Many ROS-generating natural products and drugs had been reported but their selective killing effects were sometimes not investigated [5-7]. It was warranted for further investigation about its possible selective killing effects. In contrast, it is noted that the ROS-generating natural products and drugs are not always displaying the selective killing effect.Some antioxidants were reported to have dual roles for cell survival and cell killing
in respective to different dosages , i.e., it displayed the survival effects at physiologic doses and the deleterious effects at high doses. In case of grape seed extracts, the famous natural products with an antioxidant property, it was found to be healthy to normal oral cells but inhibited the proliferation of oral cancer Ca9-22 cells at high doses .
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