Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Hydroxycholesterols”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 631 records · Page 35Linked to original sources
PubMed1978

Alteration of 86Rb+ influx and efflux following depletion of membrane sterol in L-cells.

Ouabain-sensitive uptake of 86Rb+ (an analogue of K+) was enhanced in L-cells that had been treated with 25-hydroxycholesterol or 7-ketocholesterol in order to deplete their sterol concentration. Ouabain-insensitive Rb+ efflux also increased in the sterol-depleted cells and the intracellular concentration of K+ diminished while the concentration of Na+ increased. All of these effects of 25-hydroxycholesterol were counteracted by the addition of mevalonate to the culture medium. Despite the evidence for increased active Rb+ transport in the 25-hydroxycholesterol-treated cells, the level of sodium and potassium ion-activated adenosine triphosphatase ((Na+ + K+)-activated ATPase) activity measured in homogenates and plasma membrane preparations from the treated cells was not significantly different from the control values. Rb+ uptake was more sensitive to ouabain inhibition in sterol-depleted cells than in control cells, although ATPase activity in plasma membrane fractions isolated from treated cells was not more sensitive to ouabain inhibition than was that from control cells. It is possible that the ability of the oxygenated sterols to inhibit DNA synthesis and cell division (Kandutsch, A. A., and Chen, H. W. (1977) J. Biol. Chem. 252, 409-415) is related to their effects upon cellular ion transport.

Biological Transport, Active↗
PubMed1983

Cholesterol and mevalonic acid are independent requirements for the in vitro proliferation of human bone marrow granulocyte progenitor cells: studies using ML-236B.

ML-236B is a competitive inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase, the key regulatory enzyme in the sequence that catalyzes the conversion of acetate to mevalonic acid in cholesterol biosynthesis. This compound caused marked inhibition of human bone marrow granulocyte progenitor cell (CFU-C) proliferation, the 50% inhibitory concentration (IHD50) being 2.0 X 10(6)M. Inhibition of colony formation was reversed by mevalonic acid but not by cholesterol. ML-236B also inhibited DNA synthesis and acetate incorporation into cholesterol in marrow mononuclear cells (IHD50 = 5.6 x 10(6)M and 3.2 x 10(7)M, respectively). No inhibition of mevalonate incorporation into cholesterol was observed. These results differ from those observed with 25-hydroxycholesterol, another inhibitor of HMG CoA reductase. The latter compound also inhibited CFU-C proliferation and cholesterol biosynthesis from acetate; inhibition of colony formation was reversed by cholesterol but not by mevalonic acid. In addition, 25-hydroxycholesterol inhibited cholesterol synthesis from mevalonic acid precursor. We conclude that: (1) ML-236B is a potent inhibitor of CFU-C proliferation, DNA synthesis, and cholesterol biosynthesis from acetate precursor in marrow mononuclear cells; (2) the effects of ML-236B are completely reversed by mevalonic acid but not by cholesterol, suggesting that mevalonic acid per se or one or more of its nonsterol products are critical for cell growth; (3) the inhibitory effects of 25-hydroxycholesterol on CFU-C proliferation and cholesterol biosynthesis are not solely a result of its inhibition of HMG CoA reductase, but are due in part to inhibition of enzymatic steps distal to mevalonic acid in the sterol synthetic pathway; and (4) mevalonic acid and cholesterol are independent requirements for CFU-C proliferation and differentiation in vitro.

Acetates↗
PubMed1981

Measurement of cholesterol 7 alpha-hydroxylase activity with selected ion monitoring.

Formation of 7 alpha-hydroxycholesterol by rat liver microsomes was quantitated using a gas chromatograph-mass spectrometer operated in selected ion monitoring mode. This procedure measures the mass of 7 alpha-hydroxycholesterol formed and does not require addition of labeled cholesterol to monitor the reaction, since endogenous microsomal cholesterol serves as substrate for the enzyme cholesterol 7 alpha-hydroxylase. The method requires only the extraction of lipids from microsomal incubations and injection of a small fraction of this extract into the apparatus. Microsomes from normal rat livers incubated for different periods were found to yield increased 7 alpha-hydroxycholesterol with time.

Animals↗
PubMed1981

Assay of oxysterol-binding protein in a mouse fibroblast, cell-free system. Dissociation constant and other properties of the system.

Procedures for determining a 7.5 S oxysterol-binding protein in the cytosol fraction of cultured mouse fibroblasts were developed. The methods involved precipitation of cytosolic proteins between 0.3 and 0.4 saturation with (NH4)2SO4, incubation of the proteins with 25-hydroxy[3H]cholesterol at 0 degrees C and analysis by velocity sedimentation of 7.5 S radioactivity or of specific binding using dextran-charcoal to adsorb free sterol. By these means it was shown that binding of the ligand to the protein in a citric acid-phosphate buffer was optimal at pH 5.5 and that the sedimentation rate of the complex was greater at pH 7.4 (7.5 S) than at pH 5.5 (6.9 S). The binding protein was essentially saturated at a diol concentration of about 20 X 10(-9) M. The apparent Kd of the sterol-protein complex was approximately 3.9 X 10(-9) M. Cholesterol did not bind to 25-hydroxycholesterol-binding sites on the 7.5 S protein, whereas several oxysterols that are potent suppressors of 3-hydroxy-3-methylglutaryl CoA reductase also inhibited the binding of 25-hydroxycholesterol. One of these sterols, 5 alpha-cholest-8(14)-en-3 beta-ol-15-one was shown to compete for sites occupied by 25-hydroxycholesterol.

Animals↗
PubMedDate not supplied

[Chromatomass-spectrometric determination of oxidized cholesterol derivatives in blood serum].

Content of several oxidized forms of cholesterol was studied in blood serum of patients with hypercholesterolemia using chromato-mass-spectrometry. The hydroxycholesterols detected were identified as 7-beta-hydroxycholesterol, 25-hydroxycholesterol, 7-ketocholesterol in the presence of standard substances added. Main patterns of gas chromatographic and mass spectrometric analyses of these substances are described.

Cholesterol↗
PubMed1977

Consequences of blocked sterol synthesis in cultured cells. DNA synthesis and membrane composition.

When cell cultures were incubated with certain oxygenated derivatives of cholesterol which specifically depress 3-hydroxy-3-methylglutaryl-coenzyme A reductase activity (i.e. 25-hydroxycholesterol, 7-ketocholesterol, or 20 alpha-hydroxycholesterol), a number of consequences followed the decline in enzyme activity. DNA synthesis, expressed in terms of (methyl-3H)thymidine incorporation/mg of cellular protein, declined progressively after the addition of an inhibitor to L-cell cultures and had essentially ceased by 80 h. A decline in the rate of cell growth, as determined by the measurement of cellular protein, became apparent about 24h after the addition of the inhibitor. These effects of the inhibitory sterols were reversed when mevalonate or cholesterol was added to the medium within 48 h after the addition of the inhibitor. Specific rates of uridine incorporation into RNA and of leucine into protein were not significantly altered during 80 h of incubation with the inhibitor. Sterol synthesis was suppressed; and the concentration of desmosterol in L-cells declined to about one-half of the control level within 36 h. Since phospholipid concentrations were not altered significantly by the treatment, the molar ratio of sterol to phospholipids declined to levels lower than any previously reported for mammalian cells. Changes in the molar ratio of sterol to phospholipids in plasma membranes isolated from L-cells that had been incubated with 25-hydroxycholesterol or cholesterol were in agreement with those found in cells under similar conditions. The inhibitory sterols caused a similar but slower decline in the concentrations of unesterified and total cholesterol in fetal mouse liver cell cultures and rat hepatoma cell cultures.

Cell Membrane↗
PubMedDate not supplied

Regulatory role of mevalonate in the growth of normal and neoplastic human mammary epithelial cells.

Treatment with 25-hydroxycholesterol, an inhibitor of HMG CoA reductase activity, efficiently blocked the proliferation of both human normal mammary epithelial cells (HMEC) and breast cancer cells (MDA231). Upon release of the block there was a rapid increase in the HMG CoA reductase activity, which reached a maximum 4 h after removal of the inhibitor, in both cell types. In MDA231 this increase in enzymatic activity was followed by a rapid initiation of DNA synthesis, whereas this process started considerably later in HMEC. Even in HMEC stimulated to DNA synthesis by insulin, there was first an increase in HMG CoA reductase activity with a maximum 4 h after the addition of the mitogen. If 25-hydroxycholesterol was added along with insulin, the subsequent initiation of DNA synthesis was prevented. Following a 25-hydroxycholesterol treatment as short as 4 h, the onset of DNA synthesis was delayed, indicating that a certain level of HMG CoA reductase activity (= mevalonate synthesis) in the early and mid stage of the prereplicative phase is required for the transduction of the signal leading to initiation of DNA synthesis. In concurrence with these data, it was also demonstrated that giving an exogenous supply of mevalonate to the insulin-stimulated HMEC results in a faster initiation of DNA synthesis.

Adult↗
PubMed1995

Effect of a coffee lipid (cafestol) on regulation of lipid metabolism in CaCo-2 cells.

The influence of cafestol, a lipid component found in boiled coffee, on low density lipoprotein (LDL) and lipid metabolism was investigated in CaCo-2 cells cultured on filter membranes. The rate of uptake and degradation of 125I-labeled tyramine cellobiose-LDL was increased 50% in CaCo-2 cells incubated with cafestol (20 micrograms/ml, 63 microM) for 24 h, whereas in cells incubated with 25-hydroxycholesterol (10 micrograms/ml, 25 microM) the rate of uptake and degradation showed a 30% decrease. A mixture of kahweol and cafestol, both natural components of coffee beans, modestly enhanced the rate of LDL uptake and degradation, as compared to pure cafestol. Incubation of cafestol with CaCo-2 cells induced a 3-fold up-regulation of LDL receptor mRNA, as compared to control cells. In contrast, incubation of the cells with 25-hydroxycholesterol produced a 30% decrease of LDL receptor expression. CaCo-2 cells were transfected with a promoter region containing the sterol regulatory element-1 (SRE-1) coupled to the reporter gene chloramphenicol acetyltransferase (CAT). When cells transfected with SRE-1 promoter were incubated with cafestol, there was a 20% up-regulation of CAT activity, whereas 25-hydroxycholesterol abolished this activity. Cafestol contributed to a significantly lowered secretion of cholesteryl ester and triacylglycerol, regardless of the radiolabeled precursor used ([2-14C]acetic acid, [1,2,3-3H]glycerol, [3H]water, and [1-14C]oleic acid). This reduction in secretion of lipids was accompanied by an increase in trichloroacetic acid-soluble activity when radiolabeled oleic acid was used as a tracer. We conclude that cafestol promotes an enhanced rate of uptake and degradation of LDL, probably due to an increase in transcription of LDL receptor mRNA and a reduced secretion of cholesteryl ester and triacylglycerol in CaCo-2 cells.

Cell Line↗
PubMed1996

Bile acid synthesis: 7 alpha-hydroxylation of intermediates in the sterol 27-hydroxylase metabolic pathway.

The recognition that the 7 alpha-hydroxylation of 27-hydroxycholesterol is catalyzed by an enzyme that is different from cholesterol 7 alpha-hydroxylase raises the question as to the number of similar enzymes that may be present in liver and subserve bile acid synthesis. Thus, both 3 beta-hydroxy-5-cholestenoic acid and 3 beta-hydroxy-5-cholenoic acid, further oxidation products derived from 27-hydroxycholesterol, are also 7 alpha-hydroxylated during their metabolism to chenodeoxycholic acid. Using a microsomal fraction of hamster liver and competition plot analysis, we found that the 7 alpha-hydroxylase activity for the acid substrates was approximately one-tenth that found for 27-hydroxycholesterol. Mixtures of the different substrates did not depress the total rate of 7 alpha-hydroxylation. The evidence supports the view that these substrates share the same catalytic site on a single enzyme.

Animals↗
PubMed1996

Formation of oxysterols during oxidation of low density lipoprotein by peroxynitrite, myoglobin, and copper.

Oxidation of low density lipoprotein (LDL) in the artery wall leads to the formation of cholesterol oxidation products that may result in cytotoxicity. Different mechanisms could contribute to LDL oxidation in vivo resulting in characteristic and specific modification of the cholesterol molecule. Alternatively, attack on cholesterol by chain propagating peroxyl radicals could result in the same distribution of oxidation products irrespective of the initial pro-oxidant mechanism. To distinguish between these possibilities we have monitored the formation of nine oxysterols during LDL oxidation, promoted by copper, myoglobin, peroxynitrite, or azo bis amidino propane. Regardless of the oxidant used, the pattern of oxysterol formation was essentially the same. The yields of products identified decreased in the order 7-oxocholesterol > 7 beta-hydroxycholesterol > 7 alpha-hydroxycholesterol > 5,6 beta-epoxycholesterol > 5,6 alpha-epoxycholesterol except in the case of peroxynitrite in which case a higher yield of 5, 6 beta-epoxycholesterol relative to 7-oxocholesterol was found. No formation of cholestane 3 beta, 5 alpha, 6 beta-triol, or the 24-,25-,27-hydroxycholesterols was seen. Concentration of 7-oxocholesterol levels in LDL was positively correlated with the degree of protein modification. Endogenous alpha-tocopherol in LDL or supplementation with butylated hydroxytoluene prevented oxysterol formation. Taken together these data indicate that the oxidation of cholesterol and protein in LDL occur as secondary oxidation events consequent on the attack of fatty acid peroxyl/alkoxyl radicals on the 7-position of cholesterol, and with amino acids on apoB. Furthermore, oxidant processes with atherogenic potential, such as peroxynitrite, copper, and myoglobin are capable of producing oxidized LDL containing cytotoxic mediators.

Amidines↗
PubMed1999

HMG CoA reductase and LDL receptor genes are regulated differently by 15-ketosterols in Hep G2 cells.

The ability of two 15-ketosubstituted sterols, 5alpha-cholest-8(14)-en-3beta-ol-15-one and 3beta-(2-hydroxyethoxy)-5alpha-cholest-8(14)-en-15-one, to alter the mRNA levels of 3-hydroxy-3-methylglutaryl-CoA reductase, low density lipoprotein receptor, and oxysterol binding protein was studied and compared with the effects of 25-hydroxycholesterol in Hep G2 cells. All three oxysterols decreased the level of HMG CoA reductase mRNA at concentrations of 10-30 microM, although 25-hydroxycholesterol was effective at concentrations of 1-3 microM. 25-Hydroxycholesterol lowered the level of LDL receptor mRNA more efficiently after 8 hours than after 24 hours of incubation, whereas 15-ketosterols did not decrease the mRNA level of the LDL receptor. The transcriptions of HMG CoA reductase and LDL receptor genes are therefore independently regulated by 15-ketosterols in Hep G2 cells. In addition, the level of the oxysterol binding protein mRNA is not affected by oxysterols in Hep G2 cells.

Cell Line↗
PubMed1982

Cholesterol metabolism in human monocyte-derived macrophages: stimulation of cholesteryl ester formation and cholesterol excretion by serum lipoproteins.

The role of lipoproteins and serum in the formation and accumulation of cholesteryl esters in human monocyte-derived macrophages (HMD macrophages) was investigated; studies were also carried out with IC21 cells (a cell line derived from mouse peritoneal macrophages). Following preincubation of HMD macrophages with lipoprotein-depleted serum (LPDS), both native and acetylated low density lipoprotein (LDL and AcLDL, respectively) stimulated the formation of cholesteryl esters with a resultant increase in cellular cholesteryl ester content. Cholesteryl ester formation and accumulation was also stimulated in macrophages exposed continuously to 25-hydroxycholesterol. However, the stimulation of cholesterol esterification by either lipoproteins or 25-hydroxycholesterol was not inhibited by progesterone in HMD macrophages, but was in the IC21 cells. Cholesterol efflux and the hydrolysis of cellular cholesterol ester, promoted by serum components, were studied in HMD macrophages preloaded with cholesteryl ester by incubation with 25-hydroxy cholesterol. Replacement of the medium with one devoid of 25-hydroxycholesterol resulted within 24 hr in at least a 30% decrease in the cholesteryl ester content of the HMD macrophages; replacement with a medium high in cholesterol acceptor content (LPDS or high density lipoprotein) and incubation for three days led to the most marked decreases in cellular cholesterol content. Thus, hydrolysis of the cholesteryl esters by HMD macrophages was not dependent on the presence of cholesterol acceptors in the medium, but cellular cholesterol content was.

Cholesterol↗
PubMed2006

Effects of hydroxysterols and atorvastatin on lipopolysaccharide-induced secretion of tumor necrosis factor and interleukin-10 by mouse macrophages.

Preincubation of macrophages with atorvastatin, cholesterol, 25-, 27-hydroxycholesterol, and 7-ketocholesterol reduced the level of TNF-alpha to 10, 61, 13, 64.5, and 82%, respectively. Addition of mevalonate to the preincubation medium canceled the effects atorvastatin, cholesterol, and 7-ketocholesterol, but not the effects of 25- and 27-hydroxycholesterols. Atorvastatin increased the level of IL-10 by 41%, while 7-ketocholesterol and 25-hydroxycholesterol inhibited its secretion by 48 and 55%.

Animals↗
PubMed2006

The effect of oxysterols, individually and as a representative mixture from food, on in vitro cultured bovine ovarian granulosa cells.

The cytotoxicity of five oxysterols identified in cooked fish, 7-ketocholesterol, 7beta-hydroxycholesterol, cholesterol 5alpha,6alpha-epoxide, cholestanetriol and 4-cholesten-3-one, was investigated in primary cultures of bovine ovarian granulosa cells. Cells were exposed to the oxysterols individually and to a mixture of the same oxysterols for 24 h. Cell viability as determined by trypan blue exclusion and mitochondrial integrity (3-[4,5-dimethylthiazol-2yl]-2,5-diphenyltetrazolium bromide (MTT) reduction) was reduced by 0.5 and 2.5 microM 7beta-hydroxycholesterol, cholesterol 5alpha,6alpha-epoxide, cholestanetriol and 4-cholesten-3-one, but not by 0.5 or 2.5 microM 7-ketocholesterol under the same culture conditions. A mixture of 7-ketocholesterol, 7beta-hydroxycholesterol, cholesterol 5alpha,6alpha-epoxide, cholestanetriol and 4-cholesten-3-one 0.5 microM each; 2.5 microM oxysterol in total) did not change cell viability relative to controls. Lipid peroxidation, as determined by thiobarbituric acid reactive substances assay, was unaffected by a 24-hour exposure of granulosa cells to individual oxysterols but was increased slightly by the oxysterol mixture. The specific activities of antioxidant enzymes superoxide dismutase and catalase were increased to different extents (1.17- to 6.43-fold), relative to controls, by the administration of individual oxysterols and the oxysterol mixture. These results indicate that while some individual oxysterols can induce cytotoxic effects and defensive responses in bovine ovarian granulosa cells, administration of the same oxysterols as a mixture does not elicit the same responses. In addition, the oxysterols tested exerted a pro-apoptotic effect on granulosa cells when administered individually at concentrations of 0.5 and 2.5 microM, but not when administered as a 2.5 microM oxysterol mixture. The results suggest that major oxysterols are not universally cytotoxic, they may complete with other oxysterols for receptor sites, and that the simultaneous presence of several different oxysterol species may reduce the adverse effects of individual oxysterols.

Animals↗
PubMed1986

A high-performance liquid chromatographic method for the assay of cholesterol 7 alpha-hydroxylase activity.

A high-performance liquid chromatographic method has been developed for the measurement of cholesterol 7 alpha-hydroxylase activity in liver microsomes. 7 alpha-Hydroxycholesterol generated from endogenous cholesterol was derivatized with anthroyl 1-carbonitrile, chromatographed on a reverse-phase column, and detected fluorometrically. The detection limit of 7 alpha-hydroxycholesterol was 1 ng/tube. The cholesterol 7 alpha-hydroxylase activity in rat liver microsomes was assayed by this method, and the effects of some detergents and of the addition of exogenous cholesterol together with detergents on the enzyme activity were investigated. The endogenous 7 alpha- and 7 beta-hydroxycholesterol could be also measured by this method.

Acetone↗
PubMed1984

Sterol-phospholipid interactions in model membranes. Effect of polar group substitutions in the cholesterol side-chain at C20 and C22.

The interactions of phospholipids with four different cholesterol derivatives substituted with one OH or one keto group at position C20 or C22 of the side-chain were studied. The derivatives were the 22,R-hydroxy; 22,S-hydroxy; 22-keto- and 20,S-hydroxycholesterol. Two aspects of the interactions were investigated: (1) the effect of the cholesterol derivatives on the gel leads to liquid crystalline phase transition of dipalmitoylphosphatidylcholine (DPPC) and of dielaidoylphosphatidylethanolamine (DEPE) monitored by differential scanning calorimetry and (2) The effect on the lamellar leads to hexagonal HII phase transition of DEPE monitored by DSC and by 31P-NMR to determine structural changes. The gel leads to liquid crystalline phase transition was affected by the cholesterol derivatives to a much larger extent in the case of DPPC than of DEPE. In both cases, there was a differential effect of the four derivatives, the 22,R-hydroxycholesterol being the less effective. In DPPC-sterol 1:1 systems, 22,R-hydroxycholesterol does not suppress the melting transition, the delta H values becomes 7.1 kcal X mol-1 as compared to 8.2 kcal X mol-1 for the pure lipid. 22,S-OH cholesterol has a much stronger effect (delta H = 3.1 kcal X mol-1) and 22-ketocholesterol suppresses the transition completely. In DEPE mixtures of all these compounds, the melting transition of the phospholipid is still observable. The transition temperature was shifted to lower values (-13.5 degrees C in the presence of 20,S-OH cholesterol). The delta H of the transition was lowered by these compounds except in DEPE-22,R-OH cholesterol mixtures and the cooperativity of the transition (reflected by the width at half peak height) was reduced. The lamellar leads to hexagonal HII phase transition was also affected by the presence of these cholesterol derivatives. The transition temperature value was depressed with all these compounds. 20,S-OH cholesterol was the most effective followed by 22,R-OH cholesterol. The delta H of the transition was not strongly affected. The molecular interfacial properties of these derivatives were studied by the monomolecular film technique. It is most likely that 22,R-OH cholesterol due to the hydroxyl groups at the 3 beta- and 22,R-positions orients with the sterol nucleus lying flat at the air/water interface, since the compression isotherm of either the pure sterol or the DOPC-sterol mixture (molar ratio, 1:1) monomolecular film exhibits a transition at approx. 103 A2.(ABSTRACT TRUNCATED AT 400 WORDS)

Air↗
PubMed1983

The coordination of sterol and phospholipid synthesis in cultured myogenic cells. Effect of cholesterol synthesis inhibition on the synthesis of phosphatidylcholine.

The coordination of biosynthesis of cholesterol and phosphatidylcholine has been investigated in a myoblast cell line L6, grown in lipid-depleted medium. The addition of 25-hydroxycholesterol or compactin to this medium inhibits cholesterol synthesis by over 95%. The rate of [3H]choline incorporation into phosphatidylcholine begins to decline after 6 h and eventually falls to 45% of control. Measurements of choline flux through the CDPcholine pathway and of the pool sizes of choline-containing intermediates indicate that the formation of CDPcholine is the rate-limiting step in phosphatidylcholine synthesis in L6. The rate of CDPcholine synthesis was measured in vivo by pulse-chase experiments. Culturing cells with 25-hydroxycholesterol or compactin results in an inhibition of this step, which parallels the inhibition of incorporation of [3H]choline into phosphatidylcholine. The specific activities of the enzymes of phosphatidylcholine synthesis were assayed under optimal substrate conditions. Growth in the presence of sterol-synthesis inhibitors for 24 h has a significant, but variable, effect on the activity of microsomal and cytosolic cholinephosphate cytidylytransferase. Inhibition is seen in approximately one-half of the preparations and ranges up to 60%. The degree of inhibition of the enzyme in vitro correlates with an elevation of cytosolic triacylglycerol and phospholipid levels, and is not eliminated by the inclusion of excess stimulatory phospholipids in the assay. The pool sizes of the substrates, cholinephosphate and CTP, are unaffected by cholesterol synthesis inhibition. In contrast to the effects on cholinephosphate cytidylytransferase, the microsomal enzymes glycerol-3-phosphate acyltransferase and choline phosphotransferase are stimulated 2-fold or more. Choline kinase specific activity was inhibited 2-fold after 24 h of treatment with 25-hydroxycholesterol; however, no effect on this step was observed in vivo. These results indicate that the coordination of cholesterol and phosphatidylcholine synthesis involves regulation at the cytidylytransferase-catalyzed step.

Cell Line↗
PubMed1984

Differences between the regulation of cholesterol side-chain cleavage in Leydig cells from mice and rats.

A Leydig cell culture system has been used to study the in vitro modulation by luteinizing hormone (LH) of steroidogenesis in Leydig cells isolated from mice and immature rats. Mouse Leydig cells precultured for 24 h in the presence of increasing concentrations of LH (1 ng-1 microgram/ml) showed a dose-dependent decrease of the maximal LH-stimulated testosterone production. After pretreatment with 1 microgram LH/ml, maximal LH-stimulated testosterone production. After production in the presence of excess 20 alpha-hydroxycholesterol (a cholesterol side-chain cleavage substrate) were reduced to approx. 50% of control values. The possible site of action of LH is probably prior to pregnenolone, because testosterone production in the presence of excess pregnenolone was not affected by the LH pretreatment. Immature rat Leydig cells showed no decrease of maximal steroid production after 24 h culture in the presence of 1 microgram LH/ml. These results indicate that the regulation of the cholesterol side-chain cleavage activity during long-term LH action is different in mouse and rat Leydig cells. The properties of the cholesterol side-chain cleavage enzyme in mouse and rat Leydig cells were further investigated with different hydroxylated cholesterol derivatives as substrates. Steroid production by mouse Leydig cells in the presence of (22R)-22 hydroxycholesterol was similar as in the presence of LH. In contrast, steroidogenesis in rat Leydig cells in the presence of (22R)-22 hydroxycholesterol was at least 10-fold higher than in the presence of LH. It is concluded that the cholesterol side-chain cleaving enzyme in the mouse Leydig cell operates at its maximal capacity during short-term LH stimulation and can be inhibited after long-term LH action, whereas in the rat Leydig cell only a fraction of the potential activity is used during short-term LH stimulation, which is not affected during long-term LH action.

Aging↗