Abstract: Objective To study the effects of tyrosol and oleanolic acid, two monomers of Fructus Ligustri Lucidi on the proliferation, tyrosinase activity and melanogenesis of cultured human melanocytes. Methods The cell proliferation was detected by MTT assay, the tyrosinase activity by dopa oxidase assay, the melanin content by NaOH-assay, and the mRNA level of tyrosinase (TYR) and tyrosinase related protein-1 (TRP-1) by RT-PCR. Results Incubation of tyrosol with cultured human melanocytes for 72 hours resulted in a significant stimulation of the tyrosinase activity and melanogenesis in a dose dependent manner. Compared with those in the cells without any treatment, the TYR and TRP-1 mRNA levels in the tyrosol-treated cells increased by 39.10% and 99.26%, respectively. Oleanolic acid also increased tyrosinase activity (P<0.01) and melanogenesis (P<0.05), and compared with those in the cells pretreated with absolute alcohol, the mRNA levels of TYR and TRP-1 in the cells pretreated with oleanolic acid increased by 31.88% and 17.73%, respectively. Conclusion The results suggest that tyrosol and oleanolic acid may stimulate tyrosinase activity and melanogenesis of cultured human melanocytes by upregulating the mRNA expression of TYR and TRP-1, and the two monomers may be the main active agents for the effects of Fructus Ligustri Lucidi on melanocytes.

Key words: Oleanolic acid, Ligustrum, Tyrosol, Melanocyte