The use of a novel tobacco-substitute sheet and smoke dilution to reduce toxicant yields in cigarette smoke

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.

Key Challenges for In Vitro Testing of Tobacco Products for Regulatory Applications: Recommendations for the In Vitro Mouse Lymphoma Assay

The Institute for In Vitro Sciences (IIVS) is sponsoring a series of workshops to develop recommendations for optimal scientific and technical approaches for conducting in vitro assays to assess potential toxicity within and across traditional tobacco and various tobacco and nicotine next-generation products (NGPs), including Heated Tobacco Products (HTPs) and Electronic Nicotine Delivery Systems (ENDS). This report was developed by a working group composed of attendees of the seventh IIVS workshop, 'Approaches and recommendations for conducting the mouse lymphoma gene mutation assay (MLA) and introduction to in vitro disease models', which was held virtually on 21-23 June 2022. This publication provides a background overview of the MLA, and includes the description of assay conduct and data interpretation, key challenges and recommended best practices for evaluating tobacco and nicotine products, with a focus on the evaluation of NGPs, and a summary of how the assay has been used to evaluate and compare tobacco and nicotine products.

Isolation and utilization of tobacco-based cellulose nanofiber (TCNF) for high performance reconstructed tobacco sheet (RTS)

Nowadays, wood pulp addition (such as softwood, hardwood, etc.) into manufacture reconstructed tobacco sheet (RTS) via a paper-making process is a feasible and sustainable technology. However, the addition of wood pulp in RTS would weaken the tobacco fragrance of cigarette by bring wood gas when smoking. In this study, a practical and feasible pretreatment by hot water/cooking process combined with cationic modification/homogenization treatment was proposed to directly isolate desirable cellulose nanofibers from tobacco stem, named TCNF. The obtained TCNF was applied in the preparation of RTS to improve its physical properties but with a reduced wood pulp proportion (from 25 wt% decreased to 16 wt%). Results showed that TCNF exhibit a similar morphology with wood based nanocellulose, and that the addition of TCNF (0.5 wt% based dried tobacco pulp) can substitute 9 % of wood pulp compared with that of the control at the similar physical properties.

In vitro mutagenicity of gas-vapour phase extracts from flavoured and unflavoured heated tobacco products

The in vitro mutagenic and genotoxic potential of Heated Tobacco Products (HTPs) has already been studied with the particulate phase and reported previously. This study has been designed to complement the in vitro assessment of the HTP and to determine whether the inclusion of potential flavourings would alter the in vitro response by testing the other phase of the aerosol, the gas-vapour phase (GVP). Both flavoured and unflavoured Neostik GVP samples did not show any sign of mutagenic activity in the Ames test but induced a mutagenic response in the mouse lymphoma assay (MLA), however, these responses were significantly less than those of the reference cigarette, 3R4F. The results demonstrated that GVP emissions of this HTP did not induce either new qualitative or quantitative mutagenic hazards compared to 3R4F, as assessed by the Ames test (no new responsive strains) and MLA (a lower mutagenic response), respectively. A statistical comparative analysis of the responses showed that the addition of flavourings that may thermally decompose under the conditions of use did not add to the in vitro baseline responses of the unflavoured Neostik.

Contribution of tobacco composition compounds to characteristic aroma of Chinese faint-scent cigarettes through chromatography analysis and partial least squares regression

To further explore the aroma mechanism of Chinese faint-scent cigarettes, the contribution of tobacco leaf composition, including six kinds of saccharides, eight tobacco alkaloids, seventeen kinds of organic acids, eighteen kinds of amino acids and four ions (Na+, K+, Mg2+ and Ca2+), on aroma quality characteristic (freshness, flowery and acidic notes) of faint-scent cigarettes was analyzed by chromatography and PLSR. The results showed that (i) xylose, fructose, glucose, maltose and sucrose were negatively correlated to acidic note, while galactose showed significantly positive correlation to acidic note. (ii) Phenylalanine and proline showed significant and positive correlation with characteristic aromas. Proline contributed to freshness and flowery, while leucine significantly contributed to acidic note. (iii) Most organic acids were significantly correlated to characteristic aromas. Palmitic acid and stearic acid contributed to the freshness, while dodecanoic acid and palmitic acid significantly contributed to flowery. (iv) Tobacco Na ion plays negative and significant correlation to acidic note.

Integrating chemical, toxicological and clinical research to assess the potential of reducing health risks associated with cigarette smoking through reducing toxicant emissions

The concept of a risk continuum for tobacco and nicotine products has been proposed, which differentiates products according to their propensity to reduce toxicant exposure and risk. Cigarettes are deemed the most risky and medicinal nicotine the least. We assessed whether a Reduced-Toxicant Prototype (RTP) cigarette could sufficiently reduce exposure to toxicants versus conventional cigarettes to be considered a distinct category in the risk continuum. We present findings from both pre-clinical and clinical studies in order to examine the potential for reduced smoke toxicant emissions to lower health risks associated with cigarette smoking. We conclude that current toxicant reducing technologies are unable to reduce toxicant emissions sufficiently to manifest beneficial disease-relevant changes in smokers. These findings point to a minimum toxicant exposure standard that future potentially reduced risk products would need to meet to be considered for full biological assessment. The RTP met WHO TobReg proposed limits on cigarette toxicant emissions, however the absence of beneficial disease relevant changes in smokers after six months reduced toxicant cigarette use, does not provide evidence that these regulatory proposals will positively impact risks of smoking related diseases. Greater toxicant reductions, such as those that can be achieved in next generation products e.g. tobacco heating products and electronic cigarettes are likely to be necessary to clearly reduce risks compared with conventional cigarettes.

Assessment of tobacco heating product THP1.0. Part 1: Series introduction

We have recently developed a Tobacco Heating Product (THP) comprising an electrical heating device, commercially known as Glo™, and consumable tobacco rods, commercially known as Kent Neostiks™. We refer to this system as THP1.0; Bright tobacco-flavoured variant THP1.0(T), or THP1.0(M) Menthol-flavoured variant. In this issue, we present a series of seven pre-clinical studies conducted on THP1.0,covering the following aspects of its design, development, safety and toxicological assessment, and a paper on placing THPs on an emissions continuum.

The use of charcoal in modified cigarette filters for mainstream smoke carbonyl reduction

Carbonyls are harmful and potentially harmful constituents (HPHCs) in mainstream cigarette smoke (MSS). Carbonyls, including formaldehyde and acrolein, are carcinogenic or mutagenic in a dose-dependent manner. Past studies demonstrate significant reduction of HPHCs by charcoal filtration. However, limits of charcoal filtration and cigarette design have not yet been investigated in a systematic manner. Objective data is needed concerning the feasibility of HPHC reduction in combustible filtered cigarettes. This systematic study evaluates the effect of charcoal filtration on carbonyl reduction in MSS. We modified filters of ten popular cigarette products with predetermined quantities (100-400 mg) of charcoal in a plug-space-plug configuration. MSS carbonyls, as well as total particulate matter, tar, nicotine, carbon monoxide (TNCO), and draw resistance were quantified. Significant carbonyl reductions were observed across all cigarette products as charcoal loading increased. At the highest charcoal loadings, carbonyls were reduced by nearly 99%. Tar and nicotine decreased modestly (<20%) compared to reductions in carbonyls. Increased draw resistance was significant at only the highest charcoal loadings. This work addresses information gaps in the science base that can inform the evaluation of charcoal filtration as an available technological adaptation to cigarette design which reduces levels of carbonyls in MSS.

Probing cigarette smoke-induced DNA single-strand breaks and screening natural protective compounds by use of magnetic bead-based chemiluminescence

Magnetic bead (MB)-based chemiluminescence (CL) ELISA can be a sample-thrifty, time-saving tool for evaluation of cigarette smoke-induced DNA single-strand breaks (SSBs) with high specificity. This article describes a novel approach using immobilized oligonucleotide on MBs to determine cigarette smoke-induced DNA SSBs and screen some protective natural compounds. Typically, fluorescein-labeled DNA (FAM-DNA) was immobilized on the MBs and then oxidized by the smoke in the absence or presence of natural compounds, and a part of FAM-DNA was fragmented due to cigarette smoke-induced DNA SSB and then detached from MBs whereas other non-broken FAM-DNA still remained on MBs. Then, any broken FAM-DNA fragments, complex tobacco smoke matrix, and other stuff related with natural compounds were conveniently washed away by a magnetic force, and thus possible interfering substances were completely removed. Finally, those remaining non-broken FAM-DNA on MBs were reacted with HRP-labeled anti-fluorescein antibody and then detected by CL ELISA. CL signal was converted to molar concentrations of the FAM-DNA by interpolation from a pre-determined standard linear calibration curve. The level of DNA SSBs induced by cigarette smoke was thus calculated using the method. A library of 30 natural products was subsequently screened, and two among them were found to protect DNA from oxidative damage and thus may be promising compounds for the development of new drugs. The method developed will be useful for quantitative screening of drug genotoxicity in terms of induction of DNA SSBs. Graphical abstract ᅟ.

Influence of cigarette circumference on smoke chemistry, biological activity, and smoking behaviour

Cigarettes with reduced circumference are increasingly popular in some countries, hence it is important to understand the effects of circumference reduction on their burning behaviour, smoke chemistry and bioactivity. Reducing circumference reduces tobacco mass burn rate, puff count and static burn time, and increases draw resistance and rod length burned during puff and smoulder periods. Smoulder temperature increases with decreasing circumference, but with no discernible effect on cigarette ignition propensity during a standard test. At constant packing density, mainstream (MS) and sidestream (SS) tar and nicotine yields decrease approximately linearly with decreasing circumference, as do the majority of smoke toxicants. However, volatile aldehydes, particularly formaldehyde, show a distinctly non-linear relationship with circumference and increases in the ratios of aldehydes to tar and nicotine have been observed as the circumference decreases. Mutagenic, cytotoxic and tumorigenic specific activities of smoke condensates (i.e. per unit weight of condensate) decrease as circumference decreases. Recent studies suggest that there is no statistical difference in mouth-level exposure to tar and nicotine among smokers of cigarettes with different circumferences. Commercially available slim cigarettes usually have changes in other cigarette design features compared with cigarettes with standard circumference, so it is difficult to isolate the effect of circumference on the properties of commercial products. However, available data shows that changes in cigarette circumference offer no discernible change to the harm associated with smoking.

An inventory of methods suitable to assess additive-induced characterising flavours of tobacco products

BACKGROUND

Products with strong non-tobacco flavours are popular among young people, and facilitate smoking initiation. Similar to the U.S. Food and Drug Administration Tobacco Control Act, the new European Tobacco Product Directive (TPD) prohibits cigarettes and roll-your-own tobacco with a characterising flavour other than tobacco. However, no methods are prescribed or operational to assess characterising flavours. This is the first study to identify, review and synthesize the existing peer-reviewed and tobacco industry literature in order to provide an inventory of methods suitable to assess characterising flavours.

METHODS

Authors gathered key empirical and theoretical papers examining methods suitable to assess characterising flavours. Scientific literature databases (PubMed and Scopus) and tobacco industry documents were searched, based on several keyword combinations. Inclusion criteria were relevance for smoked tobacco products, and quality of data.

RESULTS

The findings reveal that there is a wide variation in natural tobacco flavours. Flavour differences from natural tobacco can be described by both expert and consumer sensory panels. Most methods are based on smoking tests, but odour evaluation has also been reported. Chemical analysis can be used to identify and quantify levels of specific flavour additives in tobacco products.

CONCLUSIONS

As flavour perception is subjective, and requires human assessment, sensory analysis in consumer or expert panel studies is necessitated. We recommend developing validated tests for descriptive sensory analysis in combination with chemical-analytical measurements. Testing a broad range of brands, including those with quite subtle characterizing flavours, will provide the concentration above which an additive will impart a characterising flavour.

Tobacco alkaloids reduction by casings added/enzymatic hydrolysis treatments assessed through PLSR analysis

Based on encouraged development of potential reduced-exposure products (PREPs) by the US Institute of Medicine, casings (glucose and peptides) added treatments (CAT) and enzymatic (protease and xylanase) hydrolysis treatments (EHT) were developed to study their effect on alkaloids reduction in tobacco and cigarette mainstream smoke (MS) and further investigate the correlation between sensory attributes and alkaloids. Results showed that the developed treatments reduced nicotine by 14.5% and 24.4% in tobacco and cigarette MS, respectively, indicating that both CAT and EHT are potentially effective for developing lower-risk cigarettes. Sensory and electronic nose analysis confirmed the significant influence of treatments on sensory and cigarette MS components. PLSR analysis demonstrated that tobacco alkaloids were positively correlated to the off-taste, irritation and impact attributes, and negatively correlated to the aroma and softness attributes. Additionally, nicotine and anabasine from tobacco leaves positively contributed to the impact attribute, while they negatively contributed to the aroma attribute (P<0.05). Meanwhile, most alkaloids in cigarette MS positively contributed to the impact and irritation attributes (P<0.05). Hence, this study paved a way to better understand the correlation between tobacco alkaloids and sensory attributes.

Cytotoxicity and mutagenicity of sidestream cigarette smoke particulate matter of different particle sizes

Sidestream cigarette smoke, the major component of environmental tobacco smoke, is a complex and reactive aerosol. The particulate matter (PM) in sidestream smoke is one of the carriers of chemical constituents. However, particle size-dependent toxicological effects of PM are poorly understood. In this study, we evaluated the relationship between the PM size and in vitro cytotoxicity and mutagenicity of sidestream cigarette smoke. A NanoMoudi-II(™) 125A was used to collect PM samples ranging from 10 nm to 10 μm. The in vitro toxicity of PM was evaluated using a neutral red cytotoxicity assay and Salmonella mutagenicity assay. The results showed that the cytotoxicity and mutagenicity of PM larger than 1 μm was significantly lower than PM sized 10 nm-1 μm. Furthermore, there was a noticeable trend that the smaller the size of the PM of sidestream cigarette smoke, the greater the toxicity. This study suggests that the toxicity of PM in sidestream cigarette smoke is size-dependent.

A critical assessment of the scientific basis, and implementation, of regulations for the safety assessment and marketing of innovative tobacco-related products

Our scientific, logistical, ethical and animal welfare-related concerns about the latest US Food and Drug Administration (FDA) regulations for existing and so-called 'new' tobacco products, aimed at reducing harmful exposures, are explained. Such claims for sales in the USA now have to be based on a wide range of information, a key part of which will increasingly be data on safety and risk. One of the pathways to achieve marketing authorisation is to demonstrate substantial equivalence (SE) with benchmark products, called predicates. However, the regulations are insufficiently transparent with regard to: a) a rationale for the cut-off date for 'old' and 'new' products, and for exempting the former from regulation; b) the scientific validity and operation of SE; c) options for product labelling to circumvent SE; d) the experimental data required to support, and criteria to judge, a claim; and e) a strategy for risk assessment/management. Scientific problems related to the traditional animal methods used in respiratory disease and inhalation toxicology, and the use of quantitative comparators of toxicity, such as the No Observed Adverse Effect Level, are discussed. We review the advantages of relevant in vitro, mechanism-based, target tissue-oriented technologies, which an advisory report of the Institute of Medicine of the US National Academy of Sciences largely overlooked. These benefits include: a) the availability, for every major site in the respiratory tract, of organotypic human cell-based tissue culture systems, many of which are already being used by the industry; b) the accurate determination of concentrations of test materials received by target cells; c) methods for exposure to particulate and vapour phases of smoke, separately or combined; d) the ability to study tissue-specific biotransformation; and e) the use of modern, human-focused methodologies, unaffected by species differences. How data extrapolation, for risk assessment, from tissue culture to the whole animal, could be addressed, is also discussed. A cost (to animal welfare)-benefit (to society, including industry and consumers) analysis was conducted, taking into account the above information; the potential for animal suffering; the extensive data already available; the existence of other, less hazardous forms of nicotine delivery; the fact that much data will be generated solely for benchmarking; and that many smokers (especially nicotine-dependents) ignore health warnings. It is concluded that, in common with policies of several tobacco companies and countries, the use of laboratory animals for tobacco testing is very difficult, if not impossible, to justify. Instead, we propose and argue for an integrated testing scheme, starting with extensive chemical analysis of the ingredients and by-products associated with the use of tobacco products and their toxicity, followed by use of in vitro systems and early clinical studies (involving specific biomarkers) with weight-of-evidence assessments at each stage. Appropriate adjustment factors could be developed to enable concentration-response data obtained in vitro, with the other information generated by the strategy, to enable the FDA to meet its objectives. It is hoped that our intentionally provocative ideas will stimulate further debate on this contentious area of regulatory testing and public safety.

A comparative assessment of cigarette smoke aerosols using an in vitro air-liquid interface cytotoxicity test

This study describes the evaluation of a modified air-liquid interface BALB/c 3T3 cytotoxicity method for the assessment of smoke aerosols in vitro. The functionality and applicability of this modified protocol was assessed by comparing the cytotoxicity profiles from eight different cigarettes. Three reference cigarettes, 1R5F, 3R4F and CORESTA Monitor 7 were used to put the data into perspective and five bespoke experimental products were manufactured, ensuring a balanced and controlled study. Manufactured cigarettes were matched for key variables such as nicotine delivery, puff number, pressure drop, ventilation, carbon monoxide, nicotine free dry particulate matter and blend, but significantly modified for vapor phase delivery, via the addition of two different types and quantities of adsorptive carbon. Specifically manufacturing products ensures comparisons can be made in a consistent manner and allows the research to ask targeted questions, without confounding product variables. The results demonstrate vapor-phase associated cytotoxic effects and clear differences between the products tested and their cytotoxic profiles. This study has further characterized the in vitro vapor phase biological response relationship and confirmed that the biological response is directly proportional to the amount of available vapor phase toxicants in cigarette smoke, when using a Vitrocell® VC 10 exposure system. This study further supports and strengthens the use of aerosol based exposure options for the appropriate analysis of cigarette smoke induced responses in vitro and may be especially beneficial when comparing aerosols generated from alternative tobacco aerosol products.

The combination of two novel tobacco blends and filter technologies to reduce the in vitro genotoxicity and cytotoxicity of prototype cigarettes

Tobacco smoke from a combustible cigarette contains more than 6000 constituents; approximately 150 of these are identified as toxicants. Technologies that modify the tobacco blend to reduce toxicant emissions have been developed. These include tobacco sheet substitute to dilute toxicants in smoke and blend treated tobacco to reduce the levels of nitrogenous precursors and some polyphenols. Filter additives to reduce gas (vapour) phase constituents have also been developed. In this study, both tobacco blend and filter technologies were combined into an experimental cigarette and smoked to International Organisation on Standardisation and Health Canada puffing parameters. The resulting particulate matter was subjected to a battery of in vitro genotoxicity and cytotoxicity assays - the Ames test, mouse lymphoma assay, the in vitro micronucleus test and the Neutral Red Uptake assay. The results indicate that cigarettes containing toxicant reducing technologies may be developed without observing new additional genotoxic hazards as assessed by the assays specified. In addition, reductions in bacterial mutagenicity and mammalian genotoxicity of the experimental cigarette were observed relative to the control cigarettes. There were no significant differences in cytotoxicity relative to the control cigarettes.

Toxicity assessment of tobacco products in vitro

Driven by new regulatory demands to demonstrate risk reduction, the toxicity assessment of tobacco products increasingly employs innovative in vitro methods, including biphasic cell and tissue cultures exposed to whole cigarette smoke at the air-liquid interface, cell transformation assays, and genomic analyses. At the same time, novel tobacco products are increasingly compared to traditional cigarettes. This overview of in vitro toxicology studies of tobacco products reported in the last five years provides evidence to support the prioritisation of in vitro over in vivo methods by industry and their recommendation by regulatory authorities.

Approaches for the design of reduced toxicant emission cigarettes

Cigarette smoking causes serious diseases through frequent and prolonged exposure to toxicants. Technologies are being developed to reduce smokers’ toxicant exposure, including filter adsorbents, tobacco treatments and substitutes. This study examined the effect of modifications to filter ventilation, variations in cigarette circumference and active charcoal filter length and loading, as well as combinations of these features in a reduced-toxicant prototype (RTP) cigarette, on the yields of toxicants in cigarette smoke. An air-dilution mechanism, called split-tipping, was developed in which a band of porous paper in the centre of the filter tipping functions to minimise the loss of effective filter ventilation that occurs at the high flow rates encountered during human-smoking, and to facilitate the diffusional loss of volatile toxicants. As compared with conventional filter ventilation cigarettes, split-tipping reduced tar and volatile smoke constituent emissions under high flow rate machine-smoking conditions, most notably for products with a 1-mg ISO tar yield. Furthermore, mouth level exposure (MLE) to tar and nicotine was reduced among smokers of 1-mg ISO tar cigarettes in comparison to smokers of cigarettes with traditional filter ventilation. For higher ISO tar level cigarettes, however, there were no significant reductions in MLE. Smaller cigarette circumferences reduced sidestream toxicant yields and modified the balance of mainstream smoke chemistry with reduced levels of aromatic amines and benzo[a]pyrene but increased yields of formaldehyde. Smaller circumference cigarettes also had lower mainstream yields of volatile toxicants. Longer cigarette filters containing increased levels of high-activity carbon (HAC) showed reduced machine-smoking yields of volatile toxicants: with up to 97% removal for some volatile toxicants at higher HAC loadings. Split-tipping was combined with optimal filter length and cigarette circumference in an RTP cigarette that gave significantly lower mainstream (up to ~90%) and sidestream (predominately 20%–60%) smoke yields of numerous toxicants as compared with a commercial comparator cigarette under machine-smoking conditions. Significantly lower mainstream and sidestream smoke toxicant yields were observed for an RTP cigarette comprising several toxicant reducing technologies; these observations warrant further evaluation in clinical studies where real-world relevance can be tested using biomarkers of exposure and physiological effect.

Comparison of in vitro toxicity of mainstream cigarette smoke particulate matter from nano- to micro-size

In order to investigate the interrelationship between particulate matter (PM) size and in vitro toxicological effects of mainstream cigarette smoke, PM sized between 10 nm and 10 μm in mainstream cigarette smoke was sampled and divided into six stages. The in vitro cytotoxicity, genotoxicity and cell inhibition effects of PM were assessed by the neutral red cytotoxicity assay, Salmonella mutagenicity assay, micronucleus test and flow cytometry analysis, respectively. The results showed that all test samples were cytotoxic in the neutral red cytotoxicity assay. The IC50 values in the small-sized groups were significantly lower than those in the large-sized groups. Most test samples were mutagenic in the Salmonella mutagenicity assay (TA98 with S9 and TA100 with S9) and increased the frequency of micronucleated cells. Most PM disturbed the normal progression of the cell cycle, resulting in the accumulation of cells in the G0/G1 phase and the induction of apoptosis. In these tests, PM of a large size induced less toxicity compared with PM of a small size. These findings suggest that most PM samples induced toxicity in vitro, and PM of a small size was more toxic than PM of a large size.

Tobacco smoke-related health effects induced by 1,3-butadiene and strategies for risk reduction

1,3-Butadiene (BD) is a smoke component selected by the World Health Organization (WHO) study group on Tobacco Product Regulation (TobReg) for mandated lowering. We examined the tobacco smoke-related health effects induced by BD and possible health impacts of risk reduction strategies. BD levels in mainstream smoke (MSS) from international and Canadian cigarettes and environmental tobacco smoke (ETS) were derived from scientific journals and international government reports. Dose-response analyses from toxicity studies from government reports were evaluated and the most sensitive cancer and noncancer endpoints were selected. The risks were evaluated by taking the ratio (margin of exposure, MOE) from the most sensitive toxicity endpoint and appropriate exposure estimates for BD in MSS and ETS. BD is a good choice for lowering given that MSS and ETS were at levels for cancer (leukemia) and noncancer (ovarian atrophy) risks, and the risks can be significantly lowered when lowering the BD concentrations in smoke. Several risk reduction strategies were analyzed including a maximum level of 125% of the median BD value per milligram nicotine obtained from international brands as recommended by the WHO TobReg, tobacco substitute sheets, dual and triple carbon filters, and polymer-derived carbon. The use of tobacco substitute sheet with a polymer-derived carbon filter resulted in the most significant change in risk for cancer and noncancer effects. Our results demonstrate that MOE analysis might be a practical way to assess the impact of risk reduction strategies on human health in the future.

Reference change values to assess changes in concentrations of biomarkers of exposure in individuals participating in a cigarette-switching study

Background: In a previous clinical study, levels of biomarkers of exposure (BoEs) for specific toxicants were significantly reduced in smokers who switched from conventional cigarettes to reduced toxicant prototype (RTP) cigarettes. Very little is known about the biological variability of tobacco smoke BoEs within individuals and sub-groups, and the descriptive group-comparison statistics might not be sufficient to understand such changes. Therefore, we assessed how different statistical methods could be used to interpret changes in urine BoE levels at the individual level.

Methods: We used non-parametric statistical reference limits, the empirical rule and reference change values (RCVs) to assess changes in levels of BoEs related to four toxicants in cigarettes smoke. Current smokers [of 6 mg and 1 mg International Organization for Standardization (ISO) tar yields] were allocated to switching to RTP groups or non-switching control groups within their respective tar bands. There were two 6 mg tar study groups, with a non-switching group (CC6, n=46) and a group switching to an RTP containing tobacco-substitute sheet and modified filter (TSS6, n=49); and three 1 mg tar smoker groups, with one non-switching (CC1, n=42), a group switching to an RTP containing tobacco-substitute sheet and modified filter (TSS1, n=44) and one switching to an RTP containing an enzyme-treated tobacco and modified filter (BT1, n=47).

Results: Assessment of the direction of change showed that up to the 100% of subjects experienced a decrease in levels of some BoEs. Between 49% and 64% of subjects in the switching groups were classified as having decreased levels of 3-hydroxy-1-methylpropylmercapturic acid (HMPMA) by the non-parametric criterion, whereas only 2%–6% had reduced levels of N-nitrosoanatabine (NAT). Of non-switchers, in 7%–14% of those smoking 1 mg ISO tar yield cigarettes increases were classified across all BoEs. RCVs highlighted patterns with more detail, showing that most changes occurred within 14 days of switching. Among smokers who switched to 6 mg RTPs, 40%, 44%, 6% and 15%, respectively, were classified as experiencing significant decreasing levels of HPMA, 3-hydroxypropylmercapturic acid, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol and NAT, whereas in the two 1 mg switching groups 46%, 22%, 11% and 52% and 43%, 27%, 2% and 16% had decreased levels of the same biomarkers. Up to five subjects in the 6 mg non-switching group were classified as having increased levels of all BoEs.

Conclusions: Although we believe that is not possible to determine whether the observed changes in BoEs reflect biological relevance, the use of reference values enables assessment of changes in BoEs at the individual level. Estimates of the BoE variability between subjects might aid study design and setting minimum targets for smoke toxicant yields for future development of RTPs.

A single-blinded, single-centre, controlled study in healthy adult smokers to identify the effects of a reduced toxicant prototype cigarette on biomarkers of exposure and of biological effect versus commercial cigarettes

BACKGROUND

Despite universal acceptance that smoking is harmful, a substantial number of adults continue to smoke. The development of potential reduced exposure products (more recently termed modified risk tobacco products) has been suggested as a way to reduce the risks of tobacco smoking. This trial is designed to investigate whether changes in toxicant exposure after switching from a commercial to reduced toxicant prototype (RTP) cigarette (7 mg International Organisation for Standardisation (ISO) tar yield) can be assessed by measurement of biomarkers and other factors. The primary objective is to descriptively assess changes in selected biomarkers of exposure (BoE) and biomarkers of biological effect (BoBE) within participants and within and between groups after switching. Secondary objectives are to assess similarly changes in other biomarkers, quality of life, smoking behaviours, physiological measures, mouth-level exposure to toxicants and sensory perception.

METHODS/DESIGN

This trial will assess current smokers, ex-smokers and never-smokers in a single-centre single-blind, controlled clinical trial with a forced-switching design and in-clinic (residential) and ambulatory (non-residential) periods. Smokers will be aged 23-55 years (minimum legal smoking age plus 5 years) and non-smokers 28-55 years (minimum legal smoking age plus 5 years, plus minimum 5 years since last smoked). Smokers will be allowed to smoke freely at all times. We will assess changes in selected BoE and BoBE and effective dose in urine and blood after switching. Creatinine concentrations in serum, creatinine clearance in urine, cotinine concentration in saliva, diaries and collection of spent cigarette filters will be used to assess compliance with the study protocol. Mouth-level exposure to toxins will be assessed by filter analysis.

DISCUSSION

Data from this study are expected to improve scientific understanding of the effects of RTP cigarettes on BoE and BoBE, and give insights into study design for clinical assessment of potential MRTPs.

TRIAL REGISTRATION

The study was registered in the Current Controlled Trials database under the reference ISRCTN81286286.

The resolving power of in vitro genotoxicity assays for cigarette smoke particulate matter

In vitro genotoxicity assays are often used to compare tobacco smoke particulate matter (PM) from different cigarettes. The quantitative aspect of the comparisons requires appropriate statistical methods and replication levels, to support the interpretation in terms of power and significance. This paper recommends a uniform statistical analysis for the Ames test, mouse lymphoma mammalian cell mutation assay (MLA) and the in vitro micronucleus test (IVMNT); involving a hierarchical decision process with respect to slope, fixed effect and single dose comparisons. With these methods, replication levels of 5 (Ames test TA98), 4 (Ames test TA100), 10 (Ames test TA1537), 6 (MLA) and 4 (IVMNT) resolved a 30% difference in PM genotoxicity.

Lung cancer biomarkers for the assessment of modified risk tobacco products: an oxidative stress perspective

Manufacturers have developed prototype cigarettes yielding reduced levels of some tobacco smoke toxicants, when tested using laboratory machine smoking under standardised conditions. For the scientific assessment of modified risk tobacco products, tests that offer objective, reproducible data, which can be obtained in a much shorter time than the requirements of conventional epidemiology are needed. In this review, we consider whether biomarkers of biological effect related to oxidative stress can be used in this role. Based on published data, urinary 8-oxo-7,8-dihydro-2-deoxyguanosine, thymidine glycol, F2-isoprostanes, serum dehydroascorbic acid to ascorbic acid ratio and carotenoid concentrations show promise, while 4-hydroxynonenal requires further qualification.

The effect of long term storage on tobacco smoke particulate matter in in vitro genotoxicity and cytotoxicity assays

Particulate matter (PM) collected from mainstream tobacco smoke is a test article commonly used for in vitro genotoxicity and cytotoxicity testing of combustible tobacco products. However, little published data exists concerning the stability of PM. We completed a 2 year study to quantify the effect of PM storage at -80 °C, on the genotoxicity and cytotoxicity of PM generated from 3R4F and M4A reference cigarettes. The Ames test, Micronucleus assay (MNvit), Mouse Lymphoma assay (MLA) and the Neutral Red Uptake assay (NRU) were used. The majority of M4A and 3R4F PMs were genotoxic and cytotoxic at the timepoints tested. Some minor but statistically significant differences were observed for stored versus freshly prepared PM, but the magnitude of changes were within the variability observed for repeat testing.

Modification of smoke toxicant yields alters the effects of cigarette smoke extracts on endothelial migration: an in vitro study using a cardiovascular disease model

Endothelial damage plays a key role in atherosclerosis and this is impacted upon by numerous risk factors including cigarette smoking. A potential measure to reduce the cardiovascular burden associated with smoking is to reduce smoke toxicant exposure. In an in vitro endothelial damage repair assay, endothelial cell migration was inhibited by cigarette smoke particulate matter (PM) generated from several cigarette types. This inhibition was reduced when cells were exposed to PM from an experimental cigarette with reduced smoke toxicant levels. As a number of toxicants induce oxidative stress and since oxidative stress may link cigarette smoke and endothelial damage, we hypothesized that PM effects were dependent on elevated cellular oxidants. However, although PM-induced cellular oxidant production could be inhibited by ascorbic acid or n-acetylcysteine, both these antioxidants were without effect on migration responses to PM. Furthermore, reactive oxygen species production, as indicated by dihydroethidium fluorescence, was not different in cells exposed to smoke from cigarettes with different toxicant levels. In summary, our data demonstrate that a cardiovascular disease-related biological response may be modified when cells are exposed to smoke containing different levels of toxicants. This appeared independent of the induction of oxidative stress.

The effect of a novel tobacco process on the in vitro cytotoxicity and genotoxicity of cigarette smoke particulate matter

Some of the toxic effects of smoking have been attributed to the combustion of nitrogenous protein in tobacco. The effects of a treatment which reduces tobacco's protein nitrogen level, on the in vitro cytotoxicity and genotoxicity of cigarette smoke particulate matter (PM), were measured. PMs were tested in the Neutral Red Uptake (NRU) test; the Salmonella mutagenicity assay (SAL); the mouse lymphoma mammalian cell mutation assay (MLA) and the in vitro micronucleus test (IVMNT). PMs from all of the cigarettes were cytotoxic and genotoxic. PM obtained from smoking treated tobacco, showed a small, consistent and statistically significant reduced mutagenicity (revertants/μg) in TA98 with post-mitochondrial supernatant (S9). No consistent quantitative or qualitative differences were detected in the other tests. The data are discussed in relation to published information on smoke chemistry obtained from cigarettes made of tobacco treated using this technique. The observations confirm that the method did not give rise to any new qualitative or quantitative cytotoxic or genotoxic effects, and may have reduced PM's bacterial mutagenicity in TA98 with S9. Further toxicity testing is warranted, to investigate the effects of the tobacco treatment in more detail and add to the data already obtained.

Use of hazard indices for a theoretical evaluation of cigarette smoke composition

The chemical composition of cigarette mainstream smoke (MS) has been quantitatively analyzed in multiple studies, often with the objective to toxicologically evaluate and compare various types of MS. Increases and decreases in yields of constituents between MS types can only be consolidated if these yields are compared on the basis of toxicological properties of the individual constituents. For the risk assessment of various complex mixtures including MS, a hazard index (HI) approach has been used that requires weighing of the exposure to individual MS constituents by cancer and noncancer potency values. The objective of the current study is to review the past uses of the HI concept for MS and smokeless tobacco and discuss strengths and limitations of using this concept. Published information as well as information made available on the Web was used. The HI concept has been applied to MS for determining and comparing theoretical lifetime risks, for consumer communication, for the prioritization of constituents for reduction, for ingredient assessment, and for the selection of constituents for regulation. The limitations of this approach are associated with the limited number of MS constituents with available yield data, the gaps and uncertainties in available potency values, the application to relatively high exposure concentrations, and the default assumption of additivity. The derived theoretical noncancer index is dominated by acrolein to an extent that there seems to be not much advantage in using the HI concept for noncancer assessments. The derived theoretical cancer index is dominated by genotoxic carcinogens of the MS vapor phase and may thus complement currently used toxicological assays in a tiered evaluation approach. As is the case for every other assay and interpretation model, the HI concept needs to be applied with its limitations and weaknesses in mind. Its best application is for comparative purposes. It should be kept in mind that the HI concept is a theoretical concept and does not provide actual risk information.

Evaluation of the cytotoxicity of cigarette smoke condensate by a cellular impedance biosensor

In this study, a cytotoxicity assay was developed for profiling the cytotoxicity of cigarette smoke condensates (CSCs) base on a cellular impedance biosensor (CIB). Compared with the traditional in vitro cytotoxicity assays, this CIB-based method offered distinct advantages in real-time kinetic measurement which provided a comprehensive understanding of cellular responses for the entire duration of the experiment and prediction of the potential mechanism of action of a given treatment. The time-dependent cell response profiles provided valid evidences for optimization of cell number per well, cell quality control, and identification of the optimal time points for compound treatment and endpoint assays. According to the time dependent IC50 values, the CIB could provide dynamic information that can be used to identify maximum toxicity of cigarette smoke and reversibility of the toxic effects which are difficult to achieve by the endpoint assays. The comparative IC50 values indicated that the as-developed biosensor offered analytical results in good consistency with the commonly used NRU method. The features of the CIB-based cytotoxicity assay, such as no cell labeling, automatic detection, and easy operation, give this assay potential to become routine setting for evaluating the cytotoxicity of CSCs.

Design and chemical evaluation of reduced machine-yield cigarettes

Experimental cigarettes (ECs) were made by combining technological applications that individually reduce the machine measured yields of specific toxicants or groups of toxicants in mainstream smoke (MS). Two tobacco blends, featuring a tobacco substitute sheet or a tobacco blend treatment, were combined with filters containing an amine functionalised resin (CR20L) and/or a polymer-derived, high activity carbon adsorbent to generate three ECs with the potential for generating lower smoke toxicant yields than conventional cigarettes. MS yields of smoke constituents were determined under 4 different smoking machine conditions. Health Canada Intense (HCI) machine smoking conditions gave the highest MS yields for nicotine-free dry particulate matter and for most smoke constituents measured. Toxicant yields from the ECs were compared with those from two commercial comparator cigarettes, three scientific control cigarettes measured contemporaneously and with published data on 120 commercial cigarettes. The ECs were found to generate some of the lowest machine yields of toxicants from cigarettes for which published HCI smoke chemistry data are available; these comparisons therefore confirm that ECs with reduced MS machine toxicant yields compared to commercial cigarettes can be produced. The results encourage further work examining human exposure to toxicants from these cigarettes, including human biomarker studies.