Persistence of circulating endothelial microparticles in COPD despite smoking cessation

Abstract

Introduction: Increasing evidence links COPD pathogenesis with pulmonary capillary apoptosis. We previously demonstrated that plasma levels of circulating microparticles released from endothelial cells (EMPs) due to apoptosis are elevated in smokers with normal spirometry but low diffusion capacity, that is, with early evidence of lung destruction. We hypothesised that pulmonary capillary apoptosis persists with the development of COPD and assessed its reversibility in healthy smokers and COPD smokers following smoking cessation.

Methods: Pulmonary function and high-resolution CT (HRCT) were assessed in 28 non-smokers, 61 healthy smokers and 49 COPD smokers; 17 healthy smokers and 18 COPD smokers quit smoking for 12 months following the baseline visit. Total EMP (CD42b-CD31+), pulmonary capillary EMP (CD42b-CD31+ACE+) and apoptotic EMP (CD42b-CD62E+/CD42b-CD31+) levels were quantified by flow cytometry.

Results: Compared with non-smokers, healthy smokers and COPD smokers had elevated levels of circulating EMPs due to active pulmonary capillary endothelial apoptosis. Levels remained elevated over 12 months in healthy smokers and COPD smokers who continued smoking, but returned to non-smoker levels in healthy smokers who quit. In contrast, levels remained significantly abnormal in COPD smokers who quit.

Conclusions: Pulmonary capillary apoptosis is reversible in healthy smokers who quit, but continues to play a role in COPD pathogenesis in smokers who progressed to airflow obstruction despite smoking cessation.

Trial registration number: NCT00974064; NCT01776398.

Keywords: COPD ÀÜ Mechanisms; Smoking cessation; Tobacco and the lung.

Conflict of interest statement

Competing interests: Hans Bitter, Sriram Sridhar, Sreekumar G. Pillai, Holly Hilton, Gerhard Wolff, Christopher S. Stevenson, Sudha Visvanathan and Jay S. Fine were all former employees of Hoffmann-La Roche.

Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/.

Figures

Figure 1

Urine cotinine levels (ng/ml) as a measure of smoking status at baseline and at 3, 6 and 12 months in nonsmokers, healthy smokers and smokers with COPD (COPD smokers). Shown is data for nonsmokers (n=28, green circles), healthy smokers who continue to smoke (n=44, yellow circles), healthy smokers who quit smoking following baseline (n=17, light blue circles), COPD smokers who continue to smoke (n=31, red circles) and COPD smokers who quit smoking following baseline (n=18, tan circles). Data represent mean ± standard error. Dashed lines indicate urine cotinine detection level of ≤ 5 ng/ml and urine cotinine level of ≥ 104 ng/ml for active smoking (see Supplemental Methods).

Figure 2

Levels of total circulating endothelium microparticles (EMPs), ACE+ EMPs, and apoptotic EMPs in plasma at baseline. Shown is data for nonsmokers (n=28, green circles), healthy smokers (n=61, yellow circles) and smokers with COPD (n=49, red circles). A. Total CD42b−CD31+ EMPs. The gray shaded area indicates the nonsmoker mean ± 2 standard deviations. The % value above the smoker populations represents the proportion of smokers with EMP levels above that mean. B. CD42b−CD31+ACE+ EMPs. Proportion of total CD42b−CD31+ EMPs in plasma that express angiotensin converting enzyme (ACE+). The gray shaded area represents the nonsmoker mean ± 2 standard deviations. C. Ratio of CD42b−CD62E+ to CD42b−CD31+ EMPs. The dashed line indicates the lowest ratio of CD42b−CD62E+/CD42b−CD31+ EMPs in nonsmokers. The % value below the smoker populations represents the proportion of smokers with a ratio below that level. A–C; Bold dashed lines represent the mean for each group. Symbols inside the dots: A horizontal line indicates subjects with systemic hypertension; a vertical line indicates subjects with type 2 diabetes mellitus; a star indicates subjects with type 1 diabetes.

Figure 3

Total circulating CD42b−CD31+ endothelial microparticles (EMPs) and ratio of CD42b−CD62E+ to CD42b−CD31+ EMPs over time in nonsmokers (n=28, green circles), healthy smokers who continue to smoke (n=44, yellow circles), healthy smokers who quit smoking following baseline (n=17, light blue circles), smokers with COPD (COPD smokers) who continue smoking (n=31, red circles) and COPD smokers who quit smoking following baseline (n=18, tan circles). A, B. Total CD42b−CD31+ EMPs. C, D. Ratio of CD42b−CD62E+ to CD42b−CD31+ EMPs A, C. Healthy smokers who continue to smoke and healthy smokers who quit smoking vs nonsmokers. B, D. COPD smokers who continue to smoke and COPD smokers who quit smoking vs nonsmokers. A–D. Data represent mean ± standard error. P values comparing each time point to baseline within the same group are shown at the top of the panel (for the group that is above the nonsmokers at month 12) and at the bottom of the panel (for the group that is below the nonsmokers at month 12). P values comparing each time point in a smoker group to the same time point in the nonsmoker group are shown above the group if the group is above the nonsmokers at month 12 and below the group if the group is below the nonsmokers at month 12. P values comparing the subjects who continue to smoke with those who quit smoking at month 12 are to the right of the panel. NS = not significant; *, **, ***, **** indicate p<0.05, p<0.01, p<0.001 and p<0.0001, respectively.