Phospholipid requirement of epididymal testosterone 5 alpha-reductase and phospholipid composition of epididymal microsomes

Expression in Escherichia Coli, Purification, and Functional Reconstitution of Human Steroid 5α-Reductases

The potent androgen 5α-dihydrotestosterone irreversibly derives from testosterone via the activity of steroid 5α-reductases (5αRs). The major 5αR isoforms in most species, 5αR1 and 5αR2, have not been purified to homogeneity. We report here the heterologous expression of polyhistidine-tagged, codon-optimized human 5αR1 and 5αR2 cDNAs in Escherichia coli. A combination of the nonionic detergents Triton X-100 and Nonidet P-40 enabled solubilization of these extremely hydrophobic integral membrane proteins and facilitated purification with affinity and cation-exchange chromatography methods. For functional reconstitution, we incorporated the purified isoenzymes into Triton X-100-saturated dioleoylphosphatidylcholine liposomes and removed excess detergent with polystyrene beads. Kinetic studies indicated that the 2 isozymes differ in biochemical properties, with 5αR2 having a lower apparent Km for testosterone, androstenedione, progesterone, and 17-hydroxyprogesterone than 5αR1; however, 5αR1 had a greater capacity for steroid conversion, as reflected by a higher Vmax than 5αR2. Both enzymes preferred progesterone as substrate over other steroids, and the catalytic efficiency of purified reconstituted 5αR2 exhibited a sharp pH optimum at pH 5. Intriguingly, we found that the prostate-cancer drug-metabolite 3-keto-∆ 4-abiraterone is metabolized by 5αR1 but not 5αR2, which may serve as a structural basis for isoform selectivity and inhibitor design. The functional characterization results with the purified reconstituted isoenzymes paralleled trends obtained with HEK-293 cell lines stably expressing native 5αR1 and 5αR2. Access to purified human 5αR1 and 5αR2 will advance studies of these important enzymes and might help to clarify their contributions to steroid anabolism and catabolism.

Inhibition of type 1 and type 2 5alpha-reductase activity by free fatty acids, active ingredients of Permixon

In different cell systems, the lipido-sterolic extract of Serenoa repens (LSESr, Permixon inhibits both type 1 and type 2 5alpha-reductase activity (5alphaR1 and 5alphaR2). LSESr is mainly constituted of fatty acids (90+/-5%) essentially as free fatty acids (80%). Among these free fatty acids, the main components are oleic and lauric acids which represent 65% and linoleic and myristic acids 15%. To evaluate the inhibitory effect of the different components of LSESr on 5alphaR1 or 5alphaR2 activity, the corresponding type 1 and type 2 human genes have been cloned and expressed in the baculovirus-directed insect cell expression system Sf9. The cells were incubated at pH 5.5 (5alphaR2) and pH 7.4 (5alphaR1) with 1 or 3nM testosterone in presence or absence of various concentrations of LSESr or of its different components. Dihydrotestosterone formation was measured with an automatic system combining HPLC and an on-line radiodetector. The inhibition of 5alphaR1 and 5alphaR2 activity was only observed with free fatty acids: esterified fatty acids, alcohols as well as sterols assayed were inactive. A specificity of the fatty acids in 5alphaR1 or 5alphaR2 inhibition has been found. Long unsaturated chains (oleic and linolenic) were active (IC(50)=4+/-2 and 13+/-3 microg/ml, respectively) on 5alphaR1 but to a much lesser extent (IC(50)>100 and 35+/-21 microg/ml, respectively) on 5alphaR2. Palmitic and stearic acids were inactive on the two isoforms. Lauric acid was active on 5alphaR1 (IC(50)=17+/-3 microg/ml) and 5alphaR2 (IC(50)=19+/-9 microg/ml). The inhibitory activity of myristic acid was evaluated on 5alphaR2 only and found active on this isoform (IC(50)=4+/-2 microg/ml). The dual inhibitory activity of LSESr on 5alpha-reductase type 1 and type 2 can be attributed to its high content in free fatty acids.

Phospholipase A2 degradation products modulate epithelial and stromal 5alpha-reductase activity of human benign prostatic hyperplasia in vitro

BACKGROUND

Recent studies have demonstrated the inhibition of 5alpha-reductase activity in human prostate by phospholipases. Among those phospholipases, phospholipase A2 cleaves one of the acyl chains from phospholipids, thereby producing fatty acids and lysophospholipids such as LPC, LPS, and LPE. Therefore, we were interested in the effect of those lysophospholipids on 5alpha-reductase activity in human benign prostatic hyperplasia (BPH).

METHODS

In a first set of experiments, cell homogenates were incubated with phospholipase A2 either in the presence or absence of albumin, which is known to bind fatty acids and lysophospholipids. Thereafter, the effect of lysophospholipids of known structure on 5alpha-reductase activity was investigated.

RESULTS

In epithelium and stroma of human BPH, 5alpha-reductase activity was inhibited in a dose-dependent manner by phospholipase A2. In the presence of albumin, this inhibition was enhanced. In epithelium, LPC at low concentration yielded a dose-dependent stimulation of 5alpha-reductase activity up to 167%. At higher concentrations, epithelial as well as stromal 5alpha-reductase activity was inhibited significantly. As indicated by results of enzyme kinetic analyses, the LPC-mediated activation in the epithelium results from an increase of the active population of 5alpha-reductase. In contrast, LPC reduces the affinity of epithelial 5alpha-reductase to testosterone. LPE had no effect on epithelial 5alpha-reductase, whereas stromal 5alpha-reductase was inhibited in a dose-dependent manner up to 46%. Finally, LPS stimulated epithelial and stromal 5alpha-reductase activity; this stimulation was significantly stronger in epithelium (296%) than in stroma (163%). The LPC-mediated effects could be neutralized by the addition of albumin.

CONCLUSIONS

The present data on BPH tissue suggest that lysophospholipids may play a specific and structure-related role in the posttranslational regulation of human prostatic 5alpha-reductase.

In vitro modulation of steroid 5alpha-reductase activity by phospholipases in epithelium and stroma of human benign prostatic hyperplasia

Membrane components, such as phospholipids, play an important role in the regulation of prostatic 5alpha-reductase activity. To describe in more detail the impact of such regulation on 5alpha-reductase activity, epithelial and stromal cell homogenates of human BPH were treated with phospholipases to specifically alter the structure of cellular phospholipid components. Phospholipase A(2) (PLA(2)) was used to alter the structure of the nonpolar, hydrophobic region of the membrane bilayer. Various types of phospholipase C (PLC) affect the polar, hydrophilic region of phospholipids. In epithelium and stroma, 5alpha-reductase activity was dose-dependently inhibited by PLA(2) and PLC type III. In epithelium and stroma, the mean IC(50) values of PLA(2) were 9.4 +/- 1.1 and 13.9 +/- 2.6 [U/mg protein +/- SEM], respectively. The mean IC(50) values of PLC type III in epithelium and stroma were 4.5 +/- 1.2 and 1.7 +/- 0.2 [U/mg protein +/- SEM], respectively. In epithelium as well as in stroma, 5alpha-reductase activity was more greatly inhibited by PLC type III than by PLA(2). Both in epithelium and stroma, PLA(2) significantly decreased the V(max) of 5alpha-reductase whereas its K(m) remained unaffected. A similar decrease in V(max) was found with PLC type III in epithelium and stroma. Furthermore, the K(m) of epithelial 5alpha-reductase increased significantly following the addition of PLC type III. The two phospholipases, with their specific substrate affinities and sites of hydrolysis, exhibited significantly different effects on 5alpha-reductase, indicating that 5alpha-reductase activity is not unspecifically affected by modification of the hydrophilic milieu. Rather, 5alpha-reductase activity is specifically modulated by various phospholipids and/or phospholipolysis mediated degradation products. These findings suggest that the structural composition of the lipid environment plays a fundamental role in the post-translational regulation of 5alpha-reductase activity in the epithelium and stroma of human BPH. Thus, changes in membrane phospholipid content seem to be instrumental in the expression of DHT-dependent processes.

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

Immunocytochemical studies and mRNA measurements have shown that the rat epididymis--like the rat prostate--expresses both rat steroid 5alpha-reductase isozymes, i.e. type I and II. So far, enzyme activity measurements in rat epididymis homogenates, however, do not support the presence of type I 5alpha-reductase activity. Incubating homogenates of both tissues with a wide range of substrate concentrations, we were able to detect activity of both isozymes in rat prostate and epididymis tissues at neutral pH. In rat prostate the amount of type I activity, as measured by the Vmax at pH 7.0, exceeds that of type II 5alpha-reductase 50-fold. The efficiency ratio, Vmax/Km, of the type I isozyme accounts for 25% of the total in vivo potential activity. A possible anabolic role for the type I isozyme in rat prostate was thus surmised. In rat epididymis the Vmax of type I and type II 5alpha-reductase at pH 7.0 were similar. Comparison of the efficiency ratio Vmax/Km of either isozyme in the rat epididymis, however, suggested that the type II isozyme would play the major role in the 5alpha-reduction of testosterone at physiological concentrations and at neutral pH. The specific localization of the isozymes should be considered to allow for correct quantification of their in vivo contribution to dihydrotestosterone formation.