Characterization of Polyphenol Metabolites

Abstract

Dietary phytochemicals, food plant secondary metabolites, are a diverse range of low molecular weight compounds that include the flavonoids, hydroxycinnamates, glucosinolates, and allylsulfides. Consumption of plant foods is associated with a reduced risk of chronic diseases such as cardiovascular disease and cancer, as demonstrated by the results of epidemiological cohort and case-control studies [1, 2]. It is likely that at least part of the protection from plant foods results from the action of the phytochemical component [3]; this may arise through mechanisms involving (direct or indirect) antioxidant activity, modulation of enzyme activity (including inhibition of phase I enzymes and induction of phase II enzymes), and modulation of gene expression [4, 5]. In addition to this epidemiological data, the putative evidence for the biological activity of phytochemicals arises from animal studies, cell and tissue culture studies, and in vitro experiments. Frequently these studies are carried out with the phytochemicals of interest not in the form present in the diet, as metabolites (e.g., nonglycosylated or nonconjugated forms), and/or at concentrations considerably higher than those obtainable through a normal diet. Not only could such factors have a profound effect on the interpretation of the results from in vitro studies, but experimentation with nonphysiologically relevant compounds may also influence the rate and extent of absorption and the range of metabolites produced in the animal and cell culture studies. Furthermore, model systems may display qualitatively and quantitatively different metabolic pathways for phytochemicals when compared to their behavior in humans. It is also worth noting that there is considerable inter-individual variation in metabolism of phyto-chemicals due