Institute of Industrial Fermentations (CSIC), Juan de la Cierva 3, 28006 Madrid, Spain.
Food Funct. 2010 Dec;1(3):233-53. doi: 10.1039/c0fo00132e. Epub 2010 Nov 17.
Flavan-3-ols, occurring in monomeric, as well as in oligomeric and polymeric forms (also known as condensed tannins or proanthocyanidins), are among the most abundant and bioactive dietary polyphenols, but their in vivo health effects in humans may be limited because of their recognition as xenobiotics. Bioavailability of flavan-3-ols is largely influenced by their degree of polymerization; while monomers are readily absorbed in the small intestine, oligomers and polymers need to be biotransformed by the colonic microbiota before absorption. Therefore, phenolic metabolites, rather than the original high molecular weight compounds found in foods, may be responsible for the health effects derived from flavan-3-ol consumption. Flavan-3-ol phenolic metabolites differ in structure, amount and excretion site. Phase II or tissular metabolites derived from the small intestine and hepatic metabolism are presented as conjugated derivatives (glucuronic acid or sulfate esters, methyl ether, or their combined forms) of monomeric flavan-3-ols and are preferentially eliminated in the bile, whereas microbial metabolites are rather simple conjugated lactones and phenolic acids that are largely excreted in urine. Although the colon is seen as an important organ for the metabolism of flavan-3-ols, the microbial catabolic pathways of these compounds are still under consideration, partly due to the lack of identification of bacteria with such capacity. Studies performed with synthesized or isolated phase II conjugated metabolites have revealed that they could have an effect beyond their antioxidant properties, by interacting with signalling pathways implicated in important processes involved in the development of diseases, among other bioactivities. However, the biological properties of microbe-derived metabolites in their actual conjugated forms remain largely unknown. Currently, there is an increasing interest in their effects on intestinal infections, inflammatory intestinal diseases and overall gut health. The present review will give an insight into the metabolism and microbial biotransformation of flavan-3-ols, including tentative catabolic pathways and aspects related to the identification of bacteria with the ability to catabolize these kinds of polyphenols. Also, the in vitro bioactivities of phase II and microbial phenolic metabolites will be covered in detail.
黄烷-3-醇以单体、低聚体和聚合物形式（也称为缩合单宁或原花青素）存在，是最丰富和最具生物活性的膳食多酚之一，但由于它们被认为是异源生物，其在人体中的健康影响可能有限。黄烷-3-醇的生物利用度在很大程度上受到其聚合度的影响；虽然单体在小肠中很容易被吸收，但低聚体和聚合物需要被结肠微生物群生物转化后才能被吸收。因此，酚类代谢物，而不是在食物中发现的原始高分子量化合物，可能是黄烷-3-醇消费带来健康影响的原因。黄烷-3-醇酚类代谢物在结构、数量和排泄部位上有所不同。从小肠和肝脏代谢中衍生的 II 相或组织代谢物呈现为单体黄烷-3-醇的共轭衍生物（葡萄糖醛酸或硫酸盐酯、甲基醚或它们的组合形式），并优先在胆汁中排泄，而微生物代谢物则是简单的共轭内酯和酚酸，主要在尿液中排泄。尽管结肠被视为黄烷-3-醇代谢的重要器官，但这些化合物的微生物代谢途径仍在研究中，部分原因是缺乏具有这种能力的细菌的鉴定。用合成或分离的 II 相共轭代谢物进行的研究表明，它们可能具有超越抗氧化特性的作用，通过与涉及疾病发展等重要过程的信号通路相互作用。然而，微生物衍生代谢物在其实际共轭形式下的生物特性在很大程度上仍然未知。目前，人们对它们在肠道感染、炎症性肠道疾病和整体肠道健康方面的影响越来越感兴趣。本综述将深入了解黄烷-3-醇的代谢和微生物生物转化，包括暂定的代谢途径以及与鉴定具有代谢这些类多酚能力的细菌相关的方面。此外，还将详细介绍 II 相和微生物酚类代谢物的体外生物活性。
