Flavored e-cigarette liquids and cinnamaldehyde impair respiratory innate immune cell function

Introduction:
This article investigates the impact of electronic cigarette (e-cigarette) liquids on respiratory innate immune cell function. The study screens popular e-liquids for their potential to alter innate immune cell function, identifies common flavoring agents in the e-liquids eliciting a response, and investigates whether exposure to a shared flavoring agent alone could recapitulate the observed response. The authors focus on cinnamaldehyde, a flavoring chemical present in several e-liquids, and examine its effects on alveolar macrophages, neutrophils, and natural killer (NK) cells.

Key Points:

* The study selected seven flavored nicotine-free e-liquids and analyzed their chemical composition.
* alveolar macrophages, neutrophils, and NK cells were isolated from healthy nonsmoker volunteers and exposed to varying dilutions of e-liquids.
* Cinnamaldehyde, a flavoring chemical found in three e-liquids, was identified as a potential immune suppressant.
* Cinnamaldehyde exhibited dose-dependent broadly immunosuppressive effects on alveolar macrophages, neutrophils, and NK cells.
* Cinnamaldehyde-induced suppression of macrophage phagocytosis was reversed by adding a small-molecule reducing agent, suggesting protein thiol modification as a potential mechanism for cinnamaldehyde-induced immune cell dysfunction.
* The study highlights the need for further toxicological evaluation of chemical flavoring agents to inform regulation governing their use in e-liquid formulations.

Main Message:
This study underscores the potential risks associated with the use of e-cigarettes, particularly in relation to their flavoring chemicals. Cinnamaldehyde, a common flavoring agent in e-liquids, exhibits immunosuppressive effects on respiratory innate immune cells, which could increase susceptibility to respiratory infections. The findings emphasize the importance of regulating chemical flavoring agents in e-liquids to ensure the safety and public health.

Clapp, Phillip W., Erica a. Pawlak, Justin T. Lackey, James E. Keating, Steven L. Reeber, Gary L. Glish, and Ilona Jaspers. “Flavored E-Cigarette Liquids and Cinnamaldehyde Impair Respiratory Innate Immune Cell Function.” american Journal of Physiology-Lung Cellular and Molecular Physiology 313, no. 2 (august 1, 2017): L278–92. https://doi.org/10.1152/ajplung.00452.2016.