Transcriptomic response of primary human airway epithelial cells to flavoring chemicals in electronic cigarettes

Abstract

The widespread use of electronic cigarettes (e-cigarettes or e-cig) is a growing public health concern. Diacetyl and its chemical cousin 2,3-pentanedione are commonly used to add flavors to e-cig; however, little is known about how the flavoring chemicals may impair lung function. Here we report that the flavoring chemicals induce transcriptomic changes and perturb cilia function in the airway epithelium. Using RNA-Seq, we identified a total of 163 and 568 differentially expressed genes in primary normal human bronchial epithelial (NHBE) cells that were exposed to diacetyl and 2,3-pentanedione, respectively. DAVID pathway analysis revealed an enrichment of cellular pathways involved in cytoskeletal and cilia processes among the set of common genes (142 genes) perturbed by both diacetyl and 2,3-pentanedione. Consistent with this, qRT-PCR confirmed that the expression of multiple genes involved in cilia biogenesis was significantly downregulated by diacetyl and 2,3-pentanedione in NHBE cells. Furthermore, immunofluorescence staining showed that the number of ciliated cells was significantly decreased by the flavoring chemicals. Our study indicates that the two widely used e-cig flavoring chemicals impair the cilia function in airway epithelium and likely contribute to the adverse effects of e-cig in the lung.

Life-threatening bronchiolitis related to electronic cigarette use in a Canadian youth

“…57 Bronchiolitis obliterans from diacetyl exposure is also known as "popcorn worker's lung" owing to its initial description in patient clusters of microwave-popcorn factory workers exposed to diacetylbased flavouring agents. [55][56][57] Diacetyl and another flavouring agent, 2,3-pentanedione, can alter gene expression pathways related to cilia and cytoskeletal processes in normal human bronchial epithelial cells, 72 and cause epithelial cell injury and bronchiolitis obliterans in rodents. 73,74 Although the mechanisms behind bronchiolitis obliterans remain incompletely understood, inhaled diacetyl influences human cellular matrix remodelling and may stimulate fibroproliferative changes in human airways.…”

Chemical Characterization of Electronic Cigarette (e-cigs) Refill Liquids Prior to EU Tobacco Product Directive Adoption: Evaluation of BTEX Contamination by HS-SPME-GC-MS and Identification of Flavoring Additives by GC-MS-O

“…Extensive scientific research on diacetyl has been carried out from then both confirming preliminary hypothesis on exposure-occurrence of lung disease association and adding new relevant scientific data [53]. Recently published papers have highlighted both neurotoxicity and impairment of cilia function in human airway epithelium [54,55]. Therefore, in light of the knowledge progressively acquired, the inclusion of diacetyl as flavoring additive in the manufacturing process of liquid formulations for e-cigs has rapidly become a much-debated issue in the scientific community due to foreseeable toxicological implications from direct inhalation exposure.…”

A Summary of In Vitro and In Vivo Studies Evaluating the Impact of E-Cigarette Exposure on Living Organisms and the Environment

“…Some chemicals in e-liquids exert a harmful effect on the lungs [83]. Diacetyl and 2,3-pentanedione impair cilia function in NHBE cells by downregulating the genes taking part in cilia biogenesis [84]. Recent studies have highlighted the role of flavoring agents on airway tract cells and the consequence of inhaling them on ROS release, cytotoxic response, immune-mediated responses, DNA damage and mucociliary clearance [30].…”