Effects of uptake of flavonoids on oxidative stress induced by hydrogen peroxide in human intestinal Caco-2 cells

The relation between the uptake of flavonoids and the response of human colon adenocarcinoma Caco-2 cells exposed to oxidative stress induced by hydrogen peroxide (H2O2) was examined. Flavonoid aglycones were incorporated into Caco-2 cells in a concentration- and time-dependent manner, but neither glycosides nor unstable myricetin were incorporated. into the cells. The incorporated flavonoids reduced the reactive oxygen species (ROS) induced by H2O2 in the cells in proportion to the amount incorporated and the radical scavenging activity of flavonoids. But, flavonoids with high radical scavenging activity also generated H2O2. The activity decreasing intracellular ROS was inversely related to the H2O2 scavenging activity of flavonoids. Therefore, the decrease in the amount of intracellular ROS induced by H2O2 was not directly due to the scavenging of H2O2, but rather to the scavenging of ROS generated from H2O2. These results suggest that strong antioxidative flavonoids have both a cytoprotective effect owing to the scavenging of ROS and cytotoxic effect caused by the generation of H2O2.