Tobacco and e-cigarettes exposure
Exposure to tobacco has been associated with oxidative imbalance and
stress, which may change barrier function of the epithelial layer by
reducing ciliary beating and enhancing mucus production, epithelial to
mesenchymal transition, and immune dysfunction [73]. Moreover, some
cigarette smoke derivates may disrupt epithelial cellular junctions,
allowing a deeper penetration of toxins and allergens [73]. Oxidate
stress related to exposure to tobacco may activate the transcription of
factors involved in inflammatory responses, which are responsible for
sustained immune cell recruitment and activation. Furthermore, prolonged
exposure to tobacco may enhances both Th2- and Th1-mediated inflammatory
responses, being associated with a more severe asthma phenotype
[74]. In utero exposure to nicotine may affect lung development in
the fetus, consequently leading to impaired lung function and an
increased risk of asthma [75]. Nicotine has been also associated
with epigenetic changes, such as DNA methylation or changed microRNA
expression, which may modulate epithelial differentiation, immune cell
differentiation, or both, in a permanent way [76].
The chemical compounds, including reactive carbonyls, resulting from
heating in e-cigarettes are also known for their toxic and irritant
effect on the airways, causing airway construction, direct damage to
airway epithelium and changes in gene expression [77]. Similar to
exposure to cigarettes, acute exposure to SHS to e-cigarettes was also
associated with altered lung cells, including the small airway
epithelium, alveolar macrophages, and circulating endothelial
microparticles [78].
Prevention and mitigation of the effects of air pollution on
childhood asthma
Actions against the well-known childhood asthma risk factors, industrial
activities, TRAP, cleaning and consumer products, and smoking, should be
taken simultaneously. Global, national, local, and individual action
plans should be implemented considering each situation and need to be
planned and implemented by engaging policymakers, governments, civil
society, and each individual (Figure 3 ).