Antioxidant and pro-oxidant properties of ascorbic acid and gallic acid

The antioxidant and pro-oxidant properties of ascorbic acid (AA) and gallic acid (GA) were investigated. AA and GA, at a concentration of 1.65 mM, accelerate the oxidation of deoxyribose induced by Fe3+–EDTAJH2O2. The reducing power of these two compounds increased upon increasing the concentration. AA and GA showed no chelating ability toward iron (II). At a concentration of 4.17 mM, AA and GA exhibited 42.1 and 43.9% scavenging effects on DPPH radicals, respectively. They exhibited 60% scavenging effects on hydrogen peroxide at a concentration of 4.17 mM. No toxicity was found in AA and GA toward human lymphocytes. AA, at 0.82 mM, and GA, at 0.6 mM, exhibited the maximal DNA damage, the means of tail DNA% were 14.8 and 28.8%, respectively. When AA and GA were mixed with H2O2, they exhibited a slight inhibitory effect on DNA damage induced by H2O2 on pre-incubating both the compounds with human lymphocytes for 30 min before exposure to H2O2. The antioxidant activities of AA and GA at a higher concentration were mainly due to the scavenging of hydrogen peroxide in this system. The pro-oxidant mechanism for AA and GA acid is most likely due to the strong reducing power and weak metalchelating ability.