Koyama E, Chiba K, Tani M, Ishizaki T
Department of Clinical Pharmacology, Research Institute, International Medical Center of Japan, Tokyo.
J Pharmacol Exp Ther. 1997 Jun;281(3):1199-210.
Cytochrome P450 (CYP) involved in the two major pathways of imipramine (IMI) was reappraised using human liver microsomes phenotyped for S-mephenytoin 4'-hydroxylation in vitro and 11 recombinant human CYP isoforms. Individual Eadie-Hoffstee plots for IMI N-demethylation and 2-hydroxylation showed a monophasic profile in microsomes obtained from three putative S-mephenytoin poor metabolizer (PM) livers, whereas the plots gave a biphasic relationship (except for one case in 2-hydroxylation) in those from the three extensive metabolizer (EM) livers. Effects of CYP-selective inhibitor/substrate probes on the two metabolic reactions were examined at the two IMI concentrations (2 and 400 microM) with microsomes obtained from the two PM and three EM livers. S-mephenytoin inhibited IMI N-demethylation by 50% at the low concentration in microsomes from the EM livers with no discernible effect on this pathway in those from the PM livers. Furafylline inhibited the N-demethylation by about 60% at the low and high substrate concentrations in microsomes from both the EM and PM livers. Quinidine abolished the 2-hydroxylation at the low and high concentrations in microsomes from both the EM and the PM livers. Among the recombinant human CYPs, CYP2C19, 2C18, 2D6, 1A2, 3A4 and 2B6 in rank order catalyzed the N-demethylation, whereas CYP2D6, 2C19, 1A2, 2C18 and 3A4 catalyzed the 2-hydroxylation. The Km values obtained from recombinant CYP2C19 and 1A2 approximated those of the high- and low-affinity components from human liver microsomes for IMI N-demethylation, respectively. For IMI 2-hydroxylation, the respective Km values obtained from recombinant CYP2D6 and 2C19 were close to those of the high- and low-affinity components from human liver microsomes. Our human liver microsomal study using the near-therapeutic IMI concentration (2 microM) suggests that 1) CYP2C19 and 1A2 are involved in the N-demethylation and the 2-hydroxylation is mediated exclusively by CYP2D6 and partially by CYP2C19 in the EM livers, and 2) CYP1A2 and 2D6 play a major role in IMI N-demethylation and 2-hydroxylation, respectively, in the PM livers. Our recombinant human CYP isoform study, in general, supports this conclusion.
利用体外S-美芬妥因4'-羟化表型的人肝微粒体和11种重组人CYP同工型，对参与丙咪嗪（IMI）两条主要代谢途径的细胞色素P450（CYP）进行了重新评估。IMI N-去甲基化和2-羟化的个体伊迪-霍夫斯蒂图在来自三名推定的S-美芬妥因慢代谢者（PM）肝脏的微粒体中呈单相分布，而在来自三名快代谢者（EM）肝脏的微粒体中，这些图呈现双相关系（2-羟化中有一个病例除外）。在两种IMI浓度（2和400μM）下，用来自两名PM和三名EM肝脏的微粒体检测了CYP选择性抑制剂/底物探针对这两种代谢反应的影响。S-美芬妥因在低浓度时可使EM肝脏微粒体中的IMI N-去甲基化抑制50%，而对PM肝脏微粒体中的该途径无明显影响。呋拉茶碱在低底物浓度和高底物浓度下，均可使EM和PM肝脏微粒体中的N-去甲基化抑制约60%。奎尼丁在低浓度和高浓度下均可消除EM和PM肝脏微粒体中的2-羟化。在重组人CYP中，CYP2C19、2C18、2D6、1A2、3A4和2B6按催化N-去甲基化的能力排序，而CYP2D6、2C19、1A2、2C18和3A4催化2-羟化。从重组CYP2C19和1A2获得的Km值分别近似于人肝微粒体中IMI N-去甲基化的高亲和力组分和低亲和力组分的Km值。对于IMI 2-羟化，从重组CYP2D6和2C19获得的各自Km值分别与人肝微粒体中高亲和力组分和低亲和力组分的Km值接近。我们使用接近治疗浓度的IMI（2μM）进行的人肝微粒体研究表明：1）在EM肝脏中，CYP2C19和1A2参与N-去甲基化，2-羟化仅由CYP2D6介导，部分由CYP2C19介导；2）在PM肝脏中，CYP1A2和2D6分别在IMI N-去甲基化和2-羟化中起主要作用。我们的重组人CYP同工型研究总体上支持这一结论。
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