The anti-melanogenic activity of essential oils of Alpinia nantoensis and their bioactive ingredients were investigated in vitro. Treatment with leaf (LEO) and rhizome (REO) essential oils of A. nantoensis, significantly reduced forskolin-induced melanin production followed by down-regulation of tyrosinase (TYR) and tyrosinase related protein-1 (TRP-1) expression at both transcriptional and translational levels. Further studies revealed that down-regulation TYR and TRP-1 were caused by LEO/REO-mediated suppression of Microphthalmia-associated transcription factor (MITF), as evidenced by reduced nuclear translocation of MITF. Also, we found that LEO/REO induce the sustained activation of ERK1/2, which facilitate subsequent proteasomal degradation of MITF, as confirmed by that LEO/REO failed to inhibits MITF activity in ERK1/2 inhibitor treated cells. In addition, a significant increase of ubiquitinated MITF was observed after treatment with LEO and REO. Furthermore, the chemical composition of LEO and REO were characterized by gas chromatography-mass spectrometry (GC-MS) resulted that camphor, camphene, α-pinene, β-pinene, isoborneol and D-limonene were the major compounds in both LEO and REO. Further studies revealed that α-pinene and D-limonene were the active components responsible for the anti-melanogenic properties of LEO and REO. Based on the results, this study provided a strong evidence that LEO and REO could be promising natural sources for the development of novel skin-whitening agents for the cosmetic purposes.

Calocedrus formosana (Cupressaceae) is one of the five precious woods of Taiwan. In this study, we investigated the anti-melanogenic activity of C. formosana wood essential oil (CFEO) and its bioactive components in vitro. Initially, CFEO exhibited strong mushroom tyrosinase activity in the cell-free mushroom tyrosinase assay system with an IC50 value of 2.72 µg/mL. Next, treatment with CFEO significantly as well as dose-dependently reduced a combination of a-melanocyte-stimulating hormone and forskolin (a-MSH-FSK)-induced melanin synthesis in B16-F10 cells. Indeed, 80 mg/mL CFEO completely inhibited melanin production, which is similar to that of control cells. Further studies revealed that treatment with CFEO significantly inhibited melanogenesis regulatory proteins, including TRP-1, TRP-2, and MITF, whereas tyrosinase was unaffected by either a-MSH-FSK or CFEO. In addition, the composition of the CFEO was characterized. The major components of CFEO were α-terpineol (23.47%), shonanic acid (10.45%), terpinen-4-ol (12.23%), thymol (5.3%), piperitone (3.44%), berbenone (2.81%), thujic acid (1.65%), and chaminic acid (0.13%). Among them, shonanic acid (1), thujic acid (2), and chaminic acid (3) were uncommon constitutes in essential oils, which could be the index compounds of CFEO, and the structure of these compounds were confirmed by spectral analysis. Furthermore, we found that thymol is an active ingredient responsible for CFEO’s anti-melanogenic activity. Based on these results, we suggest that CFEO or thymol could be a potential candidate for the development of skin whitening products for cosmetic purposes.