Gossypol inhibits 5α-reductase 1 and 3α-hydroxysteroid dehydrogenase: Its possible use for the treatment of prostate cancer.

Gossypol is a yellow polyphenol isolated from cotton seeds. It has the antitumor activity and it is being tested to treat prostate cancer. However, its underlying mechanisms are still not well understood. The present study investigated the inhibitory effects of gossypol acetate on rat 5α-reductase 1, 3α-hydroxysteroid dehydrogenase, and retinol dehydrogenase 2 for androgen metabolism. Rat 5α-reductase 1, 3α-hydroxysteroid dehydrogenase, and retinol dehydrogenase 2 were expressed in COS-1 cells. Immature Leydig cells that contain these enzymes were isolated from 35-day-old male Sprague Dawley rats. The potency and mode of action of gossypol acetate to inhibit these enzymes in both enzyme-expressed preparations and immature Leydig cells were examined. Molecular docking study of gossypol on the crystal structure of 3α-hydroxysteroid dehydrogenase was performed. Gossypol acetate inhibited 5α-reductase 1 and 3α-hydroxysteroid dehydrogenase with IC50 values of 3.33 ±â€¯0.07 and 0.52 ±â€¯0.06 × 10-6 M in the expressed enzymes as well as 8.512 ±â€¯0.079 and 1.032 ±â€¯0.068 × 10-6 M in intact rat immature Leydig cells, respectively. Gossypol acetate inhibited rat 5α-reductase 1 in a noncompetitive mode and 3α-hydroxysteroid dehydrogenase in a mixed mode when steroid substrates were supplied. Gossypol acetate weakly inhibited retinol dehydrogenase 2 with IC50 value over 1 × 10-4 M. Molecular docking analysis showed that gossypol partially bound to the steroid-binding site of the crystal structure of rat 3α-hydroxysteroid dehydrogenase. Gossypol acetate is a potent inhibitor of rat 5α-reductase 1 and 3α-hydroxysteroid dehydrogenase, possibly inhibiting the formation of androgen in the prostate cancer cells.

Taxifolin inhibits rat and human 11ß-hydroxysteroid dehydrogenase 2.

Taxifolin is a flavonoid in food plants. Kidney 11ß-hydroxysteroid dehydrogenase 2 (11ß-HSD2) is an NAD+-dependent oxidase that inactivates glucocorticoid cortisol (human) or corticosterone (rodents) into biologically inert 11 keto glucocorticoids. The present study investigated the effects of taxifolin on rat and human kidney microsomal 11ß-HSD2. Taxifolin noncompetitively inhibited rat and human 11ß-HSD2 against steroid substrates, with IC50 values of 33.08 and 13.14µM, respectively. Administration of 5 and 10mg/kg taxifolin for 30min ex vivo inhibited 11ß-HSD2 significantly and also in vivo decreased cortisol metabolism, as shown in the significant increase of area under curve (AUC). This result shows that taxifolin is a potent 11ß-HSD2 inhibitor, possibly causing side effects.