High density lipoprotein composition in insulin-dependent diabetes mellitus.

Although atherosclerotic cardiovascular disease (ASCVD) is the leading cause of death in insulin-dependent diabetics, plasma levels of high density lipoprotein (HDL) cholesterol (an independent "negative" risk factor for ASCVD) have been reported to be normal or high. To test whether alterations in HDL composition might increase potential risk of insulin-dependent diabetics to ASCVD, their major constituent apolipoproteins, A-I and A-II, were measured and compared with levels in controls. HDL cholesterol levels were slightly higher (P = NS) in diabetics than in controls. The HDL cholesterol/LDL cholesterol ratio (an inverse index of relative risk of developing ASCVD) was significantly higher in diabetic men than in controls (P less than 0.02). HDL composition differed markedly in diabetics and controls: the apolipoprotein A-I/A-II ratio was significantly higher (P less than 0.001) in both diabetic men and women (diabetic men--4.1 +/- 0.5, mean +/- SD, controls 3.6 +/- 0.4; diabetic women--4.6 +/- 0.4, controls 3.9 +/- 0.5). Subsequent analysis of plasma from four patients by analytic ultracentrifugation demonstrated a high correlation (r = 0.993, P less than 0.01) between the apolipoprotein A-I/A-II ratio and HDL2, the cholesterol-rich lighter subclass of HDL thought to be the group of particles involved in reduced risk of ASCVD. Therefore, the alteration of HDL composition in insulin-dependent diabetics appears similar to that associated with reduced risk in nondiabetics. Thus, whether a genetic or acquired abnormality, the high apolipoprotein A-I/A-II ratio in insulin-dependent diabetics does not appear to counteract their increased risk of developing ASCVD.