[Mechanisms Involved in the Inhibition of Melanin Synthesis by Bushen Quban Granule]

Objective To observe the molecular mechanism of Bushen Quban Granule (BQG) for inhibiting the synthesis of intracellular melanin. Methods Twenty SPF grade female SD rats were di- vided into four groups by completely randomized method, i.e., the control group (fed with normal saline) , high, middle, and low dose BQG groups (administered with BQG at 4. 8, 2. 4, 1. 2 g/kg by gastrogavage, equivalent to 24, 12, and 6 times clinical doses, respectively, twice per day for 3 days in total) , 5 in each group. Drug containing serum was collected. Expressions of melanocortin 1 receptor (MC1 R) , mi- crophthalmia-associated transcription factor ( MITF) , tyrosinase ( TYP) , tyrosinase-related protein I (TYRP1) , and tyrosinase-related protein 2 (TYRP2) at the mRNA level were detected by RT-PCR. Ex- pressions of phosphorylated-extracellular regulated MAP kinasel/2 (p-ERK) , TYP, TYRP1 and TYRP2 at the protein level were detected by Western blot. Intracellular melanin contents were determined by NaOH dissolving method. Activities of tyrosinase were determined by Dopa pigment method, and the cell viability was detected by MTT. Results Compared with the control group, expressions of MC1R, MITF, TYP, TYRP1 and TYRP2 at the mRNA level were down-regulated (P0. 05), and those of TYP, TYRP1 and TYRP2 at the protein level were also down-regulated (P0. 05), intracellular contents of melanin and the activity of tyrosinase decreased (P0. 05) , but the level of p-ERK and the proliferation of cells increased in each medicated group (P0. 05). When ERK was inhibited by its inhibitor PD98059, there was no sta- tistical difference in expressions of MC1 R or MITF at the mRNA level among all medicated groups (P0. 05). Compared with the control group, mRNA expressions of TYP, TYRP1 and TYRP2 decreased in the high dose BQG group (P0. 05), but with no significant difference in protein expressions of p-ERK, TYP, TYRP1 and TYRP2 (P0. 05). There was no statistical difference in the content of melanin, the activity of TYP, or the proliferation of cells between the control group and the high dose BQG group (P0. 05). Con- clusion BQG could inhibit the synthesis of intracellular melanin through up-regulating p-ERK to inhibit the expression of tyrosinase and its related proteins.