Flavonoids, apigenin and icariin exert potent melanogenic activities in murine B16 melanoma cells

We aimed to screen for melanogenic agents among 35 botanical compounds. The compounds were first assessed with regard to their effects on tyrosinase activity in B16 cells. At 100μM, 13 compounds showed tyrosinase activity-enhancing effects, ranging from 2.6 to 372.8% activation. Five of them showed more than 50% enhancement and were further tested for their EC₅₀ values. Compared with 8-Methoxypsoralen, an effective tyrosinase activator with an EC₅₀ of 7.26μM, 3 compounds exhibited smaller EC₅₀ values (apigenin, 0.45μM; hyperosid, 0.92μM; and icariin, 1.01μM for enhancing tyrosinase activity). The 3 compounds significantly increased cellular melanin contents without affecting cell proliferation. Compared with 8-Methoxypsoralen (EC₅₀, 35.94μM for stimulating pigmentation), apigenin (EC₅₀, 17.46μM) and icariin (EC₅₀, 32.77μM) showed better melanogenic activity, while hyperosid (EC₅₀, 70.4μM) was less potent. Western blot analysis demonstrated that the 3 compounds could differentially increase the expression levels of tyrosinase, and tyrosinase-related proteins 1 and 2. Together these data suggest that apigenin and icariin exert potent melanogenic activities through, at least in part, upregulating the protein expression levels of melanogenic enzymes in B16 cells. Thus, further investigations are merited to ascertain their potential application in treating hypopigmentation disorders.