Carbonyl Profiles of Electronic Nicotine Delivery System (ENDS) Aerosols Reflect Both the Chemical Composition and the Numbers of E-Liquid Ingredients–Focus on the In Vitro Toxicity of Strawberry and Vanilla Flavors

Abstract

Propylene glycol (PG) and glycerin (G) are the most widely used humectants in electronic nicotine delivery system (ENDS) devices. Carbonyls are present in aerosols produced when ENDS devices heat PG and G. Whether aerosolized PG and G are innocuous to the lungs has not been established. Here, we determined the chemical profiles of ENDS aerosols containing three humectant ratios (30/70, 50/50 and 70/30, PG/VG), for three flavors (strawberry, vanilla and Catalan cream) containing either 12 or 18 mg/mL of nicotine. Additionally, we examined the in vitro toxicity of the strawberry- and vanilla-flavored ENDS aerosol in human lung epithelial cells (BEAS-2B) exposed at the air-liquid interface for 1 h. For strawberry- and vanilla-flavored aerosols produced by a 3rd-generation ENDS device with the same PG/G ratio, the e-liquid nicotine content of 12 and 18 mg/mL did not transfer to the aerosol with substantial differences in concentrations. Our data also indicate the presence of carbonyls in all three flavored e-cig aerosols analyzed, with levels exceeding 1 µg/puff for acetone, butyraldehyde, and acetaldehyde, in strawberry-, vanilla, and Catalan cream-flavored e-cig aerosols, respectively. Furthermore, closed-system ENDS of the fourth generation emitted trace levels of carbonyls in the aerosols (<0.3 µg/puff), while open-system tank-style ENDS of the third generation produced elevated levels of harmful chemicals, including acrolein (>1 µg/puff), formaldehyde (>5 µg/puff), and m- & p-tolualdehyde (>4 µg/puff). Moreover, under non-cytotoxic conditions, BEAS-2B cells exposed to strawberry-flavored aerosols exhibited significantly increased reactive oxygen and nitric oxide species (ROS/NOS) levels in cell media compared to air controls, while vanilla-flavored ENDS aerosols up-regulated the expression of pro-inflammatory and oxidative stress markers. Our data suggest (a) that ENDS aerosol chemical composition will vary based upon the presence and concentration of the initial e-liquid ingredients, with a pronounced impact of the flavoring components; and (b) short-term exposures to flavored ENDS aerosols may impair lung cells’ redox signaling in a flavor-specific manner.

Sex-Specific Alterations of the Lung Transcriptome at Birth in Mouse Offspring Prenatally Exposed to Vanilla-Flavored E-Cigarette Aerosols and Enhanced Susceptibility to Asthma

“…We conducted real-time and offline characterization of the e-cig aerosols via a MicroDustPro (Casella) and traditional gravimetric sampling methods, respectively, as previously described [ 22 , 28 ]. The chemical analysis of the vanilla-flavored e-cig aerosol produced under the same conditions as those in this study was published by our research group elsewhere [ 33 ] and revealed that this vanilla-flavored e-cig aerosol contained high concentrations of PG and G (>2 mg/puff) in addition to having elevated levels of butyraldehyde (>1 µg/puff).…”

Physical and chemical characterizations of a reference e-cigarette used in animal testing

“…On the grounds of these observations, it is evident that this approach is based on the worst toxicological conditions, with the highest risks for users. A similar approach can be found in many articles using these worst risk exposure conditions in studying the effects of EC emissions on cell cultures 4 – 6 and on laboratory animals 7 – 9 .…”

Effects of Electronic Cigarette E-Liquids on the Adhesion and Growth of Osteoblast Cells

“…Another e-liquid component linked to e-cigarette toxicity is flavoring agents (Herbert et al, 2023;Noël and Ghosh, 2022;Shen et al, 2016). In their analysis of e-liquid cytotoxicity on human MG-63 and Saos-2 osteoblast-like cells, (Otero et al, 2019) reported a decrease in cell viability, suggesting a toxic effect independent of the presence of nicotine.…”

“…PG and VG are humectants that mimic cigarette smoke and transport nicotine during vaping. While VG provides visual smoke and improves taste and smell, PG is associated with health issues such as sore throat, headache, and dizziness (Harvanko et al, 2019;Guo et al, 2022;Noël and Ghosh, 2022). These main e-liquid constituents have been generally considered to be safe ingredients for oral ingestion (FDA, 1980).…”