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Journal of Environmental Microbiology

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During hypoxia, ageing hepg2 cells complete the Krebs cycle by switching from the aminotransferase glutaminolytic pyruvate utilisation pathway

Author(s): Arnold Aletrino*

A Hepatocellular carcinoma in humans HepG2 cells are forced to undergo Oxidative Phosphorylation (OXPHOS) when grown in aglycemic conditions with galactose and glutamine.These OXPHOS cells serve as a prototype for cancer cells' combined aerobic glycolysis and OXPHOS bioenergetics. It was our goal to identify the portions of the glutaminolytic pathway that involved the aminotransferase reaction that supplied 2-oxoglutarate (2OG) to the Krebs cycle active segment with Aconitase And Isocitrate Dehydrogenase-3 (ACO-IDH3), which is typically inactive in cancer cells because citrate is exported from the mitochondria. At normoxia, the aminotransferase inhibitor Aminooxyacetate (AOA) or AOA combined with the glutamatedehydrogenase inhibitor Bithionol reduced OXPHOS cell respiration to 15% and 10%, respectively.When combined with AOA, the ratio of phosphorylating to non-phosphorylating respiration decreased from >6.5 to 1.9 and then to nil. Thus, glutaminolysis plays a major role in normoxic OXPHOS HepG2 cells. The immediate partial restoration of respiration upon addition of membrane-permeant dimethyl-2- oxoglutarate to inhibited cells demonstrated the absence of 2OGdehydrogenase substrate post aminotransferase inhibition.Surprisingly, the AOA (bithionol) inhibition stopped after 72 hours of 5% O2 hypoxia, and respiration was fully recovered. As a result, the glycolysis pathway in diabetic HepG2 cells was accelerated by the Hypoxia-Induced Factor (HIF), which was preceded by galactolysis. Pyruvate was then redirected toward ACO-IDH3 via the still partially blocked pyruvate dehydrogenase. A greater activity of the Leloir pathway in OXPHOS cells was clearly matched by an increase in the glycolytic flux under hypoxia. NADPH oxidase activity was raised 2-fold in hypoxic OXPHOS cells but decreased in hypoxic glycolytic cells. At 5 mM glucose, OXPHOS cells and glycolytic cells experienced a reduction in; Contrary to aglycemic cells, glycolytic HepG2 cells showed the conventional HIF-mediated adaptation when exposed to hypoxia, i.e., even with unlimited respiratory substrate availability for 72 hours at 5% O2. Nevertheless, dm2OG significantly increased their ATP content compared to when it wasn't present during hypoxic adaptation. Thus, under conditions frequently established for solid tumours in vivo, such as aglycemia and hypoxia, the metabolic flexibility of cancer cells is demonstrated. Therefore, it is wrong to widely accept the exclusive and irreversible Warburg phenotype in cancer cells