Kojo A, Viitala P, Pasanen M, Pelkonen O, Raunio H, Juvonen R
Department of Pharmacology and Toxicology, University of Kuopio, Finland.
Arch Toxicol. 1998 May;72(6):336-41. doi: 10.1007/s002040050511.
Mouse liver CYP2A5 is induced by several structurally unrelated compounds. In intact mouse liver, pyrazole (PYR) and 4-hydroxypyrazole (4-OH) induce selectively the expression of CYP2A5 while expression of other CYPs is decreased. In this study we exposed mouse primary hepatocytes to PYR, 4-OH, 4-methylpyrazole (4Me; 0.1-20 mM) and 4-iodopyrazole (4-I; 0.1-5.0 mM). PYR and its derivatives increased coumarin 7-hydroxylase activity, with 4-1 and 4-OH being the strongest inducers, by 114-fold and 41-fold, respectively. However, only 4-1 treatment increased markedly the CYP2A5 protein content. CYP2B9/10-mediated pentoxyresorufin O-deethylase activity (PROD) was decreased by 80% by 4-Me and 4-1, and by 50% by 4-OH while PYR had no marked effect. PYR and 4-Me increased 2- to 3-fold the CYPA1/2-mediated ethoxyresorufin O-deethylase activity (EROD) while 4-OH and 4-1 had no marked effect on this enzyme. The time of exposure markedly affected the inducibility of 4-OH such that induction was 7-fold stronger when it was added to the incubation medium 24 h after the isolation of hepatocytes compared to exposure 3 h after their isolation. Cimetidine prevented the induction of coumarin 7-hydroxylase activity by PYR and 4-OH by 46 and 74%, respectively indicating that their effects on the expression of CYP2A5 are, at least partly, mediated via their metabolites. The data demonstrate that the regulation of CYP2A5 is different from other monooxygenases and that the effects of pyrazole and its derivatives are different in vivo and in vitro. Also, the timing of exposure markedly affects the inducibility of 4-OH in hepatocytes.
小鼠肝脏CYP2A5可被几种结构不相关的化合物诱导。在完整的小鼠肝脏中，吡唑（PYR）和4-羟基吡唑（4-OH）选择性地诱导CYP2A5的表达，而其他细胞色素P450（CYPs）的表达则降低。在本研究中，我们将小鼠原代肝细胞暴露于PYR、4-OH、4-甲基吡唑（4Me；0.1 - 20 mM）和4-碘吡唑（4-I；0.1 - 5.0 mM）。PYR及其衍生物增加了香豆素7-羟化酶活性，其中4-I和4-OH是最强的诱导剂，分别增加了114倍和41倍。然而，只有4-I处理显著增加了CYP2A5蛋白含量。4-Me和4-I使CYP2B9/10介导的戊氧基试卤灵O-脱乙基酶活性（PROD）降低了80%，4-OH使其降低了50%，而PYR没有显著影响。PYR和4-Me使CYPA1/2介导的乙氧基试卤灵O-脱乙基酶活性（EROD）增加了2至3倍，而4-OH和4-I对该酶没有显著影响。暴露时间显著影响4-OH的诱导能力，与肝细胞分离后3小时暴露相比，在肝细胞分离后24小时将其添加到孵育培养基中时，诱导作用强7倍。西咪替丁分别使PYR和4-OH对香豆素7-羟化酶活性的诱导作用降低了46%和74%，表明它们对CYP2A5表达的影响至少部分是通过其代谢产物介导的。数据表明，CYP2A5的调节与其他单加氧酶不同，吡唑及其衍生物在体内和体外的作用也不同。此外，暴露时间显著影响肝细胞中4-OH的诱导能力。
