The endocrine activities of 8-prenylnaringenin and related hop (Humulus lupulus L.) flavonoids

The female flowers of the hop plant have long been used as a presentative and a flavoring agent in beer, but they are now being included in some herbal preparations for women for breast enhancement. This study investigated the relative estrogenic, androgenic and progestogenic activities of the known phytoestrogen, 8-prenylnaringenin, and structurally related hop flavonoids. 6-Prenylnaringenin, 6,8-diprenylnaringenin and 8-geranylnaringenin exhibited some estrogenicity, but their potency was less than 1% of that of 8-prenylnaringenin. 8-Prenylnaringenin alone competed strongly with 17 beta -estradiol for binding to both the alpha- and beta -estrogen receptors. None of the compounds (xanthohumol, isoxanthohumol, 8-prenylnaringenin, 6-prenylnaringenin, 3'-geranylchalconaringenin, 6-geranylnaringenin, 8-geranylnaringenin, 4'-O-methyl-3'-prenylchalconarinagenin and 6,8-diprenylnaringenin) nor polyphenolic hop extracts showed progestogenic or androgenic bioactivity. These results indicate that the endocrine properties of hops and hop products are due to the very high estrogenic activity of 8-prenylnaringenin and concern must be expressed about the unrestricted use of hops in herbal preparations for women.