Lower Temperatures Exacerbate NLRP3 Inflammasome Activation by Promoting Monosodium Urate Crystallization, Causing Gout

IL1A regulates the inflammation in gout through the Toll-like receptors pathway

Objective: Gout is a dangerous metabolic condition related to monosodium urate (MSU). Our aim is to study the molecular mechanisms underlying gout and to identify potential clinical biomarkers by bioinformatics analysis and experimental validation. Methods: In this study, we retrieved the overlapping genes between GSE199950-Differential Expressed Genes (DEGs) dataset and key module in Weighted Gene Co-Expression Network Analysis (WGCNA) on GSE199950. These genes were then analyzed by protein-protein interaction (PPI) network, expression and Gene Set Enrichment Analysis to identify the hub gene related to gout. Then, the gene was investigated by peripheral blood mononuclear cells (PBMCs), immunoassay and cell experiments like western blotting to uncover its underlying mechanism in gout cells. Results: From the turquoise module and 83 DEGs, we identified 62 overlapping genes, only 11 genes had mutual interactions in PPI network and these genes were highly expressed in MSU-treated samples. Then, it was found that the IL1A (interleukin 1 alpha) was the only one gene related to Toll-like receptor signaling pathway that was associated with the occurrence of gout. Thus, IL1A was determined as the hub gene in this study. In immunoassay, IL1A was significantly positively correlated with B cells and negatively correlated with macrophages. Moreover, IL1A is highly expressed in gout patients,it has a good clinical diagnostic value. Finally, the results of in vitro experiments showed that after knocking down IL1A, the expressions of pro-inflammatory cytokines and Toll-like receptor signaling pathway-related proteins (TLR2, TLR4, MyD88) were all reduced. Conclusion: It is confirmed that IL1A is a promoting gene in gout with a good diagnostic value, and specifically it affects the inflammation in gout through Toll-like receptor pathway. Our research offers fresh perspectives on the pathophysiology of gout and valuable directions for future diagnosis and treatment.

The landscape of pathophysiology guided therapeutic strategies for gout treatment

INTRODUCTION

Gout is a common autoinflammatory disease caused by hyperuricemia with acute and/or chronic inflammation as well as tissue damage. Currently, urate-lowering therapy (ULT) and anti-inflammatory therapy are used as first-line strategies for gout treatment. However, traditional drugs for gout treatment exhibit some unexpected side effects and are not suitable for certain patients due to their comorbidity with other chronic disease.

AREAS COVERED

In this review, we described the pathophysiology of hyperuricemia and monosodium urate (MSU) crystal induced inflammatory response during gout development in depth and comprehensively summarized the advances in the investigation of promising ULT drugs as well as anti-inflammatory drugs that might be safer and more effective for gout treatment.

EXPERT OPINION

New drugs that are developed based on these molecular mechanisms exhibited great efficacy on reduction of disease burden both in vitro and in vivo, implying their potential for clinical application. Moreover, hyperthermia also showed regulation effect on MSU crystals formation and the signaling pathways involved in inflammation.

Comparison of the different monosodium urate crystals in the preparation process and pro-inflammation

OBJECTIVES

The deposition of monosodium urate (MSU) crystals within synovial joints and tissues is the initiating factor for gout arthritis. Thus, MSU crystals are a vital tool for studying gout's molecular mechanism in animal and cellular models. This study mainly compared the excellence and worseness of MSU crystals prepared by different processes and the degree of inflammation induced by MSU crystals.

METHODS

MSU crystals were prepared using neutralization, alkali titration, and acid titration methods. The crystals' shape, length, quality, and uniformity were observed by polarized light microscopy and calculated by the software Image J. The foot pad and air pouch models were used to assess the different degrees of inflammation induced by the MSU crystals prepared by the three different methods at different time points. Paw swelling was evaluated by caliper. In air pouch lavage fluid, inflammatory cell recruitment was measured by hemocytometer, and the level of IL-1β, TNF-α, and IL-18 by ELISA. Inflammatory cell infiltration was assayed by immunohistochemistry of air pouch synovial slices.

RESULTS

For the preparation of MSU crystals with the same uric acid, the quantity acquired by the alkalization method was highest, followed by neutralization, with the acid titration method being the lowest. The crystals prepared by neutralization were the longest. The swelling index of the foot pad induced by MSU crystals prepared by acid titration was significantly lower than that of the other methods at 24 h. The inflammatory cell recruitment and level of IL-1β, TNF-α, and IL-18 in air pouch lavage fluid were lowest in animals with crystals prepared by acid titration. IL-1β secretion induced by MSU crystals prepared by acid titration was significantly lower than that of the other two groups, but there was no significant difference in IL-18 secretion between the three groups in THP-1 macrophages and BMDMs.

CONCLUSIONS

All three methods can successfully prepare MSU crystals, but the levels of inflammation induced by the crystals prepared by the three methods were not identical. The degree of inflammation induced by MSU crystals prepared by neutralization and alkalization is greater than by acid titration, but the quantity of MSU crystals obtained by the alkalization method is higher and less time-consuming. Apparently, the window of inflammation triggered by acid titration preparation is shorter compared to other forms of crystal preparation. Overall, MSU crystals prepared by the alkaline method should be recommended for studying the molecular mechanisms of gout in animal and cellular models.

A Preliminary Study of Mild Heat Stress on Inflammasome Activation in Murine Macrophages

Inflammation and mitochondrial-dependent oxidative stress are interrelated processes implicated in multiple neuroinflammatory disorders, including Alzheimer's disease (AD) and depression. Exposure to elevated temperature (hyperthermia) is proposed as a non-pharmacological, anti-inflammatory treatment for these disorders; however, the underlying mechanisms are not fully understood. Here we asked if the inflammasome, a protein complex essential for orchestrating the inflammatory response and linked to mitochondrial stress, might be modulated by elevated temperatures. To test this, in preliminary studies, immortalized bone-marrow-derived murine macrophages (iBMM) were primed with inflammatory stimuli, exposed to a range of temperatures (37-41.5 °C), and examined for markers of inflammasome and mitochondrial activity. We found that exposure to mild heat stress (39 °C for 15 min) rapidly inhibited iBMM inflammasome activity. Furthermore, heat exposure led to decreased ASC speck formation and increased numbers of polarized mitochondria. These results suggest that mild hyperthermia inhibits inflammasome activity in the iBMM, limiting potentially harmful inflammation and mitigating mitochondrial stress. Our findings suggest an additional potential mechanism by which hyperthermia may exert its beneficial effects on inflammatory diseases.

Effects of NLRP3 on implants placement

Bone stability is precisely controlled by osteoclast-mediated bone resorption and osteoblast-mediated bone formation. When the balance is broken, the integrity of the bone structure will be destroyed. Inflammasomes are important protein complexes in response to pathogen-related molecular models or injury-related molecular models, which can promote the activation and secretion of proinflammatory cytokines and activate a local inflammatory response. NOD-like receptor thermal protein domain associated protein (NLRP) 3 inflammasome can promote bone resorption through the activation of the proinflammatory cytokines interleukin (IL)-1β, IL-18 and the induction of caspase-1-mediated pyroptosis. Inhibiting the production of NLRP3 inflammasome may be beneficial to improve comfort and bone stability. The presence of metal particles and microorganisms around implants can activate NLRP3 and promote bone absorption. NLRP3 inflammasome plays an important role in the maintenance of bone stability around implants, however, most studies focus on orthopedic implants and periodontitis. This article reviews the effects of NLRP3 inflammasome on bone formation, resorption and pain induced by implants, and the possibility of NLRP3 as a target for preventing peri-implantitis is discussed.

The preventive effect of Chinese sumac fruit against monosodium urate-induced gouty arthritis in rats by regulating several inflammatory pathways

Chinese sumac (Rhus chinensis Mill.) fruit is a traditional Chinese medicinal material that can be consumed daily. This study aimed to investigate whether the ethanol extract of sumac fruits can ameliorate monosodium urate-induced gouty arthritis in rats from the perspective of inflammation. Results showed that the extract of Chinese sumac fruits can obviously prevent monosodium urate-induced gouty arthritis in rats. Further analyses revealed that this bioactivity may be mainly achieved by modulating several inflammatory pathways, including NLRP3, NF-κB, and MAPK pathways. In addition, the extract can also improve oxidative stress by reducing the levels of malondialdehyde and myeloperoxidase, increasing the contents of superoxide dismutase and glutathione. In conclusion, this study revealed that the Chinese sumac fruit can alleviate the pathological symptoms of gouty arthritis by inhibiting inflammatory responses and oxidative stress, which can provide a theoretical basis for the use of Chinese sumac fruits as a Chinese herbal medicine and health food for the prevention and treatment of gouty arthritis.

Polydatin protects against gouty nephropathy by inhibiting renal tubular cell pyroptosis

OBJECTIVE

To investigate the protective effect and mechanism of polydatin (PD) against gouty nephropathy (GN) in mice.

METHODS

Twenty-four mice were randomly divided into three groups: the control group (no treatment), the GN group (300 mg/kg hypoxanthine + 150 mg/kg potassium oxonate), and the GN + PD group (300 mg/kg hypoxanthine + 150 mg/kg potassium oxonate + 50 mg/kg PD). Histological changes in the kidneys and the levels of uric acid (UA), blood urea nitrogen (BUN), and serum creatinine (SCr) in the sera were measured. In addition, the expression of gasdermin D (GSDMD) protein in renal tubular epithelial cells, and the expression of NOD-like receptor protein 3 (NLRP3), GSDMD, and caspase-1 proteins in the kidney tissues were determined by immunohistochemistry, immunofluorescence, and Western blot.

RESULTS

In vitro, PD inhibited the expression of NLRP3, caspase-1, and GSDMD and protected the renal tubular epithelial cells from pyroptosis. In vivo, PD treatment significantly ameliorated the pathological changes in kidney tissue, and reversed the decrease of serum UA and BUN in GN model mice. The expression of NLRP3, GSDMD, and caspase-1 proteins was also decreased in the PD-treated GN mice.

CONCLUSION

The results suggest that PD has a protective effect on mice with GN, which may be related to the downregulation of NLRP3, GSDMD, and caspase-1 proteins and the inhibition of renal tubular epithelial cells pyroptosis.

JC2-11, a benzylideneacetophenone derivative, attenuates inflammasome activation

Dysregulation of inflammasome activation induces chronic and excess inflammation resulting in several disorders, such as metabolic disorders and cancers. Thus, screening for its regulator derived from natural materials has been conducted progressively. JC2-11 (JC) was designed to enhance the antioxidant activity based on a chalcone, which is abundant in edible plants and a precursor of flavonoids. This study examined the effects of JC on inflammasome activation in human and murine macrophages. JC inhibited the secretion of interleukin (IL)-1β and lactate dehydrogenases, and the cleavage of caspase-1 and gasdermin D in response to the tested activators (i.e., NLRP3, NLRC4, AIM2, and non-canonical inflammasome triggers). In addition, JC attenuated IL-1β secretion from lipopolysaccharide (LPS)-injected mice, an inflammasome-mediating disease model. Mechanistically, JC blocked the expression of the inflammasome components during the priming step of the inflammasome, and interrupted the production of mitochondrial reactive oxygen species. In addition, JC inhibited the activity of caspase-1. In conclusion, JC may be a candidate pan-inflammasome inhibitor.

Lipoxin A4 attenuates MSU-crystal-induced NLRP3 inflammasome activation through suppressing Nrf2 thereby increasing TXNRD2

Gout is a common inflammatory disease. The activation of NLRP3 inflammasome induced by monosodium urate (MSU) crystals has a critical role in gout, and its prevention is beneficial for patients. Lipoxin A4 (LXA4) is an endogenous lipoxygenase-derived eicosanoid mediator with powerful anti-inflammatory properties. However, whether LXA4 can suppress NLRP3 inflammasome activation induced by MSU crystals remains unclear. This study aimed to investigate the protective effect of LXA4 on MSU-crystal-induced NLRP3 inflammasome activation and its underlying molecular mechanisms. We found that LXA4 inhibited MSU-crystal-induced NLRP3 inflammasome activation, interleukin (IL)-1β maturation, and pyroptosis. More specifically, LXA4 suppressed the assembly of the NLRP3 inflammasome, including oligomerization and speck formation of ASC, and ASC-NLRP3 interaction. Furthermore, LXA4 suppressed oxidative stress, the upstream events for NLRP3 inflammasome activation, as evidenced by the fact that LXA4 eliminated total reactive oxygen species (ROS) generation and alleviated nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activation and mitochondrial dysfunction. However, LXA4 also depressed the Nrf2 activation, a critical molecule in the antioxidant pathway, and then exerted an inhibitory impact on Klf9 expression and promotional impact on TXNRD2 expression, two molecules located downstream of Nrf2 in sequence. Knockdown of TXNRD2 reversed the LXA4-induced depression of ROS and NLRP3 inflammasome. Moreover, LXA4 alleviated joint inflammation and decreased the production of cleaved caspase-1 and matured IL-1β in gouty arthritis rats. Taken together, our findings demonstrate that LXA4 can attenuate MSU-crystal-induced NLRP3 inflammasome activation, probably through suppressing Nrf2 activation to increase TXNRD2 expression. The present study highlights the potential of LXA4 as an attractive new gout treatment candidate.

Maltol, a Natural Flavor Enhancer, Inhibits NLRP3 and Non-Canonical Inflammasome Activation

Maltol (3-hydroxy-2-methyl-4-pyrone) is used widely as a food and cosmetic supplement, and it has antioxidant and anti-inflammatory activities. Inflammasome causes the maturation and secretion of interleukin (IL)-1β and -18 through the activation of caspase-1 (Casp1), which contributes to various inflammatory diseases. This study examined the effects of maltol on the inflammasome activation in macrophages and mice. Lipopolysaccharide (LPS)-primed macrophages were treated with a trigger of NLRP3, NLRC4, AIM2, or non-canonical (NC) inflammasomes in the presence of maltol. The secretion of IL-1β and IL-18 and the cleavage of Casp1 were analyzed as indices of inflammasome activation. Mice were injected with LPS and an NLRP3 trigger with or without maltol, and the peritoneal IL-1β secretions were observed. The effects of maltol on reactive oxygen species (ROS) production and Casp1 activity were analyzed to determine the mechanism. Maltol inhibited the activation of NLRP3 and NC inflammasomes, but it did not alter the other inflammasomes. Maltol also attenuated IL-1β secretion resulting from the inflammasome activation in mice. The anti-inflammatory mechanism of maltol was revealed by the inhibition of ROS production and Casp1 activity. Maltol is suggested to be promising as a anti-inflammasome molecule.

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.