Defective intracellular antioxidant enzyme production in type 1 diabetic patients with nephropathy

There is an individual susceptibility to diabetic nephropathy, and oxidativ e stress is believed to play an important role in the pathogenesis of diabe tic complications. Active oxygen species induce antioxidant enzyme expressi on in tissues, an effect considered to be a defensive mechanism. To test wh ether altered intracellular antioxidant enzyme production might explain the predisposition to diabetic nephropathy, we studied the effect of long-term (12 weeks) exposure to normal (5 mmol/l) or high (22 mmol/l) glucose conce ntrations on fibroblast antioxidant enzyme gene expression and protein acti vity in type 1 diabetic patients with and without nephropathy, nondiabetic nephropathic patients, and nondiabetic control subjects. Under conditions o f normal glucose concentration in the culture media, CuZnSuperoxide-dismuta se, MnSnperoxide-dismutase, catalase, and glutathione-peroxidase activity a nd mRNA expression were not different among the four groups. Under high-glu cose conditions, CnZnSu-peroxide-dismutase mRNA and activity increased simi larly in all groups (P < 0.001 vs. basal), whereas MnSu-peroxide-dismutase did not change. In contrast, catalase mRNA and activity as well as glutathi one-peroxidase mRNA and activity increased in fibroblasts from type 1 diabe tic patients without nephropathy (P < 0.001), in fibroblasts from nondiabet ic nephropathic patients (P < 0.001), and in fibroblasts from nondiabetic c ontrol subjects (P < 0.001), but not in fibroblasts from type 1 diabetic pa tients with nephropathy. Exposure to high glucose concentrations significan tly increased Lipid peroxidation in cells, higher levels being found in cel ls from diabetic patients with nephropathy (P < 0.001). These data, while c onfirming that exposure to high glucose concentrations induces an antioxida nt defense in skin fibroblasts from normal subjects, demonstrate a failure of this defensive mechanism in cells from type 1 diabetic patients with nep hropathy, whereas skin fibroblasts from diabetic patients without complicat ions or from nondiabetic nephropathic patients have an intact antioxidant r esponse to glucose-induced oxidative stress.