Endocrine and adrenergic pharmacological intervention in diseases of the prostate

The role of dihydrotestosterone in benign prostatic hyperplasia

This article examines the role of the androgen dihydrotestosterone (DHT) in the healthy and diseased prostate and considers the implications of the data on DHT for therapeutic approaches to benign prostatic hyperplasia (BPH). Development and maintenance of the normal prostate, as well as development of BPH, depend on a functional androgen-signaling axis, components of which include: (1) testosterone synthesis in the testes and adrenal glands; (2) conversion of testosterone to DHT; (3) transport of DHT to target tissues; and (4) binding of DHT to the androgen receptor with consequent modulation of genes. DHT plays a beneficial role in the developing prostate but it can be detrimental in the adult prostate in that it causes pathologic prostate growth. The role of DHT in other adult tissues is uncertain. DHT has not been shown to perform beneficial functions unique from testosterone in the adult male, and it is believed that its fundamental effect is to amplify testosterone's weaker hormonal signal. Increased understanding of the cellular mechanisms by which the androgen-signaling axis functions has led to advances in treatment for prostate disease. In BPH, the 5alpha-reductase inhibitors--the only class of therapy to act at the pathophysiologic substrate of the disease--arrest the disease process, reduce prostate volume, improve symptoms, and reduce the risk of acute urinary retention and BPH-related surgery. The availability of dutasteride, the first dual (Type 1/Type 2) 5alpha-reductase inhibitor, offers the opportunity for rapid and consistent inhibition of DHT.

Detection of cytochrome P450 mRNA transcripts in prostate samples by RT-PCR

BACKGROUND

The expression of cytochrome P450 (CYP)-dependent mono-oxygenases in the prostate is important, as it will determine the rate of activation of potential carcinogens as well as the metabolism of hormones with implications in diseases of the prostate. In addition, the levels of cytochromes P450 in prostatic tumours may well be determinants of the outcome of therapy involving P450 substrates such as anti-androgens.

METHODS

The gene expression of 12 different CYP genes was measured by reverse transcription-polymerase chain reaction (RT-PCR) in a total of 28 human prostatic tumour and nontumour samples.

RESULTS

Intriguingly, a large number of CYP mRNAs were detected in the prostate samples, including CYP1A2, -1B1, -2C19, -2D6, -3A4, -3A5, -3A7 and -4B1. CYP1B1 was consistently expressed and CYP3A5 and CYP4B1 were expressed in a majority of the samples tested.

CONCLUSIONS

These data demonstrate a wide range of CYP genes being expressed in the prostate. The relative importance of these enzymes in the pathogenesis and treatment of prostatic disease remains an important theme for further study.

A 6-month large-scale study into the safety of tamsulosin

AIMS

Tamsulosin is an alpha1-adrenoceptor antagonist for the treatment of symptomatic benign prostatic hyperplasia with a tolerability similar to that of placebo in short-term, placebo-controlled studies with limited patient numbers. The present study was designed to test the safety of tamsulosin treatment in a large cohort of men during a prolonged period of time, particularly with regard to comedications.

METHODS

A multicentre, open-label phase IIIb study with 1784 patients receiving 0.4 mg o.d. tamsulosin for 6 months was performed according to good clinical practice guidelines. The analysis was performed on an intention-to-treat basis and powered to detect adverse events (AE) occurring in 0.15% of patients with 95% confidence.

RESULTS

During a total drug exposure time of 811 patient years, 386 AE were recorded in 253 patients (14.2%; 95% confidence intervals [CI] 12.0-15.2%). Twenty-nine patients suffered 44 serious AE including five fatal events (CI 0.12-0.73%) due to myocardial infarction (n = 3) and to pneumonia and a car accident (one each), but all deaths were judged to be unlikely to be related to study medication. The frequency of AE in patients without any comedication (n = 1095) was 13.0% (CI 11.3-14.9%). In a logistic regression analysis beta-adrenoceptor blockers, converting enzyme inhibitors, antidiabetics and diuretics did not significantly affect the odds ratio for having AE. However, concomitant alpha-adrenoceptor antagonists (a protocol violation) and treatment with verapamil (which also has alpha-adrenoceptor antagonist activity) significantly enhanced the odds ratio for having AE to 3.87 (CI 1.52-9.85) and 3.17 (CI 1.52-6.58), respectively. Minor increases in the odds ratio, which did not reach statistical significance, were also observed for Ca2+ antagonists other than verapamil and for nitrates.

CONCLUSIONS

We conclude that tamsulosin has a good safety profile relative to AE rates in the placebo arms of previous studies on tamsulosin even in the presence of most potentially complicating comedications. No major unexpected severe AE were recorded during our 6 months study.