A comparison of in vitro toxicities of cigarette smoke condensate from Eclipse cigarettes and four commercially available ultra low-"tar" cigarettes

Testicular tissue response following a 90-day subchronic exposure to HTP aerosols and cigarette smoke in rats

Background

Researches have shown that chronic inhalation of cigarette smoke (CS) disrupts male reproductive system, but it is unclear about the mechanisms behind reproductive damages by tobacco toxicants in male rats. This study was designed to explore the effects of heated tobacco products (HTP) aerosols and CS exposure on the testicular health of rats.

Materials and Methods

Experiments were performed on male SD rats exposed to filtered air, HTP aerosols at 10 μg/L, 23 μg/L, and 50 μg/L nicotine-equivalent contents, and also CS at 23 μg/L nicotine-equivalent content for 90 days in five exposure groups (coded as sham, HTP_10, HTP_23, HTP_50 and Cig_23). The expression of serum testosterone, testicular tissue inflammatory cytokines (IL-1β, IL-6, IL-10, TNF-α), reactive oxygen species (ROS), superoxide dismutase (SOD) and malondialdehyde (MDA), NLRP3 inflammasome-related mRNAs and proteins (NLRP3, ASC, and Caspase-1), the degree of pyroptosis and histopathology were investigated.

Results

The results demonstrated that HTP_50 and Cig_23 caused varying degrees of oxidative damage to rat testis, resulting in a decrease of sperm quantity and serum testosterone contents, an increase in the deformity rate, expression levels of proinflammatory cytokines, and NLRP3 inflammasome-related mRNA, and an increase in the NLRP3, ASC, and Caspase-1-immunopositive cells, pyroptosis cell indices, and histopathological damage in the testes of rats. Responses from the HTP_10 and HTP_23 groups were less than those found in the above two exposure groups.

Conclusion

These findings indicate that HTP_50 and Cig_23 induced oxidative stress in rat testes, induced inflammation and pyroptosis through the ROS/NLRP3/Caspase-1 pathway, and destroyed the integrity of thetesticular tissue structure.

Puff-resolved analysis and selected quantification of chemicals in the gas phase of E-Cigarettes, Heat-not-Burn devices and conventional cigarettes using single photon ionization time-of-flight mass spectrometry (SPI-TOFMS): A comparative study

INTRODUCTION

A wide array of alternative nicotine delivery devices (ANDD) has been developed and they are often described as less harmful than combustible cigarettes. This work compares the chemical emissions of three ANDD in comparison to cigarette smoke. All the tested ANDD are characterized by not involving combustion of tobacco.

METHOD

Single photon ionization time-of-flight mass spectrometry (SPI-TOFMS) is coupled to a linear smoking machine, which allows a comprehensive, online analysis of the gaseous phase of the ANDD aerosol and the conventional cigarette smoke (CC). The following devices were investigated in this study: a tobacco cigarette with a glowing piece of coal as a heating source, an electric device for heating tobacco and a first-generation electronic cigarette. Data obtained from a standard 2R4F research cigarette are taken as a reference.

RESULTS

The puff-by-puff profile of all products was recorded. The ANDD show a substantial reduction or complete absence of known harmful and potentially harmful substances compared to the CC. In addition, tar substances (i.e. semivolatile and low volatile aromatic and phenolic compounds) are formed to a much lower extent. Nicotine, however, is supplied in comparable amounts except for the investigated electronic cigarette.

CONCLUSIONS

The data shows that consumers switching from CC to ANDD are exposed to lower concentrations of harmful and potentially harmful substances. However, toxicological and epidemiological studies must deliver conclusive results if these reduced exposures are beneficial for users.

IMPLICATION

The comparison of puff-resolved profiles of emissions from different tobacco products, traditional and alternative, may help users switch to lower emission products. Puff-resolved comparison overcomes technical changes, use modes between products and may help in their regulation.

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.

Evaluation of flavourings potentially used in a heated tobacco product: Chemical analysis, in vitro mutagenicity, genotoxicity, cytotoxicity and in vitro tumour promoting activity

We designed a novel tobacco-heating product (THP) that heats tobacco to release nicotine and aerosolised components, such as glycerol and tobacco volatiles from a tobacco rod (Neostik). Heating tobacco significantly reduces levels of combustion-derived toxicants in the aerosol compared to cigarette smoke. This study was conducted to determine whether the inclusion of potential flavourings in the THP would add to the levels of toxicants in the emissions or alter in vitro responses. Levels of measured toxicants were similar in the flavoured and unflavoured Neostik emissions and significantly less than emissions from the reference cigarette, 3R4F. No mutagenicity was observed with the Neostiks in the Ames test or in the mouse lymphoma assay. There was evidence of a weak genotoxic response in the in vitro micronucleus test using V79 cells from both Neostiks and these responses were less than 3R4F. They did not show tumour-promoting potential in the Bhas 42 cell transformation assay and were not cytotoxic in the Neutral Red uptake assay. 3R4F elicited toxic responses in all assays at significantly lower concentrations. The addition of flavourings to the Neostik tested did not alter the chemical profile of THP emissions or change in vitro responses relative to the unflavoured Neostik.

Chronic E-Cigarette Exposure Alters the Human Bronchial Epithelial Proteome

RATIONALE

E-cigarettes vaporize propylene glycol/vegetable glycerin (PG/VG), nicotine, and flavorings. However, the long-term health effects of exposing lungs to vaped e-liquids are unknown.

OBJECTIVES

To determine the effects of chronic vaping on pulmonary epithelia.

METHODS

We performed research bronchoscopies on healthy nonsmokers, cigarette smokers, and e-cigarette users (vapers) and obtained bronchial brush biopsies and lavage samples from these subjects for proteomic investigation. We further employed in vitro and murine exposure models to support our human findings.

MEASUREMENTS AND MAIN RESULTS

Visual inspection by bronchoscopy revealed that vaper airways appeared friable and erythematous. Epithelial cells from biopsy samples revealed approximately 300 proteins that were differentially expressed in smoker and vaper airways, with only 78 proteins being commonly altered in both groups and 113 uniquely altered in vapers. For example, CYP1B1 (cytochrome P450 family 1 subfamily B member 1), MUC5AC (mucin 5 AC), and MUC4 levels were increased in vapers. Aerosolized PG/VG alone significantly increased MUC5AC protein in human airway epithelial cultures and in murine nasal epithelia in vivo. We also found that e-liquids rapidly entered cells and that PG/VG reduced membrane fluidity and impaired protein diffusion.

CONCLUSIONS

We conclude that chronic vaping exerts marked biological effects on the lung and that these effects may in part be mediated by the PG/VG base. These changes are likely not harmless and may have clinical implications for the development of chronic lung disease. Further studies will be required to determine the full extent of vaping on the lung.

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

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

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

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

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

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

Chemical analysis and in vitro toxicological evaluation of aerosol from a novel tobacco vapor product: A comparison with cigarette smoke

The recent rapid increase in the prevalence of emerging tobacco- and nicotine-containing products, such as e-cigarettes, is being driven in part by their reduced-risk potential compared to tobacco smoking. In this study, we examined emission levels for selected cigarette smoke constituents, so-called "Hoffmann analytes", and in vitro toxicity of aerosol from a novel tobacco vapor product (NTV). The NTV thermally vaporizes a nicotine-free carrier liquid to form an aerosol which then passes through tobacco, where it absorbs tobacco-derived flavors and nicotine. The NTV results were compared with those for 3R4F cigarette smoke. Chemical analysis of the NTV aerosol demonstrated that Hoffmann analyte levels were substantially lower than in 3R4F smoke and that the most were below quantifiable levels. Results from in vitro bacterial reverse mutation, micronucleus and neutral red uptake assays showed that, in contrast with 3R4F smoke, the NTV aerosol failed to demonstrate any measurable genotoxicity or cytotoxicity. The temperature of tobacco during NTV use was measured at approximately 30 °C, which may explain the lower Hoffmann analyte emission and in vitro toxicity levels. These results suggest that the aerosol from the NTV has a very different toxicological profile when compared with combustible cigarette smoke.

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.

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

Cytotoxicity assessment of combustible tobacco products by neutral red uptake (NRU) has historically used total particulate matter (TPM) or solvent captured gas vapor phase (GVP), rather than fresh whole smoke. Here, the development, validation and application of the NRU assay in Chinese Hamster Ovary (CHO) cells, following exposure to fresh whole smoke generated with the VITROCELL® VC10® system is described. Whole smoke exposure is particularly important as both particulate and vapor phases of tobacco smoke show cytotoxicity in vitro. The VITROCELL® VC10® system provides exposure at the air liquid interface (ALI) to mimic in vivo conditions for assessing the toxicological impact of smoke in vitro. Instrument and assay validations are crucial for comparative analyses.

GOALS OF THIS STUDY

1) demonstrate functionality of the VITROCELL® VC10® system by installation, operational and performance qualification, 2) develop and validate a cellular system for assessing cytotoxicity following whole smoke exposure and 3) assess the whole smoke NRU assay sensitivity for statistical differentiation between a reference combustible cigarette (3R4F) and a primarily "heat-not-burn" cigarette (Eclipse).

RESULTS

The VITROCELL® VC10® provided consistent generation and delivery of whole smoke; exposure-related changes in in vitro cytotoxicity were observed with reproducible IC50 values; comparative analysis showed that the heat-not-burn cigarette was significantly (P<0.001) less cytotoxic than the 3R4F combustible cigarette, consistent with the lower levels of chemical constituents liberated by primarily-heating the cigarette versus burning.

Quantitative analysis of the relative mutagenicity of five chemical constituents of tobacco smoke in the mouse lymphoma assay

Quantifying health-related biological effects, like genotoxicity, could provide a way of distinguishing between tobacco products. In order to develop tools for using genotoxicty data to quantitatively evaluate the risk of tobacco products, we tested five carcinogens found in cigarette smoke, 4-aminobiphenyl (4-ABP), benzo[a]pyrene (BaP), cadmium (in the form of CdCl2), 2-amino-3,4-dimethyl-3H-imidazo[4,5-f]quinoline (MeIQ) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), in the mouse lymphoma assay (MLA). The resulting mutagenicity dose responses were analyzed by various quantitative approaches and their strengths and weaknesses for distinguishing responses in the MLA were evaluated. L5178Y/Tk (+/-) 3.7.2C mouse lymphoma cells were treated with four to seven concentrations of each chemical for 4h. Only CdCl2 produced a positive response without metabolic activation (S9); all five chemicals produced dose-dependent increases in cytotoxicity and mutagenicity with S9. The lowest dose exceeding the global evaluation factor, the benchmark dose producing a 10%, 50%, 100% or 200% increase in the background frequency (BMD10, BMD50, BMD100 and BMD200), the no observed genotoxic effect level (NOGEL), the lowest observed genotoxic effect level (LOGEL) and the mutagenic potency expressed as a mutant frequency per micromole of chemical, were calculated for all the positive responses. All the quantitative metrics had similar rank orders for the agents' ability to induce mutation, from the most to least potent as CdCl2(-S9) > BaP(+S9) > CdCl2(+S9) > MeIQ(+S9) > 4-ABP(+S9) > NNK(+S9). However, the metric values for the different chemical responses (i.e. the ratio of the greatest value to the least value) for the different chemicals ranged from 16-fold (BMD10) to 572-fold (mutagenic potency). These results suggest that data from the MLA are capable of discriminating the mutagenicity of various constituents of cigarette smoke, and that quantitative analyses are available that can be useful in distinguishing between the exposure responses.

Cigarette smoke and adverse health effects: An overview of research trends and future needs

A large volume of data has accumulated on the issues of tobacco and health worldwide. The relationship between tobacco use and health stems initially from clinical observations about lung cancer, the first disease definitively linked to tobacco use. Almost 35 years ago, the Office of the Surgeon General of the United States Health Service reviewed over 7000 research papers on the topic of smoking and health, and publicly recognized the role of smoking in various diseases, including lung cancer. Since then, numerous studies have been published that substantiate the strong association of tobacco use with a variety of adverse human health effects, most prominently with cancer and cardiovascular diseases. Cigarette smoking is regarded as a major risk factor in the development of lung cancer, which is the main cause of cancer deaths in men and women in the United States and the world. Major advances have been made by applying modern genetic technologies to examine the relationship between exposure to tobacco smoke and the development of diseases in human populations. The present review summarizes the major research areas of the past decade, important advances, future research needs and federal funding trends.

Genetic toxicology and toxicogenomic analysis of three cigarette smoke condensates in vitro reveals few differences among full-flavor, blonde, and light products

Cigarette smoking leads to various detrimental health outcomes. Tobacco companies produce different brands of cigarettes that are marketed as reduced harm tobacco products. Early examples included "light" cigarettes, which differ from regular cigarettes due to filter ventilation and/or differences in chemical constituents. In order to establish baseline similarities and differences among different tobacco brands available in Canada, the present study examined the cytotoxicity, mutagenicity, clastogenicity, and gene expression profiles of cigarette smoke condensate (CSC) from three tobacco products, encompassing a full-flavor, blonde, and "light" variety. Using the Salmonella mutagenicity assay, we confirmed that the three CSCs are mutagenic, and that the potency is related to the presence of aromatic amines. Using the Muta™Mouse FE1 cell line we determined that the CSCs were clastogenic and cytotoxic, but nonmutagenic, and the results showed few differences in potencies among the three brands. There were no clear brand-specific changes in gene expression; each brand yielded highly similar expression profiles within a time point and concentration. The molecular pathways and biological functions affected by exposure included xenobiotic metabolism, oxidative stress, DNA damage response, cell cycle arrest and apoptosis, as well as inflammation. Thus, there was no appreciable difference in toxicity or gene expression profiles between regular brands and products marketed as "light," and hence no evidence of reduced harm. The work establishes baseline CSC cytotoxicity, mutagenicity, and expression profiles that can be used as a point of reference for comparison with data generated for products marketed as reduced harm and/or modified risk tobacco products.

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.

Concentration dependent effects of tobacco particulates from different types of cigarettes on expression of drug metabolizing proteins, and benzo(a)pyrene metabolism in primary normal human oral epithelial cells

The ability of tobacco smoke (TS) to modulate phase I and II enzymes and affect metabolism of tobacco carcinogens is likely an important factor in its carcinogenicity. For the first time several types of TS particulates (TSP) were compared in different primary cultured human oral epithelial cells (NOE) for their abilities to affect metabolism of the tobacco carcinogen, (BaP) to genotoxic products, and expression of drug metabolizing enzymes. TSP from, reference filtered (2RF4), mentholated (MS), reference unfiltered, (IR3), ultra low tar (UL), and cigarettes that primarily heat tobacco (ECL) were tested. Cells pretreated with TSP concentrations of 0.2-10 μg/ml generally showed increased rates of BaP metabolism; those treated with TSP concentrations above 10 μg/ml showed decreased rates. Effects of TSPs were similar when expressed on a weight basis. Weights of TSP/cigarette varied in the order: MS≈IR3>2RF4>ECL>UL. All TSPs induced the phase I proteins, cytochrome P450 1A1 (CYP1A1) and 1B1 (CYP1B1), phase II proteins, NAD(P)H dehydrogenase quinone 1 (NQO1), and microsomal glutathione S-transferase 1 (MGST1), and additionally, hydroxysteroid (17-beta) dehydrogenase 2 (HSD17B2), as assessed by qRT-PCR. The pattern of gene induction at probable physiological levels favored activation over detoxification.

Mutagenicity of 11 cigarette smoke condensates in two versions of the mouse lymphoma assay

Cigarette smoke condensate (CSC) is genotoxic in nearly all assays in which it has been tested. In this study, we investigated the mutagenicity of 11 CSCs using the microwell and soft-agar versions of the mouse lymphoma assay (MLA). These CSCs were prepared from commercial or experimental cigarettes, 10 of them were produced using International Organisation for Standardisation (ISO) conditions and one CSC was generated using intense Massachusetts Department of Public Health (MDPH) conditions. In the presence of rat liver S9, the L5178Y/Tk(+/-) mouse lymphoma cells were treated with 11 CSCs at different concentrations (25-200 μg/ml) for 4 h. All CSCs resulted in dose-dependent increases of both cytotoxicity and mutagenicity in both versions of the MLA. The mutagenic potencies of the CSCs were calculated as mutant frequency per microgram CSC from the slope of the linear regression of the dose-response curves and showed no correlations with the tar yield of the cigarette or nicotine concentrations of the CSCs. Comparing two CSCs produced from the same commercial cigarettes using two different smoking conditions, the one generated under ISO conditions was more mutagenic than the other generated under intense conditions on a per microgram CSC basis. We also examined the loss of heterozygosity (LOH) at four microsatellite loci spanning the entire chromosome 11 for the mutants induced by 11 CSCs. The most common type of mutation observed was LOH with chromosome damage spanning less than ∼34 Mbp. These results indicate that the MLA identifies different genotoxic potencies among a variety of CSCs and that the results from both versions of the assay are comparable.

In vitro micronucleus assay for cigarette smoke using a whole smoke exposure system: a comparison of smoking regimens

Previous studies on the biological assessment of cigarette smoke (CS) mainly focused on the total particulate matter (TPM) collected using a Cambridge filter or gas vapor phase (GVP) bubbled through phosphate-buffered saline (PBS). To study the effects of native CS in vitro, direct exposure methods have been developed. Meanwhile, in vitro micronucleus (MN) assays have been reported to evaluate the mutagenicity of CS. The objective of this research is to investigate the MN-inducing activity of whole smoke (WS) and GVP using a whole smoke exposure system, CULTEX((R)), which allows direct exposure of cultured cells to native CS at the air/liquid interface (ALI). CS was generated according to the International Organization for Standardization (ISO; 35ml, 2s, once per 60s) or the Health Canada Intensive (HCI; 55ml, 2s, once per 30s, with complete ventilation block) regimens and Chinese hamster lung (CHL/IU) cells were then exposed to this smoke. Dosages were adjusted according to the amount of smoke entering the actual exposure position. Under both smoking regimens, WS and GVP from 2R4F reference cigarettes induced MN responses. The concept of the dosage and similar dose-response relationships between theoretical and monitored dosage values under the two regimens enabled us to compare the MN-inducing activities of cigarettes in the direct exposure assay, even in the case of various experimental settings or different TPM amounts. MN-inducing activities of 2R4F under the ISO regimen seemed to be higher than those under HCI estimated by the TPM equivalent calculated values.

Comparison between two kinds of cigarette smoke condensates (CSCs) of the cytogenotoxicity and protein expression in a human B-cell lymphoblastoid cell line using CCK-8 assay, comet assay and protein microarray

The differences of the cytogenotoxicity and proteins expression of human B-cell lymphoblastoid cells exposed to cigarette smoke condensates (CSCs) from two kinds of cigarettes were detected with CCK-8 assay, comet assay, protein microarray and western blot assay in vitro. Human B-cell lymphoblastoid cell line was exposed to CSCs from two cigarettes (which delivers approximately 3mg tar, 0.3mg nicotine, 3mg CO per cigarette for cigarette 1 and 15mg tar, 1.3mg nicotine, 15mg CO per cigarette for cigarette 2), and the exposure doses were 2.5, 5.0, 7.5, 10.0 and 12.5x10(-3)cigarettes/ml of CSCs for 24h in CCK-8 assay, 6.0, 8.0, 10.0, 12.0 and 14.0x10(-3)cigarettes/ml of CSCs for 4h in comet assay, and 10.0x10(-3)cigarettes/ml of CSCs for 4h in protein levels analysis. The results of CCK-8 assay and comet assay in the present study suggested that the cytogenotoxicity in cigarette 2 group was significantly higher than that in cigarette 1 group. The results of protein microarray and western blot assay showed that there were the differences of the expression levels of four proteins (i.e., RAR-beta, 14-3-3 sigma, XPF, and p57(Kip2) Ab-7) between cigarette 1 group and cigarette 2 group. Hence, it is possible that the RAR-beta, 14-3-3 sigma, XPF, and p57(Kip2) Ab-7 proteins serve as the molecular biomarkers in studying the cytogenotoxicity induced by CSCs.

Evaluation of in vitro assays for assessing the toxicity of cigarette smoke and smokeless tobacco

BACKGROUND

In vitro toxicology studies of tobacco and tobacco smoke have been used to understand why tobacco use causes cancer and to assess the toxicologic impact of tobacco product design changes. The need for toxicology studies has been heightened given the Food and Drug Administration's newly granted authority over tobacco products for mandating tobacco product performance standards and evaluate manufacturers' health claims about modified tobacco products. The goal of this review is to critically evaluate in vitro toxicology methods related to cancer for assessing tobacco products and to identify related research gaps.

METHODS

PubMed database searches were used to identify tobacco-related in vitro toxicology studies published since 1980. Articles published before 1980 with high relevance also were identified. The data were compiled to examine (a) the goals of the study, (b) the methods for collecting test substances, (c) experimental designs, (d) toxicologic end points, and (e) relevance to cancer risk.

RESULTS

A variety of in vitro assays are available to assess tobacco smoke that address different modes of action, mostly using non-human cell models. However, smokeless tobacco products perform poorly in these assays. Although reliable as a screening tool for qualitative assessments, the available in vitro assays have been poorly validated for quantitative comparisons of different tobacco products. Assay batteries have not been developed, although they exist for nontobacco assessments. Extrapolating data from in vitro studies to human risks remains hypothetical.

CONCLUSIONS

In vitro toxicology methods are useful for screening toxicity, but better methods are needed for today's context of regulation and evaluation of health claims.

Cytotoxicity, mutagenicity, and tumorigenicity of mainstream smoke from three reference cigarettes machine-smoked to the same yields of total particulate matter per cigarette

The particle phase of mainstream smoke from three types of cigarettes was investigated in vitro in the Neutral Red cytotoxicity assay and the Salmonella typhimurium Reverse Mutation Assay (Ames Assay) and in vivo in the two-stage dermal tumorigenicity assay (Skin Painting Assay) in SENCAR mice. The cigarettes used were the Reference Cigarettes 1R5F, 2R4F, and 2R1F from the University of Kentucky, USA, which, when smoked according to the smoking regimen defined by the International Standards Organization (ISO), produce a yield of approximately 2, 12, and 26 mg total particulate matter (TPM)/cigarette, respectively. All cigarettes were machine smoked according to ISO and then again in such a way that the TPM yields per cigarette equaled the ISO TPM yields of the other two cigarette types. The TPM from cigarettes with inherently different smoke yields showed similar in vitro toxicity and in vivo toxicity when, with different smoking regimens, these cigarettes were smoked to the same TPM yield. More intensive smoking conditions were associated with lower in vitro and in vivo activity per gram of TPM. The strongest decrease, and the tightest correlation, in this regard was observed for dermal tumorigenicity (tumor incidence).

Assessing cytogenotoxicity of cigarette smoke condensates using three in vitro assays

Cigarette smoke condensates (CSCs) are complex mixed compounds that contain both direct and indirect mutagens/carcinogens. To detect genotoxicity of CSCs in vitro, a combination of various enzymes (e.g. activation and detoxification enzymes) called S9 is usually added. However, as S9 may induce cytotoxicity in target cells, it is unclear whether the addition of S9 can impact CSC-induced toxicity. Here, differences in cytogenotoxicity between CSCs in the presence or absence of S9 were studied using three in vitro assays (neutral red uptake assay, comet assay, and TCR gene mutation test) in human peripheral lymphocytes, which were exposed to CSCs at doses of 25, 50, 75, 100 and 125 microg/ml for 4 h. Assay results showed that both CSCs + S9 or CSCs - S9 could induce a dose-dependent elevation of cytogenotoxic effects in human lymphocytes with some differences between the two groups. The cytogenotoxicity induced by CSCs - S9 was significantly higher than that induced by CSCs + S9 in all three assays. The comet and NRU assays revealed that a dose-response relationship of cytogenotoxicity induced by CSCs + S9 was less typical than that induced by CSCs - S9, possibly due to specific cytogenotoxic agents in CSCs and enzymes contained in the S9 mixture. Thus, the three in vitro assays used in the present study are suitable for detecting cytogenotoxic effects in human lymphocytes induced by CSCs. Furthermore, the cytogenotoxicity induced by both CSCs + S9 and CSCs - S9 should be measured simultaneously when assessing and comparing the biological activity of different CSCs.

Cigarette smoke condensate and total particulate matter severely disrupts physiological angiogenesis

The cigarette smoke condensate (CSC) and total particulate matter (TPM) in cigarette smoke is extremely toxic and may produce several pathologies. In our study, we used a chicken chorioallantoic membrane assay (CAM) to study the toxicological effects of CSC and TPM on different aspects of angiogenesis. CSC and TPM from four different commercial filtered cigarettes were applied to the CAMs on day 6 of incubation. Macroscopic vascular transformations were observed among all treated CAMs. The application of CSC disks caused obliteration of main blood vessels, while the entire architecture of the secondary and tertiary vasculature was completely destroyed. Likewise, the application of TPM from all brands of cigarette caused the disproportionate thinning of all primary and secondary blood vessels. A reduction in the total area and diameter of the primary, secondary, and tertiary blood vessels was observed after treatment with CSC and TPM. Histological evaluations revealed the loss of ectodermal and mesodermal integrity with both types of treatments. We also noted a profound inflammatory reaction restricted to the disk area with a novel filopodial deformity of the endoderm in the CSC treated groups. Scanty capillary plexus formation, deterioration of the extracellular matrix, and delayed migration of blood vessels were prominent findings among all treated groups. Results obtained from the CSC treated groups were more localized, while more generalized results were recorded in the TPM treated groups. Special caution should be taken for the presence of CSC and TPM while smoking during pregnancy or after surgery because it may severely affect the process of angiogenesis, which is vital to the maintenance of pregnancy and wound healing.

Mutagenicity of native cigarette mainstream smoke and its gas/vapour phase by use of different tester strains and cigarettes in a modified Ames assay

The "Bacterial Reverse Mutation Assay" is generally accepted to analyse the genotoxic capacity of single compounds or complex mixtures such as cigarette-smoke condensates. With an adapted and modified Ames assay, the mutagenicity of native cigarette mainstream whole smoke (WS) and its gas/vapour phase (GVP) was studied. The bacteria were directly exposed to the smoke in a CULTEX1 system closely connected to a smoking robot (VC10). A variety of standard tester strains (TA98, TA100, TA1535, TA1537, TA1538, TA102, WP2uvrApKM101) and descendants of TA98 (YG1021, YG1024, YG1041) and TA100 (YG1026, YG1029 and YG1042) were exposed to whole and filtered smoke of the research cigarette K2R4F to find the most sensitive strains for analysing the mutagenic activity of these test atmospheres. Mutagenicity of WS was detected by TA98, TA100 and their YG descendant strains as well as by WP2uvrApKM101 in the presence of S9 mix. The GVP induced a mutagenic signal in TA100, YG1029 and YG1042 and WP2uvrApKM101 only in the absence of S9 mix. To detect mutagenicity in WS the presence of the plasmid pKM101 is required and a frame-shift mutation is more effective than a missense mutation. To detect mutagenicity in GVP, the presence of the plasmid pKM101 and a missense mutation are required. The differentiating capacity of this modified Ames assay was demonstrated by exposing strain TA98 to WS and TA100 to the GVP of cigarettes with different tar content. The mutagenic activity of WS and the GVP increased with rising tar content of the cigarettes with two exceptions in WS. Thus, the concept of tar content alone is misleading and does not reflect the mutagenic activity of a cigarette.

Toxicological analysis of low-nicotine and nicotine-free cigarettes

Low-nicotine and nicotine-free cigarettes are commercially available under the brand-name Quest. Some consumers may believe that these are safer cigarettes, and they may smoke more cigarettes or inhale more smoke to compensate for low nicotine yields. Thus, we have studied the toxicological effects of these two cigarettes and compared them with the Kentucky reference cigarette 2R4F. Also, the availability of nicotine-free cigarettes allows for the assessing the role of nicotine in cigarette smoke. In addition to nicotine, some tobacco-specific nitrosamines, aldehydes, and volatile organic compounds were also reduced in the Quest cigarettes compared to the 2R4F. However, aromatic amines were higher in the nicotine-free compared with low nicotine cigarettes. The Ames test revealed that cigarette smoke condensates from the nicotine-free (CSC-F), low nicotine (CSC-L) and 2R4F (CSC-R) cigarettes had a similar mutagenic potency. Exposure to any CSC caused a similar dose-dependent LDH leakage from normal human bronchial epithelial cells. However, CSC-F had more inhibitory effects on the cell growth than CSC-L and CSC-R. Adding nicotine to the CSC-F attenuated this inhibition. Both Quest CSCs decreased gap junction intercellular communication and caused cell cycle arrest. CSC exposure increased cytoplasmic nucleosomes, sub-G1/G0 population and apoptotic comet tails. Proapoptotic protein Bax increased independent of p53 induction after exposure to CSC-F. In conclusion, these studies are not consistent with a perception that low-nicotine or nicotine-free cigarettes may have less toxicity in human cells. Nicotine, as it exists in CSC, attenuates cytotoxicity possibly in part through inhibition of apoptotic pathways.

A modified Ames assay reveals the mutagenicity of native cigarette mainstream smoke and its gas vapour phase

The evaluation of the mutagenic activity of cigarette smoke is mostly based on studies with condensates or extracts in the standard Ames assay. These samples only insufficiently reflect the composition of the actual generated aerosol. Therefore, such atmospheres should be analysed in their native composition to gain a real signal of its mutagenic capacity. Based on the technical difficulties of testing native air contaminants, there are no accepted methods for effective exposure of bacteria under such conditions. Therefore, we established a new experimental approach for direct exposure of bacteria in a modified CULTEX system (Patent no. DE 19801763/PCT/EP99/00295) connected to a smoking machine. This allowed us to investigate the mutagenic activity of native mainstream smoke of the research cigarette K2R4F by exposure of Salmonella Typhimurium strains. In comparison to studies using the plate incorporation assay, the direct exposure of bacteria to smoke on the agar surface enhances contact to the aerosols. By using this modification of the Ames assay, we demonstrate that it is possible to analyse the effects of native whole smoke and the gas vapour phase of cigarettes directly and achieve a dose-dependent induction of revertants. In a number of experiments, the treatment of strains TA98 and TA100 with whole smoke and the gas vapour phase of K2R4F cigarettes resulted in the induction of revertants dependent on the dilution of smoke and the number of cigarettes smoked. Our alternative procedure of exposing bacteria directly to gases and complex mixtures offers new possibilities in the field of inhalation genotoxicology for the evaluation of genotoxicity in the Ames assay.

Effect of smoking conditions and methods of collection on the mutagenicity and cytotoxicity of cigarette mainstream smoke

There is a history for the use of in vitro bioassays to assess the toxicological properties of mainstream cigarette smoke (MSS). The results described in the literature were, for the most part, obtained with MSS collected under Federal Trade Commission (FTC) or International Organization for Standardization (ISO) conditions. However, numerous studies have shown that smokers smoke their cigarettes more intensely (e.g., they take larger puffs and/or more frequent puffs and/or partially occlude filter ventilation) than they are smoked on smoking machines operated under FTC (or ISO) conditions. It has also been reported that MSS composition changes with changes in smoking conditions. Furthermore, some governmental agencies have adopted regulations that specify more intensive protocols (i.e., Health Canada Intensive, HCI) for the collection of MSS for in vitro toxicological assays. Consequently, the performance of the Ames assay (TA98+S9, TA100+S9) and neutral red uptake assay under ISO and HCI protocols was studied with two blended (KR1R4F/KR2R4F, KR1R5F) and one flue-cured (CIM-7) reference cigarettes. The main outcome was when results were reported on a per milligram TPM (that portion of the mainstream smoke which is trapped in the smoke trap, expressed as milligrams per cigarette) basis generated under ISO conditions was more mutagenic and more cytotoxic than was TPM generated under HCI conditions. However, the decrease in biological activity could not be explained only by the increased in the water content of the TPM on going from ISO to HCI smoking conditions, and the results may be influenced by differences in smoke chemistry as a result of differing smoke collection systems.

Early specific free radical-related cytotoxicity of gas phase cigarette smoke and its paradoxical temporary inhibition by tar: An electron paramagnetic resonance study with the spin trap DEPMPO

Electron paramagnetic resonance (EPR) spin trapping studies demonstrated aqueous tar particulate matter (TPM) and gas phase cigarette smoke (GPCS) to behave as different sources of free radicals in cigarette smoke (CS) but their cytotoxic implications have been only assessed in CS due to its relevance to the natural smoking process. Using a sensitive spin trapping detection with 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline-N-oxide (DEPMPO), this study compared the respective roles of CS- and GPCS-derived free radicals on smoke-induced cytotoxicity and lipid peroxidation of filtered and unfiltered, machine-smoked experimental and reference cigarettes yielding a wide range of TPM yields. In buffer bubbled with CS the DEPMPO/superoxide spin adduct was the major detected nitroxide. Use of appropriate control experiments with nitric oxide radical (NO*) or carbonyl sulfide, and a computer analysis of spin adduct diastereoisomery showed that the hydroxyl radical (HO*) adduct of DEPMPO seen in GPCS-bubbled was rather related to metal-catalyzed nucleophilic synthesis than to direct HO* trapping. Unexpectedly a protective effect of TPM on murine 3T3 fibroblasts was observed in early (<3h) free radical-, GPCS-induced cell death, and carbon filtering decreased free radical formation, toxicity and lipid peroxidation in three cell lines (including human epithelial lung cells) challenged with GPCS. These results highlight an acute, free radical-dependent, harmful mechanism specific to the GPCS phase, possibly involving NO* chemistry, whose physical or chemical control may be of great interest with the aim of reducing the toxicity of smoke.

Smoking and reproduction: the oviduct as a target of cigarette smoke

The oviduct is an exquisitely designed organ that functions in picking-up ovulated oocytes, transporting gametes in opposite directions to the site of fertilization, providing a suitable environment for fertilization and early development, and transporting preimplantation embryos to the uterus. A variety of biological processes can be studied in oviducts making them an excellent model for toxicological studies. This review considers the role of the oviduct in oocyte pick-up and embryo transport and the evidence that chemicals in both mainstream and sidestream cigarette smoke impair these oviductal functions. Epidemiological data have repeatedly shown that women who smoke are at increased risk for a variety of reproductive problems, including ectopic pregnancy, delay to conception, and infertility. In vivo and in vitro studies indicate the oviduct is targeted by smoke components in a manner that could explain some of the epidemiological data. Comparisons between the toxicity of smoke from different types of cigarettes, including harm reduction cigarettes, are discussed, and the chemicals in smoke that impair oviductal functioning are reviewed.

Analysis of complex mixtures--cigarette smoke

Mainstream cigarette smoke is a complex mixture that is inhaled into the respiratory system. The physical characteristics and chemical composition of mainstream smoke are reviewed and briefly compared with that of sidestream smoke. Special attention is paid to ageing effects and artifact formation during the sampling and testing of cigarette smoke, with specific examples of artifact formation during sampling discussed (nitrogen dioxide, methyl nitrite, etc.). Historically, the generation of cigarette smoke for chemical and biological testing has been based on standard smoke generation procedures that are intended for product comparisons. More recently, emerging global regulations have called for alternative smoke generation methods, with emphasis on results relevant to conditions of product use, e.g., estimates of maximum smoke emissions. Strategies for establishing such alternative smoke generation methods are discussed and the potential effects of alternative smoking conditions on analytical accuracy and precision are addressed. Current regulatory requirements that include Hoffmann analyte analysis (i.e., constituents reported to be associated with the risks of cigarette smoking) are also summarized and the potential effect of alternative smoke generation methods on individual constituent yields considered. Finally, a limited critique of emerging regulation that relates to mainstream cigarette smoke measurements, including a discussion of recent WHO recommendations, is offered.

Inhibitory effects of cigarette smoke on glial inducible nitric oxide synthase and lack of protective properties against oxidative neurotoxins in vitro

Epidemiological studies consistently report an inverse correlation between cigarette smoking and associated risk for Parkinson's disease (PD). The degeneration of dopaminergic neurons may involve the toxic metabolic products of glial cell monoamine oxidase (MAO) and inducible nitric oxide synthase (iNOS). This study evaluates the direct protective effects of cigarette smoke (CS) against potential neurotoxic products of MAO, such as 1-methyl-4-phenylpyridinium (MPP+), 6-hydroxydopamine (6-OHDA) and hydrogen peroxide (H2O2) in brain neuroblastoma. Moreover, the effects of CS were also evaluated on endotoxin/cytokine activated glioma iNOS protein expression and MAO enzyme activity. Cigarette smoke condensates (CSCs) were acquired from Marlboro 20 Class A and Kentucky 2R4F reference research (2R4F) cigarettes. The CSCs did not protect against 6-OHDA or H2O2 toxicity in neuroblastoma, and exhibited a very mild protective effect [approximately 10%] against MPP+. Neither CSC demonstrated antioxidant capability, but conversely contained high concentration of NO2-. Paradoxically, in glioma cells, iNOS protein expression and endogenous enzymatic NO2- production were significantly blocked by both CSCs. Both CSCs also inhibited glioma MAO-A and MAO-B [1.4.3.4]. Kinetic analysis indicated that 2R4F-CSC displayed competitive inhibition and the Marlboro-CSC exerted potent competitive and non-competitive inhibition. In conclusion, these data suggest that cigarette smoke does not appear to directly protect against the toxicity of the selected neurotoxins. In contrast, CS exerts pronounced effects on glia, whereby its presence can simultaneously attenuate cytokine induction of iNOS and MAO.