Anti-pigmentation effect of serotonin alkaloid isolated from Korean barnyard millet (Echinochola utilis)

Investigation of the melanogenesis inhibitory effect of barnyard millet grain extracts (BME) led to isolation of compounds against mushroom tyrosinase and B16 melanoma cells. Chromatography yielded five phenolic compounds, among which n-p-coumaroyl serotonin (1, CS) exhibited potent non-competitive inhibition (IC50 =8.8 μM) compared with that of kojic acid (IC50=14.6 μM) against mushroom tyrosinase. More importantly, CS decreased melanin content to eight times lower (IC50 =11.6 μM) in B16 melanocytes than that of feruloyl serotonin (2, FS, IC50 =86.5 μM) without cytotoxicity. CS significantly inhibited the protein expression of tyrosinase, tyrosinase-related protein-1 (TRP-1), TRP-2, and microphthalmia-associated transcription factor using immunoblotting. Furthermore, molecular docking simulations were also carried out to investigate the structure related to the inhibitory activities. Therefore, BME can be used as a natural source of depigmentation to prevent melanogenesis.