Tokoronin Contained in Dioscorea tokoro Makino ex Miyabe Suppressed α-MSH-Induced Melanogenesis in B16 Cells via Suppression of Classical MAPK Pathway Activation

Naturally Occurring Polyhydroxylated Spirostanol Saponins, A Review of the Classification, Sources, Biosynthesis, Biological Activities, and Toxicity

Polyhydroxylated spirostanol saponins, characterized by three or more hydroxy substitutions in the aglycone, have various interesting biological activities. In the present study, "steroids", "saponins", "polyhydroxylated", "spirostanol saponins", and "steroidal saponins" were used as search terms to screen the literature. Cited references were collected between 1950 and 2023 from the Web of Science, SciFinder, and China National Knowledge Internet (CNKI). A total of 407 polyhydroxylated spirostanol saponins were included in this review. These saponins were classified into three types, α, β, and γ. Polyhydroxylated spirostanol saponins have potential benefits, primarily anti-inflammatory, antimicrobial, cytotoxic, and cAMP phosphodiesterase inhibitory activities. These compounds were found in 11 plant families and 36 genera. The top three families containing the most saponins were Asparagaceae, Melanthiaceae, and Amaryllidaceae, and the top five genera were Trillium, Helleborus, Allium, Dracaena, and Paris. The top five plants were Trillium tschonoskii Maxim., Ypsilandra thibetica Franch., Paris polyphylla var. yunnanensis (Franch.)Hand.-Mazz., Helleborus thibetanus Franch., and Helleborus foetidus L. On the basis of their diverse biological activities, these saponins and related plant resources are worthy of further development and utilization.

Phytochemical profiling, antioxidant, enzymatic inhibitory, and antibacterial activities of Wigandia ecuadorensis

Wigandia ecuadoriensis, a member of the Namaceae family, is a source of metabolites and has been traditionally used as an anti-inflammatory. This work aimed to determine the total phenolic content (TPC), total flavonoid content (TFC), antioxidant effect, inhibition of α-glucosidase and cholinesterase enzymes (AChE, BChE), and antibacterial activity of the methanolic extract (ME) and subfractions of Wigandia ecuadoriensis. The findings revealed that ME and its subfractions exhibited significant antioxidant capacity, with the ethyl acetate fraction being the most active, displaying an IC50 of 17.66 µg/mL against the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical and 10.31 µg/mL against 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS). This activity was attributed to its high total phenolic content (357.47 mg GAE/g). Furthermore, W. ecuadoriensis fractions showed marked antimicrobial properties against human pathogen strains with Minimum Bactericidal Concentration (MBC) values ​​of 1.56-6.25 mg/mL for S. aureus, E. faecalis and E. coli. Furthermore, aqueous fraction exhibited slight inhibition of acetylcholinesterase (IC50: 915.98 µg/mL) and butyrylcholinesterase (IC50: 380.42 µg/mL). Interestingly, EF showed the greatest inhibitory effect of α-glucosidase (IC50: 38.44 µg/mL) which is more potent than the control used, acarbose (IC50: 179.07 µg/mL). UHPLC-QTOF-MS analysis identified forty compounds, including phenolic acids, flavonoids, saponins, terpenes, and fatty acyls. As far as we know, this is the first study to evaluate the chemical composition and biological potential of W. ecuadoriensis. Our results provide the first evidence to the chemical knowledge of the species W. ecuadoriensis and demonstrate its bioactive potential as an interesting source of secondary metabolites with possible beneficial properties for health.

Phenolic acids in Panax ginseng inhibit melanin production through bidirectional regulation of melanin synthase transcription via different signaling pathways

Background

Our previous investigation indicated that the preparation of Panax ginseng Meyer (P. ginseng) inhibited melanogenesis. It comprised salicylic acid (SA), protocatechuic acid (PA), p-coumaric acid (p-CA), vanillic acid (VA), and caffeic acid (CA). In this investigation, the regulatory effects of P. ginseng phenolic acid monomers on melanin production were assessed.

Methods

In vitro and in vivo impact of phenolic acid monomers were assessed.

Results

SA, PA, p-CA and VA inhibited tyrosinase (TYR) to reduce melanin production, whereas CA had the opposite effects. SA, PA, p-CA and VA significantly downregulated the melanocortin 1 receptor (MC1R), cycle AMP (cAMP), protein kinase A (PKA), cycle AMP-response element-binding protein (CREB), microphthalmia-associated transcription factor (MITF) pathway, reducing mRNA and protein levels of TYR, tyrosinase-related protein 1 (TYRP1), and TYRP2. Moreover, CA treatment enhanced the cAMP, PKA, and CREB pathways to promote MITF mRNA level and phosphorylation. It also alleviated MITF protein level in α-MSH-stimulated B16F10 cells, comparable to untreated B16F10, increasing the expression of phosphorylation glycogen synthase kinase 3β (p-GSK3β), β-catenin, p-ERK/ERK, and p-p38/p38. Furthermore, the GSK3β inhibitor promoted p-GSK3β and p-MITF expression, as observed in CA-treated cells. Moreover, p38 and ERK inhibitors inhibited CA-stimulated p-p38/p38, p-ERK/ERK, and p-MITF increase, which had negative binding energies with MC1R, as depicted by molecular docking.

Conclusion

P. ginseng roots' phenolic acid monomers can safely inhibit melanin production by bidirectionally regulating melanin synthase transcription. Furthermore, they reduced MITF expression via MC1R/cAMP/PKA signaling pathway and enhanced MITF post-translational modification via Wnt/mitogen-activated protein kinase signaling pathway.

Computational studies on searching potential phytochemicals against DNA polymerase activity of the monkeypox virus

Objectives

The outbreak of monkeypox virus (MPXV) is an emerging epidemic of medical concern with 65353 confirmed cases of infection and a fatality of 115 worldwide. Since May 2022, MPXV has been rapidly disseminating across the globe through various modes of transmission, including direct contact, respiratory droplets, and consensual sex. Because of the limited medical countermeasures available to treat MPXV, the present study aimed to identify potential phytochemicals (limonoids, triterpenoids, and polyphenols) as antagonists to target the DNA polymerase protein of MPXV with the ultimate goal to inhibit the viral DNA replication mechanism and immune-mediated responses.

Methods

The protein-DNA and protein-ligand molecular docking were performed with the help of computational programs AutoDock Vina, iGEMDOCK and HDOCK server. The BIOVIA Discovery studio and ChimeraX were used to evaluate the protein-ligand interactions. The GROMACS 2021 was used for the molecular dynamics simulations. The ADME and toxicity properties were computed by using online servers SwissADME and pKCSM.

Results

Molecular docking of 609 phytochemicals and molecular dynamics simulations of lead phytochemicals glycyrrhizinic acid and apigenin-7-O-glucuronide generated useful data that supported the ability of phytochemicals to obstruct the DNA polymerase activity of the monkeypox virus.

Conclusions

The computational results supported that appropriate phytochemicals can be used to formulate an adjuvant therapy for the monkeypox virus.

Antimelanogenesis Effects of Theasinensin A

Theasinensin A (TSA) is a major group of catechin dimers mainly found in oolong tea and black tea. This compound is also manufactured with epigallocatechin gallate (EGCG) as a substrate and is refined after the enzyme reaction. In previous studies, TSA has been reported to be effective against inflammation. However, the effect of these substances on skin melanin formation remains unknown. In this study, we unraveled the role of TSA in melanogenesis using mouse melanoma B16F10 cells and normal human epidermal melanocytes (NHEMs) through reverse transcription polymerase chain reaction (RT-PCR), Western blotting analysis, luciferase reporter assay, and enzyme-linked immunosorbent assay analysis. TSA inhibited melanin formation and secretion in α-melanocyte stimulating hormone (α-MSH)-induced B16F10 cells and NHEMs. TSA down-regulated the mRNA expression of tyrosinase (Tyr), tyrosinase-related protein 1 (Tyrp1), and Tyrp2, which are all related to melanin formation in these cells. TSA was able to suppress the activities of certain proteins in the melanocortin 1 receptor (MC1R) signaling pathway associated with melanin synthesis in B16F10 cells: cyclic adenosine monophosphate (cAMP) response element-binding protein (CREB), protein kinase A (PKA), tyrosinase, and microphthalmia-associated transcription factor (MITF). We also confirmed α-MSH-mediated CREB activities through a luciferase reporter assay, and that the quantities of cAMP were reduced by TSA in the enzyme linked immunosorbent assay (ELISA) results. Based on these findings, TSA should be considered an effective inhibitor of hyperpigmentation.