Effect of inhaled N-acetylcysteine on hydrogen peroxide exhalation in healthy subjects

Abstract

N-acetylcysteine (NAC) has antioxidant properties and its oral administration decreased H 2O 2 exhalation in patients with chronic obstructive pulmonary disease. In this study we tested whether inhaled NAC could suppress H 2O 2 levels in exhaled breath condensate (EBC) of eight healthy subjects that have never smoked (never-smokers). Original NAC solution (ACC ® vial, 300 mg NAC in 3 ml solvent), NAC-placebo (vehicle), sterile 0.9% NaCl or distilled water were nebulized via the pneumatic De Vilbiss ® nebulizer once daily every 7 days and H 2O 2 and thiols exhalation was measured just before, 30 min and 3 h after the end of drug administration. Additional in vitro experiments were performed to evaluate NAC stability during nebulization, reactivity with H 2O 2 and possible H 2O 2 generation in aqueous NAC solutions. NAC almost completely abolished H 2O 2 exhalation 30 min after inhalation (0.02±0.04 vs. 0.21±0.09 μM, p<0.001). However, 3 h later the H 2O 2 levels raised 1.8-fold from baseline ( p<0.01). Other inhaled solutions did not affect H 2O 2 levels. Mean thiol concentration in EBC rose ( p<0.05) after treatment with NAC and reached 1.03±0.48 μM at 3 h. Although, 25 and 50 mM NAC completely inhibited H 2O 2-peroxidase-luminol-dependent chemiluminescence, detectable amounts of H 2O 2 were generated in NAC solutions. It was accompanied by moderate loss of –SH groups. Catalase and ascorbic acid prevented H 2O 2 formation in NAC solutions. In conclusion inhaled NAC revealed biphasic effect on H 2O 2 exhalation in healthy subjects, which depends on direct H 2O 2 scavenging and H 2O 2 generation related to drug oxidation. The net result of these processes may determine anti- or pro-oxidant action of inhaled NAC.