7 October 2023
Abstract
The design of popular disposable electronic cigarettes (ECs) was analyzed, and the concentrations of WS-23, a synthetic coolant, in EC fluids were determined for 22 devices from 4 different brands. All products contained WS-23 in concentrations that ranged from 1.0 to 40.1 mg/mL (mean = 21.4 ± 9.2 mg/mL). To determine the effects of WS-23 on human bronchial epithelium in isolation of other chemicals, we exposed EpiAirway 3-D microtissues to WS-23 at the air liquid interface (ALI) using a cloud chamber that generated aerosols without heating. Proteomics analysis of exposed tissues revealed that the cytoskeleton was a major target of WS-23. BEAS-2B cells were exposed to WS-23 in submerged culture to validate the main results from proteomics. F-actin, which was visualized with phalloidin, decreased concentration dependently in WS-23 treated BEAS-2B cells, and cells became immotile in concentrations above 1.5 mg/mL. Gap closure, which depends on both cell proliferation and migration, was inhibited by 0.45 mg/mL of WS-23. These data show that WS-23 is being added to popular EC fluids at concentrations that can impair processes dependent on the actin cytoskeleton and disturb homeostasis of the bronchial epithelium. The unregulated use of WS-23 in EC products may harm human health.
Introduction
Synthetic coolants (WS-3 and WS-23), which were developed by Wilkerson-Sword in the 1950s for use in consumer products such as shaving cream1, were recently introduced into fourth generation electronic cigarette (EC) liquids (e-liquids)2,3,4,5. Originally reported in low concentrations in JUUL pods3,4, synthetic coolants were subsequently found in much higher concentrations in Puff products4,5,6. WS-23 concentrations in Puff e-liquids were as high as 40 mg/mL4 and exceeded concentrations in other consumer products, such as candy, beverages, and gum7. While WS-23 is often used in ECs with “icy” or “cool” flavor names, such as Puff “Cool Mint” or “Lychee Ice”, it is also used in flavors that do not imply icy or coolness, such as Puff “Tobacco” and “Mixed Berries4”. JUUL ECs dominated the early fourth generation EC market8, but were superseded by Puff and other disposable brands, which were not initially affected by the Food and Drug Administration’s (FDA) restrictive enforcement policy on flavors in cartridge style ECs9. Because Puff ECs were disposable, not cartridge style, they were able to offer JUUL users a range of attractive flavors10.
ECs have evolved rapidly in design, fluid chemistry, and popularity4,11, and many new brands now compete with Puff. As more disposable EC devices were introduced into the market, Puff products became less popular, and many local retailers stopped carrying them. In southern California, the most popular disposable fourth generation brands are currently Flum and ELFBAR, which are both available in a range of popular flavors that have not been analyzed previously for e-liquid chemistry or toxicity. The purpose of this study was to quantify the synthetic coolants (WS-3 and WS-23) in Flum Float, ELFBAR, Puff XL, Puff Plus, and Puff Bar Plus e-liquids and to evaluate toxicity of WS-23 using 3D cultures of human bronchial epithelium (EpiAirway) that were exposed to WS-23 at the air–liquid interface (ALI) in a cloud chamber. The dominant effects of WS-23 on exposed EpiAirway were determined using proteomics analysis followed by relevant in vitro assays.
