Cartilage matrix metabolism in osteoarthritis: markers in synovial fluid, serum, and urine

How Do Cartilage Lubrication Mechanisms Fail in Osteoarthritis? A Comprehensive Review

Cartilage degeneration is a characteristic of osteoarthritis (OA), which is often observed in aging populations. This degeneration is due to the breakdown of articular cartilage (AC) mechanical and tribological properties primarily attributed to lubrication failure. Understanding the reasons behind these failures and identifying potential solutions could have significant economic and societal implications, ultimately enhancing quality of life. This review provides an overview of developments in the field of AC, focusing on its mechanical and tribological properties. The emphasis is on the role of lubrication in degraded AC, offering insights into its structure and function relationship. Further, it explores the fundamental connection between AC mechano-tribological properties and the advancement of its degradation and puts forth recommendations for strategies to boost its lubrication efficiency.

MMP-3 in the peripheral serum as a biomarker of knee osteoarthritis, 40 years after open total knee meniscectomy

BACKGROUND

To explore potential biomarkers in a meniscectomy-induced knee osteoarthritis model, at forty years after meniscectomy.

METHODS

We carried out a forty-year study of 53 patients who, as adolescents, underwent open total meniscectomy and assessed two potential synovial and serum biomarkers, namely glycosaminoglycan (GAG) and matrix metalloproteinase-3 (MMP-3). Of the 30 patients available for review, 8 had contralateral knee operations and were excluded. Of the remaining 22 patients, 17 had successful operated knee synovial fluid aspirations and 8 also had successful contralateral control knee aspirations. GAG and MMP3 levels in the synovial fluid and peripheral serum was measured using Alcian blue precipitation and ELISA quantification, respectively. Patients also had their knee radiographs assessed and their radiographic osteoarthritis classified as per the Kellgren-Lawrence and Ahlbӓck systems.

RESULTS

At forty years after meniscectomy, synovial MMP-3 levels remain increased (p = 0.0132) while GAG levels were reduced (p = 0.0487) when compared to controls and these two levels correlate inversely. Furthermore, levels of synovial MMP-3 significantly correlated (p = 0.0032, r = 0.7734; p = 0.0256, r = 0.5552) and GAG levels significantly inversely correlated (p = 0.0308, r = - 0.6220; p = 0.0135, r = - 0.6024), respectively, with both radiological scoring systems. Interestingly, we found that the levels of serum MMP-3 correlated only with the synovial fluid levels of MMP-3 in the operated knee and not with the non-operated joint (p = 0.0252, r = 0.7706 vs. p = 0.0764, r = 0.6576). Multiple regression analysis for patient's quality of life based on these biomarkers revealed an almost perfect result with an R2 of 0.9998 and a p value = 0.0087.

CONCLUSION

Our results suggest that serum levels of MMP3 could be used as a potential biomarker for knee osteoarthritis, using a simple blood test. Larger cohorts are desirable in order to prove or disprove this finding.

Relationship between weight loss in obese knee osteoarthritis patients and serum biomarkers of cartilage breakdown: secondary analyses of a randomised trial

OBJECTIVE

To explore effects of weight loss and maintenance on serum cartilage biomarkers denaturation neoepitope for Collagen2 (Coll2-1) and Fibulin3 fragment (Fib3-2), as well as correlations between Coll2-1 and Fib3-2 and symptomatic improvement, in a knee osteoarthritis (KOA) population.

DESIGN

192 obese KOA patients followed a 16 week weight loss intervention and 52 weeks weight maintenance (ClinicalTrials.gov identifier: NCT00655941). Assessments were at 0, 8, 16 and 68 weeks. Serum Coll2-1 and Fib3-2 were determined with ELISA, and symptoms by the Knee Osteoarthritis Outcome Score (KOOS) questionnaire. Changes from week 0 and association between changes from baseline in body weight and Coll2-1, Fib3-2, and the 5 KOOS domains were assessed at all time points.

RESULTS

Coll2-1 changes from baseline showed a decrease at week 8 (P = 0.0002), no change at week 16 (P = 0.49), and an increase at week 68 (P = 0.036). Fib3-2 showed an increase from baseline at week 8 (P = 0.0015) and 16 (P < 0.0001), but none at week 68 (P = 0.23). No statistically significant correlations were found between changes in body weight and Coll2-1 and Fib3-2 at any time point (r < 0.05; P > 0.49). At all time-points there were significant positive correlations between changes from baseline in Coll2-1 and in KOOS_{Sports/Recreation} (week 8, 16, 68: r = 0.17; P = 0.03; r = 0.16; P = 0.04; and r = 0.17; P = 0.04, respectively).

CONCLUSION

The clinical improvement after a substantial weight loss and weight maintenance in KOA patients was not associated with decrease in markers of cartilage breakdown Coll2-1 or Fib3-2, even with indications of a slightly negative effect.

Modificazioni morfo-funzionali della cartilagine nella senescenza e nell'osteoartrosi

La cartilagine articolare è un tessuto connettivo avascolare, aneurale che ricopre le superfici articolari. La funzione di assorbimento delle sollecitazioni meccaniche, a protezione dell'osso subcondrale, rende la supeficie articolare idonea a sostenere il carico.

Le funzioni inerenti le modalità di assorbimento della sollecitazione meccanica, che fanno sì che la deformazione sia reversibile, dipendono in larga parte dalle caratteristiche della cartilagine, intesa come struttura altamente organizzata. Nell'osteoartrosi umana e nei suoi modelli animali l'alterazione strutturale dei proteoglicani cartilaginei rappresenta l'evento centrale.

Vengono discusse, alla luce delle acquisizioni più recenti, le implicazioni sulle proprieta fisico-chimiche e morfo-strutturali della cartilagine articolare riguardanti le caratteristiche di base dei proteoglicani, la struttura dei collageni, l'organizzazione della matrice extracellulare e le sue modificazioni nella senescenza ed in corso di osteoartrosi con le relative conseguenze sulle proprietà biomeccaniche del disco intervertebrale. Le conoscenze relative alle alterazioni della struttura proteoglicanica e lo sviluppo di nuovi metodi di determinazione dei markers biochimici del danno cartilagineo potrebbero migliorare la comprensione delle relazioni fra senescenza ed osteoartrosi, nonchè il riconoscimento delle modificazioni più precoci e la valutazione della risposta terapeutica.

Effect of a 16 weeks weight loss program on osteoarthritis biomarkers in obese patients with knee osteoarthritis: a prospective cohort study

OBJECTIVE

Changes in biomarkers for bone and cartilage in knee osteoarthritis (KOA) may reflect changes in tissue turnover induced by interventions. The aim of this study was to assess the effect on osteoarthritis biomarkers of an intensive weight loss intervention in obese KOA patients.

METHODS

192 obese KOA patients followed a 16 weeks weight loss intervention (ClinicalTrials.gov: NCT00655941). Serum Cartilage Oligomeric Matrix Protein (sCOMP), Urine C-terminal telopeptide of collagen type II (uCTX-II) and type I (uCTX-I) were determined by enzyme-linked immunoassay (ELISA) at baseline and after 16 weeks. Patient-reported symptoms were assessed by the Knee Injury and Osteoarthritis Outcome Score (KOOS) Questionnaire without the sports and recreation score (KOOS-4). Change from baseline was analyzed using Analysis of CoVariance (ANCOVA) adjusting for sex, age, and body mass index (BMI). Bivariate associations were analyzed using Spearman's test of rank correlation.

RESULTS

175 patients completed the treatment and lost mean 13.4 (95% CI: 12.5-14.4) kg. sCOMP concentration decreased on average 1.1 (95% CI: -1.5 to -0.8) U/L with a correlation to weight loss (r = -0.17, P = 0.028), but not to change in KOOS-4 (r = -0.13, P = 0.091). uCTX-II increased significantly, mean 69 (95% CI: 31-106) ng/mmol creatinine, with no relation to weight loss (P = 0.14). Change in uCTX-II was reversely related to change in KOOS-4 (r = -0.28, P = 0.0003). uCTX-I increased, mean 67 (95% CI: 47-87) μg/mmol creatinine, and correlated to weight loss (r = 0.22, P = 0.0007), while not to KOOS-4 (P = 0.93).

CONCLUSION

A rapid substantial weight loss in obese KOA patients was weakly, while significantly associated with a reduction in sCOMP, and increases in both uCTX-II and uCTX-I.

Characterization of the cartilage DNA methylome in knee and hip osteoarthritis

Objective

The aim of this study was to characterize the genome-wide DNA methylation profile of chondrocytes from knee and hip cartilage obtained from patients with osteoarthritis (OA) and hip cartilage obtained from patients with femoral neck fracture, providing the first comparison of DNA methylation between OA and non-OA hip cartilage, and between OA hip and OA knee cartilage.

Methods

The study was performed using the Illumina Infinium HumanMethylation450 BeadChip array, which allows the annotation of ∼480,000 CpG sites. Genome-wide methylation was assessed in chondrocyte DNA extracted from 23 hip OA patients, 73 knee OA patients, and 21 healthy hip control patients with femoral neck fracture.

Results

Analysis revealed that chondrocytes from the hip cartilage of OA patients and healthy controls have unique methylation profiles, with 5,322 differentially methylated loci (DMLs) identified between the 2 groups. In addition, a comparison between hip and knee OA chondrocytes revealed 5,547 DMLs between the 2 groups, including DMLs in several genes known to be involved in the pathogenesis of OA. Hip OA samples were found to cluster into 2 groups. A total of 15,239 DMLs were identified between the 2 clusters, with an enrichment of genes involved in inflammation and immunity. Similarly, we confirmed a previous report of knee OA samples that also clustered into 2 groups.

Conclusion

We demonstrated that global DNA methylation using a high-density array can be a powerful tool in the characterization of OA at the molecular level. Identification of pathways enriched in DMLs between OA and OA-free cartilage highlight potential etiologic mechanisms that are involved in the initiation and/or progression of the disease and that could be therapeutically targeted.

In vivo transport of Gd-DTPA2- into human meniscus and cartilage assessed with delayed gadolinium-enhanced MRI of cartilage (dGEMRIC)

Background

Impaired stability is a risk factor in knee osteoarthritis (OA), where the whole joint and not only the joint cartilage is affected. The meniscus provides joint stability and is involved in the early pathological progress of OA. Delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) has been used to identify pre-radiographic changes in the cartilage in OA, but has been used less commonly to examine the meniscus, and then using only a double dose of the contrast agent. The purpose of this study was to enable improved early OA diagnosis by investigate the temporal contrast agent distribution in the meniscus and femoral cartilage simultaneously, in healthy volunteers, using 3D dGEMRIC at two different doses of the contrast agent Gd-DTPA^2-.

Methods

The right knee in 12 asymptomatic volunteers was examined using a 3D Look-Locker sequence on two occasions after an intravenous injection of a double or triple dose of Gd-DTPA^2- (0.2 or 0.3 mmol/kg body weight). The relaxation time (T₁) and relaxation rate (R₁ = 1/T₁) were measured in the meniscus and femoral cartilage before, and 60, 90, 120 and 180 minutes after injection, and the change in relaxation rate (ΔR₁) was calculated. Paired t-test and Analysis of Variance (ANOVA) were used for statistical evaluation.

Results

The triple dose yielded higher concentrations of Gd-DTPA^2- in the meniscus and cartilage than the double dose, but provided no additional information. The observed patterns of ΔR₁ were similar for double and triple doses of the contrast agent. ΔR₁ was higher in the meniscus than in femoral cartilage in the corresponding compartments at all time points after injection. ΔR₁ increased until 90-180 minutes in both the cartilage and the meniscus (p < 0.05), and was lower in the medial than in the lateral meniscus at all time points (p < 0.05). A faster increase in ΔR₁ was observed in the vascularized peripheral region of the posterior medial meniscus, than in the avascular central part of the posterior medial meniscus during the first 60 minutes (p < 0.05).

Conclusion

It is feasible to examine undamaged meniscus and cartilage simultaneously using dGEMRIC, preferably 90 minutes after the injection of a double dose of Gd-DTPA^2- (0.2 mmol/kg body weight).

Prediction of antiarthritic drug efficacies by monitoring active matrix metalloproteinase-3 (MMP-3) levels in collagen-induced arthritic mice using the MMP-3 probe

Active matrix metalloproteinase-3 (MMP-3) is a prognostic marker of rheumatoid arthritis (RA). We recently developed an MMP-3 probe that can specifically detect the active form of MMP-3. The aim of this study was to investigate whether detection and monitoring of active MMP-3 could be useful to predict therapeutic drug responses in a collagen-induced arthritis (CIA) model. During the period of treatment with drugs such as methotrexate (MTX) or infliximab (IFX), MMP-3 mRNA and protein levels were correlated with fluorescence signals in arthritic joint tissues and in the serum of CIA mice. Also, bone volume density and erosion in the knee joints and the paws of CIA mice were measured with microcomputed tomography (micro-CT), X-ray, and histology to confirm drug responses. In joint tissues and serum of CIA mice, strong fluorescence signals induced by the action of active MMP-3 were significantly decreased when drugs were applied. The decrease in RA scores in drug-treated CIA mice led to fluorescence reductions, mainly as a result of down-regulation of MMP-3 mRNA or protein. The micro-CT, X-ray, and histology results clearly showed marked decreases in bone and cartilage destruction, which were consistent with the reduction of fluorescence by down-regulation of active MMP-3 in drug-treated CIA mice. We suggest that the MMP-3 diagnostic kit could be used to detect and monitor the active form of MMP-3 in CIA mice serum during a treatment course and thereby used to predict the drug response or resistance to RA therapies at an earlier stage. We hope that monitoring of active MMP-3 levels in arthritis patients using the MMP-3 diagnostic kit will be a promising tool for drug discovery, drug development, and monitoring of drug responses in RA therapy.

Serum cartilage oligomeric matrix protein (COMP) in knee osteoarthritis: a novel diagnostic and prognostic biomarker

A case-control study was conducted to estimate the association of cartilage oligomeric matrix protein (COMP) with knee osteoarthritis (OA) and to examine the potential utility of COMP as a diagnostic and prognostic biomarker in early knee OA. The COMP levels were estimated in the blood sera of 150 subjects belonging to study group (n = 100) and control one (n = 50). Patients with confirmed clinical isolated knee OA diagnosed through American College of Rheumatology criteria were included and were without any other cause of knee pain. ELISA was used to determine the levels of COMP, interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α). The median (range) serum COMP levels were observed to be 1117.21 ng/ml (125.03-4209.75 ng/ml) in OA patients and 338.62 ng/ml (118-589 ng/ml) in control subjects with p < 0.001. The COMP levels of study group were negatively correlated (correlation factor -0.88) with disease duration and positively correlated with age, BMI, pain score and IL-1β with correlation factors 0.86, 0.63, 0.76, and 0.79, respectively with p < 0.001. Gender differentiation was found in study group with 52% higher COMP level in males as compared to that of females. There was no significant correlation of COMP levels with radiological grading, erythrocyte sedimentation rate (ESR), hemoglobin (Hb), and TNF-α. The serum COMP levels may be used as a diagnostic OA marker along with prognostic value in determining the patients at risk of rapidly progressing this debilitating joint disease. The serum COMP level remains significantly high in first 3 years of disease duration.

Association of plasma and synovial fluid interferon-γ inducible protein-10 with radiographic severity in knee osteoarthritis

OBJECTIVES

The objective of this study was to investigate interferon-γ inducible protein-10 (IP-10) concentrations in plasma and synovial fluid of patients with knee osteoarthritis (OA) and to analyze their relationship with disease severity.

DESIGN AND METHODS

Forty OA patients and 15 healthy controls were enrolled in this study. OA grading was performed according to the Kellgren-Lawrence criteria. IP-10 levels in plasma and synovial fluid were assessed using enzyme-linked immunosorbent assay.

RESULTS

Plasma IP-10 levels in the knee OA patients were significantly lower than those of controls (P=0.006). IP-10 levels in plasma were markedly higher with regard to paired synovial fluid (P<0.001). Furthermore, IP-10 concentrations in plasma and synovial fluid displayed significant inverse correlation with radiographic severity (r=-0.713, P<0.001 and r=-0.561, P<0.001, respectively). Subsequent analysis revealed that plasma IP-10 levels were positively correlated with synovial fluid IP-10 levels (r=0.424, P=0.006).

CONCLUSIONS

IP-10 levels in both plasma and synovial fluid were inversely associated with the severity of knee OA. Accordingly, IP-10 could serve as a biomarker for determining disease severity and might play a possible role in the pathophysiology of osteoarthritis.

Aggrecan and cartilage oligomeric matrix protein in serum and synovial fluid of patients with knee osteoarthritis

Aggrecan and cartilage oligomeric matrix protein (COMP) which are important degradation products of articular cartilage may be promising diagnostic markers in serum and/or synovial fluid for diagnosis of knee osteoarthritis (OA). Our objective was to measure serum and synovial fluid levels of aggrecan and COMP in patients with OA of the knee joint to find out if they could be of diagnostic value in OA and if their levels correlate with the clinical and radiological manifestations of the disease. Sixty-six patients suffering from primary knee OA with effusion (26 males and 40 females) were studied. Twenty individuals (six males and 14 females) with recent traumatic knee effusion matched for age and sex were chosen to serve as a control group. All subjects had thorough clinical and radiological (X-ray and MRI) evaluation. Aggrecan and COMP in serum and synovial fluid were measured by ELISA. Serum and synovial fluid aggrecan and COMP levels were significantly higher than the control. Serum and synovial fluid aggrecan and COMP levels were positively correlated with age, body mass index, disease duration, plain X-ray and MRI scores. In OA, serum and synovial fluid aggrecan and COMP levels are elevated and represent useful markers in the diagnosis. Moreover, these elevated levels positively correlated with radiological joint damage but not with clinical disease parameters. These markers have the potential to be used for monitoring articular cartilage destruction and response to different therapeutic modalities.

The influence of repeated arthrocentesis and exercise on matrix metalloproteinase and tumour necrosis factor a activities in normal equine joints

REASONS FOR PERFORMING STUDY

Matrix metalloproteinases (MMPs) and tumour necrosis factor alpha (TNF-alpha) may be useful as biomarkers of joint disease or inflammation. However, activity of both MMPs and TNF-alpha in synovial fluid (SF) may be influenced by nonpathological factors such as arthrocentesis or exercise.

OBJECTIVE

To investigate the influence of repeated arthrocentesis and exercise on MMP and TNF-alpha activities in SF from normal equine joints.

METHODS

SF was collected from the left metacarpophalangeal, radiocarpal and tarsocrural joints of 16 horses. Eight of these horses were subsequently subjected to an exercise programme on a treadmill and 8 were box-rested as controls. Arthrocentesis was repeated 14, 145, 17 and 24 days after the start of the exercise programme. General MMP and TNF-alpha activities were determined in SF.

RESULTS

Repeated arthrocentesis caused a gradual increase but the exercise regimen no significant increase in MMP activity. There was a significant increase in TNF-alpha activity in SF collected from horses 2 h after cessation of the exercise programme.

CONCLUSIONS AND POTENTIAL RELEVANCE

When using MMPs as biomarkers for joint disease, at least 14 days should elapse after previous arthrocentesis before subsequent SF collection. Moderate exercise does not increase MMP activity in SF from normal joints and it may be possible to ignore this as a source of error in evaluating MMP activity in diseased joints.

Relationship between synovial fluid levels of glycosaminoglycans, hydroxyproline and general MMP activity and the presence and severity of articular cartilage change on the proximal articular surface of P1

REASONS FOR PERFORMING STUDY

Osteoarthritis (OA) is one of the most prevalent and disabling chronic conditions affecting horses and leads to degeneration of articular cartilage. Diagnosis is based on clinical signs in combination with radiography, which is relatively insensitive and provides only an indication of accumulated damage. Alternative methods, such as molecular markers, are therefore needed that can quantitatively, reliably and sensitively detect osteoarthritic changes in the joints at an early stage of the disease. If such markers are to be used reliably, it is important to know the relationship between marker concentration and cartilage composition.

OBJECTIVES

To study the relationship between cartilage composition, synovial fluid levels of glycosaminoglycans (GAGs), hydroxyproline (Hyp) and general matrix metalloproteinase (MMP) activity, and the presence and severity of articular cartilage damage on the articular surface of P1.

METHODS

Synovial fluid (SF) was collected from the metacarpophalangeal joints of 60 mature horses, and levels of GAGs, Hyp and general MMP activity were determined. Further, GAG and denatured collagen content of the articular cartilage were determined at the dorsal articular margin of P1 (site 1) and central cavity (site 2). The presence and severity of cartilage change was quantified using the cartilage degeneration index (CDI), measured at the same 2 sites. Correlations between SF parameters, cartilage composition and degree of cartilage degeneration were sought using correlation analysis.

RESULTS

There was no correlation between GAG or Hyp content of SF and the amount of GAGs or denatured collagen, respectively, in cartilage. In joints with moderate to severe cartilage damage, the GAG content of site 1 was significantly lower than in joints with no to minimal cartilage change (P = 0.005) and there was a negative correlation between the amount of denatured collagen and GAG content at site 1 in all joints (r = -039, P = 0.002). Further, in joints with moderate to severe cartilage damage, there was a significant positive correlation between MMP activity in SF and Hyp levels in SF (r = 0.72, P < 0.001) and CDI at sites 1 (r = 0.46, P = 0.03) and 2 (r = 0.43, P = 0.04).

CONCLUSIONS

General MMP activity in joints with moderate to severe cartilage damage is related to the severity of those cartilage changes and to Hyp levels in SF. Glycosaminoglycan levels in SF are not directly related to MMP activity, GAG content of articular cartilage or severity of cartilage change.

POTENTIAL RELEVANCE

Glycosaminoglycan levels in SF are not helpful for the early detection of cartilage lesions. In damaged joints, Hyp levels may give an indication of the severity of cartilage change as they are strongly related to MMP activity, but do not qualify as markers for the presence or absence of cartilage lesions.

Collagenase-1 (MMP-1) activity in equine synovial fluid: influence of age, joint pathology, exercise and repeated arthrocentesis

REASONS FOR PERFORMING STUDY

Matrix metalloproteinases (MMPs) are considered candidate biomarkers for both physiological and pathological tissue remodelling because of their key role in articular cartilage homeostasis. As disruption of the collagenous architecture is thought to be pivotal in chronic degenerative diseases such as osteoarthritis (OA), the collagenases form an interesting subset of the MMPs. The significance of any biomarker in synovial fluid (SF) can be assessed properly only when fluctuations in patterns induced by physiological processes such as development and growth, and by external influences and interventions such as exercise and repeated arthrocentesis, are known and taken into account.

OBJECTIVES

To investigate the activity of MMP-1 in equine SF at different stages of development and in joints affected by OA, and the influence of exercise and repeated arthrocentesis thereon.

METHODS

MMP-1 activity was determined in SF of normal joints of fetal, juvenile and mature horses, and in SF of horses suffering from OA, using an internally quenched fluorogenic peptide substrate. MMP-1 activity was also measured in SF from horses subjected to an exercise regimen and those subjected to repeated arthrocentesis.

RESULTS

An age-related decline in the SF levels of active MMP-1 was observed. MMP-1 activity was 15-fold higher in fetal than in juvenile animals, which showed significantly higher MMP-1 activity levels than mature horses. In SF of OA joints, MMP-1 activity was increased. Exercise did not affect MMP-1 activity in SF, but repeated arthrocentesis (within 60 h) increased MMP-1 activity significantly.

CONCLUSIONS

The high MMP-1 activity in SF of young individuals parallels the high metabolic activity occurring during rapid growth and differentiation at early age. The elevated MMP-1 activity in SF of OA joints probably reflects pathological matrix degradation, confirming the potential of MMP-1 to serve as a biochemical marker for early joint disease. Moderate exercise is not likely to influence the outcome of MMP-1 activity measurements in equine SF, but arthrocentesis should be taken into account as a possible confounding factor.

POTENTIAL RELEVANCE

Given the crucial role of the collagen matrix for tissue integrity, MMP-1 activity may be a useful tool in diagnostic, therapeutic or prognostic studies in horses suspected of OA. However, care should be taken to exclude fluctuations in MMP-1 activity induced by physiological processes such as development and growth, and by interventions such as repeated arthrocentesis.

B Cell Clonal Expansion and Somatic Hypermutation of Ig Variable Heavy Chain Genes in the Synovial Membrane of Patients with Osteoarthritis

Inflammatory mediators have been explored as possible factors in the initiation and/or progression of osteoarthritis (OA). This study shows that synovial infiltration by B lymphocytes is present in almost half of the knee OA cases. The degree of B lymphocyte infiltration is associated with more pronounced synovial inflammation and with the presence of plasma cells and lymphoid follicles in more severe cases. To examine whether these B cells are merely bystanders or could be involved in the pathogenesis of OA, we analyzed the Ig H chain variable region (V(H)) genes of B cells recovered from the synovial membrane of five OA patients with marked B cell infiltration. Sequence analysis of CDR3 regions of rearranged VDJ genes revealed clonal or oligoclonal B cell expansions in all cases. Expanded B cell clones in four of five OA patients showed clustered somatic mutations, occurring mainly in the CDRs and with a high replacement-to-silent ratio (>2.9), indicating that these cells are postgerminal center B cells that had been positively selected through their Ag receptor. These data demonstrate the presence in inflamed knee OA synovium of clonally expanded, Ag-driven B cells that may contribute to the development or progression of the disease.

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.

Assessment of the effects of age and joint disease on hydroxyproline and glycosaminoglycan concentrations in synovial fluid from the metacarpophalangeal joint of horses

OBJECTIVE

To assess the effects of age and joint disease on hydroxyproline and glycosaminoglycan (GAG) concentrations in synovial fluid from the metacarpophalangeal joint of horses and evaluate the association of those concentrations with severity of osteoarthritis and general matrix metalloproteinase (MMP) activity.

SAMPLE POPULATION

Synovial fluid was collected from the metacarpophalangeal joints of foals at birth (n = 10), 5-month-old foals (10), 11-month-old foals (5), and adult horses (73).

PROCEDURE

Hydroxyproline and GAG concentrations were determined in synovial fluid samples. The severity of osteoarthritis in adult joints was quantified by use of a cartilage degeneration index (CDI) and assessment of general MMP-activity via a fluorogenic assay.

RESULTS

Hydroxyproline and GAG concentrations in synovial fluid were highest in neonates and decreased with age. Concentrations reached a plateau in adults by 4 years and remained constant in healthy joints. In synovial fluid from osteoarthritic joints, hydroxyproline and GAG concentrations were not increased, compared with unaffected joints, but hydroxyproline were significantly correlated with the CDI and general MMP activity. There was no significant correlation between GAG concentration and CDI value or MMP activity.

CONCLUSIONS AND CLINICAL RELEVANCE

Changes in hydroxyproline concentration in synovial fluid appeared to indicate damage to collagen of the articular cartilage. In joints with osteoarthritis, the lack of high GAG concentration in synovial fluid and the absence of a significant correlation between GAG concentration and CDI values or MMP activity may severely limit the usefulness of this marker for monitoring equine joint disease.

Correlation of urinary nitric oxide concentrations with the development of hip dysplasia in Labrador retrievers

Urinary nitric oxide was determined in terms of the ratio of the concentrations of total urinary nitrite and nitrate:creatinine in 40 juvenile labrador retrievers, and radiographic signs of hip dysplasia and distraction indices were investigated in the same dogs in later life. The ratio was correlated significantly with the Norberg angle and with subchondral sclerosis in both hips, and with the grade of dysplasia in each hip and the dogs' overall grade of hip dysplasia. No correlations were observed between the ratio and the distraction indices or other radiographic criteria for hip dysplasia.

Differential expression patterns of matrix metalloproteinases and their inhibitors during development of osteoarthritis in a transgenic mouse model

OBJECTIVE

To characterise the expression of matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) during degeneration of articular cartilage in a transgenic Del1 mouse model for osteoarthritis.

METHODS

Northern analysis was used to measure mRNA levels of MMP-2, -3, -8, -9, -13, and -14, and TIMP-1, -2, and -3 in total RNA extracted from knee joints of transgenic Del1 mice, harbouring a 15 amino acid deletion in the triple helical domain of the alpha1(II) collagen chain, using their non-transgenic littermates as controls. Immunohistochemistry was used to study the presence of cleavage products (neoepitopes) of type II collagen, and the distribution of MMP-13 and TIMP-1 in degenerating cartilage.

RESULTS

Each of the MMP and TIMP mRNAs analysed exhibited distinct expression patterns during development and osteoarthritic degeneration of the knee joint. The most striking change was up regulation of MMP-13 mRNA expression in the knee joints of Del1 mice at the onset of cartilage degeneration. However, the strongest immunostaining for MMP-13 and its inhibitor TIMP-1 was not seen in the degenerating articular cartilage but in synovial tissue, deep calcified cartilage, and subchondral bone. The localisation of type II collagen neoepitopes in chondrocytes and their pericellular matrix followed a similar pattern; they were not seen in cartilage fibrillations, but in adjacent unaffected cartilage.

CONCLUSION

The primary localisation of MMP-13 and TIMP-1 in hyperplastic synovial tissue, subchondral bone, and calcified cartilage suggests that up regulation of MMP-13 expression during early degeneration of articular cartilage is a secondary response to cartilage erosion. This interpretation is supported by the distribution of type II collagen neoepitopes. Synovial production of MMP-13 may be related to removal of tissue debris released from articular cartilage. In the deep calcified cartilage and adjacent subchondral bone, MMP-13 probably participates in tissue remodelling.

An analysis of 14 molecular markers for monitoring osteoarthritis. Relationship of the markers to clinical end-points

OBJECTIVE

To investigate whether any of 14 serum and urine molecular markers (MMs) used to monitor osteoarthritis (OA) would be associated with particular clinical end-points.

DESIGN

Thirty-nine OA patients were bled and urine collected at five time points: at baseline visit and at visits 1, 3, 6 and 12 months later. Twelve clinical measurements were made and the concentrations of each of 14 MMs were determined. Principal component analysis, stepwise linear regression with backward elimination, and logistic regression were used to determine the correlations between MMs and clinical measures.

RESULTS

Principal component analysis was used to reduce the 12 clinical measurements into three independent clinical clusters: baseline clinical assessments, changes in clinical assessments and signal joint measurements. The 14 MMs were similarly reduced to five MM clusters. Each of the three clinical clusters was correlated with a single but different MM cluster. Baseline clinical assessments were correlated with bone markers typified by hydroxylysyl pyridinoline (HP) crosslinks, swelling of the signal joint was correlated with inflammation markers, especially CRP, and the change in clinical assessments over the 1 year evaluation was correlated with TGFbeta1. There was no correlation between any of the skeletal markers and the clinical measures, a situation which draws attention to the need for a direct assessment of cartilage damage in OA to validate the use of cartilage markers.

CONCLUSIONS

This study demonstrates statistical methodology for analysis of clinical trials using multiple MMs and clinical end-points. The patient numbers are sufficient to test hypotheses of relationships of single MMs such as CRP, TGFbeta1 and HP to clinical measures, but larger clinical trials are needed to validate hypotheses.

Endogenous nitric oxide production in canine osteoarthritis: Detection in urine, serum, and synovial fluid specimens

OBJECTIVE

To measure nitric oxide (NO) concentrations in serum, urine, and synovial fluid (SF) of dogs with naturally occurring cranial cruciate ligament (CCL) rupture and normal dogs, and to compare these with clinical and histologic changes of osteoarthritis (OA).

STUDY DESIGN

Prospective clinical study including 2 groups of animals selected from the hospital population.

ANIMALS

Forty-three dogs (CCL group) with OA secondary to CCL rupture; 30 healthy dogs (control group) without CCL rupture.

METHODS

Serum, urine, and SF were collected before and during surgery in the CCL group or immediately after euthanasia in the control group. Articular cartilage and synovial membrane tissue specimens were prepared for routine histologic examination. The stable end products of NO, total nitrite and nitrate (NOt) activity, were measured in body fluids and compared with macroscopic and histologic degrees of OA. Urinary NOt concentration was compared with urinary creatinine concentration and stated as urinary NOt:creatinine ratio (UNCR). RESULTS-SF NOt concentrations were not significantly different between the 2 groups. Serum NOt concentrations (45.6 vs 28.9 micromol/L; P =.042) and the UNCR (0.007 vs 0.004; P =.035) were significantly higher in dogs of the CCL group compared with the control population. An association between UNCR and histologic and macroscopical OA grades could be demonstrated.

CONCLUSION

UNCR might be a useful indicator of nitrite and nitrate production and, therefore, osteoarthritic changes in joints.

CLINICAL RELEVANCE

UNCR could be used as a tool to evaluate the NOt production by joint tissues over time and might therefore provide a method of evaluating the effects of drugs in the control of osteoarthritis.

An analysis of 14 molecular markers for monitoring osteoarthritis: segregation of the markers into clusters and distinguishing osteoarthritis at baseline

OBJECTIVE

To investigate the relationships between serum and urinary molecular markers (MM) used to monitor osteoarthritis.

DESIGN

Forty osteoarthritis patients had blood and urine collected at baseline and 1, 3, 6 and 12 months later. Specimens from 20 controls were obtained twice at a one month interval. The concentration of 14 different markers was determined at each time point and the data were analyzed by statistical methodology.

RESULTS

The markers could be divided by the method of principal components analysis into five clusters of related markers: inflammation markers (C-reactive protein, tumor necrosis receptor type I and tumor necrosis receptor type II, interleukin 6, eosinophilic cationic protein), bone markers (bone sialoprotein, hydroxylysyl pyridinoline, lysyl pyridinoline), putative markers of cartilage anabolism (carboxypropeptide of type II procollagen, hyaluronan, epitope 846) and catabolism (keratan sulfate, cartilage oligomeric matrix protein), and transforming growth factor beta. Three markers (tumor necrosis factor receptor II, cartilage oligomeric matrix protein and epitope 846) from independent clusters discriminated osteoarthritis patients from controls. Inflammation was not a confounding factor in measurement, but a recognizable distinguishing factor in osteoarthritis.

CONCLUSIONS

The markers separated into rational groups on the basis of their covariance, a finding with independent biochemical support. The covariance of markers from the same cluster suggests the use of a representative marker from the cluster to reflect changes in osteoarthritis. If multiple markers are being measured within a single cluster, then the use of a weighted cluster 'factor' may be preferable to the separate use of individual markers.

Cartilage degradation by hyaluronate lyase and chondroitin ABC lyase: a MALDI-TOF mass spectrometric study

Matrix-assisted laser desorption ionization and time-of-flight mass spectrometry (MALDI-TOF MS) has been used to investigate degradation products of two selected polysaccharides of cartilage (chondroitin sulfate and hyaluronic acid). Testicular hyaluronate lyase and chondroitin ABC lyase were used for enzymic digestion of both polysaccharides as well as of cartilage specimens. Polysaccharide solutions and cartilage supernatants were assayed by positive and negative MALDI-TOF MS. Especially chondroitin ABC lyase produced high amounts of digestion products (unsaturated di- and tetrasaccharides) from polysaccharides as well as from cartilage, clearly monitored by MALDI-TOF MS. It is concluded that MALDI-TOF MS provides a precise and fast tool for the determination of oligosaccharides since no previous derivatization is required.

Osteoarthritis in older adults

OBJECTIVE

This review highlights the clinical and pathophysiologic features of osteoarthritis (OA) of the peripheral joints and discusses the current and future management options for this common but potentially disabling disease. This article also addresses the contribution of osteoarthritis to falls and functional impairment in older people.

DESIGN

A critical assessment of current data regarding the pathogenesis of osteoarthritis, current and future therapies, and the potential role of OA in falls and functional impairment in older people.

CONCLUSIONS

Osteoarthritis is the most prevalent articular disease in older adults. Disease markers that will detect early disease and allow early intervention with pharmacologic agents that modify, if not halt, disease progression are much needed, but they are presently unavailable. Current management should include safe and adequate pain relief using systemic and local therapies and should also include medical and rehabilitative interventions to prevent, or at least compensate for, functional deficits. Although OA can result in impaired mobility and lower extremity function, its contribution as a cause of recurrent falls or impaired self-care, relative to other comorbid conditions, remains ill-defined. Further analysis of the determinants of disability, loss of mobility and falls in older patients with OA is needed.

Oligomeric forms of the 148 kDa cartilage matrix protein

The 148 kDa cartilage matrix protein (CMP), composed of three disulphide-bonded subunits, is a cartilage-specific glycoprotein found in association with fibrils of type II collagen and possibly with aggrecan. It is probable that CMP serves a structural role. As cartilage ages, an increasing proportion of the CMP becomes insoluble and resistant to extraction. In the present study, the isolation of CMP has been improved by inclusion of a hydrophobic chromatography step, thereby removing the remaining traces of collagen and proteoglycan. Evidence of self-association of CMP is presented. Higher-molecular-mass forms of CMP, ranging in apparent molecular mass from 270 to 510 kDa and separated by SDS/PAGE, were located using a specific anti-CMP monoclonal antibody. Both CMP and its oligomeric forms are reducible to 52 kDa subunits, and only trace amounts of other proteins. The formation of oligomers, which may constitute 23% of the total cartilage matrix protein, could occur as a byproduct of the normal biosynthetic trimerization of subunits. Alternatively, the oligomers may represent a step toward the age-related cross-linking and insolubilization of CMP.

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

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

Unstable stifles without clinical or radiographic osteoarthritis in young goats: an experimental study

Thirteen young, castrated male goats had instability of one stifle (knee joint) created by surgical transection of the cranial cruciate ligament, but did not develop any signs of osteoarthritis (OA) in treated joints when confined in limited space for 8 months. At the end of the experiment, the instability in the stifles had not improved, the joints were normal at radiographic examination, there were no signs of inflammation in the synovial membrane or joint capsule, and fibrosis in these tissues was not evident. The articular cartilage was normal both visually and histologically. This may indicate that the young age of the goats and the restricted physical activity on soft floor had prevented the expected development of OA in the experimentally operated joints. Synovial fluid volumes and proteoglycan concentration were measured in the treated and control joints in 6 of the goats. There seemed to be increased quantity of the proteoglycan aggrecan in the synovial fluid from the treated joints compared to the contralateral joints throughout the course of this study. It was concluded that the turnover of aggrecan in the articular cartilage of the treated joints may have been increased.

Pathogenesis and treatment of osteoarthritis

OA represents the final common pathway of a number of pathologic processes. The challenge is to define and classify the subsets of OA to understand the causes and to devise specific therapies. Effective chondroprotective therapies will be most useful when applied to high-risk individuals before the emergence of symptomatic OA. This will be feasible only with an improved understanding of the complex interaction of genes and environment in the OA disease process. Moreover, identifying the heritable bases of this disease will provide insight into the molecular mechanisms of the complex pathway that results in OA. Clinicians who encounter and treat OA patients can look forward to the development of more effective and innovative therapies based on a rapidly improving understanding of OA.

Markers of osteoarthritis: a review of the literature

There may be a great potential in the use of diagnostic "markers" of osteoarthritis in synovial fluid to diagnose the disease in an earlier stage and perhaps assess the severity of the disease and monitor the effect of a treatment. In the present study, potential markers are characterized, discussed, and grouped according to the latest knowledge on the etiology, pathogenesis, and pathology of osteoarthritis. They are grouped according to their origin as either cartilage degradation products, or related to the mechanisms of cartilage degradation, or related to chrondrocytic anabolic activity during disease, or related to genetic disorders. Also potential markers that have not yet been studied clinically or experimentally are discussed. Examples of the progress that has been made in human medicine approaching reliable diagnostic markers that should also be tried in veterinary medicine are described.

Correlation between synovial fluid markers of cartilage and bone turnover and scintigraphic scan abnormalities in osteoarthritis of the knee

OBJECTIVE

To test the hypothesis that scintigraphic evidence of bone activity will correlate with biochemical evidence of increased matrix turnover in osteoarthritis (OA).

METHODS

Keratan sulfate epitope (5D4), chondroitin sulfate epitope (3B3), and osteocalcin (OC) were measured in synovial fluid (SF) from 35 patients with knee OA, within 1 month of bone scan.

RESULTS

SF OC levels correlated with 5D4 levels (r = 0.32, P = 0.047) and with abnormalities on scintigraphic scan. Mean OC levels were 47% higher (P = 0.016) in patients with severely abnormal findings on scans compared with levels in patients with mildly abnormal scan findings. No significant association of 5D4 or 3B3 levels and perfusion- or late (bone)-phase scintigraphic abnormalities was found.

CONCLUSION

These data support the hypothesis that there is an association between late-phase bone scan abnormalities and SF biochemical markers of bone turnover in OA.

Release of cartilage oligomeric matrix protein (COMP) into joint fluid after knee injury and in osteoarthritis

OBJECTIVE

The release of fragments of cartilage oligomeric matrix protein (COMP) and aggrecan into knee joint fluid and serum after joint injury and in post-traumatic and primary osteoarthritis was monitored in a cross-sectional study.

METHODS

Samples of joint fluid and serum were obtained from healthy volunteers and from patients with arthroscopically verified injury to anterior cruciate ligament and or meniscus of the knee at different times after injury and with different degrees of post-traumatic osteoarthritis. Samples were also obtained from patients with primary osteoarthritis. Fragments of COMP were quantified in joint fluid and in serum by enzyme-linked immunoassay. Fragments of aggrecan were quantified in joint fluid by enzyme-linked immunoassay.

RESULTS

Concentrations of COMP and aggrecan fragments in joint fluid in the study groups were increased over the reference levels of 47 (range 10-109) and 34 (range 6-59) micrograms/mL, respectively, in the volunteers with healthy knees. The ratios (w/w) of aggrecan to COMP fragments in joint fluid were also increased in all study groups over that in the reference group. Average concentrations of COMP in joint fluid were high shortly after injury and decreased with time but remained increased over reference levels for many years. Joint fluid COMP concentrations were also increased in early stage post-traumatic and primary osteoarthritis, but not in advanced osteoarthritis.

CONCLUSION

Increased amounts of aggrecan and COMP fragments are released into joint fluid after joint injury and in early stage osteoarthritis. The ratios of aggrecan to COMP in joint fluid vary with time after injury and with osteoarthritis disease stage. Although both molecules are sensitive to the agents active in matrix breakdown in joint disease, differences may thus exist in the release mechanisms and attempted repair. The concentrations of the individual markers in body fluids and their ratios may serve to monitor treatment efficacy, disease progression and repair in osteoarthritis and other joint diseases.

Candida albicans arthritis in a nonimmunocompromised patient. Complication of placebo intraarticular injections

A nonimmunocompromised 32-year-old man with arthrosis of the knee participated as a placebo control in a clinical trial of intraarticular injections of hyaluronan. After the fourth weekly injection of saline, he developed a warm and swollen knee, and synovial fluid cultures revealed growth of Candida albicans. Oral fluconazole treatment was instituted 2 weeks after onset of symptoms, but failed to eradicate the infection. The patient recovered after treatment with local and systemic amphotericin B, systemic 5-fluorocytosine and surgical synovectomy. Quantitation of joint cartilage proteoglycan fragments in synovial fluid indicated extensive breakdown of cartilage during the acute phase of arthritis but, parallel to clinical recovery, these levels returned to normal.