The role of human gut bacteria in bioactivation of polyphenolic isoflavones and pyranoanthocyanins

植物来源的黄酮类和其他多酚被认为对人类健康有有益的影响。肠道微生物区系可能在多酚化合物随食物和膳食补充剂摄入后的转化中发挥关键作用。人类肠道中存在的细菌不仅可以催化多酚类物质的脱糖和去结合作用，而且还能催化生成的苷元的转化。由此形成的细菌代谢物可能具有与母体化合物不同的生物活性。该项目旨在阐明人类肠道细菌在饮食中摄入的特定异黄酮和吡喃花青素的生物激活中所起的作用。在异黄酮类中，已知大豆苷元只被肠道细菌激活为马醇。将分离出马匹形成菌株，并使用生药大鼠模型在体内验证它们的活性。虽然已知大豆苷元是从人体肠道中的O-糖苷释放出来的，但它是由C-糖苷形成的，这一点还有待证明。因此，其8-C-葡萄糖苷葛根素形成细菌大豆苷元的相关性将通过体外发酵实验得到澄清。同样，肠道细菌的O-脱糖活性可能导致吡喃花青素的生物活化。为了验证这一假设，这些花青素衍生色素的成员，如松果苷A，将被纳入与细菌去糖基化和进一步转化相关的研究中。在该项目内获得的数据将有助于对所测试的多酚进行益处/风险评估。

Plant-derived flavonoids and other polyphenols are proposed to have beneficial effects on human health. The intestinal microbiota may play a key role in the conversion of polyphenolic compounds following their intake with food and dietary supplements. Bacteria present in the human gut have been shown to catalyze not only the deglycosylation and deconjugation of polyphenolics but also the transformation of the resulting aglycones. The bacterial metabolites thereby formed may have biological activities that differ from those of the parent compounds. The project aims to elucidate the role of human gut bacteria in the bioactivation of selected isoflavones and pyranoanthocyanins ingested with diet. Of the isoflavones, daidzein is known to be activated to equol exclusively by intestinal bacteria. Equol-forming strains will be isolated and their activity verified in vivo using a gnotobiotic rat model. Whereas daidzein is known to be released from O-glycosides in the human gut, its formation from C-glycosides still needs to be demonstrated. Thus, the relevance of bacterial daidzein formation from its 8-C-glucoside, puerarin, will be clarified by in vitro fermentation experiments. Similarly, the O-deglycosylating activity of gut bacteria may result in bioactivation of pyranoanthocyanins. To test this hypothesis, members of these anthocyanin-derived pigments, such as pinotin A, will be included in studies relating to bacterial deglycosylation and further conversion. The data obtained within the project will contribute to the benefit/risk assessment of the tested polyphenols.