The mechanisms by which ethanol causes fatty liver are complex. Reducing equivalents generated during ethanol oxidation inhibit tricarboxylic acid cycle activity and fatty acid oxidation. In addition, ethanol inhibits lipoprotein export and increases fatty acid uptake and lipid peroxidation. To test the role that alcohol metabolism by alcohol dehydrogenase (ADH) has on cellular lipid metabolism, a cell line expressing rat ADH was generated by transducing HeLa cells with an ADH-expressing retrovirus. The cells expressed high levels of ADH protein and had ADH activity similar to that of liver. Exposure of the cells to 20 mmol/LK ethanol for 24 hours led to substantial accumulation of free fatty acids and triacylglycerol in the transduced, but not wild-type, HeLa cells. The rate of synthesis of saponifiable lipid was increased significantly by ethanol under these conditions. Ethanol exposure also promoted triacylglycerol accumulation when the cells were incubated with linoleic acid. This was associated with a decrease in the rat at which the cells oxidized 1-[14-C]-linoleic acid. Fat accumulation was not prevented by including α-tocopherol in the medium, arguing against a role for lipid peroxidation. However, the presence of methylene blue completely prevented the fat accumulation. This was associated with a return of the elevated lactate/pyruvate ratio toward normal. These data suggest that generation of reducing equivalents by ADH was sufficient to cause fat accumulation in this cell model.
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