The influence of 4-hydroxy-4-androstene-3,17-dione on androgen metabolism and action in cultured human foreskin fibroblasts.
4-hydroxy-4-androstene-3,17-dione (4-OHA) has been shown to be a potent inhibitor of aromatase activity. It is effective in the control of estrogen-dependent processes in female subjects and may potentially be useful in the treatment of estrogen-dependent processes in men. Human foreskin fibroblasts grown in cell culture provide a model to investigate the effects of 4-OHA on extraglandular aromatase activity as well as the ability of the compound to influence androgen receptor binding and the 5 alpha-reduction of testosterone (T). Initial experiments were carried out to determine the potency of 4-OHA in genital skin fibroblasts by incubating cells with 4-OHA over a range of concentrations. When aromatase activity was determined at a substrate concentration close to the apparent Km of the enzyme, a 44% inhibition of enzyme activity occurred at a mean concentration of 5 nM 4-OHA. Enzyme kinetic studies analyzed by Eadie-Hofstee plots demonstrated competitive inhibition by 4-OHA with a mean apparent Ki of 2.7 nM. When 5 alpha-reductase activity was determined in the presence of 200 nM [3H]T, in the absence or presence of 4-OHA, a 50% inhibition of enzyme activity occurred at an inhibitor concentration of 3 microM. In androgen receptor binding studies, 4-OHA possessed 1% of the affinity of dihydrotestosterone (DHT) for [3H]DHT binding sites. In summary: 4-OHA is a potent and specific inhibitor of aromatase activity in human genital skin fibroblasts, the affinity of the enzyme for 4-OHA being greater than its affinity for the substrate, androstenedione. The influence of 4-OHA on 5 alpha-reductase activity and androgen receptor binding is minimal.
D000728:Androgens / Q000378:metabolism*; D000735:Androstenedione / Q000031:analogs & derivatives* / Q000494:pharmacology; D001141:Aromatase / Q000378:metabolism*; D047072:Aromatase Inhibitors; D042944:Cholestenone 5 alpha-Reductase; D013196:Dihydrotestosterone / Q000378:metabolism; D005347:Fibroblasts; D006801:Humans; D007700:Kinetics; D008297:Male; D010088:Oxidoreductases / Q000378:metabolism; D010413:Penis; D011944:Receptors, Androgen / Q000187:drug effects / Q000378:metabolism
D000728:Androgens; D047072:Aromatase Inhibitors; D011944:Receptors, Androgen; D013196:Dihydrotestosterone; D000735:Androstenedione; D010088:Oxidoreductases; D001141:Aromatase; D042944:Cholestenone 5 alpha-Reductase; C014594:formestane