Bile acid synthesis from HDL cholesterol and cholesterol ester by cultured chick embryo hepatocytes

1. 1. A comparison of the uptake and conversion of HDL cholesterol and cholesterol ester to bile acids by chick embryo hepatocytes showed the following. (a) Considerable amounts of cholesterol but not cholesterol ester accumulated in the cells. (b) Cholesterol ester was hydrolyzed to cholesterol, 60% of which was converted to bile acids. (c) Approximately 3-5-times more cholesterol ester than cholesterol were converted to bile acids. 2. 2. The degradation of ¹²⁵I-labelled HDL by the hepatocytes was negligible. 3. 3. Chloroquine did not inhibit the conversion of HDL cholesterol and cholesterol ester to bile acids. 4. 4. HDL stimulated the conversion of [¹⁴C]mevalonolactone to cholesterol, the greater part of which was found in the medium. Its conversion to bile acids was not affected. 5. 5. The cholesterol pool of hepatocytes was labelled by preincubation with [¹⁴C]mevalonolactone. Upon addition of ³H-labelled HDL cholesterol, cholesterol efflux and influx were measured simultaneously. Both processes were dependent on HDL concentration and time of incubation. Efflux exceeded influx, drawing upon the cholesterol and cholesterol ester reserves of the cell. 6. 6. Bile acids were formed simultaneously from the prelabelled [¹⁴C]cholesterol pool and the exogenously added ³H-labelled HDL cholesterol.