Age-Related Changes in bis-Retinoids of Lipofuscin Granules in Human Retinal Pigment Epithelium Cells

Lipofuscin granules (LGs) in retinal pigment epithelium (RPE) cells contain bis-retinoids and their oxidation and degradation products, rendering them photo- and cytotoxic to intracellular structures. LGs are implicated in the pathogenesis of multiple visual pathologies, including age-related macular degeneration (AMD). They exhibit strong autofluorescence, which has led to the development of fundus autofluorescence (FAF) imaging as a non-invasive diagnostic method in ophthalmology. Spectral analysis of autofluorescence can expand the capabilities of this method, including for preclinical diagnostics, as pathological conditions are often associated with increased proportions of oxidized bis-retinoid derivatives that alter LG autofluorescence parameters. However, limited knowledge of age-dependent changes in LG bis-retinoid composition remains a key limitation. In this study, we combined fluorescence spectroscopy, confocal fluorescence microscopy, and fluorescence lifetime imaging (time-correlated single-photon counting) to demonstrate that, under physiological conditions, aging is accompanied by a progressive increase in the relative abundance of oxidation and degradation products of bis-retinoids in LGs. These findings provide an age-dependent baseline for distinguishing physiological and pathological states, thereby improving the potential of FAF imaging for early (preclinical) diagnosis.