COMPARISON OF ANTIOXIDANT ACTIVITY IN LIPOPROTEIN FRACTIONS FROM INSULIN-DEPENDENT DIABETICS AND HEALTHY CONTROLS

The insulin-dependent diabetic patient is at greatly increased risk of premature atherosclerosis. Oxidative damage to lipoproteins has been implicated as an important factor in the atherogenic process. Diabetic patients are exposed to excessive oxidative stress because of non-enz ymatic glycation of proteins and a variety of defects in antioxidant s ystems. We have previously described an enhanced chemiluminescent meth od for measuring protective 'chain-breaking' antioxidant activity in p lasma lipoprotein fractions. In this study we compare the lipid conten t and antioxidant activity of plasma lipoproteins in 22 young insulin- dependent diabetics without vascular complications and 20 age- and sex -matched controls. Mean levels of haemoglobin Ale in the diabetic grou p were 8.8 +/- 0.2%. There were no significant differences in serum to tal cholesterol, apolipoprotein A, apolipoprotein B or lipoprotein(a) levels between the study groups. Serum total triglyceride levels (1.32 +/- 0.11 versus 1.01 +/- 0.08 mmol/l; P < 0.05) and LDL-associated tr iglyceride (0.28 +/- 0.04 versus 0.15 +/- 0.02 mmol/l; P < 0.05) were significantly elevated in the diabetic group. Total plasma antioxidant activity was significantly reduced in the diabetic group (272.0 +/- 1 5.4 versus 338.3 +/- 20.7 mu mol/l; P < 0.05). Antioxidant activity me asured in five lipoprotein fractions isolated by density gradient ultr acentrifugation (VLDL1, VLDL2, LDL1, LDL2 and HDL) showed no significa nt differences between groups when corrected for protein, total lipid or cholesterol content. When corrected for triglyceride content signif icantly lower antioxidant values were found in the diabetic HDL fracti on only. The results of this study imply that the susceptibility of th e insulin-dependent diabetic to the development of premature atheroscl erosis cannot be attributed to reduced antioxidant activity in circula ting plasma lipoproteins. (C) 1997 Elsevier Science Ireland Ltd.