Purchase this article with an account.
M. Zareba, G. Szewczyk, M.W. Raciti, M.M. Henry, A. Fekete, J.M. Burke, T. Sarna; Does Experimental Photodegradation of RPE Melanosomes Change Their Antioxidant Properties? . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2076.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Accumulation of oxidative damage over time by the RPE is believed to contribute to age–related diseases such as AMD. RPE melanosomes could theoretically protect cells from oxidative damage due to the antioxidant properties of melanin, which binds redox active metal ions, scavenges free radicals and absorbs light. However, the amount of RPE melanin may decrease with age, possibly as a result of photo–oxidative reactions. Here we studied the effect of experimental photodegradation of melanosomes on their antioxidant properties.
Melanosomes isolated from porcine RPE were partially degraded by exposure to high intensity visible light. The morphology of native and illuminated melanosomes was examined by transmission EM (TEM). ESR and optical spectroscopies were used to quantify melanin, iron bound to melanin, oxygen photo–consumption and the production of DMPO spin trap adducts with various radicals. The cellular effects of melanosome illumination were analyzed in ARPE–19 cells containing phagocytized particles and subjected to oxidative stress induced chemically or photically.
The morphology of native and photodegraded melanosomes by TEM was similar although illuminated particles were smaller and their electron density more variable. Melanin content was significantly decreased as shown by ESR and optical spectroscopies. Native melanosomes inhibited production of DMPO adduct with hydroxyl radicals but melanosome photodegradation decreased their iron–binding capacity, which was accompanied by a decreased ability to inhibit DMPO–OH formation. In the presence of degraded melanosomes less oxygen was consumed but more adduct of DMPO with superoxide radicals was generated during blue light illumination. No cellular effects of illuminated melanosomes were seen. However, effects on individual cells with high particle number over long time periods could remain undetected by measures of acute cytotoxicity in cell populations.
Partial degradation of melanosomes by experimental light treatment diminishes their antioxidant properties in model systems and generates potentially photoreactive species. Similar changes in situ could contribute adversely to long–term RPE cell survival.
This PDF is available to Subscribers Only