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Published on: April 14, 2023
Photoreactivity of aged human RPE melanosomes: a comparison with lipofuscin
Małgorzata Rózanowska1, Witold Korytowski, Bartosz Rózanowski
1Department of Biophysics, Institute of Molecular Biology, Jagiellonian University, Kraków, Poland. rozanowskamb@cf.ac.uk
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.
Insights
Aging increases the blue-light photoreactivity of retinal pigment epithelial (RPE) melanosomes, potentially generating reactive oxygen species and depleting cellular reductants, contributing to dysfunction alongside lipofuscin.
Area of Science:
- Ophthalmology
- Cell Biology
- Biochemistry
Background:
- Retinal pigment epithelium (RPE) cells contain melanosomes and lipofuscin, which can be photoactivated.
- Melanosomes are pigment granules involved in light absorption and photoprotection.
- Lipofuscin is an age-related pigment aggregate implicated in cellular dysfunction.
Purpose of the Study:
- To investigate age-related changes in the aerobic photoreactivity of human RPE melanosomes.
- To compare the photoreactivity of aged melanosomes with that of RPE lipofuscin.
Main Methods:
- Isolated human RPE melanosomes from donors of different ages.
- Assessed photoreactivity via blue-light-induced oxygen uptake and reactive oxygen species generation.
- Detected radical intermediates, hydrogen peroxide, singlet oxygen, and lipid hydroperoxides.
Main Results:
- Melanosome photoreactivity, including oxygen uptake and superoxide adducts, increased with donor age.
- Photoexcited melanosomes generated significant hydrogen peroxide, unlike lipofuscin.
- Melanosome photoreactivity was enhanced by ascorbate, approaching lipofuscin levels.
Conclusions:
- RPE melanosome photoreactivity is age-dependent, contributing to reactive oxygen species production.
- Increased photoreactivity may deplete cellular reductants, exacerbating age-related RPE dysfunction.
- Both melanosomes and lipofuscin may play roles in age-related cellular dysfunction.
