Expression of hepatic antioxidant enzymes in non-obese type-2 diabetic Goto–Kakizaki rats

Diabetes mellitus and its complications have been attributed in part to oxidative stress, against which antioxidant enzymes constitute a major protective mechanism. The present study was performed to investigate the effects of early stage type 2 diabetes in the absence of obesity and liver damage on hepatic antioxidant enzyme expression and oxidative stress using 9-week-old Goto-Kakizaki (GK) rats. Hepatic total antioxidant capacity determined by total oxygen radical scavenging capacity and lipid peroxidation determined by malondialdehyde in plasma and liver were not significantly different between normal Wistar rats and GK rats. These results indicated that oxidative stress is not evident in these type 2 diabetic rats. Hepatic expression levels of antioxidant enzymes, including superoxide dismutase-1, catalase, glutathione peroxidase and reductase, thioredoxin-1, mu- and pi-class glutathione S-transferase (GST), and the gamma-glutamylcysteine ligase catalytic subunit, were not different between normal rats and GK rats. But, hepatic level and activity of alpha-class GST were decreased and peroxiredoxin-1 level was increased in GK rats, suggesting that upregulation of peroxiredoxin-1 compensates for downregulation of alpha-class GST. These results suggest that alpha-class GST and peroxiredoxin-1 in liver can be altered during the early stages of type 2 diabetes in the absence of obesity and severe oxidative stress.