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

描述（由申请人提供）：心脏血运重建手术后患者的术后房颤（POAF）是一项重大的医疗保健负担，估计发生率为15 - 65%。发生这种情况的机制仍然未知，并且用于识别更易受POAF影响或更易受POAF影响的患者的生物标记物对临床医生非常有价值。 本资助提案中提出的研究将有300名通过体外循环接受择期心脏血运重建手术的成年患者作为目标队列。将在手术期间从这些患者中采集右心耳样本，并构建了以下特定目的，以测试中心假设，即手术时心肌组织中谷胱甘肽抗氧化能力降低使患者易于发生POAF，并且这种抗氧化能力降低与线粒体氧化剂排放增加有关。目标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的降低是否与POAF的发生有关。如上所述，将在心肺转流术前即刻从患者中采集右心耳样本，评估细胞内还原型（GSH）和氧化型（GSSG）谷胱甘肽的浓度。还将评估每份样本中谷胱甘肽过氧化物酶（H2O2清除）和谷胱甘肽还原酶（从GSSG再生GSH）的比活性。然后将在术后使用ECG连续监测患者直至出院，然后将每例患者的谷胱甘肽数据与该患者的术后ECG曲线进行比较，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与POAF的发生之间是否存在联系。目标2）：确定接受CABG手术的患者心肌组织中线粒体氧化剂释放速率升高是否与谷胱甘肽抗氧化能力降低有关。将在透化心房肌纤维中评估基线时和外源性Ca2+摄取后内源性底物氧化支持的线粒体H2O2排放，所述透化心房肌纤维是从心肺转流术前即刻从患者获得的右心耳样本制备的。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释放的高速率是否与心房组织中还原型谷胱甘肽含量和/或酶活性相关。临床意义：预计该项目的研究结果将导致鉴定可能能够识别患有POAF的高风险患者的生化标志物，此外还为阐明POAF发生的潜在机制迈出了第一步。 公共卫生相关性：心房颤动（不规则心跳）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中，其发病率范围为20%至40%。显著的不良反应包括中风、死亡风险增加和住院时间延长，从而给医院和诊所带来巨大的经济负担。关于这种心律失常的发展机制知之甚少，更重要的是为什么它发生在一些患者身上而不是其他人身上。本文提出的研究旨在确定一种生化标志物，可以识别术后房颤风险增加的患者，并进一步了解其发展的致病因素。

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.