Serum antioxidant activity in diabetes mellitus.

Free radical medicated oxidative damage has previously been implicated in the pathogenesis of diabetic microangiopathy. Caeruloplasmin and transferrin act as antioxidants in serum by oxidizing and chelating ferrous iron which could otherwise act as a catalyst in free radical reactions. We have measured the serum anti-oxidant activity in 67 diabetics, 25 of whom had retinopathy and in 37 controls. Serum iron concentrations were normal in diabetics in comparison with controls (21.5 +/- 10 v 19.5 +/- 6.7 mumol/L) although transferrin and iron binding capacity were increased in the diabetics (3.7 +/- 0.8 v 2.9 +/- 0.9 g/L, p less than 0.001 and 69.9 +/- 10.8 v 59.0 +/- 14 mumol/L, p less than 0.002 respectively). Caeruloplasmin, measured by its ferroxidase activity, was increased in both male (46 +/- 11 v 36 +/- 9 mu/mL, p less than 0.002) and female diabetics (57 +/- 13 v 47 +/- 11 mu/mL, p less than 0.002). Ferritin was also increased in both male (124 +/- 113 v 44 +/- 38 ng/mL, p less than 0.001) and female diabetics (132 +/- 118 v 25 +/- 12 ng/mL, p less than 0.001). The presence of retinopathy, the degree of glycaemic control and duration of diabetes had no effect on these findings. We conclude that increased concentrations of iron-oxidizing and iron-binding proteins occur in diabetic serum, and that the increased serum antioxidant activity may be a response to oxidative stress.