The pathophysiology of osteoarthritis

Serum and synovial fluid levels of CCL18 are correlated with radiographic grading of knee osteoarthritis

Background

Chemokines are involved in the pathogenesis of osteoarthritis (OA). CCL18, a member of the chemokines family, is observed in synovial fluid (SF) of OA patients. The aim of this study was to determine the association between CCL18 levels in serum and SF with radiographic knee OA.

Material/Methods

This study was conducted in a population of 308 patients with knee OA. The radiological knee OA was graded by the Kellgren-Lawrence grading system.

Results

Serum levels of CCL18 in knee OA patients were markedly higher than those in healthy controls. Serum and SF levels of CCL18 increased with the severity of KL grades and were correlated with disease severity.

Conclusions

The CCL18 levels in serum and SF are correlated with the severity of OA.

Detecting cathepsin activity in human osteoarthritis via activity-based probes

Introduction

Lysosomal cathepsins have been reported to contribute to Osteoarthritis (OA) pathophysiology due to their increase in pro-inflammatory conditions. Given the causal role of cathepsins in OA, monitoring their specific activity could provide means for assessing OA severity. To this end, we herein sought to assess a cathepsin activity-based probe (ABP), GB123, in vitro and in vivo.

Methods

Protein levels and activity of cathepsins B and S were monitored by immunoblot analysis and GB123 labeling in cultured primary chondrocytes and conditioned media, following stimuli with tumor necrosis factor alpha (TNFα) and/or Interleukin 1 beta (IL-1β). Similarly, cathepsin activity was examined in sections of intact cartilage (IC) and degraded cartilage (DC) regions of OA. Finally, synovial fluid (SF) and serum from donors with no signs of diseases, early OA, late OA and rheumatoid arthritis (RA) patients were analyzed with GB123 to detect distinct activity levels of cathepsin B and S.

Results

Cathepsin activity in cell lysates, conditioned media explants and DC sections showed enhanced enzymatic activity of cathepsins B and S. Further histological analysis revealed that cathepsin activity was found higher in superficial zones of DC than in IC. Examining serum and SF revealed that cathepsin B is significantly elevated with OA severity in serum and SF, yet levels of cathepsin S are more correlated with synovitis and RA.

Conclusions

Based on our data, cathepsin activity monitored by ABPs correlated well with OA severity and joint inflammation, directing towards a novel etiological target for OA, which possesses significant translational potential in developing means for non-invasive detection of early signs of OA.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-015-0586-5) contains supplementary material, which is available to authorized users.

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.

Effects of Adipokines and Insulin on Intracellular pH, Calcium Concentration, and Responses to Hypo-Osmolarity in Human Articular Chondrocytes from Healthy and Osteoarthritic Cartilage

OBJECTIVE

To evaluate the effects of adipokines and insulin on intracellular calcium concentration ([Ca(2+)]i) and pH (pHi) in human articular chondrocytes from healthy (CHC) and osteoarthritic cartilage (COC).

DESIGN

pHi and [Ca(2+)]i were measured using BCECF and Fura-2 fluorometric probes in CHC and COC under control conditions and following a hypotonic shock. The effects of interleukin-1β (IL1β), tumor necrosis factor-α (TNFα), insulin, leptin, resistin, and adiponectin were assessed.

RESULTS

pHi was lower in COC than in CHC. Only IL1β β decreased pHi in both cell types; all the agents enhanced pHi recovery following an ammonium prepulse in CHC, effect that was attenuated by Na(+)-H(+) exchanger inhibitors, but they had no effect in COC. Hypotonic shock (HTS) caused a pHi increase, which was significantly smaller in COC. All the hormones attenuated this response and the effect of IL1β was greater. The basal [Ca(2+)]i was similar in COC and CHC; IL1β, TNFα, and insulin increased the [Ca(2+)]i, but leptin, resistin, and adiponectin did not. These effects were greater in COC. This [Ca(2+)]i increase was dependent on extracellular Ca(2+) and attenuated by Na(+)-Ca(2+) exchanger inhibitors. HTS caused a [Ca(2+)]i increase, which was inhibited by transient receptor potential vanilloid blockers and attenuated by all the hormones tested with the exception of adiponectin.

CONCLUSIONS

These findings may help explain the association between obesity and osteoarthritis, in which these hormones are altered. The responses of CHC and COC are different, which suggests that a modification of pH and Ca(2+) homeostasis is part of the osteoarthritis pathophysiology.

Relationship between growth factors and its implication in the pathogenesis of leprosy

Leprosy is a chronic infectious disease caused by Mycobacterium leprae which affects the skin and peripheral nervous system. The immune response of the host determines the clinical course of the disease. The tuberculoid form is the result of high cell-mediated immunity characterized by a Th1 response, whereas the lepromatous form is characterized by low cell-mediated immunity and a Th2 humoral response. The neural damage established produces marked changes in the expression of growth factors such as nerve growth factor (NGF) and its receptors (NGF-R). The expression of NGF, associated with the expression of Th1 and Th2 cytokines, might be involved in the tissue damage caused by the bacillus. Therefore, the objective of this study was to correlate the immunoexpression patterns of NGF and NGF-R in the different clinical forms of leprosy, and to associate the findings with the in situ expression of TGF-β and clinical classification of the disease. TGF-β, NGF and NGF-R immunoexpression was analyzed by immunohistochemistry in paraffin-embedded material. Most patients were males with a mean age of 40.7 years. TGF-β levels were significantly higher in the lepromatous forms. No significant difference in the immunoexpression of NGF or NGF-R was observed between the clinical forms, but expression tended to be higher at the lepromatous pole. There was a significant positive correlation between NGF and NGF-R in the different clinical forms of leprosy. A significant positive correlation was observed between NGF, NGF-R and TGF-β. It can be concluded that, even existing evidence on the role of these molecules in the clinical spectrum of leprosy.

Acetylated derivative of glaucine inhibits joint inflammation in collagenase-induced arthritis

CONTEXT

Osteoarthritis (OA) has become by far the most common joint disorder. A number of studies using OA animal models have explored the effects of agents that can modulate bone metabolism.

OBJECTIVE

In the present study, we investigated the effect of acetylated derivative of plant alkaloid glaucine (ADG) on experimental OA in mice.

MATERIALS AND METHODS

Arthritis was induced by two intraarticular (i.a.) injections of collaganase. Histopathological changes were observed through hematoxylin and eosine (H&E), safranin O and toluidine blue staining. Differentiation of bone marrow (BM) cells was evaluated by tartarate-resistant acid phosphatase (TRAP) assay. The expression of phospho-Janus kinase 2 (pJAK2) and phospho signal transducer and activator of transcription3 (pSTAT3) expression in the joints was determined by immunohistochemistry.

RESULTS

We established that ADG significantly decreased cell infiltration (2.32 ± 0.14 versus 1.62 ± 0.13), cartilage loss (2.42 ± 0.12 versus 1.12 ± 0.10) and bone erosion (1.76 ± 0.13 versus 1.04 ± 0.14) in arthritic mice. It appeared that the substance inhibited in a dose-dependent manner osteoclast differentiation in vitro. ADG suppressed the expression of pJAK2 in the joint and partially affected the expression of pSTAT3.

CONCLUSION

Present results suggest that ADG is a suitable candidate for further development as an anti-arthritic agent.

Chopping off the chondrocyte proteome

The progressive nature of osteoarthritis is manifested by the dynamic increase of degenerated articular cartilage, which is one of the major characteristics of this debilitating disease. As articular chondrocytes become exposed to inflammatory stress they enter a pro-catabolic state, which leads to the secretion and activation of a plethora of proteases. In aim to detect the disease before massive areas of cartilage are destroyed, various protein and non-protein biomarkers have been examined in bodily fluids and correlated with disease severity. This review will discuss the widely research extracellular degraded products as well as products generated by affected cellular pathways upon increased protease activity. While extracellular components could be more abundant, cleaved cellular proteins are less abundant and are suggested to possess a significant effect on cell metabolism and cartilage secretome. Subtle changes in cell secretome could potentially act as indicators of the chondrocyte metabolic and biological state. Therefore, it is envisioned that combined biomarkers composed of both cell and extracellular-degraded secretome could provide a valuable platform for testing drug efficacy to halt disease progression at its early stages.

Characterization of metabolites determined by means of 1H HR MAS NMR in intervertebral disc degeneration

Object

The objective of this study is the identification of metabolites by means of ¹H high resolution magic angle spinning nuclear magnetic resonance (¹H HR MAS NMR) spectroscopy and the evaluation of their applicability in distinguishing between healthy and degenerated disc tissues.

Materials and methods

Differences between the metabolic profiles of healthy and degenerated disc tissues were studied by means of ¹H HR MAS NMR. Analysis was performed for 81 disc tissue samples (control samples n = 21, degenerated disc tissue samples n = 60). Twenty six metabolites (amino acids, carbohydrates, and alcohols) were identified and quantified.

Results

The results indicate that the metabolic profile of degenerated discs is characterized by the presence of 2-propanol and the absence of scyllo-inositol and taurine. The concentrations of 2-propanol and lactate increase with age.

Conclusion

PCA analysis of ex vivo ¹H HR MAS NMR data revealed the occurrence of two groups: healthy and degenerative disc tissues. The effects of insufficient nutrient supply of discs, leading to their degeneration and back pain, are discussed.

Electronic supplementary material

The online version of this article (doi:10.1007/s10334-014-0457-0) contains supplementary material, which is available to authorized users.

Effects of low-intensity pulsed ultrasound on integrin-FAK-PI3K/Akt mechanochemical transduction in rabbit osteoarthritis chondrocytes

The effect of low-intensity pulsed ultrasound (LIPUS) on extracellular matrix (ECM) production via modulation of the integrin/focal adhesion kinase (FAK)/phosphatidylinositol 3-kinase (PI3K)/Akt pathway has been investigated in previous studies in normal chondrocytes, but not in osteoarthritis (OA). Therefore, we investigated the LIPUS-induced integrin β1/FAK/PI3K/Akt mechanochemical transduction pathway in a single study in rabbit OA chondrocytes. Normal and OA chondrocytes were exposed to LIPUS, and mRNA and protein expression of cartilage, metalloproteinases and integrin-FAK-PI3K/Akt signal pathway-related genes was determined by quantitative reverse transcription polymerase chain reaction and Western blotting, respectively. Compared with levels in normal chondrocytes, expression levels of ECM-related genes were significantly lower in OA chondrocytes and those of metalloproteinase-related genes were significantly higher. In addition, integrin β1 gene expression and the phosphorylation of FAK, PI3K and Akt were significantly higher in OA chondrocytes. The expression of all tested genes was significantly increased except for that of metalloproteinase, which was significantly decreased in the LIPUS-treated OA group compared to the untreated OA group. LIPUS may affect the integrin-FAK-PI3K/Akt mechanochemical transduction pathway and alter ECM production by OA chondrocytes. Our findings will aid the future development of a treatment or even cure for OA.

MicroRNAs play a role in chondrogenesis and osteoarthritis (review)

Osteoarthritis (OA) is one of the most widespread degenerative joint diseases affecting the elderly. Research into the regulatory mechanisms underlying the pathogenesis of OA is therefore warranted, and over the past decade, there has been an increased focus on the functional role of microRNAs (miRNAs or miRs). In this systematic review, we aimed to review the evidence implicating miRNAs in the pathogenesis of chondrogenesis and OA. Systematic reviews of PubMed and Embase were performed to search for studies using strings of miRNAs, non-coding RNAs, cartilage, chondrocytes, chondrogenesis, chondrocytogenesis and OA. The identified studies were retrieved, and the references provided were searched. The selected studies were required to focus on the role of miRNAs in chondrogenesis and OA. The results of this review indicated that more than 25 miRNAs have been implicated in chondrogenesis and OA. In particular, chondrocytogenesis, chondrogenic differentiation, chondrocyte proliferation, chondrocyte hypertrophy, endochondral ossification, and proteolytic enzyme regulation are targeted or facilitated by more than 1 miRNA. To date, limited efforts have been performed to evaluate translational applications for this knowledge. Novel therapeutic strategies have been developed and are under investigation to selectively modulate miRNAs, which could potentially enable personalized OA therapy. miRNAs appear to be important modulators of chondrogenesis and OA. Their expression is frequently altered in OA, and many are functionally implicated in the pathogenesis of the disease. The translational roles and therapeutic potential of miRNAs remains to be evaluated.

Clinical experience with duloxetine in the management of chronic musculoskeletal pain. A focus on osteoarthritis of the knee

Duloxetine is a serotonin and norepinephrine reuptake inhibitor (SNRI) with central nervous system activity. Its analgesic efficacy in central pain is putatively related to its influence on descending inhibitory pain pathways. The analgesic efficacy of duloxetine has been demonstrated in four distinct chronic pain conditions. These include neuropathic pain associated with diabetic peripheral neuropathy, fibromyalgia, chronic low back pain, and osteoarthritis knee pain (OAKP). The purpose of this review is to examine the clinical efficacy and safety of duloxetine in the management of chronic OAKP. Three separate randomized, double-blind placebo-controlled trials have demonstrated that (1) a clinically meaningful decrease in pain severity occurs at about 4 weeks relative to placebo, (2) patients receiving duloxetine report better improvements in physical functioning relative to placebo, (3) duloxetine is safe and effective when used adjunctively with nonsteroidal anti-inflammatory drugs, and (4) that there are no new safety signals beyond what has been observed in other indications.

Tumor necrosis factor-α induces ADAMTS-4 expression in human osteoarthritis chondrocytes

Tumor necrosis factor (TNF)-α and a disintegrin and metalloproteinase with thrombospondin motifs 4 (ADAMTS-4) are important in osteoarthritis (OA) cartilage degradation. In the present study, we explored the interaction between the two proteins by examining the effect of TNF-α on ADAMTS-4 expression and activity in osteoarthritic chondrocytes. Human osteoarthritic chondrocytes were treated with TNF-α in different concentrations (5, 15, 30, 45 and 60 ng/ml) for different lengths of time (1, 6, 12, 18 and 24 h) with or without the TNF receptor 1 (TNFR1) inhibitor SPD304 or different kinase inhibitors. TNF-α increased the ADAMTS-4 mRNA level in a statistically significant dose- and time-dependent manner within 18 h, which was reflected in the dose-dependent induction of the ADAMTS-4 promoter activity, ADAMTS-4 protein expression and ADAMTS-4 activity. SPD304 (50 µM) and p38 mitogen-activated protein kinase (MAPK) siRNA and inhibitor PD169316 (25 µM) completely eradicated the promoting effect of TNF-α on ADAMTS-4 expression and activity. TNF-α induces ADAMTS-4 expression and activity in human osteoarthritic chondrocytes at the transcriptional level via TNFR1 by a p38 MAPK-dependent mechanism. To the best of our knowledge, this is the first evidence of crosstalk between TNF-α and ADAMTS-4 in relation to OA cartilage degradation, which adds novel insight into the pathophysiology of OA and cartilage degradation.

Lactoferricin enhances BMP7-stimulated anabolic pathways in intervertebral disc cells

Bone-morphogenetic protein-7 (BMP7) is a well-known anabolic and anti-catabolic growth factor on intervertebral disc (IVD) matrix and cell homeostasis. Similarly, Lactoferricin B (LfcinB) has recently been shown to have pro-anabolic, anti-catabolic, anti-oxidative and/or anti-inflammatory effects in bovine disc cells in vitro. In this study, we investigated the potential benefits of using combined peptide therapy with LfcinB and BMP7 for intervertebral disc matrix repair and to understand cellular and signaling mechanisms controlled by these factors. We studied the effects of BMP7 and LfcinB as individual treatments and combined therapy on bovine nucleus pulposus (NP) cells by assessing proteoglycan (PG) accumulation and synthesis, and the gene expression of matrix protein aggrecan and transcription factor SOX-9. We also analyzed the role of Noggin, a BMP antagonist, in IVD tissue and examined its effect after stimulation with LfcinB. To understand the molecular mechanisms by which LfcinB synergizes with BMP7, we investigated the ERK-SP1 axis as a downstream intracellular signaling regulator involved in BMP7 and LfcinB-mediated activities. Treatment of bovine NP cells cultured in alginate with LfcinB plus BMP7 synergistically stimulates PG synthesis and accumulation in part by upregulation of aggrecan gene expression. The synergism results from LfcinB-mediated activation of Sp1 and SMAD signaling pathways by (i) phosphorylation of SMAD 1/5/8; (ii) downregulation of SMAD inhibitory factors [i.e., noggin and SMAD6 (inhibitory SMAD)]; and (iii) upregulation of SMAD4 (universal co-SMAD). These data indicate that LfcinB-suppression of Noggin may eliminate the negative feedback of BMP7, thereby maximizing biological activity of BMP7 and ultimately shifting homeostasis to a pro-anabolic state in disc cells. We propose that combination growth factor therapy using BMP7 and LfcinB may be beneficial for treatment of disc degeneration.

Matrix-assisted laser desorption ionization-imaging mass spectrometry: a new methodology to study human osteoarthritic cartilage

OBJECTIVE

Information about the distribution of proteins and the modulation that they undergo in the different phases of rheumatic pathologies is essential to understanding the development of these diseases. We undertook this study to demonstrate the utility of mass spectrometry (MS)-based molecular imaging for studying the spatial distribution of different components in human articular cartilage sections.

METHODS

We compared the distribution of peptides and proteins in human control and osteoarthritic (OA) cartilage. Human control and OA cartilage slices were cut and deposited on conductive slides. After tryptic digestion, we performed matrix-assisted laser desorption ionization-imaging MS (MALDI-IMS) experiments in a MALDI-quadrupole time-of-flight mass spectrometer. Protein identification was undertaken with a combination of multivariate statistical methods and Mascot protein database queries. Hematoxylin and eosin staining and immunohistochemistry were performed to validate the results.

RESULTS

We created maps of peptide distributions at 150-μm raster size from control and OA human cartilage. Proteins such as biglycan, prolargin, decorin, and aggrecan core protein were identified and localized. Specific protein markers for cartilage oligomeric matrix protein and fibronectin were found exclusively in OA cartilage samples. Their distribution displayed a stronger intensity in the deep area than in the superficial area. New tentative OA markers were found in the deep area of the OA cartilage.

CONCLUSION

MALDI-IMS identifies and localizes disease-specific peptides and proteins in cartilage. All the OA-related peptides and proteins detected display a stronger intensity in the deep cartilage. MS-based molecular imaging is demonstrated to be an innovative method for studying OA pathology.

Yin-Yang regulation of prostaglandins and nitric oxide by PGD2 in human arthritis: reversal by celecoxib

The role of PGD2 has been recognized in allergy, innate immunity and inflammation. Western blot analysis identified 21 kDa lipocalin (L)-prostaglandin D2 (PGD2) synthase (S) in human osteoarthritis (OA)-affected cartilage, whose expression was increased by IL-1β and TNFα. Similarly, PGD2 was spontaneously released by human OA-affected cartilage (and upregulated by IL-β) in ex vivo conditions and could be inhibited by indomethacin. Addition of PGD2 to human OA-affected cartilage significantly increased accumulation of PGE2, PGF1α, PGF2α, TXB2, but inhibited LTB4 and nitric oxide (NO) accumulation. Similarly, PGD2 (but not 13,14-dihydro-15-keto PGD2) augmented IL-1β induced PGE2 but inhibited IL-β induced nitric oxide (NO) in human chondrocytes. Celecoxib (10 μM) inhibits COX-1 mediated PGD2, and nitric oxide synthase (NOS) mediated NO in human OA-affected cartilage. Furthermore, celecoxib (1 μM) counter balances (IL-1β induced+PGD2 modulated) levels of NO and PGE2 in human OA-affected cartilage and chondrocytes to basal levels. These results show concentration-dependent, pro- and anti-inflammatory activity of PGD2 in human chondrocytes and cartilage, which can be neutralized by celecoxib. In view of the broad prostaglandin dependent and independent mechanism of action of celecoxib, these observations further reaffirm the broader role of celecoxib as a "Disease Modifying Drug" for human Osteoarthritis.

Prospects for treating osteoarthritis: enzyme-protein interactions regulating matrix metalloproteinase activity

Primary osteoarthritis (OA) is a musculoskeletal disorder of unknown etiology. OA is characterized by an imbalance between anabolism and catabolism in, and altered homeostasis of articular cartilage. Matrix metalloproteinases (MMPs) and a disintegrin and metalloproteinase with thrombospondin motif are upregulated in OA joints. Extracellular matrix (ECM) proteins are critical for resistance to compressive forces and for maintaining the tensile properties of the tissue. Tissue inhibitor of metalloproteinases (TIMPs) is the endogenous inhibitor of MMPs, but in OA, TIMPs do not effectively neutralize MMP activity. Upregulation of MMP gene expression occurs in OA in a milieu of proinflammatory cytokines such as interleukin (IL)-1, IL-6 and tumor necrosis factor α. Presently, the medical therapy of OA includes mainly nonsteroidal anti-inflammatory drugs and corticosteroids which dampen pain and inflammation but appear to have little effect on restoring joint function. Experimental interventions to restore the imbalance between anabolism and catabolism include small molecule inhibitors of MMP subtypes or inhibitors of the interaction between IL-1 and its receptor. Although these agents have some positive effects on reducing MMP subtype activity they have little efficacy at the clinical level. MMP-9 is one MMP subtype implicated in the degradation of articular cartilage ECM proteins. MMP-9 was found in OA synovial fluid as a complex with neutrophil gelatinase-associated lipocalin (NGAL) which protected MMP-9 from autodegradation. Suppressing NGAL synthesis or promoting NGAL degradation may result in reducing the activity of MMP-9. We also propose initiating a search for enzyme-protein interactions to dampen other MMP subtype activity which could suppress ECM protein breakdown.

Granulocyte-macrophage colony-stimulating factor is a key mediator in experimental osteoarthritis pain and disease development

Introduction

Granulocyte-macrophage colony-stimulating factor (GM-CSF) has been shown to be important in the development of inflammatory models of rheumatoid arthritis and there is encouraging data that its blockade may have clinical relevance in patients with rheumatoid arthritis. The aims of the current study were to determine whether GM-CSF may also be important for disease and pain development in a model of osteoarthritis.

Methods

The role of GM-CSF was investigated using the collagenase-induced instability model of osteoarthritis. We studied both GM-CSF-/- mice and wild-type (C57BL/6) mice treated prophylactically or therapeutically with a monoclonal antibody to GM-CSF. Disease development (both early and late) was evaluated by histology and knee pain development was measured by assessment of weight distribution.

Results

In the absence of GM-CSF, there was less synovitis and matrix metalloproteinase-mediated neoepitope expression at week 2 post disease induction, and less cartilage damage at week 6. GM-CSF was absolutely required for pain development. Therapeutic neutralization of GM-CSF not only abolished the pain within 3 days but also led to significantly reduced cartilage damage.

Conclusions

GM-CSF is key to the development of experimental osteoarthritis and its associated pain. Importantly, GM-CSF neutralization by a therapeutic monoclonal antibody-based protocol rapidly and completely abolished existing arthritic pain and suppressed the degree of arthritis development. Our results suggest that it would be worth exploring the importance of GM-CSF for pain and disease in other osteoarthritis models and perhaps clinically for this form of arthritis.

75-kd sirtuin 1 blocks tumor necrosis factor α-mediated apoptosis in human osteoarthritic chondrocytes

OBJECTIVE

Sirtuin 1 (SirT1) has been implicated in the regulation of human cartilage homeostasis and chondrocyte survival. Exposing human osteoarthritic (OA) chondrocytes to tumor necrosis factor α (TNFα) generates a stable and enzymatically inactive 75-kd form of SirT1 (75SirT1) via cathepsin B-mediated cleavage. Because 75SirT1 is resistant to further degradation, we hypothesized that it has a distinct role in OA, and the present study was undertaken to identify this role.

METHODS

The presence of cathepsin B and 75SirT in OA and normal human chondrocytes was analyzed. Confocal imaging of SirT1 was used to monitor its subcellular trafficking following TNFα stimulation. Coimmunofluorescence staining for cathepsin B, mitochondrial cytochrome oxidase subunit IV, and lysosome-associated membrane protein 1 together with SirT1 was performed. Human chondrocytes were tested for apoptosis by fluorescence-activated cell sorter analysis and immunoblotting for caspases 3 and 8. Human chondrocyte mitochondrial extracts were obtained and analyzed for 75SirT1-cytochrome c association.

RESULTS

Confocal imaging and immunoblot analyses following TNFα challenge of human chondrocytes demonstrated that 75SirT1 was exported to the cytoplasm and colocalized with the mitochondrial membrane. Consistent with this, immunoprecipitation and immunoblot analyses revealed that 75SirT1 is enriched in mitochondrial extracts and associates with cytochrome c following TNFα stimulation. Preventing nuclear export of 75SirT1 or reducing levels of full-length SirT1 and 75SirT1 augmented chondrocyte apoptosis in the presence of TNFα. Levels of cathepsin B and 75SirT1 were elevated in OA versus normal chondrocytes. Additional analyses showed that human chondrocytes exposed to OA-derived synovial fluid generated the 75SirT1 fragment.

CONCLUSION

These data suggest that 75SirT1 promotes chondrocyte survival following exposure to proinflammatory cytokines.

Expression of the H- and L-subunits of ferritin in bone marrow macrophages of patients with osteoarthritis

Osteoarthritis is a disease characterized by an increase in the production of reactive oxygen species (ROS) in afflicted joints. Excess iron, due to its role in the production of ROS and crystal deposition in the joints, is implicated in the disease progression of osteoarthritis. Ferritin is a major regulator of the bioavailability of iron, and its functions are determined largely by the combination of H- and L-subunits present in its outer protein shell. The purpose of the study was to investigate the expression of the H- and L-subunits of ferritin in bone marrow macrophages of osteoarthritis patients. The cytokine profiles were assessed as cytokines play an important role in the expression of the ferritin subunits. The H-subunit of ferritin in the bone marrow macrophages was significantly higher (P value = 0.035) in the osteoarthritis patients compared with the controls (107.84; 69.25-167.94 counts/μm(2); n = 7 versus 71.07; 58.56-86.26 counts/μm(2); n = 19). A marginally significant increase (P value = 0.059) was shown for the expression of the L-subunit in the osteoarthritis patients compared with the controls (133.03; 104.04-170.10 counts/μm(2); n = 7 versus 104.23; 91.53-118.70 counts/μm(2); n = 19). The osteoarthritis and control groups had comparable C-reactive protein, as well as proinflammatory and anti-inflammatory cytokine concentrations. The major exception was for transforming growth factor-β (TGF-β), which was higher (P value = 0.014) in the plasma of the osteoarthritis patients (16.69; 13.09-21.28 ng/mL; n = 7 versus 8.60; 6.34-11.67 ng/mL; n = 19). Up-regulation of the ferritin subunits decreases the levels of bioavailable iron and provides protection against the unwarranted production of ROS and crystal deposition. A role for TGF-β in the up-regulation of the expression of the H-subunit, and possibly the L-subunit, of ferritin is postulated in osteoarthritis.

Pravastatin suppresses matrix metalloproteinase expression and activity in human articular chondrocytes stimulated by interleukin-1β

BACKGROUND

Matrix metalloproteinases are catabolic enzymes that play a key role in the articular cartilage degeneration evident in degenerative and inflammatory conditions of articular cartilage. The aim of this study is to assess the ability of pravastatin to modify matrix metalloproteinase (MMP) messenger RNA (mRNA) expression and enzyme activity in a culture of normal human chondrocytes stimulated by interleukin-1β.

MATERIALS AND METHODS

Normal human chondrocytes were stimulated with interleukin (IL)-1β for 6 h to induce MMP expression, simulating a catabolic state, and then treated with pravastatin (1, 5 and 10 μM) for a further 18 h before cell lysates and supernatants were harvested. Cells stimulated with IL-1β but not treated with pravastatin served as controls. Real-time polymerase chain reaction (PCR) was used to assess expression of MMP-3 and MMP-9 mRNA. MMP enzyme activity was assessed using a fluorescent MMP-specific substrate. Statistical analysis was performed using analysis of variance (ANOVA).

RESULTS

MMP-3 and MMP-9 mRNA expression was reduced at all concentrations tested with statistically significant trends in reduction (p = 0.002 and <0.001, respectively). Analysis of culture supernatants revealed that pravastatin treatment led to a reduction in total MMP activity but not to a statistically significant degree (p = 0.07).

CONCLUSIONS

Treatment with pravastatin of stimulated human chondrocytes leads to significant down-regulation of selected MMP genes and a non-significant reduction in MMP enzyme activity. Our results provide further evidence that statins may have a role to play in future treatment of disease affecting articular chondrocytes.

Effects of exercise and physical activity on knee osteoarthritis

Exercise is one of the most discussed and controversial nonpharmacologic management strategies for osteoarthritis (OA) of the knee. Health care providers and patients share varied and often pseudoscientific beliefs regarding the effects of exercise on knee OA formulated on outdated notions of the etiology, pathophysiology, and progression of the condition. Based on the contemporary literature, regular light to moderate physical activity has both preventive and therapeutic benefits for individuals with knee OA. Exercise regimens with strong evidence of benefit include those that focus on aerobic/cardiovascular conditioning and lower extremity strength training. Health care providers should confidently incorporate exercise recommendations into clinical management and offer patients evidence-based and individually tailored exercise prescriptions to help manage the painful and often disabling symptoms of this condition.

Tumor necrosis factor α-mediated cleavage and inactivation of SirT1 in human osteoarthritic chondrocytes

OBJECTIVE

The protein deacetylase SirT1 positively regulates cartilage-specific gene expression, while the proinflammatory cytokine tumor necrosis factor α (TNFα) negatively regulates these same genes. This study was undertaken to test the hypothesis that SirT1 is adversely affected by TNFα, resulting in altered gene expression.

METHODS

Cartilage-specific gene expression, SirT1 activity, and results of chromatin immunoprecipitation analysis at the α2(I) collagen enhancer site were determined in RNA, protein extracts, and nuclei of human osteoarthritic chondrocytes left untreated or treated with TNFα. Protein extracts from human chondrocytes transfected with epitope-tagged SirT1 that had been left untreated or had been treated with TNFα were analyzed by immunoblotting with SirT1 and epitope-specific antibodies. The 75-kd SirT1-reactive protein present in TNFα-treated extracts was identified by mass spectroscopy, and its amino-terminal cleavage site was identified via Edman sequencing. SirT1 activity was assayed following an in vitro cathepsin B cleavage reaction. Cathepsin B small interfering RNA (siRNA) was transfected into chondrocytes left untreated or treated with TNFα.

RESULTS

TNFα-treated chondrocytes had impaired SirT1 enzymatic activity and displayed 2 forms of the enzyme: a full-length 110-kd protein and a smaller 75-kd fragment. The 75-kd SirT1 fragment was found to lack the carboxy-terminus. Cathepsin B was identified as the TNFα-responsive protease that cleaves SirT1 at residue 533. Reducing cathepsin B levels via siRNA following TNFα exposure blocked the generation of the 75-kd SirT1 fragment.

CONCLUSION

These data indicate that TNFα, a cytokine that mediates joint inflammation in arthritis, induces cathepsin B-mediated cleavage of SirT1, resulting in reduced SirT1 activity. This reduced SirT1 activity correlates with the reduced cartilage-specific gene expression evident in these TNFα-treated cells.

Reduction in knee adduction moment via non-invasive biomechanical training: a longitudinal gait analysis study

Biomechanical non-invasive interventions have been previously reported to reduce pain and facilitate superior levels of function in patients with medial knee osteoarthritis [OA]. One such treatment is the AposTherapy, a customized program utilizing a foot-worn biomechanical device allowing center of pressure modification and continuous perturbation during gait. The influence of this intervention on objective gait metrics has yet to be determined. The aim of the current study was to prospectively examine changes in kinetic and kinematic parameters in patients enrolled in this treatment program. Twenty-five females with symptomatic bilateral medial compartment knee OA were enrolled in the customized daily treatment program. All patients underwent barefoot gait analysis testing and completed subjective questionnaires prior to treatment initiation and on two follow-up visits. Significantly reduced knee adduction moment (KAM) magnitude was noted during barefoot walking after three and nine months of treatment. On average, the knee adduction impulse and the 1st and 2nd KAM peaks were reduced by 13%, 8.4%, and 12.7%, respectively. Furthermore, moment reduction was accompanied by elevated walking velocity, significant pain reduction, and increased functional activity. In addition to symptomatic improvement, our results suggest that this treatment program can alter kinetic gait parameters in this population. We speculate that these adaptations account for the symptomatic and functional improvement reported for this intervention.

Intervertebral disk repair by protein, gene, or cell injection: a framework for rehabilitation-focused biologics in the spine

Low back pain carries an enormous socioeconomic burden. Current treatment modalities for symptomatic intervertebral disk (IVD) degeneration have limited and often inconsistent clinical benefits. Novel approaches with the potential to halt or even reverse disk degeneration and restore physiologic disk function, such as biological treatments, are therefore very attractive. The following barriers are impeding the development of successful therapeutic interventions: (1) the biology and pathophysiology of disk degeneration are not well understood, and (2) the precise relationship between IVD degeneration and low back pain remains unclear. This article reviews the structural changes that take place during IVD degeneration and their relationship to diskogenic back pain. It also presents treatment modalities that currently are under laboratory investigation and are being studied in clinical trials. The authors of recent studies have shown that the content of large proteoglycans, such as aggrecan and versican, decreases with aging and IVD degeneration, whereas the content of certain small proteoglycans, such as biglycan, increases. Proinflammatory cytokines such as interleukin-1 and tumor necrosis factor-α also are associated with IVD degeneration and are potential biomarkers of IVD degeneration and repair. Our group of investigators and others have developed in vitro models of IVD cell and explant culture in addition to in vivo animal models to study IVD degeneration and repair. With the use of these models, we have tested candidate therapeutic agents to assess their therapeutic potential for matrix restoration. When a rabbit annular puncture model of IVD degeneration was used, injections of either bone morphogenetic protein-7 (also known as osteogenic protein-1) or bone morphogenetic protein-14 (also known as growth differentiation factor-5) were shown to be effective in restoring IVD structures. On the basis of these data, the Food and Drug Administration has recently allowed the initiation of Investigational New Drug clinical trials on osteogenic protein-1 and growth differentiation factor-5 in the United States. Protein therapies such as other growth factors, inhibitors of degradation enzymes or cytokines, and cell therapies also are being investigated in laboratory settings with the goal of restoring disk function and alleviating back pain symptoms. These therapies may be used by physiatrists with the skills required to administer intradiskal injections and supervise a comprehensive rehabilitation program after the procedures. Ultimately, the clinical use of any biological treatment discussed in this article would require the collective efforts of clinicians and researchers.

Chemerin/ChemR23 pathway: a system beyond chemokines

Chemerin is a chemokine that, through the engagement of its counter-receptor, ChemR23, attracts pro-inflammatory cells. However, chemerin has been shown to play other functions and a recent study by Berg and colleagues demonstrates that chemerin/ChemR23 is a system beyond chemokines. Human articular chondrocytes produce chemerin and express ChemR23, and upon stimulation with recombinant chemerin increase the production of pro-catabolic cytokines and metalloproteinases. The latter are up-regulated in osteoarthritic cartilage and cause extracellular matrix breakdown. Since an increase of chemerin in fat tissue and serum of obese patients has been reported, this new feature of chemerin may represent a functional link between obesity and osteoarthritis.

Effect of Phellodendron amurense in protecting human osteoarthritic cartilage and chondrocytes

ETHNOPHARMACOLOGICAL RELEVANCE

Traditional medicine has been widely using Phellodendron amurense Rupr. (Rutaceae) to treat various inflammatory diseases including arthritis.

AIM OF THE STUDY

This study investigated the effects of Phellodendron amurense in protecting cartilage, including regulating the levels of aggrecanases, matrix metalloproteinases (MMPs)/tissue inhibitor of metalloproteinase (TIMP), proinflammatory cytokines and signaling of the mitogen activated protein kinase (MAPK) pathway in human osteoarticular cartilage and chondrocytes.

MATERIALS AND METHODS

Explants from human osteoarthritis cartilage were cultured alone or in IL-1α for 7 days with or without Phellodendron amurense ethanol extract or celecoxib (40, 100, 200μg/ml). The effect of Phellodendron amurense on matrix degradation induced by IL-1α in human articular cartilage was assessed by staining, and the quantities of sulfated glycosaminoglycan (GAG) and type II collagen were calculated from the culture media. The levels of aggrecanases, MMPs, TIMP, and PGE(2) in the culture media were investigated using an enzyme-linked immunosorbent assay (ELISA). In addition, reverse transcription polymerase chain reaction (RT-PCR) evaluated the mRNA expression of aggrecanases, MMPs and TIMP. Furthermore, Western blot analysis was performed to identify the roles that Phellodendron amurense played in the ERK, JNK and p38 signaling pathways.

RESULTS

Phellodendron amurense showed no evident cytotoxicity on human articular cartilage. Phellodendron amurense significantly inhibited the IL-1α-induced degradation of GAG and type II collagen from human osteoarticular cartilage in a concentration-dependent manner. Celecoxib did not significantly inhibit IL-1α-induced release of GAG and only slightly reduced type II collagen. Phellodendron amurense also dose-dependently decreased the levels of aggrecanase-1 and -2, MMP-1, -3, and -13, whereas it increased TIMP-1 expression in human osteoarticular cartilage. Celecoxib only decreased MMP-1 and MMP-13 levels in human osteoarticular cartilage. In addition, Phellodendron amurense reduced the phosphorylation of extracellular signal regulated kinase (ERK)1/2, Jun NH2-terminal kinase (JNK) and activated phospho-p38 MAPK in a dose-dependent manner in human osteoarthritic chondrocytes.

CONCLUSIONS

Phellodendron amurense inhibited osteoarticular cartilage and chondrocyte destruction by inhibiting proteoglycan release and type II collagen degradation, down-regulating aggrecanases, MMP activities and phospho-ERK1/2, JNK and p38 MAP kinase signaling, and up-regulating TIMP-1 activity. Therefore, our results suggest that Phellodendron amurense is a potential therapeutic agent to protect cartilage against OA progression.

Insulin-like growth factor 1 synergizes with bone morphogenetic protein 7-mediated anabolism in bovine intervertebral disc cells

OBJECTIVE

We undertook this study to assess the therapeutic benefits of intervertebral disc matrix repair and regeneration by evaluating the potential synergistic effect of insulin-like growth factor 1 (IGF-1) and bone morphogenetic protein 7 (BMP-7) on bovine spine discs and by elucidating the relevant molecular/cellular mechanisms.

METHODS

Bovine nucleus pulposus (NP) cells were treated with BMP-7 and IGF-1. The subsequent anabolic effects driven by NP cells were assessed for proteoglycan (PG) synthesis by (35) S-sulfate incorporation and for PG accumulation by dimethylmethylene blue assays. Matrix formation was visualized by particle exclusion assay. Key matrix components and transcription factors were analyzed by real-time reverse transcription-polymerase chain reaction to determine the signaling pathways by which IGF-1 suppresses noggin, a potent inhibitor of BMP-7. Western blotting and nuclear translocation experiments were performed to assess the activation of Smad proteins.

RESULTS

Stimulation of bovine NP cells by both IGF-1 and BMP-7 greatly potentiated anabolism through complementary and synergistic mechanisms on matrix formation compared with treatment with either growth factor alone. The exogenously added decoy ligand, noggin, attenuated the anabolic effects of BMP-7, and noggin was substantially increased by BMP-7, suggesting a negative feedback regulatory mechanism. In contrast, IGF-1 significantly suppressed noggin expression via the phosphatidylinositol 3-kinase/Akt pathway and thus potentiated BMP-7 signaling in bovine NP cells. Upon combination treatment, IGF-1 activated Smad2, while BMP-7 activated Smad1/5/8 and Smad3, thus inducing all Smad signaling pathways and mimicking the effects of the combination of transforming growth factor β and BMP-7

CONCLUSION

Combination growth factor therapy using BMP-7 and IGF-1 may have considerable promise in the treatment of spine disc degeneration.

Heteroarylimino-4-thiazolidinones as inhibitors of cartilage degradation

2-Benzo[d]thiazolyl- and 2-benzo[d]isothiazolyl-imino-5-benzylidene-4-thiazolidinone derivatives were investigated as potential metalloproteinases (MMPs) inhibitors and evaluated for their antidegenerative activity on human chondrocyte cultures stimulated by IL-1β, using an experimental model that reproduces the mechanisms involved in osteoarthritic (OA) diseases. Cell viability, the amount of glycosaminoglycans (GAGs) and the production of nitric oxide (NO) were measured. The most potent compound, 5-(4-methoxy-benzylidene)-2-(benzo[d]isothiazol-3-ylimino)-thiazolidin-4-one (4b), a MMP-13 inhibitor at nanomolar concentration (IC(50)=0.036 μM), could be considered as a lead compound for the development of novel clinical agents, inhibitors of cartilage degradation, for the treatment of OA.

Joint aging and chondrocyte cell death

Articular cartilage extracellular matrix and cell function change with age and are considered to be the most important factors in the development and progression of osteoarthritis. The multifaceted nature of joint disease indicates that the contribution of cell death can be an important factor at early and late stages of osteoarthritis. Therefore, the pharmacologic inhibition of cell death is likely to be clinically valuable at any stage of the disease. In this article, we will discuss the close association between diverse changes in cartilage aging, how altered conditions influence chondrocyte death, and the implications of preventing cell loss to retard osteoarthritis progression and preserve tissue homeostasis.

Nerve growth factor in rheumatic diseases

OBJECTIVES

The nervous system modulates the immune response in many autoimmune syndromes by neurogenic inflammation. One of the pivotal mediators is nerve growth factor (NGF), which is known for its effects on neuronal survival and growth. There is considerable evidence that NGF acts as an important mediator of many immune responses. This article reviews the role of NGF in rheumatic diseases and strategies for potential therapeutic interventions.

METHODS

We conducted a database search using Medline and Medpilot. Eight hundred abstracts containing the keyword NGF and 1 of the following terms were reviewed: arthritis, neurogenic inflammation, rheumatoid arthritis, osteoarthritis, collagen arthritis, arteritis, psoriasis, psoriatic arthritis, Sjogren syndrome, systemic lupus erythematosus, gout, osteoporosis, lower back pain, lumbar disc herniation, nerve root compression, spondyloarthritis, spondylarthropathy, algoneurodystrophy, fibromyalgia, Kawasaki syndrome, polyarteritis nodosa, cytokine, vasculitis, pain, therapy, and antagonist. Articles were analyzed based on relevance and content. Most clinical trials and studies with human specimens were included. Studies with experimental animal models were selected if they contained relevant data.

RESULTS

NGF is overexpressed in many inflammatory and degenerative rheumatic diseases. Concentrations differ to some extent and sometimes even show contradictory results. NGF is found in serum, synovial fluid, and cerebrospinal fluid, and tissue specimens. NGF concentrations can be correlated with the extent of inflammation and/or clinical activity in many conditions. In rheumatoid arthritis, NGF levels are significantly higher as compared with osteoarthritis.

CONCLUSIONS

NGF is a significant mediator and modulator of inflammation. NGF sometimes shows detrimental and sometimes regenerative activity. These findings indicate potential therapeutic interventions using either NGF antagonists or recombinant NGF.

Bimodal effect of humic acids on the LPS-induced TNF-alpha release from differentiated U937 cells

Humic substances (HS) have been reported to possess anti-inflammatory as well as pro-inflammatory properties. The anti-inflammatory activity was demonstrated in the rat paw edema model and we found a preliminary explanation in the 5-lipoxygenase inhibitory effect of humic acids (HA). The pro-inflammatory activity is reflected by the production and release of pro-inflammatory cytokines in HA-treated neutrophilic granulocytes. With regard to the potential use of HA as antiviral and UV-protective agents it appears advisable to investigate the role of HS in the inflammation process in more detail. Hence we tested four different HS preparations - two naturally occurring HA from the Altteich peatland in Germany, one fulvic acid (FA) preparation from a Finnish spruce forest and a synthetic HA-like polymer (caffeic acid oxidation product, KOP) for their influence on the lipopolysaccharide (LPS)-induced TNF-alpha release in human U937 cells. In addition, the cytotoxicity of HS was determined. The results demonstrate a concentration-dependent bimodal effect of HA on the TNF-alpha release of differentiated LPS-stimulated U937 cells for both the natural black peat HA from the Altteich peatland and the HA-like polymer KOP. Low HA concentrations (10-80 microg/ml) enhanced the TNF-alpha release by up to threefold (pro-inflammatory activity), while HA concentrations >100 microg/ml reduced it about 10-fold (anti-inflammatory activity). FA failed to enhance TNF-alpha release, but reduced it at higher concentrations (>200 microg/ml) by the half. Brown water HA did not exert any significant effect on TNF-alpha release. No HS-stimulated TNF-alpha release was also observed in the absence of exogenously supplied LPS. This means that HS, unlike endotoxin, are no inflammation-causing agents for LPS-untreated cells. Differences in the effect of individual HS on TNF-alpha release are discussed in connection with the polyanionic character of HS, their molecular mass distribution and the hitherto imperfectly known chemical structure.

Prostaglandin E2 and its cognate EP receptors control human adult articular cartilage homeostasis and are linked to the pathophysiology of osteoarthritis

OBJECTIVE

To elucidate the pathophysiologic links between prostaglandin E(2) (PGE(2)) and osteoarthritis (OA) by characterizing the catabolic effects of PGE(2) and its unique receptors in human adult articular chondrocytes.

METHODS

Human adult articular chondrocytes were cultured in monolayer or alginate beads with and without PGE(2) and/or agonists of EP receptors, antagonists of EP receptors, and cytokines. Cell survival, proliferation, and total proteoglycan synthesis and accumulation were measured in alginate beads. Chondrocyte-related gene expression and phosphatidylinositol 3-kinase/Akt signaling were assessed by real-time reverse transcription-polymerase chain reaction and Western blotting, respectively, using a monolayer cell culture model.

RESULTS

Stimulation of human articular chondrocytes with PGE(2) through the EP2 receptor suppressed proteoglycan accumulation and synthesis, suppressed aggrecan gene expression, did not appreciably affect expression of matrix-degrading enzymes, and decreased the type II collagen:type I collagen ratio. EP2 and EP4 receptors were expressed at higher levels in knee cartilage than in ankle cartilage and in a grade-dependent manner. PGE(2) titration combined with interleukin-1 (IL-1) synergistically accelerated expression of pain-associated molecules such as inducible nitric oxide synthase and IL-6. Finally, stimulation with exogenous PGE(2) or an EP2 receptor-specific agonist inhibited activation of Akt that was induced by insulin-like growth factor 1.

CONCLUSION

PGE(2) exerts an antianabolic effect on human adult articular cartilage in vitro, and EP2 and EP4 receptor antagonists may represent effective therapeutic agents for the treatment of OA.

Inflammatory response in patients with active and inactive osteoarthritis

In the present study, we have investigated comparatively the inflammatory response of patients with active and inactive osteoarthritis. The sera from 31 healthy individuals, 37 patients with active OA, and 19 patients with inactive OA were assayed for TNF-alpha, IL-6, sRANKL, RANTES, and MRP8 using ELISA in order to evaluate their potential as markers of disease activity. Also, the spontaneous and LSP-induced release of TNF-alpha and IL-6 by peripheral blood neutrophils was determined. The activation of OA is associated with elevated TNF-alpha, IL-6, and RANTES serum levels while sRANKL and MRP8 appeared to be increased in both active and inactive OA. The neutrophil spontaneous and up-regulated by LPS cytokine release can contribute to the exacerbation of OA.

The action of resveratrol, a phytoestrogen found in grapes, on the intervertebral disc

STUDY DESIGN

Basic science, biologic study.

OBJECTIVE

To determine the potential benefits of using resveratrol (RSV) for intervertebral disc (IVD) matrix repair and regeneration.

SUMMARY OF BACKGROUND DATA

The phytoestrogen RSV is a natural compound found in various plants including grapes and red wines. RSV has been reported to provide a protective effect on articular cartilage in rabbit models for arthritis, but its effect on spine cartilage is unknown. METHODS.: We studied the effect of RSV on bovine IVD cartilage homeostasis by assessing MMP-13 (potent catabolic factor) production, proteoglycan (PG) accumulation and synthesis, and the interaction between RSV and known catabolic factors such as bFGF or IL-1. To understand the molecular mechanisms by which RSV modulates MMP-13 and PG production, we also investigated its downstream target regulatory molecules.

RESULTS

Stimulation of bovine disc cells cultured in monolayer with bFGF or IL-1 augmented the production of MMP-13 and ADAMTS-4 at the transcriptional level and this augmentation was blocked by RSV. Incubation of nucleus pulposus cells with RSV for 21 days significantly increased PG accumulation per cell in a dose-dependent manner, increased PG synthesis, rescued PG losses induced by catabolic reagents bFGF and IL-1, and promoted cell survival to levels seen after incubation with the anabolic protein BMP7 100 ng/mL. Protein-DNA interaction array results suggest that RSV effectively suppresses downstream target molecules of bFGF and IL-1 responsible for oxidative stress, proliferation, and apoptosis.

CONCLUSION

Resveratrol is a potent anabolic mediator of bovine IVD cartilage homeostasis, revealing its potential as a unique biologic treatment to slow the progression of IVD degeneration. These data suggests RSV may have considerable promise in the treatment of disc degeneration.

Biological impact of the fibroblast growth factor family on articular cartilage and intervertebral disc homeostasis

Two members of the fibroblast growth factor (FGF) family, basic FGF (bFGF) and FGF-18, have been implicated in the regulation of articular and intervertebral disc (IVD) cartilage homeostasis. Studies on bFGF from a variety of species have yielded contradictory results with regards to its precise role in cartilage matrix synthesis and degradation. In contrast, FGF-18 is a well-known anabolic growth factor involved in chondrogenesis and articular cartilage repair. In this review, we examined the biological actions of bFGF and FGF-18 in articular and IVD cartilage, the specific cell surface receptors bound by each factor, and the unique signaling cascades and molecular pathways utilized to exert their biological effects. Evidence suggests that bFGF selectively activates FGF receptor 1 (FGFR1) to exert degradative effects in both human articular chondrocytes and IVD tissue via upregulation of matrix-degrading enzyme activity, inhibition of matrix production, and increased cell proliferation resulting in clustering of cells seen in arthritic states. FGF-18, on the other hand, most likely exerts anabolic effects in human articular chondrocytes by activating FGFR3, increasing matrix formation and cell differentiation while inhibiting cell proliferation, leading to dispersed cells surrounded by abundant matrix. The results from in vitro and in vivo studies suggest the potential usefulness of bFGF and FGFR1 antagonists, as well as FGF-18 and FGFR3 agonists, as potential therapies to prevent cartilage degeneration and/or promote cartilage regeneration and repair in the future.

Action of fibroblast growth factor-2 on the intervertebral disc

Introduction

Fibroblast growth factor 2 (FGF2) is a growth factor that is immediately released after cartilage injury and plays a pivotal role in cartilage homeostasis. In human adult articular cartilage, FGF2 mediates anti-anabolic and potentially catabolic effects via the suppression of proteoglycan (PG) production along with the upregulation of matrix-degrading enzyme activity. The aim of the present study was to determine the biological effects of FGF2 in spine disc cells and to elucidate the complex biochemical pathways utilized by FGF2 in bovine intervertebral disc (IVD) cells in an attempt to further understand the pathophysiologic processes involved in disc degeneration.

Methods

We studied the effect of FGF2 on IVD tissue homeostasis by assessing MMP-13 expression (potent matrix-degrading enzyme), PG accumulation, and PG synthesis in the bovine spine IVD, as well as evaluating whether FGF2 counteracts known anabolic factors such as BMP7. To understand the molecular mechanisms by which FGF2 antagonizes BMP7 activity, we also investigated the signaling pathways utilized by FGF2 in bovine disc tissue.

Results

The primary receptor expressed in bovine nucleus pulposus cartilage is FGFR1, and this receptor is upregulated in degenerative human IVD tissue compared with normal IVD tissue. Stimulation of bovine nucleus pulposus cells cultured in monolayer with FGF2 augmented the production of MMP-13 at the transcriptional and translational level in a dose-dependent manner. Stimulation of bovine nucleus pulposus cells cultured in alginate beads for 21 days with FGF2 resulted in a dose-dependent decrease in PG accumulation, due at least in part to the inhibition of PG synthesis. Further studies demonstrate that FGF2 (10 ng/ml) antagonizes BMP7-mediated acceleration of PG production in bovine nucleus pulposus cells via the upregulation of noggin, an inhibitor of the transforming growth factor beta/bone morphogenetic protein signaling pathway. Chemical inhibitor studies showed that FGF2 utilizes the mitogen-activated protein kinase and NF-κB pathways to upregulate noggin, serving as one potential mechanism for its anti-anabolic effects.

Conclusion

FGF2 is anti-anabolic in bovine spine disc cells, revealing the potential of FGF2 antagonists as unique biologic treatments for both prevention and reversal of IVD degeneration.

Extracorporeal shock waves down-regulate the expression of interleukin-10 and tumor necrosis factor-alpha in osteoarthritic chondrocytes

Background

The purpose of this study was to investigate the effects of extra corporeal shock waves (ESW) therapy on the metabolism of healthy and osteoarthritic human chondrocytes, and particularly on the expression of IL-10, TNF-alpha and beta1 integrin.

Methods

Human adult articular cartilage was obtained from 9 patients (6 male and 3 females), with primary knee osteoarthritis (OA), undergoing total joint replacement and from 3 young healthy donors (HD) (2 males, 1 female) with joint traumatic fracture. After isolation, chondrocytes underwent ESW treatment (electromagnetic generator system, MINILITH SL1, STORZ MEDICAL) at different parameters of impulses, energy levels and energy flux density. After that, chondrocytes were cultured in 24-well plate in DMEM supplemented with 10% FCS for 48 hours and then beta₁ integrin surface expression and intracellular IL-10 and TNF-alpha levels were evaluated by flow-cytometry.

Results

At baseline, osteoarthritic chondrocytes expressed significantly lower levels of beta1 integrin and higher levels and IL-10 and TNF-alpha levels. Following ESW application, while beta1 integrin expression remain unchanged, a significant decrease of IL-10 and TNF-alpha intracellular levels was observed both in osteoarthritic and healthy chondrocytes. IL-10 levels decreased at any impulses and energy levels, while a significant reduction of TNF-alpha was mainly found at middle energies.

Conclusion

Our study confirmed that osteoarthritic chondrocytes express low beta₁ integrin and high TNF-alpha and IL-10 levels. Nonetheless, ESW treatment application down-regulate the intracellular levels of TNF-alpha and IL-10 by chondrocytes, suggesting that ESW might restore TNF-alpha and IL-10 production by osteoarthritic chondrocytes at normal levels. However, further in vivo and in vitro studies are necessary to establish if ESW can represent a viable option in the treatment of OA.

Membrane type-1 matrix metalloproteinase is induced following cyclic compression of in vitro grown bovine chondrocytes

OBJECTIVE

To determine if membrane type-1 matrix metalloproteinase (MT1-MMP) will respond to cyclic compression of chondrocytes grown in vitro and the regulatory mechanisms underlying this response.

METHODS

Cyclic compression (30min, 1kPa, 1Hz) was applied to bovine chondrocytes (6-9-month-old animals) grown on top of a biodegradable substrate within 3 days of initiating culture. Luciferase assays using bovine articular chondrocytes were undertaken to demonstrate the mechanosensitivity of MT1-MMP. Semi-quantitative reverse-transcription polymerase chain reaction (RT-PCR) and western blot analysis were used to establish the time course of gene and protein upregulation in response to cyclic compression. The regulation of MT1-MMP was assessed by electrophoretic mobility shift assays, RT-PCR and western blot analysis. As well, an MT1-MMP decoy oligonucleotide and an extracellular signal-regulated kinase 1/2 (ERK1/2) pharmacological inhibitor were utilized to further characterize MT1-MMP regulation.

RESULTS

After cyclic compression, MT1-MMP showed a rapid and transient increase in gene expression. Elevated protein levels were detected within 2h of stimulation which returned to baseline by 6h. During cyclic compression, phosphorylation of the mitogen activated protein kinase ERK1/2 increased significantly. This was followed by increased gene and protein expression of the transcription factor; early growth factor-1 (Egr-1) and Egr-1 binding to the MT1-MMP promoter. Blocking Egr-1 DNA binding with a decoy MT1-MMP oligonucleotide, downregulated MT1-MMP gene expression. The ERK1/2 inhibitor U0126 also reduced Egr-1 DNA binding activity to MT1-MMP promoter sequences and subsequent transcription of MT1-MMP.

CONCLUSIONS

These data suggest that cyclic compression of chondrocytes in vitro upregulates MT1-MMP via ERK1/2 dependent activation of Egr-1 binding. Delineation of the regulatory pathways activated by mechanical stimulation will further our understating of the mechanisms influencing tissue remodeling.

Morphology, mechanisms and pathology of musculoskeletal ageing

In general terms, the recognized alterations in circulating humoral factors (hormones, cytokines, growth factors) that occur in ageing, coupled with innate cellular senescence exaggerated by the slow turnover of many connective tissue cell populations and the age-associated alterations in matrix molecule cross-linking, predispose the elderly to altered connective tissue biology. These changes can be profound, leading to poor mobility, altered ability to withstand cold, weakness and an increased risk of falls, fractures and age-associated 'degenerative' diseases, such as osteoarthritis and osteoporosis. As understanding of the causes of altered connective tissue function with age increases, it is becoming clearer that many of the predisposing factors (growth hormone, cytokines, load/life style) are potential targets for improving quality of life in the elderly.

Basic fibroblast growth factor stimulates matrix metalloproteinase-13 via the molecular cross-talk between the mitogen-activated protein kinases and protein kinase Cdelta pathways in human adult articular chondrocytes

Excessive release of basic fibroblast growth factor (bFGF) during loading and/or injury of the cartilage matrix may contribute to the onset or progression of osteoarthritis. This pathological role may be related to the ability of bFGF to decrease proteoglycan synthesis and to antagonize the activity of anabolic growth factors in cartilage such as insulin-like growth factor-1 and bone morphogenetic protein 7 (BMP7 or OP-1). Matrix metalloproteinase-13 (MMP-13), a catabolic cartilage-degrading enzyme, is dramatically up-regulated by inflammatory cytokines or by fibronectin fragments in articular chondrocytes. In this study, we investigated MMP-13 production by bFGF using human articular chondrocytes. Endogenous concentration of bFGF in synovial fluids collected from arthritis patients and asymptomatic subjects showed a good linear correlation with the endogenous levels of MMP-13. bFGF stimulation of MMP-13 was mediated at the transcriptional level and, at least in part, by stimulation of interleukin-1 production. Also, our findings suggest that bFGF stimulation of MMP-13 required the activation of multiple MAPKs (ERK, p38, and JNK) by bFGF, and more importantly, bFGF activation of protein kinase C (PKC) delta played a key role in the MMP-13 stimulation. Indeed, PKCdelta is the only isoform associated with MMP-13 stimulation among the PKC isoforms tested. PKCdelta controls the bFGF response by regulating multiple MAPK pathways. Our results suggest that PKCdelta activation is a principal rate-limiting event in the bFGF-dependent stimulation of MMP-13 in human adult articular chondrocytes. We propose that deregulation of cross-talk between MAPK and PKCdelta signaling may contribute to the etiology of osteoarthritis in human patients.

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

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

Inverse relationship between matrix remodeling and lipid metabolism during osteoarthritis progression in the STR/ORT mouse

OBJECTIVE

The biologic changes associated with osteoarthritis (OA) are incompletely understood. The aim of this study was to elucidate the molecular mechanisms underlying OA progression in an STR/Ort murine model of spontaneous disease.

METHODS

Global patterns of gene expression were assessed using microarray analysis of articular cartilage/subchondral bone from the tibial plateaus of STR/Ort mice at 3, 9, and 12 months of age. The age-dependent severity of osteophyte formation and extent of cartilage damage were determined in the corresponding femurs using microfocal computed tomography and the Mankin histologic scoring system. Pathway analysis was used to identify the functions of genes associated with OA progression, and changes in gene expression were confirmed using immunohistochemistry.

RESULTS

Six hundred twenty-one genes were associated with both osteophyte formation and cartilage damage in the STR/Ort joints. Genes involved in the development/function of connective tissue and in lipid metabolism were most significantly enriched and regulated during disease progression. Genes directly interacting with peroxisome proliferator-activated receptor alpha (PPARalpha)/PPARgamma were down-regulated, whereas those genes involved with connective tissue remodeling were up-regulated during disease progression. Associations of down-regulation of myotubularin-related phosphatase 1 (a phosphoinositide 3-phosphatase involved in lipid signaling) and up-regulation of biglycan (a member of the small leucine-rich protein family known to modulate osteoblast differentiation and matrix mineralization) with OA progression were confirmed by immunohistochemistry.

CONCLUSION

Since adipogenesis and osteogenesis are inversely related in the developing skeletal tissue, these results suggest that a shift in the differentiation of mesenchymal cells from adipogenesis toward osteogenesis is a component of the OA pathophysiologic processes occurring in the tibial plateau joints of STR/Ort mice.