Metabolism of androgens in human benign prostatic hyperplasia: aromatase and its inhibition

Estrogen and androgen signaling in the pathogenesis of BPH

Estrogens and androgens have both been implicated as causes of benign prostatic hyperplasia (BPH). Although epidemiological data on an association between serum androgen concentrations and BPH are inconsistent, it is generally accepted that androgens play a permissive role in BPH pathogenesis. In clinical practice, inhibitors of 5α-reductase (which converts testosterone to the more potent androgen dihydrotestosterone) have proven effective in the management of BPH, confirming an essential role for androgens in BPH pathophysiology. To date, multiple lines of evidence support a role for estrogens in BPH pathogenesis. Studies of the two estrogen receptor (ER) subtypes have shed light on their differential functions in the human prostate; ERα and ERβ have proliferative and antiproliferative effects on prostate cells, respectively. Effects of estrogens on the prostate are associated with multiple mechanisms including apoptosis, aromatase expression and paracrine regulation via prostaglandin E2. Selective estrogen receptor modulators or other agents that can influence intraprostatic estrogen levels might conceivably be potential therapeutic targets for the treatment of BPH.

Cutaneous androgen metabolism: basic research and clinical perspectives

The skin, especially the pilosebaceous unit composed of sebaceous glands and hair follicles, can synthesize androgens de novo from cholesterol or by locally converting circulating weaker androgens to more potent ones. As in other classical steroidogenic organs, the same six major enzyme systems are involved in cutaneous androgen metabolism, namely steroid sulfatase, 3beta-hydroxy-steroid dehydrogenase, 17beta-hydroxysteroid dehydrogenase, steroid 5alpha-reductase, 3alpha-hydroxysteroid dehydrogenase, and aromatase. Steroid sulfatase, together with P450 side chain cleavage enzyme and P450 17-hydroxylase, was found to reside in the cytoplasm of sebocytes and keratinocytes. Strong steroid sulfatase immunoreactivity was observed in the lesional skin but not in unaffected skin of acne patients. 3beta-hydroxysteroid dehydrogenase has been mainly immunolocalized to sebaceous glands, with the type 1 being the key cutaneous isoenzyme. The type 2 17beta-hydroxysteroid dehydrogenase isoenzyme predominates in sebaceous glands and exhibits greater reductive activity in glands from facial areas compared with acne nonprone areas. In hair follicles, 17beta-hydroxysteroid dehydrogenase was identified mainly in outer root sheath cells. The type 1 5alpha-reductase mainly occurs in the sebaceous glands, whereby the type II isoenzyme seems to be localized in the hair follicles. 3alpha-hydroxysteroid dehydrogenase converts dihydrotestosterone to 3alpha-androstanediol, and the use of 3alpha-androstanediol glucuronide serum level to reflect the hyperandrogenic state in hirsute women may be a reliable parameter, especially for idiopathic hirsutism. In acne patients it is still controversial if 3alpha-androstanediol glucuronide or androsterone glucuronide could serve as suitable serum markers for measuring androgenicity. Aromatase, localized to sebaceous glands and to both outer as well as inner root sheath cells of anagen terminal hair follicles, may play a "detoxifying" role by removing excess androgens. Pharmacologic development of more potent specific isoenzyme antagonists may lead to better clinical treatment or even prevention of androgen-dependent dermatoses.

Transdermal dihydrotestosterone treatment of 'andropause'

Male ageing coincides on average with progressive impairment of testicular function. The most striking plasma changes are an increase in sex hormone binding globulin (SHBG) and a decrease in non SHBG-bound testosterone, which is the only testosterone subfraction effectively bioavailable for target tissues. In healthy subjects the bioavailable testosterone declines by approximately 1% per year between 40 and 70 years but a more pronounced decline has been observed in non-healthy groups, especially in high cardiovascular risks groups. Relative androgen deficiency is likely to have unfavourable consequences on muscle, adipose tissue, bone, haematopoiesis, fibrinolysis, insulin sensitivity, central nervous system, mood and sexual function and might be treated by an appropriate androgen supplementation. The potential risk for prostate has been the main reason for limiting indications of such treatment. Testosterone (T) and dihydrotestosterone (DHT) are two potent androgens which have opposite effects regarding aromatase activity, an enzyme present in prostate stroma and suspected to have a pathogenic influence through local oestradiol synthesis. T is the main substrate for aromatase and oestradiol synthesis while DHT is not aromatizable and, at sufficient concentration, decreases T and oestradiol levels. A 1.8 years survey of 37 men aged 55-70 years treated with daily percutaneous DHT treatment suggested that high plasma levels of DHT (> 8.5 nmol/l) effectively induced clinical benefits while slightly but significantly reducing prostate size. Early stages of prostate hypertrophy require synergic stimulation by both DHT and oestradiol, and suppressing oestradiol instead of DHT seems easier and better adapted to the specific situation of aged hypogonadic men.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunohistochemical evidence of the existence and localization of aromatase in human prostatic tissues

Estrogens may be involved in normal growth of the prostate and the development of benign prostatic hyperplasia (BPH). The location of estrogen production is still unclear, and there has never been a direct evidence for the existence of the aromatase system, which converts androgens to estrogens, in the prostate. Using an avidin-biotin technique with a polyclonal anti-human placental aromatase, we demonstrated the existence of aromatase in normal prostates of young men and BPH tissue from elderly men. The staining is more pronounced in the stroma. However, positive stains were also seen in the glandular epithelium. While evidence of the existence of an enzyme system does not equal demonstration of its activity in a specific tissue site, our findings suggest that local estrogen production in the stroma and/or epithelium of the prostate may play a role in the maintenance of normal growth and development of BPH.

Androgen metabolism in control and neonatally estrogenized male mice

Reduction, oxidation, and aromatization of androgens were studied in the male genital tract of untreated control and neonatally estrogenized mice. This study shows regional differences in 5 alpha-reductase and 17 beta-hydroxysteroid oxidoreductase activities in untreated male genital tract; 3 alpha/3 beta-hydroxysteroid oxidoreductase (3 alpha/3 beta-HSOR) activity varied little between tissues. Neonatal treatment with diethylstilbestrol (DES, 2 micrograms/pup/day on days 1 through 5) caused an alteration in the androgen metabolism of the male genital tract, resulting in apparent decreased net accumulation of dihydrotestosterone (DHT). This developmentally-induced 5 alpha-reductase deficiency may play a role in the long-term inhibitory effects of early estrogenization by DES in the growth and function of male sex accessory glands. No aromatase activity could be demonstrated in the male genital tract of control or neonatally estrogenized mice.

Comparison of aromatase activity in human prostatic, testicular and placental tissues

The aromatase enzyme was quantified by the release of tritiated water from [1 beta-3H] androstenedione. Tritiated water was released by the crude homogenates in 4 of 18 samples of benign prostatic hyperplasia tissue and one of 5 samples of prostate carcinoma tissue. However, this apparent aromatase activity was not inhibited by 4-hydroxyandrostenedione (0.5 and 5.0 microM), and none of the particulate fractions (100,000 g pellet) prepared from each of the prostatic tissues exhibited aromatase activity. Particulate fractions from rat ovary (n = 3) and human testes (n = 6) displayed significant aromatase activity (mean values of 9.9 and 0.033 nmol estrone formed/g protein/h, respectively). The testicular aromatase was inhibited by aminoglutethimide, 4-hydroxyandrostenedione and CGS 16949A with IC50 values of 6.4, 0.17 and 0.0017 microM, respectively. These are of a similar order to values obtained with the aromatase enzyme from human placental microsomes (14, 0.43 and 0.0075 microM, respectively).

Aromatase and other inhibitors in breast and prostatic cancer

Estrogens have an important role in the growth of breast and other hormone-sensitive cancers. We have shown that 4-hydroxyandrostenedione (4-OHA) selectively blocks estrogen synthesis by inhibiting aromatase activity in ovarian and peripheral tissues and reduces plasma estrogen levels in rat and non-human primate species. In postmenopausal men and women, estrogens are mainly of peripheral origin. When postmenopausal breast cancer patients were administered either by daily oral or parenteral weekly treatment with 4-OHA, plasma estrogen concentrations were significantly reduced. Complete or partial response to treatment occurred in 34% of 100 patients with advanced breast cancer, while the disease was stabilized in 12%. We recently studied the effects of 4-OHA and other aromatase inhibitors, 10-propargylestr-4-ene-3,17-dione (PED) and imidazo[1,5-alpha]3,4,5,6-tetrahydropyrin-6-yl-(4-benzonitrile) (CGS 16949A) as well as 5 alpha-reductase inhibitors, N,N-diethyl-4-methyl-3-oxo-4-aza-5 alpha-androstane-17 beta-carboxyamide (4-MA) and 17 beta-hydroxy-4-aza-4-methyl-19norandrost-5-en-3-one (L651190) in prostatic tissue from 11 patients with prostatic cancer and six patients with benign prostatic hypertrophy (BPH), and from normal men at autopsy. We attempted to measure aromatase activity in tissue incubation by quantitating 3H2O released during aromatization of androstenedione or testosterone labeled at the C-1 position. The amount of 3H2O released from all samples was at least twice that of the heat inactivated tissue samples. The 3H2O release was significantly inhibited by 4-OHA and 4-MA, but not by the other aromatase inhibitors. However, when HPLC and TLC were used to isolate steroid products, no estrone or estradiol was detected in the incubates. Furthermore, no aromatase mRNA was detected following amplification by PCR. The 4-OHA was found to inhibit 5 alpha-reductase in both BPH and cancer tissue, although to a lesser extent than 4-MA. The other aromatase inhibitors were without effect. Although a mechanism involving intraprostatic aromatase is not likely, inhibitors may act to reduce peripherally-formed estrogens. In postmenopausal breast cancer, the results indicate that 4-OHA is of significant benefit.

Epitestosterone--an endogenous antiandrogen?

Epitestosterone (17 alpha-hydroxy-4-androsten-3-one), a normal constituent of human plasma and urine, prevents the testosterone induced changes in body weight and in organ weights of seminal vesicles and kidney of castrated male mice. It competes with methyltrienolone in the binding to rat prostate cytosol (Ki = 29.8 nmol.l-1. It inhibits also the activity of 5 alpha-reductase from rat prostate pellet (Ki = 1.2 mumols.l-1). Epitestosterone can be considered as a weak antiandrogen in the term of displacement of androgen from receptor binding and as an efficient inhibitor of 5 alpha-reductase.

Steroid sulfate sulfatase in human benign prostatic hyperplasia: characterization and quantification of the enzyme in epithelium and stroma

Characteristics and activities of estrone sulfate (E1S) and dehydroepiandrosterone sulfate (DHAS) sulfatases were studied in epithelium and stroma of benign hyperplastic tissues from human prostates. Tissues were obtained by suprapubic prostatectomy, and epithelium and stroma were separated mechanically by standard techniques. The assay procedure comprised homogenization in Tris-buffer, incubation of the homogenate with [3H]E1S or [3H]DHAS, separation of free steroids from nonhydrolyzed steroid sulfates by extraction with ether, and their final quantification by LSC. The main results were: (1) The pH-optimum of the sulfatase was found at pH 7.0. (2) The highest specific sulfatase activity was found in the epithelium and was associated with its nuclear fraction. (3) Michaelis-Menten constants Km (microM) were 8.7 +/- 1.4 (7) and 4.3 +/- 0.8 (5), maximum velocity rates Vmax (nmol/h x mgDNA) were 47.4 +/- 8.8 (7) and 8.4 +/- 1.5 (5) for E1S and DHAS, respectively (means +/- SEM (n]. (4) The enzymatic cleavage of E1-sulfate was competitively inhibited by DHA-sulfate and vice versa with inhibition constants Ki (microM) of 4.0 +/- 0.5 (2) for E1S and 2.7 +/- 0.4 (2) for DHAS. On the basis of these findings, possible roles of steroid sulfate-sulfatases in forming precursors of active androgens and estrogens from the high amounts of E1S and DHAS in blood are discussed.

Inhibition of human placental aromatase in a perfusion model. Comparison with kinetic, cell-free experiments

In vitro perfusion of human placenta was evaluated for characterization of aromatase inhibitors. The results were compared with those in kinetic experiments in cell-free system. Inhibition constants (Ki) were determined by measuring the release of tritiated water during coincubation of human placenta microsomes with varying amounts of [1 beta,2 beta 3H]androstenedione and inhibitor in the presence of NADPH-generating system. Irreversible inactivation constants (Kinact) were determined in a similar manner following preincubation of the microsomes with different amounts of inhibitor for varying times. Lineweaver-Burk plots indicated a competitive type of inhibition with Ki values of 37 nM for 4-hydroxy-androstenedione, 3,700 nM for testolactone, 15 nM for 1-methyl-androsta-1,4-diene-3,17-dione, and 7.5 nM for 19-azido-androstenedione. Additionally, irreversible enzyme inactivation by all four substances could be demonstrated with Kinact values of 3.64 x 10(-3), 0.57 x 10(-3), 0.34 x 10(-3), and 0.69 x 10(-3)sec-1, respectively. Perfusion of a single cotyledon of human term placenta was performed by infusing medium through catheters placed in a fetal artery and in the maternal intervillous space. Perfused medium was collected from a cannulated fetal vein and from the maternal basal plate. The medium was supplemented with [3H]androstenedione (4.2 nM) and inhibitor. The perfusates were analyzed for their [3H]estrone and estradiol content following phenolic partition and Sephadex-LH 20 chromatography. The main results were, (1) the recovery of labelled steroids increased rapidly after perfusion started and reached a plateau within 60 min, when 55 and 30% (mean values) of the infused radioactivity were recovered in the fetal and maternal perfusates, respectively, (2) similar amounts of estrone and estradiol were found in both effluates, whereas androgens (mainly androstenedione and lower amounts of 5 alpha-androstane-3,17-dione) were found nearly exclusively in the fetal perfusate, (3) formation of estrogens (estrone + estradiol) reached a plateau within 20 min of perfusion. (4) The percentage of estrogens formed was not changed by increasing androstenedione concentration in the perfusion medium unless this concentration exceeded 3.5 microM indicating limited capacity of aromatase. (5) The four aromatase inhibitors reduced estrogen formation by 50% at concentrations about 100-fold of their Ki determined in the cell-free system, (6) irreversible aromatase inhibition could not be demonstrated in the perfusion model. It was concluded that the human placenta perfusion model can be successfully used to evaluate aromatase inhibitors.