Dual Inhibition of γ-Oryzanol on Cellular Melanogenesis: Inhibition of Tyrosinase Activity and Reduction of Melanogenic Gene Expression by a Protein Kinase A-Dependent Mechanism

Abstract

The in vitro effects on melanogenesis of γ-oryzanol (1), a rice bran-derived phytosterol, were investigated. The melanin content in B16F1 cells was significantly and dose-dependently reduced (-13% and -28% at 3 and 30 μM, respectively). Tyrosinase enzyme activity was inhibited by 1 both in a cell-free assay and when analyzed based on the measurement of cellular tyrosinase activity. Transcriptome analysis was performed to investigate the biological pathways altered by 1, and it was found that gene expression involving protein kinase A (PKA) signaling was markedly altered. Subsequent analyses revealed that 1 stimulation in B16 cells reduced cytosolic cAMP concentrations, PKA activity (-13% for cAMP levels and -40% for PKA activity), and phosphorylation of the cAMP-response element binding protein (-57%), which, in turn, downregulated the expression of microphthalmia-associated transcription factor (MITF; -59% for mRNA and -64% for protein), a key melanogenic gene transcription factor. Accordingly, tyrosinase-related protein 1 (TRP-1; -69% for mRNA and -82% for protein) and dopachrome tautomerase (-51% for mRNA and -92% for protein) in 1-stimulated B16F1 cells were also downregulated. These results suggest that 1 has dual inhibitory activities for cellular melanogenesis by inhibiting tyrosinase enzyme activity and reducing MITF and target genes in the PKA-dependent pathway.

Resveratrol-Enriched Rice Down-Regulates Melanin Synthesis in UVB-Induced Guinea Pigs Epidermal Skin Tissue

“…Interestingly, RR shows synergistic effects in comparison that of each resveratrol or rice alone (Baek et al, 2013;Baek et al, 2014). Several reports show that resveratrol decreases the expression of tyrosinase (Franco et al, 2012;Zheng et al, 2012;Bae et al, 2013;Park and Boo, 2013;Park et al, 2014), and Jun et al reported that gamma-oryzanol from rice extract dually inhibited cellular melanogenesis, too (Jun et al, 2012). Because each of resveratrol and rice had anti-melanogenic effects, we expected that RR would produce synergistic antimelanogenic effects and thus have some advantages over treatment with rice or resveratrol alone.…”

Himalayan Nettle Girardinia diversifolia as a Candidate Ingredient for Pharmaceutical and Nutraceutical Applications—Phytochemical Analysis and In Vitro Bioassays

“…Previous published literature showed that phenolic constituents can act as inhibitors of these enzymes [39], thus suggesting that multiple compounds in the phytocomplex of G. diversifolia may be the responsible for the observed activity. Regarding the tyrosinase activity, literature data indicate that the phytosterol fraction indicated as oryzanol has significant inhibitory properties on this enzyme [30].…”

“…Related to the tyrosinase activity, in this case the presence of high levels of phytosterols can also be related to the observed effect. A previous paper showed a significant effect for γ-oryzanol in cellular melanogenesis owing to its inhibition of tyrosinase enzyme activity and reduction of MITF and target genes in the PKA-dependent pathway [30].…”

Gamma oryzanol loaded microspheres with improved bioavailability

“…In a study on rats with colon cancer, it was found that γ-oryzanol has the capability to improve immunity by increasing the activity of both natural killer and macrophages cells . It was also found that γ-oryzanol is able to reduce melanin concentration by decreasing its synthesis in melanoma cells (Jun et al, 2012). In addition, γ-oryzanol *Corresponding author.…”