Epigallocatechin-3-Gallate Prevents Acute Gout by Suppressing NLRP3 Inflammasome Activation and Mitochondrial DNA Synthesis

Mitochondrial DNA signals driving immune responses: Why, How, Where?

There has been a recent expansion in our understanding of DNA-sensing mechanisms. Mitochondrial dysfunction, oxidative and proteostatic stresses, instability and impaired disposal of nucleoids cause the release of mitochondrial DNA (mtDNA) from the mitochondria in several human diseases, as well as in cell culture and animal models. Mitochondrial DNA mislocalized to the cytosol and/or the extracellular compartments can trigger innate immune and inflammation responses by binding DNA-sensing receptors (DSRs). Here, we define the features that make mtDNA highly immunogenic and the mechanisms of its release from the mitochondria into the cytosol and the extracellular compartments. We describe the major DSRs that bind mtDNA such as cyclic guanosine-monophosphate-adenosine-monophosphate synthase (cGAS), Z-DNA-binding protein 1 (ZBP1), NOD-, LRR-, and PYD- domain-containing protein 3 receptor (NLRP3), absent in melanoma 2 (AIM2) and toll-like receptor 9 (TLR9), and their downstream signaling cascades. We summarize the key findings, novelties, and gaps of mislocalized mtDNA as a driving signal of immune responses in vascular, metabolic, kidney, lung, and neurodegenerative diseases, as well as viral and bacterial infections. Finally, we define common strategies to induce or inhibit mtDNA release and propose challenges to advance the field.

NLRP3 inflammasome in health and disease (Review)

Activation of inflammasomes is the activation of inflammation‑related caspase mediated by the assembly signal of multi‑protein complex and the maturity of inflammatory factors, such as IL‑1β and IL‑18. Among them, the Nod‑like receptor family pyrin domain containing 3 (NLRP3) inflammasome is the most thoroughly studied type of inflammatory corpuscle at present, which is involved in the occurrence and development of numerous human diseases. Therefore, targeting the NLRP3 inflammasome has become the focus of drug development for related diseases. In this paper, the research progress of the NLRP3 inflammasome in recent years is summarized, including the activation and regulation of NLRP3 and its association with diseases. A deep understanding of the regulatory mechanism of NLRP3 will be helpful to the discovery of new drug targets and the development of therapeutic drugs.

A Bidirectional Mendelian Randomization Study of Tea-Drinking Habits and Risk of Elevated Serum Uric Acid Levels

BACKGROUND

Although recent animal experiments have revealed that tea intake improves elevated serum uric acid (SUA) levels, a causal link between the consumption of different types of tea and SUA levels remains undetermined.

METHODS

Bidirectional Mendelian randomization (MR) analysis based on genome-wide association studies was used to assess the causal relationship between consumption of different types of tea and the risk of elevated SUA levels in European and Asian populations.

RESULTS

Forward MR analysis showed that tea intake was significantly associated with lower SUA levels (p = 0.0013). The estimated effect value (β $$ \beta $$  = $$ = $$  -0.0440) suggests that for every 1-unit increase in tea intake, there is a 0.044-unit decrease in SUA levels. However, there is no reverse causality between SUA and tea intake (p = 0.2824). No causal relationship was found between the consumption of different types of tea and risk of elevated SUA levels (p > 0.05).

CONCLUSION

Although this bidirectional MR study provided evidence of a causal relationship between tea intake and SUA levels, however, due to limitations associated with the sample size and strength of instrumental variables, a definite conclusion was not possible.

Triptolide attenuates LPS-induced chondrocyte inflammation by inhibiting inflammasome activation via the Wnt/β-catenin and NF-κB signaling pathways

Osteoarthritis (OA) is a common form of arthritis characterized by subchondral bone proliferation and articular cartilage degeneration. Recently, the Nod-like receptor pyrin domain 3 (NLRP3) inflammasome has gained attention due to its association with synovial inflammation in OA. Triptolide (TP), known for its immunosuppressive and anti-inflammatory effects, has been studied in various diseases. However, the specific impact of TP on OA and its underlying mechanism remains largely unexplored. In this study, chondrocytes were treated with a specific concentration of TP, and subsequent analysis through Western blotting and immunofluorescence staining revealed decreased expression levels of MMP-13, NLRP3, Caspase-1, ASC, β-catenin, p-p65, and IκB compared to the model group. ELISA results demonstrated significantly lower levels of IL-1β, IL-18, and TNF-α in the TP treatment group compared to the model group. In addition, triptolide ameliorates the degradation of the extracellular matrix (ECM) by enhancing the expression of collagen-II. In conclusion, our findings suggest that TP exhibits anti-inflammatory effects on chondrocytes in the presence of LPS-induced inflammation by inhibiting the activation of the NLRP3 inflammasome via the Wnt/β-catenin and NF-κB pathway. These results contribute to a better understanding of TP's potential therapeutic benefits in managing OA.

Nanostructures for Delivery of Flavonoids with Antibacterial Potential against Klebsiella pneumoniae

Flavonoids are secondary metabolites that exhibit remarkable biological activities, including antimicrobial properties against Klebsiella pneumoniae, a pathogen responsible for several serious nosocomial infections. However, oral administration of these compounds faces considerable challenges, such as low bioavailability and chemical instability. Thus, the encapsulation of flavonoids in nanosystems emerges as a promising strategy to mitigate these limitations, offering protection against degradation; greater solubility; and, in some cases, controlled and targeted release. Different types of nanocarriers, such as polymeric nanoparticles, liposomes, and polymeric micelles, among others, have shown potential to increase the antimicrobial efficacy of flavonoids by reducing the therapeutic dose required and minimizing side effects. In addition, advances in nanotechnology enable co-encapsulation with other therapeutic agents and the development of systems responsive to more specific stimuli, optimizing treatment. In this context, the present article provides an updated review of the literature on flavonoids and the main nanocarriers used for delivering flavonoids with antibacterial properties against Klebsiella pneumoniae.

Combination of Simo Decoction and Golden Bifid alleviates functional dyspepsia through a mechanism involving intestinal microbiota and short-chain fatty acids

BACKGROUND AND STUDY AIMS

The integration of traditional Chinese medicine and Western medicine holds promise for the treatment of gastrointestinal disorders, which are influenced by intestinal microbiota and metabolites. This study reports a possible mechanism for the combination of Simo Decoction and Golden Bifid in functional dyspepsia (FD) by regulating intestinal microbiota and short-chain fatty acids (SCFAs).

PATIENTS AND METHODS

A mouse model of food stagnation was constructed and treated with Simo Decoction combined with different concentrations of Golden Bifid. Meta-genomics sequencing was conducted to analyze the cecum contents of the mice. Following analyses of the composition and abundance of intestinal microbiota, gas chromatography-mass spectrometry was performed to measure SCFAs in the colonic content of mice. Finally, ELISA was utilized to determine the levels of pro-inflammatory factors in the duodenal mucosa of mice and the infiltration of eosinophils in the duodenum was observed by immunohistochemical staining.

RESULTS

Combination of Simo Decoction and Golden Bifid more significantly alleviated dyspepsia in mice with food stagnation compared with Simo Decoction alone. The optimal ratio of combined treatment was 0.0075 mL/g (body weight) Simo Decoction and 0.0032 mg/g (body weight) Golden Bifid. The combined treatment increased the abundance of Bifidobacterium and Bacteroides in the intestine. The levels of SCFAs in the colonic contents of mice were increased after the combined treatment, contributing to diminished pro-inflammatory factors in the duodenal mucosa and reduced eosinophil infiltration.

CONCLUSION

Combination of Simo Decoction and Golden Bifid increases the abundance of Bacteroides and Bifidobacterium and promotes the production of SCFAs, which is instrumental for alleviation of FD.

Harnessing the Power of Polyphenols: A New Frontier in Disease Prevention and Therapy

There are a wide variety of phytochemicals collectively known as polyphenols. Their structural diversity results in a broad range of characteristics and biological effects. Polyphenols can be found in a variety of foods and drinks, including fruits, cereals, tea, and coffee. Studies both in vitro and in vivo, as well as clinical trials, have shown that they possess potent antioxidant activities, numerous therapeutic effects, and health advantages. Dietary polyphenols have demonstrated the potential to prevent many health problems, including obesity, atherosclerosis, high blood sugar, diabetes, hypertension, cancer, and neurological diseases. In this paper, the protective effects of polyphenols and the mechanisms behind them are investigated in detail, citing the most recent available literature. This review aims to provide a comprehensive overview of the current knowledge on the role of polyphenols in preventing and managing chronic diseases. The cited publications are derived from in vitro, in vivo, and human-based studies and clinical trials. A more complete understanding of these naturally occurring metabolites will pave the way for the development of novel polyphenol-rich diet and drug development programs. This, in turn, provides further evidence of their health benefits.

A Review of Medicinal Plants and Phytochemicals for the Management of Gout

Gout, characterized by elevated uric acid levels, is a common inflammatory joint disease associated with pain, joint swelling, and bone erosion. Existing treatments for gout often result in undesirable side effects, highlighting the need for new, safe, and cost-effective anti-gout drugs. Natural products, including medicinal plants and phytochemicals, have gained attention as potential sources of anti-gout compounds. In this review, we examined articles from 2000 to 2020 using PubMed and Google Scholar, focusing on the effectiveness of medicinal plants and phyto-chemicals in managing gout. Our findings identified 14 plants and nine phytochemicals with anti-gout properties. Notably, Teucrium polium, Prunus avium, Smilax riparia, Rhus coriaria, Foenic-ulum vulgare, Allium cepa, Camellia japonica, and Helianthus annuus exhibited the highest xa-thine oxidase inhibitory activity, attributed to their unique natural bioactive compounds such as phenolics, tannins, coumarins, terpenoids, and alkaloids. Herbal plants and their phytochemicals have demonstrated promising effects in reducing serum urate and inhibiting xanthine. This review aims to report recent studies on plants/phytochemicals derived from herbs beneficial in gout and their different mechanisms.

Protective Role of Betulinic Acid against Cisplatin-Induced Nephrotoxicity and Its Antibacterial Potential toward Uropathogenic Bacteria

Acute kidney injury (AKI) is one of the major side effects of cisplatin, a remarkable anticancer agent. Therefore, there is a growing need to find an agent that could mitigate cisplatin-induced nephrotoxicity. Betulinic acid (BA) is a natural compound isolated from Silene succulenta Forssk for the first time, with miraculous biological activities and no reports of its effect on the nephrotoxicity induced by cisplatin. Mice received BA orally with doses of 30 and 50 mg/kg before the intraperitoneal injection of cisplatin. Betulinic acid was found to decrease serum levels of creatinine and tissue levels of NGAL and kidney injury molecule (KIM-1) and improve the histological changes in the kidney. In addition, BA decreased the oxidative stress marker malondialdehyde (MDA), increased superoxide dismutase (SOD) antioxidative activity and suppressed the intensity of IL-1B and NFкB immuno-staining. Interestingly, betulinic acid enhanced autophagy by increasing beclin 1, ATG5, and LC3II and decreasing p62 expressions. Thus, our findings suggest betulinic acid as a potential agent that may protect from acute kidney injury by targeting inflammation, oxidative stress, and autophagy processes. Novel drugs are needed to combat the spreading of multidrug resistance between pathogenic bacteria, especially uropathogenic isolates. So, we elucidated the antibacterial properties of BA on Pseudomonas aeruginosa, Escherichia coli, Proteus mirabilis, and Klebsiella pneumoniae. Betulinic acid had minimum inhibitory concentration values (128 to 512 µg/mL). In addition, it adversely affected the membrane integrity of the tested isolates. Accordingly, betulinic acid should be clinically investigated in the future for urinary tract diseases.

Immune and inflammatory mechanisms and therapeutic targets of gout: An update

Gout is an autoimmune disease characterized by acute or chronic inflammation and damage to bone joints induced due to the precipitation of monosodium urate (MSU) crystals. In recent years, with the continuous development of animal models and ongoing clinical investigations, more immune cells and inflammatory factors have been found to play roles in gouty inflammation. The inflammatory network involved in gout has been discovered, providing a new perspective from which to develop targeted therapy for gouty inflammation. Studies have shown that neutrophil macrophages and T lymphocytes play important roles in the pathogenesis and resolution of gout, and some inflammatory cytokines, such as those in the interleukin-1 (IL-1) family, have been shown to play anti-inflammatory or proinflammatory roles in gouty inflammation, but the mechanisms underlying their roles are unclear. In this review, we explore the roles of inflammatory cytokines, inflammasomes and immune cells in the course of gout development and the research status of therapeutic drugs used for inflammation to provide insights into future targeted therapy for gouty inflammation and the direction of gout pathogenesis research.

The Chinese patent medicine Tongfengding capsule for gout in adults: a systematic review of safety and effectiveness

BACKGROUND

Gout is a common inflammatory arthritis caused by increased serum uric acid levels. Untreated or insufficiently treated gout can lead to deposition of monosodium urate crystals in joints, cartilage, and kidneys. Although Tongfengding capsules, a Chinese patent medicine, have long been used to treat gout, their effects and safety have not been reviewed systematically. This study evaluated its efficacy and safety for gout in adults.

METHODS

Randomized controlled trials involving Tongfengding capsule for gout in adults were searched from PubMed, EMBASE, Cochrane Central Register of Controlled Trials, CBM, CNKI, and VIP databases, and analyzed using the Cochrane Handbook criteria. The primary outcome measures were the total effective rate. The secondary outcome measures including the blood uric acid (BUA), 24-h urinary total protein (24-h UTP), blood urea nitrogen (BUN), interleukin (IL)-6, IL-8, tumor necrosis factor-alpha (TNF-α) and adverse effects. The risk of bias was evaluated in all included studies. RevMan ver. 5.3.5 and GRADE profiler was used for data analysis and assessing the quality of evidence, respectively.

RESULTS

Six studies (n = 607 Chinese participants) were included. Tongfengding capsules plus conventional treatment significantly increased the total effective rate (RR 1.21, 95% CI 1.11-1.33), while reducing the BUA (MD - 66.05 µmol/L, 95% CI - 81.26 to - 50.84), 24-h UTP (MD - 0.83 g/24 h, 95% CI - 0.96 to - 0.70), BUN (MD - 0.90 mmol/L, 95% CI - 1.60 to - 0.20), IL-6 (MD - 6.99 ng/L, 95% CI - 13.22 to - 0.75), IL-8 (MD - 12.17 ng/L, 95% CI - 18.07 to - 6.27), TNF-α (MD - 8.50 ng/L, 95% CI - 15.50 to - 1.51), and adverse effects (RR 0.21, 95% CI 0.04-0.95).

CONCLUSION

Tongfengding capsules plus conventional treatment is safe and beneficial for adults with gout compared with conventional treatment.

Causal association between tea intake and risk for gout: a Mendelian randomization study

Background: Gout, an increasingly prevalent form of inflammatory arthritis, is caused by the accumulation of uric acid crystals in joints, resulting in severe pain, swelling and stiffness that adversely affect physical, mental and emotional wellbeing. The management of gout requires a combination of medication and lifestyle modifications. Recent studies suggest that tea intake may reduce the risk of developing gout; however, further research is needed to establish a causal relationship. Methods: In this study, we employed a bidirectional two-sample Mendelian randomization (MR) approach, utilizing genome-wide association study (GWAS) summary statistics, to investigate the causal association between increased tea intake and gout. We meticulously selected instrumental variables (IVs) based on rigorous criteria and employed five different MR methods. Heterogeneity was assessed using Cochran's Q statistic, and pleiotropy was evaluated using the MR Egger intercept and MR-PRESSO tests. Weak IVs were identified using F values. The Phenoscanner database was consulted to exclude single nucleotide polymorphisms associated with confounding factors or outcomes. Results: The study included one dataset related to tea intake (ukb-b-6066) and three datasets related to gout (ukb-b-12765, finn-b-M13_GOUT, and finn-b-GOUT_STRICT). Our forward MR analysis suggest a causal relationship between increased tea intake and reduced risk of gout in all three gout-related datasets [OR (95% CI): 0.9966 (0.9938-0.9993), p = 0.0167; 0.4842 (0.2683-0.8737), p-value = 0.0160; and 0.4554 (0.2155-0.9623), p = 0.0393, respectively]. The reveres MR showed increased risk of gout (ukb-b-12765) was significantly associated with low tea intake according to the IVW analysis [OR (95% CI): 0.0062 (0.0002-0.154), p = 0.0020]. However, this association was not observed in the Finn-b-M13_GOUT and Finn-b-GOUT_STRICT [OR (95% CI): 0.9992 (0.9909-1.0075), p = 0.8453 and OR (95% CI): 0.9996 (0.9932-1.0059), p = 0.8896, respectively]. No significant heterogeneity or potential pleiotropy was detected, and the possibility of weak IVs was also excluded. Conclusion: Our MR analysis suggest a causal relationship between genetically predicted tea intake and a decreased risk of gout. These findings underscore the potential advantages of increasing tea intake for preventing gout. However, further research is needed to validate these results and elucidate the underlying mechanisms.

Pro-Inflammatory of PRDM1/SIRT2/NLRP3 Axis in Monosodium Urate-Induced Acute Gouty Arthritis

PR domain-containing 1 with zinc finger domain (PRDM1) has been reported as a promoter of inflammation, which is a critical process involved in the pathogenesis of acute gouty arthritis. Herein, we sought to ascertain the function of PRDM1 in the development of acute gouty arthritis and related mechanisms. At first, peripheral blood-derived monocytes from patients with acute gouty arthritis and healthy individuals were collected as experimental samples. Then, macrophages were induced from monocytes using phorbol myristate acetate (PMA). The expression patterns of PRDM1, sirtuin 2 (SIRT2), and NLR family, pyrin domain-containing 3 (NLRP3) were characterized by RT-qPCR and Western blot assay. PMA-induced macrophages were stimulated by monosodium urate (MSU) for in vitro experimentation. Meanwhile, a murine model of MSU-induced acute gouty arthritis was established for in vivo validation. PRDM1 was highly expressed while SIRT2 poorly expressed in patients with acute gouty arthritis. Loss of PRDM1 could reduce NLRP3 inflammasome and mature IL-1β levels and downregulate inflammatory cytokines in macrophages, which contributed to protection against acute gouty arthritis. Furthermore, results showed that PRDM1 could inhibit SIRT2 expression via binding to the deacetylase SIRT2 promoter. Finally, the in vivo experiments demonstrated that PRDM1 increased NLRP3 inflammasome and mature IL-1β through transcriptional inhibition of SIRT2, whereby aggravating MSU-induced acute gouty arthritis. To sum up, PRDM1 increased NLRP3 inflammasome through inhibiting SIRT2, consequently aggravating MSU-induced acute gouty arthritis.

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.

Mechanisms of theaflavins against gout and strategies for improving the bioavailability

BACKGROUND

Gout is a crystal related arthropathy caused by monosodium urate deposition. At present, the identification of appropriate treatments and new drugs to reduce serum uric acid levels and gout risk is a major research area.

PURPOSE

Theaflavins are naturally occurring compounds characterized by a benzodiazepine skeleton. The significant benefits of theaflavins have been well documented. A large number of studies have been carried out and excellent anti-gout results have been achieved in recent years.

STUDY DESIGN

A comprehensive analysis of the mechanism of the anti-gout effect of theaflavins is presented through a literature review and network pharmacology prediction, and strategies for increasing the bioavailability of theaflavins are summarized.

METHODS

In this review, the active components and pharmacological mechanisms of theaflavins in the treatment of gout were summarized, and the relationship between theaflavins and gout, the relevant components, and the potential mechanisms of anti-gout action were clarified by reviewing the literature on the anti-gout effects of theaflavins and network pharmacology.

RESULTS

Theaflavins exert anti-gout effects by down regulating the gene and protein expression of glucose transporter 9 (GLUT9) and uric acid transporter 1 (URAT1), while upregulating the mRNA expression levels of organic anion transporter 1 (OAT1), organic cation transporter N1 (OCTN1), organic cation transporters 1/2 (Oct1/2), and organic anion transporter 2 (OAT2). Network pharmacology prediction indicate that theaflavins can regulate the AGE-RAGE and cancer signaling pathways through ATP-binding cassette subfamily B member 1 (ABCB1), recombinant mitogen activated protein kinase 14 (MAPK14), telomerase reverse tranase (TERT), signal transducer and activator of transcription 1 (STAT1), matrix metalloproteinase 2 (MMP2), B-cell lymphoma-2 (BCL2), and matrix metalloproteinase 14 (MMP14) targets for anti-gout effects.

CONCLUSION

This review presents the mechanisms of anti-gout action of theaflavins and strategies for improving the bioavailability of theaflavins, as well as providing research strategies for anti-gout treatment measures and the development of novel anti-gout drugs.

cGAS inhibition alleviates Alu RNA-induced immune responses and cytotoxicity in retinal pigmented epithelium

Background

The degeneration of retinal pigmented epithelium (RPE) cells results in severe diseases, such as age-related macular degeneration (AMD) that causes blindness in millions of individuals.

Results

We report that targeting GMP-AMP (cGAMP) synthase (cGAS) alleviates Alu RNA-induced immune responses and cytotoxicity in RPE. We find that the deletion of cGAS in RPE inhibits the Alu RNA-stimulated interferon production. cGAS deficiency also protects RPE from cell death triggered by Alu RNA. Importantly, two natural chemicals, epigallocatechin gallate (EGCG) and resveratrol (RSVL), are effective in suppressing the immunogenic and cytotoxic effect of Alu RNA in RPE.

Conclusions

Our findings further demonstrate the crucial role of cGAS in the Alu RNA-induced RPE damage and present EGCG and RSVL as potential therapies for AMD and other RPE degeneration-related conditions.

Aqueous core epigallocatechin gallate PLGA nanocapsules: characterization, antibacterial activity against uropathogens, and in vivo reno-protective effect in cisplatin induced nephrotoxicity

Epigallocatechin-3-gallate (EGCG) was isolated from Cycas thouarsii leaves for the first time and encapsulated in aqueous core poly(lactide-co-glycolide) (PLGA) nanocapsules (NCs). This work investigates antimicrobial activity and in vivo reno-protective effects of EGCG-PLGA NCs in cisplatin-induced nephrotoxicity. A double emulsion solvent evaporation process was adopted to prepare PLGA NCs loaded with EGCG. Particle size, polydispersity index (PDI), zeta potential, percent entrapment efficiency (%EE), structural morphology, and in vitro release platform were all studied in vitro. The optimum formula (F2) with particle size (61.37 ± 5.90 nm), PDI (0.125 ± 0.027), zeta potential (-11.83 ± 3.22 mV), %EE (85.79 ± 5.89%w/w), initial burst (36.85 ± 4.79), and percent cumulative release (87.79 ± 9.84) was selected for further in vitro/in vivo studies. F2 exhibited an enhanced antimicrobial activity against uropathogens as it had lower minimum inhibitory concentration (MIC) values and a more significant impact on bacterial growth than free EGCG. Forty male adult mice were randomly allocated into five groups: control vehicle, untreated methotrexate, MTX groups treated with a daily oral dose of free EGCG, placebo PLGA NCs, and EGCG PLGA NCs (F2) for 10 days. Results showed that EGCG PLGA NCs (F2) exerted promising renoprotective effects compared to free EGCG. EGCG PLGA NCs group induced a significant decrease in kidney index, serum creatinine, kidney injury molecule-1 (KIM-1), NGAL serum levels, and pronounced inhibition of NLPR-3/caspase-1/IL/1β inflammasome pathway. It also significantly ameliorated oxidative stress and decreased NFκB, Bax expression levels. Aqueous core PLGA NCs are a promising formulation strategy that provides high polymeric protection and sustained release pattern for hydrophilic therapeutic agents.

Inflammasomes and their roles in arthritic disease pathogenesis

The inflammasome is a molecular platform that is created in the cytosolic compartment to mediate the host immunological response to cellular injury and infection. Caspase-1 may be activated by the inflammasome, which leads to the generation of the inflammatory cytokines interleukin-1β (IL-1β) and IL-18 and the beginning of pyroptosis, which is a type of proinflammatory cell death. Scientists have identified a number of different inflammasomes in the last 2 decades. The NLRP3 inflammasome has been studied the most, and its activity may be triggered by a broad range of different inducers. However, activation of the NLRP3 inflammasome in a manner that is not properly controlled is also a factor in the etiology of many human illnesses. Accumulating evidence indicates that the NLRP3 inflammasome plays a significant role in the innate and adaptive immune systems and the development of various arthritic illnesses, such as rheumatoid arthritis, ankylosing spondylitis, and gout. The present review provides a concise summary of the biological properties of the NLRP3 inflammasome and presents the fundamental processes behind its activation and control. We discuss the role of the inflammasome in the pathogenesis of arthritic diseases, such as rheumatoid arthritis, ankylosing spondylitis, and gout, and the potential of newly developed therapies that specifically target the inflammasome or its products for the treatment of inflammatory diseases, with a particular emphasis on treatment and clinical application.

Phytotherapeuthics Affecting the IL-1/IL-17/G-CSF Axis: A Complementary Treatment Option for Hidradenitis Suppurativa?

Hidradenitis suppurativa (HS; also designated as acne inversa) is a chronic inflammatory disease characterized by painful skin lesions that occur in the axillary, inguinal, gluteal and perianal areas of the body. These lesions contain recurring deep-seated, inflamed nodules and pus-discharging abscesses and fistulas. Affecting about 1% of the population, this common disease has gained appropriate clinical attention in the last years. Associated with numerous comorbidities including metabolic syndrome, HS is considered a systemic disease that severely impairs the quality of life and shortens life expectancy. Therapeutic options for HS are limited, comprising long-term antibiotic treatment, the surgical removal of affected skin areas, and neutralization of TNF-α, the only approved systemic treatment. Novel treatment options are needed to close the therapeutic gap. HS pathogenesis is increasingly better understood. In fact, neutrophilic granulocytes (neutrophils) seem to be decisive for the development of the purulent destructive skin inflammation in HS. Recent findings suggest a key role of the immune mediators IL-1β, IL-17A and G-CSF in the migration into and activation of neutrophils in the skin. Although phytomedical drugs display potent immunoregulatory properties and have been suggested as complementary therapy in several chronic disorders, their application in HS has not been considered so far. In this review, we describe the IL-1/IL-17/G-CSF axis and evaluate it as potential target for an integrated phytomedical treatment of HS.

Pyroptosis in acute pancreatitis and its therapeutic regulation

Pyroptosis defines a new type of GSDMs-mediated programmed cell death, distinguishes from the classical concepts of apoptosis and necrosis-mediated cell death and is prescribed by cell swelling and membrane denaturation, leading to the extensive secretion of cellular components and low-grade inflammatory response. However, NLRP3 inflammasome activation can trigger its downstream inflammatory cytokines, leading to the activation of pyroptosis-regulated cell death. Current studies reveal that activation of caspase-4/5/11-driven non-canonical inflammasome signaling pathways facilitates the pathogenesis and progression of acute pancreatitis (AP). In addition, a large number of studies have reported that NLRP3 inflammasome-dependent pyroptosis is a crucial player in driving the course of the pathogenesis of AP. Excessive uncontrolled GSDMD-mediated pyroptosis has been implicated in AP. Therefore, the pyroptosis-related molecule GSDMD may be an independent prognostic biomarker for AP. The present review paper summarizes the molecular mechanisms of pyroptotic signaling pathways and their pathophysiological impacts on the progress of AP. Moreover, we briefly present some experimental compounds targeting pyroptosis-regulated cell death for exploring novel therapeutic directions for the treatment and management of AP. Our review investigations strongly suggest that targeting pyroptosis could be an ideal therapeutic approach in AP.

The NLRP3 Inflammasome Pathway: A Review of Mechanisms and Inhibitors for the Treatment of Inflammatory Diseases

The NLRP3 inflammasome is a multiprotein complex that plays a pivotal role in regulating the innate immune system and inflammatory signaling. Upon activation by PAMPs and DAMPs, NLRP3 oligomerizes and activates caspase-1 which initiates the processing and release of pro-inflammatory cytokines IL-1β and IL-18. NLRP3 is the most extensively studied inflammasome to date due to its array of activators and aberrant activation in several inflammatory diseases. Studies using small molecules and biologics targeting the NLRP3 inflammasome pathway have shown positive outcomes in treating various disease pathologies by blocking chronic inflammation. In this review, we discuss the recent advances in understanding the NLRP3 mechanism, its role in disease pathology, and provide a broad review of therapeutics discovered to target the NLRP3 pathway and their challenges.

The Protective Effects of Neoastilbin on Monosodium Urate Stimulated THP-1-Derived Macrophages and Gouty Arthritis in Mice through NF-κB and NLRP3 Inflammasome Pathways

Gouty arthritis (GA) is a frequent inflammatory disease characterized by pain, swelling, and stiffness of joints. Neoastilbin is a flavonoid isolated from the rhizome of Smilax glabra, which possesses various anti-inflammatory effects. However, the mechanism of neoastilbin in treating GA has not yet been clarified. Thus, this study was to investigate the protective effects of neoastilbin in both monosodium urate (MSU) stimulated THP-1-derived macrophages and the animal model of GA by injecting MSU into the ankle joints of mice. The levels of key inflammatory cytokines in MSU stimulated THP-1-derived macrophages were detected by enzyme-linked immunosorbent assay (ELISA) kits. Protein expressions of nuclear factor kappa B (NF-κB) and NOD-like receptor protein 3 (NLRP3) inflammasome pathways were further detected by Western blotting. In addition, swelling degree of ankle joints, the levels of inflammatory factors, infiltration of inflammatory cells and the expressions of related proteins were determined. Swelling degree and histopathological injury in ankle joints of MSU-injected mice were significantly decreased after being treated with neoastilbin. Moreover, neoastilbin significantly diminished the secretion of interleukin-1β (IL-1β), interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α), suppressing the activation of NF-κB and NLRP3 inflammasome pathways in both MSU stimulated THP-1-derived macrophages and the mouse model of GA. In summary, neoastilbin could alleviate GA by inhibiting the NF-κB and NLRP3 inflammasome pathways, which provided some evidence for neoastilbin as a promising therapeutic agent for GA treatment.

Cynarin suppresses gouty arthritis induced by monosodium urate crystals

The study is aimed to determine the effects of cynarin (Cyn) on mice with gouty arthritis (GA) induced by monosodium urate (MSU). We measured swelling in the hind paws of mice in vivo using Vernier calipers and ultrasound. The liver, kidney, and hind paws were stained with hematoxylin-eosin, and M1 type macrophages were detected in the hind paws using anti-F4/80 and anti-iNOS antibodies. The mRNA expression of inflammatory factors in bone marrow-derived macrophages (BMDMs) and in the hind paws was detected via quantitative reverse transcription-polymerase chain reaction (qRT-PCR). Nucleotide-binding oligomerization domain (NOD)-like receptor (NLR) family pyrin domain containing 3 (NLRP3) inflammasomes and the nuclear factor kappa B (NF-κB) and mitogen-activated protein kinase (MAPK) pathways were analyzed via western blotting. Cyn was detected in vitro using Cell Counting Kit-8 (CCK-8). Cyn treatment reduced hind paw swelling and M1 macrophage infiltration, suppressed the mRNA expression of inflammatory factors, and inhibited NLRP3 inflammasome activation in vivo, in addition to inhibiting the phosphorylation of IKKa/β, p65, and c-Jun NH 2-terminal kinase (JNK). Furthermore, Cyn exerted anti-inflammatory and anti-swelling effects in mice with GA by regulating the NF-κB and JNK pathways and NLRP3 inflammasomes.

NLRP3 Inflammasome Activation: A Therapeutic Target for Cerebral Ischemia–Reperfusion Injury

Millions of patients are suffering from ischemic stroke, it is urgent to figure out the pathogenesis of cerebral ischemia–reperfusion (I/R) injury in order to find an effective cure. After I/R injury, pro-inflammatory cytokines especially interleukin-1β (IL-1β) upregulates in ischemic brain cells, such as microglia and neuron. To ameliorate the inflammation after cerebral I/R injury, nucleotide-binding oligomerization domain (NOD), leucine-rich repeat (LRR), and pyrin domain-containing protein 3 (NLRP3) inflammasome is well-investigated. NLRP3 inflammasomes are complicated protein complexes that are activated by endogenous and exogenous danger signals to participate in the inflammatory response. The assembly and activation of the NLRP3 inflammasome lead to the caspase-1-dependent release of pro-inflammatory cytokines, such as interleukin (IL)-1β and IL-18. Furthermore, pyroptosis is a pro-inflammatory cell death that occurs in a dependent manner on NLRP3 inflammasomes after cerebral I/R injury. In this review, we summarized the assembly and activation of NLRP3 inflammasome; moreover, we also concluded the pivotal role of NLRP3 inflammasome and inhibitors, targeting the NLRP3 inflammasome in cerebral I/R injury.

(-)-Epicatechin Ameliorates Monosodium Urate-Induced Acute Gouty Arthritis Through Inhibiting NLRP3 Inflammasome and the NF-κB Signaling Pathway

Background: Gouty arthritis is a common and complex inflammatory disease that will reduce the life quality of human beings (-)-Epicatechin (EC) is famous for antioxidant and anti-inflammatory activities. Thus, the aim of this study was to investigate the therapeutic effect of EC on gouty arthritis and its mechanisms. Methods and results: EC was added into a monosodium urate (MSU)-stimulated THP-1 cell that was induced by phorbol 12-myristate 13-acetate and lipopolysaccharide (LPS) in advance to establish a gout model in vitro. The efficiency of EC on acute gouty arthritis mice induced by MSU was further investigated. The results showed that EC concentration-dependently improved the cell viability of LPS and MSU stimulated THP-1 cells, and significantly alleviated MSU-induced ankle edema in mice in a dose-dependent manner. In addition, EC inhibited the infiltration of inflammatory cells and local cascular congestion in ankle joint tissue. Furthermore, the secretion of inflammatory cytokines (IL-1β, IL-18, IL-6, and TNF-α) activation of NLRP3 inflammasome and NF-κB signaling pathway were markedly suppressed by EC in vitro and in vivo. Conclusion: These results indicated that EC could effectively improve MSU-induced acute gouty arthritis via inhibiting NLRP3 inflammasome and the NF-κB signaling pathway in vitro and in vivo, which suggested that EC might be a promising active ingredient for the prevention and treatment of gouty arthritis.

Inflammatory Response to Regulated Cell Death in Gout and Its Functional Implications

Gout, a chronic inflammatory arthritis disease, is characterized by hyperuricemia and caused by interactions between genetic, epigenetic, and metabolic factors. Acute gout symptoms are triggered by the inflammatory response to monosodium urate crystals, which is mediated by the innate immune system and immune cells (e.g., macrophages and neutrophils), the NACHT, LRR, and PYD domains-containing protein 3 (NLRP3) inflammasome activation, and pro-inflammatory cytokine (e.g., IL-1β) release. Recent studies have indicated that the multiple programmed cell death pathways involved in the inflammatory response include pyroptosis, NETosis, necroptosis, and apoptosis, which initiate inflammatory reactions. In this review, we explore the correlation and interactions among these factors and their roles in the pathogenesis of gout to provide future research directions and possibilities for identifying potential novel therapeutic targets and enhancing our understanding of gout pathogenesis.

Effect of Dietary Polyphenols on Osteoarthritis-Molecular Mechanisms

Osteoarthritis is a common crippling and degenerative disease resulting in irreversible functional changes due to damage of the cartilage and other tissues of the joint. With limited safe and effective pharmaceutical treatments, the demand and use for alternative therapeutic approaches with symptomatic relief for OA patients have increased. Clinical, pre-clinical, and in vitro studies have demonstrated that polyphenols can exert pain-relieving symptoms coupled with increased functional capacity in OA models. This review will highlight studies carried out in the last five years to define the efficacies and underlying mechanisms in polyphenols such as quercetin, resveratrol, curcumin, epigallocatechin-3-gallate, rosmarinic acid, genistein, ginger, berries, silver fir, pine bark, and Boswellia. Most of these studies indicate that polyphenols exhibit their beneficial roles through regulating changes at the biochemical and molecular levels, inducing or inhibiting various signaling pathways related to inflammation and oxidative stress. Polyphenols have also been implicated in modulating microRNA at the posttranscriptional level to counteract OA pathogenesis.

Effects and underlying mechanisms of food polyphenols in treating gouty arthritis: A review on nutritional intake and joint health

Gouty arthritis, one of the most severe and common forms of arthritis, is characterized by monosodium urate crystal deposition in joints and surrounding tissues. Epidemiological evidence indicates that gouty arthritis incidence is sharply rising globally. Polyphenols are found in many foods and are secondary metabolites in plant foods. The anti-inflammatory and antioxidant effects of food polyphenols have been extensively studied in many inflammatory chronic diseases. Research has suggested that many food polyphenols have excellent anti-gouty arthritis effects. The mechanisms mainly include (a) inhibiting xanthine oxidase activity; (b) reducing the levels of inflammatory cytokines and chemokines; (c) inhibiting the activation of signaling pathways and the NLRP3 inflammasome; and (d) reducing oxidative stress. This paper reviews the research progress and pathogenesis of gouty arthritis and introduces the mechanisms of food polyphenols in treating gouty arthritis, which aims to explore the potential of functional foods in the treatment of gouty arthritis. PRACTICAL APPLICATIONS: The incidence rate of gouty arthritis has increased sharply worldwide, which has seriously affected people's quality of life. According to the current research progress, food polyphenols alleviate gouty arthritis through anti-inflammatory and antioxidant effects. This paper reviews the research progress and molecular pathogenesis of gouty arthritis and introduces the mechanisms of food-derived polyphenols in the treatment of gouty arthritis, which is helpful to the prevention and treatment of gouty arthritis.

Immunomodulatory Effects of Green Tea Polyphenols

Green tea and its bioactive components, especially polyphenols, possess many health-promoting and disease-preventing benefits, especially anti-inflammatory, antioxidant, anticancer, and metabolic modulation effects with multi-target modes of action. However, the effect of tea polyphenols on immune function has not been well studied. Moreover, the underlying cellular and molecular mechanisms mediating immunoregulation are not well understood. This review summarizes the recent studies on the immune-potentiating effects and corresponding mechanisms of tea polyphenols, especially the main components of (-)-epigallocatechin-3-gallate (EGCG) and (-)-epicatechin-3-gallate (ECG). In addition, the benefits towards immune-related diseases, such as autoimmune diseases, cutaneous-related immune diseases, and obesity-related immune diseases, have been discussed.

MiR-223-3p inhibits inflammation and pyroptosis in monosodium urate-induced rats and fibroblast-like synoviocytes by targeting NLRP3

Down-regulated miR-223-3p was found in rheumatoid arthritis. This study aimed to further explore the level and role of miR-223-3p in gout arthritis (GA). After monosodium urate (MSU)-induced GA rat and fibroblast-like synoviocytes (FLSs) models were established, the rat paw volume and gait score were documented and the FLSs were transfected with miR-223-3p mimic/inhibitor or NLR family pyrin domain containing 3 (NLRP3) over-expression plasmids. The MiR-223-3p target was found through bioinformatics and the dual-luciferase reporter. The rat joint pathological damage was observed by hematoxylin and eosin staining. The levels of interleukin (IL)-1β, tumor necrosis factor (TNF)-α and articular elastase in rats were detected by enzyme-linked immunosorbent assay (ELISA). The viability and pyroptosis of FLSs were detected by methyl thiazolyl tetrazolium (MTT) and flow cytometry. The expressions of miR-223-3p, NLRP3, cleaved caspase-1, IL-1β, apoptosis-associated speck-like protein (AS) and cleaved N-terminal gasdermin D (GSDMD) in FLSs or rat synovial tissues were detected by reverse transcription-quantitative polymerase chain reaction (RT-qPCR), immunofluorescence, Western blot or immunohistochemistry analysis. MSU increased the paw volume, gait score, inflammation in synovial tissues and increased the levels of IL-1β, TNF-α and articular elastase in rats. MSU decreased the viability and increased the pyroptosis of FLSs, up-regulated the expression of NLRP3, ASC, cleaved caspase-1, cleaved N-terminal GSDM, and IL-1β, and down-regulated miR-223-3p expression in synovial tissues of rat joints and FLSs. MiR-223-3p mimic reversed the effect of MSU on lowering cell viability, increasing pyroptosis in FLSs, while miR-223-3p inhibitor further enhanced the effect of MSU on FLSs. NLRP3 was a target of miR-223-3p. Also, NLRP3 over-expression reversed the effects of miR-223-3p on MSU-induced FLSs. MiR-223-3p inhibited pyroptosis in MSU-induced rats and FLSs by targeting NLRP3.

Loganin Alleviates Gout Inflammation by Suppressing NLRP3 Inflammasome Activation and Mitochondrial Damage

Gout is a type of inflammatory arthritis caused by the deposition of monosodium uric acid (MSU) crystals in tissues. The etiology of gout is directly linked to the NLRP3 inflammasome, since MSU crystals are NLRP3 inflammasome activators. Therefore, we decided to search for a small-molecule inhibitor of the NLRP3 inflammasome for the prevention of gout inflammation. We found that loganin suppressed MSU crystals-induced caspase-1 (p20) and interleukin (IL)-1β production and apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) specks formation in mouse primary macrophages, showing its ability to inhibit the NLRP3 inflammasome. In an air pouch inflammation model, oral administration of loganin to mice prevented MSU crystals-induced production of mature IL-1β and IL-18 in air pouch exudates, resulting in decreased neutrophil recruitment. Furthermore, oral administration of loganin suppressed MSU crystals-induced gout inflammation in a mouse foot gout model, which was accompanied by the inhibition of the NLRP3 inflammasome. Loganin blocked de novo synthesis of mitochondrial DNA in air pouches and foot tissues injected with MSU crystals. Consistently, loganin prevented MSU crystals-induced mitochondrial damage in macrophages, as it increased mitochondrial membrane potential and decreased the amount of mitochondrial reactive oxygen species. These data demonstrate that loganin suppresses NLRP3 inflammasome activation by inhibiting mitochondrial stress. These results suggest a novel pharmacological strategy to prevent gout inflammation by blocking NLRP3 inflammasome activation and mitochondrial dysfunction.

Therapeutic regulation of the NLRP3 inflammasome in chronic inflammatory diseases

Inflammasomes are cytosolic pattern recognition receptors that recognize pathogen-associated molecular patterns (PAMPs) and danger-associated molecular patterns (DAMPs) derived from invading pathogens and damaged tissues, respectively. Upon activation, the inflammasome forms a complex containing a receptor protein, an adaptor, and an effector to induce the autocleavage and activation of procaspase-1 ultimately culminating in the maturation and secretion of IL-1β and IL-18 and pyroptosis. Inflammasome activation plays an important role in host immune responses to pathogen infections and tissue repair in response to cellular damage. The NLRP3 inflammasome is a well-characterized pattern recognition receptor and is well known for its critical role in the regulation of immunity and the development and progression of various inflammatory diseases. In this review, we summarize recent efforts to develop therapeutic applications targeting the NLRP3 inflammasome to cure and prevent chronic inflammatory diseases. This review extensively discusses NLRP3 inflammasome-related diseases and current development of small molecule inhibitors providing beneficial information on the design of therapeutic strategies for NLRP3 inflammasome-related diseases. Additionally, small molecule inhibitors are classified depending on direct or indirect targeting mechanism to describe the current status of the development of pharmacological inhibitors.

Regulation of the NLRP3 Inflammasome by Post-Translational Modifications and Small Molecules

Inflammation is a host protection mechanism that eliminates invasive pathogens from the body. However, chronic inflammation, which occurs repeatedly and continuously over a long period, can directly damage tissues and cause various inflammatory and autoimmune diseases. Pattern recognition receptors (PRRs) respond to exogenous infectious agents called pathogen-associated molecular patterns and endogenous danger signals called danger-associated molecular patterns. Among PRRs, recent advancements in studies of the NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3) inflammasome have established its significant contribution to the pathology of various inflammatory diseases, including metabolic disorders, immune diseases, cardiovascular diseases, and cancer. The regulation of NLRP3 activation is now considered to be important for the development of potential therapeutic strategies. To this end, there is a need to elucidate the regulatory mechanism of NLRP3 inflammasome activation by multiple signaling pathways, post-translational modifications, and cellular organelles. In this review, we discuss the intracellular signaling events, post-translational modifications, small molecules, and phytochemicals participating in the regulation of NLRP3 inflammasome activation. Understanding how intracellular events and small molecule inhibitors regulate NLRP3 inflammasome activation will provide crucial information for elucidating the associated host defense mechanism and the development of efficient therapeutic strategies for chronic diseases.

Epigallocatechin-3-gallate prevents inflammation and diabetes -Induced glucose tolerance through inhibition of NLRP3 inflammasome activation

Epigallocatechin-3-gallate (EGCG), the primary polyphenol component of green tea, has been shown to inhibit both oxidation and inflammation. However, the exact mechanism through which EGCG exhibits anti-inflammatory effects remains unclear. In this study, we assessed the potential pathways by which EGCG regulates NLRP3 inflammasome activity in vitro. We found that EGCG inhibits caspase-1 activation and IL-1β secretion by suppressing NLRP3 inflammasome activation in mouse bone marrow-derived macrophages (BMDMs). EGCG was also observed to block NLRP3-mediated ASC speckle formation and to alleviate pyroptosis in BMDMs. In addition, EGCG treatment could improve high-fat diet (HFD)-induced glucose tolerance and prevent NLRP3 inflammasome-dependent inflammation in a mouse model of HFD-induced type 2 diabetes (T2D). Taken together, our results show that EGCG is a general inhibitor of NLRP3 inflammasome activation and administration of EGCG in T2D mice could improve glucose tolerance in vivo.

Epigallocatechin-3-gallate attenuates acute pancreatitis induced lung injury by targeting mitochondrial reactive oxygen species triggered NLRP3 inflammasome activation

Green tea has been considered as a health-promoting beverage and is widely consumed worldwide. Epigallocatechin-3-gallate (EGCG), the most abundant polyphenol derived from green tea leaves with potent antioxidative and chemopreventive activities, has been reported to offer protection against inflammation-driven tissue damage. Here, we evaluated the protective effects of EGCG against lung injury during acute pancreatitis (AP) and further revealed the detailed mechanism. The results showed that EGCG significantly attenuated l-arginine-induced AP and the consequent pulmonary damage in mice. Moreover, EGCG substantially attenuated oxidative stress and concurrently suppressed NOD-like receptor protein 3 (NLRP3) inflammasome activation in the lung. In vitro, EGCG considerably reduced the production of mitochondrial reactive oxygen species (mtROS) and oxidized mitochondrial DNA (ox-mtDNA) in alveolar macrophages (AMs) challenged with AP-conditioned plasma. Meanwhile, the amount of ox-mtDNA bound to NLRP3 decreased significantly by the treatment with EGCG, resulting in impaired NLRP3 inflammasome activation. In addition, the antagonism of NLRP3 signaling by EGCG was affected in the presence of the mtROS stimulant rotenone or scavenger Mito-TEMPO. Altogether, EGCG possesses potent activity to attenuate lung injury during AP progression by inhibiting NLRP3 inflammasome activation. As for the mechanism, the EGCG-conferred restriction of NLRP3 inflammasome activation probably arises from the elimination of mtROS as well as its oxidative product ox-mtDNA, which consequently enables the protection against AP-associated lung injury.

Management of Gout-associated MSU crystals-induced NLRP3 inflammasome activation by procyanidin B2: targeting IL-1β and Cathepsin B in macrophages

Gout, the most prevalent inflammatory arthritis worldwide, released interleukin-1β (IL-1β) and Cathepsin B inflammatory mediators that constitute the hallmark of the disease. Herein we aimed to investigate whether procyanidin B2 (PCB2), a natural dietary compound, can suppress MSU crystals-stimulated gouty inflammation. Treated with lipopolysaccharide (LPS) plus MSU, both mouse peritoneal macrophages (MPM) and mouse bone marrow-derived macrophages (BMDM) released a large amount of mature IL-1β compared to those treated with MSU or LPS alone, while IL-1β release was blocked by TLR4 and its downstream effector inhibitors. In two mouse models of gout, oral administration of PCB2 suppressed MSU crystals-induced increasing expression of IL-1β, Cathepsin B and NLRP3 in the air pouch skin and paws, accompanied with the downregulation prostaglandin E2 (PGE2) in pouch exudates. Inflammatory immune cell infiltration including macrophages and neutrophils were significantly blocked by PCB2 in air pouch skin and paws of mice gout groups. PCB2 also suppressed the release of IL-1β and Cathepsin B induced by MSU plus LPS in MPM. Our results suggest that the inhibitory effects of PCB2 on NLRP3 inflammasome may alleviate inflammatory response in gout, and this might be a promising anti-inflammatory mechanism of PCB2 against the inflammation in gout.

Effects of Standardized Green Tea Extract and Its Main Component, EGCG, on Mitochondrial Function and Contractile Performance of Healthy Rat Cardiomyocytes

We recently showed that the long-term in vivo administration of green tea catechin extract (GTE) resulted in hyperdynamic cardiomyocyte contractility. The present study investigates the mechanisms underlying GTE action in comparison to its major component, epigallocatechin-3-gallate (EGCG), given at the equivalent amount that would be in the entirety of GTE. Twenty-six male Wistar rats were given 40 mL/day of a tap water solution with either standardized GTE or pure EGCG for 4 weeks. Cardiomyocytes were then isolated for the study. Cellular bioenergetics was found to be significantly improved in both GTE- and EGCG-fed rats compared to that in controls as shown by measuring the maximal mitochondrial respiration rate and the cellular ATP level. Notably, the improvement of mitochondrial function was associated with increased levels of oxidative phosphorylation complexes, whereas the cellular mitochondrial mass was unchanged. However, only the GTE supplement improved cardiomyocyte mechanics and intracellular calcium dynamics, by lowering the expression of total phospholamban (PLB), which led to an increase of both the phosphorylated-PLB/PLB and the sarco-endoplasmic reticulum calcium ATPase/PLB ratios. Our findings suggest that GTE might be a valuable adjuvant tool for counteracting the occurrence and/or the progression of cardiomyopathies in which mitochondrial dysfunction and alteration of intracellular calcium dynamics constitute early pathogenic factors.

Repurposing Auranofin, an Anti-Rheumatic Gold Compound, to Treat Acne Vulgaris by Targeting the NLRP3 Inflammasome

Activation of the NLRP3 inflammasome is critical for host defense as well as the progression of inflammatory diseases through the production of the proinflammatory cytokine IL-1β, which is cleaved by active caspase-1. It has been reported that overactivation of the NLRP3 inflammasome contributes to the development and pathology of acne vulgaris. Therefore, inhibiting activation of the NLRP3 inflammasome may provide a new therapeutic strategy for acne vulgaris. In this study, we investigated whether auranofin, an anti-rheumatoid arthritis agent, inhibited NLRP3 inflammasome activation, thereby effectively treating acne vulgaris. Auranofin suppressed NLRP3 inflammasome activation induced by Propionibacterium acnes, reducing the production of IL-1β in primary mouse macrophages and human sebocytes. In a P. acnes-induced acne mouse model, injection of P. acnes into the ears of mice induced acne symptoms such as redness, swelling, and neutrophil infiltration. Topical application of auranofin (0.5 or 1%) to mouse ears significantly reduced the inflammatory symptoms of acne vulgaris induced by P. acnes injection. Topical application of auranofin led to the downregulation of the NLRP3 inflammasome activated by P. acnes in mouse ear skin. These results show that auranofin inhibits the NLRP3 inflammasome, the activation of which is associated with acne symptoms. The results further suggest that topical application of auranofin could be a new therapeutic strategy for treating acne vulgaris by targeting the NLRP3 inflammasome.

Inflammation, Lipid (Per)oxidation, and Redox Regulation

Significance: Inflammation increases during the aging process. It is linked to mitochondrial dysfunction and increased reactive oxygen species (ROS) production. Mitochondrial macromolecules are critical targets of oxidative damage; they contribute to respiratory uncoupling with increased ROS production, redox stress, and a cycle of senescence, cytokine production, and impaired oxidative phosphorylation. Targeting the formation or accumulation of oxidized biomolecules, particularly oxidized lipids, in immune cells and mitochondria could be beneficial for age-related inflammation and comorbidities. Recent Advances: Inflammation is central to age-related decline in health and exhibits a complex relationship with mitochondrial redox state and metabolic function. Improvements in mass spectrometric methods have led to the identification of families of oxidized phospholipids (OxPLs), cholesterols, and fatty acids that increase during inflammation and which modulate nuclear factor erythroid 2-related factor 2 (Nrf2), peroxisome proliferator-activated receptor gamma (PPARγ), activator protein 1 (AP1), and NF-κB redox-sensitive transcription factor activity. Critical Issues: The kinetic and spatial resolution of the modified lipidome has profound and sometimes opposing effects on inflammation, promoting initiation at high concentration and resolution at low concentration of OxPLs. Future Directions: There is an emerging opportunity to prevent or delay age-related inflammation and vascular comorbidity through a resolving (oxy)lipidome that is dependent on improving mitochondrial quality control and restoring redox homeostasis.

Direct Binding to NLRP3 Pyrin Domain as a Novel Strategy to Prevent NLRP3-Driven Inflammation and Gouty Arthritis

OBJECTIVE

The NLRP3 inflammasome is closely linked to the pathophysiology of a wide range of inflammatory diseases. This study was undertaken to identify small molecules that directly bind to NLRP3 in order to develop pharmacologic interventions for NLRP3-related diseases.

METHODS

A structure-based virtual screening analysis was performed with ~62,800 compounds to select efficient NLRP3 inhibitors. The production of caspase 1-p10 and interleukin-1β (IL-1β) was measured by immunoblotting and enzyme-linked immunosorbent assay to examine NLRP3 inflammasome activation. Two gouty arthritis models and an air pouch inflammation model induced by monosodium urate monohydrate (MSU) crystal injection were used for in vivo experiments. Primary synovial fluid cells from gout patients were used to determine the relevance of NLRP3 inflammasome inhibition in human gout.

RESULTS

Beta-carotene (provitamin A) suppressed the NLRP3 inflammasome activation induced by various activators, including MSU crystals, in mouse bone marrow-derived primary macrophages (P < 0.05). Surface plasmon resonance analysis demonstrated the direct binding of β-carotene to the pyrin domain (PYD) of NLRP3 (K_D = 3.41 × 10^-6 ). Molecular modeling and mutation assays revealed the interaction mode between β-carotene and the NLRP3 PYD. Inflammatory symptoms induced by MSU crystals were attenuated by oral administration of β-carotene in gouty arthritis mouse models (P < 0.05), correlating with its suppressive effects on the NLRP3 inflammasome in inflamed tissues. Furthermore, β-carotene reduced IL-1β secretion from human synovial fluid cells isolated from gout patients (P < 0.05), showing its inhibitory efficacy in human gout.

CONCLUSION

Our results present β-carotene as a selective and direct inhibitor of NLRP3, and the binding of β-carotene to NLRP3 PYD as a novel pharmacologic strategy to combat NLRP3 inflammasome-driven diseases, including gouty arthritis.

Mitochondrial superoxide/hydrogen peroxide: An emerging therapeutic target for metabolic diseases

Mitochondria are well known for their roles as energy and metabolic factory. Mitochondrial reactive oxygen species (mtROS) refer to superoxide anion radical (^•O₂^-) and hydrogen peroxide (H₂O₂). They are byproducts of electron transport in mitochondrial respiratory chain and are implicated in the regulation of physiological and pathological signal transduction. Especially when mitochondrial ^•O₂^-/H₂O₂ production is disturbed, this disturbance is closely related to the occurrence and development of metabolic diseases. In this review, the sources of mitochondrial ^•O₂^-/H₂O₂ as well as mitochondrial antioxidant mechanisms are summarized. Furthermore, we particularly emphasize the essential role of mitochondrial ^•O₂^-/H₂O₂ in metabolic diseases. Specifically, perturbed mitochondrial ^•O₂^-/H₂O₂ regulation aggravates the progression of metabolic diseases, including diabetes, gout and nonalcoholic fatty liver disease (NAFLD). Given the deleterious effect of mitochondrial ^•O₂^-/H₂O₂ in the development of metabolic diseases, antioxidants targeting mitochondrial ^•O₂^-/H₂O₂ might be an attractive therapeutic approach for the prevention and treatment of metabolic diseases.

The Functional Medicine Approach to COVID-19: Virus-Specific Nutraceutical and Botanical Agents

As the novel infection with SARS-CoV-2 emerges, objective assessment of the scientific plausibility of nutraceutical and botanical interventions for prevention and treatment is important. We evaluate twelve such interventions with mechanisms of action that modulate the immune system, impair viral replication, and/or have been demonstrated to reduce severity of illness. These are examples of interventions that, mechanistically, can help protect patients in the presence of the prevalent and infectious SARS-CoV-2 virus. While there are limited studies to validate these agents to specifically prevent COVID-19, they have been chosen based upon their level of evidence for effectiveness and safety profiles, in the context of other viral infections. These agents are to be used in a patient-specific manner in concert with lifestyle interventions known to strengthen immune response (see related article in this issue of IMCJ).

Sweroside Prevents Non-Alcoholic Steatohepatitis by Suppressing Activation of the NLRP3 Inflammasome

Non-alcoholic steatohepatitis (NASH), a type of non-alcoholic fatty liver disease, is characterized as steatosis and inflammation in the liver. NLRP3 inflammasome activation is associated with NASH pathology. We hypothesized that suppressing the NLRP3 inflammasome could be effective in preventing NASH. We searched substances that could inhibit the activation of the NLRP3 inflammasome and identified sweroside as an NLRP3 inhibitor. We investigated whether sweroside can be applied to prevent the pathological symptoms associated with NASH in a methionine–choline-deficient (MCD) diet-induced NASH mouse model. The activation of the NLRP3 inflammasome was determined by detecting the production of caspase-1 and IL-1β from pro-caspase-1 and pro-IL-1β in primary mouse macrophages and mouse liver. In a NASH model, mice were fed an MCD diet for two weeks with daily intraperitoneal injections of sweroside. Sweroside effectively inhibited NLRP3 inflammasome activation in primary macrophages as shown by a decrease in IL-1β and caspase-1 production. In a MCD diet-induced NASH mouse model, intraperitoneal injection of sweroside significantly reduced serum aspartate transaminase and alanine transaminase levels, hepatic immune cell infiltration, hepatic triglyceride accumulation, and liver fibrosis. The improvement of NASH symptoms by sweroside was accompanied with its inhibitory effects on the hepatic NLRP3 inflammasome as hepatic IL-1β and caspase-1 were decreased. Furthermore, sweroside blocked de novo synthesis of mitochondrial DNA in the liver, contributing to suppression of the NLRP3 inflammasome. These results suggest that targeting the NLRP3 inflammasome with sweroside could be beneficially employed to improve NASH symptoms.