Cartilage oligomeric matrix protein/thrombospondin-5 (COMP/TSP-5) levels do not correlate to functional class in patients with rheumatoid arthritis

Abstract

Rheumatoid arthritis (RA) can be an incapacitating disorder. The cartilage oligomeric matrix protein/thrombospondin-5 (COMP/TSP-5), a member of extracellular proteins involved in tissue genesis and remodeling, has been considered a potential prognostic marker of RA [1]. Data on the association of functional status of RA with COMP/TSP-5 levels are virtually nonexistent. In the current study, we set up to determine the serum levels of COMP/TSP-5 in RA patients of different functional classes and in healthy controls. The study was cross-sectional. Fifty-eight patients with RA [2] followed in the Outpatient Rheumatology Clinic of Sao Lucas Hospital of PUCRS comprised the target population. The Hochberg classification [3] was used to estimate the functional status of RA patients. The control group included 100 consecutive blood donors. Levels of COMP/TSP-5 were evaluated by immunoenzimatic assay (AnaMar Medical TM, Lund, Sweden). Levels above 12 U/L were considered positive [4]. Comparison of groups was obtained by analysis of variation. A 5% significance level was considered for P values. The medium age was 48±6 years for the control group and of 54±14 years for RA patients (P>0.05). The female gender predominated in patients with RA (P<0.05). After adjustment for sex and age, the average levels of COMP/ TSP-5 were 7.0 U/L (95% CI 6.1–7.9) for the control group and 12.6 U/L (95% CI 11.1–14.1) for RA patients (P<0.01). Among RA patients, 25 showed functional class I (43.1%), 14 functional class II (24.13%), 10 functional class III (17.2%), and 9 functional class IV (15.5%). With the exception of individuals in class III, patients from other functional status presented higher frequency of positive test for COMP/TSP-5 as compared to controls (P<0.001). In each of the functional classes, the average levels of COMP/ TSP-5 were significantly higher than those of the control group (P<0.05). The 28 RA patients with elevated COMP/ TSP-5 were distributed uniformly in all four functional classes (P=0.65). COMP/TSP-5 serum levels may be a predicting factor for joint damage in RA [5]. High COMP/TSP-5 levels were described in patients with early RA [6]. A positive correlation of COMP/TSP-5 levels with cartilage damage (as measured by the Larsen radiographic score) was described in 62 RA patients [7]. RA patients with severe joint damage had higher COMP/TSP-5 and C-reactive protein levels than patients with milder disease [8]. Nevertheless, other authors reported low levels of COMP/ TSP-5 in patients with decreased functional status, probably due to cartilage degradation [9]. A recent report showed that neither baseline serum COMP/TSP-5 levels nor its individual change after 3 months from start of intensive F. D. Andrade :A. L. Bender : I. G. da Silveira :H. Stein : C. A. von Muhlen :H. L. Staub Rheumatology Department, Sao Lucas Hospital, Faculty of Medicine of Pontiphical Catholic University of Rio Grande do Sul (PUCRS), Porto Alegre, Brazil