E-cigarette vapour from base components propylene glycol and vegetable glycerine inhibits the inflammatory response in macrophages and epithelial cells

E-cigarettes are a highly popular nicotine replacement therapy in the process of smoking cessation. Despite this, research on the effects of E-vapours to human health remains limited. The popularity of vaping and mass production of cheap E-liquids has led to compromised safety regulations, with contaminants such as heavy metals and alkaloids detected in multiple liquids. Vaporised E-liquids increase cellular ROS generation and inflammatory cytokine release from pulmonary macrophages. This suggests that E-cigarette usage might activate inflammasomes. Common food additives vegetable glycerine (VG) and propylene glycol (PG) form the base of all E-liquids, but little is known about their inflammatory potential once inhaled. Here, the effect of base components PG and VG on inflammasome activation and cytokine release was investigated in macrophages and epithelial cells exposed to E-liquids and vaporised E-liquid extract (E-vapour). Base E-liquid and E-vapour did not induce cellular cytotoxicity and non-vapourised E-liquid had no effect on IL-8 release. However, basic PG/VG E-vapour inhibited both IL-8 release and conventional inflammasome activation by known inflammatory activators in macrophages and epithelial cells. These results propose a novel inhibitory effect of basic E-vapour components to inflammatory challenges.