Gut Microbiota as a Novel Tool to Dissect the Complex Structures of Black Tea Polymers.

Thearubigins, polymers of tea catechins, account for more than 20% of the black tea polyphenols and have been reported to be the active components in black tea. However, the chemical structures and underlying mechanisms regarding how the thearubigins, being poorly bioavailable, generate in vivo health benefits are still largely unknown. Using germ-free and specific pathogen-free husbandry conditions combined with LC/MS-based nontargeted and targeted metabolomic analyses, we investigated the role of intestinal bacteria in thearubigin metabolism. Theaflavins and theasinensins were identified as the major microbial metabolites of thearubigins, suggesting that these molecules are the building units for the complex thearubigins. To further confirm this, thearubigin depolymerization was done using menthofuran in an acidic condition. Menthofuran-conjugated theaflavins, theasinensins, and catechins as well as their free forms were detected as the major degradation products of thearubigins. This indicated that theaflavins and theasinensins could be further polymerized through B-type proanthocyanidin linkages. Furthermore, four microbial degradation products were able to be detected in urine samples, suggesting that they can be absorbed into the circulatory system. Using the combination of microbial degradation, metabolomics, and chemical degradation, our results demonstrate that thearubigins are the complex polymers of theaflavins, theasinensins, and catechins and can be metabolized by gut microbiota to their corresponding bioactive and bioavailable smaller molecular metabolites.

Black Tea Theaflavin Detoxifies Metabolic Toxins in the Intestinal Tract of Mice.

SCOPE: This study is to determine the in vivo efficacy of black tea theaflavin (TF) to detoxify two metabolic toxins, ammonia and methylglyoxal (MGO), in mice METHODS AND RESULTS: Under in vitro conditions, TF is able to react with ammonia, MGO, and hydrogen peroxide to produce its aminated, MGO conjugated, and oxidized products, respectively. In TF-treated mice, the aminated TF, the MGO conjugates of TF and aminated TF, and the oxidized TF are searched using LC-MS/MS. The results provide the first in vivo evidence that the unabsorbed TF is able to trap ammonia to form the aminated TF; furthermore, both TF and the aminated TF have the capacity to trap MGO to generate the corresponding mono-MGO conjugates. Moreover, TF is oxidized to dehydrotheaflavin, which underwent further amination in the gut. By exposing TF to germ-free (GF) mice and conventionalized mice (GF mice colonized with specific-pathogen-free microbiota), the gut microbiota is demonstrated to facilitate the amination and MGO conjugation of TF. CONCLUSION: TF has the capacity to remove the endogenous metabolic toxins through oxidation, amination, and MGO conjugation in the intestinal tract, which can potentially explain why TF still generates in vivo efficacy while showing a poor systematic bioavailability.

Microbiota facilitates the formation of the aminated metabolite of green tea polyphenol (-)-epigallocatechin-3-gallate which trap deleterious reactive endogenous metabolites.

The in vivo mechanism of tea polyphenol-mediated prevention of many chronic diseases is still largely unknown. Studies have shown that accumulation of toxic reactive cellular metabolites, such as ammonia and reactive carbonyl species (RCS), is one of the causing factors to the development of many chronic diseases. In this study, we investigated the in vivo interaction between (-)-epigallocatechin-3-gallate (EGCG), the most abundant polyphenol in tea leaves, and ammonia and RCS. We found that EGCG could be oxidized to EGCG quinone in mice, and then rapidly react with ammonia to generate the aminated EGCG metabolite, 4'-NH2-EGCG. Both EGCG and its aminated metabolite could further scavenge RCS, such as methylglyoxal (MGO), malondialdehyde (MDA), and trans-4-hydroxy-2-nonenal (4-HNE), to produce the RCS conjugates of EGCG and the aminated EGCG. Both the aminated and the RCS conjugated metabolites of EGCG were detected in human after drinking four cups of green tea per day. By comparing the levels of the aminated and the RCS conjugated metabolites in EGCG exposed germ-free (GF) mice and specific-pathogen-free (SPF) mice, we demonstrated that gut microbiota facilitate the formation of the aminated metabolite of EGCG, the RCS conjugates of EGCG, and the RCS conjugates of the aminated EGCG. By comparing the trapping capacities of EGCG and its aminated metabolite under aerobic and anaerobic conditions, we found that oxygen is not essential for the trapping of reactive species by EGCG and 4'-NH2-EGCG suggesting that EGCG and its aminated metabolite could scavenge RCS in the GI track and in the circulation system. Altogether, this study provides in vivo evidences that EGCG has the capacity to scavenge toxic reactive metabolic wastes. This finding opens a new window to understand the underlying mechanisms by which drinking tea could prevent the development of chronic diseases.

Effects of Lactobacillus helveticus on murine behavior are dependent on diet and genotype and correlate with alterations in the gut microbiome.

Modulation of the gut microbiota with diet and probiotic bacteria can restore intestinal homeostasis in inflammatory conditions and alter behavior via the gut-brain axis. The purpose of this study was to determine whether the modulatory effects of probiotics differ depending on diet and mouse genotype. At weaning, wild type (WT) and IL-10 deficient (IL-10(-/-)) 129/SvEv mice were placed on a standard mouse chow or a Western-style diet (fat 33%, refined carbohydrate 49%)±Lactobacillus helveticus ROO52 (10(9)cfu/d) for 21 days. Animal weight and food eaten were monitored weekly. Intestinal immune function was analysed for cytokine expression using the Meso Scale Discovery platform. Spatial memory and anxiety-like behavior was assessed in a Barnes maze. Terminal restriction fragment length polymorphism (TRFLP) was used to analyze the fecal microbiota. Both WT and IL-10(-/-) mice on a Western diet had increased weight gain along with changes in gut microbiota and cytokine expression and altered anxiety-like behavior. The ability of L. helveticus to modulate these factors was genotype- and diet-dependent. Anxiety-like behavior and memory were negatively affected by Western-style diet depending on inflammatory state, but this change was prevented with L. helveticus administration. However, probiotics alone decreased anxiety-like behavior in WT mice on a chow diet. Mice on the Western diet had decreased inflammation and fecal corticosterone, but these markers did not correlate with changes in behavior. Analysis of bacterial phyla from WT and IL-10(-/-)mice showed discrete clustering of the groups to be associated with both diet and probiotic supplementation, with the diet-induced shift normalized to some degree by L. helveticus. These findings suggest that the type of diet consumed by the host and the presence or absence of active inflammation may significantly alter the ability of probiotics to modulate host physiological function.