Enzyme to Know: Pyruvate Dehydrogenase

“Energy depletion itself is an excitatory state, that calls for increased fuel and oxygen. But when cells are exposed to PUFA, their ability to use glucose is blocked, increasing their exposure to the fats. Saturated fats activate the pyruvate dehydrogenase enzyme that is essential for the efficient use of glucose, while PUFA block it.” -Ray Peat, PhD

“Estrogen impairs the mitochondria in multiple ways, including blocking the function of cytochrome oxidase, decreasing the activity of ATP synthase, increasing heme oxygenase which produces carbon monoxide and free iron, damaging mitochondrial DNA, and shifting metabolism from glucose oxidation to fat oxidation, especially by inhibiting the mitochondrial pyruvate dehydrogenase complex. These changes, including the loss of cytochrome oxidase, are seen in the Alzheimer’s brain. The fact that this kind of energy impairment can be produced by estrogen doesn’t imply that estrogen is the cause, since many other things can cause similar effects–radiation, aluminum, and endotoxin, for example.” -Ray Peat, PhD

Biochim Biophys Acta. 1993 Aug 11;1169(2):126-34.
Dietary polyunsaturated fats suppress the high-sucrose-induced increase of rat liver pyruvate dehydrogenase levels.
Da Silva LA, De Marcucci OL, Kuhnle ZR.
Pyruvate dehydrogenase complex (PDC) has a key role in the regulation of hepatic lipogenesis by dietary factors. We have investigated the effects of dietary carbohydrate and fat on hepatic PDC. Sucrose-based or starch-based diets were administered for 15 days. A positive correlation between PDC activity and the lipogenic potential of the diet was found. A high-sucrose, fat-free diet caused a 3-fold increase in total activity whereas a high-starch, fat-free diet caused a 1.5-fold increase, as compared with chow-fed rats. Dietary polyunsaturated fat (PUF) caused a marked inhibitory effect on total and active PDC; fish oil being more effective than corn oil. Dietary saturated fat (butter) failed to inhibit the sucrose-induced elevation in total activity, but was almost as effective as fish oil in depressing percent active enzyme. Changes in total PDC activity closely correlated with modifications in the content of enzyme quantitated by immunoblotting, indicating that increased enzyme content and not activation is the predominant mechanism underlying the adaptive response to high-sucrose feeding. This response is suppressed by dietary PUF. Inhibition of hepatic lipogenesis by PUF involves a reduction of PDC content as well as that of several lipogenic enzymes. The relevant mechanisms remain to be established.

Biochemistry. 1998 Nov 10;37(45):15835-41.
Selective inactivation of alpha-ketoglutarate dehydrogenase and pyruvate dehydrogenase: reaction of lipoic acid with 4-hydroxy-2-nonenal.
Humphries KM, Szweda LI.
Previous research has established that 4-hydroxy-2-nonenal (HNE), a highly toxic product of lipid peroxidation, is a potent inhibitor of mitochondrial respiration. HNE exerts its effects on respiration by inhibiting alpha-ketoglutarate dehydrogenase (KGDH). Because of the central role of KGDH in metabolism and emerging evidence that free radicals contribute to mitochondrial dysfunction associated with numerous diseases, it is of great interest to further characterize the mechanism of inhibition. In the present study, treatment of rat heart mitochondria with HNE resulted in the selective inhibition of KGDH and pyruvate dehydrogenase (PDH), while other NADH-linked dehydrogenases and electron chain complexes were unaffected. KGDH and PDH are structurally and catalytically similar multienzyme complexes, suggesting a common mode of inhibition. To determine the mechanism of inhibition, the effects of HNE on purified KGDH and PDH were examined. These studies revealed that inactivation by HNE was greatly enhanced in the presence of substrates that reduce the sulfur atoms of lipoic acid covalently bound to the E2 subunits of KGDH and PDH. In addition, loss of enzyme activity induced by HNE correlated closely with a decrease in the availability of lipoic acid sulfhydryl groups. Use of anti-lipoic acid antibodies indicated that HNE modified lipoic acid in both purified enzyme preparations and mitochondria and that this modification was dependent upon the presence of substrates. These results therefore identify a potential mechanism whereby free radical production and subsequent lipid peroxidation lead to specific modification of KGDH and PDH and inhibition of NADH-linked mitochondrial respiration.

The ability of the mitochondria to oxidize pyruvic acid and glucose is characteristically lost to some degree in cancer. When this oxidation fails, the disturbed redox balance of the cell will usually lead to the cell’s death, but if it can survive, this balance favors growth and cell division, rather than differentiated function. This was Otto Warburg’s discovery, that was rejected by official medicine for 75 years. Cancer researchers have become interested in this enzyme system that controls the oxidation of pyruvic acid (and thus sugar) by the mitochondria, since these enzymes are crucially defective in cancer cells (and also in diabetes). The chemical DCA, dichloroacetate, is effective against a variety of cancers, and it acts by reactivating the enzymes that oxidize pyruvic acid. Thyroid hormone, insulin, and fructose also activate these enzymes. These are the enzymes that are inactivated by excessive exposure to fatty acids, and that are involved in the progressive replacement of sugar oxidation by fat oxidation, during stress and aging, and in degenerative diseases; for example, a process that inactivates the energy-producing pyruvate dehydrogenase in Alzheimer’s disease has been identified (Ishiguro, 1998). Niacinamide, by lowering free fatty acids and regulating the redox system, supporting sugar oxidation, is useful in the whole spectrum of metabolic degenerative diseases. -Ray Peat, PhD

J Biol Chem. 2008 Aug 15;283(33):22700-8. Epub 2008 Jun 9.
Pyruvate dehydrogenase complex activity controls metabolic and malignant phenotype in cancer cells.
McFate T, Mohyeldin A, Lu H, Thakar J, Henriques J, Halim ND, Wu H, Schell MJ, Tsang TM, Teahan O, Zhou S, Califano JA, Jeoung NH, Harris RA, Verma A.
High lactate generation and low glucose oxidation, despite normal oxygen conditions, are commonly seen in cancer cells and tumors. Historically known as the Warburg effect, this altered metabolic phenotype has long been correlated with malignant progression and poor clinical outcome. However, the mechanistic relationship between altered glucose metabolism and malignancy remains poorly understood. Here we show that inhibition of pyruvate dehydrogenase complex (PDC) activity contributes to the Warburg metabolic and malignant phenotype in human head and neck squamous cell carcinoma. PDC inhibition occurs via enhanced expression of pyruvate dehydrogenase kinase-1 (PDK-1), which results in inhibitory phosphorylation of the pyruvate dehydrogenase alpha (PDHalpha) subunit. We also demonstrate that PDC inhibition in cancer cells is associated with normoxic stabilization of the malignancy-promoting transcription factor hypoxia-inducible factor-1alpha (HIF-1alpha) by glycolytic metabolites. Knockdown of PDK-1 via short hairpin RNA lowers PDHalpha phosphorylation, restores PDC activity, reverts the Warburg metabolic phenotype, decreases normoxic HIF-1alpha expression, lowers hypoxic cell survival, decreases invasiveness, and inhibits tumor growth. PDK-1 is an HIF-1-regulated gene, and these data suggest that the buildup of glycolytic metabolites, resulting from high PDK-1 expression, may in turn promote HIF-1 activation, thus sustaining a feed-forward loop for malignant progression. In addition to providing anabolic support for cancer cells, altered fuel metabolism thus supports a malignant phenotype. Correction of metabolic abnormalities offers unique opportunities for cancer treatment and may potentially synergize with other cancer therapies.

Rinsho Byori. 1998 Oct;46(10):1003-7.
[Involvement of tau protein kinase in amyloid-beta-induced neurodegeneration].
[Article in Japanese]
Ishiguro K.
Histopathological features of Alzheimer’s disease (AD) include extracellular deposits of amyloid beta (A beta) fibrils in the cores of senile plaques, intracellular neurofibrillary tangles (NFT) which are composed of paired helical filaments (PHF), and neuronal cell loss. The main component of PHF is highly phosphorylated tau protein. We identified a protein kinase converting normal tau into a PHF-like state. The kinase is tau protein kinase (TPK) I/glycogen synthase kinase (GSK)-3 beta. Using a neuronal cell culture system as an AD model, it was recognized that TPK I/GSK-3 beta plays a central role in AD pathology. We hypothesize that A beta-induced neuronal cell death occurs by the following mechanism. A beta inactivates PI3-kinase and activates TPK I/GSK-3 beta, which in turn phosphorylates and inactivates both tau and pyruvate dehydrogenase (PDH). After the ability of tau to promote microtubule assembly is diminished by phosphorylation, soluble tau molecules aggregate into PHF by an unknown mechanism. Destabilization of microtubule arrays causes inhibition of axonal transport and accumulation of amyloid precursor protein (APP). Phosphorylation of PDH inhibits the reaction converting pyruvate to acetyl-CoA, resulting in inhibition of energy metabolism and a decrease in acetylcholine, both of which are also characteristics of AD. These changes may lead to neuronal cell death.

Otto Warburg established that lactic acid production even in the presence of oxygen is a fundamental property of cancer. It is, to a great degree, the lactic acid which triggers the defensive reactions of the organism, leading to tissue wasting from excessive glucocorticoid hormone. The cancer’s production of lactic acid creates the same kind of internal imbalance produced by hyperventilation, and if we look at the physiology of hyperventilation in the light of Warburg’s description of cancer, hyperventilation imitates cancer metabolism, by producing lactic acid “even in the presence of oxygen.” Lactate, a supposedly benign metabolite of the cancer cells, which appears in all the other degenerative conditions, including obesity, diabetes, Alzheimer’s disease, multiple sclerosis, is itself a factor in the degenerative process. -Ray Peat, PhD

Lactic acid itself, and the longer chain fatty acids, inhibit the regulatory enzyme pyruvate dehydrogenase (which is activated by insulin), reducing the oxidative production of energy. Drugs to activate this enzyme are being studied by the pharmaceutical industry as treatments for diabetes and cancer. (for example, DCA, dichloroacetate). -Ray Peat, PhD

Nihon Geka Gakkai Zasshi. 1996 Sep;97(9):726-32.
[Energy substrate metabolism during stress].
[Article in Japanese]
Sugimoto H.
Energy substrate metabolism during stress is characterized by increased REE (resting energy expenditure), hyperglycemia, hyperlactatemia and protein catabolism. This stress-induced hypermetabolic responses are closely related to increased secretion of neurohormonal and cytokine mediators. The insulin resistance hyperglycemia has been called “stress diabetes” or “surgical diabetes”. Glucose disposal has been thought to be impaired in this condition. However, glucose uptake in most tissue is non-insulin mediated. Recent studies showed glucose uptake elevated in sepsis or TNF infusion. Insulin-regulatable glucose transporter (GLUT4) is present only in muscle, heart and adipose tissues. It was demonstrated that insulin binding to membrane receptors in these tissues was intact. This hyperglycemia in stress diabetes results from a postreceptor mechanism. Stress hyperlactatemia is thought to be caused by decreased pyruvate dehydrogenase activity rather than tissue hypoperfusion. Hyperlactatemia may promote gluconeogenesis. Glucose is a essential energy substrate in some tissues such as brain, erythrocyte and leukocyte. Hyperglycemia may be viewed as a beneficial response during stress.

J Appl Physiol. 2008 Jan;104(1):1-9. Epub 2007 Oct 18.
The acute effects of differential dietary fatty acids on human skeletal muscle pyruvate dehydrogenase activity.
Bradley NS, Heigenhauser GJ, Roy BD, Staples EM, Inglis JG, LeBlanc PJ, Peters SJ.
Pyruvate dehydrogenase (PDH) is an important regulator of carbohydrate oxidation during exercise, and its activity can be downregulated by an increase in dietary fat. The purpose of this study was to determine the acute metabolic effects of differential dietary fatty acids on the activation of the PDH complex (PDHa activity) at rest and at the onset of moderate-intensity exercise. University-aged male subjects (n = 7) underwent two fat-loading trials spaced at least 2 wk apart. Subjects consumed approximately 300 g saturated (SFA) or n-6 polyunsaturated fatty acid (PUFA) fat over the course of 5 h. Following this, participants cycled at 65% of their maximum oxygen uptake for 15 min. Muscle biopsies were taken before and following fat loading and at 1 min exercise. Plasma free fatty acids increased from 0.15 +/- 0.07 to 0.54 +/- 0.19 mM over 5 h with SFA and from 0.11 +/- 0.04 to 0.35 +/- 0.13 mM with n-6 PUFA and were significantly lower throughout the n-6 PUFA trial. PDHa activity was unchanged following fat loading but increased at the onset of exercise in the SFA trial, from 1.18 +/- 0.27 to 2.16 +/- 0.37 mmol x min(-1) x kg wet wt(-1). This effect was negated in the n-6 PUFA trial (1.04 +/- 0.20 to 1.28 +/- 0.36 mmol x min(-1) x kg wet wt(-1)). PDH kinase was unchanged in both trials, suggesting that the attenuation of PDHa activity with n-6 PUFA was a result of changes in the concentrations of intramitochondrial effectors, potentially intramitochondrial NADH or Ca(2+). Our findings suggest that attenuated PDHa activity contributes to the preferential oxidation of n-6 PUFA during moderate-intensity exercise.

PLoS One. 2013 Oct 7;8(10):e77280. doi: 10.1371/journal.pone.0077280. eCollection 2013.
Rapid Inhibition of Pyruvate Dehydrogenase: An Initiating Event in High Dietary Fat-Induced Loss of Metabolic Flexibility in the Heart
Clair Crewe, Michael Kinter, Luke I. Szweda
Cardiac function depends on the ability to switch between fatty acid and glucose oxidation for energy production in response to changes in substrate availability and energetic stress. In obese and diabetic individuals, increased reliance on fatty acids and reduced metabolic flexibility are thought to contribute to the development of cardiovascular disease. Mechanisms by which cardiac mitochondria contribute to diet-induced metabolic inflexibility were investigated. Mice were fed a high fat or low fat diet for 1 d, 1 wk, and 20 wk. Cardiac mitochondria isolated from mice fed a high fat diet displayed a diminished ability to utilize the glycolytically derived substrate pyruvate. This response was rapid, occurring within the first day on the diet, and persisted for up to 20 wk. A selective increase in the expression of pyruvate dehydrogenase kinase 4 and inhibition of pyruvate dehydrogenase are responsible for the rapid suppression of pyruvate utilization. An important consequence is that pyruvate dehydrogenase is sensitized to inhibition when mitochondria respire in the presence of fatty acids. Additionally, increased expression of pyruvate dehydrogenase kinase 4 preceded any observed diet-induced reductions in the levels of glucose transporter type 4 and glycolytic enzymes and, as judged by Akt phosphorylation, insulin signaling. Importantly, diminished insulin signaling evident at 1 wk on the high fat diet did not occur in pyruvate dehydrogenase kinase 4 knockout mice. Dietary intervention leads to a rapid decline in pyruvate dehydrogenase kinase 4 levels and recovery of pyruvate dehydrogenase activity indicating an additional form of regulation. Finally, an overnight fast elicits a metabolic response similar to that induced by high dietary fat obscuring diet-induced metabolic changes. Thus, our data indicate that diet-induced inhibition of pyruvate dehydrogenase may be an initiating event in decreased oxidation of glucose and increased reliance of the heart on fatty acids for energy production.

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