LpA-I levels do not reflect preβ1-HDL levels in human plasma

High-density lipoprotein (HDL) containing apo A-I but no apo A-II (LpA-I) can promote cholesterol efflux from cells, while HDL containing apo A-I and apo A-II can not. Preβ1-HDL, a minor fraction of LpA-I, is the initial acceptor of cellular cholesterol. To determine whether the preβ1-HDL:LpA-I ratio is constant in human plasma, we measured LpA-I levels by differential electroimmunoassay, and HDL subfraction levels by nondenaturing 2-dimensional gel electrophoresis in 26 subjects. We found that the preβ1-HDL:LpA-I ratio was higher in hypercholesterolemia (0.21±0.09; n=11, P<0.05), coronary artery disease (0.26±0.13; n=5, P=0.08) and hypertriglyceridemia (0.39±0.22; n=3, P=0.16) than in normolipidemia (0.11±0.03, n=5). LpA-I levels were significantly correlated with HDL2b (r=0.771, P=0.000001), HDL2a (r=0.438, P<0.01), and preβ2-HDL levels (r=0.496, P<0.005) but not with preβ1-HDL or HDL3 levels. In conclusion, the preβ1-HDL:LpA-I ratio is not constant in human plasma. These findings strongly suggest that size distribution of LpA-I may change in various disorders.