Zhao X J, Yokoyama H, Chiba K, Wanwimolruk S, Ishizaki T
Department of Clinical Pharmacology, International Medical Center of Japan, Tokyo, Japan.
J Pharmacol Exp Ther. 1996 Dec;279(3):1327-34.
Studies using human liver microsomes and nine recombinant human cytochrome P450 (CYP) isoforms (CYP1A1, 1A2, 2A6, 2B6, 2C9, 2C19, 2D6, 2E1 and 3A4) were performed to identify the CYP isoform(s) involved in the major metabolic pathway (3-hydroxylation) of quinine in humans. Eadie-Hofstee plots for the formation of 3-hydroxyquinine exhibited apparently monophasic behavior for all of the 10 different microsomal samples studies. There was interindividual variability in the kinetic parameters, as follows: 1.8-, 3.2- and 3.5-fold for K(m) Vmax and Vmax/K(m), respectively. The mean +/- S.D. values for K(m), Vmax and Vmax/K(m) were 106.1 +/- 19.3 microM, 1.33 +/- 0.48 nmol/mg protein/min and 12.8 +/- 5.1 microliters/mg protein/min, respectively. With 10 different human liver microsomes, the relationships between the 3-hydroxylation of quinine and the metabolic activities for substrates of the respective CYP isoforms were evaluated. The 3-hydroxylation of quinine showed an excellent correlation (r = 0.986, P < .001) with 6 beta-hydroxylation of testosterone, a marker substrate for CYP3A4. A significant correlation (r = 0.768, P < .01) between the quinine 3-hydroxylase and S-mephenytoin 4'-hydroxylase activities was also observed. However, no significant correlation existed between the 3-hydroxylation of quinine and the oxidative activities for substrates for CYP1A2 (phenacetin), 2C9 (diclofenac), 2D6 (desipramine) and 2E1 (chlorzoxazone). Ketoconazole and troleandomycin (inhibitors of CYP3A4) inhibited the 3-hydroxylation of quinine by human liver microsomes with respective mean IC50 values of 0.026 microM and 28.9 microM. Anti-CYP3A antibodies strongly inhibited quinine 3-hydroxylation, whereas weak inhibition was observed in the presence of S-mephenytoin or anti-CYP2C antibodies. Among the nine recombinant human CYP isoforms, CYP3A4 exhibited the highest catalytic activity with respect to the 3-hydroxylation of quinine, compared with the minor activity of CYP2C19 and little discernible or no effect of other CYP isoforms. Collectively, these data suggest that the 3-hydroxylation of quinine is mediated mainly by CYP3A4 and to a minor extent by CYP2C19. Other CYP isoforms used herein appear to be of negligible importance in this major pathway of quinine in humans.
开展了使用人肝微粒体和9种重组人细胞色素P450（CYP）同工酶（CYP1A1、1A2、2A6、2B6、2C9、2C19、2D6、2E1和3A4）的研究，以确定参与奎宁在人体内主要代谢途径（3-羟基化）的CYP同工酶。在所有10种不同的微粒体样品研究中，3-羟基奎宁形成的伊迪-霍夫斯泰因图均表现出明显的单相行为。动力学参数存在个体间差异，具体如下：米氏常数（K(m)）、最大反应速度（Vmax）和Vmax/K(m)分别为1.8倍、3.2倍和3.5倍。K(m)、Vmax和Vmax/K(m)的平均值±标准差分别为106.1±19.3微摩尔、1.33±0.48纳摩尔/毫克蛋白/分钟和12.8±5.1微升/毫克蛋白/分钟。利用10种不同的人肝微粒体，评估了奎宁的3-羟基化与各CYP同工酶底物代谢活性之间的关系。奎宁的3-羟基化与睾酮的6β-羟基化（CYP3A4的标记底物）表现出极好的相关性（r = 0.986，P <.001）。还观察到奎宁3-羟化酶与S-美芬妥因4'-羟化酶活性之间存在显著相关性（r = 0.768，P <.01）。然而，奎宁的3-羟基化与CYP1A2（非那西丁）、2C9（双氯芬酸）、2D6（地昔帕明）和2E1（氯唑沙宗）底物的氧化活性之间不存在显著相关性。酮康唑和三乙酰竹桃霉素（CYP3A4抑制剂）抑制人肝微粒体对奎宁的3-羟基化，其平均半数抑制浓度（IC50）值分别为0.026微摩尔和28.9微摩尔。抗CYP3A抗体强烈抑制奎宁3-羟基化，而在存在S-美芬妥因或抗CYP2C抗体时观察到弱抑制作用。在9种重组人CYP同工酶中，与CYP2C19的微弱活性以及其他CYP同工酶几乎无明显作用或无作用相比，CYP3A4对奎宁的3-羟基化表现出最高的催化活性。总体而言，这些数据表明奎宁的3-羟基化主要由CYP3A4介导，CYP2C19介导的程度较小。本文使用的其他CYP同工酶在奎宁在人体内的这一主要途径中似乎重要性可忽略不计。
