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

Vidyashankar, Satyakumar, Nandakumar, Krishna S., Patki, Pralhad S.
Toxicology 2012 v.302 no.1 pp. 34-39
acetates, alanine transaminase, alcohol dehydrogenase, alcohol drinking, antioxidants, biosynthesis, cell viability, cholesterol, cytotoxicity, enzyme activity, ethanol, fatty liver, glutathione, glutathione peroxidase, human cell lines, lipid peroxidation, lipogenesis, phospholipids, secretion, superoxide dismutase, toxicology, triacylglycerols, tumor necrosis factor-alpha, vitamin E
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 100mM concentration caused 40% cytotoxicity at 72h as determined by MTT assay. The incorporation of labeled [2-¹⁴C] acetate into triacylglycerol and phospholipid was increased by 40% and 26% respectively upon 24h 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 (10mM) 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.