Modulating the γ-ray Protection Properties of Melanin via a Highly Conjugated Catechol Structure

Melanin is a dark pigment found in many organisms that interacts with various forms of electromagnetic radiation, such as X-rays, γ-rays, and Ultraviolet visible light, providing protection against radiation damage to the host. The mechanism by which melanin protects against ionizing radiation involves dissipating energy around the cell nucleus to form a perinuclear cap. Additionally, melanin reacts with the free radicals produced by the radiolysis of water, quenching reactive oxygen species. In this study, we introduced a conjugated monomer, hexahydroxytriphenylene (HHTP), which has a rigid planar structure, into selenomelanin. The aim was to increase the physical shielding ability of selenomelanin while increasing its free radical content. Our findings indicated that incorporating HHTP molecules into selenomelanin effectively increased the unpaired electron content of selenomelanin and protected immortalized human keratinocyte (HaCaT) cells from 10 Gy γ-rays exposure. Additionally, eumelanin supplemented with HHTP molecules demonstrated excellent biocompatibility and offered similar protection to HaCaT cells exposed to 10 Gy γ-rays at high concentrations. This study is important for optimizing the functionality of melanin through the modulation of its conjugated structure.