Refill liquids for electronic cigarettes display peculiar toxicity on human endothelial cells

Abstract

The electronic cigarettes mimic combustible cigarettes through a heating technology that vaporizes a refill liquid consisting of solvents, flavors, and nicotine. E-cigarettes are sometimes still used as a support for smoking cessation, even if in 2019 an acute lung injury outbreak occurred in the USA, affecting mainly adolescents and young adults, and was correlated to eCigs. Therefore, due to the lack of a definite knowledge about the mechanism(s) of refill liquid toxicity and considering that previous investigations gave controversial results, the aim of the present study was the cytotoxicity assessment of different refill liquids on human endothelial cells, evaluated by means of two different in vitro approaches, i.e. the resazurin and the LDH release assays. Our results clearly demonstrated that different refill liquids (6 samples) display different levels of cytotoxicity in our cellular model, although their cytotoxicity was always lower than that observed for the condensate obtained from traditional cigarettes (3 samples). These results suggest that accurate evaluations should be provided for refill liquids, in particular to correlate their toxicity to their chemical composition, with the final aim of obtaining useful information for the agencies involved in the regulation of their components.

Keywords: Cytotoxicity; ENDS, electronic nicotine delivery systems; EVALI; EVALI, e-vaping acute lung injury; Electronic cigarettes; HUVEC, human umbilical vein endothelial cells; LDH, lactate dehydrogenase; Refill liquids; e-Cig, electronic cigarette.

Graphical abstract

Fig. 1

Cytotoxic effect of e-cigarette condensates evaluated by means of the resazurin assay. Data are reported as mean ± SEM of two independent experiments, each run in triplicates. *p < 0.05, ** p < 0.01, ****p < 0.0001 vs. control cells treated with medium.

Fig. 2

Cytotoxic effect of e-cigarettes evaluated by means of the LDH release assay. Data are reported as mean ± SEM of two independent experiments, each run in triplicates. ****p < 0.0001 vs. control cells treated with medium.

Fig. 3

Cytotoxic effect of traditional cigarettes evaluated by means of resazurin assay (left column) and LDH release (right column). Data are reported as mean ± SEM of two independent experiments, each run in triplicates. ** p < 0.01, ****p < 0.0001 vs. control cells treated only with medium.

Fig. 4

Comparison of cytotoxic effect of e-cigarettes and traditional cigarettes evaluated by means of resazurin and LDH assays. Data are reported as mean ± SEM of two independent experiments, each run in triplicates. *p < 0.5 and ****p < 0.0001 vs. the corresponding e-cig concentration treatment.