Effect of abatacept treatment on serum osteoclast-related biomarkers in patients with rheumatoid arthritis (RA): A multicenter RA ultrasound prospective cohort in Japan.

We evaluated the effect of abatacept treatment on osteoclast-related biomarkers and explored whether the biomarkers are associated with the therapeutic response in rheumatoid arthritis (RA) patients treated with abatacept.We enrolled 44 RA patients treated with abatacept from a multicenter prospective ultrasound cohort study of patients who received biologic or targeted synthetic disease-modifying antirheumatic drug therapy. We evaluated the disease activity score (DAS) 28-CRP (C-reactive protein), musculoskeletal ultrasound scores including the total grayscale score (GS)/power Doppler (PD) score and the serum concentrations of isoform 5b of tartrate-resistant acid phosphate (TRACP-5b) and soluble receptor activator of nuclear factor-κB ligand (sRANKL) at baseline and at 3 and 6 months of treatment. "PD responder" was defined as a patient whose Δtotal PD score over 6 months was greater than the median change of that.Abatacept significantly improved DAS28-CRP as well as the total GS/PD score over 6 months. Serum TRACP-5b was significantly elevated and serum sRANKL was significantly decreased at 6 months (P < .0001 and P < .01, respectively). At 6 months, serum sRANKL was significantly decreased in the patients who achieved DAS28-CRP remission and the PD responders but not in those who did not. However, serum TRACP-5b rose regardless of the therapeutic response.Among RA patients treated with abatacept, serum sRANKL decreased in the patients with a good therapeutic response, but serum TRACP-5b elevated paradoxically regardless of the therapeutic response.