Germinated Riceberry Rice Enhanced Protocatechuic Acid and Vanillic Acid to Suppress Melanogenesis through Cellular Oxidant-Related Tyrosinase Activity in B16 Cells

Abstract

The anti-melanogenic bioactivities of phytophenolic compounds have been well recognized. Riceberry rice contains a rich source of phenolic compounds that act as melanin inhibitors through their antioxidant and anti-tyrosinase properties. Germination has been shown to be an effective process to improve targeted phenolic compounds. In this study, germinated riceberry rice extract was tested for antioxidant activity. Total phenolic content was determined while the tyrosinase inhibitory effect was screened by the in vitro mushroom tyrosinase assay. Cytotoxicity of germinated riceberry rice extract was investigated in B16 cells before evaluating its activities on cellular tyrosinase, melanogenesis, melanin excretion, morphological appearance, and cellular oxidants. Germinated riceberry rice extract showed increased potency of antioxidants and was also twice as effective for mushroom tyrosinase inhibition when compared with ungerminated riceberry rice extract. In B16 cells, the extract inhibited cellular tyrosinase, melanogenesis, and cellular oxidants in a dose-dependent manner when compared with untreated cells. Germinated riceberry rice extract also displayed an effect on B16 cells morphology by reducing the number of melanin-containing cells and their dendriticity. Additionally, the germination of riceberry rice dominantly enhanced two phenolic acids, protocatechuic acid and vanillic acid, which have the potential for antioxidant-associated hyperpigmentation control. Thus, the restricted germination of riceberry rice tended to promote protocatechuic acid and vanillic acid, which dominantly displayed antioxidants and tyrosinase-related melanogenic inhibition.Antioxidants 2020, 9, 247 2 of 12 acid, chlorogenic acid, syringic acid, p-coumaric acid, and ferulic acid [10,11] that act as tyrosinase inhibitors. Previously, a suitable germination process promoted both the quantitative and qualitative aspects of these valuable phenolic compounds [12][13][14][15]. In this study, riceberry rice was enhanced for anti-melanogenesis by the germination process. Germinated riceberry rice extract could be further developed as a novel agent for hyperpigmentation control. Materials and Methods Rice GerminationRiceberry rice was obtained from Phayao province, Thailand. A hundred grams of rice were soaked in reverse osmosis water, pH 7.2-7.4 for 1 h. Soaked riceberry rice was germinated in a polyethylene tray (22 × 22 × 5 cm) at room temperature in the dark for 6 h. Subsequently, germinated riceberry rice was lyophilized and then ultracentrifugally powdered. The riceberry rice powder was then sieved through 345 µm and stored at −20 • C until extraction.

Modified Riceberry rice extract suppresses melanogenesis-associated cell differentiation through tyrosinase-mediated MITF downregulation on B16 cells and in vivo zebrafish embryos

“…Riceberry rice was obtained from Payao province, northern Thailand. The biomodification of the rice sample was performed based on the researchers’ previous study with some modifications ( 14 ). The rice samples were soaked in reverse osmosis water at pH 7.2-7.4 for 60 min.…”

“…The cytotoxicity of MRB was determined on B16 cells using a modified method of MTT assay ( 14 ). Briefly, 3 × 10 4 of B16 cells were treated with the MRB extract at 10 to 40 mg/mL for 24 h. Treated cells were incubated with 1.2 mM MTT solution for 4 h. Formazan crystals were solubilized by absolute DMSO and determined at 530 nm.…”

“…Intracellular and excreted melanin pigments of B16 cells were determined as described previously ( 14 ). Briefly, 1.0 × 10 5 of B16 cells were treated with the MRB extract dissolved in phenol red-free DMEM at indicated concentrations for 72 h. Excreted melanin pigments were determined in the culture medium at 405 nm.…”

“…TYR enzymatic activity in B16 cells was determined using the previous method ( 14 ). Briefly, 1.0 × 10 5 of B16 cells were treated with the MRB extract at indicated concentrations for 72 h. The cells were solubilized with PBS, pH 7.1 containing 1% Triton™ X-100, and clarified the lysate by centrifugation at 15,000 g for 15 min.…”

Antioxidants and Skin Protection

“…Another two original articles of this Special Issue include the study of the relationship between antioxidant compounds and melanin production, with the aim of characterising new whitening ingredients from germinated riceberry rice extract [9] and sesamol [10]. This kind of ingredient is interesting not only from a cosmetic point of view but also can be very useful in diseases that induce skin hyperpigmentation, such as melasma or Addison's disease, or even normal physiological conditions such as pregnancy.…”