Role of acid lipase in cholesteryl ester accumulation during atherogenesis: Correlation of enzyme activity with acid lipase-containing macrophages in rabbit and human lesions

Purified acid lipase was previously shown to hydrolyze the artificial substrate, α-naphthyl palmitate, as well as triglycerides and cholesteryl esters and to form cholesteryl esters. To determine to what extent these activities are associated with acid lipase-containing cells in atherosclerotic plaques, we examined rabbit aortas at different stages of experimental lesion induction and human atherosclerotic arteries. Assays of cholesteryl ester formation, and α-naphthyl palmitate and cholesteryl ester hydrolysis were performed on homogenates of lesions and the hydrolysis of the artificial fatty acid ester was used as a histochemical marker to identify acid lipase positive foam cells in sections of the same lesions. The volume of lesions occupied by cells stained for acid lipase correlated strongly with the enzyme activities of the arterial homogenates. These results suggest that acid lipase-containing cells may mediate the accumulation of cholesteryl ester during atherogenesis. Since acid lipase activity marks macrophages, these methods may be useful for relating macrophage distribution and function to lesion progression, regression, and complication.