Ohnishi Shiho, Hiraku Yusuke, Hasegawa Keishi, Hirakawa Kazutaka, Oikawa Shinji, Murata Mariko, Kawanishi Shosuke
Faculty of Pharmaceutical Sciences, Suzuka University of Medical Science, 3500-3, Minamitamagaki, Suzuka, Mie 513-8670, Japan.
Department of Environmental and Molecular Medicine, Mie University Graduate School of Medicine, Tsu, Mie 514-8507, Japan.
Mutat Res Genet Toxicol Environ Mutagen. 2018 Mar;827:42-49. doi: 10.1016/j.mrgentox.2018.01.005. Epub 2018 Jan 16.
Naphthalene is a carcinogenic polycyclic aromatic hydrocarbon, to which humans are exposed as an air pollutant. Naphthalene is metabolized in humans to reactive intermediates such as 1,2-hydroxynaphthalene (1,2-NQH), 1,4-NQH, 1,2-naphthoquinone (1,2-NQ), and 1,4-NQ. We examined oxidative DNA damage by these naphthalene metabolites using P-labeled DNA fragments from human cancer-relevant genes. 1,2-NQH and 1,4-NQH induced DNA damage in the presence of Cu(II). The DNA-damaging activity of 1,2-NQH was significantly increased in the presence of the reduced form of nicotinamide adenine dinucleotide (NADH), whereas that of 1,4-NQH was not. In the presence of NADH, 1,2-NQ induced Cu(II)-dependent DNA damage, whereas 1,4-NQ did not. The calculated energy of the lowest unoccupied molecular orbital (LUMO), which corresponds to the reduction potential, was estimated to be -0.67 eV for 1,2-NQ and -0.75 eV for 1,4-NQ. These results suggest that 1,2-NQ was reduced more easily than 1,4-NQ. Furthermore, 1,2-NQH, 1,4-NQH, and 1,2-NQ plus NADH formed 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) as an oxidative DNA marker. Catalase and bathocuproine inhibited DNA damage, suggesting that HO and Cu(I) were involved. These results indicate that NQHs are oxidized to the corresponding NQs via semiquinone radicals, and that HO and Cu(I) are generated during oxidation. 1,2-NQ is reduced by NADH to form the redox cycle, resulting in enhanced DNA damage. The formation of the corresponding semiquinone radicals was supported by an electron paramagnetic resonance (EPR) study. In conclusion, the redox cycle of 1,2-NQ/1,2-NQH may play a more important role in the carcinogenicity of naphthalene than that of 1,4-NQ/1,4-NQH.
萘是一种致癌性多环芳烃，人类会作为空气污染物接触到它。萘在人体内代谢为活性中间体，如1,2 - 羟基萘（1,2 - NQH）、1,4 - NQH、1,2 - 萘醌（1,2 - NQ）和1,4 - NQ。我们使用来自人类癌症相关基因的P标记DNA片段，研究了这些萘代谢物引起的氧化性DNA损伤。1,2 - NQH和1,4 - NQH在Cu(II)存在的情况下诱导DNA损伤。在烟酰胺腺嘌呤二核苷酸（NADH）的还原形式存在时，1,2 - NQH的DNA损伤活性显著增加，而1,4 - NQH的则没有。在NADH存在时，1,2 - NQ诱导Cu(II)依赖性DNA损伤，而1,4 - NQ则不会。对应于还原电位的最低未占据分子轨道（LUMO）的计算能量，估计1,2 - NQ为 - 0.67 eV，1,4 - NQ为 - 0.75 eV。这些结果表明，1,2 - NQ比1,4 - NQ更容易被还原。此外，1,2 - NQH、1,4 - NQH以及1,2 - NQ加NADH形成了8 - 氧代 - 7,8 - 二氢 - 2'-脱氧鸟苷（8 - 氧代 - dG）作为氧化性DNA标记物。过氧化氢酶和bathocuproine抑制DNA损伤，表明羟基自由基（HO）和Cu(I)参与其中。这些结果表明，萘醌半醌自由基（NQHs）通过半醌自由基氧化为相应的萘醌（NQs），并且在氧化过程中产生HO和Cu(I)。1,2 - NQ被NADH还原形成氧化还原循环，导致DNA损伤增强。电子顺磁共振（EPR）研究支持了相应半醌自由基的形成。总之，1,2 - NQ/1,2 - NQH的氧化还原循环在萘的致癌性中可能比1,4 - NQ/1,4 - NQH发挥更重要的作用。
