Microfluorometric and fluorometric lipofuscin spectral discrepancies: a concentration-dependent metachromatic effect?

The fluorescent spectral patterns of some lipid peroxidation products and their derivatives have been investigated. A significant concentration-dependent fluorescence shift was found. A variety of suggested age pigment fluorophores, 1,4-dihydropyridines, Schiff base and MDA polymers, all demonstrated a potential for spectral shifts. Along with increased concentration, the fluorescence peaks of these fluorophores shifted from blue (400-490 nm) to golden-yellow or orange-red (500-600 nm). The demonstrated metachromasia is supposed to be an inner-filter effect resulting from molecular polymerization or stacking. Thus, the striking differences between lipofuscin fluorescence spectra obtained by different investigators may be explained as due to large differences in lipofuscin concentration during measurement with different techniques. The pigments are either studied in situ by morphologists and recorded by microscopic fluorometry or by biochemists using spectrofluorometers to measure the extracted and dissolved pigments.