Antioxidant status in patients with uncomplicated insulin-dependent and non-insulin-dependent diabetes mellitus

Oxidative damage by free radicals has been implicated in the pathogenesis of vascular disease in diabetes. We compared the radical-scavenging antioxidant activity of serum from 28 patients with insulin-dependent diabetes mellitus and 24 patients with non-insulin-dependent diabetes mellitus uncomplicated by vascular disease with age-matched non-diabetic control subjects. Patients with insulin-dependent diabetes had significantly reduced total antioxidant activity (320.2 +/- 11.3 vs. 427.5 +/- 19.2 mumol L-1; P < 0.001). This was attributable to lower urate (209.4 +/- 10.4 vs. 297.1 +/- 16.7 mumol L-1; P < 0.001) and vitamin C levels (63.6 +/- 6.0 vs. 87.5 +/- 4.9 mumol L-1; P < 0.01). Patients with non-insulin-dependent diabetes had lower total antioxidant activity than age-matched control subjects (433.8 +/- 25.4 vs. 473.9 +/- 30.2 mumol L-1; NS), reflecting lower urate (299.5 +/- 19.4 vs. 324.8 +/- 21.4 mumol L-1; NS) and vitamin C levels (38.6 +/- 5.7 vs. 58.5 +/- 5.3 mumol L-1; P < 0.05). Multiple regression analysis showed that urate, vitamin C and vitamin E were the major contributors to serum total antioxidant activity. These results show that diabetic patients have significant defects of antioxidant protection, which may increase vulnerability to oxidative damage and the development of diabetic complications.