5α-Reductase Inhibitory Components as Antiandrogens From Herbal Medicine

We investigated medicinal plant sources with 5α-reductase inhibitory activity. These compounds have been used in several remedies against androgen-dependent diseases including benign prostatic hyperplasia. The 50% ethanol extract of Polygonum multiflorum Thunb (Polygoni Multiflori Radix; Polygonaceae) showed potent 5α-reductase inhibitory activity. The fraction responsible for this activity was purified, and the active constituent was isolated and identified as emodin, an anthraquinone compound. Although emodin showed considerably less potent inhibitory activity than riboflavin, the inhibitory activity of the compound was more potent than that of alizarin (1,2-dihydroxyanthraquinone), an anthraquinone-type positive control. Also, anthraquinone itself was substantially inactive against 5α-reductase, in dicating that the hydroxyl group on the structure of emodin is an important structural moiety for displaying inhibitory activity.