Abstract
BackgroundExposure to electronic-cigarette (e-cig) aerosols induces potentially fatal e-cig or vaping-associated lung injury (EVALI). The cellular and molecular mechanisms underlying these effects, however, are unknown. We used an air–liquid interface (ALI) in vitro model to determine the influence of two design characteristics of third-generation tank-style e-cig devices—resistance and voltage—on (1) e-cig aerosol composition and (2) cellular toxicity.MethodsHuman bronchial epithelial cells (H292) were exposed to either butter-flavored or cinnamon-flavored e-cig aerosols at the ALI in a Vitrocell exposure system connected to a third-generation e-cig device. Exposures were conducted following a standard vaping topography profile for 2 h per day, for 1 or 3 consecutive days. 24 h after ALI exposures cellular and molecular outcomes were assessed.ResultsWe found that butter-flavored e-cig aerosol produced under ‘sub-ohm’ conditions (< 0.5 Ω) contains high levels of carbonyls (7–15 μg/puff), including formaldehyde, acetaldehyde and acrolein. E-cig aerosol produced under regular vaping conditions (resistance > 1 Ω and voltage > 4.5 V), contains lower carbonyl levels (< 2 μg/puff). We also found that the levels of carbonyls produced in the cinnamon-flavored e-cig aerosols were much lower than that of the butter-flavored aerosols. H292 cells exposed to butter-flavored or cinnamon-flavored e-cig aerosol at the ALI under ‘sub-ohm’ conditions for 1 or 3 days displayed significant cytotoxicity, decreased tight junction integrity, increased reactive oxygen species production, and dysregulated gene expression related to biotransformation, inflammation and oxidative stress (OS). Additionally, the cinnamon-flavored e-cig aerosol induced pro-oxidant effects as evidenced by increases in 8-hydroxy-2-deoxyguanosine protein levels. Moreover, we confirmed the involvement of OS as a toxicity process for cinnamon-flavored e-cig aerosol by pre-treating the cells with N-acetyl cysteine (NAC), an antioxidant that prevented the cells from the OS-mediated damage induced by the e-cig aerosol.ConclusionThe production of high levels of carbonyls may be flavor specific. Overall, inhaling e-cig aerosols produced under ‘sub-ohm’ conditions is detrimental to lung epithelial cells, potentially via mechanisms associated with OS. This information could help policymakers take the necessary steps to prevent the manufacturing of sub-ohm atomizers for e-cig devices.
Highlights
Exposure to electronic-cigarette (e-cig) aerosols induces potentially fatal e-cig or vaping-associated lung injury (EVALI)
Sub‐ohm vaping increases the levels of carbonyls in butter‐flavored e‐cig aerosols We found that high voltage sub-ohm vaping significantly increases the levels of acetaldehyde, acrolein and formaldehyde present in butter-flavored e-cig aerosols
3 Days of butter‐flavored e‐cig aerosol exposure under sub‐ohm conditions decreases viable cell numbers and dysregulates gene expression to a greater extent than under regular vaping conditions Since butter-flavored e-cig aerosols generated under sub-ohm (0.15 Ω) conditions produced higher levels of toxic chemicals than regular vaping conditions (1.5 Ω) (Fig. 1a), we investigated whether this difference in vaping conditions would translate into toxicological responses of lung cells
Summary
Exposure to electronic-cigarette (e-cig) aerosols induces potentially fatal e-cig or vaping-associated lung injury (EVALI). This creates major challenges for ENDS-related research, as (1) standardized assessments are absent; (2) there are more than 2800 different models of ENDS from 466 identified brands [8]; plus (3) over 7700 unique e-liquid flavors [8] This is a significant public health concern, since, as demonstrated by the 2019–2020 outbreak in the United States, exposures to ENDS aerosols can induce potentially fatal e-cigarette or vaping-associated lung injury (EVALI) [9]. This clearly demonstrates that little is known regarding the long-term pulmonary effects of inhaling ENDS heated and aerosolized humectants, nicotine as well as flavors
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