A comparison of scavenging abilities of antioxidants against hydroxyl radicals.

The reactivities of various antioxidative compounds including catechol derivatives and endogenous radical scavengers toward hydroxyl radical (.OH) were investigated by an electron spin resonance-spin trapping method, thiobarbituric acid method, and DNA strand scission assay. Hydroxyl radical was generated by both the reaction of Cu(II) complex with hydrogen peroxide (H2O2) and ultraviolet (uv) photolysis of H2O2. At physiological pH, catechol derivatives such as protocatechuic acid and catechin greatly suppressed the DNA strand scission by .OH produced from the reaction of Cu(en)2 with H2O2, whereas ascorbic acid and acetylcysteine accelerated DNA strand scission. The former case is due to the chelation of catechol derivatives to Cu(II) ion, forming of Cu(II) complexes being unable to react with H2O2, and the latter case is due to the acceleration of the reduction rate of Cu(II) to Cu(I). On the other hand, all compounds used here suppressed the DNA strand scission by .OH produced from uv photolysis of H2O2. The differences of the reactivities between the reaction system of Cu(en)2-H2O2 and the uv photolysis of H2O2 have been discussed.