Osteoarthritis, an inflammatory disease: potential implication for the selection of new therapeutic targets

Noggin haploinsufficiency differentially affects tissue responses in destructive and remodeling arthritis

OBJECTIVE

The balance between destruction and homeostatic or reparative responses determines the outcome of arthritis. Increasing evidence suggests a role for signaling pathways, essential for development and growth, in the maintenance of tissue homeostasis and attempts at repair. Inappropriate activation of such pathways may also have a role in disease progression. We undertook this study to determine the effect of shifting the balance in bone morphogenetic protein (BMP) signaling in different mouse models of arthritis.

METHODS

Endogenous levels of noggin, a BMP antagonist, were reduced using heterozygous noggin(+/LacZ) mice in a model of inflammation-driven destruction (methylated bovine serum albumin [mBSA]-induced monarthritis), a model of systemic autoimmune arthritis (collagen-induced arthritis [CIA]), and a model of joint ankylosis (spontaneous arthritis in DBA/1 mice). In addition, we studied BMP inactivation by adenoviral noggin overexpression in destructive arthritis. Cartilage damage and activation of BMP signaling were studied by digital image analysis using Safranin O sulfated glycosaminoglycan staining and immunohistochemistry for phosphorylated Smads (Smads 1, 5, and 8), respectively.

RESULTS

Noggin haploinsufficiency provided protection for articular cartilage against destruction in mBSA-induced arthritis. Antagonist overexpression rendered cartilage more vulnerable in this model. Noggin gene transfer in knees affected by CIA also enhanced cartilage damage. Haploinsufficiency did not affect CIA, but noggin(+/LacZ) mice had an increased number of CD4-positive cells with normal immune responses. In noggin(+/LacZ) DBA/1 mice with spontaneous arthritis, we observed delayed progression from cartilage to bone formation.

CONCLUSION

Tight spatiotemporal control of BMP signaling appears to be critical in the response of joint tissues in models of arthritis.

Extracellular superoxide dismutase and oxidant damage in osteoarthritis

OBJECTIVE

To use human cartilage samples and a mouse model of osteoarthritis (OA) to determine whether extracellular superoxide dismutase (EC-SOD) is a constituent of cartilage and to evaluate whether there is a relationship between EC-SOD deficiency and OA.

METHODS

Samples of human cartilage were obtained from femoral heads at the time of joint replacement surgery for OA or femoral neck fracture. Samples of mouse tibial cartilage obtained from STR/ort mice and CBA control mice were compared at 5, 15, and 35 weeks of age. EC-SOD was measured by enzyme-linked immunosorbent assay, Western blotting, and immunohistochemistry techniques. Real-time quantitative reverse transcription-polymerase chain reaction was used to measure messenger RNA for EC-SOD and for endothelial cell, neuronal, and inducible nitric oxide synthases. Nitrotyrosine formation was assayed by Western blotting in mouse cartilage and by fluorescence immunohistochemistry in human cartilage.

RESULTS

Human articular cartilage contained large amounts of EC-SOD (mean +/- SEM 18.8 +/- 3.8 ng/gm wet weight of cartilage). Cartilage from patients with OA had an approximately 4-fold lower level of EC-SOD compared with cartilage from patients with hip fracture. Young STR/ort mice had decreased levels of EC-SOD in tibial cartilage before histologic evidence of disease occurred, as well as significantly more nitrotyrosine formation at all ages studied.

CONCLUSION

EC-SOD, the major scavenger of reactive oxygen species in extracellular spaces, is decreased in humans with OA and in an animal model of OA. Our findings suggest that inadequate control of reactive oxygen species plays a role in the pathophysiology of OA.

Macroscopic and microscopic features of synovial membrane inflammation in the osteoarthritic knee: correlating magnetic resonance imaging findings with disease severity

OBJECTIVE

To determine the magnetic resonance imaging (MRI), macroscopic, and microscopic characteristics of synovial membrane inflammation, to study the relationship between disease severity and the degree of synovial inflammation on MRI and on macroscopic and microscopic examination, and to look for colocalization of chondral lesions and synovial inflammation.

METHODS

Thirty-nine patients with knee osteoarthritis (OA) were classified into 2 groups according to the severity of cartilage lesions as revealed by chondroscopy. Group 1 (n = 14) had mild cartilage lesion(s) without exposure of subchondral bone. Group 2 (n = 25) had severe cartilage lesion(s) with focal or diffuse exposure of subchondral bone. Synovitis was evaluated on T1-weighted MRI sequences according to the degree of synovial thickening on a 4-point scale (ranging from 0 to 3) in 5 regions of interest. Synovial membrane was macroscopically scored, and biopsies were performed on the 5 preselected sites for histologic scoring.

RESULTS

The mean +/- SD synovial thickening score on MRI was 1.55 +/- 0.90, with no significant difference between groups 1 and 2. Intra- and interobserver reproducibility of the total synovial score was excellent, and interobserver reproducibility of the MRI grade was good. Synovitis was diffuse and associated with chondral lesions only in the medial femorotibial compartment (r = 0.49, P = 0.001). The degree of synovial thickening on MRI correlated with qualitative macroscopic analysis (r(s) = 0.58, P < 0.001) and with microscopic features (synovial lining cells [r(s) = 0.23, P < 0.007], surface fibrin deposition [r(s) = 0.12, P < 0.01], fibrosis [r(s) = 0.31, P < 0.006], edema [r(s) = 0.17, P = 0.07], congestion [r(s) = 0.30, P < 0.005], and infiltration [r(s) = 0.46, P < 0.0001]). Fibrin and infiltration parameters were more severe in end-stage disease (P = 0.009 and P = 0.02, respectively).

CONCLUSION

Synovitis may be present from the onset of OA and may be evaluated on MRI. MRI evaluation of synovitis could be used to classify OA patients in clinical trials and could help to identify those who could benefit from synovium-targeted therapy.

Increased matrix metalloproteinase-13 production with aging by human articular chondrocytes in response to catabolic stimuli

Chondrocyte anabolic activity has been shown to decline with aging, but catabolic activity has received little attention. In this study, the effect of aging on the chondrocyte catabolic response was determined by stimulating isolated human chondrocytes with fibronectin fragments (FN-f) or interleukin-1beta and measuring matrix metalloproteinase-13 (MMP-13) production as a catabolic response. A significant age-related increase in chondrocyte MMP-13 production was noted. FN-f stimulation of MMP-13 expression was blocked using a nuclear factor kappa-B (NFkappaB) inhibitor suggesting a role for NFkappaB in this chondrocyte catabolic response. Chondrocyte production of the NFkappaB-regulated cytokine interleukin-1beta was also found to increase with donor age in unstimulated cells. These results demonstrate a significant age-related increase in chondrocyte catabolic responsiveness which could contribute to the development of osteoarthritis in older adults.

Analysis of pharmacologic and nonpharmacologic prescription patterns of general practitioners and specialists in the AMICA study

OBJECTIVE

To evaluate the prescription modalities of general practitioners (GPs) and specialists in symptomatic osteoarthritis (OA) patients enrolled in the AMICA study.

PATIENTS AND METHODS

This study started in 2001 as a cohort investigation of OA patients seen by 2764 GPs and 316 specialists. Enrolled were 28,981 patients with symptomatic OA of the hand, hip, or knee.

RESULTS

GPs and physical medicine specialists treated OA less frequently with pharmacological therapy than rheumatologists (OR 0.35; CI 0.26 to 0.47) or orthopedic surgeons (OR 0.65; CI 0.54 to 0.77). Pharmacological therapies (alone or in association with nonpharmacological modalities) were selected by 97% of the GPs, 96% of the rheumatologists, 94% of the orthopedic surgeons, and 85% of the physical medicine specialists. In comparison with GPs, all of the specialists more frequently used disease-modifying OA drugs (DMOADs) (rheumatologists: OR 6.86, CI 6.03 to 7.80; orthopedic surgeons: OR 2.20, CI 1.94 to 2.49; physical medicine specialists: OR 2.11, CI 1.69 to 2.63). Nonpharmacological therapies were selected by 44% of the GPs, 54% of the rheumatologists, 71% of the orthopedic surgeons, and 90% of the physical medicine specialists. They were used alone uncommonly (by 3% of the GPs, 3% of the rheumatologists, 6% of the orthopedic surgeons, and 15% of the physical medicine specialists). GPs use nonpharmacological treatment less than specialists: OR 0.53; CI 0.47 to 0.60 versus rheumatologists; OR 0.20; CI 0.18 to 0.21 versus orthopedic surgeons; and OR 0.07; CI 0.05 to 0.09 versus physical medicine specialists. Ultrasound (US) (11%) and transcutaneous electrical nerve stimulation (TENS) (7%) were the nonpharmacological therapies most frequently prescribed by GPs. Among the specialists, physical medicine specialists most frequently prescribed US (35%) and TENS (21%); US was also preferred by rheumatologists, whereas the orthopedic surgeon's choice was magnetotherapy (21%). Exercises and other passive or active rehabilitation strategies were prescribed for only 13% of the patients seen by GPs, but all 3 categories of specialists prescribed exercises and manual techniques far more frequently: rheumatologists, OR 1.63: 1.40 to 1.63; orthopedic surgeons, OR 1.67: 1.48 to 1.88; physical medicine specialists, OR 3.19: 2.66 to 3.82.

CONCLUSIONS

Italian rheumatologists and orthopedic surgeons are the specialists who most frequently use pharmacological treatment for OA. Nonpharmacological treatment is used commonly among both GPs and specialists but rarely as single therapy. Exercise and passive or active rehabilitation strategies are not frequently prescribed, although they are recommended by all the published guidelines.

Osteoarthritis: an overview of the disease and its treatment strategies

Osteoarthritis (OA) is currently defined by the American College of Rheumatology as a "heterogeneous group of conditions that leads to joint symptoms and signs which are associated with defective integrity of articular cartilage, in addition to related changes in the underlying bone at the joint margins." Its prevalence after the age of 65 years is about 60% in men and 70% in women. The etiology of OA is multifactorial, with inflammatory, metabolic, and mechanical causes. A number of environmental risk factors, such as obesity, occupation, and trauma, may initiate various pathological pathways. OA indicates the degeneration of articular cartilage together with changes in subchondral bone and mild intraarticular inflammation. The principal treatment objectives are to control pain adequately, improve function, and reduce disability. Acetaminophen is frequently used for symptomatic OA with mild to moderate pain. Nonsteroidal antiinflammatory drugs (NSAIDs) are more effective in the case of moderate-severe pain, but they have an increased risk of serious upper gastrointestinal adverse events. The newer cyclooxygenase COX-2 specific inhibitors (Coxibs) are as efficacious as traditional NSAIDs and have a better gastrointestinal safety profile. Other compounds (eg, chondroitin sulfate, diacerein, glucosamine sulfate) have a symptomatic effect that is slower and less than that of NSAIDs. The structure-modifying effects of drugs are currently being evaluated, and both glucosamine sulfate and diacerein have been shown in some trials to have a beneficial structural effect. Nonpharmacological interventions are frequently and widely used in the management of OA patients, but there is little evidence that they are effective: the best studied and most successful nonpharmacological interventions are patient education, self-management, and exercise. There is some evidence for the pain-relieving efficacy of thermotherapy and transcutaneous electrical nerve stimulation (TENS) but not of electrotherapy, acupuncture, homeopathy, or manual therapy. The value of interventions aimed at improving function and maximizing independence (occupational therapy, walking aids, workplace adaptation) is also unclear. The disease course and patient's requirements often change over time, thus requiring a periodic review and readjustment of therapy rather than the rigid continuation of a single treatment.

New biochemical insights into the pathogenesis of osteoarthritis and the role of laboratory investigations in clinical assessment

Osteoarthritis (OA) is among the most frequent diseases in the population and a common cause of pain and disability in adults. The principal disease hallmarks for assessment of OA are still clinical observation and radiographic aspects. However, the efficacy of therapeutic interventions is complicated by the time required to observe radiographic signs, useful for both diagnosis and assessment. Thus, laboratory markers have received growing attention in recent years, in an attempt to improve diagnosis, assessment of disease activity and severity, and evaluation of therapeutic effects. Many biomarkers have been proposed, in particular those reflecting cartilage and bone turnover and synovitis. Among these, COMP, antigenic keratan sulphate, hyaluronan, YKL-40, type III collagen N-propeptide, and urinary glucosyl-galactosyl pyridinoline appear to be the most promising. However, serum or urinary determinations of these molecules are difficult to interpret adequately due to their complex metabolism. New ultrasensitive methods for C-reactive protein have improved the usefulness of this marker, especially in the assessment of disease activity. Routine examination of synovial fluid is still essential for diagnosis and includes leukocyte count and crystal detection; specialized testing includes the evaluation of the levels of markers of local inflammation such as metalloproteinases and cytokines, which appear to be crucial to the pathogenesis of OA.

Evaluation of coexpression of microsomal prostaglandin E synthase-1 and cyclooxygenase-2 in interleukin-1- stimulated equine articular chondrocytes

OBJECTIVE

To characterize expression of cyclooxygenase-2 (COX-2) and microsomal prostaglandin E synthase-1 (mPGES-1) and regulation of prostaglandin E2 (PGE2) production by equine articular chondrocytes.

SAMPLE POPULATION

Articular cartilage from the metacarpophalangeal joints of 7 adult horses.

PROCEDURE

Equine chondrocyte monolayer cultures were stimulated with different concentrations (2.5, 5, 10, and 20 ng/mL) of recombinant human interleukin-1beta (rhIL-1beta) for 24 hours and then with rhIL-1beta (5 ng/mL) for 3, 6, 9, 12, and 24 hours. Concentration of PGE2 in the media was measured via radioimmunoassay. Total RNA was extracted from harvested chondrocytes, and regulation of COX-2 and mPGES-1 mRNA was studied via reverse transcriptase-polymerase chain reaction assay and Southern blot analysis with equine-specific probes. Western blot analyses were performed on cellular extracts to characterize expression of COX-2 and mPGES-1 protein.

RESULTS

Stimulation with 5, 10, and 20 ng of rhIL-1beta/mL caused a significant increase in PGE2 concentrations in the culture media, and incubation of cells with rhIL-1beta (5 ng/mL) for 6 to 24 hours increased PGE2 production significantly. The increase in prostaglandin production was associated with an induction of COX-2 and mPGES-1 transcripts. There also was an rhIL-1beta-dependent induction in COX-2 and mPGES-1 protein expression.

CONCLUSIONS AND CLINICAL RELEVANCE

Collectively, results indicated that the rhIL-1beta-dependent increase in PGE2 production in equine chondrocytes in monolayer culture was associated with coordinated upregulation of COX-2 and mPGES-1 expression. The pathophysiologic consequences of upregulated COX-2 and mPGES-1 expression and of PGE2 synthesis in rhIL-1beta-stimulated equine chondrocytes remain to be elucidated.

Expression and regulation of antimicrobial peptides in articular joints

Articular joint infection is a surprisingly rare event considering the frequency of joint arthrocentesis and other invasive procedures applied to limb joints. This observation led us to the hypothesis that a local "chemical shield" in the form of antimicrobial proteins provides synovial membrane and articular cartilage with resistance to infection. We subsequently began a systematic analysis of in vitro and in vivo antimicrobially active proteins in healthy articular joints and in disease states such as pyogenic arthritis, rheumatoid arthritis, and osteoarthritis. An anatomical approach with systematic characterization combined with antimicrobial testing revealed expression and production of human antibiotic peptides and proteins. In this review, we focus on the most prominent antimicrobial proteins in articular joints, which we have identified as lysozyme, lactoferrin, secretory phospholipase A2, RNase 7, CAP37, the cathelicidin LL37, and especially the human beta-defensin-2 and -3 (HBD-2/-3). Activation pathways and possible antimicrobial functions are discussed and the involvement in non-antimicrobial processes such as tissue remodelling is also considered.

PD-0200347, an alpha2delta ligand of the voltage gated calcium channel, inhibits in vivo activation of the Erk1/2 pathway in osteoarthritic chondrocytes: a PKCalpha dependent effect

OBJECTIVE

To explore the in vivo effects of PD-0200347, an alpha(2)delta ligand of voltage gated Ca(2+) channels, on cell signalling in osteoarthritic (OA) chondrocytes from an experimental dog model, and examine the effect of PD-0200347 on the major signalling pathways involved in OA cartilage degradation.

METHODS

OA was surgically induced in dogs by sectioning the anterior cruciate ligament. OA dogs were divided into three groups and treated orally with (a) placebo; (b) 15 mg/kg/day PD-0200347, or (c) 90 mg/kg/day PD-0200347. The animals were killed 12 weeks after surgery. Cartilage specimens from femoral condyles and tibial plateaus were processed for immunohistochemistry. Specific antibodies against the phosphorylated form of PKCalpha, Ras, c-Raf, the MAP kinases Erk1/2, p38, JNK, and the transcription factors, CREB and Elk-1, were used.

RESULTS

Levels of all the tested signalling mediators were increased in the placebo treated (OA) group compared with the normal group. PD-0200347 treatment significantly reduced the levels of the active forms of PKCalpha, c-Raf, Erk1/2, and Elk-1; however, the levels of the active forms of Ras, p38, JNK, and CREB were not affected by the PD-0200347 treatment.

CONCLUSION

The action of PD-0200347 on OA chondrocytes is probably mediated through the inhibition of Erk1/2 activation via a Ras independent mechanism. This effect is associated with reduction of the activation of transcription factors such as Elk-1, which leads to the inhibition of the induction of the major catabolic factors involved in the degradation process of OA cartilage.

The validation of simple scoring methods for evaluating compartment-specific synovitis detected by MRI in knee osteoarthritis

OBJECTIVES

Synovitis is common in osteoarthritis (OA) of the knee. In order to evaluate its importance, valid and reliable quantification methods are required. The aim of this study was to compare simple, semiquantitative synovitis scores with detailed volume assessments in subjects with knee OA using magnetic resonance imaging (MRI) as the investigative tool.

METHODS

Thirty-five subjects with clinically diagnosed OA of the knee were assessed for synovitis using gadolinium-enhanced MRI. The volume measurement of synovitis was assessed at four sites (medial and lateral parapatellar recesses, intercondylar notch and suprapatellar pouch). The semiquantitative scoring of synovitis was scored on a 0-3 scale. Establishment of a correlative relationship was undertaken using Spearman's rho for the individual site-specific measurements. Ordinal regression modelling was undertaken in order to establish the capacity of the synovitis scoring to predict the volume measurement.

RESULTS

A total of 140 sites were assessed. There were good correlations between the semiquantitative scores and the volume measurements, ranging from rho = 0.86 (P < 0.00) for the medial parapatellar recess to rho = 0.71 (P < 0.00) for the lateral parapatellar recess. The ordinal regression suggested that, while the synovitis scores predicted between 50 and 70% (R2 = 0.53, P < 0.00 to R2 = 0.71, P < 0.00) of the volume measurements, there was some minor overlap, particularly in the mid-range synovitis scores.

CONCLUSIONS

These results suggest that semiquantitative synovitis scores are valid and will enable feasible evaluation of the synovium in OA cohorts.

Human beta-defensin 3 mediates tissue remodeling processes in articular cartilage by increasing levels of metalloproteinases and reducing levels of their endogenous inhibitors

OBJECTIVE

Beta-defensins are broad-spectrum antimicrobial peptides (APs) that are components of innate immunity. Recent investigations showed the induction of beta-defensins in synovial membranes of osteoarthritic (OA) joints and suggested that they have functions other than the ability to kill microbes. As a result of these findings, we undertook this study to investigate the production of human beta-defensin 3 (HBD-3) in OA cartilage and to determine its influence on chondrocyte function.

METHODS

Healthy and OA cartilage were assessed for HBD-3 expression by reverse transcriptase-polymerase chain reaction (RT-PCR) and immunohistochemistry. HBD-3 expression in C28/I2 chondrocytes after administration of tumor necrosis factor alpha (TNFalpha) and interleukin-1 (IL-1) was determined by real-time RT-PCR and immunodot blot. Enzyme-linked immunosorbent assay experiments were used to study the effects of HBD-3 in cultured articular chondrocytes and in healthy and OA cartilage discs. Immunohistochemical analyses were performed to study the expression of mouse beta-defensins (MBDs) in OA cartilage of STR/Ort mice.

RESULTS

HBD-3 was induced in OA cartilage without bacterial challenge. Cytokines involved in the pathogenesis of OA, namely, TNFalpha and IL-1, were strong inducers of HBD-3 in cultured chondrocytes. Application of the recombinant HBD-3 protein to cultured chondrocytes and cartilage discs resulted in increased production of cartilage-degrading matrix metalloproteinases and in down-regulation of their endogenous regulators, tissue inhibitors of metalloproteinases 1 and 2. Furthermore, STR/Ort mice, which are genetically predisposed to develop OA-like lesions in the knee joint, demonstrated an increased expression of MBDs 3 and 4 in cartilage compared with that in healthy animals.

CONCLUSION

These findings widen our knowledge of the functional spectrum of APs and demonstrate that HBD-3 is a multifunctional AP with the ability to link host defense mechanisms and inflammation with tissue-remodeling processes in articular cartilage. Moreover, our data suggest that HBD-3 is an additional factor in the pathogenesis of OA.

Expression of Jak3, STAT1, STAT4, and STAT6 in inflammatory arthritis: unique Jak3 and STAT4 expression in dendritic cells in seropositive rheumatoid arthritis

BACKGROUND

Modulation of Jak-STAT signalling may provide an effective therapeutic strategy in inflammatory arthritis.

OBJECTIVE

To document Jak-STAT expression in a cohort of patients with active rheumatoid arthritis (RA), spondyloarthritis (SpA), and osteoarthritis (OA) and compare these subsets with normal synovial tissue.

METHODS

Synovial tissue biopsy specimens from patients with RA, OA, and SpA and histologically normal tissue (n = 10 in each arthritis group) were examined for the presence of Jak3, STAT1, STAT4, and STAT6 expression using immunohistochemistry. Phenotyping was performed using immunohistochemistry and immunofluorescence. Clinical and serological characteristics of patients with RA expressing Jak3-STAT4 were assessed.

RESULTS

STAT1, STAT4, and Jak3 protein expression was generally increased in inflammatory arthritis. In contrast, STAT6 expression was relatively heterogeneous. A subpopulation of CD1a positive dendritic cells unique to seropositive patients with RA was detected. These cells showed intense protein expression for Jak3, STAT4, and STAT6.

CONCLUSION

CD1a positive dendritic cells intensely express Jak3, STAT4, and STAT6 in seropositive RA tissue and may be an alternative marker for dendritic cells in their early stages of activation as well as providing a tool for identifying RA at the level of the synovium. Jak3 inhibition may be a potential therapeutic target to prevent dendritic cell maturation in RA. STAT1 expression is increased in inflammatory arthritis, suggesting that its pro-apoptotic and anti-inflammatory effects cannot effectively counteract inflammation. STAT6 expression is heterogeneous in synovium, suggesting a possible homoeostatic role in addition to any anti-inflammatory effects.

The protective effect of licofelone on experimental osteoarthritis is correlated with the downregulation of gene expression and protein synthesis of several major cartilage catabolic factors: MMP-13, cathepsin K and aggrecanases

This study sought to evaluate the levels of mRNA expression and protein synthesis of MMP-13, cathepsin K, aggrecanase-1 (ADAMTS-4), aggrecanase-2 (ADAMTS-5) and 5-lipoxygenase (5-LOX) in cartilage in the experimental anterior cruciate ligament (ACL) dog model of osteoarthritis (OA), and to examine the effects of treatment with licofelone, a 5-lipoxygenase (LOX)/cyclooxygenase (COX) inhibitor, on the levels of these catabolic factors. Sectioning of the ACL of the right knee was performed in three experimental groups: group 1 received no active treatment (placebo group); and groups 2 and 3 received therapeutic concentrations of licofelone (2.5 or 5.0 mg/kg/day orally, respectively) for 8 weeks, beginning the day following surgery. A fourth group consisted of untreated dogs that were used as normal controls. Specimens of cartilage were selected from lesional areas of OA femoral condyles and tibial plateaus, and were processed for real-time quantitative PCR and immunohistochemical analyses. The levels of MMP-13, cathepsin K, ADAMTS-4, ADAMTS-5 and 5-LOX were found to be significantly increased in OA cartilage. Licofelone treatment decreased the levels of both mRNA expression and protein synthesis of the factors studied. Of note was the marked reduction in the level of 5-LOX gene expression. The effects of the drug were about the same at both tested dosages. In vivo treatment with therapeutic dosages of licofelone has been found to reduce the degradation of OA cartilage in experimental OA. This, coupled with the results of the present study, indicates that the effects of licofelone are mediated by the inhibition of the major cartilage catabolic pathways involved in the destruction of cartilage matrix macromolecules. Moreover, our findings also indicate the possible auto-regulation of 5-LOX gene expression by licofelone in OA cartilage.

Menisci of the rabbit knee require mechanical loading to maintain homeostasis: cyclic hydrostatic compression in vitro prevents derepression of catabolic genes

BACKGROUND

The purpose of this study was to examine the influence of removing menisci from their in vivo loading environment on gene expression patterns and to determine whether in vitro loading can maintain the tissues in their in vivo phenotype.

METHODS

Lateral and medial rabbit meniscal explants from one leg were cultured in vitro and subjected to intermittent cyclic hydrostatic pressure (CHP) of 1 MPa at 0.5 Hz for 1 min and a rest period of 14 min (4 h of culture). The contralateral menisci were incubated at atmospheric pressure for 4 h. Menisci from both legs of another set of rabbits were frozen immediately to yield time zero values reflective of in vivo mRNA levels. Total RNA was isolated from all groups and processed for reverse transcription-polymerase chain reaction analysis for a subset of relevant genes (matrix molecules, cytokines, proteinases and inhibitors, enzymes).

RESULTS

It was found that mRNA levels for MMP-1, MMP-3, TIMPs, iNOS, COX-2, interleukin-1beta in both menisci, and interleukin-6 in medial menisci were significantly elevated in tissues cultured under nonloading conditions compared to the time zero controls. Subjecting menisci to CHP significantly prevented these increases in mRNA levels for nearly all of the indicated molecules. In contrast, there were no significant differences in mRNA levels for collagens, biglycan, MMP-13, or TIMP-4 between the time zero values and those cultured under either nonloading or loading conditions.

CONCLUSIONS

These studies demonstrate that removing rabbit menisci from their normal in vivo mechanical environment leads to an apparent up-regulation of a subset of potent effector molecules that could mediate catabolic activities, and that in vitro CHP can largely prevent this apparent up-regulation.

Pharmaceutical and nutraceutical management of canine osteoarthritis: present and future perspectives

Osteoarthritis (OA) is one of the most common chronic musculoskeletal diseases and causes of lameness in the dogs. The osteoarthritic disease process involves the entire synovial joint, encompassing the synovium, cartilage and underlying bone. Joint failure results from an abnormal mechanical strain causing damage to normal tissue or failure of pathologically impaired articular cartilage and bone under the influence of normal physiological strain or a combination of both. In both cases, the end point is cartilage loss and joint impairment. Osteoarthritic chondrocytes show an altered phenotype characterised by an excess production of catabolic factors, including metalloproteinases and reactive oxygen species. These factors constitute potential therapeutic targets and some new drugs and nutraceuticals have been proposed to promote the return to homeostasis. Until now, the therapeutic management of OA in dogs has been dominated by nonsteroidal anti-inflammatory drugs, but some new compounds, including diacerhein, with potential structure-modifying effects, are already used to treat OA in humans and could be helpful to manage OA in the dog. In addition, novel nutraceuticals, such as avocado/soybean unsaponifiable substances, have shown symptomatic effects in knee OA in humans, and could offer an alternative to prevent OA progression. This paper provides an overview of recent discoveries in the pathophysiology and in the therapeutic management of osteoarthritis in dogs.

Retinoic acid blocks pro-inflammatory cytokine-induced matrix metalloproteinase production by down-regulating JNK-AP-1 signaling in human chondrocytes

The development of osteoarthritis (OA) has recently been implicated as a result of immune-mediated damage of chondrocytes and their supporting matrixes. Pro-inflammatory cytokines like interleukin (IL)-1 and tumor necrosis factor alpha (TNF-alpha) play pivotal roles in immunopathogenesis of OA. Because vitamins preserving anti-oxidative effects are suggested to provide protection in OA patients from joint damage, in the present study, we examined the effects and mechanisms of all-trans retinoic acid (t-RA) in suppressing pro-inflammatory cytokine-induced matrix metalloproteinases (MMPs) production in human chondrocytes. Chondrocytes were prepared from cartilage specimens of OA patients receiving total hip or total knee replacement. The protein concentration was measured by ELISA, the mRNA expression by reverse transcriptase-polymerase chain reaction, the protein expression by Western blotting, the transcription factor DNA-binding activity by electrophoretic mobility shift assay and the protein kinase activity by kinase assay. We showed that both MMP-1 and MMP-13 mRNA expression, protein production and enzyme activity induced by either IL-1 or TNF-alpha were suppressed by t-RA or different retinoid derivatives. The molecular investigation revealed that the t-RA-mediated suppression was likely through blocking p38 kinase and c-Jun N-terminal kinase-activator protein-1 signaling pathways. In contrast, t-RA had no effect on extracellular signal-regulated kinase activity, nuclear factor (kappa)B (NF-(kappa)B) DNA-binding activity and I(kappa)B(alpha) degradation. Furthermore, we showed that t-RA could reduce IL-1-induced TNF-alpha production in chondrocytes. Our results suggest that vitamin A may protect OA patients from pro-inflammatory cytokine-mediated damage of chondrocytes and their supporting matrixes.

Histamine, histamine receptors (H1 and H2), and histidine decarboxylase expression by chondrocytes of osteoarthritic cartilage: an immunohistochemical study

Degeneration and loss of articular cartilage are the characteristic features of osteoarthritis (OA), with the appearance of fibrillations, cell clusters, matrix depletion, and changes in matrix composition all apparent. Histamine has a recognised role in allergic and inflammatory reactions, and is reported to affect several aspects of chondrocyte behaviour. The immunohistochemical (IHC) studies reported here have demonstrated histamine (H), both H1 and H2 receptors, and the histamine-producing enzyme histidine decarboxylase (HDC) in a variable proportion of human articular chondrocytes in OA cartilage specimens. Such observations were especially evident within the degenerative, superficial zone, and more so in late-stage disease. By contrast, "normal" age-matched cartilage specimens showed relatively little immunopositive staining for histamine and HDC. These findings strongly suggest that histamine and H-receptor expression by HAC in OA cartilage is potentially an important contributor to the atypical, aberrant phenotype of OA chondrocytes.

Association of the risk of osteoarthritis with high innate production of interleukin-1beta and low innate production of interleukin-10 ex vivo, upon lipopolysaccharide stimulation

OBJECTIVE

In a sibpair study of osteoarthritis (OA) patients, we investigated whether, upon stimulation with lipopolysaccharide (LPS), variations in the innate ex vivo production of interleukin-1beta (IL-1beta), IL-1 receptor antagonist (IL-1Ra), IL-10, and tumor necrosis factor alpha (TNFalpha) in whole-blood assays contribute to the risk of OA.

METHODS

Data from 305 patients with OA at multiple sites (hand, knee, hip, and spine), whose median age was 60 years (range 43-79 years), were compared with those from 137 controls. OA was defined in accordance with the American College of Rheumatology criteria. Whole-blood samples were stimulated with LPS (10 ng/ml). In the supernatants, cytokines were measured by enzyme-linked immunosorbent assay. Odds ratios (ORs) were used as measures of the relative risk of OA in relation to quartiles of IL-1beta, IL-1Ra, TNFalpha, and IL-10 production. The ORs were adjusted for sex and age, and 95% confidence intervals (95% CIs) were computed using robust standard errors to take into account the intrafamily effect.

RESULTS

Subjects in the highest quartile of IL-1beta and IL-1Ra had an increased risk of OA (OR 3.3, 95% CI 1.4-7.9 and OR 8.0, 95% CI 3.7-17.4, respectively), while subjects in the lowest quartile of IL-10 had a 3-fold increased risk of OA (OR 3.1, 95% CI 1.5-6.5). High innate ex vivo production of TNFalpha was not associated with an increased risk of OA.

CONCLUSION

Subjects with a high innate ex vivo production of IL-1beta and IL-1Ra and low innate ex vivo production of IL-10 have an increased risk of OA. These results suggest that a proportion of the genetic susceptibility to OA may be encoded for by variations in innate cytokine activity.

Calcium-containing crystals and osteoarthritis: implications for the clinician

The clinical implication of articular deposits of calcium-containing crystals (specifically of calcium pyrophosphate dihydrate and hydroxyapatite) in osteoarthritis is unknown. Recent longitudinal studies have suggested that in some instances calcium crystals are direct participants in cartilage damage, while in other situations they are merely markers of joint damage. Better understanding of the mechanisms of crystal formation, especially in relation to inorganic pyrophosphate regulation, has lead to potential avenues for therapeutic intervention. The current treatment of osteoarthritis associated with calcium-containing crystals should involve nonsteroidal anti-inflammatory drugs, intra-articular steroids, and in resistant cases, joint irrigation can be considered. While preliminary studies suggest the possibility of favorable benefits from colchicine and hydroxycholorquine in this osteoarthritis disease subset, more rigorous studies need to be conducted to establish their roles.

Development of comprehensive functional genomic screens to identify novel mediators of osteoarthritis

OBJECTIVE

The aim of this study was to develop high-throughput assays for the analysis of major chondrocyte functions that are important in osteoarthritis (OA) pathogenesis and methods for high-level gene expression and analysis in primary human chondrocytes.

METHODS

In the first approach, complementary DNA (cDNA) libraries were constructed from OA cartilage RNA and full-length clones were selected. These cDNAs were transferred into a retroviral vector using Gateway Technology. Full-length clones were over-expressed in human articular chondrocytes (HAC) by retroviral-mediated gene transfer. The induction of OA-associated markers, including aggrecanase-1 (Agg-1), matrix metalloproteinase-13 (MMP-13), inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), collagen IIA and collagen X was measured by quantitative real-time polymerase chain reaction (QPCR). Induction of a marker gene was verified by independent isolation of 2-3 clones per gene, re-transfection followed by QPCR as well as nucleotide sequencing. In the second approach, whole cDNA libraries were transduced into chondrocytes and screened for chondrocyte cluster formation in three-dimensional agarose cultures.

RESULTS

Using green fluorescent protein (eGFP) as a marker gene, it was shown that the retroviral method has a transduction efficiency of >90%. A total of 40 verified hits were identified in the QPCR screen. The first set of 19 hits coordinately induced iNOS, COX-2, Agg-1 and MMP-13. The most potent of these genes were the tyrosine kinases Axl and Tyro-3, receptor interacting kinase-2 (RIPK2), tumor necrosis factor receptor 1A (TNFR1A), fibroblast growth factor (FGF) and its receptor FGFR, MUS81 endonuclease and Sentrin/SUMO-specific protease 3. The second set of seven hits induced both Agg-1 and MMP-13 but none of the other markers. Five of these seven genes regulate the phosphoinositide-3-kinase pathway. The most potently induced OA marker was iNOS. This marker was induced 20-500 fold by seven genes. Collagen IIA was also induced by seven genes, the most potent being transforming growth factor beta (TGFbeta)-stimulated protein TSC22, vascular endothelial growth factor (VEGF) and splicing factor 3a. This screening assay did not identify inducers of collagen X. The second chondrocyte cluster formation screen identified 14 verified hits. Most of the genes inducing cluster formation were kinases. Additional genes had not been previously known to regulate chondrocyte cluster formation or any other chondrocyte function.

CONCLUSIONS

The methods developed in this study can be applied to screen for genes capable of inducing an OA-like phenotype in chondrocytes on a genome-wide scale and identify novel mediators of OA pathogenesis. Thus, coordinated functional genomic approaches can be used to delineate key genes and pathways activated in complex human diseases such as OA.

Octacalcium phosphate crystals directly stimulate expression of inducible nitric oxide synthase through p38 and JNK mitogen-activated protein kinases in articular chondrocytes

Basic calcium phosphate (BCP) crystals, including hydroxyapatite, octacalcium phosphate (OCP) and carbonate-apatite, have been associated with severe osteoarthritis and several degenerative arthropathies. Most studies have considered the chondrocyte to be a bystander in the pathogenesis of calcium crystal deposition disease, assuming that synovial cell cytokines were the only triggers of chondrocyte activation. In the present study we identified direct activation of articular chondrocytes by OCP crystals, which are the BCP crystals with the greatest potential for inducing inflammation. OCP crystals induced nitric oxide (NO) production and inducible nitric oxide synthase (NOS) mRNA expression by isolated articular chondrocytes and cartilage fragments, in a dose-dependent manner and with variations over time. OCP crystals also induced IL-1β mRNA expression. Using pharmacological and cytokine inhibitors, we observed that OCP crystals induced NO production and inducible NOS mRNA activation were regulated at both the transcriptional and the translational levels; were independent from IL-1β gene activation; and involved p38 and c-Jun amino-terminal kinase (JNK) mitogen-activated protein kinase (MAPK) pathways, as further confirmed by OCP crystal-induced p38 and JNK MAPK phosphorylation. Taken together, our data suggest that the transcriptional inducible NOS response to OCP crystals involved both the p38 and the JNK MAPK pathways, probably under the control of activator protein-1. NO, a major mediator of cartilage degradation, can be directly produced by BCP crystals in chondrocytes. Together with synovial activation, this direct mechanism may be important in the pathogenesis of destructive arthropathies triggered by microcrystals.

EULAR report on the use of ultrasonography in painful knee osteoarthritis. Part 1: prevalence of inflammation in osteoarthritis

OBJECTIVES

To assess the prevalence of inflammation in subjects with chronic painful knee osteoarthritis (OA), as determined by the presence of synovitis or joint effusion at ultrasonography (US); and to evaluate the correlation between synovitis, effusion, and clinical parameters.

METHODS

A cross sectional, multicentre, European study was conducted under the umbrella of EULAR-ESCISIT.

SUBJECTS

had primary chronic knee OA (ACR criteria) with pain during physical activity >or=30 mm for at least 48 hours. Clinical parameters were collected by a rheumatologist and an US examination of the painful knee was performed by a radiologist or rheumatologist within 72 hours of the clinical examination. Ultrasonographic synovitis was defined as synovial thickness >or=4 mm and diffuse or nodular appearance, and a joint effusion was defined as effusion depth >or=4 mm.

RESULTS

600 patients with painful knee OA were analysed. At US 16 (2.7%) had synovitis alone, 85 (14.2%) had both synovitis and effusion, 177 (29.5%) had joint effusion alone, and 322 (53.7%) had no inflammation according to the definitions employed. Multivariate analysis showed that inflammation seen by US correlated statistically with advanced radiographic disease (Kellgren-Lawrence grade >or=3; odds ratio (OR)=2.20 and 1.91 for synovitis and joint effusion, respectively), and with clinical signs and symptoms suggestive of an inflammatory "flare", such as joint effusion on clinical examination (OR=1.97 and 2.70 for synovitis and joint effusion, respectively) or sudden aggravation of knee pain (OR=1.77 for joint effusion).

CONCLUSION

US can detect synovial inflammation and effusion in painful knee OA, which correlate significantly with knee synovitis, effusion, and clinical parameters suggestive of an inflammatory "flare".

Synovitis: a potential predictive factor of structural progression of medial tibiofemoral knee osteoarthritis -- results of a 1 year longitudinal arthroscopic study in 422 patients

OBJECTIVE

To evaluate the prevalence of synovitis in painful medial tibiofemoral knee osteoarthritis (OA) and to evaluate correlation between synovitis and the structural severity and progression of tibiofemoral cartilage damage.

STUDY

Multicenter, longitudinal, 1-year duration.

PATIENTS

Primary painful knee OA (ACR criteria) of the medial tibiofemoral compartment, with pain of the signal knee on at least 30 days in the past 2 months, medial joint space width > or = 2mm, at least 10% of one cartilage surface of the medial compartment affected by superficial fibrillation or worse at baseline arthroscopy. ARTHROSCOPIC PARAMETERS: Knee arthroscopy under local anesthesia was performed and videorecorded at entry and after 1 year. Medial chondropathy was scored by using Societe Francaise d'Arthroscopie (SFA) score (0-100) and reader's overall assessment (VAS score, 100 mm). Progression of medial chondropathy was defined by a change in SFA and VAS scores over 4.5 and 8.0 mm after 1 year, respectively. Medial perimeniscal synovium was scored as normal (few translucent and slender villi, fine vascular network), reactive (proliferation of opaque villi), or inflammatory (hypervascularization and/or proliferation of hypertrophic and hyperemic villi). Medial chondropathy and synovitis were scored by a single reader blind to chronology of paired videotapes.

RESULTS

Four hundred and twenty-two patients were enrolled (mean age: 61 years, females: 59%, body mass index: 31, mean disease duration: 4 years) and completed the 1-year study. Synovial abnormalities were present in 50% of the patients with reactive and inflammatory aspects in 29% and 21% of the patients, respectively. Patients with a reactive or inflammatory medial synovium had a more severe medial chondropathy. The worsening in medial chondropathy after 1 year was statistically more severe in the group of patients with an inflammatory perimeniscal synovial membrane at baseline compared to patients with normal and reactive aspects, with no difference between these two latter groups. The odds ratio for progression in VAS score after 1 year was 3.11 (95% CI [1.07, 5.69]) for patients with inflammatory synovium at baseline compared to patients with normal synovium.

CONCLUSIONS

This study suggests that abnormalities of the medial perimeniscal synovium are a common feature of painful medial knee OA, associated with more severe medial chondropathy. It also suggests that an inflammatory aspect of the medial perimeniscal synovium could be considered as a predictive factor of subsequent increased degradation of medial chondropathy.

Recent advances in the genetic investigation of osteoarthritis

Osteoarthritis (OA) demonstrates considerable clinical heterogeneity, generating heated debate over whether OA is a single disease or a complex mix of disparate diseases and concerning which tissues are principally involved in disease initiation and progression. Epidemiological studies have demonstrated a major genetic component to OA risk. However, these studies have also revealed differences in risk between males and females and for disease at different skeletal sites. This observation has resulted in the concept of genes for specific sites rather than a generalised OA phenotype. Recent breakthroughs have shed considerable light on the nature of OA genetic susceptibility. Many candidate genes have been confirmed, such as the interleukin-1 gene cluster and the oestrogen alpha-receptor gene ESR1. Genome-wide linkage scans have revealed several regions harbouring novel loci, some of which are beginning to yield their genes.

Pain related behaviour in two models of osteoarthritis in the rat knee

Osteoarthritis (OA) is a major healthcare burden, with increasing incidence. Pain is the predominant clinical feature, yet therapy is ineffective for many patients. While there are considerable insights into the mechanisms underlying tissue remodelling, there is poor understanding of the link between disease pathology and pain. This is in part owing to the lack of animal models that combine both osteoarthritic tissue remodelling and pain. Here, we provide an analysis of pain related behaviours in two models of OA in the rat: partial medial meniscectomy and iodoacetate injection. Histological studies demonstrated that in both models, progressive osteoarthritic joint pathology developed over the course of the next 28 days. In the ipsilateral hind limb in both models, changes in the percentage bodyweight borne were small, whereas marked mechanical hyperalgesia and tactile allodynia were seen. The responses in the iodoacetate treated animals were generally more robust, and these animals were tested for pharmacological reversal of pain related behaviour. Morphine was able to attenuate hyperalgesia 3, 14 and 28 days after OA induction, and reversed allodynia at days 14 and 28, providing evidence that this behaviour was pain related. Diclofenac and paracetamol were effective 3 days after arthritic induction only, coinciding with a measurable swelling of the knee. Gabapentin varied in its ability to reverse both hyperalgesia and allodynia. The iodoacetate model provides a basis for studies on the mechanisms of pain in OA, and for development of novel therapeutic analgesics.

Etiology and pathophysiology of osteoarthritis

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

A benefit/risk assessment of existing therapeutic alternatives for the treatment of painful inflammatory conditions

Pain remains the leading reason for which patients consult their doctors. Pain also motivates over-the-counter sales of analgesic medicines, to be taken orally or even transcutaneously. Prescription medicines usually follow attempts at self-medication that fail to achieve the desired results. Acute pain usually subsides spontaneously but medicines are needed until that occurs; in arthritic conditions--especially osteoarthritis--anti-inflammatory drugs work best in short-term administration for flares that aggravate chronic but tolerable pain. In cases of chronic pain that exceeds the level of easy tolerance, anti-inflammatory drugs can reduce the pain to tolerable levels more effectively than simple analgesics and narcotic combinations. The non-steroidal anti-inflammatory drugs (NSAIDs) are among the most useful medicines providing an array of drugs that differ chiefly in time of onset of action, duration of action and persistence in the blood. The benefit they provide is pain amelioration; none is curative. The risks are well known and do not differ greatly among the drugs; unwanted gastrointestinal (GI) effects are the most common, but the skin, kidneys, liver and blood forming organs may also be affected. As the benefits are similar, when balancing risk and benefit it is important to: consider the cause and expected duration of pain, balance the risks (GI unwanted effects far outnumber others), assess the severity and likelihood of specific reactions, and consider the costs--not only of the medicines themselves but also those of treating untoward reactions. Thus NSAIDs number among the most successful therapeutic options of modern medicine and, as pain will continue to require intervention, will likely continue--at least as ancillary medications--even as more definitive treatments are developed. In addition, the target population, its characteristics and the duration and acceptance of the intervention need to be considered.

A Pilot trial evaluating meta050, a proprietary combination of reduced iso-alpha acids, rosemary extract and oleanolic acid in patients with arthritis and fibromyalgia

The aim of this open-label, 8-week observational trial was to investigate the efficacy of Meta050 (a proprietary, standardized combination of reduced iso-alpha-acids from hops, rosemary extract and oleanolic acid) on pain in patients with rheumatic disease. Osteoarthritis, rheumatoid arthritis and fibromyalgia patients were given 440 mg Meta050 three times a day for 4 weeks, which was changed to 880 mg twice a day for the subsequent 4 weeks in the majority of patients. Pain and condition-specific symptoms were assessed using a standard visual analog scale (VAS), an abridged arthritis impact measurement scale (AIMS2) and the fibromyalgia impact questionnaire. Fifty-four subjects with rheumatic disease completed the trial. Following treatment, a statistically significant decrease in pain of 50% and 40% was observed in arthritis subjects using the VAS (p < 0.0001; Wilcoxon-ranked sums) and AIMS2 (p < 0.0001), respectively. Fibromyalgia subject scores did not significantly improve. A decreasing trend of C-reactive protein, a marker for inflammation, was also observed in those subjects who presented with elevated C-reactive protein. No serious side effects were observed. These observations suggest that Meta050 at a dosage of 440 mg three times a day has a beneficial effect on pain in arthritis subjects.

Oral treatment with PD-0200347, an ?2? ligand, reduces the development of experimental osteoarthritis by inhibiting metalloproteinases and inducible nitric oxide synthase gene expression and synthesis in cartilage chondrocytes

OBJECTIVE

To examine the in vivo effects of PD-0200347, an alpha(2)delta ligand of voltage-activated Ca(2+) channels and a compound chemically related to pregabalin and gabapentin, on the development of cartilage structural changes in an experimental dog model of osteoarthritis (OA). The effects of PD-0200347 on the major pathways involved in OA cartilage degradation, including matrix metalloproteinases (MMPs) and the inducible form of nitric oxide synthase (iNOS), were also studied.

METHODS

OA was surgically induced in dogs by sectioning the anterior cruciate ligament. OA dogs were randomly distributed into 3 groups and treated orally with either 1) placebo, 2) 15 mg/kg/day of PD-0200347, or 3) 90 mg/kg/day of PD-0200347. Dogs were killed 12 weeks after surgery. The severity of the lesions was scored macroscopically and histologically. Cartilage specimens from the femoral condyles and tibial plateaus were processed for RNA extraction and quantitative reverse transcription-polymerase chain reaction (RT-PCR) or immunohistochemistry. Specific probes and antibodies were used to study the messenger RNA and protein levels of iNOS, MMP-1, MMP-3, and MMP-13.

RESULTS

No clinical signs of drug toxicity were noted in the treated animals. Treatment with PD-0200347 at both dosages tested (15 and 90 mg/kg/day) reduced the development of cartilage lesions. There was a reduction in the score of lesions, with a statistically significant (P = 0.01) difference when the highest dosage of the drug was administered. The reduction in the score was mainly related to a decrease in the surface size of the lesions. Quantitative RT-PCR showed that PD-0200347 significantly reduced the expression of MMP-13, a key mediator in OA. Immunohistochemical analyses showed that treatment with PD-0200347 significantly reduced the synthesis of all key OA mediators studied.

CONCLUSION

This study demonstrated the efficacy of PD-0200347 in reducing the progression of cartilage structural changes in a dog model of OA. It also showed that this effect is linked to the inhibition of the major pathophysiologic mediators responsible for cartilage degradation.

Role of interleukin-8 in PiT-1 expression and CXCR1-mediated inorganic phosphate uptake in chondrocytes

OBJECTIVE

The proinflammatory chemokine interleukin-8 (IL-8) induces chondrocyte hypertrophy. Moreover, chondrocyte hypertrophy develops in situ in osteoarthritic (OA) articular cartilage and promotes dysregulated matrix repair and calcification. Growth plate chondrocyte hypertrophy is associated with expression of the type III sodium-dependent inorganic phosphate (Pi) cotransporter phosphate transporter/retrovirus receptor 1 (PiT-1). This study was undertaken to test the hypothesis that IL-8 promotes chondrocyte hypertrophy by modulating chondrocyte PiT-1 expression and sodium-dependent Pi uptake, and to assess differential roles in this activity.

METHODS

The selective IL-8 receptor CXCR1 and the promiscuous chemokine receptor CXCR2 were used. Human knee OA cartilage, cultured normal bovine knee chondrocytes, and immortalized human articular chondrocytic CH-8 cells were transfected with CXCR1/CXCR2 chimeric receptors in which the 40-amino acid C-terminal cytosolic tail domains were swapped and site mutants of a CXCR1-specific region were generated.

RESULTS

Up-regulated PiT-1 expression was detected in OA cartilage. IL-8, but not IL-1 or the CXCR2 ligand growth-related oncogene alpha, induced PiT-1 expression and increased sodium-dependent Pi uptake by >40% in chondrocytes. The sodium/phosphate cotransport inhibitor phosphonoformic acid blocked IL-8-induced chondrocyte hypertrophic differentiation. Signaling mediated by kinase Pyk-2 was essential for IL-8 induction of PitT-1 expression and Pi uptake. Signaling through the TSYT(346-349) region of the CXCR1 cytosolic tail, a region divergent from the CXCR2 cytosolic tail, was essential for IL-8 to induce Pi uptake.

CONCLUSION

Our results link low-grade IL-8-mediated cartilaginous inflammation in OA to altered chondrocyte differentiation and disease progression through PiT-1 expression and sodium-dependent Pi uptake mediated by CXCR1 signaling.

Nitric oxide decreases IGF-1 receptor function in vitro; glutathione depletion enhances this effect in vivo

Insulin-like growth factor-1 (IGF) helps maintain healthy articular cartilage; however, arthritic cartilage becomes less responsive to the anabolic actions of IGF. We previously showed that high concentrations of nitric oxide (NO) decrease IGF receptor tyrosine phosphorylation and response to IGF in intact chondrocytes. The current studies evaluate direct effects of NO on IGF receptor kinase (IGF-RK) in vitro. NO from S-nitroso-N-acetyl-d,l-penicillamine (SNAP) or 1-hydroxy-2-oxo-3-(N-3-methyl-aminopropyl)-3-methyl-1-triazene (NOC-7) inhibits IGF-RK auto- and substrate phosphorylation in a dose and time dependent manner. There is a linear correlation between inhibition of auto- and substrate phosphorylation (r(2)=0.98). Increasing either dithiothreitol or reduced glutathione (GSH) content of the phosphorylation buffer to protect thiol groups blocks NO inhibition of IGF-RK substrate phosphorylation. Increased S-nitrosylation of cysteines in IGF-RK after exposure to SNAP suggests that NO may react with sulfhydryl groups, form S-nitrosothiols, which may result in functional modifications. NO blockade of IGF-1 stimulated proteoglycan synthesis in intact cells is enhanced when chondrocyte glutathione is depleted. The in vitro system shows that there can be direct effects of NO on IGF-RK that modify receptor function; the intact cell studies suggest that the mechanisms identified in vitro may be important in intact chondrocyte insensitivity to IGF-1 in cells exposed to NO.

Up-regulation of microsomal prostaglandin E synthase 1 in osteoarthritic human cartilage: critical roles of the ERK-1/2 and p38 signaling pathways

OBJECTIVE

Microsomal prostaglandin E synthase 1 (mPGES-1) is the final enzyme of the cascade that produces prostaglandin E(2) (PGE(2)), a key actor in arthritis. To study mPGES-1 synthesis in human cartilage and its regulation by interleukin-1beta (IL-1beta), we used human cartilage and an immortalized human chondrocyte cell line. Furthermore, we investigated the signaling pathways involved in mPGES-1 expression.

METHODS

We used real-time quantitative reverse transcription-polymerase chain reaction, Northern blotting, and Western blotting to measure mPGES-1 messenger RNA (mRNA) and protein expression in human chondrocytes. PGE(2) production was measured by enzyme-linked immunosorbent assay.

RESULTS

Cartilage specimens from osteoarthritis (OA) patients contained far greater amounts of mPGES-1 and cyclooxygenase 2 (COX-2) mRNA than did normal cartilage. Incubation with IL-1beta markedly increased mPGES-1 mRNA and protein in a dose-dependent and time-dependent manner, in parallel with an increase in PGE(2) levels. Both PD98059, an ERK pathway inhibitor, and SB203580, a p38alpha/beta MAPK inhibitor, abolished the increases in mPGES-1 mRNA and protein in response to IL-1beta. The specific p38alpha MAPK inhibitor SC906 suppressed IL-1beta-induced COX-2 expression but not IL-1beta-induced mPGES-1 expression, suggesting preferential involvement of p38beta MAPK in IL-1beta-induced mPGES-1 expression.

CONCLUSION

This study is the first to show that mPGES-1 is stimulated in human chondrocytes by the proinflammatory cytokine IL-1beta via activation of both ERK-1/2 and p38 MAPK in an isoform-specific manner. We postulate that mPGES-1 may be a novel target for OA therapy.

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.

Inflammatory cytokines released from the facet joint tissue in degenerative lumbar spinal disorders

STUDY DESIGN

A prospective study of surgical cases of degenerative lumbar spinal disorders demonstrated inflammatory cytokines in the facet joint tissue.

OBJECTIVE

To quantify various inflammatory cytokines released from the facet joint tissue in surgical cases of degenerative lumbar spinal disorders.

SUMMARY OF BACKGROUND DATA

In degenerative lumbar spinal disorders, pain is often caused by osteoarthritis of a facet joint. There are inflammatory mediators such as prostaglandins and leukotrienes in facet joint tissue in lumbar spinal degeneration. However, no reports have studied if there are also inflammatory cytokines in the facet joint, which generated arthropathic changes in degenerative lumbar spinal disorder and if pain is caused by chemical factors associated with inflammation such as inflammatory cytokines.

METHODS

Forty patients with degenerative lumbar disorders who had undergone operative treatment were included in this study. Fifty-five joint cartilages and 67 synovia were harvested from the lumbar facet joints in responsible intervertebral levels of patients. There were 24 male and 16 female subjects with average ages of 50 and 67 years, respectively, in 11 cases of lumbar disc herniation and 29 cases of lumbar spinal canal stenosis. Using ELISA and CLEIA methods, joint cartilage and synovial tissues were harvested during surgery from the facet joint at the responsible upper levels to measure IL-1beta, TNF-alpha, and IL-6 in individual tissues.

RESULTS

IL-1beta was detected in joint cartilage and synovium in both groups and its positive reaction rate was higher in LSCS than in LDH. There was no difference in IL-1beta concentration in cartilage tissue between the two groups. There was TNF-alpha in the synovium of LSCS. IL-6 was high in joint cartilage and synovium in both groups. The concentration was significantly higher in LSCS than in LDH.

CONCLUSIONS

There are inflammatory cytokines in facet joint tissue at high levels in degenerative lumbar spinal disorders. Inflammatory cytokines have a higher concentration rate in lumbar spinal canal stenosis than in lumbar disc herniation. This finding suggests that inflammatory cytokines in degenerated facet joints may have some relation to the cause of pain in degenerative lumbar disorders.

Dose-response relationship for exercise on severity of experimental osteoarthritis in rats: a pilot study

OBJECTIVE

To investigate the influence of a calibrated exercise on the progression of structural lesions in an experimental model of osteoarthritis (OA) in the rat, and to explore the effect of exercise on the level of chondrocyte caspase-dependent apoptosis and of Hsp70.

METHODS

The OA model was induced by anterior cruciate ligament transection (ACLT). Rats were placed in 4 experimental groups: operated (ACLT) free moving rats, and 3 exercise groups (slight, moderate and intense) subjected to running training. Rats were killed 14 and 28 days after surgery.

RESULTS

On D14 histological assessment demonstrated a beneficial influence of a slight and a moderate exercise vs control ACLT group. Hsp70 increased significantly in the moderate group vs controls. On D28, histological lesions strongly decreased in the slight and moderate exercise groups vs ACLT group, while an intense effort abolished this beneficial trend. Interestingly, the concomitant course of apoptotic events (caspase 3-positive cells) and the co-expression of Hsp70 in the various groups varied, when significant, in an inverse manner. In the intense group this overexpression was not noted, as a "burn out" appeared, thus leading to a loss of this protective effect.

CONCLUSION

This study shows that a calibrated slight or moderate exercise exerts a beneficial influence on the severity of chondral lesions in ACLT rats. Conversely, a strong effort abolishes this chondroprotective effect. This effect could be related to a reduced level of chondrocyte apoptosis through anti-apoptotic capacities of stress-induced Hsp70 overexpression.

The inflammatory side of human chondrocytes unveiled by antibody microarrays

Although being largely used for pathobiological models of cartilage diseases such as osteoarthritis (OA), human chondrocytes are still enigmatic cells, in as much as a large part of their secretome is unknown. We took advantage of the recent development of antibody-based microarrays to study multiple protein expression by human chondrocytes obtained from one healthy and five osteoarthritic joints, in unstimulated conditions or after stimulation by the proinflammatory cytokines interleukin-1 (IL-1) or tumour necrosis factor (TNF). The secretion media of chondrocytes were incubated with array membranes consisting of 79 antibodies directed against cytokines, chemokines, and angiogenic or growth factors. Several proteins were identified as new secretion products of chondrocytes, including the growth or angiogenic factors EGF, thrombopoietin, GDNF, NT-3 and -4, and PlGF, the chemokines ENA-78, MCP-2, IP-10, MIP-3alpha, NAP-2, PARC, and the cytokines MIF, IL-12, and IL-16. Most of the newly identified chemokines were increased intensely after stimulation by IL-1 or TNF, as for other proteins of the array, including GRO proteins, GM-CSF, IL-6, IL-8, MIP-1beta, GCP-2, and osteoprotegerin. The up-regulation by cytokines suggested that these proteins may participate in the destruction of cartilage and/or in the initiation of chemotactic events within the joint during OA. In conclusion, the microarray approach enabled to unveil part of an as yet unexplored chondrocyte secretome. Our findings demonstrated that chondrocytes were equipped with a proinflammatory arsenal of proteins which may play an important part in the pathogenesis of OA and/or its drift towards an inflammatory, rheumatoid phenotype.

Cytokines as therapeutic targets for osteoarthritis

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

Effect of histamine on the production of matrix metalloproteinases-1, -3, -8 and -13, and TNF? and PGE2 by human articular chondrocytes and synovial fibroblasts in vitro: a comparative study

Histamine has many regulatory activities and is well recognised for its importance in allergic and inflammatory disorders. Recently, histamine has been implicated in the pathophysiological processes of both rheumatoid and osteoarthritis, where human articular chondrocytes (HACs) and rheumatoid synovial fibroblasts (RSFs) are reported to express histamine receptors. This study has demonstrated H(1) and H(2) histamine receptors using immunohistochemistry on HACs and RSFs in vitro and has compared the effects of histamine (20 microM) on both cell types with regard to the production of matrix metalloproteinases (MMPs-1, -3, -8 and -13), the proinflammatory cytokine tumour necrosis factor alpha (TNFalpha) and prostaglandin E(2) (PGE(2)). On incubation with histamine, HACs showed increased production of MMP-3, MMP-13, TNFalpha and PGE(2) (statistical significance P=0.02, 0.005, 0.008 and 0.03, respectively, student's t-test), but MMP-1 expression was unaffected. In contrast, the RSF showed a histamine-induced increase in MMP-1 ( P=0.028) and an approximate 10-fold level of MMP-3 and PGE(2) release over that of HACs, each being stimulated by histamine ( P=0.02 and 0.032, respectively, student's t-test). However, MMP-8, MMP-13 and TNFalpha were not detected for RSF cultures. Our results show that histamine modifies the behaviour of both HACs and RSFs in vitro, but different effects were observed for the production of specific MMPs and TNFalpha by the two cell types.

Apoptosis in osteoarthritis

Many studies have shown that apoptotic cell death occurs at an increased rate in osteoarthritic cartilage. Whichever type of cell death takes places in articular cartilage, it is important to prevent, because it is detrimental to articular cartilage maintenance. Thus, it is important to characterize events going on during cellular degeneration in more detail. Overall, physicians have reached a reasonable level of understanding of the extent of cell death occurring in the disease process, but they are still at an early stage in the understanding of the mechanisms underlying this process and the means of intervening in this facet of cartilage destruction.

Angiogenesis in osteoarthritis and spondylosis: successful repair with undesirable outcomes

PURPOSE OF REVIEW

Osteoarthritis and spondylosis are frequently described as "wear-and-tear" arthritis, apparently contradicting modern management, which focuses on continuing and progressive exercise. Laboratory findings, including the growth of new blood vessels, encourage comparisons with repair processes. This review aims to place recent evidence in the context of previous work emphasizing the dynamic nature of tissues in these conditions.

RECENT FINDINGS

Synovitis has now become recognized as a common and important feature of osteoarthritis, and vascular growth is enhanced in osteoarthritic synovia when infiltrating macrophages generate angiogenic factors. As the molecular balance between angiogenic and antiangiogenic factors is disturbed, new blood vessels are permitted to grow into normally avascular structures, such as the articular cartilage and intervertebral disc. Angiogenesis is a key factor in new bone formation in osteophytes and at the osteochondral junction, thereby contributing to radiologic disease progression. Innervation of new blood vessels may contribute importantly to chronic pain.

SUMMARY

Reconceptualizing osteoarthritis and spondylosis as reparative processes provides a pathologic model consistent with current advice to exercise, when exercise facilitates repair. Repair does not, however, lead to normal tissue, and understanding the mechanisms by which changes in joint innervation may occur as a consequence of angiogenesis should lead to novel therapies that alleviate the common symptoms of these highly prevalent conditions.

IL-17, IL-1beta and TNF-alpha stimulate VEGF production by dedifferentiated chondrocytes

OBJECTIVE

To verify the involvement of proinflammatory cytokines IL-17, IL-1beta and tumor necrosis factor alpha (TNF-alpha) in cartilage vascularization by stimulating the production of vascular endothelial growth factor (VEGF) by chondrocytes isolated from patients with osteoarthritis (OA), in comparison with patients with rheumatoid arthritis (RA) and patients with femoral or humeral neck fracture (FP).

DESIGN

Chondrocytes isolated from patients with OA were maintained in monolayer culture for several passages. Chondrocyte dedifferentiation was monitored by the synthesis of cathepsin B by these cells. Chondrocytes freshly isolated at each subculture (subcultures 1-3) were stimulated with IL-17, IL-1beta or TNF-alpha. Supernatants were collected, immunoassayed for the production of VEGF and cathepsin B and assayed as the source of VEGF on the VEGF sensible ECV304 cell line. The cells were used to quantify intracellular cathepsin B enzymatic activity.

RESULTS

In differentiated conditions IL-1beta and TNF-alpha, but not IL-17, can inhibit the spontaneous secretion of VEGF by human OA, RA and FP chondrocytes, and IL-17 can restore the decrease in VEGF secretion caused by TNF-alpha. IL-17, together with IL-1beta and TNF-alpha, can enhance VEGF secretion to various extents by dedifferentiated OA chondrocytes. This change in effect with respect to primary culture was observable for all cytokines at the beginning of dedifferentiation, when the production of VEGF by chondrocytes had dramatically fallen and the cathepsin B synthesis had increased. The amount of VEGF induced by cytokines on dedifferentiated chondrocytes never reached the amount of VEGF produced by differentiated chondrocytes. VEGF produced by chondrocytes stimulated the ECV304 cell line proliferation.

CONCLUSIONS

These results indicate that dedifferentiated OA chondrocytes secrete VEGF after stimulation with proinflammatory cytokines. This event may be responsible for neovascularization found in OA cartilage.

Detection of differentially expressed genes in synovial fibroblasts by restriction fragment differential display

OBJECTIVE

To identify differentially expressed genes in synovial fibroblasts and examine the effect on gene expression of exposure to TNF-alpha and IL-1beta.

METHODS

Restriction fragment differential display was used to isolate genes using degenerate primers complementary to the lysophosphatidic acid acyl transferase gene family. Differential gene expression was confirmed by reverse transcription-polymerase chain reaction and immunohistochemistry using a variety of synovial fibroblasts, including cells from patients with osteoarthritis and self-limiting parvovirus arthritis.

RESULTS

Irrespective of disease process, synovial fibroblasts constitutively produced higher levels of IL-6 and monocyte chemoattractant protein 1 (MCP-1) (CCL2) than skin fibroblasts. Seven genes were differentially expressed in synovial fibroblasts compared with skin fibroblasts. Of these genes, four [tissue factor pathway inhibitor 2 (TFPI2), growth regulatory oncogene beta (GRObeta), manganese superoxide dismutase (MnSOD) and granulocyte chemotactic protein 2 (GCP-2)] were all found to be constitutively overexpressed in synoviocytes derived from patients with osteoarthritis. These four genes were only weakly expressed in other synovial fibroblasts (rheumatoid and self-limiting parvovirus infection). However, expression in all types of fibroblasts was increased after stimulation with TNF-alpha and IL-1beta. Three other genes (aggrecan, biglycan and caldesmon) were expressed at higher levels in all types of synovial fibroblasts compared with skin fibroblasts even after stimulation with TNF-alpha and IL-1.

CONCLUSIONS

Seven genes have been identified with differential expression patterns in terms of disease process (osteoarthritis vs rheumatoid arthritis), state of activation (resting vs cytokine activation) and anatomical location (synovium vs skin). Four of these genes, TFPI2, GRObeta (CXCL2), MnSOD and GCP-2 (CXCL6), were selectively overexpressed in osteoarthritis fibroblasts rather than rheumatoid fibroblasts. While these differences may represent differential behaviour of synovial fibroblasts in in vitro culture, these observations suggest that TFPI2, GRObeta (CXCL2), MnSOD and GCP-2 (CXCL6) may represent new targets for treatments specifically tailored to osteoarthritis.

Oral enzyme combination versus diclofenac in the treatment of osteoarthritis of the knee ? a double-blind prospective randomized study

The aim of this study was to compare the efficacy and safety of an oral enzyme-rutosid combination (ERC) containing rutosid and the enzymes bromelain and trypsin, with that of diclofenac in patients with osteoarthritis (OA) of the knee. A total of 103 patients presenting with painful episodes of OA of the knee were treated for 6 weeks in two study centers in a randomized, double-blind, parallel group trial. Altogether, 52 patients were treated in the ERC group and 51 patients were treated in the diclofenac group. Primary efficacy criteria were Lequesne's Algofunctional Index (LFI) and a 'complaint index', including pain at rest, pain on motion and restricted function. The efficacy criteria were analyzed by applying the Wilcoxon-Mann-Whitney test that provides the Mann-Whitney estimator (MW) as a measure of relevance. Non-inferiority was considered to be proven if the lower bound of the 97.5% one-sided confidence interval (CI-LB) was higher than MW = 0.36 (benchmark of not yet relevant inferiority). Both treatments resulted in clear improvements. Within the 6-week observation period, the mean value of the LFI decreased from 13.0 to 9.4 in the ERC group and from 12.5 to 9.4 in the diclofenac group. Non-inferiority of ERC was demonstrated by both primary criteria, LFI (MW = 0.5305; CI-LB = 0.4171) and complaint index (MW = 0.5434; CI-LB = 0.4296). Considerable improvements were also seen in secondary efficacy criteria, with a slight tendency towards superiority of ERC. The global judgment of efficacy by physician resulted in at least good ratings for 51.4% of the ERC patients, and for 37.2% of the diclofenac patients. In the majority of patients tolerability was judged in both drug groups as very good or good. The current study indicates that ERC can be considered as an effective and safe alternative to NSAIDs such as diclofenac in the treatment of painful episodes of OA of the knee. Placebo-controlled studies are now needed to confirm these results.