Antioxidant properties of (-)-epicatechin-3-gallate and its inhibition of Cr(VI)-induced DNA damage and Cr(IV)- or TPA-stimulated NF-κB activation

Electron spin resonance (ESR) spin trapping was utilized to investigate the scavenging effects on hydroxyl radicals (OH) and superoxide radicals (O₂^-) by (-)-epigallocatechin-3-gallate (EGCG), one of the major anticancer compounds in tea. The spin trap used was 5,5-dimethyl-pyrroline N-oxide (DMPO). The Fenton reaction (Fe²⁺ + H₂O₂ → Fe³⁺ + OH + OH^-) was used as a source of OH radicals. EGCG efficiently scavenges OH radicals with reaction rate of 4.62 x 10¹¹ M^-1 sec^-1, which is an order of magnitude higher than several well recognized antioxidants, such as ascorbate, glutathione and cysteine. It also scavenges O₂^-radicals as demonstrated by using xanthine and xanthine oxidase system as a source of O₂^- radicals. Through its antioxidant properties, EGCG exhibited a protective effect against DNA damage induced by Cr(VI). EGCG also inhibited activation of nuclear transcription factor NF-κB induced by Cr(IV) and 12-o- tetradecanoylphorbol-13-acetate (TPA). The present studies provide a mechanistic basis for the reported anticarcinogenic properties of EGCG and related tea products.