Differential effects of IL-8, LIF (pro-inflammatory) and IL-11 (anti-inflammatory) on TNF-alpha-induced PGE(2)release and on signalling pathways in human OA synovial fibroblasts

A prospective randomized double-blind clinical trial to assess the effects of leukocyte-reduced platelet-rich plasma on pro-inflammatory, degradative, and anabolic biomarkers after closed pilon fractures

Posttraumatic osteoarthritis (PTOA) significantly affects patients with pilon fractures even after adequate anatomical reduction, and treatment strategies targeting the biologic mediators of PTOA are needed. This study was designed to determine the effects of intra-articular injection of platelet-rich plasma (PRP) on synovial fluid (SF) biomarkers for patients undergoing open reduction and internal fixation (ORIF) of pilon fractures. Patients undergoing staged management of pilon fractures were enrolled in a prospective, double-blinded, randomized, and placebo-controlled clinical trial to determine the effects of a single intra-articular injection of leukocyte-reduced PRP on SF biomarkers. Arthrocentesis of the injured and uninjured ankles was performed at the time of external skeletal fixation (ESF) and ORIF. Patients were randomized to receive either autogenous leukocyte-reduced PRP or saline (control) via intra-articular injection into the injured ankle at the time of ESF. SF biomarker concentrations were compared-uninjured, injured pretreatment, and saline-injected or PRP-injected. Eleven patients (PRP, n = 5; saline, n = 6) completed the study. Twenty-one uninjured, and 11 injured pretreatment, five PRP-treated, and six saline-treated SF samples were analyzed. PRP-treated SF contained significantly higher levels of PDGF-AA (p = 0.046) and significantly lower levels of MMP-3 (p = 0.042), MMP-9 (p = 0.009), IL-1β (p = 0.049), IL-6 (p < 0.01), IL-8 (p = 0.048), and PGE2 (p < 0.04). This study provided mechanistic data to suggest that a single intraarticular injection of leukocyte-reduced PRP is associated with anti-inflammatory, anti-degradative, and anabolic responses compared with saline control. These findings provide the impetus for investigating long-term clinical outcomes after PRP injection as an orthobiologic adjunct to ORIF for mitigating the incidence and severity of PTOA after pilon fractures.

Oxidative stress and inflammation in osteoarthritis pathogenesis: Role of polyphenols

Osteoarthritis (OA) is the most prevalent joint degenerative disease leading to irreversible structural and functional changes in the joint and is a major cause of disability and reduced life expectancy in ageing population. Despite the high prevalence of OA, there is no disease modifying drug available for the management of OA. Oxidative stress, a result of an imbalance between the production of reactive oxygen species (ROS) and their clearance by antioxidant defense system, is high in OA cartilage and is a major cause of chronic inflammation. Inflammatory mediators, such as interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) are highly upregulated in OA joints and induce ROS production and expression of matrix degrading proteases leading to cartilage extracellular matrix degradation and joint dysfunction. ROS and inflammation are interdependent, each being the target of other and represent ideal target/s for the treatment of OA. Plant polyphenols possess potent antioxidant and anti-inflammatory properties and can inhibit ROS production and inflammation in chondrocytes, cartilage explants and in animal models of OA. The aim of this review is to discuss the chondroprotective effects of polyphenols and modulation of different molecular pathways associated with OA pathogenesis and limitations and future prospects of polyphenols in OA treatment.

Genetics in Cartilage Lesions: Basic Science and Therapy Approaches

Cartilage lesions have a multifactorial nature, and genetic factors are their strongest determinants. As biochemical and genetic studies have dramatically progressed over the past decade, the molecular basis of cartilage pathologies has become clearer. Several homeostasis abnormalities within cartilaginous tissue have been found, including various structural changes, differential gene expression patterns, as well as altered epigenetic regulation. However, the efficient treatment of cartilage pathologies represents a substantial challenge. Understanding the complex genetic background pertaining to cartilage pathologies is useful primarily in the context of seeking new pathways leading to disease progression as well as in developing new targeted therapies. A technology utilizing gene transfer to deliver therapeutic genes to the site of injury is quickly becoming an emerging approach in cartilage renewal. The goal of this work is to provide an overview of the genetic basis of chondral lesions and the different approaches of the most recent systems exploiting therapeutic gene transfer in cartilage repair. The integration of tissue engineering with viral gene vectors is a novel and active area of research. However, despite promising preclinical data, this therapeutic concept needs to be supported by the growing body of clinical trials.

Metabolic responses of osteochondral allografts to re-warming

Symptomatic chondral and osteochondral defects affect a large and growing number of patients. A safe and effective surgical treatment for large articular defects is osteochondral allograft (OCA) transplantation. One of the major causes of failure for OCA transplantation is loss of essential chondrocyte viability during the preservation and storage period. It is also possible that metabolic responses of the OCA when transitioning from storage temperature to body temperature may contribute to mechanisms causing failure. The present study was designed to compare MOPS^SM -preserved OCAs to those stored using the current standard of care (SOC) method with respect to metabolic responses when rewarmed for transplantation to and maintenance at body temperature (37°C). It was theorized that grafts stored using the MOPS^SM protocol would maintain significantly higher chondrocyte viability and produce significantly lower levels of inflammatory mediators and degradative enzymes, and significantly higher levels of chemokines compared to grafts stored using the SOC protocol. Left over SOC and MOPS^SM -stored OCA tissues were collected after surgery, and cartilage explants were cultured for 6 days. Media was analyzed for biomarkers using commercially available assays. Cartilage from SOC grafts released significantly higher levels of PGE2, MMP-1, MMP-2, and MMP-13, and significantly lower levels of IL-8 and Gro-α, compared to cartilage from MOPS^SM -stored grafts. Clinical significance: These data suggest that OCAs stored using the MOPS^SM protocol have potentially less detrimental initial inflammatory and degradative responses to re-warming for transplantation compared to OCAs stored using the current tissue bank protocols. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1530-1536, 2019.

Opposing Regulation of Interleukin-8 and NF-kB Responses by Lipoxin A4 and Serum Amyloid a via the Common Lipoxin a Receptor

Lipoxin A4 (LXA4) is a potent eicosanoid that inhibits IL-1β-induced activation of human fibroblast-like synoviocytes (FLS) via the LXA4 receptor (ALXR). Serum amyloid A (SAA) is an acute phase reactant with cytokine-like properties. SAA has been shown to bind the same seven transmembrane G protein-coupled receptor ligated by LXA4. Here we compared the inflammatory responses of lipid (LXA4) and peptide (SAA) ligands in human FLS via the shared ALX and characterized their downstream signaling. LXA4 induced stimulation of tissue inhibitors of metalloproteinase-2, whereas SAA induced interleukin-8 and matrix metalloproteinase-3 production. SAA up-regulated NF-kB and AP-1 DNA binding activity, while LXA4 markedly inhibited these responses after IL-1β stimulation. A human IL-8 promoter luciferase construct was transfected into CHO cells stably expressing ALXR in order to determine the role of NF-kB and/or AP-1 in the regulation of IL-8 gene expression. The NF-kB pathway proved to be the preeminent for the biological responses elicited by both ligands. These findings suggest that two endogenous molecules, targeting a common receptor, could participate in the pathogenesis of inflammatory arthritis by differentially regulating inflammatory responses in tissues expressing the ALXR.

JNK activation is essential for activation of MEK/ERK signaling in IL-1β-induced COX-2 expression in synovial fibroblasts

The proinflammatory cytokine interleukin 1β (IL-1β) induces prostaglandin E₂ (PGE₂) production via upregulation of cyclooxygenase-2 (COX-2) expression in synovial fibroblasts. This effect of IL-1β is involved in osteoarthritis. We investigated MAPK signaling pathways in IL-1β-induced COX-2 expression in feline synovial fibroblasts. In the presence of MAPK inhibitors, IL-1β-induced COX-2 expression and PGE₂ release were both attenuated. IL-1β induced the phosphorylation of p38, JNK, MEK, and ERK1/2. A JNK inhibitor prevented not only JNK phosphorylation but also MEK and ERK1/2 phosphorylation in IL-1β-stimulated cells, but MEK and ERK1/2 inhibitors had no effect on JNK phosphorylation. A p38 inhibitor prevented p38 phosphorylation, but had no effect on MEK, ERK1/2, and JNK phosphorylation. MEK, ERK1/2, and JNK inhibitors had no effect on p38 phosphorylation. We also observed that in IL-1β-treated cells, phosphorylated MEK, ERK1/2, and JNK were co-precipitated with anti-phospho-MEK, ERK1/2, and JNK antibodies. The silencing of JNK1 in siRNA-transfected fibroblasts prevented IL-1β to induce phosphorylation of MEK and ERK1/2 and COX-2 mRNA expression. These observations suggest that JNK1 phosphorylation is necessary for the activation of the MEK/ERK1/2 pathway and the subsequent COX-2 expression for PGE₂ release, and p38 independently contributes to the IL-1β effect in synovial fibroblasts.

Serum and knee synovial fluid matrixmetalloproteinase-13 and tumor necrosis factor-alpha levels in patients with late stage osteoarthritis

Objective

To compare the levels of MMP-13 and TNF-α in late stage osteoarthritis, define their predominant pathways and investigate their correlation with McMaster Universities Arthritis Index scores.

Patients and methods

A total of 42 patients (mean age 64 ± 8.8) with grade 3 and grade 4 knee osteoarthritis according to Kellegren- Lawrence criteria and who were scheduled for total knee arthroplasty were enrolled in the study. TNF-alpha and MMP-13 levels were measured preoperatively from venous blood samples and intraoperatively from knee synovial fluid via ELISA. Preoperative and 1 month postoperative knee functions were assessed by McMaster Universities Arthritis Index.

Results

Grade 4 synovial fluid MMP-13 (4.76 ± 5.82) was elevated compared to grade 3 (3.95 ± 4.45) (p = 0.438), whereas grade 3 serum MMP-13 (1.128 ± 0.308) was found elevated compared to grade 4 (1.038 ± 0.204) (p = 0.430). Grade 4 serum TNF-α (0.253 ± 0.277) was elevated compared to grade 3 (0.206 ± 0.219) whereas grade 3 synovial fluid TNF-α (0.129 ± 0.052) was elevated compared to grade 4 (0.118 ± 0.014). Positive correlation was observed between synovial fluid MMP-13 levels and postoperative WOMAC scores. Mean serum TNF-α level (0.226 ± 0.246 pg/ml) was found higher compared to synovial level (0.124 ± 1.59), synovial MMP-13 level (4.31 ± 1.24) was found higher compared to serum level (1.089 ± 1.519).

Conclusion

Despite the systemic increase in TNF-α levels concordant with osteoarthritis grade, MMP-13 levels are elevated via local manner with a significant correlation with WOMAC scores.

Level of evidence

Level IV, Diagnostic study.

Epigenetic regulation of interleukin-8, an inflammatory chemokine, in osteoarthritis

OBJECTIVE

To determine whether altered IL8 methylation status is associated with increased expression of IL8 in human osteoarthritic (OA) chondrocytes.

METHODS

IL8 expression levels and the percentage CpG methylation in human chondrocytes were quantified by qRT-PCR and pyrosequencing in OA patients and in non-OA osteoporotic controls. The effect of CpG methylation on IL8 promoter activity was determined using a CpG-free vector; co-transfections with expression vectors encoding nuclear factor-kappa B (NF-κB), AP-1 and C/EBP were subsequently undertaken to analyse for IL8 promoter activity in response to changes in methylation status.

RESULTS

IL8 expression in OA patients was 37-fold higher than in osteoporotic controls. Three CpG sites in the IL8 promoter were significantly demethylated in OA patients. Multiple regression analysis revealed that the degree of methylation of the CpG site located at -116-bp was the strongest predictor of IL8 expression. In vitro DNA methylation was noted to decrease IL8 promoter basal activity. Furthermore, NF-κB, AP-1 and C/EBP strongly enhanced IL8 promoter activity whilst DNA methylation inhibited the effects of these three transcription factors.

CONCLUSIONS

The present study demonstrates the key role of DNA methylation status on the expression of IL8 in human chondrocytes. We demonstrate a quantitative relationship between percentage methylation and gene expression within clinical samples. These studies provide direct evidence linking the activation of IL8, DNA demethylation and the induction of the OA process with important therapeutic implications therein for patients with this debilitating disease.

Serum concentrations of canine interleukin-1 receptor antagonist protein in healthy dogs after incubation using an autologous serum processing system

The objectives of this study were to optimize and validate a canine IL-1RA ELISA using commercially available reagents and to determine the effect of an autologous serum processing system (IRAP II) on IL-1RA concentrations in canine serum. The clinical detection limit of the optimized ELISA was 188.8 to 39,965.6 pg/mL. The observed-to-expected ratio (O:E) for three serial dilutions for four serum samples ranged from 109.6 to 132.2%. The O:E for four serum samples spiked with four concentrations of canine IL-1 RA ranged from 98.7 to 114.3%. Coefficients of variances for intra- and interassay variability ranged from 1.4 to 3.0 and 6.3 to 9.8, respectively. The ELISA was sensitive, linear, accurate, precise, and reproducible. Mean±SD serum concentration of IL-1RA in 12 healthy dogs was 396.6±208.0 pg/mL. There was a significant increase in IL-1RA when blood was incubated in the IRAP II system (15,955.0±6421.0 pg/mL, P<0.0001).

Cytokines as biochemical markers for knee osteoarthritis

Osteoarthritis (OA) is a debilitating degenerative joint disease particularly affecting weightbearing joints within the body, principally the hips and knees. Current radiographic techniques are insufficient to show biochemical changes within joint tissue which can occur many years before symptoms become apparent. The need for better diagnostic and prognostic tools is heightened with the prevalence of OA set to increase in aging and obese populations. As inflammation is increasingly being considered an important part of OAs pathophysiology, cytokines are being assessed as possible candidates for biochemical markers. Cytokines, both pro- and anti-inflammatory, as well as angiogenic and chemotactic, have in recent years been studied for relevant characteristics. Biochemical markers show promise in determination of the severity of disease in addition to monitoring of the efficacy and safety of disease-modifying OA drugs, with the potential to act as diagnostic and prognostic tools. Currently, the diagnostic power of interleukin (IL)-6 and the relationship to disease burden of IL-1β, IL-15, tumor necrosis factor-α, and vascular endothelial growth factor make these the best candidates for assessment. Grouping appropriate cytokine markers together and assessing them collectively alongside other bone and cartilage degradation products will yield a more statistically powerful tool in research and clinical applications, and additionally aid in distinguishing between OA and a number of other diseases in which cytokines are known to have an involvement. Further large scale studies are needed to assess the validity and efficacy of current biomarkers, and to discover other potential biomarker candidates.

A novel rose hip preparation with enhanced anti-inflammatory and chondroprotective effects

Rose hip powder (RHP) alleviates osteoarthritis (OA) due to its anti-inflammatory and cartilage-protective properties. Substances contained in RHP might contribute to its clinical efficacy. The activity of two RHP (i.e., RH-A, from the whole fruit, RH-B, from fruits without seeds) was investigated in human peripheral blood leukocytes (PBL) and primary chondrocytes (NHAC-kn). RH-A and RH-B diminished the secretion of chemokines and cytokines in LPS/IFN-γ-activated PBL, including CCL5/RANTES, CXCL10/IP-10, interleukin- (IL-) 6, and IL-12. Most effects were transcriptional, since gene expression levels were significantly influenced by RH-A and RH-B. In IL-1β treated normal chondrocytes (NHAC-kn), both RH preparations reduced the expression of matrix metalloproteinase- (MMP-) 1, MMP-3, and MMP-13 and ADAMTS-4. These changes are associated with diminished inflammatory damage or cartilage erosion. Principal component analysis revealed that (1) RH-A and RH-B modified a large pattern of biomarkers, and (2) RH-B outperformed RH-A. Furthermore, RH-B contained more chondroprotective and anti-inflammatory constituents than RH-A. Thus, RHP contributed to restore cellular homeostasis in PBL and chondrocytes. RH preparations from fruits without seeds are thus expected to have an improved OA-preventive or OA-therapeutic profile, as subsequently shown in a related clinical trial.

Anti-inflammatory strategies in cartilage repair

Cartilage defects are normally concomitant with posttraumatic inflammation and pose a major challenge in cartilage repair. Due to the avascular nature of cartilage and its inability to surmount an inflammatory response, the cartilage is easily attacked by proinflammatory factors and oxidative stress; if left untreated, osteoarthritis may develop. Suppression of inflammation has always been a crux for cartilage repair. Pharmacological drugs have been successfully applied in cartilage repair; however, they cannot optimally work alone. This review article will summarize current pharmacological drugs and their application in cartilage repair. The development of extracellular matrix-based scaffolds and preconditioned tissue-specific stem cells will be emphasized because both of these tissue engineering components could contribute to an enhanced ability not only for cartilage regeneration but also for anti-inflammation. These strategies could be combined to boost cartilage repair under inflammatory conditions.

Fluid shear stress-induced osteoarthritis: roles of cyclooxygenase-2 and its metabolic products in inducing the expression of proinflammatory cytokines and matrix metalloproteinases

The mechanical overloading of cartilage is involved in the pathophysiology of osteoarthritis (OA) by both biochemical and mechanical pathways. The application of fluid shear stress to chondrocytes recapitulates the earmarks of OA, as evidenced by the release of proinflammatory cytokines (PICs), matrix metalloproteinases (MMPs), and apoptotic factors. Dysregulations or mutations in these genes might directly cause OA in addition to determining the stage at which OA becomes apparent, the joint sites involved, and the severity of the disease and how rapidly it progresses. However, the underlying mechanisms remain unknown. In this review, we propose that the dysregulation of cyclooxygenase-2 (COX-2) is associated with fluid shear stress-induced OA via its metabolic products at different stages of the disease. Indeed, high fluid shear stress rapidly induces the production of PICs and MMPs via COX-2-derived prostaglandin (PG)E2 at the early stage of OA. In contrast, prolonged shear exposure (>12 h) aggravates the condition by concurrently up-regulating the expression of proapoptotic genes and down-regulating the expression of antiapoptotic genes in a 15-deoxy-Δ (12,14)-prostaglandin J2 (15d-PGJ2)-dependent manner at the late stage of disease. These observations may help to resolve long-standing questions in OA progression and provide insight for development of strategies to treat and combat OA.

Rebamipide attenuates pain severity and cartilage degeneration in a rat model of osteoarthritis by downregulating oxidative damage and catabolic activity in chondrocytes

OBJECTIVE

The objectives were to investigate the in vivo effects of treatment with rebamipide on pain severity and cartilage degeneration in an experimental model of rat osteoarthritis (OA) and to explore its mode of action.

MATERIALS AND METHODS

OA was induced in rats by intra-articular injection of monosodium iodoacetate (MIA). Oral administration of rebamipide was initiated on the day of MIA injection, 3 or 7 days after. Limb nociception was assessed by measuring the paw withdrawal latency and threshold. We analyzed the samples macroscopically and histomorphologically, and used immunohistochemistry to investigate the expression of matrix metalloproteinase-13 (MMP-13), interleukin-1β (IL-1β), hypoxia-inducible factor-2α (HIF-2α), inducible nitric oxide synthase (iNOS), and nitrotyrosine in knee joints. Real-time quantitative reverse transcription-polymerase chain reaction was used to quantify the mRNA for catabolic and anticatabolic factors in human OA chondrocytes.

RESULTS

Rebamipide showed an antinociceptive property and attenuated cartilage degeneration. Rebamipide reduced the expression of MMP-13, IL-1β, HIF-2α, iNOS, and nitrotyrosine in OA cartilage in a dose-dependent manner. Nitrotyrosine expression in the subchondral bone region was decreased in the rebamipide-treated joints. mRNA expression of MMP-1, -3, and -13, and ADAMTS5 was attenuated in IL-1β-stimulated human OA chondrocytes. By contrast, rebamipide induced the mRNA expression of tissue inhibitor of metalloproteinase-1 and -3.

CONCLUSION

The results show the inhibitory effects of rebamipide on pain production and cartilage degeneration in experimentally induced OA. The suppression of oxidative damage and the restoration of extracellular matrix homeostasis of articular chondrocyte suggest that rebamipide is a potential therapeutic strategy for OA.

Impact of inflammation on the osteoarthritic niche: implications for regenerative medicine

Osteoarthritis (OA) is the most common form of arthritis worldwide and is the sixth leading cause of disability. It costs the UK economy approximately 1% of gross national product per annum. With an aging population, the cost of chronic conditions such as OA continues to rise. Historically, treatments for OA have been limited to painkillers, physiotherapy and joint injections. When these fail, patients are referred for joint replacement surgery. With the advent of tissue engineering strategies aimed at generating new bone and cartilage for repair of osteochondral defects, there has been considerable interest in exploiting these techniques to devise new treatments for OA. To date, little consideration has been given to the OA niche and attendant inflammatory milieu for any regenerative skeletal strategy. This review highlights the importance of understanding the osteoarthritic niche in order to modify existing tissue engineering and regenerative medicine strategies for the future treatment of OA.

Rose hip and its constituent galactolipids confer cartilage protection by modulating cytokine, and chemokine expression

Background

Clinical studies have shown that rose hip powder (RHP) alleviates osteoarthritis (OA). This might be due to anti-inflammatory and cartilage-protective properties of the complete RHP or specific constituents of RHP. Cellular systems (macrophages, peripheral blood leukocytes and chondrocytes), which respond to inflammatory and OA-inducing stimuli, are used as in vitro surrogates to evaluate the possible pain-relief and disease-modifying effects of RHP.

Methods

(1) Inflammatory processes were induced in RAW264.7 cells or human peripheral blood leukocytes (PBL) with LPS. Inflammatory mediators (nitric oxide (NO), prostaglandin E₂ (PGE₂) and cytokines/chemokines) were determined by the Griess reaction, EIA and multiplex ELISA, respectively. Gene expression was quantified by RT-PCR. RHP or its constituent galactolipid, GLGPG (galactolipid (2S)-1, 2-di-O-[(9Z, 12Z, 15Z)-octadeca-9, 12, 15-trienoyl]-3-O-β-D-galactopyranosyl glycerol), were added at various concentrations and the effects on biochemical and molecular parameters were evaluated. (2) SW1353 chondrosarcoma cells and primary human knee articular chondrocytes (NHAC-kn) were treated with interleukin (IL)-1β to induce in vitro processes similar to those occurring during in vivo degradation of cartilage. Biomarkers related to OA (NO, PGE₂, cytokines, chemokines, metalloproteinases) were measured by multiplex ELISA and gene expression analysis in chondrocytes. We investigated the modulation of these events by RHP and GLGPG.

Results

In macrophages and PBL, RHP and GLGPG inhibited NO and PGE₂ production and reduced the secretion of cytokines (TNF-α, IFN-γ, IL-1β, IL-6, IL-12) and chemokines (CCL5/RANTES, CXCL10/IP-10). In SW1353 cells and primary chondrocytes, RHP and GLGPG diminished catabolic gene expression and inflammatory protein secretion as shown by lower mRNA levels of matrix metalloproteinases (MMP-1, MMP-3, MMP-13), aggrecanase (ADAMTS-4), macrophage inflammatory protein (MIP-2, MIP-3α), CCL5/RANTES, CXCL10/IP-10, IL-8, IL-1α and IL-6. The effects of GLGPG were weaker than those of RHP, which presumably contains other chondro-protective substances besides GLGPG.

Conclusions

RHP and GLGPG attenuate inflammatory responses in different cellular systems (macrophages, PBLs and chondrocytes). The effects on cytokine production and MMP expression indicate that RHP and its constituent GLGPG down-regulate catabolic processes associated with osteoarthritis (OA) or rheumatoid arthritis (RA). These data provide a molecular and biochemical basis for cartilage protection provided by RHP.

CCL20 Stimulates Proinflammatory Mediator Synthesis in Human Fibroblast-like Synoviocytes Through a MAP Kinase-dependent Process with Transcriptional and Posttranscriptional Control

Objective.

To compare levels of the chemokine CCL20 and its receptor CCR6 in donor, osteoarthritic (OA), and rheumatoid arthritis (RA) synovium; and to determine the molecular mechanism of cellular activation induced by chemokine/receptor ligation in human fibroblast-like synoviocytes (FLS).

Methods.

Synovia and isolated FLS from donor, OA, and RA joints were analyzed for CCL20 and CCR6 expression by RT-PCR and immunohistochemistry. The effect of CCL20 on cytokines and mediators of cartilage degradation was examined by PCR for mRNA expression levels and ELISA, and Western blotting for protein. CCL20-dependent transcriptional and posttranscriptional activation of target genes was monitored using reporter constructs and luciferase assays in transfected donor FLS.

Results.

CCL20 and CCR6 proteins were abundantly expressed in RA synovial lining cells compared to donor or OA synovia as judged by immunohistochemistry. RT-PCR of synovial extracts confirmed the predominance of CCL20/CCR6 mRNA expression in RA synovium. CCL20 mRNA expression was low in donor FLS, but increased dramatically after stimulation with recombinant human (rh) interleukin 1ß (IL-1ß). rhCCL20 increased mRNA and protein expression of COX-2, IL-1ß, tumor necrosis factor-α, IL-6, and the matrix-destructive metalloprotease MMP-3 in donor FLS cultures. High constitutive levels of IL-6 were released from RA synovia; CCL20-induced expression of IL-6 occurred through an NSAID/COXIB-sensitive process. CCL20-induced expression of COX-2 was mediated by a PLCP1/PKCα/MEK1/2/ERK1/2-dependent pathway involving both transcriptional and posttranscriptional mechanisms.

Conclusion.

CCL20/CCR6 may play an important role in the pathogenesis of RA by assembling the molecular and cellular components orchestrating synovitis.

Epigallocatechin-3-gallate suppresses the global interleukin-1beta-induced inflammatory response in human chondrocytes

Introduction

Epigallocatechin-3-gallate (EGCG) is a bioactive polyphenol of green tea and exerts potent anti-inflammatory effects by inhibiting signaling events and gene expression. Interleukin-1beta (IL-1β) is the principal cytokine linked to cartilage degradation in osteoarthritis (OA). The objective of this study was to evaluate the global effect of EGCG on IL-1β-induced expression of proteins associated with OA pathogenesis in human chondrocytes.

Methods

Primary OA chondrocytes were pretreated with EGCG (10 to 100 uM) and then stimulated with IL-1β (5 ng/ml) for 24 hours. Culture supernatants were incubated with cytokine antibody arrays and immunoreactive proteins (80 proteins) were visualized by enhanced chemiluminiscence. Effect of EGCG on IL-1β-induced expression of 18 selected genes was verified by Real time-PCR and effect on IL-6, IL-8 and tumor necrosis factor-alpha (TNF-α) production was determined using specific ELISAs. Western immunoblotting was used to analyze the effect of EGCG on the interleukin-1 receptor-associated kinase 1 (IRAK-1) and TNF receptor-associated factor 6 (TRAF-6) proteins in IL-1β-stimulated chondrocytes. The role of nuclear factor kappa-B (NF-κB) and mitogen activated protein kinases (MAPKs) in the regulation of selected genes and the mechanism involved in EGCG mediated modulation of these genes was determined by using specific inhibitors for NF- κB (MG132) and MAPKs (p38-MAPK, SB202190; JNK-MAPK, SP600125, ERK-MAPK, PD98059).

Results

Out of 80 proteins present on the array, constitutive expression of 14% proteins was altered by EGCG treatment. No significant stimulatory effect was observed on the proteins associated with cartilage anabolic response. Stimulation with IL-1β enhanced the expression of 29 proteins. Expression of all 29 proteins up-regulated by IL-1β was found to be suppressed by EGCG. EGCG also inhibited the expression of the signaling intermediate TRAF-6 at 50 and 100 uM concentrations (P < 0.05). Our results identified several new targets of EGCG, including epithelial neutrophil activating peptide-78 (ENA-78), granulocyte macrophage colony stimulation factor (GM-CSF), growth- related oncogene (GRO), GRO-α, IL-6, IL-8, monocyte chemotactic protein-1 (MCP-1), MCP-3, macrophage inflammatory protein-1beta (MIP-1β), granulocyte chemotactic protein-2 (GCP-2), MIP-3alpha, interferon-gamma-inducible protein-10 (IP-10), nucleosome assembly protein-2 (NAP-2) and leukemia inhibitory factor (LIF). The inhibitory effects of EGCG were mainly mediated by inhibiting the activation of NF-κB and c-Jun N-terminal Kinase (JNK)-MAPK in human chondrocytes.

Conclusions

Our results suggest that the potential of EGCG in OA treatment/prevention may be related to its ability to globally suppress the inflammatory response in human chondrocytes. These results identify additional new targets of EGCG and advocate that EGCG may be a potent chondroprotective agent in OA.

Role of proinflammatory cytokines in the pathophysiology of osteoarthritis

Osteoarthritis (OA) is associated with cartilage destruction, subchondral bone remodeling and inflammation of the synovial membrane, although the etiology and pathogenesis underlying this debilitating disease are poorly understood. Secreted inflammatory molecules, such as proinflammatory cytokines, are among the critical mediators of the disturbed processes implicated in OA pathophysiology. Interleukin (IL)-1β and tumor necrosis factor (TNF), in particular, control the degeneration of articular cartilage matrix, which makes them prime targets for therapeutic strategies. Animal studies provide support for this approach, although only a few clinical studies have investigated the efficacy of blocking these proinflammatory cytokines in the treatment of OA. Apart from IL-1β and TNF, several other cytokines including IL-6, IL-15, IL-17, IL-18, IL-21, leukemia inhibitory factor and IL-8 (a chemokine) have also been shown to be implicated in OA and could possibly be targeted therapeutically. This Review discusses the current knowledge regarding the role of proinflammatory cytokines in the pathophysiology of OA and addresses the potential of anticytokine therapy in the treatment of this disease.

Analysing the role of endogenous matrix molecules in the development of osteoarthritis

Osteoarthritis (OA) is the most common form of arthritis worldwide. In this condition, damage to the extracellular matrix (ECM) of cartilage occurs, resulting in joint destruction. Factors mediating cartilage damage include mechanical injury, cytokine and superoxide release on a background of genetic susceptibility and obesity. Studies of arthritic cartilage show increased production of ECM molecules including type II collagen, cartilage oligomeric matrix protein, fibronectin (FN) and fibromodulin. Recent reports suggest that ECM proteins may become endogenous catabolic factors during joint damage. Activation of pro-inflammatory pathways by ECM proteins has led to their description as damage-associated molecular patterns (DAMPs). The ECM proteins involved include fibromodulin, which activates the complement pathway and may promote the persistence of joint inflammation. Fragmentation of type II collagen, FN and hyaluronan reveals cryptic epitopes that stimulate proteolytic enzymes including matrix metalloproteinases and aggrecanases (ADAMTSs - a disintegrin and metalloproteinase with thrombospondin type 1 motifs). Proteolytic fragments also stimulate the release of nitric oxide, chemokines and cytokines and activation of the MAP kinases. Reports are emerging that the receptors for the fragments described involve interaction with integrins and toll-like receptors. In this review the contribution of endogenous ECM molecules to joint destruction will be discussed. A deeper understanding of the pathways stimulated by endogenous ligands could offer potential avenues for novel therapies in the future.

Ciliary neurotrophic factor (CNTF) plus soluble CNTF receptor alpha increases cyclooxygenase-2 expression, PGE2 release and interferon-gamma-induced CD40 in murine microglia

BACKGROUND

Ciliary neurotrophic factor (CNTF) has been regarded as a potent trophic factor for motor neurons. However, recent studies have shown that CNTF exerts effects on glial cells as well as neurons. For instance, CNTF stimulates astrocytes to secrete FGF-2 and rat microglia to secrete glial cell line-derived neurotrophic factor (GDNF), which suggest that CNTF exerts effects on astrocytes and microglia to promote motor neuron survival indirectly. As CNTF is structurally related to IL-6, which can stimulate immune functions of microglia, we hypothesized that CNTF might exert similar effects.

METHODS

We performed 2-D and 1-D proteomic experiments with western blotting and flow cytometry to examine effects of CNTF on primary microglia derived from neonatal mouse brains.

RESULTS

We show that murine microglia express CNTF receptor alpha (CNTFRalpha), which can be induced by interferon-gamma (IFNgamma). Whereas IL-6 activated STAT-3 and ERK phosphorylation, CNTF did not activate these pathways, nor did CNTF increase p38 MAP kinase phosphorylation. Using 2-D western blot analysis, we demonstrate that CNTF induced the dephosphorylation of a set of proteins and phosphorylation of a different set. Two proteins that were phosphorylated upon CNTF treatment were the LYN substrate-1 and beta-tubulin 5. CNTF weakly stimulated microglia, whereas a stronger response was obtained by adding exogenous soluble CNTFRalpha (sCNTFRalpha) as has been observed for IL-6. When used in combination, CNTF and sCNTFRalpha collaborated with IFNgamma to increase microglial surface expression of CD40 and this effect was quite pronounced when the microglia were differentiated towards dendritic-like cells. CNTF/sCNTFRalpha complex, however, failed to increase MHC class II expression beyond that induced by IFNgamma. The combination of CNTF and sCNTFRalpha, but not CNTF alone, enhanced microglial Cox-2 protein expression and PGE2 secretion (although CNTF was 30 times less potent than LPS). Surprisingly, Cox-2 production was enhanced 2-fold, rather than being inhibited, upon addition of a gp130 blocking antibody.

CONCLUSION

Our studies indicate that CNTF can activate microglia and dendritic-like microglia similar to IL-6; however, unlike IL-6, CNTF does not stimulate the expected signaling pathways in microglia, nor does it appear to require gp130.

Concepts in gene therapy for cartilage repair

Once articular cartilage is injured, it has a very limited capacity for self repair. Although current surgical therapeutic procedures for cartilage repair are clinically useful, they cannot restore a normal articular surface. Current research offers a growing number of bioactive reagents, including proteins and nucleic acids, that may be used to augment various aspects of the repair process. As these agents are difficult to administer effectively, gene-transfer approaches are being developed to provide their sustained synthesis at sites of repair. To augment regeneration of articular cartilage, therapeutic genes can be delivered to the synovium or directly to the cartilage lesion. Gene delivery to the cells of the synovial lining is generally considered more suitable for chondroprotective approaches, based on the expression of anti-inflammatory mediators. Gene transfer targeted at cartilage defects can be achieved by either direct vector administration to cells located at or surrounding the defects, or by transplantation of genetically modified chondrogenic cells into the defect. Several studies have shown that exogenous cDNAs encoding growth factors can be delivered locally to sites of cartilage damage, where they are expressed at therapeutically relevant levels. Furthermore, data is beginning to emerge indicating that efficient delivery and expression of these genes is capable of influencing a repair response toward the synthesis of a more hyaline cartilage repair tissue in vivo. This review presents the current status of gene therapy for cartilage healing and highlights some of the remaining challenges.

Site-specific proteolysis of cyclooxygenase-2: A putative step in inflammatory prostaglandin E2 biosynthesis

Cyclooxygenase-2 (COX-2) catalyzes the rate-limiting step in inflammatory prostanoid biosynthesis. Transcriptional, post-transcriptional, and post-translational covalent modifications have been defined as important levels of regulation for COX-2 gene expression. Here, we describe a novel regulatory mechanism in primary human cells involving regulated, sequence-specific proteolysis of COX-2 that correlates with its catalytic activity and ultimately, the biosynthesis of prostaglandin E(2) (PGE(2)). Proinflammatory cytokines induced COX-2 expression and its proteolysis into stable immunoreactive fragments of 66, 42-44, 34-36, and 28 kDa. Increased COX-2 activity (PGE(2) release) was observed coincident with the timing and degree of COX-2 proteolysis with correlation analysis confirming a linear relationship (R(2) = 0.941). Inhibition of induced COX-2 activity with non-steroidal anti-inflammatory drugs (NSAIDs) and COX-2 selective inhibitors also abrogated cleavage. To determine if NSAID inhibition of proteolysis was related to drug-binding-induced conformational changes in COX-2, we assayed COX-inactive NSAID derivatives that fail to bind COX-2. Interestingly, these compounds suppressed COX-2 activity and cleavage in a correlated manner, thus suggesting that the observed NSAID-induced inhibition of COX-2 cleavage occurred through COX-independent mechanisms, presumably through the inhibition of proteases involved in COX-2 processing. Corroborating this observation, COX-2 cleavage and activity were mutually suppressed by calpain/cathepsin protease inhibitors. Our data suggest that the nascent intracellular form of COX-2 may undergo limited proteolysis to attain full catalytic capacity.

Cytokines as therapeutic targets for osteoarthritis

Osteoarthritis (OA) is a debilitating, progressive disease of diarthrodial joints associated with the aging process. With the exception of anti-inflammatory corticosteroids and nonsteroidal anti-inflammatory drugs which inhibit cyclo-oxygenase-2, the enzyme responsible for prostaglandin biosynthesis in inflammation, no specific therapy based on fundamental intracellular pathways of chondrocytes and synoviocytes exists for the medical management of OA. At the molecular level, OA is characterized by an imbalance between chondrocyte anabolism and catabolism. Disruption of chondrocyte homeostasis primarily affects the cartilage extracellular matrix (ECM), which is responsible for the biomechanical properties of the tissue. Recent evidence has implicated cytokines, among which interleukin (IL)-1, tumor necrosis factor-alpha, IL-6, and IL-17 seem most involved in the OA process of cartilage destruction. The primary role of these cytokines is to modulate the expression of matrix metalloproteinases and cartilage ECM proteins. Cartilage repair that could restore the functional integrity of the joint is also impaired because chondrocytes in OA cartilage appear unable to respond to insulin-like growth factor-1 or respond abnormally to transforming growth factor-beta. As these growth factors also modulate cytokine expression, they may prove useful in designing strategies for suppressing 'chondrocyte activation'. Although cytokines and growth factors provide a potential therapeutic target for OA, it will be necessary to elucidate the fundamental mechanisms that cytokines employ to cause chondrocyte and synoviocyte dysfunction before 'anti-cytokine' therapy can be employed in the medical management of the disease.

Participation of cyclooxygenase-1 in prostaglandin E2 release from synovitis tissue in primary osteoarthritis in vitro

OBJECTIVES

To investigate the relative contribution of the cyclooxygenase (COX) isoenzymes COX-1 and COX-2 to prostaglandin E2 (PGE2) release from inflamed synovial tissue in N=10 patients with primary osteoarthritis (OA) in vitro and to determine possible effects of COX inhibitors on the gene expression of synovial COX-1 and COX-2.

DESIGN

The effects of a COX-unspecific nonsteroidal anti-inflammatory drug (NSAID; diclofenac), a selective COX-1 inhibitor (SC-560) and a selective COX-2 inhibitor (SC-58125) on PGE2 release from inflamed synovial tissue (0.1-10 microM, 3 and 6 h incubation time) were compared. Release of PGE2 into the incubation media was measured by means of the enzyme-linked immunosorbent assay. Expression of synovial COX-1/-2 was quantified by means of real-time reverse transcriptase polymerase chain reaction (RT-PCR).

RESULTS

All agents inhibited synovial PGE2 release dose-dependently. Compared to short-term incubations, the inhibitory potency of diclofenac, SC-58125 and SC-560 was increased (0.1-10 microM) and decreased (0.1-1 microM), respectively, during 6 h: At 10 microM, SC-560 and SC-58125 had obviously lost their specificity for COX-1 and COX-2, respectively, indicated by a comparable inhibitory potency of the selective COX-1 inhibitor (86.6%) and the selective COX-2 inhibitor (96.6%) within identical tissue specimens. In contrast, at 1 microM, 83% and 62.8% inhibition was seen for diclofenac and SC-58125, respectively. SC-560 showed 30.6% inhibition (P<0.05). In contrast to synovial COX-1, RT-PCR revealed a significant induction of COX-2 through PGE2.

CONCLUSIONS

With respect to the concentrations studied, the data suggest that in inflamed synovial tissue in OA, up to 30% of PGE2 might be generated via the COX-1 pathway. In therapy of OA, the relative contribution of COX-1 in synovial inflammation should be considered, weighing the potency of COX-unspecific NSAID against the assumed superior gastrointestinal safety profile of selective COX-2 inhibitors.

Cyclooxygenase-2 and prostaglandins in articular tissues

OBJECTIVES

To provide an overview on: 1) the expression of cyclooxygenase (COX)-2 in articular tissues; 2) the role of prostaglandin E2 (PGE2) in these tissue functions; and 3) clinical trials with COX-2-selective nonsteroidal anti-inflammatory drugs (NSAIDs) (coxibs).

METHODS

MEDLINE search was performed using the key words "cyclooxygenase," "prostaglandin," "osteoarthritis" (OA), and "rheumatoid arthritis" (RA). Selected publications related to clinical trials with coxibs also are included.

RESULTS

COX-2 is upregulated in inflamed joint tissues and is responsible for elevated PGE2 production. The overexpression of COX-2 is likely induced by proinflammatory mediators such as interleukin-1beta (IL-1beta) and tumor necrosis factor (TNF) alpha. However, the exact molecular mechanisms through which the expression of COX-2 is regulated remain to be elucidated. Several studies suggest that PGE2 is involved in inflammation, apoptosis, angiogenesis, and possibly structural changes that characterize arthritic diseases. NSAIDs are prescribed for the treatment of OA and RA and provide effective relief from symptoms; however, serious gastrointestinal complications occur with their use. The clinical efficacy of NSAIDs is primarily related to the inhibition of COX-2, whereas much of the toxicity is related to COX-1 inhibition. Selective COX-2 inhibitors (coxibs) that spare COX-1 at therapeutic doses are more effective than placebo and as effective as other NSAIDs for relief of symptoms of OA and RA, and have significantly improved gastrointestinal safety and tolerability. However, some studies showed that COX-2-selective inhibitors still have classic NSAID complications.

CONCLUSIONS

Overexpression of COX-2 protein in articular tissues is a characteristic feature of arthritic diseases. However, the molecular mechanisms involved in the regulation of COX-2 expression and activity are still unclear. Elucidating the mechanisms of COX-2 expression and PGE2 production and action will help identify novel and more selective potential drug targets in the treatment of arthritic diseases.

Peroxisome proliferator-activated receptor gamma activators inhibit MMP-1 production in human synovial fibroblasts likely by reducing the binding of the activator protein 1

OBJECTIVE

To investigate the expression and activity of PPARgamma in human synovial fibroblasts and the effects of PPARgamma agonists on the expression of MMP-1. The molecular mechanisms by which PPARgamma agonists modulate MMP-1 expression were also examined.

METHODS

PPARgamma expression and activity were measured using reverse-transcription polymerase chain reaction (RT-PCR) and transient transfection assays. Human synovial fibroblasts were cultured with IL-1beta in the absence or presence of PPARgamma activators, and the expression and production of MMP-1 were evaluated by Northern blot and ELISA, respectively. The effect of 15d-PGJ(2) on MMP-1 promoter activation was analysed in transient transfection experiments, while electrophoretic mobility shift assays were performed to study the binding activity of the transcription factor AP-1.

RESULTS

PPARgamma was expressed and transcriptionally functional in human synovial fibroblasts. PPARgamma activators (15d-PGJ(2) and BRL 49653) inhibited IL-1beta-induced MMP-1 synthesis in a dose-dependent manner. Similarly, both activators inhibited IL-1-induced MMP-1 mRNA expression. Activation of the human MMP-1 promoter was also attenuated by 15d-PGJ(2), indicating that the inhibitory effect of 15d-PGJ(2) occurs at the transcriptional level. Interestingly, 15d-PGJ(2) reduced both basal and IL-1beta-induced AP-1 binding activity.

CONCLUSIONS

These data indicate that PPARgamma agonists inhibit MMP-1 gene expression by transcriptional mechanisms, and suggest that they may be useful in reducing joint tissue destruction.

Cell biology of osteoarthritis: the chondrocyte's response to injury

Cartilage is comprised of a large amount of functional extracellular matrix that is made and maintained by a small number of chondrocytes, the sole resident cell type. Normal cartilage exists in a relatively steady state: that is, the anabolic processes (those that result in the synthesis of cartilage matrix components) are in equilibrium with the catabolic processes (those that result in the normal turnover of matrix molecules). If the functional extracellular matrix is disturbed by physical or molecular means, the cells respond in an attempt to repair the matrix. This stimulated activity does not result in repair due to the extent and complexity of the extracellular matrix. Eventually, the newly synthesized and activated catabolic enzymes degrade the matrix components. This review presents the cellular and molecular mechanisms that account for this activity and provides some possible solutions.

Anticytokine therapy for osteoarthritis

Osteoarthritis (OA) is a joint disease that involves degeneration of articular cartilage, weakening of the subchondral bone and limited intra-articular inflammation manifested by synovitis. Since the pathogenesis of OA involves multiple aetiologies, including mechanical, biochemical and genetic factors, it has been difficult to identify unique targets for therapy. Current pharmacological interventions focus primarily on improving symptoms. The rationale for the use of anticytokine therapy in OA is based on evidence from studies in vitro and in vivo that interleukin-1 (IL-1) and tumour necrosis factor (TNF)-alpha are the predominant pro-inflammatory and catabolic cytokines involved in the initiation and progression of articular cartilage destruction. Since the increased levels of catabolic enzymes, prostaglandins, nitric oxide (NO) and other markers in OA fluids and tissues appear to be related to elevated levels of IL-1 and TNF-alpha, therapies that interfere with the expression or actions of these cytokines are most promising. Other cytokines that are anti-inflammatory and are often detected, paradoxically, in OA tissues are also potential therapeutic agents for counteracting the cartilage destruction in OA. Identification of methods for early diagnosis is of key importance, since therapeutic interventions aimed at blocking or reversing structural damage will be more effective when there is the possibility of preserving normal homeostasis. At later stages, cartilage tissue engineering with or without gene therapy will also require anticytokine therapy to block damage to newly repaired cartilage. This review will focus on experimental approaches currently under study that may lead to elucidation of effective strategies for therapy in OA, with special emphasis on anticytokine therapy.

Osteoarthritis and cartilage: the role of cytokines

The pathogenesis of osteoarthritis involves multiple etiologies, including mechanical, biochemical, and genetic factors that contribute to the imbalance in the synthesis and destruction of articular cartilage. It is now well documented that interleukin-1 and tumor necrosis factor-alpha are the predominant proinflammatory and catabolic cytokines involved in disease initiation and progression. Other proinflammatory cytokines may amplify or modulate this process, whereas anti-inflammatory cytokines, which are often detected, paradoxically, in osteoarthritis tissues, may counteract the tissue destruction and inflammation. This review focuses on the role of cytokines in the pathogenesis of osteoarthritis with special emphasis on how findings in culture and animal models may be reflected in the human disease process.