Effect of inhaled and oral n-acetylcysteine on airway defense mechanism

Aim: N-acetylcysteine is the prototype of mucolytic agents. The aim of this study was to evaluate the acute and chronic effect of inhaled and oral N-acetylcysteine on airway reactivity, cough reflex and ciliary beat frequency and parameters of mentioned defense mechanisms were assessed in physiological conditions. Methods: An experiment was performed using healthy guinea pigs treated with inhaled (0.6 M; 5min) and oral N-acetylcysteine (20 mg/kg), administrated either acutely as a single dose or chronically during 7 days. The cough reflex and specific airway resistance were assessed by in vivo method, using a double chamber plethysmograph box. The ciliary beat frequency was evaluated in in vitro conditions on tracheal brushed samples using light microscope coupled to high speed video camera. Results: Inhaled and oral N-acetylcysteine, either administrated as a single dose or during 7 days, have shown a tendency to decrease sensitivity of the cough reflex and increase the airway reactivity. Acute administration of inhaled and oral N-acetylcysteine had no statistically relevant effect on the ciliary beat frequency, whereas chronic administration of both inhaled and oral N-acetylcysteine led to a marked reduction in the ciliary beat frequency. Conclusion : Chronic administration of oral and inhaled N-acetylcysteine had a negative impact on the ciliary beat frequency, which represents one of the key factors determining the rate of mucociliary clearance. Thus, administration of N-acetylcysteine is less likely to increase the expulsion of mucus by ciliary movement. In addition, the observed tendency of inhaled and oral N-acetylcysteine to increase the airway reactivity may limit its use in conditions with severe airflow obstruction.