Dynamic compression counteracts IL-1 beta-induced release of nitric oxide and PGE2 by superficial zone chondrocytes cultured in agarose constructs

Compressive mechanical stress enhances susceptibility to interleukin-1 by increasing interleukin-1 receptor expression in 3D-cultured ATDC5 cells

Background

Mechanical overload applied on the articular cartilage may play an important role in the pathogenesis of osteoarthritis. However, the mechanism of chondrocyte mechanotransduction is not fully understood. The purpose of this study was to assess the effects of compressive mechanical stress on interleukin-1 receptor (IL-1R) and matrix-degrading enzyme expression by three-dimensional (3D) cultured ATDC5 cells. In addition, the implications of transient receptor potential vanilloid 4 (TRPV4) channel regulation in promoting effects of compressive mechanical loading were elucidated.

Methods

ATDC5 cells were cultured in alginate beads with the growth medium containing insulin-transferrin-selenium and BMP-2 for 6 days. The cultured cell pellet was seeded in collagen scaffolds to produce 3D-cultured constructs. Cyclic compressive loading was applied on the 3D-cultured constructs at 0.5 Hz for 3 h. The mRNA expressions of a disintegrin and metalloproteinases with thrombospondin motifs 4 (ADAMTS4) and IL-1R were determined with or without compressive loading, and effects of TRPV4 agonist/antagonist on mRNA expressions were examined. Immunoreactivities of reactive oxygen species (ROS), TRPV4 and IL-1R were assessed in 3D-cultured ATDC5 cells.

Results

In 3D-cultured ATDC5 cells, ROS was induced by cyclic compressive loading stress. The mRNA expression levels of ADAMTS4 and IL-1R were increased by cyclic compressive loading, which was mostly prevented by pyrollidine dithiocarbamate. Small amounts of IL-1β upregulated ADAMTS4 and IL-1R mRNA expressions only when combined with compressive loading. TRPV4 agonist suppressed ADAMTS4 and IL-1R mRNA levels induced by the compressive loading, whereas TRPV4 antagonist enhanced these levels. Immunoreactivities to TRPV4 and IL-1R significantly increased in constructs with cyclic compressive loading.

Conclusion

Cyclic compressive loading induced mRNA expressions of ADAMTS4 and IL-1R through reactive oxygen species. TRPV4 regulated these mRNA expressions, but excessive compressive loading may impair TRPV4 regulation. These findings suggested that TRPV4 regulates the expression level of IL-1R and subsequent IL-1 signaling induced by cyclic compressive loading and participates in cartilage homeostasis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-021-04095-x.

Anti-inflammatory effects of olive-derived hydroxytyrosol on lipopolysaccharide-induced inflammation in RAW264.7 cells

The control of inflammation, which arises from complex biological responses to harmful stimuli, is an important determinant of both clinical outcomes and patient comfort. However, the side effects of many current therapies such as non-steroidal anti-inflammatory drugs mean that new safe treatments are required. We previously reported that 12.5 µg/ml hydroxytyrosol (HT) suppressed gene expression of the inducible nitric oxide (NO) synthase (iNOS) isoform and NO production, in mouse peritoneal macrophages treated with lipopolysaccharide (LPS), where nuclear factor-κB (NF-κB) gene expression was not altered. The present study evaluated the anti-inflammatory effects of various concentrations of HT in LPS-induced RAW264.7 mouse macrophages. HT suppressed NF-κB signaling and downregulated LPS-mediated expression of iNOS, cyclooxygenase-2, tumor necrosis factor alpha, and interleukin-1β at 12.5 µg/ml, resulting in reduced production of NO and prostaglandin E₂. At lower concentrations, HT seemed to act via another signaling pathway to regulate the inflammatory response. In contrast, HT did not suppress LPS-induced expression of phosphorylated p44/42 mitogen-activated protein kinase. This study showed that HT had anti-inflammatory effects on LPS-stimulated RAW264.7 cells. HT is already available as a nutritional supplement and no toxic effects have been reported. Hence, HT represents a potential novel anti-inflammatory agent.

Effect of biomechanical stress on endogenous antioxidant networks in bovine articular cartilage

Mechanosensitve pathways in chondrocytes are essential for maintaining articular cartilage homeostasis. Traumatic loading increases cartilage oxidation and causes cell death and osteoarthritis. However, sub-lethal doses of the pro-oxidant molecule tert-Butyl hydroperoxide (tBHP) protects against loading-induced chondrocyte death. We hypothesized that compressive cyclic loading at moderate strains (<20%) causes sub-lethal cartilage oxidation that induces an adaptive increase in the endogenous antioxidant defense network. We tested this hypothesis by subjecting healthy bovine articular cartilage explants to in vitro static or cyclic (1 Hz) compressive loading at 50 kPa (15% strain, "physiologic") versus 300 kPa (40% strain, "hyper-physiologic") for 12 h per day for 2 days. We also treated unloaded explants with 100 μM tBHP for 12 h per day for 2 days to differentiate between biomechanical and chemical pro-oxidant stimulation. All loading conditions induced glutathione oxidation relative to unloaded controls, but only the 50 kPa cyclic loading condition increased total glutathione content (twofold). This increase was associated with a greater expression of glutamate-cysteine ligase, the rate-limiting step in glutathione synthesis, compared to 300 kPa cyclic loading. 50 kPa cyclic loading also increased the expression of superoxide dismutase-1 and peroxiredoxin-3. Like 50 kPa loading, tBHP treatment also increased total glutathione content. However, tBHP treatment and 50 kPa cyclic loading differed in their effect on the expression of genes regulating antioxidant defense and cartilage matrix synthesis and degradation. These findings suggest that glutathione metabolism is a mechanosensitive antioxidant defense pathway in chondrocytes and that intermittent pro-oxidant treatment alone is insufficient to account for all changes in mediators of cartilage homeostasis associated with cyclic loading. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:760-769, 2018.

Effect of Dynamic Compression on in vitro Chondrocyte Metabolism

Background

Chondrocytes can detect and respond to the mechanical environment by altering their metabolism. This study was designed to explore the effects of dynamic compression on chondrocyte metabolism.

Methods

Chondrocytes were harvested from newborn Wistar rats. After 7 days of expansion, chondrocytes embedded in agarose discs underwent uniaxial unconfined dynamic compression loads at different amplitudes (5%, 10%, and 15%) and frequencies (0.5 Hz, 1.0 Hz, 2.0 Hz, and 3.0 Hz) with a duration of 24 hours. The delayed effects on the chondrocytes were studied at 1, 3, and 7 days after the experiment.

Results

The results showed that at 10% strain, higher-frequency compression pressure can enhance the proliferation of chondrocytes. The synthesis of glycosaminoglycan (GAG) increased at 10%-15% strain and a 1-Hz load. The synthesis of nitric oxide (NO) increased at the 0.5-Hz load; while decreasing at the 15% strain. With 10% strain, 1 Hz dynamic compression, the proliferation of chondrocytes and GAG synthesis increased and persisted for 7 days, and NO synthesis decreased at the third and seventh days of culture.

Conclusions

This study showed that chondrocytes respond metabolically to compressive loading, which is expected to modulate the growth and the resultant biomechanical properties of these tissue-engineered constructs during culture.

Gentiopicroside prevents interleukin-1 beta induced inflammation response in rat articular chondrocyte

ETHNOPHARMACOLOGICAL RELEVANCE

In traditional Chinese medicine, Gentiana macrophylla Pall have been prescribed for the treatment of pain and inflammatory conditions. In addition, it is a common Tibetan medicinal herb used for the treatment of tonsillitis, urticaria, and rheumatoid arthritis (RA), while the flowers of G. macrophylla Pall have been traditionally treated as an anti-inflammatory agent to clear heat in Mongolian medicine. The secoiridoid glycosides and their derivatives are the primary active components of G. macrophylla and have been demonstrated to be effective as anti-inflammatory agents.

MATERIALS AND METHODS

Solvent extraction and D101 macroporous resin columns were employed to concentratethe gentiopicroside. Gentiopicroside cytotoxicity was assessed by 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay; the toxicity of gentiopicroside in chondrocytes was reconfirmed using Hoechst staining. Western blotting, reverse transcriptase-polymerase chain reaction (RT-PCR) and immunohistochemistry were utilized to explore the protective effects and mechanisms of gentiopicroside prevents interleukin-1 beta induced inflammation response in rat articular chondrocyte.

RESULTS

The MTT assay demonstrated that 50, 500, and 1,500 μg/mL of gentiopicroside exhibited no significant toxicity to chondrocytes (P>0.05) after 24h. Using immunohistochemistry, ELISA, RT-PCR, Western blot method to explore the protective effect and mechanism of gentiopicroside on chondrocytes induced by IL-1β. The results showed some pathways of IL-1β signal transduction were inhibited by gentiopicroside in rat chondrocytes: p38, ERK and JNK. Meanwhile, gentiopicroside showed inhibition in the IL-1β-induced release of MMPs while increasing Collagen type II expression.

CONCLUSIONS

The current study demonstrated that gentiopicroside exhibited a potent protective effect on IL-1β induced inflammation response in rat articular chondrocyte. Thus, gentiopicroside could be a potential therapeutic strategy for treatment of OA.

Role of miR-146a in human chondrocyte apoptosis in response to mechanical pressure injury in vitro

MicroRNA (miR)-146a is known to be overexpressed in osteoarthritis (OA). However, the role of miR-146a in OA has not yet been fully elucidated. In the present study, we applied mechanical pressure of 10 MPa to human chondrocytes for 60 min in order to investigate the expression of miR-146a and apoptosis following the mechanical pressure injury. Normal human chondrocytes were transfected with an miR-146a mimic or an inhibitor to regulate miR-146a expression. Potential target genes of miR-146a were predicted using bioinformatics. Moreover, luciferase reporter assay confirmed that Smad4 was a direct target of miR-146a. The expression levels of miR-146a, Smad4 and vascular endothelial growth factor (VEGF) were quantified by quantitative reverse transcription PCR and/or western blot analysis. The effects of miR-146a on apoptosis were detected by Annexin V-fluorescein isothiocyanate (FITC)/propidium iodide (PI) flow cytometry. The results indicated that mechanical pressure affected chondrocyte viability and induced the early apoptosis of chondrocytes. Mechanical pressure injury increased the expression levels of miR-146a and VEGF and decreased the levels of Smad4 in the chondrocytes. In the human chondrocytes, the upregulation of miR-146a induced apoptosis, upregulated VEGF expression and downregulated Smad4 expression. In addition, the knockdown of miR-146a reduced cell apoptosis, upregulated Smad4 expression and downregulated VEGF expression. Smad4 was identified as a direct target of miR-146a by harboring a miR‑146a binding sequence in the 3'-untranslated region (3'-UTR) of its mRNA. Furthermore, the upregulation of VEGF induced by miR‑146a was mediated by Smad4 in the chondrocytes subjected to mechanical pressure injury. These results demonstrated that miR-146a was overexpressed in our chondrocyte model of experimentally induced human mechanical injury, accompanied by the upregulation of VEGF and the downregulation of Smad4 in vitro. Moreover, our data suggest that miR-146a is involved in human chondrocyte apoptosis in response to mechanical injury, and may contribute to the mechanical injury of chondrocytes, as well as to the pathogenesis of OA by increasing the levels of VEGF and damaging the transforming growth factor (TGF)-β signaling pathway through the targeted inhibition of Smad4 in cartilage.

Combination of intermittent hydrostatic pressure linking TGF-β1, TNF-α on modulation of proteoglycan 4 metabolism in rat temporomandibular synovial fibroblasts

OBJECTIVE

This study was designed to evaluate the combined effects of intermittent hydrostatic pressure (IHP) and TGF-β1 or TNF-α on proteoglycan4 (PRG4) expression in rat temporomandibular synovial fibroblasts (SFs).

STUDY DESIGN

Rat SFs were isolated and expanded in monolayer cultures and subjected to IHP in the presence of TGF-β1 or TNF-α. Quantitative real-time RT-PCR was applied to analyze the PRG4 expression levels. Enzyme-linked immunosorbent assay was also used for the quantification of PRG4 accumulation in the culture medium while immunofluorescence staining was used to detect intracellular PRG4 protein expression.

RESULTS

The combination of IHP and TGF-β1 induced greater PRG4 expression than either stimulus alone. In contrast, TNF-α inhibited PRG4 expression, and this was partially alleviated by IHP.

CONCLUSIONS

Our study demonstrates a beneficial role of IHP, which can be used successfully in combination with TGF-β1 to enhance PRG4 production, and can partially counteract TNF-α-induced PRG4 inhibition in isolated rat SFs.

Single photon counting fluorescence lifetime detection of pericellular oxygen concentrations

Fluorescence lifetime imaging microscopy offers a non-invasive method for quantifying local oxygen concentrations. However, existing methods are either invasive, require custom-made systems, or show limited spatial resolution. Therefore, these methods are unsuitable for investigation of pericellular oxygen concentrations. This study describes an adaptation of commercially available equipment which has been optimized for quantitative extracellular oxygen detection with high lifetime accuracy and spatial resolution while avoiding systematic photon pile-up. The oxygen sensitive fluorescent dye, tris(2,2'-bipyridyl)ruthenium(II) chloride hexahydrate [Ru(bipy)(3)](2+), was excited using a two-photon excitation laser. Lifetime was measured using a Becker & Hickl time-correlated single photon counting, which will be referred to as a TCSPC card. [Ru(bipy)(3)](2+) characterization studies quantified the influences of temperature, pH, cellular culture media and oxygen on the fluorescence lifetime measurements. This provided a precisely calibrated and accurate system for quantification of pericellular oxygen concentration based on measured lifetimes. Using this technique, quantification of oxygen concentrations around isolated viable chondrocytes, seeded in three-dimensional agarose gel, revealed a subpopulation of cells that exhibited significant spatial oxygen gradients such that oxygen concentration reduced with increasing proximity to the cell. This technique provides a powerful tool for quantifying spatial oxygen gradients within three-dimensional cellular models.

Mechanical Loading of Articular Cartilage Reduces IL-1-Induced Enzyme Expression

OBJECTIVE: Exposure of articular cartilage to interleukin-1 (IL-1) results in increased synthesis of matrix degrading enzymes. Previously mechanical load applied together with IL-1 stimulation was found to reduce aggrecan cleavage by ADAMTS-4 and 5 and MMP-1, -3, -9, and -13 and reduce proteoglycan loss from the extracellular matrix. To further delineate the inhibition mechanism the gene expression of ADAMTS-4 and 5; MMP-1, -3, -9, and -13; and TIMP-1, -2, and -3 were measured. DESIGN: Mature bovine articular cartilage was stimulated with a 0.5 MPa compressive stress and 10 ng/ml of IL-1α for 3 days and then allowed to recover without stimulation for 1 additional day. The media was assayed for proteoglycan content on a daily basis, while chondrocyte gene expression (mRNA) was measured during stimulation and 1 day of recovery. RESULTS: Mechanical load alone did not change the gene expression for ADAMTS, MMP, or TIMP. IL-1 caused an increase in gene expression for all enzymes after 1 day of stimulation while not affecting the TIMP levels. Load applied together with IL-1 decreased the expression levels of ADAMTS-4 and -5 and MMP-1 and -3 and increased TIMP-3 expression. CONCLUSIONS: A mechanical load appears to modify cartilage degradation by IL-1 at the cellular level by reducing mRNA.

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.

Quantification of mRNA using real-time PCR and Western blot analysis of MAPK events in chondrocyte/agarose constructs

In vitro models of chondrocyte mechanobiology have been used to compare the intracellular signalling pathways altered in normal and osteoarthritis-affected cartilage. However, differences in the model system and type of loading configuration have led to complicated pathways. This chapter is a follow-on of previous studies from our group utilising 3D agarose as a physiological model to study mechanotransduction pathways. Experimental methods are described to assess targets at the protein and gene expression level by Western blot analysis and real-time PCR, respectively. This chapter provides a quantitative gene expression approach to explore the intracellular pathways activated by both mechanical loading and inflammatory mediators and examine upstream phosphorylation events. Ultimately, development of methods used to analyse mechano-sensitive pathways will provide important information for the identification of appropriate pharmacological and physiotherapeutic agents for the treatment of osteoarthritis.

Mechanical loading, cartilage degradation, and arthritis

Joint tissues are exquisitely sensitive to their mechanical environment, and mechanical loading may be the most important external factor regulating the development and long-term maintenance of joint tissues. Moderate mechanical loading maintains the integrity of articular cartilage; however, both disuse and overuse can result in cartilage degradation. The irreversible destruction of cartilage is the hallmark of osteoarthritis and rheumatoid arthritis. In these instances of cartilage breakdown, inflammatory cytokines such as interleukin-1 beta and tumor necrosis factor-alpha stimulate the production of matrix metalloproteinases (MMPs) and aggrecanases (ADAMTSs), enzymes that can degrade components of the cartilage extracellular matrix. In order to prevent cartilage destruction, tremendous effort has been expended to design inhibitors of MMP/ADAMTS activity and/or synthesis. To date, however, no effective clinical inhibitors exist. Accumulating evidence suggests that physiologic joint loading helps maintain cartilage integrity; however, the mechanisms by which these mechanical stimuli regulate joint homeostasis are still being elucidated. Identifying mechanosensitive chondroprotective pathways may reveal novel targets or therapeutic strategies in preventing cartilage destruction in joint disease.

Phenotypic variations in chondrocyte subpopulations and their response to in vitro culture and external stimuli

Articular cartilage defects have limited capacity to self-repair, and cost society up to 60 billion dollars annually in both medical treatments and loss of working days. Recent developments in cartilage tissue engineering have resulted in many new products coming to market or entering clinical trials. However, there is a distinct lack of treatments which aim to recreate the complex zonal organization of articular cartilage. Cartilage tissue withstands repetitive strains throughout an individual's lifetime and provides frictionless movement between joints. The structure and composition of its intricately organized extracellular matrix varies with tissue depth to provide optimal resistance to loading, ensure ease of movement, and integrate with the subchondral bone. Each tissue zone is specially designed to resist the load it experiences, and maximize the tissue properties needed for its location. It is unlikely that a homogenous solution to tissue repair will be able to optimally restore the function of such a heterogeneous tissue. For zonal engineering of articular cartilage to become practical, maintenance of phenotypically stable zonal cell populations must be achieved. The chondrocyte phenotype varies considerably by zone, and it is the activity of these cells that help achieve the structural organization of the tissue. This review provides an examination of literature which has studied variations in cellular phenotype between cartilage zones. By doing so, we have identified critical differences between cell populations and highlighted areas of research which show potential in the field. Current research has made the morphological and metabolic variations between these cell populations clear, but an ideal way of maintaining these differences in vitro culture is yet to be established. Combinations of delivered growth factors, mechanical loading, and layered three-dimensional culture systems all show potential for achieving this goal. Furthermore, differentiation of progenitor cell populations into chondrocyte subpopulations may also hold promise for achieving large numbers of zonal chondrocytes. Success of the field lies in establishing methods of retaining phenotypically stable cell populations for in vitro culture.

Mechanical signals control SOX-9, VEGF, and c-Myc expression and cell proliferation during inflammation via integrin-linked kinase, B-Raf, and ERK1/2-dependent signaling in articular chondrocytes

Introduction

The importance of mechanical signals in normal and inflamed cartilage is well established. Chondrocytes respond to changes in the levels of proinflammatory cytokines and mechanical signals during inflammation. Cytokines like interleukin (IL)-1β suppress homeostatic mechanisms and inhibit cartilage repair and cell proliferation. However, matrix synthesis and chondrocyte (AC) proliferation are upregulated by the physiological levels of mechanical forces. In this study, we investigated intracellular mechanisms underlying reparative actions of mechanical signals during inflammation.

Methods

ACs isolated from articular cartilage were exposed to low/physiologic levels of dynamic strain in the presence of IL-1β. The cell extracts were probed for differential activation/inhibition of the extracellular signal-regulated kinase 1/2 (ERK1/2) signaling cascade. The regulation of gene transcription was examined by real-time polymerase chain reaction.

Results

Mechanoactivation, but not IL-1β treatment, of ACs initiated integrin-linked kinase activation. Mechanical signals induced activation and subsequent C-Raf-mediated activation of MAP kinases (MEK1/2). However, IL-1β activated B-Raf kinase activity. Dynamic strain did not induce B-Raf activation but instead inhibited IL-1β-induced B-Raf activation. Both mechanical signals and IL-1β induced ERK1/2 phosphorylation but discrete gene expression. ERK1/2 activation by mechanical forces induced SRY-related protein-9 (SOX-9), vascular endothelial cell growth factor (VEGF), and c-Myc mRNA expression and AC proliferation. However, IL-1β did not induce SOX-9, VEGF, and c-Myc gene expression and inhibited AC cell proliferation. More importantly, SOX-9, VEGF, and Myc gene transcription and AC proliferation induced by mechanical signals were sustained in the presence of IL-1β.

Conclusions

The findings suggest that mechanical signals may sustain their effects in proinflammatory environments by regulating key molecules in the MAP kinase signaling cascade. Furthermore, the findings point to the potential of mechanosignaling in cartilage repair during inflammation.

Biomechanical modulation of collagen fragment-induced anabolic and catabolic activities in chondrocyte/agarose constructs

INTRODUCTION

The present study examined the effect of collagen fragments on anabolic and catabolic activities by chondrocyte/agarose constructs subjected to dynamic compression.

METHODS

Constructs were cultured under free-swelling conditions or subjected to continuous and intermittent compression regimes, in the presence of the N-terminal (NT) and C-terminal (CT) telopeptides derived from collagen type II and/or 1400 W (inhibits inducible nitric oxide synthase (iNOS)). The anabolic and catabolic activities were compared to the amino-terminal fibronectin fragment (NH2-FN-f) and assessed as follows: nitric oxide (NO) release and sulphated glycosaminoglycan (sGAG) content were quantified using biochemical assays. Tumour necrosis factor-alpha (TNFalpha) and interleukin-1beta (IL-1beta) release were measured by ELISA. Gene expression of matrix metalloproteinase-3 (MMP-3), matrix metalloproteinase-13 (MMP-13), collagen type II and fibronectin were assessed by real-time quantitative polymerase chain reaction (qPCR). Two-way ANOVA and the post hoc Bonferroni-corrected t-test was used to examine data.

RESULTS

The presence of the NT or CT peptides caused a moderate to strong dose-dependent stimulation of NO, TNFalpha and IL-1beta production and inhibition of sGAG content. In some instances, high concentrations of telopeptides were just as potent in stimulating catabolic activities when compared to NH2-FN-f. Depending on the concentration and type of fragment, the increased levels of NO and cytokines were inhibited with 1400 W, resulting in the restoration of sGAG content. Depending on the duration and type of compression regime employed, stimulation with compression or incubation with 1400 W or a combination of both, inhibited telopeptide or NH2-FN-f induced NO release and cytokine production and enhanced sGAG content. All fragments induced MMP-3 and MMP-13 expression in a time-dependent manner. This effect was reversed with compression and/or 1400 W resulting in the restoration of sGAG content and induction of collagen type II and fibronectin expression.

CONCLUSIONS

Collagen fragments containing the N- and C-terminal telopeptides have dose-dependent catabolic activities similar to fibronectin fragments and increase the production of NO, cytokines and MMPs. Catabolic activities were downregulated by dynamic compression or by the presence of the iNOS inhibitor, linking reparative activities by both types of stimuli. Future investigations which examine the signalling cascades of chondrocytes in response to matrix fragments with mechanical influences may provide useful information for early osteoarthritis treatments.

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.

Influence of cartilaginous matrix accumulation on viscoelastic response of chondrocyte/agarose constructs under dynamic compressive and shear loading

A method has been developed to restore cartilage defects by culturing autologous chondrocytes to create a three dimensional tissue and then implanting the cultured tissue. In this kind of approach, it is important to characterize the dynamic mechanical behavior of the regenerated cartilaginous tissue, because these tissues need to bear various dynamic loadings in daily life. The objectives of this study were to evaluate in detail the dynamic viscoelastic responses of chondrocyte-seeded agarose gel cultures in compression and torsion (shear) and to determine the relationships between these mechanical responses and biochemical composition. The results showed that both the dynamic compressive and shear stiffness of the cultured constructs increased during culture. The relative energy dissipation in dynamic compression decreased, whereas that in dynamic shear increased during culture. Furthermore, correlation analyses showed that the sulfated glycosaminoglycan (sGAG) content of the cultured construct showed significant correlations with the dynamic modulus in both compression and shear situations. On the other hand, the loss tangent in dynamic compression, which represents the relative energy dissipation capability of the constructs, showed a low correlation with the sGAG content, whereas this capability in shear exhibited moderate correlation. In conclusion, we explored the dynamic viscoelasticity of the tissue-engineered cartilage in dynamic compression and shear, and determined correlations between viscoelasticity and biochemical composition.

Physiologic deformational loading does not counteract the catabolic effects of interleukin-1 in long-term culture of chondrocyte-seeded agarose constructs

An interplay of mechanical and chemical factors is integral to cartilage maintenance and/or degeneration. Interleukin-1 (IL-1) is a pro-inflammatory cytokine that is present at elevated concentrations in osteoarthritic joints and initiates the rapid degradation of cartilage when cultured in vitro. Several short-term studies have suggested that applied dynamic deformational loading may have a protective effect against the catabolic actions of IL-1. In the current study, we examine whether the long-term (42 days) application of dynamic deformational loading on chondrocyte-seeded agarose constructs can mitigate these catabolic effects. Three studies were carried out using two IL-1 isoforms (IL-1alpha and IL-1beta) in chemically defined medium supplemented with a broad range of cytokine concentrations and durations. Physiologic loading was unable to counteract the long-term catabolic effects of IL-1 under any of the conditions tested, and in some cases led to further degeneration over unloaded controls.

IL-1 and iNOS gene expression and NO synthesis in the superior region of meniscal explants are dependent on the magnitude of compressive strains

OBJECTIVE

Partial meniscectomy is known to cause osteoarthritis (OA) of the underlying cartilage as well as alter the load on the remaining meniscus. Removal of 30-60% of the medial meniscus increases compressive strains from a maximum of approximately 10% to almost 20%. The goal of this study is to determine if meniscal cells produce catabolic molecules in response to the altered loading that results from a partial meniscectomy.

METHOD

Relative changes in gene expression of interleukin-1 (IL-1), inducible nitric oxide synthase (iNOS) and subsequent changes in the concentration of nitric oxide (NO) released by meniscal tissue in response to compression were measured. Porcine meniscal explants were dynamically compressed for 2 h at 1 Hz to simulate physiological stimulation at either 10% strain or 0.05 MPa stress. Additional explants were pathologically stimulated to either 0% strain, 20% strain or, 0.1 MPa stress.

RESULTS

iNOS and IL-1 gene expression and NO release into the surrounding media were increased at 20% compressive strain compared to other conditions. Pathological unloading (0% compressive strain) of meniscal explants did not significantly change expression of IL-1 or iNOS genes, but did result in an increased amount of NO released compared to physiological strain of 10%.

CONCLUSION

These data suggest that meniscectomies which reduce the surface area of the meniscus by 30-60% will increase the catabolic activity of the meniscus which may contribute to the progression of OA.

Dynamic compression inhibits fibronectin fragment induced iNOS and COX-2 expression in chondrocyte/agarose constructs

Mechanical loading and the fibronectin fragments (FN-fs) are known to stimulate the anabolic and catabolic processes in articular cartilage, possible through pathways mediated by *NO. This study examined the combined effects of dynamic compression and the NH(2)-hep I or COOH-hep II FN-fs on the expression levels of iNOS and COX-2 and production of *NO and PGE(2) release. Both types of fragments induced iNOS and COX-2 expression and stimulated the production of *NO release. This response was inhibited by dynamic compression. Inhibitor experiments indicated that both dynamic compression and the iNOS inhibitor were important in restoring cell proliferation and proteoglycan synthesis in the presence of the FN-fs. This is the first study which demonstrates a downregulation of the FN-f-induced iNOS and COX-2 expression by dynamic compression. The combination of mechanical and pharmacological interventions makes this study a powerful tool to examine further the interactions of biomechanics and cell signalling in osteoarthritis.

Dynamic compression counteracts IL-1beta induced inducible nitric oxide synthase and cyclo-oxygenase-2 expression in chondrocyte/agarose constructs

Background

Nitric oxide and prostaglandin E₂ (PGE₂play pivotal roles in both the pathogenesis of osteoarthritis and catabolic processes in articular cartilage. These mediators are influenced by both IL-1β and mechanical loading, and involve alterations in the inducible nitric oxide synthase (iNOS) and cyclo-oxygenase (COX)-2 enzymes. To identify the specific interactions that are activated by both types of stimuli, we examined the effects of dynamic compression on levels of expression of iNOS and COX-2 and involvement of the p38 mitogen-activated protein kinase (MAPK) pathway.

Methods

Chondrocyte/agarose constructs were cultured under free-swelling conditions with or without IL-1β and/or SB203580 (inhibitor of p38 MAPK) for up to 48 hours. Using a fully characterized bioreactor system, constructs were subjected to dynamic compression for 6, 12 and 48 hours under similar treatments. The activation or inhibition of p38 MAPK by IL-1β and/or SB203580 was analyzed by western blotting. iNOS, COX-2, aggrecan and collagen type II signals were assessed utilizing real-time quantitative PCR coupled with molecular beacons. Release of nitrite and PGE₂ was quantified using biochemical assays. Two-way analysis of variance and the post hoc Bonferroni-corrected t-test were used to examine data.

Results

IL-1β activated the phosphorylation of p38 MAPK and this effect was abolished by SB203580. IL-1β induced a transient increase in iNOS expression and stimulated the production of nitrite release. Stimulation by either dynamic compression or SB203580 in isolation reduced the IL-1β induced iNOS expression and nitrite production. However, co-stimulation with both dynamic compression and SB203580 inhibited the expression levels of iNOS and production of nitrite induced by the cytokine. IL-1β induced a transient increase in COX-2 expression and stimulated the cumulative production of PGE₂ release. These effects were inhibited by dynamic compression or SB203580. Co-stimulation with both dynamic compression and SB203580 restored cytokine-induced inhibition of aggrecan expression. This is in contrast to collagen type II, in which we observed no response with the cytokine and/or SB203580.

Conclusion

These data suggest that dynamic compression directly influences the expression levels of iNOS and COX-2. These molecules are current targets for pharmacological intervention, raising the possibility for integrated pharmacological and biophysical therapies for the treatment of cartilage joint disorders.

Regulation of chondrocytic gene expression by biomechanical signals

Cartilage is a mechanosensitive tissue, which means that it can perceive and respond to biomechanical signals. Despite the known importance of biomechanical signals in the etiopathogenesis of arthritic diseases and their effectiveness in joint restoration, little is understood about their actions at the cellular level. Recent molecular approaches have revealed that specific biomechanical stimuli and cell interactions generate intracellular signals that are powerful inducers or suppressors of proinflammatory and reparative genes in chondrocytes. Biomechanical signals are perceived by cartilage in magnitude-, frequency-, and time-dependent manners. Static and dynamic biomechanical forces of high magnitudes induce proinflammatory genes and inhibit matrix synthesis. Contrarily, dynamic biomechanical signals of low/physiologic magnitudes are potent antiinflammatory signals that inhibit interleukin-1beta (IL-1beta)-induced proinflammatory gene transcription and abrogate IL-1beta/tumor necrosis factor-alpha-induced inhibition of matrix synthesis. Recent studies have identified nuclear factor-kB (NF-kB) transcription factors as key regulators of biomechanical signal-mediated proinflammatory and antiinflammatory actions. These signals intercept multiple steps in the NF-kappaB signaling cascade to regulate cytokine gene expression. Taken together, these findings provide insight into how biomechanical signals regulate inflammatory and reparative gene transcription, underscoring their potential in enhancing the ability of chondrocytes to curb inflammation in diseased joints.

Hydrogel effects on bone marrow stromal cell response to chondrogenic growth factors

The aim of this study was to investigate the effects of alginate and agarose on the response of bone marrow stromal cells (BMSCs) to chondrogenic stimuli. Rat BMSCs were expanded in monolayer culture with or without FGF-2 supplementation. Cells were then seeded in 2% alginate and agarose gels and cultured in media with or without TGF-beta1 or dexamethasone (Dex). Sulfated glycosaminoglycans (sGAGs), collagen type II, and aggrecan were expressed in all groups that received TGF-beta1 treatment during hydrogel culture. Expansion of rat BMSCs in the presence of FGF-2 increased production of sGAG in TGF-beta1-treated groups over those cultures that were treated with TGF-beta1 alone in alginate cultures. However, in agarose, cells exposed to FGF-2 during expansion produced less sGAG within TGF-beta1-supplemented groups over those cultures treated with TGF-beta1 alone. Dex was required for optimal matrix synthesis in both hydrogels, but was found to decrease cell viability in agarose constructs. These results indicate that the response of BMSCs to a chondrogenic growth factor regimen is scaffold dependent.

Prostaglandin E2 synthesis in cartilage explants under compression: mPGES-1 is a mechanosensitive gene

Knee osteoarthritis (OA) results, at least in part, from overloading and inflammation leading to cartilage degradation. Prostaglandin E2 (PGE₂) is one of the main catabolic factors involved in OA. Its synthesis is the result of cyclooxygenase (COX) and prostaglandin E synthase (PGES) activities whereas NAD+-dependent 15 hydroxy prostaglandin dehydrogenase (15-PGDH) is the key enzyme implicated in the catabolism of PGE₂. For both COX and PGES, three isoforms have been described: in cartilage, COX-1 and cytosolic PGES are constitutively expressed whereas COX-2 and microsomal PGES type 1 (mPGES-1) are inducible in an inflammatory context. COX-3 (a variant of COX-1) and mPGES-2 have been recently cloned but little is known about their expression and regulation in cartilage, as is also the case for 15-PGDH. We investigated the regulation of the genes encoding COX and PGES isoforms during mechanical stress applied to cartilage explants. Mouse cartilage explants were subjected to compression (0.5 Hz, 1 MPa) for 2 to 24 hours. After determination of the amount of PGE₂ released in the media (enzyme immunoassay), mRNA and proteins were extracted directly from the cartilage explants and analyzed by real-time RT-PCR and western blotting respectively. Mechanical compression of cartilage explants significantly increased PGE₂ production in a time-dependent manner. This was not due to the synthesis of IL-1, since pretreatment with interleukin 1 receptor antagonist (IL1-Ra) did not alter the PGE₂ synthesis. Interestingly, COX-2 and mPGES-1 mRNA expression significantly increased after 2 hours, in parallel with protein expression, whereas COX-3 and mPGES-2 mRNA expression was not modified. Moreover, we observed a delayed overexpression of 15-PGDH just before the decline of PGE₂ synthesis after 18 hours, suggesting that PGE₂ synthesis could be altered by the induction of 15-PGDH expression. We conclude that, along with COX-2, dynamic compression induces mPGES-1 mRNA and protein expression in cartilage explants. Thus, the mechanosensitive mPGES-1 enzyme represents a potential therapeutic target in osteoarthritis.

The effects of radial shock waves on the metabolism of equine cartilage explantsin vitro

AIM

To investigate, in vitro, the effects of radial shock waves on the release of nitric oxide (NO) and synthesis of prostaglandin E2 (PGE2) and glycosaminoglycan (GAG), and liberation of GAG, from equine articular cartilage explants.

METHODS

Equine cartilage from normal metacarpophalangeal and metatarsophalangeal joints was exposed to radial shock waves at various impulse doses and then maintained as explants in culture for 48 h. Shock waves were delivered at 1,876 Torr pressure and a frequency of 10 Hz. Treatment groups consisted of a negative control group, or application of 500, 2,000, or 4,000 impulses by use of either a convex handpiece (Group A) or concave handpiece (Group B). Synthesis of GAG was measured using incorporation of 35S-labelled sodium sulphate. Additionally, the synthesis of NO and PGE2, and content of GAG of the explants and media were determined.

RESULTS

No significant effects (p>0.05) of radial shock-wave treatment were evident on the synthesis of NO or PGE2, or release of GAG by cartilage explants. However, radial shock waves decreased synthesis of GAG measured 48 h after exposure for all treatment groups other than the 500-impulse Group-A explants (p<0.05).

CONCLUSIONS

Radial shock waves impact the metabolism of GAG in chondrocytes in equine articular cartilage. Further studies will be required to fully investigate the impact of this effect on the health of joints, and to elucidate the clinical impact.

Therapeutic ultrasound effects on interleukin-1beta stimulated cartilage construct in vitro

A low-intensity ultrasound (LIUS) was examined for its possible therapeutic effects on degenerative osteoarthritic cartilage. Along with the daily treatment of 5 ng interleukin-1beta (IL-1beta) for 5 d, an engineered 3D neocartilage construct was used as an in vitro OA model. Followed by 24 h preincubation with the first dose of IL-1beta, the constructs were then given ultrasonic stimulation (frequency 1.5 MHz and SATA 30 mW/cm(2)) once a day up to 5 d for the predetermined time. Fresh IL-1beta was added before the stimulation. The difference in the cell number and viability was insignificant between control (US-/IL+) and LIUS-stimulated groups. As the daily stimulation time was extended, the GAG contents in the constructs themselves significantly increased with 50 min stimulation but those released into the culture medium remained unaffected by LIUS. While the gene expression level of aggrecan was similar between control and LIUS (50 min) group, the ratio of collagen type II to type I was found to be higher in the control. The mRNA level of matrix metalloproteinase (MMP)-1 was substantially downregulated in the stimulated construct and that of MMP-13 was indifferent between control and stimulated one. The endogenous expression of transforming growth factor (TGF)-beta1 and beta3 was barely responsive to the LIUS stimulation. From histologic analysis, more intense GAG deposition was clearly identified with the LIUS-stimulated constructs. This study indicates that LIUS may have a significant potential to be a chondroprotective stimulant for osteoarthritic cartilage.

Biomechanical signals suppress proinflammatory responses in cartilage: early events in experimental antigen-induced arthritis

Although biomechanical signals generated during joint mobilization are vital in maintaining integrity of inflamed cartilage, the molecular mechanisms of their actions are little understood. In an experimental model of arthritis, we demonstrate that biomechanical signals are potent anti-inflammatory signals that repress transcriptional activation of proinflammatory genes and augment expression of anti-inflammatory cytokine IL-10 to profoundly attenuate localized joint inflammation.

Biomechanical strain regulates TNFR2 but not TNFR1 in TMJ cells

We sought to examine whether cyclic tensile strain (CTS) regulates the gene expression of tumor necrosis factor (TNF)-alpha, its receptors TNFR1 and TNFR2, and inducible nitric oxide synthase (iNOS) under inflammatory conditions, and whether these effects of CTS are sustained. Rat temporomandibular joint disc cells (TDC) were exposed to CTS in the presence or absence of interleukin (IL)-1beta for 4 and 24h. Cells were also stimulated with IL-1beta for 24h while being subjected to CTS only for the initial 1, 2, 4, 8, and 12h or the entire 24h incubation time. Furthermore, cells were incubated with IL-1beta for 24, 36, or 48 h while being exposed to CTS only for the initial 8h. Gene expression of TNF-alpha, its receptors, and iNOS was analyzed by RT-PCR, whereas protein synthesis was determined by ELISA for TNF-alpha, immunofluorescence for TNFRs, and Griess reaction for nitric oxide. CTS inhibited the IL-1beta-stimulated synthesis of TNF-alpha, TNFR2, and iNOS. TNFR1 was constitutively expressed but not regulated by IL-1beta or CTS. Application of CTS for only 1 or 2h during a 24h incubation with IL-1beta was sufficient to inhibit IL-1beta-induced upregulation of TNF-alpha, TNFR2, and iNOS. However, for maximal inhibition of these genes a longer exposure of CTS was required. These findings are the first to show that biomechanical signals regulate the expression of TNFR2 but not TNFR1 under inflammatory conditions. Furthermore, the antiinflammatory effects of biomechanical signals on TDC are maintained for prolonged periods of time but are transient.

Biomechanical signals exert sustained attenuation of proinflammatory gene induction in articular chondrocytes

OBJECTIVES

Physical therapies are commonly used for limiting joint inflammation. To gain insight into their mechanisms of actions for optimal usage, we examined persistence of mechanical signals generated by cyclic tensile strain (CTS) in chondrocytes, in vitro. We hypothesized that mechanical signals induce anti-inflammatory and anabolic responses that are sustained over extended periods.

METHODS

Articular chondrocytes obtained from rats were subjected to CTS for various time intervals followed by a period of rest, in the presence of interleukin-1beta (IL-1beta). The induction for cyclooxygenase (COX-2), inducible nitric oxide synthase (iNOS), matrix metalloproteinase (MMP)-9, MMP-13 and aggrecan was analyzed by real-time polymerase chain reaction (PCR), Western blot analysis and immunofluorescence.

RESULTS

Exposure of chondrocytes to constant CTS (3% CTS at 0.25 Hz) for 4-24 h blocked more than 90% (P<0.05) of the IL-1beta-induced transcriptional activation of proinflammatory genes, like iNOS, COX-2, MMP-9 and MMP-13, and abrogated inhibition of aggrecan synthesis. CTS exposure for 4, 8, 12, 16, or 20 h followed by a rest for 20, 16, 12, 8 or 4h, respectively, revealed that 8h of CTS optimally blocked (P<0.05) IL-1beta-induced proinflammatory gene induction for ensuing 16 h. However, CTS for 8h was not sufficient to inhibit iNOS expression for ensuing 28 or 40 h.

CONCLUSIONS

Data suggest that constant application of CTS blocks IL-1beta-induced proinflammatory genes at transcriptional level. The signals generated by CTS are sustained after its removal, and their persistence depends upon the length of CTS exposure. Furthermore, the sustained effects of mechanical signals are also reflected in their ability to induce aggrecan synthesis. These findings, once extrapolated to human chondrocytes, may provide insight in obtaining optimal sustained effects of physical therapies in the management of arthritic joints.

Cyclooxygenases and prostaglandin E2 receptors in growth plate chondrocytes in vitro and in situ--prostaglandin E2 dependent proliferation of growth plate chondrocytes

Prostaglandin E₂ (PGE₂) plays an important role in bone development and metabolism. To interfere therapeutically in the PGE₂ pathway, however, knowledge about the involved enzymes (cyclooxygenases) and receptors (PGE₂ receptors) is essential. We therefore examined the production of PGE₂ in cultured growth plate chondrocytes in vitro and the effects of exogenously added PGE₂ on cell proliferation. Furthermore, we analysed the expression and spatial distribution of cyclooxygenase (COX)-1 and COX-2 and PGE₂ receptor types EP1, EP2, EP3 and EP4 in the growth plate in situ and in vitro. PGE₂ synthesis was determined by mass spectrometry, cell proliferation by DNA [³H]-thymidine incorporation, mRNA expression of cyclooxygenases and EP receptors by RT-PCR on cultured cells and in homogenized growth plates. To determine cellular expression, frozen sections of rat tibial growth plate and primary chondrocyte cultures were stained using immunohistochemistry with polyclonal antibodies directed towards COX-1, COX-2, EP1, EP2, EP3, and EP4. Cultured growth plate chondrocytes transiently secreted PGE₂ into the culture medium. Although both enzymes were expressed in chondrocytes in vitro and in vivo, it appears that mainly COX-2 contributed to PGE₂-dependent proliferation. Exogenously added PGE₂ stimulated DNA synthesis in a dose-dependent fashion and gave a bell-shaped curve with a maximum at 10^-8 M. The EP1/EP3 specific agonist sulprostone and the EP1-selective agonist ONO-D1-004 increased DNA synthesis. The effect of PGE₂ was suppressed by ONO-8711. The expression of EP1, EP2, EP3, and EP4 receptors in situ and in vitro was observed; EP2 was homogenously expressed in all zones of the growth plate in situ, whereas EP1 expression was inhomogenous, with spared cells in the reserve zone. In cultured cells these four receptors were expressed in a subset of cells only. The most intense staining for the EP1 receptor was found in polygonal cells surrounded by matrix. Expression of receptor protein for EP3 and EP4 was observed also in rat growth plates. In cultured chrondrocytes, however, only weak expression of EP3 and EP4 receptor was detected. We suggest that in growth plate chondrocytes, COX-2 is responsible for PGE₂ release, which stimulates cell proliferation via the EP1 receptor.

Integrin-mediated mechanotransduction in IL-1 beta stimulated chondrocytes

Mechanical loading and interleukin-1 beta (IL-1 beta) influence the release of nitric oxide (*NO) and prostaglandin E2 (PGE2) from articular chondrocytes via distinct signalling mechanisms. The exact nature of the interplay between the respective signalling pathways remains unclear. Recent studies have shown that integrins act as mechanoreceptors and may transduce extracellular stimuli into intracellular signals, thereby influencing cellular response. The current study demonstrates that the application of dynamic compression induced an inhibition of *NO and an upregulation of cell proliferation and proteoglycan synthesis in the presence and absence of IL-1 beta. PGE2 release was not affected by dynamic compression in the absence of IL-1 beta but was inhibited in the presence of the cytokine. The integrin binding peptide, GRGDSP, abolished or reversed the compression-induced alterations in all four parameters assessed in the presence and absence of IL-1 beta. The non-binding control peptide, GRADSP, had no effect. These data clearly demonstrate that the metabolic response of the chondrocytes to dynamic compression in the presence and absence of IL-1 beta, are integrin mediated.

Anti-inflammatory effects of IL-4 and dynamic compression in IL-1β stimulated chondrocytes

Mechanical loading can counteract inflammatory pathways induced by IL-1beta by inhibiting *NO and PGE2, catabolic mediators known to be involved in cartilage degradation. The current study investigates the potential of dynamic compression, in combination with the anti-inflammatory cytokine, IL-4, to further abrogate the IL-1beta induced effects. The data presented demonstrate that IL-4 alone can inhibit nitrite release in the presence and absence of IL-1beta and partially reverse the IL-1beta induced PGE2 release. When provided in combination, IL-4 and dynamic compression could further abrogate the IL-1beta induced nitrite and PGE2 release. IL-1beta inhibited [3H]thymidine incorporation and this effect could be reversed by IL-4 or dynamic strain alone or both in combination. By contrast, 35SO4 incorporation was not influenced by IL-4 and/or dynamic strain in IL-1beta stimulated constructs. IL-4 and mechanical loading may therefore provide a potential protective mechanism for cartilage destruction as observed in OA.

The influence of oxygen tension on the induction of nitric oxide and prostaglandin E2 by mechanical stress in articular cartilage

OBJECTIVES

Articular cartilage is an avascular tissue that exists at low oxygen tension. Oxygen tension can influence the production of the pro-inflammatory mediators nitric oxide (NO) and prostaglandin E2 (PGE(2)) in cartilage, which are increased in osteoarthritis (OA). The synthesis of these molecules can be stimulated by mechanical stress, which is an important risk factor for OA. The objective of this study was to determine the influence of oxygen tension on the induction of NO and PGE(2) production in articular cartilage in response to mechanical stress.

DESIGN

Intermittent mechanical compression (0.05MPa, 0.5Hz for 24h) was applied to full thickness skeletally mature porcine articular cartilage explants at either 20%, 5%, or 1% O(2). NO, PGE(2) and peroxynitrite formation were measured, and the effect of the selective nitric oxide synthase 2 inhibitor 1400W was tested.

RESULTS

Incubating articular cartilage at 5% O(2) significantly increased (P<0.001) baseline NO production, as compared with 1% or 20% O(2). Peroxynitrite formation was lower at reduced oxygen tension. Mechanical compression significantly increased (P<0.001) NO production at 20% O(2) but not at 5% or 1% O(2), and significantly increased (P<0.001) PGE(2) production at 20% O(2) (50 fold) and 5% O(2) (4 fold) but not at 1% O(2). 1400W blocked mechanically induced NO production and further increased PGE(2) production at 5% O(2) (P<0.05).

CONCLUSIONS

Oxygen tension influences the endogenous production of NO and PGE(2) in cartilage and can have a significant effect on the induction of these inflammatory mediators in response to mechanical compression.

Effect of hyaluronic acid (MW 500-730 kDa) on proteoglycan and nitric oxide production in human osteoarthritic chondrocyte cultures exposed to hydrostatic pressure

OBJECTIVE

This study investigated the in vitro effects of hyaluronic acid (HA) of molecular weight (MW) 500-730 kDa on human articular chondrocytes cultivated for 48 h in the presence of interleukin-1beta (IL-1beta) with and without hydrostatic cyclical pressure.

DESIGN

The effects of 10 and 100 microg/ml HA with and without IL-1beta were assessed in the culture medium of cells exposed to pressurization cycles in the form of sinusoidal waves (minimum pressure 1MPa, maximum pressure 5MPa) at a frequency of 0.25Hz for 3h, by the immunoenzymatic method on microplates for the quantitative measurement of human proteoglycans (PG) and by the Griess method for nitrites (NO). Morphological analyses were performed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM).

RESULTS

The presence of IL-1beta determines a significant decrease in PG and a significant increase in NO concentrations measured in the culture medium. When the cells are cultured in the presence of IL-1beta and HA at the two concentrations, a statistically significant restoration of PG and a decrease in NO levels are observed. Under pressurization conditions, we observed that the PG concentration in the medium of cells presented a very significant increase in all the conditions used in the study, except for IL-1beta alone. NO production decreased very significantly in the presence of IL-1beta+HA 10 and IL-1beta+HA 100. The results of metabolic evaluation are confirmed by morphological findings obtained by TEM and SEM.

CONCLUSIONS

These in vitro studies confirm both the protective role of HA (MW 500-730 kDa), which counteracts the IL-1beta-induced effects, and the importance of pressure on chondrocyte metabolism and morphology.

Etiology and pathophysiology of osteoarthritis

Acute or chronic insult, including normal wear and tear, age, obesity, and joint injury, may initiate an imbalance between matrix synthesis and matrix degradation in healthy cartilage that promotes chondral loss and prevents cartilage self-repair. The structure of healthy cartilage and the pathophysiological mechanisms of its degradation are described, followed by descriptions of endogenous and exogenous factors believed to be involved in the progressive course of osteoarthritis. Studies cited include research from the community of sports medicine.

Comparative effects of ginger root (Zingiber officinale Rosc.) on the production of inflammatory mediators in normal and osteoarthrotic sow chondrocytes

Ginger root was previously demonstrated to exert anti-arthritic effects in sow cartilage explants. This study further investigated the comparative effects of ginger root extract (GRE) on the production of inflammatory mediators, including nitric oxide (NO) and prostaglandin E2 (PGE2), in normal chondrocytes (NC) and osteoarthrotic chondrocytes (OC) isolated from sow cartilage explants. The sow chondrocyte cells were isolated and grown in Ham's F-12/Dulbecco's modified Eagle's medium supplemented with 10% fetal bovine serum and 1% antibiotics. GRE was then added at different concentrations (0-2,000 microg/mL), and the cells were allowed to grow for 24 hours in the presence of cytokine inducer. The culture media were collected and assayed for NO by the Griess reaction and for PGE2 by radioimmunoassay. When GRE was not used, the NC had lower PGE2 and NO than the OC. With GRE treatment, both PGE2 and NO decreased linearly in both the NC and the OC. As GRE concentrations increased, the rate of PGE(2) decrease was the same in the NC and the OC, whereas the rate of NO decrease was greater for the OC than for the NC. Collectively, OC produce more inflammatory mediators than do NC, and the production of inflammatory mediators was reduced when GRE was added to both the OC and the NC. The inhibitory effects of GRE on NO and PGE2 production by sow OC observed in this study suggest an important role for GRE as an anti-arthritic agent.