Katz M L, Stientjes H J, Gao C L, Christianson J S
University of Missouri School of Medicine, Mason Institute of Ophthalmology, Columbia 65212.
Invest Ophthalmol Vis Sci. 1993 Oct;34(11):3161-71.
One of the most prominent changes that occurs in the retinal pigment epithelium during senescence is the progressive accumulation of the autofluorescent pigment lipofuscin. Experiments were conducted to evaluate the role of nonenzymatic oxidation of photoreceptor outer segments in retinal pigment epithelium lipofuscin formation.
Albino Fischer rats were given intravitreal injections of ferrous sulfate, a catalyst that promotes nonenzymatic lipid oxidation. At 2 hours, 24 hours, and 7 days after ferrous sulfate administration, the retinas were examined with fluorescence microscopy to assess the formation of fluorescent products. At these same time intervals, organic solvent extracts of the retinas and retinal pigment epithelium-choroid complexes were prepared. The extracts were analyzed with thin layer chromatography to assay for the presence of soluble fluorophores. The ultrastructural appearances of the retinas were examined at the same time points.
At both 2 hours and 24 hours after the ferrous sulfate treatment, the photoreceptor outer segments displayed a yellow-green fluorescence emission that was not present in untreated eyes. Associated with this in situ fluorescence were a number of blue-green emitting fluorophores in organic solvent extracts that did not correspond to any of the fluorophores extracted from the retinal pigment epithelium of old animals. One week after the ferrous sulfate treatment, the photoreceptor cells had degenerated and the retinal pigment epithelium contained large amounts of an autofluorescent pigment with a golden-yellow emission typical of lipofuscin. The iron-induced fluorophores could not be extracted from this pigment into either chloroform or dichloromethane.
The initial fluorophores that were formed as a result of nonenzymatic oxidation of outer segment components did not appear to be the same as those responsible for retinal pigment epithelium lipofuscin fluorescence. However, after the oxidized outer segments were phagocytosed by the retinal pigment epithelium, the latter cells became filled with a yellow-emitting fluorescent pigment that was similar in its fluorescence properties to lipofuscin. These observations suggest that lipofuscin fluorophores are not direct products of nonenzymatic lipid oxidation. However, some of these oxidation products may be modified after uptake by the retinal pigment epithelium to form insoluble lipofuscin fluorophores.
视网膜色素上皮细胞在衰老过程中最显著的变化之一是自发荧光色素脂褐质的逐渐积累。进行实验以评估光感受器外段的非酶氧化在视网膜色素上皮细胞脂褐质形成中的作用。
给白化费希尔大鼠玻璃体内注射硫酸亚铁，一种促进非酶脂质氧化的催化剂。在给予硫酸亚铁后2小时、24小时和7天，用荧光显微镜检查视网膜，以评估荧光产物的形成。在相同的时间间隔，制备视网膜和视网膜色素上皮-脉络膜复合体的有机溶剂提取物。提取物用薄层色谱法分析，以检测可溶性荧光团的存在。在相同时间点检查视网膜的超微结构外观。
在硫酸亚铁处理后2小时和24小时，光感受器外段均显示出黄绿色荧光发射，而未处理的眼睛中不存在这种荧光。与这种原位荧光相关的是有机溶剂提取物中一些发出蓝绿色荧光的荧光团，它们与从老年动物视网膜色素上皮细胞中提取的任何荧光团都不对应。硫酸亚铁处理一周后，光感受器细胞退化，视网膜色素上皮细胞含有大量具有脂褐质典型金黄色发射的自发荧光色素。铁诱导的荧光团不能从这种色素中提取到氯仿或二氯甲烷中。
由于外段成分的非酶氧化而形成的初始荧光团似乎与导致视网膜色素上皮细胞脂褐质荧光的荧光团不同。然而，氧化的外段被视网膜色素上皮细胞吞噬后，后者细胞充满了发出黄色荧光的色素，其荧光特性与脂褐质相似。这些观察结果表明，脂褐质荧光团不是非酶脂质氧化的直接产物。然而，这些氧化产物中的一些在被视网膜色素上皮细胞摄取后可能会被修饰，以形成不溶性的脂褐质荧光团。
