The mechanism of action of bufalin in inhibition of lipid droplet accumulation in mouse macrophages

Abstract

A cardiotonic glycoside, bufalin, originally isolated from the dried white venom of Chinese toad Bufo gargarizans, was found to inhibit lipid droplet accumulation in mouse macrophages. Bufalin selectively inhibited synthesis of [14C]cholesteryl ester (CE), a main component of lipid droplet, from [14C]oleic acid and [14C]cholesterol with IC50 values of 8.6 Μm and 10 Μm, respectively. The postlysosomal metabolism of cholesterol to CE in macrophages was also inhibited by the compound with a similar IC50 value of 13.2 Μm. However, the compound exhibited almost no effect on acyl-CoA : cholesterol acyltransferase, a key enzyme in CE synthesis localized in the endoplasmic reticulum (ER). From the fluorescent microscopic observation of cellular lipids, bufalin-treated macrophages increased the accumulation of free cholesterol in lysosomes and caused to enlarge the shape and volume of lysosomes as well as pregnenolone-treated macrophages. These findings suggest that bufalin inhibited the postlysosomal metabolism of cholesterol, leading to a reduction of lipid droplets in mouse macrophages without cytotoxicity. © 2013 The Pharmaceutical Society of Japan.