Sub-ohm vaping increases the levels of carbonyls, is cytotoxic, and alters gene expression in human bronchial epithelial cells exposed at the air-liquid interface

Respir Res. 2020 Nov 19;21(1):305. doi: 10.1186/s12931-020-01571-1.


Background: Exposure 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.

Methods: Human 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.

Results: We 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.

Conclusion: The 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.

Keywords: Carbonyls; Cellular toxicity; Electronic nicotine delivery systems (ENDS); Electronic-cigarette; Sub-ohm; Vaping.

MeSH terms

  • Aerosols
  • Antioxidants / pharmacology
  • Bronchi / cytology
  • Bronchi / drug effects*
  • Bronchi / metabolism
  • Cell Differentiation / drug effects
  • Cell Differentiation / physiology
  • Cell Line
  • Cytotoxins / toxicity*
  • Electronic Nicotine Delivery Systems*
  • Flavoring Agents / toxicity*
  • Gene Expression
  • Humans
  • Lung / cytology
  • Lung / drug effects
  • Lung / metabolism
  • Oxidative Stress / drug effects
  • Oxidative Stress / physiology
  • Reactive Oxygen Species / metabolism
  • Respiratory Mucosa / drug effects*
  • Respiratory Mucosa / metabolism
  • Vaping / adverse effects*


  • Aerosols
  • Antioxidants
  • Cytotoxins
  • Flavoring Agents
  • Reactive Oxygen Species