The importance of pyruvate availability to PDC  activation and anaplerosis in human skeletal muscle

No studies have singularly investigated the relationship between pyruvate availability, pyruvate dehydrogenase complex (PDC) activation, and anaplerosis in skeletal muscle. This is surprising given the functional importance attributed to these processes in normal and disease states. We investigated the effects of changing pyruvate availability with dichloroacetate (DCA), epinephrine, and pyruvate infusions on PDC activation and accumulation of acetyl groups and tricarboxylic acid (TCA) cycle intermediates (TCAI) in human muscle. DCA increased resting PDC activity sixfold ( P < 0.05) but decreased the muscle TCAI pool (mmol/kg dry muscle) from 1.174 ± 0.042 to 0.747 ± 0.055 ( P < 0.05). This was probably a result of pyruvate being diverted to acetyl-CoA and acetylcarnitine after near-maximal activation of PDC by DCA. Conversely, neither epinephrine nor pyruvate activated PDC. However, both increased the TCAI pool (1.128 ± 0.076 to 1.614 ± 0.188, P < 0.05 and 1.098 ± 0.059 to 1.385 ± 0.114, P < 0.05, respectively) by providing a readily available pool of pyruvate for anaplerosis. These data support the hypothesis that TCAI pool expansion is principally a reflection of increased muscle pyruvate availability and, together with our previous work (J. A. Timmons, S. M. Poucher, D. Constantin-Teodosiu, V. Worrall, I. A. Macdonald, and P. L. Greenhaff. J. Clin. Invest. 97: 879–883, 1996), indicate that TCA cycle expansion may be of little functional significance to TCA cycle flux. It would appear therefore that the primary effect of DCA on oxidative ATP provision is to provide a readily available pool of acetyl groups to the TCA cycle at the onset of exercise rather than increasing TCA cycle flux by expanding the TCAI pool.

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Evidence for reverse flux through pyruvate kinase in skeletal muscle

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.90935.2008 ◽

2009 ◽

Vol 296 (4) ◽

pp. E748-E757 ◽

Cited By ~ 8

Author(s):

Eunsook S. Jin ◽

A. Dean Sherry ◽

Craig R. Malloy

Keyword(s):

Skeletal Muscle ◽

Glucose Production ◽

Tca Cycle ◽

Hepatic Glycogen ◽

Direct Transfer ◽

The Tca Cycle ◽

Tca Cycle Intermediates ◽

Minced Muscle ◽

Labeling Pattern

Conversion of lactate to glucose was examined in myotubes, minced muscle tissue, and rats exposed to 2H2O or 13C-enriched substrates. Myotubes or minced skeletal muscle incubated with [U-13C3]lactate released small amounts of [1,2,3-13C3]- or [4,5,6-13C3]glucose. This labeling pattern is consistent with direct transfer from lactate to glucose without randomization in the tricarboxylic acid (TCA) cycle. After exposure of incubated muscle to 2H2O, [U-13C3]lactate, glucose, and glutamine, there was minimal release of synthesized glucose to the medium based on a low level of 2H enrichment in medium glucose but 50- to 100-fold greater 2H enrichment in glucosyl units from glycogen. The 13C enrichment pattern in glycogen from incubated skeletal muscle was consistent only with direct transfer of lactate to glucose without exchange in TCA cycle intermediates. 13C nuclear magnetic resonance (NMR) spectra of glutamate from the same tissue showed flux from lactate through pyruvate dehydrogenase but not flux through pyruvate carboxylase into the TCA cycle. Carbon from an alternative substrate for glucose production that requires metabolism through the TCA cycle, propionate, did not enter glycogen, suggesting that TCA cycle intermediates do not exchange with phospho enolpyruvate. In vivo, the 13C labeling patterns in hepatic glycogen and plasma glucose after administration of [U-13C3]lactate did not differ significantly. However, skeletal muscle glycogen was substantially enriched in [1,2,3-13C3]- and [4,5,6-13C3]glucose units that could only occur through skeletal muscle glyconeogenesis rather than glycogenesis. Lactate serves as a substrate for glyconeogenesis in vivo without exchange into symmetric intermediates of the TCA cycle.

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Tricarboxylic acid cycle intermediate pool size and estimated cycle flux in human muscle during exercise

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.1998.275.2.e235 ◽

1998 ◽

Vol 275 (2) ◽

pp. E235-E242 ◽

Cited By ~ 37

Author(s):

Martin J. Gibala ◽

Dave A. MacLean ◽

Terry E. Graham ◽

Bengt Saltin

Keyword(s):

Skeletal Muscle ◽

Maximal Exercise ◽

Tricarboxylic Acid Cycle ◽

Tca Cycle ◽

Tricarboxylic Acid ◽

Pool Size ◽

Intense Exercise ◽

The Tca Cycle ◽

Small Change ◽

The Relationship

We examined the relationship between tricarboxylic acid (TCA) cycle intermediate (TCAI) pool size, TCA cycle flux (calculated from leg O2uptake), and pyruvate dehydrogenase activity (PDHa) in human skeletal muscle. Six males performed moderate leg extensor exercise for 10 min, followed immediately by intense exercise until exhaustion (3.8 ± 0.5 min). The sum of seven measured TCAI (ΣTCAI) increased ( P ≤ 0.05) from 1.39 ± 0.11 at rest to 2.88 ± 0.31 after 10 min and to 5.38 ± 0.31 mmol/kg dry wt at exhaustion. TCA cycle flux increased ∼70-fold during submaximal exercise and was ∼100-fold higher than rest at exhaustion. PDHa corresponded to 77 and 90% of TCA cycle flux during submaximal and maximal exercise, respectively. The present data demonstrate that a tremendous increase in TCA cycle flux can occur in skeletal muscle despite a relatively small change in TCAI pool size. It is suggested that the increase in ΣTCAI during exercise may primarily reflect an imbalance between the rate of pyruvate production and its rate of oxidation in the TCA cycle.

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Acetyl-CoA provision and the acetyl group deficit at the onset of contraction in ischemic canine skeletal muscle

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.00441.2003 ◽

2005 ◽

Vol 288 (2) ◽

pp. E327-E334 ◽

Cited By ~ 14

Author(s):

Paul A. Roberts ◽

Susan J. G. Loxham ◽

Simon M. Poucher ◽

Dumitru Constantin-Teodosiu ◽

Paul L. Greenhaff

Keyword(s):

Skeletal Muscle ◽

Energy Production ◽

Pyruvate Dehydrogenase Complex ◽

Tca Cycle ◽

Treated Group ◽

Acetyl Coa ◽

Tension Development ◽

The Tca Cycle ◽

Work Transition ◽

Acetyl Group

We examined the effects of increasing acetylcarnitine and acetyl-CoA availability at rest, independent of pyruvate dehydrogenase complex (PDC) activation, on energy production and tension development during the rest-to-work transition in canine skeletal muscle. We aimed to elucidate whether the lag in PDC-derived acetyl-CoA delivery toward the TCA cycle at the onset of exercise can be overcome by increasing acetyl group availability independently of PDC activation or is intimately dependent on PDC-derived acetyl-CoA. Gracilis muscle pretreated with saline or sodium acetate (360 mg/kg body mass) (both n = 6) was sampled repeatedly during 5 min of ischemic contraction. Acetate increased acetylcarnitine and acetyl-CoA availability (both P < 0.01) above control at rest and throughout contraction ( P < 0.05), independently of differences in resting PDC activation between treatments. Acetate reduced oxygen-independent ATP resynthesis ∼40% ( P < 0.05) during the first minute of contraction. No difference in oxygen-independent ATP resynthesis existed between treatments from 1 to 3 min of contraction; however, energy production via this route increased ∼25% ( P < 0.05) above control in the acetate-treated group during the final 2 min of contraction. Tension development was ∼20% greater after 5-min contraction after acetate treatment than in control ( P < 0.05). In conclusion, at the immediate onset of contraction, when PDC was largely inactive, increasing cellular acetyl group availability overcame inertia in mitochondrial ATP regeneration. However, after the first minute, when PDC was near maximally activated in both groups, it appears that PDC-derived acetyl-CoA, rather than increased cellular acetyl group availability per se, dictated mitochondrial ATP resynthesis.

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The Metabolic Fates of Pyruvate in Normal and Neoplastic Cells

Cells ◽

10.3390/cells10040762 ◽

2021 ◽

Vol 10 (4) ◽

pp. 762

Author(s):

Edward V. Prochownik ◽

Huabo Wang

Keyword(s):

Metabolic Pathways ◽

Redox State ◽

Pyruvate Dehydrogenase Complex ◽

Tca Cycle ◽

Vascular Supply ◽

Extrinsic Factors ◽

The Tca Cycle ◽

Initial Substrate ◽

Numerous Cell ◽

Bio Synthesis

Pyruvate occupies a central metabolic node by virtue of its position at the crossroads of glycolysis and the tricarboxylic acid (TCA) cycle and its production and fate being governed by numerous cell-intrinsic and extrinsic factors. The former includes the cell’s type, redox state, ATP content, metabolic requirements and the activities of other metabolic pathways. The latter include the extracellular oxygen concentration, pH and nutrient levels, which are in turn governed by the vascular supply. Within this context, we discuss the six pathways that influence pyruvate content and utilization: 1. The lactate dehydrogenase pathway that either converts excess pyruvate to lactate or that regenerates pyruvate from lactate for use as a fuel or biosynthetic substrate; 2. The alanine pathway that generates alanine and other amino acids; 3. The pyruvate dehydrogenase complex pathway that provides acetyl-CoA, the TCA cycle’s initial substrate; 4. The pyruvate carboxylase reaction that anaplerotically supplies oxaloacetate; 5. The malic enzyme pathway that also links glycolysis and the TCA cycle and generates NADPH to support lipid bio-synthesis; and 6. The acetate bio-synthetic pathway that converts pyruvate directly to acetate. The review discusses the mechanisms controlling these pathways, how they cross-talk and how they cooperate and are regulated to maximize growth and achieve metabolic and energetic harmony.

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Differential and shared effects of eicosapentaenoic acid and docosahexaenoic acid on serum metabolome in subjects with chronic inflammation

Scientific Reports ◽

10.1038/s41598-021-95590-7 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Wan-Chi Chang ◽

Jisun So ◽

Stefania Lamon-Fava

Keyword(s):

Metabolic Syndrome ◽

Docosahexaenoic Acid ◽

Eicosapentaenoic Acid ◽

Chronic Inflammation ◽

Cell Function ◽

Tca Cycle ◽

Differential Effects ◽

Epa And Dha ◽

The Tca Cycle ◽

Tca Cycle Intermediates

AbstractThe omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) affect cell function and metabolism, but the differential effects of EPA and DHA are not known. In a randomized, controlled, double-blind, crossover study, we assessed the effects of 10-week supplementation with EPA-only and DHA-only (3 g/d), relative to a 4-week lead-in phase of high oleic acid sunflower oil (3 g/day, defined as baseline), on fasting serum metabolites in 21 subjects (9 men and 12 post-menopausal women) with chronic inflammation and some characteristics of metabolic syndrome. Relative to baseline, EPA significantly lowered the tricarboxylic acid (TCA) cycle intermediates fumarate and α-ketoglutarate and increased glucuronate, UDP-glucuronate, and non-esterified DHA. DHA significantly lowered the TCA cycle intermediates pyruvate, citrate, isocitrate, fumarate, α-ketoglutarate, and malate, and increased succinate and glucuronate. Pathway analysis showed that both EPA and DHA significantly affected the TCA cycle, the interconversion of pentose and glucuronate, and alanine, and aspartate and glutamate pathways (FDR < 0.05) and that DHA had a significantly greater effect on the TCA cycle than EPA. Our results indicate that EPA and DHA exhibit both common and differential effects on cell metabolism in subjects with chronic inflammation and some key aspects of metabolic syndrome.

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Glutamate availability is important in intramuscular amino acid metabolism and TCA cycle intermediates but does not affect peak oxidative metabolism

Journal of Applied Physiology ◽

10.1152/japplphysiol.90394.2008 ◽

2008 ◽

Vol 105 (2) ◽

pp. 547-554 ◽

Cited By ~ 8

Author(s):

M. Mourtzakis ◽

T. E. Graham ◽

J. González-Alonso ◽

B. Saltin

Keyword(s):

Oxidative Metabolism ◽

Acid Metabolism ◽

Glutamate Uptake ◽

Knee Extensor ◽

Tca Cycle ◽

Peak Oxygen Consumption ◽

Peak Exercise ◽

Early Exercise ◽

The Tca Cycle ◽

Tca Cycle Intermediates

Muscle glutamate is central to reactions producing 2-oxoglutarate, a tricarboxylic acid (TCA) cycle intermediate that essentially expands the TCA cycle intermediate pool during exercise. Paradoxically, muscle glutamate drops ∼40–80% with the onset of exercise and 2-oxoglutarate declines in early exercise. To investigate the physiological relationship between glutamate, oxidative metabolism, and TCA cycle intermediates (i.e., fumarate, malate, 2-oxoglutarate), healthy subjects trained (T) the quadriceps of one thigh on the single-legged knee extensor ergometer (1 h/day at 70% maximum workload for 5 days/wk), while their contralateral quadriceps remained untrained (UT). After 5 wk of training, peak oxygen consumption (V̇o2peak) in the T thigh was greater than that in the UT thigh ( P < 0.05); V̇o2peak was not different between the T and UT thighs with glutamate infusion. Peak exercise under control conditions revealed a greater glutamate uptake in the T thigh compared with rest (7.3 ± 3.7 vs. 1.0 ± 0.1 μmol·min−1·kg wet wt−1, P < 0.05) without increase in TCA cycle intermediates. In the UT thigh, peak exercise (vs. rest) induced an increase in fumarate (0.33 ± 0.07 vs. 0.02 ± 0.01 mmol/kg dry wt (dw), P < 0.05) and malate (2.2 ± 0.4 vs. 0.5 ± 0.03 mmol/kg dw, P < 0.05) and a decrease in 2-oxoglutarate (12.2 ± 1.6 vs. 32.4 ± 6.8 μmol/kg dw, P < 0.05). Overall, glutamate infusion increased arterial glutamate ( P < 0.05) and maintained this increase. Glutamate infusion coincided with elevated fumarate and malate ( P < 0.05) and decreased 2-oxoglutarate ( P < 0.05) at peak exercise relative to rest in the T thigh; there were no further changes in the UT thigh. Although glutamate may have a role in the expansion of the TCA cycle, glutamate and TCA cycle intermediates do not directly affect V̇o2peak in either trained or untrained muscle.

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Tricarboxylic acid cycle intermediates in human muscle at rest and during prolonged cycling

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.1997.272.2.e239 ◽

1997 ◽

Vol 272 (2) ◽

pp. E239-E244 ◽

Cited By ~ 16

Author(s):

M. J. Gibala ◽

M. A. Tarnopolsky ◽

T. E. Graham

Keyword(s):

Fiber Type ◽

Tricarboxylic Acid Cycle ◽

Vastus Lateralis ◽

Tca Cycle ◽

Tricarboxylic Acid ◽

Human Muscle ◽

Pool Size ◽

Recruitment Pattern ◽

Total Pool ◽

Tca Cycle Intermediates

Previous studies have used the muscle concentration of citrate + malate + fumarate to estimate tricarboxylic acid (TCA) cycle pool size in humans [e.g., Am. J. Physiol. 259 (Cell Physiol. 28): C834-C841, 1990]. Our purpose was to quantify changes in individual TCA cycle intermediates (TCAI) and total pool size by measuring the concentrations of the eight TCAI in human muscle. Eight males cycled to exhaustion (Exh) at approximately 70% of their maximal oxygen uptake, and biopsies were obtained from the vastus lateralis at rest and during exercise. Succinyl-CoA was not consistently detectable, but the sum of the other seven TCAI was 1.23 +/- 0.04 mmol/kg dry wt at rest, 4.80 +/- 0.25 and 4.87 +/- 0.30 mmol/kg after 5 and 15 min of exercise, respectively, and 3.08 +/- 0.15 mmol/kg at Exh. Pool size during exercise was approximately 50% higher than that seen in rodent muscle after intense electrical stimulation (Eur. J. Biochem. 110: 371-377, 1980). Relative changes in individual TCAI were not uniform, and no one intermediate was "representative" of the changes in total pool size. We conclude that changes in specific intermediates or total pool size cannot be used as indicators of cycle flux and that the apparent species differences in total pool size may reflect differences in fiber type composition, recruitment pattern, or relative intensity of contraction.

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Targeting Altered Energy Metabolism in Colorectal Cancer: Oncogenic Reprogramming, the Central Role of the TCA Cycle and Therapeutic Opportunities

Cancers ◽

10.3390/cancers12071731 ◽

2020 ◽

Vol 12 (7) ◽

pp. 1731 ◽

Cited By ~ 1

Author(s):

Carina Neitzel ◽

Philipp Demuth ◽

Simon Wittmann ◽

Jörg Fahrer

Keyword(s):

Colorectal Cancer ◽

Energy Metabolism ◽

Pyruvate Dehydrogenase ◽

Pyruvate Dehydrogenase Complex ◽

Tca Cycle ◽

Dietary Factors ◽

Pyruvate Dehydrogenase Kinase ◽

Driver Mutations ◽

The Tca Cycle

Colorectal cancer (CRC) is among the most frequent cancer entities worldwide. Multiple factors are causally associated with CRC development, such as genetic and epigenetic alterations, inflammatory bowel disease, lifestyle and dietary factors. During malignant transformation, the cellular energy metabolism is reprogrammed in order to promote cancer cell growth and proliferation. In this review, we first describe the main alterations of the energy metabolism found in CRC, revealing the critical impact of oncogenic signaling and driver mutations in key metabolic enzymes. Then, the central role of mitochondria and the tricarboxylic acid (TCA) cycle in this process is highlighted, also considering the metabolic crosstalk between tumor and stromal cells in the tumor microenvironment. The identified cancer-specific metabolic transformations provided new therapeutic targets for the development of small molecule inhibitors. Promising agents are in clinical trials and are directed against enzymes of the TCA cycle, including isocitrate dehydrogenase, pyruvate dehydrogenase kinase, pyruvate dehydrogenase complex (PDC) and α-ketoglutarate dehydrogenase (KGDH). Finally, we focus on the α-lipoic acid derivative CPI-613, an inhibitor of both PDC and KGDH, and delineate its anti-tumor effects for targeted therapy.

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Ammonia inhibits energy metabolism in astrocytes in a rapid and glutamate dehydrogenase 2-dependent manner

Disease Models & Mechanisms ◽

10.1242/dmm.047134 ◽

2020 ◽

Vol 13 (10) ◽

pp. dmm047134

Author(s):

Leonie Drews ◽

Marcel Zimmermann ◽

Philipp Westhoff ◽

Dominik Brilhaus ◽

Rebecca E. Poss ◽

...

Keyword(s):

Amino Acids ◽

Energy Metabolism ◽

Glutamate Dehydrogenase ◽

Mitochondrial Respiration ◽

Tca Cycle ◽

Dependent Manner ◽

Independent Manner ◽

The Tca Cycle ◽

Branched Chain ◽

Tca Cycle Intermediates

ABSTRACTAstrocyte dysfunction is a primary factor in hepatic encephalopathy (HE) impairing neuronal activity under hyperammonemia. In particular, the early events causing ammonia-induced toxicity to astrocytes are not well understood. Using established cellular HE models, we show that mitochondria rapidly undergo fragmentation in a reversible manner upon hyperammonemia. Further, in our analyses, within a timescale of minutes, mitochondrial respiration and glycolysis were hampered, which occurred in a pH-independent manner. Using metabolomics, an accumulation of glucose and numerous amino acids, including branched chain amino acids, was observed. Metabolomic tracking of 15N-labeled ammonia showed rapid incorporation of 15N into glutamate and glutamate-derived amino acids. Downregulating human GLUD2 [encoding mitochondrial glutamate dehydrogenase 2 (GDH2)], inhibiting GDH2 activity by SIRT4 overexpression, and supplementing cells with glutamate or glutamine alleviated ammonia-induced inhibition of mitochondrial respiration. Metabolomic tracking of 13C-glutamine showed that hyperammonemia can inhibit anaplerosis of tricarboxylic acid (TCA) cycle intermediates. Contrary to its classical anaplerotic role, we show that, under hyperammonemia, GDH2 catalyzes the removal of ammonia by reductive amination of α-ketoglutarate, which efficiently and rapidly inhibits the TCA cycle. Overall, we propose a critical GDH2-dependent mechanism in HE models that helps to remove ammonia, but also impairs energy metabolism in mitochondria rapidly.

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Tricarboxylic Acid (TCA) Cycle Intermediates: Regulators of Immune Responses

10.20944/preprints202012.0810.v1 ◽

2020 ◽

Author(s):

Inseok Choi ◽

Hyewon Son ◽

Jea-Hyun Baek

Keyword(s):

Immune Responses ◽

Molecular Mechanisms ◽

Tricarboxylic Acid Cycle ◽

Tca Cycle ◽

Tricarboxylic Acid ◽

Cell Stress ◽

Danger Signals ◽

Cellular Processes ◽

The Tca Cycle ◽

Tca Cycle Intermediates

Tricarboxylic acid cycle (TCA) is a series of chemical reactions in aerobic organisms used to generate energy via the oxidation of acetyl-CoA derived from carbohydrates, fatty acids, and proteins. In the eukaryotic system, the TCA cycle completely occurs in mitochondria, while the intermediates of the TCA cycle are retained in mitochondria due to their polarity and hydrophilicity. Under conditions of cell stress, mitochondria become disrupted and release their contents, which act as danger signals in the cytosol. Of note, the TCA cycle intermediates may also leak from dysfunctioning mitochondria and regulate cellular processes. Increasing evidence shows that the metabolites of the TCA cycle are substantially involved in the regulation of immune responses. In this review, we aimed to provide a comprehensive systematic overview of the molecular mechanisms of each TCA cycle intermediate that may play key roles in regulating cellular immunity in cell stress and discuss their implications for immune activation and suppression.

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