title: A2E-epoxides damage DNA in retinal pigment epithelial cells. Vitamin E and other antioxidants inhibit A2E-epoxide formation.
abstract: 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.
authors.affiliation: Department of Ophthalmology and Chemistry, Columbia University, New York, New York 10028, USA. jrs88@columbia.edu
authors.forename: Janet R
authors.initials: JR
authors.lastname: Sparrow
authors.forename: Heidi R
authors.initials: HR
authors.lastname: Vollmer-Snarr
authors.forename: Jilin
authors.initials: J
authors.lastname: Zhou
authors.forename: Young P
authors.initials: YP
authors.lastname: Jang
authors.forename: Steffen
authors.initials: S
authors.lastname: Jockusch
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Itagaki
authors.forename: Koji
authors.initials: K
authors.lastname: Nakanishi
mesh_terms: D000080242:8-Hydroxy-2'-Deoxyguanosine; D000975:Antioxidants / Q000494:pharmacology*; D017209:Apoptosis; D001205:Ascorbic Acid / Q000494:pharmacology; D002244:Carbon / Q000737:chemistry; D002470:Cell Survival; D002478:Cells, Cultured; D002839:Chromans / Q000494:pharmacology; D002851:Chromatography, High Pressure Liquid; D020552:Comet Assay; D004249:DNA Damage; D003849:Deoxyguanosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D006801:Humans; D008027:Light; D013058:Mass Spectrometry; D008956:Models, Chemical; D010100:Oxygen / Q000378:metabolism; D010857:Pigment Epithelium of Eye / Q000166:cytology*; D010879:Piperazines / Q000494:pharmacology; D011726:Pyridinium Compounds / Q000737:chemistry / Q000494:pharmacology*; D012176:Retinoids / Q000737:chemistry / Q000494:pharmacology*; D014810:Vitamin E / Q000494:pharmacology
chemical_list: C112040:A2-E (N-retinylidene-N-retinylethanolamine); D000975:Antioxidants; D002839:Chromans; D010879:Piperazines; D011726:Pyridinium Compounds; D012176:Retinoids; C066382:U 78517F; D014810:Vitamin E; D002244:Carbon; D000080242:8-Hydroxy-2'-Deoxyguanosine; D003849:Deoxyguanosine; D001205:Ascorbic Acid; D010100:Oxygen