Differential Inhalation Toxicity Induced by E-Cigarette Aerosol Flavorings in Association with Nicotine

Abstract

Significance. There is a significant need for data on respiratory effects of chemical constituents including flavorings in e-cigarettes (EC) aerosols to inform the regulatory science and communicate with the public about EC safety.Methods. Cytotoxicity and inflammatory response of human airway epithelial cells in a submerged culture were measured by MTT and immunoassay at 18 hours post-exposure to EC aerosols collected in an impinger. Aerosols were generated from an EC with heating coil power of 8.9 W using a program-controlled, customized smoking system following CRM No.81 and ISO puffing regimes. Four differently flavored e-liquids (i.e., non-flavor, menthol, sweet, tobacco) of 50:50 propylene glycol and vegetable glycerin with two nicotine concentrations (0% and 1.8%) for each flavor were tested in dose-response manner.Results. We found differential cytotoxicity and repressed immune response associated with flavorings. The menthol-flavored aerosols induced cytotoxicity in dose-response manner with 20% cytotoxicity at the highest dose as compared to the other two flavorings that showed 10% or less. Non-flavored aerosols showed little cytotoxicity that did not vary by dose and nicotine level, suggesting the vehicle and additives other than flavorings have little cytotoxicity for the condition we used to generate aerosols. Very low nicotine dose slightly improved cell viability, agreeing with previous reports in the literature. IL-8 production was reduced with increased dose, but not for menthol or sweet flavors.Conclusion. EC flavorings have a significant impact on the degree and variability of respiratory toxicity. Certain flavoring such as menthol together with nicotine would synergistically increase harmful effects in user’s lung. More efforts that investigate the link between flavorings chemical composition in association with nicotine and respiratory health effects are needed to support regulation of harmful constituents in the EC products.