Inflammation and Oxidative Stress in Hyperglycemic Exacerbation of Infarct Size

描述（由申请人提供）：在糖尿病和非糖尿病患者中，急性高血糖与较大的心肌梗死（MI）大小和左室功能受损独立相关。然而，急性高血糖加剧心肌损伤的机制尚不清楚，特别是在非糖尿病患者中。急性高血糖与氧化应激增加、内皮功能障碍、凝血激活和炎症增强有关。我们的初步研究表明，在非糖尿病小鼠缺血前引起的急性高血糖显著增强再灌注损伤，并消除缺血前和后适应。此外，我们已经证明，在再灌注前立即用特异性激动剂激活腺苷2A受体（A2AR），就像用强抗氧化剂MPG治疗一样，可以消除心肌损伤的高血糖加剧。这些研究表明，非糖尿病患者的急性高血糖通过中断内源性心脏保护机制、增加氧化应激和引发先天炎症反应来增加心肌梗死的大小。越来越多的证据表明，急性高血糖期间晚期糖基化终产物（AGEs）的形成通过与AGE受体（RAGE）的相互作用，在心肌梗死大小加剧中起着核心作用。我们之前的工作表明，CD4+ T细胞上的A2ARs在调节炎症反应中起关键作用，这对心肌梗死的大小有重要影响，并且在再灌注前激活A2ARs可以减少梗死面积。我们的初步研究表明，A2ARs的激活也可以防止心肌损伤的高血糖加剧。因此，我们假设急性高血糖通过RAGE刺激和增加氧化应激增强CD4+ T细胞介导的先天免疫反应，从而加剧梗死面积。为了在体内验证这一假设，我们将使用急性高血糖的心肌缺血/再灌注损伤小鼠模型来解决以下具体目标：1)确定氧化应激、AGE/RAGE轴和胰岛素葡萄糖正常化在高血糖加剧心肌梗死（MI）大小中的机制作用。这一目标将通过在小鼠心肌梗死模型中应用特定的药理学探针（强效抗氧化剂、AGE抑制剂、可溶性RAGE和胰岛素）来实现，然后评估它们对梗死面积和再灌注后炎症反应的影响。2)确定体内携带介导和调节梗死面积高血糖加重的AGE、A2A和IL-18受体的细胞类型。本研究将采用一系列敲除小鼠（CD4- null, RAGE-null， A2AR-null和IL18R-null）来验证CD4+ T细胞上这些受体的存在在介导/调节高血糖对心肌梗死大小的有害影响中起关键作用的假设。3)应用从目标1和目标2中收集的机制见解，确定一种临床相关的治疗策略，能够最大限度地减少血糖正常/高血糖小鼠的心肌梗死大小，并使用心脏MRI的尖端技术确认这对左室结构和功能具有持久的积极影响。公共卫生相关性：缺血性心脏病仍然是美国唯一的主要死亡原因，占死亡人数的五分之一。心肌梗死（心脏病发作）和由心脏病发作引起的心力衰竭占缺血性心脏病相关死亡和疾病的绝大多数。有些人在心脏病发作时出现高血糖（高血糖症），即使他们之前没有高血糖史。这些患者死于心脏病发作的几率比没有高血糖的患者高得多。这个研究项目将增加我们对为什么高血糖会使心脏病患者的临床结果恶化的理解，并将确定新药物和现有药物的最佳组合，以减少高血糖（或非高血糖）患者心脏病发作的规模。

DESCRIPTION (provided by applicant): Acute hyperglycemia is independently associated with larger myocardial infarct (MI) size and impaired LV function in both diabetic and non-diabetic patients. However, the mechanisms underlying the exacerbation of myocardial injury by acute hyperglycemia remain unclear, especially in non-diabetics. Acute hyperglycemia is associated with increased oxidative stress, endothelial dysfunction, activation of coagulation and enhanced inflammation. Our preliminary studies show that acute hyperglycemia, induced shortly before ischemia in non- diabetic mice, significantly enhances reperfusion injury and abolishes both ischemic pre- and post-conditioning. Furthermore, we have shown that activation of Adenosine 2A Receptors (A2AR) with a specific agonist immediately before reperfusion abrogates the hyperglycemic exacerbation of myocardial injury, as does treatment with the potent antioxidant MPG. These studies indicate that acute hyperglycemia in non-diabetics increases the size of MI by interrupting endogenous cardioprotective mechanisms, increasing oxidative stress and provoking innate inflammatory responses. Growing evidence now indicates that the formation of advanced glycated end products (AGEs) during acute hyperglycemia plays a central role in exacerbating MI size through their interaction with the AGE receptor (RAGE). Our previous work showed that A2ARs on CD4+ T cells play a critical role in regulating the inflammatory responses that contribute importantly to MI size, and that infarct size is reduced by activating A2ARs prior to reperfusion. Our preliminary studies show that activation of A2ARs also prevents the hyperglycemic exacerbation of myocardial injury. We therefore hypothesize that acute hyperglycemia exacerbates infarct size by enhancing CD4+ T cell-mediated innate immune responses via RAGE stimulation and increasing oxidative stress. To test the hypothesis in vivo, we will use a mouse model of myocardial ischemia/reperfusion injury with acute hyperglycemia to address the following specific aims: 1) Determine the mechanistic roles of oxidative stress, the AGE/RAGE axis and glucose normalization with insulin in the hyperglycemic exacerbation of myocardial infarct (MI) size. This Aim will be pursued by applying specific pharmacologic probes (potent antioxidants, AGE inhibitors, soluble RAGE and insulin) in the murine model of MI, then assessing their impact on infarct size and post-reperfusion inflammatory responses. 2) Determine the identity of the cell types carrying the AGE, A2A and IL-18 receptors that mediate and regulate the hyperglycemic exacerbation of infarct size in vivo. This aim will employ an array of knockout mice (CD4- null, RAGE-null, A2AR-null & IL18R-null) to test the hypothesis that the presence of each of these receptors on CD4+ T cells plays a critical role in mediating/regulating the deleterious effects of hyperglycemia on MI size. 3) Apply the mechanistic insights gleaned from Aims 1 & 2 to identify a clinically-relevant treatment strategy capable of minimizing MI size in euglycemic/hyperglycemic mice and confirm that this has an enduring, positive impact on LV structure and function using cutting-edge techniques in cardiac MRI. PUBLIC HEALTH RELEVANCE: Ischemic heart disease remains the single leading cause of death in the United States, accounting for fully one out of every five deaths. Myocardial infarction (heart attack) and heart failure resulting from heart attack account for the vast majority of the death and illness associated with ischemic heart disease. Some people have high blood sugar (hyperglycemia) when they experience a heart attack, even if they have no prior history of high blood sugar. These patients die from their heart attack much more often than patients without high blood sugar. This research project will increase our understanding of why high blood sugar worsens clinical outcome in patients with heart attack, and will identify the best combination of new and existing drugs to reduce the size of heart attack in patients with (and without) high blood sugar.