Wang Hongbing, Chanas Brian, Ghanayem Burhan I
Laboratory of Pharmacology and Chemistry, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina 27709, USA.
J Toxicol Environ Health A. 2002 Apr 12;65(7):523-37. doi: 10.1080/15287390252807984.
Tissue-specific induction of cytochrome P-450s (CYP) followed by increased in situ bioactivation may contribute to chemical-induced site-specific toxicity. In rats, methacrylonitrile (MAN) is metabolized by cytochrome P-450 2E1 (CYP2E1) to acetone, which is eliminated along with parent MAN in breath. Gavage administration of MAN to rats causes olfactory epithelial damage and liver enlargement. It was hypothesized that treatment of rats with MAN may result in differential expression of CYP2E1 in tissues leading to tissue-specific toxicity via increased in situ formation of cytotoxic MAN metabolites. In this study, male F344 rats received 60 mg MAN/kg and were sacrificed 6, 12, or 24 h after a single dose, or 24 h after 7 consecutive daily doses. Liver, lung, and nasal tissues were collected. Reverse-transcription polymerase chain reaction (RT-PCR), Western blotting, and immunohistochemical staining were used to assess CYP2E1 expression and localization, and chlorzoxazone hydroxylation was used as a measure of CYP2E1 catalytic activity. Present results showed that CYP2E1 mRNA was increased in lung and nasal tissues with minimal effects in liver of MAN-treated rats. Induction of CYP2E1 protein expression was detected in lung. CYP2E1 activity was higher in liver and lung microsomes from MAN-treated rats when compared to control animals. To compare the effects of MAN and acetone, male F344 rats received a single acetone dose (5 ml/kg) by gavage. After 12 h, acetone treatment resulted in a significant increase in the levels of CYP2E1 mRNA and protein in lung and nasal tissues, with no obvious change noted in the liver. Overall, these data suggest that administration of MAN to rats causes increased expression of CYP2E1 in lung, liver, and nasal tissues. These results also show that acetone induces the expression of CYP2E1 at both the mRNA and protein levels in rat nasal and lung tissues. In conclusion, MAN increased the expression of CYP2E1, and this effect varied as a function of time, length of exposure, and tissue examined. While the damage in the olfactory mucosa due to MAN treatment may not be explained by the observed induction of CYP2E1, it is possible that other CYPs may play a role in the in situ bioactivation of MAN.
细胞色素P-450（CYP）的组织特异性诱导随后原位生物活化增加可能导致化学物质诱导的位点特异性毒性。在大鼠中，甲基丙烯腈（MAN）通过细胞色素P-450 2E1（CYP2E1）代谢为丙酮，丙酮与母体MAN一起通过呼吸排出。给大鼠灌胃MAN会导致嗅觉上皮损伤和肝脏肿大。据推测，用MAN处理大鼠可能导致CYP2E1在组织中的差异表达，通过增加细胞毒性MAN代谢物的原位形成导致组织特异性毒性。在本研究中，雄性F344大鼠接受60mg MAN/kg，单次给药后6、12或24小时处死，或连续7天每日给药后24小时处死。收集肝脏、肺和鼻组织。采用逆转录聚合酶链反应（RT-PCR）、蛋白质印迹法和免疫组织化学染色评估CYP2E1的表达和定位，并以氯唑沙宗羟化作为CYP2E1催化活性的指标。目前的结果表明，在经MAN处理的大鼠中，肺和鼻组织中CYP2E1 mRNA增加，而肝脏中影响最小。在肺中检测到CYP2E1蛋白表达的诱导。与对照动物相比，经MAN处理的大鼠肝脏和肺微粒体中的CYP2E1活性更高。为了比较MAN和丙酮的作用，雄性F344大鼠通过灌胃接受单次丙酮剂量（5ml/kg）。12小时后，丙酮处理导致肺和鼻组织中CYP2E1 mRNA和蛋白水平显著增加，肝脏中未观察到明显变化。总体而言，这些数据表明给大鼠施用MAN会导致肺、肝脏和鼻组织中CYP2E1表达增加。这些结果还表明，丙酮在大鼠鼻和肺组织中诱导CYP2E1在mRNA和蛋白水平的表达。总之，MAN增加了CYP2E1的表达，并且这种作用随时间、暴露时间长度和所检查的组织而变化。虽然MAN处理导致的嗅觉粘膜损伤可能无法用观察到的CYP2E1诱导来解释，但其他CYPs可能在MAN的原位生物活化中起作用。
