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 100 μM, 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 EC(50) values. Compared with 8-Methoxypsoralen, an effective tyrosinase activator with an EC(50) of 7.26 μM, 3 compounds exhibited smaller EC(50) values (apigenin, 0.45 μM; hyperosid, 0.92 μM; and icariin, 1.01 μM for enhancing tyrosinase activity). The 3 compounds significantly increased cellular melanin contents without affecting cell proliferation. Compared with 8-Methoxypsoralen (EC(50), 35.94 μM for stimulating pigmentation), apigenin (EC(50), 17.46 μM) and icariin (EC(50), 32.77 μM) showed better melanogenic activity, while hyperosid (EC(50), 70.4 μM) 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.
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