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Effects of Photodegradation on the Physical and Antioxidant Properties of Melanosomes Isolated from Retinal Pigment Epithelium
Author(s) -
Zareba Mariusz,
Szewczyk Grzegorz,
Sarna Tadeusz,
Hong Lian,
Simon John D.,
Henry Michele M.,
Burke Janice M.
Publication year - 2006
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1562/2006-03-08-ra-836
Subject(s) - melanosome , retinal pigment epithelium , melanin , photodegradation , biophysics , antioxidant , photochemistry , chemistry , irradiation , oxidative stress , retinal , biology , biochemistry , photocatalysis , physics , nuclear physics , catalysis
Melanosomes of the retinal pigment epithelium (RPE) are relatively long‐lived organelles that are theoretically susceptible to changes induced by exposure to visible light. Here melanosomes were isolated from porcine RPE cells and subjected to high intensity visible light to determine the effects of illumination on melanosome structure and on the content and antioxidant properties of melanin. As compared to untreated melanosomes, illuminated granules showed morphologic changes consistent with photodegradation, which included variable reductions in electron density demonstrated by transmission electron microscopy (TEM), and particle fragmentation and surface disruption revealed by scanning electron microscopy (SEM) and atomic force microscopy. Illuminated melanosomes had lower melanin content, indicated by measures of absorbance and electron spin resonance (ESR) signal intensity, and reduced ability to bind iron, shown by chemical and ESR analyses. Compared to untreated melanosomes, ESR‐spin trapping analyses further indicated that illuminated melanosomes show increased photogeneration of superoxide anion and reduced ability to inhibit the iron ion‐catalyzed free radical decomposition of hydrogen peroxide. It appears therefore that visible light irradiation can disrupt the structure of RPE melanosomes and reduce the amount and antioxidant properties of melanin. Some of these changes occur in human RPE melanosomes with aging and the results obtained here suggest that visible light irradiation is at least partly responsible. The consequence of light‐induced changes in RPE melanosomes may be a diminished capacity of melanin to help protect aged cells from oxidative damage, perhaps increasing the risk of diseases with an oxidative stress component such as age‐related macular degeneration.