A simple and precise assay of the enzymatic conversion of cholesterol into pregnenolone

Physiology and Pathophysiology of Steroid Biosynthesis, Transport and Metabolism in the Human Placenta

The steroid hormones progestagens, estrogens, androgens, and glucocorticoids as well as their precursor cholesterol are required for successful establishment and maintenance of pregnancy and proper development of the fetus. The human placenta forms at the interface of maternal and fetal circulation. It participates in biosynthesis and metabolism of steroids as well as their regulated exchange between maternal and fetal compartment. This review outlines the mechanisms of human placental handling of steroid compounds. Cholesterol is transported from mother to offspring involving lipoprotein receptors such as low-density lipoprotein receptor (LDLR) and scavenger receptor class B type I (SRB1) as well as ATP-binding cassette (ABC)-transporters, ABCA1 and ABCG1. Additionally, cholesterol is also a precursor for placental progesterone and estrogen synthesis. Hormone synthesis is predominantly performed by members of the cytochrome P-450 (CYP) enzyme family including CYP11A1 or CYP19A1 and hydroxysteroid dehydrogenases (HSDs) such as 3β-HSD and 17β-HSD. Placental estrogen synthesis requires delivery of sulfate-conjugated precursor molecules from fetal and maternal serum. Placental uptake of these precursors is mediated by members of the solute carrier (SLC) family including sodium-dependent organic anion transporter (SOAT), organic anion transporter 4 (OAT4), and organic anion transporting polypeptide 2B1 (OATP2B1). Maternal-fetal glucocorticoid transport has to be tightly regulated in order to ensure healthy fetal growth and development. For that purpose, the placenta expresses the enzymes 11β-HSD 1 and 2 as well as the transporter ABCB1. This article also summarizes the impact of diverse compounds and diseases on the expression level and activity of the involved transporters, receptors, and metabolizing enzymes and concludes that the regulatory mechanisms changing the physiological to a pathophysiological state are barely explored. The structure and the cellular composition of the human placental barrier are introduced. While steroid production, metabolism and transport in the placental syncytiotrophoblast have been explored for decades, few information is available for the role of placental-fetal endothelial cells in these processes. With regard to placental structure and function, significant differences exist between species. To further decipher physiologic pathways and their pathologic alterations in placental steroid handling, proper model systems are mandatory.

Steroidogenesis in plants--Biosynthesis and conversions of progesterone and other pregnane derivatives

In plants androstanes, estranes, pregnanes and corticoids have been described. Sometimes 17β-estradiol, androsterone, testosterone or progesterone were summarized as sex hormones. These steroids influence plant development: cell divisions, root and shoot growth, embryo growth, flowering, pollen tube growth and callus proliferation. First reports on the effect of applicated substances and of their endogenous occurrence date from the early twenties of the last century. This caused later on doubts on the identity of the compounds. Best investigated is the effect of progesterone. Main steps of the progesterone biosynthetic pathway have been analyzed in Digitalis. Cholesterol-side-chain-cleavage, pregnenolone and progesterone formation as well as the stereospecific reduction of progesterone are described and the corresponding enzymes are presented. Biosynthesis of androstanes, estranes and corticoids is discussed. Possible progesterone receptors and physiological reactions on progesterone application are reviewed.

A novel activity for a group of sesquiterpene lactones: inhibition of aromatase

A group of eleven sesquiterpene lactones isolated from different Asteraceae species from north-western Argentina were investigated for their inhibitory action on the estrogen biosynthesis. Seven of them, of different skeleton types, were found to inhibit the aromatase enzyme activity in human placental microsomes, showing IC50 values ranging from 7 to 110 microM. The most active were the guaianolides 10-epi-8-deoxycumambrin B (compound 1), dehydroleucodin (compound 2) and ludartin (compound 3). These compounds were competitive inhibitors with an apparent Ki = 4 microM, Ki = 21 microM and Ki = 23 microM, respectively. Compounds 1 and 2 acted as type II ligands to the heme iron present in the active site of aromatase cytochrome P450 (P450arom). Besides, all of them failed to affect the cholesterol side-chain cleavage enzyme activity on human placental mitochondrias. This is the first report on the aromatase inhibitory activity of this group of natural compounds.

Synthesis and evaluation of azole-substituted tetrahydronaphthalenes as inhibitors of P450 arom, P450 17, and P450 TxA2

In search of potential drugs for the treatment of estrogen- and androgen-dependent cancer as well as the prophylaxis of metastases, tetralones, tetralins, and dihydronaphthalenes bearing a OCH3 substituent at the benzene nucleus and an imidazol-4-yl, imidazol-1-yl, or 1,2,4-triazol-1-yl substituent in 2-position were synthesized with and without C1-spacer between the rings (compounds 2-26). The compounds were tested in vitro for inhibition of the three targets enzymes P450 arom (human placental microsomes), P450 17 (rat testicular microsomes), and P450 TxA2 (citrated human whole blood). To examine selectivity, some compounds were further tested in vitro for inhibition P450 18 (bovine adrenal mitochondria), P450 scc (bovine adrenal mitochondria) and corticoid formation (aldosterone, corticosterone; ACTH stimulated rat adrenal tissue). In vitro, selected compounds were examined in Sprague Dawley rats regarding P450 TxA2 inhibition, reduction of plasma testosterone concentration, antiuterotrophic activity (inhibition of the uterotrophic activity of androstenedione), reduction of plasma estradiol concentration (pregnant mares' serum gonadotropin-primed rats), and mammary tumor inhibiting activity (dimethylbenzanthracene-induced tumor; pre-and postmenopausal model). In the series of imidazol-4-yl compounds, which represent a novelty in the field of azole inhibitors of steroidogenic P450 enzymes, strong inhibitors of P450 arom and/or P450 17 were found; 7-OCH3-2-(imidazol-4-ylmethylene)-1-tetralone (4) and 7-OCH3-2-(imidazol-4-ylmethyl)-tetralin (12) are among the most potent inhibitors of P450 arom in vitro known so far. Compound 4 is a selective inhibitor, whereas 12 shows in addition strong inhibition of P450 17. In contrast to 12, the 6-OCH3 derivative (compound 11) is a selective inhibitor of P450 17, being 50 times more potent than ketoconazole. Some imidazol-1-yl compounds show a marked inhibition of P450 TxA2: 2-(imidazol-1-ylmethyl)-1-tetralone (13) is a selective inhibitor of P450 TxA2, whereas 7-OCH3-2-(imidazol-1-ylmethyl)-tetralin (17) as well 2-(imidazol-1-ylmethyl)-tetralin (16) and 7-OCH3-2-imidazol-1-yl-3, 4-dihydronaphthalene (25) additionally show strong inhibition of P450 arom and P450 17. Regarding the other steroidogenic P450 enzymes as well as corticosterone formation, the compounds show only little inhibitory activity. Aldosterone formation, however, is inhibited at low concentrations. Nevertheless, 4 and 12 are more selective, i.e. inhibit aldosterone synthesis less than the well known inhibitor of P450 arom fadrozole. The compounds show activity in the aforementioned in vivo tests.

Effect of a diphenylethylenediamine platinum complex on steroidogenesis in rats

Although less cytotoxic, the new platinum complex [meso-1,2-bis(2,6-difluoro-4-hydroxyphenyl)-ethylenediamine]sulfatopl atinum (II) (2) is equipotent to cisplatin (1) in the oestrogen-dependent MXT mammary tumour of the mouse. As this may be due to oestrogen level-lowering properties, we compared the effect of 1 and 2 on steroidogenesis in the rat. A single dose of 1 and 2 (20 mumol/kg s.c.) decreased plasma testosterone level in male rats by 90% (1, day 3) and 80% (2, day 7). Luteinizing hormone level remained unchanged in intact and in ovariectomized rats. The activities of the following testicular enzymes were decreased (day 7): cholesterol side-chain cleavage enzyme (1: 33%; 2: 36%), 3 beta-hydroxysteroid dehydrogenase/delta 4,delta 5-isomerase (1: 31%; 2: 48%) and 17 alpha-hydroxylase/17,20-lyase (1: 21%; 2: 15%). Testicular microsomal cytochrome P450 content was also diminished (1: 60%; 2: 49%, day 7). Corticosterone level in plasma and biosynthesis in adrenal explants was not affected, indicating the selectivity of action at the gonadal level. In vitro, neither 1 nor 2 (2 and 20 microM) influenced binding of human chorionic gonadotropin to testis interstitial cells during an observation period up to 21 h. These results suggest that 1 and 2 act at the gonadal level by inhibiting the expression of the steroidogenic enzymes. They do not, however, inactivate the luteinizing hormone receptor.

TCDD alters pituitary-adrenal function. I: Adrenal responsiveness to exogenous ACTH

Plasma ACTH concentrations in 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD)-treated rats (50 micrograms/kg; single, oral dose) were 2.1-, 2.1-, 2.9-, 1.7-, 1.5-, 2.0- and 3.0-fold greater than control values, respectively, at days 1, 3, 5, 7, 10, and 14. At days 1 and 5 plasma corticosterone concentrations were increased 5.1- and 8.0-fold, respectively; whereas, at days 10 and 14 they were depressed to values of 50% and 39% of controls, respectively. Adrenal glands were excised from rats treated with TCDD and corticosterone production was assessed. Basal corticosterone concentrations produced by treated adrenals were depressed to 81%, 72%, and 71% of control values at days 5, 7, and 14, respectively. Corticosterone secretion by ACTH stimulated adrenals was equivalent to controls. These findings suggest that TCDD exposure decreases the bioactivity of the ACTH secreted by the anterior pituitary.

Some 1-, and 3-substituted 3-(4'-aminophenyl)pyrrolidine-2,5-diones as selective inhibitors of aromatase

1-Alkyl-3-(4'aminophenyl)pyrrolidine-2,5-diones (7,R = C3H7-C7H15) are potent inhibitors of aromatase in vitro, the 1-hexyl (Ki = 62nM) being about 100-fold more potent than aminoglutethimide (AG), and more selective in their ratio of aromatase:CSCC inhibitory potency. The 1-pentyl, 1-hexyl and 1-heptyl derivatives are more stable to liver microsomal metabolism in vitro than AG possibly due to inhibition of the liver cytochrome P450s. 1,3-Dialkyl-3(4'-aminophenyl)pyrrolidine-2,5-diones (9) have been synthesised by a novel method. Although the higher homologues (di-pentyl and di-hexyl) are more potent in vitro as inhibitors of aromatase than AG, they are less active than their 1-alkyl counterparts with the same alkyl substituent.

Evaluation of the racemate and the enantiomers of a new highly active and selective aromatase inhibitor of the aminoglutethimide type

Compound 1 [3-(4-aminophenyl)-3-cyclohexylpiperidine-2,6-dione] is a highly potent nonsteroidal aromatase inhibitor of the aminoglutethimide (AG)-type containing an asymmetric carbon atom. 1 and its enantiomers (+)-1 and (-)-1 inhibited human placental aromatase by 50% at 0.3, 0.15, and 4.6 microM, respectively (IC50 AG = 37 microM). A competitive type of inhibition was observed for 1 and (+)-1 (Ki 1 = 3.9 nM, Ki (+)-1 = 2.0 nM, Ki AG = 408 nM). Using solubilized high spin aromatase, 1 showed a type II difference spectrum indicating the interaction of the amino nitrogen with the central Fe(III)-ion of the cytochrome P450 heme component. 1 and (+)-1 inhibited cholesterol side chain cleavage enzyme (desmolase) by 50% at 67 and 82 microM, respectively (IC50 AG = 29 microM). In ACTH-stimulated rat adrenal tissue in vitro, 1 was less active in inhibiting aldosterone and corticosterone production compared to AG (IC50s, 1, 130 and 140 microM, AG, 80 and 50 microM, respectively). In vivo, 1 was superior to AG, too: it showed a stronger inhibition of the plasma estradiol concentration of pregnant mares' serum gonadotropin-primed SD rats, the activity residing mainly in the (+)-enantiomer [ovarian vein: (+)-1, 0.31 mg/kg: 81% inhibition, (-)-1, 0.31 mg/kg: 6%, AG, 1.25 mg/kg: 35%]. Furthermore 1 was much more active in inhibiting the testosterone-stimulated tumor growth of the ovariectomized 9,10-dimethyl-1,2-benzanthracene tumor-bearing SD rat (postmenopausal model). Up to a dose of 600 mg/kg of 1 no central nervous symptom depressive effects were observed in the motility test and the rotarod experiment, whereas AG exhibited ED50s of 62 and 164 mg/kg, respectively.

Cholesterol side-chain cleavage by mitochondria from the human placenta. Studies using hydroxycholesterols as substrates

The side-chain cleavage of cholesterol by cytochrome P-450scc in mitochondria from the human placenta was studied using hydroxycholesterol substrates and intermediates of the reaction. 25-Hydroxycholesterol inhibited 3 beta-hydroxy-5-pregnen-20-one (pregnenolone) production by placental mitochondria. It was converted to pregnenolone at a maximum velocity of only 19% of that for cholesterol. Addition of 20 alpha-hydroxycholesterol or 22R-hydroxycholesterol to placental mitochondria caused a lag in pregnenolone synthesis which was concentration dependent. Measurement of the concentration of 20 alpha,22R-dihydroxycholesterol during incubation of placental mitochondria with 22R-hydroxycholesterol revealed that the lag in pregnenolone production was caused by accumulation of 20 alpha,22R-dihydroxycholesterol. This intermediate of the reaction dissociated from the active site of cytochrome P-450scc. Only after its concentration had increased, presumably to a level where it could compete with 22R-hydroxycholesterol for binding to cytochrome P-450scc, was it converted to pregnenolone. These results indicate a lack of kinetic stabilization of the cytochrome P-450scc-20 alpha,22R-dihydroxycholesterol complex with dissociation occurring more rapidly than the final hydroxylation. Similar measurements of side-chain cleavage of 22R-hydroxycholesterol by mitochondria from the bovine adrenal cortex showed that kinetic stabilization of the cytochrome P-450scc-20 alpha,22R-dihydroxycholesterol complex does not occur in that tissue either. The relative hydroxylation rates of 20 alpha-hydroxycholesterol, 22R-hydroxycholesterol and 20 alpha,22R-dihydroxycholesterol indicate that all three hydroxylations catalysed by human cytochrome P-450scc occur at approximately the same rate.

Neurosteroids: oligodendrocyte mitochondria convert cholesterol to pregnenolone

Oligodendrocyte mitochondria from 21-day-old Sprague-Dawley male rats were incubated with 100 nM [3H]cholesterol. It yielded [3H]pregnenolone at a rate of 2.5 +/- 0.7 and 5-[3H]pregnene-3 beta, 20 alpha-diol at a rate of 2.5 +/- 1.1 pmol per mg of protein per hr. Cultures of glial cells from 19- to 21-day-old fetuses (a mixed population of astrocytes and oligodendrocytes) were incubated for 24 hr with [3H]mevalonolactone. [3H]Cholesterol, [3H]pregnenolone, and 5-[3H]pregnene-3 beta, 20 alpha-diol were characterized in cellular extracts. The formation of the 3H-labeled steroids was increased by dibutyryl cAMP (0.2 mM) added to the culture medium. The active cholesterol side-chain cleavage mechanism, recently suggested immunohistochemically and already observed in cultures of C6 glioma cells, reinforces the concept of "neurosteroids" applied to delta 5-3 beta-hydroxysteroids previously isolated from brain.

Discovery and development of a novel class of nonsteroidal aromatase inhibitors

Efforts to develop a novel class of nonsteroidal aromatase inhibitors began with the discovery that the infertility in male rats exposed to high levels of the agricultural fungicide, fenarimol (alpha-(2-chlorophenyl)-alpha-(4-chlorophenyl)-5-pyrimidine-methanol), was attributable to the inhibition of aromatase activity within the central nervous system during the critical neonatal period. Although fenarimol was not particularly potent in inhibiting rat ovarian microsome aromatase activity in vitro (50% inhibition (IC50) = 4.1 microM). Subsequent testing of a number of analogues led to the identification of LY56110 (alpha,alpha-bis(4-chlorophenyl)-5-methylpyrimidine) which exhibited an IC50 of 29 nM. LY56110 was orally active, blocking the testosterone-induced increase of uterine weight and ovarian estrogen biosynthesis in immature female rats. In rats with established DMBA-induced mammary carcinoma, complete tumor regression was observed in 80% of the animals. Development of LY56110 was, however, stopped because of its effects on hepatic microsomal enzymes and an unacceptably long half-life. Structural modifications resulted in the development of the indenopyrimidines. LY113174 (8-chloro-5-(4-chlorophenyl)-5H-indeno less than 1, 2D greater than pyrimidine) was highly effective in vitro (IC50 = 24 nM) and in vivo but was far less potent than LY56110 with respect to induction of hepatic microsomal enzymes. LY113174 exhibited an acceptable biological half-life and had no effect on cholesterol side-chain cleavage. The indenopyrimidines appear to be a novel class of nonsteroidal aromatase inhibitors which may prove useful in the treatment of estrogen-dependent diseases.

The stimulation by calcium and its inhibition by ADP of cholesterol side-chain cleavage activity in adrenal mitochondria

Cholesterol side-chain cleavage activity (cholesterol SCC) in a mitochondrial preparation is increased by calcium in a sigmoidal manner. A 5-10-fold increase is obtained and an effect may be seen at 20 microM CaCl2. ADP inhibits the stimulation by calcium with a shift of the sigmoid curve to the right and 10 microM ADP results in a 4-fold increase in the amount of CaCl2 required to obtain one-half the maximal stimulation value. The inhibition is specific for ADP and inhibition by ATP is due to the formation of ADP. The characteristics of the calcium-ADP modulation are such that a suitable ADP-inhibited level of cholesterol sidechain cleavage activity will be stimulated by a given increment of calcium to a greater extent than in the absence of the added ADP. Steroid 11 beta-hydroxylation is also stimulated in a sigmoidal manner by calcium and this stimulation is inhibited by ADP. The 11 beta-hydroxylation, however, is less sensitive to calcium and ADP so that changes in cholesterol SCC are obtained at concentration of calcium and ADP where minimal effects on 11 beta-hydroxylation are found. Calmodulin-like activity is present in the mitochondrial preparation. No evidence, however, for a role for calmodulin in the calcium-ADP effects could be obtained, but the possibility of its involvement cannot be excluded. The calcium-ADP modulations are of a magnitude and take place at sufficiently low concentrations to suggest a physiological role in the regulation of mitochondrial steroidogenesis.

An early steroidogenic defect in hormone-induced Leydig cell desensitization

To define the nature of the lesion of the early steroidogenic pathway (prior to pregnenolone formation) in gonadotropin-induced desensitization of rat testicular Leydig cells, we evaluated cholesterol side-chain cleavage activity in isolated mitochondria by measurement of pregnenolone synthesis and [14C]isocaproic acid formation from [26-14C]cholesterol. The enzyme activity was shown to be reduced after in vivo treatment with 10 micrograms hCG when compared to that of mitochondria from control animals only when measured in the presence of limiting NADPH concentrations (100 microM). Sonication of mitochondria from control and hCG-treated rats caused complete loss of cholesterol side-chain cleavage activity. When acetone-powdered adrenal cell mitochondria were employed as the source of the enzyme, the addition of sonicated Leydig cell mitochondria from control and hCG-treated animals caused the same differences as those observed with intact Leydig cell mitochondria in the presence of low concentration of NADPH. The Km value of the adrenal enzyme for NADPH incubated with Leydig cell mitochondria increased from 0.111 mM in control to 0.37 mM after hCG, with no changes in Vmax. Moreover, cholesterol side-chain cleavage activity of adrenal mitochondria assayed in the presence of 100 microM cholesterol was progressively inhibited by increasing amounts of acetone powder from Leydig cell mitochondria of control and hCG-treated rats, with ID50 of 500 and 280 micrograms protein, respectively. The inhibiting factor was not a lipid or steroid but a heat-labile protein, with an approximate Stokes radius of 4.8 nm and an isoelectric point of 5.05 +/- 0.23 SD (n = 8). The inhibitory effect was confined to the Leydig cell mitochondrial membrane, and was not related to changes in oxidative phosphorylation. NADPH was not directly oxidized or immobilized by the mitochondrial factor, and this inhibiting substance was not adsorbed on 2',5' ADP-Sepharose 4B. These results have demonstrated that a heat-labile inhibiting protein factor is present in mitochondria from normal Leydig cells and is markedly activated or increased by hCG treatment. This substance that competitively modulates cholesterol side-chain cleavage activity could contribute to the early steroidogenic lesion, and also serve as an endogenous modulator of steroid hormone biosynthesis.

Inhibition of human placental progesterone synthesis by danazol in vitro

In vitro, danazol showed a slight dose-dependent inhibition of the mitochondrial cholesterol side chain cleavage enzyme isolated from early gestational (8th to 12th week of gestation) placenta. In the presence of 100 microM danazol, the enzyme activity was 65% of controls. Danazol inhibits dose-dependently the mitochondrial 3 beta-hydroxysteroid dehydrogenase (I50 = 3.1 microM; Ki = 1 microM) (noncompetitive inhibition) and the cytoplasmic 20 alpha-hydroxysteroid dehydrogenase (I50 = 1.4 microM; Ki = 2.6 microM) (competitive inhibition). The inhibition of human placental progesterone synthesis by danazol in vitro is a further example for the direct interference of danazol with steroidogenesis.

Inhibition of human placental progesterone synthesis and aromatase activity by synthetic steroidogenic inhibitors in vitro

The inhibitory effect in vitro of four synthetic steroids on enzyme systems of placental progesterone synthesis at term was analyzed. Cholesterol side chain cleavage enzyme (CSCC) was not influenced by azastene, trilostane, and WIN 32,729. A 50% inhibition of CSCC was found by 10 microM cyanoketone. The 3 beta-hydroxysteroid dehydrogenase was dose-dependently inhibited by azastene (I50 = 1 microM, trilostane (I50 = 4 nM), cyanoketone (I50 = 3 nM), and WIN 32,729 (I50 = 5 nM). A competitive inhibition of the 20 alpha-hydroxysteroid dehydrogenase (20 alpha-HSDH) by azastene (I50 = 0.6 microM), trilostane (I50 = 4.1 microM), cyanoketone (I50 = 0.6 microM), and WIN 32,729 (I50 = 1.5 microM) was observed. No difference in the effect of steroids on the 20 alpha-HSDH of early gestational and term placenta was found. The four steroidogenic inhibitors did not affect the activity of placental aromatase in vitro. Our results allow a comparison of inhibitory potencies of four steroidogenic inhibitors on different steroidogenic enzymes in vitro.

Modulation of the kinetics of cholesterol side-chain cleavage by an activator and by an inhibitor isolated from the cytosol of the cortex of bovine adrenals

Two modulators of sterol side-chain cleavage activity have been detected in the cytosol from the cortex of bovine adrenals. One is an inhibitor of side-chain cleavage which increases the Km of a purified and reconstituted mitochondrial side-chain cleavage system for both cholesterol and cholesterol sulfate. It also lowers the Vmax of cleavage when cholesterol sulfate is the substrate. The other modulator is a low molecular weight protein which in the reconstituted system increases the Vmax of cleavage for both substrates but does not affect the Km of either. Side-chain cleavage activity was also found in bovine adrenocortical cytosol and this appears to differ from that present in mitochondria.

Characterization of human cholesterol side chain cleavage enzyme (EC 1.14.15x) of human term placental mitochondria

The cholesterol side chain cleavage enzyme (EC 1.14.15x) in mitochondria of a human term placenta was partially characterized. Enzyme activity was determined by separation of [26-14C]-cholesterol and [5-14C]-isocaproic acid formed by side chain cleavage. Since the amounts of unlabeled cholesterol were too large, a KM of cholesterol could not be determined. The apparent KM value of NADPH is 6.25 x 10(-4) M. A pH optimum was found at pH 9.5 (Tris buffer) and a temperature optimum at 40 C. The metal ions Sr2+ and Ba2+ showed no inhibition at 1 and 10 mM and a moderate inhibition at 100 mM. In low concentrations (1 mM), Mg2+ and Ca2+ slightly stimulated the enzyme whereas in higher concentrations (100 mM) an inhibitory effect was observed. A strong inhibition was achieved with 1 mM Zn2+, Cd2+, Cu2+ and by 10 and 100 mM Fe2+, Mn2+, Co2+ and Ni2+. During preincubation of the enzyme without radioactive substrate, a rapid loss in enzyme activity in relation to enzyme concentration was observed (initial activity = 100%) (preincubation time in hours): 0.5 h (97%), 1 h (55%) and 1.5 h (34%). A dose-dependent inhibition of the enzyme by the following proteins was achieved: bovine serum protein, human serum protein, human immunoglobulin G and ovalbumin. Furthermore, a dose-dependent inhibition was found with the membrane lipids lecithin and sphingosine.

Solid-phase reagents for the isolation and protection of carbonyl compounds

Resins which can serve as solid-phase Girard reagents have been prepared. These consist of porous cross-linked polystyrene-divinylbenzene matrices functionalized either with acid hydrazide groups, 1 or with O-alkylhydroxylamine groups, 2. Both resins react rapidly, under acid catalysis, with steroidal ketones and with glucose to form resin bound carbonyl derivatives. The carbonyl compound can be recovered by exchange with acetone under mildly acidic conditions. Resin 2 was used to extract steroidal ketones from an extract of bovine adrenals. By protecting the C-20 ketone group of allopregnanolone, resin 2 was used to prepare the counterpart of the steroid bearing tritium in the 3 alpha-position.

Partial characterization of placental 3 beta-hydroxysteroid dehydrogenase (EC 1.1.1.145), delta 4-5isomerase (EC 5.3.3.1) in human term placental mitochondria

A partial characterization of human term placental 3 beta-HSDH in mitochondria is reported. Apparent KM of pregnenolone: 70 nM. A dose-dependent stimulation of 3 beta-HSDH by NAD+ or NADP+ was observed in the range from 10(-6) to 10(-3) M (KM value of NAD+: 20 microM). At equimolar concentrations NAD+ is more than 10-fold as effective a cofactor of the 3 beta-HSDH than NADP+. pH optimum: 9.5 (glycine-NaOH buffer). Temperature optimum 40-45 degrees C. A rapid loss of 3 beta-HSDH activity was found after preincubation of the enzyme at 37 degrees C after 30 min; less than 50% of initial enzyme activity is present. No inhibition was obtained by Mg2+, Ca2+ Sr2+ and Ba2+ (1-100 mM). A strong inhibition was achieved with 1 mM Zn2+, Cd2+, Cu2+ and 10 mM and 100 mM Fe2+, Mn2+, Co2+ and Ni2+.

A new assay and solubilization procedure for steroid 17,20-lyase from rat testes

We report an assay for testicular 17,20-lyase which depends on the use of [21-14C]progesterone as a substrate. The method is made possible by a simplified procedure for the synthesis of [21-14C]progesterone. A chromatographic separation of the unreacted substrate and the 2-carbon by-product on mini silica gel columns permitted a quantitative assay of the lyase activity. The lyase complex from rat testes has been solubilized by treatment with Triton CF-54 detergent. The solubilized enzyme complex catalyzes the formation of androstenedione (4-androstene-3,17-dione) from progesterone without equilibrium with added 17-hydroxyprogesterone and the solubilized enzyme complex responds to the presence of cytosol activator. Both of these characteristics are similar to the properties of the intact microsomes. Thus, solubilization with this detergent preserves the special properties of the microsome bound enzyme complex.

New assays for the enzymatic conversion of cholesterol to pregnenolone

Cholesterol side chain cleavage is determined by means of separation of (26-C14)-cholesterol and its radioactively labeled side chain (1-C14)k-isocaproic acid. Alumina minicolumn assay (AMCA): adsorption of cholesterol from an aqueous phase by aluminium oxide, while isocaproic acid can percolate through the column. In modification of a previously described technique (1), cholesterol is quantitatively eluted by ethanol. Filter assay (FA): retention of cholesterol by a membrane filter (pore size less than or equal to 0.1 um) while isocaproic acid can pass the filter. Two-phase scintillation assay (TPSA): pH-dependent partition of isocaproic acid between an organic scintillation mixture and an aqueous phase. The TPSA can be applied for all enzymatic reaction in which the polarity of the radioactive residue which is split off depends on pH values or when the total charge of a polar molecule is changed to an apolar state by cleaving one non-radioactive group (e.g. steroid sulfates) and vice versa. The criteria or reliability of the test systems are described. Bovine adrenal mitochondria were incubated and the side chain cleavage of (26-C14)-cholesterol was studied by the new tests systems and compared to the conversion rates of (4-C14)-cholesterol to its metabolites are determined by thin layer chromatography. A good agreement of all tests was found.

Modification of enzymatic activity and difference spectra of cytochrome P-450 from various sources by cholesterol side chain cleavage inhibitors

Several groups of compounds were tested for their ability to inhibit cholesterol side chain cleavage and induce spectral change in cytochrome P-450 from bovine corpus luteum, bovine adrenal cortex, and human placental mitochondria. The substances tested include: steroids, pyridines, glutarimides, anilines and imidazoles. Good correlation was found between spectral change and enzymatic inhibition, especially in the corpus luteum which has only a single P-450-linked steroid hydroxylase. The cholesterol side chain cleavage enzyme systems from each of the three sources appear to have similar affinities for the inhibitors, which adds further support to the concept that these cytochrome P-450s are functionally identical.

Unreliability of tritiated cholesterol: studies with [1,2-3H]-cholesterol and [24,25-3H]cholesterol in humans

Over the past 18 months different lots of [1,2-3H]cholesterol and [24,25-3H]cholesterol were found to be radiochemically acceptable by conventional chemical and other in vitro tests, yet, when co-administered with [4-14C]cholesterol to human subjects, an abrupt fall in the 3H/14C specific activity ratio in plasma cholesterol was discovered in every case. We have concluded that all batches of [3H]cholesterol should be regarded as radiochemically unreliable unless they are shown to behave identically in all respects to [4-14C]cholesterol in an appropriate in vivo assay system.

Detection in bovine adrenal cortex of a lipoidal substance that yields pregnenolone upon treatment with alkali

Bovine adrenal cortical tissue contains a lipoidal derivative of pregnenolone (3beta-hydroxy-pregn-5-en-20-one) from which the free steroid can be liberated by treatment with alkali. Evidence for the presence of such an entity comes from examination of a nonpolar extract of tissue from which pregnenolone and its sulfate had been removed by chromatography. Treatment of the nonpolar fraction with alkali followed by exhaustive chromatographic analysis led to the detection of pregnenolone. The steroid was identified by both gas chromatography/mass spectrometry and double isotope procedures. Quantitative analysis indicated that the three forms of pregnenolone are present in bovine adrenal cortical tissue in the following amounts (mug/kg): lipoidal derivative, 290; free steroid, 435; and sulfate, 65. Because the only known metabolic function of pregnenolone is to serve as a precursor of the steroid hormones, these findings have far-reaching implications for steroid hormone biochemistry.

Implication of ligand modified spectra of cytochrome P-450 associated with pregnenolone synthesis in mitochondria from corpus luteum

The implications of ligand modified spectra of cytochrome P-450 in mitochondria from corpus luteum are considered. Mitochondria from bovine corpus luteum contain a single cytochrome P-450 which oxidizes cholesterol to pregnenolone and isocaproaldehyde. These mitochondria and the cytochrome P-450 purified from these mitochondria yield Type I spectral changes with substrates, reverse Type I spectral changes with certain steroid substrates, steroid products and unrelated steroid ligands. Nitrogenous ligands yield Type II spectral changes. Mitochondrial and purified cytochrome P-450 preparations are equivalent in this study. The inhibitory effects on the cholesterol monooxygenase are directly related to the spectral changes induced by Type II ligands. Lastly, it is suggested that a similar relationship exists with reverse Type I ligands.