A survey of aerosol exposure systems relative to the analysis of cytotoxicity: A Cooperation Centre for Scientific Research Relative to Tobacco (CORESTA) perspective

Abstract

During a Cooperation Centre for Scientific Research Relative to Tobacco (CORESTA) meeting, the in vitro toxicity testing Sub-Group (IVT SG) met to discuss the evolving field of aerosol exposure research. Given the diversity of exposure parameters and biological endpoints being used, it was considered a high priority to investigate and contextualise the responses obtained. This is particularly driven by the inability to compare between studies on different exposure systems due to user preferences and protocol differences. Twelve global tobacco and contract research companies met to discuss this topic and formulate an aligned approach on how this diverging field of research could be appropriately compared. Something that is becoming increasingly important, especially in the light of more focused regulatory scrutiny. A detailed and comprehensive survey was conducted on over 40 parameters ranging from aerosol generation, dilution and data analysis across eight geographically independent laboratories. The survey results emphasise the diversity of in vitro exposure parameters and methodologies employed across the IVT SG and highlighted pockets of harmonisation. For example, many of the biological protocol parameters are consistent across the Sub-Group. However, variables such as cell type and exposure time remain largely inconsistent. The next steps for this work will be to map parameters and system data against biological findings and investigate whether the observed inconsistencies translate into increased biological variability. The results from the survey provide improved awareness of parameters and nuances, that may be of substantial benefit to scientists in intersecting fields and in the development of harmonised approaches.

Characterisation of a smoke/ aerosol exposure in vitro system (SAEIVS) for delivery of complex mixtures directly to cells at the air‐liquid interface

“…The experimentation carried out using any such system should therefore be subject to a level of standardisation to ensure reproducible results. This is already in place in terms of ISO smoking regimes, which have demonstrated reproducibility between in vitro set‐ups (Thorne, Wieczorek, et al, 2021); however, more standardisation is required with regards to smoke generation equipment. Additionally, pre‐conditioning of the system is important to ensure replacement of dead volumes of air, for example, within the distribution manifold and within valves, and therefore continuous flow of smoke/ aerosol.…”

“…Many exposure systems have the functions to dilute the whole smoke/ aerosols generated (with air) to operator‐defined puffing regimes, and to smoke multiple products at the same time, to support specific study designs and dose–response testing. A number of in vitro smoke exposure systems have been characterised for their smoke delivery and dilution effectiveness (Scian, Oldham, Kane, et al, 2009; Steiner et al, 2017), and additionally for their ability to generate smoke to defined standardised puffing regimes (Thorne, Wieczorek, et al, 2021). For example, the VitroCell VC‐10 S rotary smoking robot is a commonly used, commercially available, exposure system where smoke is carried and diluted via a continuous flow of air through the system, following which cells can be exposed within an exposure module by setting the vacuum rate to draw air from the main air stream into the exposure modules and over the apical surface of the cell layer (Behrsing et al, 2018; Keyser et al, 2019; Thorne & Adamson, 2013).…”

Key challenges for in vitro testing of tobacco products for regulatory applications: Recommendations for dosimetry

“…31,32,46,63 To efficiently use quantitative measures of aerosol constituents, researchers need to characterize the levels of those compounds generated by the product prior to performing whole-aerosol exposures. A recent publication 122 and offline methods (analyzed after the experiment) in ALI in vitro studies (Table 3).…”

Characterization of smoke and aerosol deliveries from combustible cigarettes, heated tobacco products and electronic nicotine delivery systems in the Vitrocell® Mammalian 6/48 exposure module

“…Historically, assessments pertaining to the toxicity of cigarette smoke (CS) have been those that incorporate the gaseous or particulate fractions (or a combination thereof) into assays primarily designed to assess the potential effects of single chemicals to human health and the environment [13] , [32] , [34] , [7] , [8] . While extremely robust, these assays were not conceived with the intention of assessing complex mixtures and as such there is interest in investigating approaches that look at the interaction of freshly generated aerosol with cellular assays that are exposed at the air liquid interface (ALI) or equivalent [10] rather than under submerged conditions [42] . By performing exposures at the air liquid interface, direct cell-aerosol interactions occur with both gaseous and particulate phases simultaneously and allow for a more biologically relevant approximation of exposure, without the impact of dissolution.…”