Lee Sang Yoon, Jang Himchan, Lee Ji-Yoon, Kwon Kwang-il, Oh Soo Jin, Kim Sang Kyum
College of Pharmacy, Chungnam National University, Daejeon 305-764, Republic of Korea.
Bio-Evaluation Center, KRIBB, 685-1 Yangcheong-ri, Ochang-eup, Cheongwon-gun, Chungbuk 363-883, Republic of Korea.
Toxicol Lett. 2014 Aug 17;229(1):33-40. doi: 10.1016/j.toxlet.2014.06.006. Epub 2014 Jun 5.
Although cytochrome P450 inhibition is the major drug-drug interaction (DDI) mechanism in clinical pharmacotherapy, DDI of a number of well-established drugs have not been investigated. Rifampicin, isoniazid, pyrazinamide and ethambutol combination therapy inhibits clearance of theophylline in patients with tuberculosis. We determined the inhibitory effects of ethambutol on the activities of nine CYP isoforms including CYP1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1 and 3A4 in pooled human liver microsomes (HLM). As measured by liquid chromatography-electrospray ionization tandem mass spectrometry, ethambutol exhibited strong inhibitory potential against CYP1A2 and CYP2E1, moderate against CYP2C19 and CYP2D6 and weak against CYP2A6, CYP2C9 and CYP3A4, based on the IC50 values. The K(i) value of ethambutol for CYP1A2 was 1.4 μM and for CYP2E1 was 2.9 μM. Inhibition of CYP1A2 and CYP2E1 was not increased by preincubation with ethambutol and β-nicotinamideadenine dinucleotide phosphate (NADPH), suggesting that the ethambutol-induced CYP inhibition may not be metabolism-dependent. Kinetic analysis showed that the inhibition of CYP1A2 and CYP2E1 by ethambutol was best fit to a competitive inhibition model. Formation of 1-methylxanthene and 1,3-dimethyluric acid from theophylline in HLM was decreased to 47% and 36%, respectively, by 3.0 μM ethambutol, which is comparable to its IC50 value against CYP1A2. Considering its maximal plasma concentrations of ~10 μM and long half-life of ~22 h, our findings raise the possibility that ethambutol causes significant DDIs in clinical situations with drugs with narrow therapeutic index, such as theophylline, in clinical situations.
尽管细胞色素P450抑制是临床药物治疗中主要的药物相互作用（DDI）机制，但许多已确立药物的DDI尚未得到研究。利福平、异烟肼、吡嗪酰胺和乙胺丁醇联合疗法会抑制结核病患者体内茶碱的清除。我们测定了乙胺丁醇对包括CYP1A2、2A6、2B6、2C8、2C9、2C19、2D6、2E1和3A4在内的九种CYP同工酶在人肝微粒体（HLM）中的活性抑制作用。通过液相色谱-电喷雾电离串联质谱法测定，根据IC50值，乙胺丁醇对CYP1A2和CYP2E1表现出强抑制潜力，对CYP2C19和CYP2D6表现出中度抑制，对CYP2A6、CYP2C9和CYP3A4表现出弱抑制。乙胺丁醇对CYP1A2的K(i)值为1.4 μM，对CYP2E1的K(i)值为2.9 μM。乙胺丁醇与β-烟酰胺腺嘌呤二核苷酸磷酸（NADPH）预孵育后，对CYP1A2和CYP2E1的抑制作用并未增强，这表明乙胺丁醇诱导的CYP抑制可能不依赖于代谢。动力学分析表明，乙胺丁醇对CYP1A2和CYP2E1的抑制最符合竞争性抑制模型。在HLM中，3.0 μM乙胺丁醇可使茶碱生成1-甲基黄嘌呤和1,3-二甲基尿酸的量分别降至47%和36%，这与其对CYP1A2的IC50值相当。考虑到其最大血浆浓度约为10 μM，半衰期约为22小时，我们的研究结果增加了乙胺丁醇在临床情况下与治疗指数窄的药物（如茶碱）发生显著DDI的可能性。
