The flavoring and not the nicotine content is a decisive factor for the effects of refill liquids of electronic cigarette on the redox status of endothelial cells.

Introduction:
This article investigates the effects of three common liquids with ranging nicotine concentrations used as refill for electronic cigarettes on the redox status of human vascular endothelial cells. The study aimed to evaluate five redox biomarkers, namely GSh, ROS, TaC, TBaRS, and CaRBS levels, to understand the role of the tested e-liquids on cell redox equilibrium.

Key Points:

* The study used three tobacco-flavored e-liquids, two apple/mint-flavored e-liquids, and two vanilla-flavored e-liquids with varying nicotine concentrations.
* The Ea.hy926 endothelial cell line was used for the experiment, and the cells were treated with increasing concentrations of each e-liquid sample in serum-free medium for 24 hours.
* The XTT Cell Proliferation assay was used to assess cell viability, and the absorbance was measured at 450nm and 630nm as a reference wavelength.
* The cells were then treated with e-liquids at different concentrations, and the intracellular GSh and ROS levels were determined using flow cytometry.
* The TBaRS levels were measured to evaluate lipid peroxidation, TaC was determined to assess the total antioxidant capacity, and protein carbonyls were measured to evaluate protein oxidation.
* The study found that the tobacco-flavored e-liquids increased ROS levels and TBaRS levels, indicating lipid peroxidation.
* The vanilla-flavored e-liquid with 12mg/ml nicotine increased GSh levels, but also increased ROS levels and TBaRS levels.
* The apple/mint-flavored e-liquid with 12mg/ml nicotine decreased ROS levels, TBaRS levels, and protein carbonyls levels, indicating a protective effect on endothelial cells.

Main Message:
The study suggests that the flavorings in e-liquids play a crucial role in the oxidative stress-induced toxicity of electronic cigarettes. While tobacco-flavored e-liquids showed a pro-oxidant effect, the apple/mint-flavored e-liquid showed an antioxidant effect, indicating that the flavoring compounds can modulate the redox status of endothelial cells. Therefore, further studies are required to understand the mechanisms involved and to evaluate the long-term effects of e-cigarette use on human health.

Kerasioti E, Veskoukis aS, Skaperda Z, et al. The flavoring and not the nicotine content is a decisive factor for the effects of refill liquids of electronic cigarette on the redox status of endothelial cells. Toxicology reports. 2020;7:1095-1102. doi:10.1016/j.toxrep.2020.08.029