Mobilization of acyl chains from endogenous cellular phospholipids into cholesteryl esters during foam-cell formation in mouse peritoneal macrophages.

We previously showed that phosphatidylserine-containing liposomes (phosphatidylserine liposomes) are effectively metabolized and induce foam-cell formation in cultured macrophages (Nishikawa, K., Arai, H. and Inoue, K. (1990) J. Biol. Chem. 265, 5226-5231). When cultured mouse peritoneal macrophages were incubated with phosphatidylserine liposomes of different cholesterol content, cholesteryl esters were formed in the cells in proportion to the cholesterol content of the liposomes added to the culture. Cholesteryl esters were formed only when the cells took up more than a certain amount of cholesterol (approx. 160% above the basal cell level). Fatty acyl moiety derived from the exogenous phospholipids were utilized preferentially for cholesteryl ester formation. Once cholesterol as an acceptor is exhausted within cells, the acyl chain may be utilized for triacylglycerol formation. Not only exogenous lipid acyl chains but also endogenous phospholipid acyl chains were also utilized for cholesteryl ester and triacylglycerol formation under the present conditions, since the radioactivity in phospholipids was incorporated into both cholesteryl esters and triacylglycerols in macrophages whose endogenous phospholipids had been prelabeled with radioactive fatty acids. Among phospholipid classes, phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, and phosphatidylinositol served as the acyl donor, whereas sphingomyelin and cardiolipin did not. Mobilization of acyl chains from endogenous phospholipids to the neutral lipid fraction was also observed during foam-cell formation induced by acetyl low-density lipoprotein. The substance(s) produced within cell in the process of foam-cell formation may trigger the acyl chain mobilization from endogenous phospholipids.