Effect of chronic ethanol feeding on lipid peroxidation and protein oxidation in relation to liver pathology

Liver lipid peroxidation, nonheme iron, antioxidants, and protein oxidation were investigated in experimental alcohol‐induced liver disease in the rat. Wistar male rats were intragastrically and continuously infused for 4 weeks with a high‐fat diet plus an ethanol or an isocaloric amount of dextrose, maintaining a high blood alcohol level (200‐300 mg%). This model induced fatty liver, spotty necrosis, and focal inflammation. This pathology was associated with an enhanced lipid peroxidation and a decrease in the major antioxidant factors. Hepatic alpha‐tocopherol and glutathione concentrations were significantly decreased in ethanol‐fed rats. Glutathione peroxidase (GPx) was also decreased, whereas glutathione S‐transferase (GST) was unaffected. The nonheme iron level was significantly decreased. Protein oxidation was assessed through three parameters: protein thiols, protein carbonyl groups, and the activity of glutamine synthetase (GS), a centrilobular enzyme particularly susceptible to free‐radical‐ mediated damage. Ethanol‐fed rats had decreased protein thiol concentrations and reduced GS activity, together with increased protein carbonyls. A significant correlation between GS activity and the pathological score was observed. This study confirms the ethanol‐related increase in lipid peroxidation and shows that ethanol impairs the hepatic antioxidant potential. Furthermore, evidence of oxidative protein damage is given, including decreased activity of a key enzyme of ammonia metabolism. These protein disturbances may contribute to the pathogenesis of the observed liver damage.