Inhibitors of cholesterol biosynthesis. Further studies of the metabolism of 5α-cholest-8(14)-en-3β-ol-15-one in rat liver preparations

5α-Cholest-8(14)-en-3β-ol-15-one is a potent inhibitor of sterol biosynthesis in mammalian cells in culture and has significant hypocholesterolemic activity upon oral administration to rodents and non-human primates. The conversion of the 15-ketosterol to cholesterol upon incubation with the 10,000 × g supernatant fraction of rat liver homogenate preparations under aerobic conditions has been reported (D.J. Monger, E.J. Parish and G.J. Schroepfer, Jr. (1980) J. Biol. Chem. 255, 11122–11129). Presented herein are results of studies of the metabolism of [2,4- 3H]5α-cholest-8(14)-en-3β-ol-15-one obtained upon incubation with the microsomal, cytosolic and the 10,000 × g supernatant fractions of liver homogenates of female rats under a variety of conditions. The results of these studies indicated metabolism of the 15-ketosterol to materials with the chromatographic properties of fatty acid esters of the 15-ketosterol, fatty acid esters of C 27-monohydroxysterols, a component similar to the 15-ketosterol (possibly an isomer of the Δ 8(14)-15-ketosterol), and a polar component. Detailed studies of the C 27-monohydroxysterols obtained from incubation of the 15-ketosterol under anaerobic conditions indicated the formation of labeled 5α-cholesta-8, 14-dien-3β-ol and a 5α-cholest-7-en-3β-ol which were characterized by their behavior on silicic acid column chromatography, by the behavior of their acetate derivatives on medium pressure liquid chromatography on alumina-AgNO 3 columns, and by co-crystallization of the labeled sterols with authentic unlabeled standards. The identification of 5α-cholesta-8, 14-dien-3β-ol and 5α-cholest-7-en-3β-ol as metabolites of the 15-ketesterol, coupled with previous studies of the metabolism of 5α-cholesta-8, 14-dien-3β-ol and of 5α-cholest-8(14)-ene-3β, 15α-diol and 5α-cholest-8(14)-ene-3β, 15β-diol has permitted the formulation of a scheme for the overall metabolism of the 15-ketosterol to cholesterol.