title: Lack of correlation between the spatial distribution of A2E and lipofuscin fluorescence in the human retinal pigment epithelium.
abstract: OBJECTIVE
  The accumulation of lipofuscin in the RPE is a hallmark of aging in the eye. The best characterized component of lipofuscin is A2E, a bis-retinoid byproduct of the normal retinoid visual cycle, which exhibits a broad spectrum of cytotoxic effects in vitro. The purpose of our study was to correlate the distribution of lipofuscin and A2E across the human RPE.
  
  
  METHODS
  Lipofuscin fluorescence was imaged in flat-mounted RPE from human donors of various ages. The spatial distributions of A2E and its oxides were determined using matrix-assisted laser desorption-ionization imaging mass spectrometry (MALDI-IMS) on flat-mounted RPE tissue sections and retinal cross-sections.
  
  
  RESULTS
  Our data support the clinical observations of strong RPE fluorescence, increasing with age, in the central area of the RPE. However, there was no correlation between the distribution of A2E and lipofuscin, as the levels of A2E were highest in the far periphery and decreased toward the central region. High-resolution MALDI-IMS of retinal cross-sections confirmed the A2E localization data obtained in RPE flat-mounts. Singly- and doubly-oxidized A2E had distributions similar to A2E, but represented <10% of the A2E levels.
  
  
  CONCLUSIONS
  This report to our knowledge is the first description of the spatial distribution of A2E in the human RPE by imaging mass spectrometry. These data demonstrate that the accumulation of A2E is not responsible for the increase in lipofuscin fluorescence observed in the central RPE with aging.
authors.affiliation: Department of Ophthalmology, Medical University of South Carolina, Charleston, South Carolina 29425, USA. ablonczy@musc.edu
authors.forename: Zsolt
authors.initials: Z
authors.lastname: Ablonczy
authors.forename: Daniel
authors.initials: D
authors.lastname: Higbee
authors.forename: David M
authors.initials: DM
authors.lastname: Anderson
authors.forename: Mohammad
authors.initials: M
authors.lastname: Dahrouj
authors.forename: Angus C
authors.initials: AC
authors.lastname: Grey
authors.forename: Danielle
authors.initials: D
authors.lastname: Gutierrez
authors.forename: Yiannis
authors.initials: Y
authors.lastname: Koutalos
authors.forename: Kevin L
authors.initials: KL
authors.lastname: Schey
authors.forename: Anne
authors.initials: A
authors.lastname: Hanneken
authors.forename: Rosalie K
authors.initials: RK
authors.lastname: Crouch
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000378:metabolism*; D015415:Biomarkers / Q000378:metabolism; D002648:Child; D002675:Child, Preschool; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008062:Lipofuscin / Q000096:biosynthesis*; D008875:Middle Aged; D011726:Pyridinium Compounds; D012162:Retinal Degeneration / Q000378:metabolism* / Q000473:pathology; D055213:Retinal Pigment Epithelium / Q000378:metabolism* / Q000473:pathology; D012176:Retinoids / Q000096:biosynthesis*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D055815:Young Adult
chemical_list: C112040:A2-E (N-retinylidene-N-retinylethanolamine); D015415:Biomarkers; D008062:Lipofuscin; D011726:Pyridinium Compounds; D012176:Retinoids
keywords: A2E; human; imaging; lipofuscin; mass spectrometry; retinal degeneration; retinoids