New assays for the enzymatic conversion of cholesterol to pregnenolone

Cytochrome P-450 levels of immature rat ovaries during early follicular development: quantification, cellular and subcellular distribution, enzymatic activity and response to FSH in vivo and in vitro

Absolute values of cytochrome P-450 (cyt. P-450) content were determined by dual beam spectrophotometry in mitochondrial and microsomal fractions of granulosa cells and stroma (theca and interstitial cells) obtained from ovaries of immature rats treated with diethylstilbestrol (DES) or with DES and FSH. Cholesterol side-chain cleavage activity and aromatase activity were also measured in relevant cell fractions. The cyt. P-450 content in the granulosa cell mitochondria was significantly increased in FSH-treated animals (cyt.P-450 in nmols/mg protein, mean +/- SE: DES-treated 0.027 +/- 0.00213, N = 9; DES/FSH-treated 0.0668 +/- 0.0120, N = 13, P = 0.014). The increased cyt. P-450 content was associated with an increase in cholesterol side-chain cleavage activity confirming the functional relevance of the spectrophotometric measurements. The increase in cyt. P-450 content in stroma after FSH treatment was not statistically significant but there was a significant increase in cholesterol side-chain cleavage activity. The cholesterol side-chain cleavage activity of intact granulosa cells from secondary follicles of DES-treated rats was significantly stimulated by in vitro exposure to FSH during 2 hr assay incubations. A significant cyt. P-450 content was detected in the microsomal fraction of granulosa cells from DES-treated rats which was not associated with aromatase activity. Granulosa cell microsomal cyt. P-450 content was not significantly altered by in vivo FSH treatment despite a dramatic increase in aromatase activity of such microsomal preparations.

Endocrine properties of the testosterone 5 alpha-reductase inhibitor turosteride (FCE 26073)

Turosteride was tested in a series of studies for its effect on 5 alpha-reductase and for its possible influence on other steroidogenic enzymes and on steroid receptors. The compound was found to inhibit human and rat prostatic 5 alpha-reductases with IC50 values of 55 and 53 nM, respectively, whereas it caused a less marked inhibition of the dog enzyme (IC50 2.2 microM). Turosteride showed no relevant effect on rat adrenal C20,22-desmolase (IC50 254 microM) and human placental aromatase (IC50 > 100 microM), and only at relatively high concentrations it caused inhibition of human placental 5-ene-3 beta-hydroxysteroid dehydrogenase-isomerase (3 beta-HSD-I) (IC50 2.5 microM). Turosteride was found to be a selective 5 alpha-reductase inhibitor showing no noteworthy binding to receptors for androgens (relative binding affinity, RBA, 0.004%), estrogens (< or = 0.005%), progesterone (< 0.005%), glucocorticoids (< 0.01%) and mineralocorticoids (< 0.03%). Its biochemical profile was similar to that of finasteride, whereas 4-MA (17 beta-N,N-diethyl-carbamoyl-4-methyl-4-aza-5 alpha-androstan-3-one) was confirmed to be a non-selective 5 alpha-reductase inhibitor, showing a degree of binding affinity to the androgen receptor (RBA 0.1%) and a marked inhibition of 3 beta-HSD-I (IC50 32 nM). When given orally in immature castrated rats together with subcutaneous testosterone propionate (TP) for 7 consecutive days, turosteride reduced the ventral prostate and seminal vesicle growth promoting effect of TP, with IC50 values of approximately 5 and 6.7 mg/kg/day, whereas levator ani weight was unchanged. In comparison, 4-MA was approx. 3-fold less potent than turosteride in reducing the prostate and seminal vesicle weights and caused a marked reduction of levator ani weight, thus showing its unselectivity.

Steroidogenic enzyme activity in the hypogonadal (hpg) mouse testis and effect of treatment with luteinizing hormone

The hypogonadal (hpg) mouse, which lacks circulating gonadotrophins during development, has been used (a) to determine whether initial expression of steroidogenic enzyme activity is dependent upon gonadotrophins and (b) to examine the responsiveness of these enzymes to luteinizing hormone (LH) stimulation. Activities of 17 alpha-hydroxylase, 17-ketosteroid reductase and 5 alpha-reductase were very low but detectable in the hpg testis while cholesterol side-chain cleavage (CSCC) activity was undetectable. In contrast, 3 beta-hydroxysteroid dehydrogenase (3 beta HSD) activity was high (11% of normal testis). Treatment with LH increased CSCC and 17 alpha-hydroxylase activity more than 11-fold within 24 h. 5 alpha-Reductase activity was increased 3-fold after 3 days treatment while 17-ketosteroid reductase and 3 beta HSD activities did not respond until after 10 days of treatment. The overall increases in 5 alpha-reductase (4-fold) and 3 beta HSD (6-fold) activities were low while changes in 17-ketosteroid reductase (20-fold) and, particularly, CSCC (greater than 130-fold) and 17 alpha-hydroxylase (153-fold) were more marked. Results show (1) that expression of 3 beta HSD activity may be independent of gonadotrophins, (2) that activity of 17 alpha-hydroxylase, 17-ketosteroid reductase and 5 alpha-reductase is expressed, though at low levels, in the absence of gonadotrophins and (3) that prior exposure to gonadotrophins is not required for a rapid response to LH stimulation, particularly with respect to the cytochrome P-450 enzymes.

4-Aminoandrostenedione derivatives: a novel class of irreversible aromatase inhibitors. Comparison with FCE 24304 and 4-hydroxyandrostenedione

FCE 24928 (4-aminoandrosta-1,4,6-triene-3,17-dione) was selected among a series of 4-aminoandrostenedione derivatives as a novel irreversible aromatase inhibitor. Its in vitro and in vivo properties have been studied and compared to FCE 24304 (6-methylenandrosta-1,4-diene-3,17-dione) and 4-OHA (4-hydroxyandrostenedione). FCE 24928 caused time-dependent inhibition of human placental aromatase with a t1/2 of 4 min and Ki of 59 nM. Enzyme inactivation by FCE 24928 was faster than by FCE 24304 (t1/2 13.9 min). In PMSG-treated rats, microsomal ovarian aromatase activity was reduced 24 h after FCE 24928 dosing by both the s.c. (ED50 1.2 mg/kg) and the oral (ED50 14.1 mg/kg) routes. The compound was more potent than FCE 24304 and 4-OHA (ED50 1.8 and 3.1 mg/kg s.c.). FCE 24928 did not show any interference with 5 alpha-reductase and desmolase activity nor any significant binding affinity for androgen and estrogen receptors. Slight binding affinity for androgen receptor was observed with FCE 24304 and 4-OHA (0.21 and 0.25% of DHT). In immature, castrated rats, FCE 24928 did not show any intrinsic androgenic activity, up to 100 mg/kg/day s.c., in contrast to a slight androgenic activity observed with FCE 24304 at 10 mg/kg s.c.

Luteolytic effect of the antiprogestin and antiglucocorticoid agent RU486 in rats

Ovarian cells of pregnant rats were cultured with synthetic progestins (R5020, R2323), dexamethasone and RU486. Progesterone and 20 alpha-hydroxy-pregn-4-en-3-one (20 alpha-dihydroprogesterone) in the medium were measured by specific radioimmunoassay. Both R5020 and R2323 increased concentrations of these intrinsic progestins. RU486 decreased concentrations of progesterone, however, the addition of R5020 or R2323 counteracted this action. Immature hypophysectomized rats treated with pregnant mare serum gonadotropin (PMS) and human chorionic gonadotropin (hCG) were administered with RU486; the serum levels of progesterone and 20 alpha-dihydroprogesterone tended to decrease. R5020 and R2323 inhibited the effect of 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD), whereas RU486 did not. Inhibition of the cholesterol side chain cleavage enzyme (CSCC) by RU486 was more marked than that by R5020 or R2323. These results show that RU486 decreases progesterone synthesis in cultured ovarian cells. A part of the mechanism may involve an inhibition of CSCC.

Regulation of human placental progesterone synthesis in vitro by naturally occurring steroids

A regulatory model of human placental progesterone synthesis is based on studies with isolated placental enzymes. Steroids causing a dose-dependent inhibition are listed in the standing order of their inhibitory potency (I50 (microM)/Ki value (microM)/type of inhibition: c = competitive and nc = non competitive). Cholesterol side chain cleavage enzyme (mitochondria): Mainly regulated by hydroxylated cholesterol derivates. No inhibition was observed by cholesterylesters and by other naturally occurring steroids tested. 5-ene-3 beta-hydroxysteroid dehydrogenase-isomerase (mitochondria): 6 beta-hydroxyprogesterone (nc), dehydroepiandrosterone (0.32/0.82/c), 20 alpha-dihydroprogesterone (0.38/-/nc), progesterone (0.46/-), estrone (0.56/0.1/c), estradiol (0.1/0.8/c), 17 alpha-hydroxyprogesterone (2.1/-/nc), 17 alpha-hydroxypregnenolone (0.4/-/c), dehydroepiandrosterone sulfate (2.5/-/c), cortisone (5.0/-), cortisol (100/-). 20 alpha-hydroxysteroid dehydrogenase (cytoplasmic): estrone (0.26/0.7/c), estradiol (0.28/0.9/c), pregnenolone (4.4/9.2/c), 5 alpha-pregnan-3 beta-ol-20-one (4.6/-/nc), estriol (5.1/11.5/c); dehydroepiandrosterone (7.2/14.0/c), 5 alpha-dihydrotestosterone (26.0/-/nc), progesterone (33.0/48.0/c), dehydroepiandrosterone sulfate (50.0/23.0/nc), and testosterone (59.0/63.0/c). An autoregulatory mechanism of placental progesterone synthesis is postulated which is in good agreement with data published by others proving that placental progesterone synthesis is independent of the endocrine organs of the mother and the fetus.

Cholesterol side-chain cleavage activity in human placenta and bovine adrenals: an one-step method for separation of pregnenolone formed in vitro

Cholesterol side-chain cleavage (CSCC) activity towards exogenous cholesterol was quantified by an one-step reversed-phase minicolumn method for the separation of pregnenolone formed in the reaction. The assay is rapid and reproducible. The method is linear for up to 2 mg of placental mitochondrial protein and up to 1 mg of bovine adrenal mitochondrial protein in the incubata over 30 min and 5 min reaction times, respectively. Average Km and Vmax values were 14.1 microM and 3.4 pmol/min/mg for the placental preparation and 1.5 microM and 20.7 pmol/min/mg for the bovine adrenal mitochondrial preparation. In human placenta, the mitochondrial fraction contained most of the CSCC activity. Inhibition studies showed that aminoglutethimide (500 microM) inhibited both placental and bovine adrenal activities at the same level (about 80-90% inhibition) but androstenedione (500 microM), metyrapone (500 microM), benzo(a)pyrene (800 microM) and Emulgen 911 (0.05%) were more effective in human placental preparations. Neither of the activities were inhibited to any great extent by alpha-naphthoflavone (500 microM), SKF 525A (500 microM) or 7-ethoxycoumarin (1 mM).

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.

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.

New aromatase assay and its application for inhibitory studies of aminoglutethimide on microsomes of human term placenta

A new, simple, fast and highly practicable aromatase assay and its application is described. This test depends on the release of tritiated water after aromatization of [1 beta,2 beta-3H]- or [1,2-3H]-androstendione or testosterone. In tests with [1 beta,2 beta-3H]-androstendione, nonradioactivity labeled estrogens are formed whereas in tests using [1,2-3H]-androstendione as substrate both estrogens and water contain tritium atoms. Tritiated water is determined by a two-phase scintillation technique depending on the limited emulsifying capacity of dioxane-based scintillation solution for water. A small volume (0.1 ml) of water is completely emulsified by the scintillation solution (10 ml) and all tritium-labeled substances can be measured. After addition of 2 ml distilled water 95% of the tritiated water is partitioned in the aqueous phase and only (1 beta,2 beta-3H]-androstendione or [1,2-3H]-androstendione and tritium labeled estrogens can be counted. The amount of tritiated water in each test can be calculated by impulse differences before and after addition of 2 ml distilled water. This aromatase assay using [1,2-3H]-androstendione was compared to a method described by Thompson and Siiteri [1] depending on extraction of steroids prior to scintillation counting. A good agreement of both methods was found. In tests with human term placenta aromatase in microsomes the apparent Km of androstendione was determined to be 8.9 nM. Aminoglutethimide showed a 50% inhibition of the placental microsomal aromatase at 0.6 microM.

Endogenous inhibition of the 20 alpha-hydroxysteroid dehydrogenase (EC 1.1.1.149) in the human term placenta in vitro

Human placental 20 alpha-hydroxysteroid dehydrogenase (20 alpha-HSDH) interconverts progesterone and 20 alpha-dihydroprogesterone (20 alpha-DHP). In this study, an endogenous inhibitor of the cytoplasmic 20 alpha-HSDH isolated from human term placenta is demonstrated. Characterization of the endogenous inhibitor was carried out by adding heat-denatured fractions of the 20 alpha-HSDH enzyme stock solution to the incubations. The aqueous phase of the 20 alpha-HSDH (after diethylether extraction) using 8-fold concentration of the enzyme inhibited the 20 alpha-HSDH activity by 50%. After ultrafiltration of the aqueous phase, this inhibitory effect (50%) was found in the aqueous fraction with a molecular weight above 12,800. No inhibition of the 20 alpha-HSDH was shown using the ether phase or the aqueous ultrafiltrate with a molecular weight below 12,800. The 20 alpha-HSDH was stimulated by human and bovine serum albumins up to 290% and 420% respectively. Bovine serum albumin showed a higher stimulatory effect on the oxidative (420%) than on the reductive (190%) pathway of the 20 alpha-HSDH. Ovalbumin and immunoglobulin G had no effect. The endogenous inhibitor of the cytoplasmic 20 alpha-HSDH isolated from the human term placenta is heat stable (100 degrees C), water soluble, not soluble in diethylether and has a molecular weight above 12,800. The stimulatory effect of serum albumins in 20 alpha-HSDH may be caused by binding and inactivation of the endogenous inhibitor.

Partial characterization of the cytoplasmic 20 alpha-hydroxysteroid dehydrogenase (EC 1.1.1.149) of the human placenta at term

The 20 alpha-hydroxysteroid dehydrogenase (20 alpha-HSDH) is a key enzyme in human fetal and maternal progesterone metabolism. In this paper, the cytoplasmic 20 alpha-HSDH of human term placenta is partially characterized in vitro. A 14-fold concentration of the 20 alpha-HSDH was prepared by ultracentrifugation and ammonium sulfate precipitation. The apparent Km values for the substrates progesterone (Km: 4.8 x 10(-5) M) and 20 alpha-DHP (Km: 6.2 x 10(-5) M) and for the cofactors NADPH (Km: 1.9 x 10(-4)) and NADH (Km: 2.6 x 10(-4)) were determined. The temperature optimum for the oxidation of 20 alpha-DHP is 40--50 degrees C. The pH optimum for the reduction of progesterone was found to be pH 6.2 and for the oxidation of 20 alpha-DHP pH 6.5. The addition of glycerol (3 M) to the incubation medium inhibited the conversion rate of 20 alpha-HSDH by 70%. No influence of EDTA could be found. Various bivalent metal ions (1--100 mM) showed a dose-dependent inhibition of 20 alpha-HSDH; a complete inhibition was achieved at 100 mM: Cu2+, Zn2+, Cd2+, Fe2+ and Ni2+.