Cartilage-pannus Junction Research Articles

Osteoclast-Associated Receptor (OSCAR) Distribution in the Synovial Tissues of Patients with Active RA and TNF-α and RANKL Regulation of Expression by Osteoclasts In Vitro.

Osteoclast-associated receptor (OSCAR) is a co-stimulatory receptor in osteoclastogenesis. Synovial tissues from active rheumatoid arthritis (RA) patients express higher levels of OSCAR compared with osteoarthritic and normal patients; however, the comparison of OSCAR levels in different regions of active RA synovium has not been reported. The regulation of OSCAR by TNF-α and receptor activator of NF kappa β ligand (RANKL) in pre-osteoclasts/osteoclasts in vitro is unclear. OSCAR and tartrate-resistant acid phosphatase (TRAP) expression levels did not differ between the cartilage pannus junction (CPJ) and non-CPJ regions in active RA. We demonstrate a similar pattern of OSCAR expression in the CPJ and non-CPJ synovial tissue from patients with active RA. OSCAR was associated with mononuclear cells in both the lining and sub-lining and endothelial cells (von Willebrand factor positive). Pre-osteoclasts (TRAP-positive cells) were present in the lining and sub-lining of both regions. OSCAR messenger RNA (mRNA) expression and release by pre-oscteoclasts/osteoclasts was modulated by RANKL with/without TNF-α in vitro. Osteoclast resorption on dentine slices was significantly greater with TNF-α pre-treatment and RANKL (10ng/ml) than RANKL 10 or 50ng/ml alone or RANKL 10ng/ml with TNF-α given from day 3 post-RANKL. The lower levels of OSCAR mRNA expression corresponded with high osteoclast activity levels.

Serum Calprotectin in Rheumatoid Arthritis: A Promising Diagnostic Marker, How Far Is It Related to Activity and Sonographic Findings?

BackgroundIn the past 2 decades, there has been increasing interest in calprotectin. It is released and detected in serum and body fluids as a potentially useful clinical inflammatory marker. The protein has been described in synovial tissue in rheumatoid arthritis (RA) patients, specifically in the lining layer adjacent to the cartilage–pannus junction, which is the primary site of cartilage destruction and bone erosion. Assessment of inflammatory activity in RA is of pivotal importance for the optimal treatment. Our aim in this study is to measure the serum calprotectin levels in RA patients and to assess its association—if there is any—with disease activity score and radiological findings using the musculoskeletal ultrasound. Patients and methodsIn our case control study, we included 44 RA patients (Group I) and 20 age- and sex-matched healthy volunteers who served as the control group (Group II). Both groups were subjected to full history taking and thorough clinical examination. Assessment of RA disease activity state was done for all RA patients using the Disease Activity Score 28. Laboratory investigations included the measurement of complete blood cell count, erythrocyte sedimentation rate, C-reactive protein, rheumatoid factor, anticitrullinated peptide antibodies, kidney, liver functions; serum calprotectin levels were determined using enzyme-linked immunosorbent assay and radiological joint assessment was done using musculoskeletal ultrasound score. ResultsThere was a statistically significant elevation of serum calprotectin levels among RA patients when compared with healthy controls. Statistically significant correlations were also found between serum calprotectin and the ultrasound grading score, Disease Activity Score 28, and erythrocyte sedimentation rate, which reflect the degree of inflammatory activity in the affected joints in RA patients. Moreover, the study yielded a significant correlation between serum calprotectin levels and rheumatoid autoantibodies (rheumatoid factor and anticitrullinated peptide antibodies), which are strong predictors of the aggressiveness of the disease. Serum calprotectin at a cutoff level of 93.9 μg/dL had 88.6% sensitivity and 100% specificity for diagnosis of RA. ConclusionCalprotectin was found to have high association with laboratory and ultrasonography markers of inflammation in RA patients, so it is recommended for use as a marker of inflammatory activity in RA patients especially for the follow-up of patients on biological therapy to assess its efficacy.

Calprotectin as a biomarker for rheumatoid arthritis: a systematic review.

Calprotectin (myeloid-related protein 8/14), a heterodimeric complex of calcium-binding proteins, is expressed in granulocytes and monocytes. Calprotectin levels are high in synovial tissue, particularly in activated cells adjacent to the cartilage-pannus junction. This systematic review evaluates the use of calprotectin as an indicator of disease activity, therapeutic response, and prognosis in rheumatoid arthritis (RA). Medline, Scopus, and the Cochrane Library (1970-2013) were searched for studies containing original data from patients with RA in whom calprotectin levels were measured in plasma/serum and/or synovial fluid (SF). We included studies examining associations between calprotectin levels and clinical and laboratory assessments, disease progression, and therapeutic response. There were no restrictions for sample size, disease duration, or length of followup. We evaluated 17 studies (1988-2013) with 1065 patients enrolled; 11 were cross-sectional and 8 had longitudinal designs with 2 studies reporting cross-sectional and longitudinal data. Systemic and SF levels of calprotectin were raised in RA. There was a wide range of levels and marked interstudy and intrastudy variability. Calprotectin levels were high in active disease and were particularly high in rheumatoid factor (RF)-positive patients. Levels fell with effective treatment. Longitudinal data showed that calprotectin was a significant and independent predictor of erosive progression and therapeutic responses, particularly in patients who received effective biological treatments. SF calprotectin levels are high, suggesting there is substantial local production by inflamed synovium. Blood calprotectin levels, though highly variable, are elevated in active RA and fall with effective therapy. High baseline calprotectin levels predict future erosive damage.

Beneficial effects of tumour necrosis factor-alpha (TNF-alpha) blockade in rheumatoid arthritis (RA)

The biological properties of TNF-alpha make it a candidate therapeutic target in RA. Our studies have demonstrated that TNF-alpha and its receptors are up-regulated and co-expressed in the synovium and cartilage-pannus junction of RA joints. Neutralizing TNF-alpha antibodies reduce the production of the many pro-inflammatory cytokines, including IL-1 and granulocyte-macrophage colony-stimulating factor (GM-CSF), produced by mononuclear cells from RA in culture. When injected into DBA/1 mice with collagen-induced arthritis and TNF-alpha transgenic mice with arthritis, anti-TNF MoAbs decrease inflammatory damage of joints. Clinical trials employing cA2, a chimaeric anti-TNF-alpha MoAb, in open-label and randomized placebo-controlled studies have demonstrated a dose-dependent efficacy with impressive improvement in disease activity and acute-phase responses lasting several weeks. We conclude that TNF-alpha is a critical mediator of inflammation in RA, and is an important therapeutic target in this disease.

SAT0069 Regulation of syndecan-1 expression in monocytes/macrophages in chronic inflammatory arthritis

BackgroundThe syndecans (SDCs) are integral cell surface heparan sulfate proteoglycans (HSPGs) that are expressed in a cell, tissue and development specific manner. To date, the regulation of SDC-1 expression in...

Macrophages in Synovial Inflammation

Synovial macrophages are one of the resident cell types in synovial tissue and while they remain relatively quiescent in the healthy joint, they become activated in the inflamed joint and, along with infiltrating monocytes/macrophages, regulate secretion of pro-inflammatory cytokines and enzymes involved in driving the inflammatory response and joint destruction. Synovial macrophages are positioned throughout the sub-lining layer and lining layer at the cartilage–pannus junction and mediate articular destruction. Sub-lining macrophages are now also considered as the most reliable biomarker for disease severity and response to therapy in rheumatoid arthritis (RA). There is a growing understanding of the molecular drivers of inflammation and an appreciation that the resolution of inflammation is an active process rather than a passive return to homeostasis, and this has implications for our understanding of the role of macrophages in inflammation. Macrophage phenotype determines the cytokine secretion profile and tissue destruction capabilities of these cells. Whereas inflammatory synovial macrophages have not yet been classified into one phenotype or another it is widely known that TNFα and IL-l, characteristically released by M1 macrophages, are abundant in RA while IL-10 activity, characteristic of M2 macrophages, is somewhat diminished. Here we will briefly review our current understanding of macrophages and macrophage polarization in RA as well as the elements implicated in controlling polarization, such as cytokines and transcription factors like NFκB, IRFs and NR4A, and pro-resolving factors, such as LXA4 and other lipid mediators which may promote a non-inflammatory, pro-resolving phenotype, and may represent a novel therapeutic paradigm.

The history of erosions in rheumatoid arthritis: Are erosions history?

Small joint periarticular erosions have occupied center stage in the understanding of the pathogenesis of rheumatoid arthritis (RA) for well over 50 years (1). Such erosions have diagnostic and prognostic significance and have served as a valuable outcome measure in the evaluation of therapeutic responses to drugs for disease (2). The RA erosion paradigm extends well beyond these immediately clinically relevant issues. An understanding of the proinflammatory milieu at the cartilage–pannus junction, the putative site where erosion formation was thought to be initiated, was considered to represent a key event toward the development of biologic therapies in RA (3). Ongoing efforts seek to link the immunopathogenetic basis for erosion formation to emergent genome-wide association studies to further elucidate the basis for joint disease in RA. The importance of erosions in the immunopathogenesis of RA is almost dwarfed by the importance that their early detection has assumed. Erosions represent 1 of the 3 diagnostic criteria for RA when combined with clinical and serologic parameters (2). With the advent of more sophisticated imaging techniques, most notably, magnetic resonance imaging (MRI) and ultrasound (US), rheumatologists are increasingly interested in detecting these seemingly diagnostic and prognostic features in early RA to facilitate a definitive diagnosis and to initiate the most appropriate therapy, at the earliest possible opportunity. Why this is the case and why it merits reconsideration based on work reported by Stach et al in this issue of Arthritis & Rheumatism (4) and based on other recent data are the subjects of this perspective. History of erosion immunopathogenesis

Interaction of Human Recombinant Tumor Necrosis Factor-Related Apoptosis-Inducing Ligand and Osteoprotegerin Could Contribute to Enhancement of the Erosive Processes Induced by Human Synovial Cells

To the Editor: Rheumatoid arthritis (RA) is a chronic inflammatory disease for which the etiology is unknown. Patients with RA are known to have lower bone mineral density and are at risk of pathological fracture caused by cytokines produced by RA synovial fibroblasts, which have the potential to promote osteoclast formation and bone resorption. It is now clear that osteoclast formation and activation at the cartilage-pannus junction is an essential step in the destruction of bone matrix in RA1,2. Our aim was to investigate key factors that regulate focal bone erosion in RA, and their relationships with human recombinant tumor necrosis factor (TNF)-related apoptosis-inducing ligand (hr-TRAIL), in order to propose a strategy to block bone destruction in RA. A number of inflammatory cytokines found in the RA synovial tissue [interleukin 1 (IL-1), IL-1s, IL-6, TNF-α, and macrophage colony-stimulating factor] have the potential to promote osteoclast formation and bone resorption3,4. Cells within RA synovial fibroblasts also are substantial sources of soluble receptor activator of nuclear factor-κB (sRANKL) and osteoprotegerin … Address reprint requests to Dr. V. Nicolin; E-mail: nicolin{at}units.it

Cadherin 11 promotes invasive behavior of fibroblast‐like synoviocytes

To define the expression pattern of cadherin 11 in the destructive pannus tissue of patients with rheumatoid arthritis, and to determine whether cadherin 11 expression in fibroblast-like synoviocytes controls their invasive capacity. Cadherin 11 expression in rheumatoid synovial tissue was evaluated using immunohistochemistry. To examine the role of cadherin 11 in regulating the invasive behavior of fibroblast-like synoviocytes, we generated L cell clones expressing wild-type cadherin 11, mutant cadherin 11, and empty vector-transfected controls. The invasive capacity of L cell transfectants and cultured fibroblast-like synoviocytes treated with a blocking cadherin 11-Fc fusion protein or control immunoglobulin was determined in Matrigel invasion assays. Immunohistochemical analysis revealed that cadherin 11 is abundantly expressed in cells at the cartilage-pannus junction in rheumatoid synovitis. Assays to determine invasion demonstrated a 2-fold increased invasive capacity of cadherin 11-transfected L cells compared with L cells transfected with E-cadherin or control vector. The invasive behavior of L cells stably transfected with a cadherin 11 construct that lacked the juxtamembrane cytoplasmic domain was diminished to the level of vector control L cells. Furthermore, treatment with the cadherin 11-Fc fusion protein diminished the invasive capacity of fibroblast-like synoviocytes. The results of these in vitro studies implicate a role for cadherin 11 in promoting cell invasion and contribute insight into the invasive nature of fibroblast-like synoviocytes in chronic synovitis and rheumatoid arthritis.

Membrane type 1 matrix metalloproteinase is a crucial promoter of synovial invasion in human rheumatoid arthritis

A hallmark of rheumatoid arthritis (RA) is invasion of the synovial pannus into cartilage, and this process requires degradation of the collagen matrix. The aim of this study was to explore the role of one of the collagen-degrading matrix metalloproteinases (MMPs), membrane type 1 MMP (MT1-MMP), in synovial pannus invasiveness. The expression and localization of MT1-MMP in human RA pannus were investigated by Western blot analysis of primary synovial cells and immunohistochemical analysis of RA joint specimens. The functional role of MT1-MMP was analyzed by 3-dimensional (3-D) collagen invasion assays and a cartilage invasion assay in the presence or absence of tissue inhibitor of metalloproteinases 1 (TIMP-1), TIMP-2, or GM6001. The effect of adenoviral expression of a dominant-negative MT1-MMP construct lacking a catalytic domain was also examined. MT1-MMP was highly expressed at the pannus-cartilage junction in RA joints. Freshly isolated rheumatoid synovial tissue and isolated RA synovial fibroblasts invaded into a 3-D collagen matrix in an MT1-MMP-dependent manner. Invasion was blocked by TIMP-2 and GM6001 but not by TIMP-1. Invasion was also inhibited by the overexpression of a dominant-negative MT1-MMP, which inhibits collagenolytic activity and proMMP-2 activation by MT1-MMP on the cell surface. Synovial fibroblasts also invaded into cartilage in an MT1-MMP-dependent manner. This process was further enhanced by removing aggrecan from the cartilage matrix. MT1-MMP serves as an essential collagen-degrading proteinase during pannus invasion in human RA. Specific inhibition of MT1-MMP-dependent invasion may represent a novel therapeutic strategy for RA.

Cellular responses to human chondrocytes: absence of allogeneic responses in the presence of HLA-DR and ICAM-1

To assess the accessory cell function of human articular chondrocytes, we assessed the ability of human chondrocytes to stimulate allogeneic peripheral blood mononuclear cells (PBMC) and to support phytohaemagglutinin (PHA)-induced proliferation of highly purified T cells. We also examined the surface expression of HLA-DR and ICAM-1 on the chondrocytes both unstimulated and stimulated with cytokines in vitro. Chondrocytes failed to stimulate allogeneic PBMC despite the constitutive expression of MHC class I molecules and the cytokine-induced expression of class II molecules but were able to support T cell proliferation to PHA, IFN-gamma and to a limited extent, IL-1 beta, induced class II expression on chondrocytes. ICAM-1 was present on 94-99% of freshly isolated cells; this declined with culture (17-59%; P < 0.005) but was readily induced by IFN-gamma, IL-1 beta, and tumour necrosis factor-alpha. Alloreactivity and, presumably, autoreactivity to chondrocytes requires factors in addition to the surface expression of DR and ICAM-1. However the presence of these molecules suggests a capacity for cell-cell interactions in inflammatory sites such as the cartilage pannus junction.

Microarray analysis for molecular characterization of disease activity and measuring outcomes of anti-tumour necrosis factor therapy in rheumatoid arthritis

In the pathogenesis of rheumatoid arthritis (RA), macrophages (Mφ) play a pivotal role in synovitis, especially at the cartilage–pannus junction. Both Mφ and peripheral blood monocytes (MO) are activated and release proinflammatory cytokines (IL-1β, tumour necrosis factor [TNF] alpha). Neutralization of IL1-β and TNF-α leads to clinical improvement in RA.

Regional variation and differential response to therapy for knee synovitis adjacent to the cartilage-pannus junction and suprapatellar pouch in inflammatory arthritis: implications for pathogenesis and treatment.

To use magnetic resonance imaging (MRI) to investigate the importance of knee joint synovitis at the cartilage-pannus junction (CPJ) in rheumatoid arthritis (RA) as compared with synovitis at a distant site in the suprapatellar pouch (SPP) and as compared with CPJ synovitis in the spondylarthropathies (SpA), and to assess the relative response of knee joint synovitis to therapy at the CPJ and SPP sites. Dynamic contrast-enhanced MRI (DEMRI) of actively involved knee joints in 24 patients (13 with RA and 11 with SpA) was undertaken. The area of synovitis was calculated at the CPJ and SPP regions of interest in patients with RA and in patients with SpA. Differences in CPJ and SPP synovitis were determined using calculated DEMRI parameters which included the initial rate of contrast enhancement (IRE) and the maximal enhancement (ME). Changes in the synovial area at the CPJ and SPP were also measured in 10 patients with early RA, following treatment with disease-modifying antirheumatic drugs (DMARDs) (either methotrexate or leflunomide). In patients with RA or SpA, the area of synovitis was significantly larger immediately adjacent to the CPJ compared with a distant site at the SPP (in RA, mean synovitis area 162 mm2 at the CPJ versus 114 mm2 at the SPP [P = 0.010]; in SpA, mean synovitis area 214 mm2 at the CPJ versus 143 mm2 at the SPP [P = 0.002]), but the differences in the areas of synovitis at these sites were not significant between the RA and SpA patients. The IRE and ME values were also higher at the CPJ compared with the SPP, both in the RA patients (IRE P = 0.054, ME P = 0.018) and in the SpA patients (IRE P = 0.002, ME P = 0.001). A larger reduction in the area of synovitis was seen at the SPP compared with the CPJ following DMARD therapy in the RA patients (mean reduction 35% at the SPP [P = 0.023] and 12% at the CPJ [P not significant]). The non-disease-specific variations in synovitis and the differential responses to therapy in RA patients have implications for improving our understanding of CPJ synovitis. The results suggest that the pathophysiologic events at the CPJ reflect common anatomic, immune system, or biomechanical factors that play a role in modulating the severity of arthritis, and these events are not specific to RA since the same process was observed in other arthritides.

Increased synovial tissue NF-kappa B1 expression at sites adjacent to the cartilage-pannus junction in rheumatoid arthritis.

To compare the expression of the Rel/NF-kappa B subunits, NF-kappa B1 (p50) and RelA (p65), in paired synovial tissue samples selected from sites adjacent to and remote from the cartilage-pannus junction (CPJ) in patients with inflammatory arthritis. Synovial tissue was selected at arthroscopy from sites adjacent to the CPJ and from the suprapatellar pouch of patients who were referred to an early arthritis clinic. Tissue samples from patients with osteoarthritis (OA) undergoing knee arthroplasty were also studied. Rel/NF-kappa B subunit activation and expression were measured by electrophoretic mobility shift assay and supershift analyses and by immunohistochemistry. Tissue samples were obtained from 10 patients with rheumatoid arthritis (RA), 7 with a seronegative arthropathy (SnA), and 6 with OA. Rel/NF-kappa B was abundantly expressed in all samples. In both RA and SnA synovial tissue, the absolute number of NF-kappa B1+ cells at the CPJ was significantly higher than at non-CPJ sites (P = 0.006 and P = 0.02, respectively). The proportion of cells expressing NF-kappa B1 was also significantly higher at the CPJ compared with non-CPJ sites (P = 0.003 in RA, P = 0.009 in SnA). The numbers of RelA+ cells were consistently lower throughout. In RA synovial tissue, but not in SnA synovial tissue, both the absolute number and the proportion of RelA+ cells were significantly higher at the CPJ than at non-CPJ sites (P = 0.003 and P = 0.01, respectively). In OA synovial tissue, the numbers of cells expressing NF-kappa B1 and RelA were similar to those observed at the non-CPJ sites in all inflammatory tissues studied. In this study of early inflammatory arthritis, expression of NF-kappa B1 in synovial tissue was highest at sites most likely to be associated with joint erosion. These observations are consistent with a critical role of NF-kappa B1 in joint destruction, and support the rationale for specific therapeutic inhibition of NF-kappa B in RA.

Dynamic expression of transforming growth factor-betas (TGF-beta) and their type I and type II receptors in the synovial tissue of arthritic rats.

A well characterized animal model that shares many characteristic features with rheumatoid arthritis (RA) is collagen-induced arthritis (CIA) in DA rats. Recent studies have demonstrated that TGF-beta, a multifunctional cytokine, is an important modulator of the immune response in CIA, and possibly also in RA. In this study we have investigated the expression of the precursor forms of TGF-beta1, TGF-beta2, TGF-beta3, as well as TGF-beta type I receptor (TGF-betaRI) and TGF-beta type II receptor (TGF-betaRII) in the synovial tissue of arthritic rats during the course of the disease. By using immunohistochemical techniques, an abundant expression of all three TGF-beta isoforms and their receptors was observed in the arthritic synovia, an expression that increased with time after onset of disease. Antibodies to TGF-beta1, TGF-beta2, TGF-betaRI and TGF-betaRII stained blood vessels intensively, already at the early onset of inflammation, whereas the synovial lining layer and chondrocytes expressed strong immunoreactivity later on in the inflammatory process. The most intense staining with these antibodies was detected in fibroblasts within fibrotic tissue, in particular at the cartilage pannus junction. Interestingly, TGF-beta3 only stained macrophage-like cells and chondrocytes in the synovia. The data suggest that the abundant expression of TGF-beta1, TGF-beta2, TGF-beta3 as well as TGF-betaRI and TGF-betaRII in the synovia, is of pathogenic importance in the development of CIA, although the question of how the different TGF-beta isoforms may enhance or counteract different arthritogenic events remains open.

Cytokine production in synovial tissue of mice with collagen-induced arthritis (CIA)

The kinetics of cytokine production in arthritic limbs of mice with CIA was determined by using modified immunohistochemical techniques. Tissue cryostat sections of undecalcified whole paws were analysed for the presence of tumour necrosis factor-alpha (TNF-alpha), IL-6, IL-2, IL-4, IL-5 interferon-gamma (IFN-gamma), transforming growth factor-beta 2 (TGF-beta2) and TGF-beta3. Locally produced TNF-alpha, IL-6 and TGF-beta2 were observed within the lining layer, sublining and pannus at all stages of disease. The staining of TNF-alpha was particularly intense at the cartilage-pannus junction. In contrast to the monokines, IFN-gamma and TGF-beta3 were only expressed in scattered cells within the deeper layers of the synovia. Interestingly, IFN-gamma was not present in the late phase of CIA, despite the continued presence of TNF-alpha and IL-6 in the pannus. Production of IL-2, IL-4 or IL-5 was not detected in any joint. The observed pattern of a relative paucity of T cell-derived cytokines and an abundance of monokines during the late phase of T cell-dependent CIA indicates that the synovial cytokine pattern previously described in rheumatoid arthritis (RA) is fully compatible with a pathogenic role of T cells. The temporal as well as spatial dissociation between expression of T cell-derived cytokines and monokines indicates that T cell-independent mechanisms may also be of importance in the triggering of monokine production during arthritis.

Leukotrienes, mast cells, and T cells

Leukotrienes, mast cells, and T cells

Involvement of the peripheral benzodiazepine receptor in the development of rheumatoid arthritis in Mrl/lpr mice

In this study, the effects of different peripheral benzodiazepine receptor ligands: PK 11195 [1-(2-chloro-phenyl)- N-methyl- N-(1-methylpropyl)-1-isoquinoline carboxamide], Ro5-4864 [7-chloro-5-(4-chlorophenyl)-1,3-dihydro-1-methyl-2 H-1,4-benzodiazepin-2-one] and the newly described SSR 180575 (7-chloro- N, N,5-trimethyl-4-oxo-3-phenyl-3,5-dihydro-4 H-pyridozine[4,5-b] indole-1-acetamide) were analysed on the progression and severity of rheumatoid arthritis in vivo in the Mrl/lpr mice model, following chronic treatment (at 3 mg/kg, i.p. for 30 days). We found that peripheral benzodiazepine receptor ligands have significant beneficial therapeutic action on the development of spontaneous rheumatoid arthritis-like signs. Concomitantly, we mapped immunoreactive peripheral benzodiazepine receptor in inflamed tissues, and we observed that in addition to the infiltrated leukocytes, peripheral benzodiazepine receptor was expressed in synovial membranes, at the cartilage pannus junction and in chondrocytes. Interestingly, we observed that peripheral benzodiazepine receptor expression in chondrocytes was reduced when Mrl/lpr mice developed the pathology and restored upon peripheral benzodiazepine receptor ligand treatment. Altogether, our data provide further evidence of a role played by peripheral benzodiazepine receptor in the regulation of inflammation processes and support new therapeutic applications for specific potent peripheral benzodiazepine receptor ligands.

Cartilage destruction and bone erosion in arthritis: the role of tumour necrosis factor α

Rheumatoid arthritis (RA) is a chronic disabling disease characterised by synovitis, destruction of cartilage and bone and, ultimately, loss of joint function. A great deal of research in rheumatology over...

Participation of substance P distribution in the cytokine production of rheumatoid synovium

Based on findings which suggested the involvement of the neuropeptide substance P in the pathogenesis of rheumatoid arthritis (RA), we investigated the mechanism of synovial pannus formation in RA, and examined the interaction between the cytokine production of synovial tissues and the concentration of substance P in the cartilage–pannus junction (CPJ). The CPJ and other peripheral synovial tissues were separately obtained from each part of the synovium from the knee joints of seven RA patients. The concentrations of substance P and the cytokines interleukin (IL)-1β and IL-6 in the CPJ and peripheral synovial tissues were determined by enzyme-linked immunosorbent assays. In addition, synovial cells were isolated from the CPJ and peripheral synovial tissues and treated with substance P or neurokinin-1 receptor antagonist to analyze the changes in cytokine production. The substance P levels were 211.2 and 50.5 pg/mg protein in the CPJ and the peripheral synovium, respectively. The IL-1β and IL-6 levels in the CPJ were 24.6 and 12.8 pg/mg protein, respectively. In the peripheral synovium, these levels were 4.3 and 2.5 pg/mg protein, respectively. In the CPJ, the IL-1β and IL-6 levels in tissue containing a high concentration of substance P (>200 pg/mg protein) were 39.4 and 21.6 pg/mg protein, respectively, and those in tissue containing a low concentration of substance P (≤200 pg/mg protein) were 11.6 and 5.1 pg/mg protein, respectively. Synovial cells from the CPJ produced higher levels of IL-1β and IL-6 than those from peripheral tissues. In addition, treatment of the cells with an NK-1 antagonist significantly reduced the production of these cytokines by the synovial cells. The theory that substance P plays a role in the pathogenesis of RA via the upregulation of cytokine production should be considered in further studies on the immunomodulatory properties of substance P in arthritis.