Cheng Tao, Wang Mingjun, Chen Zhiwei, Robert A Eisenberg

Zhang Yu，Zou Yaohong, Deng Yingsu, Wang Mian and Zhou Ling

Background Bone damage around the joints is one of the major pathophysiological mechanisms that leads to rheumatoid arthritis (RA) chronic disability. Serum tartrate-resistant acid phosphatase 5b (TRACP-5b) is secreted by osteoclasts, its activity can be used as a clinically relevant bone resorption marker. The aim of this study was to test whether the measurement of serum levels of TRACP-5b in patients with RA would correlate with measures of disease activity and with responses to therapy.

Methods Fifty-six patients were randomly assigned to receive recombinant human cytotoxic tlymphocyte-associated antigen-4 immunoglobulin (RhCTLA4-Ig), infliximab or methotrexate (MTX). The clinical and serologic indicators of RA activity were evaluated at baseline and at 24 weeks. Serum TRACP-5b was measured by Enzyme-linked Immunosorbent Assay (ELISA) at 0, 12 and 24 weeks. Hand X-rays were obtained at baseline.

Results At baseline, the levels of TRACP-5b correlated with the severity of X-ray damage, disease duration (r=0.332, P=0.012), and tender joint count (r=0.408, P=0.002). The 24 weeks values of TRACP-5b for RhCTLA4-Ig group and infliximab group differed significantly from the baseline values in each group (P <0.05; P <0.05), whereas only the value for RhCTLA4-Ig group differed significantly from the 24 weeks value for the MTX group (P <0.01). Considering the two biologics-treated groups together, the TRACP-5b levels at 24 weeks differed significantly from the baseline values only in those patients who reached an ACR70 level (P <0.05).

Conclusions Measurement of serum TRACP-5b in RA patients reflects clinical and radiological measures of disease activity, treatment with certain biologics, and degree of response to therapy. TRACP-5b should be investigated further as a potential biomarker to predict response to therapy, including slowing of radiographic progression.