Ito Shosuke, Kikuta Marina, Koike Shota, Szewczyk Grzegorz, Sarna Michal, Zadlo Andrzej, Sarna Tadeusz, Wakamatsu Kazumasa
Department of Chemistry, Fujita Health University School of Health Sciences, Toyoake, Aichi, Japan.
Department of Biophysics, Faculty of Biochemistry, Biophysics, and Biotechnology, Jagiellonian University, Krakow, Poland.
Pigment Cell Melanoma Res. 2016 May;29(3):340-51. doi: 10.1111/pcmr.12469.
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.
真黑素可保护色素沉着组织免受紫外线（UV）损伤。然而，UVA诱导的晒黑似乎源于已有黑色素的光氧化作用，且无助于光保护。我们利用5,6 - 二羟基吲哚 - 2 - 羧酸（DHICA） - 黑色素在中性缓冲液中的溶解性，并采用差示分光光度法检测其结构的细微变化，研究了UVA诱导的DHICA - 黑色素降解机制。我们的方法适用于检测与活性氧（ROS）相互作用的各种试剂的效果，以确定ROS如何参与UVA诱导的氧化修饰。结果表明，UVA辐射可诱导真黑素中的DHICA氧化为吲哚 - 5,6 - 醌 - 2 - 羧酸，然后该物质被裂解形成光降解的吡咯部分，最终形成游离的吡咯 - 2,3,5 - 三羧酸。研究表明超氧自由基和单线态氧可能参与了氧化过程。通过直接测量单线态氧磷光证实了DHICA - 黑色素对单线态氧的产生和猝灭作用。
