Sparrow Janet R, Vollmer-Snarr Heidi R, Zhou Jilin, Jang Young P, Jockusch Steffen, Itagaki Yasuhiro, Nakanishi Koji
Department of Ophthalmology and Chemistry, Columbia University, New York, New York 10028, USA.
J Biol Chem. 2003 May 16;278(20):18207-13. doi: 10.1074/jbc.M300457200. Epub 2003 Mar 19.
The autofluorescent pigments that accumulate in retinal pigment epithelial cells with aging and in some retinal disorders have been implicated in the etiology of macular degeneration. The major constituent is the fluorophore A2E, a pyridinium bisretinoid. Light-exposed A2E-laden retinal pigment epithelium exhibits a propensity for apoptosis with light in the blue region of the spectrum being most damaging. Efforts to understand the events precipitating the death of the cells have revealed that during irradiation (430 nm), A2E self-generates singlet oxygen with the singlet oxygen in turn reacting with A2E to generate epoxides at carbon-carbon double bonds. Here we demonstrate that A2E-epoxides, independent of singlet oxygen, exhibit reactivity toward DNA with oxidative base changes being at least one of these lesions. Mass spectrometry revealed that the antioxidants vitamins E and C, butylated hydroxytoluene, resveratrol, a trolox analogue (PNU-83836-E), and bilberry extract reduce A2E-epoxidation, whereas single cell gel electrophoresis and cell viability studies revealed a corresponding reduction in the incidence of DNA damage and cell death. Vitamin E, a lipophilic antioxidant, produced a more pronounced decrease in A2E-epoxidation than vitamin C, and treatment with both vitamins simultaneously did not confer additional benefit. Studies in which singlet oxygen was generated by endoperoxide in the presence of A2E revealed that vitamin E, butylated hydroxytoluene, resveratrol, the trolox analogue, and bilberry reduced A2E-epoxidation by quenching singlet oxygen. Conversely, vitamin C and ginkgolide B were not efficient quenchers of singlet oxygen under these conditions.
随着年龄增长以及在某些视网膜疾病中，视网膜色素上皮细胞中积累的自发荧光色素被认为与黄斑变性的病因有关。其主要成分是荧光团A2E，一种吡啶鎓双视黄醛。暴露于光下的载有A2E的视网膜色素上皮细胞表现出凋亡倾向，光谱中蓝色区域的光最具破坏性。为了解导致细胞死亡的事件所做的努力表明，在照射（430nm）期间，A2E自身产生单线态氧，而单线态氧又与A2E反应，在碳 - 碳双键处生成环氧化物。在这里，我们证明A2E环氧化物独立于单线态氧，对DNA具有反应性，氧化碱基变化至少是其中一种损伤。质谱分析表明，抗氧化剂维生素E和C、丁基化羟基甲苯、白藜芦醇、一种曲洛克斯类似物（PNU - 83836 - E）和越橘提取物可减少A2E环氧化，而单细胞凝胶电泳和细胞活力研究表明DNA损伤和细胞死亡的发生率相应降低。维生素E是一种亲脂性抗氧化剂，比维生素C更能显著降低A2E环氧化，同时用两种维生素处理并没有带来额外益处。在A2E存在下由内过氧化物产生单线态氧的研究表明，维生素E、丁基化羟基甲苯、白藜芦醇、曲洛克斯类似物和越橘通过淬灭单线态氧减少A2E环氧化。相反，在这些条件下，维生素C和银杏内酯B不是有效的单线态氧淬灭剂。
