Cartilage proteoglycans in synovial fluid and serum in patients with inflammatory joint disease. Relation to systemic treatment

Biomarkers and proteomic analysis of osteoarthritis

Our friend and colleague, Dr. Dick Heinegård, contributed greatly to the understanding of joint tissue biochemistry, the discovery and validation of arthritis-related biomarkers and the establishment of methodology for proteomic studies in osteoarthritis (OA). To date, discovery of OA-related biomarkers has focused on cartilage, synovial fluid and serum. Methods, such as affinity depletion and hyaluronidase treatment have facilitated proteomics discovery research from these sources. Osteoarthritis usually involves multiple joints; this characteristic makes it easier to detect OA with a systemic biomarker but makes it hard to delineate abnormalities of individual affected joints. Although the abundance of cartilage proteins in urine may generally be lower than other tissue/sample sources, the protein composition of urine is much less complex and its collection is non-invasive thereby facilitating the development of patient friendly biomarkers. To date however, relatively few proteomics studies have been conducted in OA urine. Proteomics strategies have identified many proteins that may relate to pathological mechanisms of OA. Further targeted approaches to validate the role of these proteins in OA are needed. Herein we summarize recent proteomic studies related to joint tissues and the cohorts used; a clear understanding of the cohorts is important for this work as we expect that the decisive discoveries of OA-related biomarkers rely on comprehensive phenotyping of healthy non-OA and OA subjects. Besides the common phenotyping criteria that include, gender, age, and body mass index (BMI), it is essential to collect data on symptoms and signs of OA outside the index joints and to bolster this with objective imaging data whenever possible to gain the most precise appreciation of the total burden of disease. Proteomic studies on systemic biospecimens, such as serum and urine, rely on comprehensive phenotyping data to unravel the true meaning of the proteomic results.

Toll-like receptors and chondrocytes: The lipopolysaccharide-induced decrease in cartilage matrix synthesis is dependent on the presence of toll-like receptor 4 and antagonized by bone morphogenetic protein 7

OBJECTIVE

To assess the presence of Toll-like receptors (TLRs) 1-9 in human articular cartilage, and to investigate the effects of lipopolysaccharide (LPS)-induced activation of TLR-4 on biosynthetic activity and matrix production by human articular chondrocytes.

METHODS

TLRs 1-9 were assessed in human articular cartilage by reverse transcription-polymerase chain reaction (RT-PCR); TLR-4 was also analyzed by Western blotting and immunohistochemistry. Articular chondrocytes were isolated from human donors and from wild-type or TLR-4(-/-) mice. Chondrocyte monolayer cultures were incubated with interleukin-1beta (IL-1beta) and LPS in the absence or presence of bone morphogenetic protein 7 (BMP-7) and IL-1 receptor antagonist (IL-1Ra). Neosynthesis of sulfated glycosaminoglycans (sGAG) was measured by (35)S-sulfate incorporation. Endogenous gene expression of cartilage markers as well as IL-1beta was examined using RT-PCR. The involvement of p38 kinase or p44/42 kinase (ERK-1/2) in LPS-mediated TLR-4 signaling was investigated by immunoblotting, RT-PCR, and sGAG synthesis.

RESULTS

TLRs 1-9 were found on the messenger RNA (mRNA) level in human articular chondrocytes. The presence of TLR-4 was also observed on the protein level. In murine and human articular chondrocytes, but not in chondrocytes derived from TLR-4(-/-) mice, stimulation with LPS resulted in a decrease in total proteoglycan synthesis. IL-1beta mRNA expression was increased by TLR-4 activation, whereas expression of aggrecan and type II collagen was significantly decreased. The presence of BMP-7 and IL-1Ra antagonized the anti-anabolic effects of LPS. Blocking of p38, but not ERK-1/2, resulted in inhibition of both LPS-mediated IL-1beta gene expression and the negative effects of LPS on matrix biosynthesis.

CONCLUSION

These data demonstrate the presence of TLRs in human articular cartilage. The suppressive effects of LPS on cartilage biosynthetic activity are dependent on the presence of TLR-4, are governed, at least in part, by an up-regulation of IL-1beta, and are mediated by p38 kinase. These in vitro data indicate an anti-anabolic effect of TLR-4 in articular chondrocytes that may hamper cartilage repair in various joint diseases.

Markers of disease in rheumatoid arthritis

Substantial progress can be noted in the efforts to demonstrate the usefulness of tissue-related markers of disease in rheumatoid arthritis and other joint diseases. The most informative studies use longitudinal analyses of well-characterized patient groups. Emphasis should be on searching for markers which can be of prognostic significance. New markers need to be assessed in relation to existing ones, such as C-polysaccharide reacting protein and erythrocyte sedimentation rate, which, although not specific, are hard to beat as measures of inflammation. A newly identified matrix component, cartilage intermediate layer protein, has features which make it attractive as a potential cartilage specific marker. Many markers may not in the end prove clinically useful. They will, however, give important insight into pathogenic processes, and may help in evaluating new therapy. Finally, markers originally identified in humans have now proven their value in experimental arthritis.

The role of crystals in articular tissue degeneration

The deposition of calcium-containing crystals in articular tissues is probably an underrecognized event. Clinical observations indicate that exaggerated and uniquely distributed cartilage degeneration is associated with these deposits. Perhaps the most compelling argument favoring a role for crystals in causing osteoarthritis stems from their in vitro effects on articular tissues. In this short review, we will discuss the fact that crystals can cause the degeneration of articular tissues in 2 separate pathways. In the "Direct" pathway, crystals directly induce fibroblast-like synoviocytes to proliferate and produce metalloproteinases and prostaglandins. The other "Paracrine pathway" involves the interaction between crystals and macrophages/monocytes, which leads to synthesis and release of cytokines that can reinforce the action of crystals on synoviocytes and induce chondrocytes to secrete enzymes, eventually causing the degeneration of articular tissues.

The role of crystals in osteoarthritis

The deposition of calcium-containing crystals in articular tissues is probably an under-recognized event. Clinical observations indicate that an exaggerated and uniquely distributed cartilage degeneration is associated with these deposits. Measurements of putative markers of cartilage breakdown suggest that the presence of these crystals magnifies the degenerative process. In vitro studies indicate two potential mechanisms by which crystals cause degeneration. These involve the stimulation of mitogenesis in synovial fibroblasts and the secretion of proteases by cells that phagocytose these crystals. Approaches that might ameliorate the degenerative process may ensue from new information about how crystals form and how they exert their biologic effects.

Serum markers of articular cartilage damage and repair

Joint cartilage is a dynamic tissue that reacts to trauma, inflammation, and other insults by attempting to repair its matrix. This reaction results in the release of cartilage macromolecules into the body fluids. Analysis of these fluids has identified a limited number of at least somewhat tissue-specific markers of altered cartilage metabolism. Analyses of serum are less specific and less sensitive than analyses of synovial fluid, but their use as research tools in clinical studies, drug development, and experimental work in animal models is increasing.

What is the current status of biochemical markers in the diagnosis, prognosis and monitoring of osteoarthritis?

Biochemical markers for osteoarthritis (OA) may serve different purposes. Since markers reflect ongoing dynamic metabolic processes in the joint tissues (cartilage, synovium, bone, etc.), they are most likely to be useful to predict prognosis and response to treatment, to monitor response to treatment, and for disease staging. Markers are currently being used at the research level for these purposes. The goal of using these markers to assess the disease process in the OA clinical trial setting or in the clinical routine has, however, not yet been reached.

Correlation of morphologic and biochemical changes in the natural history of spontaneous osteoarthrosis in guinea pigs

OBJECTIVE

To study how the concentrations of proteoglycans (PGs) and collagen change in various parts of tibial articular cartilage during aging, and to evaluate the development of spontaneous osteoarthrosis (OA) in guinea pigs.

METHODS

PGs were extracted from guinea pig cartilage samples using 4M guanidine hydrochloride, and the amount of hydroxyproline was determined in the extraction remainder. The molecular size and aggregation of PGs were analyzed by electrophoresis, and the glycosaminoglycan composition was assessed by high-performance liquid chromatography.

RESULTS

The PG concentration was proportional to the load distribution. However, when OA became histologically manifest, the PG concentration decreased by 50% (from a mean of 44 microg to 22 microg per mg fresh tissue) and the collagen level decreased by 40% (from a mean of 17 microg to 10 microg per mg fresh tissue), while the proportion of water increased by 13% (from a mean of 710 mg to 800 mg per mg fresh tissue).

CONCLUSION

Unmineralized cartilage can, within physiologic load limits, respond to increased mechanical demands by increasing the PG and collagen concentrations. Beyond a certain limit, however, the cartilage can no longer compensate for further increases in stress, which results in cartilage degeneration and losses of matrix constituents. These losses seemed to appear earlier in the disease process than has been described in previous animal models of secondary OA.

Intra-articular morphine and saline injections induce release of large molecular weight proteoglycans into equine synovial fluid

Both morphine and physiologic saline injected intra-articularly into healthy equine tarsocrural joints induced a release of large molecular size proteoglycan (PG) subunits into the synovial fluid (SF) analysed 24 h postinjection. High-performance liquid chromatography (HPLC) with a size-exclusion column was used to assess the high molecular weight proteoglycans in equine synovial fluid (SF). The PG peaks of SF samples eluated separately from SF hyaluronate and other molecular components of the SF in the HPLC chromatographies indicating no interaction between hyaluronate and PG in the SF. Individual elution profiles varied between joints and horses. The amount of PG release was measured by relative area index from the HPLC chromatograms. The synovial fluid PG content was significantly increased (P < 0.05) after morphine but not in saline injected joints compared with pretreatment but there were no significant differences between the two groups. It was concluded that intra-articular injections of both morphine and physiologic saline are able to elicit a marked PG release into the SF from articular cartilage within 24 h of injection.

Cytokines in osteoarthritis: mediators or markers of joint destruction?

OBJECTIVE

The integrity of articular cartilage is maintained by the balance between cytokine-driven anabolic and catabolic processes. Unregulated or excess influences of these molecules are thought to play a part in the pathophysiology of many joint diseases. However, the role of cytokines in osteoarthritis (OA) is not well established. Our aims are twofold: firstly to consider the evidence for the contribution of cytokines to the pathophysiology of OA and secondly to evaluate their potential as markers of disease activity in OA.

METHODS

Cytokine homeostasis, the role of catabolic and anabolic cytokines in maintaining cartilage integrity, and the contribution of such cytokines to destructive processes in OA were examined. Consideration was given to the interrelationship between cartilage, bone, and synovium in OA; metabolites produced by such structures were compared with cytokines as indicators of disease activity.

RESULTS

The evidence reviewed suggests that interleukin-1 (IL-1) and the less potent tumor necrosis factor alpha (TNF alpha) are mediators of joint damage in OA. The cytokines interleukin-6 (IL-6) and leukemia inhibitory factor (LIF) were implicted in both destructive and protective mechanisms, suggesting a dual role. Metabolites of the different components of the joint provided a better measure of disease activity than cytokines.

CONCLUSIONS

Experimental evidence is emerging that catabolic cytokines are mediators of joint damage in OA, although their usefulness as markers of disease activity is limited because of the need to monitor a wide range of ligands and their inhibitors simultaneously. In contrast, metabolites released from cells within bone, synovium, and cartilage related to disease activity and provided prognostic information.

Markers of cartilage matrix metabolism in human joint fluid and serum: the effect of exercise

The concentrations of cartilage proteoglycan (aggrecan), stromelysin-1, tissue inhibitor of metalloproteinases-1 (TIMP-1) and procollagen II C-propeptide in knee joint fluid and the levels of aggrecan, hyaluronan and keratan sulfate in serum were measured before and after exercise in 33 healthy athletes. The samples before exercise were obtained after 24 h rest from running or soccer and the samples after exercise were obtained 30-60 min after the exercise. Nine athletes ran on a treadmill for 60 min, 16 ran on road for 80 min and 8 played one soccer game (90 min). A reference group of 28 patients with knee pain but not evidence of joint pathology or injury was used for comparison. In joint fluid no single marker from the degradative processes in cartilage matrix changed significantly with exercise but all showed a rising trend. All markers except stromelysin showed lower concentrations in athletes at rest compared to the reference group. In serum from runners before exercise the concentration of keratan sulfate was significantly higher than in both the soccer and reference groups and further increased after exercise. The increase in markers after exercise may reflect an effect of mechanical loading in combination with a possible high turnover rate of body cartilage matrix in these individuals.

Increased release of bone sialoprotein into synovial fluid reflects tissue destruction in rheumatoid arthritis

OBJECTIVE

Bone sialoprotein (BSP) was quantified in synovial fluids and sera from rheumatoid arthritis (RA) patients to elucidate whether its release from bone relates to the degree of joint tissue destruction. Osteocalcin was assayed for comparison.

METHODS

BSP and osteocalcin levels were determined by immunoassays of knee synovial fluids and of sera from RA patients who were selected on the basis of radiographic knee joint tissue damage.

RESULTS

Synovial fluid concentrations of BSP increased with increasing degrees of knee joint damage (rs = 0.6848, P < 0.001). Synovial fluid concentrations of osteocalcin did not relate to the degree of joint damage. Serum concentrations of BSP were increased, but did not relate to the degree of joint damage. Serum concentrations of osteocalcin were normal, but increased within the range of normal during progression of joint destruction (rs = 0.4567, P < 0.001).

CONCLUSION

Quantification of BSP in synovial fluid holds promise as a useful means of assessing the degree of tissue damage at the molecular level in patients with RA.

Migration and homing of lymphocytes to lymphoid and synovial tissues in proteoglycan-induced murine arthritis

OBJECTIVE

To describe the migration and homing of labeled donor lymphocytes to the lymphoid organs and synovial tissues of host animals, during the development of cartilage proteoglycan (PG)-induced arthritis adoptively transferred to syngeneic BALB/c mice.

METHODS

Lymphocytes from either nonarthritic or arthritic donor animals were labeled with either fluorescent or radioactive cell linkers (PKH-GL) and injected into syngeneic, immunosuppressed mice. The homing patterns of donor lymphocytes following the injection of labeled cells were studied by fluorescence microscopy and by measurement of radioactivity in tissue samples.

RESULTS

Lymphocytes from arthritic donors retained their ability to transfer the disease after labeling. In the lymphoid organs, arthritic and nonarthritic donor lymphocytes exhibited similar homing patterns, although remarkable differences were found in the number of homing cells derived from nonarthritic and arthritic donors. However, labeled cells only from arthritic animals migrated to the synovial tissue of the recipient mice, and their appearance was associated with the onset of arthritis.

CONCLUSION

Lymphocytes from mice with PG-induced arthritis, in contrast to lymphocytes from non-arthritic donors, exhibit preferential homing to the synovial tissue of the host. Adoptive transfer of arthritis is linked to the appearance of these cells in the synovium.

Differential levels of synovial fluid aggrecan aggregate components in experimental osteoarthritis and joint disuse

The levels of proteoglycan aggregate components (link protein, keratan sulfate epitope, and total sulfated glycosaminoglycan) were determined in the synovial fluid lavages of dogs with experimental osteoarthritis or disuse atrophy. A model of experimental osteoarthritis was created by transection of the anterior cruciate ligament of the right knee; studies were carried out 6 and 12 weeks after surgery. Joint disuse was studied at 4 and 8 weeks after initiation of the disuse. Recovery after disuse also was studied in joints that had 3 weeks of remobilization after 4 or 8 weeks of disuse. Synovial fluid lavages from the right knee joints of untreated animals were used as controls. The concentrations of keratan sulfate epitope, sulfated glycosaminoglycan, and link protein in the synovial fluid lavages at 6 and 12 weeks after transection of the anterior cruciate were elevated compared with the control values. Similar analysis of the fluid after disuse showed that the levels of keratan sulfate epitope and sulfated glycosaminoglycan were increased compared with the control levels and the levels after transection. However, the concentration of link protein in the fluid after disuse was not significantly different from the control level. The levels of keratan sulfate epitope and sulfated glycosaminoglycan in the synovial fluid lavages after disuse with recovery were high, but the levels of link protein remained low. The results indicate that the catabolism of proteoglycan aggregates in articular cartilage during early osteoarthritis and disuse is different. The determination of keratan sulfate epitope in synovial fluid lavages appears to provide a relatively general indication of proteoglycan catabolism, whereas increased levels of link protein may be more indicative of cartilage degeneration.

Changes in cartilage metabolism in arthritis are reflected by altered serum and synovial fluid levels of the cartilage proteoglycan aggrecan. Implications for pathogenesis

The metabolism of the cartilage proteoglycan aggrecan was studied in patients with osteoarthritis (OA, n = 83), rheumatoid arthritis (RA, n = 127), and in controls (n = 117) using monoclonal antibody-based radioimmunoassays for glycosaminoglycans in the serum and synovial fluid (SF) to detect epitope 846 on chondroitin sulfate (probably only on recently synthesized molecules) and a keratan sulfate (KS) epitope AN9PI, present on intact and degraded molecules. Epitope 846 levels were always elevated in SF over serum (mean 38-fold in OA and 8.6-fold in RA) being highest in OA patients with the longest disease duration and greatest loss of cartilage, and lowest in RA joints with high leucocyte counts. Serum levels were more often elevated in RA (56%) than in OA (19%) and probably reflect increased aggrecan synthesis in diseased joints. KS levels were higher in SF than in serum in 69% of patients (up to 2.3-fold); levels were inversely (OA) and directly (RA) related to SF leucocyte counts. Serum KS was reduced in both diseases and in RA was inversely related to both systemic and joint inflammation markers. SF 846 levels were inversely related to SF KS in both diseases. These epitopes may provide a measure of the balance between cartilage synthesis and degradation in these diseases.

Measurement of glycosaminoglycans and keratan sulphate in canine arthropathies

Glycosaminoglycans (GAG) and keratan sulphate (KS) were measured in sera and synovial fluids from dogs with either osteoarthritis (OA) or rupture of the cranial cruciate ligament (CCL) and normal dogs. The dogs with OA had higher synovial fluid GAG levels (P < 0.002) and serum KS (P < 0.03) compared to the normal dogs. No significant differences in serum GAG were found in either group. In both OA and rupture of the CCL, GAG levels were increased in the synovial fluid from the affected joint compared with the clinically normal (inactive) contralateral joint. Neither GAG nor KS measurements correlated with serum and synovial fluid antibodies to collagen type II, synovial fluid white cell count or age of dog. It is unlikely that the measurement of these cartilage breakdown products is of value for diagnostic or prognostic use in canine arthropathies.

Determination of chondroitin-6-sulphate by a competitive enzyme immunoassay using a biotinylated antigen

A competitive enzyme immunoassay was developed to determine chondroitin-6-sulphate in body fluids and cell cultures. The assay uses a monoclonal anti-chondroitin-6-sulphate antibody, immobilised to microtitre plates, and it involves a competitive binding reaction between chondroitin-6-sulphate in the samples and the biotinylated antigen. This assay enables the quantification of chondroitin-6-sulphate in the low concentration range of 16-120 micrograms/l. The intra-assay and inter-assay coefficients of variation are below 6.5% and 9.0%, respectively. More than 90% of chondroitin-6-sulphate was recovered when added to 0.1 mol/l phosphate-buffered saline, an albumin solution (40 g/l in phosphate-buffered saline) and cell culture medium (containing 100 ml/l foetal calf serum). Chondroitin-6-sulphate was also determined in sera of healthy male (n = 90) and female (n = 90) blood donors. The normal range was 55-169 micrograms/l. In men the mean value was estimated at 102.2 +/- 37.1 micrograms/l and in women at 98.7 +/- 26.4 micrograms/l. No age or sex dependence was observed. The urine excretion of chondroitin-6-sulphate in men (n = 16) was 44.5 +/- 21.1 mg/kg creatinine (mean +/- standard deviation) and in females (n = 10) 53.5 +/- 21.3 mg/kg creatinine. The clearance rate in men was 0.41 +/- 0.22 ml x min-1 and in women 0.38 +/- 0.15 ml x min-1. No sex dependence was found. Furthermore, the enzyme immunoassay was modified to measure the specific incorporation of a radioactively labelled precursor ([14C]galactosamine) into chondroitin-6-sulphate.(ABSTRACT TRUNCATED AT 250 WORDS)

ELISA for the core protein of the cartilage large aggregating proteoglycan, aggrecan: comparison with the concentrations of immunogenic keratan sulphate in synovial fluid, serum and urine

Immunological assays for fragments of the cartilage large aggregating proteoglycan, aggrecan, have been widely used to monitor cartilage turnover. These assays have commonly employed the monoclonal keratan sulphate antibody, 5D4. Keratan sulphate, however, is present in many tissues and 5D4 affinity is critically dependent on antigen structure. We have therefore raised and characterized a monoclonal antibody (1-F21) that reacts with the core protein of aggrecan without interference from the glycosaminoglycan side chains and, using this antibody, we have optimized a sensitive, competitive ELISA. The within-assay and between-assay coefficients of variation were 4.9-8.9% and 11.1-13.0%, respectively. The mean concentrations of core protein in synovial fluid, serum and urine were 76.4 micrograms/ml, 104.0 ng/ml and 81.0 ng/ml, respectively. In synovial fluids the concentrations were closely correlated with the concentrations of keratan sulphate as determined by 5D4 (r = 0.94), whereas in serum and urine there was no obvious correlation between the determinations. These findings show that measurement of both core protein and keratan sulphate results in a more precise description of aggrecan turnover.

The structure of aggrecan fragments in human synovial fluid. Evidence that aggrecanase mediates cartilage degradation in inflammatory joint disease, joint injury, and osteoarthritis

OBJECTIVE

To determine the proteolytic fragmentation patterns and N-terminal sequence of aggrecan fragments in human synovial fluid from patients with inflammatory arthritides, joint injury, or osteoarthritis (OA).

METHODS

Knee synovial fluid was obtained from patients with joint injury, OA, acute pyrophosphate arthritis (pseudogout), reactive arthritis, psoriatic arthritis, or juvenile rheumatoid arthritis. Chondroitin sulfate-substituted aggrecan fragments present in the fluid were purified by cesium chloride gradient centrifugation and enzymatically deglycosylated. Core protein species were determined by N-terminal analysis and by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) with electroblotting and detection with monoclonal antibody 3B3.

RESULTS

Samples from patients with joint injury, OA, and inflammatory joint disease all showed a similar 3-band pattern, with core sizes of approximately 200 kd, 170 kd, and 135 kd. In all samples, diffuse immunoreactive products were also seen, with an apparent size of > 250 kd. N-terminal analysis of core preparations of all samples showed a consistent single predominant sequence, beginning at alanine 374 of the human aggrecan core protein.

CONCLUSION

The aggrecan fragments present in joint fluids from patients with various inflammatory arthritides, joint injury, or OA result from a predominant cleavage of the human aggrecan core protein at the glutamate 373-alanine 374 bond within the interglobular domain, between the G1 and G2 domains. The consistent pattern of fragments seen on SDS-PAGE and the single predominant N-terminal sequence suggest a common degradative mechanism of aggrecan in these different joint conditions. The identity of the proteolytic agent (aggrecanase), however, remains unknown. These results appear to have important implications with regard to the development of therapies to protect cartilage from degradation in patients with joint disease.

Intrasynovial levels of sulphated glycosaminoglycans and autoantibodies to type II collagen in rheumatoid arthritis: a correlative analysis

It is uncertain whether the autoantibodies to type II collagen that occur frequently in the serum and synovial fluid of patients with rheumatoid arthritis (RA), but rarely in other articular diseases, are primary or secondary to cartilage damage. Hence, we measured antibodies in synovial fluid from patients with RA and other articular diseases and related these to the concentration of sulphated glycosaminoglycans, as a measure of ongoing cartilage catabolism. Synovial fluids from 42 patients with RA and 30 patients with other articular diseases were studied. We found that levels of antibodies to native and denatured collagen were significantly higher in RA than in all other articular diseases, whereas concentrations of sulphated glycosaminoglycans were similar. The absence of any correlation between levels of sulphated glycosaminoglycans and antibodies to collagen weighs against the occurrence of such antibodies in RA as a secondary effect of cartilage damage.

Effects of intraarticular corticosteroid and sodium hyaluronate injections on synovial fluid production and synovial fluid content of sodium hyaluronate and proteoglycans in normal equine joints

Hyaluronate and cartilage proteoglycan fragments in synovial fluid from normal equine joints were determined after repeated intraarticular injections of beta-methasone, methylprednisolone, hyaluronate, saline and a combination of beta-methasone + hyaluronate and methylprednisolone + hyaluronate. The experimental intraarticular treatments were given at the beginning of the study and after one and two weeks. Synovial samples were obtained at the onset of the study and after 1, 2, 3, 4, 6, and 8 weeks. The synovial volume was determined and showed no significant changes after the repeated arthrocenteses and the experimental treatments. Corticosteroid injections resulted in increased levels of hyaluronate in the synovial fluid which indicated a stimulatory effect on the synoviocytes to produce hyaluronate. The corticosteroids also resulted in high levels (up to 20 times the initial level) of proteoglycans which indicated joint cartilage degradation. A combined injection of corticosteroids and high molecular weight hyaluronate reduced proteoglycan breakdown which indicated a protective effect of hyaluronate on the articular cartilage.

Release of cartilage macromolecules into the synovial fluid in patients with acute and prolonged phases of reactive arthritis

OBJECTIVE

Extensive changes in articular cartilage metabolism occur during the acute phase of reactive arthritis, as indicated by altered release of cartilage macromolecules into synovial fluid (SF) demonstrated immunochemically. Nevertheless, permanent cartilage lesions are rare in this disease. To monitor specific events during the evolution of reactive arthritis, we investigated the content of cartilage macromolecules in sequentially obtained SF samples from 22 patients.

METHODS

Two groups of proteoglycan epitopes, the glycosaminoglycan-rich region of aggrecan (referred to as proteoglycan) and its hyaluronan-binding region (HABr), as well as one matrix protein, cartilage oligomeric matrix protein (COMP), were quantified by immunoassay.

RESULTS

SF proteoglycan concentrations, which were initially elevated, decreased significantly with prolonged arthritis, whereas COMP levels changed less markedly and levels of HABr remained stable. There was a positive correlation between SF and serum concentrations of COMP in samples obtained during the early phase of the disease.

CONCLUSION

Cartilage involvement in reactive arthritis is transient, in contrast to findings in rheumatoid arthritis. Reactive arthritis should therefore be a suitable model for studies of repair processes in cartilage, which will facilitate understanding of the pathophysiology of cartilage involvement in arthritis.

Cellular immunity to cartilage proteoglycans: relevance to the pathogenesis of ankylosing spondylitis

Cellular immunity to cartilage proteoglycans may be responsible for sustaining chronic inflammation in ankylosing spondylitis. This hypothesis was examined by measuring peripheral blood and synovial fluid mononuclear cell proliferation in five preparations of human cartilage proteoglycan monomer in vitro. Peripheral blood mononuclear cells from 25 patients and synovial fluid mononuclear cells from five patients were compared with those from normal and disease control subjects matched for age. No significant differences were found between the three groups. This suggests that autoimmune responses to cartilage proteoglycans are unlikely to play a significant part in the pathogenesis of ankylosing spondylitis.

Markers of bone and collagen breakdown in early inflammatory arthritis

Inflammatory arthritis has the potential to cause irreversible erosive damage to cartilage and bone. This may occur very early in the course of the disease. At present it is not possible at diagnosis to identify those patients who will develop erosive damage. If this were possible, it would enable aggressive therapy to be targeted to those patients at greatest risk. There is therefore a need for sensitive markers to detect and quantify joint damage at as early a stage as possible. In this chapter we review potential biochemical markers of such damage and assess their clinical usefulness.

Increased release of matrix components from articular cartilage in experimental canine osteoarthritis

The release rates of specific components of the proteoglycan aggregates (G1 domain, the chondroitin sulfate and keratan sulfate containing portion of the protein core, and link protein) of the articular cartilage of mature beagles were studied at early stages of canine experimental osteoarthritis (OA), generated by transection of the anterior cruciate ligament. Analysis of cartilage explants and synovial fluids indicates that at early stages of experimental OA, there is increased release of the proteoglycan aggregates of the articular cartilage. This involves a release from the tissue of the components of the proteoglycan that are specifically involved with aggregation together with the glycosaminoglycans of the proteoglycan. These components were detected at elevated levels in the media of explants of cartilage from the operated joint, and in the synovial fluids of the operated joints.

Glycosaminoglycans in normal and osteoarthrotic human temporomandibular joint disks

Glycosaminoglycans in normal and osteoarthrotic temporomandibular joint disks were studied by means of high-performance liquid chromatography methods. Normal disk tissue contains galactosaminoglycans (chondroitin sulfate and dermatan sulfate) as the main polysaccharides and with smaller amounts of hyaluronate and heparan sulfate. The galactosaminoglycans are mainly sulfated in 6-position, and some of the disaccharides contain iduronic acid. There was a slight general variation in glycosaminoglycan concentration with increasing age. In the severely arthrotic disks the content of glycosaminoglycans was considerably lower than in normal disk tissue. This decrease was far more extensive than that observed in relation to age in normal tissue. The 4/6-sulfate ratio of the galactosaminoglycans was increased, whereas the proportion of iduronic acid was markedly decreased.

Comparison of keratan sulphate concentrations and the size distribution of proteoglycans in the synovial fluid of patients with osteoarthritis and pyrophosphate arthropathy

In order to evaluate the effect of calcium pyrophosphate dihydrate (CPPD) deposition on articular cartilage catabolism, the proteoglycans released into normal synovial fluid were compared with those in synovial fluid obtained from patients with osteoarthritis (OA), chronic pyrophosphate arthropathy (CPA) and acute pyrophosphate arthropathy (APA). Keratan sulphate (KS) was measured by the modified 1,9-dimethylmethylene blue (DMB) assay in synovial fluids treated with chondroitin ABC lyase. This enzyme was found to eliminate all of the sulphated glycosaminoglycans in synovial fluid except KS. In OA, CPA and APA the concentrations of KS were found to be significantly higher than in normal synovial fluid (NSF) (P less than 0.01). Similar KS concentrations were observed in CPA and APA. In CPA they were significantly higher than in OA (P less than 0.02). The size distribution of proteoglycan fragments varied between different patients with the same disease, but only minor differences were observed in patients with OA and CPA who were matched for age, sex and disease severity. Furthermore, the size distribution of proteoglycan fragments in the acute and chronic phases of pyrophosphate arthritis was similar. Thus although in pyrophosphate arthritis the rate at which proteoglycans are released from the cartilage may be greater than in OA or normal joints, the fundamental processes governing the release of these macromolecules may be the same.

Proteoglycan epitope in synovial fluid in gonarthrosis. 28 cases of tibial osteotomy studied prospectively for 2 years

High tibial osteotomy was performed for medial gonarthrosis in 28 patients. Preoperatively, and at 3, 12, and 24 months after surgery, clinical and radiographic examinations were made, and joint-fluid samples were aspirated. Arthroscopy was performed preoperatively and at 24 months. Immunoassay of proteoglycan epitope in joint fluid showed an increase in concentration at all times as compared with a reference population with normal knee joints. An increase in both the concentration and the total amount of proteoglycan epitope in joint fluid was noted at 3 months postoperatively with a return to preoperative values at later times. Regrowth of fibrocartilage did not correlate with proteoglycan epitope data.

Glycosaminoglycans in horses with osteoarthritis

Horse articular cartilage glycosaminoglycans (GAGs) were measured in synovial fluids from 48 joints affected with osteoarthritis (OA), 22 normal joints, four joints with osteochondritis, three joints with traumatic arthritis and seven joints infected with bacteria. Serum and urine from individual horses were also examined for the presence of GAGs. High levels of GAGs were found in synovial fluids (SF) from horses with OA. In each case, the level was higher in the synovial fluid than in the serum or urine from the same horse. Horses with OA showed high GAG levels in SF, serum and urine compared to horses with normal and infected joints. High levels were also found in horses with osteochondritis and traumatic arthritis. Levels of synovial fluid GAG reflect cartilage destruction in arthritis and may be useful for monitoring disease progression in the equine species.

A new sandwich-ELISA method for the determination of keratan sulphate peptides in biological fluids employing a monoclonal antibody and labelled avidin biotin technique

A new sandwich-ELISA for the determination of keratan sulphate peptides in biological fluids is described. The technique involves binding a commercially available monoclonal antibody against keratan sulphate to microtitre plates, adding the unknown keratan sulphate antigen then interacting the keratan sulphate-antibody complex with a biotin-monoclonal antibody conjugate which was also specific for keratan sulphate peptides. Alkaline phosphatase conjugated streptravidin was then added and the amount which bound to the biotin was determined by measuring the release of chromogen from an added chromogenic substrate. Using this assay, keratan sulphate peptides in biological fluids within the range 10-1000 ng/ml could be quantitated. This method was found to be more sensitive than presently used techniques. The intra- and inter-assay coefficients of variation were 11% and 13%, respectively.

Stimulation of rheumatoid synovial and blood T cells and lines by synovial fluid and interleukin-2: characterization of clones and recognition of a co-stimulatory effect

Rheumatoid arthritis (RA) is characterized by the presence of interleukin-2 (Il-2) receptor-positive T cells in the peripheral blood and synovial compartments. Utilizing the limiting dilution technique, the precursor frequencies of Il-2 responsive T cells were determined in peripheral blood and synovial sites from RA patients and in the blood of normal donors. The frequencies of Il-2 responsive T cells were significantly higher in RA patients (range from 1/180 to 1/7432) compared to normal donors (range from 1/400 to 1/8163). T-cell clones raised by the addition of Il-2 alone were predominantly of the CD4-positive phenotype. Peripheral blood T cells, synovial T-cell clones and lines derived from RA patients were co-stimulated with Il-2 and synovial fluid or supernatants from cultured synovial lining cells. This co-stimulation induced a strikingly enhanced proliferative T-cell response while synovial fluid alone was without effect. This stimulatory activity was found in the high molecular weight range (approximately 150 kDa) and could not be attributed to the action of immunoglobulins or known cytokines such as Il-2 or interleukin-1 (Il-1), suggesting the activity of a material that modulates the Il-2-dependent growth of T cells. The co-stimulatory capacity of synovial fluid with Il-2 may be relevant to the activated state, especially of synovial T cells.

Cytidine deaminase activity in synovial fluid of patients with rheumatoid arthritis: relation to lactoferrin, acidosis, and cartilage proteoglycan release

It is claimed that cytidine deaminase activity reflects local granulocyte turnover or activity in the synovial fluid of patients with rheumatoid arthritis, but cytidine deaminase is not a granulocyte specific enzyme. Lactoferrin is a granulocyte specific protein that is released from the secondary granulae during activation. We measured cytidine deaminase activity and lactoferrin concentrations in 33 rheumatic synovial fluid samples. Cytidine deaminase activity and lactoferrin concentrations correlated closely, indicating that both analyses reflect similar events in the joint-that is, result in their release from granulocytes. Cytidine deaminase activity and granulocyte concentrations correlated less closely, suggesting that there are additional factors besides the cell number which contribute to this release. Joint acidosis may be one such factor, as pH and cytidine deaminase activity correlated inversely. There was no association with synovial fluid proteoglycan concentrations, a marker of cartilage degradation.

Inflammation and cartilage metabolism in rheumatoid arthritis. Studies of the blood markers hyaluronic acid, orosomucoid, and keratan sulfate

Single analyses of peripheral blood of rheumatoid arthritis (RA) patients showed a significant reduction in the mean value for keratan sulfate (KS) compared with that in control subjects, but the mean value for orosomucoid (OM) was elevated compared with that in control subjects. Some RA patients displayed highly elevated levels of hyaluronic acid (HA), while others exhibited normal levels. There was a significant inverse correlation between OM and KS content in RA patients, as well as a direct correlation between HA and OM. In longitudinal studies of RA patients, parallel changes in OM and HA and inverse changes between KS and OM or HA were commonly observed. Clinical analyses revealed that there was an inverse correlation between KS and morning stiffness, and direct correlations between the number of tender joints and HA, and between HA or the erythrocyte sedimentation rate and the number of joints with effusions. The reason(s) for the inverse correlation between KS and OM as an index of systemic inflammation remains to be established. Circulating HA represents an index of joint inflammation, for which a marker has not been previously available.

Increased levels of proteoglycan fragments in knee joint fluid after injury

We measured levels of cartilage proteoglycan (PG) fragments in knee joint synovial fluid obtained from patients with previous trauma of the knee, early gonarthrosis, or pyrophosphate synovitis, and in age-matched control subjects. During the initial 3-4 weeks after rupture of the anterior cruciate ligament or the meniscus (confirmed by arthroscopy), markedly increased PG fragment levels were found. At later times after trauma (up to 4 years), many of these patients still had significantly elevated levels of cartilage PG fragments in the joint fluid. In a group of older patients with gonarthrosis, these levels were only moderately elevated, while in patients with acute pseudogout, greatly increased levels were observed. Although longitudinal studies are needed to validate the significance, PG fragments in joint fluid may be a marker for early posttraumatic arthrosis.

Immunohistologic demonstration of type II collagen in synovial fluid phagocytes of osteoarthritis and rheumatoid arthritis patients

We were able to demonstrate type II collagen in synovial phagocytes of osteoarthritis (OA) and rheumatoid arthritis (RA) patients, using a monoclonal antibody to human type II collagen and immunoperoxidase staining. In addition, using immunoelectron microscopy, we demonstrated labeled fragments in synovial phagocytes of both RA and OA patients. This immunohistochemical assay may prove to be a sensitive indicator of cartilage erosion in patients with OA and RA.

Involvement of nonarticular cartilage, as demonstrated by release of a cartilage-specific protein, in rheumatoid arthritis

Analysis of human cartilage extracts by radioimmunoassay showed that the noncollagenous 148-kd cartilage matrix protein was present in extracts of tracheal cartilage but was undetectable in normal or arthritic joint cartilage, corroborating previous results with bovine cartilage samples. Concentrations of the protein in the circulation, as studied by radioimmunoassay, were greatly elevated in patients with rheumatoid arthritis and polyarticular juvenile rheumatoid arthritis. In contrast, patients with reactive arthritis and oligoarticular juvenile rheumatoid arthritis, as well as rheumatoid arthritis patients treated with low-dose glucocorticoids, had levels similar to those in healthy controls. The serum concentrations were not related to age. A patient with polychondritis and tracheal involvement had a high serum concentration of the protein, which decreased during plasma exchange and cyclophosphamide treatment. Studies of the release of this cartilage matrix protein, which is present in nonarticular cartilage but not in articular cartilage, should aid in the understanding of the mechanisms of cartilage involvement in disease, and the protein may become a clinically useful marker.

Application of an enzyme-linked immunosorbent-inhibition assay to quantitate the release of KS peptides into fluids of the rat subcutaneous air-pouch model and the effects of chondroprotective drugs on the release process

The effects of the chondroprotective agents (Arteparon, SP-54 and DH40J) on the release of proteoglycan degradation products (as keratan sulphate peptide fragments) from articular cartilage implanted into rat subcutaneous air pouches have been investigated by using an enzyme-linked immunosorbent-inhibition assay (ELISIA). The ELISIA technique was capable of quantitating the keratan sulphate peptides (KS peptides) in fluids within the range of 100-2,000 ng/ml by using the monoclonal antibody line 1/20/5-D-4 and human articular cartilage KS peptides as standard reagents. It was found that the levels of KS peptides present in the air-pouch fluid of rats treated with the chondroprotective drugs was significantly less than in fluid aspirated from the pouches of non-drug-treated control animals. On the basis of these findings we suggest that the assessment of KS peptide by ELISIAs may provide a useful means of monitoring proteoglycan breakdown products in biological fluids (e.g. synovial fluids or blood) and for evaluating the effects that antiarthritic drugs may have on this process.

Cartilage proteoglycan depletion in acute and chronic antigen-induced arthritis

We examined the kinetics of proteoglycan (PG) depletion in rabbits with antigen-induced arthritis. There was a rapid loss of PG from arthritic cartilage, reaching 35-40% at day 7. Thereafter, the rate of PG depletion declined, and by day 42, the maximum loss was 55-60%. The initial loss of PG was accompanied by the appearance of large amounts of sulfated glycosaminoglycans (GAGs) in the joint fluid (measured as total sulfated GAGs by dye binding and as keratan sulfate by radioimmunoassay). However, by day 14, the levels of sulfated GAGs in arthritic joint fluid declined to control levels, even though the cartilage demonstrated a sustained depletion of PG. The cartilage PG degradation observed in antigen-induced arthritis could also be produced in normal animals by a single intraarticular injection of recombinant interleukin-1. The acute loss of cartilage PG occurred independently of neutrophil accumulation, both in the case of antigen-induced arthritis and after injection of interleukin-1.

Measurement of sulphated glycosaminoglycans and proteoglycan fragments in arthritic synovial fluid

Immunoreactive proteoglycans (iPGs) and sulphated glycosaminoglycans (GAGs) were assayed in synovial fluid obtained from 22 patients with osteoarthritis (OA), 21 with rheumatoid arthritis (RA), 13 with gout, and five with Reiter's syndrome. A strong positive linear correlation was observed between concentrations of sulphated GAGs and iPGs in RA (r = 0.95) and gout (r = 0.94). A linear correlation was also observed in OA (r = 0.65). Patients with gout and Reiter's syndrome had significantly higher concentrations of sulphated GAGs and iPGs than patients with OA or RA. Patients with gout also had significantly higher total quantities of sulphated GAGs and iPGs in the knee joint cavity than patients with OA or RA. In all four diseases similar profiles were observed when comparisons were made between the total quantities and concentrations of sulphated GAGs and iPGs in synovial fluid. These results indicate that the observed differences in concentrations are not simply a function of dilution. The concentrations of sulphated GAGs and iPGs did not correlate closely with the type or number of inflammatory cells in the synovial fluid. Considerable variation was noted in the sulphated GAG/iPG ratios, suggesting that different mechanisms may be contributing to the release of proteoglycans in the diseases studied.

Increased concentrations of proteoglycan components in the synovial fluids of patients with acute but not chronic joint disease

Synovial fluid samples (139) from 121 patients with rheumatoid arthritis, osteoarthritis, pseudogout, chronic pyrophosphate arthritis, gout, and reactive arthritis were analysed for cartilage proteoglycan components. Keratan sulphate (KS) epitope was determined by a competitive radioimmunoassay, and total sulphated glycosaminoglycans (S-GAG) were determined after papain digestion by a specific dye binding assay. Increased concentration of both KS epitope and S-GAG were found in synovial fluid from joints with acute inflammatory arthropathy (gout, pseudogout, and reactive arthritis). Analysis of consecutive samples from the same joint at different stages showed that the concentration of KS epitope or total S-GAG varied with acute inflammatory activity. In samples from patients with chronic conditions during active and inactive inflammatory phases concentrations were much lower and not distinguishable among these disease groups. The detection of raised concentration of proteoglycan components may reflect the rapid depletion or greatly increased turnover of proteoglycan in the articular cartilage during acute inflammation in the joint. This did not appear to be sustained in most patients with chronic joint diseases.

Proteoglycans of joint cartilage. Structure, function, turnover and role as markers of joint disease

Joint cartilage consists of cells embedded in a matrix of fibrous collagen within a concentrated water-proteoglycan gel. The integrity of this matrix is crucial for the biomechanical properties of the joint cartilage. The different components of the matrix are synthesized and degraded by the cartilage cells, a process regulated by the amount of mechanical stress applied to the chondrocytes as well as by peptide factors and hormones present in synovial fluid. The proteoglycans are large macromolecules consisting of a protein core to which are attached multiple chains of glycosaminoglycans and oligosaccharides. During normal and pathological turnover, degradation products are released to the synovial fluid and to the circulation. Newly developed assays allow the sensitive and specific detection of these fragments in joint fluid and serum. Results of experimental and clinical investigations suggest that these assays will be of value in efforts to diagnose, grade and predict the outcome of inflammatory and degenerative joint disease.

Proteoglycan concentration in synovial fluid: predictor of future cartilage destruction in rheumatoid arthritis?

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