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Nutrient Physiology, Metabolism, and Nutrient-Nutrient Interactions

The Prenylflavonoid Isoxanthohumol from Hops (Humulus lupulus L.) Is Activated into the Potent Phytoestrogen 8-Prenylnaringenin In Vitro and in the Human Intestine¹

Sam Possemiers^*, Selin Bolca^*,, Charlotte Grootaert^*, Arne Heyerick, Karel Decroos^*, Willem Dhooge^**, Denis De Keukeleire, Sylvie Rabot, Willy Verstraete^* and Tom Van de Wiele^*,2

^* Laboratory of Microbial Ecology and Technology (LabMET), Faculty of Bioscience Engineering, Ghent University-UGent, B-9000 Gent, Belgium; Laboratory of Pharmacognosy and Phytochemistry, Faculty of Pharmaceutical Sciences, Ghent University-UGent, B-9000 Gent, Belgium; ^** Department of Endocrinology, Ghent University Hospital, B-9000 Gent, Belgium; and Unit on Ecology and Physiology of the Digestive Tract (UEPSD), National Institute for Agricultural Research (INRA), F-78352 Jouy-en-Josas Cedex, France

² To whom correspondence should be addressed. E-mail: tom.vandewiele{at}ugent.be.

Hops, an essential beer ingredient, are a source of prenylflavonoids, including 8-prenylnaringenin (8-PN), one of the most potent phytoestrogens. Because 8-PN concentrations in beers are generally low, its health effects after moderate beer consumption were considered negligible. However, human intestinal microbiota may activate up to 4 mg/L isoxanthohumol (IX) in beer into 8-PN. Depending on interindividual differences in the intestinal transformation potential, this conversion could easily increase the 8-PN exposure 10-fold upon beer consumption. Here, we present a further investigation of the process both in vitro and in vivo. In vitro experiments with the dynamic SHIME model showed that hop prenylflavonoids pass unaltered through the stomach and small intestine and that activation of IX into 8-PN (up to 80% conversion) occurs only in the distal colon. In vitro incubations of 51 fecal samples from female volunteers with IX enabled us to separate the fecal microbiota into high (8 of 51), moderate (11 of 51) and slow (32 of 51) 8-PN producers, clearly illustrating an interindividual variability. Three women, selected from the respective groups, received a daily dose of 5.59 mg IX for 4 d. Intestinal IX activation and urinary 8-PN excretion were correlated (R² = 0.6417, P < 0.01). These data show that intestinal conversion of IX upon moderate beer consumption can lead to 8-PN exposure values that might fall within the range of human biological activity.

KEY WORDS: • phytoestrogens • hops • 8-prenylnaringenin • intestinal bacteria • SHIME

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