Air pollution-induced airway epithelial barrier dysfunction in COPD: a narrative review of mechanisms and therapeutic...

Air pollution is particularly harmful to people with chronic obstructive pulmonary disease (COPD). Exposure to air pollution from sources such as biomass burning leads to a unique COPD phenotype. This phenotype mainly shows airway damage, with less emphysema than typical smoking-related phenotypes. Across various COPD phenotypes, airway epithelial barrier dysfunction is a basic pathological mechanism. This narrative review summarises the current available evidence on how different types of airborne pollutants, including particulate matter (PM), ozone (O₃), diesel exhaust and microplastics, damage the airway epithelial barrier. The toxicity of fine PM with a diameter of ≤2.5 µm, one of its main constituents, largely depends on its chemical composition. Some metals or organic chemicals with redox properties can initiate oxidation reactions and induce pathologic responses. The main injury mechanisms are direct physical damage to apical junctional complexes, serious impairment of mucociliary clearance and induction of oxidative stress. Apart from these immediate harms, pollutants also create epigenetic modifications and disturbed epithelium-immune cell cross-talk, which breaks down the equilibrium of the airway epithelial barrier. These system-wide effects are exacerbated through the gut-lung axis, which aggravates local lung damage via microbiome dysregulation. We evaluate emerging therapeutic strategies that aim to restore barrier integrity, including antioxidants, natural compounds, inhibitors directing specific pathways (e.g. epidermal growth factor receptor (EGFR), NLR family pyrin domain containing 3 (NLRP3)) and microbiome modulation via probiotics. Protection and repair of the airway epithelial barrier offer a promising approach to reducing the onset and progression of pollution-related COPD in populations vulnerable to highly polluted environments.