Effects of the melanogenic inhibitor, uracil, derived from Lactobacillus plantarum TWK10-fermented soy milk on anti-melanogenesis in B16F0 mouse melanoma cells

The anti-melanogenic ingredient from aqueous extracts of soy milk fermented by Lactobacillus plantarum TWK10 (TWK10) was isolated and identified as uracil. In addition, the mechanism by which uracil inhibits melanogenesis in α-melanocyte stimulating hormone (α-MSH)-stimulated B16 melanoma cells was investigated. Concentrations of uracil less than 100 µg/mL had no cytotoxic effect on α-MSH-stimulated B16 melanoma cells, nor any effect on their cell cycle distribution, but did reduce melanin content in the cells. The mechanisms by which uracil inhibited melanin production included down-regulating the transcription of the gene encoding melanocortin 1 receptor, decreasing the phosphorylation of cyclic adenosine monophosphate response element-binding protein, and repressing the expression of microphthalmia-associated transcription factor (MITF). In addition, a uracil-mediated suppression of phosphorylation of p38 mitogen-activated protein kinase, leading to concomitant decrease in MITF levels, was observed. The reduction in MITF levels leads to decreases in the expression of tyrosinase, tyrosinase-related protein-1, and tyrosinase-related protein-2, resulting in lower melanin production in α-MSH-stimulated B16 melanoma cells. These results indicate that uracil, derived from aqueous extracts of TWK10-fermented soy milk, is a substance that is safe to use on B16 melanoma cells and has anti-melanogenic effects. It may be used to develop functional foods and cosmetics, and to increase the range of applications of traditional agricultural products.