A 6-month inhalation toxicology study in Apoe−/− mice demonstrates substantially lower effects of e-vapor aerosol compared with cigarette smoke in the respiratory tract

Abstract

Cigarette smoking is the major cause of chronic obstructive pulmonary disease. Considerable attention has been paid to the reduced harm potential of nicotine-containing inhalable products such as electronic cigarettes (e-cigarettes). We investigated the effects of mainstream cigarette smoke (CS) and e-vapor aerosols (containing nicotine and flavor) generated by a capillary aerosol generator on emphysematous changes, lung function, and molecular alterations in the respiratory system of female Apoe−/− mice. Mice were exposed daily (3 h/day, 5 days/week) for 6 months to aerosols from three different e-vapor formulations—(1) carrier (propylene glycol and vegetable glycerol), (2) base (carrier and nicotine), or (3) test (base and flavor)—or to CS from 3R4F reference cigarettes. The CS and base/test aerosol concentrations were matched at 35 µg nicotine/L. CS exposure, but not e-vapor exposure, led to impairment of lung function (pressure–volume loop area, A and K parameters, quasi-static elastance and compliance) and caused marked lung inflammation and emphysematous changes, which were confirmed histopathologically and morphometrically. CS exposure caused lung transcriptome (activation of oxidative stress and inflammatory responses), lipidome, and proteome dysregulation and changes in DNA methylation; in contrast, these effects were substantially reduced in response to the e-vapor aerosol exposure. Compared with sham, aerosol exposure (carrier, base, and test) caused a slight impact on lung inflammation and epithelia irritation. Our results demonstrated that, in comparison with CS, e-vapor aerosols induced substantially lower biological and pathological changes in the respiratory tract associated with chronic inflammation and emphysema.

Assessment of inhalation toxicity of cigarette smoke and aerosols from flavor mixtures: 5‐week study in A/J mice

“…Potential technical variation in BALF recovery could explain the lower cell and protein/analyte recovery in the female PG/VG/N/F (nicotine with flavor) group. The minimal lung inflammation in the e‐vapor groups is supported by the results of other flavor‐containing e‐vapor aerosol exposure studies (Ho et al, 2020; Larcombe et al, 2017; Olfert et al, 2018; Werley, Kirkpatrick, et al, 2016; Wong et al, 2021). The robustness of the increased total and differential leukocyte counts present in BALF supporting increased lung inflammation was substantiated by the corresponding changes in the concentration of inflammatory mediators, total protein content, and increased histopathology severity scores.…”

“…While inhalation studies have been valuable in assessing the long‐term impact of specific flavors or flavored e‐cigarette products (Ha et al, 2015; Olfert et al, 2018; Werley, Kirkpatrick, et al, 2016; Wong et al, 2021), it is not always feasible to test the large number of individual flavor ingredients or combinations of formulations (Zhu et al, 2014) because of the great amount of time and number of laboratory animals required for such testing. To comprehensively test the large number of diverse flavor compounds used in e‐cigarettes, we previously performed a 90‐day sub‐chronic inhalation study in rats by employing the “read‐across” and “flavor toolbox” concepts (Ho et al, 2020; Sciuscio et al, 2022).…”

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

“…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. 30,31,37,47,50,52,[56][57][58][59]61,64 Persistent histological changes in the nasal cavity and larynx included: mild epithelial hyperplasia and squamous metaplasia, and mucus hypersecretion. In the submandibular gland, ductal dilation, connective tissue thickening, and epithelial degeneration with cytoplasmic vacuolization were observed.…”

“…Twenty-five studies [13][14][15][16][19][20][21][22][23]26,27,32,35,37,40,41,45,46,49,51,55,58,61,63,64 directly compared the effects of exposure to e-cigarette vapor versus traditional cigarette smoke. In general, exposure to traditional cigarette smoke/condensate resulted in increased cytotoxicity, intracellular oxidative stress, DNA damage, and upregulated proinflammatory response compared with exposure to e-cigarette aerosol/condensate (±nicotine).…”

Use of Capillary Aerosol Generator in Continuous Production of Controlled Aerosol for Non-Clinical Studies

“…Current e-liquid in vivo toxicology studies are limited in reproducing e-cigarette aerosols due to the logistical complexity to meet the scale of aerosol required, such as in an OECD TG 413 study 20 . The protocol presented in this study gives an overview on the CAG assembly and settings used at Philip Morris International for aerosol generation in in vivo long-term exposure studies 18 . These data can serve as a good starting point for further fine-tuning in another laboratory environment (e.g., drug delivery systems 21 ) or for adaptation to specific requirements of a particular study.…”