INCREASED HYDROLYSIS OF CHOLESTERYL ESTER WITH PROSTACYCLIN IS POTENTIATED BY HIGH-DENSITY-LIPOPROTEIN THROUGH THE PROSTACYCLIN STABILIZATION

Prostacyclin (PGI2) has been reported to stimulate activities of acid cholesteryl ester hydrolase (ACEH; EC 3.1.1.13) and neutral cholesteryl ester hydrolase (NCEH; EC 3.1.1.13) in the smooth muscle cells leading to a decrease in intracellular cholesteryl ester. Recently, we have found that the half-life of PGI2 was prolonged through stabilization by HDL. HDL is known to have anti-atherogenic properties, although its precise mechanism has not been fully clarified. We therefore hypothesized that HDL can exert anti-atherogenic action by augmenting PGI2-stimulated increases in the activities of ACEH and NCEH. After incubation with PGI2 and HDL, a cell homogenate was made from which the activities of ACEH and NCEH were assessed. HDL significantly augmented the PGI2-induced increase in the activities of both enzymes. This effect of HDL was abolished in the absence of PGI2. Elevated intracellular levels of cyclic AMP were maintained for longer periods by HDL. The increase in both intracellular cyclic AMP levels and enzyme activities disappeared in the presence of an inhibitor of adenylate cyclase, 2′5′-dideoxyadenosine. Radiolabeled smooth muscle cells demonstrated a significant loss in total cholesterol and cholesteryl ester after treatment with PGI2 and HDL, due to the increase in cholesteryl ester hydrolytic activities. These data suggest that HDL enhanced the PGI2-stimulated hydrolysis of cholesteryl ester and augmented the PGI2-induced reduction of cellular cholesteryl ester content by stabilizing PGI2.