Effects of vitamin E supplementation on intracellular antioxidant enzyme production in adolescents with type 1 diabetes and early microangiopathy

Defective intracellular antioxidant enzyme production (IAP) has been demonstrated in adults with diabetic nephropathy. To evaluate the effects on IAP of vitamin E administration in adolescents with type I diabetes and early signs of microangiopathy, 12 adolescents (aged 11-21 y; diabetes duration 10-18) were studied. Eight had retinopathy [background (four), preproliferative (three), or proliferative (one)], four had persistent microalbuminuria, and seven had both. Skin fibroblasts were obtained by biopsies and cultured in Dulbecco's modified Eagle's medium. CuZn superoxide dismutase (SOD), MnSOD, catalase (CAT), and glutathione-peroxidase (GPX) activity and mRNA expression were measured before and after 3 mo of synthetic vitamin E supplementation (600 mg twice daily); on both occasions, IAP was evaluated at different ex vivo glucose concentrations (5 and 22 mM). Ten adolescents with type I diabetes (aged 12-20 y) without angiopathy and eight healthy volunteers (aged 15-22 y) participated as control subjects. Vitamin E serum levels were measured throughout the study. In normal glucose concentrations, CuZnSOD, MnSOD, CAT, and GPX activity and mRNA expression were not different among the groups. In high glucose, CuZnSOD activity and mRNA increased similarly in all groups [angiopathics: 0.96 +/- 0.30 U/mg protein; 9.9 +/- 3.2 mRNA/glyceraldehyde-3-phosphate dehydrogenase). CAT and GPX activity and mRNA did not increase in high glucose only in adolescents with angiopathy (0.35 +/- 0.09; 4.2 +/- 0.1 and 0.52 +/- 0.14; 2.4 +/- 0.9, respectively). MnSOD did not change in any group. Vitamin E supplementation had no effect on any enzymatic activity and mRNA in both normal and hyperglycemic conditions. Adolescents with early signs of diabetic angiopathy have defective IAP and activity, which are not modified by vitamin E.