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Basic Calcium Phosphate Crystals Induce Monocyte/Macrophage IL-1β Secretion through the NLRP3 Inflammasome In Vitro

Basic calcium phosphate (BCP) crystals are associated with severe osteoarthritis and acute periarticular inflammation. Three main forms of BCP crystals have been identified from pathological tissues: octacalcium phosphate, carbonate-substituted apatite, and hydroxyapatite. We investigated the proinflammatory effects of these BCP crystals in vitro with special regard to the involvement of the NLRP3–inflammasome in THP-1 cells, primary human monocytes and macrophages, and mouse bone marrow-derived macrophages (BMDM). THP-1 cells stimulated with BCP crystals produced IL-1β in a dose-dependent manner. Similarly, primary human cells and BMDM from wild-type mice also produced high concentrations of IL-1β after crystal stimulation. THP-1 cells transfected with short hairpin RNA against the components of the NLRP3 inflammasome and mouse BMDM from mice deficient for NLRP3, apoptosis-associated speck-like protein, or caspase-1 did not produce IL-1β after BCP crystal stimulation. BCP crystals induced macrophage apoptosis/necrosis as demonstrated by MTT and flow cytometric analysis. Collectively, these results demonstrate that BCP crystals induce IL-1β secretion through activating the NLRP3 inflammasome. Furthermore, we speculate that IL-1 blockade could be a novel strategy to inhibit BCP-induced inflammation in human disease.

Octacalcium phosphate crystals directly stimulate expression of inducible nitric oxide synthase through p38 and JNK mitogen-activated protein kinases in articular chondrocytes

Basic calcium phosphate (BCP) crystals, including hydroxyapatite, octacalcium phosphate (OCP) and carbonate-apatite, have been associated with severe osteoarthritis and several degenerative arthropathies. Most studies have considered the chondrocyte to be a bystander in the pathogenesis of calcium crystal deposition disease, assuming that synovial cell cytokines were the only triggers of chondrocyte activation. In the present study we identified direct activation of articular chondrocytes by OCP crystals, which are the BCP crystals with the greatest potential for inducing inflammation. OCP crystals induced nitric oxide (NO) production and inducible nitric oxide synthase (NOS) mRNA expression by isolated articular chondrocytes and cartilage fragments, in a dose-dependent manner and with variations over time. OCP crystals also induced IL-1β mRNA expression. Using pharmacological and cytokine inhibitors, we observed that OCP crystals induced NO production and inducible NOS mRNA activation were regulated at both the transcriptional and the translational levels; were independent from IL-1β gene activation; and involved p38 and c-Jun amino-terminal kinase (JNK) mitogen-activated protein kinase (MAPK) pathways, as further confirmed by OCP crystal-induced p38 and JNK MAPK phosphorylation. Taken together, our data suggest that the transcriptional inducible NOS response to OCP crystals involved both the p38 and the JNK MAPK pathways, probably under the control of activator protein-1. NO, a major mediator of cartilage degradation, can be directly produced by BCP crystals in chondrocytes. Together with synovial activation, this direct mechanism may be important in the pathogenesis of destructive arthropathies triggered by microcrystals.

Inhibition of bone resorption blunts osteoarthritis in mice with high bone remodelling.

Background Osteoarthritis (OA) is characterised by cartilage degradation and bone lesions. Subchondral bone may be involved in the pathogenesis of cartilage matrix breakdown. Objective To assess the role of bone remodelling in OA by studying the effect of bisphosphonate on OA development in mice with high bone remodelling. Methods Mice overexpressing Runx2 (Runx2-Tg) under the control of collagen type I that displayed high bone remodelling were used. Joint instability was performed by partial medial meniscectomy to induce OA. Results Six weeks after surgery, tibial cartilage of Runx2-Tg mice displayed an increased number of ADAMTS-4- and ADAMTS-5-expressing chondrocytes compared with controls (p<0.05). This increase was higher in Runx2-Tg mice than in wild-type mice, although their OA score did not differ (2.5±0.6 vs 2.4±0.2, P=NS). Pamidronate reduced the OA score in Runx2-Tg mice but not in wild-type littermates (1.2±0.5 vs 2.7±0.4; p<0.05) despite the reduction of bone resorption and of the expression of cartilage proteases in both genotypes. Conclusions These findings support the hypothesis that the level of bone resorption influences cartilage metabolism and that inhibition might prevent the progression of OA. Targeting bone resorption might therefore provide an approach to the treatment of high bone resorbing forms of OA.

Advances in understanding calcium-containing crystal disease.

Purpose of reviewCalcium pyrophosphate dihydrate and basic calcium phosphate crystals are the two most common calcium-containing crystals involved in rheumatic diseases. Recent literature concerning their role in the pathogenesis of osteoarthritis is reviewed. Recent findingsIn some instances, these calcium crystals might worsen osteoarthritis cartilage destruction. Laboratory investigations have identified determinants of cartilage calcification, especially a better characterization of matrix vesicle content and a better understanding of the regulation of inorganic pyrophosphate and phosphate concentration. In-vitro studies have highlighted new pathogenic mechanisms of calcium crystal-induced cell activation. Several intracellular signalling pathways are activated by calcium crystals. Recent studies suggested the implication of the inflammasome complex and a pivotal role for IL-1 in pseudogout attacks and chondrocyte apoptosis in basic calcium phosphate crystal-related arthropathies. SummaryAnimal models of osteoarthritis and in-vitro studies using calcium pyrophosphate dihydrate and basic calcium phosphate crystals will improve our knowledge of these common crystals and could suggest new targets for drugs, as these common diseases are ‘orphan’ with respect to therapy.

Efficacy of anakinra in gouty arthritis: a retrospective study of 40 cases

IntroductionGout is a common arthritis that occurs particularly in patients who frequently have associated comorbidities that limit the use of conventional therapies. The main mechanism of crystal-induced inflammation is interleukin-1 production by activation of the inflammasome. We aimed to evaluate the efficacy and tolerance of anakinra in gouty patients.MethodsWe conducted a multicenter retrospective review of patients receiving anakinra for gouty arthritis. We reviewed the response to treatment, adverse events and relapses.ResultsWe examined data for 40 gouty patients (32 men; mean age 60.0 ± 13.9 years) receiving anakinra. Mean disease duration was 8.7 ± 8.7 years. All patients showed contraindications to and/or failure of at least two conventional therapies. Most (36; 90%) demonstrated good response to anakinra. Median pain on a 100-mm visual analog scale was rapidly decreased (73.5 (70.0 to 80.0) to 25.0 (20.0 to 32.5) mm, P <0.0001), as was median C-reactive protein (CRP) level (130.5 (55.8 to 238.8) to 16.0 (5.0 to 29.5) mg/l, P <0.0001). After a median follow-up of 7.0 (2.0 to 13.0) months, relapse occurred in 13 patients after a median delay of 15.0 (10.0 to 70.0) days. Seven infectious events, mainly with long-term use of anakinra, were noted.ConclusionsAnakinra may be efficient in gouty arthritis, is relatively well tolerated with short-term use, and could be a relevant option in managing gouty arthritis when conventional therapies are ineffective or contraindicated. Its long-term use could be limited by infectious complications.

Scleritis: A Paradoxical Effect of Etanercept? Etanercept-associated Inflammatory Eye Disease

Objective. To describe 3 cases of scleritis associated with etanercept use for rheumatoid arthritis (RA) and to review the literature related to inflammatory eye diseases associated with the use of etanercept. Methods. Three cases of severe scleritis during etanercept therapy were analyzed. A systematic review of the literature in PubMed, Embase, and the Cochrane Library was performed, from 1962 to July 2010. Results. Three patients with seropositive RA developed scleritis 7–28 months after initiation of etanercept, for the first time during their long-lasting disease. In all patients the underlying disease had responded well to anti-tumor necrosis factor therapy. Ocular inflammation went into remission after discontinuation of etanercept, and no other relapses were observed. One patient experienced a dechallenge-rechallenge phenomenon (improvement in symptoms following discontinuation of the agent, then reappearance or worsening of symptoms on reexposure to the agent). Forty-two cases of inflammatory eye diseases believed to be associated with the use of etanercept have been reported in the literature: 33 uveitis, 8 scleritis, 1 orbital myositis, concerning 16 patients with RA, 10 with juvenile idiopathic arthritis, 14 with ankylosing spondylitis, and 2 with psoriatic spondyloarthropathy. Dechallenge was performed in 28 patients, leading to resolution of symptoms. Rechallenge was done in 6 cases, with clear exacerbation. Conclusion. Ocular inflammation is paradoxically a potential adverse effect of etanercept, even in previously uninvolved eyes.

Loss of sclerostin promotes osteoarthritis in mice via β-catenin-dependent and -independent Wnt pathways

IntroductionSclerostin is a Wnt inhibitor produced by osteocytes that regulates bone formation. Because bone tissue contributes to the development of osteoarthritis (OA), we investigated the role of sclerostin in bone and cartilage in a joint instability model in mice.MethodsTen-week-old SOST-knockout (SOST-KO) and wild-type (WT) mice underwent destabilization of the medial meniscus (DMM). We measured bone volume at the medial femoral condyle and osteophyte volume and determined the OA score and expression of matrix proteins. Primary murine chondrocytes were cultured with Wnt3a and sclerostin to assess the expression of matrix proteins, proteoglycan release and glycosaminoglycan accumulation.ResultsSclerostin was expressed in calcified cartilage of WT mice with OA. In SOST-KO mice, cartilage was preserved despite high bone volume. However, SOST-KO mice with DMM had a high OA score, with increased expression of aggrecanases and type X collagen. Moreover, SOST-KO mice with OA showed disrupted anabolic–catabolic balance and cartilage damage. In primary chondrocytes, sclerostin addition abolished Wnt3a-increased expression of a disintegrin and metalloproteinase with thrombospondin motifs, matrix metalloproteinases and type X collagen by inhibiting the canonical Wnt pathway. Moreover, sclerostin inhibited Wnt-phosphorylated c-Jun N-terminal kinase (JNK) and rescued the expression of anabolic genes. Furthermore, sclerostin treatment inhibited both Wnt canonical and non-canonical JNK pathways in chondrocytes, thus preserving metabolism.ConclusionSclerostin may play an important role in maintaining cartilage integrity in OA.

Pathogenic role of basic calcium phosphate crystals in destructive arthropathies.

Background basic calcium phosphate (BCP) crystals are commonly found in osteoarthritis (OA) and are associated with cartilage destruction. BCP crystals induce in vitro catabolic responses with the production of metalloproteases and inflammatory cytokines such as interleukin-1 (IL-1). In vivo, IL-1 production induced by BCP crystals is both dependant and independent of NLRP3 inflammasome. We aimed to clarify 1/ the role of BCP crystals in cartilage destruction and 2/ the role of IL-1 and NLRP3 inflammasome in cartilage degradation related to BCP crystals. Methodology/ Principal Findings synovial membranes isolated from OA knees were analysed by alizarin Red and FTIR. Pyrogen free BCP crystals were injected into right knees of WT, NLRP3 -/-, ASC -/-, IL-1α -/- and IL-1β-/- mice and PBS was injected into left knees. To assess the role of IL-1, WT mice were treated by intra-peritoneal injections of anakinra, the IL-1Ra recombinant protein, or PBS. Articular destruction was studied at d4, d17 and d30 assessing synovial inflammation, proteoglycan loss and chondrocyte apoptosis. BCP crystals were frequently found in OA synovial membranes including low grade OA. BCP crystals injected into murine knee joints provoked synovial inflammation characterized by synovial macrophage infiltration that persisted at day 30, cartilage degradation as evidenced by loss of proteoglycan staining by Safranin-O and concomitant expression of VDIPEN epitopes, and increased chondrocyte apoptosis. BCP crystal-induced synovitis was totally independent of IL-1α and IL-1β signalling and no alterations of inflammation were observed in mice deficient for components of the NLRP3-inflammasome, IL-1α or IL-1β. Similarly, treatment with anakinra did not prevent BCP crystal effects. In vitro, BCP crystals elicited enhanced transcription of matrix degrading and pro-inflammatory genes in macrophages. Conclusions/ Significance intra-articular BCP crystals can elicit synovial inflammation and cartilage degradation suggesting that BCP crystals have a direct pathogenic role in OA. The effects are independent of IL-1 and NLRP3 inflammasome.

GOSPEL: prospective survey of gout in France. Part I: design and patient characteristics (n = 1003).

OBJECTIVES To assess diagnoses and management of acute and chronic gout in primary care and rheumatology settings relative to 2006 European League Against Rheumatism (EULAR) gout recommendations. Secondary objectives were to describe patient demographics, clinical features, lifestyle modifications, and short- and mid-term outcomes. METHODS Prospective, cross-sectional, descriptive survey of patients with chronic gout, acute gout, or suspected gout, included by randomly selected general practitioners (GPs, n = 398) and rheumatologists (n = 109) between October 2008 and September 2009, in France. At the first visit, a structured questionnaire was completed. Each patient completed self-questionnaires at the first visit and 3 to 6 months later. RESULTS We included 1003 patients, including 879 (87.6%) males (mean age, 61.6 ± 11.4 years; 28.1% obese) and 124 (12.4%) females (70.2 ± 11.9 years; 33.1% obese). Mean disease duration was 8.0 ± 8.3 years and mean time since hyperuricemia diagnosis 8.2 ± 8.4 years. Mean annual number of flares was 1.9 ± 1.5. ACR criteria for gout were met in 855 pts. Gout was acute in 487 (48.6%) patients and chronic in 241 (24.4%). Tophi (19.4% of patients) were associated with disease duration but not gender or chronic kidney disease (CKD). The main co-morbidities were hypertension (53.8%), dyslipidemia (47.2%), and hyperglycemia/diabetes mellitus (15.0%). CKD 3-5 was present in 43% of patients but was identified by physicians in only 5.2%. CKD severity was significantly associated with age, gender, hypertension, and diuretic use. CONCLUSION This cohort will prove valuable for addressing the concordance with EULAR recommendations and for future studies of gout in everyday practice, most notably regarding metabolic syndrome, other co-morbidities, and identification of difficult-to-treat patients.

Severe gouty arthritis and mild neurologic symptoms due to F199C, a newly identified variant of the hypoxanthine guanine phosphoribosyltransferase.

A deficiency in hypoxanthine guanine phosphoribosyltransferase (HPRT) activity leads to overproduction of uric acid. According to the degree of enzymatic deficiency, a large spectrum of neurologic features can also be observed, ranging from mild or no neurologic involvement to complete Lesch-Nyhan disease. Herein, we describe a patient with hyperuricemia, juvenile-onset gouty arthritis, nephrolithiasis, and mild neurologic symptoms, attributed to a newly identified variant of the hprt gene, c.596T>G, resulting in the amino acid change p.F199C. Residual HPRT activity (8%) protected against severe neurologic involvement in this patient. Modeling of the mutated protein was used to predict the mechanisms that led to partial enzymatic activity. Careful neurologic examination is warranted in juvenile and middle-aged patients with gout, in order to detect mild symptoms that may lead to a diagnosis of HPRT deficiency.