AM-251 and SR144528 are acyl CoA:cholesterol acyltransferase inhibitors.

Oxysterol-induced macrophage apoptosis may have a role in atherosclerosis. Macrophages lacking the type 2 cannabinoid receptor (CB2) are partially resistant to apoptosis induced by 7-ketocholesterol (7KC). AM-251 and SR144528 are selective antagonists of CB1 and CB2 receptors, respectively. We observed that both compounds reduce 7KC-induced apoptosis in Raw 264.7 macrophages. As oxysterol-induced macrophage apoptosis requires acyl-coenzymeA:cholesterol acyltransferase (ACAT) activity, we tested their affects on ACAT activity. AM-251 and SR144528 both reduced cholesteryl ester synthesis in unstimulated and acetylated LDL-stimulated Raw 264.7 macrophages, CB2(+/+) and CB2(-/-) peritoneal macrophages, as well as in vitro, in mouse liver microsomes. Consistent with inhibition of ACAT, the development of foam cell characteristics in macrophages by treatment with acetylated LDL was reduced by both compounds. This work is the first evidence that AM-251 and SR144528 are inhibitors of ACAT and as a result, might have anti-atherosclerotic activities independent of their affect on cannabinoid signaling.