Oxidative Stress and Left Ventricular Diastolic Function

描述（由申请人提供）：大约一半的心力衰竭病例发生在保留收缩功能的患者中，使舒张性心力衰竭成为一个实质性的健康问题。舒张功能障碍的患病率一直在增加，死亡率大致相当于收缩期心力衰竭患者的死亡率，并且与收缩期心力衰竭不同，死亡率不受当前治疗方法的影响。在某种程度上，这源于缺乏对这种情况的机制理解。高血压是舒张功能障碍的主要危险因素之一，本应用将探讨高血压导致舒张功能障碍的可能机制。一氧化氮（NO）已被证明能增强舒张舒张。高血压导致氧化应激，通过一氧化氮合酶（NOS）解偶联导致NO的损失，这种情况的特征是四氢生物蝶呤（BH4）的损失。BH4是NOS电子传递链中的重要辅助因子。不耦合的NOS发生在BH4被氧化时。当不耦合时，NOS产生超氧化物而不是NO。因此，少量的氧化应激可以导致一个正反馈循环，最终耗尽大部分NO合成能力。最近，我们已经证明BH4优先被过氧亚硝酸盐氧化，并且NAD(P)H氧化酶（NOX）衍生的过氧亚硝酸盐是NOS解耦的核心。基于高血压与舒张功能障碍的强烈临床关联，我们建立了一种小鼠舒张功能障碍模型，使用醋酸脱氧皮质酮盐诱导的小鼠高血压。我们已经证明，该模型通过一氧化氮依赖机制产生氧化应激。在初步研究中，通过超声心动图和血流动力学测量，我们发现这些小鼠存在心脏氧化应激、BH4降低、内皮细胞NOS （eNOS）解耦和舒张功能障碍。膳食补充BH4可防止eNOS解偶联和舒张功能障碍的发生，提示NOS解偶联可能在这种形式的高血压引起的舒张功能障碍的发病机制中起核心作用。因此，我们假设高血压期间活性氧（ROS）的持续过量产生导致恶性循环，过量的ROS产生导致心肌BH4的氧化消耗和NOS的解耦，这反过来又使超氧化物的过量产生持续存在，进一步消耗BH4并降低心肌NO的生物利用度。一氧化氮在心脏中的生物利用度降低导致心肌细胞舒张舒张受损。此外，我们将测试是否像在脉管系统中一样，NOXs对于产生心脏中初始NOS解耦所必需的ROS至关重要。我们将测试清除ROS是否会防止BH4耗竭、非偶联NOS和舒张功能障碍。最后，由于NOXs是血管紧张素II依赖性的，心脏血管紧张素II似乎在舒张功能障碍中发挥作用，我们将测试以降低肾素-血管紧张素系统激活为目标的药物治疗是否会防止BH4耗竭、解偶联NOS和舒张功能障碍。

DESCRIPTION (provided by applicant): Approximately half of all heart failure cases occur in patients with preserved systolic function, making diastolic heart failure a substantial health problem. The prevalence of diastolic dysfunction has been increasing, the mortality rate is roughly equivalent to that of patients with systolic heart failure, and, unlike in systolic heart failure, mortality has been unaffected by current therapies. In part, this stems from a lack of mechanistic understanding about this condition. Hypertension is among the leading risk factors for diastolic dysfunction, and this application will explore a possible mechanism whereby hypertension may cause diastolic dysfunction. Nitric oxide (NO) has been shown to enhance diastolic relaxation. Hypertension results in an oxidative stress that leads to loss of NO through nitric oxide synthase (NOS) uncoupling, a condition characterized by the loss of tetrahydrobiopterin (BH4). BH4 is a critical co-factor in the NOS electron transport chain. Uncoupled NOS occurs when BH4 becomes oxidized. When uncoupled, NOS produces superoxide rather than NO. Therefore, a small amount of oxidant stress can lead to a positive feedback loop that ultimately depletes most NO synthetic capacity. Recently, we have shown that BH4 is preferentially oxidized by peroxynitrite and that NAD(P)H oxidase (NOX)-derived peroxynitrite is central to NOS uncoupling. Based on the strong clinical association of hypertension and diastolic dysfunction, we developed a murine model of diastolic dysfunction using mice with deoxycorticosterone acetate-salt induced hypertension. We have shown that this model generates oxidative stress through an NOX-dependent mechanism. In preliminary studies, we show these mice have cardiac oxidative stress, reduced BH4, uncoupled endothelial NOS (eNOS), and diastolic dysfunction by echocardiographic and hemodynamic measures. Dietary supplementation with BH4 prevents the onset of eNOS uncoupling and diastolic dysfunction, suggesting that NOS uncoupling may play a central role in the pathogenesis of diastolic dysfunction induced by this form of hypertension. Therefore, we hypothesize that persistent overproduction of reactive oxygen species (ROS) during hypertension results in a vicious cycle where excess ROS production leads to oxidative depletion of myocardial BH4 and NOS uncoupling, which in turn perpetuates the overproduction of superoxide, further depleting BH4 and reducing myocardial NO bioavailability. A decreased NO bioavailability in the heart results in impaired diastolic relaxation of cardiomyocytes. Furthermore, we will test whether, as in the vasculature, if NOXs are central to generating the ROS necessary for initial NOS uncoupling in the heart. We will test whether scavenging of ROS will prevent BH4 depletion, uncoupled NOS, and diastolic dysfunction. Finally, since NOXs are angiotensin II- dependent and cardiac angiotensin II seems to play a role in diastolic dysfunction, we will test whether pharmacological therapy targeting at reducing renin-angiotensin system activation will prevent BH4 depletion, uncoupled NOS, and diastolic dysfunction. Project Narrative: Diastolic heart failure is a major and growing public health problem in the United States. Despite the increasing prevalence and ominous implications for life expectancy, there are currently no approved therapies for diastolic heart failure, in part due to our overall poor understanding of the mechanisms underlying diastolic dysfunction. This project will investigate a novel potential mechanism that might open the way for new therapies for this poorly understood disorder.