Effect of LDL+VLDL oxidizability and hyperglycemia on blood cholesterol, phospholipid and triglyceride levels in type-I diabetic patients.

Oxidative modification of low-density lipoproteins has been implicated in impaired lipid metabolism and its deposition in the arterial wall, and atherosclerosis. This study was carried out to determine the relationship between the in vitro oxidizability of low-density lipoprotein (LDL) and very-low-density lipoprotein (VLDL) and the cholesterol, phospholipid and triglyceride (TG) levels in the blood of Type-I diabetic patients. LDL+VLDL was isolated using a micro-affinity column from serum of diabetic patients (n = 34) and age-matched normal individuals (n = 22). The oxidative susceptibility of LDL+VLDL was determined by treatment with 25 microM CuCl(2) for 1.5 h. The levels of total-, LDL-, and HDL-cholesterol, phospholipids and triglycerides, as well as glycated hemoglobin (HbA(t)), were measured in the blood using standard methods. The diabetics had significantly higher levels of triglycerides and phospholipids, but cholesterol levels were similar between Type-I diabetics and age-matched normals. However, among diabetics, there was a significant correlation between the in vitro oxidation of LDL+VLDL at 1.5 h and total cholesterol (r = 0.49, P<0.002), and LDL cholesterol (r = 0.54, P<0.001) and TG (r = 0.34, P<0.05) levels. The level of in vitro oxidizability of LDL+VLDL did not have any correlation with HDL-cholesterol or phospholipid levels. The level of glycemic control (HbA(1)) did not have any correlation with levels of LDL- or HDL-cholesterol or triglycerides, but was significantly correlated with phospholipid levels (r = 0.48, P<0.005). This study suggests that the levels of LDL-cholesterol and triglycerides in the blood are directly related to the degree of in vitro oxidative susceptibility of low-density lipoproteins in Type-1 diabetic patients.