Cholesteryl ester metabolism in tissue culture cells. I. Accumulation in Fu5AH rat hepatoma cells

Exposure of Fu5AH rat hepatoma tissue culture cells to hyperlipemic rabbit serum results in the accumulation of cellular cholesteryl esters. Accumulation is not a characteristic of all cells in culture, as evidenced by the lack of response of mouse and human fibroblasts. Fu5AH cells grown for 24 hr on 5% hyperlipemic rabbit serum have an 8‐ to 12‐fold increase of cellular cholesteryl esters, small increases in free cholesterol and triglycerides, and no change in phospholipids, when compared to cells grown in normal rabbit serum. Rapid accumulation of cholesteryl esters occurs during the first 8–12 hr of incubation, and maximum cellular concentration is achieved within 24 hr. The maximum level of cellular cholesteryl esters obtained with individual samples of hyperlipemic rabbit serum is correlated with the cholesterol content of the original sera, even when the incubation medium is adjusted to a constant concentration of cholesterol. Heating hyperlipemic rabbit serum (60 C/30 min) does not destroy activity; however, no cholesteryl ester accumulation occurs in heated cells. The stimulatory activity of hyperlipemic rabbit serum primarily is associated with lipoproteins having densities <1.006. High levels of cellular cholesteryl ester are associated with the appearance of cytoplasmic vacuoles containing cholesteryl esters. The increase in cellular cholesteryl esters is accompanied by a decrease of the cholesteryl esters in the growth medium. Cellular cholesteryl esters are not rapidly hydrolyzed or released upon removal of hyperlipemic rabbit serum.