Oikawa Shinji, Furukawaa Ayako, Asada Hideyuki, Hirakawa Kazutaka, Kawanishi Shosuke
Department of Environmental and Molecular Medicine, Mie University School of Medicine, Edobashi 2-174, Tsu, Mie 514-8507, Japan.
Free Radic Res. 2003 Aug;37(8):881-90. doi: 10.1080/1071576031000150751.
Green tea catechins have antimutagenic and anticarcinogenic activities. On the other hand, several epidemiological studies have indicated significant positive relationship between green tea consumption and cancer. Catechins enhance colon carcinogenesis in rats initiated with chemical carcinogen. To clarify the mechanism underlying the potential carcinogenicity, we investigated the DNA-damaging ability of catechins in human cultured cells. Catechin increased the formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), a characteristic oxidative DNA lesion, in human leukemia cell line HL-60 but not in HP100, a hydrogen peroxide (H2O2)-resistant cell line derived from HL-60. The catechin-induced formation of 8-oxodG in HL-60 cells significantly decreased by bathocuproine. Furthermore, we investigated DNA damage and its site-specificity induced by catechins, using 32P-labeled DNA fragments. Catechin and epicatechin induced extensive DNA damage in the presence of Cu(II). Catechin caused piperidine-labile sites at thymine and cytosine residues in the presence of Cu(II). Catalase and bathocuproine inhibited the DNA damage, indicating the involvement of H2O2 and Cu(I). NADH enhanced catechins plus Cu(II)-induced 8-oxodG formation in calf thymus DNA, suggesting the redox cycle between catechins and their corresponding quinones, the oxidized forms of catechins. The DNA-damaging ability of epicatechin is stronger than that of catechin, possibly due to the greater turnover frequency of the redox cycle. The difference in their redox properties could be explained by their redox potentials estimated form an ab initio molecular orbital calculation. The present study demonstrated that catechins could induce metal-dependent H2O2 generation during the redox reactions and subsequently damage to cellular and isolated DNA. Therefore, it is reasonably considered that green tea catechins may have the dual function of anticarcinogenic and carcinogenic potentials.
绿茶儿茶素具有抗诱变和抗癌活性。另一方面，多项流行病学研究表明绿茶消费与癌症之间存在显著的正相关关系。儿茶素会增强经化学致癌物启动的大鼠的结肠癌发生。为阐明潜在致癌性的潜在机制，我们研究了儿茶素在人培养细胞中的DNA损伤能力。儿茶素在人白血病细胞系HL-60中增加了8-氧代-7,8-二氢-2'-脱氧鸟苷（8-氧代dG）的形成，这是一种典型的氧化性DNA损伤，但在HP100中未增加，HP100是一种源自HL-60的抗过氧化氢（H2O2）细胞系。儿茶素诱导的HL-60细胞中8-氧代dG的形成被铜试剂显著降低。此外，我们使用32P标记的DNA片段研究了儿茶素诱导的DNA损伤及其位点特异性。儿茶素和表儿茶素在Cu(II)存在下诱导广泛的DNA损伤。儿茶素在Cu(II)存在下导致胸腺嘧啶和胞嘧啶残基处出现哌啶不稳定位点。过氧化氢酶和铜试剂抑制了DNA损伤，表明H2O2和Cu(I)的参与。NADH增强了儿茶素加Cu(II)诱导的小牛胸腺DNA中8-氧代dG的形成，表明儿茶素与其相应醌（儿茶素的氧化形式）之间的氧化还原循环。表儿茶素的DNA损伤能力强于儿茶素，这可能是由于氧化还原循环的周转频率更高。它们氧化还原性质的差异可以通过从头算分子轨道计算估计的氧化还原电位来解释。本研究表明，儿茶素在氧化还原反应过程中可诱导金属依赖性H2O2生成，随后对细胞和分离的DNA造成损伤。因此，合理认为绿茶儿茶素可能具有抗癌和致癌潜力的双重功能。
