Ageing and smoking contribute to plasma surfactant proteins and protease imbalance with correlations to airway obstruction

BMC Pulm Med. 2011 Apr 19;11:19. doi: 10.1186/1471-2466-11-19.


Background: A significant number of young people start smoking at an age of 13-15, which means that serious smoking-evoked changes may have been occurred by their twenties. Surfactant proteins (SP) and matrix metalloproteinases (MMPs) and their tissue inhibitors (TIMPs) have been linked to cigarette smoke induced lung remodelling and chronic obstructive pulmonary disease (COPD). However, the level of these proteins has not been examined during ageing or in young individuals with short smoking histories.

Methods: Plasma levels of SP-A, SP-D, MMP-9, and TIMP-1 were measured by EIA/ELISA from young (18-23 years) non-smoking controls (YNS) (n = 36), smokers (YS) (n = 51), middle aged/elderly (37-77 years) non-smoking controls (ONS) (n = 40), smokers (OS) (n = 64) (FEV1/FVC >0.7 in all subjects) and patients with COPD (n = 44, 35-79 years).

Results: Plasma levels of SP-A increased with age and in the older group in relation to smoking and COPD. Plasma SP-D and MMP-9 levels did not change with age but were elevated in OS and COPD as compared to ONS. The TIMP-1 level declined with age but increased in chronic smokers when compared to ONS. The clearest correlations could be detected between plasma SP-A vs. age, pack years and FEV1/FVC. The receiver operating characteristic (ROC) curve analysis revealed SP-A to be the best marker for discriminating between patients with COPD and the controls (area under ROC curve of 0.842; 95% confidence interval, 0.785-0.899; p < 0.001).

Conclusions: Age has a significant contribution to potential markers related to smoking and COPD; SP-A seems to be the best factor in differentiating COPD from the controls.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Aging / metabolism*
  • Case-Control Studies
  • Female
  • Forced Expiratory Volume / physiology
  • Humans
  • Male
  • Matrix Metalloproteinase 9 / blood
  • Middle Aged
  • Peptide Hydrolases / blood*
  • Pulmonary Disease, Chronic Obstructive / metabolism*
  • Pulmonary Disease, Chronic Obstructive / physiopathology
  • Pulmonary Surfactant-Associated Protein A / blood
  • Pulmonary Surfactant-Associated Protein D / blood
  • Pulmonary Surfactants / blood*
  • ROC Curve
  • Smoking / metabolism*
  • Tissue Inhibitor of Metalloproteinase-1 / blood
  • Vital Capacity / physiology
  • Young Adult


  • Pulmonary Surfactant-Associated Protein A
  • Pulmonary Surfactant-Associated Protein D
  • Pulmonary Surfactants
  • Tissue Inhibitor of Metalloproteinase-1
  • Peptide Hydrolases
  • Matrix Metalloproteinase 9