Informed development of a multi-species biofilm in chronic obstructive pulmonary disease.

Recent evidence indicates that microbial biofilm aggregates inhabit the lungs of COPD patients and actively contribute towards chronic colonization and repeat infections. However, there are no contextually relevant complex biofilm models for COPD research. In this study, a meta-analysis of the lung microbiome in COPD was used to inform development of an optimized biofilm model composed of genera highly associated with COPD. Bioinformatic analysis showed that although diversity matrices of COPD microbiomes were similar to healthy controls, and internal compositions made it possible to accurately differentiate between these cohorts (AUC = 0.939). Genera that best defined these patients included Haemophilus, Moraxella and Streptococcus. Many studies fail to account for fungi; therefore, Candida albicans was included in the creation of an interkingdom biofilm model. These organisms formed a biofilm capable of tolerating high concentrations of antimicrobial therapies with no significant reductions in viability. However, combined therapies of antibiotics and an antifungal resulted in significant reductions in viable cells throughout the biofilm (p < 0.05). This biofilm model is representative of the COPD lung microbiome and results from in vitro antimicrobial challenge experiments indicate that targeting both bacteria and fungi in these interkingdom communities will be required for more positive clinical outcomes.

Destabilization of the Medial Meniscus and Cartilage Scratch Murine Model of Accelerated Osteoarthritis.

Osteoarthritis is the most prevalent musculoskeletal disease in people over 45, leading to an increasing economic and societal cost. Animal models are used to mimic many aspects of the disease. The present protocol describes the destabilization and cartilage scratch model (DCS) of post-traumatic osteoarthritis. Based on the widely used destabilization of the medial meniscus (DMM) model, DCS introduces three scratches on the cartilage surface. The current article highlights the steps to destabilize the knee by transecting the medial meniscotibial ligament followed by three intentional superficial scratches on the articular cartilage. The possible analysis methods by dynamic weight-bearing, microcomputed tomography, and histology are also demonstrated. While the DCS model is not recommended for studies that focus on the effect of osteoarthritis on the cartilage, it enables the study of osteoarthritis development in a shorter time window, with special focus on (1) osteophyte formation, (2) osteoarthritic and injury pain, and (3) the effect of cartilage damage in the whole joint.

The Serpin Superfamily and Their Role in the Regulation and Dysfunction of Serine Protease Activity in COPD and Other Chronic Lung Diseases.

Chronic obstructive pulmonary disease (COPD) is a debilitating heterogeneous disease characterised by unregulated proteolytic destruction of lung tissue mediated via a protease-antiprotease imbalance. In COPD, the relationship between the neutrophil serine protease, neutrophil elastase, and its endogenous inhibitor, alpha-1-antitrypsin (AAT) is the best characterised. AAT belongs to a superfamily of serine protease inhibitors known as serpins. Advances in screening technologies have, however, resulted in many members of the serpin superfamily being identified as having differential expression across a multitude of chronic lung diseases compared to healthy individuals. Serpins exhibit a unique suicide-substrate mechanism of inhibition during which they undergo a dramatic conformational change to a more stable form. A limitation is that this also renders them susceptible to disease-causing mutations. Identification of the extent of their physiological/pathological role in the airways would allow further expansion of knowledge regarding the complexity of protease regulation in the lung and may provide wider opportunity for their use as therapeutics to aid the management of COPD and other chronic airways diseases.

Trypsin-Like Proteases and Their Role in Muco-Obstructive Lung Diseases.

Trypsin-like proteases (TLPs) belong to a family of serine enzymes with primary substrate specificities for the basic residues, lysine and arginine, in the P1 position. Whilst initially perceived as soluble enzymes that are extracellularly secreted, a number of novel TLPs that are anchored in the cell membrane have since been discovered. Muco-obstructive lung diseases (MucOLDs) are characterised by the accumulation of hyper-concentrated mucus in the small airways, leading to persistent inflammation, infection and dysregulated protease activity. Although neutrophilic serine proteases, particularly neutrophil elastase, have been implicated in the propagation of inflammation and local tissue destruction, it is likely that the serine TLPs also contribute to various disease-relevant processes given the roles that a number of these enzymes play in the activation of both the epithelial sodium channel (ENaC) and protease-activated receptor 2 (PAR2). More recently, significant attention has focused on the activation of viruses such as SARS-CoV-2 by host TLPs. The purpose of this review was to highlight key TLPs linked to the activation of ENaC and PAR2 and their association with airway dehydration and inflammatory signalling pathways, respectively. The role of TLPs in viral infectivity will also be discussed in the context of the inhibition of TLP activities and the potential of these proteases as therapeutic targets.

Losartan protects endothelium-dependent relaxation in vivo in a murine model of rheumatoid arthritis.

Angiotensin II-type 1 receptor stimulation is recognised to promote inflammation, a state central to the development and maintenance of rheumatoid arthritis. Herein we examined the use of losartan, an angiotensin II-type 1 receptor antagonist, on vascular reactivity, knee joint diameter and behavioural assessment of pain in a Freund's complete adjuvant (FCA) mouse model of joint inflammation. Monoarthritis was induced via FCA in the presence or absence of losartan with naive mice serving as controls. Knee joint swelling, joint pain (assessed by dynamic weight bearing of limb use), knee joint artery reactivity (assessed ex vivo) and blood perfusion of the knee joint (assessed in vivo) were determined. FCA mediated a significant increase in knee joint diameter and reduced weight-bearing (a surrogate for pain sensation) of the affected limb. Notably, these phenomena were substantially reduced when mice were prophylactically treated with losartan. Assessment of arterial relaxation and blood perfusion with acetylcholine stimulation revealed that FCA resulted in significant vascular dysfunction, which was resolved to naïve levels with losartan treatment. Through the actions of losartan, these findings indicate that the angiotensin II-type 1 receptor is a likely therapeutic target of importance in the development of the physical changes, pain sensation and vascular dysfunction found in inflammatory arthritis.

Protease activated receptor 2 and matriptase expression in the joints of cats with and without osteoarthritis.

OBJECTIVES: The aim of this study was to determine the presence of protease-activated receptor 2 (PAR2) and matriptase proteins and quantify PAR2 and matriptase mRNA expression in the articular cartilage and synovial membrane of cats with and without osteoarthritis (OA). METHODS: A total of 28 articular cartilage samples from adult cats (14 OA and 14 normal), 10 synovial membranes from adult cats (five OA and five normal) and three cartilage samples from 9-week-old fetal cats were used. The presence of PAR2 and matriptase in the cartilage and synovial membrane of the adult samples was detected by immunohistochemical (IHC) staining, while real-time PCR was used for mRNA expression analyses in all samples. RESULTS: PAR2 was detected in all OA and normal articular cartilage and synovial membrane samples but confined to only a few superficial chondrocytes in the normal samples. Matriptase was only detected in OA articular cartilage and synovial membrane samples. PAR2 and matriptase mRNA expression were, however, detected in all cartilage and synovial membrane samples. PAR2 and matriptase mRNA expression levels in OA articular cartilage were five (P <0.001) and 3.3 (P <0.001) times higher than that of the healthy group, respectively. There was no significant difference (P = 0.05) in the OA synovial membrane PAR2 and matriptase mRNA expression compared with the normal samples. CONCLUSIONS AND RELEVANCE: Detection of PAR2 and matriptase proteins and gene expression in feline articular tissues is a novel and important finding, and supports the hypothesis that serine proteases are involved in the pathogenesis of feline OA. The consistent presence of PAR2 and matriptase protein in the cytoplasm of OA chondrocytes suggests a possible involvement of proteases in cartilage degradation. Further investigations into the PAR2 and matriptase pathobiology could enhance our understanding of the proteolytic cascades in feline OA, which might lead to the development of novel therapeutic strategies.

Exosomes in intercellular communication and implications for osteoarthritis.

Osteoarthritis (OA) is the most prevalent of the musculoskeletal conditions and represents a significant public health burden. While degeneration of articular cartilage is a key feature, it is now increasingly recognized as a complex condition affecting the whole joint, with synovial inflammation present in a significant proportion of patients. As a secretory tissue, the OA synovium is a rich source of both soluble inflammatory mediators and extracellular vesicles, including exosomes, which have been implicated in cell-cell communication. Exosome cargo has been found to include proteins, lipids and various RNA subtypes such as mRNA and miRNA, potentially capable of regulating gene expression in target cells and tissues. Profiling of exosome cargo and understanding effects on cartilage could elucidate novel regulatory mechanisms within the joint, providing insight for targeted treatment. The aim of this article is to review current literature on exosome biology, highlighting the relevance and application for OA pathogenesis.

Rheumatic Disease: Protease-Activated Receptor-2 in Synovial Joint Pathobiology.

Protease-activated receptor-2 (PAR2) is one member of a small family of transmembrane, G-protein-coupled receptors. These receptors are activated via cleavage of their N terminus by serine proteases (e.g., tryptase), unveiling an N terminus tethered ligand which binds to the second extracellular loop of the receptor. Increasing evidence has emerged identifying key pathophysiological roles for PAR2 in both rheumatoid arthritis (RA) and osteoarthritis (OA). Importantly, this includes both pro-inflammatory and destructive roles. For example, in murine models of RA, the associated synovitis, cartilage degradation, and subsequent bone erosion are all significantly reduced in the absence of PAR2. Similarly, in experimental models of OA, PAR2 disruption confers protection against cartilage degradation, subchondral bone osteosclerosis, and osteophyte formation. This review focuses on the role of PAR2 in rheumatic disease and its potential as an important therapeutic target for treating pain and joint degradation.

Endothelium-derived contraction in a model of rheumatoid arthritis is mediated via angiotensin II type 1 receptors.

A role for endothelium-derived constricting factors (EDCF), and the angiotensin II type 1 receptor (AT1R) pathway, in the vascular impairment found in the rat Freund's complete adjuvant (FCA)-model of rheumatoid arthritis (RA) was examined. FCA arthritis was induced in rats±losartan. Vehicle-treated rats served as controls. Knee-joint swelling and red blood cell (RBC) aggregation were measured as indicators of inflammation and endothelium reactivity assessed by response to acetylcholine (ACh) on aortic rings. Results show that knee-joint swelling and RBC aggregation were elevated in the FCA+vehicle group and restored to control levels in the FCA+losartan-treated animals. ACh-induced relaxation of aortic rings taken from FCA+vehicle animals was significantly impaired compared to vehicle-controls and this vasoreactivity was restored to control levels in the FCA+losartan-treated group. Further examination of aorta from the FCA+vehicle animals revealed an EDCF that was reliant on cyclooxygenase-2 (but not cyclooxygenase-1), generation of superoxide anion generation (but not hydrogen peroxide) and activation of thromboxane-prostanoid receptor. Losartan administration in vivo or ex vivo (to aortic rings) prevented the generation of the EDCF. In summary, this is the first evidence of an EDCF in a model of RA and identifies this mechanism as potentially significant in the cardiovascular disorder associated with the disease.

Proteinase-activated receptor 2 modulates OA-related pain, cartilage and bone pathology.

OBJECTIVE: Proteinase-activated receptor 2 (PAR2) deficiency protects against cartilage degradation in experimental osteoarthritis (OA). The wider impact of this pathway upon OA-associated pathologies such as osteophyte formation and pain is unknown. Herein, we investigated early temporal bone and cartilage changes in experimental OA in order to further elucidate the role of PAR2 in OA pathogenesis. METHODS: OA was induced in wild-type (WT) and PAR2-deficient (PAR2-/-) mice by destabilisation of the medial meniscus (DMM). Inflammation, cartilage degradation and bone changes were monitored using histology and microCT. In gene rescue experiments, PAR2-/- mice were intra-articularly injected with human PAR2 (hPAR2)-expressing adenovirus. Dynamic weight bearing was used as a surrogate of OA-related pain. RESULTS: Osteophytes formed within 7 days post-DMM in WT mice but osteosclerosis was only evident from 14 days post induction. Importantly, PAR2 was expressed in the proliferative/hypertrophic chondrocytes present within osteophytes. In PAR2-/- mice, osteophytes developed significantly less frequently but, when present, were smaller and of greater density; no osteosclerosis was observed in these mice up to day 28. The pattern of weight bearing was altered in PAR2-/- mice, suggesting reduced pain perception. The expression of hPAR2 in PAR2-/- mice recapitulated osteophyte formation and cartilage damage similar to that observed in WT mice. However, osteosclerosis was absent, consistent with lack of hPAR2 expression in subchondral bone. CONCLUSIONS: This study clearly demonstrates PAR2 plays a critical role, via chondrocytes, in osteophyte development and subchondral bone changes, which occur prior to PAR2-mediated cartilage damage. The latter likely occurs independently of OA-related bone changes.

Angiotensin II Type 1 receptor blockade protects endothelium-derived hyperpolarising factor-mediated relaxation in a rat model of monoarthritis.

AIMS: Rheumatoid arthritis (RA) is associated with high cardiovascular mortality. Impaired endothelial cell (EC) function and elevated angiotensin II levels may be central to the link between vascular dysfunction and RA. Here we investigated the action of angiotensin type 1 receptor (AT1R) blockade on endothelium-dependent relaxation of the isolated saphenous artery in a rat model of monoarthritis. MAIN METHODS: Adjuvant arthritis was induced in rats with and without prophylactic losartan (AT1R antagonist) treatment. Vehicle-treated rats were used as controls. Wire myography was employed to investigate EC function of isolated rings of saphenous artery. KEY FINDINGS: EC-dependent relaxation in arteries from non-inflamed control rats was mediated by both nitric oxide (NO) and endothelium-derived hyperpolarising factor (EDHF) with the EDHF response dependent principally on functional myoendothelial gap junctions. While NO-dependent relaxation remained unaffected, the EDHF-mediated response was abolished in arteries from arthritic rats (P<0.001), however, substantial protection (approximately 50%) of the EDHF-relaxation was found in arthritic rats treated with losartan (P<0.01). Thus, the attenuated EDHF response found in the saphenous artery of arthritic rats was significantly reversed by AT1R blockade. SIGNIFICANCE: These results suggest a key role for the angiotensin system in the EC dysfunction found in chronic joint inflammation and highlights AT1R as a potential therapeutic target to redress the vascular impairment and mortality associated with RA.

Proteinase-activated receptor-2 modulates human macrophage differentiation and effector function.

Proteinase-activated receptor-2 (PAR-2) was shown to influence immune regulation; however, its role in human macrophage subset development and function has not been addressed. Here, PAR-2 expression and activation was investigated on granulocyte macrophage (GM)-CSF(M1) and macrophage (M)-CSF(M2) macrophages. In both macrophages, the PAR-2-activating peptide, SLIGKV, increased PAR-2 expression and regulated TNF-α and IL-10 secretion in a manner similar to LPS. In addition, HLA-DR on M1 cells also increased. Monocytes matured to an M1 phenotype in the presence of SLIGKV had reduced cell area, and released less TNF-α after LPS challenge compared with vehicle (P < 0.05, n = 3). Cells matured to an M2 phenotype with SLIGKV also had a reduced cell area and made significantly more TNF-α after LPS exposure compared to vehicle (P < 0.05, n = 3) with reduced IL-10 secretion (P < 0.05, n = 3). Thus, PAR-2 activation on macrophage subsets regulates HLA-DR and PAR-2 surface expression, and drives cytokine production. In contrast, PAR-2 activation during M1 or M2 maturation induces altered cell morphology and skewing of phenotype, as evidenced by cytokine secretion. These data suggest a complex role for PAR-2 in macrophage biology and may have implications for macrophage-driven disease in which proteinase-rich environments can influence the immune process directly.

Immunomodulatory role of proteinase-activated receptor-2.

OBJECTIVE: Proteinase-activated receptor-2 (PAR(2)) has been implicated in inflammatory articular pathology. Using the collagen-induced arthritis model (CIA) the authors have explored the capacity of PAR(2) to regulate adaptive immune pathways that could promote autoimmune mediated articular damage. METHODS: Using PAR(2) gene deletion and other approaches to inhibit or prevent PAR(2) activation, the development and progression of CIA were assessed via clinical and histological scores together with ex vivo immune analyses. RESULTS: The progression of CIA, assessed by arthritic score and histological assessment of joint damage, was significantly (p<0.0001) abrogated in PAR(2) deficient mice or in wild-type mice administered either a PAR(2) antagonist (ENMD-1068) or a PAR(2) neutralising antibody (SAM11). Lymph node derived cell suspensions from PAR(2) deficient mice were found to produce significantly less interleukin (IL)-17 and IFNγ in ex vivo recall collagen stimulation assays compared with wild-type littermates. In addition, substantial inhibition of TNFα, IL-6, IL-1ß and IL-12 along with GM-CSF and MIP-1α was observed. However, spleen and lymph node histology did not differ between groups nor was any difference detected in draining lymph node cell subsets. Anticollagen antibody titres were significantly lower in PAR(2) deficient mice. CONCLUSION: These data support an important role for PAR(2) in the pathogenesis of CIA and suggest an immunomodulatory role for this receptor in an adaptive model of inflammatory arthritis. PAR(2) antagonism may offer future potential for the management of inflammatory arthritides in which a proteinase rich environment prevails.

Correlation of protease-activated receptor-2 expression and synovitis in rheumatoid and osteoarthritis.

Protease-activated receptor-2 (PAR-2) is known to be pro-inflammatory and increasing evidence points to an inflammatory component in osteoarthritis. This investigation examined the relationship between synovitis and PAR-2 expression, histological and immunohistochemical analysis being performed on synovial samples obtained from OA and RA patients, along with non-arthritic samples obtained by post mortem (PM). Samples were also analysed for PAR-4 expression, this receptor also having putative pro-inflammatory roles. Analysis involved comparison of inflammatory indices (synovial thickness and monocyte infiltration) with expression of PAR-2 and PAR-4. Synovial explants were also analysed for TNFα generation in the presence of a PAR-2 antagonist (ENMD-1068) or vehicle. OA synovia showed heterogeneity of inflammatory indicators, some samples overlapping with those from the RA cohort whilst others appeared similar to the PM cohort. PAR-2 expression, both in the lining layer and the interstitium, correlated strongly and significantly with synovial thickness (r = 0.91) and monocyte infiltration (r = 0.83), respectively (P < 0.001 in both cases), and this remains significant on individual cohort analysis. PAR-2 was co-localised to CD3 and CD68 cells in RA and OA synovium as well as fibroblasts derived from these synovia. PAR-4 was also expressed, but the relationship with inflammatory indicators was substantially weaker. Inflammatory indicators in OA synovia showed considerable variability, but correlated strongly with PAR-2 expression, suggesting PAR-2 upregulation in synovitis. Heterogeneity of inflammatory indicators was paralleled by wide variation in TNFα generation between samples. Secretion of this cytokine was dose-dependently inhibited by ENMD-1068, providing evidence of a functional role for PAR-2 in promoting synovitis.

Protease-activated receptor 2: a novel pathogenic pathway in a murine model of osteoarthritis.

OBJECTIVE: Osteoarthritis is a global clinical challenge for which no effective disease-modifying agents currently exist. This study identified protease-activated receptor 2 (PAR-2) as a novel pathogenic mechanism and potential therapeutic target in osteoarthritis. METHODS: Experimental osteoarthritis was induced in wild-type and PAR-2-deficient mice by sectioning the medial meniscotibial ligament (MMTL), leading to the development of a mild arthropathy. Cartilage degradation and increased subchondral bone formation were assessed as indicators of osteoarthritis pathology. RESULTS: Four weeks following MMTL section, cartilage erosion and increased subchondral bone formation was evident in wild-type mice but was substantially reduced in PAR-2-deficient mice. Crucially, the therapeutic inhibition of PAR-2 in wild-type mice, using either a PAR-2 antagonist or a monoclonal antibody targeting the protease cleavage site of PAR-2, was also equally effective at reducing osteoarthritis progression in vivo. PAR-2 was upregulated in chondrocytes of wild-type but not sham-operated mice. Wild-type mice showed further joint degradation 8 weeks after the induction of osteoarthritis, but PAR-2-deficient mice were still protected. CONCLUSIONS: The substantial protection from pathology afforded by PAR-2 deficiency following the induction of osteoarthritis provides proof of concept that PAR-2 plays a key role in osteoarthritis and suggests this receptor as a potential therapeutic target.

Matriptase is a novel initiator of cartilage matrix degradation in osteoarthritis.

OBJECTIVE: Increasing evidence implicates serine proteinases in pathologic tissue turnover. The aim of this study was to assess the role of the transmembrane serine proteinase matriptase in cartilage destruction in osteoarthritis (OA). METHODS: Serine proteinase gene expression in femoral head cartilage obtained from either patients with hip OA or patients with fracture to the neck of the femur (NOF) was assessed using a low-density array. The effect of matriptase on collagen breakdown was determined in cartilage degradation models, while the effect on matrix metalloproteinase (MMP) expression was analyzed by real-time polymerase chain reaction. ProMMP processing was determined using sodium dodecyl sulfate-polyacrylamide gel electrophoresis/N-terminal sequencing, while its ability to activate proteinase-activated receptor 2 (PAR-2) was determined using a synovial perfusion assay in mice. RESULTS: Matriptase gene expression was significantly elevated in OA cartilage compared with NOF cartilage, and matriptase was immunolocalized to OA chondrocytes. We showed that matriptase activated proMMP-1 and processed proMMP-3 to its fully active form. Exogenous matriptase significantly enhanced cytokine-stimulated cartilage collagenolysis, while matriptase alone caused significant collagenolysis from OA cartilage, which was metalloproteinase-dependent. Matriptase also induced MMP-1, MMP-3, and MMP-13 gene expression. Synovial perfusion data confirmed that matriptase activates PAR-2, and we demonstrated that matriptase-dependent enhancement of collagenolysis from OA cartilage is blocked by PAR-2 inhibition. CONCLUSION: Elevated matriptase expression in OA and the ability of matriptase to activate selective proMMPs as well as induce collagenase expression make this serine proteinase a key initiator and inducer of cartilage destruction in OA. We propose that the indirect effects of matriptase are mediated by PAR-2, and a more detailed understanding of these mechanisms may highlight important new therapeutic targets for OA treatment.

Expression and proinflammatory role of proteinase-activated receptor 2 in rheumatoid synovium: ex vivo studies using a novel proteinase-activated receptor 2 antagonist.

OBJECTIVE: Serine proteinases activate the G protein-coupled receptor, proteinase-activated receptor 2 (PAR-2), via cleavage and exposure of a tethered ligand. PAR-2 is known to exert proinflammatory actions in a murine model of arthritis, since PAR-2-deficient mice exhibit strikingly reduced articular inflammation. This study was undertaken to examine synovial PAR-2 expression and to determine the effect of a novel PAR-2 antagonist on synovial cytokine production, in order to investigate the hypothesis that PAR-2 plays a critical role in the pathogenesis of rheumatoid arthritis (RA). METHODS: Using a monoclonal antibody to human PAR-2, expression in RA synovium and cultured synovial fibroblasts was characterized. The novel PAR-2 antagonist, ENMD-1068, was added to primary cultures of RA synovial tissue, from which spontaneous cytokine release was measured. RESULTS: PAR-2 was substantially up-regulated in RA synovium compared with control synovial tissue from patients with osteoarthritis or seronegative inflammatory arthritis, neither of which exhibited significant PAR-2 expression. Importantly, spontaneous release of tumor necrosis factor alpha and interleukin-1beta from RA synovium was substantially inhibited by ENMD-1068, in a dose-dependent manner. CONCLUSION: These findings identify PAR-2 as a novel upstream regulator of proinflammatory cytokine production in RA and indicate its potential as a novel therapeutic target in inflammatory arthritis.

The therapeutic potential of proteinase-activated receptors in arthritis.

Proteinase-activated receptors are a family of seven-transmembrane G-protein-coupled receptors. Activation of PARs is initiated through cleavage of the N-terminus, unmasking a tethered ligand that can then interact with the receptor and lead to its activation. PARs exhibit both anti- and pro-inflammatory properties, although recent evidence has pointed towards a detrimental role for PARs, particularly PAR-2, in arthritis. Initial research using PAR-2 knockout mice identified PAR-2 as a key mediator of chronic joint inflammation. Further research examined the role of PAR-2 in human articular cell types, demonstrating upregulation of PAR-2 in cells from an inflammatory background compared with non-inflammatory cells, with PAR-2 levels being further upregulated by pro-inflammatory cytokines and growth factors. To date, there is no clinical evidence of a role for PAR-2 in vivo in humans, although recent studies utilizing human joint tissue and articular cells are emerging.

Therapeutic promise of proteinase-activated receptor-2 antagonism in joint inflammation.

Biological therapies such as tumor necrosis factor-alpha inhibitors have advanced the treatment of rheumatoid arthritis, but one-third of patients do not respond to such therapy. Furthermore, these inhibitors are now usually administered in combination with conventional disease-modifying antirheumatic drugs, suggesting they have not achieved their early promise. This study investigates a novel therapeutic target, proteinase-activated receptor (PAR)-2, in joint inflammation. Intra-articular carrageenan/kaolin (C/K) injection in mice resulted in joint swelling that was associated with synovial PAR2 up-regulation. Inhibiting receptor up-regulation using small interfering RNA technology, as confirmed by immunoblotting, substantially reduced the inflammatory response in the joint. Serine proteinase-induced joint swelling was mediated primarily via PAR2 activation, since the response to exogenous application of trypsin and tryptase was absent in PAR2 knockout mice. Furthermore, serine proteinase inhibitors were effective anti-inflammatory agents in this model. Disrupting proteolytic activation of PAR2 using antiserum (B5) directed to the receptor cleavage/activation site also attenuated C/K-induced inflammation, as did the similarly targeted PAR2 monoclonal antibody SAM-11. Finally, we report the activity of a novel small molecule PAR2 antagonist, N1-3-methylbutyryl-N4-6-aminohexanoyl-piperazine (ENMD-1068), that dose dependently attenuated joint inflammation. Our findings represent a major advance in collectively identifying PAR2 as a novel target for the future treatment of arthritis.

Pathophysiology of vascular dysfunction in a rat model of chronic joint inflammation.

The impact of chronic joint inflammation on articular vascular function in rats was investigated to address whether joint swelling and the associated vascular dysfunction are dependent upon a common prostanoid mechanism. Urinary nitrate/nitrite (NO(x)) and PGE(2) excretion, knee joint diameter and body weight were measured following induction of adjuvant-induced arthritis (AIA). Ten days postinduction of AIA, joint vascular reactivity was assessed by measuring the perfusion response using a laser Doppler imager (LDI) to topical application of acetylcholine (ACh) and sodium nitroprusside (SNP). Four groups were compared: a non-inflamed control group and three AIA groups treated i.p. with vehicle, indomethacin or SC-236 (at equimolar doses). The selective cyclooxygenase-2 (COX-2) inhibitor (SC-236) was used to differentiate between COX-1 and -2-derived prostaglandins. Urinary NO(x) and PGE(2) levels increased substantially during the early phase of AIA but decreased thereafter. Toxicity to indomethacin but not SC-236 was observed, as indicated by a marked decrease in body weight. Joint swelling was similarly attenuated by indomethacin and SC-236 (P= 0.0001 cf. vehicle-treated AIA; n= 5-6 per group), indicating that this is due to COX-2 and not COX-1 inhibition. The AIA-induced changes in urinary NO(x) and PGE(2) were corrected by both COX inhibitors. While vascular reactivity to ACh and SNP was significantly attenuated by AIA (P < 0.002; n= 5-10 per group), the perfusion responses to these vasodilating agents were similar in all three AIA groups, demonstrating that the vascular dysfunction was not corrected by inhibition of either COX-1 or COX-2 enzymes. Furthermore, the attenuation of both ACh and SNP-induced responses in AIA suggest that vascular dysfunction was not exclusively endothelial in nature. In conclusion, the joint swelling and vascular dysfunction associated with AIA appear to be mediated, at least in part, by independent mechanisms. While COX-1/COX-2 inhibition reduced joint swelling, vascular dysfunction in AIA is independent of constitutive or inducible prostanoid mechanisms, and appears not to be solely endothelial-derived, but to involve other components such as the vascular smooth muscle.