Comparison of proteoglycans from bovine articular cartilage

Characterization of ex vivo-generated bovine and human cartilage by immunohistochemical, biochemical, and magnetic resonance imaging analyses

Osteoarthritis (OA) is a prevalent age-associated disease involving altered chondrocyte homeostasis and cartilage degeneration. The avascular nature of cartilage and the altered chondrocyte phenotype characteristic of OA severely limit the capacity for in vivo tissue regeneration. Cell- and tissue-based repair has the potential to revolutionize treatment of OA, but those approaches have exhibited limited clinical success to date. In this study, we test the hypothesis that bovine and human chondrocytes in a collagen type I scaffold will form hyaline cartilage ex vivo with immunohistochemical, biochemical, and magnetic resonance (MR) endpoints similar to the original native cartilage. Chondrocytes were isolated from 1- to 3-week-old calf knee cartilage or from cartilage obtained from human total knee arthroplasties, suspended in 2.7 mg/mL collagen I, and plated as 300 microL spot cultures with 5 x 10(6) each. Medium formulations were varied, including the amount of serum, the presence or absence of ascorbate, and treatments with cytokines. Bovine chondrocytes generated metachromatic territorial and interstitial matrix and accumulated type II collagen over time. Type VI collagen was confined primarily to the pericellular region. The ex vivo-formed bovine cartilage contained more chondroitin sulfate per dry weight than native cartilage. Human chondrocytes remained viable and generated metachromatic territorial matrix, but were unable to support interstitial matrix accumulation. MR analysis of ex vivo-formed bovine cartilage revealed evidence of progressively maturing matrix, but MR-derived indices of tissue quality did not reach those of native cartilage. We conclude that the collagen-spot culture model supports formation and maturation of three-dimensional hyaline cartilage from active bovine chondrocytes. Future studies will focus on determining the capacity of human chondrocytes to show comparable tissue formation.

Tensile mechanical properties of bovine articular cartilage: variations with growth and relationships to collagen network components

One approach to repairing articular defects is to regenerate cartilage by recapitulating the changes that occur during fetal and postnatal growth into adulthood, and to thereby restore functional biomechanical properties, especially those of the normally strong superficial region. The objectives of this study were (1) to characterize and compare tensile biomechanical properties of the superficial region of articular cartilage of the patellofemoral groove (PFG) and femoral condyle (FC) from bovine animals over a range of growth stages (third-trimester fetal, 1-3 week-old calf, and adult), and (2) to determine if these properties were correlated with collagen network components. With growth from the fetus to the adult, the equilibrium and dynamic tensile moduli and strength of cartilage samples increased by an average of 391-1060%, while the strain at the failure decreased by 43%. The collagen concentration (per wet weight) increased by 98%, and the pyridinoline cross-link concentration increased by 730%, while the glycosaminoglycan concentration remained unchanged or decreased slightly. Some growth-associated changes were location-specific, with tensile moduli and strength attaining higher values in the PFG than the FC. The growth-associated variation in tensile moduli and strength were associated strongly with variation in the contents of collagen and pyridinoline cross-link, but not sulfated glycosaminoglycan. The marked changes in the tensile properties and collagen network components of articular cartilage with growth suggest that such parameters may be used to evaluate the degrees to which regenerated cartilage recapitulates normal development and 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.

Compressive properties and function-composition relationships of developing bovine articular cartilage

The composition of cartilage is known to change during fetal and postnatal development. The objectives of this study were to characterize the compressive biomechanical properties of the 1 mm thick articular layer of cartilage of the distal femur from third-trimester bovine fetuses, from 1 to 3 week old bovine calf and from young adult bovine knees, and to correlate these properties with tissue components. The confined compression modulus increased 180% from the fetus to the calf and adult. The hydraulic permeability at 45% offset compression (relative to the free-swelling thickness) decreased by 70% from fetus to adult. These development-associated changes in biomechanical properties were primarily associated with a marked (approximately 2-3-fold) increase during development in collagen content and no detectable change in glycosaminoglycan (GAG) content. A role for collagen in the compressive properties of cartilage and the gradual increase in collagen during development suggest that collagen metabolism is critical for cartilage tissue engineering and repair therapies.

Extracellular matrix composition of different regions of the knee joint cartilage in cattle

Articular cartilage covering the bone ends at the joint shows different chemical composition in different regions, depending on the mechanical and biological properties of that region. Several studies have shown a relationship between the chemical composition of the cartilage and biomechanical forces. In the present study we analysed five different knee joints divided into the following regions: F1-medial and lateral border of the patellar surface, F2-patellar surface of the femur, F3-medial and lateral condyles, P-articular surface of the patella and T-medial and lateral condyle of the tibia. The main glycosaminoglycan (GAG) present in these regions was chondroitin sulfate. Analysis of total GAG after digestion of the tissue with papain showed that in F2 and F3 there was a larger quantity of GAG/mg tissue, probably due to the dynamic character of the biomechanical forces in these regions. No significant differences were found for the extract and D1 fractions of the different regions. Analysis of the D4 fraction showed that the protein content was higher in the F3 and P regions than in their opposite T and F2 regions. The differences among the five regions may be a result of the non-uniform presence of biomechanical forces supported by these regions. It is important to consider that the intensity and direction of stress in different parts of a tissue may influence the composition of the extracellular matrix.

Cartilage response to mechanical force in high-density chondrocyte cultures

High-density cultures of chick embryonic chondrocytes were exposed to intermittent compressive force (ICF) of physiologic magnitude for 24 hours. Proteoglycan synthesis was significantly increased in chondrocyte cultures exposed to ICF as compared with control cultures. Similar effects were found in explants of epiphyseal cartilage. Proteoglycans extracted with guanidine-HCl from cultures exposed to ICF aggregated better with hyaluronic acid than did control cultures, as shown by Sepharose 2B gel chromatography. In addition, the amount of non-extractable proteoglycans was increased in ICF cultures. We conclude that ICF not only increases the synthesis of proteoglycans but also improves the aggregating capacity of proteoglycans and the coherence of proteoglycans with other matrix components. High-density cultures of epiphyseal chondrocytes provide a suitable model to study the processes involved in the perception of and the subsequent cellular response to compressive force by cartilage.

Factors influencing articular cartilage wear in vitro

The in vitro wear of articular cartilage in oscillating and impulsively loaded bovine metatarsophalangeal joints was studied. Articular cartilage scarification had little effect on cartilage wear, but stiffening of the subchondral bone with methyl methacrylate greatly increased the rate of cartilage loss, whether or not it had previously been scarified. Glutaraldehyde treatment of articular cartilage for 30 minutes decreased is wear rate. Guanidinium chloride extraction of the cartilage before wear testing caused it to peel off its subchondral bed. This effect could be spared by prior glutaraldehyde fixation.

Degradative enzymes of cartilage. Effects of freeze-thawing of the tissue prior to extraction, and of protease inhibitors, on proteoglycans extracted with iso-osmotic neutral salt and 4 M guanidinium chloride

The effects of freeze-thawing of the tissue, and of protease inhibitors, on proteoglycans extracted sequentially from pig laryngeal cartilage with 0.15 M sodium acetate and 4 M guanidinium chloride were examined. Freeze-thawing of the tissue prior to extraction resulted in an increase in the proportion of smaller-sized proteoglycans in the sodium acetate extracts and a decrease in the proportion of aggregated proteoglycans in 4 M guanidinium extracts. In addition, a slight decrease in the hydrodynamic size of purified disaggregated proteoglycans was noted after freeze-thawing of the cartilage. When the protease inhibitors EDTA, 6-aminohexanoic acid and benzamidine hydrochloride were added to the sodium acetate buffer the yields of proteoglycans from fresh and freeze-thawed cartilage were diminished, but the inhibitors had no effect on the hydrodynamic size of the proteoglycans extracted with sodium acetate. Addition of the protease inhibitors to the 4 M guanidinium solvent increased the proportion of proteoglycans present in aggregates. The highest proportion of aggregated proteoglycans was obtained when fresh tissue was extracted in the presence of the inhibitors.

Failure of proteoglycans to form aggregates in morphologically normal aged human hip cartilage

The macromolecular organization of proteoglycans in morphologically and histochemically normal hip cartilage from aged humans has been studied. In contrast to findings in articular and nonarticular cartilage from other sources, most of the proteoglycans in these tissues did not exist in large aggregates. Treatment with hyaluronic acid beta1 leads to 3 hydrolase failed to diminish the size of proteoglycans prepared under conditions favoring aggregation, a finding suggesting that they were not complexed with hyaluronic acid. Polyacrylamide gel electrophoresis failed to demonstrate the presence of link glycoproteins associated with the proteoglycans. After incubation in vitro with hyaluronic acid, minimal augmentation of hydrodynamic size of the preparation occurred, an indication that hyaluronate-proteoglycan interaction had not taken place. These results suggest that proteoglycan aggregation was diminished because of a defect in the core protein of the proteoglycans resulting in an impaired ability of these molecules to interact with hyaluronic acid.

Heterogeneity of proteoglycans in developing chick limb cartilage

Proteoglycan heterogeneity was studied during the maturation of embryonic-chick limb cartilage in vivo. The results suggest that during the differentiation of limb-bud cartilage the aggregated forms of proteoglycans increase between stages 24 and 35, whereas the non-aggregated or monomeric forms decrease. Only one link protein is found in stage-24 limb buds, whereas two are present at stage 35. Evidence suggests that the synthesis of link proteins may be a regulatory factor in limb chondrogenesis.