Although reactive oxygen species (ROS) have been implicated in the etiology of alcohol-induced liver disease, neither their relative contribution to cell death nor the cellular mechanisms mediating their formation are known. The purpose of this study was to test the hypothesis that acute and chronic ethanol exposure enhances the mitochondrial generation of ROS in fresh, isolated hepatocytes. Acute ethanol exposure stimulated ROS production, increased the cellular NADH/NAD ؉ ratio, and decreased hepatocyte viability slightly, which was prevented by pretreatment with 4-methylpyrazole (4-MP), an inhibitor of alcohol dehydrogenase. Similarly, xylitol, an NADHgenerating compound, enhanced hepatocyte ROS production and decreased viability. Incubation with pyruvate, an NADH-oxidizing compound, and cyanamide, an inhibitor of aldehyde dehydrogenase, significantly decreased ROS levels in acute ethanol-treated hepatocytes. Chronic ethanol consumption produced a sixfold increase in hepatocyte ROS production compared with levels measured in controls. Hepatocytes from ethanol-fed rats were less viable compared with controls, e.g., viability was 68% ؎ 2% (ethanol) versus 83% ؎ 1% (control) after 60 minutes of incubation. Antimycin A increased ROS production and decreased cell viability; however, the toxic effect of antimycin A was more pronounced in ethanol-fed hepatocytes. These results suggest that acute and chronic ethanol exposure exacerbates mitochondrial ROS production, contributing to cell death. (HEPATOLOGY 1998;28:1318-1326.)The mechanisms responsible for alcohol-induced liver disease are presently unknown; however, attention has focused on the role of reactive oxygen species (ROS). The first reports of ROS involvement in alcoholic liver disease were published in the early 1960s and were attributed to observations that ethanol exposure enhanced lipid peroxidation which could be prevented by antioxidants.

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Chronic ethanol consumption results in a generalized depression in hepatic mitochondrial energy metabolism. Both the rate and efficiency of ATP synthesis via the oxidative phosphorylation system are decreased. Alterations in the activities of several components of the oxidative phosphorylation system contribute to the overall decrease in the capacity for ATP synthesis. There appears to be no alteration in any particular component which is rate-limiting. Although changes in membrane lipids may play a minor role, it appears that the decreased levels of mitochondria-derived polypeptide components of the oxidative phosphorylation system are primarily responsible for the depression in both the rate and efficiency of ATP synthesis. The concentrations of these mitochondrial gene products are lowered due to effects of chronic ethanol consumption on the mitochondrial translational process.

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