Modification of the cellular antioxidant activity (CAA) assay to study phenolic antioxidants in a Caco-2 cell line

In vitro assays are widely used to analyze the antioxidant potential of compounds, but they cannot accurately predict antioxidant behavior in living systems. Cell-based assays, like the cellular antioxidant activity (CAA) assay, are gaining importance as they provide a biological perspective. When the CAA assay was employed to study phenolic antioxidants using hepatocarcinoma (HepG2) cells, quercetin showed antioxidant activity in HepG2 cells; 25 and 250 mu M quercetin reduced fluorescence by 17.1 +/- 0.9% and 58.6 +/- 2.4%, respectively. (+)-Catechin, a phenolic antioxidant present in many foods, bestowed virtually no CAA in HepG2 cells. When Caco-2 cells were employed, more robust antioxidant activity was observed; 50 mu M (+)-catechin and quercetin reduced fluorescence by 54.1 +/- 1.4% and 63.6 +/- 0.9%, respectively. Based on these results, likely due to differences in active membrane transport between the cell types, the Caco-2-based CAA assay appears to be a more appropriate method for the study of certain dietary phenolics.