PHOTOPHYSICAL STUDIES ON HUMAN RETINAL LIPOFUSCIN

Fluorescent material generated in the human retina accumulates within lipofuscin granules of the retinal pigment epithelium (RPE) during agi ng. Its presence has been suggested to contributed to various diseases including age-related macular degeneration. Because this material abs orbs light at wave lengths as long as 550 nm, photophysical studies we re performed to determine whether lipofuscin could contribute to light damage and to determine if its composition is similar to a synthetica lly prepared lipofuscin. Time-resolved experiments were performed to m onitor (1) fluorescence decay, (2) the UV-visible absorption of longer -lived excited states and (3) the formation and decay of singlet oxyge n at 1270 nm. Steady-state and time-resolved fluorescence studies indi cate that human and synthetic lipofuscin have fluorophores in common. Time-resolved absorption experiments on human retinal lipofuscin and s ynthetic lipofuscin showed the presence of at least two transient spec ies, one absorbing at 430 nm (lifetime ca 7 mu s) and a second absorbi ng at 580 nm, which decays via second order kinetics. In addition, the re is a third absorbing species stable to several hundred milliseconds . The transient species at 430 nm is quenched by oxygen, suggesting th at it is a triplet state. Subsequent studies showed the formation of s inglet oxygen, which was monitored by its phosphorescence decay at 127 0 nm. These studies demonstrate that lipofuscin can act as a sensitize r for the generation of reactive oxygen species that may contribute to the age-related decline of RPE function and blue light damage.