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B.–L.L. Seagle, E.M. Gasyna, K.A. Rezaei, W.F. Mieler, J.R. Norris; Melanin Photoprotection in Human Retinal Pigment Epithelium Cells as Revealed by Time–Resolved Electron Paramagnetic Resonance Spectroscopy . Invest. Ophthalmol. Vis. Sci. 2006;47(13):5530.
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© ARVO (1962-2015); The Authors (2016-present)
In order to elucidate the role of melanin in the RPE, time–resolved electron paramagnetic resonance (EPR) spectroscopy was used to study melanin photochemistry in human fetal retinal pigment epithelium (RPE) cells.
RPE cells were isolated and cultured from human fetal eyes. Time–resolved EPR experiments were performed on whole RPE cell samples under varying conditions of oxygenation/deoxygenation, light wavelength, and light intensity. Radiation, either 532 nm or 355 nm, was provided by a Nd:yttrium/aluminum garnet laser. Flow cytometry was used to determine RPE apoptosis rates.
EPR spectra from RPE cells reveal in vivo light–induced melanin free radical photochemistry consistent with melanin photoprotective mechanisms. Spectra are consistent with photoproduction of melanin radical pairs from excited triplet states, free radical migration within melanin aggregates, and free radical recombination chemistry. Additionally, we show that a single species of melanin free radical, existing in both the intrinsic and extrinsic radical populations, scavenges photogenerated reactive oxygen species in RPE cells. The rate of blue light–induced apoptosis of RPE cells can be correlated with EPR detected photochemistry and with overall melanin content within the RPE cells.
Melanin plays a protective role in the RPE as a light absorber and as a versatile redox and reactive species buffer. Increased melanin content within RPE cells correlates with significantly decreased RPE blue–light induced apoptosis.
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