Linking redox chemistry and mitochondria in atrium to post-operative arrhythmia

描述（由申请人提供）：心脏血运重建术后患者的术后心房颤动（POAF）是一项重大的医疗负担，估计发生率在15-65%之间。这种情况发生的机制尚不清楚，识别那些更容易或易患POAF的患者的生物标志物对临床医生来说是非常有价值的。本研究将纳入300名接受体外循环择期心脏血管重建术的成年患者。将在手术期间从这些患者中获得右心房附件样本，并构建以下特定目的来验证中心假设，即手术时心肌组织中谷胱甘肽抗氧化能力的降低易使患者发生POAF，并且这种抗氧化能力的降低与线粒体氧化剂释放增加有关。目的1)：确定手术时患者心房谷胱甘肽含量或谷胱甘肽相关酶活性的降低是否与POAF的发生有关。细胞内还原性谷胱甘肽（GSH）和氧化性谷胱甘肽（GSSG）的浓度将在上述体外循环机构之前直接从患者的右心耳样本中进行评估。每个样品的谷胱甘肽过氧化物酶（清除H2O2）和谷胱甘肽还原酶（从GSSG中再生谷胱甘肽）的特定活性也将被评估。术后将持续监测患者的心电图直至出院，然后将每位患者的谷胱甘肽数据与该患者的术后心电图资料进行比较，以确定手术时患者心房谷胱甘肽含量和/或谷胱甘肽相关酶活性与POAF的发生之间是否存在联系。目的2)：确定冠状动脉搭桥手术患者心肌组织中线粒体氧化剂释放率升高是否与谷胱甘肽抗氧化能力下降有关。在基线和外源性Ca2+摄取后，由内源性底物氧化支持的线粒体H2O2排放将在从体外循环机构直接获得的患者右心房附件样品制备的渗透性心房肌纤维中进行评估。然后将这些数据与谷胱甘肽数据一起进行分析，以确定线粒体H2O2排放率高是否与心房组织中谷胱甘肽含量和/或酶活性降低有关。临床意义：预计该项目的研究结果将导致鉴定生化标记物，这些标记物可能能够识别发生POAF的高风险患者，此外还为阐明POAF发生的潜在机制提供了第一步。

DESCRIPTION (provided by applicant): Post-operative atrial fibrillation (POAF) in patients following cardiac revascularization surgery is a significant health care burden and estimates of occurrence range from 15-65%. The mechanisms by which this occurs remain unknown, and a bio-marker for identifying those patients that are more vulnerable, or pre-disposed, to POAF would be highly valuable to clinicians. The studies proposed in this grant proposal will have a target cohort of 300 adult patients undergoing elective cardiac revascularization surgery via cardiopulmonary bypass. Samples of right atrial appendage will be obtained from these patients during surgery, and the following Specific Aims have been constructed to test the CENTRAL HYPOTHESIS that a diminished glutathione antioxidant capacity in myocardial tissue at the time of surgery pre-disposes a patient to developing POAF, and that this diminished antioxidant capacity is linked to increased mitochondrial oxidant emission. Aim 1): To determine if decreased glutathione content or glutathione-related enzyme activity in a patient's atrium at the time of surgery is linked to the development of POAF. The concentration of intracellular reduced (GSH) and oxidized (GSSG) glutathione will be assessed in samples of right atrial appendage obtained from patients directly prior to institution of cardiopulmonary bypass as outlined above. The specific activities of glutathione peroxidase (H2O2 scavenging) and glutathione reductase (regenerates GSH from GSSG) will also be assessed in each sample. Patients will then be continuously monitored with ECG post-operatively until discharge from hospital, and the glutathione data for each patient will then be compared with the post-operative ECG profile of that patient to determine whether there is a link between glutathione content and/or glutathione-related enzyme activity in a patient's atrium at the time of surgery and the development of POAF. Aim 2): To determine whether elevated rates of mitochondrial oxidant emission are linked to diminished glutathione antioxidant capacity in myocardial tissue of patients undergoing CABG surgery. Mitochondrial H2O2 emission supported by endogenous substrate oxidation at baseline and following exogenous Ca2+ uptake will be assessed in permeabilized atrial myofibers prepared from samples of right atrial appendage obtained from patients directly prior to institution of cardiopulmonary bypass. These data will then be analyzed together with the glutathione data, to establish whether high rates of mitochondrial H2O2 emission are associated with reduced glutathione content and/or enzyme activity in atrial tissue. CLINICAL SIGNIFICANCE: It is anticipated that the findings from this project will result in identification of biochemical markers that may be able to identify patients at higher risk for developing POAF, in addition to providing a first step towards elucidating a potential mechanism by which POAF occurs. PUBLIC HEALTH RELEVANCE: Atrial fibrillation (irregular heartbeat) is one of the most common complications after open heart surgery. Its incidence ranges from 20% to 40% in most published series. Significant adverse effects include stroke, increased risk of death, and increased length of stay in hospital, resulting in a large financial burden to hospitals and clinics. Little is known about the mechanism for the development of this arrhythmia, and more importantly why it occurs in some patients and not in others. The studies proposed here are directed towards identifying a biochemical marker which could identify patients who are at increased risk of developing postoperative atrial fibrillation, and towards further understanding of the causative factors underlying its development.