title: Roles of reactive oxygen species in UVA-induced oxidation of 5,6-dihydroxyindole-2-carboxylic acid-melanin as studied by differential spectrophotometric method.
abstract: Eumelanin photoprotects pigmented tissues from ultraviolet (UV) damage. However, UVA-induced tanning seems to result from the photooxidation of preexisting melanin and does not contribute to photoprotection. We investigated the mechanism of UVA-induced degradation of 5,6-dihydroxyindole-2-carboxylic acid (DHICA)-melanin taking advantage of its solubility in a neutral buffer and using a differential spectrophotometric method to detect subtle changes in its structure. Our methodology is suitable for examining the effects of various agents that interact with reactive oxygen species (ROS) to determine how ROS is involved in the UVA-induced oxidative modifications. The results show that UVA radiation induces the oxidation of DHICA to indole-5,6-quinone-2-carboxylic acid in eumelanin, which is then cleaved to form a photodegraded, pyrrolic moiety and finally to form free pyrrole-2,3,5-tricarboxylic acid. The possible involvement of superoxide radical and singlet oxygen in the oxidation was suggested. The generation and quenching of singlet oxygen by DHICA-melanin was confirmed by direct measurements of singlet oxygen phosphorescence.
authors.affiliation: Department of Chemistry, Fujita Health University School of Health Sciences, Toyoake, Aichi, Japan.
authors.forename: Shosuke
authors.initials: S
authors.lastname: Ito
authors.affiliation: Department of Chemistry, Fujita Health University School of Health Sciences, Toyoake, Aichi, Japan.
authors.forename: Marina
authors.initials: M
authors.lastname: Kikuta
authors.affiliation: Department of Chemistry, Fujita Health University School of Health Sciences, Toyoake, Aichi, Japan.
authors.forename: Shota
authors.initials: S
authors.lastname: Koike
authors.affiliation: Department of Biophysics, Faculty of Biochemistry, Biophysics, and Biotechnology, Jagiellonian University, Krakow, Poland.
authors.forename: Grzegorz
authors.initials: G
authors.lastname: Szewczyk
authors.affiliation: Department of Biophysics, Faculty of Biochemistry, Biophysics, and Biotechnology, Jagiellonian University, Krakow, Poland.
authors.forename: Michal
authors.initials: M
authors.lastname: Sarna
authors.affiliation: Department of Biophysics, Faculty of Biochemistry, Biophysics, and Biotechnology, Jagiellonian University, Krakow, Poland.
authors.forename: Andrzej
authors.initials: A
authors.lastname: Zadlo
authors.affiliation: Department of Biophysics, Faculty of Biochemistry, Biophysics, and Biotechnology, Jagiellonian University, Krakow, Poland.
authors.forename: Tadeusz
authors.initials: T
authors.lastname: Sarna
authors.affiliation: Department of Chemistry, Fujita Health University School of Health Sciences, Toyoake, Aichi, Japan.
authors.forename: Kazumasa
authors.initials: K
authors.lastname: Wakamatsu
mesh_terms: D000818:Animals; D001205:Ascorbic Acid / Q000494:pharmacology; D001894:Borohydrides / Q000494:pharmacology; D002417:Cattle; D006861:Hydrogen Peroxide / Q000494:pharmacology; D007211:Indoles / Q000737:chemistry* / Q000528:radiation effects; D049449:Luminescence; D008543:Melanins / Q000737:chemistry* / Q000528:radiation effects; D010084:Oxidation-Reduction / Q000187:drug effects / Q000528:radiation effects; D017382:Reactive Oxygen Species / Q000378:metabolism*; D026082:Singlet Oxygen / Q000378:metabolism; D013053:Spectrophotometry / Q000379:methods*; D019265:Spectroscopy, Near-Infrared; D013997:Time Factors; D014466:Ultraviolet Rays
chemical_list: D001894:Borohydrides; D007211:Indoles; D008543:Melanins; D017382:Reactive Oxygen Species; C461099:dihydroxyindole-melanin; D026082:Singlet Oxygen; C030692:5,6-dihydroxy-2-indolylcarboxylic acid; C025364:sodium borohydride; D006861:Hydrogen Peroxide; D001205:Ascorbic Acid
keywords: 5,6-dihydroxyindole-2-carboxylic acid; UVA; eumelanin; reactive oxygen species; singlet oxygen