Effect of Aging on Kinetic Parameters of 5α-Reductase in Epithelium and Stroma of Normal and Hyperplastic Human Prostate*

Abstract

Altered 5 alpha-dihydrotestosterone (DHT) metabolism and stromal-epithelial cell interactions are two factors hypothesized to explain the development of benign prostatic hyperplasia (BPH). Furthermore, the development of BPH is clearly age dependent. Therefore, we studied the age-dependent alteration of 5 alpha-reductase, the enzyme that catalyzes the irreversible conversion of testosterone to DHT in epithelium and stroma of the human prostate. For this purpose kinetic parameters [Km Vmax] of 5 alpha-reductase were determined separately in epithelium and stroma of normal prostatic tissue (NPR) from 5 and BPH tissue from 20 men, and the results were correlated with the age of the donors (15-86 yr). The mean Km in epithelium [NPR, 14.3 +/- 1.8 (+/- SE); BPH, 29.5 +/- 2.7 nmol/L] was significantly (P less than 0.0001) lower than that in stroma (NPR, 78.4 +/- 8.5; BPH, 185.8 +/- 13.6 nmol/L). The mean Vmax in epithelium [NPR, 23.8 +/- 3.9 (+/- SE); BPH, 27.9 +/- 3.0 pmol/mg protein.h] was significantly (P less than 0.0001) lower than that in stroma (NPR, 68.3 +/- 4.4; BPH, 173.8 +/- 12.2 pmol/mg protein.h). The DHT-forming index (Vmax/Km) in NPR epithelium [1.6 +/- 0.2 (+/- SE)] was significantly (P less than 0.01) higher than that in NPR stroma (0.9 +/- 0.1), while in BPH the DHT-forming index was nearly identical in epithelium (1.1 +/- 0.1) and stroma (1.0 +/- 0.1). The Km values in epithelium and stroma both correlated positively (P less than 0.01) with age, but the Vmax values correlated positively with age (P less than 0.0001) only in stroma. The DHT-forming index decreased significantly with age in epithelium (P less than 0.01), but remained constant in stroma. These results indicate that there is a nonuniform age-dependent alteration of Km and Vmax in epithelium and stroma of the human prostate independent of the presence of BPH, which might have an impact on the conversion rate of testosterone to DHT with advancing age.

Enzyme Activities in Tissue of Human Benign Prostatic Hyperplasia after Three Months' Treatment with the Sabalserrulata Extract IDS 89 (Strogen®) or Placebo

“…Our study has been focussed on the 5a-reductase and the 3a(ß)-HSORred, because in the pros tate those enzymes are catalyzing the irreversible conver sion of testosterone to the highly potent DHT and the con version of DHT to the biologically per se inactive 5a-androstanediols, respectively [11,12], In this context, our own in vitro studies have demonstrated that in BPH tis IDS 89 treatment would denote a conflicting fact, because it is under discussion whether an increased estrogen level might play a pathogenetic role in BPH development [13]. Alternatively, the significant increase of Ymax of the CK in BPH stroma could merely be the adaptation of the stro mal cells to a higher energy demand, the latter being somehow induced by IDS 89.…”

“…Measurement of 5a-Reductase and 3a(ß)-HSORrect Activity 5a-Reductase and 3a(ß)-HSORrecj activity were measured under optimized incubation conditions as described earlier [11,12]. The incubation mixtures (final volume 202 pi) were composed of bufferdiluted epithelial or stromal homogenate (200-500 pg protein, pH 7.4), a NADPH-regenerating system (5 mM glucose-6-phosphate, 0.6 U glucose-6-phosphate dehydrogenase), and varying concentra tions of the respective steroid substrate (either as tritium-labeled ste roid alone or tritium-labeled plus -unlabeled steroid).…”

“…The dried steroids were re-dissolved in 50 pi acetonitrile containing 100 pg of the following steroids as trac ers: (1) forthe determination of 5a-reductase: testosterone, DHT, 5a-androstane-3a,17ß-diol, and 5a-androstane-3ß,17ß-diol, and (2) for the determination of 3a(ß)-HSORrelj: DHT, 5a-androstane-3a,17ß-diol, and 5a-androstane-3ß,17ß-diol. The steroids were separated by reversed-phase high-performance liquid chromatography as de scribed in detail earlier [11]. The eluant was composed of a fil tered and helium-degassed mixture of acetonitrile:methanol:H20 (53:12:35, v/v/v).…”

“…So, in BPH tissue from patients being treated for 3 months with either IDS 89 or placebo, the amount (Vmax) and substrate affinity (Km) of the DHTforming 5a-reductase and the DHT-removing 3a-and 3ß-hydroxysteroid oxidoreductase (3a(ß)-HSORred) have been analyzed. Previous studies have demonstrated sig nificant differences between epithelium and stroma con cerning 5a-reductase [11] and 3a(ß)-HSORred activity [12], Moreover, it is interesting to note that epithelium and stroma are two compartments which are probably under the influence of a different endogenous androgento-estrogen ratio [13]. Therefore, the in vivo effect of IDS 89 on intraprostatic enzyme activities has been investi gated in separated epithelial and stromal tissue homoge nates.…”

Fatty acid composition of phospholipids in epithelium and stroma of human benign prostatic hyperplasia

“…Earlier own studies have shown significant differences in the 5␣-reductase activity between epithelium and stroma of the human prostate [3,[6][7][8]. The highest DHT-forming capacity was found in epithelium of the normal prostate.…”