Romach E H, Zhao C Q, Del Razo L M, Cebrián M E, Waalkes M P
Inorganic Carcinogenesis Section, Laboratory of Comparative Carcinogenesis, National Cancer Institute at the National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina, USA.
Toxicol Sci. 2000 Apr;54(2):500-8. doi: 10.1093/toxsci/54.2.500.
Arsenic (As) is a human carcinogen. Our prior work showed that chronic (>18 weeks) low level (500 nM) arsenite (As3+) exposure induced malignant transformation in a rat liver epithelial cell line (TRL 1215). In these cells, metallothionein (MT) is hyper-expressible, a trait often linked to metal tolerance. Thus, this study examined whether the adverse effects of arsenicals and other metals were altered in these chronic arsenite-exposed (CAsE) cells. CAsE cells, which had been continuously exposed to 500 nM arsenite for 18 to 20 weeks, and control cells, were exposed to As3+, arsenate (As5+), dimethylarsinic acid (DMA), monomethylarsonic acid (MMA), antimony (Sb3+), cadmium (Cd2+), cisplatin (cis-Pt), and nickel (Ni2+) for 24 h and cell viability was determined by metabolic integrity. The lethal concentration for 50% of exposed cells (LC50) for As3+ was 140 microM in CAsE cells as compared to 26 microM in control cells, a 5.4-fold increase in tolerance. CAsE cells were also very tolerant to the acute toxic effects of As5+ (LC50 > 4000 microM) compared to control (LC50 = 180 microM). The LC50 for DMA was 4.4-fold higher in CAsE cells than in control cells, but the LC50 for MMA was unchanged. There was a modest cross-tolerance to Sb3+, Cd2+, and cis-Pt in CAsE cells (LC50 1.5-2.0-fold higher) as compared to control. CAsE cells were very tolerant to Ni2+ (LC50 > 8-fold higher). Culturing CAsE cells in As(3+)-free medium for 5 weeks did not alter As3+ tolerance, implicating an irreversible phenotypic change. Cellular accumulation of As was 87% less in CAsE cells than control and the accumulated As was more readily eliminated. Although accumulating much less As, a greater portion was converted to DMA in CAsE cells. Altered glutathione (GSH) levels were not linked with As tolerance. A maximal induction of MT by Zn produced only a 2.5-fold increase in tolerance to As3+ in control cells. Cell lines derived from MT normal mice (MT+/+) were only slightly more resistant (1.6-fold) to As3+ than cells from MT null mice (MT-/-). These results show that CAsE cells acquire tolerance to As3+, As5+, and DMA. It appears that this self-tolerance is based primarily on reduced cellular disposition of the metalloid and is not accounted for by changes in GSH or MT.
砷（As）是一种人类致癌物。我们之前的研究表明，长期（>18周）低水平（500 nM）亚砷酸盐（As3+）暴露可诱导大鼠肝上皮细胞系（TRL 1215）发生恶性转化。在这些细胞中，金属硫蛋白（MT）可过度表达，这一特性通常与金属耐受性相关。因此，本研究检测了在这些长期暴露于亚砷酸盐（CAsE）的细胞中，砷化合物和其他金属的不良反应是否发生改变。将连续18至20周暴露于500 nM亚砷酸盐的CAsE细胞和对照细胞暴露于As3+、砷酸盐（As5+）、二甲基砷酸（DMA）、一甲基砷酸（MMA）、锑（Sb3+）、镉（Cd2+）、顺铂（cis-Pt）和镍（Ni2+）24小时，并通过代谢完整性测定细胞活力。As3+对50%暴露细胞的致死浓度（LC50）在CAsE细胞中为140 microM，而在对照细胞中为26 microM，耐受性增加了5.4倍。与对照（LC50 =为180 microM）相比，CAsE细胞对As5+的急性毒性作用也具有很强耐受性（LC50 > 4000 microM）。DMA的LC50在CAsE细胞中比对照细胞高4.4倍，但MMA的LC50没有变化。与对照相比，CAsE细胞对Sb3+、Cd2+和顺铂具有一定程度的交叉耐受性（LC50高1.5 - 2.0倍）。CAsE细胞对Ni2+具有很强耐受性（LC50 > 8倍以上）。在无As(3+)的培养基中培养CAsE细胞5周并未改变对As3+的耐受性，这意味着发生了不可逆的表型变化。CAsE细胞中As的细胞蓄积量比对照细胞少87%，且蓄积的As更容易被清除。尽管CAsE细胞蓄积的As少得多，但其中较大一部分在CAsE细胞中转化为DMA。谷胱甘肽（GSH）水平的改变与As耐受性无关。锌对MT的最大诱导仅使对照细胞对As3+的耐受性增加2.5倍。源自MT正常小鼠（MT+/ +）的细胞系对As3+的抗性仅比来自MT基因敲除小鼠（MT-/-）的细胞略高（1.6倍）。这些结果表明，CAsE细胞对As3+、As5+和DMA具有耐受性。这种自我耐受性似乎主要基于类金属在细胞内分布的减少，而不是由GSH或MT的变化引起的。
