Electronic cigarette aerosol condensate is cytotoxic and increases ACE2 expression in human airway epithelial cells: implications for COVID-19

Abstract

<b>Background:</b> Tobacco smoking increases ACE2 expression in the lung, enhancing susceptibility to SARS-CoV-2 infection and progression to COVID-19. Electronic cigarettes (e-cig) have the capability to deliver large hits of nicotine, therefore they can also be an avoidable risk factor. <b>Aim:</b> We investigated the cytotoxicity profile of e-cig aerosol condensates and whether e-cig vaping can also elevate ACE2 expression in large and small airway epithelial cells (SAECs). <b>Methods:</b> Bronchial (BEAS-2B) and primary SAECs were exposed to e-cig aerosol condensates produced from PG/VG or watermelon e-liquid (± added nicotine), and cigarette smoke extract (CSE). Cytotoxicity (CCK-8), membrane integrity (LDH), and ACE2 protein expression (IF) and gene expression (qPCR) were measured in BEAS-2Bs and SAECs for both 4 and 24-hours treatments. <b>Results:</b> Nicotine-free condensates (p&lt;0.0001) and higher concentrations of nicotine-containing condensates (p&lt;0.0001; p&lt;0.01) were cytotoxic. Reduced membrane integrity was evident in BEAS-2B cells treated for 24 hours with higher concentrations of nicotine-containing condensates (p&lt;0.0001; p&lt;0.05). ACE2 protein expression in BEAS-2Bs was increased significantly in condensates containing 18mg/mL of nicotine for both time points. ACE2 protein expression is observably increased in all SAEC treatments compared to media controls. Select increases in ACE2 gene expression were measured. CSE had greatest effect on increased ACE2 expression (p&lt;0.01). <b>Conclusions:</b> Our data suggests that vaping is cytotoxic and can increase lung ACE2 expression. Vaping should be avoided, particularly during the COVID-19 pandemic.