Effects of tenidap on the progression of osteoarthritic lesions in a canine experimental model. Suppression of metalloprotease and interleukin-1 activity

Assessment of the effects of diet and physical rehabilitation on radiographic findings and markers of synovial inflammation in dogs following tibial plateau leveling osteotomy

OBJECTIVE To determine the effects of an omega-3 fatty acid and protein-enriched diet, physical rehabilitation, or both on radiographic findings and markers of synovial inflammation in dogs following tibial plateau leveling osteotomy and arthroscopic surgery for treatment of cranial cruciate ligament disease. DESIGN Randomized, prospective clinical trial. ANIMALS 48 dogs with unilateral cranial cruciate ligament disease. PROCEDURES Dogs were randomly assigned to receive a dry omega-3 fatty acid and protein-enriched dog food formulated to support joint health (test food [TF]), a dry food formulated for adult canine maintenance (control food [CF]), TF plus rehabilitation, or CF plus rehabilitation after surgery. Synovial fluid prostaglandin (PG) E₂ and interleukin-1β concentrations, radiographic osteoarthritis scores, osteotomy site healing, and patellar ligament thickness were assessed at predetermined time points up to 6 months after surgery. RESULTS Dogs that received CF had significantly higher PGE₂ concentrations over time following surgery than did dogs that received TF, regardless of rehabilitation status. Synovial fluid interleukin-1β concentrations did not change over time in any groups. Diet and rehabilitation were both associated with osteoarthritis scores, with significantly lower scores over time for dogs that received TF versus CF and for dogs that underwent rehabilitation versus those that did not. Proportions of dogs with complete osteotomy healing 8 and 24 weeks after surgery were significantly lower for dogs that received TF than for dogs that received CF, regardless of rehabilitation status. CONCLUSIONS AND CLINICAL RELEVANCE Results suggested that feeding the TF can result in lower synovial fluid PGE₂ concentrations and that both the TF and rehabilitation can reduce progression of osteoarthritis in the 6 months following tibial plateau leveling osteotomy; clinical relevance of slower osteotomy healing in dogs fed the TF was unclear.

Osteophytes: relevance and biology

OBJECTIVE

Osteophytes are common features of osteoarthritis. This review summarizes the current understanding of the clinical relevance and biology of osteophytes.

METHOD

This review summarizes peer-reviewed articles published in the PubMed database before May 2006. In addition this review is supplemented with own data and theoretical considerations with regard to osteophyte formation.

RESULTS

Osteophytes can contribute both to the functional properties of affected joints and to clinical relevant symptoms. Osteophyte formation is highly associated with cartilage damage but osteophytes can develop without explicit cartilage damage. Osteophytes are mainly derived from precursor cells in the periosteum and growth factors of the TGFbeta superfamily appear to play a crucial role in their induction.

CONCLUSION

Osteophyte formation is an integral component of OA pathogenesis and understanding the biology of osteophyte formation can give insights in the disturbed homeostasis in OA joints.

Differential direct effects of cyclo-oxygenase-1/2 inhibition on proteoglycan turnover of human osteoarthritic cartilage: an in vitro study

Treatment of osteoarthritis (OA) with nonsteroidal anti-inflammatory drugs (NSAIDs) diminishes inflammation along with mediators of cartilage destruction. However, NSAIDs may exert adverse direct effects on cartilage, particularly if treatment is prolonged. We therefore compared the direct effects of indomethacin, naproxen, aceclofenac and celecoxib on matrix turnover in human OA cartilage tissue. Human clinically defined OA cartilage from five different donors was exposed for 7 days in culture to indomethacin, naproxen, aceclofenac and celecoxib – agents chosen based on their cyclo-oxygenase (COX)-2 selectivity. As a control, SC-560 (a selective COX-1 inhibitor) was used. Changes in cartilage proteoglycan turnover and prostaglandin E₂ production were determined. OA cartilage exhibited characteristic proteoglycan turnover. Indomethacin further inhibited proteoglycan synthesis; no significant effect of indomethacin on proteoglycan release was found, and proteoglycan content tended to decrease. Naproxen treatment was not associated with changes in any parameter. In contrast, aceclofenac and, prominently, celecoxib had beneficial effects on OA cartilage. Both were associated with increased proteoglycan synthesis and normalized release. Importantly, both NSAIDs improved proteoglycan content. Inhibition of prostaglandin E₂ production indirectly showed that all NSAIDs inhibited COX, with the more COX-2 specific agents having more pronounced effects. Selective COX-1 inhibition resulted in adverse effects on all parameters, and prostaglandin E₂ production was only mildly inhibited. NSAIDs with low COX-2/COX-1 selectivity exhibit adverse direct effects on OA cartilage, whereas high COX-2/COX-1 selective NSAIDs did not show such effects and might even have cartilage reparative properties.

Long term NSAID treatment inhibits COX-2 synthesis in the knee synovial membrane of patients with osteoarthritis: differential proinflammatory cytokine profile between celecoxib and aceclofenac

OBJECTIVE

To compare the effect of celecoxib with that of a classic non-steroidal anti-inflammatory drug (NSAID) on synovial inflammation and on the synovial expression of proinflammatory genes in patients with knee osteoarthritis (OA).

METHODS

30 patients with severe knee OA scheduled for total knee replacement surgery were included in a 3 month clinical trial. They were randomised to two groups: patients treated with celecoxib (CBX) (200 mg/24 h) and patients treated with aceclofenac (ACF) (100 mg/12 h). Those patients with OA who did not want to be treated with NSAIDs served as a control group. During knee surgery, synovial fluid (SF) and synovial membrane (SM) were collected. A SM specimen was fixed and embedded in paraffin and another part was frozen for molecular biology studies.

RESULTS

At the end of study both CBX and ACF treated patients showed a significant improvement in pain and knee function compared with controls. Both drugs significantly reduced prostaglandin E(2) (PGE(2)) SF concentration and down regulated COX-2 mRNA and protein expression at the SM. However, synovial macrophage infiltration (CD68 antigen staining) and expression of proinflammatory mediators, such as interleukin 1beta and tumour necrosis factor alpha, were decreased only by CBX treatment.

CONCLUSION

Both drugs improved joint pain and function, inhibited SF PGE(2) concentration, and induced a decrease in synovial COX-2 expression and synthesis not related to the tissue inflammatory status. These data suggest that PGE(2) blocking agents may decrease PGE(2) production not only by direct COX-2 inhibition but also by down regulating COX-2 expression and synthesis. However, CBX and ACF appear to have different anti-inflammatory profiles in controlling OA synovial macrophage infiltration and proinflammatory expression.

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.

Subchondral and trabecular bone metabolism regulation in canine experimental knee osteoarthritis

OBJECTIVE

To determine trabecular and subchondral bone metabolic changes in experimental canine osteoarthritis (OA).

METHODS

OA was induced in 19 dogs by transection of the anterior cruciate ligament (ACL) of the right knee through a stab wound. Dogs were sacrificed at 8 (n=7) and 12 weeks (n=12) after surgery. Non-operated normal dogs (n=6) were used as controls. After sacrifice, samples were obtained from the weight-bearing area of medial tibial plateaus. Explants and cell cultures were prepared from subchondral and trabecular bone. Osteocalcin (Oc), cellular alkaline phosphatase (ALPase), urokinase plasminogen-activator (uPA), prostaglandin E2 (PGE2), metalloproteinase (MMP) and nitric oxide (NO) were measured using standard procedures.

RESULTS

ALPase production was significantly increased only at week 12 in subchondral and trabecular bone, while an increase in Oc was noted at week 8. uPA and MMP activity were increased significantly at week 12 in subchondral bone, while PGE2 levels were significantly higher in subchondral and trabecular bone at week 12 compared to normal. A decrease in NO production appeared late at week 12 in trabecular bone, whereas NO levels from subchondral bone were significantly increased compared to normal at week 8.

DISCUSSION

Intense bone remodeling takes place in both subchondral and trabecular bone in the knee following ACL transection. This process seems to occur around week 12, although Oc and NO appeared to be involved earlier at 8 weeks. These results suggest that not only subchondral but also trabecular bone metabolism is altered in this OA model.

Effects of ibuprofen on molecular markers of cartilage and synovium turnover in patients with knee osteoarthritis

OBJECTIVE

The aim of this study was to evaluate the effect of ibuprofen on the urinary excretion of C-terminal crosslinking telopeptide of type II collagen (CTX-II) and urinary glucosyl galactosyl pyridinoline (Glc-Gal-PYD), two new molecular markers of cartilage and synovial tissue metabolism, respectively, in patients with knee osteoarthritis (OA).

METHODS

We studied 201 patients with knee pain and radiographic evidence of knee OA who were on treatment with non-steroidal anti-inflammatory drugs (NSAIDs) prior to study initiation. After an initial screening visit, patients were withdrawn from their pre-study NSAID and, following a flare of their OA symptoms, were randomised to ibuprofen (2400 mg/day) or placebo. Urinary CTX-II and Glc-Gal-PYD levels were measured at time of randomisation (baseline) and after 4-6 weeks of treatment.

RESULTS

After 4 to 6 weeks, urinary CTX-II (+17%, p = 0.023) and Glc-Gal-PYD (+10%, p = 0.020) increased significantly from baseline in the placebo group whereas marginal or no increase was observed in the ibuprofen group (CTX-II +2%, NS and Glc-Gal-PYD +4%, p = 0.045). For urinary CTX-II, the difference in the change from baseline between placebo and ibuprofen treated groups was significant (13%, p = 0.017). At baseline, urinary levels of CTX-II and Glc-Gal-PYD were higher in patients with knee swelling (n = 127) than in those without (n = 74) (p<0.02 for both markers). When patients were stratified according to presence or absence of knee swelling at baseline, the increases over 4-6 weeks of urinary CTX-II and Glc-Gal-PYD in the placebo group were restricted to patients with knee swelling (+22% from baseline, p = 0.001 and +12%, p = 0.011, for urinary CTX-II and Glc-Gal-PYD respectively). In patients with knee swelling who were treated with ibuprofen this increase was not observed and the difference from placebo was significant for urinary CTX-II (p = 0.014).

CONCLUSION

In patients with a flare of knee OA, specifically in patients with evidence of joint inflammation documented by knee swelling, there was a significant increase in markers reflecting cartilage and synovium metabolism that could partly be prevented by high doses of ibuprofen. These data suggest that patients with a flare of knee OA are characterised by increased cartilage and synovial tissue degradation, which may be partly prevented by high doses of NSAIDs.

Gelatinase activity in synovial fluid and synovium obtained from healthy and osteoarthritic joints of dogs

OBJECTIVE

To determine matrix metalloproteinase (MMP) activity in synovial fluid (SF) obtained from the joints of dogs with degenerative joint disease (DJD) secondary to various underlying conditions.

SAMPLE POPULATION

35 samples of SF obtained from 18 clinically normal (control) dogs and 34 samples of SF obtained from 17 dogs with DJD; dogs with DJD were from 2 populations (client-owned dogs and research dogs that had DJD secondary to the lysosomal storage disease mucopolysaccharidosis VII).

PROCEDURE

MMP activity in samples of SF was semiquantitatively examined by use of gelatin or casein zymography. Western blot analysis was performed by use of antibodies for MMP-2 and MMP-9. In addition, in situ MMP activity was observed in sections of synovial membrane obtained from healthy and osteoarthritic joints.

RESULTS

Samples of SF from osteoarthritic joints had higher MMP-2 activity and dramatically increased MMP-9 activity, compared with values for healthy joints. Substrate-overlay analyses indicated minimal gelatin-degrading activity in synoviocytes obtained from control dogs, whereas greater activity was seen in osteoarthritic synoviocytes, with additional activity in the underlying tissue.

CONCLUSIONS AND CLINICAL RELEVANCE

Higher MMP-2 activity and dramatic increases in MMP-9 activity were associated with the osteoarthritic state, even though MMP-2 activity was detected in healthy joints. This study expands information on MMP production in SF of osteoarthritic joints in other species and documents the similarity of MMP activity patterns regardless of the cause of DJD.

Arthroscopic evaluation of potential structure-modifying drug in osteoarthritis of the knee. A multicenter, randomized, double-blind comparison of tenidap sodium vs piroxicam

OBJECTIVE

To test the hypothesis that tenidap has a structure-modifying effect in human knee osteoarthritis.

DESIGN

STUDY

multicenter, prospective, randomized, double blind, 1 year duration.

PATIENTS

primary painful knee osteoarthritis (ACR criteria) of the medial tibiofemoral compartment, 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. STUDY MEDICATION: once daily dosage of either tenidap 40 mg, tenidap 120 mg or piroxicam 20mg. STUDY ENDPOINTS: bilateral extended weight-bearing X-rays and knee arthroscopy under local anaesthesia were done at entry and after 1 year. Joint space width was measured in millimeters at the narrowest point of the medial compartment. Chondropathy was scored by using reader's overall assessment (VAS score, 100mm) and Société Française d'Arthroscopie (SFA) score (0-100).

RESULTS

Patients (665) were randomized and 494 completed the study. After 1 year, intra-group radiological changes and radiological difference between both tenidap groups and the piroxicam group did not reach statistical significance. The intra-group arthroscopic deterioration of chondropathy was low, but statistically significant in the three study groups. However, there was no statistically significant difference between both tenidap groups and the piroxicam group.

CONCLUSIONS

This study failed to demonstrate any difference between the treatment arms with regard to the structural progression of medial knee osteoarthritis as measured by radiography and arthroscopy. Arthroscopy did, however, appears to be more sensitive in detecting disease progression than the weight-bearing radiographs with fully extended knees. This study shows that it is possible to complete a large international trial using arthroscopy as an outcome measure of articular cartilage.

Modulation of IL-1beta, IL-6, TNF-alpha and PGE(2) by pharmacological agents in explants of membranes from failed total hip replacement

Introduction and goal Proinflammatory cytokines and prostaglandin E(2) (PGE(2)) play an important role in the pathophysiology of osteolysis and implant loosening. The aim of this study was to evaluate the role of pharmacological agents in the inhibition of Interleukin-1 (IL-1), interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) and PGE(2) in explants of interface membranes from failed total hip replacements (fTHR). Material and methods Membranes from fTHR were retrieved (N=20) and explants were incubated for 72h in the absence or presence of tenidap at three different concentrations (5, 20 or 50 microg/ml) or diclofenac (125 microg/l). IL-1beta, IL-6, TNF-alpha, and PGE(2) levels were measured in the culture medium using ELISA Capture or EIA kits. Statistical analysis was done using the Mann-Whitney U-test. Results A statistically significant inhibition in IL-1beta synthesis was found at tenidap concentrations of 20 microg/ml (71.3%, P< 0.05) and 50 microg/ml (79.3%,P< 0.02). Tenidap reduced IL-6 levels by 90.4% at 20 microg/ml (P< 0.005) and 96.0% (P< 0.05) at 50 microg/ml. Tenidap also reduced the synthesis of TNF-alpha by 66.9% (P< 0.05) and 77.4% at concentrations of 20 microg/ml and 50 microg/ml. Tenidap had a marked suppressive effect of over 90% (P< 0.0001) on PGE(2) synthesis in all three concentrations. Diclofenac (125 microg/l) decreased PGE(2) production by 95% (P< 0.0001), but had no significant effect in IL-1beta, IL-6, and TNF-alpha levels in the culture medium. Conclusion The ability to simultaneously suppress the release of proinflammatory cytokines and PGE(2) may help control osteolysis and prevent aseptic loosening of THR. This effect could increase implant longevity and lead the way to the pharmacological treatment of this pathology.

Cyclooxygenase-2 modulates brain inflammation-related gene expression in central nervous system radiation injury

Although the contribution of cyclooxygenase-2 (COX-2) to peripheral inflammation is well documented, little is known about its role in brain inflammation. For this purpose we studied COX-2 expression in the mouse brain following ionizing radiation in vivo, as well as in murine glial cell cultures in vitro. The possible role of COX-2 in modulating brain inflammation was examined utilizing NS-398, a COX-2 selective inhibitor. Our results indicate that COX-2 is significantly induced in astrocyte and microglial cultures by radiation injury as well as in brain. Increased levels of prostaglandin E(2) in irradiated brain were reduced by NS-398. Moreover, NS-398 administration significantly attenuated levels of induction for the majority of inflammatory mediators examined, including TNFalpha, IL-1beta, IL-6, iNOS, ICAM-1, and MMP-9. In contrast, the chemokines MIP-2 and MCP-1 showed enhanced levels of induction following NS-398 administration. These results indicate that COX-2 modulates the inflammatory response in brain following radiation injury, and suggest the use of COX-2 selective inhibitors for the management of CNS inflammation.

Do NSAIDs affect the progression of osteoarthritis?

NSAIDs are widely used to alleviate the symptoms of OA. It remains controversial as to what effects these agents have on the progression of OA. In vitro studies showed several types of NSAIDs (e.g., sodium salicylate, indomethacin) inhibited the synthesis of cartilage matrix component, but some types of NSAIDs (e.g., aceclofenac, meloxicam, nimesulide) increased the matrix component synthesis and protected the chondrocytes against apoptosis, while others (e.g., piroxicam) had no effects. Studies in animal models verified that NSAIDs had favourable or detrimental action on OA progression, even the same NSAID (e.g., naproxen, tiaprofenic acid) had reverse effects on articular cartilage in different studies. Preliminary clinical trials revealed some NSAIDs such as indomethacin had a negative influence on joint structure, other NSAIDs such as diclofenac and naproxen had no acceleration of radiographic damage to OA within 2-years of treatment. So far, there are no convincing data to show the widely used NSAIDs and recommended selective COX-2 inhibitor have favourable effects on cartilage. Therefore, it is necessary and valuable to clarify the effects of these NSAIDs on cartilage in patients with OA using validated non-invasive methods such as MRI.

In vivo dual inhibition of cyclooxygenase and lipoxygenase by ML-3000 reduces the progression of experimental osteoarthritis: suppression of collagenase 1 and interleukin-1beta synthesis

OBJECTIVE

To study the therapeutic effectiveness of ML-3000, a new antiinflammatory drug that has balanced dual inhibitory activity against 5-lipoxygenase and cyclooxygenase, on the development of lesions in the experimental osteoarthritis (OA) dog model, and to determine the action of ML-3000 on the synthesis of collagenase 1 in cartilage and interleukin-1beta (IL-1beta) in synovial membrane.

METHODS

The anterior cruciate ligament of the right stifle joint of 21 mongrel dogs was sectioned with a stab wound. Dogs were divided into 3 groups: group 1 (n = 7) received placebo; groups 2 (n = 7) and 3 (n = 7) were treated with therapeutic dosages of oral ML-3000 at 2.5 mg/kg/day and 5 mg/kg/day, respectively. The dogs began receiving medication the day after surgery and were killed 8 weeks later. The size and grade of cartilage erosions on both the condyles and plateaus were evaluated, and the severity of the cartilage lesions and synovial inflammation was examined histologically. Levels of collagenase 1 in cartilage and IL-1beta in the synovial membrane were measured by immunohistochemistry. In addition, levels of prostaglandin E2 (PGE2) in the synovial fluid and leukotriene B4 (LTB4) in cultured synovial membrane explants were determined using specific enzyme immunoassays.

RESULTS

Serum levels of ML-3000 in treated dogs were within the therapeutic range. ML-3000 significantly decreased the size and grade of the cartilage lesions in tibials and plateaus, compared with placebo. At the histologic level, the severity of cartilage lesions was also decreased in the ML-3000-treated dogs versus the placebo-treated dogs in both the condyles and the plateaus. All 3 OA groups exhibited a notable and similar level of synovial inflammation. ML-3000 significantly decreased the level of PGE2 in synovial fluid and LTB4 production by synovium. It also markedly reduced the levels of collagenase 1 in cartilage and IL-1beta in synovial membrane.

CONCLUSION

ML-3000 significantly reduced the development of lesions in experimental dog OA. The drug acts by reducing the synthesis of the inflammation mediators PGE2 and LTB4 and catabolic factors such as collagenase 1 and IL-1beta, which are known to play an important role in the pathophysiology of OA lesions. The effect of the drug on catabolic factors could possibly be related to its inhibitory action on LTB4 synthesis.

Long-term temporal evaluation of ground reaction forces during development of experimentally induced osteoarthritis in dogs

OBJECTIVE

To describe changes in vertical ground reaction forces (GRF) over 48 months in dogs with osteoarthritis (OA) of the stifle joint induced by transection of a cranial cruciate ligament (CCL).

ANIMALS

12 clinically normal adult dogs.

PROCEDURE

Vertical GRF (eg, peak force and impulse) were determined prior to and 1, 2, 3, 6, 10, and 12 months after transection of the right CCL. In 7 dogs, data were also collected 24, 32, 38, 42, and 48 months after transection.

RESULTS

Vertical peak force and impulse were significantly decreased in the right hind limb at all times after transection, compared with baseline values. From 10 through 48 months after transection, vertical GRF remained essentially static. Ground reaction forces in the unoperated (left) hind limb also changed significantly during the study. Left vertical impulse significantly increased 3 months after transection, whereas at 24, 38, 42, and 48 months after transection, left vertical peak force was significantly decreased, compared with the baseline value. Mean intradog coefficients of variation (CV) for peak vertical force and impulse ranged from 738 and 9.32, respectively, 1 month after transection to 1.96 and 2.76, respectively, at 42 months.

CONCLUSIONS AND CLINICAL RELEVANCE

Vertical GRF in the affected hind limb equilibrated approximately 10 months after CCL transection. Prior to this, force transmission across the affected stifle joint changed significantly over time. Intradog CV were small, indicating that GRF may be an appropriate outcome measurement for evaluation of OA development induced by CCL transection in dogs.

Novel strategies for the treatment of osteoarthritis

Osteoarthritis is a worldwide heterogeneous group of conditions that leads to joint symptoms, which are associated with defective integrity of articular cartilage, in addition to related changes in the underlying bone at the joint margins. The prevalence of the disease after the age of 65 years, is about 60% in men and 70% in women. The aetiology of osteoarthritis is multifactorial, with the end result being mechanical joint failure and varying degrees of loss of joint function. The pathophysiological events associated with osteoarthritis are beginning to be understood. Essential inflammatory cytokines, such as IL-1beta and TNF-alpha, are involved initiating a vicious cycle of catabolic and degradative events in cartilage, mediated by metalloproteinases, which degrade cartilage extracellular matrix. The role of inflammation in the pathophysiology and progression of early osteoarthritis is supported further by the observation that C-reactive protein levels are raised in women with early knee osteoarthritis and higher levels predict those whose disease will progress. The synovium from osteoarthritis joints stains for IL-1beta and TNF-alpha. Nitric oxide, which exerts pro-inflammatory effects, is released during inflammation. Cartilage from patients with rheumatoid arthritis and osteoarthritis spontaneously produces nitric oxide in vitro. In experimental osteoarthritis, nitric oxide induces chondrocyte apoptosis, thus contributing to cartilage degradation. Hence unregulated nitric oxide production in humans plays a part in the pathophysiology of the disease. These recent observations suggest that therapy can now be targeted at specific sites of pathophysiological pathways involved in the pathogenesis of osteoarthritis. The novel strategies under consideration for the treatment of osteoarthritis can be divided into five main areas. These are COX-2 inhibitors, nitric oxide synthesis inhibitors and anti-oxidants, chondrocyte and bone growth promoters, metalloproteinase and cytokine inhibitors and gene therapy.

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

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

Pharmacotherapy and osteoarthritis

Therapy for osteoarthritis (OA) is aimed at relieving symptoms and at maximizing function. Therapies can be considered as either symptom modifying OA drugs (SMOADs) or as disease modifying OA drugs (DMOADs). Currently available agents fall into the category of SMOADs. Analgesic medications, particularly paracetamol and capsaicin, have proven efficacy in OA and are recommended first line therapies. Non-steroidal anti-inflammatory drugs (NSAIDs) do appear to provide extra symptomatic benefit for some patients but have greater toxicity. Newer generation NSAIDs may have safety advantages which remain to be confirmed in practice. Further therapies are being developed which aim to prevent cartilage damage and/or aid cartilage restoration, but these DMOADs remain in the experimental stage.