Inhibition of cholesterol esterification in macrophages and vascular smooth muscle foam cells: evaluation of E5324, an acyl-CoA cholesterol acyltransferase inhibitor.

Cholesteryl esters (CE) comprise the principal lipid class that accumulates within macrophages and smooth muscle cells of the atherosclerotic lesion. Acyl-CoA cholesterol acyl-transferase (ACAT) is the major enzyme responsible for esterification of intracellular cholesterol. We evaluated the ability of E5324 (n-butyl-N'-[-2-[3-(5-ethyl-4-phenyl-1H-imidazol-1-yl)propoxy]-6- methyl-phenyl]urea), a novel, orally absorbable ACAT inhibitor, to inhibit esterification of fatty acids to cholesterol and CE accumulation in macrophages and in smooth muscle cells. E5324 significantly inhibited cholesterol esterification in rat aortic smooth muscle cells and in macrophages. In addition, E5324 reduced the cellular mass of CE, the significant measure of the efficacy of drugs designed to modulate cholesterol metabolism. E5324 treatment of macrophages exposed to acetylated low-density lipoprotein reduced CE mass by 97%, and treatment of lipid-loaded smooth muscle cells reduced CE mass by 29%. Although free cholesterol increased approximately twofold, this free cholesterol would presumably be accessible to the membrane for efflux in vivo (reverse cholesterol transport). These results demonstrate that E5324 can inhibit cholesterol esterification and CE mass in atherosclerotic foam cells, derived from either macrophages or arterial smooth muscle cells.