Application of dosimetry tools for the assessment of e-cigarette aerosol and cigarette smoke generated on two different in vitro exposure systems

Characterization of mass distribution in a biomimetic aerosol exposure system

OBJECTIVE

Lack of biomimicry in geometry and flow conditions of emissions systems for analytical testing and biological exposure has led to fundamental limitations, including a poor understanding of dose delivered to specific airway locations. This work characterizes mass distribution of a JUUL® brand e-cigarette in a Biomimetic Aerosol Exposure System (BAES).

MATERIALS AND METHODS

A combination of mass balance, direct measurements, and inferences based on direct measurements were used to characterize regional and local dose as a function of system flow path configuration and emissions topography profile.

RESULTS

Doses produced by the emissions topography profile with only puffing were significantly different from profiles with clean air inhalation following puffs. Mass characterization results support that dose can be manipulated using flow path geometry. Local and regional deposition was mapped throughout the system.

DISCUSSION AND CONCLUSIONS

We estimate the fraction of yield to the mouth deposited at several locations throughout the system for a variety of puffing and respiration topographies and show that emissions topography profile and system flow path geometry affect dose. This work provides proof-of-concept for assessing mass distribution as a function of aerosol generator (e-cigarette product), user airway geometry, and inhalation and puffing topography.

Vaping product exposure system (VaPES): a novel in vitro aerosol deposition system

OBJECTIVE

Due to recent increases in the use of vaping devices, there is a high demand for research addressing the respiratory health effects of vaping products. Given the constantly changing nature of the vaping market with new devices, flavors, metals, and other chemicals rapidly emerging, there is a need for inexpensive and highly adaptable vaping device exposure systems. Here, we describe the design and validation of a novel in vitro aerosol exposure system for toxicity testing of vaping devices.

MATERIALS AND METHODS

We developed an inexpensive, open-source in vitro vaping device exposure system that produces even deposition, can be adapted for different vaping devices, and allows for experiments to be performed under physiological conditions. The system was then validated with deposition testing and a representative exposure with human bronchial epithelial cells (hBECs).

RESULTS

The Vaping Product Exposure System (VaPES) produced sufficient and uniform deposition for dose-response studies and was precise enough to observe biological responses to vaping exposures. VaPES was adapted to work with both pod and cartridge-based vaping devices.

CONCLUSION

We have designed and validated a novel vaping device exposure system that will eliminate the need to use high-cost commercial exposure systems, lowering the barrier to entry of physiologically relevant vaping studies.

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

In vitro testing is important to characterise biological effects of consumer products, including nicotine delivery products such as cigarettes, e-cigarettes and heated tobacco products. Users' cells are exposed to these products' aerosols, of variant chemical compositions, as they move along the respiratory tract. In vitro exposure systems are available to model such exposures, including delivery of whole aerosols to cells, and at the air-liquid interface. Whilst there are clear advantages of such systems, factors including time to aerosol delivery, aerosol losses and number of cell cultures that can be exposed at one time could be improved. This study aimed to characterise a custom-built smoke/ aerosol exposure in vitro system (SAEIVS) using 1R6F reference cigarette smoke. This system contains five parallel smoking chambers and delivers different dilutions of smoke/ aerosol to two separate cell culture exposure chambers in <10 s. Using two dosimetry measures (optical density 400 nm [OD⁴⁰⁰ ]; mass spectrometric nicotine quantification), the SAEIVS demonstrated excellent linearity of smoke dilution prior to exposure (R²  = 0.9951 for mass spectrometric quantification; R²  = 0.9965 for OD⁴⁰⁰ ) and consistent puff-wise exposures across 24 and 96 well plates in cell culture relevant formats (e.g., within inserts). Smoke loss was lower than previously reported for other systems (OD⁴⁰⁰ : 16%; nicotine measurement: 20%). There was good correlation of OD⁴⁰⁰ and nicotine measurements, indicating that OD was a useful surrogate for exposure dosimetry for the product tested. The findings demonstrated that the SAEIVS is a fit-for-purpose exposure system for the reproducible dose-wise exposure assessment of nicotine delivery product aerosols.

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

The rapid development associated with Next Generation Tobacco Products (NGTP) has necessitated the development of high throughput methodologies to test their genotoxic potential in vitro when compared to conventional cigarette smoke (CS). An assessment of two Vitrocell® Mammalian 6/48 exposure modules in three independent experiments was made by comparing results from multiple dosimetric techniques applied to aerosol generated from 3R4F Kentucky Reference cigarettes, commercially available electronically heated tobacco product (eHTP) and Electronic Nicotine Delivery System (ENDS) using the Vitrocell® VC10®. Real-time aerosol particle concentration was assessed by means of light scattering photometers and expressed as area under the curve (∑AUC). Nicotine concentrations were determined analytically by LC/MS. Humectant amount and distribution was assessed for eHTP and ENDS by the quantification of free glycerol in a phosphate buffered saline (PBS) trap, whereas total particulate matter (TPM) was assessed in the 3R4F cigarettes by the fluorescence of the particulate at 485 nm in anhydrous dimethyl sulfoxide (DMSO) trap within the exposure. Dose was adjusted by means of the addition of ambient air to dilute the whole smoke/aerosol in L/min and sampled into the system at a rate of 5 mL/min. Dilution of CS ranged from 8.0 to 0.5 L/min and for the eHTP and ENDS ranged from 4 to 0 L/min (undiluted). Dosimetric analysis of the system showed good concordance within replicates (p-values ranged from p = 0.3762 to p = 0.8926) and showed that the Vitrocell® Mammalian 6/48 is a viable means for genotoxic assessment of aerosol generated from both conventional cigarettes and NGTP. Results demonstrate the need to tailor dosimetry approaches to different aerosols due to variations in the physio-chemical composition, with a multi-dosimetry approach recommended.

Considerations on dosimetry for in vitro assessment of e-cigarette toxicity

Electronic cigarettes (or e-cigarettes) can be used as smoking cessation aid. Some studies tend to show that they are less hazardous than tobacco cigarettes, even if it does not mean they are completely safe. The huge variation in study designs assessing in vitro toxicity of e-cigarettes aerosol makes it difficult to make comparisons and draw robust and irrefutable conclusions. In this paper, we review this heterogeneity (in terms of e-cigarette products, biological models, and exposure conditions) with a special focus on the wide disparity in the doses used as well as in the way they are expressed. Finally, we discuss the major issue of dosimetry and show how dosimetry tools enable to align data between different exposure systems or data from different laboratories and therefore allow comparisons to help further exploring the risk potential of e-cigarettes.

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.

Review of data on chemical content in an aerosol resulting from heating a tobacco or a solution used in e-cigarettes and in the smoke generated from the reference cigarettes

BACKGROUND

The article presents a review of the literature on the chemical composition of smoke generated from a standard cigarette and the aerosol generated after heating tobacco and chemical compounds formed in the aerosol of electronic cigarettes.

METHODS

The literature review was carried out on the PubMed online bibliographic database, Google search engine, Google Scholar based on science articles published in recent 20 years.

RESULTS

The bibliographic analysis shows that: replacing smoking in the traditional way by heating tobacco modifies significantly the content of chemical substances found in aerosol, the substances found in aerosols generated by e-cigarettes have proven toxic effects, e.g. pro-inflammatory effect on lung epithelial cells (e.g. crotonaldehyde) or a mutagenic effect (e.g. NNK), using e-cigarette aerosol does not rule out a health risk for people, which is not fully recognized at present.

CONCLUSIONS

Replacing smoking in the traditional way by heating tobacco modifies significantly the content of chemical substances found in aerosol. Using e-cigarette aerosol does not rule out a health risk for people, because the substances found in aerosols generated by e-cigarettes have proven toxic effects.

The development of an in vitro 3D model of goblet cell hyperplasia using MUC5AC expression and repeated whole aerosol exposures

Goblet cell hyperplasia and overproduction of airway mucin are characteristic features of the lung epithelium of smokers and COPD patients. Tobacco heating products (THPs) are a potentially less risky alternative to combustible cigarettes, and through continued use solus THPs may reduce smoking-related disease risk. Using the MucilAir™ in vitro lung model, a 6-week feasibility study was conducted investigating the effect of repeated cigarette smoke (1R6F), THP aerosol and air exposure. Tissues were exposed to nicotine-matched whole aerosol doses 3 times/week. Endpoints assessed were dosimetry, tight-junction integrity, cilia beat frequency (CBF) and active area (AA), cytokine secretion and airway mucin MUC5AC expression. Comparison of incubator and air exposed controls indicated exposures did not have a significant effect on the transepithelial electrical resistance (TEER), CBF and AA of the tissues. Cytokine secretion indicated clear differences in secretion patterns in response to 1R6F and THP exposure. 1R6F exposure resulted in a significant decrease in the TEER and AA (p=0.000 and p=0.000, respectively), and an increase in MUC5AC positive cells (p=0.002). Repeated THP exposure did not result in a significant change in MUC5AC positive cells. This study demonstrates repeated cigarette smoke whole aerosol exposure can induce these morphological changes in vitro.

Nicotine dosimetry and stability in cambridge filter PADs (CFPs) following different smoking regime protocols and storage conditions

Despite the growing numbers of studies on cigarettes and electronic nicotine delivery products (ENDs), no standard assessment of nicotine stability in various matrix post exposure is currently available. The aim of the present study was to evaluate the optimal standard condition to store Cambridge Filter Pads (CFPs) before chemical analysis in order to guarantee the titer of nicotine.We further performed data normalization according to different smoking or vaping runs. Smoke and vapor generated respectively by a reference tobacco cigarette (1R6F) and ENDs under different exposure regimes (ISO, HCI and CRM81) were collected on CFPs as total particulate matter (TPM) and subsequently analyzed for nicotine content. For each exposure, some CFPs were analyzed at time zero, whereas the others were stored under different conditions for nicotine assessment after 30 days. Principal Component Analysis (PCA) showed the best correlation between nicotine on CFPs and TPM for normalization. This study suggests that different exposure regimes and products can affect the preservation of nicotine titer on CFPs while samples storage at -80 °C may prevent the loss of nicotine. Finally, normalization of nicotine with TPM is strongly recommended for regulatory purpose.

An interlaboratory in vitro aerosol exposure system reference study

Given the complexity of inhaled substances, the aerosol exposure environment has seen diversification and development of setups in conjunction with the evolving in vitro toxicology space. Each laboratory uses its in vitro exposure system differently (different protocols, adaptations, and biological analysis). Unfortunately, as systems diversify, so does the complexity of comparing multiple systems in a “standardized” manner. As yet, no one has compared simply whether these diverse systems can all generate a consistent aerosol stream, which is paramount prior to transit and exposure. This study has compared, at source, aerosol generation (using nicotine as an exposure marker) in nine in vitro whole-aerosol exposure setups (seven different systems) across five distinct geographically independent locations, including the UK, the USA, Switzerland, Germany, and Japan. The results demonstrate that, despite system-wide differences (adaptations, nuances, and application), these systems—when appropriately maintained and used under a prescribed set of established conditions can all generate a consistent and statistically comparable aerosol stream. These data will be invaluable for new researchers and established laboratories, so they may benchmark against this study. Finally, this interlaboratory comparison combined with the wealth of transit and exposure interface data, may help the environment move towards a truly validated and consistent approach to aerosol exposure. Such an approach could be replicated for other aerosolized products, such as e-cigarettes and heated tobacco products.

Acute electronic vapour product whole aerosol exposure of 3D human bronchial tissue results in minimal cellular and transcriptomic responses when compared to cigarette smoke

The use of electronic vapour products (EVPs) continues to increase worldwide and with advances in cell culture systems, molecular biology and the computational sciences there is also accumulating evidence of their potential reduced toxicity and reduced potential harm when compared to cigarette smoke. To further understand the potential risks and health effects associated with exposure to EVP aerosols we have assessed the cellular and transcriptomic response from a commercially available lung tissue culture system (MucilAirTM) following a single sub-cytotoxic exposure to cigarette smoke and the equivalent nicotine delivered dose of EVP aerosol. The transcriptomic, cellular (cilia beat frequency (CBF) and percent active area (%AA), trans epithelial electrical resistance (TEER), histology) and cytokine release were assessed at 4- and 48- hours following recovery from air, EVP aerosol (8.4% V/V: mybluTM blueberry flavour, 2.4% nicotine) and 3R4F smoke (3.5% V/V: exposure). No pathological changes were observed at either recovery time point from any exposure. Air and EVP aerosol exposure had no effect on CBF, %AA nor TEER at 48 hours. Exposure to cigarette smoke resulted in a decrease in TEER, an increase in CBF and the release of proinflammatory cytokines at both recovery time points. Although the number of significantly expressed genes was minimal following exposure to EVP aerosol, exposure to 3R4F smoke resulted in a significant upregulation of several disease relevant pathways. These data provide evidence that following an acute exposure to EVP aerosol there is significantly less damage to lung cells in culture than the equivalent, nicotine based, dose of cigarette smoke.

The Era of E-Cigarettes: A Cross-Sectional Study of Vaping Preferences, Reasons for Use and Withdrawal Symptoms Among Current E-Cigarette Users in the United Arab Emirates

Electronic cigarette (E-cig) use has increased substantially among the young population, who adopt using E-cig for various reasons. Our present study aimed to explore vaping preferences and reasons for using E-cig among current users in the United Arab Emirates (UAE) and to assess physical and psychological symptoms experienced while using E-cig during intermittent fasting. A cross-sectional study was conducted from April 23 to May 22, 2020, to solicit responses from current E-cig users in the UAE. Data were collected about sociodemographic profile, tobacco cigarette smoking, vaping preferences, reasons for use, and withdrawal symptoms during fasting in Ramadan. A convenience sample of 591 adult E-cig users were initially recruited, of whom 392 participants with complete responses were included in our analysis. The majority of participants were males (n = 275, 70.2%) and around 28.6% (n = 112) were dual users. Vape tank/Box-mod was the most used type of E-cig (50.3%). Most of the participants (n = 317; 80.9%) believed that E-cigs are less harmful than tobacco cigarettes. During fasting time, around 46.2% (n = 181) of E-cig users have experienced various physical symptoms, while 51.0% (n = 200) of users have experienced various psychological symptoms. E-cig use is gaining popularity within the UAE after the recent legalization as these devices are commonly advertised and claimed by manufacturers to aid smoking cessation. The effectiveness of E-cig in aiding smoking cessation should be investigated with a higher level of evidence, especially in a new context of usage as the UAE, considering various types of devices, hundreds of E-liquid brands, and the influence of concurrent poly-tobacco use.

In Vitro Toxicity and Chemical Characterization of Aerosol Derived from Electronic Cigarette Humectants Using a Newly Developed Exposure System

In the United States, the recent surge of electronic cigarette (e-cig) use has raised questions concerning the safety of these devices. This study seeks to assess the pro-inflammatory and cellular stress effects of the vaped humectants propylene glycol (PG) and glycerol (GLY) on airway epithelial cells (16HBE cells and differentiated human bronchial epithelial cells) with a newly developed aerosol exposure system. This system allows for chemical characterization of e-cig generated aerosol particles as well as in vitro exposures of 16HBE cells at an air-liquid interface to vaped PG and GLY aerosol. Our data demonstrate that the process of vaping results in the formation of PG- and GLY-derived oligomers in the aerosol particles. Our in vitro data demonstrate an increase in pro-inflammatory cytokines IL-6 and IL-8 levels in response to vaped PG and GLY exposures. Vaped GLY also causes an increase in cellular stress signals HMOX1, NQO1, and carbonylated proteins when the e-cig device is operated at high wattages. Additionally, we find that the exposure of vaped PG causes elevated IL-6 expression, while the exposure of vaped GLY increases HMOX1 expression in human bronchial epithelial cells when the device is operated at high wattages. These findings suggest that vaporizing PG and GLY results in the formation of novel compounds and the exposure of vaped PG and GLY are detrimental to airway cells. Since PG and/or GLY is universally contained in all e-cig liquids, we conclude that these components alone can cause harm to the airway epithelium.

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.

Genotoxicity evaluation of tobacco and nicotine delivery products: Part One. Mouse lymphoma assay

Conduct of the mouse lymphoma assay (MLA) is underpinned by Organisation for Economic Co-operation and Development (OECD) Test Guideline 490 and International Conference on Harmonisation S2(R1) guidance and is a recognised in vitro genotoxicity test battery assay. It has been used on a limited number of occasions for the assessment of some tobacco and nicotine products, such as e-cigarettes and tobacco heating products (THP). The aim of this study was to assess the suitability of the MLA for genotoxicity testing with a variety of tobacco and nicotine products. Total particulate matter (TPM) from a 3R4F cigarette was compared against a commercial electronic cigarette liquid (e-liquid), electronic cigarette (e-cigarette) aerosol matter captured from the same e-liquid, and TPM from a commercial THP. Treatment conditions included 3 h exposures with and without metabolic activation and a longer 24 h exposure without metabolic activation (-S9) at concentrations up to 500 μg/mL. Under all treatment conditions, 3R4F produced a clear positive response with regard to induction of mutation. In contrast, no marked induction of mutation was observed for the e-liquid, e-cigarette aerosol or THP. Additionally, data are presented as a function of nicotine equivalents for comparisons between these different tobacco products and test matrices.

A Device for measuring the in-situ response of Human Bronchial Epithelial Cells to airborne environmental agents

Measuring the time evolution of response of Normal Human Bronchial Epithelial (NHBE) cells to aerosols is essential for understanding the pathogenesis of airway disease. This study introduces a novel Real-Time Examination of Cell Exposure (RTECE) system, which enables direct in situ assessment of functional responses of the cell culture during and following exposure to environmental agents. Included are cell morphology, migration, and specialised responses, such as ciliary beat frequency (CBF). Utilising annular nozzles for aerosol injection and installing windows above and below the culture, the cells can be illuminated and examined during exposure. The performance of RTECE is compared to that of the commercial Vitrocell by exposing NHBE cells to cigarette smoke. Both systems show the same mass deposition and similar trends in smoke-induced changes to monolayer permeability, CBF and transepithelial resistance. In situ measurements performed during and after two exposures to smoke show that the CBF decreases gradually during both exposures, recovering after the first, but decreasing sharply after the second. Using Particle image velocimetry, the cell motions are monitored for twelve hours. Exposure to smoke increases the spatially-averaged cell velocity by an order of magnitude. The relative motion between cells peaks shortly after each exposure, but remains elevated and even increases further several hours later.

Characterisation of the borgwaldt LM4E system for in vitro exposures to undiluted aerosols from next generation tobacco and nicotine products (NGPs)

Traditional in vitro exposure to combustible tobacco products utilise exposure systems that include the use of smoking machines to generate, dilute and deliver smoke to in vitro cell cultures. With reported lower emissions from next generation tobacco and nicotine products (NGPs), including e-cigarettes and tobacco heating products (THPs), diluting the aerosol is potentially not required. Herein we present a simplified exposure scenario to undiluted NGP aerosols, using a new puffing system called the LM4E. Nicotine delivery from an e-cigarette was used as a dosimetry marker, and was measured at source across 4 LM4E ports and in the exposure chamber. Cell viability studies, using Neutral Red Uptake (NRU) assay, were performed using H292 human lung epithelial cells, testing undiluted aerosols from an e-cigarette and a THP. E-cigarette mean nicotine generated at source was measured at 0.084 ± 0.005 mg/puff with no significant differences in delivery across the 4 different ports, p = 0.268 (n = 10/port). Mean nicotine delivery from the e-cigarette to the in vitro exposure chamber (measured up to 100 puffs) was 0.046 ± 0.006 mg/puff, p = 0.061. Aerosol penetration within the LM4E was 55% from source to chamber. H292 cells were exposed to undiluted e-cigarette aerosol for 2 h (240 puffs) or undiluted THP aerosol for 1 h (120 puffs). There were positive correlations between puff number and nicotine in the exposed culture media, R² = 0.764 for the e-cigarette and R² = 0.970 for the THP. NRU determined cell viability for e-cigarettes after 2 h' exposure resulted in 21.5 ± 17.0% cell survival, however for the THP, full cytotoxicity was reached after 1-h exposure.

Next-generation tobacco and nicotine products

A framework for the assessment of novel next-generation tobacco and nicotine products with the potential to reduce health risks compared with cigarettes should integrate scientific studies incorporating nonclinical, clinical, and population studies approaches. These products should have lower emissions and exhibit reduced biological effects compared with those of cigarettes, ideally approaching those of smoking cessation. The products should also be acceptable cigarette alternatives for current smokers, while not appealing to nonsmokers or former smokers. Validating harm reduction and promoting regulatory acceptance of the assessment methods require a collaborative approach by industry, independent reviewers, the public health community, and regulatory agencies. This article summarizes the science and approaches applied and considered to substantiate tobacco harm reduction in the light of regulatory requirements, presented at the 53rd Congress of the European Societies of Toxicology, 2017.

Assessing modified risk tobacco and nicotine products: Description of the scientific framework and assessment of a closed modular electronic cigarette

Cigarette smoking causes many human diseases including cardiovascular disease, lung disease and cancer. Novel tobacco products with reduced yields of toxicants compared to cigarettes, such as tobacco-heating products, snus and electronic cigarettes, hold great potential for reducing the harms associated with tobacco use. In the UK several public health agencies have advocated a potential role for novel products in tobacco harm reduction. Public Health England has stated that "The current best estimate is that e-cigarettes are around 95% less harmful than smoking" and the Royal College of Physicians has urged public health to "Promote e-cigarettes widely as substitute for smoking". Health related claims on novel products such as 'reduced exposure' and 'reduced risk' should be substantiated using a weight of evidence approach based on a comprehensive scientific assessment. The US FDA, has provided draft guidance outlining a framework to assess novel products as Modified Risk Tobacco Products (MRTP). Based on this, we now propose a framework comprising pre-clinical, clinical, and population studies to assess the risk profile of novel tobacco products. Additionally, the utility of this framework is assessed through the pre-clinical and part of the clinical comparison of a commercial e-cigarette (Vype ePen) with a scientific reference cigarette (3R4F) and the results of these studies suggest that ePen has the potential to be a reduced risk product.

Assessment of tobacco heating product THP1.0. Part 5: In vitro dosimetric and cytotoxic assessment

Tobacco heating products (THPs) represent a subset of the next-generation nicotine and tobacco product category, in which tobacco is typically heated at temperatures of 250-350 °C, thereby avoiding many of the harmful combustion-related toxicant emissions of conventional cigarettes. In this study, we have assessed aerosol generation and cytotoxicity from two commercially available THPs, THP1.0 and THS, relative to tobacco smoke from 3R4F reference cigarettes, using an adapted Borgwaldt RM20S Smoking Machine. Quantification of nicotine in the exposed cell-culture media showed greater delivery of nicotine from both THPs than from the cigarette. Using Neutral Red Uptake assay, THPs demonstrated reduced in vitro cytotoxicity in H292 human bronchial epithelial cells as compared with 3R4F cigarette exposure at the air-liquid interface (p < 0.0001). Both THPs demonstrated a statistically similar reduction in biological response, with >87% viability relative to 3R4F at a common aerosol dilution (1:40, aerosol:air). A similar response was observed when plotted against nicotine; a statistical difference between 3R4F and THPs (p < 0.0001) and no difference between the THPs (p = 0.0186). This pre-clinical in vitro biological testing forms part of a larger package of data to help assess the safety and risk reduction potential of next-generation tobacco products relative to cigarettes, using a weight of evidence approach.

A novel hybrid tobacco product that delivers a tobacco flavour note with vapour aerosol (Part 2): In vitro biological assessment and comparison with different tobacco-heating products

This study assessed the toxicological and biological responses of aerosols from a novel hybrid tobacco product. Toxicological responses from the hybrid tobacco product were compared to those from a commercially available Tobacco Heating Product (c-THP), a prototype THP (p-THP) and a 3R4F reference cigarette, using in vitro test methods which were outlined as part of a framework to substantiate the risk reduction potential of novel tobacco and nicotine products. Exposure matrices used included total particulate matter (TPM), whole aerosol (WA), and aqueous aerosol extracts (AqE) obtained after machine-puffing the test products under the Health Canada Intense smoking regime. Levels of carbonyls and nicotine in these matrices were measured to understand the aerosol dosimetry of the products. The hybrid tobacco product tested negative across the in vitro assays including mutagenicity, genotoxicity, cytotoxicity, tumour promotion, oxidative stress and endothelial dysfunction. All the THPs tested demonstrated significantly reduced responses in these in vitro assays when compared to 3R4F. The findings suggest these products have the potential for reduced health risks. Further pre-clinical and clinical assessments are required to substantiate the risk reduction of these novel products at individual and population levels.

Reduced biological effect of e-cigarette aerosol compared to cigarette smoke evaluated in vitro using normalized nicotine dose and RNA-seq-based toxicogenomics

Electronic cigarettes (e-cigarettes) use has increased globally and could potentially offer a lower risk alternative to cigarette smoking. Here, we assessed the transcriptional response of a primary 3D airway model acutely exposed to e-cigarette aerosol and cigarette (3R4F) smoke. Aerosols were generated with standard intense smoking regimens with careful consideration for dose by normalizing the exposures to nicotine. Two e-cigarette aerosol dilutions were tested for equivalent and higher nicotine delivery compared to 3R4F. RNA was extracted at 24 hrs and 48 hrs post exposure for RNA-seq. 873 and 205 RNAs were differentially expressed for 3R4F smoke at 24 hrs and 48 hrs using a pFDR < 0.01 and a [fold change] > 2 threshold. 113 RNAs were differentially expressed at the highest dose of e-cigarette aerosol using a looser threshold of pFDR < 0.05, 3 RNAs exceeded a fold change of 2. Geneset enrichment analysis revealed a clear response from lung cancer, inflammation, and fibrosis associated genes after 3R4F smoke exposure. Metabolic/biosynthetic processes, extracellular membrane, apoptosis, and hypoxia were identified for e-cigarette exposures, albeit with a lower confidence score. Based on equivalent or higher nicotine delivery, an acute exposure to e-cigarette aerosol had a reduced impact on gene expression compared to 3R4F smoke exposure in vitro.

The comparative in vitro assessment of e-cigarette and cigarette smoke aerosols using the γH2AX assay and applied dose measurements

DNA damage can be caused by a variety of external and internal factors and together with cellular responses, can establish genomic instability through multiple pathways. DNA damage therefore, is considered to play an important role in the aetiology and early stages of carcinogenesis. The DNA-damage inducing potential of tobacco smoke aerosols in vitro has been extensively investigated; however, the ability of e-cigarette aerosols to induce DNA damage has not been extensively investigated. E-cigarette use has grown globally in recent years and the health implications of long term e-cigarette use are still unclear. Therefore, this study has assessed the induction of double-strand DNA damage in vitro using human lung epithelial cells to e-cigarette aerosols from two different product variants (a "cigalike" and a closed "modular" system) and cigarette smoke. A Vitrocell^® VC 10 aerosol exposure system was used to generate and dilute cigarette smoke and e-cigarette aerosols, which were delivered to human bronchial epithelial cells (BEAS-2Bs) housed at the air-liquid-interface (ALI) for up to 120min exposure (diluting airflow, 0.25-1L/min). Following exposure, cells were immediately fixed, incubated with primary (0.1% γH2AX antibody in PBS) and secondary antibodies (DyLight™ 549 conjugated goat anti-mouse IgG) containing Hoechst dye DNA staining solution (0.2% secondary antibody and 0.01% Hoechst in PBS), and finally screened using the Cellomics Arrayscan VTI platform. The results from this study demonstrate a clear DNA damage-induced dose response with increasing smoke concentrations up to cytotoxic levels. In contrast, e-cigarette aerosols from two product variants did not induce DNA damage at equivalent to or greater than doses of cigarette smoke aerosol. In this study dosimetry approaches were used to contextualize exposure, define exposure conditions and facilitate comparisons between cigarette smoke and e-cigarette aerosols. Quartz crystal microbalance (QCM) technology and quantified nicotine delivery were both assessed at the exposure interface. Nicotine was eluted from the QCM surface to give a quantifiable measure of exposure to support deposited mass. Dose measured as deposited mass (μg/cm²) and nicotine (ng/mL) demonstrated that in vitro e-cigarette exposures were conducted at doses up to 12-28 fold to that of cigarette smoke and demonstrated a consistent negative finding.