Pan L P, De Vriendt C, Belpaire F M
Heymans Institute of Pharmacology, University of Gent Medical School, Belgium.
Pharmacogenetics. 1998 Oct;8(5):383-9. doi: 10.1097/00008571-199810000-00003.
In-vitro studies were performed using human liver microsomes and c-DNA-expressed human P450 isoforms to identify the cytochrome P450 isoenzyme(s) involved in the back oxidation and N-dealkylation of reduced haloperidol. Back oxidation and N-dealkylation of reduced haloperidol were assessed by measuring the formation of haloperidol and 4-(4-chlorophenyl)-4-hydroxypiperidine (CPHP), respectively. The haloperidol and CPHP formation rates as a function of substrate concentration, measured in three livers, followed monophasic enzyme kinetics. For haloperidol formation Km values ranged from 51-59 microM, and Vmax values from 190-334 pmol mg(-1) min(-1); for CPHP formation Km values were 44-49 microM, and Vmax values 74-110 pmol mg(-1) min(-1). Haloperidol and CPHP formation rates in the nine liver preparations were significantly correlated with dextromethorphan N-demethylase activity (a marker of CYP3A4 activity), but not with the CYP2D6, CYP1A2 and CYP2C9 activity. Ketoconazole and troleandomycin, inhibitors of CYP3A4, inhibited competitively both haloperidol and CPHP formation, with a Ki value lower than 0.2 microM for ketoconazole and lower than 0.3 microM for troleandomycin. Sulphaphenazole (CYP2C9), furafylline (CYP1A2) and quinidine and paroxetine (CYP2D6) gave only little inhibition (IC50 > 60 microM). CPHP and haloperidol formation were, moreover, enhanced by alpha-naphthoflavone, an effect known for CYP3A4 mediated reactions. Anti-CYP3A4 antibodies strongly inhibited haloperidol and CPHP formation, whereas CYP2D6 antibodies did not. Among the recombinant human CYP isoforms tested, CYP3A4 exhibited the highest activity with respect to haloperidol and CPHP formation rates, with no detectable effect of CYP1A2, CYP2D6 and CYP2C9. These results strongly suggest that back oxidation and N-dealkylation of reduced haloperidol in human liver microsomal preparations are mediated by CYP3A4.
利用人肝微粒体和cDNA表达的人细胞色素P450同工酶进行体外研究，以鉴定参与还原氟哌啶醇的回氧化和N-脱烷基化的细胞色素P450同工酶。分别通过测量氟哌啶醇和4-(4-氯苯基)-4-羟基哌啶(CPHP)的生成来评估还原氟哌啶醇的回氧化和N-脱烷基化。在三个肝脏中测得的氟哌啶醇和CPHP生成速率作为底物浓度的函数，遵循单相酶动力学。对于氟哌啶醇生成，Km值范围为51 - 59μM，Vmax值为190 - 334 pmol mg(-1) min(-1)；对于CPHP生成，Km值为44 - 49μM，Vmax值为74 - 110 pmol mg(-1) min(-1)。九种肝脏制剂中氟哌啶醇和CPHP的生成速率与右美沙芬N-脱甲基酶活性(一种CYP3A4活性的标志物)显著相关，但与CYP2D6、CYP1A2和CYP2C9活性无关。CYP3A4抑制剂酮康唑和三乙酰竹桃霉素竞争性抑制氟哌啶醇和CPHP的生成，酮康唑的Ki值低于0.2μM，三乙酰竹桃霉素的Ki值低于0.3μM。磺胺苯吡唑(CYP2C9)、呋拉茶碱(CYP1A2)、奎尼丁和帕罗西汀(CYP2D6)仅有微弱抑制作用(IC50 > 60μM)。此外，α-萘黄酮增强了CPHP和氟哌啶醇的生成，这是CYP3A4介导反应的已知效应。抗CYP3A4抗体强烈抑制氟哌啶醇和CPHP的生成，而CYP2D6抗体则无此作用。在所测试的重组人CYP同工酶中，CYP3A4在氟哌啶醇和CPHP生成速率方面表现出最高活性，而CYP1A2、CYP2D6和CYP2C9无明显作用。这些结果强烈表明，人肝微粒体制剂中还原氟哌啶醇的回氧化和N-脱烷基化由CYP3A4介导。
