BETA-VLDL-INDUCED CHOLESTEROL ESTER DEPOSITION IN MACROPHAGES MAY BE REGULATED BY NEUTRAL CHOLESTEROL ESTERASE-ACTIVITY

We examined the role of enzyme activities involved in cholesterol ester metabolism in the accumulation of cholesterol ester in macrophages. When [H-3] cholesterol linoleate-beta-very low density lipoproteins (beta-VLDLs) were incubated with rat resident peritoneal macrophages, (RPMs), thioglycolate-elicited macrophages (TEMs), or alveolar macrophages (AMs), cholesterol ester accumulation was the greatest in TEMs and the least in AMs. The uptake of [H-3] cholesterol linoleate-beta-VLDL into AMs was four times that into RPMs, and the uptake into TEMs was twice that into RPMs. The [H-3] cholesterol released from [H-3] cholesterol linoleate-beta-VLDL-loaded AMs was five times higher than from TEMs and RPMs, whereas those from RPMs and TEMs were almost the same. In studies using cell homogenates, the acid cholesterol esterase activity in AMs was 1.7 times that in TEMs and six times that in RPMs. The acyl-coenzyme A:cholesterol acyltransferase (ACAT) activities in AMs and TEMs were similar but were higher than that in RPMs. The neutral cholesterol esterase activity was seven times higher in AMs than in RPMs and TEMs. In the study using intact cells, the hydrolysis of loaded [H-3] cholesterol linoleate-beta-VLDL in the presence of the ACAT inhibitor CL277,082 and the cholesterol [C-14] oleate synthesis from [C-14] oleate were enhanced in AMs about twofold compared with RPMs and TEMs. The reduction of de novo synthesized cholesterol [C-14] oleate in the presence of CL277,082 was enhanced in AMs four times compared with TEMs or RPMs. These results suggest that the accumulation of cholesterol ester is regulated not only by the uptake of lipoprotein but also by the cholesterol release and that the cholesterol release from macrophages might depend on the neutral cholesterol esterase activity.