In vitro cholesterol esterification in human serum

We report a simple, convenient, and reproducible method, involving the use of radiolabeled cholesterol dispersed in Tween 20 as a tracer and endogenous lipoproteins as a substrate, for measuring the rate of serum cholesterol esterification in vitro. The reaction of lecithin acyltransferase (EC 2.3.1.43) was enhanced by the presence of Tween 20, which probably accelerates the exchange between radiolabeled cholesterol and endogenous lipoprotein cholesterol. In sera from 65 normal subjects, the in vitro cholesterol esterification rate was significantly correlated (r = 0.47, P = 0.001) with age. The mean rate of esterification of 31 subjects 30 years old or younger was significantly lower than that of 34 subjects 31 to 64 years of age. We found no significant difference in the rate of esterification between men and women. The rate of cholesterol esterification (nmol/ml per h) was significantly correlated with the concentration of endogenous free cholesterol in serum, but the fractional rate (the percentage of radiolabeled cholesterol esterified per hour) was inversely proportional to the endogenous free cholesterol. The fatty acid composition of the cholesteryl esters formed by the acyltransferase reaction may provide an index in recognizing some specific disorder.