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

Effect of ceramic calcium-phosphorus ratio on chondrocyte-mediated biosynthesis and mineralization

The osteochondral interface functions as a structural barrier between cartilage and bone, maintaining tissue integrity postinjury and during homeostasis. Regeneration of this calcified cartilage region is thus essential for integrative cartilage healing, and hydrogel-ceramic composite scaffolds have been explored for calcified cartilage formation. The objective of this study is to test the hypothesis that Ca/P ratio of the ceramic phase of the composite scaffold regulates chondrocyte biosynthesis and mineralization potential. Specifically, the response of deep zone chondrocytes to two bioactive ceramics with different calcium-phosphorus ratios (1.35 ± 0.01 and 1.41 ± 0.02) was evaluated in agarose hydrogel scaffolds over two weeks in vitro. It was observed that the ceramic with higher calcium-phosphorus ratio enhanced chondrocyte proliferation, glycosaminoglycan production, and induced an early onset of alkaline phosphorus activity, while the ceramic with lower calcium-phosphorus ratio performed similarly to the ceramic-free control. These results underscore the importance of ceramic bioactivity in directing chondrocyte response, and demonstrate that Ca/P ratio is a key parameter to be considered in osteochondral scaffold design. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2694-2702, 2017.

Fact versus artifact: avoiding erroneous estimates of sulfated glycosaminoglycan content using the dimethylmethylene blue colorimetric assay for tissue-engineered constructs

The 1,9-dimethylmethylene blue (DMMB) assay is widely used to quantify sulfated glycosaminoglycan (sGAG) contents of engineered tissues, culture media, tissue samples and bodily fluids, but the assay is subject to interference from polyanions such as hyaluronic acid (HA), DNA and RNA. We examined whether specific combinations of dye pH and absorbance wavelength could minimize non-sGAG artifacts without compromising DMMB assay sensitivity. HA and DNA solutions generated substantial signal at pH 3 but not at pH 1.5. Reducing dye pH did not significantly alter sGAG measurements for normal cartilage and meniscus tissues, but eliminated anomalously high apparent sGAG contents for enzymatically isolated chondrocytes, adipose-derived stem cell (ADSC)-agarose constructs and ADSC pellets. In a cartilage tissue-engineering case study, pH 3 dye indicated high apparent sGAG readings throughout culture in both basal and chondrogenic media, with a marked decline between day 14 and 21 for chondrogenic constructs. The pH 1.5 dye, however, indicated minimal sGAG accumulation in basal medium and stable sGAG content throughout culture in chondrogenic medium. As it is often difficult to know a priori whether all groups in a study will have sGAG contents high enough to overwhelm artifacts, we recommend modifying the standard DMMB assay to reduce the risk of spurious findings in tissue engineering and clinical research. Specifically, we recommend shifting to a pH 1.5 DMMB dye and basing quantification on the absorbance difference between 525 nm (µ peak) and 595 nm (β peak) to compensate for the moderate loss of sensitivity associated with reducing the dye pH.

A functional agarose-hydroxyapatite scaffold for osteochondral interface regeneration

Regeneration of the osteochondral interface is critical for integrative and functional cartilage repair. This study focuses on the design and optimization of a hydrogel-ceramic composite scaffold of agarose and hydroxyapatite (HA) for calcified cartilage formation. The first study objective was to compare the effects of HA on non-hypertrophic and hypertrophic chondrocytes cultured in the composite scaffold. Specifically, cell growth, biosynthesis, hypertrophy, and scaffold mechanical properties were evaluated. Next, the ceramic phase of the scaffold was optimized in terms of particle size (200 nm vs. 25 μm) and dose (0-6 w/v%). It was observed that while deep zone chondrocyte (DZC) biosynthesis and hypertrophy remained unaffected, hypertrophic chondrocytes measured higher matrix deposition and mineralization potential with the addition of HA. Most importantly, higher matrix content translated into significant increases in both compressive and shear mechanical properties. While cell hypertrophy was independent of ceramic size, matrix deposition was higher only with the addition of micron-sized ceramic particles. In addition, the highest matrix content, mechanical properties and mineralization potential were found in scaffolds with 3% micro-HA, which approximates both the mineral aggregate size and content of the native interface. These results demonstrate that the biomimetic hydrogel-ceramic composite is optimal for calcified cartilage formation and is a promising design strategy for osteochondral interface regeneration.

A hydrogel-mineral composite scaffold for osteochondral interface tissue engineering

Osteoarthritis is the leading cause of physical disability among Americans, and tissue engineered cartilage grafts have emerged as a promising treatment option for this debilitating condition. Currently, the formation of a stable interface between the cartilage graft and subchondral bone remains a significant challenge. This study evaluates the potential of a hybrid scaffold of hydroxyapatite (HA) and alginate hydrogel for the regeneration of the osteochondral interface. Specifically, the effects of HA on the response of chondrocytes were determined, focusing on changes in matrix production and mineralization, as well as scaffold mechanical properties over time. Additionally, the optimal chondrocyte population for interface tissue engineering was evaluated. It was observed that the HA phase of the composite scaffold promoted the formation of a proteoglycan- and type II collagen-rich matrix when seeded with deep zone chondrocytes. More importantly, the elevated biosynthesis translated into significant increases in both compressive and shear moduli relative to the mineral-free control. Presence of HA also promoted chondrocyte hypertrophy and type X collagen deposition. These results demonstrate that the hydrogel-calcium phosphate composite supported the formation of a calcified cartilage-like matrix and is a promising scaffold design for osteochondral interface tissue engineering.

Calcium Concentration Effects on the Mechanical and Biochemical Properties of Chondrocyte-Alginate Constructs

Alginate gel crosslinked by calcium ions (Ca(2+)) has been widely used in cartilage tissue engineering. However, most studies have been largely performed in vitro in medium with a calcium concentration ([Ca(2+)]) of 1.8mM, while the calcium level in the synovial fluid of the human knee joints, for example, has been reported to be 4mM or even higher. To simulate the synovial environment, the two studies in this paper were designed to investigate how the alginate scaffold alone, as well as the chondrocytes seeded alginate gel responds to variations in medium [Ca(2+)]. In Study A, the mechanical properties of 2% alginate hydrogel were tested in 0.15M NaCl and various [Ca(2+)] (1.0mM, 1.8mM, and 4mM). In Study B, primary bovine chondrocytes was seeded in alginate gel, and biochemical contents and mechanical properties were determined after incubation for 28 days in three [Ca(2+)] (1.8mM, 4mM, and 8mM). For both studies, it was found that the magnitude of the complex shear modulus (|G*|) at 1Hz doubled and the corresponding phase angle shift angle (δ) increased > 2° as a result of the approximate 4-fold change in [Ca(2+)]. At high [Ca(2+)], the chondrocyte glycosaminogylcan (GAG) production inside the chondrocyte-alginate constructs was suppressed significantly. This is likely due to a decrease in the porosity of the chondrocyte-alginate constructs as a result of compaction in structure caused by an increased crosslinking density with [Ca(2+)]. These may be important considerations in the eventual successful implementation of cartilage tissue-engineered constructs in the clinical setting.

Heterogeneous transmural proteoglycan distribution provides a mechanism for regulating residual stresses in the aorta

The arterial wall contains a significant amount of charged proteoglycans, which are inhomogeneously distributed, with the greatest concentrations in the intimal and medial layers. The hypothesis of this study is that the transmural distribution of proteoglycans plays a significant role in regulating residual stresses in the arterial wall. This hypothesis was first tested theoretically, using the framework of mixture theory for charged hydrated tissues, and then verified experimentally by measuring the opening angle of rat aorta in NaCl solutions of various ionic strengths. A three-dimensional finite element model of aortic ring, using realistic values of the solid matrix shear modulus and proteoglycan fixed-charge density, yielded opening angles and changes with osmolarity comparable to values reported in the literature. Experimentally, the mean opening angle in isotonic saline (300 mosM) was 15 +/- 17 degrees and changed to 4 +/- 19 degrees and 73 +/- 18 degrees under hypertonic (2,000 mosM) and hypotonic (0 mosM) conditions, respectively (n = 16). In addition, the opening angle in isotonic (300 mosM) sucrose, an uncharged molecule, was 60 +/- 16 degrees (n = 11), suggesting that the charge effect, not cellular swelling, was the major underlying mechanism for these observations. The extent of changes in opening angle under osmotic challenges suggests that transmural heterogeneity of fixed-charge density plays a crucial role in governing the zero-stress configuration of the aorta. A significant implication of this finding is that arterial wall remodeling in response to altered wall stresses may occur via altered deposition of proteoglycans across the wall thickness, providing a novel mechanism for regulating mechanical homeostasis in vascular tissue.

The effect of gamma irradiation on anterior cruciate ligament allograft biomechanical and biochemical properties in the caprine model at time zero and at 6 months after surgery

BACKGROUND

High levels of gamma irradiation are required to eliminate the risk of bacterial and viral transmission during implantation of musculoskeletal allografts. The effects of high levels of gamma irradiation on anterior cruciate ligament allograft biomechanics are still not known.

HYPOTHESIS

High-dose gamma irradiation (4 Mrad) adversely affects anterior cruciate ligament allograft biomechanics at surgery and at 6 months after surgery and affects biochemistry at 6 months.

STUDY DESIGN

Controlled laboratory study.

METHODS

Bilateral anterior cruciate ligament reconstructions were performed in 18 adult goats, with one knee receiving an irradiated patellar tendon allograft (4 Mrad) and the other receiving a frozen control allograft (0 Mrad). In 6 recipients (time zero group), graft pairs were tested immediately after sacrifice, and load relaxation of the femur-allograft-tibia preparation was measured during cyclic anterior displacement. Twelve recipients received bilateral anterior cruciate ligament reconstructions, staged 2 months apart, and were sacrificed a mean of 6 months postoperatively. Load relaxation and tensile failure testing were performed, followed by allograft biochemistry assessment.

RESULTS

At time zero, irradiated grafts showed less load relaxation than did contralateral controls, but by 6 months, the trend had reversed because of decreases in control graft relaxation, with no changes in irradiated graft relaxation. By 6 months, irradiated grafts showed lower stiffness and maximum force compared to controls but no differences in modulus, maximum stress, or biochemistry.

CONCLUSION

High levels of gamma irradiation affect anterior cruciate ligament allograft subfailure viscoelastic and structural properties but not material or biochemical properties over time.

CLINICAL RELEVANCE

Although high levels of gamma irradiation may inactivate infectious agents, this treatment is not a feasible clinical option because of altered allograft biomechanics.

Separation of keratan-sulfate-derived disaccharides by high-performance liquid chromatography and postcolumn derivatization with 2-cyanoacetamide and fluorimetric detection

In this paper, we report a rapid, sensitive, and quantitative procedure to conduct disaccharide compositional analyses of keratan sulfates (KS) by means of high-performance liquid chromatography (HPLC) separation and postcolumn derivatization with 2-cyanoacetamide and fluorimetric detection of products generated by hydrolysis of this glycosaminoglycan with Bacillus sp. keratanase II or Escherichia freundii endo-beta-galactosidase. Following E. freundii endo-beta-galactosidase digestion of bovine corneal KS, the monosulfated disaccharide glcNAc6sbeta(1-->3)gal, accounting for approximately equals 95% nmol and 50% yield products, is produced. On the contrary, bovine corneal KS treated with endo-beta-N-acetylglucosaminidase (keratanase II) from Bacillus sp. generates two major products, the monosulfated disaccharide galbeta(1-->4)glcNAc6s ( approximately equals 50% nmol product) and the disulfated disaccharide gal6sbeta(1-->4)glcNAc6s ( approximately equals 40% nmol product) for over 90% nmol products. These disaccharides are separated and readily determined within 30 min by using a linear-gradient strong anion-exchange separation. A linear relationship was found for the two purified disaccharides over a wide range of concentrations, from approximately equals 108 pmol, 50 ng, to 2,160 pmol, 1,000 ng, for the disaccharide galbeta(1-->4)glcNAc6s, and from 92 pmol, 50 ng, to 1,840 pmol, 1,000 ng, for the disaccharide gal6sbeta(1-->4)glcNAc6s. HPLC analysis was applied to the quantitative and qualitative determination of KS produced by 3T3-J2 murine fibroblasts in the cell medium. The amount of KS was found to be 2.80+/-0.34 microg/ml/10(6) cells and composed of approximately equals 71% nmol of disaccharide galbeta(1-->4)glcNAc6s and 18% nmol of the disulfated disaccharide gal6sbeta(1-->4)glcNAc6s having approximately equals 1.20 sulfate groups/disaccharide. Our data illustrate that the HPLC procedure reported represents an improved approach for the quantitative and compositional microanalyses of KS, especially applicable to experimentation involving small amounts ( approximately 50 ng) of this glycosaminoglycan and in relation to its biological function and pathological importance.

Keratan sulfate disaccharide composition determined by FACE analysis of keratanase II and endo-beta-galactosidase digestion products

Many tissues contain glycoproteins and proteoglycans, which are substituted with N-or O-linked keratan sulfate, a glycosaminoglycan in which the lactosamine (-galbeta1,4glcNAc-) disaccharide backbone is variably modified by sulfation, fucosylation, and sialylation. We report here a rapid, sensitive, and quantitative procedure for obtaining a complete disaccharide compositional analyses for keratan sulfates after FACE separation of products generated by hydrolysis of the glycosaminoglycans with B. fragillis keratanase II and E. freundii endo-beta-galactosidase. Seven digestion end products are separable in a single electrophoretic step using Monosaccharide composition gels. These are: the unsulfated disaccharide, glcNAcbeta1,3gal, the fucosylated trisaccharide, galbeta1,2[fucalpha1,3]glcNAc6S, the mono- and disulfated disaccharides, galbeta1,4glcNAc6S or gal6Sbeta1,4glcNAc6S from the chain interior, and the sialylated mono- and disulfated trisaccharides neuAalpha2,3galbeta1,4glcNAc6S or neuAalpha2,3gal6Sbeta1,4glcNAc6S from the nonreducing terminus. FACE analyses also revealed the presence of a contaminant beta-galactosidase activity in keratanase II enzyme preparations which cleaves the disaccharide, galbeta1,4glcNAc6S to its constituent monosaccharides, gal and glcNAc6S. It was particularly prominent at enzyme concentrations > 2 mU per nmole substrate glcNH(2) or after prolonged digestion times (> 12 h), and was not inhibitable by thiogalactosides or N-acetyl-lactosamine. As these monosaccharide products would not be detectable using the commonly described analytical methods for KS hydrolase products, such as (1)H-NMR and HPLC analyses, our data illustrate that the FACE procedure represents an improved approach for accurate compositional microanalyses of corneal and skeletal keratan sulfates, especially applicable to experimentation involving small amounts (1-2 microg) of this glycosaminoglycan.

Osteoarthritic changes in the biochemical composition of thumb carpometacarpal joint cartilage and correlation with biomechanical properties

The biochemical composition and biomechanical properties of articular cartilage from 53 human thumb carpometacarpal (CMC) joints from cadavers aged 20 to 79 years were measured and studied in normal, mildly fibrillated, and advanced osteoarthritic (OA) joints. Statistical analyses were performed to determine the correlations between the compositional measures and biomechanical properties. For these CMC joint tissues we found that water content increased, proteoglycan content decreased, and collagen content per dry weight remained unaltered with progression of OA degeneration. We also found that with disease progression, as defined by an OA staging score, the aggregate modulus (ie, compressive stiffness) decreased, along with an unexpected moderate decrease in permeability. This latter finding appears to be specific to CMC cartilage degeneration since articular cartilage from knees and hips generally demonstrates an increase in permeability with water content and OA score. Correlations between biochemical composition and biomechanical properties were found to be stronger in joints with OA than in joints without OA. This finding suggests that OA changes in biochemical composition, relative to baseline normal values, directly affect the biomechanical properties of cartilage, even though the baseline compositional values themselves do not directly determine the magnitude of the biomechanical properties in normal tissue.

Functional tissue engineering of articular cartilage through dynamic loading of chondrocyte-seeded agarose gels

Due to its avascular nature, articular cartilage exhibits a very limited capacity to regenerate and to repair. Although much of the tissue-engineered cartilage in existence has been successful in mimicking the morphological and biochemical appearance of hyaline cartilage, it is generally mechanically inferior to the natural tissue. In this study, we tested the hypothesis that the application of dynamic deformational loading at physiological strain levels enhances chondrocyte matrix elaboration in cell-seeded agarose scaffolds to produce a more functional engineered tissue construct than in free swelling controls. A custom-designed bioreactor was used to load cell-seeded agarose disks dynamically in unconfined compression with a peak-to-peak compressive strain amplitude of 10 percent, at a frequency of 1 Hz, 3 x (1 hour on, 1 hour off)/day, 5 days/week for 4 weeks. Results demonstrated that dynamically loaded disks yielded a sixfold increase in the equilibrium aggregate modulus over free swelling controls after 28 days of loading (100 +/- 16 kPa versus 15 +/- 8 kPa, p < 0.0001). This represented a 21-fold increase over the equilibrium modulus of day 0 (4.8 +/- 2.3 kPa). Sulfated glycosaminoglycan content and hydroxyproline content was also found to be greater in dynamically loaded disks compared to free swelling controls at day 21 (p < 0.0001 and p = 0.002, respectively).

Knee joint immobilization decreases aggrecan gene expression in the meniscus

Aggrecan is the major proteoglycan of the meniscus, and its primary function is to give the meniscus its viscoelastic compressive properties. The objective of this study was to determine the effect of joint immobilization on aggrecan gene expression in the meniscus. The right hindlimbs of six mature beagles were knee cast-immobilized in 90 degrees of flexion and supported by a sling to prevent weightbearing, while the contralateral limb was left free to bear weight. The animals were sacrificed at 4 weeks, and the anterior and posterior halves of the medial and lateral menisci were analyzed separately. Analysis of aggrecan gene expression by quantitative polymerase chain reaction showed decreased aggrecan gene expression in menisci from immobilized knees (P < 0.01, two-way analysis of variance). Aggrecan gene expression decreased by a factor of 2 to 5.5 in the different regions examined. Analysis of the composition of the meniscus also showed decreased proteoglycan content and increased water content with immobilization (P < 0.05, two-way analysis of variance). These results show that joint immobilization can significantly affect meniscal cellular activity and composition and can therefore potentially affect meniscal function.

Proteoglycans in the synovial fluid of the temporomandibular joint as an indicator of changes in cartilage metabolism during primary and secondary osteoarthritis

PURPOSE

The specific aim of this investigation was to assess differences between primary and secondary osteoarthritis (OA) of the temporomandibular joint (TMJ) using clinical evaluation and synovial fluid analysis for proteoglycans.

MATERIALS AND METHODS

Arthroscopic surgery was performed on 101 TMJs from patients with significant pain or dysfunction and who had failed to respond to treatment. Joints were assessed for primary and secondary osteoarthritis. Synovial fluid aspirates were obtained and analyzed to determine the levels of keratan sulfate (KS) epitope and a novel 3B3(-) epitope by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Fifty-four patients and 67 joints had OA diagnosed by both clinical examination and arthroscopy. Primary OA was diagnosed in 14 joints (20%), and the remaining 53 joints were regarded as having secondary OA. No differences were detected in the levels of KS in the synovial fluid from the primary and secondary OA joints. Furthermore, the 3B3(-) epitope was not detectable in the synovial fluid aspirates of any TMJ.

CONCLUSION

Secondary OA is a common disorder of the TMJ. However, there is no apparent difference in the metabolism of the joints with primary and secondary OA as assessed by proteoglycans in the synovial fluid. The apparent absence of the 3b3(-) epitope, in contrast to its presence in OA of other major synovial joints, suggests that there are some differences between the cartilage metabolism of the TMJ and these other joints during OA.

Differences in patellofemoral joint cartilage material properties and their significance to the etiology of cartilage surface fibrillation

OBJECTIVE

To determine if differences in biomechanical properties and biochemical composition exist between human patellar articular cartilage and the opposing femoral articular cartilage.

DESIGN

The biomechanical properties and biochemical composition of the articular cartilage of 17 knees from 13 donors were determined for four sites on the patella and three sites on the femur representing regions of contact at 30 degrees and 90 degrees of flexion. The material properties were determined by biphasic indentation testing, yielding the compressive aggregate modulus, HA, permeability, k, and Poisson's ratio, vs. The thickness of the cartilage at the indentation site, h, was also measured using a needle probe. Full-thickness samples of cartilage adjacent to each indentation site were used for wet weight, sulfated glycosaminoglycan content and hydroxyproline content determinations.

RESULTS

The patellar cartilage was found to have a lower compressive aggregate modulus by 30% (P < 0.001), higher permeability to fluid flow by 66% (P < 0.001) and greater thickness by 23% (P = 0.017) than that of the opposing femoral cartilage. The Poisson's ratios for both surfaces were found to be nearly zero. The water content of the patella was higher by 5% (P = 0.031) and the proteoglycan content lower by 19% (P = 0.030) than that of the femur. However, no differences were found between the collagen contents of the cartilages.

CONCLUSIONS

Significant differences were found between the intrinsic material properties of the patellar cartilage and those of the femoral-trochlear cartilage. This variability of cartilage material properties with the patellofemoral joint may help explain why patellar cartilage has been frequently observed clinically to exhibit earlier and more severe fibrillation changes than the opposing femoral cartilage.

Biochemical markers in synovial fluid identify early osteoarthritis of the glenohumeral joint

The objective of this study on the glenohumeral joint was to assess the (1) accuracy of clinical diagnosis of osteoarthritis compared with arthroscopic diagnosis, and (2) the ability of biochemical markers in synovial fluid to detect osteoarthritis. Patients (96) were examined clinically and the preoperative diagnosis of osteoarthritis was recorded. At surgery (arthroscopy or arthroplasty), the glenohumeral joint was inspected for signs of osteoarthritis, and the joint osteoarthritis grade (I-IV) was recorded. At surgery, synovial fluid lavage was obtained from the joint, and later analyzed to determine levels of aggrecan components: total sulfated glycosaminoglycan and keratan sulfate epitope, link protein and the chondroitin sulfate epitope recognized by antibody 3B3 (3B3(-)). Compared with arthroscopic diagnosis of osteoarthritis, the results showed that the clinical diagnosis did not wrongly identify joints without osteoarthritis, and was always able to identify joints with advanced (Grade IV) osteoarthritis. Grade II osteoarthritis was rarely identified (10% of the time), and Grade III osteoarthritis was identified 50% of the time. Biochemical assessment of the synovial fluid showed that the catabolic markers (sulfated glycosaminoglycan, keratan sulfate and link protein) were elevated in fluids from joints with moderate (Grade III) and advanced osteoarthritis (Grade IV), and the 3B3(-) epitope was elevated in Grades II, III, and IV. These results show that arthroscopic diagnosis for osteoarthritis, of the glenohumeral joint is particularly useful for early and moderate osteoarthritis, where clinical (nonarthroscopic) diagnosis is poor, and that biochemical analysis of the synovial fluids corresponds well to arthroscopic diagnosis of shoulder osteoarthritis.

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.

Mechanical and biochemical changes in the superficial zone of articular cartilage in canine experimental osteoarthritis

The changes in the tensile mechanical properties and biochemical composition of the superficial zone of articular cartilage were examined in a canine model of early osteoarthritis generated by transection of the anterior cruciate ligament. Sixteen weeks following ligament transection, the tensile stiffness of the articular cartilage was decreased by 44% and the ion-induced stress relaxation of the tissue was increased by 57% compared with the contralateral control. Biochemical analyses indicated that the water content of the experimental tissue was increased by 13%, which was reflected as an apparent 37% decrease in the proteoglycan content and a 36% decrease in the collagen content (expressed per wet weight). The hydroxypyridinium crosslink density was decreased in the experimental tissue by 11%. A significant negative correlation was found between the ion-induced stress relaxation and the hydroxypyridinium crosslink density in both control tissue (R = -0.56) and experimental tissue (R = -0.70). No correlation was noted between the tensile stiffness and the biochemical composition of the tissue. These results suggest that, in the superficial zone of articular cartilage, the structure of the tissue may play a more important role than the composition in the determination of its mechanical properties. A major event observed in the model of early osteoarthritis appears to be the disruption and remodeling of the collagen network in the superficial zone of the articular cartilage.

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.

The sulphation pattern in chondroitin sulphate chains investigated by chondroitinase ABC and ACII digestion and reactivity with monoclonal antibodies

We have used progressive chondroitinase digestion of pig aggrecan in conjunction with ELISA assays and disaccharide analysis to derive information about the pattern of 4- and 6-sulphation in chondroitin sulphate chains. Digestion with chondroitinase ABC resulted in the release of mainly disaccharides from the nonreducing terminal of chondroitin sulphate chains but there was also the release of some tetra- and hexa-saccharides which were degraded to disaccharides with more extensive digestion. Chondroitinase ACII, in contrast, released only disaccharides. Analysis of the disaccharide composition of the intact and digested products at different stages of digestion showed that there was a slight increase in 6-sulphate content of the chains as they were shortened. Reaction of the partially digested proteoglycans with monoclonal antibodies 3-B-3 and 3-D-5 which recognise chains terminating in 6- or 4-sulphated disaccharides, respectively, showed major differences between chondroitinase ABC and ACII products. The results suggested that chondroitinase ABC preferentially cleaved next to 4-sulphated, rather than 6-sulphated disaccharides and this resulted in some oligosaccharides as well as disaccharide being released. Chondroitinase ACII also cleaved an additional disaccharide next to the linkage to protein of chondroitin sulphate, which was not removed by chondroitinase ABC and this disaccharide was mainly nonsulphated.

Cloning and expression in Escherichia coli of the gene encoding the Proteus vulgaris chondroitin ABC lyase

The structural gene encoding chondroitin ABC lyase from Proteus vulgaris was cloned and sequenced. This gene consists of a single open reading frame of 3,063 bp, including a sequence (72 bp) for a possible secretory protein leader peptide, preceded by a Shine-Dalgarno ribosomal binding site. Promoter-like and rho-independent terminator sequences were detected upstream and downstream of the open reading frame, respectively. The G+C content of the coding region was 38.6%. The transcription startpoint was located 41-bp upstream of the initiation codon (ATG). Chondroitin ABC lyase is composed of 997 amino acids, and has a relative molecular mass of 112,635. When the 5.2-kb fragment containing the 1.2-kb upstream from the gene was inserted into pSTV29, and cloned in Escherichia coli, chondroitin ABC lyase was induced in the medium containing chondroitin-6-sulfate as the carbon source. On the other hand, when a 4.2-kb fragment containing only 0.2 kb upstream was inserted into pSTV29(pCHS delta 6), and pCHS delta 6 was introduced into E. coli, the enzyme was constitutively produced, even in medium containing glucose as the carbon source. By immunoblot analysis, the polypeptide synthesized by E. coli cells carrying pCHS delta 6 appeared to be the same as that of the purified chondroitin ABC lyase from P. vulgaris.

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.