Imaging of Retinal Hydroxyapatite as an Early Screen for AMD

视网膜相关性黄斑变性（AMD）是发达国家中老年人失明的最常见原因。 影响超过1000万美国人。该病的发病是渐进的，症状很少，大多数 患者直到通过眼部检查发现不可逆转的视力丧失才意识到。人们普遍认为， 视网膜中脂肪和蛋白质的沉积，其中最著名的是所谓的玻璃疣，导致死亡的人。 感光细胞在那里。虽然不太常见的"湿性" AMD（CNV）可以通过称为 VEGF抑制剂，更常见的"干"形式（GA）目前无法治疗，尽管有几种治疗方法， 发展最近，我们发现玻璃疣含有羟基磷灰石（HAP）的微观球体， 一种磷酸钙的形式，在骨骼和牙齿中含量丰富，并有证据表明， 使视网膜中的玻璃疣生长成核。我们发现荧光染色是用来研究骨骼生长的 也会对小球进行染色，使它们能够通过视网膜的荧光成像进行研究。我们 推测通过这种体内成像方法早期检测HAP小球可能预测HAP的发生。 玻璃疣的出现和因此AMD的发展;这在至少一些病例中得到证实。 因此，这项生物工程研究资助的重点是开发和验证视网膜成像方法 用于筛查和早期检测AMD，以提示治疗，并跟踪疾病的进程， 评估治疗。一些合成的用于动物模型骨研究的染料在体外表现良好，但 它们的行为和安全性在动物身上知之甚少，根本没有人体研究。但也有 四环素类抗生素在与骨矿物质结合时也会发出明亮的荧光，我们发现， 在这些条件下的明显荧光寿命，可以从背景中分辨出来 通过荧光寿命成像的视网膜荧光。四环素类药物具有众所周知的特性， 很可能是口服的，对人体非常安全。用四环素对小球成像 染色，我们必须构建一个荧光寿命成像检眼镜（FLIO），可用于人类或 唯一好的AMD动物模型，猕猴（猴子）。我们将构建一个FLIO基于现有的 仪器，完善我们的程序供体尸体，然后测试FLIO和染色程序对老年人 猕猴（其形成小球）和日本猕猴（其早期且快速地形成玻璃疣， 高脂肪饮食的结果。需要回答的关键问题是小球的出现如何可靠地预测 玻璃疣的发展和AMD的进展，以及成像程序对猴子的安全性; 令人满意的结果将可能导致在人体中进行试验。

Age-related macular degeneration (AMD) is the most common cause of blindness in the elderly in developed countries, affecting over ten million Americans. The disease onset is gradual, with few symptoms and most patients unaware until irreversible vision loss is detected by eye examination. It is accepted that the buildup of deposits of fats and protein in the retina, the best known of which are called drusen, causes the death of the light-sensitive cells there. While the less common, “wet” form of AMD (CNV) can be arrested by drugs called VEGF inhibitors, the more common, “dry” form (GA) is currently untreatable, although several treatments are in development. Recently, we discovered that drusen contain microscopic spherules of hydroxyapatite (HAP), a form of calcium phosphate abundant in bones and teeth, and developed evidence indicating that the spherules nucleate the growth of drusen in the retina. We found that fluorescent stains developed to study bone growth would also stain the spherules, permitting them to be studied by fluorescence imaging of the retina. We inferred that detecting the HAP spherules early by such an imaging approach used in vivo might predict the appearance of the drusen and thus AMD development; this was confirmed in at least some cases. Thus, the thrust of this Bioengineering Research Grant is to develop and validate a retinal imaging approach for screening and early detection of AMD, both to cue treatment, and to follow the course of the disease to assess treatment. Some of the stains synthesized for bone studies in animal models perform well in vitro, but their behavior and safety is little known in animals, and there are no human studies at all. However, some tetracycline antibiotics also give bright fluorescence when bound to bone mineral, and we found that they have a distinct fluorescence lifetime under these conditions, which can be resolved from the background fluorescence of the retina by fluorescence lifetime imaging. The tetracyclines have well known behavior, can probably be administered orally, and are very safe in humans. To image the spherules with tetracycline staining we must construct a fluorescence lifetime imaging ophthalmoscope (FLIO), usable on humans or the only good animal model for AMD, macaques (monkeys). We will construct a FLIO based on an existing instrument, refine our procedures on donor cadavers, then test the FLIO and staining procedures on aged macaques (which develop spherules) and a Japanese macaque which develops drusen early and rapidly as a result of a high fat diet. Key questions to be answered are how reliably the appearance of spherules predicts the development of drusen and progression to AMD, and how safe the imaging procedure is for the monkeys; satisfactory results will likely lead to trials in humans.