Obesity/Insulin Resistance and Endothelial t-PA Release

描述（由申请人提供）：动脉粥样硬化性血管疾病是2型糖尿病发病率和死亡率的主要原因。尽管对2型糖尿病发病的病理生理机制有了更深入的了解，但2型糖尿病中血管过度风险的机制尚不清楚。在肥胖/胰岛素抵抗的糖尿病前期，纤维蛋白溶解功能受损被认为是2型糖尿病患者动脉粥样硬化血栓形成速度加快的原因之一。然而，肥胖/胰岛素抵抗中低纤溶状态的潜在机制尚不清楚。事实上，目前尚不清楚血管内皮释放组织型纤溶酶原激活剂（t-PA）的能力是否在肥胖/胰岛素抵抗中受损。这一点至关重要，因为决定内源性溶栓潜力的是t-PA的局部内皮释放率，而不是循环血浆纤维蛋白溶解浓度。t-PA是启动纤维蛋白溶解的关键酶。因此，本提案的具体目的将是确定：1)肥胖/胰岛素抵抗的成年人血管内皮释放组织型纤溶酶原激活剂的能力是否降低；2)肥胖/胰岛素抵抗导致内皮组织型纤溶酶原激活物释放减少是否由于氧化应激增加；3)内皮组织型纤溶酶原激活剂释放减少与肥胖/胰岛素抵抗是否与慢性亚临床炎症有关。为了实现这些目标，48名中年肥胖/胰岛素抵抗和非肥胖/胰岛素敏感的成年人将被研究。血管内皮局部释放t-PA的能力将在体内评估，以响应臂内输注缓动素（12.5-50 ng/ 100ml组织/min）和硝普钠（1.0-4.0 mL / 100ml组织/min）。通过前臂血管对每种药物刺激的t-PA净释放/摄取将被计算为动静脉浓度梯度和前臂血浆流量的乘积。为了确定氧化应激对内皮细胞t-PA释放的影响，将在抗氧化剂维生素C （12 mg/100 mL组织/min）的联合输注下重复缓激肽和硝普钠的剂量反应曲线。血浆炎症生物标志物与t-PA释放之间的关系也将被检查。预期的结果将为肥胖/胰岛素抵抗的前驱糖尿病状态下观察到的动脉粥样硬化血栓形成的过度风险提供机制见解，并为未来旨在减少/预防2型糖尿病相关心血管并发症的抗氧化剂补充试验提供实验支持。

DESCRIPTION (provided by applicant): Atherothrombotic vascular disease is the leading cause of morbidity and mortality in type 2 diabetes. Despite a greater understanding of the pathophysiologic mechanisms responsible for the development of type 2 diabetes, the mechanisms responsible for the excess vascular risk in type 2 diabetes are unclear. Impaired fibrinolytic function occurring in the obese/insulin resistant prediabetic stage is thought to contribute to the accelerated rate of atherothrombosis in type 2 diabetes. However, the underlying mechanisms responsible for the hypofibrinolytic state in obesity/insulin resistance are not well understood. Indeed, it is currently unknown whether the capacity of the vascular endothelium to release tissue-type plasminogen activator (t-PA) is impaired in obesity/insulin resistance. This is critically important because it is the local endothelial release rate of t-PA, the key enzyme in initiating fibrinolysis, and not circulating plasma fibrinolytic concentrations that determines endogenous thrombolysis potential. Accordingly, the specific aims of the present proposal will be to determine: 1) if the capacity of the vascular endothelium to release tissue-type plasminogen activator is reduced in obese/insulin resistant adult humans; 2) if the postulated decrease in endothelial tissue-type plasminogen activator release with obesity/insulin resistance is due to increased oxidative stress; and 3) if the postulated decrease in endothelial tissue-type plasminogen activator release with obesity/insulin resistance is associated with chronic subclinical inflammation. To address these aims, 48 middle-aged obese/insulin resistant and non-obese/insulin sensitive adults will be studied. Capacity of the vascular endothelium to locally release t-PA will be assessed, in vivo, in response to intrabrachial infusions of bradykinin (12.5-50 ng/100 mL tissue/min) and sodium nitroprusside (1.0-4.0 ml/100 ml tissue/min). Net release/uptake of t-PA across the forearm vasculature to each pharmacological stimulus will be calculated as the product of the arteriovenous concentration gradient and forearm plasma flow. To determine the effects of oxidative stress on endothelial t-PA release, the bradykinin and sodium nitroprusside dose response curves will be repeated with a coinfusion of the antioxidant vitamin C (12 mg/100 mL tissue/min). The relation between plasma biomarkers of inflammation and t-PA release will also be examined. The expected results should provide mechanistic insight into the excess risk of atherothrombosis observed in the obese/insulin resistant prediabetic state, and experimental support for future antioxidant supplementation trials aimed at reducing/preventing cardiovascular complications associated with type 2 diabetes.