Importance of cholesterol and oxysterols metabolism in the pharmacology of tamoxifen and other AEBS ligands

Tamoxifen is one of the major drugs used for the hormonotherapy of estrogen receptor positive breast cancers. However, its therapeutic efficacy can be limited by acquired resistance and tumor recurrence can occur after several years of treatment. Tamoxifen is known as the prototypical modulator of estrogen receptors, but other targets have been identified that could account for its pharmacology. In particular, tamoxifen binds with high affinity to the microsomal antiestrogen binding site (AEBS) and inhibits cholesterol esterification at therapeutic doses. We have recently shown that the AEBS was a hetero-oligomeric complex composed of 3β-hydroxysterol-Δ(8)-Δ(7)-isomerase and 3β-hydroxysterol-Δ(7)-reductase, that binds different structural classes of ligands, including selective estrogen receptor modulators, several sigma receptor ligands, poly-unsaturated fatty acids and ring B oxysterols. We established a link between the modulation of cholesterol metabolism by tamoxifen and other AEBS ligands and their capacity to induce breast cancer cell differentiation, apoptosis and autophagy. Moreover, we showed that the AEBS carries out cholesterol-5,6-epoxide hydrolase activity and established that cholesterol-5,6-epoxide hydrolase is a new target for tamoxifen and other AEBS ligands. Finally in this review, we report on recent data from the literature showing how the modulation of cholesterol and oxysterol metabolism can be linked to the antitumor and chemopreventive properties of tamoxifen, and give new perspectives to improve the clinical outcome of the hormonotherapy of breast cancers.     

Sterol synthesis: studies of the metabolism of 14 alpha-methyl-5 alpha-cholest-7-en-3 beta-ol

[3 alpha-3H]14 alpha-Methyl-5 alpha-cholest-7-en-3 beta-ol has been prepared by chemical synthesis. The metabolism of this compound has been studied in the 10,000 g supernatant fraction of liver homogenates of female rats. Efficient conversion to cholesterol was observed. Other labeled compounds recovered after incubation of [3 alpha-3H]14 alpha-methyl-5 alpha-cholest-7-en-3 beta-ol with the enzyme preparations include the unreacted substrate, 5 alpha-cholesta-7,14-dien-3 beta-ol, 5 alpha-cholesta-8,14-dien-3 beta-ol, cholesta-5,7-dien-3 beta-ol, 5 alpha-cholest-8(14)-en-3 beta-ol, 5 alpha-cholest-8-en-3 beta-ol, and 5 alpha-cholest-7-en-3 beta-ol. In addition, significant amounts of incubated radioactivity were recovered in steryl esters. The steroidal components of these esters were found to contain labeled 14 alpha-methyl-5 alpha-cholest-7-en-3 beta-ol, 5 alpha-cholesta-8,14-dien-3 beta-ol, 5 alpha-cholesta-7,14-dien-3 beta-ol, 5 alpha-cholest-8-en-3 beta-ol, 5 alpha-cholest-7-en-3 beta-ol, and cholesterol.     

Correlation between serum levels of some cholesterol precursors and activity of HMG-CoA reductase in human liver

The possibility that the serum concentrations of various cholesterol precursors may reflect the activity of the hepatic HMG-CoA reductase was investigated in humans under different conditions. The serum levels of squalene, free and esterified lanosterol, (4 alpha, 4 beta, 14 alpha-trimethyl-5 alpha-cholest-8, 24-dien-3 beta-ol), two dimethylsterols (4 alpha, 4 beta-dimethyl-5 beta-cholest-8-en-3 beta-ol and 4 alpha, 4 beta-dimethyl-5 alpha-cholest-8, 24-dien-3 beta-ol), two methostenols (4 alpha-methyl-5 alpha-cholest-7-en-3 beta-ol and 4 alpha-methyl-5 alpha-cholest-8-en-3 beta-ol), two lathosterols (5 alpha-cholest-7-en-3 beta-ol and 5 alpha-cholest-8-en-3 beta-ol) and desmosterol (cholest-5, 24-dien-3 beta-ol) were measured in untreated patients (n = 7) and patients treated with cholestyramine (QuestranR, 8 g twice daily for 2-3 weeks, n = 5) or chenodeoxycholic acid (15 mg/kg body weight daily for 3-4 weeks, n = 8) prior to elective cholecystectomy. The activity of the hepatic microsomal HMG-CoA reductase was measured in liver biopsies taken in connection with the operation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Inhibition of sterol synthesis by delta 5-sterols in a sterol auxotroph of yeast defective in oxidosqualene cyclase and cytochrome P-450

Synthesis of ergosterol is demonstrated in the GL7 mutant of Saccharomyces cerevisiae. This sterol auxotroph has been thought to lack the ability to synthesize sterols due both to the absence of 2,3-oxidosqualene cyclase and to a heme deficiency eliminating cytochrome P-450 which is required in demethylation at C-14. However, when the medium sterol was 5 alpha-cholestan-3 beta-ol, 5 alpha-cholest-8(14)-en-3 beta-ol, or 24 beta-methyl-5 alpha-cholest-8(14)-en-3 beta-ol, sterol synthesis was found to proceed yielding 1-3 fg/cell of ergosterol (24 beta-methylcholesta-5,7,22E-trien-3 beta-ol). Ergosterol was identified by mass spectroscopy, gas and high performance liquid chromatography, ultraviolet spectroscopy, and radioactive labeling from [3H]acetate. Except for some cholest-5-en-3 beta-ol (cholesterol) which was derived from the 5 alpha-cholestan-3 beta-ol, the stanol and the two 8(14)-stenols were not significantly metabolized confirming the absence of an isomerase for migration of the double bond from C-8(14) to C-7. Drastic reduction of ergosterol synthesis to not more than 0.06 fg/cell was observed when the medium sterol either had a double bond at C-5, as in the case of cholesterol, or could be metabolized to a sterol with such a bond. Thus, both 5 alpha-cholest-8(9)-en-3 beta-ol and 5 alpha-cholest-7-en-3 beta-ol (lathosterol) were converted to cholesta-5,7-dien-3 beta-ol (7-dehydrocholesterol), and the presence of the latter dienol depressed the level of ergosterol. The most attractive of the possible explanations for our observations is the assumption of two genetic compartments for synthesis of sterols, one of which has and one of which has not been affected by the two mutations. The ability, despite the mutations, to synthesize small amounts of ergosterol which could act to regulate the cell cycle may also explain why this mutant can grow aerobically with cholesterol (acting in the bulk membrane role) as the sole exogenous sterol.     

Chemical synthesis of three 14 alpha-hydroxymethyl cholestenols.

Reported herein are chemical syntheses of 14 alpha-hydroxymethyl-5 alpha-cholest-8-en-3 beta-ol, 14 alpha-hydroxymethyl-5 alph-cholest-7-en-3 beta-ol, and 14 alpha-hydroxymethyl-5 alpha-cholest-6-en 3 beta-ol. These compounds were obtained in pure form after repeated medium-pressure column chromatography of the mixture obtained by treatment of 3 beta-acetoxy-7 alpha,32-epoxy-14 alpha-methyl-5 alpha-cholestane with pyridine hydrochloride in refluxing acetic anhydride followed by reduction with lithium aluminum hydride. The compounds were characterized by their chromatographic properties and by the results of infrared, optical rotation, nuclear magnetic resonance, and low and high resolution mass spectral studies.     

The conversion of cholest-5-en-3beta-ol into cholest-7-en-3beta-ol by the echinoderms Asterias rubens and Solaster papposus.

1. The echinoderms Asterias rubens and Solaster papposus (Class Asteroidea) metabolize injected [4(-14)C]cholest-5-en-3beta-ol to produce labelled 5alpha-cholestan-3beta-ol and 5alpha-cholest-7-en-3beta-ol. 2. Conversion of 5alpha-[4(-14)C]cholestan-3beta-ol into 5alpha-cholest-7-en-3beta-ol was demonstrated in A. Rubens. 3. Incubations of A. rubens with [4(-14)C]cholest-4-en-3-one resulted in the production of labelled 5alpha-cholestan-3-one, 5alpha-cholestan-3beta-ol and 5alpha-cholest-7-en-3beta-ol. 4. [4(-14)C]Sitosterol was metabolized by A. rubens to give 5alpha-stigmastan-3beta-ol and 5alpha-stigmast-7-en-3beta-ol. 5. The significance of these results in relation to the presence of alpha7 sterols in starfish is discussed.     

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

5 alpha-Cholest-8(14)-en-3 beta-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 x 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]5 alpha-cholest-8(14)-en-3 beta-ol-15-one obtained upon incubation with the microsomal, cytosolic and the 10,000 x 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 C27-monohydroxysterols, a component similar to the 15-ketosterol (possibly an isomer of the delta 8(14)-15-ketosterol), and a polar component. Detailed studies of the C27-monohydroxysterols obtained from incubation of the 15-ketosterol under anaerobic conditions indicated the formation of labeled 5 alpha-cholesta-8,14-dien-3 beta-ol and 5 alpha-cholest-7-en-3 beta-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-AgNO3 columns, and by co-crystallization of the labeled sterols with authentic unlabeled standards. The identification of 5 alpha-cholesta-8,14-dien-3 beta-ol and 5 alpha-cholest-7-en-3 beta-ol as metabolites of the 15-ketesterol, coupled with previous studies of the metabolism of 5 alpha-cholesta-8,14-dien-3 beta-ol and of 5 alpha-cholest-8(14)-ene-3 beta, 15 alpha-diol and 5 alpha-cholest-8(14)-ene-3 beta, 15 beta-diol has permitted the formulation of a scheme for the overall metabolism of the 15-ketosterol to cholesterol.     

Palmitates of isomeric 15-oxygenated delta8(14)-sterols

3 beta-Hexadecanoyloxy-5 alpha-cholest-8(14)-en-15-one, 3 alpha-hexadecanoyloxy-5 alpha-cholest-8(14)-en-15-one, 15 beta- hexadecanoyloxy-5 alpha-cholest-8(14)-en-3 beta-ol, 15 alpha-hexadecanoyloxy-5 alpha-cholest-8(14)-en-3 beta-ol, 15 beta-hexadecanoyloxy-5 alpha-cholest-8(14)-en-3-one, and 15 alpha-hexadecanoyloxy-5 alpha-cholest-8(14)-en-3-one were synthesized and their chromatographic and 1H NMR characteristics were determined. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2004, vol. 30, no. 2; see also http://www.maik.ru.     

Studies of the oxysterol inhibition of tumor cell growth

The oxysterols 3 beta-hydroxy-5 alpha-cholest-8-en-11-one, 3 beta-hydroxy-5 alpha-cholest-8-en-7-one, 3 beta-hydroxy-5 alpha-cholest-8(14)-en-7-one, 3 beta-hydroxy-4,4'-dimethylcholest-5-ene-7 one, 4,4'-dimethylcholest-5-ene-3 beta, 7 alpha-diol, 4,4'-dimethylcholest-5-ene-3 beta, 7 beta-diol, lanost-8-ene-3 beta, 25-diol, 25-hydroxylanost-8-en-3-one, 9 alpha, 11 alpha-epoxy-5 alpha-cholest-7-en-3 beta-ol, 3 beta-hydroxycholest-5 alpha-en-22-one, and 3 beta-hydroxycholest-5-en-22-one oxime were evaluated with respect to their ability to inhibit cell growth. All of the sterols were found to possess cytotoxicity when incubated with hepatoma (HTC) and lymphoma (RDM-4) cells in culture at 10-30 microM concentrations.     

Sterols of scallop. Part II. Structure of unknown sterols by combination gas-liquid chromatography and mass spectrometry.

Four sterols, isolated from the scallop Pacopecten magellanicus have been identified as 24-nor-5alpha-cholest-22-en-3beta-ol; 24-norcholest-5-en-3beta-ol; 5alpha-cholest-22-en-3beta-ol; and (E) -24-propylidenecholest-5-en-3beta-ol. These bring to seventeen the total number of sterols identified in this marine mollusc. A fifth newly detected sterol, closely similar in its mass spectrometric properties is 22-cis and trans-cholesta-5, 22-dien-3beta-ol, was clearly distinguished from these by its shorter retention time by GLC.     

Stereospecific reduction of keto group in 3beta-triphenylmethoxy-5alpha-cholest-8(14)-en-15-one

The reduction of 3 beta-triphenylmethoxy-5 alpha-cholest-8(14)-en-15-one with lithium aluminum hydride resulted in a quantitative yield of 3 beta-triphenylmethoxy-5 alpha-cholest-8(14)-en-15 beta-ol.     

Inhibitors of sterol synthesis. Chemical syntheses, properties and effects of 4,4-dimethyl-15-oxygenated sterols on sterol synthesis and on 3-hydroxy-3-methylglutaryl coenzyme A reductase activity in cultured mammalian cells

The chemical syntheses of a number of 4,4-dimethyl substituted 15-oxygenated sterols have been pursued to permit evaluation of their activity in the inhibition of the biosynthesis of cholesterol and other biological effects. Described herein are the first chemical syntheses of 4,4-dimethyl-14 alpha-ethyl-5 alpha-cholest-7-en-3 beta-ol-15-one, 3 beta,15 alpha-diacetoxy-4,4-dimethyl-14 alpha-ethyl-5 alpha-cholest-7-ene, 3 beta-acetoxy-4,4-dimethyl-14 alpha-ethyl-5 alpha-cholest-7-en-15 beta-ol, 4,4-dimethyl-14 alpha-ethyl-5 alpha-cholest-7-ene-3 beta,15 alpha-diol, 4,4-dimethyl-14 alpha-ethyl-5 alpha-cholest-7-ene-3 beta,15 beta-diol, 4,4-dimethyl-14 alpha-ethyl-5 alpha-cholest-7-en-15 alpha-ol-3-one, 3 beta-benzoyloxy-4,4-dimethyl-5 alpha-cholest-8(14)-ene-7 alpha,15 alpha-diol, 7 alpha,15 alpha-diacetoxy-3 beta-benzoyloxy-4,4-dimethyl-5 alpha-cholest-8(14)-ene, 4,4-dimethyl-5 alpha-cholest-8(14)-en-3 beta-ol-15-one and 3 beta,7 alpha,15 alpha-tri-o-bromobenzoyloxy-5 alpha-cholest-8(14)-ene. Also prepared for use in the biological experiments were 4,4-dimethyl-5 alpha-cholest-7-ene-3 beta,15 alpha-diol, 4,4-dimethyl-5 alpha-cholest-8-ene-3 beta,15 alpha-diol and 4,4-dimethyl-5 alpha-cholest-8(14)-ene-3 beta,7 alpha,15 alpha-triol. The effects of twelve 4,4-dimethyl substituted 15-oxygenated sterols and of four 4,4-dimethyl substituted 32-oxygenated sterols on sterol synthesis and on the level of 3-hydroxy-3-methylglutaryl coenzyme A reductase activity were evaluated in mouse L cells. With the exception of 4,4-dimethyl-5 alpha-cholest-8(14)-ene-3 beta,7 alpha,15 alpha-triol, all of the 4,4-dimethyl substituted 15-oxygenated sterols caused a 50% inhibition of sterol synthesis at less than 10(-6) M and six of the 4,4-dimethyl substituted 15-oxygenated sterols caused a 50% inhibition of sterol synthesis at less than 10(-7) M. 4,4-Dimethyl-14 alpha-ethyl-5 alpha-cholest-7-ene-3 beta,15 alpha-diol caused a 50% decrease in sterol synthesis at 10(-8) M. The potencies of the 4,4-dimethyl substituted 15-oxygenated and C-32-oxygenated sterols with respect to inhibition of sterol synthesis and suppression of 3-hydroxy-3-methylglutaryl coenzyme A reductase activity have been compared with those of the corresponding sterols lacking the 4,4-dimethyl substitution.     

Synthesis, properties and reactions of 3 beta-benzoyloxy-7 alpha-15 beta-dichloro-5 alpha-cholest-8(14)-ene.

Treatment of 3 beta-benzoyloxy-14 alpha,15 alpha-epoxy-5 alpha-cholest-7-ene (I) with gaseous HCl in chloroform at -40 degrees C gave, in 87% yield, 3 beta-benzoyloxy-7 alpha,15 beta-dichloro-5 alpha cholest-8(14)-ene (III). Reduction of the latter compound with lithium aluminum hydride in ether at room temperature for 20 min gave, in 86% yield, 7 alpha-15 beta-dichloro-5 alpha-cholest-8(14)-en-3 beta-ol (IV). The latter compound was fully characterized and assignments of the individual carbon peaks in the 13C nuclear magnetic resonance spectra of this sterol have been completed. Reduction of III with excess lithium aluminum hydride in refluxing ether for 4 days gave, in 74% yield, 5 alpha-cholesta-7,14-dien-3 beta-ol (VI). Reduction of the dichloro-steryl benzoate III with lithium triethylborohydride in tetrahydrofuran gave, in 88% yield, 5 alpha-cholest-8(14)-en-3 beta-ol (VII). A similar reduction using lithium triethylborodeuteride led to the formation of [7 beta, 15 xi-2 H2]-VIIa. Treatment of III with concentrated HCl in a mixture of chloroform and methanol gave, in 79% yield, 3 beta-benzoyloxy-5 alpha-cholest-8(14)-en-15-one (II) which was characterized as such and as the corresponding free sterol.     

The sterols of the echinoderm Asterias rubens

1. Twenty-two sterols were identified in the starfish Asterias rubens (Phylum, Echinodermata; Class, Asteroidea). 2. The major 4-demethyl sterols had a Delta(7) bond and the C(27) compound 5alpha-cholest-7-en-3beta-ol predominated over other mono- and di-unsaturated sterols belonging to the C(26), C(27), C(28) and C(29) series. 3. Small amounts of cholest-5-en-3beta-ol and 5alpha-cholestan-3beta-ol were also present. 4. The minor sterols identified all contained either one or two methyl groups at C-4 and are considered to be potential biosynthetic precursors of 5alpha-cholest-7-en-3beta-ol. 5. Three sterols possessing a 9beta,19-cyclopropane ring were also isolated and were probably derived by the starfish from a dietary source.     

Novel nuclear methylation of sterols by the nematode Caenorhabditis elegans

Caenorhabditis elegans possesses a unique sterol methylation pathway not reported to occur in any other organism and also removes the C-24 ethyl group of sitosterol (a plant sterol). This nematode produced substantial quantities of 4 alpha-methyl-5 alpha-cholest-8(14)-en-3 beta-ol and smaller amounts of lophenol from dietary cholesterol, desmosterol or sitosterol. When C. elegans was propagated in media containing sitosterol plus 25-azacoprostane hydrochloride (25-aza-5 beta-cholestane hydrochloride), an inhibitor of delta 24-sterol reductase in insects, its 4 alpha-methylsterol fraction largely consisted of equal amounts of 4 alpha-methyl-5 alpha-cholesta-7,24-dien-3 beta-ol and 4 alpha-methyl-5 alpha-cholesta-8(14),24-dien-3 beta-ol. Thus 25-azacoprostane hydrochloride inhibited both a delta 24-sterol reductase and a delta 7-sterol isomerase in C. elegans.     

In vitro inhibition of rat liver cholest-5en-3 beta-ol (cholesterol) biosynthesis by non-mercurial sulfhydryl reagents.

In vitro conversion of 2-14C-mevalonate to cholest-5en-3 beta-ol (cholesterol) in rat liver homogenates is inhibited by arsenite, beta-mercaptoethanol, dithiothreitol and ethanethiol. Two sterols containing 20 carbon atoms accumulate under these conditions. One of these is identified as 4,4 dimethyl-5alpha-cholest-8en-3beta-ol and the other tentatively identified as 4,4 dimethyl-5alpha-cholest-8,24-dien-3beta-ol. Based on these observations, these non-mercurial sulfhydryl reagents do not inhibit 5alpha-lanosta-8,24-dien-3beta-ol 14alpha demethylase.     

Sterol biosynthesis in the echinoderm Asterias rubens.

1. [2(-14)C]Mevalonic acid injected into the echinoderm Asterias rubens (Class Asteroidea) was effectively incorporated into the non-saponifiable lipid. 2. The most extensively labelled compounds were squalene and the 4,4-dimethyl sterols with much lower incorporations into the 4alpha-monomethyl and 4-demethyl sterol fractions. 3. Labelled compounds identified were squalene, lanosterol, 4,4-dimethyl-5alpha-cholesta-8,24-dien-3beta-ol and 4alpha-methyl-5alpha-cholest-7-en-3beta-ol; these are all intermediates in sterol biosynthesis. 4. The major sterol in A. rubens, 5alpha-cholest-7-en-3beta-ol, was also labelled showing that this echinoderm is capable of sterol biosynthesis de novo. 5. No evidence was obtained for the incorporation of [2(-14)C]mevalonic acid into the C28 and C29 components of the 4-demethyl sterols or 9beta,19-cyclopropane sterols found in A. rubens and it is assumed that these sterols are of dietary origin. 6. Another starfish Henricia sanguinolenta also incorporated [2(-14)C]mevalonic acid into squalene and lanosterol. 7. Various isolated tissues of A. rubens were all capable of incorporation of [2(-14)C]mevalonic acid into the nonsaponifiable lipid. With the body-wall and stomach tissues radioactivity accumulated in squalene and the 4,4-dimethyl sterols, but with the gonads and pyloric caecae there was a more efficient incorporation of radioactivity into the 4-demethyl sterols, principally 5alpha-cholest-7-en-3beta-ol.     

Concerning the chemical synthesis of 3 beta-hydroxy-5 alpha-cholest-8(14)-en-15-one, a novel regulator of cholesterol metabolism

A four-step synthesis of 3 beta-hydroxy-5 alpha-cholest-8(14)-en-15-one (I) from 7-dehydrocholesterol is described. This synthesis, which is efficient and suitable for kilogram scale work, was carried out in a 33% overall average yield (39% overall best yield). A major byproduct of the hydrolysis of 3 beta-benzoyloxy-14 alpha,15 alpha-epoxy-5 alpha-cholest-7-ene to I was found to be the ring C aromatic sterol 12-methyl-18-nor-5 alpha-cholesta-8,11,13-trien-3 beta-ol. Several other intermediates and byproducts of these reactions were also identified. All new sterols were characterized by 1H- and 13C-NMR.     

Delta8(14)-steroids in the bacterium Methylococcus capsulatus.

The 4,4-dimethyl and 4alpha-methyl sterols of the bacterium Methylococcus capsulatus were identified as 4,4-dimethyl- and 4alpha-methyl-5alpha-cholest-8(14)-en-3beta-ol and 4,4-dimethyl- and 4alpha-methyl-5alpha-cholesta-8(14),24-dien-3beta-ol. Sterol biosynthesis is blocked at the level of 4alpha-methyl delta8(14)-sterols.     

Further studies on the inhibition of sterol biosynthesis in animal cells by 15-oxygenated sterols

The chemical syntheses of a number of C27 15-oxygenated sterols 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 3 alpha-benzoyloxy-5 alpha-cholest-8(14)-en-15-one, 5 alpha-cholest-8(14)-en-3 alpha-ol-15-one, 5 alpha-cholest-8(14)-en-15-one-3 beta-yl pyridinium sulfate, 5 alpha-cholest-8(14)-en-15-one-3 beta-yl potassium sulfate (monohydrate), 5 alpha-cholest-8(14)-en-15-one-3 alpha-yl pyridinium sulfate, 5 alpha-cholest-8(14)-en-3 alpha-yl potassium sulfate (monohydrate), 5 alpha-cholest-8(14)-en3,7,15-trione, 5 alpha-cholest-8(14)-en-15 alpha-ol-3-one, 5 alpha, 14 alpha-cholestan-3 beta, 15 beta-diol diacetate, 5 alpha, 14 beta-cholestan-3 beta, 15 beta-diol diacetate, 5 alpha, 14 alpha-cholestan-3 beta, 15 alpha-diol, 5 alpha, 14 alpha-cholestan-15 alpha-ol-3-one, 5 alpha, 14 beta-cholestan-3 beta, 15 beta-diol, 5 alpha, 14 alpha-cholestan-3,15-dione, and 5 alpha, 14 beta-cholestan-3,5-dione. The effects of 8 of the above compounds and of 5 alpha-cholesta-6,8(14)-dien-3 beta-ol-15-one, 3 beta-he misuccinoyloxy-5 alpha-cholest-8(14)-en-15 one, 3 beta-hexadecanoyloxy-5 alpha-cholest-8(14)-en-15-one, 5 alpha-cholest-8(14)-en-3,15-dione, 5 alpha-cholesta-6,8(14)-dien-3,15-dione, 5 alpha-cholest-8-en-3 beta, 15 alpha-diol, 5 alpha-cholest-7-en-3 beta, 15 alpha-diol, 5 alpha-cholest-8(14)-en-15 alpha-ol-3-one, 5 alpha-cholest-8-en-15 alpha-ol-3-one, and 5 alpha-cholest-7-en-15 alpha-ol-3-one on the synthesis of digitonin-precipitable sterols and on levels of HMG-CoA reductase activity have been investigated and compared with previously published data on 7 other C27 15-oxygenated sterols.