Role of CYP2J2 in Xenobiotic Induced QT-prolongation

描述（由申请方提供）：本研究提案的长期目标是阐明CYP2J2在某些外源性物质的QT延长、心脏毒性作用中的作用。CYP2J2在心肌细胞中含量丰富，并参与花生四烯酸代谢为具有生物活性的环氧二十碳三烯酸（E3）。在各种细胞模型中，雌二醇对心脏离子通道和QT周期的电生理作用已有充分的记录。我们已经证明，CYP2J2被70%的与QT延长强烈相关的药物抑制。因此，预计CYP2J2抑制剂引起的组织EET浓度变化对心肌细胞具有毒性作用。该项目围绕两个假设和四个具体目标展开。假设1指出，可以鉴定出与尖端扭转型室性心动过速相关的药物，这些药物强烈抑制CYP2J2，但在生理浓度下对hERG的影响极小。设计了两个特定目的来检验这一假设，重点是表征在重组系统和心脏表达CYP2J2的转基因小鼠的心脏微粒体中引起QT延长的药物对CYP2J2抑制的生理作用。第二个假设指出，抑制CYP2J2的药物通过降低EET水平，进而导致KATP电流降低，从而有助于延长小鼠心肌细胞的动作电位。为了检验第二个假设，开发了具体目标3和4，以确定用具体目标1和2中确定的强效CYP2J2抑制剂长期治疗小鼠，导致小鼠心脏组织中内源性雌二醇水平降低，最后，具体目标4利用从野生型和转基因小鼠中分离的心肌细胞的电生理学研究来确定抑制CYP2J2对KATP的影响电流和动作电位持续时间。这些目标的成功完成将首次证明代谢在致室性心动过速药物毒性机制中的重要性，通过表征位于药物和内源性底物代谢界面的独特酶（CYP 2J2）的功能相互作用。

DESCRIPTION (provided by applicant): The long term objective of this research proposal is to elucidate the role of CYP2J2 in the QT- prolonging, cardiotoxic effect of certain xenobiotics. CYP2J2 is abundant in cardiac myocytes and is involved in the metabolism of arachidonic acid to biologically active epoxyeicosatrienoic acids (EETs). EETs have well documented electrophysiological effects on cardiac ion channels and the QT-period in various cell models. We have demonstrated that CYP2J2 is inhibited by 70% of drugs that are strongly associated with QT-prolongation. Therefore, alterations in tissue EET(s) concentrations caused by CYP2J2 inhibitors could be expected to have toxic effects on cardiomyocytes. This project is developed around two hypotheses and four specific aims. Hypothesis one states that drugs associated with torsade de pointes can be identified that strongly inhibit CYP2J2, but have minimal effect on hERG at physiological concentrations. Two specific aims were designed to test this hypothesis and are focused on characterizing the physiological effect of CYP2J2 inhibition by drugs that cause QT- prolongation in both a recombinant system and cardiac microsomes from transgenic mice that express CYP2J2 in their hearts. The second hypothesis states that drugs that inhibit CYP2J2 contribute to prolongation of the action potential in mouse cardiac myocytes by reducing EET levels, which in turn leads to reduction in KATP currents. To test the second hypothesis, specific aims 3 and 4 were developed to determine if chronic treatment of mice with potent CYP2J2 inhibitors, identified in specific aims 1 and 2, leads to reduction in endogenous EETs levels in mouse cardiac tissue and finally specific aim 4 utilizes electrophysiological studies in cardiac myocytes isolated from wild type and transgenic mice to determine the consequences of inhibiting CYP2J2 on KATP currents and the action potential duration. Successful completion of these aims will demonstrate, for the first time, the importance of metabolism in the mechanism of toxicity of torsadogenic drugs, by characterizing the functional interactions of a unique enzyme (CYP2J2) that is situated at the interface of drug and endogenous substrate metabolism.