To determine whether circulating levels of osteopontin (OPN), osteoprotegerin (OPG), total soluble receptor activator of nuclear factor-kappa B ligand (total sRANKL), and high-sensitivity C-reactive protein (hsCRP) change in patients with rheumatoid arthritis (RA) during immunosuppressive therapy.
Twenty-five active RA patients were randomized to treatment with either etanercept alone or in combination with methotrexate (MTX). The treatment response after 16 weeks was assessed using the European League Against Rheumatism (EULAR) response criteria. Blood samples were taken before the start of and every fourth week during the study. OPN, OPG, and total sRANKL were measured by enzyme-linked immunosorbent assays (ELISAs) and hsCRP by highly sensitive turbidometry.
At baseline, OPN and hsCRP were significantly (p<0.001) elevated compared to healthy persons. Compared to baseline only hsCRP levels decreased significantly (p<0.05 to p<0.001) in the EULAR responders through the study. OPN remained significantly (p<0.05) elevated at 16 weeks in patients with a low disease activity score (DAS< or =3.2). Total sRANKL increased significantly (p<0.05) from baseline to week 12. No statistically significant changes were observed in the non-responders.
Active RA patients showed increased circulating levels of hsCRP and OPN, but only hsCRP decreased during etanercept therapy. Our findings suggest that OPN, OPG, total sRANKL, and hsCRP reflect different aspects of the inflammatory process in RA.