Retinyl Palmitate and the Blue-Light-Induced Phototoxicity of Human Ocular Lipofuscin

Lipofuscin accumulation in the retinal pigment epithelium is associated with the onset of age-related macular degeneration. Lipofuscin is phototoxic and affects cellular function through the photochemical generation of reactive oxygen intermediates. Mass spectral analysis of solvent extracts of human retinal lipofuscin granules reveals the presence of retinyl palmitate, the substrate for the enzymatic regeneration of 11-cis-retinal. Retinyl palmitate has an appreciable binding constant for phosphatidylcholine liposomes, and based on the glycophospholipids present in lipofuscin, retinal palmitate likely accumulates within the lipid content of the granule. Photochemical oxidation of retinal palmitate generates anhydroretinol, an intracellular signaling retinoid in the signal transduction cascade from the plasma membrane that causes apoptosis by generating reactive oxygen intermediates. These data are used to propose a model for the phototoxicity of lipofuscin.