Molecular mechanisms for E-cigarette vapor-induced mucociliary dysfunction: role of nicotinic acetylcholine and TRP receptors

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Use of e-cigarettes (E-cigs), known as “vaping”, is becoming widely adopted amongst adolescents who are attracted by their novelty, synthetic flavors, and belief of reduced toxicity. Previous smokers also use E-cigs as a smoking cessation tool that is an alternative nicotine delivery system with milder social stigma. However, “vaping” is an emerging public health problem, especially concerning young people with no smoking history, due to the lack of informative respiratory studies on E-cig vapor components. Past inhaled nicotine studies examined its effects mainly on airway smooth muscle and the central nervous system as opposed to the ciliated airway epithelia, the major barrier for inhaled E-cig vapor, and few studies investigated nicotine in isolation of tobacco smoke constituents. Additionally, toxicology studies of most E-cig flavorings were never completed for inhalation exposure. This research proposal, which doubles as a mentored postdoctoral training plan, aims to elucidate effects of E-cig vapor on the functional human ciliated airway epithelium. The airway epithelium expresses several isoforms of nicotinic acetylcholine receptors (nAChRs), transient receptor potential (TRP) cation channel member A1 (TRPA1), and other TRP channels, which are all calcium (Ca2+)-permeant. Nicotine is reported to stimulate both nAChRs and TRPA1, and some E-cig flavors are TRP agonists, such as cinnamaldehyde (TRPA1), vanillin (TRPV1), and menthol (TRPM8). The basic hypothesis of this proposal is that E-cig vapor components nicotine and cinnamaldehyde compromise mucociliary function by stimulating nAChRs and TRPA1 to cause sustained Ca2+ influx. Research goals for this study are to identify a molecular mechanism(s) for how E-cig vapor impairs mucociliary function and to develop novel high-throughput methodology for establishing continuous mucociliary transport in vitro. The latter will be used to probe adverse/therapeutic effects of aerosolized compounds. These goals will be tested in primary human bronchial epithelial cells differentiated at the air-liquid interface, using physiologically-relevant exposures, and measuring in vitro parameters of mucociliary function such as mucociliary transport, ciliary beating, and airway surface hydration. Training goals for this proposal are to develop expertise in studying pulmonary effects of inhaled toxicants and to become immersed in translational research by working in a diverse team composed of clinicians and scientists. Completion of this study will fulfill the unmet need for clarification and information regarding effects of inhaled nicotine and E-cig flavorings. Use of relevant exposures and primary cultures will provide a compelling biological rationale to adapt public health policy. It will also inform clinicians on the `pro & cons' of E-cigs as smoking cessation tools as well as the impact on young never-smoking subjects who take up “vaping”. Lastly, completion of this training plan will generate data and expertise necessary for career transition from postdoctoral trainee to independent investigator.