Effects of human intestinal flora on plasma and caecal isoflavones, and effects of isoflavones on the composition and metabolism of flora in human flora-associated (HFA) mice

Abstract

Much attention has focused on the isoflavones present in soybeans. In this study, we investigated the influence of human intestinal flora on plasma and caecal isoflavones using human flora-associated (HFA) mice. The GI (germfree-isoflavone) and HI (HFA-isoflavone) mice were administered daidzein and genistein and the GC (germ-free control) and HC (HFA control) mice were administered solvent over a 4-day period. The plasma and caecal isoflavones were analysed by high-performance liquid chromatography (HPLC). Caecal bacterial β-glucosidase and β-glucuronidase activities were also measured. The composition of intestinal flora was analysed. The total amounts of daidzein and genistein in the caecum were significantly higher in the GI mice than in the HI mice. Equol was detected only in the plasma and caecal contents of the HI mice. The caecal β-glucosidase activity was significantly lower in the HFA mice administered isoflavones (p < 0.05). Isoflavone administration led to a significant increase in faecal clostridia in the faeces of the HI mice. The present study suggests that the human intestinal flora plays an important role in the metabolism and absorption of isoflavones. The HFA mice employed in this study may be useful tools for studying the role of human intestinal flora on the effects of dietary isoflavones on the host in vivo.