EVALUATION OF THE ANTIOXIDANT AND PROOXIDANT ACTIONS OF GALLIC ACID AND ITS DERIVATIVES

The antioxidant and prooxidant activities of gallic acid and its propyl, methyl, and (where solubility allowed) lauryl esters were investigated. Gallic acid (GA), propyl gallate (PG), and gallic acid methyl ester (GM) were able to scavenge hypochlorous acid at a rate sufficient to protect alpha-1-antiproteinase against inactivation by this molecule. When dissolved in ethanol, gallic acid lauryl ester (GL), PG, and GM decreased the peroxidation of ox brain phospholipids. GA had only a weak inhibitory effect. GM, GL, and PG reacted with CCl3O2. (trichloromethyl peroxyl radical) with rate constants of 1.23 X 10(7), 2.33 x 10(7), and 1.67 x 10(7) M-1 s-1, respectively. Gallic acid was much less reactive with a rate constant of 4.47 x 10(5) M-1 s-1. By contrast to these antioxidant properties, GA, GM, and PG accelerated damage to the sugar deoxyribose in the presence of ferric-EDTA and H2O2. GA also accelerated DNA damage by a ferric-bleomycin system. GM was less effective but GL had no effect. Reaction of NBT and cytochrome c by O2.- was only slightly inhibited by PG, GM, and GA, indicating that their rates of reaction with O2.- are low. Our data confirm the antioxidant actions of gallic acid lauryl, propyl, and methyl esters. However, they also show that both the prooxidant and antioxidant actions of ''proposed antioxidants'' should be fully characterized.