The genotoxicological assessment of a tobacco heating product relative to cigarette smoke using the in vitro micronucleus assay

Genotoxicity and cytotoxicity evaluation of a heat-not-burn product

'Heat-not-burn' products (HnBP) contain lower levels of harmful substances than traditional cigarettes, but the use of these products warrants further toxicological evaluation. We have compared the cytotoxicity and genotoxicity of a heat-not burn product with conventional cigarettes, in vivo and in vitro. Male Sprague Dawley rats were exposed to mainstream smoke from conventional cigarettes or a HnBP, for 4 or 28 days, followed by isolation of bone marrow polychromatic erythrocytes (PCE) and histological examination of the testes. Chinese hamster lung fibroblast cells were exposed in vitro to total particulate matter from cigarette smoke obtained through Cambridge filters. The cytotoxicity and genotoxicity of total particulate matter were assessed by the neutral red uptake assay, chromosome aberration assay, in vitro micronucleus test, comet assay, and Ames assay. In the short-term exposure rat models, only the conventional-cigarettes group showed a significant increase in the ratio of micronuclei to total PCE. There was no significant difference in rat testis histology in the long-term exposure models. In vitro, in the neutral red uptake assay, the HnBP product showed lower cytotoxicity than conventional cigarettes. Conventional cigarettes showed greater genotoxicity in the chromosome aberration assay, high-dose Ames tests with exogenous metabolic activation, and micronucleus tests. In summary, our results suggest that HnBP have lower cytotoxicity and genotoxicity than conventional cigarettes.

A Scoping Review of Behavioural Studies on Heated Tobacco Products

Heated tobacco products (HTPs) are electronic devices that heat tobacco sticks to temperatures much lower than those which cause pyrolysis and combustion in cigarettes. While this electrical heating causes the formation of an inhalable aerosol which contains nicotine, the aerosol from HTPs contains significantly fewer and lower levels of the harmful and potentially harmful chemicals found in cigarette smoke. As a result, HTP use potentially conveys reduced risks to health compared to cigarette smoking. While this relative reduction in individual health risk is becoming clearer, what is less certain is the impact of HTPs on overall population‑level health, taking into account both the potential positive impact on adult smokers who completely switch to using HTPs and any unintended impacts such as use by tobacco non‑users and particularly by youth. The aim of this scoping review was to collate and evaluate the published scientific evidence to date, with a cut‑off of 1 January 2024, investigating the impact of HTPs on population‑level health. This evaluation suggests that HTP use is almost exclusively observed among those with a history of cigarette smoking, and there is a growing body of evidence for the ability of HTPs to provide support for adult smokers to transition away from cigarette smoking, in the absence of any significant "gateway" into tobacco use initiation. Many studies have reported a significant degree of dual use of cigarettes and HTPs, and efforts to assess the reasons for such patterns of use, whether these provide overall exposure reductions, and whether dual use acts as a bridge towards a complete transition away from cigarette smoking, requires further investigation. In addition, correction of the widespread and increasing misperceptions of HTPs among adult smokers is recommended to promote HTP uptake as a potentially less harmful alternative to smoking in this population.

Evaluation of Cytotoxic and Genotoxic Effects in Buccal Mucosal Cells in Non-Smokers and Users of Traditional Combustible Tobacco Products and Non-Combustible Alternatives

AIMS/OBJECTIVES

The aim of this cross-sectional observational study was to investigate cytogenetic damage to the buccal mucosa in non-smokers and consumers of traditional combustible tobacco products and non-combustible alternatives.

METHODS

A total of 160 participants were divided into four groups according to the type of product used, including non-smokers, users of conventional combustible tobacco (cigarettes), heated tobacco, and electronic, tobacco-free vapor products (e-cigarettes). Buccal mucosa samples were analyzed using the micronucleus cytome assay to assess cytotoxic and genotoxic damage.

RESULTS

E-cigarette users showed significantly higher values for all tested parameters in the micronucleus test compared to non-smokers (p < 0.05). Similarly, users of tobacco heating products showed an increase in all parameters (p < 0.05), with the exception of the number of cells with micronuclei. Conventional cigarette smokers showed a notable increase in the number of binucleated cells and cells with karyorrhexis and karyolysis (p ≤ 0.05). When assessing the differences between users of traditional combustible tobacco products and non-combustible alternatives, these did not appear to be significant, except for e-cigarette users, who had significantly more cells with condensed chromatin (p ≤ 0.001), while users of tobacco heating products had more pyknotic cells (p ≤ 0.001).

CONCLUSION

The results of this study underscore the heightened occurrence of cytotoxic and genotoxic damage in users of both conventional combustible tobacco products and non-combustible alternatives compared to non-smokers, emphasizing the detrimental impact of these products on the oral mucosa.

Impact of Electronic Cigarettes, Heated Tobacco Products and Conventional Cigarettes on the Generation of Oxidative Stress and Genetic and Epigenetic Lesions in Human Bronchial Epithelial BEAS-2B Cells

Electronic cigarettes (e-cig) and heated tobacco products (HTP) are often used as smoking cessation aids, while the harm reduction effects of these alternatives to cigarettes are still the subject of controversial debate, in particular regarding their carcinogenic potential. The objective of this study is to compare the effects of e-cig, HTP and conventional cigarette emissions on the generation of oxidative stress and genetic and epigenetic lesions in human bronchial epithelial BEAS-2B cells. Our results show that HTP were less cytotoxic than conventional cigarettes while e-cig were not substantially cytotoxic in BEAS-2B cells. E-cig had no significant effect on the Nrf2 pathway, whereas HTP and cigarettes increased the binding activity of Nrf2 to antioxidant response elements and the expression of its downstream targets HMOX1 and NQO1. Concordantly, only HTP and cigarettes induced oxidative DNA damage and significantly increased DNA strand breaks and chromosomal aberrations. Neither histone modulations nor global DNA methylation changes were found after acute exposure, regardless of the type of emissions. In conclusion, this study reveals that HTP, unlike e-cig, elicit a biological response very similar to that of cigarettes, but only after a more intensive exposure: both tobacco products induce cytotoxicity, Nrf2-dependent oxidative stress and genetic lesions in human epithelial pulmonary cells. Therefore, the health risk of HTP should not be underestimated and animal studies are required in order to determine the tumorigenic potential of these emerging products.

Multiple endpoint in vitro toxicity assessment of a prototype heated tobacco product indicates substantially reduced effects compared to those of combustible cigarette

This study aimed to compare the aerosol chemistry and in vitro toxicological profiles of two prototype Heated Tobacco Product (p-HTP) variants to the 1R6F Reference Cigarette. In the neutral red uptake screen the p-HTPs were 37-39-fold less potent than 1R6F, in the micronucleus assay, responses to the p-HTPs were 8-22-fold less, and in the Ames test mutagenicity was weak or removed compared to 1R6F. The cardiovascular scratch wound assay revealed 58-fold greater wound healing impairment following exposure to 1R6F smoke extracts than the p-HTPs. Furthermore, in seven cell stress-related high content screening endpoints (cell count, cytochrome c release, mitochondrial membrane potential, GSH depletion, NFkB translocation, phosphorylation of c-jun and phosphorylation of H2AX), at 4 and 24 h, responses were substantially greater to 1R6F smoke extracts at comparable nicotine levels. The reduced in vitro effects of the p-HTPs were attributed to substantial reductions (90-97%) in selected HPHCs measured compared to in 1R6F smoke. The multiple endpoint in vitro assessment approach provides greater mechanistic insight and the first reported toxicological characterisation of these p-HTPs in the literature. Overall, the findings contribute to the growing weight of evidence that HTPs may offer a reduced harm mode of nicotine delivery to adult smokers.

Chemical and in vitro toxicological comparison of emissions from a heated tobacco product and the 1R6F reference cigarette

It has previously been found that, compared with cigarette smoke, the aerosols generated by heated tobacco products contain fewer and lower harmful and potentially harmful constituents (HPHCs) and elicit lower biological activity in in vitro models and lower smoking-related exposure biomarker levels in clinical studies. It is important to accumulate such scientific evidences for heated tobacco products with a novel heating system, because different heating system may affect the quantitative aspect of the amount of HPHCs and the qualitative aspect of the biological activity of the aerosol generated. Here, the chemical properties of, and toxicological responses to aerosols emitted by DT3.0a, a new heated tobacco product with a novel heating system, and cigarette smoke (CS) were compared, using chemical analyses, in vitro battery (standardized genotoxicity and cytotoxicity) assays, and mechanistic (ToxTracker and two-dimensional cell culture) assays. Regular- and menthol-flavored DT3.0a and standard 1R6F reference cigarettes were tested. Selected HPHC yields were lower in DT3.0a aerosol than 1R6F CS. The genotoxicity-related assays indicated that DT3.0a aerosol was not genotoxic, regardless of metabolic activation. The other biological assays indicated that less cytotoxicity induction and oxidative stress response were elicited by DT3.0a aerosol compared with 1R6F CS. Similar results were found for both regular and menthol DT3.0a. Like previous reports for heated tobacco products with other heating systems, the results of this study indicated that DT3.0a aerosols have chemical and biological properties less likely to be harmful than 1R6F CS.

Evaluation of behavioural, chemical, toxicological and clinical studies of a tobacco heated product glo™ and the potential for bridging from a foundational dataset to new product iterations

Background

Tobacco Heating Products (THPs) are tobacco products that heat rather than burn tobacco with temperatures less than 350 °C. Because of this operating principle, they produce substantially fewer and lower levels of tobacco smoke toxicants than combustible cigarette smoke produced when tobacco is burnt, which occurs at much higher temperatures of around 900 °C. This paper analyses data on a THP, glo™, and assesses whether its use would result in reduced health risks compared to the health risks of smoking cigarettes. It also looks at the possibility of bridging datasets across the different variants of the glo™ product.

Methods

The approach is to consider whether datasets from behavioural, chemical, toxicological and clinical studies provide consistent findings of reductions in toxicant exposure with glo™ use by subjects who switch completely from smoking cigarettes to using glo™ and whether these reductions are similar to those who stop smoking cigarettes without switching to glo™ or any other tobacco or nicotine product. We also examine the similarities and differences of different versions of the glo™ product and benchmark it against a THP from another manufacturer.

Results

The studies indicate that the use of the glo™ results in substantial and prolonged reductions in toxicant exposure for smokers who switch to glo™ completely. A long-term clinical study shows substantial reductions in toxicant exposure over a period of time, similar to reduction of some biomarkers of exposure found following smoking cessation without switching to glo™ or any other tobacco product, and biomarkers of potential harm trending in a favourable manner for both groups that switch to glo™ and that quit all tobacco and nicotine use. Data suggests that all iterations of glo™ result in substantial reductions in toxicant exposure compared to smoking cigarettes and that bridging across datasets is feasible.

Conclusions

Given the accumulated scientific data summarised in this paper, and particularly the findings from a long-term clinical study, the data demonstrate that glo™ is a reduced exposure product compared to combustible cigarettes and is reasonably deemed to reduce the risk of smoking-related diseases and supports the conclusion that smokers who would have otherwise continued to smoke and instead switch entirely to THP glo™ use, will reduce their relative risk of developing smoking-related diseases as compared to continued smoking. The extent of reduction in risk compared to continuing to smoke is likely to vary by smoking-related disease and by an individuals' smoking history, other risk factors and an individual's susceptibility to disease. Use of the THP will present some level of increased health risk as compared to cessation of tobacco and nicotine products and will cause dependence. As long as the principles of heat-not-burn are maintained, THP use will result in substantially reduced exposure to smoke toxicants as compared to continued conventional cigarette smoking. It is possible to use bridging or read across to apply these conclusions to new iterations of the glo™ product, extending the utility and validity of the evidence generated through study of prior iterations.

A novel clinical method to measure skin staining reveals activation of skin damage pathways by cigarette smoke

BACKGROUND

Long-term use of cigarettes can result in localised staining and aging of smokers' skin. The use of tobacco heating products (THPs) and electronic cigarettes (ECs) has grown on a global scale; however, the long-term effect of these products' aerosols on consumers' skin is unknown. This pilot clinical study aimed to determine whether THP or EC aerosol exposure results in skin staining or activation of biomarkers associated with oxidative stress.

MATERIALS AND METHODS

Eight areas were identified on the backs of 10 subjects. Two areas were used for air control, and two areas exposed to 32-puffs of cigarette smoke (CS), THP or EC aerosols, which were delivered to the skin using a 3-cm diameter exposure chamber and smoke engine. Skin colour was measured using a Chromameter. Squalene (SQ), SQ monohydroperoxide (SQOOH) and malondialdehyde (MDA) levels were measured in sebum samples by mass spectrometry and catalase colorimetry.

RESULTS

CS exposure significantly increased skin staining, SQOOH and MDA levels and SQOOH/SQ ratio. THP and EC values were significantly lower than CS; EC values being comparable to air control. THP values were comparable to EC and air control at all endpoints, apart from skin staining. SQ and catalase levels did not change with exposure.

CONCLUSIONS

CS stained skin and activated pathways known to be associated with skin damage. THPs and ECs produced significantly lower values, suggesting they could offer hygiene and cosmetic benefits for consumers who switch exclusively from smoking cigarettes. Further studies are required to assess longer-term effects of ECs and THPs on skin function.

Effects of antioxidant capacity on micronucleus induction by cigarette smoke in mammalian cells

We have compared micronucleus (MN) induction by cigarette smoke in the L5178Y, TK6, and CHL/IU cell lines. The test sample was total particulate matter of 3R4F reference cigarette smoke, suspended in DMSO. After 3-h treatment, with or without a rat liver S9 metabolic activation system, followed by 24-h recovery, dose-dependent MN increases were seen in all cell lines. However, CHL/IU and TK6 cells were more resistant than L5178Y cells (comparison by Benchmark Doses with PROAST software). 3R4F smoke generates reactive oxygen species (ROS). Therefore, we explored the relationship between the sensitivities to 3R4F smoke and the antioxidant capacities of the cell lines. While the total antioxidant capacities were not significantly different among the cell lines, cellular glutathione (GSH) was higher in CHL/IU cells than in L5178Y cells. Pretreatment of CHL/IU cells with a GSH precursor, N-acetylcysteine (NAC), reduced the genotoxicity/cytotoxicity of 3R4F, whereas an inhibitor of GSH biosynthesis, buthionine sulfoximine (BSO), enhanced it. The effects of NAC and BSO were also seen after treatment with allyl isothiocyanate, a ROS-generating chemical, but not with mitomycin C, a ROS-independent genotoxicant. Pretreatment with NAC increased cellular thiol levels. From the present results, the genotoxicity and cytotoxicity of cigarette smoke differs among these cell lines in a manner that may be related to their antioxidant thiol levels.

Novel Solvent-Free Extraction Method for Analyzing Tobacco Heating Product Aerosols: An Analytical and In Vitro Toxicological Five-Way Product Comparison

Harmful and potentially harmful constituents (HPHCs) in tobacco smoke are thought to be responsible for the increased health risks. Tobacco heating products (THPs) heat tobacco instead of burning it to achieve significantly fewer toxicants than conventional cigarettes. To assess the toxicity of THP aerosols, it is often desirable to extract the main constituents using a solvent method. In this study, we developed a high-speed centrifugal method for extracting the total particulate matter (TPM) from THPs to quantitatively compare the toxicity of different THPs and conventional cigarettes. Its TPM extraction efficiency exceeded 85%, and the primary aerosol components and typical HPHCs were comparable to those of the solvent method. The TPMs extracted from five THPs were subjected to 14 in vitro toxicology assessments, and the results were compared with those of a 3R4F reference cigarette. Physical separation can improve biases from solvent selectivity and potential interactions between solvent and aerosol constituents. By eliminating solvent influence, the extraction method could achieve high-dose exposures, enabling the toxicity comparison of different THPs. The relative toxicity of the THPs differed under different dosage units, including the TPM concentration, nicotine equivalent, and puff number.

Short-term whole body cigarette smoke exposure induces regional differences in cellular response in the mouse larynx

The larynx is an essential organ in the respiratory tract and necessary for airway protection, respiration, and phonation. Cigarette smoking is a significant risk factor associated with benign and malignant laryngeal diseases. Despite this association, the underlying mechanisms by which cigarette smoke (CS) drives disease development are not well elucidated. In the current study, we developed a short-term murine whole body inhalation model to evaluate the first CS-induced cellular responses in the glottic [i.e. vocal fold (VF)] and subglottic regions of the larynx. Specifically, we investigated epithelial cell proliferation, cell death, surface topography, and mucus production, at various time points (1 day, 5 days, 10 days) after ∼ 2 h exposure to 3R4F cigarettes (Delivered dose: 5.6968 mg/kg per cigarette) and following cessation for 5 days after a 5 day CS exposure (CSE). CSE elevated levels of BrdU labeled proliferative cells and p63 labeled epithelial basal cells on day 1 in the VF. CSE increased proliferative cells in the subglottis at days 5, 10 and following cessation in the subglottis. Cleaved caspase-3 apoptotic activity was absent in VF at all time points and increased at day 1 in the subglottis. Evaluation of the VF surface by scanning electron microscopy (SEM) revealed significant epithelial microprojection damage at day 10 and early signs of necrosis at days 5 and 10 post-CSE. SEM visualizations additionally indicated the presence of deformed cilia at days 5 and 10 after CSE and post-cessation in the respiratory epithelium lined subglottis. In terms of mucin content, the impact of short-term CSE was observed only at day 10, with decreasing acidic mucin levels and increasing neutral mucin levels. Overall, these findings reveal regional differences in murine laryngeal cellular responses following short-term CSE and provide insight into potential mechanisms underlying CS-induced laryngeal disease development.

Systematic review of biomarker findings from clinical studies of electronic cigarettes and heated tobacco products

BACKGROUND

Worldwide adoption of electronic cigarettes (e-cigarettes) and heated tobacco products (HTPs) has increased exponentially over the past decade. These products have been proposed as non-combustible alternatives to traditional tobacco products such as cigarettes and may thus reduce the negative health consequences associated with tobacco smoke. However, the overall health impact and safety of using these products remains unclear. This review seeks to provide an updated summary of available evidence on changes to levels of tobacco-related biomarkers to aid the overall assessment of the consequences of using e-cigarettes and HTPs.

METHODS

A systematic review was conducted through major databases (Medline/PubMed, Scopus, EMBASE) searching for articles directly comparing biomarker levels in humans using e-cigarettes or HTPs and those using combustible cigarettes. We included peer reviewed articles with comparative or longitudinal design and extracted key information for our purpose (type of population, demographics, biomarkers measurements, and health effects). An initial qualitative analysis was performed followed by a summary of findings.

RESULTS

A total of 44 studies were included from initial citations. The vast majority of the literature reported reductions in levels of biomarkers of tobacco smoke exposure (BOE), especially nicotine, MHBMA, 3-HPMA, S-PMA, 1-OHP and NNAL, when using e-cigarettes and HTPs compared to combustible cigarettes. There was a slight tendency toward a larger reduction in these biomarkers levels with the use of e-cigarettes, although direct comparisons between e-cigarettes and HTPs were lacking. There was also a trend toward positive changes in levels of biomarkers of biological effect (BOBE) with the use of e-cigarettes and HTPs.

CONCLUSIONS

A comparison of levels of biomarkers of tobacco-related exposure collected in clinical studies revealed that the use of e-cigarettes and HTPs could lead to a significant reduction in exposure to harmful substances compared to combusted cigarettes. In tandem, the health status of e-cigarettes and HTP users, indexed by levels of biomarkers of biological effect showed potential for improvement compared to smoking. However, larger and longer-term population-based studies are needed to further clarify these findings.

Comparative and cumulative quantitative risk assessments on a novel heated tobacco product versus the 3R4F reference cigarette

Novel tobacco products that heat rather than burn tobacco (heated tobacco products or HTPs) have been shown to produce lower levels of harmful and potentially harmful constituents than conventional combusted cigarettes. The present study uses a quantitative risk assessment approach to compare non-cancer and cancer risk estimates for emissions generated by an HTP with smoke from a reference cigarette (3R4F). Fifty-four analytes were evaluated from the HTP aerosol and the 3R4F cigarette smoke. Emissions were generated using the ISO and the Health Canada Intense smoking regimes. The measured values were extrapolated to define a conservative exposure assumption for per day use and lifetime use based on an estimated maximum usage level of 400 puffs per day i.e., approximately 8 HTP tobacco capsules or 40 combustible cigarettes. Non-cancer and cancer risk estimates were calculated using these exposure assumptions for individual and per health outcome domains based on toxicological reference values derived by regulatory and/or public health agencies. The results of this assessment showed a reduction of non-cancer and cancer risk estimates by more than 90 % for the HTP versus the 3R4F cigarette, regardless of the smoking regime.