Ocular Oxygen Metabolism and the Etiology of Open Angle Glaucoma

描述（由申请人提供）：了解青光眼（第二大致盲原因）的发病机制是视觉研究的重要目标。许多研究已经确定了小梁网（TM）细胞的氧化损伤，导致流出功能降低和眼内压升高。虽然将氧化损伤与青光眼联系起来的证据很强，但青光眼中氧化损伤的原因尚不清楚。在拟定的研究中，我们将检验TM的氧化损伤是由过度暴露于分子氧和/或其代谢产物引起的假设。我们的假设是基于氧分压（pO 2）的测量，在手术过程中使用薄的，灵活的，光纤探头在人眼。我们确定了前房中大而稳定的氧梯度和前房角中接近TM的pO 2的严格调节。我们还注意到pO 2和青光眼的重要危险因素之间的强相关性，包括中央角膜厚度，非洲裔美国人的遗传和玻璃体切除术的历史。我们相信我们的研究是第一个将生理变量，前房（AC）中的pO 2与青光眼发展的风险联系起来的研究。我们的第一个具体目标是测试玻璃体切除术后青光眼风险的增加是否是由于AC中pO 2的增加导致TM损伤。我们将与威斯康星大学麦迪逊分校的同事合作，对老年恒河猴进行纵向研究，这些恒河猴将依次接受玻璃体切除术和白内障摘除术。我们将绘制pO 2水平，并测量每个阶段的房水抗氧化剂和流出设施。在研究结束时，我们将确定TM细胞损失的程度，并量化TM细胞及其细胞外基质的结构和氧化损伤。通过这种方式，我们可以将pO 2与TM的氧化损伤相关联。我们的第二个目的是确定非裔美国人的pO 2增加是否与房水中的生化变化相关。我们将扩大我们的初步研究的代谢物在房水中，这表明种族差异的线粒体代谢。我们还将分析房水的总抗氧化潜力和已知抗氧化剂（如抗坏血酸盐）的浓度;研究将确定pO 2与前房中氧化剂-抗氧化剂平衡之间是否存在相关性。我们假设较高的pO 2与抗氧化剂的消耗有关。我们的第三个具体目标是确定是否角膜氧代谢的非侵入性措施预测眼内pO 2。我们假设较低的角膜耗氧量与AC中pO 2的增加相关。如果正确的话，这项测试可能会提供一个重要的手段，以确定那些在发展青光眼的风险。它还将提供一种方法来确定眼内氧的差异是否是遗传的，并确定相关的基因。我们的新方法将通过识别导致房水流出功能丧失的因素，提供有关开角型青光眼病理生理学的重要信息。这些研究中获得的知识可能会导致新的治疗方法和预防这种疾病的策略。 公共卫生相关性：大量研究支持氧化应激（破坏性自由基分子与身体抗氧化防御机制之间的不平衡）通过损害眼睛引流中的小梁网细胞以及还通过潜在地损害视神经细胞而在青光眼中起作用的理论。我们假设这种损伤的来源是由于小梁细胞过度暴露于氧气和/或其代谢产物引起的。我们将在动物模型中评估氧水平升高对小梁网功能和细胞变化的影响，我们已经将氧水平升高与先前确定的几个青光眼风险因素相关联。我们还将研究与氧化应激相关的眼内液体的生化变化，并测量角膜对氧气的使用，避免使用接触透镜进行侵入性测量。相关性：青光眼是全球第二大致盲原因，也是美国视力损害的常见原因，是一个重要的公共卫生问题。通过扩展我们对这种情况的原因的理解，这项研究提案也将扩大潜在的治疗和预防途径。

DESCRIPTION (provided by applicant): Understanding the pathogenesis of glaucoma, the second leading cause of blindness, is an important goal of vision research. Many studies have identified oxidative damage to the trabecular meshwork (TM) cells, leading to decreased outflow facility and increased intraocular pressure. Although the evidence linking oxidative damage to glaucoma is strong, the causes of oxidative damage in glaucoma are not known. In the proposed studies, we will test the hypothesis that oxidative damage to the TM is caused by excessive exposure to molecular oxygen and/or its metabolites. Our hypothesis is based on measurements of oxygen partial pressure (pO2), made in the human eye during surgery using a thin, flexible, fiberoptic probe. We identified large, stable oxygen gradients in the anterior chamber and tight regulation of pO2 in the anterior chamber angle, close to the TM. We also noted strong correlations between pO2 and important risk factors for glaucoma, including central corneal thickness, African-American heritage, and history of vitrectomy surgery. We believe that our studies are the first to link a physiologic variable, pO2 in the anterior chamber (AC), to these risks of glaucoma development. Our first specific aim will test whether the increased risk of glaucoma after vitrectomy is due to increased pO2 in the AC, causing damage to the TM. We will collaborate with colleagues at the University of Wisconsin-Madison for a longitudinal study in older Rhesus macaques that will sequentially undergo vitrectomy surgery and cataract extraction. We will map pO2 levels and measure aqueous humor antioxidants and outflow facility at each stage. At the conclusion of the study, we will determine the extent of TM cell loss and quantify the structural and oxidative damage to TM cells and their extracellular matrix. In this manner, we may correlate pO2 with oxidative damage to the TM. Our second aim is to determine whether the increased pO2 in African- Americans correlates with biochemical changes in the aqueous humor. We will expand our pilot study of metabolites in the aqueous humor, which suggested racial differences in mitochondrial metabolism. We will also analyze aqueous humor for its total antioxidant potential and concentration of known antioxidants, like ascorbate; studies that will determine whether there is a correlation between pO2 and the oxidant-antioxidant balance in the anterior chamber. We hypothesize that higher pO2 will be associated with depletion of anti- oxidants. Our third specific aim is to determine whether a non-invasive measure of corneal oxygen metabolism predicts intraocular pO2. We hypothesize that lower corneal oxygen consumption will correlate with increased pO2 in the AC. If correct, this test may provide an important means to determine those at risk of developing glaucoma. It will also offer a method to determine whether differences in intraocular oxygen are inherited and to identify the genes involved. Our novel approach will provide important information about the pathophysiology of open angle glaucoma by identifying factors responsible for the loss of aqueous outflow facility. The knowledge gained in these studies may lead to new therapies for and strategies to prevent this disease. PUBLIC HEALTH RELEVANCE: Numerous studies provide support for the theory that oxidative stress, the imbalance between damaging free radical molecules and the body's antioxidant defense mechanisms, plays a role in glaucoma by damaging the trabecular meshwork cells in the drain of the eye and also by potentially damaging the cells of the optic nerve. We hypothesize that the source of this damage is caused by excessive exposure of the trabecular meshwork cells to oxygen and/or its metabolites. We will evaluate the effects of elevated levels of oxygen, which we have correlated to several previously identified glaucoma risk factors, on the function and cellular changes of the trabecular meshwork in an animal model. We will also study the fluids of the eye for biochemical changes associated with oxidative stress and measure the cornea's use of oxygen and avoid invasive measurements with a contact lens. Relevance: Glaucoma, the second leading cause of blindness worldwide and frequent cause of visual impairment in the U.S., is an important public health issue. By extending our understanding of the causes of this condition, this research proposal will also expand potential pathways of therapy and prevention.