Inhibition of cartilage degradation and changes in physical properties induced by IL-1beta and retinoic acid using matrix metalloproteinase inhibitors

In vitro models for investigation of the effects of acute mechanical injury on cartilage

Traumatic injury to a joint is known to increase the risk for the development of secondary osteoarthritis, but it is unclear how this process occurs. The existence of such a discrete event that can lead to an increased risk of osteoarthritis has spurred interest in developing in vitro models of traumatic joint injury. The current authors review some of the recent insights gained from these model systems into the pathogenesis of osteoarthritis, including the evidence for an initial, irreversible insult to chondrocytes during mechanical injury, the occurrence of apoptotic chondrocyte death, and attempts to identify the effects of trauma on chondrocyte metabolic response. Results also are presented from the authors' ongoing studies of the degradative pathways initiated by traumatic mechanical loads, the mechanism by which chondrocytes are affected during compression, and possible contributions of the joint capsule to posttraumatic cartilage degradation.

Use of an antineoepitope antibody for identification of type-II collagen degradation in equine articular cartilage

OBJECTIVE

To develop an antibody that specifically recognizes collagenase-cleaved type-II collagen in equine articular cartilage.

SAMPLE POPULATION

Cartilage specimens from horses euthanatized for problems unrelated to the musculoskeletal system.

PROCEDURE

A peptide was synthesized representing the carboxy- (C-) terminus (neoepitope) of the equine type-II collagen fragment created by mammalian collagenases. This peptide was used to produce a polyclonal antibody, characterized by western analysis for reactivity to native and collagenase-cleaved equine collagens. The antibody was evaluated as an antineoepitope antibody by ELISA, using peptides +/- an amino acid at the C-terminus of the immunizing peptide. Collagen cleavage was assayed from equine articular cartilage cultured with interleukin-1 (IL-1), +/- a synthetic MMP inhibitor, BAY 12-9566. Cartilage specimens from osteoarthritic and nonarthritic joints were compared for antibody staining.

RESULTS

An antibody, 234CEQ, recognized only collagenase-generated 3/4-length fragments of equine type-II collagen. This was a true antineoepitope antibody, as altering the C-terminus of the immunizing peptide significantly decreased competition for binding in an inhibition ELISA. The IL-1-induced release of type-II collagen fragments from articular cartilage was prevented with the MMP inhibitor. Cartilage from an osteoarthritic joint of a horse had increased staining with the 234CEQ antibody, compared with normal articular cartilage.

CONCLUSIONS AND CLINICAL RELEVANCE

We generated an antineoepitope antibody recognizing collagenase-cleaved type-II collagen of horses. This antibody detects increases in type-II collagen cleavage in diseased equine articular cartilage. The 234CEQ antibody has the potential to aid in the early diagnosis of arthritis and to monitor treatment responses.

Host metalloproteinases in Lyme arthritis

OBJECTIVE

To assess the role of matrix metalloproteinases (MMPs) in cartilage and bone erosions in Lyme arthritis

METHODS

We examined synovial fluid from 10 patients with Lyme arthritis for the presence of MMP-2, MMP-3, MMP-9, and "aggrecanase" activity using gelatinolytic zymography and immunoblot analysis. We developed an in vitro model of Lyme arthritis using cartilage explants and observed changes in cartilage degradation in the presence of Borrelia burgdorferi and/or various protease inhibitors.

RESULTS

Synovial fluid from patients with Lyme arthritis was found to contain at least 3 MMPs: gelatinase A (MMP-2), stromelysin (MMP-3), and gelatinase B (MMP-9). In addition, there was evidence in 2 patients of "aggrecanase" activity not accounted for by the above enzymes. Infection of cartilage explants with B. burgdorferi resulted in induction of MMP-3, MMP-9, and "aggrecanase" activity. Increased induction of these enzymes by B. burgdorferi alone was not sufficient to cause cartilage destruction in the explants as measured by glycosaminoglycan (GAG) and hydroxyproline release. However, addition of plasminogen, which can act as an MMP activator, to cultures resulted in significant GAG and hydroxyproline release in the presence of B. burgdorferi. The MMP inhibitor batimastat significantly reduced the GAG release and completely inhibited the collagen degradation.

CONCLUSION

MMPs are found in synovial fluids from patients with Lyme arthritis and are induced from cartilage tissue by the presence of B. burgdorferi. Inhibition of MMP activity prevents B. burgdorferi-induced cartilage degradation in vitro.

Calcium pentosan polysulfate inhibits the catabolism of aggrecan in articular cartilage explant cultures

OBJECTIVE

The catabolism of aggrecan and loss of aggrecan fragments from articular cartilage is a key event in the pathogenesis of arthritic diseases such as osteoarthritis. The catabolism of aggrecan is mediated by the specific proteolytic activity termed aggrecanase. The aim of this study was to investigate the effect of the chondroprotective agent calcium pentosan polysulfate (CaPPS) on the aggrecanase-mediated catabolism of aggrecan.

METHODS

The catabolism of 35S-labeled aggrecan and loss of tissue glycosaminoglycans (GAGs) were investigated using bovine articular cartilage explant cultures maintained in medium containing varying concentrations of CaPPS (1-100 microg/ml) in the presence or absence of 10(-6)M retinoic acid or 7 ng/ml recombinant human interleukin-1alpha (rHuIL-1alpha). In addition, the effect of CaPPS on the degradation of aggrecan monomers by aggrecanase activity present in conditioned medium from joint capsule explant cultures was investigated.

RESULTS

CaPPS inhibited the catabolism of 35S-labeled aggrecan in a dose-dependent manner, particularly when retinoic acid or rHuIL-1alpha was used to stimulate aggrecan catabolism. These effects were reflected in the tissue levels of GAG remaining in these cultures at the end of the experiment. CaPPS inhibited the degradation of aggrecan monomers by soluble aggrecanase activity.

CONCLUSION

CaPPS inhibits the catabolism of aggrecan by articular cartilage in a dose-dependent manner, particularly when the processes responsible for aggrecan loss are stimulated. This effect occurs, at least in part, through direct inhibition of aggrecanase activity. CaPPS did not adversely affect overall chondrocyte metabolism, as shown by the incorporation of 35S-sulfate and 3H-leucine into macromolecules and by lactate production in cartilage explant cultures.

Matrix metalloproteinases 19 and 20 cleave aggrecan and cartilage oligomeric matrix protein (COMP)

Matrix metalloproteinase (MMP)-19 and MMP-20 (enamelysin) are two recently discovered members of the MMP family. These enzymes are involved in the degradation of the various components of the extracellular matrix (ECM) during development, haemostasis and pathological conditions. Whereas MMP-19 mRNA is found widely expressed in body tissues, including the synovium of normal and rheumatoid arthritic patients, MMP-20 expression is restricted to the enamel organ. In this study we investigated the ability of MMP-19 and MMP-20 to cleave two of the macromolecules characterising the cartilage ECM, namely aggrecan and the cartilage oligomeric matrix protein (COMP). Both MMPs hydrolysed aggrecan efficiently at the well-described MMP cleavage site between residues Asn(341) and Phe(342), as shown by Western blotting using neo-epitope antibodies. Furthermore, the two enzymes cleaved COMP in a distinctive manner, generating a major proteolytic product of 60 kDa. Our results suggest that MMP-19 may participate in the degradation of aggrecan and COMP in arthritic disease, whereas MMP-20, due to its unique expression pattern, may primarily be involved in the turnover of these molecules during tooth development.

Expression of hyaluronan synthases in articular cartilage

OBJECTIVE

To investigate the mRNA expression profiles of three mammalian hyaluronan synthases (HAS1, HAS2 and HAS3) in chondrocytes from normal (undiseased) animal cartilage and osteoarthritic human cartilage maintained in experimental culture systems and exposed to catabolic or anabolic stimuli provided by cytokines, growth factors and retinoic acid.

DESIGN

Chondrocytes isolated from normal bovine, porcine or from osteoarthritic human cartilage were cultured as monolayers or embedded in agarose. Cultures were maintained for 3-5 days in the presence or absence of catabolic stimuli (IL-1, TNF-alpha or retinoic acid) or anabolic stimuli (TGF-beta or IGF-1) followed by extraction of RNA and analysis of HAS mRNA expression by RT-PCR.

RESULTS

Whereas mRNA for HAS1 was not detected in any sample, the mRNAs for HAS2 and HAS3 were expressed in human, bovine and porcine chondrocytes. HAS2 mRNA was present in chondrocytes from all cartilages and under all culture conditions, whereas HAS3 did not show such constitutive expression. In agarose cultures of bovine and porcine chondrocytes HAS2 mRNA was present in control, IL-1 and retinoic acid treated cultures, whereas HAS3 mRNA was only detected in IL-1 stimulated cultures. Mature bovine chondrocytes cultured in monolayers expressed mRNAs for both HAS2 and HAS3 in the presence of IL-1, TNF-alpha, TGF-beta and IGF-1, however immature bovine chondrocytes in monolayer cultures displayed virtually no HAS3 mRNA expression in the presence of these cytokines and growth factors. HAS2 and HAS3 mRNAs were also expressed by bovine chondrocytes isolated from either the superficial or deep zone of articular cartilage, and by human chondrocytes cultured either in the absence or presence of IL-1 and retinoic acid.

CONCLUSIONS

Our data indicate that HAS2 and HAS3 (but not HAS1) mRNAs are expressed in several mammalian cartilages. Chondrocyte HAS2 mRNA appears to be constitutively expressed while chondrocyte HAS3 mRNA expression can be differentially regulated in an age-dependent fashion, and may be affected by local and/or systemic catabolic or anabolic stimuli provided by cytokines or growth factors.

Nitric oxide inhibits aggrecan degradation in explant cultures of equine articular cartilage

Arthroses are debilitating diseases of articular joints which result in erosion of the cartilage extracellular matrix. Nitric oxide (NO) is a major component of the inflammatory response, and has been implicated as a mediator of some of the effects of the proinflammatory cytokine, interleukin-1 (IL-1). In this study, we investigated the role of NO in the regulation of proteoglycan degradation in equine articular cartilage. NO fully mediated the suppressive effect of IL-1 on proteoglycan synthesis. However, NO was also antagonistic to proteoglycan degradation, irrespective of whether degradation was initiated by 10 ng/ml IL-1 or 1 micromol/l all-trans retinoic acid (RA) which (unlike IL-1) does not elevate NO production. This was confirmed using the NO donor 2,2'-(hydroxynitrosohydrazono) bis-ethanamine (DETA-NONOate) and the iNOS inhibitor L-N5-iminoethyl ornithine (dihydrochloride) (L-NIO). The G1 fragments of aggrecan were detected in the media and extracts of cartilage explant cultures treated with all-trans RA, DETA-NONOate and L-NIO. The presence of exogenous NO in culture resulted in a decrease in the appearance of the 'aggrecanase' cleavage epitope. Therefore, changes in the appearance of the G1 fragment expressing the 'aggrecanase' cleavage epitope in the media emulated the glycosaminoglycan loss from the tissue. These results lend further support to the hypothesis that NO has an anticatabolic role in equine cartilage proteoglycan degradation, and suggest that this may be mediated by the regulation of 'aggrecanase' activity. Therefore, any pharmacological intervention using NO as a target must take into account both its catabolic and anticatabolic roles in joint tissue turnover.

Differential effects of interleukin-1 on hyaluronan and proteoglycan metabolism in two compartments of the matrix formed by articular chondrocytes maintained in alginate

Phenotypically stable young adult bovine articular chondrocytes suspended in beads of alginate gel were first cultured for 5 days, using daily changes of medium containing 10% fetal bovine serum and supplements. The cells in the beads were then maintained in culture for a further 3 days in the presence or absence of interleukin-1alpha at 1 ng/ml in the daily change of medium. The exposure to interleukin-1alpha caused the incorporation of (35)S-sulfate into the predominant cartilage proteoglycan, aggrecan, to decrease by approximately 60%. In addition, proteoglycans that had accumulated into the cell-associated matrix during the first 5 days of culture in the absence of interleukin-1alpha moved into the matrix further removed from the cells and from there into the medium. In contrast, the exposure to interleukin-1alpha was found to markedly promote the rate of synthesis of hyaluronan, especially during the first 24 h. Over the 3 days of culture in the presence of interleukin-1alpha, a large proportion of the newly synthesized hyaluronan molecules, as well as those that had previously become residents of the cell-associated matrix, moved out of this compartment and appeared to become permanent residents of the further removed matrix. These results demonstrate that exposure of young adult articular chondrocytes to interleukin-1alpha has profound effects on the metabolism of hyaluronan, a molecule that plays a critical role in the retention of proteoglycan molecules in the matrix. Importantly, the results suggest that exposure of chondrocytes to interleukin-1 in inflamed joints, such as occurs in rheumatoid arthritis, leads to the rapid loss of coordination of the synthesis of aggrecan and hyaluronan, two of the critical constituents of the proteoglycan aggregate. In addition, we present evidence that these interleukin-1-induced effects differentially alter the metabolism of hyaluronan in the metabolically active cell-associated matrix and the metabolically inactive matrix further removed from the chondrocytes.

Mannosamine inhibits aggrecanase-mediated changes in the physical properties and biochemical composition of articular cartilage

The enzymatic processes underlying the degradation of aggrecan in cartilage and the corresponding changes in the biomechanical properties of the tissue are an important part of the pathophysiology of osteoarthritis. Recent studies have demonstrated that the hexosamines glucosamine (GlcN) and mannosamine (ManN) can inhibit aggrecanase-mediated cleavage of aggrecan in IL-1-treated cartilage cultures. The term aggrecanase describes two or more members of the ADAMTS family of metalloproteinases whose glutamyl endopeptidase activity is known to be responsible for much of the aggrecan degradation seen in human arthritides. In this study we examined the effect of ManN and GlcN on aggrecanase-mediated degradation of aggrecan induced by IL-1alpha and the corresponding tissue mechanical properties in newborn bovine articular cartilage. After 6 days of culture in 10 ng/ml IL-1 plus ManN, mechanical testing of explants in confined compression demonstrated that ManN inhibited the IL-1alpha-induced degradation in tissue equilibrium modulus, dynamic stiffness, streaming potential, and hydraulic permeability, in a dose-dependent fashion, with peak inhibition ( approximately 75-100% inhibition) reached by a concentration of 1.35 mM. Aggrecan from explants cultured in IL-1 was found by Western analysis to be almost entirely processed down to the G1-NITEGE(373) end product. Addition of ManN or GlcN was found to produce 75-90% inhibition of this cleavage, but the proportion of aggrecan remaining in the tissue which was cleaved at aggrecanase sites in the chondroitin sulfate (CS)-rich region (Glu(1501) and Glu(1687)) was higher than with IL-1 alone. This result suggests that the preservation of mechanical properties by hexosamines in explants is primarily due to inhibition of cleavage at the Glu(373) site in the interglobular domain. While the precise mechanism by which hexosamines function in this system is unclear, the present analysis suggests that the mechanical properties examined may be predominantly a function of electrostatic repulsion due to the charged CS chains in the tightly packed repetitive sequences of the CS-1 region.

Chondrocyte-mediated catabolism of aggrecan: evidence for a glycosylphosphatidylinositol-linked protein in the aggrecanase response to interleukin-1 or retinoic acid

The control of chondrocyte-mediated degradation of aggrecan has been studied in rat chondrosarcoma cells and bovine cartilage explants treated with either IL-1 or retinoic acid. The capacity of glucosamine to inhibit the aggrecanase-mediated response (J. D. Sandy, D. Gamett, V. Thompson, and C. Verscharen (1998) Biochem. J. 335, 59-66) has been extended to an investigation of the effect of other hexosamines. Mannosamine inhibits the aggrecanase response to both IL-1 and RA at about one-tenth the concentration of glucosamine in both rat cell and bovine explant systems. This effect of mannosamine appears to be due to its capacity to inhibit the synthesis of glycosylphosphatidylinositol (GPI)-linked proteins by chondrocytes since the GPI synthesis inhibitor 2-deoxyfluoroglucose (2-DFG) also inhibited the aggrecanase response to IL-1b and RA in rat cells. Moreover, phosphatidylinositol-specific phospholipase C (PIPLC) treatment of rat cells markedly inhibited the aggrecanase response to IL-1b and RA. These inhibitory effects of mannosamine, 2-DFG, and PIPLC in rat cells did not appear to be due to an interference with general biosynthetic activity of the cells as measured by [3H]proline incorporation into secreted proteins. We suggest that the aggrecanase response by chondrocytes to IL-1 and RA is dependent on the activity of a GPI-anchored protein on the chondrocyte cell surface.

The surface contour of articular cartilage in an intact, loaded joint

The friction coefficients measured in diarthrodial joints are small. Theories of joint lubrication attribute this efficiency to entrapment or movement of synovial fluid, yet anatomical models of the surface are based on studies of isolated fragments of cartilage, not functional joints. To investigate the functional interrelationship of joint surfaces and synovial fluid, the ultrastructure of loaded joints was examined. Twenty-four New Zealand white rabbit knee joints were loaded either statically or moved ex vivo using simulated muscle forces and then plunge-frozen under load. After fixation in the frozen/loaded state by freeze-substitution fixation, the medial joint compartments were embedded in epoxy resin while still articulated. Bone was trimmed away from the articular surfaces, permitting the cartilage to be sectioned for light and electron microscopy. These joint surfaces were then compared with controls which were not loaded, not moved or had been disarticulated prior to embedding. Articular surfaces of loaded joints were smooth at magnifications from x 35 to x 7500, whereas the tibial surfaces of nonloaded joints were irregular. Small pools of joint fluid were observed at the meniscal edge and beneath the anterior horn of the meniscus. At magnifications of x 40000, the joint surfaces were separated by a uniform 100 nm space containing fluid. An amorphous, electron dense articular surface lamina was present but, when loaded, was thicker and flatter than previously reported. No surface pits or bumps were visible in embedded, loaded joints. This is the first ultrastructural study of intact loaded joints. The findings suggest that fluid film lubrication is present in diarthrodial joints, but the fluid sequestration postulated in several models is not apparent.

Physical and biological regulation of proteoglycan turnover around chondrocytes in cartilage explants. Implications for tissue degradation and repair

The development of clinical strategies for cartilage repair and inhibition of matrix degradation may be facilitated by a better understanding of (1) the chondrocyte phenotype in the context of a damaged extracellular matrix, and (2) the roles of biochemical and biomechanical pathways by which matrix metabolism is mediated. Using methods of quantitative autoradiography, we examined the cell-length scale patterns of proteoglycan deposition and turnover in the cell-associated matrices of chondrocytes in adult bovine and calf cartilage explants. Results highlight a rapid turnover in the pericellular matrix, which may indicate spatial organization of PG metabolic pools, and specific biomechanical roles for different matrix regions. Subsequent to injurious compression of calf explants, which resulted in grossly visible tissue cracks and caused a decrease in the number of viable chondrocytes within explants, cell-mediated matrix catabolic processes appeared to increase, resulting in apparently increased rates of proteoglycan turnover around active cells. Furthermore, the influences of cell-stimulatory factors such as IL-1 beta appeared to be delayed in their effects subsequent to injurious compression, suggesting interactions between biomechanical and biochemical pathways of PG degradation. These results may provide a useful reference point in the development of in vitro models for cartilage injury and disease, and hint at possible new approaches in the development of cartilage repair strategies.

Differential expression of aggrecanase and matrix metalloproteinase activity in chondrocytes isolated from bovine and porcine articular cartilage

The release of aggrecan catabolites from cartilage is an early event in the pathogenesis of degenerative joint diseases. The enzymes involved in this process are unknown, controversial, and the subject of intense investigation. In this paper we have utilized a recombinant substrate containing the interglobular domain (IGD) of aggrecan to study specifically aggrecanase versus matrix metalloproteinase (MMP) catabolism in this domain of aggrecan. Our studies have shown that (i) there are species differences in the expression of latent versus active MMP activity on the aggrecan IGD; (ii) interleukin-1alpha exposure induces both aggrecanase and MMP activities, whereas retinoic acid induces only aggrecanase activity and inhibits the MMP activity on the aggrecan IGD; (iii) activators of latent MMP activity (p-aminophenylmercuric acetate and trypsin) significantly reduce aggrecanase activity; (iv) the time course of the appearance of aggrecanase versus the MMP catabolism of aggrecan IGD differs; (v) aggrecanase is a protease with metalloprotease characteristics; however (vi) the physiological (tissue) inhibitors of MMPs show weak inhibition (TIMP-1) or no inhibition (TIMP-2) of aggrecanase activity. Collectively, these studies show that aggrecanase and MMP catabolism of the aggrecan IGD are independent and uncoupled.

Chondrocyte-mediated catabolism of aggrecan: aggrecanase-dependent cleavage induced by interleukin-1 or retinoic acid can be inhibited by glucosamine

A rat chondrosarcoma cell line and bovine cartilage explants have been used to study the control of aggrecan degradation by chondrocytes treated with interleukin-1 (IL-1) or retinoic acid (RA). Aggrecan fragment analysis with anti-neo-epitope antibodies suggests that aggrecanase (an as yet unidentified enzyme) is the only aggrecan-degrading proteinase active in these cultures. With rat cells, aggrecanase converts the aggrecan core protein into two major G1-domain-bearing products (60 kDa with a C-terminal Glu-373, and 220 kDa with a C-terminal Glu-1459). Both products were quantified on a standardized Western analysis system with a G1-specific antibody. Immunoblots were analysed by scanning densitometry and the sensitivity, linearity and reproducibility of the assay were established. With rat cells the aggrecanase response to IL-1 was optimal at about 2 mM glutamine, but was progressively inhibited at higher concentrations, with about 90% inhibition at 10 mM glutamine. Such inhibition by glutamine was not, however, observed with bovine explants. On the other hand, marked inhibition of aggrecanase-dependent cleavage was observed with both rat cells and bovine explants when d(+)-glucosamine was included at concentrations above 2 mM. Inhibition was apparently not due to cytotoxicity or interference with IL-1 signalling, since biosynthetic activity was not inhibited and inhibition of the aggrecanase response was also obtained when RA was used as the catabolic stimulator. Possible mechanisms for the inhibition of the aggrecanase response by glucosamine in chondrocytes treated with IL-1 or RA are discussed.