Quercetin negatively regulates IL-1β production in Pseudomonas aeruginosa-infected human macrophages through the inhibition of MAPK/NLRP3 inflammasome pathways

Therapeutic implications of quercetin and its derived-products in COVID-19 protection and prophylactic

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a novel human coronavirus, which has triggered a global pandemic of the coronavirus infectious disease 2019 (COVID-19). Outbreaks of emerging infectious diseases continue to challenge human health worldwide. The virus conquers human cells through the angiotensin-converting enzyme 2 receptor-driven pathway by mostly targeting the human respiratory tract. Quercetin is a natural flavonoid widely represented in the plant kingdom. Cumulative evidence has demonstrated that quercetin and its derivatives have various pharmacological properties including anti-cancer, anti-hypertension, anti-hyperlipidemia, anti-hyperglycemia, anti-microbial, antiviral, neuroprotective, and cardio-protective effects, because it is a potential treatment for severe inflammation and acute respiratory distress syndrome. Furthermore, it is the main life-threatening condition in patients with COVID-19. This article provides a comprehensive review of the primary literature on the predictable effectiveness of quercetin and its derivatives docked to multi-target of SARS-CoV-2 and host cells via in silico and some of validation through in vitro, in vivo, and clinically to fight SARS-CoV-2 infections, contribute to the reduction of inflammation, which suggests the preventive and therapeutic latency of quercetin and its derived-products against COVID-19 pandemic, multisystem inflammatory syndromes (MIS), and long-COVID.

Quercetin attenuates Pseudomonas aeruginosa-induced acute lung inflammation by inhibiting PI3K/AKT/NF-κB signaling pathway

Pseudomonas aeruginosa is an opportunistic pathogen that commonly causes infections in immunocompromised individuals with significant morbidity and mortality. Quercetin is a natural flavonoid abundantly present in fruits and vegetables, exerting potent anti-inflammatory effects in treatment of various diseases. However, the molecular mechanisms of quercetin in treatment of P. aeruginosa-induced acute lung inflammation are unclear. In this study, we exploited network pharmacology- and molecular docking-based approach to explore the potential mechanisms of quercetin against P. aeruginosa pneumonia, which was further validated via in vivo and in vitro experiments. The in vivo experiments demonstrated that quercetin alleviated the P. aeruginosa-induced lung injury by diminishing neutrophil infiltration and production of proinflammatory cytokines (IL-1β, IL-6, and TNF), which was associated with decreased mortality. Moreover, the quercetin-treated mice displayed decreased phosphorylation levels of PI3K, AKT, IκBα, and NF-κB p65 in lung tissues compared to non-drug-treated mice. Similarly, the in vitro study showed that the phosphorylation of these regulatory proteins and production of the proinflammatory cytokines were impaired in the quercetin-pretreated macrophages upon P. aeruginosa infection. Altogether, this study suggested that quercetin reduced the P. aeruginosa-induced acute lung inflammation by suppressing PI3K/AKT/NF-κB signaling pathway.

Quercetin counteracts monosodium glutamate to mitigate immunosuppression in the thymus and spleen via redox-guided cellular signaling

BACKGROUND

Chronic inflammation brought on by oxidative stress can result in several immunopathologies. Natural compounds with antioxidant characteristics, like quercetin, have shown effectiveness in reducing oxidative damage and regulating the immune response.

PURPOSE

The commonly used food additive monosodium glutamate (M) causes immunosuppression by disrupting redox equilibrium and inducing oxidative stress. The goal of this work is to examine the therapeutic potential of quercetin against immunotoxicity brought on by M, revealing the molecular route implicated in such immunopathology by targeting the thymus and spleen, to support the development of future anti-inflammatory and antioxidant therapies.

STUDY DESIGN AND METHODS

M-fed rats were employed as an immunotoxicity model and were supplemented with quercetin for four weeks. Hematological and biochemical parameters were measured; H&E staining, immunohistochemistry, flow cytometry, real-time quantitative PCR, and western blotting were performed.

RESULTS

Based on the findings, TLR4 was activated by M to cause oxidative stress-mediated inflammation, which was alleviated by the supplementation of quercetin by modulating redox homeostasis to neutralize free radicals and suppress the inflammatory response. To prevent M-induced inflammation, quercetin demonstrated anti-inflammatory functions by blocking NF-kB activation, lowering the production of pro-inflammatory cytokines, and increasing the release of anti-inflammatory cytokines. By normalizing lipid profiles and lowering the potential risk of immunological deficiency caused by M, quercetin also improves lipid metabolism. Additionally, it has shown potential for modifying insulin levels, suggesting a possible function in controlling M-induced alteration in glucose metabolism. The addition of quercetin to M enhanced the immune response by improving immunoglobulin levels and CD4/CD8 expression in the thymus and spleen. Additionally, quercetin inhibited apoptosis by controlling mitochondrial caspase-mediated cellular signaling, suggesting that it may be able to halt cell death in M-fed rats.

CONCLUSION

The results of this study first indicate that quercetin, via modulating redox-guided cellular signaling, has a promising role in reducing immune disturbances. This study illuminates the potential of quercetin as a safe, natural remedy for immunopathology caused by M, including thymic hypoplasia and/or splenomegaly, and paves the way for future anti-inflammatory and antioxidant supplements.

The pomegranate-derived peptide Pug-4 alleviates nontypeable Haemophilus influenzae-induced inflammation by suppressing NF-kB signaling and NLRP3 inflammasome activation

The respiratory pathogen nontypeable Haemophilus influenzae (NTHi) is the most common cause of exacerbation of chronic obstructive pulmonary disease (COPD), of which an excessive inflammatory response is a hallmark. With the limited success of current medicines there is an urgent need for the development of novel therapeutics that are both safe and effective. In this study, we explored the regulatory potential of pomegranate-derived peptides Pug-1, Pug-2, Pug-3, and Pug-4 on NTHi-induced inflammation. Our results clearly showed that to varying degrees the Pug peptides inhibited NTHi-induced production of IL-1β, a pivotal cytokine in COPD, and showed that these effects were not related to cytotoxicity. Pug-4 peptide exhibited the most potent inhibitory activity. This was demonstrated in all studied cell types including murine (RAW264.7) and human (differentiated THP-1) macrophages as well as human lung epithelial cells (A549). Substantial reduction by Pug-4 of TNF-α, NO and PGE2 in NTHi-infected A549 cells was also observed. In addition, Pug-4 strongly inhibited the expression of nuclear-NF-κB p65 protein and the NF-κB target genes (determined by IL-1β, TNF-α, iNOS and COX-2 mRNA expression) in NTHi-infected A549 cells. Pug-4 suppressed the expression of NLRP3 and pro-IL-1β proteins and inhibited NTHi-mediated cleavage of caspase-1 and mature IL-1β. These results demonstrated that Pug-4 inhibited NTHi-induced inflammation through the NF-κB signaling and NLRP3 inflammasome activation. Our findings herein highlight the significant anti-inflammatory activity of Pug-4, a newly identified peptide from pomegranate, against NTHi-induced inflammation. We therefore strongly suggest the potential of the Pug-4 peptide as an anti-inflammatory medicine candidate for treatment of NTHi-mediated inflammation.

Function and inhibition of P38 MAP kinase signaling: Targeting multiple inflammation diseases

Inflammation is a natural host defense mechanism that protects the body from pathogenic microorganisms. A growing body of research suggests that inflammation is a key factor in triggering other diseases (lung injury, rheumatoid arthritis, etc.). However, there is no consensus on the complex mechanism of inflammatory response, which may include enzyme activation, mediator release, and tissue repair. In recent years, p38 MAPK, a member of the MAPKs family, has attracted much attention as a central target for the treatment of inflammatory diseases. However, many p38 MAPK inhibitors attempting to obtain marketing approval have failed at the clinical trial stage due to selectivity and/or toxicity issues. In this paper, we discuss the mechanism of p38 MAPK in regulating inflammatory response and its key role in major inflammatory diseases and summarize the synthetic or natural products targeting p38 MAPK to improve the inflammatory response in the last five years, which will provide ideas for the development of novel clinical anti-inflammatory drugs based on p38 MAPK inhibitors.

Oral pectin/oligochitosan microspheres for colon-specific controlled release of quercetin to treat inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic, life quality-reducing disease with no cures available yet. To develop an effective medication suitable for long-term use is an urgent but unmet need. Quercetin (QT) is a natural dietary flavonoid with good safety and multifaceted pharmacological activities against inflammation. However, orally administrated quercetin yields unproductive outcomes for IBD treatment because of its poor solubility and extensive metabolism in the gastrointestinal tract. In this work, a colon-targeted QT delivery system (termed COS-CaP-QT) was developed, of which the pectin (PEC)/Ca²⁺ microspheres were prepared and then crosslinked by oligochitosan (COS). The drug release profile of COS-CaP-QT was pH-dependent and colon microenvironment-responsive, and COS-CaP-QT showed preferential distribution in the colon. The mechanism study showed that QT triggered the Notch pathway to regulate the proliferation of T helper 2 (Th2) cells and group 3 innate lymphoid cells (ILC3s) and the inflammatory microenvironment was remodeled. The in vivo therapeutic results revealed that COS-CaP-QT could relieve the colitis symptoms and maintain the colon length and intestinal barrier integrity.

Regulatory Roles of Flavonoids in Caspase-11 Non-Canonical Inflammasome-Mediated Inflammatory Responses and Diseases

Inflammasomes are multiprotein complexes that activate inflammatory responses by inducing pyroptosis and secretion of pro-inflammatory cytokines. Along with many previous studies on inflammatory responses and diseases induced by canonical inflammasomes, an increasing number of studies have demonstrated that non-canonical inflammasomes, such as mouse caspase-11 and human caspase-4 inflammasomes, are emerging key players in inflammatory responses and various diseases. Flavonoids are natural bioactive compounds found in plants, fruits, vegetables, and teas and have pharmacological properties in a wide range of human diseases. Many studies have successfully demonstrated that flavonoids play an anti-inflammatory role and ameliorate many inflammatory diseases by inhibiting canonical inflammasomes. Others have demonstrated the anti-inflammatory roles of flavonoids in inflammatory responses and various diseases, with a new mechanism by which flavonoids inhibit non-canonical inflammasomes. This review discusses recent studies that have investigated the anti-inflammatory roles and pharmacological properties of flavonoids in inflammatory responses and diseases induced by non-canonical inflammasomes and further provides insight into developing flavonoid-based therapeutics as potential nutraceuticals against human inflammatory diseases.

A wild rice-derived peptide R14 ameliorates monosodium urate crystals-induced IL-1β secretion through inhibition of NF-κB signaling and NLRP3 inflammasome activation

Gout is an inflammatory arthritis initiated by the deposition of monosodium urate crystals (MSU) around the joints and surrounding tissues. MSU crystals activate the nucleotide-binding oligomerization domain-like receptor containing pyrin domain 3 (NLRP3) inflammasome to the release of interleukin-1β (IL-1β). Gout can have a substantial impact on patient's quality of life, and currently available medicines are unable to meet all the clinical needs. This study explored anti-gout potentials of the Rice14 (R14) peptide, a peptide derived from leaves of wild rice Oryza minuta. The effects of R14 peptide on IL-1β secretion in THP-1 macrophages with MSU crystals-induced inflammation were examined. Our results clearly showed that the R14 peptide significantly inhibited the secretion of IL-1β in MSU crystals-induced macrophages, and the effects were dose-related. For safety testing, the R14 peptide did not show both cytotoxicity and hemolytic activity. In addition, the R14 peptide strongly suppressed the phospho-IκB-α and nuclear factor kappa-B (NF-κB) p65 proteins in NF-κB signaling pathway, reduced the NLRP3 expression and inhibited the MSU crystals-mediated cleavage of caspase-1 as well as mature IL-1β. The R14 peptide also reduced MSU-triggered intracellular ROS levels in macrophages. Taken together, these results indicated that R14 peptide inhibited MSU crystals-induced IL-1β production through NF-κB and NLRP3 inflammasome activation. Our findings demonstrated that R14 peptide, the newly recognized peptide from wild rice, possessed potent regulatory activity against IL-1β production in MSU crystals-induced inflammation, and we therefore propose that the R14 peptide is a promising molecule with potential clinical application in the treatment of MSU crystals-induced inflammation.

YY1 was indispensable for the alleviation of quercetin on diabetic nephropathy-associated tubulointerstitial inflammation

BACKGROUND

The emergence of tubulointerstitial inflammation (TI) could accelerate the development of tubulointerstitial fibrosis (TIF) of diabetic nephropathy (DN). Yin Yang 1 (YY1) was a new pro-inflammatory mediator and became the important target of DN-related TIF. Quercetin performed an effective role in anti-inflammation and was probable to bind to YY1. However, the role of YY1 in quercetin's anti-inflammatory effect on DN-related TIF was uncovered.

PURPOSE

To investigate the potential effect and mechanism of quercetin against DN-related TI.

STUDY DESIGN AND METHODS

The protein levels of YY1 were examined in the renal tubular epithelial cells (RTECs) of db/db mice and HG-cultured HK-2 cells. Molecular modeling studies and YY1 overexpression lentivirus vector were selected to further confirm the indispensable part of YY1 in quercetin's TI protection in vitro. Luciferase assay and chromatin immunoprecipitation (ChIP) assay were carried out to identify whether YY1 directly regulated IL-6/STAT3 signaling by binding to the IL-6 promoter in quercetin's TI protection in vitro. At last, the important role of YY1-mediated IL-6/STAT3 signaling in quercetin's TIF protection effect was further identified by using of YY1 overexpression lentivirus vector and IL-6 specific inhibitor tocilizumab.

RESULTS

Along with the alleviated tubulointerstitial injury by quercetin in the RTECs of db/db mice and HK-2 cells stimulated by HG, YY1-mediated IL-6/STAT-3 pathway involved in TI protection of quercetin in vivo and in vitro. Quercetin bound to YY1 and decreased its protein expression, and YY1 directly suppressed IL-6 transcription by bounding to its promoter, resulting in the alleviation of inflammation by inactivating of IL-6/STAT-3 pathway in vitro. YY1-mediated IL-6/STAT-3 pathway was also indispensable for the alleviation of quercetin on DN-associated TIF.

CONCLUSION

YY1 could not be absent from quercetin's anti-inflammatory effect on DN-associated TIF via alleviating IL-6/STAT-3 pathway mediated TI.

Convergence of Fructose-Induced NLRP3 Activation with Oxidative Stress and ER Stress Leading to Hepatic Steatosis

High fructose flux enhances hepatocellular triglyceride accumulation (hepatic steatosis), which is a prime trigger in the emergence of hepatic ailments. Nevertheless, the pathophysiology underlying the process is not completely understood. Emerging evidences have revealed the inputs from multiple cues including inflammation, oxidative stress, and endoplasmic reticulum (ER) stress in the development of hepatic steatosis. Here, we substantiated the role of NLRP3 inflammasome and its convergence with oxidative and ER stress leading to hepatic steatosis under high fructose diet feeding. Male SD rats were fed on 60% high fructose diet (HFrD) for 10 weeks and treated with antioxidant quercetin or NLRP3 inflammasome inhibitor glyburide during the last 6 weeks, followed by metabolic characterization and analysis of hepatic parameters. HFrD-induced hepatic steatosis was associated with the activation of NLRP3 inflammasome, pro-inflammatory response, oxidative, and ER stress in liver. Treatment with quercetin abrogated HFrD-induced oxidative stress, along with attenuation of NLRP3 activation in the liver. On the other hand, inhibition of NLRP3 signaling by glyburide suppressed HFrD-induced oxidative and ER stress. Both glyburide or quercetin treatment significantly attenuated hepatic steatosis, associated with mitigated expression of the lipogenic markers in liver. Our findings verified the association of NLRP3 inflammasome with oxidative and ER stress in fructose-induced lipogenic response and indicate that in addition to be a target of oxidative/ER stress, NLRP3 can act as a trigger for oxidative/ER stress to activate a vicious cycle where these cues act in a complex manner to propagate inflammatory response, leading to hepatic steatosis.

Gallium-modified gelatin nanoparticles loaded with quercetin promote skin wound healing via the regulation of bacterial proliferation and macrophage polarization

Background: Wound healing is a complicated process involving multiple cell components and can help the re-establishment of the skin's barrier function. Previous studies have pointed out that bacterial infection and sustained inflammatory reactions are the main causes of the delay of wound closure and scar formation during wound healing. The effect of current approaches for scar-free wound repair still faces many challenges, and alternative therapeutic methods are urgently needed to be established. Methods: The basic characteristics of the new-designed nanoparticles were clarified through the characterization of the material. The biocompatibility of the nanoparticles, as well as its effect on fibroblast function, anti-bacterial capacity, inflammation suppressive role, and the underlying mechanism were further verified by a panel of biochemical assays in vitro. Ultimately, pre-clinical rat model was employed to testify its role in wound healing and scar formation in vivo. Results: Firstly, gallium-modified gelatin nanoparticles loaded with quercetin was successfully established, displaying good biocompatibility and facilitative effect on fibroblast function. In addition, the nanoparticles showed prominent anti-bacterial and inflammation-suppressive effects. What's more important, the nanoparticles could also induce the polarization of macrophages from M1 to M2 phenotype to exert its inflammatory inhibitory role through TGF-β/Smad signaling pathway. Ultimately, in vivo experiment showed that the nanoparticles could effectively promote wound repair and inhibit scar formation during the process of wound healing. Conclusion: Taken together, the new nanoparticles have good anti-bacterial and anti-scar formation effects and great potential in the field of skin wound repair, which provides a promising therapeutic strategy for wound treatment.

Moringa concanensis L. Alleviates DNCB-Induced Atopic Dermatitis-like Symptoms by Inhibiting NLRP3 Inflammasome-Mediated IL-1β in BALB/c Mice

Atopic dermatitis (AD) is a chronic inflammatory skin disease characterized by pruritus, dry skin and redness on the face and inside elbows or knees. Most patients with AD are children and youths, but it can also develop in adults. In the therapeutic aspect, treatment with corticosteroids for AD has several side effects, such as weight loss, atrophy and acne. In the current study, we examined the anti-inflammatory effect of Moringa concanensis leaves on HaCaT keratinocytes and 2,4-dinitrochlorobenzene (DNCB)-induced atopic dermatitis-like symptoms in BALB/c mice. We observed that M. concanensis treatment exhibited significant inhibition in the production of inflammatory mediators and proinflammatory cytokines, such as IL-1β, in LPS-induced HaCaT keratinocytes by downregulating the NLRP3 inflammasome activation. Moreover, M. concanensis inhibited the activation of JNK, AP-1 and p65, which resulted in the deformation of NLRP3 in LPS-stimulated HaCaT cells. In mice with DNCB-induced AD-like skin lesions, the administration of M. concanensis ameliorated the clinical symptoms, such as the dermatitis score, thickness of lesional ear skin and TEWL. Furthermore, M. concanensis could attenuate the activation of the immune system, such as reducing the spleen index, concentration of the IgE levels and expression of the NLRP3 inflammasome in ear tissues. Therefore, our results suggest that M. concanensis exerts anti-atopic dermatitis effects by inhibiting the NLRP3 inflammasome-mediated IL-1β.

Flavonoids Enhance Lipofection Efficiency and Ameliorate Cytotoxicity in Colon26 and HepG2 Cells via Oxidative Stress Regulation

The generation of reactive oxygen species (ROS) can affect cationic liposome-mediated transfection. In this study, we focused on a specific class of antioxidants, flavonoids, to investigate the transfection efficiency using cationic liposome/plasmid DNA complexes (lipoplexes) in 2D and 3D cultures of Colon26 and HepG2 cells, respectively. All tested flavonoids enhanced the transfection efficiency in 2D Colon26 and HepG2 cells. Among the tested flavonoids, 25 µM quercetin showed the highest promotion effect of 8.4- and 7.6-folds in 2D Colon26 and HepG2 cells, respectively. Transfection was also performed in 3D cultures of Colon26 and HepG2 cells using lipoplexes with quercetin. Quercetin (12.5 µM) showed the highest transfection efficiency at all transfection timings in 3D Colon26 and HepG2 cells with increased cell viability. Flow cytometry revealed that quercetin treatment reduced the population of gene expression-negative cells with high ROS levels and increased the number of gene expression-positive cells with low ROS levels in HepG2 cells. Information from this study can be valuable to develop strategies to promote transfection efficiency and attenuate cytotoxicity using lipoplexes.

Flavonoids: Nutraceuticals for Rheumatic Diseases via Targeting of Inflammasome Activation

Inflammation, an innate immune response that prevents cellular damage caused by pathogens, consists of two successive mechanisms, namely priming and triggering. While priming is an inflammation-preparation step, triggering is an inflammation-activation step, and the central feature of triggering is the activation of inflammasomes and intracellular inflammatory protein complexes. Flavonoids are natural phenolic compounds predominantly present in plants, fruits, and vegetables and are known to possess strong anti-inflammatory activities. The anti-inflammatory activity of flavonoids has long been demonstrated, with the main focus on the priming mechanisms, while increasing numbers of recent studies have redirected the research focus on the triggering step, and studies have reported that flavonoids inhibit inflammatory responses and diseases by targeting inflammasome activation. Rheumatic diseases are systemic inflammatory and autoimmune diseases that primarily affect joints and connective tissues, and they are associated with numerous deleterious effects. Here, we discuss the emerging literature on the ameliorative role of flavonoids targeting inflammasome activation in inflammatory rheumatic diseases.