Studies on toxicity and inflammatory reactions induced by e-cigarettes: In vitro exposure of human nasal mucosa cells to propylene glycol at the air–liquid interface

Abstract

Background: The e‑cigarette has become increasingly popular in recent years. However, the question of toxicity is not yet clear and there is global uncertainty regarding the use of e‑cigarettes. This is intensified by the fact that there is a lack of declaration of the liquid ingredients. Objective: The present paper investigates propylene glycol, a major component of the liquids, for possible acute inflammatory reactions as well as cytotoxic and genotoxic effects on human nasal mucosa cells. Materials and methods: The nasal mucosa cells from 10 volunteers were cultivated at the air–liquid interface and then exposed to different concentrations of propylene glycol. The analysis was carried out using the trypan blue test, comet assay, micronucleus test, and interleukin (IL)-6 and IL‑8 sandwich ELISA. Results: The trypan blue test showed no reduction in vitality. No increase in IL‑6 and IL‑8 concentrations were detected in the sandwich ELISA. In the comet assay, the Olive tail moment showed a dose-dependent increase in DNA fragmentation compared to the negative control at all examined concentrations. A difference between the pure substance and the negative control was shown in the micronucleus test. Conclusion: Possibly repairable dose-dependent DNA fragmentation and profound DNA alterations at high concentrations of propylene glycol warrant enhanced genotoxicological studies. These should include long-term exposure studies and assessment of further ingredients of the liquids. Consequently, the manufacturers need to be forced to declare the latter.