Reduction in the structural changes of experimental osteoarthritis by a nitric oxide inhibitor

Developing anti-inflammatory therapeutics for patients with osteoarthritis

OA is the most common joint disorder in the world, but there are no approved therapeutics to prevent disease progression. Historically, OA has been considered a wear-and-tear joint disease, and efforts to identify and develop disease-modifying therapeutics have predominantly focused on direct inhibition of cartilage degeneration. However, there is now increasing evidence that inflammation is a key mediator of OA joint pathology, and also that the link between obesity and OA is not solely due to excessive load-bearing, suggesting therefore that targeting inflammation in OA could be a rewarding therapeutic strategy. In this review we therefore re-evaluate historical clinical trial data on anti-inflammatory therapeutics in OA patients, highlight some of the more promising emerging therapeutic targets and discuss the implications for future clinical trial design.

On the predictive utility of animal models of osteoarthritis

Animal models of osteoarthritis are extensively used for investigating disease pathways and for preclinical testing of novel therapies. Their predictive utility, however, has often been questioned, mainly because preclinical efficacy of novel therapeutics is poorly translated in clinical trials. In the current narrative review, we consider the preclinical models that were used to support undertaking clinical trials for disease-modifying osteoarthritis drugs, and compare outcomes between clinical and preclinical studies. We discuss this in light of the 1999 Food and Drug Administration draft guidelines for industry for use in the development of drugs, devices, and biological products intended for the treatment of osteoarthritis, which raised five considerations on the usefulness of osteoarthritis models. We systematically discuss what has been learnt regarding these five points since 1999, with emphasis on replicating distinct risk factors and subtypes of human osteoarthritis, and on comprehensive evaluation of the disease in animals, including pathology of all joint tissues, biomarker analysis, and assessment of pain and joint function. Finally, we discuss lessons learnt and propose some recommendations for how the evidence from preclinical research might be strengthened with a view to improving success in clinical translation.

A dual role for NOTCH signaling in joint cartilage maintenance and osteoarthritis

Loss of NOTCH signaling in postnatal murine joints results in osteoarthritis, indicating a requirement for NOTCH during maintenance of joint cartilage. However, NOTCH signaling components are substantially increased in abundance in posttraumatic osteoarthritis in humans and mice, suggesting either a reparative or a pathological role for NOTCH activation in osteoarthritis. We investigated a potential dual role for NOTCH in joint maintenance and osteoarthritis by generating two mouse models overexpressing the NOTCH1 intracellular domain (NICD) within postnatal joint cartilage. The first mouse model exhibited sustained NOTCH activation to resemble pathological NOTCH signaling, whereas the second model had transient NOTCH activation, which more closely reflected physiological NOTCH signaling. Sustained NOTCH signaling in joint cartilage led to an early and progressive osteoarthritic-like pathology, whereas transient NOTCH activation enhanced the synthesis of cartilage matrix and promoted joint maintenance under normal physiological conditions. Through RNA-sequencing, immunohistochemical, and biochemical approaches, we identified several targets that could be responsible for NOTCH-mediated cartilage degradation, fibrosis, and osteoarthritis progression. These targets included components of the interleukin-6 (IL-6)-signal transducer and activator of transcription 3 (STAT3) and mitogen-activated protein kinase signaling pathways, which may also contribute to the posttraumatic development of osteoarthritis. Together, these data suggest a dual role for the NOTCH pathway in joint cartilage, and they identify downstream effectors of NOTCH signaling as potential targets for disease-modifying osteoarthritis drugs.

Effect of S-methylisothiourea, an inducible nitric oxide synthase inhibitor, in joint pain and pathology in surgically induced model of osteoarthritis

The aim of the present study was to evaluate in vivo modulatory effect of S-methylisothiourea (SMT), a preferential inhibitor of inducible nitric oxide synthase (iNOS) on pain and pathology in the surgical model of osteoarthritis (OA) in rats. The OA was produced by the anterior cruciate ligament transection (ACLT) and medial meniscectomy (MMx) of right knee. SMT was administered 1 day prior to the production of OA and continued up to day 42 postoperation. Mechanical hyperalgesia, thermal hyperalgesia, tail flick latency after repeated flexion and extension of OA knee and knee diameter of right knee were determined at weekly intervals. Serum levels of IL-1β, TNF-α and nitrite concentration were determined at the end of the experiment. Glycosaminoglycan (GAG) content, collagen content and histopathological evaluation of articular cartilage were also determined at the end of the experiment. SMT reduced mechanical hyperalgesia and the serum levels of IL-1β, TNF-α and nitrite. Further, SMT reduced the loss of GAG from articular cartilage. Microscopically, SMT reduced the severity of the cartilage lesion. The results indicate the effectiveness of SMT in attenuating the pain and pathology of experimental OA phase by reducing the production of nitric oxide and interleukin-1β and tumor necrosis factor-α, which are known to play a major role in the pathophysiology of OA.

The hallmarks of osteoarthritis and the potential to develop personalised disease-modifying pharmacological therapeutics

Osteoarthritis (OA) is an age-related condition and the leading cause of pain, disability and shortening of adult working life in the UK. The incidence of OA increases with age, with 25% of the over 50s population having OA of the knee. Despite promising preclinical data covering various molecule classes, there is regrettably at present no approved disease-modifying OA drugs (DMOADs). With the advent of next generation sequencing technologies, other therapeutic areas, in particular oncology, have experienced a paradigm shift towards defining disease by its molecular composition. This paradigm shift has enabled high resolution patient stratification and supported the emergence of personalised or precision medicines. In this review we evaluate the potential for the development of OA therapeutics to undergo a similar paradigm shift given that OA is increasingly being recognised as a heterogeneous disease affecting multiple joint tissues. We highlight the evidence for the role of these tissues in OA pathology as different "hallmarks" of OA biology and review the opportunities to identify and develop targeted disease-modifying pharmacological therapeutics. Finally, we consider whether it is feasible to expect the emergence of personalised disease-modifying medicines for patients with OA and how this might be achieved.

Urocortin protects chondrocytes from NO-induced apoptosis: a future therapy for osteoarthritis?

Osteoarthritis (OA) is characterized by a loss of joint mobility and pain resulting from progressive destruction and loss of articular cartilage secondary to chondrocyte death and/ or senescence. Certain stimuli including nitric oxide (NO) and the pro-inflammatory cytokine tumor necrosis factor α (TNF-α have been implicated in this chondrocyte death and the subsequent accelerated damage to cartilage. In this study, we demonstrate that a corticotrophin releasing factor (CRF) family peptide, urocortin (Ucn), is produced by a human chondrocyte cell line, C-20/A4, and acts both as an endogenous survival signal and as a cytoprotective agent reducing the induction of apoptosis by NO but not TNF-α when added exogenously. Furthermore, treatment with the NO donor S-nitroso-N-acetyl-D-L-penicillamine upregulates chondrocyte Ucn expression, whereas treatment with TNF-α does not. The chondroprotective effects of Ucn are abolished by both specific ligand depletion (with an anti-Ucn antibody) and by CRF receptor blockade with the pan-CRFR antagonist α-helical CRH(9-41). CRFR expression was confirmed by reverse transcription-PCR with subsequent amplicon sequence analysis and demonstrates that C-20/A4 cells express both CRFR1 and CRFR2, specifically CRFR1α and CRFR2β. Protein expression of these receptors was confirmed by western blotting. The presence of both Ucn and its receptors in these cells, coupled with the induction of Ucn by NO, suggests the existence of an endogenous autocrine/paracrine chondroprotective mechanism against stimuli inducing chondrocyte apoptosis via the intrinsic/mitochondrial pathway.

Key Pathways to Prevent Posttraumatic Arthritis for Future Molecule-Based Therapy

Joint injuries are common, especially among young adults aged 18 to 44 years. They are accompanied by a cascade of events that increase the risk of posttraumatic osteoarthritis (PTOA). Therefore, understanding of biological responses that predispose to PTOA should help in determining treatment modalities to delay and/or prevent the onset and progression of the disease. The vast majority of the literature pointed to chondrocyte death and apoptosis, inflammation and matrix damage/fragmentation being the earliest events that follow joint trauma. Together these events lead to the development of osteoarthritis-like focal cartilage lesions that if untreated have a tendency to expand and progress to fully developed disease. Currently, the only treatments available for joint trauma are surgical interventions. Experimental biologic approaches involve engineering of cartilage with the use of cells (stem cells or chondrocytes), juvenile or adult cartilage pieces, scaffolds, and various polymeric matrices. The major challenge for all of them is regeneration of normal functional mature hyaline cartilage that can sustain the load, resist compression, and most important, integrate with the host tissue. If the tissue is spontaneously repaired it fails to reproduce original structure and function and thus, may be more susceptible to re-injury. Thus, there is a critical need to develop novel molecular mechanism-based therapeutic approaches to biologic chondral and/or osteochondral repair. The focus of this review is on the earliest molecular and cellular manifestations of injury that can be grouped based on the following therapeutic options for PTOA: chondroprotection, anti-inflammatory, matrix protection, and matrix remodeling/matrix synthesis.

Effect of iNOS inhibitor S-methylisothiourea in monosodium iodoacetate-induced osteoathritic pain: implication for osteoarthritis therapy

Much information is available on the role of nitric oxide (NO) in osteoarthritis (OA). However, its role has not been studied in the monosodium iodoacetate (MIA)-induced model of osteoarthritic pain. The present study was undertaken in rats to investigate the effect of iNOS inhibitor S-methylisothiourea (SMT) in MIA-induced osteoathritic pain and disease progression in rats. Osteoarthritis was produced by single intra-articular injection of the MIA in the right knee joint on day 0. Treatment groups were orally gavazed with different doses of SMT (10, 30 and 100mg/kg) and etoricoxib (10mg/kg) daily for 21 days. On days 0, 3, 7, 14 and 21, pain was measured and histopathology of right knee joint was done on day 21. SMT produced analgesia in a dose-dependent manner as shown by mechanical, heat hyperalgesia, knee vocalization, knee squeeze test, and spontaneous motor activity test. SMT reduced NO production in synovial fluid. Histopathological findings indicated that SMT reduced disease progression as evident from complete cartilage formation in rats treated with SMT at 30 mg/kg. In conclusion, the results indicate that SMT attenuates the MIA-induced pain and histopathological changes in the knee joint. The antinociceptive and antiarthritic effects of SMT were mediated by inhibiting cartilage damage and suppression of NO in synovial fluid. It is suggested that SMT has potential as a therapeutic modality in the treatment of osteoarthritis.

Nutritional care for aging cats and dogs

Veterinarians need to be prepared to provide nutritional advice for healthy pets as well as for pets that are ill. Before instituting a dietary change in any patient, especially an older dog or cat, a nutritional evaluation should be completed. This should include an evaluation of the patient, the current diet, and feeding management. Diets should be appropriate to the unique needs of the individual patient. Many diseases in senior pets are “diet-sensitive” meaning that diet can play a role in managing the effects of the disease. Common examples discussed include cognitive dysfunction of aging, osteoarthritis, and obesity.

Hypoxia, RONS and energy metabolism in articular cartilage

OBJECTIVE

Increased pro-inflammatory cytokines and reactive oxygen and nitrogen species (RONS) occur in osteoarthritis (OA). Oxygen tension can alter the levels of RONS induced by interleukin-1 (IL-1). RONS such as nitric oxide (NO) can alter energy metabolism. The aim of this study was to determine if oxygen tension alters energy metabolism, in articular cartilage, in response to IL-1 or NO and to determine if cell death occurred.

DESIGN

Porcine articular chondrocytes were incubated with IL-1 or the NO donor NOC-18 for 48 h in either 1, 5 or 20% O(2). Adenosine triphosphate (ATP) levels were measured and immunoblots for adenosine monophosphate-activated protein kinase (AMPK) were done. Protein translation was measured by S6 activation. Senescence and autophagy were determined by increased caveolin or conversion of LC3-I to LC3-II respectively.

RESULTS

One percent O(2) significantly reduced ATP levels compared with 20% O(2). Five percent O(2) significantly increased ATP levels compared with 20% O(2). One percent O(2) significantly increased phospho-AMPK (pAMPK) protein expression compared with 5 or 20% O(2). Oxygen tension had no effects on pS6, caveolin or LC3-II levels. IL-1-induced NO production was significantly reduced with decreased oxygen tension, and significantly reduced ATP levels at all oxygen tensions, but pAMPK was only significantly increased at 5% O(2). IL-1 significantly reduced pS6 at all oxygen tensions. IL-1 had no effects on caveolin and significantly increased LC3-II at 20% O(2) only. NOC-18 significantly reduced ATP levels at all oxygen tensions, and significantly increased pAMPK at 5% O(2) only, and significantly decreased pAMPK at 1% O(2). NOC-18 significantly reduced pS6 at 1% O(2) and significantly increased caveolin at 5% O(2), and LC3-II at 1% O(2).

CONCLUSION

Our data suggest 5% O(2) is optimal for energy metabolism and protective to some effects of IL-1 and NO. NO has the greatest effects on ATP levels and the induction of autophagy at 1% O(2).

Systematic review of the management of canine osteoarthritis

This review assesses the evidence for the efficacy of therapies used in the management of osteoarthritis in dogs on the basis of papers published in peer-reviewed journals in English between 1985 and July 2007. Sixty-eight papers were identified and evaluated. They considered four alternative therapies, one use of functional food, two intra-articular agents, six nutraceutical agents, 21 pharmacological agents, two physical therapies, three surgical techniques and two combinations of weight control. There was a high level of comfort (strong evidence) for the efficacy of carprofen, firocoxib and meloxicam, and a moderate level of comfort for the efficacy of etodolac in modifying the signs of osteoarthritis. There was a moderate level of comfort for the efficacy of glycosaminoglycan polysulphate, licofelone, elk velvet antler and a functional food containing green-lipped mussel for the modification of the structures involved in the disease. There was weak or no evidence in support of the use of doxycycline, electrostimulated acupuncture, extracorporeal shockwave therapy, gold wire acupuncture, hyaluronan, pentosan polysulphate, P54FP (extract of turmeric), tiaprofenic acid or tibial plateau levelling osteotomy.

Oxidative DNA damage in osteoarthritic porcine articular cartilage

Osteoarthritis (OA) is associated with increased levels of reactive oxygen species. This study investigated if increased oxidative DNA damage accumulates in OA articular cartilage compared with non-OA articular cartilage from pigs with spontaneous OA. Additionally, the ability of nitric oxide (NO) or peroxynitrite (ONOO(-)) induced DNA damage in non-OA chondrocytes to undergo endogenous repair was investigated. Porcine femoral condyles were graded for the stage of OA, macroscopically by the Collins Scale, and histologically by the modified Mankin Grade. Levels of DNA damage were determined in non-OA and OA cartilage, using the comet assay. For calibration, DNA damage was measured by exposing non-OA chondrocytes to 0-12 Gray (Gy) of X-ray irradiation. Non-OA articular chondrocytes were treated with 0-500 microM of NO donors (NOC-18 or SIN-1), and DNA damage assessed after treatment and 5 days recovery. A significant increase (P < 0.01) in oxidative DNA damage occurred in OA chondrocytes in joints with Mankin Grades 3 or greater, compared to non-OA chondrocytes. The percentage of nuclei containing DNA damage increased significantly (P < 0.001) from early to late grades of OA. An increase of approximately 0.65-1.7 breaks/1,000 kb of DNA occurred in OA, compared to non-OA nuclei. NOC-18 or SIN-1 caused significant DNA damage (P < 0.001) in non-OA chondrocytes that did not undergo full endogenous repair after 5 days (P < 0.05). Our data suggest significant levels of oxidative DNA damage occur in OA chondrocytes that accumulates with OA progression. Additionally, DNA damage induced by NO and ONOO(-) in non-OA chondrocytes does not undergo full endogenous repair.

Animal models of osteoarthritis: lessons learned while seeking the "Holy Grail"

PURPOSE OF REVIEW

Difficulties in studying osteoarthritis in humans that stem from both the low sensitivity of diagnostic tools and the low availability of diseased tissues explain why research on animal models remains highly dynamic. This review will summarize the recent advances in this field.

RECENT FINDINGS

With regard to the etiology of osteoarthritis, synovial macrophages mediate osteophyte formation, whereas increased ligament laxity could be responsible for spontaneous osteoarthritis in guinea pigs. The concomitant changes in subchondral bone and cartilage reported in several models, and the structure-modifying effects of some bone inhibitors have confirmed the importance of bone in osteoarthritis. With regard to cartilage pathobiology, ADAMTS-5 is the major aggrecanase responsible for cartilage destruction, whereas inadequate control of oxidative stress and decreased expression of transforming growth factor-beta receptors could predispose to osteoarthritis. New models include a postmenopausal rat model, the groove model and a joint-specific bone morphogenetic receptor-deficient mouse. The iodoacetate model was also validated as the first pain model of osteoarthritis.

SUMMARY

In view of the multiple animal models available, there is a need to reach a consensus on one or several gold standard animal model(s). New studies indicate that important differences in therapeutic response exist between young and old animals, and between spontaneous and surgical models, suggesting that not all models are adequate models of osteoarthritis.

The development of posttraumatic arthritis after articular fracture

Posttraumatic arthritis (PTA) is one of the most frequent causes of disability after trauma involving weight-bearing joints and is estimated to be responsible for approximately 10% of the 21 million Americans who have osteoarthritis. Despite a number of similarities in the pathology and end-stage disease of PTA with primary osteoarthritis, the mechanisms involved in the onset and progression of joint degeneration after articular fracture are poorly understood. The largest area of study regarding articular fractures and the development of arthritic changes has focused on the role of adequate surgical reduction of the articular surfaces. However, it is now apparent that a number of complex and interacting biomechanical, biochemical, and, possibly, genetic factors contribute to the development of osteoarthritic changes in the joint after joint trauma, ranging from the cell and molecular level to the joint and systemic level. In this paper, we discuss the potential roles of the initial impact and fracture as well as the subsequent alterations in joint loading, biomechanical and metabolic properties of the cartilage, local and systemic inflammatory cytokines, and viability of chondrocytes in the progression of PTA. An improved understanding of the mechanisms involved in the development of PTA will hopefully lead to the improvement of surgical and nonsurgical therapies for this disease.

Interaction between inhibitors of inducible nitric oxide synthase and cyclooxygenase in adjuvant-induced arthritis in female albino rats: an isobolographic study

We studied the interaction of S-methylisothiourea (a selective inducible nitric oxide synthase inhibitor) with rofecoxib (a selective cyclooxygenase-2 inhibitor) and mefenamic acid (a non-selective cyclooxygenase inhibitor) in adjuvant-induced arthritis in female albino Wistar rats, applying the isobolographic analysis. Each drug was effective in reducing the progressive increase in paw volume less than 50% except rofecoxib, when used alone. Log dose-response curve was obtained for each drug along with the corresponding ED(25). Following isobolographic analysis, combination of S-methylisothiourea with rofecoxib and mefenamic acid revealed supra-additive or synergistic interaction. Experimental ED(25) of the combinations was significantly lower than the theoretical ED(25) of the corresponding drug combination which substantiated the synergistic type of interaction between inducible nitric oxide synthase and cyclooxygenase in adjuvant-induced arthritis in female albino rats. Results suggest that NO regulates the cyclooxygenase enzyme activity as the activity of cyclooxygenase enzymes in the LPS-stimulated leukocyte lysates was significantly low or hardly detectable in the presence of varying concentrations of S-methylisothiourea. Simultaneous inhibition of inducible nitric oxide synthase and cyclooxygenase appears to offer an alternative approach for ameliorating the progression of arthritis.

Calcium crystal deposition diseases: update on pathogenesis and manifestations

Basic calcium phosphate (BCP) and calcium pyrophosphate dihydrate crystals are the most common types of pathologic calcium-containing crystals. Although these crystals long have been associated with a variety of rheumatic syndromes, recent evidence implicates BCP crystals in the pathogenesis of breast cancer and atherosclerosis. Although understanding of molecular mechanisms involved in generating these pathologic effects has been advanced significantly in recent years, they still are understood incompletely. Such advances are essential to the ongoing search for effective therapies for crystal-associated diseases.

Prospects for disease modification in osteoarthritis

Osteoarthritis (OA) can be a progressive, disabling disease, leading to diminished quality of life, and, for over 500,000 individuals annually in the US, total joint replacement. The etiology of OA will vary among individuals, with potential roles for systemic factors (such as genetics and obesity) as well as for local biomechanical factors (such as muscle weakness, joint laxity and traumatic injury). Joint deterioration occurs over extended periods of time, and the diverse molecular mechanisms that mediate pathogenic events of early, mid and late disease are not yet fully understood. The success of biologic therapies in the treatment of rheumatoid arthritis has demonstrated that the blockade of a single dominant cytokine or regulatory molecule can prevent cartilage destruction in a complex disease, and has raised expectations that mechanism-based treatments could also be developed for patients with OA. In this review, we will address the biological mechanisms that mediate structural damage in OA and examine current targets that are candidates for disease modification. The challenges to drug development and the obstacles to disease modification strategies will also be addressed.

Basic calcium phosphate crystals: pathways to joint degeneration

PURPOSE OF REVIEW

Basic calcium phosphate crystals have long been associated with rheumatic syndromes. Although an understanding of the molecular mechanisms involved in generating these pathological effects has been significantly advanced in recent years, it is still incomplete.

RECENT FINDINGS

Basic calcium phosphate crystals have been shown to increase prostaglandin E(2) production in human fibroblasts, mediated by the induction of both cyclooxygenases 1 and 2. Basic calcium phosphate crystals have also been found to upregulate IL-1beta in fibroblasts and chondrocytes. The upregulation of inducible nitric oxide synthase and stimulation of nitric oxide production in chondrocytes by octacalcium phosphate crystals has been demonstrated. The involvement of protein kinase C isoforms in basic calcium phosphate crystal-mediated matrix metalloproteinase 1 and 3 expression in human fibroblasts has been clarified. Two pathways are involved: protein kinase Calpha mediates the calcium-dependent pathway, whereas protein kinase Cmu activates the extracellular-regulated kinase pathway in a calcium-independent cascade. In addition, basic calcium phosphate crystals activate the transcription factor Egr-1, an effect that may contribute to the mitogenic effect of these crystals on fibroblasts.

SUMMARY

Recent findings have emphasized the potential for basic calcium phosphate crystals to stimulate the production of a variety of inflammatory mediators such as prostaglandin E(2), nitric oxide, IL-1beta and matrix metalloproteinases, and have helped to elucidate the mechanisms of these effects. Such advances are essential for the ongoing search for effective therapies for basic calcium phosphate crystal-associated diseases.

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.

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.

Arthroscopy -- a potential "gold standard" for the diagnosis of the chondropathy of early osteoarthritis

OBJECTIVES

The aims of this study were to: 1. Evaluate the performance of arthroscopy for the diagnosis of chondropathy and to compare it to that of direct non-arthroscopic assessments; 2. Determine intra-observer reliability of arthroscopic assessments; 3. Evaluate the effects of the arthroscopic video quality and probing upon diagnostic performance.

DESIGN

The ovine medial meniscectomy (MMx) model of early osteoarthritis (OA) was used assuming that pre-MMx articular cartilage (AC) was "normal" and post-MMx AC "chondropathic". Video recordings of arthroscopic assessments of each stifle compartment were evaluated. Scores were given for the quality of the video and the amount of probing. The diagnostic performances of dynamic shear modulus (G), light microscopic assessment and superficial zone collagen birefringence assessments were evaluated and compared to that of arthroscopy. Intra-observer reliability of arthroscopic assessments was also evaluated.

RESULTS

Arthroscopic assessments had high sensitivity (91-100%), specificity (62-88%) and accuracy (75-93%) for the diagnosis of chondropathy 16 weeks after MMx. Arthroscopy compared favourably with the direct non-arthroscopic assessments in the lateral compartment and was found to have extremely high intra-observer reliability (kappa 0.78-1.00). The quality of arthroscopic video recordings and the amount of probing did not significantly influence accuracy or reliability.

CONCLUSIONS

Arthroscopy performs as well as direct non-arthroscopic assessments of AC for diagnosis of early OA. These results suggest that arthroscopy can be used as a "gold standard" for the validation of non-invasive assessments like magnetic resonance imaging and that arthroscopic diagnosis can be based on small amounts of video footage without AC probing.

Disposition and pharmacokinetics of L-N6-(1-iminoethyl)lysine-5-tetrazole-amide, a selective iNOS inhibitor, in rats

The metabolism, pharmacokinetics, tissue distribution, and excretion of L-N6-(1-iminoethyl)lysine-5-tetrazole-amide (L-NIL-TA), a selective inducible NO synthase (iNOS) inhibitor, were investigated in rats. [(14)C]L-NIL-TA is extensively metabolized after either oral or IV administration with a minor amount (<1%) excreted as the prodrug. L-NIL-TA is metabolized via a single hydrolysis pathway to form the active drug, L-N6-(1-iminoethyl)lysine (L-NIL). The oxidative deamination of 2-amino group of L-NIL forms a 2-keto metabolite (M5), which further loses carbon dioxide to yield a carboxylic acid metabolite (M6). Acetylation of L-NIL and M5 resulted in the formations of metabolites M7 and M4, respectively. Complete recovery of the radioactive dose was achieved after either oral (91.2% in urine and 4.66% in feces) and IV (99.3% in urine and 5.11% in feces) administration. L-NIL-TA-related material was extensively distributed to the tissues, with the highest concentration of radioactivity being found in muscle. Maximal concentration of radioactivity was reached between 0.5 and 1 h post-dose in the majority of tissues, with the exception of muscle and skin where the maximal concentrations were achieved at 8 h post-dose.

Accuracy and reliability of arthroscopic estimates of cartilage lesion size in a plastic knee simulation model

PURPOSE

The goal of the study was to determine the accuracy and reliability of arthroscopic percent area estimates in a plastic knee simulation model. A second goal was to determine the effect of lesion location within the knee and lesion size on accuracy and reliability.

TYPE OF STUDY

Cross-sectional study of arthroscopic estimates of cartilage lesion size.

METHODS

Three experienced arthroscopists performed 3 sets arthroscopic percent area estimates in 5 different plastic knees. Each knee had lesions drawn on 5 surfaces (patellar, medial and lateral femoral condyle, medial and lateral tibial plateaus). Accuracy and reliability were studied using Bland and Altman limits of agreement (LOA) and intraclass correlation coefficients.

RESULTS

There was a strong tendency to overestimate lesion size by over 100% on the femoral and patellar surfaces. Intraobserver and interobserver reliabilities were generally poor. The range for the 95% LOA (+/- 1.96 standard deviation [SD] of the difference scores) between repeated measurements was almost 6 times the size of the lesion itself. Reliability of estimates was poorest for the largest lesions and worse at femoral, lateral tibial, and patellar sites.

CONCLUSIONS

Assessments of arthroscopic measurements using LOA found that accuracy and reliability were generally poor, although results were better at the medial tibial plateau and for smaller lesions. In spite of these problems, arthroscopy remains a promising measurement tool because it permits physical assessment of cartilage integrity. This study sets the foundations for improvement in techniques of arthroscopic measurement of cartilage lesion size.

Intercellular signaling as a cause of cell death in cyclically impacted cartilage explants

Recently, in vitro cartilage studies have shown that impact loading can produce structural damage and osteoarthritis-like changes, including tissue swelling, collagen denaturation, and cell death.

OBJECTIVE

This study was to determine whether a signal for cell death moves through the cartilage matrix, resulting in the spread of cell death over time from impacted to unimpacted regions.

DESIGN

Cyclic impacts were applied to the 2 mm core of 4 mm cartilage discs. Post-impact culturing extended for 3, 6 or 21 days and occurred in one of two ways. In one, discs were cultured intact. In the second, cores were removed immediately after cessation of impact and cores and rings cultured separately. Cells in apoptosis and later stage necrosis were monitored using the TUNEL assay.

RESULTS

The extent of cell death in impacted samples increased with increased duration of post-impact culturing. At the early time, the majority of cell death was located in the regions of direct impact whereas after extended culture, the extent of cell death was similar in the surrounding unimpacted regions and in the impacted core region. However, the physical separation of the impacted core from the surrounding, non-impacted ring regions immediately after impact, and prior to independent culture, kept the level of cell death in the surrounding ring close to control levels, even after 21 days of incubation.

DISCUSSION

These findings indicate that soluble intercellular signalling is involved in the spreading of cell death through the cartilage matrix, and that its effects can be prevented by physical isolation of the surrounding ring from the impacted core.

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.

Peroxisome proliferator--activated receptor gamma activators inhibit interleukin-1beta-induced nitric oxide and matrix metalloproteinase 13 production in human chondrocytes

OBJECTIVE

To determine the effects of peroxisome proliferator-activated receptor gamma (PPARgamma) agonists on interleukin-1 (IL-1) induction of nitric oxide (NO) and matrix metalloproteinase 13 (MMP-13) in human chondrocytes.

METHODS

PPARgamma expression and synthesis in human chondrocytes were determined by reverse transcriptase-polymerase chain reaction (RT-PCR) and immunohistochemistry, respectively. Chondrocytes were cultured with IL-1beta, tumor necrosis factor alpha (TNFalpha), and IL-17 in the presence or absence of PPARgamma agonists, and NO and MMP-13 synthesis and expression levels were measured. Transient transfection experiments were performed with the 7-kb inducible NO synthase (iNOS) and 1.6-kb MMP-13 human promoters, as well as with the PPARgamma expression vector and the activator protein 1 (AP-1) and nuclear factor kappaB (NF-kappaB) reporter constructs.

RESULTS

RT-PCR and immunohistochemical analysis revealed that human chondrocytes expressed and produced PPARgamma. Treatment of chondrocytes with PPARgamma ligands BRL 49653 and 15-deoxy-delta12,14-prostaglandin J2 (15d-PGJ2), but not with PPARalpha ligand Wy 14643, decreased IL-1beta-induced NO and MMP-13 production in a dose-dependent manner. In addition, both iNOS and MMP-13 messenger RNA were inhibited in the presence of 15d-PGJ2. The inhibitory effect of PPARgamma activation was not restricted to IL-1beta, since TNFalpha- and IL-17-induced NO and MMP-13 production were also inhibited by 15d-PGJ2. In transient transfection experiments, we showed that a constitutively active form of mitogen-activated protein kinase kinase kinase 1 (AMEKK-1) induced the MMP-13 and iNOS human promoter activity. This process was reduced by 15d-PGJ2 and further inhibited by cotransfection with a PPARgamma expression vector. Similarly, in a PPARgamma-dependent manner, 15d-PGJ2 inhibited deltaMEKK-1-induced AP-1- and NF-kappaB-luciferase reporter plasmid activation.

CONCLUSION

The findings of this study demonstrate that PPARgamma agonists inhibit IL-1beta induction of both NO and MMP-13 in human chondrocytes. The inhibition occurs at least at the transcriptional level through a PPARgamma-dependent pathway, probably by interfering with the activation of AP-1 and NF-kappaB.

Reduced NO accumulation in arthrotic cartilage by exposure to methylene blue

Nitric oxide (NO) appears to be a final common inflammation mediator of cartilage degradation. Halting the pathological formation of excessive NO, by suppressing the inducible NO synthase (iNOS) activity, may help to preserve cartilage integrity. We used fresh ex-vivo human articular cartilage explants from normal and arthrotic joints for assessment of NO levels, as determined by its nitrite degradation products and nitric oxide synthase expression. We measured matrix proteoglycan content, assessed by image analysis of alcian blue staining, and proteoglycan synthesis, assessed by sulfate incorporation into proteoglycans. The effect of methylene blue, a nitric oxide synthase inhibitor, on matrix preservation was evaluated. Cartilage discs in vitro, derived from normal appearing joints, secreted about one tenth as much NO compared to discs derived from arthrotic cartilage. Cartilage explants showed a time-dependent reduction in the amount of aggrecan within the cartilaginous matrix. Addition of methylene blue to the growth medium lowered nitric oxide accumulation and prevented matrix degradation in the cultured cartilage discs. The cartilage matrix preservation effect was mediated through downregulation of all three isoforms of NOS, i.e., the neuronal NOS, endothelial NOS and inducible NOS and upregulation of TGF beta receptor in the chondrocytes. Our findings indicate that inhibition of NOS activity preserves cartilage matrix in vitro.

Mitochondrial oxidative phosphorylation is a downstream regulator of nitric oxide effects on chondrocyte matrix synthesis and mineralization

OBJECTIVE

Increased chondrocyte nitric oxide (NO) and peroxynitrite production appears to modulate decreased matrix synthesis and increased mineralization in osteoarthritis (OA). Because NO inhibits mitochondrial respiration, this study was undertaken to directly assess the potential role of chondrocyte mitochondrial oxidative phosphorylation (OXPHOS) in matrix synthesis and mineralization.

METHODS

We studied cultured human articular chondrocytes and immortalized costal chondrocytes (TC28 cells). We also assessed the effects of antimycin A and oligomycin (inhibitors of mitochondrial complexes III and V, respectively) on chondrocyte mitochondrial respiration, ATP synthesis, and inorganic pyrophosphate (PPi) generation, and the mineralizing potential of released matrix vesicles (MV).

RESULTS

Articular chondrocytes and TC28 cells respired at comparable rates. Peroxynitrite and NO donors markedly suppressed respiration and ATP generation in chondrocytes. Because NO exerts multiple effects on chondrocytes, we investigated the primary functions of mitochondrial respiration and OXPHOS. To do so, we identified minimally cytotoxic doses of antimycin and oligomycin, which both induced intracellular ATP depletion (by 50-80%), attenuated collagen and proteoglycan synthesis, and blocked transforming growth factor beta from increasing intracellular ATP and elaboration of PPi, a critical inhibitor of hydroxyapatite deposition. Antimycin and oligomycin also abrogated the ability of the ATP-hydrolyzing enzyme plasma cell membrane glycoprotein 1 (PC-1) to increase chondrocyte PPi generation. Finally, MV from cells treated with antimycin or oligomycin contained less PPi and precipitated >50% more 45Ca.

CONCLUSION

Chondrocyte mitochondrial reserve, as NO-sensitive mitochondrial respiration-mediated ATP production, appears to support matrix synthesis and PPi elaboration and to regulate MV composition and mineralizing activity. NO-induced depression of chondrocyte respiration could modulate matrix loss and secondary cartilage mineralization in OA.

Anabolic and destructive mediators in osteoarthritis

Osteoarthritis is a joint disease that is characterized by focal degradation of articular cartilage. In addition to the degeneration of articular cartilage, attempts at repair are found in the affected tissue. Cartilage cells (chondrocytes) play a key role, not only in the destructive process, but also in the repair response. It has become apparent that anabolic and catabolic mediators, released from chondrocytes themselves or from other joint cells, drive both destructive and repair activities in the osteoarthritic joint.