title: Determination of N-retinylidene-N-retinylethanolamine (A2E) levels in central and peripheral areas of human retinal pigment epithelium.
abstract: The bis-retinoid N-retinylidene-N-retinylethanolamine (A2E) is one of the major components of lipofuscin, a fluorescent material that accumulates with age in the lysosomes of the retinal pigment epithelium (RPE) of the human eye. Lipofuscin, as well as A2E, exhibit a range of cytotoxic properties, which are thought to contribute to the pathogenesis of degenerative diseases of the retina such as Age-related Macular Degeneration. Consistent with such a pathogenic role, high levels of lipofuscin fluorescence are found in the central area of the human RPE, and decline toward the periphery. Recent reports have however suggested a surprising incongruence between the distributions of lipofuscin and A2E in the human RPE, with A2E levels being lowest in the central area and increasing toward the periphery. To appraise such a possibility, we have quantified the levels of A2E in the central and peripheral RPE areas of 10 eyes from 6 human donors (ages 75-91 years) with HPLC and UV/VIS spectroscopy. The levels of A2E in the central area were on average 3-6 times lower than in peripheral areas of the same eye. Furthermore, continuous accumulation of selected ions (CASI) imaging mass spectrometry showed the presence of A2E in the central RPE, and at lower intensities than in the periphery. We have therefore corroborated that in human RPE the levels of A2E are lower in the central area compared to the periphery. We conclude that the levels of A2E cannot by themselves provide an explanation for the higher lipofuscin fluorescence found in the central area of the human RPE.
authors: Department of Ophthalmology, Medical University of South Carolina, Charleston, SC, USA. koutalo@musc.edu.
authors: Leopold
authors: L
authors: Adler
authors: Department of Ophthalmology, Medical University of South Carolina, Charleston, SC, USA. koutalo@musc.edu.
authors: Nicholas P
authors: NP
authors: Boyer
authors: Mass Spectrometry Research Center, Vanderbilt School of Medicine, Nashville, TN, USA.
authors: David M
authors: DM
authors: Anderson
authors: Mass Spectrometry Research Center, Vanderbilt School of Medicine, Nashville, TN, USA.
authors: Jeffrey M
authors: JM
authors: Spraggins
authors: Mass Spectrometry Research Center, Vanderbilt School of Medicine, Nashville, TN, USA.
authors: Kevin L
authors: KL
authors: Schey
authors: Department of Molecular and Experimental Medicine, The Scripps Research Institute, La Jolla, CA, USA.
authors: Anne
authors: A
authors: Hanneken
authors: Department of Ophthalmology, Medical University of South Carolina, Charleston, SC, USA. koutalo@musc.edu.
authors: Zsolt
authors: Z
authors: Ablonczy
authors: Department of Ophthalmology, Medical University of South Carolina, Charleston, SC, USA. koutalo@musc.edu.
authors: Rosalie K
authors: RK
authors: Crouch
authors: Department of Ophthalmology, Medical University of South Carolina, Charleston, SC, USA. koutalo@musc.edu.
authors: Yiannis
authors: Y
authors: Koutalos
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D006801:Humans; D055213:Retinal Pigment Epithelium / Q000737:chemistry*; D012176:Retinoids / Q000032:analysis*
chemical_list: C112040:A2-E (N-retinylidene-N-retinylethanolamine); D012176:Retinoids