Isolation and Characterization of Hydroxymethylglutaryl Coenzyme A Reductase Inhibitors from Fermented Soybean Extracts

The present study was carried out to isolate and identify the 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMG-CoA reductase)-inhibiting agents in the lipids of fermented soybeans, Tempeh, since oral feeding of an alcohol extract of Tempeh to hypercholesterolemic rabbits reduced their level of serum cholesterol. Fermented soybeans were extracted with hexane:ethanol, and the extract was separated into different fractions by silica gel column chromatography. One fraction obtained, SF1, inhibited the rat liver microsomal enzyme 94% at a dose of 0.625μg lipid/μl of incubation contents; 0.17μg/μl lead to 50% inhibition. Analysis of SF1 by gas chromatography/mass-spectrometry and fast-atom-bombardment (FAB)/mass-spectrometry revealed the presence of palmitic, stearic, oleic, linolenic, arachidic, and behenic acids. Oleic acid inhibited HMG-CoA reductase 94% at a dose of 0.625μg/μl of incubation contents, and 0.055μg/μl inhibited 50% of the enzyme activity. Enzyme kinetics showed the inhibition was of a mixed type. Linolenic acid, 0.625μg/μl of incubation contents, inhibited the enzyme 100%; and 0.085μg/μl lead to 50% inhibition. The inhibition was competitive. The other fatty acids were less inhibitory (1-18%). Methyl esters of oleic acid and linolenic acid maximally inhibited the enzyme 20 and 15%, respectively.