Our understanding of the molecular mechanisms and their relationship to the development of cancer has enabled the creation of a set of predictive tools that can be applied across a range of existing and new tobacco products to inform risk for cancer. These tools are accurate in short-term assays, applicable to human progenitor cells for cancer, and recapitulate changes seen in primary cancer that can take decades to develop. Quantitative results from such assays should be highly useful for establishing regulatory policies and communicating relative risk. We have developed an in vitro pre-malignancy model using metabolically competent immortalized human bronchial epithelial cells that will now be extended to three oral epithelial cell lines to test the acute and chronic effects of exposure to electronic cigarette (E-cig) aerosols containing nicotine and common classes of flavor chemicals. The E-cig industry is in a major period of evolution with the release of more than one hundred delivery devices that afford the user the opportunity to adjust the voltage for aerosol generation and to customize their nicotine solution with a menu of >7764 unique flavor chemicals. Most of these flavor chemicals are confectionary in nature, food grade, and generally recognized as safe when used as food constituents. However, the toxicological effects of flavors when inhaled after heating or burning and how they may influence the deposition profile of the components released from nicotine (e.g., NNK, formaldehyde) are unknown. For example, diacetyl and acetyl propionyl are associated with respiratory disease when inhaled, found in 74% of 159 tested flavorings, and readily detected in the generated aerosols at levels that exceed consumer safety. The 12 major classes of flavor chemicals with and without the addition of a standard nicotine solution generated at a low and high voltage will be studied to provide a comprehensive assessment of the toxicological effects of the aerosols generated from these complex mixtures on the oral epithelial cell. The aerosols generated from the different nicotine-flavor chemical mixtures with respect to toxicological components, the effect of increased voltage on aerosol composition, and how these variables impact the deposition profile within the oral-tracheal tract will be characterized. A sensitive readout will be obtained by acute and chronic in vitro exposure of these oral epithelial cell lines to the different E-cig aerosols to inform many aspects related o the cytotoxic, genotoxic, and carcinogenic potential of these E-cig products. The compilation of these findings will support development of a risk model that links chemical constituents within the E-cig aerosol to the detrimental biological effects observed in the in vitro studies.
The E-cigarette industry is evolving with development of new devices that allow the adjustment of voltage for aerosol development and the increasing user population to customize their nicotine solution with flavor chemicals that contain hazardous compounds. Our studies will characterize the deposition profile in the oral-trachea region and identify toxic chemicals present within E-cigarette aerosols generated from the major classes of flavor chemicals with and without nicotine. A set of predictive tools developed by our group will be interrogated in an in vitro model of metabolically competent immortalized human oral epithelial cells exposed to the same aerosols to evaluate cytotoxicity, genotoxicity, and pre-malignant endpoints to provide a comprehensive assessment regard to exposure, toxicant yield, and oral cancer risk.
