title: Redox Active Transition Metal ions Make Melanin Susceptible to Chemical Degradation Induced by Organic Peroxide.
abstract: 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.
authors.affiliation: Department of Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Krakow, Poland. andrzej.zadlo@uj.edu.pl.
authors.forename: Andrzej
authors.initials: A
authors.lastname: Zadlo
authors.affiliation: Department of Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Krakow, Poland.
authors.forename: Anna
authors.initials: A
authors.lastname: Pilat
authors.affiliation: Department of Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Krakow, Poland.
authors.forename: Michal
authors.initials: M
authors.lastname: Sarna
authors.affiliation: Department of Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Krakow, Poland.
authors.forename: Anna
authors.initials: A
authors.lastname: Pawlak
authors.affiliation: Department of Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Krakow, Poland.
authors.forename: Tadeusz
authors.initials: T
authors.lastname: Sarna
mesh_terms: D000818:Animals; D002417:Cattle; D056831:Coordination Complexes / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D007477:Ions / Q000737:chemistry; D008027:Light; D008054:Lipid Peroxides / Q000378:metabolism; D008543:Melanins / Q000737:chemistry* / Q000378:metabolism; D020460:Melanosomes / Q000378:metabolism; D018625:Microscopy, Atomic Force; D010084:Oxidation-Reduction; D010092:Oximetry; D010100:Oxygen / Q000032:analysis; D010316:Particle Size; D055213:Retinal Pigment Epithelium / Q000187:drug effects / Q000378:metabolism; D013056:Spectrophotometry, Ultraviolet; D028561:Transition Elements / Q000737:chemistry*; D020122:tert-Butylhydroperoxide / Q000737:chemistry* / Q000494:pharmacology
chemical_list: D056831:Coordination Complexes; D007477:Ions; D008054:Lipid Peroxides; D008543:Melanins; D028561:Transition Elements; D020122:tert-Butylhydroperoxide; D010100:Oxygen
keywords: Antioxidant; Melanin; Melanosomes; Organic peroxides; Oxidative degradation; Transition metal ions