Whitening Effect of Storage Protein 2 from Silkworm Hemolymph

This study investigated the effects of silkworm hemolymph-derived storage protein 2 (SP2) on the whitening process in mouse B16F1 melanoma cells. After the cells were treated with various concentrations of SP2 (0.1 - 1.0 mg/mL), cytotoxicity, melanin contents, and differences in mRNA and protein expression associated with melanogenesis were observed. No cytotoxicity was observed when cells were treated with SP2, even with increased SP2 concentrations of up to 2.0 mg/mL. When treated with various SP2 concentrations in the cells, the protein and mRNA expression of tyrosinase were dose-dependently decreased, respectively, and inhibition of tyrosinase was further increased by 50.0% with increasing SP2 concentration of 1.0 mg/mL. Expression mRNAs coding tyrosinase related protein-1 and protein-2 (TRP-1 and TRP-2) was also significantly decreased in a dose dependent manner. When measuring the melanin content in melanoma cells, SP2 at 1 mg/mL inhibited melanin synthesis by 73.5% compared with non-treated cells. The inhibitory effect was 2.8-fold higher than that obtained using arbutin as a positive control. This study demonstrates that SP2, as a whitening material, is capable of suppressing melanin synthesis through the downregulation of proteins and genes in the melanin biosynthesis pathway.