Cytokine-induced cartilage proteoglycan degradation is mediated by aggrecanase

Modeling early changes associated with cartilage trauma using human-cell-laden hydrogel cartilage models

BACKGROUND

Traumatic impacts to the articular joint surface are known to lead to cartilage degeneration, as in post-traumatic osteoarthritis (PTOA). Limited progress in the development of disease-modifying OA drugs (DMOADs) may be due to insufficient mechanistic understanding of human disease onset/progression and insufficient in vitro models for disease and therapeutic modeling. In this study, biomimetic hydrogels laden with adult human mesenchymal stromal cells (MSC) are used to examine the effects of traumatic impacts as a model of PTOA. We hypothesize that MSC-based, engineered cartilage models will respond to traumatic impacts in a manner congruent with early PTOA pathogenesis observed in animal models.

METHODS

Engineered cartilage constructs were fabricated by encapsulating adult human bone marrow-derived mesenchymal stem cells in a photocross-linkable, biomimetic hydrogel of 15% methacrylated gelatin and promoting chondrogenic differentiation for 28 days in a defined medium and TGF-β3. Constructs were subjected to traumatic impacts with different strains or 10 ng/ml IL-1β, as a common comparative method of modeling OA. Cell viability and metabolism, elastic modulus, gene expression, matrix protein production and activation of catabolic enzymes were assessed.

RESULTS

Cell viability staining showed that traumatic impacts of 30% strain caused an appropriate level of cell death in engineered cartilage constructs. Gene expression and histo/immunohistochemical analyses revealed an acute decrease in anabolic activities, such as COL2 and ACAN expression, and a rapid increase in catabolic enzyme expression, e.g., MMP13, and inflammatory modulators, e.g., COX2. Safranin O staining and GAG assays together revealed a transient decrease in matrix production 24 h after trauma that recovered within 7 days. The decrease in elastic modulus of engineered cartilage constructs was coincident with GAG loss and mediated by the encapsulated cells. The acute and transient changes observed after traumatic impacts contrasted with progressive changes observed using continual IL-1β treatment.

CONCLUSIONS

Traumatic impacts delivered to engineered cartilage constructs induced PTOA-like changes in the encapsulated cells. While IL-1b may be appropriate in modeling OA pathogenesis, the results of this study indicate it may not be appropriate in understanding the etiology of PTOA. The development of a more physiological in vitro PTOA model may contribute to the more rapid development of DMOADs.

Genetic markers for psoriatic arthritis in patients with psoriasis. Part I: non-HLA genes

Psoriatic arthritis often develops in patients with psoriasis and can lead to joint deformity, stiffness, dysfunction, and disability. Psoriatic arthritis is a polygenic disease. and the issue of personalizing the prognosis of its development can only be resolved taking into account the variability of plenty genomic loci associated with the development of the disease. The personification of the prognosis of the disease can be solved taking into account the variability of the set of genomic loci with which its development is associated. The review examines genomic polymorphisms associated with the development of psoriatic arthritis not psoriasis, except of HLA polymorphisms. Genome regions containing polymorphisms, allelic variants of which are associated both with the development of psoriatic arthritis and reducing the likelihood of its occurrence, are described. It has been reported that the predisposition to the development of psoriatic arthritis in patients with psoriasis is determined by genes encoding proteins involved in inflammation and bone metabolism.

IL-37 diminishes proteoglycan loss in human OA cartilage: donor-specific link between IL-37 and MMP-3

OBJECTIVE

A hallmark of osteoarthritis (OA) is degradation of articular cartilage proteoglycans. In isolated human OA chondrocytes, the anti-inflammatory cytokine Interleukin-37 (IL-37) lowers the expression of the proteolytic MMP and ADAMTS enzymes, which mediate this degradation. Therefore, we investigated if IL-37 protects against proteoglycan loss in freshly obtained human OA explants.

MATERIAL AND METHODS

Human OA cartilage explants were incubated with IL-37. Release of sulphated proteoglycans (sGAGs) was measured with the dimethylmethylene-blue assay. Production and degradation of newly synthesized proteoglycans was measured using ³⁵S-sulphate. Proteoglycan and proteolytic enzyme expression were analyzed by qPCR and Western Blot. Proteolytic activity was determined by measuring MMP- and ADAMTS-generated aggrecan neo-epitopes with ELISA and by using MMP-3-, MMP-13- or ADAMTS-5-inhibitors.

RESULTS

Over time, a linear release of sGAGs from OA cartilage was measured. IL-37 reduced this release by 87 μg/ml (24%) 95%CI [21.04-141.4]. IL-37 did not affect ³⁵S-sulphate incorporation or proteoglycan gene expression. In contrast, IL-37 reduced loss of ³⁵S-sulphate labeled GAGs and reduced MMP-3 protein expression, indicating that IL-37 inhibits proteoglycan degradation. Remarkably, we observed two groups of patients; one group in which MMP-3-inhibition lowered sGAG release, and one group in which ADAMTS5-inhibition had this effect. Remarkably, IL-37 was only functional in the group of patients that responded to MMP-3-inhibition.

CONCLUSION

We identified a relationship between IL-37 and reduced sGAG loss in OA cartilage. Most likely, this effect is mediated by inhibition of MMP-3 expression. These results suggest that IL-37 could be applied as therapy in a subgroup of OA patients, in which cartilage degradation is mediated by MMP-3.

Genetic variation at the glycosaminoglycan metabolism pathway contributes to the risk of psoriatic arthritis but not psoriasis

OBJECTIVE

Psoriatic arthritis (PsA) is a chronic inflammatory arthritis affecting up to 30% of patients with psoriasis (Ps). To date, most of the known risk loci for PsA are shared with Ps, and identifying disease-specific variation has proven very challenging. The objective of the present study was to identify genetic variation specific for PsA.

METHODS

We performed a genome-wide association study in a cohort of 835 patients with PsA and 1558 controls from Spain. Genetic association was tested at the single marker level and at the pathway level. Meta-analysis was performed with a case-control cohort of 2847 individuals from North America. To confirm the specificity of the genetic associations with PsA, we tested the associated variation using a purely cutaneous psoriasis cohort (PsC, n=614) and a rheumatoid arthritis cohort (RA, n=1191). Using network and drug-repurposing analyses, we further investigated the potential of the PsA-specific associations to guide the development of new drugs in PsA.

RESULTS

We identified a new PsA risk single-nucleotide polymorphism at B3GNT2 locus (p=1.10e-08). At the pathway level, we found 14 genetic pathways significantly associated with PsA (p_FDR<0.05). From these, the glycosaminoglycan (GAG) metabolism pathway was confirmed to be disease-specific after comparing the PsA cohort with the cohorts of patients with PsC and RA. Finally, we identified candidate drug targets in the GAG metabolism pathway as well as new PsA indications for approved drugs.

CONCLUSION

These findings provide insights into the biological mechanisms that are specific for PsA and could contribute to develop more effective therapies.

Degradation alters the lubrication of articular cartilage by high viscosity, hyaluronic acid-based lubricants

Hyaluronic acid (HA) is widely injected as a viscosupplement in the treatment of osteoarthritis. Despite its extensive use, it is not currently known if cartilage degradation alters how HA-based solutions lubricate the articular surface. In this study we utilized a model of cartilage degradation by IL-1β along with a recently developed framework to study role of cartilage degradation on lubrication by clinically-approved HA-based lubricants with high viscosities. Cartilage explants were cultured up to 8 days with 10 ng/ml IL-1β. After culture, samples were examined histologically, immunohistochemically, biochemically, mechanically, topographically, and tribologically. The tribological testing analyzed both boundary and mixed lubrication modes to assess individual effects of viscosity and boundary lubricating ability. Friction testing was carried out using PBS and two clinically approved HA-based viscosupplements in a cartilage-glass configuration. After culture with IL-1β, boundary mode friction was elevated after both 4 and 8 days. Additionally, friction in mixed mode lubrication, where HA is most effective as a lubricant, was significantly elevated after 8 days of culture. As cartilage became rougher, softer, and more permeable after culture, the boundary mode plateau was extended, and as a result, significantly increased lubricant viscosities or sliding speeds were necessary to achieve effective mixed lubrication. Overall, this study revealed that lubrication of cartilage by HA is degradation-dependent and coincides with changes in mechanics and roughness. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1456-1464, 2018.

Sensitivity of serum concentration of cartilage biomarkers to 21-days of bed rest

The objective of the study was to test the hypothesis that serum levels of cartilage oligomeric matrix protein (COMP) would decrease and serum levels of tumor-necrosis factor alpha (TNF-α) and selected matrix metalloproteinases (MMPs) would increase in response to bed rest (BR) and that these changes are unaffected by the intake of potassium bicarbonate or whey protein. Seven and nine healthy male subjects participated in two 21-day 6° head down tilt crossover BR-studies with nutrition interventions. Serum samples were taken before, during, and after BR and biomarker concentrations were measured using commercial enzyme-linked immunosorbent assays. MMP-3 during BR was significantly lower than at baseline (reduction greater 20%; p < 0.001). MMP-3 increased significantly from 14 to 21 days of BR (+7%; p = 0.049). COMP during BR was significantly lower than at baseline (reduction greater 20%; p < 0.001). MMP-3 and COMP returned to baseline within 1 day after BR. MMP-9 on day 3 of BR was significantly lower than at baseline (-31%; p < 0.033) and on days 3, 5, and 14 of BR significantly lower than at the end of and after BR (reduction greater 35%; p < 0.030). The nutritional countermeasures did not affect these results. The observed changes in cartilage biomarkers may be caused by altered cartilage metabolism in response to the lack of mechanical stimulus during BR and inflammatory biomarkers may play a role in changes in biomarker levels.

CLINICAL RELEVANCE

Immobilization independently from injury can cause altered cartilage biomarker concentration. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1465-1471, 2018.

Do model polymer therapeutics sufficiently diffuse through articular cartilage to be a viable therapeutic route?

The ability of a polymer therapeutic to access the appropriate subcellular location is crucial to its efficacy and is defined to a large part by the many and complex cellular biological and biochemical barriers such that a construct must traverse. It is shown here that model dextrin conjugates are able to pass through a cartilaginous extracellular matrix into chondrocytes, with little perturbation of the matrix structure, indicating that targeting of potential therapeutics through a cartilaginous extracellular matrix should be proven possible. Rapid chondrocytic targeting of drugs which require intra cellularisation for their activity and uniform extracellular concentrations of drugs with an extracellular target, is thus enabled though polymer conjugation.

Adipokines induce catabolism of newly synthesized matrix in cartilage and meniscus tissues

PURPOSE

Altered synovial levels of various adipokines (factors secreted by fat as well as other tissues) have been associated with osteoarthritis (OA) onset and progression. However, the metabolic effects of adipokines on joint tissues, in particular the fibrocartilaginous menisci, are not well understood. This study investigated effects of several adipokines on release of recently synthesized extracellular matrix in bovine cartilage and meniscus tissue explants.

MATERIALS AND METHODS

After labeling newly synthesized proteins and sulfated glycosaminoglycans (sGAGs) with ³H-proline and ³⁵S-sulfate, respectively; bovine cartilage and meniscus tissue explants were cultured for 6 days in basal medium (control) or media supplemented with adipokines (1 µg/ml of leptin, visfatin, adiponectin, or resistin) or 20 ng/ml interleukin-1 (IL-1). Release of radiolabel and sGAG to the media during culture and the final explant water, DNA, sGAG, and retained radiolabel were measured. Matrix metalloproteinase (MMP-2) and MMP-3 activities were assessed using gelatin and casein zymography, respectively.

RESULTS

Water and DNA contents were not significantly altered by any treatment. Visfatin, adiponectin, resistin, and IL-1 stimulated sGAG release from meniscus, whereas only IL-1 stimulated sGAG release from cartilage. Release of ³H and ³⁵S was stimulated not only by resistin and IL-1 in meniscus but also by IL-1 in cartilage. Retained ³H was unaltered by any treatment, while retained ³⁵S was reduced by visfatin, resistin, and IL-1 in meniscus and by only IL-1 in cartilage. Resistin and IL-1 elevated active MMP-2 and total MMP-3 in meniscus, whereas cartilage MMP-3 activity was elevated by only IL-1.

CONCLUSIONS

Resistin stimulated rapid and extensive catabolism of meniscus tissue, similar to IL-1, whereas adipokines minimally affected cartilage. Release of newly synthesized matrix was similar to overall release in both tissues. These observations provide further indications that meniscal tissue is more sensitive to pro-inflammatory factors than cartilage and also suggest further study of resistin's role in OA.

Traditional Chinese Medicine Formula "Xiaofeng granules" suppressed gouty arthritis animal models and inhibited the proteoglycan degradation on chondrocytes induced by monosodium urate

ETHNOPHARMACOLOGICAL RELEVANCE

Xiaofeng Granules (XF) is a kind of granules prepared by the famous traditional Chinese medicine formula for its efficiency in treating gouty diseases.

AIM OF THE STUDY

We investigated the relevance between XF that made from Modified simiaowan (MSW) as the anti-gouty arthritis drugs and protective mechanisms for cartilage matrix in order to provide the evidence for new drug application.

MATERIALS AND METHODS

In the present study, we evaluated the anti-gouty arthritis activity of XF in rats and rabbits models induced by MSU together with chondrocytes focusing on the link to proteoglycan degradation in vitro studies.

RESULTS

The results demonstrated that XF significantly reduced the swelling rate and attenuated the pathological changes in joints. The XF-containing serum were used medicated serum in cellular experiments. The in vitro data were in accordance with the in vivo results, showing that the constituents in XF-containing serum had obvious inhibitory effects on the activation of pro-inflammatory mediators in chondrocytes. Moreover, XF-containing serum substantially inhibited MSU-induced expression of glycosaminoglycans(GAG) and hydroxyproline(Hyp), and up regulated proteoglycan, which might be associated with the regulation of the balance of MMP-3/TIMP-1and ADAMTS-4/TIMP-3 inchondrocytes.

CONCLUSION

In conclusion, XF that made from MSW showed obvious effects on acute gouty arthritis, which also provided an effective protection on cartilage matrix degradation.

Controlled release of anti-inflammatory peptides from reducible thermosensitive nanoparticles suppresses cartilage inflammation

Characterized by pain, cartilage degradation, and inflammation, osteoarthritis is often treated with anti-inflammatory therapies that provide short-term relief but can have adverse side effects; intra-articular drug delivery systems with controlled release of anti-inflammatory peptides using degradable poly(N-isopropylacrylamide) (pNIPAM) nanoparticles could prolong relief and minimize these side effects. Nanoparticles provide a biocompatible drug carrier that can protect encapsulated therapeutics from enzymatic degradation and increase payload delivery upon encountering a degradation stimulus. Here we demonstrate passive targeting of inflamed cartilage ex vivo by uptake of PEGylated pNIPAM nanoparticles with degradable disulfide crosslinks (abbreviated as NGPEGSS) into chondrocytes and subsequent intracellular release of an anti-inflammatory peptide KAFAKLAARLYRKALARQLGVAA (KAFAK). The KAFAK-loaded NGPEGSS treatment reduced ex vivo inflammation to a greater extent compared to its non-degradable counterparts. This study highlights a nanoparticle system that delivers therapeutics intracellularly with improved efficacy by triggered degradation and suppresses inflammation in multiple cell types within an inflamed joint.

Glucosamine Hydrochloride but Not Chondroitin Sulfate Prevents Cartilage Degradation and Inflammation Induced by Interleukin-1α in Bovine Cartilage Explants

OBJECTIVE

Glucosamine hydrochloride (GH) and chondroitin sulfate (CS) are commonly used for the treatment of osteoarthritis (OA). The aim of this study was to assess their effects, alone and in combination, on preventing aggrecan degradation and inflammation in an in vitro model of OA.

DESIGN

To test the effects of GH and/or CS as a preventative treatment, cartilage explants were pretreated with the compound(s) using concentrations that showed no detrimental effect on chondrocyte viability. Interleukin-1α (IL-1α) was added to induce cartilage degradation, supernatant and explants were analyzed for proteoglycan degradation products, aggrecanase mRNA expression and activity, and for the release of inflammatory markers.

RESULTS

Following treatment with IL-1α, 2 mg/mL dose of GH pretreatment was associated with a reduction of glycosaminoglycan release, reduced generation of the pathological interglobular domain aggrecan catabolites, decreased mRNA levels of ADAMTS-4 and -5 and reduced activity of ADAMTS-4. In contrast, CS alone did not have a significant effect on IL-1α-induced cartilage degradation and the addition of 0.4 mg/mL CS to 2 mg/mL GH did not further inhibit IL-1α-induced activity. Pretreatment with 2 mg/mL GH also reduced the release of inflammatory markers, prostaglandin E2 and nitric oxide induced by IL-1α while CS did not have a significant effect.

CONCLUSIONS

The results suggest that GH prevents cartilage degradation mediated by aggrecanases ADAMTS-4 and -5, and may also reduce inflammation. This could be part of the mechanisms by which GH is effective in maintaining joint integrity and function, and preventing or delaying early symptoms of OA.

Inhibition of aggrecanases as a therapeutic strategy in osteoarthritis

Over the last decade, there has been a large effort to target aggrecanases, which are responsible for the degradation of the aggrecan in the extracellular matrix of joints, in order to hopefully lead to new treatments for osteoarthritis. Only a few inhibitors have been effective in explants or rodent models and thus only a few have reached the clinic, none of which have proven to be effective. In this article, a survey of chemical series is described, covering historical and recent inhibitors and highlighting how some of their problems were resolved, with a critical overview of the challenges encountered. A large effort should be undertaken in designing smaller compounds with higher residence times, defining new interaction sites on the aggrecanases and exploiting target flexibility.

Absolute quantification of selected proteins in the human osteoarthritic secretome

Osteoarthritis (OA) is characterized by a loss of extracellular matrix which is driven by catabolic cytokines. Proteomic analysis of the OA cartilage secretome enables the global study of secreted proteins. These are an important class of molecules with roles in numerous pathological mechanisms. Although cartilage studies have identified profiles of secreted proteins, quantitative proteomics techniques have been implemented that would enable further biological questions to be addressed. To overcome this limitation, we used the secretome from human OA cartilage explants stimulated with IL-1β and compared proteins released into the media using a label-free LC-MS/MS-based strategy. We employed QconCAT technology to quantify specific proteins using selected reaction monitoring. A total of 252 proteins were identified, nine were differentially expressed by IL-1 β stimulation. Selected protein candidates were quantified in absolute amounts using QconCAT. These findings confirmed a significant reduction in TIMP-1 in the secretome following IL-1β stimulation. Label-free and QconCAT analysis produced equivocal results indicating no effect of cytokine stimulation on aggrecan, cartilage oligomeric matrix protein, fibromodulin, matrix metalloproteinases 1 and 3 or plasminogen release. This study enabled comparative protein profiling and absolute quantification of proteins involved in molecular pathways pertinent to understanding the pathogenesis of OA.

Transport and binding of tumor necrosis factor-α in articular cartilage depend on its quaternary structure

The effect of tumor necrosis factor-α (TNFα) on cartilage matrix degradation is mediated by its transport and binding within the extracellular matrix (ECM) of the tissue, which mediates availability to cell receptors. Since the bioactive form of TNFα is a homotrimer of monomeric subunits, conversion between trimeric and monomeric forms during intratissue transport may affect binding to ECM and, thereby, bioactivity within cartilage. We studied the transport and binding of TNFα in cartilage, considering the quaternary structure of this cytokine. Competitive binding assays showed significant binding of TNFα in cartilage tissue, leading to an enhanced uptake. However, studies in which TNFα was cross-linked to remain in the trimeric form revealed that the binding of trimeric TNFα was negligible. Thus, binding of TNFα to ECM was associated with the monomeric form. Binding of TNFα was not disrupted by pre-treating cartilage tissue with trypsin, which removes proteoglycans and glycoproteins but leaves the collagen network intact. Therefore, proteoglycan loss during osteoarthritis should only alter the passive diffusion of TNFα but not its binding interaction with the remaining matrix. Our results suggest that matrix binding and trimer-monomer conversion of TNFα both play crucial roles in regulating the accessibility of bioactive TNFα within cartilage.

Biomimetic aggrecan reduces cartilage extracellular matrix from degradation and lowers catabolic activity in ex vivo and in vivo models

Aggrecan, a major macromolecule in cartilage, protects the extracellular matrix (ECM) from degradation during the progression of osteoarthritis (OA). However, aggrecan itself is also susceptible to proteolytic cleavage. Here, the use of a biomimetic proteoglycan (mAGC) is presented, which functionally mimics aggrecan but lacks the known cleavage sites, protecting the molecule from proteolytic degradation. The objective of this study is to test the efficacy of this molecule in ex vivo (human OA synovial fluid) and in vivo (Sprague-Dawley rats) osteoarthritic models. These results indicate that mAGC's may protect articular cartilage against the loss of key ECM components, and lower catabolic protein and gene expression in both models. This suppression of matrix degradation has the potential to provide a healthy environment for tissue repair.

Genetic polymorphisms associated with intervertebral disc degeneration

BACKGROUND CONTEXT

Disc degeneration (DD) is a multifaceted chronic process that alters the structure and function of the intervertebral discs and can lead to painful conditions. The pathophysiology of degeneration is not well understood, but previous studies suggest that certain genetic polymorphisms may be important contributing factors leading to an increased risk of DD.

PURPOSE

To review the genetic factors in DD with a focus on polymorphisms and their putative role in the pathophysiology of degeneration. Elucidating the genetic components that are associated with degeneration could provide insights into the mechanism of the process. Furthermore, defining these relationships and eventually using them in a clinical setting may allow an identification and early intervention for those who are at a high risk for painful DD.

STUDY DESIGN

Literature review.

METHODS

This literature review focused on the studies concerning genetic polymorphisms and their associations with DD.

RESULTS

Genetic polymorphisms in 20 genes have been analyzed in association with DD, including vitamin D receptor, growth differentiation factor 5 (GDF5), aggrecan, collagen Types I, IX, and XI, fibronectin, hyaluronan and proteoglycan link protein 1 (HAPLN1), thrombospondin, cartilage intermediate layer protein (CILP), asporin, MMP1, 2, and 3, parkinson protein 2, E3 ubiquitin protein ligase (PARK2), proteosome subunit β type 9 (PSMB9), tissue inhibitor of metalloproteinase (TIMP), cyclooxygenase-2 (COX2), and IL1α, IL1β, and IL6. Each genetic polymorphism codes for a protein that has a functional role in the pathogenesis of DD.

CONCLUSIONS

There are known associations between several genetic polymorphisms and DD. Of the 20 genes analyzed, polymorphisms in vitamin D receptor, aggrecan, Type IX collagen, asporin, MMP3, IL1, and IL6 show the most promise as functional variants. Genetic studies are crucial for understanding the mechanism of the degeneration. This genetic information could eventually be used as a predictive model for determining a patient's risk for symptomatic DD.

Cell-penetrating peptides released from thermosensitive nanoparticles suppress pro-inflammatory cytokine response by specifically targeting inflamed cartilage explants

Cell-penetrating anti-inflammatory peptide KAFAKLAARLYRKALARQLGVAA (KAFAK) has the ability to suppress pro-inflammatory cytokines TNF-α and IL-6 when released from degradable and non-degradable poly(NIPAm-AMPS) nanoparticles. In vitro human macrophage model with THP1 human monocytes and ex vivo bovine knee cartilage tissue both showed a dose-dependent suppression of pro-inflammatory cytokines when treated with KAFAK-loaded poly(NIPAm-AMPS) nanoparticles. When bovine knee cartilage explants were treated with KAFAK-loaded poly(NIPAm-AMPS) nanoparticles, rapid and highly selective targeting of only damaged tissue occurred. This study has demonstrated selective targeting and therapeutic efficacy of KAFAK when released from both degradable and non-degradable poly(NIPAm-AMPS) nanoparticles in in vitro and ex vivo models. As a result, poly(NIPAm-AMPS) nanoparticles loaded with KAFAK could be a very effective tool to treat osteoarthritis.

FROM THE CLINICAL EDITOR

Inflammatory arthritis remains a major medical problem with substantial socio-economic impact. Anti-inflammatory KAFAK peptide when released from degradable and non-degradable poly(NIPAm-AMPS) nanoparticles has the ability to penetrate cells and suppress pro-inflammatory cytokines, resulting in rapid and highly selective targeting of only damaged tissue in bovine knee cartilage explants. This approach may provide a very effective future tool in addressing osteoarthritis.

The association between changes in synovial fluid levels of ARGS-aggrecan fragments, progression of radiographic osteoarthritis and self-reported outcomes: a cohort study

OBJECTIVE

To investigate whether change in concentrations over time of aggrecanase generated ARGS-aggrecan in synovial fluid (SF ARGS) associates with progression of radiographic knee osteoarthritis (OA) and patient-reported outcome in subjects with previous meniscectomy.

METHODS

We studied 141 subjects at two time points after meniscectomy. Time point A was on average 18 years after meniscectomy, time point B was on average 7.5 years later; 74 subjects had SF available from both examinations. We measured SF ARGS by an electrochemiluminescence immunoassay, graded radiographic features of tibiofemoral or patellofemoral OA according to the Osteoarthritis Research Society International (OARSI) atlas, and scored patient-reported outcomes using the Knee Injury and Osteoarthritis Outcome Score (KOOS). Using logistic regression (adjusted for age, gender, body mass index, time between examinations, and SF ARGS at first examination) we assessed associations between change in SF ARGS between first and second examinations and progression of radiographic OA and KOOS.

RESULTS

In subjects with decreasing SF ARGS between examinations, the likelihood of loss of joint space and worsening of KOOS pain between examinations was increased 6- and 4-fold respectively compared to those increasing in SF ARGS (odds ratio (OR) 5.72; 95% confidence interval (CI) 1.53-21.4 and 3.66; 1.01-13.2, respectively). No significant associations were seen between decreasing SF ARGS and progression of osteophytes (OR 0.88; 0.28-2.78), or for patient-reported outcomes other than KOOS pain.

CONCLUSION

Having decreasing levels of SF ARGS over time was associated with an increased risk of loss of joint space and pain worsening, but showed no association with other patient-reported outcomes or osteophyte progression.

Chondrocyte AMP-activated protein kinase activity suppresses matrix degradation responses to proinflammatory cytokines interleukin-1β and tumor necrosis factor α

OBJECTIVE

Interleukin-1β (IL-1β) and tumor necrosis factor α (TNFα) stimulate chondrocyte matrix catabolic responses, thereby compromising cartilage homeostasis in osteoarthritis (OA). AMP-activated protein kinase (AMPK), which regulates energy homeostasis and cellular metabolism, also exerts antiinflammatory effects in multiple tissues. This study was undertaken to test the hypothesis that AMPK activity limits chondrocyte matrix catabolic responses to IL-1β and TNFα.

METHODS

Expression of AMPK subunits was examined, and AMPKα activity was ascertained by the phosphorylation status of AMPKα Thr(172) in human knee articular chondrocytes and cartilage by Western blotting and immunohistochemistry, respectively. Procatabolic responses to IL-1β and TNFα, such as release of glycosaminoglycan, nitric oxide, and matrix metalloproteinases 3 and 13 were determined by dimethylmethylene blue assay, Griess reaction, and Western blotting, respectively, in cartilage explants and chondrocytes with and without knockdown of AMPKα by small interfering RNA.

RESULTS

Normal human knee articular chondrocytes expressed AMPKα1, α2, β1, β2, and γ1 subunits. AMPK activity was constitutively present in normal articular chondrocytes and cartilage, but decreased in OA articular chondrocytes and cartilage and in normal chondrocytes treated with IL-1β and TNFα. Knockdown of AMPKα resulted in enhanced catabolic responses to IL-1β and TNFα in chondrocytes. Moreover, AMPK activators suppressed cartilage/chondrocyte procatabolic responses to IL-1β and TNFα and the capacity of TNFα and CXCL8 (IL-8) to induce type X collagen expression.

CONCLUSION

Our findings indicate that AMPK activity is reduced in OA cartilage and in chondrocytes following treatment with IL-1β or TNFα. AMPK activators attenuate dephosphorylation of AMPKα and procatabolic responses in chondrocytes induced by these cytokines. These observations suggest that maintenance of AMPK activity supports cartilage homeostasis by protecting cartilage matrix from inflammation-induced degradation.

Investigating ADAMTS-mediated aggrecanolysis in mouse cartilage

Proteolysis of the cartilage proteoglycan aggrecan is a feature of arthritis. We present a method for analyzing aggrecanolysis in in vitro cultures of 3-week-old mouse femoral head cartilage based on traditional methods developed for large animal species. Investigators can choose either a simple analysis that detects several aggrecan fragments released into culture medium only or a more comprehensive study that detects all fragments present in both the medium and the cartilage matrix. The protocol comprises (i) cartilage culture and optional cartilage extraction, (ii) a quick and simple colorimetric assay for quantitating aggrecan and (iii) neoepitope western blotting to identify specific aggrecan fragments partitioning to the medium or cartilage compartments. The crucial difference between the methods for mice and larger animals is that the proportion of aggrecan in a given sample is normalized to total aggrecan rather than to tissue wet weight. This necessary break from tradition arises because tiny volumes of liquid clinging to mouse cartilage can increase the apparent tissue wet weight, causing unacceptable errors. The protocol has broad application for the in vitro analysis of transgenic mice, particularly those with mutations that affect cartilage remodeling, arthritic disease and skeletal development. The protocol is robust, reliable and takes 7-11 d to complete.

Eicosapentaenoic acid and docosahexaenoic acid reduce interleukin-1β-mediated cartilage degradation

INTRODUCTION

In inflammatory joint disease, such as osteoarthritis (OA), there is an increased level of proinflammatory cytokines, such as interleukin (IL)-1β. These cytokines stimulate the production of matrix metalloproteinases (MMPs), which leads to the degradation of the cartilage extracellular matrix and the loss of key structural components such as sulphated glycosaminoglycan (sGAG) and collagen II. The aim of this study was to examine the therapeutic potential of n-3 polyunsaturated fatty acids (PUFAs) in an in vitro model of cartilage inflammation.

METHODS

Two specific n-3 compounds were tested, namely, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), each at 0.1, 1 and 10 μM. Full thickness bovine cartilage explants, 5 mm in diameter, were cultured for 5 days with or without IL-1β and in the presence or absence of each n-3 compound. The media were replaced every 24 hours and assayed for sGAG content using the 1,9-dimethylmethylene blue (DMB) method. Chondrocyte viability was determined at the end of the culture period using fluorescence microscopy to visualise cells labelled with calcein AM and ethidium homodimer.

RESULTS

Treatment with IL-1β (10 ng.ml⁻¹) produced a large increase in sGAG release compared to untreated controls, but with no effect on cell viability, which was maintained above 80% for all treatments. In the absence of IL-1β, both n-3 compounds induced a mild catabolic response with increased loss of sGAG, particularly at 10 μM. By contrast, in the presence of IL-1β, both EPA and DHA at 0.1 and 1 μM significantly reduced IL-1β-mediated sGAG loss. The efficacy of the EPA treatment was maintained at approximately 75% throughout the 5-day period. However, at the same concentrations, the efficacy of DHA, although initially greater, reduced to approximately half that of EPA after 5 days. For both EPA and DHA, the highest dose of 10 μM was less effective.

CONCLUSIONS

The results support the hypothesis that n-3 compounds are anti-inflammatory through competitive inhibition of the arachidonic acid oxidation pathway. The efficacy of these compounds is likely to be even greater at more physiological levels of IL-1β. Thus we suggest that n-3 PUFAs, particularly EPA, have exciting therapeutic potential for preventing cartilage degradation associated with chronic inflammatory joint disease.

Development of an in vitro model of feline cartilage degradation

Osteoarthritis is the most common arthropathy of mammalian species including cats. Cartilage degradation is central to the disorder and here we present, for the first time, an in vitro model of feline cartilage degradation which will be useful for further studies in this target species. Feline articular cartilage explant cultures were maintained for 28 days and in the presence of oncostatin M with and without interleukin (IL)-17, tumour necrosis factor (TNF), IL-1α, or IL-1β. Media samples and digested cartilage explants were analysed for glycosaminoglycan (GAG) and collagen content. The combination of IL-1β and OSM, both at 20 ng/ml, was able to promote GAG release to the greatest extent at 14 days. At 28 days, all groups showed relatively high release of GAG. At 14 days, only IL-1β and OSM in combination were associated with a statistically significant increase in collagen release over and above control tissue. IL-1β dose-response studies showed that an IL-1β dose of 10 ng/ml promotes a statistically significant increase in GAG breakdown when used with OSM, and higher doses of IL-1β did not result in significantly greater response. The model demonstrated both GAG and collagen degradation and will be of use for further understanding of feline cartilage metabolism and for screening of potential structure-modifying agents to be used in cats.

Transport and equilibrium uptake of a peptide inhibitor of PACE4 into articular cartilage is dominated by electrostatic interactions

The availability of therapeutic molecules to targets within cartilage depends on transport through the avascular matrix. We studied equilibrium partitioning and non-equilibrium transport into cartilage of Pf-pep, a 760 Da positively charged peptide inhibitor of the proprotein convertase PACE4. Competitive binding measurements revealed negligible binding of Pf-pep to sites within cartilage. Uptake of Pf-pep depended on glycosaminoglycan charge density, and was consistent with predictions of Donnan equilibrium given the known charge of Pf-pep. In separate transport experiments, the diffusivity of Pf-pep in cartilage was measured to be approximately 1 x 10(-6) cm(2)/s, close to other similarly-sized non-binding solutes. These results suggest that small positively charged therapeutics will have a higher concentration within cartilage than in the surrounding synovial fluid, a desired property for local delivery; however, such therapeutics may rapidly diffuse out of cartilage unless there is additional specific binding to intra-tissue substrates that can maintain enhanced intra-tissue concentration for local delivery.

Mechanical load inhibits IL-1 induced matrix degradation in articular cartilage

OBJECTIVE

Osteoarthritis is a disease process of cellular degradation of articular cartilage caused by mechanical loads and inflammatory cytokines. We studied the cellular response in native cartilage subjected to a mechanical load administered simultaneously with an inflammatory cytokine interleukin-1 (IL-1), hypothesizing that the combination of load and cytokine would result in accelerated extracellular matrix (ECM) degradation.

METHODS

Mature bovine articular cartilage was loaded for 3 days (stimulation) with 0.2 and 0.5 MPa stresses, with and without IL-1 (IL-1alpha, 10 ng/ml), followed by 3 days of no stimulation (recovery). Aggrecan and collagen loss were measured as well as aggrecan cleavage using monoclonal antibodies AF-28 and BC-3 for cleavage by aggrecanases (ADAMTS) and matrix metalloproteinases (MMPs), respectively.

RESULTS

Incubation with IL-1 caused aggrecan cleavage by aggrecanases and MMPs during the 3 days of stimulation. A load of 0.5 MPa inhibited the IL-1-induced aggrecan loss while no inhibition was found for the 0.2 MPa stress. There was no collagen loss during the treatments but upon load and IL-1 removal proteoglycan and collagen loss increased. Load itself under these conditions was found to have no effect when compared to the unloaded controls.

CONCLUSIONS

A mechanical load of sufficient magnitude can inhibit ECM degradation by chondrocytes when stimulated by IL-1. The molecular mechanisms involved in this process are not clear but probably involve altered mechanochemical signal transduction between the ECM and chondrocyte.

Proteinases involved in matrix turnover during cartilage and bone breakdown

The joint is a discrete unit that consists of cartilage, bone, tendon and ligaments. These tissues are all composed of an extracellular matrix made of collagens, proteoglycans and specialised glycoproteins that are actively synthesised, precisely assembled and subsequently degraded by the resident connective tissue cells. A balance is maintained between matrix synthesis and degradation in healthy adult tissues. Different classes of proteinases play a part in connective tissue turnover in which active proteinases can cleave matrix protein during resorption, although the proteinase that predominates varies between different tissues and diseases. The metalloproteinases are potent enzymes that, once activated, degrade connective tissue and are inhibited by tissue inhibitors of metalloproteinases (TIMPs); the balance between active matrix metalloproteinases and TIMPs determines, in many tissues, the extent of extracellular matrix degradation. The serine proteinases are involved in the initiation of activation cascades and some, such as elastase, can directly degrade the matrix. Cysteine proteinases are responsible for the breakdown of collagen in bone following the removal of the osteoid layer and the attachment of osteoclasts to the exposed bone surface. Various growth factors increase the synthesis of matrix and proteinase inhibitors, whereas cytokines (alone or in combination) can inhibit matrix synthesis and stimulate proteinase production and matrix destruction.

Composition-function relationships during IL-1-induced cartilage degradation and recovery

OBJECTIVE

To examine the relationships between biochemical composition and mechanical properties of articular cartilage explants during interleukin-1 (IL-1)-induced degradation and post-exposure recovery.

DESIGN

Bovine articular cartilage explants were cultured for up to 32 days with or without 20 ng/mL IL-1. The dynamic shear modulus |G*(dyn)| and equilibrium and dynamic unconfined compression moduli (E(equil) and |E*(dyn)|) were measured at intervals throughout the culture period. In a subsequent recovery study, explants were cultured for 4 days with or without 20ng/mL IL-1 and for an additional 16 days in control media. The dynamic moduli |E*(dyn)| and |G*(dyn)| were measured at intervals during degeneration and recovery. Conditioned media and explant digests were assayed for sulfated glycosaminoglycans (sGAG) and collagen content.

RESULTS

Continuous IL-1 stimulation triggered progressive decreases in E(equil), |E*(dyn)|, and |G*(dyn)| concomitant with the sequential release of sGAG and collagen from the explants. Brief IL-1 exposure resulted in a short release of sGAG but not collagen, followed by a gradual and incomplete repopulation of sGAG. The temporary sGAG depletion was associated with decreases in both |E*(dyn)| and |G*(dyn)| which also recovered after removal of IL-1. During IL-1-induced degradation and post-exposure recovery, explant mechanical properties correlated well with tissue sGAG concentration.

CONCLUSIONS

As previously shown for developing cartilages and engineered cartilage constructs, cytokine-induced changes in sGAG concentration (i.e., fixed charge density) are coincident with changes in compressive and shear properties of articular cartilage. Further, recovery of cartilage mechanical properties can be achieved by relief from proinflammatory stimuli and subsequent restoration of tissue sGAG concentration.

Catabolic responses of chondrocyte-seeded peptide hydrogel to dynamic compression

This study investigated the role of matrix metalloproteases and aggrecanases during dynamic compression-induced aggrecan catabolism in chondrocyte-seeded self-assembling peptide hydrogel. One- to two-week-old bovine chondrocytes were encapsulated into peptide hydrogel and cultured for 14 days prior to the application of an alternate day loading protocol. Dynamic compression-induced aggrecan catabolism was explored by evaluating GAG loss to the culture medium, zymography for matrix metalloproteases (MMPs), gene expression of MMPs and ADAMTS proteases, and Western blot analysis for aggrecan fragments. The application of loading over 4 days increased GAG loss to the medium three- to four-fold relative to free-swelling controls. Zymogram analysis detected increased concentrations of latent MMP-9 and MMP-3 in the culture medium relative to free-swelling culture. Real-time PCR showed expression levels of MMPs and ADAMTS proteases in loaded samples that ranged from 2.5- to 95-fold higher than free-swelling culture. Aggrecan fragment analysis did not detect small (50-80 kDa) molecular weight fragments in free-swelling culture; however, dynamic compression samples contained 60-80 kDa fragments that were detected by both anti-G1 and NITEGE probes, demonstrating ADAMTS but not MMP degradation. These data suggest that partially mature cartilage tissue engineering constructs may be susceptible to catabolic degradation.

Modified expression of the ADAMTS enzymes and tissue inhibitor of metalloproteinases 3 during human intervertebral disc degeneration

OBJECTIVE

Intervertebral disc degeneration is linked to loss of extracellular matrix (ECM), particularly the early loss of aggrecan. A group of metalloproteinases called aggrecanases are important mediators of aggrecan turnover. The present study was undertaken to investigate the expression of the recognized aggrecanases and their inhibitor, tissue inhibitor of metalloproteinases 3 (TIMP-3), in human intervertebral disc tissue.

METHODS

Twenty-four nondegenerated and 30 degenerated disc samples were analyzed for absolute messenger RNA (mRNA) copy number of ADAMTS 1, 4, 5, 8, 9, and 15 and TIMP-3 by real-time reverse transcription-polymerase chain reaction. Thirty-six formalin-fixed embedded intervertebral disc samples of varying grades of degeneration were used for immunohistochemical analyses. In addition, samples from 8 subjects were analyzed for the presence of matrix metalloproteinase (MMP)- and aggrecanase-generated aggrecan products.

RESULTS

Messenger RNA for all the aggrecanases other than ADAMTS-8 was identified in intervertebral disc tissue, as was mRNA for TIMP-3. Levels of mRNA expression of ADAMTS 1, 4, 5, and 15 were significantly increased in degenerated tissue compared with nondegenerated tissue. All these aggrecanases and TIMP-3 were also detected immunohistochemically in disc tissue, and numbers of nucleus pulposus cells staining positive for ADAMTS 4, 5, 9, and 15 were significantly increased in degenerated tissue compared with nondegenerated tissue. Aggrecan breakdown products generated by MMP and aggrecanase activities were also detected in intervertebral disc tissue.

CONCLUSION

The aggrecanases ADAMTS 1, 4, 5, 9, and 15 may contribute to the changes occurring in the ECM during intervertebral disc degeneration. Targeting these enzymes may be a possible future therapeutic strategy for the prevention of intervertebral disc degeneration and its associated morbidity.

Effects of alendronate on a disintegrin and metalloproteinase with thrombospondin motifs expression in the developing epiphyseal cartilage in rats

A disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS) have been reported to play a role in the degradation of aggrecan, a major component of cartilage. This study was performed to examine the effects of alendronate on the expression of ADAMTS in developing femoral epiphyseal cartilage. Primary cultured chondrocytes from this cartilage were treated with alendronate in vitro and postnatal day 1 rats were injected subcutaneously with alendronate (1 mg/kg) every second day in vivo. The number of cultured chondrocytes and their aggrecan mRNA levels were unaffected by the alendronate treatment at 10(-6) to 10(-4) M concentrations. The mRNA levels of ADAMTS-1, -2 and -9 in chondrocytes were also unaffected. However, the levels of ADAMTS-5 and -4 were reduced significantly by the same treatment. The thickness of the proliferating chondrocyte layers and the aggrecan mRNA levels in the epiphysis were unaffected by the alendronate treatment in vivo. However, the hypertrophied chondrocyte layers became significantly thicker, and the size of the secondary ossification centre was reduced significantly by the same treatment (P < 0.05). Both ADAMTS-4 and -5 mRNA expressions were also reduced significantly in vivo. The immunoreactivity against ADAMTS-4 was seen in hypertrophied chondrocytes and reduced significantly by the alendronate treatment. These results suggested that alendronate can inhibit the degradation of aggrecan in the articular cartilage by downregulating the expression of matrix enzymes such as ADAMTS-4 and -5.

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.

Characterization of an ADAMTS-5-mediated cleavage site in aggrecan in OSM-stimulated bovine cartilage

OBJECTIVE

In a previous study, we identified a 50-kDa G3-containing aggrecan degradation product in bovine cartilage, released from the tissue after interleukin-1 (IL-1) stimulation in the presence of oncostatin M (OSM). Our objective was to purify, determine the N-terminal sequence of this fragment and verify whether this cleavage could be attributed to a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)-4 and ADAMTS-5 action in vitro.

METHODS

Collected media from bovine cartilage explant cultures stimulated with IL-1+OSM were subjected to anion-exchange chromatography. The N-terminal sequence of the fragment of interest in the purified fractions was determined by automated Edman sequencing. Fetal bovine aggrecan was digested with full-length recombinant ADAMTS-4 and ADAMTS-5 and resulting degradation products were analyzed by sodium dodecyl sulfate/polyacrylamide gel electrophoresis (SDS/PAGE) and immunoblotting using an anti-G3 antiserum and an anti-neoepitope antibody that had been generated to the new N-terminus of the G3 fragment.

RESULTS

Characterization of the 50-kDa fragment showed that it possesses chondroitin sulfate (CS) and is the result of a cleavage within the C-terminal portion of the CS-2 domain, adjacent to the G3 region. Sequence analysis identified the cleavage region as TQRPAE(2047)-(2048)ARLEIE, suggesting an aggrecanase-derived product. Using an anti-neoepitope antibody specific for the additional cleavage site, it was shown that the product is generated in vitro upon digestion of aggrecan by ADAMTS-5 and, to a much lesser extent, by ADAMTS-4.

CONCLUSIONS

The abundance and rapid rate of release of this degradation product in organ cultures in the presence of OSM suggest that it could result from a unique aggrecan proteolysis mediated by aggrecanases.

Evidence of a novel aggrecan-degrading activity in cartilage: Studies of mice deficient in both ADAMTS-4 and ADAMTS-5

OBJECTIVE

To characterize aggrecan catabolism and the overall phenotype in mice deficient in both ADAMTS-4 and ADAMTS-5 (TS-4/TS-5 Delta-cat) activity.

METHODS

Femoral head cartilage from the joints of TS-4/TS-5 Delta-cat mice and wild-type mice were cultured in vitro, and aggrecan catabolism was stimulated with either interleukin-1alpha (IL-1alpha) or retinoic acid. Total aggrecan release was measured, and aggrecanase activity was examined by Western blotting using neoepitope antibodies for detecting cleavage at EGE 373-374 ALG, SELE 1279-1280 GRG, FREEE 1467-1468 GLG, and AQE 1572-1573 AGEG. Aggrecan catabolism in vivo was examined by Western blotting of cartilage that had been extracted immediately ex vivo.

RESULTS

TS-4/TS-5 Delta-cat mice were viable, fertile, and phenotypically normal. TS-4/TS-5 Delta-cat cartilage explants did not release aggrecan in response to IL-1alpha, and there was no detectable increase in aggrecanase neoepitopes. TS-4/TS-5 Delta-cat cartilage explants released aggrecan in response to retinoic acid. There was no retinoic acid-stimulated cleavage at either EGE 373-374 ALG or AQE 1572-1573 AGEG. There was a low level of cleavage at SELE 1279-1280 GRG and major cleavage at FREEE 1467-1468 GLG. Ex vivo, cleavage at FREEE 1467-1468 GLG was substantially reduced, but still present, in TS-4/TS-5 Delta-cat mouse cartilage compared with wild-type mouse cartilage.

CONCLUSION

An aggrecanase other than ADAMTS-4 and ADAMTS-5 is expressed in mouse cartilage and is up-regulated by retinoic acid but not IL-1alpha. The novel aggrecanase appears to have different substrate specificity from either ADAMTS-4 or ADAMTS-5, cleaving E-G bonds but not E-A bonds. Neither ADAMTS-4 nor ADAMTS-5 is required for normal skeletal development or aggrecan turnover in cartilage.

Promotion of the articular cartilage proteoglycan degradation by T-2 toxin and selenium protective effect

OBJECTIVE

To identify the relationship between T-2 toxin and Kashin-Beck disease (KBD), the effects of T-2 toxin on aggrecan metabolism in human chondrocytes and cartilage were investigated in vitro.

METHODS

Chondrocytes were isolated from human articular cartilage and cultured in vitro. Hyaluronic acid (HA), soluble CD44 (sCD44), IL-1beta and TNF-alpha levels in supernatants were measured by enzyme-linked immunosorbent assay (ELISA). CD44 content in chondrocyte membrane was determined by flow cytometry (FCM). CD44, hyaluronic acid synthetase-2 (HAS-2) and aggrecanases mRNA levels in chondrocytes were determined using reverse transcription polymerase chain reaction (RT-PCR). Immunocytochemical method was used to investigate expressions of BC-13, 3-B-3(-) and 2-B-6 epitopes in the cartilage reconstructed in vitro.

RESULTS

T-2 toxin inhibited CD44, HAS-2, and aggrecan mRNA expressions, but promoted aggrecanase-2 mRNA expression. Meanwhile, CD44 expression was found to be the lowest in the chondrocytes cultured with T-2 toxin and the highest in control plus selenium group. In addition, ELISA results indicated that there were higher sCD44, IL-1beta and TNF-alpha levels in T-2 toxin group. Similarly, higher HA levels were also observed in T-2 toxin group using radioimmunoprecipitation assay (RIPA). Furthermore, using monoclonal antibodies BC-13, 3-B-3 and 2-B-6, strong positive immunostaining was found in the reconstructed cartilage cultured with T-2 toxin, whereas no positive staining or very weak staining was observed in the cartilage cultured without T-2 toxin. Selenium could partly inhibit the effects of T-2 toxin above.

CONCLUSION

T-2 toxin could inhibit aggrecan synthesis, promote aggrecanases and pro-inflammatory cytokines production, and consequently induce aggrecan degradation in chondrocytes. These will perturb metabolism balance between aggrecan synthesis and degradation in cartilage, inducing aggrecan loss in the end, which may be the initiation of the cartilage degradation.

Nitric oxide enhances aggrecan degradation by aggrecanase in response to TNF-alpha but not IL-1beta treatment at a post-transcriptional level in bovine cartilage explants

OBJECTIVE

The objective of this study was to determine the role of nitric oxide (NO) in tumor necrosis factor alpha (TNF-alpha)-induced matrix damage, compared to interleukin 1 beta (IL-1beta), in bovine cartilage explant cultures.

METHODS

Cartilage explants were subjected to treatment with TNF-alpha (100ng/ml), IL-1beta (10 ng/ml) and to the nitric oxide synthase inhibitor, N-methyl-arginine (L-NMA; 1.25 mM) for 26, 50 or 120 h (5 days). The collected medium was analyzed for sulfated glycosaminoglycan (sGAG), nitrate and nitrite, matrix metalloproteinase (MMP) activity by zymography, and aggrecan degradation by immunoblotting of aggrecan-G1 and aggrecan-G1-NITEGE fragments. RNA was extracted from the 26 and 50 h treated explants for real time quantitative PCR analyses.

RESULTS

TNF-alpha and IL-1beta treatment caused a 3-5 fold increase in sGAG release with an increase in aggrecanase-specific aggrecan breakdown and an increase in nitrate and nitrite production. L-NMA treatment inhibited almost 50% of the sGAG release caused by TNF-alpha treatment, with concomitant decrease in the aggrecanase-specific-NITEGE neo-epitope of aggrecan released into the medium. No L-NMA effect was identified with IL-1beta. TNF-alpha and IL-1beta both increased a disintegrin and matrix metalloproteinase with thrombospondin motif (ADAMTS)4 and ADAMTS5 transcription with no effect by L-NMA, suggesting that NO regulates aggrecanase activity at a post-transcriptional level in response to TNF-alpha. TNF-alpha and IL-1beta both caused an increase in protease transcription (MMP-3, MMP-13, ADAMTS4 and ADAMTS5) and in pro-inflammatory enzymes, inducible nitric oxide synthase and cyclooxygenase (COX)-2, as well as a decrease in matrix protein transcription, including collagen II, aggrecan, fibromodulin and link protein (IL-1beta only), and an increase in MMP-3 and MMP-9 secretion. L-NMA had no effect on gene transcription or MMP secretion.

CONCLUSION

NO regulates aggrecanase activity at a post-transcriptional level in response to TNF-alpha treatment while having no effect on IL-1beta treated cartilage explants.

Low molecular weight isoforms of the aggrecanases are responsible for the cytokine-induced proteolysis of aggrecan in a porcine chondrocyte culture system

OBJECTIVE

The major proteases responsible for aggrecan turnover in articular cartilage are the aggrecanases (ADAMTS-4 and ADAMTS-5). Although several studies have demonstrated C-terminal truncation of these aggrecanases, the mechanism and importance of this processing are poorly understood. The objective of this study was to further investigate ADAMTS-4 and ADAMTS-5 C-terminal truncation in a porcine model in vitro culture system.

METHODS

Chondrocyte-agarose cultures with well-established extracellular matrices were treated with or without interleukin-1 (IL-1), for a variety of different culture time periods. Cultures were analyzed for release of sulfated glycosaminoglycan, aggrecanase-generated interglobular domain (IGD)-aggrecan cleavage, and the presence of ADAMTS-4 and ADAMTS-5 isoforms. Inhibition of aggrecanase activity with monoclonal antibodies, tissue inhibitor of metalloproteinases 3 (TIMP-3), and cycloheximide pretreatment were used to identify ADAMTS isoforms involved in IGD-aggrecan catabolism.

RESULTS

Multiple isoforms, including possible zymogens, of ADAMTS-4 and ADAMTS-5 were sequestered within the extracellular matrix formed by 3-week chondrocyte-agarose cultures. IL-1 exposure induced production of a low molecular weight (37 kd) isoform of ADAMTS-4. This isoform was capable of degrading exogenous aggrecan at the IGD-aggrecanase site, was inhibited by TIMP-3, was blocked after preincubation with an antibody to a sequence in the catalytic domain of ADAMTS-4, and required de novo synthesis in the presence of IL-1 for its generation.

CONCLUSION

In porcine chondrocyte-agarose cultures, a 37-kd ADAMTS-4 isoform appears to be the major matrix protease responsible for the IGD-aggrecanase activity detected in response to exposure to IL-1. This conclusion contradicts that of recent studies of transgenic knockout mice and highlights the need to determine the roles of the different aggrecanase(s) in human disease.

Aggrecanases and aggrecanase-generated fragments in the human intervertebral disc at early and advanced stages of disc degeneration

STUDY DESIGN

A comparative study of aggrecanases and aggrecan fragmentation profile in the human intervertebral disc at early and advanced stages of disc degeneration.

OBJECTIVE

To determine differences in the content of the aggrecanases and the profile of aggrecan fragmentation in early and advanced stages of disc degeneration using cadaveric human intervertebral discs.

SUMMARY OF BACKGROUND DATA

Aggrecanases and aggrecanase-generated aggrecan fragments have been found in human degenerated discs. However, the association between the grade of disc degeneration and the content of the aggrecanases and the profile of aggrecan fragments has not been well studied.

METHODS

A total of 108 cadaveric donor spines were assessed by MRI T2 imaging and graded based on the Thompson scale. Twelve donor spines (average age, 63 years), each specifically exhibiting 2 different stages (Grade 2 and Grade 4) of disc degeneration at different disc levels, were included in this study. After harvesting the preselected discs, tissue samples were obtained from the center of the nucleus pulposus (NP) and the middle zone of the anulus fibrosus (AF). The amount of the aggrecanases, specifically ADAMTS-4 and ADAMTS-5, and the pattern of aggrecan fragmentation in the isolated tissues were assessed by western blot using specific antibodies.

RESULTS

In both NP and the AF tissues, the amount of ADAMTS-4 detected was higher in disc tissues with a higher level of degeneration (Grade 4) than in Grade 2 disc tissues with a lower level of degeneration. However, the amount of ADAMTS-5 detected did not differ between the 2 disc tissue grades. The aggrecan fragmentation analysis of these samples demonstrated the presence of aggrecanase-mediated fragmentation in both groups; however, there was no apparent difference in the aggrecan fragmentation profile between discs at early and advanced stages of disc degeneration.

CONCLUSION

Aggrecanases are involved in aggrecanolysis at both the early and advanced stages of disc degeneration. The aggrecan fragmentation profile analysis demonstrates the involvement of aggrecanases, as well as that of matrix metalloproteinases and/or cathepsins, during disc degeneration.

The matrix metalloproteinases as pharmacological target in osteoarthritis: Statins may be of therapeutic benefit

Osteoarthritis (OA) is a common joint disease; however, current pharmacologic agents for OA are only symptomatic and they can not prevent the disease progression. Matrix metalloproteinases (MMPs) produced by chondrocytes play an important role in the development of cartilage destruction in OA, and agents that can target against MMPs activity may be of therapeutical value. There were reports that statins can inhibit the secretion of MMPs in vitro and in vivo, which were believed to account for the plaque stabilizing effects of statins in the treatment of atherosclerosis. We based our hypothesis on that atherosclerosis possesses some aspects that are similar to that of osteoarthritis, such as inflammation and matrix degradation. Since statins have displayed great benefits in modifying the progression of atherosclerosis via anti-inflammatory and matrix-stabilizing mechanisms, it is conceivable that statins may also prevent the disease progression of osteoarthritis. Further work are needed to verify if statins can protect cartilage from destruction through inhibition of MMP secretion by chondrocytes, and their potential to be used as therapeutic agents in OA should be investigated.

Analysis of cartilage matrix fixed charge density and three-dimensional morphology via contrast-enhanced microcomputed tomography

Small animal models of osteoarthritis are often used for evaluating the efficacy of pharmacologic treatments and cartilage repair strategies, but noninvasive techniques capable of monitoring matrix-level changes are limited by the joint size and the low radiopacity of soft tissues. Here we present a technique for the noninvasive imaging of cartilage at micrometer-level resolution based on detecting the equilibrium partitioning of an ionic contrast agent via microcomputed tomography. The approach exploits electrochemical interactions between the molecular charges present in the cartilage matrix and an ionic contrast agent, resulting in a nonuniform equilibrium partitioning of the ionic contrast agent reflecting the proteoglycan distribution. In an in vitro model of cartilage degeneration we observed changes in x-ray attenuation magnitude and distribution consistent with biochemical and histological analyses of sulfated glycosaminoglycans, and x-ray attenuation was found to be a strong predictor of sulfated glycosaminoglycan density. Equilibration with the contrast agent also permits direct in situ visualization and quantification of cartilage surface morphology. Equilibrium partitioning of an ionic contrast agent via microcomputed tomography thus provides a powerful approach to quantitatively assess 3D cartilage composition and morphology for studies of cartilage degradation and repair.

Interleukin-1alpha induction of tensile weakening associated with collagen degradation in bovine articular cartilage

OBJECTIVE

To determine whether interleukin-1alpha (IL-1alpha) induces tensile weakening of articular cartilage that is concomitant with the loss of glycosaminoglycans (GAGs) or the subsequent degradation of the collagen network.

METHODS

Explants of young adult bovine cartilage obtained from the superficial (including the articular surface), middle, and deep layers were cultured with or without IL-1alpha for 1 week or 3 weeks. Then, portions of the explants were analyzed for their tensile properties (ramp modulus, strength, and failure strain); other portions of explants and spent culture medium were analyzed for the amount of GAG and the amount of cleaved, denatured, and total collagen.

RESULTS

The effect of IL-1alpha treatment on cartilage tensile properties and content was dependent on the duration of culture and the depth of the explant from the articular surface. The tensile strength and failure strain of IL-1alpha-treated samples from the superficial and middle layers were lower after 3 weeks of culture, but not after 1 week of culture. However, by 1 week of culture, IL-1alpha had already induced release of the majority of tissue GAGs into the medium, without detectable loss or degradation of collagen. In contrast, after 3 weeks of culture, IL-1alpha induced significant collagen degradation, as indicated by the amount of total, cleaved, or denatured collagen in the medium or in explants from the superficial and middle layers.

CONCLUSION

IL-1alpha-induced degradation of cartilage results in tensile weakening that occurs subsequent to the depletion of GAG and concomitant with the degradation of the collagen network.

Selective and non-selective metalloproteinase inhibitors reduce IL-1-induced cartilage degradation and loss of mechanical properties

Articular cartilage undergoes matrix degradation and loss of mechanical properties when stimulated with proinflammatory cytokines such as interleukin-1 (IL-1). Aggrecanases and matrix metalloproteinases (MMPs) are thought to be principal downstream effectors of cytokine-induced matrix catabolism, and aggrecanase- or MMP-selective inhibitors reduce or block matrix destruction in several model systems. The objective of this study was to use metalloproteinase inhibitors to perturb IL-1-induced matrix catabolism in bovine cartilage explants and examine their effects on changes in tissue compression and shear properties. Explanted tissue was stimulated with IL-1 for up to 24 days in the absence or presence of inhibitors that were aggrecanase-selective, MMP-selective, or non-selective. Analysis of conditioned media and explant digests revealed that aggrecanase-mediated aggrecanolysis was delayed to varying extents with all inhibitor treatments, but that aggrecan release persisted. Collagen degradation was abrogated by MMP- and non-selective inhibitors and reduced by the aggrecanase inhibitor. The inhibitors delayed but did not reduce loss of the equilibrium compression modulus, whereas the losses of dynamic compression and shear moduli were delayed and reduced. The data suggest that non-metalloproteinase mechanisms participate in IL-1-induced matrix degradation and loss of tissue material properties.

Understanding the role of tissue degrading enzymes and their inhibitors in development and disease

Cartilage and the underlying bone are destroyed in severe cases of arthritis preventing joints from functioning normally. Cartilage and bone collagen can be specifically cleaved by the collagenases, members of the matrix metalloproteinase family (MMPs), whilst cartilage aggrecan is degraded by members of the ADAMTS (A Disintegrin And Metalloproteinase with ThromboSpondin repeats) family of proteinases. Intracellular cysteine proteinases are involved in bone resorption by osteoclasts and the serine proteinases are involved in activating MMPs. Together, these enzymes act in concert during normal growth and development, especially within the growth plate; however they are also involved in tissue destruction during disease. Synthetic MMP inhibitors have been investigated as a means to block tissue destruction in arthritis but have been unsuccessful, although recent trials with doxycycline suggest this may block joint destruction in osteoarthritis. It is likely that combinations of therapy will be required to ensure that joint destruction is prevented in arthritis patients.

Drug delivery strategies for cathepsin inhibitors in joint diseases

Cathepsins play important roles in the development of joint and bone diseases such as osteoporosis, rheumatoid arthritis (RA) and osteoarthritis (OA). Cathepsin inhibitors are presently in development and clinical testing for use as novel disease-modifying drugs for the improved treatment of osteoporosis. They may also be applicable for the treatment of joint diseases. However, some barriers still hamper their clinical applications in these indications. Based on pathophysiological features of RA and OA, the authors discuss six potential drug delivery strategies for the effective delivery of cathepsin inhibitors or other antiarthritic drugs to the arthritic joint tissue. Successful application of these strategies may significantly contribute to a more effective and safe treatment of RA and OA.

Effects of interleukin-1 on calcium signaling and the increase of filamentous actin in isolated and in situ articular chondrocytes

OBJECTIVE

To determine whether interleukin-1 (IL-1) initiates transient changes in the intracellular concentration of [Ca2+]i and the organization of filamentous actin (F-actin) in articular chondrocytes.

METHODS

Articular chondrocytes within cartilage explants and enzymatically isolated chondrocytes were loaded with Ca(2+)-sensitive fluorescence indicators, and [Ca2+]i was measured using confocal fluorescence ratio imaging during exposure to 10 ng/ml IL-1alpha. Inhibitors of Ca2+ mobilization (Ca(2+)-free medium, thapsigargin [inhibitor of Ca-ATPases], U73122 [inhibitor of phospholipase C], and pertussis toxin [inhibitor of G proteins]) were used to determine the mechanisms of increased [Ca2+]i. Cellular F-actin was quantified using fluorescently labeled phalloidin. Toxin B was used to determine the role of the Rho family of small GTPases in F-actin reorganization.

RESULTS

In isolated cells on glass and in in situ chondrocytes within explants, exposure to IL-1 induced a transient peak in [Ca2+]i that was generally followed by a series of decaying oscillations. Thapsigargin, U73122, and pertussis toxin inhibited the percentage of cells responding to IL-1. IL-1 increased F-actin content in chondrocytes in a manner that was inhibited by toxin B.

CONCLUSION

Both isolated and in situ chondrocytes respond to IL-1 with transient increases in [Ca2+]i via intracellular Ca2+ release mediated by the phospholipase C and inositol trisphosphate pathways. The influx of Ca2+ from the extracellular space and the activation of G protein-coupled receptors also appear to contribute to these mechanisms. These findings suggest that Ca2+ mobilization may be one of the first signaling events in the response of chondrocytes to IL-1.

Development and characterization of a highly specific and sensitive sandwich ELISA for detection of aggrecanase-generated aggrecan fragments

OBJECTIVE

To develop an enzyme linked immunosorbent assay (ELISA) to quantify the levels of specific aggrecan fragments generated by aggrecanase-mediated cleavage at the 373Glu-374 Ala bond within the aggrecan interglobular domain.

METHODS

The ELISA employs a commercially available monoclonal antibody to capture aggrecan fragments containing keratan sulfate (KS). Aggrecan fragments generated by cleavage at the Glu-Ala bond were then detected using a monoclonal neoepitope antibody (mAb OA-1) that specifically recognizes the N-terminal sequence 'ARGSVIL'.

RESULTS

The mAb OA-1 antibody was highly specific for the immunizing neoepitope peptide since neither peptides spanning the cleavage site nor mutated peptides were detected. Aggrecan fragments generated by ADAMTS-4 digested human aggrecan monomers and from IL-1-stimulated human cartilage explants were quantified by the ELISA, and we observed increased sensitivity of the ELISA compared to mAb OA-1 Western analysis. We also observed that the basal, as well as IL-1-stimulated production of ARGS aggrecan fragments from human articular cartilage explants was blocked by a selective aggrecanase inhibitor, consistent with generation of the ARGS neoepitope in human articular cartilage being mediated by aggrecanase. Using purified human aggrecan digested by ADAMTS-4 as standard to quantify ARGS aggrecan fragments in human synovial fluids, we determined that the calculated amount of ARGSVIL-aggrecan fragments by ELISA measurement is in agreement with the published levels of these fragments, supporting its potential utility as a biomarker assay for osteoarthritis.

CONCLUSION

We have developed an assay that detects and quantifies specific aggrecan fragments generated by aggrecanase-mediated cleavage. Because aggrecanase mediates degradation of human articular aggrecan in joint disease, the KS/mAb OA-1 ELISA may serve as a biomarker assay for evaluation of preclinical and clinical samples.