Exposure to aldehyde cherry e-liquid flavouring and its vape by-product disrupts pulmonary surfactant biophysical function

Abstract

Over the last decade there has been a surge in vaping device usage, especially among adolescents, raising concerns for potentially related lung damage. Notoriously, there have been many e-cigarette or vaping-related lung injury (EVALI) cases resulting in hospitalisations and deaths. Although the vaping component vitamin E acetate has been linked to a large proportion of EVALI cases resulting in its widespread banning, one fifth of the cases remain unexplained. Furthermore, the overall long-term impact of vaping on respiratory health is poorly understood. A likely driver behind EVALI is pulmonary surfactant disruption, as it is the first point of contact for any inhaled toxicant in the alveoli, and abnormalities of its function are linked to some symptoms presented in EVALI cases. Aberrant biophysical function of the surfactant results in alveolar surface tension increase, causing alveolar collapse. Vaping chemicals with the potential to disrupt surfactant function must be hydrophobic molecules able to interact with surfactant components at the alveolar air-liquid interface. Recent findings have recorded the synthesis of highly hydrophobic acetal by-products of the base vaping chemical propylene glycol and common flavouring aldehydes, including the cherry flavouring benzaldehyde, not identified in preliminary e-liquid safety tests. This study provides evidence that benzaldehyde and its by-product, benzaldehyde propylene glycol acetal, have the potential to significantly disrupt surfactant biophysical function via interactions with surfactant proteins SP-B and/or SP-C, which may provide stable interactions within the surfactant film by forming associations with the sublayer of surfactant three-dimensional structure present at high lateral compression, i.e., expiration breathing. Data also suggest considerable vaping chemical loss to the experimental subphase, indicating potential further implications to the alveolar epithelial layer beneath.