Gout, Urate, and Crystal Deposition Disease

Gout and calcium pyrophosphate crystal deposition disease (CPPD) are frequently associated with comorbid disorders, including coronary artery disease and osteoarthritis, in which ectopic calcification with basic calcium phosphate crystals commonly affects arteries and articular cartilage, respectively. Accepting the 2024 G-CAN Gold Medal, I review my research philosophy for translational etiopathogenesis investigation in gout and CPPD, atherosclerosis, responses to arterial injury, and osteoarthritis. Since molecular homeostasis points to pathophysiology and vice versa, I have followed selected molecular players and pathways to phenotypes. Typically, behind each disease target is another target. Illuminating passageways between etiopathogenic pathways is especially productive when using approaches beyond conventional “omics” to reveal the impact of specific post-translational protein modifications, and changes in protein conformation, complex assembly, and interactomes. Highlighting these concepts, I review my past studies on specific molecular pathways, and current perspectives for the following: (i) PP_i, NPP1, ANKH, and transglutaminase 2 (TG2); (ii) relationships between NPP1, ANKH, Vanin-1 Pantetheinase, and ectopic chondrogenesis; (iii) intersections between adenosine, AMPK, CXCL8 and its receptor CXCR2, the receptor for advanced glycation endproducts (RAGE) and chondrocyte hypertrophy; (iv) lubricin homeostasis and proteolysis; (v) receptor for advanced glycation endproducts (RAGE) and TG2-catalyzed post-translational calgranulin modification; (vi) complement activation and C5b-9 assembly, and the nucleotide-bound conformation of TG2. The inescapable conclusion is that these molecular pathways tightly knit crystal arthropathy with both arterial and osteoarthritis comorbidity. 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

This review provides an overview of the most significant developments in gout pathophysiology research published in 2024. Thirteen studies were selected based on originality, scientific rigor, and potential clinical impact and grouped into four major categories: inflammation and pain mechanisms (LRRC8 anion channels, CXCL5-CXCR2 axis, CD38 and NAD⁺ metabolism, PLK1 and NLRP3 inflammasome localization, and IFN1 suppression), biomarkers and proteomics (scRNA-seq reveals monocyte and T-cell flare signatures, and Olink serum profiling reveals a proinflammatory signature in hyperuricemia and also identifies TNFSF14 as a novel flare biomarker, while a multi-omics integrative study implicates TRIM46 as a key causal gene), gut virome, and novel therapies (vagus nerve stimulation, biomimetic nanosystem, and restoration of Urate Oxidase (Uox) function). The studies selected focused primarily on work on subjects other than on hyperuricemia. The findings collectively expand our understanding of gout’s complex pathophysiology and highlight potential strategies for diagnosis, management, and innovative treatments. Full article

The 3rd Annual Meeting of the International Network on Ectopic Calcification (INTEC) was held in Faro, Portugal on 12–13 September 2024. This hybrid meeting brought together researchers and clinicians focused on the molecular, (patho)physiological, and clinical aspects of ectopic calcification in hereditary and acquired conditions, as well as in aging. The findings presented in this year’s meeting emphasised the complexity of the field, offering new insights into both mechanistic pathways and translational hurdles. The abstracts of this year’s meeting are collected in this conference paper, with permission from the corresponding authors. Full article

The evidence regarding allopurinol’s effects on renal function among people with hyperuricemia and gout has been conflicting, though clinicians are often cautious about using allopurinol in chronic kidney disease (CKD). We sought to examine the relation between allopurinol use in those with gout and CKD and the risk of worsening renal function. We conducted a time-stratified propensity score (PS)-matched cohort study on the IQVIA Medical Research Data representative of the UK general population. Among participants 18–89 years old with gout and CKD 3–4 not on urate-lowering therapy within one year prior, we identified new users of allopurinol and matched them 1:1 with a non-user. We analyzed the relation between incident allopurinol use and the changes in the eGFR at one year of follow-up using linear regression adjusted for the potential confounders included in the PS model. We PS-matched 10,716 allopurinol initiators to 10,716 non-users, among whom 42% were female, the mean age was 74 years and 7% had CKD4. The progression to dialysis or kidney transplant was similar in both groups. The mean eGFR prior to the study entry was 48.4 mL/min among allopurinol initiators and 49.5 mL/min among non-users, while the last eGFR within one year was 49.4 and 49.7 mL/min, respectively. The allopurinol initiators had an adjusted mean increase in the eGFR of 0.81 mL/min (95% CI 0.57–1.05) greater than that of non-users. Among those with gout and CKD 3–4, allopurinol did not worsen renal function and may have slightly improved it, suggesting that allopurinol is not detrimental to patients with gout who have CKD. 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

The tenth annual international G-CAN research symposium was held in Alexandria, VA on the 13th and 14th of November 2024. This hybrid meeting, a live face-to-face and virtual live symposium, was attended by 201 participants. Over 20 research abstract submissions were received from early career investigators, for plenary oral and poster presentations. Here, we present the 22 accepted, lightly edited abstracts from the early career presenters consenting to have their materials published. We thank and congratulate the presenters for their work and contributions to the meeting. Full article

Xanthine oxidoreductase (XOR) is the only enzyme responsible for uric acid production and is essential for preventing gout. While XOR inhibitors effectively reduce serum urate levels, they also influence purine salvage and de novo pathways, as well as energy metabolism, raising concerns about metabolic adaptation and rebound effects upon treatment discontinuation. In this review, we outline the fundamental regulatory mechanisms of purine metabolism and summarize the mechanisms of action of XOR inhibitors and their associated metabolic effects with reference to XOR deficiency, type I xanthinuria. Furthermore, we discuss the impact of discontinuing XOR inhibitors and examine their potential for rebound. Full article

Background: Mendelian randomization (MR) is a genetic epidemiological method used to infer causal relationships between exposures and outcomes. Its application in hyperuricemia and gout has grown exponentially owing to the ready availability of summary statistics from genome-wide association studies and the ease of applying the two-sample MR technique. However, indications of poor study quality suggest the need for systematic evaluation. Objective: This study evaluated the quality of two-sample MR studies on hyperuricemia and gout and developed a scoring system to help reviewers and readers assess their quality and validity. Methods: A systematic review was conducted on 86 two-sample MR studies published between 2016 and 2024. Studies were assessed using a scoring system encompassing study design, statistical methods, result interpretation, and adherence to STROBE-MR guidelines. Scores could range between −9 and 21. Trends in quality over time were analyzed using regression models. Results: Study quality scores ranged from 0 to 19, with a mean of 9.1 and median of 11, demonstrating wide variability. High-quality studies adhered to MR assumptions, used independent datasets, and conducted replication analyses, while lower-quality studies often failed to correct the p-value when needed, test for confounders, address dataset overlap, or report study power. Despite the increased publication of MR studies, overall quality has not improved over time. Conclusion: There is variability in two-sample MR study quality. Our proposed scoring system offers a practical framework for evaluating MR studies, aiding researchers and clinicians in identifying robust findings while promoting higher methodological standards. Full article

Monosodium urate, calcium pyrophosphate, and basic calcium phosphate crystals are the most common types of crystals found in the joints. Each type of crystal has been associated with the onset of different joint diseases. However, the mechanisms identified for one type of crystal are often generalized to the others; thus, overlooking the specific and distinct molecular and cellular responses activated by each type of crystal. This review describes the similarities and differences of the main molecules and mechanisms underlying the diseases associated with the three different types of crystals. Specifically, current knowledge on crystal properties and formation, on the induction and resolution of inflammation, on mechanisms involved in pain processing and senescence, and on the role of mitochondria and genomic instability are elucidated. A more complete and detailed study of the specific molecular mechanisms induced by different crystals is necessary to advance our understanding of the pathogenesis and to help identify innovative opportunities for prevention and treatment of crystal deposition disease. Full article

Genetic association studies in gout have identified genetic variants in or near genes involved in the biosynthesis and transport of urate and in immunological pathways. However, the causal role of the remaining genetic variants, genes, and pathways in gout is not clear. Here, we present the results from a genetic colocalization analysis of gout-associated signals with metabolite quantitative trait loci (mQTL), shedding light on the metabolites that are likely directly affected by genetic variants associated with gout. We identified 141 candidate metabolites with evidence of colocalization with at least one gout-associated genetic signal, of which 29 showed evidence of a causal relationship with gout by Mendelian randomization. Among the 29 metabolites were lysophosphatidylcholines, which may affect the inflammatory response by binding to the TLR-2/4 receptors, providing plausible candidate metabolites for future studies that link metabolites with inflammatory processes in gout. Full article

Calcium pyrophosphate deposition disease (CPPD) has been shown to be associated with inflammatory arthritis such as rheumatoid arthritis. However, few studies have investigated the correlation between CPPD and psoriatic arthritis (PsA). Our study aimed to determine whether there were higher rates of PsA in patients with CPPD than controls. A retrospective cohort study was conducted using the Veterans Affairs’ Corporate Data Warehouse. Individuals with a CPPD ICD code were matched with controls and diagnoses of PsA and psoriasis were collected. A total of 41,084 CPPD patients were matched with 119,192 controls. The proportion of CPPD patients with PsA diagnosis was more than double that of controls (1.07% vs. 0.37%; p < 0.0001), and more CPPD patients were diagnosed with psoriasis (3.05% vs. 2.52%; p < 0.0001). Those with CPPD had higher odds of a PsA diagnosis (OR 3.550, 95% CI 2.602–4.844). A total of 61.59% of PsA diagnoses preceded the CPPD diagnoses by at least one year. This is the first case–control study demonstrating an association between CPPD and PsA, potentially related to the fact that both PsA and CPPD could be triggered by trauma, and are closely associated with osteoarthritis. It also is possible that inflammatory pathways contribute to CPP crystal deposition in joints. Full article

This review examines the concept of “psout”, an overlap syndrome of hyperuricemic psoriatic arthritis (HU-PsA) and co-existing gout and PsA. The manuscript explores its epidemiology, pathophysiology, clinical implications, and treatment strategies, focusing on emerging data since its first description in 2020. The psout concept is sustained by shared inflammatory and metabolic pathways between gout and PsA, contributing to a broad spectrum of phenotypes and moderate-to-severe clinical manifestations. Monosodium urate crystals and hyperuricemia are central to this overlap, influencing cytokine production, keratinocyte activation, and immune responses, being able to activate both innate and acquired immunity. Clinical management is complex due to diagnostic challenges and therapeutic considerations not yet implemented in international recommendations. Emerging data from clinical trials underscore the significance of hyperuricemia in worsening PsA outcomes while highlighting the potential of personalized treatments. Future research into shared pathophysiological mechanisms, the accurate description of the diversity of phenotypes, innovative imaging assessments, and therapeutic strategies could provide insights into the interplay of these two conditions and enhance patient outcomes. Full article

Gout management strategies remain a topic of debate, particularly regarding the efficacy of treat-to-target (T2T) and treat-to-avoid-symptoms (T2S) approaches. T2T, endorsed by major rheumatology societies, involves systematic serum urate (sUA) monitoring and urate-lowering therapy (ULT) dose escalation to maintain sUA below a predefined threshold. In contrast, T2S, which focuses on symptom relief rather than routine sUA monitoring, is supported by alternative guidelines. Despite the widespread adoption of T2T in other chronic diseases, its clinical benefits beyond biochemical parameters, such as serum urate reduction, remain uncertain in gout. This study evaluates current evidence on T2T and T2S, analyzing data from a pragmatic multicenter trial comparing both strategies. Findings suggest that while T2T is effective in reducing sUA levels, its superiority in preventing flares and improving patient-reported outcomes remains inconclusive. Some studies report reduced tophus burden and better adherence with T2T, whereas others find negligible differences in pain relief and functional improvement between the two strategies. The lack of high-quality comparative trials underscores the need for further investigation. Future research should prioritize long-term, patient-centered outcomes and pragmatic implementation strategies. Full article

Lifelong urate-lowering therapy (ULT) is recommended for gout to prevent flares and urate deposition. However, concerns about its adherence, long-term side effects, and the necessity of continuous treatment after achieving remission raise critical questions. Two randomised controlled trials (RCTs), GO TEST Finale and STING, aim to evaluate the safety and feasibility of ULT discontinuation in gout patients in remission. The GO TEST Finale is a superiority trial involving 310 patients in the Netherlands, comparing a treat-to-target (T2T) ULT continuation strategy with ULT discontinuation. Patients in the discontinuation arm resume ULT only after flare recurrence or tophi development. The primary outcomes focus on remission criteria failure over 24 months, while the secondary outcomes explore predictors of successful discontinuation and cost-effectiveness. The STING study, a non-inferiority trial in France, includes 450 patients without ultrasound (US) evidence of urate deposits. Patients in the discontinuation group resume ULT if a US detects urate deposition during follow-up, minimising flare risk. The primary outcomes measure the proportion of patients experiencing flares at two years, with the secondary outcomes examining the long-term health impacts and cost-effectiveness. These trials provide an opportunity for translational research into the immunological and epigenetic effects of rising serum urate levels. The results could inform personalised strategies for a drug-free period and address the critical question of whether lifelong ULT is necessary for gout management. The complementary findings from both trials are expected to contribute significantly to resolving this ongoing clinical debate. Full article

Gout is a common inflammatory joint disease in China. In recent years, the prevalence of gout in China has been increasing and the onset age of gout has been trending younger. The common risk factors for gout in China include hyperuricemia, age, sex, obesity, hypertension, metabolic syndrome, use of drugs (e.g., diuretics), dietary factors, chronic kidney disease (CKD), ethnicity, and income. Chinese clinical guidelines recommend the diagnosis of subclinical gout, refractory gout, and clinical classification of hyperuricemia in gout patients with early-onset or family history. Maintaining a consistently low level of serum urate is crucial for the effective long-term treatment of gout. However, the Chinese guidelines recommend paying special attention to allopurinol hypersensitivity when considering urate-lowering drugs. The adherence rate to urate-lowering therapy (ULT) in Chinese patients with gout ranges from 9.6% to 40.7%. Patient education and reducing drug side effects are effective approaches to improve the adherence to ULT and the rate of achieving the target urate level. The development of new treatment principles based on clinical trials, such as ULT based on the classification of hyperuricemia and urine alkalization, is recommended to improve patient outcomes and reduce potential side effects. The study of genetics, metabolites, and intestinal microbiota has yielded new findings that may aid in the diagnosis, classification, and pathogenesis of gout in China. Full article

Gout is the most common inflammatory arthritis, with a growing global disease burden. This conference report summarizes nine impactful publications dating from 11/2022 to 10/2023 to inform and improve clinical care in gout. The articles we present here collectively address diverse facets of gout research, including gout epidemiology, predictive biomarkers, the occurrence of complications relating to gout flares, and gout management strategies. Full article

We assessed changes in vascular inflammation and monosodium urate (MSU)-coded deposits after administration of Pegloticase in the vasculature of tophaceous gout patients using ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) Positron emission tomography/computed tomography (PET/CT) and dual-energy CT (DECT). Ten patients with tophaceous gout, intolerant or refractory to urate-lowering therapy (ULT), were treated with Pegloticase every two weeks for six months. ¹⁸F-FDG PET/CT and DECT were performed at baseline and after Pegloticase therapy to detect vessel wall inflammation (Standard uptake value, SUVmean, and SUVmax) and vascular MSU-coded deposition (MSU volume). Data were summarized using means and standard deviations. Baseline and follow-up values were compared for each variable using mixed-effect models. Significant decreases in SUVmean (p = 0.0003) and SUVmax (p = 0.009) were found with a trend towards a decrease in vessel wall MSU volume after treatment. There was a significant decrease in serum urate, correlating with reduction in SUVmean (R² = 0.65), with a trend towards a decrease in CRP and blood pressure in all patients. Despite the small sample size, we were able to demonstrate a decrease in vessel wall inflammation and a trend towards a decrease in MSU volume by intensively lowering serum urate. These findings suggest that MSU-coded deposits and hyperuricemia may play a role in vascular wall inflammation. It remains to be seen whether this correlates with a decrease in adverse cardiovascular outcomes. Full article