Effects of waterpipe smoking on lung pathobiology and carcinogenesis remain sparse despite the worldwide emergence of this tobacco vector. To address this gap, we investigated the effects of chronic waterpipe smoke (WPS) exposure on lung pathobiology, host immunity, and tumorigenesis using an experimental animal model that is prone to tobacco carcinogens and an exploratory observational analysis of human waterpipe smokers and non-smokers. Mice exhibited elevated incidence of lung tumors following heavy WPS exposure (five days/week for 20 weeks) compared to littermates with light WPS (once/week for 20 weeks) or control air. Lungs of mice exposed to heavy WPS showed augmented CD8+ and CD4+ T cells counts along with elevated pro-tumor immune phenotypes including increased IL-17A in T/B cells, PD-L1 on tumor and immune cells, and the pro-inflammatory cytokine IL-1β in myeloid cells. RNA-sequencing (RNA-seq) analysis showed reduced anti-tumor immune gene signatures in animals exposed to heavy WPS relative to control air. We also performed RNA-seq analysis of airway epithelia from bronchial brushings of cancer-free waterpipe smokers and non-smokers undergoing diagnostic bronchoscopy. Transcriptomes of normal airway cells in waterpipe smokers, relative to waterpipe non-smokers, harbored gene programs that were associated with poor clinical outcomes in lung adenocarcinoma (LUAD) patients, alluding to a WPS-associated molecular injury, like that established in response to cigarette smoking. Our findings support the notion that WPS exhibits carcinogenic effects and constitutes a possible risk factor for lung cancer as well as warrant future studies that can guide evidence-based policies for mitigating waterpipe smoking.

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