(−)-Epigallocatechin gallate causes oxidative damage to isolated and cellular DNA

Abstract

Green tea catechins, especially (−)-epigallocatechin gallate (EGCG), are believed to mediate much of the cancer chemopreventive effects of tea. However, it was reported that green tea catechins enhanced colon carcinogenesis in rats. Experiments using 32 P -labeled DNA fragments obtained from human cancer-related genes showed that catechins induced DNA damage in the presence of metals such as Cu(II) and Fe(III) complexes. In the presence of Fe(III)EDTA, the order of DNA damaging ability was EGCG ≈ (−)-epigallocatechin > (−)-epicatechin gallate ⪢ catechin. Catechins plus Fe(III)EDTA caused DNA damage at every nucleotide, most likely due to OH generation from H 2O 2. In the presence of Cu(II), the order was (−)-epigallocatechin > catechin > EGCG > (−)-epicatechin gallate. Cu(II)-mediated DNA damage by EGCG occurred most frequently at T and G residues, especially of 5′-TG-3′ and GG sequences. Catalase and bathocuproine inhibited the Cu(II)-mediated DNA damage, suggesting the involvement of H 2O 2 and Cu(I). In the presence of metal ions, increased amounts of 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxodG) were found in DNA treated with EGCG. Furthermore, EGCG increased amounts of 8-oxodG in HL-60 cells, but not in the H 2O 2-resistant clone HP100. When GSH was reduced by l-buthionine-[ S, R]-sulfoximine, a low concentration of EGCG increased amounts of 8-oxodG in HL-60 cells, further supporting the involvement of H 2O 2 in cellular DNA damage . It is concluded that EGCG can induce H 2O 2 generation and subsequent damage to isolated and cellular DNA, and that oxidative DNA damage may mediate the potential carcinogenicity of EGCG.