Mechanical Ventilation and Diaphragmatic Oxidant Injury

描述（由申请人提供）：机械通气（MV）用于无法维持足够肺泡通气的患者维持肺部气体交换。从患者身上撤出MV被称为“断奶”，断奶过程中出现的问题是经常发生的。研究表明，膈肌无力是断奶困难的关键因素。重要的是，我们发现mv引起的膈肌无力与膈肌的氧化损伤有关。此外，我们最近的研究表明，mv诱导的氧化应激抑制膈肌比力的产生，促进蛋白质水解，导致膈肌萎缩。目前，mv诱导细胞产生氧化剂的机制尚不清楚。因此，这些实验将确定负责mv诱导的隔膜氧化损伤的氧化途径。基于初步实验，我们的工作假设是mv诱导的膈膜氧化应激是由于4种氧化产生途径之间的相互作用而发生的：1)NAD(P)H氧化酶产生超氧自由基；2)通过黄嘌呤氧化酶途径产生超氧自由基；3)通过一氧化氮合酶生产一氧化氮；4)通过增加细胞活性铁水平形成羟基自由基。这一假设将在大鼠脑脊液模型中进行验证，采用一种创新和全面的实验方法。首先，我们将使用一组已建立的技术来测量mv诱导的隔膜氧化损伤。其次，我们将研究每个氧化剂产生途径的关键元素，以确定这些成分是否在MV动物的膈膜中升高。此外，我们将采用已证实的每种氧化途径的药理抑制剂来确定该途径在mv诱导的膈肌氧化损伤和收缩功能障碍中的相对重要性。描述紫外线诱导的隔膜氧化产生的生化途径对于开发一种有效的方法来对抗这一破坏性过程至关重要。这些实验将提供关于横膈膜氧化剂来源的新的重要机制信息，可用于制定最佳的临床策略，以延缓mv诱导的横膈膜氧化应激和收缩功能障碍。

DESCRIPTION (provided by applicant): Mechanical ventilation (MV) is used to sustain pulmonary gas exchange in patients incapable of maintaining adequate alveolar ventilation. The withdrawal of MV from patients is called "weaning" and problems in weaning are frequent. Studies reveal that diaphragmatic weakness is a key contributor to weaning difficulties. Importantly, we have discovered that MV-induced diaphragmatic weakness is associated with oxidative damage to the diaphragm. Moreover, our recent work reveals that MV-induced oxidative stress depresses diaphragmatic specific force production and promotes proteolysis leading to diaphragmatic atrophy. At present, the mechanism(s) responsible for MV-induced production of cellular oxidants are unknown. Therefore, these experiments will determine the oxidant pathway(s) responsible for MV-induced oxidative injury in the diaphragm. Based upon preliminary experiments, our working hypothesis is that MVinduced diaphragmatic oxidative stress occurs due to interactions between 4 oxidant-producing pathways: 1) production of superoxide radicals by NAD(P)H oxidase; 2) generation of superoxide radicals by the xanthine oxidase pathway; 3) nitric oxide production via nitric oxide synthase; and 4) formation of hydroxyl radicals by increased cellular levels of reactive iron. This hypothesis will be tested in a rat model of MV using an innovative and comprehensive experimental approach. First, we will measure MV-induced oxidative injury in the diaphragm using a panel of established techniques. Secondly, we will investigate critical elements of each oxidant production pathway to determine if these components are elevated in diaphragms from MV animals. Further, we will employ proven pharmacological inhibitors of each oxidant pathway to determine the relative importance of the pathway in MV-induced diaphragmatic oxidative injury and contractile dysfunction. Delineating the biochemical pathways responsible for MV-induced oxidant production in the diaphragm is essential to developing an effective approach to oppose this damaging process. These experiments will provide new and important mechanistic information about the source of oxidants in the diaphragm that can be used to develop optimal clinical strategies to retard MV-induced diaphragmatic oxidant stress and contractile dysfunction.