Susceptibility of low- and high-density lipoproteins from diabetic subjects to in vitro oxidative modification

Aims To investigate the hypothesis that lipid peroxidation of both low-dens ity lipoproteins (LDL) and high-density lipoproteins (HDL) is important in the development of atherosclerosis. Methods We have investigated whether LDL and HDL from patients with Type 1 diabetes mellitus (DM, n = 16) and Type 2 DM (n = 15) is more susceptible t o Cu2+- induced lipid peroxidation than LDL and HDL from a similar number o f nondiabetic controls matched for age, gender and serum cholesterol. Results The vitamin E content of LDL and HDL from both groups of diabetic p atients was not significantly different from controls. The LDL from Type 2 diabetic patients and HDL from both diabetic groups were significantly rich er in triglyceride than controls. Phospholipid was decreased in LDL from Ty pe 2 diabetic patients and protein was decreased in HDL in Type 1 DM, but o therwise the composition of LDL and HDL in diabetic subjects was similar to controls. No significant differences were observed in the generation of co njugated dienes or lipid peroxides in either LDL or HDL when the two groups were compared with each other or with their respective controls. Conclusions Increased lipid peroxidation occurring in vivo in diabetes is u nlikely to be the result of increased susceptibility of lipoproteins to lip id peroxidation, but rather to increased generation of free radicals, to ox idation of lipids other than those present in serum lipoproteins or to decr eases in antioxidant systems other than the fat-soluble antioxidants presen t in lipoproteins.