Moraxella catarrhalis acquisition, airway inflammation and protease-antiprotease balance in chronic obstructive pulmonary disease

Abstract

Background: Moraxella catarrhalis causes approximately 10% of exacerbations in chronic obstructive pulmonary disease (COPD) and also colonizes the lower airway in stable patients. Little is known about the effects of colonization by M. catarrhalis on airway inflammation and protease-antiprotease balance, and how these changes compare to those seen during exacerbations. Since COPD is a progressive inflammatory disease, elucidating the effects of bacterial colonization and exacerbation on airway inflammation is relevant to understanding disease progression in COPD. Our aims were (1) Analyze changes in airway inflammation in colonization and exacerbation of COPD due to M. catarrhalis; (2) Explore protease-antiprotease balance in colonization and exacerbation due to M. catarrhalis. Our hypothesis were (1) Acquisition of a new strain of M. catarrhalis in COPD increases airway inflammation from baseline and alters the protease-antiprotease balance towards a more proteolytic environment; (2) These changes are greater during exacerbations associated with M. catarrhalis as compared to colonization.

Methods: Thirty-nine consecutive COPD patients with 76 acquisitions of a new strain of M. catarrhalis over a 6-year period were identified in a prospective study. Seventy-six pre-acquisition sputum supernatant samples, obtained just before acquisition of M catarrhalis, and 76 acquisition samples (34 were associated with exacerbation, 42 with colonization) were analyzed for IL-8, TNF-alpha, Neutrophil Elastase (NE) and Secretory leukocyte protease inhibitor (SLPI). Changes were compared in paired samples from each patient.

Results: IL-8, TNF-alpha and NE were significantly elevated after acquisition of M. catarrhalis, compared to pre-acquisition samples (p =< 0.001 for all three). These changes were present in colonization (p = 0.015 for IL-8; p =< 0.001 for TNF-alpha and NE) as well as in exacerbation (p =< 0.001 for all three), compared to pre-acquisition levels. SLPI was significantly lower after acquisition (p =< 0.001), in colonization (p =< 0.001) as well as in exacerbation (p = 0.004), compared to pre-acquisition levels. SLPI levels correlated negatively with NE levels (R2 = 0.07; p = 0.001).

Conclusion: Acquisition of M. catarrhalis in COPD causes increased airway inflammation and worsening protease-antiprotease imbalance during exacerbations and also in colonization, even in the absence of increased symptoms. These effects could contribute to progression of airway disease in COPD.

Figure 1

Log₁₀ change from IL-8 pre-acquisition levels for colonization and exacerbation samples (Box-plots showing means and 95% CI); c = colonization; e = exacerbation.

Figure 2

Log₁₀ change from TNF-α pre-acquisition levels for colonization and exacerbation samples (Box-plots showing means and 95% CI); c = colonization; e = exacerbation.

Figure 3

Linear regression showing relationship of log-SLPIand log-NE levels for all samples (acquisition and pre-acquisition samples included) (R² = 0.07; p = 0.001).

Figure 4

Log₁₀ change from NE pre-acquisition levels for colonization and exacerbation samples (Box-plots showing means and 95% CI); c = colonization; e = exacerbation.

Figure 5

Log₁₀ change from SLPI pre-acquisition levels for colonization and exacerbation samples (Box-plots showing means and 95% CI); c = colonization; e = exacerbation.

Figure 6

Linear regression showing relationship of log-SLPI and log-NE levels for exacerbation samples only (R² = 0.1; p = 0.06).

Figure 7

Linear regression showing relationship of log-SLPI and log-NE levels for colonization samples only (R² = 0.02; p = 0.43).

Figure 8

Linear regression showing relationship of log-IL-8 and log-NE levels for colonization samples only (R² = 0.38; p =< 0.001).

Figure 9

Linear regression showing relationship of log-TNF-α and log-NE levels for colonization samples only (R² = 0.38; p =< 0.001).