There is a smoking product that has risen from the proverbial “ashes” of tobacco cigarettes, namely the electronic cigarette (e-cig). E-cigs have become a popularized alternative to the traditional tobacco cigarette. They can also be referred to as “vaping devices” that portable and battery powered that heat an internal coil to vaporize an e-liquid cartridge. E-liquids (e-juices are composed of several chemicals including the active ingredient (THC, CBD, nicotine), diluents (cutting agents), solvents (humectants), and flavoring agents (terpenes). E-cigs are regarded as the “safe alternative” to traditional cigarettes, but have contribiuted to a new public health concern in the demographic of middle and high school students. The CDC defined a respiratory disease known as “E-cig or Vaping product use-Associated Lung Injury (EVALI) due to an influx of patient deaths who had a history of e-cig use. There is a need to determine the toxicological effects of e-liquid ingredients on biological models. The aim of this study is to investigate the chemical interactions between binary mixtures of diluents and terpenes based on combined cytotoxicity on human bronchial epithelial cells (BEAS-2B).   Triethyl citrate (diluent) and limonene (terpene) served as the set of exposures. Cells were exposed to each constituent separaely as well as in combination for 24 hours and subseuqntly analysed via the MTS assay.  A dose-response curve was used to calculate the LC50 value using extrapolation. Mixtures of the diluent and terpene were used in equimolar ratios of 30:70, 50:50, and 70:30. Isobologram analyses was used to determine the synergistic, additive, or antagonistic effects at different ratios of diluent:terpene mixtures. Our results show that diluent-only and terpene-only exposures resulted in progressive cell death over dose. Co-exposures of diluent and terpene mixtures showed that combined effects resulted in a synergistic interaction, i.e. more progressive cell death at lower inoculating doses. Results were repeated using aerosol exposure of the same mixtures to the same cells at the air liquid interface. We conclude that aerosol transformations of e-liquids must be tested on biological models to further understand the potential toxicity that can result from the heating of e-liquid chemicals.

Environmental health effects after vaping: Mechanistic analyses resulting from terpene and diluent co-exposures

ACS Fall 2021

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