Kinetic analysis of rat steroid 5alpha-reductase activity in prostate and epididymis homogenates at neutral pH: evidence for type I activity in epididymis

5α-Reductase, an enzyme regulating glucocorticoid action in the testis of Rhinella arenarum (Amphibia: Anura)

The reduction of A-ring of glucocorticoids to produce 5α-dihydro-derivatives by 5α-reductases has been considered as a pathway of irreversible inactivation. However, 5α-reduced metabolites of corticosterone and testosterone have significant biological activity. In this paper, we investigated whether toad testicular 5α-reductase (5α-Red) is able to transform corticosterone into 5α-dihydrocorticosterone. Furthermore, we studied the role of 5α-reduced metabolite of corticosterone as a glucocorticoid receptor (GR) agonist. The activity of 5α-Red was assayed in subcellular fractions with [(3)H]corticosterone or [(3)H]testosterone as substrate. The enzyme localizes in microsomes and its optimal pH is between 7 and 8. The activity is not inhibited by finasteride. These results support the conclusion that toad 5α-Red resembles mammalian type 1 isoenzyme. Kinetic studies indicate that neither K(m) nor V(max) for both corticosterone and testosterone were significantly different among reproductive periods. The K(m) value for testosterone was significantly higher than that for corticosterone, indicating that the C-21 steroid is the preferred substrate for the enzyme. Studies of the binding capacity of 5α-dihydrocorticosterone (5α-DHB) to the testicular GR show that 5α-DHB is able to displace the binding of [(3)H]dexamethasone to testicular cytosol with a similar potency than corticosterone. The inhibition constant (Ki) values for corticosterone and 5α-DHB were similar, 31.33±2.9 nM and 35.24±2.3 nM, respectively. In vitro experiments suggest that 5α-DHB is an agonist of toad testicular GR, decreasing the activity of the key enzyme for androgen synthesis, the cytochrome P450 17-hydroxylase, C17,20-lyase.

Determination method for steroid 5alpha-reductase activity using liquid chromatography/atmospheric pressure chemical ionization-mass spectrometry

A determination method for steroid 5alpha-reductase activity using liquid chromatography/atmospheric pressure chemical ionization-mass spectrometry (LC/APCI-MS) in the positive-ion mode has been developed. The rat prostatic enzyme source was used and the enzymatically formed 5alpha-dihydrotestosterone and 5a-androstane-3alpha,17beta-diol were determined by LC/APCI-MS using absolute calibration curve method. The sum of the formed products was used as a measurement of the enzyme activity. This method was applied to kinetic study of this enzyme and inhibitory experiments using Finasteride as a model inhibitor.

CHEMOPREVENTION OF PROSTATE CANCER IN MEN AT HIGH RISK: RATIONALE AND DESIGN OF THE REDUCTION BY DUTASTERIDE OF PROSTATE CANCER EVENTS (REDUCE) TRIAL

PURPOSE

Chemoprevention may significantly impact the natural history of prostate cancer. The most potent intraprostatic androgen, dihydrotestosterone, has a significant role in the pathophysiology of prostate cancer. It represents a biologically plausible target for chemoprevention through the inhibition of 5alpha-reductase isoenzymes.

MATERIALS AND METHODS

The Reduction by Dutasteride of Prostate Cancer Events clinical trial is an international, multicenter, double-blind, placebo controlled chemoprevention study designed to determine if dutasteride 0.5 mg daily decreases the risk of biopsy detectable prostate cancer. A total of 8,000 men will be randomized to receive dutasteride or placebo for 4 years. Eligible men must be 50 to 75 years old, have a serum prostate specific antigen of 2.5 to 10 ng/ml (ages 50 to 60 years) or 3.0 to 10 ng/ml (older than 60 years). Men must have a negative 6 to 12 core biopsy within 6 months prior to enrollment. Repeat biopsies will be taken at 2 and 4 years. The rates of prostate cancer for each treatment group will be compared. Genetic and protein biomarkers of prostate cancer, and the effect of dutasteride on benign prostatic hyperplasia and prostatitis symptomatology and histopathology will also be assessed.

RESULTS

Results remain to be determined.

CONCLUSIONS

The study will examine the effects of the dual 5alpha-reductase inhibitor dutasteride on the natural history of prostate cancer in men at increased risk for this malignancy. It affords a unique opportunity to examine biomarkers and genetic linkage for prostate cancer, and assess a range of prostate health outcome measures.

Pharmacodynamic analysis of steroid 5alpha-reductase inhibitory actions of Z-350 in rat prostate

The pharmacodynamics of (S)-4-[3-[4-[1-(4-methylphenyl)-3-[4-(2-methoxyphenyl)piperazine-1-yl]propoxy]benzoyl]indole-1-yl] butyric acid hydrochloride (Z-350), which has alpha(1)-adrenoceptor antagonistic and steroid 5alpha-reductase inhibitory effects, were investigated in rats. The disposition of Z-350 was a function of linear kinetics at doses from 1 to 30 mg/kg; the bioavailability was calculated to be 65.2%. The inhibition of 5alpha-reductase was dependent on the concentration of Z-350 in plasma and in the prostate. Analysis of the relationship between the concentration in the prostate and the inhibition seen after a single oral administration showed that the Hill constant was almost 1.0 and EC(50)(n(H)) was 47.4 ng/g of tissue; these parameters did not change after multiple administration. Z-350 inhibited 5alpha-reductase 1 h after oral administration at a dose of 3 mg/kg; maximum inhibition was observed after 2-4 h, and the inhibition (%) was maintained for 24 h after oral administration.

Identification and partial characterization of two steroid 5 alpha-reductase isozymes in the canine prostate

BACKGROUND

The dog has been extensively used as an in vivo model to test the pharmacokinetics and effects on pathological prostatic growth of 5 alpha-reductase inhibitors. However, no information is available on the existence or characteristics of canine 5 alpha-reductase isozymes.

METHODS

The 5 alpha-reduction of testosterone is analyzed in dog prostatic homogenates. Three human-specific inhibitors are tested for their activity against dog 5 alpha-reductase.

RESULTS

Two pH optima of 5 alpha-reductase activity in dog prostatic homogenates are described, comparable to the pH optima of rat and human 5 alpha-reductase isozymes. Kinetic analysis of 5 alpha-reductase enzymatic activity at pH 7.0 revealed isozymes with a low apparent affinity constant (Km = 2.67 nM) and a high apparent affinity constant (Km = 1.23 microM). These apparent affinity constants compare favorably to the human and rat isozymes types II and I, respectively. The human type II inhibitor finasteride selectively inhibited the low Km isozyme, whereas the human type I inhibitor MK386 preferentially inhibited the high Km isozyme. The human type I inhibitor LY306089 was nonspecific for the dog isozymes.

CONCLUSIONS

We postulate that the high and low Km isozymes described here represent the dog type I and type II 5 alpha-reductase isozymes, respectively.