Rapid labeling of lipoproteins in plasma with radioactive cholesterol. Application for measurement of plasma cholesterol esterification.

In order to efficiently and rapidly label lipoproteins in plasma with [3H]cholesterol, micelles consisting of lysophosphatidylcholine (lysoPC) and [3H]cholesterol (molar ratio, 50:1) were prepared. When trace amounts of these micelles were injected into plasma, [3H]cholesterol rapidly equilibrated among the plasma lipoproteins, as compared to [3H]cholesterol from an albumin-stabilized emulsion. The distributions of both [3H]cholesterol and unlabeled free cholesterol in plasma lipoproteins were similar in labeled plasma samples. This method of labeling can be used for the measurement of cholesterol esterification, or lecithin:cholesterol acyltransferase activity, in small amounts (20-40 microliters) of plasma samples.