Increased cholesterol-ester formation during forced cholesterol synthesis in rat hepatocytes

Abstract

By comparing the incorporation of 3H20 and [14C]mevalonate into cholesterol in suspensions of rat hepatocytes, it was calculated that the cholesterol biosynthesis could be stimulated 4--7-fold by addition of mevalonate. The addition of 3.3--6.7 mM mevalonate also caused a 5--6-fold increase in the proportion of newly synthesized cholesterol that was esterifield. The esterification of radioactive cholesterol, entering the cells by exchange with surrounding plasma lipoproteins was also increased, indicating that a true increase in the rate of cholesterol ester formation rather than a more selective utilization of newly synthesized cholesterol for esterification, occurred. The increase in cholesterol esterification was not abolished by cycloheximide, indicating that it did not require an increased synthesis of cholesterol esterifying enzyme. Instead the data suggest that the supply of cholesterol to the esterifiable pool may be an important factor, regulating the rate of cholesterol ester formation in rat liver. The addition of 0.5 mM oleic acid to the medium did not increase the degree of cholesterol esterification significantly, whereas 2 mM oleic acid bound to 1% albumin increased the proportion of newly synthesized cholesterol that was esterified, by about 70%. The cells secreted radioactive cholesterol esters into the medium. Cycloheximide inhibited this secretion to about 80% but did not affect the rate at which newly synthesized cholesterol was transferred to surrounding plasma lipoproteins.