Evidence of the direct aromatization of testosterone and different aromatization sites for testosterone and androstenedione in human placental microsomes

Synthesis and biological evaluation of nandrolone-bodipy conjugates

Here, we report synthesis and biological evaluation of fluorescent nandrolone-3-carboxymethyloxime derivatives conjugated with green-emitting bodipy dye via PEG linkers. All the newly-synthesized compounds were evaluated for their effect on cell proliferation in vitro in MCF-7, LNCaP, PC-3 and HEK 293T model cell lines using WST-1 assay. By means of live-cell fluorescence microscopy, the intracellular localization of nandrolone-bodipy conjugates was revealed in endoplasmic reticulum. Moreover, we performed competitive localization study with nonfluorescent nandrolone, metandrolone, boldenone, trenbolone, and testosterone.

Structure-activity relationships of 3-deoxy androgens as aromatase inhibitors. Synthesis and biochemical studies of 4-substituted 4-ene and 5-ene steroids

As part of our investigation into the structure-activity relationship of a novel class of aromatase inhibitors, two series of 3-deoxy androgens, androst-5-en-17-ones with a non-polar alkoxy (5 and 6), alkyl (20-22), or phenylalkyl (23 and 24) group at C-4beta and 4-acyloxyandrost-4-en-17-ones (29-32, and 34) were synthesized and evaluated. The 4beta-alkyl and 4beta-phenylalkyl compounds were obtained through reaction of 4alpha,5alpha-epoxy steroid (8) with RMgBr (R: alkyl and phenylalkyl) followed by dehydration of the 4beta-substituted 5alpha-hydroxy products (15-19) with SOCl(2) as key reactions. Acylation of 4alpha,5alpha-diol (25) with (RCO)(2)O in pyridine and subsequent dehydration with SOCl(2) gave the 4-acyloxy steroids. All of the steroids studied, except for 4-acetoxy-19-ol (34) that was a non-competitive inhibitor of human placental aromatase, blocked aromatase activity in a competitive manner. 4-Benzoyloxy- and 4-acetoxy steroids (31) and (32) were the most powerful inhibitors of aromatase (K(i)=70 and 60nM, respectively). Elongation of an acetoxy group in a series of 4-acyloxy steroids or a methyl group in a series of 4beta-alkyl steroids decreased affinity for aromatase principally in relation to carbon number of the acyl or alkyl function. The present findings are potentially useful for understanding the spatial and electronic nature of the binding site of aromatase as well as for developing effective aromatase inhibitors.

Aromatase inhibition by 4 beta,5 beta-epoxides of 16 alpha-hydroxyandrostenedione and its 19-oxygenated analogs, potential precursors of estriol production in the feto-placental unit

To gain insight into the nature of the substrate binding site and the catalytic function of aromatase, we studied the inhibition of androstenedione aromatization by 4beta,5beta-epoxy-16alpha-hydroxyandrostenedione (4) and its 19-hydroxy and 19-oxo derivatives, 5 and 6, as well as the biochemical aromatization of these steroids in human placental microsomes. The 19-methyl and 19-oxo compounds, 4 and 6, were weak competitive inhibitors of aromatase, with apparent K(i) values of 246 microM and 270 microM, respectively, whereas the 19-hydroxy compound 5 inhibited aromatase in a non-competitive manner with the K(i) of 135 microM. The 19-methyl compound 4 inactivated aromatase in a time-dependent manner with k(inact) of 0.213 min(-1) in the presence of NADPH in air, but the other two did not cause it. The conversion of the three epoxides into estrogen, as well as 19-oxygenation of 19-methyl steroid 4 with human placental microsomes in the presence of NADPH in air, were not detected by gas chromatography-mass spectrometry. The present results are consistent with the two binding sites theory in the active site of aromatase.

Aromatization of 16alpha-hydroxyandrostenedione by human placental microsomes: effect of preincubation with suicide substrates of androstenedione aromatization

Estrogen synthase (aromatase) catalyzes the aromatization of androstenedione (AD) as well as 16alpha-hydroxyandrostenedione (16alpha-OHAD) leading to estrone and estriol, respectively. We found that several steroid analogs including 4-hydroxyandrostenedione (1), 6-oxoandrostenedione (6-oxoAD, 2) and its 19-hydroxy analog (3), 10beta-acetoxyestr-5-ene-7,17-dione (4), androst-5-ene-4,7,17-trione (5), and 17alpha-ethynyl-19-norteststerone (6), which are known suicide inactivators of AD aromatization, are not effective in inactivating 16alpha-OHAD aromatization in a time-dependent manner. The compounds were tested with the use of human placental microsomes and 1beta-tritiated-16alpha-OHAD as the substrate. The results of the tritium water method of 16alpha-OHAD aromatization was confirmed by the gas chromatography-mass spectrometry (GC-MS) method of estriol formation. The 1beta-tritiated-AD was used to measure AD aromatization as a positive control for these experiments. The compounds were tested at concentrations up to 40-fold higher than the K(i)'s determined for inhibition of AD aromatization. These studies suggest that differences exist in the binding site structures responsible for aromatization of 16alpha-OHAD and AD.

Lack of evidence for aromatase expression in human ovarian epithelial carcinoma

It is controversial whether ovarian epithelial carcinoma possesses steroidogenic enzymes. We investigated aromatase expression in ovarian epithelial carcinoma, and compared it with the normal ovary and placenta. Samples were obtained from an ovarian carcinoma cell line SK-OV-3, ovarian tumour tissues from four patients with epithelial carcinoma and one patient with dysgerminoma. Aromatase enzymatic activity was measured in microsome fractions by quantitating 3H2O released from [1-3H] androstenedione and [3H]oestrone converted from [1,2,6,7-3H] androstenedione. Aromatase messenger ribonucleic acid (mRNA) was determined by reverse transcription-polymerase chain reaction (RT-PCR) using oligonucleotide primers synthesized according to the published human aromatase gene sequence. No aromatase activity was detected in either of two mucinous cystadenocarcinoma specimens or in SK-OV-3 cells, while aromatization proceeded with apparent Michaelis-Menten kinetics in the normal ovaries and placentas. The apparent Km value was 200 nmol/L for the ovary. Aromatase mRNA was detected in dysgerminoma, and the normal ovary and placenta, but not in any of three mucinous cystadenocarcinoma specimens, one serous cystadenocarcinoma specimen and SK-OV-3 cells. These results for both enzyme activity and gene expression suggest that the human ovarian epithelial carcinoma lacks aromatase. The demonstration of absence of aromatase gene expression raises the possibility that aromatase activity in ovaries bearing epithelial carcinoma may be associated with hyperplastic stromal rather than tumour cells.

19-Aldehydo-4-androstene-3,17-dione: an estrogen precursor that inhibits sebaceous secretion in a rat model

19-aldehydo-4-androstene-3,17-dione (A; R = CHO), a biogenetic precursor of estrone in the body, has been found to suppress sebum secretion in the ovariectomized testosterone-treated Wistar rat at 1/2000 times the dose of cyproterone acetate required to produce an equivalent effect. The action of this steroid must therefore be analogous to that of an estrogen even though, in striking contrast to estradiol, it is without effect on uterine weight or vaginal cornification. It is postulated that 19-aldehydo-4-androstene-3,17-dione (A; R = CHO) is converted locally into estrone (B) by aromatase present in skin but only in low concentrations in vagina and uterus. The potential of biogenetic precursors (I) of estrogens for therapy of acne or alleviation of the worst effects of skin aging is worth investigation.

Human placental estrogen synthetase (aromatase). Effect of environment on the kinetics of protein-protein and substrate-protein interactions and the production of 19-oxygenated androgen intermediates in the purified reconstituted cytochrome P450 enzyme system

Estrogen synthetase (aromatase) catalyzes the conversion of androgen into estrogen via two hydroxylations at C19 and a subsequent C19-10 lyase reaction. We report here the results of a reconstitution study using a highly purified aromatase cytochrome P450 monooxygenase enzyme system, with both protein components (cytochrome P450 and NADPH-cytochrome P450 reductase) obtained from human term placental microsomes. By varying one of the components (amounts of cytochrome P450, NADPH-cytochrome P450 reductase, or androgen substrate) as the other two were held constant in four different environments (phospholipid, non-ionic detergent, mixture of phospholipid and non-ionic detergent and buffer alone), we obtained evidence supporting the following conclusions. The reconstituted enzyme is more active and the protein components exhibit much lower apparent Km values in the detergent and/or lipid environment compared with buffer alone. Although the apparent Km and Vmax values for each aromatase protein component differ significantly in most cases with the particular limiting component and environment, the catalytic efficiency (Kcat/Km) was independent of the limiting protein component and varied with the environment only (highest in the lipid-detergent mixture and lowest in lipid alone). When the concentration of androgen substrate (androstenedione or testosterone) was varied at constant amounts of the aromatase protein components (NADPH-cytochrome P450 reductase saturating), the Km was lower and the Vmax was higher for adrostenedione. The specificity constant (Vmax/Km) was a function of the reconstitution environment (highest in lipid alone and lowest in detergent alone) and was, on average, about 4-fold higher for androstenedione in a particular environment. The extent of production of 19-oxygenated androgen intermediates (19-hydroxy and 19-oxo androstenedione) was examined at three different levels of aromatase cytochrome P450 (subsaturating, saturating, super-saturating) relative to the NADPH-cytochrome P450 reductase component in the three different hydrophobic environments using androstenedione as substrate. Both 19-oxygenated androgens, each made in comparable amounts relative to control, were isolatable in greatest amounts under cytochrome P450 super-saturating conditions in the detergent-lipid mixed environment, and in least amounts under cytochrome P450 subsaturating conditions in the lipid-only environment. Based on these data, we propose that 19-oxygenated androgen intermediates are biosynthesized sequentially in a step-wise fashion as the cytochrome P450 and NADPH-cytochrome P450 reductase form transient complexes, and that the amount of isolatable 19-oxygenated androgen is proportional to the amount of excess cytochrome P450 component.

Androgen and 19-norandrogen aromatization by equine and human placental microsomes

The ability of equine and human placental microsomes to aromatize testosterone and 19-nortestosterone was studied. When 3 microM [1 beta,2 beta-3H]testosterone was used as substrate, the specific activity of equine placental microsomal aromatase was 2.5 times higher than that of the human microsomal enzyme. Although 19-nortestosterone was aromatized 67 times more rapidly by equine than by human aromatase, we found that equine aromatase exhibited a markedly weaker affinity for this substrate than did the human enzyme. Competitive inhibition of testosterone aromatization by 19-nortestosterone occurred with both equine and human aromatases. While having no effect on mare placental microsomes, Na+ and K+ (500 mM) stimulated testosterone aromatization by human placental microsomes by 73 and 52% respectively. If indeed a single enzyme is responsible for the aromatization of testosterone and 19-nortestosterone, which seems to be the case in both equine and human placental aromatase, our results show that differences in the structure of the active sites exist between equine and human aromatases.

Mechanisms of action of aminoglutethimide as endocrine therapy of breast cancer

During the last decade aminoglutethimide has been recognised as a valuable alternative in endocrine therapy for advanced breast cancer. Although some side effects do occur, most often these are initial effects which subside within a few weeks, and cessation of therapy is not usually indicated. Aminoglutethimide was originally introduced as an inhibitor of steroidogenesis in the adrenal cortex. It was soon recognised, however, that inhibition of the non-glandular aromatase, blocking the conversion of androgenic prohormones to oestrogens, was more important, resulting in decreased blood levels of oestrogens. In this review the role of aromatase inhibition as the only important aspect of the mechanism of action of aminoglutethimide is challenged. Evidence has accumulated during the last few years that aminoglutethimide is a most potent inducer of microsomal enzymes. In addition to the pharmacological implications this has (suggesting important interactions), it also points to the possibility that levels of oestrogens are decreased due to accelerated metabolism of these hormones. Based on new experimental data, and also clinical work with alternative aromatase inhibitors, it appears that the antitumour activity of aminoglutethimide may be due to both aromatase inhibition and accelerated metabolism of oestrogens. This seriously challenges the importance of aromatase inhibition alone as a strategy in endocrine therapy of breast cancer, and furthermore suggests that accelerated metabolism of key hormones is an alternative strategy to be explored.

Aromatization of testosterone and 19-nortestosterone by a single enzyme from equine testicular microsomes. Differences from human placental aromatase

A single enzyme in the stallion testis was able to aromatize both testosterone and nortestosterone. This enzyme had a much lower affinity for nortestosterone than for testosterone. In contrast to human placental estrogen synthetase, this enzyme aromatized testosterone and 19-nortestosterone with similar efficiency. The differences observed (effects of monovalent cations, inhibition of androstenedione aromatization by testosterone and 19-nortestosterone and, above all, rate of norandrogen aromatization) suggest that the aromatase in the horse testis is not the same as that in the human placenta.

Reduced estradiol production by a substituted triazole results in delayed ovulation in rats

Ovulation in the rat is delayed by a single administration of the substituted triazole R151885 (1,1-di(4-fluorophenyl)-2-(1,2,4-triazol-1-yl)-ethanol). This delay results from a 24-hr shift in the preovulatory luteinizing hormone (LH) surge since administration of chorionic gonadotrophin on proestrus restores ovulation. Plasma levels of estradiol are markedly reduced (42-45%) 6-12 hr after administration of R151885. The restoration of ovulation in R151885-pretreated rats, by administration of exogenous estradiol benzoate, indicates that the reduced estradiol levels play a pivotal role in the delay of ovulation. Granulosa cells isolated from rat ovaries produce estradiol and progesterone in vitro in the presence of both follicle-stimulating hormone and testosterone. The addition of R151885 to such cultures results in a dose-dependent inhibition of estradiol production (69% by 1 microM) without a significant effect on progesterone production. This inhibition occurs at concentrations of R151885 similar to those measured in vivo. R151885 is a competitive inhibitor of human placental aromatase (apparent Ki with androstenedione substrate of 410 nM) and produces a type II spectral perturbation of cytochrome P-450 from placental microsomes. Pituitaries isolated from R151885-treated rats have reduced LH output in response to gonadotrophin-releasing hormone stimulation compared with those of controls. It is proposed that R151885 competitively inhibits aromatase activity in developing ovarian follicles. The resultant temporary reduction of plasma estradiol levels at a critical time in the estrous cycle, and consequent inadequate pituitary sensitization, produces a 24-hr delay in the preovulatory LH surge and hence ovulation is delayed by 24 hr.

In vitro and in vivo studies demonstrating potent and selective estrogen inhibition with the nonsteroidal aromatase inhibitor CGS 16949A

CGS 16949A inhibited the conversion of [4-14C]androstenedione (A) to [4-14C]estrone by human placental microsomes in a competitive manner (Ki = 1.6 nM). Aminoglutethimide, also a competitive inhibitor, had a Ki = 0.7 microM in this assay system. The Km for the aromatization of A was 0.11 microM. Using ovarian microsomes from immature rats primed with pregnant mare's serum gonadotrophin and using [4-14C]testosterone conversion to [4-14C]estradiol as a measure of aromatase activity, the Km was 42 nM. At a substrate concentration 3-fold the Km, CGS 16949A was 180 times more potent as an inhibitor than aminoglutethimide, exhibiting half-maximal inhibition at 1.7 nM as compared to 0.3 microM. In vivo CGS 16949A lowered ovarian estrogen synthesis by gonadotropin-primed, androstenedione treated, immature rats by 90% at a dose of 260 micrograms/kg (PO). A dose of 100 mg/kg of aminoglutethimide was needed to produce this same effect. CGS 16949A at a dose of 4 mg/kg (PO) induced uterine atrophy (aromatase inhibition) without inducing adrenal hypertrophy - indicating a lack of inhibition of corticosterone secretion, while aminoglutethimide at 40 mg/kg (PO) induced adrenal hypertrophy without inducing uterine atrophy. CGS 16949A was neither androgenic nor estrogenic in rats using standard bioassays. The data suggest that CGS 16949A may serve as a potent and selective agent for modulating estrogen-dependent functions.

Synthesis and evaluation of bromoacetoxy 4-androsten-3-ones as active site-directed inhibitors of human placental aromatase

2 alpha-Bromoacetoxy (II), 6-bromoacetoxy (VII and X), and 19-bromoacetoxy (XII) derivatives of androstenedione and 17 beta-bromoacetoxy compounds (III, IV, XIII-XVI) were synthesized as potential affinity-labeling reagents for aromatase. 6 alpha-Bromoacetoxy derivative VII was the most potent inhibitor of human placental microsomal aromatase activity among this series. Its inhibitory activity was higher than that of the parent 6 alpha-hydroxy compound V, although other bromoacetates showed weaker inhibition of aromatase than the corresponding alcohols. The bromoacetates (except the 6 beta-bromoacetate X) inhibited aromatase activity in a time-dependent manner in the absence of NADPH, and the enzyme inactivation was blocked by the addition of androstenedione to the incubates. Kinetic analysis of the time- and concentration-dependent inhibition by the 6 beta-bromo-17 beta-bromoacetoxy compound XV gave an apparent Ki of 25 microM and kinact of 0.027 min-1.

Estrone sulfate: a potential source of estradiol in human breast cancer tissues

Local formation of estradiol in human breast tumors could provide a more important source of estrogen than is delivered from plasma. Prior studies have suggested that estrone is primarily synthesized from estrone sulfate. The enzyme 17 beta-hydroxysteroid dehydrogenase (HSD) would be required to convert estrone to estradiol. This study characterized HSD in 1000 X g supernatants from human breast tumors. Estradiol synthesis was linearly related to tissue concentration or time over the range studied. Cofactor requirements varied with estrone concentration. High and low affinity sites were found in 50% of tissues studied, while the remainder contained only low affinity sites. Screen assays showed measurable activity in all 42 samples tested. This activity ranged from 0.73- greater than 100 nmol estrone synthesized/g protein/hr, with a median activity of 5.9 nmol/g/hr. We evaluated the biological relevance of the sulfatase-HSD pathway by testing the ability of estrone sulfate to stimulate colony formation in soft agar cultures of nitrosomethylurea-induced rat mammary tumors. The maximally effective concentration ranged from 10(-7) to 10(-4)M. Significant stimulation of colony formation was observed in 7 of 8 experiments. The estrone sulfate stimulation pattern was similar to that previously observed with estradiol. Of the 3H-estrone sulfate added to the dishes, 20-98% was recovered as estrone and 0.2-6% as estradiol. These studies suggest that the requisite enzymes are present in human breast tumors for conversion of estrone sulfate to estradiol, and that this pathway may be biologically significant.

The apparent shift in distribution of aromatase activity in the subcellular fraction of human term placenta stored at -96 degrees C

The effects of storage at -96 degrees C on the distribution of the total aromatase activity in the homogenate, 900 xg pellet and 900 xg supernatant of two human term placentas were studied. Both specific and total aromatase activities in the 900 xg pellet increased through storage at -96 degrees C, while that in the 900 xg supernatant decreased. The ratio of total aromatase activity between the 900 xg pellet and 900 xg supernatant was about 2:1 in fresh placenta, but the ratio was about 19:1 in placenta stored at -96 degrees C for 3.5 months. Total aromatase activity in the tissue homogenate remained fairly constant throughout five months of storage at -96 degrees C. These data indicate that although active microsomal aromatase is thought to be available only from fresh placenta and the activity is lost quickly during storage of the tissue, aromatase itself is stable for months at -96 degrees C and the 900 xg pellet prepared from the frozen tissue contains almost the total original aromatase activity in the fresh placental tissue.

Aromatase in breast cancer and the role of aminoglutethimide and other aromatase inhibitors

Approximately one third of human breast carcinomas are hormone dependent and regress upon reduction of circulating estrogen levels. Traditional treatment strategies utilized surgical ablative methods to lower estrogen concentrations as treatment of breast cancer. Currently, investigative emphasis is focused upon development of highly specific antiestrogens and inhibitors of estrogen production. The enzyme, aromatase, as the terminal step in estrogen biosynthesis, is a logical target for blockade with potent and specific inhibitors. The earliest available aromatase antagonist, aminoglutethimide, suppresses estrogen production to the same extent as surgical ablation and is an effective treatment for breast cancer. Aminoglutethimide, however, blocks other cytochrome P-450-mediated steroid hydroxylations, requires concomitant glucocorticoid administration, and is associated with initial side effects. Several more specific inhibitors by destroying aromatase irreversibly as well as by competitive inhibition. One of these, 4-hydroxy-androstenedione, has been intensively studied in animals and is undergoing clinical trial. New data regarding these inhibitors further emphasize the key role of aromatase in estrogen production and the practical utility of blocking this enzyme.

Enzymatic androgen assay: some properties of human placental microsomal aromatase

The androgen content of biological fluids can be determined after their conversion into estrogens using human placental microsomal aromatase (HPMA). The purpose of this paper is to report some physico-chemical properties of HPMA. Using an accurate, specific and sensitive assay for HPMA, Km values for dehydroepiandrosterone (DHEA), androstenedione and testosterone were found to increase with increasing amount of the detergent (Triton X-100) added. Analysis at substrate concentrations 5-10 times above and below the Km values did not indicate any anomalous kinetic behaviour. Triton X-100, used for enzyme solubilization, significantly decreased the rate of aromatization of the three substrates by increasing their Km values. This effect was more important for testosterone than for androstenedione or DHEA. Using a new protocol for the determination of aromatase activity, kinetic properties of aromatase before and after solubilization are described.

High-performance liquid chromatographic determination of aromatization of 16 alpha-hydroxylated androgens with human placental microsomes

A sensitive nonradiometric assay of aromatization of 16 alpha-hydroxylated androgens, 16 alpha-hydroxy-4-androstene-3,17-dione (16 alpha-OHA), and 16 alpha-hydroxytestosterone (16 alpha-OHT), has been developed using reverse-phase high-performance liquid chromatography with voltametric detector. The estrogens produced by human placental microsomes, estriol (E3) and 16 alpha-hydroxyestrone (16 alpha-OHE1), were simultaneously detected in quantities as low as 1-2 ng using 3-methoxy-1,3,5(10)-estratriene-2, 16 alpha,17 beta-triol as an internal standard. E3 was the only estrogen detected from the incubate of 16 alpha-OHT with the microsomes and NADPH, while 16 alpha-OHA gave 16 alpha-OHE1 and E3 under the same conditions. Apparent Km and Vmax of the microsomal aromatase for 16 alpha-OHA and 16 alpha-OHT were 2.56 microM and 71.4 pmol/min/mg and 13.33 microM and 15.4 pmol/min/mg, respectively.

Peripheral aromatization as a risk factor for breast and endometrial cancer in postmenopausal women: a review

In menopause, estrogens are produced almost exclusively through peripheral aromatization of androgens, especially androstenedione. Obesity increases the production rate of estrogens by means of the same mechanism. In postmenopause, plasma levels of SHBG diminish significantly. Obesity even further decreases the levels of SHBG, thus increasing "free" E2 available to target tissues. The increase in circulating estrogenic activity in menopause, whether as a result of obesity or of ingestion of estrogens, implies a risk factor for endometrial and breast cancer not only because of the permissive and stimulating effects of estrogens but also due to the special circumstance that they may act on target tissues in the almost absolute absence of the "protecting effect" of progesterone. The modifications performed by obesity on the values of SHBG and circulating estrogens are reversible, since they tend to normalize with weight loss.

Aromatization of 15 alpha and 16 alpha hydroxylated androgens in the human placental using [1,2-3H]-substrates

This in vitro study reports data on the aromatization of [1,2-3H]-C19 steroids in the human term placenta [androstenedione (III), testosterone (IV), 15 alpha-hydroxy-androstenedione (V), 15 alpha-hydroxy-testosterone (VI), 16 alpha-hydroxy-androstenedione (VII)]. The hydroxylated androgens were microbiologically synthesized from commercially radiolabelled [1,2-3H]-androstenedione and testosterone. Androstenedione and testosterone were good substrates for the human placental aromatase (low Km values, high Vmax); they strongly inhibited the 15 and 16 hydroxylated androgens aromatizations. On the other hand, these hydroxylated compounds acted as poor substrates and were only non-competitive inhibitors of the androstenedione and testosterone aromatizations. However, 15 alpha-hydroxy-androstenedione could not be disregarded as a potential precursor of 15 alpha-hydroxylated estrogens in the human placenta.

Substrate specificity of the placental microsomal aromatase

Using an accurate and sensitive assay for the human placental aromatase we have found apparent Km values for androstenedione (4-androstene-3,17-dione) and testosterone to be 14 +/- 4.0 nM and 41 +/- 12 nM respectively. These values were significantly different (p < 0.001). Analyses at substrate concentrations 5-10 fold above and below the Km values did not indicate any anomalous kinetic behavior. Mixed substrate experiments were consistent with a single enzyme metabolizing both steroids: each competitively inhibited the aromatization of the other, and the "Ki" values were the same as their apparent Km values. Sodium chloride (1.2M) significantly increased the rate of testosterone aromatization by decreasing its Km value and had no significant effect on the aromatization of androstenedione. However, in the presence of this salt testosterone still inhibited the aromatization of androstenedione competitively with a "Ki" equal to its apparent Km. Our data is therefore consistent with the proposal that human placental microsomes contain a single "high affinity" site for the aromatization of androstenedione and testosterone.

Synthesis and some reactions of 6-bromoandrogens: potential affinity ligand and inactivator of estrogen synthetase

The synthesis of epimeric 6-bromo-4-androstene-3,17-dione (1a and 1b), 6-bromotestosterone (2a and 2b) and its acetate (3a and 3b), and 6-bromo-16 alpha-acetoxy-4-androstene-3,17-dione (5a and 5b), and 6 beta-bromo-16 alpha-hydroxy-4-androstene-3,17-dione (4) is described. The interconversions among compounds 1, 2, and 3 are also studied. The 6 beta-isomer (1b, 2b, and 3b) was epimerized to the 6 alpha-isomer (1a, 2a and 3a) in carbon tetrachloride or chloroform-methanol (9:1) and the 6 alpha-isomer was isolated by fractional crystallization from the epimeric mixture. 6 alpha-Bromo isomer 1a was also epimerized back to 6 beta-bromo isomer 1b in chloroform-methanol (9:1). Two polymorphic forms of 6 beta-bromotestosterone acetate (3b) were isolated (mp. 114--117 degrees and 138--141 degrees). The 6 beta-bromo isomers were found to be unstable in methanol and decomposed to give 5 alpha-androstane-3,6-dione derivative (6). The results of irreversible inactivation of human placental androgen aromatase with some of these 6-bromoandrogens are discussed.

Steroid aromatization by a small particle fraction from porcine ovaries

Testosterone, 4-androstene-3,17-dione, 19-hydroxy-4-androstene-3,17-dione, 4alpha-5-oxido-5alpha-androstane-3,17-dione and 4beta-5-oxido-5beta-androstane-3,17-dione were compared as substrates for aromatization by the small particle fraction from sow ovaries. Relative conversion rates were: 19-hydroxy-4-androstene-3,17-dione:4-androstene-3,17-dione: testosterone: 4alpha-5-oxido-5alpha- and 4beta-5-oxido-5beta-androstane-3,17-dione; 100:32:20:congruent to O. Apparent Michaelis constants were 4.4 muM for 4-androstene-3,17-dione and 12 muM for testosterone. Maximum velocities were 0.20 pmoles/mg protein per min for androstenedione [1] and 0.16 for testosterone. The substrate preferences of the aromatizing system found in ovary are similar to those of the enzyme found in placenta.

Estrogen biosynthesis and 1beta-hydroxylation using C19 and 19-nor steroid precursors

(1) In order to study the relationship between aromatization (estrogen biosynthesis) and 1beta-hydroxylation, the effects of a variety of factors on these processes were evaluated. (2) Using the C18 substrate, 4-estrene-3,17-dione, it was found that carbon monoxide, SU-4885, amphenone B, potassium cyanide, 4-androstene-3,17-dione and 1,4-androstadiene-3,17-dione inhibited the above transformations significantly and to varying degrees. However, within a given experiment the inhibition of each process was similar. (3) SKF-525A did not inhibit either transformation. In addition, phosphate, Tris and barbital buffers, as well as pH changes from 6.9 to 7.7, had no stimulatory or inhibitory effect on the production of estrogen and 1beta-hydroxy compounds. (4) In contrast, several inhibitors affected the aromatization of C19 and C18 steroids differently. These include carbon monoxide, SU-4885 and amphenone B. (5) When a mixture of 4-[7beta-3Hi1estrene-3,17-dione and 19-[4-14C]nortestosterone were incubated together the former was preferentially converted to estrogen. This preference for the 17-keto steroidal form mimics results observed for C19 substrates. (6) We conclude that while estrogen biosynthesis and 1beta-hydroxylation appear to be mediated by the same enzyme system, the same conclusion cannot be drawn for the aromatization of C19 and C18 substrates.