Quercetin 3-O-Galactoside Isolated from Limonium tetragonum Inhibits Melanogenesis by Regulating PKA/MITF Signaling and ERK Activation

Multi-target mechanisms and potential applications of quercetin in the treatment of acne vulgaris

Acne vulgaris, a prevalent inflammatory dermatosis, afflicts approximately 90% of adolescents globally. Despite the efficacy of conventional therapies, including antibiotics and retinoids, their use is frequently limited by adverse effects and the emergence of drug resistance. Quercetin, a naturally occurring flavonoid, has garnered significant attention owing to its diverse biological activities, encompassing anti-inflammatory, antioxidant, antimicrobial, and immunomodulatory properties. This review comprehensively explores the multi-target mechanisms of quercetin in the treatment of acne, focusing on its ability to modulate inflammatory cytokine production, oxidative stress pathways, sebaceous gland activity, and microbial populations. Additionally, quercetin promotes skin barrier repair and reduces post-inflammatory hyperpigmentation and scarring through its antioxidant and anti-fibrotic effects. Despite promising in vitro and preclinical findings, challenges such as quercetin's low bioavailability and lack of robust clinical evidence necessitate further research. Advanced delivery systems, including nanoparticles and combination therapies, may optimize its therapeutic potential. This review provides insights into the molecular mechanisms and clinical applications of quercetin, highlighting its potential as a safe and effective alternative for acne management.

Molecular mechanisms underlying Tao-Hong-Si-Wu decoction treating hyperpigmentation based on network pharmacology, Mendelian randomization analysis, and experimental verification

CONTEXT

Hyperpigmentation, a common skin condition marked by excessive melanin production, currently has limited effective treatment options.

OBJECTIVE

This study explores the effects of Tao-Hong-Si-Wu decoction (THSWD) on hyperpigmentation and to elucidate the underlying mechanisms.

MATERIALS AND METHODS

We employed network pharmacology, Mendelian randomization, and molecular docking to identify THSWD's hub targets and mechanisms against hyperpigmentation. The Cell Counting Kit-8 (CCK-8) assay determined suitable THSWD treatment concentrations for PIG1 cells. These cells were exposed to graded concentrations of THSWD-containing serum (2.5%, 5%, 10%, 15%, 20%, 30%, 40%, and 50%) and treated with α-MSH (100 nM) to induce an in vitro hyperpigmentation model. Assessments included melanin content, tyrosinase activity, and Western blotting.

RESULTS

ALB, IL6, and MAPK3 emerged as primary targets, while quercetin, apigenin, and luteolin were the core active ingredients. The CCK-8 assay indicated that concentrations between 2.5% and 20% were suitable for PIG1 cells, with a 50% cytotoxicity concentration (CC50) of 32.14%. THSWD treatment significantly reduced melanin content and tyrosinase activity in α-MSH-induced PIG1 cells, along with downregulating MC1R and MITF expression. THSWD increased ALB and p-MAPK3/MAPK3 levels and decreased IL6 expression in the model cells.

DISCUSSION AND CONCLUSION

THSWD mitigates hyperpigmentation by targeting ALB, IL6, and MAPK3. This study paves the way for clinical applications of THSWD as a novel treatment for hyperpigmentation and offers new targeted therapeutic strategies.

UGT708S6 from Dendrobium catenatum, catalyzes the formation of flavonoid C-glycosides

BACKGROUND

Dendrobium catenatum is a perennial herb of the genus Dendrobium orchidaceae. It has been known as "Golden Grass, Soft Gold" since ancient times with effects of strengthening the body, benefiting the stomach, generating body fluid, nourishing Yin and clearing internal heat. The flowers of D. catenatum have anti-oxidation, immune regulation and other biological activities. The composition analysis of flowers showed that flavonoid glycosides were significantly accumulated in floral tissue. However, in the flowers of D. catenatum, there was only one case of the UDP-glycosyltransferase (UGT) responsible for the glycosylation of flavonoids has been reported.

RESULT

In this study, a new UGT (named UGT708S6) was cloned from D. catenatum flowers rich in O-glycosides and C-glycosides, and its function and biochemical properties were characterized. Through homology comparison and molecular docking, we identified the key amino acid residues affecting the catalytic function of UGT708S6. The glycosyltransferase UGT708S6 was characterized and demonstrated C-glycosyltransferase (CGT) activity in vitro assay using phloretin and 2-hydroxynaringenin as sugar acceptors. The catalytic promiscuity assay revealed that UGT708S6 has a clear sugar donor preference, and displayed O-glycosyltransferase (OGT) activity towards luteolin, naringenin and liquiritigenin. Furthermore, the catalytic characteristics of UGT708S6 were explored, shedding light on the structural basis of substrate promiscuity and the catalytic mechanism involved in the formation of flavonoid C-glycosides. R271 was a key amino acid residue site that sustained the catalytic reaction. The smaller binding pocket resulted in the production of new O-glycosides and the reduction of C-glycosides. This highlighted the importance of the binding pocket in determining whether C-glycosides or O-glycosides were produced.

CONCLUSIONS

The findings suggest that UGT708S6 holds promise as a new glycosyltransferase for synthesizing flavonoid glycosides and offer valuable insights for further understanding the catalytic mechanisms of flavonoid glycosyltransferases.

Unlocking the Bioactive Potential and Exploring Novel Applications for Portuguese Endemic Santolina impressa

The infusion of Santolina impressa, an endemic Portuguese plant, is traditionally used to treat various infections and disorders. This study aimed to assess its chemical profile by HPLC-DAD-ESI-MSn and validate its anti-inflammatory potential. In addition, the antioxidant capacity and effects on wound healing, lipogenesis, melanogenesis, and cellular senescence, all processes in which a dysregulated inflammatory response plays a pivotal role, were unveiled. The anti-inflammatory potential was assessed in lipopolysaccharide (LPS)-stimulated macrophages, cell migration was determined using a scratch wound assay, lipogenesis was assessed on T0901317-stimulated keratinocytes and melanogenesis on 3-isobutyl-1-methylxanthine (IBMX)-activated melanocytes. Etoposide was used to induce senescence in fibroblasts. Our results point out a chemical composition predominantly characterized by dicaffeoylquinic acids and low amounts of flavonols. Regarding the infusion's bioactive potential, an anti-inflammatory effect was evident through a decrease in nitric oxide production and inducible nitric oxide synthase and pro-interleukin-1β protein levels. Moreover, a decrease in fibroblast migration was observed, as well as an inhibition in both intracellular lipid accumulation and melanogenesis. Furthermore, the infusion decreased senescence-associated β-galactosidase activity, γH2AX nuclear accumulation and both p53 and p21 protein levels. Overall, this study confirms the traditional uses of S. impressa and ascribes additional properties of interest in the pharmaceutical and dermocosmetics industries.

Tribuloside acts on the PDE/cAMP/PKA pathway to enhance melanogenesis, melanocyte dendricity and melanosome transport

ETHNOPHARMACOLOGICAL RELEVANCE

Tribuloside, a natural flavonoid extracted from Chinese medicine Tribulus terrestris L., has shown potent efficacy in treating various diseases. In China, the fruits of Tribulus terrestris L. have long been utilized for relieving headache, dizziness, itchiness, and vitiligo. Water-based extract derived from Tribulus terrestris L. can enhance melanogenesis in mouse hair follicle melanocytes by elevating the expression of α-melanocyte stimulating hormone (α-MSH) and melanocortin-1 recepter (MC-1R). Nevertheless, there is a lack of information regarding the impact of tribuloside on pigmentation in both laboratory settings and living organisms.

AIM OF THE STUDY

The present research aimed to examine the impact of tribuloside on pigmentation, and delve into the underlying mechanism.

MATERIALS AND METHODS

Following the administration of tribuloside in human epidermal melanocytes (HEMCs), we utilized microplate reader, Masson-Fontana ammoniacal silver stain, transmission electron microscopy (TEM) and scanning electron microscopy (SEM) to measure melanin contents, dendrite lengths, melanosome counts; L-DOPA oxidation assay to indicate tyrosinase activity, Western blotting to evaluate the expression of melanogenic and associated phosphodiesterase (PDE)/cyclic adenosine monophosphate (cAMP)/cyclic-AMP dependent protein kinase A (PKA) pathway proteins. A PDE-Glo assay to verify the inhibitory effect of tribuloside on PDE was also conducted. Additionally, we examined the impact of tribuloside on the pigmentation in both zebrafish model and human skin samples.

RESULTS

Tribuloside had a notable impact on the production of melanin in melanocytes, zebrafish, and human skin samples. These functions might be attributed to the inhibitory effect of tribuloside on PDE, which could increase the intracellular level of cAMP to stimulate the phosphorylation of cAMP-response element binding (CREB). Once activated, it induced microphthalmia-associated transcription factor (MITF) expression and increased the expression of tyrosinase, Rab27a and cell division cycle protein 42 (Cdc42), ultimately facilitating melanogenesis, melanocyte dendricity, and melanin transport.

CONCLUSION

Tribuloside acts on the PDE/cAMP/PKA pathway to enhance melanogenesis, melanocyte dendricity, and melanosome transport; meanwhile, tribuloside does not have any toxic effects on cells and may be introduced into clinical prescriptions to promote pigmentation.

Comparative Study of Quercetin and Hyperoside: Antimicrobial Potential towards Food Spoilage Bacteria, Mode of Action and Molecular Docking

The antibacterial activities of quercetin and hyperoside were evaluated towards two major spoilage bacteria in fish, Pseudomonas aeruginosa (PA) and Shewanella putrefaciens (SP). Hyperoside showed a lower minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) towards both spoilage bacteria, PA and SP, than quercetin. Cell membrane morphology was affected when treated with hyperoside and quercetin. The release of content from the treated cells occurred, as ascertained by the release of potassium and magnesium ions and the increase in conductivity of the culture media. The morphology of cells was significantly changed, in which shrinkage and pores were obtained, when observed using SEM. Both compounds negatively affected the motility, both swimming and swarming, and the formation of extracellular polymeric substance (EPS), thus confirming antibiofilm activities. Agarose gel analysis revealed that both compounds could bind to or degrade the genomic DNA of both bacteria, thereby causing bacterial death. Molecular docking indicated that the compounds interacted with the minor groove of the DNA, favoring the adenine-thymine-rich regions. Thus, both quercetin and hyperoside could serve as potential antimicrobial agents to retard the spoilage of fish or perishable products.

6-Methylcoumarin Promotes Melanogenesis through the PKA/CREB, MAPK, AKT/PI3K, and GSK3β/β-Catenin Signaling Pathways

We investigated the effects of four coumarin derivatives, namely, 6-methylcoumarin, 7-methylcoumarin, 4-hydroxy-6-methylcoumarin, and 4-hydroxy-7-methylcoumarin, which have similar structures on melanogenesis in a murine melanoma cell line from a C57BL/6J mouse called B16F10. Our results showed that only 6-methylcoumarin significantly increased the melanin synthesis in a concentration-dependent manner. In addition, the tyrosinase, TRP-1, TRP-2, and MITF protein levels were found to significantly increase in response to 6-methylcoumarin in a concentration-dependent manner. To elucidate the molecular mechanism whereby 6-methylcoumarin-induced melanogenesis influences the melanogenesis-related protein expression and melanogenesis-regulating protein activation, we further assessed the B16F10 cells. The inhibition of the ERK, Akt, and CREB phosphorylation, and conversely, the increased p38, JNK, and PKA phosphorylation activated the melanin synthesis via MITF upregulation, which ultimately led to increased melanin synthesis. Accordingly, 6-methylcoumarin increased the p38, JNK, and PKA phosphorylation in the B16F10 cells, whereas it decreased the phosphorylated ERK, Akt, and CREB expressions. In addition, the 6-methylcoumarin activated GSK3β and β-catenin phosphorylation and reduced the β-catenin protein level. These results suggest that 6-methylcoumarin stimulates melanogenesis through the GSK3β/β-catenin signal pathway, thereby affecting the pigmentation process. Finally, we tested the safety of 6-methylcoumarin for topical applications using a primary human skin irritation test on the normal skin of 31 healthy volunteers. We found that 6-methylcoumarin did not cause any adverse effects at concentrations of 125 and 250 μM. Our findings indicate that 6-methylcoumarin may be an effective pigmentation stimulator for use in cosmetics and the medical treatment of photoprotection and hypopigmentation disorders.