Comparative studies of DNA adduct formation in mice following dermal application of smoke condensates from cigarettes that burn or primarily heat tobacco

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.

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.

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.

Extracts from presumed "reduced harm" cigarettes induce equivalent or greater toxicity in antigen-presenting cells

The tobacco industry has promoted certain cigarette products with claims that their use may be less harmful to the smoker as they purportedly deliver lower amounts of toxic chemicals compared to conventional cigarettes. This study was designed to compare the relative antigen presenting cellular toxicity of Eclipse, a presumed reduced exposure product (PREP) cigarette, when compared with the reference research 3R4F cigarettes (Kentucky University). Utilizing a murine macrophage cell line, murine bone marrow derived dendritic cells (DCs) and human monocyte-derived DCs incubated with extracts generated from Eclipse and Kentucky reference 3R4F cigarettes, we determined the relative toxic effects of the different cigarette smoke extracts on cellular viability, oxidative stress, T-helper-1 (Th-1) polarizing cytokine production and general gene expression. Eclipse and 3R4F cigarette smoke extracts induced equivalent oxidatively-mediated cellular heme oxygenase-1 (HO-1) protein levels in macrophages and DCs. Cellular viability determination demonstrated greater induction of cell death by apoptosis and necrosis by Eclipse extracts in DCs. The production of the key Th-1 polarizing cytokine interleukin-12 (IL-12) by activated DCs or macrophages was suppressed to an equivalent or greater extent by Eclipse extracts. Microarray studies performed on bone marrow derived murine DCs incubated with Eclispe or 3R4F cigarette extracts showed identical genotoxic profiles. These studies imply that presumed reduced harm Eclipse cigarettes induce equivalent or greater antigen presenting cell dysfunction relative to 3R4F cigarettes and illustrate the importance of independent validation and testing of similar products claimed to be associated with reduced toxicity relative to other cigarettes.

Clinical laboratory evaluation of potential reduced exposure products for smokers

Smoking-related cancer and other disease account for more than 400,000 U.S. deaths annually. Smoking cessation reduces smoking-related disease rates, but relapse rates are high. Thus, interest in reducing the harm of continued smoking is growing. Potential reduced exposure products (PREPs) are marketed to reduce smokers' exposure to smoke toxicants such as carbon monoxide (CO) and carcinogens and may be harm reduction tools. New PREPs are proliferating, but past experience with "low-yield" cigarettes that failed to reduce smokers' toxicant exposure suggests that comprehensive evaluation is necessary to predict if these new products are likely to alter the harm caused by smoking. The purpose of the study was to develop clinical laboratory methods for PREP evaluation. Smokers (N = 35) completed four, 5-day conditions that differed by product used: Advance, Eclipse, own brand cigarettes, or no cigarettes. Carcinogen (as assessed by one nitrosamine and one polycyclic aromatic hydrocarbon biomarker) and nicotine exposure were assessed via thrice-weekly urine sampling. Withdrawal symptoms were measured daily, and smoking behavior was assessed on the first and last day of each condition. Relative to own brand, Advance reduced exposure to the nitrosamine NNK and CO, and Eclipse reduced exposure to nicotine and the nitrosamine NNK, increased exposure to CO, and resulted in larger, longer, and more frequent puffs. No smoking reduced exposure to the nitrosamine NNK, CO, and nicotine, whereas withdrawal was elevated (all p values <.05). Clinical laboratory evaluation of PREPs for smokers is valuable for measuring users' smoke toxicant exposure, withdrawal, and smoking behavior and should be incorporated into a comprehensive PREP evaluation strategy.

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.

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.

Effect of ECE and NEP inhibition on cigarette smoke-induced cell proliferation in the rat lung

To investigate the role of endothelins in cigarette smoke-induced cell proliferation, we assessed the effect of two dual nonselective neutral endopeptidase (NEP)/endothelin-converting enzyme (ECE) inhibitors, phosphoramidon and CGS 26303, and of a specific NEP inhibitor, CGS 24592, on cell proliferation in the airways and arterial vasculature of the rat lung. Eight groups of rats were exposed to either room air (group 1, control), the smoke of 10 cigarettes (group 2, smoke only) or groups 1 and 2 in addition to a continuous iv infusion of CGS 24592, CGS 26303, or phosphoramidon (10 mg/kg/24 h). Cigarette smoke produced significant cell proliferation in the airways (epithelium and wall) and in the perialveolar ductular vessels (endothelium and wall). CGS 26303 reduced the smoke-induced proliferation in the endothelium and walls of the vessels adjacent to the alveolar ducts, and in the airway walls, but did not affect proliferation in the airway epithelium. CGS 24592 reduced cell proliferation in the airway wall. Phosphoramidon had no effect. These findings indicate that acute cigarette smoke-induced cell proliferation of the rat airways and pulmonary arterial vessels is mediated, at least in part, through release and actions of endothelins. The effectiveness of the more potent inhibitor, CGS 26303, appears to conform to its site of predominant expression.

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.

Acetaldehyde-stimulated PKC activity in airway epithelial cells treated with smoke extract from normal and smokeless cigarettes

Previously, we have found that acetaldehyde, a volatile component of cigarette smoke, stimulates the protein kinase C (PKC) pathway and inhibits ciliary motility. A "smokeless" cigarette (Eclipse) now exists in which most of the tobacco is not burned, reducing the pyrolyzed components in the extract. We hypothesized that acetaldehyde is a component of cigarette smoke that activates PKC in the airway epithelial cell, and therefore the Eclipse cigarette would not activate epithelial cell PKC. In this study, bovine bronchial epithelial cells (BBEC) were incubated with cigarette smoke extract (CSE) or Eclipse smoke extract (ESE). We found that PKC activity was significantly higher in cells exposed to 5% CSE than cells exposed to 5% ESE or media. When acetaldehyde levels of both extracts were measured by gas chromatography, CSE was found to have 15-20 times greater concentration (microM) of acetaldehyde than ESE. When BBEC were treated with 5% CSE, ciliary beating was further decreased from baseline levels. This decrease in ciliary beating was not observed in cells treated with ESE, suggesting that acetaldehyde contained in CSE slows cilia. These results suggest that volatile components such as acetaldehyde in cigarette smoke may inhibit ciliary motility via a PKC-dependent mechanism.