Nicotine promotes e-cigarette vapour-induced lung inflammation and structural alterations.

Electronic cigarette (e-cigarette) vapour is gaining popularity as an alternative to tobacco smoking and can induce acute lung injury. However, the specific role of nicotine in e-cigarette vapour and its long-term effects on the airways, lung parenchyma and vasculature remain unclear. We found that in vitro exposure to nicotine-containing e-cigarette vapour extract (ECVE) or nicotine-free extract (NF ECVE) induced changes in gene expression of epithelial cells and pulmonary arterial smooth muscle cells (PASMC), but preferentially ECVE caused functional alterations ( e.g. decrease of human or mouse PASMC proliferation by 29.3±5.3% or 44.3±8.4%, respectively). Additionally, acute inhalation of nicotine-containing e-cigarette vapour (ECV) but not nicotine-free vapour (NF ECV) increased pulmonary endothelial permeability in isolated lungs. Long-term, in vivo exposure of mice to ECV for 8 months significantly increased the number of inflammatory cells, in particular lymphocytes compared to control and NF ECV in the bronchoalveolar lavage (BAL, ECV: 853.4±150.8, control: 37.0±21.1, NF ECV: 198.6±94.9 cells·mL -1 ) and in lung tissue (ECV: 25.7±3.3, control: 4.8±1.1, NF ECV: 14.1±2.2 cells·mm -3 ). BAL-cytokines were predominantly increased by ECV. Moreover, ECV caused significant changes in lung structure and function ( e.g. increase in airspace by 17.5±1.4% compared to control), similar to mild tobacco smoke-induced alterations, which also could be detected in the NF ECV group, albeit to a lesser degree. In contrast, the pulmonary vasculature was not significantly affected by ECV or NF ECV. In conclusion, NF ECV components induce cell-type specific effects and mild pulmonary alterations, while inclusion of nicotine induces significant endothelial damage, inflammation and parenchymal alterations.