Damien Breheny

The role of oxidative stress in the biological responses of lung epithelial cells to cigarette smoke

The mechanism(s) by which cigarette smoke contributes to lung diseases, such as cancer, remains unclear. Recent developments in our knowledge of cell signalling events suggest that cigarette smoke causes oxidative stress and proinflammatory responses in cells of the lung. Cigarette smoke is a complex mixture of over 4000 compounds and high levels of oxidants and reactive oxygen species (ROS) have been detected in both mainstream and sidestream smoke. Oxidative stress that ensues, when the antioxidant defences are depleted, is accompanied by increases in ROS production in lung epithelial cells. Cigarette smoke-mediated oxidative stress produces DNA damage and activates survival signalling cascades resulting in uncontrolled cell proliferation and transformation. Intervention studies using antioxidants have provided compelling evidence that oxidative stress plays a critical role in the aetiology of smoking-related disorders.

E-cigarette aerosols induce lower oxidative stress in vitro when compared to tobacco smoke

Abstract Tobacco smoking is a risk factor for various diseases. The underlying cellular mechanisms are not fully characterized, but include oxidative stress, apoptosis, and necrosis. Electronic-cigarettes (e-cigarettes) have emerged as an alternative to and a possible means to reduce harm from tobacco smoking. E-cigarette vapor contains significantly lower levels of toxicants than cigarette smoke, but standardized methods to assess cellular responses to exposure are not well established. We investigated whether an in vitro model of the airway epithelium (human bronchial epithelial cells) and commercially available assays could differentiate cellular stress responses to aqueous aerosol extracts (AqE) generated from cigarette smoke and e-cigarette aerosols. After exposure to AqE concentrations of 0.063–0.500 puffs/mL, we measured the intracellular glutathione ratio (GSH:GSSG), intracellular generation of oxidant species, and activation of the nuclear factor erythroid-related factor 2 (Nrf2)-controlled antioxidant response elements (ARE) to characterize oxidative stress. Apoptotic and necrotic responses were characterized by increases in caspase 3/7 activity and reductions in viable cell protease activities. Concentration-dependent responses indicative of oxidative stress were obtained for all endpoints following exposure to cigarette smoke AqE: intracellular generation of oxidant species increased by up to 83%, GSH:GSSG reduced by 98.6% and transcriptional activation of ARE increased by up to 335%. Caspase 3/7 activity was increased by up to 37% and the viable cell population declined by up to 76%. No cellular stress responses were detected following exposure to e-cigarette AqE. The methods used were suitably sensitive to be employed for comparative studies of tobacco and nicotine products.

Assessing modified risk tobacco and nicotine products: Description of the scientific framework and assessment of a closed modular electronic cigarette

ABSTRACT Cigarette smoking causes many human diseases including cardiovascular disease, lung disease and cancer. Novel tobacco products with reduced yields of toxicants compared to cigarettes, such as tobacco‐heating products, snus and electronic cigarettes, hold great potential for reducing the harms associated with tobacco use. In the UK several public health agencies have advocated a potential role for novel products in tobacco harm reduction. Public Health England has stated that “The current best estimate is that e‐cigarettes are around 95% less harmful than smoking” and the Royal College of Physicians has urged public health to “Promote e‐cigarettes widely as substitute for smoking”. Health related claims on novel products such as ‘reduced exposure’ and ‘reduced risk’ should be substantiated using a weight of evidence approach based on a comprehensive scientific assessment. The US FDA, has provided draft guidance outlining a framework to assess novel products as Modified Risk Tobacco Products (MRTP). Based on this, we now propose a framework comprising pre‐clinical, clinical, and population studies to assess the risk profile of novel tobacco products. Additionally, the utility of this framework is assessed through the pre‐clinical and part of the clinical comparison of a commercial e‐cigarette (Vype ePen) with a scientific reference cigarette (3R4F) and the results of these studies suggest that ePen has the potential to be a reduced risk product. HighlightsDescription of a scientific framework to assess the risk profile of next generation products relative to cigarettes.Multi‐disciplinary studies comparing a commercial e‐cigarette (Vype ePen) with a scientific reference cigarette (3R4F).The test e‐cigarette aerosol is compositionally simpler, containing reduced levels of toxicants relative to cigarette smoke.Results from a range of multi‐disciplinary studies showed reduced responses for the test e‐cigarette relative to cigarettes.

Application of a modified gaseous exposure system to the in vitro toxicological assessment of tobacco smoke toxicants.

Tobacco smoke is a complex mixture of over 6,000 individual chemical constituents. Approximately 150 of these have been identified as ‘tobacco smoke toxicants’ due to their known toxicological effects. A number of these toxicants are present in the gaseous phase of tobacco smoke. This presents a technical challenge when assessing the toxicological effects of these chemicals in vitro. We have adapted a commercially available tobacco smoke exposure system to enable the assessment of the contribution of individual smoke toxicants to the overall toxicological effects of whole mainstream cigarette smoke (WS). Here we present a description of the exposure system and the methodology used. We use the example of a gaseous tobacco smoke toxicant, ethylene oxide (EtO), a Group 1 IARC carcinogen and known mutagen, to illustrate how this methodology can be applied to the assessment of genotoxicity of gaseous chemicals in the context of WS. In the present study we found that EtO was positive in Salmonella typhimurium strain YG1042, a strain that is sensitive to tobacco smoke. However, EtO did not increase the mutagenicity of the WS mixture when it was added at greatly higher concentrations than those found typically in WS. The findings presented here demonstrate the suitability of this exposure system for the assessment of the mutagenic potential of gases in vitro. Whilst we have focused on tobacco smoke toxicants, this system has broad application potential in studying the biological effects of exposure to a wide range of gaseous compounds that are present within complex aerosol mixtures. Environ. Mol. Mutagen. 55:662–672, 2014.

Assessment of tobacco heating product THP1.0. Part 5: In vitro dosimetric and cytotoxic assessment

ABSTRACT 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. HighlightsTHP and 3R4F aerosols were assessed using the Borgwaldt RM20S smoking machine.In vitro cytotoxicity from two THPs were compared to a 3R4F reference cigarette.THPs demonstrated significantly reduced cytotoxicity compared to 3R4F exposure.Nicotine delivery to the culture media was greater with the two THPs than 3R4F.

Assessment of novel tobacco heating product THP1.0. Part 7: Comparative in vitro toxicological evaluation

ABSTRACT In vitro studies have been widely used to support the toxicological evaluation of chemicals and complex mixtures including cigarette smoke. In this study, the total particulate matter and whole aerosol from a Kentucky reference 3R4F cigarette and two commercially available tobacco heating products (THPs) were assessed using in vitro mutagenicity, cytotoxicity and tumour‐promoting activity assays. The Ames assay assessed mutagenicity using Salmonella typhimurium tester strains TA98, TA100, TA1535, TA1537 and TA102 ± metabolic activation (S9). The mouse lymphoma assay was used with short 3 h and longer 24 h exposures. The Bhas 42 cell transformation assay was incorporated as an in vitro alternative for detecting tumour promoters, and the neutral red uptake cell viability assay provided an acute measure of cytotoxicity. To complement the approach, the Ames assay was also employed with S. typhimurium tester strains TA98, TA100, TA1535, TA97 and TA102 using a scaled down methodology for the assessment of aerosols. All the in vitro techniques employed produced a clear positive response with cigarette smoke and in contrast, a negative response to THPs at doses equivalent to or higher than a cigarette smoke test matrix. The data show little difference between the THPs assessed suggesting parity between products. HighlightsIn vitro genotoxicity and cytotoxicity assays compared responses from THPs and 3R4F.THPs were directly compared to 3R4F at equivalent doses.Clear positive activity from 3R4F cigarette smoke was observed in every assay.THPs demonstrated significantly reduced responses compared to cigarette smoke.No differences were observed between THPs in any of the tests performed.

Assessment of novel tobacco heating product THP1.0. Part 6: A comparative in vitro study using contemporary screening approaches

ABSTRACT Cigarette smoking is a major risk factor for many adverse health conditions. Novel tobacco heating products (THPs) heat tobacco, reducing exposure to many of the harmful combustion toxicants in conventional cigarette emissions. In vitro studies have been employed to support the toxicological evaluation of chemicals and complex mixtures, including cigarette smoke. The use of automated robotics platforms for in vitro toxicological screening complements traditional testing approaches. Multiparametric toxicity and oxidative stress endpoints were used to assess in vitro biological responses elicited after exposure to total particulate matter (TPM) from two commercially available THPs, and the reference tobacco product 3R4F, in human bronchial epithelial cells. A luciferase‐based reporter gene assay was used to assess antioxidant response element (ARE) transcriptional activation in stably transfected H292 cells after 6 and 24 h exposures. High‐content screening was used to assess 10 endpoints normal human bronchial epithelial cells after 4 or 24 h exposures. 3R4F TPM stimulated significant increases in ARE activation (p < 0.005) and moderate activity in HCS cell‐based assays compared to THP at comparable doses. THPs showed little or no activity in all assays. HCS techniques can extend safety assessments providing information quickly in the early stages of product innovation and development. HighlightsContemporary multiparametric toxicity screening approaches were used to assess THPs.The transcriptional activation of H292‐ARE‐Luc2P cells were assessed.10 different toxicity and oxidative‐stress endpoints were assessed in NHBEs.Compared to 3R4F, THPs were significantly reduced across all endpoints tested.No differences were observed between the THPs in the tests performed.

Comparative tumor promotion assessment of e-cigarette and cigarettes using the in vitro Bhas 42 cell transformation assay

In vitro cell transformation assays (CTA) are used to assess the carcinogenic potential of chemicals and complex mixtures and can detect nongenotoxic as well as genotoxic carcinogens. The Bhas 42 CTA has been developed with both initiation and promotion protocols to distinguish between these two carcinogen classes. Cigarette smoke is known to be carcinogenic and is positive in in vitro genotoxicity assays. Cigarette smoke also contains nongenotoxic carcinogens and is a tumour promoter and cocarcinogen in vivo. We have combined a suite of in vitro assays to compare the relative biological effects of new categories of tobacco and nicotine products with traditional cigarettes. The Bhas promotion assay has been included in this test battery to provide an in vitro surrogate for detecting tumor promoters. The activity of an electronic cigarette (e‐cigarette; Vype ePen) was compared to that of a reference cigarette (3R4F) in the promotion assay, using total particulate matter (TPM)/aerosol collected matter (ACM) and aqueous extracts (AqE) of product aerosol emissions. 3R4F TPM was positive in this assay at concentrations ≥6 µg/mL, while e‐cigarette ACM did not have any promoter activity. AqE was found to be a lesssuitable test matrix in this assay due to high cytotoxicity. This is the first study to use the Bhas assay to compare tobacco and nicotine products and demonstrates the potential for its future application as part of a product assessment framework. These data add to growing evidence suggesting that e‐cigarettes may provide a safer alternative to traditional cigarettes. Environ. Mol. Mutagen. 58:190–198, 2017.

Abstract 2423: Acute in vitro exposure to cigarette smoke particulate matter does not induce epithelial-mesenchymal transition in lung epithelial cells

The epithelial-mesenchymal transition (EMT) program was first identified from studies on embryogenesis and organ development, but has since been found to play vital roles in tissue remodelling and tumorigenesis. EMT is a biological process during which epithelial cells change their morphology to adopt fibroblast-like characteristics. During EMT, cell adhesion is lost while cells become more motile. A number of distinct molecular events are required for a cell to undergo EMT including transcription factor activation, cytoskeletal rearrangement, changes in cell adhesion molecule expression and increased production of extracellular matrix-degrading enzymes. EMT has recently been linked to chronic inflammation and cigarette smoke exposure in the lung and is believed to be involved in lung carcinogenesis. As the specific genes and proteins involved in EMT have been well defined, they can serve as markers to demonstrate the passage of cells through EMT in the context of cigarette smoking. The purpose of this study was to develop an in vitro model of EMT using immortalised human bronchial epithelial (BEAS-2B) cells. EMT was induced in BEAS-2B cells using a 72 hour treatment with 5 ng/mL TGF-β1. Expression of the following EMT markers were assessed at the transcript level using reverse transcription real time-polymerase chain reaction (RT-PCR): alpha smooth muscle actin (α-SMA), collagen 1, fibronectin, vimentin, e-cadherin, slug and snail. Protein levels of α-SMA, fibronectin, β-catenin, e-cadherin and zonular occludin-1 were evaluated using immunocytochemistry techniques. This model was then used to determine the effects of acute (72 hour) cigarette smoke particulate matter treatment on EMT in BEAS-2B cells. Cells were treated with particulate matter alone, and in combination with TGF-β1. Particulate matter did not induce EMT directly, nor did it influence EMT induced by TGF-β1 under the treatment conditions used in this study, based on marker expression. It is possible that a more prolonged exposure to particulate matter is required for EMT induction in BEAS-2B cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2423. doi:1538-7445.AM2012-2423