Fabrizi L, Gemma S, Testai E, Vittozzi L
Department of Comparative Toxicology and Ecotoxicology, Istituto Superiore di Sanità, Rome, Italy.
J Biochem Mol Toxicol. 1999;13(1):53-61. doi: 10.1002/(sici)1099-0461(1999)13:1<53::aid-jbt7>3.0.co;2-2.
The metabolism of diazinon, an organo-phosphorothionate pesticide, to diazoxon and pyrimidinol has been studied in incubations with hepatic microsomes from control Sprague-Dawley (SD) rats or SD rats treated with different P450-specific inducers (phenobarbital, dexamethasone, beta-napthoflavone, and pyrazole). Results obtained indicate an involvement of CYP2C11, CYP3A2, and CYP2B1/2, whereas CYP2E1 and CYP1A1 do not contribute to the pesticide oxidative metabolism. Indeed, diazinon was metabolized by microsomes from control rats; among the inducers, phenobarbital and dexamethasone only increased the production of either metabolites, although to different extents. The production of the two metabolites is self-limiting, due to P450 inactivation; therefore, the inhibition of CYP-specific monooxygenase activities after diazinon preincubation has been used to selectively identify the competent CYPs in diazinon metabolism. Results indicate that, after diazinon preincubation, CYP3A2-catalyzed reactions (2beta- and 6beta-testosterone hydroxylation) are very efficiently inhibited; CYP2C11- and CYP2B1/2-catalyzed reactions (2alpha- and 16beta-testosterone hydroxylation, respectively) are weakly inhibited, while CYP2E1-, CYP2A1/2-, and CYP1A1/2-related activities were unaffected. Results obtained by using chemical inhibitors or antibodies selectively active against specific CYPs provide a direct evidence for the involvement of CYP2C11, CYP3A2, and CYP2B1/2, indicating that each of them contributed about 40-50% of the diazinon metabolism, in hepatic microsomes from untreated, phenobarbital-, and dexamethasone-treated rats, respectively. The higher diazoxon/pyrimidinol ratio observed after phenobarbital-treatment together with the significantly more effective inhibition toward diazoxon production exerted by metyrapone in microsomes from phenobarbital-treated rats supports the conclusion that CYP2B1/2 catalyze preferentially the production of diazoxon.
已在来自对照斯普拉格 - 道利（SD）大鼠或用不同的P450特异性诱导剂（苯巴比妥、地塞米松、β - 萘黄酮和吡唑）处理的SD大鼠的肝微粒体孵育中，研究了有机磷硫代磷酸酯农药二嗪农向二嗪磷和嘧啶醇的代谢。所得结果表明CYP2C11、CYP3A2和CYP2B1/2参与其中，而CYP2E1和CYP1A1对该农药的氧化代谢无贡献。实际上，二嗪农可被对照大鼠的微粒体代谢；在诱导剂中，苯巴比妥和地塞米松仅增加了两种代谢物的生成量，不过程度不同。由于P450失活，两种代谢物的生成是自我限制的；因此，二嗪农预孵育后对CYP特异性单加氧酶活性的抑制已被用于选择性鉴定二嗪农代谢中起作用的细胞色素P450（CYPs）。结果表明，二嗪农预孵育后，CYP3A2催化的反应（2β - 和6β - 睾酮羟基化）受到非常有效的抑制；CYP2C11和CYP2B1/2催化的反应（分别为2α - 和16β - 睾酮羟基化）受到较弱的抑制，而CYP2E1、CYP2A1/2和CYP1A1/2相关活性未受影响。使用对特定CYPs具有选择性活性的化学抑制剂或抗体获得的结果，为CYP2C11、CYP3A2和CYP2B1/2的参与提供了直接证据，表明在未处理的、苯巴比妥处理的和地塞米松处理的大鼠的肝微粒体中，它们各自对二嗪农代谢的贡献约为40 - 50％。苯巴比妥处理后观察到的较高的二嗪磷/嘧啶醇比率，以及甲吡酮对苯巴比妥处理的大鼠微粒体中二嗪磷生成的抑制作用明显更有效，支持了CYP2B1/2优先催化二嗪磷生成的结论。
