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

Electron spin resonance (ESR) spin trapping was utilized to investigate the scavenging effects on hydroxyl radicals ((OH)-O-.) and superoxide radicals (O-2(.-)) by (-)-epigallocatechin-3-gallate (EGCG), one of the major antic ancer compounds in tea. The spin trap used was 5,5-dimethyl-pyrroline N-oxi de (DMPO). The Fenton reaction (Fe2+ + H2O2 --> Fe3+ + (OH)-O-. + OH-) was used as a source of (OH)-O-. radicals. EGCG efficiently scavenges (OH)-O-. radicals with reaction rate of 4.62 x 10(11) M-1 sec(-1), which is an order of magnitude higher than several well recognized antioxidants, such as asc orbate, glutathione and cysteine. It also scavenges O-2(.-) radicals as dem onstrated by using xanthine and xanthine oxidase system as a source of O-2( .-) radicals. Through its antioxidant properties, EGCG exhibited a protecti ve effect against DNA damage induced by Cr(VI). EGCG also inhibited activat ion of nuclear transcription factor NF-kappa B induced by Cr(IV) and 12-o-t etradecanoylphorbol-13-acetate (TPA). The present studies provide a mechani stic basis for the reported anticarcinogenic properties of EGCG and related tea products.