Alcohol and antioxidant systems.

Following the pioneer report of Di Luzio (Physiologist 6, 169-173, 1963) concerning the prevention of the acute ethanol-induced fatty liver by antioxidants, many observations have shown that ethanol-induced liver injury may be linked, at least partly, to an oxidative stress resulting from increased free radical production and/or decreased antioxidant defence. The disturbances induced in the major hepatic enzymatic and non-enzymatic antioxidant systems following experimental acute and chronic ethanol administration are reviewed, emphasizing the important role of dietary alpha-tocopherol in modifying the induction of oxidative stress and its usual expression as increased lipid peroxidation. Adaptative increases in some elements of the hepatic antioxidant defence partly counteract the enhanced generation of prooxidant free radicals following chronic ethanol intake. By contrast, lipid peroxidation is favoured when ethanol is administered together with a fat-rich diet and/or various xenobiotics. Chronic ethanol feeding has also been reported to potentiate the oxidative stress resulting from an acute ethanol load. By generating potent chemoattractants for human neutrophils and/or by stimulating the expression of genes involved in collagen biosynthesis, liver lipid peroxidation may play an important role in the progression of steatosis to hepatitis and cirrhosis. Oxidative stress has been shown not to be restricted to the liver, but also to affect, under some experimental conditions of ethanol administration, extrahepatic tissues, such as the central nervous system, the heart and the testes. This stress can be partly prevented by vitamin E supplementation. Ethanol-induced antioxidant disturbances have also been reported in clinical studies in blood and liver biopsies. Pharmacological antioxidants could have beneficial effects in reducing the incidence of ethanol-induced changes in cellular lipids, proteins and nucleic acids. The antioxidants considered could act by reducing free radical production (e.g. chelators of redox-active iron derivatives), trapping free radicals themselves, interrupting the peroxidation process or reinforcing the natural antioxidant defence.