Role of Amyloid Fibrils in Enhancing the Protective Properties of Microbial Melanin against Oxidative Stress, UV Damage, and AGE-Related Cytotoxicity in Human Keratinocytes.

The biological properties of microbial melanins, whose structures resemble those of animal-derived eumelanin pigments, have been poorly investigated in mammalian cell systems, as well as the role of amyloid fibrils in modulating melanin activities. Indeed, although amyloid fibrils are known to be crucial in the melanogenesis process, their functional role is not fully understood. In this study, we have investigated, for the first time, the ability of a microbial eumelanin, biotechnologically produced and purified by Streptomyces nashvillensis DSM 40314, to act as a protective agent against oxidative stress, UV radiation damage, and cytotoxicity associated with advanced glycation end products (AGEs) in a human keratinocyte cell model. Also, the effect of amyloid fibrils on the structural and biological properties of microbial melanin has been investigated for the first time, and the results indicated that the addition of an amyloid scaffold promotes an increase of melanin antioxidant activity and provides greater cellular protection against UV irradiation and AGE-induced cytotoxicity, key events associated with skin damage and aging. This study provides new insights into the functional role of amyloid in enhancing the protective properties of biotechnologically produced microbial melanin, highlighting its potential as a substitute for animal-derived eumelanin.