Aromatic aldehydes formed during heating of cinnamon-flavored e-liquids drive pro-inflammatory responses in human...

Flavor additives can contribute to the biological effects of electronic cigarette (e-cigarette) aerosols, yet the mechanisms underlying flavor-related vascular toxicity remain poorly understood. We previously showed that exposure of human aortic smooth muscle cells (AoSMCs) to cinnamon-flavored e-cigarette aerosol induced a marked pro-inflammatory response that was amplified by heating. The present study aimed to identify thermal degradation products derived from cinnamon flavoring that may contribute to this effect. Aerosol condensates were generated from cinnamon-flavored e-liquids under controlled vaping conditions, and a chemical screening approach was used to identify degradation products. Benzaldehyde and phenylacetaldehyde were detected as specific to the heated cinnamon condensate and were subsequently selected for targeted in vitro testing. AoSMCs were exposed to aerosols, unheated e-liquids, or e-liquids supplemented with aldehydes (alone or in combination), and cytotoxicity and pro-inflammatory responses were assessed. Exposure to cinnamon aerosol induced a significant increase in IL-8 release without detectable cytotoxicity. Supplementation of e-liquids with benzaldehyde reproduced much of the IL-8 response observed with the aerosol, whereas phenylacetaldehyde alone elicited only a limited effect. Co-exposure to both aldehydes did not further enhance IL-8 production beyond that induced by benzaldehyde alone, suggesting potential interaction effects among cinnamon-derived degradation products. Taken together, these findings indicate that thermal processing of cinnamon-flavored e-liquids generates aromatic aldehydes that contribute to pro-inflammatory signaling in human vascular smooth muscle cells, with benzaldehyde emerging as a major contributor under the present experimental conditions. This study highlights the importance of considering flavor-derived degradation products when evaluating the vascular toxicity of e-cigarette emissions.