Activation of neutral metalloprotease in human osteoarthritic knee cartilage: evidence for degradation in the core protein of sulphated proteoglycan

Replacement of the knee meniscus by a porous polymer implant: a study in dogs

BACKGROUND

Meniscectomy will lead to articular cartilage degeneration in the long term. Therefore, the authors developed an implant to replace the native meniscus.

HYPOTHESIS

The porous polymer meniscus implant develops into a neomeniscus and protects the cartilage from degeneration.

STUDY DESIGN

Controlled laboratory study.

METHODS

In a dog model, a porous polymer scaffold with optimal properties for tissue infiltration and regeneration of a neomeniscus was implanted and compared with total meniscectomy. The tissue infiltration and redifferentiation in the scaffold, the stiffness of the scaffold, and the articular cartilage degeneration were evaluated.

RESULTS

Three months after implantation, the implant was completely filled with fibrovascular tissue. After 6 months, the central areas of the implant contained cartilage-like tissue with abundant collagen type II and proteoglycans in their matrix. The foreign-body reaction remained limited to a few giant cells in the implant. The compression modulus of the implant-tissue construct still differed significantly from that of the native meniscus, even at 6 months. Cartilage degeneration was observed both in the meniscectomy group and in the implant group.

CONCLUSION

The improved properties of these polymer implants resulted in a faster tissue infiltration and in phenotypical differentiation into tissue resembling that of the native meniscus. However, the material characteristics of the implant need to be improved to prevent degeneration of the articular cartilage.

CLINICAL RELEVANCE

The porous polymer implant developed into a polymer-tissue construct that resembled the native meniscus, and with improved gliding characteristics, this prosthesis might be a promising implant for the replacement of the meniscus.

The effect of IL-1beta on the expression of matrix metalloproteinases and tissue inhibitors of matrix metalloproteinases in human chondrocytes

Interleukin-1 (IL-1) plays key roles in altering cartilage matrix turnover. This turnover is regulated by matrix metalloproteinases (MMPs) and tissue inhibitors of matrix metalloproteinases (TIMPs). In the present study, we examined the effect of IL-1beta on cell proliferation, alkaline phosphatase (ALPase) activity, and the expression of MMPs, and TIMPs in chondrocytes derived from normal human femoral cartilage. The cells were cultured in Dulbecco's modified Eagle's medium containing 15% fetal bovine serum and 0, 1, 10, or 100 U/ml of IL-1beta for up to 28 days. The level of expression of MMPs and TIMPs was estimated by determining mRNA levels using real-time PCR and by determining protein levels using an enzyme-linked immunosorbent assay. Cell proliferation decreased in the presence of IL-1beta after day 21 of culture. ALPase activity decreased significantly in the presence of IL-1beta after day 10 of culture. The expression of MMP-1, -2, and -3 increased markedly in the presence of IL-1beta after day 21 of culture. MMP-13 expression increased markedly in the presence of IL-1beta on day 1 of culture, but decreased markedly after day 7. The expression of TIMP-1 increased significantly after day 14 of culture. The expression of TIMP-2 decreased significantly on day 1, but increased significantly from day 3 to day 14 of culture. These results suggest that IL-1beta may stimulate cartilage matrix turnover by increasing mainly MMP-13 production by the cells.

Presence of pannus-like tissue on osteoarthritic cartilage and its histological character

OBJECTIVE

To investigate and characterize pannus-like tissue which is often present on osteoarthritic articular cartilage.

DESIGN

Cartilage specimens from 15 knee and five hip joints of patients with osteoarthritis (OA) undergoing arthroplasty were stained for HE and Safranin-O. They were also immunostained by antitype I collagen, type II collagen, CD68, IL-1beta and MMP3 antibodies.

RESULTS

Ninety percent of joints have pannus-like tissue on the articular surface, preferentially in a marginal area. The articular cartilage was divided into three regions according to the location: the marginal zone, the intermediate zone and the paraeburnated zone. Pannuslike tissue in OA knee joint occurred 45.9%, 27.5% and 11.1% of the surface of each region respectively. Histologically, pannus-like tissue could be classified into the vascular type and the fibrous type. Extracellular matrix of both types of tissues were negative for Safranin-O and type II collagen, but positive for type I collagen. IL-1beta and MMP3 expressing cells are predominant in pannus-like tissue, whereas CD68 positive cells were infiltrated in only a few samples. Vascular type tissue kept continuity with bone marrow suggesting mesenchymal origin.

CONCLUSION

Pannus-like tissue exists in advanced OA cartilage, preferentially in the marginal zone. It expressed IL-1beta and MMP3, which strongly suggests that it contributes to cartilage degradation.

Presence and mechanism of knee articular cartilage degeneration after meniscal reconstruction in dogs

OBJECTIVE

Partial meniscectomy is the golden standard for treating a bucket-handle tear in the meniscus of the knee, but it inevitably leads to articular cartilage degeneration. Surgical creation of an access channel between the lesion and the vascularized synovial lining is intended to induce ingrowth of repair tissue and thus avoid degeneration of articular cartilage.

DESIGN

The presence and mechanism of cartilage degeneration were evaluated in 24 canine menisci after a longitudinal lesion and access channel had been created in the avascular part of the meniscus. In 12 menisci the channel was implanted with a porous polymer scaffold, while the remaining 12 were left empty. Evaluation was performed using routine histology and antibodies directed against denatured type II collagen (Col2-3/4M).

RESULTS

Articular degeneration was apparent in the polymer implant group and the empty channel group. This consisted of fibrillation, loss of chondrocytes and decreased proteoglycan content. Areas of fibrillated cartilage always showed positive labeling with the collagen degradation antibody Col2-3/4M. Collagen degradation was also visible in non-fibrillated areas. The upper zone of the cartilage showed swelling especially in the implant group, with empty cell lacunae and moderate levels of Col2-3/4M antibody labeling.

DISCUSSION

This reconstruction technique cannot be considered superior to partial meniscectomy. We propose that degradation of the collagen type II network is a result of cartilage fibrillation and vice versa.

The effect of sodium heparin on equine articular cartilage

This study compared the effect of sodium heparin and gentamicin sulphate on equine articular cartilage (AC) explants in order to investigate the possible use of sodium heparin in the treatment of infectious arthritis. Six concentrations of sodium heparin and gentamicin sulphate were tested. The supernatant and explant digest were assayed for glycosaminoglycan (GAG) content with the dimethyl-methylene blue assay and the per cent loss of GAG was calculated. A significant (P< 0.001) increase in percentage GAG loss was noted for the sodium heparin groups when compared to the control, whilst no significant increase was found among the treatment groups (P =0.782). For gentamicin, no significant difference in percentage GAG loss was found between the control and three of the five treatment groups (P =0.667). The percentage GAG loss in the sodium heparin treated AC explants was greater than for any of the gentamicin-treated AC explants. It can be concluded that sodium heparin sulphate stimulates an increase in GAG release from equine articular cartilage explants, though no firm conclusions can be drawn on its use in treating equine infectious arthritis.

Spontaneous production of nitric oxide (NO), prostaglandin (PGE2) and neutral metalloproteinases (NMPs) in media of explant cultures of equine synovial membrane and articular cartilage from normal and osteoarthritic joints

Nitric oxide (NO), prostaglandin E2 (PGE2), and the activity of neutral metalloproteinases (NMPs) were measured in conditioned media of equine synovial membrane and articular cartilage explant cultures from horses with normal joints (n = 7) and from horses affected with moderate (n = 7) or severe osteoarthritis (n = 14) as judged by macroscopic appearance. Normal articular cartilage appeared glossy and bluish-white, was of normal thickness and showed no evidence of discolouration, fibrillation or other cartilage discontinuity. Slight discolouration and fibrillation or minor clefts of the cartilage were considered as moderate OA, whereas erosions of articular cartilage down to the subchondral bone were considered as cases of severe OA. Explant cultures of equine synovial membrane and articular cartilage released the local mediators, NO and PGE2, as well as detectable levels of NMP activity into culture media. Concentrations of NO were higher in articular cartilage explants compared to synovial membrane explants, whereas concentrations of PGE2 were higher in synovial membrane explants. The NMPs with collagenolytic activities were similar in both explant cultures, whereas gelatinolytic activities were higher in synovial membrane explant cultures and caseinolytic activities were generally higher in articular cartilage explant cultures. Furthermore it was shown that concentrations or enzyme activities increased according to the severity of disease of the joints. Concentrations for NO, collagenolytic and gelatinolytic NMPs were relatively stable, whereas PGE2 and caseinolytic NMP concentrations increased over time in culture.

Osteoarthritis: Update on Pathology, Pathogenesis and Treatment

Osteoarthritis (OA) is a joint disorder that is characterized by increased degradative and decreased synthetic processes. The pathogenetic factors that have been demonstrated to influence the progression of OA are cytokines and nitric oxide. This new information serves to further elucidate the factors involved in the etiology of osteoarthritis and will aid in the development of pharmacological tools to treat this disease. As our understanding of the pathogenesis of OA grows, so does our appreciation that it is not simply a disease of passive joint degeneration. Unfortunately, therapies aimed at modifying the progression of the disease remain frustratingly difficult to identify. Primary therapy for OA thus is still largely aimed at controlling the symptoms of the disease while minimizing drug side effects. New agents with the potential to slow disease progression are beginning to emerge however. These will be discussed along with the agents that should be used first line to control symptoms.

Osteoarthritis: differential expression of matrix metalloproteinase-9 mRNA in nonfibrillated and fibrillated cartilage

Expression of matrix metalloproteinase-9 mRNA in osteoarthritic and normal cartilage was analyzed using reverse transcription-polymerase chain reaction and in situ hybridization. Fifty-four osteoarthritic cartilage samples were obtained from 24 patients undergoing total knee arthroplasty. Sixteen normal cartilage samples were obtained from non-osteoarthritic knees of four autopsy cases. With normal cartilage, reverse transcription-polymerase chain reaction analysis for matrix metalloproteinase-9 mRNA showed that chondrocytes exhibited only a trace signal. In analysis of osteoarthritic cartilage, chondrocytes of moderately and severely fibrillated cartilage exhibited a 73-fold and 110-fold increase in matrix metalloproteinase-9 mRNA signal, respectively, relative to normal cartilage. Chondrocytes of nonfibrillated osteoarthritic cartilage exhibited a 6-fold increase (p < 0.02) in matrix metalloproteinase-9 mRNA signal relative to normal cartilage. Analysis of matrix metalloproteinase-9 mRNA expression in fresh-frozen sections of normal and osteoarthritic cartilage by in situ hybridization confirmed these results. This study showed that reverse transcription-polymerase chain reaction provides a sensitive index of mRNA levels in normal and osteoarthritic cartilage samples and suggests that increased expression of matrix metalloproteinase-9 precedes fibrillation of cartilage in the development of osteoarthritis.

Histochemical and immunohistochemical studies of the effects of experimental anterior disc displacement on sulfated glycosaminoglycans, hyaluronic acid, and link protein of the rabbit craniomandibular joint

PURPOSE

The purpose of this study was to determine the effects of surgically induced anterior disc displacement (ADD) on sulfated glycosaminoglycans (GAGs) such as keratan sulfate (KS), chondroitin-4-sulfate (C4S), and chondroitin-6-sulfate (C6S), hyaluronic acid (HA), and link protein (LP) of the rabbit craniomandibular joint (CMJ) using histochemical and immunohistochemical techniques.

MATERIALS AND METHODS

The right joint of 20 rabbits was exposed surgically, and all discal attachments were severed except for the posterior attachment. The disc was then repositioned anteriorly and sutured to the zygomatic arch. The left joint served as a sham-operated control. Ten additional joints were used as nonoperated controls. Deeply anesthetized rabbits were perfused with 2% buffered formalin 2 weeks (10 rabbits) or 6 weeks (10 rabbits) after surgery. Discs, bilaminar zones, condyles, and articular eminences were excised. Condyles and articular eminences were decalcified in ethylenediaminetetraacetic acid (EDTA). All tissues were sectioned at 10 microns in a cryostat. Sections were incubated with alcian blue and monoclonal antibodies directed against KS, C4S, C6S, HA, or LP. After incubation in the appropriate fluorescein isothiocyanate (FITC)-labeled secondary antibodies, tissue sections were studied under the fluorescence microscope.

RESULTS

The results showed a reduction in alcian blue staining and KS, C4S, C6S, HA, and LP immunostaining in the disc and articular surfaces at 2 weeks after induction of ADD. This reduction was followed by an increase in their immunostaining at 6 weeks. Also, there was a progressive increase in alcian blue staining, and KS, C4S, C6S, and HA immunostaining in the bilaminar zone at 2 and 6 weeks.

CONCLUSION

It was concluded that surgical induction of ADD in the rabbit CMJ leads to alterations in KS, C4S, C6S, HA, and LP content, consistent with similar changes accompanying osteoarthritis of other synovial joints.

Phenotypic modulation of newly synthesized proteoglycans in human cartilage and chondrocytes

The proteoglycans synthesized by human osteoarthritic femoral head cartilage and nonarthritic articular cartilage age-matched to the osteoarthritic cartilage specimens was studied in explant cultures and in chondrocytes generated by explant outgrowth from the cartilages. Twenty-four hours after explanation, both nonarthritic articular cartilage and osteoarthritic cartilage synthesized principally one large proteoglycan core protein that migrated on 3-5% acrylamide gels with an apparent molecular mass (M(r)) of approximately 520 kDa after enzymatic digestion with chondroitinase ABC and keratanase. The proteoglycan was found in both the explant itself and in the medium compartment of the culture as well. This proteoglycan contained chondroitin-6-sulfate, keratan sulfate and the hyaluronan binding region as evidenced by immunoblotting with murine anti-proteoglycan monoclonal antibodies indicating that the proteoglycan was aggrecan. To a much lesser extent two additional proteoglycan core proteins were also found in the explant but were not seen in the culture medium compartment. These proteoglycans possessed apparent M(r)'s of approximately 480 kDa and approximately 390 kDa on 3-5% acrylamide gels after chondroitinase ABC and keratanase digestion. The medium compartment contained principally the approximately 520 kDa proteoglycan core protein. In osteoarthritic cartilage explants, the pattern of newly synthesized proteoglycans recovered from the tissue as assessed on 3-16% polyacrylamide gradient gels remained relatively the same from day 1 after explantation up to 36 days of culture. By contrast, the proteoglycans recovered from the culture medium contained chondroitin sulfate and keratan sulfate after 1, 7, and 21 days in culture but by 36 days appeared to contain only chondroitin sulfate. Chondrocytes generated from osteoarthritic cartilage and age-matched nonarthritic articular cartilage synthesized different patterns of large (greater than 200 kDa) proteoglycan. Whereas chondrocytes derived from osteoarthritic cartilage continued to synthesize principally the approximately 520 kDa proteoglycan core protein, the chondrocytes derived from nonarthritic cartilage synthesized in addition to this proteoglycan, abundant amounts of the other two proteoglycan core proteins as well.

Inhibition of relaxin-induced pubic symphyseal "relaxation" in guinea pigs by glycosaminoglycan polysulfates and pentosan polysulfate

There are similarities between the actions of estrogen and relaxin on the connective tissues of the pubic symphysis and those of neutral proteases on cartilage in osteoarthritis, including cartilage hydration, proteoglycan loss, and dissolution of collagen fibers. We hypothesized that compounds known to inhibit cartilage breakdown in animal models of osteoarthritis, such as polysulfated GAGs, would also antagonize the actions of estrogen and relaxin that increase the laxity and mobility of the pubic symphyses of guinea pigs. Estrogen-primed guinea pigs were injected with relaxin or with relaxin and the test compound. The pubic symphyses were manually palpated 6 h later and the degree of mobility scored. Glycosaminoglycan polysulfates and pentosan polysulfate inhibited relaxin-induced pubic symphyseal relaxation, whereas other types of agents were without effect. The guinea pig pubic symphysis assay for relaxin may thus provide a novel rapid screening test for compounds with potential chondroprotective activity.

The effects of orally administered calcium pentosan polysulfate on inflammation and cartilage degradation produced in rabbit joints by intraarticular injection of a hyaluronate-polylysine complex

OBJECTIVE

To determine the antiinflammatory and cartilage-protecting activities of orally administered calcium pentosan polysulfate (CaPPS) in a rabbit model of inflammatory arthritis.

METHODS

A single intraarticular injection of a preformed polycation complex (PC) of poly-D-lysine and hyaluronan was used to induce joint inflammation; saline was injected into the contralateral joint as a control. Animals were killed 1, 4, 7, or 10 days post-PC injection. CaPPS, at 5 mg/kg, 10 mg/kg, or 75 mg/kg, was given every 48 hours commencing 7 days prior to PC injection. Serum interleukin-6 (IL-6), synovial fluid (SF) prostaglandin E2, cell numbers, and cartilage proteoglycan (PG) content, composition, and biosynthesis were determined for PC- and saline-injected joints.

RESULTS

In PC-injected, non-drug-treated animals, serum IL-6 activity, SF leukocyte numbers, and prostaglandin E2 levels were elevated, while cartilage PG content and biosynthesis were reduced. CaPPS at 10 mg/kg, but not at 5 mg/kg, decreased serum IL-6 levels but maintained cartilage PG concentration and biosynthesis. However, SF leukocyte counts and prostaglandin E2 levels (except on day 1) were not reduced.

CONCLUSION

The ability of CaPPS to attenuate serum IL-6 levels and preserve cartilage PGs in inflamed rabbit joints suggests that this substance could be of value as an effective orally administered chondroprotective, antiarthritic drug.

Effects of nimesulide and naproxen on the degradation and metalloprotease synthesis of human osteoarthritic cartilage

The aim of this study was to examine the effects of 2 nonsteroidal anti-inflammatory drugs (NSAIDs), nimesulide and naproxen, on the proteoglycan matrix breakdown and metalloprotease synthesis of human osteoarthritic cartilage. The results showed that, under in vitro conditions, these 2 NSAIDs could significantly reduce both the degradation of proteoglycan and stromelysin synthesis. However, only nimesulide had the ability to significantly reduce collagenase synthesis. The effectiveness of these drugs on the natural course of osteoarthritis remains to be established by clinical studies.

Coordinate synthesis of stromelysin, interleukin-1, and oncogene proteins in experimental osteoarthritis. An immunohistochemical study

Metalloproteases appear to play an important role in the pathophysiology of osteoarthritis (OA) and their expression is believed to be regulated by cytokines such as interleukin-1 (IL-1). Nuclear oncogene products are suggested as mediators through which IL-1 induces metalloprotease gene expression. Little data are available on the in vivo involvement of these agents in the pathophysiology of OA. This study examined by immunohistochemistry, using specific antibodies, the distribution of stromelysin, IL-1 alpha, IL-1 beta, and oncogene products (c-FOS, c-JUN, and c-MYC) in synovium and cartilage from normal and experimental canine models of OA. In the OA synovium, stromelysin and IL-1 were localized in the cytoplasm of superficial synovial lining cells, infiltrating mononuclear cells, and endothelial and smooth muscle cells of the blood vessels, whereas oncoproteins were detected predominantly in the synovial lining cells. Normal synovial membranes demonstrated low levels of specific staining in synovial lining cells with occasional staining of blood vessel cells for IL-1 alpha, IL-1 beta, and stromelysin. In OA cartilage, chondrocytes at the superficial and middle layers as well as in fibrillated areas were found to be involved in the synthesis of stromelysin, IL-1, and oncoproteins. Diffuse staining of stromelysin and IL-1 beta in OA cartilage matrix was also identified. In normal cartilage, only a few chondrocytes at the superficial layer showed a low level of antigens. These results demonstrate the in vivo concomitant cellular and/or matrical presence of stromelysin, IL-1, and oncogene proteins in tissues from experimentally induced OA with the most intense staining at the sites of cartilage erosion and synovial proliferation. These findings suggest that they may be involved in the pathophysiology of OA, and that the regulatory mechanisms involved in the expression of these proteins may be associated.

Synthesis of low buoyant density proteoglycans by human chondrocytes in culture

Human chondrocyte strains were derived from explant outgrowth of nonarthritic or osteoarthritic human cartilage. Chondrocytes radiolabeled with [35SO4] or [35S]-methionine were used to measure the biosynthesis of proteoglycans recovered from the most buoyant fraction (A4) of a CsCl density gradient centrifugation performed under associative conditions. The proteoglycans isolated from the A4 fraction (rho < 1.47 g/ml) were hydrodynamically small and contained both large and small glycosaminoglycan chains. When assessed by SDS/PAGE using 3-16% gradient gels, two subpopulations of small proteoglycans (smPG) were identified. The larger of the two species (smPG-I) migrated slower than the 200 kDa marker protein; when reassessed on 3-5% acrylamide gels, its apparent molecular mass was larger than the 480 kDa and 440 kDa alpha and beta heavy chains of dynein. We estimated the apparent molecular size of this smPG to be approximately 520 kDa. The smaller smPG (smPG-II) had an apparent average molecular mass of 180 kDa (range 170-210 kDa) after 3-16% SDS/PAGE. Three monoclonal antibodies, 1C6, 5D4, and S103L, reactive with the hyaluronic acid binding region of the aggregating proteoglycan core protein, keratan sulfate, and a core protein domain in the chondroitin sulfate attachment region, respectively, reacted with a single protein (apparent molecular mass, 180 kDa) that was similar in size to smPG-II.

Cartilage matrix metabolism in osteoarthritis: markers in synovial fluid, serum, and urine

Osteoarthritis is a major cause of disability and early retirement. Yet we lack the means to diagnose the disease in its early stages or to monitor the effects of treatment on the target tissue, the joint cartilage. Neither can we identify the disease mechanisms at the tissue or cell level. Current research focuses on the use of markers of cartilage matrix metabolism in body fluids as a means to diagnose and monitor osteoarthritis. Cartilage proteoglycan, collagen and glycoprotein fragments, as well as proteinases and their inhibitors, are being suggested for this purpose. Structural information on matrix molecule fragments released into body fluids may also help to identify the enzymes active in the destruction of the cartilage, a central issue in osteoarthritis.

Quinolone arthropathy--acute toxicity to immature articular cartilage

A class effect of quinolone antibacterial agents observed during animal toxicity testing is a specific arthropathy (QAP). Despite the growing list of laboratory animals susceptible to QAP and reports of arthralgia in patients treated with quinolones, the potential for QAP development in humans remains unknown. This review discusses current concepts in the biology of articular cartilage and how these concepts elucidate QAP pathogenesis. Biomechanical forces within synovial joints and toxicokinetic properties of quinolones contribute to QAP induction. Since a limited number of mechanistic pathways exist for acute articular damage, QAP may serve as a research tool to probe the pathobiology of injury to articular cartilage.

Markers of cartilage metabolism in arthrosis. A review

The mechanisms involved in the disease process in arthrosis are largely unknown, with genetics, joint malalignment, overload or trauma, obesity, and aging as some of the known or suspected contributing factors. Even less well known is how these general factors are translated into disease mechanisms at the cell and tissue levels. However, it may be argued that degradation of cartilage matrix is a key event at some time in the development of arthrosis. During this process, fragments of matrix molecules and other chondrocyte products are released into the joint fluid and eventually into other body fluids. These molecules can be used as markers of cartilage metabolism to monitor joint disease. In addition, by identifying the proteases and the structure of the released matrix fragments, we may improve our understanding of the cellular mechanisms active in cartilage degradation. Such information offers improved diagnostic and prognostic tools for rational treatment aimed at retarding cartilage destruction in arthrosis.

Metalloproteinase digestion of cartilage proteoglycan. Pattern of cleavage by stromelysin and susceptibility to collagenase

The action of purified rabbit bone stromelysin was investigated on proteoglycan aggregates from pig laryngeal cartilage. The enzyme caused a rapid fall in viscosity of proteoglycan aggregate solution (6 mg/ml), and the products of a partial digest (60% loss of relative viscosity) and a complete digest (95% loss of relative viscosity) were characterized. Analysis by gel chromatography on Sepharose 2B under associative conditions showed that 95% of the glycosaminoglycans in the complete digest were in small-sized fragments, whereas most of the hyaluronan-binding G1 domain and link protein remained intact and bound to hyaluronan. In contrast, there was extensive digestion of the G2 domain which resulted in 76% loss in its detection by immunoassay. Analysis of the partial digest also showed considerable loss (40%) of detection of the G2 domain, but the glycosaminoglycan-rich fragments were much larger than in the complete digest. There was also much less cleavage to create small fragments containing the G1 domain. This was evident on SDS/PAGE analysis where a 58 kDa G1 domain fragment was abundant in the complete digest, but was only present in small amounts in the partial digest. There was also only very limited conversion of link protein from a 44 kDa form to a 40 kDa form. The digestion of proteoglycan aggregate (6 mg/ml) by stromelysin was unaffected by the addition of a high concentration of extra chondroitin sulphate chains (14 mg/ml), and the digestion of proteoglycan monomer showed that the G1 domain was resistant to stromelysin digestion even when not bound to hyaluronan and link protein. The results show that stromelysin degrades the proteoglycan protein core with major cleavages close to, but not within, the G1 domain, and extensive cleavage in other regions. Experiments with purified collagenase, a metalloproteinase structurally related to stromelysin, showed that it too cleaved proteoglycan at several sites within the glycosaminoglycan-rich region of the core protein. Metalloproteinase attack on proteoglycan thus not only occurs with stromelysin but also with collagenase.

Synthesis of abnormal articular cartilage proteoglycans in rapidly destructive arthropathy (osteoarthritis)

Articular cartilage fragments were obtained from four femoral heads and one femoral condyle, resected in five patients undergoing prosthetic surgery for rapidly destructive arthropathy (RDA) and from one normal femoral head and one normal femoral condyle resected at autopsy. The cartilage fragments were labelled in vitro with 35SO4 and newly-synthesized proteoglycans, (35S-PGs) were then extracted with 4 M guanidinium hydrochloride (GuHCl) and analyzed. In three cases a much greater and in one case a significantly increased proportion of small 35S-PGs enriched in dermatan sulfate (DS) was demonstrated in diseased tissues in comparison with control samples. These DS 35S-PGs were completely unable to interact with hyaluronan (HA) and had longer glycosamino-glycan (GAG) side chains than large 35S-PGs. Also, large 35S-PGs extracted from diseased tissue interacted poorly under associative conditions with exogenous HA when this was added to the crude extract. However, they interacted much better following the addition of exogenous HA to the purified high density proteoglycans. This suggests the presence of an inhibitor of PG-HA interaction in the crude extract which is lost during PG purification. The synthesis of an abnormally large proportion of small PGs by articular chondrocytes and impaired aggregation of large PGs may account for the accelerated destruction of articular cartilage in this condition.

Proteinase-mediated cartilage degradation in osteoarthritis

Osteoarthritis (OA) is a disease of complex etiology that results in articular cartilage breakdown. Current experimental evidence strongly suggests that proteinases may be involved in this loss of cartilage matrix. The present review summarizes the evidence for implicating proteinases in the etiopathogenesis of OA and suggests that blockade of proteinase activity may provide a rational basis for new therapeutic agents.

Are cytokines involved in osteoarthritic pathophysiology?

The putative role and mechanism of action of cytokines in the progression of arthritic diseases such as osteoarthritis (OA) has received particular attention because of the important interaction between articular cartilage and synovium in the pathophysiology of the diseased state. Maintaining matrix homeostasis in the normal adult cartilage phenotype requires normal turnover of matrix components, principally collagen and proteoglycan. Chondrocytes and synovial fibroblasts are targeted, via specific cell-surface receptors, by cytokines like interleukin 1 (IL-1) and tumor necrosis factor alpha (TNF-alpha) to produce matrix proteases and to suppress the synthesis of collagen and proteoglycan. Thus, cytokines not only favor tissue destruction, but also inhibit tissue repair. A structurally heterogeneous group of factors capable of directly antagonizing cytokine action is described, which acts either by blocking cytokine-receptor binding, inhibiting local cytokine synthesis, or complexing the cytokine into an inactive form. Furthermore, many growth factors, such as transforming growth factor-beta (TGF-beta), can counteract the net effect of cytokines by stimulating the synthesis of matrix components or natural inhibitors of cartilage degrading enzymes.

Serum keratan sulfate. Quantitative and qualitative comparisons in inflammatory versus noninflammatory arthritides

The concentration of keratan sulfate (KS) epitope was measured in the serum of patients with osteoarthritis (OA) or rheumatoid arthritis (RA) by enzyme-linked immunosorbent assay and compared with that in the serum of patients with primary fibromyalgia syndrome (PFS) and of controls who had no joint disease. By Student's tau-test, the mean serum KS concentrations in OA and RA patients measured with monoclonal antibodies (MAb) 5-D-4 and 2-D-3 were significantly increased over those in the PFS and normal groups; similar findings were observed using a nonparametric test, except that levels in RA patients showed no difference from those in PFS patients and normal subjects. There was no significant correlation between joint scores or disease duration and KS levels in OA or RA patients. Gel filtration of sera revealed mainly large, polydisperse KS-bearing fragments which eluted in a broad profile. KS purified from sera by immunoaffinity chromatography consisted mainly of high-density proteoglycans. Electrophoresis of pooled high-density KS fractions in polyacrylamide-agarose gels followed by Western blotting with MAb 5-D-4 showed diffuse bands with relative mobilities corresponding to large proteoglycans. These findings are consistent with attachment of KS to protein core fragments of various sizes; KS in patient sera is comparable in size with that in normal sera. Elevations of serum KS levels occur in the presence of cartilage degradation, but do not quantitatively define the extent or duration of articular involvement.

The role of proteinases in cartilage destruction

Most of the organic, extracellular matrix of articular cartilage consists of collagens and proteoglycans. Their degradation is initiated extra- or peri-cellularly by proteinases produced locally by cells in and around the joint. Although enzymes from all four classes of proteinases can degrade the cartilagenous matrix, serine proteinases, particularly plasmin, and various neutral metalloproteinases (NMPs) are likely to be the key enzymes in this process. Much attention has been paid to members of the latter group, which are synthesised both by the resident, mesenchymal cells of the joint and by various types of white blood cells which colonise it during inflammation. NMPs can be conveniently grouped into three classes, the collagenases, the stromelysins and the gelatinases. Two members are known for each class, with the recently identified "pump" (Putative Metalloproteinase) probably constituting a third member of the stromelysin group. Regulation of these enzymes is complex. Cells normally synthesise NMPs at low rates, but their production increases markedly following cellular activation by cytokines or certain other stimuli. Major control points for enzyme synthesis occur at the levels of transcription and the conversion of proenzyme to active enzyme; enzyme activity is further regulated through the action of inhibitors. Alpha-2 macroglobulin is the major systemic inhibitor, while a number of tissue inhibitors act as local regulators. These include at least two TIMPs and several IMPs. Pharmacologic manipulation of NMP activity holds promise as an approach to anti-erosive therapy in arthritis.

In vivo activity of human recombinant tissue inhibitor of metalloproteinases (TIMP). Activity against human stromelysin in vitro and in the rat pleural cavity

Recombinant human tissue inhibitor of metalloproteinase (rhTIMP) suppressed the ability of native human stromelysin to degrade [3H]transferrin in vitro. Maximum inhibition occurred at molar ratios (TIMP: stromelysin) of 2:1 and 1:1. Reduced and alkylated tissue inhibitor of metalloproteinases (TIMP) lost its ability to suppress stromelysin activity. rhTIMP also inhibited stromelysin from degrading proteoglycan monomer in vitro. When injected into the rat pleural cavity prior to stromelysin, rhTIMP inhibited the ability of the enzyme to degrade aggregating cartilage proteoglycan monomer. Marked inhibition of stromelysin-mediated proteoglycan degradation in vivo occurred at molar ratios (TIMP: enzyme) of 2:1 and 1:1, with less inhibition at molar ratios of 0.5:1 and 0.25:1. Reduction and alkylation prevented rhTIMP from suppressing stromelysin-mediated degradation of proteoglycan monomer in vivo. By comparison, an equimolar concentration of the serine proteinase inhibitor, alpha 1-proteinase inhibitor (alpha 1-PI), did not inhibit stromelysin activity in the rat pleural cavity. This study demonstrates that rhTIMP is effective in inhibiting native human stromelysin both in vitro and in vivo.

Early-onset primary osteoarthritis and mild chondrodysplasia. Radiographic and pathologic studies with an analysis of cartilage proteoglycans

Three generations of a nonconsanguineous family with premature onset of primary (idiopathic) osteoarthritis (OA) were studied for clues to the etiopathogenesis of their disorder. Articular symptoms began in their second and third decades of life and involved multiple joints, both typical and atypical for primary OA. Radiographs of the majority of involved peripheral joints showed abnormalities typical of primary OA. Evidence of chondrodysplasia was found in the spines. Pathologic examination of femoral heads obtained at total hip arthroplasty from 3 affected family members showed moderate to severe OA. Articular cartilage proteoglycans from these specimens were evaluated for aggregatability with hyaluronic acid, levels of chondroitin sulfate and keratan sulfate, and core protein structure. The results from each patient's specimen differed from the results of the other specimens. We conclude that this family's disorder, primary OA associated with a mild chondrodysplasia, was a late-onset overlap form of an epiphyseal dysplasia, that a defect common to hyaline articular and physeal cartilage was primary, and that a single structural proteoglycan abnormality was not likely to be the underlying cause.

Passive role of articular chondrocytes in quinolone-induced arthropathy in guinea pigs

The role of articular chondrocytes and matrix degrading enzymes such as collagenase and neutral protease in the pathogenesis of quinolone-induced cartilage degeneration was investigated in immature guinea pigs. Articular cartilage from nalidixic acid (NA) treated guinea pigs was examined for the presence of protease activity or the ex vivo synthesis of collagenase at various times post-treatment. Histologic evaluation of knee joints confirmed the presence of degenerative changes in the matrix, but increased collagenase synthesis or protease activity were not detected. A separate group of animals was used to determine the importance of articular chondrocytes in the lesion generation. These cells were killed by intra-articular injection of the glycolysis inhibitor iodoacetic acid (IA) prior to treatment of the animals with NA. Typical "blister-like" their presence was not required for lesion development. Cartilage exposed to IA only did not exhibit "blister-like" lesions indicating that chondrocyte death and proteoglycan loss in conjunction with frictional forces associated with load-bearing were not sufficient to induce major matrical disruptive changes during the period of this study. These results indicate that articular chondrocytes are not actively involved in inducing the degenerative changes and provide no evidence for involvement of collagenase or neutral protease in the pathogenesis of the lesion.