Comparison of antioxidant and anti-melanogenic activity of γ-oryzanol and gallic acid by inhibiting tyrosinase activity in B16F10 mouse melanoma cells

Abstract

Abstract The beneficial effects of rice bran consumption must consider the synergic interaction of all these bioactive constituents. Rice bran is abundant in gallic acid due to the tannins which upon hydrolysis yields gallic acid. Also, hydroxycinnamic acids such as ferulic, p-coumaric and caffeic acids were also found in the extracts. γ-Oryzanol comprises a mixture of ferulic acid esters and phytosterols (sterols and triterpenic alcohols). At least 10 steryl ferulates were determined in γ-oryzanol. To better understand the mechanisms of the two important bioactive compounds of rice bran, we compared the antioxidant and anti melanogenic activities of gallic acid and γ-oryzanol for the treatment of disorders caused by hyperpigmentation. The antioxidant activity was measured by 2, 2′-diphenyl-1-picrylhydrazyl radical (DPPH) and ferric reducing antioxidant power (FRAP) methods. Then, its effects on viability, reactive oxygen species (ROS) production, mushroom tyrosinase and melanin content as well as amount of MITF and tyrosinase proteins was investigated on B16F10 murine melanoma cell line. The antioxidant effects of were γ-oryzanol higher than gallic acid in DPPH and FRAP tests. Concentrations of 0.001 to 100 μM γ-oryzanol and gallic acid did not show significant cytotoxic effect at all concentrations after 24 and 48 h, and also reduced the amount of ROS, but did not have a significant effect in comparison with each other. In addition, the reduction of mushroom tyrosinase activity in γ-oryzanol was more than gallic acid and the concentrations of 10, 25, 50 and 100 μM showed significant effects. A decrease in melanin content was observed in different concentrations of γ-oryzanol and gallic acid, but this decrease in two compounds was not significant in comparison to each other. Finally, western blotting results showed that the decrease in the expression of MITF and tyrosinase proteins in γ-oryzanol is higher than in gallic acid, and this decrease was significant in concentrations of 01, 5 and 10 μM. According to the obtained results and the comparison of measured parameters between γ-oryzanol and gallic acid compounds, it can be concluded that γ-oryzanol has more antioxidant effects than gallic acid. In addition, γ-oryzanol shows higher inhibitory effects in the expression pathway of proteins involved in melanin synthesis in B16F10 cells. According to the obtained results γ-oryzanol was superior to gallic acid in case of antioxidant and anti-melanogenic activity in B16F10 cells and may has higher potential in treating disorders caused by hyperpigmentation compared to gallic acid.