Oxidation causes melanin fluorescence. Invest Ophthamol Vis Sci

Article (PDF Available)inInvestigative Ophthalmology & Visual Science 42(1):241-6 · February 2001with113 Reads
Source: PubMed
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.
    • "These are lipophilic and are therefore potentially able to enter the nucleus. In addition, melanin polymer rapidly solubilizes when exposed to hydrogen peroxide [43] and its degradation by peroxidation or UVphotoionization had been proposed to involve dioxetane and triplet carbonyls [44,45]. We found that a triplet state could be created in melanin by a cell-free system: synthetic melanin oxidized with peroxynitrite and incubated with DBAS generated chemiluminescence. "
    [Show abstract] [Hide abstract] ABSTRACT: Sunlight’s ultraviolet wavelengths induce cyclobutane pyrimidine dimers (CPDs), which then cause mutations that lead to melanoma or to cancers of skin keratinocytes. In pigmented melanocytes, we found that CPDs arise both instantaneously and for hours after UV exposure ends. Remarkably, the CPDs arising in the dark originate by a novel pathway that resembles bioluminescence but does not end in light: First, UV activates the enzymes nitric oxide synthase (NOS) and NADPH oxidase (NOX), which generate the radicals nitric oxide (NOradical dot) and superoxide (O2radical dot−); these combine to form the powerful oxidant peroxynitrite (ONOO−). A fragment of the skin pigment melanin is then oxidized, exciting an electron to an energy level so high that it is rarely seen in biology. This process of chemically exciting electrons, termed “chemiexcitation”, is used by fireflies to generate light but it had never been seen in mammalian cells. In melanocytes, the energy transfers radiationlessly to DNA, inducing CPDs. Chemiexcitation is a new source of genome instability, and it calls attention to endogenous mechanisms of genome maintenance that prevent electronic excitation or dissipate the energy of excited states. Chemiexcitation may also trigger pathogenesis in internal tissues because the same chemistry should arise wherever superoxide and nitric oxide arise near cells that contain melanin.
    Full-text · Article · May 2016
    • "Therefore it was concluded that an increased fluorescence is a strong indicator of oxidized melanins. In contrast to a previous study [10] the increase in fluorescence was not requiring UV radiation for activation. A B C DFigure 1. Example of untreated hair: light reddish-blond hair without cosmetic treatment (subject 6,Figure 2. Dark-blond hair from a volunteer bleached with H 2 O 2 in alkaline medium. "
    [Show abstract] [Hide abstract] ABSTRACT: In assessing abstinence from drug or alcohol abuse, hair analysis plays an important role. Cosmetic hair treatment influences the content of deposited drugs which is not always detectable during analysis. Since oxidation of melanin leads to an increase in fluorescence, a microscopic method was developed to distinguish natural from cosmetically treated hair. For validation, natural hair samples were treated with different types of cosmetics and inspected by fluorescence microscopy. Hair samples from 20 volunteers with documented cosmetic treatment and as a proof of concept 100 hair samples from forensic cases were analyzed by this method. Apart from autofluorescence with excitation at 365 nm, no obvious fluorescence was observed in untreated hair samples. Tinting and a natural plant product had no influence on fluorescence, but dyeing procedures including oxidation led to a marked increase in fluorescence. Proof of cosmetic treatment was achieved in hair samples from the 20 volunteers. In 100 forensic cases, 13 samples were characterized as oxidatively treated, which was in accordance with the respective disclosure except for one case where treatment was not admitted. This fluorescence microscopic procedure proved to be fast, easy, and reliable to identify oxidatively treated hair samples, which must be considered especially in evaluating cases of negative drug results. Copyright © 2015 John Wiley & Sons, Ltd.
    Article · Sep 2015
    • "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]. "
    [Show abstract] [Hide abstract] ABSTRACT: This review attempts to summarize molecular mechanisms, spectral and intensity properties, detection techniques and applications of ultra-weak photon emission. Ultra-weak photon emission is the chemiluminescence from biological systems where electronically excited species are formed during oxidative metabolic or oxidative stress processes. It is generally accepted that photons are emitted (1) at near UVA, visible, and near IR spectral ranges from 350 to 1300nm and (2) at the intensity of photon emission in the range of several units to several hundreds (oxidative metabolic process) and several hundreds to several thousands (oxidative stress process) photons s(-1)cm(-2). Current development in detection using low-noise photomultiplier tubes and imaging using highly sensitive charge coupled device cameras allows temporal and spatial visualization of oxidative metabolic or oxidative stress processes, respectively. As the phenomenon of ultra-weak photon emission reflects oxidative metabolic or oxidative stress processes, it can be widely used as a non-invasive tool for monitoring of the physiological state of biological systems.
    Full-text · Article · Feb 2014
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