Differences in DNA-damage in non-smoking men and women exposed to environmental tobacco smoke (ETS)

Dysregulation of immunity by cigarette smoking promotes inflammation and cancer: A review

Smoking is a serious global health issue. Cigarette smoking contains over 7000 different chemicals. The main harmful components include nicotine, acrolein, aromatic hydrocarbons and heavy metals, which play the key role for cigarette-induced inflammation and carcinogenesis. Growing evidences show that cigarette smoking and its components exert a remarkable impact on regulation of immunity and dysregulated immunity promotes inflammation and cancer. Therefore, this comprehensive and up-to-date review covers four interrelated topics, including cigarette smoking, inflammation, cancer and immune system. The known harmful chemicals from cigarette smoking were summarized. Importantly, we discussed in depth the impact of cigarette smoking on the formation of inflammatory or tumor microenvironment, primarily by affecting immune effector cells, such as macrophages, neutrophils, and T lymphocytes. Furthermore, the main molecular mechanisms by which cigarette smoking induces inflammation and cancer, including changes in epigenetics, DNA damage and others were further summarized. This article will contribute to a better understanding of the impact of cigarette smoking on inducing inflammation and cancer.

Human Variation in DNA Repair, Immune Function, and Cancer Risk

DNA damage constantly threatens genome integrity, and DNA repair deficiency is associated with increased cancer risk. An intuitive and widely accepted explanation for this relationship is that unrepaired DNA damage leads to carcinogenesis due to the accumulation of mutations in somatic cells. But DNA repair also plays key roles in the function of immune cells, and immunodeficiency is an important risk factor for many cancers. Thus, it is possible that emerging links between inter-individual variation in DNA repair capacity and cancer risk are driven, at least in part, by variation in immune function, but this idea is underexplored. In this review we present an overview of the current understanding of the links between cancer risk and both inter-individual variation in DNA repair capacity and inter-individual variation in immune function. We discuss factors that play a role in both types of variability, including age, lifestyle, and environmental exposures. In conclusion, we propose a research paradigm that incorporates functional studies of both genome integrity and the immune system to predict cancer risk and lay the groundwork for personalized prevention.

Environmental Tobacco Smoke in Occupational Settings: Effect and Susceptibility Biomarkers in Workers From Lisbon Restaurants and Bars

Environmental tobacco smoke (ETS) has been recognized as a major health hazard by environmental and public health authorities worldwide. In Portugal, smoke-free laws are in force for some years, banning smoking in most indoor public spaces. However, in hospitality venues such as restaurants and bars, owners can still choose between a total smoke-free policy or a partial smoking restriction with designated smoking areas, if adequate reinforced ventilation systems are implemented. Despite that, a previous study showed that workers remained continuously exposed to higher ETS pollution in Lisbon restaurants and bars where smoking was still allowed, comparatively to total smoke-free venues. This was assessed by measurements of indoor PM2.5 and urinary cotinine, a biomarkers of tobacco smoke exposure, demonstrating that partial smoking restrictions do not effectively protect workers from ETS. The aim of the present work was to characterize effect and susceptibility biomarkers in non-smokers from those hospitality venues occupationally exposed to ETS comparatively to non-exposed ones. A group of smokers was also included for comparison. The sister chromatid exchange (SCE), micronucleus (MN) and comet assays in whole peripheral blood lymphocytes (PBLs) and the micronucleus assay in exfoliated buccal cells, were used as biomarkers of genotoxicity. Furthermore, a comet assay after ex vivo challenge of leukocytes with an alkylating agent, ethyl methanesulfonate (EMS), was used to analyze the repair capacity of those cells. Genetic polymorphisms in genes associated with metabolism and DNA repair were also included. The results showed no clear association between occupational exposure to ETS and the induction of genotoxicity. Interestingly, the leukocytes from non-smoking ETS-exposed individuals displayed lower DNA damage levels in response to the ex vivo EMS challenge, in comparison to those from non-exposed workers, suggesting a possible adaptive response. The contribution of individual susceptibility to the effect biomarkers studied was unclear, deserving further investigation.

Metabolomic profiling of in vivo plasma responses to dioxin-associated dietary contaminant exposure in rats: implications for identification of sources of animal and human exposure

Dioxin contamination of the food chain typically occurs when cocktails of combustion residues or polychlorinated biphenyl (PCB) containing oils become incorporated into animal feed. These highly toxic compounds are bioaccumulative with small amounts posing a major health risk. The ability to identify animal exposure to these compounds prior to their entry into the food chain may be an invaluable tool to safeguard public health. Dioxin-like compounds act by a common mode of action and this suggests that markers or patterns of response may facilitate identification of exposed animals. However, secondary co-contaminating compounds present in typical dioxin sources may affect responses to compounds. This study has investigated for the first time the potential of a metabolomics platform to distinguish between animals exposed to different sources of dioxin contamination through their diet. Sprague-Dawley rats were given feed containing dioxin-like toxins from hospital incinerator soot, a common PCB oil standard and pure 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) (normalized at 0.1 μg/kg TEQ) and acquired plasma was subsequently biochemically profiled using ultra high performance liquid chromatography (UPLC) quadropole time-of-flight-mass spectrometry (QTof-MS). An OPLS-DA model was generated from acquired metabolite fingerprints and validated which allowed classification of plasma from individual animals into the four dietary exposure study groups with a level of accuracy of 97-100%. A set of 24 ions of importance to the prediction model, and which had levels significantly altered between feeding groups, were positively identified as deriving from eight identifiable metabolites including lysophosphatidylcholine (16:0) and tyrosine. This study demonstrates the enormous potential of metabolomic-based profiling to provide a powerful and reliable tool for the detection of dioxin exposure in food-producing animals.

DNA and protein adducts in human tissues resulting from exposure to tobacco smoke

Tobacco smoke contains a variety of genotoxic carcinogens that form adducts with DNA and protein in the tissues of smokers. Not only are these biochemical events relevant to the carcinogenic process, but the detection of adducts provides a means of monitoring exposure to tobacco smoke. Characterization of smoking-related adducts has shed light on the mechanisms of smoking-related diseases and many different types of smoking-derived DNA and protein adducts have been identified. Such approaches also reveal the potential harm of environmental tobacco smoke (ETS) to nonsmokers, infants and children. Because the majority of tobacco-smoke carcinogens are not exclusive to this source of exposure, studies comparing smokers and nonsmokers may be confounded by other environmental sources. Nevertheless, certain DNA and protein adducts have been validated as biomarkers of exposure to tobacco smoke, with continuing applications in the study of ETS exposures, cancer prevention and tobacco product legislation. Our article is a review of the literature on smoking-related adducts in human tissues published since 2002.

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone is correlated with 8-hydroxy-2'-deoxyguanosine in humans after exposure to environmental tobacco smoke

Cigarette smoking and exposure to environmental tobacco smoke (ETS) are important risk factors for many cancers. However, exposure doses have usually not been quantitatively assessed in human studies. In humans 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol and its glucuronate conjugate (defined as total NNAL) are the major metabolites of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, a cigarette-specific carcinogen. Although animal studies have shown that exposure to cigarette smoke increases tissue oxidative DNA damage, the relationship between cigarette smoke and 8-hydroxydeoxyguanosine (8-OHdG) is not consistent in human studies. In the present study, we have developed a simple, sensitive, and robust LC-MS/MS method for quantifying total NNAL and 8-OHdG concentrations in human plasma. We quantified total NNAL and 8-OHdG in plasma as well as 8-OHdG in urine of 121 healthy male subjects. Total NNAL levels were significantly higher in ever-smokers than in never-smokers. Furthermore, total NNAL levels in plasma were increased with numbers of cigarettes smoked per day in ever-smokers. It suggests that total NNAL in plasma is a good biomarker for cigarette smoke exposure. After stratifying by smoking status and adjusting for age, ETS exposure and occupation category, total NNAL was associated with plasma and urinary 8-OHdG in never-smokers, but not in ever-smokers. Since total NNAL levels in nonsmokers represented the ETS exposure, it appears that 8-OHdG levels are dose-dependently correlated with their ETS exposure dose. Furthermore, this correlation supports the hypothesis that oxidative DNA damage is one of major adverse effects induced by ETS exposure in humans.

Reduction in oxidatively generated DNA damage following smoking cessation

Background

Cigarette smoking is a known cause of cancer, and cancer may be in part due to effects of oxidative stress. However, whether smoking cessation reverses oxidatively induced DNA damage unclear. The current study sought to examine the extent to which three DNA lesions showed significant reductions after participants quit smoking.

Methods

Participants (n = 19) in this study were recruited from an ongoing 16-week smoking cessation clinical trial and provided blood samples from which leukocyte DNA was extracted and assessed for 3 DNA lesions (thymine glycol modification [d(T^gpA)]; formamide breakdown of pyrimidine bases [d(T^gpA)]; 8-oxo-7,8-dihydroguanine [d(G^h)]) via liquid chromatography tandem mass spectrometry (LC-MS/MS). Change in lesions over time was assessed using generalized estimating equations, controlling for gender, age, and treatment condition.

Results

Overall time effects for the d(T^gpA) (χ²(3) = 8.068, p < 0.045), d(P^fpA) (χ²(3) = 8.477, p < 0.037), and d(G^h) (χ²(3) = 37.599, p < 0.001) lesions were seen, indicating levels of each decreased significantly after CO-confirmed smoking cessation. The d(T^gpA) and d(P^fpA) lesions show relatively greater rebound at Week 16 compared to the d(G^h) lesion (88% of baseline for d(T^gpA), 64% of baseline for d(P^fpA), vs 46% of baseline for d(G^h)).

Conclusions

Overall, results from this analysis suggest that cigarette smoking contributes to oxidatively induced DNA damage, and that smoking cessation appears to reduce levels of specific damage markers between 30-50 percent in the short term. Future research may shed light on the broader array of oxidative damage influenced by smoking and over longer durations of abstinence, to provide further insights into mechanisms underlying carcinogenesis.

Impact of Environmental Tobacco Smoke on the Incidence of Mutations in Epidermal Growth Factor Receptor Gene in Never-Smoker Patients With Non–Small-Cell Lung Cancer

Purpose

Active tobacco smoking has been associated with the incidence of epidermal growth factor receptor (EGFR) mutations. However, the impact of environmental tobacco smoke (ETS) on EGFR mutations has been unknown. We investigated an association between ETS exposure and EGFR mutations in never smokers with non–small-cell lung cancer (NSCLC).

Patients and Methods

We enrolled 179 consecutive never smokers who were newly diagnosed with NSCLC. The history of ETS exposure was obtained with a standardized questionnaire that included exposure period, place, and duration. The nucleotide sequences of exons 18 to 21 on EGFR gene were determined using nested polymerase chain reaction amplification.

Results

The incidence of EGFR mutations was significantly lower in patients with ETS exposure than in those without (38.5% v 61.4%; P = .008). In a logistic regression model that adjusted for sex and histology, an adjusted odds ratio (AOR) for the risk of EGFR mutations with exposure to ETS was 0.40 (95% CI, 0.20 to 0.81; P = .011). In quartile groups based on total smoker-year, the AORs for the lowest- to highest-quartile groups were 0.59 (95% CI, 0.23 to 1.49), 0.50 (95% CI, 0.17 to 1.50), 0.48 (95% CI, 0.20 to 1.18), and 0.22 (95% CI, 0.08 to 0.62; Ptrend = .028). Among the types of ETS exposure, adulthood ETS and household ETS were significantly associated with the incidence of EGFR mutations. Patients with ETS exposure showed a lower response rate to EGFR tyrosine kinase inhibitors than did patients without ETS exposure (24.6% v 44.8%; P = .053).

Conclusion

ETS exposure is negatively associated with EGFR mutations in never smokers with NSCLC.

Mechanisms of leukemia translocations

PURPOSE OF REVIEW

This review highlights recent findings about the known DNA repair machinery, its impact on chromosomal translocation mechanisms and their relevance to leukemia in the clinic.

RECENT FINDINGS

Chromosomal translocations regulate the behavior of leukemia. They not only predict outcome but they define therapy. There is a great deal of knowledge on the products of leukemic translocations, yet little is known about the mechanism by which those translocations occur. Given the large number of DNA double-strand breaks that occur during normal progression through the cell cycle, especially from V(D)J recombination, stalled replication forks or failed decatenation, it is surprising that leukemogenic translocations do not occur more frequently. Fortunately, hematopoietic cells have sophisticated repair mechanisms to suppress such translocations. When these defenses fail leukemia becomes far more common, as seen in inherited deficiencies of DNA repair. Analyzing translocation sequences in cellular and animal models, and in human leukemias, has yielded new insights into the mechanisms of leukemogenic translocations.

SUMMARY

New data from animal models suggest a two hit origin of leukemic translocations, where there must be both a defect in DNA double-strand break repair and a subsequent failure of cell cycle arrest for leukemogenesis.

Second hand smoke, age of exposure and lung cancer risk

BACKGROUND

Exposure to second hand smoke (SHS) has been identified as a risk factor for lung cancer for three decades. It is also known that the lung continues to grow from birth to adulthood, when lung growth stops. We hypothesize that after adjusting for active cigarette smoking, if SHS exposure took place during the period of growth, i.e. in the earlier part of life (0-25 years of age) the risk of lung cancer is greater compared to an exposure occurring after age 25.

METHOD

Second hand smoke exposure was self-reported for three different activities (leisure, work and at home) for this study population of 1669 cases and 1263 controls. We created variables that captured location of exposure and timing of first exposure with respect to a study participant's age (0-25, >25 years of age). Multiple logistic regressions were used to study the association between SHS exposure and lung cancer, adjusting for age, gender and active smoking variables.

RESULT

For study participants that were exposed to SHS at both activities (work and leisure) and compared to one or no activity, the adjusted odds ratio (AOR) for lung cancer was 1.30 (1.08-1.57) when exposure occurred between birth and age 25 and 0.66 (0.21-1.57) if exposure occurred after age 25 years. Respective results for non-smokers were 1.29 (0.82-2.02) and 0.87 (0.22-3.38), and current and ex-smokers combined 1.28 (1.04-1.58) and 0.66 (0.15-2.85).

CONCLUSION

All individuals exposed to SHS have a higher risk of lung cancer. Furthermore, this study suggests that subjects first exposed before age 25 have a higher lung cancer risk compared to those for whom first exposure occurred after age 25 years.

Induction of V(D)J-mediated recombination of an extrachromosomal substrate following exposure to DNA-damaging agents

V(D)J recombinase normally mediates recombination signal sequence (RSS) directed rearrangements of variable (V), diversity (D), and joining (J) germline gene segments that lead to the generation of diversified T cell receptor or immunoglobulin proteins in lymphoid cells. Of significant clinical importance is that V(D)J-recombinase-mediated rearrangements at immune RSS and nonimmune cryptic RSS (cRSS) have been implicated in the genomic alterations observed in lymphoid malignancies. There is growing evidence that exposure to DNA-damaging agents can increase the frequency of V(D)J-recombinase-mediated rearrangements in vivo in humans. In this study, we investigated the frequency of V(D)J-recombinase-mediated rearrangements of an extrachromosomal V(D)J plasmid substrate following exposure to alkylating agents and ionizing radiation. We observed significant dose- and time-dependent increases in V(D)J recombination frequency (V(D)J RF) following exposure to ethyl methanesulfonate (EMS) and methyl methanesulfonate (MMS) but not a nonreactive analogue, methylsulfone (MeSulf). We also observed a dose-dependent increase in V(D)J RF when cells were exposed to gamma radiation. The induction of V(D)J rearrangements following exposure to DNA-damaging agents was not associated with an increase in the expression of RAG 1/2 mRNA compared to unexposed controls or an increase in expression of the DNA repair Ku70, Ku80 or Artemis proteins of the nonhomologous end joining pathway. These studies demonstrate that genotoxic alkylating agents and ionizing radiation can induce V(D)J rearrangements through a cellular response that appears to be independent of differential expression of proteins involved with V(D)J recombination.

Second Hand Smoke Exposure and Survival in Early-Stage Non–Small-Cell Lung Cancer Patients

PURPOSE

Second hand smoke (SHS) exposure is associated with higher risk of lung cancer. However, the role of SHS in lung cancer survival is not clear.

EXPERIMENTAL DESIGN

We examined the association between self-reported SHS exposure before diagnosis and overall survival and recurrence-free survival in 393 early-stage non-small-cell lung cancer patients. SHS exposure was analyzed by both duration and location of exposure using log-rank test and Cox proportional hazard models, adjusting for covariates including pack-years of smoking.

RESULTS

The median follow-up time was 66 months (range, 0.2-140 months). There were 135 recurrences and 213 deaths. The 5-year overall survival rates were 71% [95% confidence interval (95% CI), 62-81%], 61% (51-72%), 49% (38-60%), and 47% (37-58%), respectively, for patients with the lowest to highest quartile of SHS exposure durations (P < 0.001, log-rank test), with the adjusted hazard ratio (AHR) of 1.57 (95% CI, 1.02-2.41) for the highest versus lowest quartile of SHS exposure durations (P(trend) = 0.04). For different SHS exposure locations, a stronger association was found for SHS exposure at work (AHR of the highest versus lowest quartile, 1.71; 95% CI, 1.12-2.61; P(trend) = 0.03) than for exposure at home (AHR, 1.26; 95% CI, 0.86-1.86; P(trend) = 0.20) or leisure places (AHR, 1.28; 95% CI, 0.83-1.95; P(trend) = 0.16). Similar associations were observed when SHS exposure durations were dichotomized into two or three groups and between SHS exposure and recurrence-free survival.

CONCLUSIONS

SHS exposure is associated with worse survival in early-stage non-small-cell lung cancer patients, especially for SHS exposure at the work.