Al metabolism of theaflavin esters (TFDG, TF3G, and TF39G) are consistent with previous findings that microbial enzymes cleave the gallate group of (?-epigallocatechin 3-O-gallate (EGCG) and (?-epicatechin 3-O-gallate (ECG) [13,28]. PG was reported as the major metabolite detected in both plasma and urine of rats fed ECG indicating that PG can be absorbed from the colon and then enters into the circulating system [29]. Both 2-O-sulfate-pyrogallol and 4-O-methyl-gallic acid were identified as the markers for black tea intake in human [30,31], which further demonstrated that lower molecular weight microbial metabolites can be absorbed by the host. Unbiased metagenomics sequencing has revealed that the human distal intestinal microbiota 
comprises two predominant phyla, the Firmicutes and Bacteroidetes, with lesser contributions from Proteobacteria and Actinobacteria, and minor contributions from Fusobacteria, Verrucomicrobia and Cyanobacteria [32,33]. Remarkably, at the phylum level the murine microbiota is very similar to the one observed in human [34]. Our study shows a similar profile of microbial metabolites of TFDG between miceand human, suggesting that functional studies on these metabolites could be performed in mice. Anlotinib Nevertheless, our human fecal batch fermentation experiment has identified PG as metabolite of TFDG, TF3G, TF39G, and GA suggesting that the human gut microbiota has a slightly different capacity to metabolize theaflavins as compared to the murine microbiota. This would be consistent with the unique profile of human microbiota compared to the murine one at the genus levels [34]. Future experiments using human fecal transplantation in mice are currently 520-26-3 web underway to better define the role of human biota in TFDG metabolism. Another important finding is the interindividual variation on the metabolism rate of GA to PG between human donors. The interindividual variability on the biotransformation of polyphenols into their microbial metabolites has been reported and recognized as an essential part of personalized nutrition approaches [14,22,35]. For example, only 25?0 of the adult population of Western countries and 50?0 23727046 of the adults from Japan, Korea, or China produce equol, the microbial metabolite of soy isoflavone daidzein [35]. It has been reported that isoflavone treatment in equol producer differentially affects gene expression as compared with nonproducers and a stronger effect on some putative estrogen-responsive genes was observed in equol produc-Microbial Metabolites of TheaflavinsFigure 5. HPLC-ECD chromatograms of microbial metabolites of TF3G after incubation with human fecal bacteria (A ). A, B and C represent the three human volunteers, respectively. TF3G: theaflavin 3-digallate. doi:10.1371/journal.pone.0051001.gers than in nonproducers [36]. In our study, subject B can hardly metabolize GA to PG, whereas, 15755315 subject C almost completely metabolizes 
GA to PG within 48 h incubation. Subject A has moderate activity in terms of metabolizing GA to PG. This suggests that microbial composition may impact on the ability of a given individual to generate theaflavins-derived metabolites. Nextgeneration sequencing on fecal material would help identify bacterial community associated with theaflavins-derived metabolites. These experiments may prove important in defining the human population better suited to generate theaflavins-derived metabolites. This population may include better responders of theaflavins-mediated bene.Al metabolism of theaflavin esters (TFDG, TF3G, and TF39G) are consistent with previous findings that microbial enzymes cleave the gallate group of (?-epigallocatechin 3-O-gallate (EGCG) and (?-epicatechin 3-O-gallate (ECG) [13,28]. PG was reported as the major metabolite detected in both plasma and urine of rats fed ECG indicating that PG can be absorbed from the colon and then enters into the circulating system [29]. Both 2-O-sulfate-pyrogallol and 4-O-methyl-gallic acid were identified as the markers for black tea intake in human [30,31], which further demonstrated that lower molecular weight microbial metabolites can be absorbed by the host. Unbiased metagenomics sequencing has revealed that the human distal intestinal microbiota comprises two predominant phyla, the Firmicutes and Bacteroidetes, with lesser contributions from Proteobacteria and Actinobacteria, and minor contributions from Fusobacteria, Verrucomicrobia and Cyanobacteria [32,33]. Remarkably, at the phylum level the murine microbiota is very similar to the one observed in human [34]. Our study shows a similar profile of microbial metabolites of TFDG between miceand human, suggesting that functional studies on these metabolites could be performed in mice. Nevertheless, our human fecal batch fermentation experiment has identified PG as metabolite of TFDG, TF3G, TF39G, and GA suggesting that the human gut microbiota has a slightly different capacity to metabolize theaflavins as compared to the murine microbiota. This would be consistent with the unique profile of human microbiota compared to the murine one at the genus levels [34]. Future experiments using human fecal transplantation in mice are currently underway to better define the role of human biota in TFDG metabolism. Another important finding is the interindividual variation on the metabolism rate of GA to PG between human donors. The interindividual variability on the biotransformation of polyphenols into their microbial metabolites has been reported and recognized as an essential part of personalized nutrition approaches [14,22,35]. For example, only 25?0 of the adult population of Western countries and 50?0 23727046 of the adults from Japan, Korea, or China produce equol, the microbial metabolite of soy isoflavone daidzein [35]. It has been reported that isoflavone treatment in equol producer differentially affects gene expression as compared with nonproducers and a stronger effect on some putative estrogen-responsive genes was observed in equol produc-Microbial Metabolites of TheaflavinsFigure 5. HPLC-ECD chromatograms of microbial metabolites of TF3G after incubation with human fecal bacteria (A ). A, B and C represent the three human volunteers, respectively. TF3G: theaflavin 3-digallate. doi:10.1371/journal.pone.0051001.gers than in nonproducers [36]. In our study, subject B can hardly metabolize GA to PG, whereas, 15755315 subject C almost completely metabolizes GA to PG within 48 h incubation. Subject A has moderate activity in terms of metabolizing GA to PG. This suggests that microbial composition may impact on the ability of a given individual to generate theaflavins-derived metabolites. Nextgeneration sequencing on fecal material would help identify bacterial community associated with theaflavins-derived metabolites. These experiments may prove important in defining the human population better suited to generate theaflavins-derived metabolites. This population may include better responders of theaflavins-mediated bene.
