Ultimate carcinogenetic compound of arsenic : the chemical structure and the toxicity

我们先前的研究显示，在大鼠长期口服二甲基胂酸（DMAV）后，在尿液和粪便中检测到未鉴定的代谢产物M1、M2和M3。此外，我们还报道了大肠杆菌A3-6将DMAV转化为M-2和M-3，将氧化三甲基胂（TMAO）转化为M1，并且DMAV转化为M-2和M-3需要半胱氨酸（Cys）。在这项研究中，我们研究了这些未知的代谢产物在体外和体内的生产机制。在体外研究中，DMAV在Cys和A3-6存在下转化为M2并进一步转化为M3。TMAO迅速转化为M1。在Cys/DMA比为2时观察到M2的最大浓度，当该比超过3时观察到M3的最大浓度。体内试验结果表明，日粮半胱氨酸和大肠杆菌影响M2和M3的产生。此外，我们通过LC-ICP-MS和LC/MS检查了M-2的化学性质。M2被过氧化氢氧化为DMAV，表明M2可能是DMA复合物。M2与DMAV与偏亚硫酸氢盐-硫代硫酸盐试剂的反应物一致。M-2的分子量为154，是一种含硫代谢产物。在V79细胞中，M2的细胞毒性高于DMAV、M1和M3。加入超氧化物歧化酶后，M2对HL-60细胞的毒性降低，提示M2的细胞毒性可能与产生活性氧有关。

Our previous study revealed that unidentified metabolites, M1, M2, and M3, were detected in urine and feces after long-term oral administration of dimethylarsinic acid (DMAV) to rats. In addition, we reported that the E.coli A3-6 converted DMAV to M-2 and M-3 and converted Trimethylarsine oxide (TMAO) to M1, and the conversion of DMAV to M2 and M-3 by E.coli A3-6 required cysteine (Cys). In this study we examined the mechanism of production of these unknown metabolites in vitro and in vivo. In vitro study, DMAV was converted to M2 and further to M3 in the presence of Cys and A3-6. TMAO was rapidly converted to M1. The maximum concentration of M2 was observed at a Cys/DMA ratio of 2, and the maximum of M3 was observed when the ratio exceeded 3. In vivo experiment, the results indicated that dietary Cys and E.coli affected the production of M2 and M3. In addition, we examined the chemical properties of M-2 by LC-ICP-MS and LC/MS. M2 was oxidized to DMAV by hydrogen peroxide, suggesting that M2 may be a DMA complex. M2 was consistent with the reactant of DMAV with metabisulfite-thiosulfate reagent. The molecular weight of M-2 was 154 and M-2 was a sulfur-containing metabolite.The cytotoxicity of the unidentified metabolites was investigated. M2 was more cytotoxic than DMAV, M1, and M3 in V79 cells. Cytotoxicity of M2 in HL-60 cells was decreased by the addition of superoxide dismutase, suggesting that the cytotoxicity of M2 might be due to the production of reactive oxygen species.