Effect of Aspergilus oryzae-fermented broken rice, brewers’ rice and rice bran on melanogenesis in highly pigmented human melanoma, MNT-1

The food and beauty sectors are developing strategies to establish a link between nutrient consumption and skin health, as nutraceuticals offer a promising treatment option for some skin disorders such as hyperpigmentation and premature ageing. As a result, the consumption of food ingredients and supplements claiming to lower the risk of developing such skin problems is increasing. In this study, anti-tyrosinase potential of Aspergillus oryzae-fermented rice by-product water extracts namely fermented broken rice (FBR), brewers’ rice (FBrR), and rice bran (FRB) was assessed through in vitro study using highly pigmented human melanoma MNT-1 cells. The fermented extracts were evaluated for cytotoxicity, anti-tyrosinase activity using intracellular tyrosinase assay as well as melanin content analysis. Their effect on the gene expression of three melanogenic enzymes: tyrosinase (TYR), tyrosinase-related protein-1 (TRP-1) and tyrosinase-related protein 2 (TRP-2) was also assessed by qPCR analysis. As a result, all extracts at tested concentrations of 50 and 100 µg/mL have a low cytotoxicity effect. Together with the positive control kojic acid, the FBR at both concentrations and the FRB at 50 µg/mL significantly decreased intracellular tyrosinase activity. However, their melanin content was not significantly reduced. The qPCR analysis indicated that FBR at 50 and 100 µg/ mL significantly reduced TYR gene expression by up to 71% and 61%, respectively. On the other hand, FBR (100 µg/mL) increased TRP-1 gene expression, whilst FRB (100 µg/ mL) elevated both TRP-1 and TRP-2 gene expression. The positive control kojic acid significantly reduced TYR, TRP-1 and TRP-2 gene expression. However, FBrR demonstrated no significant effect in any of the analyses. Based on these findings, FBR and FRB at 50 µg/mL possess anti-tyrosinase potential. However, further investigation is needed to dissect deeper mechanisms underlying their potential as functional bioingredients for nutraceutical or cosmeceutical applications.