Peripheral Osteoblastogenesis in Rheumatoid Arthritis Is Enhanced after TNF Blocker Treatment, Irrespective of Systemic Inflammation

초록

Background/Purpose: We investigated osteoclastogenesis and osteoblastogenesis in peripheral blood before and 6 months after TNF blocker treatment in seropositive RA patients. Methods: Seventeen seropositive RA patients who received TNF blocker treatment including infliximab, adalimumab and etanercept were enrolled. Peripheral blood mononuclear cells (PBMCs) were collected at baseline and 6 months after TNF blocker treatment. For osteoblast culture, PBMCs were cultured and stained with alizarin S to detect calcified nodules. The optical density (OD) of alizarin S was measured for quantitative analysis. We also evaluated serum level of bone formation markers including osteocalcin, bone specific alkaline phosphatase (BSALP) using enzyme linked immunosorbent assay (ELISA). For osteoclast culture, PBMCs (1 x 106 cells/well) were cultured and stained with tartrate resistant acid phosphatase (TRAP). TRAP positive cells with more than 3 nuclei were regarded as osteoclasts. To assess resorption potential of osteoclasts, PBMCs were cultured on bone slices and resorption pits were visualized with 0.1% toluidine blue. The areas of pits were quantified using our own devised computerized image analysis program (Fig. 1). Inflammatory markers including erythrocyte sedimentation rate (ESR), c-reactive protein (CRP) and IL-6 were measured. Results: The OD of calcified nodules and bone formation markers including osteocalcin and BSALP all increased after TNF blocker treatment (Table 1). There was a positive correlation between differences of osteocalcin and that of BSALP (p = 0.002, r = 0.696). The number of cultured osteoclasts and the area of resorption pit by osteoclasts decreased after treatment. The difference of numbers of circulating monocytes showed negative correlation with difference of BSALP (p = 0.008, r= - 0.617) and that of osteocalcin (p = 0.005, r= - 0.651). Inflammatory markers did not respond to the treatment. Conclusion: Increase both in bone forma