Dysregulation of the endothelial nitric oxide pathway is associated with airway inflammation in COPD

Abstract

Background: Chronic obstructive pulmonary disease (COPD) is related to endothelial dysfunction and the impaired generation of nitric oxide (NO) from L-arginine by the endothelial NO synthase (eNOS). The relationship between eNOS dysfunctionality and airway inflammation is unknown. We assessed serum asymmetric and symmetric dimethylarginine (ADMA and SDMA) and nitrite/nitrate concentrations, indicators of eNOS function, in patients with COPD and correlated them with markers of inflammation.

Methods: We recruited 15 control smokers, 29 patients with stable and 32 patients with exacerbated COPD requiring hospitalization (20 of them were measured both at admission and discharge). Serum L-arginine, ADMA, SDMA, nitrite and nitrate were measured and correlated with airway inflammatory markers (fractional exhaled nitric oxide concentration - FENO, sputum nitrite and nitrate, sputum cellularity), serum C-reactive protein - CRP, white blood cell count, lung function and blood gases. ANOVA, t-tests and Pearson correlation were used (mean ± SD or geometric mean ± geometric SD for nitrite/nitrate).

Results: Serum L-arginine/ADMA, a marker of substrate availability for eNOS, was lower in stable (214 ± 58, p < 0.01) and exacerbated COPD (231 ± 68, p < 0.05) than in controls (287 ± 64). The serum concentration of SDMA, a competitor of L-arginine transport, was elevated during an exacerbation (0.78 ± 0.39 μM) compared to stable patients (0.53 ± 0.14 μM, p < 0.01) and controls (0.45 ± 0.14 μM, p < 0.001). ADMA correlated with blood neutrophil percentage (r = 0.36, p < 0.01), FENO (r = 0.42, p < 0.01) and a tendency for positive association was observed to sputum neutrophil count (r = 0.33, p = 0.07). SDMA correlated with total sputum inflammatory cell count (r = 0.61, p < 0.01) and sputum neutrophil count (r = 0.62, p < 0.01). Markers were not related to lung function, blood gases or CRP. L-arginine/ADMA was unchanged, but serum SDMA level decreased (0.57 ± 0.42 μM, p < 0.05) after systemic steroid treatment of the exacerbation. Serum nitrite level increased in stable and exacerbated disease (4.11 ± 2.12 and 4.03 ± 1.77 vs. control: 1.61 ± 1.84 μM, both p < 0.001).

Conclusions: Our data suggest impaired eNOS function in stable COPD, which is transiently aggravated during an exacerbation and partly reversed by systemic steroid treatment. Serum ADMA and SDMA correlate with airway inflammatory markers implying a possible effect of anti-inflammatory therapy on endothelial dysfunction. Serum nitrite can serve as a compensatory pool for impaired endothelial NO generation.

Keywords: Airway inflammation; Cardiovascular comorbidity; Chronic obstructive pulmonary disease; Endothelial dysfunction; Exacerbation; Nitric oxide.

Fig. 1

Serum L-arginine/ADMA in smoking controls and patients with COPD. Serum L-arginine/ADMA was analysed among smoking control and patients with stable and exacerbated COPD (a, ANOVA with post-hoc test) and between the onset and the recovery of an acute severe exacerbation (b, paired t-test). Correlation between serum ADMA concentration and blood neutrophil percentage and FENO was also analysed in patients with stable and exacerbated COPD (c and d, Pearson correlation). Control: smoking control subjects, S-COPD: stable COPD, E-COPD: exacerbation of COPD, FENO: fractional exhaled nitric oxide concentration. *p < 0.05, **p < 0.01 vs. Control. Data are shown as mean and standard deviation

Fig. 2

Serum SDMA concentration in smoking controls and patients with COPD. Serum SDMA concentration was compared among smoking controls and patients with stable and exacerbated COPD (a, ANOVA) and between the onset and the recovery of an acute severe exacerbation (b; paired t-test). Correlation between serum SDMA concentration and sputum inflammatory cell count and neutrophil count was also analysed in patients with E-COPD (c and d, Pearson correlation). Control: smoking control subjects, S-COPD: stable COPD, E-COPD: exacerbation of COPD. **p < 0.01, ***p < 0.001 vs. Control. ^##p < 0.01 vs. S-COPD, ^&p < 0.05 vs. Onset. Data are shown as mean and standard deviation

Fig. 3

Serum nitrate and nitrite concentration in smoking controls and patients with COPD. Logarithmically transformed serum nitrate and nitrite concentrations were analysed among smoking control and patients with stable and exacerbated COPD (a and c; ANOVA with post-hoc analysis, ***p < 0.001) and between the onset and the recovery of an acute severe exacerbation (b and d; paired t-test). Control: smoking control subjects, S-COPD: stable COPD, E-COPD: exacerbation of COPD. Data were analysed after log transformation and are shown as geometric mean and geometric standard deviation

Fig. 4

Sputum nitrate and nitrite concentration in COPD. Sputum nitrate and nitrite concentrations were analysed between patients with stable and exacerbated COPD (a and c; unpaired t-test, *p < 0.05), and between the onset and the recovery of an acute severe exacerbation (b and d; paired t-test, ^&p = 0.06). S-COPD: stable COPD, E-COPD: exacerbation of COPD. Data were analysed after log transformation and are shown as geometric mean and geometric standard deviation