Hepatotoxicity induced by iron overload and alcohol. Studies on the role of chelatable iron, cytochrome P450 2E1 and lipid peroxidation.

BACKGROUND/AIMS: Clinical experience and studies with experimental animal models indicate a synergistic hepatotoxic effect of dietary iron overload and chronic alcohol ingestion. In order to elucidate the mechanism underlying this synergism, we examined the hepatic levels of ethanol-inducible cytochrome P450 2E1, glutathione and malondialdehyde, and the effect of iron chelation with desferrioxamine, in livers from rats treated with iron and/or ethanol.

METHODS

Animals received diets with or without 2.5-3% carbonyl iron for 6-9 weeks, followed by an ethanol-containing diet or a liquid control diet for 5-9 weeks. Desferrioxamine was administered subcutaneously with mini-osmotic pumps. Alanine aminotransferase activity in serum and hepatic contents of glutathione and malondialdehyde were determined. The hepatic level of cytochrome P450 2E1 was determined with Western Blotting using a specific polyclonal antibody.

RESULTS

The combination of iron and alcohol led to a marked increase in serum alanine aminotransferase activity as compared with all other treatment groups, and iron chelation with desferrioxamine reversed these increases. Treatment with alcohol alone led to slightly increased aminotransferases compared with controls. The level of cytochrome P450 2E1 was significantly elevated in microsomes isolated from ethanol-treated rats, but neither additional iron supplementation nor desferrioxamine influenced this level significantly. Glutathione contents were increased in the livers of animals treated with iron and/or ethanol. Malondialdehyde values were increased in iron-treated animals, whereas neither ethanol nor desferrioxamine altered malondialdehyde levels significantly.

CONCLUSIONS

The toxic effects exerted by the combination of iron overload and chronic ethanol feeding on rat liver are dependent on a pool of chelatable iron. The hepatic level of cytochrome P450 2E1 is markedly induced by ethanol but not further altered by iron overload. Neither increased lipid peroxidation nor depletion of hepatic glutathione levels can explain the synergistic hepatotoxic effects of iron and ethanol in this model.