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A. Wang, E. M. Gasyna, W. F. Mieler, J. R. Norris, Jr.; Synthetic Melanin as a Photoprotector Against Radical Oxygen Species. Invest. Ophthalmol. Vis. Sci. 2007;48(13):5955.
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Melanin, a major pigment found in RPE cells, contains intrinsic free radicals that can serve as detectors of potentially harmful reactive oxygen species. Melanin can serve as a photoprotector, quenching free radical species, particularly reactive oxygen species (ROS). Recently, the protective quenching of reactive oxygen species by melanin has been observed by the technique of time-resolved electron paramagnetic resonance spectroscopy (TREPR). However, how melanin quenches ROS is poorly understood. In addition, TREPR is difficult to perform on RPE cells because of limited sample sizes. To provide the necessary data for interpreting the photochemistry of melanin in RPE cells, readily available melanin such as synthetic melanin and sepia melanin can be used as a model system for exploration by TREPR. The goal is to characterize the free radical chemistry of melanin immediately after light irradiation in the presence and absence of oxygen. A better understanding of melanin’s interaction with oxygen is expected to provide new insight to the origin, prevention and treatment of age related macular degeneration (AMD).
The melanin photochemistry is initiated with 15 nanosecond long light pulses at 355 nm as provided by a Nd:yttrium/aluminum garnet laser. The ensuing photochemistry is followed by TREPR preformed on melanin samples with and without oxygen.
The TREPR spectra of melanin exposed to oxygen shows a decrease in free radical intensity at a very early time period with a quick return to baseline that is not present in melanin not exposed to oxygen.
The rapid decrease in TREPR intensity in the presence of oxygen indicates that melanin radicals are either interacting with oxygen by quenching singlet oxygen or by reacting with ROS that arises from singlet oxygen. This quenching mechanism is compatible with melanin serving a photoprotection role in RPE cells.
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