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Ankylosing spondylitis patients displayed lower osteoprotegerin levels
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Patients with ankylosing spondylitis had significantly lower osteoprotegerin and bone mineral density levels compared with healthy controls, but other bone turnover-related biomarkers and cytokines appeared similar, according to study results.
In a cross-sectional study, researchers in Turkey evaluated 55 patients (median age, 36 years; 48 men) with ankylosing spondylitis (AS) and 33 healthy controls (median age, 39 years; 24 men). Spinal mobility and radiologic changes were assessed, and Bath Ankylosing Disease Activity Index was measured, with scores equal to or greater than 4 considered active disease. Researchers also measured bone mineral density (BMD) via dual energy X-ray absorptiometry.
Researchers studied 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. All were similar between groups (P>.05), with the exception of BMD and OPG. Femoral neck BMD (0.8 g/cm2 [0.5-1.1] vs. 0.9 g/cm2 [0.6-1.1]) and OPG levels (339 pg/mL [52-1,118] vs. 527 pg/mL [16-1,030]) were significantly lower in AS patients.
In subgroup analysis, patients with active AS had a significantly higher OPG concentration than patients with inactive disease (P=.004). Patients with AS, whether active or inactive, also displayed other similar biomarkers and cytokines of bone turnover. Patients treated with anti-tumor necrosis factor-alpha drugs had significantly lower OPG concentrations than patients receiving conventional therapy (P=.04), and they had significantly higher levels of bone-specific alkaline phosphatase (P=.04) and DKK-1 (P=.03).
“We showed that OPG levels were significantly downregulated in AS patients compared to healthy subjects,” the researchers concluded. “Serum concentrations of OPG tend to be higher in patients with disease state, suggesting a trend favoring osteoblastic activity. The levels of Wnt signaling pathway inhibitors seem not altered in AS. Ongoing ectopic bone formation, one of the hallmark features of AS, may be related to dysfunction of these molecules at the cellular level.”
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