Rin K, Kawaguchi K, Yamanaka K, Tezuka M, Oku N, Okada S
School of Pharmaceutical Sciences, University of Shizuoka, Japan.
Biol Pharm Bull. 1995 Jan;18(1):45-8. doi: 10.1248/bpb.18.45.
We previously reported that dimethylarsinic acid (DMAA), a major metabolite of inorganic arsenics, induced DNA single-strand breaks (ssb) both in vivo and in cultured alveolar type II (L-132) cells in vitro, possibly via the production of dimethylarsenic peroxyl radicals. Here, the interaction of superoxide anion radicals (O2-) in the induction of ssb in L-132 cells was investigated using paraquat, an O2(-)-producing agent. A significant enhancement of ssb formation was observed in the DMAA-exposed cells when coexposed to paraquat. This enhancement occurred even when post-exposed to DMAA after washing, suggesting that the DMAA exposure caused some modification of DNA such as DNA-adducts, which was recognized by active oxygens to form ssb. An experiment with UV-irradiation, which was likely to induce ssb at the modified region, supported the possibility of DNA modification by DMAA exposure. An ESR study indicated that O2- produced by paraquat in DMAA-exposed cells was more consumed than in non-exposed cells, assumingly through the reaction with the dimethylarsenic-modified region of DNA. The species of active oxygens were estimated by using diethyldithiocarbamate, aminotriazole, diethylmaleate, hydrogen peroxide (H2O2), gamma-irradiation and ethanol. O2- but neither H2O2 nor hydroxyl radicals was very likely to contribute to the ssb-enhancing action of paraquat.
我们之前报道过，无机砷的主要代谢产物二甲基次胂酸（DMAA）在体内及体外培养的肺泡II型（L-132）细胞中均可诱导DNA单链断裂（ssb），可能是通过产生二甲基砷过氧自由基实现的。在此，使用百草枯（一种产生O2-的试剂）研究超氧阴离子自由基（O2-）在L-132细胞中诱导ssb的相互作用。当DMAA暴露的细胞与百草枯共同暴露时，观察到ssb形成显著增强。即使在洗涤后再暴露于DMAA时这种增强也会出现，这表明DMAA暴露导致了DNA的某些修饰，如DNA加合物，其被活性氧识别从而形成ssb。一项紫外线照射实验（可能在修饰区域诱导ssb）支持了DMAA暴露导致DNA修饰的可能性。电子自旋共振研究表明，百草枯在DMAA暴露细胞中产生的O2-比未暴露细胞中消耗得更多，推测是通过与DNA的二甲基砷修饰区域反应实现的。使用二乙基二硫代氨基甲酸盐、氨基三唑、马来酸二乙酯、过氧化氢（H2O2）、γ射线照射和乙醇来估计活性氧的种类。O2-而非H2O2或羟基自由基很可能对百草枯增强ssb的作用有贡献。
