Transforming growth factor-beta causes partial inhibition of interleukin 1-stimulated cartilage degradation in vitro

Inhibitors of collagenase but not of gelatinase reduce cartilage explant proteoglycan breakdown despite only low levels of matrix metalloproteinase activity

Aims-To investigate the level of matrix metalloproteinase activity during the time-course of cartilage explant proteoglycan breakdown; to determine the effects of selective small-molecule inhibitors of matrix metalloproteinases on proteoglycan degradation.Methods-The levels of matrix metalloproteinase activity in cartilage explant cultures and conditioned media were monitored by use of a quenched fluorescent substrate. The constants for inhibition of certain matrix metalloproteinases by a series of synthetic inhibitors were determined. Bovine and human cartilage explant cultures were treated with interleukin-1, tumor necrosis factor or retinoic acid and the amount of proteoglycan released into the culture medium in the absence and presence of the inhibitors was quantified. Control experiments, examining the inhibition of other proteinases, and investigating possible toxic or non-specific effects of the inhibitors, were carried out.Results-The profile of inhibition of proteoglycan release suggested the involvement of interstitial collagenase-like, rather than gelatinase- or possibly stromelysin-like, proteinases. No evidence was found for toxic or non-specific mechanisms of inhibition. Very low levels of activity of the known matrix metalloproteinases were present during the time-course of aggrecan breakdown.Conclusions-A novel collagenase-like proteinase(s) may be involved in cartilage proteoglycan breakdown. Gelatinase-type matrix metalloproteinases do not seem to be involved in this process. Specific collagenase inhibitors may be therapeutically efficacious in the treatment of arthritis.

TGF-beta inhibits IL-1beta-activated PAR-2 expression through multiple pathways in human primary synovial cells

To investigate the mechanism how Transforming growth factor-β(TGF-β) represses Interleukin-1β (IL-1β)-induced Proteinase-Activated Receptor-2 (PAR-2) expression in human primary synovial cells (hPSCs). Human chondrocytes and hPSCs isolated from cartilages and synovium of Osteoarthritis (OA) patients were cultured with 10% fetal bovine serum media or serum free media before treatment with IL-1β, TGF-β1, or Connective tissue growth factor (CTGF). The expression of PAR-2 was detected using reverse transcriptase-polymerase chain reaction (RT-PCR) and western blotting. Collagen zymography was performed to assess the activity of Matrix metalloproteinases-13 (MMP-13). It was demonstrated that IL-1β induces PAR-2 expression via p38 pathway in hPSCs. This induction can be repressed by TGF-β and was observed to persist for at least 48 hrs, suggesting that TGF-β inhibits PAR-2 expression through multiple pathways. First of all, TGF-β was able to inhibit PAR-2 activity by inhibiting IL-1β-induced p38 signal transduction and secondly the inhibition was also indirectly due to MMP-13 inactivation. Finally, TGF-β was able to induce CTGF, and in turn CTGF represses PAR-2 expression by inhibiting IL-1β-induced phospho-p38 level. TGF-β could prevent OA from progression with the anabolic ability to induce CTGF production to maintain extracellular matrix (ECM) integrity and to down regulate PAR-2 expression, and the anti-catabolic ability to induce Tissue inhibitors of metalloproteinase-3 (TIMP-3) production to inhibit MMPs leading to avoid PAR-2 over-expression. Because IL-1β-induced PAR-2 expressed in hPSCs might play a significantly important role in early phase of OA, PAR-2 repression by exogenous TGF-β or other agents might be an ideal therapeutic target to prevent OA from progression.

Fibroblast growth factor 2 inhibits induction of aggrecanase activity in human articular cartilage

OBJECTIVE

Articular chondrocytes are surrounded by an extracellular pool of fibroblast growth factor 2 (FGF-2). We undertook this study to investigate the possible role of FGF-2 in aggrecan catabolism by aggrecanase in human articular cartilage.

METHODS

Aggrecan catabolism was induced by interleukin-1alpha (IL-1alpha) in normal human articular cartilage and assessed by measuring the release of glycosaminoglycan (GAG) and aggrecanase-dependent fragments by Western blotting with antibodies against neoepitopes. ADAMTS-4 and ADAMTS-5 messenger RNA (mRNA) expression was measured by quantitative real-time reverse transcriptase-polymerase chain reaction. Production of matrix metalloproteinases (MMPs) 1, 3, and 13 and tissue inhibitors of metalloproteinases (TIMPs) 1 and 3 was measured by Western blotting. IL-6 and IL-8 were measured by enzyme-linked immunosorbent assay. Proteoglycan synthesis was monitored by 35S-sulfate incorporation.

RESULTS

IL-1alpha caused cleavage of aggrecan in cultured human articular cartilage explants, with release of GAG and aggrecan fragments containing ARGS and AGEG neoepitopes. This was inhibited by FGF-2 (1-100 ng/ml). Tumor necrosis factor alpha and retinoic acid also stimulated release of neoepitope, and this was also suppressed by FGF-2. IL-1alpha induced ADAMTS-4 and ADAMTS-5 mRNA in primary human chondrocytes, and this was inhibited by FGF-2. IL-1alpha-induced aggrecan breakdown was inhibited by TIMP-1 or by the N-terminal portion of TIMP-3, although FGF-2 did not affect production of the inhibitors TIMP-1 and TIMP-3 when IL-1alpha was present. FGF-2 did not prevent IL-1alpha suppression of proteoglycan synthesis and did not negate its ability to stimulate the production of IL-6, IL-8, and MMPs 1, 3, and 13.

CONCLUSION

Our findings suggest that FGF-2 may play a chondroprotective role in human articular cartilage by controlling the expression and activity of the aggrecanases ADAMTS-4 and ADAMTS-5.

The multicomponent phytopharmaceutical SKI306X inhibits in vitro cartilage degradation and the production of inflammatory mediators

Clinical studies have demonstrated that SKI306X, a purified preparation of three medicinal plants, relieves joint pain and improves functionality in osteoarthritis patients. To study the biological action of SKI306X, bovine cartilage explants and human peripheral blood mononuclear cells (PBMC) were stimulated with IL-1 beta and lipopolysaccharide (LPS) respectively, in the presence or absence of SKI306X and its individual composites. All tested compounds inhibited dose-dependently IL-1 beta-induced proteoglycan release and nitric oxide production by cartilage, indicating cartilage protective activity. SKI306X and two of its compounds inhibited PGE(2), TNF-alpha and IL-1 beta production by LPS-stimulated PBMC, indicating anti-inflammatory activity. These results demonstrate that the biological effect of SKI306X is at least bipartite: (1) cartilage protective and (2) anti-inflammatory. The observed anti-inflammatory effects may provide an explanation for the outcome of the clinical studies. Long-term clinical trails are necessary to elucidate whether the in vitro cartilage protective activity results in disease-modifying effects.

Effects of transforming growth factor-beta on aggrecanase production and proteoglycan degradation by human chondrocytes in vitro

OBJECTIVE

Aggrecan is degraded by Aggrecanases (ADAMTS-4 and -5) and MMPs, which cleave its core protein at different sites. Transforming growth factor (TGF)beta is known to stimulate matrix formation in cartilage, and ADAMTS-4 production in synoviocytes. The aim of this in-vitro study was to examine the effects of TGFbeta on aggrecanase production in human cartilage.

DESIGN

Expression of ADAMTS-4 and -5 in chondrocyte cultures from normal or osteoarthritic cartilage was studied at mRNA level by RT-PCR. Aggrecanase activity was examined by western blot of aggrecanase-generated neoepitope NITEGE, and by measure of proteoglycan degradation in cartilage explants.

RESULTS

TGFbeta strongly increased mRNA levels of ADAMTS-4, while ADAMTS-5 was expressed in a constitutive way in chondrocytes from normal and osteoathritic cartilage. TGFbeta also increased NITEGE levels and proteoglycan degradation. Addition of an aggrecanase inhibitor blocked the increase of NITEGE, and partially inhibited proteoglycan degradation.

CONCLUSIONS

TGFbeta stimulates ADAMTS-4 expression and aggrecan degradation in cartilage. This catabolic action seems to be partially mediated by aggrecanases. It is, therefore, proposed that the role of TGFbeta in cartilage matrix turnover is not limited to anabolic and anti-catabolic actions, but also extends to selective degradation of matrix components such as aggrecan.

Regulation of osteogenic proteins by chondrocytes

The purpose of this review is to summarize the current scientific knowledge of bone morphogenetic proteins (BMPs) in adult articular cartilage. We specifically focus on adult cartilage, since one of the major potential applications of the members of the BMP family may be a repair of adult tissue after trauma and/or disease. After reviewing cartilage physiology and BMPs, we analyze the data on the role of recombinant BMPs as anabolic agents in tissue formation and restoration in different in vitro and in vivo models following with the endogenous expression of BMPs and factors that regulate their expression. We also discuss recent transgenic modifications of BMP genes and subsequent effect on cartilage matrix synthesis. We found that the most studied BMPs in adult articular cartilage are BMP-7 and BMP-2 as well as transforming growth factor-beta (TGF-beta). There are a number of contradicting reports for some of these growth factors, since different models, animals, doses, time points, culture conditions and devices were used. However, regardless of the experimental conditions, only BMP-7 or osteogenic protein-1 (OP-1) exhibits the most convincing effects. It is the only BMP studied thus far in adult cartilage that demonstrates strong anabolic activity in vitro and in vivo with and without serum. OP-1 stimulates the synthesis of the majority of cartilage extracellular matrix proteins in adult articular chondrocytes derived from different species and of different age. OP-1 counteracts the degenerative effect of numerous catabolic mediators; it is also expressed in adult human, bovine, rabbit and goat articular cartilage. This review reveals the importance of the exploration of the BMPs in the cartilage field and highlights their significance for clinical applications in the treatment of cartilage-related diseases.

Inhibition of endogenous TGF-beta during experimental osteoarthritis prevents osteophyte formation and impairs cartilage repair

Osteoarthritis has as main characteristics the degradation of articular cartilage and the formation of new bone at the joint edges, so-called osteophytes. In this study enhanced expression of TGF-beta1 and -beta3 was detected in developing osteophytes and articular cartilage during murine experimental osteoarthritis. To determine the role of endogenous TGF-beta on osteophyte formation and articular cartilage, TGF-beta activity was blocked via a scavenging soluble TGF-beta-RII. Our results clearly show that inhibition of endogenous TGF-beta nearly completely prevented osteophyte formation. In contrast, treatment with recombinant soluble TGF-beta-RII markedly enhanced articular cartilage proteoglycan loss and reduced the thickness of articular cartilage. In conclusion, we show for the first time that endogenous TGF-beta is a crucial factor in the process of osteophyte formation and has an important function in protection against cartilage loss.

Catechins from green tea (Camellia sinensis) inhibit bovine and human cartilage proteoglycan and type II collagen degradation in vitro

Polyphenolic compounds from green tea have been shown to reduce inflammation in a murine model of inflammatory arthritis, but no studies have been undertaken to investigate whether these compounds are protective to joint tissues. We therefore investigated the effects of catechins found in green tea on cartilage extracellular matrix components using in vitro model systems. Bovine nasal and metacarpophalangeal cartilage as well as human nondiseased, osteoarthritic and rheumatoid cartilage were cultured with and without reagents known to accelerate cartilage matrix breakdown. Individual catechins were added to the cultures and the amount of released proteoglycan and type II collagen was measured by metachromatic assay and inhibition ELISA, respectively. Possible nonspecific or toxic effects of the catechins were assessed by lactate output and proteoglycan synthesis. Catechins, particularly those containing a gallate ester, were effective at micromolar concentrations at inhibiting proteoglycan and type II collagen breakdown. No toxic effects of the catechins were evident. We conclude that some green tea catechins are chondroprotective and that consumption of green tea may be prophylactic for arthritis and may benefit the arthritis patient by reducing inflammation and slowing cartilage breakdown. Further studies will be required to determine whether these compounds access the joint space in sufficient concentration and in a form capable of providing efficacy in vivo.

Photodynamic treatment has chondroprotective effects on articular cartilage

Osteoarthritis (OA) is a disabling joint disease for which there is currently no cure. It is characterized by the destruction of articular cartilage. One strategy that is being explored for protecting the cartilage in OA is the administration of transforming growth factor-beta, which in vitro antagonizes cartilage degradation initiated by catabolic stimulants such as interleukin-1 (IL-1). The problems associated with selective delivery of the growth factor to chondrocytes, undesirable side-effects on joint tissues, and short biological half-life have led us to explore modalities aimed at activating transforming growth factor-beta that is stored in the cartilage as latent complexes. Photodynamic therapy is a two-step protocol of tissue sensitization with a light-activatable chemical called a photosensitizer followed at some interval by irradiation with the appropriate wavelength visible light. Biological effects are typically elicited through oxygen-dependent photochemistry without heat generation. Transforming growth factor-beta1 can be activated by oxidative mechanism(s), prompting us to explore whether photodynamic technology can be harnessed to modulate cartilage metabolism. Disks of bovine articular cartilage were photosensitized by incubation with a chlorin(e6)-succinylated polylysine conjugate and irradiated with 1-2 J/cm2 red light (lambdamax = 671 nm). This two-step regimen dramatically inhibited IL-1-stimulated proteoglycan degradation and concomitantly increased latent and active transforming growth factor-beta1 in culture medium. This research may lead to the development of minimally invasive photodynamic therapy in which light is delivered to locally activate a chondroprotective program in photosensitized cartilage in the context of OA.

Synergistic effects of glycoprotein 130 binding cytokines in combination with interleukin-1 on cartilage collagen breakdown

OBJECTIVE

To determine whether other glycoprotein 130 (gp130) binding cytokines can mimic the effects of oncostatin M (OSM) in acting synergistically with interleukin-1alpha (IL-1alpha) to induce cartilage collagen breakdown and collagenase expression, and to determine which receptors mediate these effects.

METHODS

The release of collagen and proteoglycan was assessed in bovine and human cartilage explant cultures. Messenger RNA (mRNA) and protein production from immortalized human chondrocytes (T/C28a4) was analyzed by Northern blotting and specific enzyme-linked immunosorbent assays. Collagenase activity was measured by bioassay. Cell surface receptors were detected by flow cytometry.

RESULTS

OSM in combination with IL-1alpha caused a rapid synergistic induction of matrix metalloproteinase 1 mRNA, which was sustained over a 72-hour period. Flow cytometric analyses detected both the OSM-specific receptor and the gp130 receptor at the chondrocyte cell surface, but failed to detect the leukemia inhibitory factor receptor (LIFR). Cartilage degradation assays revealed that, of the gp130 binding cytokines, only OSM and IL-6, in the presence of its soluble receptor (sIL-6R), were able to act synergistically with IL-1alpha to promote collagen release.

CONCLUSION

This study demonstrates that IL-6 can mimic OSM in synergizing with IL-1alpha to induce chondrocyte-mediated cartilage collagen breakdown and collagenase production. In order to have this effect, IL-6 requires the presence of its soluble receptor. The apparent absence of LIFR explains why other gp130 binding cytokines do not act in synergy with IL-1alpha. Since OSM, IL-6, and sIL-6R levels have all been shown to be elevated in the rheumatoid joint, our findings suggest that these cytokines may be key mediators of cartilage collagen catabolism in the inflammatory arthritides.

Potential biologic agents for treating rheumatoid arthritis

The encouraging clinical results observed in trials using anti-TNF therapy clearly warrant further studies to determine whether TNF inhibitors are capable of modifying the destructive component of this disease in long-term follow-up studies as well as to assess the safety of long-term use (see the article by Keystone in this issue). It is also reasonable to propose that interfering with the cytokine cascade earlier in the course of disease may be of even greater therapeutic benefit. As the pathogenetic mechanisms in RA are more clearly defined, especially in early disease and in those individuals destined to develop severe disease, the potential of other biologic agents to specifically inhibit these critical pathways may provide better treatments for our patients. Many potential targets in the immune-mediated process of RA are currently being rigorously evaluated in clinical trials. Use of combinations of biologic therapies, perhaps in human patients with RA, should be of considerable interest in future trials.

Insulin-like growth factor 1 blocks collagen release and down regulates matrix metalloproteinase-1, -3, -8, and -13 mRNA expression in bovine nasal cartilage stimulated with oncostatin M in combination with interleukin 1alpha

OBJECTIVE

To investigate the effect of insulin-like growth factor 1 (IGF1) on the release of collagen, and the production and expression of matrix metalloproteinases (MMPs) induced by the proinflammatory cytokine interleukin 1alpha (IL1alpha) in combination with oncostatin M (OSM) from bovine nasal cartilage and primary human articular chondrocytes.

METHODS

Human articular chondrocytes and bovine nasal cartilage were cultured with and without IGF1 in the presence of IL1alpha or IL1alpha + OSM. The release of collagen was measured by an assay for hydroxyproline. Collagenase activity was determined with the diffuse fibril assay using 3H acetylated collagen. The expression of MMP-1, MMP-3, MMP-8, MMP-13, and tissue inhibitor of metalloproteinase 1 (TIMP-1) mRNA was analysed by northern blot.

RESULTS

IGF1 can partially inhibit the release of collagen induced by IL1alpha or IL1alpha + OSM from bovine nasal cartilage. This was accompanied by a reduced secretion and activation of collagenase by bovine nasal cartilage. IGF1 can also down regulate IL1alpha or IL1alpha + OSM induced MMP-1, MMP-3, MMP-8, and MMP-13 mRNA expression in human articular chondrocytes and bovine chondrocytes. It had no significant effect on the production and expression of TIMP-1 mRNA in chondrocytes.

CONCLUSION

This study shows for the first time that IGF1 can partially block the release of collagen from cartilage and suggests that down regulation of collagenases by IGF1 may be an important mechanism in preventing cartilage resorption initiated by proinflammatory cytokines.

Age-related effects of TGF-beta on proteoglycan synthesis in equine articular cartilage

The synthesis of proteoglycans was measured in normal equine articular cartilage of ages 9 months to 20 years and the effect of TGF-beta1 on this activity was investigated. The rate of incorporation of [(35)S]Na(2)SO(4) decreased with age as did the responsiveness of the tissue to the growth factor. The enhanced synthesis of proteoglycan induced at all ages by TGF-beta1 was down-regulated by IL-1 beta and retinoic acid. The expression of mRNA for TGF-beta1, 2, and 3 was also measured, and although the level of TGF-beta1 was highest at all ages, the expression of each growth factor decreased with age.

Transforming growth factor beta1 blocks the release of collagen fragments from boving nasal cartilage stimulated by oncostatin M in combination with IL-1alpha

Oncostatin M in combination with interleukin-1 (IL-1) induced a rapid and reproducible release of collagen from bovine nasal cartilage in culture. This release was accompanied by a high collagenolytic activity and low or absent tissue inhibitor of metalloproteinase-1 activity in the culture medium. Transforming growth factor-beta1 was able to block this release of collagen from the tissue, and reduce the expression and secretion of collagenases whilst maintaining TIMP-1 levels from bovine nasal chondrocytes. This study shows for the first time that TGF-beta1 can protect cartilage collagen from destruction.

The role of oncostatin M in animal and human connective tissue collagen turnover and its localization within the rheumatoid joint

OBJECTIVE

To study the interaction of interleukin-1alpha (IL-1alpha) and oncostatin M (OSM) in promoting cartilage collagen destruction.

METHODS

Bovine, porcine, and human cartilage and human chondrocytes were studied in culture. The levels of collagenase (matrix metalloproteinase 1 [MMP-1]) and tissue inhibitor of metalloproteinases 1 (TIMP-1) were measured by bioassay and enzyme-linked immunosorbent assay (ELISA). The levels of OSM in rheumatoid synovial fluid were measured by ELISA.

RESULTS

When combined with OSM, IL-1alpha, IL-1beta, and tumor necrosis factor alpha released proteoglycan and collagen from cartilage. OSM was the only member of the IL-6 family to have this effect. Human tendon also responded to IL-1alpha and OSM. OSM increased the production of MMP-1 and TIMP-1 but when combined with IL-1alpha, synergistically promoted MMP-1 production in human chondrocytes and synovial fibroblasts. High levels of OSM were found in human rheumatoid synovial fluids, and confocal microscopy showed that OSM was produced by macrophages in rheumatoid synovial tissue.

CONCLUSION

These results highlight an important new mechanism by which there is irreversible loss of collagen from cartilage.

Expression of cartilage-specific functional matrix chondromodulin-I mRNA in rabbit growth plate chondrocytes and its responsiveness to growth stimuli in vitro

Cartilage-specific functional matrix chondromodulin-I (ChM-I) is a 25 kDa glycoprotein purified from fetal bovine epiphyseal cartilage which stimulates the growth of rabbit chondrocytes and the colony formation of the cells in agarose. In the present study, we isolated rabbit ChM-I precursor CDNA by reverse transcription-polymerase chain reactions. Northern blot analysis revealed that the expression of ChM-I mRNA occurred in a tissue-specific manner in cartilage. Moreover, the ChM-I mRNA level was markedly changed in response to growth and differentiation stimuli in primary cultured chondrocytes. Among others, fibroblast growth factor-2, transforming growth factor-beta, and parathyroid hormone related peptide each markedly down-regulated the expression of ChM-I mRNA in chondrocytes. These results indicated that the expression ChM-I was placed under the dynamic control of local growth and differentiation factors.

Proteoglycan breakdown from bovine nasal cartilage is increased, and from articular cartilage is decreased, by extracellular ATP

The addition of ATP, but not ADP or AMP, to the culture media of bovine nasal cartilage explants caused an acceleration in the rate of proteoglycan loss from the tissue. The ATP-stimulated loss of proteoglycan was not inhibited by the IL1-receptor antagonist protein, but was partially inhibited by the presence of ADP or AMP. The proteolytic events resulting from the presence of ATP were found to be similar to those following treatment with IL1, in that inhibitors of the cysteine-peptidase cathepsin B, serine-proteinases with trypsin-like specificity, and of some of the matrixins, could all prevent proteoglycan loss, which was mediated, at least in part, by the action of 'aggrecanase'. In contrast to its effects on nasal cartilage, ATP inhibited basal and stimulated proteoglycan release from articular cartilage. Both ADP and AMP had no effect on proteoglycan release in articular cartilage but enhanced the response to ATP when added concurrently. We conclude that extracellular ATP, probably acting via P2-purinoceptors, stimulates proteoglycan breakdown from bovine nasal cartilage and thus, may have a role in diseases which primarily involve destruction of non-articular cartilage. Extracellular ATP has, in contrast, a chondroprotective effect on bovine articular cartilage.

Bone morphogenetic protein 2 stimulates articular cartilage proteoglycan synthesis in vivo but does not counteract interleukin-1alpha effects on proteoglycan synthesis and content

OBJECTIVE

To study the effect of bone morphogenetic protein 2 (BMP-2) on articular cartilage proteoglycan (PG) synthesis in vivo and to investigate whether BMP-2 is able to counteract the effects of interleukin-1 (IL-1) on articular cartilage PG synthesis and content.

METHODS

BMP-2 alone or in combination with IL-1alpha was injected into murine knee joints. PG synthesis was measured by 35S-sulfate incorporation using an ex vivo method or autoradiography. Cartilage PG content was analyzed by measuring Safranin O staining intensity on histologic sections.

RESULTS

BMP-2 appeared to be a potent stimulator of articular cartilage PG synthesis in vivo. However, BMP-2 was not able to counteract the deleterious effects of IL-1alpha on articular cartilage PG synthesis and content. In addition, intraarticular injections of BMP-2 induced chondrophytes.

CONCLUSION

Although BMP-2 is a very potent stimulator of cartilage PG synthesis in vivo, the therapeutic applications of BMP-2 are limited due to the inability of BMP-2 to counteract the effects of IL-1 and the induction of chondrophytes.

Cytokines modulate routes of collagen breakdown. Review with special emphasis on mechanisms of collagen degradation in the periodontium and the burst hypothesis of periodontal disease progression

In this paper, we review recent work on collagen degradation, 2 main routes of breakdown are described and their relevance during healthy and inflammatory conditions of the periodontium is discussed. Special attention is paid to the possible role of cytokines, in particular interleukin 1 (IL-1) and transforming growth factor beta (TGF-beta), on the modulation of collagen phagocytosis and metalloproteinase production. IL-1 has been shown to have a dual function in collagen digestion. It inhibits the intracellular phagocytic pathway, but at the same time, it strongly promotes extracellular digestion by inducing the release of collagenolytic enzymes like collagenase. TGF-beta has an opposite effect on both pathways and antagonizes IL-1. Collagenase is released in an inactive form, and a considerable fraction of the proenzyme may become incorporated in the extracellular matrix. This reservoir of latent enzyme can be activated (for instance by plasmin), leading to a sudden and extensive breakdown of the collagenous fibre meshwork. It is suggested that this phenomenon may also take place during progressive periodontitis and could explain an episodic nature of collagenolysis, clinically resulting in bursts of attachment loss (burst hypothesis).

Interleukin-4 blocks the release of collagen fragments from bovine nasal cartilage treated with cytokines

Interleukin-1 (IL-1) in combination with other cytokines can induce a reproducible release of collagen fragments from bovine nasal cartilage in culture. Over 70% of the total collagen is released by day 14 and this release is accompanied by the appearance of collagenolytic activity in the medium that cleaves collagen specifically at the one quarter/three quarter position. Interleukin-4 is able to prevent the release of collagen fragments from the tissue and this is accompanied by a reduced secretion and activation of collagenase (MMP-1) with an increase in tissue inhibitor of metalloproteinases-1 (TIMP-1). IL-4, especially in the presence of IL-1, increased TIMP secretion by bovine nasal cartilage in culture. These results suggest that IL-4 is able to specifically block cartilage collagen resorption by down-regulating the production of collagenase (MMP-1) and up-regulating TIMP-1 by chondrocytes within the cartilage.

Modulation of the catabolic effects of interleukin-1 beta on human articular chondrocytes by transforming growth factor-beta

The effects of IL-1 beta and TGF-beta on the biosynthesis of extracellular matrix structural components relative to the metalloproteinases and their inhibitor TIMP1 in human articular chondrocytes were investigated. It has been proposed that TGF-beta, acting as a positive regulator of matrix accretion, can counteract the increased loss of cartilage matrix induced by IL-1 beta. To allow a comparison of their effects on mRNA levels for these different components, quantitation by competitive RT/PCR was employed. This method was found to give reproducible estimates of mRNA levels and the observed effects of IL-1 beta and TGF-beta on individual components of this system agree with qualitative data obtained by northern blotting. IL-1 beta had a more pronounced effect on aggrecan mRNA levels than on those for type II collagen. Similar quantitative differences were observed between collagenase and stromelysin mRNA levels. TGF-beta generally counteracted the effects of IL-1 beta, and new steady state levels were attained within 24 h. However, the reversal of IL-1 beta induced suppression of matrix protein mRNA levels appeared more effective than its suppression of the increase in stromelysin and collagenase mRNA levels. Similarly TGF-beta did not reduce the extent of IL-1 beta induced secretion of stromelysin at the protein level. TIMP1 mRNA levels were only slightly reduced by IL-1 beta; however this cytokine effectively suppressed its induction by TGF-beta. The higher concentrations of TGF-beta and longer exposure times required to overcome the suppressive effects of IL-1 beta suggest that the interaction between IL-1 beta and TGF-beta in the regulation of TIMP1 expression follows a different mechanism to that operating for the metalloproteinases and matrix proteins. Thus the overall potential of TGF-beta to inhibit proteolysis is attenuated by its much slower effect on TIMP1 mRNA levels.

Effect of retinoic acid in combination with platelet-derived growth factor-BB or transforming growth factor-beta on tissue inhibitor of metalloproteinases and collagenase secretion from human skin and synovial fibroblasts

This report shows for the first time that platelet-derived growth factor-BB (PDGF-BB) and transforming growth factor-beta (TGF-beta) can interact in a synergistic manner with retinoic acid to stimulate the production of tissue inhibitor of metalloproteinases (TIMP) from human skin and synovial fibroblasts. When cells are treated with 1, 10, and 100 ng/ml of either of these growth factors in combination with 10(-5) M retinoic acid, this results in a dose-dependent synergistic induction of TIMP protein secretion which is greater than the additive effect of the agents by up to fourfold. These responses can be inhibited by the presence of specific neutralising antibodies to the growth factors, demonstrating that they are not the result of an experimental artefact such as contamination with bacterial endotoxin. The mechanisms of these synergistic responses may involve the induction of receptors for retinoic acid, PDGF, or TGF-beta or may result from synergistic effects on TIMP gene transcription. We have also found that retinoic acid potently down-regulates PDGF-BB-stimulated collagenase in both types of fibroblast and that the effect of PDGF-BB alone on collagenase secretion from skin fibroblasts is biphasic. Finally, this study reports that retinoic acid and TGF-beta do not act in an additive fashion to inhibit the production of collagenase from skin fibroblasts.

Collagenase: a key enzyme in collagen turnover

The primary agents responsible for cartilage and bone destruction in joint diseases are active proteinases that degrade collagen and proteoglycan. All four main classes of proteolytic enzymes are involved in either the normal turnover of connective tissue or its pathological destruction. These proteinases are made by different cells found within the joints. Both extracellular and intracellular pathways exist and individual enzymes can be inhibited by specific proteinaceous inhibitors that block their activity. Recent research has implicated the matrix metalloproteinases (MMPs) in many of the processes involved in joint diseases. The metalloproteinases are capable of degrading all components of the extracellular matrix. This family of proteinases contains a group of at least three collagenases that are capable of degrading native fibrillar collagen. Collagen degradation within joint disease is recognized as the irreversible step in the destruction of cartilage that leads to a failure in joint function. The collagenases are the enzymes necessary to initiate collagen turnover in normal connective tissue turnover and in disease.

Metalloproteinase inhibitors and the prevention of connective tissue breakdown

The primary agents responsible for cartilage and bone destruction in joint diseases are active proteinases degrading collagen and proteoglycan. All four main classes of proteolytic enzymes are involved in either the normal turnover of connective tissue or its pathological destruction. These proteinases are made by different cells found within the joints. Both extracellular and intracellular pathways exist, and individual enzymes can be inhibited by specific proteinaceous inhibitors that block their activity. Recent research has implicated the matrix metalloproteinases in many of the processes involved in joint diseases. Conventional treatments do little to affect the underlying disease processes, and recently, the use of proteinase inhibitors has been suggested as a new therapeutic approach. A large variety of different synthetic approaches have been used and highly effective metalloproteinase inhibitors have been designed, synthesised and tested. These metalloproteinase inhibitors can prevent the destruction of animal cartilage in model systems and slow the progression of human tumours. Future patient trials will test the effectiveness of these compounds in vivo for the treatment of joint diseases.

Standardization of nutrient media for isolated human articular chondrocytes in gelified agarose suspension culture

Human articular cartilage cells were cultured in 1.5% agarose in Dulbecco's modified Eagle's medium (DMEM) with 10% fetal calf serum or in serum-free DMEM with 0.15% bovine serum albumin. 35S-aggrecan synthesis in serum-free DMEM was between 20% and 30% of the value observed in DMEM supplemented with 10% fetal calf serum. The extent to which different growth or differentiation factors were able to restore 35S incorporation in aggrecan in serum-free DMEM was determined: human serum transferrin had no effect on aggrecan synthesis levels; bovine pancreas insulin, insulin-like growth factor (IGF)-1 and IGF-2 restored 35S-aggrecan synthesis to 35-50% of the control levels. The effects were dose-dependent, to level off at 100 ng/mL for the three factors. No cumulative or synergistic activities were observed when these factors were combined. Transforming growth factor (TGF)-beta, at concentrations ranging from 10-50 ng/mL stimulated aggrecan synthesis to approximately 50% of the control values in the chondrocytes obtained from two out of four donors, while the cells of the other two maintained within the range of the control levels. In th presence of insulin (100 ng/mL) 10 ng/mL of TGF-beta stimulated aggrecan synthesis to more than 90% of the control level in the chondrocytes of all donors.

IL-1 beta and TGF-beta 1 modulate the sulphation grade of chondro-disaccharides in porcine articular cartilage: a capillary electrophoresis study

This report describes the effect of interleukin-1 beta (IL-1 beta) and transforming growth factor-beta 1 (TGF-beta 1) on proteoglycan release from cartilage explants and modification at the sulphation level. Matrix proteoglycans purified by ion-exchange chromatography were composed of two distinct peaks (1 and 2) each showing a different Kav value when they were subjected to size-exclusion chromatography on a Sepharose CL-2B column. Glycosaminoglycans (GAGs) of conditioned medium and extracellular matrix proteoglycans were digested by chondroitin ABC and AC lyase, suggesting that chondroitin sulphate (CS) is the major GAG present (80-90%). Structural analysis of disaccharides, by capillary zone electrophoresis, revealed a different pattern of sulphated glycosaminoglycans when cartilage was treated with either IL-1 beta or TGF-beta 1. Analysis of GAGs released into the medium from TGF-beta 1 treated cartilage showed a reduction in the level of 4-S-disaccharide (delta Di4S) and an increase in non-sulphated disaccharides (delta Di0S), while no significant changes were found in IL-1 beta treated cartilage. In the extracellular matrix, IL-1 beta and TGF-beta 1 induced a more complex rearrangement of the GAGs. The level of non-sulphated disaccharides was increased whereas that of total sulphated disaccharides was reduced. Taken together, these results suggest that both cytokines modify the structure of GAGs, probably by interfering with the activity or the synthesis of sulphotransferases involved in GAG turnover.

In vivo protection against interleukin-1-induced articular cartilage damage by transforming growth factor-beta 1: age-related differences

OBJECTIVES

Transforming growth factor-beta (TGF-beta) has been shown to antagonise interleukin-1 (IL-1) effects in different systems. Investigations were carried out to study whether TGF-beta 1 modulates IL-1 induced inflammation and IL-1 effects on articular cartilage in the murine knee joint.

METHODS

IL-1, TGF-beta 1 or both factors together were injected into the knee joint. Inflammation was studied in whole knee histological sections. Patellar cartilage proteoglycan synthesis was measured using 35S-sulphate incorporation while patellar cartilage glycosaminoglycan content was determined with automated image analysis on joint sections.

RESULTS

Co-injection of TGF-beta 1 and IL-1 resulted in synergistic attraction of inflammatory cells. In contrast, TGF-beta 1 counteracted IL-1 induced suppression of articular cartilage proteoglycan synthesis. Proteoglycan depletion was similar shortly after the last injection of IL-1 or IL-1/TGF-beta 1, but accelerated recovery was found with the combination at later days. This protective effect of TGF-beta 1 could not be demonstrated in older mice.

CONCLUSIONS

TGF-beta 1 aggravates IL-1 induced knee joint inflammation, but counteracts the deleterious effects of IL-1 on articular cartilage proteoglycan synthesis and content. The data indicate that TGF-beta 1 could play an important part in articular cartilage restoration after IL-1 induced proteoglycan depletion.

Using inhibitors of metalloproteinases to treat arthritis. Easier said than done?

Collagenase and stromelysin have a premier role in the irreversible degradation of the extracellular matrix seen in rheumatic disease. It is therefore no surprise that considerable attention has been devoted to developing strategies to reduce their levels in diseased joints. Most efforts have focused on inhibiting the activity of the enzymes, either by increasing the concentration of natural inhibitors such as the TIMPs or by introducing into the joint synthetic compounds that will complex with the enzymes and inactivate them. There have also been studies directed at inhibiting enzyme synthesis. These preclinical studies have been carried out in cell-free and/or cell culture systems and in animal models. Despite promising preclinical data, there have been no stunning successes in the clinical arena. The reasons for this are several. In part, they are rooted in the technical difficulties associated with designing inhibitors of enzyme activity that are of high affinity, and then delivering them to the affected joints while still maintaining specificity and efficacy. The complicated structure of the proteoglycan and collagen that comprise articular cartilage, along with the biochemistry of inflamed synovial tissue, only compound the difficulties. In addition to these technical problems, the lack of fundamental knowledge about the biochemistry and molecular biology of the enzymes has handicapped our efforts. We are just resolving the crystal structure of the metalloproteinases (108) and beginning to understand the mechanisms controlling gene expression (67, 68, 70-72). These advances represent significant achievements in metalloproteinase enzymology and biology and should form the scientific basis for a new generation of effective therapies. For example, knowledge of the active site as derived from the crystal structure of the enzymes may facilitate the development of tightly-binding specific inhibitors which function well in vivo. Similarly, based on our current understanding of mechanisms controlling the regulation of both the TIMP genes and the MMP genes, we are beginning to elucidate how to turn these genes on or off, and hopefully, to modulate disease accordingly. Indeed, although some studies are still at a preclinical level, these possible approaches are becoming a reality (109). Arthritic diseases in general, and rheumatoid arthritis in particular, represent a complicated multifaceted set of clinical disorders. The clinical symptoms and pathologic features result from a cascade of biologic pathways that involve acute and chronic inflammation, the immune response, and metalloproteinase biochemistry.(ABSTRACT TRUNCATED AT 400 WORDS)

Cytokine modulation of plasminogen activator inhibitor-1 (PAI-1) production by human articular cartilage and chondrocytes. Down-regulation by tumor necrosis factor alpha and up-regulation by transforming growth factor-B basic fibroblast growth factor

Recombinant human cytokines were examined for their effects on plasminogen activator inhibitor-1 (PAI-1) production by human articular cartilage and chondrocyte monolayer cultures. Cartilage and chondrocytes were cultured with and without added cytokines and the conditioned media assayed for PAI-1 by a specific enzyme-linked immunosorbent assay, and mRNA levels determined by Northern blot analysis. Tumor necrosis factor alpha (TNF alpha) reduced, and transforming growth factor-beta (TGF-beta) and basic fibroblast growth factor (bFGF) increased, the levels of PAI-1 antigen and mRNA in the culture fluids and cell extracts, respectively. The effects of TNF alpha and TGF-beta on PAI-1 antigen levels were both time- and concentration-dependent; optimum doses being 10-100 pM TNF alpha and 0.4-0.8 nM TGF-beta, with each cytokine exerting its effect on PAI-1 antigen levels within 8 h of addition to culture. TNF alpha (and interleukin-1 alpha) also countered the effects of TGF-beta and bFGF. The anti-inflammatory drugs, indomethacin and dexamethasone, did not appear to modulate PAI-1 levels in cultures of cartilage tissue. The inhibition of PAI-1 levels by cytokines and reagents which stimulate cartilage resorption (i.e., TNF alpha, interleukin-1 alpha, retinoic acid) and enhancement by cytokines which counter it (i.e., TGF-beta, bFGF) further implicate plasminogen activator in the mechanism(s) of cartilage degradation in diseases such as arthritis.

Nitric oxide and energy production in articular chondrocytes

Addition of human, recombinant interleukin-1 beta (hrIL-1 beta) to cultures of lapine articular chondrocytes provoked a delayed increase in the production of both nitric oxide (NO) and lactate. These two phenomena followed a similar time course and shared a parallel dose-response sensitivity to hrIL-1 beta. A causal relationship is suggested by the ability of N-monomethyl-L-arginine (NMA), an inhibitor of NO synthase, to blunt the glycolytic response to hrIL-1 beta. Furthermore, addition of S-nitroso-N-acetylpenicillamine (SNAP), which spontaneously generates NO in culture, increased lactate production to the same degree as IL-1. However, 8-Br-cGMP and isobutylmethylxanthine (IBMX) had no effect either in the presence or absence of IL-1. Even under standard, aerobic, cell culture conditions, chondrocytes consumed little oxygen, either in the presence or absence of IL-1 or NMA. Furthermore, cyanide at concentrations up to 100 microM had no effect upon NO synthesis or lactate production. Thus, the increases in glycolysis under study were not secondary to reduced mitochondrial activity. Although cells treated with IL-1 had increased rates of glycolysis, their concentrations of ATP fell below those of untreated chondrocytes in a time-dependent, but NMA-independent, manner. Transforming growth factor-beta (TGF-beta) and synovial cytokines (CAF) also increased lactate production. However, TGF-beta failed to induce NO, and its effect on glycolysis was independent of NMA. Furthermore, cells treated with TGF-beta were not depleted in ATP. These data are consistent with hypotheses that rates of proteoglycan synthesis are, in part, regulated by the intracellular concentration of ATP or by changes in pericellular pH. These two possibilities are not mutually exclusive.

Synovial fluid cytokine concentrations as possible prognostic indicators in the ACL-deficient knee

Approximately 44% of patients develop osteoarthritis (OA) following rupture of the anterior cruciate ligament (ACL) if the injury is left unrepaired. Restoring knee stability through reconstruction, while providing symptomatic relief, has not been shown to reduce the incidence of degenerative changes. In fact, recent studies have shown that 50%-60% of ACL-reconstructed patients go on to develop degenerative changes or frank osteoarthritis. In light of these data, our group suggests that the cause of post-traumatic osteoarthritis is not biomechanical but biochemical. To test this hypothesis, we measured levels of nine cytokines which are important in modulating physiological and pathophysiological metabolism of cartilage in knee joint synovial fluid following ACL rupture. Our patient population contained both acute and chronic ACL ruptures. A total of 84 samples were collected and analyzed by enzyme-linked immunosorbent assay. On the basis of the data collected, we were able to identify subgroups of patients who, on the basis of their synovial fluid cytokine profile, may be at greater or lesser risk of developing post-traumatic OA. In general, patients displayed concentrations of interleukin-1 alpha (IL-1 alpha), basic fibroblastic growth factor (bFGF), transforming growth factor-beta (TGF-beta), granulocyte/macrophage-colony stimulating factor (GM-CSF), IL-6, and IL-8 that we interpreted as being consistent with an inflammatory reaction. Of great interest is the fact that the levels of these cytokines were very similar in patients 4 weeks after injury and in chronic patients, leading us to hypothesize that a chronic smoldering inflammatory reaction persists after resolution of the acute effusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Cytokines and proteoglycans

Cytokines play an important regulatory role in the metabolism of proteoglycans. Proteoglycans are found in plasma membranes, but predominantly in the extra-cellular matrix. In the latter they are quantitatively and qualitatively essential components. Especially in a tissue like cartilage without any blood vessels, the cells are dependent on cytokines for the communication among themselves in the extra-cellular matrix and also for communication with the 'outside world'. Various cytokines have been found to be able to penetrate the extra-cellular matrix and inhibit, respectively stimulate the proteoglycan synthesis. Also, the degradation of proteoglycans can be stimulated, respectively inhibited by several cytokines. In addition, some cytokines have been found which regulate the effects of the other cytokines. With respect to proteoglycan metabolism a complex cytokine network is emerging. Furthermore it is becoming increasingly clear that proteoglycans are connected to the cytokine network by their own bioactive functions. First, they possibly possess cytokine activities themselves. Second, they can function as receptors, protectors, inactivators and storage ligands for cytokines. So the proteoglycans are clearly involved in the feedback signalling from the extra-cellular matrix to the cells that are synthesizing this extra-cellular matrix. Together with agonistic or antagonistic cytokines they are involved in the regulation of proteoglycan turnover during balanced or unbalanced metabolism in normal, respectively pathological situations.

Cytokines and proteoglycans

Cytokines play an important regulatory role in the metabolism of proteoglycans. Proteoglycans are found in plasma membranes, but predominantly in the extra-cellular matrix. In the latter they are quantitatively and qualitatively essential components. Especially in a tissue like cartilage without any blood vessels, the cells are dependent on cytokines for the communication among themselves in the extra-cellular matrix and also for communication with the 'outside world'. Various cytokines have been found to be able to penetrate the extra-cellular matrix and inhibit, respectively stimulate the proteoglycan synthesis. Also, the degradation of proteoglycans can be stimulated, respectively inhibited by several cytokines. In addition, some cytokines have been found which regulate the effects of the other cytokines. With respect to proteoglycan metabolism a complex cytokine network is emerging. Furthermore it is becoming increasingly clear that proteoglycans are connected to the cytokine network by their own bioactive functions. First, they possibly possess cytokine activities themselves. Second, they can function as receptors, protectors, inactivators and storage ligands for cytokines. So the proteoglycans are clearly involved in the feedback signalling from the extra-cellular matrix to the cells that are synthesizing this extra-cellular matrix. Together with agonistic or antagonistic cytokines they are involved in the regulation of proteoglycan turnover during balanced or unbalanced metabolism in normal, respectively pathological situations.

Identification of tissue inhibitor of metalloproteinase-2 (TIMP-2)-progelatinase complex as the third metalloproteinase inhibitor peak in rheumatoid synovial fluid

The metalloproteinases are a family of enzymes that can degrade all the components of the extracellular matrix. These potent enzymes are often found in proenzyme forms and require activation before the substrate can be digested. To prevent unlimited connective tissue destruction a number of inhibitors exist to limit their activity. In a previous study it was found that metalloproteinases in proenzyme form and metalloproteinase inhibitors were often present in rheumatoid synovial fluids. Two of these inhibitors were identified in rheumatoid synovial fluid as alpha 2 macroglobulin and tissue inhibitor of metalloproteinase (TIMP), the specific metalloproteinase inhibitor. A third inhibitory peak was unidentified. In the study reported here it was shown that this third inhibitor can be purified using gelatin-Sepharose chromatography and consists of TIMP-2 bound to progelatinase (relative molecular weight 72,000) in a similar way to that found in concentrated connective tissue culture medium. The importance of these proteinase inhibitors in synovial fluid is discussed.

Protection from interleukin 1 induced destruction of articular cartilage by transforming growth factor beta: studies in anatomically intact cartilage in vitro and in vivo

The modulation of interleukin 1 (IL-1) effects on proteoglycan metabolism in intact murine patellar cartilage by transforming growth factor beta (TGF-beta) was investigated in vitro and in vivo. In vitro TGF-beta (400 pmol/l) had no effect on basal proteoglycan degradation. Proteoglycan degradation induced by IL-1, however, was suppressed by TGF-beta in serum free medium alone and in medium supplemented with 0.5 micrograms/ml insulin-like growth factor 1. This suggests a specific regulatory role for TGF-beta under pathological conditions. In contrast with the suppression of breakdown, synthesis of proteoglycans was stimulated by TGF-beta for both basal and IL-1 suppressed proteoglycan synthesis in cultures without insulin-like growth factor. In the presence of insulin-like growth factor no extra effect of TGF-beta on proteoglycan synthesis was observed. With insulin-like growth factor, however, TGF-beta potentiated the ex vivo recovery of IL-1 induced suppression of proteoglycan synthesis. Analogous to the in vitro effects, TGF-beta injected intraarticularly suppressed IL-1 induced proteoglycan degradation. Furthermore, TGF-beta injected into the joint counteracted IL-1 induced suppression of proteoglycan synthesis. This indicates that in vivo also TGF-beta can ameliorate the deleterious effects of IL-1 on the cartilage matrix.

The measurement of collagenase, tissue inhibitor of metalloproteinases (TIMP), and collagenase-TIMP complex in synovial fluids from patients with osteoarthritis and rheumatoid arthritis

OBJECTIVE

To compare the levels of collagenase, tissue inhibitor of metalloproteinases (TIMP), and collagenase-TIMP complex in synovial fluid (SF) from patients with rheumatoid arthritis (RA) and patients with osteoarthritis (OA). This study aims to clarify existing data from previously used enzyme or inhibitor activity assays performed following separation by gel filtration, by using a 1-step enzyme-linked immunosorbent assay (ELISA) for each component.

METHODS

Total collagenase, free TIMP, and collagenase-TIMP complex were measured using a newly developed, specific double-antibody sandwich ELISA:

RESULTS

Levels of both collagenase and TIMP were significantly higher in RA patients (collagenase 1,560 +/- 150 ng/ml [mean +/- SEM], TIMP 1,610 +/- 130 ng/ml; n = 80) than OA patients (collagenase 420 +/- 90 ng/ml, TIMP 1,050 +/- 60 ng/ml; n = 80), with the difference being especially striking for collagenase. Sixteen RA fluids had detectable levels of collagenase-TIMP complex, compared with only 3 OA fluids.

CONCLUSION

The level of total collagenase in SF is greater in RA than OA, while levels of free TIMP show more overlap between the 2 diseases; this may simply reflect the increased inflammation seen in RA, or it may reflect a different disease mechanism.

A synthetic peptide metalloproteinase inhibitor, but not TIMP, prevents the breakdown of proteoglycan within articular cartilage in vitro

IL1-stimulated pig articular cartilage fragments were cultured in the and absence of various metalloproteinase inhibitors. Tissue inhibitor of metalloproteinases (TIMP) was unable to stop the release of proteoglycan from the cartilage. Incubation of cartilage with a potent synthetic metalloproteinase inhibitor inhibited the release of proteoglycan in a dose-dependent fashion. The results suggest that low-M(r) metalloproteinase inhibitors may have therapeutic potential in limiting connective tissue breakdown in conditions such as rheumatoid arthritis.

Induction of swelling, synovial hyperplasia and cartilage proteoglycan loss upon intra-articular injection of transforming growth factor beta-2 in the rabbit

Transforming growth factor beta (TGF-beta) is a multifunctional homodimeric polypeptide with potent actions upon many target cells, including those of mesenchymal and haemopoietic lineage. The recent reports of high levels of the cytokine in rheumatoid synovium and synovial fluid, prompted this study into the effect of intra-articular injection of TGF beta-2 into rabbit knee-joints. Four daily injections of 1 microgram caused swelling, probably as a consequence of prostaglandin E2 production, synovial fibroblastic hyperplasia and a striking loss of femoral condyle proteoglycan. Using the polymerase chain reaction, no evidence could be obtained for the induction of interleukin-1 alpha gene expression in either synovial tissue or synovial fluid cells. These findings suggest that the TGF-beta present in the rheumatoid joint may contribute directly to the pathogenesis of rheumatoid arthritis.

Effects of anti-inflammatory drugs and agents that modify intracellular transduction signals or metabolic activities in inflammatory cells on interleukin-1 induced cartilage proteoglycan resorption in vitro

The actions of (a) anti-inflammatory drugs possessing a wide range of chemical structures and pharmacological actions, and (b) agents which modify intracellular transduction signals or metabolic functions were investigated for their potential to modify in vitro the proteoglycan (PrGn) resorption in bovine nasal cartilage induced by interleukin-1 alpha (IL-1). It was found that: (a) none of the conventional anti-inflammatory agents exhibited any inhibitory effects on IL-1 induced resorption of PrGns with the exception of the weak effects observed with the iron chelator, desferrioxamine, a cryogenine derivative JB-1-0, and myalex; (b) the antitumour agent cisplatin was a potent inhibitor but the analogue, transplatin, which does not inhibit DNA synthesis was without effect; (c) suramin, an inhibitor of cartilage degrading enzymes from leucocytes, also inhibited IL-1 induced resorption, as did natural somatomedin C (insulin-like growth factor = IGF alpha) but not agents previously shown to inhibit the lymphocyte mitogenic responses to IL-1 (e.g. alpha-melanocyte stimulating hormone, phenylglyoxal); (d) while no effects were observed with drugs that alter the intracellular production of cyclic AMP, those which affect uptake of calcium ions did inhibit proteoglycan resorption by IL-1. The results suggest that IL-1 induced cartilage PrGn degradation can be regulated at the level of transcriptional production of intracellular PrGn degrading enzymes or their activity, regulating calcium uptake into chondrocytes or by overcoming the PrGn degradation from IL-1 by stimulating the synthesis of these macromolecules.

The synovial activation of chondrocytes: evidence for complex cytokine interactions involving a possible novel factor

Preparations of lapine synovial 'chondrocyte activating factors' (CAF) were analyzed for the presence of individual cytokines which modulate the production of neutral metalloproteinases (NMPs) and prostaglandin E2 (PGE2) by articular chondrocytes. A combination of different biochemical analyses suggested that synovial fibroblasts secrete IL-1 alpha, which activated chondrocytes directly, bFGF, which potentiated the activity of IL-1, and TGF-beta 1, which produced a bivalent response. TGF-beta 1 suppressed NMP synthesis by chondrocytes, but enhanced PGE2 synthesis. The IL-1 receptor antagonist protein (IRAP) eliminated chondrocyte activation by IL-1, but only partially inhibited activation by CAF. Thus, CAF may contain a cytokine in addition to IL-1 which activates chondrocytes. This putative additional factor was more thermosensitive than IL-1, and had an apparent molecular weight of approx. 20,000 when estimated by size exclusion chromatography. Of a variety of purified cytokines tested for their ability to induce NMPs in chondrocytes, only IL-1 was active. This favours the possibility that the activity which resists suppression by IRAP reflects the presence of a novel cytokine.

Detection of mRNA for the transforming growth factor beta family in human articular chondrocytes by the polymerase chain reaction

The Transforming Growth Factor-beta (TGF beta) family of polypeptides elicits diverse biological actions on a wide range of cell types. There are known to be several isoforms of TGF beta coded for by different genes, with possibly differential expression and potencies. We have demonstrated that there is constitutive expression of three forms of transforming growth factor beta in adult human articular chondrocytes. The presence of 10% fetal calf serum in the culture medium may influence expression. The addition of transforming growth factor beta or interleukin 1 beta to the culture medium does not appear to consistently influence the expression of TGF beta by the cells.

Transforming growth factor beta stimulates the production of the tissue inhibitor of metalloproteinases (TIMP) by human synovial and skin fibroblasts

IL-1 stimulates the secretion of metalloproteinases by a variety of connective tissue cells and is thought to be the primary inducing agent of connective tissue breakdown in rheumatoid arthritis. Transforming growth factor-beta (TGF-beta) is known to be capable of inhibiting the synthesis of metalloproteinases and to be able to partially inhibit interleukin-1 (IL-1) induced cartilage degradation. The present paper examines the ability of TGF-beta to modulate the action of IL-1 on fibroblasts of synovial and skin origin and investigates the secretion of the tissue inhibitor of metalloproteinases (TIMP) by these cells after exposure to TGF-beta and IL-1. The principal findings are that when four out of five fibroblast lines were exposed to TGF-beta and IL-1 in combination they displayed a significant increase in TIMP secretion; furthermore, in two of these cell lines a significant stimulation of TIMP secretion was induced by TGF-beta alone.

In vivo effects of interleukin-1 on articular cartilage. Prolongation of proteoglycan metabolic disturbances in old mice

We investigated the effects of intraarticular injections of interleukin-1 alpha (IL-1 alpha) into the knee joints of young (3-month-old) and old (18-month-old) C57Bl/10 mice. In this in vivo study, 35S-sulfate incorporation and release were used to compare the effects of IL-1 on patellar cartilage proteoglycan metabolism. IL-1-induced stimulation of proteoglycan degradation was confined to the first 24 hours after injection in both young and old animals, and was only slightly lower in old cartilage than in young. In old patellar cartilage, IL-1-induced suppression of proteoglycan synthesis appeared to be more prolonged. Also, the amount of time needed to restore the cartilage matrix, characterized by proteoglycan synthesis above normal levels, was longer in old animals. Histologic analysis confirmed the retarded recovery in the cartilage of old mice. Autoradiography showed that the chondrocytes of the medial side of the femorotibial area were most vulnerable to IL-1-induced suppression of proteoglycan synthesis, especially the medial tibial plateau. As with the patellar cartilage, IL-1-induced suppression of proteoglycan synthesis in this area of articular cartilage was more prolonged in old animals. Our data indicated that the impact of IL-1 on articular cartilage is higher in old mice and that, consistent with certain loci found to be at risk in experimental osteoarthritis, there are sites at which IL-1 is more likely to act.

Physiological and pharmacological regulation of biological calcification

Biological calcification is a highly regulated process which occurs in diverse species of microorganisms, plants, and animals. Calcification provides tissues with structural rigidity to function in support and protection, supplies the organism with a reservoir for physiologically important ions, and also serves in a variety of specialized functions. In the vertebrate skeleton, hydroxyapatite crystals are laid down on a backbone of type I collagen, with the process being controlled by a wide range of noncollagenous proteins present in the local surroundings. In bone, cells of the osteoblast lineage are responsible for the synthesis of the bone matrix and many of these regulatory proteins. Osteoclasts, on the other hand, are continually resorbing bone to both produce changes in bone shape and maintain skeletal integrity, and to establish the ionic environment needed by the organism. The proliferation, differentiation, and activity of these cells is regulated by a number of growth factors and hormones. While much has already been discovered over the past few years about the involvement of various regulators in the process of mineralization, the identification and functional characterization of these factors remains an area of intense investigation. As with any complex, biological system that is in a finely tuned equilibrium under normal conditions, problems can occur. An imbalance in the processes of formation and resorption can lead to calcification disorders, and the resultant diseases of the skeletal system have a major impact on human health. A number of pharmacological agents have been, and are being, investigated for their therapeutic potential to correct these defects.(ABSTRACT TRUNCATED AT 250 WORDS)