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PubMed1996

Relationship between the serum concentration of 7 alpha-hydroxycholesterol and fecal bile acid excretion in humans.

BACKGROUND: Serum levels of 7 alpha-hydroxycholesterol have been shown to reflect the activity of cholesterol 7 alpha-hydroxylase, the key enzyme of bite acid synthesis in the liver, but a comparison with direct measurements of bile acid synthesis rates has never been performed. METHODS: 7 alpha-Hydroxycholesterol was measured by gas-liquid chromatography/mass spectrometry and bile acid synthesis by the fecal balance method in 35 subjects. RESULTS: A significant correlation was found between 7 alpha-hydroxycholesterol concentration in serum and bile acid synthesis (r = 0.863, p < 0.001). Serum levels of 7 alpha-hydroxycholesterol in 20 patients treated with a 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitor did not differ from levels obtained in healthy volunteers (78 +/- 7 ng/ml versus 63 +/- 5 ng/ml; NS). Treatment with fenofibrate reduced 7 alpha-hydroxycholesterol concentrations in six patients from 107 +/- 47 ng/ml to 61 +/- 12 ng/ml (p < 0.05). CONCLUSIONS: We conclude that the concentration of 7 alpha-hydroxycholesterol in serum is an indicator of bile acid synthesis and that serum levels of 7 alpha-hydroxycholesterol are not affected in patients treated with HMG-CoA reductase inhibitors but are affected in those treated with fenofibrate.

Acyl Coenzyme A↗
PubMed2000

Fluorocholesterols, in contrast to hydroxycholesterols, exhibit interfacial properties similar to cholesterol.

We used an automated Langmuir-Pockels surface balance to characterize the air-water interfacial properties of cholesterol (CH) and its derivatives with hydrophilic OH and F substitutions at isologous sites on the sterol body or side chain. We studied 6-fluorocholesterol, 25-fluorocholesterol, 25,26,26,26,27,27,27-heptafluorocholesterol, 7alpha-hydroxycholesterol, 7beta-hydroxycholesterol, 25-hydroxycholesterol and 27-hydroxycholesterol, alone and in mixtures with 1-palmitoyl-2-oleoyl-sn-3-glycero-phosphocholine (POPC). Pressure;-area isotherms of the fluorocholesterols were essentially indistinguishable from CH and all condensed POPC monomolecular layers (monolayers) to variable degrees. Both nucleus-substituted hydroxycholesterols formed expanded monolayers, with lift-offs from baseline 22-26 A(2)/molecule larger than CH, suggesting interfacial tilting; furthermore, in binary mixtures, they condensed POPC monolayers less than CH. In contrast, the side chain hydroxylated CHs were oriented horizontally in the interface at large molecular areas, and became vertical below 140 A(2)/molecule with the side chain-OH rather than 3-OH group anchored in the subphase, as evidenced by low collapse pressures and smaller molecular areas than CH. Both side chain hydroxycholesterols expanded POPC monolayers at molar ratios <30%, but induced condensation with higher ratios, suggesting that OH-acyl chain (POPC) repulsion is superceded at higher mole fractions by lateral phase separation and intersteroidal H-bonding. These studies predict that fluorocholesterols should exhibit intramembrane spatial occupancy nearly identical to CH, whereas nucleus and especially side chain hydroxycholesterols will perturb membrane lipid packing notably.

Cholesterol↗
PubMedDate not supplied

Serum 7alpha-hydroxycholesterol levels during liver regeneration after hepatectomy in humans.

BACKGROUND/AIMS: Changes in bile acid synthesis during liver regeneration after hepatectomy is little known in humans. Since it has been reported that the serum 7 alpha-hydroxycholesterol levels reflect the hepatic bile acid synthesis and that the determination of bile acid synthesis is useful to assess the liver regeneration rate, we determined the serum 7 alpha-hydroxycholesterol level during liver regeneration after hepatectomy in clinical patients. METHODOLOGY: The serum 7 alpha-hydroxycholesterol levels were determined by gas-liquid chromatography-mass spectrometry-selected ion monitoring method before and on days 1, 3, 5, 7, 14 and 21 after hepatectomy in twenty consecutive patients. RESULTS: The 7 alpha-hydroxycholesterol levels became lower between days 1 and 7, were increased on day 14, and then decreased on day 21 after hepatectomy. The patients with preoperative external biliary drainage showed a higher serum 7 alpha-hydroxycholesterol level than those without biliary drainage before hepatectomy. The former showed lower serum 7 alpha-hydroxycholesterol levels than the latter throughout the 21 days after hepatectomy. In patients whose liver resection rate was more than 50%, the serum 7 alpha-hydroxycholesterol levels were kept lower until 21 days after hepatectomy compared with those whose liver was excised less than 50%. CONCLUSIONS: It is concluded that the patients who had preoperative biliary drainage or major hepatic resection seem to have less hepatic reserve capacity for bile acid synthesis after hepatectomy.

Bile Acids and Salts↗
PubMed1993

Cholesterol and 27-hydroxycholesterol 7 alpha-hydroxylation: evidence for two different enzymes.

The use of 2-hydroxypropyl-beta-cyclodextrin as a vehicle for solubilizing cholesterol and 27-hydroxycholesterol has led to a study of their rates of 7 alpha-hydroxylation in microsomal preparations from hamster liver and HepG2 cells. Addition of the vehicle alone to the cholesterol 7 alpha-hydroxylase assay always caused a several-fold increase in activity. Preloading the vehicle with cholesterol further augmented the rate of 7 alpha-hydroxycholesterol formation. Preloading the vehicle with 27-hydroxycholesterol or 27-hydroxycholestanol (molar ratio 1/1.2) minimally decreased cholesterol 7 alpha-hydroxylase activity (-12%), compared with preloading with cholestanol (-50%), a known competitive inhibitor of the enzyme. Microsomes from hamster liver yielded rates of 7 alpha,27-dihydroxcholesterol formation of 1.5 to 3.0 nmol/min per mg protein, compared with 0.3 nmol/min per mg protein for 7 alpha-hydroxycholesterol. Although cholesterol and cholestanol had minimal effects on the rate of 7 alpha-hydroxylation of 27-hydroxycholesterol, addition of an approximately equimolar amount of 27-hydroxycholestanol inhibited the rate of formation by 65%. Attempts to separate and identify the two C-27 sterol 7 alpha-hydroxylases chromatographically led to the finding that Emulgen 913 selectively inactivates 7 alpha-hydroxylation of 27-hydroxycholesterol. These results indicate that the metabolic pathway for bile acid synthesis from 27-hydroxycholesterol is not governed by cholesterol 7 alpha-hydroxylase.

2-Hydroxypropyl-beta-cyclodextrin↗
PubMed1984

25-Hydroxycholesterol-induced elevation in 45Ca uptake: correlation with depressed DNA synthesis.

The mechanism whereby 25-hydroxycholesterol, an inhibitor of the synthesis of cholesterol, depresses DNA synthesis in cycling P815 mastocytoma cells was investigated. The uptake of 45Ca into P815 cells treated with 1 microgram/ml 25-hydroxycholesterol began to rise above control levels by 6 hours after initiation of treatment and was increased tenfold by 15 hours. Kinetic data of calcium uptake indicated the presence of at least two components of calcium uptake, fast and slow. The fast phase of calcium exchange at the cell surface was changed little by treatment with 25-hydroxycholesterol. The slow phase of calcium exchange with the intracellular compartment was markedly affected by treatment with the inhibitor, there being a large increase in the flux and half-time of uptake, and a fall in the rate constant. This resulted in a large elevation of the intracellular compartment size. Incorporation of [3H]thymidine into DNA began to decline between 9 and 12 hours posttreatment in these cultures. Uptake of calcium and depression of DNA synthesis were shown to be directly related to the dose of 25-hydroxycholesterol used. The changes in 45Ca uptake and DNA synthesis due to 25-hydroxycholesterol treatment were abolished by addition of exogenous cholesterol to the incubation medium. The results are consistent with the hypothesis that 25-hydroxycholesterol, by inhibiting cholesterol production, depresses DNA synthesis via an elevation in the uptake of calcium into the cell to a level incompatible with continued DNA replication.

Animals↗
PubMed1995

Accumulation of 7 alpha-hydroxycholesterol in liver tissue of patients with cholesterol gallstones.

Patients with cholesterol gallstones have a reduced pool of bile acids. This study was undertaken to clarify the mechanism by which bile acid biosynthesis does not increase to supranormal levels to cause a reexpansion of the pool. We investigated the first two steps of the bile acid biosynthesis pathway by assaying the activities of cholesterol 7 alpha-hydroxylase, the rate-limiting enzyme in this pathway, and 3 beta-hydroxy-delta 5-C27-steroid dehydrogenase/isomerase, and by measuring the concentrations of 7 alpha-hydroxycholesterol and 7 alpha-hydroxy-4-cholesten-3-one in liver specimens from ten patients with cholesterol gallstones and ten gallstone-free controls. In the patients with gallstones, cholesterol 7 alpha-hydroxylase activity, 3 beta-hydroxy-delta 5-C27-steroid dehydrogenase/isomerase activity, and hepatic 7 alpha-hydroxy-4-cholesten-3-one concentration did not significantly different from levels in controls, but hepatic 7 alpha-hydroxycholesterol concentration was more than twofold that of controls (12.9 +/- 2.6 vs 5.3 +/- 1.2 nmol/g liver, P < 0.01). The concentration of 7 alpha-hydroxycholesterol positively correlated with the ratio of cholesterol 7 alpha-hydroxylase activity to 3 beta-hydroxy-delta 5-C27-steroid dehydrogenase/isomerase activity (r = 0.93; P < 0.005) in the gallstone-free controls. In contrast, this correlation disappeared in the patients with gallstones. These results suggest a derangement of the normal 7 alpha-hydroxycholesterol metabolism in the patients with gallstones. The reason for the accumulation of 7 alpha-hydroxycholesterol remains unclear; however, it is possible that, in patients with cholesterol gallstone, the accumulated 7 alpha-hydroxycholesterol causes inappropriate suppression of cholesterol 7 alpha-hydroxylase activity by product inhibition.

3-Hydroxysteroid Dehydrogenases↗
PubMed2005

Combined effect of 25-hydroxycholesterol and IL-1beta on IL-8 production in human colon carcinoma cell line (Caco-2).

Interleukin-1 beta (IL-1beta) is an important mediator in intestinal inflammation. IL-1beta promotes IL-8 production, which can be modulated by a number of factors, including oxidative stress. Interestingly, oxysterols, which are thought to contribute to inflammation in atherosclerotic plaques, are also produced by intestinal epithelial cells. Thus, we investigated the effect of oxysterols, including 25-hydroxycholesterol and 7beta-hydroxycholesterol, on IL-1beta-induced IL-8 production in Caco-2 cells (a human colon carcinoma cell line). Pre-treatment of Caco-2 cells with 25-hydroxycholesterol significantly enhanced IL-1beta-induced IL-8 expression at both mRNA and protein levels. However, 7beta-hydroxycholesterol showed very little effect on IL-8 production. Furthermore, pre-treatment with 25-hydroxycholesterol, followed by IL-1beta stimulation, enhanced IL-8 promoter activity beyond that observed with IL-1beta alone. These results suggest that 25-hydroxycholesterol enhances IL-1beta-induced IL-8 production, possibly by enhancing promoter activity.

Adenocarcinoma↗
PubMed1999

Effects of cholestyramine on hepatic cholesterol 7alpha-hydroxylase and serum 7alpha-hydroxycholesterol in the hamster.

Cholestyramine increases activities of hepatic cholesterol 7alpha-hydroxylase and serum levels of 7alpha-hydroxycholesterol. To examine if serum 7alpha-hydroxycholesterol levels parallel with enzyme activity, 0, 0.5, 1, 2, 4, and 10% of cholestyramine was administered to female golden Syrian hamsters for 28 d in the dose-dependent study, and 2% cholestyramine for 0, 1, 3, 7, 14, 21, and 28 d in the time-dependent study. In the dose-dependent study, hepatic and serum cholesterol levels were significantly decreased dose-dependently when more than 0.5% of cholestyramine was fed for 28 d. Cholestyramine increased the cholesterol 7alpha-hydroxylase activity in a dose-dependent manner, while the serum 7alpha-hydroxycholesterol level was essentially unchanged. No correlation was found between the serum level and the hepatic enzyme activity. In the time-dependent study, hepatic and serum cholesterol levels markedly decreased when 2% cholestyramine was fed for longer than 3 d. The serum triglyceride level increased significantly for the first 7 d and then decreased. Cholesterol 7alpha-hydroxylase activity increased significantly as early as day 1, reached maximum activity level on day 7, and then kept the significantly high values until day 28. The serum 7alpha-hydroxycholesterol level significantly increased for the first 7 d and decreased to the pretreatment level thereafter. 7Alpha-hydroxycholesterol levels significantly correlated with serum cholesterol and triglyceride levels. We conclude that the serum 7alpha-hydroxycholesterol level does not always reflect the activity of hepatic cholesterol 7alpha-hydroxylase, when cholesterol metabolism is severely disturbed by cholestyramine.

Animals↗
PubMed1992

Effect of 22R-hydroxycholesterol on the action of sphingomyelinase from Bacillus cereus toward bovine erythrocytes.

The incorporation of 22R-hydroxycholesterol [(22R)-5-cholestene-3 beta,22-diol] into the bovine erythrocyte membranes remarkably enhanced the degradation of sphingomyelin in erythrocyte membranes by the action of sphingomyelinase from Bacillus cereus, causing much faster hemolysis of erythrocytes. The stimulative effect of 22R-hydroxycholesterol on the breakdown of sphingomyelin was maximal in the presence of Mg2+. On the other hand, in spite of the presence of 22R-hydroxycholesterol, the breakdown of sphingomyelin was inhibited by increasing concentrations of Ca2+. Also, the incorporation of 22R-hydroxycholesterol into the erythrocyte membranes facilitated the specific adsorption of the enzyme onto the surface of the erythrocyte membranes. The specific adsorption of sphingomyelinase amounted to 20-40% of the total activity in the presence of Mg2+ and the absence of divalent metal ions. In the presence of Ca2+, the incorporation of 22R-hydroxycholesterol enhanced the enzyme adsorption, exceeding more than 90% of the total activity. Therefore, the incorporation of 22R-hydroxycholesterol into bovine erythrocyte membranes remarkably accelerates the breakdown of sphingomyelin in the presence of Mg2+, and the specific adsorption of sphingomyelinase onto erythrocytes in the presence of Ca2+.

Adsorption↗
PubMed2006

Cytotoxicity of myeloperoxidase/nitrite-oxidized low-density lipoprotein toward endothelial cells is due to a high 7beta-hydroxycholesterol to 7-ketocholesterol ratio.

Oxygenated cholesterols (oxysterols) formed during oxidation of low-density lipoprotein (LDL) are associated with endothelial dysfunction and atherogenesis. We compared the profile of oxysterols in modified human LDL obtained on reaction with myeloperoxidase/H2O2 plus nitrite (MPO/H2O2/nitrite-oxLDL) with that on Cu2+ -catalyzed oxidation. The 7beta-hydroxycholesterol/7-ketocholesterol ratio was markedly higher in MPO/H2O2/nitrite-oxLDL than in Cu2+ -oxidized LDL (7.9 +/- 3.0 versus 0.94 +/- 0.10). Like MPO/H2O2/nitrite-oxLDL, 7beta-hydroxycholesterol was cytotoxic toward endothelial cells through eliciting oxidative stress. Cytotoxicity was accompanied by DNA fragmentation and was prevented by the NADPH oxidase inhibitor apocynin, suggesting stimulation of NADPH oxidase-mediated O2-* formation. 7-Ketocholesterol was only cytotoxic when added alone, whereas a 1:1-mixture with 7beta-hydroxycholesterol surprisingly was noncytotoxic. We conclude from our data that (i) 7beta-hydroxycholesterol is a pivotal cytotoxic component of oxidized LDL, (ii) 7-ketocholesterol protects against 7beta-hydroxycholesterol in oxysterol mixtures or oxLDL, (iii) the 7beta-hydroxycholesterol/7-ketocholesterol ratio is a crucial determinant for cytotoxicity of oxidized LDL species and oxysterol mixtures, and (iv) the low share of 7-ketocholesterol explains the higher cytotoxicity of MPO/H2O2/nitrite-oxLDL than other forms of oxidized LDL. The dietary polyphenol (-)-epicatechin inhibited not only formation but also cytotoxic actions of both oxLDL and oxysterols.

Catechin↗
PubMed2005

High circulating levels of 7beta- and 7alpha-hydroxycholesterol and presence of apoptotic and oxidative markers in arterial lesions of normocholesterolemic atherosclerotic patients undergoing endarterectomy.

In previous investigations, we found that 7beta-hydroxycholesterol had potent pro-apoptotic, and pro-oxidative properties. So, we asked whether the circulating level of this oxysterol was enhanced in atherosclerotic patients undergoing endarterectomy of the superficial femoral artery. To this end, 7beta-hydroxycholesterol serum concentrations were determined and compared with common lipid parameters in atherosclerotic patients, and in healthy subjects. 7alpha-hydroxycholesterol was simultaneously measured to evaluate the reliability of the method used for oxysterol analysis. On normal and atherosclerotic arterial fragments from patients, markers of oxidation (4-hydroxynonenal (4-HNE) adducts), and apoptosis (activated caspase-3; condensed/fragmented nuclei) were studied. Interestingly, high serum concentrations of 7beta- and 7alpha-hydroxycholesterol were found in normocholesterolemic atherosclerotic patients. However, in statin-treated patients, the circulating levels of 7beta- and 7alpha-hydroxycholesterol tend towards normal values. Therefore, 7beta- as well as 7alpha-hydroxycholesterol could be more appropriate markers of lipid metabolism disorders than cholesterol or LDL in normocholesterolemic patients with atherosclerosis of the lower limbs, and statins could normalize their serum concentrations. At the arterial level, apoptotic cells were mainly identified in low grade lesions and no statin effects were found on oxidation and apoptosis.

Aged↗
PubMed2006

Species differences among various rodents in the conversion of 7alpha-hydroxycholesterol in liver microsomes.

Our previous study demonstrated that there are species differences among vertebrates in their conversion of 7alpha-hydroxycholesterol (7HC) to 7-ketocholesterol (7KC). To examine this further, we investigated the differences in the products of 7alpha-hydroxycholesterol in various species of male muroid rodents. Adult male Syrian hamsters (Mesocricetus auratus), dwarf hamsters (Phodopus rovolovskii), Djungarian hamsters (Phodopus sungorus), Chinese hamsters (Cricetulus griseus), rat-like hamsters (Tscherskia triton), and hispid cotton rats (Sigmodon hispidus) were used. Microsomal fractions were prepared from their livers, and the activities of the enzymes that participate in the dehydrogenation of 7alpha-hydroxycholesterol were determined by measuring the products using high-performance liquid chromatography. 7alpha-hydroxycholesterol was converted to both 7alpha-hydroxy-4-cholesten-3-one (7HCO) and 7-ketocholesterol in all of the hamsters tested. However, in the rat-like hamster and the hispid cotton rat, 7alpha-hydroxycholesterol was converted mostly to 7alpha-hydroxy-4-cholesten-3-one, as also observed in the rat (Rattus norvegicus). The results suggest that microsomal enzyme activity in the conversion of 7alpha-hydroxycholesterol to 7-ketocholesterol varies considerably, even within the subfamily Cricetinae and the family Muridae.

Animals↗
PubMed1995

A novel nonhepatic hydroxycholesterol 7 alpha-hydroxylase that is markedly stimulated by interleukin-1 beta. Characterization in the immature rat ovary.

During studies on the regulation of rat ovarian steroidogenic enzymes by interleukin-1 beta (IL-1 beta), we observed substantial metabolism of 25-hydroxycholesterol to two unusual polar products. This unexpected effect was observed both in isolated granulosa cells and in whole ovarian dispersates and was also induced by tumor necrosis factor alpha, but not by insulin-like growth factor I or follicle-stimulating hormone. The effect was dependent on time and the dose of IL-1 beta and was blocked by and IL-1 receptor antagonist. The formation of the polar metabolites was inhibited by ketoconazole and trilostane, but not by aminoglutethimide. Subsequent purification of these novel metabolites and analysis by gas chromatography/ mass spectrometry, NMR, and high performance liquid chromatography revealed them to be related 7 alpha-hydroxylated hydroxycholesterols (cholest-4-ene-7 alpha,25-diol-3-one and cholest-5-ene-3 beta,7 alpha,25-triol). IL-1 beta-stimulated ovarian 7 alpha-hydroxylase activity (3-10 pmol/min/mg of cellular protein) was nearly 4-fold that of control levels using 25-hydroxycholesterol as substrate. Activities at or below control levels were observed when IL-1 beta-treated cell sonicates were boiled or assayed in the presence of NADH (rather than NADPH), indicating that involvement of a nonenzymatic process was unlikely. IL-1 beta-stimulated 7 alpha-hydroxylase activity was inhibited to basal levels by a 10-fold excess of unlabeled 25- or 27-hydroxycholesterol, but not by cholesterol, pregnenolone, progesterone, testosterone, or dehydroepiandrosterone, suggesting that ovarian 7 alpha-hydroxylase is specific for hydroxycholesterols. Furthermore, when IL-1 beta-treated ovarian cultures were incubated with radiolabeled cholesterol or testosterone, no 7 alpha-hydroxylated products were observed. We were also unable to detect any mRNA transcripts for liver cholesterol 7 alpha-hydroxylase in IL-1 beta-stimulated ovarian cultures. This study describes an ovarian hydroxycholesterol 7 alpha-hydroxylase that differs from liver cholesterol 7 alpha-hydroxylase and from other nonhepatic progestin/ androgen 7 alpha-hydroxylases. The novel finding of the regulation of a 7 alpha-hydroxylase by IL-1 beta (and tumor necrosis factor alpha) suggests a unique role for cytokines in the regulation of cholesterol metabolism in the ovary and possibly other tissues.

Animals↗
PubMed2000

Plasma 24S-hydroxycholesterol: a peripheral indicator of neuronal degeneration and potential state marker for Alzheimer's disease.

The conversion of brain cholesterol into 24S-hydroxycholesterol and its subsequent release into the periphery is probably an important step for the maintenance of brain cholesterol homeostasis. Recent findings suggest that plasma 24S-hydroxycholesterol may be elevated in Alzheimer's disease (AD) and vascular dementia at least at some stage of the disease, suggesting increased brain cholesterol turnover during neurodegeneration. We investigated whether plasma 24S-hydroxycholesterol concentrations depend on the severity of AD and on the apolipoprotein E (apoE) genotype. Severity of AD and inheritance of the apoE4 allele were independently associated with reduced plasma 24S-hydroxycholesterol/cholesterol ratios. The results suggest that the decrease of plasma 24S-hydroxycholesterol/cholesterol in severely affected AD patients is a peripheral marker for loss of cholesterol 24S-hydroxylase in the CNS. Inheritance of the apoE4 allele may be associated with increased apoE-mediated transport of brain cholesterol to the periphery or with decreased activity of the 24S-hydroxylase. Longitudinal studies will assess the validity of the ratio plasma 24S-hydroxycholesterol/cholesterol as a state marker for AD.

Aged↗
PubMed1985

25-Hydroxycholesterol-supported and 8-bromo-adenosine 3',5'-monophosphate-stimulated testosterone production by primary cultures of two populations of rat Leydig cells.

Previous studies from this laboratory have demonstrated the presence of two populations of rat Leydig cells (I and II), which differ in their capacity for hCG- or cAMP-stimulated testosterone production. In the present study, we examined the metabolism of 25-hydroxycholesterol in primary cultures of both populations of Leydig cells. 25-Hydroxycholesterol bypasses the cAMP-dependent transport mechanism to the mitochondrial cytochrome P-450 side-chain cleavage enzyme (P-450scc) required by cholesterol and thus provides an index of the relative activity of P-450scc. Incubation of Leydig cells with increasing concentrations of 25-hydroxycholesterol resulted in a concentration-dependent increase in the amount of testosterone produced, with maximal amounts in both populations being reached at 25-hydroxycholesterol concentrations of 5 microM or greater. Population II produced more than twice as much testosterone as population I Leydig cells, whether incubated with 25-hydroxycholesterol or with 8-bromo-cAMP. Each population of Leydig cells produced 2.5-fold greater amounts of testosterone when incubated with 25-hydroxycholesterol than when incubated with 8-bromo-cAMP. In both populations of Leydig cells, cAMP-stimulated testosterone production was not different in cells cultured for 24 h from that in freshly isolated Leydig cells. These data suggest that cholesterol transport to P-450scc limits maximal testosterone production, and that the difference in hCG- or cAMP-stimulated testosterone production between the two populations of Leydig cells is primarily due to differences in P-450scc activity between the two populations and is not a result of population I consisting mostly of damaged Leydig cells.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1992

Effect of 25-hydroxycholesterol on cytotoxicity and prostacyclin production in cultured human umbilical arterial endothelial cells.

The effect of cholesterol or 25-hydroxycholesterol on DNA synthesis and prostacyclin synthesis by cultured human umbilical arterial endothelial cells was investigated. Cells incubated with 25-hydroxycholesterol showed an increased rate of cell death, decreased [3H]-thymidine incorporation and increased prostacyclin production as compared to either the control or the pure cholesterol group. 25-hydroxycholesterol caused a concentration- and time-dependent increase in prostacyclin synthesis. The intracellular free calcium concentration of endothelial cells incubated with 25-hydroxycholesterol was markedly increased in a time-dependent manner. Calcium uptake by endothelial cells incubated with 25-hydroxycholesterol for 24 h was markedly increased. It is suggested that 25-hydroxycholesterol may depress DNA synthesis and increase prostacyclin synthesis via an elevation in the intracellular free calcium concentration of endothelial cells.

Calcium↗
PubMed1995

Movement of 25-hydroxycholesterol from the plasma membrane to the rough endoplasmic reticulum in cultured hepatoma cells.

Oxysterols serve as both substrates and signal molecules in the cholesterol-utilizing pathways of mammalian cells. Their distribution and movement within these cells, however, have not been well characterized; therefore we have undertaken such an analysis. Radiolabeled cholesterol and 25-hydroxycholesterol were pulsed into the cell surface membranes of rat hepatoma cells and their esterification was determined. The esterification of both probes was stimulated by feeding cells lipoproteins, even though lipoprotein cholesterol might be viewed as a competitor. Unlabeled 25-hydroxycholesterol, another potential competitor, also stimulated the esterification of the cell-surface probes. Esterification of both sterols was inhibited by a variety of amphiphilic agents. This inhibition was reversed by unlabeled 25-hydroxycholesterol. In cells incubated at 15 degrees C the fractional rate of esterification of the oxysterol was more than 100 times greater than that of cholesterol. Furthermore, the time course of esterification of plasma membrane cholesterol but not that of 25-hydroxycholesterol, was lagged. In contrast, the rate of esterification of the two probes was similar in broken cells supplied with saturating cholesterol. Finally, the transfer of 25-hydroxycholesterol from red blood cells to plasma lipoproteins was approximately 2000-fold faster than that of cholesterol. We conclude that 25-hydroxycholesterol and cholesterol are moved between the plasma membrane and endoplasmic reticulum by a common transport mechanism but that the oxysterol enters this pathway much more rapidly, possibly through a passive transfer step akin to its unmediated transfer from red cells to plasma.

Animals↗
PubMed1998

Serum 27-hydroxycholesterol in patients with primary biliary cirrhosis suggests alteration of cholesterol catabolism to bile acids via the acidic pathway.

Reduced cholesterol synthesis has been reported in patients with primary biliary cirrhosis but no data are available on changes in cholesterol catabolism induced by the disease. Serum levels of 7alpha-hydroxycholesterol and 27-hydroxycholesterol have been measured in 25 patients (either normocholesterolemic or hypercholesterolemic) with primary biliary cirrhosis and in control subjects. To evaluate cholesterol synthesis, serum levels of lathosterol were measured, and campesterol and sitosterol were considered to reflect intestinal absorption and biliary elimination of sterols. In normocholesterolemic patients with primary biliary cirrhosis, lathosterol was significantly lower than in normocholesterolemic controls (P < 0.05) whereas no difference was found between hypercholesterolemic patients and hypercholesterolemic controls. Serum concentrations of sitosterol were significantly higher in both normocholesterolemic and hypercholesterolemic patients with primary biliary cirrhosis as compared with the respective controls (P < 0.01). In patients with primary biliary cirrhosis, serum 7alpha-hydroxycholesterol was slightly higher than in controls. 27-Hydroxycholesterol was significantly higher in hypercholesterolemic compared to normocholesterolemic controls (P < 0.05) and a significant linear correlation (r = 0.771; P < 0.001) was found between 27-hydroxycholesterol and cholesterol. In contrast, in patients with primary biliary cirrhosis, high cholesterol concentrations were not associated with increased serum levels of 27-hydroxycholesterol. Our data confirm that in patients with primary biliary cirrhosis, cholesterol synthesis and biliary elimination of sterols are impaired and also suggest that both the feedback regulation of retained bile acids on cholesterol 7alpha-hydroxylase and the scavenger effect on elevated serum cholesterol by cholesterol 27-hydroxylase are deficient in these patients. acids via the acidic pathway.

Aged↗