The effects of dual IQOS and cigarette smoke exposure on airway epithelial cells: implications for lung health and respiratory disease pathogenesis.

Background: Cigarette smoking remains a primary cause of chronic lung diseases. After a steady decline, smoking rates have recently increased especially with the introduction of newer electronic nicotine delivery devices, and it is also emerging that dual- or poly-product usage is on the rise. Additionally, with the introduction of IQOS (a heated tobacco product) globally, its impact on human health needs to be investigated. In this study we tested if dual exposure (cigarette smoke (CS)+IQOS) is detrimental to lung epithelial cells when compared with CS or IQOS exposure alone. Methods: Human airway epithelial cells (BEAS-2B) were exposed to either CS, IQOS or their dual combination (CS+IQOS) at concentrations of 0.1%, 1.0%, 2.5% and 5.0%. Cytotoxicity, oxidative stress, mitochondrial homeostasis, mitophagy and effects on epithelial-mesenchymal transition (EMT) signalling were assessed. Results: Both CS and IQOS alone significantly induced loss of cell viability in a concentration-dependent manner which was further enhanced by dual exposure compared with IQOS alone (p<0.01). Dual exposure significantly increased oxidative stress and perturbed mitochondrial homeostasis when compared with CS or IQOS alone (p<0.05). Additionally, dual exposure induced EMT signalling as shown by increased mesenchymal (α-smooth muscle actin and N-cadherin) and decreased epithelial (E-cadherin) markers when compared with CS or IQOS alone (p<0.05). Conclusion: Collectively, our study demonstrates that dual CS+IQOS exposure enhances pathogenic signalling mediated by oxidative stress and mitochondrial dysfunction leading to EMT activation, which is an important regulator of small airway fibrosis in obstructive lung diseases.