AB0884 Serum fibroblast growth factor-23 levels were higher in patients with axial spondyloartrhritis and may be associated with disease activity
Authors: O. Gercik, E. Coban, B. Ozbek Iptec, G. Avcioglu, D. Solmaz, O. Bayindir, G. Kabadayi, D. Kozaci, S. Akar
Journal: Annals of the Rheumatic Diseases (2018)

<h3>Background</h3> Axial spondyloarthritis (axSpA) is a chronic inflammatory disease that mainly affects axial skeleton. The disease is characterised by new bone formation; it usually starts with the bony fusion of sacroiliac joints (SIJs) and also causes syndesmophyte formation in the intervertebral space, enthesophytes in the tendon and ligament insertion sites. Underlying mechanisms of new bone formation in axSpA patients is not completely understood and low levels of sclerostin may be associated with the development of syndesmophyte in patients with ankylosing spondylitis (AS). Beside sclerostin another osteocyte factor is fibroblast growth factor-23 (FGF-23) and it has been first described as a phosphaturic hormone. It was also shown that FGF-23 may inhibit osteoblast differentiation and matrix mineralization. <h3>Objectives</h3> To evaluate serum FGF-23 and sclerostin levels in patients with axSpA and to compare them with those of healthy control subjects. We also assessed relationship between the serum FGF-23, sclerostin levels and disease related variables in particular the presence of structural changes. <h3>Methods</h3> In total 109 axSpA patients according to ASAS classification criteria and age- and sex-matched 57 healthy control subjects were included in the analysis. Subjects with renal failure and significant comorbid conditions and axial SpA patients who were using anti-TNF agents were excluded. Demographic and disease related characteristics were collected by using a standard questionnaire. Serum levels of FGF-23 and sclerostin were measured using commercially available enzyme-linked immunosorbent assay (ELISA) kits in accordance with the supplier's instructions. <h3>Results</h3> In the present study there were 55 patients with non-radiographic axSpA and 54 patients with AS. Serum levels of FGF-23 levels were significantly higher in axSpA patients than healthy subjects. Although there was a trend towards a lower sclerostin levels in axSpA patients this difference did not show statistical significance (table 1). In axSpA patients serum FGF-23 levels were found to be correlated with erythrocyte sedimentation rate (ESR) (p<i>=</i>0.006 and r=0.265), C-reactive protein (CRP) (p<i>=</i>0.017 and r=0.229) and patients' height (p<i>=</i>0.027 and r=−0.221). There was no relationship between FGF-23 and mSASSS score or the presence of syndesmophyte. Subgroup analysis revealed that the duration of disease (p<i>=</i>0.005), ESR (p<i>=</i>0.007), CRP (p<i>&lt;</i>0.001) and mSASSS (p<i>=</i>0.008) scores were significantly higher in AS patients than nr-axSpA patients. However serum sclerostin levels were significantly higher in nr-axSpA patients (1464.4±728.1 vs 1150.8±754.3 pg/mL and p<i>=</i>0.029). <h3>Conclusions</h3> Our results suggested that serum FGF-23 is increased in axSpA patients. And also disease activity may contribute to an up-regulation in serum FGF-23 levels. <h3>Disclosure of Interest</h3> None declared