Jacobs J, Roussel R, Roberts M, Marek D, Wood S, Walton H, Dwyer B, Sinclair P, Sinclair J
Department of Microbiology, Dartmouth Medical School, Hanover, New Hampshire 03755, USA.
Toxicol Appl Pharmacol. 1998 Jun;150(2):376-82. doi: 10.1006/taap.1998.8436.
In earlier studies, treatment with sodium arsenite was shown to decrease total hepatic CYP in rats. A concomitant increase in heme oxygenase, the rate-limiting step in heme degradation to biliverdin, was considered responsible for the decrease in CYP. Here we investigated the effect of sodium arsenite on induction of CYP2H, CYP1A, and heme oxygenase in primary cultures of chicken embryo hepatocytes. When added simultaneously with inducer, arsenite inhibited phenobarbital-mediated increases in CYP2H and 3-methylcholanthrene-mediated increases in CYP1A, as measured enzymatically and immunochemically. Near maximal decreases were observed in these forms of CYP at a concentration of 2.5 microM sodium arsenite. The concentration-dependent decreases in CYP2H and CYP1A by sodium arsenite were concomitant with increases in heme oxygenase. Sodium arsenite was not toxic at concentrations as high as 10 microM, as indicated by protein synthesis and the reduction of MTT by intact cells. Sodium arsenite had no effect on induction of CYP2H1 mRNA, suggesting that the decreases in this form of CYP occurred post-transcriptionally. Treatment of cells with tin mesoporphyrin (SnMeso), an inhibitor of heme oxygenase, resulted in inhibition of arsenite-induced heme oxygenase. However, SnMeso did not alter the effect of arsenite to prevent phenobarbital-mediated increases in CYP2H protein. SnMeso alone inhibited phenobarbital-mediated increases in CYP2H. Inclusion of 2 or 5 microM exogenous heme with arsenite did not prevent the arsenite-mediated decrease in CYP2H. Combined treatment with heme and phenobarbital induced heme oxygenase to the same extent as treatment with heme, arsenite, and phenobarbital. However, CYP2H activity was decreased only when the treatment included arsenite. These results suggest that elevated levels of heme oxygenase alone are not responsible for arsenite-mediated decreases in CYP2H.
在早期研究中，已表明用亚砷酸钠处理可使大鼠肝脏中的总细胞色素P450（CYP）减少。血红素加氧酶是血红素降解为胆绿素的限速步骤，其伴随性增加被认为是导致CYP减少的原因。在此，我们研究了亚砷酸钠对鸡胚肝细胞原代培养物中CYP2H、CYP1A和血红素加氧酶诱导的影响。当与诱导剂同时添加时，通过酶法和免疫化学方法测定，亚砷酸盐抑制了苯巴比妥介导的CYP2H增加以及3-甲基胆蒽介导的CYP1A增加。在2.5微摩尔/升亚砷酸钠浓度下，观察到这些形式的CYP接近最大程度的减少。亚砷酸钠对CYP2H和CYP1A的浓度依赖性降低与血红素加氧酶的增加同时发生。如完整细胞的蛋白质合成和MTT还原所示，亚砷酸钠在高达10微摩尔/升的浓度下无毒。亚砷酸钠对CYP2H1 mRNA的诱导没有影响，这表明这种形式的CYP减少发生在转录后。用血红素加氧酶抑制剂锡中卟啉（SnMeso）处理细胞导致亚砷酸盐诱导的血红素加氧酶受到抑制。然而，SnMeso并没有改变亚砷酸盐阻止苯巴比妥介导的CYP2H蛋白增加的作用。单独使用SnMeso抑制了苯巴比妥介导的CYP2H增加。将2或5微摩尔/升的外源性血红素与亚砷酸盐一起添加并不能阻止亚砷酸盐介导的CYP2H减少。血红素和苯巴比妥联合处理诱导血红素加氧酶的程度与血红素、亚砷酸盐和苯巴比妥联合处理相同。然而，只有当处理包括亚砷酸盐时，CYP2H活性才会降低。这些结果表明，仅血红素加氧酶水平升高并非亚砷酸盐介导的CYP2H减少的原因。
