Evaluation of e-liquid toxicity using an open-source high-throughput screening assay

Abstract

The e-liquids used in electronic cigarettes (E-cigs) consist of propylene glycol (PG), vegetable glycerin (VG), nicotine, and chemical additives for flavoring. There are currently over 7,700 e-liquid flavors available, and while some have been tested for toxicity in the laboratory, most have not. Here, we developed a 3-phase, 384-well, plate-based, high-throughput screening (HTS) assay to rapidly triage and validate the toxicity of multiple e-liquids. Our data demonstrated that the PG/VG vehicle adversely affected cell viability and that a large number of e-liquids were more toxic than PG/VG. We also performed gas chromatography–mass spectrometry (GC-MS) analysis on all tested e-liquids. Subsequent nonmetric multidimensional scaling (NMDS) analysis revealed that e-liquids are an extremely heterogeneous group. Furthermore, these data indicated that (i) the more chemicals contained in an e-liquid, the more toxic it was likely to be and (ii) the presence of vanillin was associated with higher toxicity values. Further analysis of common constituents by electron ionization revealed that the concentration of cinnamaldehyde and vanillin, but not triacetin, correlated with toxicity. We have also developed a publicly available searchable website (www.eliquidinfo.org). Given the large numbers of available e-liquids, this website will serve as a resource to facilitate dissemination of this information. Our data suggest that an HTS approach to evaluate the toxicity of multiple e-liquids is feasible. Such an approach may serve as a roadmap to enable bodies such as the Food and Drug Administration (FDA) to better regulate e-liquid composition.

Immunological and pathological effects of electronic cigarettes

“…Moreover, cells exposed to PG or VG showed higher levels of oxidative stress than when exposed to air . PG/VG mixture also had negative effects on cell viability of embryonic kidney 293 cells, human adenocarcinoma alveolar basal epithelial cells and human airway smooth muscle cells, in a dose‐dependent manner …”

“…33 PG/VG mixture also had negative effects on cell viability of embryonic kidney 293 cells, human adenocarcinoma alveolar basal epithelial cells and human airway smooth muscle cells, in a dose-dependent manner. 88 More than seven thousand flavourings for E-cigarettes are now available, with over 70% of E-liquids containing greater than 1% flavoured chemical levels by weight. 89 Although most of the flavourings are defined as safe to be used in food products, the potential toxicity associated with degradation products generated by vaping at high temperatures is unknown.…”

Epigenetic reprogramming in periodontal disease: Dynamic crosstalk with potential impact in oncogenesis

“…Cigarette smoking is one of the major risk factors for various oral disorders including periodontal diseases and oral cancers . In a recent systematic review, the impact of smoking cessation on the risk of periodontitis onset and progression was compared between smokers and nonsmokers.…”

“…125 It has been proposed by electronic cigarette manufacturers that because these products do not burn tobacco they are less toxic and therefore a safer alternative to cigarette smoking. 126 In an recently published study in a murine model, electronic cigarette exposure was shown to stimulate DNA damage and downregulate DNA-repair function; the data showed DNA damage provoked by nitrosamines in vivo, and found that nitrosation of nicotine occurred in different organs of mice exposed to electronic cigarette smoke; and the authors also discussed the potential carcinogenic effect of electronic cigarette smoke via nitrosamine metabolites induction of methylation. 121 In an in vitro study it was demonstrated that direct exposure to electronic cigarettes' aerosol mixtures stimulates oxidative/carbonyl stress and inflammatory cytokine release, including cyclooxygenase-2 and prostaglandin-E2 in cultured human periodontal ligament fibroblasts, human gingival epithelium progenitor cells, pooled cells, and 3D MatTek's EpiGingival TM tissues (MatTek Corporation, Ashland, MA, USA) tissues.…”

Vaping Perpetuates Cardiac Electrical Instability

“…Several studies investigated the toxicity of e-liquids, and it was shown that flavoring aldehydes could be harmful in cell culture [7][8][9][10][11][12][13][14][15][16][17][18] , however, the possible cardiac electrophysiological toxicity of vaping has not been systematically examined and is not completely understood. Here, we will assess the cardiac electrophysiological toxicity of 3 eliquids of different flavors and we will test the hypothesis that vaping results in cardiac electrophysiological instability and arrhythmogenesis.…”