Objective: To investigate the potential mechanism of betulin in treatment of chloasma. Method: The A375 cell lines in logarithmic phase were cultured for 24 hours

and then the liquid was discarded. The cultured cells were divided and added with different concentrations of 200 μL drug liquid

and then divided into blank group

estradiol group (1×10-3 μmol·L-1 estradiol)

betulin group (at set concentration)

with 6 wells in each group. A375 cells were treated with betulin and then methyl thiazdyl tetrazolium(MTT) assay was used to detect cells activity;NaOH schizolysis method and L-dopa oxidation method were respectively used to detect amount of melanin and the activity of tyrosinase (TYR). Reverse transcription-polymerase chain reaction(RT-PCR) was applied to measure the expression levels of tyrosinase (TYR)

tyrosinase related protein-1 (TRP-1) and tyrosinase related protein-2 (TRP-2)

as well as the mRNA expression levels of the key protein kinases ERK1

ERK2 and JNK2 in MAPK signal pathways. Result: As compared with the blank group

betulin of 1

1×10-1

1×10-2

1×10-3 μmol·L-1 can significantly inhibit melanin formation of A375 cells and activity of tyrosinase (TYR);betulin of 1 μmol·L-1 can significantly down-regulate mRNA expression levels of TYR

TRP-1

TRP-2 as well as ERK1

ERK2 and JNK2 (P < 0.05

P < 0.01). Conclusion: Betulin can inhibit the melanogenesis of A375 cells probably by inhibiting TYR activity and/or down-regulating TYR

TRP-1 and TRP-2 mRNA expression levels

and this effect may be associated with inhibition of the expression of ERK1

ERK2 and JNK2 levels.