Serum cartilage oligomeric matrix protein (COMP) decreases in rheumatoid arthritis patients treated with infliximab or etanercept

Abstract

Changes in serum cartilage oligomeric matrix protein (COMP) were studied during a 6-month period from initiation of treatment of rheumatoid arthritis patients with either infliximab or etanercept, to elucidate whether the favourable results of tissue protection reported in clinical trials are corroborated by changing levels of circulating COMP. Rheumatoid arthritis patients commencing treatment with infliximab (N = 32) or etanercept (N = 17) were monitored in accordance with a structured protocol. Only patients who were not receiving glucocorticoids or who were on a stable dose of oral prednisolone (<10 mg daily) were included. Serum COMP was measured by a sandwich immunoassay based on two monoclonal antibodies against human COMP in samples obtained at treatment initiation and at 3 and 6 months. Serum COMP decreased at 3 months in both infliximab- and etanercept-treated patients (P < 0.001 and <0.005, respectively) and remained low at 6 months. There was no significant correlation between changes in or concentrations of serum COMP and serum C-reactive protein at any time point. A decrease in serum COMP was seen both in ACR20 responders (patients meeting the American College of Rheumatology criteria for 20% improvement) and in nonresponders. The pattern of changes of serum COMP, a marker for cartilage turnover, in these patient groups supports the interpretation that infliximab and etanercept have a joint protective effect. Serum COMP has potential as a useful marker for evaluating tissue effects of novel treatment modalities in rheumatoid arthritis.

Figure 1

Serum COMP (S-COMP) at baseline and after 3 and 6 months in rheumatoid arthritis patients treated with etanercept. Serum COMP was lower than at baseline after 3 months (P < 0.005). The levels remained low after 6 months, although not significantly lower than at baseline (P = 0.07). See text for details. COMP = cartilage oligomeric matrix protein (thrombospondin-5).

Figure 2

Serum COMP (S-COMP) at baseline and after 3 and 6 months in rheumatoid arthritis patients treated with infliximab. Serum COMP was lower than at baseline after 3 months (P < 0.001). The levels remained low after 6 months (P < 0.001 compared with baseline). For details, see text. COMP = cartilage oligomeric matrix protein (thrombospondin-5).

Figure 3

Serum COMP (S-COMP) at baseline and after 3 months in rheumatoid arthritis patients treated with etanercept (a) or infliximab (b), grouped according to whether they were ACR20 responders (i.e., met the American College of Rheumatology criteria for 20% improvement) or nonresponders. Serum COMP was lower than at baseline after 3 months in all groups (P < 0.05 or better). For details, see text and Table 1.