Distribution of lipids and apolipoproteins in human plasma by vertical spin ultracentrifugation

A study on the fractionation of human plasma into various lipoprotein classes was performed by single spin vertical ultracentrifugation. Detailed apolipoprotein (A-I, A-II, B, C-III, and E) and lipid (cholesterol, cholesterol ester, and triacylglycerol) analyses were performed on the fractions obtained by single spin vertical ultracentrifugation. ApoB was located primarily in the low-density lipoprotein (LDL) fraction whereas Lp(a) was detected in the fractions extending into the high-density lipoprotein region. The distributions of ApoA-I and ApoA-II varied among individuals, suggesting heterogeneity in the composition of HDL, and this was confirmed by the distributions of ApoC-III, ApoD, and ApoE. ApoC-III and ApoD were associated primarily with HDL3 while ApoE showed the most variation among subjects, spreading across the entire density spectrum. Distributions of cholesterol and cholesterol ester coincided with the elution of major apolipoproteins A-I and B while the distribution of triacylglycerol was variable. An immunoassay for lecithin:cholesterol acyltransferase (LCAT) demonstrated that the majority of LCAT was present in the high- to very high-density lipoprotein region, but LCAT was also detected in LDL and the immunoreactivity extended into the very low-density lipoprotein region. The presence of apolipoproteins A-I and A-II, as well as LCAT in the intermediate lipoprotein density region (LDL1) was consistent with these species representing lipolytic remnants. This study indicated that rapid (3 h) single spin vertical ultracentrifugation offers insights into the heterogeneity of lipoproteins and offers a useful tool for monitoring perturbations of the plasma lipid transport system. In conjunction with immunosorbers, immunoassays, and micro lipid analyses, this procedure offers a method to isolate and characterize various lipoprotein subspecies.