A 7-month inhalation toxicology study in C57BL/6 mice demonstrates reduced pulmonary inflammation and emphysematous changes following smoking cessation or switching to e-vapor products

Abstract

Cigarette smoking causes serious diseases, including lung cancer, atherosclerotic coronary artery disease, peripheral vascular disease, chronic bronchitis, and emphysema. While cessation remains the most effective approach to minimize smoking-related disease, alternative non-combustible tobacco-derived nicotine-containing products may reduce disease risks among those unable or unwilling to quit. E-vapor aerosols typically contain significantly lower levels of smoke-related harmful and potentially harmful constituents; however, health risks of long-term inhalation exposures are unknown. We designed a 7-month inhalation study in C57BL/6 mice to evaluate long-term respiratory toxicity of e-vapor aerosols compared to cigarette smoke and to assess the impact of smoking cessation (Cessation group) or switching to an e-vapor product (Switching group) after 3 months of exposure to 3R4F cigarette smoke (CS). There were no significant changes in in-life observations (body weights, clinical signs) in e-vapor groups compared to the Sham Control. The 3R4F CS group showed reduced respiratory function during exposure and had lower body weight and showed transient signs of distress post-exposure. Following 7 months of exposure, e-vapor aerosols resulted in no or minimal increase in pulmonary inflammation, while exposure to 3R4F CS led to impairment of lung function and caused marked lung inflammation and emphysematous changes. Biological changes observed in the Switching group were similar to the Cessation group. 3R4F CS exposure dysregulated the lung and nasal tissue transcriptome, while these molecular effects were substantially lower in the e-vapor group. Results from this study demonstrate that in comparison with 3R4F CS, e-vapor aerosols induce substantially lower biological responses including pulmonary inflammation and emphysematous changes, and that complete switching from CS to e-vapor products significantly reduces biological changes associated with CS in C57BL/6 mice.

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

“…Other organ weight changes seen in this study—including the higher adrenal gland weights in the female sham mice than in the male sham mice—are consistent with sex‐dependent growth effects on the organs (Biedermann et al, 2014). The lower adrenal gland weight observed in the CS group was consistent with the findings of a previous studies (Kumar et al, 2021; Wong et al, 2020), even though no histopathological findings of biological significance were found. Marginal reductions in ovary weights were previously observed in response to chronic exposure to CS and aerosol of a heated tobacco product (Wong et al, 2020).…”

“…Similar changes have been observed in previous CS and nicotine-exposure studies (Oviedo et al, 2016;Phillips et al, 2017;Wong et al, 2016Wong et al, , 2020, which were likely attributable to increased stress hormone levels Sundar et al, 2014). Flavor ingredients did not impact general stress responses in previous inhalation studies (Ho et al, 2020;Kumar et al, 2021;Lee et al, 2018;Szostak et al, 2020). The animal strain, flavor composition, and (very high) flavor concentrations used in this study may have an impact on the biological outcomes.…”

Toxicological Assessment of Flavor Ingredients in E-Vapor Products

“…For instance, Ghosh et al (2019) reported elevated neutrophil elastase matrix metalloproteinases activities in bronchoalveolar lavage fluid of both vapers and smokers relative to non-smokers and suggested that e-vapor product aerosol might adversely affect the lung parenchyma. In contrast, other repeated inhalation studies of e-vapor product aerosol exposures have demonstrated reduced risk potential in animal models compared to cigarette smoke ( Wong et al, 2020 ; Kumar et al, 2021 ). These apparently conflicting results warrant a robust toxicity assessment of flavor ingredients in e-vapor product aerosol via long-term inhalation exposures.…”

Predicted aerosol dosimetry for mouse models of chronic obstructive pulmonary disease, cardiovascular disease and lung cancer

“…Acquisition of the necessary respiratory tract anatomy has evolved from various manual digitization techniques [5][6][7] to non-invasive scanning methods (e.g., magnetic resonance imaging, computed tomography-CT. 8 Recently, micro-CT techniques were used to obtain the tracheobronchial tract anatomy of several mouse strains, [9][10][11][12] including those mouse strains used as in vivo models of human disease, such as chronic obstructive pulmonary disease (COPD; C57BL/6 mice), cardiovascular disease (CVD; ApoE-/-mice) and lung cancer (AJ mice). Numerous inhalation studies have used the C57BL/6 mouse as a model of COPD, [13][14][15][16][17][18] the ApoE-/-mouse (derived from the C57BL/ 6 mouse and is apolipoprotein E-deficient) as a model of CVD [19][20][21][22][23] and the AJ mouse as a model of lung cancer. [24][25][26][27] Unlike the other two mouse strains, the C57BL6 mouse when not exposed to inhaled toxicants (e.g., mainstream tobacco smoke), is considered a wildtype mouse that does not exhibit features of COPD.…”