Inhibition of Melanogenesis by Some Well-Known Polyphenolics: A Review

Melanogenesis is simply defined as the production of melanin in melanosomes by melanocytes through a complex process. Melanin, a pigment derived from L-tyrosine, comes into two forms, namely eumelanin (brownish to black) and pheomelanin (red to yellow). Melanin synthesis starts via the hydroxylation of L-tyrosine to L-3,4-Dihydroxyphenylalanine (DOPA) catalyzed by the enzyme known as Tyrosinase (TYR), which triggers further conversion reaction to DOPAquinone and then to DOPAchrome. Additionally, this process is also related to two more proteins, i.e., oxygenase TYR-related Protein 1 (TYRP1), and Dopachrome Tautomerase TYRP2 (or DCT). However, TYR located in the melanosomal membrane still stands as the key enzyme to initiate the whole process of melanogenesis. Due to some deficits, melanogenesis may emerge as hypo- or hyperpigmentation in the skin. High production of melanin in melanocytes leads to hyperpigmentation- related skin disorders, including freckles, melasma, melanoma, etc., that may cause displeasure in personal appearance and reduce quality of life. Consequently, several melanogenesis inhibitors of synthetic and natural origins have been developed up to date, though most of them have been reported with serious side effects. For this reason, extensive research is still going on to find novel and more effective melanogenesis inhibitors with less side effects. In this sense, particularly flavonoids, catechins, and stilbenes from plants have been a hope to discover new inhibitors which gain significant attention from scientists. In this review, promising natural products effective in melanogenesis inhibition will be scrutinized.