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Posts Tagged ‘Mitochondrion’


Reversal of Cardiac mitochondrial dysfunction

Curator: Larry H Bernstein, MD, FACP

This article is the FOURTH in a four-article Series covering the topic of the Roles of the Mitochondria in Cardiovascular Diseases. They include the following;

  • Mitochondria and Cardiovascular Disease: A Tribute to Richard Bing, Larry H Bernstein, MD, FACP

https://pharmaceuticalintelligence.com/2013/04/14/chapter-5-mitochondria-and-cardiovascular-disease/

  • Mitochondrial Metabolism and Cardiac Function, Larry H Bernstein, MD, FACP

https://pharmaceuticalintelligence.com/2013/04/14/mitochondrial-metabolism-and-cardiac-function/

  • Mitochondrial Dysfunction and Cardiac Disorders, Larry H Bernstein, MD, FACP

https://pharmaceuticalintelligence.com/2013/04/14/mitochondrial-dysfunction-and-cardiac-disorders/

https://pharmaceuticalintelligence.com/2013/04/14/reversal-of-cardiac-mitochondrial-dysfunction/

 

Mitochondrial metabolism and cardiac function

There is sufficient evidence to suggest that, even with optimal therapy, there is an

  • attenuation or loss of effectiveness of neurohormonal antagonism as heart failure worsens.

The production of oxygen radicals is increased in the failing heart, whereas

  • normal antioxidant enzyme activities are preserved.

Mitochondrial electron transport is an enzymatic source of oxygen radical generation and

  • can be a therapeutic target against oxidant-induced damage in the failing myocardium.

Therefore, future therapeutic targets

  • must address the cellular and molecular mechanisms that contribute to heart failure.

Furthermore, since  fundamental characteristics of the failing heart are 

  • defective mitochondrial energetics and
  • abnormal substrate metabolism

we might expect that substantial benefit may be derived from the development of therapies aimed at

  • preserving cardiac mitochondrial function and
  • optimizing substrate metabolism.

Nutrition and physiological function

Blockade of electron transport in isolated, perfused guinea pig hearts –
before ischaemia with the reversible complex I inhibitor amobarbital
  • decreased superoxide production and
  • preserved oxidative phosphorylation in cardiac mitochondria,
  • decreased myocardial damage.
But when ascorbic acid was administered orally to chronic heart failure patients, there were improvements
  • in endothelial function but
  • no improvement in skeletal muscle energy metabolism.
Angiotensin I-converting enzyme (ACE) inhibitors with trandolapril treatment  in models of heart failure
  • appear to preserve mitochondrial function
  • improving cardiac energy metabolism and
  • function in rats with chronic heart failure.
Similarly perindopril treatment   – in rat skeletal muscle after myocardial infarction -restored :
  • levels of the mitochondrial biogenesis transcription factors PPARg coactivator-1a and
  • nuclear respiratory factor-2a, and
  • prevented mitochondrial dysfunction
Tissue effects of ACE inhibition, such as
might activate intracellular signalling cascades that
  • stimulate mitochondrial biogenesis and
  • improve energy metabolism.
Clearly, the mechanisms of metabolic regulation by
  • existing cardioprotective agents require further investigation.

Substrate metabolism in the failing heart

Increased sympathetic drive in heart failure patients causes adipose tissue lipolysis, thus
  • elevating plasma FFA concentrations.
Myocardial FFA uptake rates are largely determined by circulating FFA concentrations.
In addition to being a major fuel in heart,
  • fatty acids are ligands for the peroxisome proliferator-activated receptors (PPARs),
    •  members of the nuclear hormone receptor (NHR) family.
One PPAR subtype, PPARa, is highly expressed in heart and skeletal muscle. PPARs regulate gene expression by
binding to response elements in the promoter region of target genes that control fatty acid metabolism, including
It has been known for many years that high plasma FFA concentrations are detrimental to the heart,
  • increasing oxygen consumption for any given workload.
Decreased myocardial oxygen efficiency could result, in part,
  • from the inherent stoichiometric inefficiency of fatty acid oxidation,
  • which accounts for the consumption of 12% more oxygen per ATP synthesized than glucose oxidation.

High levels of plasma FFAs have been associated with increased cardiac UCP3 levels in patients undergoing CABG(Fig) and

  • are believed to activate the uncoupling action of UCP3.

http://htmlimg1.scribdassets.com/8o5pfgywg0lyerj/images/4-244729cb6a.jpg

Fig .  Metabolic modulation of the failing heart can be achieved by inhibiting mitochondrial beta-oxidation with trimetazidine, or
  • free fatty acid (FFA) uptake via the carnitine palmitoyltransferase (CPT) system with perhexiline,
    • giving rise to more oxygen-efficient glucose oxidation.
Alternatively, CPT is inhibited by malonyl-coenzyme A (CoA),
  • synthesized from cytosolic acetyl-CoA by acetyl-CoA  carboxylase.
Pharmacological inhibition, or mutation, of
  • malonyl-CoA decarboxylase, which normally converts malonyl-CoA back to acetyl-CoA,
  • elevates malonyl-CoA levels, inhibiting mitochondrial FFA uptake and thus protects the failing heart.

Nutritional Support for the Mitochondria

Human Studies                                       Animal or In Vitro Studies

Alpha lipoic acid                                                    Resveratrol
Co-Enzyme Q10                                                      EgCG
Acetyl-L-Carnitine                                                Curcumin

Lipoic Acid & Acetyl-L-Carnitine

Alpha lipoic acid is known to be a mitochondrial antioxidant that preserves or improves mitochondrial function.

  •  lipoic acid can prevent arterial calcification, and
  • arterial calcification may be related to mitochondrial dysfunction
  • methods are under study to increase lipoic acid synthase production, the enzyme responsible for making lipoic acid in the body.

Co-Enzyme Q10

It is well known that statin drugs taken for high cholesterol severely reduce CoQ10 levels, and causes other negative cardiovascular side effects.
A  study on CAD patients has shown that over 8 weeks of supplementing with 300mg of CoQ10 reversed

  • mitochondrial dysfunction (as measured by a reduced lactate:pyruvate ratio) and
  • improved endothelial function (as measured by increased flow-mediated dilation)

Other Mitochondrial Antioxidants

Other natural compounds that have been shown to have antioxidant effects in the mitochondria include

  • resveratrol, found in wine and grapes,
  • curcumin from turmeric and
  • EGCG, found abundantly in green tea extract.

But no studies have been conducted for these compounds in CVD.

Metabolic syndrome and serum carotenoids: findings of a cross-sectional study
in Queensland, Australia

Metabolic syndrome and serum carotenoids.

T Coyne, TI Ibiebele, PD Baade, CS McClintock and JE Shaw.
Viertel Center for Research in Cancer Control, Cancer Council Queensland, and School of Public Health,
Queensland University of Technology and University of Queensland, Brisbane, Australia
Several components of the metabolic syndrome are known to be oxidative stress-related conditions
  1. diabetes and
  2. cardiovascular disease,
Carotenoids are compounds derived primarily from plants and several have been shown to be potent antioxidant nutrients.
Both diabetes and cardiovascular disease are known to be oxidative stress-related conditions such that
  • antioxidant nutrients may play a protective role in these conditions.
Several cross–sectional surveys have found lower levels of serum carotenoids among those with impaired glucose metabolism or type 2 diabetes.
Carotenoids are compounds derived primarily from plants, several of which are known to be potent antioxidants.
Epidemiological evidence indicates that some serum carotenoids may play a protective role against the development of chronic diseases such as
  1. atherosclerosis,
  2. stroke,
  3. hypertension,
  4. certain cancers,
  5. inflammatory diseases and
  6. diabetic retinopathy.

The primary carotenoids found in human serum are

  1. α-carotene
  2. β-carotene
  3. β-cryptoxanthin
  4. lutein/zeaxanthin
  5. lycopene.
The aim of this study was to examine the associations between metabolic syndrome status and major serum carotenoids in adult Australians.
Data on the presence of the metabolic syndrome, based on International Diabetes Federation 2005 criteria, were collected from 1523 adults
aged 25 years and over in six randomly selected urban centers in Queensland, Australia, using a cross sectional study design.
The following were determined:
  1. Weight
  2. height
  3. BMI
  4. waist circumference
  5. blood pressure
  6. fasting and 2-34 hour blood glucose
  7. lipids
  8. five serum carotenoids.
Criteria used to assess the number of metabolic syndrome components present in a 171 participant using the
2005 International Diabetes Federation definition are as follows:
Components = 0 -none of the metabolic syndrome components (i.e. abdominal obesity, raised triglyceride,
reduced HDL-cholesterol, raised blood pressure, and impaired fasting plasma glucose) are present;
  1. Components = any 1 one of the five metabolic syndrome components is present ;
  2. Components = 2 – any two of the five components are present;
  3. Components = 3 any three of the components are present;
  4. Components = 4 – any four of the components are present;
  5. Components = 5 = all five metabolic syndrome components are present.
This study investigated the relationships between these five primary serum carotenoids and the metabolic syndrome
in a cross-sectional population-based study in Queensland, Australia.  Distributions of serum carotenoids were skewed
and therefore natural logarithmically transformed to better approximate the normal distribution for regression analyses.
Association between log transformed serum carotenoids as dependent variables and metabolic syndrome status were
assessed using multiple linear regression analysis. Results are reported as back transformed geometric means.
Analysis was performed for each serum carotenoid separately, and the sum of the five carotenoids,
adjusting for the following potential confounders:
  1. age
  2. sex
  3. education
  4. BMI
  5. smoking
  6. alcohol intake
  7. physical activity
  8. vitamin use.
Mean serum alpha-carotene, beta-carotene and the sum of the five carotenoid concentrations were significantly lower (p<0.05)
in persons with the metabolic syndrome (after adjusting for age,sex, education, BMI status, alcohol intake, smoking, physical activity
status and vitamin/mineral use) than persons without the syndrome. Alpha, beta and total carotenoids also decreased significantly
(p<0.05) with increased number of components of the metabolic syndrome, after adjusting for these confounders. These differences
were significant among former smokers and non-smokers, but not in current smokers. Low concentrations of serum
  • alpha-carotene,
  • beta carotene and
  • the sum of five carotenoids
appear to be associated with metabolic syndrome status.
The overall prevalence of the syndrome was 24% and was significantly higher among males than females. As would be expected, significant
differences in prevalence of the syndrome were seen with
  • body mass index
  • waist circumference
  • systolic and diastolic blood pressure
  • blood lipids.
Significant differences were also evident by
  • age group, smoking status, educational status and income.
Income was marginally inversely associated. The prevalence increased with age, and was lower in those with post graduate education.
No significant differences were seen by alcohol intake, physical activity levels,  vitamin usage, or fruit intake. There was actually an
  • inverse relationship between vegetable intake (not fruit) and serum carotenoids.
Those who consumed 4 serves or more of vegetable were less likely to have the metabolic syndrome
  • compared to those who consumed 1 serve or less of vegetables.
The mean concentrations of serum alpha-carotene, beta-carotene and the sum of the five carotenoids were significantly lower for participants
  • with the metabolic syndrome present compared with those without the syndrome, after adjusting for potential confounding variables.
Concentrations of alpha-carotene, beta-carotene and the sum of the five carotenoids decreased significantly as
  • the number of components of the metabolic syndrome increased after adjusting for potential confounding variables.
Similarly there was an inverse association between quartiles of
  • individual and total serum carotenoids and metabolic syndrome status and each of its components.
This study was designed to investigate the association between several serum carotenoids and the metabolic syndrome.
The data from the present population study suggest that several serum carotenoids are inversely related to the metabolic syndrome.
The study showed significantly lower concentrations present among those with the metabolic syndrome of
  1. α-carotene,
  2. β-carotene and
  3. the sum of the five carotenoids
 compared to those without.We also found decreasing concentrations of all the carotenoids tested as

  • the number of the metabolic syndrome components increased.
This was significant for
  1. α-carotene,
  2. β-carotene,
  3. β-cryptoxanthin
  4. total carotenoids.
    (not lycopenes)
These findings are consistent with data reported from the third National Health and Nutrition Examination Survey (NHANES III).
In the NHANES III study, significantly lower concentrations of all the carotenoids, except lycopene, were found among persons
with the metabolic syndrome compared with those without, after adjusting for confounding factors similar to those in our study.

Carnitine: A novel health factor-An overview. 

CD Dayanand, N Krishnamurthy, S Ashakiran, KN Shashidhar
Int J Pharm Biomed Res 2011; 2(2): 79-89.  ISSN No: 0976-0350
Carnitine comprises L-carnitine, acetyl –L-carnitine and Propionyl –L-carnitine. Carnitine is
  • obtained in greater amount from animal dietary sources than from plant sources.
The endogenous synthesis of carnitine takes place in animal tissues like
  • liver
  • kidney
  • brain
using precursor amino acids lysine and methionine by a pathway
  • dependent on iron, vitamin C, niacin, pyridoxine .
This is the basis of vegans generally depending on carnitine in larger proportion
  • through in vivo synthesis than omnivorous subjects.
The concentration of tri-methyl lysine residues and the tissue specificity of  butyro-betaine dehydrogenase
  • plays a significant role in regulating the carnitine biosynthesis.
Carnitine transport from the site of synthesis to target tissue occurs via blood.
The measurement of plasma carnitine concentration represents –
  • the balance between the rate of synthesis and rate of excretion
    • through specific transporter proteins.
The cellular functional role of carnitine depends on the uptake into cells through
  1. carnitine transport proteins and
  2. transport into mitochondrial matrix.
The function of carnitine is to traverse Long-chain Fatty Acids across inner mitochondrial membrane
  • for β-oxidation, thereby, generating ATP.
Carnitine deficiency results in muscle disorders.  The deficiency states are primary and secondar.
The primary is of systemic or myopathic, characterized by a defect of high affinity organic cation transporter protein (CTP)
  • present on the plasma membrane of liver and kidney and
  • also due to dysfunction of carnitine reabsorbtion through
    • similar transport proteins in renal tubules.
Secondary carnitine deficiency is associated with
  1. mitochondrial disorders and also
  2. defective β-oxidation such as CPT-II and acyl CoA dehydrogenase.
In recent times, carnitine has been extensively studied in various research activities to explore the therapeutic benefit.
Thus, carnitine justifies as a novel health factor.

Propionyl-L-carnitine Corrects Metabolic and Cardiovascular Alterations in
Diet-Induced Obese Mice and Improves Liver Respiratory Chain Activity

C Mingorance,  L Duluc, M Chalopin, G Simard, et al.
PLC improved the insulin-resistant state and reversed the increased total cholesterol
but not the increase in free fatty acid, triglyceride and HDL/LDL ratio induced by high-fat diet.
Vehicle-HF exhibited a reduced

  • cardiac output/body weight ratio,
  • endothelial dysfunction and
  • tissue decrease of NO production,

all of them being improved by PLC treatment.
The decrease of hepatic mitochondrial activity by high-fat diet was reversed by PLC.

Oral administration of PLC improves the insulin-resistant state developed by obese animals and
decreases the cardiovascular risk associated with the metabolically impaired mitochondrial function.

Omega-3 Fatty Acid and cardioprotection

The Benefits of Flaxseed    

By Elaine Magee, MPH, RD    WebMD Expert Column
Some call it one of the most powerful plant foods on the planet. There’s some evidence it may help reduce your risk of

  • heart disease, cancer, stroke, and diabetes.

That’s quite a tall order for a tiny seed that’s been around for centuries.

Flaxseed was cultivated in Babylon as early as 3000 BC. In the 8th century, King Charlemagne believed so strongly in the
health benefits of flaxseed that he passed laws requiring his subjects to consume it. Now, thirteen centuries later, some
experts say we have preliminary research to back up what Charlemagne suspected.

http://img.webmd.com/dtmcms/live/webmd/consumer_assets/site_images/article_
thumbnails/features/benefits_of_flaxseed_features/375x321_benefits_of_flaxseed_features.jpg

Not only has consumer demand for flaxseed grown, agricultural use has also increased.
Flaxseed is what’s used to feed all those chickens that are laying eggs with higher levels of omega-3 fatty acids.
Although flaxseed contains all sorts of healthy components, it owes its primary healthy reputation to three of them:

  1. Omega-3 essential fatty acids, have been shown to have heart-healthy effects.  1.8 grams of plant omega-3s/tablespoon ground.
  2. Lignans, which have both plant estrogen and antioxidant qualities.  75 to 800 times more lignans than other plant foods.
  3. Fiber. Flaxseed contains both the soluble and insoluble types.

Omega-3 Polyunsaturated Fatty Acids and Cardiovascular Diseases

CJ Lavie, RV Milani, MR Mehra, and HO Ventura.
J. Am. Coll. Cardiol. 2009;54;585-594.   http://dx.doi.org/10.1016/j.jacc.2009.02.084
Fish oil is obtained in the human diet by eating oily fish, such as
  • herring, mackerel, salmon, albacore tuna, and sardines, or
  • by consuming fish oil supplements or cod liver oil.
Fish do not naturally produce these oils, but obtain them through the ocean food chain from the marine microorganisms
  • that are the original source of the omega-3 polyunsaturated fatty acids (ω-3 PUFA) found in fish oils.
Numerous prospective and retrospective trials from many countries, including the U.S., have shown that moderate
  • fish oil consumption decreases the risk of major cardiovascular (CV) events, such as
  1. myocardial infarction (MI),
  2. sudden cardiac death (SCD),
  3. coronary heart disease (CHD),
  4. atrial fibrillation (AF), and most recently,
  5. death in patients with heart failure (HF).
Most of the evidence for benefits of the ω-3 PUFA has been obtained for
  • eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), the long-chain fatty acids in this family.
There is support for a benefit from alpha-linolenic acid (ALA),
  • the plant-based precursor of EPA.
The American Heart Association (AHA) has currently endorsed the use of ω-3 PUFA in patients with documented CHD

  • at a dose of approximately 1 g/day of combined DHA and EPA, either in the form of fatty fish or fish oil supplements
The health benefits of these long chain fatty acids are numerous and remain an active area of research.
Omega-3 polyunsaturated fatty acid (ω-3 PUFA) therapy continues to show great promise in primary and,
  • particularly in secondary prevention of cardiovascular (CV) diseases.
This portion of discussion summarizes the current scientific data on the effects of the long chain ω-3 PUFA
  • in the primary and secondary prevention of various CV disorders.
The most compelling evidence for CV benefits of ω-3 PUFA comes from 4 controlled trials
  • of nearly 40,000 participants randomized to receive eicosapentaenoic acid (EPA)
  • with or without docosahexaenoic acid (DHA) in studies of patients
    • in primary prevention,
    • after myocardial infarction, and
    • with heart failure (HF).
The evidence from retrospective epidemiologic studies and from large randomized controlled trials
show the benefits of ω-3 PUFA, specifically EPA and DHA, in primary and secondary CV prevention
and provide insight into potential mechanisms of these observed benefits.

Background Epidemiologic Evidence

During the past 3 decades, numerous epidemiologic and observational studies have been published on the CV benefits of ω-3 PUFA.
As early as 1944, Sinclair described the rarity of CHD in Greenland Eskimos, who consumed a diet high in whale, seal, and fish.
More than 30 years ago, Bang and Dyberg reported that despite a diet low in fruit, vegetables, and complex carbohydrates but
high in saturated fat and cholesterol, serum cholesterol and triglycerides were lower in Greenland Inuit than in age-matched residents
of Denmark, and the risk of MI was markedly lower in the Greenland population compared with the Danes. These initial observations raised
speculation on the potential benefits of ω-3 PUFA (particularly EPA and DHA) as the protective “Eskimo factor”.
Potential EPA and DHA Effects   
  1. Antiarrhythmic effects
  2. Improvements in autonomic function
  3. Decreased platelet aggregation
  4. Vasodilation
  5. Decreased blood pressure
  6. Anti-inflammatory effects
  7. Improvements in endothelial function
  8. Plaque stabilization
  9. Reduced atherosclerosis
  10. Reduced free fatty acids and triglycerides
  11. Up-regulated adiponectin synthesis
  12. Reduced collagen deposition
The target EPA + DHA consumption should be at least 500 mg/day for individuals without underlying overt CV disease
  • and at least 800 to 1,000 mg/day for individuals with known coronary heart disease and HF.
Further studies are needed to determine optimal dosing and the relative ratio of DHA and EPA ω-3 PUFA that
  • provides maximal cardioprotection in those at risk of CV disease
  • as well in the treatment of atherosclerotic, arrhythmic, and primary myocardial disorders.
Lavie et al.  Omega-3 PUFA and CV Diseases  J Am Coll Cardiol 2009; 54(7): 585–94

Assessing Appropriateness of Lipid Management Among Patients With Diabetes Mellitus

Moving From Target to Treatment.   AJ Beard, TP Hofer, JR Downs, et al. and Diabetes Clinical Action Measures Workgroup
Performance measures that emphasize only a treat-to-target approach may motivate ove-rtreatment with high-dose statins,
  • potentially leading to adverse events and unnecessary costs.
We developed a clinical action performance measure for lipid management in patients with diabetes mellitus that is designed
  • to encourage appropriate treatment with moderate-dose statins while minimizing over-treatment.
We examined data from July 2010 to June 2011 for 964 818 active Veterans Affairs primary care patients ≥18 years of age with diabetes mellitus.
We defined 3 conditions as successfully meeting the clinical action measure for patients 50 to 75 years old:
  1.  having a low-density lipoprotein (LDL) <100 mg/dL,
  2. taking a moderate-dose statin regardless of LDL level or measurement, or
  3. receiving appropriate clinical action (starting, switching, or intensifying statin therapy) if LDL is ≥100 mg/dL.
We examined possible over-treatment for patients ≥18 years of age by examining the proportion of patients
  • without ischemic heart disease who were on a high-dose statin.
We then examined variability in measure attainment across 881 facilities using 2-level hierarchical multivariable logistic models.
Of 668 209 patients with diabetes mellitus who were 50 to 75 years of age, 84.6% passed the clinical action measure:
  1. 67.2% with LDL <100 mg/dL,
  2. 13.0% with LDL ≥100 mg/dL and either on a moderate-dose statin (7.5%) or with appropriate clinical action (5.5%), and
  3. 4.4% with no index LDL on at least a moderate-dose statin. Of the entire cohort ≥18 years of age, 13.7% were potentially over-treated.
Use of a performance measure that credits appropriate clinical action indicates that almost 85% of diabetic veterans 50 to 75 years of age
  • are receiving appropriate dyslipidemia management.

Exercise training and mitochondria in heart failure

The beneficial effects of exercise in the rehabilitation of patients with heart failure are well established,
with improvements observed in
  • exercise capacity,
  • quality of life,
  • hospitalization rates and
  • morbidity/mortality.
There is no evidence of training-induced
improvements in cardiac energy metabolism or
  • mitochondrial function, and
  • no modification of myocardial oxidative capacity,
  • oxidative enzymes, or
  • energy transfer enzymes
in exercising rats with experimental heart failure, but there is  evidence of
There are also improvements in
  • skeletal muscle oxidative capacity with
  • increased mitochondrial density
following endurance training in heart failure patients associated with alleviation of symptoms such as
  • exercise intolerance and
  • chronic fatigue.
The mechanism underlying improvements in mitochondrial function may perhaps be a result of
  • more effective peripheral oxygen delivery following training,
  • alleviating tissue hypoxia and oxidative stress.

Treating Type 2 diabetes, and lowering cardiovascular disease risk

Treating Diabetes and Obesity with an FGF21-Mimetic Antibody
Activating the βKlotho/FGFR1c Receptor Complex

IN Foltz, S Hu, C King, Xinle Wu, et al.  Amgen and Texas A&M HSC, Houston, TX.
Sci Transl Med  Nov 2012; 4(162), p. 162ra153
http://dx.doi.org/10.1126/scitranslmed.3004690

Fibroblast growth factor 21 (FGF21) is a distinctive member of the FGF family with potent beneficial effects on

  1. lipid
  2. body weight
  3. glucose metabolism

A monoclonal antibody, mimAb1, binds to βKlotho with high affinity and specifically

  • activates signaling from the βKlotho/FGFR1c (FGF receptor 1c) receptor complex.

Injection of mimAb1 into obese cynomolgus monkeys led to FGF21-like metabolic effects:

  1. decreases in body weight,
  2. plasma insulin,
  3. triglycerides, and
  4. glucose during tolerance testing.

Mice with adipose-selective FGFR1 knockout were refractory to FGF21-induced improvements

  • in glucose metabolism and body weight.

mimAb1 depends on βKlotho to activate FGFR1c, but

  • it is not expected to induce side effects caused by activating FGFR1c alone.

The results in obese monkeys (with mimAb1) and in FGFR1 knockout mice (with FGF21) demonstrated

  • the essential role of FGFR1c in FGF21 function and
  • suggest fat as a critical target tissue for the cytokine and antibody.

This antibody activates FGF21-like signaling through cell surface receptors, and  provided

  • preclinical validation for an innovative therapeutic approach to diabetes and obesity.

Influencing Factors on Cardiac Structure and Function Beyond Glycemic Control
in Patients With Type 2 Diabetes Mellitus (T2DM)

R Ichikawa, M Daimon, T Miyazaki, T Kawata, et al.     Cardiovasc Diabetol. 2013;12(38)

We studied 148 asymptomatic patients with T2DM without overt heart disease.
Early (E) and late (A) diastolic mitral flow velocity and early diastolic mitral annular velocity (e’)

  • were measured for assessing left ventricular (LV) diastolic function.

In addition

  • insulin resistance,
  • non-esterified fatty acid,
  • high-sensitive CRP,
  • estimated glomerular filtration rate,
  • waist/hip ratio,
  • abdominal visceral adipose tissue (VAT),
  • subcutaneous adipose tissue (SAT)

In T2DM (compared to controls),

  • E/A and e’ were significantly lower, and
  • E/e’, left atrial volume and LV mass were significantly greater

VAT  and age were independent determinants of

  • left atrial volume (β =0.203, p=0.011),
  • E/A (β =−0.208, p=0.002), e’ (β =−0.354, p<0.001) and
  • E/e’ (β=0.220, p=0.003).

Independent determinants of LV mass were

  • systolic blood pressure,
  • waist-hip ratio (β=0.173, p=0.024)
  • VAT/SAT ratio (β=0.162, p=0.049)

Excessive visceral fat accompanied by adipocyte dysfunction may play a greater role than

  • glycemic control in the development of diastolic dysfunction and LV hypertrophy in T2DM

Inhibition of oxidative stress and mtDNA damage

Novel pharmacological agents are needed that

  • optimize substrate metabolism and
  • maintain mitochondrial integrity,
  • improve oxidative capacity in heart and skeletal muscle, and
  • alleviate many of the clinical symptoms associated with heart failure.

The evidence for the attenuation or loss of effectiveness of neurohormonal antagonism as heart failure worsens

  • indicates future therapeutic targets must address the cellular and molecular mechanisms that contribute to heart failure.

Pharmacological Targets of oxidative stress and mitochondrial damage

Defective mitochondrial energetics and abnormal substrate metabolism are fundamental characteristics of CHF.

A significant benefit may be derived from developing therapies aimed at

  • preserving cardiac mitochondrial function and
  • optimizing substrate metabolism.
Oxidative stress is enhanced in myocardial remodelling and failure. The increased production of oxygen radicals in the failing heart
  • with preserved antioxidant enzyme activities suggests
  • mitochondrial electron transport as a source of oxygen radical generation
  • can be a therapeutic target against oxidant-induced damage in the failing myocardium.
Chronic increases in oxygen radical production in the mitochondria
  • leads to mitochondrial DNA (mtDNA) damage,
  • functional decline,
  • further oxygen radical generation, and
  • cellular injury.
MtDNA defects may thus play an important role in the
  • development and progression of myocardial remodelling and failure.
Reactive oxygen species induce
  1. myocyte hypertrophy,
  2. apoptosis, and
  3. interstitial fibrosis
  4. by activating matrix metallo-proteinases,
  5. promoting the development and
  6. progression of maladaptive myocardial remodelling and failure.
Oxidative stress has direct effects on cellular structure and function and
  • may activate integral signalling molecules in myocardial remodelling and failure (Figure).
ROS result in a phenotype characterized by
  • hypertrophy and apoptosis in isolated cardiac myocytes.
Therefore, oxidative stress and mtDNA damage are good therapeutic targets.
Overexpression of the genes for
  • peroxiredoxin-3 (Prx-3), a mitochondrial antioxidant, or
  • mitochondrial transcription factor A (TFAM),
    • could ameliorate the decline in mtDNA copy number in failing hearts.
Consistent with alterations in mtDNA, the
  • decrease in mitochondrial function was prevented,
  • proving that the activation of Prx-3 or TFAM gene expression
  • could ameliorate the pathophysiological processes seen
  1. in mitochondrial dysfunction and
  2. myocardial remodelling.
Inhibition of oxidative stress and mtDNA damage
  • could be novel and effective treatment strategies for heart failure.
Proposed mechanisms through which overexpression of the
  • mitochondrial transcription factor A (TFAM) gene prevents
  • mitochondrial DNA (mtDNA) damage,
  • oxidative stress, and
  • myocardial remodelling and failure.
In wild-type mice, mitochondrial transcription factor A
  • directly interacts with mitochondrial DNA to form nucleoids.
Stress such as ischaemia causes mitochondrial DNA damage, which
  1. increases the production of reactive oxygen species (ROS)
  2. leading to a catastrophic cycle of mitochondrial electron transport impairment,
  3. further reactive oxygen species generation, and mitochondrial dysfunction.
TFAM overexpression may protect mitochondrial DNA from damage by
  1. directly binding and stabilizing mitochondrial DNA and
  2. increasing the steady-state levels of mitochondrial DNA
ameliorating mitochondrial dysfunction and thus the development and progression of heart failure.

Conclusion

Heart failure is a multifactorial syndrome that is characterized by
  • abnormal energetics and substrate metabolism in heart and skeletal muscle.
Although existing therapies have been beneficial, there is a clear need for new approaches to treatment.
Pharmacological targeting of the cellular stresses underlying mitochondrial dysfunction, such as
  • elevated fatty acid levels,
  • tissue hypoxia and oxidative stress and
  • metabolic modulation of heart and skeletal muscle mitochondria,
    • appears to offer a promising therapeutic strategy for tackling heart failure.
Murray AJ, Anderson RE, Watson GC, et al. Uncoupling proteins in human heart. Lancet 2004; 364:1786.
Delarue J, Magnan C. Free fatty acids and insulin resistance. Curr Opin ClinNutr Metab Care 2007; 10:142
Lee L, Campbell R, Scheuermann-Freestone M, et al. Metabolic modulation with perhexiline in chronic heart failure: a randomized, controlled trialof short-term use of a novel treatment. Circulation 2005; 112:3280
Tsutsui H, Kinugawa S, Matsushima S. Mitochondrial oxidative stress and dysfunction in myocardial remodelling. Cardiovasc Res. 2009;81(3):449-56. http://dxdoi.org/10.1093/cvr/cvn280.
C Maack, M Böhm. Targeting Mitochondrial Oxidative Stress in Heart Failure. J Am Coll Cardiol. 2011;58(1):83-86. http://dx.doi.org/10.1016/j.jacc.2011.01.032

 References

Mitochondrial dynamics and cardiovascular diseases    Ritu Saxena
https://pharmaceuticalintelligence.com/2012/11/14/mitochondrial-dynamics-and-cardiovascular-diseases/

Mitochondrial Damage and Repair under Oxidative Stress   larryhbern
https://pharmaceuticalintelligence.com/2012/10/28/mitochondrial-damage-and-repair-under-oxidative-stress/

Mitochondria: Origin from oxygen free environment, role in aerobic glycolysis, metabolic adaptation   larryhbern
http://pharmaceuticalintelligence.com/2012/09/26/mitochondria-origin-from-oxygen-free-environment-role-in-aerobic-glycolysis-metabolic-adaptation/

Ca2+ signaling: transcriptional control     larryhbern
http://pharmaceuticalintelligence.com/2013/03/06/ca2-signaling-transcriptional-control/

MIT Scientists on Proteomics: All the Proteins in the Mitochondrial Matrix identified  Aviva Lev-Ari
http://pharmaceuticalintelligence.com/2013/02/03/mit-scientists-on-proteomics-all-the-proteins-in-the-mitochondrial-matrix-identified/

Nitric Oxide has a ubiquitous role in the regulation of glycolysis -with a concomitant influence on mitochondrial function    larryhbern
http://pharmaceuticalintelligence.com/2012/09/16/nitric-oxide-has-a-ubiquitous-role-in-the-regulation-of-glycolysis-with-a-concomitant-influence-on-mitochondrial-function/

Ubiquinin-Proteosome pathway, autophagy, the mitochondrion, proteolysis and cell apoptosis  larryhbern
http://pharmaceuticalintelligence.com/2013/02/14/ubiquinin-proteosome-pathway-autophagy-the-mitochondrion-proteolysis-and-cell-apoptosis-reconsidered/

Low Bioavailability of Nitric Oxide due to Misbalance in Cell Free Hemoglobin in Sickle Cell Disease – A Computational Model   Anamika Sarkar
http://pharmaceuticalintelligence.com/2012/11/09/low-bioavailability-of-nitric-oxide-due-to-misbalance-in-cell-free-hemoglobin-in-sickle-cell-disease-a-computational-model/

The rationale and use of inhaled NO in Pulmonary Artery Hypertension and Right Sided Heart Failure    larryhbern
http://pharmaceuticalintelligence.com/2012/08/20/the-rationale-and-use-of-inhaled-no-in-pulmonary-artery-hypertension-and-right-sided-heart-failure/

Mitochondria and Cardiovascular Disease: A Tribute to Richard Bing, Larry H Bernstein, MD, FACP
https://pharmaceuticalintelligence.com/2013/04/14/chapter-5-mitochondria-and-cardiovascular-disease/

Mitochondrial Metabolism and Cardiac Function, Larry H Bernstein, MD, FACP
https://pharmaceuticalintelligence.com/2013/04/14/mitochondrial-metabolism-and-cardiac-function/

Mitochondrial Dysfunction and Cardiac Disorders, Larry H Bernstein, MD, FACP
https://pharmaceuticalintelligence.com/2013/04/14/mitochondrial-dysfunction-and-cardiac-disorders/

Reversal of Cardiac mitochondrial dysfunction, Larry H Bernstein, MD, FACP
https://pharmaceuticalintelligence.com/2013/04/14/reversal-of-cardiac-mitochondrial-dysfunction/

Clinical Trials Results for Endothelin System: Pathophysiological role in Chronic Heart Failure, Acute Coronary Syndromes and MI – Marker of Disease Severity or Genetic Determination? Aviva Lev-Ari, PhD, RN 10/19/2012
https://pharmaceuticalintelligence.com/2012/10/19/clinical-trials-results-for-endothelin-system-pathophysiological-role-in-chronic-heart-failure-acute-coronary-syndromes-and-mi-marker-of-disease-severity-or-genetic-determination/

Endothelin Receptors in Cardiovascular Diseases: The Role of eNOS Stimulation, Aviva Lev-Ari, PhD, RN 10/4/2012
https://pharmaceuticalintelligence.com/2012/10/04/endothelin-receptors-in-cardiovascular-diseases-the-role-of-enos-stimulation/

Inhibition of ET-1, ETA and ETA-ETB, Induction of NO production, stimulation of eNOS and Treatment Regime with PPAR-gamma agonists (TZD): cEPCs Endogenous Augmentation for Cardiovascular Risk Reduction – A Bibliography, Aviva Lev-Ari, PhD, RN 10/4/2012
https://pharmaceuticalintelligence.com/2012/10/04/inhibition-of-et-1-eta-and-eta-etb-induction-of-no-production-and-stimulation-of-enos-and-treatment-regime-with-ppar-gamma-agonists-tzd-cepcs-endogenous-augmentation-for-cardiovascular-risk-reduc/

Genomics & Genetics of Cardiovascular Disease Diagnoses: A Literature Survey of AHA’s Circulation Cardiovascular Genetics, 3/2010 – 3/2013, L H Bernstein, MD, FACP and Aviva Lev-Ari,PhD, RN  3/7/2013
https://pharmaceuticalintelligence.com/2013/03/07/genomics-genetics-of-cardiovascular-disease-diagnoses-a-literature-survey-of-ahas-circulation-cardiovascular-genetics-32010-32013/

Cardiovascular Disease (CVD) and the Role of agent alternatives in endothelial Nitric Oxide Synthase (eNOS) Activation and Nitric Oxide Production, Aviva Lev-Ari, PhD, RN 7/19/2012 https://pharmaceuticalintelligence.com/2012/07/19/cardiovascular-disease-cvd-and-the-role-of-agent-alternatives-in-endothelial-nitric-oxide-synthase-enos-activation-and-nitric-oxide-production/

Cardiovascular Risk Inflammatory Marker: Risk Assessment for Coronary Heart Disease and Ischemic Stroke – Atherosclerosis. Aviva Lev-Ari, PhD, RN 10/30/2012
https://pharmaceuticalintelligence.com/2012/10/30/cardiovascular-risk-inflammatory-marker-risk-assessment-for-coronary-heart-disease-and-ischemic-stroke-atherosclerosis/

Cholesteryl Ester Transfer Protein (CETP) Inhibitor: Potential of Anacetrapib to treat Atherosclerosis and CAD.     Aviva Lev-Ari, PhD, RN 4/7/2013
https://pharmaceuticalintelligence.com/2013/04/07/cholesteryl-ester-transfer-protein-cetp-inhibitor-potential-of-anacetrapib-to-treat-atherosclerosis-and-cad/

Hypertriglyceridemia concurrent Hyperlipidemia: Vertical Density Gradient Ultracentrifugation a Better Test to Prevent Undertreatment of High-Risk Cardiac Patients, Aviva Lev-Ari, PhD, RN  4/4/2013  https://pharmaceuticalintelligence.com/2013/04/04/hypertriglyceridemia-concurrent-hyperlipidemia-vertical-density-gradient-ultracentrifugation-a-better-test-to-prevent-undertreatment-of-high-risk-cardiac-patients/

Fight against Atherosclerotic Cardiovascular Disease: A Biologics not a Small Molecule – Recombinant Human lecithin-cholesterol acyltransferase (rhLCAT) attracted AstraZeneca to acquire AlphaCore.
Aviva Lev-Ari, PhD, RN 4/3/2013
https://pharmaceuticalintelligence.com/2013/04/03/fight-against-atherosclerotic-cardiovascular-disease-a-biologics-not-a-small-molecule-recombinant-human-lecithin-cholesterol-acyltransferase-rhlcat-attracted-astrazeneca-to-acquire-alphacore/

High-Density Lipoprotein (HDL): An Independent Predictor of Endothelial Function & Atherosclerosis, A Modulator, An Agonist, A Biomarker for Cardiovascular Risk.   Aviva Lev-Ari, PhD, RN 3/31/2013
https://pharmaceuticalintelligence.com/2013/03/31/high-density-lipoprotein-hdl-an-independent-predictor-of-endothelial-function-artherosclerosis-a-modulator-an-agonist-a-biomarker-for-cardiovascular-risk/

Peroxisome proliferator-activated receptor (PPAR-gamma) Receptors Activation: PPARγ transrepression for Angiogenesis in Cardiovascular Disease and PPARγ transactivation for Treatment of Diabetes.
Aviva Lev-Ari, PhD, RN 11/13/2012
https://pharmaceuticalintelligence.com/2012/11/13/peroxisome-proliferator-activated-receptor-ppar-gamma-receptors-activation-pparγ-transrepression-for-angiogenesis-in-cardiovascular-disease-and-pparγ-transactivation-for-treatment-of-dia/

Sulfur-Deficiciency and Hyperhomocysteinemia, L H Bernstein, MD, FACP
https://pharmaceuticalintelligence.com/2013/04/04/sulfur-deficiency-and-hyperhomocusteinemia/

Structure of the human mitochondrial genome.

Structure of the human mitochondrial genome. (Photo credit: Wikipedia)

English: Treatment Guidelines for Chronic Hear...

English: Treatment Guidelines for Chronic Heart Failure (Photo credit: Wikipedia)

English: Oxidative stress process Italiano: Pr...

English: Oxidative stress process Italiano: Processo dello stress ossidativo (Photo credit: Wikipedia)

Diagram taken from the paper "Dissection ...

Diagram taken from the paper “Dissection of mitochondrial superhaplogroup H using coding region SNPs” (Photo credit: Asparagirl)

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Mitochondrial Metabolism and Cardiac Function

Curator: Larry H Bernstein, MD, FACP

This article is the SECOND in a four-article Series covering the topic of the Roles of the Mitochondria in Cardiovascular Diseases. They include the following;

The mitochondrion serves a critical role as a platform for
  • energy transduction,
  • signaling, and
  • cell death pathways
relevant to common diseases of the myocardium such as heart failure. This review focuses on the molecular regulatory events involved in mitochondrial energy metabolism.
This is followed by the derangements known to occur in the development of heart failure.

 Cardiac Energy Metabolism

All cellular processes are driven by ATP-dependent pathways. The heart has perpetually high energy demands related to
  • the maintenance of specialized cellular processes, including
    • ion transport,
    • sarcomeric function, and
    • intracellular Ca2+ homeostasis.
Myocardial workload (energy demand) and energy substrate availability (supply) are in continual flux. Thus, ATP-generating pathways must

  • respond proportionately to dynamic fluctuations in physiological demands and fuel delivery.
In order to support contractile activity, the human heart requires
  • a daily synthesis of approximately 30kg of ATP, via
    • oxidative phosphorylation at
    • the inner mitochondrial membrane.
These metabolic  processes are regulated, involving
  • allosteric control of enzyme activity,
  • signal transduction events, and
  • the activity of genes encoding
    • rate-limiting enzymes and proteins.
Catabolism of exogenous substrates ,such as
  • fatty acids,
  • glucose,
  • pyruvate,
  • lactate and
  • ketone bodies,
generates most of the reduced compounds,
  • NADH (nicotinamide adenine dinucleotide, reduced) and
  • FADH2 (flavin adenine dinucleotide, reduced),
which are necessary for mitochondrial electron transport (Fig. 1).
Fig 1  Fatty acid beta-oxidation and the Krebs cycle produce
  1. nicotinamide adenine dinucleotide, reduced (NADH) and
  2. flavin adenine dinucleotide, reduced(FADH2),
which are oxidized by complexes I and II, respectively, of
Electrons are transferred through the chain to the final acceptor, namely oxygen(O2).
The free energy from electron transfer
  1. is used to pump hydrogen out of the mitochondria and
  2. generate an electrochemical gradient across the inner mitochondrial membrane.
This gradient is the driving force for ATP synthesis via the ATP synthase. Alternatively,
H can enter the mitochondria by a mechanism not coupled to ATP synthesis, via
  • the uncoupling proteins(UCPs), which results in the dissipation of energy.

[ANT, adenine nucleotide translocase; CoA, coenzymeA; FAT, fatty acid transporter; GLUT, glucose transporter;

NAD, nicotinamide adenine dinucleotide; TCA, tricarboxylic acid].

Cardiac Energy Metabolic Pathways

 Oxidation of free fatty acids (FFAs) and glucose in mitochondria
  • accounts for the vast majority of ATP generation in the healthy adult heart.
FFAs are the preferred substrate in the adult myocardium,
  • supplying 70-90% of total ATP.
FAs derived from circulating triglyceride-rich lipoproteins and albumin bound nonesterified FAs
  • are oxidized in the mitochondrial matrix by the process of beta-oxidation (FAO), whereas
pyruvate derived from glucose and lactate
  • is oxidized by the pyruvate-dehydrogenase (PDH) complex,
    • localized within the inner mitochondrial membrane.
Acetyl-CoA, derived from both pathways,
  • enters the tricarboxylic acid (TCA) cycle.
Reduced flavin adenine dinucleotide (FADH2) and NADH are generated, respectively, via
  • substrate flux through the
The reducing equivalents enter the electron transport (ET) chain,
  • producing an electrochemical gradient across the mitochondrial membrane
  • that drives ATP synthesis in the presence of molecular oxygen (oxidative phosphorylation).
The relative contributions of each of these substrates are determined
  • by their availability
  • cardiac workload and
  • hormonal status
In the healthy, normal heart, the ATP requirement is largely met in the actively metabolic mitochondria by
  • the catabolism of free fatty acids (FFAs) via beta-oxidation,
  • the tricarboxylic acid cycle and
  • oxidative phosphorylation
giving rise to a greater ATP yield per C2 unit than with glucose.
The relative contribution of glucose to the mitochondrial acetyl-coenzyme A (CoA) pool increases
  • during the postprandial period,
    • when the heart is insulin stimulated, and
  • during exercise
  • hypoxia, or
  • ischemia
when glucose is favored as a more oxygen-efficient substrate than
  • FFAs (greater ATP yield per oxygen molecule consumed).
Substrate switching in the heart can also be achieved by
  • acute alterations in transcriptional regulation of key metabolic enzymes
  • in response to alterations in substrate levels and oxygen availability, or
  • indeed by the intracellular circadian clock.
This continual process of fine adjustment in fuel selection
  • allows cardiac mitochondria to function
  • under a range of metabolic conditions to meet the high energy demands of the heart.
Mitochondrial enzymes are encoded by both nuclear and mitochondrial genes.
All of the enzymes of
  1. beta-oxidation and the TCA cycle, and
  2. most of the subunits of Electron Transfer/Oxidative Phosphorylation,
    • are encoded by nuclear genes.
The mitochondrial genome is comprised of
  • 1 circular double-stranded chromosome that encodes
  • 13 ET chain subunits within complexes I, III, and IV.
Since mitochondrial number and function require both nuclear and mitochondrial-encoded genes,
  • coordinated mechanisms exist to regulate the 2 genomes and
  • determine overall cardiac oxidative capacity.
In addition, distinct pathways exist to coordinately regulate
  • nuclear genes encoding component mitochondrial pathways.

Early Postnatal Low-protein Nutrition, Metabolic Programming and
the Autonomic Nervous System in Adult Life.

JC de Oliveira, S Grassiolli, C Gravena, PCF de Mathias  Nutr Metab. 2012;9(80)

The developmental origins of health and disease (DOHaD) hypothesis stipulates that adult metabolic disease

  • may be programmed during the perinatal stage.

A large amount of evidence suggests that the etiology of obesity is not only related to food abundance

  • but also to food restriction during early life.

Protein restriction during lactation has been used as a rat model of metabolic programming

  • to study the impact of perinatal malnutrition on adult metabolism.

In contrast to protein restriction during fetal life, protein restriction during lactation did not appear to cause

  • either obesity or the hallmarks of metabolic syndrome, such as hyperinsulinemia, when individuals reached adulthood.

Protein restriction provokes body underweight and hypoinsulinemia.
Hypoinsulinemia programs adult rats to maintain normoglycemia,

  • pancreatic β-cells are less sensitive to secretion stimuli:
  1.  glucose and
  2. cholinergic agents.

These pancreatic dysfunctions are attributed to an imbalance of ANS activity

  • recorded in adult rats that experienced maternal protein restriction

Several studies have reported that the ANS activity is altered in under- or malnourished organisms. After weaning,

  • rats fed a chronically protein-deficient diet exhibited low activity of the vagus nerve,
  • whereas high sympathetic activity was recorded

These data were in agreement with a low insulin response to glucose.
Pancreatic islets isolated from protein-restricted rats showed

  • weak glucose and cholinergic insulin tropic responses
  • suggesting that pancreatic β-cell dysfunction may be attributed to altered ANS activity

Food abundance or restriction with regard to body weight control involves changes in

  • metabolic homeostasis and ANS balance activity.

Although the secretion of insulin by the pancreatic β-cells is increased in people who were overweight,

  • it is diminished in people who were underweight.

Changes in the ANS activity may constitute the mechanisms underlying the β-cell dysfunction:

  • the high PNS tonus observed in obese individuals constantly potentiates insulin secretion,
  • whereas the low activity reported in underweight individuals is associated with a weak cholinergic insulin tropic effect.

Under Nutrition Early in Life and Epigenetic Modifications, Association With Metabolic Diseases Risk

relevant to this issue is the role of epigenetic changes in the increased risk of developing metabolic diseases,

  • such as type 2 diabetes and obesity, later in life.

Epigenetic mechanisms, such as DNA methylation and/or nucleoprotein acetylation/methylation, are

  • crucial to the normal/physiological development of several tissues in mammals, and
  • they involve several mechanisms to guarantee fluctuations of enzymes and other proteins that regulate the metabolism.

The intrauterine phase of development is particularly important for the genomic processes related to genes associated with metabolic pathways.
This phase of life may be particularly important for nutritional disturbance. In humans who experienced the Dutch famine Winter in 1944–1945 and
in rats that were deprived of food in utero, epigenetic modifications were detected in

  • the insulin-like growth factor 2 (IGF2) and
  • pancreatic and duodenal home box 1 (Pdx1),

the major factors involved in pancreas development and pancreatic β-cell maturation.
The pancreas and the pancreatic β-cells develop during the embryonic phase, but the postnatal life is also crucial for

  • the maintenance processes that control the β-cell mass:
  1. proliferation,
  2. neogenesis
  3. apoptosis.

Nutritional Restriction to the Fetus: A Risk of Obesity Onset

If an abundant diet is offered to people who have been undernourished during the perinatal life,

  • this opportunity induces a metabolic shift toward the storage of energy and high fat tissue accumulation

The concept of Developmental Origins of Health and Disease extends to any type of stressful situations that may

  • predispose babies or pups to develop metabolic disorders when they reach adulthood.

Programmed Metabolism and Insulin Secretion-coupling Process

What are the mechanisms involved in the low glucose insulin tropic response observed in low protein-programmed lean rats?
The pancreatic β-cells secrete insulin when stimulated mostly by glucose. However, several nutrients, such as

  • amino acids,
  • fatty acids,
  • and their metabolites,

stimulate cellular metabolism and increase ATP production.

ATP-sensitive potassium channels (KATP) are inactivated by an increased ATP/ADP ratio. This provokes

  • membrane depolarization and
  • the activation of voltage-dependent calcium channels.

These ionic changes increase the intracellular calcium concentration, which is involved in

  • the export of insulin to the bloodstream.

Glucose may also stimulate insulin secretion by alternative pathways involving KATP channels.

Programmed Metabolism and Insulin Tropic Effects of Neurotransmitters

Insulin release is modulated by non-nutrient secretagogues, such as neurotransmitters, which

  • enhance or inhibit glucose-stimulated insulin secretion.

Pancreatic β-cells contain several receptors for neurotransmitters and Neuropeptide, such as

  • adrenoceptors and cholinergic muscarinic receptors (mAChRs).

These receptors are stimulated by efferent signals from the central nervous system, including the ANS,

  • throughout their neural ends for pancreatic β-cells.

During blood glucose level oscillations, the β-cells receive inputs from

  • the parasympathetic and sympathetic systems to participate in glycemic regulation.

Overall, acetylcholine promotes the potentiation of glucose-induced insulin secretion,

  • whereas noradrenaline and adrenaline inhibit this response.

Functional studies of mAChR subtypes have revealed that M1 and particularly M3 are the receptors that are involved in

  • the insulin tropic effect of acetylcholine.

Interestingly, it was reported that M3mAChR gene knockout mice are

  • underweight,
  • hypophagic and
  • hypoinsulinemic,

as are adult rats that were protein-restricted during lactation.
The pancreatic islets from M3mAChR mice (-/-) showed a reduced secretory response to cholinergic agonists.
In studies using transgenic mice in which the pancreatic β-cell M3mAChRs are chronically stimulated,

  • an improvement of glycemic control has been observed

Adult male rat offspring from whose mothers were protein-restricted during lactation

  • exhibit a low PNS activity.

Evidence suggests that ANS changes may contribute to the impairment of glycemic homeostasis in metabolically programmed rats.

Pathways involved in cardiac energy metabolism.

FA and glucose oxidation are the main ATP-generating pathways in the adult mammalian heart.
Acetyl-CoA derived from FA and glucose oxidation is
  • further oxidized in the TCA cycle to generate NADH and FADH2, which
  • enter the ET/oxidative phosphorylation pathway and drive ATP synthesis.
Genes encoding enzymes involved at multiple steps of these metabolic pathways
  1. uptake,
  2. esterification,
  3. mitochondrial transport,
  4. and oxidation
are transcriptionally regulated by PGC-1a
  • with its nuclear receptor partners, including PPARs and ERRs .
Glucose uptake/oxidation and electron transport/oxidative phosphorylation pathways are also regulated by PGC-1a via
  • other transcription factors, such as MEF-2 and NRF-1.

[Cyt c, cytochrome c]

 Fetal metabolism of carbohydrate utilization

This reviewer poses the question of whether the fetal cardiac metabolism, which is characterized by a (facultative) anaerobic glycolysis,
  • results in lactate production that is not redirected into the TCA cycle.
An unexamined, but related question is whether there is an associated change in the ratio of
  • mitochondrial to cytoplasmic malate dehydrogenase isoenzyme activity (m-MDH:c-MDH).
The fetal heart operates without oxygenation from a functioning lung, bathed in amniotic fluid.
An enzymatic feature might be expressed in a facultative anaerobic cytplasmic glycolytic pathway characterized by
  • a decrease in the h-type lactate dehydrogenase (LD) isoenzyme(s) (LD1, LD2) with a predominance of
  • the m-type LD isoenzymes (LD3, LD4, LD5).
The observation here is that the heart muscle is a syncytium, and it functions at a highly regulated rate,
  • not with the spurts of activity seen in skeletal muscle.
In another article in this series, there are morphological changes that occur in the heart mitochondria, and
  • there are three locations, as if the organelle itself were an organ.
The normal functioning myocardium can utilize lactic acid accumulated in the bloodstream during extreme exercise as fuel.
This is a virtue of mitochondrial function.  There is a significant functional difference between the roles of the h- and m-type LD isoenzymes.
The h-type is a regulatory enzyme that forms a complex as NADH is converted to NAD+ between the
  • LD (H4, H3M; LD1, LD2),
  • oxidized pyridine nucleotide coenzyme, and
  • pyruvate
The complex forms in 200 msec as observed in the Aminco-Morrow stop-flow analyzer.  This is not the case for the m-type isoenzyme.
I presume that it is not a factor in embryonic heart.  It would become a factor after birth with the expansion of the lungs.
This would also bring to the discussion the effect of severe restrictive lung disease on cardiac metabolism.

Related References:

LH Bernstein,  patents: Malate dehydrogenase method,  The lactate dehydrogenase method
LH Bernstein, J Everse. Determination of the isoenzyme levels of lactate dehydrogenase. Methods Enzymol 1975; 41 47-52    ICID: 825516
LH Bernstein, J Everse, N Shioura, PJ Russell. Detection of cardiac damage using a steady state assay for lactate dehydrogenase isoenzymes in serum.   J Mol Cell Cardiol 1974; 6(4):297-315  ICID: 825597
LH Bernstein, MB Grisham, KD Cole, J Everse . Substrate inhibition of the mitochondrial and cytoplasmic malate dehydrogenases. J Biol Chem 1978; 253(24):8697-8701. ICID: 825513
R Belding, L Bernstein, G Reynoso. An evaluation of the immunochemical LD1 method in routine clinical practice. Clin Chem 1981; 27(10):1027-1028.   ICID: 844981
J Adan, L H Bernstein, J Babb. Lactate dehydrogenase isoenzyme-1/total ratio: accurate for determining the existence of myocardial infarction. Clin Chem 1986; 32(4):624-628.  ICID: 825540
MB Grisham, LH Bernstein, J Everse. The cytoplasmic malate dehydrogenase in neoplastic tissues; presence of a novel isoenzyme? Br J Cancer 1983; 47(5):727-731. ICID: 825551
LH Bernstein, P Scinto. Two methods compared for measuring LD-1/total LD activity in serum. Clin Chem 1986; 32(5):792-796.   ICID: 825581

PGC-1a: an inducible integrator of transcriptional circuits

 The PPAR³ coactivator-1 (PGC-1) family of transcriptional coactivators is involved in regulating mitochondrial metabolism and biogenesis.
PGC-1a was the first member discovered through its functional interaction with the nuclear receptor PPAR³ in brown adipose tissue (BAT).
There are two PGC-1a related coactivators,
  1. PGC-1² (also called PERC) and
  2. PGC-1–related coactivator (PRC).
PRC coactivates transcription in mitochondrial biogenesis, with PGC-1a and PGC-1² . Both are expressed in tissues with high oxidative capacity, such as
  1. heart
  2. slow-twitch skeletal muscle, and
  3. BAT
They serve critical roles in the regulation of mitochondrial functional capacity. PGC-1a  also regulates
  • hepatic gluconeogenesis and
  • skeletal muscle glucose uptake.
PGC-1² appears to be important in regulating energy metabolism in the heart, but
  • PGC-1a is distinct from other PGC-1 family members, indeed from most coactivators, in its broad responsiveness to
  1. developmental alterations in energy metabolism and
  2. physiological and pathological cues at the level of expression and transactivation.
In the heart, PGC-1a expression increases at birth coincident with an increase in cardiac oxidative capacity and
  • a perinatal shift from reliance on glucose metabolism to the oxidation of fats for energy.
PGC-1a is induced by physiological stimuli that increase ATP demand and
  • stimulate mitochondrial oxidation, including
  1. cold exposure,
  2. fasting, and
  3. exercise.
Activation of this regulatory cascade increases cardiac mitochondrial oxidative capacity in the heart. In cardiac myocytes in culture, it
  1. increases mitochondrial number,
  2. upregulates expression of mitochondrial enzymes, and
  3. increases rates of FA oxidation and coupled respiration.
Thus, PGC-1a is an inducible coactivator that coordinately regulates
  • cardiac fuel selection and
  • mitochondrial ATP-producing capacity.
 PGC-1a activates expression of nuclear respiratory factor-1 (NRF-1) and NRF-2 and
  • directly coactivates NRF-1 on its target gene promoters.
NRF-1 and NRF-2 regulate expression of mitochondrial transcription factor A (Tfam),
  • a nuclear-encoded transcription factor that binds regulatory sites on mitochondrial DNA and is essential for
  1. replication,
  2. maintenance, and
  3. transcription of the mitochondrial genome.
Furthermore, NRF-1 and NRF-2 regulate the expression of nuclear genes encoding
  • respiratory chain subunits and other proteins required for mitochondrial function.
PGC-1a  also
  • coactivates the PPAR and ERR nuclear receptors, critical regulators of myocardial FFA utilization.
  • regulates genes involved in the cellular uptake and mitochondrial oxidation of FFAs.
  • is an integrator of the transcriptional network regulating mitochondrial biogenesis and function.
Numerous signaling pathways, by increasing either PGC-1a expression or activity, such as –
  • Ca2+-dependent,
  • NO,
  • MAPK, and
  • beta-adrenergic pathways (beta3/cAMP),
    • activate the PGC-1a directly
Additionally, the p38_MAPK pathway
  • selectively activates PPARa, which may bring about synergistic activation in the presence of PGC-1a,
  • whereas ERK-MAPK has the opposite effect.
These signaling pathways transduce physiological stimuli to the PGC-1a pathway:
  1. stress
  2. fasting
  3. exercise
PGC-1a, in turn, coactivates transcriptional partners,which regulate mitochondrial biogenesis and FA-oxidation pathways:
  • NRF-1 and -2,
  • ERRa, and
  • PPARa,
 Insights into the physiological responsiveness of the PGC-1a pathway come from
  • identification of signal transduction pathways that modulate the activity of PGC-1a and its downstream partners.
PGC-1a is upregulated in response to beta-adrenergic signaling, consistent with the involvement of this pathway in thermogenesis.
The stress-activated  p38_MAPK activates PGC-1a by increasing PGC-1a protein stability and promoting dissociation of a repressor.
p38 increases mitochondrial FAO through selective activation of the PGC-1a partner, PPARa. Conversely, the ERK-MAPK pathway
  • inactivates the PPARa/RXRa complex via direct phosphorylation.
Therefore, distinct limbs of the MAPK pathway exert
  • opposing regulatory influences on the PGC-1a cascade.
Recently, NO has emerged as a novel signaling molecule proposed to integrate pathways involved in
  • regulating mitochondrial biogenesis by inducing mitochondrial proliferation.

 A Paradox

Mitochondria are like little cells within our cells. They are the energy producing organelles of the body. The more energy a certain tissue requires
  • such as the brain and the heart
    • the more mitochondria those cells contain.
Conventional transmission electron microscopy of mammalian cardiac tissue reveals mitochondria to be
  1. elliptical individual organelles situated either in clusters beneath the sarcolemma (subsarcolemmal mitochondria, SSM) or
  2. in parallel, longitudinal rows ensconced within the contractile apparatus (interfibrillar mitochondria, IFM).
The two mitochondrial populations differ in their cristae morphology, with
  1. a lamelliform orientation in SSM, whereas
  2. the cristae orientation in IFM is tubular.
The morphology of mitochondria is responsive to changes in cardiomyocytes.
 Mitochondrial oxidative phosphorylation relies
  • not only on the activities of individual complexes, but also on
  • the coordinated action of supramolecular assemblies (respirasomes) of the electron transport chain (ETC) complexes
in both normal and failing heart.
Mitochondria have their own set of DNA and
  • the more energy they generate,
  • the more DNA-damaging free radicals they produce.
Mitochondrial DNA damage is incurred by generation of energy in ATP production, so that
  • the process that sustains life also is the source of toxic damage that causes the dysfunction and mitogeny in the cell.
In human mtDNA mutant cybrids with impaired mitochondrial respiration, the recovery of mitochondrial function
  • correlates with the formation of respirasomes suggesting that
  • respirasomes represent regulatory units of mitochondrial oxidative phosphorylation
    • by facilitating the electron transfer between the catalytic sites of the ETC.
We recently reported a decrease in mitochondrial respirasomes in CHF that fits in the category of a new mitochondrial cytopathy.
 ATP utilized by the heart is synthesized mainly by means of oxidative phosphorylation in the inner mitochondrial membrane,
  • a process that involves the coupling of electron transfer and oxygen consumption with phosphorylation of ADP to ATP.
The catabolism of exogenous substrates (FAs, glucose, pyruvate, lactate, and ketone bodies) provides the reduced intermediates,
  1. NADH (nicotinamide adenine dinucleotide, reduced) and
  2. FADH2 (flavin adenine dinucleotide, reduced),
as donors for mitochondrial electron transport.
The contribution of glucose to the acetyl CoA pool in the heart is
  • increased by insulin during the postprandial period and during exercise.
 All cells and tissues require
  • adenine,
  • pyridine, and
  • flavin nucleotides for energy
by way of Krebs cycle metabolism of fatty acids and carbohydrate substrates.
If DNA holds the blueprint for the proper function of a cell, then any change in the blueprint will change how the cell functions.
If the mitochondria do not function properly, then they cannot fulfill their role in producing energy:
  •  the cell will lose its ability to function adequately.

 Related articles

 References

Mitochondrial dynamics and cardiovascular diseases    Ritu Saxena
https://pharmaceuticalintelligence.com/2012/11/14/mitochondrial-dynamics-and-cardiovascular-diseases/
Mitochondrial Damage and Repair under Oxidative Stress   larryhbern
https://pharmaceuticalintelligence.com/2012/10/28/mitochondrial-damage-and-repair-under-oxidative-stress/
Mitochondria: Origin from oxygen free environment, role in aerobic glycolysis, metabolic adaptation   larryhbern
http://pharmaceuticalintelligence.com/2012/09/26/mitochondria-origin-from-oxygen-free-environment-role-in-aerobic-glycolysis-metabolic-adaptation/ Ca2+ signaling: transcriptional control     larryhbern
http://pharmaceuticalintelligence.com/2013/03/06/ca2-signaling-transcriptional-control/ MIT Scientists on Proteomics: All the Proteins in the Mitochondrial Matrix identified  Aviva Lev-Ari
http://pharmaceuticalintelligence.com/2013/02/03/mit-scientists-on-proteomics-all-the-proteins-in-the-mitochondrial-matrix-identified/
Nitric Oxide has a ubiquitous role in the regulation of glycolysis -with a concomitant influence on mitochondrial function    larryhbern
http://pharmaceuticalintelligence.com/2012/09/16/nitric-oxide-has-a-ubiquitous-role-in-the-regulation-of-glycolysis-with-a-concomitant-influence-on-mitochondrial-function/
Ubiquinin-Proteosome pathway, autophagy, the mitochondrion, proteolysis and cell apoptosis  larryhbern
http://pharmaceuticalintelligence.com/2013/02/14/ubiquinin-proteosome-pathway-autophagy-the-mitochondrion-proteolysis-and-cell-apoptosis-reconsidered/
Low Bioavailability of Nitric Oxide due to Misbalance in Cell Free Hemoglobin in Sickle Cell Disease – A Computational Model   Anamika Sarkar
http://pharmaceuticalintelligence.com/2012/11/09/low-bioavailability-of-nitric-oxide-due-to-misbalance-in-cell-free-hemoglobin-in-sickle-cell-disease-a-computational-model/
The rationale and use of inhaled NO in Pulmonary Artery Hypertension and Right Sided Heart Failure    larryhbern
http://pharmaceuticalintelligence.com/2012/08/20/the-rationale-and-use-of-inhaled-no-in-pulmonary-artery-hypertension-and-right-sided-heart-failure/
Mitochondria and Cardiovascular Disease: A Tribute to Richard Bing, Larry H Bernstein, MD, FACP
https://pharmaceuticalintelligence.com/2013/04/14/chapter-5-mitochondria-and-cardiovascular-disease/
Mitochondrial Metabolism and Cardiac Function, Larry H Bernstein, MD, FACP
https://pharmaceuticalintelligence.com/2013/04/14/mitochondrial-metabolism-and-cardiac-function/
Mitochondrial Dysfunction and Cardiac Disorders, Larry H Bernstein, MD, FACP
https://pharmaceuticalintelligence.com/2013/04/14/mitochondrial-dysfunction-and-cardiac-disorders/
Reversal of Cardiac mitochondrial dysfunction, Larry H Bernstein, MD, FACP
https://pharmaceuticalintelligence.com/2013/04/14/reversal-of-cardiac-mitochondrial-dysfunction/
Clinical Trials Results for Endothelin System: Pathophysiological role in Chronic Heart Failure, Acute Coronary Syndromes and MI – Marker of Disease Severity or Genetic Determination? Aviva Lev-Ari, PhD, RN 10/19/2012
https://pharmaceuticalintelligence.com/2012/10/19/clinical-trials-results-for-endothelin-system-pathophysiological-role-in-chronic-heart-failure-acute-coronary-syndromes-and-mi-marker-of-disease-severity-or-genetic-determination/
Endothelin Receptors in Cardiovascular Diseases: The Role of eNOS Stimulation, Aviva Lev-Ari, PhD, RN 10/4/2012
https://pharmaceuticalintelligence.com/2012/10/04/endothelin-receptors-in-cardiovascular-diseases-the-role-of-enos-stimulation/
Inhibition of ET-1, ETA and ETA-ETB, Induction of NO production, stimulation of eNOS and Treatment Regime with PPAR-gamma agonists (TZD): cEPCs Endogenous Augmentation for Cardiovascular Risk Reduction – A Bibliography, Aviva Lev-Ari, PhD, RN 10/4/2012
https://pharmaceuticalintelligence.com/2012/10/04/inhibition-of-et-1-eta-and-eta-etb-induction-of-no-production-and-stimulation-of-enos-and-treatment-regime-with-ppar-gamma-agonists-tzd-cepcs-endogenous-augmentation-for-cardiovascular-risk-reduc/
Genomics & Genetics of Cardiovascular Disease Diagnoses: A Literature Survey of AHA’s Circulation Cardiovascular Genetics, 3/2010 – 3/2013, L H Bernstein, MD, FACP and Aviva Lev-Ari,PhD, RN  3/7/2013
https://pharmaceuticalintelligence.com/2013/03/07/genomics-genetics-of-cardiovascular-disease-diagnoses-a-literature-survey-of-ahas-circulation-cardiovascular-genetics-32010-32013/
Cardiovascular Disease (CVD) and the Role of agent alternatives in endothelial Nitric Oxide Synthase (eNOS) Activation and Nitric Oxide Production, Aviva Lev-Ari, PhD, RN 7/19/2012
https://pharmaceuticalintelligence.com/2012/07/19/cardiovascular-disease-cvd-and-the-role-of-agent-alternatives-in-endothelial-nitric-oxide-synthase-enos-activation-and-nitric-oxide-production/
Cardiovascular Risk Inflammatory Marker: Risk Assessment for Coronary Heart Disease and Ischemic Stroke – Atherosclerosis. Aviva Lev-Ari, PhD, RN 10/30/2012
https://pharmaceuticalintelligence.com/2012/10/30/cardiovascular-risk-inflammatory-marker-risk-assessment-for-coronary-heart-disease-and-ischemic-stroke-atherosclerosis/
Cholesteryl Ester Transfer Protein (CETP) Inhibitor: Potential of Anacetrapib to treat Atherosclerosis and CAD, Aviva Lev-Ari, PhD, RN 4/7/2013
https://pharmaceuticalintelligence.com/2013/04/07/cholesteryl-ester-transfer-protein-cetp-inhibitor-potential-of-anacetrapib-to-treat-atherosclerosis-and-cad/
Hypertriglyceridemia concurrent Hyperlipidemia: Vertical Density Gradient Ultracentrifugation a Better Test to Prevent Undertreatment of High-Risk Cardiac Patients, Aviva Lev-Ari, PhD, RN  4/4/2013 https://pharmaceuticalintelligence.com/2013/04/04/hypertriglyceridemia-concurrent-hyperlipidemia-vertical-density-gradient-ultracentrifugation-a-better-test-to-prevent-undertreatment-of-high-risk-cardiac-patients/
Fight against Atherosclerotic Cardiovascular Disease: A Biologics not a Small Molecule – Recombinant Human lecithin-cholesterol acyltransferase (rhLCAT) attracted AstraZeneca to acquire AlphaCore, Aviva Lev-Ari, PhD, RN 4/3/2013
https://pharmaceuticalintelligence.com/2013/04/03/fight-against-atherosclerotic-cardiovascular-disease-a-biologics-not-a-small-molecule-recombinant-human-lecithin-cholesterol-acyltransferase-rhlcat-attracted-astrazeneca-to-acquire-alphacore/
High-Density Lipoprotein (HDL): An Independent Predictor of Endothelial Function & Atherosclerosis, A Modulator, An Agonist, A Biomarker for Cardiovascular Risk, Aviva Lev-Ari, PhD, RN 3/31/2013 

https://pharmaceuticalintelligence.com/2013/03/31/high-density-lipoprotein-hdl-an-independent-predictor-of-endothelial-function-artherosclerosis-a-modulator-an-agonist-a-biomarker-for-cardiovascular-risk/
Peroxisome proliferator-activated receptor (PPAR-gamma) Receptors Activation: PPARγ transrepression for Angiogenesis in Cardiovascular Disease and PPARγ transactivation for Treatment of Diabetes, Aviva Lev-Ari, PhD, RN 11/13/2012
https://pharmaceuticalintelligence.com/2012/11/13/peroxisome-proliferator-activated-receptor-ppar-gamma-receptors-activation-pparγ-transrepression-for-angiogenesis-in-cardiovascular-disease-and-pparγ-transactivation-for-treatment-of-dia/
Sulfur-Deficiciency and Hyperhomocysteinemia, L H Bernstein, MD, FACP
https://pharmaceuticalintelligence.com/2013/04/04/sulfur-deficiency-and-hyperhomocusteinemia/

 

 

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Mitochondria structure: 1 : inner membrane 2 :...

Mitochondria structure: 1 : inner membrane 2 : outer membrane 3 : cristae 4 : matrix (Photo credit: Wikipedia)

English: mechanism of fatty acids and L-carnit...

English: mechanism of fatty acids and L-carnitine going through mitochondrial membrane (Photo credit: Wikipedia)

English: Acyl-CoA from the cytosol to the mito...

English: Acyl-CoA from the cytosol to the mitochondrial matrix. Français : Transport de l’Acyl-CoA du Cytosol jusqu’à la matrice mitochondriale. (Photo credit: Wikipedia)

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Author: Ziv Raviv, PhD

Mitochondria are recognized as essential for both life and death fates of cells. Mitochondria are the site where oxidative phosphorylation happens, the process that is responsible for the majority of energy production of the cell in the form of adenosine triphosphate (ATP) synthesis. Therefore mitochondria are considered as the main power station of the cell. On the other hand, both apoptotic and necrotic cell death may result from mitochondrial perturbation [1]. In cancer cells, mitochondria are different from those of normal cells by several aspects: (i) In cancer cells the mitochondrial membrane potential is higher than that of normal cells, (ii) there is expression modulation of permeability transition pore complex (PTPC) components which include the voltage-dependent anion channel (VDAC), the adenine nucleotide translocator (ANT), and cyclophilin D, and (iii) there are enhanced rates of glycolysis even in the presence of oxygen, a phenomena that is known as the Warburg effect [2]. In fact, many chemotherapeutic drugs induce mitochondrial-mediated apoptotic cell death (intrinsic apoptosis pathway) and act via mitochondrial perturbation, causing mitochondrial membrane permeability transition (MPT), membrane depolarization, osmotic swelling, and release of cytochrome c leading to cancer cell death.

Hexokinase (HK) is the initial enzyme of glycolysis that catalyzes the phosphorylation of glucose to glucose-6-phosphate (G6P), which is also the rate-limiting step in glycolysis and sequesters glucose inside the cells.  In cancer cells, HK (mainly HK-II) is overexpressed and found mostly bound to mitochondria through VDAC1  [3]. An enhanced expression of HK is found in aggressive tumors such as gliomas [4], and hepatomas [5]. HK overexpression, along with its glucose phosphorylation activity, is suggested to play a pivotal role in cancer cell growth rate and survival [6]. Thus, mitochondrial-bound HK overexpression may contribute to the Warburg effect by facilitating the access  to ATP, the substrate of HK [7]. In addition, as one of the hallmarks of cancer [8] is evading apoptotic cell death, owing in part to overexpression of anti-apoptotic proteins of the Bcl-2 family and that of HK, the elevated levels of mitochondria-bound HK in cancer cells contribute to the protection against mitochondria-mediated cell death [6].  All together, these characteristics make HK attractive target for cancer therapy.

Anti-cancer agents targeting HK-mitochondria interactions:

Jasmonates

The jasmonates plant stress hormones aside from their natural function against microbial pathogens in plants were also discovered to have toxic activities towards mammalian cancer cells. These activities consist of two important characteristics for anti-cancer drugs: high selectivity towards cancer cells, and the ability to act against drug resistant cancer cells [9]. The main mechanism of action of jasmonates–induced cancer cell death is suggested to involve direct mitochondrial perturbation. Methyl jasmonate (MJ) is able to reduce intracellular levels of ATP in various cancer cells, preceding cell death induction. Thus, the impaired ability of cancer cell mitochondria to generate ATP renders them more sensitive to the rapid ATP depletion induced by MJ. In addition, MJ induces mitochondrial membrane depolarization and cytochrome c release in cancer cells, as well as swelling and cytochrome c release in isolated mitochondria derived from cancer cells in a PTPC-mediated manner, but not of normal cells [10]. These findings demonstrate that the jasmonates selective toxicity towards cancer cells relies on the differential mitochondrial status of cancer cells vs. non-cancerous cells. Most relevant, it was clearly demonstrated that MJ binds specifically to HK and disrupts its interaction with mitochondrial VDAC1, leading to detachment of HK from the mitochondria followed by cytochrome c release and subsequent cell death [11]. The direct interaction of MJ with HK was demonstrated using real-time surface plasmon resonance (SPR).  In addition, it was demonstrated that the susceptibility of cancer cells and mitochondria to MJ  depends on the expression of HK and its mitochondrial association [11]. Therefore, MJ-induced HK detachment from mitochondria perturbs mitochondrial permeability and induce overall cellular energy crises, leading to cell death (see figure). Jasmonates thus describe for the first time of a cytotoxic mechanism based on direct interaction between an anti-cancer agent and HK. This finding may stimulate the development of a novel class of small anticancer compounds that inhibit the HK-VDAC1 interaction [12].

Image

VDAC1-based peptides

As described above, the HK association to mitochondria in cancer cells mediated through VDAC1 [13]. It has been shown that HK–VDAC1 interaction prevents induction of apoptosis in tumor-derived cells. Thus interfering with HK binding to VDAC1, promoting detachment of HK would form the basis for novel cancer treatment. Two main classes of agents might affect the HK-VDAC1 association: inhibitors of HK activity, or compounds that compete with VDAC1 for HK binding.

Detailed studies were performed in order to elucidate the domains on VDAC1 sequence that are essential for its interactions with HK.  These studies were based upon VDAC1 biochemical/functional structural prediction and the recently elucidated VDAC1 3D structure. By mutagenesis and functional studies, suspected domains on VDAC1 were examined as for their role in VDAC1-HK interactions [14]. According to these studies selected cell-penetrable VDAC1-based peptides were designed and were demonstrated to directly interact with purified HK in vitro and to detach HK bound to mitochondria isolated from tumor cells. Not only that, it was clearly demonstrated that these peptides are capable to selectively kill cancer cells while spearing normal cells [15], all together supporting the notion that interfering with the binding of HK to mitochondria by VDAC1-based peptides indeed may offer a novel strategy by which to induce selective cancer cell death.

Further directions

In order to evaluate the potential of using the HK-mitochondrial interactions as valid targets for cancer therapy, more steps are needed to be taken on the road. The selectiveness of this therapy relays on the fact that cancer cells bare much more mitochondrial-bound HK than normal cells, which might serve as an Achilles heel of the cancer cell. As peptides could be easily degraded in the plasma, the VDAC1-based peptides efficacy against cancer should be evaluated in vivo as well as their plasma stability should be examined. New generation and formulations of VDAC1-based peptides should be developed based upon research progress. As for jasmonates, their main deficiency is the need of using relatively high concentration (at the range of millimolar) to exert their action. Therefore, in order to develop valid jasmonate-based therapies, there is an urgent need for the development of jasmonate analogs that actually work in much lower dosage, with increased solubility, yet still effective and potent against cancer. Furthermore, it is not clear yet what is the exact domain on HK that MJ is interacting with. Elucidating the plausible interaction site(s) of MJ with HK would give the opportunity to design other small molecules directed to that specific HK domain with the hope to achieve more effective anti-cancer agents.

References

1. Newmeyer DD, Ferguson-Miller S (2003) Mitochondria: releasing power for life and unleashing the machineries of death. Cell 112 (4):481-490

2. Warburg O (1956) On the origin of cancer cells. Science 123 (3191):309-314

3. Pedersen PL, Mathupala S, Rempel A, Geschwind JF, Ko YH (2002) Mitochondrial bound type II hexokinase: a key player in the growth and survival of many cancers and an ideal prospect for therapeutic intervention. Biochim Biophys Acta 1555 (1-3):14-20

4. Pastorino JG, Hoek JB (2003) Hexokinase II: the integration of energy metabolism and control of apoptosis. Curr Med Chem 10 (16):1535-1551

5. Gelb BD, Adams V, Jones SN, Griffin LD, MacGregor GR, McCabe ER (1992) Targeting of hexokinase 1 to liver and hepatoma mitochondria. Proc Natl Acad Sci U S A 89 (1):202-206

6. Mathupala SP, Ko YH, Pedersen PL (2006) Hexokinase II: cancer’s double-edged sword acting as both facilitator and gatekeeper of malignancy when bound to mitochondria. Oncogene 25 (34):4777-4786

7. Pedersen PL (2007) Warburg, me and Hexokinase 2: Multiple discoveries of key molecular events underlying one of cancers’ most common phenotypes, the “Warburg Effect”, i.e., elevated glycolysis in the presence of oxygen. J Bioenerg Biomembr 39 (3):211-222

8. Hanahan D, Weinberg RA (2011) Hallmarks of cancer: the next generation. Cell 144 (5):646-674

9. Raviv Z, Cohen S, Reischer-Pelech D (2013) The anti-cancer activities of jasmonates. Cancer Chemother Pharmacol 71 (2):275-285

10. Rotem R, Heyfets A, Fingrut O, Blickstein D, Shaklai M, Flescher E (2005) Jasmonates: novel anticancer agents acting directly and selectively on human cancer cell mitochondria. Cancer Res 65 (5):1984-1993

11. Goldin N, Arzoine L, Heyfets A, Israelson A, Zaslavsky Z, Bravman T, Bronner V, Notcovich A, Shoshan-Barmatz V, Flescher E (2008) Methyl jasmonate binds to and detaches mitochondria-bound hexokinase. Oncogene 27 (34):4636-4643

12. Galluzzi L, Kepp O, Tajeddine N, Kroemer G (2008) Disruption of the hexokinase-VDAC complex for tumor therapy. Oncogene 27 (34):4633-4635

13. Shoshan-Barmatz V, Zakar M, Rosenthal K, Abu-Hamad S (2009) Key regions of VDAC1 functioning in apoptosis induction and regulation by hexokinase. Biochim Biophys Acta 1787 (5):421-430

14. Abu-Hamad S, Zaid H, Israelson A, Nahon E, Shoshan-Barmatz V (2008) Hexokinase -I protection against apoptotic cell death is mediated via interaction with the voltage-dependent anion channel-1: Mapping the site of binding. J Biol Chem 19:13482-13490

15. Arzoine L, Zilberberg N, Ben-Romano R, Shoshan-Barmatz V (2009) Voltage-dependent anion channel 1-based peptides interact with hexokinase to prevent its anti-apoptotic activity. J Biol Chem 284 (6):3946-3955.

pharmaceuticalintelligence.com

https://pharmaceuticalintelligence.com/2012/10/17/is-the-warburg-effect-the-cause-or-the-effect-of-cancer-a-21st-century-view/

https://pharmaceuticalintelligence.com/2012/09/01/mitochondria-and-cancer-an-overview/

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Reporter: Aviva Lev-Ari, PhD, RN

 

02/01/2013
Ashley Yeager

For the first time, scientists have identified all the proteins in the mitochondrial matrix, which is where the cell’s energy is generated. How? Find out…

 

Between the maze-like inner membranes of the mitochondria, there’s a thick, sticky region called the matrix. This region serves an important role in the generation of the cell’s energy, but the proteins that actually make up this matrix have remained a mystery. But now, researchers at the Massachusetts Institute of Technology (MIT) have catalogued all the proteins in the mitochondrial matrix, identifying 31 proteins not previously associated with mitochondria. They did this by combining the strengths of two methods: microscopy and mass spectrometry.

 

Electron microscopy of human embryonic kidney cells expressing mito-APEX. Credit: Alice Ting, MIT

“This method is really a new paradigm for doing mass spec proteomics because we’re recording proteomics in living cells,” said Alice Ting, a chemist at MIT and author of a paper published online yesterday in Science that describes the technique (1).Microscopy and mass spectrometry are valuable for studying proteins, but each has its drawbacks. While microscopy can show where a protein is located within a cell, it can only do so for a small number of a cell’s roughly 20,000 proteins at once. Meanwhile, mass spectrometry can identify all the proteins within a cell, but destroys the cell membrane in the process of releasing the cell’s contents, resulting in a mixture of proteins from different cell regions and organelles.

To overcome these limitations, Ting’s group genetically engineered the mitochondrial matrix to express a newly designed peroxidase called APEX. When biotin-phenol was added to these cells, APEX stripped an electron and a proton from the biotin molecule, creating highly reactive biotin-phenoxyl radicals. These radicals quickly bound to nearby proteins to stabilize themselves, effectively tagging the proteins in the matrix.

The scientists then identified these tagged proteins with fluorescent imaging, dissolved the cell membrane, and isolated the proteins from the mitochondrial matrix. Using mass spectrometry, the team then identified 495 proteins in the mitochondrial matrix, 31 of which had not been previously linked to the mitochondrial region.

One of the biggest surprises was the discovery that the enzyme PPOX is in the matrix. PPOX helps synthesize heme, the pigment in red blood cells and a cofactor of the protein hemoglobin. Previously, biologists believed that PPOX was located within the space between the outer and inner membranes of the mitochondria, but Ting’s team found that it was actually within the matrix, which the team said is an example of how locally precise their biotin-tagging technique is.

Now, Ting and her team are looking at proteins in the mitochondrial intermembrane space. In addition, the researchers are tweaking their labeling system to map proteins in the cell membrane and to detect specific protein-protein interactions.

Reference

1. Rhee, H.-W., P. Zou, N. D. Udeshi, J. D. Martell, V. K. Mootha, S. A. Carr, and A. Y. Ting. 2013. Proteomic mapping of mitochondria in living cells via spatially restricted enzymatic tagging. Science (January).

SOURCE:

http://www.biotechniques.com/news/biotechniquesNews/biotechniques-339645.html#.UQ37hRxiB0w

 

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English: ATP producing pathways of glucose met...

English: ATP producing pathways of glucose metabolism in aerobic respiration (Photo credit: Wikipedia)

Author: Larry H. Bernstein, MD, FCAP,  

Writer, Author, Responder Clinical Pathologist, Biochemist, and Transfusion Physician _____________________________________________________________________________________________________________________________________________

Heterogeneity The heterogeneity is a problem that will take at least another decade to unravel because of the number of signaling pathways and the crosstalk that is specifically at issue. I must refer back to the work of Frank Dixon, Herschel Sidransky, and others, who did much to develop a concept of neoplasia occurring in several stages – minimal deviation and fast growing. These have differences in growth rates, anaplasia, and biochemical. This resembles the multiple “hit” theory that is described in “systemic inflammatory” disease leading to a final stage, as in sepsis and septic shock.

Tumor heterogeneity is problematic because of differences among the metabolic variety among types of gastrointestinal (GI) cancers, confounding treatment response and prognosis. A group of investigators from Sunnybrook Health Sciences Centre, University of Toronto, Ontario, Canada who evaluated the feasibility and safety of magnetic resonance (MR) imaging–controlled transurethral ultrasound therapy for prostate cancer in humans. Their study’s objective was to prove that using real-time MRI guidance of HIFU treatment is possible and it guarantees that the location of ablated tissue indeed corresponds to the locations planned for treatment.  The real-time MRI guidance is an improvement in imaging technology.

The ability to allow resection with removal of the tumor, and adjacent tissue at risk is unproved, and is related to the length of remission.

See comment written for :

Knowing the tumor’s size and location, could we target treatment to THE ROI by applying…..

https://pharmaceuticalintelligence.com/2012/10/16/knowing-the-tumors-size-and-location-could-we-target-treatment-to-the-roi-by-applying-imaging-guided-intervention/

 

The Response vs. Recurrence Free Interval Conundrum

There is a difference between expected response to esophageal or gastric neoplasms both biologically and in expected response, even given variability within a class. The expected time to recurrence is usually longer in the latter case, but the confounders are –

  1. age at time of discovery,
  2. biological time of detection,
  3. presence of lymph node and/or
  4. distant metastasis, microscopic vascular invasion.

There is a long latent period in abdominal cancers before discovery, unless a lesion is found incidentally in surgery for another reason. The undeniable reality is that it is not difficult to identify the main lesion, but it is difficult to identify adjacent epithelium that is at risk (transitional or pretransitional). Pathologists have a very good idea about precancerous cervical neoplasia.

The heterogeneity rests within each tumor and between the primary and metastatic sites, which is expected to be improved by targeted therapy directed by tumor-specific testing. Despite rapid advances in our understanding of targeted therapy for GI cancers, the impact on cancer survival has been marginal. Brücher BLDM, Bilchik A, Nissan A, Avital I & Stojadinovic A. Can tumor response to therapy be predicted, thereby improving the selection of patients for cancer treatment?  Future Oncology 2012; 8(8): 903-906 , DOI 10.2217/fon.12.78 (doi:10.2217/fon.12.78)   The heterogeneity is a problem that will take at least another decade to unravel because of the number of signaling pathways and the crosstalk that is specifically at issue.

Anaerobic Glycolysis and Respiratory Impairment  In 1920, Otto Warburg received the Nobel Prize for his work on respiration. He postulated that cancer cells become anaerobic compared with their normal counterpart that uses aerobic respiration to meet most energy needs. He attributed this to “mitochondrial dysfunction. In fact, we now think that in response to oxidative stress, the mitochondrion relies on the Lynen Cycle to make more cells and the major source of energy becomes glycolytic, which is at the expense of the lean body mass (muscle), which produces gluconeogenic precursors from muscle proteolysis (cancer cachexia).

There is a loss of about 26 ATP ~Ps in the transition. The mitochondrial gene expression system includes the mitochondrial genome, mitochondrial ribosomes, and the transcription and translation machinery needed to regulate and conduct gene expression as well as mtDNA replication and repair. Machinery involved in energetics includes the enzymes of the Kreb’s citric acid or TCA (tricarboxylic acid) cycle, some of the enzymes involved in fatty acid catabolism (β-oxidation), and the proteins needed to help regulate these systems. The inner membrane is central to mitochondrial physiology and, as such, contains multiple protein systems of interest. These include the protein complexes involved in the electron transport component of oxidative phosphorylation and proteins involved in substrate and ion transport. ________________________________________________________________________________________________________________________________________________________________________________ Mitochondrial Roles in Cellular Homeostasis Mitochondrial roles in, and effects on, cellular homeostasis extend far beyond the production of ATP, but the transformation of energy is central to most mitochondrial functions. Reducing equivalents are also used for anabolic reactions. The energy produced by mitochondria is most commonly thought of to come from the pyruvate that results from glycolysis, but it is important to keep in mind that the chemical energy contained in both fats and amino acids can also be converted into NADH and FADH2 through mitochondrial pathways.

The major mechanism for harvesting energy from fats is β-oxidation; the major mechanism for harvesting energy from amino acids and pyruvate is the TCA cycle. Once the chemical energy has been transformed into NADH and FADH2 (also discovered by Warburg and the basis for a second Nobel nomination in 1934), these compounds are fed into the mitochondrial respiratory chain. The hydroxyl free radical is extremely reactive. It will react with most, if not all, compounds found in the living cell (including DNA, proteins, lipids and a host of small molecules).

The hydroxyl free radical is so aggressive that it will react within 5 (or so) molecular diameters from its site of production. The damage caused by it, therefore, is very site specific. The reactions of the hydroxyl free radical can be classified as hydrogen abstraction, electron transfer, and addition. The formation of the hydroxyl free radical can be disastrous for living organisms. Unlike superoxide and hydrogen peroxide, which are mainly controlled enzymatically, the hydroxyl free radical is far too reactive to be restricted in such a way – it will even attack antioxidant enzymes. Instead, biological defenses have evolved that reduce the chance that the hydroxyl free radical will be produced and, as nothing is perfect, to repair damage. ________________________________________________________________________________________________________________________________________________________________________________ Oxidative Stress and Mitochondrial Impairment Currently, some endogenous markers are being proposed as useful measures of total “oxidative stress” e.g., 8-hydroxy-2’deoxyguanosine in urine. The ideal scavenger must be non-toxic, have limited or no biological activity, readily reach the site of hydroxyl free radical production (i.e., pass through barriers such as the blood-brain barrier), react rapidly with the free radical, be specific for this radical, and neither the scavenger nor its product(s) should undergo further metabolism. Nitric oxide has a single unpaired electron in its π*2p antibonding orbital and is therefore paramagnetic. This unpaired electron also weakens the overall bonding seen in diatomic nitrogen molecules so that the nitrogen and oxygen atoms are joined by only 2.5 bonds. The structure of nitric oxide is a resonance hybrid of two forms. In living organisms nitric oxide is produced enzymatically. Microbes can generate nitric oxide by the reduction of nitrite or oxidation of ammonia.

In mammals nitric oxide is produced by stepwise oxidation of L-arginine catalyzed by nitric oxide synthase (NOS). Nitric oxide is formed from the guanidino nitrogen of the L-arginine in a reaction that consumes five electrons and requires flavin adenine dinucleotide (FAD), flavin mononucleotide (FMN) tetrahydrobiopterin (BH4), and iron protoporphyrin IX as cofactors. The primary product of NOS activity may be the nitroxyl anion that is then converted to nitric oxide by electron acceptors. The thiol-disulfide redox couple is very important to oxidative metabolism. GSH is a reducing cofactor for glutathione peroxidase, an antioxidant enzyme responsible for the destruction of hydrogen peroxide.

Thiols and disulfides can readily undergo exchange reactions, forming mixed disulfides. Thiol-disulfide exchange is biologically very important. For example, GSH can react with protein cystine groups and influence the correct folding of proteins, and it GSH may play a direct role in cellular signaling through thiol-disulfide exchange reactions with membrane bound receptor proteins (e.g., the insulin receptor complex), transcription factors (e.g., nuclear factor κB), and regulatory proteins in cells. Conditions that alter the redox status of the cell can have important consequences on cellular function.  So the complexity of life is not yet unravelled.

_________________________________________________________________________________________________________________________________________________________________________________

Warburgh Effect

Cells seem to be well-adjusted to glycolysis. While Otto Warburg first proposed that cancer cells show increased levels of glucose consumption and lactate fermentation even in the presence of ample oxygen (known as “Warburg Effect”), which requires oxidative phosphorylation to switch to glycolysis promoting the proliferation of cancer cells., many studies have demonstrated glycolysis as the main metabolic pathway in cancer cells. It is now accepted that glycolysis provides cancer cells with the most abundant extracellular nutrient, glucose, to make ample ATP metabolic intermediates, such as ribose sugars, glycerol and citrate, nonessential amino acids, and the oxidative pentose phosphate pathway, which serve as building blocks for cancer cells.

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Dampened Mitochondrial Respiration
Since, cancer cells have increased rates of aerobic glycolysis, investigators argue over the function of mitochondria in cancer cells. Mitochondrion, a one of the smaller organelles, produces most of the energy in the form of ATP to supply the body. In Warburg’s theory, the function of cellular mitochondrial respiration is dampened and mitochondria are not fully functional. There are many studies backing this theory. A recent review on hypoxia nicely summarizes some current studies and speculates that the “Warburg Effect” provides a benefit to the tumor not by increasing glycolysis but by decreasing mitochondrial activity.

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Glycolysis
Glycolysis is enhanced and beneficial to cancer cells. The mammalian target of rapamycin (mTOR) has been well discussed in its role to promote glycolysis; recent literature has revealed some new mechanisms of how glycolysis is promoted during skin cancer development.

On the other hand, Akt is not only involved in the regulation of mitochondrial metabolism in skin cancer but also of glycolysis. Activation of Akt has been found to phosphorylate FoxO3a, a downstream transcription factor of Akt, which promotes glycolysis by inhibiting apoptosis in melanoma. In addition, activated Akt is also associated with stabilized c-Myc and activation of mTOR, which both increase glycolysis for cancer cells.
Nevertheless, ras mutational activation prevails in skin cancer. Oncogenic ras induces glycolysis. In human squamous cell carcinoma, the c-Jun NH(2)-terminal Kinase (JNK) is activated as a mediator of ras signaling, and is essential for ras-induced glycolysis, since pharmacological inhibitors if JNK suppress glycolysis. CD147/basigin, a member of the immunoglobulin superfamily, is high expressed in melanoma and other cancers.
Glyoxalase I (GLO1) is a ubiquitous cellular defense enzyme involved in the detoxification of methylglyoxal, a cytotoxic byproduct of glycolysis. In human melanoma tissue, GLO1 is upregulated at both the mRNA and protein levels.
Knockdown of GLO1 sensitizes A375 and G361 human metastatic melanoma cells to apoptosis.
The transcription factor HIF-1 upregulates a number of genes in low oxygen conditions including glycolytic enzymes, which promotes ATP synthesis in an oxygen independent manner. Studies have demonstrated that hypoxia induces HIF-1 overexpression and its transcriptional activity increases in parallel with the progression of many tumor types. A recent study demonstrated that in malignant melanoma cells, HIF-1 is upregulated, leading to elevated expression of Pyruvate Dehydrogenase Kinase 1 (PDK1), and downregulated mitochondrial oxygen consumption.
The M2 isoform of Pyruvate Kinase (PKM2), which is required for catalyzing the final step of aerobic glycolysis, is highly expressed in cancer cells; whereas the M1 isoform (PKM1) is expressed in normal cells. Studies using the skin cell promotion model (JB6 cells) demonstrated that PKM2 is activated whereas PKM1 is inactivated upon tumor promoter treatment. Acute increases in ROS inhibited PKM2 through oxidation of Cys358 in human lung cancer cells. The levels of ROS and stage of tumor development may be pivotal for the role of PKM2.

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Dampening Mitochondrial Both Cause and Effect 

Warburg effect is both, a cause and effect of cancer…Review article mentioned in link below explains how different factors can contribute to metabolic reprogramming and Warburg effect….The Supply-based model and Traditional model clearly explains how the cancer cells will progress during different availability of growth factors and nutrients…And recent studies including my project (under process of getting published) will also suggest that growth factors can drive cancer cells to undergo Warburg effect regardless of the presence of oxygen…

Otto Warburg proposed that “EVEN IN THE PRESENCE OF OXYGEN, cancer cells can reprogram their glucose metabolism, and thus their energy production, by limiting their energy metabolism largely to glycolysis” . http://www.ncbi.nlm.nih.gov/pubmed

Metabolic reprogramming: a cancer hallmark even warburg did not anticipate (Ward & Thompson) Posted by Nirav Patel

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The autophagic tumor stroma model of cancer metabolism.
Cancer cells induce oxidative stress in adjacent cancer-associated fibroblasts (CAFs). This activates reactive oxygen species (ROS) production and autophagy. ROS production in CAFs, via the bystander eff ect, serves to induce random mutagenesis in epithelial cancer cells, leading to double-strand DNA breaks and aneuploidy. Cancer cells mount an anti-oxidant defense and upregulate molecules that protect them against ROS and autophagy, preventing them from undergoing apoptosis. So, stromal fibroblasts conveniently feed and mutagenize cancer cells, while protecting them against death. See the text for more details. A+, autophagy positive; A-, autophagy negative; AR, autophagy resistant.

1. Recycled Nutrients
2. Random Mutagenesis
3. Protection Against Apoptosis

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The reverse Warburg effect.
Via oxidative stress, cancer cells activate two major transcription factors in adjacent stromal fibroblasts (hypoxia-inducible factor (HIF)1α and NFκB).
This leads to the onset of both autophagy and mitophagy, as well as aerobic glycolysis, which then produces recycled nutrients (such as lactate, ketones, and glutamine).
These high-energy chemical building blocks can then be transferred and used as fuel in the tricarboxylic acid cycle (TCA) in adjacent cancer cells.
The outcome is high ATP production in cancer cells, and protection against cell death. ROS, reactive oxygen species.

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The choline dependent methylation of PP2A is the brake, the “antidote”, which limits “the poison” resulting from an excess of insulin signaling. Moreover, it seems that choline deficiency is involved in the L to M2 transition of PK isoenzymes. The negative regulation of Ras/MAP kinase signals mediated by PP2A phosphatase seems to be complex.

The serine-threonine phosphatase does more than simply counteracting kinases; it binds to the intermediate Shc protein on the signaling cascade, which is inhibited. The targeting of PP2A towards proteins of the signaling pathway depends of the assembly of the different holoenzymes.

The relative decrease of methylated PP2A in the cytosol, not only cancels the brake over the signaling kinases, but also favors the inactivation of PK and PDH, which remain phosphorylated, contributing to the metabolic anomaly of tumor cells. In order to prevent tumors, one should then favor the methylation route rather than the phosphorylation route for choline metabolism.

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Martin Canazales observes….

(http://www.cellsignal.com/reference/pathway/warburg_effect.html), is responsible of overactivation of the PI3K…

the produced peroxide via free radicals over activate the cyclooxigenase and consequently the PI3K pathway, thereby activating  the most important protein-kinase.  This brakes the Warburg effect, and stops the PI3K activation.

(http://www.cellsignal.com/reference/pathway/Akt_PKB.html)

Then all the cancer protein related with the generation of tumor (pAKT,pP70S6K, Cyclin D1, HIF1, VEGF, EGFrc, GSK, Myc, etc, etc, etc)  get down regulated. That is what happens when one knocks down the new protein-kinase in pancreatic cancer cell lines.  These pancreatic cancer cell lines divide very-very-very slowly.

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I now transition from what is understood about the metabolic signatures of cancer that tend to behave more alike than the cell of origin, but not initially.  This is perhaps a key to therapeutics.  >>>

Time of intervention>>> and right intervention.

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Can tumor response to therapy be predicted, thereby improving the selection of patients for cancer treatment? The goal is not just complete response. Histopathological response seems to be related post-treatment histopathological assessment but it is not free from the challenge of accurately determining treatment response, as this method cannot delineate whether or not there are residual cancer cells. Functional imaging to assess metabolic response by 18-fluorodeoxyglucose PET also has its limits, as the results are impacted significantly by several variables:

  1. tumor type
  2. sizing
  3. doubling time
  4. anaplasia?
  5. extent of tumor necrosis
  6. presence of tumor at the margin of biopsy
  7. lymph node and/or distant metastasis
  8. vascular involvement
  9. type of antitumor therapy and the time when response was determined.

The new modality should be based on individualized histopathology as well as tumor molecular, genetic and functional characteristics, and individual patients’ characteristics, a greater challenge in an era of ‘minimally invasive treatment’. This has been pointed out by Brücher et al. if the International Consortium on Cancer with respect to the shortcoming of MIS as follows: Minimally Invasive Surgery (MIS) vs. conventional surgery dissection applied to cancer tissue with the known pathophysiology of recurrence and remission cycles has its short term advantages.

  1. in many cases MIS is not the right surgical decision
  2. predicting the uncertain future behavior of the tumor with respect to its response to therapeutics bears uncertain outcomes.

An increase in the desirable outcomes of MIS as a modality of treatment, will be assisted in the future, when anticipated progress is made in the field of

  • Cancer Research,
  • Translational Medicine and
  • Personalized Medicine,

when each of the cancer types, above,  will already have a Genetic Marker allowing the Clinical Team to use the marker(s) for:

  • prediction of Patient’s reaction to Drug induction
  • design of Clinical Trials to validate drug efficacy on small subset of patients predicted to react favorable to drug regimen, increasing validity and reliability
  • Genetical identification of patients at no need to have a drug administered if non sensitivity to the drug has been predicted by the genetic marker.

See listing of cancers provided by Dr. Aviva Lev-Ari.

Lev-Ari A. Personalized Medicine: Cancer Cell Biology and Minimally Invasive Surgery (MIS). ________________________________________________________________________________________________________________________________________________________________________________ See comment: 

Judging the ‘Tumor response’-there is more food for thought 

 

That is an optimistic order to effectively carry out in the face of the statistical/mathematical challenge imposed for any real success.

Brücher BLDM, Bilchik A, Nissan A, Avital I & Stojadinovic A. Can tumor response to therapy be predicted, thereby improving the selection of patients for cancer treatment?  Future Oncology 2012; 8(8): 903-906 , DOI 10.2217/fon.12.78 (doi:10.2217/fon.12.78) _________________________________________________________________________________________________________________________________________________________________________________ A Model Based on Kullback Entropy and Identifying and Classifying Anomalies This listing suggests that for every cancer the following data has to be collected (except doubling time). If there are 8 variables, the classification based on these alone would calculate to be very sizable based on Eugene Rypka’s feature extraction and classification. But looking forward,

Treatment for cure is not the endpoint, but the best that can be done is to extend the time of survival to a realistic long term goal and retain a quality of life. Brücher BLDM, Piso P, Verwaal V et al. Peritoneal carcinomatosis: overview and basics. Cancer Invest.30(3),209–224 (2012). Brücher BLDM, Swisher S, Königsrainer A et al. Response to preoperative therapy in upper gastrointestinal cancers. Ann. Surg. Oncol.16(4),878–886 (2009). Miller AB, Hoogstraten B, Staquet M, Winkler A. Reporting results of cancer treatment. Cancer47(1),207–214 (1981). Therasse P, Arbuck SG, Eisenhauer EA et al. New guidelines to evaluate the response to treatment in solid tumors. European Organization for Research and Treatment of Cancer, National Cancer Institute of the United States, National Cancer Institute of Canada. J. Natl Cancer Inst.92(3),205–216 (2000). Brücher BLDM, Becker K, Lordick F et al. The clinical impact of histopathological response assessment by residual tumor cell quantification in esophageal squamous cell carcinomas. Cancer106(10),2119–2127 (2006). _________________________________________________________________________________________________________________________________________________________________________________

The critical question encountered by the pathologist is that key histological stains have been used for some time, such as Her2, and a number of others to establish tumor cell type, and differences with cell types.  The number will grow as the genomic identifiers are explored and put to use.  It doesn’t appear that the pathologist will be displaced any time soon.  This is separate from older observations of nuclear polymorphism, anaplastic changes related to cell adhesion, etc.  These do not displace the information gained from staging criteria.  Clearly, there is much information that is used for individual decisions about therapeutic approach, which will undergo further refinement even before the end of this decade.

_________________________________________________________________________________________________________________________________________________________________________________ Melanoma Example A marker for increased glycolysis in melanoma is the elevated levels of Lactate Dehydrogenase (LDH) in the blood of patients with melanoma, which has proven to be an accurate predictor of prognosis and response to treatments. LDH converts pyruvate, the final product of glycolysis, to lactate when oxygen is absent. High concentrations of lactate, in turn, negatively regulate LDH. Therefore, targeting acid excretion may provide a feasible and effective therapeutic approach for melanoma. For instance, JugloSne, a main active component in walnut, has been used in traditional medicines.

Studies have shown that Juglone causes cell membrane damage and increased LDH levels in a concentration-dependent manner in cultured melanoma cells. As one of the rate-limiting enzyme of glycolysis, 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase isozyme 3 (PFKFB3) is activated in neoplastic cells. Studies have confirmed that an inhibitor of PFKFB3, 3-(3-pyridinyl)-1-(4-pyridinyl)-2-propen-1-one (3PO), suppresses glycolysis in neoplastic cells. In melanoma cell lines, the concentrations of Fru-2, 6-BP, lactate, ATP, NAD+, and NADH are diminished by 3PO. Therefore, targeting PFKFB3 using 3PO and other PFKFB3 specific inhibitors could be effective in melanoma chemotherapy.

This is only one example of the encouraging results from targeted therapy. An unexplored idea was provided to me that is interesting and be highly conditional, by loading with high concentrations of ketones to offset the glycolytic pathway redirected bypass of mitochondrial pathways.  There is an inherent problem with muscle proteolysis raising the glucose level from gluconeogenesis. The effect is uncertain with respect to TCA cycle intermediates. It seems plausible that cure is not necessarily attainable due to inability to identify portions of proximate local tumor, modification and drug resistance. The reliable extension of disease free survival and maintaining a patient acceptable quality of life is improvable. __________________________________________________________________________________________________________________________________________________________________________________

Ward PS, Thompson CB. Metabolic Reprogramming: A Cancer Hallmark Even Warburg Did Not Anticipate. Cancer Cell. 2012; 21(3):297-308.

  1. Quiescent versus Proliferating Cells: Both Use Mitochondria, but to Different Ends
  2. Altered Metabolism Is a Direct Response to Growth-Factor Signaling
  3. PI3K/Akt/mTORC1 Activation: Driving Anabolic Metabolism and Tumorigenesis by Reprogramming Mitochondria

Full-size image (51 K) Bhowmick NA. Metastatic Ability: Adapting to a Tissue Site Unseen.  Cancer Cell  2012; 22(5): 563-564. _____________________________________________________________________________________________________________________________________________________________________________ Therapeutic strategies that target glycolysis and biosynthetic pathways in cancer cells are currently the main focus of research in the field of cancer metabolism. In this issue of Cancer Cell, Hitosugi and colleagues show that targeting PGAM1 could be a way of “killing two birds with one stone”. Chaneton B, Gottlieb E. PGAMgnam Style: A Glycolytic Switch Controls Biosynthesis. Cancer Cell 2012; 22(5): 565-566. ______________________________________________________________________________________________________________________________________________________________________________ The Polycomb epigenetic silencing protein EZH2 is affected by gain-of-function somatic mutations in B cell lymphomas. Two recent reports describe the development of highly selective EZH2 inhibitors and reveal mutant EZH2 as playing an essential role in maintaining lymphoma proliferation. EZH2 inhibitors are thus a promising new targeted therapy for lymphoma. Melnick A. Epigenetic Therapy Leaps Ahead with Specific Targeting of EZH2. Cancer Cell 22(5): 569-570. _______________________________________________________________________________________________________________________________________________________________________________ The microenvironment of the primary as well as the metastatic tumor sites can determine the ability for a disseminated tumor to progress. In this issue of Cancer Cell, Calon and colleagues find that systemic TGF-β can facilitate colon cancer metastatic engraftment and expansion. Calon A, Espinet E, Palomo-Ponce S, Tauriello DVF, et al.  Dependency of Colorectal Cancer on a TGF-β-Driven Program in Stromal Cells for Metastasis Initiation.  Cancer Cell 2012;22(5): 571-584. image

_______________________________________________________________________________________________________________________________________________________________________________ An analysis of what is possible, but who knows how far into the accelerating future? Tumor response criteria: are they appropriate? The International Consortium is centered at the Billroth Institute, in Munich. Interesting it is that Billroth was the father of abdominal surgery and performed the first esophagectomy and the firat gastrectomy. He also pioneered in keeping a record of treatments and outcomes in the 19th century, which Halsted studied. I need not repeat what has been stated in the post. The pathologist’s role is still important, as the editorial in Future Oncology gets at.  This also requires necessary and sufficient features to extract differentiating classifiers.  I don’t think we shall see pathologists the likes of many who were masters until the 1990′s. The surgical pathologist today cannot have complete command of the large knowledge base, but the tumor registry and the cancer committee has evolved to a better stage than in the 1960′s. Surgical grand rounds have been used for teaching and evaluating the practice since at least the 1960′s. What is asked is that we go beyond that.

See comment written for:

Knowing the tumor’s size and location, could we target treatment to THE ROI by applying…..

https://pharmaceuticalintelligence.com/2012/10/16/knowing-the-tumors-size-and-location-could-we-target-treatment-to-the-roi-by-applying-imaging-guided-intervention/

________________________________________________________________________________________________________________________________________________________________________________ Evidence-based medicine Evidence-based medicine is substantially flawed because of reliance on meta-analysis to arrive at conclusions from underpowered and inconsistent studies, discarding more than half of the studies examined that don’t meet the inclusion criteria.

  1. – There can be no movement forward without the systematic collection of data into a functionally well designed repository.
  2. – The current construct of the EMR probably has to be “remodeled” if not “remade”.
  3. – The studies will have to use real data, not aggregates of studies with “missing information”.
  4. – Bioinformatics is an emerging field that is only supported in the top two tiers of academic medical centers, which would include the well known cancer centers in Boston, Houston, and New York.

I don’t place much hope in “Watson” coming to the rescue, because you have to collect both a lot of information and “sufficient” information.

  1. -”Sufficient” information has been precluded by years of cost-elimination without paying attention to the real impact of “technologies” on costs, and an inherent competition between labor and “capital” investment.
  2. – Despite the progress in genomics, the heterogeneity of these solid tumors is a natural adaptation that occurs in carcinogenesis.
  3. The heterogeneity traced over a time-span should have information about stage in carcinogenesis.
  4. The pathologist can see and interpret histologic grades in the evolution that may have a better relationship to the evolutionary studies of genomics and signaling pathways than to stage of disease, but by combining the best available evidence, you move to a better classification. Without good classification, I don’t see how you can arrive at “science based” personalized medicine.

there is still a Rubicon to cross in going from genomics to translational medicine, which extends to diet and lifestyle.

Search Results for ‘cancer’ on this web site

Cancer Genomics – Leading the Way by Cancer Genomics Program at UC Santa Cruz Closing the gap towards real-time, imaging-guided treatment of cancer patients. Lipid Profile, Saturated Fats, Raman Spectrosopy, Cancer Cytology

mRNA interference with cancer expression

Pancreatic cancer genomes: Axon guidance pathway genes – aberrations revealed Biomarker tool development for Early Diagnosis of Pancreatic Cancer: Van Andel Institute and Emory University

Is the Warburg Effect the cause or the effect of cancer: A 21st Century View?

Crucial role of Nitric Oxide in Cancer Targeting Glucose Deprived Network Along with Targeted Cancer Therapy Can be a Possible Method of Treatment

Structure of the human mitochondrial genome.

Structure of the human mitochondrial genome. (Photo credit: Wikipedia)

English: ATP production in aerobic respiration

English: ATP production in aerobic respiration (Photo credit: Wikipedia)

 

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Is the Warburg Effect the Cause or the Effect of Cancer: A 21st Century View?

Author: Larry H. Bernstein, MD, FCAP  

A Critical Review

What is the Warburg effect?

“Warburg Effect” describes the preference of glycolysis and lactate fermentation rather than oxidative phosphorylation for energy production in cancer cells. Mitochondrial metabolism is an important and necessary component in the functioning and maintenance of the organelle, and accumulating evidence suggests that dysfunction of mitochondrial metabolism plays a role in cancer. Progress has demonstrated the mechanisms of the mitochondrial metabolism-to-glycolysis switch in cancer development and how to target this metabolic switch.
In vertebrates, food is digested and supplied to cells mainly in the form of glucose. Glucose is broken down further to make Adenosine Triphosphate (ATP) by two pathways. One is via anaerobic metabolism occurring in the cytoplasm, also known as glycolysis. The major physiological significance of glycolysis lies in making ATP quickly, but in a minuscule amount. The breakdown process continues in the mitochondria via the Krebs’s cycle coupled with oxidative phosphorylation, which is more efficient for ATP production. Cancer cells seem to be well-adjust to glycolysis. In the 1920s, Otto Warburg first proposed that cancer cells show increased levels of glucose consumption and lactate fermentation even in the presence of ample oxygen (known as “Warburg Effect”). Based on this theory, oxidative phosphorylation switches to glycolysis which promotes the proliferation of cancer cells. Many studies have demonstrated glycolysis as the main metabolic pathway in cancer cells.
Why cancer cells prefer glycolysis, an inefficient metabolic pathway?

It is now accepted that glycolysis provides cancer cells with the most abundant extracellular nutrient, glucose, to make ample ATP metabolic intermediates, such as ribose sugars, glycerol and citrate, nonessential amino acids, and the oxidative pentose phosphate pathway, which serve as building blocks for cancer cells.
Since, cancer cells have increased rates of aerobic glycolysis, investigators argue over the function of mitochondria in cancer cells. Mitochondrion, a one of the smaller organelles, produces most of the energy in the form of ATP to supply the body. In Warburg’s theory, the function of cellular mitochondrial respiration is dampened and mitochondria are not fully functional. There are many studies backing this theory. A recent review on hypoxia nicely summarizes some current studies and speculates that the “Warburg Effect” provides a benefit to the tumor not by increasing glycolysis but by decreasing mitochondrial activity.
Glycolysis
Glycolysis is enhanced and beneficial to cancer cells. The mammalian target of rapamycin (mTOR) has been well discussed in its role to promote glycolysis; recent literature has revealed some new mechanisms of how glycolysis is promoted during skin cancer development.
On the other hand, Akt is not only involved in the regulation of mitochondrial metabolism in skin cancer but also of glycolysis. Activation of Akt has been found to phosphorylate FoxO3a, a downstream transcription factor of Akt, which promotes glycolysis by inhibiting apoptosis in melanoma. In addition, activated Akt is also associated with stabilized c-Myc and activation of mTOR, which both increase glycolysis for cancer cells.
Nevertheless, ras mutational activation prevails in skin cancer. Oncogenic ras induces glycolysis. In human squamous cell carcinoma, the c-Jun NH(2)-terminal Kinase (JNK) is activated as a mediator of ras signaling, and is essential for ras-induced glycolysis, since pharmacological inhibitors if JNK suppress glycolysis. CD147/basigin, a member of the immunoglobulin superfamily, is high expressed in melanoma and other cancers.
Glyoxalase I (GLO1) is a ubiquitous cellular defense enzyme involved in the detoxification of methylglyoxal, a cytotoxic byproduct of glycolysis. In human melanoma tissue, GLO1 is upregulated at both the mRNA and protein levels.
Knockdown of GLO1 sensitizes A375 and G361 human metastatic melanoma cells to apoptosis.
The transcription factor HIF-1 upregulates a number of genes in low oxygen conditions including glycolytic enzymes, which promotes ATP synthesis in an oxygen independent manner. Studies have demonstrated that hypoxia induces HIF-1 overexpression and its transcriptional activity increases in parallel with the progression of many tumor types. A recent study demonstrated that in malignant melanoma cells, HIF-1 is upregulated, leading to elevated expression of Pyruvate Dehydrogenase Kinase 1 (PDK1), and downregulated mitochondrial oxygen consumption.
The M2 isoform of Pyruvate Kinase (PKM2), which is required for catalyzing the final step of aerobic glycolysis, is highly expressed in cancer cells; whereas the M1 isoform (PKM1) is expressed in normal cells. Studies using the skin cell promotion model (JB6 cells) demonstrated that PKM2 is activated whereas PKM1 is inactivated upon tumor promoter treatment. Acute increases in ROS inhibited PKM2 through oxidation of Cys358 in human lung cancer cells. The levels of ROS and stage of tumor development may be pivotal for the role of PKM2.

Mitochondrial metabolism and glycolysis targeting for cancer drug delivery
In cancer cells including skin cancer cells, the metabolic shift is composed of increased glycolysis, activation of anabolic pathways including amino acid and pentose phosphate production, and increased fatty acid biosynthesis. More and more studies have converged on particular glycolytic and mitochondrial metabolic targets for cancer drug discovery.
A marker for increased glycolysis in melanoma is the elevated levels of Lactate Dehydrogenase (LDH) in the blood of patients with melanoma, which has proven to be an accurate predictor of prognosis and response to treatments. LDH converts pyruvate, the final product of glycolysis, to lactate when oxygen is absent. High concentrations of lactate, in turn, negatively regulate LDH. Therefore, targeting acid excretion may provide a feasible and effective therapeutic approach for melanoma. For instance, JugloSne, a main active component in walnut, has been used in traditional medicines. Studies have shown that Juglone causes cell membrane damage and increased LDH levels in a concentration-dependent manner in cultured melanoma cells. As one of the rate-limiting enzyme of glycolysis, 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase isozyme 3 (PFKFB3) is activated in neoplastic cells. Studies have confirmed that an inhibitor of PFKFB3, 3-(3-pyridinyl)-1-(4-pyridinyl)-2-propen-1-one (3PO), suppresses glycolysis in neoplastic cells. In melanoma cell lines, the concentrations of Fru-2, 6-BP, lactate, ATP, NAD+, and NADH are diminished by 3PO. Therefore, targeting PFKFB3 using 3PO and other PFKFB3 specific inhibitors could be effective in melanoma chemotherapy.
A new NO (nitric oxide) donating compound [(S,R)-3-phenyl-4,5-dihydro-5-isoxazole acetic acid–nitric oxide (GIT-27NO)] has been tested in treating melanoma cells. The results suggest that GIT-27/NO causes a dose-dependent reduction of mitochondrial respiration in treated A375 human melanoma cells.

At least two mitochondrial enzymes are affected by angiostatin which include malate dehydrogenase, a member of the Kreb’s cycle enzymes; and adenosine triphosphate synthase. Both are identified potential angiostatin-binding partners. Treated with angiostatin, the ATP concentrations of A2058 cells were decreased. Meanwhile, using siRNA of these two enzymes also inhibited the ATP production. PKM2 is up regulated in the early stage of skin carcinogenesis, therefore, targeting PKM2 could serve as a new approach for skin cancer prevention and therapy.
The signaling pathways critical for this glycolytic activation could serve as preventive and therapeutic targets for human skin cancer.

The Historical Challenge posed by the Warburg Hypothesis.

Impaired cellular energy metabolism is the defining characteristic of nearly all cancers regardless of cellular or tissue origin. In contrast to normal cells, which derive most of their usable energy from oxidative phosphorylation, most cancer cells become heavily dependent on substrate level phosphorylation to meet energy demands. Evidence is reviewed supporting a general hypothesis that genomic instability and essentially all hallmarks of cancer, including aerobic glycolysis (Warburg effect), can be linked to impaired mitochondrial function and energy metabolism.
In a landmark review, six essential alterations in cell physiology could underlie malignant cell growth. These six alterations were described as the hallmarks of nearly all cancers and included,

  • self-sufficiency in growth signals,
  • insensitivity to growth inhibitory (antigrowth) signals,
  • evasion of programmed cell death (apoptosis),
  • limitless replicative potential,
  • sustained vascularity (angiogenesis), and
  • tissue invasion and metastasis.

Genome instability, leading to increased mutability, was considered the essential enabling characteristic for manifesting the six hallmarks. The loss of genomic “caretakers” or “guardians”, involved in sensing and repairing DNA damage, was proposed to explain the increased mutability of tumor cells. The loss of these caretaker systems would allow genomic instability thus enabling pre-malignant cells to reach the six essential hallmarks of cancer.
In addition to the six recognized hallmarks of cancer, aerobic glycolysis or the Warburg effect is also a robust metabolic hallmark of most tumors. Aerobic glycolysis in cancer cells involves elevated glucose uptake with lactic acid production in the presence of oxygen. This metabolic phenotype is the basis for tumor imaging using labeled glucose analogues and has become an important diagnostic tool for cancer detection and management. Genes for glycolysis are overexpressed in the majority of cancers examined.
Although aerobic glycolysis and anaerobic glycolysis are similar in that lactic acid is produced under both situations, aerobic glycolysis can arise in tumor cells from damaged respiration whereas anaerobic glycolysis arises from the absence of oxygen. As oxygen will reduce anaerobic glycolysis and lactic acid production in most normal cells (Pasteur effect), the continued production of lactic acid in the presence of oxygen can represent an abnormal Pasteur effect. This is the situation in most tumor cells.
Warburg proposed with considerable certainty and insight that irreversible damage to respiration was the prime cause of cancer. Warburg’s biographer, Hans Krebs, mentioned that Warburg’s idea on the primary cause of cancer, i.e., the replacement of respiration by fermentation (glycolysis), was only a symptom of cancer and not the cause. While there is renewed interest in the energy metabolism of cancer cells, it is widely thought that the Warburg effect and the metabolic defects expressed in cancer cells arise primarily from genomic mutability selected during tumor progression. Emerging evidence, however, questions the genetic origin of cancer and suggests that cancer is primarily a metabolic disease.
Genomic mutability and essentially all hallmarks of cancer, including the Warburg effect, can be linked to impaired respiration and energy metabolism. In brief, damage to cellular respiration precedes and underlies the genome instability that accompanies tumor development. Once established, genome instability contributes to further respiratory impairment, genome mutability, and tumor progression. In other words, effects become causes. This hypothesis is based on evidence that nuclear genome integrity is largely dependent on mitochondrial energy homeostasis and that all cells require a constant level of useable energy to maintain viability. While Warburg recognized the centrality of impaired respiration in the origin of cancer, he did not link this phenomenon to what are now recognize as the hallmarks of cancer.
Abnormal metabolism of tumors, a selective advantage
The initial observation of Warburg 1916 on tumor glycolysis with lactate production is still a crucial observation. Two fundamental findings complete the metabolic picture:

  • the discovery of the M2 pyruvate kinase (PK) typical of tumors
  • and the implication of tyrosine kinase signals and subsequent phosphorylations in the M2 PK blockade.

A typical feature of tumor cells is a glycolysis associated to an inhibition of apoptosis. Tumors overexpress the high affinity hexokinase 2, which strongly interacts with the mitochondrial ANT-VDAC-PTP complex. In this position, close to the ATP/ADP exchanger (ANT), the hexokinase receives efficiently its ATP substrate. As long as hexokinase occupies this mitochondria site, glycolysis is efficient. However, this has another consequence, hexokinase pushes away from the mitochondria site the permeability transition pore (PTP), which inhibits the release of cytochrome C, the apoptotic trigger. The site also contains a voltage dependent anion channel (VDAC) and other proteins. The repulsion of PTP by hexokinase would reduce the pore size and the release of cytochrome C. Thus, the apoptosome-caspase proteolytic structure does not assemble in the cytoplasm. The liver hexokinase or glucokinase, is different it has less interaction with the site, has a lower affinity for glucose; because of this difference, glucose goes preferentially to the brain.
Further, phosphofructokinase gives fructose 1-6 bisphosphate; glycolysis is stimulated if an allosteric analogue, fructose 2-6 bis phosphate increases in response to a decrease of cAMP. The activation of insulin receptors in tumors has multiple effects, among them; a decrease of cAMP, which will stimulate glycolysis. Another control point is glyceraldehyde P dehydrogenase that requires NAD+ in the glycolytic direction. If the oxygen supply is normal, the mitochondria malate/aspartate (MAL/ASP) shuttle forms the required NAD+ in the cytosol and NADH in the mitochondria. In hypoxic conditions, the NAD+ will essentially come via lactate dehydrogenase converting pyruvate into lactate. This reaction is prominent in tumor cells; it is the first discovery of Warburg on cancer.
At the last step of glycolysis, pyruvate kinase (PK) converts phospho-enolpyruvate (PEP) into pyruvate, which enters in the mitochondria as acetyl- CoA, starting the citric acid cycle and oxidative metabolism. To explain the PK situation in tumors we must recall that PK only works in the glycolytic direction, from PEP to pyruvate, which implies that gluconeogenesis uses other enzymes for converting pyruvate into PEP. In starvation, when cells need glucose, one switches from glycolysis to gluconeogenesis and ketogenesis; PK and pyruvate dehydrogenase (PDH) are off, in a phosphorylated form, presumably following a cAMP-glucagon-adrenergic signal. In parallel, pyruvate carboxylase (Pcarb) becomes active.
Moreover, in starvation, much alanine comes from muscle protein proteolysis, and is transaminated into pyruvate. Pyruvate carboxylase first converts pyruvate to OAA and then, PEP carboxykinase converts OAA to PEP etc…, until glucose. The inhibition of PK is necessary, if not one would go back to pyruvate. Phosphorylation of PK, and alanine, inhibit the enzyme.
PK and a PDH of tumors are inhibited by phosphorylation and alanine, like for gluconeogenesis, in spite of an increased glycolysis! Moreover, in tumors, one finds a particular PK, the M2 embryonic enzyme [2,9,10] the dimeric, phosphorylated form is inactive, leading to a “bottleneck “. The M2 PK has to be activated by fructose 1-6 bis P its allosteric activator, whereas the M1 adult enzyme is a constitutive active form. The M2 PK bottleneck between glycolysis and the citric acid cycle is a typical feature of tumor cell glycolysis.
Above the bottleneck, the massive entry of glucose accumulates PEP, which converts to OAA via mitochondria PEP carboxykinase, an enzyme requiring biotine-CO2-GDP. This source of OAA is abnormal, since Pcarb, another biotin-requiring enzyme, should have provided OAA. Tumors may indeed contain “morule inclusions” of biotin-enzyme suggesting an inhibition of Pcarb, presumably a consequence of the maintained citrate synthase activity, and decrease of ketone bodies that normally stimulate Pcarb. The OAA coming via PEP carboxykinase and OAA coming from aspartate transamination or via malate dehydrogenase condenses with acetyl CoA, feeding the elevated tumoral citric acid condensation starting the Krebs cycle.
Thus, tumors have to find large amounts of acetyl CoA for their condensation reaction; it comes essentially from lipolysis and β oxidation of fatty acids, and enters in the mitochondria via the carnitine transporter. This is the major source of acetyl CoA. It is as if the mechanism switching from gluconeogenesis to glycolysis was jammed in tumors, PK and PDH are at rest, like for gluconeogenesis, but citrate synthase is on. Thus, citric acid condensation pulls the glucose flux in the glycolytic direction, which needs NAD+; it will come from the pyruvate to lactate conversion by lactate dehydrogenase (LDH) no longer in competition with a quiescent Pcarb.
Since the citrate condensation consumes acetyl CoA, ketone bodies do not form; while citrate will support the synthesis of triglycerides via ATP citrate lyase and fatty acid synthesis… The cytosolic OAA drives the transaminases in a direction consuming amino acid. The result of these metabolic changes is that tumors burn glucose while consuming muscle protein and lipid stores of the organism. In a normal physiological situation, one mobilizes stores for making glucose or ketone bodies, but not while burning glucose!
The 21st Century Genomic Challenge?
According to the modern understanding of cancer, it is a disease caused by genetic and epigenetic alterations. Although this is now widely accepted, perhaps more emphasis has been given to the fact that cancer is a genetic disease. Numerous studies, including our earlier works, have supported the notion that carcinogenesis involves the activation of tumor-promoting oncogenes and the inactivation of growth-inhibiting tumor suppressor genes. It should be noted that in the post-genome sequencing project period of the 21st century, an in depth investigation of the factors associated with tumorigenesis is required for achieving it. Extensive research is warranted in two areas, namely, tumor bioenergetics and the cancer stem cell (CSC) hypothesis, neither of which received the required attention after the success of the genome sequencing project. An investigation of these two concepts would give rise to a new era in the study of cancer biology. Indeed, recent studies have indicated that the two apparently distinct fields might be related to each other and can converge more rapidly than previously recognized.
Warburg Effect Revisited
Cancer cells rarely depend on mitochondria for respiration and obtain almost half of their ATP by directly metabolizing glucose to lactic acid, even in the presence of oxygen. However, with the discovery that tumors do not show any shift to glycolysis, Warburg’s cancer theory (high lactate production and low mitochondrial respiration in tumor under normal oxygen pressure) was gradually discredited. Otto Warburg won a Nobel Prize in 1931 for the discovery of tumor bioenergetics, which is now commonly used as the basis of positron emission tomography (PET), a highly sensitive noninvasive technique used in cancer diagnosis. The increasing number of recent reports on the Warburg effect has reestablished the significance of this effect in tumorigenesis, indicating that bioenergetics may play a critical role in malignant transformation. Furthermore, it has been reported that TP53, which is one of the most commonly mutated genes in cancer, can trigger the Warburg effect. Glycolytic conversion is initiated in the early stages in cells that are genetically engineered to become cancerous, and the conversion was enhanced as the cells became more malignant. Therefore, the Warburg effect might directly contribute to the initiation of cancer formation not only by enhanced glycolysis but also via decreased respiration in the presence of oxygen, which suppresses apoptosis. This effect may also produce a metabolic shift to enhanced glycolysis and play a role in the early stages of multistep tumorigenesis in vivo.

Cancer Stem Cells (CSC) and Embryonic Stem Cells (ESC)
The importance of the cancer stem cell (CSC) hypothesis in therapy-related resistance and metastasis has been recognized during the past 2 decades. Accumulating evidence suggests that tumor bioenergetics plays a critical role in CSC regulation; this finding has opened up a new era of cancer medicine, which goes beyond cancer genomics.

Embryonic stem (ES) cells and immortalized primary and cancerous cells show a common concerted metabolic shift, including:

  • enhanced glycolysis,
  • decreased apoptosis, and
  • reduced mitochondrial respiration.

This finding reinforces the use of somatic stem cells or metastatic tumor cells in hypoxic niches. Hypoxia appears to regulate the functions of hematopoietic stem cells in the bone marrow and metastatic tumor cells by preserving important stem cell functions, such as:

  • cell cycle control,
  • survival,
  • metabolism, and
  • protection against oxidative stress.

Several companies and laboratories are now attempting to evaluate the bioenergetics associated with tumorigenesis by testing and challenging the available anticancer drugs.

A small population of cancer-initiating cells plays a very important role in current investigations. These CSCs may cause resistance to chemotherapy or radiation therapy or lead to post-therapy recurrence even when most of the cancer cells appear to be dead. In addition to their genetic alterations, CSCs are believed to mimic normal adult stem cells with regard to properties like self-renewal and undifferentiated status, which eventually leads to the formation of differentiated cells. Unlike well-differentiated daughter cells, small populations of CSCs are believed to be more resistant to toxic injuries and chemoradiotherapy. Indeed, the conventional cancer therapies have always been targeted toward proliferating cells. The control of CSCs, which is often exercised in the dormant phase of the cell cycle, can now be applied to achieve complete tumor regression.
Identification of cancer-specific markers
Due to their potential use in clinical applications, the surface markers of CSCs have been studied and identified. Adult stem cells and their malignant counterparts share similar intrinsic and extrinsic factors that regulate the

  • self renewal,
  • differentiation, and
  • proliferation pathways.

The following are the examples of candidate markers: musashi-1 (Msi-1), hairy and enhancer of split homolog-1 (Hes-1), CD133 (prominin-1, Prom1), epithelial cellular adhesion molecule (EpCam), claudin-7,29 CD44 variant isoforms, Lgr5,30Hedgehog (Hh), bone morphogenic protein (Bmp), Notch, and Wnt.
Is cancer a metabolic disease and genomic instability a secondary effect?
Bioenergetics of Cancer Stem Cells
The bioenergetics associated with the adaptation of CSCs to their micro-environment still requires extensive research. Although numerous studied suggested the association between Warburg effect and reduced oxidative stress in cancer, the relevant molecular mechanism was not known until very recently when Ruckenstuhl, et al. reported their findings in a yeast model.

How cancer cells achieve one of the most common phenotypes, namely, the “Warburg effect,” i.e., elevated glycolysis in the presence of oxygen, is still a topic of hypothesis, unless the involvement of glycolysis genes is considered.
The Warburg effect has been observed in differentiating cancer cells (e.g., cells that undergo epithelial-to-mesenchymal and mesenchymal-to-amoeboid transition), cells resistant to anoikis, and cells which interact with the stromal components of the metastatic niche. The epithelial-to-mesenchymal transition is involved in the resistance to chemotherapy in gastrointestinal cancer cells.

Cancer metastasis can be regarded as an integrated “escape program” triggered by redox changes. These alterations might be associated with avoiding oxidative stress in the niche of the tumor cells, or presumably with the response to treatments aimed at genetic targets, such as chemotherapy and radiation.
The introduction of induced pluripotent stem (iPS) cell genes was necessary for inducing the expression of immature status-related proteins in gastrointestinal cancer cells, and that the induced pluripotent cancer (iPC) cells were distinct from natural cancer cells with regard to their sensitivity to differentiation inducing treatment. For the complete eradication of cancer, however, future efforts should be directed toward improving translational research.
Cancer metabolism.
Glycolysis is elevated in tumors, but a pyruvate kinase (PK) “bottleneck” interrupts phosphoenol pyruvate (PEP) to pyruvate conversion. Thus, alanine following muscle proteolysis transaminates to pyruvate, feeding lactate dehydrogenase, converting pyruvate to lactate, (Warburg effect) and NAD+ required for glycolysis. Cytosolic malate dehydrogenase also provides NAD+ (in OAA to MAL direction). Malate moves through the shuttle giving back OAA in the mitochondria. Below the PK-bottleneck, pyruvate dehydrogenase (PDH) is phosphorylated (second bottleneck). However, citrate condensation increases: acetyl-CoA, will thus come from fatty acids b-oxydation and lipolysis, while OAA sources are via PEP carboxy kinase, and malate dehydrogenase, (pyruvate carboxylase is inactive). Citrate quits the mitochondria, (note interrupted Krebs cycle). In the cytosol, ATP citrate lyase cleaves citrate into acetyl CoA and OAA.
Acetyl CoA will make fatty acids-triglycerides. Above all, OAA pushes transaminases in a direction usually associated to gluconeogenesis! This consumes protein stores, providing alanine (ALA); like glutamine, it is essential for tumors. The transaminases output is aspartate (ASP) it joins with ASP from the shuttle and feeds ASP transcarbamylase, starting pyrimidine synthesis. ASP in not processed by argininosuccinate synthetase, which is blocked, interrupting the urea cycle.
Arginine gives ornithine via arginase, ornithine is decarboxylated into putrescine by ornithine decarboxylase. Putrescine and SAM form polyamines (spermine spermidine) via SAM decarboxylase. The other product 5-methylthioadenosine provides adenine. Arginine deprivation should affect tumors. The SAM destruction impairs methylations, particularly of PP2A, removing the “signaling kinase brake”, PP2A also fails to dephosphorylate PK and PDH, forming the “bottlenecks”.

Insulin or IGF actions boost the cellular influx of glucose and glycolysis. However, if the signaling pathway gets out of control, the tyrosine kinase phosphorylations may lead to a parallel PK blockade explaining the tumor bottleneck at the end of glycolysis. Since an activation of enyme kinases may indeed block essential enzymes (PK, PDH and others); in principle, the inactivation of phosphatases may also keep these enzymes in a phosphorylated form and lead to a similar bottleneck and we do know that oncogenes bind and affect PP2A phosphatase. In sum, a perturbed MAP kinase pathway, elicits metabolic features that would give to tumor cells their metabolic advantage.

Warburg effect and the prognostic value of stromal caveolin-1 as a marker of a lethal tumor microenvironment
Cancer cells show a broad spectrum of bioenergetic states, with some cells using aerobic glycolysis while others rely on oxidative phosphorylation as their main source of energy. In addition, there is mounting evidence that metabolic coupling occurs in aggressive tumors, between epithelial cancer cells and the stromal compartment, and between well-oxygenated and hypoxic compartments. We recently showed that oxidative stress in the tumor stroma, due to aerobic glycolysis and mitochondrial dysfunction, is important for cancer cell mutagenesis and tumor progression. More specifically, increased autophagy/mitophagy in the tumor stroma drives a form of parasitic epithelial-stromal metabolic coupling. These findings explain why it is effective to treat tumors with either inducers or inhibitors of autophagy, as both would disrupt this energetic coupling. We also discuss evidence that glutamine addiction in cancer cells produces ammonia via oxidative mitochondrial metabolism.

Ammonia production in cancer cells, in turn, could then help maintain autophagy in the tumor stromal compartment. In this vicious cycle, the initial glutamine provided to cancer cells would be produced by autophagy in the tumor stroma. Thus, we believe that parasitic epithelial-stromal metabolic coupling has important implications for cancer diagnosis and therapy, for example, in designing novel metabolic imaging techniques and establishing new targeted therapies. In direct support of this notion, we identified a loss of stromal caveolin-1 as a marker of oxidative stress, hypoxia, and autophagy in the tumor microenvironment, explaining its powerful predictive value. Loss of stromal caveolin-1 in breast cancers is associated with early tumor recurrence, metastasis, and drug resistance, leading to poor clinical outcome.
The conventional ‘Warburg effect’ versus oxidative mitochondrial metabolism
Warburg’s original work indicated that while glucose uptake and lactate production are greatly elevated, a cancer cell’s rate of mitochondrial respiration is similar to that of normal cells. He, however, described it as a ‘respiratory impairment’ due to the fact that, in cancer cells, mitochondrial respiration is smaller, relative to their glycolytic power, but not smaller relative to normal cells. He recognized that oxygen consumption is not diminished in tumor cells, but that respiration is disturbed because glycolysis persists in the presence of oxygen. Unfortunately, the perception of his original findings was simplified over the years, and most subsequent papers validated that cancer cells undergo aerobic glycolysis and produce lactate, but did not measure mitochondrial respiration, and just presumed decreased tricarboxylic acid (TCA) cycle activity and reduced oxidative phosphorylation [1,2]. It is indeed well documented that, as a consequence of intra-tumoral hypoxia, the hypoxia-inducible factor (HIF)1α pathway is activated in many tumors cells, resulting in the direct up-regulation of lactate dehydrogenase (LDH) and increased glucose consumption.
It is now clear that cancer cells utilize both glycolysis and oxidative phosphorylation to satisfy their metabolic needs. Experimental assessments of ATP production in cancer cells have demonstrated that oxidative pathways play a signifi cant role in energy generation, and may be responsible for about 50 to 80% of the ATP generated. several studies now clearly indicate that mitochondrial activity and oxidative phosphorylation support tumor growth. Loss-of-function mutations in the TCA cycle gene IDH1 (isocitrate dehydrogenase 1) are found in about 70% of gliomas, but, interestingly, correlate with a better prognosis and improved survival, suggesting that severely decreased activity in one of the TCA cycle enzymes does not favor tumor aggressiveness. The mitochondrial protein p32 was shown to maintain high levels of oxidative phosphorylation in human cancer cells and to sustain tumorigenicity in vivo. In addition, STAT3 is known to enhance tumor growth and to predict poor prognosis in human cancers. Interestingly, a pool of STAT3 localizes to the mitochondria, to sustain high levels of mitochondrial respiration and to augment transformation by oncogenic Ras. Similarly, the mitochondrial transcription factor A (TFAM), which is required for mitochondrial DNA replication and oxidative phosphorylation, is also required for K-Ras induced lung tumorigenesis.
There is also evidence that pro-oncogenic molecules regulate mitochondrial function. Cyclin D1 inhibits mitochondrial function in breast cancer cells. Overexpression of cyclin D1 is observed in about 50% of invasive breast cancers and is associated with a good clinical outcome, indicating that inhibition of mitochondrial activity correlates with favorable prognosis. Importantly, it was shown that the oncogene c-Myc stimulates mitochondrial biogenesis, and enhances glutamine metabolism by regulating the expression of mitochondrial glutaminase, the first enzyme in the glutamine utilization pathway. Glutamine is an essential metabolic fuel that is converted to alpha-ketoglutarate and serves as a substrate for the TCA cycle or for glutathione synthesis, to promote energy production and cellular biosynthesis, and to protect against oxidative stress. Interestingly, pharmacological targeting of mitochondrial glutaminase inhibits cancer cell transforming activity, suggesting that glutamine metabolism and its role in fueling and replenishing the TCA cycle are required for neoplastic transformation.
Reverse Warburg Effect.
It is increasingly apparent that the tumor microenvironment regulates neoplastic growth and progression. Activation of the stroma is a critical step required for tumor formation. Among the stromal players, cancer associated fi broblasts (CAFs) have recently taken center stage [25]. CAFs are activated, contractile        fibroblasts that display features of myo-fibroblasts, express muscle specific actin, and show an increased ability to secrete and remodel the extracellular matrix. They are not just neutral spectators, but actively support malignant transformation and metastasis, as compared to normal resting fibroblasts.

Importantly, the tumor stroma dictates clinical outcome and constitutes a source of potential biomarkers. Expression profiling has identified a cancer-associated stromal signature that predicts good and poor clinical prognosis in breast cancer patients, independently of other factors.

A loss of caveolin-1 (Cav-1) in the stromal compartment is a novel biomarker for predicting poor clinical outcome in all of the most common subtypes of human breast cancer, including the more lethal triple negative subtype. A loss of stromal Cav-1 predicts early tumor recurrence, lymph node metastasis, tamoxifen-resistance, and poor survival.

Overall, breast cancer patients with a loss of stromal Cav-1show a 20% 5-year survival rate, compared to the 80% 5-year survival of patients with high stromal Cav-1 expression. In triple negative patients, the 5-year survival rate is 75.5% for high stromal Cav-1 versus 9.4% for absent stromal Cav-1. A loss of stromal Cav-1 also predicts progression to invasive disease in ductal carcinoma in situ patients, suggesting that a loss of Cav-1 regulates tumor progression. Similarly, a loss of stromal Cav-1 is associated with advanced disease and metastasis, as well as a high Gleason score, in prostate cancer patients.

The autophagic tumor stroma model of cancer metabolism.
Cancer cells induce oxidative stress in adjacent cancer-associated fibroblasts (CAFs). This activates reactive oxygen species (ROS) production and autophagy. ROS production in CAFs, via the bystander eff ect, serves to induce random mutagenesis in epithelial cancer cells, leading to double-strand DNA breaks and aneuploidy. Cancer cells mount an anti-oxidant defense and upregulate molecules that protect them against ROS and autophagy, preventing them from undergoing apoptosis. So, stromal fibroblasts conveniently feed and mutagenize cancer cells, while protecting them against death. See the text for more details. A+, autophagy positive; A-, autophagy negative; AR, autophagy resistant.

1. Recycled Nutrients
2. Random Mutagenesis
3. Protection Against Apoptosis
The clinical use of PET is well established in Hodgkin’s lymphomas which are composed of less than 10% tumor cells, the rest being stromal and inflammatory cells. Yet, Hodgkin’s lymphomas are very PET avid tumors, suggesting that 2-deoxy-glucose uptake may be associated with the tumor stroma. That the fibrotic component may be glucose avid is further supported by the notion that PET is clinically used to assess the therapeutic response in gastrointestinal stromal tumors (GIST), which are a subset of tumors of mesenchymal origin.
The reverse Warburg effect can be described as ‘metabolic coupling’ between supporting glycolytic stromal cells and oxidative tumor cells. Metabolic cooperativity between adjacent cell-compartments is observed in several normal physiological settings.
The reverse Warburg effect.
Via oxidative stress, cancer cells activate two major transcription factors in adjacent stromal fibroblasts (hypoxia-inducible factor (HIF)1α and NFκB).
This leads to the onset of both autophagy and mitophagy, as well as aerobic glycolysis, which then produces recycled nutrients (such as lactate, ketones, and glutamine).
These high-energy chemical building blocks can then be transferred and used as fuel in the tricarboxylic acid cycle (TCA) in adjacent cancer cells.
The outcome is high ATP production in cancer cells, and protection against cell death. ROS, reactive oxygen species.
The methylation hypothesis and the role of PP2A phosphatase
Diethanolamine decreased choline derivatives and methyl donors in the liver, like seen in a choline deficient diet. Such conditions trigger tumors in mice, particularly in the B6C3F1 strain. Again, the historical perspective recalled by Newberne’s comment brings us back to insulin. Indeed, after the discovery of insulin in 1922, Banting and Best were able to keep alive for several months depancreatized dogs, treated with pure insulin. However, these dogs developed a fatty liver and died. Unlike pure insulin, the total pancreatic extract contained a substance that prevented fatty liver: a lipotropic substance identified later as being choline. Like other lipotropes, (methionine, folate, B12) choline supports transmethylation reactions, of a variety of substrates, that would change their cellular fate, or action, after methylation. In the particular case concerned here, the removal of triglycerides from the liver, as very low-density lipoprotein particles (VLDL), requires the synthesis of lecithin, which might decrease if choline and S-adenosyl methionine (SAM) are missing. Hence, a choline deficient diet decreases the removal of triglycerides from the liver; a fatty liver and tumors may then form. In sum, we have seen that pathways exemplified by the insulin-tyrosine kinase signaling pathway, which control anabolic processes, mitosis, growth and cell death, are at each step targets for oncogenes; we now find that insulin may also provoke fatty liver and cancer, when choline is not associated to insulin.

We know that after the tyrosine kinase reaction, serine-threonine kinases take over along the signaling route. It is thus highly probable that serine-threonine phosphatases will counteract the kinases and limit the intensity of the insulin or insulin like signals. One of the phosphatases involved is PP2A, itself the target of DNA viral oncogenes (Polyoma or SV40 antigens react with PP2A subunits and cause tumors). We found a possible link between the PP2A phosphatase brake and choline. the catalytic C subunit of PP2A is associated to a structural subunit A. When C receives a methyl, the dimer recruits a regulatory subunit B. The trimer then targets specific proteins that are dephosphorylated. choline, via SAM, methylates PP2A, which is targeted toward the serine-threonine kinases that are counteracted along the insulin-signaling pathway.

The choline dependent methylation of PP2A is the brake, the “antidote”, which limits “the poison” resulting from an excess of insulin signaling. Moreover, it seems that choline deficiency is involved in the L to M2 transition of PK isoenzymes. The negative regulation of Ras/MAP kinase signals mediated by PP2A phosphatase seems to be complex. The serine-threonine phosphatase does more than simply counteracting kinases; it binds to the intermediate Shc protein on the signaling cascade, which is inhibited. The targeting of PP2A towards proteins of the signaling pathway depends of the assembly of the different holoenzymes.

The relative decrease of methylated PP2A in the cytosol, not only cancels the brake over the signaling kinases, but also favors the inactivation of PK and PDH, which remain phosphorylated, contributing to the metabolic anomaly of tumor cells. In order to prevent tumors, one should then favor the methylation route rather than the phosphorylation route for choline metabolism. This would decrease triglycerides, promote the methylation of PP2A and keep it in the cytosol, reestablishing the brake over signaling kinases. Moreover, PK, and PDH would become active after the phosphatase action. One would also gain to inhibit their kinases as recently done with dichloroacetate for PDH kinase. The nuclear or cytosolic targeting of PP2A isoforms is a hypothesis also inspired by several works.
Hypoxic adaptations in the presence of oxygen
Through different biochemical and biophysical pathways, which are characteristic to cancer cells, tumor cells adopt this phenotype, i.e., high glycolysis and decreased respiration, in the presence of oxygen. It has been shown that although the induction of hypoxia and cellular proliferation engage entirely different cellular pathways, they often coexist during tumor growth. The ability of cells to grow during hypoxia results, in part, from the crosstalk between hypoxia-inducible factors (Hifs) and the proto-oncogene c-Myc. These genes partially regulate the development of complex adaptations of tumor cells growing in low O2, and contribute to fine tuning the adaptive responses of cells to hypoxic environments.

Hypoxic conditions seem to trigger back the expression of the fetal gene packet via HIF1-Von-Hippel signals. The mechanism would depend of a double switch since not all fetal genes become active after hypoxia. First, the histones have to be in an acetylated form, opening the way to transcription factors, this depends either of histone eacetylase (HDAC) inhibition or of histone acetyltransferase (HAT) activation, and represents the main switch

Growth hormone-IGF actions, the control of asymmetrical mitosis
When IGF – Growth hormone operate, the fatty acid source of acetyl CoA takes over. Indeed, GH stimulates a triglyceride lipase in adipocytes, increasing the release of fatty acids and their b oxidation. In parallel, GH would close the glycolytic source of acetyl CoA, perhaps inhibiting the hexokinase interaction with the mitochondrial ANT site. This effect, which renders apoptosis possible, does not occur in tumor cells. GH mobilizes the fatty acid source of acetyl CoA from adipocytes, which should help the formation of ketone bodies. Since citrate synthase activity is elevated in tumors, ketone bodies do not form. This result silences several genes like PETEN, P53, or methylase inhibitory genes. It is probable that the IGFBP gene gets silent as well.

Uncoupling Proteins in Cancer
Uncoupling proteins (UCPs) are a family of inner mitochondrial membrane proteins whose function is to allow the re-entry of protons to the mitochondrial matrix, by dissipating the proton gradient and, subsequently, decreasing membrane potential and production of reactive oxygen species (ROS). Due to their pivotal role in the intersection between energy efficiency and oxidative stress, UCPs are being investigated for a potential role in cancer.

Mitochondria have been shown to be key players in numerous cellular events tightly related with the biology of cancer. Although energy production relies on the glycolytic pathway in cancer cells, these organelles also participate in many other processes essential for cell survival and proliferation such as ROS production, apoptotic and necrotic cell death, modulation of oxygen concentration, calcium and iron homeostasis, and certain metabolic and biosynthetic pathways. Many of these mitochondrial-dependent processes are altered in cancer cells, leading to a phenotype characterized, among others, by higher oxidative stress, inhibition of apoptosis, enhanced cell proliferation, chemoresistance, induction of angiogenic genes and aggressive fatty acid oxidation. Uncoupling proteins, a family of inner mitochondrial membrane proteins specialized in energy-dissipation, has aroused enormous interest in cancer due to their relevant impact on such processes and their potential for the development of novel therapeutic strategies.
Briefly, oxidation of reduced nutrient molecules, such as carbohydrates, lipids, and proteins, through cellular metabolism yields electrons in the form of reduced hydrogen carriers NADH+ and FADH2. These reduced cofactors donate electrons to a series of protein complexes embedded in the inner mitochondrial membrane known as the electron transport chain (ETC). These complexes use the energy released from electron transport for active pumping of protons across the inner membrane, generating an electrochemical gradient. Mitochondria orchestrate conversions between different forms of energy, coupling aerobic respiration to phosphorylation.
Conversion of metabolic fuel into ATP is not a fully efficient process. Some of the energy of the electrochemical gradient is not coupled to ATP production due to a phenomenon known as proton leak, which consists of the return of protons to the mitochondrial matrix through alternative pathways that bypass ATP synthase. Although this apparently futile cycle of protons is physiologically important, accounting for 20-25% of basal metabolic rate, its function is still a subject of debate. Several different functions have been suggested for proton leak, including thermogenesis, regulation of energy metabolism, and control of body weight and attenuation of reactive oxygen species (ROS) production. Although a part of the proton leak may be attributed to biophysical properties of the inner membrane, such as protein/lipid interfaces, the bulk of the proton conductance is linked to the action of a family of mitochondrial proteins termed uncoupling proteins.

Mitochondria are the major sources of reactive oxygen species (ROS). Aerobic respiration involves the complete reduction of oxygen to water, which is catalysed by complex IV (or cytochrome c oxidase). Nevertheless, during the transfer of electrons along the electron transport complexes, single electrons sometimes escape and result in a single electron reduction of molecular oxygen to form a superoxide anion, which, in turn is the precursor of other ROS.

One of the most interesting functions attributed to UCPs is their ability to decrease the formation of mitochondrial ROS. Mitochondria are the main source of ROS in cells. Superoxide formation is strongly activated under resting (state 4) conditions when the membrane potential is high and the rate of electron transport is limited by lack of ADP and Pi. Thus, there is a well established strong positive correlation between membrane potential and ROS production.
A small increase in membrane potential gives rise to a large stimulation of ROS production, whereas a small decrease in membrane potential (10 mV) is able to inhibit ROS production by 70% . Therefore, mild uncoupling, i.e., a small decrease in membrane potential, has been suggested to have a natural antioxidant effect.

Consistent with such a proposal, the inhibition of UCPs by GDP in mitochondria has been shown to increase membrane potential and mitochondrial ROS production. The loss of UCP2 or UCP3 in knockouts yielded increased ROS production concurrent with elevated membrane potential specifically in those tissues normally expressing the missing protein.
The hypothesis of UCPs as an antioxidant defense has been strongly supported by the fact that these proteins have been shown to be activated by ROS or by-products of lipid peroxidation, showing that UCPs would form part of a negative feed-back mechanism aimed to mitigate excessive ROS production and oxidative damage.
ROS and Cancer
ROS are thought to play multiple roles in tumor initiation, progression and maintenance, eliciting cellular responses that range from proliferation to cell death. In normal cells, ROS play crucial roles in several biological mechanisms including phagocytosis, proliferation, apoptosis, detoxification and other biochemical reactions. Low levels of ROS regulate cellular signaling and play an important role in normal cell proliferation. During initiation of cancer, ROS may cause DNA damage and mutagenesis, while ROS acting as second messengers stimulate proliferation and inhibit apoptosis, conferring growth advantage to established cancer cells. Cancer cells have been found to have increased ROS levels.

One of the functional roles of these elevated ROS levels during tumor progression is constant activation of transcription factors such as NF-kappaB and AP-1 which induce genes that promote proliferation and inhibit apoptosis. In addition, oxidative stress can induce DNA damage which leads to genomic instability and the acquisition of new mutations, which may contribute to cancer progression.

Role of ROS in control of proliferation and apoptosis
ROS are also essential mediators of apoptosis which eliminates cancer and other cells that threaten our health [81–86]. Many chemotherapeutic drugs and radiotherapy are aimed at increasing ROS levels to promote apoptosis by stimulating pro-apoptotic singaling molecules such as ASK1, JNK and p38. Because of the pivotal role of ROS in triggering apoptosis, antioxidants can inhibit this protective mechanism by depleting ROS. Thus, antioxidant mechanisms are thought to interfere with the therapeutic activity of anticancer drugs that kill advanced stage cancer cells by apoptosis.

Effect of uncoupling proteins on proliferation and apoptosis in relation to ROS levels

Uncoupling-to-survive hypothesis (proposed by Brand)

  • the ability of UCP2 to increase lifespan is mediated by decreased ROS production and oxidative stress.
  • the ability of mild uncoupling to avoid ROS formation, gives a reasonable argument to hypothesize about a role for UCPs in cancer prevention

Consistently, Derdák et al. showed that Ucp2−/− mice treated with the carcinogen azoxymethane were found to develop more aberrant crypt foci and colon tumours than Ucp2+/+ in relation with increased oxidative stress and enhanced NF-kappaB activation.

Roles of UCPs in Cancer Progression
The growth of a tumor from a single genetically altered cell is a stepwise progression requiring the alterations of several genes which contribute to the acquisition of a malignant phenotype. Such genetic alterations are positively selected when in the tumor, they confer a proliferative, survival or treatment resistance advantage for the host cell. In addition, several mutations, such as those silencing tumour suppressor genes, trigger the probability of accumulating new mutations, so the process of malignant transformation is progressively self-accelerated.

Considering the ability of UCPs to modulate mutagenic ROS, as well as mitochondrial bioenergetics and membrane potential, both involved in regulation of cell survival, an interesting question is whether UCPs can be involved in the progression of cancer.

Increased uncoupled respiration may be a mechanism to lower cellular oxygen concentration and, thus, alter molecular pathways of oxygen sensing such as those regulated by hypoxia-inducible factor (HIF). In normoxia, the alpha subunit of HIF-1 is a target for prolyl hydroxylase, which makes HIF-1alpha a target for degradation by the proteasome. During hypoxia, prolyl hydroxylase is inhibited since it requires oxygen as a cosubstrate. Thus, hypoxia allows HIF to accumulate and translocate into the nucleus for induction of target genes regulating glycolysis, angiogenesis and hematopoiesis. By this mechanism, UCPs activity may contribute to increase the expression of genes related to the formation of blood vessels, and thus promote tumor growth.

Roles of UCPs in Cancer Energy Metabolism
Lynen and colleagues proposed that the root of the Warburg effect is not in the inability of mitochondria to carry out respiration, but rather would rely on their incapacity to synthesize ATP in response to membrane potential.

The ability of UCPs to uncouple ATP synthesis from respiration and the fact that UCP2 is overexpressed in several chemoresistant cancer cell lines and primary human colon cancers have lead to speculate about the existence of a link between UCPs and the Warburg effect. As mentioned above, uncoupling induced by overexpression of UCP2 has been shown to prevent ROS formation, and, in turn, increase apoptotic threshold in cancer cells, providing a pro-survival advantage and a resistance mechanism to cope with ROS-inducing chemo-therapeutic agents.

Mitochondrial Krebs cycle is one of the sources for these anabolic precursors. The export of these metabolites to cytoplasm for anabolic purposes involves the replenishment of the cycle intermediates by anaplerotic substrates such as pyruvate and glutamate. Thus, glycolysis-derived pyruvate, as well as alpha-ketoglutarate derived from glutaminolysis, may be necessary to sustain anaplerotic reactions. At the same time, to keep Krebs cycle functional, the reduced cofactors NADH and FADH2 would have to be re-oxidized, a function which relies on the mitochondrial respiratory chain. Once again, uncoupling may be crucial for cancer cell mitochondrial metabolism, allowing Krebs cycle to be kept functional to meet the vigorous biosynthetic demand of cancer cells.

Several cancer cells resistant to chemotherapeutics and radiation often exhibit higher rates of fatty acid oxidation and it has been observed that inhibition of fatty acid oxidation potentiates apoptotic death induced by chemotherapeutic agents. These findings are in agreement with the proposed need of fatty acid for the activity of UCPs, suggesting that the lack of these potential substrates or activators would decrease uncoupling activity, subsequently increasing membrane potential, ROS production and therefore lowering apoptotic threshold.

Roles of UCPs in Cancer Cachexia
Cachexia is a wasting syndrome characterized by weakness, weight and fat loss, and muscle atrophy which is often seen in patients with advanced cancer or AIDS. Cachexia has been suggested to be responsible for at least 20 % of cancer deaths and also plays an important part in the compromised immunity leading to death from infection. The imbalance between energy intake and energy expenditure underlying cachexia cannot be reversed nutritionally.

Alterations leading to high energy expenditure, such as excessive proton leak or mitochondrial uncoupling, are likely mechanisms underlying cachexia. In fact, increased expression of UCP1 in BAT and UCP2 and UCP3 in skeletal muscle have been shown in several murine models of cancer cachexia

Roles of UCPs in Chemoresistance

Cancer cells acquire drug resistance as a result of selection pressure dictated by unfavorable microenvironments. Although mild uncoupling may clearly be useful under normal conditions or under severe or chronic metabolic stress such as hypoxia or anoxia, it may be a mechanism to elude oxidative stress-induced apoptosis in advanced cancer cells. Several anti-cancer treatments are based on promotion of ROS formation, to induce cell growth arrest and apoptosis. Thus, increased UCP levels in cancer cells, rather than a marker of oxidative stress, may be a mechanisms conferring anti-apoptotic advantages to the malignant cell, increasing their ability to survive in adverse microenvironments, radiotherapy and chemotherapy. UCPs appear to play a permissive role in tumor cell survival and growth.

Expression of UCPs promote bioenergetics adaptation and cell survival. UCPs appear to be critical to determine the sensitivity of cancer cells to several chemotherapeutic agents and radiotherapy, interfering with the activation of mitochondria driven apoptosis.

From a therapeutic viewpoint, inhibition of glycolysis in UCP2 expressing tumours or specific inhibition of UCP2 are, respectively, attractive strategies to target the specific metabolic signature of cancer cells.

Hypoxia-inducible factor-1 in tumour angiogenesis
HIF-b subunits, is a heterodimeric transcriptional activator. In response to
hypoxia,

  • stimulation of growth factors, and
  • activation of oncogenes as well as carcinogens,

HIF-1a is overexpressed and/or activated and targets those genes which are required for angiogenesis, metabolic adaptation to low oxygen and promotes survival.

Several dozens of putative direct HIF-1 target genes have been identified on the basis of one or more cis-acting hypoxia-response elements that contain an HIF-1 binding site. Activation of HIF-1 in combination with activated signaling pathways and regulators is implicated in tumour progression and prognosis.
In order for a macroscopic tumour to grow, adequate oxygen delivery must be effected via tumor angiogenesis that results from an increased synthesis of angiogenic factors and a decreased synthesis of anti-angiogenic factors. The metabolic adaptation of tumor cells to reduced oxygen availability by increasing glucose transport and glycolysis to promote survival are important consequences in response to hypoxia.

Hypoxia and HIF-1
Hypoxia is one of the major drivers to tumour progression as hypoxic areas form in human tumours when the growth of tumour cells in a given area outstrips local neovascularization, thereby creating areas of inadequate perfusion. Although several transcriptional factors have been reported to be involved
in the response to hypoxic stress such as AP-1, NF-kB and HIF-1, HIF-1 is the most potent inducer of the expression of genes such as those encoding for glycolytic enzymes, VEGF and erythropoietin.

HIF-a subunit exists as at least three isoforms, HIF-1a, HIF-2a and HIF-3a. HIF-1a and HIF-2a can form heterodimers with HIF-b. Although HIF-b subunits are constitutive nuclear proteins, both HIF-1a andHIF-2a subunits are strongly induced by hypoxia in a similar manner. HIF-1a is up-regulated in hypoxic tumour cells and activates the transcription of target genes by binding to cis-acting enhancers, hypoxic responsive element (HRE) close to the promoters of these genes with a result of tumour cellular adaptation to hypoxia and tumour angiogenesis, and promotion of further growth of the primary tumour. Studies have shown HIF-1a to be over-expressed by both tumour cells and such stromal cells as macrophages in many forms of human malignancy.

Regulation of HIF-1
The first regulator of HIF-1 is oxygen. HIF-1α appears to be the HIF-1 subunit regulated by hypoxia. The oxygen sensors in the HIF-1α pathway are two kinds of oxygen dependent hydroxylases. One is prolyl hydroxylase which could hydroxylize the proline residues 402 and 564 at the oxygen dependent domain (ODD) of HIF-1 in the presence of oxygen and iron with a result of HIF-α degradation. The other is hydroxylation of Asn803 at the C-terminal transactivation domain (TAD-C) by FIH-1, which could inhibit the interaction of HIF-1α with co-activator p300 with a subsequent inhibition of HIF-1α transactivity. The hydroxylation of proline 564 at ODD of HIF-1α under normoxia was shown using a novel hydroxylation-specific antibody to detect hydroxylized HIF-1α.

Oncogene comes as the second regulator. Many oncogenes have effects on HIF-1α. Among them, some function in regulation of HIF-1α protein stability or degradation, others play roles in several activated signaling pathways. Tumor suppressor genes as p53 and von Hippel-Lindau (VHL) influence the levels and functions of HIF-1. The wild type (wt) form of p53 protein was involved in inhibiting HIF-1 activity by targeting the HIF-1a subunit for Mdm2-mediated ubiquitination and proteasomal degradation, and in inducing inhibitors of angiogenesis such as thrombospondin-1, while loss of wt p53 (by gene deletion or mutation) could enhance HIF-1α accumulation in hypoxia.

The third regulator is a battery of growth factors and cytokines from stromal and parenchymal cells such as

  • EGF,
  • transforming growth factor-α,
  • insulin-like growth factors 1 and 2,
  • heregulin, and interleukin-1b

via autocrine and paracrine pathways. These regulators not only induce the expression of HIF-1α protein, HIF-1 DNA binding activity and transactivity, but also make HIF-1 target gene expression under normoxia or hypoxia.
The fourth one is a group of reactive oxygen species (ROS) resulting from carcinogens such as Vanadate and Cr (VI) or stimulation of cytokines such as angiotensin and TNFa. However, it seems controversial when it comes to the production of ROS under hypoxia and their individual role in regulation of HIF-1a. It is well known that ROS plays an important role in carcinogenesis induced by a variety of carcinogens.

Signaling Pathways Involved in Regulation of HIF-1α
HIF-1 is a phosphorylated protein and its phosphorylation is involved in HIF-1a subunit expression and/or stabilization as well as in the regulation of HIF-1 transcriptional activity. Three signaling pathways involved in the regulation of HIF-1α have been reported to date.

  • The PI-3k pathway has been mainly and frequently implicated in regulation of HIF-1α protein expression and stability.
  • Akt is also activated by hypoxia. Activated Akt initiates two different pathways in regulation of HIF-1α. The function of these two pathways appears to show consistent impact on HIF-1α activation.
  • Signal transduction pathway in HIF-1α regulation.Oncogenes, growth factors and hypoxia have been documented to regulate HIF-1α protein and increase its transactivity. GSK and mTOR were two target events of Akt and could contribute to decreasing HIF-1α degradation and increasing HIF-1α protein synthesis. Activated ERK1/2 could mainly up-regulate.

HIF-1a, Angiogenesis and Tumour Prognosis
Hypoxia, oncogenes and a variety of growth factors and cytokines increase HIF-1α stability and/or synthesis and transactivation to initiate tumour angiogenesis, metabolic adaptation to hypoxic situation and promote cell survival or anti-apoptosis resulting from a consequence of more than sixty putative direct HIF-1 target gene expressions.

The crucial role of HIF-1 in tumour angiogenesis has sparked scientists and clinical researchers to try their best to understand the whole diagram of HIF-1 so as to find out novel approaches to inhibit HIF-1 overexpression. Indeed, the combination of anti-angiogenic agent and inhibitor of HIF-1 might be particularly efficacious, as the angiogenesis inhibitor would cut off the tumour’s blood supply and HIF-1 inhibitor would reduce the ability of tumour adaptation to hypoxia and suppress the proliferation and promote apoptosis. Screens for small-molecule inhibitors of HIF-1 are underway and several agents that inhibit HIF-1, angiogenesis and xenograft growth have been identified.

Hypoxia, autophagy, and mitophagy in the tumor stroma
Metabolomic profiling reveals that Cav-1(-/-) null mammary fat pads display a highly catabolic metabolism, with the increased release of several metabolites, such as amino acids, ribose and nucleotides, and a shift towards gluconeogenesis, as well as mitochondrial dysfunction. These changes are consistent with increased autophagy, mitophagy and aerobic glycolysis, all processes that are induced by oxidative stress. Autophagy or ‘self-eating’ is the process by which cells degrade their own cellular components to survive during starvation or to eliminate damaged organelles after oxidative stress. Mitophagy, or mitochondrial-autophagy, is particularly important to remove damaged ROS-generating mitochondria.

An autophagy/mitophagy program is also triggered by hypoxia. Hypoxia is a common feature of solid tumors, and promotes cancer progression, invasion and metastasis. Interestingly, via induction of autophagy, hypoxia is sufficient to induce a dramatic loss of Cav-1 in fibroblasts. The hypoxia-induced loss of Cav-1 can be inhibited by the autophagy inhibitor chloroquine, or by pharmacological inhibition of HIF1α. Conversely, small interfering RNA-mediated Cav-1 knock-down is sufficient to induce pseudo-hypoxia, with HIF1α and NFκB activation, and to promote autophagy/mitophagy, as well as a loss of mitochondrial membrane potential in stromal cells. These results indicate that a loss of stromal Cav-1 is a marker of hypoxia and oxidative stress.

In a co-culture model, autophagy in cancer-associated fibroblasts was shown to promote tumor cell survival via the induction of the pro-autophagic HIF1α and NFκB pathways in the tumor stromal microenvironment. Finally, the mitophagy marker Bnip3L is selectively upregulated in the stroma of human breast cancers lacking Cav-1, but is notably absent from the adjacent breast cancer epithelial cells.

Metabolome profiling of several types of human cancer tissues versus corresponding normal tissues have consistently shown that cancer tissues are highly catabolic, with the significant accumulation of many amino acids and TCA cycle metabolites. The levels of reduced glutathione were decreased in primary and metastatic prostate cancers compared to benign adjacent prostate tissue, suggesting that aggressive disease is associated with increased oxidative stress. Also, these data show that the tumor microenvironment has increased oxidative-stress-induced autophagy and increased catabolism.

Taken together, all these findings suggest an integrated model whereby
A loss of stromal Cav-1 induces autophagy/mitophagy in the tumor stroma, via oxidative stress.

This creates a catabolic micro-environment with the local accumulation of chemical building blocks and recycled nutrients (such as amino acids and nucleotides), directly feeding cancer cells to sustain their survival and growth.
This novel idea is termed the ‘autophagic tumor stroma model of cancer’ .
This new paradigm may explain the ‘autophagy paradox’, which is based on the fact that both the systemic inhibition and systemic stimulation of autophagy prevent tumor formation.

What is presented suggests that vectorial energy transfer from the tumor stroma to cancer cells directly sustains tumor growth, and that interruption of such metabolic coupling will block tumor growth. Autophagy inhibitors (such as chloroquine) functionally block the catabolic transfer of metabolites from the stroma to the tumor, inducing cancer cell starvation and death. Conversely, autophagy inducers (such as rapamycin) promote autophagy in tumor cells and induce cell death. Thus, both inhibitors and inducers of autophagy will have a similar effect by severing the metabolic coupling of the stroma and tumor cells, resulting in tumor growth inhibition (cutting ‘off ’ the fuel supply).

This model may also explain why enthusiasm for antiangiogenic therapy has been dampened. In most cases, the clinical benefits are short term, and more importantly, new data suggest an unexpected link between anti-angiogenic treatments and metastasis. In pre-clinical models, anti-vascular endothelial growth factor (anti-VEGF) drugs (sunitinib and anti-VEGFR2 blocking antibodies) were shown to inhibit localized tumor formation, but potently induced relapse and metastasis. Thus, by inducing hypoxia in the tumor microenvironment, antiangiogenic drugs may create a more favorable metastatic niche.
Glutamine, glutaminolysis.
In direct support that cancer cells use mitochondrial oxidative metabolism, many investigators have shown that cancer cells are ‘addicted’ to glutamine. Glutamine is a non-essential amino acid that is metabolized to glutamate and enters the TCA cycle as α-ketoglutarate, resulting in high ATP generation via oxidative phosphorylation. Recent studies also show that ammonia is a by-product of glutaminolysis. In addition, ammonia can act as a diffusible inducer of autophagy. Given these observations, glutamine addiction in cancer cells provides another mechanism for driving and maintaining autophagy in the tumor micro-environment .

In support of this idea, a loss of Cav-1 in the stroma is sufficient to drive autophagy, resulting in increased glutamine production in the tumor micro-environment. Thus, this concept defines a new vicious cycle in which autophagy in the tumor stroma transfers glutamine to cancer cells, and the by-product of this metabolism, ammonia, maintains autophagic glutamine production. This model fits well with the ‘autophagic tumor stroma model of cancer metabolism’, in which energy rich recycled nutrients (lactate, ketones, and glutamine) fuel oxidative mitochondrial metabolism in cancer cells.

Glutamine utilization in cancer cells and the tumor stroma. Oxidative mitochondrial metabolism of glutamine in cancer cells produces ammonia. Ammonia production is sufficient to induce autophagy. Thus, autophagy in cancer-associated fibroblasts provides cancer cells with an abundant source of glutamine. In turn, the ammonia produced maintains the autophagic phenotype of the adjacent stromal fibroblasts.

Lessons from other paradigms

an infectious parasitic cancer cell that metastasizes and captures mitochondrial DNA from host cells
Cancer cells behave like ‘parasites’, by inducing oxidative stress in normal host fibroblasts, resulting in the production of recycled nutrients via autophagy.

This is exactly the same mechanism by which infectious parasites (such as malaria) obtain nutrients and are propagated by inducing oxidative stress and autophagy in host cells. In this regard, malaria is an ‘intracellular’ parasite, while cancer cells may be thought of as ‘extracellular’ parasites. This explains why chloroquine is both an effective antimalarial drug and an effective anti-tumor agent, as it functions as an autophagy inhibitor, cutting off the ‘fuel supply’ in both disease states.

Human cancer cells can ‘steal’ live mitochondria or mitochondrial DNA from adjacent mesenchymal stem cells in culture, which then rescues aerobic glycolysis in these cancer cells. This is known as mitochondrial transfer. Interestingly, metastatic breast cancer cells show the up-regulation of numerous mitochondrial proteins, specifically associated with oxidative phosphorylation, as seen by unbiased proteomic analysis.

Thus, increased mitochondrial oxidative metabolism may be a key driver of tumor cell metastasis. In further support of this argument, treatment of MCF7 cancer cells with lactate is indeed sufficient to induce mitochondrial biogenesis in these cells.

To determine if these findings may be clinically relevant, a lactate-induced gene signature was recently generated using MCF7 cells. This gene signature shows that lactate induces ‘stemness’ in cancer cells, and this lactate induced gene signature predicts poor clinical outcome (including tumor recurrence and metastasis) in breast cancer patients.

REFERENCES

Li W and Zhao Y. “Warburg Effect” and Mitochondrial Metabolism in Skin Cancer. Epidermal Pigmentation, Nucleotide Excision Repair and Risk of Skin Cancer. J Carcinogene Mutagene 2012; S4:002 doi:10.4172/2157-2518.
Seyfried TN, Shelton LM. Cancer as a metabolic disease. Nutrition & Metabolism 2010; 7:7(22 pg). doi:10.1186/1743-7075-7-7
Israël M, Schwartz L. The metabolic advantage of tumor cells. Molecular Cancer 2011, 10:70-82. http://www.molecular-cancer.com/content/10/1/70
Valle A, Oliver J, Roca P. Role of Uncoupling Proteins in Cancer. Cancers 2010, 2, 567-591; doi:10.3390/cancers2020567
Ishii H, Doki Y, Mori M. Perspective beyond Cancer Genomics: Bioenergetics of Cancer Stem Cells. Yonsei Med J 2010; 51(5):617-621. DOI 10.3349/ymj. 2010.51.5.617 pISSN: 0513-5796, eISSN: 1976-2437
Sotgia F, Martinez-Outschoorn, Pavlides S,Howell A . Understanding the Warburg effect and the prognostic value of stromal caveolin-1 as a marker of a lethal tumor microenvironment. Breast Cancer Research 2011, 13:213-26. http://breast-cancer-research.com/content/13/4/213
Yong-Hong Shi, Wei-Gang Fang. Hypoxia-inducible factor-1 in tumour angiogenesis. World J Gastroenterol 2004; 10(8): 1082-1087. http:// wjgnet.com /1007-9327/10/1082.asp

English: Glycolysis pathway overview.

English: Glycolysis pathway overview. (Photo credit: Wikipedia)

Adenosine triphosphate

 

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Warburg Effect, glycolysis, pyruvate kinase, PKM2, PIM2, mtDNA, complex I, NSCLC

Ribeirão Preto Area, Brazil|Government Relations
Current- University, USP-FMRP Physiology – Biochemistry
Previous- Imperial Cancer Research Fund Lab, Instituto de Investigaciones Bioquimicas, Luta armada e CIA
Education – FMRP-USP
While exile interrupted ny graduation in Medicine, started a port grade at Leloir´s Instituto Investigaciones bioquímicas Buenos Aires Argentina Jan 1970 – jan 1972. PhD from 1972- jan 1976 FMRP-USP . Post Doc ICRF London England 1979 -1980

“Those…..whose acquitance with scientific research is derived chiefly from its practical results easily develop a completely false notion of the { scientific } mentality.”

My goal and previous experience besides laboratory work was dedicated to solve this apparent conflict.

When Pasteur did his work studying the chemistry outside yeast-cells, he was able to perceive that in anaerobiosis yeast cells were able to convert sugar at a great velocity to its end products. While the same yeast cells, therefore with the same genome did it at a very slow speed in aerobiosis. Warburg tested tumor cells for the same and found that while normal cells from the organ in which he has found tumors presented a similar metabolic regulatory response to anaerobic/aerobic transition tumor cells did not. Tumos cells continued to display strong acidification (producing great amounts of lactate in the culture media) in aerobiosis.

Tumor cells displayed a failure in this regulatory mechanism that, he O. Warburg, named Pasteur effect. He also noticed that this defect continues from old cancer cells to newer ones. Therefore, for him, it is a genetic defect. Furthermore, as mitochondria generates newer mitochondria in the cells, the genetic component is in the mitochondria that were the site of core metabolism in aerobiosis.

Larry Bernstein
Part of what you describe is in Warburg biography by Hans Krebs (out of print). He also refers to a Meyerhof Quotient to express the degree of metabolic anaerobiosis. I don’t recall a reference to a mitochondrial “genetic” defect. That is farsighted. He did conclude that once the cancer cells were truly anaplastic, metastatic behavior was irreversible. It was only later that another Nobelist who described fatty acid synthesis, I think, concluded that the synthetic process tied up the same aerobic pathway so that anaerobic glycolysis became essential for the cells energetics. You can correct me if I’m in error. Where does the substrate come from? Lean body mass breaks down to provide gluconeogenic precursors. Points of concern are – deamination of branch chain AAs, the splitting of a 6 carbon sugar into 2 3-carbon chains, and the conversion of pyruvate to lactate with the reverse reaction blocked. There is also evidence that there is an impairment in the TCA cycle at the point of fumarase. Then there is never any consideration of the flow of substrates back and forth across the mitochondrial membrane (malate, aspartate), and the redox potentials.

Jose: For reasons independent of my will, the copy of Science,123(3191):309-14,1956 translation of O Warburg original article is not in my hands. Some that do not find any alternative form to respond to my critics concerning molecular biology distortion of biochemistry left on purpose, almost all of my older reprints on the rain. Anyway, O. Warburg refers to mitochondria using the expression of “grana” or “grains” if my recollections are correct. The original work of O Warburg is one of 1924 – Biochemisch ZeiTschrift.,152:51-60.1924. “Weberssert method zur messing der atmung un glycolyse, drese zeitschr.” Other aspects of your interesting comment I will try to comment latter.

By Jose Eduardo de Salles Roselino
Larry Bernstein, not as a correction but , following my line of reasoning about carbono fluxes…It is almost impossible to figure out what was really inside the mind-set of a scientific researcher at the time he has performed his work. Anyway, by the knowledge available at his time, we may conjecture about, even when we acknowledge that, what he may have had in mind at the start could be quite different from what he have latter published from his results.
In case, we try to present the ideas behind Warburg´s works we may take into account the following pre-existing knowledge: Lavoisier (done by 1779-1784) measured very carefully the amount of heat released by respiration and chemical oxidative processes. Reached the conclusion that respiration was slower but essentially similar to carbon combustion by chemical oxidative processes. By early XIX caloric values for gram of sugar, lipids and proteins where made clear. T Schwann recognized that yeast cells convert sugar in ethanol plus a volatile acid (carbon dioxide). Pasteur-effect was seen just as a change in the velocity of product production from a same sugar and/or a decrease in sugar concentration in the growth medium. This is a change in carbon flux velocity in the oxidative process calorimetrically measured by Lavoisier.
In Germany, however, the preponderance of organic chemical point of view has great scientists as Berzelius, Liebig etc. to consider that yeast where similar to inorganic catalysts. The oxidative process was caused by oxygen only. You may amuse yourself reading, how they attack T. Schwann proposal in Annalen, 29: 100 (1839). When O Warburg paid tribute to L. Pasteur, we can see clearly on which side he was. Furthermore, his apparatus, in which I was introduced to this line of research, a rather modern version at that time (1960s) that look like a very futuristic robotic version of the original with a pair of blinking red and green round lights as two eyes on a metallic head, offers a very important clue about the change in carbon flow.
Inside a Warburg glass flask, kept at very finely controlled temperature to avoid changes in pressure derived from changes in the temperature, you would certainly find a central well in which the volatile acid must be trapped in order to determine a pressure reduction only due to the decrease in oxygen pressure. Inside this central well, you could determine one product (carbon dioxide) and in the outside of it where tissues or cells where in the media you could also determine the other end product of the oxidative combustion of sugar (lactate). This has provide him with the result that indicate not only a change in the velocity as originally found by Pasteur in yeast cells but in the organic flow of sugar carbons.

comment –  E-mail: vbungau11@yahoo.com

-About carcinogenesis- Electronegativity is a nucleus of an atom’s ability to attract and maintain a cloud of electrons. Copper atom electronegativity is higher than the Iron atom electronegativity. Atom with lower electronegativity (Iron),remove the atom with higher electronegativity (Copper) of combinations. This means that,in conditions of acidosis, we have cytochrome oxidase with iron (red, neoplastic), instead of cytochrome oxidase with copper (green, normal).I think this is the key to carcinogenesis. Siincerely, Dr. Viorel Bungau

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

Mitochondria are responsible for more than 90% of a cell’s energy production via ATP (adenosine triphosphate) generation, in addition to playing a significant role in respiration and many signaling events within most eukaryotic cells. These intracellular powerhouses range in size and quantity within each cell depending on the organism and overall cell function.

Mitochondria consist of a semi-permeable outer membrane, a thin inter-membrane space where oxidative phosphorylation occurs, an impermeable inner membrane that is intricately folded to create layered compartments—or christae—and the matrix that contains ATP-producing enzymes and the organelle’s own independent genome. Each section has a highly specialized function, and any impairment within the organelle can lead to disease or disorders within the overall organism.

Mitochondrial dysfunction may be due to:

1. Hereditary:

Inherited mitochondrial disorders can play a role in prevalent diseases such as cardiac disease and diabetes, and can also result in rare diseases such as Pearson syndrome or Leigh’s disease.

2. Drug Toxicity:

Mitochondrial toxicity as a result of pharmaceutical use may damage key organs, such as the liver and heart. For example:

nefazodone—a depression treatment—was withdrawn from the U.S. market after it was shown to significantly inhibit mitochondrial respiration in liver cells, leading to liver failure.

Troglitazone, an anti-diabetic and anti-inflammatory, was withdrawn from all markets after research concluded that it caused acute mitochondrial membrane depolarization, also leading to liver failure.

Drug recalls are costly to a manufacturer’s bottom line and reputation, and more importantly, can be harmful or even fatal to users. As drug discovery continues to evolve, much lead compound research now includes careful review of its interaction and potential toxicity with mitochondria.

Cell-based mitochondrial assays in microplate format may include mitochondrial membrane potential, total energy metabolism, oxygen consumption, and metabolic activity; and offer a truer environment for mitochondrial function in the presence of drug compounds compared to isolated mitochondria-based tests. Combining more than one assay in a multiplex format increases the amount of data per well while decreasing data variability arising from running the assays separately. The aggregated data also provides a more encompassing analysis of the drug’s effect on mitochondria than a single test.

One example, when testing compound effects on mitochondria, would be to measure cell membrane integrity as a function of cytotoxicity and mitochondrial function via ATP production concurrently, thus distinguishing between compounds that exhibit mitochondrial toxicity versus overt cytotoxicity.

General cytotoxicity is characterized by a decrease in ATP production and a loss of membrane integrity whereas mitochondrial toxicity results in decreased ATP production with little to no change in membrane integrity.

The assay’s efficiency is further enhanced via automation.

Robotic instrumentation ensures repeatable operation within the microplate wells when performing tasks such as cell dispensing, serial titration and transfer of compounds, and reagent dispensing. Additionally, by automating tasks within the assay process, researchers are free to attend to other tasks, reducing overall active time spent on the assay. Multi-mode microplate readers are compact instruments that can detect both fluorescent and luminescent signals. In addition, an automated process—including liquid handling and detection—can increase throughput capacity compared to manual methods.

Multiplexed cell-based mitochondrial assays increase sample throughput and decrease variability, costs, and overall time for project completion. Automating the process with robotic instrumentation allows for rapid compound profiling, repeatability, further throughput increase, and decreased per-assay and overall project time.

source:

http://www.dddmag.com/articles/2012/08/detecting-potential-toxicity-mitochondria?et_cid=2794933&et_rid=45527476&linkid=http%3a%2f%2fwww.dddmag.com%2farticles%2f2012%2f08%2fdetecting-potential-toxicity-mitochondria

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