The female flowers of the hop plant are used as a preservative and as a flavoring agent in beer. However, a recurring suggestion has been that hops have a powerful estrogenic activity and that beer may also be estrogenic. In this study, sensitive and specific in vitro bioassays for estrogens were used for an activity-guided fractionation of hops via selective solvent extraction and appropriate HPLC separation. We have identified a potent phytoestrogen in hops, 8-prenylnaringenin, which has an activity greater than other established plant estrogens. The estrogenic activity of this compound was reflected in its relative binding affinity to estrogen receptors from rat uteri. The presence of 8-prenylnaringenin in hops may provide an explanation for the accounts of menstrual disturbances in female hop workers. This phytoestrogen can also be detected in beer, but the levels are low and should not pose any cause for concern.

The female flowers of the hop plant (hop cones) are used as a preservative and as a flavouring agent in beer. A novel phyto-oestrogen, 8-prenylnaringenin, was recently identified in hops and this study was undertaken to characterize the oestrogenic activity of this compound using a combination of in vitro and in vivo assays. Natural and semi-synthetic 8-prenylnaringenin showed similar bioactivities both in a yeast screen transfected with the human oestrogen receptor and in oestrogen-responsive human Ishikawa Var-I cells. 8-Prenylnaringenin showed comparable binding activity to both oestrogen receptor isoforms (ER alpha and ER beta). 8-Prenylnaringenin extracted from hops contains similar amounts of both (R)- and (S)- enantiomers, indicating that the compound is normally formed non-enzymatically. Both enantiomers showed similar bioactivity in vitro and similar binding characteristics to ER alpha and ER beta. The oestrogenic activity of 8-prenyl-naringenin in vitro was greater than that of established phyto-oestrogens such as coumestrol, genistein and daidzein. The high oestrogenic activity was confirmed in an acute in vivo test using uterine vascular permeability as an end point. When the compound was given to ovariectomized mice in their drinking water, oestrogenic stimulation of the vaginal epithelium required concentrations of 100 mug ml(-1) (about 500-fold greater than can be found in any beer).

The in vii effcts ofxenoestrogens are ofinterest in relation to their potential health risk and/or beneficial efficts on humans and animals. However, the apparent in yim potency of the examined response can be confounded by a short half-ife, and the metabolism of estogens is very dependent on the nature of conversion and/or inactivation. To minimize such variables, we examined the estrogenic potency of a range of xenoestrogens in an acute in vivo assay-the stimulation of increased uterine vascular permeability in ovariectomized mice 4 hr after subcutaneous administra. tion. While estradiol (E2) and estriol (F3; a relatily weak natural estrogen) readily induced vascular responses [median effiv dose (ED50) 10-9 mol], much higher amounts of xenoestrogens were required. Bisphenol A was about 10,000-fold less potent than E4 and E, and octylphenol and nonylphenol were about 100,000-fold less potent; dioctyl phthalat, beyl buty ptalate, dibutyl phtbalate, and trichlorinated biphenol produced no effect. Coumestrol was the most active phytoestrogen, with an ED50 between 10-6 and 10-7 mol; genistein wa about 10-fold less potent than coumestrol, and neither daidzein nor formononetin produced any marked efflect, even at doses up to 1O5mol. All increases in vascular permeability could be blocked by the pure antiestrogen ICI 182,780. There was no evidence that any ofthe compounds could act as an aniesrogen in his assay or that they could exert ynegistc ef in. combion. These results indicate that even short-term exposure to most of the xenobiotic estogens can induce typical estrogenic efFecs in vivo, but their esuogenic potency is very weak even when assessed in an acute response.

The female flowers of the hop plant have long been used as a preservative 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 17ss-estradiol for binding to both the alpha- and ss-estrogen receptors. None of the compounds (xanthohumol, isoxanthohumol, 8-prenyl-naringenin, 6-prenylnaringenin, 3'-geranylchalconaringenin, 6-geranylnaringenin, 8-geranylnaringenin, 4'-O:-methyl-3'-prenylchalconaringenin 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.

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