Neurotoxic and neurodegenerative risks from chronic exposure to metal mixtures in e-cigarette aerosol

PROJECT SUMMARY Electronic cigarettes (e-cigs), battery-operated devices that heat liquids to generate an inhaled aerosol vapor, are increasingly popular, especially among younger users. E-cigs are seen as an increasingly attractive alternative to tobacco cigarettes; however, little is known about the human health effects arising from chronic exposure to these aerosols. A growing number of studies have examined potential e-cig risks for cancer, respiratory, and cardiovascular diseases. New data from our laboratory and others, however, raise additional human health concerns about exposure to potentially neurotoxic metals released from the heated coil wire and other e-cig components. For example, we found that in a large fraction e-cig aerosol samples we collected, nickel, chromium, and lead levels exceeded EPA national ambient air quality standards or ATSDR minimum risk levels (MRL). Notably, this was true for manganese (Mn), a prime suspect in sporadic Parkinson’s disease (PD) etiology. Others have found that vanadium, copper and selenium (all suspected for a potential role in PD) were higher in blood of e-cig users as compared to tobacco smokers. We hypothesize that hazardous metals released by e-cigs may accumulate in the brain and pose significant neurotoxic risk(s) for neurodegenerative diseases upon chronic exposure. We will test our hypothesis in three ways. First, we will determine the levels of potentially neurotoxic metals in the aerosol produced by several popular e-cigs operated under different conditions and with e-liquids differing in flavor and nicotine content. Second, we will examine the neurotoxic effect of chronic e-cig aerosol exposure in neuronal cell cultures derived from human subjects carrying incompletely-penetrant mutations linked to PD or from healthy controls, and identify metal mixtures of particular neurotoxic concern. Third, we will measure metal concentrations in brain tissue of chronically e-cig exposed mice, which are wildtype controls or knock-in for a mutation that increases the risk for PD; we will also determine the metals’ potential adverse effects on motor function and cognition in the mouse models. Findings from this study are likely to provide crucial and heretofore unavailable information to policy makers and will enable them to evaluate potential neurotoxic health risks arising from second-hand exposure to e-cig aerosol. We hypothesize that health risks are significantly influenced by genetic susceptibility to neurodegenerative disease, as well as by e-cig device construction, operating conditions, e-liquid flavoring, and nicotine content.