The lack of a safe and reliable alternative to hormone therapy (HT) for treating menopausal symptoms underscores the need for alternative therapies. OBJECTIVE: The purpose of this study was to assess the in vivo estrogenic effects of the botanical dietary supplements Trifolium pratense (red clover) and Humulus lupulus (hops), and two compounds obtained from H. lupulus, isoxanthohumol and 8-prenylnaringenin (8-PN) using the ovariectomized uterotrophic adult rat model. A H. lupulus extract and a 30% isoflavone extract of T. pratense were tested at three escalating doses as was one dose of isoxanthohumol for 21 days. 8-Prenylnaringenin, the major estrogen in H. lupulus, was also tested at three relevant escalating doses. In order to determine the in vivo metabolism of 8-PN, the major Phase I and Phase II metabolites were also identified. The primary outcome measure, uterus weight gain, indicated that H. lupulus and T. pratense did not have an estrogenic effect on the uterus, and none of the secondary outcome measures were positive. In contrast, there was a clear dose response when 8-PN was evaluated where the middle and high doses of 8-PN were active. 8-Prenylnaringenin in rat plasma, liver, and mammary gland was measured and the major Phase I and Phase II 8-PN metabolites were detected. Our findings suggest that while both the H. lupulus and T. pratense extracts do not have an effect on the rat uterus, 8-PN at equivalent doses to those previously used in humans did have an effect, and may therefore have a deleterious effect in women.
IntroductionSymptoms associated with menopause such as insomnia, loss of libido, vaginal atrophy, depression, and hot flashes can greatly affect the quality of life for women. Many women have used hormone therapy (HT) to alleviate menopausal symptoms; however, with the publication The strobiles of Humulus lupulus L. (Cannabaceae) (hops) are primarily used to flavor beer, and have been studied since 1953 for a potential estrogenic mechanism of action [13][14][15]. In the past, the flavonoids 8-PN and 6-PN, and the chalcone, isoxanthohumol (IX), have been isolated and reported to be estrogenic in vitro and/or in vivo [16,17]. The most potent estrogen in H. lupulus is 8-PN, which is in actuality an artifact formed through isomerization of the precursor chalcone, desmethylxanthohumol [18,19]. 8-Prenylnaringenin has been shown in a variety of in vitro assays to be estrogenic in the nanomolar range [16,17,20,21]. It can also be formed from precursors such as IX, and xanthohumol (XH), through metabolism [22].In previous metabolic studies, it has been shown that human liver microsomes convert 8-PN to 12 metabolites [22]. Among them, are the most abundant monooxygenated metabolites (Figure 1). The estrogenicities of the 8-PN alcohols have been previously determined [23] and were found to be ∼10 fold less estrogenic than 8-PN. Phase II metabolites of 8-PN, including glucuronides and sulfate conjugates, have been identified in incubations with human Caco-2 cells and human hepatocytes [2...