The Late Stages of Melanogenesis: Exploring the Chemical Facets and the Application Opportunities

Abstract

In the last decade, the late stages of melanin biosynthesis involving the oxidative polymerization of 5,6-dihydroxyindole (DHI) and 5,6-dihydroxyindole-2-carboxylic acid (DHICA) have been extensively investigated. Most of the information derived from a biomimetic approach in which the oxidation of melanogenic indoles was carried out under conditions mimicking those occurring in the biological environment. Characterization of the early oligomers allowed for drawing a structural picture of DHI and DHICA melanins, providing also an interpretative basis for the different properties exhibited by these pigments, e.g., the chromophore and the antioxidant ability. The improved knowledge has opened new perspectives toward the exploitation of the unique chemistry of melanins and its precursors in cosmetic and health care applications. A noticeable example is the development of an innovative hair dyeing system that is based on the marked ease of DHI to give rise to black melanin on air oxidation under slightly alkaline conditions. The advantage of this method for a step-wise coverage of gray hair with a natural shade pigmentation on repeated treatment with a DHI-based formulation with respect to traditional dyes is presented. A variant of DHICA melanin combining solubility in water-miscible organic solvents, an intense chromophore in the UltraViolet-A UV-A region, and a marked antioxidant potency was evaluated as an ingredient for cosmetic formulations.

Natural and Bioinspired Phenolic Compounds as Tyrosinase Inhibitors for the Treatment of Skin Hyperpigmentation: Recent Advances

“…Tyrosinase related protein 1 (TRP-1) is believed to catalyze the oxidation of DHICA to melanin. Although all the three enzymes, tyrosinase, TRP-1, and TRP-2 are involved in the melanogenesis pathway, tyrosinase is exclusively necessary for melanogenesis [11,[23][24][25][26][27][28][29][30].…”

Photoprotection and Skin Pigmentation: Melanin-Related Molecules and Some Other New Agents Obtained from Natural Sources

“…In addition to the enzymatic activity, TRP1 is also a stabilizing protein for tyrosinase, as its role is still unclear depending on the metal cofactor found at the active site [14,15]. DHI as well DHICA can be oxidized in the absence of any enzyme to their respective o-quinones by oxygen and ROS generated during previous reactions [16]. In any case, eumelanin is basically a polymer with mixture of decarboxylated (DHI) and carboxylated (DHICA) 5,6-oxygenated indole units at different oxidation degrees (5,6-dihydroxy, semiquinone and 5,6-quinone units).…”

“…Alternatively, in the last years, other melanin-related compounds have been proposed to increase the absorption and general properties of natural melanin in order to be used in cosmeceutics. In this regard, in exploring the maintenance role of the carboxyl group in polymers, studies revealed that the use of DHICA methyl ester improves the antioxidant and protective effects of the final polymer, particularly by the higher absorption of UVA light [16,44].…”

A Melanin-Related Phenolic Polymer with Potent Photoprotective and Antioxidant Activities for Dermo-Cosmetic Applications

“…Melanins are the primary determinants of skin, hair and exoskeletal pigmentation in mammals, birds and insects [1][2][3][4][5][6], and their importance has been growing over the past few years not only from a biological point of view, related to their role in the human body, but also for the exploitation of their unique properties in biomedicine or in the cosmetic and health sectors [7][8][9][10][11][12][13][14][15][16]. These pigments are biosynthesized in melanocytes, starting with the oxidation of tyrosine to dopaquinone catalyzed by the enzyme tyrosinase ( Figure 1) [1,17,18].…”