Advertisement

Photophysical Studies of A2-E, Putative Precursor of Lipofuscin, in Human Retinal Pigment Epithelial Cells

Authors


*To whom correspondence should be addressed at: Fordham University, Department of Natural Sciences, 113 West 60th Street, New York, NY 10023, USA. E-mail:jroberts@mary.fordham.edu

Abstract

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-l-cyclohexen-l-yl)-lE,3E:,5E,7E-octa-tetraenyl]-l-(2-hydroxyethyl)-4-[4-methyl-6-(2,6,6-tri-methyl-1 -cyclohexen-1 -y 1)- IE, 3E, 5E-hexatrienyl] -pyridi-nium (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 μM. Time-resolved fluorescence measurements of 1 μM 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 μM A2-E, the fluorescence decay was significantly faster, with the marked presence (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.

Ancillary