Formaldehyde and the transient receptor potential ankyrin-1 contribute to electronic cigarette aerosol-induced endothelial dysfunction in mice

Electronic nicotine delivery systems (ENDS) aerosol exposures can induce endothelial dysfunction (ED) in healthy young humans and animals. Thermal degradation of ENDS solvents, propylene glycol, and vegetable glycerin (PG: VG), generates abundant formaldehyde (FA) and other carbonyls. Because FA can activate the transient receptor potential ankyrin-1 (TRPA1) sensor, we hypothesized that FA in ENDS aerosols provokes TRPA1-mediated changes that include ED and "respiratory braking"-biomarkers of harm. To test this, wild-type (WT) and TRPA1-null mice were exposed by inhalation to either filtered air, PG: VG-derived aerosol, or FA (5 ppm). Short-term exposures to PG: VG and FA-induced ED in female WT but not in female TRPA1-null mice. Moreover, acute exposures to PG: VG and FA stimulated respiratory braking in WT but not in TRPA1-null female mice. Urinary metabolites of FA (ie, N-1,3-thiazolidine-4-carboxylic acid, TCA; N-1,3-thiazolidine-4-carbonyl glycine, TCG) and monoamines were measured by LC-MS/MS. PG: VG and FA exposures significantly increased urinary excretion of both TCA and TCG in both WT and TRPA1-null mice. To confirm that inhaled FA directly contributed to urinary TCA, mice were exposed to isotopic 13C-FA gas (1 ppm, 6 h). 13C-FA exposure significantly increased the urine level of 13C-TCA in the early collection (0 to 3 h) supporting a direct relationship between inhaled FA and TCA. Collectively, these data suggest that ENDS use may increase CVD risk dependent on FA, TRPA1, and catecholamines, yet independently of either nicotine or flavorants. This study supports that levels of FA in ENDS-derived aerosols should be lowered to mitigate CVD risk in people who use ENDS. Graphical Abstract. Endothelial dysfunction (ED) in aorta ex vivo after short-term exposure of female WT mice to PG: VG-derived aerosol or formaldehyde (FA) was absent in similarly exposed female TRPA1-null mice indicating a role of TRPA1. TRPA1-dependent nervous system-mediated respiratory braking response (lightning bolt in WT mice) was absent in female TRPA1-null mice. FA exposure also induced ED in WT but not in TRPA1-null mice. Irritant compounds such as FA in PG: VG-derived aerosols promote ED through a TRPA1-dependent mechanism. Notably, PG: VG-derived aerosol exposure in TRPA1-null mice induced a compensatory response in the aorta (excessive relaxation with ACh). These findings suggest exposures to E-cig-derived aerosols have complex effects on the vasculature, and thus, long-term E-cig use likely will induce ED and increase CVD risk. Created with BioRender.com.