Plasma lipid peroxidation and hyperglycaemia: a connection through hyperinsulinaemia?

Increased lipid peroxidation has been commonly observed in diabetic patients as compared to control subjects. However, studies on the relationship to metabolic control have yielded conflicting results and no data are available on the relationship of hyperinsulinaemia to lipid peroxidation. We investigated, in well-characterized groups of 93 patients with non-insulin-dependent diabetes mellitus, 22 subjects with impaired glucose tolerance (IGT) and 96 subjects with normal glucose tolerance (NGT), the determinants of plasma lipid peroxidation measured by plasma thiobarbituric acid reactive substances (TBARS). These were significantly higher in subjects with IGT (1.04 +/- 0.48 mumol I-1) and in NIDDM patients (1.00 +/- 0.48 mumol I-1) than in those with NGT (0.75 +/- 0.46 mumol I-1; p < 0.05). The glucose tolerance status was the major determinant of increased lipid peroxidation even after controlling for the effects of age, sex, body mass index, physical activity, use of alcohol, smoking, and the use of diuretics. In regression analyses the major determinants of plasma TBARS were fasting plasma glucose, insulin, and apolipoprotein A1 (inversely) levels. To conclude, plasma TBARS were increased in impaired glucose tolerance and in diabetes and they were related to prevailing plasma glucose and insulin levels, suggesting a role for insulin resistance in increased lipid peroxidation process. On the contrary, apolipoprotein A1 may have protective effects in this respect.