Metabolism of soy isoflavones by bacteria of intestinal origin

Trabajo presentado en el 7th Congress of European Microbiologists (FEMS 2017), celebrado en Valencia (España), del 9 al 13 de julio de 2017[Backgrounds] High intake of soy or purified isoflavones has been associated with less intense menopause symptoms and a reduced risk of hormone-mediated diseases. Isoflavones from the diet can be metabolized into fully-active compounds or inactive metabolites by bacteria from the human gastrointestinal tract, which at present are poorly characterized. [Objectives] In this work, we assessed the metabolism of the two majority soy isoflavones (daidzein and genistein) by cultures of faecal slurries from menopausal woman with a positive or negative equol-production phenotype. [Methods] Faecal samples of five women were homogenized and inoculated in a general medium for colon bacteria. Faecal homogenates, bulk cultures and isolated colonies from the counting plates were incubated in GAM+0.5% arginine supplemented with 100 mM daidzein or genistein. Isoflavones and their metabolites in the cultures were analysed by UHPLC. In addition, microbial DNA was purified and used in conventional and real-time PCR analysis in order to identify and quantify specific genes involved in equol formation from daidzein. [Conclusions] Equol was only present in cultures derived from equol-producing women inoculated with homogenates and bulk colonies from the counting plates. Variable amounts of genistein and dihydrogenistein were scored when this isoflavone was added. Both ddr and tdr genes, encoding reductases involved in equol production, were detected in similar amounts in DNA from faeces and cultures thereof of equol-producing women. Occasionally, these genes were also correlated with genistein-derived metabolites. The biological significance of the presence/absence of tdr and ddr in isoflavone metabolism is currently under study.Peer reviewe