Triheptanoin alters [U-13C6]-glucose incorporation into glycolytic intermediates and increases TCA cycling by normalizing the activities of pyruvate dehydrogenase and oxoglutarate dehydrogenase in a chronic epilepsy mouse model

Triheptanoin is anticonvulsant in several seizure models. Here, we investigated changes in glucose metabolism by triheptanoin interictally in the chronic stage of the pilocarpine mouse epilepsy model. After injection of [U-13C6]-glucose (i.p.), enrichments of 13C in intermediates of glycolysis and the tricarboxylic acid (TCA) cycle were quantified in hippocampal extracts and maximal activities of enzymes in each pathway were measured. The enrichment of 13C glucose in plasma was similar across all groups. Despite this, we observed reductions in incorporation of 13C in several glycolytic intermediates compared to control mice suggesting glucose utilization may be impaired and/or glycogenolysis increased in the untreated interictal hippocampus. Triheptanoin prevented the interictal reductions of 13C incorporation in most glycolytic intermediates, suggesting it increased glucose utilization or – as an additional astrocytic fuel – it decreased glycogen breakdown. In the TCA cycle metabolites, the incorporation of 13C was reduced in the interictal state. Triheptanoin restored the correlation between 13C enrichments of pyruvate relative to most of the TCA cycle intermediates in “epileptic” mice. Triheptanoin also prevented the reductions of hippocampal pyruvate dehydrogenase and 2-oxoglutarate dehydrogenase activities. Decreased glycogen breakdown and increased glucose utilization and metabolism via the TCA cycle in epileptogenic brain areas may contribute to triheptanoin's anticonvulsant effects.

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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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Effect of thermal injury on the TCA cycle enzymes of Staphylococcus aureus MF 31 and Salmonella typhimurium 7136

Canadian Journal of Microbiology ◽

10.1139/m71-121 ◽

1971 ◽

Vol 17 (6) ◽

pp. 759-765 ◽

Cited By ~ 22

Author(s):

Richard I. Tomlins ◽

Merle D. Pierson ◽

Z. John Ordal

Keyword(s):

Lactate Dehydrogenase ◽

Malate Dehydrogenase ◽

Thermal Injury ◽

Specific Activity ◽

Fumarate Hydratase ◽

Tca Cycle ◽

Tca Cycle Enzymes ◽

The Tca Cycle ◽

Oxoglutarate Dehydrogenase ◽

Metabolic Activities

The heating of S. aureus MF-31 and S. typhimurium 7136 at 52C and 48C respectively, produced a sublethal heat injury. When injured cells were placed in fresh growth medium they recovered. The recovery of S. aureus was not inhibited by chloramphenicol. The metabolic activities of tricarboxylic acid (TCA) cycle enzymes, as well as other selected enzymes in crude extracts of normal and heat-injured cells of both microorganisms were assayed. In extracts from S. typhimurium there was some loss of specific activity with fumarate hydratase, glutamate dehydrogenase, fructose diphosphate aldolase, lactate dehydrogenase, and the NAD(P) oxidases as a result of heating. In extracts from S. aureus oxoglutarate dehydrogenase, malate dehydrogenase and lactate dehydrogenase were severely inactivated after heating. Other enzymes in comparison were only moderately sensitive to heat. No significant increase in enzyme activity was observed in extracts from injured cells of either microorganism. Re-naturation of lactate dehydrogenase and malate dehydrogenase occurred during the recovery of S. aureus both in the presence and absence of chloramphenicol. No renaturation of oxoglutarate dehydrogenase was found under the same conditions.

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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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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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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 (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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Complete Remission with Devimistat (CPI-613) in Refractory Burkitt Lymphoma

Blood ◽

10.1182/blood-2021-153662 ◽

2021 ◽

Vol 138 (Supplement 1) ◽

pp. 4555-4555

Author(s):

Liana Nikolaenko ◽

Timothy Pardee ◽

Raphel Steiner ◽

Jeremy S. Abramson ◽

Steven M. Horwitz ◽

...

Keyword(s):

Pyruvate Dehydrogenase ◽

Research Funding ◽

Study Drug ◽

Tca Cycle ◽

Mitochondrial Enzymes ◽

Advisory Committees ◽

Cancer Cell Death ◽

Redox Active ◽

The Tca Cycle ◽

Alpha Ketoglutarate Dehydrogenase

Abstract Introduction: Patients (pts) with primary refractory or relapsed high-grade lymphoma (HGL) including Burkitt lymphoma (BL) and high-grade B-cell lymphoma with rearrangements of MYC and BCL2 and/or BCL6 (double-hit lymphoma, DHL) have a dismal prognosis with patients almost never achieving a meaningful remission to second line therapy. No standard second line therapeutic approach exists, particularly for BL. The characteristic hallmark of these diseases is a dysregulated MYC oncogene with both downstream effects on proliferation and a high metabolic fluxes which use tricarboxylic acid (TCA) cycle intermediates as biosynthetic precursors. CPI-613 (devimistat) is a non-redox active analogue of lipoic acid, a required cofactor for two key mitochondrial enzymes of the TCA cycle, pyruvate dehydrogenase and alpha ketoglutarate dehydrogenase. Disruption of mitochondrial function by CPI-613 results in a shutdown of ATP and biosynthetic-intermediate production, leading to cancer cell death by apoptosis or necrosis. In the initial phase I trial (n=26) one patient with multiply refractory BL had a partial remission sustained for over one year and then consolidated by surgical resection. She remains alive 7 years later. As of July 2021, 20 clinical studies for various cancers have been conducted (ongoing/completed) with devimistat with over 700 patients having received study drug. We initiated a phase II trial to further explore efficacy in HGL. Devimistat has FDA orphan status for BL and 4 other cancers. Methods: NCT03793140 is a multicenter study aiming to enroll 17 patients on each of two cohorts, BL and DHL, with a Simon's 2-stage design for each cohort, requiring one response among the first 9 treated patients to expand to 17. Patients must have had at least one prior line of therapy or are refusing standard of care and must be more than 3 months after a prior stem cell transplant. Active central nervous system (CNS) parenchymal disease is excluded, but prior leptomeningeal disease is allowed if the CSF is negative for more than 4 weeks at enrollment and maintenance intrathecal therapy is ongoing. Devimistat is given by central line over 2 hours daily x 5 days for two 14-day cycles and then as maintenance x5 days every 21 days. Pts were evaluable for response if they received at least 4 infusions over 5 days of the first cycle. Results: 9 pts were enrolled in the DHL/THL arm. Mediannumber of prior therapies were 3 (range, 1-6). No responses were seen, with only 1 patient achieving stable disease as best response, resulting in cohort closure. Thus far, 8 BL pts were enrolled. Median number of prior therapies was 3 (range, 2-4). Two patients were inevaluable for response. 1/6 patients had stable disease through cycle 7 and one had a complete response (CR). This CR patient (HIV+) with 4 prior therapies entered the study with only a biopsy proven thigh mass. He was not a transplant candidate for social reasons. He had a near complete metabolic remission after 4 cycles of devimistat and a CR after cycle 7. (Table and Figure) As of July 2021, he is in cycle 11, having had a 4-week treatment delay of cycle 5 due to CoVID 19 infection. ECOG improved from 3 to 0. Adverse events (AE): As of July30, 2021, no patient experienced a serious adverse event related to study drug. Four patients had grade 3 events at least possibly related: 2 neutropenia, 1 thrombocytopenia and 1 elevated bilirubin. 1 patient had a dose reduction for grade 2 alanine aminotransferase increase. Conclusions: Although our results are preliminary, the complete remission in this patient is promising in a disease where no viable treatment options exist in the relapsed, refractory BL. Enrollment to the BL cohort is ongoing. Figure 1 Figure 1. Disclosures Nikolaenko: Pfizer: Research Funding; Rafael Pharmaceuticals: Research Funding. Pardee: Celgene/BMS: Consultancy, Speakers Bureau; Amgen: Consultancy, Speakers Bureau; Pharmacyclics: Consultancy, Speakers Bureau; Janssen: Consultancy, Speakers Bureau; AbbVie: Membership on an entity's Board of Directors or advisory committees; CBM Biopharma: Membership on an entity's Board of Directors or advisory committees; Karyopharm: Research Funding; Rafael Pharmaceuticals: Research Funding. Abramson: Genentech: Consultancy; Kymera: Consultancy; Karyopharm: Consultancy; AbbVie: Consultancy; Seagen Inc.: Research Funding; Allogene Therapeutics: Consultancy; Astra-Zeneca: Consultancy; Incyte Corporation: Consultancy; BeiGene: Consultancy; Bluebird Bio: Consultancy; Genmab: Consultancy; EMD Serono: Consultancy; Bristol-Myers Squibb Company: Consultancy, Research Funding; C4 Therapeutics: Consultancy; Morphosys: Consultancy; Kite Pharma: Consultancy; Novartis: Consultancy. Horwitz: Vividion Therapeutics: Consultancy; Shoreline Biosciences, Inc.: Consultancy; Tubulis: Consultancy; Verastem: Research Funding; ONO Pharmaceuticals: Consultancy; Myeloid Therapeutics: Consultancy; SecuraBio: Consultancy, Research Funding; Trillium Therapeutics: Consultancy, Research Funding; Seattle Genetics: Consultancy, Research Funding; Millennium /Takeda: Consultancy, Research Funding; Kura Oncology: Consultancy; Janssen: Consultancy; Kyowa Hakko Kirin: Consultancy, Research Funding; Forty Seven, Inc.: Research Funding; Daiichi Sankyo: Research Funding; C4 Therapeutics: Consultancy; Celgene: Research Funding; Aileron: Research Funding; Affimed: Research Funding; Acrotech Biopharma: Consultancy; ADC Therapeutics: Consultancy, Research Funding. Matasar: GlaxoSmithKline: Honoraria, Research Funding; Teva: Consultancy; Janssen: Honoraria, Research Funding; Bayer: Consultancy, Honoraria, Research Funding; Genentech, Inc.: Consultancy, Honoraria, Research Funding; Merck Sharp & Dohme: Current holder of individual stocks in a privately-held company; F. Hoffmann-La Roche Ltd: Consultancy, Honoraria, Research Funding; IGM Biosciences: Research Funding; Merck: Consultancy; Juno Therapeutics: Consultancy; TG Therapeutics: Consultancy, Honoraria; Seattle Genetics: Consultancy, Honoraria, Research Funding; Memorial Sloan Kettering Cancer Center: Current Employment; Pharmacyclics: Honoraria, Research Funding; Daiichi Sankyo: Consultancy; ImmunoVaccine Technologies: Consultancy, Honoraria, Research Funding; Takeda: Consultancy, Honoraria; Rocket Medical: Consultancy, Research Funding. Noy: Rafael Parhma: Research Funding; Morphosys: Consultancy; Targeted Oncology: Consultancy; Medscape: Consultancy; Pharmacyclics: Consultancy, Research Funding; Janssen: Consultancy, Honoraria; Epizyme: Consultancy. OffLabel Disclosure: CPI-613 (devimistat) is a non-redox active analogue of lipoic acid, a required cofactor for two key mitochondrial enzymes of the TCA cycle, pyruvate dehydrogenase and alpha ketoglutarate dehydrogenase. Disruption of mitochondrial function by CPI-613 results in a shutdown of ATP and biosynthetic-intermediate production, leading to cancer cell death by apoptosis or necrosis

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Procyclic trypanosomes recycle glucose catabolites and TCA cycle intermediates to stimulate growth in the presence of physiological amounts of proline

PLoS Pathogens ◽

10.1371/journal.ppat.1009204 ◽

2021 ◽

Vol 17 (3) ◽

pp. e1009204

Author(s):

Oriana Villafraz ◽

Marc Biran ◽

Erika Pineda ◽

Nicolas Plazolles ◽

Edern Cahoreau ◽

...

Keyword(s):

Carbon Sources ◽

Tca Cycle ◽

Central Carbon Metabolism ◽

Tsetse Fly ◽

Growth Defect ◽

Insect Vector ◽

Metabolic Intermediates ◽

The Tca Cycle ◽

Production And Consumption ◽

Tca Cycle Intermediates

Trypanosoma brucei, a protist responsible for human African trypanosomiasis (sleeping sickness), is transmitted by the tsetse fly where the procyclic forms of the parasite develop in the proline-rich (1–2 mM) and glucose-depleted digestive tract. Proline is essential for the midgut colonization of the parasite in the insect vector, however other carbon sources could be available and used to feed its central metabolism. Here we show that procyclic trypanosomes can consume and metabolize metabolic intermediates, including those excreted from glucose catabolism (succinate, alanine and pyruvate), with the exception of acetate, which is the ultimate end-product excreted by the parasite. Among the tested metabolites, tricarboxylic acid (TCA) cycle intermediates (succinate, malate and α-ketoglutarate) stimulated growth of the parasite in the presence of 2 mM proline. The pathways used for their metabolism were mapped by proton-NMR metabolic profiling and phenotypic analyses of thirteen RNAi and/or null mutants affecting central carbon metabolism. We showed that (i) malate is converted to succinate by both the reducing and oxidative branches of the TCA cycle, which demonstrates that procyclic trypanosomes can use the full TCA cycle, (ii) the enormous rate of α-ketoglutarate consumption (15-times higher than glucose) is possible thanks to the balanced production and consumption of NADH at the substrate level and (iii) α-ketoglutarate is toxic for trypanosomes if not appropriately metabolized as observed for an α-ketoglutarate dehydrogenase null mutant. In addition, epimastigotes produced from procyclics upon overexpression of RBP6 showed a growth defect in the presence of 2 mM proline, which is rescued by α-ketoglutarate, suggesting that physiological amounts of proline are not sufficient per se for the development of trypanosomes in the fly. In conclusion, these data show that trypanosomes can metabolize multiple metabolites, in addition to proline, which allows them to confront challenging environments in the fly.

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

Life ◽

10.3390/life11010069 ◽

2021 ◽

Vol 11 (1) ◽

pp. 69

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

The tricarboxylic acid cycle (TCA) is a series of chemical reactions used in aerobic organisms to generate energy via the oxidation of acetylcoenzyme A (CoA) derived from carbohydrates, fatty acids and proteins. In the eukaryotic system, the TCA cycle occurs completely in mitochondria, while the intermediates of the TCA cycle are retained inside mitochondria due to their polarity and hydrophilicity. Under cell stress conditions, mitochondria can 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 its implication for immune activation and suppression.

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