Abstract
Gallic acid is one of the major flavonoids found in plants. It acts as an antioxidant, and seems to have anti-inflammatory, anti-viral, and anti-cancer properties. In this study, we investigated the effects of gallic acid on melanogenesis, including the activation of melanogenesis signaling pathways. Gallic acid significantly inhibited both melanin synthesis and tyrosinase activity in a dose- and time-dependent manner, and decreased the expression of melanogenesis-related proteins, such as microphthalmia-associated transcription factor (MITF), tyrosinase, tyrosinase-related protein-1 (TRP1), and dopachrome tautomerase (Dct). In addition, gallic acid also acts by phosphorylating and activating melanogenesis inhibitory proteins such as Akt and mitogen-activated protein kinase (MEK)/extracellular signal-regulated kinase (ERK). Using inhibitors against PI3K/Akt (LY294002) or MEK/ERK-specific (PD98059), the hypopigmentation effect was suppressed, and the gallic acid-initiated activation of MEK/ERK and PI3K/Akt was also revoked. Gallic acid also increased GSK3β and p-β-catenin expression but down-regulated p-GSK3β. Moreover, GSK3β-specific inhibitor (SB216763) restored gallic acid-induced melanin reduction. These results suggest that activation of the MEK/ERK, PI3K/Akt, and inhibition of Wnt/β-catenin signaling pathways is involved in the melanogenesis signaling cascade, and that activation by gallic acid reduces melanin synthesis via down-regulation of MITF and its downstream signaling pathway. In conclusion, gallic acid may be a potentially agent for the treatment of certain skin conditions.
Highlights
Melanocytes are located in the basal layer of the epidermis and are responsible for producing melanin, a substance that gives skin and hair their pigments
The results indicated that gallic acid was slightly cytotoxic to B16F10 cells at a concentration higher than 200 μM (Figure 1)
Tyrosinase activity staining, tyrosinase activity and cellular melanin contents were dose-dependently decreased by exposure to gallic acid. These results suggested that gallic acid has inhibitory effects on melanin synthesis through regulating tyrosinase and subsequently inhibiting melanin synthesis in B16F10 cells
Summary
Melanocytes are located in the basal layer of the epidermis and are responsible for producing melanin, a substance that gives skin and hair their pigments. Abnormal melanogenesis causes pigmentary disorders, including medical conditions such as hypopigmentation (vitiligo and albinism) or hyperpigmentation (solar lentigo, chlosma, and freckles) [2]. The expression and activation of tyrosinase is important in the control of melanogenesis, since it acts as the catalyst in the rate limiting reaction of the melanogenic pathway [3]. Inhibitors of tyrosinase have been used in skin-whitening and cosmetic products. Melanin synthesis is activated by several signal transduction pathways, including the cAMP-mediated pathway, which plays an important role in melanogenesis regulation [4]
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