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Respir Res. 2016 May 17;17(1):57. doi: 10.1186/s12931-016-0369-9.

Airway epithelial cell exposure to distinct e-cigarette liquid flavorings reveals toxicity thresholds and activation of CFTR by the chocolate flavoring 2,5-dimethypyrazine.

Author information

1
Asthma and Airway Disease Research Center, Arizona Health Sciences Center, 1501 N. Campbell Avenue, Tucson, AZ, 85724-5030, USA. caras@email.arizona.edu.
2
Bio5 Collaborative Research Institute, Arizona Health Sciences Center, Tucson, AZ, USA. caras@email.arizona.edu.
3
Asthma and Airway Disease Research Center, Arizona Health Sciences Center, 1501 N. Campbell Avenue, Tucson, AZ, 85724-5030, USA.
4
Bio5 Collaborative Research Institute, Arizona Health Sciences Center, Tucson, AZ, USA.
5
Department of Physiology, Arizona Health Sciences Center, Tucson, AZ, USA.

Abstract

BACKGROUND:

The potential for adverse respiratory effects following exposure to electronic (e-) cigarette liquid (e-liquid) flavorings remains largely unexplored. Given the multitude of flavor permutations on the market, identification of those flavor constituents that negatively impact the respiratory tract is a daunting task. In this study we examined the impact of common e-liquid flavoring chemicals on the airway epithelium, the cellular monolayer that provides the first line of defense against inhaled particulates, pathogens, and toxicants.

METHODS:

We used the xCELLigence real-time cell analyzer (RTCA) as a primary high-capacity screening tool to assess cytotoxicity thresholds and physiological effects of common e-liquid flavoring chemicals on immortalized human bronchial epithelial cells (16HBE14o-). The RTCA was used secondarily to assess the capability of 16HBE14o- cells to respond to cellular signaling agonists following a 24 h exposure to select flavoring chemicals. Finally, we conducted biophysical measurements of well-differentiated primary mouse tracheal epithelial (MTE) cells with an Ussing chamber to measure the effects of e-cigarette flavoring constituents on barrier function and ion conductance.

RESULTS:

In our high-capacity screens five of the seven flavoring chemicals displayed changes in cellular impedance consistent with cell death at concentrations found in e-liquid. Vanillin and the chocolate flavoring 2,5-dimethylpyrazine caused alterations in cellular physiology indicative of a cellular signaling event. At subcytotoxic levels, 24 h exposure to 2,5-dimethylpyrazine compromised the ability of airway epithelial cells to respond to signaling agonists important in salt and water balance at the airway surface. Biophysical measurements of 2,5-dimethylpyrazine on primary MTE cells revealed alterations in ion conductance consistent with an efflux at the apical airway surface that was accompanied by a transient loss in transepithelial resistance. Mechanistic studies confirmed that the increases in ion conductance evoked by 2,5-dimethylpyrazine were largely attributed to a protein kinase A-dependent (PKA) activation of the cystic fibrosis transmembrane conductance regulator (CFTR) ion channel.

CONCLUSIONS:

Data from our high-capacity screening assays demonstrates that individual e-cigarette liquid flavoring chemicals vary in their cytotoxicity profiles and that some constituents evoke a cellular physiological response on their own independent of cell death. The activation of CFTR by 2,5-dimethylpyrazine may have detrimental consequences for airway surface liquid homeostasis in individuals that use e-cigarettes habitually.

KEYWORDS:

2,5-dimethylpyrazine; Airway epithelium; CFTR; Electronic cigarettes; Odorant receptor; xCELLigence RTCA

PMID:
27184162
PMCID:
PMC4869201
DOI:
10.1186/s12931-016-0369-9
[Indexed for MEDLINE]
Free PMC Article

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