Photoprotection of chronic macular photochemical injury

慢性黄斑光化学损伤的光保护

• 批准号: 7212381
• 负责人: Robert F Bonner
• 金额: --
• 依托单位: EUNICE KENNEDY SHRIVER NATIONAL INSTITUTE OF CHILD HEALTH & HUMAN DEVELOPMENT
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/7212381
• 关键词: aging; biological models; biophysics; cataract surgery; cytotoxicity; disease /disorder prevention /control; eye injury; family genetics; fluorescent dye /probe; free radical oxygen; ionophores; lipofuscin; macular degeneration; model design /development; molecular pathology; oxidative stress; photochemistry; photoprotection; photoprotective agent; retina; retinal pigment epithelium; retinography; retinoids; rod cell; singlet oxygen

The associations of age-related macular degeneration (AMD) with cataracts, prior cataract surgery, cumulative exposure to sunlight and pigmentation all support the hypothesis that chronic photochemical injury drives macular changes with age and AMD progression. Lipofuscin accumulates with age in the retinal pigment epithelium (RPE) and colocalizes with acute photosensitization of reactive oxygen intermediates (ROI) in the primate retina. We model the normal accumulation of potentially damaging photoproducts with age in the RPE and Bruch?s Membrane (BM) complex as well as changes induced by additional spectral filtering of light reaching the macula. Lipofuscin granules contain at least 10 different fluorescent photochemical products includng A2E (N-retinylidene-N-retinylethanolamine), its epoxides and other as yet chemically unidentified A2E-related fluorophores. The precursors of these fluorophores originate from reactions of all-trans-retinal within the rod outer segment (ROS) discs during periods associated with significant rhodopsin bleaching (i.e., normal daylight). Although RPE lysosomal processing enzymatically digests over 99% of the shed ROS contents, A2E and related fluorophores are not digested, but are concentrated into lipofuscin granules. By age 60 years, the average concentration of A2E within RPE cells reaches ~400 microM in normal eyes. However, A2E is toxic to cellular membranes at much lower concentrations. We hypothesize that segregation of A2E into lipofuscin granules and prevention of its redistribution into critical membranes is required for RPE health. We developed a biophysical model using normal values of pupil size, lens transmission, and rod dark adaptation time constant trh to determine average retinal spectral irradiance, steady-state concentration of all-trans-retinal, all-trans-retinal photosensitization of oxidative damage, all-trans-retinal reactions to form A2E-related species in the ROS, and A2E photo-oxidation within RPE lipofuscin granules as a function of age and ambient light intensity. Our model predicts a decline of about one third in the action spectra-weighted short-wavelength macular irradiance with each decade and a nearly constant production rate of A2E-related fluorophores in the RPE during the first 60 years (falling significantly thereafter). A similar age dependence of total lipofuscin granule volume and total fluorescence per RPE cell was reported recently in human cadaver eyes. Since the rates of lipofuscin increase with age are slower than the rate of decrease in short-wavelength macular irradiance in the phakic eye with age, ROI photosensitization in the RPE should also fall with increasing age. Photo-oxidative stress in the outer retina might arise from the smaller amounts of A2E-related fluorophores observed in critical membranes of the RPE/BM complex. However, if the RPE/BM complex were the site of photo-oxidative injury driving AMD progression, the magnitude and rate of this oxidative injury would be expected to increase dramatically (not observed) following cataract removal and intraocular lens (IOL) implantation. Consequently, we propose a novel hypothesis that singlet oxygen generation by RPE lipofuscin allows the chemical alteration of accumulating A2E, thereby limiting the steady-state levels of A2E ([A2E]ss) in the RPE, the redistribution of A2E into retinal membranes, and A2E chemical toxicity. Singlet oxygen generated photochemically within the lipofuscin granule reacts with its A2E to form A2E epoxides which then react to form increasingly complex cross-linked molecules. As short-wavelength macular irradiance falls with age, the rate of A2E photo-oxidation falls approximately up to 20-fold, causing [A2E]ss in the normal phakic eye to increase even as rod bleaching and A2E production decrease. Our theoretical model of macular aging reproduces the normal age dependence of lipofuscin and A2E and provides a primary cytotoxic mechanism in which, once A2E reaches a threshold concentration in the RPE cell, A2E redistribution into critical membranes causes damage with or without additional photo-activation. In our model, it is primarily the yellowing of the lens with age that distorts the original spectral balance between rate of production and rate of photo-oxidation found in youth, and allows the [A2E]ss to rise with age. We are evaluating noninvasive retinal imaging methods that might permit clinical validation of our predictions of photochemical changes following cataract surgery and our predictions of the benefits of specific spectral photo-protective filters. Our proposed specific spectrally selective ?sunglasses? reduce both rod activation in bright ambient light and the accumulation of toxic photoproducts in the RPE. In addition, we are seeking to distinguish different RPE photoproducts by their fluorescence spectra to evaluate the potential for noninvasive monitoring of the molecular effects of such filters in patients. In collaboration with the NEI and the Eye Institute of the Russian Academy of Medicine, we are designing clinical studies of the effects of such filters on progression of both early and moderate AMD following cataract surgery and IOL implantation and macular changes in subjects with genetic predisposition to generation of increased A2E and lipofuscin at younger ages.

年龄相关性黄斑变性 (AMD) 与白内障、既往白内障手术、累积的阳光照射和色素沉着的关联都支持这样的假设：慢性光化学损伤会随着年龄和 AMD 进展而导致黄斑变化。脂褐素随着年龄的增长在视网膜色素上皮 (RPE) 中积累，并与灵长类动物视网膜中活性氧中间体 (ROI) 的急性光敏作用共定位。我们模拟了随着年龄的增长，RPE 和布鲁赫膜 (BM) 复合体中潜在破坏性光产物的正常积累，以及到达黄斑的光的额外光谱过滤引起的变化。脂褐质颗粒含有至少 10 种不同的荧光光化学产品，包括 A2E（N-亚视黄基-N-视黄乙醇胺）、其环氧化物和其他化学上尚未鉴定的 A2E 相关荧光团。这些荧光团的前体源自视杆外节 (ROS) 盘内的全反式视网膜在与视紫质显着漂白相关的时期（即正常日光）的反应。尽管 RPE 溶酶体加工酶消化了超过 99% 的脱落 ROS 含量，但 A2E 和相关荧光团没有被消化，而是浓缩成脂褐素颗粒。到 60 岁时，正常眼中 RPE 细胞内 A2E 的平均浓度达到约 400 µM。然而，A2E 在低得多的浓度下对细胞膜具有毒性。我们假设，RPE 健康需要将 A2E 分离成脂褐质颗粒并防止其重新分布到关键膜中。 我们开发了一个生物物理模型，使用瞳孔大小、晶状体透射率和杆暗适应时间常数 trh 的正常值来确定平均视网膜光谱辐照度、全反式视网膜的稳态浓度、氧化损伤的全反式视网膜光敏化、在 ROS 中形成 A2E 相关物种的全反式视网膜反应，以及 RPE 脂褐质颗粒内的 A2E 光氧化 作为年龄和环境光强度的函数。我们的模型预测，作用光谱加权短波长黄斑辐照度每十年下降约三分之一，并且在前 60 年中，RPE 中 A2E 相关荧光团的产生率几乎恒定（此后显着下降）。最近在人类尸体眼睛中报道了类似的总脂褐质颗粒体积和每个 RPE 细胞总荧光的年龄依赖性。由于脂褐质随年龄增长的速率比有晶状体眼中短波长黄斑辐照度随年龄增长的下降速率慢，因此 RPE 中的 ROI 光敏性也应随年龄的增长而下降。外视网膜中的光氧化应激可能是由于在 RPE/BM 复合体的关键膜中观察到的少量 A2E 相关荧光团引起的。然而，如果 RPE/BM 复合体是驱动 AMD 进展的光氧化损伤部位，那么在白内障摘除和人工晶状体 (IOL) 植入后，这种氧化损伤的程度和速度预计会急剧增加（未观察到）。 因此，我们提出了一个新的假设，即 RPE 脂褐素产生的单线态氧允许积累的 A2E 发生化学变化，从而限制 RPE 中 A2E ([A2E]ss) 的稳态水平、A2E 重新分布到视网膜膜中以及 A2E 化学毒性。脂褐素颗粒内光化学产生的单线态氧与其 A2E 反应形成 A2E 环氧化物，然后反应形成越来越复杂的交联分子。由于短波长黄斑辐照度随着年龄的增长而下降，A2E 光氧化速率下降约 20 倍，导致正常有晶状体眼中的 [A2E]ss 增加，即使视杆漂白和 A2E 产生减少。我们的黄斑衰老理论模型再现了脂褐质和 A2E 的正常年龄依赖性，并提供了一种主要的细胞毒性机制，其中一旦 A2E 在 RPE 细胞中达到阈值浓度，A2E 重新分布到关键膜中，无论有或没有额外的光激活，都会引起损伤。在我们的模型中，主要是晶状体随着年龄的增长而变黄，扭曲了年轻时发现的生产速率和光氧化速率之间的原始光谱平衡，并使 [A2E]ss 随着年龄的增长而上升。 我们正在评估无创视网膜成像方法，这些方法可能允许临床验证我们对白内障手术后光化学变化的预测以及我们对特定光谱光防护滤光片的好处的预测。我们提出的特定光谱选择性“太阳镜”？减少明亮环境光下视杆细胞的激活以及视网膜色素上皮中有毒光产物的积累。此外，我们正在寻求通过荧光光谱来区分不同的 RPE 光产品，以评估无创监测此类过滤器对患者的分子效应的潜力。我们与 NEI 和俄罗斯医学院眼科研究所合作，正在设计临床研究，研究此类滤光器对白内障手术和人工晶状体植入后早期和中度 AMD 进展的影响，以及对年轻时 A2E 和脂褐素生成增加的遗传倾向的受试者的黄斑变化的影响。