Redox Activities of Melanins Investigated by Electrochemical Reverse Engineering: Implications for their Roles in Oxidative Stress

Melanins, the main epidermal pigments of man, have been viewed traditionally as performing photo-protective and antioxidant functions, yet increasing evidence indicates they also possess detrimental prooxidant activities. Understanding this duality in functional activity (anti- vs. pro-oxidant) is important because oxidative stress is believed to play a central role in melanoma pathophysiology. Here, we review current knowledge of melanin's structure and functional activities and their relevance to redox biology and oxidative stress. We especially focus on recent efforts to develop an in vitro experimental methodology to characterize melanin's redox activities and suggest the implications of these in vitro observations.