Screening of different cytotoxicity methods for the assessment of ENDS toxicity relative to tobacco cigarettes.

Introduction:
This text provides an analysis of various cytotoxicity methods used to assess the toxicity of Electronic Nicotine Delivery Systems (ENDS) compared to tobacco cigarettes. The study compares two e-cigarettes, two Tobacco heating Products (ThPs), and the 1R6F reference tobacco cigarette using human bronchial epithelial cells exposed to smoke/vapor at the air-liquid interface.

Key Points:

* The study used five different cytotoxicity assays: Neutral Red Uptake (NRU), MTT, annexin V apoptosis, high Content Screening (hCS), and Real Time Cell analysis (RTCa) to compare the toxicity of ENDS and tobacco cigarettes.
* The NRU assay showed that all used products had a significant difference, with a significant reduction in cell viability after exposure to 1R6F smoke compared to aIR-hCI control.
* The MTT assay showed a considerable reduction in h292 cell viability after exposure to 1R6F smoke, but no significant differences between the other products and their respective aIR controls.
* The annexin V apoptosis assay showed a significant decrease in viable cells after exposure to 1R6F cigarette smoke compared to NRU and MTT assays, with a substantial percentage of cells in advanced apoptosis.
* The NRU imaging assay and RTCa data generated time-dependent growth/mortality profiles, indicating a strong deviation from other assays at 24 hours, particularly for the 1R6F cigarette smoke and ThP vapor exposure.
* The study found that MTT assay applied to the assessment of cytotoxicity induced by cigarette smoke and ENDS vapors could suffer from potential interference due to the intrinsic nature of these chemical mixtures.
* The NRU assay is a more appropriate test for assessing the cytotoxicity induced by these products, but it should be combined with a time-resolved test to increase toxicological sensitivity.

Main Message:
The study suggests that the NRU assay may be a suitable test for assessing the cytotoxicity induced by ENDS, especially when combined with a time-resolved test. The study also highlights the importance of considering the limitations of each assay when interpreting the results and emphasizes the need to combine different methods to increase toxicological sensitivity. The findings of this study can inform regulatory bodies about the safety profile of ENDS and their potential harm reduction benefits compared to tobacco cigarettes.

Caruso M, Emma R, Rust S, et al. Screening of different cytotoxicity methods for the assessment of ENDS toxicity relative to tobacco cigarettes. Regulatory toxicology and pharmacology : RTP. 2021;125:105018. doi:10.1016/j.yrtph.2021.105018