title: Photophysical studies of A2-E, putative precursor of lipofuscin, in human retinal pigment epithelial cells.
abstract: With age, human retinal pigment epithelial cells accumulate lipofuscin that can absorb photons in the visible range leading to light-induced damage and impaired vision. A putative precursor of lipofuscin, 2-[2,6-dimethyl-8-(2,6,6-trimethyl-1-cyclohexen-1-yl)-1E,3E, 5E,7E- octatetraenyl]-1-(2-hydroxyethyl)-4-[4-methyl-6-(2,6,6-trimethyl-1 - cyclohexen-1-yl)-1E,3E,5E-hexatrienyl]-pyridinium (A2-E), has recently been isolated and characterized from aged human retinal pigment epithelial cells. We have found that A2-E inhibits the growth of human retinal pigment epithelial cells at concentrations greater than 1 microM. Time-resolved fluorescence measurements of 1 microM A2-E in solution, performed under 413 nm excitation, showed that fluorescence wave forms integrated across the spectrum (450-600 nm) were best-fitted with three decay times in the nanosecond and subnanosecond time scale: 6.6, 1.9 and 0.33 ns. Untreated retinal pigment epithelial cells were characterized by three fluorescence lifetimes: 6.3, 1.7 and 0.35 ns. In retinal pigment epithelial cells treated with 1 microM A2-E, the fluorescence decay was significantly faster, with the marked presence (approximately equal to 30%) of a fourth short lifetime (0.12 ns). These fluorescence decay times for A2-E bound to human retinal pigment epithelial cells are similar to those of lipofuscin granules isolated from aged human retinal pigment epithelial cells. This similarity supports the hypothesis that A2-E is a precursor of lipofuscin and suggests that A2-E may play a role in the overall light damage associated with age-related retinal diseases.
authors.affiliation: INFM-Department of Physics and CEQSE-CNR, Politecnico di Milano, Italy.
authors.forename: R
authors.initials: R
authors.lastname: Cubeddu
authors.forename: P
authors.initials: P
authors.lastname: Taroni
authors.forename: D N
authors.initials: DN
authors.lastname: Hu
authors.forename: N
authors.initials: N
authors.lastname: Sakai
authors.forename: K
authors.initials: K
authors.lastname: Nakanishi
authors.forename: J E
authors.initials: JE
authors.lastname: Roberts
mesh_terms: D000375:Aging / Q000378:metabolism; D002478:Cells, Cultured; D006801:Humans; D008062:Lipofuscin / Q000737:chemistry / Q000528:radiation effects; D010777:Photochemistry; D010857:Pigment Epithelium of Eye / Q000737:chemistry / Q000528:radiation effects*; D012168:Retinal Pigments / Q000737:chemistry / Q000528:radiation effects*; D012176:Retinoids / Q000737:chemistry / Q000528:radiation effects*; D013050:Spectrometry, Fluorescence
chemical_list: C112040:A2-E (N-retinylidene-N-retinylethanolamine); D008062:Lipofuscin; D012168:Retinal Pigments; D012176:Retinoids