Kinetics of extraction of proteoglycans from human cartilage

A cartilage growth mixture model for infinitesimal strains: solutions of boundary-value problems related to in vitro growth experiments

A cartilage growth mixture (CGM) model is linearized for infinitesimal elastic and growth strains. Parametric studies for equilibrium and nonequilibrium boundary-value problems representing the in vitro growth of cylindrical cartilage constructs are solved. The results show that the CGM model is capable of describing the main biomechanical features of cartilage growth. The solutions to the equilibrium problems reveal that tissue composition, constituent pre-stresses, and geometry depend on collagen remodeling activity, growth symmetry, and differential growth. Also, nonhomogeneous growth leads to nonhomogeneous tissue composition and constituent pre-stresses. The solution to the nonequilibrium problem reveals that the tissue is nearly in equilibrium at all time points. The results suggest that the CGM model may be used in the design of tissue engineered cartilage constructs for the repair of cartilage defects; for example, to predict how dynamic mechanical loading affects the development of nonuniform properties during in vitro growth. Furthermore, the results lay the foundation for future analyses with nonlinear models that are needed to develop realistic models of cartilage growth.

A growth mixture theory for cartilage with application to growth-related experiments on cartilage explants

In this paper, we present a growth mixture model for cartilage. The main features of this model are illustrated in a simple equilibrium boundary-value problem that is chosen to illustrate how a mechanical theory of cartilage growth may be applied to growth-related experiments on cartilage explants. The cartilage growth mixture model describes the independent growth of the proteoglycan and collagen constituents due to volumetric mass deposition, which leads to the remodeling of the composition and the mechanical properties of the solid matrix. The model developed here also describes how the material constants of the collagen constituent depend on a scalar parameter that may change over time (e.g., crosslink density); this leads to a remodeling of the structural and mechanical properties of the collagen constituent. The equilibrium boundary-value problem that describes the changes observed in cartilage explants harvested at different stages of a growth or a degenerative process is formulated. This boundary-value problem is solved using existing experimental data for developing bovine cartilage explants harvested at three developmental stages. The solution of the boundary-value problem in conjunction with existing experimental data suggest the types of experimental studies that need to be conducted in the future to determine model parameters and to further refine the model.

Depth- and strain-dependent mechanical and electromechanical properties of full-thickness bovine articular cartilage in confined compression

Compression tests have often been performed to assess the biomechanical properties of full-thickness articular cartilage. We tested whether the apparent homogeneous strain-dependent properties, deduced from such tests, reflect both strain- and depth-dependent material properties. Full-thickness bovine articular cartilage was tested by oscillatory confined compression superimposed on a static offset up to 45%. and the data fit to estimate modulus, permeability, and electrokinetic coefficient assuming homogeneity. Additional tests on partial-thickness cartilage were then performed to assess depth- and strain-dependent properties in an inhomogeneous model, assuming three discrete layers (i = 1 starting from the articular surface, to i = 3 up to the subchondral bone). Estimates of the zero-strain equilibrium confined compression modulus (H(A0)), the zero-strain permeability (kp0) and deformation dependence constant (M), and the deformation-dependent electrokinetic coefficient (ke) differed among individual layers of cartilage and full-thickness cartilage. HiA0 increased from layer 1 to 3 (0.27 to 0.71 MPa), and bracketed the apparent homogeneous value (0.47 MPa). ki(p0) decreased from layer 1 to 3 (4.6 x 10(-15) to 0.50 x 10(-15) m2/Pa s) and was less than the homogeneous value (7.3 x 10(-15) m2/Pa s), while Mi increased from layer 1 to 3 (5.5 to 7.4) and became similar to the homogeneous value (8.4). The amplitude of ki(e) increased markedly with compressive strain, as did the homogeneous value: at low strain, it was lowest near the articular surface and increased to a peak in the middle-deep region. These results help to interpret the biomechanical assessment of full-thickness articular cartilage.

Glycation induced crosslinking of link proteins, in vivo and in vitro

OBJECTIVE

Reducing sugars have the ability to crosslink proteins through creation of advanced glycosylated end products (AGE). In this study, we determined the ability of AGE to induce crosslinking of link proteins and aggrecan proteoglycans.

METHODS

Aggrecan proteoglycans and link proteins were purified from adult human articular cartilage and from young bovine nasal cartilage for in vivo and in vitro studies, respectively. In vitro studies concerned incubation of aggrecan aggregates or link proteins with ribose under physiological conditions. After 30 days, aggregates were centrifuged dissociatively to obtain aggrecan monomers and link proteins. Aggrecan monomers were analyzed by immunoblot assay. Incubated link proteins were analyzed by SDS-PAGE and Sephacryl-200 column chromatography.

RESULTS

After extensive purification, adult human cartilage aggrecan continued to show the presence of link protein antigens by immunoblot analysis. Immunoblot analysis of purified aggrecan derived from ribose-treated aggregates also showed the presence of link protein antigens. Ribose treatment of link protein lead to polymerization that was confirmed by Sephacryl-200.

CONCLUSIONS

These studies suggest that human link proteins tend to become crosslinked to aggrecan in adult cartilage. A likely cause of the crosslinking is formation of AGE due to reducing sugars.

The proteoglycan metabolism of mature bovine articular cartilage explants superimposed to continuously applied cyclic mechanical loading

This study describes the effect of load magnitude, frequency and duration on proteoglycan (PG) biosynthesis and loss in mature bovine articular cartilage explants. Cultured full thickness cartilage discs were subjected to a continuously applied, uniaxial compressive cyclic load. The loads were applied using a sinusoidal waveform of 0.001, 0.01, 0.1 or 0.5 Hz-frequency and a peak stress of 0.1, 1.0, 2.5, or 5.0 MPa for a period of 1, 3 or 6 days. Increasing the load magnitude, as well as the duration of loading, reduced the PG biosynthesis. Reducing the load frequency abolished the inhibitory effect of a given load magnitude on PG biosynthesis, even though explants were more compressed. Increasing the load magnitude stimulated the release of newly synthesized PGs from explants, whereas an elevated duration of loading significantly decreased the release of endogenous PGs. Explants loaded for 1 or 3 days were viable as determined biochemically, whereas 6 days of loading resulted in a slightly diminished viability of explants. This study demonstrates that the duration and intensity of loading influences the inhibition of PG biosynthesis, while PG loss is only modulated by the magnitude and duration of loading.

Effects of meloxicam, compared with other NSAIDs, on cartilage proteoglycan metabolism, synovial prostaglandin E2, and production of interleukins 1, 6 and 8, in human and porcine explants in organ culture

Some non-steroidal anti-inflammatory drugs (NSAIDs) can accelerate joint damage in osteoarthritis by enhancing the production of pro-inflammatory cytokines or inhibiting cartilage proteoglycan synthesis. Meloxicam, a new NSAID, was compared with standard NSAIDs for its effect on proteoglycan synthesis and degradation in human and porcine cartilage explants, as well as the production of prostaglandin E2 (PGE2) and interleukins 1 and 6 by human synovial tissue explants in-vitro. Meloxicam at submicromolar concentrations inhibited synovial PGE2 production but, up to therapeutic drug concentrations (< or = 4 microM), did not affect synovial production of the pro-inflammatory cytokine IL-1. In contrast, hydrocortisone, 10 microM, a positive control, inhibited release of this cytokine, and indomethacin, 100 microM, increased its production. The lack of effects of meloxicam were evident irrespective of intrinsic IL-1 bioactivity of the synovia, production of IL-1 inhibitors or time of incubation. Production of the part anti-inflammatory cytokine IL-6, was significantly increased by therapeutic concentrations of meloxicam, as well as by indomethacin. Another major pro-inflammatory cytokine, IL-8, was unaffected by therapeutic concentrations of meloxicam. Meloxicam, 0.1-4.0 microM, did not affect cartilage proteoglycan production whereas indomethacin, 100 microM, significantly reduced synthesis of these macromolecules. Thus meloxicam, at concentrations within the therapeutic range and at which pronounced inhibition of prostaglandin production is evident, affects neither cartilage proteoglycan production nor the production of those cytokines likely to be important in cartilage destruction.

Quantitative and qualitative analyses of proteoglycans in cartilage extracts by precipitation with 1,9-dimethylmethylene blue

The dye 1,9-dimethylmethylene blue may be used for the specific and quantitative precipitation of sulphated glycosaminoglycans as well as proteoglycans from the extracts of articular cartilage. The consumption of the dye DMMB enables to determine the amount of the proteoglycans present in the extract, by measuring the decrease of the absorption at 595 nm. The precipitated complex of DMMB and proteoglycans is used for qualitative investigations into the electrophoretic mobility of the different proteoglycans in agarose slab gel and their immunological characterization after blotting. Because of its higher sensitivity and greater simplicity the method described in this report is a promising alternative to the procedure based on alcian blue.

Comparison of the Ruthenium hexammine trichloride method to other methods of chemical fixation for preservation of avian physeal cartilage

Several methods of chemical fixation of avian physeal cartilage were compared. The Ruthenium hexammine trichloride method was compared to isotonic glutaraldehyde and neutral buffered formalin for light microscopy and paraffin embedment, and to two osmium-ferrocyanide methods and a combination of 1% glutaraldehyde and 4% formaldehyde for electron microscopy. Only the Ruthenium hexammine trichloride method prevented the loss of matrix proteoglycans and shrinkage of chondrocytes. In undecalcified paraffin-embedded cartilage, preservation of matrix and cellular detail was excellent, but Ruthenium hexammine trichloride interfered with Haematoxylin and Eosin staining. Glutaraldehyde gave more intense eosinophilia than neutral buffered formalin. Ultrastructurally, the Ruthenium hexammine trichloride method was the most consistent and gave the best overall fixation. Matrix elements and cellular and nuclear membranes were well preserved. It did result in vacuolation of the cytoplasm and mitochondria, and it increased granularity of the cytoplasm, chromatin, and rough endoplasmic reticulum. Other fixatives produced minimal vacuolation and finer granularity, but preservation was less consistent, cell/matrix contrast was often excessive, and they caused shrinkage of all chondrocytes. Large dilatations of the rough endoplasmic reticulum that appear to be cytoplasmic inclusions by light microscopy are described for the first time in avian cartilage.

Effects of compression on the loss of newly synthesized proteoglycans and proteins from cartilage explants

The effects of mechanical compression of calf cartilage explants on the catabolism and loss into the medium of proteoglycans and proteins radiolabeled with [35S]sulfate and [3H]proline were examined. A single 2- or 12-h compression of 3-mm diameter cartilage disks from a thickness of 1.25 to 0.50 mm, or slow cyclic compression (2 h on/2 h off) from 1.25 mm to 1.00, 0.75, or 0.50 mm for 24 h led to transient alterations and/or sustained increases in loss of radiolabeled macromolecules. The effects of imposing or removing loads were consistent with several compression-induced physical mediators including fluid flow, diffusion, and matrix disruption. Cyclic compression induced convective fluid flow and enhanced the loss of 35S- and 3H-labeled macromolecules from tissue into medium. In contrast, prolonged static compression induced matrix consolidation and appeared to hinder the diffusional transport and loss of 35S- and 3H-labeled macromolecules. Since high amplitude cyclic compression led to a sustained increase in the rate of loss of 3H- and 35S-labeled macromolecules that was accompanied by an increase in the rate of loss of [3H]hydroxyproline residues and an increase in tissue hydration, such compression may have caused disruption of the collagen meshwork. The 35S-labeled proteoglycans lost during such cyclic compression were of smaller average size than those from controls, but contained a similarly low proportion (approximately 15%) that could form aggregates with excess hyaluronate and link protein. The size distribution and aggregability of the remaining tissue proteoglycans and 35S-labeled proteoglycans were not markedly affected. The loss of tissue proteoglycan paralleled the loss of 35S-labeled macromolecules. This study provides a framework for elucidating the biophysical mechanisms involved in the redistribution, catabolism, and loss of macromolecules during cartilage compression.

Chondrons from articular cartilage (II): Analysis of the glycosaminoglycans in the cellular microenvironment of isolated canine chondrons

A chondron rich preparation was isolated from mature canine tibial cartilage using low-speed homogenization techniques. Proteoglycans were extracted from this preparation by exhaustive treatment with 4M guanidine-HCl. A significant proportion of the total proteoglycan, measured as uronic acid, was resistant to extraction and represented 27.9% in intact cartilage chips and 18.6% in the chondron fraction. Histochemical examination of chondrons confirmed that extraction resistant proteoglycans remained within the capsule of the chondron after 4M guanidine-HCl treatment. Electrophoretic analysis of the glycosaminoglycans extracted from intact cartilage chips and the chondron fraction showed approximately equivalent amounts of chondroitin sulphate (79.3%), keratan sulphate (16.3%) and hyaluronic acid (4.3%) present. In contrast, the extraction resistant residue in the chondron fraction was significantly enriched for hyaluronic acid (10.5%, p less than 0.05) but was depleted of chondroitin sulphate (70.9%, p less than 0.05). The major chondroitin sulphate isomer in the resistant fraction was chondroitin 6-sulphate while in the soluble fraction, the quantities of the two isomers were approximately equivalent. Comparison with previously published data suggests a role for minor collagens in the retention of proteoglycans in the cellular microenvironment.

Comparative effects of azapropazone on cellular events at inflamed sites. Influence on joint pathology in arthritic rats, leucocyte superoxide and eicosanoid production, platelet aggregation, synthesis of cartilage proteoglycans, synovial production and actions of interleukin-1 in cartilage resorption correlated with drug uptake into cartilage in-vitro

Azapropazone (APZ) has been compared with standard NSAIDs in title systems to establish aspects of its mode of action on cellular events at inflamed sites. APZ (150 mg kg-1 day-1) given for 10-13 days exhibited a reduction in joint pathology in established adjuvant arthritis in rats comparable with that of indomethacin (2 mg kg-1 day-1) and clobuzarit (20 mg kg-1 day-1). APZ was shown to be a potent inhibitor of the production of leucocyte superoxide and synovial interleukin-1 (IL-1)-like activity and stimulated articular cartilage proteoglycan synthesis, but was ineffective as an inhibitor of platelet aggregation or IL-1 induced cartilage degradation in-vitro. These in-vitro effects may have relevance to the mode of action of this weak inhibitor of prostaglandin synthesis.

Maturation of proteoglycan matrix in articular cartilage under increased and decreased joint loading. A study in young rabbits

The right knees of 4-month-old NZW rabbits were splinted in extension for 1 to 8 weeks. Biochemical changes of the knee articular cartilage were noted after decreased (splinted leg) and increased loading (created by the shift of body weight onto the left, contralateral limb). Increased loading accelerated changes associated with maturation of articular cartilage, which include accumulation of hyaluronic acid (HA) and keratan sulfate-rich proteoglycans (KS, PG) that are tightly bound to the tissue. After 8-weeks of splinting the content of extractable PGs in the tibial medial condyle decreased. The lost material was apparently replaced by PGs with a higher degree of sulfation of the chondroitin sulfate (Ch-S) chains. Reduced loading disturbed normal maturation as evidenced by inhibition of the accumulation of KS-rich, non-extractable PGs. Collagen content increased in all samples of different joint sites and groups during the 8-week experiment. The content of extractable PGs decreased slightly, while the content of non-extractable, especially KS-rich PGs increased. The greatest changes occurred in the tibial medial condyle, where the KS content was highest.

Quantitation of glycosaminoglycan metabolism in anatomically intact articular cartilage of the mouse patella: in vitro and in vivo studies with 35S-sulfate, 3H-glucosamine, and 3H-acetate

We investigated the usefulness of the whole mouse patella to quantitate the synthesis of the glycosaminoglycan (GAG) backbone and its sulfation by intact murine articular cartilage, both in vitro and in vivo. Using 35S-sulfate, 3H-glucosamine, or 3H-acetate as precursors of GAG synthesis, it was found that more than 90% of the incorporated radioactivity was confined to the patellar cartilage layer compared to the whole patella. Overnight papain digestion was enough to liberate more than 95% of the incorporated radiolabels, except for 3H-acetate for which 15-25% was not digestible. Comparison of radioactivity in the patella and that in quantitatively isolated GAGs revealed that for 35S-sulfate incorporation studies the whole patella can be used as a reliable measure for sulfated GAG synthesis. The situation was different for the GAG backbone precursors 3H-glucosamine and 3H-acetate; more than 50% of the 3H labels were incorporated into compounds other than GAGs or non-covalently associated with matrix components. Hence, in studying GAG-backbone metabolism, polysaccharides must be isolated quantitatively from cartilage. In vivo studies made it clear that both 35S-sulfate and 3H-glucosamine are incorporated into patellar GAGs in amounts high enough to enable proper quantitation and that the route of administration (intraperitoneally or intravenously) is of minor importance. Due to its low specificity for cartilage GAGs, 3H-acetate is not suitable for such studies.

An in vitro model of ageing of human articular cartilage sulphated-proteoglycans

Six cases of non-pathological articular cartilage were studied by organ explant culture to assess alterations in tissue sulphated proteoglycans (PGs) as a function of time in culture and donor age. Neosynthesized, 35SO4-labeled and endogenous, or already existing, uronic acid-containing PG populations were studied at several time points over 3-4 weeks. PG extractability did not vary with donor age. The proportion of non-extractable endogenous, but not of neosynthesized, PGs increased with time in culture. Sepharose CL-2B chromatography of neosynthesized and endogenous PGs eluted with associate buffer (0.5 M sodium acetate, pH 5.8) revealed 4 PG subpopulations with Kavs of 0.05, 0.28, 0.68 and 0.9-1.0. With culture time, the percentage distribution of newly synthesized PG subpopulations of large hydrodynamic size increased significantly with a concomitant decrease in the relative amount of smaller PGs. Isopycnic cesium chloride density gradients were performed on pooled Sepharose CL-2B peaks under associative (0.5 M GuHCl) and dissociative (4 M GuHCl) conditions to assess component subclasses of PG aggregates and PG monomers within each PG subpopulation. An analysis of the Kav, 0.05 subpopulation indicated an enrichment in dense PG aggregate (A1) and PG monomer (D1). Both A1 and D1 decreased with in vitro age parallelled by an increase in the respective subclasses of least buoyant density, A4 and D4. Sepharose CL-2B chromatography of D1 fractions within this PG subpopulation indicated a progressive decrease in PG monomer hydrodynamic size with time in culture. In contrast to these age-in-culture related alterations in neosynthesized PGs, the endogenous PGs showed neither a significant change in distribution of PG subpopulations nor PG subclasses over the time period of study. These findings showed the ability of human articular cartilage to alter the profile of neosynthesized PG while maintaining the in situ PG population during in vitro cartilage aging. Such findings suggest that this system may be useful in the elucidation of specific changes in articular cartilage PGs associated with time in culture.