McNeil C M, Murray M
Department of Medicine, University of Sydney, Westmead Hospital, NSW, Australia.
Biochem Pharmacol. 1996 Jan 12;51(1):15-20. doi: 10.1016/0006-2952(95)02105-1.
N-Monoalkyl substituted tricyclic antidepressants like desipramine (DES) undergo cytochrome P450 (P450)-mediated biotransformation in liver to produce inhibitory metabolite-intermediate (MI) complexes with the enzyme. However, additional oxidation pathways that generate isolable metabolites have also been identified, so that the relationship between MI complexation and total oxidative metabolism is unclear. The present study investigated the capacity of DES and three putative metabolites (2-hydroxy- and 10-hydroxy-DES and N,N-didesmethylimipramine; DIDES) to elicit MI complexation and inhibit P450-dependent activities in rat liver. MI complexation of P450 was produced by DES, but not with the three metabolites, in NADPH-supplemented microsomes. Consistent with this finding, inhibition of testosterone hydroxylation pathways was enhanced markedly by prior incubation of DES with NADPH and microsomes. Direct addition of DIDES to incubations resulted in significant inhibition of P450 activities (IC50s of 35 and 29 microM against estradiol 6 beta- and 16 alpha-hydroxylation mediated by P450s 3A2 and 2C11, respectively). Neither 2-hydroxy- nor 10-hydroxy-DES directly inhibited testosterone hydroxylation (IC50s > 100 microM). However, after a preincubation step between these metabolites and NADPH-fortified microsomes, enhanced inhibition of reactions mediated by P450 3A2 and P450 2C11/2A1 was produced by 2-hydroxy-DES and 10-hydroxy-DES, respectively. Metabolism of DES to DIDES and 2-hydroxy-DES was estimated as 7.77 +/- 0.48 nmol/mg protein/hr (10-hydroxy-DES was not detected). It is likely that secondary oxidized metabolites derived from 2-hydroxy-DES, as well as the primary metabolite DIDES, may contribute to the inhibition of P450 activity during DES biotransformation. These results indicate that the 2-hydroxy-, 10-hydroxy-, and N-desmethyl-metabolites of DES are not involved in MI complexation, but complexation is not the sole mechanism by which DES inhibits microsomal drug oxidation that may lead to pharmacokinetic drug interactions.
像地昔帕明（DES）这样的N-单烷基取代三环类抗抑郁药在肝脏中会经历细胞色素P450（P450）介导的生物转化，从而与该酶生成抑制性代谢物-中间体（MI）复合物。然而，也已鉴定出产生可分离代谢物的其他氧化途径，因此MI复合物形成与总氧化代谢之间的关系尚不清楚。本研究调查了DES和三种假定的代谢物（2-羟基-和10-羟基-DES以及N，N-双去甲基丙咪嗪；DIDES）在大鼠肝脏中引发MI复合物形成和抑制P450依赖性活性的能力。在补充了NADPH的微粒体中，DES可产生P450的MI复合物形成，但三种代谢物则不会。与这一发现一致，预先将DES与NADPH和微粒体一起孵育可显著增强对睾酮羟化途径的抑制作用。直接将DIDES添加到孵育体系中会导致对P450活性的显著抑制（对由P450 3A2和2C11介导的雌二醇6β-和16α-羟化反应的IC50分别为35和29μM）。2-羟基-DES和10-羟基-DES均未直接抑制睾酮羟化（IC50>100μM）。然而，在这些代谢物与NADPH强化的微粒体进行预孵育步骤后，2-羟基-DES和10-羟基-DES分别对由P450 3A2和P450 2C11/2A1介导的反应产生了增强的抑制作用。DES代谢为DIDES和2-羟基-DES的速率估计为7.77±0.48 nmol/mg蛋白质/小时（未检测到10-羟基-DES）。源自2-羟基-DES的二级氧化代谢物以及初级代谢物DIDES可能在DES生物转化过程中对P450活性的抑制起作用。这些结果表明，DES的2-羟基、10-羟基和N-去甲基代谢物不参与MI复合物形成，但复合物形成并非DES抑制微粒体药物氧化从而可能导致药代动力学药物相互作用的唯一机制。
