Spectral photoprotection of chronic macular photochemical injury

年龄相关性黄斑变性（AMD）和Stargardts营养不良沿着的自发荧光变化与对不同光化学在荧光双类视色素的产生和修饰中的作用的新理解的关联支持了RPE和光感受器内的双类视色素的稳态水平升高诱导慢性应激和细胞损伤的假设。我们的生物物理模型的bisretinoids途径与年龄在人类预测，光谱太阳镜可以消除不同的光化学过程之间的慢性不平衡1）在光感受器外节中产生bisretinoids和2）在RPE脂褐质中解毒bisretinoids。由于在人类视网膜中双视黄酸的产生速率预期随着视紫红质活化速率的平方而增加，因此累积暴露于明亮日光应主导其产生。因此，我们提出，朱红，视紫红质保护光谱太阳镜应显着减少bisetinoid生产，同时允许更短的波长，以解毒积累的lipofsucin。 一种常见的替代假设是，在存在较高水平的视黄醇和累积的双类视色素的情况下，视网膜内的蓝紫光光化学通过活性氧物质（ROS）的产生和反应驱动对RPE和光感受器的慢性损伤。为了验证这些假设，我们设计了一种双色太阳镜，其中一只眼睛提供了一个专门保护视紫红质的朱红绿色阻挡滤光片，另一只眼睛提供了一个专门保护短波光化学损伤的黄蓝紫阻挡滤光片。当在明亮的阳光下佩戴时，这种太阳镜允许我们比较两只眼睛的变化，其中只有光谱辐照度发生变化，而遗传学，生理学和环境暴露是相同的。 我们假设A2 E分离成脂褐质颗粒并防止其重新分布到关键膜中是RPE健康所需的。为了进行定量预测，我们开发了一个生物物理模型，使用瞳孔大小、透镜透射率和视杆暗适应时间常数（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A2 E相关物质的全反式视网膜反应，和作为年龄和环境光强度的函数的RPE脂褐质颗粒内的A2 E光氧化。我们的模型预测，在行动光谱加权短波长黄斑辐照度下降约三分之一，每十年和一个几乎恒定的生产率A2 E相关的荧光团在RPE在第一个60年（下降显着此后）。最近在人尸体眼中报道了总脂褐素颗粒体积和每个RPE细胞的总荧光的类似年龄依赖性。由于脂褐素随年龄增加的速率慢于有晶状体眼中短波长黄斑辐照度随年龄降低的速率，RPE中的ROI光敏化也应该随着年龄的增加而下降。外层视网膜的光氧化应激可能是由于较安全的脂褐素储存区以外的关键膜中A2 E相关荧光团的数量较少所致。然而，如果RPE/BM复合物是驱动AMD进展的光氧化损伤的位点，则在白内障摘除和眼内透镜（IOL）植入后，这种氧化损伤的程度和速率将预期显著增加（未观察到）。 为了解释bisretinoids和黄斑变性之间的关系，我们提出了一个新的假设，即由RPE脂褐素产生的单线态氧允许积累A2 E的化学改变，从而限制了RPE中A2 E（A2 Ess）的稳态水平，A2 E重新分布到视网膜膜中，以及相关的A2 E化学毒性。在脂褐质颗粒内光化学产生的单线态氧与其A2 E反应以形成A2 E环氧化物，其然后化学反应以在脂褐质内形成尚未表征的日益复杂的交联分子。由于短波长黄斑辐照度随着年龄的增长而福尔斯，A2 E光氧化的速率福尔斯约20倍，导致正常有晶状体眼的A2 Ess增加，即使杆漂白和A2 E产生减少。我们的黄斑老化的理论模型再现了脂褐素和A2 E的正常年龄依赖性，并提供了一个主要的细胞毒性机制，其中，一旦A2 E超过RPE细胞中的细胞毒性阈值浓度，A2 E重新分布到关键膜中，在有或没有额外的光活化的情况下，导致RPE功能的损伤和丧失。在我们的模型中，随着年龄的增长，透镜变黄，扭曲了正常青年中发现的生产率和光氧化率之间的光谱平衡，并允许A2 Ess随着年龄的增长而上升。在Stargardts患者中，ABCA 4翻转酶的突变导致双维甲酸的产生速率相对于我们提出的RPE光化学解毒的速率增加>5倍，其导致细胞毒性水平和年轻时的视力丧失。在这些患者中，较高的双视黄酸荧光和较低的透镜自发荧光的贡献，应使识别光谱诱导的双视黄酸途径内的变化更容易。

The associations of autofluorescence changes in age-related macular degeneration (AMD) and Stargardts Dystrophy along with new understanding of role of different photochemistries in creation and modification of the fluorescent bisretinoids support the hypothesis that rising steady-state levels of bisretinoids within the RPE and photoreceptors induce chronic stress and cellular injury. Our biophysical model of bisretinoid pathways with age in humans predicts that spectral sunglasses can remove chronic imbalances between the distinct photochemical processes 1)that create bisretinoids in the photoreceptor outer segments and 2) those that detoxify bisretinoids within the RPE lipofuscin. Since rates of bisretinoid production in the human retina are expected to increase with the square of rate of activation of rhodopsin, cumulative exposures to bright daylight should dominate their production. Therefore we proposed that vermilion, rhodopsin-protecting spectral sunglasses should dramatically reduce bisetinoid production while allowing shorter wavelengths to detoxify accumulated lipofsucin. A common alternative hypothesis is that blue-violet light photochemistries within the retina in the presence of higher levels of retinaldehydes and accumulated bisretinoids drive chronic injury to RPE and photoreceptors through the generation and reaction of reactive oxygen species (ROS). To test these alternative hypotheses, we designed bicolored sunglasses in which one eye is provided a vermilion green-blocking filter that specifically protects rhodopsin and the other eye a yellow blue-violet-blocking filter that specifically protects from short-wavelength photochemical injury. When worn whenever in bright sunlight, such sunglasses allow us to compare changes in both eyes in which only spectral irradiance is changed while genetics, physiology and environmental exposures are otherwise the same. We hypothesize that segregation of A2E into lipofuscin granules and prevention of its redistribution into critical membranes is required for RPE health. To make quantitative predictions, 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 in critical membranes outside of safer lipofuscin stores. 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. To explain the relationship between bisretinoids and macular degenerations, 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 (A2Ess) 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 chemically react to form the increasingly complex cross-linked molecules within the lipofuscin that have not been characterized. As short-wavelength macular irradiance falls with age, the rate of A2E photo-oxidation falls approximately up to 20-fold, causing A2Ess 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, the yellowing of the lens with age that distorts the spectral balance between rate of production and rate of photo-oxidation found in normal youth, and allows the A2Ess to rise with age. In Stargardts patients mutations in the ABCA4 flippase leads to >5-fold increased production rates of bisretinoids relative to the rates of our proposed RPE photochemical detoxification that results in cytotoxic levels and visual loss at younger ages. In these patients the higher bisretinoid fluorescence and lower contributions of lens autofluorescence, should make identification of spectrally-induced changes within the bisretinoid pathways easier.