Project Summary / Abstract: Project 1 Electronic cigarettes (EC) have gained increasing popularity due, in part, to the perception of them as a less harmful nicotine delivery device as compared to cigarettes. However, EC aerosols contain a number of harmful or potentially harmful constituents including free radicals and other oxidants that may impact the safety of EC. The diversity of products and rapidly evolving EC market poses a challenge for researchers seeking to understand the potential harms associated with their use, and for regulators who are asked to make determinations regarding their safety and seek data on device characteristics that impact EC harm. Our in vitro data show that EC temperature and e-liquid propylene glycol (PG) concentration are the major factors regulating the production of highly reactive free radicals and other oxidants. Further, our preliminary in vivo animal data suggest that these oxidants increase biomarkers of oxidative stress and inflammation. These data suggest the potential for harm in EC users and a potential link with specific EC design features. This proposed research provides valuable data for regulatory product standard development related to current and future ECs. It addresses our overall TCORS theme to better understand how the physical design and chemical constituents affect the toxicity and addictiveness of tobacco products with a focus on harm generated from oxidants. In Aim 1 we will conduct controlled animal exposure studies to determine the effects of temperature and PG concentration on biomarkers of exposure and harm, focusing on inflammation and oxidant stress. In Aim 2 we will conduct studies of current EC users, performing controlled inhalation exposure studies as well as naturalistic studies to determine the effects of EC temperature and e- liquid PG concentration on biomarkers of exposure and harm. We will use a randomized 4-treatment 4-period crossover design to compare low and high temperature and low and high PG e-liquid concentration. Acute effects including biomarkers of exposure, inflammation, oxidant stress and cardiorespiratory function will be measured before and immediately after rigidly controlled inhalation sessions, after a two-week period of naturalistic use and after on-site ad libitum use. In Aim 3 we will test for associations between solvent PG content and free radical production and biomarkers of exposure & harm in popular commercially available pod- type EC devices. Given the popularity of these devices, it is critical that the impact of important design features on free radical production and oxidative stress-related biomarkers in individuals using these products be investigated. Overall, this project addresses the well-established need for research regarding how variation in EC product design characteristics impact constituent exposure and toxicity and development of biomarkers to assess EC-related exposure and related harm or toxicity. As such, this research directly addresses the Toxicity domain of the TCORS 3.0 RFA.