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Posts Tagged ‘Transthyretin’


Cancer and Nutrition

Writer and Curator: Larry H. Bernstein, MD, FCAP

The following discussions have been a topic of great interest and much controversy. In this discussion I shall not cover the topics related to Alternative and Complementary Medicine that is discussed elsewhere.  However, there is significant reason to explore the relationships of vitamin and micronutrient insufficiencies to cancer. The following nutritional subjects will be the focus of these discussions.

  1. Transthyretin (TTR)
  2. Vitamin A (retinoids and retinol) and retinol-binding protein (RBP)
  3. Vitamin C
  4. Vitamin D
  5. Magnesium (Mg++)

Cancer, homocysteine, Alzheimer’s Disease, and cardiovascular disease

1 Transthyretin

1.1 Plasma Transthyretin Indicates the Direction of both Nitrogen Balance and Retinoid Status in Health and Disease

Ingenbleek Yves1 and Bienvenu Jacques2,3,*

1Laboratory of Nutrition, Faculty of Pharmacy, University Louis Pasteur Strasbourg 1, France; 2Laboratory of Immunology, Hospices Civils de Lyon and 3INSERM U 851, University Claude Bernard Lyon 1, France

The Open Clinical Chemistry Journal, 2008;  1:1-12
Abstract: Whatever the nutritional status and the disease condition, the actual transthyretin (TTR) plasma level is determined by opposing influences between anabolic and catabolic alterations. Rising TTR values indicate that synthetic processes prevail over tissue breakdown with a nitrogen balance (NB) turning positive as a result of efficient nutritional support and / or anti-inflammatory therapy. Declining TTR values point to the failure of sustaining NB as an effect of maladjusted dietetic management and / or further worsening of the morbid condition. Serial measurement of TTR thus appears as a dynamic index defining the direction of NB in acute and chronic disorders, serving as a guide to alert the physician on the validity of his therapeutic strategy. The level of TTR production by the liver also works as a limiting factor for the cellular bioavailability of retinol and retinoid derivatives which play major roles in the brain ageing process. Optimal protein nutritional status, as assessed by TTR values within the normal range, prevents the occurrence of vascular and cerebral damages while maintaining the retinoid-mediated memory, cognitive and behavioral activities of elderly persons.

INTRODUCTION  Measurement of transthyretin (TTR, formerly called prealbumin) was proposed as nutritional marker in The Lancet in 1972 [1]. This proposal was largely disregarded by the scientific community during the decade following its publication. TTR testing is now the most utilized nutritional marker worldwide, having received the strong support of the Prealbumin Consensus Group [2].  A minority of workers, however, remain doubtful [3] or even reluctant [4] to adopt TTR as nutritional index, stressing the point that its synthesis is also influenced by inflammatory conditions [3,4] and by other extra-nutritional factors such as natural or synthetic corticosteroids [5] and androgens [6]. The aim of the present review paper is to clarify the complex relationships linking malnutrition and inflammation, throwing further insight into a nutrition domain of increasing public health.

EVOLUTION, STRUCTURE AND FUNCTIONS  TTR is a highly conserved protein in vertebrate species already secreted by the choroid plexus of reptiles 300 millions years ago and remaining confined within the cerebrospinal fluid (CSF) [10]. Synthesis and secretion of TTR by the liver evolved much later, about 100 millions years ago, in birds and eutherian mammals [11]. Production of TTR by the liver and by the choroid plexus is regulated separately [12]. The human TTR gene has been localized on the long arm of the chromosome 18q23 [13]. The nucleotide sequences of the entire TTR gene, including the 5′ (transcription initiating site) and the 3′ (untranslated site) flanking regions have been described [14,15]. The gene spans 6.9 kilobases (kb) and consists of 4 exons and 3 introns [14,15]. The hepatic TTR mRNA measures 0.7 kb encoding a pro-TTR-monomer undergoing a cleaving process to release the native TTR monomer [16]. Four identical subunits each 127 amino acids (AAs) length coalesce noncovalently to generate the fully mature nonglycosylated molecule whose molecular mass (MM) reaches 55 kDa [17]. Two binding sites for thyroid hormones are buried inside the central channel of the TTR heterodimer [18]. The secondary, tertiary and quarternary conformation structures of the TTR protein have been reported using 1.8 Å Fourier analysis [18]. One TTR  monomer binds to a small companion protein (21 kDa MM) to which a single retinol is bound (all-trans-retinol), hence its RBP denomination [19]. X-ray crystallographic studies have shown that RBP possesses an eight-stranded -barrel core that completely encapsulates the retinol molecule [20]. Under usual circumstances, RBP is almost entirely saturated with retinol, explaining that the 3 components of the retinol circulating complex (RCC) of 76 kDa MM has a close 1:1:1 stoichiometry [21]. Aggregation of TTR to holo-RBP occurs within the endoplasmic reticulum prior to extracellular RCC secretion [22].  The TTR protein was first discovered in human CSF in 1942 [23] and soon after in human serum. Human TTR transports about 20% of the intravascular pool of both thyroid hormones (Thyroxine [T4], triiodothyronine [T3]) and at least 90-95% of the retinol circulating pool. The term transthyretin was recommended by the International Nomenclature Committee [26] stressing the dual conveying role played by TTR in all eutherians.

The biological half-life of TTR is approximately 2 days [27] whereas that of holo-RBP (RBP + bound retinol) is half a day [28]. By contrast, apo-RBP devoid of its retinol ligand displays a significantly reduced half-life of 3.5 hr [28] and undergoes rapid glomerular leakage with subsequent tubular disintegration and recycling of its AA residues. It is therefore assumed that TTR plays an important role in the safeguard of the retinol pool. The catabolic site of TTR is mainly the liver, followed by muscle mass, skin and kidneys [29].  The TTR molecule displays microheterogeneity [30] and tissue deposits occur throughout the normal ageing processes [31]. In contrast, TTR is characterized by a very large genetic polymorphism affecting about 100 different point mutations [32], leading to misfolded forms of the protein and occurrence of amyloid disorders in several organs. The tetrameric TTR protein is recognized as a component of the normal pancreatic cell structure, preserving its integrity against the risk of apoptosis [40]. Finally, normal TTR production is required for the maturation of brain neural stem cells [41] and for the control of spatial reference memory performances [42].

SIGNIFICANCE OF TTR THROUGHOUT THE HUMAN LIFESPAN  Significant alterations in the levels of protein intakes by humans affect protein synthesis, turnover and breakdown and determine the outcome of total body N (TBN).  Anabolism occurs when the rate of AA incorporation into protein exceeds that of oxidative losses, yielding a positive NB. Catabolism is the result of protein breakdown prevailing over protein synthesis [43]. Increasing gestational age is accompanied by a slow and predictable rise in TTR values correlated with birth weight and proved useful in distinguishing between small, appropriate and large for gestational age infants [47,48]. Starting from birth until 100 years of age, our reference TTR values [54] are those collected in the monograph ” Serum Proteins in Clinical Medicine ” edited by the Foundation for Blood Research. The plasma TTR concentrations in healthy neonates are approximately two thirds those measured in healthy mothers and thereafter increase slowly until the onset of puberty without displaying sexual differences. The rate of protein synthesis similarly increases linearly during the prepubertal period [55], consistent with superimposable N accretion rates [56]. Human puberty is characterized by major hormonal and metabolic alterations leading to increased height velocity and weight gain [60]. The onset of puberty requires close interrelationships between the effects triggered by growth hormone and  insulin-like growth factors, by thyroid and steroid hormones, by insulin and sex hormones [60]. Whereas androgens strongly promote the development of muscle mass in males and lipolytic effects on visceral and subcutaneous fat, estrogens have minimal effect on the female musculature while stimulating the accrual of subcutaneous fat depots [60]. Body composition studies indicate prepubertal redistribution of FM and FFM with a significantly higher S-shaped elevation of FFM in male adolescents compared with the blunted curve recorded in teenaged girls [61,62]. TTR values manifest closely paralleled sex- and age-peculiarities in process of time that are best explained by the deeper androgenic impregnation of male subjects [6,43]. The musculature is by weight the main component of FFM, representing 37% of body mass [61].  In healthy adults, the sex-related difference in plasma TTR-RBP concentrations is maintained at plateau levels after sexual maturity [54,63]. Normal TTR plasma values are stabilized around 290-320 mg/L in males and around 250-280 mg/L in females [54,63]. Starting from the sixties, TTR concentrations progressively decline over time, disclosing a steeper slope in elderly men that reflects a relatively more rapid deterioration of their muscle mass [43]. As a result, the earlier TTR sexual difference disappears by about the age of 70 years [43]. This correlates with the age-dependent curvilinear drop of TBN, characterized by an accelerated decrease after 65 years [64]. Taken together, the plasma TTR evolutionary patterns reveal a parallelism with FFM so that TTR serves as an indicator of muscle mass. The data show that age and gender are significant co-variates of TTR which require separate blood reference values [54].

TTR AS INDEX OF PROTEIN DEPLETION / REPLETION STATES  There exists a long-lasting debate aimed at identifying the most effective protein sources, level of energy-yielding substrates and the proportion among these for the support of protein metabolism. Under usual conditions, glucose functions as the major energy substrate for protein synthesis. If the carbohydrate energy is lacking, glucose must be synthesized by gluconeogenesis, mainly from the conversion of endogenous or dietary protein [65]. This corresponds to a form of nutritional wastage which augments the cost of protein synthesis, as documented by an increased urinary excretion of urea. The above metabolic pattern stands in broad conformity with the concept that ” protein synthesis occurs in the flame of sugars ” [66].

FAO/WHO/UNU recommends for healthy adults the safe level of 0.75 g k-1 day-1 protein intake [67]. Although this amount of protein sustains normal growth and keeps unmodified the concentration of most biological parameters, such intake appears to be marginally inadequate to maintain the metabolic reserve capacities that are required to mount optimal responses to stress [68]. Studies have disclosed that TTR plasma level and pool size remain unaltered because its synthetic and catabolic rates are both downregulated concomitantly [69]. Changes occurring during prolonged starvation causes the N balance to turn negative despite efforts to minimize protein catabolism [70]. There is a direct correlation between the rate of liver protein synthesis and intrahepatic concentrations of individual free AAs [71]. It is likely that the dietary limitation of some AAs such as tryptophan [72] or leucine [73] could specifically exert inhibitory effects on the transcriptional [74] or translational [75] regulation of protein synthesis. Consequently, protein depletion causes a decrease in TTR mRNA [72,74,76].

Transcription of the TTR gene in the liver is directed by CCAAT/enhancer binding protein (C/EBP) bound to nuclear factor 1 (NF1) [74]. Multiple hepatocyte nuclear factors (HNFs) function in the regulation of TTR gene expression [77]. It has been recently shown that one of them (HNF-4) plays prominent roles before and after injury [78]. The drop of liver TTR mRNA levels to about half as an effect of protein deprivation [74] is accompanied by a corresponding diminished secretion of mature TTR molecules in the bloodstream.

The rapidly turning over TTR protein is exquisitely sensitive to any change in protein and/or energy supply, being clearly situated on the cutting edge of the equipoise. This is documented in preterm infants in whom AA supply is responsible for maintaining normal protein synthesis which may be somewhat modulated by fluctuations in energy intake [79]. In the declared stage of protein malnutrition, the serial measurement of TTR may serve to grade the severity of the disease spectrum, from mild [90] to severe [1] forms. Both metabolic and structural N compartments undergo exhausting processes as documented by the fall of nitrogenous compounds in the urine of protein-depleted subjects [91]. The relative dominance of urea over ammonia catabolites [92] reflects the more intense turnover rate of tissues belonging to the readily mobilizable N pool. Decreased TTR plasma values are indeed correlated with the involution of the gut mucosa [93] and with the extent of liver dysfunction, more pronounced in the kwashiorkor disease with massive hepatic steatosis than in marasmus with limited fatty liver infiltration [1]. The structural N compartment nevertheless participates in the loss of body protein reserves, consistent with the reduced urinary output of creatinine [91], 3-methylhistidine [94] and soluble hydroxyproline [95]. The resulting sarcopenia [96,97] and the concomitant depression of immune mechanisms [98,99] render an account of the higher morbidity / mortality rates affecting TBN-depleted patients identified by the lowest TTR and RBP plasma concentrations [100]. The mortality risk of malnourished children in Central Africa becomes likely when SA and TTR reach the threshold of 16 g /L and 65 mg /L, respectively [101].

During nutritional rehabilitation from protein malnutrition, the restoration of visceral proteins occurs at different rates depending on the type of protein and the size of its plasma pool. TTR and RBP recovery appears as the main result of increased production rates by the liver [102]. Most studies contend the view that the trajectory outlined for TTR correlates with the fluctuations of body N mass, especially during the anabolic phase of growth and clinical recovery from protein malnutrition. Using impedance parameters for assessing the N compartment still remaining in place in the stressed body of adults undergoing renal dialysis, nephrologists were able to demonstrate close relationships between TTR and phase angle, reactance and resistance values [105]. In elderly noninfected persons, FFM index measured by dual X-ray absorptiometry exhibits the highest correlation with TTR (r = 0.64) compared to RBP (r = 0.52) [106]

TTR AS NITROGEN INDEX IN INFLAMMATORY DISORDERS  Inflammatory disorders of any cause are initiated by activated leukocytes releasing a shower of cytokines working as autocrine, paracrine and endocrine molecules [107]. Cytokines regulate the overproduction of acute-phase proteins (APPs), notably that of CRP, 1-acid glycoprotein (AGP), fibrinogen, haptoglobin, 1-antitrypsin and antichymotrypsin [107]. APPs contribute in several ways to defense and repair mechanisms, being characterized by proper kinetic and functional properties [107]. Interleukin-6 (IL-6) is regarded as a key mediator governing both the acute and chronic inflammatory processes, as documented by data recorded on burn [108], sepsis [109] and AIDS [110] patients. IL-6-NF possesses a high degree of homology with C/EBP-NF1 and competes for the same DNA response element of the IL-6 gene [111]. IL-6-NF is not expressed under normal circumstances, explaining why APP concentrations are kept at baseline levels. In stressful conditions, IL-6-NF causes a dramatic surge in APP values [107,112] with a concomitant suppressed synthesis of TTR as demonstrated in animal [113] and clinical [114] experiments.  Under acute stressful conditions, protein turnover is strongly stimulated by augmented tissue breakdown (mainly in the muscle mass) and enhanced specific tissues synthesis (mainly in the liver and at the site of injury). Proteolysis releases AA residues which are preferentially incorporated into the hepatic precursor pool involved in the production of APPs [115,116]. The rate at which proteins are degraded generally exceeds the rate of AA mobilization for protein synthesis [117,118] yielding a net negative NB associated with an increased urinary output of urea and ammonia [119]. Creatininuria and 3-methylhistidinuria are significantly elevated and remain highly correlated (r = 0.97) attesting to the substantial participation of the skeletal musculature to the stress responses [117]. The gap between degradative and synthetic processes widens in proportion to the severity of injury, resulting in correspondingly increased urinary N catabolites [43]. Serious injury affecting otherwise healthy adults may trigger urinary N losses reaching 40 g/day or 250 g/week, which corresponds to about 15% of TBN [43]. In long-lasting debilitating disorders, the persisting negative NB may deplete the baseline body cell mass by about 45%, carrying ominous prognostic significance [120].

Inadequate nutritional management [122], multiple injuries, occurrence of severe sepsis and metabolic complications result in persistent proteolysis [124] and subnormal TTR concentrations [66]. The evolutionary patterns of urinary N output and of TTR thus appear as mirror images of each other, which supports the view that TTR might well reflect the depletion of TBN in both acute and chronic disease processes. Even in the most complex stressful conditions, the synthesis of visceral proteins is submitted to opposing anabolic or catabolic influences yielding ultimately TTR as an end-product reflecting the prevailing tendency. Whatever the nutritional and/or inflammatory causal factors, the actual TTR plasma level and its course in process of time indicates the exhaustion or restoration of the body N resources, hence its likely (in)ability to assume defense and repair mechanisms. The serial measurement of TTR appears as a dynamic tool pointing to the direction and magnitude of NB, predicting therefore the disease outcome. Hundreds of studies are reporting the clinical usefulness of TTR measurement.  TTR is recommended for the assessment and nutritional follow-up of a large panel of hospitalized patients in internal medicine settings [130,131], in general surgery [132,133] and intensive care units [134,135]. Low TTR values thus appear to nonspecifically reflect the extent of liver damage rather than its etiology. Liver N tissue only represents by weight a minor proportion of TBN but its intense turnover rate (10 to 20-fold more rapid than that of muscle tissue) [43] and its critical involvement in the orchestration of most major metabolic and immune pathways [145] explains why liver failure of any cause is usually associated with varying degrees of clinical malnutrition [142].

The nutritional management of kidney patients has met noticeable improvement along the past decades. Until the mid 1980s TTR was regarded as unreliable and discarded, leaving the way for the general use of SA in kidney studies. The turning point came in 1987 when a careful statistical analysis stated that TTR was the most representative marker within a large battery of currently measured parameters [149]. The most recent studies clearly incline towards the common use of TTR superseding that of SA [8, 151-155]. It has been confirmed, mainly in intensive care renal units, that the serial measurement of TTR works as a strong independent predictor of long-term survival, allowing identification of the patients in need of nutritional intervention [151,155] or at risk of reduced life expectancy [154, 155]. Using proportional hazards regression models, the relative risk of death was inversely related to TTR concentrations in 8,157 hemodialyzed patients [155]. TTR is currently measured as nutritional marker in tropical areas where bacterial, viral and parasitic diseases are still highly prevalent, usually in connection with defective immune and vitamin A status, including malaria[156], trypanosomiasis [157], schistosomiasis [158], measles[159], shigellosis [160], and AIDS patients exhibit declining TTR values as the morbid condition worsens [161].

In westernized societies, elderly persons constitute a growing population group. A substantial proportion of them may develop a syndrome of frailty characterized by weight loss, clumsy gait, impaired memory and sensorial aptitudes, poor physical, mental and social activities, depressive trends. Hallmarks of frailty combine progressive depletion of both structural and metabolic N compartments [162]. Sarcopenia and limitation of muscle strength are naturally involutive events of normal ageing which may nevertheless be accelerated by cytokine-induced underlying inflammatory disorders [163,164]. Depletion of visceral resources is substantiated by the shrinking of FFM and its partial replacement by FM, mainly in abdominal organs, and by the down-regulation of indices of growth and protein status [162]. Due to reduced tissue reserves and diminished efficiency of immune and repair mechanisms, any stressful condition affecting old age may trigger more severe clinical impact whereas healing processes require longer duration with erratical setbacks. As a result, protein malnutrition is a common finding in most elderly patients [165] with significantly increased morbidity and mortality rates [166,167].

Measurement of visceral protein status is proved useful throughout the entire ageing lifespan. A wide range of co-morbidities associated with defective protein nutritional status is described in aging persons who become more prone to develop pressure sores [163], osteoporosis [170], oral candidiasis [171] and nuclear cataract [172].  The isolation and purification of rat TTR [173] has allowed to set up animal models. In normal rats, TTR manifests highly significant correlations with nutrient intakes and with visceral and carcass N stores [174]. In tumor-bearing rats, the progressive exhaustion of body protein mass towards cachexia states is correlated with declining TTR values [175]. TTR is currently utilized as indicator of protein nutritional status in cancer patients [176,177]. TTR is held as the most powerful test overall for evaluating visceral protein status of children with solid tumors [178] and leukemias [179] both at the time of diagnosis and throughout chemotherapy. In bone marrow transplantation for malignancies, TTR accurately reflects at any point changes in the patient’s clinical status [180]. TTR has proved to be a useful marker of nutritional alterations with prognostic implications in large bowel cancer [181], bronchopulmonary carcinoid tumor [182], ovarian carcinoma [183] and bladder epithelioma [184]. Many oncologists have observed a rapid TTR fall 2 or 3 months prior to the patient’s death [181]. In cancer patients submitted to surgical intervention, most postoperative complications occurred in subjects with preoperative TTR  180 mg/L [185]. Two independent studies came to the same conclusion that a TTR threshold of 100 mg/L is indicative of extremely weak survival likelihood and that these terminally ill patients better deserve palliative care rather than aggressive therapeutic strategies [185,186].

The AGP/TTR couple is recommended in chronic inflammatory disorders, notably in several cancer types [192,193]. Working along the same lines is the prognostic inflammatory and nutritional index (PINI) [194] which is successfully applied on large cohorts of patients. TTR also participates in the development of screening formulas recently generated by innovative analytical tools such as surface-enhanced laser desorption/ionization (SELDI) or matrix-assisted laser desorption/ionization (MALDI) coupled with time of flight mass spectrometry (TOF-MS). The advent of these sophisticated and costly proteomic fingerprinting studies of serum or other biological fluids are nevertheless promising in that they tentatively strive to identify the early stages of several disease conditions such as hepatitis B [195], tuberculosis [196], Alzheimer’s disease [197] or neoplastic disorders [198]. These proteomic detecting systems usually combine classical APP reactants with some minor biological compounds scarcely measured in routine laboratory practice such as cathepsin D, hemopexin, neopterin or vitronectin. The fact that most, if not all, of these fingerprinting formulas embody TTR measurement indicates that there exists among workers a large consensus considering this carrier-protein as the most reliable indicator of protein depletion in morbid circumstances.

PROGRESS IN TTR RESEARCH : THE BRAIN AGEING PROCESS  Dementia, defined as significant memory impairment and loss of intellectual functions, is a common and devastating public health problem, affecting an estimated 2-4% individuals over the age of 65 years. Two distinct clinicopathological conditions are usually taken into consideration as causative factors: Alzheimer’s disease (AD), a chronic and continuously progressing illness for which the only widely accepted risk conditions are age and family history of the disease; and cerebral infarction, a brain deteriorating process evolving along episodic and repetitive bouts so as to generate a syndrome of multi-infarct dementia (MID) [199]. The rates of both AD and MID increase dramatically with age, leading to coexisting pathologies with intermingled symptomatology [200]. In support to this mixed cases concept are the report of equally increased blood-brain barrier permeability in both AD and MID patients [201] and the accumulation of amyloid -protein in the brain of MID subjects mimicking AD pathology [202]. There exists considerable overlap between AD and MID clinical symptoms, giving rise to a continuum of patients in whom pure AD and pure MID represent the two extreme poles [200].  The elevated homocysteine (Hcy) values found in AD patients [208,209] are reportedly associated with dementia [208,210].

The choroid plexus is the sole site of mammalian brain involved in TTR production [214]. Its synthesis rate by the choroid epithelium is estimated 25 to 100 times higher than that of the liver on a weight basis [215]. As a result, TTR is a major component of CSF, constituting 10 to 25 % of total ventricular proteins [216] conveying up to 80% of intrathecal thyroxine [217]. TTR thus constitutes an hormonal carrierprotein fulfilling important ontogenic and functional properties in mammalian nervous structures, a concept further corroborated by the observation of its increased CSF concentration during the neonatal period [218]. The data imply that choroidal TTR facilitates the uptake of thyroxine from the bloodstream, governing its transport and delivery to brain tissues following a kinetic model developed by Australian workers [219]. In comparison, CSF contains 10 to 100 times lower RBP and retinol concentrations than plasma whilst retinyl esters from dietary origin are virtually absent [220]. Although it has been reported that minute amounts of RBP could be produced within the neuraxis [221], the sizeable proportion of retinol molecules required for brain maturation utilizes the RCC transport system to reach the choroid plexus. The very high receptor binding affinity expressed by neural tissues for RBP molecules [222] is confined within the endothelial cells of the brain microvasculature and within the choroidal epithelial cells, the two primary sites of the mammalian blood-brain barrier [223]. The contrast between high RBP binding affinities and low intrathecal concentrations makes it likely that holo-RBP does not experience significant transchoroidal diffusion, strongly suggesting that its retinol ligand is released in free form and readily taken up by membrane or intracellular receptors of neural cells. The dual TTR production, plasma-derived and choroid-secreted, allows complementary stimulation of brain activities. Thyroid hormones and retinoids indeed function in concert through the mediation of common heterodimeric motifs bound to DNA response elements [224,225]. The data also imply that the provision of thyroid molecules within the CSF works as a relatively stable secretory process, poorly sensitive to extracerebral influences [12] as opposed to the delivery of retinoid molecules whose plasma concentrations are highly dependent on nutritional and/or inflammatory alterations [66]. This last statement is documented by mice experiments [226] and clinical investigations [227] showing that the level of TTR production by the liver operates as a limiting factor for retinol transport. Defective TTR synthesis determines the occurrence of secondary hyporetinolemia which nevertheless results from entirely different kinetic mechanisms in the two quoted studies [226,227].

In the TTR knock-out mice model, holo-RBP molecules are normally synthetized and secreted by the liver but undergo rapid kidney leakage in the absence of stabilizing TTR molecules [228]. Despite very low levels of plasma retinol (about 5 % of wild type), these targeted mutated animals remain healthy and fertile, implying that efficient compensatory mechanisms take place. No such increased urinary output of RBP molecules occurs in malnourished patients who develop in proportion to their declining protein status electroretinographic abnormalities and ocular lesions which are pathognomonic symptoms of vitamin A deficiency [229]. During nutritional rehabilitation of malnourished subjects, the 3 RCC components gradually return to normal ranges even without retinol or carotene supplementation, indicating that the retinyl esters normally sequestered in liver stellate cells mandatorily need diet-induced synthesis of new TTR molecules before undergoing retinol conversion and binding as holo-RBP ligand [227]. The prominent place occupied by TTR in defining distal retinoid bioavailability has been too long unrecognized despite the warning expressing that ” overlooking the crucial role of TTR in vitamin A-metabolism results in unachieved or even misleading conclusions ” [66].

Retinol is a precursor substrate that must undergo a two step oxidation procedure to release firstly retinal and thereafter the two active all-trans- and 13-cis-retinoic acids (RAs) [225,230]. The latter converting steps are regulated by retinaldehyde dehydrogenase (RALDH) enzymes whose major sites of expression are the olfactory bulb, the striatum and the hippocampus [231,232]. The intracellular activities exerted by retinoid compounds are mediated by a large variety of specific receptors among which are cellular-RBP (CRBP), cellular-RA-BP (CRABP), RA-nuclear receptors (RARs) and retinoid X receptors (RXRs), each composed of 3 subtypes [225,232]. Retinol is the rate-limiting determinant of the concentration of both RA derivatives [233], implying that any fluctuation in protein status might entail corresponding alterations in the cellular bioavailability of retinoid compounds, with all the more rapid effects as all-trans-RA has a short biological half-life of less than 1 hr [234]. Because protein malnutrition is a common finding in as much as 50 % of elderly AD and MID patients [235], many of them could well suffer permanent hyporetinolemia still accelerating the declining concentration of retinoid molecules observed over the course of normal ageing [231].  Dietary vitamin A is required to modulate early development of brain structure and differentiation [236] together with neuronal plasticity, memory functioning and neurotransmitter signaling during adulthood [237].

The normal decrease of brain retinoid molecules throughout the ageing process principally affects the above-described major sites of RA synthesis [238], a regressive alteration even more pronounced in AD patients [231]. In murine models, early depletion of retinoids causes deposition of amyloid -peptides [239], initiating the formation of Alzheimer plaques. In aged animals, cognitive and memory deficits are associated with down-regulation of the expression of retinoid receptors which may recover their full activities under RA supplementation [240]. Administration of RA similarly restores expression of proteins involved in the control of amyloidogenic pathways [241]. Along the same preventive line is the demonstration that retinol disaggregates preformed amyloid fibrils, more effectively than does RA [242].  Alternatively, TTR participates in the maintenance of memory and normal cognitive processes during ageing by acting on the retinoid signalling pathway as recently reported on TTR-null knock-out mice model [42,243]. Moreover, TTR may bind amyloid -peptide in vitro, preventing its transformation into amyloid neurofibrils [244].

Protein malnutrition, as assessed by diminished TTR plasma values, causes the elevation of Hcy concentrations [245]. There exists an inverse correlation between both TTR and Hcy parameters, explaining why malnourished elderly persons incur increasing risk of Hcy-depended thrombovascular complications [213]. The defective mechanism is situated at the level of cystathionine–synthase (CS), an enzyme governing the crossroad of remethylation and transsulfuration pathways [246]. Japanese workers have recently provided experimental validation of the metabolic anomaly, showing that rats given methionine (Met)-deprived nutriture manifest depressed CS activity with subsequent elevation of Hcy plasma levels [247]. Among all essential AAs consumed in human nutrition, Met is regarded as the most critically available because its withdrawal from the customary diet causes the deepest negative NB, being almost as great as when a protein-free regimen is ingested [248]. Met is implicated in a large spectrum of metabolic and enzyme activities and participates in the conformation of a large number of molecules of survival importance [213]. Due to the fact that plant products are relatively Met-deficient, vegan subjects are more exposed than omnivorous to develop hyperhomocysteinemia – related disorders [249]. Dietary protein restriction may promote supranormal Hcy concentrations which appears as the dark side of adaptive attempts developed by the malnourished and/or stressed body to preserve Met homeostasis.  Summing up, we assume that the low TTR concentrations reported in the blood [235] and CSF [250] of AD or MID patients result in impairment of their normal scavenging capacity [244] and in the excessive accumulation of Hcy in body fluids [245], hence causing direct harmful damage to the brain and cardiac vasculature. In addition, depressed TTR concentrations indirectly inhibit the multitude of retinoid-dependent cerebral functioning pathways [231,243] allowing the development of amyloidogenic processes [239]. The practical consequences of these findings imply that the correct assessment of nutritional status is recommended in all elderly patients. The mental and cognitive dysfunctions of old age that are not genetically programmed but result from varying energy, protein and vitamin-deficiencies may be substantially prevented and sometimes improved provided that appropriate nutritional measures are undertaken.

CONCLUDING REMARKS  In spite of classical criticisms [3,4], TTR is regarded as a robust and reliable indicator of protein nutritional. Taking into account the gender- and age-specificities, TTR appears as the sole plasma protein reflecting the fluctuations of TBN pools. The relationship linking alterations of TTR plasma levels with body N reserves are documented both in animal models [175] and in human subjects [105,106].  Uncomplicated malnutrition primarily affects the metabolic N pool, reducing protein syntheses and NB to levels compatible with survival, an adaptive response well identified by declining TTR values. In inflammatory disorders, both metabolic and structural N pools participate in varying proportions in the cytokine-induced responses of the stressed body, resulting in TBN shrinking and concomitant depression of TTR concentrations. Abatement of the stressful condition and/or efficient nutritional rehabilitation allows restoration to normal levels of both TBN pools and TTR values following parallel slopes. TTR thus appears as a dynamic index predicting the outcome of the disease. We attached more importance to the trend outlined by its serial appraisal than to any single measurement.  Whatever the causal factor, depletion of TBN reserves attenuates the body’s capacity to mount appropriate immune and repair mechanisms. A number of clinical investigations have advocated the level of plasma TTR as predictor of the length of hospital stay (LOS) and of mortality rate [252, 255]. Not surprisingly, unrecognized malnutrition entails longer LOS, increased number of complications and higher care costs whereas early detection and treatment of high risk patients significantly alleviate the financial burden of hospitalization while improving the prognostic outcome of the patients [252-256]. The last statement is documented by the first prospective and randomized survey showing that reduced morbidity and mortality rates are depending on protein N intake and correlated with rising TTR concentrations [257]. Providing elderly persons with optimal protein nutritional status in order to insure their protection against the risk of neurodeterioration is the last message released by the fascinating TTR plasma protein.

Points to consider:

  1. Protein energy malnutrition has an unlikely causal relationship to carcinogenesis. Perhaps the opposite is true. However, cancer has a relationship to protein energy malnutrition without any doubt.  PEM is the consequence of cachexia, whether caused by dietary insufficiency, inflammatory or cancer.
  2. Protein energy malnutrition leads to hyperhomocysteinemia, and by that means, the relationship of dietary insufficiency of methionine has a relationship to heart disease. This is the significant link between veganism and cardiovascular disease, whether voluntary or by unavailability of adequate source.

1.2 Downsizing of Lean Body Mass is a Key Determinant of Alzheimer’s Disease

Yves Ingenbleek, and Larry H. Bernstein
Journal of Alzheimer’s Disease 44 (2015) 745–754
http://dx.doi.org:/10.3233/JAD-141950

Lean body mass (LBM) encompasses all metabolically active organs distributed into visceral and structural tissue compartments and collecting the bulk of N and K stores of the human body. Transthyretin (TTR) is a plasma protein mainly secreted by the liver within a trimolecular TTR-RBP-retinol complex revealing from birth to old age strikingly similar evolutionary patterns with LBM in health and disease. TTR is also synthesized by the choroid plexus along distinct regulatory pathways. Chronic dietary methionine (Met) deprivation or cytokine-induced inflammatory disorders generates LBM downsizing following differentiated physiopathological processes. Met-restricted regimens downregulate the transsulfuration cascade causing upstream elevation of homocysteine (Hcy) safeguarding Met homeostasis and downstream drop of hydrogen sulfide (H2S) impairing anti-oxidative capacities. Elderly persons constitute a vulnerable population group exposed to increasing Hcy burden and declining H2S protection, notably in plant-eating communities or in the course of inflammatory illnesses. Appropriate correction of defective protein status and eradication of inflammatory processes may restore an appropriate LBM size allowing the hepatic production of the retinol circulating complex to resume, in contrast with the refractory choroidal TTR secretory process. As a result of improved health status, augmented concentrations of plasma-derived TTR and retinol may reach the cerebrospinal fluid and dismantle senile amyloid plaques, contributing to the prevention or the delay of the onset of neurodegenerative events in elderly subjects at risk of Alzheimer’s disease.

Transthyretin and Lean Body Mass in Stable and Stressed State

https://pharmaceuticalintelligence.com/2013/12/01/transthyretin-and-lean-body-mass-in-stable-and-stressed-state/

A Second Look at the Transthyretin Nutrition Inflammatory Conundrum

https://pharmaceuticalintelligence.com/2012/12/03/a-second-look-at-the-transthyretin-nutrition-inflammatory-conundrum/

Stabilizers that prevent transthyretin-mediated cardiomyocyte amyloidotic toxicity

https://pharmaceuticalintelligence.com/2013/12/02/stabilizers-that-prevent-transthyretin-mediated-cardiomyocyte-amyloidotic-toxicity/

Thyroid Function and Disorders

https://pharmaceuticalintelligence.com/2015/02/05/thyroid-function-and-disorders/

Proteomics, Metabolomics, Signaling Pathways, and Cell Regulation: a Compilation of Articles in the Journal http://pharmaceuticalintelligence.com

https://pharmaceuticalintelligence.com/2014/09/01/compilation-of-references-in-leaders-in-pharmaceutical-intelligence-about-proteomics-metabolomics-signaling-pathways-and-cell-regulation-2/

Malnutrition in India, high newborn death rate and stunting of children age under five years

https://pharmaceuticalintelligence.com/2014/07/15/malnutrition-in-india-high-newborn-death-rate-and-stunting-of-children-age-under-five-years/

Vegan Diet is Sulfur Deficient and Heart Unhealthy

https://pharmaceuticalintelligence.com/2013/11/17/vegan-diet-is-sulfur-deficient-and-heart-unhealthy/

How Methionine Imbalance with Sulfur-Insufficiency Leads to Hyperhomocysteinemia

https://pharmaceuticalintelligence.com/2013/04/04/sulfur-deficiency-leads_to_hyperhomocysteinemia/

Amyloidosis with Cardiomyopathy

https://pharmaceuticalintelligence.com/2013/03/31/amyloidosis-with-cardiomyopathy/

Advances in Separations Technology for the “OMICs” and Clarification of Therapeutic Targets

https://pharmaceuticalintelligence.com/2012/10/22/advances-in-separations-technology-for-the-omics-and-clarification-of-therapeutic-targets/

Sepsis, Multi-organ Dysfunction Syndrome, and Septic Shock: A Conundrum of Signaling Pathways Cascading Out of Control

https://pharmaceuticalintelligence.com/2012/10/13/sepsis-multi-organ-dysfunction-syndrome-and-septic-shock-a-conundrum-of-signaling-pathways-cascading-out-of-control/

Automated Inferential Diagnosis of SIRS, sepsis, septic shock

https://pharmaceuticalintelligence.com/2012/08/01/automated-inferential-diagnosis-of-sirs-sepsis-septic-shock/

 

 

1.3 Transthyretin Blocks Retinol Uptake and Cell Signaling by the Holo-Retinol-Binding Protein Receptor STRA6

Daniel C. Berry, Colleen M. Croniger, Norbert B. Ghyselinck, Noa Noya
Vitamin A is secreted from cellular stores and circulates in blood bound to retinol-binding protein (RBP). In turn, holo-RBP associates in plasma with transthyretin (TTR) to form a ternary RBP-retinol-TTR complex. It is believed that binding to TTR prevents the loss of RBP by filtration in the kidney. At target cells, holo-RBP is recognized by STRA6, a plasma membrane protein that serves a dual role: it mediates uptake of retinol from extracellular RBP into cells, and it functions as a cytokine receptor that, upon binding holo-RBP, triggers a JAK/STAT signaling cascade. We previously showed that STRA6-mediated signaling underlies the ability of RBP to induce insulin resistance. TTR blocks the ability of holo-RBP to associate with STRA6 and thereby effectively suppresses both STRA6-mediated retinol uptake and STRA6-initiated cell signaling. Consequently, TTR protects mice from RBP-induced insulin resistance, reflected by reduced phosphorylation of insulin receptor and glucose tolerance tests. The data indicate that STRA6 functions only under circumstances where the plasma RBP level exceeds that of TTR and demonstrate that, in addition to preventing the loss of RBP, TTR plays a central role in regulating holo-RBP/STRA6 signaling.

1.4 Transthyretin Amyloidosis

1.4.1 (Adapted from a Review in Amyloid: Int J Exp Clin Invest 3:44-56, 1996)

While it was expected that variations in clinical presentation (FAP-I, II, III, IV) were the result of heterogeneity in etiology or pathogenesis of the hereditary amyloidosis, it was not until the discovery by Costa, et al., in 1978 showing transthyretin as a constituent of the fibril deposits, that the biochemical basis of these syndromes could be pursued (Costa, et al., 1978).  This resulted in the discovery of the first variant form of transthyretin mutation reported in 1983.  In 1989 there were approximately 12 known mutations and in 2002 there are at least 90.  Over 80 of these mutations are associated with amyloidosis.  In addition, there is evidence that normal transthyretin may for amyloid especially in the heart and be the basis for senile cardiac amyloidosis (Westermark, 1990).

The transthyretin amyloidoses by definition are all associated with tissue deposits of fibrils having transthyretin as a major protein constituent.  While there are a number of other constituents of the amyloid deposits, including proteoglycan, amyloid P component, and various lipoproteins, it is transthyretin that is the essential ingredient in this type of amyloid.

It would appear that the signals for down regulating production of transthyretin (cytokines such as IL1 and IL6) are the same as those which cause the positive acute phase response of serum amyloid A and C reactive protein (Costa, et al., 1986).  The negative acute phase phenomenon of transthyretin is used by clinicians to monitor nutritional status of their patients.

Transthyretin is firmly entrenched in the phylogenetic evolution of vertebrate species being present in both birds and reptiles and its primary structure has been stable throughout evolution (Richardson, 1994).

While plasma transthyretin is predominantly synthesized by the adult liver, it is also synthesized by the choroids plexus of the brain and mRNA is also present in the retinal pigment epithelium, pituitary and pancreas19, 20 .  Choroid plexus synthesis would appear to be necessary for the thyroid hormone across the basement membrane into the cerebral spinal space.

The binding of RBP to transthyretin saves this small protein (21,000 daltons) from plasma clearance via filtration in the kidney.  However, when the complex gives up retinal, RBP dissociates from transthyretin and goes to meet its fate.  Transthyretin evidently can recirculate to bind more RBP-vitamin A.  Plasma residence time of transthyretin is approximately 20-24 hours, representing a plasma half-life of no more than 15 hours  (Benson, et al., 1996).  This is really very rapid turnover for a plasma protein, compared to plasma residence time of apolipoprotein AI which is 5 days, and that of albumin which is approximately 27 days (t ½ =19 days).

Most variants of transthyretin are not associated with amyloidosis.  Most variants of transthyretin are not associated with any postulated “hot spots” in the coding region.  The Ser6 variant is the only known polymorphism, prevalence of approximately 12% in the Caucasian population.  All the other mutations are present in less than 2% of the population, except in the restricted areas of Northern Sweden where greater than 2% of inhabitants have the Met30 gene and in African Americans, when considered as a group, where approximately 3% have a Val122Ile mutation.  One possible explanation of the large number of pathogenic mutations in transthyretin is that the amyloidosis is a delayed onset disease and, therefore, there is a lessened degree of selection against perpetuation of a pathogenic mutation.

Variations on the theme include the involvement of the vitreous of the eye in a number of the kindreds.  Approximately a third of transthyretin mutations are associated with vitreous deposits of amyloid; however, this finding is not uniform within families.  In different kindreds, a single mutation may have different presentations.  Most notably, Swedish patients with Met30 transthyretin have a high incidence of vitreous opacities with presentation at a fairly advanced age (58 years); whereas Portuguese patients have a lower incidence of vitreous opacities, but have presentation of neuropathy at an early age (mean 32 or 33 years).  Some transthyretin variants present as pure cardiomyopathy (e.g. Met111) (Frederikson, et al., 1962).   The Indiana/Swiss kindred (Ser84) has 100% incidence of cardiomyopathy (Benson and Dwulet, 1983) and this also appears to be true for the Appalachian kindred (Ala60) (Benson, et al., 1987).

Significant renal amyloidosis is less common than cardiac amyloidosis in most of the kindreds.  Recently attention has been directed toward kindreds having transthyretin amyloidosis with extensive leptomeningeal amyloid.  This is the hallmark of the Ohio kindred with oculoleptomeningeal amyloidosis (Gly30) (Goren, et al., 1980; Peterson, et al., 1997) and a recently reported kindred from Hungary (Gly18) in which the first clinical manifestation is dementia (Vidal, et al.,1996).  The His69 mutation has been associated with vitreous opacities alone (Zeldenrust, et al., 1994), but in another family causes oculoleptomeningeal amyloidosis.   Features of the disease in particular kindreds make familiarity with the different clinical expressions of the various transthyretin variants essential.

1.4.2 An insight to the conserved water mediated dynamics of catalytic His88 and its recognition to thyroxin and RBP binding residues in human transthyretin

Avik Banerjeea & Bishnu P. Mukhopadhyaya
http://dx.doi.org:/10.1080/07391102.2014.984632

Human transthyretin (hTTR) is a multifunctional protein involved in several amyloidogenic diseases. Besides transportation of thyroxin and vitamin-A, its role towards the catalysis of apolipoprotein-A1 and Aβ-peptide are also drawing interest. The role of water molecules in the catalytic mechanism is still unknown. Extensive analyses of 14 high-resolution X-ray structures of human transthyretin and MD simulation studies have revealed the presence of eight conserved hydrophilic centres near its catalytic zone which may be indispensable for the function, dynamics and stability of the protein. Three water molecules (W1, W2 and W3) form a cluster and play an important role in the recognition of the catalytic and RBP-binding residues. They also induce the reorganisation of the His88 for coupling with other catalytic residues (His90, Glu92). Another water molecule (W5) participate in inter-monomer recognition between the catalytic and thyroxin binding sites. The rest four water molecules (W6, W*, W# and W†) form a distorted tetrahedral cluster and impart stability to the catalytic core of hTTR. The conserved water mediated recognition dynamics of the different functional sites may provide some rational clues towards the understanding of the activity and mechanism of hTTR.

1.4.3 Amyloid Formation by Human Carboxypeptidase D Transthyretin-like Domain under Physiological Conditions*

Javier Garcia-Pardo, Ricardo Graña-Montes, Marc Fernandez-Mendez, et al.

Proteins can form amyloid aggregates from initially folded states. The transthyretin-like domain of human carboxypeptidase D forms amyloid aggregates without extensive unfolding. The monomeric transthyretin fold has an inherent propensity to aggregate due to the presence of preformed amyloidogenic structural elements. Generic aggregation from initially folded states would have a huge impact on cell proteostasis.

1.5 Evolutionary changes to transthyretin: evolution of transthyretin biosynthesis Samantha J. Richardson
FEBS Journal 276 (2009) 5342–53
http://dx.doi.org:/10.1111/j.1742-4658.2009.07244.x

Thyroid hormones are involved in growth and development, particularly of the brain. Thus, it is imperative that these hormones get from their site of synthesis to their sites of action throughout the body and the brain. This role is fulfilled by thyroid hormone distributor proteins. Of particular interest is transthyretin, which in mammals is synthesized in the liver, choroid plexus, meninges, retinal and ciliary pigment epithelia, visceral yolk sac, placenta, pancreas and intestines, whereas the other thyroid hormone distributor proteins are synthesized only in the liver. Transthyretin is synthesized by all classes of vertebrates; however, the tissue specificity of transthyretin gene expression varies widely between classes. This review summarizes what is currently known about the evolution of transthyretin synthesis in vertebrates and presents hypotheses regarding tissue-specific synthesis of transthyretin in each vertebrate class.

1.6  Distinctive binding and structural properties of piscine transthyretin

C Folli, N Pasquato, I Ramazzina, R Battistutta, G Zanotti, R Berni
FEBS Letters 555 (2003) 279-284
http://dx.doi.org:/10.1016/S0014-5793(03)01248-1

The thyroid hormone binding protein transthyretin (TTR) forms a macromolecular complex with the retinol-specific carrier retinol binding protein (RBP) in the blood of higher vertebrates. Piscine TTR is shown here to exhibit high binding affinity for L-thyroxine and negligible affinity for RBP. The 1.56 Ang resolution X-ray structure of sea bream TTR, compared with that of human TTR, reveals a high degree of conservation of the thyroid hormone binding sites. In contrast, some amino acid di¡erences in discrete regions of sea bream TTR appear to be responsible for the lack of protein-protein recognition, providing evidence for the crucial role played by a limited number of residues in the interaction between RBP and TTR. Overall, this study makes it possible to draw conclusions on evolutionary relationships for RBPs and TTRs of phylogenetically distant vertebrates.

1.7 Protein  Synthesis  at the Blood-Brain Barrier: The Major Proteins  Ecreted By Amphibian Choroid Plexus Is A Lipocalin

  1. Achen, PJ. Harms, T Thomas, SJ. Richardson, REH. Wettenhall, G Schreiber J Biol Chemistry Nov 1992; 267(32): 23167-70Among the proteins secreted by choroid plexus of vertebrates, one protein is much more  abundant than all others. In  mammals, birds, and reptiles  this protein is transthyretin, a tetramer of identical 15-kDa sub- units. In this study choroid plexus from frogs, tadpoles, and toads incubated in  vitro were found to synthesize and secrete one predominant protein. However, this consisted of one single 20-kDa polypeptide chain. It was expressed throughout  amphibian metamorphosis. Part of its amino acid sequence was determined and used for construction of oligonucleotides for polymerase chain reaction. The amplified DNA was used to screen a toad choroid plexus cDNA library. Full-length cDNA clones were isolated and sequenced. The derived amino acid sequence for the encoded protein was 183 amino acids long, including a 20-amino acid preseg- ment. The calculated molecular weight of the mature protein was 18,500. Sequence comparison with other proteins showed that the protein belonged to the lipocalin superfamily. Its expression was highest in choroid plexus, much lower in other brain areas, and absent from liver.  Since no transthyretin was detected in proteins secreted from amphibian choroid plexus, abundant synthesis and secretion of transthyretin in choroid plexus must have  evolved only after the stage of the amphibians.

2 Vitamin A

2.1 Retinoic acid pathways and cancer

2.1.1 Vitamin A, Cancer Treatment and Prevention: The New Role of Cellular Retinol Binding Proteins

Elena Doldo,Gaetana Costanza,Sara Agostinelli,Chiara Tarquini, et al.
BioMed Research International 2015; Article ID 624627, 14 pages
http://dx.doi.org/10.1155/2015/624627

Retinol and vitamin A derivatives influence cell differentiation, proliferation, and apoptosis and play an important physiologic role in a wide range of biological processes. Retinol is obtained from foods of animal origin. Retinol derivatives are fundamental for vision, while retinoic acid is essential for skin and bone growth. Intracellular retinoid bioavailability is regulated by the presence of specific cytoplasmic retinol and retinoic acid binding proteins (CRBPs and CRABPs). CRBP-1, the most diffuse CRBP isoform, is a small 15KD acytosolic protein widely expressed and evolutionarily conserved in many tissues. CRBP-1 acts as chaperone and regulates the uptake, subsequent esterification, and bioavailability of retinol. CRBP-1 plays a major role in wound healing and arterial tissue remodeling processes. In the last years, the role of CRBP-1-related retinoid signaling during cancer progression became object of several studies. CRBP-1 downregulation associates with a more malignant phenotype in breast, ovarian, and nasopharyngeal cancers.Reexpression of CRBP-1 increased retinol sensitivity and reduced viability of ovarian cancer cells in vitro. Further studies are needed to explore new therapeutic strategies aimed at restoring CRBP-1-mediated intracellular retinol trafficking and the meaning of CRBP-1 expression in cancer patients’ screening for a more personalized and efficacy retinoid therapy.

Metabolism of Retinol and Its Derivatives. Vitamin A can be acquired from the diet either as preformed vitamin A (primarily as retinyl ester, retinol, and in much smaller amount as retinoic acid) or provitamin A carotenoids (Figure1). Dietary retinyl esters are converted to retinol within the lumen of the small intestine or the intestinal mucosa and then reesterified to form retinyl ester (RE) within the enterocyte [1]. Provitamin A carotenoids, absorbed by the mucosal cells, are converted first to retinaldehyde and then to retinol [1]. After secretion of the nascent chylomicrons into the lymphatic system, the bulk of dietary vitamin A is taken up by hepatocytes and hydrolyzed again.The free retinol binds the epididymal retinoic acid binding protein (ERABP) and the retinol binding protein (RBP) [2] and into plasma transthyretin. Free retinol can be transferred to hepatic stellate cells for storage. Hepatocytes and hepatic stellate cells are very rich in retinyl ester hydrolases and in cellular retinol binding protein type 1 (CRBP-1). CRBP-1 is necessary to solubilize retinol in the aqueous environment of the cell [1].

Intracellular Trafficking of Retinoids. A cell-surface receptor named stimulated by retinoic acid 6 (STRA6) mediates vitamin A uptake from RBP [3]. Intracellular retinoid bioavailability is regulated by the presence of specific cytoplasmic retinol and retinoic acid binding proteins, CRBPs and CRABPs (Figure2). In the cytoplasm vitamin A and derivatives are bound to cytoplasmic proteins: cellular retinol binding proteins (CRBPs) which comprised four isoforms, CRBP-1 and CRBP-2 and CRBP-3 and CRBP-4. CRBP-1, are the most represented isoform in many tissues. Cellular retinoic acid binding proteins (CRABPs) comprised two isoforms, CRABP-1 and CRABP-2. CRBPs specifically bind retinol, while CRABPs and well-characterized members of the fatty acid binding proteins (FABPs) bind retinoic acid (RA). These proteins control the availability of ligands and determine the physiological response of cells and tissues to vitamin A [4]. Cellular retinoic acid binding proteins may regulate the interactions between retinoic acids and their nuclear receptors by regulating the concentrationof present retinoic acids [5]. Retinoids can activate gene expression by specific nuclear retinoid acid receptors. Two distinct classes of nuclear proteins, the retinoic acid receptors (RARs), and the retinoid X receptors (RXRs) have been identified. Each class consists of 𝛼, 𝛽,and 𝛾 subtypes. RARs and RXRs form either homodimers or heterodimers and function as transacting nuclear transcriptional factors [6]. RAR can be activated by both all-trans and 9-cis RA, whereas RXR is only activated by 9-cis-RA.

2.1.2 Retinoids, retinoic acid receptors, and cancer.

Tang XH1, Gudas LJ.
Annu Rev Pathol. 2011; 6:345-64
http://dx.doi.org:/10.1146/annurev-pathol-011110-130303

Retinoids (i.e., vitamin A, all-trans retinoic acid, and related signaling molecules) induce the differentiation of various types of stem cells. Nuclear retinoic acid receptors mediate most but not all of the effects of retinoids. Retinoid signaling is often compromised early in carcinogenesis, which suggests that a reduction in retinoid signaling may be required for tumor development. Retinoids interact with other signaling pathways, including estrogen signaling in breast cancer. Retinoids are used to treat cancer, in part because of their ability to induce differentiation and arrest proliferation. Delivery of retinoids to patients is challenging because of the rapid metabolism of some retinoids and because epigenetic changes can render cells retinoid resistant. Successful cancer therapy with retinoids is likely to require combination therapy with drugs that regulate the epigenome, such as DNA methyltransferase and histone deacetylase inhibitors, as well as classical chemotherapeutic agents. Thus, retinoid research benefits both cancer prevention and cancer treatment.
2.1.3 Molecular pathways: current role and future directions of the retinoic acid pathway in cancer prevention and treatment.

Connolly RM1Nguyen NKSukumar S.
Clin Cancer Res. 2013 Apr 1; 19(7):1651-9
http://dx.doi.org:/10.1158/1078-0432.CCR-12-3175

Retinoids and their naturally metabolized and synthetic products (e.g., all-trans retinoic acid, 13-cis retinoic acid, bexarotene) induce differentiation in various cell types. Retinoids exert their actions mainly through binding to the nuclear retinoic acid receptors (α, β, γ), which are transcriptional and homeostatic regulators with functions that are often compromised early in neoplastic transformation. The retinoids have been investigated extensively for their use in cancer prevention and treatment. Success has been achieved with their use in the treatment of subtypes of leukemia harboring chromosomal translocations. Promising results have been observed in the breast cancer prevention setting, where fenretinide prevention trials have provided a strong rationale for further investigation in young women at high risk for breast cancer. Ongoing phase III randomized trials investigating retinoids in combination with chemotherapy in non-small cell lung cancer aim to definitively characterize the role of retinoids in this tumor type. The limited treatment success observed to date in the prevention and treatment of solid tumors may relate to the frequent epigenetic silencing of RARβ. Robust evaluation of RARβ and downstream genes may permit optimized use of retinoids in the solid tumor arena.

Vitamin A is derived from animal and plant food sources and has critical functions in many aspects of human biology. Its natural derivatives and metabolized products (retinoids) such as β-carotene, retinol, retinal, isotetrinoin, all-trans retinoic acid (ATRA), 9-cis retinoic acid, and 13-cis retinoic acid have important roles in cell differentiation, growth, and apoptosis (1). Synthetic retinoids are also available and include bexarotene and fenretinide. In clinical practice, retinoids have a wide range of dermatologic indications including for psoriasis, acneiform, and keratinization disorders (2). Systemic retinoids are approved by the U.S. Food and Drug Administration (FDA) for the treatment of cutaneous T-cell lymphoma (3) and acute promyelocytic leukemia (APL; refs. 4, 5). However, the chemopreventive and therapeutic effects of retinoids in solid tumors remain controversial. Therefore, an overview of the research to date and future directions in this area is the focus of this review.

Retinoic acid and the retinoic acid receptor pathway

Retinoic acids (RA) exert their functions through their specific receptors. The 2 distinct classes of receptors are retinoic acid receptors (RAR) and retinoic X receptors (RXR). Each class contains 3 different subtypes—α, β, and γ (6). ATRA and fenretinide can bind specifically to RARS, 13-cis RA and bexarotene only to RXRS, and 9-cis RA to RARS or RXRS (refs. 1, 5; Table 1). The expression of these receptors is regulated by the receptors themselves, other nuclear receptors such as ERα, or by other subtypes in the same family (5, 7). Upon the binding of ligands, RARs and RXRs form heterodimers and function as ligand-dependent transcription factors to activate their downstream effectors by binding to the retinoic acid response elements (RARE) located in the 5′-region of RA downstream genes (5). The above model of RAR or RXR function via binding to RARE is considered the RA classical or genomic pathway. Activation of the classical pathway will trigger cell differentiation, cell arrest, and eventual apoptosis (8).

Table 1. Select clinical trials evaluating retinoids in solid tumors

Retinoid Other names Target Clinical trial setting
ATRA Tretinoin RAR Advanced NSCLC Phase II randomized (n = 107)
13-cis RA Isotretinoin Roaccutane Accutane RXR Primary prevention: H+N cancer
Advanced solid tumorsPhase I (n = 13)
Metastatic breast cancer Phase II randomized (n = 99)
9-cis RA Alitretinoin RAR RXR Metastatic breast cancerPhase I (n = 12)
Fenretinide 4-OH Phenylretinamide RAR Primary prevention: women at high risk of breast cancer Randomized double-blind 2 × 2 design (n = 235)
Secondary prevention: early breast cancerPhase III randomized (n = 2,867)
Bexarotene RXR Chemotherapy-naïve advanced NSCLC Phase III randomized (n = 623)
Metastatic  breast cancer Phase II single arm (n = 148)

The function of RA and its receptors involves not only the classical pathway but also multiple other important pathways. RAs have been shown to regulate NF-κB (9), IFN-γ (10), TGF-β (11), VEGF (12), mitogen-activated protein kinase (MAPK; ref. 13), and chromatin remodeling (14). Furthermore, RARs and RXRs can form heterodimers with other types of receptors, including the estrogen receptor-α (ERα; refs. 7, 15), AP-1 receptor (16), peroxisome proliferator-activated receptor (PPAR; ref. 17), liver X receptors (LXR; refs. 18, 19), and vitamin D receptor (VDR; ref. 20; Fig. 1). When RARs/RXRs heterodimerize with these receptors, they are involved in regulating their partner receptor’s pathways, referred to as nonclassical or nongenomic pathways (5). Interestingly, these pathways often regulate processes that have functions opposite to the classical pathway. For example, a study has shown that RA activation of the PPARβ/δ pathway resulted in upregulation of prosurvival genes (17), contrary to the known differentiation function of RARs and RXRs in response to RA. The function of RAs, which involves nongenomic pathways, may provide opportunities for cancer cells to develop resistance to RA treatment, discussed later in this review. Another important function of RARA is the regulation of stem cell differentiation (11). RAs target stem cells via both genomic and nongenomic pathways such as the Notch pathway and inflammation (10, 11). In summary, RAs and their receptors play important roles as regulators of critical processes in cells.

RARs and their action

RARs and their action

The RARs and their action. In a series of enzymatic steps, vitamin A (retinol) is metabolized through the oxidizing action of retinaldehyde (RDH) to retinal, and by retinaldehyde dehydrogenase (RALDH), to RA. RA has 3 different isomers: all-trans, 9-cis, and 13-cis RA. RA is transported to the nucleus by the protein cellular RA–binding protein (CRABP) and delivered to the RARα. RARα heterodimerizes with and binds to RARE present most often in gene promoters. In the classical pathway of RA action, RA binds to dimers of RARα and RXRs (α, β, or γ) to induce expression of its downstream target genes, including RARβ. Upon activation, RARβ can regulate its own expression and that of its downstream genes, the function of which is mainly to inhibit cell growth. Alternatively, RA can be bound and transported to the nucleus by other factors such as FABP5. This delivers RA to other nonclassical receptors such as PPARβ/δ and ERα which activate nongenomic pathways such as PDK-1/Akt or the ERα pathway. Contrary to the differentiation functions attributed to the classical pathway, the nongenomic pathways exert strong antiapoptotic and proliferative effects on cancer cells. It is believed that the classical and nongenomic pathways are controlled by the relative abundance of their own ligands. RA has a stronger affinity for RARs than for the other receptors, and the classical pathway plays a dominant role over the nongenomic pathways. Thus, if RA is present with other ligands such as estrogen, signaling through the classical pathway is preferred to result in cell differentiation and growth inhibition.

http://clincancerres.aacrjournals.org/content/19/7/1651/F1.small.gif

Retinoids and cancer

The retinoids have been investigated extensively for the prevention and treatment of cancer, predominantly because of their ability to induce cellular differentiation and arrest proliferation. RA-regulated tumor suppressor genes, when expressed, can inhibit tumor growth (21). Among the 3 RARs, RARβ has been well known for its tumor-suppressive effects in epithelial cells (5822). Exogenous expression of the RARβ gene can cause RA-dependent and -independent apoptosis and growth arrest (23). RARβ-induced growth arrest and apoptosis is mediated through RARα (24). As RA ligand-bound RARα binds to the RARE on the RARβ promoter, multiple activator proteins assemble at the site and result in the upregulation of the RARβ gene (5). The expression of RARβ results in the transactivation and expression of a number of its target genes that mediate cell differentiation and death (5, 68). The ability of ATRA to initiate differentiation of promyelocytic leukemic cells to granulocytes is the basis of the dramatic success of retinoic acid therapy for acute promyelocytic leukemia harboring the RAR/PML translocation (4) and confirms the important role of RARβ in tumor growth inhibition. It is also becoming increasingly clear that RARβ expression is lost early in carcinogenesis or is epigenetically silenced (25) in many solid tumors, providing an opportunity for novel treatment strategies to be investigated using retinoids together with epigenetic modifiers that promote reexpression of silenced genes, described further below.

The retinoids have an established role in the treatment of certain hematologic malignancies, with FDA approval for use in cutaneous T-cell lymphoma and APL. Bexarotene (an RXR-selective retinoid or rexinoid) is associated with an overall response rate of approximately 50% in patients with refractory advanced-stage mycosis fungoides, a cutaneous T-cell lymphoma (3). ATRA, a synthetic retinoid, exhibited improvements in disease-free and overall survival when compared with chemotherapy alone in APL, with long-term remissions occurring in almost 70% of cases (4). The success of retinoids in treating this disease relates to the underlying chromosomal translocation and production of the PML/RARα fusion protein and the ability of retinoids to induce differentiation and inhibition of cell growth in this setting (26, 27). Clinical trials investigating the role of retinoids in the prevention and treatment of solid tumors will now be outlined with a focus on cancers of the upper aerodigestive tract (oropharyngeal and lung) and breast (Table 1).

2.1.4 Retinoid Pathway and Cancer Therapeutics

Nathan Bushue and Yu-Jui Yvonne Wan
Adv Drug Deliv Rev. 2010 Oct 30;  62(13): 1285–1298.
http://dx.doi.org/10.1016%2Fj.addr.2010.07.003

The retinoids are a class of compounds that are structurally related to vitamin A. Retinoic acid, which is the active metabolite of retinol, regulates a wide range of biological processes including development, differentiation, proliferation, and apoptosis. Retinoids exert their effects through a variety of binding proteins including cellular retinol binding protein (CRBP), retinol-binding proteins (RBP), cellular retinoic acid-binding protein (CRABP), and nuclear receptors i.e. retinoic acid receptor (RAR) and retinoid × receptor (RXR). Because of the pleiotropic effects of retinoids, understanding the function of these binding proteins and nuclear receptors assists us in developing compounds that have specific effects. This review summarizes our current understanding of how retinoids are processed and act with the emphasis on the application of retinoids in cancer treatment and prevention.

Vitamin A and its derivatives (retinoids) exert a wide range of effects on embryonic development, cell growth, differentiation, and apoptosis. Vitamin A has been used as a treatment for thousands of years. The Egyptian papyruses Kahun 1 (ca. 1825 B.C.) and Ebers (ca. 1500 B.C.) described how the liver was used to cure eye diseases such as night blindness. Greek scholar Hippocrates (460-327 B.C.) described in the second book of “Prognostics” a method for curing night blindness: “raw beef liver, as large as possible, soaked in honey, to be taken once or twice by mouth.” Chinese medicine used pigs’ liver as a remedy for night blindness, as described by Sun-szu-mo (7th century A.D.) in his “1000 Golden Remedies”. Given that the liver is where the body stores excess vitamin A, the liver represents the best source of vitamin A available for treatment in the pre-pharmaceutical world.

The effect of vitamin A on growth was first described in a mouse experiment done by G. Lunin (1881) [2], in which one group of mice was fed pure casein, fat, sucrose, minerals, and water, and another group was fed whole dried milk. The milk-fed group was healthy and grew normally, while the other group was sick and ultimately died. Thus, something in milk was essential for survival. Elmer McCollum at University of Wisconsin-Madison as well as Lafayette Mendel and Thomas Burr Osborne at Yale University independently discovered vitamin A. McCollum began his study in 1907 by feeding cows hay with wheat, oats, or yellow maize.

Wheat-fed cows did not thrive, became blind and gave birth to dead calves prematurely. Oat-fed cows fared somewhat better, but the yellow maize-fed cows were in excellent condition, produced vigorous calves, and had no miscarriages. McCollum postulated that performing the same nutritional study using small animals, such as rodents, which require less food, provide faster reproduction and experimental outcome. Using rats, he found a diet of pure protein, pure milk sugar, minerals, and lard (or olive oil) inhibited growth, while addition of butterfat or an ether extract of egg yolk to the diet restored health. Thinking that he had found a fat-soluble factor that promoted growth in rats, he saponified butterfat, extracted the unsaponifiable mixture into ether, and added the extract to oliveoil and that extract could support growth. This essential component to support growth and development was named “fat-soluble factor A,” and later renamed vitamin A [1].

There are over 4,000 natural and synthetic molecules structurally and/or functionally related to vitamin A. Vitamin A cannot be synthesized by any animal species and is only obtained through diet in the form of retinol, retinyl ester, or β-carotene (Figure 1). Ingested vitamin A is stored as retinyl esters in hepatic stellate cells. Retinol is reversibly oxidized by retinol dehydrogenases to yield retinal. Subsequently, retinal may be irreversibly oxidized to all-trans retinoic acid (all-trans RA) by retinal dehydrogenases and further oxidized by cytochrome P450 enzymes (mainly CYP26) in hepatic tissue. Retinol has six biologically active isoforms that include all-trans, 11-cis, 13-cis, 9, 13-di-cis, 9-cis, and 11, 13-di-cis, with all-trans being the predominant physiological form. Endogenous retinoids with biological activity include all-trans RA, 9-cis RA, 11-cis retinaldehyde, 3,4-didehydro RA, and perhaps 14-hydroxy-4, 14-retro retinol, 4-oxo RA, and 4-oxo retinol [35]. All-trans RA isomerizes under experimental and physiological conditions. Different isomers activate different receptors and thus lead to different biological effects. RAs designed to be receptor specific can improve efficacy and avoid unwanted side effects. Retinoids that specifically bind to RXR are called rexinoids and have been effective in cancer treatment. Retinoids are comprised of three units: a bulky hydrophobic region, a linker unit, and a polar terminus, which is usually a carboxylic acid. Modification of each unit has generated many more compounds. Please refer to recent reviews [68].

2.1.4.1 Retinoid Pathway 

Retinoid Pathway  nihms229611f1

Retinoid Pathway nihms229611f1

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2991380/bin/nihms229611f1.jpg

Retinoids absorbed from food are converted to retinol and bound to CRBP in the intestine. Then, retinol is converted to retinyl esters and enters into blood circulation. The liver up takes retinyl esters, which are converted to retinol-RBP complex in the hepatocyte. In the serum, the retinol-RBP complex is bound to transthyretin (TTR) in a 1:1 ratio to prevent elimination by the kidney and to ensure retinol is delivered to the target cell. The uptake of retinol by the target cell is mediated by a trans-membrane protein named “stimulated by retinoic acid 6” (STRA6), which is a RBP receptor. In the target cell, retinol either binds to CRBP or is oxidized to retinaldehyde by retinol dehydrogenase (RDH) in a reversible reaction. Then, retinaldehyde can be oxidized by retinaldehyde dehydrogenase (RALDH) to RA. In the target cell, RA either binds to CRABP or enters the nucleus and binds to nuclear receptors to regulate gene transcription. Alternatively, RA can mediate via nongenomic mechanism and regulate cellular function. Hepatocytes not only process retinoids, but also are the target cells. In addition, hepatocytes located next to the storage site (stellate cell). Thus, retinoid-mediated signaling must have a profound effect in regulating hepatocyte function and phenotype [36190191].

2.1.4.2 Retinoid Binding Proteins

There are various types of retinoid-binding proteins, which locate in intracellular and extracellular compartments and associate with isomeric forms of retinoids. Hence, retinoids are either associated with cellular membranes or bound to a specific retinoid binding protein. These binding proteins along with nuclear receptors mediate the action of retinoids. Their interactions are summarized in figure 1. Retinoid-binding proteins solubilize and stabilize retinoids in aqueous spaces. In addition to this general role, specific retinoid-binding proteins have distinct functions in regulating transport and metabolism of specific retinoids. For example, the parent vitamin A molecule, all-trans retinol, circulates in blood bound to serum retinol binding protein (RBP). Inside the cells, all-trans retinol and its oxidation product, all-trans retinal, are associated with different isoforms of cellular retinol-binding proteins (CRBP), while all-trans RA intracellularly binds to cellular retinoic acid-binding protein isoforms (CRABP).

2.1.4.3 RBP

Retinol is secreted from its storage pools and circulates in blood by binding to RBP. The main storage site for vitamin A and the main site of synthesis of RBP is the liver, although other tissues (including adipose tissue, kidney, lung, heart, skeletal muscle, spleen, eye and testis) also express this protein. Secretion of RBP from the liver is regulated by the availability of retinol [9]. Vitamin A deficiency inhibits RBP secretion, leading to protein accumulation in the endoplasmic reticulum of hepatic parenchymal cells. In the presence of retinol, RBP associates with retinol, moves to the Golgi apparatus and is secreted into blood. The mechanism by which retinol initiates RBP secretion from cells is not known. In blood, RBP is bound to the small protein transthyretin, which in addition to associating with RBP functions as a carrier protein for thyroid hormones. Binding of RBP to transthyretin prevents the loss of this smaller protein by filtration in the renal glomeruli. The transthyretin-RBP-retinol complex transports retinol in the circulation and delivers it to target tissues [10].

Important insights into the biological role of RBP have been obtained by studies of mice and humans in which the RBP gene is disrupted. RBP-deficient mice display both reduced blood retinol levels and impaired visual function during the first months of life. When maintained on a vitamin A-sufficient diet, they acquire normal vision by 5 months of age, even though their blood retinol level remains low. A striking phenotype of the RBP-null mice is that they possess larger than normal hepatic vitamin A storage, but are dependent on a continuous dietary intake of vitamin A [11], further proving the importance of RBP as a transporting protein. A study of two human siblings that harbored point mutations in their RBP gene and exhibited undetectable plasma RBP levels revealed that these sisters suffered from night blindness and mild retinal dystrophy but did not exhibit other clinical symptoms of vitamin A deficiency [12]. Taken together, RBP is critical for the mobilization of retinol from hepatic storage pools; however, RBP is not essential for the delivery of retinol to target tissues. Supply of vitamin A to target tissues in the absence of RBP is likely to be accomplished via newly absorbed retinyl esters or β-carotene present in circulating chylomicrons. Increased RBP has been shown to contribute to insulin resistance and type 2 diabetes [11]. All-trans RA has recently been shown to increase insulin sensitivity in diabetic mice while lowering RBP [13]. The effect on binding proteins must be considered when retinoids are used for disease treatment.

2.1.4.4 SRA6

The stimulated by retinoic acid gene 6 (STRA6) encodes the cell surface RBP receptor, which binds specifically to RBP and mediates retinol uptake from holo-RBP [14]. STRA6 is a widely expressed transmembrane protein. In mouse mammary epithelial cells, STRA6 expression can be up regulated by Wnt1 and retinoids. In addition, STRA6 mRNA levels are up regulated in mouse mammary gland tumors and human colorectal tumors [15]. Importantly, while the RBP-null mice and humans give rise to relative mild phenotypes, STRA6-null mice develop anophthalmia, congenital heart defects, diaphragmatic hernias, alveolar capillary dysplasia, lung hypoplasia, and mental retardation. These findings suggest that STRA6 may have additional functions that are not related to RBP transport [16].

2.1.4.5 CRBP

CRBPs belong to the family of fatty acid binding proteins in which expression of CRBP family members are tissue specific. For example, CRBP-II is expressed only in the enterocytes of the intestine, while CRBP-I and -III are expressed throughout embryonic and adult tissues [17]. Knockout studies for CRBP isoforms have identified differences in function due to altered tissue localization. CRBP-I knockout mice are healthy. However, they have low levels of hepatic retinyl esters [18], and their hepatic lipid droplets appear to be smaller and less abundant than in wild type littermates. CRBP-II-null mice have impaired retinol uptake, but they develop and reproduce normally under vitamin A-enriched diet, albeit with reduced retinol storage [19]. Reduction of vitamin A in the maternal diet of CRBP-II-null mice during gestation results in neonatal mortality immediately following birth [19]. CRBP-III null mice have impaired vitamin A incorporation into milk, but they are otherwise healthy [20]. CRBP-I and CRBP-III compensate for each other to maintain normal retinoid homeostasis, but the compensation is incomplete during lactation [20]. The binding affinity of CRBP-I towards retinol is about 100-fold higher than that of CRBP-II. They display a similar binding affinity towards retinal and CRBP-II associates with retinol and retinal with similar affinities. CRBPs, and especially CRBP-I with its high affinity for retinol, may sequester retinol from its ability to disrupt cell membranes. Epigenetic silencing of CRBP is a common event in human cancers [21]. Silencing CRBP reduces the availability of retinyl esters in the bloodstream and decreases the body’s ability to metabolize retinol [22].

2.1.4.6 CRABP

CRABP-I and -II have been identified with a high affinity for all-trans RA. In humans, these isoforms display 74 percent sequence identity and are highly conserved among species; however, these CRABP isoforms display different patterns of expression across cells and developmental stages. In adults, CRABP-I is expressed ubiquitously, while CRABP-II is only expressed in the skin, uterus, ovary, and the choroid plexus. Both CRABPs are widely expressed in the embryo, although they do not usually co-exist in the same cells. The biological functions of CRABPs are not completely understood. In mouse knockout stu dies, disruption of either CRABP-I or -II only display mild defects in limb development [23], which suggests CRABPs may be involved in generation of appropriate RA concentration gradients in the developing limb bud. Both CRABP isoforms are present in cytosol and nucleus and thus may deliver the ligand directly to the nuclear receptor. The differential role of these two binding proteins remains to be studied (reviewed in [24] and [25]). Increased CRABP-I expression may also contribute to RA resistance of cancer cells [26]. The effect of CRABP on cancer therapy deserves more attention.

2.1.4.7 Retinoic Acid Receptors

The major breakthrough in understanding RA’s function occurred upon identifying and cloning the receptors for RA [2728]. RA regulates gene expression by binding to its nuclear receptors, which in turn activates transcription of their downstream target genes. Thus, retinoids exert their biological functions primarily by regulating gene expression. This was predicted by Sporn and Roberts in 1983, when they wrote: “Ultimately, it would appear that the problem of the molecular mechanism of action of retinoids in control of differentiation and carcinogenesis is converging on one of the central problems of all biology, the control of gene expression.” [29]

2.1.4.8 RAR and RXR

Two distinct classes of receptors for retinoids have been identified: retinoic acid receptors (RAR) and retinoid × receptors (RXR). Each class of receptor contains three subtypes – α, β, and γ. RARs can be activated by both all-trans and 9-cis-RA, while, RXRs are exclusively activated by 9-cis RA. However, due to the conversion of all-trans to 9-cis RA, high concentrations (10−5 M) of all-trans RA can also activate gene transcription in cells transfected with RXRs [30].

RXRs can form homo- and heterodimers with other receptors. In fact, RXRs are promiscuous receptors forming heterodimers with many different kinds of receptors, which include receptors for fatty acids [peroxisomal proliferator activated receptors (PPAR)], bile acids [farnesoid × receptor (FXR)], oxysterols [liver × receptor (LXR)], xenobiotics [pregnane × receptor (PXR) and constitutive androstane receptor (CAR)], vitamin D [vitamin D receptor (VDR)], and RA (RAR). RXRs can also form homodimers. Hypervitaminosis A leads to bone fracture suggesting that vitamin A and D compete for the same receptor [31]. Within these heterodimers, RXRs can exist as both active and silent partners. When it serves as an active partner, 9-cis RA and the ligand for the heterodimeric partner can activate the heterodimer, and addition both ligands give synergistic induction in gene transcription. For example, RXR is an active partner for PPAR. Similarly, heterodimeric complexes of RXR with LXR or FXR also retain 9-cis RA responsiveness. Thus, RAs can regulate PPAR- and FXR-mediated pathways [32]. Recently, we demonstrated that RAs could also activate PXR-, VDR, and CAR-mediated signaling and thus regulated xenobiotic metabolism and potentially its own oxidation [3335]. When RXR serves as a silent partner, the heterodimer of RXR and its partner does not respond to RA. Regardless of their active or silent role, RXRs must be present in order to exert biological actions of various nuclear receptors. Using hepatocyte RXRα-deficient mice [3637], we have demonstrated that RXRα does play vital roles in xenobiotic (alcohol, acetaminophen) and endobiotic (fatty acid, cholesterol, amino acid, and carbohydrate) metabolism [3340]. Thus, RXR functions as an auxiliary factor and determines the effects of other hormones, making RXR a master regulator. The structure of nuclear receptors is summarized in recent review articles [738].

Existing data suggest that the binding protein and receptor work together to exert the specific effect of RAs. For example, RAs can bind to both PPARβ, the receptor for fatty acids, and RAR. Fatty acid-binding protein 5 (FABP5) and CRABP-II are specific binding proteins that channel RAs from the cytosol into the nucleus for binding to either PPARβ or RAR, respectively [39]. The ratio of FABP5/CRABP-II concentrations determines which receptor is activated. By activating PPARβ, RAs induce expression of genes affecting lipid and glucose homeostasis, such as the insulin-signaling gene pyruvate dehydrogenase kinase 1 (PDK1), which enhances insulin action. Hence, RAs stimulate lipolysis and reduce triglyceride content. RA implantation into obese mice causes up regulation of PPARβ as well as an increased expression of PPARβ target genes, including PDK1, which led to weight loss [40].

2.1.4.9 Retinoids and Cancer

Retinoids are widely used to treat visual and dermatological diseases. Their effect on cancer prevention and treatment has received a lot of attention. This review focuses on the action of retinoids on cancer. Retinoids have been used as potential chemotherapeutic or chemopreventive agents because of their differentiation, anti-proliferative, pro-apoptotic, and anti-oxidant effects. Epidemiological studies show that lower vitamin A intake results in a higher risk of developing cancer, which aligns with observations of vitamin A-deficient animals [61]. Altered expression of RA receptors is also associated with malignant transformation of animal tissues or cultured cells. Furthermore, retinoids suppress carcinogenesis in tumorigenic animal models for skin, oral, lung, breast, bladder, ovarian, and prostate [6268]. In humans, retinoids reverse premalignant human epithelial lesions, induce the differentiation of myeloid cells, and prevent lung, liver, and breast cancer [6973].

The following is a summary of how major retinoids may work in cancer treatment or prevention.

2.1.4.9.1 All-trans RA (tretinoin)

All-trans RA is the most abundant natural retinoid and has been widely studied for many years. It is currently in clinical trials for the treatment of lymphoma, leukemia, melanoma, lung cancer, cervical cancer, kidney cancer, neuroblastoma, and glioblastoma. The most effective clinical usage of all-trans RA in human disease was demonstrated in treatment of a rare leukemia, acute promyelocytic leukemia (APL). APL is characterized by selected expansion of immature myeloid precursors or malignant myeloid cells blocked at the promyelocytic stage of hemopoietic development. APL cells invariably express aberrant fusion proteins involving the DNA and ligand binding domain of RARα [7475]. Other fusion partners include the promyelocytic leukemia zinc finger gene, the nucleophosmin gene, the nuclear mitotic apparatus gene, and the Stat5b gene, while the most common fusion partner is promyelocytic leukemia protein (PML). The PML-RARα chimeric receptor is created by a balanced reciprocal chromosomal translocation, t(15;17)(q22:q11). The expressed PML-RARα chimeric receptor alters normal function of RARs. PML-RARα can form a homodimer through the coiled-coil motif of PML, inhibiting RARα’s ability to bind to RA responsive elements, thereby preventing activation of downstream target genes [7677]. In addition, RXR is an essential component of the oncogenic PML/RARα complex suggesting RXR can be a drug target for APL [7879]. In 1995, the FDA approved all-trans RA for treating APL. The all-trans RA-induced differentiation of APL cells is due to both its ability to promote the degradation of the mutant PML-RARα and the dissociation of its co-repressors [80]. All-trans RA also causes cell cycle arrest at G1 phase and inhibits cell proliferation [81]. In addition, high concentration of all-trans RA induces post-maturation apoptosis of APL-blasts through the induction of the tumor-selective death ligand tumor necrosis factor-related apoptosis-inducing ligand TRAIL [82].

RA syndrome is a life-threatening complication seen in APL patients treated with all-trans RA. This syndrome is characterized by dyspnea, fever, weight gain, hypotension, and pulmonary infiltrates. It can be effectively treated by giving dexamethasone and holding off all-trans RA treatment in severe cases. An elevated white count is sometimes associated with this syndrome, but is not a prerequisite. The etiology of RA syndrome is not clear; several causes have been speculated including a capillary leak syndrome from cytokine release from the differentiating myeloid cells. Alternatively, all-trans RA may cause the maturing myeloid cells to acquire the ability to infiltrate organs such as the lung [83].

2.1.4.9.2. 9-cis RA (alitretinoin)

9-cis RA differentiates itself from all-trans RA in its ability to activate both RAR and RXR. In addition, 9-cis RA activates PPAR, FXR, PXR, VDR, and CAR via RXR. In preclinical studies, 9-cis RA is effective in the prevention of mammary and prostate cancer [8485] and it has also been FDA-approved for the topical treatment of cutaneous lesions of Kaposi’s sarcoma [86]. In addition, 9-cis RA and all-trans RA can individually induce apoptosis of human liver cancer cells [87]. 9-cis RA not only regulates nuclear genes, but also mitochondria gene transcription [88].

2.1.4.9.3. 13-cis RA (isotretinoin)

13-cis RA is unique that it exhibits immunomodulatory and anti-inflammatory responses. It inhibits ornithine decarboxylase, thereby decreasing polyamine synthesis and keratinization [89]. 13-cis RA noticeably reduces the production of sebum and shrinks the sebaceous glands [90]. It stabilizes keratinization and prevents comedones formation [9192]. The exact mechanism of action is unknown. This combination of regulating proliferation, differentiation, and inflammation could make 13-cis RA a more effective drug in comparison to other retinoids, which may cause inflammation and irritation [93].

13-cis RA is in clinical trial for different types of cancers, and thyroid cancer received a lot of attention. In follicular thyroid cancer cells, 13-cis RA induces radioiodine avidity of cells formerly unable to accumulate radioiodine [94]. In human thyroid carcinoma cell lines, retinoids induce the expression of type I iodothyronine-5′-deiodinase and sodium/iodide-symporter, which are the thyroid differentiation markers [95]. However, approximately 30% of thyroid tumors dedifferentiate after treatment and thus develop into highly malignant anaplastic thyroid carcinomas [96]. 13-cis RA is also used to treat non-operable thyroid follicular tumors, which fail to uptake radioiodine. 13-cis RA increases the radioiodide uptake in some patients. The beneficial outcome of this treatment was interpreted as partial re-differentiation of thyroid cancer cells. This effect of 13-cis RA requires the existence of functional RXR [96]. The effect of 13-cis RA on thyroid cancer has been reviewed extensively [97]. Besides thyroid cancer, utilizing 13-cis RA for maintenance therapy has significantly improved the outcome of patients with a high-risk form of neuroblastoma [98]. Along the same line of work, Krüppel zinc-finger protein ZNF423 is critical for RA signaling and is likely a prognostic marker for neuroblastoma [99]. 13-cis RA is also effective in preventing head and neck cancer, which is discussed below.

2.1.4.9.4. Synthetic Retinoids

N-(4-hydroxyphenyl) retinamide (Fenretinide or 4HPR) was first synthesized in the late 1960s by R. W. Pharmaceuticals. Since then, the biological properties of fenretinide have been of great interest. Currently, fenretinide is one of the most promising clinically tested retinoids. The modification of the carboxyl end of all-trans RA with an N-4-hydroxyphenyl group resulted in increased efficacy as a chemoprevention agent as well as reduced toxicity when compared with other retinoids [100]. Animal models have demonstrated that treatment with fenretinide prevents chemically induced cancers of the breast, prostate, bladder, and skin [101104]. Furthermore, the combination of tamoxifen with fenretinide produces efficacy greater than either chemical alone [105].

Natural retinoids like all-trans RA induce differentiation and/or cytostasis in target cells [106108], while fenretinide has distinct biologic effects including the induction of apoptosis by generating reactive oxygen species (ROS) and lipid second messengers [104]. The apoptotic effect of fenretinide has been documented in a variety of cancer cells including transformed T cells, B cells and breast epithelial cells, as well as bladder, breast, cervical, colon, embryonal, esophageal, head and neck, lung, ovarian, pancreatic, prostate, and skin carcinomas [100]. Furthermore, fenretinide does not induce point mutations or chromosomal aberrations, and is therefore not genotoxic [109]. These qualities suggest that fenretinide could be used for a long-term chemopreventive modality. In animal models, fenretinide has demonstrated chemopreventive efficacy against carcinogenesis of the breast [110], prostate, pancreas, and skin [104111112]. Moreover, in a clinical setting, fenretinide slowed the progression of prostate cancer in men diagnosed with an early stage of the disease [113]. Fenretinide protected against the development of ovarian cancer and a second breast malignancy in premenopausal women who had been treated to prevent the progression of early-stage breast cancer [114]. It also prevented relapse and the formation of secondary primary lesions in patients following the surgical removal of oral leukoplakia [115]. Recent studies also illustrated the anti-angiogenic [116] and anti-fibrotic [117] effect of fenretinide. Furthermore, long-term fenretinide treatment prevents high-fat diet-induced obesity, insulin resistance, and hepatic steatosis [118].

The mechanisms associated with fenretinide-induced apoptosis have been explored, but are not well-understood [100]. The components that lead to ROS generation and cause cell death are largely unknown. Depending on cell types and models used, the effect of fenretinide has been shown to be RARβ-dependent or -independent [119]. Our data showed that fenretinide-induced apoptosis of human liver cancer cells was RARβ-dependent [120]. Furthermore, induction and cytoplasmic localization of Nur77 dictates the sensitivity of liver cancer cell to fenretinide-induced apoptosis [121]. It seems that fenretinide enriches the cytoplasmic Nur77 to target mitochondria and induce cell death. The relationship between RARβ and Nur77 in mediating fenretinide-induced apoptosis remains to be determined.

A retinoid-related molecule 6-[3-(1-adamantyl)-4-hydroxyphenyl]-2-naphthalenecar-boxylic acid (AHPN) (also called CD437) and it’s analog (E)-4-[3-(1-adamantyl)-4-hydroxyphenyl]-3-chlorocinnamic acid (3-Cl-AHPC) also have Nur77-dependent apoptotic effects [122124]. AHPN is structurally distinct from fenretinide. AHPN-induced apoptosis activates JNK [125127], which is required for maximal apoptosis induction and precedes mitochondrial depolarization. Induction of apoptosis of breast and prostate cancer cells by AHPN is also associated with its inhibition of Akt activity [128]. Thus, induction of JNK and inhibition of Akt phosphorylation of Nur77 contribute to Nur77 nuclear export mediated by AHPN [129].

While many synthesized RAs are promising for cancer treatment, only a few are FDA-approved or currently undergoing clinical trials for cancer therapy. A number of retinoids, which have been FDA-approved for dermatological purposes, have potential for cancer treatment. Bexarotene (Targretin) is a synthetic retinoid approved by the FDA to treat skin problems caused by cutaneous T-cell lymphoma that are unresponsive to other treatments [130]. Other synthetic retinoids, such as TAC-101 (Taiho Pharmaceutical, Tokyo, Japan) has shown efficacy in inhibiting tumor growth in the liver and markedly increases survival in both the primary HCC and metastatic colon cancer models [131]. TAC-101 is currently in phase II trial for hepatocellular carcinoma and has shown good preliminary success [132]. Another, Tazarotene (AVAGE) (Allergan, Irvine, CA) is in phase I trials for the treatment of lymphoma [133]. Please see table 1 for a brief characterization of some of retinoids that are in use or in clinical trials.

3  Vitamin C

3.1 American Cancer Society

http://www.cancer.org/treatment/treatmentsandsideeffects/complementaryandalternativemedicine/herbsvitaminsandminerals/vitamin-c

Vitamin C is an essential vitamin the human body needs to function well. It is a water-soluble vitamin that cannot be made by the body, and must be obtained from foods or other sources. Vitamin C is found in abundance in citrus fruits such as oranges, grapefruit, and lemons, and in green leafy vegetables, tomatoes, potatoes, strawberries, red or green peppers, and cantaloupe.

Vitamin C is found in many vegetables and fruits, especially oranges, grapefruits, and peppers. Many studies have shown a link between eating foods rich in vitamin C, such as fruits and vegetables, and a reduced risk of cancer. On the other hand, the few studies in which vitamin C has been given as a supplement have not shown a reduced cancer risk.

This suggests that the activity of fruits and vegetables in preventing cancer is due to a combination of many things such as vitamins, fiber, and other phytochemicals and not to vitamin C alone (see Phytochemicals). Clinical trials of high doses vitamin C as a treatment for cancer have not shown any benefit. High doses of vitamin C can cause side effects in some people.

3.2 Intravenous vitamin C for cancer

Oct 4, 2013 | By Dr. Ronald Hoffman

For more than 20 years, the Hoffman Center has been using high-dose vitamin C drips in its cancer support protocols. The initial impetus was from Linus Pauling who, together with Ewan Cameron, pioneered the use of high-dose C in cancer in the 1960s.

Now, there’s new interest in this modality for fighting cancer based on new, exciting research under way at the National Institutes of Health.

Cameron and Pauling found that vitamin C helped cancer patients live about four times longer than cancer patients not given vitamin C. They administered high-dose vitamin C in the form of sodium ascorbate given orally and intravenously to treat more than 1,000 cancer patients.

Nonetheless, vitamin C for cancer suffered a setback when Dr. Charles Moertel of the Mayo Clinic, an arch foe of nutritional therapies for cancer, sought to disprove Pauling’s thesis. But he did not follow the Pauling/Cameron instructions or regimen.

Moertel selected a cohort of terminal colon cancer patients who had not responded to all forms of conventional treatment, including surgery, chemo and radiation, and administered 10 grams of vitamin C to them orally. When the patients failed to demonstrate improved survival over patients not receiving vitamin C in the study, Moertel pronounced the vitamin C/cancer hypothesis defunct.

Moertel failed to note that the benefits achieved by Pauling and Cameron’s patients were obtained via both IV and oral C. He ultimately succumbed to cancer himself years later.

Alternative practitioners, meanwhile, sought to resurrect IV vitamin C as a tool in the treatment of cancer, but not until recently has serious academic research resumed.

Dr. Hugh Riordan of Kansas treated hundreds of cancer patients with doses of vitamin C up to 200,000 mg (200 grams) per day in infusions lasting 4-12 hours several times a week. He compiled a series of case histories documenting impressive responses but passed recently, before his work was generally acknowledged.

His protegee, Dr. Jeanne Drisko, Director, KU Integrative Medicine, has undertaken a series of clinical trials to validate the benefits of IV vitamin C in cancer. An FDA approved trial is now underway.

Research at the National Institutes of Health is beginning to suggest that vitamin C deserves another chance to find its niche in the arsenal of anti-cancer therapies. Studies now suggest that even high dose vitamin C given by mouth is poorly absorbed. Blood levels “max out” at doses of 500 mg given several times during the day.

But vitamin C given intravenously is another story. When delivered in a “drip,” much higher concentrations of C can be attained. At these higher concentrations, vitamin C has different characteristics than if given orally. While oral vitamin C boosts immunity and assists tissue repair, it is too weak to do much to kill or inhibit cancer cells. But at high doses delivered directly into the bloodstream, it may act to increase levels of hydrogen peroxide deep in the tissues where cancer cells lurk. Peroxide-mediated killing is one of the white blood cells’ key mechanisms for fighting infection and cancer.

Research currently under way has shown that high concentrations of vitamin C can stop the growth or even kill a wide range of cancer cells. Only intravenous administration of vitamin C can deliver the high doses found to be effective against cancer.

IV vitamin C, when administered by a trained, experienced physician, is safe and well-tolerated, even at doses as high as 100,000 mg (100 grams) per day. Proper blood tests must be done to ensure that it is well-tolerated, and the patient must be monitored. Doses must be gradually adjusted upward. Not all patients are candidates for IV vitamin C. Vitamin C can be safely administered even while patients are undergoing chemo and radiation; in fact, the FDA-approved trial at the University of Kansas Medical Center explicitly permits the co-administration of vitamin C with conventional treatments.

3.3 IV Vitamin C Kills Cancer Cells

by Dr. Julian Whitaker

By now, most people know that vitamin C is a potent antioxidant that has the power to boost immune function, increase resistance to infection, and protect against a wide range of diseases.

But there’s an entirely different and largely unknown role of vitamin C, and that is its ability—when administered in very high doses by intravenous (IV) infusions—to kill cancer cells.

Vitamin C interacts with iron and other metals to create hydrogen peroxide. In high concentrations, hydrogen peroxide damages the DNA and mitochondria of cancer cells, shuts down their energy supply, and kills them outright. Best of all—and unlike virtually all conventional chemotherapy drugs that destroy cancer cells—it is selectively toxic. No matter how high the concentration, vitamin C does not harm healthy cells.

Lab studies reveal that this therapy is effective against many types of cancer, including lung, brain, colon, breast, pancreatic, and ovarian. Animal studies show that when human cancers are grafted into animals, high-dose IV vitamin C decreases tumor size by 41 to 53 percent “in diverse cancer types known for both their aggressive growth and limited treatment options.” Additionally, numerous patient case reports have been written up in medical journals.

Why IV Administration Is Essential

The only way to get blood levels of vitamin C to the concentrations required to kill cancer cells is to administer it intravenously. The body tightly controls levels of this vitamin by limiting intestinal absorption. If you took 10 g (10,000 mg) of vitamin C by mouth at one time, you would only absorb around 500 mg—and you’d get a serious case of diarrhea!

Intravenous administration, however, bypasses this control mechanism, and blood levels rise in a dose-dependent manner. For example, 10 g of IV vitamin C raises blood levels 25 times higher than the same dose taken orally, and this increases up to 70-fold as doses get larger.

4 Expert Q&A: Vitamin D and Cancer Risk

http://www.cancer.net/navigating-cancer-care/prevention-and-healthy-living/diet-and-nutrition/expert-qa-vitamin-d-and-cancer-risk

Vitamin D is one of several nutrients that the body needs to stay healthy. It may also play a role in reducing the risk of cancer, and several research studies are exploring this link. Cancer.Net talked with Richard Goldberg, MD, to learn more about current research on vitamin D and what people should know.

Q: What is the role of vitamin D in the body, and what are some sources of this vitamin?

A: One role of vitamin D is to regulate the absorption of calcium by the body. Calcium is the main component of bones and is important in the function of all cells in the body, particularly the heart. People who are vitamin D deficient (don’t get enough) can have weakened bones (a condition called osteoporosis in adults and rickets or osteomalacia in children). Too little calcium (called hypocalcemia) in the body can lead to irregular heartbeat and muscle spasms.

Milk, fish, eggs, and fortified cereals and orange juice are good sources of vitamin D. Milk manufactured in the United States is generally fortified with vitamin D as a way to prevent deficiencies from occurring. Supplemental vitamins are also a source.

Unlike other vitamins that the body cannot produce by itself, vitamin D can either be absorbed directly from the intestine or made from compounds in foods. The body can make vitamin D from nutrients related to cholesterol. These nutrients are then converted to vitamin D as they circulate in the blood when a person’s skin is exposed to sunlight.

Too much vitamin D can also be bad for a person, leading to drowsiness, kidney stones, bone or muscle weakness, and elevated blood calcium, a condition called hypercalcemia that can cause confusion and, in extreme cases, death.

Q: When getting vitamin D from sunlight, how long should a person be exposed to the sun? What are the risks of too much sun exposure?

A: While 90% of the body’s vitamin D comes from exposure to sun (in the absence of vitamin D supplements), the amount of sun exposure needed to produce adequate vitamin D levels is actually quite limited. Sun exposure at the equator is far more intense than in such northern cities as Boston or London, for instance, and is more intense anywhere in summer than in winter. However, it takes only five to ten minutes of exposing the hands and face three times a week to receive adequate sun exposure in the summer in Boston. Exposure of more skin, such as when wearing a bathing suit, requires only a very short time in the sun. Use of sunblock is very important when sun exposure is longer than that to prevent skin cancer, including melanoma, and other sun-induced damage such as wrinkling and pigmentation changes (sunspots). Learn more about protecting your skin from the sun.

Q: How might vitamin D work to help lower the risk of cancer?

A: Laboratory studies have shown that vitamin D deficiency can lead to decreased communication between cells and leads them to stop sticking to one another, a condition that could cause cancer cells to spread. Compared with normal cells, cancer cells remain in an immature state, and vitamin D appears to have a role in making cells mature. Vitamin D also appears to play a role in regulating cellular reproduction, which malfunctions (doesn’t work properly) in cancer. Higher levels of vitamin D lead to cellular adherence, maturation, and communication between cells, all of which may lower cancer risk.

Q: What does research show about vitamin D levels and cancer?

A: Studies in populations have shown that low vitamin D levels are a risk factor for cancer in general, and particularly for prostatecolorectal, and breast cancers.

There are also data that correlate high blood levels of vitamin D with a reduced risk of breast and colorectal cancers. These levels can best be achieved by taking supplemental vitamin D. In colorectal cancer, calcium supplementation may also reduce the risk of polyps (noncancerous growths that may develop on the inner wall of the colon and rectum) and cancer. Numerous studies have tested cancer risk by giving patients supplemental vitamin D, with or without calcium supplementation. While the results are somewhat variable, substantial reduction (on the order of 50%) in the odds of breast and colon cancers with supplementation, have been noted in some studies. People with a personal history of these types of cancer and their relatives may wish to discuss supplementation with their doctors.

5 Magnesium and Cancer Research

5.1  Dr Sircus on Mar 18, 2010
http://drsircus.com/medicine/magnesium/magnesium-and-cancer

Aleksandrowicz et al in Poland conclude that inadequacy of magnesium and antioxidants are important risk factors in predisposing to leukemias.[2] Other researchers found that 46% of the patients admitted to an ICU in a tertiary cancer center presented hypomagnesemia. They concluded that the incidence of hypomagnesemia in critically ill cancer patients is high.[3]In animal studies we find that magnesium deficiency has caused lymphopoietic neoplasms in young rats. A study of rats surviving magnesium deficiency sufficient to cause death in convulsions during early infancy in some, and cardiorenal lesions weeks later in others, disclosed that some of survivors had thymic nodules or lymphosarcoma.[4]

One would not normally think that Magnesium (Mg) deficiency can paradoxically increase the risk of, or protect against cancer yet we will find that just as severe dehydration or asphyxiation can cause death magnesium deficiency can directly lead to cancer. When you consider that over 300 enzymes and ion transport require magnesium and that its role in fatty acid and phospholipids acid metabolism affects permeability and stability of membranes, we can see that magnesium deficiency would lead to physiological decline in cells setting the stage for cancer. Anything that weakens cell physiology will lead to the infections that surround and penetrate tumor tissues. These infections are proving to be an integral part of cancer. Magnesium deficiency poses a direct threat to the health of our cells. Without sufficient amounts our cells calcify and rot. Breeding grounds for yeast and fungi colonies they become, invaders all too ready to strangle our life force and kill us.

Over 300 different enzymes systems rely upon magnesium to facilitate their catalytic action, including ATP metabolism, creatine-kinase activation, adenylate-cyclase, and sodium-potassium-ATPase.[5]

It is known that carcinogenesis induces magnesium distribution disturbances, which cause magnesium mobilization through blood cells and magnesium depletion in non-neoplastic tissues. Magnesium deficiency seems to be carcinogenic, and in case of solid tumors, a high level of supplemented magnesium inhibits carcinogenesis.[6] Both carcinogenesis and magnesium deficiency increase the plasma membrane permeability and fluidity. Scientists have in fact found out that there is much less Mg++ binding to membrane phospholipids of cancer cells, than to normal cell membranes.[7]

Magnesium protects cells from aluminum, mercury, lead, cadmium, beryllium and nickel.

Magnesium in general is essential for the survival of our cells but takes on further importance in the age of toxicity where our bodies are being bombarded on a daily basis with heavy metals.Glutathione requires magnesium for its synthesis.[8] Glutathione synthetase requires ?-glutamyl cysteine, glycine, ATP, and magnesium ions to form glutathione.[9] In magnesium deficiency, the enzyme y-glutamyl transpeptidase is lowered.[10] According to Dr. Russell Blaylock, low magnesium is associated with dramatic increases in free radical generation as well as glutathione depletion and this is vital since glutathione is one of the few antioxidant molecules known to neutralize mercury.[11]Without the cleaning and chelating work of glutathione (magnesium) cells begin to decay as cellular filth and heavy metals accumulates; excellent environments to attract deadly infection/cancer.

There is drastic change in ionic flux from the outer and inner cell membranes both in the impaired membranes of cancer, and in Mg deficiency.

Anghileri et al[12],[13] proposed that modifications of cell membranes are principal triggering factors in cell transformation leading to cancer. Using cells from induced cancers, they found that there is much less magnesium binding to membrane phospholipids of cancer cells, than to normal cell membranes.[14] It has been suggested that Mg deficiency may trigger carcinogenesis by increasing membrane permeability.[15] Magnesium deficient cells membranes seem to have a smoother surface than normal, and decreased membrane viscosity, analogous to changes in human leukemia cells.[16],[17] There is drastic change in ionic flux from the outer and inner cell membranes (higher Ca and Na; lower Mg and K levels), both in the impaired membranes of cancer, and of Mg deficiency. And we find that lead (Pb) salts, are more leukemogenic when given to Mg deficient rats, than when they are given to Mg-adequate rats, suggesting that Mg is protective.[18]

Magnesium has an effect on a variety of cell membranes through a process involving calcium channels and ion transport mechanisms. Magnesium is responsible for the maintenance of the trans-membrane gradients of sodium and potassium.

Long ago researchers postulated that magnesium supplementation of those who are Mg deficient, like chronic alcoholics, might decrease emergence of malignancies[19] and now modern researchers have found that all types of alcohol — wine, beer or liquor — add equally to the risk of developing breast cancer in women. The researchers, led by Dr. Arthur Klatsky of the Kaiser Permanente Medical Care Program in Oakland, Calif., revealed their findings at a meeting of the European Cancer Organization in Barcelona in late 2007. It was found that women who had one or two drinks a day increased their risk of developing breast cancer by 10 percent. Women who had more than three drinks a day raised their risk by 30 percent. The more one drinks the more one drives down magnesium levels.

Breast cancer is the second most common cancer killer of women, after lung cancer. It will be diagnosed in 1.2 million people globally this year and will kill 500,000.

According to data published in the British Journal of Cancer in 2002, 4 percent of all breast cancers — about 44,000 cases a year — in the United Kingdom are due to alcohol consumption. It’s an important question though, and one not asked by medical or health officials, is it the alcohol itself or the resultant drop in magnesium levels that is cancer provoking? Though some studies have shown that light- to moderate alcohol use can protect against heart attacks it does us no good to drink if it causes cancer. Perhaps if magnesium was supplemented in women drinkers who were studied there would have been no increase of cancer from drinking.

Alcohol has always been known to deplete magnesium, and is one of the first supplements given to alcoholics when they stop and attempt to detoxify and withdraw.

Researchers from the School of Public Health at the University of Minnesota have just concluded thatdiets rich in magnesium reduced the occurrence of colon cancer.[20] A previous study from Sweden[21] reported that women with the highest magnesium intake had a 40 per cent lower risk of developing the cancer than those with the lowest intake of the mineral.

Magnesium stabilizes ATP[22], allowing DNA and RNA transcriptions and repairs.[23]

The anti-colon cancer effects of calcium are linked to magnesium levels, says a new study. Researchers from Vanderbilt University found that low ratios of the minerals were associated with reduced risk of colorectal cancer, according to findings presented at the Seventh Annual American Association for Cancer Research International Conference on Frontiers in Cancer Prevention Research. Both high magnesium and calcium levels have been linked to reduced risks of colon cancer but studies have also shown that high calcium levels inhibit the absorption of magnesium. According to Qi Dai, MD, PhD, and co-workers, Americans have high calcium intake, but also a high incidence of colorectal cancer. “If calcium levels were involved alone, you’d expect the opposite direction. There may be something about these two factors combined – the ratio of one to the other – that might be at play,” said Dai. The risk of colorectal cancer adenoma recurrence was reduced by 32 per cent among those with baseline calcium to magnesium ratio below the median in comparison to no reduction for those above the median,” said Dai.[24]

Pre-treatment hypomagnesemia has been reported in young leukemic children, 78% of whom have histories of anorexia, and have excessive gut and urinary losses of Mg.[25]

Several studies have shown an increased cancer rate in regions with low magnesium levels in soil and drinking water, and the same for selenium. In Egypt the cancer rate was only about 10% of that in Europe and America. In the rural fellah it was practically non-existent. The main difference was an extremely high magnesium intake of 2.5 to 3g in these cancer-free populations, ten times more than in most western countries.[26]

5.2 Magnesium and cancer: a dangerous liason.

Castiglioni S, Maier JA.
Magnes Res. 2011 Sep; 24(3):S92-100
http://dx.doi.org:/10.1684/mrh.2011.0285

A complex relationship links magnesium and cancer. The aim of this review is to revisit current knowledge concerning the contribution of magnesium to tumorigenesis, from transformed cells to animal models, and ending with data from human studies. Cultured neoplastic cells tend to accumulate magnesium. High intracellular levels of the cation seem to confer a metabolic advantage to the cells, contribute to alterations of the genome, and promote the acquisition of an immortal phenotype. In magnesium-deficient mice, low magnesium both limits and fosters tumorigenesis, since inhibition of tumor growth at its primary site is observed in the face of increased metastatic colonization. Epidemiological studies identify magnesium deficiency as a risk factor for some types of human cancers. In addition, impaired magnesium homeostasis is reported in cancer patients, and frequently complicates therapy with some anti-cancer drugs. More studies should be undertaken in order to disclose whether a simple and inexpensive intervention to optimize magnesium intake might be helpful in the prevention and treatment of cancer.

Even though cancer-associated death rates are falling steadily, the global burden of cancer continues to increase primarily as a result of an aging population, but also because of the adoption of cancer-causing behaviors, including smoking and a western-type diet [1]. In particular, statistical and epidemiological data point to diet as responsible for about 35% of human cancer mortality [2]. There is general agreement about the inverse correlation between the risk of cancer and the regular consumption of fruit, cereals and vegetables, rich sources of many beneficial micronutrients, vitamins and minerals. Magnesium, which is predominantly obtained by eating unprocessed grains and green leafy vegetables, is an essential micronutrient implicated in a wide variety of regulatory, metabolic and structural activities [3]. The occidental diet is relatively deficient in magnesium Presented in part at the European Magnesium Meeting – EUROMAG Bologna 2011, San Giovanni in Monte, Bologna, Italy, June 8-10, 2011. because of the processing of many food items and the preference for calorie-rich, micronutrient-poor foods [4]. Magnesium deficiency complicates chronic gastrointestinal and renal diseases, diabetes mellitus, alcoholism, and therapies with some classes of diuretics and anticancer drugs [4]. A review of the literature reveals the relationship between magnesium and cancer, from the cellular level through to animal models and humans. Although controversy exists about the role of magnesium in tumors, most of the results available point to low magnesium as a factor contributing to tumorigenesis.

5.1.1 Magnesium acts as a secondary messenger, and activates a vast array of enzymes [3, 5]. Since magnesium participates in all major metabolic processes, as well as redox reactions, it is no surprise that it has a direct role in controlling cell survival and growth. In normal diploid cells, the total concentration of magnesium increases throughout the G1 and S phases of the cell cycle. Accordingly, low extracellular magnesium markedly inhibits their proliferation [3]. Conversely, neoplastic cells are refractory to the proliferative inhibition by low extracellular magnesium but, being extremely avid for the cation, it accumulates in these cells even when cultured in low magnesium levels [6]. This avidity is due, at least in part, to an impairment of Na-dependent magnesium extrusion [7], and to the overexpression of one of the magnesium transporters, namely transient receptor potential melastatin (TRPM)7 [8]. High intracellular magnesium seems to provide a selective advantage for the transformed cells since magnesium contributes to regulating enzymes of various metabolic pathways and of the systems involved in DNA repair. Indeed, magnesium forms complexes with ATP, ADP and GTP, necessary for the activity of enzymes implicated in the transfer of phosphate groups such as glucokinase, phosphofructokinase, phosphoglycerate kinase and pyruvate kinase [9], enzymes of glycolysis known to be the pathway used preferentially by neoplastic cells to produce energy [10]. Magnesium also forms complexes with DNA polymerase, ribonucleases, adenylcyclase, phosphodiesterases,guanylate-cyclase, ATPases and GTPases, being therefore implicated in the metabolism of nucleic acids and proteins, and in signal transduction [9]. Since mutation is a driving force in the development of cancer, it is worth noting that magnesium is involved in the inhibition of N-methylpurine DNA-glycosidase, which initiates base excision repair in DNA by removing a wide variety of alkylated, deaminated, and lipid peroxidation-induced purine adducts [11]. In addition, the nuclear Ser/Thr phosphatase PPM1D (also known as WIP1), which is overexpressed in various human primary tumors, requires magnesium for its activity. PPM1D is involved in the regulation of several essential signaling pathways implicated in tumorigenesis [12, 13]. In particular, PPM1D dephosphorylates and, therefore, inactivates the p53 tumor suppressor gene, a canonical suppressor of proliferation. It also complements several oncogenes, such as Ras, Myc, and HER-2/neu, for cellular transformation both in vitro and in vivo [12].

On these bases, it is possible to conclude that high intracellular magnesium has a role in promoting genetic instability. Another peculiarity of tumor cells is their limitless proliferative potential [14, 15]. It is therefore relevant to point out that magnesium is required to activate telomerase [16-18], a specialized DNA polymerase that extends telomeric DNA and counters the progressive telomere erosion associated with cell duplication. The presence of telomerase activity correlates with a resistance to induction of both senescence and apoptosis which are considered to be crucial anticancer defenses [14, 15]. These points are summarized in figure 1, which also underlines the contribution of high intracellular magnesium to some of the hallmarks of cancer, as highlighted by Hanahan and Weinberg [14, 15]. Mentioning only studies performed on neoplastic cells would be simplistic, since tumors are more than just masses of proliferating cancer cells. Rather, they are complex, heterotypic tissues where normal cells in the stroma, far from being passive bystanders, actively collaborate to cancer development and progression [14, 15]. Many of the growth signals driving the proliferation of and invasion by carcinoma cells originate from the stromal cell components of the tumor mass. It is therefore worth noting that low magnesium modulates the functions of a variety of normal cells present in the tumor microenvironment. In particular, endothelial cells cultured in low magnesium release higher amounts of metalloproteases and growth factors [19]. Similar results were obtained in cultured human fibroblasts (unpublished results). In addition, low magnesium promotes endothelial and fibroblast senescence [20], and senescent cells can modify the tissue environment in a way that synergizes with oncogenic mutations to promote the progression of cancers [21]. Only the behavior of microvascular endothelial cells cultured in low magnesium seems not to fit with the picture described above. It is well known that angiogenesis is crucial to nourish the tumor and facilitate its spreading, but low extracellular magnesium impairs acquisition of the angiogenic phenotype by microvascular endothelial cells. Exposure to low magnesium retards endothelial proliferation, migration and differentiation in vitro ([22] and manuscript submitted). Accordingly, magnesium-deficient mice develop tumors which are significantly less vascularized than the controls [23].

Figure 1. Neoplastic cells tend to have high intracellular concentrations of magnesium, which contribute to the regulation of various metabolic pathways and of systems involved in DNA repair, thus providing a selective advantage for the transformed cells. The figure also links the effects of high intracellular concentrations of magnesium on cell functions to some hallmarks of cancer as highlighted by Hanahan and Weinberg [14, 15].

5.1.2 Low magnesium and cancer: a focus on human studies

Several epidemiological studies have provided evidence that a correlation exists between dietary magnesium and various types of cancer. High levels of magnesium in drinking water protect against oesophageal and liver cancer [36, 37]. In addition, magnesium concentration in drinking water is inversely correlated with death from breast, prostate, and ovarian cancers, whereas no correlation existed for other tumors [36, 38, 39]. Epidemiological studies conducted in various countries demonstrate an association between low intake of magnesium and the risk of colon cancer [40-43]. In addition, a large population-based prospective study in Japan shows a significant inverse correlation between dietary intake of magnesium and colon cancer in men but not in women [44]. Intriguingly, the association between low intake of magnesium and colon cancer is linked to the increased formation of N-nitroso compounds, most of which are potent carcinogens [43]. A further link between magnesium and colon neoplasia is highlighted by the association of adenomatous and hyperplastic polyps, which might progress to carcinoma, with a genetic polymorphism of TRPM7 [45], an ubiquitous ion channel with a central role in magnesium uptake and homeostasis [46]. Results concerning the contribution of magnesium to lung cancer are controversial. A first case-control study correlates low dietary magnesium with increased lung cancer risk both in men and women [47]. This link is more evident in the elderly, current smokers, drinkers and in those with a late-stage disease. To explain the protective effect of magnesium against lung cancer, the authors recall that magnesium regulates cell multiplication, protects against the oxidative stress invariably associated with magnesium deficiency [48], and maintains genomic stability. A recent prospective analysis however, does not support the previous report [49]. These contrasting data could result from recall bias, the difficulty in evaluating diet composition and the fact that smoking is a very strong risk factor for lung cancer.

Conclusion Although the evidence is still fragmentary, most of the data available point to magnesium as a chemopreventive agent, so that optimizing magnesium intake might represent an effective and low-cost preventive measure to reduce cancer risk. Doubts remain about supplementing cancer patients with magnesium. The recently revived interest in the relationship between magnesium and tumors, both in experimental and clinical oncology, should encourage more studies that would advance our understanding of the role of magnesium in tumors, and could explore the possibility that optimizing magnesium homeostasis might prevent cancer or help in its treatment.

5.3 A Magnesium Deficiency Increases Cancer Risk Significantly

Wed, May 21, 2008 by: Mark Sircus

http://www.naturalnews.com/023279_magnesium_cancer_calcium.html#ixzz3ZCT65Fiv

Aleksandrowicz et al in Poland conclude that inadequacy of Mg (Magnesium) and antioxidants are important risk factors in predisposing to leukemias. Other researchers found that 46% of the patients admitted to an ICU (Intensive Care Unit) in a tertiary cancer center presented hypomagnesemia.

They concluded that the incidence of hypomagnesemia in critically ill cancer patients is high. In animal studies we find that Mg deficiency has caused lymphopoietic neoplasms in young rats. A study of rats surviving Mg deficiency sufficient to cause death in convulsions during early infancy in some, and cardiorenal lesions weeks later in others, disclosed that some of survivors had thymic nodules or lymphosarcoma.

One would not normally think that Magnesium (Mg) deficiency can paradoxically increase the risk of, or protect against cancer yet we will find that just as severe dehydration or asphyxiation can cause death, magnesium deficiency can directly lead to cancer. When you consider that over 300 enzymes and ion transport require magnesium and that its role in fatty acid and phospholipid acid metabolism affects permeability and stability of membranes, we can see that magnesiumdeficiency would lead to physiological decline in cells setting the stage for cancer. Anything that weakens cell physiology will lead to the infections that surround and penetrate tumor tissues. These infections are proving to be an integral part of cancer. Magnesium deficiency poses a direct threat to the health of our cells. Without sufficient amounts, our cells calcify and rot in. Breeding grounds for yeast and fungi colonies they become, invaders all too ready to strangle our life force and kill us.

Over 300 different enzymes systems rely upon magnesium to facilitate their catalytic action, including ATP metabolism, creatine-kinase activation, adenylate-cyclase, and sodium-potassium-ATPase.

It is known that carcinogenesis induces magnesium distribution disturbances, which cause magnesium mobilization through blood cells and magnesium depletion in non-neoplastic tissues. Magnesium deficiency seems to be carcinogenic, and in case of solid tumors, a high level of supplemented magnesium inhibits carcinogenesis. Both carcinogenesis and magnesium deficiency increase the plasma membrane permeability and fluidity. Scientists have in fact found out that there is much less Mg++ binding to membrane phospholipids of cancer cells, than to normal cell membranes.

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More Complexity in Protein Evolution

Author and Curator: Larry H. Bernstein, MD, FCAP 

Lactate dehydrogenase like crystallin: a potentially protective shield for Indian spiny-tailed lizard (Uromastix ltardwickit) lens against environmental stress?
A Atta, A Ilyas, Z Hashim, A Ahmed and S Zarina
The Protein Journal 2014; 33(2), p. 128-34.
http://dx.doi.org/10.1007/s10930-014-9543-4

Taxon specific lens crystallins in ve1iebrates are either similar or identical with various metabolic enzymes. These bifunctional crystallins serve as structural protein in lens along with their catalytic role. In the present study, we have partially purified and characterized lens crystallin from Indian spiny-tailed lizard (Uroma stix hardwickii). We have found lactate dehydrogenase (LDH) activity in lens indicating presence of an enzyme crystallin with dual functions. Taxon specific lens crystallins are product of gene sharing or gene duplication phenomenon where a pre-existing enzyme is recruited as lens crystallin in addition to structural role. In lens, same gene adopts refractive role in lens without modification or loss of pre-existing function during gene sharing phenomenon. Apart from conventional role of structural protein, LDH activity containing crystallin in Uromastix hardwickii lens is likely to have adaptive characteristics to offer protection against toxic effects of oxidative stress and ultraviolet light, hence justifying its recruitment. Taxon specific crystallins may serve as good models to understand structure-function relationship of these proteins.

αB-Crystallin and 27-kd Heat Shock Protein Are Regulated by Stress Conditions in the Central Nervous System and Accumulate in Rosenthal Fibers
T Iwaki, A Iwaki, J Tateishi, Y Sakaki, and JE Goldmant
Ameri J Pathol  1993; 143(2):487-495.

To understand the significance of the accumulation of αB-crystallin in Rosenthal fibers within astrocytes, the expression and metabolism of αB-crystallin in glioma cell lines were examined under the conditions of heat and oxidative stress. αB-crystallin mRNA was increased after both stresses, and αB-crystallin protein moved from a detergent-soluble to a detergent-insoluble form. In addition, Western blotting of Alexander’s  disease brain homogenates revealed that the 27-kd heat shock protein (HSP27), which is related to αB-crystallin, accumulates along with αB-crystallin. The presence of HSP27 in Rosenthal fibers was directly demonstrated by immunohistochemistry. Our results suggest that astrocytes in Alexander’s disease may be involved in an as yet unknown kind of stress reaction that causes the accumulation of αB-ccystallin and HSP27 and results in Rosenthal fiber formation.

α-Crystallin can function as a molecular chaperone
Joseph Horwitz
Proc. Nadl. Acad. Sci. USA Nov 1992; 89: 10449-10453. Biochemistry

The α-crystallins (αA and αB) are major lens structural proteins of the vertebrate eye that are related to the small heat shock protein family. In addition, crystallins (especially αB) are found in many cells organs outside the lens, and aα is overexpressed in several neurological disorders and in cell lines under stress conditions. Here I show that α-crystallin can function as a molecular chaperone. Stoichiometric amounts of αA and αB suppress thermally induced aggregation of various enzymes. In particular, α-crystalln is very efficient in suppressing the thermally induced aggregation of β- and y-crystallins, the two other major mammalian stuctural lens proteins. α-Crystallin was also effective in preventing aggregation and in refolding guanidine hydrochloride-denatured y-crystallin, as judged by circular dichroism spectroscopy. My results thus indicate that α-crystallin refracts light and protects proteins from aggregation in the transparent eye lens and that in nonlens cells α-crystallin may have other functions in addition to its capacity to suppress aggregation of proteins.

Gene sharing by δ-crystallin and argininosuccinate Iyase
J Piatigorsky, WE O’Brient, BL Norman, K Kalumuckt, GJ Wistow, T Borras, et al.
Proc. Natl. Acad. Sci. USA  May 1988; 85: 3479-3483. Evolution.

The lens structural protein δ-crystallin and the metabolic enzyme argininosuccinate lyase (ASL; Largininosuccinate argine-lyase, EC 4.3.2.1) have striking sequence similarity. We have demonstrated that duck δ-crystallin has enormously high ASL activity, while chicken δ-crystallin has lower but significant activity. The lenses of these birds had much greater ASL activity than other tissues, suggesting that ASL is being expressed at unusually high levels as a structural component. In Southern blots of human genomic DNA, chicken δ1-crystallin cDNA hybridized only to the human ASL gene; moreover, the two chicken δ-crystallin genes accounted for all the sequences in the chicken genome able to cross-hybridize with a human ASL cDNA, with preferential hybridization to the δ2 gene. Correlations of enzymatic activity and recent data on mRNA levels in the chicken lens suggest that ASL activity depends on expression of the δ2-crystallin gene. The data indicate that the same gene, at least in ducks, encodes two different functions, an enzyme (ASL) and a structural protein (δ-crystallin), although in chickens specialization and separation of functions may have occurred.

Gecko i-crystallin: How cellular retinol-binding protein became an eye lens ultraviolet filter
PJ L Werten, Beate Roll, DMF van Aalten, and WW de Jong
PNAS Mar 2000; 97(7): 3282–3287 http://pnas.org/cgi/doi/10.1073ypnas.050500597

Eye lenses of various diurnal geckos contain up to 12% i-crystallin. This protein is related to cellular retinol-binding protein type I (CRBP I) but has 3,4-didehydroretinol, rather than retinol, as a ligand. The 3,4-didehydroretinol gives the lens a yellow color, thus protecting the retina by absorbing short-wave radiation. i-Crystallin could be either the gecko’s housekeeping CRBP I, recruited for an additional function in the lens, or the specialized product of a duplicated CRBP I gene. The finding of the same CRBP I-like sequence in lens and liver cDNA of the gecko Lygodactylus picturatus now supports the former option. Comparison with i-crystallin of a distantly related gecko, Gonatodes vittatus, and with mammalian CRBP I, suggests that acquiring the additional lens function is associated with increased amino acid changes. Compared with the rat CRBP I structure, the i-crystallin model shows reduced negative surface charge, which might facilitate the required tight protein packing in the lens. Other changes may provide increased stability, advantageous for a long-living lens protein, without frustrating its role as retinol transporter outside the lens. Despite a number of replacements in the ligand pocket, recombinant i-crystallin binds 3,4-didehydroretinol and retinol with similar and high affinity (1.6 nM). Availability of ligand thus determines whether it binds 3,4-didehydroretinol, as in the lens, or retinol, in other tissues. i-Crystallin presents a striking example of exploiting the potential of an existing gene without prior duplication.

Expression of βA3/A1-crystallin in the developing and adult rat eye
G Parthasarathy, Bo Ma, C Zhang, C Gongora, JS Zigler, MK Duncan, D Sinha
J Molec Histol 2011; 42(1): 59-69. http://dx.doi.org:/10.1007/s10735-010-9307-1

Crystallins are very abundant structural proteins of the lens and are also expressed in other tissues. We have previously reported a spontaneous mutation in the rat βA3/A1-crystallin gene, termed Nuc1, which has a novel, complex, ocular phenotype. The current study was undertaken to compare the expression pattern of this gene during eye development in wild type and Nuc1 rats by in situ hybridization (ISH) and immunohistochemistry (IHC).
βA3/A1-crystallin expression was first detected in the eyes of both wild type and Nuc1 rats at embryonic (E) day 12.5 in the posterior portion of the lens vesicle, and remained limited to the lens fibers throughout fetal life.
After birth, βA3/A1-crystallin expression was also detected in the neural retina (specifically in the astrocytes and ganglion cells) and in the retinal pigmented epithelium (RPE).
This suggested that βA3/A1-crystallin is not only a structural protein of the lens, but has cellular function(s) in other ocular tissues.
In summary, expression of βA3/A1-crystallin is controlled differentially in various eye tissues with lens being the site of greatest expression.
Similar staining patterns, detected by ISH and IHC, in wild type and Nuc1 animals suggest that functional differences in the protein, rather than changes in mRNA/protein level of expression likely account for developmental abnormalities in Nuc1.

βA3/A1Crystallin controls anoikis-mediated cell death in astrocytes by modulating PI3K/AKT/mTOR and ERK survival pathways through the PKD/Bit1-signaling axis
B Ma, T Sen, L Asnaghi, M Valapala, F Yang, S Hose, D S McLeod, Y Lu, et la.
Cell Death and Disease 2011; 2(10). http://dx.doi.org:/10.1038/cddis.2011.100

During eye development, apoptosis is vital to the maturation of highly specialized structures such as the lens and retina. Several forms of apoptosis have been described, including anoikis, a form of apoptosis triggered by inadequate or inappropriate cell–matrix contacts. The anoikis regulators, Bit1 (Bcl-2 inhibitor of transcription-1) and protein kinase-D (PKD), are expressed in developing lens when the organelles are present in lens fibers, but are downregulated as active denucleation is initiated.
We have previously shown that in rats with a spontaneous mutation in the Cryba1 gene, coding for βA3/A1-crystallin, normal denucleation of lens fibers is inhibited. In rats with this mutation (Nuc1), both Bit1 and PKD remain abnormally high in lens fiber cells. To determine whether βA3/A1-crystallin has a role in anoikis, we induced anoikis in vitro and conducted mechanistic studies on astrocytes, cells known to express βA3/A1-crystallin.
The expression pattern of Bit1 in retina correlates temporally with the development of astrocytes. Our data also indicate that loss of βA3/A1-crystallin in astrocytes results in a failure of Bit1 to be trafficked to the Golgi, thereby suppressing anoikis. This loss of βA3/A1-crystallin also induces insulin-like growth factor-II, which increases cell survival and growth by modulating the phosphatidylinositol-3-kinase (PI3K)/AKT/mTOR and extracellular signal-regulated kinase pathways. We propose that βA3/A1-crystallin is a novel regulator of both life and death decisions in ocular astrocytes.

βA3/A1-crystallin in astroglial cells regulates retinal vascular remodeling during development
D Sinha, A Klise, Y Sergeev, S Hose, IA Bhutto, L Hackler Jr., T Malpic-llanos, et al.
Molec Cell Neurosci 2008; 37(1): 85-95.

http://dx.doi.org:/10.1016/j.mcn.2007.08.016

Vascular remodeling is a complex process critical to development of the mature vascular system. Astrocytes are known to be indispensable for initial formation of the retinal vasculature; our studies with the Nuc1 rat provide novel evidence that these cells are also essential in the retinal vascular remodeling process.
Nuc1 is a spontaneous mutation in the Sprague–Dawley rat originally characterized by nuclear cataracts in the heterozygote and microphthalmia in the homozygote. We report here that the Nuc1 allele results from mutation of the βA3/A1-crystallin gene, which in the neural retina is expressed only in astrocytes. We demonstrate striking structural abnormalities in Nuc1 astrocytes with profound effects on the organization of intermediate filaments. While vessels form in the Nuc1 retina, the subsequent remodeling process required to provide a mature vascular network is deficient. Our data implicate βA3/A1-crystallin as an important regulatory factor mediating vascular patterning and remodeling in the retina.

A developmental defect in astrocytes inhibits programmed regression of the hyaloid vasculature in the mammalian eye
C Zhang, L Asnaghi, C Gongora, B Patek, S Hose, Bo Ma, MA Fard, L Brako, et al.
Eur J Cell Biol 2011; 90(5): 440-448.
http://dx.doi.org:/10.1016/j.ejcb.2011.01.003

Previously we reported the novel observation that astrocytes ensheath the persistent hyaloid artery, both in the Nuc1 spontaneous mutant rat, and in human PFV (persistent fetal vasculature) disease (Developmental Dynamics 234:36–47, 2005). We now show that astrocytes isolated from both the optic nerve and retina of Nuc1 rats migrate faster than wild type astrocytes. Aquaporin 4 (AQP4), the major water channel in astrocytes, has been shown to be important in astrocyte migration. We demonstrate that AQP4 expression is elevated in the astrocytes in PFV conditions, and we hypothesize that this causes the cells to migrate abnormally into the vitreous where they ensheath the hyaloid artery. This abnormal association of astrocytes with the hyaloid artery may impede the normal macrophage-mediated remodeling and regression of the hyaloid system.

βA3/A1-crystallin is required for proper astrocyte template formation and vascular remodeling in the retina.
D Sinha; WJ Stark; M Valapala; IA Bhutto; M Cano; S Hose; GA Lutty; et al.  Transgenic research 2012; 21(5):1033-42.

Nuc1 is a spontaneous rat mutant resulting from a mutation in the Cryba1 gene, coding for βA3/A1-crystallin. Our earlier studies with Nuc1 provided novel evidence that astrocytes, which express βA3/A1-crystallin, have a pivotal role in retinal remodeling. The role of astrocytes in the retina is only beginning to be explored. One of the limitations in the field is the lack of appropriate animal models to better investigate the function of astrocytes in retinal health and disease. We have now established transgenic mice that overexpress the Nuc1 mutant form of Cryba1, specifically in astrocytes. Astrocytes in wild type mice show normal compact stellate structure, producing a honeycomb-like network. In contrast, in transgenics over-expressing the mutant (Nuc1) Cryba1 in astrocytes, bundle-like structures with abnormal patterns and morphology were observed. In the nerve fiber layer of the transgenic mice, an additional layer of astrocytes adjacent to the vitreous is evident. This abnormal organization of astrocytes affects both the superficial and deep retinal vascular density and remodeling. Fluorescein angiography showed increased venous dilation and tortuosity of branches in the transgenic retina, as compared to wild type. Moreover, there appear to be fewer interactions between astrocytes and endothelial cells in the transgenic retina than in normal mouse retina. Further, astrocytes overexpressing the mutant βA3/A1-crystallin migrate into the vitreous, and ensheath the hyaloid artery, in a manner similar to that seen in the Nuc1 rat. Together, these data demonstrate that developmental abnormalities of astrocytes can affect the normal remodeling process of both fetal and retinal vessels of the eye and that βA3/A1-crystallin is essential for normal astrocyte function in the retina.

Ontogeny of oxytocin and vasopressin receptor binding in the lateral septum in prairie and montane voles
Z. Wang, L.J. Young
Developmental Brain Research 1997; 104:191–195.

Adult prairie (Microtus ochrogaster). and montane voles (M. montanus). differ in the distribution of oxytocin OT. and vasopressin AVP receptor binding in the brain. The present study examined the ontogenetic pattern of these receptor bindings in the lateral septum in both species to determine whether adult differences in the receptor binding are derived from a common pattern in development. In both species, OT and AVP receptor binding in the lateral septum were detected neonatally, increased during development, and reached the adult level at weaning third week. The progression of OT and AVP receptor differed, as OT receptor binding increased continually until weaning while AVP receptor binding did not change in the first week, increased rapidly in the second week, and was sustained thereafter. For both receptors, the binding increased more rapidly in montane than in prairie voles, resulting in species differences in receptor binding at weaning and in adulthood. Together, these data indicate that OT and AVP could affect the brain during development in a peptide- and species-specific manner in voles.

Evolution of the vasopressin/oxytocin superfamily: Characterization of a cDNA encoding a vasopressin-related precursor, preproconopressin, from the mollusc Lymnaea stagnalis
RE Van Kesteren, AB Smit, RW Dirksi, ND De With, WPM Geraerts, and J Joosse
Proc. Nadl. Acad. Sci. USA May 1992; 89: 4593-4597. Neurobiology

Although the nonapeptide hormones vasopressin, oxytocin, and related peptides from vertebrates and some nonapeptides from invertebrates share similarities in amino acid sequence, their evolutionary relationships are not dear. To investigate this issue, we doned a cDNA encoding a vasopressin-related peptide, Lys-conopressin, produced in the central nervous system of the gastropod mollusc Lymnaea stagnalis. The predicted preproconopressin has the overall architecture of vertebrate preprovasopressins, with a signal peptide, Lys-conopressin, that is flanked at the C terminus by an amidation signal and a pair of basic residues, followed by a neurophysin domain. The Lymnaea neurophysin and the vertebrate neurophysins share high sequence identity, which includes the conservation of all 14 cysteine residues. In addition, the Lymnaea neurophysin possesses unique structural characteristics. It contains a putative N-linked glycosylation site at a position in the vertebrate neurophysins where a strictly conserved tyrosine residue, which plays an essential role in binding of the nonapptide hormones, is found. The C-terminal copeptin homologous extension of the Lymnaea neurophysin has low sequence identity with the vertebrate counterparts and is probably not cleaved from the prohormone, as are the mammalin copeptins. The conopressin gene is expressed in only a few neurons in both pedal ganglia of the central nervous system. The conopressin transcript is present in two sizes, due to alternative use of polyadenylylation signals. The data presented here demonstrate that the typical organization of the prohormones of the vasopressin/oxytocin superfamily must have been present in the common ancestors of vertebrates and invertebrates.

A common allele in the oxytocin receptor gene (OXTR) impacts prosocial temperament and human hypothalamic-limbic structure and function
H Tosta, B Kolachanaa, S Hakimia, H Lemaitrea, BA Verchinskia, et al.
PNAS Aug 3, 2010; 107(31): 13936–13941
http://pnas.org/cgi/doi/10.1073/pnas.1003296107

The evolutionarily highly conserved neuropeptide oxytocin is a key mediator of social and emotional behavior in mammals, including humans. A common variant (rs53576) in the oxytocin receptor gene (OXTR) has been implicated in social-behavioral phenotypes, such as maternal sensitivity and empathy, and with neuropsychiatric disorders associated with social impairment, but the intermediate neural mechanisms are unknown. Here, we used multimodal neuroimaging in a large sample of healthy human subjects to identify structural and functional alterations in OXTR risk allele carriers and their link to temperament. Activation and interregional coupling of the amygdala during the processing of emotionally salient social cues was significantly affected by genotype. In addition, evidence for structural alterations in key oxytocinergic regions emerged, particularly in the hypothalamus. These neural characteristics predicted lower levels of reward dependence, specifically in male risk allele carriers. Our findings identify sex-dependent mechanisms impacting the structure and function of hypothalamic-limbic circuits that are of potential clinical and translational significance.
Test of Association Between 10 SNPs in the Oxytocin Receptor Gene and Conduct Disorder
JT Sakai, TJ Crowley, MC Stallings, M McQueen, JK Hewitt, C Hopfer, et al.
Psychiatr Genet. 2012 Apr; 22(2): 99–102. http://dx.doi.org:/10.1097/YPG.0b013e32834c0cb2

Animal and human studies have implicated oxytocin (OXT) in affiliative and prosocial behaviors. We tested whether genetic variation in the OXT receptor (OXTR) gene is associated with conduct disorder (CD).
Utilizing a family-based sample of adolescent probands recruited from an adolescent substance abuse treatment program, control probands and their families (total sample n=1,750), we conducted three tests of association with CD and 10 SNPs (single nucleotide polymorphisms) in the OXTR gene: (1) family-based comparison utilizing the entire sample; (2) within-Whites, case control comparison of adolescent patients with CD and controls without CD; and (3) within-Whites case-control comparison of parents of patients and parents of controls.
Family-based association tests failed to show significant results (no results p<0.05). While strictly correcting for the number of tests (α=0.002), adolescent patients with CD did not differ significantly from adolescent controls in genotype frequency for the OXTR SNPs tested; similarly, comparison of OXTR genotype frequencies for parents failed to differentiate patient and control family type, except a trend association for rs237889 (p=0.004). In this sample, 10 SNPs in the OXTR gene were not significantly associated with CD.

Leu55Pro transthyretin accelerates subunit exchange and leads to rapid formation of hybrid tetramers
CA Keetch, EHC Bromley, MG McCammon, N Wang, J Christodoulou, CV Robinson
JBC  Oct 11, 2005 M508753200. http://jbc.org/cgi/doi/10.1074/jbc.M508753200

Transthyretin is a tetrameric protein associated with the commonest form of

systemic amyloid disease. Using isotopically labeled proteins and mass spectrometry we compared subunit exchange in wild-type transthyretin with that of the variant associated with the most aggressive form of the disease, Leu55Pro. Wild-type subunit exchange occurs via both monomers and dimers , while exchange via dimers is the dominant mechanism for the Leu55Pro variant. Since patients with the Leu55Pro mutation are heterozygous, expressing both proteins simultaneously, we also analyzed the subunit exchange reaction between wild-type and Leu55Pro tetramers . We found that hybrid tetramers containing two or three Leu55Pro subunits dominate in the early stages of the reaction. Surprisingly we also found that in the presence of Leu55Pro transthyretin, the rate of dissociation of wild-type transthyretin is increased. This implies interactions between the two proteins that accelerate the formation of hybrid tetramers, a result with important implications for transthyretin amyloidos is.

Beyond Genetic Factors in Familial Amyloidotic Polyneuropathy: Protein Glycation and the Loss of Fibrinogen’s Chaperone Activity
G da Costa, RA Gomes, A Guerreiro, E Mateus, E Monteiro, et al.
PLoS ONE 2011; 6(10): e24850. http://dx.doi.org:/10.1371/journal.pone.0024850

Familial amyloidotic polyneuropathy (FAP) is a systemic conformational disease characterized by extracellular amyloid fibril formation from plasma transthyretin (TTR). This is a crippling, fatal disease for which liver transplantation is the only effective therapy. More than 80 TTR point mutations are associated with amyloidotic diseases and the most widely accepted disease model relates TTR tetramer instability with TTR point mutations. However, this model fails to explain two observations. First, native TTR also forms amyloid in systemic senile amyloidosis, a geriatric disease. Second, age at disease onset varies by decades for patients bearing the same mutation and some mutation carrier individuals are asymptomatic throughout their lives. Hence, mutations only accelerate the process and non-genetic factors must play a key role in the molecular mechanisms of disease. One of these factors is protein glycation, previously associated with conformational diseases like Alzheimer’s and Parkinson’s. The glycation hypothesis in FAP is supported by our previous discovery of methylglyoxal-derived glycation of amyloid fibrils in FAP patients. Here we show that plasma proteins are differentially glycated by methylglyoxal in FAP patients and that fibrinogen is the main glycation target. Moreover, we also found that fibrinogen interacts with TTR in plasma. Fibrinogen has chaperone activity which is compromised upon glycation by methylglyoxal. Hence, we propose that methylglyoxal glycation hampers the chaperone activity of fibrinogen, rendering TTR more prone to aggregation, amyloid formation and ultimately, disease.

Aromatic Sulfonyl Fluorides Covalently Kinetically Stabilize Transthyretin to Prevent Amyloidogenesis while Affording a Fluorescent Conjugate
NP Grimster, S Connelly, A Baranczak, J Dong, …, JW Kelly
J Am Chem Soc. 2013 Apr 17; 135(15): 5656–5668. http://dx.doi.org:/10.1021/ja311729d

Molecules that bind selectively to a given protein and then undergo a rapid chemoselective reaction to form a covalent conjugate have utility in drug development. Herein a library of 1,3,4-oxadiazoles substituted at the 2 position with an aryl sulfonyl fluoride and at the 5 position with a substituted aryl known to have high affinity for the inner thyroxine binding subsite of transthyretin (TTR) were conceived of by structure-based design principles and were chemically synthesized. When bound in the thyroxine binding site, most of the aryl sulfonyl fluorides react rapidly and chemoselectively with the pKa-perturbed K15 residue, kinetically stabilizing TTR and thus preventing amyloid fibril formation, known to cause polyneuropathy. Conjugation t50s range from 1 to 4 min, ~ 1400 times faster than the hydrolysis reaction outside the thyroxine binding site. Xray crystallography confirms the anticipated binding orientation and sheds light on the sulfonyl fluoride activation leading to the sulfonamide linkage to TTR. A few of the aryl sulfonyl fluorides efficiently form conjugates with TTR in plasma. A few of the TTR covalent kinetic stabilizers synthesized exhibit fluorescence upon conjugation and therefore could have imaging applications as a consequence of the environment sensitive fluorescence of the chromophore.

Identification of S-sulfonation and S-thiolation of a novel transthyretin Phe33Cys variant from a patient diagnosed with familial transthyretin amyloidosis
A Lim, T Prokaeva, ME Mccomb, LH Connors, M Skinner, and CE Costello
Protein Science 2003; 12:1775–1786.
http://proteinscience.org/cgi/doi/10.1110/ps.0349703.

Familial transthyretin amyloidosis (ATTR) is an autosomal dominant disorder associated with a variant form of the plasma carrier protein transthyretin (TTR). Amyloid fibrils consisting of variant TTR, wild-type TTR, and TTR fragments deposit in tissues and organs. The diagnosis of ATTR relies on the identification of pathologic TTR variants in plasma of symptomatic individuals who have biopsy proven amyloid disease. Previously, we have developed a mass spectrometry-based approach, in combination with direct DNA sequence analysis, to fully identify TTR variants. Our methodology uses immunoprecipitation to isolate TTR from serum, and electrospray ionization and matrix-assisted laser desorption/ionization mass spectrometry (MS) peptide mapping to identify TTR variants and posttranslational modifications. Unambiguous identification of the amino acid substitution is performed using tandem MS (MS/MS) analysis and confirmed by direct DNA sequence analysis. The MS and MS/MS analyses also yield information about posttranslational modifications. Using this approach, we have recently identified a novel pathologic TTR variant. This variant has an amino acid substitution (Phe — Cys) at position 33. In addition, like the Cys10 present in the wild type and in this variant, the Cys33 residue was both S-sulfonated and S-thiolated (conjugated to cysteine, cysteinylglycine, and glutathione). These adducts may play a role in the TTR fibrillogenesis.

Evolutionary relationships of lactate dehydrogenases (LDHs) from mammals, birds, an amphibian, fish, barley, and bacteria: LDH cDNA sequences from Xenopus, pig, and rat
S Tsuji, MA Qureshi, EW Hou, WM Fitch, and S S.-L. Li
Proc. Natl. Acad. Sci. USA Sep 1994; 91: 9392-9396. Evolution

The nucleotide sequences of the cDNAs encoding LDH (EC 1.1.1.27) subunits LDH-A (muscle), LDH-B (liver), and LDH-C (oocyte) from Xenopus laevis, LDH-A (muscle) and LDH-B (heart) from pig, and LDH-B (heart) and LDH-C (testis) from rat were determined. These seven newly deduced amino acid sequences and 22 other published LDH sequences, and three unpublished fish LDH-A sequences kindly provided by G. N. Somero and D. A. Powers, were used to construct the most parsimonious phylogenetic tree of these 32 LDH subunits from mammals, birds, an amphibian, fish, barley, and bacteria. There have been at least six LDH gene duplications among the vertebrates. The Xenopus LDH-A, LDH-B, and LDH-C subunits are most closely related to each other and then are more closely related to vertebrate LDH-B than LDH-A. Three fish LDH-As, as well as a single LDH of lamprey, also seem to be more related to vertebrate LDH-B than to land vertebrate LDH-A. The mammalian LDH-C (testis) subunit appears to have diverged very early, prior to the divergence of vertebrate LDH-A and LDH-B subunits, as reported previously.

Evidence for neutral and selective processes in the recruitment of enzyme-crystallins in avian lenses
Graeme Wistow, Andrea Anderson, and Joram Piatigorsky
Proc. Natl. Acad. Sci. USA Aug 1990; 87: 6277-6280, Evolution

In apparent contrast to most other tissues, the ocular lenses in vertebrates show striking differences in protein composition between taxa, most notably in the recruitment of different enzymes as major structural proteins. This variability appears to be the result of at least partially neutral evolutionary processes, although there is also evidence for selective modification in molecular structure. Here we describe a bird, the chimney swift (Chaetura pelagica), that lacks δ-crystallin/ argininosuccinate lyase, usually the major crystallin of avian lenses. Clearly, δ-crystallin is not specifically required for a functionally effective avian lens. Furthermore the lens composition of the swift is more similar to that of the related hummingbirds than to that of the barn swallow (Hirundo rustica), suggesting that phylogeny is more important than environmental selection in the recruitment of crystallins. However differences in ε-crystallin/lactate dehydrogenase-B sequence between swift and hummingbird and other avian and reptilian species suggest that selective pressures may also be working at the molecular level. These differences also confirm the close relationship between swifts and hummingbirds.

Enzyme/crystallins and extremely high pyridine nucleotide levels in the eye lens.
Zigler, J. S., Jr.; Rao, P. V.
FASEB J. 1991; 3: 223-225.

Taxon-specific crystallins are proteins present in high abundance in the lens of phylogenetically restricted groups of animals. Recently it has been found that these proteins are actually enzymes which the lens has apparently adopted to serve as structural proteins. Most of these proteins have been shown to be identical to, or related to, oxidoreductases. In guinea pig lens, which contains zeta-crystallin, a protein with an NADPH dependent oxidoreductase activity, the levels of both NADPH and NADP* are extremely high and correlate with the concentration of zeta-crystallin. We report here nucleotide assays on lenses from vertebrates containing other enzyme/crystallins. In each case where the enzyme/crystallin is a pyridine nucleotide-binding protein the level of that particular nucleotide is extremely high in the lens. The presence of an enzyme/crystallin does not affect the lenticular concentrations of those nucleotides which are not specifically bound. The possibility that nucleotide binding may be a factor in the selection of some enzymes to serve as enzyme/crystallins is considered.

Comparison of stability properties of lactate dehydrogenase B4/ε-crystallin from different species
CEM Voorter, LTM Wintjes, PWH Heinstra, H Bloemendal and WW De Jong
Eur. J. Biochem. 1993; 211: 643-648

ε-Crystallin occurs as an abundant lens protein in many birds and in crocodiles and has been identified as heart-type lactate dehydrogenase (LDH-B4). Lens proteins have, due to their longevity and environmental conditions, extraordinary requirements for structural stability. To study lens protein stability, we compared various parameters of LDH-B4/ε-crystallin from lens and/or heart of duck, which has abundant amounts of this enzyme in its lenses, and of chicken and pig, which have no λ-crystallin. Measuring the thermostability of LDH-B4 from the different sources, the t50 values (temperature at which 50% of the enzyme activity remains after a 20-min period) for LDH-B4 from duck heart, duck lens and chicken heart were all found to be around 76°C whereas pig heart LDHB4 was less thermostable, having a t50 value of 625°C. A similar tendency was found with urea inactivation studies. Plotting the first-order rate constants obtained from inactivation kinetic plots against urea concentration, it was clear that LDH-B4 from pig heart was less stable in urea than the homologous enzymes from duck heart, chicken heart and duck lens. The duck and chicken enzymes were also much more resistant against proteolysis than the porcine enzyme. Therefore, it is concluded that avian LDH-B4 is structurally more stable than the homologous enzyme in mammals. This greater stability might make it suitable to function as a ε-crystallin, as in duck, but is not necessarily associated with high lens expression, as in chicken.

Duck lens ε-crystallin and lactate dehydrogenase B4 are identical: A single-copy gene product with two distinct functions
W Hendriks, JWM Mulders, MA Bibby, C Slingsby, H Bloemendal, and WW De Jong
Proc. Natl. Acad. Sci. USA Oct 1988; 85: 7114-7118. Biochemistry

To investigate whether or not duck lens ε-crystaliin and duck heart lactate dehydrogenase (LDH) B4 are the product of the same gene, we have isolated and sequenced cDNA clones of duck ε-crystallin. By using these clones we demonstrate that there is a single-copy Ldh-B gene in duck and in chicken. In the duck lens this gene is overexpressed, and its product is subject to posttranslational modification. Reconstruction of the evolutionary history of the LDH protein family reveals that the mammalian Ldh-C gene most probably originated from an ancestral Ldh-A gene and that the amino acid replacement rate in LDH-C is approximately 4 times the rate in LDH-A. Molecular modeling of LDH-B sequences shows that the increased thermostability of the avian tetramer might be explained by mutations that increase the number of ion pairs. Furthermore, the replacement of bulky side chains by glycines on the corners of the duck protein suggests an adaptation to facilitate close packing in the lens.

Lactate Dehydrogenase A as a Highly Abundant Eye Lens Protein in Platypus (Ornithorhynchus anatinus): Upsilon (υ)-Crystallin
T van Rheede,  R Amons, N Stewart, and WW de Jong
Mol. Biol. Evol. 2003; 20(06):994–998. http://dx.doi.org:/10.1093/molbev/msg116

Vertebrate eye lenses mostly contain two abundant types of proteins, the α-crystallins and the β/λ-crystallins. In addition, certain housekeeping enzymes are highly expressed as crystallins in various taxa. We now observed an unusual approximately 41-kd protein that makes up 16% to 18% of the total protein in the platypus eye lens. Its cDNA sequence was determined, which identified the protein as muscle-type lactate dehydrogenase A (LDH-A). It is the first observation of LDH-A as a crystallin, and we designate it upsilon (υ)-crystallin. Interestingly, the related heart-type LDH-B occurs as an abundant lens protein, known as ε-crystallin, in many birds and crocodiles. Thus, two members of the ldh gene family have independently been recruited as crystallins in different higher vertebrate lineages, suggesting that they are particularly suited for this purpose in terms of gene regulatory or protein structural properties. To establish whether platypus LDH-A/υ-crystallin has been under different selective constraints as compared with other vertebrate LDH-A sequences, we reconstructed the vertebrate Ldh-A gene phylogeny. No conspicuous rate deviations or amino acid replacements were observed.

Isozymes, moonlighting proteins and promiscous enzymes
M Nath Gupta, M Kapoor, AB Majumder and V Singh
Current Science Apr 2011; 100(8): 1152-1162.

The structures of isoenzymes differ and yet these catalyse the same type of reaction. These structures evolved to suit the physiological needs and are located in different parts of cells or tissues. Moonlighting proteins represent the same structure performing very different biological functions. Biological promiscuity reveals that the same active sites can catalyse different types of reactions. These three different phenomena, all illustrate similar evolutionary strategies. Viewed together, it emerges that biologists need to take a hard look at the ‘structure–function’ paradigm as well as the notions of biological specificity. Meanwhile, biotechnologists  continue to exploit the opportunities which ‘nonspecificity’ offers.

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Malnutrition in India, High Newborn Death Rate and Stunting of Children Age Under Five Years

Curator: Larry H Bernstein, MD, FCAP

 

A lead report in the New York Times focuses on a major public health problem in India today, with the irony of high growth rate and malnutrition and stunting of children under age 5 years that occurs in the majority and wealthy Hindu population, but not to any comparable degree in the Muslim population or in Bangladesh.  This is prevalent along the Ganges River, which crosses India below the Himalaya Mountains.  The inference is that the problem is perhaps solely related to poor sanitation, which is to a large degree indisputable, and the disease is related to the gut microbiome (not so stated), that leaves an intestinal mucosa with flattened epithelia, and no observation is made of the submucosal thymic-derived T-cell lymphocyte population, the largest in the human body.

Moreover, I might point out that the turnover of the intestinal epithelium with its large surface area is very high under normal metabolic circumstances.  The result is that the children are malnourished, and they have visceral protein losses as well as somatic protein loss (stunted growth, probably affecting both skeletal muscle and the metaphyseal growth plates of long bones).  This is not quite stated this way.

The irony is that they have sufficient food supply, except that if there is a diarrhea or intestinal malabsorption at an early age, the children just might not eat, except for perhaps soft foods.  So it is not explicitly cleat that their is sufficient animal protein in the diet, which has a S:N ratio that is roughly twice that of an exclusively plant diet.  The distinction is made between marasmus and kwashiorkor in that in kwashiorkor the protein deficiency is in the visceral compartment.  Consequently, there is a reprioriotization of the liver to synthesize acute phase proteins with a decline in albumin, transthyretin, and retinol-binding protein.  This is not insignificant, even though there may also be an inflammatory state, as from repeated infections.

I certainly would be interested in seeing data from the ongoing study that measures the serum protein analytes, and also a measurement of serum red cell Hb, serum cysteine, homocysteine, and glutathione, and perhaps a muscle biopsy.

I go directly to the article at this point.

Poor Sanitation in India May Afflict Well-Fed Children With Malnutrition

By GARDINER HARRIS      JULY 13, 2014
http://www.nytimes.com/2014/07/15/world/asia/poor-sanitation-in-india-may-afflict-well-fed-children-with-malnutrition.html

SHEOHAR DISTRICT, India — He wore thick black eyeliner to ward off the evil eye, but Vivek, a tiny 1-year-old living in a village of mud huts and diminutive people, had nonetheless fallen victim to India’s great scourge of malnutrition.

His parents seemed to be doing all the right things. His mother still breast-fed him. His family had six goats, access to fresh buffalo milk and a hut filled with hundreds of pounds of wheat and potatoes. The economy of the state where he lives has for years grown faster than almost any other. His mother said she fed him as much as he would eat and took him four times to doctors, who diagnosed malnutrition. Just before Vivek was born in this green landscape of small plots and grazing water buffalo near the Nepali border, the family even got electricity.

So why was Vivek malnourished?

‘Bihar grew at 12% last 7 years’

Abhay Singh, TNN | Feb 15, 2014, 02.15AM IST

 

Bihar's average annual growth rate has been 12% in the last seven fiscal years

Bihar’s average annual growth rate has been 12% in the last seven fiscal years

 

 

The report has taken 1999-2006 as the cut-off period to highlight spectacular Bihar turnaround story achieved under CM Nitish Kumar.

PATNA: Bihar’s average annual growth rate has been 12% in the last seven fiscal years, one of the highest among all Indian states, on the back of high growth rate achieved in the agriculture and allied sectors. Besides, advancement has also been made in healthcare and education.

The state’s Economic Survey Report for 2013-14, which was tabled in the assembly on Friday, has concluded this. The summary of the report said, “During 1990-91 to 2005-06, the state’s income at constant prices grew at an annual rate of 5.7%.” It said after that the economy witnessed a turnaround and grew at an annual rate of 12%. “The rate of growth achieved by the economy during 2006-13 is not only much higher, but also one of the highest among all Indian states.”

The report has taken 1999-2006 as the cut-off period to highlight spectacular Bihar turnaround story achieved under CM Nitish Kumar.

 

Poor Sanitation Linked to Malnutrition in India

New research on malnutrition, which leads to childhood stunting, suggests that a root cause may be an abundance of human waste polluting soil and water, rather than a scarcity of food.

SANITATION - bathing in Ganges River contaminated by human waste

SANITATION – bathing in Ganges River contaminated by human waste

 

 

Like almost everyone else in their village, Vivek and his family have no toilet, and the district where they live has the highest concentration of people who defecate outdoors. As a result, children are exposed to a bacterial brew that often sickens them, leaving them unable to attain a healthy body weight no matter how much food they eat.

“These children’s bodies divert energy and nutrients away from growth and brain development to prioritize infection-fighting survival,” said Jean Humphrey, a professor of human nutrition at Johns Hopkins Bloomberg School of Public Health. “When this happens during the first two years of life, children become stunted. What’s particularly disturbing is that the lost height and intelligence are permanent.”

Two years ago, Unicef, the World Health Organization and the World Bank released a major report on child malnutrition that focused entirely on a lack of food. Sanitation was not mentioned. Now, Unicef officials and those from other major charitable organizations said in interviews that they believe that poor sanitation may cause more than half of the world’s stunting problems.

“Our realization about the connection between stunting and sanitation is just emerging,” said Sue Coates, chief of water, sanitation and hygiene at Unicef India. “At this point, it is still just an hypothesis, but it is an incredibly exciting and important one because of its potential impact.”

This research has quietly swept through many of the world’s nutrition and donor organizations in part because it resolves a great mystery: Why are Indian children so much more malnourished than their poorer counterparts in sub-Saharan Africa?

A child raised in India is far more likely to be malnourished than one from the Democratic Republic of Congo, Zimbabwe or Somalia, the planet’s poorest countries. Stunting affects 65 million Indian children under the age of 5, including a third of children from the country’s richest families.

This disconnect between wealth and malnutrition is so striking that economists have concluded that economic growth does almost nothing to reduce malnutrition.

Half of India’s population, or at least 620 million people, defecate outdoors. And while this share has declined slightly in the past decade, an analysis of census data shows that rapid population growth has meant that most Indians are being exposed to more human waste than ever before.

In Sheohar, for instance, a toilet-building program between 2001 and 2011 decreased the share of households without toilets to 80 percent from 87 percent, but population growth meant that exposure to human waste rose by half.

“The difference in average height between Indian and African children can be explained entirely by differing concentrations of open defecation,” said Dean Spears, an economist at the Delhi School of Economics. “There are far more people defecating outside in India more closely to one another’s children and homes than there are in Africa or anywhere else in the world.”

 

SANITATION-children defecate outside - 162 million malnourished and stunted

SANITATION-children defecate outside – 162 million malnourished and stunted

 

Not only does stunting contribute to the deaths of a million children under the age of 5 each year, but those who survive suffer cognitive deficits and are poorer and sicker than children not affected by stunting. They also may face increased risks for adult illnesses like diabetes, heart attacks and strokes.

“India’s stunting problem represents the largest loss of human potential in any country in history, and it affects 20 times more people in India alone than H.I.V./AIDS does around the world,” said Ramanan Laxminarayan, vice president for research and policy at the Public Health Foundation of India.

India is an increasingly risky place to raise children. The country’s sanitation and air quality are among the worst in the world. Parasitic diseases and infections like tuberculosis, often linked with poor sanitation, are most common in India. More than one in four newborn deaths occur in India.

Open defecation has long been an issue in India. Some ancient Hindu texts advised people to relieve themselves far from home, a practice that Gandhi sought to curb.

“The cause of many of our diseases is the condition of our lavatories and our bad habit of disposing of excreta anywhere and everywhere,” Gandhi wrote in 1925.

SANITATION-disposing of excreta anywhere and everywhere

SANITATION-disposing of excreta anywhere and everywhere

 

 

Other developing countries have made huge strides in improving sanitation. Just 1 percent of Chinese and 3 percent of Bangladeshis relieve themselves outside compared with half of Indians. Attitudes may be just as important as access to toilets. Constructing and maintaining tens of millions of toilets in India would cost untold billions, a price many voters see no need to pay — a recent survey found that many people prefer going to the bathroom outside.

Few rural households build the sort of inexpensive latrines that have all but eliminated outdoor waste in neighboring Bangladesh.

“We need a cultural revolution in this country to completely change people’s attitudes toward sanitation and hygiene,” said Jairam Ramesh, an economist and former sanitation minister.

India’s government has for decades tried to resolve the country’s stubborn malnutrition problems by distributing vast stores of subsidized food. But more and better food has largely failed to reverse early stunting, studies have repeatedly shown.

India now spends about $26 billion annually on food and jobs programs, and less than $400 million on improving sanitation — a ratio of more than 60 to 1.

Lack of food is still an important contributor to malnutrition for some children, and some researchers say the field’s sudden embrace of sanitation has been overdone. “In South Asia, a more important factor driving stunting is diet quality,” said Zulfiqar A. Bhutta, a director of the Center for Global Child Health at the Hospital for Sick Children in Toronto.

Studies are underway in Bangladesh, Kenya and Zimbabwe to assess the share of stunting attributable to poor sanitation. “Is it 50 percent? Ninety percent? That’s a question worth answering,” said Dr. Stephen Luby, a professor of medicine at Stanford University who is overseeing a trial in Bangladesh that is expected to report its results in 2016. “In the meantime, I think we can all agree that it’s not a good idea to raise children surrounded by poop.”

Better sanitation in the West during the 19th and early 20th centuries led to huge improvements in health long before the advent of vaccines and antibiotics, and researchers have long known that childhood environments play a crucial role in child death and adult height.

The present research on gut diseases in children has focused on a condition resulting from repeated bacterial infections that flatten intestinal linings, reducing by a third the ability to absorb nutrients. A recent study of starving children found that they lacked the crucial gut bacteria needed to digest food.

In a little-discussed but surprising finding, Muslim children in India are 17 percent more likely to survive infancy than Hindus, even though Muslims are generally poorer and less educated. This enormous difference in infant mortality is explained by the fact that Muslims are far more likely to use latrines and live next to others also using latrines, a recent analysis found.

So widespread housing discrimination that confines many Muslims to separate slums may protect their children from increased exposure to the higher levels of waste in Hindu communities and, as a result, save thousands of Indian Muslim babies from death each year.

SANITATION-one in 4 newborn deaths related to sanitation

SANITATION-one in 4 newborn deaths related to sanitation

 

 

Discussion:

The coexistence of poor sanitation, where has a very large cultural barrier, with serious protein-energy malnutrition, is a toxic mix.  There is the comparison with the Muslim population at the adjoining border of the Ganges River outflow in Bangladesh.  One might also look at the catholic Portuguese population in Goa, the Jewish population in Mumbai and Kochi, and the nearby Catholic population.  There is no malnutrition in those populations, or in the Siiks.  This is undoubtedly a cultural phenomenon of ancient origin.  (The migration of the jews and of the catholics to Kochi occurred around the Indian Ocean at the time of Christ.  The catholic population in Goa was from Portugal.

I don’t think we have enough of the story here.  The Ganges river flows centrally across India, and is not far from the Himalayas.  This has some significance in the sufficiency of animal protein availability, and most importantly, of what I might expect of the tissue S:N ratio, which is critical for availability of methionine, S-adenosyl methionine, and mitochondrial energy reactions.  These are also mediated by transsulfuration reactions and by cystathionine beta-synthase.  Detailed discussions are available elsewhere.   It has been pointed out by Vernon Young and Yve Ingenbleek that sulfur is insufficient in the soil where there is not a lava flow of volcanic ash, which could be the case here.  So it is at best not a good geographic situation, even before compounding the issue.

The relationship to heart attack and stroke is established for elevated homocysteine.

Homocysteine and Vascular Disease
STEVEN E . S. MINER , M.D. , DAVID E .C. COLE *, M.D. , PHD. AND DUNCAN J . STEWART, M.D.
Cardiology Rounds   A U G U S T 1 9 9 6 ;  I(5)

Homocysteine is a naturally occurring, sulfur-containing amino acid. Continuously formed and catabolized in vivo, its metabolism is dependent on a complex interaction of genetics and physiology (Fig. 1). Its relevance is based on the increasing recognition of the correlation between elevated levels of homocysteine and human disease.

Table 1
Selected Determinants of Plasma Homocysteine*
1. Genetic
• Cystathionine-beta-synthase:
heterozygote mutations 0.5-1.5% {451}
• Methionine synthase: rare
• MTHFR: heterozygote mutations
approximately 50% {403}
2. Physiologic
• age: Hcy increases with increasing age {336}
• sex: pre-and post-menopausal women
have lower levels than men {247}
• diet: related to methionine and vitamin cofactor
(folate, vitamins B6 and B12) intake {437}
• alcohol: relationship unclear {375}
3. Pathologic
• vitamin deficiency: increased homocysteine
concentrations {10}
• renal disease: increase correlated
with increasing serum creatinine {81}
• transplantation: increased levels {149, 435}
• post stroke: transiently decreased levels {341}
• severe psoriasis: elevated levels {438}
4. Medications
• oral contraceptives/hormone replacement:
decreased levels {269}
• corticosteriods: increased {159}
• cyclosporine: increased {393}
• smoking: increased {336}

Abstracts of Interest
Serum total homocysteine and coronary heart disease in middleaged
British men.
IJ PERRY, H REFSUM, RW MORRIS, SB EBRAHIM, PM UELAND, AG SHAPER.
D E PA RTMENT OF PRIMARY CARE & POPULATION SCIENCES, ROYAL FREE
H O S P I TAL SCHOOL OF MEDICINE, LONDON, AND DEPA RTMENT OF CLINICAL
B I O L O G Y, UNIVERSITY OF BERGEN, NORWAY.
Serum total homocysteine (tHcy) levels are inversely associated with dietary intake of folic acid and B vitamins. Raised tHcy levels have been linked with coronary heart disease (CHD). We have examined the association between tHcy concentration and the subsequent risk of CHD, using a nested case control study design, within a prospective study of cardiovascular disease in British men. tHcy concentration was measured in serum samples, stored at entry to the study, from 110 incident cases of myocardial infarction and 118 controls. Cases were randomly sampled from events which occured after the first five years of follow-up. Cases and controls were frequency matched by town and age group. Levels of homocysteine [geometric mean (95% CI)] were significantly higher in cases than controls: homocysteine 13.5 (12.6 – 14.3) μmol/L vs 11.9 (11.3 – 12.6) μmol/L; p=0.005. There was a graded increase in the relative risk (odds ratio; OR) of CHD in the 2nd, 3rd and 4th quartile of tHcy (OR 1.4, 1.9, 2.2; trend p=0.006) relative to the first quartile. Adjustment for age, town, social class, body mass index, smoking, physical activity, alcohol intake, hypertensive status, serum cholesterol, and serum creatinine did not attenuate this association, (OR 2.1, 2.3, 2.7; trend p=0.04). tHcy levels were higher at baseline in men with evidence of pre-existing CHD and (as expected) adjustment for this factor attenuated the linear association between tHcy and subsequent events, trend p=0.07. The findings suggest that homocysteine is an independent risk factor for CHD
with no threshold level.
Reprinted from Heart, Volume 75 /Number 5 (Supplement 1), May 1996.
Homocysteine and Coronary Atherosclerosis
ELLEN L. MAYER, MD, DONALD W. JACOBSEN, PHD, KILLIAN ROBINSON, MD,
FACC, CLEVELAND, OHIO
The conventional risk factors for premature coronary artery disease include smoking, hyperlipidemia, hypertension, diabetes and a positive family history. However, many patients have precocious atherosclerosis without having any of these standard risk factors. Identification of other markers that increase the risk of coronary disease may improve our understanding of the pathophysiologic mechanisms of this disorder and allow the development of new preventive or therapeutic measures. An elevated plasma homocysteine level has recently received greater attention as an important risk factor for vascular disease, including coronary atherosclerosis. This review discusses the biochemistry of homocysteine and the related metabolic importance of folate, vitamin B6 (pyridoxine) and B12 (cobalamin) as well as a number of essential enzymes. The major factors that influence homocysteine concentration are genetic, nutritional and pathologic.
There is a large body of experimental and clinical evidence for high plasma homocysteine to be a risk factor for vascular disease, including coronary atherosclerosis.
Excerpted from Journal of the American College of Cardiology 1996;27:517-27

An important meta-analysis by Boushey et al in 1995 further quantified the magnitude of risk. In their analysis of all major studies available at that time, they found a linear, independent risk  for increments in homocysteine. There were no levels above or below which an incremental rise in homocysteine did not affect cardiovascular risk. Specifically, every 5 μmol/L increment in homocysteine was found to be associated with odds ratios of 1.6 for m e n ; (95% Cl 1.4-1.7) and 1.8 for women; (95% CI 1.3-1.9) for coronary artery disease.

Cystathionine beta synthase (CBS) catalyzes the reaction taking homocysteine to cystathionine. This enzyme requires pyridoxine as a co-factor and is an integral part of the transsulfuration or
pyridoxine – dependent pathway. 33 distinct mutations have been identified with heterozygosity occurring at a prevalence of 0.5-1.5%. The majority of heterozygotes will have normal fasting homocysteine levels, but can be detected with a methionine load test.

Hyperhomocysteinemia is a Biomarker of Sulfur-Deficiency in Human Morbidities

Yves Ingenbleek
Laboratory of Nutrition, University Louis Pasteur Strasbourg, France
The Open Clinical Chemistry Journal, 2009, 2, 49-60

Abstract: Methionine (Met) is crucially involved in the synthesis of S-compounds endowed with molecular, structural and functional properties of survival value. Dietary Met may undergo transmethylation processes to release homocysteine (Hcy) which may either be regenerated to Met following remethylation (RM) pathways or catabolized along the transsulfuration
(TS) cascade. The activity of enzymes governing RM and TS pathways is depending on pyridoxine, folate and cobalamin bioavailability. Dietary restriction in any of these watersoluble B-vitamins may lead to hyperhomocysteinemia (HHcy) causing a panoply of cardiovascular disorders. Taken together, the vitamin triad only affords partial account of Hcy variance, prompting the search for additional causal factor(s). Body composition studies demonstrate that nitrogen (N) and sulfur (S) maintain tightly correlated concentrations in tissues of both healthy subjects and diseased patients. Any morbid condition characterized by insufficient N intake or assimilation, as seen in protein malnutrition or intestinal malabsorption, reduces body S accretion rates. Excessive urinary N-losses, as reported in acute or chronic inflammatory disorders, entail proportionate obligatory S-losses. As a result, lean body mass (LBM) undergoes downsizing and concomitant depletion of N and S body stores which depresses the activity of cystathionine-􀀁-synthase, thereby promoting upstream accumulation of Hcy and overstimulation of RM processes. HHcy thus appears as the dark side of efforts developed by S-deprived patients to safeguard Met homeostasis. Irrespective of vitamin-B status, Hcy values are negatively correlated with LBM shrinkage well identified by the serial measurement of plasma transthyretin (TTR). The S deprivation theory fulfills the gap and allows full causal coverage of the metabolic anomaly, hence providing together with vitamin-deficiencies an unifying overview of the main nutritional determinants implicated in HHcy epidemiology.

The Oxidative Stress of Hyperhomocysteinemia Results from Reduced Bioavailability of Sulfur-Containing Reductants

Yves Ingenbleek
Laboratory of Nutrition, Faculty of Pharmacy, University Louis Pasteur Strasbourg, France
The Open Clinical Chemistry Journal, 2011, 4, 34-44

Abstract: Vegetarian subjects consuming subnormal amounts of methionine (Met) are characterized by subclinical protein malnutrition causing reduction in size of their lean body mass (LBM) best identified by the serial measurement of plasma transthyretin (TTR). As a result, the transsulfuration pathway is depressed at cystathionine-beta-synthase (C-b-S) level triggering the upstream sequestration of homocysteine (Hcy) in biological fluids and promoting its conversion to Met. Maintenance of beneficial Met homeostasis is counterpoised by the drop of cysteine (Cys) and glutathione (GSH) values downstream to CbS causing in turn declining generation of hydrogen sulfide (H2S) from enzymatic sources. The biogenesis of H2S via non-enzymatic reduction is further inhibited in areas where earth’s crust is depleted in elemental sulfur (S8) and sulfate oxyanions. Combination of subclinical malnutrition and S8-deficiency thus maximizes the defective production of Cys, GSH and H2S reductants, explaining persistence of unabated oxidative burden. The clinical entity increases the risk of developing cardiovascular diseases (CVD) and stroke in underprivileged plant-eating populations regardless of Framingham criteria and vitamin-B status. Although unrecognized up to now, the nutritional disorder is one of the commonest worldwide, reaching top prevalence in populated regions of Southeastern Asia. Increased risk of hyperhomocysteinemia and oxidative stress may also affect individuals suffering from intestinal malabsorption or westernized communities
having adopted vegan dietary lifestyles.

 

 

 

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Transthyretin and Lean Body Mass in Stable and Stressed State

Curator: Larry H Bernstein, MD, FCAP

Chapter 20
Plasma Transthyretin Reflects the Fluctuations
of Lean Body Mass in Health and Disease
Yves Ingenbleek
Abstract

Transthyretin (TTR) is a 55-kDa protein secreted mainly by the choroid plexus and the liver. Whereas its intracerebral production appears as a stable secretory process allowing even distribution of intrathecal thyroid hormones, its hepatic synthesis is influenced by nutritional and inflammatory circumstances working concomitantly. Both morbid conditions are governed by distinct pathogenic mechanisms leading to the reduction in size of lean body mass (LBM). The liver production of TTR integrates the dietary and stressful components of any disease spectrum, explaining why it is the sole plasma protein whose evolutionary patterns closely follow the shape outlined by LBM fluctuations. Serial measurement of TTR therefore provides unequalled information on the alterations affecting overall protein nutritional status. Recent advances in TTR physiopathology emphasize the detecting power and preventive role played by the protein in hyperhomocysteinemic states, acquired metabolic disorders currently ascribed to dietary restriction in water-soluble vitamins. Sulfur (S)-deficiency is proposed as an additional causal factor in the sizeable proportion of hyperhomocysteinemic patients characterized by adequate vitamin intake but experiencing varying degrees of nitrogen (N)-depletion. Owing to the fact that N and S coexist in plant and animal tissues within tightly related concentrations, decreasing LBM as an effect of dietary shortage and/or excessive hypercatabolic losses induces proportionate S-losses. Regardless of water-soluble vitamin status, elevation of homocysteine plasma levels is negatively correlated with LBM reduction and declining TTR plasma levels. These findings occur as the result of impaired cystathionine-b-synthase activity, an enzyme initiating the transsulfuration pathway and whose suppression promotes the upstream accumulation and remethylation of homocysteine molecules. Under conditions of N- and S-deficiencies,the maintenance of methionine homeostasis indicates high metabolic priority.
Y. Ingenbleek
Laboratory of Nutrition, University Louis Pasteur Strasbourg
e-mail: yves.ingenbleek@wanadoo.fr
S.J. Richardson and V. Cody (eds.), Recent Advances in Transthyretin Evolution, 329
Structure and Biological Functions,
DOI: 10.1007/978‐3‐642‐00646‐3_20, # Springer‐Verlag Berlin Heidelberg 2009

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Vegan Diet is Sulfur Deficient and Heart Unhealthy

Larry H. Bernstein, MD, FCAP, Curator

 

The following is a reblog of “Heart of the Matter: Plant-Based Diets Lead to High Homocysteine, Low Sulfur and Marginal B12 Status”
Posted on September 26, 2011 by Dr Kaayla Daniel in WAPF Blog and tagged B12, Forks over Knives, Kaayla T. Daniel, Kilmer S. McCully, Yves Ingenbleek

It is a report of a scientific study carried out by Kilmer S. Cully and Yves Ingenbleek, Harvard Pathology and Univ Louis Pasteur.  I have previously written about the conundrum of transthyretin as an accurate marker of malnutrition, but also being lowered by the septic state.  This is accounted for by the catabolic state that sets off autocannabalization of skeletal muscle and lean body mass to provide gluconeogenic precursors to sustain life.  While serum albumin and transthyretin both decline, the former has a half-life of 20 days, while the latter is 48 hours.  Much work has been done to gain a better understand this rapid turnover protein that transports thyroxine, and the immediate result of the decline in concentration is a shift the the hormone protein binding equilibrium increasing the free thyroxine, a euthyroid hyperthyroid effect.  However, much work by Prof. Inglenbleek, some ion collaboration with Vernon Young, at MIT, showed that transthyretin reflects the sulfur stores of animals.  The sulfur to nitrogen ratio of plants is 1:20, but it is 1:12 in man, so the dietary intake would affect an omnivorous animal.  Recall that S is carried on amino acids that take part in disulfide linkage.  A deficiency in S containing amino acids would have a negative health effect.  The story is presented here.

The World Health Organization (WHO) reports that 16.7 million deaths occur worldwide each year due to cardiovascular disease, and more than half of those deaths occur in developing countries where plant-based diets high in legumes and starches are eaten by the vast majority of the people.

Yet “everyone knows” plant-based diets prevent heart disease.  Indeed this myth  is repeated so often that massive numbers of educated, health-conscious individuals in first world countries are consciously adopting third world style diets in the hope of preventing disease, optimizing health and maximizing longevity.   But if the WHO statistics are correct, plant-based diets might not be protective at all.   And today’s fashionable experiment in veganism could end very badly indeed.

A study out August 26 in the journal Nutrition makes a strong case against plant-based diets for prevention of heart disease.  The title alone  –  “Vegetarianism produces subclinical malnutrition, hyperhomocysteinemia and atherogenesis” — sounds a significant warning.   The article establishes  why subjects who eat mostly vegetarian diets develop morbidity and mortality from cardiovascular disease unrelated to vitamin B status and Framingham criteria.

Co-author Kilmer S. McCully, MD, “Father of the Homocysteine Theory of Heart Disease,” is familiar to WAPF members as winner of the Linus Pauling Award, WAPF’s Integrity in Science Award, and author of numerous articles published in peer-reviewed journals as well as the popular books The Homocysteine Revolution and The Heart Revolution.   In 2009 Dr. McCully was one of the signers of the Weston A. Price Foundation’s petition to the FDA in which we asked the agency to retract its unwarranted 1999 soy/heart disease health claim.  (http://www.westonaprice.org/soy-alert/soy-heart-health-claim)

Dr. McCully teamed up with Yves Ingenbleek, MD, of the University Louis Pasteur in Strasbourg, France, which funded the research.   Dr. Ingenbleek is well known for his work on malnutrition, the essential role of sulfur to nitrogen, and sulfur deficiency as a cause of  hyperhomocysteinemia.

The study took place in Chad, and involved 24 rural male subjects age 18 to 30, and 15 urban male controls, age 18-29.   (Women in this region of Chad could not be studied because of their animistic beliefs and proscriptions against collecting their urine.)

The rural men were apparently healthy, physically active farmers with good lipid profiles.  Their staple foods included cassava, sweet potatoes, beans, millet and ground nuts.   Cassava leaves, cabbages and carrots provided good levels of carotenes, folates and pyridoxine (B6).  The diet is plant-based there because of a shortage of grazing lands and livestock, but subjects occasionally consume  some B12-containing foods, mostly poultry and eggs, though very little dairy or meat.   Their diet could be described as high carb, high fiber,  low in both protein and fat, and low in the sulfur containing amino acids.    In brief, the very diet recommended by many of today’s nutritional “experts” for overall good health and heart disease prevention.

The urban controls were likewise healthy and ate a similar diet, but with beef, smoked fish and canned or powdered milk regularly on the menus.  Their diet was thus higher in protein, fat and the sulfur-containing amino acids though roughly equivalent in calories.

Dr. McCully’s research over the past 40 years on the pathogenesis of atherosclerosis has shown the role of homocysteine in free radical damage and the protective effect of  vitamins B6, B12 and folate.   Indeed, many doctors today recommend taking this trio of B vitamins as an inexpensive heart disease “insurance policy.”

In Chad, both groups showed adequate levels of B6 and folate.  The B12 levels of the vegetarian group were lower, but the difference was only of “borderline significance.”   However, as the researchers point out, ”A previous study undertaken in the same Chadian area in a larger group of 60 rural participants did demonstrate a weak inverse correlation between B12 and homocysteine concentrations in the 20 subjects most severely protein depleted .  .  .  It is therefore likely that the hyperhomocysteinemia status of some of our rural subjects in the present survey might have resulted from combined B12 and protein deficiencies.   The correlation of B12 deficiency with hyperhomocysteinemia could well reach statistical significance if a larger groups of subjects were studied.”

Clearly it’s wise for people on plant-based diets to supplement their diets with B12, but protein malnutrition must also be addressed.   And the issue is not just getting enough protein to eat, but the right kind.   Quality, not just quantity.   The bottom line is we must eat  protein rich in bioavailable, sulfur-containing amino acids — and that means animal products.   (Vegans at this point will surely claim the issue is insufficient protein and trot out soy as the solution.   Soy is indeed a  complete plant based protein, but notoriously low in methionine.  It does contain decent levels of cysteine, but the cysteine is bound up in protease inhibitors, making it largely  biounavailable. (For more information, read  my book The Whole Soy Story: The Dark Side of America’s Favorite Health Food, endorsed by Dr. McCully, as well as our petition to the FDA noted above.)

So what did  Drs. Ingenbleek and  McCully find among the study group of protein-deficient people?   Higher levels of homocysteine, of course.  Also significant alterations in body composition,  lean body mass, body mass index and plasma transthyretin levels.  In plain English, the near-vegetarian subjects were thinner, with poorer muscle tone and showed subclinical signs of protein malnutrition.   (So much for popular ideas of extreme thinness being healthy. )

The plant-based diet of the study group was low in all of the sulfur-containing amino acids.   As would be expected, labwork on these men showed lower plasma cysteine and glutathione levels compared to the controls.  Methionine levels, however,  tested comparably.   The explanation for this is  “adaptive response.”   In brief, mammals trying to function with insufficient sulfur-containing amino acids will do whatever’s necessary to survive.   Given the essential role of methionine in metabolic processes, that means deregulating the transsulfuration pathway, increasing homocysteine levels, and methylating homocysteine to make methionine.

Ultimately, it all boils down to our need for sulfur.   As Stephanie Seneff, PhD, and many others have written in Wise Traditions and on this website, sulfur is vital for disease prevention and maintenance of good health.   In terms of heart disease, Drs. Ingenbleek and McCully have shown sulfur deficiency not only leads to high homocysteine levels, but is the likeliest reason some clinical trials using B6, B12 and folate interventions have proved ineffective for the prevention of cardiovascular and cerebrovascular diseases.    Over the past few years, headlines from such studies have led to widespread dismissal of Dr. McCully’s  “Homocysteine Theory of Heart Disease” and renewed media focus on cholesterol, c-reactive protein and other possible culprits that can be treated by statins and other profitable drugs.   In contrast, Drs. McCully and Ingenbleek research suggests we can better prevent heart disease with three inexpensive B vitamins and traditional diets rich in the sulfur-containing amino acids found in animal foods.

In the blaze of publicity surrounding Forks Over Knives and other blasts of vegan propaganda, few people are likely to hear about this study.   That’s sad, for it provides an important missing piece in our knowledge of heart disease development, a strong argument against the plant-based fad, and a bright new chapter in what the New York Times has called “The Fall and Rise of Kilmer McCully.”

*  *  *  *  *

Thanks to Sylvia Onusic PhD who was able to access a full text copy of this article to share with  me.

This entry was posted in WAPF Blog and tagged B12, Forks over Knives, Kaayla T. Daniel, Kilmer S. McCully, Naughty Nutritionist, soy, sulfur, Yves Ingenbleek. Bookmark the permalink.

Sylvia says:

September 26, 2011 at 5:32 pm

Kaayla, I found the article but you brought it to life- what a great explanation backed by high levels of knowledge and analysis. We are grateful for your numerous contributions to the field of health!
Thanks so much.

Sylvia Onusic

 

 

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Amyloidosis with Cardiomyopathy

Author: Larry H Bernstein, MD, FACP
Introduction
Amyloidosis describes the various clinical syndromes that occur as a result of damage by amyloid deposits in tissues and organs throughout the body.  Systemic amyloidosis is a relatively rare multisystem disease caused by the deposition of misfolded protein in various tissues and organs. The term amyloid describes the deposition in the extracellular space of certain proteins in a highly characteristic, insoluble fibrillar form.  The disease entity is a disorder of misfolded or misassembled proteins.  There is extracellular amyloid fiber laid down as cross β-sheets disrupting organ function, which may affect the pancreas, kidney, autonomic nervous system, the heart, and in one form causes carpal tunnel syndrome.
It may present to almost any specialty, and diagnosis is frequently delayed. Cardiac involvement is a leading cause of morbidity and mortality, especially in primary light chain (AL) amyloidosis and in both wild-type and hereditary transthyretin amyloidosis. The heart is also occasionally involved in acquired serum amyloid A type (AA) amyloidosis and other rare hereditary types. Clinical phenotype varies greatly between different types of amyloidosis, and even the cardiac presentation has a great spectrum. The incidence of amyloidosis is uncertain, but it is thought that the most frequently diagnosed AL amyloidosis has an annual incidence of 6 to 10 cases per million population in the United Kingdom and United States.
The molecular basis for this particular phenomenon came with the extensive work done on multiple myeloma, antibody structure, and light chains.  In 1950, the discovery of a familial amyloid polyneuropathy was described in Portugal, and there were similar diseases in Sweden and Japan.  There were 72 known variants of transthyretin (TTR) in 1995, and now there are 100.  In addition, the occurance of different TTR associated variants with and without (amyloid) is found is Brazil, UK, US, Israel, Spain, France, Germany, Denmark, and Africa.  The table of variants, organ damage, and geographic location is too large to place on this document. If we refer to amyloid cardiomyopathy, it is exclusively a primary amyloidopathy, not secondary to light chain disorders or an inflammatory disease.  If we consider amyloidosis, we also have to consider family history, organ dysfunction, and we have to make a distinction between primary cardiac involvement, autonomic nervous system instability, and the two coexisting.  Familial amyloid polyneuropathy (FAP) is an extremely debilitating and progressive disease that is only treatable by liver transplantation.  Primary amyloid cardiomyopathy has been treated by heart transplant.  The qualifying statement here is, it depends.

Primary and Secondary Amyloidoses

Amyloid was originally described by pathologists based on microscopy. Amyloidoses are a systemic primary or secondary disease. There are distinctions to be made based on location and type.  The clinical significance of amyloid disease varies enormously, ranging from incidental asymptomatic deposits to localized disease through to rapidly fatal systemic forms that can affect multiple vital organs.
Common causes of secondary amyloidosis are – light chain production (AL) as in plasma cell dyscrasia, amyloid A (AA), senile systemic amyloidosis (diagnosed rarely in life).  The systemic amyloidoses are designated by a capital A (for amyloid) followed by the abbreviation for the chemical identity of the fibril protein. Thus, TTR amyloidosis is abbreviated ATTR, and immunoglobulin light chain type amyloidosis is abbreviated AL. Both normal-sequence TTR and variant-sequence TTR form amyloidosis. Normal-sequence TTR forms cardiac amyloidosis in elderly people, termed senile cardiac amyloidosis (SCA). When it was recognized that SCA is often accompanied by microscopic deposits in many other organs, the alternative name senile systemic amyloidosis (SSA) was proposed. Both terms are now used.
Currently available therapy is focused on reducing the supply of the respective amyloid fibril precursor protein and supportive medical care, which together have greatly improved survival. Chemotherapy and anti-inflammatory treatment for the disorders that underlie AL and AA amyloidosis are guided by serial measurements of the respective circulating amyloid precursor proteins, i.e. serial serum free light chains in AL and serum amyloid A protein in AA type.
Quality of life and prognosis of some forms of hereditary systemic amyloidosis can be improved by liver and other organ transplants. Various new therapies, ranging from silencing RNA, protein stabilizers to monoclonal antibodies, aimed at inhibiting fibril precursor supply, fibril formation or the persistence of amyloid deposits, are in development; some are already in clinical phase.
Ann Clin Biochem May 2012; 49(3 ): 229-241   http://acb.2011.011225v1 49/3/229

What is transthyretin (TTR)?

TTR is a  tetramer of 4 127 amino acid subunits synthesized by the liver that circulates as a transporter of thyroxin, and with retinol-binding protein, transports vitamin A.  It was originally defined by the migration in electrophoresis more anodal to albumin, hence, prealbumin.  It is present in cerebrospinal fluid, secreted by the choroid plexus.  The TTR monomer contains 8 antiparallel beta pleated sheet domains. TTR can be found in plasma and in cerebrospinal fluid and is synthesized by the choroid plexus of the brain and, to a lesser degree, by the retina. Its gene is located on the long arm of chromosome 18 and contains 4 exons and 3 introns.
The concentration in serum can be expected to be above 20 mg/dL in a health adult, but the protein decreases by 1 mg/dL/day postoperatively, and it decreases with acute or chronic renal failure, pneumonia or sepsis, rising again with the onset of anabolism.  Patients in the pulmonary intensive care unit have TTR levels that remain low for 7-10 days, but followup data for the remainder of the hospital stay or in relationship to readmission in the six months after release from hospital care was not part of the study.
A decrease in TTR is associated with the systemic inflammatory response, whereby, the liver reprioritizes the synthesis of proteins with an increase in acute phase reactants (APRs), namely, C-reactive protein (CRP) and a-1 acid glycoprotein, and decreased albumin and TTR.  The inflammatory condition maintains a euthyroid status with decreased TTR because of the availability of free thyroxine in equilibrium with the lower binding protein.  This has been referred to sick euthyroid status. The role in thyroxine transport is not insignificant, as chronic protein malnutrition is associated with hypothyroidism, as originally described by Prof. Yves Ingenbleek, Univ. Louis Pateur, Starsbourg, Fr. in Senegalese children with Kwashiorkor.  However, the importance of TTR as a unique biomarker is not to be downgraded because of what is often refered to as “an inverted APR”.
Transthyretin was discovered to be a good reflection of the “lean body mass”, by Vernon Young, MIT, and Ingenbleek, as a result of 3 decades of study. The ratio of S:N being 1:20 in plant proteins and 1:12.5 in animal sources, is closely related to methylation reactions and sustained deficiency of S intake results in elevated homocysteine level.

What is FAP?

Familial amyloid polyneuropathy (FAP), also called transthyretin-related hereditary amyloidosis, transthyretin amyloidosis or Corino de Andrade’s disease, is an autosomal dominant neurodegenerative disease. It is a form of amyloidosis, and was first identified and described by Portuguese neurologist Mário Corino da Costa Andrade, in the 1950s.FAP is distinct from senile systemic amyloidosis (SAS), which is not inherited, and which was determined to be the primary cause of death for 70% of supercentenarians who have been autopsied.
Familial amyloid polyneuropathy (FAP) is an extremely debilitating and progressive disease that is only treatable by liver transplantation.  Primary amyloid cardiomyopathy has been treated by heart transplant.  The qualifying statement here is, it depends.  Those patients with TTR-amyloidopathy have a specific gene substitution in the TTR gene. Consequently, there is circulation TTR, but it is not effectively involved in thyroxine transport.

Characteristics.

Usually manifesting itself between 20 and 40 years of age, it is characterized by pain, paresthesia, muscular weakness and autonomic dysfunction. In its terminal state, the kidneys and the heart are affected. FAP is characterized by the systemic deposition of amyloidogenic variants of the transthyretin protein, especially in the peripheral nervous system, causing a progressive sensory and motor polyneuropathy. The age at symptom onset, pattern of organ involvement, and disease course vary, but most mutations are associated with cardiac and/or nerve involvement. The gastrointestinal tract, vitreous, lungs, and carpal ligament are also frequently affected. When the peripheral nerves are prominently affected, the disease is termed familial amyloidotic polyneuropathy (FAP). When the heart is involved heavily but the nerves are not, the disease is called familial amyloid cardiomyopathy (FAC). Regardless of which organ is primarily targeted, the general term is simply amyloidosis-transthyretin type, abbreviated ATTR.

Genetics.

  1. TTR mutations accelerate the process of TTR amyloid formation and are the most important risk factor for the development of clinically significant ATTR. More than 85 amyloidogenic TTR variants cause systemic familial amyloidosis. The variant TTR is mostly produced by the liver. Amyloidogenic TTR mutations destabilize TTR monomers or tetramers, allowing the molecule to more easily attain an amyloidogenic intermediate conformation. The tetramer has to dissociate into misfolded monomers to aggregate into a variety of structures including amyloid fibrils. Because most patients are heterozygotes, they deposit both mutant and wild type TTR subnits.
  2. Familial amyloid polyneuropathy has an autosomal dominant pattern of inheritance. FAP is caused by a mutation of the TTR gene, located on human chromosome 18q12.1-11.2. A replacement of valine by methionine at position 30 (TTR V30M) is the mutation most commonly found in FAP.
  3. The disease in the TTR V30M kindreds was termed FAP because early symptoms arose from peripheral neuropathy, but these patients actually have systemic amyloidosis, with widespread deposits often involving the heart, gastrointestinal tract, eye, and other organs.
  4. TTR V122I: This variant, carried by 3.9% of African Americans and over 5% of the population in some areas of West Africa, increases the risk of late-onset (after age 60 years) cardiac amyloidosis. It appears to be the most common amyloid-associated TTR variant worldwide. Affected patients usually do not have peripheral neuropathy.
  5. TTR T60A: This variant causes late-onset systemic amyloidosis with cardiac, and sometimes neuropathic, involvement. This variant originated in northwest Ireland and is found in Irish and Irish American patients.
  6. TTR L58H: Typically affecting the carpal ligament and nerves of the upper extremities, this variant originated in Germany. It has spread throughout the United States but is most common in the mid-Atlantic region.
  7. TTR G6S: This is the most common TTR variant, but it appears to be a neutral polymorphism not associated with amyloidosis. It is carried by about 10% of people of white European descent.

Cardiac transthyretin (TTR) amyloidosis

Cardiac amyloidosis of transthyretin fibril protein (ATTR) type is an infiltrative cardiomyopathy characterised by ventricular wall thickening and diastolic heart failure. More than 27 different precursor proteins have the propensity to form amyloid fibrils. The particular precursor protein that misfolds to form amyloid fibrils defines the amyloid type and predicts the patient’s clinical course. Several types of amyloid can infiltrate the heart, resulting in progressive diastolic and systolic dysfunction, congestive heart failure, and death.  Increased access to cardiovascular magnetic resonance imaging has led to a marked increase in referrals to St George’s University of London, London (Dr. Jason Dungu) of Caucasian patients with wild-type ATTR (senile systemic) amyloidosis and Afro-Caribbean patients with the hereditary ATTR V122I type. Both subtypes present predominantly as isolated cardiomyopathy. The differential diagnosis includes cardiac amyloid light-chain (AL) amyloidosis, which has a poorer prognosis and can be amenable to chemotherapy.

Clinical Presentation

Cardiac amyloidosis, irrespective of type, presents as a restrictive cardiomyopathy characterized by progressive diastolic and subsequently systolic biventricular dysfunction and arrhythmia.1 Key “red flags” to possible systemic amyloidosis include nephrotic syndrome, autonomic neuropathy (eg, postural hypotension, diarrhea), soft-tissue infiltrations (eg, macroglossia, carpal tunnel syndrome, respiratory disease), bleeding (eg, cutaneous, such as periorbital, gastrointestinal), malnutrition/cachexia and genetic predisposition (eg, family history, ethnicity). Initial presentations may be cardiac, with progressive exercise intolerance and heart failure. Other organ involvement, particularly in AL amyloidosis, may cloud the cardiac presentation (eg, nephrotic syndrome, autonomic neuropathy, pulmonary or bronchial involvement). Pulmonary edema is not common early in the disease process, but pleural and pericardial effusions and atrial arrhythmias are often seen. Syncope is common and a poor prognostic sign. It is typically exertional or postprandial as part of restrictive cardiomyopathy, sensitivity to intravascular fluid depletion from loop diuretics combined with autonomic neuropathy, or conduction tissue involvement (atrioventricular or sinoatrial nodes) or ventricular arrhythmia. The latter may rarely cause recurrent syncope. Disproportionate septal amyloid accumulation mimicking hypertrophic cardiomyopathy with dynamic left ventricular (LV) outflow tract obstruction is rare but well documented. Myocardial ischemia can result from amyloid deposits within the microvasculature. Atrial thrombus is common, particularly in AL amyloidosis

Diagnosis and Treatment

imaging – Cardiovascular Magnetic Resonance in Cardiac Amyloidosis*.

Cardiac amyloidosis can be diagnostically challenging. Cardiovascular magnetic resonance (CMR) can assess abnormal myocardial interstitium. In cardiac amyloidosis, CMR shows a characteristic pattern of global subendocardial late enhancement coupled with abnormal myocardial and blood-pool gadolinium kinetics. The findings agree with the transmural histological distribution of amyloid protein and the cardiac amyloid load.
 *AM Maceira; J Joshi; SK Prasad; J Charles Moon, et al. Royal Brompton Hospital, London;
The diagnosis of amyloidosis requires histological identification of amyloid deposits. Congo Red staining renders amyloid deposits salmon pink by light microscopy, with a characteristic apple green birefringence under polarized light conditions. Additional immunohistochemical staining for precursor proteins identifies the type of amyloidosis.  Ultimately, immunogold electron microscopy and mass spectrometry confer the greatest sensitivity and specificity for amyloid typing.
Treatment of cardiac amyloidosis is dictated by the amyloid type and degree of involvement. Consequently, early recognition and accurate classification are essential.
Novel diagnostic and surveillance approaches using imaging (echocardiography, cardiovascular magnetic resonance), biomarkers (brain natriuretic peptide [BNP], high-sensitivity troponin), new histological typing techniques, and current and future treatments, including approaches directly targeting the amyloid deposits.

Etiology

Amyloidosis is caused by the extracellular deposition of autologous protein in an abnormal insoluble β-pleated sheet fibrillary conformation—that is, as amyloid fibrils. More than 30 proteins are known to be able to form amyloid fibrils in vivo, which cause disease by progressively damaging the structure and function of affected tissues. Amyloid deposits also contain minor nonfibrillary constituents, including serum amyloid P component (SAP), apolipoprotein E, connective tissue components (glycosaminoglycans, collagen), and basement membrane components (fibronectin, laminin). Amyloid deposits can be massive, and cardiac or other tissues may become substantially replaced. Amyloid fibrils bind Congo red stain, yielding the pathognomonic apple-green birefringence under cross-polarized light microscopy that remains the gold standard for identifying amyloid deposits.

AL Amyloidosis

AL amyloidosis is caused by deposition of fibrils composed of monoclonal immunoglobulin light chains and is associated with clonal plasma cell or other B-cell dyscrasias. The spectrum and pattern of organ involvement is very wide, but cardiac involvement occurs in half of cases and is sometimes the only presenting feature. Cardiac AL amyloidosis may be rapidly progressive. Low QRS voltages, particularly in the limb leads, are common. Thickening of the LV wall is typically mild to moderate and is rarely >18 mm even in advanced disease. Cardiac AL amyloid deposition is accompanied by marked elevation of the biomarkers BNP and cardiac troponin, even at an early stage. Involvement of the heart is the commonest cause of death in AL amyloidosis and is a major determinant of prognosis; without cardiac involvement, patients with AL amyloidosis have a median survival of around 4 years, but the prognosis among affected patients with markedly elevated BNP and cardiac troponin (Mayo stage III disease) is on the order of 8 months.

Hereditary Amyloidoses

Mutations in several genes, such as transthyretin, fibrinogen, apolipoprotein A1, and apolipoprotein A2 can be responsible for hereditary amyloidosis, but by far the most common cause is variant ATTR amyloidosis (variant ATTR) caused by mutations in the transthyretin gene causing neuropathy and, often, cardiac involvement.

TTR gene mutation

 The most common is the Val122Ile mutation. In a large autopsy study that included individuals with cardiac amyloidosis, the TTR Val122Ile allele was present in 3.9% of all African Americans and 23% of African Americans with cardiac amyloidosis. Penetrance of the mutation is not truly known and is associated with a late-onset cardiomyopathy that is indistinguishable from senile cardiac amyloidosis.

Pathology, Presentation, and Management of Amyloidoses

More than 100 genetic variants of TTR are associated with amyloidosis. Most present as the clinical syndrome of progressive peripheral and autonomic neuropathy. Unlike wild-type ATTR or variant ATTR Val122Ile, the features of other variant ATTR include vitreous amyloid deposits or, rarely, deposits in other organs. Cardiac involvement in variant ATTR varies by mutations and can be the presenting or indeed the only clinical feature. For example, cardiac involvement is rare in variant ATTR associated with Val30Met (a common variant in Portugal or Sweden), but it is almost universal and develops early in individuals with variant ATTR due to Thr60Ala mutation (a mutation common in Ireland).

Senile Systemic Amyloidosis (Wild-Type ATTR)

Wild-type TTR amyloid deposits are found at autopsy in about 25% of individuals >80 years of age.  The prevalence of wild-type TTR deposits leading to the clinical syndrome of wild-type ATTR cardiac amyloidosis is unknown. Wild-type ATTR is a predominantly cardiac disease, and the only other significant extracardiac feature is a history of carpal tunnel syndrome, often preceding heart failure by 3 to 5 years. Extracardiac involvement is most unusual.
Both wild-type ATTR and ATTR due to Val122Ile are diseases of the >60-year age group and are often misdiagnosed as hypertensive heart disease. Wild-type ATTR has a strong male predominance, and the natural history remains poorly understood, but studies suggest a median survival of about 7 years from presentation. Recent developments in cardiac magnetic resonance (CMR), which have greatly improved detection of cardiac amyloid during life, suggest that wild-type ATTR is more common than previously thought: It accounted for 0.5% of all patients seen at the UK amyloidosis center until 2001 but now accounts for 7% of 1100 cases with amyloidosis seen since the end of 2009. There appears to be an association between wild-type ATTR and history of myocardial infarctions, G/G (Val/Val) exon 24 polymorphism in the alpha2-macroglobulin (alpha2M), and the H2 haplotype of the tau gene36; the association of tau with Alzheimer’s disease raises interesting questions as both are amyloid-associated diseases of aging.
ECG of a patient with cardiac AL amyloidosis showing small QRS voltages (defined as ≤6 mm height), predominantly in the limb leads and pseudoinfarction pattern in the anterior leads.
Echocardiography is characteristic. Typical findings include concentric ventricular thickening with right ventricular involvement, poor biventricular long-axis function with normal/near-normal ejection fraction and valvular thickening (particularly in wild-type or variant ATTR). Diastolic dysfunction is the earliest echocardiographic abnormality and may occur before cardiac symptoms develop. Biatrial dilatation in presence of biventricular, valvular, and interatrial septal thickening 53 is a useful clue to the diagnosis.
Transthoracic echocardiogram with speckle tracking. The red and yellow lines represent longitudinal motion in the basal segments, whereas the purple and green lines represent apical motion. This shows loss of longitudinal ventricular contraction at the base compared to apex.

Biomarkers.

High-sensitivity troponin is abnormal in >90% of cardiac AL patients, and the combination of BNP/NT-proBNP plus troponin measurements is used to stage and risk-stratify patients with AL amyloidosis at diagnosis. Very interestingly, the concentration of BNP/NT-proBNP in AL amyloidosis may fall dramatically within weeks after chemotherapy that substantially reduces the production of amyloidogenic light chains. The basis for this very rapid phenomenon, which is not mirrored by changes on echocardiography or CMR, remains uncertain, but a substantial fall is associated with improved outcomes.

Cardiac Magnetic Resonance.

CMR provides functional and morphological information on cardiac amyloid in a similar way to echocardiography, though the latter is superior for evaluating and quantifying diastolic abnormalities. An advantage of CMR is in myocardial tissue characterization. Amyloidotic myocardium reveals subtle precontrast abnormalities (T1, T2), but extravascular contrast agents based on chelated gadolinium provide the key information.

CMR with the classic amyloid global, subendocardial late gadolinium enhancement pattern in the left ventricle with blood and mid-/epimyocardium nulling together.
Recently, the technique of equilibrium contrast CMR has demonstrated much higher extracellular myocardial volume in cardiac amyloid than any other measured disease. It is anticipated that accurate measurements of the expanded interstitium in amyloidosis will prove useful in serial quantification of cardiac amyloid burden.
Sequential static images from a CMR TI scout sequence. As the inversion time (TI) increases, myocardium nulls first (arrow in image 3), followed by blood afterwards (arrow in image 6), implying that there is more gadolinium contrast in the myocardium than blood—a degree of interstitial expansion such that the “myocrit” is smaller than the hematocrit.

Tissue biopsy.

To confirm amyloidosis, including familial TTR amyloidosis, the demonstration of amyloid deposition on biopsied tissues is essential. With Congo red staining, amyloid deposits show a characteristic yellow-green birefringence under polarized light. Tissues suitable for biopsy include: subcutaneous fatty tissue of the abdominal wall, skin, gastric or rectal mucosa, sural nerve, and peritendinous fat from specimens obtained at carpal tunnel surgery. Sensitivity of endoscopic biopsy of gastrointestinal mucosa is around 85%; biopsy of the sural nerve is less sensitive. It is ideal to show that these amyloid deposits are specifically immunolabeled by anti-TTR antibodies.

Serum variant TTR protein.

TTR protein normally circulates in serum or plasma as a soluble protein having a tetrameric structure [Kelly 1998, Rochet & Lansbury 2000]. Normal plasma TTR concentration is 20-40 mg/dL (0.20-0.40 mg/mL).  Pathogenic mutations in TTR cause conformational change in the TTR protein molecule, disrupting the stability of the TTR tetramer, which is then more easily dissociated into pro-amyloidogenic monomers.

After immunoprecipitation with anti-TTR antibody, serum variant TTR protein can be detected by mass spectrometry. Approximately 90% of TTR variants so far identified are confirmed by this method. Mass shift associated with each variant TTR protein is indicated.

Molecular genetic testing.

  • TTR is the only gene in which mutations are known to cause familial TTR amyloidosis.
  • Identified in many individuals of different ethnic backgrounds; found in large clusters in Portugal, Sweden, and Japan.
  • The gene has four exons; and all the hitherto-identified mutations are in exons 2, 3, or 4.
GeneReviews designates a molecular genetic test as clinically available only if the test is listed in the GeneTests Laboratory Directory by either a US CLIA-licensed laboratory or a non-US clinical laboratory.
  • Molecular genetic testing of TTR by sequence analysis (may be preceded by targeted mutation analysis)
  • Although deletion/duplication testing is available clinically, no exonic or whole-gene deletions or duplications involving TTR have been reported to cause familial transthyretin amyloidosis.
  • However, with newly available deletion/duplication testing methods, it is theoretically possible that such mutations may be identified in affected individuals in whom prior testing by sequence analysis of the entire coding region was negative.
  • Predictive testing for at-risk asymptomatic adult family members requires prior identification of the disease-causing mutation in the family.
  • Prenatal diagnosis and preimplantation genetic diagnosis (PGD) for at-risk pregnancies require prior identification of the disease-causing mutation in the family.

Genetically Related (Allelic) Disorders

Familial euthyroid hyperthyroxinemia is caused by normal allelic variants in TTR, including Gly6Ser, Ala109Thr, Ala109Val, and Thr119Met (see Table 5) [Nakazato 1998, Benson 2001, Saraiva 2001]. The TTR protein binds approximately 15% of serum thyroxine. These mutations increase total serum thyroxine concentration because of their increased affinity for thyroxine, however, they increase neither free thyroxine nor free triiodothyronine. Therefore, individuals with these sequence variants develop no clinical symptoms (i.e., they are euthyroid).
Senile systemic amyloidosis (SSA; previously called senile cardiac amyloidosis) results from the pathologic deposition of wild-type TTR, predominantly in the heart. Pathologic deposits are also seen in the lungs, blood vessels, and the renal medulla of the kidneys [Westermark et al 2003]. SSA affects mainly the elderly but is rarely diagnosed during life.
Sensorimotor neuropathy and autonomic neuropathy progress over ten to 20 years. Various types of cardiac conduction block frequently appear. Cachexia is a common feature at the late stage of the disease. Affected individuals usually die of cardiac failure, renal failure, or infection.

Cardiac amyloidosis.

Cardiac amyloidosis, mainly characterized by progressive cardiomyopathy, has been reported with more than two thirds of TTR mutations. In some families with specific TTR mutations, such as Asp18Asn, Val20Ile, Pro24Ser, Ala45Thr, Ala45Ser, His56Arg, Gly57Arg, Ile68Leu, Ala81Thr, Ala81Val, His88Arg, Glu92Lys, Arg103Ser, Leu111Met, or Val122Ile, cardiomyopathy without peripheral neuropathy is a main feature of the disease.

Cardiac amyloidosis is usually late onset. Most individuals develop cardiac symptoms after age 50 years; cardiac amyloidosis generally presents with restrictive cardiomyopathy. The typical electrocardiogram shows a pseudoinfarction pattern with prominent Q wave in leads II, III, aVF, and V1-V3, presumably resulting from dense amyloid deposition in the anterobasal or anteroseptal wall of the left ventricle. The echocardiogram reveals left ventricular hypertrophy with preserved systolic function. The thickened walls present “a granular sparkling appearance.”
Among the mutations responsible for cardiac amyloidosis, Val122Ile is notable for its prevalence in African Americans. Approximately 3.0%-3.9% of African Americans are heterozygous for Val122Ile . The high frequency of Val122Ile partly explains the observation that in individuals in the US older than age 60 years, cardiac amyloidosis is four times more common among blacks than whites.

Leptomeningeal (oculoleptomeningeal) amyloidosis.

Amyloid deposition is seen in the pial and arachnoid membrane, as well as in the walls of vessels in the subarachnoid space associated with TTR mutations including Leu12Pro, Asp18Gly, Ala25Thr, Val30Gly, Ala36Pro, Gly53Glu, Gly53Ala, Phe64Ser, Tyr69His, or Tyr114Cys.  Individuals with leptomeningeal amyloidosis show CNS signs and symptoms including: dementia, psychosis, visual impairment, headache, seizures, motor paresis, ataxia, myelopathy, hydrocephalus, or intracranial hemorrhage. When associated with vitreous amyloid deposits, leptomeningeal amyloidosis is known as familial oculolepto-meningeal amyloidosis (FOLMA). In leptomeningeal amyloidosis protein concentration in the cerebrospinal fluid is usually high, and gadolinium-enhanced MRI typically shows extensive enhancement of the surface of the brain, ventricles, and spinal cord.

Genotype-Phenotype Correlations.

In subsets of families with the Val30Met mutation, considerable variation in phenotypic manifestations and age of onset is observed. It is hypothesized that genetic modifiers and non-genetic factors contribute to the pathogenesis and progression of familial TTR amyloidosis. The vast majority of individuals with familial TTR amyloidosis are heterozygous for a TTR mutation. It has been clinically and experimentally demonstrated that the normal allelic variant c.416C>T (Thr119Met) has a protective effect on amyloidogenesis in individuals who have the Val30Met mutation.

Cardiac amyloidosis is caused by Asp18Asn, Val20Ile, Pro24Ser, Ala45Thr, Ala45Ser, His56Arg, Gly57Arg, Ile68Leu, Ala81Thr, Ala81Val, His88Arg, Glu92Lys, Arg103Ser, Leu111Met, or Val122Ile. Peripheral and autonomic neuropathy are absent or less evident in persons with these mutations.
Leptomeningeal amyloidosis is associated with Leu12Pro, Asp18Gly, Ala25Thr, Val30Gly, Ala36Pro, Gly53Glu, Gly53Ala, Phe64Ser, Tyr69His, or Tyr114Cys.

Penetrance.

It is generally accepted that the penetrance is much higher in individuals in endemic foci than outside of endemic foci. In Portugal, cumulative disease risk in individuals with the Val30Met mutation is estimated at 80% by age 50 and 91% by age 70 years, whereas the risk in French heterozygotes is 14% by age 50 and 50% by age 70 years. In Sweden, the penetrance is much lower: 1.7% by age 30, 5% by age 40, 11% by age 50, 22% by age 60, 36% by age 70, 52% by age 80, and 69% by age 90, respectively.

Nomenclature

The neuropathy associated with TTR mutations, now called familial TTR amyloidosis, was formerly referred to as one of the following:
  • Familial amyloid polyneuropathy type I (or the Portuguese-Swedish-Japanese type)
  • Familial amyloid polyneuropathy type II (or the Indiana/Swiss or Maryland/German type)

Prevalence

The Val30Met mutation, found worldwide, is the most widely studied TTR variant and is responsible for the well-known large foci of individuals with TTR amyloid polyneuropathy in Portugal, Sweden, and Japan. Numerous families with various non-Val30Met mutations have also been identified worldwide.

 Small transthyretin (TTR) ligands as possible therapeutic agents in TTR amyloidoses.

Almeida MR, Gales L, Damas AM, Cardoso I, Saraiva MJ. Porto, Portugal.
Curr Drug Targets CNS Neurol Disord. 2005 Oct;4(5):587-96.
In transthyretin (TTR) amyloidosis TTR variants deposit as amyloid fibrils giving origin, in most cases, to peripheral polyneuropathy, cardiomyopathy, carpal tunnel syndrome and/or amyloid deposition in the eye. The amino acid substitutions in the TTR variants destabilize the tetramer, which may dissociate into non native monomeric intermediates that aggregate and polymerize in amyloid fibrils that further elongate. Since this is a multi-step process there is the possibility to impair TTR amyloid fibril formation at different stages of the process namely by tetramer stabilization, inhibition of fibril formation or fibril disruption. Based on the proposed mechanism for TTR amyloid fibril formation we discuss the action of some of the proposed TTR stabilizers such as derivatives of some NSAIDs (diflunisal, diclofenac, flufenamic acid, and derivatives) and the action of amyloid disrupters such as 4′-iodo-4′-deoxydoxorubicin (I-DOX) and tetracyclines. Among all these compounds, TTR stabilizers seem to be the most interesting since they would impair very early the process of amyloid formation and could also have a prophylactic effect.

Clusterin regulates transthyretin amyloidosis.

Lee KW, Lee DH, Son H, Kim YS, Park JY, et al.  Gyeongnam National University, South Korea
Biochem Biophys Res Commun 2009;388(2):256-60.   http://dx.doi.org/10.1016/j.bbrc.2009.07.166.
Clusterin has recently been proposed to play a role as an extracellular molecular chaperone, affecting the fibril formation of amyloidogenic proteins. The ability of clusterin to influence amyloid fibril formation prompted us to investigate whether clusterin is capable of inhibiting TTR amyloidosis. Here, we report that clusterin strongly interacts with wild-type TTR and TTR variants V30M and L55P under acidic conditions, and blocks the amyloid fibril formation of TTR variants. In particular, the amyloid fibril formation of V30M TTR in the presence of clusterin is reduced to level similar to wild-type TTR. We also demonstrated that clusterin is an effective inhibitor of L55P TTR amyloidosis, the most aggressive form of TTR diseases. The mechanism by which clusterin inhibits TTR amyloidosis appears to be through stabilization of TTR tetrameric structure.

Prognosis.

Cardiac amyloidosis in general has a poor prognosis, but this differs according to amyloid type and availability and response to therapy. Treatment may be classified as follows: supportive therapy (ie, modified heart-failure treatment including device therapy); therapies that suppress production of the respective amyloid fibril precursor protein (eg, chemotherapy in AL amyloidosis); and novel strategies to inhibit amyloid fibril formation or to directly target the amyloid deposits or stabilize the precursor protein (especially in ATTR with drugs such as tafamidis or diflunisal). Cardiac transplantation, although rarely feasible, can be very successful in carefully selected patients.

Reducing Amyloid Fibril Precursor Protein Production

Treatment of amyloidosis is currently based on the concept of reducing the supply of the respective amyloid fibril precursor protein. In AL amyloidosis, therapy is directed toward the clonal plasma cells using either cyclical combination chemotherapy or high-dose therapy with autologous stem cell transplantation.
The newer treatment options include bortezomib (a proteosome inhibitor)105 and the newer immunomodulatory drugs lenalidomide and pomalidomide. Bortezomib combinations appear to be especially efficient in amyloidosis with high rates of near-complete clonal responses, which appear to translate into early cardiac responses.106–108 Phase II (bortezomib in combination with cyclophosphamide or doxorubicin) and phase III (bortezomib, melphalan, and dexamethasone compared to melphalan and dexamethasone as front-line treatment) trials are underway.
AA amyloidosis is the only other type of amyloidosis in which production of the fibril precursor protein can be effectively suppressed by currently available therapies. Anti-inflammatory therapies, such as anti-tumor necrosis factor agents in rheumatoid arthritis, can substantially suppress serum amyloid A protein production, but very little experience has been obtained regarding cardiac involvement, which is very rare in this particular type of amyloidosis.
TTR is produced almost exclusively in the liver, and TTR amyloidosis has lately become a focus for novel drug developments aimed at reducing production of TTR through silencing RNA and antisense oligonucleotide therapies. ALN-TTR01, a systemically delivered silencing RNA therapeutic, is already in phase I clinical trial. Liver transplantation has been used as a treatment for variant ATTR for 20 years, to remove genetically variant TTR from the plasma. Although this is a successful approach in ATTR Val30Met, it has had disappointing results in patients with other ATTR variants, which often involve the heart. The procedure commonly results in progressive cardiac amyloidosis through ongoing accumulation of wild-type TTR on the existing template of variant TTR amyloid. The role of liver transplantation in non-Val30Met–associated hereditary TTR amyloidosis thus remains very uncertain.

Inhibition of Amyloid Formation

Amyloid fibril formation involves massive conformational transformation of the respective precursor protein into a completely different form with predominant β-sheet structure. The hypothesis that this conversion might be inhibited by stabilizing the fibril precursor protein through specific binding to a pharmaceutical has lately been explored in TTR amyloidosis. A key step in TTR amyloid fibril formation is the dissociation of the normal TTR tetramer into monomeric species that can autoaggregate in a misfolded form. In vitro studies identified that diflunisal, a now little used nonsteroidal anti-inflammatory analgesic, is bound by TTR in plasma, and that this enhances the stability of the normal soluble structure of the protein. Studies of diflunisal in ATTR are in progress. Tafamidis is a new compound without anti-inflammatory analgesic properties that has a similar mechanism of action. Tafamidis has just been licensed for neuropathic ATTR, but its role in cardiac amyloidosis remains uncertain, and clinical trial results are eagerly awaited. Higher-affinity “superstabilizers” are also in development.

Conclusion

Cardiac amyloidosis remains challenging to diagnose and to treat. Key “red flags” that should raise suspicion include clinical features indicating multisystem disease and concentric LV thickening on echocardiography in the absence of increased voltage on ECG; the pattern of gadolinium enhancement on CMR appears to be very characteristic. Confirmation of amyloid type is now possible in most cases through a combination of immunohistochemistry, DNA analysis, and proteomics. A variety of novel specific therapies are on the near horizon, with potential to both inhibit new amyloid formation and enhance clearance of existing deposits.

Future Prospects

Jeffery W. Kelly, the former Dean of Graduate Studies (2000-2008) and Vice President of Academic Affairs (2000-2006), currently is the Chairman of Molecular and Experimental Medicine and the Lita Annenberg Hazen Professor of Chemistry within the Skaggs Institute of Chemical Biology at The Scripps Research Institute in La Jolla, California.
The work on folding proteins by the Kelly Group focuses on
[1] understanding protein misfolding and aggregation and on developing both chemical
[2] and biological strategies
[3] to ameliorate diseases caused by protein misfolding and/or aggregation.
Besides studying the structural and energetic basis behind protein folding, his laboratory also studies the etiology of neurodegenerative diseases linked to protein aggregation, including Alzheimer’s disease, Parkinson’s Disease, and the familial gelsolin and transthyretin-based amyloidoses–publishing over 250 peer-reviewed papers in this area to date. He has also provided insight into genetic diseases associated with loss of protein function, such as lysosomal storage diseases.
Kelly has cofounded three biotechnology companies, FoldRx Pharmaceuticals (with Susan Lindquist), now owned by Pfizer, Proteostasis Therapeutics, Inc. (with Andrew Dillin and Richard Morimoto) (a private corporation) and Misfolding Diagnostics (with Xin Jiang and Justin Chapman; a private corporation). The Kelly laboratory discovered the first regulatory agency-approved drug that slows the progression of a human amyloid disease using a structure-based design approach. This drug, now called Tafamidis or Vyndaqel, slowed the progression of familial amyloid polyneuropathy in an 18 month placebo controlled trial and in an 18 month extension study sponsored by FoldRx Pharmaceuticals (acquired by Pfizer in 2010). Vyndaqel or Tafamidis  was approved for the treatment of Familial amyloid Polyneuropathy by the European Medicines Agency in late 2011. Kelly also discovered that diflunisal kinetically stabilizes transthyretin, enabling a placebo controlled clinical trial with it to ameliorate familial amyloid polyneuropathy–the results of which will be announced in 2013. Proteostasis Therapeutics, Inc. is developing first-in-class drugs that adapt the proteostasis network to ameliorate both loss-of-function misfolding diseases and gain-of-toxic function diseases linked to protein aggregation.
In addition to discovering the first drug that slows the progression of a human amyloid disease, the Kelly Laboratory is credited with demonstrating that transthyretin conformational changes alone are sufficient for amyloidogenesis, discovering the first example of functional amyloid in mammals, making major contributions toward understanding β-sheet folding, discovering the “enhanced aromatic sequon”–sequences that are more efficiently glycosylated by cells and sequences which stabilize the proteins that they are incorporated into as a consequence of N-glycosylation and was corresponding author on and contributed some of the key experimental data demonstrating that altering cellular proteostasis capacity has the potential to alleviate protein misfolding and aggregation diseases.
Native state kinetic stabilization as a strategy to ameliorate protein misfolding diseases: a focus on the transthyretin amyloidoses. Johnson SM, Wiseman RL, Sekijima Y, Green NS, Adamski-Werner SL, Kelly JW.  http://www.ncbi.nlm.nih.gov/pubmed/16359163
Small molecule-mediated protein stabilization inside or outside of the cell is a promising strategy to treat protein misfolding/misassembly diseases. Herein we focus on the transthyretin (TTR) amyloidoses and demonstrate that preferential ligand binding to and stabilization of the native state over the dissociative transition state raises the kinetic barrier of dissociation (rate-limiting for amyloidogenesis), slowing and in many cases preventing TTR amyloid fibril formation. Since T119M-TTR subunit incorporation into tetramers otherwise composed of disease-associated subunits also imparts kinetic stability on the tetramer and ameliorates amyloidosis in humans, it is likely that small molecule-mediated native state kinetic stabilization will also alleviate TTR amyloidoses.
Energetic characteristics of the new transthyretin variant A25T may explain its atypical central nervous system pathology.
Sekijima Y, Hammarström P, Matsumura M, Shimizu Y, Iwata M, Tokuda T, Ikeda S, Kelly JW.
Lab Invest. 2003 Mar;83(3):409-17.   http://www.ncbi.nlm.nih.gov/pubmed/12649341
Transthyretin (TTR) is a tetrameric protein that must misfold to form amyloid fibrils. Misfolding includes rate-limiting tetramer dissociation, followed by fast tertiary structural changes that enable aggregation. Amyloidogenesis of wild-type (WT) TTR causes a late-onset cardiac disease called senile systemic amyloidosis. The aggregation of one of > 80 TTR variants leads to familial amyloidosis encompassing a collection of disorders characterized by peripheral neuropathy and/or cardiomyopathy. Prominent central nervous system (CNS) impairment is rare in TTR amyloidosis. Herein, we identify a new A25T TTR variant in a Japanese patient who presented with CNS amyloidosis at age 42 and peripheral neuropathy at age 44. The A25T variant is the most destabilized and fastest dissociating TTR tetramer published to date, yet, surprising, disease onset is in the fifth decade. Quantification of A25T TTR in the serum of this heterozygote reveals low levels relative to WT, suggesting that protein concentration influences disease phenotype. Another recently characterized TTR CNS variant (D18G TTR) exhibits strictly analogous characteristics, suggesting that instability coupled with low serum concentrations is the signature of CNS pathology and protects against early-onset systemic amyloidosis. The low A25T serum concentration may be explained either by impaired secretion from the liver or by increased clearance, both scenarios consistent with A25T’s low kinetic and thermodynamic stability. Liver transplantation is the only known treatment for familial amyloid polyneuropathy. This is a form of gene therapy that removes the variant protein from serum preventing systemic amyloidosis. Unfortunately, the choroid plexus would have to be resected to remove A25T from the CSF-the source of the CNS TTR amyloid. Herein we demonstrate that small-molecule tetramer stabilizers represent an attractive therapeutic strategy to inhibit A25T misfolding and CNS amyloidosis. Specifically, 2-[(3,5-dichlorophenyl)amino]benzoic acid is an excellent inhibitor of A25T TTR amyloidosis in vitro.
Prevention of Transthyretin Amyloid Disease by Changing Protein Misfolding Energetics
Per Hammarström*, R. Luke Wiseman*, Evan T. Powers, Jeffery W. Kelly†
Science 31 Jan 2003; 299(5607):713-716    http://dx.doi.org/10.1126/science.1079589
Genetic evidence suggests that inhibition of amyloid fibril formation by small molecules should be effective against amyloid diseases. Known amyloid inhibitors appear to function by shifting the aggregation equilibrium away from the amyloid state. Here, we describe a series of transthyretin amyloidosis inhibitors that functioned by increasing the kinetic barrier associated with misfolding, preventing amyloidogenesis by stabilizing the native state. The trans-suppressor mutation, threonine 119 → methionine 119, which is known to ameliorate familial amyloid disease, also functioned through kinetic stabilization, implying that this small-molecule strategy should be effective in treating amyloid diseases.
R104H may suppress transthyretin amyloidogenesis by thermodynamic stabilization, but not by the kinetic mechanism characterizing T119 interallelic trans-suppression.
Sekijima Y, Dendle MT, Wiseman RL, White JT, D’Haeze W, Kelly JW.
Amyloid. Jun 2006;13(2):57-66.    http://www.ncbi.nlm.nih.gov/pubmed/16911959
The tetrameric protein transthyretin (TTR) forms amyloid fibrils upon dissociation and subsequent monomer misfolding, enabling misassembly. Remarkably, the aggregation of one of over 100 destabilized TTR variants leads to familial amyloid disease. It is known that trans-suppression mediated by the incorporation of T119M subunits into tetramers otherwise composed of the most common familial variant V30M, ameliorates disease by substantially slowing the rate of tetramer dissociation, a mechanism referred to as kinetic stabilization of the native state. R104H TTR has been reported to be non-pathogenic, and recently, this variant has been invoked as a trans-suppressor of amyloid fibril formation. Here, we demonstrate that the trans-suppression mechanism of R104H does not involve kinetic stabilization of the tetrameric structure, instead its modest trans-suppression most likely results from the thermodynamic stabilization of the tetrameric TTR structure. Thermodynamic stabilization increases the fraction of tetramer at the expense of the misfolding competent monomer decreasing the ability of TTR to aggregate into amyloid fibrils. As a consequence of this stabilization mechanism, R104H may be capable of protecting patients with modestly destabilizing mutations against amyloidosis by slightly lowering the overall population of monomeric protein that can misfold and form amyloid.
Amyloidosis, Node, Congo Red. The amyloid depo...

Amyloidosis, Node, Congo Red. The amyloid deposits are strongly congophilic when viewed before white light. (Photo credit: Wikipedia)

Amyloidosis

Amyloidosis (Photo credit: Boonyarit Cheunsuchon)

English: Intermed. mag. (H&E). Image:Cardiac a...

English: Intermed. mag. (H&E). Image:Cardiac amyloidosis high mag he.jpg (Photo credit: Wikipedia)

English: Intermed. mag. (H&E). Image:Cardiac a...

English: Intermed. mag. (H&E). Image:Cardiac amyloidosis high mag he.jpg (Photo credit: Wikipedia)

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A Second Look at the Transthyretin Nutrition Inflammatory Conundrum

Subtitle: Transthyretin and the Systemic Inflammatory Response

 

Author and Curator: Larry H. Bernstein, MD, FACP, Clinical Pathologist, Biochemist, and Transfusion Physician

 

Brief introduction

Transthyretin  (also known as prealbumin) has been widely used as a biomarker for identifying protein-energy malnutrition (PEM) and for monitoring the improvement of nutritional status after implementing a nutritional intervention by enteral feeding or by parenteral infusion. This has occurred because transthyretin (TTR) has a rapid removal from the circulation in 48 hours and it is readily measured by immunometric assay. Nevertheless, concerns have been raised about the use of TTR in the ICU setting, which prompted a review of the  benefit of using this test in acute and chronic care. TTR is easily followed in the underweight and the high risk populations in an ambulatory setting, which has a significant background risk of chronic diseases. It is sensitive to the systemic inflammatory response syndrome (SIRS), and needs to be understood in the context of acute illness to be used effectively. There are a number of physiologic changes associated with SIRS and the injury/repair process that affect TTR. The most important point is that in the context of an ICU setting, the contribution of TTR is significant in a complex milieu.  A much better understanding of the significance of this program has emerged from studies of nitrogen and sulfur in health and disease.

Transthyretin protein structure

Transthyretin protein structure (Photo credit: Wikipedia)

Age-standardised disability-adjusted life year...

Age-standardised disability-adjusted life year (DALY) rates from Protein-energy malnutrition by country (per 100,000 inhabitants). (Photo credit: Wikipedia)

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The systemic inflammatory response syndrome C-reactive protein and transthyretin conundrum.
Larry H Bernstein
Clin Chem Lab Med 2007; 45(11):0
ICID: 939932
Article type: Editorial

The Transthyretin Inflammatory State Conundrum
Larry H. Bernstein
Current Nutrition & Food Science, 2012, 8, 00-00

Keywords: Tranthyretin (TTR), systemic inflammatory response syndrome (SIRS), protein-energy malnutrition (PEM), C- reactive protein, cytokines, hypermetabolism, catabolism, repair.

Transthyretin has been widely used as a biomarker for identifying protein-energy malnutrition (PEM) and for monitoring the improvement of nutritional status after implementing a nutritional intervention by enteral feeding or by parenteral infusion. This has occurred because transthyretin (TTR) has a rapid removal from the circulation in 48 hours and it is readily measured by immunometric assay. Nevertheless, concerns have been raised about the use of TTR in the ICU setting, which prompts a review of the actual benefit of using this test in a number of settings. TTR is easily followed in the underweight and the high risk populations in an ambulatory setting, which has a significant background risk of chronic diseases. It is sensitive to the systemic inflammatory response syndrome (SIRS), and needs to be understood in the context of acute illness to be used effectively.

There are a number of physiologic changes associated with SIRS and the injury/repair process that affect TTR and  in the context of an ICU setting, the contribution of TTR is essential.  The only consideration is the timing of initiation since the metabolic burden is sufficiently high that a substantial elevation is expected in the first 3 days post admission, although the level of this biomarker is related to the severity of injury. Despite the complexity of the situation, TTR is not to be considered a test “for all seasons”. In the context of age, prolonged poor meal intake, chronic or acute illness, TTR needs to be viewed in a multivariable lens, along with estimated lean body mass, C-reactive protein, the absolute lymphocyte count, presence of neutrophilia, and perhaps procalcitonin if there is remaining uncertainty. Furthermore, the reduction of risk of associated complication requires a systematized approach to timely identification, communication, and implementation of a suitable treatment plan.

The most important point is that in the context of an ICU setting, the contribution of TTR is significant in a complex milieu.

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Title: The Automated Malnutrition Assessment
Accepted 29 April 2012. http://www.nutritionjrnl.com. Nutrition (2012), doi:10.1016/j.nut.2012.04.017.
Authors: Gil David, PhD; Larry Howard Bernstein, MD; Ronald R Coifman, PhD
Article Type: Original Article

Keywords: Network Algorithm; unsupervised classification; malnutrition screening; protein energy malnutrition (PEM); malnutrition risk; characteristic metric; characteristic profile; data characterization; non-linear differential diagnosis

We have proposed an automated nutritional assessment (ANA) algorithm that provides a method for malnutrition risk prediction with high accuracy and reliability.  The problem of rapidly identifying risk and severity of malnutrition is crucial for minimizing medical and surgical complications. These are not easily performed or adequately expedited. We characterized for each patient a unique profile and mapped similar patients into a classification. We also found that the laboratory parameters were sufficient for the automated risk prediction.

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Title: The Increasing Role for the Laboratory in Nutritional Assessment
Article Type: Editorial
Section/Category: Clinical Investigation
Accepted 22 May 2012. http://www.elsevier.com/locate/clinbiochem.
Clin Biochem (2012), doi:10.1016/j.clinbiochem.2012.05.024
Keywords: Protein Energy Malnutrition; Nutritional Screening; Laboratory Testing
Author: Dr. Larry Howard Bernstein, MD

The laboratory role in nutritional management of the patient has seen remarkable growth while there have been dramatic changes in technology over the last 25 years, and it is bound to be transformative in the near term. This editorial is an overview of the importance of the laboratory as an active participant in nutritional care.

The discipline emerged divergently along separate paths with unrelated knowledge domains in physiological chemistry, pathology, microbiology, immunology and blood cell recognition, and then cross-linked emerging into clinical biochemistry, hematology-oncology, infectious diseases, toxicology and therapeutics, genetics, pharmacogenomics, translational genomics and clinical diagnostics.

In reality, the more we learn about nutrition, the more we uncover of metabolic diversity of individuals, the family, and societies in adapting and living in many unique environments and the basic reactions, controls, and responses to illness. This course links metabolism to genomics and individual diversity through metabolomics, which will be enlightened by chemical and bioenergetic insights into biology and translated into laboratory profiling.

Vitamin deficiencies were discovered as clinical entities with observed features as a result of industrialization (rickets and vitamin D deficiency) and mercantile trade (scurvy and vitamin C)[2].  Advances in chemistry led to the isolation of each deficient “substance”.  In some cases, a deficiency of a vitamin and what is later known as an “endocrine hormone” later have confusing distinctions (vitamin D, and islet cell insulin).

The accurate measurement and roles of trace elements, enzymes, and pharmacologic agents was to follow within the next two decades with introduction of atomic absorption, kinetic spectrophotometers, column chromatography and gel electrophoresis.  We had fully automated laboratories by the late 1960s, and over the next ten years basic organ panels became routine.   This was a game changer.

Today child malnutrition prevalence is 7 percent of children under the age of 5 in China, 28 percent in sub-Saharan African, and 43 percent in India, while under-nutrition is found mostly in rural areas with 10 percent of villages and districts accounting for 27-28 percent of all Indian underweight children. This may not be surprising, but it is associated with stunting and wasting, and it has not receded with India’s economic growth. It might go unnoticed viewed alongside a growing concurrent problem of worldwide obesity.

The post WWII images of holocaust survivors awakened sensitivity to nutritional deprivation.

In the medical literature, Studley [HO Studley.  Percentage of weight loss. Basic Indicator of surgical risk in patients with chronic peptic ulcer.  JAMA 1936; 106(6):458-460.  doi:10.1001/jama.1936.02770060032009] reported the association between weight loss and poor surgical outcomes in 1936.  Ingenbleek et al [Y Ingenbleek, M De Vissher, PH De Nayer. Measurement of prealbumin as index of protein-calorie malnutrition. Lancet 1972; 300[7768]: 106-109] first reported that prealbumin (transthyretin, TTR) is a biomarker for malnutrition after finding very low TTR levels in African children with Kwashiorkor in 1972, which went unnoticed for years.  This coincided with the demonstration by Stanley Dudrick  [JA Sanchez, JM Daly. Stanley Dudrick, MD. A Paradigm ShiftArch Surg. 2010; 145(6):512-514] that beagle puppies fed totally through a catheter inserted into the superior vena cava grew, which method was then extended to feeding children with short gut.  Soon after Bistrian and Blackburn [BR Bistrian, GL Blackburn, E Hallowell, et al. Protein status of general surgical patients. JAMA 1974; 230:858; BR Bistrian, GL Blackburn, J Vitale, et al. Prevalence of malnutrition in general medicine patients, JAMA, 1976, 235:1567] showed that malnourished hospitalized medical and surgical patients have increased length of stay, increased morbidity, such as wound dehiscence and wound infection, and increased postoperative mortality, later supported by many studies.

Michael Meguid,MD, PhD, founding editor of Nutrition [Elsevier] held a nutrition conference “Skeleton in the Closet – 20 years later” in Los Angeles in 1995, at which a Beckman Prealbumin Roundtable was held, with Thomas Baumgartner and Michael M Meguid as key participants.  A key finding was that to realize the expected benefits of a nutritional screening and monitoring program requires laboratory support. A Ross Roundtable, chaired by Dr. Lawrence Kaplan, resulted in the first Standard of Laboratory Practice Document of the National Academy of Clinical Biochemists on the use of the clinical laboratory in nutritional support and monitoring. Mears then showed a real benefit to a laboratory interactive program in nutrition screening based on TTR [E Mears. Outcomes of continuous process improvement of a nutritional care program incorporating serum prealbumin measurements. Nutrition 1996; 12 (7/8): 479-484].

A later Ross Roundtable on Quality in Nutritional Care included a study of nutrition screening and time to dietitian intervention organized by Brugler and Di Prinzio that showed a decreased length of hospital stay with $1 million savings in the first year (which repeated), which included reduced cost for dietitian evaluations and lower complication rates.

Presentations were made at the 1st International Transthyretin Congress in Strasbourg, France by Mears [E Mears.  The role of visceral protein markers in protein calorie malnutrition. Clin Chem Lab Med 2002; 40:1360-1369] on the impact of TTR in screening for PEM in a public hospital in Louisiana, and by Potter [MA Potter, G Luxton. Prealbumin measurement as a screening tool for patients with protein calorie malnutrition in emergency hospital admissions: a pilot study.  Clin Invest Med. 1999; 22(2):44-52] that indicated a 17% in-hospital mortality rate in a Canadian hospital for patients with PCM compared with 4% without PCM (p < 0.02), while only 42% of patients with PCM received nutritional supplementation. Cost analysis of screening with prealbumin level projected a saving of $414 per patient screened.  Ingenbleek and Young [Y Ingenbleek, VR Young.  Significance of transthyretin in protein metabolism.  Clin Chem Lab Med. 2002; 40(12):1281–1291.  ISSN (Print) 1434-6621, DOI: 10.1515/ CCLM.2002.222, December 2002. published online: 01/06/2005] tied the TTR to basic effects reflected in protein metabolism.

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Transthyretin as a marker to predict outcome in critically ill patients.
Arun Devakonda, Liziamma George, Suhail Raoof, Adebayo Esan, Anthony Saleh, Larry H Bernstein
Clin Biochem 2008; 41(14-15):1126-1130
ICID: 939927
Article type: Original article

TTR levels correlate with patient outcomes and are an accurate predictor of patient recovery in non-critically ill patients, but it is uncertain whether or not TTR level correlates with level of nutrition support and outcome in critically ill patients. This issue has been addressed only in critically ill patients on total parenteral nutrition and there was no association reported with standard outcome measures. We revisit this in all patients admitted to a medical intensive care unit.

Serum TTR was measured on the day of admission, day 3 and day 7 of their ICU stay. APACHE II and SOFA score was assessed on the day of admission. A registered dietician for their entire ICU stay assessed the nutritional status and nutritional requirement. Patients were divided into three groups based on initial TTR level and the outcome analysis was performed for APACHE II score, SOFA score, ICU length of stay, hospital length of stay, and mortality.

TTR showed excellent concordance with the univariate or multivariate classification of patients with PEM or at high malnutrition risk, and followed for seven days in the ICU, it is a measure of the metabolic burden.  TTR levels decline from day 1 to day 7 in spite of providing nutritional support. Twenty-five patients had an initial TTR serum concentration more than 17 mg/dL (group 1), forty-eight patients had mild malnutrition with a concentration between 10 and 17 mg/dL (group 2), Forty-five patients had severe malnutrition with a concentration less than 10 mg/dL (group 3).  Initial TTR level had inverse correlation with ICU length of stay, hospital length of stay, and APACHE II score, SOFA score; and predicted mortality, especially in group 3.

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A simplified nutrition screen for hospitalized patients using readily available laboratory and patient
information.
Linda Brugler, Ana K Stankovic, Madeleine Schlefer, Larry Bernstein
Nutrition 2005; 21(6):650-658
ICID: 825623
Article type: Review article
The role of visceral protein markers in protein calorie malnutrition.
Linda Brugler, Ana Stankovic, Larry Bernstein, Frederick Scott, Julie O’Sullivan-Maillet
Clin Chem Lab Med 2002; 40(12):1360-1369
ICID: 636207
Article type: Original article

The Automated Nutrition Score is a data-driven extension of continuous quality improvement.

Larry H Bernstein
Nutrition 2009; 25(3):316-317
ICID: 939934

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Transthyretin: its response to malnutrition and stress injury. clinical usefulness and economic implications.
LH Bernstein, Y Ingenbleek
Clin Chem Lab Med 2002; 40(12):1344-1348
ICID: 636205
Article type: Original article

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THE NUTRITIONALLY-DEPENDENT ADAPTIVE DICHOTOMY (NDAD) AND STRESS HYPERMETABOLISM
Yves Ingenbleek  MD  PhD  and  Larry Bernstein MD
J CLIN LIGAND ASSAY  (out of print)

The acute reaction to stress is characterized by major metabolic, endocrine and immune alterations. According to classical descriptions, these changes clinically present as a succession of 3 adaptive steps – ebb phase, catabolic flow phase, and anabolic flow phase. The ebb phase, shock and resuscitation, is immediate, lasts several hours, and is characterized by hypokinesis, hypothermia, hemodynamic instability and reduced basal metabolic rate. The catabolic flow phase, beginning within 24 hours and lasting several days, is characterized by catabolism with the flow of gluconeogenic substrates and ketone bodies in response to the acute injury. The magnitude of the response depends on the acuity and the severity of the stress. The last, a reparative anabolic flow phase, lasts weeks and is characterized by the accretion of amino acids (AAs) to rebuilding lean body mass.

The current opinion is that the body economy is reset during the course of stress at novel thresholds of metabolic priorities. This is exemplified mainly by proteolysis of muscle, by an effect on proliferating gut mucosa and lymphoid tissue as substrates are channeled to support wound healing, by altered syntheses of liver proteins with preferential production of acute phase proteins (APPs) and local repair in inflamed tissues (3). The first two stages demonstrate body protein breakdown exceeding the rate of protein synthesis, resulting in a negative nitrogen (N) balance, muscle wasting and weight loss. In contrast, the last stage displays reversed patterns, implying progressive recovery of endogenous N pools and body weight.

These adaptive alterations undergo continuing elucidation. The identification of cytokines, secreted by activated macrophages/monocytes or other reacting cells, has provided further insights into the molecular mechanisms controlling energy expenditure, redistribution of protein pools, reprioritization of syntheses and secretory processes.

The free fraction of hormones bound to specific binding-protein(s) [BP(s)] manifests biological activities, and any change in the BP blood level modifies the effect of the hormone on the end target organ.  The efficacy of these adaptive responses may be severely impaired in protein-energy malnourished (PEM) patients. This is especially critical with respect to changes of the circulating levels of transthyretin (TTR), retinol-binding protein (RBP) and corticosteroid-binding globulin (CBG) conveying thyroid hormones (TH), retinol and cortisol, respectively.  This reaction is characterized by cytokine mediated autocrine, paracrine and endocrine changes. Among the many inducing molecules identified, interleukins 1 and 6 (Il-1, Il-6) and tumor necrosis factor a (TNF) are associated with enhanced production of 3 counterregulatory hormonal families (cortisol, catecholamines and glucagon). Growth hormone (GH) and TH also have roles in these metabolic adjustments.

There is overproduction of cortisol mediated by several cytokines acting on both the adrenal cortex (10) and on the pituitary through hypothalamic CRH with loss of feedback regulation of ACTH production (11). Hypercortisolemia is a major finding observed after surgery (12), sepsis (13), and medical insults, usually correlated with severity of insult and of complications. Rising cortisol values parallel hyperglycemic trends, as an effect of both gluconeogenesis and insulin resistance. Working in concert with TNF, glucocorticoids govern the breakdown of muscle mass, which is regarded as the main factor responsible for the negative N balance.

Under normal conditions, GH exerts both lipolytic and anabolic influences in the whole body economy under the dual control of the hypothalamic hormones somatocrinin (GHRH) and somatostatin (SRIH). GH secretion is usually depressed by rising blood concentrations of glucose and free fatty acids (FFAs) but is paradoxicaly elevated despite hyperglycemia in stressed patients.

The oversecretion of counterregulatory hormones working in concert generates subtle equilibria between glycogenolytic/glycolytic/gluconeogenic adaptive processes. The net result is the neutralization of the main hypoglycemic and anabolic activities of insulin and the development of a persisting and controlled hyperglycemic tone in the stressed body. The molecular mechanisms whereby insulin resistance occurs in the course of stress refer to
cytokine-  and  hormone-induced  phosphorylation abnormalities affecting receptor signaling. The insulin-like anabolic processes of GH are mediated by IGF1 working as relay agent. The expected high IGF1 surge associated with GH oversecretion is not observed in severe stress as plasma values are usually found at the lower limit of normal or even in the subnormal range.  The end result of this dissociation between high GH and low IGF1 levels is to favor the proteolysis of muscle mass to release AAs for gluconeogenesis and the breakdown of adipose tissue to provide ketogenic substrates.

The acute stage of stress is associated with the onset of a low T3 syndrome typically delineated by the drop of both total (TT3) and free (FT3) triiodothyronine plasma levels in the subnormal range. In contrast, both total (TT4) and free (FT4) thyroxine values usually remain within normal ranges with declining trends observed for TT4 and rising tendencies for FT4 (44). This last free compound is regarded as the sensor reflecting the actual thyroid status and governing the release of TSH whereas FT3 works as the active hormonal mediator at nuclear receptor level. The maintenance of an euthyroid sick syndrome is compatible with the down-regulation of most metabolic and energetic processes in healthy tissues. These inhibitory effects , negatively affecting all functional steps of the hypothalamo-pituitary-thyroid axis concern TSH production, iodide uptake, transport and organification into iodotyrosyl residues, peroxidase coupling activity as well as thyroglobulin synthesis and TH leakage. Taken together, the above-mentioned data indicate that the development of hyperglycemia and of insulin-resistance in healthy tissues – mainly in the muscle mass – are hallmarks resulting from the coordinated activities of the counterregulatory hormones.

A growing body of recent data suggest that the stressed territory, whatever the causal agent – bacterial or viral sepsis, auto-immune disorder, traumatic or toxic shock, burns, cancer – manifest differentiated metabolic and immune reactions. The amplitude, duration and efficacy of these responses are reportedly impaired along several ways in PEM patients. These last detrimental effects are accompanied by a number of medical, social and economical consequences, such as extended length of hospital stay and increased complication / mortality rates. It is therefore mandatory to correctly identify and follow up the nutritional status of hospitalized patients. Such approaches are prerequisite to timely and scientifically grounded nutritional and pharmacological mediated interventions.

Contrary to the rest of the body, energy requirements of the inflamed territory are primarily fulfilled by anaerobic glycolysis, an effect triggered by the inhibition of key-enzymes of carbohydrate metabolism, notably pyruvate-dehydrogenase. This non-oxidative combustion of glucose reveals low conversion efficiency but offers the major advantage to maintain, in the context of hyperglycemia, fuel provision to poorly irrigated and/or edematous tissues. The depression of the 5’-monodeiodinating activity (5’-DA) plays a pivotal role in these adaptive changes, yielding inactive reverse T3 (rT3) as index of impaired T4 to T3 conversion rates, but at the same time there is an augmented supply of bioactive T3 molecules and local overstimulation of thyro-dependent processes characterized by thyroid down-regulation.  The same differentiated evolutionary pattern applies to IGF1. In spite of lowered plasma total concentrations, the proportion of IGF1 released in free form may be substantially increased owing to the proteolytic degradation of IGFBP-3 in the intravascular compartment. The digestion of  BP-3 results from the surge of several proteases occurring the course of stress, yielding biologically active IGF1 molecules available for the repair of damaged tissues. In contrast, healthy receptors oppose a strong resistance to IGF1 ligands freed in the general circulation, likely induced by an acquired phosphorylation defect very similar in nature to that for the insulin transduction pathway.

PEM is the generic denomination of a broad spectrum of nutritional disorders, commonly found in hospital settings, and whose extreme poles are identified as marasmus and kwashiorkor. The former condition is usually regarded as the result of long-lasting starvation leading to the loss of lean body mass and fat reserves but relatively well-preserved liver function and immune capacities. The latter condition is typically the consequence of (sub)acute deprivation predominantly affecting the protein content of staplefood, an imbalance causing hepatic steatosis, fall of visceral proteins, edema and increased vulnerability to most stressful factors. PEM may be hypometabolic or hypermetabolic, usually coexists with other diseased states and is frequently associated with complications. Identification of PEM calls upon a large set of clinical and analytical disciplines comprising anthropometry, immunology, hematology and biochemistry.

CBG, TTR and RBP share in common the transport of specific ligands exerting their metabolic effects at nuclear receptor level. Released from their specific BPs in free form, cortisol, FT4 and retinol immediately participe to the strenghtening of the positive and negative responses to stressful stimuli. CBG is a relatively weak responder to short-term nutritional influences (73)  although long-lasting PEM is reportedly capable of causing its significant diminution (74). The dramatic drop of CBG in the course of stress appears as the combined effect of Il-6-induced posttranscriptional blockade of its liver synthesis (75) and peripheral overconsumption by activated neutrophils (61). The divergent alterations outlined by CBG and total cortisolemia result in an increased disposal of free ligand reaching proportions considerably higher than the 4 % recorded under physiological conditions.

The appellation of negative APPs that was once given to the visceral group of carrier-proteins. The NDAD concept takes the opposite view, defending the opinion that their suppressed synthesis releases free ligands which positively contribute to strengthen all aspects of the stress reaction, justifying the ABR denomination. This implies that the role played by ABRs should no longer be interpreted in terms of concentrations but in terms of functionality.

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THE OXIDATIVE STRESS OF HYPERHOMOCYSTEINEMIA RESULTS FROM REDUCED BIOAVAILABILITY OF SULFUR-CONTAINING REDUCTANTS.
Yves Ingenbleek. The Open Clinical Chemistry Journal, 2011, 4, 34-44.

Vegetarian subjects consuming subnormal amounts of methionine (Met) are characterized by subclinical protein malnutrition causing reduction in size of their lean body mass (LBM) best identified by the serial measurement of plasma transthyretin (TTR). As a result, the transsulfuration pathway is depressed at cystathionine-β-synthase (CβS) level triggering the upstream sequestration of homocysteine (Hcy) in biological fluids and promoting its conversion to Met. Maintenance of beneficial Met homeostasis is counterpoised by the drop of cysteine (Cys) and glutathione (GSH) values downstream to CβS causing in turn declining generation of hydrogen sulfide (H2S) from enzymatic sources. The biogenesis of H2S via non-enzymatic reduction is further inhibited in areas where earth’s crust is depleted in elemental sulfur (S8) and sulfate oxyanions. Combination of subclinical malnutrition and S8-deficiency thus maximizes the defective production of Cys, GSH and H2S reductants, explaining persistence of unabated oxidative burden. The clinical entity increases the risk of developing cardiovascular diseases (CVD) and stroke in underprivileged plant-eating populations regardless of Framingham criteria and vitamin-B status. Although unrecognized up to now, the nutritional disorder is one of the commonest worldwide, reaching top prevalence in populated regions of Southeastern Asia. Increased risk of hyperhomocysteinemia and oxidative stress may also affect individuals suffering from intestinal malabsorption or westernized communities having adopted vegan dietary lifestyles.

Metabolic pathways: Met molecules supplied by dietary proteins are submitted to TM processes allowing to release Hcy which may in turn either undergo Hcy – Met RM pathways or be irreversibly committed into TS decay. Impairment of CbS activity, as described in protein malnutrition, entails supranormal accumulation of Hcy in body fluids, stimulation of activity and maintenance of Met homeostasis. This last beneficial effect is counteracted by decreased concentration of most components generated downstream to CbS, explaining the depressed CbS- and CbL-mediated enzymatic production of H2S along the TS cascade. The restricted dietary intake of elemental S further operates as a limiting factor for its non-enzymatic reduction to H2S which contributes to downsizing a common body pool. Combined protein- and S-deficiencies work in concert to deplete Cys, GSH and H2S from their body reserves, hence impeding these reducing molecules to properly face the oxidative stress imposed by hyperhomocysteinemia.

see also …

McCully, K.S. Vascular pathology of homocysteinemia: implications for the pathogenesis of arteriosclerosis. Am. J. Pathol., 1996, 56, 111-128.

Cheng, Z.; Yang, X.; Wang, H. Hyperhomocysteinemia and endothelial dysfunction. Curr. Hypertens. Rev., 2009, 5,158-165.

Loscalzo, J. The oxidant stress of hyperhomocyst(e)inemia. J. Clin.Invest., 1996, 98, 5-7.

Ingenbleek, Y.; Hardillier, E.; Jung, L. Subclinical protein malnutrition is a determinant of hyperhomocysteinemia. Nutrition, 2002, 18, 40-46.

Ingenbleek, Y.; Young, V.R. The essentiality of sulfur is closely related to nitrogen metabolism: a clue to hyperhomocysteinemia. Nutr. Res. Rev., 2004, 17, 135-153.

Hosoki, R.; Matsuki, N.; Kimura, H. The possible role of hydrogen sulfide as an endogenous smooth muscle relaxant in synergy with nitric oxide. Biochem. Biophys. Res. Commun., 1997, 237, 527-531.

Tang, B.; Mustafa, A.; Gupta, S.; Melnyk, S.; James S.J.; Kruger, W.D. Methionine-deficient diet induces post-transcriptional downregulation of cystathionine-􀀁-synthase. Nutrition, 2010, 26, 1170-1175.

Elshorbagy, A.K.; Valdivia-Garcia, M.; Refsum, H.; Smith, A.D.; Mattocks, D.A.; Perrone, C.E. Sulfur amino acids in methioninerestricted rats: Hyperhomocysteinemia. Nutrition, 2010, 26, 1201- 1204.

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Yves Ingenbleek. Plasma Transthyretin Reflects the Fluctuations of Lean Body Mass in Health and Disease. Chapter 20. In S.J. Richardson and V. Cody (eds.), Recent Advances in Transthyretin Evolution, Structure and Biological Functions, DOI: 10.1007/978‐3‐642‐00646‐3_20, # Springer‐Verlag Berlin Heidelberg 2009.

Transthyretin (TTR) is a 55-kDa protein secreted mainly by the choroid plexus and the liver. Whereas its intracerebral production appears as a stable secretory process allowing even distribution of intrathecal thyroid hormones, its hepatic synthesis is influenced by nutritional and inflammatory circumstances working concomitantly. Both morbid conditions are governed by distinct pathogenic mechanisms leading to the reduction in size of lean body mass (LBM). The liver production of TTR integrates the dietary and stressful components of any disease spectrum, explaining why it is the sole plasma protein whose evolutionary patterns closely follow the shape outlined by LBM fluctuations. Serial measurement of TTR therefore provides unequalled information on the alterations affecting overall protein nutritional status. Recent advances in TTR physiopathology emphasize the detecting power and preventive role played by the protein in hyperhomocysteinemic states, acquired metabolic disorders currently ascribed to dietary restriction in water-soluble vitamins. Sulfur (S)-deficiency is proposed as an additional causal factor in the sizeable proportion of hyperhomocysteinemic patients characterized by adequate vitamin intake but experiencing varying degrees of nitrogen (N)-depletion. Owing to the fact that N and S coexist in plant and animal tissues within tightly related concentrations, decreasing LBM as an effect of dietary shortage and/or excessive hypercatabolic losses induces proportionate S-losses. Regardless of water-soluble vitamin status, elevation of homocysteine plasma levels is negatively correlated with LBM reduction and declining TTR plasma levels. These findings occur as the result of impaired cystathionine-b-synthase activity, an enzyme initiating the transsulfuration pathway and whose suppression promotes the upstream accumulation and remethylation of homocysteine molecules. Under conditions of N- and S-deficiencies, the maintenance of methionine homeostasis indicates high metabolic priority.

Schematically, the human body may be divided into two major compartments, namely fat mass (FM) and FFM that is obtained by substracting
FM from body weight (BW). The fat cell mass sequesters about 80% of the total body lipids, is poorly hydrated and contains only small quantities of lean tissues and nonfat constituents. FFM comprises the sizeable part of lean tissues and minor mineral compounds among which are Ca, P, Na, and Cl pools totaling about 1.7 kg or 2.5% of BW in a healthy man weighing 70 kg. Subtraction of mineral mass from FFM provides LBM, a composite aggregation of organs and tissues with specific functional properties. LBM is thus nearly but not strictly equivalent to FFM. With extracellular mineral content subtracted, LBM accounts for most of total body proteins (TBP) and of TBN assuming a mean 6.25 ratio between protein and N content.

SM accounts for 45% of TBN whereas the remaining 55% is in nonmuscle lean tissues. The LBM of the reference man contains 98% of total
body potassium (TBK) and the bulk of total body sulfur (TBS). TBK and TBS reach equal intracellular amounts (140 g each) and share distribution patterns (half in SM and half in the rest of cell mass).  The body content of K and S largely exceeds that of magnesium (19 g), iron (4.2 g) and zinc (2.3 g). The average hydration level of LBM in healthy subjects of all age is 73% with the proportion of the intracellular/extracellular fluid spaces being 4:3. SM is of particular relevance in nutritional studies due to its capacity to serve as a major reservoir of amino acids (AAs) and as a dispenser of gluconeogenic substrates. An indirect estimate of SM size consists in the measurement of urinary creatinine, end-product of the nonenzymatic hydrolysis of phosphocreatine which is limited to muscle cells.

During ageing, all the protein components of the human body decrease regularly. This shrinking tendency is especially well documented for SM  whose absolute amount is preserved until the end of the fifth decade, consistent with studies showing unmodified muscle structure, intracellular K content and working capacit. TBN and TBK are highly correlated in healthy subjects and both parameters manifest an age-dependent curvilinear decline
with an accelerated decrease after 65 years.  The trend toward sarcopenia is more marked and rapid in elderly men than in elderly women decreasing strength and functional capacity. The downward SM slope may be somewhat prevented by physical training or accelerated by supranormal cytokine status as reported in apparently healthy aged persons suffering low-grade inflammation. 2002) or in critically ill patients whose muscle mass undergoes proteolysis and contractile dysfunction.

The serial measurement of plasma TTR in healthy children shows that BP values are low in the neonatal period and rise linearly with superimposable concentrations in both sexes during infant growth consistent with superimposable N accretion and protein synthesis rates. Starting from the sixties, TTR values progressively decline showing steeper slopes in elderly males. The lowering trend seems to be initiated by the attenuation of androgen influences and trophic stimuli with increasing age. The normal human TTR trajectory from birth to death has been well documented by scientists belonging to the Foundation for Blood Research. TTR is the first plasma protein to decline in response to marginal protein restricion, thus working as an early signal warning that adaptive mechanisms maintaining homeostasis are undergoing decompensation.

TTR was proposed as a marker of protein nutritional status following a clinical investigation undertaken in 1972 on protein-energy malnourished (PEM) Senegalese children (Ingenbleek et al. 1972). By comparison with ALB and transferrin (TF) plasma values, TTR revealed a much higher degree of sensitivity to changes in protein status that has been attributed to its shorter biological half-life (2 days) and to its unusual Trp richness (Ingenbleek et al. 1972, 1975a). Transcription of the TTR gene in the liver is directed by CCAAT/enhancer binding protein (C/EBP) bound to hepatocyte nuclear factor 1 (HNF1) under the control of several other HNFs. The mechanism responsible for the suppressed TTR synthesis in PEM-states is a restricted AA and energy supply working as limiting factors (Ingenbleek and Young 2002). The rapidly turning over TTR protein is highly responsive to any change in protein flux and energy supply, being clearly situated on the cutting edge of the equipoise.

LBM shrinking may be the consequence of either dietary restriction reducing protein syntheses to levels compatible with survival or that of cytokine-induced tissue proteolysis exceeding protein synthesis and resulting in a net body negative N balance. The size of LBM in turn determines plasma TTR concentrations whose liver production similarly depends on both dietary provision and inflammatory conditions. In animal cancer models, reduced TBN pools were correlated with decreasing plasma TTR values and provided the same predictive ability. In kidney patients, LBM is proposed as an excellent predictor of outcome working in the same direction as TTR plasma levels.  High N intake, supposed to preserve LBM reserves, reduces significantly the mortality rate of kidney patients and is positively correlated with the alterations of TTR plasma concentrations appearing as the sole predictor of final outcome. It is noteworthy that most SELDI or MALDI workers interested in defining protein nutritional status have chosen TTR as a biomarker, showing that there exists a large consensus considering the BP as the most reliable indicator of protein depletion in most morbid circumstances.

Total homocysteine (tHcy) is a S-containing AA not found in customary diets but endogenously produced in the body of mammals by the enzymatic transmethylation of methionine (Met), one of the eight IAAs supplied by staplefoods. tHcy may either serve as precursor substrate for the synthesis of new Met molecules along the remethylation (RM) pathway or undergo irreversible kidney leakage through a cascade of derivatives defining the transsulfuration (TS) pathway. Hcy is thus situated at the crossroad of RM and TS pathways that are regulated by three water-soluble vitamins (pyridoxine, B6; folates, B9; cobalamins, B12).

Significant positive correlations are found between tHcy and plasma urea and plasma creatinine, indicating that both visceral and muscular tissues undergo proteolytic degradation throughout the course of rampant inflammatory burden. In healthy individuals, tHcy plasma concentrations maintain positive correlations with LBM and TTR from birth until the end of adulthood. Starting from the onset of normal old age, tHcy values become disconnected from LBM control and reveal diverging trends with TTR values. Of utmost importance is the finding that, contrary to all protein
components which are downregulated in protein-depleted states, tHcy values are upregulated.  Hyperhomocysteinemia is an acquired clinical entity characterized by mild or moderate elevation in tHcy blood values found in apparently healthy individuals (McCully 1969). This distinct morbid condition appears as a public health problem of increasing importance in the general population, being regarded as an independent and graded risk factor for vascular pathogenesis unrelated to hypercholesterolemia, arterial hypertension, diabetes and smoking.

Studies grounded on stepwise multiple regression analysis have concluded that the two main watersoluble vitamins account for only 28% of tHcy variance whereas vitamins B6, B9, and B12, taken together, did not account for more than 30–40% of variance. Moreover, a number of hyperhomocysteinemic conditions are not responsive to folate and pyridoxine supplementation. This situation prompted us to search for other causal factors which might fill the gap between the public health data and the vitamin triad deficiencies currently incriminated. We suggest that S – the forgotten element – plays central roles in nutritional epidemiology (Ingenbleek and Young 2004).

Aminoacidemia studies performed in PEM children, adult patients and elderly subjects have reported that the concentrations of plasma IAAs invariably display lowering trends as the morbid condition worsens. The depressed tendency is especially pronounced in the case of tryptophan and for the so-called branched-chain AAs (BCAAs, isoleucine, leucine, valine) the decreases in which are regarded as a salient PEM feature following the direction outlined by TTR (Ingenbleek et al. 1986). Met constitutes a notable exception to the above described evolutionary profiles, showing unusual stability in chronically protein depleted states.

Maintenance of normal methioninemia is associated with supranormal tHcy blood values in PEMadults (Ingenbleek et al. 1986) and increased tHcy leakage in the urinary output of PEM children. In contrast, most plasma and urinary S-containing compounds produced along the TS pathway downstream to CbSconverting step (Fig. 20.1) display significantly diminished values. This is notably the case for cystathionine (Ingenbleek et al. 1986), glutathione, taurine, and sulfaturia. Such distorted patterns are reminiscent of abnormalities defining homocystinuria, an inborn disease of Met metabolism characterized by CbS refractoriness to pyridoxine stimuli, thereby promoting the upstream retention of tHcy in biological fluids. It
was hypothesized more than 20 years ago (Ingenbleek et al. 1986) that PEM is apparently able to similarly depress CbS activity, suggesting that the enzyme is a N-status sensitive step working as a bidirectional lockgate, overstimulated by high Met intake (Finkelstein and Martin 1986) and downregulated under N-deprivation conditions (Ingenbleek et al. 2002). Confirmation that N dietary deprivation may inhibit CbS activity has recently provided. The tHcy precursor pool is enlarged in biological fluids, boosting Met remethylation processes along the RM pathway, consistent with studies showing overstimulation of Met-synthase activity in conditions of protein restriction. In other words, high tHcy plasma concentrations observed in PEM states are the dark side of adaptive mechanisms for maintaining Met homeostasis. This is consistent with the unique role played by Met in the preservation of N body stores.

The classical interpretation that strict vegans, who consume plenty of folates in their diet and manifest nevertheless higher tHcy plasma concentrations than omnivorous counterparts, needs to be revisited. On the basis of hematological and biochemical criteria, cobalamin deficiency is one of the most prevalent vitamin-deficiencies wordwide, being often incriminated as deficient in vegan subjects. It seems, however, likely that its true causal impact on rising tHcy values is substantially overestimated in most studies owing to the modest contribution played by cobalamins on tHcy
variance analyses. In contrast, there exists a growing body of converging data indicating that the role played by the protein component is largely underscored in vegan studies. It is worth recalling that S is the main intracellular anion coexisting with N within a constant mean S:N ratio (1:14.5) in animal tissues and dietary products of animal origin (Ingenbleek 2006). The mean S:N ratio found in plant items ranges from 1:20 to 1:35, a proportion that does not optimally meet human tissue requirements (Ingenbleek 2006), paving the way for borderline S and N deficiencies.

A recent Taiwanese investigation on hyperhomocysteinemic nuns consuming traditional vegetarian regimens consisting of mainly rice, soy products,
vegetables and fruits with few or no dairy items illustrates such clinical misinterpretation (Hung et al. 2002). The authors reported that folates and cobalamins, taken together, accounted for only 28.6% of tHcy variance in the vegetarian cohort whereas pyridoxine was inoperative (Hung et al. 2002). The daily vegetable N and Met intakes were situated highly significantly (p < 0.001) below the recommended allowances for humans (FAO/WHO/United Nations University 1985), causing a stage of unrecognized PEM documented by significantly depressed BCAA plasma
concentrations. Met levels escaped the overall decline in IAAs levels, emphasizing that efficient homeostatic mechanisms operate at the expense of an acquired hyperhomocysteinemic state. The diagnosis of subclinical PEM was missed because the authors ignored the exquisitely sensitive TTR detecting power. A proper PEM identification would have allowed the authors to confirm the previously described TTR–tHcy relationship that was established in Western Africa from comparable field studies involving country dwellers living on plant products.

The concept that acute or chronic stressful conditions may exert similar inhibitory effects on CbS activity and thereby promote hyperhomocysteinemic states is founded on previous studies showing that hypercatabolic states are characterized by increased urinary N and S losses maintaining tightly correlated depletion rates (Cuthbertson 1931; Ingenbleek and Young 2004; Sherman and Hawk 1900) which reflect the S:N ratio found in tissues undergoing cytokine induced proteolysis. This has been documented in coronary infarction and in acute pancreatitis where tHcy elevation evolves too rapidly to allow for a nutritional vitamin B-deficit explanation.  tHcy is considered stable in plasma and the two investigations report unaltered folate and cobalamin plasma concentrations.

The clinical usefulness of TTR as a nutritional biomarker, described in the early seventies (Ingenbleek et al. 1972) has been substantially disregarded by the scientific community for nearly four decades. This long-lasting reluctance expressed by many investigators is largely due to the fact that protein malnutrition and stressful disorders of various causes have combined inhibitory effects on hepatic TTR synthesis. Declining TTR plasma concentrations may result from either dietary protein and energy restrictions or from cytokine-induced transcriptional blockade (Murakami et al. 1988) of its hepatic synthesis. The proposed marker was therefore seen as having high sensitivity but poor specificity. Recent advances in protein metabolism settle the controversy by throwing further light on the relationships between TTR and the N-components of body composition.

The developmental patterns of LBM and TTR exhibit striking similarities. Both parameters rise from birth to puberty, manifest gender dimorphism during full sexual maturity then decrease during ageing. Uncomplicated PEM primarily affects both visceral and structural pools of LBM with distinct kinetics, reducing protein synthesis to levels compatible with prolonged survival. In acute or chronic stressful disorders, LBM undergoes muscle proteolysis exceeding the upregulation of protein syntheses in liver and injured areas, yielding a net body negative N balance. These adaptive responses are well identified by the measurement of TTR plasma concentrations which therefore appear as a plasma marker for LBM fluctuations.
Attenuation of stress and/or introduction of nutritional rehabilitation restores both LBM and TTR to normal values following parallel slopes. TTR fulfills, therefore, a unique position in assessing actual protein nutritional status, monitoring the efficacy of dietetic support and predicting the patient’s outcome (Bernstein and Pleban 1996).

see also…

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Bernstein LH, Ingenbleek Y (2002) Transthyretin: Its response to malnutrition and stress injury. Clinical usefulness and economical implications. Clin Chem Lab Med 40:1344–1348.

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