Correlation of bone metabolism serum markers with clinical parameters of the disease progression during 2-year follow-up in patients with chronic obstructive pulmonary disease.

Objectives: Although chronic obstructive pulmonary disease (COPD) primarily affects the lungs, it is accepted that COPD is a complex multicomponent disease characterized by chronic systemic inflammation, often with other comorbidities, which are important determinants associated with increased risk of health deterioration, hospitalization, and mortality. One of the most common comorbidities in COPD is osteoporosis. The aim of the study was to explore the possible role of three serum markers of bone metabolism, 25-hydroxyvitamin D₃ (25[OH]D₃), osteoprotegerin (OPG), and osteopontin (OPN) as indicators of COPD progression.

Materials and methods: We assessed the serum levels of these markers in 23 control individuals and in 58 patients with COPD, followed for 2 years after recruitment in the current study.

Results: All examined serum markers were significantly lower in COPD patients in comparison to controls (P < 0.0001). Serum OPN was significantly lower in patients with early GOLD stages (stage 1 and 2) than in advanced (stage 3 and 4) (P = 0.035) and had a weak negative correlation with forced expiratory volume in 1 s (FEV1%) predicted at the beginning (Rho = -0.254, P = 0.054) and at the end of the follow-up period (Rho = -0.296, P = 0.028). In contrast, serum OPG tended to be higher in patients with early stages (P = 0.086) and to correlate positively with the spirometric lung function indexes FEV1/forced vital capacity (FVC%) at the beginning (Rho = 0.276, P = 0.041) and with FEV1% at the end of the study period (Rho = 0.232, P = 0.098). OPG was significantly higher in patients without deterioration of the lung functions during the follow-up period than those who had a decrease in FEV1% predicted (P = 0.045) and decreased FEV1/FVC% (P = 0.034). Moreover, OPG correlated negatively with the COPD assessment test scores in the beginning of the study period (Rho = -0.323, P = 0.016) and with the number of the hospitalization (Rho = -0.303, P = 0.025). There was a reliable trend for negative correlation of serum 25(OH) D₃ with the number of exacerbations during the study period (Rho = -0.291, P = 0.055) and a significant positive correlation with FEV1% predicted (Rho = 0.728, P = 0.003) but only in patients with advanced stages.

Conclusion: The results suggest that the higher serum OPG and Vitamin D₃ might be markers for improving the COPD patient conditions and lung function, while the serum OPN might determine worsening.