Spectral photoprotection of chronic macular photochemica

慢性黄斑光化学的光谱光保护

• 批准号: 7334142
• 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/7334142
• 关键词: Spectral; photoprotection; chronic; macular; photochemica

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 (A2PE and A2PEH2) of these fluorophores originate from reactions of all-trans-retinal within the receptor outer segments (ROS) 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 associated 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 exceeds a cytotoxic threshold concentration in the RPE cell, A2E redistribution into critical membranes causes damage and loss of RPE function 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. We have designed and had manufactured "bicolored" sunglasses with two different specific spectrally selective lenses that provide equivalent spectral photoactivation of lipofuscin photosensitization of singlet oxygen but very different degrees of rod activation in bright ambient light. Our model predicts that in young eyes or elderly pseudophakes the levels of A2PEH2 production in the rods and the [A2E]ss levels in the RPE will be remarkably divergent in individuals wearing these sunglasses over a period of a few months of significant outdoor daylight activity. In order to distinguish the steady-state levels of different RPE photoproducts in the retina noninvasively, we are developing spectral imaging capabilities by modifying confocal scanning laser ophthalmoscopes and fundus cameras. We are currently evaluating the potential of these modified clinical instruments for noninvasive monitoring of the molecular effects of such filters in patients. Furthermore, we expect that improved spectral separation of the different species in the "A2E pathway" along with high resolution noninvasive imaging of the human retina, should enable us to quantify early microscopic abnormalities that we believe are the earliest stages in age-related maculopathy leading to AMD as well as genetically -linked diseases such as Stargardt's macular dystrophy. Such quantitative early intermediate endpoints may prove critical in developing new more efficient clinical studies of AMD prevention. 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. In parallel laboratory experimentation, we are studying RPE cell cultures, human autopsy eyes, and animal models to better characterize the pathways and rates of A2E photo-oxidation and chemical modification. In collaboration with our sister NICHD lab (Steve Coon), we are planning to test our hypothesis of spectral imbalance by raising ABCA4 (-)/(-) and (-)/(+) knockout mice (that produce large amounts of A2E) in cyclic ambient light spectrally filtered eitehr with the rod-sparing vermilion filter or the amber filter which does not spare rods but provides the equivalent amount of protection from blue-light photo-oxidation reactions within the retina. This model system should validate our noninvasive spectral imaging separation of components by comparing with HPLC-MS of lipofuscin extracts from the whole retina at sacrifice and provide a stronger experimental rationale for our proposed clinical studies by validate the basic hypothesis that spectral imbalances of retinal irradiance can induce high A2E steady state levels in teh RPE.

老年性黄斑变性（AMD）与白内障、既往白内障手术、日积月晒和色素沉着的关系都支持慢性光化学损伤驱动黄斑病变随年龄和AMD进展的假设。随着年龄的增长，脂褐素在视网膜色素上皮（RPE）中积累，并与灵长类动物视网膜中活性氧中间体（ROI）的急性光敏共定位。我们在RPE和Bruch？膜（BM）复合物以及到达黄斑的光的额外光谱过滤所引起的变化。脂褐素颗粒含有至少10种不同的荧光光化学产物，包括A2E （n -视黄醛- n -视黄醛乙醇胺）、其环氧化物和其他尚未化学鉴定的A2E相关荧光团。这些荧光团的前体（A2PE和A2PEH2）源于与显著视紫红质漂白（即正常日光）相关的时期（即正常日光）中受体外段（ROS）内的全反式视网膜反应。虽然RPE溶酶体加工酶消化了超过99%的脱落ROS含量，但A2E和相关的荧光团没有被消化，而是被浓缩成脂褐素颗粒。到60岁时，正常眼RPE细胞内A2E的平均浓度达到~400 microM。然而，低浓度的A2E对细胞膜是有毒的。我们假设A2E分离成脂褐素颗粒并防止其重新分布到关键膜是RPE健康所必需的。