Exposure Assessment of Arsenic Compounds and Study of Their Disturbing Activity of Cell Cycle

本文报道了二甲基胂酸（DMA）在体内诱导中国仓鼠V79细胞、培养的人淋巴细胞和骨髓细胞发生有丝分裂阻滞和四倍体或非整倍体。本研究发现，DMA在体外抑制微管蛋白的正常组装，并抑制V79细胞有丝分裂中纺锤体的正常发育，DMA抑制微管蛋白的GTP活性。这些结果表明，DMA通过降低微管蛋白的GTP活性来干扰微管蛋白的正常组装，并诱导有丝分裂停滞。其次，我们发现半胱氨酸强烈增强DMA的细胞毒性和诱导染色体畸变。本研究试图阐明大鼠长期口服DMA后产生未知代谢产物M-1和M-2的机制。谷胱甘肽（GSH）消耗减少TMAO消除，表明GSH在大鼠DMA甲基化为TMAO中起重要作用。单次经口给药后，GSH耗竭大鼠中M-1或M-2的尿液消除量高于对照组，表明在肝脏甲基化过程中不能形成M-1和M-2。腹腔给药后，M-1和M-2的消除量低于经口给药后的消除量;在20周的DMA暴露后，在粪便中检测到一种新的代谢产物M-3，其为DMA的代谢产物。未鉴别代谢物M-1、M-2和M-3主要以粪便代谢物的形式与未代谢的DMA一起沿着排泄。体外研究表明，两株E.从大鼠盲肠分离的大肠杆菌将DMA代谢为M-2或M-3，将TMAO代谢为M-1。这些发现表明，M-1、M-2和M-3可能在肠道中产生。半胱氨酸是肠道细菌代谢DMA所必需的。

We had reported that dimethylarsinic acid (DMA) induced mitotic arrest and tetraploids or aneuploids in Chinese hamster V79 cells, cultured human lymphocytes or bone marrow cells (in vivo). In this study we revealed that DMA inhibits normal assembly of tublin in vitro and also inhibits normal development of spindles in V79 mitotic cells, DMA inhibits tublin's GTP activity. These results suggest that DMA disturbs normal assembly of tublin by lowering tublin's GTP activity and induces mitotic arrest. Next we found that cysteine enhances strongly cytotoxicity and induction of chromosome aberration of DMA. This result suggest that cysteine participates in carcinogenicity of DMA.We attempted to clarify the mechanism of production of unknown metabolites, M-1 and M-2, which were excreted in urine after long-term oral administration of DMA in rats. Glutathione (GSH) depletion decreased in TMAO elimination, suggesting that GSH plays important roles in the methylation of DMA to TMAO in rats. The amounts of urinary elimination of either M-1 or M-2 in GSH-depleted rats were higher than controls after a single oral administration, suggesting that M-1 and M-2 cannot be formed during methylation in the liver. The amounts of elimination of M-1 and M-2 were less after intraperitoneal administration than after oral administration.A new unidentified metabolite, M-3, was detected in feces as a metabolite of DMA after 20-week exposure to DMA. The unidentified metabolites M-1, M-2, and M-3 were excreted mainly as fecal metabolites along with unmetabolized DMA. In vitro study showed that two strains of E. coli isolated from rat ceca metabolized DMA to M-2 or M-3 and TMAO to M-1. These findings suggest that M-1, M-2, and M-3 might be produced in the intestinal tract. Cysteine was required for metabolism of DMA by the intestinal bacteria.