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

Hae-Ryung Park,Quan Lu,Michael O’Sullivan,Jose Vallarino,Jin-Ah Park,David C Christiani,Maya Shumyatcher,Joseph Allen,Blanca E Himes

doi:10.1038/s41598-018-37913-9

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.

Highlights

Electronic cigarettes (e-cigarettes or e-cig) have gained popularity as a substitute for cigarettes or cigars, and they have been a gateway to cigarettes for those who never smoked[1]
normal human bronchial epithelial (NHBE) cells cultured under air–liquid interface (ALI) after 14 days differentiate into a mixture of ciliated cells, goblet cells as well as some remaining basal cells (Fig. 1A), closely mimicking human airway epithelium in vivo[30]
The rationale for choosing 25 ppm diacetyl is that the previous study indicates that no observable adverse effect level for sub-chronic inhalation may be less than 25 ppm diacetyl[28]

Summary

Introduction

Electronic cigarettes (e-cigarettes or e-cig) have gained popularity as a substitute for cigarettes or cigars, and they have been a gateway to cigarettes for those who never smoked[1]. The most common flavoring compound added to e-cig is diacetyl[15,16], which is a small, volatile compound with butter-like aroma[18]. Diacetyl was the most prominent chemical in the butter flavorings and its effect was dose-dependent[20,21,22,23]. Because of the known link between diacetyl and “popcorn lung”, 2,3-pentanedione, which has similar flavor properties to diacetyl, was used as a substitute in some e-cig[24]. Despite the widespread use of these flavoring chemicals in e-cig, there is a paucity of studies on potential adverse effects of these chemicals to e-cig users. (B,C) Volcano plot of RNA-seq results with top 10 genes annotated in diacetyl or 2,3-pentanedione-exposed NHBE cells for 24 h. (D,E) qPCR validation of top 10 genes identified by RNA-seq with diacetyl or 2,3-pentanedione.

Methods

Results

Discussion

Conclusion