Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/5/2009
Publication Date: 10/13/2009
Citation: Bialonska, D., Kasimsetty, S.G., Khan, S.I., Ferreira, D. 2009. Urolithins, Intestinal Microbial Metabolites of Pomegranate Ellagitannins, Exhibit Potent Antioxidant Activity in Cell-Based Assay. Journal of Agricultural and Food Chemistry. 57(21):10181-10186. Interpretive Summary: As part of a study on beneficial effects of pomegranate, antioxidant potential of urolithins were evaluated. Ellagitannins are the main components of pomegranate which are metabolized by gut bacteria to urolithins which enter the circulation. Urolithin C and Urolithin D were most potent in exhibiting antioxidant property. They were more potent than the parent ellagic acid and punicalagins. This study indicated that the beneficial effects of pomegranate could be accounted for the microbial transformation of its ellagitannins to urolithins which are responsible for potential antioxidant effects.
Technical Abstract: Many health benefits of pomegranate products have been attributed to the potent antioxidant action of their tannin components, mainly punicalagins and ellagic acid. While moving through the intestines, ellagitannins are metabolized by gut bacteria into urolithins that readily enter systemic circulation. In this study, the antioxidant properties of seven urolithin derivatives were evaluated in a cell-based assay. This method is biologically more relevant because it reflects bioavailability of the test compound to the cells, and the antioxidant action is determined in the cellular environment. Our results showed that the antioxidant activity of urolithins was correlated with the number of hydroxy groups as well as the lipophilicity of the molecule. The most potent antioxidants are urolithins C and D with IC50 values of 0.16 and 0.33 µM, respectively, when compared to IC50 values of 1.1 and 1.4 µM of the parent ellagic acid and punicalagins, respectively. The dihydroxylated urolithin A showed weaker antioxidant activity, with an IC50 value 13.6 µM, however, the potency was within the range of urolithin A plasma concentrations. Therefore, products of the intestinal microbial transformation of pomegranate ellagitannins may account for systemic antioxidant effects.