Structure-activity relationships of the inhibition of human placental aromatase by imidazole drugs including ketoconazole

The aim of the present study was to investigate the effectiveness of several imidazole drugs to inhibit human placental aromatase compared with the known inhibitors of aromatase, 4-hydroxyandrostenedione (4-OHA) and aminoglutethimide (AG). Inhibition was similar with both androstenedione and testosterone as substrates. The order of decreasing inhibitory effect (determined from ID50 values) was: 4-OHA greater than tioconazole greater than econazole greater than bifonazole greater than clotrimazole greater than micomazole greater than isoconazole greater than ketoconazole greater than AG greater than nimorazole. The imidazole drugs and AG were reversible inhibitors of aromatase activity, in contrast 4-OHA was an irreversible inhibitor. Astemizole inhibited less than 40% whereas metronidazole, carbimazole, mebendazole, tinidazole and thiabendazole inhibited less than 20% of aromatase activity at 100 mumol/l. The imidazole drugs and AG were without effect on 3 beta-hydroxysteroid dehydrogenase-isomerase (3 beta-HSD-I) and 17 beta-hydroxysteroid oxidoreductase activity. In contrast 4-OHA was found to be a potent, reversible inhibitor of 3 beta-HSD-I with an ID50 value of 2.15 mumol/l. A common structural feature of the imidazole drugs having an inhibitory effect was the presence of one or more aromatic rings on the N-1 substituent. In contrast, the imidazole drugs having the imidazole ring fused to a benzene ring, i.e. benzimidazoles (astemizole, mebendazole, thiabendazole) and those having an aliphatic side chain on the N-1 of the imidazole ring (carbimazole, metronidazole, nimorazole, tinidazole) were only weak inhibitors of aromatase.     

Inhibition of testicular 17 alpha-hydroxylase and 17,20-lyase but not 3 beta-hydroxysteroid dehydrogenase-isomerase or 17 beta-hydroxysteroid oxidoreductase by ketoconazole and other imidazole drugs

Ketoconazole, an orally active antifungal drug, is known to inhibit testicular androgen production both in vitro and in vivo. The aim of the present study was to examine the effect of ketoconazole and 13 other imidazole drugs on rat testicular microsomal 17 alpha-hydroxylase, 17,20-lyase, 3 beta-hydroxysteroid dehydrogenase-isomerase (3 beta-HSD-I) and 17 beta-hydroxysteroid oxidoreductase (17 beta-HSOR). The order of decreasing inhibitory effect (determined from Ki values) on 17 alpha-hydroxylase (substrate [3H]progesterone; Km = 89 +/- 0.65 nmol/l; SEM, n = 8) was bifonazole (Ki = 86 +/- 3.3 nmol/l; SEM, n = 4) greater than ketoconazole (160 +/- 4.92) greater than clotrimazole (170 +/- 5.81) greater than miconazole (599 +/- 7.22) greater than econazole (688 +/- 6.98) greater than tioconazole (901 +/- 1.71) greater than isoconazole (1090 +/- 6.96) and on 17,20-lyase (substrate, [3H]17 alpha-hydroxyprogesterone; Km = 250 +/- 0.75 nmol/l; SEM, n = 8) was bifonazole (56.5 +/- 3.4) greater than clotrimazole (81.5 +/- 3.1) greater than ketoconazole (84 +/- 3.5) greater than miconazole (243 +/- 6.3) greater than econazole (325 +/- 5.1) greater than tioconazole (505 +/- 5.2) greater than isoconazole (610 +/- 6.34). However, these imidazole drugs did not inhibit the 3 beta-HSD-I or 17 beta-HSOR activities. A common structural feature of the imidazole drugs having an inhibitory effect was the presence of one or more aromatic rings on the imidazole side chain. In contrast, the imidazole drugs having the imidazole ring fused to a benezene ring, i.e. benzimidazoles (astemizole, mebendazole, thiabendazole) and those having an aliphatic side chain on the N-1 of the imidazole ring (carbimazole, metronidazole, nimorazole, tinidazole) did not inhibit 17 alpha-hydroxylase, 3 beta-HSD-I or 17 beta-HSOR enzyme activities. However some did inhibit 17,20-lyase activity but only at high concentrations. The results of the present study suggest that some imidazole drugs may be useful in clinical situations requiring the suppression of androgen production, for example in the treatment of hormone-dependent prostatic cancer.     

In vitro inhibition by ketoconazole of human testicular steroid oxidoreductases

An oral antimycotic agent, ketoconazole has been demonstrated to be an inhibitor of cytochrome P-450-dependent monooxygenases. To investigate its effect on steroid oxidoreductases, in vitro studies were carried out using subcellular fractions of human testes. Ketoconazole competitively inhibited activities of 3 beta-hydroxy-5-ene-steroid oxidoreductase/isomerase and NADH-linked 20 alpha-hydroxysteroid oxidoreductase for steroid substrate and the Ki values were 2.9 and 0.9 microM, respectively. In contrast, ketoconazole inhibited neither 17 beta-hydroxysteroid oxidoreductase nor NADPH-linked 20 alpha-hydroxysteroid oxidoreductase, indicating that the two 20 alpha-hydroxysteroid oxidoreductases are distinct. Further, ketoconazole inhibited non-competitively the above enzyme activities for the corresponding cofactors of NAD and NADH. From the binding mode of ketoconazole to cytochrome P-450 and the present findings, it appears likely that the agent binds to a site which is different from that of steroids or pyridine nucleotides.     

Inhibition of leucocytic lysosomal enzymes by glycosaminoglycans in vitro.

1. A lysosomal fraction was separated by density-gradient centrifugation from a highly purified human polymorphonuclear leucocyte suspension. 2. Some 23 different lysosomal enzymes were assayed for activity in the presence of various concentrations of glycosaminoglycans. 3. The 21 acid hydrolases assayed were strongly inhibited to different degrees by low (0-12 mmol/l) concentrations of glycosaminoglycans in a pH-dependent manner. Thus inhibitions were stronger below pH4.5, with activity returning to control values at about pH5.0. 4. On a molar basis, the inhibitory activity for the several glycosaminoglycans studied was: heparin greater than chondroitin sulphate greater than hyaluronic acid. 5. Once the glycosaminoglycan-acid hydrolase complex was formed, it was partially dissociated by slight elevations in the pH of the incubation medium, by increasing the ionic strength of the incubation medium, or by adding several cationic proteins (e.g. histone, protamine). 6. As leucocytic lysosomes contain large amounts of chondroitin sulphate, and have a strongly acid intragranular pH, we suggest that glycosaminoglycans may modify lysosomal function through the formation of complexes with lysosomal enzymes, by inhibiting the digestive activity of the acid hydrolases when the intralysosomal pH is below their pI.     

Effects of ketoconazole on rat testicular steroidogenic enzymatic activities

Ketoconazole (K) is an antifungal imidazole derivative which has been shown to be a potent inhibitor of testosterone (T) biosynthesis in rodents and humans. To study the effect of K on rat testicular steroidogenesis we measured the activities of five testicular microsomal steroidogenic enzymes in K-treated rats and controls. Thirty male adult rats were given either 2 mg K or water every 12 hours by mouth during 5 days. Mean testicular weight was similar in both groups of animals. The K-treated group had a T serum concentration of 83 +/- 14 ng/dL whereas it was 94 +/- 16 ng/dL in the control group (NS). The K-treated animals had decreased activities of the 3 beta-hydroxysteroid dehydrogenase (830 +/- 48 vs 2,245 +/- 109 pmol/mg protein/min, P less than 0.001), 17-hydroxylase (243 +/- 5 vs 676 +/- 17 pmol/mg protein/min, P less than 0.001), 17-ketosteroid reductase (31 +/- 2 vs 169 +/- 7 pmol/mg protein/min, P less than 0.001), and aromatase enzymes (92 +/- 6 vs 123 +/- 7 pmol/mg protein/min, P less than 0.01). The 17,20-desmolase activity was similar in both groups of animals (210 +/- 4 vs 171 +/- 18 pmol/mg protein/min). We conclude that K given orally to rats inhibits the activity of several testicular steroidogenic enzymes.     

Upregulation of steroidogenic enzymes and ovarian 17beta-estradiol in human granulosa-lutein cells by Cordyceps sinensis mycelium

There is increasing evidence that 17beta-estradiol (E2) directly influences the quality of maturing oocytes and thus the outcome of assisted reproduction treatment. Although Cordyceps sinensis (CS) mycelium, a Chinese herbal medicine, is believed to enhance libido and fertility in both sexes, the mechanism of its effect in women has not been determined. The aim of the present study was to evaluate the effects of CS on steroidogenic enzyme expression and E2 biosynthesis in human granulosa-lutein cells (GLC). We found that CS induced E2 production by GLC in a dose- and time-dependent manner and that a 3-h treatment with CS induced increased levels of mRNAs coding for the P450 side chain cleavage enzyme (P450scc), 3beta-hydroxysteroid dehydrogenase (3beta-HSD), and aromatase. Western blot analysis demonstrated that, after treatment with CS for 3 h, protein levels of steroidogenic acute regulatory protein (StAR) and aromatase were upregulated while P450scc and 3beta-HSD levels showed no substantial change. New protein synthesis was required for CS-induced E2 production because it was abrogated by cycloheximide pretreatment. Addition of 22(R)-hydroxycholesterol, thus bypassing the need for StAR protein, did not induce as much E2 production as CS treatment, indicating that upregulation of StAR protein was not the only factor contributing to CS-induced steroidogenesis. Cotreatment of GLCs with CS and aminoglutethimide, an aromatase inhibitor, completely abolished CS-induced E2 production. In conclusion, treatment of GLCs with CS results in increased E2 production due, at least in part, to increased StAR and aromatase expression. These data may help in the development of treatment regimens to improve the success rate of in vitro fertilization.     

Inhibition of membrane-bound adrenodoxin-adrenodoxin reductase activity by puromycin and cycloheximide,which antagonize the adrenal steroidogenic action of ACTH

Inhibition of NADPH-dependent adrenodoxin reductase activity in adrenocortical mitochondria by puromycin and cycloheximide was observed at 0.1 mM and 1 mM, respectively. NADPH-dependent reduction of cytochrome P450 was also inhibited at similar concentrations, while solubilized enzymes were unaffected by the antibiotics. Further, puromycin induces high-to-low spin spectral changes with dissociation constants of 0.2 mM and 1.0 mM for membrane-bound and soluble cytochrome P450, respectively. Cycloheximide caused no spin changes.     

Inhibition of human in vitro osteoclastogenesis by Equisetum arvense

Objectives

Equisetum arvense has long been used in traditional medicines to treat different disorders, including bone pathologies. In this study a hydromethanolic extract of E. arvense was assessed for its effects on human osteoclastogenesis.

Materials and methods

Osteoclast precursors were maintained in non‐stimulated and stimulated (presence of M‐CSF and RANKL) conditions, or in co‐cultures with osteoblasts. Cell cultures were treated with 0.00016–0.5 mg/ml of a hydromethanolic E. arvense extract.

Results

The extract did not affect spontaneous osteoclastogenesis. In osteoclast precursors committed to osteoclastogenesis (stimulated or co‐cultured with osteoblasts), E. arvense caused dose‐dependent inhibitory effect that became statistically significant at concentrations ≥0.004 mg/ml. This was observed using different osteoclast differentiation and activation markers. Cell response was associated with changes in relative contribution of MEK and NFkB signalling pathways, as well as PGE2 production. As there were differences in the response of osteoclast precursors maintained in the presence of inductive factors, or co‐cultured with osteoblastic cells, it seems that E. arvense extract had the ability to modulate osteoclastogenesis, either by acting directly on osteoclast precursor cells, and/or via osteoblasts.

Conclusions

Equisetum appeared to have a negative effect on human osteoclastogenesis, which is in line with its putative beneficial role in pathophysiological conditions associated with increased osteoclastic activity, and might suggest potential utility for treatment with bone regeneration strategies.     

Inhibition of 17 beta-hydroxysteroid dehydrogenase activity in human endometrium by adrenal androgens

The effect of dehydroepiandrosterone sulphate (DHA-S) and its metabolites dehydroepiandrosterone (DHA) and 5-androstene-3 beta, 17 beta-diol (ADIOL) on the activity of 17 beta-hydroxysteroid dehydrogenase in human endometrial tissue was investigated by an isotope ratio technique. The apparent KM for oestradiol was 1.59 X 10(-6) M. All three androgens inhibited the metabolism of oestradiol and the apparent Ki values were: ADIOL, 2.05 X 10(-6) M; DHA-S and DHA, 1.59 X 10(-6) M. However, ADIOL acted by direct competition with oestradiol for the active enzyme site whereas inhibition by DHA and its sulphate was non-competitive. DHA-S and DHA were more potent inhibitors of oestradiol metabolism than was ADIOL. These results support the hypothesis that adrenal androgens could be involved in the development of endometrial hyperplasia and adenocarcinoma. Inhibition of oestradiol metabolism could increase the concentration of oestradiol in endometrial tissue and if unopposed by progesterone, e.g. after the menopause or in subjects with ovulatory defects, could stimulate abnormal endometrial growth.     

Secretion of lysosomal enzymes by human placental villi in vitro

Summary Chorionic villi from first trimester and term human placentas have been incubated in vitro and shown to release the lysosomal enzymes, -hexosaminidase, -glucosidase and -gluctlronidase. There was negligible release of the cytoplasmic enzyme, lactate dehydrogenase, under the same conditions. The first trimester villi released proportionally more of their lysosomal enzyme content than did the term villi. Extracellular levels of -hexosaminidase were raised and those of -glucosidase and, -glucuronidase were lowered when tissue was incubated with 1 M colchicine, suggesting that microtubules are involved in the control of lysosomal enzyme release from placental villi.     

60-Hz electric field alters the steroidogenic response of rat adrenal tissue, in vitro

Exposure to a 60-Hz electric field at 10 kV/m but not at 5 kV/m, 100 kV/m or 1000 kV/m caused a highly significant, threefold elevation in the steroidogenic response of rat adrenal cortical tissue after the administration of 10 mU of adrenocorticotrophic hormone (ACTH) under in vitro, superfusion conditions. A 60-Hz electric field can directly influence the function of mammalian tissue in the absence of central-nervous-system mediation.     

Structure of genes encoding steroidogenic enzymes

Synthesis of adrenal steroid hormones from cholesterol entails the actions of only five enzymes, four of which are specific forms of cytochrome P450. These cytochrome P450 enzymes have all been isolated and their activities reconstituted in vitro, showing that each enzyme catalyses multiple steroidal conversions. Genes or complementary DNAs have been cloned for human P450scc (the cholesterol side-chain cleavage enzyme), P450c17 (17 alpha-hydroxylase/17,20 lyase) and P450c21 (21-hydroxylase). The sequences for microsomal P450c17 and P450c21 are much more closely related to one another than either is to the sequence for mitochondrial P450scc. Each of these P450 enzymes is encoded by a single human gene; the gene for P450scc lies on chromosome 15, that for P450c17 lies on chromosome 10, and that for P450c21 lies on chromosome 6. The human, mouse and bovine genomes each have two P450c21 genes. While only one of these is active in mouse and man, both genes may be active in cattle. A wide variety of lesions in the human P450c21(B) gene causes congenital adrenal hyperplasia, a common genetic disorder.     

Inhibition of human P450 enzymes by nicotinic acid and nicotinamide

Nicotinic acid has been used as a cholesterol-lowering agent for a few decades already, whereas the cytoprotective and antiviral properties of nicotinamide are slowly gaining attention. In both cases however, very high doses are needed to achieve a therapeutic effect, resulting in blood concentrations sometimes as high as 15 mM. Based on their common pyridine functionality, we hypothesized that these two molecules could inhibit human P450 enzymes. In vitro inhibition studies demonstrate that, at their therapeutic concentrations, both nicotinic acid and nicotinamide inhibit CYP2D6 (Ki = 3.8 +/- 0.3 and 19 +/- 4 mM, respectively). Nicotinamide also inhibits CYP3A4 (Ki = 13 +/- 3 mM) and CYP2E1 (Ki = 13 +/- 8 mM). As expected for nitrogen-containing heteroaromatic molecules, spectrophotometric analysis indicates that the inhibition occurs via coordination of the pyridine nitrogen atom to the heme iron.     

Comparative in vitro responses of fetal, pregnant and non-pregnant rabbits' adrenal glands to steroidogenic agents

The in vitro secretion of aldosterone and corticosterone by the adrenal glands of fetal (day 30), pregnant and non-pregnant rabbits was examined under basal and stimulated conditions. In general, non-pregnant animals basally secreted less aldosterone than either pregnant or fetal rabbits, whereas basal corticosterone secretion by pregnant animals exceeded that of either fetal or non-pregnant animals. At similar doses of adrenocorticotropin (ACTH), fetal and pregnant adrenal glands produced comparatively more aldosterone than non-pregnant animals, while corticosterone secretion was accelerated to a greater degree in fetal rabbits than in the other groups. Angiotensin II had its greatest effect on the aldosterone secretory rates of fetal and non-pregnant animals without affecting corticosterone secretion in any group. Elevated potassium (K+) enhanced the secretory rates of aldosterone and corticosterone in fetal animals, while increasing only aldosterone secretion in non-pregnant rabbits. Serotonin accelerated aldosterone secretion in all animals, whereas it increased corticosterone secretion only in non-pregnant animals. These results suggest that (1) in fetal rabbits, the secretory rates of both aldosterone and corticosterone are regulated primarily by ACTH and to a much lesser extent by angiotensin II and K+, (2) the corticosterone secretory rates of pregnant and non-pregnant rabbits are controlled mainly by ACTH, and (3) aldosterone secretion by non-pregnant animals is regulated primarily by angiotensin II and secondarily by ACTH and K+, while in pregnant animals ACTH may be the primary regulator of aldosterone secretion as it is in the fetus.