二甲基胂酸致小鼠肺肿瘤促进作用中诱发氧化应激

Induction of oxidative stress during dimethylarsenic-induced lung tumor promoting process in mice

目的研究无机砷在体内甲基化代谢的主要产物二甲基肿酸（dimethylarsinic acid，DMA）在致肺肿瘤促进作用过程中是否诱发氧化应激。方法应用免疫组织化学方法和免疫电子显微镜胶体金染色法，检测400ppm DMA经饮水给药0～25周，小鼠肺组织中脂质过氧化的主要代谢产物4-羟烯酸（4-hydroxy-2-nonenal，4HNE）的表达及定位。结果DMA给药25周，肺组织的姬姆（HE）染色与对照组比较未观察到明显的形态学改变。免疫组织化学方法检测到肺终末细支气管上皮细胞胞浆中有棕色颗粒的4HNE阳性染色，染色细胞数明显高于对照组（P〈0．05）。从DMA给药8周开始4HNE阳性染色细胞数随给药时间延长而增多，并且与对照组比较，差异有统计学意义（P〈0．05）。免疫电子显微镜胶体金染色法观察到肺终末细支气管上皮细胞中呈阳性染色的为无纤毛的Clara细胞。DMA给药导致小鼠肺Clara细胞发生滑面内质网扩张、增生及核周水肿等超微结构的形态学改变。结论口服DMA诱发氧化应激，并且在DMA诱发肿瘤促进作用过程中一直起着十分重要的作用。我们首次指出，口服DMA致小鼠肺肿瘤促进作用过程中，DMA诱发的氧化应激特异地发生在肺肿瘤的靶细胞Clara细胞。

Objective To clarify the involvement of the induction of oxidative stress in lung tumor promotion by dimethylarsinic acid （DMA）, a main metabolite of inorganic arsenics in mammals. Methods Immunohistochemistry and post-embedding immunogold electron microscopy analysis were performed using a specific antibody against 4-hydroxy-2-nonenal （4HNE） adducts, which were major aldehydic metabolites of lipid peroxidation. Results 4HNE-medified proteins existed specifically in the secretory granules in terminal bronchiolar Clara cells. Furthermore, the degree of positive staining increased with the duration of DMA administration. Transmission electron microscopy revealed morphological changes in the Clara cells of DMA-treated mice. Conclusion These results suggest that Clara cells are the major target cell for DMA-induced oxidative stress, and the cells may play an important role in the lung tumor promotion process in mice.