Abstract:

Objective To estimate the effects of ginsenoside Rb1 on melanogenesis in human melanocytes and underlying mechanisms. Methods Epidermal melanocytes were obtained from circumcision specimens of children, and subjected to primary culture. After 2 to 5 passages, the melanocytes were treated with different concentrations of ginsenoside Rb1, dimethyl sulfoxide （DMSO, vehicle control）, forskolin at 10 μmol/L （positive control） or remained untreated （blank control）. After additional culture for 72 hours, methyl thiazolyl tetrazolium （MTT） assay and NaOH lysis method were used to evaluate cell viability and melanin content in melanocytes respectively, spectrophotometer to determine dopa oxidase activity of tyrosinase, Western blot to quantify the protein level of tyrosinase, microphthalmia-associated transcription factor （MITF）, phosphorylated and total cAMP response element binding protein （p-CREB and t-CREB） in melanocytes. Results After treatment with ginsenoside Rb1 of 25, 50 and 100 μmol/L for 72 hours, the melanocytes experienced no significant changes in viability （P > 0.05）, but a significant dose-dependent increase in melanin content （112.4% ± 5.7%, 155.7% ± 6.3%, 217.2% ± 11.7% vs. 100%, P < 0.05 or 0.01） and tyrosinase activity（117.9% ± 5.7%, 158.2% ± 9.6%, 182.6% ± 10.0% vs. 100%, P < 0.05 or 0.01） compared with the vehicle control melanocytes. The protein expressions of tyrosinase, MITF and p-CREB were statistically higher in melanocytes treated with ginsenoside Rb1 of 100 μmol/L for 72 hours than in the vehicle control melanocytes （225.4% ± 12.8% vs. 100% ± 7.9%, 313.5% ± 16.7% vs. 100% ± 9.8%, 322.5% ± 21.1% vs. 100% ± 9.1%, all P < 0.01）. The increase in MITF protein expression was inapparent in melanocytes at 8 hours after the treatment with ginsenoside Rb1 of 100 μmol/L, but statistically significant at 24 hours compared with the melanocytes at baseline （P < 0.01）. The pretreatment with H-89 （a selective inhibitor of PKA） at 10 μmol/L, significantly suppressed the ginsenoside Rb1 （100 μmol/L for 72 hours） -induced phosphorylation of CREB, increase in MITF, tyrosinase expression, as well as tyrosinase activity and melanin content in melanocytes （all P < 0.01）. Conclusions Ginsenoside Rb1 could enhance the melanogenesis and tyrosinase activity in normal human melanocytes. The PKA/CREB/MITF/tyrosinase signaling pathway may contribute to the pro-melanogenic effect of ginsenoside Rb1.

Key words: Melanogenesis