Intracellular Polyphenols: How Little We Know.

In vitro cell studies are used by scientists to determine mechanisms that can be operating in vivo and pave the way for animal and human studies. Polyphenols, the major antioxidants in plants and the human diet, have been extensively studied in cells within thousands of publications. However, glucuronides, sulfates, and methyl metabolites and not the original polyphenols are generally present in the circulation and often have weaker beneficial effects in cell studies. The number of articles in the literature involving their cellular metabolites is quite small. We will critically examine the knowledge we have up to the present regarding polyphenols and cells in five areas: stability in in vitro cell culture media, metabolites, conjugation/deconjugation, transport to cells, and cells in vivo. Also, the future research needs in the field of polyphenols and their metabolites with cells will be outlined.