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

我们先前的研究表明，长期口服二甲基砷酸(DMAV)后，在大鼠的尿液和粪便中检测到不明代谢物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，并将氧化三甲基砷(TMAO)转化为M1，而将DMAV转化为M2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代谢物在体外和体内的产生机制。在体外研究中，在Cys和A3-6的存在下，DMAV被转化为M2，进而转化为M3。TMAO迅速转化为M1。当Cys/DMA比为2时，M2的浓度最大，超过3时，M3的浓度最大。体内实验结果表明，饲料中的半胱氨酸和大肠杆菌对M2和M3的产生有影响。此外，我们还用LC-ICPMS和LC/MS对M-2的化学性质进行了研究。M2被过氧化氢氧化成了DMAV，表明M2可能是一种DMA络合物。M2与DMAV与焦亚硫酸盐-硫代硫酸盐试剂的反应物一致。M-2的相对分子质量为154，为含硫代谢产物，并对其细胞毒性进行了研究。在V79细胞中，M2的细胞毒作用强于DMAV、M1和M3。加入超氧化物歧化酶后，M2对HL-60细胞的细胞毒作用减弱，提示M2的细胞毒作用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.