Serum markers of bone metabolism correlate with clinical parameters for disease progression during 2 years follow-up in patients with COPD

The aim of the study was to explore the possible role of three serum markers of bone metabolism, 25-hydroxyvitamin D [25(OH)D], osteoprotegerin (OPG) and osteopontin (OPN) as indicators of COPD progression. We assessed the serum levels in 58 patients with COPD followed for 2 years and in 23 control individuals. All studied 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 weak negative correlation with FEV1% at the beginning (p=0.054) and at the end of the follow-up period (p=0.028). On opposite, serum OPG tended to be higher in patients with early stages and to correlate positively with FEV1/FVC% at the beginning and with FEV1% in the end of the study period. OPG was significantly higher in patients which during the follow-up period did not worsen their lung function than those which had decrease in FEV1% (p=0.045) and decreased FEV1/FVC% (p=0.034). Moreover, OPG correlated negatively with the CAT scores in the beginning of the study period (p=0.016) and with the number of the hospitalization (p=0.025). The serum 25(OH)D negatively correlated with the number of exacerbations during the study period (p=0.055) and had significant positive correlations with FEV1% (Rho=0.728, p=0.003) and FVC% (Rho=0.638, p=0.014) but only in patients with advance stages. The results suggest that the higher serum OPG and vitamin D might be markers for improving the COPD patient conditions and lung function, while the serum OPN might determine worsening.