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Photoreactivity of aged human RPE melanosomes: A comparison with lipofuscin

Rozanowska, Malgorzata Barbara, Korytowski, Witold, Rozanowski, Bartosz, Skumatz, Christine, Boulton, Michael Edwin, Burke, Janice M. and Sarna, Tadeusz 2002. Photoreactivity of aged human RPE melanosomes: A comparison with lipofuscin. Investigative Ophthalmology and Visual Science 43 (7) , pp. 2088-2096.

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Abstract

purpose. To determine whether aging is accompanied by changes in aerobic photoreactivity of retinal pigment epithelial (RPE) melanosomes isolated from human donors of different ages, and to compare the photoreactivity of aged melanosomes with that of RPE lipofuscin. methods. Human RPE pigment granules were isolated from RPE cells pooled into groups according to the age of the donors. Photoreactivity was determined by blue-light-induced oxygen uptake and photogeneration of reactive oxygen species. Short-lived radical intermediates were detected by spin-trapping, hydrogen peroxide by an oxidase electrode, singlet oxygen by cholesterol assay, and lipid hydroperoxides by iodometric assay. results. Blue-light photoexcitation of melanosomes resulted in age-related increases in both oxygen uptake and the accumulation of superoxide anion spin adducts. The efficiencies of these processes, however, were still significantly lower than that induced by photoexcited lipofuscin. During irradiation of melanosomes, a substantial amount of oxygen was converted into hydrogen peroxide, whereas for lipofuscin, hydrogen peroxide accounted for not more than 3% of oxygen consumed. In contrast to lipofuscin, photoexcited melanosomes did not substantially increase the rate of oxidative reactions in the presence of polyunsaturated lipids or albumin. However, oxygen uptake was significantly elevated in the presence of ascorbate. Thus, the rate of photo-induced oxygen uptake in samples containing both ascorbate and melanosomes approached that observed in lipofuscin samples. conclusions. Blue-light-induced photoreactivity of melanosomes increases with age, perhaps providing a source of reactive oxygen species and leading to depletion of vital cellular reductants, which, together with lipofuscin, may contribute to cellular dysfunction.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Optometry and Vision Sciences
Additional Information: Confirmation received by publisher on 21 February 2014 that publisher's pdf can be self-archived 6 months after publication.
Publisher: Association for Research in Vision and Ophthalmology
ISSN: 0146-0404
Date of First Compliant Deposit: 30 March 2016
Last Modified: 04 Jun 2017 01:36
URI: http://orca-mwe.cf.ac.uk/id/eprint/820

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