Regulation of neutral cholesterol esterase activity by phospholipids containing negative charges in substrate liposome.

The effect of phospholipids on cholesteryl ester hydrolysis by neutral cholesterol esterase in alveolar macro- phages was studied. Among the phospholipids used as emul- sifiers, those with a negative charge, such as phosphatidylser- ine, phosphatidic acid, phosphatidylinositol, and cardiolipin, gave a higher level of hydrolysis by neutral cholesterol esterase than other less negatively charged phospholipids, such as phosphatidylcholine, lysophosphatidylcholine, phos- phatidylethanolamine, and sphingomyelin. Phospholipase D treatment of liposomes emulsified with phosphatidylcholine produced phosphatidic acid and enhanced cholesteryl ester hydrolysis. Phospholipase AS treatment produced lysophos- phatidylcholine and decreased the hydrolysis. The hydrolysis of cholesteryl ester in lipid droplets obtained from choles- terol-laden macrophages elicited by thioglycollate in the rat peritoneal cavity was low compared to artificial liposomes emulsified with phosphatidylcholine. The reason for this was speculated to be that lipid droplets were low in total phos- pholipids and poor in phospholipids with strong negative charges but rich in phosphatidylethanolamine and sphin- gomyelin. M These results suggest that the polar heads of phospholipids may play an important role in cholesteryl ester hydrolysis by neutral cho1esterolesterase.-Ishii, I., R. Onozaki, E. Takahashi, S. Takahashi, N. Fujio, T. Harada, N. Morisaki, K. Shirai, Y. Saito, and S. Hirose. Regulation of neutral cholesterol esterase activity by phospholipids contain- ing negative charges in substrate 1iposome.J Lipid Res. 1995. 36 2303-2310.