Electronic cigarette derived free radicals, oxidative stress and inflammation in lung cancer development

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Project Abstract Electronic cigarettes (e-cig) have been promoted as electronic nicotine (NIC) delivery systems (ENDS) without the adverse effects of tobacco cigarette smoking (CS). However, recent studies have reported a wide range of e-cig-induced toxicities with severe inflammatory lung disease observed in e-cig users. While there is a strong association between CS-induced oxidative stress, inflammation and cancer, this has not been established for e-cig use. E-cig generate toxic species, including free radicals and reactive acetaldehydes with the levels of these toxicants increased with increasing device power. These toxic chemicals produce reactive oxygen species (ROS), which can lead to uncontrolled inflammation and DNA damage with dysregulated cell proliferation that trigger carcinogenesis. In our chronic mouse e-cig exposure model, we observed that e-cig aerosol, generated from e-cig liquid containing NIC, induced lung tumors in 50% of the mice studied at 50 weeks of exposure, as first detected by micro-CT imaging. Histopathological examination of the tumors showed adenocarcinoma or adenoma with focal mixed broncho-alveolar neoplastic and pre-malignant cells. Superoxide radicals, inflammation, DNA damage and stemness markers were detected in the alveoli and bronchioles, preceding cancer development at earlier exposure times. The free radicals and high levels of aldehydes in e-cig aerosol, as well as the NIC derived iminium metabolite, can trigger processes of cellular ROS generation and this may serve as a central trigger of carcinogenesis. Based on the critical public health implications of this work, it is imperative to expand these observations to measure the exposure intensity/duration relationships, and the role of e-cig aerosol free radical levels and NIC in cancer development. Thus, we will perform longitudinal studies with the requisite group size needed to definitively address the critical questions: 1) What is the exposure intensity and duration required for lung cancer initiation/progression? 2) What is the incidence rate of e-cig-induced lung cancer? 3) Is cancer onset and/or progression NIC- dependent? 4) How is it effected by device power and resultant aerosol free radical levels? 5) Is cancer onset and/or progression gender-dependent? 6) What are the mechanisms by which e-cig exposure triggers ROS generation and inflammation in the lung? Studies with longitudinal micro-CT, MRI, EPR spectroscopy, EPR- MRI co-imaging and blood tumor markers followed by biochemical assays and histopathology will determine the role of exposure duration, ENDS power, NIC, and gender on initiation and/or progression of lung cancer. ROS generation, lung inflammation and secondary epithelial mesenchymal transition will be evaluated as triggers or steps leading to carcinogenesis. With knowledge of the role of these mechanisms and evaluation of inhibitors that block them, we will identify therapeutic interventions that could be used to ameliorate e-cig induced lung inflammation and carcinogenesis. Thus, this research will provide important insights defining the carcinogenesis risk of e-cig use, and its underlying exposure-dependent triggers and mechanisms.