title: Spatial localization of A2E in the retinal pigment epithelium.
abstract: OBJECTIVE
  Lipofuscin, a fluorescent lysosomal pigment made of lipophilic molecules, is associated with age-related pathophysiological processes in the retinal pigment epithelium (RPE). The best-characterized components of lipofuscin are A2E and its oxides, but a direct spatial correlation with lipofuscin has not previously been possible.
  
  
  METHODS
  Lipofuscin fluorescence was mapped across the RPE of Abca4(-/-) and Sv129 (background strain control) mice. In the same tissues, they determined the spatial distribution of A2E and its oxides by using the high molecular specificity of matrix-assisted laser desorption-ionization imaging mass spectrometry (MALDI-IMS). The fluorescence and tandem mass spectra taken directly from the tissue were compared with those of synthetic A2E standard.
  
  
  RESULTS
  In 2-month-old mice, A2E was found in the center of the retinal pigment epithelial tissue; with age, A2E increased across the tissue. With high levels of A2E, there was a marked correlation between A2E and lipofuscin, but with low levels this correlation diminished. The distributions of the oxidized forms of A2E were also determined. The amount of oxidation on A2E remained constant over 6 months, implying that A2E does not become increasingly oxidized with age in this time frame.
  
  
  CONCLUSIONS
  This report is the first description of the spatial imaging of a specific retinoid from fresh tissue and the first description of a direct correlation of A2E with lipofuscin. The molecule-specific imaging of lipofuscin components from the RPE suggests wide applicability to other small molecules and pharmaceuticals for the molecular characterization and treatment of age-related macular degeneration.
authors.affiliation: Department of Optometry and Vision Science, University of Auckland, Auckland, New Zealand.
authors.forename: Angus C
authors.initials: AC
authors.lastname: Grey
authors.forename: Rosalie K
authors.initials: RK
authors.lastname: Crouch
authors.forename: Yiannis
authors.initials: Y
authors.lastname: Koutalos
authors.forename: Kevin L
authors.initials: KL
authors.lastname: Schey
authors.forename: Zsolt
authors.initials: Z
authors.lastname: Ablonczy
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics* / Q000378:metabolism; D000818:Animals; D005260:Female; D008062:Lipofuscin / Q000235:genetics / Q000378:metabolism*; D008268:Macular Degeneration / Q000378:metabolism* / Q000473:pathology; D008297:Male; D051379:Mice; D057507:Mice, 129 Strain; D008817:Mice, Mutant Strains; D008856:Microscopy, Fluorescence / Q000379:methods; D010084:Oxidation-Reduction; D010087:Oxides / Q000378:metabolism; D011726:Pyridinium Compounds / Q000737:chemistry / Q000378:metabolism*; D055213:Retinal Pigment Epithelium / Q000378:metabolism* / Q000473:pathology; D012176:Retinoids / Q000737:chemistry / Q000378:metabolism*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: C112040:A2-E (N-retinylidene-N-retinylethanolamine); D018528:ATP-Binding Cassette Transporters; C512841:Abca4 protein, mouse; D008062:Lipofuscin; D010087:Oxides; D011726:Pyridinium Compounds; D012176:Retinoids