Obesity-Mediated Atrial Fibrillation: Underlying Mechanisms and Responsiveness to Antiarrhythmic Therapy

心房颤动（AF）是退伍军人中最常见的持续性心律失常， 增加中风、心力衰竭和死亡的风险。受AF影响的美国人数量是 预计到2050年将激增至约1600万人。虽然因果关系 肥胖和房颤之间的联系，其潜在的病理生理机制和 它们对抗糖尿病药物（AAD）治疗反应的影响仍不清楚。新出现的证据 支持降低心脏Na+通道表达作为一种潜在的促成机制。以来 阻断心脏Na+通道（Nav1.5）的I类AAD通常用于治疗AF， 该提案的首要目标是阐明潜在的电生理（EP）和分子 肥胖增加AF风险和调节对Na+通道阻滞剂反应的机制 在饮食诱导的肥胖（DIO）小鼠中。具体目标1将检验肥胖诱导的房颤是 与DIO小鼠中氧化应激增加相关，这种作用部分由 调节心脏Na+通道。我们将测量心房的生物标志物（4-羟基壬烯醛，4-HNE; 硝化蛋白，YNO 2）和全身性（F2-异前列烷，IsoPs）氧化应激， 将其与精益控制进行比较。这一目标建立在我们以前的工作基础上，表明SCN 5A缺失- 功能突变通过降低Nav1.5表达和电流（INa）增加AF风险，试点数据 表明DIO小鼠比瘦对照组更容易发生AF，这种风险部分由以下因素介导： Nav1.5下调和氧化应激增加。尽管最近在基于导管的 尽管AAD治疗的疗效不佳，但AAD仍常用于治疗症状性AF。 个体患者是高度可变，且膜活性药物与严重毒性相关。 因此，一个主要的知识缺口是预测哪些AF患者最有可能对AAD有反应。 我们在JBVA/UIC AF登记处获得的初步数据不仅表明肥胖调节了 对抗心律失常治疗有反应，但对Na+通道与K+通道的反应不同 通道阻断剂AAD。这就提出了在具体目标2中检验的假设，即氟卡尼（Na+ 通道阻滞剂）在治疗DIO小鼠AF方面劣于索他洛尔（K+通道阻滞剂）。肥胖的老鼠会 接受快速经食管心房起搏以诱发AF，然后急性接受AAD治疗，或 以房颤负担作为主要结局。这一目标建立在我们的临床和动物数据基础上 显示氟卡尼在肥胖患者和DIO小鼠中治疗AF的疗效降低 分别我们的研究表明，肥胖介导的房颤与氧化应激增加有关。 应激，这部分是通过调节心脏Na+通道介导的。第3章将 定义肥胖增加DIO小鼠AF风险的潜在分子机制：i） 确定ROS产生的来源和特定途径; ii）确定Nav1.5是否直接 iii）评估氧化应激如何影响表达 和心脏Na+通道的活性。这一目标建立在我们早期的研究和试点数据的基础上， 显示用靶向抗氧化剂治疗的DIO小鼠的AF负荷显著降低 （MitoTEMPO）.拟议研究的直接影响将阐明潜在的EP和分子 肥胖增加AF风险的机制;确定氧化应激的新心房生物标志物 这将转化为患者;揭示ROS产生的特定途径，用于治疗靶向; 并验证小鼠模型的结果可以转化为更好的抗肿瘤药物的假设， 肥胖AF患者的治疗。 1

Atrial fibrillation (AF), the most common sustained cardiac arrhythmia in Veterans, is associated with increased risk for stroke, heart failure, and death. The number of Americans affected by AF is expected to surge to approximately 16 million by the year 2050. Although a causal relationship between obesity and AF was recently established, the underlying pathophysiological mechanisms and their impact on response to antiarrhythmic drug (AAD) therapy remain unclear. Emerging evidence supports reduced cardiac Na+ channel expression as one potential contributing mechanism. Since Class I AADs, which block the cardiac Na+ channel (Nav1.5), are commonly used to treat AF, the overarching goal of this proposal is to elucidate the underlying electrophysiologic (EP) and molecular mechanisms by which obesity increases risk of AF and modulates response to Na+ channel blockers in diet-induced obese (DIO) mice. Specific Aim 1 will test the hypothesis that obesity-induced AF is associated with increased oxidative stress in DIO mice and this effect is in part mediated by modulating the cardiac Na+ channel. We will measure biomarkers of atrial (4-hydroxynonenal, 4-HNE; nitrated proteins, YNO2) and systemic (F2-isoprostanes, IsoPs) oxidative stress in DIO mice and compare them with lean controls. This aim builds on our previous work showing that SCN5A loss-of- function mutations increase AF risk by reducing Nav1.5 expression and current (INa), pilot data showing that DIO mice are more prone to AF than lean controls and this risk is mediated in part by downregulation of Nav1.5 and increased oxidative stress. Despite recent advances in catheter-based therapies, AADs continue to be commonly used to treat symptomatic AF. However, response in an individual patient is highly variable and membrane-active drugs are associated with serious toxicities. Thus, a major knowledge gap is predicting which patients with AF are most likely to respond to AADs. Our pilot data, generated in the JBVA/UIC AF Registry, not only shows that obesity modulates response to antiarrhythmic therapy but that there is a differential response to Na+ channel versus K+ channel blocker AADs. This raises the hypothesis to be tested in Specific Aim 2 that flecainide (Na+ channel blocker) is inferior to sotalol (K+ channel blocker) in treating AF in DIO mice. Obese mice will undergo rapid transesophageal atrial pacing to induce AF and then be treated with AADs acutely or chronically with AF burden as the primary outcome. This aim builds on our clinical and animal data that shows reduced efficacy of flecainide in treatment of AF in obese patients and DIO mice respectively. Our studies have shown that obesity-mediated AF is associated with increased oxidative stress and this is mediated in part by modulation of the cardiac Na+ channel. Specific Aim 3 will define the underlying molecular mechanisms by which obesity increases risk of AF in DIO mice by: i) identifying the sources and specific pathways of ROS production; ii) determining if Nav1.5 is directly targeted by increased oxidative stress; and iii) evaluating how oxidative stress impacts the expression and activity of the cardiac Na+ channel. This aim builds on our earlier studies and pilot data where we show significant reduction in AF burden in DIO mice treated with a mitochondria-targeted antioxidant (MitoTEMPO). Direct impact of the proposed studies will elucidate the underlying EP and molecular mechanisms by which obesity increases risk of AF; identify novel atrial biomarkers of oxidative stress that will translate to patients; uncover specific pathways of ROS production for therapeutic targeting; and test the hypothesis that results from mouse models can be translated into better antiarrhythmic therapy in obese patients with AF. 1