Formation of flavorant-propylene Glycol adducts With Novel Toxicological Properties in Chemically Unstable E-Cigarette Liquids.

Introduction:
This article investigates the chemical stability of e-cigarette liquids (e-liquids) and the formation of potentially harmful compounds that may result from the reaction between flavor aldehydes and the e-liquid solvent propylene glycol (PG). The study aims to determine the extent of these reactions, the stability of the resulting compounds, and their potential toxicological effects.

Key Points:

* Flavor aldehydes, such as benzaldehyde, cinnamaldehyde, citral, ethylvanillin, and vanillin, rapidly react with PG in e-liquids, forming flavor aldehyde PG acetals.
* Upward of 40% of flavor aldehyde content is converted to flavor aldehyde PG acetals, which were also detected in commercial e-liquids.
* Vaping experiments showed carryover rates of 50%-80% of acetals to e-cigarette vapor.
* acetals remained stable in physiological aqueous solution, with half-lives above 36 hours, suggesting they persist when inhaled by the user.
* acetals activated aldehyde-sensitive TRPa1 irritant receptors and aldehyde-insensitive TRPV1 irritant receptors.
* The formation of flavor aldehyde PG acetals in e-liquids is potentially reactive and can result in new compounds with unexpected toxicological effects.
* a rigorous process is advised to monitor the changing composition of e-liquids and e-vapors over time to identify possible health hazards.

Main Message:
The study highlights the potential risks associated with the chemical instability of e-liquids and the formation of harmful compounds that can result from the reaction between flavor aldehydes and PG. The study suggests that a comprehensive risk assessment of e-liquids should include an analytical workflow to detect newly formed compounds and their potential toxicological effects. This is crucial for regulatory risk analysis and ensuring the safety of e-cigarette users.

Erythropel hC, Jabba SV, DeWinter TM, et al. Formation of flavorant-propylene Glycol adducts With Novel Toxicological Properties in Chemically Unstable E-Cigarette Liquids. Nicotine & tobacco research : official journal of the Society for Research on Nicotine and Tobacco. 2019;21(9):1248-1258. doi:10.1093/ntr/nty192