Transcriptomic Evidence That Switching from Tobacco to Electronic Cigarettes Does Not Reverse Damage to the Respiratory Epithelium

Abstract

The health benefits of switching from tobacco to electronic cigarettes (ECs) are neither confirmed nor well characterized. To address this problem, we used RNA-seq analysis to compare the nasal epithelium transcriptome from the following groups (n = 3 for each group): (1) former smokers who completely switched to second generation ECs for at least 6 months, (2) current tobacco cigarette smokers (CS), and (3) non-smokers (NS). Group three included one former cigarette smoker. The nasal epithelial biopsies from the EC users vs. NS had a higher number of differentially expressed genes (DEGs) than biopsies from the CS vs. NS and CS vs. EC sets (1817 DEGs total for the EC vs. NS, 407 DEGs for the CS vs. NS, and 116 DEGs for the CS vs. EC comparison). In the EC vs. NS comparison, enriched gene ontology terms for the downregulated DEGs included cilium assembly and organization, whereas gene ontologies for upregulated DEGs included immune response, keratinization, and NADPH oxidase. Similarly, ontologies for cilium movement were enriched in the downregulated DEGs for the CS vs. NS group. Reactome pathway analysis gave similar results and also identified keratinization and cornified envelope in the upregulated DEGs in the EC vs. NS comparison. In the CS vs. NS comparison, the enriched Reactome pathways for upregulated DEGs included biological oxidations and several metabolic processes. Regulator effects identified for the EC vs. NS comparison were inflammatory response, cell movement of phagocytes and degranulation of phagocytes. Disease Ontology Sematic Enrichment analysis identified lung disease, mouth disease, periodontal disease and pulmonary fibrosis in the EC vs. NS comparison. Squamous metaplasia associated markers, keratin 10, keratin 13 and involucrin, were increased in the EC vs. NS comparison. Our transcriptomic analysis showed that gene expression profiles associated with EC use are not equivalent to those from non-smokers. EC use may interfere with airway epithelium recovery by promoting increased oxidative stress, inhibition of ciliogenesis, and maintaining an inflammatory response. These transcriptomic alterations may contribute to the progression of diseases with chronic EC use.

The Toxicological Effects of e‐Cigarette Use in the Upper Airway: A Scoping Review

“…These included elevated levels of secreted soluble inflammatory mediators (IL-1α, IL-1β, IL-2, IL-4, IL-6, IL-8, IL-10, IL-12p70, IL-13, tumor necrosis factorα, interferon-γ, CCL-5, CXCL-10, MCP-1, matrix metalloproteinase [MMP]-2, MMP-9, MMP-13, MUC5AC, MUC5B), increased expression of genes or proteins involved in inflammatory signaling (ERK1/2, p38, COX-2, JNK, and NF-kB), and enrichment of gene sets or pathways associated with inflammatory processes. 16,18,25,28,30,35,40,[42][43][44][45][46]49,53,62 Genotoxicity was seen primarily in the oral cavity, but also in the oropharynx and larynx, and was detected by increased DNA fragmentation, adducts, double-or single-strand breaks, appearance of micronuclei or metanuclear abnormalities, or increased expression of genes or proteins involved with DNA damage or repair pathways. 14,19,[22][23][24][25]27,32,51 Histological changes associated with acute and subchronic e-cigarette aerosol exposure in animal models were seen in the oral cavity, submandibular gland, nasal cavity, larynx, and trachea; however, the majority of these changes were considered adaptive and resolved following a recovery period.…”

“…Pozuelos et al 46 Significantly increased number of differentially expressed genes in primary human nasal epithelial cells of cigarette smokers and e-cigarette users (407 genes, 1817 genes, respectively) vs nonsmokers. Enriched gene ontology terms for the downregulated genes between e-cigarette users and nonsmokers included "cilium assembly and function" and for the upregulated genes included "immune response", "neutrophil activation," "leukocyte degranulation," and "granulocyte activation.…”

Early Transcriptional Responses of Human Nasal Epithelial Cells to Infection with Influenza A and SARS-CoV-2 Virus Differ and Are Influenced by Physiological Temperature

“…Alternatively, keratinization also plays a role in wound healing and may be a sign that these cells were able to recover from viral infection damage more quickly, which may explain why there is greater persistence of infection at lower temperature with the maintenance of newly differentiated, susceptible cell types [ 71 ]. Keratinization has also been associated with the damage response in the nasal epithelium due to cigarette use [ 72 ]. Hyper-keratinization can also be a response to chronic irritation, again a likely response to increased persistence of infection at lower temperatures [ 71 ].…”

Early transcriptional responses of human nasal epithelial cells to infection with Influenza A and SARS-CoV-2 virus differ and are influenced by physiological temperature

“…Hyper-keratinization can also be a response to chronic irritation, again a likely response to increased persistence of infection at lower temperatures 38 . A study investigating asthma-mediated protection from SCV2 infection reports higher keratinization of the cells, mediated through IL-13 signaling, to be a mechanism of protection against high viral loads 86 .However, more research is needed to identify how temperature impacts keratinization, as well as the impact of keratinization on viral replication.…”