In vitro inhibitory effect of sulfated galactans isolated from red alga Gracilaria fisheri on melanogenesis in B16F10 melanoma cells

Hyperpigmentation of the skin results from excessive melanin formation in melanocytes, and overproduction of melanin frequently leads to melanoma. The aim of this study was to investigate the potential of sulfated galactans (SG) from Gracilaria fisheri to inhibit melanin formation or melanogenesis. Cellular and molecular mechanisms of inhibition were also investigated. SG was evaluated in vitro for its inhibitory effect on mushroom tyrosinase activity, cell-free tyrosinase activity, and cellular tyrosinase activity. B16F10 mouse melanoma cells were cultured with SG and their tyrosinase activity and melanin content was compared with kojic acid, a known tyrosinase inhibitor. Moreover, the levels of expression of melanogenesis-related genes and proteins were determined by quantitative RT-PCR and enzyme-linked immunosorbent assay (ELISA), respectively. The result showed that SG had no inhibitory effect on mushroom tyrosinase activity and cell-free tyrosinase activity. However, SG significantly suppressed cellular tyrosinase activity and melanin production in B16F10 melanoma cells without any apparent cytotoxicity. Quantitative RT-PCR and ELISA revealed that SG downregulated the expression of microphthalmia-associated transcription factor (MITF), tyrosinase-related protein-1 (TRP-1), tyrosinase-related protein-2 (TRP-2), and tyrosinase mRNA and proteins. Taken together, the data suggest that SG may act as an anti-melanogenic agent by inhibiting the expression of MITF and cellular tyrosinase activity. SG may show potential as an ingredient in skin-whitening cosmetics or as a topical agent for the treatment of hyperpigmentation disorders.