Partial amelioration of a chronic cigarette-smoke-induced phenotype in mice by switching to electronic cigarettes

Electronic cigarettes ("e-cigarettes") are often marketed as smoking cessation tools and are used by smokers to reduce/quit cigarette smoking. The objective of this study was to assess the health effects of switching to e-cigarettes after long-term smoking in a mouse model and compare these effects with continued smoking, or quitting entirely. Adult BALB/c mice were whole-body exposed to mainstream cigarette smoke (2 h/day, 5 days/week) for 12 weeks prior to switching to flavoured e-cigarette aerosol (50:50 propylene glycol and glycerine) containing 18 mg/mL nicotine (2 h/day and 5 days/week), continuing cigarette smoking (2 h/day and 5 days/week), or quitting entirely for an additional 2 weeks. We then assessed a range of respiratory health outcomes including lung function and structure, pulmonary inflammation and changes in gene expression in the lung. Switching to e-cigarettes led to improvements in some aspects of respiratory health in mice compared with continued smoking, such as reduced neutrophilic inflammation in the lung. However, total cellular lung inflammation was still elevated and lung function was still impaired, in terms of airway responsiveness to methacholine, for e-cigarette use compared with quitting. Larger effects were typically seen in female mice compared to male. This study shows that switching to e-cigarettes after long-term cigarette smoking leads to improvements in some aspects of respiratory health, such as neutrophilic inflammation and the volume dependence of lung function compared with continued smoking. However, switching to e-cigarettes was not as effective as quitting smoking entirely.