In the early stage of atherosclerogenesis, macrophages which have penetrated into the intima efficiently take up modified low density lipoprotein store cholesterol and fatty acids as a form of neutral lipids such as cholesteryl ester and triacylglycerol in the cytosolic lipid droplets, and are converted into foam cells, leading to the development of atherosclerosis in the arterial wall. During the course of our screening program for anti-atherosclerotic agents of microbial origin, a culture broth of Beauveria sp. FO-6979 was found to inhibit lipid droplet formation in mouse peritoneal macrophages. Eight structurally related cyclodepsipeptides, beauveriolide I and III to IX, were isolated by solvent extraction, column chromatographies and HPLC from the mycelium fraction cultured in the tryptone-supplemented medium. Beauveriolide I was previously reported as an insectcidal agent and beauveriolide IX was identical to beauverolide Fa, but the others were found to be new. Beauveriolide III was white powder, and its molecular formula was established as C_<27>H_<41>N_3O_5 by high resolution FAB-MS. The structure of beauveriolide III was elucidated to be cyclo-[(3S,4S)-3-hydroxy-4-methyloctanoyl-L-phenylalanyl-L-alanyl-D-alloisoleucyl] by NMR spectral analyses and chemical degradation. Addition of L-Ile to the culture medium yielded a high and selective production of beauveriolide III. Beauveriolides I and III caused a reduction in the number and size of cytosolic lipid droplets in macrophages at 10μM without any cytotoxic effect. Studies on the mode of action revealed that they inhibit ACAT activity specifically. Their in vivo efficiency was shown in LDL receptor knockout mice, reducing the atherogenic lesion in aortas and hearts after 2-month oral administration of beauveriolides. Beauveriolides are expected to develop as a lead for a new type of anti-atherosclerotic drugs.
