cholesterol-alpha-oxide and 7-ketocholesterol

Mitochondria play a central role in the irreversible damages induced to the heart by a prolonged period of ischemia followed by reperfusion. We previously demonstrated that (1) myocardial ischemia-reperfusion induces mitochondrial accumulation of cholesterol and oxysterols that are deleterious for the organelle; (2) inhibition of cholesterol and oxysterol accumulation prevents mitochondrial injury at reperfusion; (3) exercise is cardioprotective and remains efficient in the presence of co-morbidities such as obesity. The aim of this study was to investigate whether regular exercise limits mitochondrial cholesterol and oxysterol accumulation in wild-type and obese mice. Wild-type C57BL/6J and obese (ob/ob) mice were assigned to sedentary conditions or regular treadmill exercise and submitted to 30min of coronary artery occlusion followed by 15min of reperfusion. Regular exercise improved oxidative phosphorylation, restored the antioxidant capacity of the heart by increasing the expression of SOD1 and catalase and reduced the mitochondrial generation of oxysterols in wild-type as well as in ob/ob mice. In wild-type animals, exercise limited the production of oxysterols. In ob/ob mice, despite hypercholesterolemia, chronic exercise abolished the mitochondrial accumulation of cholesterol and concomitantly reduced the generation of 7α-hydroxycholesterol, 7-ketocholesterol and cholesterol-5α,6α-epoxide. In conclusion, regular exercise prevents the mitochondrial accumulation of cholesterol and oxysterols which occurs during early reperfusion of an ischemic myocardium in mice. This effect is observed in normo and hypercholesterolemic animals. It may be partly responsible for the antioxidant properties of regular exercise and contribute to its cardioprotective effect in obese conditions.

Topics: Animals; Biological Transport; Catalase; Cholesterol; Coronary Stenosis; Gene Expression; Hydroxycholesterols; Hypercholesterolemia; Ketocholesterols; Male; Mice; Mice, Inbred C57BL; Mice, Obese; Mitochondria, Heart; Myocardial Reperfusion Injury; Oxidative Phosphorylation; Physical Conditioning, Animal; Superoxide Dismutase-1

Oxysterols, the major components of oxidized low-density lipoproteins (ox-LDLs), are present in atherosclerotic plaque and are suggested to play an active role in plaque development. The formation of an atherosclerotic lesion occurs through activation of cellular events that include vascular smooth muscle cell (SMC) migration and proliferation. Therefore, we investigated the roles of two common oxysterols, 7-ketocholesterol (7-keto) and cholesterol-5alpha,6alpha-epoxide (alpha-epoxide) on SMCs. Our results showed that 7-keto and alpha-epoxide promoted SMC migration by a chemotactic assay, and induced mitogenic effects by MTT assay and BrdU assay. Specific inhibitors confirmed that MMPs, EGFR and PI3K are involved in oxysterol-induced SMC migration, while EGFR, ERK, Akt, and sphingomyelin/ceramide pathways might play a role in SMC proliferation. More, the co-immunoprecipitation study indicated that 7-keto and alpha-epoxide caused EGFR phosphorylation and there was an interaction between EGFR and PI3K. At protein expression level, Akt and ERK were activated, at messenger RNA level, MMP-2/9 mRNA was transcribed, at enzyme activity level, the MMP-2/9 enzyme activity were increased in SMCs treated with 7-keto and alpha-epoxide according to Western bolt, RT-PCR and a fluorogenic substrate. Taken together, we concluded that 7-keto and alpha-epoxide may be an atherogenic factor by stimulating SMC migration and proliferation.

Topics: Animals; Aorta; Cell Movement; Cell Proliferation; Ceramides; Cholesterol; ErbB Receptors; Extracellular Signal-Regulated MAP Kinases; Intracellular Signaling Peptides and Proteins; Ketocholesterols; Matrix Metalloproteinase 2; Matrix Metalloproteinase 9; Muscle, Smooth, Vascular; Myocytes, Smooth Muscle; Phosphatidylinositol 3-Kinases; Phosphorylation; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins c-akt; Rats; RNA, Messenger; Signal Transduction; Sphingomyelins; TOR Serine-Threonine Kinases

Oxidative stress plays an important role in the pathophysiology of diabetes mellitus. The aim of this study was to evaluate the formation of cholesterol oxides (ChOx) as biomarkers of oxidative stress in subjects with impaired glucose tolerance (IGT) and diabetes.. Blood plasma levels of cholesterol oxidation products were determined in the following groups: type 1 diabetes mellitus (DM1), type 2 diabetes (DM2), impaired glucose tolerance (IGT), children without diabetes (C1) and adults without diabetes (C2). The serum levels of cholest-5-ene-3alpha,7alpha-diol (7alpha-hydroxycholesterol, 7alpha-OH), cholest-5-ene-3beta,7beta-diol (7beta-hydroxycholesterol, 7beta-OH), 3beta-hydroxycholest-5-7-one (7-ketocholesterol, 7-K), 5alpha-cholestane-3beta,5,6beta-triol (cholestanetriol), 5,6alpha-epoxy-5alpha-cholestan-3alpha-ol (cholesterol-5alpha,6alpha-epoxide,), 5,6beta-epoxy-5beta-cholestan-3beta-ol (cholesterol-5beta,6beta-epoxide) and cholest-5-eno-3beta,25-diol (25-hydroxycholesterol, 25-OH) (trivial name and abbreviations indicated in parentheses) were quantified by gas chromatography using flame ionization detection.. The levels of total ChOx were elevated in the DM1 and DM2 groups compared to age-matched subjects without diabetes (p < 0.05). The concentrations of 7beta-hydroxycholesterol, cholesterol-alpha-epoxide and cholesterol-beta-epoxide were higher in the blood plasma of subjects in the DM2 group than in the blood plasma of subjects in the C2 and IGT groups (p < 0.05). Treatment of type 2 diabetic patients with oral hypoglycemic drugs associated with insulin resulted in lower concentrations of nitrotyrosine in the blood plasma without significant changes in the concentrations of glucose and glycated hemoglobin. Moreover, combination with statins in both treatments decreased the concentrations of ChOx.. ChOx are suitable biomarkers of oxidative stress and may be useful in clinical studies to follow drug effects on lipid oxidative modifications in diabetic patients.

Topics: Adolescent; Adult; Aged; Angiotensin-Converting Enzyme Inhibitors; Biomarkers; Child; Cholestanols; Cholesterol; Diabetes Mellitus, Type 1; Diabetes Mellitus, Type 2; Female; Glucose Intolerance; Humans; Hydroxycholesterols; Hypoglycemic Agents; Insulin; Ketocholesterols; Male; Middle Aged; Oxidative Stress

The mutagenicity of oxysterols, cholesterol-3beta,5alpha,6beta-triol (alpha-Triol), 7-keto-cholesterol (7-Keto) and cholesterol-5alpha,6alpha-epoxide (alpha-Epox) were examined by the Ames method and chromosome aberration test in this study. Only alpha-Triol concentration-dependently caused an increase of bacterial revertants in the absence of metabolic activating enzymes (S9), but not 7-keto and alpha-Epox. The mutagenic effect of alpha-Triol was reduced by the addition of S9. On the other hand, although alpha-Triol significantly induced chromosome aberration in CHO-K1 cells with and without S9. However, the addition of S9 reduced the degree of abnormal structure chromosome compared to without S9 mix. Catalase and superoxide dismutase (SOD) inhibited alpha-Triol induced increase of revertants in Salmonella typhimurium and chromosome aberration frequency in CHO cells, suggesting that reactive oxygen species (ROS) might be involved in the genotoxic effect of alpha-Triol. Treatment with alpha-Triol increased the ROS production in CHO cells, which could be attenuated by catalase and SOD. Results in this study suggested, for the first time that alpha-Triol, causes genotoxic effect in an ROS-dependent manner.

Topics: Animals; Catalase; CHO Cells; Cholestanols; Cholesterol; Chromosome Aberrations; Cricetinae; Cricetulus; DNA Damage; Ketocholesterols; Mutagenicity Tests; Reactive Oxygen Species; Salmonella; Superoxide Dismutase

The cytotoxicity of the oxysterols 25-hydroxycholesterol, 7beta-hydroxycholesterol, cholesterol-5alpha,6alphaepoxide, cholesterol-5beta,6beta-epoxide, 19-hydroxycholesterol and 7-ketocholesterol was examined in U937 cells, a human monocytic blood cell line. 7beta-Hydroxycholesterol, cholesterol-5beta,6beta-epoxide, and 7-ketocholesterol, at 30 micromol/L concentration, were found to be cytotoxic to this cell line and the mode of cell death was by apoptosis. 25-Hydroxycholesterol, cholesterol-5alpha,6beta-epoxide and 19-hydroxycholesterol (30 micromol/L) did not induce apoptosis in this cell line. Since it has been suggested that the generation of an oxidative stress may occur in the early stages of the apoptotic process, the glutathione concentration and the activity of superoxide dismutase were also measured in the oxysterol-treated cells. 7beta-Hydroxycholesterol was shown to increase the superoxide dismutase activity and decrease the glutathione concentration. However, cholesterol-5beta,6beta-epoxide and 7-ketocholesterol, which were also shown to induce apoptosis, did not affect the glutathione concentration or the superoxide dismutase activity in the U937 cells. Therefore, oxysterol-induced apoptosis may not be dependent on the generation of an oxidative stress.

Topics: Apoptosis; Cell Count; Cell Line; Cell Membrane Permeability; Cell Survival; Cholesterol; Cholesterol, Dietary; DNA Fragmentation; Free Radical Scavengers; Glutathione; Humans; Hydroxycholesterols; Ketocholesterols; Monocytes; Oxidation-Reduction; Superoxide Dismutase

Recent studies have demonstrated that, unlike cholesterol, cholesterol oxidized at position 7 can reduce the maximal endothelium-dependent relaxation of isolated rabbit aortas (Circulation. 1997;95:723-731). The aim of the current study was to determine whether cholesterol oxides reduce the release of nitric oxide (NO) from human umbilical vein endothelial cells (HUVECs). The amount of NO released by histamine-stimulated HUVECs was determined by differential pulse amperometry using a nickel porphyrin- and Nafion-coated carbon microfiber electrode. The effects of cholesterol (preserved from oxidation by butylated hydroxytoluene), 7-ketocholesterol, 7beta-hydroxycholesterol, 5alpha,6alpha-epoxycholesterol, 19-hydroxycholesterol (60 microg/mL), and alpha-lysophosphatidylcholine (10 microg/mL) were compared. Pretreatment of HUVECs with cholesterol, 5alpha,6alpha-epoxycholesterol, or 19-hydroxycholesterol did not alter histamine-activated NO production. In contrast, pretreatment with 7-ketocholesterol or 7beta-hydroxycholesterol significantly decreased NO release. The inhibitory effect of 7-ketocholesterol was time and dose dependent and was maintained in the presence of L-arginine. In the absence of serum, lysophosphatidylcholine also reduced NO production. In ionomycin-stimulated cells, pretreatment with 7-ketocholesterol did not inhibit NO release. These results demonstrate that cholesterol derivatives oxidized at the 7 position, the main products of low density lipoprotein oxidation, reduce histamine-activated NO release in HUVECs. Such an inhibitory effect of cholesterol oxides may account, at least in part, for the ability of oxidized low density lipoprotein to reduce the endothelium-dependent relaxation of arteries.

Topics: Arginine; Cells, Cultured; Cholesterol; Endothelium, Vascular; Histamine; Humans; Hydroxycholesterols; Ionomycin; Ketocholesterols; Lysophosphatidylcholines; Nitric Oxide; Umbilical Veins

Increasing the energy value of diets with dietary fat, particularly fats rich in saturated fatty acids, can result in the elevation of plasma total and lipoprotein cholesterol. In the present study, experimental diets were designed to examine the effects of increasing the energy content of diets with a saturated fat source and cholesterol in a non-purified diet on hyperlipoproteinaemia and aortic plaque composition in the atherosclerosis-susceptible Japanese quail (Coturnix japonica) model of human atherosclerosis. Commercial poultry diets containing two levels (i.e. 60 or 120 g/kg) of beef tallow as the primary source of saturated fat were balanced for endogenous cholesterol or supplemented with cholesterol (i.e. 0.5 or 5.0 g/kg) and fed to quail for 9 weeks to examine the effects on whole plasma, lipoprotein and aortic plaque lipid composition in relation to aortic plaque formation. Hypercholesterolaemia (P < 0.001) was confirmed in birds fed on high-cholesterol (HC) diets only. An interaction (P = 0.05) between dietary cholesterol and fat intake level was observed for plasma triacylglycerols (TG) and was specific to changes observed in VLDL composition. Diet-induced changes in lipoprotein total cholesterol, TG and phospholipid composition were greatest in the portomicron and VLDL fractions in birds fed on atherogenic diets. Hyperlipoproteinaemia induced by the 60 g/kg added beef tallow-HC diet resulted in significant (P < 0.001) aortic plaque deposition, which was further enhanced in birds fed on the 120 g/kg beef tallow-HC diet. Quail fed on 120 g/kg beef tallow-HC diets exhibited the most severe aortic plaque formation, with marked increases in aortic tissue cholesterol content and quantifiable amounts of several cholesterol oxides (5,6 alpha-epoxy-5 alpha-cholesterol, 7 beta-hydroxycholesterol, cholestanetriol, 7-ketocholesterol and 25-hydroxycholesterol). In summary, hyperlipoproteinaemia associated with HC diets with a greater proportion of energy from saturated fat produced a combined effect in altering plasma and lipoprotein lipid composition as well as aortic tissue cholesterol and cholesterol oxide content in the Japanese quail.

Topics: Analysis of Variance; Animals; Aorta; Arteriosclerosis; Bird Diseases; Cholestanols; Cholesterol; Cholesterol, Dietary; Coturnix; Dietary Fats; Disease Models, Animal; Energy Intake; Hydroxycholesterols; Hypolipidemic Agents; Ketocholesterols; Lipids; Lipoproteins; Male; Regression Analysis

The effects of the cholesterol oxides on low density lipoprotein receptor (LDLR) gene expression were investigated. Cultured rabbit aortic smooth muscle cells were incubated with 1, 2, and 5 micrograms/ml culture medium concentrations of pure cholesterol, 25-hydroxycholesterol (25-OH), 7-ketocholesterol (7-keto), cholestane-3 beta, 5 alpha, 6 beta-triol (triol) and cholesterol-5 alpha, 6 alpha-epoxide (epoxide) for 12 hours and with vehicle only as control. Total mRNAs were extracted and electrophoresed. Northern blot hybridization analyses were performed. The results showed mRNA expressions of LDLR gene were inhibited to 16.1 +/- 4.4%, 33.8 +/- 0.6%, 42.8 +/- 1.8% and 46.9 +/- 3.9% of control by 25-OH, 7-keto, epoxide and triol respectively. Pure cholesterol showed only minimal inhibition. The inhibitions were time dependent. Although cholesterol oxides have been shown to alter many membrane-related functions and the LDLR domain are located in the cell membrane. The findings of this study suggested that the cholesterol oxides exerted their repressive actions on LDLR function primarily by down-regulating LDLR gene expression rather than directly upon cell membrane.

Topics: Animals; Blotting, Northern; Cells, Cultured; Cholestanols; Cholesterol; Gene Expression Regulation; Hydroxycholesterols; Ketocholesterols; Muscle, Smooth, Vascular; Rabbits; Receptors, Lipoprotein; RNA, Messenger

A method for isolation, detection and quantification of cholesterol oxidation products based on solid phase extraction in combination with preparative HPLC and gas chromatography-mass spectrometry selected ion monitoring has been developed for dairy products. The isolation procedure had a high recovery and artifact formation was minimal, as shown by isotope labelling. The limits of detection ranged from 0.3 to 35 pg/microliters of the isomeric forms of 7-hydroxycholesterol, 20 alpha-hydroxycholesterol, the isomeric forms of cholesterol-5,6-epoxides, cholestanetriol, 25-hydroxycholesterol and 7-ketocholesterol corresponding to a limit of quantification of 2-6 ng oxysterol/g lipid in the dairy product, depending on the nature of the cholesterol oxidation product.

Topics: Cholestanols; Cholesterol; Cholesterol Esters; Chromatography, High Pressure Liquid; Dairy Products; Gas Chromatography-Mass Spectrometry; Hydroxycholesterols; Ketocholesterols; Mass Spectrometry; Oxidation-Reduction; Oxides; Triglycerides

The application of gas chromatography and high-pressure liquid chromatography/mass spectrometry techniques for analysis of plasma cholesterol oxidation products is described. Cholesterol oxides that are widely identified in biological samples were subjected to gas (GC) and high-pressure liquid chromatographic (HPLC) separations, and their detection and characterization by mass spectrometry (MS) were compared. Analysis of cholesterol oxides from plasma samples revealed distinct advantages for each method according to the specific cholesterol oxide in question. Whereas HPLC/MS analysis of cholesterol oxides provided less resolution and lower sensitivity as compared to GC/MS, a distinct advantage was evident for direct measurements of cholesterol-7-hydroperoxides and 7-ketocholesterol. These two cholesterol oxides are particularly sensitive to storage in solvents, derivatization procedures, and analytical conditions used for GC analysis, which are minimized or avoided using the HPLC/MS conditions described. Analysis of human and rabbit plasma samples identified cholest-5-ene-3 beta, 7 beta-diol (7 beta-hydroxycholesterol); 5,6 alpha-epoxy-5 alpha-cholestan-3 beta-ol (cholesterol-5 alpha, 6 alpha-epoxide); 5 alpha-cholestane-3 beta, 5,6 beta-triol (cholestanetriol); 3 beta-hydroxycholest-5-ene-7-one (7-ketocholesterol); and 5,6 beta-epoxy-5 beta-cholestan-3 beta-ol (cholesterol-5 beta,6 beta-epoxide) as commonly occurring components (trivial names indicated in parentheses). The latter two compounds were dramatically increased in hypercholesterolemic samples and were found in approximately equal amounts in the free cholesterol and cholesteryl ester fractions. Although most of the plasma cholesterol oxides are found in the dietary cholesterol, others are not, particularly cholesterol-5 beta,6 beta-epoxide, suggesting that at least some of these compounds are formed by in vivo oxidation of cholesterol. Despite the readily measurable levels of the above cholesterol oxides, as well as other less prominent oxides, there was no evidence of cholesterol-7-hydroperoxides associated with plasma free cholesterol. Although several of the plasma cholesterol oxides may derive from cholesterol-7-hydroperoxides, it appears that the latter are either unstable and decompose in plasma, are metabolized to other cholesterol oxidation products, or break down during their isolation.

Topics: Animals; Cholesterol; Chromatography, High Pressure Liquid; Gas Chromatography-Mass Spectrometry; Humans; Ketocholesterols; Lipid Peroxides; Male; Mass Spectrometry; Oxidation-Reduction; Rabbits

The homogenizing effect of cholesterol and its oxidative derivatives, 7-ketocholesterol, cholesterol 5 alpha, 6 alpha-epoxide and 25-hydroxycholesterol, in liquid-crystalline 1,2-dioleoyl-sn-glycero-3-phosphocholine(DOPC) bilayer vesicles was studied using the fluorescence lifetimes of 2-(3-(diphenylhexatrienyl)propanoyl)-1-hexadecanoyl-sn-glycero-3-p hosphocholine (DPH-PC). The phase and modulation data were fitted either to discrete exponential models or to models characterized by continuous distributional lifetimes. Among all the models tested, it was found that the best one to account for the experimental data was the unimodal Lorentzian distribution. Thus, the DPH-PC lifetime was adequately described by a distributional center and a full width at half-maximum, for DOPC vesicles these values being 6.23 and 0.48 ns, respectively. Increasing the concentration of cholesterol, 7-ketocholesterol, or cholesterol 5 alpha, 6 alpha-epoxide from 0 to 30 mol% resulted in an increase of the lifetime center (e.g., 7.16 ns at 30 mol% cholesterol) and a decrease of the distributional width (e.g., 0.05 ns at 30 mol% cholesterol). On the other hand, up to 30 mol% of 25-hydroxycholesterol incorporated into the bilayer vesicles showed little influence on both lifetime parameters. Our results support the use of lifetime distributional width to evaluate membrane heterogeneity and suggest that oxysterols, depending on their molecular structural particulars, may exert cholesterol-like homogenizing effect in membranes.

Topics: Cholesterol; Diphenylhexatriene; Hydroxycholesterols; Ketocholesterols; Lipid Bilayers; Membrane Fluidity; Membrane Lipids; Phosphatidylcholines; Spectrometry, Fluorescence

A spectrum of cholesterol oxidation derivatives (oxysterols) is generated in food products exposed to heat or radiation in the presence of oxygen. One of these derivatives (cholestan-3 beta,5 alpha,6 beta-triol) was shown to compromise the selective barrier function of cultured vascular endothelial cell monolayers, an action that may initiate atherosclerotic lesion formation. This study sought to investigate the relationship of cholesterol synthesis inhibition by several naturally occurring oxysterols to depression of vascular endothelial cell monolayer barrier function, determined as an increase in albumin transfer across cultured endothelial monolayers. All oxysterols tested caused a variable time- and dose-dependent elevation in trans-endothelial albumin transfer, and they were also able to inhibit cholesterol biosynthesis to varying degrees. Pure cholesterol was without effect on both counts. The correlation between the increase in albumin transfer related to oxysterol exposure and the ability of oxysterols to suppress cholesterol biosynthesis was, however, poor. Moreover, mevinolin, a water-soluble competitive inhibitor of cholesterol synthesis, reduced the rate of cholesterol synthesis to 0.9% of control but did not significantly increase albumin transfer. Cholestan-3 beta,5 alpha,6 beta-triol caused a 660% elevation in albumin transfer while cholesterol synthesis remained at 11% of control. We conclude that changes in endothelial barrier function caused by exposure to the oxysterols examined, but not pure cholesterol, are probably related to factors other than the well-known action of cholesterol biosynthesis inhibition. These findings may have implications in the development of atherosclerosis.

Topics: Animals; Biological Transport; Cell Membrane Permeability; Cholestanes; Cholestanols; Cholesterol; Dehydrocholesterols; Disease Models, Animal; Dose-Response Relationship, Drug; Endothelium; Hydroxycholesterols; Hypolipidemic Agents; In Vitro Techniques; Ketocholesterols; Lovastatin; Serum Albumin; Swine; Time Factors

Human umbilical vein endothelial cells and rabbit aortic smooth muscle cells in culture were incubated for intervals up to 24 hrs with varying concentrations of cholesterol, 7-ketocholesterol, 25-hydroxycholesterol, cholestane-3 beta,5 alpha,6 beta-triol or cholesterol-5 alpha, 6 beta-epoxide. Endocytosis, as measured by uptake of horseradish peroxidase (HRP), was inhibited in a dose and time dependent manner in both endothelial and smooth muscle cell cultures by cholestane-3 beta,5 alpha,6 beta-triol and 25-hydroxycholesterol. Inhibition by 7-ketocholesterol in endothelial cells occurred only at higher concentrations, and cholesterol and cholesterol epoxide showed no significant inhibitory effects. The viability of the cells exposed to the cholesterol oxides at the concentrations that inhibited the uptake of HRP was not changed. Cholesterol oxides induce functional endothelial injury, not morphologically apparent, which may be involved in atherogenesis.

Topics: Animals; Aorta; Cells, Cultured; Cholestanols; Cholesterol; Endocytosis; Endothelium, Vascular; Horseradish Peroxidase; Humans; Hydroxycholesterols; Hypolipidemic Agents; Ketocholesterols; Kinetics; Muscle, Smooth, Vascular; Rabbits; Umbilical Veins

Hepatic cholesterol-epoxide hydrolase is a microsomal enzyme which appears to be catalytically distinct from the epoxide hydrolase responsible for the catabolism of a wide variety of aromatic and aliphatic epoxides. The diastereomeric forms of cholesterol epoxide, cholesterol 5 alpha,6 alpha-, and cholesterol 5 beta,6 beta-epoxides are converted to cholestane-3 beta,5 alpha,6 beta-triol with equal facility. Kinetic analysis of cholesterol-epoxide hydrolase demonstrated that both diastereomers bind to a common catalytic site. Apparent Km values of 3.69 and 4.42 microM were derived for cholesterol 5 alpha,6 alpha- and cholesterol 5 beta,6 beta-epoxide, respectively. In addition, enzyme activity with both diastereomers was product-inhibited by cholestanetriol through a competitive mechanism with the apparent Ki for cholestanetriol being 10.8 and 6.8 microM against cholesterol alpha- and beta-epoxides, respectively. This inhibitory effect of cholestanetriol may account for the difference observed in the hydration rates for the cholesterol epoxide isomers when they are incubated together in the presence of liver microsomes. Inhibitors of epoxide hydrolase were studied, and three oxidation products were found to be particularly effective against cholesterol-epoxide hydrolase while producing no significant inhibition of styrene-epoxide hydrolase. These inhibitors were 7-ketocholesterol, 6-ketocholestanol, and 7-ketocholestanol, the latter displaying an apparent Ki lower than the Km for either cholesterol epoxide isomer. None of the xenobiotic epoxide hydrolase inhibitors or activators studied affected cholesterol-epoxide hydrolase activity.

Topics: Animals; Cholesterol; Chromatography, High Pressure Liquid; Cytosol; Epoxide Hydrolases; Hydrogen-Ion Concentration; Ketocholesterols; Kinetics; Liver; Male; Microsomes, Liver; Rats; Rats, Inbred Strains; Stereoisomerism