Abstract: Objective This study was undertaken to explore the expression of Dkk-1 and its potential role in patients with ankylosing spondylitis (AS). Methods Serum Dkk-1 levels were measured by sandwich enzyme linked immunosorbent assay (ELISA). Two groups of AS subjects were tested. The first group consisted of patients who have not been treated with biological agents. In the second group, patients had been receiving anti- TNFα treatment more than 12 weeks. These were compared to serum samples from 8 patients with rheumatoid arthritis (RA) and 20 healthy subjects. Disease activity assessment was performed using the Bath AS Disease Activity Index (BASDAI) in patients with AS, the Disease Activity Score in 28 joints (DAS28) in patients with RA. All patients with AS and RA had active disease. Markers of inflammation (erythrocyte sedimentation rate [ESR] and C-reactive protein [CRP] levels) were measured in all patients. Results Serum Dkk-1 levels were significantly decreased in AS patients who have not been treated with biological agents as compared with patients with RA (p=0.037), and normal subjects (p=0.012). The BASDAI，ESR and CRP in patients with AS did not correlate with serum Dkk-1 levels. Patients with AS receiving anti-TNFα treatment had significantly higher serum Dkk-1 levels compared with patients with AS not receiving this treatment (p=0.000). Conclusion Our results indicate that the levels of serum Dkk-1 in patients with AS, a prototype bone-forming disease, is decrease. No association between circulating Dkk-1 levels and disease activity or markers of inflammation (ESR and CRP) in any AS patient group. Furthermore, TNFα could induce the expression of Dkk-1 in patients with AS.

Key words: Spondylitis, ankylosing, Dkk-1