Enhanced osteoclastogenesis in patients with tophaceous gout: Urate crystals promote osteoclast development through interactions with stromal cells

Urate crystal deposition and bone erosion in gout: 'inside-out' or 'outside-in'? A dual-energy computed tomography study

Background

It is currently unknown whether bone erosion in gout occurs through an ‘inside-out’ mechanism due to direct intra-osseous crystal deposition or through an ‘outside-in’ mechanism from the surface of bone. The aim of this study was to examine the mechanism (‘outside-in’ vs. ‘inside-out’) of monosodium urate (MSU) crystal deposition in bone erosion in gout. Specifically, we used three-dimensional dual-energy computed tomography (DECT) to analyse the positional relationship between bone and MSU crystal deposition in tophaceous gout, and to determine whether intra-osseous crystal deposition occurs in the absence of erosion.

Methods

One hundred forty-four participants with gout and at least one palpable tophus had a DECT scan of both feet. Two readers independently scored all metatarsal heads (1433 bones available for scoring). For bones in contact with urate, the bone was scored for whether urate was present within an erosion, on the surface of bone or within bone only (true intra-osseous deposit). Data were analysed using generalised estimating equations.

Results

Urate in contact with bone was present in 370 (54.3 %) of 681 joints with urate deposition. For those bones in contact with urate, deposition was present on the surface of bone in 143 (38.6 %) of 370 joints and within erosion in 227 (61.4 %) of 370. True intra-osseous urate deposition was not observed at any site (p < 0.0001). For all bones with apparent intra-osseous deposition in one plane, examination in other planes revealed urate deposition within an en face erosion.

Conclusions

In tophaceous gout, MSU crystal deposition is present within the joint, on the bone surface and within bone erosion, but it is not observed within bone in the absence of a cortical break. These data support the concept that MSU crystals deposit outside bone and contribute to bone erosion through an ‘outside-in’ mechanism.

Simplified Radiographic Damage Index for Affected Joints in Chronic Gouty Arthritis

The aim of this study was to develop and validate a new radiographic damage scoring method (DAmagE index of GoUt; DAEGU) in chronic gout using plain radiography. Two independent observers scored foot x-rays from 15 patients with chronic gout according to the DAEGU method and the modified Sharp/van der Heijde (SvdH) method. The 10 metatarsophalangeal (MTP) and 2 interphalangeal (IP) joints of the first toes of both feet were scored to assess the degrees of erosion and joint space narrowing (JSN). The intraobserver and interobserver reliabilities were analyzed by calculating the intraclass correlation coefficient (ICC) and minimal detectable change (MDC). The correlation between the DAEGU and SvdH methods was analyzed by calculating the Spearman's rho correlation coefficients and Kappa coefficients. The DAEGU method was found to be highly reproducible (0.945-0.987 for the intraobserver and 0.993-0.996 for the interobserver ICC values). The erosion, JSN, and total scores exhibited strong positive correlations between the DAEGU and SvdH methods and also within each method (r = 0.860-0.969, P < 0.001 for all parameters). The DAEGU and SvdH methods were in very good agreement as determined by Kappa coefficient analysis [0.732 (0.387-1.000) for erosion and 1.000 (1.000-1.000) for JSN]. In conclusion, this study revealed that DAEGU method was a reliable and feasible tool in the assessment of radiographic damage in chronic gout. The DAEGU method may provide a more easy assessment of structural damage in chronic gout in the real clinical practice.

Path Analysis Identifies Receptor Activator of Nuclear Factor-κB Ligand, Osteoprotegerin, and Sclerostin as Potential Mediators of the Tophus-bone Erosion Relationship in Gout

OBJECTIVE

To determine the relationship between tophus, erosion and bone remodeling factors in gout.

METHODS

Computed tomography bone erosion and circulating bone factors were measured in adults with tophaceous gout. Multiple regression modeling and path analysis were used to determine predictors of erosion.

RESULTS

Tophus number, Māori or Pacific ethnicity, creatinine, receptor activator of nuclear factor-κB ligand (RANKL), osteoprotegerin (OPG), and sclerostin were independently associated with erosion. Path analysis showed a direct effect of tophus number on erosion, partially mediated through OPG, RANKL, and sclerostin.

CONCLUSION

Tophus number is strongly associated with bone erosion in gout. Circulating RANKL, OPG, and sclerostin are potential mediators of tophus-related erosion.

Hyperuricaemia with deposition: latest evidence and therapeutic approach

This article reviews recent evidence on urate deposition and the opportunity for a therapeutic approach. We reviewed Pubmed 2013-2015 literature using the search terms 'deposition' with 'hyperuricaemia', 'gout', 'ultrasonography', 'DECT' (dual-energy computed tomography), 'radiography', 'CT'(computed tomography), 'MRI' (magnetic resonance imaging), or 'cardiovascular', in addition to a digital bibliographic library compiled by the authors with 2072 papers on hyperuricaemia and gout. Relevant papers on the topic were selected. Recent evidence, mostly based on imaging studies, showed a continuum from hyperuricaemia to deposition and clinical manifestations. Chronic inflammation and structural damage may be present even in asymptomatic patients with crystal-proved deposition. The impact of early intervention in patients with asymptomatic deposition either on vascular outcomes or further structural joint damage has not been demonstrated yet. In conclusion, a worldwide definition of gout is still lacking, stages from hyperuricaemia to clinical gout not being definitively defined. Although there is increasing interest on the impact of early deposits on joint damage and cardiovascular outcomes, robust evidence is still lacking to fully support interventions.

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.

Gouty arthropathy: Review of clinico-pathologic and imaging features

Gout is a common inflammatory arthropathy in adults, with the prevalence increasing in males of older age. It occurs when monosodium urate (MSU) crystals are deposited in joints and connective tissue causing inflammation. The gold standard for the diagnosis of gout is the demonstration of negatively birefringent, needle-shaped MSU crystals through synovial fluid aspiration. However, this is an invasive technique and may not always be conclusive or feasible. Imaging techniques have been developed to aid in diagnosis of gout non-invasively. Radiography has a low utility in the early diagnosis of gout and demonstrates erosions in late stages. Ultrasound (US) has a high overall sensitivity in diagnosing gout with the 'double contour' sign having a high specificity. Magnetic resonance imaging is good at detecting tophi, bone marrow oedema and erosions, but has a limited role in diagnosis because of its high cost and limited availability. Conventional computed tomography (CT) has no role in the routine diagnosis of gout before development of erosions and tophi. A newer technology, dual-energy CT (DECT) has been shown to be able to detect MSU crystals burden with high accuracy. It has a higher specificity and lower sensitivity that US in gout diagnosis. However, because of radiation exposure and cost, it has a better utility in diagnosing clinically suspected gout complicated by other concurrent rheumatologic conditions or if radiography, US and synovial aspiration are inconclusive or not feasible. This paper will review the clinico-pathologic and imaging features of gouty arthropathy.

Monosodium Urate in the Presence of RANKL Promotes Osteoclast Formation through Activation of c-Jun N-Terminal Kinase

The aim of this study was to clarify the role of monosodium urate (MSU) crystals in receptor activator of nuclear factor kB ligand- (RANKL-) RANK-induced osteoclast formation. RAW 264.7 murine macrophage cells were incubated with MSU crystals or RANKL and differentiated into osteoclast-like cells as confirmed by staining for tartrate-resistant acid phosphatase (TRAP) and actin ring, pit formation assay, and TRAP activity assay. MSU crystals in the presence of RANKL augmented osteoclast differentiation, with enhanced mRNA expression of NFATc1, cathepsin K, carbonic anhydrase II, and matrix metalloproteinase-9 (MMP-9), in comparison to RAW 264.7 macrophages incubated in the presence of RANKL alone. Treatment with both MSU crystals and RANKL induced osteoclast differentiation by activating downstream molecules in the RANKL-RANK pathway including tumor necrosis factor receptor-associated factor 6 (TRAF-6), JNK, c-Jun, and NFATc1. IL-1b produced in response to treatment with both MSU and RANKL is involved in osteoclast differentiation in part through the induction of TRAF-6 downstream of the IL-1b pathway. This study revealed that MSU crystals contribute to enhanced osteoclast formation through activation of RANKL-mediated pathways and recruitment of IL-1b. These findings suggest that MSU crystals might be a pathologic causative agent of bone destruction in gout.

Serum urate levels and the risk of hip fractures: data from the Cardiovascular Health Study

PURPOSE

Uric acid inhibits vitamin D activation experimentally and higher serum urate levels are associated with higher parathyroid hormone levels in humans suggesting a link between uric acid and bone health. We hypothesized that hyperuricemia may increase the risk of fractures in older adults.

METHODS

1963 men and 2729 women ≥65 years of age who participated in the Cardiovascular Health Study and had baseline serum urate levels were included in the study. The primary outcome was incident hip fracture, assessed prospectively through June, 2008 by inpatient and outpatient records. The analysis was stratified by sex a priori.

RESULTS

There was a U-shaped relationship between serum urate levels and hip fractures in men. Men in the lowest and the highest urate quartiles (<4.88 and ≥6.88 mg/dL respectively) had a significantly higher rate of fractures in unadjusted analysis. However, upon multivariate adjustment, only the HR for hip fracture in highest quartile versus the reference remained significant (HR 1.9; 95% C.I. 1.1, 3.1; p value 0.02). High serum urate levels were not associated with hip fractures in women.

CONCLUSION

In this large prospective cohort of community-dwelling older adults, increased serum urate levels were associated with an increased risk of hip fractures in men. Further studies are needed to confirm these findings and to understand the mechanisms that underlie them.

Lemnalol attenuates mast cell activation and osteoclast activity in a gouty arthritis model

OBJECTIVES

In this study, we investigated the effects of a soft coral-derived anti-inflammatory compound, lemnalol, on mast cell (MC) function and osteoclast activity in rats with monosodium urate (MSU) crystal-induced gouty arthritis.

METHODS

In this study, we examined the therapeutic effects of lemnalol on intra-articular injection of MSU induces gouty arthritis with the measurement of ankle oedema. Toluidine blue staining were used to analyse the infiltration and the percentage degranulation MCs. Immunohistochemical analysis showed CD117, transforming growth factor beta 1 (TGF-β1), matrix metalloproteinase 9 (MMP-9), the osteoclast markers cathepsin K and tartrate-resistant acid phosphatase (TRAP) protein expression in ankle tissue.

KEY FINDINGS

We found that both infiltration and degranulation of MCs increased at 24 h after MSU injection in the ankle joint. Immunohistochemical analysis showed that MSU induced upregulation of TGF-β1, MMP-9, the osteoclast markers cathepsin K and TRAP in ankle tissues. Administration of lemnalol ameliorated MSU-induced TGF-β1, MMP-9, cathepsin K and TRAP protein expression.

CONCLUSIONS

Taken together, our results show that MSU-induced gouty arthritis is accompanied by osteoclast-related protein upregulation and that lemnalol treatment may be beneficial for the attenuation of MC infiltration and degranulation and for suppressing osteoclast activation in gouty arthritis.

Exploring cartilage damage in gout using 3-T MRI: distribution and associations with joint inflammation and tophus deposition

OBJECTIVE

Few imaging studies have investigated cartilage in gout. Magnetic resonance imaging (MRI) can image cartilage damage and also reveals other features of gouty arthropathy. The objective was to develop and validate a system for quantifying cartilage damage in gout.

METHODS

3-T MRI scans of the wrist were obtained in 40 gout patients. MRI cartilage damage was quantified using an adaptation of the radiographic Sharp van der Heijde score. Two readers scored cartilage loss at 7 wrist joints: 0 (normal), 1 (partial narrowing), 2 (complete narrowing) and concomitant osteoarthritis was recorded. Bone erosion, bone oedema and synovitis were scored (RAMRIS) and tophi were assessed. Correlations between radiographic and MRI cartilage scores were investigated, as was the reliability of the MRI cartilage score and its associations.

RESULTS

The GOut MRI Cartilage Score (GOMRICS) was highly correlated with the total Sharp van der Heijde (SvdH) score and the joint space narrowing component (R = 0.8 and 0.71 respectively, p < 0.001). Reliability was high (intraobserver, interobserver ICCs = 0.87 [0.57-0.97], 0.64 [0.41-0.79] respectively), and improved on unenhanced scans; interobserver ICC = 0.82 [0.49-0.95]. Cartilage damage was predominantly focal (82% of lesions) and identified in 40 out of 280 (14%) of joints. Cartilage scores correlated with bone erosion (R = 0.57), tophus size (R = 0.52), and synovitis (R = 0.55), but not bone oedema scores.

CONCLUSIONS

Magnetic resonance imaging can be used to investigate cartilage in gout. Cartilage damage was relatively uncommon, focal, and associated with bone erosions, tophi and synovitis, but not bone oedema. This emphasises the unique pathophysiology of gout.

Methods of assessment of tophus and bone erosions in gout using dual-energy CT: reproducibility analysis

This study aims to evaluate the intraobserver and interobserver reproducibility of the tophus urate volume, erosion volume, and the erosion score measurements in patients with gout by using dual-energy CT (DECT) scans comparing their bone erosion volumes against bone erosion scores and also to determine a valid measure of joint destruction in chronic gout. Sixty-six subjects underwent DECT scans of the hands or feet. Two independent observers measured the tophus urate volumes and bone erosion volumes using automated volume assessment software and the erosion scores based on the rheumatoid arthritis magnetic resonance imaging score (RAMRIS). The intraobserver and interobserver reproducibility were analyzed by intraclass correlation coefficient (ICC) and limits of agreements analysis. The relationship between erosion volumes and erosion scores was analyzed. The intraobserver and interobserver ICC for tophus urate volume measurements (n = 636) were 1.000 (95 % confidence interval (95 % CI) 1.000 to 1.000) and 1.000 (95 % CI 1.000 to 1.000), 0.999 (0.999, 0.999) and 0.999 (0.999, 0.999) for bone erosion volumes (n = 350), 0.937 (0.928, 0.946) and 0.899 (0.883, 0.912) for erosion scores (n = 350). Strong positive correlations were demonstrated between individual erosion volumes and scores (r s = 0.914, p < 0.001) as well as total erosion volume and score per patient (r = 0.838-0.867, p < 0.001). This study demonstrated a high reproducibility of tophus urate volumes, erosion volumes, and erosion score measurements using DECT. Erosion volumes show to be a more direct and accurate method to evaluate bone erosion compared with erosion score, strongly supporting it as a superior and standard measure of structural joint damage in gout.

The emerging role of biotechnological drugs in the treatment of gout

One of the most important therapeutic advances obtained in the field of rheumatology is the availability of the so-called bio(techno)logical drugs, which have deeply changed treatment perspectives in diseases such as rheumatoid arthritis and ankylosing spondylitis. According to the steadily increasing attention on gout, due to well-established prognostic and epidemiology implications, in the last 5 years, the same change of perspective has been observed also for this disease. In fact, several bio(techno)logical agents have been investigated both for the management of the articular gout symptoms, targeting mainly interleukin-1β, as well as urate-lowering therapies such as recombinant uricases. Among the IL-1β inhibitors, the majority of studies involve drugs such as anakinra, canakinumab, and rilonacept, but other compounds are under development. Moreover, other potential targets have been suggested, as, for example, the TNF alpha and IL-6, even if data obtained are less robust than those of IL-1β inhibitors. Regarding urate-lowering therapies, the recombinant uricases pegloticase and rasburicase clearly showed their effectiveness in gout patients. Also in this case, new compounds are under development. The aim of this review is to focus on the various aspects of different bio(techno)logical drugs in gouty patients.

Interactions between tenocytes and monosodium urate monohydrate crystals: implications for tendon involvement in gout

OBJECTIVES

Advanced imaging studies have demonstrated that urate deposition in periarticular structures, such as tendons, is common in gout. The aim of this study was to investigate the effects of monosodium urate monohydrate (MSU) crystals on tenocyte viability and function.

METHODS

The histological appearance of tendons in joints affected by advanced gout was examined using light microscopy. In vitro, colorimetric assays and flow cytometry were used to assess cell viability in primary rat and primary human tenocytes cultured with MSU crystals. Real-time PCR was used to determine changes in the relative mRNA expression levels of tendon-related genes, and Sirius red staining was used to measure changes in collagen deposition in primary rat tenocytes.

RESULTS

In joint samples from patients with gout, MSU crystals were identified within the tendon, adjacent to and invading into tendon, and at the enthesis. MSU crystals reduced tenocyte viability in a dose-dependent manner. MSU crystals decreased the mRNA expression of tendon collagens, matrix proteins and degradative enzymes and reduced collagen protein deposition by tenocytes.

CONCLUSIONS

These data indicate that MSU crystals directly interact with tenocytes to reduce cell viability and function. These interactions may contribute to tendon damage in people with advanced gout.

Exploratory study of radiographic change in patients with tophaceous gout treated with intensive urate-lowering therapy

OBJECTIVE

Tophi are strongly associated with structural damage in gout, and urate-lowering therapy reduces tophus size. Pegloticase leads to dramatic reductions in serum urate and subcutaneous tophi in treatment responders. The aim of this analysis was to examine whether profound urate lowering can alter radiographic findings in gout.

METHODS

Serial plain radiographs of the hands and feet were obtained from 8 patients with tophaceous gout treated with pegloticase. Radiographs were scored for erosion and joint space narrowing (JSN) according to the gout-modified Sharp/van der Heijde method. Scorers were blinded to each other's scores and to the clinical characteristics of the patients (including the clinical response to pegloticase). A detailed qualitative site-by-site analysis was undertaken to define additional changes observed from baseline.

RESULTS

All patients experienced a profound urate-lowering response (serum urate level <1 mg/dl) during pegloticase treatment. For the entire group, the median total radiographic scores reduced from 69.25 (range 1.5-138) at baseline to 57.25 (range 1.5-110) at 12 months (P = 0.02). Median erosion scores reduced over 1 year (P = 0.008), but JSN scores did not change (P = 0.50). Further reductions were observed in total scores and erosion scores in 5 patients with 24-month followup films (one-way analysis of variance P = 0.009 for total score, 0.02 for erosion, and 0.95 for JSN). Qualitative site-by-site analysis identified regression of soft tissue masses, increased sclerosis, and filling in of erosions in the followup films.

CONCLUSION

This exploratory study suggests that profound urate lowering can lead to improvement in structural damage, particularly bone erosion, in patients with tophaceous gout.

First metatarsophalangeal joint arthrodesis for the treatment of tophaceous gouty arthritis

In tophaceous gouty arthritis, surgeons face the choice between preservation of the involved joint and arthrodesis after tophi excision. Magnetic resonance imaging (MRI) can allow evaluation of the distribution of tophaceous deposits, which can be difficult to visualize on radiography. The goal of this study was to evaluate the characteristic MRI features of tophaceous lesions and to compare the clinical outcomes of arthrodesis after tophi excision with those of simple tophi excision. The authors reviewed 16 feet in 15 consecutive patients diagnosed with tophaceous gouty arthritis of the first metatarsophalangeal (MTP) joint who underwent surgery. Nine feet (group A) were treated with simple tophi excision, whereas the other 7 (group B) underwent first MTP joint arthrodesis after tophi excision. For clinical evaluation, the visual analog scale (VAS) for pain, American Orthopaedic Foot and Ankle Society (AOFAS) score, Tegner activity scale, and patient satisfaction assessments were used. Magnetic resonance imaging was performed to evaluate the characteristics of tophaceous deposits in the first MTP joint. Mean VAS and AOFAS scores and patient satisfaction significantly differed between the 2 groups at final follow-up (P=.007, .005, and .002, respectively). In group A, progression of arthritis of the first MTP joint was observed in 6 of 9 cases at final follow-up. The tophaceous lesions of these 6 cases were found to be located intra-articularly on MRI. Arthrodesis after tophi excision should be considered for treating tophaceous gouty arthritis of the first MTP joint when tophi are located intra-articularly and loss of cartilage involved is greater than 50% of the entire joint.

The Effects of Monosodium Urate Monohydrate Crystals on Chondrocyte Viability and Function: Implications for Development of Cartilage Damage in Gout

Objective.

Cartilage damage is frequently observed in advanced destructive gout. The aim of our study was to investigate the effects of monosodium urate monohydrate (MSU) crystals on chondrocyte viability and function.

Methods.

The alamarBlue assay and flow cytometry were used to assess the viability of primary human chondrocytes and cartilage explants following culture with MSU crystals. The number of dead chondrocytes in cartilage explants cultured with MSU crystals was quantified. Real-time PCR was used to determine changes in the relative mRNA expression levels of chondrocytic genes. The histological appearance of cartilage in joints affected by gout was also examined.

Results.

MSU crystals rapidly reduced primary human chondrocyte and cartilage explant viability in a dose-dependent manner (p < 0.01 for both). Cartilage explants cultured with MSU crystals had a greater percentage of dead chondrocytes at the articular surface compared to untreated cartilage (p = 0.004). Relative mRNA expression of type II collagen and the cartilage matrix proteins aggrecan and versican was decreased in chondrocytes following culture with MSU crystals (p < 0.05 for all). However, expression of the degradative enzymes ADAMTS4 and ADAMTS5 was increased (p < 0.05 for both). In joints affected by gout, normal cartilage architecture was lost, with empty chondrocyte lacunae observed.

Conclusion.

MSU crystals have profound inhibitory effects on chondrocyte viability and function. Interactions between MSU crystals and chondrocytes may contribute to cartilage damage in gout through reduction of chondrocyte viability and promotion of a catabolic state.

Imaging of gout: an overview

The diverse clinical states and sites of pathology in gout provide challenges when considering the features apparent on imaging. Ideally, an imaging modality should capture all aspects of disease including monosodium urate crystal deposition, acute inflammation, tophus, tissue remodelling and complications of disease. The modalities used in gout include conventional radiography, ultrasonography, magnetic resonance imaging, computed tomography and dual-energy computed tomography. This review discusses the role of each of these imaging modalities in gout, focussing on the imaging characteristics, role in gout diagnosis and role for disease monitoring. Ultrasonography and dual-energy computed tomography are particularly promising methods for both non-invasive diagnosis and monitoring of disease. The observation that ultrasonographic appearances of monosodium urate crystal deposition can be observed in patients with hyperuricaemia but no other clinical features of gout raises important questions about disease definitions.

No reduction in circulating preosteoclasts 18 months after treatment with zoledronate: analysis from a randomized placebo controlled trial

The conventional model that bisphosphonates bind to the bone surface and inhibit mature osteoclasts does not convincingly explain the prolonged duration of action of zoledronate. We hypothesized that zoledronate on the bone surface adjacent to marrow cells impairs osteoclastogenesis, contributing to sustained inhibition of resorption. In this case, numbers of circulating preosteoclasts may be reduced after zoledronate treatment. This study assessed this possibility in subjects from a clinical trial. Twenty-two osteopenic women participating in a randomized, controlled trial comparing zoledronate 5 mg with placebo were recruited, 18 months after administration of study drug. Peripheral blood mononuclear cells were analyzed for the presence of osteoclast precursors using flow cytometry for preosteoclast markers and the ability to form osteoclast-like cells in culture with RANKL and M-CSF. There was no difference in the percentage of CD14(+)/CD11b(+) cells in peripheral blood between the two groups. The numbers of TRAP(+) multinucleated cells in cultures in the absence of RANKL and M-CSF were very low in both groups, but a significantly higher number of these cells was observed in the zoledronate group compared with the placebo group (p = 0.01). The number of TRAP(+) multinucleated cells and resorption pits following culture with RANKL and M-CSF did not differ between the two groups. Serum P1NP was reduced 53 % at 18 months in the zoledronate group but unchanged in the placebo group. These results do not support the hypothesis that the inhibitory action of zoledronate contributes to its prolonged action on preosteoclasts within bone marrow.

Rheumatology meets radiology in the hot soup of Gutta

If left untreated, gout may result in radiographic abnormalities, that is, cartilage loss and periarticular osteopenia plus more-or-less gout-specific radiographic abnormalities: spurs, sclerosis, and periostal new bone formation. In the current issue, Dalbeth and colleagues describe findings from about 800 joints in 20 mostly tophaceous patients, which can help clinicians to identify osteopathologic gout: spurs, osteosclerosis, ankylosis and periostal new bone formation, all symptoms of advanced, untreated gout. These are hallmarks of chronic untreated gout and are to be prevented.

Adipokines in psoriatic arthritis patients: the correlations with osteoclast precursors and bone erosions

Significant bone remodeling with disordered osteoclastogenesis has been implicated in the pathogenesis of psoriatic arthritis (PsA). And there is a high prevalence of the metabolic syndrome (MS) in PsA patients. Adipokines, especially leptin and adiponectin, have recently been reported to be involved in the development and regulation of some autoimmune diseases. In this study, we examined the alternation of circulating osteoclastogenesis related cytokines [tumor necrosis factor-α (TNF-α), osteoprotegerin (OPG) and receptor activator of nuclear factor-κB ligand (RANKL)] and adipokines (leptin, adiponectin, resistin, chemerin, omentin) in PsA patients, and analysed the correlations between these factors and osteoclast precursors numbers, radiographic damage scores, and disease activity index. 41 PsA patients, 20 psoriasis patients, and 24 healthy controls were recruited. Blood samples were obtained for detecting the levels of TNF-α, OPG, RANKL and the adipokines. The numbers of osteoclast precursors (OCs) in peripheral blood were assessed. Radiographs of affected joints in PsA patients were scored for erosion, joint-space narrowing, osteolysis, and new bone formation. Compared with healthy controls, patients with PsA had higher TNF-α, RANKL, OCs, leptin and omentin but lower adiponectin and chemerin. Increased serum levels of TNF-α, RANKL, leptin, and omentin were positively correlated with OCs numbers. In contrast, serum adiponectin levels were decreased in PsA patients and negatively correlated with OCs numbers. TNF-α, RANKL and leptin were positively correlated with Psoriatic Arthritis Joint Activity Index (PsAJAI). Only TNF-α was positively correlated with radiographic damage scores. Our data demonstrated that systemic expression of soluble mediators of osteoclastogenesis and adipokines were disordered in PsA. Certain adipokines were elevated in the circulation of patients with PsA and might contribute to pathogenesis of arthritis. Prospective studies will be of interest to determine the pluripotent effects of adipokines on osteoclastogenesis in chronic inflammatory rheumatic diseases. Future studies may lead to novel therapeutic strategies.

Characterization of new bone formation in gout: a quantitative site-by-site analysis using plain radiography and computed tomography

INTRODUCTION

Radiographic descriptions of gout have noted the tendency to hypertrophic bone changes. The aim of this study was to characterize the features of new bone formation (NBF) in gout, and to determine the relationship between NBF and other radiographic features of disease, particularly erosion and tophus.

METHODS

Paired plain radiographs (XR) and computed tomography (CT) scans of 798 individual hand and wrist joints from 20 patients with gout were analyzed. Following a structured review of a separate set of images, films were scored for the presence of the following features of NBF: spur, osteophyte, periosteal NBF, ankylosis and sclerosis. The relationship between NBF and other radiographic features was analyzed.

RESULTS

The most frequent forms of NBF were bone sclerosis and osteophyte. Spur and periosteal NBF were less common, and ankylosis was rare. On both XR and CT, joints with bone erosion were more likely to have NBF; for CT, if erosion was present, the odds ratios (OR) was 45.1 for spur, 3.3 for osteophyte, 16.6 for periosteal NBF, 26.6 for ankylosis and 32.3 for sclerosis, P for all < 0.01. Similarly, on CT, joints with intraosseous tophus were more likely to have NBF; if tophus was present, the OR was 48.4 for spur, 3.3 for osteophyte, 14.5 for periosteal NBF, 35.1 for ankylosis and 39.1 for sclerosis; P for all < 0.001.

CONCLUSIONS

This detailed quantitative analysis has demonstrated that NBF occurs more frequently in joints affected by other features of gout. This work suggests a connection between bone loss, tophus, and formation of new bone during the process of joint remodelling in gout.

The epidemiology and treatment of gout

The development and expression of gout depends on three key steps: (1) chronic hyperuricemia, (2) the growth of monosodium urate (MSU) crystals, and (3) interaction between MSU crystals and the inflammatory system. Epidemiological studies have continued to improve our understanding of the environmental and genetic factors which influence chronic hyperuricemia and gout. The influence of obesity, alcohol, race, sex, age, and specific dietary components will be discussed below. The primary mechanism of hyperuricemia is insufficient renal clearance of uric acid which in turn is dependent on transport of uric acid in the proximal renal tubule. Knowledge of the transport mechanisms has improved understanding of the genetic influences on gout and is relevant to understanding of the effects of drugs which can increase or decrease renal uric acid clearance. The application of established principles of management including diagnosis through crystal identification, the gradual introduction of hypouricemic therapy with the use of prophylaxis to reduce the risk of flares, identification of a suitably low target of plasma urate, a progressive increase in therapy to achieve the target and taking steps to encourage good compliance, has the potential to improve outcomes for patients with this very common affliction. The potential role for new therapies will also be discussed.

T cells as key players for bone destruction in gouty arthritis?

The deposition of monosodium urate (MSU) crystals in synovial fluid and tissue leads to gouty arthritis frequently associated with synovial inflammation and bone erosions. The cellular mechanism that links MSU crystals to an increased number of osteoclasts has not yet been fully understood. In a recent issue of Arthritis Research & Therapy Lee and colleagues proposed that bone destruction in chronic gouty arthritis is at least in part dependent on expression by T cells of receptor activator of NF-κB ligand (RANKL). The authors showed that pro-resorptive cytokines such as IL-1β, IL-6, and TNFα are expressed within tophi and stromal infiltrates. In vitro stimulation with MSU crystals revealed monocytes as a source for these cytokines, whereas T cells produce RANKL, the major trigger of osteoclastogenesis.

Lineage-committed osteoclast precursors circulate in blood and settle down into bone

Osteoclasts are derived from the monocyte/macrophage lineage, but little is known about osteoclast precursors in circulation. We previously showed that cell cycle-arrested quiescent osteoclast precursors (QOPs) were detected along bone surfaces as direct osteoclast precursors. Here we show that receptor activator of NF-κB (RANK)-positive cells isolated from bone marrow and peripheral blood possess characteristics of QOPs in mice. RANK-positive cells expressed c-Fms (receptors of macrophage colony-stimulating factor) at various levels, but scarcely expressed other monocyte/granulocyte markers. RANK-positive cells failed to exert phagocytic and proliferating activities, and differentiated into osteoclasts but not into dendritic cells. To identify circulating QOPs, collagen disks containing bone morphogenetic protein-2 (BMP disks) were implanted into mice, which were administered bromodeoxyuridine daily. Most nuclei of osteoclasts detected in BMP-2-induced ectopic bone were bromodeoxyuridine-negative. RANK-positive cells in peripheral blood proliferated more slowly and had a much longer lifespan than F4/80 (a macrophage marker)-positive macrophages. When BMP disks and control disks were implanted in RANK ligand-deficient mice, RANK-positive cells were observed in the BMP disks but not in the controls. F4/80-positive cells were distributed in both disks. Administration of FYT720, a sphingosine 1-phosphate agonist, promoted the egress of RANK-positive cells from hematopoietic tissues into bloodstream. These results suggest that lineage-determined QOPs circulate in the blood and settle in the bone.

Imaging in gout--what can we learn from MRI, CT, DECT and US?

There are many exciting new applications for advanced imaging in gout. These modalities employ multiplanar imaging and allow computerized three-dimensional rendering of bone and joints (including tophi) and have the advantage of electronic data storage for later retrieval. High-resolution computed tomography has been particularly helpful in exploring the pathology of gout by investigating the relationship between bone erosions and tophi. Magnetic resonance imaging and ultrasonography can image the inflammatory nature of gouty arthropathy, revealing synovial and soft tissue inflammation, and can provide information about the composition and vascularity of tophi. Dual-energy computerized tomography is a new modality that is able to identify tophi by their chemical composition and reveal even small occult tophaceous deposits. All modalities are being investigated for their potential roles in diagnosis and could have important clinical applications in the patient for whom aspiration of monosodium urate crystals from the joint is not possible. Imaging can also provide outcome measures, such as change in tophus volume, for monitoring the response to urate-lowering therapy and this is an important application in the clinical trial setting.

Bone destruction by receptor activator of nuclear factor κB ligand-expressing T cells in chronic gouty arthritis

INTRODUCTION

The purpose of this study was to analyze the cellular expressions of pro-resorptive cytokines in gouty tophus tissues, to determine the capacity of monosodium urate monohydrate (MSU) crystals to induce these cytokines, and to understand the mechanisms of bone destruction in chronic gout.

METHODS

Fourteen fixed, paraffin-embedded, uninfected tophus samples were analyzed immunohistochemically. Peripheral blood mononuclear cells (PBMCs) were cultured in vitro with MSU crystals, and gene expression was assessed by reverse transcription-polymerase chain reaction. In vitro osteoclastogenesis was performed using PBMCs and synovial fluid mononuclear cells (SFMCs).

RESULTS

CD4+ T cells, CD8+ T cells, CD20+ B cells and mast cells infiltrated tophus tissues. Tartrate-resistant acid phosphatase (TRAP)+ osteoclasts were present around tophi and in osteolytic lesions. Interleukin (IL)-1, IL-6 and tumor necrosis factor (TNF)-alpha were produced from infiltrated mononuclear cells, whereas receptor activator of nuclear factor κB ligand (RANKL) was strongly expressed in T cells. However, osteoprotegerin (OPG) was not or was weakly expressed in tophus tissues. MSU crystals induced the expressions of IL-1, IL-6, TNF-alpha and RANKL in PBMCs, but inhibited OPG expression. In addition, the pro-resorptive cytokines were highly expressed in SFMCs of gouty arthritis patients. Furthermore, in vitro osteoclastogenesis was enhanced in SFMC cultures, but inhibited in T cell-depleted SFMC cultures.

CONCLUSIONS

Our study demonstrates that RANKL-expressing T cells and TRAP+ osteoclasts are present within gouty tophus tissues, and that infiltrating cells express pro-resorptive cytokines. Furthermore, our data show that MSU crystals have the potential to induce pro-resorptive cytokines, and T cells are involved in osteoclastogenesis in chronic gout.

Osteoblast retraction induced by adherent neutrophils promotes osteoclast bone resorption: implication for altered bone remodeling in chronic gout

Bone destruction in chronic gout is correlated with deposits of monosodium urate (MSU) crystals. Bone with MSU tophi were histopathologically shown to have altered remodeling and cellular distribution. We investigated the impact of neutrophils in bone remodeling associated with MSU and demonstrated that neutrophils, through elastase localized at their surface, induced retraction of confluent osteoblasts (OBs) previously layered on calcified matrix. This OB retraction allowed osteoclasts to resorb cell-free areas of the matrix. This neutrophil effect was concentration dependent and time dependent and required direct contact with OBs. Exposure of OBs to MSU greatly promoted neutrophil adherence to OBs. Neutrophil membrane at the contact zone with OBs showed concentrated fluorescence of dye PKH-67, indicating a cellular contact. Neutrophil-OB interaction increased the survival of neutrophils, reduced their release of lactoferrin in presence of MSU and did not change OB-mediated mineralization. The adhesion of neutrophils to OBs was heterotypic through neutrophil CD29/CD49d and OB-fibronectin peptide CS1. Leukotriene B₄ (LTB₄) and platelet-activating factor (PAF) were also involved in neutrophil adherence to OBs, as shown by the blocking effect of selective LTB₄ and PAF receptor antagonists, and a cytosolic phospholipase A(2α) (cPLA(2α)) inhibitor. Blockade of CD49d/CS1 and inhibition of the cPLA(2α) had subadditive effects, reducing by 60% the adherence of neutrophils to OBs. Taken together, these data showed that neutrophil adhesion to MSU-activated OBs was mediated by the β₁ integrin CD29/CD49d-fibronectin peptide CS1 receptors and cPLA(2α)-derived metabolites and impacts on OB and osteoclast functions. These interactions could be involved in the local bone remodeling process of gout.

Serum uric acid is associated with bone health in older men: a cross-sectional population-based study

Serum uric acid (UA) is a strong endogenous antioxidant. Since oxidative stress has been linked to osteoporosis, we examined the association between serum UA levels and bone mineral density (BMD), prevalent vertebral and nonvertebral fractures, and laboratory measures such as calcitropic hormones and bone turnover marker levels. This cross-sectional analysis consisted of 1705 community-dwelling men aged 70 years or over who participated in the baseline part of the Concord Health and Ageing in Men Project (CHAMP), a population-based study of older men in Sydney, Australia. BMD at all sites was significantly higher among men with serum UA levels above the group median than among men with UA levels below the median. In multiple regression analyses adjusted for potential confounders, serum UA remained associated with BMD at all sites (β = 0.12 to 0.14, p < .001), serum calcium (β = 0.11, p = .001), parathyroid hormone (β = 0.09, p = .002), 25-hydroxyvitamin D (β = 0.09, p = .005), and was negatively associated with urinary excretion amino-terminal cross-linked telopeptide of type 1 collagen (β = -0.09, p = .006). Overall, serum UA accounted for 1.0% to 1.44% of the variances in BMD (R(2)  = 0.10 to 0.22). In multiple logistic regression analyses, above-median serum UA levels were associated with a lower prevalence of osteoporosis at the femoral neck [odds ratio (OR) = 0.42, 95% confidence interval (CI) 0.22-0.81, p = .010) and lumbar spine (OR = 0.44, 95% CI 0.23-0.86, p = .016) and a lower prevalence of vertebral (OR = 0.62, 95% CI 0.43-0.91, p = .015) and nonvertebral (OR = 0.51, 95% CI 0.29-0.89, p = .018) fractures. In conclusion, higher serum UA levels are associated with higher BMD at all skeletal sites and with a lower prevalence of vertebral and nonvertebral fractures in older men.

Total ankle replacement in patients with gouty arthritis

BACKGROUND

Gout is the most common cause of inflammatory arthritis in men and older women. The purpose of this review was to assess prosthetic component stability, postoperative pain relief, functional outcome, and quality of life of patients with gouty ankle arthritis who were treated with total ankle replacement.

METHODS

Sixteen patients (nineteen ankles) with chronic gout and a mean age (and standard deviation) of 65.2 ± 5.5 years were treated with a non-constrained three-component total ankle arthroplasty because of painful ankle arthritis. The average duration of follow-up was 5.1 ± 2.5 years. Component stability was assessed with use of weight-bearing radiographs. Clinical outcomes were analyzed with use of a visual analogue scale (VAS) for pain, a 36-item short-form health survey (SF-36), and the American Orthopaedic Foot & Ankle Society (AOFAS) hindfoot score.

RESULTS

There were no intraoperative complications. In one patient, both arthroplasties were revised 4.7 years postoperatively because of painful prosthetic loosening. The average VAS score for pain decreased significantly from 7.5 ± 1.8 (range, 5 to 10) to 1.2 ± 1.3 (range, 0 to 3) (p < 0.001). All eight categories of the SF-36 score showed significant improvement (all p < 0.001). The average AOFAS hindfoot score increased significantly from 38 ± 15 (range, 15 to 77) preoperatively to 75 ± 13 (range, 54 to 92) postoperatively (p < 0.001).

CONCLUSIONS

Total ankle replacement in patients with painful gouty ankle arthritis is associated with a low risk of intraoperative and postoperative complications and leads to significant pain relief, high patient satisfaction, and good functional results.

Radiographic bone damage in chronic gout is negatively associated with the inflammatory cytokines soluble interleukin 6 receptor and osteoprotegerin

OBJECTIVE

We investigated the risk factors for radiographic bone damage to foot joints in patients with chronic gout among various patient characteristics and serum inflammatory cytokines such as interleukin 1ß (IL-1ß), IL-6, soluble IL-6 receptor (sIL-6R), osteoprotegerin (OPG), and receptor activator of nuclear factor-κB ligand (RANKL).

METHODS

Fifty consecutive male patients with gout and 54 age-matched healthy male controls were enrolled. Serum levels of cytokines including IL-1ß, IL-6, sIL-6R, OPG, and RANKL were measured using ELISA. Radiographic damage indices including erosion scores, narrowing scores, and total scores for foot joints were assessed according to a modified Sharp-van der Heijde system.

RESULTS

There were significant differences in serum IL-1ß, IL-6, sIL-6R, OPG, and RANKL levels between patients with gout and the controls, after adjustment for confounding factors such as age, body mass index, blood urea nitrogen, creatinine, triglyceride, and fasting blood glucose (p = 0.034 for IL-1ß, p < 0.001 for IL-6, p = 0.040 for sIL-6R, p = 0.002 for OPG, and p = 0.018 for RANKL). Radiographic damage indices (erosion, narrowing, and total scores) were negatively associated with serum sIL-6R and OPG levels in multivariable-adjusted regression analysis. Serum sIL-6R levels in patients without radiographic damage were higher than in those with damage (p = 0.006).

CONCLUSION

Radiographic damage in patients with chronic gouty arthritis was negatively associated with serum sIL-6R and OPG. Further study on the role of inflammatory cytokines in the pathogenesis of radiographic damage in gout is needed.

Alendronate reduces osteoclast precursors in osteoporosis

This study evaluates the effect of alendronate on osteoclastogenesis, cytokine production, and bone resorption in postmenopausal women. We suggest that it acts on mature bone resorbing osteoclasts after 3 months of treatment, whereas, after 1 year, it diminishes their formation by reducing their precursors and serum RANKL.

INTRODUCTION

Osteoclasts are the target cells of bisphosphonates, though the most drug-sensitive steps of their formation and activity have not been determined. The present study evaluates the effect of alendronate on osteoclastogenesis, cytokine production, and bone resorption in postmenopausal women.

METHODS

The study was conducted on 35 osteoporotic women; 15 were pretreated with alendronate 70 mg/week, whereas, 20 were treated with calcium 1 g/day and vitamin D 800 IU/day. After 3 months, 30 received alendonate 70/mg, vitamin D 2800 IU/week, and calcium 1 g/day for 12 months (combined therapy), whereas, the other five patients remained on calcium 1 g/day and vitamin D 800 IU/day. The following parameters were assessed before and after therapy: changes in bone resorption markers, circulating osteoclast precursors, formation of osteoclasts in peripheral blood mononuclear cell cultures, their viability, and variations in cytokines production.

RESULTS

After 3 months of alendronate, there was no significant reduction in the number of osteoclast precursors, osteoclast formation and viability, and cytokine levels, whereas, there was a significant reduction of bone resorption markers. One year of the combined therapy, on the other hand, reduced osteoclast precursors, osteoclast formation, and serum RANKL, whereas, calcium plus vitamin D alone had no effect.

CONCLUSIONS

We suggest that alendronate mainly acts on mature bone resorbing osteoclasts in the short term, whereas, its long-term administration diminishes their formation by reducing their precursors and serum RANKL.

Circulating mediators of bone remodeling in psoriatic arthritis: implications for disordered osteoclastogenesis and bone erosion

Introduction

Diverse bone pathologies are observed in patients with psoriatic arthritis (PsA). Uncoupling of bone remodeling with disordered osteoclastogenesis has been implicated in the pathogenesis of PsA. The aim of this study was to examine the role of soluble mediators of bone remodeling within the circulation of patients with PsA.

Methods

Patients with PsA (n = 38), with psoriasis (n = 10), and healthy controls (n = 12) were studied. Serum was obtained for testing of Dikkopf-1 (Dkk-1), macrophage-colony stimulating factor (M-CSF), osteoprotegerin (OPG), and receptor activator of nuclear factor-κB ligand (RANKL) with ELISA. Patients with PsA also had bone densitometry, plain radiographs of the hands and feet, and assessment of peripheral blood osteoclast precursors. Radiographs were scored for erosion, joint-space narrowing, osteolysis, and new bone formation.

Results

Compared with those with psoriasis and healthy controls, patients with PsA had higher circulating concentrations of Dkk-1 and M-CSF. In patients with PsA, M-CSF and RANKL, but not Dkk-1, concentrations positively correlated with radiographic erosion, joint-space narrowing, and osteolysis scores. Mediators of bone remodeling did not correlate with the number of joints with new bone formation or with total hip-bone mineral density. Peripheral blood CD14⁺/CD11b⁺ cells, and the number of osteoclast-like cells and resorptive pits after culture with RANKL and M-CSF also correlated with radiographic damage scores. Circulating M-CSF concentrations correlated with the percentage of peripheral blood CD14⁺/CD11b⁺ cells.

Conclusions

Systemic expression of soluble factors that promote osteoclastogenesis is disordered in patients with PsA and may contribute to periarticular bone loss in this disease.

Management of gout: beyond allopurinol

The basic concepts of the pathogenesis and management of gout have not altered for many years. Monosodium urate monohydrate crystals drive the disease and identification of these crystals is required for certain diagnosis. In contrast, our understanding of the mediators of gouty inflammation, the appropriate target serum urate concentration during treatment, the drugs available and the best ways to use those drugs have all advanced in recent years and will be the focus of this review.

Cellular characterization of the gouty tophus: a quantitative analysis

OBJECTIVE

To characterize the cellular architecture of the tophus and to determine the presence of cytokines implicated in the initiation and resolution of gouty inflammation.

METHODS

Sixteen fixed, paraffin-embedded, uninfected tophus samples were surgically obtained from 12 patients with microscopically proven gout and were analyzed by quantitative immunohistochemistry. The number of cells present in the corona and fibrovascular zones of the tophus was analyzed by Genmod mixed models analysis.

RESULTS

Numerous CD68+ mononucleated and multinucleated cells were present within the corona zone. Mast cells were identified in all tophus samples and at similar densities throughout the corona and fibrovascular zones. In contrast, neutrophils were rarely observed. Plasma cells were present in very high numbers within the corona zone. The overall number of CD20+ B cells was much lower. However, in 6 of 12 patients (50%), at least 1 B cell aggregate was present in the fibrovascular zone. Large numbers of cells expressing interleukin-1beta (IL-1beta) were observed in the corona zone. Transforming growth factor beta1 (TGFbeta1)-expressing mononucleated cells were also identified. The number of CD68+ cells correlated with the number of cells expressing IL-1beta (r = 0.691, P = 0.009) and the number expressing TGFbeta1 (r = 0.518, P = 0.04).

CONCLUSION

The tophus represents a complex and organized chronic inflammatory tissue response to monosodium urate monohydrate crystals involving both innate and adaptive immune cells. The coexpression of IL-1beta and TGFbeta1 suggests that both proinflammatory and antiinflammatory factors present within the tophus contribute to a cycle of chronic inflammation, attempted resolution, and tissue remodeling.