Bidirectional Interactions between Green Tea (GT) Polyphenols and Human Gut Bacteria

Abstract

Green tea (GT) polyphenols undergo extensive metabolism within gastrointestinal tract (GIT), where their derivatives compounds potentially modulate the gut microbiome. This biotransformation process involves a cascade of exclusive gut microbial enzymes which chemically modify the GT polyphenols influencing both their bioactivity and bioavailability in host. Herein, we examined the in vitro interactions between 37 different human gut microbiota and the GT polyphenols. UHPLC-LTQ-Orbitrap-MS/MS analysis of the culture broth extracts unravel that genera Adlercreutzia, Eggerthella and Lactiplantibacillus plantarum KACC11451 promoted C-ring opening reaction in GT catechins. In addition, L. plantarum also hydrolyzed catechin galloyl esters to produce gallic acid and pyrogallol, and also converted flavonoid glycosides to their aglycone derivatives. Biotransformation of GT polyphenols into derivative compounds enhanced their antioxidant bioactivities in culture broth extracts. Considering the effects of GT polyphenols on specific growth rates of gut bacteria, we noted that GT polyphenols and their derivate compounds inhibited most species in phylum Actinobacteria, Bacteroides, and Firmicutes except genus Lactobacillus. The present study delineates the likely mechanisms involved in the metabolism and bioavailability of GT polyphenols upon exposure to gut microbiota. Further, widening this workflow to understand the metabolism of various other dietary polyphenols can unravel their biotransformation mechanisms and associated functions in human GIT.

Keywords: Gut microbiota; LC-MS/MS; biotransformation; green tea; polyphenols.

Fig. 1. Chemical structures of major GT polyphenol classes used in this study.

(A) GT catechins, and (B) flavonoids. Here, G represents gallate moiety.

Fig. 2. Proposed biotransformation mechanisms and heat-map showing the relative levels of major GT phenolics in spent media extracts from four gut bacteria.

The colored squares indicate the fold changes (blue - to - red) normalized by the average abundance of the corresponding compounds in samples. Bacterial strain codes are the following: A: Adlercreutzia equolifaciens; E: Eggerthella lenta; AP: Lactiplantibacillus plantarum APsulloc 331261; LP: Lactiplantibacillus plantarum KACC11451.

Fig. 3. Proposed biotransformation pathways and heat-map showing the relative levels of major GT flavonoids in spent media extracts from four gut bacteria.

The colored squares indicate the fold changes (blue - to - red) normalized by the average abundance of the corresponding compounds in samples. Bacterial strain codes are the following: A: Adlercreutzia equolifaciens; E: Eggerthella lenta; AP: Lactiplantibacillus plantarum APsulloc 331261; LP: Lactiplantibacillus plantarum KACC11451.

Fig. 4. Bioactivity phenotypes for gut microbial spent media extracts following GT treatment.

The bar graphs represent, (A) antioxidant activity, (B) total phenolic contents, and (C) total flavonoid content, for gut microbial cultures. The bar colors represent different time points - white color: 0 h; gray color: mid harvest point; black color: final harvest point. All values are expressed as the average of three biological replicates with standard deviation. The bar graph denoted by the same letter indicates absence of statistical differences, according to Duncan’s multiple range test (p < 0.05).

Fig. 5. Pearson’s correlation analysis between bioactivity phenotypes and GT metabolites biotransformed in gut bacteria cultures.

Herein, the bioactivity phenotypes including antioxidant activity (ABTS), total flavonoid contents (TFC), and total phenolic contents (TPC) were correlated with GT polyphenols and their derivatives. Strength of Pearson’s correlation coefficient values (r) between GT metabolites and bioactivity phenotypes is represented with heat-map. Red and blue a indicate positive (0 < r < 1) and negative (-1 < r < 0) correlation, respectively. (*p < 0.05, ^aTFC represents the Total Flavonoid Contents; ^bTPC represents the Total Phenolic Contents).

Fig. 6. The growth modulatory effects of green tea (GT) polyphenols and derivatives on growth rates (μ_max) of gut microbes used in this study.

The variation in growth rates are indicated with heap-map and the values in colored squares represent the fold changes (blue - to - red) normalized with growth rate for corresponding control cultures.

Fig. 7. The growth modulatory effect of green tea (GT) extracts and their major flavonoids on selected gut microbe growth rates (μ_max).

The values in heat-map represent the fold changes (blue - to - red) values for growth rates normalized with corresponding control cultures.