Towards an in-vitro multi-cellular human airways model for evaluating the effects of Electronic cigarettes

Despite being poor representations of human airways architecture, innumerable animals, especially rodents, have been used in cigarette smoking studies. The advent of Electronic-cigarettes (ECs) could herald a further escalation, with data from in-vivo experiments already increasingly published. The current study aims to demonstrate the application of a human in-vitro model for evaluation of EC, providing alternatives to the outdated in-vivo models. The human airways model consists of relevant cell types that would be directly encountered during vaping. Human bronchial epithelial cells and pulmonary fibroblasts were co-cultured at air-liquid interface (ALI) under conditions that promote mucociliary differentiation, tight junction formation and mucin production. An in-house built smoking machine was used to deliver vapour from a commercially available EC (ECV) or whole cigarette smoke (WCS) to the co-culture model according to ISO standard. This methodology closely mimics human smoking behaviour, as opposed to enforced nasal inhalation in rodent smoking/vaping model. 24h post exposure, XTT cell viability analysis showed that WCS caused a significant decrease (p<0.0001) in cell viability (<70%) compared to control cells exposed to air only. ECV on the other hand did not have a significant impact on cell viability, thus suggesting low cytotoxicity. This difference in effect correlates with a number of existing in-vitro and in-vivo ECV/WCS studies, illustrating that the current model is a relevant, more realistic platform for EC studies compared to animal models. Further, such an airways model resembling in-vivo physiology can be used to study COPD progression and development, a condition difficult to replicate in rodents.