Fluorophores of the human retinal pigment epithelium: separation and spectral characterization

Ten fluorescent fractions originating from the chloroform extracts of retinal pigment epithelial (RPE) cells of human donor eyes (ages 52-98 yr) have been separated and characterized by UV-vis absorbance and corrected fluorescence spectroscopy. The semipurified fluorophores fall into four categories based upon their spectral properties: green-emitting fluorophores, a golden yellow-emitting fluorophore, yellow-green-emitting fluorophores and orange-red-emitting fluorophores. All share common absorbance peaks around 280- and 330 nm, and the orange-red-emitting fluorophores also exhibit a strong absorbance peak at 420 nm. No significant visible-emitting fluorophores were detected in the methanol-water phase of these extracts. While these fluorophores are abundant in extracts from adult-derived RPE, most of the fluorophores occur in much lower amounts in RPE extracts from human donors under 10 yr of age. Eyes from child human donors also have much less RPE lipofuscin than those from adult donors, suggesting that most of the fluorophores are lipofuscin derived. This interpretation is supported by the previous finding that all of the fluorophores from whole RPE are also present in extracts of purified lipofuscin granules. Characterization of the chromatographic and spectral properties of the chloroform-soluble fluorescent components from the human RPE provides an important tool for determining the mechanism of RPE lipofuscin fluorophore formation. The absorbance properties defined here are of significance to investigations into the photobiology of the RPE and to those using laser therapy in treatment of age-related retinal diseases.