The accumulation of lipofuscin has previously been implicated in several retinal diseases including Best's macular dystrophy, Stargardt's disease and age-related macular degeneration (AMD). Previously one of the major fluorophores of lipofuscin was identified as a bis-retinoid pyridinium salt called A2E, which is known to photochemically cause damage. In addition to A2E, there are numerous components in RPE lipofuscin that are unidentified. These compounds were determined to be structurally related to A2E by their fragmentation pattern with losses of 106, 190, 174 and/or 150 amu from the parent ion and the formation of fragments of ca 592 amu. The vast majority consists of relatively hydrophobic components corresponding to derivatized A2E with molecular weights in discrete groups of 800–900, 970–1080 and > 1200 m/z regions. In order to determine the mechanism of these modifications, A2E was chemically modified by; (1) the formation of specific esters, (2) reaction with specific aldehydes and (3) spontaneous auto-oxidation. The contribution of ester formation to the naturally occurring components of lipofuscin was discounted since their fragmentation patterns were different to those found in vivo. Alternatively, reactions with specific aldehydes result in nearly identical products as those found in vivo. Artificial aging of RPE lipofuscin gives a complex mixture of structurally related components. This results from the auto- and/or photooxidation of A2E to form aldehydes, which then back react with A2E giving a series of higher molecular weight products. The majority of these modifications result in compounds that are much more hydrophobic than A2E. These higher molecular weight materials have increased values of log P compared to A2E. This increase in hydrophobicity most likely aids in the sequestering of A2E into granules with the concomitant diminution of its reactivity. Therefore, these processes may serve as protective mechanisms for the RPE. Copyright © 2010 John Wiley & Sons, Ltd.
脂褐素的积累与多种视网膜疾病有关,包括贝斯特黄斑营养不良症、斯塔尔加特病和老年性黄斑变性(
AMD)。此前,脂褐素的主要荧光团之一被确认为一种名为 A2E 的双
维甲酸吡啶鎓盐,众所周知,A2E 会造成光
化学损伤。除 A2E 外,RPE 脂褐素中还有许多成分尚未确定。这些化合物的结构与 A2E 有关,因为它们的碎裂模式是母离子损失 106、190、174 和/或 150
AMu,并形成约 592
AMu 的碎片。其中绝大部分由相对疏
水的成分组成,这些成分与分子量在 800-900、970-1080 和大于 1200 m/z 区域的衍生化 A2E 相对应。为了确定这些修饰的机理,对 A2E 进行了
化学修饰:(1) 形成特定的酯,(2) 与特定的醛反应,(3) 自发自动氧化。由于脂褐素天然成分的碎裂模式与在体内发现的不同,因此酯的形成对脂褐素天然成分的贡献被排除在外。另外,与特定
醛类反应也会产生与体内几乎相同的产物。RPE 脂褐质的人工老化产生了结构相关成分的复杂混合物。这是 A2E 自氧化和/或光氧化形成
醛类的结果,
醛类再与 A2E 发生逆反应,产生一系列分子量更高的产物。这些改性的大部分结果是产生比 A2E 更疏
水的化合物。与 A2E 相比,这些高分子量材料的对数 P 值会增加。疏
水性的增加很可能有助于将 A2E 封闭在颗粒中,同时降低其反应活性。因此,这些过程可作为 RPE 的保护机制。Copyright © 2010 John Wiley & Sons, Ltd. All Rights Reserved.