In vitro and in vivo studies have shown that carbon monoxide (CO) has both anti-inflammatory and anti-oxidant capacities. Since chronic obstructive pulmonary disease (COPD) is characterised by inflammation and oxidative stress, low-dose CO could be of therapeutic use. The aim of the present study was to investigate the feasibility and anti-inflammatory effects of 100-125 ppm CO inhalation in patients with stable COPD. In total, 20 ex-smoking COPD patients with post-bronchodilator forced expiratory volume in one second (FEV(1)) >1.20 L and FEV(1)/forced vital capacity <70% were enrolled in a randomised, placebo-controlled, crossover study. Effects on inflammation were measured in induced sputum and blood. CO inhalation was feasible and patients' vital signs were unaffected; 2 h.day(-1) inhalation of low-dose CO on 4 consecutive days led to a maximal individual carboxyhaemoglobin level of 4.5%. Two exacerbations occurred in the CO period. CO inhalation led to trends in reduced sputum eosinophils (median reduction 0.25% point) and improved responsiveness to methacholine (median provocative concentration causing a 20% fall in FEV(1) 0.85 versus 0.63 mg.mL(-1)). Inhalation of 100-125 ppm carbon monoxide by patients with chronic obstructive pulmonary disease in a stable phase was feasible and led to trends in reduction of sputum eosinophils and improvement of responsiveness to methacholine. Further studies need to confirm the safety and efficacy in inflammatory lung diseases.
Trial registration: ClinicalTrials.gov NCT00122694.