Human prostatic steroid 5 alpha-reductase isoforms--a comparative study of selective inhibitors.
The present study describes the independent expression of the type 1 and 2 isoforms of human 5 alpha-reductase in the baculovirus-directed insect cell expression system and the selectivity of their inhibition. The catalytic properties and kinetic parameters of the recombinant isozymes were consistent with published data. The type 1 isoform displayed a neutral (range 6-8) pH optimum and the type 2 isoform an acidic (5-6) pH optimum. The type 2 isoform had higher affinity for testosterone than did the type 1 isoform (Km = 0.5 and 2.9 microM, respectively). Finasteride and turosteride were selective inhibitors of the type 2 isoform (Ki (type 2) = 7.3 and 21.7 nM compared to Ki (type 1) = 108 and 330 nM, respectively). 4-MA and the lipido-sterol extract of Serenoa repens (LSESr) markedly inhibited both isozymes (Ki (type 1) = 8.4 nM and 7.2 micrograms/ml, respectively; Ki (type 2) = 7.4 nM and 4.9 micrograms/ml, respectively). The three azasteroids were competitive inhibitors vs substrate, whereas LSESr displayed non-competitive inhibition of the type 1 isozyme and uncompetitive inhibition of the type 2 isozyme. These observations suggest that the lipid component of LSESr might be responsible for its inhibitory effect by modulating the membrane environment of 5 alpha-reductase. Partially purified recombinant 5 alpha-reductase type 1 activity was preserved by the presence of lipids indicating that lipids can exert either stimulatory or inhibitory effects on human 5 alpha-reductase.
Iehlé
C
C
Laboratoire de Cancérologie Expérimentale, Faculté de Médecine, Marseille, France.
Délos
S
S
Guirou
O
O
Tate
R
R
Raynaud
J P
JP
Martin
P M
PM
D000818:Animals; D001378:Azasteroids / Q000494:pharmacology; D001667:Binding, Competitive; D042944:Cholestenone 5 alpha-Reductase; D013196:Dihydrotestosterone / Q000031:analogs & derivatives / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D018120:Finasteride / Q000031:analogs & derivatives* / Q000494:pharmacology; D006801:Humans; D007313:Insecta; D007527:Isoenzymes / Q000037:antagonists & inhibitors* / Q000302:isolation & purification; D008297:Male; D010088:Oxidoreductases / Q000037:antagonists & inhibitors* / Q000302:isolation & purification; D011467:Prostate / Q000201:enzymology*; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000302:isolation & purification; D014162:Transfection
D001378:Azasteroids; D004791:Enzyme Inhibitors; D007527:Isoenzymes; D011994:Recombinant Proteins; D013196:Dihydrotestosterone; D018120:Finasteride; C031563:17-N,N-diethylcarbamoyl-4-methyl-4-azaandrostane-3-one; D010088:Oxidoreductases; D042944:Cholestenone 5 alpha-Reductase; C084634:turosteride