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Justyna Anna Furso, Andrzej Zadlo, Grzegorz Szewczyk, Tadeusz Sarna; Complexation of A2E with a model protein increases photoreactivity of the bis-retinoid in selected model systems. Invest. Ophthalmol. Vis. Sci. 2021;62(8):254.
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It has been postulated that the age pigment lipofuscin mediates photochemical reactions, which can contribute to oxidative stress in the outer retina. Chronic oxidative stress may lead to the onset of age-related macular degeneration (AMD). Lipofuscin is a composite granule with several chromophores, including a pyridinium bis-retinoid A2E, which according to the common belief, is responsible for photoreactivity and phototoxicity of this age pigment. Even though in simple model systems the photochemical reactivity of A2E was shown to be moderate or even low, it exhibited significant phototoxicity in retinal pigment epithelium cells in vitro. This vitamin A-derivative accumulates with senescence in retinal tissues and by forming adducts with biomolecules, may induce potential phototoxicity. In this study, we examined if the complexation of A2E with a model protein affected photoreactivity of this bis-retinoid.
The formation of non-covalent complexes of A2E with bovine serum albumin (BSA) was determined by UV-Vis absorption and emission spectrophotometry. The photochemical reactivity of bis-retinoid A2E and its complex with BSA was analyzed by time-resolved singlet oxygen phosphorescence, electron paramagnetic resonance (EPR)-spin trapping, and EPR-oximetry, using an appropriated spin trap and spin probe, respectively, and oxidation of the fluorogenic coumarin boronic acid probe.
The obtained data indicate that A2E after complexation with the model protein exhibited enhanced photoreactivity generating, upon irradiation with blue light, reactive oxygen species, particularly singlet oxygen. Aerobic photoexcitation of A2E-BSA complexes resulted in the formation of protein hydroperoxides suggesting that A2E was able to oxidize this model protein in vitro.
The ability of A2E to oxidize model protein upon excitation with blue light suggests that the pyridinium bis-retinoid may also oxidatively modify cellular proteins and change their key properties.
This is a 2021 ARVO Annual Meeting abstract.
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