Analysis of intraarticular fibrinolytic pathways in patients with inflammatory and noninflammatory joint diseases

Prognostic model to predict the incidence of radiographic knee osteoarthritis

OBJECTIVE

Early diagnosis of knee osteoarthritis (KOA) in asymptomatic stages is essential for the timely management of patients using preventative strategies. We develop and validate a prognostic model useful for predicting the incidence of radiographic KOA (rKOA) in non-radiographic osteoarthritic subjects and stratify individuals at high risk of developing the disease.

METHODS

Subjects without radiographic signs of KOA according to the Kellgren and Lawrence (KL) classification scale (KL=0 in both knees) were enrolled in the OA initiative (OAI) cohort and the Prospective Cohort of A Coruña (PROCOAC). Prognostic models were developed to predict rKOA incidence during a 96-month follow-up period among OAI participants based on clinical variables and serum levels of the candidate protein biomarkers APOA1, APOA4, ZA2G and A2AP. The predictive capability of the biomarkers was assessed based on area under the curve (AUC), and internal validation was performed to correct for overfitting. A nomogram was plotted based on the regression parameters. Model performance was externally validated in the PROCOAC.

RESULTS

282 participants from the OAI were included in the development dataset. The model built with demographic, anthropometric and clinical data (age, sex, body mass index and WOMAC pain score) showed an AUC=0.702 for predicting rKOA incidence during the follow-up. The inclusion of ZA2G, A2AP and APOA1 data significantly improved the model's sensitivity and predictive performance (AUC=0.831). The simplest model, including only clinical covariates and ZA2G and A2AP serum levels, achieved an AUC=0.826. Both models were internally cross-validated. Predictive performance was externally validated in an independent dataset of 100 individuals from the PROCOAC (AUC=0.713).

CONCLUSION

A novel prognostic model based on common clinical variables and protein biomarkers was developed and externally validated to predict rKOA incidence over a 96-month period in individuals without any radiographic signs of disease. The resulting nomogram is a useful tool for stratifying high-risk populations and could potentially lead to personalised medicine strategies for treating OA.

The Roles of Fibrinolytic Factors in Bone Destruction Caused by Inflammation

Chronic inflammatory diseases, such as rheumatoid arthritis, spondyloarthritis, systemic lupus erythematosus, Crohn's disease, periodontitis, and carcinoma metastasis frequently result in bone destruction. Pro-inflammatory cytokines such as tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), IL-6, and IL-17 are known to influence bone loss by promoting the differentiation and activation of osteoclasts. Fibrinolytic factors, such as plasminogen (Plg), plasmin, urokinase-type plasminogen activator (uPA), its receptor (uPAR), tissue-type plasminogen activator (tPA), α2-antiplasmin (α2AP), and plasminogen activator inhibitor-1 (PAI-1) are expressed in osteoclasts and osteoblasts and are considered essential in maintaining bone homeostasis by regulating the functions of both osteoclasts and osteoblasts. Additionally, fibrinolytic factors are associated with the regulation of inflammation and the immune system. This review explores the roles of fibrinolytic factors in bone destruction caused by inflammation.

Platelet-Rich Fibrin-Augmented Gap-Bridging Strategy in Rabbit Anterior Cruciate Ligament Repair

BACKGROUND

We assessed the efficacy of a novel platelet-rich fibrin (PRF)-augmented repair strategy for promoting biological healing of an anterior cruciate ligament (ACL) midsubstance tear in a rabbit model. The biological gap-bridging effect of a PRF scaffold alone or in combination with rabbit ligamentocytes on primary ACL healing was evaluated both in vitro and in vivo.

HYPOTHESIS

A PRF matrix can be implanted as a provisional fibrin-platelet bridging scaffold at an ACL defect to facilitate functional healing.

STUDY DESIGN

Controlled laboratory study.

METHODS

The biological effects of PRF on primary rabbit ligamentocyte proliferation, tenogenic differentiation, migration, and tendon-specific matrix production were investigated for treatment of cells with PRF-conditioned medium (PRFM). Three-dimensional (3D) lyophilized PRF (LPRF)-cell composite was fabricated by culturing ligamentocytes on an LPRF patch for 14 days. Cell-scaffold interactions were investigated under a scanning electron microscope and through histological analysis. An ACL midsubstance tear model was established in 3 rabbit groups: a ruptured ACL was treated with isolated suture repair in group A, whereas the primary repair was augmented with LPRF and LPRF-cell composite to bridge the gap between ruptured ends of ligaments in groups B and C, respectively. Outcomes-gross appearance, magnetic resonance imaging, and histological analysis-were evaluated in postoperative weeks 8 and 12.

RESULTS

PRFM promoted cultured ligamentocyte proliferation, migration, and expression of tenogenic genes (type I and III collagen and tenascin). PRF was noted to upregulate cell tenogenic differentiation in terms of matrix production. In the 3D culture, viable cells formed layers at high density on the LPRF scaffold surface, with notable cell ingrowth and abundant collagenous matrix depositions. Moreover, ACL repair tissue and less articular cartilage damage were observed in knee joints in groups B and C, implying the existence of a chondroprotective phenomenon associated with PRF-augmented treatment.

CONCLUSION

Our PRF-augmented strategy can facilitate the formation of stable repair tissue and thus provide gap-bridging in ACL repair.

CLINICAL RELEVANCE

From the translational viewpoint, effective primary repair of the ACL may enable considerable advancement in therapeutic strategy for ACL injuries, particularly allowing for proprioception retention and thus improved physiological joint kinematics.

Effects of radiation dose and nitrogen purge on collagen scaffold properties

Sterilization of medical devices is commonly performed using radiation methods. However, collagen materials can be damaged when using standard radiation doses (25 kGy). Small increases of radiation dose can allow for increases in the acceptable initial bioburden load of aseptically manufactured devices while maintaining required sterility assurance levels, which is often critical in early stage translational settings. In this study, we hypothesized that small increases in radiation dose from 15 to 20 kGy would result in significant changes to several key characteristics of collagen scaffolds. Scaffolds were manufactured by lyophilizing the pepsin digest of dense bovine connective tissue in cylindrical molds and were irradiated at either 0, 15, 17.5, or 20 kGy with an additional group packaged in nitrogen and irradiated at 17.5 kGy. Groups were evaluated for changes to the soluble collagen and glycosaminoglycan mass fractions, protein banding patterns in electrophoresis, a collagen fragmentation assay, and resistance to enzymatic degradation. All parameters were statistically analyzed using one-way analysis of variance with Tukey's correction for multiple comparisons. The soluble collagen mass fraction was significantly decreased in the 20 kGy group; however, there was no significant effect of radiation dose or a nitrogen-rich environment on the other measured parameters, including protein banding patterns, fragmented collagen content, and resistance to enzymatic degradation.Statement of Clinical Significance: Collagen scaffolds have proven useful in clinical applications but can be damaged by standard radiation doses. Low-dose sterilization may be a viable alternative that minimally impacts key properties of these scaffolds.

Fibrin-Based Biomaterial Systems to Enhance Anterior Cruciate Ligament Healing

Anterior cruciate ligament (ACL) tears are a common and potentially career-ending injury, particularly for athletes and soldiers. Partial and complete ruptures of this ligament cause instability in the knee, and the ACL does not have the capacity for healing due, in part, to its position within the highly thrombolytic synovial fluid environment of the knee joint. Traditional methods of ACL reconstruction, such as graft replacement with attached bone anchors for bone integration, restore stability, but do not prevent the development of post-traumatic osteoarthritis. To enhance therapeutic treatment options, novel fibrin-based technologies and repair techniques have been recently explored and show promise for improved patient outcomes. Through modification of existing surgical methods, such as the use of fibrin glues incorporating growth factors and cells and the implementation of scaffolds containing platelet-rich plasma, platelet-rich fibrin, and other blood derivatives, surgeons are attempting to overcome the shortcomings of traditional treatments. This mini-review will detail current efforts using fibrin-based treatments and discuss opportunities to further enhance ACL healing.

The importance of plasmin for the healing of the anterior cruciate ligament

Aims

The anterior cruciate ligament (ACL) is known to have a poor wound healing capacity, whereas other ligaments outside of the knee joint capsule such as the medial collateral ligament (MCL) apparently heal more easily. Plasmin has been identified as a major component in the synovial fluid that varies among patients. The aim of this study was to test whether plasmin, a component of synovial fluid, could be a main factor responsible for the poor wound healing capacity of the ACL.

Methods

The effects of increasing concentrations of plasmin (0, 0.1, 1, 10, and 50 µg/ml) onto the wound closing speed (WCS) of primary ACL-derived ligamentocytes (ACL-LCs) were tested using wound scratch assay and time-lapse phase-contrast microscopy. Additionally, relative expression changes (quantitative PCR (qPCR)) of major LC-relevant genes and catabolic genes were investigated. The positive controls were 10% fetal calf serum (FCS) and platelet-derived growth factor (PDGF).

Results

WCS did not differ significantly among no plasmin versus each of the tested concentrations (six donors). The positive controls with PDGF and with FCS differed significantly from the negative controls. However, we found a trend demonstrating that higher plasmin concentrations up-regulate the expression of matrix metalloproteinase 13 (MMP13), 3 (MMP3), and tenomodulin (TNMD).

Conclusion

The clinical relevance of this study is the possibility that it is not solely the plasmin, but also additional factors in the synovial fluid of the knee, that may be responsible for the poor healing capacity of the ACL.

Cite this article: Bone Joint Res 2020;9(9):543–553.

Intra-articular TSG-6 delivery from heparin-based microparticles reduces cartilage damage in a rat model of osteoarthritis

As a potential treatment for osteoarthritis (OA), we have developed hydrolytically degradable heparin-based biomaterials for the intra-articular delivery of tumor necrosis factor-alpha stimulated gene-6 (TSG-6).

Haemarthrosis stimulates the synovial fibrinolytic system in haemophilic mice

Recurrent joint bleeding is the most common manifestation of haemophilia resulting in haemophilic arthropathy (HA). The exact pathophysiology is unknown, but it is suggested that arthropathy is stimulated by liberation of fibrinolytic activators from the synovium during haemarthrosis. The aim of this study was to test the hypothesis that haemarthrosis activates the local synovial fibrinolytic system in a murine haemophilia model. The right knees of haemophilic and control mice were punctured to induce haemarthrosis. The left knees served as internal control joints. Synovial levels of urokinase-type plasminogen activator (uPA), plasminogen activator inhibitor 1 (PAI-1), plasmin, and alpha-2-antiplasmin (A2AP) were compared between the punctured and control knees. In haemophilic mice, an increase in synovial cells expressing urokinase-type plasminogen activator (uPA) in the right punctured knee versus the left unaffected knee was observed: (47% vs 43%) (p=0.03). Additionally, in haemophilic mice, haemar-throsis induced an increase in uPA (0.016 ng/ml vs 0.01 ng/ml) (p=0.03) and plasmin (0.53 μg/ml vs 0.46 μg/ml) (p=0.01) as promoters of fibrinolysis. Synovial levels of PAI-1 (0.32 ng/ml vs 0.17 ng/ ml) (p<0.01) was also increased, whereas synovial levels of A2AP were unchanged: (0.021 μg/ml vs 0.021 μg/ml) (p=0.15). Enhanced uPA production was confirmed in human stimulated synovial fibroblast cultures and elevated levels of plasmin were confirmed harmful to human cartilage tissue explants. In this study we demonstrate that haemarthrosis in haemophilic mice induces synovial uPA expression and results in an increase in synovial plasmin levels, making the joint more vulnerable to prolonged and subsequent bleedings, and adding directly to cartilage damage.

Perioperative Blood Loss During Total Hip Arthroplasty Among Patients With Ankylosing Spondylitis

Intraoperative blood loss is frequently an overarching concern during total hip arthroplasty (THA) for patients who have ankylosing spondylitis with hip involvement. However, the factors that affect blood loss have not been identified. The goal of this study was to investigate these factors among patients with ankylosing spondylitis. Patients in the authors' department who had ankylosing spondylitis and underwent unilateral THA from 2011 to 2016 were studied retrospectively. Demographic characteristics, perioperative laboratory values, intraoperative data, transfusion rate, transfusion volume, and data on hemostatic use were collected and analyzed statistically. Multiple and univariate linear regression analyses were performed. As a result, 44 patients were eligible for inclusion in the study. Mean age was 31.7±10.6 years, and mean disease duration was 9.7±5.8 years. Mean body mass index was 21.30±3.01 kg/m². Mean volume of blood loss during THA was 1735.19±756.04 mL. Multiple linear regression analysis showed that perioperative blood loss was positively associated with Ankylosing Spondylitis Disease Activity Score (ASDAS), fibrinogen concentration, and surgical time. Further evaluation with univariate linear regression analysis suggested that ASDAS, red blood cell transfusion, and change of hematocrit concentration from preoperatively to postoperatively were correlated with blood loss. Disease activity, allogeneic blood transfusion volume, and change of hematocrit concentration from preoperatively to postoperatively appeared to be positively associated with perioperative blood loss during THA for patients with ankylosing spondylitis. For these patients, disease activity and the potential for allogeneic transfusion should be considered carefully before surgery. [Orthopedics. 2017; 40(5):e904-e910.].

Changes in concentrations of haemostatic and inflammatory biomarkers in synovial fluid after intra-articular injection of lipopolysaccharide in horses

Background

Septic arthritis is a common and potentially devastating disease characterized by severe intra-articular (IA) inflammation and fibrin deposition. Research into equine joint pathologies has focused on inflammation, but recent research in humans suggests that both haemostatic and inflammatory pathways are activated in the joint compartment in arthritic conditions. The aim of this study was to characterize the IA haemostatic and inflammatory responses in horses with experimental lipopolysaccharide (LPS)-induced joint inflammation. Inflammation was induced by IA injection of LPS into one antebrachiocarpal joint of six horses. Horses were evaluated clinically with subjective grading of lameness, and blood and synovial fluid (SF) samples were collected at post injection hours (PIH) -120, −96, −24, 0, 2, 4, 8, 16, 24, 36, 48, 72 and 144. Total protein (TP), white blood cell counts (WBC), serum amyloid A (SAA), haptoglobin, iron, fibrinogen, thrombin-antithrombin (TAT) and d-dimer concentrations were assessed in blood and SF.

Results

Intra-articular injection of LPS caused local and systemic signs of inflammation including increased rectal temperature, lameness and increased joint circumference and skin temperature. Most of the biomarkers (TP, WBC, haptoglobin, fibrinogen and TAT) measured in SF increased quickly after LPS injection (at PIH 2–4), whereas SAA and d-dimer levels increased more slowly (at PIH 16 and 144, respectively). SF iron concentrations did not change statistically significantly. Blood WBC, SAA, haptoglobin and fibrinogen increased and iron decreased significantly in response to the IA LPS injection, while TAT and d-dimer concentrations did not change. Repeated pre-injection arthrocenteses caused significant changes in SF concentrations of TP, WBC and haptoglobin.

Conclusion

Similar to inflammatory joint disease in humans, joint inflammation in horses was accompanied by an IA haemostatic response with changes in fibrinogen, TAT and d-dimer concentrations. Inflammatory and haemostatic responses were induced simultaneously and may likely interact. Further studies of interactions between the two responses are needed for a better understanding of pathogenesis of joint disease in horses. Knowledge of effects of repeated arthrocenteses on levels of SF biomarkers may be of value when markers are used for diagnostic purposes.

Purification and characterization of tenerplasminin-1, a serine peptidase inhibitor with antiplasmin activity from the coral snake (Micrurus tener tener) venom

A plasmin inhibitor, named tenerplasminin-1 (TP1), was isolated from Micrurus tener tener (Mtt) venom. It showed a molecular mass of 6542Da, similarly to Kunitz-type serine peptidase inhibitors. The amidolytic activity of plasmin (0.5nM) on synthetic substrate S-2251 was inhibited by 91% following the incubation with TP1 (1nM). Aprotinin (2nM) used as the positive control of inhibition, reduced the plasmin amidolytic activity by 71%. Plasmin fibrinolytic activity (0.05nM) was inhibited by 67% following incubation with TP1 (0.1nM). The degradation of fibrinogen chains induced by plasmin, trypsin or elastase was inhibited by TP1 at a 1:2, 1:4 and 1:20 enzyme:inhibitor ratio, respectively. On the other hand, the proteolytic activity of crude Mtt venom on fibrinogen chains, previously attributed to metallopeptidases, was not abolished by TP1. The tPA-clot lysis assay showed that TP1 (0.2nM) acts like aprotinin (0.4nM) inducing a delay in lysis time and lysis rate which may be associated with the inhibition of plasmin generated from the endogenous plasminogen activation. TP1 is the first serine protease plasmin-like inhibitor isolated from Mtt snake venom which has been characterized in relation to its mechanism of action, formation of a plasmin:TP1 complex and therapeutic potential as anti-fibrinolytic agent, a biological characteristic of great interest in the field of biomedical research. They could be used to regulate the fibrinolytic system in pathologies such as metastatic cancer, parasitic infections, hemophilia and other hemorrhagic syndromes, in which an intense fibrinolytic activity is observed.

Effect of low-temperature ethylene oxide and electron beam sterilization on the in vitro and in vivo function of reconstituted extracellular matrix-derived scaffolds

Reconstituted extracellular matrix (ECM)-derived scaffolds are commonly utilized in preclinical tissue engineering studies as delivery vehicles for cells and growth factors. Translation into clinical use requires identifying a sterilization method that effectively removes bacteria but does not harm scaffold function. To determine effectiveness of sterilization and impact on ECM scaffold integrity and function, low-temperature ethylene oxide and 15 kGy electron beam irradiation techniques were evaluated. Scaffold sterility was assessed in accordance to United States Pharmacopeia Chapter 71. Scaffold matrix degradation was determined in vitro using enzymatic resistance tests and gel electrophoresis. Scaffold mechanics including elastic modulus, yield stress and collapse modulus were tested. Lastly, 14 Yorkshire pigs underwent ACL transection and bio-enhanced ACL repair using sterilized scaffolds. Histologic response of ligament, synovium, and lymph nodes was compared at 4, 6, and 8 weeks. Ethylene oxide as well as electron beam irradiation yielded sterile scaffolds. Scaffold resistance to enzymatic digestion and protein integrity slightly decreased after electron beam irradiation while ethylene oxide altered scaffold matrix. Scaffold elastic modulus and yield stress were increased after electron beam treatment, while collapse modulus was increased after ethylene oxide treatment. No significant changes in ACL dimensions, in vivo scaffold resorption rate, or histologic response of synovium, ligament, and lymph nodes with either terminal sterilization technique were detectable. In conclusion, this study identifies two methods to terminally sterilize an ECM scaffold. In vitro scaffold properties were slightly changed without significantly influencing the biologic responses of the surrounding tissues in vivo. This is a critical step toward translating new tissue engineering strategies to clinical trials.

Proteomic analysis of synovial fluid from the osteoarthritic knee: comparison with transcriptome analyses of joint tissues

OBJECTIVE

The pathophysiology of the most common joint disease, osteoarthritis (OA), remains poorly understood. Since synovial fluid (SF) bathes joint cartilage and synovium, we reasoned that a comparative analysis of its protein constituents in health and OA could identify pathways involved in joint damage. We undertook this study to perform a proteomic analysis of knee SF from OA patients and control subjects and to compare the results to microarray expression data from cartilage and synovium.

METHODS

Age-matched knee SF samples from 10 control subjects, 10 patients with early-stage OA, and 10 patients with late-stage OA were compared using 2-dimensional difference-in-gel electrophoresis and mass spectrometry (MS). MS with a multiplexed peptide selected reaction monitoring assay was used to confirm differential expression of a subset of proteins in an independent OA patient cohort. Proteomic results were analyzed by Ingenuity Pathways Analysis and compared to published synovial tissue and cartilage messenger RNA profiles.

RESULTS

Sixty-six proteins were differentially present in healthy and OA SF. Three major pathways were identified among these proteins: the acute-phase response signaling pathway, the complement pathway, and the coagulation pathway. Differential expression of 5 proteins was confirmed by selected reaction monitoring assay. A focused analysis of transcripts corresponding to the differentially present proteins indicated that both synovial and cartilage tissues may contribute to the OA SF proteome.

CONCLUSION

Proteins involved in the acute-phase response signaling pathway, the complement pathway, and the coagulation pathway are differentially regulated in SF from OA patients, suggesting that they contribute to joint damage. Validation of these pathways and their utility as biomarkers or therapeutic targets in OA is warranted.

Natural and engineered plasmin inhibitors: applications and design strategies

The serine protease plasmin is ubiquitously expressed throughout the human body in the form of the zymogen plasminogen. Conversion to active plasmin occurs through enzymatic cleavage by plasminogen activators. The plasminogen activator/plasmin system has a well-established function in the removal of intravascular fibrin deposition through fibrinolysis and the inhibition of plasmin activity; this has found widespread clinical use in reducing perioperative bleeding. Increasing evidence also suggests diverse, although currently less defined, roles for plasmin in a number of physiological and pathological processes relating to extracellular matrix degradation, cell migration and tissue remodelling. In particular, dysregulation of plasmin has been linked to cancer invasion/metastasis and various chronic inflammatory conditions; this has prompted efforts to develop inhibitors of this protease. Although a number of plasmin inhibitors exist, they commonly suffer from poor potency and/or specificity of inhibition that either results in reduced efficacy or prevents clinical use. Consequently, there is a need for further development of high-affinity plasmin inhibitors that maintain selectivity over other serine proteases. This review summarises clearly defined and potential applications for plasmin inhibition. The properties of naturally occurring and engineered plasmin inhibitors are discussed in the context of current knowledge regarding plasmin structure, specificity and function. This includes design strategies to obtain the potency and specificity of inhibition in addition to controlled temporal and spatial distribution tailored for the intended use.

The Effect of Synovial Fluid Enzymes on the Biodegradability of Collagen and Fibrin Clots

Recently there has been a great deal of interest in the use of biomaterials to stimulate wound healing. This is largely due to their ability to centralize high concentrations of compounds known to promote wound healing at a needed location. Joints present a unique challenge to using scaffolds because of the presence of enzymes in synovial fluid which are known to degrade materials that would be stable in other parts of the body. The hypothesis of this study was that atelocollagen scaffolds would have greater resistance to enzymatic degradation than scaffolds made of gelatin, fibrin and whole blood. To test this hypothesis, collagen and fibrin-based scaffolds were placed in matrix metallopeptidase-1 (MMP-1), elastase, and plasmin solutions at physiologic concentrations, and the degradation of each scaffold was measured at varying time points. The atelocollagen scaffolds had a significantly greater resistance to degradation by MMP-1, elastase and plasmin over the fibrin based scaffolds. The results suggest that atelocollagen-based scaffolds may provide some protection against premature degradation by synovial fluid enzymes over fibrin-based matrices.

Fibrinolysis is down-regulated in mouse collagen-induced arthritis, but its normalization does not alleviate the course of disease

OBJECTIVE

Down-regulation of fibrinolysis and increased fibrin deposition in joints are hallmarks of rheumatoid arthritis (RA), and are believed to be involved in disease progression. The mouse model of collagen-induced arthritis (CIA) closely resembles RA and has been used to explore mechanism and treatments of RA, but neither the fibrinolytic system nor pro-fibrinolytic therapies were investigated in CIA.

MATERIALS AND METHODS

Plasmin activity, levels of plasminogen activator inhibitor (PAI-1), D-dimer, and IL-6 were measured in plasma of CIA mice. Fibrin deposition and PAI-1 levels were also measured in inflamed joints. Mice were treated with plasminogen activators uPA (urokinase-type plasminogen activator) or tPA (tissue-type plasminogen activator). Effects of treatment on disease severity and fibrinolytic system were assessed.

RESULTS

CIA caused decrease in plasmin activity, accompanied by increase in PAI-1 levels, in both blood and inflamed joints. This resulted in massive fibrin deposition in synovium. PAI-1 levels correlated negatively with plasmin activity and positively with IL-6. Treatments with uPA and tPA improved plasmin activity and removed fibrin deposits in inflamed joints. However, disease severity remained unchanged.

CONCLUSIONS

Fibrinolytic changes in CIA parallel changes in RA, making CIA a suitable model to study fibrinolysis in RA. Normalization of plasmin activity in CIA after treatment with plasminogen activators had no effect on disease severity.

How the surface nanostructure of polyethylene affects protein assembly and orientation

Protein adsorption plays a key role in the biological response to implants. We report how nanoscale topography, chemistry, crystallinity, and molecular chain anisotropy of ultrahigh molecular weight polyethylene (UHMWPE) surfaces affect the protein assembly and induce lateral orientational order. We applied ultraflat, melt drawn UHMWPE films to show that highly oriented nanocrystalline lamellae influence the conformation and aggregation into network structures of human plasma fibrinogen by atomic force microscopy with unprecedented clarity and molecular resolution. We observed a transition from random protein orientation at low concentrations to an assembly guided by the UHMWPE surface nanotopography at a close to full surface coverage on hydrophobic melt drawn UHMWPE. This assembly differs from the arrangement at a hydrophobic, on the nanoscale smooth UHMWPE reference. On plasma-modified, hydrophilic melt drawn UHMWPE surfaces that retained their original nanotopography, the influence of the nanoscale surface pattern on the protein adsorption is lost. A model based on protein-surface and protein-protein interactions is proposed. We suggest these nanostructured polymer films to be versatile model surfaces to provide unique information on protein interactions with nanoscale building blocks of implants, such as nanocrystalline UHMWPE lamellae. The current study contributes to the understanding of molecular processes at polymer biointerfaces and may support their future design and molecular scale tailoring.

A suppressive effect of prostaglandin E2 on the expression of SERPINE1/plasminogen activator inhibitor-1 in human articular chondrocytes: An in vitro pilot study

Prostaglandin E₂ (PGE₂) is expressed in articular joints with inflammatory arthropathy and may exert catabolic effects leading to cartilage degradation. As we observed in a preliminary experiment that PGE₂ suppressed the expression of SERPINE1/plasminogen activator inhibitor (PAI)-1 mRNA in chondrocytes, we focused on the effect of PGE₂ on PAI-1 in a panel of cultured chondrocytes obtained from osteoarthritic patients. Specifically, articular cartilage specimens were obtained from patients with osteoarthritis who underwent joint surgery. Isolated chondrocytes were cultured in vitro as a monolayer and stimulated with PGE₂. Stimulated cells and culture supernatants were analyzed using Western blotting and enzyme-linked immunosorbent assay. The results confirmed that the in vitro PGE₂ stimulation suppressed the expression of PAI-1 in the tested chondrocyte samples. The inhibitory effect was partly abrogated by an antagonist of EP4 receptor of PGE₂, but not by an EP2 antagonist. Although PGE₂ induced activations of mitogen-activated protein kinases (MAPK), blocking of the MAPK did not abrogate the suppressive effect of PGE₂, implying a distinct signaling pathway. In summary, prostaglandin is suggested to modulate the plasminogen system in chondrocytes. Further elucidation of the interaction might open a new avenue to understand the degradative process of cartilage.

Discreplasminin, a plasmin inhibitor isolated from Tityus discrepans scorpion venom

Tityus discrepans venom (TdV) produces digestive hemorrhages, disseminated intravascular coagulation, alveoli fibrin deposition and/or prothrombin and partial thromboplastin time alterations in humans. T. discrepans venom presents an in vitro tissue plasminogen activator-like (tPA-like), fibrino(geno)lytic and plasmin inhibitory activities. The plasmin inhibitor, called discreplasminin, was isolated from TdV. Discreplasminin has a pI of 8.0 and a relative molecular weight of <6,000 Da. Discreplasminin and aprotinin strongly inhibited plasmin activity and moderately tPA activity, while epsilon amino caproic acid (EACA) moderately inhibited both enzymes. In presence and absence of fibrin, the plasmin generation by tPA was completely inhibited by aprotinin and discreplasminin. EACA in the absence of fibrin partially inhibited plasmin generation (37%); however, it produced a total inhibition of plasmin generation on a fibrin surface. The tPA-clot lysis assay showed that discreplasminin acts like aprotinin inducing a slight delay in lysis time and lysis rate; in contrast, EACA presented a total inhibitory effect on fibrin lysis. These results suggest that discreplasminin presents an anti-fibrinolytic mechanism similar to aprotinin. Discreplasminin probably interacts with the active sites of plasmin and tPA. The presence of discreplasminin and other similar components in scorpion venom could partially explain the generalized fibrin deposition which was found previously in rams.

High abundance synovial fluid proteome: distinct profiles in health and osteoarthritis

The development of increasingly high-throughput and sensitive mass spectroscopy-based proteomic techniques provides new opportunities to examine the physiology and pathophysiology of many biologic fluids and tissues. The purpose of this study was to determine protein expression profiles of high-abundance synovial fluid (SF) proteins in health and in the prevalent joint disease osteoarthritis (OA). A cross-sectional study of 62 patients with early OA (n = 21), patients with late OA (n = 21), and control individuals (n = 20) was conducted. SF proteins were separated by using one-dimensional PAGE, and the in-gel digested proteins were analyzed by electrospray ionization tandem mass spectrometry. A total of 362 spots were examined and 135 high-abundance SF proteins were identified as being expressed across all three study cohorts. A total of 135 SF proteins were identified. Eighteen proteins were found to be significantly differentially expressed between control individuals and OA patients. Two subsets of OA that are not dependent on disease duration were identified using unsupervised analysis of the data. Several novel SF proteins were also identified. Our analyses demonstrate no disease duration-dependent differences in abundant protein composition of SF in OA, and we clearly identified two previously unappreciated yet distinct subsets of protein profiles in this disease cohort. Additionally, our findings reveal novel abundant protein species in healthy SF whose functional contribution to SF physiology was not previously recognized. Finally, our studies identify candidate biomarkers for OA with potential for use as highly sensitive and specific tests for diagnostic purposes or for evaluating therapeutic response.

Comparison of Textilinin-1 with Aprotinin as Serine Protease Inhibitors and as Antifibrinolytic Agents

Textilinin-1 (Q8008) was isolated from the venom of the Pseudonaja textilis and has a 47% sequence identity to the antihaemorrhagic therapeutic agent aprotinin. When equimolar concentrations of enzyme and aprotinin were pre-incubated, plasmin was inhibited 100%, plasma kallikrein 58%, and tissue kallikrein 99%. Under the same conditions, textilinin-1 inhibited plasmin 98%, plasma kallikrein 16% and tissue kallikrein 17%. Whole blood clot lysis was inhibited strongly by both aprotinin and textilinin-1, as shown by thrombelastography. At 2 microM inhibitor lysis initiated by t-PA was greater than 99% inhibited by aprotinin (LY60 = 0.4 +/- 0.1) whereas textilinin-1, inhibited lysis by 91% (LY60 = 8.9 +/- 0.7). The same trend was found with the lysis of euglobulin fractions. From these data textilinin-1 appears to be a more specific plasmin inhibitor than aprotinin but aprotinin inhibits clot lysis to a greater extent.

The plasminogen activator/plasmin system is essential for development of the joint inflammatory phase of collagen type II-induced arthritis

The plasminogen activator (PA) system has been proposed to have important roles in rheumatoid arthritis. Here we have used the autoimmune collagen type II (CII)-induced arthritis (CIA) model and mice deficient for urokinase-type PA (uPA) or plasminogen to investigate the role of the PA system for development of arthritis. Our data revealed that uPA-deficient mice have a lower severity and incidence of CIA than wild-type mice. Furthermore, although >80% of wild-type control mice developed CIA, we found that none of the 50 plasminogen-deficient littermates that were tested developed CIA within a 40-day period. Antibody generation after CII immunization as well as the binding of labeled anti-CII antibodies to the surface of cartilage were similar in wild-type and plasminogen-deficient mice. No sign of inflammation was seen when plasminogen-deficient mice were injected with a mixture of monoclonal antibodies against CII. However, after daily injections of human plasminogen, these mice developed arthritis within 5 days. Our finding that infiltration of inflammatory cells into the synovial joints was impaired in plasminogen-deficient mice suggests that uPA and plasminogen are important mediators of joint inflammation. Active plasmin is therefore essential for the induction of pathological inflammatory joint destruction in CIA.

A fibrin based model for rheumatoid synovitis

Intracavitary fibrin clots may initiate pannus formation and the immunopathology of RA. Two critical steps, probably host dependent, may determine the development of RA: an altered regulation of extravascular haemostasis or an aberrant reactivity of synovial fibroblasts to the adhered fibrin clots. Current treatments for RA target events downstream of fibrin deposition, perhaps agents acting at an earlier stage should be tried.

Urokinase, a constitutive component of the inflamed synovial fluid, induces arthritis

Urokinase plasminogen activator (uPA) is an important regulator of fibrinolysis in synovial fluid. An increase of uPA activity and expression of its receptor have been reported in joints of patients with rheumatoid arthritis (RA). The aim of the present study was to assess the arthritogenic capacity of uPA and the mechanisms by which this effect is mediated. uPA was injected into the knee joints of healthy mice, and morphological signs of arthritis were assessed 4 days after the injection. The prerequisite of different leukocyte populations for the development of uPA-triggered arthritis was assessed by selective cell depletion. The inflammatory capacity of uPA was assessed in vitro. Finally, levels of uPA were measured in 67 paired blood and synovial fluid samples from RA patients. The synovial fluid from RA patients displayed higher levels of uPA compared with blood samples. Morphological signs of arthritis were found in 72% of uPA-injected joints compared with in only 18% of joints injected with PBS (P < 0.05). Synovitis was characterised by infiltration of CD4-Mac-1+ mononuclear cells, by the formation of pannus and by occasional cartilage destruction. The absence of monocytes and lymphocytes diminished the frequency of synovitis (P < 0.01), indicating an arthritogenic role of both these leukocyte populations. Synthetic uPA inhibitor downregulated the incidence of uPA-triggered arthritis by 50%. uPA induced arthritis, stimulating the release of proinflammatory cytokines IL-6, IL-1beta and tumour necrosis factor alpha. Accumulation of uPA locally in the joint cavity is a typical finding in erosive RA. uPA exerts potent arthritogenic properties and thus may be viewed as one of the essential mediators of joint inflammation.

Effects of polysulfated glycosaminoglycan and triamcinolone acetonid on the production of proteinases and their inhibitors by IL-1alpha treated articular chondrocytes

In this study we determined the in vitro effects of polysulfated glycosaminoglycan (PSGAG) and the glucocorticoid triamcinolone acetonid (TA) on the IL-1 altered expression and activity of matrix metalloproteinases (MMP-1, MMP-3), tissue inhibitor of metalloproteinases-1, the plasminogen activators tPA and uPA and plasminogen activator inhibitor 1 by articular chondrocytes. Bovine chondrocytes were cultured in alginate gel beads. Cells were treated with interleukin-1alpha (IL-1alpha) in the presence of vehicle or drugs at various concentrations. After 48hr mRNA expression of MMP-1, MMP-3, TIMP-1, uPA, tPA and PAI-1 was analyzed by RT-PCR-ELISA. The protein synthesis of TIMP-1 and MMP-3 was determined by immunoprecipitation, PAI-1 protein was quantitated by ELISA. The activity of enzymes and inhibitors was measured by functional assays. Treating chondrocytes with IL-1 induced the expression of MMPs and downregulated TIMP-1 but stimulated both the expression of PAs and PAI-1. Both drugs significantly reduced collagenase and proteoglycanase activities which was accompanied by inhibition of the expression of MMP-1 and MMP-3. The IL-1 decreased expression of TIMP-1 was further reduced by TA, which resulted in a significant loss of TIMP activity. No effects on TIMP activity or TIMP-1 biosynthesis were observed after treatment of chondrocytes with PSGAG. Both drugs inhibited the IL-1-induced mRNA expression of tPA, whereas expression of uPA was only mildly reduced by PSGAG, which also induced PAI-1 above IL-1 stimulated levels. As inhibition of collagenase activities and tPA expression by PSGAG occurred at physiological concentrations it might be of clinical relevance, indicating that PSGAG could help reducing cartilage degradation and has a strong anti-fibrinolytic potential. Due to their co-regulation of MMPs and TIMP(s) glucocorticoids should be carefully studied for their overall effect on extracellular matrix proteolysis.

Activation of procollagenases is a key control point in cartilage collagen degradation: interaction of serine and metalloproteinase pathways

OBJECTIVE

Bovine and human cartilages in explant culture respond to proinflammatory cytokines with the up-regulation of procollagenases. In stimulated bovine nasal cartilage (BNC), >90% of collagen is released by day 14 of culture, but collagen release is rarely seen before day 7. The aim of this study was to investigate if activation of procollagenases is a rate-limiting step in cartilage collagen breakdown.

METHODS

BNC and human articular cartilage explants were cultured with interleukin-1alpha (IL-1alpha) and/or oncostatin M (OSM) with or without test reagents. Collagen levels were determined by assay of hydroxyproline. Collagenase activity was measured using the diffuse fibril assay.

RESULTS

The addition of procollagenase activators, matrix metalloproteinase 3 (MMP-3), and APMA to IL-1alpha/OSM-stimulated BNC resulted in early release of collagen. The release with APMA was completely blocked by the addition of tissue inhibitor of metalloproteinases 1. This shows that procollagenases are present early in the culture period, but cartilage collagen breakdown does not happen until activation occurs. The addition of plasminogen to IL-1alpha/OSM-stimulated cartilage produced early collagen release in bovine and a significant increase in human cartilage. Thus, plasminogen activators (PAs) are present and convert plasminogen to plasmin, a known activator of several MMPs, including collagenases. Addition of alpha1-proteinase inhibitor or a urokinase-type PA inhibitor, 7-amino-4-chloro-3-(3-isothiureidopropoxy) isocoumarin, partially blocked the breakdown of collagen from IL-1alpha/OSM-treated bovine cartilage. This suggests that serine proteinases are involved in the activation cascades of procollagenases that result in cartilage collagen breakdown.

CONCLUSION

The activation of procollagenases is a key control point in cartilage collagen breakdown, and serine proteinase pathways activate MMPs.

Effects of ceramide on aggrecanase activity in rabbit articular cartilage

Ceramide participates in signal transduction of IL-1 and TNF, two cytokines likely involved in cartilage degradation in osteoarthritis. We previously showed that ceramide stimulates proteoglycan degradation, mRNA expression of matrix metalloproteinase (MMP)-1, -3, and -13, and pro-MMP-3 production in rabbit cartilage. Since aggrecan, the main cartilage proteoglycan, can be cleaved by metalloproteinases both of MMP and aggrecanase type, the aim of this study was to determine if ceramide stimulates aggrecanase action and, if that is the case, in which measure aggrecanase mediates the degradative effect of ceramide. To this end, antibodies were used against the C terminal aggrecan neoepitopes generated by aggrecanases (NITEGE(373)) and MMPs (DIPEN(341)). Ceramide C(2) at 10(-5) to 10(-4) M dose-dependently increased NITEGE signal, without changing that of DIPEN, in cultured explants of rabbit cartilage. The effects of 10(-4) M C(2) on NITEGE signal and proteoglycan degradation were similarly antagonized by the metalloproteinase inhibitor batimastat, with return to the basal level at 10(-6) M. These results show that, similarly to IL-1 and TNF, ceramide-induced aggrecan degradation is mainly due to aggrecanases. That no increase of MMP activity was detected, despite stimulation of MMP expression, was probably due to lack of proenzyme conversion to mature form, since addition of a MMP activator to C(2)-treated cartilage increased both DIPEN signal and proteoglycan degradation. These findings support the hypothesis that cytokine-induced ceramide could play a mediatory role in situations of increased degradation of cartilage matrix.

Fibrin(ogen)-induced expression of ICAM-1 and chemokines in human synovial fibroblasts

It has long been recognized that in most inflamed arthritic joints the coagulation system is activated, leading to the local generation of fibrin, and it has long been hypothesized that the local fibrin deposition promotes inflammation and tissue destruction. However, only recently has the direct effect of fibrin on the inflammatory process been seriously investigated, and specific roles assigned to fibrin or its products as mediators of the inflammatory process. Although fibrin and/or fibrinogen (fibrin(ogen)) is abundantly present in inflamed tissues and joints rich in fibroblastic cells, no significant data on fibrin(ogen)-induced gene expression by fibroblasts have been published. We now demonstrate that coculture of human synovial fibroblasts with fibrin(ogen) results in the up-regulation of ICAM-1 as well as increased production of the chemokines IL-8 and growth-related oncogene-alpha. Increased ICAM-1 expression was fibrin(ogen) dose-dependent and was demonstrated by ELISA, flow cytometry, and functional adhesion assays. Levels of ICAM-1 induced by fibrin(ogen) were comparable to those that could be induced by cytokine stimulation. Fibrin(ogen) stimulation of ICAM-1 could be suppressed by pyrrolidinedithiocarbamate, an inhibitor of NF-kappaB activation. Chemokine production was induced by fibrin(ogen) in cell culture supernatants >100-fold as compared with controls. Thus, through its activation of synovial fibroblasts, fibrin(ogen) deposition may promote the recruitment (via chemokines) and retention (via adhesion molecules) of lymphocytes within the arthritic joint.

Soluble urokinase plasminogen activator receptor in plasma of patients with inflammatory rheumatic disorders: increased concentrations in rheumatoid arthritis

OBJECTIVE

Urokinase type plasminogen activator (uPA) catalyses the formation of the proteolytic enzyme plasmin, which is involved in matrix degradation in the processes of tissue remodelling. Because of a surface bound uPA receptor (uPAR), expressed by some cell types (for example, macrophages, malignant cells and inflammatory activated synoviocytes), the action of uPA can be localised and intensified. uPAR seems to have a role in the mechanisms leading to invasive growth of malignant tissue and the rheumatoid pannus. uPAR may become cleaved at its cell surface anchor, thus forming a free soluble receptor (suPAR). suPAR is detectable in low but constant values in plasma of healthy people, while increased concentrations are found in patients with disseminated malignant disease, so that suPAR may be an indicator of invasive growth and tissue remodelling. suPAR concentrations in plasma have not previously been measured in rheumatic patients. A controlled cross sectional measurement was performed of suPAR in plasma of patients with various inflammatory rheumatic disorders with special reference to rheumatoid arthritis (RA).

METHODS

suPAR in plasma was measured by ELISA technique in patients with RA (n=51), reactive arthritis (ReA) (n=23), primary Sjögren's syndrome (PSS) (n=42) and sex and age matched healthy controls (n=53).

RESULTS

In the control group suPAR (median) was 0. 91 (range 0.56-1.94) microg/l. Median suPAR value in RA was 1.47 (range 0.65-6.62) microgram/l; in ReA 0.68 microgram/l (range 0.52-1.48) and in PSS 1.12 microgram/l (range 0.76-1.92); p versus controls <0.001 in all patient groups. suPAR values in RA were also significantly increased compared with ReA (p<0.001) and PSS (p=0.004) groups. suPAR in RA was positively correlated to C reactive protein (CRP) (p<0.01) and erythrocyte sedimentation rate (p<0.05) and number of swollen joints (p<0.05). The ReA group had the highest CRP values of all groups, but at the same time the lowest suPAR concentrations in plasma.

CONCLUSIONS

Increased suPAR concentrations were found in plasma in RA, and to a smaller extent also in PSS, but not in ReA. In RA suPAR is related to disease activity. suPAR seems though not merely to be an acute phase reactant like CRP. Increased suPAR values might reflect erosive activity in RA.

Increased vulnerability of postarthritic cartilage to a second arthritic insult: accelerated MMP activity in a flare up of arthritis

OBJECTIVE

Murine antigen induced arthritis (AIA) is a chronic, smouldering inflammation. Flares of arthritis can be induced by antigen rechallenge or exposure to inflammatory mediators like interleukin 1 (IL1). These flares are characterised by a fast and marked proteoglycan (PG) depletion if compared with the initial arthritis. This study investigated the involvement of metalloproteinases in both the initial and the flare phase of arthritis.

METHODS

Murine AIA was induced and a flare up of arthritis was induced by injection of 10 ng of IL1beta. Messenger RNA levels of MMP-1 and -3 were studied by RT-PCR. MMP activity in cartilage, during both primary AIA as well as the flare up of arthritis, was studied by immunodetection of MMP specific neoepitopes in aggrecan (VDIPEN). Cartilage just before flare induction was analysed for presence of MMPs at the mRNA level as well as at the protein level by zymography.

RESULTS

At the onset of AIA, a fast upregulation of mRNA for stromelysin and collagenase was noted. However, no VDIPEN epitopes were detected during this early phase of arthritis. They appeared when PG depletion was severe at day 7 of arthritis and disappeared when cartilage was repaired. IL1 injection into a knee joint at week 4 of AIA caused a flare up of arthritis, coinciding with a fast and marked PG degradation. This degradation was characterised by accelerated expression of VDIPEN epitopes if compared with the expression in primary AIA. Analysis of cartilage at week 4 of AIA showed still increased mRNA levels of MMP-1 and -3. Moreover, increased levels of latent MMPs were present as well, as APMA activation induced profound VDIPEN epitope. In vitro exposure to IL1 did show increased PG breakdown but no VDIPEN expression, suggesting that factors in addition to IL1 are needed to cause the in vivo VDIPEN expression.

CONCLUSIONS

The fast and marked PG depletion seen in a flare up of AIA coincides with accelarated expression of MMP induced neoepitopes compared with expression during primary AIA. This accelerated expression is probably linked to increased levels of latent enzyme, which were found to be present in the cartilage before induction of a flare up.

Synoviocytes from osteoarthritis and rheumatoid arthritis produce plasminogen activators and plasminogen activator inhibitor-1 and display u-PA receptors on their surface

The production of plasminogen activators and their inhibitors was studied in vitro in osteoarthritic (OA) and rheumatoid arthritic (RA) synovial fibroblasts (SF), obtained from RA and OA patients undergoing joint surgery. Subcultured SF were cultivated for 2, 4, 6, 8, 10 and 13 days and the medium assayed for the presence of both plasminogen activators (PAs) and plasminogen activator inhibitor-1 (PAI-1). The presence of urokinase-Plasminogen Activator (u-PA) receptors (u-PAR) on the surface of synovial cells was investigated by radio-ligand binding assay and cross-linking and by transmission electron microscopy (TEM) of a gold-u-PA complex. Our results showed a low production of tissue-type-Plasminogen Activator (t-PA) in both OA and RA SF, but relatively high levels of u-PA, until confluence, both in OA and in RA. SF were also able to produce plasminogen activator inhibitor in large amounts, in particular in RA since the very beginning of the culture. Receptors for u-PA were evident on both RA and OA SF. Our data show that SF in vitro produce mainly u-PA, the most important plasminogen activator involved in tissue modifications. The demonstration of u-PA receptors on the surface of OA and RA SF represents a step forward in the understanding of the possible role of fibrinolytic and tissue destructive proteinase cascade in joint inflammation.

Human urinary trypsin inhibitor inhibits the activation of pro-matrix metalloproteinases and proteoglycans release in rabbit articular cartilage

Treatment of primary cultured chondrocytes from rabbit articular cartilage with interleukin-1 (IL-1)alpha and plasminogen induced the production of pro-matrix metalloproteinase 1 (proMMP-1/interstitial collagenase), proMMP-3 (stromelysin 1) and proMMP-9 (gelatinase B), as well as their active forms. Human urinary trypsin inhibitor (UTI), a multipotent inhibitor of serine proteases, including plasmin inhibited the activation of proMMP-1, proMMP-3 and proMMP-9 when added to the culture medium together with IL-1alpha and plasminogen, in a dose-dependent manner. Moreover, UTI inhibited the release of proteoglycans induced by IL-1alpha and plasminogen from rabbit articular cartilage explants. These findings strongly suggest that UTI inhibits the destruction of articular cartilage induced by plasmin and/or MMPs. Thus, UTI probably exert an anti-osteoarthritic action via inactivation of proMMPs.

Intracellular Pool of Vascular Endothelial Growth Factor in Human Neutrophils

Vascular endothelial growth factor (VEGF ), an endothelial cell mitogen, is a potent angiogenic factor produced by several cell types. Whether human neutrophils are potential producers of VEGF has not yet been described. The present work shows that phorbol-12-myristate 13-acetate (PMA), fMet-Leu-Phe, and tumor necrosis factor-α (TNF-α) triggered a time-dependent secretion of VEGF by human neutrophils. Cells incubated with 50 ng/mL of PMA released significant amounts of VEGF after 15 minutes. Because the extracellular content of VEGF in human neutrophils supernatants remained constant over a period of 2 to 24 hours and because PMA is a potent inducer of human neutrophil degranulation, the PMA-induced secretion of VEGF may be due to a pre-existing intracellular pool of this molecule. This hypothesis was reinforced by the absence of cycloheximide effect on the PMA-induced secretion of VEGF. The existence of an intracellular pool of VEGF was confirmed by measuring the intracellular content of VEGF in resting neutrophils. A dosedependent inhibition of PMA-induced VEGF secretion was observed when the cells were incubated in the presence of pentoxifylline, a methylxanthine known to inhibit neutrophil degranulation. To confirm the implication of neutrophil degranulation in VEGF release, the effects of two inducers of physiologic degranulation, fMet-Leu-Phe and TNF-α, were determined. Both agonists induced a release of VEGF in the absence of cytochalasin B, confirming the involvement of neutrophil degranulation and suggesting the intracellular localization of VEGF in the specific granule fraction. In addition, the kinetics of fMet-Leu-Phe– and TNF-α–induced secretion of lactoferrin were similar to those of VEGF release induced by these two both agonists. The subcellular fractionation of human neutrophils showed a granule-specific distribution of the intracellular pool of VEGF in resting neutrophils. The finding that human neutrophils contain an intracellular pool of VEGF, secreted in the extracellular space under PMA-, fMet-Leu-Phe–, and TNF-α–induced degranulation, suggests a role for human neutrophils as cellular effectors of physiologic as well as pathologic angiogenesis.

Plasminogen activation in synovial tissues: differences between normal, osteoarthritis, and rheumatoid arthritis joints

OBJECTIVE

To analyse the functional activity of the plasminogen activators urokinase (uPA) and tissue type plasminogen activator (tPA) in human synovial membrane, and to compare the pattern of expression between normal, osteoarthritic, and rheumatoid synovium. The molecular mechanisms underlying differences in PA activities between normal and pathological synovial tissues have been further examined.

METHODS

Synovial membranes from seven normal (N) subjects, 14 osteoarthritis (OA), and 10 rheumatoid arthritis (RA) patients were analysed for plasminogen activator activity by conventional zymography and in situ zymography on tissue sections. The tissue distribution of uPA, tPA, uPA receptor (uPAR), and plasminogen activator inhibitor type-1 (PAI-1) was studied by immunohistochemistry. uPA, tPA, uPAR, and PAI-1 mRNA values and mRNA distribution were assessed by northern blot and in situ hybridisations respectively.

RESULTS

All normal and most OA synovial tissues expressed predominantly tPA catalysed proteolytic activity mainly associated to the synovial vasculature. In some OA, tPA activity was expressed together with variable amounts of uPA mediated activity. By contrast, most RA synovial tissues exhibited considerably increased uPA activity over the proliferative lining areas, while tPA activity was reduced when compared with N and OA synovial tissues. This increase in uPA activity was associated with increased levels of uPA antigen and its corresponding mRNA, which were localised over the synovial proliferative lining areas. In addition, in RA tissues, expression of the specific uPA receptor (uPAR) and of the plasminogen activator inhibitor-type 1

Up-regulation of the alpha2-macroglobulin signaling receptor on rheumatoid synovial fibroblasts

In the present study, we demonstrate that the alpha2-macroglobulin (alpha2M) signaling receptor is up-regulated on rheumatoid synovial fibroblasts. In rheumatoid cells, 125I-alpha2M-methylamine bound to two sites; namely, one of high affinity (Kd approximately 52 pM) and the second of lower affinity (Kd approximately 9.7 nM). In normal synovial fibroblasts only one site for 125I-alpha2M-methylamine (Kd approximately 5.36 nM) was present. Receptor-associated protein did not inhibit the binding of alpha2M-methylamine to the high affinity binding sites, but it caused a 70-80% reduction in its binding to low affinity binding sites establishing its identity as the low density lipoprotein receptor-related protein/alpha2M receptor. Binding of alpha2M-methylamine to rheumatoid but not normal synovial fibroblasts caused a rapid rise in inositol 1,4,5-trisphosphate synthesis with a peak reached within 10 s of ligand exposure. Concomitantly, rheumatoid but not normal cells showed a rise in intracellular Ca2+. Pretreatment of rheumatoid cells with Receptor-associated protein or pertussis toxin did not affect the alpha2M-methylamine-induced increase in intracellular Ca2+. These are characteristic properties of ligation by alpha2M-methylamine of the alpha2M signaling receptor but not the lipoprotein receptor-related protein/alpha2M receptor. Binding of alpha2M-methylamine to rheumatoid synovial fibroblasts significantly increased the synthesis of DNA compared with normal synovial fibroblasts treated similarly.

Significance of serine proteinase and matrix metalloproteinase systems in the destruction of human articular cartilage

1. During the destruction of articular cartilage, fibrinolytic enzymes and matrix metalloproteinases (MMP) may contribute to the related pathology. The activities, antigens and messenger RNA (mRNA) levels of urokinase-type plasminogen activator (uPA) and plasminogen activator inhibitor-1 (PAI-1) in articular cartilage were measured in patients with no history of joint diseases (control), those with osteoarthritis (OA) classified into osteophyte-formed site (OS) and weight-bearing site (WS), and in patients with rheumatoid arthritis (RA). 2. The uPA content was higher in WS and RA compared to normal. The PAI-1 content was higher in OS and RA compared to normal. Weight-bearing site patients expressed a high uPA mRNA level but a low PAI-1 mRNA level. Osteophyte-formed site patients expressed a low uPA mRNA level but a high PAI-1 mRNA level. 3. The levels of the MMP and mRNA of tissue inhibitors of metalloproteinases (TIMP) were measured in WS, OS, and RA. In WS, the levels of MMP were high and levels of TIMP mRNA expression low. In OS, the levels of TIMP were high and levels of MMP mRNA were low. In RA, the levels of MMP and TIMP mRNA were high. 4. These findings suggest that regulation of fibrinolysis may play an important role in the matrix of articular cartilage with arthropathy.

Plasminogen modulation of IL-1-stimulated degradation in bovine and human articular cartilage explants. The role of the endogenous inhibitors: PAI-1, alpha 2-antiplasmin, alpha 1-PI, alpha 2-macroglobulin and TIMP

The studies described here examine the involvement of the fibrinolytic cascade and its endogenous inhibitors in the regulation of activity of matrix metalloproteinases and cartilage degradation related to non-inflammatory joint disease, like osteoarthritis. An interleukin-1-induced model of degradation using [35S]-labeled bovine and human articular cartilage explants was utilized. One goal of these studies was to compare the responses of bovine and human articular cartilage. Degradation was not inhibited by alpha 1-PI, PAI-1, alpha 2-macroglobulin, alpha 2-antiplasmin or TIMP-2, when IL-1 alone was added. Addition of human plasminogen to bovine explants, at concentrations found in human synovial fluid, increased degradation by three to four-fold. Under these conditions, the degradation was inhibited effectively by all of the endogenous inhibitors tested, indicating the presence of a cascade where activated chondrocytes are a source of u-PA. Plasminogen activated by u-PA gives plasmin, which is known to further activate pro-stromelysin. Stromelysin is essential for activation of collegenase. Not only TIMP, but also inhibitors at earlier steps of activation like PAI-1, alpha 2-antiplasmin, alpha 1-PI and alpha 2-macroglobulin inhibited degradation, and could provide cartilage protection in vivo. An experiment with human articular cartilage explants showed that very little or no degradation occurred when human articular cartilage explants were stimulated with interleukin-1 alone. Addition of human plasminogen (at physiologically relevant concentrations) resulted in significant degradation, which was inhibited in the same manner as in bovine explants, by inhibitors of the fibrinolytic cascade and TIMP. TIMP is much more efficient in human explants, indicating the limited participation of human plasmin in the degradation of human cartilage. Although speculative, it is possible that in vivo, cartilage degradation could be promoted not only by TIMP/MMP imbalance, but also accelerated by decreased levels of certain serpins in synovial fluid (e.g. PAIs, alpha 2-antiplasmin and alpha 1-PI).

Plasminogen activators and their inhibitors in synovial fluids from normal, osteoarthritis, and rheumatoid arthritis knees

OBJECTIVES

To establish baseline concentrations of plasminogen activators and their inhibitors in normal knee synovial fluids, and to compare them with well characterised osteoarthritis (OA) and rheumatoid arthritis (RA) knee fluids.

METHODS

A total of 26 normal subjects, 71 patients with OA, and 17 patients with RA underwent knee aspiration. Patients with OA were subclassified according to presence of nodal generalised OA (NGOA) and synovial fluid calcium pyrophosphate crystals. Clinical assessment of inflammation (graded 0-6) was undertaken in OA and RA patients. Plasminogen activator (PA), plasminogen activator inhibitor (PAI), and urokinase-type PA receptor (uPAR) antigen concentrations were determined by enzyme linked immunosorbent assay. The species of PAs present were determined by sodium dodecyl sulphate-polyacrylamide gel electrophoresis.

RESULTS

Concentrations of all antigens (uPA, tissue-type PA (tPA), uPAR, and PAI-1), were significantly greater in RA than OA; those in OA were significantly greater than normal. The concentrations showed no direct association with clinically assessed inflammation of the knee. In normal fluids, no associations with age were observed. Antigen concentrations (uPA, tPA, and uPAR) in NGOA differed from those in other subclasses of OA, but the species of PA present did not appear to vary between disease groups. The predominant PA appeared to have identity with uPA.

CONCLUSION

Because of the greater concentrations of these antigens in OA compared with normal fluids, OA cannot be used as a surrogate normal control in studies of the PA/PAI system. Alteration of the PA/PAI system was confirmed in RA and OA knee fluids, with greater changes evident in RA. The finding of different concentrations of PA antigens in NGOA compared with other OA fluids further supports a different pathogenic mechanism in this subset.

A solid-phase antibody capture assay for the measurement of C1-inhibitor consumption in vivo

C1-inhibitor (C1-Inh) is a serine esterase proteinase inhibitor (serpin) which plays an important role in regulating serine proteinases of the early inflammatory response. In this study, we describe a novel and versatile polyclonal antibody capture assay to examine C1-Inh consumption in vivo. This assay has advantages over previously described methods of measuring C1-Inh consumption as it allows the assessment of the relative amounts of native, complexed and cleaved inhibitor circulating in plasma. By using polyclonal antibodies specific for other complement proteins, the C1-Inh capture assay was adapted to measure in vivo activation of C3, C4 and factor B. C1-Inh consumption and complement activation were examined in the plasma of 21 normal individuals, 24 individuals with systemic lupus erythematosus (SLE), nine individuals with adult respiratory distress syndrome (ARDS) and in the paired plasma and synovial fluid from 18 patients with rheumatoid arthritis (RA). The C1-Inh capture assay revealed native, cleaved and complexed C1-Inh migrating at 115 kDa, 96 kDa and 209-225 kDa respectively, in normal plasma. C1-Inh consumption was increased in the plasma of all the inflammatory disorders examined, in comparison to normal plasma. It is proposed that this serpin capture assay could be adapted to the study of serpin involvement in a wide variety of inflammatory disorders.

Proteolytic inactivation of alpha 1-antitrypsin and alpha 1-antichymotrypsin by neutrophils in arthritic joints

OBJECTIVE

In vitro, activated neutrophils create a microenvironment in which proteinase inhibitors are inactivated through the coordinate action of reactive oxygen species and released elastase. We investigated whether such a mechanism may contribute to the destruction of the joint tissues in arthritis.

METHODS

We analyzed the state of alpha 1-antitrypsin (alpha 1AT) and alpha 1-antichymotrypsin (alpha 1ACT), the two major inhibitors of the neutrophilic serine proteinases, in synovial fluid (SF) from patients with inflammatory arthropathies (n = 71) and osteoarthritis (OA) (n = 11), and related the results to neutrophil activation in SF.

RESULTS

The ratio of functional to antigenic levels of alpha 1AT in SF of patients with inflammatory joint diseases was similar to that of alpha 1AT in normal plasma, whereas that of alpha 1ACT was significantly decreased. Patients with inflammatory arthropathies had significantly higher levels of inactivated alpha 1AT (i alpha 1AT) and inactivated alpha 1ACT (i alpha 1ACT) in SF (as determined with monoclonal antibodies specific for the inactivated [i.e., proteolytically inactivated and/or complexed] forms of these inhibitors) than patients with OA (P < 0.005). Inactivated alpha 1AT and i alpha 1ACT levels corresponded to 0.3-11% and 3-99%, respectively, of the total amount of these inhibitors in SF. Most of the i alpha 1AT in SF had a lower M(r) than that of native alpha 1AT. Inactivated alpha 1ACT in SF had an M(r) identical to that of nonfunctional alpha 1ACT in plasma treated with chymotrypsin. Levels of both i alpha 1AT and i alpha 1ACT correlated significantly with lactoferrin and elastase levels.

CONCLUSION

These results suggest that alpha 1AT and alpha 1ACT in arthritic joints are inactivated in part by activated neutrophils, suggesting a role for these cells in impairment of the local balance between proteinases and their inhibitors in arthritis.