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 prooxidant
mechanism for AA and GA acid is most likely due to the strong reducing power and weak metalchelating ability. # 2002
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