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

Abstract

Most flavors used in e‐liquids are generally recognized as safe for oral consumption, but their potential effects when inhaled are not well characterized. In vivo inhalation studies of flavor ingredients in e‐liquids are scarce. A structure‐based grouping approach was used to select 38 flavor group representatives (FGR) on the basis of known and in silico‐predicted toxicological data. These FGRs were combined to create prototype e‐liquid formulations and tested against cigarette smoke (CS) in a 5‐week inhalation study. Female A/J mice were whole‐body exposed for 6 h/day, 5 days/week, for 5 weeks to air, mainstream CS, or aerosols from (1) test formulations containing propylene glycol (PG), vegetable glycerol (VG), nicotine (N; 2% w/w), and flavor (F) mixtures at low (4.6% w/w), medium (9.3% w/w), or high (18.6% w/w) concentration or (2) base formulation (PG/VG/N). Male A/J mice were exposed to air, PG/VG/N, or PG/VG/N/F‐high under the same exposure regimen. There were no significant mortality or in‐life clinical findings in the treatment groups, with only transient weight loss during the early exposure adaptation period. While exposure to flavor aerosols did not cause notable lung inflammation, it caused only minimal adaptive changes in the larynx and nasal epithelia. In contrast, exposure to CS resulted in lung inflammation and moderate‐to‐severe changes in the epithelia of the nose, larynx, and trachea. In summary, the study evaluates an approach for assessing the inhalation toxicity potential of flavor mixtures, thereby informing the selection of flavor exposure concentrations (up to 18.6%) for a future chronic inhalation study.

Chemical and in vitro toxicological comparison of emissions from a heated tobacco product and the 1R6F reference cigarette

“…Propylene glycol and glycerol are widely used in food, pharmaceuticals, cosmetics, and tobacco products. Additionally, it was demonstrated that the whole-body exposure of aerosol from the base formulation containing these two humectants to A/J mice produced no significant mortality or in-life clinical findings in 5-week study [33] . Therefore, these liquid constituents were yielded higher in DT3.0a aerosol than in 1R6F CS, suggesting less toxic property of DT3.0a aerosol compared with 1R6F CS.…”

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

“…After the removal of duplicates, 822 unique abstracts were screened, resulting in the inclusion of 53 studies (Figure 1, Table 1). 12‐64 Out of the 53 included articles, 34 (64%) analyzed the effects of e‐cigarette use on human subjects or cell lines, 16 (30%) utilized an animal model to investigate the in vivo effects of e‐cigarette aerosol exposure, and 3 (6%) studied both human and animal models. Human studies included: (1) in vitro assessments of e‐cigarette aerosol, condensate, or e‐liquid exposure on primary cultured cells or immortalized cell lines derived from upper airway tissue, or (2) clinical studies using samples obtained from current or former e‐cigarette users.…”

Repeated intratracheal instillation of whole‐cigarette smoke condensate to assess lung damage in a rat model

“…Previous studies have shown that smoking causes weight loss and deficient lung function 19,20 . According to Wong et al, 21 CS for 1 h daily for 5 weeks in female A/J mice induced weight loss and increased lung weight. Similarly, the instillation of WCSC in this study reduced the body weight of rats compared to the control (Figure 2A,B).…”

“…Previous studies have shown that smoking causes weight loss and deficient lung function. 19,20 According to Wong et al, 21 Inflammation plays a key role in most interstitial lung diseases, and various immune cells such as macrophages, neutrophils, and lymphocytes are actively involved in the inflammatory response. 22,23 Exposure to CS is known to increase the number of immune cells in the BALF, 24,25 which increases the risk of tissue damage by releasing toxic mediators such as proteolytic enzymes and reactive oxygen species.…”