Rheumatology Advance Access originally published online on August 18, 2006
Rheumatology 2006 45(10):1308-1309; doi:10.1093/rheumatology/kel271
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
LETTERS TO THE EDITOR |
Associations between cartilage oligomeric matrix protein and several articular tissues in early knee joint osteoarthritis
Department of Laboratory Medicine, Tartu University and 1Department of Radiology, Tartu University Clinics, Estonia
Correspondence to: J. Kumm, L. Puusepa 1A-4022, Tartu 50406, Estonia. E-mail: Jaanika.Kumm{at}kliinikum.ee
SIR, Knee osteoarthritis (OA) involves different joint tissues. Nevertheless, main focus has been placed on the changes in articular cartilage. Therefore, components of the cartilage have been studied thoroughly as progression markers for early stage OA [1, 2]. Recently, with the help of the whole panel of cartilage biomarkers, Sharif et al. [3] found that only serum cartilage oligomeric matrix protein (S-COMP) levels differentiated between the subsets of tibiofemoral (TF) and patellofemoral (PF) OA, being higher in the former subset.
However, it is not clear which structural changes are related to high levels of biomarkers in knee OA. S-COMP is not an entirely cartilage-specific macromolecule but is also found in tendons, ligaments, menisci and synovium [4]. Usually, the radiographic diagnosis of OA is a combination of joint space narrowing (JSN) and/or presence of osteophytes. To the best of our knowledge, the relationship between S-COMP and the above mentioned features of OA have not been investigated separately. We made an attempt to investigate what kind of knee-joint structures might be associated with increased levels of S-COMP in subjects with early knee OA.
A population-based cohort of 158 subjects, aged 32–55 (mean 45) yrs, with chronic knee pain (>3 months) and/or other knee joint limitations was examined clinically and radiologically. The study was approved by the Ethical Committee of Human Research, Tartu University. From each subject written, informed consent for participation was obtained according to the Declaration of Helsinki. Among them, 99 (63%) were women and 59 (37%) were men. Serum levels of COMP were measured by ELISA (AnaMar Medical, Uppsala, Sweden).
The radiographs from both knee joints were performed in a standing frontal antero-posterior position for the assessment of the TF joints and in a lying position, with the knee joint in 60° flexion, for PF joints. The radiographs were graded independently by two radiologists for osteoarthritic changes (presence of JSN and/or osteophytes) according to the grading system (grades 0–III) of Nagaosa et al. [5].
Fifty-five (34%) individuals in the study group had knee-joint symptoms but no radiographic findings, 85 (53%) were diagnosed with knee OA grade I, among them 20 with only tibiofemoral OA, 35 with only patellofemoral OA and 30 had both knee joint compartments affected in combination. Twenty-one subjects (13%) had OA grade II or III, predominantly in the PF region. Radiographic findings of osteophytes and JSN were distributed in the OA group as follows: one-third had only osteophytes, another third had only JSN and the rest had both simultaneously.
The knees were examined ultrasonographically using a multi-frequency linear 7.5 MHz probe. The presence of osteophytes, thickness of tendons, PF cartilage, meniscal changes and synovial effusion was assessed according to the EULAR guidelines [6] and graded in 0/1 scale.
For statistical evaluations non-parametric methods (Spearman's rank correlations, Mann–Whitney U-test) were used. P-values < 0.05 were considered significant.
S-COMP median values for male and female subjects were 12.0 and 9.8 U/l, respectively, P = 0.0001. Data demonstrated obvious gender differences with regard to associations between the S-COMP levels and the other parameters (Table 1). S-COMP values correlated with age only in female subjects (
= 0.284, P = 0.004). Additional investigations showed that the S-COMP values were significantly higher in the female subjects with osteophytes compared with those without any radiographic changes (P = 0.05, by Mann–Whitney U-test). More detailed analysis revealed that only TF osteophytes influence S-COMP levels. No correlation was found when the diagnosis was based solely on JSN.
|
Our results are in accordance with the findings of Sharif et al. [3] that S-COMP is higher in men and in the case of TFOA. Our results, which are based on the subjects about 20 yrs younger than those in the material by Sharif et al., indicate that in some women, at least in early stage OA, the appearance of osteophytes involves increased S-COMP levels. Investigating subjects of the same age range as those in our study, Boegard et al. [7] found that TF osteophytes might be important signs of cartilage defects detectable by MRI. Therefore, being the expression of chondroneogenesis [8], osteophytes could be accompanied by cartilage damage not yet visible on plain radiographs. The possible link between S-COMP levels and osteophytes needs further investigation.
Also, the gender differences in COMP levels, which have not been taken account in the majority of studies, definitely require more attention. Up to now conflicting results have been published concerning gender differences [3, 9]. Nevertheless, both groups have stressed a significant increase in serum COMP levels at the age >65 yrs, especially in women. At present, we cannot exclude gender specific differences in development of early knee OA.
Our findings, based on the correlations between S-COMP levels and changes in the soft tissues confirm the standpoint that COMP is a more general marker of the joint tissues which might explain the finding that only S-COMP levels differentiated between the TF and PF OA groups, unlike other cartilage biomarkers (GAG, KS, YKL-40) [3]. Compared with other biomarkers, S-COMP might reflect better the changes in the joint as COMP consists of the contributions of different articular tissues.
 |
Acknowledgements |
|---|
 Top Acknowledgements References |
|---|
This study was supported by grant No. 5308 by the Estonian Science Foundation.
The authors have declared that there are no conflicts of interest.
|
References |
|---|
|
TopAcknowledgementsReferences |
|---|
- Wollheim FA. (2003) Early stages of osteoarthritis: the search for sensitive predictors. Ann Rheum Dis 62:1031–2.
[Free Full Text] - Reijman M, Hazes J, Bierma-Zeinstra S, et al. (2004) A new marker for osteoarthritis: cross-sectional and longitudinal approach. Arthritis Rheum 50:2471–8.[CrossRef][Web of Science][Medline]
- Sharif M, Granell R, Johansen J, Clarke S, Elson C, Kirwan J. (2006) Serum cartilage oligomeric matrix protein and other biomarker profiles in tibiofemoral and patellofemoral osteoarthritis of the knee. Rheumatology 45:522–6.
[Abstract/Free Full Text] - Petersson I, Boegard T, Svensson B, Heinegard D, Saxne T. (1998) Changes in cartilage and bone metabolism identified by serum markers in early osteoarthritis of the knee joint. Br J Rheumatol 37:46–50.
[Abstract/Free Full Text] - Nagaosa Y, Mateus M, Hassan B, et al. (2000) Development of logically devised line drawing atlas for grading of knee osteoarthritis. Ann Rheum Dis 59:587–95.
[Abstract/Free Full Text] - Backhaus M, Burmester G, Gerber T, Grassi W, Machold K, Swen W. (2001) Guidelines for musculoskeletal ultrasound in rheumatology. Ann Rheum Dis 60:641–9.
[Free Full Text] - Boegard T, Rudling O, Petersson I, Jonsson K. (1998) Correlation between radiographically diagnosed osteophytes and magnetic resonance detected cartilage defects in the tibiofemoral joint. Ann Rheum Dis 57:401–7.
[Abstract/Free Full Text] - Gelse K, Söder S, Eger W, Diemtar T, Aigner T. (2003) Osteophyte development – molecular characterization of differentation stages. Osteoarthritis Cartilage 11:141–8.[CrossRef][Web of Science][Medline]
- Clarke A, Jordan J, Vilim V, et al. (1999) Serum cartilage oligomeric matrix protein reflects osteoarthritis presence and severity. Arthritis Rheum 42:2356–64.[CrossRef][Web of Science][Medline]
CiteULike 
Connotea 
Del.icio.us What's this?
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||