Glutamate–oxaloacetate transaminase activity promotes palmitate lipotoxicity in rat hepatocytes by enhancing anaplerosis and citric acid cycle flux

Abstract

Edited by Jeffrey E. PessinHepatocyte lipotoxicity is characterized by aberrant mitochondrial metabolism, which predisposes cells to oxidative stress and apoptosis. Previously, we reported that translocation of calcium from the endoplasmic reticulum to mitochondria of palmitate-treated hepatocytes activates anaplerotic flux from glutamine to ␣-ketoglutarate (␣KG), which subsequently enters the citric acid cycle (CAC) for oxidation. We hypothesized that increased glutamine anaplerosis fuels elevations in CAC flux and oxidative stress following palmitate treatment. To test this hypothesis, primary rat hepatocytes or immortalized H4IIEC3 rat hepatoma cells were treated with lipotoxic levels of palmitate while modulating anaplerotic pathways leading to ␣KG. We found that culture media supplemented with glutamine, glutamate, or dimethyl-␣KG increased palmitate lipotoxicity compared with media that lacked these anaplerotic substrates. Knockdown of glutamate-oxaloacetate transaminase activity significantly reduced the lipotoxic effects of palmitate, whereas knockdown of glutamate dehydrogenase (Glud1) had no effect on palmitate lipotoxicity. 13 C flux analysis of H4IIEC3 cells cotreated with palmitate and the pan-transaminase inhibitor aminooxyacetic acid confirmed that reductions in lipotoxic markers were associated with decreases in anaplerosis, CAC flux, and oxygen consumption. Taken together, these results demonstrate that lipotoxic palmitate treatments enhance anaplerosis in cultured rat hepatocytes, causing a shift to aberrant transaminase metabolism that fuels CAC dysregulation and oxidative stress.

Increased glycolysis is an early consequence of palmitate lipotoxicity mediated by redox signaling

“…In fact, added palmitate was not oxidized, since etomoxir, a CPT1 inhibitor which prevents uptake of the fatty acid into mitochondria [ 49 ], had no effects on OCRs or ECARs ( Fig S1 ). Cytosolic palmitate has previously been found to rewire the citric acid cycle and promote modified use of carbon sources [ 50 ], which is compatible with our results showing metabolic plasticity promoted by this fatty acid in the cytosol.…”

Heavy metal toxicity in Buriganga river alters the immunology of Nile tilapia (Oreochromis niloticus L)

“…Li et al [75] suggested that the organism increased the metabolic rate to mitigate the stress condition. The liver in fish metabolizes the essential biomolecules and repair any physiological and biochemical disorder which include GOT and GPT activities [76]. The findings of the current study have showed increased GOT and GPT activity in O. niloticus which is presumed due to the alteration of the muscle and hepatic tissues.…”

ATP Production Relies on Fatty Acid Oxidation Rather than Glycolysis in Pancreatic Ductal Adenocarcinoma

“…The transfer of cytosolic NADH into mitochondria in cancer cells requires the MAS, which is composed of two antiporters, the malate-α-KG antiporter (SLC25A11 or OGC) and the glutamate-aspartate antiporter (SLC25A12 or aspartate-glutamate carrier isoform 1), as well as glutamic-oxaloacetic transaminase 1 and 2 (GOT1 and 2), and malate dehydrogenase 1 and 2 [ 22 , 29 ]. The MAS can be blocked by AOA, which inhibits GOT1 and 2 [ 30 ]. In this study, blocking MAS using AOA decreased OCR and ATP production by up to 90% in PDAC cells ( Figure 4 A), whereas it had no effect on OCR and ATP production in HPNE normal cells ( Figure 4 B).…”