Search Results (61)

Gout is the most common form of inflammatory arthritis in men, driven by hyperuricemia and the deposition of monosodium urate (MSU) crystals. The innate immune response to these crystals leads to acute inflammatory episodes, called flares, characterized by intense joint pain, swelling, and temporary disability. Although gout flares are self-limiting, they impose a considerable burden on patients’ quality of life and contribute to increased healthcare utilization. A detailed understanding of the inflammatory processes triggered by MSU crystals is critical for developing targeted therapies to prevent and manage flares effectively. This review provides an overview of experimental models used to study the inflammatory phase of gout, with a focus on both in vivo and in vitro models of MSU crystal-induced inflammation. We concentrate on models that reproduce the acute inflammatory response following MSU crystal deposition, including the air pouch, intraarticular injection, and peritonitis rodent models, alongside the larval zebrafish model. In addition, we discuss in vitro approaches using primary immune cells and cell lines. We discuss the strengths, limitations, and translational relevance of these models and highlight some examples of how they have contributed to our understanding of the etiology of gout. Of note, models of hyperuricemia are not included here as these have been extensively reviewed elsewhere. Full article

Gouty arthritis (GA) is a debilitating autoinflammatory disorder precipitated by the deposition of monosodium urate (MSU) crystals, leading to intense, recurrent joint inflammation and systemic metabolic dysregulation. While hyperuricemia is a prerequisite, the transition to clinical gout involves complex intercellular signaling cascades that are not fully understood. Emerging evidence has identified exosomes,— nanoscale extracellular vesicles, —as critical mediators in this pathological process. Exosomes function as intercellular carriers, transporting a diverse cargo of bioactive molecules, including proteins, lipids, and nucleic acids (e.g., microRNAs), which profoundly influence immune cell activation, inflammasome regulation, and metabolic pathways. This review provides a critical analysis of the dual role of exosomes in both propagating and potentially resolving inflammation in GA. We delve into the intricate mechanisms of exosome-mediated pathogenesis, including the modulation of purine metabolism, lysosomal function, and complement–inflammasome crosstalk. Furthermore, we explore the burgeoning field of exosome-based therapeutics, critically evaluating strategies such as engineered exosomes for targeted drug delivery, mesenchymal stem cell (MSC)-derived exosomes for immunomodulation, and the development of exosomal biomarkers for diagnostics. Additionally, we examine how chemical drugs and herbal compounds may exert therapeutic effects by modulating exosome pathways, offering new insights into integrative treatment approaches. By synthesizing recent findings from proteomic, transcriptomic, and functional studies, we aim to unravel the complexities of exosome signaling in GA and to propose innovative therapeutic avenues that target these pathways to improve patient outcomes. Full article

This review introduces and elaborates a novel temporal paradigm, the “Gout Inflammation Time Programming” model, conceptualized through the Gout-STAT™ framework. This model redefines gout inflammation as a dynamic continuum progressing through three precisely timed phases: an acute Perception phase (0–24 h) initiated by monosodium urate (MSU) crystal recognition, triggering the NOD-like receptor thermal protein domain associated protein 3 (NLRP3) inflammasome and neutrophil-driven burst; a critical Adaptation phase (24–72 h) where outcomes are determined by immunometabolic reprogramming of macrophages and synovial fibroblasts; and a chronic Tissue Injury phase (>72 h) driven by epigenetic memory, leading to irreversible osteoarticular destruction. Deciphering this programmed timeline reveals distinct therapeutic windows. We propose a shift towards stage-specific precision interventions, targeting upstream triggers (e.g., mitochondrial reactive oxygen species(ROS), neutrophil extracellular trap formation (NETosis)) in the acute phase, correcting metabolic checkpoints (e.g., succinate accumulation, impaired autophagy) during adaptation, and employing tissue-protective strategies (e.g., epigenetic modulators) in the chronic phase. Furthermore, we highlight the pivotal role of cutting-edge translational technologies, such as intelligent drug delivery systems and digital twin joint models, in achieving spatiotemporal precision. Understanding this intrinsic molecular clock is fundamental for advancing gout management from reactive treatment to a predictive, preventive, and personalized 4P medicine approach. Full article

The diagnosis of crystal-induced arthritis is routinely established by synovial fluid analysis. However, a synovial effusion is not always present, fluid aspiration is not always possible or practical, and synovial fluid analysis is occasionally subject to false negative results. When there is a high suspicion of crystal-induced arthritis, but crystals are not identified in the synovial fluid, a biopsy of the synovium in search of crystals can assist in making a diagnosis. In this manuscript, we review the utility of ultrasound-guided needle biopsy of synovial tissue in the identification of crystal-induced arthritis, briefly describe the procedure, and recommend best practices for specimen handling and tissue processing. Full article

Objective: Monosodium urate (MSU) crystallization in human joints is poorly understood. This study aimed to investigate whether the length of MSU crystals varies in relation to organized ultrasound deposits, which may lead to longer crystals. Methods: Observational, cross-sectional study analyzing MSU crystals from synovial fluid samples of patients with crystal-proven gout. Using light microscopy, we measured crystal lengths (in µm) and noted the presence of long crystals, defined by cutoffs at the 66th, 75th, and 90th percentiles. We evaluated their association with two ultrasound-defined crystal deposition models: (1) grade 2–3 double-contour (DC) sign, tophi, and/or aggregates; and (2) grade 2–3 DC sign and/or tophi. Results: In a total of 1076 MSU crystals from 28 joints, median length was 23.3 µm (95% confidence interval 22.1–24.5). MSU crystal length was similar regardless of ultrasound deposition: in model 1 (20 joints, 71.4%), 22.5 µm in joints with deposits vs. 21.7 µm without; p = 0.42; in model 2 (15 joints, 53.6%), 22.8 µm vs. 21.2 µm, respectively; p = 0.12. Joints fulfilling model 2 criteria had more long crystals (>66th percentile), both in absolute and relative terms. Long crystals mildly correlated with serum urate levels and were numerically more frequent in patients with tophaceous gout. Conclusions: Most MSU crystals in synovial fluid gathered around a common length, regardless of ultrasound deposition. Long crystals were more common in joints with DC signs or tophi. Our finding is in keeping with two different mechanisms of MSU crystallization in humans. Full article

Endothelial dysfunction is an early driver of atherosclerosis, yet the direct impact of endogenous crystals such as cholesterol crystals and monosodium urate on endothelial activation remains incompletely understood. In this study, we examine how crystalline stimuli modulate human umbilical vein endothelial cells by assessing inflammatory signaling, mitochondrial respiration, and neutrophil recruitment. Using dose- and time-controlled experiments, we show that CC and MSU are internalized by endothelial cells, activating NF-κB and STAT3 signaling pathways and inducing a robust pro-inflammatory cytokine profile. Notably, CC caused marked mitochondrial dysfunction, evidenced by impaired respiratory capacity and loss of membrane potential, revealing a novel bioenergetic vulnerability in endothelial cells. Both direct crystal stimulation and exposure to crystal-primed conditioned media triggered endothelial adhesion molecule expression and promoted neutrophil adhesion, indicating that soluble mediators released upon crystal stimulation can propagate vascular inflammation. These findings demonstrate that crystalline stimuli are potent vascular danger signals capable of driving endothelial inflammation, mitochondrial impairment, and immune cell engagement, which are hallmarks of early atherogenesis. By elucidating these multifaceted endothelial responses, this study provides important mechanistic insights into how crystal-induced signals may contribute to vascular dysfunction and the early stages of atherogenesis. Full article

Gout is a form of sterile inflammatory arthritis in which monosodium urate (MSU) crystals deposit and provoke a neutrophil-predominant response, primarily driven by activation of the NACHT, leucine-rich repeat, and pyrin domain-containing protein 3 (NLRP3) inflammasome. Here, we show that auranofin, a Food and Drug Administration (FDA)-approved anti-rheumatic agent, exerts anti-inflammatory effects in both in vitro and in vivo models of gout. Auranofin inhibited NLRP3 inflammasome activation in human THP-1 cells and murine macrophages, leading to reduced cleavage of caspase-1, interleukin-1β (IL-1β), and interleukin-18 (IL-18). In MSU crystal-induced mouse models, auranofin treatment reduced paw swelling, serum cytokine levels, and tissue inflammation. Notably, auranofin suppressed neutrophil migration and decreased expression of C-X-C motif chemokine ligand 1 (CXCL1) in inflamed foot tissue and air-pouch exudates. Mechanistically, auranofin disrupted the interleukin-33 (IL-33)/suppression of tumorigenicity 2 (ST2) axis, a key signaling pathway promoting neutrophil recruitment. Overexpression of IL-33 abolished the anti-inflammatory effects of auranofin, highlighting the central role of IL-33 in gout pathogenesis. Together, our findings suggest that auranofin alleviates MSU-induced inflammation by concurrently inhibiting NLRP3 inflammasome activation and IL-33-mediated neutrophil recruitment, supporting its potential as a dual-action therapeutic candidate for gout. Full article

Gout is a chronic inflammatory disease characterized by the deposition of monosodium urate (MSU) crystals within joints, leading to recurrent acute flares and long-term tissue damage. While various hypotheses have been proposed to explain the self-limiting nature of acute gout attacks, we posit that aggregated neutrophil extracellular traps (aggNETs) play a central role in this process. This review focuses on the mechanisms underlying MSU crystal-induced formation of neutrophil extracellular traps (NETs) and explores their dual role in the clinical progression of gout. During the initial phase of acute flares, massive NET formation is accompanied by the release of preformed inflammatory mediators, which is a condition that amplifies inflammatory cascades. As neutrophil recruitment reaches a critical threshold, the NETs tend to form high-order aggregates (aggNETs). The latter encapsulate MSU crystals and further pro-inflammatory mediators within their three-dimensional scaffold. High concentrations of neutrophil serine proteases (NSPs) within the aggNETs facilitate the degradation of soluble inflammatory mediators and eventually promote the resolution of inflammation in a kind of negative inflammatory feedback loop. In advanced stages of gout, MSU crystal deposits are often visible via dual-energy computed tomography (DECT), and the formation of palpable tophi is frequently observed. Based on the mechanisms of resolution of inflammation and the clinical course of the disease, building on the traditional static model of “central crystal–peripheral fibrous encapsulation,” we have expanded the NETs component and refined the overall concept, proposing a more dynamic, multilayered, multicentric, and heterogeneous model of tophus maturation. Notably, in patients with late-stage gout, tophi exist in a stable state, referred to as “silent” tophi. However, during clinical tophus removal, the disruption of the structural or functional stability of “silent” tophi often leads to the explosive reactivation of inflammation. Considering these findings, we propose that future therapeutic strategies should focus on the precise modulation of NET dynamics, aiming to maintain immune equilibrium and prevent the recurrence of gout flares. Full article

Objectives: Identification of monosodium urate (MSU) and calcium pyrophosphate (CPP) crystals in synovial fluid should ideally be performed within 24 h to ensure optimal diagnostic accuracy for gout and CPP arthritis. However, crystal identification is often delayed in community-based healthcare facilities due to limited access to specialists or necessary equipment. This study aimed to determine whether MSU and CPP crystals remain detectable in synovial fluid after two weeks of storage at 4 °C and −20 °C. Methods: Anonymized synovial fluid samples were obtained from Thammasat University Hospital between February and March 2024. All samples underwent an initial round of crystal identification using compensated polarized light microscopy, conducted by two experienced examiners blinded to the clinical diagnosis. Following the initial analysis, each sample was divided into two equal portions and placed in ethylenediaminetetraacetic acid (EDTA)-coated tubes. One portion was stored at 4 °C, while the other was frozen at −20 °C. After two weeks, all samples underwent a second round of crystal identification. Results: Forty-nine samples were included for the first evaluation; MSU and CPP crystals were identified in 14 and 6 samples, respectively. On the second examination, MSU crystals were detectable in 13/14 (92.8%) samples stored at 4 °C and 12/14 (85.7%) samples stored at −20 °C. However, CPP crystals were detectable in 2/6 (33.3%) samples stored at both temperatures. No new crystal formation in initially negative samples was observed. Conclusion: MSU crystals remain detectable in synovial fluid for up to two weeks when stored in a standard refrigerator or freezer. However, the identification rate of CPP crystals tends to decline over this period. These findings may help inform best practices for handling synovial fluid samples in cases where immediate access to a specialist or necessary equipment is unavailable. Full article

Objectives: (1) To compare cytokine levels in participants with serum urate (SU) < 360 µmol/L, SU ≥ 360 µmol/L with and without monosodium urate (MSU) crystal deposition, respectively, and inter-critical gout. (2) To explore the association of IL-1β, IL-6 and high-sensitivity (hs) CRP with disease duration and the frequency of self-reported gout flares. Methods: Samples and data from 184 participants from studies conducted at Academic Rheumatology, Nottingham City Hospital, were included. Serum high-sensitivity CRP and cytokines involved in the pathogenesis of gouty inflammation were measured. MANCOVA and multivariate linear regression were used, as appropriate, and were adjusted for age, sex, body mass index and self-reported comorbidities. p values were adjusted for multiple testing using a 5% false-discovery rate. Results: Participants with inter-critical gout had greater levels of IL-1β (p_corr = 0.009), IL-18 (p_corr = 0.02), IL-6 (p_corr < 0.0001), IP-10 (p_corr < 0.0001), TNF-α (p_corr < 0.0001), GRO-α (p_corr = 0.0006) and hsCRP (p_corr = 0.009) compared to other groups in multivariate analyses and after correcting for multiple testing. There were no differences in cytokine and hsCRP levels in participants with SU < 360 µmol/L and in participants with SU ≥ 360 µmol/L with or without MSU crystal deposition. There was a statistically non-significant trend for association between IL-6 levels and number of self-reported gout flares. Conclusions: Our findings suggest that gout is a chronic inflammatory condition. The pre-clinical phases of gout were not associated with systemic inflammation, potentially due to the modest sample size. Further research is required to understand whether treating gout by targeting the complete dissolution of MSU crystals would reduce systemic inflammation in inter-critical gout. Full article

Gout, a metabolic and autoinflammatory disease, is the most common form of inflammatory arthritis worldwide. Hyperuricemia may result in monosodium urate (MSU) crystals forming and depositing in joints and surrounding tissues, triggering an autoinflammatory response. Effective urate-lowering therapies, as well as anti-inflammatory medications, are used to treat gout. Over the past few decades, new antihyperglycemic drug classes with different modes of action have been added to treat hyperglycemia in type 2 diabetes mellitus (T2DM). Two of these drug classes, sodium–glucose co-transporter-2 (SGLT2) inhibitors and glucagon-like peptide-1 (GLP-1) receptor agonists (RAs), have reduced cardiovascular and renal events and mortality. Several clinical studies have demonstrated that SGLT2 inhibitors possess urate-lowering properties, which may be beneficial for treating gout patients, particularly those with comorbid T2DM. Regarding SGLT2 inhibitors, some researchers have suggested that their benefits are partly explained by their ability to reduce serum urate (SU) levels, probably through increased urinary uric acid excretion. The effect of GLP-1 RA on SU levels and urinary excretion of uric acid in humans is unclear. This paper reviews the mechanisms of action of SGLT2 inhibitors and GLP-1RA, both approved and in development. Additionally, it examines what is known about their structure–activity relationships, uricosuric effects, pharmacokinetic profiles, and adverse effects. Full article

Background/Objectives: 7-Methylxanthine (7-MX) is a naturally occurring metabolite of caffeine and theobromine that can inhibit the crystallization of monosodium urate (MSU) and may be useful for the prevention or treatment of gout. However, the pharmacokinetics and ex vivo activity of 7-MX remain poorly characterized. Methods: The present study assessed the pharmacokinetics of 7-MX in Sprague Dawley rats following a single oral dose (30 mg/kg), and the ex vivo inhibition of MSU crystallization by 7-MX in rat plasma after the repeated administration of oral 7-MX. Results: The pharmacokinetic analysis showed that 7-MX reached peak plasma concentration (C_max ≈ 30 µM) at 30 min after administration (t_max), the terminal half-life was approximately 1.4 h, and there was no evidence of accumulation after repeated daily dosing. After repeated administration, the relationship between dose (30 or 60 mg/kg) and plasma concentration was proportional. In vitro and ex vivo crystallization assays demonstrated that 7-MX inhibited MSU crystallization in a concentration-dependent manner. The in vitro studies showed that 100 µM 7-MX inhibited up to 74% of MSU crystallization under supersaturated conditions (400 mg/L urate). The ex vivo experiments indicated that plasma from rats that received 30 or 60 mg/kg of 7-MX had 41.4% and 52.6% inhibition of crystallization, consistent with the measured plasma concentrations. Conclusions: These findings confirm that oral administration of 7-MX to rats led to a plasma level that was sufficient to decrease MSU crystallization in plasma, and there were no observable toxicities. These results support the potential of 7-MX as a safe oral treatment for gout, especially in combination with urate-lowering therapies, such as allopurinol. Further clinical investigations are warranted to confirm the therapeutic potential of 7-MX in humans. Full article

Background/Objectives: Gouty arthritis (GA) is a chronic inflammatory condition characterized by hyperuricemia and NLRP3 inflammasome activation, leading to joint damage and systemic inflammation. Although allopurinol (ALP), a xanthine oxidase inhibitor, effectively lowers serum urate levels, it has limited anti-inflammatory effects. This study investigated whether combining disulfiram (DSF), a known NLRP3 inflammasome inhibitor, with ALP enhances therapeutic outcomes in a rat model of gout. Methods: Thirty male Albino Wistar rats (150–200 g) were randomly assigned to five groups (n = 6): control, disease control, ALP-treated, DSF-treated, and ALP + DSF combination. Hyperuricemia was induced using potassium oxonate, followed by MSU crystal injection to trigger acute gout. Treatment lasted 30 days. Efficacy was assessed through clinical scoring, paw swelling, serum uric acid levels, ELISA-based cytokine profiling (IL-1β, TNF-α, IL-6), renal function tests, radiography, and histopathology. Results: Combination therapy with ALP + DSF significantly reduced paw swelling (p < 0.05), inflammation index (p < 0.001), serum uric acid (p < 0.001), and pro-inflammatory cytokines compared to monotherapy. Histopathology revealed preserved synovial architecture and reduced inflammatory infiltration. Radiographic imaging showed attenuated soft tissue swelling and joint erosion. Renal function markers were also improved in the combination group. Conclusions: The combination of ALP and DSF provided superior anti-inflammatory and urate-lowering effects compared to individual treatments. These findings support the potential of disulfiram as an adjunct to conventional ULTs in gout management through dual modulation of urate metabolism and inflammasome-driven inflammation. Full article

Hyperuricemia, induced by monosodium urate (MSU) crystals that accumulate in articular joints and periarticular soft tissues, can impair macrophages. Possible causes of macrophage injury include uric acid-induced oxidative stress or inflammation. This study examined the dried fruits of guava (DFG) as a complementary medicine with urate-lowering properties, utilizing THP-1 macrophages to determine if high uric acid-induced cellular damage could be mitigated through the reduction of oxidative stress and inflammation via treatment with a phytochemical extract. The active extract was prescreened using a xanthine oxidase (XO) inhibition assay coupled with fractionation and component analysis. The DFG extracts were used to identify, through an in vitro study of THP-1 cells. The results indicated that the DFG extracts with the highest total flavonoids (12.08 ± 0.81 mg/g DW) exhibited the XO inhibition activity. High-performance liquid chromatography–tandem mass spectrometry analysis showed that DFG extract contained 85.32% flavonoids, including quercetin and kaempferol derivatives. Furthermore, fractionation results of DFG extracts indicated a significant reduction in MSU-induced cytotoxicity in THP-1 cells obtained from the 75% ethanol-eluted fraction (Fr-75). Additionally, kaempferol, an active compound in Fr-75, effectively mitigated MSU-induced NF-κB and NLRP3 gene overexpression. These findings suggest that the prepared Fr-75 is a promising hyperuricemia therapeutic candidate. Full article

Background: Crystal arthritides represent the most common inflammatory rheumatologic condition. While the prevalence of gouty arthritis by monosodium urate (MSU) is well established, the prevalences of calciumpyrophosphat (CPP) and basic calcium pyrophosphate (ARP) arthritis are less clear. We herein sought to assess the prevalence and inflammatory characteristics of crystal arthritides at our institution, the biggest tertiary center in Switzerland. Methods: A total of 5036 synovial fluid (SF) samples were analyzed with regard to crystal positivity as well as joint, age, and sex distribution in affected patients. We furthermore compared inflammatory and non-inflammatory SF samples for yields of their Polymorphonuclear (PMN) fractions. Results: About half of all samples were derived from knee joints, a male/female ratio up to 10.1:1 among the MSU-positive, and a clear shift towards elder patients with CPP–arthritis was seen. These findings were in line with previous studies and suggest good comparability of our cohort. Of note, 21.9% of all samples were CPP positive, whereas 15.3% and 9.5% were positive for MSU and ARP/alizarin-red positive, respectively. Importantly, CPP crystals were predominant in inflammatory (58.9%) and non-inflammatory (65.7%) samples. By contrast, MSU crystals were significantly more often associated with synovitis (p < 0.001). Interestingly, higher PMN fractions were found in non-inflammatory MSU-positive samples (p < 0.01), whereas a similar trend was seen in CPP-positive samples. Conclusions: CPP arthritis represented the most frequent crystal arthritis form at our center. Higher PMN fractions in non-inflammatory samples with CPP and MSU crystals suggest subclinical inflammation and provide further arguments for earlier anti-inflammatory and uric acid-lowering therapies in patients with crystal deposits. Full article