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Daplan E, Turin L. Free radical production induced by visible light in live fruit flies. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY. B, BIOLOGY 2024; 255:112925. [PMID: 38703451 DOI: 10.1016/j.jphotobiol.2024.112925] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/28/2024] [Revised: 04/22/2024] [Accepted: 04/25/2024] [Indexed: 05/06/2024]
Abstract
Visible light triggers free radical production in alive and intact Drosophila melanogaster. We exposed fruit flies to red (613-631 nm), green (515-535 nm), and blue (455-475 nm) light while we monitored changes in unpaired electron content with an electron spin resonance spectrometer (ESR/EPR). The immediate response to light is a rapid increase in spin content lasting approximately 10 s followed by a slower, linear increase for approximately 170 s. When the light is turned off, the spin population promptly decays with a similar time course, though never fully returning to baseline. The magnitude and time course of the spin production depends on the wavelength of the light. Initially, we surmised that eumelanin might be responsible for the spin change because of its documented ability for visible light absorption and its highly stable free radical content. To explore this, we utilized different fruit fly strains with varying eumelanin content and clarified the relation of melanin types with the spin response. Our findings revealed that flies with darker cuticle have at least three-fold more unpaired electrons than flies with yellow cuticle. However, to our surprise, the increase in unpaired electron population by light was not drastically different amongst the genotypes. This suggests that light-induced free radical production may not exclusively rely on the presence of black melanin, but may instead be dependent on light effects on quinone-based cuticular polymers.
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Affiliation(s)
| | - Luca Turin
- University of Buckingham, United Kingdom
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Lyu Y, Tschulakow AV, Wang K, Brash DE, Schraermeyer U. Chemiexcitation and melanin in photoreceptor disc turnover and prevention of macular degeneration. Proc Natl Acad Sci U S A 2023; 120:e2216935120. [PMID: 37155898 PMCID: PMC10194005 DOI: 10.1073/pnas.2216935120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2022] [Accepted: 04/03/2023] [Indexed: 05/10/2023] Open
Abstract
Age-related macular degeneration, Stargardt disease, and their Abca4-/- mouse model are characterized by accelerated accumulation of the pigment lipofuscin, derived from photoreceptor disc turnover in the retinal pigment epithelium (RPE); lipofuscin accumulation and retinal degeneration both occur earlier in albino mice. Intravitreal injection of superoxide (O2•-) generators reverses lipofuscin accumulation and rescues retinal pathology, but neither the target nor mechanism is known. Here we show that RPE contains thin multi-lamellar membranes (TLMs) resembling photoreceptor discs, which associate with melanolipofuscin granules in pigmented mice but in albinos are 10-fold more abundant and reside in vacuoles. Genetically over-expressing tyrosinase in albinos generates melanosomes and decreases TLM-related lipofuscin. Intravitreal injection of generators of O2•- or nitric oxide (•NO) decreases TLM-related lipofuscin in melanolipofuscin granules of pigmented mice by ~50% in 2 d, but not in albinos. Prompted by evidence that O2•- plus •NO creates a dioxetane on melanin that excites its electrons to a high-energy state (termed "chemiexcitation"), we show that exciting electrons directly using a synthetic dioxetane reverses TLM-related lipofuscin even in albinos; quenching the excited-electron energy blocks this reversal. Melanin chemiexcitation assists in safe photoreceptor disc turnover.
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Affiliation(s)
- Yanan Lyu
- Division of Experimental Vitreoretinal Surgery, Centre for Ophthalmology, University of Tuebingen, Tuebingen72076, Germany
| | - Alexander V. Tschulakow
- Division of Experimental Vitreoretinal Surgery, Centre for Ophthalmology, University of Tuebingen, Tuebingen72076, Germany
- OcuTox GmbH, Preclinical Drug Assessment, Hechingen72379, Germany
| | - Kun Wang
- Division of Experimental Vitreoretinal Surgery, Centre for Ophthalmology, University of Tuebingen, Tuebingen72076, Germany
| | - Douglas E. Brash
- Department of Therapeutic Radiology, Yale University School of Medicine, New Haven, CT06520-8040
- Yale Comprehensive Cancer Center, Yale University School of Medicine, New Haven, CT06520-8028
| | - Ulrich Schraermeyer
- Division of Experimental Vitreoretinal Surgery, Centre for Ophthalmology, University of Tuebingen, Tuebingen72076, Germany
- OcuTox GmbH, Preclinical Drug Assessment, Hechingen72379, Germany
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Mostert AB. Melanin, the What, the Why and the How: An Introductory Review for Materials Scientists Interested in Flexible and Versatile Polymers. Polymers (Basel) 2021; 13:1670. [PMID: 34065580 PMCID: PMC8161012 DOI: 10.3390/polym13101670] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2021] [Revised: 05/18/2021] [Accepted: 05/18/2021] [Indexed: 01/13/2023] Open
Abstract
Today, western society is facing challenges to create new medical technologies to service an aging population as well as the ever-increasing e-waste of electronic devices and sensors. A key solution to these challenges will be the use of biomaterials and biomimetic systems. One material that has been receiving serious attention for its biomedical and device applications is eumelanin. Eumelanin, or commonly known as melanin, is nature's brown-black pigment and is a poly-indolequinone biopolymer, which possess unique physical and chemical properties for material applications. Presented here is a review, aimed at polymer and other materials scientists, to introduce eumelanin as a potential material for research. Covered here are the chemical and physical structures of melanin, an overview of its unique physical and chemical properties, as well as a wide array of applications, but with an emphasis on device and sensing applications. The review is then finished by introducing interested readers to novel synthetic protocols and post synthesis fabrication techniques to enable a starting point for polymer research in this intriguing and complex material.
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Affiliation(s)
- A Bernardus Mostert
- Department of Chemistry, Swansea University, Singleton Park, Wales SA2 8PP, UK
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Ostrovsky MA, Zak PP, Dontsov AE. Vertebrate Eye Melanosomes and Invertebrate Eye Ommochromes as Screening Cell Organelles. BIOL BULL+ 2019. [DOI: 10.1134/s1062359018060109] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Mostert AB, Rienecker SB, Noble C, Hanson GR, Meredith P. The photoreactive free radical in eumelanin. SCIENCE ADVANCES 2018; 4:eaaq1293. [PMID: 29600273 PMCID: PMC5873843 DOI: 10.1126/sciadv.aaq1293] [Citation(s) in RCA: 52] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/04/2017] [Accepted: 02/13/2018] [Indexed: 05/12/2023]
Abstract
Melanin is the primary photoprotecting pigment in humans as well as being implicated in the development of deadly melanoma. The material also conducts electricity and has thus become a bioelectronic model for proton-to-electron transduction. Central to these phenomena are its spin properties-notably two linked species derived from carbon-centered and semiquinone radicals. Using a novel in situ photoinduced electron paramagnetic resonance technique with simultaneous electrical measurements, we have elucidated for the first time the distinct photoreactivity of the two different radical species. We find that the production of the semiquinone is light- and water-driven, explaining the electrical properties and revealing biologically relevant photoreactivity.
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Affiliation(s)
- Albertus B. Mostert
- Department of Chemistry, Swansea University, Singleton Park, Swansea, Wales SA2 8PP, UK
| | - Shermiyah B. Rienecker
- Centre for Advanced Imaging, University of Queensland, St Lucia, Brisbane, Queensland 4072, Australia
- School of Chemistry and Molecular Biosciences, University of Queensland, St Lucia, Brisbane, Queensland 4072, Australia
| | - Christopher Noble
- Centre for Advanced Imaging, University of Queensland, St Lucia, Brisbane, Queensland 4072, Australia
| | - Graeme R. Hanson
- Centre for Advanced Imaging, University of Queensland, St Lucia, Brisbane, Queensland 4072, Australia
| | - Paul Meredith
- Department of Physics, Swansea University, Singleton Park, Swansea, Wales SA2 8PP, UK
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Effect of UV radiation and hydrogen peroxide on the antiradical and antioxidant activities of DOPA-melanin and melanosomes from retinal pigment epithelial cells. Russ Chem Bull 2016. [DOI: 10.1007/s11172-015-1051-y] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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Mostert AB, Hanson GR, Sarna T, Gentle IR, Powell BJ, Meredith P. Hydration-controlled X-band EPR spectroscopy: a tool for unravelling the complexities of the solid-state free radical in eumelanin. J Phys Chem B 2013; 117:4965-72. [PMID: 23600769 DOI: 10.1021/jp401615e] [Citation(s) in RCA: 69] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Melanin, the human skin pigment, is found everywhere in nature. Recently it has gained significant attention for its potential bioelectronic properties. However, there remain significant obstacles in realizing its electronic potential, in particular, the identity of the solid-state free radical in eumelanin, which has been implicated in charge transport. We have therefore undertaken a hydration-controlled continuous-wave electron paramagnetic resonance study on solid-state eumelanin. Herein we show that the EPR signal from solid-state eumelanin arises predominantly from a carbon-centered radical but with an additional semiquinone free radical component. Furthermore, the spin densities of both of these radicals can be manipulated using water and pH. In the case of the semiquinone radical, the comproportionation reaction governs the pH- and hydration-dependent behavior. In contrast, the mechanism underlying the carbon-centered radical's pH- and hydration-dependent behavior is not clear; consequently, we have proposed a new destacking model in which the intermolecular structure of melanin is disordered due to π-π destacking, brought about by the addition of water or increased pH, which increases the proportion of semiquinone radicals via the comproportionation reaction.
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Affiliation(s)
- A Bernardus Mostert
- Centre for Organic Photonics and Electronics, School of Mathematics and Physics, The University of Queensland, Brisbane, QLD 4072, Australia
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Mostert AB, Powell BJ, Pratt FL, Hanson GR, Sarna T, Gentle IR, Meredith P. Role of semiconductivity and ion transport in the electrical conduction of melanin. Proc Natl Acad Sci U S A 2012; 109:8943-7. [PMID: 22615355 PMCID: PMC3384144 DOI: 10.1073/pnas.1119948109] [Citation(s) in RCA: 264] [Impact Index Per Article: 22.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Melanins are pigmentary macromolecules found throughout the biosphere that, in the 1970s, were discovered to conduct electricity and display bistable switching. Since then, it has been widely believed that melanins are naturally occurring amorphous organic semiconductors. Here, we report electrical conductivity, muon spin relaxation, and electron paramagnetic resonance measurements of melanin as the environmental humidity is varied. We show that hydration of melanin shifts the comproportionation equilibrium so as to dope electrons and protons into the system. This equilibrium defines the relative proportions of hydroxyquinone, semiquinone, and quinone species in the macromolecule. As such, the mechanism explains why melanin at neutral pH only conducts when "wet" and suggests that both carriers play a role in the conductivity. Understanding that melanin is an electronic-ionic hybrid conductor rather than an amorphous organic semiconductor opens exciting possibilities for bioelectronic applications such as ion-to-electron transduction given its biocompatibility.
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Affiliation(s)
- Albertus B. Mostert
- Centre for Organic Photonics and Electronics, School of Mathematics and Physics, University of Queensland, Brisbane St. Lucia QLD 4072, Australia
| | - Benjamin J. Powell
- Centre for Organic Photonics and Electronics, School of Mathematics and Physics, University of Queensland, Brisbane St. Lucia QLD 4072, Australia
| | - Francis L. Pratt
- ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX, United Kingdom
| | - Graeme R. Hanson
- Centre for Advanced Imaging, University of Queensland, Brisbane St. Lucia QLD 4072, Australia
| | - Tadeusz Sarna
- Department of Biophysics, Faculty of Biochemistry, Biophysics, and Biotechnology, Jagiellonian University, 31-007, Krakow, Poland; and
| | - Ian R. Gentle
- Centre for Organic Photonics and Electronics, School of Chemistry and Molecular Biosciences, University of Queensland, Brisbane St. Lucia QLD 4072, Australia
| | - Paul Meredith
- Centre for Organic Photonics and Electronics, School of Mathematics and Physics, University of Queensland, Brisbane St. Lucia QLD 4072, Australia
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Chakraborty DP, Roy S. CHEMICAL AND BIOLOGICAL ASPECTS OF MELANIN. THE ALKALOIDS: CHEMISTRY AND BIOLOGY 2003; 60:345-91. [PMID: 14593860 DOI: 10.1016/s0099-9598(03)60006-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/10/2023]
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SCHOFFA G. Anwendung der Elektronenspinresonanz in der Biologie und Medizin. BIOMED ENG-BIOMED TE 1964. [DOI: 10.1515/bmte.1964.9.1-4.199] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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Reversible free radical generation in the melanin granules of the eye by visible light. Arch Biochem Biophys 1963. [DOI: 10.1016/0003-9861(63)90058-4] [Citation(s) in RCA: 79] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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