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Open Access Highly Accessed Research article

Biomarkers and cytokines of bone turnover: extensive evaluation in a cohort of patients with ankylosing spondylitis

Ali Taylan1*, Ismail Sari2, Baris Akinci3, Safak Bilge4, Didem Kozaci5, Servet Akar2, Ayfer Colak6, Hulya Yalcin6, Necati Gunay7 and Nurullah Akkoc2

Author Affiliations

1 Izmir Tepecik Training and Research Hospital, Department of Rheumatology, Izmir, Turkey

2 Dokuz Eylul University School of Medicine, Department of Internal Medicine, Division of Rheumatology, Izmir, Turkey

3 Izmir Tepecik Training and Research Hospital, Department of Endocrinology, Izmir, Turkey

4 Izmir Tepecik Training and Research Hospital, Department of Physical medicine and Rehabilitation, Izmir, Turkey

5 Adnan Menderes University School of Medicine, Department of Biochemistry, Aydin, Turkey

6 Izmir Tepecik Training and Research Hospital, Department of Biochemistry, Izmir, Turkey

7 Adnan Menderes University, Bilim ve Teknoloji Araştirma ve Uygulama Merkezi (ADU-BILTEM), Aydin, Turkey

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BMC Musculoskeletal Disorders 2012, 13:191  doi:10.1186/1471-2474-13-191

Published: 2 October 2012

Abstract

Background

Ankylosing spondylitis (AS) is a chronic inflammatory disease of spine and sacroiliac joints; it is characterized by new bone formation, and the disease processes can be accompanied by osteoporosis. In the present study, we investigated changes in bone mineral density (BMD) and in the levels of various bone turnover-related biomarkers and cytokines in a cohort of AS patients, with regard to clinical parameters, disease activity, and treatment regimen.

Methods

55 AS patients and 33 healthy controls included in the study. Spinal mobility was assessed by the Bath Ankylosing Spondylitis Metrology Index (BASMI), and radiologic changes were scored by the Bath Ankylosing Spondylitis Radiologic Index (BASRI). Patients were also evaluated with the Bath Ankylosing Spondylitis Functional Index (BASFI) and the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI). Bone mineral density (BMD) assessed by dual energy X-ray absorptiometry. Various biomarkers and cytokines of bone turnover including osteoprotegerin (OPG), serum band 5 tartrate-resistant acid phosphatase (TRAP-5), soluble receptor activator of nuclear factor kappa-B ligand (sRANKL), secreted frizzled-related protein 1 (sFRP-1), Dickkopf-related protein 1 (DKK-1), and sclerostin were studied.

Results

The levels of TRAP-5, NTX, sRANKL, sclerostin, sFRP-1, DKK-1, and IFNγ, were similar between the patients and controls (p > 0.05), while BMD of femoral neck, and OPG levels were significantly lower in AS patients (p < 0.05). In a subgroup analysis, patients with active disease had significantly higher concentrations of OPG compared with the inactive group. Rest of the biomarkers and cytokines of bone turnover were similar between the active and inactive disease groups. Subgroup analysis of patients receiving anti-TNFα agents and conventional therapy revealed that OPG concentrations were significantly lower in the patients receiving biological drugs, while BAP and DKK-1 were significantly higher in the patients treated with conventional agents.

Conclusions

In this cross-sectional study we showed that OPG levels were significantly lower in AS patients compared to healthy subjects. On the other hand, the levels of wingless (Wnt) signal pathway inhibitors seem not altered. Ectopic bone formation in AS may be related to dysfunction of these molecules at the cellular level.

Keywords:
Ankylosing spondylitis; Bone mineral density; OPG; RANKL; DKK-1