Gap junction intercellular communication and cytotoxicity in normal human cells after exposure to smoke condensates from cigarettes that burn or primarily heat tobacco

Connexins and Gap Junctions in Cancer of the Urinary Tract

This review focuses on connexins and nexus or gap junctions in the genesis, progression, and therapy of carcinomas of the human urinary tract. Some decades ago, the idea was born that gap junctional intercellular communication might prevent both the onset and the progression of cancer. Later evidence indicated that, on the contrary, synthesis and the presence of connexins as a prerequisite for gap junctional intercellular communication might promote the occurrence of cancer and metastases. The research history of urinary bladder cancer is a good example of the development of scientific perception. So far, the role of gap junctional intercellular communication in carcinogenesis and cancer progression, as well as in therapeutical approaches, remains unclear.

Smoking and Lung Cancer: Future Research Directions

The aim of future research in this area is to provide the mechanistic understanding and the tools for effective prevention, early diagnosis, and therapy of lung cancer. With the established causal link between cigarette smoking and the risk of developing lung cancer, the most effective prevention is certainly not to smoke. A much better mechanistic understanding of lung cancer and its variability will support the development and evaluation of potentially reduced risk products for those who maintain smoking as well as for the development of early diagnostic tools and targeted therapies. Because of the complexity of lung cancer and the long duration for its development, nonclinical and clinical research efforts need to complement each other. Recent promising advances in this research area are the understanding of the interaction between genotoxic and epigenetic effects of smoking, the development of laboratory animal models for lung tumorigenesis by smoke inhalation, the unraveling of molecular pathways and signatures in clinical lung cancer research useful for developing diagnostic tools and therapeutic approaches, and the first successful therapy for lung cancer—although less suitable for smokers. The above—in combination with emerging data sets from explorative non-clinical and clinical studies as well as improved modeling approaches—are setting the stage for accelerated progress towards developing successful early diagnostic tools and therapies as well as for the assessment of new consumer products with potentially reduced risk.

A Safer Cigarette? A Comparative Study. A Consensus Report

This special issue describes the scientific progress and scientific review process to develop a safer cigarette. A peer-review panel, the ECLIPSE Expert Panel, was convened to critically review the potential health hazards of this new cigarette to a reference, conventional cigarette that bums tobacco. This new cigarette is lit and smoked much like other cigarettes, but it burns very little tobacco and paper. Also, unlike other cigarettes, it does not burn down to a butt, nor does it produce loose ash. Such a product would be expected to have less "tar" and other combustion products than cigarettes that burn tobacco and should greatly reduce any sidestream smoke. This panel assessed the chemistry and physical characteristics, as well as the biological activity, of this new cigarette.

Impact of obesity on 7,12-dimethylbenz[a]anthracene-induced altered ovarian connexin gap junction proteins in female mice

The ovarian gap junction proteins alpha 4 (GJA4 or connexin 37; CX37), alpha 1 (GJA1 or connexin 43; CX43) and gamma 1 (GJC1 or connexin 45; CX45) are involved in cell communication and folliculogenesis. 7,12-dimethylbenz[a]anthracene (DMBA) alters Cx37 and Cx43 expression in cultured neonatal rat ovaries. Additionally, obesity has an additive effect on DMBA-induced ovarian cell death and follicle depletion, thus, we investigated in vivo impacts of obesity and DMBA on CX protein levels. Ovaries were collected from lean and obese mice aged 6, 12, 18, or 24 wks. A subset of 18 wk old mice (lean and obese) were dosed with sesame oil or DMBA (1mg/kg; ip) for 14days and ovaries collected 3days thereafter. Cx43 and Cx45 mRNA and protein levels decreased (P<0.05) after 18 wks while Cx37 mRNA and protein levels decreased (P<0.05) after 24 wks in obese ovaries. Cx37 mRNA and antral follicle protein staining intensity were reduced (P<0.05) by obesity while total CX37 protein was reduced (P<0.05) in DMBA exposed obese ovaries. Cx43 mRNA and total protein levels were decreased (P<0.05) by DMBA in both lean and obese ovaries while basal protein staining intensity was reduced (P<0.05) in obese controls. Cx45 mRNA, total protein and protein staining intensity level were decreased (P<0.05) by obesity. These data support that obesity temporally alters gap junction protein expression and that DMBA-induced ovotoxicity may involve reduced gap junction protein function.

Regulation of gene expression by tobacco product preparations in cultured human dermal fibroblasts

Skin fibroblasts comprise the first barrier of defense against wounds, and tobacco products directly contact the oral cavity. Cultured human dermal fibroblasts were exposed to smokeless tobacco extract (STE), total particulate matter (TPM) from tobacco smoke, or nicotine at concentrations comparable to those found in these extracts for 1h or 5h. Differences were identified in pathway-specific genes between treatments and vehicle using qRT-PCR. At 1h, IL1α was suppressed significantly by TPM and less significantly by STE. Neither FOS nor JUN was suppressed at 1h by tobacco products. IL8, TNFα, VCAM1, and NFκB1 were suppressed after 5h with STE, whereas only TNFα and NFκB1 were suppressed by TPM. At 1h with TPM, secreted levels of IL10 and TNFα were increased. Potentially confounding effects of nicotine were exemplified by genes such as ATF3 (5h), which was increased by nicotine but suppressed by other components of STE. Within 2h, TPM stimulated nitric oxide production, and both STE and TPM increased reactive oxygen species. The biological significance of these findings and utilization of the gene expression changes reported herein regarding effects of the tobacco product preparations on dermal fibroblasts will require additional research.

Characterization of a gap-junctional intercellular communication (GJIC) assay using cigarette smoke

Inhibition of gap-junctional intercellular communication (GJIC) via exposure to various toxic substances has been implicated in tumor promotion. In the present study, cigarette smoke total particulate matter (TPM), a known inhibitor of GJIC, were used to characterize a new GJIC screening assay in three independent experiments. The main features of this assay were automated fluorescence microscopy combined with non-invasive parachute technique. Rat liver epithelial cells (WB-F344) were stained with the fluorescent dye Calcein AM (acetoxymethyl) and exposed to TPM from the Kentucky Reference Cigarette 2R4F (a blend of Bright and Burley tobaccos) and from two single-tobacco cigarettes (Bright and Burley) for 3h. Phorbol-12-myristate-13-acetate (TPA) was used as positive control and 0.5% dimethyl sulfoxide (DMSO) as solvent control. The transfer of dye to adjacent cells (percentage of stained cells) was used as a measure of cellular communication. A clear and reproducible dose-response of GJIC inhibition following TPM exposure was seen. Reproducibility and repeatability measurements for the 2R4F cigarette were 3.7% and 6.9%, respectively. The half-maximal effective concentration values were 0.34ng/ml for TPA, 0.050mg/ml for the 2R4F, 0.044mg/ml for the Bright cigarette, and 0.060mg/ml for the Burley cigarette. The assay was able to discriminate between the two single-tobacco cigarettes (P<0.0001), and between the single-tobacco cigarettes and the 2R4F (P=0.0008, 2R4F vs. Burley and P<0.0001, 2R4F vs. Bright). Thus, this assay can be used to determine the activity of complex mixtures such as cigarette smoke with high throughput and high precision.

The use of in vitro systems to assess cancer mechanisms and the carcinogenic potential of chemicals

Carcinogenesis is a highly complex, multi-stage process that can occur over a relatively long period before its clinical manifestation. While the sequence in which a cancer cell acquires the necessary traits for tumour formation can vary, there are a number of mechanisms that are common to most, if not all, cancers across the spectrum of possible causes. Many aspects of carcinogenesis can be modelled in vitro. This has led to the development of a number of mechanistically driven, cell-based assays to assess the pro-carcinogenic and anti-carcinogenic potential of chemicals. A review is presented of the current in vitro models that can be used to study carcinogenesis, with examples of cigarette smoke testing in some of these models, in order to illustrate their potential applications. We present an overview of the assays used in regulatory genotoxicity testing, as well as those designed to model other aspects that are considered to be hallmarks of cancer. The latter assays are described with a view to demonstrating the recent advances in these areas, to a point where they should now be considered for inclusion in an overall testing strategy for chemical carcinogens.

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.

Gap junctional intercellular communication as a target for liver toxicity and carcinogenicity

Direct communication between hepatocytes, mediated by gap junctions, constitutes a major regulatory platform in the control of liver homeostasis, ranging from hepatocellular proliferation to hepatocyte cell death. Inherent to this pivotal task, gap junction functionality is frequently disrupted upon impairment of the homeostatic balance, as occurs during liver toxicity and carcinogenicity. In the present paper, the deleterious effects of a number of chemical and biological toxic compounds on hepatic gap junctions are discussed, including environmental pollutants, biological toxins, organic solvents, pesticides, pharmaceuticals, peroxides, metals and phthalates. Particular attention is paid to the molecular mechanisms that underlie the abrogation of gap junction functionality. Since hepatic gap junctions are specifically targeted by tumor promoters and epigenetic carcinogens, both in vivo and in vitro, inhibition of gap junction functionality is considered as a suitable indicator for the detection of nongenotoxic hepatocarcinogenicity.

Two new lipoaminoacids with complementary modes of action: new prospects to fight out against skin aging

The mode of action of two cosmetic active ingredients (AIs), palmitoyl glycine (PG) and cocoyl alanine (CA) was studied with cDNA array experiments and quantitative PCR confirmations, which were performed on experimentally aged human fibroblasts. These preliminary studies revealed complementary profiles. Thus, specific supplementary investigations were then carried out for each AI. Protocols used were based either on in vitro models: (i) biochemical assays, (ii) monolayer cell culture (primary human fibroblasts and keratinocytes) and (iii) the model of capillary-like tube formation by human endothelial cells or on ex vivo models, i.e. topically treated skin explants and both immunohistochemical and Chromameter(TM) investigations. New prospects are proposed to fight out against skin aging. Indeed, PG and CA showed complementary properties and thus enabled a regulation or a restoration effect on main aging-associated disorders. Thus, they can not only act on tissue architecture, cell-cell interactions and extracellular matrix protection but also on inflammation, cell longevity, skin immune system protection, skin radiance and stem cell survey. Finally, a clinical trial performed on Caucasian women confirmed AI anti-wrinkle efficacy, which was superior to that of a market reference ingredient. In the future, complementary experiments enabling a better understanding of the aging-induced decline of epidermal stem cells would be of a great interest.

Toxicity Assessment of Industrial Chemicals and Airborne Contaminants: Transition fromIn VivotoIn VitroTest Methods: A Review

Exposure to occupational and environmental contaminants is a major contributor to human health problems. Inhalation of gases, vapors, aerosols, and mixtures of these can cause a wide range of adverse health effects, ranging from simple irritation to systemic diseases. Despite significant achievements in the risk assessment of chemicals, the toxicological database, particularly for industrial chemicals, remains limited. Considering there are approximately 80,000 chemicals in commerce, and an extremely large number of chemical mixtures, in vivo testing of this large number is unachievable from both economical and practical perspectives. While in vitro methods are capable of rapidly providing toxicity information, regulatory agencies in general are still cautious about the replacement of whole-animal methods with new in vitro techniques. Although studying the toxic effects of inhaled chemicals is a complex subject, recent studies demonstrate that in vitro methods may have significant potential for assessing the toxicity of airborne contaminants. In this review, current toxicity test methods for risk evaluation of industrial chemicals and airborne contaminants are presented. To evaluate the potential applications of in vitro methods for studying respiratory toxicity, more recent models developed for toxicity testing of airborne contaminants are discussed.

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.

Gene expression in normal human bronchial epithelial (NHBE) cells following in vitro exposure to cigarette smoke condensate

Cigarettes that burn tobacco produce a complex mixture of chemicals, including mutagens and carcinogens. Cigarettes that primarily heat tobacco produce smoke with marked reductions in the amount of mutagens and carcinogens and demonstrate reduced mutagenicity and carcinogenicity in a battery of toxicological assays. Chemically induced oxidative stress, DNA damage, and inflammation may alter cell cycle regulation and are important biological events in the carcinogenic process. The objective of this study was to characterize and compare the effects of smoke condensates from cigarettes that burn tobacco and those that primarily heat tobacco on gene expression in NHBE cells. For this comparison, we used quantitative RT/PCR and further evaluated the effects on cell cycling using flow cytometry. Cigarette smoke condensates (CSCs) were prepared from Kentucky 1R4F cigarettes (a tobacco-burning product designed to represent the average full-flavor, low "tar" cigarette in the US market) and Eclipse (a cigarette that primarily heats tobacco) using FTC machine smoking conditions. The CSC from 1R4F cigarettes induced statistically significant increases in the mRNA levels of genes responsive to DNA damage (GADD45) and involved in cell cycle regulation (p21;WAF1/CIP1), compared to the CSC from Eclipse cigarettes. In addition, genes coding for cyclooxygenase-2 (COX-2) and interleukin 8 (IL-8), which are associated with oxidative stress and inflammation, respectively, were increased statistically significantly more by CSC from 1R4F than by that from Eclipse. Furthermore, a dose-dependent increase in IL-8 protein secretion into cell culture media was stimulated by 1R4F exposure, whereas minimal IL-8 protein was secreted after Eclipse treatment. The biological relevance of the differential effect on gene expression was reflected in differential cell cycle regulation, as cells exposed to 1R4F CSC exhibited more significant S phase and G2 phase accumulation than cells exposed to Eclipse CSC. These data indicate that the simplified smoke chemistry of the tobacco-heating Eclipse cigarette yields statistically significant reductions in the expression of key genes involved in DNA damage, oxidative stress, inflammatory response, and cell cycle regulation in normal human bronchial epithelial cells compared to a representative tobacco-burning cigarette.

Comparative assessment of toxicities of mainstream smoke from commercial cigarettes

Three cigarette types were compared using an experimental approach for quantifying selected toxicological effects of diluted fresh whole cigarette mainstream smoke in vitro. The test procedure involved automatic smoking of cigarettes according to the FTC/ISO standard, online monitoring of generated smoke aerosols with respect to particulate and gas-phase components, and direct exposure of a human type II-like lung cell line (A549) using exposure conditions relevant to human smoking. Test specimens were the K1R4F standard research cigarettes (9.2 mg tar/cigarette) and two commercial European light filter cigarettes (brand 1, brand 2) having the same tar content (7.0 mg/cigarette). As a representative of the toxicological effect of smoke, intracellular reduced glutathione was analyzed directly after exposure of cells. Results revealed statistically significant different quantitative effects with regard to glutathione depletion when comparing whole smoke and filtered smoke from all three cigarettes. ED50 values revealed a depletion of reduced glutathione by brand 1 cigarettes that was more than twice the depletion caused by brand 2 cigarettes on a per cigarette basis. Also, quantitatively different effects were found on a per particle and on a per CO concentration basis using whole or filtered smoke from the cigarettes. We conclude that the methods we employed provide sensitive and reproducible ways of detecting differences in the toxicological action of smoke from various types of cigarettes.

A responsive, sensitive, and reproducible dermal tumor promotion assay for the comparative evaluation of cigarette smoke condensates

The mouse dermal initiation/promotion bioassay has been used for several decades to study cigarette smoke condensates (CSCs). However, these studies have used highly variable methodologies that differ in the manner of CSC collection, duration of treatment, mouse strain, number of mice and endpoints measured. In this report, a protocol that uses female SENCAR mice and standardizes many of the procedures is presented. A reference cigarette (University of Kentucky 1R4F), readily available to researchers, was used. This report presents the combined data from four independent studies. Female, SENCAR mice (40/group) were treated with a single dose (75microg) of dimethylbenz[a]anthracene (DMBA) as an initiator, followed 1 week later by treatment (three times/week) with 10, 20 or 40mg "tar"/application of 1R4F CSC for 29 weeks. There were no treatment-related effects on body weights. Histological diagnosis of all masses at study termination indicated a dose-dependent increase in the number of tumor-bearing mice and total tumor number. These studies support the conclusion that the 1R4F cigarette is suitable for use as a reference standard and the protocol presented is an appropriate and standardized model suitable for the comparative evaluation of CSC.

A review of in vitro methods to assess the biological activity of tobacco smoke with the aim of reducing the toxicity of smoke

In the last few years tobacco companies have been developing several research strategies in order to reduce the risks associated with smoking. These strategies include, for example, the refining of alternative cigarette designs that reduce the amount of hazardous chemicals in the mainstream smoke by introducing modified filters, and/or reducing the amount of biologically significant ingredients in tobacco-burning cigarettes. In the last few decades numerous studies have been published to assess the biological activity of tobacco smoke using in vivo and in vitro test systems. In this scenario a general scientific consensus on how to measure and characterize the risk associated with cigarette smoke is still lacking. Short-term in vitro assays, which are widely accepted by regulatory agencies around the world, are useful tools to evaluate both the biological activity and the progress towards a reduction of tobacco smoke toxicity. These assays could be mainly applied to evaluate cytotoxicity and genotoxicity properties on whole cigarette smoke as well as condensates or fractions of whole smoke. Cytotoxicity induction can be measured as cellular viability and growth rates using different end-points. Otherwise, the target of genotoxicity studies is the DNA molecule. For genotoxicity evaluation, the end-points and cell systems should be chosen from those that are relevant and appropriate as clinical surrogate markers. In this respect, the occurrence of early biological effect markers, such as mutational or clastogenic events (point mutations, frameshifts, micronuclei, SCE, DNA adducts) in bacterial and mammalian cells should be studied in a tiered approach following the guidelines of regulatory agencies. The choice of criteria shall be matter of discussion.

An improved in vitro model for testing the pulmonary toxicity of complex mixtures such as cigarette smoke

Numerous approaches have been employed for testing the biological activity of cigarette smoke in vitro. None of them has managed to expose cultured lung cells in a realistic manner to the complex gaseous and particulate mixture that constitutes cigarette smoke. We have devised a system that makes this possible. The system presented here enables the direct exposure of human lung cells to native, unmodified cigarette mainstream smoke. It consists of a smoking machine, a dilution device for the smoke, analytical devices for online monitoring and a specially adapted exposure module based on the Cultex** cell cultivation system that is equipped with a gas-exposure top. Due to the special design of the exposure device and the optimised exposure conditions, this equipment allows cultured human lung cells to be exposed to freshly generated cigarette mainstream smoke. Exploratory experiments revealed that the smoke could be diluted over a wide concentration range in a reproducible way with respect to gas and particulate phases, and also demonstrated reproducible particle deposition depending on smoke concentration. Furthermore, it was shown that the exposed cells maintained their viability. Native cigarette mainstream smoke induced dose-dependent cellular effects in exposed cells with respect to cellular viability (viable cell number monitored by tetrazolium salt cleavage) and intracellular parameters (ATP and glutathione content). Therefore, fresh, physically and chemically unmodified cigarette mainstream smoke can be tested using this novel system.

Genomic and transcriptional alterations in mouse fetus liver after transplacental exposure to cigarette smoke

The transplacental exposure of fetuses to maternal cigarette smoke may increase the risk of developmental impairments, congenital diseases, and childhood cancer. The whole-body exposure of Swiss mice to environmental cigarette smoke (ECS) during pregnancy decreased the number of fetuses per dam, placenta weight, and fetus weight. ECS increased DNA adducts, oxidative nucleotide alterations, and cytogenetic damage in fetus liver. Evaluation by cDNA array of 746 genes showed that 61 of them were expressed in fetus liver under basal conditions. The oral administration of N-acetylcysteine (NAC) during pregnancy enhanced the expression of three genes only, including two glutathione S-transferases and alpha1-antitrypsin precursor, whose deficiency plays a pathogenetic role in congenital emphysema. Transplacental ECS upregulated the expression of 116 genes involved in metabolism, response to oxidative stress, DNA and protein repair, and signal transduction. NAC inhibited the ECS-related genetic damage and upregulation of most genes. ECS stimulated pro-apoptotic genes and genes downregulating the cell cycle, which may justify growth impairments in the developing fetus. Thus, both genetic and epigenetic mechanisms were modulated by ECS. Moreover, hypoxia-related genes and several oncogenes and receptors involved in proliferation and differentiation of leukocytes were induced in the fetal liver, which also bears hematopoietic functions.

Sharing signals: connecting lung epithelial cells with gap junction channels

Gap junction channels enable the direct flow of signaling molecules and metabolites between cells. Alveolar epithelial cells show great variability in the expression of gap junction proteins (connexins) as a function of cell phenotype and cell state. Differential connexin expression and control by alveolar epithelial cells have the potential to enable these cells to regulate the extent of intercellular coupling in response to cell stress and to regulate surfactant secretion. However, defining the precise signals transmitted through gap junction channels and the cross talk between gap junctions and other signaling pathways has proven difficult. Insights from what is known about roles for gap junctions in other systems in the context of the connexin expression pattern by lung cells can be used to predict potential roles for gap junctional communication between alveolar epithelial cells.

The role of glutathione in the toxicity of smoke condensates from cigarettes that burn or heat tobacco

Inhalation of cigarette smoke aerosol via active smoking is associated with the development of pulmonary inflammation. The cytotoxic potential of cigarette smoke has been hypothetically related to development of pulmonary inflammation since the release of intracellular contents from dead and dying cells has been reported to induce inflammatory foci. In this study, cigarette smoke condensates (CSCs) were prepared from Kentucky 1R4F reference cigarettes and cigarettes that primarily heat tobacco (Eclipse). The two CSCs were then compared for their ability to induce killing in human-hamster A(L) hybrid cells. CSCs prepared from Eclipse were much less cytotoxic than those prepared from reference cigarettes. At 60 microg CSC/ml culture medium, survival for CSC from Eclipse cigarettes was approximately 70% compared with 1% for CSC from burned K1R4F cigarettes. The observed reduction in CSC-Eclipse cytotoxicity toward these mammalian cells is consistent with the previously published observation of a 30% decline in pulmonary white cell count and 40% reduction in visual bronchitis index in human smokers who switched to Eclipse for 2 months. Results with N-acetylcysteine and buthionine-S-R-sulfoximine indicate that glutathione markedly reduces the cytoxicity of both CSCs.

Subchronic inhalation by rats of mainstream smoke from a cigarette that primarily heats tobacco compared to a cigarette that burns tobacco

A subchronic, nose-only inhalation study comparing the potential biological activity of mainstream smoke from a cigarette that primarily heats tobacco (Eclipse) to mainstream smoke from a 1R4F reference cigarette was conducted using Sprague-Dawley rats of each gender. Smoke exposures were for 1 h/day, 5 days/wk for 13 wk, at concentrations of 0, 0.16, 0.32, or 0.64 mg wet total particulate matter (WTPM)/L air. Smoke was generated at the Federal Trade Commission standard of a 2-s puff of 35 ml, taken once per minute. Clinical signs, body and organ weights, clinical chemistry, hematology, carboxyhemoglobin, serum nicotine, plethysmography, gross pathology, and histopathology were determined. Plethysmography indicated that respiratory rate was decreased at all concentrations of 1R4F smoke, but only at the high concentration of Eclipse smoke. Tidal volume was depressed and minute volume was lower for all smoke-exposed rats. Rats exposed to Eclipse smoke inhaled more smoke at the low and mid-concentration exposures than rats exposed to equivalent concentrations 1R4F smoke. Carboxyhemoglobin and serum nicotine were directly related to the exposure concentrations of carbon monoxide (CO) and nicotine in an exposure-dependent manner. Body weights were slightly lower in smoke-exposed rats, while no treatment-related effects were seen in clinical signs, clinical chemistry, hematology, or gross changes at necropsy. The only treatment-related effect seen in organ weights was an increase in heart weight in females in the Eclipse high-concentration exposure group, attributed to higher CO in the Eclipse exposure atmosphere. Higher CO resulted from the lower dilution of Eclipse smoke required to maintain WTPM concentrations equal to those of the 1R4F smoke, and not from a higher CO yield from Eclipse cigarettes. Nasal epithelial hyperplasia and ventral laryngeal squamous metaplasia were noted after exposure to either the 1R4F or Eclipse smoke. The degree of change was less in Eclipse smoke-exposed rats. Lung macrophages were increased to a similar extent in the Eclipse and 1R4F smoke-exposed groups. Brown/gold pigmented macrophages were detected in the lungs of rats exposed to 1R4F smoke, but not those exposed to Eclipse smoke. Subsets of rats from each group were maintained for an additional 13 wk without smoke exposures. Most of the changes noted at the end of the smoke exposures had disappeared, while those that remained were regressing toward normal. Evaluation of these findings indicated the overall biological activity of Eclipse smoke was less than 1R4F smoke at comparable exposure concentrations.