The In Vivo Turnover of Individual Cholesterol Esters in Human Plasma Lipoproteins *

Abstract

Studies were conducted of the turnover rates of individual cholesterol esters in whole plasma and in each of 3 plasma lipoprotein fractions in man. Two normal fasting men were injected intravenously with C14-mevalonic acid, and serial plasma samples were then collected. Plasma lipoprotein fractions were separated by ultracentrifugation at densities of 1.019, 1.063 and 1.21. Following silicic acid column chromatography of the lipid extracts, the specific radioactivity of each of the 4 cholesterol ester groups (saturated, mono-, di-, and tetraunsaturated esters) was determined by a combination of gas-liquid and thin-layer chromatography. Marked differences were observed in the relative rates of appearance of radioactivity in the cholesterol esters of the different plasma lipoproteins. Both subjects showed the greatest fractional turnover rate in the high density lipoprotein cholesterol esters, and the smallest fractional turnover rate in the low density (density 1.019 to 1.063) lipoprotein cholesterol esters. Within each lipoprotein, all the different cholesterol esters turned over at the same fractional rate.