Photoaging of retinal pigment epithelial melanosomes: The effect of photobleaching on morphology and reactivity of the pigment granules

Wnuk

et al. 2018

Sci Rep

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Retinal pigment epithelium (RPE) is an important part of the blood-retina barrier (BRB) that separates the retina from the choroid. Although melanin granules contribute to the mechanical stability of the BRB complex, it is unknown if the age pigment lipofuscin affects mechanical properties of the tissue. To address this issue the effect of sub-lethal photic stress mediated by phagocytized lipofuscin granules, isolated from RPE of human donors, on morphology and mechanical properties of ARPE-19 cells was investigated. Nanomechanical analysis using atomic force spectroscopy revealed that irradiation of cells containing lipofuscin granules with blue light induced significant softening of the cells, which was accompanied by substantial reorganization of the cell cytoskeleton due to peroxidation of cellular proteins. Our results indicate that lipofuscin-mediated photic stress can cause significant modification of the RPE cells with the potential to disturb biological function of the BRB complex.

Section: Resultsmentioning

confidence: 95%

Lipofuscin-mediated photodynamic stress induces adverse changes in nanomechanical properties of retinal pigment epithelium cells

Wiktor

Wnuk

et al. 2018

Sci Rep

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“…This could change, if the pigment granule morphology is substantially modified by oxidative degradation and if the oxidized melanin constituents lose their efficiency to quench/scavenge reactive oxygen species. We recently demonstrated that melanosomes isolated from retinal pigment epithelium of bovine eyes, subjected to experimental photobleaching, and exhibited significantly altered morphology with loose structure allowing for easier penetration of the granules by different reagents (Zadlo et al, ). In addition, such partially photobleached pigment granules showed higher photoreactivity, reduced efficiency to quench singlet oxygen and lower antioxidant capacity (Zareba et al, ; Zadlo et al, ).…”

Section: Resultsmentioning

confidence: 99%

“…We recently demonstrated that melanosomes isolated from retinal pigment epithelium of bovine eyes, subjected to experimental photobleaching, and exhibited significantly altered morphology with loose structure allowing for easier penetration of the granules by different reagents (Zadlo et al, ). In addition, such partially photobleached pigment granules showed higher photoreactivity, reduced efficiency to quench singlet oxygen and lower antioxidant capacity (Zareba et al, ; Zadlo et al, ). The reduced efficacy of photobleached synthetic pheomelanin to quench singlet oxygen is consistent with our postulate that the photoreactivity and phototoxicity of the skin pheomelanin could significantly increase with its in situ aerobic photolysis.…”

Section: Resultsmentioning

confidence: 99%

Photobleaching of pheomelanin increases its phototoxic potential: Physicochemical studies of synthetic pheomelanin subjected to aerobic photolysis

Szewczyk

Pigment Cell Melanoma Res

Camenisch

et al. 2018

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Although melanin is a photoprotective pigment, its elevated photochemical reactivity could lead to various phototoxic processes. Photoreactivity of synthetic pheomelanin, derived from 5‐S‐cysteinyldopa (5SCD‐M) and its photodegradation products obtained by subjecting the melanin to aerobic irradiation with UV‐visible light, was examined employing an array of advanced physicochemical methods. Extensive photolysis of 5SCD‐M was accompanied by partial bleaching of the melanin, modification of its paramagnetic properties, and significant increase in the ability to photogenerate singlet oxygen. The changes correlated with a substantial decrease in the melanin content of benzothiazine (BT) units and increase of modified benzothiazole (BZ) units. Synthetically prepared BZ exhibited higher efficiency to photogenerate singlet oxygen than the synthetic BT, and the free radical form of BZ, unlike that of BT, did not show measurable spin density on nitrogen atom, which was confirmed by quantum chemical calculations. Formation of modified BZ units in the photobleached 5SCD‐M is responsible for the paramagnetic and photochemical changes of the melanin and its elevated phototoxic potential. Given a relatively constant pheomelanin–eumelanin ratio, such undesirable changes could occur in individual of all skin types.

“…Average sizes of the studied melanosomes are shown in Table 1 . In our previous work we have shown that in vitro photoaging of bovine RPE melanosomes induces morphological changes of the pigment granules, exposing melanin nanoaggregates [ 21 ]. In this study, we observed similar effects induced by chemical degradation.…”

Section: Resultsmentioning

confidence: 99%

Redox Active Transition Metal ions Make Melanin Susceptible to Chemical Degradation Induced by Organic Peroxide

Piłat

Pawlak

et al. 2017

Cell Biochem Biophys

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With aging, retinal pigment epithelium melanosomes, by fusion with the age pigment lipofuscin, form complex granules called melanolipofuscin. Lipofuscin granules may contain oxidized proteins and lipid hydroperoxides, which in melanolipofuscin could chemically modify melanin polymer, while transition metal ions present in melanin can accelerate such oxidative modifications. The aim of this research was to examine the effect of selected transition metal ions on melanin susceptibility to chemical modification induced by the water-soluble tert-butyl hydroperoxide used as an oxidizing agent. Synthetic melanin obtained by DOPA autooxidation and melanosomes isolated from bovine retinal pigment epithelium were analyzed. To monitor tert-butyl hydroperoxide-induced oxidative changes of DMa and BMs, electron paramagnetic resonance spectroscopy, UV-vis absorption spectroscopy, dynamic light scattering, atomic force microscopy and electron paramagnetic resonance oximetry were employed. These measurements revealed that both copper and iron ions accelerated chemical degradation induced by tert-butyl hydroperoxide, while zinc ions had no effect. Strong prooxidant action was detected only in the case of melanosomes and melanin degraded in the presence of iron. It can be postulated that similar chemical processes, if they occur in situ in melanolipofuscin granules of the human retinal pigment epithelium, would modify antioxidant properties of melanin and its reactivity.