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

Effects of glycosaminoglycan content in extracellular matrix of donor cartilage on the functional properties of osteochondral allografts evaluated by micro-CT non-destructive analysis

Osteochondral allograft (OCA) is an important surgical procedure used to repair extensive articular cartilage damage. It is known that chondrocyte viability is crucial for maintaining the biochemical and biomechanical properties of OCA, which is directly related to the clinical success of the operation and is the only standard for preoperative evaluation of OCA. However, there is a lack of systematic research on the effect of the content of cellular matrix in OCA cartilage tissue on the efficacy of transplantation. Therefore, we evaluated the effect of different GAG contents on the success of OCA transplantation in a rabbit animal model. Each rabbit OCA was treated with chondroitinase to regulate glycosaminoglycan (GAG) content in the tissue. Due to the different action times of chondroitinase, they were divided into 4 experimental groups (including control group, 2h, 4h, and 8h groups). The treated OCAs of each group were used for transplantation. In this study, transplant surgery effects were assessed using micro-computed tomography (μCT) and histological analysis. Our results showed that tissue integration at the graft site was poorer in the 4h and 8h groups compared to the control group at 4 and 12 weeks in vivo, as were the compressive modulus, GAG content, and cell density reduced. In conclusion, we evaluated the biochemical composition of OCAs before and after surgery using μCT analysis and demonstrated that the GAG content of the graft decreased, it also decreased during implantation; this resulted in decreased chondrocyte viability after transplantation and ultimately affected the functional success of OCAs.

Insulin Signaling in Arthritis

Inflammatory arthritis is burdened by an increased risk of metabolic disorders. Cytokines and other mediators in inflammatory diseases lead to insulin resistance, diabetes and hyperlipidemia. Accumulating evidence in the field of immunometabolism suggests that the cause-effect relationship between arthritis and metabolic abnormalities might be bidirectional. Indeed, the immune response can be modulated by various factors such as environmental agents, bacterial products and hormones. Insulin is produced by pancreatic cells and regulates glucose, fat metabolism and cell growth. The action of insulin is mediated through the insulin receptor (IR), localized on the cellular membrane of hepatocytes, myocytes and adipocytes but also on the surface of T cells, macrophages, and dendritic cells. In murine models, the absence of IR in T-cells coincided with reduced cytokine production, proliferation, and migration. In macrophages, defective insulin signaling resulted in enhanced glycolysis affecting the responses to pathogens. In this review, we focalize on the bidirectional cause-effect relationship between impaired insulin signaling and arthritis analyzing how insulin signaling may be involved in the aberrant immune response implicated in arthritis and how inflammatory mediators affect insulin signaling. Finally, the effect of glucose-lowering agents on arthritis was summarized.

Growth factor levels in leukocyte-poor platelet-rich plasma and correlations with donor age, gender, and platelets in the Japanese population

BACKGROUND

Clinical application of platelet-rich-plasma (PRP) has been accelerated to investigate early recovery from various musculoskeletal conditions. It involves the promotion of tissue damage repair through the action of multiple growth factors at physiological concentrations. The composition of PRP differs based on many factors, which may include age and gender. Therefore, we analyzed correlations between age, gender, and platelet counts in PRP with growth factors in Japanese subjects.

METHOD

Peripheral blood was drawn from 39 healthy volunteers between 20 and 49 years of age (age, mean ± standard deviation = 33 ± 8.7 years; gender ratio, male:female = 19:20; BMI, mean ± standard deviation = 22 ± 4.0) and prepared through centrifugation (volume, 6 mL per sample). After being activated with CaCl₂, the supernatant was stored. The mean platelet count in PRP was 41.4 ± 12.2 × 10⁴/μL. PRP concentration rate (i.e., PRP/peripheral platelet counts) was 1.8 ± 0.4 times. Growth factor levels (platelet-derived growth factor-BB, transforming growth factor-β1, vascular endothelial growth factor, epidermal growth factor, fibroblast growth factor, insulin-like growth factor-1, and hepatocyte growth factor) were measured using enzyme-linked immunosorbent assay (ELISA), and correlations with age, gender, and PRP platelet counts were statistically analyzed by calculating Spearman's rank correlation coefficients (r).

RESULTS

Age was negatively correlated with platelet-derived growth factor-BB and insulin-like growth factor-1 (r = - 0.32, - 0.39), and gender had no influence on growth factors. Platelet counts in PRP positively correlated with platelet-derived growth factor-BB, transforming growth factor-β1, epidermal growth factor, and hepatocyte growth factor (r = 0.39, 0.75, 0.71, and 0.48, respectively).

CONCLUSIONS

This clinical study shows a significant variation of PRP among individual patients and that this variation is influenced by the age and the platelet counts of the subjects. Our data demonstrate that patient characteristics account for the differences in PRP physiological activity.

Men and Women Differ in the Biochemical Composition of Platelet-Rich Plasma

BACKGROUND

Autologous platelet-rich plasma (PRP) is widely used for a variety of clinical applications. However, clinical outcome studies have not consistently shown positive effects. The composition of PRP differs based on many factors. An improved understanding of factors influencing the composition of PRP is important for the optimization of PRP use.

HYPOTHESIS

Age and sex influence the PRP composition in healthy patients.

STUDY DESIGN

Controlled laboratory study.

METHODS

Blood from 39 healthy patients was collected at a standardized time and processed into leukocyte-poor PRP within 1 hour of collection using the same laboratory centrifuge protocol and frozen for later analysis. Eleven female and 10 male patients were "young" (aged 18-30 years), while 8 male and 10 female patients were "older" (aged 45-60 years). Thawed PRP samples were assessed for cytokine and growth factor levels using a multiplex assay and enzyme-linked immunosorbent assay. The platelet count and high-sensitivity C-reactive protein levels were measured. Two-way analysis of variance determined age- and sex-based differences.

RESULTS

Platelet and high-sensitivity C-reactive protein concentrations were similar in PRP between the groups ( P = .234). Male patients had higher cytokine and growth factor levels in PRP compared with female patients for inflammatory cytokines such as interleukin-1 beta (IL-1β) (9.83 vs 7.71 pg/mL, respectively; P = .008) and tumor necrosis factor-alpha (TNF-α) (131.6 vs 110.5 pg/mL, respectively; P = .048); the anti-inflammatory IL-1 receptor antagonist protein (IRAP) (298.0 vs 218.0 pg/mL, respectively; P < .001); and growth factors such as fibroblast growth factor-basic (FGF-basic) (237.9 vs 194.0 pg/mL, respectively; P = .01), platelet-derived growth factor (PDGF-BB) (3296.2 vs 2579.3 pg/mL, respectively; P = .087), and transforming growth factor-beta 1 (TGF-β1) (118.8 vs 92.8 ng/mL, respectively; P = .002). Age- but not sex-related differences were observed for insulin-like growth factor-1 (IGF-1) ( P < .001). Age and sex interaction terms were not significant. While mean differences were significant, there was also substantial intragroup variability.

CONCLUSION

This study in healthy patients shows differences in the composition of PRP between men and women, with sex being a greater factor than age. There was also proteomic variability within the groups. These data support a personalized approach to PRP treatment and highlight the need for a greater understanding of the relationships between proteomic factors in PRP and clinical outcomes.

CLINICAL RELEVANCE

Variability in the proteomic profile of PRP may affect tissue and clinical responses to treatment. These data suggest that clinical studies should account for the composition of PRP used.

Long-term delivery of rhIGF-1 from biodegradable poly(lactic acid)/hydroxyapatite@Eudragit double-layer microspheres for prevention of bone loss and articular degeneration in C57BL/6 mice

Insulin-like growth factor (IGF-1) has encouraged researchers to investigate its various potential therapeutic uses such as in the treatment of osteoporosis and repair of articular cartilage.

IGF-1R signalling contributes to IL-6 production and T cell dependent inflammation in rheumatoid arthritis

BACKGROUND

Signalling through insulin-like growth factor 1 receptor (IGF-1R) is essential for cell survival, but may turn pathogenic in uncontrolled tissue growth in tumours. In rheumatoid arthritis (RA), the IGF-1R signalling is activated and supports expansion of the inflamed synovia.

AIM

In the present study, we assess if disruption of IGF-1R signalling resolves arthritis.

MATERIAL AND METHODS

Clinical associations of IGF-1R expression in leukocytes of the peripheral blood were studied in 84 RA patients. Consequences of the IGF-1R signalling inhibition for arthritis were studied in mBSA immunised Balb/c mice treated with NT157 compound promoting degradation of insulin receptor substrates.

RESULTS

In RA patients, high expression of IGF-1R in leukocytes was associated with systemic inflammation as verified by higher expression of NF-kB, serum levels of IL6 and erythrocyte sedimentation rate, and higher pain perception. Additionally, phosphorylated IGF-1R and STAT3 enriched T cells infiltrate in RA synovia. Treatment with NT157 inhibited the phosphorylation of IGF-1R and STAT3 in synovia, and alleviated arthritis and joint damage in mice. It also reduced expression of IGF-1R and despaired ERK and Akt signalling in spleen T cells. This limited IL-6 production, changed RoRgt/FoxP3 balance and IL17 levels.

CONCLUSION

IGF-1R signalling contributes to T cell dependent inflammation in arthritis. Inhibition of IGF-1R on the level of insulin receptor substrates alleviates arthritis by restricting IL6-dependent formation of Th17 cells and may open for new treatment strategies in RA.

Implantation of rAAV5-IGF-I transduced autologous chondrocytes improves cartilage repair in full-thickness defects in the equine model

Cartilage injury often precipitates osteoarthritis which has driven research to bolster repair in cartilage impact damage. Autologous chondrocytes transduced with rAAV5-IGF-I were evaluated in chondral defects in a well-established large animal model. Cartilage was harvested from the talus of 24 horses; chondrocytes were isolated and stored frozen. Twenty million cells were cultured and transduced with 10(5) AAV vg/cell prior to implantation. Chondrocytes from eight horses were transduced with rAAV5-IGF-I, chondrocytes from eight horses with rAAV5-GFP, and chondrocytes from eight horses were not transduced. A 15 mm full-thickness chondral defect was created arthroscopically in the lateral trochlear ridge of the femur in both femoropatellar joints. Treated defects were filled with naive or gene-enhanced chondrocytes, in fibrin vehicle. Control defects in the opposite limb received fibrin alone. rAAV5-IGF-I transduced chondrocytes resulted in significantly better healing at 8 week arthroscopy and 8 month necropsy examination when compared to controls. At 8 months, defects implanted with cells expressing IGF-I had better histological scores compared to control defects and defects repaired with naive chondrocytes. This included increased chondrocyte predominance and collagen type II, both features of hyaline-like repair tissue. The equine model closely approximates human cartilage healing, indicating AAV-mediated genetic modification of chondrocytes may be clinically beneficial to humans.

Modeling the Insulin-Like Growth Factor System in Articular Cartilage

IGF signaling is involved in cell proliferation, differentiation and apoptosis in a wide range of tissues, both normal and diseased, and so IGF-IR has been the focus of intense interest as a promising drug target. In this computational study on cartilage, we focus on two questions: (i) what are the key factors influencing IGF-IR complex formation, and (ii) how might cells regulate IGF-IR complex formation? We develop a reaction-diffusion computational model of the IGF system involving twenty three parameters. A series of parametric and sensitivity studies are used to identify the key factors influencing IGF signaling. From the model we predict the free IGF and IGF-IR complex concentrations throughout the tissue. We estimate the degradation half-lives of free IGF-I and IGFBPs in normal cartilage to be 20 and 100 mins respectively, and conclude that regulation of the IGF half-life, either directly or indirectly via extracellular matrix IGF-BP protease concentrations, are two critical factors governing the IGF-IR complex formation in the cartilage. Further we find that cellular regulation of IGF-II production, the IGF-IIR concentration and its clearance rate, all significantly influence IGF signaling. It is likely that negative feedback processes via regulation of these factors tune IGF signaling within a tissue, which may help explain the recent failures of single target drug therapies aimed at modifying IGF signaling.

Autologous platelet-poor plasma decreases the bronchial stump necrosis in rat

BACKGROUND

Necrosis of the bronchial stump is a very important trigger for bronchopleural fistula. The administration of local autologous platelet-poor plasma (PPP) could protect the bronchial stump.

MATERIALS AND METHODS

Left pneumonectomy was performed in 25 Sprague-Dawley rats. Animals were randomly assigned to a control group (n=13) and PPP group (n=12). PPP was locally administered on the bronchial stump after pneumonectomy. We analyzed histologic changes in the bronchial stump and messenger RNA expression changes of genes involved in wound repair at 10 and 20 d.

RESULTS

Local PPP treatment produced a mass of fibrous tissue surrounding the bronchial stump and significantly decreased the presence of necrosis at 20 d. PPP increased the expression of insulin like growth factor 1 at 10 d although it did not reach statistical significance.

CONCLUSIONS

Our findings indicate that local PPP treatment of the bronchial stump after pneumonectomy decreased necrosis and could have a protective effect on the bronchial stump.

Intraarticular injection of platelet-rich plasma reduces inflammation in a pig model of rheumatoid arthritis of the knee joint

OBJECTIVE

Treatment options for rheumatoid arthritis range from symptomatic approaches to modern molecular interventions such as inhibition of inflammatory mediators. Inhibition of inflammation by platelet-rich plasma (PRP) has been proposed as a treatment for tendinitis and osteoarthritis. The present study was undertaken to investigate the effect of PRP on antigen-induced arthritis (AIA) of the knee joint in a large animal model.

METHODS

Six-month-old pigs (n = 10) were systemically immunized by bovine serum albumin (BSA) injection, and arthritis was induced by intraarticular BSA injection. PRP was injected into the knee joints of 5 of the animals after 2 weeks. An additional 5 animals received no systemic immunization (controls). Signs of arthritis were documented by plain histologic analysis, Safranin O staining, and immunohistochemistry analysis for type II collagen (CII), interleukin-6 (IL-6), and vascular endothelial growth factor (VEGF). Interleukin-1β (IL-1β), IL-6, tumor necrosis factor α (TNFα), VEGF, and insulin-like growth factor 1 (IGF-1) protein content was measured by Luminex assay.

RESULTS

In the pigs with AIA, plain histologic analysis revealed severe arthritic changes in the synovium. Safranin O and CII staining showed decreased proteoglycan and CII content in cartilage. Immunohistochemistry analysis revealed increased levels of IL-6 and VEGF in synovium and cartilage, and protein concentrations of IL-6, VEGF, IL-1β, and IGF-1 in synovium and cartilage were elevated as well; in addition, TNFα protein was increased in cartilage. Treatment with PRP led to attenuation of these arthritic changes in the synovium and cartilage.

CONCLUSION

We have described a porcine model of AIA. Experiments using this model demonstrated that PRP can attenuate arthritic changes as assessed histologically and based on protein synthesis of typical inflammatory mediators in the synovial membrane and cartilage.

Insulin-like growth factor-1 suspended in hyaluronan improves cartilage and subchondral cancellous bone repair in osteoarthritis of temporomandibular joint

This study sought to evaluate the effects of intra-articular injection of insulin-like growth factor-1 (IGF-1) suspended in hyaluronan (HA) on the cartilage and subchondral cancellous bone repair in osteoarthritis (OA) of the temporomandibular joint (TMJ). Disc perforation was performed bilaterally in rabbit TMJs to induce OA. Four groups of animals (n=12) received OA induction only, and either intra-articular HA injection alone, intra-articular IGF-1 injection alone, or a combination of HA and IGF-1 injection. All therapy was begun 4 weeks after OA induction. The animals were killed 12 or 24 weeks after the first injection, for histology and micro-CT examinations. Two additional animals were used as normal controls. Typical cartilage and subchondral cancellous bone lesions were observed in the OA group. No protective effect on cartilage and subchondral cancellous bone was found in the HA or IGF-1 alone groups. Better histological repair and nearly normal micro-architectural properties of the subchondral cancellous bone were observed in the HA+IGF-1 group compared with the HA or IGF-1 alone groups. HA may be used as an effective carrier for intra-articular injection of IGF-1 and the combination of HA/IGF-1 shows promise as a new rational approach to therapy of TMJ OA.

A dose titration of triamcinolone acetonide on insulin-like growth factor-1 and interleukin-1-conditioned equine cartilage explants

REASONS FOR PERFORMING STUDY

Previous in vitro pilot studies have defined a potentially beneficial effect of insulin-like growth factor-1 (IGF-1) and triamcinolone acetonide (TA) on interleukin-1 (IL-1)-conditioned equine cartilage. Furthermore, an optimal dose for IGF-1 treatment alone has been documented previously using the same test system as in the current project.

OBJECTIVES

To perform a dose titration of TA on IL-1-conditioned equine articular cartilage explants in the presence of an optimised IGF-1 dose, in order to optimise a triamcinolone concentration for use in combination with IGF-1 for future investigations.

METHODS

Cartilage explants were harvested from the distal femur of a normal horse. The effect of a clinically relevant TA dose range was evaluated in the presence of IL-1 and IGF-1 through measurement of proteoglycan (PG) matrix metabolism (synthesis and degradation).

RESULTS

TA and IGF-1 in combination inhibited the IL-1-induced release of PG matrix components (glycosaminoglycan or GAG) from the articular cartilage, as well as producing a significant increase in GAG synthesis.

CONCLUSIONS

This experiment provided proof of principle that a combination treatment appears to be able to combat the IL-1-induced matrix depletion, while enhancing anabolic metabolism within the articular cartilage.

POTENTIAL RELEVANCE

The use of IGF-1 in conjunction with TA in vivo has the potential to provide beneficial anabolic effects not seen with TA alone.

Stimulation of ankle cartilage: other emerging technologies (cellular, electricomagnetic, etc.)

Advances in understanding age-related changes in articular cartilage, joint homeostasis, the natural healing process after cartilage injury, and improved standards for evaluation of a joint surface made the ultimate goal of cartilage repair a possibility. New strategies for enhancement of articular cartilages' limited healing potential and biologic regeneration include advances in tissue engineering and the use of electromagnetic fields. This article reviews developments in basic science and clinical research made with these emerging technologies concerning treatment of articular cartilage defects and treatment of osteoarthritis of the ankle.

A novel role for suppressor of cytokine signaling 3 in cartilage destruction via induction of chondrocyte desensitization toward insulin-like growth factor

OBJECTIVE

An important mechanism contributing to cartilage destruction in arthritis is chondrocyte desensitization toward its main anabolic factor, insulin-like growth factor 1 (IGF-1). In this study, we sought to determine the role of suppressor of cytokine signaling 3 (SOCS-3) in the induction of IGF-1 desensitization of murine chondrocytes.

METHODS

Chondrocyte responsiveness to IGF-1 was assessed by 35S-sulfate incorporation into proteoglycans (PGs), via aggrecan messenger RNA expression, using quantitative real-time polymerase chain reaction or insulin receptor substrate 1 (IRS-1) tyrosine phosphorylation (Western blot analysis). IGF-1 desensitization of patellar chondrocytes was studied in zymosan-induced arthritis. IGF-1 desensitization was induced in patellar cartilage explants or the H4 chondrocyte cell line, exposed to interleukin-1alpha (IL-1alpha). SOCS-3 protein expression was assessed by immunohistochemistry or by Western blot analysis of protein extracts. The role of SOCS-3 in IGF-1 signaling was elucidated by adenoviral overexpression.

RESULTS

Exposure of murine articular cartilage to IL-1 caused a significant decrease in IGF-1-induced PG synthesis. This effect also occurred in inducible nitric oxide synthase-knockout mice, revealing the involvement of a secondary IL-1-induced factor other than nitric oxide. We showed that IL-1 significantly up-regulated SOCS-3 transcription and protein synthesis in H4 chondrocytes. In contrast, IL-18 was unable to induce SOCS-3 expression and failed to induce chondrocyte IGF-1 desensitization. Histologic analysis of samples from arthritic knee joints revealed high expression of SOCS-3 in chondrocytes. Through adenoviral overexpression of SOCS-3, we obtained direct evidence that SOCS-3 inhibits IGF-1-mediated cell signaling, since IRS-1 phosphorylation was reduced.

CONCLUSION

This study demonstrates that IL-1-induced SOCS-3 expression is a novel mechanism of IGF-1 desensitization in chondrocytes; in conjunction with nitric oxide it can contribute to cartilage damage during arthritis.

Chondroprotective drugs in degenerative joint diseases

Catabolic cytokine and anabolic growth factor pathways control destruction and repair in osteoarthritis (OA). A unidirectional TNF-alpha/IL-1-driven cytokine cascade disturbs the homeostasis of the extracellular matrix of articular cartilage in OA. Although chondrocytes in OA cartilage overexpress anabolic insulin-like growth factor (IGF) and its specific receptor (IGFRI) autocrine TNF-alpha released by apoptotic articular cartilage cells sets off an auto/paracrine IL-1-driven cascade that overrules the growth factor activities that sustain repair in degenerative joint disease. Chondroprotection with reappearance of a joint space that had disappeared has been documented unmistakably in peripheral joints of patients suffering from spondyloarthropathy when treated with TNF-alpha-blocking agents that repressed the unidirectional TNF-alpha/IL-1-driven cytokine cascade. A series of connective tissue structure-modifying agents (CTSMAs) that directly affect IL-1 synthesis and release in vitro and down-modulate downstream IL-1 features, e.g. collagenase, proteoglycanase and matrix metalloproteinase activities, the expression of inducible nitric oxide synthase, the increased release of nitric oxide, and the secretion of prostaglandin E(2), IL-6 and IL-8, have been shown to possess disease-modifying OA drug (DMOAD) activities in experimental models of OA and in human subjects with finger joint and knee OA. Examples are corticosteroids, some sulphated polysaccharides, chemically modified tetracyclines, diacetylrhein/rhein, glucosamine and avocado/soybean unsaponifiables.

Homeostasis of the extracellular matrix of normal and osteoarthritic human articular cartilage chondrocytes in vitro

OBJECTIVE

In normal articular cartilage cells, the IGFRI/insulin-like growth factor 1 (IGF-1) autocrine pathway was shown to overrule the catabolic effects of the IL-1/IL-1RI pathway by up-regulation of the IL-1RII decoy receptor. The activity of the IGF-1/IGFR1 and IL-1/IL-1R pathways, and of the IL-1RII control mechanism in the synthesis and turnover of the extracellular matrix (ECM) by chondrocytes from normal and osteoarthritic (OA) articular cartilage was compared in order to identify possible therapeutic targets of this disease.

METHODS

Phenotypically stable human articular cartilage cells were obtained from normal and OA cartilage of the same knee showing focal OA. The cells were cultured in alginate beads over 1 week to re-establish the intracellular cytokine and growth factors, to reexpress the respective plasma membrane receptors and to reach equilibrium in accumulated cell-associated matrix (CAM) compounds. Following liberation of the cells from the alginate beads, the levels of cell-associated matrix (CAM) aggrecan, type II collagen and fibronectin, of intracellular IGF-1, IL-1alpha and beta and of their respective plasma membrane-bound receptors, IGFR1, IL-1RI and the decoy receptor IL-1RII, were assayed using flow cytometry.

RESULTS

Coordinated production and accumulation of CAM aggrecan and type II collagen under the effect of the IGFR1/IGF-1 autocrine pathway-as documented for chondrocytes from healthy controls-was absent when the chondrocytes had been obtained from OA joints. When compared with cells obtained from normal tissues, chondrocytes from fibrillated OA cartilage expressed significantly higher intracellular IGF-1 levels and plasma membrane-bound IGFR1. At the same time, significantly higher intracellular IL-1alpha and beta levels and upregulated plasma membrane-bound IL-1RI were observed. Plasma membrane-bound IL-1RII decoy receptor was downregulated in OA chondrocytes. The levels of CAM aggrecan, type II collagen and fibronectin were significantly reduced in the chondrocytes obtained from pathological tissue.

CONCLUSION

Paired analysis of normal and OA chondrocytes from the same knee joint has shown an enhanced capacity of chondrocytes from OA cartilage to produce ECM macromolecules. However, the same cells have increased catabolic signalling pathways. As a consequence of this increased IL-1 activity and the reduced amounts of IL-1RII decoy receptor, less of the produced ECM macromolecules may persist in the CAM of the OA chondrocytes.

Insulin-like growth factor 1-induced interleukin-1 receptor II overrides the activity of interleukin-1 and controls the homeostasis of the extracellular matrix of cartilage

OBJECTIVE

We examined the effect of the insulin-like growth factor 1 (IGF-1)/IGF receptor I (IGFRI) autocrine/paracrine anabolic pathway on the extracellular matrix (ECM) of human chondrocytes and the mechanism by which IGF-1 reverses the catabolic effects of interleukin-1 (IL-1).

METHODS

Phenotypically stable human articular cartilage cells were obtained from normal cartilage and maintained in culture in alginate beads for 1 week to reach equilibrium of accumulated cell-associated matrix (CAM) compounds. Levels of CAM components aggrecan and type II collagen (CII) and levels of intracellular IGF-1, IL-1alpha, and IL-1beta and their respective plasma membrane-bound receptors IGFRI, IL-1 receptor I (IL-1RI), and the decoy receptor IL-1RII were assayed using flow cytometry to investigate the relationship between the autocrine/paracrine pathways and the homeostasis of ECM molecules in the CAM. The effects of IGF-1 on the expression of IGF-1, IL-1alpha, and IL-1beta and their respective receptor systems, the aggrecan core protein, and CII were determined by flow cytometry.

RESULTS

Cause-effect relationship experiments showed that IGF-1 up-regulates the levels of IGF-1, IGFRI, aggrecan, and CII in the CAM. No effects on the expression of IL-1alpha and IL-1beta and their signaling receptor IL-1RI were observed. However, IGF-1 was able to reverse IL-1beta-mediated degradation of aggrecan and the repression of the aggrecan synthesis rate. Interestingly, levels of aggrecan and CII in the CAM strongly correlated not only with IGF-1, but also with IL-1RII, which acts as a decoy receptor for IL-1alpha and IL-1beta. This suggests that IGF-1 and IL-1RII may cooperate in regulating ECM homeostasis. Additional experiments demonstrated that IGF-1 up-regulated IL-1RII, thereby overriding the catabolic effects of IL-1.

CONCLUSION

These findings reveal a new paradigm by which IGF-1 influences chondrocyte metabolism, by reversing the IL-1-mediated catabolic pathway through up-regulation of its decoy receptor.

Growth factors and cartilage repair

Growth factors are obvious tools to enhance cartilage repair. Understanding of reactivities in normal and arthritic cartilage and potential side effects on other compartments in the joint will help to identify possibilities and limitations. Growth factor responses have been evaluated in normal and diseased murine knees. The main cartilage anabolic factor, insulinlike growth factor-1, shows great safety, but has little contribution in diseased cartilage because of insulinlike growth factor nonresponsiveness of arthritic chondrocytes. Transforming growth factor-beta can overrule interleukin-1 catabolic effects and can enhance cartilage repair in arthritic tissue, unlike bone morphogenetic protein-2 that only is capable of enhancing chondrocyte proteoglycan synthesis in the absence of interleukin-1. Transforming growth factor-beta and bone morphogenetic protein-2 induce chondrophyte formation at the margins of the joint. Studies with scavenging transforming growth factor beta soluble receptor identified endogenous transforming growth factor-beta involvement in spontaneous cartilage repair and chondrophyte and subsequent osteophyte formation in arthritic conditions. Osteophyte induction may hamper intraarticular transforming growth factor-beta application in the joint and warrants targeted growth factor application to cartilage lesion sites only.

Differential metabolic responses to local administration of TGF-beta and IGF-1 in temporomandibular joint cartilage of aged mice

Osteoarthritis is a degenerative joint disease characterized by destruction of the articular cartilage in aging and senescence. The aim of this study was to study the possible treatment of this disease by intraarticular injection of growth factors to osteoarthritic joints of aged animals. 20-month-old female ICR mice were injected with insulin-like growth factor (IGF-1), transforming growth factor-beta (TGF-beta) or TGF-beta+IGF-1 on days 1, 4, and 7. On day 9 the joints were dissected and cultured in the presence of 35S-sulfate and 3H-thymidine. Combined treatment of TGF-beta and IGF-1 resulted in elevated 3H-thymidine incorporation and DNA and protein contents, reduction of 35S-sulfate incorporation and alkaline phosphatase activity, with no significant change in the activity of acid phosphatase. Following injections of TGF-beta, contents of DNA and protein, and incorporations of 3H-thymidine were induced, and 35S-sulfate and alkaline phosphatase activity were reduced. Treatment with IGF-1 resulted in reduced incorporation of 3H-thymidine with no significant changes in the activity of acid phosphatase. Atypically hypertrophic chondrocytes were observed along the articular surface and the endogenous production of TGF-beta and of IGF-1, as revealed by immunohistochemistry, was reduced. It is concluded that although 3H-thymidine incorporation and alkaline phosphatase activity appeared to be induced by TGF-beta and IGF-1, the overall responsiveness of cartilage from aged mice to these growth factors appeared to be inhibitory. Moreover, their effects appeared to be limited to specific cell populations in the cartilage itself.

Metabolic and mitogenic activities of insulin-like growth factor-1 in interleukin-1-conditioned equine cartilage

OBJECTIVE

To determine response of interleukin-1alpha (IL-1alpha)-conditioned equine articular cartilage explants to insulin-like growth factor-1 (IGF-1). Sample Population-Cartilage from the trochlea and condyles of the femur of a clinically normal 4-year-old horse.

PROCEDURE

Effects of IGF-1 (0 to 500 ng/ml) after addition of IL-1alpha were evaluated by assessing matrix responses, using a sulfated glycosaminoglycan (GAG) assay, matrix 35SO4 GAG incorporation, and release of GAG. Mitogenic response was assessed by 3H-thymidine incorporation into DNA and fluorometric assay of total DNA concentration.

RESULTS

Human recombinant IL-1alpha (40 ng/ml) increased the amount of labeled GAG released and decreased labeled and total GAG remaining in explants, and IL-1alpha decreased mitogenic response. Addition of IGF-1 counteracted effects seen with IL-1alpha alone. In general, IGF-1 decreased total and labeled GAG released into the medium, compared with IL-1alpha-treated explants (positive-control sample). Values for these variables did not differ significantly from those for negative-control explants. A significant increase in total and newly synthesized GAG in the explants at termination of the experiment was observed with 500 ng of IGF-1/ml. Labeled GAG remaining in explants was greater with treatment at 50 ng of IGF-1/ml, compared with treatment with IL-1alpha alone. Concentrations of 200 ng of IGF-1/ml abolished actions of IL-1alpha and restored DNA synthesis to values similar to those of negative-control explants.

CONCLUSIONS AND CLINICAL RELEVANCE

IGF-1 at 500 ng/ml was best at overcoming detrimental effects associated with IL-1alpha in in vitro explants. These beneficial effects may be useful in horses with osteoarthritis.

Enhanced repair of extensive articular defects by insulin-like growth factor-I-laden fibrin composites

Stem cells indigenous to the cancellous spaces of the bone bed in an acute injury provide an important source of pluripotent cells for cartilage repair. Insulin-like growth factor-I facilitates chondrogenesis of bone marrow-derived stem cells in long-term culture and may enhance chondrogenesis in healing cartilage lesions in vivo. This study examined the impact of insulin-like growth factor-I, gradually released from fibrin clots polymerized in situ, on the recruitable stem-cell pool in a full-thickness critical cartilage defect model. Twelve full-thickness 15-mm cartilage lesions in the femoropatellar articulations of six young mature horses were repaired by an injection of autogenous fibrin containing 25 microg of human recombinant insulin-like growth factor-I or, in control joints, fibrin without the growth factor. All horses were killed at 6 months, and cartilage repair tissue and surrounding cartilage were assessed by histology, histochemistry, types I and II collagen immunohistochemistry, types I and II collagen in situ hybridization, and matrix biochemical determinations. White tissue filled grafted and control lesions, with the growth factor-treated defects being more completely filled and securely attached to the subchondral bone. A moderately improved chondrocyte population, more columnar cellular organization, and better attachment to the underlying bone were evident on histological evaluation of growth factor-treated defects. Type-II procollagen mRNA was abundantly present in the deeper half of the treated sections compared with moderate message expression in control tissues. Immunolocalization of type-II collagen showed a preponderance of the collagen in growth factor-treated lesions, confirming translation of type-II message to protein. Composite histologic healing scores for treated defects were significantly improved over those for control defects. DNA content in the cartilage defects was similar in treated and control joints. Matrix proteoglycan content was similar in treated and control defects and lower in the defects than in the intact surrounding and remote cartilage of the treated and control joints. The proportion of type-II collagen significantly increased in growth factor-treated tissues. Fibrin polymers laden with insulin-like growth factor-I improved the histologic appearance and the proportion of type-II collagen in healing, full-thickness cartilage lesions. However, none of the biochemical or morphologic features were consistent with those of normal articular cartilage.

Reduced cartilage proteoglycan loss during zymosan-induced gonarthritis in NOS2-deficient mice and in anti-interleukin-1-treated wild-type mice with unabated joint inflammation

OBJECTIVE

To investigate the role of nitric oxide (NO) and interleukin-1 in (IL-1) joint inflammation and cartilage destruction during zymosan-induced gonarthritis (ZIA).

METHODS

Monarticular arthritis was elicited by intraarticular injection of zymosan. The effect of NO deficiency on arthritis was studied in mice with genetically disrupted NOS2. The role of IL-1 was examined by treating wild-type mice with neutralizing anti-murine IL-1(alpha+beta) antibodies. Joint swelling was measured externally by the increased uptake of circulating 99mtechnetium pertechnetate. Proteoglycan (PG) synthesis was assessed using 35S-sulfate incorporation into patellae ex vivo. Histology evaluated exudation and infiltration of leukocytes and the extent of cartilage destruction.

RESULTS

The proinflammatory mediators NO, IL-1, and IL-6 were released by the articular tissues during the first hours of inflammation. Interestingly, anti-IL-1 treatment moderately reduced, and NOS2 deficiency moderately enhanced, joint swelling. However, the influx of neutrophils into the joint occurred independently of IL-1 and NOS2 activities. In the first week of inflammation, chondrocyte PG synthesis was significantly suppressed and chondrocytes became unresponsive to their essential anabolic factor, insulin-like growth factor 1 (IGF-1). Anti-IL-1 treatment or NOS2 deficiency prevented the inhibition of PG synthesis, and the chondrocytes remained IGF-1 responsive. Intraarticular injections of IL-1alpha into NOS2-deficient mice did not affect PG synthesis, thus proving that NO mediated this IL-1 effect in vivo. Furthermore, histology showed that cartilage PG loss was markedly ameliorated in NOS2-deficient and anti-IL-1-treated mice. Intermediate cartilage pathology was found in mice that were heterozygous for disrupted NOS2.

CONCLUSION

IL-1 and NO play a minor role in edema and neutrophil influx, but a major role in cartilage destruction of ZIA. In this model of murine arthritis, cartilage destruction was, for the most part, caused by pronounced suppression of PG synthesis and IGF-1 unresponsiveness of the chondrocytes, which were induced by de novo-synthesized IL-1 and were mediated by NOS2 activation.

Articular cartilage destruction in experimental inflammatory arthritis: insulin-like growth factor-1 regulation of proteoglycan metabolism in chondrocytes

Rheumatoid arthritis, a disease of unknown aetiology, is characterized by joint inflammation and, in its later stages, cartilage destruction. Inflammatory mediators may exert not only suppression of matrix synthesis but also cartilage degradation, which eventually leads to severe cartilage depletion. Systemically and locally produced growth factors and hormones regulate cartilage metabolism. Alterations in levels of these factors or in their activity can influence the pathogenesis of articular cartilage destruction in arthritic joints. The main topic of the present review is the role of the anabolic factor insulin-like growth factor-1 in the regulation of chondrocyte metabolic functions in normal and in diseased cartilage. This is the most important growth factor that balances chondrocytes proteoglycan synthesis and catabolism to maintain a functional cartilage matrix. A brief overview of how chondrocytes keep the cartilage matrix intact, and how catabolic and anabolic factors are thought to be involved in pathological cartilage destruction precedes the review of the role of this growth factor in proteoglycan metabolism in cartilage.

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.