Ashika Chhana

Monosodium urate monohydrate crystals inhibit osteoblast viability and function: implications for development of bone erosion in gout

Background Bone erosion is a common manifestation of chronic tophaceous gout. Objectives To investigate the effects of monosodium urate monohydrate (MSU) crystals on osteoblast viability and function. Methods The MTT assay and flow cytometry were used to assess osteoblast cell viability in the MC3T3-E1 and ST2 osteoblast-like cell lines, and primary rat and primary human osteoblasts cultured with MSU crystals. Quantitative real-time PCR and von Kossa stained mineralised bone formation assays were used to assess the effects of MSU crystals on osteoblast differentiation using MC3T3-E1 cells. The numbers of osteoblasts and bone lining cells were quantified in bone samples from patients with gout. Results MSU crystals rapidly reduced viability in all cell types in a dose-dependent manner. The inhibitory effect on cell viability was independent of crystal phagocytosis and was not influenced by differing crystal length or addition of serum. Long-term culture of MC3T3-E1 cells with MSU crystals showed a reduction in mineralisation and decreased mRNA expression of genes related to osteoblast differentiation such as Runx2, Sp7 (osterix), Ibsp (bone sialoprotein), and Bglap (osteocalcin). Fewer osteoblast and lining cells were present on bone directly adjacent to gouty tophus than bone unaffected by tophus in patients with gout. Conclusions MSU crystals have profound inhibitory effects on osteoblast viability and differentiation. These data suggest that bone erosion in gout occurs at the tophus–bone interface through alteration of physiological bone turnover, with both excessive osteoclast formation, and reduced osteoblast differentiation from mesenchymal stem cells.

Mechanisms of joint damage in gout: evidence from cellular and imaging studies

The clinical course of gout is initially characterized by acute self-limited joint inflammation, but long-standing disease is often associated with chronic inflammation followed by the development of erosive joint damage, which can result in long-term functional impairment. Preventing joint damage is now a major focus of therapeutic intervention in gout. New light has been shed on the mechanisms leading to cartilage and bone damage in patients with this disease. Here, we discuss basic science studies focusing on the cellular immunology of bone and cartilage in gout and the effects of monosodium urate crystals on signaling pathways, cytokine release and the function of osteoclasts, osteoblasts and chondrocytes. We then explore the use of advanced imaging modalities (including MRI, ultrasonography, CT and dual-energy CT) to investigate pathology in gout, as they provide new ways to visualize joint tissues. These modalities vary in their ability to detect the various pathological features of gout and have different clinical applications. Imaging provides information about the inflammatory nature of the joint lesion, position and size of tophaceous deposits, and extent of bone and cartilage damage. Imaging is also increasingly being used to monitor the progression of joint damage and regression of tophi with effective urate-lowering therapy.

Molecular mechanisms involved in the mitogenic effect of lactoferrin in osteoblasts

Lactoferrin, an iron-binding glycoprotein present in milk and other exocrine secretions in mammals, is anabolic to bone at physiological concentrations. Lactoferrin stimulates the proliferation, differentiation and survival of osteoblasts, as well as potently inhibiting osteoclastogenesis in bone marrow cultures. In the current study we further investigated the mechanism of action of lactoferrin in osteoblasts. We used low-density arrays to measure the level of expression of 45 genes in MC3T3-E1 osteoblast-like cells treated with lactoferrin, and identified transient, dose-dependent increases in the transcription levels of interleukin-6, of the pro-inflammatory factor prostaglandin-endoperoxide synthase 2 (Ptgs2), and of the transcription factor nuclear factor of activated T cells (Nfatc1). We demonstrated similar changes in primary osteoblast cultures from human and rat. Levels of prostaglandin E2 were increased in conditioned media collected from osteoblasts treated with lactoferrin, indicating that the activity of the enzyme cyclooxygenase 2 (COX2), which is encoded by Ptgs2, was also up-regulated. Using a luciferase reporter construct we showed that lactoferrin induced transcription from the NFAT consensus sequence. We found that inhibiting either COX2 or NFATc1 activity blocked the mitogenic effect of lactoferrin in osteoblasts and that inhibition of NFATc1 activity partially blocked the transcriptional activation of Ptgs2. Our study has provided the first evidence that COX2 and NFATc1 activities are increased by lactoferrin, and demonstrated a role for each of these molecules as mediators of the mitogenic effects of lactoferrin in osteoblasts.

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.

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.

Structural Joint Damage in Gout

This article summarizes the structural damage that is observed in advanced gout and current understanding of the mechanisms by which this damage occurs. Interactions between monosodium urate crystals and cells within the joint are described as well as knowledge gained from imaging studies. Future research directions and potential therapeutic strategies for the prevention and treatment of joint damage in gout are also discussed.

Zoledronate for prevention of bone erosion in tophaceous gout: a randomised, double-blind, placebo-controlled trial

Objectives The osteoclast has been implicated in development of bone erosion in gout. The aim of this study was to determine whether zoledronate, a potent antiosteoclast drug, influences bone erosion in people with tophaceous gout. Methods This was a 2-year, randomised, double-blind, placebo-controlled trial of 100 people with tophaceous gout. Participants were randomised to annual administration of 5 mg intravenous zoledronate or placebo. The primary endpoint was change in the foot CT bone erosion score from baseline. Secondary endpoint was change in plain radiographic damage scores. Other endpoints were change in bone mineral density (BMD), bone turnover markers and the OMERACT-endorsed core domains for chronic gout studies. Results There was no change in CT erosion scores over 2 years, and no difference between the two treatment groups at Year 1 or 2 (p(treat)=0.10, p(time)=0.47, p(treat*time)=0.23). Similarly, there was no change in plain radiographic scores over 2 years, and no difference between the two groups at Year 1 or 2. By contrast, zoledronate increased spine, neck of femur, total hip and total body BMD. Zoledronate therapy also reduced the bone turnover markers P1NP and β-CTX compared with placebo. There was no difference between treatment groups in OMERACT-endorsed core domains. Conclusions Despite improvements in BMD and suppression of bone turnover markers, antiosteoclast therapy with zoledronate did not influence bone erosion in people with tophaceous gout. These findings suggest a disconnect between responses in the healthy skeleton and at sites of focal bone erosion in tophaceous gout.

Advanced imaging assessment of gout: comparison of dual-energy CT and MRI with anatomical pathology

Dual-energy CT (DECT) and MRI are advanced imaging methods used to visualise gout pathology. DECT can identify monosodium urate (MSU) crystals in people with gout,1 ,2 and also has conventional CT properties, allowing assessment of tophus and bone pathology.3 ,4 MRI is used to assess inflammation, bone erosion and cartilage damage in gout.5–7 This study aimed to compare DECT and MRI with corresponding anatomical pathology in the assessment of gout. Cadaveric joint specimens were obtained from two donors; a donor aged 82 years with crystal-proven tophaceous gout and a control donor aged 89 years without gout (12 joints from each). All joints were scanned by DECT (SOMATOM Definition Flash, Siemens Medical, Erlangen, Germany) and MRI (3T MAGNETOM Skyra, Siemens Medical), and then processed for histology, including digital photography of sectioned digits (sagittal plane) for macroscopic analysis, and preparation of histology slides from each individual joint for microscopic analysis. Slides were stained with H&E or 1% toluidine blue. Collection and use of cadaveric tissue was in accordance with the New Zealand Human Tissue Act 2008. All images and histology data were systematically assessed for gout pathology by experienced readers who were blinded to diagnosis and each others scores. …

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.

Monosodium urate crystals reduce osteocyte viability and indirectly promote a shift in osteocyte function towards a proinflammatory and proresorptive state

BackgroundBone erosion is a frequent complication of gout and is strongly associated with tophi, which are lesions comprising inflammatory cells surrounding collections of monosodium urate (MSU) crystals. Osteocytes are important cellular mediators of bone remodeling. The aim of this study was to investigate the direct effects of MSU crystals and indirect effects of MSU crystal-induced inflammation on osteocytes.MethodsFor direct assays, MSU crystals were added to MLO-Y4 osteocyte cell line cultures or primary mouse osteocyte cultures. For indirect assays, the RAW264.7 macrophage cell line was cultured with or without MSU crystals, and conditioned medium from these cultures was added to MLO-Y4 cells. MLO-Y4 cell viability was assessed using alamarBlue® and LIVE/DEAD® assays, and MLO-Y4 cell gene expression and protein expression were assessed by real-time polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA), respectively. Histological analysis was used to examine the relationship between MSU crystals, inflammatory cells, and osteocytes in human joints affected by tophaceous gout.ResultsIn direct assays, MSU crystals reduced MLO-Y4 cell and primary mouse osteocyte viability but did not alter MLO-Y4 cell gene expression. In contrast, conditioned medium from MSU crystal-stimulated RAW264.7 macrophages did not affect MLO-Y4 cell viability but significantly increased MLO-Y4 cell expression of osteocyte-related factors including E11, connexin 43, and RANKL, and inflammatory mediators such as interleukin (IL)-6, IL-11, tumor necrosis factor (TNF)-α and cyclooxygenase-2 (COX-2). Inhibition of COX-2 in MLO-Y4 cells significantly reduced the indirect effects of MSU crystals. In histological analysis, CD68+ macrophages and MSU crystals were identified in close proximity to osteocytes within bone. COX-2 expression was also observed in tophaceous joint samples.ConclusionsMSU crystals directly inhibit osteocyte viability and, through interactions with macrophages, indirectly promote a shift in osteocyte function that favors bone resorption and inflammation. These interactions may contribute to disordered bone remodeling in gout.