DNA damage response induced by exposure of human lung adenocarcinoma cells to smoke from tobacco- and nicotine-free cigarettes

The tobacco-free fallacy: What paediatricians should know about herbal smoking products

While e-cigarette and combustible cigarette use remains more common among youth, herbal smoking products are gaining interest and popularity among children and adolescents. Herbal smoking products are often touted as a safer alternative to tobacco smoking or nicotine vaping; however, research suggests that they emit significant levels of toxicants and carcinogens posing risks to child and adolescent health. The low perceived risk coupled with youth-friendly flavours and easy access may entice youth to use herbal smoking products and increase the risk of subsequent tobacco and substance use. We discuss what is known about the use, health effects, and regulations of herbal smoking products and present strategies for policymakers and paediatric providers to reduce the risks associated with these products for Canadian youth.

Factors to Consider for the Correct Use of γH2AX in the Evaluation of DNA Double-Strand Breaks Damage Caused by Ionizing Radiation

People exposed to ionizing radiation (IR) both for diagnostic and therapeutic purposes is constantly increasing. Since the use of IR involves a risk of harmful effects, such as the DNA DSB induction, an accurate determination of this induced DNA damage and a correct evaluation of the risk-benefit ratio in the clinical field are of key relevance. γH2AX (the phosphorylated form of the histone variant H2AX) is a very early marker of DSBs that can be induced both in physiological conditions, such as in the absence of specific external agents, and by external factors such as smoking, heat, background environmental radiation, and drugs. All these internal and external conditions result in a basal level of γH2AX which must be considered for the correct assessment of the DSBs after IR exposure. In this review we analyze the most common conditions that induce H2AX phosphorylation, including specific exogenous stimuli, cellular states, basic environmental factors, and lifestyles. Moreover, we discuss the most widely used methods for γH2AX determination and describe the principal applications of γH2AX scoring, paying particular attention to clinical studies. This knowledge will help us optimize the use of available methods in order to discern the specific γH2AX following IR-induced DSBs from the basal level of γH2AX in the cells.

Psychosocial stress and cancer risk: a narrative review

BACKGROUND

It is unclear which psychological factors (stressors, emotional correlates, and psychophysiological markers) induce cancer risk. This currently limits the potential for prevention strategies.

PURPOSE

The aim of this review is to bring forth evidence of stress as a determinant of cancer risk from a public health perspective, written for a broad public of practitioners and scientists.

METHODS

Based on a semisystematic literature search, the impact of different aspects/types of stress and the potential physiological and behavioral pathways are summarized, while highlighting further research, public health and clinical implications.

RESULTS

Between 2007 and 2020, 65 case-control or cohort studies have been identified. Apart from overall cancer ( N = 24), 12 cancer types have been associated with psychological stress with most for breast ( N = 21), colorectal ( N = 11) and lung/prostate/pancreas cancer ( N = 8 each). Although the evidence regarding the mechanisms is still scarce, cancer development in relation to stress might be due to interacting and combined effects of different stress(or) types, but such interaction has not really been tested yet. The path from stress towards cancer incidence consists of a biological pathway with endocrinology and immunology as well as stress-induced behavioral pathways, including smoking, alcoholism, sleep disruption, an unhealthy diet, and low physical activity together with the related phenomenon of obesity.

CONCLUSION

Not only the stress but also the stress-induced lifestyle should be targeted for cancer prevention and treatment. Future research should include a more diverse spectrum of cancer types (not only hormonal related like breast cancer) and of stress measures while also considering behavioral covariates.

Systematic content analysis of online information on herbal smoking products

BACKGROUND

Herbal smoking products (HSPs) are marketed as a safer alternative to tobacco. These are easily available at affordable prices in the online retail websites. This study aimed to analyze the HSP-related informational content available in the most popular online platforms.

METHODS

Google, Yahoo, Bing and YouTube online platforms were searched for HSP related content using appropriate keywords. First 50 search results were retrieved and screened for potential eligibility. The included web-pages were categorized as video and still records. From each included record, information regarding source, primary theme, health benefits/hazards and tone was abstracted. Additionally, video production quality, like ratio and video power index was also computed for each video record. All included records were subjected to descriptive statistics and Chi-square test, as appropriate. Level of significance was set at <0.05.

RESULTS

174 still and 94 video records were included. 35.6% of the included still records were sourced by manufacturers/suppliers while that of scientific origin was 12.1%. 83% of the video-records were posted by general public. About 90% of the included records had not mentioned anything regarding age restrictions. 67.8% of the still records and 87.2% of the video records promoted the use of HSPs.

CONCLUSIONS

The informational content presented online is huge, mostly posted by the general public without any scientific rationale and exclusively favors the use of HSPs. There is no age restriction as to who can access the information, making this content easily accessible to people of all ages. Such spread of information may mislead the public in adopting the smoking of these herbal products. Since HSPs may act as a potential gateway to tobacco smoking, there is an urgent need to regulate the content available online.

Electronic Cigarettes Induce Mitochondrial DNA Damage and Trigger TLR9 (Toll-Like Receptor 9)-Mediated Atherosclerosis

OBJECTIVE

Electronic cigarette (e-cig) use has recently been implicated in promoting atherosclerosis. In this study, we aimed to investigate the mechanism of e-cig exposure accelerated atherosclerotic lesion development. Approach and Results: Eight-week-old ApoE^-/- mice fed normal laboratory diet were exposed to e-cig vapor (ECV) for 2 hours/day, 5 days/week for 16 weeks. We found that ECV exposure significantly induced atherosclerotic lesions as examined by Oil Red O staining and greatly upregulated TLR9 (toll-like receptor 9) expression in classical monocytes and in the atherosclerotic plaques, which the latter was corroborated by enhanced TLR9 expression in human femoral artery atherosclerotic plaques from e-cig smokers. Intriguingly, we found a significant increase of oxidative mitochondria DNA lesion in the plasma of ECV-exposed mice. Administration of TLR9 antagonist before ECV exposure not only alleviated atherosclerosis and the upregulation of TLR9 in plaques but also attenuated the increase of plasma levels of inflammatory cytokines, reduced the plaque accumulation of lipid and macrophages, and decreased the frequency of blood CCR2⁺ (C-C chemokine receptor type 2) classical monocytes. Surprisingly, we found that cytoplasmic mitochondrial DNA isolated from ECV extract-treated macrophages can enhance TLR9 activation in reporter cells and the induction of inflammatory cytokine could be suppressed by TLR9 inhibitor in macrophages.

CONCLUSIONS

E-cig increases level of damaged mitochondrial DNA in circulating blood and induces the expression of TLR9, which elevate the expression of proinflammatory cytokines in monocyte/macrophage and consequently lead to atherosclerosis. Our results raise the possibility that intervention of TLR9 activation is a potential pharmacological target of ECV-related inflammation and cardiovascular diseases.

Anthocyanin-rich haskap (Lonicera caerulea L.) berry extracts reduce nitrosamine-induced DNA damage in human normal lung epithelial cells in vitro

Diets rich in polyphenols are known to reduce cancer among high-risk populations. Haskap (Lonicera caerulea L.) berry has abundant phenolic acids and flavonoids, especially anthocyanins. Tobacco-specific nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) present in cigarette smoke, is a major lung carcinogenic factor. We analyzed the efficacy of anthocyanin-rich haskap berry extracts in preventing DNA damage induced by 4-[(acetoxymethyl) nitrosamino]-1-(3-pyridyl)-1-butanone (NNKOAc), a precursor of NKK, in human lung epithelial BEAS-2B cells in vitro. A cocktail of monomeric polyphenols from haskap berries was extracted separately in ethanol and water and profiled. Sub-lethal concentrations of NNKOAc were used to induce DNA damage in BEAS-2B cells, and a cell viability assay was performed to confirm that the tested concentrations of haskap extracts were not cytotoxic to BEAS-2B cells. Cells were pre-treated with the haskap extracts prior to NNKOAc exposure. Dose-dependent DNA damage was observed with carcinogenic NNKOAc, but did not occur in the presence of the haskap extracts. Pre-treatment of the cells with the haskap extracts significantly reduced NNKOAc-induced DNA damage, DNA fragmentation, and intracellular reactive oxygen species and upregulated the ATM-dependent DNA damage repair cascade compared to non-treated BEAS-2B cells. The protective effect of haskap extracts could be related to their polyphenol content and high antioxidant capacity.

Assessing the lung cancer risk reduction potential of candidate modified risk tobacco products

Smoking is the major cause of lung cancer. While the risk of lung cancer increases with the number of cigarettes smoked and the duration of smoking, it also decreases upon smoking cessation. The development of candidate modified risk tobacco products (cMRTP) is aimed at providing smokers who will not quit with alternatives to cigarettes that present less risk of harm and smoking-related disease. It is necessary to assess the risk reduction potential of cMRTPs, including their potential to reduce the risk of lung cancer. Assessing the lung cancer risk reduction potential of cMRTPs is hampered by (i) the absence of clinical risk markers that are predictive of future lung cancer development, (ii) the latency of lung cancer manifestation (decades of smoking), and (iii) the slow reduction in excess risk upon cessation and a fortiori upon switching to a cMRTP. It is, therefore, likely that only long-term epidemiology will provide definitive answers to this question and allow to first verify that a cMRTP reduces the risk of lung cancer and if it does, to quantify the reduction in excess lung cancer risk associated with a cMRTP. For this to be possible, the cMRTP would need to be available in the market and used exclusively by a large portion of current smokers. Here, we propose that a mechanism-based approach represents a solid alternative to show in a pre-market setting that switching to a cMRTP is likely to significantly reduce the risk of lung cancer. This approach is based on the causal chain of events that leads from smoking to disease and leverages both non-clinical and clinical studies as well as the principles of systems toxicology. We also discuss several important challenges inherent to the assessment of cMRTPs as well as key aspects regarding product use behavior.

Tobacco and bone fractures: A review of the facts and issues that every orthopaedic surgeon should know

Objectives

The aim of this study was to review the impact of smoking tobacco on the musculoskeletal system, and on bone fractures in particular.

Methods

English-language publications of human and animal studies categorizing subjects into smokers and nonsmokers were sourced from MEDLINE, The Cochrane Library, and SCOPUS. This review specifically focused on the risk, surgical treatment, and prevention of fracture complications in smokers.

Results

Smokers have an increased risk of fracture and experience more complications with delayed bone healing, even if they have already stopped smoking, because some adverse effects persist for a prolonged period. Some risks can be reduced during and after surgery by local and general prevention, and smoking cessation is an important factor in lessening this risk. However, if a patient wants to stop smoking at the time of a fracture, the cessation strategies in reducing tobacco use are not easy to implement. The patient should also be warned that using e-cigarettes or other tobaccos does not appear to reduce adverse effects on health.

Conclusion

The evidence reviewed in this study shows that smoking has a negative effect in terms of the risk and treatment of fractures.

Cite this article: J. Hernigou, F. Schuind. Tobacco and bone fractures: A review of the facts and issues that every orthopaedic surgeon should know. Bone Joint Res 2019;8:255–265. DOI: 10.1302/2046-3758.86.BJR-2018-0344.R1.

Cell type-specific properties and environment shape tissue specificity of cancer genes

One of the biggest mysteries in cancer research remains why mutations in certain genes cause cancer only at specific sites in the human body. The poor correlation between the expression level of a cancer gene and the tissues in which it causes malignant transformations raises the question of which factors determine the tissue-specific effects of a mutation. Here, we explore why some cancer genes are associated only with few different cancer types (i.e., are specific), while others are found mutated in a large number of different types of cancer (i.e., are general). We do so by contrasting cellular functions of specific-cancer genes with those of general ones to identify properties that determine where in the body a gene mutation is causing malignant transformations. We identified different groups of cancer genes that did not behave as expected (i.e., DNA repair genes being tissue specific, immune response genes showing a bimodal specificity function or strong association of generally expressed genes to particular cancers). Analysis of these three groups demonstrates the importance of environmental impact for understanding why certain cancer genes are only involved in the development of some cancer types but are rarely found mutated in other types of cancer.

Tobacco and lung cancer: risks, trends, and outcomes in patients with cancer

Tobacco use, primarily associated with cigarette smoking, is the largest preventable cause of cancer mortality, responsible for approximately one-third of all cancer deaths. Approximately 85% of lung cancers result from smoking, with an additional fraction caused by secondhand smoke exposure in nonsmokers. The risk of lung cancer is dose dependent, but can be dramatically reduced with tobacco cessation, especially if the person discontinues smoking early in life. The increase in lung cancer incidence in different countries around in the world parallels changes in cigarette consumption. Lung cancer risks are not reduced by switching to filters or low-tar/low-nicotine cigarettes. In patients with cancer, continued tobacco use after diagnosis is associated with poor therapeutic outcomes including increased treatment-related toxicity, increased risk of second primary cancer, decreased quality of life, and decreased survival. Tobacco cessation in patients with cancer may improve cancer treatment outcomes, but cessation support is often not provided by oncologists. Reducing the health related effects of tobacco requires coordinated efforts to reduce exposure to tobacco, accurately assess tobacco use in clinical settings, and increase access to tobacco cessation support. Lung cancer screening and coordinated international tobacco control efforts offer the promise to dramatically reduce lung cancer mortality in the coming decades.

Analysis of global gene expression profiles in tobacco roots under drought stress

Tobacco (Nicotiana tabacum L.) is an economically important and relatively drought-tolerant crop grown around the world. However, the molecular regulatory mechanisms involved in tobacco root development in response to drought stress are not wellknown. To gain insight into the transcriptome dynamics associated with drought resistance, genome-wide gene expression profiling of roots from a tobacco cultivar (Honghua Dajinyuan, a major flue-cured tobacco cultivar in Southwest China) under 20% PEG6000 treatment for 0, 6 h and 48 h were conducted using Solexa sequencing (Illumina Inc., San Diego, CA, USA). Over five million tags were generated from tobacco roots, including 229,344, 221,248 and 242,065 clean tags in three libraries, respectively. The most differentially expressed tags, with either log2FC > 2.0 for up-regulated genes or log2FC < -2.0 for down regulated genes (p < 0.001), were analyzed further. In comparison to the control, 1476 up-regulated and 1574 down-regulated differentially expressed genes (DEGs) were identified, except for unknown transcripts, which were grouped into 43 functional categories involved in seven significant pathways. The most enriched categories were those that were populated by transcripts involved in metabolism, signal transduction and cellular transport. Many genes and/or biological pathways were found to be common among the three libraries, for example, genes participating in transport, stress response, auxin transport and signaling, etc. Next, the expression patterns of 12 genes were assessed with quantitative real-time PCR, the results of which agreed with the Solexa analysis. In conclusion, we revealed complex changes in the transcriptome during tobacco root development related to drought resistance, and provided a comprehensive set of data that is essential to understanding the molecular regulatory mechanisms involved. These data may prove valuable in future studies of the molecular mechanisms regulating root development in response to drought stress in tobacco and other plants.

Common genetic variants on 3q28 contribute to non-small cell lung cancer susceptibility: evidence from 10 case-control studies

The association between common variations (rs10937405, rs4488809) on 3q28 and lung cancer has been widely evaluated in various ethnic groups, since it was first identified through genome-wide association approach. However, the results have been inconclusive. To derive a more precise estimation of the relationship and the effect of factors that might modify the risk, we performed this meta-analysis. The random-effects model was applied, addressing heterogeneity and publication bias. A total of 10 articles involving 36,221 cases and 58,108 controls were included. Overall, the summary per-allele OR of 1.19 (95 % CI 1.14-1.25, P < 10(-5)) and 1.17 (95 % CI 1.10-1.23, P < 10(-5)) was found for the rs10937405 and rs4488809 polymorphisms, respectively. Significant results were also observed in heterozygous and homozygous when compared with wild genotype for these polymorphisms. Significant results were found in East Asians when stratified by ethnicity, whereas no significant associations were found among Caucasians. After stratifying by sample size, study design, control source and sex, significant associations were also obtained. In addition, our data indicate that these polymorphisms are involved in lung cancer susceptibility and confer its effect primarily in lung adenocarcinoma when stratified by histological subtype. Furthermore, significant associations were also detected both never-smokers and smokers for these polymorphisms. In conclusion, this meta-analysis demonstrated that rs10937405 and rs4488809 are a risk factor associated with increased non-small cell lung cancer susceptibility, particularly for East Asian populations.

Smoking cessation reverses DNA double-strand breaks in human mononuclear cells

OBJECTIVE

Cigarette smoking is a major risk factor for atherosclerotic cardiovascular disease, which is responsible for a significant proportion of smoking-related deaths. However, the precise mechanism whereby smoking induces this pathology has not been fully delineated. Based on observation of DNA double-strand breaks (DSBs), the most harmful type of DNA damage, in atherosclerotic lesions, we hypothesized that there is a direct association between smoking and DSBs. The goal of this study was to investigate whether smoking induces DSBs and smoking cessation reverses DSBs in vivo through examination of peripheral mononuclear cells (MNCs).

APPROACH AND RESULTS

Immunoreactivity of oxidative modification of DNA and DSBs were increased in human atherosclerotic lesions but not in the adjacent normal area. DSBs in human MNCs isolated from the blood of volunteers can be detected as cytologically visible "foci" using an antibody against the phosphorylated form of the histone H2AX (γ-H2AX). Young healthy active smokers (n = 15) showed increased γ-H2AX foci number when compared with non-smokers (n = 12) (foci number/cell: median, 0.37/cell; interquartile range [IQR], 0.31-0.58 vs. 4.36/cell; IQR, 3.09-7.39, p<0.0001). Smoking cessation for 1 month reduced the γ-H2AX foci number (median, 4.44/cell; IQR, 4.36-5.24 to 0.28/cell; IQR, 0.12-0.53, p<0.05). A positive correlation was noted between γ-H2AX foci number and exhaled carbon monoxide levels (r = 0.75, p<0.01).

CONCLUSIONS

Smoking induces DSBs in human MNCs in vivo, and importantly, smoking cessation for 1 month resulted in a decrease in DSBs to a level comparable to that seen in non-smokers. These data reinforce the notion that the cigarette smoking induces DSBs and highlight the importance of smoking cessation.

Assessing tobacco use by cancer patients and facilitating cessation: an American Association for Cancer Research policy statement

When diagnosed with cancer, patients can immediately make a meaningful positive impact on their health by stopping their tobacco use. Scientific evidence clearly shows that tobacco use in patients with cancer leads to poorer outcomes. The specific biological processes driving tobacco consumption's interference in cancer therapy are the subject of continuing research, but the evidence is clear that tobacco use in patients with cancer leads to decreased treatment efficacy and safety, decreased survival, decreased quality of life, increased treatment-related toxicity, and increased risk of cancer recurrence and second primary tumors. Data suggest that tobacco cessation can improve outcomes and survival in patients with cancer, yet full execution of evidence-based cessation interventions is infrequent in oncology settings. Therefore, both improved provision of cessation assistance to all patients with cancer who use tobacco or have recently quit and further study of the deleterious effects of tobacco use and benefits of tobacco cessation on cancer progression and treatment are needed and recommended by the American Association for Cancer Research. Progress on both fronts begins with universal assessment and documentation of tobacco use as a standard of quality cancer care regardless of treatment setting and will be further facilitated through the development of reliable, valid, and standard measures of tobacco use, incorporation of evidence-based procedures into quality and accreditation procedures, and the development of appropriate training, clinical infrastructure, and incentives for delivery of tobacco cessation interventions.

Construction of a computable network model for DNA damage, autophagy, cell death, and senescence

Towards the development of a systems biology-based risk assessment approach for environmental toxicants, including tobacco products in a systems toxicology setting such as the “21st Century Toxicology”, we are building a series of computable biological network models specific to non-diseased pulmonary and cardiovascular cells/tissues which capture the molecular events that can be activated following exposure to environmental toxicants. Here we extend on previous work and report on the construction and evaluation of a mechanistic network model focused on DNA damage response and the four main cellular fates induced by stress: autophagy, apoptosis, necroptosis, and senescence. In total, the network consists of 34 sub-models containing 1052 unique nodes and 1538 unique edges which are supported by 1231 PubMed-referenced literature citations. Causal node-edge relationships are described using the Biological Expression Language (BEL), which allows for the semantic representation of life science relationships in a computable format. The Network is provided in .XGMML format and can be viewed using freely available network visualization software, such as Cytoscape.

Perinatal exposure to nicotine and implications for subsequent obstructive lung disease

Many diseases are due to gene-environment or epigenetic-environment interactions resulting in a change in the program that controls tissue structure and function. Changes in the in utero and external environment during perinatal development due to parental smoking, or nicotine exposure, may reduce the capacity of the offspring to protect themselves against environmental stressors. Nicotine is genotoxic and also induces reactive oxygen species [ROS] production. It also reduces the antioxidant capacity of the lung. The lungs of the offspring are therefore developing in an environment of an oxidant-antioxidant imbalance with the concomitant adverse effects of the oxidants and nicotine on cell integrity. Consequently, they are more prone to develop respiratory diseases such as asthma and emphysema later in life. The use of NRT by pregnant or lactating females is therefore not an appropriate strategy to quit smoking.

Nicotine and lung cancer

Tobacco use in cancer patients is associated with increased cancer treatment failure and decreased survival. Nicotine is one of over 7,000 compounds in tobacco smoke and nicotine is the principal chemical associated with addiction. The purpose of this article is to review the tumor promoting activities of nicotine. Nicotine and its metabolites can promote tumor growth through increased proliferation, angiogenesis, migration, invasion, epithelial to mesenchymal transition, and stimulation of autocrine loops associated with tumor growth. Furthermore, nicotine can decrease the biologic effectiveness of conventional cancer treatments such as chemotherapy and radiotherapy. Common mechanisms appear to involve activation of nicotinic acetylcholine receptors and beta-adrenergic receptors leading to downstream activation of parallel signal transduction pathways that facilitate tumor progression and resistance to treatment. Data suggest that nicotine may be an important mechanism by which tobacco promotes tumor development, progression, and resistance to cancer treatment.

DNA damage signaling assessed in individual cells in relation to the cell cycle phase and induction of apoptosis

Reviewed are the phosphorylation events reporting activation of protein kinases and the key substrates critical for the DNA damage signaling (DDS). These DDS events are detected immunocytochemically using phospho-specific Abs; flow cytometry or image-assisted cytometry provide the means to quantitatively assess them on a cell by cell basis. The multiparameter analysis of the data is used to correlate these events with each other and relate to the cell cycle phase, DNA replication and induction of apoptosis. Expression of γH2AX as a possible marker of induction of DNA double strand breaks is the most widely studied event of DDS. Reviewed are applications of this multiparameter approach to investigate constitutive DDS reporting DNA damage by endogenous oxidants byproducts of oxidative phosphorylation. Also reviewed are its applications to detect and explore mechanisms of DDS induced by variety of exogenous agents targeting DNA such as exogenous oxidants, ionizing radiation, radiomimetic drugs, UV light, DNA topoisomerase I and II inhibitors, DNA crosslinking drugs and variety of environmental genotoxins. Analysis of DDS induced by these agents provides often a wealth of information about mechanism of induction and the type of DNA damage (lesion) and is reviewed in the context of cell cycle phase specificity, DNA replication, and induction of apoptosis or cell senescence. Critically assessed is interpretation of the data as to whether the observed DDS events report induction of a particular type of DNA lesion.

SIRT1 pathway dysregulation in the smoke-exposed airway epithelium and lung tumor tissue

Cigarette smoke produces a molecular field of injury in epithelial cells lining the respiratory tract. However, the specific signaling pathways that are altered in the airway of smokers and the signaling processes responsible for the transition from smoking-induced airway damage to lung cancer remain unknown. In this study, we use a genomic approach to study the signaling processes associated with tobacco smoke exposure and lung cancer. First, we developed and validated pathway-specific gene expression signatures in bronchial airway epithelium that reflect activation of signaling pathways relevant to tobacco exposure, including ATM, BCL2, GPX1, NOS2, IKBKB, and SIRT1. Using these profiles and four independent gene expression datasets, we found that SIRT1 activity is significantly upregulated in cytologically normal bronchial airway epithelial cells from active smokers compared with nonsmokers. In contrast, this activity is strikingly downregulated in non-small cell lung cancer. This pattern of signaling modulation was unique to SIRT1, and downregulation of SIRT1 activity is confined to tumors from smokers. Decreased activity of SIRT1 was validated using genomic analyses of mouse models of lung cancer and biochemical testing of SIRT1 activity in patient lung tumors. Together, our findings indicate a role of SIRT1 in response to smoke and a potential role in repressing lung cancer. Furthermore, our findings suggest that the airway gene expression signatures derived in this study can provide novel insights into signaling pathways altered in the "field of injury" induced by tobacco smoke and thus may impact strategies for prevention of tobacco-related lung cancer.

γH2AX as a novel endpoint to detect DNA damage: applications for the assessment of the in vitro genotoxicity of cigarette smoke

Histone H2AX is rapidly phosphorylated to become γH2AX after exposure to DNA-damaging agents that cause double-strand DNA breaks (DSBs). γH2AX can be detected and quantified by numerous methods, giving a direct correlation with the number of DSBs. This relationship has made γH2AX an increasingly utilised endpoint in multiple scientific fields since its discovery in 1998. Applications include its use in pre-clinical drug assessment, as a biomarker of DNA damage and in in vitro mechanistic studies. Here, we review current in vitro regulatory and non-regulatory genotoxicity assays proposing the γH2AX assay as a potential complement to the current test battery. Additionally, we evaluate the use of the γH2AX assay to measure DSBs in vitro in tobacco product testing.

DNA repair gene polymorphisms and tobacco smoking in the risk for colorectal adenomas

DNA damage is thought to play a critical role in the development of colorectal adenoma. Variation in DNA repair genes may alter their capacity to correct endogenous and exogenous DNA damage. We explored the association between common single-nucleotide polymorphisms (SNPs) in DNA repair genes and adenoma risk with a case-control study nested in the Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial. A total of 1338 left sided, advanced colorectal adenoma cases and 1503 matched controls free of left-sided polyps were included in the study. Using DNA extracted from blood, 3144 tag SNPs in 149 DNA repair genes were successfully genotyped. Among Caucasians, 30 SNPs were associated with adenoma risk at P < 0.01, with four SNPs remaining significant after gene-based adjustment for multiple testing. The most significant finding was for a non-synonymous SNP (rs9350) in Exonuclease-1 (EXO1) [odds ratio (OR) = 1.30, 95% confidence interval (CI) = 1.11-1.51, P = 0.001)], which was predicted to be damaging using bioinformatics methods. However, the association was limited to smokers with a strong risk for current smokers (OR = 2.15, 95% CI = 1.27-3.65) and an intermediate risk for former smokers (OR = 1.45, 95% CI = 1.14-1.82) and no association for never smokers (OR = 0.98, 95% CI = 0.76-1.25) (P(interaction) = 0.002). Among the top findings, an SNP (rs17503908) in ataxia telangiectasia mutated (ATM) was inversely related to adenoma risk (OR = 0.75, 95% CI = 0.63-0.91). The association was restricted to never smokers (OR = 0.55, 95% CI = 0.40-0.76) with no increased risk observed among smokers (OR = 0.89, 95% CI = 0.70-1.13) (P(interaction) = 0.006). This large comprehensive study, which evaluated all presently known DNA repair genes, suggests that polymorphisms in EXO1 and ATM may be associated with risk for advanced colorectal adenoma with the associations modified by tobacco-smoking status.

New biomarkers probing depth of cell senescence assessed by laser scanning cytometry

The imaging analytical capabilities of laser scanning cytometer (LSC) have been used to assess morphological features considered to be typical of the senescent phenotype. The characteristic “flattening” of senescent cells was reflected by the decline in the density of staining (intensity of maximal pixel) of DNA-associated fluorescence [4,6-diamidino-2-phenylindole (DAPI)] paralleled by an increase in nuclear size (area). The decrease in ratio of maximal pixel to nuclear area was even more sensitive senescence biomarker than the change in maximal pixel or nuclear area, each alone. The saturation cell density at plateau phase of growth recorded by LSC was found to be dramatically decreased in cultures of senescent cells, thereby also serving as an additional marker. The induction of cyclin dependent kinase inhibitors p21^WAF1 and p27^KIP1 and γH2AX and activation of ATM markers of DNA damage response were measured in parallel with DNA/DAPI maximal pixel and nuclear area. These biomarker indices were expressed in quantitative terms by reporting them as a fraction of the respective controls. The effect of treatment of A549 and WI-38 cells with different concentrations of mitoxantrone (Mxt) and trichostatin A for various time periods was studied to assess the degree (depth) of cell senescence. Also assessed was the effect of 2-deoxy-d-glucose, the agent attenuating metabolic cell activity, on the depth of senescence induced by Mxt. A relationship between the ability of cells to synthesize RNA (incorporate 5-ethynyluridine) that leads to growth imbalance and induction of cell senescence was also studied. The data show that morphometric analysis of cellular attributes by LSC offers an attractive tool to detect cell senescence and measure its degree particularly in assessing effects of the factors that enhance or attenuate this process. This methodology is of importance in light of the evidence that cellular senescence is not only a biological process that is fundamental for organismal aging but also impedes formation of induced-pluripotent stem cells providing the barrier for neoplastic transformation and is the major mechanism of induction of reproductive cell death during treatment of solid tumors. © 2010 International Society for Advancement of Cytometry.

Analysis of individual molecular events of DNA damage response by flow- and image-assisted cytometry

This chapter describes molecular mechanisms of DNA damage response (DDR) and presents flow- and image-assisted cytometric approaches to assess these mechanisms and measure the extent of DDR in individual cells. DNA damage was induced by cell treatment with oxidizing agents, UV light, DNA topoisomerase I or II inhibitors, cisplatin, tobacco smoke, and by exogenous and endogenous oxidants. Chromatin relaxation (decondensation) is an early event of DDR chromatin that involves modification of high mobility group proteins (HMGs) and histone H1 and was detected by cytometry by analysis of the susceptibility of DNA in situ to denaturation using the metachromatic fluorochrome acridine orange. Translocation of the MRN complex consisting of Meiotic Recombination 11 Homolog A (Mre11), Rad50 homolog, and Nijmegen Breakage Syndrome 1 (NMR1) into DNA damage sites was assessed by laser scanning cytometry as the increase in the intensity of maximal pixel as well as integral value of Mre11 immunofluorescence. Examples of cytometric detection of activation of Ataxia telangiectasia mutated (ATM), and Check 2 (Chk2) protein kinases using phospho-specific Abs targeting Ser1981 and Thr68 of these proteins, respectively are also presented. We also discuss approaches to correlate activation of ATM and Chk2 with phosphorylation of p53 on Ser15 and histone H2AX on Ser139 as well as with cell cycle position and DNA replication. The capability of laser scanning cytometry to quantify individual foci of phosphorylated H2AX and/or ATM that provides more dependable assessment of the presence of DNA double-strand breaks is outlined. The new microfluidic Lab-on-a-Chip platforms for interrogation of individual cells offer a novel approach for DDR cytometric analysis.

Measuring the impact of cigarette smoke on the UPR

The unfolded protein response (UPR) is a set of pathways activated by the accumulation of improperly folded proteins. It can be triggered by a broad range of stressful conditions which disrupt successful maturation of proteins in the endoplasmic reticulum (ER) by interfering with proper folding, assembly, and posttranslational modification. Recent studies have demonstrated the induction of ER stress and activation of elements of the UPR in human lung cells exposed to diesel exhaust particles, airborne particulate matter, and tobacco smoke. ER stress has been found to play a role in a variety of lung maladies, including cancer, infections, idiopathic pulmonary fibrosis, and chronic obstructive pulmonary disease. Lung cancer is one of the few diseases where the etiological agent, cigarette smoke (CS), is well known. It is, therefore, desirable to measure dysregulation of the UPR pathway in samples representing both the earliest events (cells exposed to CS in vitro) and in clinical samples from healthy smokers and individuals with smoking-related lung diseases. We hereby provide a detailed description of methods for assessing the degree and timing of cellular response to CS with respect to the three major UPR pathways.

LKB1/PEA3/ΔNp63 pathway regulates PTGS-2 (COX-2) transcription in lung cancer cells upon cigarette smoke exposure

This is the first study to show that cigarette smoking induced the LKB1/PEA 3/ΔNp63-dependent transcriptional regulation of inflammatory molecules, such as COX-2/PTGS-2. Using mainstream smoke extract (MSE) and sidestream smoke extract (SSE) as modeling tools for primary and secondhand smoking, we found that both MSE and SSE downregulated protein levels for LKB1, while upregulated protein levels for PEA 3 and COX-2 in a dose-dependent manner. Using the endogenous ChIP analysis, we further found that the C/EBPβ, NFκB, NF-Y (CHOP), PEA 3 (ETS) and ΔNp63 proteins bound to the specific area (-550 to -130) of the COX-2 promoter, while forming multiple protein complexes in lung cancer cells exposed to MSE and SSE. Our results define a novel link between various transcription factors occupying the COX-2 promoter and cellular response to cigarette smoke exposure bringing a new component, ΔNp63α, showing a critical role for cooperation between various chromatin components in regulation of COX-2 expression and, therefore strengthening the central role of inflammatory process in tumorigenesis of epithelial cells, especially after cigarette smoke exposure (both primary and secondhand).