Identification of 17-methyl-18-norandrosta-5,13(17-dien-3beta-ol, the C19 fragment formed by adrenal side chain cleavage of a 20-aryl analog of (20S)-20-hydroxycholesterol.
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Incubation of (20R)-20-phenyl-5-pregnene-3beta,20-diol, an aromatic analog of (23S)-20-hydroxycholesterol, with an adrenal mitochondrial preparation leads to the formation of four compounds: pregnenolone, phenol, a C8 ketone, acetophenone, and a nonpolar C19 compound. This latter compound has now been identified by reverse isotope dilution analysis and by gas chromatography/mass spectrometry as 17-methyl-18-norandrosta-5,13(17)-dien-3beta-ol. From these results it is evident that enzymatic fission of the C-17,20 bond of this synthetic derivative occurs. On the other hand, when (20S)-20-hydroxy[21-14C]cholesterol was used as substrate, the analogous cleavage did not take place. Thus, substitution of an aromatic group on C-20 facilitates side chain cleavage between that carbon atom and the nucleus whereas neither of the naturally occuring precursors, cholesterol or its 20-hydroxylated counterpart, are metabolized to a C8 fragment. (+info)
The 7alpha-hydroxysteroids produced in human tonsils enhance the immune response to tetanus toxoid and Bordetella pertussis antigens.
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Human tonsils were assessed for their ability to 7alpha-hydroxylate pregnenolone (PREG), dehydroepiandrosterone (DHEA) and 3-epiandrosterone (EPIA). Both 7alpha-hydroxy-DHEA and 7alpha-hydroxy-EPIA were produced by homogenates of either whole tonsils or of lymphocyte-depleted tonsil fractions. In contrast, isolated lymphocytes were found to be unable to carry out 7alpha-hydroxylation. When co-cultures of tonsil-derived T and B lymphocytes were set up under stimulatory conditions, IgGs were released in the supernatants and could be quantitated, and immunomodulating properties of different steroids were monitored. When PREG was added to a mixture of tonsil-derived B and T lymphocytes, a decrease of non-specific and specific IgG was observed. An increase in specific anti-tetanus toxoid and anti-Bordetella pertussis antigen IgGs was obtained with either 1 microM 7alpha-hydroxy-DHEA or 1 microM 7alpha-hydroxy-EPIA. In contrast, DHEA and EPIA were unable to trigger such an effect. When cultures of isolated tonsillar B cells were used, none of the steroids tested showed significant effects on specific IgG productions. These data led to the conclusion that human tonsillar cells transform DHEA and EPIA, but not PREG, into 7alpha-hydroxylated metabolites. These metabolites could act on target tonsillar T lymphocytes which in turn act upon B lymphocytes for increasing specific IgG production. (+info)
Dexamethasone-induced apoptosis of mouse thymocytes: prevention by native 7alpha-hydroxysteroids.
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Dehydroepiandrosterone (DHEA) has been shown to decrease the dexamethasone (DEX)-induced apoptosis of thymocytes and to be one of the native 3beta-hydroxysteroids extensively 7alpha-hydroxylated in thymus. This led us to question whether DHEA or 7alpha-hydroxy-DHEA is responsible for the decrease in DEX-induced apoptosis of thymocytes and whether this property is shared with other native 3beta-hydroxysteroids and their 7alpha-hydroxylated metabolites. Treatment of mice with DHEA or 7alpha-hydroxy-DHEA prior to DEX led to a smaller decrease in thymus weight than with DEX alone and to a disappearance of the DEX-induced changes in thymocyte phenotypes. Thymocyte apoptosis induced by DEX treatment was significantly lowered in DHEA- and 7alpha-hydroxy-DHEA-treated thymi, even after 18 h culture with additional 10-6 mol/L DEX. Extensive apoptosis of thymocytes cultured with 10-7 mol/L DEX was brought back to control levels when 10-5 mol/L 7alpha-hydroxy-DHEA or 10-5 mol/L 7alpha-hydroxy-epiandrosterone was added. After use of DHEA and epiandrosterone or pregnenolone, less significant and no significant changes were obtained, respectively. These findings imply that the 7alpha-hydroxylation of 3beta-hydroxysteroids may be a prerequisite for an exquisite regulation of the thymocyte-positive selection driven by the glucocorticoids produced in thymic epithelial cells. (+info)
Biosynthesis of bile acids in man. Hydroxylation of the C27-steroid side chain.
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The first step in the degradation of the steroid side chain during biosynthesis of bile acids from cholesterol in man was studied in microsomal and mitochondrial fraction of homogenate of livers from 14 patients. The microsomal fraction was found to catalyze an efficient 25-hydroxylation of 5,8-cholestane-3a,7a,12atriol. A small extent of 23-, 24-, and 26-hydroxylation of the same substrate was observed. 53-Cholestane-3a,7adiol was hydroxylated in the 25-position only to a very small extent. The mitochondrial fraction was found to catalyze 26-hydroxylation of cholesterol, 5-cholestene-3P,7a-diol, 5P-cholestane-3a,7a-diol, 7a-hydroxy-4-cholesten-3-one, and 5,0-cholestane-3a,7a,12a-triol. Addition of Mg++ stimulated the 26-hydroxylation of cholesterol but had no effect or an inhibitory effect on 26-hydroxylation of the other substrates, indicating a heterogeneity of the mitochondrial 26-hydroxylating system. The level of 26-hydroxylase activity towards different substrates varied considerably with different mitochondrial preparations. The roles of the microsomal and mitochondrial 26- hydroxylations as well as the microsomal 25-hydroxylation in biosynthesis of bile acids in man are discussed. The results indicate that microsomal 26-hydroxylation is less important than mitochondrial 26-hydroxylation under normal conditions. The possibility that microsomal 25-hydroxylation is important cannot be ruled out. (+info)
A unique case of central diabetes insipidus (DI) associated with transient pituitary stalk enlargement: close observation over several years using magnetic resonance imaging (MRI) and hypophysial endocrine tests.
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We had the opportunity to closely observe a unique case of central diabetes insipidus (DI), in which dramatic changes in both radiological findings and hypophysial functions were seen. A 63-year-old female developed central DI, and magnetic resonance imaging (MRI) revealed a mild thickening of the pituitary stalk and lack of hyperintense signal associated with normal neurohypophysis on T1-weighted images. About three months later, the stalk was found to be remarkably expanded like neoplasm; however, anterior pituitary functions were almost normal on that occasion, except for the absence of GH response to an insulin tolerance test. About nine months after the onset of DI, secondary hypoadrenalism and hypothyroidism, which required replacement therapy, developed transiently, but recovered about one year later. Results of hypophysial endocrine tests during this period showed that the dysfunction was predominantly suprapituitary in nature. As time passed, the stalk lesion began to shrink spontaneously and another MRI, obtained five years after the onset of DI, disclosed normal findings for the infundibulo-hypophysial system, except for lack of the hyperintense signal of the neurohypophysis. The patient has since been healthy, except for the DI, which has been controlled by treatment with vasopressin. We report here a unique case of central DI associated with transient pituitary stalk enlargement. (+info)
Microsomal 12alpha-hydroxylation of 7alpha-[12alpha, 12beta-2H2]hydroxy-4-cholesten-3-one.
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The synthesis of 7alpha-[12alpha, 12beta-2 H2]hydroxy-4-cholesten-3-one is described. It was shown with different techniques that this compound was 12alpha-hydroxylated by the microsomal fraction of a rat liver homogenate without marked isotope effect, indicating that cleavage of the C--H bond is not the rate-limiting step in this hydroxylation. The rate of 12alpha-hydroxylation was decreased by about 20% when performed in a medium containing deuterated water. The findings were discussed with reference to the specific properties of the 12alpha-hydroxylating system and to the results of previous studies on rate-limiting step in microsomal hydroxylation of steroids. (+info)
Cholesterol ester formation in cultured human fibroblasts. Stimulation by oxygenated sterols.
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Incubation of monolayers of cultured human fibroblasts with oxygenated sterols (25-hydroxycholesterol, 7-ketocholesterol, or 6-ketocholestanol) markedly enhanced the rate at which the cells esterified their endogenous cholesterol and produced an increase in the cellular content of cholesterol esters. The enhanced esterification capacity was associated with an increase in the activity of a membrane-bound fatty acyl-CoA:cholesteryl acyltransferase. Incubation of cells for 5 hours with 5 mug/ml of 25-hydroxycholesterol produced an 8-fold increase in the specific activity of this enzyme when assayed in cell-free extracts. Since the oxygenated sterols that elevated the activity of fatty acyl-CoA:cholesteryl acyl-transferase also suppressed the activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase, the data suggest that the processes of cholesterol ester formation and cholesterol synthesis in human fibroblasts are regulated in a reciprocal manner by coordinate changes in the activities of these two membrane-bound enzymes. (+info)
Identification of pentahydroxy bile alcohols in cerebrotendinous xanthomatosis: characterization of 5beta-cholestane-3alpha, 7alpha, 12alpha, 24xi, 25-pentol and 5beta-cholestane-3alpha, 7alpha, 12alpha, 23xi, 25-pentol.
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This paper describes studies dealing with the nature of the C27 pentahydroxy bile alcohols present in the bile and feces of two patients with cerebrotendinous xanthomatosis (CTX). The presence of a bile alcohol having the structure 5beta-cholestane-3alpha,7alpha,12alpha,24alpha,25-pentol was confirmed by separation of the two 24-hydroxy epimers of 5beta-cholestane-3alpha,7alpha,12alpha,24,25-pentol and characterization of the dpimers by gas-liquid chromatography and infrared and mass spectrometry. Tentative assignment of the 24alpha and 24beta configuration was made on the basis of molecular rotation differences. A second major bile alcohol excreted by the CTX subjects was 5beta-cholestane-3alpha,7alpha,12alpha,23xi,25-pentol. Its structure was determined by infrared spectrometry, proton magnetic resonance spectrometry, and mass spectrometry because a reference compound was not available. (+info)