Electronic cigarettes and pulmonary effects : a translational approach

Despite the observed health hazards associated with using e-cigarettes, the popularity of e-cigarettes remains high, with millions of users worldwide. The lungs are the primary organs targeted by inhaled external stimuli, including the constituents in e-cigarette vapours. This thesis investigated the use of e- cigarettes and their pulmonary effects to contribute to a better understanding and knowledge in this area.

In Paper I, we found that 3.9% of young adults in the BAMSE cohort were current e-cigarette users at the 24-year follow-up. We observed significant associations between e-cigarette use, male gender, and cigarette smoking. E-cigarette users reported higher chronic bronchitis-like symptoms, such as cough and mucous production, compared to non-users. Additionally, dual use of e-cigarettes and traditional cigarettes was linked to an increased risk of respiratory symptoms. We concluded that although the prevalence of e-cigarette use was low, the increased prevalence of respiratory symptoms in e-cigarette users poses a risk to respiratory health, even considering the short duration of e-cigarette use in our participants.

In Paper II, the levels of biomarker for local airway inflammation FeNO were higher in e-cigarette users and lower in traditional cigarette smokers compared to healthy non-smokers. Bronchial responsiveness also increased in e-cigarette users, like conventional cigarette smokers. The percentages of IL13-positive and IFNy-positive cells increased in e-cigarette users and dual users. Additionally, the innate immune receptors TLR2 on blood granulocytes and TLR2 and TLR4 on sputum immune cells were higher in e-cigarette users and dual users. Moreover, total cellular ROS was higher in both e-cigarette and dual users in blood and sputum. The concentration of TIMP1 decreased in sputum, while MMP9 increased significantly in saliva in both e-cigarette users and dual users. Considering that markers of inflammation, oxidative stress, and innate immune receptors were induced both locally in sputum/saliva and systemically in blood/serum not only in e-cigarette users but also in dual users of e-cigarettes and traditional cigarettes, we conclude that e-cigarettes and dual users had developed altered inflammatory and innate immune response both locally and systemically.

In Paper III, we observed that exposure of bronchial mucosa models to e- cigarette fruit flavour 1 increased inflammation and oxidative stress markers at the transcript level when nicotine was present. Similarly, exposure of bronchial mucosa models to e-cigarette fruit flavour 2 resulted in increased markers of inflammation and oxidative stress at the transcript level, regardless of the presence of nicotine. On the other hand, exposing alveolar mucosa models to e- cigarette fruit flavour 1 increased inflammation and oxidative stress markers at the transcript level in the absence of nicotine. However, exposure of alveolar mucosa models to e-cigarette fruit flavour 2 decreased inflammatory mediators at the transcript level, regardless of the presence of nicotine. In conclusion, our findings suggest that the toxic effects differed between models and flavours, indicating that different lung regions react differently and that different flavour compositions have different exposure effects.

In Paper IV, exposure of bronchial mucosa models to e-cigarette vapours in vitro increased transcript expression of mucociliary markers FOXJ1, CFTR, and KCNMA1. Exposure of alveolar mucosa models to e-cigarette vapours decreased transcript expression of epithelial junction protein marker claudin. On the other hand, exposure to CSC and dual exposure to e-cigarettes and CSC increased junction protein markers in alveolar models. In bronchial models, exposure to e-cigarettes and dual exposures increased transcript expression of inflammatory (IL6 and IL8) and oxidative stress (HMOX1) markers. HMOX1 also increased after CSC exposures. In alveolar models, markers of inflammation and oxidative stress were decreased after e-cigarette exposures. Exposure to CSC and dual exposures increased total cellular ROS and surface TLR expression in both bronchial and alveolar models. In contrast, exposure to e-cigarettes showed no significant changes in either type of cell model. In conclusion, exposure to e-cigarettes had different effects in bronchial and alveolar lung mucosa models. Additionally, exposure to e-cigarettes or CSC had varying effects in the lung models.

List of scientific papers

I. Sompa SI, Zettergren A, Ekström S, Upadhyay S, Ganguly K, Georgelis A, Ljungman P, Pershagen G, Kull I, Melen E, Palmberg L, Bergström A. Predictors of electronic cigarette use and its association with respiratory health and obesity in young adulthood in Sweden; findings from the population-based birth cohort BAMSE. Environmental Research. 2022 May 15;208:112760. https://doi.org/10.1016/j.envres.2022.112760

II. Sompa SI, Ji J, Rahman M, Sjögren B, Upadhyay S, Ganguly K, Olin AC, Bergström A, Palmberg L. Local and systemic effects in e-cigarette users compared to cigarette smokers, dual users, and non-smokers. [Manuscript]

III. Ganguly K, Nordström A, Thimraj TA, Rahman M, Ramström M, Sompa SI, Lin EZ, O'Brien F, Koelmel J, Ernstgård L, Johanson G, Pollitt KJG, Palmberg L, Upadhyay S. Addressing the challenges of E-cigarette safety profiling by assessment of pulmonary toxicological response in bronchial and alveolar mucosa models. Scientific reports. 2020 Nov 24;10(1):20460. https://doi.org/10.1038/s41598-020-77452-w

IV. Sompa SI, Upadhyay S, Ganguly K, Bergström A, Ji J#, Palmberg L#. Epithelial effects of exposure to e-cigarettes alone or in combination with cigarette smoke using multicellular lung mucosa models. #Equally contributed [Manuscript]