The specificity of the 3beta-hydroxysteroid dehydrogenase activity of bovine ovaries toward dehydroepiandrosterone and pregnenolone: evidence for multiple enzymes

Estrogen receptors alpha (ERα) and beta (ERβ): subtype-selective ligands and clinical potential

Estrogen receptors alpha (ERα) and beta (ERβ) are nuclear transcription factors that are involved in the regulation of many complex physiological processes in humans. Modulation of these receptors by prospective therapeutic agents is currently being considered for prevention and treatment of a wide variety of pathological conditions, such as, cancer, metabolic and cardiovascular diseases, neurodegeneration, inflammation, and osteoporosis. This review provides an overview and update of compounds that have been recently reported as modulators of ERs, with a particular focus on their potential clinical applications.

Delta (5)3 beta hydroxysteroid dehydrogenase activity of the rat corpus luteum exhibits positive substrate-binding co-operativity: a continuous monitoring microdensitometric study with unfixed ovarian tissue sections

delta (5)3 beta hydroxysteroid dehydrogenase activity transforms biologically inactive delta (5)3 beta hydroxy steroids into the active delta (4)3-keto products (e.g. pregnenolone to progesterone). Using a cytochemical procedure which allows for the continuous microdensitometric monitoring of an enzyme reaction as it proceeds and a well described cytochemical assay for delta (5)3 beta HSD we have analysed the initial velocity rates (Vo) for dehydroepiandrosterone (DHEA) binding to this enzyme in regressing (i.e. 20 alpha hydroxy steroid dehydrogenase positive) corpus luteum (CL) cells in unfixed tissue sections (5 micron) of the dioestrous and proestrous rat ovary. The results are mean +/- S.E.M. The relationship between DHEA concentration (0 to 50 microM) and delta (5)3 beta HSD activity in the dioestrous corpora lutea was sigmoidal and had an atypical 1/Vo versus 1/S plot, the x intercept being positive. Using a 1/Vo versus 1/S2 plot the Vmax was determined to be 1.0 +/- 0.08 mumol min-1 mg-1 CL (n = 6). The Hill constant was 2.7 +/- 0.02 (n = 6) suggesting a high degree of positive co-operativity for DHEA binding. The S concentration for half maximal activity was 17 +/- 1 mumoles (n = 6). In the corpora lutea cells of the proestrous ovary, the Vmax for DHEA transformation was unchanged (0.95 +/- 0.04 mumol min-1 mg-1, n = 3) whilst the S0.5 was significantly increased to 27 +/- 0.1 (p less than 0.01, n = 3). The Hill constant remained positive being 2.9 +/- 0.2 (n = 3).(ABSTRACT TRUNCATED AT 250 WORDS)

3 beta-Hydroxysteroid dehydrogenase in human placental microsomes and mitochondria: co-solubilization of androstene and pregnene activities

3 beta-Hydroxysteroid dehydrogenase (3 beta-HSD) was solubilized from human term-placental microsomes and mitochondria using the non-ionic detergent, polyoxyethylene 20 cetyl ether (BrijR-58). Electron photomicrographs showed microsomes and mitochondria well disrupted by the detergent. The pregnene (C-21) and androstene (C-19) activities co-solubilized over a range (0.04-0.44) of BrijR-58/protein (B/P) concentration ratios (w/w). Optimal solubilization of the C-19 and C-21 activities were 63.3 +/- 2.6% (mean +/- SEM) from mitochondria (B/P ratio 0.37) and 71.8 +/- 2.1% from microsomes (B/P ratio 0.34). Detergent treatment of microsomes and mitochondria--varying time (5-90 min, pH 7.4) or varying pH (6.0-7.8, 90 min)--yielded C-19 activities identical with C-21 activities. The C-21/C-19 specific activity ratios of 3 beta-HSD in particulate, solubilized and chromatographed preparations were 2.28 +/- 0.16 (mean +/- SEM) for mitochondria and 1.97 +/- 0.07 for microsomes. 3 beta-HSD molecular weight estimates were 208,000 (microsomes) and 220,000 (mitochondria). These studies argue that a single protein is responsible for both the C-19 and C-21 activities of 3 beta-HSD and that this protein is the same in microsomes and mitochondria.

The application of continuous monitoring microdensitometry to an analysis of NAD+ binding and 3 beta-hydroxy-delta 5-steroid dehydrogenase activity in the regressing corpus luteum of the pro-oestrous rat ovary

A technique which allows for the continuous microdensitometric monitoring (at 3.3 s intervals) of an enzyme reaction has been applied to a study of 3 beta-hydroxy-delta 5-steroid dehydrogenase activity in regressing corpora lutea cells of unfixed tissue sections (5 micron thick) of the pro-oestrous rat ovary. Initial reaction rates for NAD+ reduction by the activity of the enzyme were maintained for less than 3 min at all the concentrations (0-500 mumol/l) of co-factor employed. The relationship between NAD+ concentration and enzyme activity under initial velocity rate conditions was hyperbolic and maximum enzyme activity was seen when the NAD+ concentration was greater than 250 mumol/l. The apparent Michaelis-Menten constant (Km) was 29 mumol/l and Vmax 0.63 mumol NAD+ reduced/min/cm3 corpora lutea.

Kinetic studies on the enzymes involved in estrogen biosynthesis and evidence for existence of a single 5-Ene-3beta-hydroxysteroid dehydrogenase complex in the ovary of the freshwater catfish, Clarias batrachus

Substrate velocity kinetics and other characteristics of two key enzymes involved in estrogen biosynthesis in the ovary of the catfish, Clarias batrachus, were studied. Enzyme reactions were measured spectrophotometrically during the initial phase of vitellogenesis. 5-Ene-3beta-hydroxysteroid dehydrogenase (5-ene-3beta-HSD) was found to have a different Michaelis-Menten constant (Km) for each of three 5-ene-3beta-hydroxysteroids, (pregnenolone (P5), 17alpha-hydroxypregnenolone (17alpha-P5), and dehydroepiandrosterone (DHA) but the constant for 17beta-hydroxysteroid dehydrogenase (17beta-HSD) was similar for both the substrates androstendione (A-dione) and estradiol-17beta (E2). 5-Ene-3beta-HSD required exclusively NAD as cofactor for the conversion of P5, 17alpha-P5, and DHA. A-dione was converted into testosterone (T) by a NADP-dependent 17beta-HSD, whereas there was an obligatory requirement of NAD for the conversion of E2 to estrone (E1). P5 was utilized more efficiently as substrate by 5-ene-3beta-HSD than DHA, as indicated by its lower Km/Vmax ratio. The rate of the combined substrate reaction was less than the sum of the rate of reactions measured separately for each of the three sets of substrate pairs. These results indicate that a single enzyme is responsible for the oxidation of three types of 5-ene-3beta-hydroxysteroids studied.

Inhibition of 3-beta-hydroxy steroid dehydrogenase activity in first trimester human pregnancy with trilostane and WIN 32729

The effects of equivalent doses of two inhibitors of the 3-beta-hydroxy steroid dehydrogenase enzyme system--WIN 24540 (trilostane) and WIN 32729--on the secretion of progesterone in early human pregnancy are described. Patients and controls less than 12 weeks pregnant were given a single dose of either drug and the resultant hormonal changes monitored for 7 1/2 h. A consistent fall in plasma progesterone concentrations occurred at all doses and, at the highest dose, they fell to less than 50% of pre-treatment levels. However, whilst with trilostane the associated increase in plasma concentrations of pregnenolone was always accompanied by a rise in plasma DHA concentrations, with WIN 32729 there appeared to be no adrenal effect at the lower dosage levels. These data demonstrate inhibition of progesterone secretion in human pregnancy using non-hormonally active steroids. The pattern of steroid precursors indicates that while both drugs inhibit 3-beta-hydroxy steroid dehydrogenase activity, WIN 32729 is more selective and only interferes with adrenal steroid biosynthesis at high doses.

Kinetic analysis of the placental microsomal 3 beta-hydroxysteroid dehydrogenase activity

A sensitive accurate assay for the placental microsomal 3 beta-hydroxysteroid dehydrogenase (E.C.1.1.1.51) has been developed using tritiated substrates. Kinetic analysis of the enzyme with 3 beta-hydroxy-5-androsten-17-one and 3 beta-hydroxy-5-pregnen-20-one indicates that the apparent Km values for these substrates are orders of magnitude less than previously described. Analyses were carried out with microsomal preparations from two different placentas. For placenta 1 the apparent Km value for 3 beta-hydroxy-5-androsten-17-one was 14 nM and for 3 beta-hydroxy-5-pregnen-20-one was 36 nM; for placental 2 apparent Km values were 19 nM and 42 nM respectively. The analyses were performed over wide ranges of substrate concentration (about 200 fold), both above and below the Km values and no deviation from linearity of Eadie-Hoftsee plots was observed.

Steroid specificity of human placental 5-ene-3 beta-hydroxysteroid oxidoreductase

The properties of 5-ene-3 beta hydroxysteroid oxidoreductase (3 beta-HSD) from human placental homogenates were studied in vitro. The apparent Michaelis constants for 3 beta-HSD with the substrates pregnenolone (delta 5P) and dehydroepiandrosterone (DHA) were 170 nM and nM respectively. The optimal pH for both these substrates was between 10 and 12. With NAD as the substrate, the Km for the pregnenolone was 20 microM and for DHA, 17 microM. The activity of 3 beta-HSD was inhibited by various steroids. Competitive inhibitors (pregnenolone substrate) included: ethynylestradiol (inhibition constant Ki=7.3 nM), DHA (Ki=46 nM), estradiol-17 beta (Ki=46 nM), cholesterol (Ki=0.68 microM) and 16 alpha-hydroxydehydroepiandrosterone (16 alphaOHDHA) (Ki=2.2 microM). When the substrate was DHA, competitive inhibition occurred with the following steroids: ethynylestradiol (Ki=6.4 nM), estradiol-17 beta (Ki=69 nM), pregnenolone (Ki=91 nM), cholesterol (Ki=1.3 microM) and 16 alphaOHDHA (Ki=1.9 microM). 4-Ene-3-ketosteroids such as androstenedione, progesterone (delta 4P), norethindrone and chlormadinone acetate acted as noncompetitive inhibitors towards both substrates.

3beta-Hydroxysteroid dehydrogenase activity in human fetal membranes

A 3beta-hydroxysteroid dehydrogenase (3betaHSD) was demonstrated in term human fetal membranes (chorion and amnion) with both dehydroepiandrosterone (3beta-hydroxy-5-androsten-17-one) and pregnenolone (3beta-hydroxy-5-pregnen-20-one as substrates, and the subcellular distribution substrate and nucleotide specificity of the enzyme was studied. In both membranes the microsomal fraction (particles which sedimented at 105,000 g after 90 min) had the highest specific activity. The chorion was more active than the amnion but the enzyme in both tissues had similar substrate and nucleotide specificity. NAD was the preferred cofactor, and pregnenolone was a better substrate than dehydroepiandrosterone in the presence of NAD. However, with NADP as cofactor both steroids were equally good substrates. When the 3beta-hydroxysteroid dehydrogenase activity of chorion microsomes was compared with that of placental microsomes, the specific activities were found to be of the same order of magnitude, and the substrate, nucleotide specificity and steroid binding properties were almost identical.

Solubilization and separation of delta5,3beta-hydroxysteroid dehydrogenase and 3-oxosteroid-delta4-delta5-isomerase from bovine adrenal cortex microsomes

A physical separation of delta5,3beta-hydroxysteroid dehydrogenase and 3-oxosteroid delta4-delta5-isomerase solubilized from bovine adrenocortical microsomes is described for the first time. The solubilization as well as the separation was carried out with a mixture of a detergent: a substituted betaine (Empigen BB/P) and sodium cholate. This latter detergent protects isomerase from complete inactivation by Empigen and is necessary for the recovery of a significant amount of soluble isomerase. Separation of dehydrogenase and isomerase was successfully accomplished by the use of a DEAE-Biogel A anion-exchanger. Dehydrogenase activity was eluted, while the isomerase was retained. Measurements of dehydrogenase activity with androst-5-en-3beta-ol-17-one, pregnen-3beta-ol-20-one and pregn-5-en-(3beta,17alpha)-diol-20-one and of isomerase activity with androst-5-en-(3,17)-dione and pregn-5-en-(3,20)-dione suggested that more than one isomerase and more than one dehydrogenase form were present.