Bulky DNA Adducts, Tobacco Smoking, Genetic Susceptibility, and Lung Cancer Risk

DNA adduct formation in Saccharomyces cerevisiae following exposure to environmental pollutants, as in vivo model for molecular toxicity studies

DNA adduction in the model yeast Saccharomyces cerevisiae was investigated after exposure to the fungicide penconazole and the reference genotoxic compound benzo(a)pyrene, for validating yeasts as a tool for molecular toxicity studies, particularly of environmental pollution. The effect of the toxicants on the yeast's growth kinetics was determined as an indicator of cytotoxicity. Fermentative cultures of S. cerevisiae were exposed to 2 ppm of Penconazole during different phases of growth; while 0.2 and 2 ppm of benzo(a)pyrene were applied to the culture medium before inoculation and on exponential cultures. Exponential respiratory cultures were also exposed to 0.2 ppm of B(a)P for comparison of both metabolisms. Penconazole induced DNA adducts formation in the exponential phase test; DNA adducts showed a peak of 54.93 adducts/109 nucleotides. Benzo(a)pyrene induced the formation of DNA adducts in all the tests carried out; the highest amount of 46.7 adducts/109 nucleotides was obtained in the fermentative cultures after the exponential phase exposure to 0.2 ppm; whereas in the respiratory cultures, 14.6 adducts/109 nucleotides were detected. No cytotoxicity was obtained in any experiment. Our study showed that yeast could be used to analyse DNA adducts as biomarkers of exposure to environmental toxicants.

Comparative analyses of transcriptome sequencing and carcinogenic exposure toxicity of nicotine and 6-methyl nicotine in human bronchial epithelial cells

Electronic cigarettes have become a purported safer alternative to the conventional cigarettes in recent years. Nicotine is the main component of electronic cigarettes, and other nicotinic compounds are synthesized as alternatives to nicotine. However, scientific data on the potential health effects of electronic cigarettes are scarce. Herein, we evaluated the cytotoxicity of nicotine and its analog 6-methyl nicotine (6-MN) on human bronchial epithelial cells (BEAS-2B cells) in vitro. Furthermore, we performed transcriptome sequencing to systematically assess the effects of nicotine and 6-MN on BEAS-2B cells. The cytotoxicity assay revealed that BEAS-2B cells were more sensitive to 6-MN than to nicotine. Transcriptome sequencing revealed 1208 differentially expressed cancer-related proteins (CRP) in the 6-MN groups relative to that with CRP in the control group. In addition, 6-MN had a greater negative effect on the CRP expression than nicotine. Bioinformatic analysis revealed that the differentially expressed genes and proteins in the 6-MN group were significantly enriched in the cancer-related pathways, unlike those in the nicotine group. Further validations of some lung cancer-related proteins, such as NF-κB p65, EGFR, and MET, were conducted by immunoblotting and real-time PCR, which revealed that 6-MN may have a greater negative effect on tumor development and metastasis than nicotine. Taken together, our findings suggest that new electronic cigarettes with 6-MN might offer some advantages over conventional electronic cigarettes containing nicotine.

Effect of Guanine Adduct Size, Shape, and Linker Type on the Conformation of Adducted DNA: A DFT and Molecular Dynamics Study

DNA is damaged through various exogenous sources (e.g., automobile exhaust, tobacco smoke, and processed foods), which can yield diverse C8-dG bulky aryl adducts. Adducts are known to induce structural changes to DNA that can lead to various biological outcomes, ranging from cell death to diseases such as cancer. Unfortunately, the relationship between the chemical composition of the damaged product, the adducted DNA structure, and the biological consequences is not well understood, which limits the development of disease detection and prevention strategies. The present study uses density functional theory (DFT) calculations and quintuplicate 1 μs molecular dynamics (MD) simulations to characterize the structure of DNA containing 21 model C8-dG adducts that systematically differ in size (phenyl to pyrenyl), shape (α (2,3), β (3,4) fusion, or ring substitution), and nucleobase-aryl group linkage (N, O, and C-linked). DFT calculations reveal that the inherent structural features of the G nucleobase adducts are impacted by linker type and bulky moiety shape, but not size, with the conformational flexibility reducing with α-ring fusion and linker composition as N > O > C. These structural properties are maintained in nucleoside models, which also reveal an increased propensity for anti-to-syn rotation about the glycosidic bond with N < O < C linker type. Although these diverse chemical features do not influence the global structure of adducted DNA, the adducts differentially impact the conformation local to the adducted site, including the relative populations of structures with the bulky moiety in the major groove (B conformer) and intercalated (stacked) into the helix (S conformer). Specifically, while the smallest phenyl adducts favor the B conformation and the largest pyrenyl-derived adducts stabilize the S conformation, the B/S ratio decreases with an increase in ring size and N > O > C linker composition. The shape and size (length) of the adduct can further finetune the B/S ratio, with β-fused naphthyl or α-fused phenanthryl N-linked adducts and O or C-linked adducts containing ring substitution increasing the prevalence of the S adducted DNA conformation. Overall, this work uncovers the significant effect of bulky moiety size and linker type, as well as the lesser impact of aryl group shape, on adducted DNA structure, which suggests differential replication and repair outcomes, and thereby represents an important step toward rationalizing connections between the structure and biological consequences of diverse DNA adducts.

Traffic-Related Air Pollution and Ground-Level Ozone Associated Global DNA Hypomethylation and Bulky DNA Adduct Formation

Studies have indicated that air pollution, including surface-level ozone (O₃), can significantly influence the risk of chronic diseases. To better understand the carcinogenic mechanisms of air pollutants and identify predictive disease biomarkers, we examined the association between traffic-related pollutants with DNA methylation alterations and bulky DNA adducts, two biomarkers of carcinogen exposure and cancer risk, in the peripheral blood of 140 volunteers-95 traffic police officers, and 45 unexposed subjects. The DNA methylation and adduct measurements were performed by bisulfite-PCR and pyrosequencing and ³²P-postlabeling assay. Airborne levels of benzo(a)pyrene [B(a)P], carbon monoxide, and tropospheric O₃ were determined by personal exposure biomonitoring or by fixed monitoring stations. Overall, air pollution exposure was associated with a significant reduction (1.41 units) in global DNA methylation (95% C.I. -2.65-0.04, p = 0.026). The decrement in ALU repetitive elements was greatest in the policemen working downtown (95% C.I. -3.23--0.49, p = 0.008). The DNA adducts were found to be significantly increased (0.45 units) in the municipal officers with respect to unexposed subjects (95% C.I. 0.02-0.88, p = 0.039), mainly in those who were controlling traffic in downtown areas (95% C.I. 0.39-1.29, p < 0.001). Regression models indicated an increment of ALU methylation at higher B(a)P concentrations (95% C.I. 0.03-0.60, p = 0.032). Moreover, statistical models showed a decrement in ALU methylation and an increment of DNA damage only above the cut-off value of 30 µg/m³ O₃. A significant increment of 0.73 units of IL-6 gene methylation was also found in smokers with respect to non-smokers. Our results highlighted the role of air pollution on epigenetic alterations and genotoxic effects, especially above the target value of 30 µg/m³ surface-level O₃, supporting the necessity for developing public health strategies aimed to reduce traffic-related air pollution molecular alterations.

An investigation of DNA damage and DNA repair in chemical carcinogenesis triggered by small-molecule xenobiotics and in cancer: Thirty years with the comet assay

In the present review we addressed the determination of DNA damage induced by small-molecule carcinogens, considered their persistence in DNA and mutagenicity in in vitro and in vivo systems over a period of 30 years. The review spans from the investigation of the role of DNA damage in the cascade of chemical carcinogenesis. In the nineties, this concept evolved into the biomonitoring studies comprising multiple biomarkers that not only reflected DNA/chromosomal damage, but also the potential of the organism for biotransformation/elimination of various xenobiotics. Since first years of the new millennium, dynamic system of DNA repair and host susceptibility factors started to appear in studies and a considerable knowledge has been accumulated on carcinogens and their role in carcinogenesis. It was understood that the final biological links bridging the arising DNA damage and cancer onset remain to be elucidated. In further years the community of scientists learnt that cancer is a multifactorial disease evolving over several decades of individual´s life. Moreover, DNA damage and DNA repair are inseparable players also in treatment of malignant diseases, but affect substantially other processes, such as degeneration. Functional monitoring of DNA repair pathways and DNA damage response may cast some light on above aspects. Very little is currently known about the relationship between telomere homeostasis and DNA damage formation and repair. DNA damage/repair in genomic and mitochondrial DNA and crosstalk between these two entities emerge as a new interesting topic.

Artificial Intelligence Predictive Models of Response to Cytotoxic Chemotherapy Alone or Combined to Targeted Therapy for Metastatic Colorectal Cancer Patients: A Systematic Review and Meta-Analysis

Tailored treatments for metastatic colorectal cancer (mCRC) have not yet completely evolved due to the variety in response to drugs. Therefore, artificial intelligence has been recently used to develop prognostic and predictive models of treatment response (either activity/efficacy or toxicity) to aid in clinical decision making. In this systematic review, we have examined the ability of learning methods to predict response to chemotherapy alone or combined with targeted therapy in mCRC patients by targeting specific narrative publications in Medline up to April 2022 to identify appropriate original scientific articles. After the literature search, 26 original articles met inclusion and exclusion criteria and were included in the study. Our results show that all investigations conducted on this field have provided generally promising results in predicting the response to therapy or toxic side-effects. By a meta-analytic approach we found that the overall weighted means of the area under the receiver operating characteristic (ROC) curve (AUC) were 0.90, 95% C.I. 0.80-0.95 and 0.83, 95% C.I. 0.74-0.89 in training and validation sets, respectively, indicating a good classification performance in discriminating response vs. non-response. The calculation of overall HR indicates that learning models have strong ability to predict improved survival. Lastly, the delta-radiomics and the 74 gene signatures were able to discriminate response vs. non-response by correctly identifying up to 99% of mCRC patients who were responders and up to 100% of patients who were non-responders. Specifically, when we evaluated the predictive models with tests reaching 80% sensitivity (SE) and 90% specificity (SP), the delta radiomics showed an SE of 99% and an SP of 94% in the training set and an SE of 85% and SP of 92 in the test set, whereas for the 74 gene signatures the SE was 97.6% and the SP 100% in the training set.

Cruciferous Vegetable Intake and Bulky DNA Damage within Non-Smokers and Former Smokers in the Gen-Air Study (EPIC Cohort)

Epidemiologic studies have indicated that cruciferous vegetables can influence the cancer risk; therefore, we examined with a cross-sectional approach the correlation between the frequent consumption of the total cruciferous vegetables and the formation of bulky DNA damage, a biomarker of carcinogen exposure and cancer risk, in the Gen-Air study within the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort. DNA damage measurements were performed in the peripheral blood of 696 of those apparently healthy without cancer controls, including 379 never-smokers and 317 former smokers from seven European countries by the 32P-postlabeling assay. In the Gen-Air controls, the median intake of cruciferous vegetables was 6.16 (IQR 1.16−13.66) g/day, ranging from 0.37 (IQR 0−6.00) g/day in Spain to 11.34 (IQR 6.02−16.07) g/day in the UK. Based on this information, participants were grouped into: (a) high consumers (>20 g/day), (b) medium consumers (3−20 g/day) and (c) low consumers (<3.0 g/day). Overall, low cruciferous vegetable intake was correlated with a greater frequency of bulky DNA lesions, including benzo(a)pyrene, lactone and quinone-adducts and bulky oxidative lesions, in the adjusted models. Conversely, a high versus low intake of cruciferous vegetables was associated with a reduction in DNA damage (up to a 23% change, p = 0.032); this was particularly evident in former smokers (up to a 40% change, p = 0.008). The Generalized Linear Regression models indicated an overall Mean Ratio between the high and the low consumers of 0.78 (95% confidence interval, 0.64−0.97). The current study suggests that a higher intake of cruciferous vegetables is associated with a lower level of bulky DNA adducts and supports the potential for cancer prevention strategies through dietary habit changes aimed at increasing the consumption of cruciferous vegetables.

Radon, Tobacco Exposure and Non-Small Cell Lung Cancer Risk Related to BER and NER Genetic Polymorphisms

INTRODUCTION

Tobacco consumption and radon exposure are considered the first and second most common causes of lung cancer, respectively. The aim of this study was to analyze both whether selected genetic polymorphisms in loci that are in DNA repair pathways, are related to non-small-cell lung cancer (NSCLC) and whether they may modulate the association between residential radon exposure and lung cancer in both smokers and never smokers.

METHODS

A multicentre, hospital-based, case-control study with 826 cases and 1201 controls was designed in a radon-prone area. Genotyping was determined in whole blood and residential radon exposure was measured in participants' dwellings.

RESULTS

Attending to tobacco exposure, the variant in the gene NBN (rs1805794) was associated with lung cancer in never smokers (OR 2.72; 95%1.44-5.2) and heavy smokers (OR 3.04; 95%CI 1.21-7.69). The polymorphism with the highest lung cancer association was OGG1 (rs125701), showing an OR of 8.04 (95%CI 1.64-58.29) for its homozygous variant genotype in heavy smokers. Attending to indoor radon exposure (>200Bq/m3), rs1452584, for its homozygous variant genotype, showed the highest association (OR 3.04 (95%CI 1.15-8.48).

CONCLUSION

The genes analyzed seem to have no association with the fully adjusted model, but they might modulate lung cancer association when different categories of tobacco consumption are considered (i.e. heavy smokers). This association may similarly be elevated for those individuals having high indoor radon exposures, though at a minor extent.

Alcohol and Head and Neck Cancer: Updates on the Role of Oxidative Stress, Genetic, Epigenetics, Oral Microbiota, Antioxidants, and Alkylating Agents

Head and neck cancer (HNC) concerns more than 890,000 patients worldwide annually and is associated with the advanced stage at presentation and heavy outcomes. Alcohol drinking, together with tobacco smoking, and human papillomavirus infection are the main recognized risk factors. The tumorigenesis of HNC represents an intricate sequential process that implicates a gradual acquisition of genetic and epigenetics alterations targeting crucial pathways regulating cell growth, motility, and stromal interactions. Tumor microenvironment and growth factors also play a major role in HNC. Alcohol toxicity is caused both directly by ethanol and indirectly by its metabolic products, with the involvement of the oral microbiota and oxidative stress; alcohol might enhance the exposure of epithelial cells to carcinogens, causing epigenetic modifications, DNA damage, and inaccurate DNA repair with the formation of DNA adducts. Long-term markers of alcohol consumption, especially those detected in the hair, may provide crucial information on the real alcohol drinking of HNC patients. Strategies for prevention could include food supplements as polyphenols, and alkylating drugs as therapy that play a key role in HNC management. Indeed, polyphenols throughout their antioxidant and anti-inflammatory actions may counteract or limit the toxic effect of alcohol whereas alkylating agents inhibiting cancer cells’ growth could reduce the carcinogenic damage induced by alcohol. Despite the established association between alcohol and HNC, a concerning pattern of alcohol consumption in survivors of HNC has been shown. It is of primary importance to increase the awareness of cancer risks associated with alcohol consumption, both in oncologic patients and the general population, to provide advice for reducing HNC prevalence and complications.

Attenuation of Polycyclic Aromatic Hydrocarbon (PAH)-Mediated Pulmonary DNA Adducts and Cytochrome P450 (CYP)1B1 by Dietary Antioxidants, Omega-3 Fatty Acids, in Mice

Numerous human and animal studies have reported positive correlation between carcinogen-DNA adduct levels and cancer occurrence. Therefore, attenuation of DNA adduct levels would be expected to suppress tumorigenesis. In this investigation, we report that the antioxidants omega 3-fatty acids, which are constituents of fish oil (FO), significantly decreased DNA adduct formation by polycyclic aromatic hydrocarbons (PAHs). B6C3F1 male mice were fed an FO or corn oil (CO) diet, or A/J male mice were pre-fed with omega-3 fatty acids eicosapentaenoic acid (EPA) and/or docosahexaenoic acid (DHA). While the B6C3F1 mice were administered two doses of a mixture of seven carcinogenic PAHs including benzo(a)pyrene (BP), the A/J mice were treated i.p. with pure benzo[a]pyrene (BP). Animals were euthanized after 1, 3, or 7 d after PAH treatment. DNA adduct levels were measured by the ³²P-postlabeling assay. Our results showed that DNA adduct levels in the lungs of mice 7 d after treatment were significantly decreased in the FO or EPA/DHA groups compared with the CO group. Interestingly, both qPCR and Western blot analyses revealed that FO, DHA and EPA/DHA significantly decreased the expression of cytochrome P450 (CYP) 1B1. CYP1B1 plays a critical role in the metabolic activation of BP to DNA-reactive metabolites. qPCR also showed that the expression of some metabolic and DNA repair genes was induced by BP and inhibited by FO or omega-3 fatty acids in liver, but not lung. Our results suggest that a combination of mechanism entailing CYP1B1 inhibition and the modulation of DNA repair genes contribute to the attenuation of PAH-mediated carcinogenesis by omega 3 fatty acids.

Effect of EGCG on bronchial epithelial cell premalignant lesions induced by cigarette smoke and on its CYP1A1 expression

Epigallocatechin-3-gallate (EGCG) has been demonstrated to exhibit anticancer effects; however, the mechanisms behind these are not yet clear. The objective of the present study was to assess the effect of EGCG on smoking-induced, precancerous, bronchial epithelial cell lesions and determine a potential protective mechanism. Human bronchial epithelial (HBE) cells were treated with cigarette smoke extract (CSE). Benzopyrene-DNA adducts were detected by immunofluorescence cytochemistry. Changes to microRNA (miRNA) expression levels were detected via microarray. The effects of EGCG on smoke-induced benzopyrene-DNA adduct formation and the subsequent change in miRNA expression were analyzed. Subsequently, the protective effect of EGCG on smoke inhalation-induced precancerous lesions was investigated. The expression levels of miRNA target genes were also analyzed. After CSE treatment, benzopyrene-DNA adducts appeared in HBE cells, along with a resultant change in miRNA expression. EGCG inhibited the effects of CSE exposure; benzopyrene-DNA adduct formation was reduced and miRNA expression changes were suppressed. In vivo, EGCG significantly reduced benzopyrene-DNA adduct formation and the subsequent development of precancerous lesions in rat lungs induced by cigarette smoke inhalation. Moreover, EGCG downregulated CYP1A1 overexpression, a target gene of multiple smoking-induced miRNAs, in rat lungs. EGCG may reduce the risk of lung cancer by downregulating the expression of the key gene CYP1A1, preventing the formation of smoking-induced benzopyrene-DNA adducts and alleviating smoking-induced bronchial epithelial dysplasia and heterogeneity.

Genome-wide mapping of genomic DNA damage: methods and implications

Exposures from the external and internal environments lead to the modification of genomic DNA, which is implicated in the cause of numerous diseases, including cancer, cardiovascular, pulmonary and neurodegenerative diseases, together with ageing. However, the precise mechanism(s) linking the presence of damage, to impact upon cellular function and pathogenesis, is far from clear. Genomic location of specific forms of damage is likely to be highly informative in understanding this process, as the impact of downstream events (e.g. mutation, microsatellite instability, altered methylation and gene expression) on cellular function will be positional—events at key locations will have the greatest impact. However, until recently, methods for assessing DNA damage determined the totality of damage in the genomic location, with no positional information. The technique of “mapping DNA adductomics” describes the molecular approaches that map a variety of forms of DNA damage, to specific locations across the nuclear and mitochondrial genomes. We propose that integrated comparison of this information with other genome-wide data, such as mutational hotspots for specific genotoxins, tumour-specific mutation patterns and chromatin organisation and transcriptional activity in non-cancerous lesions (such as nevi), pre-cancerous conditions (such as polyps) and tumours, will improve our understanding of how environmental toxins lead to cancer. Adopting an analogous approach for non-cancer diseases, including the development of genome-wide assays for other cellular outcomes of DNA damage, will improve our understanding of the role of DNA damage in pathogenesis more generally.

Silencing LINC00504 inhibits cell proliferation, invasion as well as migration and promotes cell apoptosis in lung cancer cells via upregulating miR-876-3p

LINC00504 acts as an oncogene and associates with unfavorable prognosis in patients with lung cancer. Silencing LINC00504 may be a promising strategy for treatment of lung cancer and its effects were firstly investigated in lung cancer cells this study. The gene expression level of miR-876-3p as well as LINC00504 were measured via PCR assay. The cell proliferation was investigated through Cell Counting Kit-8 (CCK-8) assay and colony formation assay. Flow cytometry was applied for detection of cell apoptosis. Wound healing and transwell assay were performed for measurement of cell migration and invasion respectively. The apoptosis related protein expressions were measured by western blot. Luciferase report assay was conducted for verification the target gene. LINC00504 was higher expressed in five types of lung cancer cells studied herein when compared with the control normal cells. LINC00504 knockdown exerted inhibitory effects on cell apoptosis, cell migration as well as cell invasion and promoted cell apoptosis. All the effects mentioned above were counteracted by miR-876-3p inhibitor. Silencing LINC00504 possessed anti-proliferation, repression of cell invasion as well as migration and pro-apoptosis effects via targeting up-regulation of miR-876-3p in lung cancer cells, proving the new therapeutic targets and highlighting the potential application in future diagnosis and treatment in lung cancer.

Oxidative Stress and DNA Damage in Chronic Disease and Environmental Studies

Humans are continually exposed to a large number of environmental carcinogens [...].

Wood dust and urinary 15-F2t isoprostane in Italian industry workers

Wood dust is one of the most common occupational exposures, with about 3.6 million of workers in the wood industry in Europe. Wood particles can deposit in the nose and the respiratory tract and cause adverse health effects. Occupational exposure to wood dust has been associated with malignant tumors of the nasal cavity and paranasal sinuses. The induction of oxidative stress and the generation of reactive oxygen species through activation of inflammatory cells could have a role in the carcinogenicity of respirable wood dust. Therefore, we conducted a cross-sectional study to evaluate the prevalence of urinary 15-F_2t isoprostane (15-F_2t-IsoP), a biomarker of oxidative stress and peroxidation of lipids, in 123 wood workers compared to 57 unexposed controls living in Tuscany region, Italy. 15-F_2t-IsoP generation was measured by ELISA. The main result of the present study showed that a statistically significant excess of this biomarker occurred in the workers exposed to 1.48 mg/m³ of airborne wood dust with respect to the unexposed controls. The overall mean ratio (MR) between the workers exposed to wood dust and the controls was 1.36, 95% Confidence Interval (C.I.) 1.18-1.57, after correction for age and smoking habits. A significant increment of 15-F_2t-IsoP (43%) was observed in the smokers as compared to the non-smokers. The urinary excretion of 15-F_2t-IsoP was significantly associated with co-exposure to organic solvents, i.e., MR of 1.41, 95% C.I. 1.17-1.70, after adjustment for age and smoking habits. A 41% excess was observed in long-term wood workers, 95% C.I. 1.14-1.75. Multivariate regression analysis showed that the level of 15-F_2t-IsoP was linearly correlated to the length of exposure, regression coefficient (β) = 0.244 ± 0.002 (SE). The overall increment by exposure group persisted after stratification for smoking habits. For instance, in smokers, a 53% excess was detected in the wood workers as compared to the controls, 95% C.I. 1.23-1.91. Our data support the hypothesis that oxidative stress and lipid peroxidation can have a role in the toxicity of wood dust F₂-IsoP measure can be a tool for the evaluation of the effectiveness of targeted interventions aimed to reduce exposures to environmental carcinogens.

Recent Studies on DNA Adducts Resulting from Human Exposure to Tobacco Smoke

DNA adducts are believed to play a central role in the induction of cancer in cigarette smokers and are proposed as being potential biomarkers of cancer risk. We have summarized research conducted since 2012 on DNA adduct formation in smokers. A variety of DNA adducts derived from various classes of carcinogens, including aromatic amines, polycyclic aromatic hydrocarbons, tobacco-specific nitrosamines, alkylating agents, aldehydes, volatile carcinogens, as well as oxidative damage have been reported. The results are discussed with particular attention to the analytical methods used in those studies. Mass spectrometry-based methods that have higher selectivity and specificity compared to 32P-postlabeling or immunochemical approaches are preferred. Multiple DNA adducts specific to tobacco constituents have also been characterized for the first time in vitro or detected in vivo since 2012, and descriptions of those adducts are included. We also discuss common issues related to measuring DNA adducts in humans, including the development and validation of analytical methods and prevention of artifact formation.

Carcinogens and DNA damage

Humans are variously and continuously exposed to a wide range of different DNA-damaging agents, some of which are classed as carcinogens. DNA damage can arise from exposure to exogenous agents, but damage from endogenous processes is probably far more prevalent. That said, epidemiological studies of migrant populations from regions of low cancer risk to high cancer risk countries point to a role for environmental and/or lifestyle factors playing a pivotal part in cancer aetiology. One might reasonably surmise from this that carcinogens found in our environment or diet are culpable. Exposure to carcinogens is associated with various forms of DNA damage such as single-stand breaks, double-strand breaks, covalently bound chemical DNA adducts, oxidative-induced lesions and DNA-DNA or DNA-protein cross-links. This review predominantly concentrates on DNA damage induced by the following carcinogens: polycyclic aromatic hydrocarbons, heterocyclic aromatic amines, mycotoxins, ultraviolet light, ionising radiation, aristolochic acid, nitrosamines and particulate matter. Additionally, we allude to some of the cancer types where there is molecular epidemiological evidence that these agents are aetiological risk factors. The complex role that carcinogens play in the pathophysiology of cancer development remains obscure, but DNA damage remains pivotal to this process.

Reactive Chemicals and Electrophilic Stress in Cancer: A Minireview

Exogenous reactive chemicals can impair cellular homeostasis and are often associated with the development of cancer. Significant progress has been achieved by studying the macromolecular interactions of chemicals that possess various electron-withdrawing groups and the elucidation of the protective responses of cells to chemical interventions. However, the formation of electrophilic species inside the cell and the relationship between oxydative and electrophilic stress remain largely unclear. Derivatives of nitro-benzoxadiazole (also referred as nitro-benzofurazan) are potent producers of hydrogen peroxide and have been used as a model to study the generation of reactive species in cancer cells. This survey highlights the pivotal role of Cu/Zn superoxide dismutase 1 (SOD1) in the production of reactive oxygen and electrophilic species in cells exposed to cell-permeable chemicals. Lipophilic electrophiles rapidly bind to SOD1 and induce stable and functionally active dimers, which produce excess hydrogen peroxide leading to aberrant cell signalling. Moreover, reactive oxygen species and reactive electrophilic species, simultaneously generated by redox reactions, behave as independent entities that attack a variety of proteins. It is postulated that the binding of the electrophilic moiety to multiple proteins leading to impairing different cellular functions may explain unpredictable side effects in patients undergoing chemotherapy with reactive oxygen species (ROS)-inducing drugs. The identification of proteins susceptible to electrophiles at early steps of oxidative and electrophilic stress is a promising way to offer rational strategies for dealing with stress-related malignant tumors.

Monocyte-derived exosomes upon exposure to cigarette smoke condensate alter their characteristics and show protective effect against cytotoxicity and HIV-1 replication

Smoking is known to exacerbate HIV-1 pathogenesis, especially in monocytes, through the oxidative stress pathway. Exosomes are known to alter HIV-1 pathogenesis through inter-cellular communication. However, the role of exosomes in smoking-mediated HIV-1 pathogenesis is unknown. In this study, we investigated the effect of cigarette smoke condensate (CSC) on the characteristics of monocyte-derived exosomes and their influence on HIV-1 replication. Initially, we demonstrated that CSC reduced total protein and antioxidant capacity in exosomes derived from HIV-1-infected and uninfected macrophages. The exosomes from CSC-treated uninfected cells showed a protective effect against cytotoxicity and viral replication in HIV-1-infected macrophages. However, exosomes derived from HIV-1-infected cells lost their protective capacity. The results suggest that the exosomal defense is likely to be more effective during the early phase of HIV-1 infection and diminishes at the latter phase. Furthermore, we showed CSC-mediated upregulation of catalase in exosomes from uninfected cells, with a decrease in the levels of catalase and PRDX6 in exosomes derived from HIV-1-infected cells. These results suggest a potential role of antioxidant enzymes, which are differentially packaged into CSC-exposed HIV-1-infected and uninfected cell-derived exosomes, on HIV-1 replication of recipient cells. Overall, our study suggests a novel role of exosomes in tobacco-mediated HIV-1 pathogenesis.

Linking the generation of DNA adducts to lung cancer

Worldwide, lung cancer is the leading cause of cancer death. DNA adducts are considered a reliable biomarker that reflects carcinogen exposure to tobacco smoke, but the central question is what is the relationship of DNA adducts and cancer? Therefore, we investigated this relationship by a meta-analysis of twenty-two studies with bronchial adducts for a total of 1091 subjects, 887 lung cancer cases and 204 apparently healthy individuals with no evidence of lung cancer. Our study shows that these adducts are significantly associated to increase lung cancer risk. The value of Mean Ratio_lung-cancer (MR) of bronchial adducts resulting from the random effects model was 2.64, 95% C.I. 2.00-3.50, in overall lung cancer cases as compared to controls. The significant difference, with lung cancer patients having significant higher levels of bronchial adducts than controls, persisted after stratification for smoking habits. The MR_lung-cancer value between lung cancer patients and controls for smokers was 2.03, 95% C.I. 1.42-2.91, for ex-smokers 3.27, 95% C.I. 1.49-7.18, and for non-smokers was 3.81, 95% C.I. 1.85-7.85. Next, we found that the generation of bronchial adducts is significantly related to inhalation exposure to tobacco smoke carcinogens confirming its association with volatile carcinogens. The MR_smoking estimate of bronchial adducts resulting from meta-regression was 2.28, 95% Confidence Interval (C.I.) 1.10-4.73, in overall smokers in respect to non-smokers. The present work provides strengthening of the hypothesis that bronchial adducts are not simply relate to exposure, but are a cause of chemical-induced lung cancer.