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PubMed1994

A microstructural model for the elastic response of articular cartilage.

A model of articular cartilage is developed in which the continuum stiffness tensor is related to the tissue's microstructure. The model consists of bilinear elastic fibers embedded in an elastic matrix. Homogenization techniques are used to relate this level of organization to the macroscopic response of the tissue. The model includes the effects of spatial orientation of fibers, pre-stress in the fibers and matrix resulting from matrix swelling, slipping at the interface between the fibers and the matrix, fiber buckling in compression, and deformation-induced fiber reorientation. The model predicts increased axial stiffness with increasing stretch due to fiber reorientation, reduced axial and shear stiffness with slipping between fiber and matrix and a sensitivity of the tissue response to the swelling pressure in the matrix, the matrix modulus and the bonding of the fiber matrix interface.

Algorithms↗

PubMed1983

Proteinase inhibitors of human articular cartilage.

Extracts of human articular cartilage contain a variety of inhibitors to serine, cysteine and metallo-proteinases. By gel filtration chromatography, inhibitory activity towards serine proteinases was resolved into two components of apparent molecular weights 62,000 and 12,000 daltons; whereas inhibitory activity towards cysteine proteinases eluted with an apparent molecular weight of 13,000 daltons. In both cases the low molecular weight inhibitors were further resolved into two components by ion-exchange chromatography. Inhibitory activity towards metallo-proteinases resolved into two components of apparent molecular weights 35,000 and 25,000 daltons. No inhibitor of aspartic proteinases was detected. Although most of the inhibitory activities to serine and cysteine proteinases could be extracted from cartilage with 1 M NaCl, the complete removal of metalloproteinase inhibitory activities required extraction with 4 M guanidinium chloride. This suggests that they are more strongly associated with the cartilage.

Aged↗

PubMed1998

The effects of pH and ionic strength on intrafibrillar hydration in articular cartilage.

The hydration of articular cartilage is an essential determinant of its load bearing capacity. Here we have examined the dependence of the amount of intrafibrillar water, associated with the collagen molecules in both native and PG-depleted cartilage specimens, on the pH and ionic strength of the bathing solution, in the presence and absence of an externally applied pressure. We found that high ionic strength reduces the collagen intermolecular spacing over a large pH range: this is consistent with the electrostatic nature of the interactions between the charged groups within the intrafibrillar space. We also found that as the pH is lowered from neutral to approximately 3, there is, as expected, a gradual increase in the overall positive charge of the intrafibrillar compartment. However, surprisingly, this is not accompanied by an increase in the intrafibrillar hydration; only at pH 1.8 does the amount of intrafibrillar water increase markedly. We suggest that, rather than overall intrafibrillar charge, it is specific local axial and azimuthal relationships among collagen molecules in the fibril, and more particularly, among their charged amino acid residues, that determine the intermolecular collagen spacing, and hence intrafibrillar hydration.

Adult↗

PubMed1993

Direct evidence for active metalloproteinases mediating matrix degradation in interleukin 1-stimulated human articular cartilage.

When adult human articular cartilage was maintained in organ culture in the presence of interleukin 1 beta, increased destruction of the extracellular matrix was observed, as judged by increased type II collagen degradation in situ determined immunohistochemically and the increased release of proteoglycan into the culture medium. Concomitant with these changes was the increased release of latent metalloproteinases into the culture medium. Culture of cartilage in the presence of a peptidylhydroxamate metalloproteinase inhibitor indicated a key role for the active forms of these enzymes in situ, since it produced a marked reduction in both proteoglycan release and collagen degradation. This compound had no detectable cytotoxic effects in organ culture and did not reduce the secretion of the metalloproteinases. The results of this study provide direct evidence that the latent metalloproteinase precursors, whose release is greatly stimulated by interleukin 1, are indeed activated to some degree and participate in cartilage matrix degradation.

Adolescent↗

PubMed1984

Proteoglycan association with collagen d band in hyaline articular cartilage.

Proteoglycans of canine articular cartilage were labelled for transmission electron microscopy using the cationic copper phthalocyanin dye, cupromeronic blue, in a critical electrolyte concentration method. Much of the proteoglycan appeared to be structurally unrelated to collagen but a small proportion was positioned close to fibrils. On demonstrating the characteristic collagen banding pattern with uranyl acetate and phosphotungstic acid, it was evident that proteoglycan interacted with collagen at the d band.

Animals↗

PubMed1988

Age-related changes in small proteoglycans of low buoyant density of human articular cartilage.

Proteoglycans extracted from articular cartilage of large joints of humans aged 4, 11, 70 and 75, were fractionated on associative density gradients. The top fraction (A3) was purified by ion-exchange chromatography and subsequent gel filtration on Sepharose CL 4B in 4 M GuCl, 0.5% Triton x 100. Proteoglycans from young cartilages yielded a narrow rapid migrating band on gel electrophoresis, had a Kav of 0.43 and 0.44 on Sepharose CL 4B, a glucosamine/galactosamine ratio of 0.11 and 0.12 and a glycoprotein core rich in aspartic acid and leucine with a Mr of about 47,000. Proteoglycans from old cartilages gave a wider and slower migrating band on gel electrophoresis, had a wide peak with a Kav of 0.38 and 0.40 on Sepharose CL 4B, a glucosamine/galactosamine ratio of 5.1 and 3.2, a glycoprotein core rich in glutamic acid and glycine, and with a Mr of about 170,000-180,000. Analysis using monoclonal antibodies detected epitopes of keratarn sulfate and of hyaluronic acid binding region in the fractions from old but not in those from young cartilages. Small proteoglycans not derived from the large monomers are the major component of low-buoyant-density fractions of proteoglycans from young cartilages. Fragments of large monomers containing keratan sulfate and hyaluronic acid binding region are the major component of similar fractions from old cartilage.

Aged↗

PubMed1991

Influence of polysulfated glycosaminoglycan on equine articular cartilage in explant culture.

Articular cartilage explants from 3 horses were maintained in tissue culture to test the effects of a polysulfated glycosaminoglycan on proteoglycan biosynthesis. Cultures were exposed to concentrations of 0, 50, or 200 micrograms of the drug/ml for either 2 days or 6 days, and labeled with 35S, before measuring the content of sulfated proteoglycan in the culture media and in extracts of cartilage. In a second experiment, the explants were incubated with the isotope and subsequently exposed to the same concentrations of the polysulfated glycosaminoglycan for 4 days. Subsequently, the amount of remaining labeled proteoglycan was determined. Gel filtration chromatography was used to compare the hydrodynamic size of proteoglycans from the cartilage explants in each experiment. Polysulfated glycosaminoglycan caused a dose-dependent depression of sulfated proteoglycan synthesis, which was statistically significant after 6 days of exposure. Radioactive proteoglycan content in explants was similar in the experiment involving isotopic labeling prior to exposure to the drug. Proteoglycan monomer size was similar in all treatment groups. It was concluded that polysulfated glycosaminoglycan caused a modest depression in proteoglycan synthesis, had little effect on endogenous proteoglycan degradation, and did not influence the size of sulfated proteoglycans synthesized by normal equine chondrocytes in explant culture.

Animals↗

PubMed1991

Mechanisms of proteoglycan degradation in human articular cartilage.

Aging of human articular cartilage is associated with proteolytic degradation of its constituent proteoglycan aggregates. Similar events are thought to be associated with proteoglycan loss in osteoarthritis. Degradative changes in link protein have been characterized and can be used as an indicator of the causative proteolytic agents. In the neonate, proteolysis results in cleavage of the N-terminal 16 amino acids, at a site characteristic for the metalloproteinase stromelysin. In the adult, further cleavage occurs in the N-terminal region and the adjacent disulfide bonded loop, indicating the action of additional proteolytic agents. In osteoarthritis, link protein cleavage occurs at sites identical to those observed in the normal adult.

Aging↗

PubMed1985

The role of link protein in mediating the interaction between hyaluronic acid and newly secreted proteoglycan subunits from adult human articular cartilage.

Normal adult human articular cartilage in organ culture secretes proteoglycan subunits that cannot initially interact in a normal manner with hyaluronic acid unless the latter is present at high concentrations and a neutral pH is employed. However, if the newly secreted subunit is allowed to mature in the cartilage matrix for up to 12 h, then its ability to interact is indistinguishable from that of its more mature counterparts. This conversion does not take place if the proteoglycan subunits are incubated in dilute solutions in the absence of the cartilage, and it is prevented by culturing at low temperature. The newly secreted proteoglycan subunits can, however, be induced to interact with hyaluronic acid by the presence of link proteins. The complex formed by these three components cannot be dissociated in the presence of hyaluronic acid oligosaccharides, suggesting a normal aggregate configuration. It is thus possible that proteoglycan aggregate formation within the cartilage is initially mediated by the presence of link proteins, which induce a conformational change with the hyaluronic acid-binding region of the proteoglycan subunits, although additional modification may be necessary to render any such change irreversible.

Adult↗

PubMed1996

Purification and characterisation of 6 and 58 kDa forms of the endogenous serine proteinase inhibitory proteins of ovine articular cartilage.

The major ovine articular cartilage (AC) serine proteinase inhibitory protein (SPI), a 58 kDa glycoprotein (SPI-58), was purified to homogeneity by sequential Sephacryl S-300 gel permeation, concanavalin A affinity, Mono Q anion exchange and Superose 12 FPLC. If precautions to prevent degradation of the native 58 kDa SPI were not undertaken during the early stages of its purification a SPI of approximately 6 kDa (SPI-6) was generated. SPI-6 could also be generated from SPI-58 by chymotrypsin affinity chromatography, suggesting that SPI-6 could be produced from SPI-58 in vivo by proteolytic processing within the tissue. SPI-6 was indistinguishable from the Kunitz inhibitor, bovine pancreatic trypsin inhibitor (BPTI) by SDS-PAGE under both reducing and non reducing conditions and showed a strong homology to BPTI in N-terminal sequence. These data suggest that the BPTI-like 6 kDa SPI constituted the inhibitory domain of the native 58 kDa SPI of ovine AC. Detection of [14C]-lysine-SPI-6 and SPI-58 in the serum free culture medium from ovine chondrocytes cultured in alginate beads in the presence of [14C]-lysine indicated that these SPIs were chondrocyte biosynthetic products. The inhibitory profiles of SPI-58 and SPI-6 differed somewhat suggesting that each may have an independent role in vivo.

Animals↗

PubMed2002

Ultrasound detection of trypsin-treated articular cartilage: its association with cartilaginous proteoglycans assessed by histological and biochemical methods.

We studied the correlation between histological imaging quantification and the biochemical assessment of proteoglycan (PG) content in articular cartilage in vitro, which served as a basis for the validation of ultrasound detection as a noninvasive tool in the assessment of PG changes in full-thickness articular cartilage. Articular cartilage of 14 intact fresh bovine femoral condyles was used for trypsin digestion. Full-thickness articular cartilage cylinders, 3 mm in diameter, were harvested at time intervals of 0.5, 1, 2, and 3 h after trypsin digestion. Each cartilage cylinder was then cut into two equal parts for either histomorphometric quantification of the PG area fraction stained with Safranine O or conventional biochemical assessment of uronic acid content. In addition, five fresh mature bovine patellae were used for the validation of an ultrasound compression system developed for testing the potential layered biomechanical properties of articular cartilage, including the equilibrium compressive modulus, i.e., the slope of the linear regression of the equilibrium stress-strain curve. Results showed that PG content in the articular cartilage was significantly decreased with increasing time of trypsin digestion, both histologically and biochemically, with a significant correlation of r = 0.502 ( P < 0.001). Ultrasound measurements demonstrated differences in the equilibrium compressive moduli of the digested zone, the undigested zone, and the entire articular cartilage layer, as well as a characteristically large ultrasound reflection signal detected in the interface of the trypsin digestion front of articular cartilage. The results of this study suggested that the histomorphometric quantification of PG content could be used to reflect not only PG quantity but also its spatial distribution; also, the ultrasound compression system might have potential for the non-invasive detection of pathological changes in articular cartilage.

Animals↗

PubMed2004

Delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) and T2 characteristics of human knee articular cartilage: topographical variation and relationships to mechanical properties.

The macromolecular structure and mechanical properties of articular cartilage are interrelated and known to vary topographically in the human knee joint. To investigate the potential of delayed gadolinium-enhanced MRI of cartilage (dGEMRIC), T1, and T2 mapping to elucidate these differences, full-thickness cartilage disks were prepared from six anatomical locations in nonarthritic human knee joints (N = 13). Young's modulus and the dynamic modulus at 1 Hz were determined with the use of unconfined compression tests, followed by quantitative MRI measurements at 9.4 Tesla. Mechanical tests revealed reproducible, statistically significant differences in moduli between the patella and the medial/lateral femoral condyles. Typically, femoral cartilage showed higher Young's (>1.0 MPa) and dynamic (>8 MPa) moduli than tibial or patellar cartilage (Young's modulus < 0.9 MPa, dynamic modulus < 8 MPa). dGEMRIC moderately reproduced the topographical variation in moduli. Additionally, T1, T2, and dGEMRIC revealed topographical differences that were not registered mechanically. The different MRI and mechanical parameters showed poor to excellent linear correlations, up to r = 0.87, at individual test sites. After all specimens were pooled, dGEMRIC was the best predictor of compressive stiffness (r = 0.57, N = 77). The results suggest that quantitative MRI can indirectly provide information on the mechanical properties of human knee articular cartilage, as well as the site-dependent variations of these properties. Investigators should consider the topographical variation in MRI parameters when conducting quantitative MRI of cartilage in vivo.

Adult↗

PubMed2006

Protein profile of osteoarthritic human articular cartilage using tandem mass spectrometry.

Articular cartilage contains both chondrocyte cells and extracellular matrix (ECM) components. Currently, comprehensive information concerning the protein composition of human articular cartilage tissue is somewhat lacking. In this report we detail the use of tandem mass spectrometry (MS/MS) for a preliminary global identification of proteins from human articular knee cartilage tissue from patients diagnosed with osteoarthritis. Knee cartilage supernatant was fractionated using one-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis (1D-SDS-PAGE), in-gel digested and peptide sequences were then determined by performing on-line nano-liquid chromatography (LC)/MS/MS experiments using an ion trap mass spectrometer. Altogether, over 100 different proteins from nearly 700 unique peptide sequences were detected by MS/MS. The majority of the proteins identified are involved in ECM organization (35%), signal transduction and cell communication (14%), immune response (11%) and metabolism and energy pathways (11%). Proteins observed included several well-known cartilage components as well as lower abundant lesser known ECM proteins. Possible degradation products in the cartilage sample, such as from cartilage link protein, could also be detected by our mass spectrometry methods. We show here that mass spectrometry can be utilized as a tool for a fast, accurate and sensitive analysis of a complex mixture of cartilage proteins. It is believed that this type of proteomic analysis will aid future work centered on investigating the pathology of this and other related joint diseases.

Adult↗

PubMed1983

Movement of interstitial water through loaded articular cartilage.

Water transport through articular cartilage and across the articular surface is a major factor controlling the amount and rate of tissue deformation. To study water movement concentration profiles within the tissue were determined using radiotracer techniques. Water movement was spatially and temporally mapped for unloaded, undeformed tissue, after cyclic and dead weight creep, and for recovery following dead weight creep using a uniaxial confined compression configuration to produce one-dimensional fluid movement. In unloaded tissue diffusion rapidly exchanged water by 15 minutes while the gross efflux of fluid during cyclic and dead weight creep compression effectively inhibited any external water influx. During recovery fluid inhibition was restricted when a small surface load was present, and only after complete removal of all surface traction was a large fluid efflux found. The compression and/or collapse of the uppermost surface layer of the tissue is believed responsible for controlling tissue fluid transport and mechanical response.

Animals↗

PubMed2002

Specific enzymatic treatment of bovine and human articular cartilage: implications for integrative cartilage repair.

OBJECTIVE: Chondrocyte death in articular cartilage wound edges and the subsequent lack of matrix-producing cells in the interface area are considered to be a major cause of impaired cartilage wound healing and poor integrative cartilage repair. This study was undertaken to investigate whether enzymatic matrix digestion can be used to stimulate integrative cartilage repair via a mechanism of local increase in the amount of vital chondrocytes in cartilage wound edges. METHODS: Full-thickness bovine articular cartilage samples were cultured in vitro for 14 days in standard medium. Samples were either left untreated or treated for 48 hours with 0.3% hyaluronidase or 30 units/ml highly purified collagenase VII. Nuclear and cytoplasmic changes were analyzed to determine cell viability, and the number of vital chondrocytes in wound edges was determined. Subsequently, we investigated whether increased chondrocyte density in the lesion edges resulted in better wound healing. Finally, full-thickness human tibial plateau cartilage explants were tested with similar enzyme treatment protocols to determine the clinical value of our results. RESULTS: In bovine explants a rapid onset of chondrocyte death was observed in wound edges in all treatment groups. This led to low chondrocyte density in a band of 0-150 microm from the lesion edges in untreated and hyaluronidase-treated explants. Treatment with 30 units/ml collagenase resulted in a significant increase in chondrocyte density in this area. The integration experiments demonstrated improved integration of the lesion edges after treatment with collagenase. In human articular cartilage an increase in chondrocyte density at the lesion edges could also be achieved, but only when proteoglycans were depleted from the wound edges prior to collagenase treatment. CONCLUSION: Treatment with highly purified collagenase improves integrative cartilage repair, possibly by increasing the cell density at cartilage wound edges.

Adult↗

PubMed1983

Investigational approaches to articular cartilage preservation.

A brief review of articular cartilage preservation identifies several directions and concerns for modern investigators. First, storage of intact cartilage in such solutions as alcohol, merthiolate, plasma, and saline may not be as good as storage in air. Second, viable cartilage appears to fare better than nonviable cartilage after transplantation. Third, freezing of isolated cartilage cells appears to be a satisfactory method for preserving viability, but the same may not be true for cartilage tissue slices, slivers, or explants. Fourth, tissue culture of slices seems to provide excellent preservation of cells in their matrix. Fifth, freezing of intact cartilage presents problems of water diffusion, as well as penetration of cryopreservative. Extremely slow freezing may provide an answer to these problems. Sixth, transplantation of isolated chondrocytes into cartilage defects does not seem to provide regeneration of articular cartilage, but transplantation of slices or larger pieces may restore a more normal appearance to the joint surface. Further investigation is obviously necessary and should continue to provide information and knowledge toward the goal of successful preservation of functional articular cartilage.

Animals↗

PubMed1986

Metabolism of a cartilage matrix glycoprotein in normal and osteoarthritic canine articular cartilage.

We have recently described a 550,000-dalton noncollagenous cartilage matrix glycoprotein (CMGP), with subunits of 130,000, which is present in hyaline cartilage and fibrocartilage. Biosynthetic studies indicated that CMGP was synthesized by short-term organ cultures of normal canine articular cartilage, representing approximately 9% of the total 3H-leucine incorporated into protein in 24-hour cultures. There was no incorporation of 35S-sulfate or 3H-mannose into CMGP under these conditions, but the protein did incorporate 32P-phosphate. The majority of the 3H-leucine-labeled CMGP was removed after 24 hours of chase with unlabeled leucine, and only a small amount remained at 72 hours, which suggests that there was rapid metabolism of the protein. CMGP was not detected in cartilage after addition of cycloheximide to the culture medium; this confirms its short half-life. Cultures of osteoarthritic cartilage obtained from dogs 8-10 weeks after anterior cruciate ligament transection revealed no difference in the metabolism of CMGP in this tissue compared with that found in cultures of normal articular cartilage.

Animals↗

PubMedDate not supplied

Articular cartilage repair by means of biodegradable scaffolds.

INTRODUCTION: Articular cartilage has a limited capacity for self-repair; untreated injuries of cartilage may lead to osteoarthritis. In severe cases the only choice a total joint replacement, may be inadequate in young patients. This problem demands new effective methods to reconstruct articular cartilage. The aim of this study was to evaluate the application of collagen matrix for the reconstruction of articular cartilage. MATERIALS AND METHODS: A group of 28 rabbits had a defect penetrating into the subchondral constructed and either filled with collagen scaffold (group I) or remained empty (group II). The results were observed after 4 and 12 weeks. Macroscopic and microscopic evaluations were performed. RESULTS: In the first group we observed the presence of hyalinelike cartilage resembling normal articular cartilage. In the second group fibrous tissue dominated. The surface of regenerated tissue was smooth, intact, and the defect completely filled with regenerated tissue, showing good structural integrity. In the second group, superficial irregularities, disorders of structural integrity, and necrotic features were noticed. CONCLUSIONS: This study showed better results of articular cartilage reconstruction by means of a biodegradable scaffold.

Animals↗