Active constituents from Sophora japonica exhibiting cellular tyrosinase inhibition in human epidermal melanocytes

Aim of the Study: There is greater consumer awareness of plant-based skin-care products. Sophora japonica L. (Fabaceae) has been used traditionally as a hemostatic agent and also has skin-care and whitening benefits. The effect of the isolated active compounds of Sophora japonica L. (Fabaceae) that inhibits tyrosinase activity in human epidermal melanocytes (HEMn) was examined. Materials and methods: We used the mushroom tyrosinase inhibitory assay to isolate active constituents from the extracts. The structures of these constituents were characterized by physical and spectroscopic analyses. Cellular tyrosinase kinetics were analyzed and showed by Lineweaver-Burk plot. Results: A new compound, N-feruloyl-N′-cis-feruloyl-putrescine (8), together with four flavonoids and three putrescine derivatives were obtained after assay-guided isolation of S. japonica. In HEMn, compound 8 was minimally cytotoxic (cell viability >90% at 100 μM) and the IC₅₀ value for suppression of cellular tyrosinase activity was estimated as 85.0 μM. Zymography analysis demonstrated the compound's concentration-dependent effects and the kinetic analysis indicated the compound's mixed-inhibitory action. Conclusions: We concluded that the new compound 8 is the most potent component of S. japonica yet discovered. Its pigment inhibition activity may be exploitable cosmetically.