Association of higher levels of serum cartilage oligomeric matrix protein and N-telopeptide crosslinks with the development of radiographic hip osteoarthritis in elderly women

A Comprehensive, Multidisciplinary Assessment for Knee Osteoarthritis Following Traumatic Unilateral Lower Limb Loss in Service Members

INTRODUCTION

Knee osteoarthritis (KOA) is a primary source of long-term disability and decreased quality of life (QoL) in service members (SM) with lower limb loss (LL); however, it remains difficult to preemptively identify and mitigate the progression of KOA and KOA-related symptoms. The objective of this study was to explore a comprehensive cross-sectional evaluation, at the baseline of a prospective study, for characterizing KOA in SM with traumatic LL.

MATERIALS AND METHODS

Thirty-eight male SM with traumatic unilateral LL (23 transtibial and 15 transfemoral), 9.5 ± 5.9 years post-injury, were cross-sectionally evaluated at initial enrollment into a prospective, longitudinal study utilizing a comprehensive evaluation to characterize knee joint health, functionality, and QoL in SM with LL. Presences of medial, lateral, and/or patellofemoral articular degeneration within the contralateral knee were identified via magnetic resonance imaging(for medically eligible SM; Kellgren-Lawrence Grade [n = 32]; and Outerbridge classification [OC; n = 22]). Tri-planar trunk and pelvic motions, knee kinetics, along with temporospatial parameters, were quantified via full-body gait evaluation and inverse dynamics. Concentrations of 26 protein biomarkers of osteochondral tissue degradation and inflammatory activity were identified via serum immunoassays. Physical function, knee symptoms, and QoL were collected via several patient reported outcome measures.

RESULTS

KOA was identified in 12 of 32 (37.5%; KL ≥ 1) SM with LL; however, 16 of 22 SM presented with patellofemoral degeneration (72.7%; OC ≥ 1). Service members with versus without KOA had a 26% reduction in the narrowest medial tibiofemoral joint space. Biomechanically, SM with versus without KOA walked with a 24% wider stride width and with a negative correlation between peak knee adduction moments and minimal medial tibiofemoral joint space. Physiologically, SM with versus without KOA exhibited elevated concentrations of pro-inflammatory biomarker interleukin-7 (+180%), collagen breakdown markers collagen II cleavage (+44%), and lower concentrations of hyaluronic acid (-73%) and bone resorption biomarker N-telopeptide of Type 1 Collagen (-49%). Lastly, there was a negative correlation between patient-reported contralateral knee pain severity and patient-reported functionality and QoL.

CONCLUSIONS

While 37.5% of SM with LL had KOA at the tibiofemoral joint (KL ≥ 1), 72.7% of SM had the presence of patellofemoral degeneration (OC ≥ 1). These findings demonstrate that the patellofemoral joint may be more susceptible to degeneration than the medial tibiofemoral compartment following traumatic LL.

Emerging microfluidics-enabled platforms for osteoarthritis management: from benchtop to bedside

Osteoarthritis (OA) is a prevalent debilitating age-related joint degenerative disease. It is a leading cause of pain and functional disability in older adults. Unfortunately, there is no cure for OA once the damage is established. Therefore, it promotes an urgent need for early detection and intervention of OA. Theranostics, combining therapy and diagnosis, emerges as a promising approach for OA management. However, OA theranostics is still in its infancy. Three fundamental needs have to be firstly fulfilled: i) a reliable OA model for disease pathogenesis investigation and drug screening, ii) an effective and precise diagnostic platform, and iii) an advanced fabrication approach for drug delivery and therapy. Meanwhile, microfluidics emerges as a versatile technology to address each of the needs and eventually boost the development of OA theranostics. Therefore, this review focuses on the applications of microfluidics, from benchtop to bedside, for OA modelling and drug screening, early diagnosis, and clinical therapy. We first introduce the basic pathophysiology of OA and point out the major unfilled research gaps in current OA management including lack of disease modelling and drug screening platforms, early diagnostic modalities and disease-modifying drugs and delivery approaches. Accordingly, we then summarize the state-of-the-art microfluidics technology for OA management from in vitro modelling and diagnosis to therapy. Given the existing promising results, we further discuss the future development of microfluidic platforms towards clinical translation at the crossroad of engineering and biomedicine.

Prognostic factors for progression of osteoarthritis of the hip: a systematic review

Background

Predicting which patients with hip osteoarthritis are more likely to show disease progression is important for healthcare professionals. Therefore, the aim of this review was to assess which factors are predictive of progression in patients with hip osteoarthritis.

Methods

A literature search was made up until 14 March 2019. Included were cohort and case-control studies evaluating the association between factors and progression (either clinical, radiological, or THR). Excluded were studies with a follow-up < 1 year or specific underlying pathologies of osteoarthritis. Risk of bias was assessed using the QUIPS tool. A best-evidence synthesis was conducted.

Results

We included 57 articles describing 154 different factors. Of these, a best-evidence synthesis was possible for 103 factors, separately for clinical and radiological progression, and progression to total hip replacement. We found strong evidence for more clinical progression in patients with comorbidity and more progression to total hip replacement for a higher Kellgren and Lawrence grade, superior or (supero) lateral femoral head migration, and subchondral sclerosis. Strong evidence for no association was found regarding clinical progression for gender, social support, pain medication, quality of life, and limited range of motion of internal rotation or external rotation. Also, strong evidence for no association was found regarding radiological progression for the markers CTX-I, COMP, NTX-I, PINP, and PIIINP and regarding progression to total hip replacement for body mass index.

Conclusion

Strong evidence suggested that 4 factors were predictive of progression of hip osteoarthritis, whereas 12 factors were not predictive of progression. Evidence for most of the reported factors was either limited or conflicting.

Protocol registration

PROSPERO, CRD42015010757

Electronic supplementary material

The online version of this article (10.1186/s13075-019-1969-9) contains supplementary material, which is available to authorized users.

Cartilage oligomeric matrix protein, C-terminal cross-linking telopeptide of type II collagen, and matrix metalloproteinase-3 as biomarkers for knee and hip osteoarthritis (OA) diagnosis: a systematic review and meta-analysis

OBJECTIVE

This study was design to examine the diagnostic performance of cartilage oligomeric matrix protein (COMP), C-terminal cross-linking telopeptide of type II collagen (CTX-II), and matrix metalloproteinase-3 (MMP-3) as biomarker for knee and hip OA.

METHODS

Systematic search on multiple databases was completed in January 2018 using certain keywords. COMP, CTX-II, MMP-3 levels in knee and hip OA patients and healthy individuals were collected and calculated. Differences between subgroups were expressed as standardized mean differences (SMD). Subgroup analyses were performed to compare COMP, CTX-II, and MMP-3 performance between measuring sources, genders, large and small sample size and diagnostic criteria for OA patients.

RESULTS

A moderate performance of COMP in distinguishing between knee (SMD: 0.68; 95% confidence intervals (CI): 0.43-0.93; P < 0.0001) or hip (SMD: 0.25; 95% CI, 0.10, 0.40; P = 0.0008) OA patients and controls were found. CTX-II showed a moderated standardised mean differences (SMD) of 0.48 (95% CI, 0.32, 0.64; P < 0.0001) in the detection of knee OA and a large SMD of 0.76 (95% CI, 0.09, 1.42; P = 0.03) in diagnosing hip OA. A small SMD of 0.32 (95% CI, -0.03, 0.67; P = 0.07) was found for MMP-3 performance and the results did not reach statistic significance. Progression study revealed potential effectiveness of serum COMP in predicting OA progression. Subgroup analysis showed that serum COMP and urinary CTX-II performed better in male than female. Study size and diagnostic criteria did not significantly influence the pooled SMD, but they might be the sources of heterogeneity among studies.

CONCLUSION

The overall results indicates that serum COMP and urinary CTX-II can distinguish between knee or hip OA patients and control subjects. Serum COMP is effective in predicting OA progression.Further researches with rigorous study design and a larger sample size are required to validate our findings.

Biochemical Markers for the Early Identification of Osteoarthritis: Systematic Review and Meta-Analysis

BACKGROUND

There is a desperate need for the reliable detection of osteoarthritis (OA) at the early stage when patients are likely to benefit most from disease interventions. A variety of biochemical markers have been proposed, but their reliability varies among studies.

OBJECTIVE

In this review, we aimed to answer the following questions: (1) are there biochemical markers that are differentially expressed in early OA versus healthy subjects, and (2) if so, what is the diagnostic value of these biomarkers for early OA?

METHODS

Embase, PubMed, and Web of Science were searched to obtain all relevant studies up to March 2018, and studies comparing the biochemical markers between early OA and healthy controls were selected. The Downs and Black checklist was used to assess the risk of bias. Biomarkers that were investigated in five or more different populations were pooled for meta-analysis. A meta-regression analysis was performed to explore possible explanations for the heterogeneity of studies.

RESULT

In total, 26 articles met the criteria for the qualitative synthesis and 17 articles for the final quantitative synthesis. N-terminal crosslinked telopeptide of type I collagen (NTX-I) was the only biomarker found to be differently expressed in patients with early OA versus controls, without significant heterogeneity among studies (I2 = 0%, [Formula: see text] = 1.695, p = 0.792). The meta-regression analysis identified that sample size and affected joint possibly explained the heterogeneity among studies.

CONCLUSION

Although a wide range of biomarkers has been previously investigated in early OA, the diagnostic value of these biomarkers could not be determined because due to a low number of studies regarding any given biomarker. Large prospective and adequately powered studies are therefore required to validate these (and other) biomarkers for identifying early OA.

Toward classification criteria for early osteoarthritis of the knee

OBJECTIVE

To propose draft classification criteria for early stage osteoarthritis (OA) of the knee for use in a primary care setting.

METHODS

A group of basic scientists, physician-scientists, rheumatologists, orthopedic surgeons, and physiotherapists in a workshop setting discussed potential classification criteria for early osteoarthritis of the knee. The workshop was divided into sessions around relevant topics with short state of the art presentations followed by breakout sessions, consensus discussions, and consolidation into a consensus document.

RESULTS

Three classes of criteria were agreed: (1) Pain, symptoms/signs, self-reported function, and quality of life using tools such as KOOS: scoring ≤85% in at least 2 out of these 4 categories; (2) Clinical examination: at least 1 present out of joint line tenderness or crepitus; (3) Knee radiographs: Kellgren & Lawrence (KL) grade of 0 or 1. MRI is at present not recommended as an aid to identify or define early OA in routine clinical practice or primary care, in light of the absence of validated consensus criteria and the high population prevalence of structural joint changes detected by this method. Biomarkers may have future utility in early OA classification, but no individual or set of biomarkers is yet robust enough.

CONCLUSION

Based on our consensus proposal, draft classification criteria for early OA of the knee for use in clinical studies should include patient reported outcomes such as pain and function, together with clinical signs and KL grade 0-1 on radiographs.

COMP serum levels: A new non-invasive biomarker of liver fibrosis in patients with chronic viral hepatitis

BACKGROUND & AIMS

Recently we have shown that cartilage oligomeric matrix protein (COMP), a fibrillar collagen assembly regulator, is strongly associated with cirrhosis and hepatocellular carcinoma progression. Therefore, we assessed whether serum COMP levels can be used as a non-invasive fibrosis marker in patients with chronic viral hepatitis (CVH) and compared this marker with standard methods for disease stage assessment [histology, transient elastography (TE), APRI, FIB-4].

METHODS

Sera from 116 CVH patients, 66 HBV [24 female; median age 53(22-76)] and 50 HCV [21 female; median age 48.5(25-69)] were investigated by COMP-ELISA. APRI and FIB-4 score was calculated in all along with TE. Liver biopsy was performed in 61. Patients were divided into two groups (F1/F2 and F3/F4) according to Metavir score.

RESULTS

55/116 (47%) CVH patients were classified in F3/F4-group according to TE [14.3(9.3-75)kPa]. APRI score was >1.5 in 21/116 and FIB-4>3.25 in 20/116. Liver histology revealed 24/61 (39%) patients with significant fibrosis (stage 3-4), while 12/61 (19.7%) had cirrhosis. COMP levels correlated with TE measurements (r=0.5; p<0.001) and APRI score (r=0.23; p<0.02). The diagnostic accuracy of COMP in detecting cirrhosis was as good as TE, APRI and FIB-4 index (AUC 0.884) with sensitivity and specificity of 83.3% and 83.7% (cut-off 11.5U/L).

CONCLUSIONS

COMP serum levels performed as well as TE, APRI and FIB4 score in detecting cirrhosis in CVH patients, suggesting COMP as a sensitive non-invasive, easy to perform biomarker of liver fibrosis. Further studies are needed in order to validate our findings in CVH patients.

Racial differences in associations between baseline patterns of radiographic osteoarthritis and multiple definitions of progression of hip osteoarthritis: the Johnston County Osteoarthritis Project

Background

To identify baseline radiographic features that predict hip osteoarthritis (HOA) progression, and to explore differences in these associations by race.

Methods

Radiographs from the community-based Johnston County OA Project were scored using Kellgren-Lawrence (KL) grade and for presence and location of joint space narrowing (JSN), osteophytes, and subchondral changes. Associations between these features and HOA progression (increase of at least 1 KL grade, interval hip replacement, range of motion [ROM, a reduction of ≥10° in internal rotation], or disability [increase of ≥0.2 in Health Assessment Questionnaire scores], or Any of these) were assessed using logistic regression, adjusting for age, gender, race, hip injury, BMI, education, smoking and follow-up time, accounting for multiple comparisons. Race interactions were assessed and analyses stratified as indicated.

Results

The sample (n = 1,422) included 40 % men and 26 % African American (AA) participants, with mean age 61 years and BMI 29 kg/m². The baseline frequency of radiographic hip OA (RHOA) between Caucasians and AAs was similar (23 %), although some radiographic features differed. AAs were more likely to have progression defined by ROM or disability or Any progression; Caucasians were more likely to have RHOA progression. JSN, subchondral sclerosis, and medial osteophytes were associated with increased RHOA progression overall; JSN was associated with disability progression only in AAs, while lateral osteophytes were associated with ROM progression only in Caucasians.

Conclusions

AAs and Caucasians exhibited differences in the radiographic presentation and progression patterns of HOA, with AAs reporting progressive pain and disability, while Caucasians had more RHOA progression.

The Natural History of Femoroacetabular Impingement

Femoroacetabular impingement (FAI) is a clinical syndrome resulting from abnormal hip joint morphology and is a common cause of hip pain in young adults. FAI has been posited as a precursor to hip osteoarthritis (OA); however, conflicting evidence exists and the true natural history of the disease is unclear. The purpose of this article is to review the current understanding of how FAI damages the hip joint by highlighting its pathomechanics and etiology. We then review the current evidence relating FAI to OA. Lastly, we will discuss the potential of hip preservation surgery to alter the natural history of FAI, reduce the risk of developing OA and the need for future arthroplasty.

What is the utility of biomarkers for assessing the pathophysiology of hip osteoarthritis? A systematic review

BACKGROUND

Innovations in biologics offer great promise in the treatment of patients with orthopaedic conditions and in advancing our ability to monitor underlying disease pathophysiology. Our understanding of the pathophysiology of hip osteoarthritis (OA) has improved significantly in the last decade. Femoroacetabular impingement (FAI) and hip dysplasia are increasingly recognized and treated as forms of prearthritic hip disease, yet the inability of radiographic and MR imaging to identify patients before the onset of irreversible articular cartilage injury limits their use for early diagnosis and treatment of patients with these conditions. Molecular biomarkers, as objectively measureable indicators of the pathophysiology of hip OA, have the potential to improve diagnosis, disease staging, and prognosis of hip OA and prearthritic hip disease. Although research into molecular biomarkers of hip OA has been conducted, investigations in prearthritic hip disease have only recently begun.

QUESTIONS/PURPOSES

The purpose of our review was to assess the use of molecular biomarkers in the pathophysiology of hip OA, including (1) diagnosis; (2) disease staging; and (3) prognosis. We additionally aimed to summarize the available literature investigating the use of biomarkers in (4) prearthritic hip disease, including FAI and hip dysplasia.

METHODS

We conducted a systematic review of molecular biomarkers associated with hip OA or prearthritic hip disease by searching four major electronic databases for keywords "hip", "osteoarthritis", "biomarker", and all synonyms. The search terms "femoroacetabular impingement" and "hip dysplasia" were also included. The biologic source of biomarkers was limited to serum, plasma, urine, and synovial fluid. The literature search yielded a total of 2740 results. Forty studies met all criteria and were included in our review. Studies were categorized regarding their relevance to (1) diagnosis; (2) disease staging; (3) prognosis; and/or (4) prearthritic hip disease.

RESULTS

Biomarker studies were characterized as relevant to diagnosis (16 studies), disease staging (15 studies), prognosis (11 studies), and prearthritic hip disease (three studies). Sixteen different biomarkers demonstrated associations relevant to the diagnosis of hip OA, 16 biomarkers demonstrated similar associations for disease staging, and six for prognosis. Six biomarkers seemed to be the most promising, demonstrating associations with hip OA in multiple studies, including: urinary level of type II collagen telopeptide (n = 5 studies), serum cartilage oligomeric protein (n = 4 studies), and serum C-reactive protein (n = 4 studies). Only three studies investigated the role of biomarkers in prearthritic hip disease, including two in FAI and one in unspecified etiology of pain. There were no studies about biomarkers in hip dysplasia.

CONCLUSIONS

Molecular biomarkers are increasingly investigated for their use in evaluating the pathophysiology of hip OA, but less so for prearthritic hip disease. Several biomarkers have demonstrated significant associations with hip OA across multiple studies. Further validation of these biomarkers is needed to assess their clinical use and potential application to prearthritic hip disease.

Biomarkers for osteoarthritis: Can they be used for risk assessment? A systematic review

The identification of early biochemical predictors of osteoarthritis (OA) has been the focus of much research over the past few years. However, it still is unclear whether current biochemical markers can be used in prognostic risk assessment of OA. The aim of this systematic review is to evaluate the possible prognostic application of blood and urinary biochemical markers of knee and hip OA. Abstract and full text selection was done by two independent reviewers. A total of 25 relevant publications including 37 biochemical markers of bone and cartilage turnover and inflammation associated with some aspects of OA were reviewed. Most of those biomarkers were studied only once or twice. Due to heterogeneity of both OA-phenotype and determinant among the publications, meta-analysis of the studied biochemical markers was not possible. There was strong evidence for urinary C-terminal telopeptide of collagen type II (uCTX-II) as a prognostic marker for knee OA progression and serum cartilage oligomeric protein (COMP) level as prognostic marker for incidence of knee and hip OA. Evidence for prognostic value of C-reactive protein is still inconclusive. International standardization of future investigations should be pursued to obtain more high-quality, homogenous data on the full spectrum of biochemical OA markers.

Biomarkers of cartilage and surrounding joint tissue

The identification and clinical demonstration of efficacy and safety of osteo- and chondro-protective drugs are met with certain difficulties. During the last few decades, the pharmaceutical industry has, in the field of rheumatology, experienced disappointments associated with the development of disease modification. Today, the vast amount of patients suffering from serious, chronic joint diseases can only be offered treatments aimed at improving symptoms, such as pain and acute inflammation, and are not aimed at protecting the joint tissue. This huge, unmet medical need has been the driver behind the development of improved analytical techniques allowing better and more efficient clinical trial design, implementation and analysis. With this review, we aim to provide a brief and general overview of biochemical markers of joint tissue, with special focus on neoepitopes. Furthermore, we highlight recent studies applying biochemical markers in joint degenerative diseases. These disorders, including osteoarthritis, rheumatoid arthritis and spondyloarthropathies, are the most predominant disorders in Europe and the USA, and have enormous socioeconomical impact.

Associations between biomarkers of joint metabolism, hand osteoarthritis, and hand pain and function: the Johnston County Osteoarthritis Project

OBJECTIVE

To determine the associations between joint metabolism biomarkers and hand radiographic osteoarthritis [(rOA), based on Kellgren Lawrence (KL) grade ≥ 2], symptoms, and function.

METHODS

Cross-sectional data were available for 663 participants (mean age 63 yrs, 63% white, 49% women). Three definitions of hand rOA were considered: (1) a composite measure involving at least 3 hand joints distributed bilaterally with 2 of 3 in the same joint group, including ≥ 1 distal interphalangeal joint, without metacarpophalangeal (MCP) swelling; (2) rOA in at least 1 joint of a group; and (3) number of joints with KL ≥ 2. We assessed hand symptoms and the 15-item Australian Canadian Hand Osteoarthritis Index (AUSCAN; Likert format). We measured serum cartilage oligomeric matrix protein (sCOMP), hyaluronic acid (sHA), carboxy-terminal propeptide of type II collagen, type II collagen degradation product, urinary C-terminal crosslinked telopeptide of type II collagen, and urinary N-terminal crosslinked telopeptide. Linear regression models were performed to assess associations between each biomarker with hand rOA, AUSCAN, and symptoms, adjusting for age, sex, race, current smoking/drinking status, body mass index, and hip and knee rOA.

RESULTS

In adjusted analyses, MCP (p < 0.0001) and carpometacarpal rOA (p = 0.003), and a higher number of hand joints with rOA (p = 0.009), were associated with higher levels of sHA. Positive associations were seen between AUSCAN and hand symptoms and levels of sCOMP (p ≤ 0.003) and sHA (p ≤ 0.048).

CONCLUSION

Hand symptoms and higher AUSCAN scores were independently associated with higher levels of both sCOMP and sHA; hand rOA was associated only with sHA levels.

Association between serum and urine biomarkers and lumbar spine individual radiographic features: the Johnston County Osteoarthritis Project

OBJECTIVE

(1) To determine associations between radiographic features of lumbosacral (LS) spine disc space narrowing (DSN) and osteophytes (OST) and joint metabolism biomarkers (serum cartilage oligomeric matrix protein (COMP), hyaluronic acid (HA), collagen neoepitope (C2C), C-propeptide of type II procollagen (CP-II), urine C-terminal cross-linking telopeptide (CTX-II) and N-terminal telopeptide (NTX-I)). (2) To explore interactions with race, gender and low back symptoms.

DESIGN

Cross-sectional analysis of 547 participants enrolled in the Johnston County (JoCo) Osteoarthritis Project from 2003 to 2004. Mean biomarker levels were estimated with linear regression. Proportional and partial-proportional odds models were used to estimate associations. Interactions were tested with likelihood ratio tests at a P-value < 0.10. Biomarkers were natural log (ln) transformed.

RESULTS

Significant differences in mean biomarker levels were found across severity of DSN for lnHA and lnC2C and lnCTX-II across severity of both DSN and OST. Moderate-to-strong associations were found between biomarkers of type II collagen and DSN, whereas associations with OST were weak. An association between lnHA and DSN was seen in women (adjusted odds ratio [aOR] = 1.34 (95% confidence intervals (CI) 1.08, 1.65)) but no association among men (aOR = 0.90 (95% CI 0.63, 1.26)). In Caucasians there was a decreased association with NTX-I and OST (aOR = 0.67 (95% CI 0.49, 0.91)) and no association in African Americans (AAs) (aOR = 1.06 (95% CI 0.76, 1.47)). There was a positive association of lnCOMP with DSN among those with low back symptoms (aOR = 1.82 (95% CI 1.02, 3.27)), but no association in those without low back symptoms (aOR = 0.65 (95% CI 0.35, 1.20)).

CONCLUSION

Joint metabolism biomarkers suggest biological differences in the pathologic process involved in DSN and OST that may be gender (HA) and ethnicity (NTX-I) specific.

Diabetic foot osteomyelitis: bone markers and treatment outcomes

AIMS

Novel bone turnover markers could help with the diagnosis and monitoring of osteomyelitis patients. We compared levels of two bone turnover markers, serum amino-terminal telopeptides (NTx) and bone alkaline phosphatase (BAP), in diabetic patients with and without osteomyelitis.

METHODS

Matched case-control study was conducted with diabetic patients with and without osteomyelitis. Cases not undergoing immediate amputation were followed with repeat measurements after osteomyelitis treatment and for outcome determination.

RESULTS

Analysis included 54 subjects, 27 cases and 27 controls. Median BAP levels were similar between cases and controls at enrollment (p=.55) as were median NTx levels (p=.43). Cases with follow-up data (n=18) had similar bone marker levels at enrollment and 6 weeks. No significant differences in BAP or NTx levels at enrollment or follow-up were seen between cases with poor versus favorable outcomes.

CONCLUSIONS

No differences in NTx or BAP levels were seen between cases and controls. Cases with follow-up data had similar levels at enrollment and 6 weeks. Lack of difference may be due to small sample size, small areas of bone involved in foot osteomyelitis, or limitations of these specific markers. More research is needed.

Biological markers in osteoarthritis

Osteoarthritis (OA) is considered as a chronic disease with a long "silent" period. The diagnosis is generally based on clinical symptoms and radiographic changes. However X-ray has a poor sensitivity and a relatively large precision error that does not allow an early detection of OA or the monitoring of joint damage progression. The limitations of the tools that are currently available for OA assessment have been the impetus to identify specific biological markers that reflect quantitative and dynamic variations in joint remodeling. Research has focused on the structural components of cartilage matrix, especially type II collagen degradation markers. In spite of a significant increase of some markers in individuals with early stage of OA, the large overlap with control subjects indicates that the current biomarkers used alone have limited diagnostic potential. However, the combination of specific markers seems to improve the prediction of disease progression at the individual level. Several types of treatment have been investigated but the lack of medications with definitively demonstrated chondroprotective activity has limited the assessment of the potential role of biomarkers for monitoring patients' responses to the treatment of OA. In this review, we will use the BIPED classification that appeared in 2006 for OA markers to describe the potential usage of a given marker [5]. This article is part of a Special Issue entitled "Osteoarthritis".

Protein modification by deamidation indicates variations in joint extracellular matrix turnover

As extracellular proteins age, they undergo and accumulate nonenzymatic post-translational modifications that cannot be repaired. We hypothesized that these could be used to systemically monitor loss of extracellular matrix due to chronic arthritic diseases such as osteoarthritis (OA). To test this, we predicted sites of deamidation in cartilage oligomeric matrix protein (COMP) and confirmed, by mass spectroscopy, the presence of deamidated (Asp(64)) and native (Asn(64)) COMP epitopes (mean 0.95% deamidated COMP (D-COMP) relative to native COMP) in cartilage. An Asp(64), D-COMP-specific ELISA was developed using a newly created monoclonal antibody 6-1A12. In a joint replacement study, serum D-COMP (p = 0.017), but not total COMP (p = 0.5), declined significantly after replacement demonstrating a joint tissue source for D-COMP. In analyses of 450 participants from the Johnston County Osteoarthritis Project controlled for age, gender, and race, D-COMP was associated with radiographic hip (p < 0.0001) but not knee (p = 0.95) OA severity. In contrast, total COMP was associated with radiographic knee (p < 0.0001) but not hip (p = 0.47) OA severity. D-COMP was higher in soluble proteins extracted from hip cartilage proximal to OA lesions compared with remote from lesions (p = 0.007) or lesional and remote OA knee (p < 0.01) cartilage. Total COMP in cartilage did not vary by joint site or proximity to the lesion. This study demonstrates the presence of D-COMP in articular cartilage and the systemic circulation, and to our knowledge, it is the first biomarker to show specificity for a particular joint site. We believe that enrichment of deamidated epitope in hip OA cartilage indicates a lesser repair response of hip OA compared with knee OA cartilage.

Biomarkers of incident radiographic knee osteoarthritis: do they vary by chronic knee symptoms?

OBJECTIVE

To explore the ability of osteoarthritis (OA)-related biomarkers to predict incident radiographic knee OA in a large sample of African American and Caucasian men and women.

METHODS

Baseline levels of serum cartilage oligomeric matrix protein (COMP), hyaluronan (HA), high-sensitivity C-reactive protein (hsCRP), and keratan sulfate (KS) and baseline and followup radiographs were available for 353 knees without baseline osteophyte formation and for 446 knees without baseline joint space narrowing (JSN). Cox models estimated the hazard ratio (HR) and 95% confidence interval (95% CI) for incident knee OA for a 1-unit increase in the ln of each biomarker, with adjustment for age, race, sex, body mass index, and knee OA of the contralateral limb. Report of chronic knee symptoms was explored as a modifier of the association.

RESULTS

The hazard of incident knee osteophytes (HR 2.16 [95% CI 1.39-3.37]) and incident JSN (HR 1.82 [95% CI 1.15-2.89]) increased with higher baseline ln(COMP) levels. The hazard of incident knee JSN increased with higher ln(HA) levels (HR 1.46 [95% CI 1.14-1.87]). Baseline ln(hsCRP) and ln(KS) did not predict incident knee outcomes. HRs per unit increase in ln(COMP), ln(HA), and ln(KS) were higher among knees with chronic symptoms than among those without symptoms.

CONCLUSION

Higher baseline ln(COMP) and ln(HA) levels were associated with incident knee OA over an average followup period of 6.3 years. These results represent detection of a molecular stage of OA prior to radiographic manifestations. Further exploration is needed to determine how chronic knee symptoms modify the biomarker-incident knee OA association.

Active shape modeling of the hip in the prediction of incident hip fracture

The objective of this study was to evaluate right proximal femur shape as a risk factor for incident hip fracture using active shape modeling (ASM). A nested case-control study of white women 65 years of age and older enrolled in the Study of Osteoporotic Fractures (SOF) was performed. Subjects (n = 168) were randomly selected from study participants who experienced hip fracture during the follow-up period (mean 8.3 years). Controls (n = 231) had no fracture during follow-up. Subjects with baseline radiographic hip osteoarthritis were excluded. ASM of digitized right hip radiographs generated 10 independent modes of variation in proximal femur shape that together accounted for 95% of the variance in proximal femur shape. The association of ASM modes with incident hip fracture was analyzed by logistic regression. Together, the 10 ASM modes demonstrated good discrimination of incident hip fracture. In models controlling for age and body mass index (BMI), the area under receiver operating characteristic (AUROC) curve for hip shape was 0.813, 95% confidence interval (CI) 0.771-0.854 compared with models containing femoral neck bone mineral density (AUROC = 0.675, 95% CI 0.620-0.730), intertrochanteric bone mineral density (AUROC = 0.645, 95% CI 0.589-0.701), femoral neck length (AUROC = 0.631, 95% CI 0.573-0.690), or femoral neck width (AUROC = 0.633, 95% CI 0.574-0.691). The accuracy of fracture discrimination was improved by combining ASM modes with femoral neck bone mineral density (AUROC = 0.835, 95% CI 0.795-0.875) or with intertrochanteric bone mineral density (AUROC = 0.834, 95% CI 0.794-0.875). Hips with positive standard deviations of ASM mode 4 had the highest risk of incident hip fracture (odds ratio = 2.48, 95% CI 1.68-3.31, p < .001). We conclude that variations in the relative size of the femoral head and neck are important determinants of incident hip fracture. The addition of hip shape to fracture-prediction tools may improve the risk assessment for osteoporotic hip fractures.

New developments in osteoarthritis. Sex differences in magnetic resonance imaging-based biomarkers and in those of joint metabolism

Sex differences in the prevalence, incidence, and severity of osteoarthritis (OA) have long been known. Some differences in the evaluation of this issue across studies may be related to differences in study design, sampling, study size, study populations, targeted joint sites, and definitions of OA. This report highlights recent studies of sex differences in individual joint components imaged by magnetic resonance imaging and in systemic biomarkers of joint metabolism. Particularly important are those studies that examine this issue in young unaffected adults and children before the development of disease. Despite some variation across studies, women appear for the most part to have a thinner and more reduced volume of cartilage in the knee than men, and this may occur from early childhood. It is not clear whether women have a more accelerated rate of cartilage volume loss than men. Few data exist on sex differences in systemic biomarkers of joint metabolism. In these studies, it is critically important to characterize the total body burden of OA and the presence of comorbid conditions likely to influence a given biomarker. Lastly, future research should dovetail studies of sex differences in imaging and biochemical biomarkers with genetics to maximize insight into the mechanisms behind observed sex differences.

Improving the routine management of rheumatoid arthritis: the value of tight control

Evidence is mounting that adopting a tight control approach to the management of patients with rheumatoid arthritis (RA) yields superior clinical outcomes including inhibition of progressive structural damage. While this approach has been successfully implemented in other chronic diseases, such as diabetes, its use in RA is less straightforward as there is not a simple "gold standard" measure for disease activity. A key component of the tight control approach is the availability of easily implemented and clinically relevant assessment measures of disease activity that allow physicians to monitor progress toward preset goals. This article summarizes the evidence from clinical trials demonstrating the benefits of achieving tight control and surveys the instruments available to assess patient progress in a consistent manner. A case study clearly demonstrates the benefits of the tight control approach in routine clinical practice.

Value of entheseal ultrasonography and serum cartilage oligomeric matrix protein in the preclinical diagnosis of psoriatic arthritis

Objective:

To evaluate the utility of entheseal ultrasonography and serum COMP in the preclinical diagnosis of psoriatic arthritis.

Methods:

60 psoriatic patients were divided into: 30 patients with psoriasis (group I) and 30 patients with psoriatic arthritis as control (group II). They underwent independent clinical and ultrasonographic examination of both lower limbs at the calcaneal insertions of Achilles tendons. Psoriatic arthritis disease activity and severity was assessed by modified DAS28 and Steinbrockers scores. Serum levels of COMP were measured for all patients by ELISA.

Results:

On clinical examination, no entheseal abnormalities were detected in group I while they were present in 23.3% of group II with statistically significant difference between them (P < 0.001). Ultrasonographic entheseal abnormalities were detected in 33.3% of group I and in 46.7% of group II with no significant difference between them (P > 0.05). Serum COMP were significantly elevated in group I and II with no statistically significant difference between them (mean ± SD 5.9 ± 3 and 6.8 ± 12 respectively, P > 0.05). Entheseal ultrasound was more specific (67%) while serum COMP was more sensitive (87%) in the preclinical diagnosis of psoriatic arthritis. Serum COMP levels were significantly correlated with CRP in both groups and with DAS28 and Steinbrockers scores in group II (P < 0.01).

Conclusion:

Entheseal ultrasonography and serum COMP levels may be used complementary to each other for preclinical diagnosis of psoriatic arthritis. Serum COMP seems to be promising prognostic marker for psoriatic arthritis patients.

The association of proximal femoral shape and incident radiographic hip OA in elderly women

PURPOSE

Variations in femoral head shape are reported to predict incident hip osteoarthritis (OA). This study evaluated if proximal femur shape at baseline was a risk factor for incident radiographic hip OA (RHOA) after 8.3 years of follow-up in a cohort of elderly Caucasian women.

METHODS

Supine pelvic radiographs were obtained as part of the Study of Osteoporotic Fractures (SOF) at baseline and Visit 5 (8.3 years later), and were scored for RHOA. A nested case-control study was performed: hips were eligible for inclusion if they had no prevalent RHOA in either hip at baseline. Cases of incident RHOA were defined as no RHOA at baseline and RHOA in their right hip present at Visit 5 [or right total hip replacement (THR) for OA between baseline for follow-up] and a random selection of one half of all incident RHOA cases plus right THR cases (n=102) were chosen. A random selection (n=249) of control subjects who had no RHOA in their right hip at both baseline and follow-up visit were included for comparison. The shape of the right proximal femur was outlined on a digitized baseline radiograph and a statistical image analysis technique, Active Shape Modeling (ASM), was used to generate 10 unique and independent "modes" or variations in shape, which explained 95% of the variance in the shape of the proximal femurs studied. Any hip shape was therefore described as the average shape plus a linear combination of these 10 independent modes of variation. The values for each of these 10 modes for each hip analyzed were entered into a logistic regression model as independent predictors of incident RHOA adjusting for covariates.

RESULTS

The incident RHOA cases were slightly taller, heavier and had higher total hip bone mineral density (BMD) than control subjects (P<0.05), but were otherwise similar demographically. Results of ASM showed that Modes 1, 2 and 3 together explained 81% of the variance in proximal femur shape among all subjects analyzed. Modes 3, 5, 9 which accounted for 8.9%, 3.3% and 0.8% of the variance respectively, were significant predictors of incident RHOA with adjusted odds-ratios ranging from 1.61 to 1.99 (P<0.001) for every 1 standard deviation (SD) increase in the mode score.

CONCLUSION

These results suggest that variations in the relative sizes of the femoral head and neck at baseline are modest determinants of incident RHOA in elderly Caucasian women.

Association of biomarkers with pre-radiographically defined and radiographically defined knee osteoarthritis in a population-based study

OBJECTIVE

To evaluate 10 biomarkers in magnetic resonance imaging (MRI)-determined, pre-radiographically defined osteoarthritis (pre-ROA) and radiographically defined OA (ROA) in a population-based cohort of subjects with symptomatic knee pain.

METHODS

Two hundred one white subjects with knee pain, ages 40-79 years, were classified into OA subgroups according to MRI-based cartilage (MRC) scores (range 0-4) and Kellgren/Lawrence (K/L) grades of radiographic severity (range 0-4): no OA (MRC score 0, K/L grade<2), pre-ROA (MRC score>or=1, K/L grade<2), or ROA (MRC score>or=1, K/L grade>or=2). Urine and serum samples were assessed for levels of the following biomarkers: urinary biomarkers C-telopeptide of type II collagen (uCTX-II), type II and types I and II collagen cleavage neoepitopes (uC2C and uC1,2C, respectively), and N-telopeptide of type I collagen, and serum biomarkers sC1,2C, sC2C, C-propeptide of type II procollagen (sCPII), chondroitin sulfate 846 epitope, cartilage oligomeric matrix protein, and hyaluronic acid. Multicategory logistic regression was performed to evaluate the association of OA subgroup with individual biomarker levels and biomarker ratios, adjusted for age, sex, and body mass index.

RESULTS

The risk of ROA versus no OA increased with increasing levels of uCTX-II (odds ratio [OR] 3.12, 95% confidence interval [95% CI] 1.35-7.21), uC2C (OR 2.13, 95% CI 1.04-4.37), and uC1,2C (OR 2.07, 95% CI 1.06-4.04), and was reduced in association with high levels of sCPII (OR 0.53, 95% CI 0.30-0.94). The risk of pre-ROA versus no OA increased with increasing levels of uC2C (OR 2.06, 95% CI 1.05-4.01) and uC1,2C (OR 2.06, 95% CI 1.12-3.77). The ratios of type II collagen degradation markers to collagen synthesis markers were better than individual biomarkers at differentiating the OA subgroups, e.g., the ratio of [uCTX-II][uC1,2C] to sCPII was associated with a risk of ROA versus no OA of 3.47 (95% CI 1.34-9.03) and a risk of pre-ROA versus no OA of 2.56 (95% CI 1.03-6.40).

CONCLUSION

Different cartilage degradation markers are associated with pre-ROA than are associated with ROA, indicating that their use as diagnostic markers depends on the stage of OA. Biomarker ratios contrasting cartilage degradation with cartilage synthesis are better able to differentiate OA stages compared with levels of the individual markers.

High Serum Cartilage Oligomeric Matrix Protein Determines the Subset of Patients with Early-Stage Rheumatoid Arthritis with High Serum C-Reactive Protein, Matrix Metalloproteinase-3, and MRI-Proven Bone Erosion

Objective.

To identify the significance of serum cartilage oligomeric matrix protein (COMP), a marker of cartilage turnover, in patients with early-stage rheumatoid arthritis (RA) in relation to other serologic variables and magnetic resonance imaging (MRI) features.

Methods.

Ninety-eight patients with early-stage RA, whose disease duration from onset was less than 2 years, were enrolled. The objective measures at baseline were Disease Activity Score (DAS28), serum C-reactive protein (CRP), serum matrix metalloproteinase-3 (MMP-3), serum antibodies against cyclic citrullinated peptide (anti-CCP), and MRI features of both wrist and finger joints. The MRI features included the number of sites scored positive for synovitis, bone edema, and bone erosion.

Results.

Serum COMP concentration was not different among groups identified with low, moderate, and high DAS28-CRP values. However, COMP values were statistically high in subjects positive for bone erosions on MRI compared with the subjects who were negative for bone erosions. A positive correlation of COMP with CRP and with MMP-3 values was also identified.

Conclusion.

Elevation of COMP may reflect joint damage that is dependent on the synovial inflammatory process in early-stage RA.

Inverse association of general joint hypermobility with hand and knee osteoarthritis and serum cartilage oligomeric matrix protein levels

OBJECTIVE

Extensive joint hypermobility, lower serum cartilage oligomeric matrix protein (COMP) levels, and early-onset osteoarthritis (OA) are phenotypes of inherited pseudoachondroplasia and multiple epiphyseal dysplasia. However, few studies have evaluated the association between articular hypermobility and primary OA. We undertook the present study to evaluate this association and to test the hypothesis that COMP levels are associated with hypermobility in patients with OA and individuals without OA.

METHODS

Two separate cohorts were available for analysis, the CARRIAGE (CARolinas Region Interaction of Aging Genes and Environment) extended family and a subset of the GOGO (Genetics of Generalized Osteoarthritis) sibpair cohort. In the CARRIAGE family, we performed hand and knee examinations and hypermobility evaluations (Beighton criteria) and obtained sera for measurement of COMP and hyaluronan (HA). Data on COMP and HA levels and extensive joint radiographic and hypermobility data were also available for the GOGO cohort.

RESULTS

The prevalence of hypermobility was 13% in the CARRIAGE family and 5% in the GOGO cohort. In the CARRIAGE family, hypermobility was associated with a significantly reduced prevalence of hand (especially proximal interphalangeal joint) and knee OA and lower mean serum COMP levels, both in the total cohort and in non-hand-OA subgroups. These results were further validated in the GOGO subsets without radiographic OA, in which hypermobility was also associated with a significantly reduced mean serum COMP level (P < 0.0001 adjusted for age). Serum HA levels did not differ in relation to hypermobility in either cohort.

CONCLUSION

The present results indicate that there is an inverse relationship between hypermobility and hand and knee OA, and that hypermobility is associated with lower serum COMP levels. Genetic variations of the COMP gene may account for some subgroups of benign joint hypermobility.

Biomarkers in the development of novel disease-modifying therapies for osteoarthritis

Identification and utilization of biomarkers is vitally important for the successful development of disease-modifying osteoarthritis drugs. Biochemical and imaging platforms hold great promise to deliver such biomarkers. Studies indicate a marked increase in biochemical products arising from the breakdown and biosynthesis of collagen, extracellular matrix and bone in osteoarthritis. These molecules have been associated with disease severity and may also have prognostic value as indicators of disease progression. However, issues including biological variability and lack of tissue specificity currently hinder the utility of these molecular markers in drug development. Imaging technologies hold great potential for sensitive and accurate measurement of disease-related structural damage. Drawbacks, including expense, need for validation and limited accessibility also limit the utility of these technologies. In this article, the potential value and challenges in developing and utilizing biomarkers in disease-modifying osteoarthritis drug development will be discussed.

Change in serum measurements of cartilage oligomeric matrix protein and association with the development and worsening of radiographic hip osteoarthritis

OBJECTIVE

To determine the association between changes in serum levels of cartilage oligomeric matrix protein (COMP) and serum N-telopeptide crosslinks (NTX) over a 6-year interval with the development and progression of radiographically apparent hip osteoarthritis (RHOA) in a community sample of elderly women over 8.3 years of follow-up.

METHODS

Pelvic radiographs were obtained a mean of 8.3 years apart in Caucasian women > or =65 years of age enrolled in the Study of Osteoporotic Fractures. From a cohort of 5928 subjects, we randomly sampled study subjects ( approximately 170 per group) to perform two nested case-control studies, one of RHOA incidence and the other of RHOA progression. Baseline and year 6 serum COMP and serum NTX levels were measured by enzyme linked immunosorbent assay in duplicate and percentage change in serum levels was calculated. Odds ratios (ORs) and 95% confidence intervals (CIs) for 1 standard deviation (SD) change in the serum COMP and NTX level differences were calculated using logistic regression analysis and used to predict the development or progression of RHOA, adjusting for potential covariates.

RESULTS

The percentage change in the level of serum COMP from baseline to year 6 was found to be a risk factor for the development of incident RHOA [adjusted OR of 1.58 per 1 SD increase (95% CI: 1.19-2.09)], and reduction of progression of RHOA [adjusted OR of 0.74 per 1 SD increase (95% CI: 0.58-0.96)]. Quartile analysis of serum COMP changes revealed that the three highest quartiles of change in serum COMP were associated with (1) a five-fold greater risk of developing incident RHOA [adjusted OR=5.42 (95% CI: 2.80-10.60)], and (2) a 50% decreased risk of developing progression of RHOA [adjusted OR=0.48 (95% CI: 0.30-0.80)]. No significant association was found between changes in serum NTX levels from baseline to year 6 with either incident RHOA or the progression of existing RHOA.

CONCLUSION

Measurement of serum COMP at two distinct timepoints may be a method of identifying patients at risk for developing incident RHOA and those with baseline RHOA that will not rapidly progress.

Biochemical markers of bone turnover in aseptic loosening in hip arthroplasty

The aim of this study was to determine the diagnostic value of systemic biochemical markers of bone turnover in aseptic loosening in hip arthroplasty, namely the urine levels of three bone resorption peptides - crosslinked n-telopeptides (NTX), c-telopeptides (CTX I) and deoxypyridinoline (DPD). We compared 52 patients with surgically proven component loosening with 52 patients without clinical or radiological signs of endoprosthetic loosening and 52 healthy individuals. All three markers were measured using commercially available enzyme-linked immunoassays. We found significantly increased levels of DPD in the loosening group (p < 0.05), but there was no significant difference between the loosening group and the two reference groups for the other two markers tested. Our data suggest that DPD can be used as an additional tool in the diagnosis of aseptic loosening in hip arthroplasty but CTX I and NTX have no predictive value in this context.

Estrogen receptor alpha genotype is associated with a reduced prevalence of radiographic hip osteoarthritis in elderly Caucasian women

PURPOSE

This study evaluated the association between polymorphisms in the estrogen receptor (ER) alpha gene (ESR1) and prevalent and incident radiographic hip osteoarthritis (RHOA) in a large, well-defined prospective cohort of elderly Caucasian women.

METHODS

Prevalent and incident RHOA was evaluated from all available pelvis X-rays obtained from the Study of Osteoporotic Fractures at baseline and after a mean of 8.3 years. Evaluable DNA samples were available from 4746 of these subjects. RHOA cases were defined by published methods. The ESR1 polymorphisms at intron I (Pvu II for a T/C substitution and Xba I for an A/G substitution) were genotyped in the context of a multiplex polymerase chain reaction (PCR) amplification followed by allele-specific single nucleotide polymorphism (SNP) detection with immobilized oligonucleotide probes in linear arrays. Multiple logistic regression was performed to estimate odds ratios (ORs) and 95% confidence intervals (95% CI) associated with the T/C and A/G polymorphisms.

RESULTS

RHOA was present in 12.1% of subjects, of whom 325 had joint space narrowing (JSN) score > or =3 and 130 had an osteophyte score > or =2 and JSN score > or =2. There was a significant reduction in the odds of prevalent RHOA for individuals with the C/C compared to T/T genotype at the Pvu II site with an OR of 0.71 (95% CI: 0.55-0.92) (P=0.01). Adjustments for age, weight, height, hip Bone mineral density (BMD) and estrogen use did not alter the relationship between the C/C genotype and reduced risk of RHOA, with an OR of 0.71 (95% CI: 0.54-0.94) (P=0.01). The risk of incident RHOA was reduced for the Pvu II C/C compared to the T/T genotype (P=0.11). Also, the reduced risk of incident RHOA in C/C subjects varied by estrogen use. There was no association between the Xba I G/G or G/A genotypes and RHOA with OR of 0.82 (95% CI: 0.61-1.10) (P=0.19) compared to women with A/A genotype.

CONCLUSIONS

We conclude that the C/C genotype of the ER alpha Pvu II polymorphism was associated with a modestly reduced risk of prevalent and incident RHOA in elderly Caucasian women. Additional work is required to understand how the intron I ESR1 polymorphism may alter joint degeneration.

Biological markers in osteoarthritis

Osteoarthritis (OA) is a progressive disorder characterized by destruction of articular cartilage and subchondral bone, and by synovial changes. The diagnosis of OA is generally based on clinical and radiographic changes, which occur fairly late during disease progression and have poor sensitivity for monitoring disease progression. Progression of joint damage is likely to result primarily from an imbalance between cartilage degradation and repair, so measuring markers of these processes would seem a promising approach to improve the prediction of disease progression at the individual level. Moreover, genetic markers might be useful predictors of prognosis. The lack of fully effective, chondroprotective medications has limited the use of such potential markers to monitor the effect of treatment for OA. Nevertheless, owing to their dynamic changes in response to treatment, biological markers might provide relevant information more rapidly than imaging techniques (such as radiography and MRI) can, and should contribute to our understanding of mechanisms that underlie the clinical efficacy of OA treatments. Most of the identified genes involved in OA encode signal-transduction proteins, which provide the potential for novel therapeutic approaches. In this Review, we will use the recently proposed BIPED (i.e. burden of disease, investigative, prognostic, efficacy of intervention and diagnostic) classification of OA markers to describe the potential usage of a given marker.

Unique matrix structure in the rough endoplasmic reticulum cisternae of pseudoachondroplasia chondrocytes

Mutations in cartilage oligomeric matrix protein (COMP) cause two skeletal dysplasias, pseudoachondroplasia (PSACH) and multiple epiphyseal dysplasia (MED/EDM1). Because COMP exists as a homopentamer, only one mutant COMP subunit may result in an abnormal complex that is accumulated in expanded rough endoplasmic reticulum (rER) cisternae, a hallmark of PSACH. Type IX collagen and matrilin-3 (MATN3), also accumulate in the rER cisternae of PSACH chondrocytes, but it is unknown how mutant COMP interacts with these proteins. The studies herein focus on defining the organization of these intracellularly retained proteins using fluorescence deconvolution microscopy. A unique matrix organization was identified in which type II procollagen formed a central core surrounded by a protein network of mutant COMP, type IX collagen, and MATN3. This pattern of matrix organization was found in multiple cisternae from single chondrocytes and in chondrocytes with different COMP mutations, indicating a common pattern of interaction. This suggests that stalling of mutant COMP and an interaction between mutant COMP and type II procollagen are initiating events in the assembly of matrix in the rER, possibly explaining why the material is not readily cleared from the rER. Altogether, these data suggest that mutant COMP initiates and perhaps catalyzes premature intracellular matrix assembly.

Serum matrix metalloproteinase 3 is an independent predictor of structural damage progression in patients with ankylosing spondylitis

OBJECTIVE

In prospective studies, only baseline radiographic damage has been identified as an independent predictor of radiographic progression in ankylosing spondylitis (AS). Several biomarkers have been identified as independent predictors of radiographic progression in rheumatoid arthritis, however, and these may be of use in AS. This study was undertaken to analyze serologic biomarkers as predictors of radiographic progression in AS.

METHODS

We measured a panel of biomarkers reflecting cartilage turnover and osteoclasis. These biomarkers were cartilage oligomeric matrix protein, human cartilage gp-39 (YKL-40), type II collagen epitopes detected by the C2C and C1,2C degradation assays and the CPII synthesis assay, aggrecan 846 epitope, osteoprotegerin, and matrix metalloproteinase 3 (MMP-3). The analysis was performed in a cohort of AS patients from the Netherlands, Belgium, and France enrolled in a longitudinal study, the Outcome Assessments in Ankylosing Spondylitis International Study. We examined 2-year radiographic progression data scored using the modified Stoke AS Spine Score (mSASSS).

RESULTS

Complete data were available on 97 patients. Only the biomarkers YKL-40 and MMP-3 showed weak to moderate univariate correlation with 2-year progression. After adjustment for sex, age, disease duration, C-reactive protein level, and baseline mSASSS, only MMP-3 was significantly associated with 2-year progression (beta = 0.29, P = 0.004). Logistic regression analysis revealed MMP-3 (cutoff 68 ng/ml; odds ratio 9.4 [95% confidence interval 1.6-56]) and baseline mSASSS (cutoff 10 mSASSS units; odds ratio 18.6 [95% confidence interval 2.5-138]) as the only independent predictors of 2-year progression (cutoff 3 mSASSS units; model R(2) = 50%). MMP-3 was primarily contributory in patients who already had substantial baseline damage (>10 mSASSS units).

CONCLUSION

These results indicate that MMP-3 is a significant independent predictor of radiographic progression in patients with AS, particularly in those with preexisting radiographic damage.

New biochemical markers of osteoarthritis

Osteoarthritis is characterized by the progressive destruction of articular cartilage and subchondral bone and synovial reaction. Radiological findings that form the basis of the diagnosis of osteoarthritis are poorly sensitive for detecting early disease and monitoring progression of joint damage. New specific and sensitive biochemical markers of cartilage and synovial tissue turnover, including assays for Type II collagen synthesis and degradation, have been developed. Recent prospective studies indicate that blood and urine levels of these new markers are associated with the progression of joint damage. Biological markers respond rapidly to treatment, and thus will certainly play an important role in the development and monitoring of disease-modifying therapies. As osteoarthritis involves different tissues and complex biological processes, a combination of different biochemical markers appears to be the most promising diagnostic strategy.