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

描述(由申请人提供)：心脏血管重建术后患者的术后心房颤动(POAF)是一种重大的医疗负担，估计发生率在15%-65%之间。发生这种情况的机制尚不清楚，而识别那些更易患POAF或易患POAF的患者的生物标志物对临床医生来说将具有很高的价值。这项拨款提案中提出的研究将以300名成年患者为目标队列，这些患者通过体外循环接受择期心脏血管重建术。手术期间将从这些患者身上获取右心耳样本，并构建了以下特定目标来验证以下中心假设：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排放的增加有关。目的1)：确定手术时患者心房内谷胱甘肽含量或谷胱甘肽相关酶活性降低是否与POAF的发生有关。细胞内还原型谷胱甘肽(GSH)和氧化型谷胱甘肽(GSSG)的浓度将在如上所述的体外循环前直接从患者的右心耳样本中进行评估。还将在每个样本中评估谷胱甘肽过氧化物酶(清除过氧化氢)和谷胱甘肽还原酶(从谷胱甘肽中再生谷胱甘肽)的特定活性。然后，患者将在手术后持续进行心电监测，直到出院，然后将每个患者的谷胱甘肽数据与该患者手术后的心电图图谱进行比较，以确定手术时患者心房中的谷胱甘肽含量和/或谷胱甘肽相关酶活性是否与POAF的发生有关。目的：探讨冠脉搭桥术患者心肌组织线粒体氧化剂释放率升高是否与心肌组织谷胱甘肽抗氧化能力降低有关。我们将在体外循环前直接从患者的右心耳标本制备的通透性心房肌纤维中评估内源性底物氧化和外源性钙摄取所支持的线粒体H_2O_2释放。然后将这些数据与谷胱甘肽数据一起进行分析，以确定线粒体过氧化氢释放的高率是否与心房组织中谷胱甘肽含量和/或酶活性的降低有关。临床意义：预计该项目的发现将导致识别生化标记物，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。 公共卫生意义：房颤(心律不齐)是心脏直视手术后最常见的并发症之一。在大多数已发表的系列文章中，其发病率从20%到40%不等。严重的不良影响包括中风、死亡风险增加和住院时间增加，给医院和诊所带来了巨大的经济负担。人们对这种心律失常的发生机制知之甚少，更重要的是，为什么它发生在一些患者身上，而不是发生在其他患者身上。本研究旨在找出一种生化标记物，以确定哪些患者术后发生房颤的风险增加，并进一步了解房颤发生的原因。

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.