E-Cigarette Vapor Decreases Cellular Proliferation through Nicotine-Dependent Mechanisms

Abstract

Electronic cigarette (e-cigarette) use has risen as individuals look for healthier nicotine delivery systems than conventional cigarettes, but recent studies have demonstrated variable physiological responses to e-cigarette vapor. The safety of e-cigarette vapor remains an open question. We investigated the molecular cellular response of adenocarcinoma human alveolar basal epithelial (A549) cells to flavored e-cigarette vapor. E-cigarette and cigarette vapor were extracted via a vacuum-percolating system into PBS. The effects of a flavored e-liquid containing nicotine (eCSE) and nicotine free e-liquid (NFeCSE) were compared to cigarette smoke extract (CSE), pure nicotine, glycerol, and PBS. Cells exposed to eCSE and NFeCSE had decreased cell viability and proliferation. An increase in active caspase-3 was observed in cells exposed to NFeCSE, while cells exposed to eCSE and CSE displayed no change, suggesting nicotine-mediated protection from apoptosis. However, phosphorylated Akt, which regulates cellular proliferation, was elevated in response to eCSE, NFeCSE, CSE, and glycerol. As the glutathione-oxidative stress response was known to integrate cellular factors including carcinogenesis, inflammation, and cell proliferation, GSH/GSSG levels were measured in cells exposed to e-cigarette smoke. An increase in oxidative stress was observed in cells treated with CSE, but not eCSE, suggesting components in CSE independent of nicotine may be contributing to an imbalance in the stress response. These results indicate e-cigarette vapor affects A549 cell viability dependent on nicotine, and is distinct from CSE-induced mechanisms of oxidative-stress.