Development, qualification, validation and application of the neutral red uptake assay in Chinese Hamster Ovary (CHO) cells using a VITROCELL® VC10® smoke exposure system

In vitro toxicological evaluation of glo menthol and non-menthol heated tobacco products

Heated tobacco products (HTPs) are non-combustible, inhaled tobacco products that generate an aerosol with fewer and lower levels of toxicants, with a potential to reduce risk relative to cigarette smoking. Here, we assessed in vitro toxicological effects of three menthol (glo neo neoCLICK, neo Smooth Menthol and Fresh Menthol) and one non-menthol (neo Smooth Tobacco) variants of glo HTP, along with market comparators for cigarettes and HTPs. Limited chemical characterization of the study products revealed significantly lower levels of acetaldehyde, acrolein, crotanaldehyde and formaldehyde in test samples from HTPs than those from cigarettes. The glo HTPs were non-mutagenic in the bacterial reverse mutagenesis assay. Although, the whole aerosol exposures of glo HTPs were classified as genotoxic in the in vitro micronucleus assay, and cytotoxic in the NRU (monolayer) and MTT (3 dimensional EpiAirway™ tissues) assays, the cigarette comparators were the most toxic study products in each of these assessments. Further, glo HTPs elicited oxidative stress responses only at the highest dose tested, whereas the cigarette comparators were potent inducers of oxidative stress at substantially lower doses in the EpiAirway tissues. The comparator (non-glo) HTP results were similar to the glo HTPs in these assays. Thus, the glo HTPs exhibit substantially lower toxicity compared to cigarettes.

Multidimensional assessment of the biological effects of electronic cigarettes on lung bronchial epithelial cells

Cigarette smoke (CS) exposure is known to cause injury to respiratory tract epithelial cells and is a contributing factor in the development of chronic obstructive pulmonary disease and lung cancer. Electronic cigarettes (e-cigarettes) are gaining popularity as a potential substitute for conventional cigarettes due to their potential for aiding smoking cessation. However, the safety of e-cigarettes remains uncertain, and scientific evidence on this topic is still limited. In this study, we aimed to investigate the effects of CS and e-cigarette smoke (ECS) of different flavors on human lung bronchial epithelial cells. Real-time smoke exposure was carried out using an air-liquid interface system, and cell viability was assessed. RNA-Seq transcriptome analysis was performed to compare the differences between CS and ECS. The transcriptome analysis revealed a significantly higher number of differentially expressed genes in CS than in ECS. Moreover, the impact of mint-flavored e-cigarettes on cells was found to be greater than that of tobacco-flavored e-cigarettes, as evidenced by the greater number of differentially expressed genes. These findings provide a reference for future safety research on traditional cigarettes and e-cigarettes, particularly those of different flavors. The use of omics-scale methodologies has improved our ability to understand the biological effects of CS and ECS on human respiratory tract epithelial cells, which can aid in the development of novel approaches for smoking cessation and lung disease prevention.

Evaluation of Cytotoxicity and Oxidative Stress of Whole Aerosol from Vuse Alto ENDS Products

Assessment of in vitro cytotoxicity is an important component of tobacco product toxicological evaluations. However, current methods of regulatory testing involve exposing monolayer cell cultures to various preparations of aerosols from cigarettes or other emerging products such as electronic nicotine delivery systems (ENDS), which are not representative of human exposure. In the present study, a whole aerosol (WA) system was used to expose lung epithelial cultures (2D and 3D) to determine the potential of six Vuse Alto ENDS products that varied in nicotine content (1.8%, 2.4%, and 5%) and flavors (Golden Tobacco, Rich Tobacco, Menthol, and Mixed Berry), along with a marketed ENDS and a marked cigarette comparator to induce cytotoxicity and oxidative stress. The WA from the Vuse Alto ENDS products was not cytotoxic in the NRU and MTT assays, nor did it activate the Nrf2 reporter gene, a marker of oxidative stress. In summary, Vuse Alto ENDS products did not induce cytotoxic or oxidative stress responses in the in vitro models. The WA exposures used in the 3D in vitro models described herein may be better suited than 2D models for the determination of cytotoxicity and other in vitro functional endpoints and represent alternative models for regulatory evaluation of tobacco products.

Metallic nanoparticle contamination from environmental atmospheric particulate matter in the last slab of the trophic chain: Nanocrystallography, subcellular localization and toxicity effects

Atmospheric particulate material (PM) from mining and steel industries comprises several metallic contaminants. PM₁₀ samples collected in a Brazilian region with a recognized influence of the steel and iron pelletizing industries were used to investigate metallic nanoparticle incorporation into human fibroblast cells (MRC-5). MRC-5 cells were exposed to 0 (control, ultrapure water), 2.5, 5, 10, 20 and 40 μg PM₁₀ mL^-1, for 24 h. Cytotoxic and genotoxic dose-response effects were observed on lysosome and DNA structure, and concentrations high as 20 and 40 μg PM₁₀ mL^-1 induced elevated cell death. Ultrastructure analyses showed aluminosilicate, iron, and the emerging metallic contaminants titanium, bismuth, and cerium nanoparticles were incorporated into lung cells, in which the nanocrystallography analysis indicated the bismuth as Bi₂O₃. All internalized metallic nanoparticles were free and unbound in the cytoplasm and nucleus thereby indicating bioavailability and potential interaction to biological processes and cellular structures. Pearson's correlation analysis showed Fe, Ni, Al, Cr, Pb and Hg as the main cytotoxic elements which are associated with the stainless steel production. The presence of internalized nanoparticles in human lung cells exposed to environmental atmospheric matter highlights the need for a greater effort by regulatory agencies to understand their potential damage and hence the need for future regulation, especially of emerging metallic contaminants.

Pulmonary in vitro instruments for the replacement of animal experiments

Advanced in vitro systems often combine a mechanical-physical instrument with a biological component e.g. cell culture models. For testing of aerosols, it is of advantage to consider aerosol behavior, particle deposition and lung region specific cell lines. Although there are many good reviews on the selection of cell cultures, articles on instruments are rare. This article focuses on the development of in vitro instruments targeting the exposure of aerosols on cell cultures. In this context, guidelines for toxicity investigation are taken into account as the aim of new methods must be the prediction of human relevant data and the replacement of existing animal experiments. We provide an overview on development history of research-based instruments from a pharmaceutical point of view. The standardized commercial devices resulting from the research-based instruments are presented and the future perspectives on pulmonary in vitro devices are discussed.

Signaling pathway perturbation analysis for assessment of biological impact of cigarette smoke on lung cells

Exposure to cigarette smoke (CS) results in injury to the epithelial cells of the human respiratory tract and has been implicated as a causative factor in the development of chronic obstructive pulmonary disease and lung cancers. The application of omics-scale methodologies has improved the capacity to understand cellular signaling processes underlying response to CS exposure. We report here the development of an algorithm based on quantitative assessment of transcriptomic profiles and signaling pathway perturbation analysis (SPPA) of human bronchial epithelial cells (HBEC) exposed to the toxic components present in CS. HBEC were exposed to CS of different compositions and for different durations using an ISO3308 smoking regime and the impact of exposure was monitored in 2263 signaling pathways in the cell to generate a total effect score that reflects the quantitative degree of impact of external stimuli on the cells. These findings support the conclusion that the SPPA algorithm provides an objective, systematic, sensitive means to evaluate the biological impact of exposures to CS of different compositions making a powerful comparative tool for commercial product evaluation and potentially for other known or potentially toxic environmental smoke substances.

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

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.

An experimental aerosol air-agar interface mouse lymphoma assay methodology

This work investigates a completely novel and experimental concept of exposing L5178Y cells at the air-agar-interface to mainstream cigarette smoke aerosol (Kentucky reference 3R4F). This study highlights the associated challenges of combining a suspension cell line alongside an in vitro aerosol exposure system. To achieve a monolayer, cells were 'seeded' in a concentrated cell super-mix suspension onto an RPMI/agar-matrix -base. The resulting cell suspension media was adsorbed into the agar base leaving the L5178Y cells lightly suspended on the agar surface, approximating a monolayer. Cells were deemed supportable on the agar-matrix, viable and recoverable. Using Vitrocell VC 10 exposure system and the Ames 4 exposure module, L5178Y cells were successfully exposed to a dynamic cigarette smoke aerosol, recovered and assessed for mutant frequencies, using standard assay procedures. Method development included assessment of flowing air conditions, plating efficiency and recovery of L5178Y cells from the agar-matrix surface. Positive controls MMS and B[a]P were successfully incorporated into the agar-matrix and metabolic activation was achieved by S-9 incorporation into the same agar-base-matrix. B[a]P demonstrated metabolic activation and positive response, suggesting a clear cellular interaction with the agar-matrix. Whole smoke exposed cells in the presence of metabolic activation showed a clear dose response and increasing mutant frequencies, well in excess of the controls (air and incubator) and the global evaluation factor following a 2 or 3 day expression period. This experimental concept demonstrates that L5178Y cells can be exposed to cigarette smoke aerosol, using a completely novel and a previously untested approach. Although this work successfully demonstrates the approach is viable and cells can be plated and maintained on an agar-matrix, more optimisation and robustness assessment is required before it can be considered fully adapted and used alongside other whole aerosol methodologies for the assessment of cigarette smoke and other inhaled aerosols.

Investigation of multiple whole smoke dosimetry techniques using a VITROCELL®VC10® smoke exposure system

The Vitrocell® VC10® smoke exposure system offers multiple platforms for air liquid interface (ALI) and air agar interface (AAI) exposure that mimic in vivo conditions for assessing toxicological impact of whole smoke using in vitro assays. The aim of this study was to investigate and compare multiple dosimetry techniques that may be employed during combustible cigarette whole smoke exposure using the Vitrocell® VC10® smoking robot. The following techniques were assessed: (1) quartz crystal microbalances (QCMs), (2) aerosol photometers (using area under curve, AUC), and (3) fluorescence of anhydrous dimethyl sulfoxide (DMSO)-captured smoke constituents. Results showed that each of the dosimetry techniques was able to distinguish different levels of whole smoke airflow in a concentration-related manner. When compared to each other, the three techniques showed a high level of consistency and all were considered efficient tools in quantifying dose during an exposure, although higher variation was observed at the higher airflows tested. Overall, the dosimetry tools investigated here provide effective measures of the whole smoke concentrations tested during the exposure.

[Systematic analysis of the scientific literature on heated tobacco]

INTRODUCTION

The tobacco industry (TI) reports that heated tobacco reduces risk of tobacco use and will replace cigarettes. An analysis of the scientific literature was conducted in order to enlighten professionals and decision-makers.

METHOD

After a Medline query in February 2018, a systematic analysis was conducted.

RESULTS

Of the 100 papers published in 2008-2018, 75 have authors affiliated or linked to TI. Emissions contain gases, droplets and solid particles, so are smokes. The main products are: THS2.2 (Iqos®) which heats mini-cigarettes at 340°C, the THP1.0 (Glo®) which heats at 240°C sticks delivering about half as much nicotine, Ploom® which uses reconstituted tobacco microcapsules heated at 180°C. Under the experimental conditions, there is a reduction of toxic emissions and biological effects, but the expected risk reduction is not demonstrated. Symptoms related to passive smoking are described. The 4 epidemiological articles report that heated tobacco is used in 10 to 45% of cases by non-smokers and demonstrate the effectiveness of TI promotion campaigns. Thus, the THS2.2 is more a gateway to smoking (20%) than an exit door (11%); moreover, it is not expected risk reduction among the 69% who are mixed users.

CONCLUSIONS

While reducing emissions is documented, reducing the risk to the smoker who switches to heated-tobacco remains to be demonstrated. On the other hand, the worsening of the global tobacco risk related to the promotion of the products by the TI is anticipated, justifying that the authorities take the appropriate measures to control the promotion of heated tobacco.

Application of a direct aerosol exposure system for the assessment of biological effects of cigarette smoke and novel tobacco product vapor on human bronchial epithelial cultures

Recent advancements in in vitro exposure systems and cell culture technology enable direct exposure to cigarette smoke (CS) of human organotypic bronchial epithelial cultures. MucilAir organotypic bronchial epithelial cultures were exposed, using a Vitrocell exposure system, to mainstream aerosols from the 3R4F cigarette or from a recently developed novel tobacco vapor product (NTV). The exposure aerosol dose was controlled by dilution flow and the number of products smoked; there were five exposure conditions for 3R4F smoke and three for NTV vapor. The amount of nicotine delivered to the tissues under each condition was analyzed and that of the total particulate matter (TPM) was estimated using nicotine data. The nicotine dose was similar for the two products at the highest dose, but the estimated TPM levels from the NTV were 3.7 times the levels from the 3R4F. Following 3R4F smoke exposure, a dose dependent increase was observed in cytotoxicity, cytokine secretion, and differential gene expression. However, no changes were detected in these endpoints following NTV vapor exposure, suggesting the biological effects of NTV vapor are lower than those of conventional combustible CS. Our study design, which includes collection of biological data and dosimetry data, is applicable to assessing novel tobacco products.

Development, qualification, validation and application of the Ames test using a VITROCELL® VC10® smoke exposure system

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Smoke-induced mutagenicity at air agar interface was developed and validated.

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The VITROCELL^® VC10^® system was validated by equipment qualification protocols.

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Differentiation of mutagenicity by 3R4F and Eclipse cigarettes was demonstrated.

The Ames test has established use in the assessment of potential mutagenicity of tobacco products but has generally been performed using partitioned exposures (e.g. total particulate matter [TPM], gas vapor phase [GVP]) rather than whole smoke (WS). The VITROCELL^®VC10^® smoke exposure system offers multiple platforms for air liquid interface (ALI), or air agar interface (AAI) in the case of the Ames test exposure to mimic in vivo-like conditions for assessing the toxicological impact of fresh WS in in vitro assays.

The goals of this study were to 1) qualify the VITROCELL^®VC10^® to demonstrate functionality of the system, 2) develop and validate the Ames test following WS exposure with the VITROCELL^®VC10^® and 3) assess the ability of the Ames test to differentiate between a reference combustible product (3R4F Kentucky reference cigarette) and a primarily tobacco heating product (Eclipse). Based on critical function assessments, the VITROCELL^®VC10^® was demonstrated to be fit for the purpose of consistent generation of WS. Assay validation was conducted for 5 bacterial strains (TA97, TA98, TA100, TA1535 and TA102) and reproducible exposure–related changes in revertants were observed for TA98 and TA100 in the presence of rat liver S-9 following exposure to 3R4F WS. In the comparative studies, exposure-related changes in in vitro mutagenicity following exposure of TA98 and TA100 in the presence of S9 to both 3R4F and Eclipse WS were observed, with the response for Eclipse being significantly less than that for 3R4F (p < 0.001) which is consistent with the fewer chemical constituents liberated by primarily-heating the product.

Evaluation of whole cigarette smoke induced oxidative stress in A549 and BEAS-2B cells

Cigarette smoke is a complex and oxidative aerosol. Previous researches on the hazards of cigarette smoke mainly focused on the adverse bioeffects induced by its condensates or gas vapor phase, which ignored the dynamic processes of smoking and the cigarette smoke aging. To overcome these disadvantages, we performed air-liquid interface exposure of whole smoke, which used native and unmodified smoke and ensured the exposure similar to physiological inhalation. Our results indicated that whole cigarette smoke induced lung epithelial cells (A549) and bronchial epithelial cells (BEAS-2B) damages in cytotoxicity assays (methyl thiazoly tetrazolium and neutral red uptake assays). In addition, A549 and BEAS-2B cells showed oxidative damages in whole smoke exposure, with concentration change of several biomarkers (reduced and oxidized glutathione, malondialdehyde, 4-hydroxyhydroxy-2-nonenal, extracellular superoxide dismutase, and 8-hydroxyl deoxyguanosine). These results indicate that whole smoke-induced oxidative stress occurs in two different kinds of cells at air-liquid interface.