Inhibitors of sterol synthesis. Chemical synthesis, structure, and biological activities of (25R)-3 beta,26-dihydroxy-5 alpha-cholest-8(14)-en-15-one, a metabolite of 3 beta-hydroxy-5 alpha-cholest-8(14)-en-15-one

A Facile Synthesis of 3β,25-dihydroxy-5α-Cholest-7-ene, the Precursor to HMG-CoA Reductase Inhibitor

An efficient four-step procedure is described for the synthesis of 3β,25-dihydroxy-5α-cholest-7-ene from 3β-hydroxy-5α-cholesta-7,24-diene in an overall yield of 34%. This product can serve as a precursor for the synthesis of an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase. The 3β-toluene- p-sulfonate ester of 5α-cholesta-7,24-diene was obtained from natural lanolin followed by treatment with toluene- p-sulfonyl chloride. The key step in the synthesis is a very mild method for the hydroxybromination of this ester with N-bromosuccinimide in water, followed by reduction with LiAlH4to obtain the 3β-toluene- p-sulfonate ester of 25-hydroxy-5α-cholesta-7-ene. The final product was obtained after desulfonation of 3β-toluene- p-sulfonyoxy-25-hydroxy-5α-cholesta-7-ene to afford 3β,25-dihydroxy-5α-cholest-7-ene in excellent yield. The reagents are all relatively cheap, non-toxic and stable.

The Effect of Small Molecules on Sterol Homeostasis: Measuring 7-Dehydrocholesterol in Dhcr7-Deficient Neuro2a Cells and Human Fibroblasts

Well-established cell culture models were combined with new analytical methods to assess the effects of small molecules on the cholesterol biosynthesis pathway. The analytical protocol, which is based on sterol derivation with the dienolphile PTAD, was found to be reliable for the analysis of 7-DHC and desmosterol. The PTAD method was applied to the screening of a small library of pharmacologically active substances, and the effect of compounds on the cholesterol pathway was determined. Of some 727 compounds, over 30 compounds decreased 7-DHC in Dhcr7-deficient Neuro2a cells. The examination of chemical structures of active molecules in the screen grouped the compounds into distinct categories. In addition to statins, our screen found that SERMs, antifungals, and several antipsychotic medications reduced levels of 7-DHC. The activities of selected compounds were verified in human fibroblasts derived from Smith-Lemli-Opitz syndrome (SLOS) patients and linked to specific transformations in the cholesterol biosynthesis pathway.

A highly sensitive method for analysis of 7-dehydrocholesterol for the study of Smith-Lemli-Opitz syndrome

We describe a highly sensitive method for the detection of 7-dehydrocholesterol (7-DHC), the biosynthetic precursor of cholesterol, based on its reactivity with 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD) in a Diels-Alder cycloaddition reaction. Samples of biological tissues and fluids with added deuterium-labeled internal standards were derivatized with PTAD and analyzed by LC-MS. This protocol permits fast processing of samples, short chromatography times, and high sensitivity. We applied this method to the analysis of cells, blood, and tissues from several sources, including human plasma. Another innovative aspect of this study is that it provides a reliable and highly reproducible measurement of 7-DHC in 7-dehydrocholesterol reductase (Dhcr7)-HET mouse (a model for Smith-Lemli-Opitz syndrome) samples, showing regional differences in the brain tissue. We found that the levels of 7-DHC are consistently higher in Dhcr7-HET mice than in controls, with the spinal cord and peripheral nerve showing the biggest differences. In addition to 7-DHC, sensitive analysis of desmosterol in tissues and blood was also accomplished with this PTAD method by assaying adducts formed from the PTAD "ene" reaction. The method reported here may provide a highly sensitive and high throughput way to identify at-risk populations having errors in cholesterol biosynthesis.

Stereoselective synthesis and hormonal activity of novel dafachronic acids and naturally occurring steroids isolated from corals

A stereoselective synthesis of (25S)-Δ(1)-, (25S)-Δ(1,4)-, (25S)-Δ(1,7)-, (25S)-Δ(8(14))-, (25S)-Δ(4,6,8(14))-dafachronic acid, methyl (25S)-Δ(1,4)-dafachronate and (25S)-5α-hydroxy-3,6-dioxocholest-7-en-26-oic acid is described. (25S)-Δ(1,4)-Dafachronic acid and its methyl ester are natural products isolated from corals and have been obtained by synthesis for the first time. (25S)-5α-Hydroxy-3,6-dioxocholest-7-en-26-oic acid represents a promising synthetic precursor for cytotoxic marine steroids.

Synthesis and activity of dafachronic acid ligands for the C. elegans DAF-12 nuclear hormone receptor

The nuclear hormone receptor DAF-12 from Caenorhabditis elegans is activated by dafachronic acids, which derive from sterols upon oxidation by DAF-9, a cytochrome P450. DAF-12 activation is a critical checkpoint in C. elegans for acquisition of reproductive competence and for entry into adulthood rather than dauer diapause. Previous studies implicated the (25S)-Delta(7)-dafachronic acid isomer as the most potent compound, but the (25S)-Delta(4)-isomer was also identified as an activator of DAF-12. To explore the tolerance of DAF-12 for structural variations in the ligand and to enable further studies requiring large amounts of ligands for DAF-12 and homologs in other nematodes, we synthesized (25R)- and (25S)-isomers of five dafachronic acids differing in A/B-ring configurations. Both the (25S)- and (25R)-Delta(7)-dafachronic acids are potent transcriptional activators in a Gal4-transactivation assay using HEK-293 cells, with EC(50) values of 23 and 33 nm, respectively, as are (25S)- and (25R)-Delta(4)-dafachronic acids, with EC(50) values of 23 and 66 nm, respectively. The (25S)- and (25R)-Delta(5)-isomers were much less potent, with EC(50) values approaching 1000 nm, and saturated 5alpha- and 5beta-dafachronic acids showed mostly intermediate potencies. Rescue assays using daf- 9-null mutants confirmed the results from transactivation experiments, but this in vivo assay accentuated the greater potencies of the (25S)-epimers, particularly for the (25S)-Delta(7)-isomer. We conclude that DAF-12 accommodates a large range of structural variation in ligand geometry, but (25S)-Delta(7)-dafachronic acid is the most potent and probably biologically relevant isomer. Potency derives more from the A/B-ring configuration than from the stereochemistry at C-25.

Cellular toxicity of oxycholesterols

Oxycholesterols (OS) are formed from cholesterol or its immediate precursors by enzymatic or free radical action in vivo, or they may be derived from food. OS exhibit a wide spectrum of biological activities. In OS cytotoxicity, several mechanisms seem to be involved: e.g. inhibition of HMG-CoA reductase activity, antiproliferative action, apoptosis induction, replacement of cholesterol by OS in membranes followed by changes in cellular membrane structure and functionality, and immune system functions alteration. Furthermore, OS may be mutagenic and carcinogenic and may serve as intracellular signaling or regulatory molecules. Here we review OS cellular activities with special attention to the cytotoxic action in vivo and in vitro using experimental models.

Disrupted coordinate regulation of farnesoid X receptor target genes in a patient with cerebrotendinous xanthomatosis

Cerebrotendinous xanthomatosis (CTX), sterol 27-hydroxylase (CYP27A1) deficiency, is associated with markedly reduced chenodeoxycholic acid (CDCA), the most powerful activating ligand for farnesoid X receptor (FXR). We investigated the effects of reduced CDCA on FXR target genes in humans. Liver specimens from an untreated CTX patient and 10 control subjects were studied. In the patient, hepatic CDCA concentration was markedly reduced but the bile alcohol level exceeded CDCA levels in control subjects (73.5 vs. 37.8 +/- 6.2 nmol/g liver). Cholesterol 7alpha-hydroxylase (CYP7A1) and Na+/taurocholate-cotransporting polypeptide (NTCP) were upregulated 84- and 8-fold, respectively. However, small heterodimer partner (SHP) and bile salt export pump were normally expressed. Marked CYP7A1 induction with normal SHP expression was not explained by the regulation of liver X receptor alpha (LXRalpha) or pregnane X receptor. However, another nuclear receptor, hepatocyte nuclear factor 4alpha (HNF4alpha), was induced 2.9-fold in CTX, which was associated with enhanced mRNA levels of HNF4alpha target genes, CYP7A1, 7alpha-hydroxy-4-cholesten-3-one 12alpha-hydroxylase, CYP27A1, and NTCP. In conclusion, the coordinate regulation of FXR target genes was lost in CTX. The mechanism of the disruption may be explained by a normally stimulated FXR pathway attributable to markedly increased bile alcohols with activation of HNF4alpha caused by reduced bile acids in CTX liver.

Benzophenone-containing cholesterol surrogates: synthesis and biological evaluation

Eight analogs of cholesterol (1) containing a benzophenone group have been synthesized as prospective photoaffinity labels for studies in cellular sterol efflux and HDL formation. Six of these compounds (4-9) have the photophore replacing different portions of the cholesterol alkyl side chain, and two (10 and 11) have it attached via nitrogen at carbon 3. The suitability of these analogs as cholesterol surrogates was determined by examining their ability to replace [3H]1 in fibroblasts preequilibrated with [3H]1. All eight analogs were effective in replacing natural 1 in competition with [3H]1 for apolipoprotein A-I-induced efflux. These are the first compounds shown to replace cholesterol successfully in a complex pathway of multiple intracellular steps. The results suggest an unexpected tolerance of biological membranes regarding the incorporation of sterols of differing chemical structure.

Significance of plasma 7alpha-hydroxy-4-cholesten-3-one and 27-hydroxycholesterol concentrations as markers for hepatic bile acid synthesis in cholesterol-fed rabbits

Plasma 7alpha-hydroxy-4-cholesten-3-one has been used as an index of hepatic bile acid synthesis. The aim of the current study was to ascertain whether the level of this oxysterol reflects hepatic cholesterol 7alpha-hydroxylase activity when plasma cholesterol concentrations are markedly changed. In addition, the relationship of hepatic sterol 27-hydroxylase activity with plasma concentrations of 27-hydroxycholesterol and 3beta-hydroxy-5-cholestenoic acid was studied. We used New Zealand white rabbits fed 2% cholesterol for 5 or 10 days and/or constructed bile fistula. Feeding cholesterol markedly increased and bile drainage reduced plasma cholesterol concentrations. Initially, in these models there was no correlation between plasma 7alpha-hydroxy-4-cholesten-3-one concentrations and hepatic cholesterol 7alpha-hydroxylase activities (r = -0.24, n = 10). Cholesterol feeding was associated with downregulated 7alpha-hydroxylase activities, while plasma 7alpha-hydroxy-4-cholesten-3-one concentrations were elevated in the presence of increased plasma cholesterol levels. However, this discrepancy was overcome and significant correlation was observed (r = 0.73, P <.05, n = 10) by expressing 7alpha-hydroxy-4-cholesten-3-one levels relative to cholesterol. In contrast, hepatic sterol 27-hydroxylase activities were not significantly correlated with plasma absolute (r = 0.23, difference not significant [NS], n = 10) nor cholesterol-related levels of 27-hydroxycholesterol (r = -0.13, NS, n = 10), or 3beta-hydroxy-5-cholestenoic acid concentrations (r = 0.30, NS, n = 10). In conclusion, plasma 7alpha-hydroxy-4-cholesten-3-one concentrations reflected hepatic cholesterol 7alpha-hydroxylase activities when the sterol levels were adjusted to plasma cholesterol concentrations in rabbits with hypercholesterolemia. The results suggest that plasma 7alpha-hydroxy-4-cholesten-3-one relative to cholesterol is a better marker for hepatic cholesterol 7alpha-hydroxylase activity than the absolute concentration when hypercholesterolemia is present. In contrast, 27-hydroxycholesterol and 3beta-hydroxy-5-cholestenoic acid levels in plasma did not reflect hepatic sterol 27-hydroxylase activities even if the levels were adjusted to plasma cholesterol concentrations.

Identification of naturally occurring spirostenols preventing beta-amyloid-induced neurotoxicity

22R-Hydroxycholesterol is an intermediate in the steroid biosynthesis pathway shown to exhibit a neuroprotective property against beta-amyloid (1-42) (Abeta) toxicity in rat PCl2 and human NT2N neuronal cells by binding and inactivating Abeta. In search of potent 22R-hydroxycholesterol derivatives, we assessed the ability of a series of naturally occurring entities containing the 22R-hydroxycholesterol structure to protect PC12 cells against Abeta-induced neurotoxicity, determined by measuring changes in membrane potential, mitochondrial diaphorase activity, ATP levels and trypan blue uptake. 22R-Hydroxycholesterol derivatives sharing a common spirost-5-en-3-ol or a furost-5-en-3-ol structure were tested. Although some of these compounds were neuroprotective against 0.1 microM Abeta, only three protected against the 1-10 microM Abeta-induced toxicity and, in contrast to 22R-hydroxycholesterol, all were devoid of steroidogenic activity. These entities shared a common structural feature, a long chain ester in position 3 and common stereochemistry. The neuroprotective property of these compounds was coupled to their ability to displace radiolabeled 22R-hydroxycholesterol from Abeta, suggesting that the Abeta-22R-hydroxycholesterol physicochemical interaction contributes to their beneficial effect. In addition, a 22R-hydroxycholesterol derivative inhibited the formation of neurotoxic amyloid-derived diffusible ligands. Computational docking simulations of 22R-hydroxycholesterol and its derivatives on Abeta identified two binding sites. Chemical entities, as 22R-hydroxycholesterol, seem to bind preferentially only to one site. In contrast, the presence of the ester chain seems to confer the ability to bind to both sites on Abeta, leading to neuroprotection against high concentrations of Abeta. In conclusion, these results suggest that spirost-5-en-3-ol naturally occurring derivatives of 22R-hydroxycholesterol might offer a new approach for Alzheimer's disease therapy.

Origin of oxysterols in hepatic bile of patients with biliary infection

OBJECTIVES

Oxysterols are ubiquitous in the body and are potential cytotoxic agents in addition to being metabolic regulators. Although bile contains high concentrations of cholesterol, oxysterol concentrations in bile and the effect of infection on oxysterol levels have not been measured, nor has their origin been studied. The purpose of this study was to determine if infection of the biliary tract was associated with increased concentrations of oxysterols in the bile and, if so, which oxysterols showed a significant change.

METHODS

Hepatic bile was obtained from eight patients with biliary tract disease by means of a naso-biliary catheter. Oxysterols were extracted and purified by solid-phase extraction, derivatized and measured by gas chromatography-mass spectrometry.

RESULTS

The following were quantified in hepatic bile: 7-alpha-hydroxycholesterol, 7-beta-hydroxycholesterol, cholestan-3-beta,5-alpha,6-beta-triol, 25-hydroxycholesterol, 26-hydroxycholesterol, 7-ketocholesterol, and 7-alpha-hydroxy-4-cholesten-3-one. Total oxysterols in hepatic bile ranged from 0.133 mumol/L to 7.748 mumol/L (1.47 +/- 2.55 mumol/L). Levels of 7-alpha-hydroxycholesterol and 7-beta-hydroxycholesterol were increased in infected bile (14.2 +/- 15.1 x 10(-3)% of cholesterol vs 1.9 +/- 0.5 x 10(-3)% of cholesterol, p < 0.05, and 22.0 +/- 25.0 x 10(-3)% of cholesterol vs 1.6 +/- 1.2 x 10(-3)% of cholesterol, p < 0.05, respectively). Serum C-reactive protein levels correlated positively with biliary levels of 7-alpha-hydroxycholesterol (R = 0.948), 7-beta-hydroxycholesterol (R = 0.976), cholestan-3-beta,5-alpha,6-beta-triol (R = 0.823), 7-alpha-hydroxy-4-cholesten-3-one (R = 0.846,) and 7-ketocholesterol (R = 0.973). Different oxysterols were found in gallstones, chiefly 3-keto-cholest-4-ene (624 +/- 316 parts per million [ppm] of dry weight), 3-keto-cholesta-4,6-diene (240 +/- 329 ppm) and 7-keto-cholesterol (77 +/- 81 ppm). Incubation of human leukocytes with model bile in the presence of bacterial lipopolysaccharide resulted in changes in sterol composition, including increases in oxysterols. We have identified and quantified oxysterols from uninfected and infected human hepatic bile and from gallstones and gallbladder bile. Biliary infection may be involved in the biogenesis of oxysterols in bile through the production of reactive oxygen species from activated leukocytes.

Effects of dietary 27-hydroxycholesterol on cholesterol metabolism and bile acid biosynthesis in the hamster

27-hydroxycholesterol (27OH-Chol) is an important endogenous oxysterol resulting from the action of sterol 27-hydroxylase (CYP27A1) on cholesterol in the liver and numerous extrahepatic tissues. It may act as a modulator of cholesterol and bile acid metabolism. The effects of 27OH-Chol on the main enzymes and receptors of cholesterol metabolism were investigated by feeding male hamsters a diet supplemented with 27OH-Chol (0.1% w/w) for 1 week. Intestinal scavenger class B, type I (SR-BI) protein level was decreased (–65%), but hepatic expression was increased (+34%). Liver 3β-hydroxy-3β-methyl glutaryl coenzyme A reductase (–58%), cholesterol 7α-hydroxylase (–54%), oxysterol 7α-hydroxylase (–44%), and sterol 12α-hydroxylase (–70%) activities were all decreased. Bile acid composition was changed (fourfold increase in the chenodeoxycholic/cholic acid ratio). This study demonstrates that dietary 27OH-Chol modulates major enzymes of cholesterol metabolism and alters the biliary bile acid profile, making it more hydrophobic, at least at this level of intake. Its effects on SR-BI protein levels are organ dependent. The properties of 27OH-Chol or its metabolites on cholesterol metabolism probably result from the activation of specific transcription factors. Key words: cholesterol 7α-hydroxylase (CYP7A1), sterol 12α-hydroxylase (CYP8B1), sterol 27-hydroxylase (CYP27A1), 3β-hydroxy-3β-methyl glutaryl coenzyme A reductase (HMGCoAR), scavenger receptor class B type I (SR-BI).

27-Hydroxylation of 7- and 8-dehydrocholesterol in Smith-Lemli-Opitz syndrome: a novel metabolic pathway

Smith-Lemli-Opitz syndrome (SLOS) is attributable to mutations in the gene coding for 7-dehydrocholesterol reductase. Low to absent enzyme activity accounts for the accumulation of both 7-dehydrocholesterol and 8-dehydrocholesterol in plasma and other tissues. Since oxysterols can participate in the regulation of cholesterol homeostasis, we examined the possibility that they are formed from these dehydrocholesterol intermediates. In patients with SLOS, we found serum levels of 27-hydroxy-7-dehydrocholesterol ranging from 0.1 to 0.25micro M and evidence for circulating levels of 27-hydroxy-8-dehydrocholesterol (0.04-0.51 micro M). Picomolar quantities of 27-hydroxy-7-dehydrocholesterol were identified in normal individuals. Biologic activities of 27-hydroxy-7-dehydrocholesterol were found to include inhibition of sterol synthesis and the activation of nuclear receptor LXRalpha but not that of LXRbeta. These activities occurred at concentrations found in plasma and presumably at those existing in tissues. Thus, patients with SLOS have increased levels of metabolites derived from intermediates in cholesterol synthesis that are biologically active and may contribute to the regulation of cholesterol synthesis in vivo.

Chromatographic behavior of oxygenated derivatives of cholesterol

Oxygenated derivatives of cholesterol have important functions in many biochemical processes. These oxysterols are difficult to study because of their low physiological concentrations, the facile formation of cholesterol autoxidation artifacts, and lack of information on their chromatographic behavior. Focusing on metabolites and autoxidation products of cholesterol, we have documented the chromatographic mobilities of 35 oxysterols under a variety of conditions: eight solvent systems for thin-layer chromatography on silica gel, several mobile phases for reversed-phase high-performance liquid chromatography (HPLC), and two types of stationary phase for capillary gas chromatography (GC) using trimethylsilyl derivatives. Notable differences in selectivity could be obtained by modifying the stationary or mobile phases. Separations of oxysterol pairs isomeric at side-chain carbons or C-7 were achieved on normal-phase, reversed-phase, chiral, or silver-ion HPLC columns. Chromatographic behavior is also described for side-chain hexadeuterated and heptafluorinated oxysterols, which are useful as standards in isotope dilution analyses and autoxidation studies, respectively. The overall results are relevant to many problems of oxysterol analysis, including the initial separation of oxysterols from cholesterol, determination of highly polar and nonpolar oxysterols, separation of isomeric pairs, selection of derivatization conditions for GC analysis, and quantitation of the extent of cholesterol autoxidation.

Synthesis of (25R)-26-hydroxycholesterol

We describe the synthesis of (25R)-cholest-5-en-3beta,26-diol ((25R)-26-hydroxycholesterol) from diosgenin in four steps in 58% overall, yield via a modified Clemmensen reduction followed by a Barton deoxygenation reaction.

Studies toward the synthesis of the shark repellent pavoninin-5

Sharks are the most dangerous predators of people in the sea, resulting in people being mauled and killed each year. A shark repellent could help to diminish this danger. The aglycone of the shark repellent pavoninin-5, (25R)-cholest-5-en-3beta,15alpha,26-triol (5a), was synthesized from diosgenin (9). Removing mercury from the Clemmensen reduction of 9 gave a higher yield of (25R)-cholest-5-en-3beta,16beta,26-triol, 10a, and was also more environmentally friendly. Attempted methods for the transposition of the C-16beta hydroxyl to the 15alpha position are described. A successful method for this transposition via the 15alpha-hydroxy-16-ketone, 8a, using the Barton deoxygenation reaction on the 16-alcohol 14b, is reported.

Selective inhibition of CYP27A1 and of chenodeoxycholic acid synthesis in cholestatic hamster liver

The aim of this study was to explore the regulation of serum cholic acid (CA)/chenodeoxycholic acid (CDCA) ratio in cholestatic hamster induced by ligation of the common bile duct for 48 h. The serum concentration of total bile acids and CA/CDCA ratio were significantly elevated, and the serum proportion of unconjugated bile acids to total bile acids was reduced in the cholestatic hamster similar to that in patients with obstructive jaundice. The hepatic CA/CDCA ratio increased from 3.6 to 11.0 (P<0.05) along with a 2.9-fold elevation in CA concentration (P<0.05) while the CDCA level remained unchanged. The hepatic mRNA and protein level as well as microsomal activity of the cholesterol 7alpha-hydroxylase, 7alpha-hydroxy-4-cholesten-3-one 12alpha-hydroxylase and 5beta-cholestane-3alpha,7alpha,12alpha-triol 25-hydroxylase were not significantly affected in cholestatic hamsters. In contrast, the mitochondrial activity and enzyme mass of the sterol 27-hydroxylase were significantly reduced, while its mRNA levels remained normal in bile duct-ligated hamster. In conclusion, bile acid biosynthetic pathway via mitochondrial sterol 27-hydroxylase was preferentially inhibited in bile duct-ligated hamsters. The suppression of CYP27A1 is, at least in part, responsible for the relative decreased production of CDCA and increased CA/CDCA ratio in the liver, bile and serum of cholestatic hamsters.

Side chain hydroxylations in bile acid biosynthesis catalyzed by CYP3A are markedly up-regulated in Cyp27-/- mice but not in cerebrotendinous xanthomatosis

The accumulation of various 25-hydroxylated C(27)-bile alcohols in blood and their excretion in urine are characteristic features of cerebrotendinous xanthomatosis (CTX) a recessively inherited inborn error of bile acid synthesis caused by mutations in the mitochondrial sterol 27-hydroxylase (CYP27) gene. These bile alcohols may be intermediates in the alternative cholic acid side chain cleavage pathway. The present study was undertaken to identify enzymes and reactions responsible for the formation of these bile alcohols and to explain why Cyp27(-/-) mice do not show CTX-related abnormalities. Microsomal activities of 5beta-cholestane-3alpha,7alpha,12alpha-triol 25- and 26-hydroxylases, 5beta-cholestane-3alpha,7alpha,12alpha,25-tetrol 23R-, 24S-, and 27-hydroxylases and testosterone 6beta-hydroxylase, a marker enzyme for CYP3A, in Cyp27(-/-) mice livers were markedly up-regulated (5.5-, 3.5-, 6.5-, 7.5-, 2.9-, and 5.4-fold, respectively). In contrast, these enzyme activities were not increased in CTX. The activities of 5beta-cholestane-3alpha,7alpha,12alpha-triol 25- and 26-hydroxylases and 5beta-cholestane-3alpha,7alpha,12alpha,25-tetrol 23R-, 24R-, 24S-, and 27-hydroxylases were strongly correlated with the activities of testosterone 6beta-hydroxylase in control human liver microsomes from eight unrelated donors. Troleandomycin, a specific inhibitor of CYP3A, markedly suppressed these microsomal side chain hydroxylations in both mouse and human livers in a dose-dependent manner. In addition, experiments using recombinant overexpressed human CYP3A4 confirmed that these microsomal side chain hydroxylations were catalyzed by a single enzyme, CYP3A4. The results demonstrate that microsomal 25- and 26-hydroxylations of 5beta-cholestane-3alpha,7alpha,12alpha-triol and microsomal 23R-, 24R-, 24S-, and 27-hydroxylations of 5beta-cholestane-3alpha,7alpha,12alpha,25-tetrol are mainly catalyzed by CYP3A in both mice and humans. Unlike Cyp27(-/-) mice, CYP3A activity was not up-regulated despite marked accumulation of 5beta-cholestane-3alpha,7alpha,12alpha-triol in CTX.

Synthesis of 7alpha-hydroxy derivatives of regulatory oxysterols

7alpha-Hydroxy derivatives of oxysterols are of considerable interest because of their possible involvement in regulation of cholesterol metabolism. This paper describes stereoselective syntheses and complete characterization of the 7alpha-hydroxy derivatives of four key oxysterols: 25-hydroxycholesterol, 27-hydroxycholesterol, 24(S)-hydroxycholesterol, and 24(S), 25-epoxycholesterol.

Oxysterols: modulators of cholesterol metabolism and other processes

Oxygenated derivatives of cholesterol (oxysterols) present a remarkably diverse profile of biological activities, including effects on sphingolipid metabolism, platelet aggregation, apoptosis, and protein prenylation. The most notable oxysterol activities center around the regulation of cholesterol homeostasis, which appears to be controlled in part by a complex series of interactions of oxysterol ligands with various receptors, such as the oxysterol binding protein, the cellular nucleic acid binding protein, the sterol regulatory element binding protein, the LXR nuclear orphan receptors, and the low-density lipoprotein receptor. Identification of the endogenous oxysterol ligands and elucidation of their enzymatic origins are topics of active investigation. Except for 24, 25-epoxysterols, most oxysterols arise from cholesterol by autoxidation or by specific microsomal or mitochondrial oxidations, usually involving cytochrome P-450 species. Oxysterols are variously metabolized to esters, bile acids, steroid hormones, cholesterol, or other sterols through pathways that may differ according to the type of cell and mode of experimentation (in vitro, in vivo, cell culture). Reliable measurements of oxysterol levels and activities are hampered by low physiological concentrations (approximately 0.01-0.1 microM plasma) relative to cholesterol (approximately 5,000 microM) and by the susceptibility of cholesterol to autoxidation, which produces artifactual oxysterols that may also have potent activities. Reports describing the occurrence and levels of oxysterols in plasma, low-density lipoproteins, various tissues, and food products include many unrealistic data resulting from inattention to autoxidation and to limitations of the analytical methodology. Because of the widespread lack of appreciation for the technical difficulties involved in oxysterol research, a rigorous evaluation of the chromatographic and spectroscopic methods used in the isolation, characterization, and quantitation of oxysterols has been included. This review comprises a detailed and critical assessment of current knowledge regarding the formation, occurrence, metabolism, regulatory properties, and other activities of oxysterols in mammalian systems.

Synthesis of (25R)-26-hydroxy-15-ketosterols

(25R)-3beta,26-Dihydroxy-5alpha-cholest-8(14)-en-15-one (1) and (25R)-3beta,26-dihydroxy-5alpha,14beta-cholest-16-en-1 5-one (2) were synthesized from (25R)-3beta,26-dibenzoyloxy-5alpha,14alpha-chole st-16-ene (4). Oxidation of 4 with CrO3-3,5-dimethylpyrazole at -20 degrees C gave (25R)-3beta,26-dibenzoyloxy-5alpha,14alpha-chole st-16-en-15-one (5) along with (25R)-3beta,26-dibenzoyloxy-5alpha-cholest-16alpha+ ++,17alpha-epoxide (6). Oxidation of 5 with selenium dioxide afforded (25R)-3beta,26-dibenzoyloxy-5alpha-cholest-8(14),16-++ +dien-15-one (7) and (25R)-3beta,26-dibenzoyloxy-5alpha,14beta-choles t-16-en-15-one (8). Selective hydrogenation of 7 followed by hydrolysis in alcoholic potassium hydroxide yielded (25R)-3beta,26-dihydroxy-5alpha-cholest-8(14)-en-15-one (1). Hydrolysis of 5 and 8 in alcoholic potassium hydroxide provided (25R)-3beta,26-dihydroxy-5alpha,14beta-cholest-16-en-1 5-one (2).

Sterol synthesis. Preparation and characterization of fluorinated and deuterated analogs of oxygenated derivatives of cholesterol

Oxygenated sterols, including both autoxidation products and sterol metabolites, have many important biological activities. Identification and quantitation of oxysterols by chromatographic and spectroscopic methods is greatly facilitated by the availability of authentic standards, and deuterated and fluorinated analogs are valuable as internal standards for quantitation. We describe the preparation, purification and characterization of 43 oxygenated sterols, including the 4 beta-hydroxy, 7 alpha-hydroxy, 7 beta-hydroxy, 7-keto, and 19-hydroxy derivatives of cholesterol and their analogs with 25,26,26,26,27,27,27-heptafluoro (F7) and 26,26,26,27,27,27-hexadeuterio (d6) substitution. The 7 alpha-hydroxy, 7 beta-hydroxy, and 7-keto derivatives of (25R)-cholest-5-ene-3 beta, 26-diol (1d) and their 16,16-dideuterio analogs were also prepared. These d2-26-hydroxysterols and [16,16-2H2]-(25R)-cholest-5-ene-3 beta, 26-diol (1e) were synthesized from [16,16-2H2]-(25R)-cholest-5-ene-3 beta, 26-diol diacetate (2e), which can be prepared from diosgenin. The highly specific deuterium incorporation at C-16 in 1e and 2e should be useful in mass spectral analysis of 26-hydroxycholesterol samples by isotope dilution methods. The delta 5-3 beta, 7 alpha, 26- and delta 5-3 beta, 7 beta, 26-triols were regioselectively oxidized/isomerized to the corresponding delta 4-3-ketosteroids with cholesterol oxidase. Also described are 5,6 alpha-epoxy-5 alpha-cholestan-3 beta-ol, its 5 beta,6 beta-isomer, cholestane-3 beta, 5 alpha,6 beta-triol, their F7 and d6 derivatives, and d3-25-hydroxycholesterol, which was prepared from 3 beta-acetoxy-27-norcholest-5-en-25-one (30). The 43 oxysterols and most synthetic intermediates were isolated in high purity and characterized by chromatographic and spectroscopic methods, including mass spectrometry and nuclear magnetic resonance (NMR) spectroscopy. Detailed mass spectral assignments are presented, and 1H NMR stereochemical assignments are derived for the C-19 protons of 19-hydroxysterols and for the side-chain protons of 30.

Sterol synthesis. Synthesis of 3 beta-hydroxy-25,26,26,26,27,27,27-heptafluorocholest-5-en-7-one and its effects on HMG-CoA reductase activity in Chinese hamster ovary cells, on ACAT activity in rat jejunal microsomes, and serum cholesterol levels in rats

3 beta-Hydroxycholest-5-en-7-one (I; 7-ketocholesterol) is an oxysterol of continuing interest in biology and medicine. In the present study, we have prepared a side-chain fluorinated analog, 3 beta-hydroxy-25,26,26,26,27,27,27-heptafluorocholest-5-en-7-one (VI), with the anticipation that the F7 substitution would block major metabolism of the 7-ketosterol, and thereby enhance its potential in vivo effects on serum cholesterol levels and other parameters. Chromium trioxide/dimethyl pyrazole oxidation of the acetate derivative of the previously described 25,26,26,26,27,27,27-heptafluorocholest-5-en-3 beta-ol (Swaminathan et al., 1993. J. Lipid Res. 34, 1805-1823) followed by mild alkaline hydrolysis gave VI. The effects of VI on 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase activity in Chinese hamster ovary (CHO-K1) cells, on acyl coenzyme A-cholesterol acyltransferase (ACAT) activity in rat jejunal microsomes, and on serum cholesterol levels and other parameters in male Sprague-Dawley rats were determined and compared with those obtained with I and with another alpha, beta-unsaturated ketosterol, i.e. 3 beta-hydroxy-5 alpha-cholest-8(14)-en-15-one (II). I and VI showed essentially the same potency, considerably less than that of II, in lowering the levels of HMG-CoA reductase activity in CHO-K1 cells. Whereas addition of II to rat jejunal microsomes inhibited ACAT activity (IC50 approximately 3 microM), I and VI had no effect under the conditions studied (from 1 to 16 microM). Dietary administration of I, at levels of 0.1 and 0.15%, had no effect on food consumption, gain in body weight, or serum cholesterol levels. At 0.2%, I caused a modest decrease in body weight gain and a slight decrease in serum cholesterol levels (relative to ad libitum but not pair-fed control animals). The F7-7-ketosterol VI, at 0.26% in diet (the molar equivalent of 0.2% I), had no effect on food consumption, body weight, or serum cholesterol levels. Administration of I (0.1, 0.15 or 0.2% in diet) caused increases in the weight of small intestine. In contrast, no effect of VI (0.26% in diet) on small intestinal weight was observed.

Synthesis of [3 alpha-3H]7-dehydrocholesterol via stable tritiated 4-phenyl-1,2,4-triazoline-3,5-dione derivative

Synthesis of [3 alpha-3H]7-dehydrocholesterol is described via protection of the 5,7-diene system in 7-dehydrocholesterol as the Diels-Alder adduct with 4-phenyl-1,2,4-triazoline-3,5-dione followed by oxidation of the hydroxyl group to give the 3-oxo adduct. Reduction of the keto adduct with [3H]sodium borohydride produced the adduct of [3 alpha-3H]7-dehydrocholesterol from which the radiolabeled sterol was obtained via treatment with lithium aluminum hydride. The advantage of the method is that highly labeled [3 alpha-3H]7-dehydrocholesterol can be prepared. Further, unlike 7-dehydrocholesterol, its adduct with 4-phenyl-1,2,4-triazoline-3,5-dione is stable and can be stored. This allows the preparation of small batches of [3 alpha-3H]7-dehydrocholesterol for immediate use in biological experiments, and losses due to decomposition of excess radiolabeled 7-dehydrocholesterol are minimized.

Inhibitors of sterol synthesis. Synthesis and spectral properties of 3 beta-hydroxy-25,26,26,26,27,27,27-heptafluoro-5 alpha-cholestan-15-one

3 beta-Hydroxy-25,26,26,26,27,27,27-heptafluoro-5 alpha-cholestan-15-one (4) has been prepared as part of a program to synthesize 15-ketosterols that are not readily metabolized to cholesterol or side-chain oxygenated species. Saponification of 3 beta-acetoxy-5 alpha-chola-8(14),23-dien-15-one (5) followed by lithium-ammonia reduction with a bromobenzene quench gave 3 beta-hydroxy-5 alpha-chol-23-en-15-one (6). Addition of (CF3)2CFI to 6 in the presence of triethylborane gave an iodide preparation, which was reduced to 4 with tributyltin hydride (71% overall yield of 4 from 5). The 23-iodide preparations consisted of 6:1 mixtures of (23R)-3 beta-hydroxy-23-iodo-25,26,26,26,27,27,27-heptafluoro-5 alpha-cholestan-15-one (9a) and its C-23 epimer 9b with variable amounts of 4. Compound 4 was also prepared by lithium-ammonia reduction of the delta 8(14) analogs of 4 and iodides 9a and 9b. The presence of small amounts of 6 in the latter product suggested a side reaction involving cleavage of the C24-C25 bond with loss of a (CF3)2CF radical. Also prepared were 25,26,26,26,27,27,27-heptafluoro-5 alpha-cholestane-3 beta, 15 alpha-diol, its 15 beta epimer, the 7 alpha-methyl analog of 4, 3 beta-hydroxy-7 alpha-methyl-5 alpha-cholestan-15-one (16), and (25R)-3 beta,26-dihydroxy-5 alpha-cholestan-15-one. Full 1H and 13C-NMR data of high precision with complete signal assignments are given for all new compounds. Definitive 1H-NMR stereochemical assignments of the C-24 protons were established for most sterols with a C8H17 side chain based on analysis of the downfield H-24 resonance in a 750-MHz spectrum of 16. Detailed electron-impact mass spectral data are presented together with a summary of major fragmentation patterns for 15-hydroxy- and 15-ketosteroids with and without a delta 8(14) bond.

27-hydroxylated low density lipoprotein (LDL) cholesterol can be converted to 7alpha,27-dihydroxy-4-cholesten-3-one (cytosterone) before suppressing cholesterol production in normal human fibroblasts. Evidence that an altered metabolism of ldl cholesterol can underlie a defective feedback control in malignant cells

The formation of oxysterols in cultured human fibroblasts and their physiological roles as intracellular regulators of cholesterol production have been investigated. In the presence of low density lipoproteins (LDL), normal fibroblasts converted LDL cholesterol to 27hydroxycholesterol, which was further metabolized to 7alpha, 27-dihydroxycholesterol, 7alpha,27-dihydroxy-4-cholesten-3-one, and 7alpha-hydroxy-3-oxo-4-cholestenoic acid. Autooxidation products of cholesterol contaminating the lipoproteins were also metabolized in the cells. 7alpha-Hydroxycholesterol was converted to 7alpha-hydroxy-4-cholesten-3-one prior to 27-hydroxylation and further oxidation to 7alpha-hydroxy-3-oxo-4-cholestenoic acid. 7beta-Hydroxycholesterol and 7-oxocholesterol were 27-hydroxylated and then oxidized to C27-acids. Oxidation of the 7beta-hydroxy group also occurred. 25-Hydroxycholesterol was 7alpha-hydroxylated and further oxidized to 7alpha,25-dihydroxy-4-cholesten-3-one. 25-Hydroxylation of sterols was observed only under specific conditions. In contrast, only small amounts of oxysterols were formed in virus-transformed human fibroblasts when incubated with lipoproteins. This was due to very low activities of the 27- and 7alpha-hydroxylating enzymes. The rate of oxidation at C-3 was also decreased moderately. A defective suppression of 3-hydroxy-3-methylglutaryl coenzyme A reductase by LDL and autooxidation products of cholesterol observed in the transformed fibroblasts could be caused by the deficiencies of the sterol-metabolizing enzymes, since these cells responded normally to the sterol metabolites 7alpha,27-dihydroxy-4-cholesten-3-one, 7alpha, 25-dihydroxy-4-cholesten-3-one, and 27-hydroxy-7-oxo-cholesterol. These metabolites, which all possessed an oxo group with a conjugated double bond in the steroid nucleus and a hydroxyl group in the side chain, did not seem to require further metabolism in order to be active. An impaired response to LDL was also seen in other human tumor cells, including breast carcinoma, colonic carcinoma, and malignant melanoma cells. Common to all the malignant cells was an intracellular shortage of 7alpha, 27-dihydroxy-4-cholesten-3-one caused by a decreased formation or an increased metabolism.

Review of progress in sterol oxidations: 1987-1995

Material dealing with the chemistry, biochemistry, and biological activities of oxysterols is reviewed for the period 1987-1995. Particular attention is paid to the presence of oxysterols in tissues and foods and to their physiological relevance.

Chemical synthesis of 15-ketosterols and their inhibitions of cholesteryl ester transfer protein

Described herein are the chemical syntheses of 3 beta-hydroxy-5 alpha-cholest-8(14)-en-15-one and 3 beta-hydroxy-5 alpha-cholest-8(14),16-dien-15-one from diosgenin and the examinations of their ability to inhibit the cholesteryl ester transfer protein (CETP). Clemmensen reduction of diosgenin gave cholest-5-ene-3 beta, 16 beta,26-triol. Tosylation of the latter compound gave cholest-5-ene-3 beta,16 beta,26-triol 26-tosylate which, upon reduction with LiAIH4, gave cholest-5-ene-3 beta,16 beta-diol. Hydrogenation-benzoylation of the latter to 5 alpha-cholest-3 beta,16 beta-diol 3 beta-benzoate followed by mesylation-elimination gave 5 alpha-cholest-16-ene-3 beta-ol 3 beta-benzoate. Controlled oxidation of the latter with CrO3-dimethylpyrazole gave 3 beta-hydroxy-5 alpha, 14 alpha-cholest-16-en-15-one 3 beta-benzoate. Oxidation of delta 16-15-one with SeO2 gave 3 beta-hydroxy-5 alpha-cholest-8(14),16-dien-15-one 3 beta-benzoate along with 3 beta-hydroxy-5 alpha, 14 beta-cholest-16-en-15-one 3 beta-benzoate. Selective hydrogenation of the delta 8(14),16-15-ketosteryl ester, followed by base hydrolysis gave 3 beta-hydroxy-5 alpha-cholest-8(14)-en-15-one. Hydrolysis of 3 beta-hydroxy-5 alpha-cholest-8(14),16-dien-15-one 3 beta-benzoate in basic media gave 3 beta-hydroxy-5 alpha-cholest-8(14),16-dien-15-one. The effects of the 15-ketosterols on the CETP activity were studied in vitro by incubating cholesteryl ester donor (HDL), cholesteryl ester acceptor (LDL) and human plasma as a CETP source at 37 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibitors of sterol synthesis. An improved chemical synthesis of 26-oxygenated delta 8(14)-15-ketosterols having the 25R configuration

(25R)-3 beta,26-Dihydroxy-5 alpha-cholest-8(14)-en-15-one (I) was synthesized in four steps from (25R)-3 beta,26-diacetoxycholesta-5,7-diene (III) in 30% overall yield. Isomerization of III with HCl in chloroform-dichloromethane at -60 degrees C gave (25R)-3 beta,26-diacetoxy-5 alpha-cholesta-7,14-diene together with the 5 alpha-delta 8,14 and 5 beta-delta 8,14 isomers in a 5:1:1 ratio. Epoxidation of the crude diene mixture with m-chloroperbenzoic acid, followed by hydrolysis in acetone containing concentrated HClO4 (0.1%) gave (25R)-3 beta,26-diacetoxy-5 alpha-cholest-8(14)-en-15-one (VIII), accompanied by numerous minor byproducts, including the 5 alpha,14 beta-delta 7, 5 alpha, 14 beta-delta 8 and 5 beta,14 beta-delta 8 isomers of VIII. All four 15-ketosterol esters were isolated by chromatography and fully characterized by mass spectrometry and 1H and 13C nuclear magnetic resonance. Treatment of VIII with potassium carbonate in degassed methanol gave I.

Efficient preparation of steroidal 5,7-dienes of high purity

Protected forms of dehydroepiandrosterone, delta 5 cholenic acid, (25R)-26-hydroxycholesterol and diosgenin were converted to the corresponding delta 5,7 dienes by successive treatment with 1,3-dibromo-5,5-dimethylhydantoin (dibromantin), tetrabutylammonium bromide and tetrabutylammonium fluoride. The crude products, which contained the delta 5,7 species contaminated by minor amounts of the delta 5 and delta 4,6 steroids, were purified by silica gel-AgNO3 chromatography to give the following steroids in approximately 99% purity and at least 50% yield: 3 beta-acetoxyandrosta-5,7-dien-17-one, methyl 3 beta-acetoxychola-5,7-dien-24-oate, (25R)-3 beta,26-diacetoxycholesta-5,7-diene and (25R)-3 beta-acetoxyspirosta-5,7-diene. Analogous treatment of acetate derivatives of pregnenolone and stigmasterol gave 3 beta-acetoxypregna-5,7-dien-20-one and 3 beta-acetoxystigmasta-5,7,22-triene in approximately 50% yield but of lower purity. Full 1H and 13C NMR assignments are given for seven delta 5,7 steroid acetates and the corresponding delta 5 starting materials. Coupling constants for rings A, B and C of delta 5,7 steroids are presented and stereochemical assignments have been made for the following 1H NMR signals: the C-11 protons of delta 5,7 steroids, the C-16 protons of sterols and bile acids, the C-22 and C-23 protons of bile acid esters and the C-28 protons of stigmasterol derivatives.