In vivo effects of interleukin-1 on articular cartilage. Prolongation of proteoglycan metabolic disturbances in old mice

Network-based cytokine inference implicates Oncostatin M as a driver of an inflammation phenotype in knee osteoarthritis

Inflammatory cytokines released by synovium after trauma disturb the gene regulatory network and have been implicated in the pathophysiology of osteoarthritis. A mechanistic understanding of how aging perturbs this process can help identify novel interventions. Here, we introduced network paradigms to simulate cytokine-mediated pathological communication between the synovium and cartilage. Cartilage-specific network analysis of injured young and aged murine knees revealed aberrant matrix remodeling as a transcriptomic response unique to aged knees displaying accelerated cartilage degradation. Next, network-based cytokine inference with pharmacological manipulation uncovered IL6 family member, Oncostatin M (OSM), as a driver of the aberrant matrix remodeling. By implementing a phenotypic drug discovery approach, we identified that the activation of OSM recapitulated an "inflammatory" phenotype of knee osteoarthritis and highlighted high-value targets for drug development and repurposing. These findings offer translational opportunities targeting the inflammation-driven osteoarthritis phenotype.

Meta-analysis Integrated With Multi-omics Data Analysis to Elucidate Pathogenic Mechanisms of Age-Related Knee Osteoarthritis in Mice

Increased mechanistic insight into the pathogenesis of knee osteoarthritis (KOA) is needed to develop efficacious disease-modifying treatments. Though age-related pathogenic mechanisms are most relevant to the majority of clinically presenting KOA, the bulk of our mechanistic understanding of KOA has been derived using surgically induced posttraumatic OA (PTOA) models. Here, we took an integrated approach of meta-analysis and multi-omics data analysis to elucidate pathogenic mechanisms of age-related KOA in mice. Protein-level data were integrated with transcriptomic profiling to reveal inflammation, autophagy, and cellular senescence as primary hallmarks of age-related KOA. Importantly, the molecular profiles of cartilage aging were unique from those observed following PTOA, with less than 3% overlap between the 2 models. At the nexus of the 3 aging hallmarks, advanced glycation end product (AGE)/receptor for AGE (RAGE) emerged as the most statistically robust pathway associated with age-related KOA. This pathway was further supported by analysis of mass spectrometry data. Notably, the change in AGE-RAGE signaling over time was exclusively observed in male mice, suggesting sexual dimorphism in the pathogenesis of age-induced KOA in murine models. Collectively, these findings implicate dysregulation of AGE-RAGE signaling as a sex-dependent driver of age-related KOA.

Inflammasomes and the IL-1 Family in Bone Homeostasis and Disease

PURPOSE OF REVIEW

Inflammasomes are multimeric protein structures with crucial roles in host responses against infections and injuries. The importance of inflammasome activation goes beyond host defense as a dysregulated inflammasome and subsequent secretion of IL-1 family members is believed to be involved in the pathogenesis of various diseases, some of which also produce skeletal manifestations. The purpose of this review is to summarize recent developments in the understanding of inflammasome regulation and IL-1 family members in bone physiology and pathology and current therapeutics will be discussed.

RECENT FINDINGS

Small animal models have been vital to help understand how the inflammasome regulates bone dynamics. Animal models with gain or loss of function in various inflammasome components or IL-1 family signaling have illustrated how these systems can impact numerous bone pathologies and have been utilized to test new inflammasome therapeutics. It is increasingly clear that a tightly regulated inflammasome is required not only for host defense but for skeletal homeostasis, as a dysregulated inflammasome is linked to diseases of pathological bone accrual and loss. Given the complexities of inflammasome activation and redundancies in IL-1 activation and secretion, targeting these pathways is at times challenging. Ongoing research into inflammasome-mediated mechanisms will allow the development of new therapeutics for inflammasome/IL-1 diseases.

Rheumatoid arthritis: current therapeutics compendium

Rheumatoid arthritis is a common chronic inflammatory disease with substantial economic, social, and personal costs. Its pathogenesis is multifactorial and complex. The ultimate goal of rheumatoid arthritis treatment is stopping or slowing down the disease progression. In the past two decades, invention of new medicines, especially biologic agents, revolutionized the management of this disease. These agents have been associated with an improved prognosis and clinical remission, especially in patients who did not respond to traditional disease-modifying anti-rheumatic drugs (DMARDs). Improvement in the understanding of the rheumatoid arthritis pathogenesis leads to the development of novel biologic therapeutic approaches. In the present paper, we summarized the current therapeutics, especially biologic agents, available for the treatment of rheumatoid arthritis.

Cartilage tissue engineering: From proinflammatory and anti‑inflammatory cytokines to osteoarthritis treatments (Review)

Osteoarthritis (OA), one of the most common joint diseases, is characterized by fibrosis, rhagadia, ulcers and attrition of articular cartilage due to a number of factors. The etiology of OA remains unclear, but its occurrence has been associated with age, obesity, inflammation, trauma and genetic factors. Inflammatory cytokines are crucial for the occurrence and progression of OA. The intra-articular proinflammatory and anti-inflammatory cytokines jointly maintain a dynamic balance, in accordance with the physiological metabolism of articular cartilage. However, dynamic imbalance between proinflammatory and anti-inflammatory cytokines can cause abnormal metabolism in knee articular cartilage, which leads to deformation, loss and abnormal regeneration, and ultimately destroys the normal structure of the knee joint. The ability of articular cartilage to self-repair once damaged is limited, due to its inability to obtain nutrients from blood vessels, nerves and lymphatic vessels, as well as limitations in the extracellular matrix. There are several disadvantages inherent to conventional repair methods, while cartilage tissue engineering (CTE), which combines proinflammatory and anti-inflammatory cytokines, offers a new therapeutic approach for OA. The aim of the present review was to examine the proinflammatory factors implicated in OA, including IL-1β, TNF-α, IL-6, IL-15, IL-17 and IL-18, as well as the key anti-inflammatory factors reducing OA-related articular damage, including IL-4, insulin-like growth factor and TGF-β. The predominance of proinflammatory over anti-inflammatory cytokine effects ultimately leads to the development of OA. CTE, which employs mesenchymal stem cells and scaffolding technology, may prevent OA by maintaining the homeostasis of pro- and anti-inflammatory factors.

Applying chlorogenic acid in an alginate scaffold of chondrocytes can improve the repair of damaged articular cartilage

Damaged cartilage has very low regenerative potential which has led to the search for novel tissue-engineering approaches to help treat cartilage defects. While various approaches have been reported, there is no perfect treatment currently. In this study we evaluated the effects of a plant extract, chlorogenic acid (CGA), as part of chondrocyte transplantation on a model of knee joint injury in chicks. First, primary cultured chondrocytes used to evaluate the effects of CGA on chondrogenesis. Then using an articular cartilage injury model of chick knee we assessed the functional recovery after transplantation of the complexes containing chondrocytes and CGA in an alginate scaffold. Histological analysis, PCR, and western blot were further used to understand the underlying mechanisms. We showed that 60 μM CGA in alginate exhibited notable effects on stimulating chondrogenesis in vitro. Secondly, it was shown that the application of these complexes accelerated the recovery of injury-induced dysfunction by gait analysis when followed for 21 days. Histochemical analysis demonstrated that there was less abnormal vasculature formation, more chondrocyte proliferation and cartilage matrix synthesis in the presence of the complexes containing CGA. We discovered CGA treated transplantation up-regulated the expressions of Sox9 and Col2a1 which were responsible for the stimulation of chondrogenesis. Furthermore, the application of these complexes could suppress the abnormal angiogenesis and fibrosis at the injury site. Lastly, the elevated levels of inflammatory cytokines IL-1β, TNF-α, p-p65, and MMPs expression were decreased in the presence of CGA. This may be caused through adjusting cellular redox homeostasis associated with Nrf2. This study suggests that combining chondrocytes and CGA on an alginate scaffold can improve the recovery of damaged articular cartilage.

Safety, tolerability, and pharmacodynamics of an anti-interleukin-1α/β dual variable domain immunoglobulin in patients with osteoarthritis of the knee: a randomized phase 1 study

OBJECTIVE

To investigate the safety, tolerability, pharmacokinetics, and pharmacodynamics of ABT-981, a human dual variable domain immunoglobulin simultaneously targeting interleukin (IL)-1α and IL-1β, in patients with knee osteoarthritis (OA).

METHOD

This was a randomized, double-blind, placebo-controlled, single-center study of multiple subcutaneous (SC) injections of ABT-981 in patients with mild-to-moderate OA of the knee (NCT01668511). Three cohorts received ABT-981 (0.3, 1, or 3 mg/kg) or placebo every other week for a total of four SC injections, and one cohort received ABT-981 (3 mg/kg) or placebo every 4 weeks for a total of three SC injections. Assessment of safety and tolerability were the primary objectives. A panel of serum and urine biomarkers of inflammation and joint degradation were evaluated.

RESULTS

A total of 36 patients were randomized (ABT-981, n = 28; placebo, n = 8); 31 (86%) completed the study. Adverse event (AE) rates were comparable between ABT-981 and placebo (54% vs 63%). The most common AE reported with ABT-981 vs placebo was injection site erythema (14% vs 0%). ABT-981 significantly reduced absolute neutrophil count and serum concentrations of IL-1α/IL-1β, high-sensitivity C-reactive protein, and matrix metalloproteinase (MMP)-derived type 1 collagen. Serum concentrations of MMP-derived type 3 collagen and MMP-degraded C-reactive protein demonstrated decreasing trends with ABT-981. Antidrug antibodies were found in 37% of patients but were not associated with the incidence or severity of AEs.

CONCLUSION

ABT-981 was generally well tolerated in patients with knee OA and engaged relevant tissue targets, eliciting an anti-inflammatory response. Consequently, ABT-981 may provide clinical benefit to patients with inflammation-driven OA.

IL37 dampens the IL1β-induced catabolic status of human OA chondrocytes

Objective

A crucial feature of OA is cartilage degradation. This process is mediated by pro-inflammatory cytokines, among other factors, via induction of matrix-degrading enzymes. Interleukin 37 (IL37) is an anti-inflammatory cytokine and is efficient in blocking the production of pro-inflammatory cytokines during innate immune responses. We hypothesize that IL37 is therapeutic in treating the inflammatory cytokine cascade in human OA chondrocytes and can act as a counter-regulatory cytokine to reduce cartilage degradation in OA.

Methods

Human OA cartilage was obtained from patients undergoing total knee or hip arthroplasty. Immunohistochemistry was applied to study IL37 protein expression in cartilage biopsies from OA patients. Induction of IL37 expression by IL1β, OA synovium-conditioned medium and TNFα was investigated in human OA chondrocytes. Adenoviral overexpression of IL37 followed by IL1β stimulation was performed to investigate the anti-inflammatory potential of IL37.

Results

IL37 expression was detected in cartilage biopsies of OA patients and induced by IL1β. After IL1β stimulation, increased IL1β, IL6 and IL8 expression was observed in OA chondrocytes. Elevated IL37 levels diminished the IL1β-induced IL1β , IL6 and IL8 gene levels and IL1β and IL8 protein levels. In addition to the reduction in pro-inflammatory cytokine expression, IL37 reduced MMP1 , MMP3 , MMP13 and disintegrin and metalloproteinase with thrombospondin motifs 5 gene levels and MMP3 and MMP13 protein levels.

Conclusion

IL37 is induced by IL1β, and IL37 itself reduced IL1β, IL6 and IL8 production, indicating that IL37 is able to induce a counter-regulatory anti-inflammatory feedback loop in chondrocytes. In addition, IL37 dampens catabolic enzyme expression. This supports IL37 as a potential therapeutic target in OA.

Revisiting the Role of Interleukin-1 Pathway in Osteoarthritis: Interleukin-1α and -1β, and NLRP3 Inflammasome Are Not Involved in the Pathological Features of the Murine Menisectomy Model of Osteoarthritis

Background: Innate immune response components such as toll-like receptors (TLRs) and NLRP3-inflammasome act in concert to increase IL-1α/β secretion by synovial macrophages. Previous results suggest that IL-1α/β could be an important mediator involved in the pathogenesis of osteoarthritis (OA). Objectives: The aim of our study was to evaluate the role of NLRP3, IL-1β, and IL-1α in the menisectomy (MNX) model of murine OA. Methods: Murine chondrocytes (CHs) and bone marrow-derived machrophages (BMDM) were stimulated with hydroxyapatite (HA) crystals, a form of calcium-containing crystal found in human OA, and IL-1β and IL-6 secretion assayed by ELISA.Conversely, the ability of IL-1β and IL-6 to induce CHs calcification was assessed in vitro by Alizarin red staining. Knees from 8 to 10 weeks old C57Bl/6J wild-type (WT) (n = 7), NLRP3^-/- (n = 9), IL-1α^-/- (n = 5), and IL-1β^-/- (n = 5) mice were menisectomized, using the sham-operated contralateral knee as control. 8 weeks later, knee cartilage degradation and synovial inflammation were evaluated by histology. In addition, apoptotic chondrocytes, metalloproteases activity, and collagen-type 2 expression were evaluated in all mice. Joint calcification and subchondral bone parameters were quantified by CT-scan in WT and IL-1β^-/- menisectomized knees. Results:In vitro, HA crystals induced significant increased IL-6 secretion by CHs, while IL-1β remained undetectable.Conversely, both IL-6 and IL-1β were able to increase chondrocytes mineralization. In vivo, operated knees exhibited OA features compared to sham-operated knees as evidenced by increased cartilage degradation and synovial inflammation. In menisectomized KO mice, severity and extent of cartilage lesions were similar (IL-1α^-/- mice) or exacerbated (IL-1β^-/- and NLRP3^-/- mice) compared to that of menisectomized WT mice. Metalloproteases activity, collagen-type 2 expression, chondrocytes apoptosis, and synovial inflammation were similar between KO and WT mice menisectomized knees. Moreover, the extent of joint calcification in osteoarthritic knees was comparable between IL-1β^-/- and WT mice. Conclusions: MNX knees recapitulated features of OA, i.e, cartilage destruction, synovial inflammation, cell death, and joint calcification. Deficiency of IL-1α did not impact on the severity of these features, whereas deficiency of IL-1β or of NLRP3 led to increased cartilage erosion. Our results suggest that IL-1α and IL-1β are not key mediators in this murine OA model and may explain the inefficiency of IL-1 targeted therapies in OA.

Interleukin-1 is not involved in synovial inflammation and cartilage destruction in collagenase-induced osteoarthritis

OBJECTIVE

Interleukin-1 (IL-1) is an alleged important cytokine in osteoarthritis (OA), although the exact contribution of IL-1 to joint destruction remains unclear. Here we investigated the involvement of IL-1α and IL-1β in joint pathology during collagenase-induced OA (CiOA).

METHODS

CiOA was induced in wild type (WT) and IL-1αβ^-/- mice. Additionally, IL-1 signaling was inhibited in WT mice with CiOA using osmotic pumps containing IL-1RA. Joint pathology was assessed using histology. Activity of cartilage-degrading enzymes was determined using antibodies against aggrecan neo-epitopes VDIPEN and NITEGE. Synovial gene expression was analyzed using quantitative real-time polymerase chain reaction (qRT-PCR). Serum protein levels were measured with Luminex or enzyme-linked immunosorbent assay (ELISA).

RESULTS

Synovial IL-1β expression was strongly elevated 7 days after induction of CiOA in WT mice but decreased afterwards, whereas S100A8/A9, previously described to aggravate OA, remained elevated for 21 days. Remarkably, synovial inflammation was comparable between WT and IL-1αβ^-/- mice on day 7 of CiOA. In line, synovial mRNA expression of genes involved in IL-1 signaling and inflammatory mediators was comparable between WT and IL-1αβ^-/- mice, and serum levels for Keratinocyte Chemoattractant (KC)/IL-6/S100A8/S100A9/IL-10 were equal. Synovial matrix metalloproteinase (MMP)/aggrecanase expression and activity in cartilage was not different in WT and IL-1αβ^-/- mice on day 7 of CiOA. Cartilage destruction on day 42 was not different between WT and IL-1αβ^-/- mice, which was supported by our finding that IL-1RA treatment in WT mice with CiOA did not alter joint destruction.

CONCLUSIONS

IL-1α and IL-1β are not involved in synovial inflammation and cartilage destruction during CiOA, implicating that other mediators are responsible for the joint damage.

Non-invasive mouse models of post-traumatic osteoarthritis

Animal models of osteoarthritis (OA) are essential tools for investigating the development of the disease on a more rapid timeline than human OA. Mice are particularly useful due to the plethora of genetically modified or inbred mouse strains available. The majority of available mouse models of OA use a joint injury or other acute insult to initiate joint degeneration, representing post-traumatic osteoarthritis (PTOA). However, no consensus exists on which injury methods are most translatable to human OA. Currently, surgical injury methods are most commonly used for studies of OA in mice; however, these methods may have confounding effects due to the surgical/invasive injury procedure itself, rather than the targeted joint injury. Non-invasive injury methods avoid this complication by mechanically inducing a joint injury externally, without breaking the skin or disrupting the joint. In this regard, non-invasive injury models may be crucial for investigating early adaptive processes initiated at the time of injury, and may be more representative of human OA in which injury is induced mechanically. A small number of non-invasive mouse models of PTOA have been described within the last few years, including intra-articular fracture of tibial subchondral bone, cyclic tibial compression loading of articular cartilage, and anterior cruciate ligament (ACL) rupture via tibial compression overload. This review describes the methods used to induce joint injury in each of these non-invasive models, and presents the findings of studies utilizing these models. Altogether, these non-invasive mouse models represent a unique and important spectrum of animal models for studying different aspects of PTOA.

Asporin and osteoarthritis

OBJECTIVE

To provide an overview of the literature describing the role of asporin, a small leucine-rich proteoglycan (SLRP), in osteoarthritis (OA).

METHOD

A literature search was performed and reviewed using the narrative approach.

RESULTS

As a class I SLRP member, asporin, is distinct from other SLRPs. Accumulating evidence demonstrates the involvement of asporin in OA pathogenesis. Many human studies have been conducted to explore the association between the D-repeat polymorphisms and OA susceptibility, but these yield inconsistent results. Possible mechanisms for the involvement of asporin in OA pathology include its influence on TGF-β (transforming growth factor-β) signaling pathways and collagen mineralization. To date, no studies were found to use an asporin-deficient animal model that would help to understand disease mechanisms. Many issues must be addressed to clarify the link between asporin and OA to provide a novel therapeutic strategy for OA, perhaps through controlling and modifying the TGF-β-ECM system.

CONCLUSIONS

Studies examined demonstrate the involvement of asporin in OA pathogenesis, and possible mechanisms by which asporin may be involved in this process have been proposed. However, large-scale interracial studies should be conducted to investigate the association between asporin and OA, and further investigations are needed to obtain a better understanding of the disease mechanism, develop novel therapeutic strategies, and explore new approaches for diagnosis of OA.

Annexin A6 interacts with p65 and stimulates NF-κB activity and catabolic events in articular chondrocytes

OBJECTIVE

ANXA6, the gene for annexin A6, is highly expressed in osteoarthritic (OA) articular chondrocytes but not in healthy articular chondrocytes. This study was undertaken to determine whether annexin A6 affects catabolic events in these cells.

METHODS

Articular chondrocytes were isolated from Anxa6-knockout mice, wild-type (WT) mice, and human articular cartilage in which ANXA6 was overexpressed. Cells were treated with interleukin-1β (IL-1β) or tumor necrosis factor α (TNFα), and expression of catabolic genes and activation of NF-κB were determined by real-time polymerase chain reaction and luciferase reporter assay. Anxa6(-/-) and WT mouse knee joints were injected with IL-1β or the medial collateral ligament was transected and partial resection of the medial meniscus was performed to determine the role of Anxa6 in IL-1β-mediated cartilage destruction and OA progression. The mechanism by which Anxa6 stimulates NF-κB activity was determined by coimmunoprecipitation and immunoblot analysis of nuclear and cytoplasmic fractions of IL-1β-treated Anxa6(-/-) and WT mouse chondrocytes for p65 and Anxa6.

RESULTS

Loss of Anxa6 resulted in decreased NF-κB activation and catabolic marker messenger RNA (mRNA) levels in IL-1β- or TNFα-treated articular chondrocytes, whereas overexpression of ANXA6 resulted in increased NF-κB activity and catabolic marker mRNA levels. Annexin A6 interacted with p65, and loss of Anxa6 caused decreased nuclear translocation and retention of the active p50/p65 NF-κB complex. Cartilage destruction in Anxa6(-/-) mouse knee joints after IL-1β injection or partial medial meniscectomy was reduced as compared to that in WT mouse joints.

CONCLUSION

Our data define a role of annexin A6 in the modulation of NF-κB activity and in the stimulation of catabolic events in articular chondrocytes.

Inducible chondrocyte-specific overexpression of BMP2 in young mice results in severe aggravation of osteophyte formation in experimental OA without altering cartilage damage

OBJECTIVES

In osteoarthritis (OA) chondrocytes surrounding lesions express elevated bone morphogenetic protein 2 (BMP2) levels. To investigate the functional consequence of chondrocyte-specific BMP2 expression, we made a collagen type II dependent, doxycycline (dox)-inducible BMP2 transgenic mouse and studied the effect of elevated BMP2 expression on healthy joints and joints with experimental OA.

METHODS

We cloned a lentivirus with BMP2 controlled by a tet-responsive element and transfected embryos of mice containing a collagen type II driven cre-recombinase and floxed rtTA to gain a mouse expressing BMP2 solely in chondrocytes and only upon dox exposure (Col2-rtTA-TRE-BMP2). Mice were treated with dox to induce elevated BMP2 expression. In addition, experimental OA was induced (destabilisation of the medial meniscus model) with or without dox supplementation and knee joints were isolated for histology.

RESULTS

Dox treatment resulted in chondrocyte-specific upregulation of BMP2 and severely aggravated formation of osteophytes in experimental OA but not in control mice. Moreover, elevated BMP2 levels did not result in alterations in articular cartilage of young healthy mice, although BMP2-exposure did increase VDIPEN expression in the articular cartilage. Strikingly, despite apparent changes in knee joint morphology due to formation of large osteophytes there were no detectible differences in articular cartilage: none with regard to structural damage nor in Safranin O staining intensity when comparing destabilisation of the medial meniscus with or without dox exposure.

CONCLUSIONS

Our data show that chondrocyte-specific elevation of BMP2 levels does not alter the course of cartilage damage in an OA model in young mice but results in severe aggravation of osteophyte formation.

Sphingosine 1-phosphate counteracts the effects of interleukin-1β in human chondrocytes

Objective

The lipid mediator sphingosine 1-phosphate (S1P) is found in the synovial fluid of osteoarthritis (OA) patients. S1P protects bovine cartilage by counteracting the effects of interleukin-1β (IL-1β). This study was undertaken to examine the interaction of S1P and IL-1β in human OA chondrocytes.

Methods

Human cartilage was obtained from patients undergoing total knee joint replacement. Chondrocytes were cultured in monolayer and treated with IL-1β and S1P. Expression of S1P receptor subtypes and genes involved in cartilage degradation was evaluated using real-time polymerase chain reaction, immunohistochemistry, and Western blotting. S1P signaling was evaluated using inhibitors of S1P receptors and small interfering RNA (siRNA) knockdown of the S1P₂ receptor. Phosphorylation of MAP kinases and NF-κB in response to IL-1β and S1P was detected by Western blotting.

Results

S1P₂ was identified as the most prevalent S1P receptor subtype in human OA cartilage and chondrocytes in vitro. S1P reduced expression of inducible nitric oxide synthase (iNOS) in IL-1β–treated chondrocytes. Reduction of ADAMTS-4 and matrix metalloproteinase 13 expression by S1P correlated with S1P₂ expression. Pharmacologic inhibition of the S1P₂ receptor, but not the S1P₁ and S1P₃ receptors, abrogated the inhibition of iNOS expression. Similar results were observed using siRNA knockdown. S1P signaling inhibited IL-1β–induced phosphorylation of p38 MAPK.

Conclusion

In human chondrocytes, S1P reduces the induction of catabolic genes in the presence of IL-1β. Activation of the S1P₂ receptor counteracts the detrimental phosphorylation of p38 MAPK by IL-1β.

Prolactin promotes cartilage survival and attenuates inflammation in inflammatory arthritis

Chondrocytes are the only cells in cartilage, and their death by apoptosis contributes to cartilage loss in inflammatory joint diseases, such as rheumatoid arthritis (RA). A putative therapeutic intervention for RA is the inhibition of apoptosis-mediated cartilage degradation. The hormone prolactin (PRL) frequently increases in the circulation of patients with RA, but the role of hyperprolactinemia in disease activity is unclear. Here, we demonstrate that PRL inhibits the apoptosis of cultured chondrocytes in response to a mixture of proinflammatory cytokines (TNF-α, IL-1β, and IFN-γ) by preventing the induction of p53 and decreasing the BAX/BCL-2 ratio through a NO-independent, JAK2/STAT3-dependent pathway. Local treatment with PRL or increasing PRL circulating levels also prevented chondrocyte apoptosis evoked by injecting cytokines into the knee joints of rats, whereas the proapoptotic effect of cytokines was enhanced in PRL receptor-null (Prlr(-/-)) mice. Moreover, eliciting hyperprolactinemia in rats before or after inducing the adjuvant model of inflammatory arthritis reduced chondrocyte apoptosis, proinflammatory cytokine expression, pannus formation, bone erosion, joint swelling, and pain. These results reveal the protective effect of PRL against inflammation-induced chondrocyte apoptosis and the therapeutic potential of hyperprolactinemia to reduce permanent joint damage and inflammation in RA.

Scientific evidence and rationale for the development of curcumin and resveratrol as nutraceutricals for joint health

Interleukin 1β (IL-1β) and tumor necrosis factor α (TNF-α) are key cytokines that drive the production of inflammatory mediators and matrix-degrading enzymes in osteoarthritis (OA). These proinflammatory cytokines bind to their respective cell surface receptors and activate inflammatory signaling pathways culminating with the activation of nuclear factor κB (NF-κB), a transcription factor that can be triggered by a host of stress-related stimuli including, excessive mechanical stress and ECM degradation products. Once activated, NF-κB regulates the expression of many cytokines, chemokines, adhesion molecules, inflammatory mediators, and several matrix-degrading enzymes. Therefore, proinflammatory cytokines, their cell surface receptors, NF-κB and downstream signaling pathways are therapeutic targets in OA. This paper critically reviews the recent literature and outlines the potential prophylactic properties of plant-derived phytochemicals such as curcumin and resveratrol for targeting NF-κB signaling and inflammation in OA to determine whether these phytochemicals can be used as functional foods.

A stable isotope method for the simultaneous measurement of matrix synthesis and cell proliferation in articular cartilage in vivo

OBJECTIVE

Measurements of cell proliferation and matrix synthesis in cartilage explants have identified regulatory factors [e.g., interleukin-1 (IL-1)] that contribute to osteoarthritis and anabolic mediators [e.g., bone morphogenic protein-7 (BMP-7)] that may have therapeutic potential. The objective of this study was to develop a robust method for measuring cell proliferation and glycosaminoglycan synthesis in articular cartilage that could be applied in vivo.

METHODS

A stable isotope-mass spectrometry approach was validated by measuring the metabolic effects of IL-1 and BMP-7 in cultures of mature and immature bovine cartilage explants. The method was also applied in vivo to quantify physiologic turnover rates of matrix and cells in the articular cartilage of normal rats. Heavy water was administered to explants in the culture medium and to rats via drinking water, and cartilage was analyzed for labeling of chondroitin sulfate (CS), hyaluronic acid (HA) and DNA.

RESULTS

As expected, IL-1 inhibited the synthesis of DNA and CS in cartilage explants. However, IL-1 inhibited HA synthesis only in immature cartilage. Furthermore, BMP-7 was generally stimulatory, but immature cartilage was significantly more responsive than mature cartilage, particularly in terms of HA and DNA synthesis. In vivo, labeling of CS and DNA in normal rats for up to a year indicated half-lives of 22 and 862 days, respectively, in the joint.

CONCLUSIONS

We describe a method by which deuterium from heavy water is traced into multiple metabolites from a single cartilage specimen to profile its metabolic activity. This method was demonstrated in tissue culture and rodents but may have significant clinical applications.

Intra-articular injection of tumor necrosis factor-alpha in the rat: an acute and reversible in vivo model of cartilage proteoglycan degradation

OBJECTIVE

To develop an in vivo model for rapid assessment of cartilage aggrecan degradation and its pharmacological modulation.

DESIGN

Tumor necrosis factor-alpha (TNFalpha) was injected intra-articularly (IA) in rat knees and aggrecan degradation was monitored at various times following challenge. Articular cartilage was assessed for aggrecan content by Safranin O staining and by immunohistochemistry for the NITEGE epitope. Synovial fluids (SFs) were analyzed for sulfated glycosaminoglycans (GAGs) using the dimethylmethylene blue dye assay and for aggrecan fragments generated by specific cleavage at aggrecanase-sensitive sites by Western blot analysis with neoepitope antibodies. Indomethacin, dexamethasone, and an aggrecanase inhibitor were evaluated for their ability to modulate TNFalpha-induced proteoglycan degradation in vivo.

RESULTS

(1) IA injection of TNFalpha in the knee joint of rats resulted in transient aggrecan degradation and release of aggrecanase-generated aggrecan fragments from the articular cartilage into the SF; (2) a correlation was observed between histologically assessed depletion of aggrecan from the articular cartilage and the appearance of specific neoepitopes in the SF; (3) aggrecan degradation was inhibited by an aggrecanase inhibitor as well as by dexamethasone, but not by the non-steroidal anti-inflammatory drug (NSAID), indomethacin.

CONCLUSION

TNFalpha injection in the knee joints of rats results in rapid transient cartilage proteoglycan degradation, mediated by cleavage at the aggrecanase sites. Biomarker read-out of specific neoepitopes in the SF enables the use of this mechanism-based model for rapid evaluation of aggrecanase-mediated aggrecan degradation in vivo.

The contribution of the synovium, synovial derived inflammatory cytokines and neuropeptides to the pathogenesis of osteoarthritis

Osteoarthritis (OA) is one of the most common and disabling chronic joint disorders affecting horses, dogs and humans. Synovial inflammation or synovitis is a frequently observed phenomenon in osteoarthritic joints and contributes to the pathogenesis of OA through formation of various catabolic and pro-inflammatory mediators altering the balance of cartilage matrix degradation and repair. Catabolic mediators produced by the inflamed synovium include pro-inflammatory cytokines, nitric oxide, prostaglandin E(2) and several neuropeptides, which further contribute to the pathogenesis of OA by increasing cartilage degradation. Recent studies suggest that substance P, corticotropin-releasing factor, urocortin and vasoactive intestinal peptide may also be involved in OA development, but the precise role of these neuropeptides in the pathogenesis of OA is not known. Since increased production of matrix metalloproteinases by the synovium is stimulated by pro-inflammatory cytokines, future anti-inflammatory therapies should focus on the synovium as a means of controlling subsequent inflammatory damage.

Elevated extracellular matrix production and degradation upon bone morphogenetic protein-2 (BMP-2) stimulation point toward a role for BMP-2 in cartilage repair and remodeling

Bone morphogenetic protein-2 (BMP-2) has been proposed as a tool for cartilage repair and as a stimulant of chondrogenesis. In healthy cartilage, BMP-2 is hardly present, whereas it is highly expressed during osteoarthritis. To assess its function in cartilage, BMP-2 was overexpressed in healthy murine knee joints and the effects on proteoglycan (PG) synthesis and degradation were evaluated. Moreover, the contribution of BMP in repairing damage induced by interleukin-1 (IL-1) was investigated. Ad-BMP-2 was injected intra-articularly into murine knee joints, which were isolated 3, 7, and 21 days after injection for histology, immunohistochemistry, and autoradiography. In addition, patellar and tibial cartilage was isolated for RNA isolation or measurement of PG synthesis by means of ³⁵SO₄ ^2- incorporation. To investigate the role for BMP-2 in cartilage repair, cartilage damage was induced by intra-articular injection of IL-1. After 2 days, Ad-BMP-2, Ad-BMP-2 + Ad-gremlin, Ad-gremlin, or a control virus was injected. Whole knee joints were isolated for histology at day 4 or patellae were isolated to measure ³⁵SO₄^2- incorporation. BMP-2 stimulated PG synthesis in patellar cartilage on all days and in tibial cartilage on day 21. Aggrecan mRNA expression had increased on all days in patellar cartilage, with the highest increase on day 7. Collagen type II expression showed a similar expression pattern. In tibial cartilage, collagen type II and aggrecan mRNA expression had increased on days 7 and 21. BMP-2 overexpression also induced increased aggrecan degradation in cartilage. VDIPEN staining (indicating matrix metalloproteinase activity) was elevated on day 3 in tibial cartilage and on days 3 and 7 in patellar cartilage, but no longer was by day 21. Increased NITEGE staining (indicating aggrecanase activity) was found on days 7 and 21. In IL-1-damaged patellar cartilage, BMP-2 boosted PG synthesis. Blocking of BMP activity resulted in a decreased PG synthesis compared with IL-1 alone. This decreased PG synthesis was associated with PG depletion in the cartilage. These data show that BMP-2 boosts matrix turnover in intact and IL-damaged cartilage. Moreover, BMP contributes to the intrinsic repair capacity of damaged cartilage. Increased matrix turnover might be functional in replacing matrix molecules in the repair of a damaged cartilage matrix.

TGF beta-induced cartilage repair is maintained but fibrosis is blocked in the presence of Smad7

Cartilage damage in osteoarthritis (OA) is considered an imbalance between catabolic and anabolic factors, favoring the catabolic side. We assessed whether adenoviral overexpression of transforming growth factor-β (TGFβ) enhanced cartilage repair and whether TGFβ-induced fibrosis was blocked by local expression of the intracellular TGFβ inhibitor Smad7. We inflicted cartilage damage by injection of interleukin-1 (IL-1) into murine knee joints. After 2 days, we injected an adenovirus encoding TGFβ. On day 4, we measured proteoglycan (PG) synthesis and content. To examine whether we could block TGFβ-induced fibrosis and stimulate cartilage repair simultaneously, we injected Ad-TGFβ and Ad-Smad7. This was performed both after IL-1-induced damage and in a model of primary OA. In addition to PG in cartilage, synovial fibrosis was measured by determining the synovial width and the number of procollagen I-expressing cells. Adenoviral overexpression of TGFβ restored the IL-1-induced reduction in PG content and increased PG synthesis. TGFβ-induced an elevation in PG content in cartilage of the OA model. TGFβ-induced synovial fibrosis was strongly diminished by simultaneous synovial overexpression of Smad7 in the synovial lining. Of great interest, overexpression of Smad7 did not reduce the repair-stimulating effect of TGFβ on cartilage. Adenoviral overexpression of TGFβ stimulated repair of IL-1- and OA-damaged cartilage. TGFβ-induced synovial fibrosis was blocked by locally inhibiting TGFβ signaling in the synovial lining by simultaneously transfecting it with an adenovirus overexpressing Smad7.

Reduced transforming growth factor-beta signaling in cartilage of old mice: role in impaired repair capacity

Osteoarthritis (OA) is a common joint disease, mainly effecting the elderly population. The cause of OA seems to be an imbalance in catabolic and anabolic factors that develops with age. IL-1 is a catabolic factor known to induce cartilage damage, and transforming growth factor (TGF)-beta is an anabolic factor that can counteract many IL-1-induced effects. In old mice, we observed reduced responsiveness to TGF-beta-induced IL-1 counteraction. We investigated whether expression of TGF-beta and its signaling molecules altered with age. To mimic the TGF-beta deprived conditions in aged mice, we assessed the functional consequence of TGF-beta blocking. We isolated knee joints of mice aged 5 months or 2 years, half of which were exposed to IL-1 by intra-articular injection 24 h prior to knee joint isolation. Immunohistochemistry was performed, staining for TGF-beta1, -2 or -3, TGF-betaRI or -RII, Smad2, -3, -4, -6 and -7 and Smad-2P. The percentage of cells staining positive was determined in tibial cartilage. To mimic the lack of TGF-beta signaling in old mice, young mice were injected with IL-1 and after 2 days Ad-LAP (TGF-beta inhibitor) or a control virus were injected. Proteoglycan (PG) synthesis (³⁵S-sulfate incorporation) and PG content of the cartilage were determined. Our experiments revealed that TGF-beta2 and -3 expression decreased with age, as did the TGF-beta receptors. Although the number of cells positive for the Smad proteins was not altered, the number of cells expressing Smad2P strongly dropped in old mice. IL-1 did not alter the expression patterns. We mimicked the lack of TGF-beta signaling in old mice by TGF-beta inhibition with LAP. This resulted in a reduced level of PG synthesis and aggravation of PG depletion. The limited response of old mice to TGF-beta induced-IL-1 counteraction is not due to a diminished level of intracellular signaling molecules or an upregulation of intracellular inhibitors, but is likely due to an intrinsic absence of sufficient TGF-beta receptor expression. Blocking TGF-beta distorted the natural repair response after IL-1 injection. In conclusion, TGF-beta appears to play an important role in repair of cartilage and a lack of TGF-beta responsiveness in old mice might be at the root of OA development.

The role of cytokines in cartilage matrix degeneration in osteoarthritis

Chondrocytes are the single cellular component of hyaline cartilage. Under physiologic conditions, they show steady-state equilibrium between anabolic and catabolic activities that maintains the structural and functional integrity of the cartilage extracellular matrix. Implicit in the loss of cartilage matrix that is associated with osteoarthritis is that there is a disturbance in the regulation of synthetic (anabolic) and resorptive (catabolic) activities of the resident chondrocytes that results in a net loss of cartilage matrix components and deterioration in the structural and functional properties of the cartilage. Multiple mechanisms likely are involved in the disturbance of chondrocyte remodeling activities in OA. They include the development of acquired or age-related alterations in chondrocyte function, the effects of excessive mechanical loading, and the presence of dysregulated cytokine activities. Cytokines are soluble or cell-surface molecules that play an essential role in mediating cell-cell interactions. It is possible to classify the cytokines that regulate cartilage remodeling as catabolic, acting on target cells to increase products that enhance matrix degradation; as anticatabolic, tending to inhibit or antagonize the activity of the catabolic cytokines; and as anabolic, acting on chondrocytes to increase synthetic activity. This review will focus on the role of proinflammatory cytokines and their roles in mediating the increased matrix degradation that characterizes the osteoarthritic cartilage lesion.

Intracellular interleukin-1 receptor antagonist in osteoarthritis chondrocytes

The objective of the current study was to determine whether the balance of interleukin-1 and intracellular interleukin-1 receptor antagonist in chondrocytes in osteoarthritic human joints favors agonist action. Chondrocytes were isolated from cartilage specimens taken at the time of joint arthroplasty. Interleukin-1alpha, interleukin-1beta, and intracellular interleukin-1 receptor antagonist messenger ribonucleic acids were assessed by reverse transcriptase-polymerase chain reaction, and chondrocyte lysates were analyzed by enzyme-linked immunosorbent assay for the respective proteins. Type I intracellular interleukin receptor antagonist transcripts were the only intracellular variant detected in osteoarthritis chondrocytes. In cartilage graded as advanced osteoarthritis both interleukin proteins in chondrocyte lysates decreased, correlating with decreased interleukin-1alpha and beta messenger ribonucleic acids. Interleukin-1 receptor antagonist exceeded interleukin-1alpha in chondrocyte lysates by one order of magnitude except that in moderate osteoarthritis, antagonist was only two- to fourfold in excess. Interleukin-1alpha and interleukin-1beta proteins were correlated closely in individual lysates, with interleukin-1beta exceeding interleukin-1beta by one order of magnitude. In moderately degenerated cartilage, intracellular antagonist may not be sufficiently abundant to block postulated intracellular functions of precursor interleukin-1alpha. Furthermore, if stored interleukin-1alpha, interleukin-1beta, and interleukin receptor antagonist are released from chondrocytes, the localized antagonist would be insufficient to prevent signaling through cell surface receptors. Chondrocyte-derived interleukin-1alpha and interleukin-1beta may locally overwhelm inhibition by interleukin receptor antagonist to promote the early degenerative changes in osteoarthritis.

Phenotypic characterization of inflammatory cells from osteoarthritic synovium and synovial fluids

Osteoarthritis (OA) is considered a degenerative joint disorder caused by mechanical wear to the articular surface. However, while joint injury, obesity, and mutations in collagen increase the risk of developing OA, evidence implicates inflammatory mechanisms in disease progression and chronicity. To address this question we used FACS analysis, immunohistochemistry, and in vitro cell culture to evaluate inflammatory mechanisms in synovial fluids and joint tissues obtained after arthrocentesis or knee replacement surgery. Immunohistochemistry revealed a significant T cell infiltrate in six of nine tissue specimens. T cells were present throughout the synovial membrane and were particularly localized around vasculature and in large cellular aggregates. Cells within the aggregates expressed markers associated with immune activation and antigen presentation. T cells from OA synovial fluids expressed an activated phenotype and synthesized interferon-gamma following in vitro stimulation. These data support the hypothesis that inflammatory cells play a significant role in OA disease progression and chronicity.

Phenotypic differences in murine chondrocyte cell lines derived from mature articular cartilage

OBJECTIVE

To obtain well characterized immortalized murine chondrocyte cell lines. The cell lines were obtained from mature articular chondrocytes, instead of embryonal cells which are used in most other studies.

METHODS

Pieces of articular cartilage were cut from murine patellae and femoral heads. Chondrocytes were isolated by digestion with collagenase. These cells were cultured in monolayer and immortalized by transfection of the SV40 large T antigen gene. To preserve the differentiated phenotype, the resulting clones were cultured in three-dimensional carriers, alginate beads. The phenotypes of the cells were characterized using the following parameters: Cell morphology (light microscopy), messenger RNA (RT-PCR) and protein (immunohistochemistry) levels of extracellular matrix molecules. Moreover, responsiveness to interleukin-1(IL-1) was determined by measuring production of proteoglycans ((35)S-sulfate incorporation) and of nitric oxide (Griess reaction).

RESULTS

Sixteen clones were obtained, ten (P1 to P10) derived from patellar cartilage, and six (H1 to H6) from femoral head cartilage. In seven cell lines (P2, P5, H1, H3, H4, H5, H6) high production of type II collagen corresponded with high levels of mRNA of type II collagen (and prevalence of the IIB type) and with high IL-1-induced suppression of proteoglycan synthesis. Like intact murine articular cartilage, all cell lines produced type I and type X collagens, but mRNA levels of both types of collagen were never higher in the cell lines as compared with intact cartilage.

CONCLUSION

Our results demonstrate that it is possible to immortalize mature murine articular chondrocytes. Each of the obtained chondrocyte cell lines appeared to have a stable phenotype. Both relatively differentiated and relatively dedifferentiated chondrocyte cell lines could be identified.

Effects of anti-arthritic drugs on proteoglycan synthesis by equine cartilage

The concentration-effect relationships of phenylbutazone, indomethacin, betamethasone, pentosan polysulphate (PPS) and polysulphated glycosaminoglycan (PSGAG), on proteoglycan synthesis by equine cultured chondrocytes grown in monolayers, and articular cartilage explants were measured. The effect of PSGAG on interleukin-1beta induced suppression of proteogycan synthesis was also investigated. Proteoglycan synthesis was measured by scintillation assay of radiolabelled sulphate (35SO4) incorporation. Polysulphated glycosaminoglycan and PPS stimulated proteoglycan synthesis in chondrocyte monolayers in a concentration-related manner with maximal effects being achieved at a concentration of 10 microg/mL. Polysulphated glycosaminoglycan reversed the concentration-related suppression of proteoglycan synthesis induced by interleukin-1beta. Neither PSGAG nor PPS exerted significant effects on radiolabel incorporation in cartilage explants. Betamethasone suppressed proteoglycan synthesis by both chondrocytes and explants at high concentrations (0.1-100 microg/mL), but the effect was not concentration-related. At low concentrations (0.001-0.05 microg/mL) betamethasone neither increased nor decreased proteoglycan synthesis. Phenylbutazone and indomethacin increased radiolabel incorporation in chondrocyte cultures but not in cartilage explants at low (0.1, 1 and 10 microg/mL), but not at high (20 and 100 microg/mL) concentrations. These findings may be relevant to the clinical use of these drugs in the treatment of equine disease.

Effect of interleukin 17 on proteoglycan degradation in murine knee joints

OBJECTIVE

To evaluate the effect of murine interleukin 17 (IL17) on cartilage catabolism and joint inflammation by direct intra-articular injection of the cytokine into murine knee joints.

METHODS

Knees of normal C57 Bl mice were injected once or repeatedly with recombinant IL17 or IL1beta. Inflammation was estimated by technetium-99m pertechnetate ((99)Tc) uptake and histological scoring of tissue sections. Proteoglycan depletion was evaluated by histological scoring of safranin O stained sections. Effects on proteoglycan synthesis were studied by (35)SO(4) incorporation.

RESULTS

A single intra-articular injection of IL17 (10 ng/knee) produced effects very similar to those of IL1beta (10 ng/knee). No inflammation was detected at six or 24 hours by (99)Tc uptake. However, safranin O staining showed depletion of proteoglycan at 48 hours. Repeated injections of IL17 induced joint inflammation and cartilage proteoglycan depletion as shown by histological scoring. Unlike IL1beta, proteoglycan depletion induced by IL17 seemed to be the result of increased degradation only, as no suppression of (35)SO(4) incorporation was seen.

CONCLUSION

These findings confirm, in vivo, the catabolic effects of IL17 on cartilage. IL17 is thus the first T cell cytokine showing a direct catabolic effect on cartilage in addition to stimulatory effects on macrophages and synoviocytes, making it a potentially important cytokine in the pathogenesis of arthritis.

The role of cytokines as inflammatory mediators in osteoarthritis: lessons from animal models

Studies in animal models of osteoarthritis (OA) have been used extensively to gain insight into the pathogenesis of OA, but early studies largely ignored inflammation except as a secondary phenomenon. Synovitis has often been noted as a feature in experimental OA, and more recent work has established a central role for inflammatory cytokines as biochemical signals which stimulate chondrocytes to release cartilage-degrading proteinases. Thus, proteinase inhibitors, cytokine antagonists and receptor blocking antibodies, and growth/differentiation factors have been considered as potential therapeutic agents and targets for gene therapy. Although there is some disagreement, it is generally accepted that IL-1 is the pivotal cytokine at early and late stages, while TNF-alpha is involved primarily in the onset of arthritis. Other cytokines released during the inflammatory process in the OA joint may be regulatory (IL-6, IL-8) or inhibitory (IL-4, IL-10, IL-13, IFN-gamma). Furthermore, studies in animal models have illustrated the potentially beneficial effects of anticytokine therapy with monoclonal antibodies or receptor antagonists, although local rather than systemic delivery would be necessary for the largely localized OA in humans. Transgenic or knockout mice have also provided insights into general mechanisms of cytokine-induced cartilage degradation but have not directly addressed OA pathogenesis. Similarly, animals with spontaneous or transgenic modifications in cartilage matrix components, growth/differentiation factors, or developmentally regulated transcription factors have provided information about potential gene defects that predispose to OA without addressing the role of inflammatory mediators in cartilage destruction. Although the multiple etiologies of human OA indicate that it is more complex than any animal model, the use of appropriate, well-defined animal models will establish the feasibility of novel forms of therapy.

Oncostatin M induces leukocyte infiltration and cartilage proteoglycan degradation in vivo in goat joints

OBJECTIVE

To evaluate the effect of intraarticular injections of recombinant human oncostatin M (rHuOSM) in the goat joint.

METHODS

One milliliter of endotoxin-free normal saline (vehicle) containing either 40 ng, 200 ng, or 1,000 ng of rHuOSM was injected into the right radiocarpal joints (RCJs) of 12 male angora goats, while the left RCJs were injected with an equivalent volume of vehicle alone. In subsequent studies, the right and left RCJs of 8 male angora goats were injected with 200 ng of rHuOSM, and 1 hour later, the right RCJs were injected with either 5 microg of recombinant murine leukemia inhibitory factor binding protein (rMuLBP) or 1 mg of recombinant human interleukin-1 receptor antagonist (rHuIL-1Ra) in 1 ml of vehicle, while the left RCJs received 1 ml of vehicle alone. Goat joints were examined for clinical features of inflammation, and synovial fluid (SF) was aspirated on day 0 (before injection) and at days 2 and 6 postinjection.

RESULTS

Injections of rHuOSM stimulated dose-dependent increases in the carpal:metacarpal ratio, SF volume, and SF leukocyte numbers, and stimulated dose-dependent decreases in the cartilage proteoglycan (PG) content ex vivo and PG synthesis. No significant changes were observed in the control joints that received saline alone, or between RCJs that were injected with 200 ng rHuOSM followed by 5 microg rMuLBP and RCJs that were injected with 200 ng of rHuOSM alone, except in respect to synovial fluid keratan sulfate concentrations, where a modest statistically significant reduction was observed in the joints injected with the combination of rHuOSM and rMuLPB. In contrast, RCJs injected with 200 ng rHuOSM followed by 1 mg of rHuIL-1Ra had significantly lower SF volumes (P<0.0001) and a significantly higher rate of ex vivo PG synthesis (P<0.0001).

CONCLUSION

These results indicate that rHuOSM stimulates inflammation and modulates cartilage PG metabolism in vivo. Some of the effects of rHuOSM in vivo appear to be due, in part, to elaboration of IL-1. Even at very high doses, however, the rHuIL-1Ra did not attenuate OSM-mediated cartilage PG resorption. Thus, OSM has the potential to contribute to synovitis in vivo and can stimulate cartilage PG resorption in vivo, independent of IL-1.

Cartilage protection by nitric oxide synthase inhibitors after intraarticular injection of interleukin-1beta in rats

OBJECTIVE

To evaluate the effect of nitric oxide synthase (NOS) inhibitors on proteoglycan synthesis following intraarticular administration of interleukin-1beta (IL-1beta) in rats.

METHODS

Recombinant human IL-1beta and NOS inhibitors with different selectivity for inducible NOS (N-monomethyl-L-arginine [L-NMA], N-iminoethyl-L-ornithine [L-NIO], and S-methylisothiourea [SMT]) were simultaneously administered in rats by a single intraarticular injection in each knee. L-NMA was also infused for 72 hours using an Alzet mini osmotic pump implanted into the peritoneal cavity 24 hours before IL-1beta challenge. NO production was determined as nitrate and nitrite, either in synovial fluid or ex vivo in supernatants of synovium and patellae. Proteoglycan synthesis was measured by ex vivo incorporation of 35SO4(2-) into patellar cartilage.

RESULTS

IL-1beta induced a time-dependent increase in NO production in synovial fluid. Synovium and patellae released large amounts of nitrate and nitrite under ex vivo conditions, indicating that both tissues are effective sources of NO within the joint. This production of NO was accompanied by a delayed inhibition of proteoglycan synthesis. The intraarticular administration of L-NMA and L-NIO reduced NO release in synovial fluid and resulted in a partial recovery of proteoglycan synthesis. Under our experimental conditions, SMT failed to reduce NO synthesis and to restore proteoglycan synthesis. The protection of cartilage was improved by the systemic and sustained delivery of L-NMA. However, the complete inhibition of NO production in synovial fluid was not sufficient to fully restore cartilage anabolism.

CONCLUSION

Our findings show that in rats: 1) NO may be an early mediator of the effect of IL-1beta on cartilage, 2) NO inhibition may have therapeutic relevance, although it is not sufficient to fully reverse the deleterious effects of IL-1beta, 3) among NOS inhibitors tested, only amino acid derivatives are effective, 4) protection can be achieved by local administration of NOS inhibitors, and 5) systemic and sustained delivery of the NOS inhibitor with the highest efficacy after intraarticular injection provides the most benefit.

Niacinamide therapy for osteoarthritis--does it inhibit nitric oxide synthase induction by interleukin 1 in chondrocytes?

Fifty years ago, Kaufman reported that high-dose niacinamide was beneficial in osteoarthritis (OA) and rheumatoid arthritis. A recent double-blind study confirms the efficacy of niacinamide in OA. It may be feasible to interpret this finding in the context of evidence that synovium-generated interleukin-1 (IL-1), by inducing nitric oxide (NO) synthase and thereby inhibiting chondrocyte synthesis of aggrecan and type II collagen, is crucial to the pathogenesis of OA. Niacinamide and other inhibitors of ADP-ribosylation have been shown to suppress cytokine-mediated induction of NO synthase in a number of types of cells; it is therefore reasonable to speculate that niacinamide will have a comparable effect in IL-1-exposed chondrocytes, blunting the anti-anabolic impact of IL-1. The chondroprotective antibiotic doxycycline may have a similar mechanism of action. Other nutrients reported to be useful in OA may likewise intervene in the activity or synthesis of IL-1. Supplemental glucosamine can be expected to stimulate synovial synthesis of hyaluronic acid; hyaluronic acid suppresses the anti-catabolic effect of IL-1 in chondrocyte cell cultures, and has documented therapeutic efficacy when injected intra-articularly. S-adenosylmethionine (SAM), another proven therapy for OA, upregulates the proteoglycan synthesis of chondrocytes, perhaps because it functions physiologically as a signal of sulfur availability. IL-1 is likely to decrease SAM levels in chondrocytes; supplemental SAM may compensate for this deficit. Adequate selenium nutrition may down-regulate cytokine signaling, and ample intakes of fish oil can be expected to decrease synovial IL-1 production; these nutrients should receive further evaluation in OA. These considerations suggest that non-toxic nutritional regimens, by intervening at multiple points in the signal transduction pathways that promote the synthesis and mediate the activity of IL-1, may provide a substantially superior alternative to NSAIDs (merely palliative and often dangerously toxic) in the treatment and perhaps prevention of OA.

Modulation of IL-1 effects on cartilage by NO synthase inhibitors: pharmacological studies in rats

Objective To compare the ability of L-arginine (L-arg) analog nitric oxide synthase (NOS) inhibitors and isothioureas to restore the interleukin-1 (IL-1) induced inhibition of proteoglycan (PG) synthesis in rat.Methods Chondrocytes beads and patellae were challenged with IL-1betain vitro and monitored for NO production and proteoglycan synthesis. Rats injected with IL-1beta in knee joints were monitored for NO(2)( - )+NO(3)( - )levels in joint tissues and ex-vivo(35)S sulfate incorporation in patellae. NOS inhibitors were either added to culture medium or injected concomittantly to IL-1beta. Results Ability of NOS inhibitors to reduce NO(2)( - )levels decreased from chondrocytes beads to patellae. Partial restoration of PG synthesis was restricted to L-arg analogs in patellae. After IL-1 injection, NO was produced from patella and synovium. L-arg analogs restored partly PG synthesis when decreasing significantly NO(2)( - )+NO(3)( - )levels in synovial fluid. Isothioureas were ineffective. Conclusions NO accounts importantly for IL-1 induced inhibition of cartilage anabolism in rat. L-arg analog NOS inhibitors are more effective than isothioureas in restoring PG synthesis and have chondroprotective potency when administered locally in diseased joint.

The proinflammatory and chondral activities of leukemia inhibitory factor in goat joints are partially a function of interleukin-1

We wished to determine if the effects of injected recombinant human leukemia inhibitory factor (LIF) are a function of endogenous goat interleukin-1 (IL-1) production and, conversely, if the effects of injected recombinant human IL-1 are a function of endogenous LIF production in goat radiocarpal joints (RCJ). In preliminary experiments, murine LIF binding protein (MuLBP) and recombinant HuIL-1RA were found to independently attenuate the cartilage proteoglycan resorbing activity of goat synovial membrane-conditioned medium (GSMCM), implying activity against goat LIF and goat IL-1, respectively. The present study shows that the proinflammatory and chondral actions of rHuLIF in goat RCJ are partially attenuated by rHuIL-1RA. This implies that a small but important component of the in vivo activity of rHuLIF is a result of IL-1 production in the synovial joint. With the exception of proteoglycan synthesis, the absence of significant effects by MuLBP on the actions of rHuIL-1alpha in goat RCJ suggests that the proinflammatory and chondral effects of IL-1alpha in vivo are probably not mediated by LIF.

Treatment of rheumatoid arthritis with recombinant human interleukin-1 receptor antagonist

OBJECTIVE

To evaluate the efficacy and safety of interleukin-1 receptor antagonist (IL-1Ra) in patients with rheumatoid arthritis (RA).

METHODS

Patients with active and severe RA (disease duration <8 years) were recruited into a 24-week, double-blind, randomized, placebo-controlled, multicenter study. Doses of nonsteroidal antiinflammatory drugs and/or oral corticosteroids (< or =10 mg prednisolone daily) remained constant throughout the study. Any disease-modifying antirheumatic drugs that were being administered were discontinued at least 6 weeks prior to enrollment. Patients were randomized to 1 of 4 treatment groups: placebo or a single, self-administered subcutaneous injection of IL-1Ra at a daily dose of 30 mg, 75 mg, or 150 mg.

RESULTS

A total of 472 patients were recruited. At enrollment, the mean age, sex ratio, disease duration, and percentage of patients with rheumatoid factor and erosions were similar in the 4 treatment groups. The clinical parameters of disease activity were similar in each treatment group and were consistent with active and severe RA. At 24 weeks, of the patients who received 150 mg/day IL-1Ra, 43% met the American College of Rheumatology criteria for response (the primary efficacy measure), 44% met the Paulus criteria, and statistically significant improvements were seen in the number of swollen joints, number of tender joints, investigator's assessment of disease activity, patient's assessment of disease activity, pain score on a visual analog scale, duration of morning stiffness, Health Assessment Questionnaire score, C-reactive protein level, and erythrocyte sedimentation rate. In addition, the rate of radiologic progression in the patients receiving IL-1Ra was significantly less than in the placebo group at 24 weeks, as evidenced by the Larsen score and the erosive joint count. IL-1Ra was well tolerated and no serious adverse events were observed. An injection-site reaction was the most frequently observed adverse event, and this resulted in a 5% rate of withdrawal from the study among those receiving IL-1Ra at 150 mg/day.

CONCLUSION

This study confirmed both the efficacy and the safety of IL-1Ra in a large cohort of patients with active and severe RA. IL-1Ra is the first biologic agent to demonstrate a beneficial effect on the rate of joint erosion.

Basal and induced nitric oxide and cGMP productions are decreased in senescent cultured rat articular chondrocytes

The effects of interleukin-1 (IL-1), tumor necrosis factor-alpha (TNF-alpha), and lipopolysaccharide (LPS) on the productions of nitric oxide (NO) and cGMP by cultured articular chondrocyte (AC) monolayers from 1-, 8- and 18-month old male Wistar rats were studied. It was found that basal NO and cGMP productions decrease with the age of animals. The productions were more than 2-fold greater in cells from 1-month old rats then in cells from older animals. IL-1, TNF-alpha, and LPS stimulated all three types of cells to produce NO and cGMP in a time- and concentration-dependent manner. Although the cells from young animals produced more NO per microg DNA, the older counterparts were more sensitive to these agents since they produced more NO upon stimulation then the corresponding non-stimulated controls. At the concentration of 10(-3) M, the nitric oxide synthase (NOS) inhibitor, Ng-monomethyl-L-arginine (L-NMA), blocked, although incompletely, both the basal and stimulated NO and cGMP productions in cells from the 1 and 8-month old rats and only induced productions in 18-month old counterparts. These results show a decreased capacity of unstimulated- and stimulated-AC from old rats to produce NO and cGMP in culture, which may affect the ageing cells in some yet unknown way.

Complexity of IL-1 beta induced gene expression pattern in human articular chondrocytes

The mRNA fingerprinting technique, differential display reverse transcription polymerase chain (DDRT-PCR), was used to detect changes in the overall pattern of gene expression in human articular knee chondrocytes-induced by interleukin-1 beta (IL-1 beta), the prototypical inducer of catabolic responses in degenerate joint diseases. One hundred different primer combinations generated approximately 10,000 different PCR fragments for IL-1 beta treated, as well as for untreated human chondrocytes, cultivated in alginate beads. This represented 53% of all expressed chondrocyte genes as based on statistical considerations. Side by side comparisons of differential display patterns originating from two different donor tissues yielded 44 reproducibly, differentially-displayed cDNA fragments, which were subcloned and sequenced. Sequence homology searches revealed sequence identities to the human necrosis factor alpha (TNF-alpha) and IL-1 regulated gene TSG-6, fibronectin, osteopontin, calnexin, and the DNA repair enzyme ERCC5. The differential expression was confirmed with Northern and quantitative PCR analyses. The known function of these genes and their known IL-1 responsiveness indicate that the employed model system reflects the pleiotropic effects of IL-1 on the overall gene expression in human articular chondrocytes and identifies genes involved in very different biochemical pathways. Twenty-seven cDNAs lacked sequence homologies to known genes and may represent novel genes.

Interleukin 1 beta and stromelysin (MMP3) activity of synovial fluid as possible markers of osteoarthritis in the temporomandibular joint

PURPOSE

This study investigated the early signs of synovitis and cartilage degradation by means of synovial fluid analysis in temporomandibular joints (TMJs) with internal derangement (closed lock) or osteoarthritis (OA).

PATIENTS AND METHODS

Synovial fluid was obtained from 25 TMJs in 22 patients diagnosed with closed lock and from 15 asymptomatic TMJs of 12 normal controls. IL-1 beta concentrations were measured using enzyme-linked immunosorbent assay (ELISA), and proteinase activity was detected by means of gelatin enzymography.

RESULTS

Nine of the 25 TMJs with closed lock (CL group) exhibited osteolytic changes on the surface of the condyle. TMJs in the normal control group did not show any bony changes. Mean IL-1 beta concentration in the synovial fluid (SF) protein in the CL group was 330.1 +/- 347.7 pg per 100 micrograms protein, which was significantly higher than in the normal control (76.7 +/- 95.3 pg/100 micrograms SF-protein). Synovial fluid from the TMJs with osteolytic changes contained higher levels of IL-1 beta (531.8 +/- 379.6 pg/100 micrograms SF-protein) than those without bony changes (216.7 +/- 280.1 pg/100 micrograms SF-protein). Matrix metalloproteinase (MMP) activity with a molecular weight of 50 kd (stromelysin or MMP3) was detected in a highly augmented form in two synovial fluid samples of seven closed lock patients.

CONCLUSION

The results suggest that IL-1 beta levels in synovial fluid of the TMJ have a positive correlation with OA change. The MMP3 activity detected was greatly increased in patients with cartilage degradation. These findings suggest that both changes may be important markers of early bone deterioration in TMJs that are undetectable by radiograph imaging.

Changes in cartilage proteoglycan aggrecan after intra-articular injection of interleukin-1 in rabbits: studies of synovial fluid and articular cartilage

OBJECTIVE

To determine how acute but transient inflammation affects the cartilage proteoglycan aggrecan and the value of analyses of synovial fluid to study this.

METHODS

For 96 hours after a single intra-articular injection of rabbit knees with human interleukin-1 alpha (IL-1 alpha) or vehicle, articular cartilage and synovial fluid were examined using a putative indicator of aggrecan synthesis (aggrecan chondroitin sulphate epitope 846), immunoreactive keratan sulphate, and total glycosaminoglycan (GAG) content. Aggrecan extractability (with 0.5 M NaCl) followed by 4 M guanidine hydrochloride extraction permitted analyses of cartilage damage, total content and aggrecan heterogeneity. Aggrecan epitopes as well as GAG were assayed in synovial fluid. Changes were related to total joint leucocyte content in synovial fluid.

RESULTS

At 10 ng, IL-1 alpha produced a transient increase in synovial fluid leucocytes at six hours and 24 hours. This accompanied a reduction in content and increased extractability of GAG, which was greatest in the tibial medial compartment of the knee. Further studies of this compartment showed no change in keratan sulphate epitope content, but a transient increase in extractability in 0.5 M NaCl. Epitope 846 content and extractability were unchanged. Total contents and extractability for GAG were inversely correlated in both controls and joints injected with IL-1 alpha. These changes were accompanied by transient increases in GAG, keratan sulphate epitope, and 846 content in synovial fluid.

CONCLUSION

According to the aggrecan component measured, damage to the matrix of articular cartilage was sometimes reflected by a transient increased extractability and a net loss of aggrecan. There was always an increased release of GAG, and keratan sulphate, and 846 epitopes into synovial fluid. These studies show that changes in aggrecan epitopes and GAG in synovial fluid reflect changes in cartilage metabolism induced by acute transient inflammation.

The superficial layer of human articular cartilage is more susceptible to interleukin-1-induced damage than the deeper layers

OBJECTIVE

To compare the responses of chondrocytes from superficial and deep layers of normal human articular cartilage to interleukin-1 (IL-1) and IL-1 receptor antagonist protein (IRAP), and to evaluate the binding sites for IL-1 on these cells.

METHODS

Cartilage and chondrocytes from superficial and deeper layers of human femoral condyles were cultured with and without IL-1 in the presence and absence of IRAP. The effect of these agents on 35S- proteoglycan synthesis and catabolism and production of stromelysin and tissue inhibitor of metalloproteinases 1 (TIMP-1) were measured by biochemical and immunologic assays. Receptor binding was evaluated using 125I-labeled IL-1.

RESULTS

IL-1 induced more severe inhibition of proteoglycan synthesis and a lower ratio of secreted TIMP-l:stromelysin in chondrocytes from superficial cartilage than those from deeper cartilage. IRAP blocked responses to IL-1 more effectively in chondrocytes from deep cartilage than those from superficial cartilage. Chondrocytes from the articular surface showed approximately twice the number of high-affinity b!nding sites for IL-1 as did cells from deep cartilage.

CONCLUSION

Chondrocytes from the surface of articular cartilage show a greater vulnerability to the harmful effects of IL-1 and are less responsive to the potential therapeutic effects of IRAP than cells in the deeper layers of the tissue.

IL-1 has no direct role in the IGF-1 non-responsive state during experimentally induced arthritis in mouse knee joints

OBJECTIVE

To investigate the involvement of interleukin-1 (IL-1) in the induction or maintenance of the insulin-like growth factor 1 (IGF-1) non-responsive state of chondrocytes during experimental arthritis in mouse knee joints.

METHODS

To characterise IGF-1 nonresponsiveness during arthritis, we measured chondrocyte proteoglycan (PG) synthesis by assaying incorporation of 35S-sulphate into mouse patellar cartilage, obtained from knee joints with experimentally induced arthritis and normal knee joints, cultured with IGF-1. We investigated whether suppressive mediators produced by the arthritic synovium or chondrocytes abolished the IGF-1 stimulation of normal cartilage, and used IL-1 primed cartilage to mimic the arthritic in vivo state. Specific inflammatory mediators responsible for the maintenance of the suppressed IGF-1 response were sought. We measured IGF-1 responsiveness in normal and arthritic patellae cultured with antibodies against tumour necrosis factor (TNF) or IL-1 alpha/beta, with IL-1 receptor antagonist (IL-1ra), and with several inhibitors of proteolytic enzymes or reactive oxygen species, and analysed the role of IL-1 in the development of IGF-1 non-responsiveness by studying IGF-1 responses in cartilage treated with IL-1 antibodies in vivo, at the onset of arthritis.

RESULTS

Mediators from the surrounding tissue of both normal and arthritic cartilage suppressed chondrocyte IGF-1 responses. Priming the cartilage with IL-1 did not directly induce IGF-1 non-responsiveness, but enhanced the ability of suppressive mediators from synovium or chondrocytes to downregulate the IGF-1 responsive state. IL-1ra, IL-1 alpha/beta antibody, TNF antibody, or the inhibitors tested did not markedly improve the disturbed IGF-1 response, but treatment with anti-IL-1 at the onset of arthritis prevented the development of IGF-1 non-responsiveness.

CONCLUSION

IL-1 alone does not induce IGF-1 non-responsiveness and is not critical in the maintenance of this phenomenon. However, IL-1 does appear to be an important cofactor in the generation of the IGF-1 non-responsive state.

Chondrocyte IGF-1 receptor expression and responsiveness to IGF-1 stimulation in mouse articular cartilage during various phases of experimentally induced arthritis

OBJECTIVE

To examine the distribution of insulin like growth factor-1 (IGF-1) receptors and the biological response to IGF-1 stimulation in articular cartilage of normal mouse knee joints and arthritic joints taken at various stages of experimentally induced arthritis.

METHODS

In situ IGF-1 receptor expression and responsiveness to IGF-1 stimulation were examined in murine articular cartilage at different phases in two models of experimentally induced arthritis. IGF-1 receptor expression was visualised in joint sections with the use of anti-IGF-1 receptor antibodies and quantified by confocal laser scanning microscopy. Chondrocyte proteoglycan (PG) synthesis was measured by incorporation of 35S-sulphate.

RESULTS

In control cartilage, the majority of IGF-1 receptors were found on chondrocytes localised in the middle and deeper zones of the cartilage, whereas receptor expression in surface zone chondrocytes was very low. During culture of normal articular cartilage, IGF-1 was able to maintain chondrocyte PG synthesis at the in vivo level. Concurrently with the development of arthritis, cartilage lost its capacity to react to IGF-1, but IGF-1 stimulation recovered when the inflammatory response waned. Shortly after induction of arthritis, IGF-1 receptor expression initially declined, but it had returned to normal levels by day 1 and remained increased thereafter.

CONCLUSION

The distribution of IGF-1 receptor expression in the different zones of normal articular cartilage reflects IGF-1 stimulation and metabolic activity of chondrocytes in these layers. This correlation is disturbed in arthritic cartilage, suggesting inadequate or overruled signalling.

Inhibition of the production and effects of interleukin-1 and tumor necrosis factor alpha in rheumatoid arthritis

This review has summarized information published over the last 5 years on the presence and pathophysiologic role of IL-1 and TNF alpha in RA. The evidence to date shows that 5 of 6 criteria for identifying mediators of tissue damage in human autoimmune diseases are satisfied (Table 1). The last criterion, prevention of clinical progression in patients with RA, is currently being evaluated. Many new therapeutic approaches are currently being developed, including the use of soluble receptors to IL-1 or TNF, monoclonal antibodies to TNF alpha, a specific IL-1 receptor antagonist, and gene therapy with the latter molecule. It should be emphasized that both IL-1 and TNF alpha play important roles in normal host defense; the possible complications of blocking their production or effects need to be carefully evaluated in long-term studies. A recent review has emphasized that although IL-1 and TNF alpha have many overlapping biologic properties, each may exhibit distinct effects in joint disease (99). Anti-TNF treatment may be primarily antiinflammatory but blocking IL-1 may be more effective in preventing cartilage destruction (100). The possibility exists that simultaneous inhibition of TNF alpha and IL-1 may be more therapeutically efficacious than blockade of either agent alone, as was recently demonstrated with IL-1ra and soluble TNF receptors in bacterial cell wall-induced arthritis in rats (101). The next level of clinical studies in rheumatoid arthritis should include the use of two biologic response modifiers together, or one agent combined with a more traditional form of therapy.

In vivo protection against interleukin-1-induced articular cartilage damage by transforming growth factor-beta 1: age-related differences

OBJECTIVES

Transforming growth factor-beta (TGF-beta) has been shown to antagonise interleukin-1 (IL-1) effects in different systems. Investigations were carried out to study whether TGF-beta 1 modulates IL-1 induced inflammation and IL-1 effects on articular cartilage in the murine knee joint.

METHODS

IL-1, TGF-beta 1 or both factors together were injected into the knee joint. Inflammation was studied in whole knee histological sections. Patellar cartilage proteoglycan synthesis was measured using 35S-sulphate incorporation while patellar cartilage glycosaminoglycan content was determined with automated image analysis on joint sections.

RESULTS

Co-injection of TGF-beta 1 and IL-1 resulted in synergistic attraction of inflammatory cells. In contrast, TGF-beta 1 counteracted IL-1 induced suppression of articular cartilage proteoglycan synthesis. Proteoglycan depletion was similar shortly after the last injection of IL-1 or IL-1/TGF-beta 1, but accelerated recovery was found with the combination at later days. This protective effect of TGF-beta 1 could not be demonstrated in older mice.

CONCLUSIONS

TGF-beta 1 aggravates IL-1 induced knee joint inflammation, but counteracts the deleterious effects of IL-1 on articular cartilage proteoglycan synthesis and content. The data indicate that TGF-beta 1 could play an important part in articular cartilage restoration after IL-1 induced proteoglycan depletion.

Responsiveness of articular cartilage from normal and inflamed mouse knee joints to various growth factors

OBJECTIVE

Disturbed anabolic signalling might contribute to the decreased chondrocyte proteoglycan (PG) synthesis during joint inflammation. Articular cartilage obtained from mouse knee joints with experimentally-induced arthritis exhibits a state of nonresponsiveness towards stimulation of chondrocyte PG synthesis by insulin-like growth factor-1 (IGF-1). Investigations were carried out on the role of other growth factors apart from IGF-1 on regulation of chondrocyte PG synthesis under pathological conditions, that is, during repair after IL-1 exposure as well as during early and later arthritis.

METHODS

Mouse patellae were obtained from normal knee joints and joints injected with IL-1 or zymosan. The patellae were cultured with basic fibroblast growth factor [bFGF], platelet-derived growth factor [PDGF], epidermal growth factor [EGF] or transforming growth factor beta [TGF beta] for 24 hours in the presence or absence of IGF-1. Chondrocyte PG synthesis was measured by 35S-sulphate incorporation.

RESULTS

In normal cartilage none of the tested growth factors elicited stimulatory effects on the chondrocyte PG synthesis as caused by IGF-1. EGF and TGF beta even caused significant inhibition of chondrocyte PG synthesis. Combination of bFGF or PDGF with IGF-1 exerted significant additional stimulation of the 35S-sulphate incorporation. IL-1 exposed cartilage displayed reactivity to IGF-1 as well as to the other growth factors similar to control cartilage. Cartilage obtained from joints with experimentally-induced arthritis exhibited a state of nonresponsiveness towards all individually tested growth factors as well as growth factor combinations.

CONCLUSION

Arthritis causes nonresponsiveness to stimulation of chondrocyte PG synthesis by the tested growth factors, which might be caused by a general receptor function defect.