Chemicals of environmental concern as inhibitors of human placental 3ß-hydroxysteroid dehydrogenase 1 and aromatase: Screening and docking analysis.

Many environmental pollutants act as endocrine-disrupting compounds by inhibiting human placental 3ß-hydroxysteroid dehydrogenase/Δ5-4 isomerase type 1 (HSD3B1) and aromatase (CYP19A1) activities. In this study, we screened 13 chemicals of environmental concern for their ability to inhibit human HSD3B1 and CYP19A1 by measuring the conversion of pregnenolone to progesterone for HSD3B1 activity and the conversion of testosterone to 17ß-estradiol for CYP19A1 activity in human JEG-3 choriocarcinoma cell microsomes. HSD3B1 had an apparent Km of 0.323 µM and an apparent Vmax of 0.111 nmol/mg/min and CYP19A1 had an apparent Km of 56 nM and an apparent Vmax of 0.177 nmol/mg protein/min. 17ß-Estradiol, bisphenol A, and bisphenol AF competitively inhibited HSD3B1 with Ki values of 0.8, 284.1, and 141.2 µM, respectively, while diethylstilbestrol had a mixed inhibition on human HSD3B1 with the Ki of 8.0 µM. Ketoconazole, bisphenol A, and bisphenol AF noncompetitively inhibited CYP19A1 with Ki values of 10.3, 54.4, and 45.7 µM, respectively, while diethylstilbestrol and zearalenone competitively suppressed CYP19A1 with Ki values of 63.0 and 16.6 µM, respectively. Docking analysis showed that 17ß-estradiol, diethylstilbestrol, bisphenol A, and bisphenol AF bound the steroid binding pocket facing the catalytic residues Y155 and K159 of HSD3B1, and that ketoconazole, bisphenol A, and bisphenol AF bound heme binding pocket while diethylstilbestrol and zearalenone bound the steroid binding site of CYP19A1. In conclusion, 17ß-estradiol, diethylstilbestrol, bisphenol A, and bisphenol AF are human HSD3B1 inhibitors, and ketoconazole, zearalenone, diethylstilbestrol, bisphenol A, and bisphenol AF are human CYP19A1 inhibitors.

Trilostane, a 3ß-hydroxysteroid dehydrogenase inhibitor, suppresses growth of hepatocellular carcinoma and enhances anti-cancer effects of sorafenib.

Background Human 3ß-hydroxysteroid dehydrogenase type 1 (HSD3B1) is an enzyme associated with steroidogenesis, however its' role in hepatocellular carcinoma (HCC) biology is unknown. Trilostane is an inhibitor of HSD3B1 and has been tested as a treatment for patients with breast cancer but has not been studied in patients with HCC. Methods and Results The expression of HSD3B1 in HCC tumors in 57 patients were examined. A total of 44 out of 57 tumors (77.2%) showed increased HSD3B1 expression. The increased HSD3B1 in tumors was significantly associated with advanced HCC. In vitro, the knockdown of HSD3B1 expression in Mahlavu HCC cells by a short hairpin RNA (shRNA) led to significant decreases in colony formation and cell migration. The suppression of clonogenicity in the HSD3B1-knockdown HCC cells was reversed by testosterone and 17ß-estradiol. Trilostane-mediated inhibition of HSD3B1 in different HCC cells also caused significant inhibition of clonogenicity and cell migration. In subcutaneous HCC Mahlavu xenografts, trilostane (30 or 60 mg/kg, intraperitoneal injection) significantly inhibited tumor growth in a dose-dependent manner. Furthermore, the combination of trilostane and sorafenib significantly enhanced the inhibition of clonogenicity and xenograft growth, surpassing the effects of each drug used alone, with no documented additional toxicity to animals. HSD3B1 blockade was found to suppress the phosphorylation of extracellular signal-regulated kinase (ERK). The decreased ERK phosphorylation was reversed by testosterone or 17b-estradiol. Conclusions Trilostane significantly inhibited the growth of HCC by inhibiting HSD3B1 function and augmenting the efficacy of sorafenib.

Acephate interferes with androgen synthesis in rat immature Leydig cells.

Acephate is an organophosphate pesticide. It is widely used. However, whether it inhibits androgen synthesis and metabolism remains unclear. In the current study, we investigated the effect of acephate on the inhibition of androgen synthetic and metabolic pathways in rat immature Leydig cells after 3-h culture. Acephate inhibited basal androgen output in a dose-dependent manner with the inhibition starting at 0.5 µM. It significantly inhibited luteinizing hormone and 8-Br-cAMP stimulated androgen output at 50 µM. It significantly inhibited progesterone-mediated androgen output at 50 µM. Further study demonstrated that acephate down-regulated the expression of Hsd3b1 and its protein at ≥ 0.5 µM, Lhcgr at 5 µM and Star at 50 µM. Acephate directly blocked rat testicular HSD3B1 activity at 50 µM. Acephate did not affect other androgen synthetic and metabolic enzyme activities as well as ROS production, proliferation, and apoptosis of immature Leydig cells. In conclusion, acephate targets LHCGR, STAR, and HSD3B1, thus blocking androgen synthesis in rat immature Leydig cells and HSD3B1 is being the most sensitive target of acephate.

Human placental 3ß-hydroxysteroid dehydrogenase/steroid Δ5,4-isomerase 1: Identity, regulation and environmental inhibitors.

Human placental 3ß-hydroxysteroid dehydrogenase/steroid Δ5, 4-isomerase 1 (HSD3B1), a high-affinity type I enzyme, uses pregnenolone to make progesterone, which is critical for maintenance of pregnancy. HSD3B1 is located in the mitochondrion and the smooth endoplasmic reticulum of placental cells and is encoded by HSD3B1 gene. HSD3B1 contains GATA and TEF-5 regulatory elements. Many endocrine disruptors, including phthalates, methoxychlor and its metabolite, organotins, and gossypol directly inhibit placental HSD3B1 thus blocking progesterone production. In this review, we discuss the placental HSD3B1, its gene regulation, biochemistry, subcellular location, and inhibitors from the environment.

Inhibition of 3ß-Hydroxysteroid Dehydrogenase Type 1 Suppresses Interleukin-6 in Breast Cancer.

BACKGROUND: Recently, we demonstrated that the expression of 3ß-hydroxysteroid dehydrogenase type 1 (HSD3B1) in breast cancer is associated with shorter recurrence-free survival, and genetic or pharmacologic inhibition of HSD3B1 reduced colony formation and xenograft growth. However, the mechanisms are unclear. METHODS: Triple-negative MDA-MB-231 and BT-20 breast cancer cells underwent HSD3B1 silencing. Microarray and bioinformatic analysis were performed. The interleukin-6 (IL-6) expression and secretion were evaluated using real-time quantitative polymerase chain reaction and enzyme-linked immunosorbent assay. Clonogenic ability and cell viability were determined in the absence or presence of recombinant IL-6. RESULTS: Functional and pathway enrichment analyses showed that HSD3B1 silencing modulates the expression of several growth factors and cytokines. Cells transfected with HSD3B1-targeting small interfering RNA or treated with an HSD3B1 inhibitor (trilostane) had decreased IL-6 expression and secretion. HSD3B1 inhibition reduced colony formation, which was partially rescued by IL-6 supplementation. The HSD3B1 knockdown enhanced paclitaxel sensitivity, and IL-6 treatment partially reversed the augmented cytotoxicity. CONCLUSIONS: Our findings suggest that the therapeutic potential of targeting HSD3B1 is in part mediated by IL-6 suppression.

Endocrine disruptors of inhibiting testicular 3ß-hydroxysteroid dehydrogenase.

Testicular 3ß-hydroxysteroid dehydrogenase (HSD3B) is a steroidogenic enzyme, catalyzing the conversion of 3ß-hydroxysteroids into 3-keto-steroids. Two distinct isoforms in the human are cloned, HSD3B1 and HSD3B2, and HSD3B2 is located in the testis. HSD3B2 is a two-substrate enzyme, which binds to cofactor NAD+ and a 3ß-steroid. Many endocrine disruptors, including industrial compounds (phthalates, bisphenols, and perfluoroalkyl substances), insecticides and biocides (organochlorine insecticides and organotins), food additives (butylated hydroxyanisole, resveratrol, gossypol, flavones, and isoflavones), and drugs (etomidate, troglitazone, medroxyprogesterone acetate, and ketoconazole) inhibit testicular HSD3B, possibly interfering with androgen synthesis. In this review, we discuss the distinct testicular isoform of HSD3B, its gene, chemistry, subcellular location, and the endocrine disruptors that directly inhibit testicular HSD3B and their inhibitory modes.

Expression of 3ß-Hydroxysteroid Dehydrogenase Type 1 in Breast Cancer is Associated with Poor Prognosis Independent of Estrogen Receptor Status.

BACKGROUND: Human 3ß-hydroxysteroid dehydrogenase type 1 (HSD3B1) plays a vital role in steroidogenesis in breast tumors and may therefore be a suitable target for treatment of breast cancer. This study investigated the role of HSD3B1 in the pathogenesis of breast cancer in clinical and experimental settings. METHODS: Expression of HSD3B1 in primary tumors of 258 breast cancer patients was evaluated by immunohistochemistry. Screening of breast cancer cell lines indicated that triple-negative MDA-MB-231 cells expressed HSD3B1. The effects from genetic and pharmacologic inhibition of HSD3B1 were assessed in vitro and in vivo. RESULTS: The findings showed that 44% of the 258 breast cancers were HSD3B1-positive. The HSD3B1-positivity was associated with advanced-stage disease (p = 0.009) and reduced recurrence-free survival (p = 0.048) but not with tumor subtype or estrogen receptor status. Silencing of HSD3B1 or treatment with an HSD3B1 inhibitor (trilostane) reduced colony formation in breast cancer cells. Knockdown of HSD3B1 inhibited cell proliferation and migration. Analysis of a murine xenograft tumor model indicated that trilostane significantly slowed tumor growth. CONCLUSIONS: Expression of HSD3B1 in breast cancer is negatively associated with prognosis. The study found HSD3B1 to be a potential therapeutic target for breast cancer independent of estrogen receptor status.

The Effects of Fungicides on Human 3ß-Hydroxysteroid Dehydrogenase 1 and Aromatase in Human Placental Cell Line JEG-3.

Placenta secretes a large amount of progesterone and estradiol, which are critical for maintaining pregnancy. In human placenta, 3ß-hydroxysteroid dehydrogenase 1 (HSD3B1) catalyzes pregnenolone to form progesterone, and aromatase (CYP19A1) catalyzes testosterone into estradiol. Fungicides display antifungal activities and are widely used to prevent fungal infections in agricultural plants. These chemicals include azoles, such as tebuconazole (TEB), triadimefon (TRI), and vinclozolin (VCZ) or organotins, such as tributyltin (TBT) and tetrabutyltin (TTBT). Fungicides may disrupt the activities of these 2 enzymes. In the present study, we investigated the effects of these fungicides on steroid production in a human placental cell line JEG-3 and on HSD3B1 and CYP19A1 activities. Of all fungicides tested at 100 µmol/L, only TBT inhibited pregnenolone-mediated progesterone production in JEG-3 cells by over 50%. Except TTBT, all other 4 fungicides inhibited testosterone-mediated estradiol production by over 50%. TBT was a moderate HSD3B1 inhibitor with a half maximal inhibitory concentration (IC50) of 45.60 ± 0.12 µmol/L. When pregnenolone was used to determine the mode of inhibition, TBT was a competitive inhibitor of HSD3B1. The IC50 values of TEB, TRI, VCZ, and TBT for CYP19A1 were 56.84 ± 0.13, 58.73 ± 0.14, 57.42 ± 0.171, and 4.58 ± 0.048 µmol/L, respectively. TEB, TRI, and VCZ were noncompetitive inhibitors of CYP19A1, while TBT was a competitive inhibitor of this enzyme. Therefore, they are endocrine disruptors.

Suppressed Sex Hormone Biosynthesis by Alkylresorcinols: A Possible Link to Chemoprevention.

Alkylresorcinols (ARs, 5-n-alkylresorcinols) are amphiphilic phenolic lipids in whole grain rye and wheat, with a long odd-numbered carbon chain. A preventive effect of whole grain diet on sex hormone-dependent cancers has been recognized, but the active component(s) or mechanisms are not known. We have investigated the effects of the ARs C15:0, C19:0, and C21:0, individually and in combination, on steroid hormone production by using the human adrenocortical cell line H295R. Decreased synthesis of dehydroepiandrosterone (DHEA), testosterone, and estradiol was demonstrated at low concentrations of C15:0 and C19:0. There were no indications of additive effects on steroid secretion from the combined treatment with equimolar concentrations of the three ARs. Gene expressions of CYP21A2, HSD3B2, and CYP19A1 were downregulated and CYP11A1 was upregulated by the ARs. The results on gene expression could not explain the effects on steroidogenesis, which may be due to direct effects on enzyme activities, such as inhibition of CYP17A1. Our results demonstrate suppressed synthesis of testosterone and estradiol by ARs suggesting a novel mechanism for ARs in the chemoprevention of prostate and breast cancer.

Structure-activity relationships of phthalates in inhibition of human placental 3ß-hydroxysteroid dehydrogenase 1 and aromatase.

Phthalates are associated with preterm delivery. However, the mechanism is unclear. Progesterone formed by 3ß-hydroxysteroid dehydrogenase 1 (HSD3B1) and estradiol by aromatase (CYP19A1) in placenta are critical for maintaining pregnancy. In this study, we compared structure-activity relationships (SAR) of 14 phthalates varied in carbon atoms in alcohol moiety to inhibit human HSD3B1 in COS1 and CYP19A1 in JEG-3 cells. There were responses in that only diphthalates with 4-7 carbon atoms were competitive HSD3B1 inhibitors and diphthalates with 6 carbon atoms were CYP19A1 inhibitors. IC50s of dipentyl (DPP), bis(2-butoxyethyl) (BBOP), dicyclohexyl (DCHP), dibutyl (DBP), and diheptyl phthalate (DHP) were 50.12, 32.41, 31.42, 9.69, and 4.87µM for HSD3B1, respectively. DCHP and BBOP inhibited CYP19A1, with IC50s of 64.70 and 56.47µM. DPP, BBOP, DCHP, DBP, and DHP inhibited progesterone production in JEG-3 cells. In conclusion, our results indicate that there is clear SAR for phthalates in inhibition of HSD3B1 and CYP19A1.

Effects of Methoxychlor and Its Metabolite Hydroxychlor on Human Placental 3ß-Hydroxysteroid Dehydrogenase 1 and Aromatase in JEG-3 Cells.

Progesterone and estradiol produced by the human placenta are critical for maintenance of pregnancy and fetal development. In the human placenta, 3ß-hydroxysteroid dehydrogenase 1 (HSD3B1) is responsible for the formation of progesterone from pregnenolone and aromatase (CYP19A1) for the production of estradiol from androgen. Insecticide methoxychlor (MXC) and its metabolite hydroxychlor (HPTE) may disrupt the activities of these 2 enzymes. In this study, we investigated the effects of MXC and HPTE on steroid production in human placental JEG-3 cells and on HSD3B1 and CYP19A1 activities. MXC and HPTE inhibited progesterone and estradiol production in JEG-3 cells. MXC and HPTE were potent HSD3B1 inhibitors with the half maximal inhibitory concentration (IC50) values of 2.339 ± 0.096 and 1.918 ± 0.078 µmol/l, respectively. MXC had no inhibition on CYP19A1 at 100 µmol/l, while HPTE was a weak inhibitor with IC50 of 97.16 ± 0.10 µmol/l. When pregnenolone was used to determine the inhibitory mode, MXC and HPTE were found to be competitive inhibitors of HSD3B1. When cofactor NAD+ was used, MXC and HPTE were the noncompetitive inhibitors of HSD3B1. When testosterone was used, HPTE was a mixed inhibitor of CYP19A1. In conclusion, MXC and HPTE are potent inhibitors of human HSD3B1, and HPTE is a weak CYP19A1 inhibitor.

Gossypol enantiomers potently inhibit human placental 3ß-hydroxysteroid dehydrogenase 1 and aromatase activities.

Gossypol is a chemical isolated from cotton seeds. It exists as (+) or (-) enantiomer and has been tested for anticancer, abortion-inducing, and male contraception. Progesterone formed from pregnenolone by 3ß-hydroxysteroid dehydrogenase 1 (HSD3B1) and estradiol from androgen by aromatase (CYP19A1) are critical for the maintenance of pregnancy or associated with some cancers. In this study we compared the potencies of (+)- and (-)-gossypol enantiomers in the inhibition of HSD3B1 and aromatase activities as well as progesterone and estradiol production in human placental JEG-3 cells. (+) Gossypol showed potent inhibition on human placental HSD3B1 with IC50 value of 2.3 µM, while (-) gossypol weakly inhibited it with IC50 over 100 µM. In contrast, (-) gossypol moderately inhibited CYP19A1 activity with IC50 of 23 µM, while (+) gossypol had no inhibition when the highest concentration (100 µM) was tested. (+) Gossypol enantiomer competitively inhibited HSD3B1 against substrate pregnenolone and showed mixed mode against NAD(+). (-) Gossypol competitively inhibited CYP19A1 against substrate testosterone. Gossypol enantiomers showed different potency related to their inhibition on human HSD3B1 and CYP19A1. Whether gossypol enantiomer is used alone or in combination relies on its application and beneficial effects.

A Dietary Medium-Chain Fatty Acid, Decanoic Acid, Inhibits Recruitment of Nur77 to the HSD3B2 Promoter In Vitro and Reverses Endocrine and Metabolic Abnormalities in a Rat Model of Polycystic Ovary Syndrome.

Hyperandrogenism is the central feature of polycystic ovary syndrome (PCOS). Due to the intricate relationship between hyperandrogenism and insulin resistance in PCOS, 50%-70% of these patients also present with hyperinsulinemia. Metformin, an insulin sensitizer, has been used to reduce insulin resistance and improve fertility in women with PCOS. In previous work, we have noted that a dietary medium-chain fatty acid, decanoic acid (DA), improves glucose tolerance and lipid profile in a mouse model of diabetes. Here, we report for the first time that DA, like metformin, inhibits androgen biosynthesis in NCI-H295R steroidogenic cells by regulating the enzyme 3ß-hydroxysteroid dehydrogenase/Δ5-Δ4-isomerase type 2 (HSD3B2). The inhibitory effect on HSD3B2 and androgen production required cAMP stimulation, suggesting a mechanistic action via the cAMP-stimulated pathway. Specifically, both DA and metformin reduced cAMP-enhanced recruitment of the orphan nuclear receptor Nur77 to the HSD3B2 promoter, coupled with decreased transcription and protein expression of HSD3B2. In a letrozole-induced PCOS rat model, treatment with DA or metformin reduced serum-free testosterone, lowered fasting insulin, and restored estrous cyclicity. In addition, DA treatment lowered serum total testosterone and decreased HSD3B2 protein expression in the adrenals and ovaries. We conclude that DA inhibits androgen biosynthesis via mechanisms resulting in the suppression of HSD3B2 expression, an effect consistently observed both in vitro and in vivo. The efficacy of DA in reversing the endocrine and metabolic abnormalities of the letrozole-induced PCOS rat model are promising, raising the possibility that diets including DA could be beneficial for the management of both hyperandrogenism and insulin resistance in PCOS.

Interleukin-4 and prostaglandin E2 synergistically up-regulate 3ß-hydroxysteroid dehydrogenase type 2 in endometrioma stromal cells.

CONTEXT: Endometriosis is a chronic inflammatory disease in which immune response and production of estrogen in endometriotic tissues are involved in the development of the disease. Prostaglandin E2 (PGE2) stimulates aromatase (P450arom) expression in endometrioma stromal cells (ESCs) and increases the production of estrogens. On the other hand, an accumulating amount of evidence suggests that IL-4, a typical Th2 cytokine, plays important roles in the disease. OBJECTIVE: The objective of the investigation was to study the effect of IL-4 on the expression of 3ß-hydroxysteroid dehydrogenase (HSD3B2), a pivotal enzyme for estrogen production, in ESCs. DESIGN, PATIENTS, AND MAIN OUTCOME MEASURES: ESCs were isolated from ovarian endometrioma tissues and cultured with IL-4 and PGE2. CP-690550, a Janus protein tyrosine kinase 3 inhibitor, and HSD3B2 small interfering RNA were added to the culture. Gene expression of HSD3B2 and P450arom was examined by quantitative RT-PCR. Dehydroepiandrosterone (DHEA) was added to the culture, and then the combined enzyme activity of HSD3B2, which converts DHEA to androstenedione, and P450arom, which converts androstenedione to estrone, was examined by measuring estrone concentration in the supernatants with a specific enzyme immunoassay. RESULTS: IL-4 increased the expression of HSD3B2 mRNA in a dose-dependent manner. CP-650550 inhibited the IL-4-induced increase in HSD3B2 mRNA expression. PGE2 also increased the expression of HSD3B2 mRNA, and the combination of IL-4 and PGE2 synergistically increased the expression of HSD3B2 mRNA. IL-4 had no effect on the expression of P450arom mRNA, whereas PGE2 increased the expression of P450arom mRNA. Although PGE2 alone increased the production of estrone from DHEA, the combination of IL-4 and PGE2 significantly augmented the production of estrone from DHEA. The enhanced production of estrone by the combination of IL-4 and PGE2 was inhibited by CP-690550 and HSD3B2 small interfering RNA. CONCLUSIONS: IL-4 in combination with PGE2 may enhance estrogen production in endometriotic tissues, implying an elaborate mechanism that Th2 immune response augments inflammation-dependent progression of the disease.

3 beta-hydroxysteroid dehydrogenase isomerase (3beta-HSD) activity in the rat sciatic nerve: kinetic analysis and regulation by steroids.

We have shown that progesterone (PROG) has a stimulatory effect on myelin formation after sciatic nerve injury. PROG is synthesized from pregnenolone (PREG) by the enzyme 3 beta-hydroxysteroid dehydrogenase isomerase (3beta-HSD). At the occasion of the 15th International Symposium of the Journal of the Steroid Biochemistry and Molecular Biology, we presented some of our recent results demonstrating, expression and activity of the enzyme 3beta-HSD in the rat sciatic nerve. We determined the kinetic properties of 3beta-HSD and its regulation by PROG and estradiol. The expression of 3beta-HSD protein was assessed by Western-blot analysis, and the 3beta-HSD activity was evaluated by incubating homogenates with [3H]-PREG as substrate and NAD(+) as cofactor. Levels of steroids formed were calculated either by extrapolation of the relationship between the tritiated peaks obtained by thin layer chromatography (TLC) and the initial amount of PREG, or by gas chromatography-mass spectrometry (GC-MS) determination. A rapid increase in PROG formation was found between 0 and 50min of incubation and no significant change was observed between 1 and 4h. The calculated K(m) value was close to the values obtained for the 3beta-HSD types I and IV isoforms. Trilostane caused a potent inhibition of the rate of conversion of PREG to PROG. When we tested the effects of progesterone and estradiol on 3beta-HSD activity, a significant inhibition was obtained.

Differences in substrate and inhibitor kinetics of human type 1 and type 2 3beta-hydroxysteroid dehydrogenase are explained by the type 1 mutant, H156Y.

Two distinct genes encode the human type 1 (placenta, mammary gland) and type 2 (adrenal, gonad) isoforms of 3beta-hydroxysteroid dehydrogenase/isomerase (3beta-HSD). We have produced the Y154F, H156Y, and K158Q mutant enzymes in the Y154-P-H156-S-K158 motif of the human type 1 3beta-HSD/isomerase. The H156Y mutant was created to produce a chimera of the type 2 enzyme motif (Y154-P-Y156-S-K158) in the type 1 enzyme. The wild-type (WT) 1 and 2 plus the mutant enzymes were expressed and purified. The Km for dehydroepiandrosterone and Ki for epostane measured with both the H156Y mutant and WT 2 are 13-fold to 17-fold greater than those values obtained with the WT 1 3beta-HSD. The Y154F and K158Q mutants exhibit no 3beta-HSD but have significant isomerase activity. Thus, H156 in WT 1 vs. Y156 in WT 2 accounts for the substantially higher affinity of WT 1 3beta-HSD activity for these substrate and inhibitor steroids relative to the WT 2 enzyme.

Medroxyprogesterone acetate and dexamethasone are competitive inhibitors of different human steroidogenic enzymes.

Medroxyprogesterone acetate (MPA), a widely used progestin, can suppress the hypothalamic-pituitary-gonadal axis but can also directly inhibit gonadal steroidogenesis; the success of MPA as a treatment for gonadotropin-independent sexual precocity derives from its direct action on steroidogenic tissues. Dexamethasone, a widely used glucocorticoid, can suppress the hypothalamic-pituitary-adrenal axis, but its potential effect directly on the adrenal is unclear. Previous reports suggested that these two drugs may act on the initial steps in the rodent steroidogenic pathway; therefore, we investigated their abilities to inhibit the first three human enzymes in steroidogenesis: the cholesterol side-chain cleavage enzyme (P450scc), the 17alpha-hydroxylase/17,20-lyase (P450c17), and type II 3beta-hydroxysteroid dehydrogenase/isomerase (3betaHSDII). We found no effect of either drug on P450scc in intact human choriocarcinoma JEG-3 cells. Using microsomes from yeast expressing human P450c17 or microsomes from human adrenals, we found that dexamethasone inhibited P450c17 with a Ki of 87 micromol/L, which is about 1000 times higher than typical therapeutic concentrations, but that MPA has no detectable action on P450c17. Using microsomes from yeast expressing human 3betaHSDII, we found that this enzyme has indistinguishable apparent Km values of 5.2-5.5 micromol/L and similar maximum velocities of 0.34-0.56 pmol steroid/min x microg microsomal protein for the three principal endogenous substrates, pregnenolone, 17-hydroxypregnenolone, and dehydroepiandrosterone. In this system, MPA inhibited 3betaHSDII with a Ki of 3.0 micromol/L, which is near concentrations achieved by high therapeutic doses of 5-20 mg MPA/kg x day. These data establish the mechanism of action of MPA as an inhibitor of human steroidogenesis, and are in contrast with the results of earlier studies indicating that MPA inhibited both P450c17 and 3betaHSD in rat Leydig cells. These studies establish the "humanized yeast" system as a model for studying the actions of drugs on human steroidogenic enzymes and suggest that 3betaHSDII may be an appropriate target for pharmacological interventions in human disorders characterized by androgen excess or sex steroid dependency.

Bovine adrenal 3beta-hydroxysteroid dehydrogenase (E.C. 1.1.1. 145)/5-ene-4-ene isomerase (E.C. 5.3.3.1): characterization and its inhibition by isoflavones.

The isoflavones daidzein, genistein, biochanin A and formononetin inhibit potently and preferentially the gamma-isozymes of mammalian alcohol dehydrogenase (gammagamma-ADH), the only ADH isozyme that catalyzes the oxidation of 3beta-hydroxysteroids. Based on these results, we proposed that these isoflavones might also act on other enzymes involved in 3beta-hydroxysteroid metabolism. Recently, we showed that they indeed are potent inhibitors of a bacterial beta-hydroxysteroid dehydrogenase (beta-HSD). To extend this finding to the mammalian systems, we hereby purified, characterized and studied the effects of isoflavones and structurally related compounds on, a bovine adrenal 3beta-hydroxysteroid dehydrogenase (3beta-HSD). This enzyme catalyzes the oxidation of 3beta-hydroxysteroids but not 3alpha-, 11beta- or 17beta-hydroxysteroids. The same enzyme also catalyzes 5-ene-4-ene isomerization, converting 5-pregnen 3, 20-dione to progesterone. The K(m) values of its dehydrogenase activity determined for a list of 3beta-hydroxysteroid substrates are similar (1 to 2 microM) and that of its isomerase activity, determined with 5-pregnen 3, 20-dione as a substrate, is 10 microM. The k(cat) value determined for its isomerase activity (18.2 min(-1)) is also higher than that for its dehydrogenase activity (1.4-2.4 min(-1)). A survey of more than 30 isoflavones and structurally related compounds revealed that daidzein, genistein, biochanin A and formononetin inhibit both the dehydrogenase and isomerase activity of this enzyme. Inhibition is potent and concentration dependent. IC(50) values determined for these compounds range from 0.4 to 11 microM, within the plasma and urine concentration ranges of daidzein and genistein of individuals on vegetarian diet or semi-vegetarian diet. These results suggest that dietary isoflavones may exert their biological effects by inhibiting the action of 3beta-HSD, a key enzyme of neurosteroid and/or steroid hormone biosynthesis.

Affinity radiolabeling identifies peptides associated with the isomerase activity of human type I (placental) 3beta-hydroxysteroid dehydrogenase/isomerase.

3beta-Hydroxysteroid dehydrogenase and steroid Delta5-->4-isomerase (3beta-HSD/isomerase) were purified as a single protein from human term placenta. The affinity alkylator, 5,10-secoestr-4-yne-3,10, 17-trione (secosteroid), was incubated with the purified enzyme (30/1 secosteroid/enzyme molar ratio) to produce an 80% loss of initial isomerase activity over 90 min in a time-dependent, irreversible manner. The secosteroid inactivated 3beta-HSD by only 20% during the same 90 min. Incubations containing the isomerase substrate steroid, 5-androstene-3,17-dione, completely protected the isomerase activity from inactivation by the secosteroid and did not slow the inactivation of 3beta-HSD. The enzyme containing covalently bound steroid was separated from unreacted secosteroid by reversed phase HPLC. Ketones on the protein-bound secosteroid were radiolabeled by reduction with sodium boro[3H]hydride (specific radioactivity 50 microCi/micromol for the transferred tritium). After removal of the unreacted sodium boro[3H]hydride, the affinity-radiolabeled enzyme was digested with trypsin-TPCK, and the peptides were isolated by reversed phase HPLC. The radiolabeled peptide fractions were sequenced. The secosteroid alkylated three tryptic peptides: 251GQFYYISDDTPHQSYDNLNYTLSK274, tritiated His262; 176NGGTLYTCALR186, tritiated Cys183; and 353TVEWVGSLVDR363, tritiated Trp356. Coincubation with the isomerase substrate blocked the labeling of these three peptides and shifted the alkylation by secosteroid to a single tryptic peptide (135EIIQNGHEEEPLENTWPAPYPHSK159, tritiated His142). Using substrate protection to validate specificity, the affinity labeling secosteroid has identified peptides in the enzyme that are associated with isomerase activity.