Abstract
The 2019 United States outbreak of E-cigarette (e-cig), or Vaping, Associated Acute Lung Injury (EVALI) has been linked to presence of vitamin E acetate (VEA) in Δ8tetrahydrocannabinol (Δ8THC)-containing e-liquids, as supported by VEA detection in patient biological samples. However, the pathogenesis of EVALI and the complex physicochemical properties of e-cig emissions remain unclear, raising concerns on health risks of vaping. This study investigates the effect of Δ8THC/VEA e-liquids and e-cig operational voltage on in vitro toxicity of e-cig aerosols. A novel E-cigExposure Generation System platform was used to generate and characterize e-cig aerosols from a panel of Δ8THC/VEA or nicotine-based e-liquids at 3.7 or 5 V. Human lung Calu-3 cells and THP-1 monocytes were exposed to cell culture media conditioned with collected e-cig aerosol condensate at doses of 85 and 257 puffs/m2 lung surface for 24 h, whereafter specific toxicological endpoints were assessed (including cytotoxicity, metabolic activity, reactive oxygen species generation, apoptosis, and inflammatory cytokines). Higher concentrations of gaseous volatile organic compounds were emitted from Δ8THC/VEA compared with nicotine-based e-liquids, especially at 5 V. Emitted PM2.5 concentrations in aerosol were higher for Δ8THC/VEA at 5 V and averagely for nicotine-based e-liquids at 3.7 V. Overall, aerosols from nicotine-based e-liquids showed higher bioactivity than Δ8THC/VEA aerosols in THP-1 cells, with no apparent differences in Calu-3 cells. Importantly, presence of VEA in Δ8THC and menthol flavoring in nicotine-based e-liquids increased cytotoxicity of aerosols across both cell lines, especially at 5 V. This study systematically investigates the physicochemical and toxicological properties of a model of Δ8THC/VEA and nicotine e-cigarette condensate exposure demonstrating that pyrolysis of these mixtures can generate hazardous toxicants whose synergistic actions potentially drive acute lung injury upon inhalation.