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

Enzymatic digestion does not compromise sliding-mediated cartilage lubrication

Articular cartilage's remarkable low-friction properties are essential to joint function. In osteoarthritis (OA), cartilage degeneration (e.g., proteoglycan loss and collagen damage) decreases tissue modulus and increases permeability. Although these changes impair lubrication in fully depressurized and slowly slid cartilage, new evidence suggests such relationships may not hold under biofidelic sliding conditions more representative of those encountered in vivo. Our recent studies using the convergent stationary contact area (cSCA) configuration demonstrate that articulation (i.e., sliding) generates interfacial hydrodynamic pressures capable of replenishing cartilage interstitial fluid/pressure lost to compressive loading through a mechanism termed tribological rehydration. This fluid recovery sustains in vivo-like kinetic friction coefficients (µk<0.02 in PBS and <0.005 in synovial fluid) with little sensitivity to mechanical properties in healthy tissue. However, the tribomechanical function of compromised cartilage under biofidelic sliding conditions remains unknown. Here, we investigated the effects of OA-like changes in cartilage mechanical properties, modeled via enzymatic digestion of mature bovine cartilage, on its tribomechanical function during cSCA sliding. We found no differences in sliding-driven tribological rehydration behaviors or µk between naïve and digested cSCA cartilage (in PBS or synovial fluid). This suggests that OA-like cartilage retains sufficient functional properties to support naïve-like fluid recovery and lubrication under biofidelic sliding conditions. However, OA-like cartilage accumulated greater total tissue strains due to elevated strain accrual during initial load application. Together, these results suggest that elevated total tissue strains-as opposed to activity-mediated strains or friction-driven wear-might be the key biomechanical mediator of OA pathology in cartilage. STATEMENT OF SIGNIFICANCE: Osteoarthritis (OA) decreases cartilage's modulus and increases its permeability. While these changes compromise frictional performance in benchtop testing under low fluid load support (FLS) conditions, whether such observations hold under sliding conditions that better represent the joints' dynamic FLS conditions in vivo is unclear. Here, we leveraged biofidelic benchtop sliding experiments-that is, those mimicking joints' native sliding environment-to examine how OA-like changes in mechanical properties effect cartilage's natural lubrication. We found no differences in sliding-mediated fluid recovery or kinetic friction behaviors between naïve and OA-like cartilage. However, OA-like cartilage experienced greater strain accumulation during load application, suggesting that elevated tissue strains (not friction-driven wear) may be the primary biomechanical mediator of OA pathology.

Cartilage Tissue Engineering in Practice: Preclinical Trials, Clinical Applications, and Prospects

Articular cartilage defects significantly compromise the quality of life in the global population. Although many strategies are needed to repair articular cartilage, including microfracture, autologous osteochondral transplantation, and osteochondral allograft, the therapeutic effects remain suboptimal. In recent years, with the development of cartilage tissue engineering, scientists have continuously improved the formulations of therapeutic cells, biomaterial-based scaffolds, and biological factors, which have opened new avenues for better therapeutics of cartilage lesions. This review focuses on advances in cartilage tissue engineering, particularly in preclinical trials and clinical applications, prospects, and challenges.

Structural origins of cartilage shear mechanics

Articular cartilage is a remarkable material able to sustain millions of loading cycles over decades of use outperforming any synthetic substitute. Crucially, how extracellular matrix constituents alter mechanical performance, particularly in shear, remains poorly understood. Here, we present experiments and theory in support of a rigidity percolation framework that quantitatively describes the structural origins of cartilage's shear properties and how they arise from the mechanical interdependence of the collagen and aggrecan networks making up its extracellular matrix. This framework explains that near the cartilage surface, where the collagen network is sparse and close to the rigidity threshold, slight changes in either collagen or aggrecan concentrations, common in early stages of cartilage disease, create a marked weakening in modulus that can lead to tissue collapse. More broadly, this framework provides a map for understanding how changes in composition throughout the tissue alter its shear properties and ultimate in vivo function.

Sulforaphane-loaded hyaluronic acid-poloxamer hybrid hydrogel enhances cartilage protection in osteoarthritis models

Sulforaphane (SFN) is an isothiocyanate with anti-arthritic and immuno-regulatory activities, supported by the downregulation of NF-κB pathway, reduction on metalloproteinases expression and prevention of cytokine-induced cartilage degeneration implicated in OA progression. SFN promising pharmacological effects associated to its possible use, by intra-articular route and directly in contact to the site of action, highlight SFN as promising candidate for the development of drug-delivery systems. The association of poloxamers (PL) and hyaluronic acid (HA) supports the development of osteotrophic and chondroprotective pharmaceutical formulations. This study aims to develop PL-HA hybrid hydrogels as delivery systems for SFN intra-articular release and evaluate their biocompatibility and efficacy for osteoarthritis treatment. All formulations showed viscoelastic behavior and cubic phase organization. SFN incorporation and drug loading showed a concentration-dependent behavior following HA addition. Drug release profiles were influenced by both diffusion and relaxation of polymeric chains mechanisms. The PL407-PL338-HA-SFN hydrogel did not evoke pronounced cytotoxic effects on either osteoblast or chondrosarcoma cell lines. In vitro/ex vivo pharmacological evaluation interfered with an elevated activation of NF-κB and COX-2, increased the type II collagen expression, and inhibited proteoglycan depletion. These results highlight the biocompatibility and the pharmacological efficacy of PL-HA hybrid hydrogels as delivery systems for SFN intra-articular release for OA treatment.

Degeneration alters the biomechanical properties and structural composition of lateral human menisci

OBJECTIVE

Because the literature relating to the influence of degeneration on the viscoelasticity and tissue composition of human lateral menisci remains contradictory or completely lacking, the aim of this study was to fill these gaps by comprehensively characterising the biomechanical properties of menisci with regard to the degree of degeneration.

DESIGN

Meniscal tissue from 24 patients undergoing a total knee replacement was collected and the degeneration of each region classified according to Pauli et al. For biomechanical characterisation, compression and tensile tests were performed. Additionally, the water content was determined and infrared (IR) spectroscopy was applied to detect changes in the structural composition, particularly of the proteoglycan and collagen content.

RESULTS

With an increasing degree of degeneration, a significant decrease of the equilibrium modulus was detected, while simultaneously the water content and the hydraulic permeability significantly increased. However, the tensile modulus displayed a tendency to decrease with increasing degeneration, which might be due to the significantly decreasing amount of collagen content identified by the IR measurements.

CONCLUSION

The findings of the current study may contribute to the understanding of meniscus degeneration, showing that degenerative processes appear to mainly worsen viscoelastic properties of the inner circumference by disrupting the collagen integrity.

Sub-toxic levels of Co2+ are anti-inflammatory and protect cartilage from degradation caused by IL-1β

BACKGROUND

Cobalt ions from some orthopaedic implants induce a dose-dependent cytotoxic and pro-inflammatory response. Recent studies show that sub-toxic levels of cobalt influence actin organisation regulating fibroblasts and macrophages behaviour. However little is known about the influence of sub-toxic levels of cobalt on articular cartilage biology and biomechanics. Previously, we have reported that IL-1β signalling in chondrocytes, is regulated by primary cilia and associated intraflagellar transport. Since primary cilia expression is modulated by actin organisation, we set out to test the hypothesis that sub-toxic levels of cobalt regulate cilia expression and IL-1β signalling thereby influencing articular cartilage degradation.

METHODS

Isolated chondrocytes and bovine cartilage explants were subjected to Co²⁺ in the presence and absence of IL-1β. Primary cilia were monitored by confocal immunofluorescence. Nitric oxide and PGE₂ release were used to monitor IL-1β signalling. Degradation of cartilage matrix was assessed by the release of sGAG and the biomechanical properties of the tissue in uniaxial unconfined compression.

FINDINGS

Sub-toxic levels of Co²⁺ (50 μM) blocked IL-1β-induced primary cilia elongation in isolated chondrocytes. This was associated with disruption of pro-inflammatory signalling in both isolated chondrocytes and cartilage explants, and inhibition of cartilage matrix degradation and loss of biomechanical properties.

INTERPRETATION

This study reveals that low levels of cobalt ions are anti-inflammatory, preventing cartilage degradation in response to IL-1β. This mechanism is associated with regulation of primary cilia elongation. These observations provide new insight into the potential beneficial role of cobalt and may lead to novel mechanisms for controlling cartilage inflammation.

Activating Nrf2 signalling alleviates osteoarthritis development by inhibiting inflammasome activation

Osteoarthritis (OA), which is characterized by proliferation of subchondral bone and the degeneration of articular cartilage, is the most prevalent human arthritis. Nod-like receptor pyrin domain 3 (NLRP3) inflammasome is a hot spot in recent year and has been reported to be associated with OA synovial inflammation. However, there are few studies on NLRP3 inflammasome in chondrocyte. Licochalcone A (Lico A), a compound extracted from Glycyrrhiza species, has various biological effects such as anti-inflammation, anti-apoptotic, anti-cancer and anti-oxidation. In this study, we investigated the protective effect of Lico A on chondrocytes stimulated by lipopolysaccharide (LPS) and surgically induced OA models. In vitro, Lico A could reduce the expression of NLRP3, apoptosis-associated speck-like protein (ASC), Gasdermin D (GSDMD), caspase-1, interleukin-1beta (IL-1β) and IL-18, which indicated that Lico A attenuates LPS-induced chondrocytes pyroptosis. In addition, Lico A ameliorates the degradation of extracellular matrix (ECM) by enhancing the expression of aggrecan and collagen-II. Meanwhile, we found that Lico A inhibits NLRP3 inflammasome via nuclear factor erythroid-2-related factor 2 (Nrf2)/haeme oxygenase-1(HO-1)/nuclear factor kappa-B (NF-κB) axis. And the Nrf2 small interfering RNA (siRNA) could reverse the anti-pyroptosis effects of Lico A in mouse OA chondrocytes. In vivo, Lico A mitigates progression OA in a mouse model and reduces OA Research Society International (OARSI) scores. Thus, Lico A may have therapeutic potential in OA.

Osmotic Swelling Responses Are Conserved Across Cartilaginous Tissues With Varied Sulfated-Glycosaminoglycan Contents

Determining the influence of tissue composition on the osmotic swelling stress of articular cartilage and meniscus fibrocartilage is important to enhance our understanding of physiology and disease. This osmotic swelling stress is critical for the load-bearing capability of both tissues and results in part due to the interactions between the negatively charged sulfated glycosaminoglycan (sGAG) chains and the ionic interstitial fluid. Changes in sGAG content, as those occurring during the progression of degenerative joint disease, alter such interactions. Here, we compare the time-varying effects of altered osmotic environments on the confined compression swelling behavior of bovine tissues spanning a range of sGAG concentrations: juvenile articular cartilage, juvenile and adult meniscus, and juvenile cartilage enzymatically degraded to reduce its sGAG content. The transient response to changes in bath conditions was evaluated for explants assigned to one of three compressive offsets (5%, 10%, or 15% strain) and one of three bath conditions (0.1X, 1X, or 10X phosphate-buffered saline). Our results show that relative responses to alterations to the osmotic environment are consistent across native tissues but differ for degraded juvenile cartilage, demonstrating that changes in sGAG do not completely recapitulate the native swelling behaviors. Further, we found a strong correlation between aggregate modulus and sGAG/collagen, as well as between sGAG and collagen contents across native tissue types, suggesting some conservation of composition-function relationships across a range of tissue types with varying sGAG concentrations. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:785-792, 2020.

An ex vivo tissue model of cartilage degradation suggests that cartilage state can be determined from secreted key protein patterns

The pathophysiology of osteoarthritis (OA) involves dysregulation of anabolic and catabolic processes associated with a broad panel of proteins that ultimately lead to cartilage degradation. An increased understanding about these protein interactions with systematic in vitro analyses may give new ideas regarding candidates for treatment of OA related cartilage degradation. Therefore, an ex vivo tissue model of cartilage degradation was established by culturing tissue explants with bacterial collagenase II. Responses of healthy and degrading cartilage were analyzed through protein abundance in tissue supernatant with a 26-multiplex protein profiling assay, after exposing the samples to a panel of 55 protein stimulations present in synovial joints of OA patients. Multivariate data analysis including exhaustive pairwise variable subset selection identified the most outstanding changes in measured protein secretions. MMP9 response to stimulation was outstandingly low in degrading cartilage and there were several protein pairs like IFNG and MMP9 that can be used for successful discrimination between degrading and healthy samples. The discovered changes in protein responses seem promising for accurate detection of degrading cartilage. The ex vivo model seems interesting for drug discovery projects related to cartilage degradation, for example when trying to uncover the unknown interactions between secreted proteins in healthy and degrading tissues.

Chondrocyte and mesenchymal stem cell derived engineered cartilage exhibits differential sensitivity to pro-inflammatory cytokines

Tissue engineering is a promising approach for the repair of articular cartilage defects, with engineered constructs emerging that match native tissue properties. However, the inflammatory environment of the damaged joint might compromise outcomes, and this may be impacted by the choice of cell source in terms of their ability to operate anabolically in an inflamed environment. Here, we compared the response of engineered cartilage derived from native chondrocytes and mesenchymal stem cells (MSCs) to challenge by TNFα and IL-1β in order to determine if either cell type possessed an inherent advantage. Compositional (extracellular matrix) and functional (mechanical) characteristics, as well as the release of catabolic mediators (matrix metalloproteinases [MMPs], nitric oxide [NO]) were assessed to determine cell- and tissue-level changes following exposure to IL-1β or TNF-α. Results demonstrated that MSC-derived constructs were more sensitive to inflammatory mediators than chondrocyte-derived constructs, exhibiting a greater loss of proteoglycans and functional properties at lower cytokine concentrations. While MSCs and chondrocytes both have the capacity to form functional engineered cartilage in vitro, this study suggests that the presence of an inflammatory environment is more likely to impair the in vivo success of MSC-derived cartilage repair. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2901-2910, 2018.

Co-culture with infrapatellar fat pad differentially stimulates proteoglycan synthesis and accumulation in cartilage and meniscus tissues

PURPOSE

Although osteoarthritis is widely viewed as a disease of the whole joint, relatively few studies have focused on interactions among joint tissues in joint homeostasis and degeneration. In particular, few studies have examined the effects of the infrapatellar fat pad (IFP) on cartilaginous tissues. The aim of this study was to test the hypothesis that co-culture with healthy IFP would induce degradation of cartilage and meniscus tissues.

MATERIALS AND METHODS

Bovine articular cartilage, meniscus, and IFP were cultured isolated or as cartilage-fat or meniscus-fat co-cultures for up to 14 days. Conditioned media were assayed for sulfated glycosaminoglycan (sGAG) content, nitrite content, and matrix metalloproteinase (MMP) activity, and explants were assayed for sGAG and DNA contents.

RESULTS

Co-cultures exhibited increased cumulative sGAG release and sGAG release rates for both cartilage and meniscus, and the cartilage (but not meniscus) exhibited a substantial synergistic effect of co-culture (sGAG release in co-culture was significantly greater than the summed release from isolated cartilage and fat). Fat co-culture did not significantly alter the sGAG content of either cartilage or meniscus explants, indicating that IFP co-culture stimulated net sGAG production by cartilage. Nitrite release was increased relative to isolated tissue controls in co-cultured meniscus, but not the cartilage, with no synergistic effect of co-culture. Interestingly, MMP-2 production was decreased by co-culture for both cartilage and meniscus.

CONCLUSIONS

This study demonstrates that healthy IFP may modulate joint homeostasis by stimulating sGAG production in cartilage. Counter to our hypothesis, healthy IFP did not promote degradation of either cartilage or meniscus tissues.

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.

Bovine meniscal tissue exhibits age- and interleukin-1 dose-dependent degradation patterns and composition-function relationships

Despite increasing evidence that meniscal degeneration is an early event in the development of knee osteoarthritis, relatively little is known regarding the sequence or functional implications of cytokine-induced meniscal degradation or how degradation varies with age. This study examined dose-dependent patterns of interleukin-1 (IL-1)-induced matrix degradation in explants from the radially middle regions of juvenile and adult bovine menisci. Tissue explants were cultured for 10 days in the presence of 0, 1.25, 5, or 20 ng/ml recombinant human IL-1α. Juvenile explants exhibited immediate and extensive sulfated glycosaminoglycan (sGAG) loss and subsequent collagen release beginning after 4-6 days, with relatively little IL-1 dose-dependence. Adult explants exhibited a more graded response to IL-1, with dose-dependent sGAG release and a lower fraction of sGAG released (but greater absolute release) than juvenile explants. In contrast to juvenile explants, adult explants exhibited minimal collagen release over the 10-day culture. Compressive and shear moduli reflected the changes in explant composition, with substantial decreases for both ages but a greater relative decrease in juvenile tissue. Dynamic moduli exhibited stronger dependence on explant sGAG content for juvenile tissue, likely reflecting concomitant changes to both proteoglycan and collagen tissue components. The patterns of tissue degradation suggest that, like in articular cartilage, meniscal proteoglycans may partially protect collagen from cell-mediated degeneration. A more detailed view of functional changes in meniscal tissue mechanics with degeneration will help to establish the relevance of in vitro culture models and will advance understanding of how meniscal degeneration contributes to overall joint changes in early stage osteoarthritis. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:801-811, 2016.

Modeling IL-1 induced degradation of articular cartilage

In this study, we develop a computational model to simulate the in vitro biochemical degradation of articular cartilage explants sourced from the femoropatellar grooves of bovine calves. Cartilage explants were incubated in culture medium with and without the inflammatory cytokine IL-1α. The spatio-temporal evolution of the cartilage explant's extracellular matrix components is modelled. Key variables in the model include chondrocytes, aggrecan, collagen, aggrecanase, collagenase and IL-1α. The model is first calibrated for aggrecan homeostasis of cartilage in vivo, then for data on (explant) controls, and finally for data on the IL-1α driven proteolysis of aggrecan and collagen over a 4-week period. The model was found to fit the experimental data best when: (i) chondrocytes continue to synthesize aggrecan during the cytokine challenge, (ii) a one to two day delay is introduced between the addition of IL-1α to the culture medium and subsequent aggrecanolysis, (iii) collagen degradation does not commence until the total concentration of aggrecan (i.e. both intact and degraded aggrecan) at any specific location within the explant becomes ≤ 1.5 mg/ml and (iv) degraded aggrecan formed due to the IL-1α induced proteolysis of intact aggrecan protects the collagen network while collagen degrades in a two-step process which, together, significantly modulate the collagen network degradation. Under simulated in vivo conditions, the model predicts increased aggrecan turnover rates in the presence of synovial IL-1α, consistent with experimental observations. Such models may help to infer the course of events in vivo following traumatic joint injury, and may also prove useful in quantitatively evaluating the efficiency of various therapeutic molecules that could be employed to avoid or modify the course of cartilage disease states.

Lithium chloride prevents interleukin-1β induced cartilage degradation and loss of mechanical properties

Osteoarthritis is a chronic degenerative disease that affects the articular cartilage. Recent studies have demonstrated that lithium chloride exhibits significant efficacy as a chondroprotective agent, blocking cartilage degradation in response to inflammatory cytokines. However, conflicting literature suggests lithium may affect the physicochemical properties of articular cartilage and thus long-term exposure may negatively affect the mechanical functionality of this tissue. This study aims to investigate the effect of lithium chloride on the biomechanical properties of healthy and interleukin-1β treated cartilage in vitro and examines the consequences of long-term exposure to lithium on cartilage health in vivo. Bovine cartilage explants were treated with lithium chloride for 12 days. Chondrocyte viability, matrix catabolism and the biomechanical properties of bovine cartilage explants were not significantly altered following treatment. Consistent with these findings, long term-exposure (9 months) to dietary lithium did not induce osteoarthritis in rats, as determined by histological staining. Moreover, lithium chloride did not induce the expression of catabolic enzymes in human articular chondrocytes. In an inflammatory model of cartilage destruction, lithium chloride blocked interleukin-1β signaling in the form of nitric oxide and prostaglandin E2 release and prevented matrix catabolism such that the loss of mechanical integrity observed with interleukin-1β alone was inhibited. This study provides further support for lithium chloride as a novel compound for the treatment of osteoarthritis.

Meniscus is more susceptible than cartilage to catabolic and anti-anabolic effects of adipokines

OBJECTIVE

This study compared the effects on cartilage and meniscus matrix catabolism and biosynthesis of several adipokines implicated in osteoarthritis (OA).

DESIGN

Bovine cartilage and meniscus explants were cultured for 1 or 9 days in serum-free medium alone or with 0.02, 0.2, or 2 μg/ml of leptin, visfatin, adiponectin, or resistin. Media were supplemented with (3)H-proline or (35)S-sodium sulfate to evaluate protein and sulfated glycosaminoglycan (sGAG) accumulation on the last day of culture. Explants were assayed for radiolabel, sGAG, and DNA contents. Cultured media were assayed for sGAG, nitrite and lactate dehydrogenase.

RESULTS

Cartilage tissue was minimally affected by adipokines, with only the highest resistin dose increasing sGAG release and nitrite production compared to controls. In sharp contrast, meniscus tissue was responsive to several adipokines, with elevated sGAG and nitrite release following treatment with resistin, leptin, or visfatin. Cartilage sGAG content was unaltered by adipokine treatment whereas meniscal sGAG content significantly decreased with resistin dosage. Protein ((3)H) incorporation was unaffected by adipokine treatment in both tissues. sGAG ((35)S) incorporation did not significantly vary with adipokine treatment in cartilage but was inhibited by treatment with leptin, visfatin, and resistin in meniscus.

CONCLUSION

Our results indicate that meniscal tissue is more susceptible to adipokine-stimulated catabolism than is cartilage. Resistin had the strongest effect of the adipokines tested, inducing sGAG release in both tissues and depleting sGAG content in meniscus. These results suggest that increased adipokine levels due to obesity or joint injury may alter the mechanical integrity of the knee joint through biological pathways.

Anti-inflammatory and chondroprotective effects of atorvastatin in a cartilage explant model of osteoarthritis

OBJECTIVE

This study aimed to assess the chondroprotective potential of atorvastatin in rat's cartilage explant culture model of osteoarthritis, stimulated by interleukin-1β (IL-1β).

MATERIALS AND METHODS

The cartilage explants were treated with 20 ng/ml IL-1β alone or with 20 ng/ml IL-1β + various concentration of atorvastatin (1, 3, or 10 µM dissolved in DMSO) and incubated at 37 °C for 24 h. Also, control (0.25% DMSO), stimulated (20 ng IL-1β) and treatment (atorvastatin 10 µM) cartilage explants were incubated without and with 1400W (10 µM). After 24 h of incubation, TNF-α, PGE2, MMP-13, TIMP-1, NO, and superoxide anion formation (O2(-)) concomitant with glycosaminoglycans (GAGs) were estimated in the medium.

RESULTS

Atorvastatin inhibited IL-1β-induced GAGs release, TNF-α, MMP-13, and O2(-) with no effect on TIMP-1 and NO. In addition, the source of NO in normal and atorvastatin-treated cartilage was eNOS, while for IL-1β-stimulated cartilage it was iNOS. The cartilage degradation was associated with the combined effects of increased NO and O2 (-) rather than only NO.

CONCLUSION

The present study suggests that atorvastatin has the ability to protect cartilage degradation following IL-1β-stimulated cartilage in in vitro OA model and supports additional therapeutic application of atorvastatin in OA.

Regional variation in T1ρ and T2 times in osteoarthritic human menisci: correlation with mechanical properties and matrix composition

OBJECTIVE

Changes in T1ρ and T2 magnetic resonance relaxation times have been associated with articular cartilage degeneration, but similar relationships for meniscal tissue have not been extensively investigated. This work examined relationships between T1ρ and T2 measurements and biochemical and mechanical properties across regions of degenerate human menisci.

DESIGN

Average T1ρ and T2 relaxation times were determined for nine regions each of seven medial and 13 lateral menisci from 14 total knee replacement patients. Sulfated glycosaminoglycan (sGAG), collagen and water contents were measured for each region. Biomechanical measurements of equilibrium compressive, dynamic compressive and dynamic shear moduli were made for anterior, central and posterior regions.

RESULTS

T1ρ and T2 times showed similar regional patterns, with longer relaxation times in the (radially) middle region compared to the inner and outer regions. Pooled over all regions, T1ρ and T2 times showed strong correlations both with one another and with water content. Correlations with biochemical content varied depending on normalization to wet or dry mass, and both imaging parameters showed stronger correlations with collagen compared to sGAG content. Mechanical properties displayed moderate inverse correlations with increasing T1ρ and T2 times and water content.

CONCLUSION

Both T1ρ and T2 relaxation times correlated strongly with water content and moderately with mechanical properties in osteoarthritic menisci, but not as strongly with sGAG or collagen contents alone. While the ability of magnetic resonance imaging (MRI) to detect early osteoarthritic changes remains the subject of investigation, these results suggest that T1ρ and T2 relaxation times have limited ability to detect compositional variations in degenerate menisci.

Modeling signaling pathways in articular cartilage

Chondrocytes, the only cell type in articular cartilage, are responsible for maintaining the composition of cartilage extracellular matrix (ECM) through a complex interplay of anabolic and catabolic stimuli. Although understanding the way chondrocytes respond to stimuli is of utmost importance for shedding light into the etiology of joint diseases, an integrative approach to studying their signaling transduction mechanisms is yet to be introduced. Herein, we propose an approach that combines high throughput proteomic measurements and state of the art optimization algorithms to construct a predictive model of chondrocyte signaling network, downstream of 78 receptors of interest.

In vitro inhibition of compression-induced catabolic gene expression in meniscal explants following treatment with IL-1 receptor antagonist

BACKGROUND

Damage to the knee meniscus may result in tears that are difficult or unable to heal, and are often treated by partial removal of the damaged tissue. In vitro, 20% dynamic compressive strains on meniscal tissue explants have resulted in an increase in the release of sulfated glycosaminoglycans (GAG) and nitric oxide (NO) from the tissue explants and increased expression of matrix metalloproteinases (MMP) and interleukin-1α (IL-1α). The objective of this study was to explore the efficacy of IL-1 blockade on the expression of a wide range of genes, as well as NO and GAG release, following dynamic compression of porcine meniscal explants.

METHODS

Explants were dynamically compressed for 2 h at 1 Hz to 0, 10, or 20% strain with and without a pre-treatment of 500 ng/ml interleukin-1 receptor antagonist (IL-1RA). Relative changes in gene expression of IL-1α, MMP-1, -3, -13, A Disintegrin and Metalloproteinase with ThromboSpondin 4 (ADAMTS-4), ADAMTS-5, iNOS, aggrecan, and COX-2, as well as changes in NO and GAG release, were measured with standard biochemical assays.

RESULTS

Expression of IL-1α, MMP-3, MMP-13, and ADAMTS-4 in superficial explants was significantly downregulated at 20% dynamic strain compared to 10% strain following treatment with IL-1RA. GAG and NO release were not significantly influenced by IL-1RA treatment.

CONCLUSIONS

Treatment of meniscal explants with IL-1RA inhibited the expression of many catabolic genes following a single bout of high dynamic strain. IL-1RA may therefore be a potential therapy option during the acute phase of meniscal tear or meniscectomy treatment.

Imaging of lower limb cartilage

The cartilage of the lower limb joints is exposed to high levels of mechanical stress and therefore is a frequent site of degenerative and traumatic lesions. Magnetic resonance imaging (MRI) is the modality of choice for the assessment of these cartilage lesions. To date, clinically available sequences have focused on morphological defects and cartilage loss. Efforts have been made in recent years to depict cartilage lesions at an earlier stage, with new quantitative sequences focusing on the biochemical assessment of tissue.After a brief review of the hyaline cartilage structure, we review the current morphological imaging methods and the biochemical MRI techniques to assess the cartilage. We then illustrate the application of these MRI sequences for the most common degenerative and traumatic disorders affecting lower limb cartilage.