Topical Area: Dietary Bioactive Components
Objectives : 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. The objective of this study is to investigated the in vivo interaction between tea polyphenols and ammonia and RCS.
Methods : In mice, we gave 200 mg/kg tea polyphenol ((-)-epigallocatechin-3-gallate (EGCG) or theaflavin) to CD-1 mice, 129/SvEv specific-pathogen-free (SPF) mice, or germ-free (GF) mice. Urinary and fecal samples were collected in metabolic cages for 24 h. In humans, two healthy volunteers drank 4 cups of Lipton green tea every day for four days. On the fourth day, 24 h urinary and fecal samples were collected after consuming the first cup of tea. Using LC tandem mass, we searched the formation of the aminated and RCS conjugated metabolites of tea polyphenols. Chemical standards were synthesized to confirm the structures of these metabolites. In order to study the impact of gut microbiota on the formation of these metabolites, we also quantified the concentrations of these metabolites in SPF and GF mice.
Results : We found that both EGCG and theaflavin could rapidly react with ammonia to generate the aminated metabolites. Both tea polyphenols and their aminated metabolites could further scavenge RCS, such as methylglyoxal (MGO), malondialdehyde (MDA), and trans-4-hydroxy-2-nonenal (4-HNE), to produce the RCS conjugates of tea polyphenols and the aminated tea polyphenols. 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 or theaflavin exposed germ-free (GF) mice and specific-pathogen-free (SPF) mice, we demonstrated that gut microbiota facilitate the formation of the aminated metabolites of tea polyphenols, the RCS conjugates of tea polyphenols, and the RCS conjugates of the aminated tea polyphenols.
Conclusions : Altogether, this study provides in vivo evidences that tea polyphenols have 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.
Funding Sources : We gratefully acknowledge financial support from NIH R01 grant AT008623 to this work.