Elevated aggrecanase activity in a rat model of joint injury is attenuated by an aggrecanase specific inhibitor

Disease-modifying osteoarthritis drugs: in vitro and in vivo data on the development of DMOADs under investigation

INTRODUCTION

Osteoarthritis is a disabling affliction, and disease-modifying osteoarthritis drugs (DMOADs) would be highly desirable adjuncts to symptomatic relief as they may delay the disease process.

AREAS COVERED

This study is a comprehensive review of the recent literature on the efficacy of DMOADs in the treatment of OA. In vitro and in vivo evidence was collected using MEDLINE® (1950 to November 2012) and EMBASE (1980 to November 2012) databases. Several drugs have demonstrated DMOAD effects in OA. They can be divided into three groups based on their predominant mode of action: those targeting cartilage, inflammatory pathways and subchondral bone. OARSI guidelines recommend glucosamine and chondroitin sulphates and diacerein as DMOADS, and NICE will recommend glucosamine sulphate in the next update of guidelines. Exploration of improved outcome measures and identification of subgroups of patients most likely to benefit from different DMOADs are likely to be the most important areas of development over the coming years.

EXPERT OPINION

It is expected that a wider range of prospective clinical studies will be embarked upon in the coming years. Trials including MRI as well as joint space narrowing (JSN) should be designed in a systematic manner, powered with sufficient numbers to demonstrate clinical benefit at different stages of disease.

Tenascin-C levels in synovial fluid are elevated after injury to the human and canine joint and correlate with markers of inflammation and matrix degradation

OBJECTIVE

We have previously shown the capacity of tenascin-C (TN-C) to induce inflammatory mediators and matrix degradation in vitro in human articular cartilage. The objective of the present study was to follow TN-C release into knee synovial fluid after acute joint injury or in joint disease, and to correlate TN-C levels with markers of cartilage matrix degradation and inflammation.

METHOD

Human knee synovial fluid samples (n = 164) were from a cross-sectional convenience cohort. Diagnostic groups were knee healthy reference, knee anterior cruciate ligament rupture, with or without concomitant meniscus lesions, isolated knee meniscus injury, acute inflammatory arthritis (AIA) and knee osteoarthritis (OA). TN-C was measured in synovial fluid samples using an enzyme-linked immunosorbent assay (ELISA) and results correlated to other cartilage markers. TN-C release was also monitored in joints of dogs that underwent knee instability surgery.

RESULTS

Statistically significantly higher levels of TN-C compared to reference subjects were observed in the joint fluid of all human disease groups and in the dogs that underwent knee instability surgery. Statistically significant correlations were observed between the TN-C levels in the synovial fluid of the human patients and the levels of aggrecanase-dependent Ala-Arg-Gly-aggrecan (ARG-aggrecan) fragments and matrix metalloproteinases 1 and 3.

CONCLUSIONS

We find highly elevated levels of TN-C in human knee joints after injury, AIA or OA that correlated with markers of cartilage degradation and inflammation. TN-C in synovial fluid may serve dual roles as a marker of joint damage and a stimulant of further joint degradation.

Chondrogenesis, chondrocyte differentiation, and articular cartilage metabolism in health and osteoarthritis

Chondrogenesis occurs as a result of mesenchymal cell condensation and chondroprogenitor cell differentiation. Following chondrogenesis, the chondrocytes remain as resting cells to form the articular cartilage or undergo proliferation, terminal differentiation to chondrocyte hypertrophy, and apoptosis in a process termed endochondral ossification, whereby the hypertrophic cartilage is replaced by bone. Human adult articular cartilage is a complex tissue of matrix proteins that varies from superficial to deep layers and from loaded to unloaded zones. A major challenge to efforts to repair cartilage by stem cell-based and other tissue-engineering strategies is the inability of the resident chondrocytes to lay down a new matrix with the same properties as it had when it was formed during development. Thus, understanding and comparing the mechanisms of cartilage remodeling during development, osteoarthritis (OA), and aging may lead to more effective strategies for preventing cartilage damage and promoting repair. The pivotal proteinase that marks OA progression is matrix metalloproteinase 13 (MMP-13), the major type II collagen-degrading collagenase, which is regulated by both stress and inflammatory signals. We and other investigators have found that there are common mediators of these processes in human OA cartilage. We also observe temporal and spatial expression of these mediators in early through late stages of OA in mouse models and are analyzing the consequences of knockout or transgenic overexpression of critical genes. Since the chondrocytes in adult human cartilage are normally quiescent and maintain the matrix in a low turnover state, understanding how they undergo phenotypic modulation and promote matrix destruction and abnormal repair in OA may to lead to identification of critical targets for therapy to block cartilage damage and promote effective cartilage repair.

Future therapeutics for osteoarthritis

Osteoarthritis (OA) is a disease of the joints that affects several million individuals worldwide. This disease, which involves mainly the diarthrodial joints, is chronic and develops slowly over decades, making it very difficult to precisely identify the different etiological and risk factors that influence its onset. At present, most therapies for OA are symptomatic. This review will focus on new OA therapeutics in development that are directed toward pain relief as well as others with the potential to reduce or stop the progression of the disease (DMOADs). This article is part of a Special Issue entitled "Osteoarthritis".

Biological markers in osteoarthritis

Osteoarthritis (OA) is considered as a chronic disease with a long "silent" period. The diagnosis is generally based on clinical symptoms and radiographic changes. However X-ray has a poor sensitivity and a relatively large precision error that does not allow an early detection of OA or the monitoring of joint damage progression. The limitations of the tools that are currently available for OA assessment have been the impetus to identify specific biological markers that reflect quantitative and dynamic variations in joint remodeling. Research has focused on the structural components of cartilage matrix, especially type II collagen degradation markers. In spite of a significant increase of some markers in individuals with early stage of OA, the large overlap with control subjects indicates that the current biomarkers used alone have limited diagnostic potential. However, the combination of specific markers seems to improve the prediction of disease progression at the individual level. Several types of treatment have been investigated but the lack of medications with definitively demonstrated chondroprotective activity has limited the assessment of the potential role of biomarkers for monitoring patients' responses to the treatment of OA. In this review, we will use the BIPED classification that appeared in 2006 for OA markers to describe the potential usage of a given marker [5]. This article is part of a Special Issue entitled "Osteoarthritis".

Pentosan polysulfate increases affinity between ADAMTS-5 and TIMP-3 through formation of an electrostatically driven trimolecular complex

The semi-synthetic sulfated polysaccharide PPS (pentosan polysulfate) increases affinity between the aggrecan-degrading ADAMTSs (adamalysins with thrombospondin motifs) and their endogenous inhibitor, TIMP (tissue inhibitor of metalloproteinases)-3. In the present study we demonstrate that PPS mediates the formation of a high-affinity trimolecular complex with ADAMTS-5 and TIMP-3. A TIMP-3 mutant that lacks extracellular-matrix-binding ability was insensitive to this affinity increase, and truncated forms of ADAMTS-5 that lack the Sp (spacer) domain had reduced PPS-binding ability and sensitivity to the affinity increase. PPS molecules composed of 11 or more saccharide units were 100-fold more effective than those of eight saccharide units, indicating the involvement of extended or multiple protein-interaction sites. The formation of a high-affinity trimolecular complex was completely abolished in the presence of 0.4 M NaCl. These results suggest that PPS enhances the affinity between ADAMTS-5 and TIMP-3 by forming electrostatically driven trimolecular complexes under physiological conditions.

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.

Teriparatide as a chondroregenerative therapy for injury-induced osteoarthritis

There is no disease-modifying therapy for osteoarthritis, a degenerative joint disease that is projected to afflict more than 67 million individuals in the United States alone by 2030. Because disease pathogenesis is associated with inappropriate articular chondrocyte maturation resembling that seen during normal endochondral ossification, pathways that govern the maturation of articular chondrocytes are candidate therapeutic targets. It is well established that parathyroid hormone (PTH) acting via the type 1 PTH receptor induces matrix synthesis and suppresses maturation of chondrocytes. We report that the PTH receptor is up-regulated in articular chondrocytes after meniscal injury and in osteoarthritis in humans and in a mouse model of injury-induced knee osteoarthritis. To test whether recombinant human PTH(1-34) (teriparatide) would inhibit aberrant chondrocyte maturation and associated articular cartilage degeneration, we administered systemic teriparatide (Forteo), a Food and Drug Administration-approved treatment for osteoporosis, either immediately after or 8 weeks after meniscal/ligamentous injury in mice. Knee joints were harvested at 4, 8, or 12 weeks after injury to examine the effects of teriparatide on cartilage degeneration and articular chondrocyte maturation. Microcomputed tomography revealed increased bone volume within joints from teriparatide-treated mice compared to saline-treated control animals. Immediate systemic administration of teriparatide increased proteoglycan content and inhibited articular cartilage degeneration, whereas delayed treatment beginning 8 weeks after injury induced a regenerative effect. The chondroprotective and chondroregenerative effects of teriparatide correlated with decreased expression of type X collagen, RUNX2 (runt-related transcription factor 2), matrix metalloproteinase 13, and the carboxyl-terminal aggrecan cleavage product NITEGE. These preclinical findings provide proof of concept that Forteo may be useful for decelerating cartilage degeneration and inducing matrix regeneration in patients with osteoarthritis.

Human aggrecanase generated synovial fluid fragment levels are elevated directly after knee injuries due to proteolysis both in the inter globular and chondroitin sulfate domains

OBJECTIVE

To examine different aggrecanase generated fragments in synovial fluid (SF) from patients with acute and chronic knee injuries and from knee healthy subjects.

METHODS

We prepared SF-D1 samples from acute (n=35) and chronic (n=35) knee injury patients and knee healthy subjects (n=10). Aggrecan fragments were analyzed in the SF-D1 samples by quantitative (G1, ARGS, KEEE and G3 antibodies) and non-quantitative (GRGT and AGEG antibodies) Western blot.

RESULTS

ARGS-SELE, ARGS-chondroitin sulfate (CS)1, GRGT-, GLGS- and AGEG-G3 fragments were the main ARGS and G3 fragments in injured and reference samples. In the acute injury samples the concentrations of these fragments were increased compared to the reference, and the level of the ARGS-SELE remained elevated for at least 2 years after the joint injury. Both SF ARGS fragments and aggrecanase generated G3 fragments had high sensitivity and specificity as biomarkers in distinguishing injured from healthy knee joints, although the ARGS fragments had higher area under the receiver operating characteristic curve (AUC) values for injuries (74-86%) than the G3 fragments (AUC values 63-68%).

CONCLUSION

Our results suggest that during the acute phase after knee injury there is an increased aggrecanase activity against both the interglobular domain (IGD) and the CS2 cleavage sites of joint cartilage aggrecan. This increase in SF aggrecanolytic fragments is present for several years after the injury. SF ARGS fragments are better biomarkers than the aggrecanase generated G3-fragments in distinguishing injured from healthy knee joints.

Tenascin-C induces inflammatory mediators and matrix degradation in osteoarthritic cartilage

Background

Tenascin-C (TN-C) is an extracellular matrix glycoprotein that is involved in tissue injury and repair processes. We analyzed TN-C expression in normal and osteoarthritic (OA) human cartilage, and evaluated its capacity to induce inflammatory and catabolic mediators in chondrocytes in vitro. The effect of TN-C on proteoglycan loss from articular cartilage in culture was also assessed.

Methods

TN-C in culture media, cartilage extracts, and synovial fluid of human and animal joints was quantified using a sandwich ELISA and/or analyzed by Western immunoblotting. mRNA expression of TN-C and aggrecanases were analyzed by Taqman assays. Human and bovine primary chondrocytes and/or explant culture systems were utilized to study TN-C induced inflammatory or catabolic mediators and proteoglycan loss. Total proteoglycan and aggrecanase -generated ARG-aggrecan fragments were quantified in human and rat synovial fluids by ELISA.

Results

TN-C protein and mRNA expression were significantly upregulated in OA cartilage with a concomitant elevation of TN-C levels in the synovial fluid of OA patients. IL-1 enhanced TN-C expression in articular cartilage. Addition of TN-C induced IL-6, PGE₂, and nitrate release and upregulated ADAMTS4 mRNA in cultured primary human and bovine chondrocytes. TN-C treatment resulted in an increased loss of proteoglycan from cartilage explants in culture. A correlation was observed between TN-C and aggrecanase generated ARG-aggrecan fragment levels in the synovial fluid of human OA joints and in the lavage of rat joints that underwent surgical induction of OA.

Conclusions

TN-C expression in the knee cartilage and TN-C levels measured in the synovial fluid are significantly enhanced in OA patients. Our findings suggest that the elevated levels of TN-C could induce inflammatory mediators and promote matrix degradation in OA joints.

Proteases involved in cartilage matrix degradation in osteoarthritis

Osteoarthritis is a common joint disease for which there are currently no disease-modifying drugs available. Degradation of the cartilage extracellular matrix is a central feature of the disease and is widely thought to be mediated by proteinases that degrade structural components of the matrix, primarily aggrecan and collagen. Studies on transgenic mice have confirmed the central role of Adamalysin with Thrombospondin Motifs 5 (ADAMTS-5) in aggrecan degradation, and the collagenolytic matrix metalloproteinase MMP-13 in collagen degradation. This review discusses recent advances in current understanding of the mechanisms regulating expression of these key enzymes, as well as reviewing the roles of other proteinases in cartilage destruction. This article is part of a Special Issue entitled: Proteolysis 50 years after the discovery of lysosome.

Association between synovial fluid levels of aggrecan ARGS fragments and radiographic progression in knee osteoarthritis

Introduction

Aggrecanase cleavage at the ³⁹²Glu-³⁹³Ala bond in the interglobular domain (IGD) of aggrecan, releasing N-terminal ³⁹³ARGS fragments, is an early key event in arthritis and joint injuries. We determined whether synovial fluid (SF) levels of ARGS-aggrecan distinguish subjects with progressive radiographic knee osteoarthritis (ROA) from those with stable or no ROA.

Methods

We studied 141 subjects who, at examination A, had been given meniscectomies an average of 18 years earlier (range, 15 to 22 years). Seventeen individuals without surgery, and without known injury to the menisci or cruciate ligaments, were used as references. At examinations A and B, with a mean follow-up time of 7.5 years, we obtained SF and standing tibiofemoral and skyline patellofemoral radiographs. SF ARGS-aggrecan was measured with an electrochemiluminescence immunoassay, and we graded radiographs according to the OARSI atlas. The association between SF ARGS levels at examination A and progression of radiographic features of knee OA between examinations A and B was assessed by using logistic regression adjusted for age, gender, body mass index, and time between examinations, and stratified by ROA status at examination A.

Results

We found a weak negative association between SF ARGS concentrations and loss of joint space: the likelihood of progression of radiographic joint space narrowing decreased 0.9 times per picomole per milliliter increase in ARGS (odds ratio (OR) 0.89; 95% confidence interval (CI), 0.79 to 0.996). In subjects with and without preexisting ROA at examination A, the association was OR, 0.96; 0.81 to 1.13; and 0.77; 0.62 to 0.95, respectively. Average levels of SF ARGS 18 years after meniscectomy were no different from those of reference subjects and were not correlated to radiographic status at examination A.

Conclusions

In subjects with previous knee meniscectomy but without ROA, levels of SF ARGS-aggrecan were weakly and inversely associated with increased loss of joint space over a period of 7.5 years.