There is increasing agreement about the atherogenicity of intermediate density lipoprotein (IDL). We have previously demonstrated an increased cholesterol (Ch) concentration in the Sf20-60 lipoprotein fraction of diabetics. On the other hand, it is a matter of debate whether hyperinsulinemia too plays an important role in atherogenesis. Therefore, in order to determine the atherogenicity of IDL and insulin in diabetics, we conducted three lines of study.
First, Ch concentration in the IDL was examined in normolipidemic diabetics. Second, a lipoprotein profile, including subclasses of the triglyceride (Tg) rich lipoprotein fraction, was examined before and after the commencement of insulin treatment. Third, the particle size distribution of IDL and LDL was examined by electron microscopy. A comparison was made between control and insulin-treated diabetics.
Increased Ch concentrations were found in the IDL₁ (Sf20-60) fraction of normolipidemic diabetics, which suggests an important role of this fraction for the development of atheros-clerosis in normolipidemic diabetics. Insulin treatment raised the Ch/Tg ratio of the Tg-rich fraction (Sf 60-400). The appearance of this Ch-rich particle after insulin treatment may indicate the role of exogenous insulin for the development fo atherosclerosis. Insulin-treated diabetics had smaller and Ch-enriched VLDL remnants and larger LDL particles than did nondiabetic control subjects. Thus, we have demonstrated new evidence that insulin is deeply involved in the generation of atherogenic lipoproteins in diadetic subjects.