Myeloid-Related Proteins 8 and 14 Contribute to Monosodium Urate Monohydrate Crystal-Induced Inflammation in Gout

Data-independent LC-MS/MS analysis of ME/CFS plasma reveals a dysregulated coagulation system, endothelial dysfunction, downregulation of complement machinery

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a debilitating chronic condition that is characterized by unresolved fatigue, post-exertion symptom exacerbation (PESE), cognitive dysfunction, orthostatic intolerance, and other symptoms. ME/CFS lacks established clinical biomarkers and requires further elucidation of disease mechanisms. A growing number of studies demonstrate signs of hematological and cardiovascular pathology in ME/CFS cohorts, including hyperactivated platelets, endothelial dysfunction, vascular dysregulation, and anomalous clotting processes. To build on these findings, and to identify potential biomarkers that can be related to pathophysiology, we measured differences in protein expression in platelet-poor plasma (PPP) samples from 15 ME/CFS study participants and 10 controls not previously infected with SARS-CoV-2, using DIA LC-MS/MS. We identified 24 proteins that are significantly increased in the ME/CFS group compared to the controls, and 21 proteins that are significantly downregulated. Proteins related to clotting processes - thrombospondin-1 (important in platelet activation), platelet factor 4, and protein S - were differentially expressed in the ME/CFS group, suggestive of a dysregulated coagulation system and abnormal endothelial function. Complement machinery was also significantly downregulated, including C9 which forms part of the membrane attack complex. Additionally, we identified a significant upregulation of lactotransferrin, protein S100-A9, and an immunoglobulin variant. The findings from this experiment further implicate the coagulation and immune system in ME/CFS, and bring to attention the pathology of or imposed on the endothelium. This study highlights potential systems and proteins that require further research with regards to their contribution to the pathogenesis of ME/CFS, symptom manifestation, and biomarker potential, and also gives insight into the hematological and cardiovascular risk for ME/CFS individuals affected by diabetes mellitus.

Correlation analysis of serum TLR4 protein levels and TLR4 gene polymorphisms in gouty arthritis patients

OBJECTIVE

The Toll-like receptor (TLR) 4-mediated nuclear factor kappa B (NF-κB) signaling pathway regulates the production of inflammatory factors and plays a key role in the pathogenesis of gouty arthritis. The aim of the present study was to investigate the link among TLR4 gene polymorphisms at various loci, protein expression, and gouty arthritis susceptibility.

METHODS

Between 2016 and 2021, a case-control study was used to collect a total of 1207 study subjects, including 317 male patients with gouty arthritis (gout group) and 890 healthy males (control group). The association between gout susceptibility and different genetic models was analyzed by typing three loci of the TLR4 gene (rs2149356, rs2737191, and rs10759932) using a multiplex point mutation rapid assay, and the association between protein expression and gout was confirmed by measuring TLR4 protein concentrations using enzyme-linked immunosorbent assays (ELISAs).

RESULTS

In a codominant models AA and AG, the rs2737191 polymorphism in the gout group increased the risk of gout compared to the AA genotype (OR = 2.249, 95%CI 1.010~5.008), and the risk of gout was higher for those carrying the G allele compared to the A allele (OR = 2.227, 95%CI 1.006~4.932). TLR4 protein expression was different between the two groups with different locus genotypes. The differences in TLR4 protein expression between the gout group and control group were statistically significant between the following genotypes: the GG and GT genotypes of the rs2149356 polymorphism; the AA and AG genotypes of the rs2737191 polymorphism; and the TT and TC genotypes of the rs10759932 polymorphism(P<0.05). The TLR4 protein level in the gout group (19.19±3.09 ng/ml) was significantly higher than that in the control group (15.85±4.75 ng/ml).

CONCLUSION

The AG genotype of the TLR4 gene rs2737191 polymorphism may be correlated with the development of gouty arthritis. The level of TLR4 protein expression is significantly higher in patients with gouty arthritis than in controls, and there is a correlation between high TLR4 protein expression and the development of gouty arthritis.

Identified S100A9 as a target for diagnosis and treatment of ulcerative colitis by bioinformatics analysis

Ulcerative colitis (UC) is a chronic, recurrent inflammatory bowel disease. UC confronts with severe challenges including the unclear pathogenesis and lack of specific diagnostic markers, demanding for identifying predictive biomarkers for UC diagnosis and treatment. We perform immune infiltration and weighted gene co-expression network analysis on gene expression profiles of active UC, inactive UC, and normal controls to identify UC related immune cell and hub genes. Neutrophils, M1 macrophages, activated dendritic cells, and activated mast cells are significantly enriched in active UC. MMP-9, CHI3L1, CXCL9, CXCL10, CXCR2 and S100A9 are identified as hub genes in active UC. Specifically, S100A9 is significantly overexpressed in mice with colitis. The receiver operating characteristic curve demonstrates the excellent performance of S100A9 expression in diagnosing active UC. Inhibition of S100A9 expression reduces DSS-induced colonic inflammation. These identified biomarkers associated with activity in UC patients enlighten the new insights of UC diagnosis and treatment.

Novel Leflunomide Analog, UTLOH-4e, Ameliorates Gouty Arthritis Induced by Monosodium Urate Via NF-κB/NLRP3 Signaling Pathway

BACKGROUND

Gouty arthritis (GA) is a common form of inflammatory arthritis caused by intra-articular deposition of monosodium urate (MSU) crystals; however, there is a tremendous lack of safe and effective therapy in the clinic.

OBJECTIVE

The goal of this work was to investigate a novel leflunomide analogue, N-(2,4- dihydroxyphenyl)-5-methyl-1,2-oxazole-3-carboxamide (UTLOH-4e), for its potential to prevent/ treat gouty arthritis.

METHODS

In this study, the anti-inflammatory activity of UTLOH-4e was evaluated by MSUinduced GA model in vivo and in vitro, and the molecular docking test was applied to estimate the affinity of UTLOH-4e/UTL-5g/b for MAPKs, NF-κB, and NLRP3.

RESULTS

In vitro, UTLOH-4e (1~100 μM) treatment inhibited the inflammatory reaction with no obvious cytotoxicity in PMA-induced THP-1 macrophages exposed to MSU crystals for 24 h, involving the prominent decreased production and gene expression of IL-1β, TNF-α, and IL-6. Western blot analyses demonstrated that UTLOH-4e (1~100 μM) significantly suppressed the activation of NLRP3 inflammasomes, NF-κB, and MAPK pathways. Furthermore, the data from the experiment on gouty rats induced by intra-articular injection of MSU crystal confirmed that UTLOH-4e markedly ameliorated rat paw swelling, articular synovium inflammation and reduced the concentration of IL-1β and TNF-α in serum through down-regulating NLRP3 protein expression.

CONCLUSION

These results manifested that UTLOH-4e ameliorates GA induced by MSU crystals, which contributes to the modulation of NF-κB/ NLRP3 signaling pathway, suggesting that UTLOH- 4e is a promising and potent drug candidate for the prevention and treatment of gouty arthritis.

New drug targets for the treatment of gout arthritis: what's new?

INTRODUCTION

Gout arthritis (GA) is an intermittent inflammatory disease affecting approximately 10% of the worldwide population. Symptomatic phases (acute flares) are timely spaced by asymptomatic periods. During an acute attack, redness, joint swelling, limited movement, and excruciating pain are common symptoms. However, the current available therapies are not fully effective in reducing symptoms and offer numerous side effects. Therefore, unveiling new drug targets and effector molecules are required in developing novel GA therapeutics.

AREAS COVERED

This review discusses the pathophysiological mechanisms of GA and explores potential pharmacological targets to ameliorate disease outcome. In addition, we listed promising pre-clinical studies demonstrating effector molecules with therapeutical potential. Among those, we emphasized the importance of natural products, including traditional Chinese medicine formulas and their multitarget mechanisms of action.

EXPERT OPINION

In our search, we observed that there is a massive gap between pre-clinical and clinical knowledge. Only a minority (4.4%) of clinical trials aimed to intervene by applying natural products or current hot targets described herein. In this sense, we envisage four possibilities for GA therapeutics, which include the repurposing of existing therapies, ALX/FPR2 agonism for improvement in disease outcome, the use of multitarget drugs (e.g. natural products), and targeting the neuroinflammatory component of GA.

Surgical Management of Tophaceous Gout in the Upper Limb

PURPOSE

Gouty tophi are a clinical manifestation of hyperuricemia in advanced stages. They can produce pain, functional limitation, and severe deformities. Patients with severe symptoms require short-term symptomatic solutions that standard medical management is not able to provide. The objective of this study was to present the results obtained with the surgical management of tophaceous gout in the upper limb, as well as present a detailed characterization of the disease in the upper limb.

METHODS

Databases of the hand surgery service of a quaternary care hospital were reviewed to identify patients aged >18 years old undergoing tophi resection in the upper limbs between 2014 and 2020. Medical history records were reviewed retrospectively, and the relevant data were extracted to establish demographic profile, clinical presentation, anatomic distribution, postoperative outcomes, and additional procedures required.

RESULTS

The most frequent symptom was pain (83%), followed by limited range of motion (56%), deformity (50%), and daily living/occupational activity limitation (28%). The main indications for surgical management were the presence of deformity, pain, and/or limited range of motion. The most frequently affected anatomic sites were the metacarpophalangeal joints, followed by the elbows, proximal interphalangeal joints, and proximal phalanges. The postoperative complication rate was 28%. The most common complications were operative site infections and wound dehiscence. Decreased pain was associated with surgical resection. Additional procedures, such as extensor tenorrhaphy and local flaps, were required in 47.2% of patients.

CONCLUSION

Surgical resection of tophi can decrease pain. Although surgery is associated with a high rate of complications, most are minor.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic IV.

Inflammaging and Osteoarthritis

Osteoarthritis is a highly prevalent disease particularly in subjects over 65 years of age worldwide. While in the past it was considered a mere consequence of cartilage degradation leading to anatomical and functional joint impairment, in recent decades, there has been a more dynamic view with the synovium, the cartilage, and the subchondral bone producing inflammatory mediators which ultimately lead to cartilage damage. Inflammaging is defined as a chronic, sterile, low-grade inflammation state driven by endogenous signals in the absence of infections, occurring with aging. This chronic status is linked to the production of reactive oxygen species and molecules involved in the development of age-related disease such as cancer, diabetes, and cardiovascular and neurodegenerative diseases. Inflammaging contributes to osteoarthritis development where both the innate and the adaptive immune response are involved. Elevated systemic and local inflammatory cytokines and senescent molecules promote cartilage degradation, and antigens derived from damaged joints further trigger inflammation through inflammasome activation. B and T lymphocyte populations also change with inflammaging and OA, with reduced regulatory functions, thus implicating self-reactivity as an additional mechanism of joint damage. The discovery of the underlying pathogenic pathways may help to identify potential therapeutic targets for the management or the prevention of osteoarthritis. We will provide a comprehensive evaluation of the current literature on the role of inflammaging in osteoarthritis and discuss the emerging therapeutic strategies.

Circulating Calprotectin (cCLP) in autoimmune diseases

BACKGROUND AND AIM

Calprotectin (CLP) is a heterodimeric complex formed by two S100 proteins (S100A8/A9), which plays a pivotal role in innate immunity. Due to its intrinsic cytotoxic and proinflammatory properties, CLP controls cell differentiation, proliferation and NETosis and has been associated with a wide range of rheumatic diseases. Our review summarizes the widespread interest in circulating CLP (cCLP) as a biomarker of neutrophil-related inflammation, in autoimmune rheumatic disease (ARD) and non-ARD.

METHODS

A thorough literature review was performed using PubMed and EMBASE databases searching for circulating calprotectin and synonyms S100A8/A9, myeloid-related protein 8/14 (MRP8/MRP14), calgranulin A/B and L1 protein in addition to specific ARDs and autoimmune non-rheumatic diseases. We selected only English-language articles and excluded abstracts without the main text.

RESULTS

High cCLP serum levels are associated with worse structural outcomes in rheumatoid arthritis and to a lesser extent, in spondyloarthritis. In addition, cCLP can predict disease relapse in some autoimmune diseases including systemic lupus erythematosus (SLE), anti-neutrophil cytoplasmic antibodies-associated vasculitis (AAV) and some severe manifestations of connective tissue diseases, such as glomerulonephritis in SLE, AAV, juvenile idiopathic arthritis, adult-onset Still's disease and lung fibrosis in systemic sclerosis. Therefore, cCLP levels enable the identification of patients who need an accurate and tight follow-up. The clinical usefulness of cCLP as an inflammatory marker has been suggested for inflammatory/autoimmune non-rheumatic diseases, and especially for the monitoring of the inflammatory bowel diseases patients. Currently, there are only a few studies that evaluated the cCLP efficacy as a clinical biomarker in inflammatory/autoimmune non-rheumatic diseases with controversial results. Future studies are warranted to better clarify the role of cCLP in relation to the disease severity in myasthenia gravis, multiple sclerosis, chronic inflammatory demyelinating polyneuropathy, Graves' orbitopathy, autoimmune bullous diseases and uveitis.

CONCLUSION

Our literature review supports a relevant role of cCLP as potential prognostic biomarker mirroring local or systemic inflammation, especially in chronic inflammatory rheumatic diseases.

Immune-related potential biomarkers and therapeutic targets in coronary artery disease

Background

Coronary artery disease (CAD) is a complex illness with unknown pathophysiology. Peripheral biomarkers are a non-invasive method required to track the onset and progression of CAD and have unbeatable benefits in terms of early identification, prognostic assessment, and categorization of the diagnosis. This study aimed to identify and validate the diagnostic and therapeutic potential of differentially expressed immune-related genes (DE-IRGs) in CAD, which will aid in improving our knowledge on the etiology of CAD and in forming genetic predictions.

Methods

First, we searched coronary heart disease in the Gene Expression Omnibus (GEO) database and identified GSE20680 (CAD = 87, Normal = 52) as the trial set and GSE20681 (CAD = 99, Normal = 99) as the validation set. Functional enrichment analysis using protein-protein interactions (PPIs), Gene Ontology (GO), and Kyoto Encyclopedia of Genes and Genomes (KEGG) was carried out on the identified differentially expressed genes. Optimal feature genes (OFGs) were generated using the support vector machine recursive feature elimination algorithm and the least absolute shrinkage and selection operator (LASSO) algorithm. Furthermore, immune infiltration in CAD patients and healthy controls was compared using CIBERSORT, and the relationship between immune cells and OFGs was examined. In addition, we constructed potential targeted drugs for this model through the Drug-Gene Interaction database (DGIdb) database. Finally, we verify the expression of S100A8-dominated OFGs in the GSE20681 dataset to confirm the universality of our study.

Results

We identified the ten best OFGs for CAD from the DE-IRGs. Functional enrichment analysis showed that these marker genes are crucial for receptor-ligand activity, signaling receptor activator activity, and positive control of the response to stimuli from the outside world. Additionally, CIBERSORT revealed that S100A8 could be connected to alterations in the immune microenvironment in CAD patients. Furthermore, with the help of DGIdb and Cytoscape, a total of 64 medicines that target five marker genes were subsequently discovered. Finally, we verified the expression of the OFGs genes in the GSE20681 dataset between CAD patients and normal patients and found that there was also a significant difference in the expression of S100A8.

Conclusion

We created a 10-gene immune-related prognostic model for CAD and confirmed its validity. The model can identify potential biomarkers for CAD prediction and more accurately gauge the progression of the disease.

From bench to bedside: Calprotectin (S100A8/S100A9) as a biomarker in rheumatoid arthritis

S100A9/S100A8 (calprotectin), a member of the S100 protein family, has been shown to play a pivotal role in innate immunity activation. Calprotectin plays a critical role in the pathogenesis of rheumatoid arthritis (RA), as it triggers chemotaxis, phagocyte migration and modulation of neutrophils and macrophages. Higher calprotectin levels have been found in synovial fluid, plasma, and serum from RA patients. Recent studies have demonstrated better correlations between serum or plasma calprotectin and composite inflammatory disease activity indexes than c-reactive protein (CRP) or the erythrocyte sedimentation rate (ESR). Calprotectin serum levels decreased after treatment, independently of the DMARD type or strategy. Calprotectin has shown the strongest correlations with other sensitive techniques to detect inflammation, such as ultrasound. Calprotectin independently predicts radiographic progression. However, its value as a biomarker of treatment response and flare after tapering is unclear. This update reviews the current understanding of calprotectin in RA and discusses possible applications as a biomarker in clinical practice.

Neutrophil Extracellular Vesicles: A Delicate Balance between Pro-Inflammatory Responses and Anti-Inflammatory Therapies

Extracellular vesicles (EVs) are released in the extracellular environment during cell activation or apoptosis. Working as signal transducers, EVs are important mediators of intercellular communication through the convoying of proteins, nucleic acids, lipids, and metabolites. Neutrophil extracellular vesicles (nEVs) contain molecules acting as key modulators of inflammation and immune responses. Due to their potential as therapeutic tools, studies about nEVs have been increasing in recent years. However, our knowledge about nEVs is still in its infancy. In this review, we summarize the current understanding of the role of nEVs in the framework of neutrophil inflammation functions and disease development. The therapeutic potential of nEVs as clinical treatment strategies is deeply discussed. Moreover, the promising research landscape of nEVs in the near future is also examined.

A single-dose Qβ VLP vaccine against S100A9 protein reduces atherosclerosis in a preclinical model

The standard therapy for cardiovascular disease (CVD) is the administration of statins to reduce plasma cholesterol levels, but this requires lifelong treatment. We developed a CVD vaccine candidate that targets the pro-inflammatory mediator calprotectin by eliciting antibodies against the S100A9 protein. The vaccine, based on bacteriophage Qβ virus-like particles (VLPs) displaying S100A9 peptide epitopes, was formulated as a slow-release PLGA:VLP implant by hot-melt extrusion. The single-dose implant elicited S100A9-specific antibody titers comparable to a three-dose injection schedule with soluble VLPs. In an animal model of CVD (ApoE-/- mice fed on a high-fat diet), the implant reduced serum levels of calprotectin, IL-1β, IL-6 and MCP-1, resulting in less severe aortic lesions. This novel implant was therefore able to attenuate atherosclerosis over a sustained period and offers a novel and promising strategy to replace the repetitive administration of statins for the treatment of CVD.

Urate crystal deposition is associated with inflammatory markers and carotid artery pathology in patients with intercritical gout: results from the NOR-Gout study

BACKGROUND

Gout is of unknown reason associated with cardiovascular disease. Ultrasound is sensitive for detecting crystal deposition and plasma calprotectin is a sensitive inflammatory marker. This study explores the associations between crystal deposition, inflammation and carotid artery pathology.

METHOD

A cross-sectional analysis of baseline assessments from the NOR-Gout study was undertaken. Crystal deposition was assessed by ultrasound (double contour, tophi, aggregates) and dual-energy CT (DECT) and laboratory assessments included plasma calprotectin. The carotid arteries were bilaterally examined for carotid intima-media thickness (cIMT) and presence of plaques. Spearman correlations, Mann-Whitney tests and linear regression analyses were used to explore associations between crystal deposition, inflammatory markers,and carotid pathology.

RESULTS

202 patients with intercritical gout (95.5% men, mean (SD) age 56.5 (13.8) years, disease duration 7.9 (7.7) years) were included. Calprotectin was correlated with all scores of crystal deposition by ultrasound (r=0.26-0.32, p<0.001) and DECT (r=0.15, p<0.05). cIMT was correlated with sum score aggregates (r=0.18-0.22, p<0.05). Patients with large tophi had higher levels of calprotectin as well as more frequent carotid plaque (p<0.05).

CONCLUSIONS

Study findings point towards crystal deposition contributing to subclinical inflammation with subsequent vascular implications. However, future longitudinal studies are needed to confirm such causal relationships.

The Mechanism of the NLRP3 Inflammasome Activation and Pathogenic Implication in the Pathogenesis of Gout

The NACHT, LRR, and PYD-domains-containing protein 3 (NLRP3) inflammasome is an intracellular multi-protein signaling platform that is activated by cytosolic pattern-recognition receptors such as NLRs against endogenous and exogenous pathogens. Once it is activated by a variety of danger signals, recruitment and assembly of NLRP3, ASC, and pro-caspase-1 trigger the processing and release of pro-inflammatory cytokines including interleukin-1β (IL-1β) and IL-18. Multiple intracellular and extracellular structures and molecular mechanisms are involved in NLRP3 inflammasome activation. Gout is an autoinflammatory disease induced by inflammatory response through production of NLRP3 inflammasome-mediated proinflammatory cytokines such as IL-1β by deposition of monosodium urate (MSU) crystals in the articular joints and periarticular structures. NLRP3 inflammasome is considered a main therapeutic target in MSU crystal-induced inflammation in gout. Novel therapeutic strategies have been proposed to control acute flares of gouty arthritis and prophylaxis for gout flares through modulation of the NLRP3/IL-1 axis pathway. This review discusses the basic mechanism of NLRP3 inflammasome activation and the IL-1-induced inflammatory cascade and explains the NLRP3 inflammasome-induced pathogenic role in the pathogenesis of gout.

Transcriptomic Analysis of Circulating Neutrophils in Sheep with Mineral Element Imbalance

This experiment was designed to investigate the effects of mineral element imbalance on gene transcription in peripheral circulating neutrophils of sheep. Ten female sheep weighing 30 kg of similar age and physiological condition were randomly selected and injected via central venous catheterization with EDTA at a concentration of 4% (W/V) to construct a model of mineral element imbalance. As self-control, the sheep were divided into control [Con, before EDTA injection, time point 0 (T0)], EDTA [12 h after EDTA injection, time point 12 h (T12h)] and recovery [HF, 7 days after injection, time point 7 days (T7d)] groups. Whole blood was collected, and serum and neutrophils were separated for ionomic and transcriptomic analysis. The results showed that levels of P (P < 0.05), Zn (P < 0.01), K (P < 0.01) and some other elements were significantly lower in sheep in the EDTA group than in those in the control group, but levels of P (P > 0.05), Zn (P > 0.05) and K (P > 0.05) were similar in the recovery and control groups. Levels of Ca (P > 0.05) and Cu (P < 0.05) were higher after injection, and levels of Cu (P < 0.01) continued to increase during the recovery period. There were 1561 genes, including S100 family genes, significantly differentially expressed in neutrophils between the control and trial groups, and these genes were mainly enriched in the categories defense response, immune response, regulation of interleukin production and other functions. The top enriched signaling pathways were phagosome, NF-κB and Toll-like receptor. Mineral element homeostasis imbalance affected the gene transcriptome of circulating neutrophils, demonstrating the importance of carefully controlling the addition of mineral elements.

Systematic analysis of inflammation and pain pathways in a mouse model of gout

Gout is a prevalent and painful inflammatory arthritis, and its global burden continues to rise. Intense pain induced by gout attacks is a major complication of gout. However, systematic studies of gout inflammation and pain are lacking. Using a monosodium urate (MSU) crystal-induced gout model, we performed genome-wide transcriptome analysis of the inflamed ankle joint, dorsal root ganglion (DRG), and spinal cord of gouty mice. Our results revealed important transcriptional changes, including highly elevated inflammation and broad activation of immune pathways in both the joint and the nervous system, in gouty mice. Integrated analysis showed that there was a remarkable overlap between our RNAseq and human genome-wide association study (GWAS) of gout; for example, the risk gene, stanniocalcin-1 (STC1) showed significant upregulation in all three tissues. Interestingly, when compared to the transcriptomes of human osteoarthritis (OA) and rheumatoid arthritis (RA) joint tissues, we identified significant upregulation of cAMP/cyclic nucleotide-mediated signaling shared between gouty mice and human OA with high knee pain, which may provide excellent drug targets to relieve gout pain. Furthermore, we investigated the common and distinct transcriptomic features of gouty, inflammatory pain, and neuropathic pain mouse models in their DRG and spinal cord tissues. Moreover, we discovered distinct sets of genes with significant differential alternative splicing or differential transcript usage in each tissue, which were largely not detected by conventional differential gene expression analysis approaches. Based on these results, our study provided a more accurate and comprehensive depiction of transcriptomic alterations related to gout inflammation and pain.

Calprotectin: from biomarker to biological function

The incidence of inflammatory bowel diseases (IBD) emerged with Westernisation of dietary habits worldwide. Crohn's disease and ulcerative colitis are chronic debilitating conditions that afflict individuals with substantial morbidity and challenge healthcare systems across the globe. Since identification and characterisation of calprotectin (CP) in the 1980s, faecal CP emerged as significantly validated, non-invasive biomarker that allows evaluation of gut inflammation. Faecal CP discriminates between inflammatory and non-inflammatory diseases of the gut and portraits the disease course of human IBD. Recent studies revealed insights into biological functions of the CP subunits S100A8 and S100A9 during orchestration of an inflammatory response at mucosal surfaces across organ systems. In this review, we summarise longitudinal evidence for the evolution of CP from biomarker to rheostat of mucosal inflammation and suggest an algorithm for the interpretation of faecal CP in daily clinical practice. We propose that mechanistic insights into the biological function of CP in the gut and beyond may facilitate interpretation of current assays and guide patient-tailored medical therapy in IBD, a concept warranting controlled clinical trials.

Regulation of crystal induced inflammation: current understandings and clinical implications

Introduction: Accumulation of abnormal crystals in the body, derived from endogenous or exogenous materials can drive a wide spectrum of inflammatory disease states. It is well established that intra-articular deposition of monosodium urate (MSU) and calcium pyrophoshate (CPP) crystals contributes to joint destruction through pro-inflammatory processes.Areas covered: This review will focus on current understanding and recent novelty about the mechanisms and the clinical implications of the inflammation induced by MSU and CPP crystals.Expert opinion: Advances in molecular biology reveal that at the base of the inflammatory cascade, stimulated by MSU or CPP crystals, there are many complex cellular mechanisms mainly involving the NLRP3 inflammasome, the hallmark of autoinflammatory syndromes. The extensive studies carried out through in vitro and in vivo models along with a better clinical definition of the disease has led to an optimized use of existing drugs and the introduction of novel therapeutic strategies. In particular, the identification of IL-1 as the most important target in gout and pseudogout has made it possible to expand the pharmacological indications of anti-IL-1 biological drugs, opening new therapeutic perspectives for patients.

Neutrophil extracellular trap-associated molecules: a review on their immunophysiological and inflammatory roles

Neutrophil extracellular traps (NETs) are a defense mechanism against pathogens. They are composed of DNA and various proteins and have the ability to hinder microbial spreading and survival. However, NETs are not only related to infections but also participate in sterile inflammatory events. In addition to DNA, NETs contain histones, serine proteases, cytoskeletal proteins and antimicrobial peptides, all of which have immunomodulatory properties that can augment or decrease the inflammatory response. Extracellular localization of these molecules alerts the immune system of cellular damage, which is triggered by recognition of damage-associated molecular patterns (DAMPs) through specific pattern recognition receptors. However, not all of these molecules are DAMPs and may have other immunophysiological properties in the extracellular space. The release of NETs can lead to production of pro-inflammatory cytokines (due to TLR2/4/9 and inflammasome activation), the destruction of the extracellular matrix, activation of serine proteases and of matrix metallopeptidases (MMPs), modulation of cellular proliferation, induction of cellular migration and adhesion, promotion of thrombogenesis and angiogenesis and disruption of epithelial and endothelial permeability. Understanding the dynamics of NET-associated molecules, either individually or synergically, will help to unravel their role in inflammatory events and open novel perspectives for potential therapeutic targets. We here review molecules contained within NETS and their immunophysiological roles.

Impact of Exercise Intensity on Calprotectin Levels in Healthy Volunteers and Patients with Inflammatory Rheumatic Diseases

Exercise influences inflammatory response and immune system performance. The regular practice of a moderate activity positively regulates immunity and the inflammatory process, while intensive training depresses it and enhances inflammatory marker secretion. Calprotectin is involved in the inflammatory process, promoting neutrophil recruitment, cell degranulation, and inflammatory mediators. Furthermore, calprotectin has been associated with various inflammatory diseases, including inflammatory rheumatic diseases. The present review explores the effect of exercise on calprotectin levels in both healthy and inflammatory rheumatic conditions. Data show that the intensity duration and the type of exercise modulate calprotectin levels and participant inflammatory status. The exact role of calprotectin in the exercise response is yet unknown. Calprotectin could constitute an interesting biomarker for monitoring both the effect of exercise on the inflammatory process in healthy volunteers and the efficiency of exercise treatment programs in a patient with inflammatory rheumatic disease.

S100A11 (calgizzarin) is released via NETosis in rheumatoid arthritis (RA) and stimulates IL-6 and TNF secretion by neutrophils

S100A11 (calgizzarin), a member of S100 family, is associated with several autoimmune diseases, including rheumatoid arthritis (RA). Neutrophil extracellular traps (NETs) are implicated in the pathogenesis of RA and in the externalization of some S100 family members. Therefore, we aimed to determine the association between S100A11 and NETs in RA. For this purpose, the levels of S100A11 and NETosis markers were detected in the RA synovial fluid by immunoassays. The expression of S100A11 by neutrophils in the RA synovial tissue was assessed. Neutrophils isolated from peripheral blood were exposed to S100A11 or stimulated to release NETs. The levels of NETosis- and inflammation-associated proteins were analysed by immunoassays. NETs were visualized by immunofluorescence. We showed that S100A11 was expressed by the neutrophils in the RA synovial tissue. Moreover, S100A11 in the RA synovial fluid correlated with several NETosis markers. In vitro, S100A11 was abundantly released by neutrophils undergoing NETosis compared to untreated cells (p < 0.001). Extracellular S100A11 increased the secretion of IL-6 (p < 0.05) and TNF (p < 0.05) by neutrophils but did not induce NETosis. This study demonstrates, for the first time, that the release of S100A11 is dependent on NETosis and that extracellular S100A11 augments the inflammatory response by inducing pro-inflammatory cytokines in neutrophils.

Roles of Interactions Between Toll-Like Receptors and Their Endogenous Ligands in the Pathogenesis of Systemic Juvenile Idiopathic Arthritis and Adult-Onset Still's Disease

Systemic juvenile idiopathic arthritis (JIA) and adult-onset Still’s disease (AOSD) are systemic inflammatory disorders that manifest as high-spiking fever, joint pain, evanescent skin rash, and organomegaly. Their pathogenesis is unclear, but inflammation is triggered by activation of the innate immune system with aberrant production of proinflammatory cytokines. Along with extrinsic factors, intrinsic pathways can trigger an unexpected immune response. Damage-associated molecular patterns (DAMPs) induce the activation of innate immune cells, leading to sterile inflammation in systemic JIA and AOSD. These endogenous proteins interact with Toll-like receptors (TLRs), which are pattern recognition receptors, and mediate immune signaling following stimulation by pathogen-associated molecular patterns and DAMPs. Several DAMPs, such as S100 proteins, play a role in the development or severity of systemic JIA and AOSD, in which their interactions with TLRs are altered. Also, the expression levels of genes encoding DAMPs contribute to the susceptibility to systemic JIA and AOSD. Herein, we review reports that TLR and DAMP signaling initiates and/or maintains the inflammatory response in systemic JIA and AOSD, and their correlations with the clinical characteristics of those diseases. In addition, we assess their utility as biomarkers or therapeutics for systemic JIA and AOSD.

S100A9 plays a pivotal role in a mouse model of herpetic neuralgia via TLR4/TNF pathway

Herpetic neuralgia is a painful condition following herpes zoster disease, which results from Varicella-zoster virus reactivation in the dorsal or trigeminal sensory ganglia. Nevertheless, the pathophysiological mechanisms involved in herpetic neuralgia are not well understood. Recently, we identified, that neuroimmune-glia interactions in the sensory ganglion is a critical mechanism for the development of herpetic neuralgia. Here, we investigate the contribution of S100A9, a well-known pro-inflammatory molecule produced by myeloid cells, for the development of herpetic neuralgia using a murine model of HSV-1 infection. We found that cutaneous HSV-1 infection results in an increase of S100A9 expression in the Dorsal Root Ganglia (DRGs). Infiltrating neutrophils into the DRGs were the main source of S100A9 post HSV-1 infection. Functionally, genetic or pharmacological inhibition of S100A9 impairs the development of HSV-1 infection-induced mechanical pain hypersensitivity. Finally, we found that the pronociceptive role of S100A9 in herpetic neuralgia depends on the TLR4/TNF pathway. These results unraveled previously unknown mechanisms involved in the pathophysiology of herpetic neuralgia and indicate that S100A9 might be an important target for novel therapies aiming acute herpetic neuralgia.

Autoinflammatory Mechanisms in Crystal-Induced Arthritis

Crystal-induced arthritides have been classified as “type-1 autoinflammatory diseases” for their main features which resemble those of the monogenic autoinflammatory syndromes. They are in fact characterized by spontaneous onset, recurrence of the episodes, self-limitation and resolution, inflammasome activation with huge production of IL-1β and a prevalent involvement of the innate immune system. The term “auto” refers also to the induction of IL-1β gene expression, processing and secretion by IL-1β itself. The concept of autoinflammation in crystal-induced arthritis has been finally reinforced by the efficacy of IL-1 blockade in treating acute and chronic state of this disease. The aim of this article is to review the autoinflammatory mechanisms in crystal-induced arthritis, considering both clinical and molecular aspects.

Monosodium urate crystal interleukin-1β release is dependent on Toll-like receptor 4 and transient receptor potential V1 activation

OBJECTIVE

The present study aimed to elucidate the mechanisms involved in MSU-induced IL-1β release in a rodent animal model of acute gout arthritis.

METHODS

Painful (mechanical and thermal hypersensitivity, ongoing pain and arthritis score) and inflammatory (oedema, plasma extravasation, cell infiltration and IL-1β release) parameters were assessed several hours after intra-articular injection of MSU (100 µg/articulation) in wild-type or knockout mice for Toll-like receptor 4 (TLR4), inducible nitric oxide synthase (iNOS), transient receptor potential (TRP) V1 and the IL-1 receptor (IL-1R). Also, wild-type animals were treated with clodronate, lipopolysaccharide from Rhodobacter sphaeroides (LPS-RS) (TLR4 antagonist), spleen tyrosine kinase (SYK) inhibitor (iSYK), aminoguanidine (AMG, an iNOS inhibitor) or SB366791 (TRPV1 antagonist). Nitrite/nitrate and IL-1β levels were measured on the synovial fluid of wild-type mice, 2 h after intra-articular MSU injections, or medium from macrophages stimulated for MSU (1000 μg) for 2 h.

RESULTS

Intra-articular MSU injection caused robust nociception and severe inflammation from 2 up to 6 h after injection, which were prevented by the pre-treatment with clodronate, LPS-RS, iSYK, AMG and SB366791, or the genetic ablation of TLR4, iNOS, TRPV1 or IL-1R. MSU also increased nitrite/nitrate and IL-1β levels in the synovial fluid, which was prevented by clodronate, LPS-RS, iSYK and AMG, but not by SB366791. Similarly, MSU-stimulated peritoneal macrophages released nitric oxide, which was prevented by LPS-RS, iSYK and AMG, but not by SB366791, and released IL-1β, which was prevented by LPS-RS, iSYK, AMG and SB366791.

CONCLUSION

Our data indicate that MSU may activate TLR4, SYK, iNOS and TRPV1 to induce the release of IL-1β by macrophages, triggering nociception and inflammation during acute gout attack.

S100 family proteins in inflammation and beyond

The S100 family proteins possess a variety of intracellular and extracellular functions. They interact with multiple receptors and signal transducers to regulate pathways that govern inflammation, cell differentiation, proliferation, energy metabolism, apoptosis, calcium homeostasis, cell cytoskeleton and microbial resistance. S100 proteins are also emerging as novel diagnostic markers for identifying and monitoring various diseases. Strategies aimed at targeting S100-mediated signaling pathways hold a great potential in developing novel therapeutics for multiple diseases. In this chapter, we aim to summarize the current knowledge about the role of S100 family proteins in health and disease with a major focus on their role in inflammatory conditions.

miRNAs Regulate Cytokine Secretion Induced by Phosphorylated S100A8/A9 in Neutrophils

The release of cytokines by neutrophils constitutes an essential process in the development of inflammation by recruiting and activating additional cells. Neutrophils are also able to secrete a complex of S100A8 and S100A9 proteins (S100A8/A9), which can amplify the general inflammatory state of the host and is involved in the pathogenesis of several chronic inflammatory diseases, such as rheumatoid arthritis (RA). S100A8/A9 have received renewed attention due to their susceptibility to several function-altering post-translational modifications. In that context, it has been recently demonstrated that only the phosphorylated form of S100A8/A9 (S100A8/A9-P) is able to induce the secretion of several cytokines in neutrophils. Here, we investigate the mechanism by which this post-translational modification of S100A8/A9 can regulate the extracellular activity of the protein complex and its impact on the inflammatory functions of neutrophils. We found that S100A8/A9-P are present in large amounts in the synovial fluids from RA patients, highlighting the importance of this form of S100A8/A9 complex in the inflammation process. Using miRNA-sequencing on S100A8/A9-P-stimulated differentiated HL-60 cells, we identified a dysregulation of miR-146a-5p and miR-155-5p expression through TRL4 signaling pathways. Our data reveal that overexpression of these miRNAs in neutrophil-like cells reduces S100A8/A9-P-mediated secretion of pro-inflammatory cytokines.

Recombinant human proteoglycan-4 reduces phagocytosis of urate crystals and downstream nuclear factor kappa B and inflammasome activation and production of cytokines and chemokines in human and murine macrophages

Background

Gout is an inflammatory arthritis caused by monosodium urate monohydrate (MSU) crystals’ joint deposition. MSU phagocytosis by resident macrophages is a key step in gout pathogenesis. MSU phagocytosis triggers nuclear factor kappa B (NFκB) activation and production of cytokines and chemokines. Proteoglycan-4 (PRG4) is a glycoprotein produced by synovial fibroblasts and exerts an anti-inflammatory effect in the joint mediated by its interaction with cell surface receptor CD44. PRG4 also binds and antagonizes TLR2 and TLR4. The objective of this study is to evaluate the efficacy of recombinant human PRG4 (rhPRG4) in suppressing MSU-induced inflammation and mechanical allodynia in vitro and in vivo.

Methods

THP-1 macrophages were incubated with MSU crystals ± rhPRG4 or bovine submaxillary mucin (BSM), and crystal phagocytosis, cytokines and chemokines expression and production were determined. NFκB p65 subunit nuclear translocation, NLRP3 induction, caspase-1 activation and conversion of proIL-1β to mature IL-1β were studied. MSU phagocytosis by Prg4^+/+ and Prg4^−/− peritoneal macrophages was determined in the absence or presence of rhPRG4, BSM, anti-CD44, anti-TLR2, anti-TLR4 and isotype control antibodies. Rhodamine-labeled rhPRG4 was incubated with murine macrophages and receptor colocalization studies were performed. Lewis rats underwent intra-articular injection of MSU crystals followed by intra-articular treatment with PBS or rhPRG4. Weight bearing and SF myeloperoxidase activities were determined.

Results

rhPRG4 reduced MSU crystal phagocytosis at 4 h (p < 0.01) and IL-1β, TNF-α, IL-8 and MCP-1 expression and production at 6 h (p < 0.05). BSM did not alter MSU phagocytosis or IL-1β production in human and murine macrophages. rhPRG4 treatment reduced NFκB nuclear translocation, NLRP3 expression, caspase-1 activation and generation of mature IL-1β (p < 0.05). MSU-stimulated IL-1β production was higher in Prg4^−/− macrophages compared to Prg4^+/+ macrophages (p < 0.001). rhPRG4, anti-CD44, anti-TLR2 and anti-TLR4 antibody treatments reduced MSU phagocytosis and IL-1β production in murine macrophages (p < 0.05). rhPRG4 preferentially colocalized with CD44 on Prg4^−/− peritoneal macrophages compared to TLR2 or TLR4 (p < 0.01). rhPRG4 normalized weight bearing and reduced SF myeloperoxidase activity compared to PBS in vivo.

Conclusion

rhPRG4 inhibits MSU crystal phagocytosis and exhibits an anti-inflammatory and anti-nociceptive activity in vitro and in vivo. rhPRG4’s anti-inflammatory mechanism may be due to targeting CD44 on macrophages.

S100A8/A9 in Inflammation

S100A8 and S100A9 (also known as MRP8 and MRP14, respectively) are Ca²⁺ binding proteins belonging to the S100 family. They often exist in the form of heterodimer, while homodimer exists very little because of the stability. S100A8/A9 is constitutively expressed in neutrophils and monocytes as a Ca²⁺ sensor, participating in cytoskeleton rearrangement and arachidonic acid metabolism. During inflammation, S100A8/A9 is released actively and exerts a critical role in modulating the inflammatory response by stimulating leukocyte recruitment and inducing cytokine secretion. S100A8/A9 serves as a candidate biomarker for diagnosis and follow-up as well as a predictive indicator of therapeutic responses to inflammation-associated diseases. As blockade of S100A8/A9 activity using small-molecule inhibitors or antibodies improves pathological conditions in murine models, the heterodimer has potential as a therapeutic target. In this review, we provide a comprehensive and detailed overview of the distribution and biological functions of S100A8/A9 and highlight its application as a diagnostic and therapeutic target in inflammation-associated diseases.

Serum levels of IL-17 are elevated in patients with acute gouty arthritis

Acute gouty arthritis (AGA) is one of the most common forms of auto-inflammatory arthritis. IL-17 is a key proinflammatory cytokine which has been implicated in several autoimmune diseases. However, to date little is known about the role of IL-17 in AGA. In the present study, we show that serum IL-17 levels are significantly elevated in AGA patients early in the onset of symptoms of gout, and decrease gradually as symptoms diminish. Correlation analysis indicated that IL-17 expression is not only positively correlated with disease activity, but is also correlated with serum levels of IL-1β which plays a critical role in the differentiation of IL-17^- γδT cells into IL-17⁺γδT cells. Flow cytometry analysis indicated that γδ T cells are a major source of IL-17 production during the early onset of AGA. We therefore identify IL-17 as a potential novel biomarker for AGA and suggest that targeting the γδ T cell/IL-17 immune axis is a potential strategy for treatment of acute flares of AGA.

Secretion of the Phosphorylated Form of S100A9 from Neutrophils Is Essential for the Proinflammatory Functions of Extracellular S100A8/A9

S100A8 and S100A9 are members of the S100 family of cytoplasmic EF-hand Ca²⁺-binding proteins and are abundantly expressed in the cytosol of neutrophils. In addition to their intracellular roles, S100A8/A9 can be secreted in the extracellular environment and are considered as alarmins able to amplify the inflammatory response. The intracellular activity of S100A8/A9 was shown to be regulated by S100A9 phosphorylation, but the importance of this phosphorylation on the extracellular activity of S100A8/A9 has not yet been extensively studied. Our work focuses on the impact of the phosphorylation state of secreted S100A9 on the proinflammatory function of neutrophils. In a first step, we characterized the secretion of S100A8/A9 in different stimulatory conditions and investigated the phosphorylation state of secreted S100A9. Our results on neutrophil-like differentiated HL-60 (dHL-60) cells and purified human neutrophils showed a time-dependent secretion of S100A8/A9 when induced by phorbol 12-myristoyl 13-acetate and this secreted S100A9 was found in a phosphorylated form. Second, we evaluated the impact of this phosphorylation on proinflammatory cytokine expression and secretion in dHL-60 cells. Time course experiments with purified unphosphorylated or phosphorylated S100A8/A9 were performed and the expression and secretion levels of interleukin (IL)-1α, IL-1β, IL-6, tumor necrosis factor alpha, CCL2, CCL3, CCL4, and CXCL8 were measured by real-time PCR and cytometry bead array, respectively. Our results demonstrate that only the phosphorylated form of the complex induces proinflammatory cytokine expression and secretion. For the first time, we provide evidence that S100A8/PhosphoS100A9 is inducing cytokine secretion through toll-like receptor 4 signaling.

Monosodium urate crystals induced ICAM-1 expression and cell-cell adhesion in renal mesangial cells: Implications for the pathogenesis of gouty nephropathy

BACKGROUND

Renal disease is prevalent in gouty patients and monosodium urate (MSU) crystal deposition in the kidney can be detected in some gouty nephropathy patients. MSU crystals can induce inflammatory events, we investigated the MSU-induced expression of intercellular adhesion molecule (ICAM)-1 on human renal mesangial cells (HRMCs) and the involved signal transduction mechanisms.

METHODS

The HRMCs cell line was purchased from ScienCell Research Laboratories. MSU crystals were made by dissolving uric acid in sodium hydroxide (NaOH) solution. The involvement of MAPKs, apoptosis-associated speck-like protein containing a CARD domain (ASC), and Toll-like receptor (TLR) was investigated using pharmacological inhibitors, transfection with short hairpin RNA (shRNA), or monoclonal antibodies. Protein expression was evaluated by Western blotting. The functional activity of ICAM-1 was evaluated with cell-cell adhesion assay and immunofluorescence analysis.

RESULTS

MSU stimulation increased expression of ICAM-1 and adhesion between HRMCs and human monocytic THP-1 cells. The interaction between HRMCs and THP-1 was suppressed by ICAM-1 neutralizing antibodies. MSU stimulation induced activation of mitogen-activated protein kinases, including c-Jun N-terminal kinase (JNK), p38, and extracellular signal-regulated kinase (ERK), but only p38 was responsible for MSU-induced expression of ICAM-1 and cell-cell adhesion. ASC also play a role in MSU-induced effects. Pretreatment with monoclonal antibodies against toll-like receptor (TLR)2 or TLR4 reduced MSU-induced ICAM-1 expression, cell-cell adhesion, p38 phosphorylation but the reduction of ASC activation is insignificant.

CONCLUSION

The MSU induced ICAM-1 expression on HRMCs and cell-cell adhesion involved TLR2/4-p38-ICAM1 pathway and TLR2/4 independent ASC-p38-ICAM1 axis. These findings might partly explain the mechanisms underlying gouty nephropathy.

β-Hydroxybutyrate Deactivates Neutrophil NLRP3 Inflammasome to Relieve Gout Flares

Aging and lipotoxicity are two major risk factors for gout that are linked by the activation of the NLRP3 inflammasome. Neutrophil-mediated production of interleukin-1β (IL-1β) drives gouty flares that cause joint destruction, intense pain, and fever. However, metabolites that impact neutrophil inflammasome remain unknown. Here, we identified that ketogenic diet (KD) increases β-hydroxybutyrate (BHB) and alleviates urate crystal-induced gout without impairing immune defense against bacterial infection. BHB inhibited NLRP3 inflammasome in S100A9 fibril-primed and urate crystal-activated macrophages, which serve to recruit inflammatory neutrophils in joints. Consistent with reduced gouty flares in rats fed a ketogenic diet, BHB blocked IL-1β in neutrophils in a NLRP3-dependent manner in mice and humans irrespective of age. Mechanistically, BHB inhibited the NLRP3 inflammasome in neutrophils by reducing priming and assembly steps. Collectively, our studies show that BHB, a known alternate metabolic fuel, is also an anti-inflammatory molecule that may serve as a treatment for gout.

Inflammation in gout: mechanisms and therapeutic targets

The acute symptoms of gout are triggered by the inflammatory response to monosodium urate crystals, mediated principally by macrophages and neutrophils. Innate immune pathways are of key importance in the pathogenesis of gout, in particular the activation of the NLRP3 inflammasome, which leads to the release of IL-1β and other pro-inflammatory cytokines. The orchestration of this pro-inflammatory cascade involves multiple intracellular and extracellular receptors and enzymes interacting with environmental influences that modulate the inflammatory state. Furthermore, the resolution of inflammation in gout is becoming better understood. This Review highlights recent advances in our understanding of both positive and negative regulatory pathways, as well as the genetic and environmental factors that modulate the inflammatory response. Some of these pathways can be manipulated and present novel therapeutic opportunities for the treatment of acute gout attacks.

S100A9 potentiates the activation of neutrophils by the etiological agent of gout, monosodium urate crystals

Gout is one of the most painful types of arthritis that arises when the body mounts an acute inflammatory reaction against a crystallized form of uric acid known as monosodium urate crystals (MSUs). Although MSUs are known to activate neutrophils, the most abundant leukocyte in the synovial fluid of patients with gout, few studies have investigated the effect on neutrophils of the simultaneous stimulation with MSU and proinflammatory mediators in the inflamed joint. Herein, we focused on a protein that is highly expressed in the synovium in gout, S100A9. The predominant expression of S100A9 in and around blood vessels suggests it may prime neutrophils during their migration toward the inflamed joint. Using a combination of functional and signaling assays, we found that S100A9 enhances the production of radical oxygen species as well as IL-1 and IL-8 release by human neutrophils activated with MSU. Moreover, upstream and downstream signaling events activated by MSUs in human neutrophils were also potentiated by S100A9, including the mobilization of intracellular calcium stores, tyrosine phosphorylation, the serine phosphorylation of PKC substrates, Akt, and p38. We also show that S100A9 alone increases glycolysis in human neutrophils, which is suggestive of an additional mechanism through which neutrophils can be primed. Together, our observations indicate a novel way in which S100A9 may contribute to the pathogenesis of gout, by priming neutrophils to respond to MSUs.

Regulation of Nlrp3 inflammasome by dietary metabolites

The bidirectional communication between innate immune cells and energy metabolism is now widely appreciated to regulate homeostasis as well as chronic diseases that emerge from dysregulated inflammation. Macronutrients-derived from diet or endogenous pathways that generate and divert metabolites into energetic or biosynthetic pathways – regulate the initiation, duration and cessation of the inflammatory response. The NLRP3 inflammasome is an important innate sensor of structurally diverse metabolic damage-associated molecular patterns (DAMPs) that has been implicated in a wide range of inflammatory disorders associated with caloric excess, adiposity and aging. Understanding the regulators of immune-metabolic interactions and their contribution towards chronic disease mechanisms, therefore, has the potential to reduce disease pathology, improve quality of life in elderly and promote the extension of healthspan. Just as specialized subsets of immune cells dampen inflammation through the production of negative regulatory cytokines; specific immunoregulatory metabolites can deactivate inflammasome-mediated immune activation. Here, we highlight the role of energy substrates, alternative fuels and metabolic DAMPs in the regulation of the NLRP3 inflammasome and discuss potential dietary interventions that may impact sterile inflammatory disease.

Alarmins firing arthritis: Helpful diagnostic tools and promising therapeutic targets

Alarmins are endogenous molecules with homeostatic roles that have reached the focus of research in inflammatory arthritis in the last two decades, mostly due to their ability to indicate tissue related damage after active or passive release from injured cells. From HMGB1, S100A8/A9 and S100A12 proteins, over heat-shock proteins (HSPs) and purine metabolites (e.g. uric acid, ATP) to altered matrix proteins and interleukin-33 (IL-33), a number of alarmins have been determined until now as having a role in rheumatoid arthritis, psoriatic and juvenile idiopathic arthritis, as well as spondyloarthritis and gout. Although formerly being linked to initiation and chronification of inflammatory arthritis, driving auto- and paracrine inflammatory loops, more recent research has also unraveled the alarmins' role in the crosstalk between innate and adaptive immunity and in resolution of inflammation. Providing a state-of-the-art overview of known alarmins, this review lists the known modes of action and pathologic contribution of alarmins to inflammatory arthritis, as well as biomarker potential of alarmins in the clinical setting for tracking disease severity. Based upon research on animal experimental models (CIA, AIA) and clinical trials, a look is made into potentially viable strategies for modifying alarmin secretion and their target receptor (e.g. TLR, RAGE) interaction with the purpose of attenuating arthritic disease.

Innate immune memory: Implications for host responses to damage-associated molecular patterns

Cells of the innate immune system build immunological memory via epigenetic reprogramming after stimulations with microbial ligands. This functional readjustment allows for enhanced nonspecific inflammatory responses upon secondary challenges, a process termed "trained immunity." The epigenomic blueprint of trained monocytes has been recently reported, which revealed several important immunologic and metabolic mechanisms that underlie these changes. Interestingly, similar long-term reprogramming of cytokine production has also been described to be induced by endogenous damage-associated molecular patterns (DAMPs). Here, we present an overview of the novel data showing that endogenous alarm signals associated with tissue damage and sterile inflammation can induce trained immunity through epigenetic regulation of transcriptional programs. We describe new and old evidence of persistent effects of DAMPs in driving inflammation and enforce the concept that the influence of tissue-derived signals is critical in adjusting the magnitude and type of immune response built by the host. The better characterization of trained immunity for the persistence of inflammation induced by DAMPs would provide new possibilities for intervention in aging and autoinflammatory disorders.

TLR4 Endogenous Ligand S100A8/A9 Levels in Adult-Onset Still's Disease and Their Association with Disease Activity and Clinical Manifestations

S100A8/A9 has been suggested as a marker of disease activity in patients with adult-onset Still’s disease (AOSD). We evaluated the clinical significance of S100A8/A9 as a biomarker and its pathogenic role in AOSD. Blood samples were collected prospectively from 20 AOSD patients and 20 healthy controls (HCs). Furthermore, skin and lymph node biopsy specimens of AOSD patients were investigated for S100A8/A9 expression levels via immunohistochemistry. Peripheral blood mononuclear cells (PBMCs) of active AOSD patients and HCs were investigated for S100A8/A9 cell signals. S100A8/A9, interleukin-1β (IL-1β), and tumor necrosis factor-α (TNF-α) levels in active AOSD patients were higher than those of HCs. S100A8/A9 levels correlated positively with IL-1β, TNF-α and C-reactive protein. The inflammatory cells expressing S100A8/A9 were graded from one to three in skin and lymph node biopsies of AOSD patients. The grading for S100A8/A9 was more intense in the skin lesions with karyorrhexis, mucin deposition, and neutrophil infiltration. Like lipopolysaccharide (LPS), S100A8/A9 induced phosphorylation of p38 and c-Jun amino-terminal kinase (JNK) in PBMCs, suggesting that S100A8/A9 activates Toll-like receptor 4 signaling pathways. These findings suggest that S100A8/A9 may be involved in the inflammatory response with induction of proinflammatory cytokines and may serve as a clinicopathological marker for disease activity in AOSD.

Alarmin S100A9 Induces Proinflammatory and Catabolic Effects Predominantly in the M1 Macrophages of Human Osteoarthritic Synovium

OBJECTIVE

The alarmins S100A8 and S100A9 have been shown to regulate synovial activation, cartilage damage, and osteophyte formation in osteoarthritis (OA). Here we investigated the effect of S100A9 on the production of proinflammatory cytokines and matrix metalloprotease (MMP) in OA synovium, granulocyte macrophage colony-stimulating factor (GM-CSF)-differentiated/macrophage colony-stimulating factor (M-CSF)-differentiated macrophages, and OA fibroblasts.

METHODS

We determined which cell types in the synovium produced S100A8 and S100A9. Further, the production of proinflammatory cytokines and MMP, and the activation of canonical Wnt signaling, was determined in human OA synovium, OA fibroblasts, and monocyte-derived macrophages following stimulation with S100A9.

RESULTS

We observed that S100A8 and S100A9 were mainly produced by GM-CSF-differentiated macrophages present in the synovium, and to a lesser extent by M-CSF-differentiated macrophages, but not by fibroblasts. S100A9 stimulation of OA synovial tissue increased the production of the proinflammatory cytokines interleukin (IL) 1β, IL-6, IL-8, and tumor necrosis factor-α. Additionally, various MMP were upregulated after S100A9 stimulation. Experiments to determine which cell type was responsible for these effects revealed that mainly stimulation of GM-CSF-differentiated macrophages and to a lesser extent M-CSF-differentiated macrophages with S100A9 increased the expression of these proinflammatory cytokines and MMP. In contrast, stimulation of fibroblasts with S100A9 did not affect their expression. Finally, stimulation of GM-CSF-differentiated, but not M-CSF-differentiated macrophages with S100A9 activated canonical Wnt signaling, whereas incubation of OA synovium with the S100A9 inhibitor paquinimod reduced the activation of canonical Wnt signaling.

CONCLUSION

Predominantly mediated by M1-like macrophages, the alarmin S100A9 stimulates the production of proinflammatory and catabolic mediators and activates canonical Wnt signaling in OA synovium.

Toll-like receptors and chronic inflammation in rheumatic diseases: new developments

In the past few years, new developments have been reported on the role of Toll-like receptors (TLRs) in chronic inflammation in rheumatic diseases. The inhibitory function of TLR10 has been demonstrated. Receptors that enhance the function of TLRs, and several TLR inhibitors, have been identified. In addition, the role of the microbiome and TLRs in the onset of rheumatic diseases has been reported. We review novel insights on the role of TLRs in several inflammatory joint diseases, including rheumatoid arthritis, systemic lupus erythematosus, gout and Lyme arthritis, with a focus on the signalling mechanisms mediated by the Toll-IL-1 receptor (TIR) domain, the exogenous and endogenous ligands of TLRs, and the current and future therapeutic strategies to target TLR signalling in rheumatic diseases.

The gouty tophus: a review

The tophus is the cardinal feature of advanced gout. This review summarises recent research into the biology, impact and treatment of tophaceous gout. Microscopically, tophi are chronic foreign body granuloma-like structures containing collections of monosodium urate (MSU) crystals surrounded by inflammatory cells and connective tissue. Extracellular trap formation mediated by neutrophil interactions with MSU crystals may be a central checkpoint in tophus formation. Gouty tophi impact on many aspects of health-related quality of life. Tophi are also implicated in the development of structural joint damage and increased mortality risk in people with gout. Effective treatment of tophaceous gout requires long-term urate-lowering therapy, ideally to achieve a serum urate concentration of <5 mg/dL (300 μmol/L). Recent advances in gout therapeutics have expanded urate-lowering therapy options for patients with severe tophaceous disease to allow faster regression of tophi, improved health-related quality of life and, potentially, improved structural outcomes.

Prophylactic treatment with S100A9 inhibitor paquinimod reduces pathology in experimental collagenase-induced osteoarthritis

OBJECTIVES

Alarmins S100A8/A9 regulate pathology in experimental osteoarthritis (OA). Paquinimod is an immunomodulatory compound preventing S100A9 binding to TLR-4. We investigated the effect of paquinimod on experimental OA and human OA synovium.

MATERIALS AND METHODS

Two OA mouse models differing in level of synovial activation were treated prophylactic with paquinimod. Synovial thickening, osteophyte size and cartilage damage were measured histologically, using an arbitrary score, adapted Pritzker OARSI score or imaging software, respectively. Human OA synovia were stimulated with S100A9, with or without paquinimod.

RESULTS

Paquinimod treatment of collagenase-induced OA (CIOA) resulted in significantly reduced synovial thickening (57%), osteophyte size at the medial femur (66%) and cruciate ligaments (67%) and cartilage damage at the medial tibia (47%) and femur (75%; n=7, untreated n=6). In contrast, paquinimod did not reduce osteophyte size and reduced cartilage damage at one location only in destabilised medial meniscus, an OA model with considerably lower synovial activation compared with CIOA. In human OA synovium, paquinimod blocked proinflammatory (interleukin (IL)-6, IL-8, tumour necrosis factor-α) and catabolic (matrix metalloproteinases 1 and 3) factors induced by S100A9 (n=5).

CONCLUSIONS

Prophylactic treatment of paquinimod reduces synovial activation, osteophyte formation and cartilage damage in experimental OA with high synovial activation (CIOA) and ameliorates pathological effects of S100A9 in OA synovium ex vivo.

Soluble monosodium urate, but not its crystal, induces toll like receptor 4-dependent immune activation in renal mesangial cells

BACKGROUND

Uric acid has emerged as a novel and potential modifiable risk factor for the incidence and progression of kidney diseases, however, the deteriorate effect of uric acid on renal mesangial cells remains unclear. The present study is to examine the immune activation of soluble and crystal forms of uric acid in human mesangial cells.

METHODS

We stimulated primary human mesangial cells (HMCs) with increasing concentrations (from 50 to 200 μg/ml) of soluble monosodium urate (MSU) or MSU crystals. We examined interleukin (IL)-1β protein expression levels in cell culture by ELISA. The stimulated HMCs were further stimulated with soluble MSU or MSU crystals at 200 μg/ml with or without the pre-incubation of toll like receptor (TLR) 4 inhibitor TAK242 (1μM). TLR4, nod-like receptor protein (NLRP3, also known as NALP3), IL-1β, human leukocyte antigen (HLA)-DR and CD40 were examined by Realtime-PCR, Western blot and ELISA, respectively.

RESULTS

We found that both soluble MSU and MSU crystals increased IL-1β protein expression levels in dose-dependent fashion. Soluble MSU significantly enhanced the expression of TLR4, NLRP3, IL-1β, HLA-DR and CD40 while MSU crystals only upregulated the expression of TLR4 and IL-1β. TLR4 inhibitor TAK242 significantly blocked the up-regulation of NLRP3, IL-1β, HLA-DR and CD40 induced by soluble MSU while no TAK242 suppression effect on MSU crystals induced IL-1β up-regulation was found.

CONCLUSIONS

Our results suggested that soluble MSU, but not MSU crystals, induce NLRP3, IL-1β, HLA-DR and CD40 upregulation in a TLR4-dependent manner. These findings indicate that soluble MSU may play a pathological role in hyperuricemia induced renal mesangial injury.

Clinicopathologic characterization of visceral gout of various internal organs--a study of 2 cases from a venom and toxin research center

BACKGROUND

Gout is a metabolic disorder that results in hyperuricemia and the deposition of positively birefringent monosodium urate crystals in various parts of the body. The purpose of this study was to characterize the incidence and diagnostic features of visceral gout found at necropsy in two patients.

CASE PRESENTATION

The authors present an unusual report of untreated gout leading to major structure destructions in visceral organs. Gross post-mortem examination revealed a white powdery substance and display needle-like crystalline symmetry under the macroscopic on the visceral surfaces. Microscopically, the presence of crystalline deposits (urate tophi) were detected in visceral organs, such as; kidney, liver, lung and mesentery. Irrespective of its location, gout was observed, by H&E, as intracellular and extracellular eosinophilic deposits that compressed surrounding tissues. Moreover, numerous necrotizing granulomas of multifarious sizes were observed that were compounded by large aggregations of eosinophilic material (gout), surrounded by epithelioid macrophages, lymphoplasmacytic cells, foreign body multinucleated giant cells, fibrosis, fibroplasia and few edema. On the other hand, our results revealed that granulomatous nodules in the mesentery and kidney contained large numbers of gout foci compared with lung and liver. Furthermore, the immediate cause of death in these cases were not identified, but appeared to result from multiple factors, including the visceral gout due to unsuitable environmental conditions.

CONCLUSION

In summary, we have identified a valid histopathologic damage index for use in laboratory studies of visceral gout. This system provides a feasible method of representing visceral damage in gout, and may allow for better understanding of the natural history, pathophysiology and the management of acute attacks of gouty visceral in this disease. Finally, to the best of our knowledge, understanding of the distribution of monosodium urate crystals within the body can aid clinical diagnosis and further understanding of the resulting pathology.

VIRTUAL SLIDES

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1293547351151638 .

Proteomic analysis of plasma identifies the Toll-like receptor agonists S100A8/A9 as a novel possible marker for systemic sclerosis phenotype

BACKGROUND

Systemic sclerosis (SSc) is an autoimmune disease characterised by fibrosis of the skin and the internal organs. Except for anticentromere, antitopoisomerase I and antipolymerase III antibodies, there are no reliable circulating markers predicting susceptibility and internal organ complications. This study has exploited a proteome-wide profiling method with the aim to identify new markers to identify SSc phenotype.

METHOD

40 SSc patients were included for proteomic identification. Patients were stratified as having diffuse cutaneous SSc (dcSSc) (n=19) or limited cutaneous SSc (lcSSc) (n=21) according to the extent of skin involvement. As controls 19 healthy donors were included. Blood was drawn and plasma was stored before analysing with the SELDI-TOF-MS. For replication in serum, the cohort was extended with 60 SSc patients.

RESULTS

Proteomic analysis revealed a list of 25 masspeaks that were differentially expressed between SSc patients and healthy controls. One of the peaks was suggestive for S100A8, a masspeak we previously found in supernatant of plasmacytoid dendritic cells from SSc patients. Increased expression of S100A8/A9 in SSc patients was confirmed in replication cohort compared with controls. Intriguingly, S100A8/A9 was highest in patients with limited cutaneous SSc having lung fibrosis.

CONCLUSIONS

S100A8/A9 was robustly found to be elevated in the circulation of SSc patients, suggesting its use as a biomarker for SSc lung disease and the need to further explore the role of TLR in SSc.