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B Rozanowski, W Korytowski, A Pawlak, MB Rozanowska, M Boulton, JM Burke, T Sarna; Age-related Changes in Photoreactivity of RPE Melanosomes and Lipofuscin Granules . Invest. Ophthalmol. Vis. Sci. 2002;43(13):678.
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Purpose: The photophysical properties - absorption and fluorescence - of RPE melanosomes (MS) and lipofuscin granules (LF) change with age. The aim of this study was to determine whether their photoreactivities also undergo age-related changes. Methods: MS and LF granules were isolated from human RPE pooled into four age groups - below 40, 41-60, 61-80, and above 80 years of age. The concentrations of pigment granules were measured by counting in a hemocytometer. Photoreactivity was assessed by photo-induced oxygen uptake measured by electron spin resonance (ESR) oximetry, and photogeneration of free radicals measured by ESR spin trapping during irradiation of suspension of pigment granules with narrow or broad band blue light. Results: The rates of photo-induced oxygen uptake increased with age of pigment granule donor by a factor of 2.4 and 1.6 for MS and LF, respectively. Also the rates of photo-induced accumulation of spin adducts with superoxide increased with donors' age. Most oxygen was consumed by oxidation of intragranular components and only about 27% and 1 % of oxygen accumulated as hydrogen peroxide in the presence of photoexcited aged MS and LF, respectively. Despite the rate of broad band blue light-induced oxygen uptake mediated by aged MS was lower by a factor of about 3 than that mediated by the same concentration of LF granules, it significantly increased in the presence of 0.2 mM ascorbate and became similar to that of LF. Conclusion: Blue-light induced aerobic photoreactivity of both MS and LF granules increases with age, perhaps providing a source of reactive oxygen species and leading to depletion of vital cellular reductants, which together with increased number of LF granules may contribute to cellular dysfunction.
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