N-acetyl-L-cysteine (NAC) was initially introduced as a treatment for mucus reduction and widely used for chronic respiratory conditions associated with mucus overproduction. However, the mechanism of action for NAC extends beyond its mucolytic activity and is complex and multifaceted. Contrary to other mucoactive drugs, NAC has been found to exhibit antioxidant, anti-infective, and anti-inflammatory activity in pre-clinical and clinical reports. These properties have sparked interest in its potential for treating chronic lung diseases, including chronic obstructive pulmonary disease (COPD), bronchiectasis (BE), cystic fibrosis (CF), and idiopathic pulmonary fibrosis (IPF), which are associated with oxidative stress, increased levels of glutathione and inflammation. NAC’s anti-inflammatory activity is noteworthy, and it is not solely secondary to its antioxidant capabilities. In ex vivo models of COPD exacerbation, the anti-inflammatory effects have been observed even at very low doses, especially with prolonged treatment. The mechanism involves the inhibition of the activation of NF-kB and neurokinin A production, resulting in a reduction in interleukin-6 production, a cytokine abundantly present in the sputum and breath condensate of patients with COPD and correlates with the number of exacerbations. The unique combination of mucolytic, antioxidant, anti-infective, and anti-inflammatory properties positions NAC as a safe, cost-effective, and efficacious therapy for a plethora of respiratory conditions.

Background and objective: Hypoxemia and respiratory failure (RF) in chronic obstructive pulmonary disease (COPD) are associated with exacerbations, comorbidities and increased mortality. However, the prevalence of hypoxemia and RF in stable COPD is unknown. We aimed at investigating the prevalence and determining predictive factors for chronic gas exchange abnormalities in COPD patients. Methods: A retrospective cohort study that enrolled clinically stable COPD patients referring to a pulmonary outpatient clinic. Anthropometrics, clinical characteristics, blood gas analysis and lung function were analyzed. Patients were grouped according to hypoxemia (PaO₂ <80 and ≥60 mmHg), type 1 (PaO₂ < 60 mmHg) or type II (PaO₂ < 60 and PaCO₂ > 45 mmHg) RF. A sensitivity analysis adopting an age-adjusted definition of hypoxemia was performed. Predictive factors for hypoxemia or RF were assessed with multifactorial analysis. Results: We analyzed data from 515 patients. Fixed-ratio hypoxemia, RF type 1 and type 2 were observed in 352 (68.3%), 27 (5.2%) and 43 (8.3%) patients, respectively. Risk of hypoxemia was associated with preserved alveolar volume, residual volume/total lung capacity, and lung diffusion capacity. Heart failure, ischemic heart disease, atrial fibrillation, and metabolic syndrome were predictive factors for RF. Patients with age-adjusted hypoxemia (n = 321 patients, 62.3%) showed no difference in terms of anthropometrics, lung function, and clinical characteristics as compared with fixed-threshold hypoxemia. Conclusions: Hypoxemia is frequent in stable COPD. Lung function parameters and comorbidities can support the identification of patients at risk of RF. Blood gas analysis should be always performed in patients with COPD to allow for personalized therapy and management.