Effects of estrogen deprivation on human benign prostatic hyperplasia

Phytosterols activating nuclear receptors are involving in steroid hormone-dependent cancers: Myth or fact?

Nuclear receptors (NRs) represent intracellular proteins that function as a signaling network of transcriptional factors to control genes in response to a variety of environmental, dietary, and hormonal stimulations or serve as orphan receptors lacking a recognized ligand. They also play an essential role in normal development, metabolism, cell growth, cell division, physiology, reproduction, and homeostasis and function as biological markers for tumor subclassification and as targets for hormone therapy. NRs, including steroid hormone receptors (SHRs), have been studied as tools to examine the fundamentals of transcriptional regulation within the development of mammals and human physiology, in addition to their links to disturbances. In this regard, it is widely recognized that aberrant NR signaling is responsible for the pathological growth of hormone-dependent tumors in response to SHRs dysregulation and consequently represents a potential therapeutic candidate in a range of diseases, as in the case of prostate cancer and breast cancer. On the other hand, phytosterols are a group of plant-derived compounds that act directly as ligands for NRs and have proven their efficacy in the management of diabetes, heart diseases, and cancers. However, these plants are not suggested in cases of hormone-dependent cancer since a certain group of plants contains molecules with a chemical structure similar to that of estrogens, which are known as phytoestrogens or estrogen-like compounds, such as lignans, coumestans, and isoflavones. Therefore, it remains an open and controversial debate regarding whether consuming a phytosterol-rich diet and adopting a vegetarian lifestyle like the Mediterranean diet may increase the risk of developing steroid hormone-dependent cancers by constitutively activating SHRs and thereby leading to tumor transformation. Overall, the purpose of this review is to better understand the relevant mechanistic pathways and explore epidemiological investigations in order to establish that phytosterols may contribute to the activation of NRs as cancer drivers in hormone-dependent cancers.

The Protective Effect of Dietary Phytosterols on Cancer Risk: A Systematic Meta-Analysis

BACKGROUNDS/AIMS

Many studies have explored the association between dietary phytosterols and cancer risk, but the results have been inconsistent. We aimed to provide a synopsis of the current understanding of phytosterol intake for cancer risk through a systematic evaluation of the results from previous studies.

METHODS

We performed a literature search of PUBMED, EMBASE, CNKI, and Wanfang, and studies published before May 2019 focusing on dietary total phytosterols, β-sitosterol, campesterol, stigmasterol, β-sitostanol, and campestanol, as well as their relationships with cancer risk, were included in this meta-analysis. Summaries of the relative risks from 11 case-control and case-cohort studies were eventually estimated by randomized or fixed effects models.

RESULTS

The summary relative risk for the highest versus the lowest intake was 0.63 (95% confidence interval [CI] = 0.49-0.81) for total phytosterols, 0.74 (95% CI = 0.54-1.02) for β-sitosterol, 0.72 (95% CI = 0.51-1.00) for campesterol, 0.83 (95% CI = 0.60-1.16) for stigmasterol, 1.12 (95% CI = 0.96-1.32) for β-sitostanol, and 0.77 (95% CI = 0.65-0.90) for campestanol. In a dose-response analysis, the results suggested a linear association for campesterol and a nonlinear association for total phytosterol intake.

CONCLUSION

Our findings support the hypothesis that high phytosterol intake is inversely related to risk of cancer. Further studies with prospective designs that control for vital confounders and investigate the important anticancer effects of dietary phytosterols are warranted.

Phytosterols and Triterpenoids for Prevention and Treatment of Metabolic-related Liver Diseases and Hepatocellular Carcinoma

Background:

Liver ailments are among the leading causes of death; they originate from viral infections, chronic alcoholism, and autoimmune illnesses, which may chronically be precursors of cirrhosis; furthermore, metabolic syndrome may worsen those hepatopathies or cause Non-alcoholic Fatty Liver Disease (NAFLD) that may advance to non-alcoholic steatohepatitis (NASH). Cirrhosis is the late-stage liver disease and can proceed to hepatocellular carcinoma (HCC). Pharmacological treatment options for liver diseases, cirrhosis, and HCC, are limited, expensive, and not wholly effective. The use of medicinal herbs and functional foods is growing around the world as natural resources of bioactive compounds that would set the basis for the development of new drugs.

Review and Conclusion:

Plant and food-derived sterols and triterpenoids (TTP) possess antioxidant, metabolic-regulating, immunomodulatory, and anti-inflammatory activities, as well as they are recognized as anticancer agents, suggesting their application strongly as an alternative therapy in some chronic diseases. Thus, it is interesting to review current reports about them as hepatoprotective agents, but also because they structurally resemble cholesterol, sexual hormones, corticosteroids and bile acids due to the presence of the steroid nucleus, so they all can share pharmacological properties through activating nuclear and membrane receptors. Therefore, sterols and TTP appear as a feasible option for the prevention and treatment of chronic metabolic-related liver diseases, cirrhosis, and HCC.

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.

Polyphenol composition and antioxidant capacity of Epilobium species

Epilobium species (Onagraceae) are commonly used herbal remedies in traditional, adjuvant therapy of benignus prostate hyperplasia (BPH), however the pharmacological and clinical standardization of commercially available Epilobii herba (willow-herb) remains difficult. Willow-herb products usually consist of mixtures from various species, with different phenoloid content, often only partially identified. The present study reports comprehensive LC-MS/MS investigation on the polyphenol composition of the most common Epilobium species, emphasizing the pharmaceutical importance of a uniform standardization protocol in case of their products. The antioxidant capacity of species was evaluated by a simple spectrophotometric method, using ABTS(+) (2,2'azinobis-(3-ethylbenzthiazoline-6-sulfonic acid)). High ratio of macrocyclic tannins, mainly oenothein B was identified in all Epilobium species examined. Flavonoid composition of Epilobium extracts showed several differences, especially comparing E. angustifolium to other species. Myricetin, quercetin, kaempferol and their various glycosides were dominant in samples, but their combination and ratio were distinctive in all cases. Epilobium extracts showed high radical-scavenger activity, comparable to that of well-known antioxidants, Trolox and ascorbic acid. Among species examined, extract of Epilobium parviflorum possessed the highest antioxidant capacity (EC(50)=1.71+/-0.05 microg/ml).

Expression of enzymes involved in estrogen metabolism in human prostate

There is evidence that estrogens can directly modulate human prostate cell activity. It has also been shown that cultured human prostate cancer LNCaP can synthesize the active estrogen estradiol (E2). To elucidate the metabolism of estrogens in the human prostate, we have studied the expression of enzymes involved in the formation and inactivation of estrogens at the cellular level. 17beta-Hydroxysteroid dehydrogenase (17beta-HSD) types 1, 2, 4, 7, and 12, as well as aromatase mRNA and protein expressions, were studied in benign prostatic hyperplasia (BPH) specimens using in situ hybridization and immunohistochemistry. For 17beta-HSD type 4, only in situ hybridization studies were performed. Identical results were obtained with in situ hybridization and immunohistochemistry. All the enzymes studied were shown to be expressed in both epithelial and stromal cells, with the exception of 17beta-HSD types 4 and 7, which were detected only in the epithelial cells. On the basis of our previous results, showing that 3beta-HSD and 17beta-HSD type 5 are expressed in human prostate, and of the present data, it can be concluded that the human prostate expresses all the enzymes involved in the conversion of circulating dehydroepiandrosterone (DHEA) to E2. The local biosynthesis of E2 might be involved in the development and/or progression of prostate pathology such as BPH and prostate cancer through modulation of estrogen receptors, which are also expressed in epithelial and stromal cells.

Polymorphisms in genes involved in sex hormone metabolism may increase risk of benign prostatic hyperplasia

BACKGROUND

This study investigates associations between polymorphisms in genes involved in sex hormone metabolism and measures of benign prostatic hyperplasia (BPH).

METHODS

Community-dwelling Caucasian men (n=510, median age 60 years in 2000) from the Olmsted County, MN, participated in a longitudinal study of BPH. From 1990 through 2000, urologic measures of BPH were assessed biennially from lower urinary tract symptom severity, peak flow rates, prostate volume, serum prostate specific antigen (PSA) level, acute urinary retention, and treatment for BPH. Men were genotyped for polymorphisms in genes involved in sex hormone metabolism.

RESULTS

With the wildtype genotype as reference, men with HSD3B1 (c.1100 A/C) heterozygous genotype (hazard ratio (HR)=0.7, 95% confidence intervals (CI)=0.6, 0.9) were at decreased risk of an enlarged prostate and men with CYP19 (TTTA)(n) genotype homozygous for >or=175 TTTA repeats (HR=1.5, 95% CI=1.1, 2.1), and CYP19 (c.1531 C/T) homozygous T variant (HR=1.6, 95% CI=1.1, 2.2) were at increased risk of an enlarged prostate. The homozygous A variant of the PSA gene (g.-252 G/A), was associated with treatment for BPH (HR=2.3, 95% CI=1.2, 4.4). In multivariate analyses, the homozygous variant genotypes of AKR1C3 (c.15 G/A and c.90 G/A) were associated with a decreased risk of an enlarged prostate (HR=0.56, 95% CI=0.35, 0.90 and HR=0.57, 95% CI=0.33, 0.98).

CONCLUSIONS

Polymorphisms in HSD3B1, CYP19, AKR1C3 genes may be associated with an enlarged prostate in older men. These data provide insights into genes that should be examined further for their potential role in the pathogenesis of BPH.

Androgen Replacement Therapy

The major goal of androgen substitution is to replace testosterone at levels as close to physiological levels as is possible. For some androgen-dependent functions testosterone is a pro-hormone, peripherally converted to 5alpha-dihydrotestosterone (DHT) and 17beta-estradiol (E2), of which the levels preferably should be within normal physiological ranges. Furthermore, androgens should have a good safety profile without adverse effects on the prostate, serum lipids, liver or respiratory function, and they must be convenient to use and patient-friendly, with a relative independence from medical services. Natural testosterone is viewed as the best androgen for substitution in hypogonadal men. The reason behind the selection is that testosterone can be converted to DHT and E2, thus developing the full spectrum of testosterone activities in long-term substitution. The mainstays of testosterone substitution are parenteral testosterone esters (testosterone enantate and testosterone cipionate) administered every 2-3 weeks. A major disadvantage is the strongly fluctuating levels of plasma testosterone, which are not in the physiological range at least 50% of the time. Also, the generated plasma E2 is usually supraphysiological. A major improvement is parenteral testosterone undecanoate producing normal plasma levels of testosterone for 12 weeks, with normal plasma levels of DHT and E2 also. Subcutaneous testosterone implants provide the patient, depending on the dose of implants, with normal plasma testosterone for 3-6 months. However, their use is not widespread. Oral testosterone undecanoate dissolved in castor oil bypasses the liver via its lymphatic absorption. At a dosage of 80 mg twice daily, plasma testosterone levels are largely in the normal range, but plasma DHT tends to be elevated. For two decades transdermal testosterone preparations have been available and have an attractive pharmacokinetic profile. Scrotal testosterone patches generate supraphysiological plasma DHT levels, which is not the case with the nonscrotal testosterone patches. Transdermal testosterone gel produces fewer skin irritations than the patches and offers greater flexibility in dosage. Oromucosal testosterone preparations have recently become available. Testosterone replacement is usually of long duration and so patient compliance is of utmost importance. Therefore, the patient must be involved in the selection of type of testosterone preparation. Administration of testosterone to young individuals has almost no adverse effects. With increasing age the risk of adverse effects on the prostate, the cardiovascular system and erythropoiesis increases. Consequently, short-acting testosterone preparations are better suited for aging androgen-deficient men.

Identification of genes involved in estrogenic action in the human prostate using microarray analysis

Estrogens have profound effects on the developing prostate and are suspected to contribute to the development of benign prostatic hyperplasia, but the mechanism by which this hormone elicits its regulatory function still remains largely unknown. Using complementary RNA microarrays comprising approximately 10,000 oligonucleotide gene targets we compared differences in mRNA expression of estradiol-treated and untreated prostatic stromal cells in vitro. Based on a threshold of greater than twofold change, 228, 241, and 464 of the expressed genes were found to be regulated by estradiol after 10, 24, and 48 h of treatment, respectively. The secondary analysis of one estradiol-activated transcript, namely lipopolysaccharide-binding protein, and four estradiol-repressed genes, namely ras homolog gene family member E (RhoE/Rnd3), ubiquitin thiolesterase, interleukin 6, and interleukin 8 (IL-8), by real-time quantitative PCR confirmed the results of the microarray analysis. Moreover, IL-8 and RhoE were found to be down-regulated by estradiol at the protein level as well. We identified a set of genes involved in a wide range of cellular functions that are potentially important for understanding the molecular basis of estradiol action in the prostate.

Testosterone metabolism, dose-response relationships and receptor polymorphisms: selected pharmacological/toxicological considerations on benefits versus risks of testosterone therapy in men

In this review selected toxicological problems related to testosterone therapy in hypogonadal men are discussed. Applying "classical" pharmacological/toxicological findings (e.g. animal studies on short- and long-term toxicity) to clinical situations is not very helpful. Molecular biological knowledge and especially evaluation of epidemiological studies, as well as intervention studies, on testosterone therapy in hypogonadal men are more useful. Potential risks include overdosage for lifestyle reasons, e.g. excessive muscle building and reduction of visceral obesity, when erythrocytosis occurs concomitantly. Modern galenic formulations of testosterone administration (e.g. transdermal gel, suitable testosterone esters for intramuscular application and newer oral preparations) avoid supraphysiological serum concentrations, therefore significantly reducing the toxicological risk. A hypothetical model of the toxicological risks of testosterone therapy is given that is based on the influence of testosterone metabolism (aromatization vs. reduction) of the respective parameter/target chosen. Finally, the great influence of polymorphisms of the androgen receptor on the assessment of toxicological risk and on the individualization of androgen therapy is shown. Already existing national, continental and international guidelines or recommendations for the testosterone therapy should be harmonized.

Androgen deficiency in the aging male: benefits and risks of androgen supplementation

There is now convincing evidence that in a subset of aging men, increasing with age, plasma testosterone levels fall below a critical level resulting in hypogonadism. This state of testosterone deficiency has an impact on bone, muscle and brain function and is maybe a factor in the accumulation of visceral fat which again has a significant impact on the cardiovascular risk profile. From the above it follows that androgen replacement to selected men with proven androgen deficiency will have beneficial effects. There is, however a concern that androgen administration to aging men may be harmful in view of effects on prostate disease. Benign prostate hyperplasia (BPH) and prostate cancer are typically diseases of the aging male, steeply increasing with age. But epidemiological studies provide no clues that the levels of circulating androgen are correlated with or predict prostate disease. Similarly, androgen replacement studies in men do not suggest that these men suffer in a higher degree from prostate disease than control subjects. It seems a defensible practice to treat aging men with androgens if and when they are testosterone-deficient, but long-term studies including sufficient numbers of men are needed.

Phytosterols as anticancer dietary components: evidence and mechanism of action

Phytosterols (PS) or plant sterols are structurally similar to cholesterol. The most common PS are beta-sitosterol, campesterol and stigmasterol. Epidemiologic and experimental studies suggest that dietary PS may offer protection from the most common cancers in Western societies, such as colon, breast and prostate cancer. This review summarizes the findings of these studies and the possible mechanisms by which PS offer this protection. These include the effect of PS on membrane structure and function of tumor and host tissue, signal transduction pathways that regulate tumor growth and apoptosis, immune function of the host and cholesterol metabolism by the host. In addition, suggestions for future studies to fill the gaps in our knowledge have been given.

Role of estrogens in human benign prostatic hyperplasia

The aging process is associated with a progressive decline of plasma testosterone levels, while estrone and estradiol remain unchanged and sex hormone binding globulin (SHBG) increases, with reduction of bioavailable testosterone in prostatic tissue with benign prostatic hyperplasia (BPH) the most important androgen is dihydrotestosterone: with its receptors it is almost uniformly distributed in the epithelial and stromal compartment and is not supranormal. Intraprostatic estrogens and their receptors are elevated and concentrated in the stroma. Androgens may act on the prostate indirectly through the production of growth factors; in human BPH no clear evidence exists on the modulatory effect of estrogens on bFGF, KGF and TGFbeta formation. A western diet, characterized by high fat consumption, predisposes men to BPH, while a diet rich in flavonoids and lignanes, containing phyto-estrogens, lowers this risk. These data suggest that in the medical treatment of BPH, antiestrogens or aromatase inhibitors may be used: however, up to now the clinical results of this treatment are not promising and the improvement of the obstructive symptoms does not exceed that of placebo. A possible explanation of this unsatisfactory result could be that the estrogen reduction secondary to the use of aromatase inhibitors is counterbalanced by the rise of androgen precursors.

Relative potency of testosterone and dihydrotestosterone in preventing atrophy and apoptosis in the prostate of the castrated rat

Although dihydrotestosterone (DHT) is the principal androgen in the prostate, testosterone can also act as an androgen in this tissue. To determine the relative potencies of testosterone and DHT in preventing prostate regression, castrated rats were implanted for 4 d with varying doses of testosterone in the presence or absence of the 5alpha-reductase inhibitor finasteride. In the absence of finasteride, testosterone in the prostate is converted to DHT, creating an intraprostatic DHT dose response. In the presence of finasteride, this conversion is blocked, and an intraprostatic testosterone dose response is achieved. DHT was 2.4 times more potent than testosterone at maintaining normal prostate weight and duct lumen mass, a measure of epithelial cell function. The two androgens were equipotent at preventing DNA fragementation and expression of testosterone-repressed prostate message, two measures of apoptosis (cell death). The intraprostatic testosterone concentration that results from finasteride treatment in rats is sufficient to inhibit apoptosis but will not maintain normal epithelial cell activity. In conclusion, whereas DHT is more potent than testosterone at stimulating prostate epithelial cell function as measured by ductal mass, the two androgens are equipotent at preventing prostate cell death after castration. These results explain why finasteride causes prostate involution in the rat with minimal evidence of prostate cell death.

Effect of aromatase inhibitor, TZA-2209, on the prostate of androstenedione-treated castrated dogs: changes in prostate volume and histopathological findings

To determine whether the inhibition of estrogen-related effect in the prostate would be of value in the management of benign prostate hyperplasia (BPH), we examined the effect of TZA-2209, a new steroidal aromatase inhibitor, on the prostate in three of six castrated beagles that received 75 mg/week androstenedione. The three other animals served as controls. Sequential measurements of prostate volume by transrectal ultrasonography showed that the volume in TZA-treated dogs was significantly decreased compared with that in the controls. Prostatic aromatase activity was suppressed by TZA administration. Histopathologically, the stromal component was increased and glands were atrophied by androstenedione treatment. TZA administration increased the volume of the glands. Immunohistochemical detection of estramustine-binding protein showed more positive staining of the protein in the glands that were increased in volume by TZA administration. We concluded that the aromatase inhibitor effectively antagonized the estrogen-related stromal changes, however, this action was accompanied by stimulation of the glandular component due to the accumulation of androgens, the substrate of the aromatase. In the light of these findings, we suggest the simultaneous treatment for the androgen-glandular component route in the prostate is necessary for the effective management of BPH.

Expression of estrogen receptor in diseased human prostate assessed by non-radioactive in situ hybridization and immunohistochemistry

To understand the role of estrogen in the pathogenesis of benign prostatic hyperplasia, expressions of estrogen receptor (ER) mRNA and ER protein by in situ hybridization and by immunohistochemistry, respectively, were investigated in human prostatic tissues. In non-malignant region, ER mRNA and ER protein were found in cytoplasm and nucleus, respectively, of stromal cells, but not in glandular epithelial and basal cells. In benign regions, ER mRNA/ER protein positive cells were found in fibromyoadenomatous and myoadenomatous hyperplasia, but not in adenomatous hyperplasia. A striking feature was periacinar arrangement of ER mRNA/ER protein positive stromal cells in all prostate carcinoma treated with androgen withdrawal. The ER mRNA/ER protein positive cells were immunohistochemically identified as fibroblasts, myoblasts, and smooth muscle cells. These results indicate that stromal cells are the primary target of estrogen in prostate, and that androgen withdrawal upregulates the expression of ER gene.

Placebo controlled double-blind study to test the efficacy of the aromatase inhibitor atamestane in patients with benign prostatic hyperplasia not requiring operation. The Schering 90.062 Study Group

PURPOSE

We tested the theoretical concept that a selective decrease in estrogens has a beneficial therapeutic effect on established benign prostatic hyperplasia.

MATERIALS AND METHODS

In a double-blind study 160 patients from 14 centers were randomized between 2 groups to receive either placebo or the aromatase inhibitor atamestane (1-methyl-androsin-1,4 diene-3 17-dione, 400 mg. daily for 48 weeks).

RESULTS

The aromatase inhibitor decreased the mean estradiol level by approximately 40% and estrone by 60%. The testosterone concentration increased by more than 40% and dihydrotestosterone increased to 30%. Analysis of clinical parameters showed no difference between placebo and atamestane.

CONCLUSIONS

The counter regulatory increase in androgens may counterbalance any positive effect of the decrease in estrogens to preserve intraprostatic homeostasis.

Benign prostatic hyperplasia

Benign prostatic hyperplasia (BPH) is a pathologic disorder that develops in response to the action of dihydrotestosterone on the aging prostate and to changes in stromal and epithelial cells in this exocrine gland. The current therapies for this disorder are chosen after other causes for irritative and obstructive symptoms have been excluded and the status of the urinary tract has been assessed. This evaluation includes a detailed medical history, a thorough genitourinary and neurological examination, assessment of serum prostate specific antigen and creatinine levels, as well as a urinalysis. A urodynamic evaluation consisting of a combined pressure-flow study is required if the diagnosis of obstruction is to be made. Patients with minimal symptoms and normal test results require no therapy. Mild to moderate symptoms can be controlled, at least temporarily, with alpha-adrenergic blockers such as terazosin or doxazosin. A subset of BPH patients with obstructive symptoms respond to the 5 alpha-reductase inhibitor finasteride. Early results with minimally invasive treatments such as laser prostatectomies, hyperthermia, and ultrasonic and radiofrequency ablation appear encouraging for those with moderate symptoms of prostatism. Severe symptoms, urinary retention, gross hematuria, recurrent urinary tract infections, bladder calculi, and hydronephrosis or renal insufficiency warrant transurethral incision, resection, vaporization, or open prostatectomy (for very large neoplasms). Although the morbidities of these latter surgical therapies are not insignificant, these treatments offer the best and most durable results for relief of obstruction and amelioration of symptoms.

Effects of hormones on the prostate in adult and aging men and animals

Literature on the effect of steroid hormones (androgens, estrogens, and other steroids), of peptide hormones (e.g., prolactin), and growth factors (e.g., EGF, FGF, TGF-beta), on the effect of castration and of experimental hormone application on the prostate is reviewed. Androgens have inductive, repressive, and interactive effects. They counterbalance an agonistic effect on proliferation and an antagonistic effect on cell death; they may influence DNA synthesis and induce the synthesis of substances with mitogenic effects on the prostate. Estrogens exert direct and indirect effects on the prostate. They suppress the secretion of gonatropins, thus repressing testicular androgen secretion. They stimulate the fibromuscular stroma and induce squamous metaplasia of the epithelium. Estrogens may also be involved in the onset of benign prostatic hyperplasia. Prolactin is preferentially bound in the diseased human prostate. An abundance of information has been gained on EGF, FGF, TGF-beta, and other growth factors. They may be involved in the development of prostatic hyperplasia. Castration leads to a striking reduction in prostatic size in a short period of time due to autophagic and heterophagic processes. In castrated individuals, the prostate is enriched in androgen-independent cells. Experimental hormone application involves the substitution of androgens as well as anti-androgens, long-term application of different hormones, and application of combinations of drugs. The results of several studies are described. Further directions in the field of prostate research should concentrate on the role of growth factors in prostate development and pathology and on the effect of certain lectins on prostate diseases. We think that the investigation of interactions between steroid hormones and growth factors in normal and pathological neovascularization of the prostate is important.

Strictosidine synthase from Catharanthus roseus: purification and characterization of multiple forms

Multiple (six) forms of strictosidine synthase from Catharanthus roseus cell suspension cultures were purified and characterized. A purification protocol is presented composed of hydrophobic-interaction, gel-permeation and ion-exchange chromatography and chromatofocusing. Four of six isoforms were purified to apparent homogeneity, whereas two others were nearly homogeneous. All strictosidine synthase isoforms were found to be glycoproteins. The isoforms were also found in leaves and roots of the plant, in seedlings and in hairy root cultures. The ratio of the different isoforms differed slightly between these sources. The kinetic parameters of the isoforms showed no significant differences. The maximal velocity (300-400 nkat/mg of protein) is the highest reported so far. It was demonstrated that the apparent Michaelis constant for tryptamine (approx. 9 microM) is much lower than values reported previously. The presence of weak product inhibition (Kp approx. 35 times Km) was established, whereas substrate inhibition was not detected.

Estradiol causes the rapid accumulation of cAMP in human prostate

Androgens are widely acknowledged to be central to the pathogenesis of benign prostatic hypertrophy (BPH). However, BPH increases in prevalence as men age, at precisely the stage of life when plasma androgens are decreasing. The decrease in total plasma androgens is amplified by an age-related increase in plasma sex hormone-binding globulin (SHBG) that results in a relatively greater decrease in free androgens than in total androgens. In addition, estrogens have long been suspected to be important in BPH, but a direct effect on the human prostate has never been demonstrated. We present data that are consistent with a role for estradiol, and for a decrease in androgens and an increase in SHBG, in the pathogenesis of BPH. We show that estradiol, but not dihydrotestosterone, acts in concert with SHBG to produce an 8-fold increase in intracellular cAMP in human BPH tissue. This increase is not blocked by an antiestrogen and is not provoked by an estrogen (diethylstilbestrol) that does not bind to SHBG, thus excluding the classic estrogen receptor as being operative in these events. Conversely, dihydrotestosterone, which blocks the binding of estradiol to SHBG, completely negates the effect of estradiol. Finally, we demonstrate that the SHBG-steroid-responsive second-messenger system is primarily localized to the prostatic stromal cells and not to the prostatic epithelial cells. Thus, we have shown a cell-specific, powerful, nontranscriptional effect of estradiol on the human prostate.

Novel aromatase and 5 alpha-reductase inhibitors

Inhibitors of aromatase and 5 alpha-reductase may be of use for the therapy of postmenopausal breast cancer and benign prostatic hyperplasia, respectively. FCE 27993 is a novel steroidal irreversible aromatase inhibitor structurally related to exemestane (FCE 24304). The compound was found to be a very potent competitive inhibitor of human placental aromatase, with a Ki of 7.2 nM (4.3 nM for exemestane). In preincubation studies with placental aromatase FCE 27993, like exemestane, was found to cause time-dependent inhibition with a higher rate of inactivation (t1/2 4.5 vs 15.1 min) and a similar Ki(inact) (56 vs 66 nM). The compound was found to have a very low binding affinity to the androgen receptor (RBA 0.09% of dihydrotestosterone) and, in contrast to exemestane, no androgenic activity up to 100 mg/kg/day s.c. in immature castrated rats. Among a series of novel 4-azasteroids with fluoro-substituted-17 beta-amidic side chains, three compounds, namely FCE 28260, FCE 28175 and FCE 27837, were identified as potent in vitro and in vivo inhibitors of prostatic 5 alpha-reductase. Their IC50 values were found to be 16, 38 and 51 nM for the inhibition of the human enzyme, and 15, 20 and 60 nM for the inhibition of the rat enzyme, respectively. When given orally for 7 days in castrated and testosterone (Silastic implants) supplemented rats, the new compounds were very effective in reducing prostate growth. At a dose of 0.3 mg/kg/day inhibitions of 42, 36 and 41% were caused by FCE 28260, FCE 28175 and FCE 27837, respectively.

Hormone-nuclear receptor interactions in health and disease. The oestrogen receptor

During the past 30 years, we have learned a great deal about the molecular details whereby the ovarian hormone elicits the feminizing effects that Knauer described in his experiments over a century ago. The ER plays a pivotal role in this process, and potentially in many other physiological processes. The roles of variant receptors, the details of ER-mediated transactivation and the regulation of ER expression and activation are just a few of the important unresolved issues in this field. These are not trivial problems, and their solutions are likely to require much more investigation. This information will provide important clinical insight into breast cancer, lipid metabolism, bone metabolism, prostatic hyperplasia and other diseases. Armed with this basic knowledge, scientists will be better equipped to design rational therapeutic and preventive strategies to combat these major clinical problems.

Endocrine therapies for symptomatic benign prostatic hyperplasia

OBJECTIVE

To provide a comprehensive overview of the various endocrine therapies being developed and investigated for the treatment of symptomatic benign prostatic hyperplasia (BPH).

METHODS

Peer-reviewed reports in the medical and urologic literature were examined for pertinent information relating to the role of luteinizing hormone-releasing hormone (LHRH) agonists, antiandrogens, 5 alpha-reductase inhibitors, and aromatase inhibitors in the management of BPH. Special attention was given to the scientific rationale and clinical results for each therapy.

RESULTS

LHRH agonists, antiandrogens, and 5 alpha-reductase inhibitors all reduce the androgenic stimulation to the prostate gland. In doing so, they decrease prostate size by 25 percent, but cause a modest improvement in symptom score (3-4 points) and peak urinary flow rate (approximately 2.5 mL/sec). All of these therapies cause a significant decrease in the serum prostate-specific antigen (PSA) concentration, and an effect is maintained as long as the treatment is continued. Side effects are most pronounced for the LHRH agonists, in which impotency and decreased libido are universal phenomena, and least significant for the 5 alpha-reductase inhibitors. Aromatase inhibitors eliminate the estrogenic stimulation to the prostate gland. Although substantial evidence exists to support the role of estrogens in the development and maintenance of BPH, no data from large-scale randomized clinical trials are available to document the clinical usefulness of aromatase inhibitors in the treatment of symptomatic BPH.

CONCLUSIONS

Medications that produce a state of androgen deprivation can reduce the static component of BPH. Of these agents, the 5 alpha-reductase inhibitors have the greatest promise because of their low toxicity profile. The role of the aromatase inhibitors in the treatment of BPH remains to be determined.

Aromatase in the human testis

Low levels of testicular estrogen synthesis have been reported in a number of species, but the cellular localization has not been unequivocally established. To study aromatase in the human testis, we have combined immunocytochemistry with direct measurement of enzyme activity in the testicular 6 microns cryosections. Thus, the functionality of the immunoreaction and its sensitivity can be assessed in quantitative terms. Testes were obtained from immediate autopsy from men aged 18-53 years, from surgery from two patients with prostatic cancer (67 and 74 years) and from two normal children aged 8 months and 3 years at autopsy. Benign testicular sex cord tumors were also examined from two unrelated patients aged 5 and 8 years with gynecomastia and diagnosed with Peutz-Jeghers syndrome. Our results consistently showed low to moderate staining intensity of immunoreactive aromatase in comparison to that of normal human placental cryosections. Immunoreactive aromatase was only present in the interstitial Leydig cells and absent from the Sertoli cells of all normal adult testes showing spermatogenesis. Aromatase activity correlated well with the intensity of the immunostain. However, there was no obvious relationship between the level of aromatase activity and increasing age. Generally higher levels were present in testes of young men (18-22 years). No immunostain in any cell type was detected in one 33-year-old patient with testicular cancer. In the testes of the two normal prepubertal boys, no immunostaining was observed. However, intensely stained Sertoli cells as well as high aromatase activity were observed in the testicular tumors of the patients with Peutz-Jeghers syndrome. Our results suggest that Leydig cells are the source of aromatase in normal men but that Sertoli cells may express this enzyme under abnormal conditions. The combined methods for measuring enzyme activity and immunoreactive aromatase are suitable for application to tissues expressing low levels of aromatase.