Inhibitors of sterol synthesis. Differential effects of 14 alpha-hydroxymethyl-5 alpha-cholest-7-ene-3 beta, 15 alpha-diol and 14 alpha-hydroxymethyl-5 alpha-cholest-6-ene-3 beta, 15 alpha-diol on sterol synthesis in cell-free homogenates of rat liver

Abstract

14 alpha-Hydroxymethyl-5 alpha-cholest-7-ene-3 beta, 15 alpha-diol and 14 alpha-hydroxymethyl-5 alpha-cholest-6-ene-3 beta, 15 alpha-diol have been shown to be potent inhibitors of the synthesis of digitonin-precipitable sterols in mouse L-cells and in primary cultures of fetal mouse liver cells and to cause a reduction in the levels of activity of 3-hydroxy-3-methylglutaryl-CoA reductase in the same cells (Schroepfer, G. J., Jr., Parish, E. J., Pascal, R. A., Jr., and Kandutsch, A. A. (1980) J. Lipid Res. 21, 571-584). In the present study, we have found that both sterols have a second, but distinct, site of action, distal to the formation of mevalonic acid. 14 alpha-Hydroxymethyl-5 alpha-cholest-7-ene-3 beta, 15 alpha-diol has been found to be a potent inhibitor of the synthesis of digitonin-precipitable sterols from labeled mevalonate in cell-free preparations of rat liver. This inhibition was accompanied by a striking accumulation of labeled lanosterol and 24,25-dihydrolanosterol. The latter sterols were fully characterized by the results of chromatographic and co-crystallization experiments. In contrast, 14 alpha-hydroxymethyl-5 alpha-cholest-6-ene-3 beta, 15 alpha-diol had only a slight effect on the synthesis of digitonin-precipitable sterols from labeled mevalonate in cell-free rat liver preparations. The delta 6-3 beta, 15 alpha, 32-triol had no apparent effect on the metabolism of lanosterol and 24,25-dihydrolanosterol but caused a substantial accumulation of labeled 5 alpha-cholest-8-en-3 beta-ol which was fully characterized by the results of chromatographic and co-crystallization experiments. These findings are compatible with a specific inhibition of the metabolism of lanosterol and 24,25-dihydrolanosterol by the delta 7-3 beta, 15 alpha, 32-triol and a specific inhibition of the delta 8 leads to delta 7 isomerase by the delta 6-3 beta, 15 alpha, 32-triol. [2,4]3H]14 alpha-Hydroxymethyl-5 alpha-cholest-7-ene-3 beta, 15 alpha-diol, prepared by chemical synthesis, was not convertible to cholesterol upon incubation, under aerobic conditions, with a cell-free homogenate preparation of rat liver. The labeled delta 7-3 beta, 15 alpha, 32-triol was, however, metabolized to several polar compounds.