Comparative Evaluation of Antityrosinase and Antioxidant Activities of Dietary Phenolics and their Activities in Melanoma Cells Exposed to UVA

Background: Dietary phenolics have been shown to possess antityrosinase and antioxidant properties which account for their pharmacological effect against ultraviolet (UV)-mediated skin pigmentation. Hence, this study assessed the correlation between antityrosinase and antioxidant activities of various phenolic acids including caffeic acid (CA), ferulic acid (FA), gallic acid (GA), p-coumaric acid (PA) and quercetin using cell-free systems including mushroom tyrosinase and DPPH (1,1-diphenyl-2-picrylhydrazyl) assays and human melanoma (G361) cell culture model. Methods: Antityrosinase and free radical (FR) scavenging activities of all test phenolics were determined using mushroom tyrosinase and DPPH assays, respectively. Inhibition of cellular melanogenesis with regard to regulation of intracellular oxidant formation and glutathione (GSH) content was assessed in UVA-irradiated G361 melanoma cells. Results: The IC30 values for the mushroom tyrosinase inhibition activity showed a rank order of quercetin ≈ PA > kojic acid (KA) ≈ CA ≈ FA > GA. For the FR scavenging activity, IC30 values demonstrated a rank order of GA ≈ CA ≈ FA > quercetin > PA ≈ KA. In addition, both CA and FA were observed to suppress UVA-induced tyrosinase activity and melanin content in G361 cells, although CA exerted greater antimelanogenic effect than FA. Pretreatment with CA was also able to reduce oxidant generation and restore GSH content in irradiated cells. Conclusion: Cell-free systems showed that antityrosinase activity of test phenolics was not associated with their FR scaven-ging activity. Moreover, we have herein reported the correlation between depigmenting effect and antioxidant action of CA in G361 cells. Keywords: Phenolic acids, antioxidant, tyrosinase, melanogenesis, glutathione Siriraj Med J 2014;66:5-10