Open Access Research

Comprehensive characterisation of pulmonary and serum surfactant protein D in COPD

Carla Winkler1,2†, Elena N Atochina-Vasserman3†, Olaf Holz1, Michael F Beers3, Veit J Erpenbeck1,2, Norbert Krug1, Stefan Roepcke4, Gereon Lauer4, Martin Elmlinger4 and Jens M Hohlfeld1,2*

Author Affiliations

1 Department of Clinical Airway Research, Fraunhofer Institute for Toxicology and Experimental Medicine, Hannover, Germany

2 Department of Respiratory Medicine, Hannover Medical School, Hannover, Germany

3 Division of Pulmonary, Allergy, and Critical Care Medicine, Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia, PA, USA

4 Nycomed GmbH, Konstanz, Germany

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Respiratory Research 2011, 12:29 doi:10.1186/1465-9921-12-29

Published: 11 March 2011

Abstract

Background

Pulmonary surfactant protein D (SP-D) is considered as a candidate biomarker for the functional integrity of the lung and for disease progression, which can be detected in serum. The origin of SP-D in serum and how serum concentrations are related to pulmonary concentrations under inflammatory conditions is still unclear.

Methods

In a cross-sectional study comprising non-smokers (n = 10), young - (n = 10), elderly smokers (n = 20), and smokers with COPD (n = 20) we simultaneously analysed pulmonary and serum SP-D levels with regard to pulmonary function, exercise, repeatability and its quaternary structure by native gel electrophoresis. Statistical comparisons were conducted by ANOVA and post-hoc testing for multiple comparisons; repeatability was assessed by Bland-Altman analysis.

Results

In COPD, median (IQR) pulmonary SP-D levels were lower (129(68) ng/ml) compared to smokers (young: 299(190), elderly: 296(158) ng/ml; p < 0.01) and non-smokers (967(708) ng/ml; p < 0.001). The opposite was observed in serum, with higher concentrations in COPD (140(89) ng/ml) as compared to non-smokers (76(47) ng/ml; p < 0.01). SP-D levels were reproducible and correlated with the degree of airway obstruction in all smokers. In addition, smoking lead to disruption of the quaternary structure.

Conclusions

Pulmonary and serum SP-D levels are stable markers influenced by smoking and related to airflow obstruction and disease state. Smaller subunits of pulmonary SP-D and the rapid increase of serum SP-D levels in COPD due to exercise support the translocation hypothesis and its use as a COPD biomarker.

Trial registration

no interventional trial