HLA DRB1* typing and cartilage oligomeric matrix protein (COMP) as predictors of joint destruction in recent-onset rheumatoid arthritis

Cartilage oligomeric matrix protein: COMPopathies and beyond

Cartilage oligomeric matrix protein (COMP) is a large pentameric glycoprotein that interacts with multiple extracellular matrix proteins in cartilage and other tissues. While, COMP is known to play a role in collagen secretion and fibrillogenesis, chondrocyte proliferation and mechanical strength of tendons, the complete range of COMP functions remains to be defined. COMPopathies describe pseudoachondroplasia (PSACH) and multiple epiphyseal dysplasia (MED), two skeletal dysplasias caused by autosomal dominant COMP mutations. The majority of the mutations are in the calcium binding domains and compromise protein folding. COMPopathies are ER storage disorders in which the retention of COMP in the chondrocyte ER stimulates overwhelming cellular stress. The retention causes oxidative and inflammation processes leading to chondrocyte death and loss of long bone growth. In contrast, dysregulation of wild-type COMP expression is found in numerous diseases including: fibrosis, cardiomyopathy and breast and prostate cancers. The most exciting clinical application is the use of COMP as a biomarker for idiopathic pulmonary fibrosis and cartilage degeneration associated osteoarthritis and rheumatoid and, as a prognostic marker for joint injury. The ever expanding roles of COMP in single gene disorders and multifactorial diseases will lead to a better understanding of its functions in ECM and tissue homeostasis towards the goal of developing new therapeutic avenues.

[Biomarkers in rheumatoid arthritis]

The search for biomarkers in rheumatoid arthritis (RA) has been the object of interesting research in the past few years, although results have not always been relevant. Several biomarkers, from several different locations (blood, urine, synovial fluid, synovial tissue) and of different nature (autoantibodies, genetic markers, joint remodeling markers), and related to different outcomes, diagnostic and prognostic markers (joint destruction, disability, lack of remission, mortality, response to anti-rheumatic treatment, etc.) have been studied. The present article reviews research only on soluble biomarkers, mainly those in serum, related to the diagnosis and joint destruction in RA.

Cartilage Oligomeric Matrix Protein (COMP): A Biomarker of Arthritis

Arthritis is a chronic disease with a significant impact on the population. It damages the cartilage, synovium, and bone of the joints causing pain, impairment, and disability in patients. Current methods for diagnosis of and monitoring the disease are only able to detect clinical manifestations of arthritis late in the process. However, with the recent onset of successful treatments for rheumatoid arthritis and osteoarthritis, it becomes important to identify prognostic factors that can predict the evolution of arthritis. This is especially critical in the early phases of disease so that these treatments can be started as soon as possible to slow down progression of the disease. A valuable approach to monitor arthritis would be by measuring biological markers of cartilage degradation and repair to reflect variations in joint remodeling. One such potential biological marker of arthritis is cartilage oligomeric matrix protein (COMP). In various studies, COMP has shown promise as a diagnostic and prognostic indicator and as a marker of the disease severity and the effect of treatment. This review highlights the progress in the utilization of COMP as a biomarker of arthritis.

Serum cartilage oligomeric matrix protein (COMP) in rheumatoid arthritis and knee osteoarthritis

The cartilage oligometrix matrix protein (COMP) is a noncollagenous protein, a glycoprotein, the function of which is to bind to type II collagen fibres and stabilise the collagen fibre network in the articular cartilage. In the serum of the normal population the COMP level is 5 mug/ml. An increased level of COMP in the synovial fluid was described in the early stage of rheumatoid arthritis (RA), whereas in advanced stages of RA, the level of COMP decreased. In this study we assessed the serum COMP level in patients with RA and knee osteoarthritis (OA) and found a correlation between the serum COMP level and other markers as well as bone mass density (BMD) changes, activity of disease, disease duration and the age of the patients. The blood was collected from 30 RA patients and 30 OA patients who constituted the control group. The serum COMP level was determined using an inhibition enzyme-linked immunosorbent assay (ELISA). The average value of the serum COMP level in RA patients was 10.4+/-3.6 U/l. There was a correlation between the serum COMP level and the age of RA patients (p<0.005) and disease activity score (DAS) value (p<0.01). According to correlation coefficients, the serum COMP level was independent of stage of disease, number of painful and swollen joints, duration of morning stiffness, disease duration and titre of the Waaler-Rose test. The influence of rheumatoid nodule presence on the serum COMP level was shown (p<0.05). In RA patients with erythrocyte sedimentation rate (ESR) values below 20 mm/h compared with patients with ESR values over 60 mm/h, the serum COMP level was observed to be significantly lower (p<0.05). The average value of COMP in OA patients was 10.4+/-2.7 U/l. No correlation was found between the serum COMP level and patients' age and disease duration. There was a correlation between the serum COMP level and Western Ontario and McMaster Universities (WOMAC) index pain scale for the lower limbs (p<0.005) and T-score value of densitometry examinations (p<0.036) in OA patients. No statistical differences were found between the average serum COMP level in RA and OA patients.

Cartilage oligomeric matrix protein in serum in systemic lupus erythematosus and knee osteoarthritis. Preliminary communication

The cartilage oligomeric matrix protein (COMP) is a glycoprotein, which occurs mainly in an articular cartilage. The amount of this protein increases under the influence of cytokines and growth factors. As a result of various diseases that cause damage to cartilage, fragments of matrix protein are released into synovial fluid and then into blood. The assessment of matrix protein level in serum, for example COMP, permits the establishment of the degree of cartilage damage in inflammatory joint diseases, and permits observation of the effectiveness of the treatment. Blood was collected from 30 systemic lupus erythematosus (SLE) patients, and from 30 patients with knee osteoarthritis (OA) who constituted the control group. Serum COMP level was determined using an inhibition enzyme-linked immunosorbent assay (ELISA). The average value of the serum COMP level in SLE patients was 11.3+/-3.7 U/l. According to correlation coefficients, serum COMP level is independent of patients' age, disease duration and the clinical picture of SLE. No correlation was found between serum COMP level and bone mass density (BMD) changes. In SLE patients with decreased haemoglobin levels (<11.0 g/dl) values compared with patients with normal haemoglobin level, the serum COMP level was observed to be significantly higher (P<0.05). Both in SLE patients with erythrocyte sedimentation rate (ESR) values over 60 mm/h and in patients with ESR values below 60 mm/h, the serum COMP level was observed to be significantly higher (P<0.05). A significant positive correlation was found between serum COMP level and ESR value, as well as a number of thrombocytes. Negative correlation occurred between the serum COMP level and the value of haemoglobin. The average value of COMP in OA patients was 10.4+/-2.7 U/l. No correlation was found between serum COMP level and patients' age and disease duration. There was correlation between the serum COMP level and the T-score value of densitometry examinations in OA patients. No statistical differences were found between the average serum COMP levels for SLE and OA patients.

Serum levels of cartilage oligomeric matrix protein. A predicting factor and a valuable parameter for disease management in rheumatoid arthritis

OBJECTIVE

To examine whether cartilage oligomeric matrix protein (COMP) correlates with inflammation and/or joint destruction of patients with rheumatoid arthritis (RA) and to test COMP as predicting factor for the outcome of patients with established RA.

METHODS

Serum levels of COMP were measured in sera of 62 patients, suffering from RA according to the ACR criteria and treated in intervals in our department, over a period of 5 years. A commercially available sandwich--type ELISA-kit developed by AnaMar Medical AB, Sweden, was used. The results of serum COMP were compared with the Disease Activity Score (DAS), the Larsen Score, and clinical and laboratory parameters.

RESULTS

We found a positive correlation between serum levels of COMP at baseline and deterioration of Larsen score even after 5 years (p < 0.007; r = 0.34). To confirm serum COMP as an independent predicting factor for patients with RA we looked at a subgroup of patients (n = 17) with elevated serum levels of COMP (mean 11,7 U/l) and low clinical prognostic factors. In this subgroup we also found a significant correlation with delta Larsen score (p < 0.01; r = 0.59) after 5 years.

CONCLUSION

Serum levels of COMP is known to reflect increased cartilage turnover. The results indicate that serum COMP may be used as a prognostic marker of cartilage degradation in a patient group with established RA.

The shared epitope and severity of rheumatoid arthritis

After two decades of research involving thousands of RA patients, it is still not possible to precisely define the relation of HLA-DRB1 SE alleles to RA severity. Improvements in our understanding require more careful consideration of several factors such as ethnicity, gender, and the specific SE allele and genotype inherited. Large studies of heterogeneous groups of patients are required and indicate the need for collaborative efforts among researchers. In the interim, meta-analysis of the existing literature may provide some insight, because it allows utilization of the tremendous amount of research already completed. A preliminary meta-analysis highlighted the significant heterogeneity among the existing literature, and a more ambitious meta-analysis that uses individual patient-level data is currently ongoing. Profound implications exist for determination of the precise relationship between the SE and RA severity. This information could be valuable in identifying patients at greater risk of severe complications or as a stratification variable for clinical trials. Moreover, patients genetically predisposed to severe disease may benefit from early initiation of more aggressive therapy. Ultimately, clarification of the role of the SE may be valuable for the development of specific therapies directed toward DRB1 and related targets.

Genetic studies, clinical heterogeneity, and disease outcome studies in rheumatoid arthritis

HLA haplotypes influence various clinical RA features considered to reflect severity in case-control and cohort studies. Of particular note is the fact that HLA generally influences the development of erosive and sometimes seropositive and nodular disease; in prospective studies, it noticeably affects joint surgical intervention. These are valuable clues indicating that HLA influences RA severity and chronicity. Nevertheless, HLA influences are generally weak enough so as to require large study subject numbers for detection. As a result, HLA genotyping has restricted usefulness for prediction of clinical severity in individual patients.

Treatment strategy, disease activity, and outcome in four cohorts of patients with early rheumatoid arthritis

OBJECTIVE

To compare four different inception cohorts of patients with early rheumatoid arthritis (RA) with respect to treatment strategies, disease activity, and outcome during a five year follow up period.

METHOD

Data from cohorts of patients with early RA, with a standardised assessment at least every six months for five years from four different centres, were included in one database. Owing to slight differences in the individual study designs, linearly interpolated values were calculated to complete the standard follow up schedule.

RESULTS

Despite similar inclusion criteria, significant differences in demographic factors and baseline disease activity were found between the different cohorts. During the follow up an aggressive treatment strategy was followed in the Dutch and Finnish cohort, an intermediate strategy in the British cohort, and a conservative strategy in the Swedish cohort. A significant improvement in disease activity was seen in all cohorts, though the most rapid and striking improvement was seen in those receiving aggressive treatment. This resulted in less radiographic destruction in the long run.

CONCLUSION

This observational study of cohorts of patients with early RA confirms that early aggressive treatment results not only in a more rapid reduction of disease activity but also in less radiographic progression in the long term.

Markers of disease in rheumatoid arthritis

Substantial progress can be noted in the efforts to demonstrate the usefulness of tissue-related markers of disease in rheumatoid arthritis and other joint diseases. The most informative studies use longitudinal analyses of well-characterized patient groups. Emphasis should be on searching for markers which can be of prognostic significance. New markers need to be assessed in relation to existing ones, such as C-polysaccharide reacting protein and erythrocyte sedimentation rate, which, although not specific, are hard to beat as measures of inflammation. A newly identified matrix component, cartilage intermediate layer protein, has features which make it attractive as a potential cartilage specific marker. Many markers may not in the end prove clinically useful. They will, however, give important insight into pathogenic processes, and may help in evaluating new therapy. Finally, markers originally identified in humans have now proven their value in experimental arthritis.

Serum markers of articular cartilage damage and repair

Joint cartilage is a dynamic tissue that reacts to trauma, inflammation, and other insults by attempting to repair its matrix. This reaction results in the release of cartilage macromolecules into the body fluids. Analysis of these fluids has identified a limited number of at least somewhat tissue-specific markers of altered cartilage metabolism. Analyses of serum are less specific and less sensitive than analyses of synovial fluid, but their use as research tools in clinical studies, drug development, and experimental work in animal models is increasing.

Knee and/or hip joint destruction in rheumatoid arthritis is associated with HLA-DRB1*0405 in Japanese patients

To determine the prognostic factors for knee and/or hip joint destruction in rheumatoid arthritis (RA) patients, we typed 379 RA patients for HLA-DRB alleles and analysed the antigen frequencies. The DRB1*0405 antigen frequency in RA patients who underwent total knee replacement and/or total hip replacement was significantly higher than in those who did not have replacements, which meant that DRB1*0405 was associated with knee and/or hip joint destruction. This finding may be of value for predicting knee and/or hip joint destruction in RA.