Association between polyphenol metabolism and polymorphisms in intestinal drug metabolising enzymes and its relation to health benefits

Epidemiological studies suggest that regular consumption of black and green tea is associated with a reduction in risk of a range of pathological conditions including cardiovascular diseases and selected cancers. In vitro studies suggest that the effects seen in epidemiological studies are partially caused by catechins and polymers thereof present in tea. However, limitations in these studies are that they mostly do not take into account the very low bioavailability of polyphenols with peak plasma concentration in the sub-micromolar range. To date it is still unclear which molecular forms of polyphenols could mediate these effects, and what the potential mechanisms of action are. The poor bioavailability of polyphenols is caused inter alia by extensive biotransformation by xenobiotic metabolising enzymes. Metabolism of catechins by intestinal phase II metabolising enzymes such as catechol-O-methyl-transferase (COMT) and UDP-glucuronosyltransferases (UGT's) has been shown. In addition, in vitro data suggest that selected polyphenols can induce activity of a number of phase I metabolising enzymes such as cytochroms CYP450 1A1. In turn, activation of phase I and phase II enzymes could change bioavailability of other polyphenolic compounds. Furthermore, polymorphism in those enzymes has been suggested to influence metabolic rate and absolute bioavailability of polyphenols. Overall, there is a lack of understanding how and to which extent polyphenols are biotransformed during absorption and how this process is related to their potential health beneficial effects. The overall aim of the proposed project is therefore to discover the effects of green and black tea polyphenols on phase I, II and III enzymes using both tissue culture and a human intervention study. The goal of the project is to elucidate which different polyphenol metabolites are produced and how genetic variation might explain some of the observed between-subject differences seen in human studies. Finally, the project aims at identifying whether polyphenol metabolites are able to reduce mitochondrial DNA damage. The main objectives are to identify metabolic profiles of tea polyphenols in tissue cultures, phase I, II and III enzymes involved, and genetic differences in phase I, II and III metabolism. An important early milestone will be the identification of major tea polyphenol metabolites using appropriate in vitro models for intestinal and liver metabolism. To achieve this we will make use of established models such as intestinal microsomes, HepG2 cells and liver slices. Metabolic profiles will be determined using state-of-the-art HPLC-MS/MS methods. Results from metabolic profiling will be used to identify the major xenobiotic metabolising enzymes involved. In addition, it is planned to determine gene and protein expression of key phase I, II and III enzymes involved in metabolism of tea polyphenols in tissue cultures and buccal mucosal cells. Quantitative PCR as well as microarray analysis will highlight metabolic pathways as well as key phase I, II and III enzymes differentially regulated after tea administration. The subsequent step will be identification of common single nucleotide polymorphisms in key phase I, II and III enzymes in human buccal mucosal cells. The scientific challenge will be to link those polymorphism with a frequency >5% to metabolic profiles in humans. A human intervention study will be performed to address these questions. This project will be a major milestone in unravelling the potential health beneficial effects of tea polyphenol by shedding more light on which metabolites are produced by phase I, II and III enzymes, at which concentrations they circulate in plasma and to what extent the large observed between-subject variation in humans is linked to genetic variations in xenobiotic metabolising enzymes.