Oxidation causes melanin fluorescence. Invest Ophthamol Vis Sci

Department of Vitreoretinal Surgery, Division of Ophthalmology, University of Cologne, Germany.
Investigative Ophthalmology &amp Visual Science (Impact Factor: 3.66). 02/2001; 42(1):241-6.
Source: PubMed

ABSTRACT The goal of this study is the characterization of the strong yellow fluorescence of oxidized melanin in the retinal pigment epithelium (RPE) and the choroid.
Naturally occurring melanin in the human retina and choroid was oxidized by exposing fixed and plastic-embedded sections of a human eye to light and hydrogen peroxide. Synthetic melanin was also oxidized in vitro by exposure to light and hydrogen peroxide. The fluorescence of oxidized melanin was examined by absorption spectroscopy, fluorescence spectroscopy, and fluorescence microscopy.
Naturally occurring melanin oxidized in situ exhibited a lipofuscin-like yellow fluorescence. Oxidation of melanin in vitro degraded the melanin polymer, resulting in a fluorescent solution. Fluorescence spectroscopy gave an excitation maximum at approximately 470 nm and an emission maximum at approximately 540 nm for both natural and synthetic melanin. Increasing the time of exposure to light or hydrogen peroxide increased melanin fluorescence.
The results indicate that the strong yellow fluorescence of melanin in the RPE and choroid in situ is a property of oxidized melanin and is not due to contamination of the melanin by proteinaceous or lipid materials. The data presented allow a reinterpretation of the results obtained from fluorescence investigations of melanin-containing tissue and suggest a link between melanin degradation and lipofuscin formation.

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Available from: Peter Kayatz, Feb 07, 2014
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    • "Triplet excited carbonyls 350–550 nm [36] [75] Singlet excited pigments 360–560 nm melanin [76] [77] 680–740 nm chlorophyll [78] Triplet excited pigments 870–1000 nm chlorophyll + Dimolar singlet oxygen 634 nm, 703 nm [22] [23] [37] Monomolar singlet oxygen 1270 nm * + expected based on the singlet excited pigment emission but not yet directly confirmed as a contribution to ultra-weak photon emission. Emission wavelength from triplet excited chlorophyll is known from phosphorescence measurement [79]. "
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    • "They are ubiquitous in nature and occur in various organisms, particularly fungi and bacteria have been found to show a high melanin content which is associated with microbial pathogenesis (Gomez and Nosanchuk, 2003; Nosanchuk and Casadevall, 2003). Compared to the other age-related pigments, melanin is regarded to show only a relatively weak fluorescence, but it has been shown that oxidation significantly increases fluorescence with a emission maximum at ∼540 nm when excited at ∼470 nm (Kayatz et al., 2001). Fluorescent light emission from tetrapyrrolic compounds (i.e. "
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    • "Recently, it was reported that melanins emit fluorescence in the NIR region (820–920 nm) when excited at 785 nm [26]. Oxidation may be the cause of melanin fluorescence as it has been shown that nonoxidized melanins have very weak fluorescence compared with oxidized ones [48]. In skin tissue with melanoma, pigmented areas have much higher fluorescence intensity than nonpigmented areas with two-photon excitation at 800 nm [49]. "
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