Melanogenesis Inhibitors: Strategies for Searching for and Evaluation of Active Compounds

Hyperpigmentation disorders constitute important medical and aesthetical conditions. Dark areas or dark spots on the skin result from inappropriate amount and/or deposition of skin pigments - melanins. Several depigmenting agents, such as kojic acid, arbutin, aloesin, ellagic acid, resveratrol, azelaic acid, niacinamide, tretinoin, glycolic acid, lactic acid, and citric acid, have already been identified and are used in topical drugs or cosmetic formulations for the treatment of hyperpigmentations. However, these compounds are characterized by insufficient effectiveness and multiple adverse effects. As a result, there is still a need for searching for new active substances. The current paper summarizes strategies for searching for novel melanogenesis inhibitors. In the review, they are divided according to approach, into in silico, in vitro and in vivo experiments. In silico research includes computational studies with models of tyrosinase and di-copper complexes. The in vitro approach is based on tests using tyrosinase (a key enzyme in melanin biosynthesis), cell cultures, cell co-cultures, pigmented human skin equivalents or Streptomyces bikiniensis model. In vivo studies involve zebrafish, rodents or humans. Examples of protocols and laboratory procedures are presented, with a focus on utilization of various models for evaluation of mechanisms of action of tested compounds. The potential limitations of the methods are also discussed, together with future perspectives in the field of searching for melanogenesis inhibitors.