Antimelanogenic effects of the novel melanogenic inhibitors daidzein and equol, derived from soymilk fermented with Lactobacillus plantarum strain TWK10, in B16F0 mouse melanoma cells

Melanin functions to protect the skin; however, excessive production of melanin can cause hyperpigmentation. The antimelanogenic effects of daidzein and its microbial metabolite, equol, and the mechanisms through which they inhibit melanogenesis in B16 melanoma cells were investigated. At concentrations of less than 50 and 40 µM, respectively, daidzein and equol had no cytotoxic effects on B16 melanoma cells stimulated with α-melanocyte-stimulating hormone (α-MSH). Daidzein and equol reduced melanin content in these cells by downregulating the transcription of genes encoding melanocortin 1 receptor. Additionally, these compounds interfered with the phosphorylation of p38 mitogen-activated protein kinase and induced the phosphorylation of extracellular signal-regulated kinase 1/2 and glycogen synthase kinase 3β. Moreover, daidzein and equol decreased the expression of tyrosinase, TRP-1, and TRP-2, thereby blocking melanin production in α-MSH-stimulated B16 melanoma cells. In conclusion, daidzein and equol were noncytotoxic in B16 melanoma cells and exerted antimelanogenic effects. The functions of these bioactive compounds in fermented soymilk were confirmed, and they may be useful for developing functional foods and cosmetics, extending the range of applications of crops containing them.