Studies of a monoclonal antibody to skeletal keratan sulphate. Importance of antibody valency

The structure and degradation of aggrecan in human intervertebral disc

The ability of the intervertebral disc to resist compression is dependent on its high proteoglycan concentration. The disc proteoglycans are classified as aggregating or non-aggregating depending on their ability to interact with hyaluronan. The majority of the aggregating proteoglycans are derived from aggrecan, though their glycosaminoglycan substitution pattern has not been determined. In contrast, the origin of the non-aggregating proteoglycans is unclear, though it has been postulated that they are derived from aggrecan by proteolysis. The present work demonstrates that keratan sulfate (KS) in the glycosaminoglycan-binding region of disc aggrecan is confined to the KS-rich domain of the core protein and is not present in association with chondroitin sulfate (CS) in the CS1 and CS2 domains. It also shows that the non-aggregating disc proteoglycans are derived from aggrecan, with the large molecules possessing both the KS-rich and CS1 domains and the smaller molecules being generated from either the KS-rich or CS2 domain. The origin and spectrum of disc proteoglycan heterogeneity is the same in both the annulus fibrosus and nucleus pulposus.

The glycosaminoglycan attachment regions of human aggrecan

Aggrecan possesses both chondroitin sulfate (CS) and keratan sulfate (KS) chains attached to its core protein, which reside mainly in the central region of the molecule termed the glycosaminoglycan-attachment region. This region is further subdivided into the KS-rich domain and two adjacent CS-rich domains (CS1 and CS2). The CS1 domain of the human is unique in exhibiting length polymorphism due to a variable number of tandem amino acid repeats. The focus of this work was to determine how length polymorphism affects the structure of the CS1 domain and whether CS and KS chains can coexist in the different glycosaminoglycan-attachment domains. The CS1 domain possesses several amino acid repeat sequences that divide it into three subdomains. Variation in repeat number may occur in any of these domains, with the consequence that CS1 domains of the same length may possess different amino acid sequences. There was no evidence to support the presence of KS in either the CS1 or the CS2 domains nor the presence of CS in the KS-rich domain. The structure of the CS chains was shown to vary between the CS1 and CS2 domains, particularly in the adult, with variation occurring in chain length and the sulfation of the non-reducing terminal N-acetyl galactosamine residue. CS chains in the adult CS2 domain were shorter than those in the CS1 domain and possessed disulfated terminal residues in addition to monosulfated residues. There was, however, no change in the sulfation pattern of the disaccharide repeats in the CS chains from the two domains.

Localization of sulfated sialic acids in the dentinal tubules during tooth formation in mice

Lectin-like properties of the major enamel protein amelogenin suggest that it binds to glycoconjugates in dentinal tubules released at the dentin-enamel junction (DEJ) during enamel formation. Therefore, a detailed mapping of glycosylation in dentinal tubules during tooth formation was undertaken using histochemistry and lectin-binding assays. The tubular content exhibited sialidase-susceptible gamma-metachromasia with Toluidine Blue (pH 2.5) and staining with Alcian Blue (pH 1.0). The presence of sulfate groups was confirmed by benzidine reactions (Bracco-Curti's and tetrazonium assays). Alpha2,3-, alpha2,6- and alpha2,8-sialidases entirely abolished staining with the benzidine reactions. The presence of sialic acids in dentinal tubules was confirmed with the Bial's reaction and sialidase-susceptible binding of Limax flavus lectin suggesting that sialic acids are the major sulfated sugars in the glycoconjguates. Immunostaining with the monoclonal antibody 5-D-4 before and after treatment with chondroitin-4- and chondroitin-6-sulfatase confirmed the presence of keratan sulfate (KS), a sialylated proteoglycan, in dentinal tubules. We suggest that sulfated sialic acids are part of the KSs. The sulfated glycoconjugates are also found in dentin and the DEJ but not in predentin suggesting that amelogenin binds to the sialoconjugate during enamel formation.

An analysis of 14 molecular markers for monitoring osteoarthritis. Relationship of the markers to clinical end-points

OBJECTIVE

To investigate whether any of 14 serum and urine molecular markers (MMs) used to monitor osteoarthritis (OA) would be associated with particular clinical end-points.

DESIGN

Thirty-nine OA patients were bled and urine collected at five time points: at baseline visit and at visits 1, 3, 6 and 12 months later. Twelve clinical measurements were made and the concentrations of each of 14 MMs were determined. Principal component analysis, stepwise linear regression with backward elimination, and logistic regression were used to determine the correlations between MMs and clinical measures.

RESULTS

Principal component analysis was used to reduce the 12 clinical measurements into three independent clinical clusters: baseline clinical assessments, changes in clinical assessments and signal joint measurements. The 14 MMs were similarly reduced to five MM clusters. Each of the three clinical clusters was correlated with a single but different MM cluster. Baseline clinical assessments were correlated with bone markers typified by hydroxylysyl pyridinoline (HP) crosslinks, swelling of the signal joint was correlated with inflammation markers, especially CRP, and the change in clinical assessments over the 1 year evaluation was correlated with TGFbeta1. There was no correlation between any of the skeletal markers and the clinical measures, a situation which draws attention to the need for a direct assessment of cartilage damage in OA to validate the use of cartilage markers.

CONCLUSIONS

This study demonstrates statistical methodology for analysis of clinical trials using multiple MMs and clinical end-points. The patient numbers are sufficient to test hypotheses of relationships of single MMs such as CRP, TGFbeta1 and HP to clinical measures, but larger clinical trials are needed to validate hypotheses.

Analytical method for keratan sulfates by high-performance liquid chromatography/turbo-ionspray tandem mass spectrometry

We established a highly sensitive LC/MS/MS method for the analysis of the disaccharides produced from keratan sulfates (KS). It was revealed that the disaccharides produced by keratanase II enzymatic digestion of KS could be determined with high sensitivity by the negative-ion mode of multiple reaction monitoring. Furthermore, monosulfated and disulfated disaccharides can be separated using a short column of Capcell Pak NH2 UG80 (35 mm x 2 mm i.d.). The complete analysis of one sample can be performed within 5 min. The assay method was validated and showed satisfactory sensitivity, precision, and accuracy, which enabled quantitation at subpicomole levels. From the results of analyses of KS obtained from cornea, nasal cartilage, and brain, it was found that the degree of sulfation at the C-6 position of the galactose residues differed among those samples in the following order: nasal cartilage > cornea > brain. Our analytical method is very useful for the analyses of KS in various biological materials and for comparison of the degree of sulfation of KS from various biological samples.

Use of synovial fluid markers of cartilage synthesis and turnover to study effects of repeated intra-articular administration of methylprednisolone acetate on articular cartilage in vivo

In vivo the effects of intra-articular (IA) corticosteroids on articular cartilage remain controversial. This study was designed to examine this issue using synovial fluid (SF) markers of cartilage metabolism. Paired radiocarpal joints, without clinical or radiographic signs of joint disease, were studied in 10 adult horses. Aseptic arthrocentesis was performed weekly for 13 weeks. IA injections of methylprednisolone acetate (MPA) into the treatment joint and the vehicle into the control joint were performed at weeks 3, 5 and 7. We used radioimmunoassays on SF samples which measure a keratan sulfate epitope (KS) and the 846 epitope on cartilage aggrecan (PG) and the C-propeptide (CPII) of cartilage type II procollagen which is released following synthesis of this molecule. Gel chromatography was performed on selected SF samples to evaluate the sizes of SF PG molecules. The total joint KS and the 846 epitopes were both present on a heterogeneous population of mainly molecules which, from chromotographic analysis, appeared to be mainly fragments of the articular cartilage aggrecan. They were significantly elevated in MPA joints whereas CPII was significantly reduced compared to the control during the treatment period. These results indicate that the repeated use of IA MPA leads to a potentially harmful inhibition of procollagen II synthesis and an increased release of degradation products of the PG aggrecan from articular cartilage.

Alterations in cartilage type-II procollagen and aggrecan contents in synovial fluid in equine osteochondrosis

The etiology and pathophysiology of osteochondrosis remain poorly understood because it is difficult to obtain material from lesions in the early stage of this disease and because there is no satisfactory experimental animal model. We wished to determine whether there are changes in articular cartilage turnover in equine osteochondrosis, which closely resembles the human disease, by assaying cartilage matrix molecules in synovial fluids. We used immunoassays that measure a keratan sulfate epitope and the epitope 846 on the cartilage proteoglycan aggrecan and the C-propeptide of cartilage type-II procollagen, which is released following the synthesis of this molecule, to analyse synovial fluids from equine tarsocrural joints with and without osteochondrosis. In young horses with osteochondrosis, there was a significant increase of C-propeptide of type-II procollagen accompanied by a decrease in the 846 and keratan sulfate epitopes. The results identify differential alterations in aggrecan and type-II collagen turnover in the cartilage matrix in young animals with osteochondrosis that may contribute to the pathological degeneration of articular cartilage in this disease.

Immune responses to cartilage link protein and the G1 domain of proteoglycan aggrecan in patients with osteoarthritis

OBJECTIVE

To determine whether patients with osteoarthritis (OA) express cellular immunity to cartilage link protein (LP) and the G1 globular domain of proteoglycan (PG) aggrecan, and whether immunity to the G1 domain is influenced by the removal of keratan sulfate (KS).

METHODS

LP and the G1 globular domain of PG were isolated from human and/or bovine cartilage and used in proliferation assays with peripheral blood lymphocytes (PBL) from 42 patients with OA and 40 healthy control subjects.

RESULTS

Patients with OA expressed a higher prevalence of cellular immunity to human cartilage LP (42.4%) compared with the control group (13.3%). The prevalence of immune reactivity to bovine LP in patients with OA was lower (35.7%) compared with the immunity to human LP, but remained similar in the control group (13.8%). PBL from patients with OA exhibited low reactivity to the native G1 domain of bovine PG. However, removal of KS chains from the G1 globular domain resulted in increased cellular immune responses to the G1 domain in OA patients (45.8%) compared with the control group (7.7%).

CONCLUSION

These results indicate the presence of immunity to cartilage-derived LP and the G1 globular domain of PG aggrecan in patients with OA and the inhibitory effect of KS chains on the G1 domain on the expression of this immunity in OA patients. This immune reactivity is commonly observed in patients with inflammatory joint disease and can experimentally induce arthritis. Thus, it may be involved in the pathogenesis of OA.

Induction of arthritis in BALB/c mice by cartilage link protein: involvement of distinct regions recognized by T and B lymphocytes

Both type II collagen and the proteoglycan aggrecan are capable of inducing an erosive inflammatory polyarthritis in mice. In this study we provide the first demonstration that link protein (LP), purified from bovine cartilage, can produce a persistent, erosive, inflammatory polyarthritis when injected repeatedly intraperitoneally into BALB/c mice. We discovered a single T-cell epitope, located within residues 266 to 290 of bovine LP (NDGAQIAKVGQIFAAWKLLGYDRCD), which is recognized by bovine LP-specific T lymphocytes. We also identified three immunogenic regions in bovine LP that contain epitopes recognized by antibodies in hyperimmunized sera. One of these B-cell regions is found in the most species-variable domain of LP (residues 1 to 36), whereas the other epitopes are located in the most conserved regions (residues 186 to 230 and 286 to 310). The latter two regions contain an AGWLSDGSVQYP motif shared by the G1 globulin domain of aggrecan core protein, versican, neurocan, glial hyaluronan-binding protein, and the hyaluronan receptor CD44. Our data reveal that the induction of arthritis is associated with antibody reactivities to B-cell epitopes located at residues 1 to 19. Together, these observations show that another cartilage protein, LP, like type II collagen and the proteoglycan aggrecan, is capable of inducing an erosive inflammatory arthritis in mice and that the immunity to LP involves recognition of both T- and B-cell epitopes. This immunity may be of importance in the pathogenesis of inflammatory joint diseases, such as juvenile rheumatoid arthritis, in which cellular immunity to LP has been demonstrated.

Cellular immunity to the G1 domain of cartilage proteoglycan aggrecan is enhanced in patients with rheumatoid arthritis but only after removal of keratan sulfate

OBJECTIVE

To determine whether patients with rheumatoid arthritis (RA) express cellular immunity to the purified G1 globular domain of cartilage proteoglycan (PG) aggrecan and whether it is influenced by the removal of keratan sulfate (KS) chains from the molecule.

METHODS

The G1 globular domain of PG was purified from mature bovine articular cartilage, digested with keratanase, and used in proliferation assays with peripheral blood lymphocytes (PBL) isolated from 43 patients with RA, 11 patients with nonarticular rheumatism (NAR), including soft tissue rheumatism and mechanical back pain, and 13 healthy age- and sex-matched control subjects.

RESULTS

Removal of KS chains from the G1 globular domain resulted in significantly increased prevalence and values of cellular immune responses to G1 in RA patients compared with the control and NAR groups. In the majority of RA patients, KS chains on G1 significantly inhibited its immune recognition by PBL. There was no significant effect of KS removal on the immunity to G1 in patients with NAR and in the healthy control group.

CONCLUSION

These results reveal that immune reactivity to the G1 globular domain of the cartilage PG aggrecan is enhanced in patients with RA but only when KS chains are removed. Thus, KS chains inhibit immune responses to this domain of aggrecan. Since immunity to the G1 globular domain of aggrecan induces an erosive polyarthritis in BALB/c mice after removal of KS chains, immunity to the G1 globular domain, cleaved by proteases to remove KS chains, may play a role in the pathogenesis of RA.

Detection of aggregatable proteoglycan populations by affinity blotting using biotinylated hyaluronan

Proteoglycans (PGs) were extracted from a range of cartilaginous ovine connective tissues using 4 M GuHCl and separated by composite agarose polyacrylamide gel electrophoresis. Individual PG populations resolved by this electrophoretic system were identified in toluidine blue and Stains-All stained gel segments and also by conventional immunoblotting using a range of monoclonal antibodies to defined PG epitopes. These PG species were compared with aggregatable PG populations identified by affinity blotting using a biotinylated hyaluronan, and an avidin alkaline phosphatase/nitro blue tetrazolium 5-bromo-4-chloro indolyl phosphate detection system. Two major chondroitin sulfate- and keratan sulfate-substituted aggrecan populations were readily identified by affinity blotting in all of the connective tissue extracts. An additional slower migrating aggrecan species was also detected by affinity and immunoblotting in fetal disc extracts. This may represent an aggrecan species containing an intact carboxyl terminal G3 domain. Link protein was also detectable by affinity blotting; this was confirmed by immunoblotting using an anti-link protein monoclonal antibody (8-A-4). Fragments of aggrecan which contained a functional G1 domain were also detectable by affinity blotting. The biotinylated hyaluronan affinity blotting technique could detect as little as 100 ng (as hexuronic acid) of aggregatable PG. Affinity blotting therefore represents a useful new detection methodology which complements conventional immunoblotting protocols and yields information regarding the functional status of the G1 domain of individual PG populations.

Proteoglycans from adult worms of Schistosoma haematobium

Different types of proteoglycans (PGs) from adult worms of Schistosoma haematobium, were sequentially extracted using chaotropic agents under associative conditions (0.5 M GnCl), dissociative conditions (4 M GnCl) and detergents (Triton X-100 and SDS). The extracts were designated F1, F2, F3 and F4, respectively. The highest amount of uronic acid and carbohydrate was detected in the associative extract (F1) while the highest amount of protein was detected in the SDS extract (F4). Agarose polyacrylamide gel electrophoresis (A-PAGE) indicated the presence of a different PG in each extract with different electrophoretic mobilities. Agarose gel electrophoresis of glycosaminoglycan (GAG) separated from GnCl, associative and dissociative extracts, and the residue suggested the presence of dermatan sulphate in the two extracts and the residue, in addition to a GAG-like material found in the associative extract only. This glycosaminoglycan showed resistance to digestion with all mucopolysaccharidases and nitrous acid treatment. Gel filtration chromatography of associative extract on Sepharose CL-6B indicated the presence of three main uronic acid peaks (P1, P2 and P3). Chondroitin sulphate was the main GAG that could be detected in peak one (P1). Peak two (P2) contains carbohydrate and uronic acid but has no protein or absorbance at 280 nm. P2 has two types of GAGs: dermatan sulphate and a GAG-like material. The role of this PG in helping the adult schistosomes in evading immobilization by the host blood clotting cascade is discussed. Antibodies to peak one and peak two were detected in hamster sera infected with S. haematobium and S. mansoni using the ELISA test. The specificity of peak two was found to be evident in its low cross-reactivity (18.9%) when confronted with S. mansoni infected sera.

Contents and distributions of the proteoglycans decorin and biglycan in normal and osteoarthritic human articular cartilage

The study was designed to determine the contents and distributions of the proteoglycans decorin and biglycan in adult human femoral condylar cartilage and whether these may change in osteoarthritis. New radioimmunoassays were established using peptides representing the amino-terminal 21 amino acid sequence of each proteoglycan (to which a tyrosine was added for radioiodination) and antibodies in a rabbit antiserum raised to both these molecules. Cartilage was extracted with 4 M guanidine HCl to determine total content, and extracts were analyzed by chromatography to determine molecular sizes. Frozen sections were cut parallel to the articular surface and were extracted to determine distribution within the tissue. Gel chromatography on Sepharose CL-2B under dissociative conditions revealed molecules with a partition coefficient of 0.7-0.75 in both normal and osteoarthritic cartilage. In normal adult cartilage, the mean contents of the core proteins of biglycan and decorin were calculated to be approximately 0.34 and 0.48 mg per gram wet weight, respectively. These represented molar contents similar to that of aggrecan. In osteoarthritic cartilage, there were no overall significant changes in the content and distribution of these molecules. There was, however, considerable individual variation in both distribution and content. Analyses indicated that there was a trend in osteoarthritic cartilage toward a loss of biglycan and decorin from the more superficial layers of intact cartilage, where both these molecules are normally more concentrated. This was accompanied by maintenance of proteoglycan content deeper in the cartilage, regardless of the degree of degeneration.

Immunity to the G1 globular domain of the cartilage proteoglycan aggrecan can induce inflammatory erosive polyarthritis and spondylitis in BALB/c mice but immunity to G1 is inhibited by covalently bound keratan sulfate in vitro and in vivo

Earlier work from this laboratory showed that the human proteoglycan aggrecan from fetal cartilages can induce a CD4+ T cell-dependent inflammatory polyarthritis in BALB/c mice when injected after removal of chondroitin sulfate chains. Adult keratan sulfate (KS)-rich aggrecan does not possess this property. We found that two CD4+ T cell hybridomas (TH5 and TH14) isolated from arthritic mice recognize bovine calf aggrecan and the purified G1 domain of this molecule, which also contains a portion of the interglobular domain to which KS is bound. These hybridoma responses to G1 are enhanced by partial removal of KS by the endoglycosidase keratanase or by cyanogen bromide cleavage of core protein. KS removal results in increased cellular uptake by antigen-present cells in vitro. After removal of KS by keratanase, G1 alone can induce a severe erosive polyarthritis and spondylitis in BALB/c mice identifying it as an arthritogenic domain of aggrecan. The presence of KS prevents induction of arthritis presumably as a result of an impaired immune response as observed in vitro. These observations not only identify the arthritogenic properties of G1 but they also point to the importance of glycosylation and proteolysis in determining the arthritogenicity of aggrecan and fragments thereof.

Demonstration of immunogenic keratan sulphate in commercial chondroitin 6-sulphate from shark cartilage. Implications for ELISA assays

The prototype monoclonal keratan sulphate (KS) antibody 5D4 that is widely used for detection of KS in tissues and biological fluids reacts strongly with commercial low grade shark cartilage chondroitin 6-sulphate. Characterization of the immunogenic material by chondroitinase ABC digestion, ELISA inhibition studies, immunoblotting and HPLC analyses confirmed the presence of substantial amounts of KS, probably as a large proteoglycan (> 120 kDa). Commercial and heterogenic glycosaminoglycan preparations therefore must be used with great caution in immunological analyses. On the other hand the shark cartilage chondroitin 6-sulphate is an easy accessible source of immunogenic KS that can be used as a reference standard and as coating antigen in KS-ELISAs. The concentration of immunogenic KS in synovial fluid measured with an ELISA based solely on reagents of shark cartilage chondroitin 6-sulphate correlated well (r = 0.90) with the concentrations obtained with a traditional KS-ELISA that uses purified aggrecan as standard and coating antigen, and KS in both serum and synovial fluid could be measured with sufficient linearity.

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.

Comparison of mobility changes with histological and biochemical changes during lipopolysaccharide-induced arthritis in the hamster

Arthritis refers to a heterogeneous class of diseases characterized by impairment of movement. Yet animal models of arthritis have traditionally been based on the utilization of animals housed without the capability of extended free movement and without adjunctive measurement of mobility. To define the determinants of mobility impairment, we have established a lipopolysaccharide (LPS)-induced arthritis model in the hamster that prominently features monitoring of mobility and compares mobility changes with histological and biochemical changes during arthritis. Intraarticular LPS induces a dose-dependent inhibition of the hamster's mobility as measured by decreased daily distance on a running wheel (normal distance 9 to 12 km/day). At low concentrations of LPS (0.1 and 1 microgram/knee), daily distances returned to normal after 4 and 6 days, respectively. At higher concentrations, the mobility was still markedly suppressed after 6 days, and, at 100 micrograms/knee, irreversible chondrocyte loss was observed on the femoral condylar margins. Further studies were therefore conducted using 1 microgram LPS/knee. Histological and biochemical changes were examined to determine which resolved at the time of restoration of mobility. At the time of restoration of mobility, the synovial capsule was still edematous and heavily infiltrated with leukocytes; proteoglycan loss from the medial femoral condyle was still increasing. Plasma keratan sulfate failed to correlate with either proteoglycan loss or mobility changes. Proteoglycan synthesis, which was maximally suppressed the second day after LPS, was enhanced over controls at the time of restoration of mobility, suggesting the onset of repair. These results suggest a possible association of mobility inhibition with local cytokine synthesis. This model provides an approach to define the causes of mobility impairment.

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 quantitation of a native chondroitin sulfate epitope in synovial fluid lavages and articular cartilage from canine experimental osteoarthritis and disuse atrophy

OBJECTIVE

Previous studies have shown the presence of a native chondroitin sulfate epitope in articular cartilage proteoglycans from canine knee joints with experimental early osteoarthritis (OA), but not in normal cartilage. The objective of this study was to quantitate the native epitope recognized by monoclonal antibody 3-B-3 in synovial fluids and articular cartilage of diseased joints.

METHODS

An immunoassay with monoclonal antibody 3-B-3, which recognizes a native chondroitin-6-sulfate structure, was developed and used to analyze synovial fluid lavage material and extracts of articular cartilage from canine knee joints with early experimental OA or with mild disuse atrophy, and from control animals.

RESULTS

The concentration of epitope in the OA fluids was elevated 33-35-fold, and in the OA articular cartilage extracts it was elevated > 200-fold, compared with samples from the control group. No significant difference was detected in the levels of 3-B-3 epitope in the synovial fluid lavage material or cartilage extracts from the joints of the disuse group versus the control group.

CONCLUSION

The native 3-B-3 epitope in articular cartilage and synovial fluids may be a specific marker of ongoing anabolic events in early degenerative joint disease.

Sensitivity of monoclonal antibody, 5-D-4, for the detection of aggrecan, aggrecan fragments, and keratan sulfate

Bovine nasal septum aggrecan and selected proteinase-digested products of aggrecan were evaluated in an inhibition ELISA using the anti-keratan sulfate (KS) monoclonal antibody 5-D-4 (5D4). Undegraded aggrecan was recognized with an IC50 of 0.27 microgram/ml. When aggrecan was treated with human stromelysin (SLN), human leukocyte elastase (HLE), or papain, the degradation fragments had different hydrodynamic sizes. Treatment with SLN produced the largest fragments, HLE generated intermediate fragments, and papain the smallest fragments. Whereas degradation of aggrecan by SLN had little effect on recognition of proteoglycan in the ELISA (IC50-0.5 microgram/ml), degradation by both HLE and papain significantly decreased the sensitivity for detection of KS epitope (IC50-700 and 215 micrograms/ml, respectively). In addition, 5D4 detected single chain costal and corneal KS with much less sensitivity (IC50-21 and 469 micrograms/ml, respectively) than undegraded aggrecan (IC50-0.27 microgram/ml).

Studies of the articular cartilage proteoglycan aggrecan in health and osteoarthritis. Evidence for molecular heterogeneity and extensive molecular changes in disease

Changes in the structure of the proteoglycan aggrecan (PG) of articular cartilage were determined immunochemically by RIA and gel chromatography and related to cartilage degeneration documented histologically by the Mankin grading system. Monoclonal antibodies to glycosaminoglycan epitopes were used. In all cartilages, three chondroitin sulfate (CS)-rich populations of large size were observed in addition to a smaller keratan sulfate (KS)-rich population. In grades 7-13 OA cartilages (phase II), molecules were significantly larger than the equivalent molecules of grades 2-6 (phase I). CS chain lengths remained unchanged. In most OA cartilages, a CS epitope 846 was elevated in content, this being most marked in phase II (mean: fivefold). Loss of uronic acid, KS, and hyaluronic acid were only pronounced in phase II OA because of variations in normal contents. Aggregation of PG was unchanged (50-60%) or reduced in OA cartilages, but molecules bearing epitope 846 exhibited almost complete aggregation in normal cartilages. This study provides evidence for the capacity of OA cartilage to synthesize new aggrecan molecules to replace those damaged and lost by disease-related changes. It also defines two phases of PG change in OA: an early predominantly degenerate phase I followed by a net reparative phase II accompanied by net loss of these molecules.

Antigenic properties of keratan sulfate: influence of antigen structure, monoclonal antibodies, and antibody valency

The influence of (a) antigen structure, (b) type of monoclonal antibody, and (c) antibody bivalency on the immunochemical detection and quantification of keratan sulfate (KS) from aggrecan has been studied. Apparent KS epitope levels were determined by immunoglobulin G (IgG)-enzyme-linked immunosorbent assay (ELISA) in preparations of human aggrecan and in a defined series of lower molecular weight proteoglycan preparations generated by proteolytic and alkali treatment of aggrecan. Gel filtration chromatography showed KS epitope to be preferentially detected in the higher molecular weight fragments of the preparations. In single KS chains the epitope was detected in the chains of higher M(r). The ability of the proteoglycan to inhibit in the IgG-ELISA decreased with a reduction in proteoglycan fragment size, ranging between 6- and 260-fold, depending on the antibody used. This was considered to be a cooperative binding effect. With most antibodies, the sensitivity of the IgG-ELISA (represented by the steepness of the inhibition slope) was also reduced with smaller inhibitor sizes. The lowest limit of detectability (the amount of KS required to generate 20% inhibition) varied by up to 60-fold depending on the antibody used. The use of monovalent Fab fragments instead of the whole IgG anti-KS antibody in the ELISA showed that the bivalency of the antibody also affected the quantitation of the assay. In the Fab-ELISA the assay was found to have an increased detectability (by 9.5-fold with aggrecan as the inhibitor), and the proteoglycan fragments and aggrecan all generated parallel inhibition curves. Although the Fab-ELISA was somewhat influenced by the structural presentation of the KS, this was not apparent for small fragments and single chains. Thus the effects of cooperative binding and antibody valency could be overcome and quantitative data could be obtained for all samples, using papain-digested samples and the Fab-ELISA. Application of this assay to analysis of body fluids showed the KS-containing fragments in synovial fluid, serum, and urine were of different sizes and could be quantified.

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.

Cartilage proteoglycan-induced arthritis in BALB/c mice. Antibodies that recognize human and mouse cartilage proteoglycan and can cause depletion of cartilage proteoglycan with little or no synovitis

Human fetal cartilage proteoglycan (PG) induces the development of an erosive polyarthritis and spondylitis in BALB/c mice. We have examined the properties of 3 monoclonal antibodies (MAb) to human fetal cartilage PG isolated from immunized mice that cross-react with mouse cartilage PG. Compared with sera from arthritic mice, which contain antibodies reactive with keratan sulfate, MAb 202 (IgG1) reacted only with a protein-related epitope that is distributed on both hyaluronic acid-binding and chondroitin sulfate-attachment regions. MAb 813 (IgG1) reacted with the same fragments and recognized an epitope with the immunologic characteristics of keratan sulfate. MAb 945 (IgM) remains to be further characterized. Introduction of hybridomas secreting MAb 202 and MAb 945 into irradiated mice resulted in the loss of PG from articular cartilage and from growth plate cartilage (with MAb 202 only), as revealed by a loss of staining with toluidine blue. There was no synovial hyperplasia with MAb 202, but some hyperplasia and mononuclear cell infiltration was seen with MAb 945. This was accompanied by the binding of immunoglobulins to articular cartilage, as demonstrated by immunofluorescence. The hybridoma secreting MAb 813 produced no cartilage changes or synovitis, and there was no immunoglobulin binding to cartilage. Polymorphonuclear leukocyte infiltration was never observed with these antibodies. These studies indicate that MAb reactive with mouse cartilage PG can cause the depletion of PG from hyaline cartilage by mechanisms that may be both complement dependent and complement independent. Antibodies may serve to release and expose PG antigen to immune cells, as well as causing a loss of the mechanical properties of cartilage that are PG dependent.

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.

Monoclonal antibodies reacting with endo-beta-galactosidase-resistant epitopes on keratan sulfate-bearing fragments of bovine nasal cartilage proteoglycan

Six monoclonal antibody-producing cell lines were derived from mice immunized with keratan sulfate (KS)-bearing tryptic fragments of the core protein of bovine nasal cartilage proteoglycan monomer digested with KS-specific endo-beta-galactosidase. The monoclonal antibodies were characterized by solid-phase ELISA competition studies and SDS-PAGE immunoblotting. Two of them resemble previously described monoclonal antibodies that are directed to epitopes containing both KS and core protein. In contrast, the remaining four monoclonal antibodies are unprecedented in being directed to epitopes whose reactivity is unaffected or enhanced by endo-beta-galactosidase degradation of KS. SDS-PAGE immunoblots revealed two large KS-bearing tryptic fragments of cartilage proteoglycan and a heterogeneous population of smaller fragments not evident by non-immunological techniques. Some of the antibodies used react with all KS-bearing fragments, others react only with the two largest fragments.