Reduction of melanin content and tyrosinase and tyrosinase-related protein gene expression by horsfieldone A and maingayone D

Horsfieldone A and maingayone D purified from Horsfieldia motley, a native plant in Indonesia, were screened in this work. To determine the potential effects of these plant compounds on melanogenesis, their tyrosinase inhibitor (TYR-I) activity was evaluated using in vitro and cellular screening. Melanin content was measured in B16F10 melanoma cells. Altered transcript expression levels of the TYR, TYR-related protein 1 (TRP-1), and TRP 2 (TRP-2) encoding genes were investigated using quantitative real time reverse transcriptase (qrtRT)-PCR in MSH-treated B16F10 melanoma cells, compared to kojic acid as the positive TYR-I control. Horsfieldone A and maingayone D had an effective TYR-I activity against mushroom TYR with the half maximal inhibitory concentration (IC50 value) of 0.294 and 0.020 mM, respectively, compared with kojic acid (IC50 = 0.048 mM). Considering a relative cell viability of less than 80% at a 72-h treatment as cytotoxic, horsfieldone A and maingayone D exhibited cytotoxicity against B16F10 melanoma cells at concentrations of higher than 0.011 and 0.004 mM, whereas the less cytotoxic kojic acid required 1.407 mM, with IC50 values of 0.021, 0.019, and 10.765 mM for horsfieldone A, maingayone D, and kojic acid, respectively. Kojic acid, but neither horsfieldone A nor maingayone D, exhibited significant TYR-I activity, but all three compounds inhibited melanin production efficiently. The qrtRT-PCR assays showed that horsfieldone A reduced transcript levels of TRP-2, kojic acid reduced TRP-1, and maingayone D reduced both TRP-1 and TRP-2, but none of them reduced TYR transcript levels. Thus, horsfieldone A and maingayone D are potential TYR-Is.