Abstract: Aims: Steatosis may increase oxidative stress, which is counteracted by cellular enzymatic (cytosolic and mitochondrial superoxide dismutases (Cu/Zn‐SOD and Mn‐SOD), glutathione peroxidase (GPx), catalase) and non‐enzymatic antioxidant systems. We aimed to determine, in patients with non‐alcoholic fatty liver disease (NAFLD), the level of antioxidant defenses (1) in liver biopsies, to demonstrate the existence of oxidative stress; (2) in erythrocytes and plasma, to determine whether their antioxidant defenses reflect liver oxidative stress.

Methods: Erythrocyte and plasma antioxidant defenses were prospectively studied in two groups of 16 patients: patients with NAFLD and controls. Liver biopsies were performed in eight NAFLD patients; liver antioxidant enzyme activities were measured and compared with those in 12 control livers used for transplantation.

Results: Cu/Zn‐SOD, GPx and catalase activities were significantly higher in NAFLD livers than in controls whereas no significant differences were observed in Mn‐SOD activity, and thiobarbituric acid‐reactive substance (TBARS) concentration. No differences were observed in erythrocyte antioxidant enzyme activities (GPx, catalase, Cu/Zn‐SOD), erythrocyte TBARS concentration, and plasma α‐tocopherol concentration.

Conclusions: Liver antioxidant enzyme activities were high in patients with NAFLD, reflecting an oxidative stress possibly involved in inflammation and fibrogenesis. However, erythrocyte and plasma antioxidant defenses did not reflect intrahepatic peroxidation.