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

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.

Effect of phenylmethylsulfonyl fluoride on sterol biosynthesis in 10,000 x g supernatant fraction of rat liver homogenates

Phenylmethylsulfonyl fluoride (PMSF), a reagent commonly employed for the inhibition of serine proteases, has been found to cause significant inhibition of the incorporation of labeled acetate, but not mevalonate, into nonsaponifiable lipid and digitonin-precipitable sterols in the 10,000 X g supernatant fraction of rat liver homogenate preparations. In two experiments, the extent of inhibition of the synthesis of digitonin-precipitable sterols from acetate by PMSF at 1 mM was 81 and 65%. PMSF inhibited the synthesis of nonsaponifiable lipid from acetate at concentrations as low as 0.1 microM. Preincubation of the 10,000 X g supernatant fraction of rat liver homogenates with PMSF (1 mM) resulted in a significant reduction of the activities of acetate thiokinase and 3-hydroxy-3-methylglutaric acid (HMG)-CoA synthase, but did not affect the activities of acetoacetyl-CoA thiolase. Preincubation of rat liver microsomes with PMSF (1 mM) caused a 50% reduction in the level of HMG-CoA reductase activity. The combined results indicate that major sites of action of PMSF in the inhibition of sterol biosynthesis from labeled acetate appear to be on the activities of acetate thiokinase, HMG-CoA synthase, and HMG-CoA reductase. Another reagent used to inhibit serine proteases, diisopropylfluorophosphate, had (at a concentration of 1 mM) no effect on the activities of cytosolic acetoacetyl-CoA thiolase, HMG-CoA synthase, and HMG-CoA reductase.

Sterol synthesis. A simplified method for the synthesis of 32-oxygenated derivatives of 24,25-dihydrolanosterol

A simplified method is described for the preparation of 14 alpha-hydroxymethyl-4,4-dimethyl-5 alpha-cholest-8-en-e beta-ol, 14 alpha-hydroxymethyl-4,4-dimethyl-5 alpha-cholest-7-en-3 beta-ol, and 14 alpha-hydroxymethyl-4,4-dimethyl-5-alpha-cholest-6-en-3 beta-ol from commercial lanosterol. This method represents a modification of the approach introduced by Fried and co-workers (Fried, J., J. W. Brown, and L. Borkenhagen. 1965. Tetrahedron Lett. 2499-2504).

Sterol synthesis: a simple method for the isolation of zymosterol (5 alpha-cholesta-8, 24-dien-3 beta-ol) from yeast and spectral properties of zymosterol

A relatively simple method is described for the isolation of zymosterol (5 alpha-cholesta-8, 24-dien-3 beta-ol) of high purity from baker's yeast. Also presented are detailed spectral properties, including 13C NMR spectral analyses, of zymosterol and its acetate derivative.

15-Oxygenated sterols. Enzymatic conversion of [2,4]3H]5 alpha-cholest-8(14)-en-3 beta-ol-15-one to cholesterol in rat liver homogenate preparations

5 alpha-Cholest-8(14)-en-3 beta-ol-15-one is a very potent inhibitor of sterol biosynthesis in animal cells in culture (G. J. Schroepfer, Jr., E. J. Parish, H. W. Chen, and A. A. Kandutsch (1977) J. Biol. Chem. 252, 8975-8980) and has significant hypocholesterolemic activity upon dietary administration to normal animals (G. J. Schroepfer, Jr., D. Monger, A. S. Taylor, J. S. Chamberlain, E. J. Parish, A. Kisic, and A. A. Kandutsch (1977) Biochem. Biophys. Res. Commun. 78, 1227-1233). In the present study we have prepared [2,4-3H]5 alpha-cholest-8(14)-en-3 beta-ol-15-one by chemical synthesis. This compound has been shown to be convertible to cholesterol upon incubation with the 10,000 X g supernatant fraction of rat liver homogenates under aerobic conditions. The efficiency of this conversion was higher in preparations derived from male rats than in those obtained from female rats. Labeled 5 alpha-cholest-7-en-3 beta-ol was also isolated and characterized as a product of the metabolism of the labeled delta 8(14)-15-ketosterol. The demonstration of the enzymatic conversion of 5 alpha-cholest-8(14)-en-3 beta-ol-15-one to cholesterol in liver preparations suggests that previous estimates of the biological potency of this compound may be much lower than the true values and/or that metabolites of this compound may be the active species responsible for its biological actions.

Inhibition of sterol biosynthesis in animal cells by 14 alpha-hydroxymethyl sterols

The chemical syntheses of a number of 14 alpha-hydroxymethyl sterols and 14 alpha -hydroxymethyl-15 alpha-hydroxysterols and their derivatives have been pursued to permit evaluation of their activity in the inhibition of sterol biosynthesis in animal cells in culture. Described herein are chemical syntheses of 7 alpha,8 slpha-epoxy-14 alpha-methyl-5 alpha-cholestan-3 beta,15 alpha-diol, 14 alpha-methyl-5 alpha-cholestan-3 beta,7 alpha,15 alpha-triol, 3 beta,15 alpha-diacetoxy-14 alpha-methyl-5 alpha-cholestan-7 alpha-ol, 3 beta,15 alpha-diacetoxy-7 alpha,32-epoxy-14 alpha-methyl-5 alpha-cholestane, 14 alpha-hydroxymethyl-5 alpha-cholest-6-en-3 beta,15 alpha-diol, 14 alpha-hydroxymethyl-5 alpha-cholest-7-en-3 beta,15 alpha-diol, 7 alpha,32-epoxy-14 alpha-methyl-5 alpha-cholestan-3 beta,15 alpha-diol, 14 alpha-hydroxymethyl-5 alpha-cholest-6-en-3-one, 14 alpha-hydroxymethyl-5 alpha-cholest-7-en-3-one, and 14 alpha-hydroxymethyl-5 alpha-cholets-7-en-15 alpha-ol-3-one. The effects of eight of the above compounds and of 14 alpha-hydroxymethyl-5 alpha-cholest-8-en-3 beta-ol, 14 alpha-hydroxymethyl-5 alpha-cholest-7-en-3 beta-ol, 14 alpha-hydroxymethyl-5 alpha-cholest-6-en-3 beta-ol, and 7 alpha,32-epoxy-14 alpha-methyl-5 alpha-cholestan-3 beta-ol on the synthesis of digitonin-precipitalbe sterols and on levels of HMG-CoA reductase activity in L cells and in primary cultures of fetal mouse liver cells have been investigated. All of the 14 alpha-hydroxymethyl sterols and 14 alpha-hydroxymethyl-15 alpha-hydroxysterols were found to be potent inhibitors of sterol synthesis and to reduce the levels of HMG-CoA reductase activity in these cells. Since hydroxylation of the 14 alpha-methyl group of 14 alpha-methyl sterol precursors of cholesterol can be considered as an obligatory step in the biosynthesis of cholesterol, the finding that 14 alpha-hydroxymethyl sterols are potent inhibitors of cholesterol biosynthesis and cause a reduction in the levels of HMG-CoA reductase activity raises the possibility that oxygenated sterol precursors of cholesterol, such as 14 alpha-hydroxymethyl sterols, may play an important role in the regulation of cholesterol synthesis and in the regulation of processes dependent upon mevalonate and sterol formation.

Cycloheximide inhibits sterol biosynthesis in cell-free preparations of rat liver

Cycloheximide, frequently used as an inhibitor of protein synthesis in vivo and in vitro, has been found to cause a significant reduction of the synthesis of digitonin-precipitable sterols from acetate, but not from mevalonate, at a concentration of 1 mM in the 10,000 x g supernatant fraction of rat liver homogenate preparations. The results of studies of the metabolism of labeled leucine under the same conditions indicated that the effect of cycloheximide on sterol synthesis from acetate was not related to an effect of cycloheximide on protein synthesis. Preincubation of the 10,000 x g supernatant fraction of rat liver homogenates with cycloheximide (1 mM) caused a significant reduction in the levels of acetate thiokinase and hydroxymethylglutaryl-CoA synthase activities but not of acetoacetyl-CoA thiolase activity. Preincubation of the 100,000 x g supernatant fraction of rat liver homogenates with cycloheximide (1 mM or 0.3 mM) also caused a significant reduction of the levels of hydroxymethylglutaryl-CoA synthase activity. When cycloheximide (1 mM) was preincubated with the 100,000 x g supernatant fraction, a reduction in the level of acetate thiokinase activity was observed. Preincubation of rat liver microsomes with cycloheximide (1 mM and 3 mM) had no effect on the level of hydroxymethylglutaryl-CoA reductase activity. These results suggest that biological effects observed upon exposure of cells or tissues to high concentrations of cycloheximide may not be exclusively due to effects of the cycloheximide on the synthesis of protein.

Inhibition of sterol biosynthesis by 14 alpha-hydroxy-delta 7-sterols

5 alpha-Cholest-7-en-3 beta, 14 alpha-diol and 5 alpha-cholest-7-en-14 alpha-ol-3-one have been found to be potent inhibitors of the synthesis of digitonin-precipitable sterols in L cells in culture and to reduce the levels of HMG-CoA reductase activity in these cells.

15-Oxygenated sterols with the unnatural cis-C-D ring junction. Studies of the metabolism of 5 alpha,14 beta-cholest-7-ene-3 beta,15 alpha-diol and 5 alpha,14 beta-cholest-7-ene-3 beta,15 beta-diol

Four 15-oxygenated sterols with the "unnatural" cis-C-D ring juncture have recently been shown to be potent inhibitors of sterol synthesis in animal cells in culture (Schroepfer, G.J., Jr., Parish, E.J., Chen, H.W., and Kandutsch, A.A. (1977) J. Biol. Chem. 252, 8975-8980; Schroepfer, G.J., Jr., Pascal, R.A., Jr., and Kandutsch, A.A. (1979) Biochem. Pharmacol. 28, 249-252). In the present study we have prepared two of these sterols, [2,4-3H]5 alpha,14 beta-cholest-7-ene-3 beta,15 alpha-diol and [2,4-3H]5 alpha,14 beta-cholest-7-ene-3 beta,15 beta-diol, in labeled form, 5 alpha,14 beta-Cholest-7-ene-3 beta, 15 alpha-diol, but not its 15 beta-hydroxy epimer, was shown to be efficiently converted to cholesterol in 10,000 x g supernatant fractions of liver homogenate preparations from both male and female rats. After incubation of [2,4-3H]5 alpha,14 beta-cholest-7-ene-3 beta,15 alpha-diol with these enzyme preparations a number of labeled products, in addition to cholesterol, were isolated and characterized. These included 5 alpha-cholesta-8,14-dien-3 beta-ol, cholesta-5,7-dien-3 beta-ol, 5 alpha-cholest-8-en-3 beta-ol, and 5 alpha-cholest-7-en-3 beta-ol. A scheme to account for the enzymatic formation of cholesterol and the other sterol precursors of cholesterol is presented.

Concerning the structure of 7 alpha,15 beta-dichloro-5 alpha-cholest-8(14)-en-3 beta-ol, a novel inhibitor of cholesterol biosynthesis

Treatment of 3 beta-p-bromobenzoyloxy-14 alpha,15 alpha-epoxy-5 alpha-cholest-7-ene with gaseous HCl in chloroform at -25 degrees C gave 3 beta-p-bromobenzoyloxy-7 alpha,15 beta-dichloro-5 alpha-cholest-8(14)-ene in 93% yield. The structure of the latter compound was unequivocally established by the results of X-ray crystallographic analysis.

Sterol synthesis. Chemical synthesis of 5 alpha-cholest-7-en-3 beta, 14 alpha-diol

Reported herein is the chemical synthesis of 5 alpha-cholest-7-en-3 beta, 14 alpha-diol by mild Wolff-Kishner reduction of 3 beta-acetoxy-8 alpha, 14 alpha-epoxy-5 alpha-cholestan-7-one. The preparation of 5 alpha-cholest-7-en-14 alpha-ol-3-one from 5 alpha is also described. These compounds were fully characterized by the results of infrared, nuclear magnetic resonance, and high and low resolution mass spectral studies.

Inhibition of sterol biosynthesis in animal cells by 14 alpha-alkyl-substituted 15-oxygenated sterols

Reported herein are the results of investigations of the effects of a number of 14 alpha-alkyl-substituted 15-oxygenated sterols, prepared by chemical synthesis, on sterol biosynthesis and the levels of 3-hydroxy-3-methylglutaryl CoA reductase activity in L cells and in primary cultures of fetal mouse liver cells grown in serum-free media. Several of the compounds, most notably 14 alpha-ethyl-5 alpha-cholest-7-en-3 beta, 15 alpha-diol and 14 alpha-ethyl-5 alpha-cholest-7-en-15 alpha-ol-3-one, were found to be extraordinarily potent inhibitors of sterol synthesis in these cells. For example, the latter compound caused a 50% inhibition of the incorporation of labeled acetate into digitonin-precipitable sterols in L cells in culture at a concentration of 6 X 10(-9) M.