Circulatory osteoprotegerin is related to osteoporosis of the hip in patients with COPD

Abstract

Background: Osteoprotegerin (OPG), a potent inhibitor of osteoclastogenesis, decreases bone resorption and has protective effects on bone mineral density (BMD). Recently we have shown that the adipose-tissue derived OPG relates to BMD in patients with chronic obstructive pulmonary disease (COPD), a condition associated with increased risk of osteoporosis.

Objective: Here we aimed to investigate the potential of circulatory OPG to reflect hip BMD in patients with COPD.

Patients and methods: In 56 subjects with COPD [age, 61.7 ± 6.7 years; forced expiratory volume in 1 s (FEV1), 53.6 ± 19.2% predicted], total femur BMD was assessed by dual energy X-ray absorptiometry, serum OPG and β-crosslaps, a marker of increased bone resorption, by commercially available assays.

Results: From patients with normal hip BMD (n = 32, T-score 0.1 ± 0.8) to those with osteopenia (n = 14, T-score -1.6 ± 0.4) and osteoporosis (n = 10, T-score -3.4 ± 0.7) serum OPG levels significantly increased (6.6 ± 1.8 versus 7.2 ± 2.9 and versus 8.6 ± 1.5 pmol/l, p = 0.036). In addition, hip T-scores were directly related to FEV1, and inversely to β-crosslaps (R = 0.40, p = 0.002; R = 0.38, p = 0.01, respectively). In multivariate analysis, OPG independently predicted hip T-scores after adjustments for age, gender, FEV1, and β-crosslaps (p = 0.011, adjusted R(2) = 0.354). Area under receiver operator curve for OPG as a discriminator of osteoporosis was 0.787 (95% CI, 0.653-0.921) (p = 0.005).

Conclusions: Present results suggest that osteoporosis of the hip is associated with increased circulatory levels of OPG in patients with COPD. OPG might serve as a biomarker of this COPD-related comorbidity.

Keywords: Biomarker; Bone resorption; Chronic obstructive pulmonary disease; Osteoporosis; Osteoprotegerin.