Turnover of individual cholesterol esters in human liver and plasma.

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Abstract
The incorporation of radioactivity into the individual cholesterol esters of liver and plasma was studied in 5 subjects requiring abdominal surgery. After the injection of either cholesterol-4-C labeled lipo-proteins or 3H-mevalonic acid, the distribution of radioactivity and the fatty acid composition were measured in the separated cholesterol esters. Similar studies were carried out in the subcellular fractions of liver in one of the subjects. In the livers of 2 additional subjects, only the fatty acid composition was determined in the cholesterol esters of the subcellular fractions. The composition of cholesterol esters differed in liver and plasma in that the proportion of saturated esters (palmitate and stearate) was considerably higher in the liver, whereas that of linoleate was higher in the plasma. There were major differences in the cholesterol esters of the different subcellular fractions. The mitochondria and microsomes were particularly rich in stearate. In the liver, the distribution of radioactivity differed substantially from the fatty acid composition, especially with respect to linoleate and the saturated esters. Proportionately more radioactivity was incorporated into linoleate than into the other esters and proportionately less into the saturated esters. This heterogeneity among the esters was also found in the mitochondria and microsomes, but not in the supernatant. The distribution of radioactivity among the cholesterol esters of plasma resembled the fatty acid composition, indicating that their turnover rates were of the same order. The distribution of radioactivity among the hepatic cholesterol esters resembled to some extent that in the plasma esters, indicating a a degree of relationship between them. The results are consistent with the existence of several pools of cholesterol esters in the liver differing both in composition and metabolism.