Serum Fibroblast Growth Factor 23 (FGF23) in Patients with Rheumatoid Arthritis.

Objective Rheumatoid arthritis (RA) is a chronic inflammatory disease accompanied by periarticular and systemic osteoporosis. Fibroblast growth factor 23 (FGF23), which is mainly produced by osteocytes, circulates to the kidneys and regulates bone metabolism. We herein assessed serum FGF23 and its relationship to inflammation and osteoporosis in patients with RA. Methods Sixty-one patients with RA were included. Serum concentrations of FGF23 were determined using a sandwich enzyme-linked immunosorbent assay. Results The mean (± standard deviation) serum FGF23 concentration was 34.9±9.2 (range, 21.0-61.0) pg/mL. The serum FGF23 level was significantly and positively correlated with the erythrocyte sedimentation rate (ESR), C-reactive protein (CRP) levels, disease activity score-28 based on the ESR (DAS-28 ESR) and DAS-28 CRP (r=0.261, p=0.044, r=0.280, p=0.029, r=0.409, p=0.001 and r=0.421, p=0.001, respectively). The serum matrix metalloproteinase-3 level was also significantly and positively correlated with the serum FGF23 level (r=0.331, p=0.015). Concentrations of type I collagen cross-linked N-telopeptide in the serum was significantly correlated with the serum FGF23 level (r=0.272, p=0.034). Neither the bone mineral density in the femoral neck nor lumbar was significantly correlated with the serum FGF23 level. Serum phosphate, calcium, 25-hydroxy vitamin D, and intact parathyroid hormone were not related to the serum FGF23 level. Conclusion In patients with RA, serum FGF23 is correlated with inflammation, the disease activity of RA, and bone absorption markers. Serum FGF23 may be associated with abnormal bone absorption related to RA inflammation. Further studies are necessary to clarify the mechanism underlying this association.