Rheumatology 2001; 40: 739-742
© 2001 British Society for Rheumatology
Original Papers |
Alternatively spliced EDA-containing fibronectin in synovial fluid as a predictor of rheumatoid joint destruction
Department of Medicine and Rheumatology, Kakogawa Konan Hospital and
1 Department of Medicine and Faculty of Health Science, Kobe University School of Medicine, Kobe, Japan
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Abstract |
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Objectives. Fibronectin containing the EDA region (EDA+Fn), a molecule important for rheumatoid joint destruction, was measured in relation to the progression of joint destruction in rheumatoid arthritis (RA).
Methods. Total Fn and EDA+Fn were measured by ELISA, and the concentrations of Fn in plasma and synovial fluid were compared prospectively for 2 yr with the progression of joint destruction in 41 knee joints of 37 patients with RA. The extent of joint destruction was assessed by the Larsen score and joint space narrowing in X-ray films taken before and 2 yr after measurement of EDA+Fn.
Results. The concentration of synovial fluid EDA+Fn showed a positive correlation with the progression of joint destruction in RA (r=0.78). While total Fn in synovial fluid also showed a correlation with joint destruction (r=0.54), total Fn and EDA+Fn in plasma showed no correlation with joint destruction. The concentration of synovial fluid EDA+Fn was significantly higher in patients who underwent joint replacement after the measurement of EDA+Fn than in those who did not receive surgery (P<0.029).
Conclusion. Synovial fluid EDA+Fn can be a predictor of subsequent joint destruction in RA.
KEY WORDS: Fibronectin, EDA, Rheumatoid arthritis, Joint destruction, Prognosis.
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Introduction |
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Multiple isoforms of fibronectin (Fn) are produced from a single gene by alternative splicing at three distinct sites: EDA, EDB and IIICS. The Fn produced by hepatocytes and commonly found in plasma, i.e. plasma Fn, lacks the EDA and EDB regions, whereas the isoforms containing the EDA and EDB regions (EDA+Fn) are expressed in the early stages of fetal development, malignant transformation and wound healing [1]. Recent studies have shown that EDA+Fn synthesized by rheumatoid synovial fibroblast-like cells is highly concentrated in rheumatoid synovial fluids and detectable on rheumatoid cartilage surfaces in a disease-specific manner [2, 3]. EDA+Fn is specifically detectable in the invasive fronts of active cellular pannus [2], and we have shown that Fn on the cartilage surface specifically promotes pannus formation [4]. We have also shown that pannus invasion appears to be increased by interaction between the carboxy-terminal heparin-binding (Hep2) region of EDA+Fn and heparan sulphate proteoglycans on the synovial cells [3].
Because these findings strongly suggest that increased EDA+Fn in the joints increases rheumatoid joint destruction, we studied the contribution of EDA+Fn to subsequent progression of rheumatoid joint destruction. Patients with rheumatoid arthritis (RA) were followed prospectively for 2 yr after measurement of total Fn or EDA+Fn, and the extent of progression of joint destruction was measured by the change in the Larsen score of the knee joints. There was a positive correlation between the concentration of synovial fluid EDA+Fn and the extent of progression of joint destruction. This result is discussed in relation to the progression of rheumatoid joint destruction.
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Patients and methods |
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TopAbstractIntroductionPatients and methodsResultsDiscussionReferences |
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Forty-one knee joints of 37 patients with RA who met the American College of Rheumatology diagnostic criteria [5] were followed prospectively for 2 yr for the progression of joint destruction.
Patient characteristics were as follows: 10 men and 27 women; age 57.0±11.8 yr; disease duration 10.2±6.9 yr; functional class 1.9±0.6; Steinbroker hand X-ray stage 3.0±0.8; grip strength 138±65 mmHg; joint score (Larsen) 14.2±7.9; C-reactive protein (CRP) 4.2±3.5 mg/dl; erythrocyte sedimentation rate (ESR) 71±35 mm/h; rheumatoid factor 452±719 IU/ml. A value of CRP exceeding 0.6 mg/dl and a level of rheumatoid factor exceeding 31 IU/ml were found in 92.5 and 70% of patients respectively. Only patients treated with any one of the non-steroidal anti-inflammatory drugs daily and 5 mg methotrexate weekly were followed prospectively for 2 yr. An increase in the dose of methotrexate up to 7.5 mg weekly was permitted. Methotrexate treatment at these doses is a standard prescription, and a dose of more than 10 mg weekly is seldom prescribed for patients with active disease with RA in Japan. Patients were scheduled to be excluded from the study when other treatments, including disease-modifying anti-rheumatic drugs other than methotrexate and surgery, were changed or newly started during the 2-yr study period. All 37 patients completed the study. The concentrations of total Fn and EDA+Fn in plasma and synovial fluid were measured by ELISA [2]. X-ray films of weight-bearing anteroposterior views of knee joints were taken at the time of measurement of Fn, and were compared with X-ray films taken 2 yr afterwards. The X-ray films were assessed by means of the Larsen score [6]. Changes in the Larsen score and joint space narrowing over the 2-yr study period were compared with the concentrations of total Fn and EDA+Fn in plasma and synovial fluid. The Larsen score and the concentration of Fn were also compared with age, disease duration, joint score, grip strength, CRP, rheumatoid factor, ESR, white cell count and platelet count at the time of measurement of Fn. Joint score was assessed as described previously [7]. Statistical analyses were performed according to Motulsky [8].
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Results |
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The concentration of EDA+Fn in synovial fluids showed a positive correlation with the extent of progression of joint destruction for 2 yr (r=0.78) (Fig. 1
). The correlation between total Fn in synovial fluids and the extent of progression of joint destruction was less significant (r=0.54). The concentration of total Fn or EDA+Fn in plasma showed no correlation with joint destruction. The extent of progression of joint destruction showed no correlation with the values of clinical and laboratory variables at the time of measurement of Fn, including joint score, grip strength, CRP, ESR, rheumatoid factor and peripheral blood counts. This was also the case for the correlation between the concentrations of total Fn and EDA+Fn in synovial fluids and the clinical and laboratory variables mentioned above.
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In the patients studied, the concentrations of total Fn and EDA+Fn and the EDA+Fn/total Fn ratio in plasma were 390±95 µg/ml, 0.48±0.31 µg/ml and 0.12±0.07 respectively. Values for synovial fluid were 647±298 µg/ml, 8.97±5.86 µg/ml and 1.50±0.91 respectively, indicating that EDA+Fn is highly concentrated in rheumatoid synovial fluids. The average amount of synovial fluid in the patients was 20.5 ml per joint; the amount of synovial fluid was not significantly correlated with the concentrations of EDA+Fn and total Fn in synovial fluid (r=0.12 and r=0.09 respectively). The total amounts of EDA+Fn and total Fn in a joint, but not the concentration of EDA+Fn or total Fn, did not correlate with the progression of the Larsen score (r=0.23 and r=0.10 respectively). In contrast, the concentration of EDA+Fn in synovial fluid showed a significant correlation with the extent of progression of joint space narrowing during the 2-yr study period (r=0.66).
Joint replacement was performed on seven joints of six patients 4–41 months after the completion of the 2-yr study. All patients were followed for at least 41 months after completion of the study; in this 41-month period late synovectomy was also performed on another seven knee joints of six patients. The concentration of EDA+Fn in the synovial fluid of those who received joint replacement was 12.9±6.1 µg/ml (n=7); in those receiving late synovectomy it was 8.3±6.9 µg/ml (n=7), and in those who did not receive surgery it was 8.1±5.3 µg/ml (n=27). There were statistically significant differences between those who received joint replacement and those who underwent late synovectomy (P<0.028) and between those who received joint replacement and those who received no surgery (P<0.029).
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Discussion |
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TopAbstractIntroductionPatients and methodsResultsDiscussionReferences |
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The results showed that there was a positive correlation between the concentration of EDA+Fn in synovial fluid and the subsequent progression of joint destruction in patients with RA. Previous studies have indicated that Fn is significantly increased in synovial fluids, synovial tissues and invasive fronts of active cellular pannus in patients with RA [9–11]. Fn is present on the articular surface of rheumatoid cartilage in a disease-specific manner [12] and plays an essential role in the induction of pannus invasion [4, 11]. Recent molecular studies have shown the existence of splice variants in Fn [1]. The isoform containing the EDA and EDB regions (EDA+Fn) has been shown to be more important than total Fn, not only for cellular transformation [1] but also for rheumatoid joint destruction [2, 3]. EDA+Fn has been shown to be highly concentrated in rheumatoid synovial fluids [2] and supports the adhesion and extension of synovial cells at the Hep2 region of the molecule in association with the RGD binding complex [3].
Whether or not a particular patient decides to receive surgery depends also on the factors other than the progression of joint destruction. Nevertheless, we found that a significant proportion of rheumatoid patients with increased synovial fluid EDA+Fn received joint replacement. We found osteoarthritic changes on X-ray in four patients, of whom one received joint surgery. The concentrations of EDA+Fn and total Fn in synovial fluid in these four patients were 9.04±6.81 and 691±221 µg/ml respectively. These values were not significantly different from the average values found in rheumatoid patients, suggesting that the contribution of osteoarthritic changes was small in the present study. These findings suggest that EDA+Fn in synovial fluid may be a predictor of subsequent rheumatoid joint destruction. The present study indicates that a level of EDA+Fn in synovial fluid exceeding 10 µg/ml predicts the future progression of rheumatoid joint destruction.
It was interesting to find in the present study that there was no significant correlation between the concentration of EDA+Fn in synovial fluid and the inflammatory indices, such as CRP and ESR. These inflammatory indices also did not correlate with the extent of progression of joint destruction as revealed by the change in the Larsen score during the study period. If mesenchymal synovial cells are directly responsible for rheumatoid joint destruction, as suggested by previous morphological and recent biochemical studies [13–17], the present findings may shed some light on the mechanism of progression of rheumatoid joint destruction, especially in relation to pannus invasion [13, 15].
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Acknowledgments |
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This work was supported in part by grants-in-aid for scientific research to SS (grants 07557225 and 08457153) of the Ministry of Education, Science, Sports and Culture of Japan.
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Notes |
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Correspondence to: S. Shiozawa, Kobe University School of Medicine, Faculty of Health Science, 7-10-2 Tomogaoka, Sumaku, Kobe 654-0142, Japan.
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