Articles

Inhibition of 5 alpha-reductase in genital skin fibroblasts and prostate tissue by dietary lignans and isoflavonoids.

Author

Evans BA, Griffiths K, Morton MS

Date

11/1995

Journal

J Endocrinol

Abstract

Isoflavonoids and lignans, constituents of many plant foods, have been proposed as protective agents in those populations with a low incidence of hormone-dependent cancers. They may act by their inhibition of the metabolism of growth-promoting steroid hormones. This report describes the inhibition of 5 alpha-reductase and 17 beta- hydroxysteroid dehydrogenase by six isoflavonoids and two lignans in human genital skin fibroblast monolayers and homogenates, and in benign prostatic hyperplasia tissue homogenates. In genital skin fibroblasts, genistein, biochanin A and equol were the most potent inhibitors of 5 alpha-reductase activity, each resulting in greater than 80% inhibition at a concentration of 100 microM. The IC50 values for genistein and a seven-compound mixture were approximately 35 microM and 20 microM (2.9 microM of each compound) respectively. Of the lignans, enterolactone was the most potent inhibitor. Inhibition by biochanin A was shown to be reversible. When genital skin fibroblast homogenates were used, biochanin A was found to inhibit 5 alpha-reductase isozymes 1 and 2 to differing extents (30% and 75% respectively). Genistein was shown to inhibit 5 alpha-reductase 2 in a non-competitive nature (Vmax and Km values without and with inhibitor were 30 and 20 pmol/mg protein per h and 177 and 170 nM respectively). All of the compounds tested inhibited 17 beta- hydroxysteroid dehydrogenase activity in genital skin fibroblast monolayers. When prostate tissue homogenates were used, the compounds tested were better inhibitors of 5 alpha-reductase 1 than 2.(ABSTRACT TRUNCATED AT 250 WORDS)