Retinal Oxygenation in Diabetic Retinopathy

描述（由申请人提供）：目前对糖尿病视网膜病变的治疗并不完全成功。我们认为，如果患者患视网膜病变的风险能够在病程早期得到预测，那么治疗方法的开发和评估可能会比目前更快。我们开发了一种独特的功能性磁共振成像（fMRI）技术，可以测量受试者呼吸碳（95% O2: 5% CO2）时玻璃体内氧分压（deltaPO2）的变化。使用这种急性视网膜“应激”测试，我们已经表明，与正常人相比，糖尿病3-4个月大鼠和小鼠（在视网膜病变出现之前）的碳呼吸使视网膜deltaPO2显著减少。低于正常的deltaPO2与缺氧的存在是一致的，但它还不能明确地解释为缺氧的测量。此外，在3个月大的糖尿病大鼠中，氨基胍（AMG）治疗可以阻止视网膜deltaPO2的下降。已知AMG可以预防糖尿病大鼠视网膜病变的形成，并抑制诱导型一氧化氮合酶（iNOS）和蛋白激酶C （PKC）的活性（以及其他作用）。假设：实验性糖尿病视网膜deltaPO2亚正常与视网膜缺氧（Aims 1）、iNOS和PKC活性升高（Aims 2和3）相关，但在组织病理学出现之前。1)比较糖尿病大鼠发病前、2周、3、9个月时视网膜PO2和deltaPO2的差异。功能磁共振成像和碳挑战将用于测量视网膜δ o2。为了测量PO2，将全氟碳液滴注射到视网膜前玻璃体上或下视网膜上，并进行19F磁共振波谱。2)比较使用和不使用选择性iNOS抑制剂(L-NIL (L-N（6)-（1-亚氨基乙基赖氨酸））治疗的正常和糖尿病大鼠，以及正常、糖尿病和糖尿病iNOS敲除小鼠的视网膜deltaPO2（3个月时）和组织学（3和15个月时）。特异性目的3)比较使用和未使用选择性PKC抑制剂（LY333531）治疗的正常和糖尿病大鼠的视网膜deltaPO2（3个月时）和组织学（3和15个月时）。此外，我们将比较正常小鼠、过表达PKC β II的转基因小鼠、糖尿病小鼠和糖尿病PKC β II敲除小鼠的视网膜deltaPO2。这些研究的结果将证明视网膜deltaPO2的变化是否与视网膜缺氧或多种生化异常的发展相关，这些异常与糖尿病视网膜病变相关，但现有技术无法在体内测量。这些研究的结果可能导致一种非侵入性的实时方法的发展，用于糖尿病视网膜病变的早期评估及其治疗。

DESCRIPTION (provided by applicant): Current treatments for diabetic retinopathy are not entirely successful. We reason that therapies could be more rapidly developed and evaluated than is currently possible if a patient's risk of developing retinopathy could be predicted early in the course of the disease. We have developed a unique functional magnetic resonance imaging (fMRI) technique that measures the change in partial pressure of oxygen (deltaPO2) in the vitreous humor while the subject breathes carbogen (95% O2: 5% CO2). Using this acute retinal "stress" test, we have shown that carbogen breathing in rats and mice at 3-4 months of diabetes (before the appearance of retinal lesions) produces a significantly reduced retinal deltaPO2 compared to normals. A subnormal deltaPO2 is consistent with the presence of hypoxia but it cannot yet be unambiguously interpreted as a measure of hypoxia. In addition, in 3 month diabetic rats, aminoguanidine (AMG) treatment prevented the decrease in retinal deltaPO2. AMG is known to prevent retinal lesion formation in diabetic rats and inhibit the activity of both the inducible form of nitric oxide synthase (iNOS) and protein kinase C (PKC) (among other actions). Hypothesis: Subnormal retinal deltaPO2 in experimental diabetes is correlated with retinal hypoxia (Aim 1), and increased iNOS and PKC activity (Aims 2 and 3) but precedes the appearance of histopathology. Specific Aim 1) To compare retinal PO2 and deltaPO2 before, and at 2 wks, and 3 and 9 months of diabetes in rats. fMRI and a carbogen challenge will be used to measure the retinal deltaPO2. To measure PO2, a perfluorocarbon droplet will be injected into the preretinal vitreous over superior or inferior retina and 19F magnetic resonance spectroscopy performed. Specific Aim 2) To compare the retinal deltaPO2 (at 3 months) and histology (at 3 and 15 months) in normal and diabetic rats with and without treatment with a selective iNOS inhibitor (L-NIL (L-N(6)-(1-iminoethyl)lysine)), and in normal, diabetic, and diabetic iNOS knockout mice. Specific Aim 3) To compare the retinal deltaPO2 (at 3 months) and histology (at 3 and 15 months) in normal and diabetic rats with and without treatment with a selective PKC inhibitor (LY333531). In addition, we will compare retinal deltaPO2 in normal mice, transgenic mice that overexpress PKC beta II, diabetic mice, and diabetic PKC beta II-knockout mice. The results of the proposed studies will prove whether or not changes in retinal deltaPO2 correlate with the development of retinal hypoxia or multiple biochemical abnormalities that are associated with diabetic retinopathy but cannot be measured in vivo by existing techniques. The results of these studies could lead to the development of a non-invasive real time method for the early evaluation of diabetic retinopathy and its treatment.