INHIBITORY EFFECTS OF N-FERULOYLDOPAMINE 139 ACTIVITY OF N-FERULOYLDOPAMINE ON MELANOSOME MATURATION GENES After 48 h of incubation with N-feruloyldopamine, Protein P mRNA expression re- mained unchanged as measured using qRT-PCR methods. On the other hand, MART-1, described as a chaperone protein for Pmel17, was moderately decreased (data not shown). Finally, incubation with N-feruloyldopamine signifi cantly decreased Pmel17 mRNA expression in a dose-related manner with a statistically signifi cant 53% decrease when used at 100 μM (Figure 6) (p 0.05 Dunn’s procedure). DISCUSSION Tyrosinase catalyzes the fi rst two limiting steps of melanogenesis. It is thus the most often targeted protein for melanogenesis inhibition purposes. In our research program Figure 2. Cell viability assay. MTT assay of (A) NHEMs. (B) B16-F10 cells. Mean ± SD, n = 6. *, **Statistically signifi cant vs. untreated control, p 0.05 and p 0.01, respectively.

JOURNAL OF COSMETIC SCIENCE 140 to identify a novel tyrosinase inhibitor, we decided to screen compounds combining the structural features known to participate in the interaction between tyrosinase and its substrates or inhibitors. This way, we have selected N-feruloyldopamine as the most potent substrate-mimicking inhibitor of tyrosinase. N-feruloyldopamine has been previously isolated from Atraphaxis spinosa (22) with poor yield. We used organic synthesis to obtain this molecule in suffi cient amounts to evaluate its melanogenesis inhibition abilities in vitro. Results show that N-feruloyldopamine exerted 45% inhibition when used at 30 μM in cultured NHEMs. Using linear regression, the IC50 of N-feruloyldopamine in this model was evaluated at 48.3μM (% inhibition = −0.8042 × [N-feruloyldopamine] + 90.698 R2 = 0.9068). Contrarily, N-feruloyldopamine did not exert any inhibitory effect toward Figure 3. Measurement of (A) human and (B) mushroom tyrosinase activities. Mean ± SD, n = 6. **, ***Statistically signifi cant vs. untreated control, p 0.01 and p 0.001, respectively.