Interleukin 37 limits monosodium urate crystal-induced innate immune responses in human and murine models of gout

Anti-Inflammatory Effect of Atorvastatin and Rosuvastatin on Monosodium Urate-Induced Inflammation through IL-37/Smad3-Complex Activation in an In Vitro Study Using THP-1 Macrophages

Objective: The pleiotropic effect of hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) is responsible for potent defense against inflammatory response. This study evaluated the inhibitory effects of HMG-CoA reductase inhibitors on the monosodium urate (MSU)-induced inflammatory response through the regulation of interleukin-37 (IL-37) expression. Methods: Serum was collected from patients with gout (n = 40) and from healthy controls (n = 30). The mRNA and protein expression of the target molecules IL-1β, IL-37, caspase-1, and Smad3 were measured in THP-1 macrophages stimulated with MSU, atorvastatin, or rosuvastatin using a real-time quantitative polymerase chain reaction and Western blot assay. Transfection with IL-1β or Smad3 siRNA in THP-1 macrophages was used to verify the pharmaceutical effect of statins in uric-acid-induced inflammation. Results: Serum IL-37 levels in gout patients were significantly higher than in controls (p < 0.001) and was associated with the serum uric acid level (r = 0.382, p = 0.008). THP-1 cells stimulated with MSU markedly induced IL-37 mRNA expression and the transition of IL-37 from the cytoplasm to the nucleus. Recombinant IL-37 treatment dose-dependently inhibited activation of caspase-1 and IL-1β in MSU-induced inflammation. Atorvastatin and rosuvastatin attenuated caspase-1 activation and mature IL-1β expression but augmented translocation of IL-37 from the cytoplasm to the nucleus. Atorvastatin and rosuvastatin induced phosphorylation of Smad3 in THP-1 cells treated with MSU crystals. Statins potently attenuated translocation of IL-37 from the cytoplasm to the nucleus in THP-1 macrophages transfected with Smad3 siRNA compared to cells with negative control siRNA. Conclusions: This study revealed that statins inhibit the MSU-induced inflammatory response through phosphorylated Smad3-mediated IL-37 expression in THP-1 macrophages.

Identification of SOCS3 and PTGS2 as new biomarkers for the diagnosis of gout by cross-species comprehensive analysis

Background

Gout is the most common inflammatory arthritis in adults. Gout is an arthritic disease caused by the deposition of monosodium urate crystal (MSU) in the joints, which can lead to acute inflammation and damage adjacent tissue. Hyperuricemia is the main risk factor for MSU crystal deposition and gout. With the increasing burden of gout disease, the identification of potential biomarkers and novel targets for diagnosis is urgently needed.

Methods

For the analysis of this subject paper, we downloaded the human gout data set GSE160170 and the gout mouse model data set GSE190138 from the GEO database. To obtain the differentially expressed genes (DEGs), we intersected the two data sets. Using the cytohubba algorithm, we identified the key genes and enriched them through GO and KEGG. The gene expression trends of three subgroups (normal control group, intermittent gout group and acute gout attack group) were analyzed by Series Test of Cluster (STC) analysis, and the key genes were screened out, and the diagnostic effect was verified by ROC curve. The expression of key genes in dorsal root nerve and spinal cord of gout mice was analyzed. Finally, the clinical samples of normal control group, hyperuricemia group, intermittent gout group and acute gout attack group were collected, and the expression of key genes at protein level was verified by ELISA.

Result

We obtained 59 co-upregulated and 28 co-downregulated genes by comparing the DEGs between gout mouse model data set and human gout data set. 7 hub DEGs(IL1B, IL10, NLRP3, SOCS3, PTGS2) were screened out via Cytohubba algorithm. The results of both GO and KEGG enrichment analyses indicate that 7 hub genes play a significant role in regulating the inflammatory response, cytokine production in immune response, and the TNF signaling pathway. The most representative hub genes SOCS3 and PTGS2 were screened out by Series Test of Cluster, and ROC analysis results showed the AUC values were both up to 1.000. In addition, we found that PTGS2 expression was significantly elevated in the dorsal root ganglia and spinal cord in monosodium urate(MSU)-induced gout mouse model. The ELISA results revealed that the expression of SOCS3 and PTGS2 was notably higher in the acute gout attack and intermittent gout groups compared to the normal control group. This difference was statistically significant, indicating a clear distinction between the groups.

Conclusion

Through cross-species comprehensive analysis and experimental verification, SOCS3 and PTGS2 were proved to be new biomarkers for diagnosing gout and predicting disease progression.

Signaling pathways in uric acid homeostasis and gout: From pathogenesis to therapeutic interventions

Uric acid is a product of purine degradation, and uric acid may have multiple physiologic roles, including the beneficial effects as an antioxidant and neuroprotector, maintenance of blood pressure during low salt ingestion, and modulation of immunity. However, overproduction of metabolic uric acid, and/or imbalance of renal uric acid secretion and reabsorption, and/or underexcretion of extrarenal uric acid, e.g. gut, will contribute to hyperuricemia, which is a common metabolic disease. Long-lasting hyperuricemia can induce the formation and deposition of monosodium urate (MSU) crystals within the joints and periarticular structures. MSU crystals further induce an acute, intensely painful, and sterile inflammation conditions named as gout by NLRP3 inflammasome-mediated cleavage of pro-IL-1β to bioactive IL-1β. Moreover, hyperuricemia and gout are associated with multiple cardiovascular and renal disorders, e.g., hypertension, myocardial infarction, stroke, obesity, hyperlipidemia, type 2 diabetes mellitus and chronic kidney disease. Although great efforts have been made by scientists of modern medicine, however, modern therapeutic strategies with a single target are difficult to exert long-term positive effects, and even some of these agents have severe adverse effects. The Chinese have used the ancient classic prescriptions of traditional Chinese medicine (TCM) to treat metabolic diseases, including gout, by multiple targets, for more than 2200 years. In this review, we discuss the current understanding of urate homeostasis, the pathogenesis of hyperuricemia and gout, and both modern medicine and TCM strategies for this commonly metabolic disorder. We hope these will provide the good references for treating hyperuricemia and gout.

Regulation of SOCS3-STAT3 in urate-induced cytokine production in human myeloid cells

OBJECTIVE

Hyperuricaemia is necessary for gout. High urate concentrations have been linked to inflammation in mononuclear cells. Here, we explore the role of the suppressor of cytokine signaling 3 (SOCS3) in urate-induced inflammation.

METHODS

Peripheral blood mononuclear cells (PBMCs) from gout patients, hyperuricemic and normouricemic individuals were cultured for 24h with varying concentrations of soluble urate, followed by 24h restimulation with lipopolysaccharides (LPS)±monosodium urate (MSU) crystals. Transcriptomic profiling was performed using RNA-Sequencing. DNA methylation was assessed using Illumina Infinium® MethylationEPIC BeadChip system (EPIC array). Phosphorylation of signal transducer and activator of transcription 3 (STAT3) was determined by flow cytometry. Cytokine responses were also assessed in PBMCs from patients with JAK2 V617F tyrosine kinase mutation.

RESULTS

PBMCs pre-treated with urate produced more interleukin-1beta (IL-1β) and interleukin-6 (IL-6) and less interleukin-1 receptor anatagonist (IL-1Ra) after LPS simulation. In vitro, urate treatment enhanced SOCS3 expression in control monocytes but no DNA methylation changes were observed at the SOCS3 gene. A dose-dependent reduction in phosphorylated STAT3 concomitant with a decrease in IL-1Ra was observed with increasing concentrations of urate. PBMCs with constitutively activated STAT3 (JAK2 V617F mutation) could not be primed by urate.

CONCLUSION

In vitro, urate exposure increased SOCS3 expression, while urate priming, and subsequent stimulation resulted in decreased STAT3 phosphorylation and IL-1Ra production. There was no evidence that DNA methylation constitutes a regulatory mechanism of SOCS3. Elevated SOCS3 and reduced pSTAT3 could play a role in urate-induced hyperinflammation since urate priming had no effect in PBMCs from patients with constitutively activated STAT3.

Pathogenesis of gout: Exploring more therapeutic target

Gout is a chronic metabolic and immune disease, and its specific pathogenesis is still unclear. When the serum uric acid exceeds its saturation in the blood or tissue fluid, it is converted to monosodium urate crystals, which lead to acute arthritis of varying degrees, urinary stones, or irreversible peripheral joint damage, and in severe cases, impairment of vital organ function. Gout flare is a clinically significant state of acute inflammation in gout. The current treatment is mostly anti-inflammatory analgesics, which have numerous side effects with limited treatment methods. Gout pathogenesis involves many aspects. Therefore, exploring gout pathogenesis from multiple perspectives is conducive to identifying more therapeutic targets and providing safer and more effective alternative treatment options for patients with gout flare. Thus, this article is of great significance for further exploring the pathogenesis of gout. The author summarizes the pathogenesis of gout from four aspects: signaling pathways, inflammatory factors, intestinal flora, and programmed cell death, focusing on exploring more new therapeutic targets.

Uric acid in health and disease: From physiological functions to pathogenic mechanisms

Owing to renal reabsorption and the loss of uricase activity, uric acid (UA) is strictly maintained at a higher physiological level in humans than in other mammals, which provides a survival advantage during evolution but increases susceptibility to certain diseases such as gout. Although monosodium urate (MSU) crystal precipitation has been detected in different tissues of patients as a trigger for disease, the pathological role of soluble UA remains controversial due to the lack of causality in the clinical setting. Abnormal elevation or reduction of UA levels has been linked to some of pathological status, also known as U-shaped association, implying that the physiological levels of UA regulated by multiple enzymes and transporters are crucial for the maintenance of health. In addition, the protective potential of UA has also been proposed in aging and some diseases. Therefore, the role of UA as a double-edged sword in humans is determined by its physiological or non-physiological levels. In this review, we summarize biosynthesis, membrane transport, and physiological functions of UA. Then, we discuss the pathological involvement of hyperuricemia and hypouricemia as well as the underlying mechanisms by which UA at abnormal levels regulates the onset and progression of diseases. Finally, pharmacological strategies for urate-lowering therapy (ULT) are introduced, and current challenges in UA study and future perspectives are also described.

Upregulation of CD39 During Gout Attacks Promotes Spontaneous Remission of Acute Gouty Inflammation

Gout is a self-limiting form of inflammatory arthropathy caused by the formation of urate crystals due to hyperuricemia. The resolution of gout involves the transition of proinflammatory M1-type macrophages to anti-inflammatory M2-type macrophages, as well as neutrophil-mediated extracellular trap (NET) formation. However, the underlying mechanisms of these changes are not clear. Studies have confirmed that high expression of CD39 on macrophages and neutrophils can trigger the polarization of macrophages from a proinflammatory state to an anti-inflammatory state. Recent studies have shown that the pathogenesis of gout involves extracellular ATP (eATP), and the synergistic effect of MSU and extracellular ATP can cause gout. CD39 is a kind of ATP hydrolysis enzyme that can degrade eATP, suggesting that CD39 may inhibit the aggravation of inflammation in gout and participate in the remission mechanism of gout. To confirm this hypothesis, using data mining and flow cytometry, we first found that CD39 expression was significantly upregulated on CD14 + monocytes and neutrophils in gout patients during the acute phase. Inhibition of CD39 by lentivirus or a CD39 inhibitor in acute gout models aggravated gouty arthritis and delayed gout remission. Apyrase, a functional analog of CD39, can significantly reduce the inflammatory response and promote gout remission in acute gout model mice. Our findings confirm that the upregulation of CD39 during gout flare-ups promotes spontaneous remission of acute gouty inflammation.

Chinese herbal compound Huangqin Qingrechubi capsule reduces lipid metabolism disorder and inflammatory response in gouty arthritis via the LncRNA H19/APN/PI3K/AKT cascade

CONTEXT

Gouty arthritis (GA) is a characteristically inflammatory disease often associated with lipid metabolism disorder. Huangqin Qingrechubi capsule (HQC) has been used for the treatment of GA.

OBJECTIVE

To explore the mechanism of HQC in the treatment of GA.

MATERIALS AND METHODS

A total of 30 GA patients (GA group) and 30 healthy subjects [normal control (NC) group] were recruited. The GA group was treated with HQC (3.6 g/d) for 10 days. Lipid metabolism and inflammation indexes were detected. Five herbal names of HQC, or 'gouty arthritis', 'hyperlipidemia' and 'inflammation' were used as key words to search related databases for network pharmacological analysis. Subsequently, GA-fibroblast-like synoviocytes (FLSs) were stimulated with GA-peripheral blood mononuclear cells (PBMCs) (3:1) and treated with HQC drug-containing serum (20%). RT-qPCR, Western blot, and ELISA were conducted to further explore the mechanism of HQC in improving GA.

RESULTS

In clinical observation, HQC decreased the expression of lncRNA H19 and IL-1β, and increased the expression of adiponectin (APN) and IL-4 in the GA group (about half). Through network pharmacology, the PI3K/AKT signaling pathway was identified. Cell experiments showed that HQC treatment reduced the viability of GA-FLSs (49.61%), up-regulated the expression of IL-4 (155.18%), IL-10 (165.13%), and APN (31.24%), and down-regulated the expression of lncRNA H19 (33.70%), IL-1β (64.70%), TNF-α (78.32%), p-PI3K (48.80%), and p-AKT (53.48%).

DISCUSSION AND CONCLUSIONS

HQC improved lipid metabolism disorder and inflammatory response of GA by regulating the lncRNA H19/APN/PI3K/AKT. Maintaining the stability of lipid metabolism may be an effective way to alleviate GA.

Total Saponin Fraction of Dioscorea Nipponica Makino Improves Gouty Arthritis Symptoms in Rats via M1/M2 Polarization of Monocytes and Macrophages Mediated by Arachidonic Acid Signaling

OBJECTIVE

To explore the mechanism of effects of total saponin fraction from Dioscorea Nipponica Makino (TSDN) on M1/M2 polarization of monocytes/macrophages and arachidonic acid (AA) pathway in rats with gouty arthritis (GA).

METHODS

Seventy-two Sprague Dawley rats were randomly divided into 4 groups (n=18 in each): normal, model, TSDN at 160 mg/kg, and celecoxib at 43.3 mg/kg. Monosodium urate crystal (MSU) was injected into the rats' ankle joints to induce an experimental GA model. Blood and tissue samples were collected on the 3rd, 5th, and 8th days of drug administration. Histopathological changes in the synovium of joints were observed via hematoxylin and eosin (HE) staining. The expression levels of arachidonic acid (AA) signaling pathway were assessed via real-time polymerase chain reaction (qPCR) and Western blot. Flow cytometry was used to determine the proportion of M1 and M2 macrophages in the peripheral blood. An enzyme-linked immunosorbent assay (ELISA) was used to detect interleukine (IL)-1 β, tumor necrosis factor-alpha (TNF-α), IL-4, IL-10, prostaglandin E2 (PGE2), and leukotriene B4 (LTB4).

RESULTS

HE staining showed that TSDN improved the synovial tissue. qPCR and Western blot showed that on the 3rd, 5th and 8th days of drug administration, TSDN reduced the mRNA and protein expressions of cyclooxygenase (COX)2, microsomal prostaglandin E synthase-1 derived eicosanoids (mPGES-1), 5-lipoxygenase (5-LOX), recombinant human mothers against decapentaplegic homolog 3 (Smad3), nucleotide-binding oligomerization domain-like receptor protein 3 (NALP3), and inducible nitric oxide synthase (iNOS) in rats' ankle synovial tissues (P<0.01). TSDN decreased COX1 mRNA and protein expression on 3rd and 5th day of drug administration and raised it on the 8th day (both P<0.01). It lowered CD68 protein expression on days 3 (P<0.01), as well as mRNA and protein expression on days 5 and 8 (P<0.01). On the 3rd, 5th, and 8th days of drug administration, TSDN elevated the mRNA and protein expression of Arg1 and CD163 (P<0.01). Flow cytometry results showed that TSDN decreased the percentage of M1 macrophages while increasing the percentage of M2 in peripheral blood (P<0.05 or P<0.01). ELISA results showed that on the 3rd, 5th, and 8th days of drug administration, TSDN decreased serum levels of IL-1 β, TNF-α, and LTB4 (P<0.01), as well as PGE2 levels on days 3rd and 8th days (P<0.05 or P<0.01); on day 8 of administration, TSDN increased IL-4 serum levels and enhanced IL-10 contents on days 5 and 8 (P<0.05 or P<0.01).

CONCLUSION

The anti-inflammatory effect of TSDN on rats with GA may be achieved by influencing M1/M2 polarization through AA signaling pathway.

MSU crystal deposition contributes to inflammation and immune responses in gout remission

As a prominent feature of gout, monosodium urate (MSU) crystal deposition induces gout flares, but its impact on immune inflammation in gout remission remains unclear. Using single-cell RNA sequencing (scRNA-seq), we characterize the transcription profiling of peripheral blood mononuclear cells (PBMCs) among intercritical remission gout, advanced remission gout, and normal controls. We find systemic inflammation in gout remission with MSU crystal deposition at the intercritical and advanced stages, evidenced by activated inflammatory pathways, strengthened inflammatory cell-cell interactions, and elevated arachidonic acid metabolic activity. We also find increased HLA-DQA1high classic monocytes and PTGS2high monocytes in advanced gout and overactivated CD8+ T cell subtypes in intercritical and advanced gout. Additionally, the osteoclast differentiation pathway is significantly enriched in monocytes, T cells, and B cells from advanced gout. Overall, we demonstrate systemic inflammation and distinctive immune responses in gout remission with MSU crystal deposition, allowing further exploration of the underlying mechanism and clinical significance in conversion from intercritical to advanced stage.

Interleukin-37: associations of plasma levels and genetic variants in gout

OBJECTIVES

IL-37 is an anti-inflammatory cytokine involved in inflammatory and autoimmune diseases. We aimed to investigate the association between IL-37 genetic variants, IL-37 plasma levels, and various clinical phases of gout.

METHODS

The study included a control group with no history of primary hyperuricemia/gout, (n = 50), asymptomatic hyperuricemia (n = 74), intercritical gout (n = 200), acute gouty flare (n = 18), and chronic tophaceous gout (n = 30). Plasma IL-37 was analysed using enzyme-linked immunosorbent assay. All coding regions and intron-exon boundaries of IL-37 and exons 1-5 were amplified and sequenced.

RESULTS

Plasma levels of IL-37 were significantly higher in asymptomatic hyperuricemic (p = 0.045), intercritical gout (p = 0.001), and chronic tophaceous gout (p = 0.021) cohorts when compared to control group. The levels of IL-37 in patients with acute gouty flare were comparable to control group (p = 0.061). We identified 15 genetic variants of IL-37: eight intron (rs2708959, rs2723170, rs2708958, rs2723169 rs2466448, rs3811045, rs3811048, rs2708944) and seven non-synonymous allelic variants (rs3811046, rs3811047, rs2708943, rs2723183, rs2723187, rs2708947, rs27231927), of which rs2708959 showed an over-presentation in gouty and acute flare cohorts (p = 0.003 and 0.033, respectively) compared to European population (minor allelic frequency MAF = 0.05) but not in control and hyperuricemic cohorts (p/MAF = 0.17/0.08 and 0.71/0.05, respectively).. On the contrary, rs3811045, rs3811046, rs3811047, and rs3811048 were underrepresented among individuals with tophaceous gout (MAF = 0.57) compared to European MAF 0.70-0.71, but not compared to the control cohort (MAF = 0.67).

CONCLUSIONS

We demonstrated the up-regulation of IL-37 levels across the clinical phases of gout: asymptomatic hyperuricemia, intercritical, and chronic tophaceous gout compared to control. Moreover, 15 genetic variants of IL-37 were identified and their associations with the clinical variants of gout were evaluated.

Gout therapeutics and drug delivery

Gout is a common inflammatory arthritis caused by persistently elevated uric acid levels. With the improvement of people's living standards, the consumption of processed food and the widespread use of drugs that induce elevated uric acid, gout rates are increasing, seriously affecting the human quality of life, and becoming a burden to health systems worldwide. Since the pathological mechanism of gout has been elucidated, there are relatively effective drug treatments in clinical practice. However, due to (bio)pharmaceutical shortcomings of these drugs, such as poor chemical stability and limited ability to target the pathophysiological pathways, traditional drug treatment strategies show low efficacy and safety. In this scenario, drug delivery systems (DDS) design that overcome these drawbacks is urgently called for. In this review, we initially describe the pathological features, the therapeutic targets, and the drugs currently in clinical use and under investigation to treat gout. We also comprehensively summarize recent research efforts utilizing lipid, polymeric and inorganic carriers to develop advanced DDS for improved gout management and therapy.

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.

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.

Monosodium urate crystals alter the circadian clock in macrophages leading to loss of NLRP3 inflammasome repression: Implications for timing of the gout flare

Gout is caused by monosodium urate (MSU) crystal deposition within joints. This leads to acute episodes of inflammation ("gout flares") driven by NLRP3 inflammasome activation in macrophages. Gout flares are frequently present during late night/early morning. The reason for this timing is unclear. Recent evidence suggests the NLRP3 inflammasome is under circadian control. The purpose of this study was to determine whether MSU crystals cause changes in the circadian clock in macrophages leading to time-of-day differences in NLRP3 inflammasome activation. Levels of circadian clock components were measured in undifferentiated "monocytic" and PMA-differentiated "macrophagic" THP-1 cells cultured with/without MSU crystals. Caspase-1 activity was measured to assess NLRP3 inflammasome activity. MSU crystal exposure resulted in minimal effects on clock genes in THP-1 monocytes but BMAL1, CRY1, PER2, and REV-ERBα showed altered expression with reduced protein levels of BMAL1 and REV-ERBα in THP-1 macrophages. REV-ERBα activation or BMAL1 over-expression resulted in reduced MSU crystal-induced caspase-1 activity. BMAL1 knockdown resulted in a further increase in MSU crystal-induced caspase-1 activity, but only at times of day when BMAL1 levels were naturally high. MSU crystal-induced NLRP3 inflammasome activation was greatest at the time of day when BMAL1 levels were naturally low. MSU crystals alter the expression of circadian clock components in THP-1 macrophages leading to loss of BMAL1 and REV-ERBα-mediated repression of NLRP3 inflammasome activity and time-of-day differences in susceptibility to inflammasome activation. Our findings suggest that the nocturnal risk of gout flare is at least partially a consequence of altered circadian control of immune cell function.

Upregulated expression of FFAR2 and SOC3 genes is associated with gout

OBJECTIVE

To examine the expression of Free fatty acid receptor 2 (FFAR2) and Suppressor of cytokine signalling 3 (SOCS3) genes in asymptomatic hyperuricaemia (AH), AH with MSU crystal deposition, inter-critical gout and gout flare.

METHODS

Study participants (n = 120) comprised 34 people with serum urate (SU) <360 μmol/l, 69 with AH ± MSU crystal deposition and 17 with a gout flare. Sixteen of the 17 patients with a gout flare attended a second visit 6-12 weeks later. Gene expression levels were assessed using RT-qPCR and results computed as fold changes (FC) after normalization to the reference gene.

RESULTS

FFAR2 was significantly upregulated during gout flares (FC = 2.9) compared with normal SU, AH, and AH + MSU crystal deposition (FC = 1.1, P < 0.0001 for each comparison). FFAR2 was also significantly upregulated during inter-critical gout (FC = 1.8) compared with normal SU, AH and AH + MSU (FC = 1.1, P < 0.001 for each comparison). SOCS3 was significantly upregulated during gout flares (FC = 3.4) compared with normal SU, AH, and AH + MSU crystal deposition (FC = 1.1, 1.1 and 1.2, respectively, P < 0.0001 for each comparison). SOCS3 was also upregulated during inter-critical gout (FC = 2.1) compared with normal SU (P = 0.02) and AH (P = 0.006) (FC = 1.1 and 1.2, respectively). FFAR2 expression was upregulated during gout flare compared with inter-critical gout and SOCS3 expression showed negative correlation with flare duration (r = -0.49, P < 0.05).

CONCLUSION

FFAR2 upregulation is associated with gout and may trigger gout flares. SOCS3 may have a role in amelioration of gout flares.

Distinct macrophage polarization in acute and chronic gout

Macrophage polarization mediates the development of inflammatory diseases. However, the polarization status at various stages of gout is not fully understood. Our study aimed to define the evolution of macrophage polarization in acute and chronic gout. Normal human synovium and synovium with tophi were collected for immunofluorescence (IF). Rat gouty joints were collected for joint thickness assessment and pathological evaluation. Tissue mRNA expression of inducible nitric oxide synthase (iNOS) and arginase-1 (Arg-1) were evaluated. Mouse peritoneal macrophages and THP-1 derived macrophages were stimulated by monosodium urate (MSU) crystals and were collected for detection of interleukin (IL) -1β and IL-37 levels and iNOS/Arg-1 ratio. Arg-1 and IL-37 were highly expressed in normal synovium and synovium with tophi. In rat gouty joints, the inflammatory cell counts and ankle thickness began to increase at 2 h, peaked at 24 h, and was decreased spontaneously. An increase in macrophages preceded the neutrophils infiltration. Infiltration of M1 was positively related with the severity of arthritis. M2 appeared in an early stage (at 2 h) of inflammation. The number of M1 macrophages was comparable to that of M2 from 2 to 12 h and exceeded M2 number at 18 h and 24 h. The ratios of M2/M1 reversed at 48 h and remained reversed until 120 h. In mice gouty joints, iNOS/Arg-1 mRNA ratio was significantly higher than the that in control group at 8 h. The proportion of neutrophils and M1-macrophages reached peak at 4 h in mice model with peritoneal gout. Concentration of IL-1β and ratio of iNOS/Arg-1 were increased at 6 h, peaked at 48 h, and were then decreased at 72 h in vitro, while the concentration of IL-37 peaked at 2 h and then decreased. In summary, altered macrophage polarization was observed in various stages of gouty inflammation. Macrophages in acute gout were polarized into M1 at early stage and into M2 at later stage while the macrophages in chronic gout mainly were only polarized towards M2. The number of M1 rose with the progression of inflammation. Early increase of M2 was observed, which might be generated directly from M0.

IL-37 improves mice myocardial infarction via inhibiting YAP-NLRP3 signaling mediated macrophage programming

OBJECTIVE

Myocardial infarction is the highest cause of cardiovascular death. Previous studies found that patients with myocardial infarction have elevated serum IL-37 and IL-37 treatment significantly alleviates adverse remodeling in myocardial infarction mice. However, the underlying mechanism of IL-37 in myocardial infarction is still unknown. Here we explored the underlying mechanism of IL-37 in attenuating myocardial infarction.

METHODS

The myocardial infarction mice model was constructed by left anterior descending ligation and then submitted to recombinant IL-37 administration. The histology and cardiac function were detected by HE & Masson staining and echocardiography, respectively. The macrophage phenotypes were analyzed by flow cytometry and real-time PCR. The cytokines in serum and cell culture supernatant were determined by ELISA. In addition, THP-1 cells were used in vitro to investigate the underlying mechanisms.

RESULTS

Infarcted mice showed increased inflammatory cell infiltration and impaired cardiac function. IL-37 treatment alleviated pro-inflammatory macrophage infiltration, tissue injury, and collagen deposition in hearts on day 3 and 7 after infarction in mice. In addition, IL-37 application modulated the balance between M1 and M2 macrophages in infarcted hearts. In vitro, THP-1 cell line polarization was also regulated by IL-37, companied by YAP phosphorylation and NLRP3 inactivation. Verteporfin, a YAP inhibitor, could abolish IL-37-induced NLRP3 inhibition and M2 macrophage polarization.

CONCLUSION

Our results demonstrated that IL-37 achieves a favorable therapeutical function on myocardial infarction by modulating YAP-NLRP3 mediated macrophage programming, providing a promising drug for the treatment of myocardial infarction.

IL-37 alleviates liver granuloma caused by Schistosoma japonicum infection by inducing alternative macrophage activation

Background

Hepatic macrophages regulate liver granuloma formation and fibrosis caused by infection with Schistosoma japonicum, with the manner of regulation dependent on macrophage activation state. Interleukin (IL)-37 may have immunomodulatory effects on macrophages. However, whether IL-37 can affect liver granuloma formation and fibrosis by affecting the polarization of macrophages in S. japonicum infection remains unclear. The aim of this study was to investigate IL-37-affected macrophage polarization in liver granuloma formation and fibrosis in S. japonicum infection.

Methods

An enzyme-linked immunosorbent assay (ELISA) was used to detect the expression of IL-37 in the serum of patients with acute S. japonicum infection and in the serum of healthy people. Recombinant IL-37 (rIL-37), CPP-IgG₂Fc-IL-37 and no CPP-IgG₂Fc-IL-37 proteins were injected into S. japonicum-infected mice every 3 days for a total of 6 times from day 24 post infection onwards. Subsequently, ELISA, quantitative reverse transcription-PCR, fluorescence-activated cell sorting and western blot were used to analyze whether IL-37 inhibits the formation of liver granulomas and the development of liver fibrosis by regulating the phenotypic transition of macrophages. Finally, the three IL-37 proteins and SIS3, a Smad3 inhibitor, were co-cultured in mouse peritoneal macrophages to explore the mechanism underlying the promotion of the polarization of M0 macrophages to the M2 phenotype by IL-37.

Results

Serum IL-37 levels were upregulated in schistosomiasis patients, and this increased level of IL-37 protein apparently alleviated the liver granuloma of mice in infection models. It also could induce liver and peritoneal macrophages to polarize to the M2 phenotype in S. japonicum-infected mice. The S. japonicum-infected mice injected with CPP-IgG₂Fc-IL-37 group exhibited the most obvious improvement in inflammatory reaction against the liver granuloma. The number and ratio of M2 macrophages in the liver and peritoneal cavity were significantly higher in the three IL-37 protein groups, especially in the CPP-IgG₂Fc-IL-37 group, compared to the controls. Similar results were also found regarding liver function damage. IL-37 induced macrophage M2 polarization by promoting AMP-activated protein kinase (AMPK) phosphorylation in vitro. Among all groups, the activation of AMPK was most significant in the CPP-IgG₂Fc-IL-37 group, and it was found that SMAD3 could enhance the anti-inflammatory function of IL-37.

Conclusions

The results show that IL-37 was able to promote the polarization of macrophages to the M2 phenotype, thereby inhibiting the development of schistosomiasis. In comparison to the rIL-37 protein, the CPP-IgG₂Fc-IL-37 protein has the advantages of being effective in small doses and having fewer side effects and a better efficacy.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05420-6.

The genetic backbone of ankylosing spondylitis: how knowledge of genetic susceptibility informs our understanding and management of disease

Ankylosing spondylitis (AS) is a seronegative, chronic inflammatory arthritis with high genetic burden. A strong association with HLA-B27 has long been established, but to date its contribution to disease aetiology remains unresolved. Recent insights through genome wide studies reveal an increasing array of immunogenetic risk variants extraneous to the HLA complex in AS cohorts. These genetic traits build a complex profile of disease causality, highlighting several molecular pathways associated with the condition. This and other evidence strongly implicates T-cell-driven pathology, revolving around the T helper 17 cell subset as an important contributor to disease. This prominence of the T helper 17 cell subset has presented the opportunity for therapeutic intervention through inhibition of interleukins 17 and 23 which drive T helper 17 activity. While targeting of interleukin 17 has proven effective, this success has not been replicated with interleukin 23 inhibition in AS patients. Evidence points to significant genetic diversity between AS patients which may, in part, explain the observed refractoriness among a proportion of patients. In this review we discuss the impact of genetics on our understanding of AS and its relationship with closely linked pathologies. We further explore how genetics can be used in the development of therapeutics and as a tool to assist in the diagnosis and management of patients. This evidence indicates that genetic profiling should play a role in the clinician’s choice of therapy as part of a precision medicine strategy towards disease management.

Recent Insights Into the Role of Macrophages in Acute Gout

Gout is a common type of inflammatory arthritis characterized by the presence of monosodium urate crystals (MSU) in the joints. Macrophages are believed to be involved in gout flares. It has long been recognized that resident macrophage and monocyte derived macrophages are distinct subsets and there have been attempts to investigate their roles in acute gout, respectively. Previous studies revealed that resident macrophages initiate and drive the inflammation, while monocyte derived macrophages differentiated into M1-like macrophages in response to MSU crystals. With the advancement of technologies, subpopulations of synovial resident macrophages have been defined with the characteristics more accurately described. Resident macrophages in the synovial lining layer showed an anti-inflammatory effect in rheumatoid arthritis, but specific Trpv4 depletion of them reduced MSU crystals induced murine arthritis. CD14+ monocytes in the synovial fluid from patients with gout exhibit phenotypes of anti-inflammatory as well as pro-inflammatory characteristics. Here, we review the main aspects of macrophages in the initiation and resolution of acute gout and try to clarify the specific role of each subpopulation. Building a reliable diagram of the effect of monocytes and macrophages during MSU crystals induced arthritis will bring us closer to targeting macrophages for improving the management of gout.

Biology of interleukin‑37 and its role in autoimmune diseases (Review)

Autoimmune diseases (AIDs) are characterized by dysfunction and tissue destruction, and recent studies have shown that interleukin (IL)-37 expression is dysregulated in AIDs. Among cytokines of the IL-1 family, most are pro-inflammatory agents, and as an anti-inflammatory cytokine, IL-37 may have the potential to alleviate excessive inflammation and can be used as a ligand or transcription factor that is involved in regulating innate and adaptive immunity. IL-37 plays important roles in the development of AIDs. This review summarizes the biological characteristics and functions of IL-37 and discusses the potential of IL-37 as a therapeutic target for effective cytokine therapy and as a biomarker in AIDs.

Identification of Inflammation-Related Biomarker Pro-ADM for Male Patients With Gout by Comprehensive Analysis

Objective

Gout is a local inflammatory disease caused by the deposition of monosodium urate (MSU) crystals in joints or adjacent tissues. When some gout occurs without hyperuricemia, or its clinical symptoms and signs are not typical, the diagnosis of gout will be delayed, so there is an urgent need to find a new biomarker to predict and diagnose of gout flare. Our research attempts to find the key genes and potential molecular mechanisms of gout through bioinformatics analysis, and collected general data and blood biochemical samples of patients with gout and healthy, then analyzed and compared the expression of factors regulated by key genes.

Method

GSE160170 were downloaded from GEO database for analysis. The data were normalized to identify the differentially expressed genes (DEGs), then GO and KEGG enrichment analysis were applied. Protein-protein interaction (PPI) networks and hub genes between DEGs were identified. Then collect general information and blood samples from male patients with acute gout, hyperuricemia and healthy. ELISA method was used to detect pro-ADM levels of different groups, and the data was input into SPSS statistical software for analysis.

Result

We identified 266 DEGs (179 up-regulated and 87 down-regulated) between gout patients and healthy controls. GO analysis results show that DEGs are mostly enriched in inflammatory response, growth factor activity, cytokine activity, chemokine activity, S100 protein binding and CXCR chemokine receptor binding. KEGG pathway analysis showed that DEGs are mainly related to Chemokine signaling pathway and Cytokine-cytokine receptor interaction. ADM, CXCR1, CXCR6, CXCL3, CCL3, CCL18, CCL3L3, CCL4L1, CD69, CD83, AREG, EREG, B7RP1, HBEGF, NAMPT and S100B are the most important hub genes in the PPI network. We found that the expression of pro-ADM in the gout group and hyperuricemia group was higher than that in the healthy group, and the difference was statistically significant.

Conclusion

In this study, a series of bioinformatics analyses were performed on DEGs to identify key genes and pathways related to gout. Through clinical verification, we found that pro-ADM can be used as an inflammation-related biomarker for acute attacks of gout, providing new ideas for the diagnosis and treatment of gout.

IL-37 blocks gouty inflammation by shaping macrophages into a non-inflammatory phagocytic phenotype

OBJECTIVE

Interleukin (IL)-37 is a natural suppressor of inflammation. Macrophages play an important role in acute gout flare by dominating the inflammation and spontaneous relief. We have reported IL-37 could limit runaway inflammation in gout. Here we focus on whether IL-37 inhibits gouty inflammation by altering macrophage functions and how it does.

METHODS

Macrophage functions were evaluated in terms of phagocytosis, pyroptosis, polarization, and metabolism. Phagocytosis and polarization of macrophages were detected by side scattering and double-labelling iNOS/Arg-1 using flow cytometry, respectively. Transcription of pyroptosis-related molecules was detected by qPCR. Metabolomics was performed by liquid chromatograph mass spectrometer. Human IL-37 knock-in mice and a model with point mutation (S9A) at mouse Gsk3b locus were created by CRISPR/Cas-mediated genome engineering. MSU was injected into paws and peritoneal cavity to model acute gout. Vernier caliper was used to measure the thickness of the paws. The mice paws and human synovium tissues or tophi were collected for pathological staining. Peritoneal fluid of mice was used to enrich macrophages to detect polarization.

RESULTS

IL-37 promoted non-inflammatory phagocytic activity of macrophages, by enhancing phagocytosis of MSU, reducing pyroptosis-related proteins transcription and inflammatory cytokines releasing, protecting mitochondrial function, and mediating metabolic reprogramming in MSU-treated THP-1 cells. These multifaceted roles of IL-37 were partly depended on the mediation of glycogen synthase kinase-3β (GSK-3β).

CONCLUSIONS

Our study revealed that IL-37 could shape macrophages into a "silent" non-inflammatory phagocytic fashion. IL-37 may become a potentially valuable treatment option for patients of chronic gout, especially for those with tophi.

Reduced CXCL1 production by endogenous IL-37 expressing dendritic cells does not affect T cell activation

The dendritic cell (DC)-derived cytokine profile contributes to naive T cell differentiation, thereby directing the immune response. IL-37 is a cytokine with anti-inflammatory characteristics that has been demonstrated to induce tolerogenic properties in DC. In this study we aimed to evaluate the influence of IL-37 on DC–T cell interaction, with a special focus on the role of the chemokine CXCL1. DC were cultured from bone marrow of human IL-37 transgenic (hIL-37Tg) or WT mice. The phenotype of unstimulated and LPS-stimulated DC was analyzed (co-stimulatory molecules and MHCII by flow cytometry, cytokine profile by RT-PCR and ELISA), and T cell stimulatory capacity was assessed in mixed lymphocyte reaction. The role of CXCL1 in T cell activation was analyzed in T cell stimulation assays with anti-CD3 or allogeneic DC. The expression of the co-stimulatory molecules CD40, CD80 and CD86, and of MHCII in LPS-stimulated DC was not affected by endogenous expression of IL-37, whereas LPS-stimulated hIL-37Tg DC produced less CXCL1 compared to LPS-stimulated WT DC. T cell stimulatory capacity of LPS-matured hIL-37Tg DC was comparable to that of WT DC. Recombinant mouse CXCL1 did not increase T cell proliferation either alone or in combination with anti-CD3 or allogeneic DC, nor did CXCL1 affect the T cell production of interferon-γ and IL-17. Endogenous IL-37 expression does not affect mouse DC phenotype or subsequent T cell stimulatory capacity, despite a reduced CXCL1 production. In addition, we did not observe an effect of CXCL1 in T cell proliferation or differentiation.

Gout

Gout is a common and treatable disease caused by the deposition of monosodium urate crystals in articular and non-articular structures. Increased concentration of serum urate (hyperuricaemia) is the most important risk factor for the development of gout. Serum urate is regulated by urate transporters in the kidney and gut, particularly GLUT9 (SLC2A9), URAT1 (SLC22A12), and ABCG2. Activation of the NLRP3 inflammasome by monosodium urate crystals with release of IL-1β plays a major role in the initiation of the gout flare; aggregated neutrophil extracellular traps are important in the resolution phase. Although presenting as an intermittent flaring condition, gout is a chronic disease. Long-term urate lowering therapy (eg, allopurinol) leads to the dissolution of monosodium urate crystals, ultimately resulting in the prevention of gout flares and tophi and in improved quality of life. Strategies such as nurse-led care are effective in delivering high-quality gout care and lead to major improvements in patient outcomes.

Interleukin-37 contributes to the pathogenesis of gout by affecting PDZ domain-containing 1 protein through the nuclear factor-kappa B pathway

OBJECTIVE

Our objective was to explore the molecular pathogenesis of the onset of gout and the mechanism underlying the effect of interleukin (IL)-37 on PDZ domain-containing 1 (PDZK1) protein through the nuclear factor-κB signaling pathway.

METHODS

Real-time PCR and western blotting were used to detect expression of PDZK1 mRNA and protein, respectively, in the HK-2 cell line. The inhibitors pyrrolidine dithiocarbamate (PDTC) and wortmannin were added to HK-2 cells stimulated by IL-37, and changes in PDZK1 protein were detected by western blotting.

RESULTS

Based on our previous research, we used 10 µmol/L PDTC. We detected no significant change in PDZK1 at the mRNA level among the IL-37, PDTC+IL-37, and wortmannin+IL-37 groups. With increasing IL-37 concentration, the protein level of PDZK1 increased. After adding wortmannin, the protein level of PDZK1 increased with increasing concentration of IL-37, albeit not significantly, and the level of PDZK1 remained lower than that with IL-37 alone. After adding PDTC, the protein level of PDZK1 showed a trend to decrease with increasing concentrations of IL-37 up to 40 ng/mL. The immunofluorescence results supported the western blot results.

CONCLUSIONS

IL-37 can affect protein expression of PDZK1, but not at the translational level, in the pathogenesis of gout.

IL-37 As a Potential Biotherapeutics of Inflammatory Diseases

Interleukin-37 (IL-37) was discovered as a new member of pro-inflammatory IL-1 superfamily. However, further studies suggested that IL-37 plays a critical anti-inflammatory role in innate and adaptive immunity. IL-37 may suppress the inflammatory process via intracellular SMAD family member 3 (SMAD3) and extracellular IL-18 Receptor alpha (IL-18Rα) signaling pathway, respectively. Meanwhile, the abnormal expression of IL-37 was observed in immune-mediated inflammatory diseases, such as inflammatory bowel disease, rheumatoid arthritis, atherosclerosis, systemic lupus erythematosus, asthma, and multiple sclerosis, which suggest IL-37 is a potential therapeutic target for these diseases. In this review, we summarize the anti-inflammatory mechanism of IL-37 and discuss the critical roles of IL-37 in the pathogenesis of these diseases. Further studies are required to confirm the effectiveness of IL-37 as a novel target for these inflammatory diseases.

Elevated interleukin-37 associated with tophus and pro-inflammatory mediators in Chinese gout patients

INTRODUCTION

Interleukin-37(IL-37), a natural inhibitor of innate immunity, has been identified to protect against various inflammatory diseases, including monosodium urate (MSU)-induced inflammation. However, the association of IL-37 with clinical indexes and pro-inflammatory mediators in gout patients remains unclear. The aim of this study was to determine IL-37 level in hyperuricemia and gout patients with or without tophus, and to investigate the correlations of IL-37 with clinical indexs such as Uric Acid (UA), CRP(C-reactive protein), Creatinine Clearance Rate (Ccr), Erythrocyte Sedimentation Rate (ESR) and so on, as well as with the pro-inflammatory mediators in serum including Interleukin-1β(IL-1β), Interleukin-6(IL-6) and Interleukin-18(IL-18) from gout patients.

METHODOLOGY

The serum levels of IL-37, IL-1β, IL-6 and IL-18 levels in serum of gout patients were determined by ELISA; the correlations between IL-37 and clinical values or pro-inflammatory mediators in serum of gout were analyzed by Spearman correlation test.

RESULTS

The serum levels of IL-37 were higher in active gout patients than inactive gout patients and HCs, especially in active gout patients with tophus. No significant difference was observed in serum IL-37 levels between hyperuricemia and normal controls. IL-1β, IL-6 and IL-18 levels were significant elevated in gout patients with tophus than those without tophus; Serum IL-37 were positively correlated with CRP and ESR, as well as with IL-1β, IL-6 and IL-18, negatively correlated with Ccr, and not correlated with UA, creatinine (Cr) and triglyceride (TG) in gout patients.

CONCLUSIONS

IL-37 increased in gout patients positively associated CRP and ESR, as well as with proinflammatory mediators IL-1β, IL-6, IL-18, the presence of tophus and chronic kidney disease in gout. It may be a novel marker for predicting this pathology.

IL-37 inhibits M1-like macrophage activation to ameliorate temporomandibular joint inflammation through the NLRP3 pathway

OBJECTIVES

IL-37 has been identified as an important anti-inflammatory and immunosuppressive factor. This study was undertaken to explore how IL-37 affects M1/M2-like macrophage polarization and thus contributes to anti-inflammatory processes in the temporomandibular joint.

METHODS

Western blotting, quantitative real-time PCR (qRT-PCR) and immunofluorescence were used to verify the IL-37-induced polarization shift from the M1 phenotype to the M2 phenotype, and the related key pathways were analysed by western blotting. Human chondrocytes were stimulated with M1-conditioned medium (CM) or IL-37-pretreated M1-CM, and inflammatory cytokines were detected. siRNA-IL-1R8 and MCC-950 were used to investigate the mechanism underlying the anti-inflammatory effects of IL-37. Complete Freund's adjuvant-induced and disc perforation-induced inflammation models were used for in vivo studies. Haematoxylin and eosin, immunohistochemical and safranin-O staining protocols were used to analyse histological changes in the synovium and condyle.

RESULTS

Western blotting, qRT-PCR and immunofluorescence showed that IL-37 inhibited M1 marker expression and upregulated M2 marker expression. Western blotting and qRT-PCR showed that pretreatment with IL-37 suppressed inflammatory cytokine expression in chondrocytes. IL-37 inhibited the expression of NLRP3 and upregulated the expression of IL-1R8. Si-IL-1R8 and MCC-950 further confirmed that the anti-inflammatory properties of IL-37 were dependent on the presence of IL-1R8 and NLRP3. In vivo, IL-37 reduced synovial M1 marker expression and cartilage degeneration and increased M2 marker expression.

CONCLUSION

IL-37 shifting of the polarization of macrophages from the pro-inflammatory M1 phenotype to the beneficial anti-inflammatory M2 phenotype seems to be a promising therapeutic strategy for treating temporomandibular joint inflammation.

The role of interleukin-1 family members in hyperuricemia and gout

BACKGROUND

Interleukin (IL)-1 family cytokines and their receptors have important roles in innate and partly in adaptive immunity. The family consists of 11 members of which IL-1α, IL-1β, IL-18, IL-33, IL-36α, IL-36β and IL-36γ are considered pro-inflammatory and IL-1Ra, IL-36Ra, IL-37 and IL-38 anti-inflammatory. Whereas IL-1β has a known pivotal role in gout, increasing evidence suggests other IL-1 family members are also involved in the pathogenesis of hyperuricemia and gout flares.

FINDINGS

Studies indicate IL-1α, like IL-1β, plays an essential role in the pathogenesis of gout flares. IL-18, although elevated in patients with gout, does not contribute to MSU crystal-induced inflammation, but may be involved in the subsequent development of cardiovascular disease in individuals with gout. The role of the pro-inflammatory cytokine IL-36 in gout remains elusive. In contrast, IL-1Ra, IL-33, IL-37 and IL-38 inhibit MSU crystal-induced inflammation and therefore have therapeutic potential for treatment of gout flares. In addition to existing IL-1β blockers, several new therapeutics to treat gout are being developed either inhibiting the transcription or maturation of IL-1β.

CONCLUSION

In this review, IL-1 family cytokines are discussed in the context of hyperuricemia and gout. Finally, current and novel therapeutic options for targeting IL-1 are reviewed.

Advances in our understanding of gout as an auto-inflammatory disease

Gout, the most common inflammatory arthritis, is the result of hyperuricemia and inflammation induced by monosodium urate (MSU) crystal deposition. However, most people with hyperuricemia will never develop gout, implying a molecular-genetic contribution to the development of gout. Recent genomic studies reveal links between certain genetic variations and gout. We highlight recent advances in our understanding of gout as an auto-inflammatory disease. We review the auto-inflammatory aspects of gout, including the inflammasome and thirteen gout-associated inflammatory-pathway genes and associated comorbidities. This information provides important insights into emerging immune-modulating targets in the management of gout, and future novel therapeutic targets in gout treatment. Cumulatively, this has important implications for treating gout as an auto-inflammatory disease, as opposed to a purely metabolic disease.

Gout: a disease involved with complicated immunoinflammatory responses: a narrative review

Gout is a disease with acute and/or chronic inflammation and tissue damage induced by the precipitation of monosodium urate crystal (MSU) crystals in bone joints, kidneys, and subcutaneous sites. In recent years, with the continuous research on gout animal models and patient clinical investigations, the mechanism of inflammation activation of gout has been further discovered. Studies have shown that pro-inflammatory factors such as interleukin (IL)-1β, IL-8 and IL-17, NLRP3 inflammasome, and tumor necrosis factor alpha (TNF-α), anti-inflammatory factors such as IL-10, IL-37 are all involved in the MSU-induced gout inflammatory process. And the immune cells in gout, including neutrophils, monocytes/macrophages, and lymphocytes, all play important roles in the pathogenesis of gout. In this review, we mainly emphasize the understanding of various cytokines, inflammasome, and immune cells involved in the onset of gout, in order to provide a systematic and theoretical basis for the novel exploration of inflammatory therapeutic targets for gout.

Huzhang Tongfeng Granule Improves Monosodium Urate-Induced Inflammation of Gouty Arthritis Rat Model by Downregulation of Cyr61 and Related Cytokines

OBJECTIVE

Gouty arthritis (GA) is a noninfectious inflammatory disease characterized by self-limited and severe pain. Huzhang Tongfeng granule is one of the most effective traditional Chinese medicines in the treatment of acute GA. However, its effects on the inflammatory factors in the process of acute gout inflammation remain unknown. In the present study, we aimed to evaluate the effect of Huzhang Tongfeng granule on the expressions of Cyr61 and related inflammatory factors in both experimental gout models in vivo and in vitro.

METHODS

Huzhang Tongfeng granule was provided by the pharmaceutical preparation room of Yueyang Hospital of Integrated Traditional Chinese and Western Medicine. The expressions of Cyr61, IL-1β, TNF-α, and IL-6 in monosodium urate- (MSU-) induced rat models and fibroblast-like synoviocytes (FLSs) were determined by RT-PCR, Western blotting analysis, ELISA, immunohistochemistry, and hematoxylin and eosin staining.

RESULTS

Huzhang Tongfeng granule could downregulate the expressions of IL-1β, TNF-α, and IL-6 to some extent by inhibiting the expression of Cyr61.

CONCLUSIONS

Collectively, our findings indicated that Cyr61 was highly expressed in rat models of gout. By inhibiting the expression of Cyr61, Huzhang Tongfeng granule could partially attenuate the inflammation induced by MSU crystal.

Interleukin-37 Attenuates Lipopolysaccharide (LPS)-Induced Neonatal Acute Respiratory Distress Syndrome in Young Mice via Inhibition of Inflammation and Cell Apoptosis

Background

Neonatal acute respiratory distress syndrome (ARDS) is a common clinical syndrome caused by lung immaturity and the abnormal synthesis of pulmonary surfactant in preterm newborns, and it has high morbidity and mortality rates. The present study investigated the roles of interleukin-37 (IL-37) in the pathogenesis of neonatal ARDS and the underlying biochemical mechanism.

Material/Methods

We used 6-day-old neonatal C57BL/6 mice to establish the ARDS model. Inflammatory cytokines levels were measured with enzyme-linked immunosorbent assay (ELISA) Kits. The pathological morphology of lung tissues was observed by hematoxylin-eosin (HE) staining. The expression levels of proteins were assessed by Western blotting and apoptotic cells were detected via TUNEL assay. Further, the expression of nucleotide-bound oligomerization domain (Nod)-like receptor P3 (NLRP3) was detected with immunohistochemistry and Western blotting.

Results

IL-37 attenuated lipopolysaccharide (LPS)-induced cell apoptosis and excessive inflammatory cytokines levels, including IL-1β, IL-8, TNF-α, and MCP-1, and ameliorated lung pathological manifestations in an LPS-induced neonatal ARDS model. Moreover, IL-37 suppressed the abnormal expression of proteins related to the CXCR4/SDF-1 chemokine axis and NLRP3 inflammasome pathway.

Conclusions

The present results suggest that IL-37 protect against LPS-induced lung injury through inhibition of inflammation and apoptosis in lung tissue in an LPS-induced neonatal ARDS model. Hence, IL-37 may be considered as a potential therapeutic agent for neonatal ARDS.

Rare genetic variants in interleukin-37 link this anti-inflammatory cytokine to the pathogenesis and treatment of gout

OBJECTIVE

Gout is characterised by severe interleukin (IL)-1-mediated joint inflammation induced by monosodium urate crystals. Since IL-37 is a pivotal anti-inflammatory cytokine suppressing the activity of IL-1, we conducted genetic and functional studies aimed at elucidating the role of IL-37 in the pathogenesis and treatment of gout.

METHODS

Variant identification was performed by DNA sequencing of all coding bases of IL37 using molecular inversion probe-based resequencing (discovery cohort: gout n=675, controls n=520) and TaqMan genotyping (validation cohort: gout n=2202, controls n=2295). Predictive modelling of the effects of rare variants on protein structure was followed by in vitro experiments evaluating the impact on protein function. Treatment with recombinant IL-37 was evaluated in vitro and in vivo in a mouse model of gout.

RESULTS

We identified four rare variants in IL37 in six of the discovery gout patients; p.(A144P), p.(G174Dfs*16), p.(C181*) and p.(N182S), whereas none emerged in healthy controls (Fisher's exact p-value=0.043). All variants clustered in the functional domain of IL-37 in exon 5 (p-value=5.71×10^-5). Predictive modelling and functional studies confirmed loss of anti-inflammatory functions and we substantiated the therapeutic potential of recombinant IL-37 in the treatment of gouty inflammation. Furthermore, the carrier status of p.(N182S)(rs752113534) was associated with increased risk (OR=1.81, p-value=0.031) of developing gout in hyperuricaemic individuals of Polynesian ancestry.

CONCLUSION

Here, we provide genetic as well as mechanistic evidence for the role of IL-37 in the pathogenesis of gout, and highlight the therapeutic potential of recombinant IL-37 for the treatment of gouty arthritis.

Parsing the IL-37-Mediated Suppression of Inflammasome Function

Interleukin (IL)-37 is a member of the IL-1 family of cytokines. Although its broad anti-inflammatory properties are well described, the effects of IL-37 on inflammasome function remain poorly understood. Performing gene expression analyses, ASC oligomerization/speck assays and caspase-1 assays in bone marrow-derived macrophages (BMDM), and employing an in vivo endotoxemia model, we studied how IL-37 affects the expression and maturation of IL-1β and IL-18, inflammasome activation, and pyroptosis in detail. IL-37 inhibited IL-1β production by NLRP3 and AIM2 inflammasomes, and IL-18 production by the NLRP3 inflammasome. This inhibition was partially attributable to effects on gene expression: whereas IL-37 did not affect lipopolysaccharide (LPS)-induced mRNA expression of Il18 or inflammasome components, IL-37-transgenic BMDM displayed an up to 83% inhibition of baseline and LPS-stimulated Il1b compared to their wild-type counterparts. Importantly, we observed that IL-37 suppresses nigericin- and silica-induced ASC oligomerization/speck formation (a step in inflammasome activation and subsequent caspase-1 activation), and pyroptosis (-50%). In mice subjected to endotoxemia, IL-37 inhibited plasma IL-1β (-78% compared to wild-type animals) and IL-18 (-61%). Thus, our study adds suppression of inflammasome activity to the portfolio of anti-inflammatory pathways employed by IL-37, highlighting this cytokine as a potential tool for treating inflammasome-driven diseases.

The role of IL-37 in skin and connective tissue diseases

IL-37 was discovered as an anti-inflammatory and immunosuppressive cytokine of the IL-1 family. Significant advancements in the understanding of signaling pathways associated with IL-37 have been made in recent years. IL-37 binds to IL-18R and recruits IL-1R8 to form the IL-37/IL-1R8/IL-18Rα complex. Capase-1 plays a key role in the nuclear transduction of IL-37 signal, processing precursor IL-37 into the mature isoform, and interacting with Smad3. IL-37 exerts its role by activating anti-inflammation pathways including AMPK, PTEN, Mer, STAT3 and p62, and promoting tolerogenic dendritic cells and Tregs. In addition, IL-37 inhibits pro-inflammatory cytokines such as IL-1, IL-6, IL-8, IL-17, IL-23, TNF-α, and IFN-γ, and suppresses Fyn, MAPK, TAK1, NFκB, and mTOR signaling. The final effects of IL-37 depend on the interaction among IL-18R, IL-1R8, IL-37 and IL-18BP. Previous studies have deciphered the role of IL-37 in the development and pathogenesis of autoimmune diseases, chronic infections and cancer. In this review, we discuss the role of IL-37 in psoriasis, atopic dermatitis, Behcet's diseases, systemic lupus erythematosus, and other skin and connective tissue diseases.

Insight into interleukin-37: The potential therapeutic target in allergic diseases

Allergic diseases are ubiquitous diseases with detrimental effects on the quality of life of people worldwide. Common allergic diseases include asthma, allergic rhinitis (AR) and allergic dermatitis (AD). Recently, studies have shown that interleukin (IL)-37, a novel cytokine in the IL-1 family, exhibits broad protective properties in various diseases, such as autoimmune diseases and cancer. IL-37 displays its anti-inflammatory effect on diseases by curbing innate and acquired immunity as well as inflammatory reactions. IL-37 functions by forming a complex with IL-18Rα and IL-1R8 extracellularly and can be translocated to the nucleus upon forming a complex with mothers against decapentaplegic homolog 3 (Smad3) intracellularly, thereby affecting gene transcription and signaling pathway activation. In addition, increasing evidence confirms that IL-37 expression is aberrant in asthma, AR and AD, which indicates that IL-37 may also play essential roles in allergic diseases. Furthermore, accumulating data obtained from recombinant IL-37 (rIL-37)-treated mice and from IL-37 transgenic (IL-37tg) mice suggest a protective role for IL-37. This review will detail the role of IL-37 in the occurrence and development of allergic diseases and discuss the potential of IL-37 as a therapeutic target in allergic diseases.

IL-37b alleviates inflammation in the temporomandibular joint cartilage via IL-1R8 pathway

Objectives

Interleukin (IL)‐37 is a natural suppressor of innate inflammation. This study was conducted to explore the anti‐inflammatory effects of IL‐37 in temporomandibular joint (TMJ) inflammation.

Materials and Methods

The expression of IL‐37 in the TMJ was measured using ELISA and IHC. Human TMJ chondrocytes were treated with IL‐37b and IL‐1β, and inflammation‐related factors were detected. siRNA‐IL‐1R8 was transfected into chondrocytes, and the affected pathways were detected. IL‐37b was used in disc‐perforation‐induced TMJ inflammation in SD rats. Micro‐CT, IHC, real‐time PCR and histological staining were used to quantify the therapeutic effect of IL‐37b.

Results

IL‐37 was expressed in the synovium and the disc of patients with osteoarthritis (OA) and in the articular cartilage of condylar fracture patients. IL‐37 was highly expressed in synovial fluid of patients with synovitis than in those with OA and disc displacement and was closely related to visual analogue scale (VAS) score. In vitro, IL‐37b suppressed the expression of pro‐inflammatory factors. In addition, IL‐37b exerted anti‐inflammatory effects via IL‐1R8 by inhibiting the p38, ERK, JNK and NF‐κB activation, while silencing IL‐1R8 led to inflammation and upregulation of these signals. In disc‐perforation‐induced TMJ inflammation in SD rats, IL‐37b suppressed inflammation and inhibited osteoclast formation to protect against TMJ.

Conclusions

IL‐37b may be a novel therapeutic agent for TMJ inflammation.

Gout

Gout is a chronic disease caused by monosodium urate (MSU) crystal deposition. Gout typically presents as an acute, self-limiting inflammatory monoarthritis that affects the joints of the lower limb. Elevated serum urate level (hyperuricaemia) is the major risk factor for MSU crystal deposition and development of gout. Although traditionally considered a disorder of purine metabolism, altered urate transport, both in the gut and the kidneys, has a key role in the pathogenesis of hyperuricaemia. Anti-inflammatory agents, such corticosteroids, NSAIDs and colchicine, are widely used for the treatment of gout flare; recognition of the importance of NLRP3 inflammasome activation and bioactive IL-1β release in initiation of the gout flare has led to the development of anti-IL-1β biological therapy for gout flares. Sustained reduction in serum urate levels using urate-lowering therapy is vital in the long-term management of gout, which aims to dissolve MSU crystals, suppress gout flares and resolve tophi. Allopurinol is the first-line urate-lowering therapy and should be started at a low dose, with gradual dose escalation. Low-dose anti-inflammatory therapies can reduce gout flares during initiation of urate-lowering therapy. Models of care, such as nurse-led strategies that focus on patient engagement and education, substantially improve clinical outcomes and now represent best practice for gout management.

Pharmacological basis for use of madecassoside in gouty arthritis: anti-inflammatory, anti-hyperuricemic, and NLRP3 inhibition

Objectives: Gouty arthritis is caused by the deposition of monosodium urate (MSU) crystals in joints, which is associated with the rise of serum urate content. This study aims to investigate the therapeutic effect of Madecassoside on gouty arthritis and hyperuricemia. Methods: DBA/1 mice were intradermally injected with MSU to stimulate joint inflammation or intraperitoneally injected with MSU to trigger peritonitis. Moreover, ICR mice were exposed to potassium oxonate to stimulate hyperuricemia. Results: Madecassoside repressed MSU-triggered pad swelling, joint 99mTc uptake, and joint inflammation in DBA/1 mice with gouty arthritis. Neutrophil infiltration and IL-1β & IL-6 & MCP-1 secretion was also alleviated in lavage fluids from DBA/1 mice with peritonitis due to Madecassoside treatment. Furthermore, Madecassoside decreased MSU-induced neutrophil cytosolic factor 1, caspase-1 and NLRP3 expression in mice with peritoneal inflammation. In hyperuricemic mice, Madecassoside improved renal dysfunction. Serum uric acid, BUN, and creatinine were down-regulated by Madecassoside. Conclusion: These findings indicate that Madecassoside has potential to ameliorate inflammation in both acute gouty arthritis model and peritonitis model, probably via regulating IL-1β and NLRP3 expression. Practical point: Madecassoside also exhibited a urate-lowering effect and a renal protective effect in hyperuricemic mice.

Interleukin-37 (IL-37) Suppresses Pertussis Toxin-Induced Inflammatory Myopathy in a Rat Model

Background

Recent data have demonstrated the potential immunosuppressive roles of interleukin-37 (IL-37) in several diseases, but whether it is involved in the pathogenesis of inflammatory myopathy has not been elucidated.

Material/Methods

An experimental autoimmune myositis (EAM) model was built by subcutaneous injections of pertussis toxin (PTX) and purified rabbit myosin (10mg/kg) emulsified with an equal volume of conventional complete Freund’s adjuvant (CFA) in a Lewis model. Autoimmune myositis Lewis model rats were divided into 3 groups: group A rats (control group) were injected with CFA in saline weekly; group B (IL-37 group) rats were injected with saline with IL-37 and CFA in saline weekly; and group C (IL-37 + SIS3 group) rats were injected with IL-37, CFA, and SIS3. ELISA was also used to assess the expressions of TNF-α, IL-6, IL-1β, TGF-β1, and CK. HE staining was performed to assess pathological changes in lung and muscle tissues.

Results

The expressions of TNF-α, IL-6, IL-1β, TGF-β1, and CK significantly increased in autoimmune myositis Lewis model rats. After IL-37 treatment, the expression of TNF-α, IL-6, IL-1β, TGF-β1, and CK was significantly reduced, as were the inflammatory responses of lung and muscle. However, SIS3 reduced the effects of IL-37 on the autoimmune myositis Lewis model rats.

Conclusioans

These findings indicate that IL-37 protects against inflammatory response via regulating Smad3 in autoimmune myositis Lewis model rats.

The Role of Inhibitory Receptors in Monosodium Urate Crystal-Induced Inflammation

Inhibitory receptors are key regulators of immune responses. Aberrant inhibitory receptor function can either lead to an exacerbated or defective immune response. Several regulatory mechanisms involved in the inflammatory reaction induced by monosodium urate crystals (MSU) during acute gout have been identified. One of these mechanisms involves inhibitory receptors. The engagement of the inhibitory receptors Clec12A and SIRL-1 has opposing effects on the responses of neutrophils to MSU. We review the general concepts of inhibitory receptor biology and apply them to understand and compare the modulation of MSU-induced inflammation by Clec12A and SIRL-1. We also discuss gaps in our knowledge of the contribution of inhibitory receptors to the pathogenesis of gout and propose future avenues of research.

Association of NLRP3 polymorphisms with susceptibility to primary gouty arthritis in a Chinese Han population

The NLRP3-interleukin1β (IL1β) signaling pathway is involved in monosodium urate (MSU)-mediated inflammation. The aim of this present study was to determine whether single nucleotide polymorphisms (SNPs) in the NLRP3 gene are associated with susceptibility to gouty arthritis (GA) and whether these SNPs alter the expression of components of the NLRP3-IL1β signaling pathway. The rs10754558, rs4612666, and rs1539019 SNPs were detected in 583 patients with GA and 459 healthy subjects. NLRP3 and IL1β mRNA levels in peripheral blood mononuclear cells (PBMCs) and serum IL1β levels were measured in different genotype carriers, and correlations between the NLRP3 SNPs and NLRP3 mRNA, IL1β mRNA, and serum IL1β levels were investigated. The GG genotype of NLRP3 rs10754558 was found to be significantly associated with patients with GA compared to the healthy control subjects via multivariate logistic regression analysis (adjusted OR = 2.68, P = 0.006). The CGA haplotypes were independently associated with patients with GA compared to the healthy control subjects (adjusted OR = 1.968, P = 0.02). The levels of NLRP3 mRNA, IL1β mRNA, and serum IL1β in the patients with GA were significantly different among the three genotypes of rs10754558 (all P < 0.01). The GG genotype of rs10754558 and the CGA haplotype of rs4612666-C, rs10754558-G, and rs1539019-A are both independent risk factors for primary GA development. The rs10754558 polymorphism might participate in regulating immune and inflammation responses in patients with GA by influencing the expression of components of the NLRP3 inflammasome. Future multicenter studies aimed at replicating these findings in an independent population as well as functional tests will aid in further defining the role of these SNPs in the development of GA.

Estradiol inhibits NLRP3 inflammasome in fibroblast-like synoviocytes activated by lipopolysaccharide and adenosine triphosphate

OBJECTIVE

Nucleotide binding domain and leucine-rich repeat pyrin 3 domain (NLRP3) inflammasome is known for activating pro-inflammatory cytokines in knee osteoarthritis (OA). This study was performed to identify whether NLRP3 inflammasome can be triggered by lipopolysaccharides (LPS) and adenosine triphos adenine (ATP), which are positively related with knee OA severity in joint-spaces, in human fibroblast-like synoviocytes (FLS), and to identify whether estrogen would inhibit the activation of NLRP3 inflammasome.

METHODS

In the present study, human FLS were isolated from the knee OA in patients during arthroplasty, and were treated with LPS and ATP in the presence or absence of estradiol (E2). The messenger RNA (mRNA) and protein levels of NLRP3 components were analyzed by real-time polymerase chain reaction and western blotting, respectively. Enzyme-linked immunosorbent assay (ELISA) was used to examine interleukin (IL)-1β and IL-18 content in the supernatant. Estrogen receptor α inhibitor MPP and β inhibitor PHTPP were used to explore how E2 works.

RESULTS

Our results demonstrated that treatment with LPS and ATP increased significantly both in mRNA and protein levels of all the NLRP3 inflammasome components, and triggered the NLRP3 inflammasome, followed by upregulated IL-1β and IL-18 in the cell supernatant. E2 appeared to inhibit the activation of NLRP3 inflammasome by diminishing mRNA and protein levels of NLRP3 through estrogen receptor β, and decreased the expression of IL-1β and IL-18 as well.

CONCLUSION

These results suggested the increased LPS and ATP in joint-space may promote knee OA by NLRP3 inflammasome and E2 may exert a protective effect by inhibiting the activation of NLRP3 inflammasome in FLS.

What makes gouty inflammation so variable?

Acute gout arthritis flares contribute dominantly to gout-specific impaired health-related quality of life, representing a progressively increasing public health problem. Flares can be complex and expensive to treat, partly due to the frequent comorbidities. Unmet needs in gout management are more pressing given the markedly increasing gout flare hospital admission rates. In addition, chronic gouty arthritis can cause joint damage and functional impairment. This review addresses new knowledge on the basis for the marked, inherent variability of responses to deposited urate crystals, including the unpredictable and self-limited aspects of many gout flares. Specific topics reviewed include how innate immunity and two-signal inflammasome activation intersect with diet, metabolism, nutritional biosensing, the microbiome, and the phagocyte cytoskeleton and cell fate. The paper discusses the roles of endogenous constitutive regulators of inflammation, including certain nutritional biosensors, and emerging genetic and epigenetic factors. Recent advances in the basis of variability in responses to urate crystals in gout provide information about inflammatory arthritis, and have identified potential new targets and strategies for anti-inflammatory prevention and treatment of gouty arthritis.

SOCS molecules: the growing players in macrophage polarization and function

The concept of macrophage polarization is defined in terms of macrophage phenotypic heterogeneity and functional diversity. Cytokines signals are thought to be required for the polarization of macrophage populations toward different phenotypes at different stages in development, homeostasis and disease. The suppressors of cytokine signaling family of proteins contribute to the magnitude and duration of cytokines signaling, which ultimately control the subtle adjustment of the balance between divergent macrophage phenotypes. This review highlights the specific roles and mechanisms of various cytokines family and their negative regulators link to the macrophage polarization programs. Eventually, breakthrough in the identification of these molecules will provide the novel therapeutic approaches for a host of diseases by targeting macrophage phenotypic shift.

Molecular Pathophysiology of Gout

Three contradictory clinical presentations of gout have puzzled clinicians and basic scientists for some time: first, the crescendo of sterile inflammation in acute gouty arthritis; second, its spontaneous resolution, despite monosodium urate (MSU) crystal persistence in the synovium; and third, immune anergy to MSU crystal masses observed in tophaceous or visceral gout. Here, we provide an update on the molecular pathophysiology of these gout manifestations, namely, how MSU crystals can trigger the auto-amplification loop of necroinflammation underlying the crescendo of acute gouty arthritis. We also discuss new findings, such as how aggregating neutrophil extracellular traps (NETs) might drive the resolution of arthritis and how these structures, together with granuloma formation, might support immune anergy, but yet promote tissue damage and remodeling during tophaceous gout.