Alcohol depletes coenzyme-Q10 associated with increased TNF-alpha secretion to induce cytotoxicity in HepG2 cells

Highlights: ► Ethanol induced cytotoxicity in HepG2 cells in absence of lipogenesis. ► Ethanol inhibited HMG-CoA reductase activity. ► Ethanol induced HMG-CoA reductase inhibition is due to decreased cell viability. ► Incubation with mevalonate could not increase the cholesterol. ► Cytotoxicity brought about by CoQ10 depletion and increased TNF-alpha. -- Abstract: Alcohol consumption has been implicated to cause severe hepatic steatosis which is mediated by alcohol dehydrogenase (ADH) activity and CYP450 2E1 expression. In this context, the effect of ethanol was studied for its influence on lipogenesis in HepG2 cell which is deficient of ADH and does not express CYP450 2E1. The results showed that ethanol at 100 mM concentration caused 40% cytotoxicity at 72 h as determined by MTT assay. The incorporation of labeled [2-14C] acetate into triacylglycerol and phospholipid was increased by 40% and 26% respectively upon 24 h incubation, whereas incorporation of labeled [2-14C] acetate into cholesterol was not significantly increased. Further, ethanol inhibited HMG-CoA reductase which is a rate-limiting enzyme in the cholesterol biosynthesis. It was observed that, HMG-CoA reductase inhibition was brought about by ethanol as a consequence of decreased cell viability, since incubation of HepG2 cells with mevalonate could not increase the cholesterol content and increase the cell viability. Addition of ethanol significantly increased TNF-alpha secretion and depleted mitochondrial coenzyme-Q10 which is detrimental for cell viability. But vitamin E (10 mM) could partially restore coenzyme-Q10 and glutathione content with decreased TNF-alpha secretion in ethanol treated cells. Further, lipid peroxidation, glutathione peroxidase and superoxide dismutase enzyme activities remained unaffected. Ethanol decreased glutathione content while, GSH/GSSG ratio was significantly higher compared to other groups showing cellular pro-oxidant and antioxidant balance remained intact. Alanine amino transferase activity was increased by 4.85 folds in cells treated with ethanol confirming hepatocyte damage. Hence, it is inferred that ethanol induced cytotoxicity in HepG2 cells due to coenzyme-Q10 depletion and increased TNF-alpha secretion.