Inhibitory Effect of Phlorotannins Isolated from Ecklonia cava on Mushroom Tyrosinase Activity and Melanin Formation in Mouse B16F10 Melanoma Cells

In this study, to assess the feasibility of phlorotannins isolated from Ecklonia cava as an inhibitor of melanin formation, we evaluated its inhibitory effects on mushroom tyrosinase and 3-isobutyl-1-methylxanthine (IBMX)-induced melanin formation inhibitory effects in B16F10 melanoma cell. The ethanolic (EtOH) extract and ethyl acetate (EtOAc) soluble fraction obtained from E cava evidenced a marked inhibitory effect on mushroom tyrosinase at a concentration of 50 mu g/mL. Repeated column chromatography of the active EtOAc fraction resulted in the isolation of three phlorotannins. Their structures were elucidated on the basis of spectroscopic techniques [1D and 2D nuclear magnetic resonance (NMR)] and characterized as phloroglucinol (1), dioxinodehydroeckol (2), and 7-phloroeckol (3), respectively. Among the compounds, 7-phloroeckol (3) evidenced more potent tyrosinase inhibitory effect with an IC50 value of 0.85 mu M than arbutin (IC50 = 243.16 mu M) and kojic acid (IC50 = 40.28 mu M), which were used as positive controls. Lineweaver-Burk plots suggest that 7-phloroeckol plays as a noncompetitive inhibitor against tyrosinase. Furthermore, these compounds were evaluated for their inhibitory effects on IBMX-induced melanin formation in B16F10 melanoma cells. Treatment with 7-phloroeckol (6.25-100 mu M) resulted in a significant inhibition of melanin production in the melanoma cells. In this study, we suggest that 7-phloroeckol might prove useful as a novel inhibitor of melanin formation in cosmetic applications.