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Alzheimer’s Disease and Diabetes Mellitus

Posted in Alzheimer's Disease, Etiology, Neurodegenerative Diseases, Neurological Diseases, Neuroscience, tagged Alzheimer Disease, amylin, amyloid beta peptide, dementia, Diabetes Mellitus, Insulin, insulysin, metalloproteases, neprilysin on April 21, 2016| Leave a Comment »

Alzheimer’s Disease and Diabetes Mellitus

Larry H. Bernstein, MD, FCAP, Curator

LPBI

Unraveling Alzheimer’s:Making Sense of the Relationship between Diabetes and Alzheimer’s Disease¹

Schilling, Melissa A.^* New York University, New York, NY, USA Journal of Alzheimer’s Disease 2016; 51(4): 961-977
http://content.iospress.com/articles/journal-of-alzheimers-disease/jad150980DOI: 10.3233/JAD-150980

Numerous studies have documented a strong association between diabetes and Alzheimer’s disease (AD). The nature of the relationship, however, has remained a puzzle, in part because of seemingly incongruent findings. For example, some studies have concluded that insulin deficiency is primarily at fault, suggesting that intranasal insulin or inhibiting the insulin-degrading enzyme (IDE) could be beneficial. Other research has concluded that hyperinsulinemia is to blame, which implies that intranasal insulin or the inhibition of IDE would exacerbate the disease. Such antithetical conclusions pose a serious obstacle to making progress on treatments. However, careful integration of multiple strands of research, with attention to the methods used in different studies, makes it possible to disentangle the research on AD. This integration suggests that there is an important relationship between insulin, IDE, and AD that yields multiple pathways to AD depending on the where deficiency or excess in the cycle occurs. I review evidence for each of these pathways here. The results suggest that avoiding excess insulin, and supporting robust IDE levels, could be important ways of preventing and lessening the impact of AD. I also describe what further tests need to be conducted to verify the arguments made in the paper, and their implications for treating AD.

Alzheimer’s disease (AD) is a devastating, fatal disease that affects an estimated 5.2 million Americans, and 44 million people worldwide. It is a disease that is often harder on the families and caregivers of the patient than on the patient themselves. The direct costs to the US of AD in 2014 were estimated to total $214 billion [1]. Adding in the informal costs (the costs of family members and friends providing unpaid care to those with dementia) doubles those figures. The bulk of the financial burden of AD is not due to the cost of drugs or doctor’s visits; instead, the vast majority (75–84%) of the expenses go to nursing home care, plus formal and informal home care [2]. The drugs currently available for AD (primarily cholinesterase inhibitors and memantine) offer only incremental improvements in symptoms— they do not stop the progression of the disease [3–6]. Analysts estimate that AD will cost $1.5 trillion per year US by 2050 if a more effective treatment is not developed [7].

AD has been a difficult puzzle to solve, in part because of an abundance of seemingly incongruent findings. For example, though many studies have identified a significant association between type 2 diabetes mellitus (T2DM) and AD (see the review provided inTable 1), these studies have often come to different conclusions about the causal mechanism and its implications for treatment. Some studies, for example, have concluded that insulin deficiency is primarily at fault, suggesting that intranasal insulin or inhibiting the insulin-degrading enzyme (IDE) could be beneficial [8–11]. Other research has concluded that hyperinsulinemia is to blame, which implies that intranasal insulin or the inhibition of IDE could exacerbate the disease [12–16]. Similarly, recent studies have found a strong association between AD and amylin, a peptide hormone co-secreted with insulin [17–20]. Jackson et al. and Srodulski et al. found that amylin, like the amyloid-β (Aβ) protein thought to be central to the pathology of AD, forms amyloid plaques in the brain, leading them to conclude that amylin might be another amyloid with a causal role in dementia. Oskarsson et al. similarly found that amylin and Aβ were colocalized in plaques in the brain, leading them to draw similar conclusions. However, two other recent studies came to an opposite conclusion: they obtained results suggesting that amylin provides a neuroprotective effect that reduces the symptoms of AD [21, 22].

Despite these seemingly incongruent results, careful integration of multiple strands of research (with attention to the methods used in different studies) makes it possible to disentangle the research on AD. Such an integration points to the likelihood of a relationship between insulin, IDE, and AD that yields multiple pathways to the disease depending on the where deficiency or excess in the cycle occurs.

I posit that the weight of the evidence suggests that under normal circumstances, insulin upregulates the expression of IDE, which subsequently breaks insulin down [23, 24]. IDE, however, also plays important roles in breaking down Aβ and other amyloidogenic peptides. This system can malfunction and lead to AD in at least four different ways as outlined below (see Fig. 1) Evidence for each of these will be reviewed in turn in the sections that follow:

1) An individual with severe insulin deficiency (e.g., undertreated type 1 diabetes mellitus, T1DM) may have inadequate IDE activity, resulting in the accumulation of Aβ (and other protein aggregates) in the brain [23, 25, 26].
2) An individual with diminished IDE (or similar protease) production may end up with accumulation of Aβ and amylin plaques in the brain [27–32].
3) If an individual has exceptionally high levels of insulin (and amylin) in the body (e.g., due to early stages of T2DM), the insulin and amylin may competitively inhibit the breakdown of Aβ, resulting in AD [30, 33–35].
4) An individual may produce more than a typical level of an amyloidogenic peptide, or experience synergistic interactions between amyloidogenic peptides, leading to deposition that outpaces clearing by IDE and similar proteases [17–19, 36–42].

INSULIN, INSULIN DEGRADING ENZYME, AND ALZHEIMER’S DISEASE

The potential roles of insulin and insulin degrading enzyme in AD and other dementias came under scrutiny because of the strong association between T2DM and AD. I thus begin here by briefly reviewing the research on the relationship between T2DM and AD, and I will then review the evidence (summaries are provided in Table 1) for the pathway proposed inFig. 1 and its possible malfunctions.

Type 2 diabetes and Alzheimer’s disease

There is an abundance of studies suggesting that T2DM has a positive association with AD. Some of the most well known research in this area was based on a large population study in Rotterdam [43, 44]. The longitudinal results from this study suggested that diabetes increased the risk of dementia by 1.9 fold, and that diabetic patients treated with insulin were at even greater risk (4.3 fold). Another longitudinal cohort study from the same time frame found that T2DM was associated with an increased risk for all dementias (1.66), and AD in particular (2.27 fold for men, 1.37 fold for women) [45]. Several other longitudinal cohort studies followed, with nearly all concluding that T2DM increased the risk of AD between 1.3 fold and 1.8 fold [46–49].

When cognitive testing is used to assess AD, there is a risk that other types of dementias (notably vascular dementia) will be labeled AD. A diagnosis of AD may often be the result of multiple pathologies [50]. Using autopsies, Schneider et al., for example, found that of 179 probable AD cases, almost half exhibited mixed pathologies— most commonly vascular dementia as a result of cerebral infarctions or neocortical Lewy bodies [51]. Notably, many studies have also implicated T2DM in an increased risk of vascular dementia [46, 52, 53], and, as I will explain later, we have reason to suspect that T2DM could also increase the risk of Lewy bodies.

As noted previously, there is considerable disagreement about the mechanism by which T2DM increases the risk of AD. One line of research posits that it is the excess of insulin or glucose from T2DM that leads to AD. Several studies have found that people with AD have significantly higher levels of insulin and glucose than healthy controls [13, 15, 54]. In a large sample longitudinal study of elderly subjects, Luchsinger et al. conclude that 39% of AD in their sample was attributable to hyperinsulinemia or diabetes [55]. This is also consistent with earlier findings of Ott et al. that diabetics that were treated with insulin had far greater risk of AD [43, 44].

Another line of research, however, suggests that it is insulin deficiency (either by the relative deficiency that results from insulin resistance in early stages of T2DM, or absolute deficiency that occurs when beta cell dysfunction occurs in full-blown T2DM) that causes AD by impairing insulin’s ability to perform its roles in the brain [8, 56–61]. Insulin and its signaling pathways have been found to affect learning and memory [62, 63]. For example, some research has found that administering insulin growth factors in rats and mice enhances memory retention [63, 64], and depleting it impairs learning [65]. However, the mechanisms of insulin’s roles in the brain remain poorly understood [66]. The potential roles of insulin deficiency in AD has led some researchers to conclude that administration of intranasal insulin, or insulin sensitizers, would attenuate neurological deficits. For example, in several studies, Reger et al. found that moderate doses of intranasal insulin improved some memory symptoms in older adults with AD or mild cognitive impairment [57–59]. However, it is important to note first that patients with diabetes were excluded from the study, and second that the results were nonmonotonic in the dosages of insulin. That is, at higher levels, insulin administration impaired performance.

If insulin deficiency is one of the main culprits in AD, then we would expect a very strong relationship between undertreated T1DM (whereby an individual does not produce insulin or amylin at all) and AD. However, T1DM is much rarer than T2DM, and in the past it often resulted in much earlier mortality. Furthermore, survival of T1DM requires individuals to be treated with insulin, confounding our ability to analyze its relationship with AD. In a few studies, T1DM was induced in mice via administration of streptozotocin, and these mice exhibited AD (or AD-like) pathology [11, 24, 67, 68]¹. For example, in the study by Wang et al., inducing T1DM in mice via administration of streptozotocin resulted in increased Aβ generation, neuritic plaque formation, and spatial memory deficits in mice engineered to exhibit AD [11]. Similarly, a study by Clodfelder-Miller et al. found that within three days of insulin depletion by streptozotocin, mice exhibited a five-fold increase in tau phosphorylation [68]. There is also some evidence to suggest that having a severe insulin deficiency, as in T1DM, could result in inadequate upregulation of proteases that break down Aβ [71]. This leads, then, to the first malfunction pathway proposed above.

MALFUNCTION 1. SEVERE INSULIN DEFICIENCY MAY LEAD TO INADEQUATE PROTEASE PRODUCTION OR ACTIVITY

There is a paucity of information about what stimulates IDE and other amyloid proteases, however, the studies that do exist suggest that insulin is a primary regulator of IDE [23, 24, 26]. For example, in one study, Zhao et al. conclude that IDE upregulation requires insulin-mediated Akt (also known as protein kinase B) activation [23], and mice induced to have T1DM (and thus do not produce insulin) expressed significantly less IDE [24]. Rezende et al. also found that when insulin secretion levels were dramatically reduced in mice through protein secretion, there was a concomitant dramatic decrease in IDE expression in the liver [72]. This suggests that a severe insulin deficiency could possibly be accompanied by an IDE deficiency that could lead to or exacerbate AD. However, because severe insulin deficiency is typically fatal if untreated, this malfunction pathway is probably the least likely to be observed in situ. Furthermore, there are other proteases known to act upon Aβ (e.g., cathepsin D, endothelin-converting enzyme, neprilysin [73–77]) that may not be as reliant upon insulin, and we know relatively little about how these proteases are stimulated, which ones act on Aβ in vivo, and how they may compensate for each other. This area thus requires much further research.

MALFUNCTION 2. DIMINISHED PROTEASE PRODUCTION OR ACTIVITY RESULTS IN AMYLOID ACCUMULATION

IDE is one of the most widely studied proteases in studies of the relationship between insulin and Aβ. It is a ubiquitously expressed zinc metalloprotease that breaks down or irreversibly binds insulin [27, 33, 36, 78, 79], amylin [36], Aβ [27–31, 33, 80–86], and other amyloidogenic peptides [34, 36], including alpha synuclein [87, 88], which is implicated in Parkinson’s disease and Lewy body dementia. An individual with diminished IDE production (for example, due to the excess of an IDE inhibitor such as nitric oxide [89], or an inadequacy of zinc) might thus end up with accumulation of Aβ, amylin plaques, and alpha synuclein in the brain.

There are numerous studies showing that diminished IDE can result in accumulation of Aβ and memory deficits [27, 90, 91]. For example, Farris et al. found that IDE knockout mice had a greater than 50% decrease in Aβ degradation in both brain membrane fractions and primary neuronal cultures. [27] The mice exhibited an increase in cerebral accumulation of endogenous Aβ (consistent with AD), hyperinsulinemia, and glucose intolerance. Madani et al. found that neprilysin knockout mice had increased Aβ deposition [91], and Miller et al. found that IDE knockout mice had significantly increased levels of Aβ in the brain [92]. Vingtdeux et al. found that CALHM1 potentiates IDE activity, and CALHM1 knockout mice exhibited roughly a 50% increase in endogenous Aβ concentrations in the whole brain and primary neurons [85].

There is also research suggesting that deficiency in IDE might lead to an accumulation of insulin in the brain (hyperinsulinemia), leading to insulin resistance and glucose intolerance [27, 32]. Though the possibility of IDE regulating insulin in the brain remains to be directly tested, this possibility suggests that one of the reasons that AD and T2DM are closely associated might be because they can be caused by the same mechanism.

Diminished IDE production may also account for at least part of the association between the ApoE4 allele and AD. ApoE4 is a well-established risk factor for AD; most estimates suggest that roughly 20–25% of the population has the ApoE4 allele, yet roughly 50% of the AD population has the ApoE4 allele [21, 93, 94]. Furthermore, in their longitudinal study of 2,574 Japanese-American men (and 216 autopsies), Peila et al. found that the combination of diabetes and having one or more copies of the ApoE4 allele resulted in a dramatically higher risk of AD— 5.5 fold— than either risk alone [46]. Having a single copy of the allele is thought to triple the risk for late-onset AD; having two copies of the allele is thought to increase the risk of AD 12 fold [94]. Importantly, Cook et al. found that AD patients with the ApoE4 allele had a 50% reduction in expression of IDE compared to AD patients without the ApoE4 allele, suggesting that the ApoE4 allele may play a role in IDE deficiency leading to AD [95]. The mechanisms that underlie ApoE4’s relationship to AD remain to be more fully explored, however.

Qiu et al.’s study, and a review by Qiu and Folstein, suggest that IDE is likely to be an important protease involved in Aβ degradation [30, 35]. Furthermore, since the IDE gene plays a significant role also in diabetes, this would help to explain the strong relationship between the two pathologies. However, it is important to note that are other proteases that appear to play roles in breaking down or binding Aβ such as neprilysin, endothelin-converting enzyme, cathepsin B, or cathepsin D [73, 83, 96]. The role of these proteases in Aβ degradation and AD pathology have thus far received far less attention and warrant further study.

MALFUNCTION 3. EXCESS INSULIN OR AMYLIN COMPETITIVELY INHIBITS BREAKDOWN OF Aβ

Though IDE can break down a range of amyloidogenic peptides [34], it has a preferential affinity for insulin [33, 36]. This suggests the possibility that, consistent with Qiu et al.’s hypothesis, one of the causal mechanisms leading to sporadic AD may be the competitive inhibition of Aβ by insulin or amylin [30]. Numerous studies have shown that insulin completely competitively inhibits the breakdown of both Aβ [30, 33, 35] and amylin [36]. Furthermore, though insulin upregulates the expression of IDE, it has been shown that its ability to increase IDE diminishes at high levels [23]. This suggests that in the hyperinsulinemia of early T2DM (or obesity) [97, 98], insulin levels could outstrip IDE’s ability to break it down. If IDE preferentially targets insulin and insulin levels are outpacing IDE production, IDE’s ability to breakdown other amyloidogenic proteins will be markedly reduced. As eloquently stated in Bennett et al., “Normally, a balance exists between deposition and degradation of the amyloidogenic peptide. When the levels of the peptide exceed the capacity to degrade them, either by increased expression of the peptide, or decreased expression of the enzymatic activity of IDE, the balance is shifted from degradation to deposition.” [36] The chronic hyperinsulinemia of early T2DM and its potential to competitively inhibit the breakdown of Aβ thus likely explains a large portion of the association between T2DM and AD.

This competitive inhibition of degradation among different IDE substrates brings us to the recent amylin studies. In 2013, Jackson et al. found patients with AD had large amylin plaque deposits and mixed amylin and Aβ deposits in their brains [17]. They concluded that amylin may play a causal role in AD. Then in 2014, Srodulski et al. found that rats that were genetically modified to express human amylin accumulated amylin oligomers in their brains, and exhibited neurological deficits [18]. Oskarsson et al. also found that amylin and Aβ were colocalized in the brains of human AD patients [19]. If amylin, which is co-secreted with insulin, competes with Aβ for degradation, promotes the deposition of Aβ, or accumulates in plaques on the brain itself, this is another strong mechanism by which T2DM and dementia may be linked.

Remarkably, another set of recent studies appeared to directly counter this conclusion by finding that amylin exhibited a neuroprotective effect [21, 99, 100]. These studies found that injection of pramlintide (an amylin analog), or rat/mouse amylin, appeared to improve memory symptoms in mice engineered to exhibit AD or accelerated senescence. Furthermore, administration of pramlintide to humans appeared to improve some learning and memory measures. However, two important features of these recent studies must be noted. First, the studies used rat/mouse amylin, or pramlintide (synthetic amylin), both of which have proline substitutions at positions 25, 28, and 29 that limit amylin’s self-aggregating properties, thus rendering it non-amyloidogenic. Second, in all the studies except for Qiu et al.’s study of homebound elderly [22], the subjects were diabetes free, and thus likely had no deficiency in their IDE system or excess of competing insulin. In the Qiu et al. study of homebound elderly, the researchers found some differences in memory scores across quartiles of amylin levels across all subjects (including those with diabetes), however these differences were not monotonically increasing. Furthermore, the significant differences they report in amylin levels across AD patients, mild cognitive impairment patients, and healthy persons were only for patients without diabetes.

The preceding suggests that pramlintide might have beneficial effects for people without diabetes. This could be due to its role in preventing post-prandial glucose spikes or by inhibiting glucagon, both of which would collectively lessen insulin demand. These mechanisms of potential benefit, however, are speculative; the mechanism of pramlintide’s potential neuroprotective effect is unclear. For people with diabetes, however, pramlintide seems far less likely to be beneficial in AD. In people with diabetes, insulin and amylin levels are already high, and may have already exhausted their capacity for stimulating IDE production and activity.

MALFUNCTION 4. EXCESS PRODUCTION OF AN AMYLOIDOGENIC PROTEIN, OR POSITIVE INTERACTIONS BETWEEN AMYLOIDOGENIC PROTEINS, RESULT IN AMYLOID ACCUMULATION

Excess production of an amyloidogenic protein can result in amyloid deposition outpacing amyloid degradation, resulting in amyloid accumulation [36]. For example, mutations in the amyloid precursor protein gene (the gene associated with early-onset AD) can increase the relative production of Aβ₄₂, leading to amyloid deposition [37, 38]. Similarly, excess production of amylin (as in T2DM) may directly cause a build-up of amylin plaques on the brain [17]. There is also growing evidence that some amyloidogenic proteins can foster the formation of amyloids of other proteins, in a process known as “cross-seeding” [39–41]. For example, alpha synuclein can initiate tau amyloid formation, and then the two peptides can increase the polymerization of each other [42]. Similarly, amylin may interact with Aβ to increase its formation of plaques [17–19].

IMPLICATIONS

The implications of the preceding are very important, because the mechanism by which AD arises strongly determines what treatments are likely to be effective. If insulin deficiency is the main culprit, for example, then intranasal insulin might be of significant benefit. If, however, hyperinsulinemia and/or competitive inhibition of degradation of Aβ by a degrading protease is the main cause, then administering intranasal insulin could exacerbate the disease. Furthermore, there is evidence that hyperinsulinemia precedes the hyperglycemia of T2DM by many years and it is likely the chronic overstimulation of insulin receptors that leads to insulin resistance [35, 97, 101]. This suggests that extreme caution should be exercised in giving a diabetic or pre-diabetic individual extra insulin— it may just add fuel to the fire.

The evidence overwhelmingly suggests that testing for glucose tolerance should occur early and often. There is no downside to glucose tolerance testing other than minor cost, and the upside could be the earlier identification and treatment of pre-diabetes and diabetes. Given the evidence of a very strong association between hyperinsulinemia and AD (and other forms of dementia), every patient with AD or mild cognitive impairment should be regularly tested for glucose intolerance. Furthermore, obesity is also strongly associated with hyperinsulinemia [97] and diabetes [102], and thus, not surprisingly, increases the risk of AD [103]. Given the widespread prevalence of obesity, pre-diabetes, and diabetes, glucose intolerance testing should become a standard part of regular health screening in the broader population. According to the American Diabetes Association, of the 29.1 million Americans with diabetes in 2012, 8.1 million (28%) were undiagnosed. Furthermore, 86 million Americans are estimated to be pre-diabetic (i.e., have impaired glucose tolerance) and most will have no symptoms that are recognizable without medical testing [104]. Early identification of, and intervention for, diabetes and prediabetes could significantly lessen the impact of both diabetes and AD.

The review and arguments here suggest a few necessary future studies:

1. Insulin Deficiency versus Hyperinsulinemia

First, to test the competing hypotheses that it is insulin deficiency versus hyperinsulinemia that create or exacerbate AD (and thus the appropriateness of administering intranasal insulin) mice (including wild type, mice altered to develop AD, and mice altered to develop both AD and hyperinsulinemia) should be given chronic intranasal insulin and then subjected to both cognitive testing and quantification of amyloid burden and tauopathy. If the pathways to AD posed in this paper are correct, intranasal insulin should make AD in hyperinsulinemic mice worse. Its effects on the other mice should be very informative: if it yields moderate neurological improvements in the AD mice, this would support its use in non-hyperinsulinemic AD patients. It might, however, induce hyperinsulinemia and insulin resistance leading to T2DM in the wild type mice, and both T2DM and worsening of AD in the AD mice by competitively inhibiting the breakdown of Aβ. Ideally a range of doses of insulin will be used to assess potential curvilinear effects.

2. Neuroprotective versus Competitive Inhibition Effects of Amylin and Pramlintide

Next, to assess the neuroprotective versus competitive inhibition effects of amylin and pramlintide, in vitro studies should first be conducted to assess the degree to which pramlintide (rather than human amylin) competitively inhibits the breakdown of Aβ. If IDE responds primarily to the amyloidogenic motif rather than particular amino acid sequences, as suggested by Kurochkin [34] and others, perhaps pramlintide competes less for breakdown of IDE compared to human amylin. Next different groups of mice (wild type, mice altered to develop AD and hyperinsulinemia, mice altered to develop AD but without hyperinsulinemia, and IDE knockout mice altered to develop AD) should be chronically treated with different amylins (pramlintide, human amylin), at different dosage levels to observe the potential differential effects of amylin and pramlintide depending on the state of the insulin-IDE system of the subject. IDE inhibitors that can decrease (rather than eliminate) IDE could also be used to more precisely explore the relationships between intranasal insulin, pramlintide, IDE, and AD [32, 105]. This should be followed by cognitive testing and quantification of amyloid burden and tauopathy. If the arguments about competitive inhibition presented earlier are correct, the administration of human amylin should exacerbate AD in all but the wild-type mice. I was unable to find any studies of whether pramlintide competitively inhibits the breakdown of Aβ, so it is impossible to predict the outcome of the tests with pramlintide. If, however, it turns out that pramlintide does competitively inhibit the breakdown of Aβ, then its administration should also exacerbate AD in all but the wild-type mice.

If the results of the first set of studies above find that hyperinsulinemia rather than insulin deficiency exacerbates AD, then this implies that we should be able to significantly lower rates of AD through educating people about how to better manage their blood sugar and insulin. A very large portion of the population has little understanding of the glycemic index of carbohydrates. Furthermore, very few people know that some artificial sweeteners produce an insulin response. This also yields a potential policy implication that perhaps food should be labeled with a measure of its effect on insulin. The results of the second study should help us to identify any AD risks of administering pramlintide (which is already given to many diabetic patients in addition to insulin sensitizers) and help us to assess the overall reliability, efficacy, and safety of administering these drugs.

If the results of future studies support the arguments made in this paper, then this suggests that much more research should be done to identify the different proteases that degrade Aβin vivo, to better understand their promoters and inhibitors, and to evaluate the safety and efficacy of increasing the availability of such proteases in both AD and diabetes. Relatedly, it would be valuable to develop easily administered diagnostic tests to identify protease deficiencies.

Finally, the work here hints at some very fruitful opportunities for extending the findings in AD to better understand other neurodegenerative diseases that involve protein aggregation in the brain. For example, many of the studies cited here with IDE knockout or IDE upregulated mice should be adapted for studies of Parkinson’s disease, Lewy body dementia, and Huntington’s disease. These latter diseases have longer peptide sequences than IDE is thought to degrade (IDE has been shown to only cleave peptides of 50 amino acids or shorter [106]), but recent studies indicate that IDE nonproteolytically inhibits alpha synuclein fibril formation by binding to alpha synuclein oligomers and preventing them from forming amyloids [88], suggesting there could be great promise in this research pathway.

It should be noted that there is disagreement about the validity of a Type 1 diabetes model based on the administration of streptozotocin. Some studies have suggested that streptozotocin is neurotoxic per se [69] while others have found that streptozotocin is not directly neurotoxic [70].

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Alzheimer’s Disease Conundrum – Are We Near the End of the Puzzle?

Posted in Advanced Drug Manufacturing Technology, Biological Networks, Gene Regulation and Evolution, Biomarkers & Medical Diagnostics, Cell Biology, Signaling & Cell Circuits, Cerebrovascular and Neurodegenerative Diseases, Chemical Genetics, Disease Biology, Small Molecules in Development of Therapeutic Drugs, Genome Biology, Genomic Testing: Methodology for Diagnosis, Human Immune System in Health and in Disease, Innovations in Neurophysiology & Neuropsychology, International Global Work in Pharmaceutical, Medical Imaging Technology, Image Processing/Computing, MRI, CT, Nuclear Medicine, Ultra Sound, Molecular Genetics & Pharmaceutical, Pharmaceutical Industry Competitive Intelligence, Proteomics, Regulated Clinical Trials: Design, Methods, Components and IRB related issues, Technology Transfer: Biotech and Pharmaceutical, tagged Alois Alzheimer, Alzheimer, Alzheimer Disease, Alzheimers Disease, ApoE, BCHE brain imaging, Beta amyloid, biomarkers, cellular inflammatiory response, CLU, conitive loss, Decode Genetics, dementia, Icelanders, innovative applications, Kári Stefánsson, mapping, Massachusetts General Hospital, Picalm, plaque regression, Tau protein on March 9, 2013| 1 Comment »

Alzheimer’s Genomic Diagnosis and Treatment

Curator: Larry H Bernstein, MD, FCAP

Gene Mutation Protects Against Alzheimer’s

by Greg Miller on 11 July 2012
Brain preserver. A newly discovered gene mutation appears to protect against Alzheimer’s disease. Credit: Alzheimer’s Disease Education and Referral Center/NIA/NIH
http://news.sciencemag.org/sciencenow/2012/07/gene-mutation-protects-against-a.html

A rare mutation that alters a single letter of the genetic code protects people from the

memory-robbing dementia of Alzheimer’s disease.

The DNA change may inhibit the buildup of β amyloid, the

protein fragment that forms the hallmark plaques in the brains of Alzheimer’s patients.
The mutation affects a gene called APP,
which encodes a protein that gets broken down into pieces,
including β amyloid.

Researchers previously identified more than 30 mutations to APP, none of them good. Several of these changes increase β amyloid formation and cause

• a devastating inherited form of Alzheimer’s that afflicts people in their 30s and 40s—

• much earlier than the far more common “late-onset” form of Alzheimer’s

that typically strikes people their 70s and 80s.

The new mutation, discovered from whole-genome data from 1795 Icelanders for variations in APP that protect against Alzheimer’s, appears to do the opposite. The mutation interferes with one of the enzymes that breaks down the APP protein and causes a 40% reduction in β amyloid formation

New pharmacological strategies for treatment of Alzheimer’s disease: focus on disease modifying drugs.
Salomone S, Caraci F, Leggio GM, Fedotova J, Drago F.
University of Catania, Viale Andrea Doria 6, Catania, Italy.
Br J Clin Pharmacol. 2012 Apr;73(4):504-17. doi: 10.1111/j.1365-2125.2011.04134.x.

Current approved drug treatments for Alzheimer disease (AD) include

cholinesterase inhibitors (donepezil, rivastigmine, galantamine) and the
NMDA receptor antagonist memantine.

These drugs provide symptomatic relief but poorly affect the progression of the disease. Drug discovery has been directed, in the last 10 years, to develop ‘disease modifying drugs’ hopefully able to counteract the progression of AD. Because in a chronic, slow progressing pathological process, such as AD, an early start of treatment enhances the chance of success,

it is crucial to have biomarkers for early detection of AD-related brain dysfunction,
- usable before clinical onset.

Reliable early biomarkers need therefore to be prospectively tested for predictive accuracy,

with specific cut off values validated in clinical practice.

Disease modifying drugs developed so far include drugs to

reduce β amyloid (Aβ) production,
drugs to prevent Aβ aggregation,
drugs to promote Aβ clearance,
drugs targeting tau phosphorylation and assembly

None of these drugs has demonstrated efficacy in phase 3 studies. The failure of clinical trials with disease modifying drugs raises a number of questions, spanning from

methodological flaws to
fundamental understanding of AD pathophysiology and biology.

Diagnostic criteria applicable to presymptomatic stages of AD have now been published.

These new criteria may impact on drug development, such that future trials on disease modifying drugs will include populations susceptible to AD, before clinical onset. http://www.ncbi.nlm.nih.gov/pubmed/22035455

Gene mutation defends against Alzheimer’s disease
Rare genetic variant suggests a cause and treatment for cognitive decline.
Ewen Callaway 11 July 2012
http://www.nature.com/news/gene-mutation-defends-against-alzheimer-s-disease-1.10984

J. NIETH/CORBIS
Almost 30 million people live with Alzheimer’s disease worldwide, a staggering health-care burden that is expected to quadruple by 2050. Yet doctors can offer no effective treatment, and scientists have been unable to pin down the underlying mechanism of the disease.
Research published this week offers some hope on both counts – few people carry a genetic mutation that naturally prevents them from developing the condition – 0.5% of Icelanders have a protective gene, as are 0.2–0.5% of Finns, Swedes and Norwegians. Icelanders who carry it have a 50% better chance of reaching age 85, are more than five times more likely to reach it 85 without Alzheimer’s. The mutation seems to put a brake on the milder mental deterioration that most elderly people experience. Carriers are about 7.5 times more likely than non-carriers to reach the age of 85 without major cognitive decline, and perform better on the cognitive tests that are administered thrice yearly to Icelanders who live in nursing homes.
The discovery not only confirms the principal suspect that is responsible for Alzheimer’s, it also suggests that the disease could be

an extreme form of the cognitive decline seen in many older people.

The mutation — the first ever found to protect against the disease — lies in a gene that produces

amyloid-β precursor protein (APP),
which has an unknown role in the brain

APP was discovered 25 years ago in patients with rare,

inherited forms of Alzheimer’s that strike in middle age.
In the brain, APP is broken down into a smaller molecule called amyloid-β.

Visible clumps, or plaques, of amyloid-β found in the autopsied brains of patients are a hallmark of Alzheimer’s.
Scientists have long debated whether the plaques are a cause of the neurodegenerative condition

or a consequence of other biochemical changes associated with the disease.

The latest finding supports other genetics studies blaming amyloid-β, according to Rudolph Tanzi, a neurologist at the Massachusetts General Hospital in Boston and a member of one of the four teams that discovered APP’s role in the 1980s.
If amyloid-β plaques were confirmed as the cause of Alzheimer’s, it would bolster efforts to develop drugs that block their formation, says Kári Stefánsson, chief executive of deCODE Genetics in Reykjavik, Iceland, who led the latest research. He and his team first discovered the mutation by comparing the complete genome sequences of 1,795 Icelanders with their medical histories. The researchers then studied the variant in nearly 400,000 more Scandinavians.
This suggests that Alzheimer’s disease and cognitive decline are two sides of the same coin, with a common cause — the build-up of amyloid-β plaques in the brain, something seen to a lesser degree in elderly people who do not develop full-blown Alzheimer’s. A drug that mimics the effects of the mutation, might slow cognitive decline as well as prevent Alzheimer’s.
Stefánsson and his team discovered that the mutation introduces a single amino-acid alteration to APP. This amino acid is close to the site where an enzyme called

β-secretase 1 (BACE1) ordinarily snips APP into smaller amyloid-β chunks —
and the alteration is enough to reduce the enzyme’s efficiency.

Stefánsson’s study suggests that blocking β-secretase from cleaving APP has the potential to prevent Alzheimer’s, but Philippe Amouyel, an epidemiologist at the Pasteur Institute in Lille, France, says “it is very difficult to identify the

precise time when this amyloid toxic effect could still be modified”.

“If this effect needs to be blocked as early as possible in life to protect against Alzheimer’s disease, we will need to propose a new design for clinical trials” to identify an effective treatment.

The results demonstrate that whole-genome sequencing can uncover very rare mutations that might offer insight into common diseases.

disease risk, may be determined by genetic variants that slightly tilt the odds of developing disease
In this case a rare mutant may provide very key mechanistic insights into Alzheimer’s

Jonsson, T. et al. Nature http://dx.doi.org/10.1038/nature11283 (2012).
Kang, J. et al. Nature 325, 733–736 (1987).
Goldgaber, D., Lerman, M. I., McBride, O. W., Saffiotti, U. & Gajdusek, D. C. Science 235, 877–880 (1987).

BHCE genetic data combined with brain imaging using agent florbetapir connects the BHCE gene to AD plaque buildup. BHCE is an enzyme that breaks down acetylcholine in the brain, which is depleted early in the disease and results in memory loss. http://www.genengnews.com/

New Alzheimer’s Genes Found
Gigantic Scientific Effort Discovers Clues to Treatment, Diagnosis of Alzheimer’s Disease
By Daniel J. DeNoon
WebMD Health News Reviewed by Laura J. Martin, MD
http://www.webmd.com/alzheimers/news/20110403/new-alzheimers-genes-found

A massive scientific effort has found five new gene variants linked to Alzheimer’s disease. The undertaking involved analyzing the genomes of nearly 40,000 people with and without Alzheimer’s. This study was undertaken by two separate research consortiums in the U.S. and in Europe, which collaborated to confirm each other’s results.
Four genes had previously been linked to Alzheimer’s. Three of them affect only the risk of relatively rare forms of Alzheimer’s. The fourth is APOE, until now the only gene known to affect risk of the common, late-onset form of Alzheimer’s. Roughly 27% of Alzheimer’s disease can be attributed to the five new gene variants. Even though Alzheimer’s is a very complex disease, the new findings represent a large chunk of Alzheimer’s risk, according to Margaret A. Pericak-Vance, PhD, of the U.S. consortium –

20% of the causal risk of Alzheimer’s disease and
32% of the genetic risk.

Alzheimer’s Tied to Mutation Harming Immune Response
By GINA KOLATA Published: November 14, 2012 in NY Times
http://www.nytimes.com/2012/11/15/health/gene-mutation-that-hobbles-immune-response-is-linked-to-alzheimers.html?_r=0
Alzheimer’s researchers and drug companies have for years concentrated on one hallmark of Alzheimer’s disease: the production of toxic shards of a protein that accumulate in plaques on the brain.
Two groups of researchers working from entirely different starting points have converged on a mutated gene involved in another aspect of Alzheimer’s disease:

the immune system’s role in protecting against the disease.

The mutation is suspected of interfering with

the brain’s ability to prevent the buildup of plaque.

When the gene is not mutated, white blood cells in the brain spring into action,

gobbling up and eliminating the plaque-forming toxic protein, beta amyloid.

As a result, Alzheimer’s can be staved off or averted. People with the mutated gene have a threefold to fivefold increase in the likelihood of developing Alzheimer’s disease in old age.

Comparing Differences

Dr. Julie Williams’s, Cardiff, Wales (European team leader) report identified CLU and Picalm. A second study published in Nature Genetics, by Philippe Amouyel from Institut Pasteur de Lille in France, pinpointed CLU and CR1. The greatest inherited risk comes from the APOE gene, discovered in 1993 by a team led by Allen Roses, now director of the Deane Drug Discovery Institute at Duke UMC, in Durham, North Carolina.
The findings “are beginning to give us insight into the biology, but I don’t think you can expect treatments overnight,” Dr. Michael Owen (Cardiff, Wales) said. Instead, the genes will show a mosaic of risk, and “the key issue is what hand of cards you’re dealt,” he said.

Promise for Early Diagnosis
BHCE genetic data combined with brain imaging using agent florbetapir connects the BHCE gene to AD plaque buildup. BHCE is an enzyme that breaks down acetylcholine in the brain, which is depleted early in the disease and results in memory loss.

Dr. Bernstein’s comments:

There has been a long history of failure of drugs to slow down the progression of Alzheimer’s. Regression of the plaques has not corresponded with retention of cognitive ability, which has been behind the arguments over beta amyloid or tau.
We now have two particularly interesting mutations –
1. ApoE gene mutation that increases risk
2. APP mutation that quite dramatically affects retention of cognition

Alzheimer’s Disease: Green Tea Extract Found To Interfere With The Formation Of Amyloid Plaques (medicalnewstoday.com)
Aging Brain – The Specific Gene That Causes It (belmarrahealth.com)
The Pathogenic Aβ43 Is Enriched in Familial and Sporadic Alzheimer Disease (plosone.org)
Damaged blood vessels loaded with amyloid worsen cognitive impairment in Alzheimer’s disease (eurekalert.org)
Major step toward an Alzheimer’s vaccine (nextbigfuture.com)
Damaged blood vessels loaded with amyloid worsen cognitive impairment in Alzheimer’s disease (medicalxpress.com)
Top Signs You are at Risk for Alzheimer’s (belmarrahealth.com)
A Reliable Way to Detect Endogenous Murine β-Amyloid (plosone.org)

β-amyloid fibrils. (Photo credit: Wikipedia)

English: PET scan of a human brain with Alzheimer’s disease (Photo credit: Wikipedia)

Depiction of amyloid precursor protein processing, created by I. Peltan Ipeltan (Photo credit: Wikipedia)

English: Diagram of how microtubules desintegrate with Alzheimer’s disease Français : La protéine Tau dans un neurone sain et dans un neurone malade Español: Esquema que muestra cómo se desintegran los microtúbulos en la enfermedad de Alzheimer (Photo credit: Wikipedia)

English: Histopathogic image of senile plaques seen in the cerebral cortex in a patient with presenile onset of Alzheimer disease. Bowdian stain. The same case as shown in a file “Alzheimer_dementia_(1)_presenile_onset.jpg”. (Photo credit: Wikipedia)

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Special Considerations in Blood Lipoproteins, Viscosity, Assessment and Treatment

Posted in Bio Instrumentation in Experimental Life Sciences Research, Biological Networks, Gene Regulation and Evolution, Biomarkers & Medical Diagnostics, Cardiovascular Pharmacogenomics, Cell Biology, Signaling & Cell Circuits, Cerebrovascular and Neurodegenerative Diseases, Chemical Biology and its relations to Metabolic Disease, Coagulation Therapy and Internal Bleeding, Disease Biology, Small Molecules in Development of Therapeutic Drugs, Frontiers in Cardiology and Cardiovascular Disorders, Genome Biology, HTN, International Global Work in Pharmaceutical, Medical and Population Genetics, Medical Devices R&D Investment, Metabolomics, Molecular Genetics & Pharmaceutical, Nutrition, Origins of Cardiovascular Disease, Personalized and Precision Medicine & Genomic Research, Pharmaceutical Industry Competitive Intelligence, Pharmacotherapy of Cardiovascular Disease, Population Health Management, Genetics & Pharmaceutical, Population Health Management, Nutrition and Phytochemistry, Proteomics, Systemic Inflammatory Response Related Disorders, tagged apo(a), arterial hemodynamics, cerebral blood flow, Coagulation, CRP, dementia, Endothelium, fibronectin, fluid flow, grape seed, Heart rate, hemostasis, homocysteine, homocysteine thiolactone, hyperglycemia, hyperhomocysteinemia, hypoxic-ischemic encephalopathy, LDL, LDL-apheresis, lipoprotein (a), methionine, non-gaussian variability, plasminogen, plasminogen activator inhibitor, protease, shear stress, Stroke, TGF beta1, Thrombophilia, thrombosis related disorders, triglycerides, viscosity, VLDL, Von Willebrand factor on November 28, 2012| 10 Comments »

Special Considerations in Blood Lipoproteins, Viscosity, Assessment and Treatment

Author: Larry H. Bernstein, MD, FCAP

and

Curator: Aviva Lev-Ari, PhD, RN

This is the second of a two part discussion of viscosity, hemostasis, and vascular risk

This is Part II of a series on blood flow and shear stress effects on hemostasis and vascular disease.

See Part I on viscosity, triglycerides and LDL, and thrombotic risk.

Hemostatic Factors in Thrombophilia

Objectives.—To review the state of the art relating to elevated hemostatic factor levels as a potential risk factor for thrombosis, as reflected by the medical literature and the consensus opinion of recognized experts in the field, and to make recommendations for the use of specific measurements of hemostatic factor levels in the assessment of thrombotic risk in individual patients.

Data Sources.—Review of the medical literature, primarily from the last 10 years.

Data Extraction and Synthesis.—After an initial assessment of the literature, key points were identified. Experts were assigned to do an in-depth review of the literature and to prepare a summary of their findings and recommendations.

A draft manuscript was prepared and circulated to every participant in the College of American Pathologists Conference XXXVI: Diagnostic Issues in Thrombophilia prior to the conference. Each of the key points and associated recommendations was then presented for discussion at the conference. Recommendations were accepted if a consensus of the 27 experts attending the conference was reached. The results of the discussion were used to revise the manuscript into its final form.

Consensus was reached on 8 recommendations concerning the use of hemostatic factor levels in the assessment of thrombotic risk in individual patients.

The underlying premise for measuring elevated coagulation factor levels is that if the average level of the factor is increased in the patient long-term, then the patient may be at increased risk of thrombosis long-term. Both risk of thrombosis and certain factors increase with age (eg, fibrinogen, factor VII, factor VIII, factor IX, and von Willebrand factor). Are these effects linked or do we need age specific ranges? Do acquired effects like other diseases or medications affect factor levels, and do the same risk thresholds apply in these instances? How do we assure that the level we are measuring is a true indication of the patient’s average baseline level and not a transient change? Fibrinogen, factor VIII, and von Willebrand factor are all strong acute-phase reactants.

Risk of bleeding associated with coagulation factor levels increases with roughly log decreases in factor levels. Compared to normal (100%), 60% to 90% decreases in a coagulation factor may be associated with excess bleeding with major trauma, 95% to 98% decreases with minor trauma, and .99% decrease with spontaneous hemorrhage. In contrast, the difference between low risk and high risk for thrombosis may be separated by as little as 15% above normal.

It may be possible to define relative cutoffs for specific factors, for example, 50% above the mean level determined locally in healthy subjects for a certain factor. Before coagulation factor levels can be routinely used to assess individual risk, work must be done to better standardize and calibrate the assays used.

Detailed discussion of the rationale for each of these recommendations is presented in the article. This is an evolving area of research. While routine use of factor level measurements is not recommended, improvements in assay methodology and further clinical studies may change these recommendations in the future.

Chandler WL, Rodgers GM, Sprouse JT, Thompson AR. Elevated Hemostatic Factor Levels as Potential Risk Factors for Thrombosis. Arch Pathol Lab Med. 2002;126:1405–1414

Model System for Hemostatic Behavior

This study explores the behavior of a model system in response to perturbations in

tissue factor
thrombomodulin surface densities
tissue factor site dimensions
wall shear rate.

The classic time course is characterized by

initiation and
amplification of thrombin generation
the existence of threshold-like responses

This author defines a new parameter, the „effective prothrombotic zone‟, and its dependence on model parameters. It was found that prothrombotic effects may extend significantly beyond the dimensions of the spatially discrete site of tissue factor expression in both axial and radial directions. Furthermore, he takes advantage of the finite element modeling approach to explore the behavior of systems containing multiple spatially distinct sites of TF expression in a physiologic model. The computational model is applied to assess individualized thrombotic risk from clinical data of plasma coagulation factor levels. He proposes a systems-based parameter with deep venous thrombosis using computational methods in combination with biochemical panels to predict hypercoagulability for high risk populations.

The Vascular Surface

The ‘resting’ endothelium synthesizes and presents a number of antithrombogenic molecules including

heparan sulfate proteoglycans
ecto-adenosine diphosphatase
prostacyclin
nitric oxide
thrombomodulin.

In response to various stimuli

inflammatory mediators
hypoxia
oxidative stress
fluid shear stress

the cell surface becomes ‘activated’ and serves to organize membrane-associated enzyme complexes of coagulation.

Fluid Phase Models of Coagulation

Leipold et al. developed a model of the tissue factor pathway as a design aid for the development of exogenous serine protease inhibitors. In contrast, Guo et al. focused on the reactions of the contact, or intrinsic pathway, to study parameters relevant to material-induced thrombosis, including procoagulant surface area.

Alternative approaches to modeling the coagulation cascade have been pursued including the use of stochastic activity networks to represent the intrinsic, extrinsic, and common pathways through fibrin formation and a kinetic Monte Carlo simulation of TF-initiated thrombin generation. Generally, fluid phase models of the kinetics of coagulation are both computationally and experimentally less complex. As such, the computational models are able to incorporate a large number of species and their reactions, and empirical data is often available for regression analysis and model validation. The range of complexity and motivations for these models is wide, and the models have been used to describe various phenomena including the ‘all-or-none’ threshold behavior of thrombin generation. However, the role of blood flow in coagulation is well recognized in promoting the delivery of substrates to the vessel wall and in regulating the thrombin response by removing activated clotting factors.

Flow Based Models of Coagulation

In 1990, Basmadjian presented a mathematical analysis of the effect of flow and mass transport on a single reactive event at the vessel wall and consequently laid the foundation for the first flow-based models of coagulation. It was proposed that for vessels greater than 0.1 mm in diameter, reactive events at the vessel wall could be adequately described by the assumption of a concentration boundary layer very close to the reactive surface, within which the majority of concentration changes took place. The height of the boundary layer and the mass transfer coefficient that described transport to and from the vessel wall were shown to stabilize on a time scale much shorter than the time scale over which concentration changes were empirically observed. Thus, the vascular space could be divided into two compartments, a boundary volume and a bulk volume, and furthermore, changes within the bulk phase could be considered negligible, thereby reducing the previously intractable problem to a pseudo-one compartment model described by a system of ordinary differential equations.

Basmadjian et al. subsequently published a limited model of six reactions, including two positive feedback reactions and two inhibitory reactions, of the common pathway of coagulation triggered by exogenous factor IXa under flow. As a consequence of the definition of the mass transfer coefficient, the kinetic parameters were dependent on the boundary layer height. Furthermore, the model did not explicitly account for intrinsic tenase or prothrombinase formation, but rather derived a rate expression for reaction in the presence of a cofactor. The major finding of the study was the predicted effect of increased mass transport to enhance thrombin generation by decreasing the induction time up to a critical mass transfer rate, beyond which transport significantly decreased peak thrombin levels thereby reducing overall thrombin production.

Kuharsky and Fogelson formulated a more comprehensive, pseudo-one compartment model of tissue factor-initiated coagulation under flow, which included the description of 59 distinct fluid- and surface-bound species. In contrast to the Baldwin-Basmadjian model, which defined a mass transfer coefficient as a rate of transport to the vessel surface, the Kuharsky-Fogelson model defined the mass transfer coefficient as a rate of transport into the boundary volume, thus eliminating the dependence of kinetic parameters on transport parameters. The computational study focused on the threshold response of thrombin generation to the availability of membrane binding sites. Additionally, the model suggested that adhered platelets may play a role in blocking the activity of the TF/ VIIa complex. Fogelson and Tania later expanded the model to include the protein C and TFPI pathways.

Modeling surface-associated reactions under flow uses finite element method (FEM), which is a technique for solving partial differential equations by dividing the vascular space into a finite number of discrete elements. Hall et al. used FEM to simulate factor X activation over a surface presenting TF in a parallel plate flow reactor. The steady state model was defined by the convection-diffusion equation and Michaelis-Menten reaction kinetics at the surface. The computational results were compared to experimental data for the generation of factor Xa by cultured rat vascular smooth muscle cells expressing TF.

Based on discrepancies between numerical and experimental studies, the catalytic activity of the TF/ VIIa complex may be shear-dependent. Towards the overall objective of developing an antithrombogenic biomaterial, Tummala and Hall studied the kinetics of factor Xa inhibition by surface-immobilized recombinant TFPI under unsteady flow conditions. Similarly, Byun et al. investigated the association and dissociation kinetics of ATIII inactivation of thrombin accelerated by surface-immobilized heparin under steady flow conditions. To date, finite element models that detail surface-bound reactions under flow have been restricted to no more than a single reaction catalyzed by a single surface-immobilized species.

Models of Coagulation Incorporating Spatial Parameter

Major findings include the roles of these specific coagulation pathways in the

initiation
amplification
termination phases of coagulation.

Coagulation near the activating surface was determined by TF/VIIa catalyzed factor Xa production, which was rapidly inhibited close to the wall. In contrast, factor IXa diffused farther from the surface, and thus factor Xa generation and clot formation away from the reactive wall was dependent on intrinsic tenase (IXa/ VIIIa) activity. Additionally, the concentration wave of thrombin propagated away from the activation zone at a rate which was dependent on the efficiency of inhibitory mechanisms.

Experimental and ‘virtual’ addition of plasma-phase thrombomodulin resulted in dose-dependent termination of thrombin generation and provided evidence of spatial localization of clot formation by TM with final clot lengths of 0.2-2 mm under diffusive conditions.

These studies provide an interesting analysis of the roles of specific factors in relation to space due to diffusive effects, but neglect the essential role of blood flow in the transport analysis. Additionally, the spatial dynamics of clot localization by thrombomodulin would likely be affected by restricting the inhibitor to its physiologic site on the vessel surface.

Finite Element Modeling

Finite element method (FEM) is a numerical technique for solving partial differential equations. Originally proposed in the 1940s to approach structural analysis problems in civil engineering, FEM now finds application in a wide variety of disciplines. The computational method relies on mesh discretization of a continuous domain which subdivides the space into a finite number of ‘elements’. The physics of each element are defined by its own set of physical properties and boundary conditions, and the simultaneous solution of the equations describing the individual elements approximate the behavior of the overall domain.

Sumanas W. Jordan, PhD Thesis. A Mathematical Model of Tissue Factor-Induced Blood Coagulation: Discrete Sites of Initiation and Regulation under Conditions of Flow.

Doctor of Philosophy in Biomedical Engineering. Emory University, Georgia Institute of Technology. May 2010. Under supervision of: Dr. Elliot L. Chaikof, Departments of Surgery and Biomedical Engineering.

Blood Coagulation (Thrombin) and Protein C Pathways (Blood_Coagulation_and_Protein_C_Pathways.jpg) (Photo credit: Wikipedia)

Coagulation cascade (Photo credit: Wikipedia)

Cardiovascular Physiology: Modeling, Estimation and Signal Processing

With cardiovascular diseases being among the main causes of death in the world, quantitative modeling, assessment and monitoring of cardiovascular dynamics, and functioning play a critical role in bringing important breakthroughs to cardiovascular care. Quantification of cardiovascular physiology and its control mechanisms from physiological recordings, by use of mathematical models and algorithms, has been proved to be of important value in understanding the causes of cardiovascular diseases and assisting the diagnostic and prognostic process. This E-Book is derived from the Frontiers in Computational Physiology and Medicine Research Topic entitled “Engineering Approaches to Study Cardiovascular Physiology: Modeling, Estimation and Signal Processing.”

There are two review articles. The first review article by Chen et al. (2012) presents a unified point process probabilistic framework to assess heart beat dynamics and autonomic cardiovascular control. Using clinical recordings of healthy subjects during Propofol anesthesia, the authors demonstrate the effectiveness of their approach by applying the proposed paradigm to estimate

instantaneous heart rate (HR),
heart rate variability (HRV),
respiratory sinus arrhythmia (RSA)
baroreflex sensitivity (BRS).

The second review article, contributed by Zhang et al. (2011), provides a comprehensive overview of tube-load model parameter estimation for monitoring arterial hemodynamics.

The remaining eight original research articles can be mainly classified into two categories. The two articles from the first category emphasize modeling and estimation methods. In particular, the paper “Modeling the autonomic and metabolic effects of obstructive sleep apnea: a simulation study” by Cheng and Khoo (2012), combines computational modeling and simulations to study the autonomic and metabolic effects of obstructive sleep apnea (OSA).

The second paper, “Estimation of cardiac output and peripheral resistance using square-wave-approximated aortic flow signal” by Fazeli and Hahn (2012), presents a model-based approach to estimate cardiac output (CO) and total peripheral resistance (TPR), and validates the proposed approach via in vivo experimental data from animal subjects.

The six articles in the second category focus on application of signal processing techniques and statistical tools to analyze cardiovascular or physiological signals in practical applications. the paper “Modulation of the sympatho-vagal balance during sleep: frequency domain study of heart rate variability and respiration” by Cabiddu et al. (2012), uses spectral and cross-spectral analysis of heartbeat and respiration signals to assess autonomic cardiac regulation and cardiopulmonary coupling variations during different sleep stages in healthy subjects.

The paper “increased non-gaussianity of heart rate variability predicts cardiac mortality after an acute myocardial infarction” by Hayano et al. (2011) uses a new non-gaussian index to assess the HRV of cardiac mortality using 670 post-acute myocardial infarction (AMI) patients. the paper “non-gaussianity of low frequency heart rate variability and sympathetic activation: lack of increases in multiple system atrophy and parkinson disease” by Kiyono et al. (2012), applies a non-gaussian index to assess HRV in patients with multiple system atrophy (MSA) and parkinson diseases and reports the relation between the non-gaussian intermittency of the heartbeat and increased sympathetic activity. The paper “Information domain approach to the investigation of cardio-vascular, cardio-pulmonary, and vasculo-pulmonary causal couplings” by Faes et al. (2011), proposes an information domain approach to evaluate nonlinear causality among heartbeat, arterial pressure, and respiration measures during tilt testing and paced breathing protocols. The paper “integrated central-autonomic multifractal complexity in the heart rate variability of healthy humans” by Lin and Sharif (2012), uses a relative multifractal complexity measure to assess HRV in healthy humans and discusses the related implications in central autonomic interactions. Lastly, the paper “Time scales of autonomic information flow in near-term fetal sheep” by Frasch et al. (2012), analyzes the autonomic information flow (AIF) with kullback–leibler entropy in fetal sheep as a function of vagal and sympathetic modulation of fetal HRV during atropine and propranolol blockade.

In summary, this Research Topic attempts to give a general panorama of the possible state-of-the-art modeling methodologies, practical tools in signal processing and estimation, as well as several important clinical applications, which can altogether help deepen our understanding about heart physiology and pathology and further lead to new scientific findings. We hope that the readership of Frontiers will appreciate this collected volume and enjoy reading the presented contributions. Finally, we are grateful to all contributed authors, reviewers, and editorial staffs who had all put tremendous effort to make this E-Book a reality.

Cabiddu, R., Cerutti, S., Viardot, G., Werner, S., and Bianchi, A. M. (2012). Modulation of the sympatho-vagal balance during sleep: frequency domain study of heart rate variability and respiration. Front. Physio. 3:45. doi: 10.3389/fphys.2012.00045

Chen, Z., Purdon, P. L., Brown, E. N., and Barbieri, R. (2012). A unified point process probabilistic framework to assess heartbeat dynamics and autonomic cardiovascular control. Front. Physio. 3:4. doi: 10.3389/fphys.2012.00004

Cheng, L., and Khoo, M. C. K. (2012). Modeling the autonomic and metabolic effects of obstructive sleep apnea: a simulation study. Front. Physio. 2:111. doi: 10.3389/fphys.2011.00111

Faes, L., Nollo, G., and Porta, A. (2011). Information domain approach to the investigation of cardio-vascular, cardio-pulmonary, and vasculo-pulmonary causal couplings. Front. Physio. 2:80. doi: 10.3389/fphys.2011.00080

Fazeli, N., and Hahn, J.-O. (2012). Estimation of cardiac output and peripheral resistance using square-wave-approximated aortic flow signal. Front. Physio. 3:298. doi: 10.3389/fphys.2012.00298

Frasch, M. G., Frank, B., Last, M., and Müller, T. (2012). Time scales of autonomic information flow in near-term fetal sheep. Front. Physio. 3:378. doi: 10.3389/fphys.2012.00378

Hayano, J., Kiyono, K., Struzik, Z. R., Yamamoto, Y., Watanabe, E., Stein, P. K., et al. (2011). Increased non-gaussianity of heart rate variability predicts cardiac mortality after an acute myocardial infarction. Front. Physio. 2:65. doi: 10.3389/fphys.2011.00065

Kiyono, K., Hayano, J., Kwak, S., Watanabe, E., and Yamamoto, Y. (2012). Non-Gaussianity of low frequency heart rate variability and sympathetic activation: lack of increases in multiple system atrophy and Parkinson disease. Front. Physio. 3:34. doi: 10.3389/fphys.2012.00034

Lin, D. C., and Sharif, A. (2012). Integrated central-autonomic multifractal complexity in the heart rate variability of healthy humans. Front. Physio. 2:123. doi: 10.3389/fphys.2011.00123

Zhang, G., Hahn, J., and Mukkamala, R. (2011). Tube-load model parameter estimation for monitoring arterial hemodynamics. Front. Physio. 2:72. doi: 10.3389/fphys.2011.00072

Citation: Chen Z and Barbieri R (2012) Editorial: engineering approaches to study cardiovascular physiology: modeling, estimation, and signal processing. Front. Physio. 3:425. doi: 10.3389/fphys.2012.00425

fluctuations of cerebral blood flow and metabolic demand following hypoxia in neonatal brain

Most of the research investigating the pathogenesis of perinatal brain injury following hypoxia-ischemia has focused on excitotoxicity, oxidative stress and an inflammatory response, with the response of the developing cerebrovasculature receiving less attention. This is surprising as the presentation of devastating and permanent injury such as germinal matrix-intraventricular haemorrhage (GM-IVH) and perinatal stroke are of vascular origin, and the origin of periventricular leukomalacia (PVL) may also arise from poor perfusion of the white matter. This highlights that cerebrovasculature injury following hypoxia could primarily be responsible for the injury seen in the brain of many infants diagnosed with hypoxic-ischemic encephalopathy (HIE).

The highly dynamic nature of the cerebral blood vessels in the fetus, and the fluctuations of cerebral blood flow and metabolic demand that occur following hypoxia suggest that the response of blood vessels could explain both regional protection and vulnerability in the developing brain.

This review discusses the current concepts on the pathogenesis of perinatal brain injury, the development of the fetal cerebrovasculature and the blood brain barrier (BBB), and key mediators involved with the response of cerebral blood vessels to hypoxia.

Baburamani AA, Ek CJ, Walker DW and Castillo-Melendez M. Vulnerability of the developing brain to hypoxic-ischemic damage: contribution of the cerebral vasculature to injury and repair? Front. Physio. 2012; 3:424. doi: 10.3389/fphys.2012.00424

remodeling of coronary and cerebral arteries and arterioles

Effects of hypertension on arteries and arterioles often manifest first as a thickened wall, with associated changes in passive material properties (e.g., stiffness) or function (e.g., cellular phenotype, synthesis and removal rates, and vasomotor responsiveness). Less is known, however, regarding the relative evolution of such changes in vessels from different vascular beds.

We used an aortic coarctation model of hypertension in the mini-pig to elucidate spatiotemporal changes in geometry and wall composition (including layer-specific thicknesses as well as presence of collagen, elastin, smooth muscle, endothelial, macrophage, and hematopoietic cells) in three different arterial beds, specifically aortic, cerebral, and coronary, and vasodilator function in two different arteriolar beds, the cerebral and coronary.

Marked geometric and structural changes occurred in the thoracic aorta and left anterior descending coronary artery within 2 weeks of the establishment of hypertension and continued to increase over the 8-week study period. In contrast, no significant changes were observed in the middle cerebral arteries from the same animals. Consistent with these differential findings at the arterial level, we also found a diminished nitric oxide-mediated dilation to adenosine at 8 weeks of hypertension in coronary arterioles, but not cerebral arterioles.

These findings, coupled with the observation that temporal changes in wall constituents and the presence of macrophages differed significantly between the thoracic aorta and coronary arteries, confirm a strong differential progressive remodeling within different vascular beds.

These results suggest a spatiotemporal progression of vascular remodeling, beginning first in large elastic arteries and delayed in distal vessels.

Hayenga HN, Hu J-J, Meyer CA, Wilson E, Hein TW, Kuo L and Humphrey JD Differential progressive remodeling of coronary and cerebral arteries and arterioles in an aortic coarctation model of hypertension. Front. Physio. 2012; 3:420. doi: 10.3389/fphys.2012.00420

C-reactive protein oxidant-mediated release of pro-thrombotic factor

Inflammation and the generation of reactive oxygen species (ROS) have been implicated in the initiation and progression of atherosclerosis. Although C-reactive protein (CRP) has traditionally been considered to be a biomarker of inflammation, recent in vitro and in vivo studies have provided evidence that CRP, itself, exerts pro-thrombotic effects on vascular cells and may thus play a critical role in the development of atherothrombosis. Of particular importance is that CRP interacts with Fcγ receptors on cells of the vascular wall giving rise to the release of pro-thrombotic factors. The present review focuses on distinct sources of CRP-mediated ROS generation as well as the pivotal role of ROS in CRP-induced tissue factor expression. These studies provide considerable insight into the role of the oxidative mechanisms in CRP-mediated stimulation of pro-thrombotic factors and activation of platelets. Collectively, the available data provide strong support for ROS playing an important intermediary role in the relationship between CRP and atherothrombosis.

Zhang Z, Yang Y, Hill MA and Wu J. Does C-reactive protein contribute to atherothrombosis via oxidant-mediated release of pro-thrombotic factors and activation of platelets? Front. Physio. 2012; 3:433. doi: 10.3389/fphys.2012.00433

CRP association with Peripheral Vascular Disease

To determine whether the increase in plasma levels of C-Reactive Protein (CRP), a non-specifi c reactant in the acute-phase of systemic infl ammation, is associated with clinical severity of peripheral arterial disease (PAD).

This is a cross-sectional study at a referral hospital center of institutional practice in Madrid, Spain. These investigators took a stratifi ed random sampling of 3370 patients with symptomatic PAD from the outpatient vascular laboratory database in 2007 in the order of their clinical severity:

the fi rst group of patients with mild chronological clinical severity who did not require surgical revascularization,
the second group consisted of patients with moderate clinical severity who had only undergone only one surgical revascularization procedure and
the third group consisted of patients who were severely affected and had undergone two or more surgical revascularization procedures of the lower extremities in different areas or needed late re-interventions.

The Neyman affi xation was used to calculate the sample size with a fi xed relative error of 0.1.

A homogeneity analysis between groups and a unifactorial analysis of comparison of medians for CRP was done.

The groups were homogeneous for

age
smoking status
Arterial Hypertension
diabetes mellitus
dyslipemia
homocysteinemia and
specifi c markers of infl ammation.

In the unifactorial analysis of multiple comparisons of medians according to Scheffé, it was observed that

the median values of CRP plasma levels were increased in association with higher clinical severity of PAD

3.81 mg/L [2.14–5.48] vs.
8.33 [4.38–9.19] vs.
12.83 [9.5–14.16]; p 0.05

as a unique factor of tested ones.

Plasma levels of CRP are associated with not only the presence of atherosclerosis but also with its chronological clinical severity.

De Haro J, Acin F, Medina FJ, Lopez-Quintana A, and March JR. Relationship Between the Plasma Concentration of C-Reactive Protein and Severity of Peripheral Arterial Disease.
Clinical Medicine: Cardiology 2009;3: 1–7

Hemostasis induced by hyperhomocysteinemia

Elevated concentration of homocysteine (Hcy) in human tissues, defined as hyperhomocysteinemia has been correlated with some diseases, such as

cardiovascular
neurodegenerative
kidney disorders

L-Homocysteine (Hcy) is an endogenous amino acid, containing a free thiol group, which in healthy cells is involved in methionine and cysteine synthesis/resynthesis. Indirectly, Hcy participates in methyl, folate, and cellular thiol metabolism. Approximately 80% of total plasma Hcy is protein-bound, and only a small amount exists as a free reduced Hcy (about 0.1 μM). The majority of the unbound fraction of Hcy is oxidized, and forms dimers (homocystine) or mixed disulphides consisting of cysteine and Hcy.

Two main pathways of Hcy biotoxicity are discussed:

Hcy-dependent oxidative stress – generated during oxidation of the free thiol group of Hcy. Hcy binds via a disulphide bridge with

— plasma proteins

— or with other low-molecular plasma thiols

— or with a second Hcy molecule.

Accumulation of oxidized biomolecules alters the biological functions of many cellular pathways.

Hcy-induced protein structure modifications, named homocysteinylation.

Two main types of homocysteinylation exist: S-homocysteinylation and N-homocysteinylation; both considered as posttranslational protein modifications.

a) S-homocysteinylation occurs when Hcy reacts, by its free thiol group, with another free thiol derived from a cysteine residue in a protein molecule.

These changes can alter the thiol-dependent redox status of proteins.

b) N-homocysteinylation takes place after acylation of the free ε-amino lysine groups of proteins by the most reactive form of Hcy — its cyclic thioester (Hcy thiolactone — HTL), representing up to 0.29% of total plasma Hcy.

Homocysteine occurs in human blood plasma in several forms, including the most reactive one, the homocysteine thiolactone (HTL) — a cyclic thioester, which represents up to 0.29% of total plasma Hcy. In human blood, N-homocysteinylated (N-Hcy-protein) and S-homocysteinylated proteins (S-Hcy-protein) such as NHcy-hemoglobin, N-(Hcy-S-S-Cys)-albumin, and S-Hcyalbumin are known. Other pathways of Hcy biotoxicity might be apoptosis and excitotoxicity mediated through glutamate receptors. The relationship between homocysteine and risk appears to hold for total plasma concentrations of homocysteine between 10 and 30 μM.

Different forms of homocysteine present in human blood.

*Total level of homocysteine — the term “total homocysteine” describes the pool of homocysteine released by reduction of all disulphide bonds in the sample (Perla-Kajan et al., 2007; Zimny, 2008; Manolescu et al., 2010, modified).

The form of Hcy	The concentration in human blood
Homocysteine thiolactone (HTL)	0–35 nM
Protein N-linked homocysteine: N-Hcy-hemoglobin, N-(Hcy-S-S-Cys)-albumin	about 15.5 μM: 12.7 μM, 2.8 μM
Protein S-linked homocysteine — S-Hcy-albumin	about 7.3 μM*
Homocystine (Hcy-S-S-Hcy) and combined with cysteine to from mixed disulphides (Hcy-S-S-Cys)	about 2 μM*
Free reduced Hcy	about 0.1 μM*

As early as in the 1960s it was noted that the risk of atherosclerosis is markedly increased in patients with homocystinuria, an inherited disease resulting from homozygous CBS deficiency and characterized by episodes of

— thromboembolism

— mental retardation

— lens dislocation

— hepatic steatosis

— osteoporosis.

— very high concentrations of plasma homocysteine and methionine.

Patients with homocystinuria have very severe hyperhomocysteinemia, with plasma homocysteine concentration reaching even 400 μM, and represent a very small proportion of the population (approximately 1 in 200,000 individuals). Heterozygous lack of CBS, CBS mutations and polymorphism of the methylenetetrahydrofolate reductase gene are considered to be the most probable causes of hyperhomocysteinemia.

The effects of hyperhomocysteinemia include the complex process of hemostasis, which regulates the properties of blood flow. Interactions of homocysteine and its different derivatives, including homocysteine thiolactone, with the major components of hemostasis are:

endothelial cells
platelets
fibrinogen
plasminogen

Elevated plasma Hcy (>15 μM; Hcy) is associated with an increased risk of cardiovascular diseases

thrombosis
thrombosis related diseases
ischemic brain stroke (independent of other, conventional risk factors of this disease)

Every increase of 2.5 μM in plasma Hcy may be associated with an increase of stroke risk of about 20%. Total plasma Hcy level above 20 μM are associated with a nine-fold increase of the myocardial infarction and stroke risk, in comparison to the concentrations below 9 μM. The increase of Hcy concentration has been also found in other human pathologies, including neurodegenerative diseases

Modifications of hemostatic proteins (N-homocysteinylation or S-homocysteinylation) induced by Hcy or its thiolactone seem to be the main cause of homocysteine biotoxicity in hemostatic abnormalities.

Hcy and HTL may act as oxidants, but various polyphenolic antioxidants are able to inhibit the oxidative damage induced by Hcy or HTL. Therefore, we have to consider the role of phenolic antioxidants in hyperhomocysteinemia –induced changes in hemostasis.

The synthesis of homocysteine thiolactone is associated with the activation of the amino acid by aminoacyl-tRNA synthetase (AARS). Hcy may also undergo erroneous activation, e.g. by methionyl-t-RNA synthetase (MetRS). In the first step of conversion of Hcy to HTL, MetRS misactivates Hcy giving rise to homocysteinyl-adenylate. In the next phase, the homocysteine side chain thiol group reacts with the activated carboxyl group and HTL is produced. The level of HTL synthesis in cultured cells depends on Hcy and Met levels.

Hyperhomocysteinemia and Changes in Fibrinolysis and Coagulation Process

The fibrinolytic activity of blood is regulated by specific inhibitors; the inhibition of fibrinolysis takes place at the level of plasminogen activation (by PA-inhibitors: plasminogen activator inhibitor type-1, -2; PAI-1 or PAI-2) or at the level of plasmin activity (mainly by α2-antiplasmin). Hyperhomocysteinemia disturbs hemostasis and shifts the hemostatic mechanisms in favor of thrombosis. The recent reports indicate that the prothrombotic state observed in hyperhomocysteinemia may arise not only due to endothelium dysfunction or blood platelet and coagulation activation, but also due to impaired fibrinolysis. Hcy-modified fibrinogen is more resistant to the fibrinolytic action. Oral methionine load increases total Hcy, but may diminish the fibrinolytic activity of the euglobulin plasma fraction. Homocysteine-lowering therapies may increase fibrinolytic activity, thereby, prevent atherothrombotic events in patients with cardiovascular diseases after the first myocardial infarction.

Homocysteine — Fibronectin Interaction and its Consequences

Fibronectin (Fn) plays key roles in

cell adhesion
migration
embryogenesis
differentiation
hemostasis
thrombosis
wound healing
tissue remodeling

Interaction of FN with fibrin, mediated by factor XIII transglutaminase, is thought to be important for cell adhesion or cell migration into fibrin clots. After tissue injury, a blood clot formation serves the dual role of restoring vascular integrity and serving as a temporary scaffold for the wound healing process. Fibrin and plasma FN, the major protein components of blood clots, are essential to perform these functions. In the blood clotting process, after fibrin deposition, plasma FN-fibrin matrix is covalently crosslinked, and it then promotes fibroblast adhesion, spreading, and migration into the clot.

Homocysteine binds to several human plasma proteins, including fibronectin. If homocysteine binds to fibronectin via a disulphide linkage, this binding results in a functional change, namely, the inhibition of fibrin binding by fibronectin. This inhibition may lead to a prolonged recovery from a thrombotic event and contribute to vascular occlusion.

Grape seeds are one of the richest plant sources of phenolic substances, and grape seed extract reduces the toxic effect of Hcys and HTL on fibrinolysis. The grape seed extract (12.5–50 μg/ml) supported plasminogen to plasmin conversion inhibited by Hcys or HTL. In vitro experiments showed in the presence of grape seed extract (at the highest tested concentration — 50 μg/ml) the increase of about 78% (for human plasminogen-treated with Hcys) and 56% (for human plasma-treated with Hcys). Thus, in the in vitro model system, that the grape seed extract (12.5–50 μg/ml) diminished the reduction of thiol groups and of lysine ε-amino groups in plasma proteins treated with Hcys (0.1 mM) or HTL (1 μM). In the presence of the grape seed extract at the concentration of 50 μg/ml, the level of reduction of thiol groups reached about 45% (for plasma treated with Hcys) and about 15% (for plasma treated with HTL).

In the presence of the grape seed extract at the concentration of 50 μg/ml, the level of reduction of thiol groups reached about 45% (for plasma treated with Hcys) and about 15% (for plasma treated with HTL).Very similar protective effects of the grape seed extract were observed in the measurements of lysine ε-amino groups in plasma proteins treated with Hcys or HTL. These results indicated that the extract from berries of Aronia melanocarpa (a rich source of phenolic substances) reduces the toxic effects of Hcy and HTL on the hemostatic properties of fibrinogen and plasma. These findings indicate a possible protective action of the A. melanocarpa extract in hyperhomocysteinemia-induced cardiovascular disorders. Moreover, the extract from berries of A. melanocarpa, due to its antioxidant action, significantly attenuated the oxidative stress (assessed by measuring of the total antioxidant status — TAS) in plasma in a model of hyperhomocysteinemia.

Proposed model for the protective role of phenolic antioxidants on selected elements of hemostasis during hyperhomocysteinemia.

various antioxidants (present in human diet), including phenolic compounds, may reduce the toxic effects of Hcy or its derivatives on hemostasis. These findings give hope for the develop development of dietary supplements, which will be capable of preventing thrombosis which occurs under pathological conditions, observed also in hyperhomocysteinemia, such as plasma procoagulant activity and oxidative stress.

Malinowska J, Kolodziejczyk J and Olas B. The disturbance of hemostasis induced by hyper-homocysteinemia; the role of antioxidants. Acta Biochimica Polonica 2012; 59(2): 185–194.

Lipoprotein (a)

Lipoprotein (a) (Lp(a)), for the first time described in 1963 by Berg belongs to the lipoproteins with the strongest atherogenic effect. Its importance for the development of various atherosclerotic vasculopathies (coronary heart disease, ischemic stroke, peripheral vasculopathy, abdominal aneurysm) was recognized considerably later.

Lipoprotein(a) (Lp(a)), an established risk marker of cardiovascular diseases, is independent from other risk markers. The main difference of Lp(a) compared to low density lipoprotein (LDL) is the apo(a) residue, covalently bound to apoB is covalently by a disulfide-bridge. Apo(a) synthesis is performed in the liver, probably followed by extracellular assembly to the apoB location of the LDL.

ApoB-100_______LDL¬¬___ S-S –

Apo(a) has been detected bound to triglyceride-rich lipoproteins (Very Low Density Lipoproteins; VLDL). Corresponding to the structural similarity to LDL, both particles are very similar to each other with regard to their composition. It is a glycoprotein which underlies a large genetic polymorphism caused by a variation of the kringle-IV-type-2 repeats of the protein, characterized by a structural homology to plasminogen. Apo(a)’s structural homology to plasminogen, shares the gene localization on chromosome 6. The kringle repeats present a particularly characteristic structure, which have a high similarity to kringle IV (K IV) of plasminogen. Apo(a) also has a kringle V structure of plasminogen and also a protease domain, which cannot be activated, as opposed to the one of plasminogen. At least 30 genetically determined apo(a) isoforms were identified in man.

Features:

Non covalent binding of kringle -4 types 7 and 8 of apo (a) to apo B
Disulfide bond at Cys4326 of ApoB (near its receptor binding domain ) and the only free cysteine group in K –IV type 9 (Cys4057) of apo(a )
Binding to fibrin and cell membranes
Enhancement by small isoforms ; high concentrations compared to plasminogen and homocysteine
Binding to different lysine rich components of the coagulation system (e. g. TFPI)
Intense homology to plasminogen but no protease activity

ApoB-100_______LDL¬¬___ S-S –

The synthesis of Lp(a), which thus occurs as part of an assembly, is a two-step process.

In a first step, which can be competitively inhibited by lysine analogues, the free sulfhydryl groups of apo(a) and apoB are brought close together.
The binding of apo(a) then occurs near the apoB domain which binds to the LDL receptor, resulting in a reduced affinity of Lp(a) to the LDL-receptor.

Particles that show a reduced affinity to the LDL receptor are not able to form stable compounds with apo(a). Thus the largest part of apo(a) is present as apo(a) bound to LDL. Only a small, quantitatively variable part of apo(a) remains as free apo(a) and probably plays an important role in the metabolism and physiological function of Lp(a).

The Lp(a) plasma concentration in the population is highly skewed and determined to more than 90 % by genetic factors. In healthy subjects the Lp(a)-concentration is correlated with its synthesis.

It is assumed that the kidney has a specific function in Lp(a) catabolizm, since nephrotic syndrome and terminal kidney failure are associated with an elevation of the Lp(a) plasma concentration. One consequence of the poor knowledge of the metabolic path of Lp(a) is the fact that so far pharmaceutical science has failed to develop drugs that are able to reduce elevated Lp(a) plasma concentrations to a desirable level.

Plasma concentrations of Lp(a) are affected by different diseases (e.g. diseases of liver and kidney), hormonal factors (e.g. sexual steroids, glucocorticoids, thyroid hormones), individual and environmental factors (e.g. age, cigarette smoking) as well as pharmaceuticals (e.g. derivatives of nicotinic acid) and therapeutic procedures (lipid apheresis). This review describes the physiological regulation of Lp(a) as well as factors influencing its plasma concentration.

Apart from its significance as an important agent in the development of atherosclerosis, Lp(a) has even more physiological functions, e.g. in

wound healing
angiogenesis
hemostasis

However, in the meaning of a pleiotropic mechanism the favorable action mechanisms are opposed by pathogenic mechanisms, whereby the importance of Lp(a) in atherogenesis is stressed.

Lp(a) in Atherosclerosis

In transgenic, hyperlipidemic and Lp(a) expressing Watanabe rabbits, Lp(a) leads to enhanced atherosclerosis. Under the influence of Lp(a), the binding of Lp(a) to glycoproteins, e.g. laminin, results – via its apo(a)-part – both in

an increased invasion of inflammatory cells and in
an activation of smooth vascular muscle cells

with subsequent calcifications in the vascular wall.

The inhibition of transforming growth factor-β1 (TGF-β1) activation is another mechanism via which Lp(a) contributes to the development of atherosclerotic vasculopathies. TGF-β1 is subject to proteolytic activation by plasmin and its active form leads to an inhibition of the proliferation and migration of smooth muscle cells, which play a central role in the formation and progression of atherosclerotic vascular diseases.

In man, Lp(a) is an important risk marker which is independent of other risk markers. Its importance, partly also under consideration of the molecular weight and other genetic polymorphisms, could be demonstrated by a high number of epidemiological and clinical studies investigating the formation and progression of atherosclerosis, myocardial infarction, and stroke.

Lp(a) in Hemostasis

Lp(a) is able to competitively inhibit the binding of plasminogen to fibrinogen and fibrin, and to inhibit the fibrin-dependent activation of plasminogen to plasmin via the tissue plasminogen activator, whereby apo(a) isoforms of low molecular weight have a higher affinity to fibrin than apo(a) isoforms of higher molecular weight. Like other compounds containing sulfhydryl groups, homocysteine enhances the binding of Lp(a) to fibrin.

Pleiotropic effect of Lp(a).

Prothrombotic :

Binding to fibrin
Competitive inhibition of plasminogen
Stimulation of plasminogen activator inhibitor I and II (PAI -I, PAI -II)
Inactivation of tissue factor pathway inhibitor (TFPI)

Antithrombotic :

Inhibition of platelet activating factor acetylhydrolase (PAF -AH)
Inhibition of platelet activating factor
Inhibition of collagen dependent platelet aggregation
Inhibition of secretion of serotonin und thromboxane

Lp(a) in Angiogenesis

Lp(a) is also important for the process of angiogenesis and the sprouting of new vessels.

angiogenesis starts with the remodelling of matrix proteins and
activation of matrix metalloproteinases (MMP).

The latter ones are usually synthesised as

inactive zymogens and
require activation by proteases,

Recall that Apo(a) is not activated by proteases. The angiogenesis is also accomplished by plasminogen. Lp(a) and apo(a) and its fragments has an antiangiogenetic and metastasis inhibiting effect related to the structural homology with plasminogen without the protease activity.

Siekmeier R, Scharnagl H, Kostner GM, T. Grammer T, Stojakovic T and März W. Variation of Lp(a) Plasma Concentrations in Health and Disease. The Open Clinical Chemistry Journal, 2010; 3: 72-89.

LDL-Apheresis

In 1985, Brown and Goldstein were awarded the Nobel Prize for medicine for their work on the regulation of cholesterol metabolism. On the basis of numerous studies, they were able to demonstrate that circulating low-density lipoprotein (LDL) is absorbed into the cell through receptor linked endocytosis. The absorption of LDL into the cell is specific and is mediated by a LDL receptor. In patients with familial hypercholesterolemia, this receptor is changed, and the LDL particles can no longer be recognized. Their absorption can thus no longer be mediated, leading to an accumulation of LDL in blood.

Furthermore, an excess supply of cholesterol also blocks the 3-hydrox-3 methylglutaryl-Co enzyme A (HMG CoA), reductase enzyme, which otherwise inhibits the cholesterol synthesis rate. Brown and Goldstein also determined the structure of the LDL receptor. They discovered structural defects in this receptor in many patients with familial hypercholesterolemia. Thus, familial hypercholesterolemia was the first metabolic disease that could be tracked back to the mutation of a receptor gene.

Dyslipoproteinemia in combination with diabetes mellitus causes a cumulative insult to the vasculature resulting in more severe disease which occurs at an earlier age in large and small vessels as well as capillaries. The most common clinical conditions resulting from this combination are myocardial infarction and lower extremity vascular disease. Ceriello et al. show an independent and cumulative effect of postprandial hypertriglyceridemia and hyperglycemia on endothelial function, suggesting oxidative stress as common mediator of such effect. The combination produces greater morbidity and mortality than either alone.

As an antiatherogenic factor, HDL cholesterol correlates inversely to the extent of postprandial lipemia. A high concentration of HDL is a sign that triglyceride-rich particles are quickly decomposed in the postprandial phase of lipemia. Conversely, with a low HDL concentration this decomposition is delayed. Thus, excessively high triglyceride concentrations are accompanied by very low HDL counts. This combination has also been associated with an increased risk of pancreatitis.

The importance of lipoprotein (a) (Lp(a)) as an atherogenic substance has also been recognized in recent years. Lp(a) is very similar to LDL. But it also contains Apo(a), which is very similar to plasminogen, enabling Lp(a) to bind to fibrin clots. Binding of plasminogen is prevented and fibrinolysis obstructed. Thrombi are integrated into the walls of the arteries and become plaque components.

Another strong risk factor for accelerated atherogenesis, which must be mentioned here, are the widespread high homocysteine levels found in dialysis patients. This risk factor is independent of classic risk factors such as high cholesterol and LDL levels, smoking, hypertension, and obesity, and much more predictive of coronary events in dialysis patients than are these better-known factors. Homocysteine is a sulfur aminoacid produced in the metabolism of methionine. Under normal conditions, about 50 percent of homocysteine is remethylated to methionine and the remaining via the transsulfuration pathway.

Defining hyperhomocysteinemia as levels greater than the 90th percentile of controls and elevated Lp(a) level as greater than 30mg/dL, the frequency of the combination increased with declining renal function. Fifty-eight percent of patients with a GFR less than 10mL/min had both hyperhomocysteinemia and elevated Lp(a) levels, and even in patients with mild renal impairment, 20 percent of patients had both risk factors present.

The prognosis of patients suffering from severe hyperlipidemia, sometimes combined with elevated lipoprotein (a) levels, and coronary heart disease refractory to diet and lipid-lowering drugs is poor. For such patients, regular treatment with low-density lipoprotein (LDL) apheresis is the therapeutic option. Today, there are five different LDL-apheresis systems available: cascade filtration or lipid filtration, immunoadsorption, heparin-induced LDL precipitation, dextran sulfate LDL adsorption, and the LDL hemoperfusion. The requirement that the original level of cholesterol is to be reduced by at least 60 percent is fulfilled by all these systems.

There is a strong correlation between hyperlipidemia and atherosclerosis. Besides the elimination of other risk factors, in severe hyperlipidemia therapeutic strategies should focus on a drastic reduction of serum lipoproteins. Despite maximum conventional therapy with a combination of different kinds of lipid-lowering drugs, sometimes the goal of therapy cannot be reached. Hence, in such patients, treatment with LDL-apheresis is indicated. Technical and clinical aspects of these five different LDL-apheresis methods are depicted. There were no significant differences with respect to or concerning all cholesterols, or triglycerides observed.

High plasma levels of Lp(a) are associated with an increased risk for atherosclerotic coronary heart disease
(CHD) by a mechanism yet to be determined. Because of its structural properties, Lp(a) can have both atherogenic and thrombogenic potentials. The means for correcting the high plasma levels of Lp(a) are still limited in effectiveness. All drug therapies tried thus far have failed. The most effective therapeutic methods in lowering Lp(a) are the LDL-apheresismethods. Since 1993, special immunoadsorption polyclonal antibody columns (Pocard, Moscow, Russia) containing sepharose bound anti-Lp(a) have been available for the treatment of patients with elevated Lp(a) serum concentrations.

With respect to elevated lipoprotein (a) levels, however, the immunoadsorption method seems to be most effective. The different published data clearly demonstrate that treatment with LDL-apheresis in patients suffering from severe hyperlipidemia refractory to maximum conservative therapy is effective and safe in long-term application.

LDL-apheresis decreases not only LDL mass but also improves the patient’s life expectancy. LDL-apheresis performed with different techniques decreases the susceptibility of LDL to oxidation. This decrease may be related to a temporary mass imbalance between freshly produced and older LDL particles. Furthermore, the baseline fatty acid pattern influences pretreatment and postreatment susceptibility to oxidation.

Bambauer R, Bambauer C, Lehmann B, Latza R, and Ralf Schiel R. LDL-Apheresis: Technical and Clinical Aspects. The Scientific World Journal 2012; Article ID 314283, pp 1-19. doi:10.1100/2012/314283

Summary: This discussion is a two part sequence that first establishes the known strong relationship between blood flow viscosity, shear stress, and plasma triglycerides (VLDL) as risk factors for hemostatic disorders leading to thromboembolic disease, and the association with atherosclerotic disease affecting the heart, the brain (via carotid blood flow), peripheral circulation,the kidneys, and retinopathy as well.

The second part discusses the modeling of hemostasis and takes into account the effects of plasma proteins involved with red cell and endothelial interaction, which is related to part I. The current laboratory assessment of thrombophilias is taken from a consensus document of the American Society for Clinical Pathology. The problems encountered are sufficient for the most common problems of coagulation testing and monitoring, but don’t address the large number of patients who are at risk for complications of accelerated vasoconstrictive systemic disease that precede serious hemostatic problems. Special attention is given to Lp(a) and to homocysteine. Lp(a) is a protein that has both prothrombotic and antithrombotic characteristics, and is a homologue of plasminogen and is composed of an apo(a) bound to LDL. Unlike plasminogen, it has no protease activity. Homocysteine elevation is a known risk factor for downstream myocardial infarct. Homocysteine is a mirror into sulfur metabolism, so an increase is an independent predictor of risk, not fully discussed here. The modification of risk is discussed by diet modification. In the most serious cases of lipoprotein disorders, often including Lp(a) the long term use of LDL-apheresis is described.

see Relevent article that appears in NEJM from American College of Cardiology

Apolipoprotein(a) Genetic Sequence Variants Associated With Systemic Atherosclerosis and Coronary Atherosclerotic Burden but Not With Venous Thromboembolism

Helgadottir A, Gretarsdottir S, Thorleifsson G, et al

J Am Coll Cardiol. 2012;60:722-729

Study Summary

The LPA gene codes for apolipoprotein(a), which, when linked with low-density lipoprotein particles, forms lipoprotein(a) [Lp(a)] — a well-studied molecule associated with coronary artery disease (CAD). The Lp(a) molecule has both atherogenic and thrombogenic effects in vitro , but the extent to which these translate to differences in how atherothrombotic disease presents is unknown.

LPA contains many single-nucleotide polymorphisms, and 2 have been identified by previous groups as being strongly associated with levels of Lp(a) and, as a consequence, strongly associated with CAD. However, because atherosclerosis is thought to be a systemic disease, it is unclear to what extent Lp(a) leads to atherosclerosis in other arterial beds (eg, carotid, abdominal aorta, and lower extremity), as well as to other thrombotic disorders (eg, ischemic/cardioembolic stroke and venous thromboembolism). Such distinctions are important, because therapies that might lower Lp(a) could potentially reduce forms of atherosclerosis beyond the coronary tree.

To answer this question, Helgadottir and colleagues compiled clinical and genetic data on the LPA gene from thousands of previous participants in genetic research studies from across the world. They did not have access to Lp(a) levels, but by knowing the genotypes for 2 LPA variants, they inferred the levels of Lp(a) on the basis of prior associations between these variants and Lp(a) levels. [1] Their studies included not only individuals of white European descent but also a significant proportion of black persons, in order to widen the generalizability of their results.

Their main findings are that LPA variants (and, by proxy, Lp(a) levels) are associated with CAD, peripheral arterial disease, abdominal aortic aneurysm, number of CAD vessels, age at onset of CAD diagnosis, and large-artery atherosclerosis-type stroke. They did not find an association with cardioembolic or small-vessel disease-type stroke; intracranial aneurysm; venous thrombosis; carotid intima thickness; or, in a small subset of individuals, myocardial infarction.

Viewpoint

The main conclusion to draw from this work is that Lp(a) is probably a strong causal factor in not only CAD, but also the development of atherosclerosis in other arterial trees. Although there is no evidence from this study that Lp(a) levels contribute to venous thrombosis, the investigators do not exclude a role for Lp(a) in arterial thrombosis.

Large-artery atherosclerosis stroke is thought to involve some element of arterial thrombosis or thromboembolism, [2] and genetic substudies of randomized trials of aspirin demonstrate that individuals with LPA variants predicted to have elevated levels of Lp(a) benefit the most from antiplatelet therapy. [3] Together, these data suggest that Lp(a) probably has clinically relevant effects on the development of atherosclerosis and arterial thrombosis.

Of note, the investigators found no association between Lp(a) and carotid intima thickness, suggesting that either intima thickness is a poor surrogate for the clinical manifestations of atherosclerosis or that Lp(a) affects a distinct step in the atherosclerotic disease process that is not demonstrable in the carotid arteries.

Although Lp(a) testing is available, these studies do not provide any evidence that testing for Lp(a) is of clinical benefit, or that screening for atherosclerosis should go beyond well-described clinical risk factors, such as low-density lipoprotein cholesterol levels, high-density lipoprotein levels, hypertension, diabetes, smoking, and family history. Until evidence demonstrates that adding information on Lp(a) levels to routine clinical practice improves the ability of physicians to identify those at highest risk for atherosclerosis, Lp(a) testing should remain a research tool. Nevertheless, these findings do suggest that therapies to lower Lp(a) may have benefits that extend to forms of atherothrombosis beyond the coronary tree.

The finding of this study is interesting:

[1] It consistent with Dr. William LaFramboise.. examination specifically at APO B100, which is part of Lp(a) with some 14 candidate predictors for a more accurate exclusion of patients who don’t need intervention. Apo B100 was not one of 5 top candidates.

William LaFramboise • Our study (http://www.ncbi.nlm.nih.gov/pubmed/23216991) comprised discovery research using targeted immunochemical screening of retrospective patient samples using both Luminex and Aushon platforms as opposed to shotgun proteomics. Hence the costs constrained sample numbers. Nevertheless, our ability to predict outcome substantially exceeded available methods:

The Framingham CHD scores were statistically different between groups (P <0.001, unpaired Student’s t test) but they classified only 16% of the subjects without significant CAD (10 of 63) at a 95% sensitivity for patients with CAD. In contrast, our algorithm incorporating serum values for OPN, RES, CRP, MMP7 and IFNγ identified 63% of the subjects without significant CAD (40 of 63) at 95% sensitivity for patients with CAD. Thus, our multiplex serum protein classifier correctly identified four times as many patients as the Framingham index.

This study is consistent with the concept of CAD, PVD, and atheromatous disease is a systemic vascular disease, but the point that is made is that it appears to have no relationship to venous thrombosis. The importance for predicting thrombotic events is considered serious. The venous flow does not have the turbulence of large arteries, so the conclusion is no surprise. The flow in capillary beds is a linear cell passage with minimal viscosity or turbulence. The finding of no association with carotid artery disease is interpreted to mean that the Lp(a) might be an earlier finding than carotid intimal thickness. It is reassuring to find a recommendation for antiplatelet therapy for individuals with LPA variants based on randomized trials of aspirin substudies.

If that is the conclusion from the studies, and based on the strong association between the prothrombotic (pleiotropic) effect and the association with hyperhomocysteinemia, my own impression is that the recommendation is short-sighted.

[2] Lp(a) is able to competitively inhibit the binding of plasminogen to fibrinogen and fibrin, and to inhibit the fibrin-dependent activation of plasminogen to plasmin via the tissue plasminogen activator, whereby apo(a) isoforms of low molecular weight have a higher affinity to fibrin than apo(a) isoforms of higher molecular weight. Like other compounds containing sulfhydryl groups, homocysteine enhances the binding of Lp(a) to fibrin.

Prothrombotic :

Binding to fibrin
Competitive inhibition of plasminogen
Stimulation of plasminogen activator inhibitor I and II (PAI -I, PAI -II)
Inactivation of tissue factor pathway inhibitor (TFPI)

Nitric Oxide Function in Coagulation (pharmaceuticalintelligence.com)
Biochemistry of the Coagulation Cascade and Platelet Aggregation (pharmaceuticalintelligence.com)
The Causes of Deep Vein Thrombosis (veinspecialistshouston.com)
Coagulation: Transition from a familiar model tied to laboratory testing, and the new cellular-driven model (pharmaceuticalintelligence.com)
Discovery Of New Regulator Of The Blood Coagulation Cascade (medicalnewstoday.com)
Watching Out for Deep Venous Thrombosis: Resources for Further Reading (veinspecialistshouston.com)

Source for Lp(a)

Artherogenesis: Predictor of CVD – the Smaller and Denser LDL Particles

http://pharmaceuticalintelligence.com/2012/11/15/artherogenesis-predictor-of-cvd-the-smaller-and-denser-ldl-particles/

References on Triglycerides and blood viscosity

Lowe GD, Lee AJ, Rumley A, et al. Blood viscosity and risk of cardiovascular events: the Edinburgh Artery Study. Br J Haematol 1997; 96:168-173. 

Sloop GD. A unifying theory of atherogenesis. Med Hypotheses. 1996; 47:321-5. Smith WC, Lowe GD, et al. Rheological determinants of blood pressure in a Scottish adult population. J Hypertens 1992; 10:467-72.

Letcher RL, Chien S, et al. Direct relationship between blood pressure and blood viscosity in normal and hypertensive subjects. Role of fibrinogen and concentration. Am J Med 1981; 70:1195-1202. 

Devereux RB, Case DB, Alderman MH, et al. Possible role of increased blood viscosity in the hemodynamics of systemic hypertension. Am J Cardiol 2000; 85:1265-1268. 

Levenson J, Simon AC, Cambien FA, Beretti C. Cigarette smoking and hypertension. Factors independently associated with blood hyperviscosity and arterial rigidity. Arteriosclerosis 1987; 7:572-577. 

Sloop GD, Garber DW. The effects of low-density lipoprotein and high-density lipoprotein on blood viscosity correlate with their association with risk of atherosclerosis in humans. Clin Sci 1997; 92:473-479.

Lowe GD. Blood viscosity, lipoproteins, and cardiovascular risk. Circulation 1992; 85:2329-2331. 

Rosenson RS, Shott S, Tangney CC. Hypertriglyceridemia is associated with an elevated blood viscosity: triglycerides and blood viscosity. Atherosclerosis 2002; 161:433-9. 

Stamos TD, Rosenson RS. Low high density lipoprotein levels are associated with an elevated blood viscosity. Atherosclerosis 1999; 146:161-5. 

Hoieggen A, Fossum E, Moan A, Enger E, Kjeldsen SE. Whole-blood viscosity and the insulin-resistance syndrome. J Hypertens 1998; 16:203-10. 

de Simone G, Devereux RB, Chien S, et al. Relation of blood viscosity to demographic and physiologic variables and to cardiovascular risk factors in apparently normal adults. Circulation 1990; 81:107-17. 

Rosenson RS, McCormick A, Uretz EF. Distribution of blood viscosity values and biochemical correlates in healthy adults. Clin Chem 1996; 42:1189-95. 

Tamariz LJ, Young JH, Pankow JS, et al. Blood viscosity and hematocrit as risk factors for type 2 diabetes mellitus: The Atherosclerosis Risk in Communities (ARIC) Study. Am J Epidemiol 2008; 168:1153-60. 

Jax TW, Peters AJ, Plehn G, Schoebel FC. Hemostatic risk factors in patients with coronary artery disease and type 2 diabetes – a two year follow-up of 243 patients. Cardiovasc Diabetol 2009; 8:48. 

Ernst E, Weihmayr T, et al. Cardiovascular risk factors and hemorheology. Physical fitness, stress and obesity. Atherosclerosis 1986; 59:263-9. 

Hoieggen A, Fossum E, et al. Whole-blood viscosity and the insulin-resistance syndrome. J Hypertens 1998; 16:203-10. 

Carroll S, Cooke CB, Butterly RJ. Plasma viscosity, fibrinogen and the metabolic syndrome: effect of obesity and cardiorespiratory fitness. Blood Coagul Fibrinolysis 2000; 11:71-8. 

Ernst E, Koenig W, Matrai A, et al. Blood rheology in healthy cigarette smokers. Results from the MONICA project, Augsburg. Arteriosclerosis 1988; 8:385-8. 

Ernst E. Haemorheological consequences of chronic cigarette smoking. J Cardiovasc Risk 1995; 2:435-9. 

Lowe GD, Drummond MM, Forbes CD, Barbenel JC. The effects of age and cigarette-smoking on blood and plasma viscosity in men. Scott Med J 1980; 25:13-7. 

Kameneva MV, Watach MJ, Borovetz HS. Gender difference in rheologic properties of blood and risk of cardiovascular diseases. Clin Hemorheol Microcirc 1999; 21:357-363. 

Fowkes FG, Pell JP, Donnan PT, et al. Sex differences in susceptibility to etiologic factors for peripheral atherosclerosis. Importance of plasma fibrinogen and blood viscosity. Arterioscler Thromb 1994; 14:862-8. 

Coppola L, Caserta F, De Lucia D, et al. Blood viscosity and aging. Arch Gerontol Geriatr 2000; 31:35-42.

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Behavior of biomarkers in CSF: Differential Diagnosis of Dementia by ELISA

Posted in Alzheimer's Disease, Etiology, tagged AD, alzheimer's, Alzheimers Disease, Beta amyloid, cerebrospinal fluid, cohort study, dementia, differential diagnosis, Dr. Venkat S. Karra, ELISA, Frontotemporal lobar degeneration, Innogenetics, MCI, Mild cognitive impairment, Tau protein on July 19, 2012| 2 Comments »

Curated by: Dr. Venkat S. Karra, Ph.D.

The number of patients with dementia have been increasing exponentially with the aging of society. The development of AD research has clarified that the pathogenesis of AD is initiated by Aβ amyloidosis with secondary tauopathy and provided a strategy for investigating drugs that may improve or cure AD.

Mild cognitive impairment (MCI) as a prodromal stage of AD and the pathogenesis of Dementia with Lewy bodies (DLB) and Frontotemporal lobar degeneration (FTLD) as a non-AD type dementia have also been elucidated. Currently, a consortium study by the Alzheimer Disease Neuroimaging initiative (ADNI) is being performed to establish global clinical evidence regarding a neuropsychiatric test battery, CSF biomarkers, neuroimaging including MRI, FDG-PET, and amyloid PET to predict progression from MCI to AD and to promote studies of basic therapy for AD [1].

Several new biomarkers such as Aβ oligomer, α-synuclein, and TDP-43 are now under investigation for further determination of their usefulness to detect AD and other non-AD type dementia.

Cerebrospinal Fluid Aβ40, Aβ42, Tau, and Phosphorylated Tau biomarkers have been used for a clinical diagnosis of AD, discrimination from the Vascular dementia (VaD) and non-AD type dementia, exclusion of treatable dementia and MCI, prediction of AD onset and evaluation of the clinical trials of an anti-Aβ antibody, Aβ vaccine therapy, and secretase inhibitors [2–4].

In the current study Schoonenboom et al., [10] conducted a large cohort of patients with different types of dementia to determine how amyloid β 42 (Aβ42), total tau (t-tau), and phosphorylated tau (p-tau) levels behave in CSF.

Aβ is produced mainly in the nerve cells of the brain, and it is secreted about 12 hours later into the CSF, then excreted through the blood-brain barrier 24 hours later into blood (Aβ clearance), and finally degraded in the reticuloendothelial system. Aβ levels are regulated in strict equilibrium among the brain, CSF, and blood [6, 7]. Aβ levels are high while awake and low while a sleep suggesting the presence of a daily change in the CSF Aβ amounts and it is because Aβ amounts in CSF are controlled by orexin and thus collection of CSF by lumbar puncture early in morning in a fasting state is recommended [5].

In AD brains, Aβ42 forms insoluble amyloids and accumulates as insoluble amyloid fibrils in the brain. The reason Aβ42 levels are decreased in the CSF of AD patients is considered to be caused by deterioration of physiologic Aβ clearance into the CSF in AD brains [2, 3]. CSF total tau levels increase slightly with aging. However, CSF tau levels show a 3-fold greater increase in AD patients than in normal controls [8].

It is thought that the rise in CSF total tau is related to degeneration of axons and neurons and to severe destructive disease of the nervous system. Several diseases show slightly increased tau levels such as VaD, multiple sclerosis, AIDS dementia, head injury, and tauopathy. However, CSF tau levels show significant increases in Creutzfeldt-Jakob disease (CJD) and meningoencephalitis [8].

These biomarkers can be measured with an Amyloid ELISA Kit (Wako), which is commercially available and used worldwide. The ELISA kit was developed in Japan by Suzuki et al. and shows extremely high sensitivity and reproducibility [9]. INNOTEST β-AMYLOID1-42 (Innogenetics), for Aβ42 is used widely in Europe and America.

Several assay kits for total tau and phosphorylated tau are also used for the measurement of CSF tau. Currently, total tau is measured using INNOTEST hTau Ag (Innogenetics). There are 3 ELISA systems for measurement of phosphorylated tau that recognize the special phosphorylation sites at Ser199 (Mitsubishi Chemical Corp.), Thr181 (Innogenetics) and Thr231 (Applied NeuroSolutions Inc.), and phosphorylated tau levels are increased in CSF of AD on assays using these kits. Of these 3 kits, INNOTEST PHOSPHO-TAU (181) (Innogenetics) is commercially available and used widely. Recently, INNO-BIA AlzBio3 by Innogenetics has been able to measure Aβ1-42, total tau, and P-tau181P simultaneously in 75 μL of CSF, which is a very small amount of CSF.

In the current study researchers used the following strategy to collect Baseline CSF and Aβ42, t-tau, and p-tau (at amino acid 181) were measured in CSF by ELISA:

Types of patients with Alzheimer disease (AD) = 512 patients
Types of patients with other types of dementia (OD) = 272 patients
Types of patients with a psychiatric disorder (PSY) = 135 patients
Types of patients with subjective memory complaints (SMC) = 275 patients
Autopsy was obtained in a subgroup of about 17 patients.

The study suggested that CSF Aβ42, t-tau, and p-tau are useful in differential dementia diagnosis, whereas in DLB, FTLD, VaD, and CBD, a substantial group exhibited a CSF AD biomarker profile, which requires more autopsy confirmation in the future.

The study found a correct classification of patients with AD (92%) and patients with OD (66%) when CSF Aβ42 and p-tau were combined.
Patients with progressive supranuclear palsy had normal CSF biomarker values in 90%.

Patients with Creutzfeldt-Jakob disease demonstrated an extremely high CSF t-tau at a relatively normal CSF p-tau.

CSF AD biomarker profile was seen in

47% of patients with dementia with Lewy bodies (DLB),

38% in corticobasal degeneration (CBD), and

30% in frontotemporal lobar degeneration (FTLD) and vascular dementia (VaD).

PSY and SMC patients had normal CSF biomarkers in 91% and 88%.

Older patients are more likely to have a CSF AD profile.

Concordance between clinical and neuropathologic diagnosis was 85%.

CSF markers reflected neuropathology in 94%.

The study concluded that CSF Aβ42, t-tau, and p-tau are useful in differential dementia diagnosis. However, in DLB, FTLD, VaD, and CBD, a substantial group exhibit a CSF AD biomarker profile, which requires more autopsy confirmation in the future.

References:

1. R. C. Petersen, P. S. Aisen, L. A. Beckett et al., “Alzheimer’s Disease Neuroimaging Initiative (ADNI): clinical characterization,” Neurology, vol. 74, no. 3, pp. 201–209, 2010.

2. M. Shoji and M. Kanai, “Cerebrospinal fluid Aβ40 and Aβ42: natural course and clinical usefulness,” Journal of Alzheimer’s Disease, vol. 3, no. 3, pp. 313–321, 2001.

3. M. Shoji, M. Kanai, E. Matsubara et al., “The levels of cerebrospinal fluid Aβ40 and Aβ42(43) are regulated age-dependently,” Neurobiology of Aging, vol. 22, no. 2, pp. 209–215, 2001.

4. M. Kanai, E. Matsubara, K. Isoe et al., “Longitudinal study of cerebrospinal fluid levels of tau, Aβ1-40, and Aβ1-42(43) in Alzheimer’s disease: a study in Japan,” Annals of Neurology, vol. 44, no. 1, pp. 17–26, 1998.

5. J. E. Kang, M. M. Lim, R. J. Bateman et al., “Amyloid-β dynamics are regulated by orexin and the sleep-wake cycle,” Science, vol. 326, no. 5955, pp. 1005–1007, 2009.

6. M. Shoji, T. E. Golde, J. Ghiso et al., “Production of the Alzheimer amyloid β protein by normal proteolytic processing,” Science, vol. 258, no. 5079, pp. 126–129, 1992.

7. R. J. Bateman, E. R. Siemers, K. G. Mawuenyega et al., “A γ-secretase inhibitor decreases amyloid-β production in the central nervous system,” Annals of Neurology, vol. 66, no. 1, pp. 48–54, 2009.

8. M. Shoji, E. Matsubara, T. Murakami et al., “Cerebrospinal fluid tau in dementia disorders: a large scale multicenter study by a Japanese study group,” Neurobiology of Aging, vol. 23, no. 3, pp. 363–370, 2002.

9. N. Suzuki, T. T. Cheung, X. D. Cai et al., “An increased percentage of long amyloid β protein secreted by familial amyloid β protein precursor (βAPP) mutants,” Science, vol. 264, no. 5163, pp. 1336–1340, 1994.

Source:

10. N.S.M. Schoonenboom et al., Cerebrospinal fluid markers for differential dementia diagnosis in a large memory clinic cohort

For further insight read the following excellent review article by M. Shoji

Biomarkers of Dementia

New Bio-markers in Alzheimer’s & Stress Induced Changes in the Brains of Alzheimer’s Patients (pharmaceuticalintelligence.com)
MRI Cortical Thickness Biomarker Predicts AD-like CSF and Cognitive Decline in Normal Adults (pharmaceuticalintelligence.com)
Infection May Cause Chronic Inflammation In The Brain, Leading The Way To Alzheimer’s Disease (medicalnewstoday.com)
Test to detect Alzheimer’s disease grappled with by researchers at Vancouver convention (theprovince.com)
Pathalogical Aging may simply be an early stage of Alzheimer’s (tginnovations.wordpress.com)

Special thanks to Wikipedia for excellent relevant pictures and keyword links.

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Two Centuries of Neurology and Psychiatry in the Journal NEJM

Posted in Innovations in Neurophysiology & Neuropsychology, tagged Boston Medical Library, dementia, Denny-Brown, depression, dystonia, Neurology, New England Journal of Medicine, psychosis on July 5, 2012| Leave a Comment »

Reporter: Aviva Lev-Ari, PhD, RN

http://www.nejm.org/doi/full/10.1056/NEJMra1104781?query=TOC

Fifty years ago, when the curator of the Boston Medical Library, Henry Viets, collated a score of the most important articles that had been published in the first century and a half of the New England Journal of Medicine, 10 of the 20 related to neurologic conditions. Viets HR. A score of significant papers published in the Journal during the last hundred and fifty years. N Engl J Med 1962;266:23-28

On the occasion of its 200th anniversary, one might ask why so many articles on neurologic and psychiatric diseases have been published in the Journal and what impact these pieces have had on their respective fields. Although the Journal is replete with reports of neurologic conditions that have entered the canon of medicine, it has been the large number and the breadth of clinical trials that have redefined neurology and psychiatry as active, therapeutic specialties. This article reviews the evolution of our understanding of neurologic and psychiatric conditions during the past two centuries.

Modern scientific neurology, based on neuropathology and neurophysiology, began after World War II. By 1952, patients with tabes dorsalis and general paresis had practically disappeared from hospital wards. Antimicrobial agents had changed the course of bacterial and tuberculous meningitis, but poliomyelitis was still a nemesis. Denny-Brown‘s Shattuck Lecture on the state of neurology that year in the Journal pronounced that, freed from its preoccupation with syphilology and now separating itself from internal medicine and psychiatry, neurology had “entered on an extremely productive and virile phase.” Denny-Brown DE. The changing pattern of neurologic medicine. N Engl J Med1952;246:839-846

Denny-Brown emphasized recent contributions on the neurologic aspects of liver failure, the recognition that transient ischemic attacks were due to occlusion of the carotid artery, and the emerging understanding of increased intracranial pressure. There was little question at the time that neurologic and psychiatric diseases both acted on the same brain, but Denny-Brown’s position in his Shattuck Lecture marked the emergence of American neurology, pointedly disengaging it from the popular practice of neuropsychiatry and aligning it with internal medicine. He provided a modern manifesto for neurology, which nonetheless remained largely an elegant diagnostic specialty.

TWO INFLUENTIAL ARTICLES

A seemingly mundane clinical neurology article in the pages of the Journal had a highly felicitous effect on the relief of human suffering by addressing the problem of sciatica. That 1934 report by Mixter and Barr

Mixter WJ, Barr JS. Rupture of the intervertebral disc with involvement of the spinal canal. N Engl J Med 1934;211:210-215 established intervertebral disk rupture with nerve-root compression as the mechanism and also provided a remarkably sophisticated analysis of cervical-disk herniation and cord compression. It presented detailed instructions for the cure — in both instances, laminectomy. Twelve terse pages provided meticulous clinical descriptions and drawings of the corrective operation (Figure 1FIGURE 1Mixter and Barr’s Descriptions and Operation for Disk Rupture.). The enduring impact of that article, as well as the continuity of attention to this topic in the Journal, was affirmed by a 2007 report on a clinical trial that showed the superiority of surgery over conservative management. Peul WC, van Houwelingen HC, van den Hout WB, et al. Surgery versus prolonged conservative treatment for sciatica. N Engl J Med 2007;356:2245-2256

The excess of ill-advised laminectomies for back pain that followed Mixter and Barr’s article was not their doing; in a less frequently cited but more detailed contribution published in the Journal 6 years after their first report, they state, “We wish to emphasize at this point that a large proportion of the cases of sciatica resolve spontaneously or under conservative orthopedic treatment.” Mixter WJ, Barr JS. Protrusion of the lower lumbar intervertebral disks. N Engl J Med1940;223:523-529

Second article, An influential article in psychiatry from the New England Journal of Medicine with vast secular influence was “Neurasthenia, or Nervous Exhaustion” by George Beard, published in 1869. Beard G. Neurasthenia, or nervous exhaustion. Boston Med Surg J 1869;80:217-221

He spoke of “a condition of the system that is, perhaps, more frequently than any other in our time at least, the cause and effect of disease. . . . Both anemia and neurasthenia are most frequently met with in civilized intellectual communities. They are part of the compensation for our progress and refinement.” Beard G. Neurasthenia, or nervous exhaustion. Boston Med Surg J 1869;80:217-221

The use of the label “neurasthenia,” and probably its reported incidence, expanded greatly after Beard’s article appeared. It was called the “American disease” by the illustrious French neurologist, J.-M. Charcot, who took it up for study as a strictly neurologic condition. By medicalizing the misfortunes of life, for which care is still so frequently sought, physicians became comfortable invoking a patient’s constitutional makeup, as if it were a physical entity, as the substrate for exhaustion, melancholia, depression, discouragement, weakness, and headache.

THE RISE OF BIOLOGIC PSYCHIATRY

Some topics in every field turn out to be fraught with specious ideas, and neurology and psychiatry have grappled with many of them. We cannot know whether the absence of articles on phrenology in BMSJ was an implicit message or whether it was a reflection of Boston’s medical orthodoxy. Many positive reports of magnetism applied to nervous conditions and endorsements of autointoxication as the cause of mental diseases were, however, published in the Journal. Briggs LV. A consideration of auto-intoxication and auto-infection as cause of various mental disorders. Boston Med Surg J 1905;152:1-5, 36

Most of these quaint notions simply reflected the medical ideologies of the time. For an example of early continuity of subject matter regarding the nerves that has appeared in the Journal one has only to look at Brown-Séquard’s work on electrical activity of the nervous system and J.C. Warren’s derisive article “Animal Magnetism,” stating that the concept, “which some thirty years ago excited great attention . . . has since been viewed as one of the remarkable impositions on the credulity of mankind.” Warren JC. Animal magnetism. Boston Med Surg J 1814;3:40-46

But the use of electricity for brain disorders is now again invoked through the technology of deep-brain stimulation. Escaping from the stigma of psychosurgery, articles in the Journal have expanded the application of deep-brain stimulation well beyond its usual use in Parkinson’s disease and found substantiation for its use in intractable obsessive–compulsive disorder. Mallet L, Polosan M, Jaafari N, et al. Subthalamic nucleus stimulation in severe obsessive-compulsive disorder. N Engl J Med 2008;359:2121-2134[Erratum, N Engl J Med 2009;361:1027.] and in dystonia. Kupsch A, Benecke R, Muller J, et al. Pallidal deep-brain stimulation in primary generalized or segmental dystonia. N Engl J Med 2006;355:1978-1990 and Vidailhet M, Vercueil L, Houeto JL, et al. Bilateral deep brain stimulation of the globus pallidus in primary generalized dystonia. N Engl J Med 2005;352:459-467

When psychodynamic systems that attributed mental diseases to unconscious conflicts were popularized in the mid-20th century, there was a conspicuous absence of articles about them in theJournal. The exception was psychosomatic medicine. In a 1948 article in the Journal, A.O. Ludwig wrote that “emotional influences acting over longer or shorter periods result at first in disturbed physiology and eventually in structural change. Peptic ulcer is the simplest example . . . [u]lcerative colitis . . . asthma, hay fever and urticaria, certain skin diseases, such as eczema and neurodermatitis, migraine, possibly certain cases of epilepsy; hypertension and rheumatoid arthritis.” Ludwig AO. The practical importance of modern concepts of psychosomatic relations. N Engl J Med 1948;238:175-178. Concerning much of 20th-century psychiatry, including psychoanalysis, however, the Journal spoke through its silence. With the ascent of biologic psychiatry in the first decade of the 21st century, large pragmatic “efficacy” trials identified by their acronyms have appeared in the pages of the Journal — for depression (STAR*D), Trivedi MH, Fava M, Wisniewski SR, et al. Medication augmentation after the failure of SSRIs for depression. N Engl J Med 2006;354:1243-1252 psychosis (CATIE), Lieberman JA, Stroup TS, McEvoy JP, et al. Effectiveness of antipsychotic drugs in patients with chronic schizophrenia. N Engl J Med 2005;353:1209-1223[Erratum, N Engl J Med 2010;363:1092-3.] and dementia (CATIE-AD). Schneider LS, Tariot PN, Dagerman KS, et al. Effectiveness of atypical antipsychotic drugs in patients with Alzheimer’s disease. N Engl J Med 2006;355:1525-1538

These studies affirm the value but expose the shortcomings and risks of medical treatment for mental conditions and suggest that the field may have moved a bit too far, as in a quip by the late Leon Eisenberg, from “brainlessness to mindlessness.” Eisenberg L. Mindlessness and brainlessness in psychiatry. Br J Psychiatry 1986;148:497-508

These articles about psychiatry published in the Journal are influencing that field, as other articles have in neurology and neurosurgery, bringing the study of mental life and its diseases back into contemporary medicine and thereby rejoining the specialties of the brain.

For 200 years, the Journal has seen neurology and psychiatry evolve from a European to an international scope, from an emphasis on diagnosis to an emphasis on treatment, and has published many of the fundamental descriptions of nervous and mental diseases while cultivating a new and potent therapeutic course. One would expect the next 100 years to bring a new outlook on diseases of the nervous system that is based on fundamental biology, but the need for keen observation of the individual patient is not likely to be supplanted.