Antioxidant and tyrosinase inhibition activity of the fertile fronds and rhizomes of three different Drynaria species

Hirsutanone Isolated from the Bark of Alnus japonica Attenuates Melanogenesis via Dual Inhibition of Tyrosinase Activity and Expression of Melanogenic Proteins

Hirsutanone (Hir) and oregonin (Ore) are diarylheptanoids isolated from the bark of Alnus japonica. In this study, we investigated the anti-melanogenic activity of Hir and Ore in B16-F1 murine melanoma and normal human epidermal melanocytes (HEMn-DP) and elucidated the mechanisms of action. In B16-F1 cells, Hir and Ore suppressed melanin synthesis induced by α-melanocyte-stimulating hormone (α-MSH) without cytotoxicity. The inhibitory effect of Hir on melanin synthesis was much stronger than that of Ore. In addition, Hir reduced melanin content in HEMn-DP cells. As tyrosinase is a key enzyme in melanin synthesis, the effect of Hir on tyrosinase activity was assessed. The results demonstrated that Hir partially decreased tyrosinase activity and intracellular tyrosinase activity. Moreover, Hir suppressed the protein expression of melanogenic enzymes, including tyrosinase, tyrosinase-related protein (TRP)-1, and TRP-2, leading to reduced melanin biosynthesis. Hir also led to the suppression of cAMP response element-binding protein (CREB) phosphorylation and microphthalmia-associated transcription factor (MITF) expression, which control the expression of melanogenic enzymes. These results suggest that Hir suppressed melanin synthesis by dual inhibition of tyrosinase activity and the CREB/MITF pathway leading to the expression of melanogenic enzymes and may be a potent cosmetic and therapeutic agent for hyperpigmentation disorders.

Human Embryonic Stem Cell-Derived Neural Lineages as In Vitro Models for Screening the Neuroprotective Properties of Lignosus rhinocerus (Cooke) Ryvarden

In the biomedical field, there is growing interest in using human stem cell-derived neurons as in vitro models for pharmacological and toxicological screening of bioactive compounds extracted from natural products. Lignosus rhinocerus (Tiger Milk Mushroom) is used by indigenous communities in Malaysia as a traditional medicine to treat various diseases. The sclerotium of L. rhinocerus has been reported to have medicinal properties, including various bioactivities such as neuritogenic, anti-inflammatory, and anticancer effects. This study aims to investigate the neuroprotective activities of L. rhinocerus sclerotial extracts. Human embryonic stem cell (hESC)-derived neural lineages exposed to the synthetic glucocorticoid, dexamethasone (DEX), were used as the in vitro models. Excess glucocorticoids have been shown to adversely affect fetal brain development and impair differentiation of neural progenitor cells. Screening of different L. rhinocerus sclerotial extracts and DEX on the hESC-derived neural lineages was conducted using cell viability and neurite outgrowth assays. The neuroprotective effects of L. rhinocerus sclerotial extracts against DEX were further evaluated using apoptosis assays and Western blot analysis. Hot aqueous and methanol extracts of L. rhinocerus sclerotium promoted neurite outgrowth of hESC-derived neural stem cells (NSCs) with negligible cytotoxicity. Treatment with DEX decreased viability of NSCs by inducing apoptosis. Coincubation of L. rhinocerus methanol extract with DEX attenuated the DEX-induced apoptosis and reduction in phospho-Akt (pAkt) level in NSCs. These results suggest the involvement of Akt signaling in the neuroprotection of L. rhinocerus methanol extract against DEX-induced apoptosis in NSCs. Methanol extract of L. rhinocerus sclerotium exhibited potential neuroprotective activities against DEX-induced toxicity in hESC-derived NSCs. This study thus validates the use of human stem cell-derived neural lineages as potential in vitro models for screening of natural products with neuroprotective properties.