Associations between smoking, GST genotypes and N7-methylguanine levels in DNA extracted from bronchial lavage cells

Guanine-guided time-resolved luminescence recognition of DNA modification and i-motif formation by a terbium(III)-platinum(II) complex

Site-specific recognition of DNA modification or the formation of noncanonical structures has important applications in molecular biology, disease diagnosis, and gene expression analysis. In this study, we introduce a guanine-guided sensing tool using a terbium(III)-platinum(II) complex (TPC) as a time-resolved luminescence probe to site-specifically recognize DNA modification and i-motif formation in aqueous solution. The probe is composed of a Tb^III center as the luminescent reporter and two Pt^II units as the receptor for guanine (G) nucleobase. TPC exhibits remarkable reaction selectivity for guanine nucleotides over other nucleotides, giving rise to a significant increase in luminescence. The luminescence enhancement of TPC is mainly attributed to an energy transfer from G base to the Tb^III center after the specific coordination of Pt^II with N7 of guanine (N7-G), which would be facilitated by the phosphates through promoting the departure of coordinated water and bringing G closer to Tb^IIIvia noncovalent interactions. Based on such sensing feature, the enhanced luminescence of TPC sensitized by G nucleotides can correspondingly decrease upon N7-G modifications of DNA or i-motif formation through constructing simple guanine-guided sensing tools. This probe would provide a useful strategy for site-specific recognition of DNA for extensive purposes.

Direct-acting DNA ethylating agents associated with tobacco use primarily originate from the tobacco itself, not combustion

Unburnt tobacco and tobacco smoke contain a variety of carcinogens, exposure to which are causally associated with the incidence of several human cancers. Herein, we used isotope-dilution LC-MS/MS for the quantification of alkylated purines in DNA, following in vitro exposure to aqueous extracts of tobacco itself, and tobacco smoke. Our results demonstrated the presence of direct-acting ethylating agent(s) in unburnt tobacco, which 4.0-6.3 times exceeded that in the particulate phase of sidestream cigarette smoke and 6.8-8.9 times exceeded that in mainstream smoke. Interestingly, particulate phase of sidestream cigarette smoke exhibited higher ethylating potency than that in mainstream smoke. This finding refutes the previous assumptions that the ethylating agent(s) associated with smoking, are derived from cigarette smoke. Indeed, our data show that combustion of tobacco actually decreases the ethylating potency of tobacco. Although the identity of this agent(s) remains unknown, our data suggest that it is highly hydrophilic, and hence likely to be easily extracted by saliva. This would allow intimate contact with the tissues of the oropharyngeal cavity. Taken together, these results have profound implications for tobacco use, in particular for tobacco chewers and passive smokers, whose exposure to ethylating agent(s) is greater than previously thought.

Use of rodent data for cancer risk assessment of smokeless tobacco in the regulatory context

To support risk management decisions, information from different fields has been integrated in this presentation to provide a realistic quantitative cancer risk assessment of smokeless tobacco. Smoking among Swedish men is currently below 10%, while about 20% use a special smokeless tobacco (snus) as a substitute for cigarettes. Epidemiological data and molecular biomarkers demonstrate that rodent bioassays with tobacco specific nitrosamines (TSNA) overestimate cancer risk from snus by more than one order of magnitude. The underlying reasons are discussed. DNA damage constitutes a necessary, although not sufficient prerequisite for cancer initiation. Individuals who have not used tobacco exhibit DNA lesions identical with those induced by TSNA. No increase above this adduct background can be shown from snus, and extensive epidemiological studies in Sweden have failed to demonstrate elevated cancer risks even in long term users. A "bench mark" for acceptable risk of 1/10(6) derived from rodent data has been suggested when regulating snus. By relating similarly derived estimates for some food contaminants, the implementation even of a limit of 1/10(4) may be unrealistic. The management of smokeless tobacco products has rarely been based on a scientifically sound risk assessment, where attention is given to the outstandingly higher hazards associated with smoking.

Context Matters: Contribution of Specific DNA Adducts to the Genotoxic Properties of the Tobacco-Specific Nitrosamine NNK

The tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a potent pulmonary carcinogen in laboratory animals. It is classified as a Group 1 human carcinogen by the International Agency for Cancer Research. NNK is bioactivated upon cytochrome P450 catalyzed hydroxylation of the carbon atoms adjacent to the nitrosamino group to both methylating and pyridyloxobutylating agents. Both pathways generate a spectrum of DNA damage that contributes to the overall mutagenic and toxic properties of this compound. NNK is also reduced to form 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), which is also carcinogenic. Like NNK, NNAL requires metabolic activation to DNA alkylating agents. Methyl hydroxylation of NNAL generates pyridylhydroxybutyl DNA adducts, and methylene hydroxylation leads to DNA methyl adducts. The consequence of this complex metabolism is that NNK generates a vast spectrum of DNA damage, any form of which can contribute to the overall carcinogenic properties of this potent pulmonary carcinogen. This Perspective reviews the chemistry and genotoxic properties of the collection of DNA adducts formed from NNK. In addition, it provides evidence that multiple adducts contribute to the overall carcinogenic properties of this chemical. The adduct that contributes to the genotoxic effects of NNK depends on the context, such as the relative amounts of each DNA alkylating pathway occurring in the model system, the levels and genetic variants of key repair enzymes, and the gene targeted for mutation.

Increased N7-methyldeoxyguanosine DNA adducts after occupational exposure to pesticides and influence of genetic polymorphisms of paraoxonase-1 and glutathione S-transferase M1 and T1

There are concerns about genetic risks associated with long-term exposure to pesticides as these compounds may damage DNA, resulting in mutations that eventually lead to cancer, neurological, and reproductive adverse health effects. This study assessed DNA damage in intensive agricultural workers exposed to pesticides by determining the levels of N7-methyldeoxyguanosine (N7-MedG), an adduct known to be a robust biomarker of recent exposure to chemical methylating agents. A cohort of 39 plastic greenhouse workers was assessed for changes in lymphocyte DNA N7-MedG levels between low level and high level exposures during the course of a spraying season. The contributions of genetic polymorphisms of the pesticide-metabolizing enzymes paraoxonase-1 (PON1) and the glutathione S-transferases, GSTM1 and GSTT1, on N7-MedG levels and other potential confounders were also assessed. N7-MedG increased in the period of high pesticide exposure as compared to the low exposure period (0.23 and 0.18 µmol N7-MedG/mol dG for the unadjusted and adjusted linear mixed models, P = 0.02 and 0.08, respectively). Significant decreased levels of erythrocyte acetylcholinesterase and plasma cholinesterase were observed in the high versus low exposure period in both the unadjusted (2.85 U/g hemoglobin and 213.13 U/L, respectively) and adjusted linear mixed models (2.99 U/g hemoglobin and 230.77 U/L, respectively), indicating pesticide intake. In intensive agriculture workers, higher pesticide exposure increased DNA alkylation levels, further demonstrating the genotoxicity of pesticides in man. In addition, pesticide-exposed individuals with inherited susceptible metabolic genotypes (particularly, null genotype for GSTM1 and the PON1 192R allele) appear to have an increased risk of genotoxic DNA damage. Environ. Mol. Mutagen. 56:437-445, 2015. © 2014 Wiley Periodicals, Inc.

Exploratory study on the correlation between 14 lung cancer-related gene expression and specific clinical characteristics of NSCLC patients

Personalized medicine has become essential in the treatment of lung cancer. However, the lung cancer-related gene expression profiles in non-small cell lung cancer (NSCLC) patients have not been elucidated. In this study, the correlation between gene expression profiles and clinicopathological characteristics was investigated in NSCLC patients. A total of 95 patients were enrolled in this study. The mRNA expression levels of 14 genes were assessed by multiplex branched DNA liquidchip (MBL) technology and data on 9 clinicopathological characteristics of patients were collected simultaneously. The correlation between gene expression and clinicopathological characteristics was investigated. Out of the 9 clinicopathological parameters, 6 were associated with several of the 14 genes analyzed. Patient gender was associated with TYMS and TOP2A. Clinical stage was associated with VEGFR2, KIT and HER2. There was weak correlation between primary tumor size of ≤3 cm and the expression level of KIT. The mRNA expression levels of VEGFR2 and HER2 correlated with distant metastasis. BRCA1, TYMS, TOP2A and HER2 were associated with histological type. Smoking correlated with higher expression levels of BRCA1, TYMS and TOP2A and lower expression levels of PDGFRβ. The results were suggestive of correlation between the clinicopathological parameters of the NSCLC patients and the mRNA expression levels of certain lung cancer-related genes, including BRCA1, TYMS, TOP2A, PDGFRβ, VEGFR2, KIT and HER2.

Topographical study of O(6)-alkylguanine DNA alkyltransferase repair activity and N7-methylguanine levels in resected lung tissue

BACKGROUND

Tobacco specific nitrosamines such as 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) are genotoxic alkylating agents found within cigarette smoke that induce lung adenocarcinomas in animal models. In humans, adenocarcinomas originate most frequently in the lung periphery. The aim of this study was to determine whether peripheral lung has increased susceptibility to the genotoxic effects of alkylating agents by comparing DNA alkylation damage (N7-methylguanine: N7-meG) and repair (O(6)-alkylguanine DNA alkyltransferase: MGMT) in peripheral relative to central lung tissue.

METHODS

Macroscopically normal lung tissue, resected from patients undergoing surgery for lung cancer, was sampled at equidistant points from central to peripheral lung along a bronchus. N7-meG levels were determined using an immunoslotblot technique and MGMT activity with a [32P]-labelled oligodeoxynucleotide cleavage assay.

RESULTS

A total of 20 subjects were recruited, 12 males and 8 females with a mean age of 68.7±5.8years. There were 14 former and 6 current smokers with a mean smoking exposure of 34.0±18.3packyears. N7-meG (mean 0.75±0.57/10(6)dG, n=65 samples from 14 patients) and MGMT repair (geometric mean 9.57±1.62fmol/μg DNA, n=79 samples from 16 patients) were detected in all samples assayed. MGMT activity increased towards the lung periphery (r=0.28, p=0.023; n=16) with a highly significant association in current (r=0.53, p=0.008; n=6) but not former smokers (r=0.13; p=0.41; n=10). No correlation was seen with N7-meG levels and lung position (r=-0.18; p=0.21; n=14). N7-meG levels were higher in current compared to former smokers reaching significance in two lung positions including peripheral lung (p=0.047).

CONCLUSIONS

The findings in this study do not support the hypothesis that peripheral tissue is more susceptible to the genotoxic effects of alkylating agents than central lung tissue. In addition exposure to cigarette smoke reduced the level of MGMT in central bronchial tissue possibly through increased alkylating agent exposure.

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.

Smoking-related O4-ethylthymidine formation in human lung tissue and comparisons with bulky DNA adducts

Tobacco smoke contains many alkylating agents that can react with DNA to produce O(4)-ethylthymidine (O(4)-etT) and several other types of promutagenic base modifications. Our aims were (i) to confirm results of a pilot study (Godschalk, R., Nair, J., Schooten, F. J., Risch, A., Drings, P., Kayser, K., Dienemann, H. and Bartsch, H. (2002) Comparison of multiple DNA adduct types in tumor adjacent human lung tissue: effect of cigarette smoking. Carcinogenesis, 23, 2081-2086) on the formation of O(4)-etT in smokers' lung; (ii) to explore associations between levels of O(4)-etT and smoking status and (iii) to investigate whether a correlation exists between levels of O(4)-etT and bulky (polycyclic aromatic hydrocarbons-derived) DNA adducts. Archived DNA samples originated from histologically normal peripheral lung tissues of 64 Hungarian lung cancer patients, who underwent lung resection. O(4)-etT was determined by an immunoenriched (32)P-postlabelling-high-performance liquid chromatography method. Levels of bulky DNA adducts were determined by the nuclease P1 adduct-enriched (32)P-postlabelling. O(4)-etT levels ranged from 0.01 to 3.91 adducts/10(8) thymidines. In the combined group of subjects who smoked until surgery or gave up smoking at most 1 year before it, the mean level of O(4)-etT was 1.7-fold (P = 0.015) and of bulky DNA adducts 2.2-fold (P < 0.0001) higher than in long-term ex-smokers (LES) and never-smokers (NS) combined. We found no significant correlation between the individual levels of the two DNA adduct types. No dose-response was detected between O(4)-etT formation and smoking dose. In one-third of LES, O(4)-etT levels were above the 2.0-fold mean level of adducts found in NS, indicating its high persistence. Our results confirm the smoking-related formation of O(4)-etT in human lung DNA that should be explored as biomarker. Its long persistence in target tissue implicates a role of this potentially miscoding lesion in tobacco smoking-associated cancers.

Alkylation of sperm DNA is associated with male factor infertility and a reduction in the proportion of oocytes fertilised during assisted reproduction

Approximately one-third of IVF cases in the UK are attributed to male factor infertility and in the majority of cases the origin of male infertility is unknown. The integrity of sperm DNA is important both for the success of assisted reproduction and the implications for the off-spring. One type of DNA damage that has not been investigated with respect to fertility outcomes is the adduct N7-methyldeoxyguanosine (N7-MedG), a biomarker for exposure to alkylating agents. A prospective cohort of couples attending for IVF had their N7-MedG levels in sperm measured using an immunoslot blot technique to examine whether sperm N7-MedG levels are associated with male factor infertility, semen quality measures or assisted reproduction outcomes. Sufficient DNA for analysis was obtained from 67/97 couples and N7-MedG was detected in 94% of sperm samples analysed. Men diagnosed with male factor infertility had significantly higher mean levels of N7-MedG in their sperm DNA (P=0.03). Logistic regression analysis showed that N7-MedG levels were significantly negatively associated with the proportion of oocytes successfully fertilised irrespective of the method of fertilisation used (IVF or intra-cytoplasmic sperm injection; ICSI, P<0.001). Therefore exposure to DNA alkylating agents is significantly associated with male infertility and the proportion of oocytes fertilised during assisted reproduction. Reducing such exposure may improve male fertility but further work is required to determine the relative importance of exogenous and endogenous sources of exposure.

The formation and biological significance of N7-guanine adducts

DNA alkylation or adduct formation occurs at nucleophilic sites in DNA, mainly the N7-position of guanine. Ever since identification of the first N7-guanine adduct, several hundred studies on DNA adducts have been reported. Major issues addressed include the relationships between N7-guanine adducts and exposure, mutagenesis, and other biological endpoints. It became quickly apparent that N7-guanine adducts are frequently formed, but may have minimal biological relevance, since they are chemically unstable and do not participate in Watson Crick base pairing. However, N7-guanine adducts have been shown to be excellent biomarkers for internal exposure to direct acting and metabolically activated carcinogens. Questions arise, however, regarding the biological significance of N7-guanine adducts that are readily formed, do not persist, and are not likely to be mutagenic. Thus, we set out to review the current literature to evaluate their formation and the mechanistic evidence for the involvement of N7-guanine adducts in mutagenesis or other biological processes. It was concluded that there is insufficient evidence that N7-guanine adducts can be used beyond confirmation of exposure to the target tissue and demonstration of the molecular dose. There is little to no evidence that N7-guanine adducts or their depurination product, apurinic sites, are the cause of mutations in cells and tissues, since increases in AP sites have not been shown unless toxicity is extant. However, more research is needed to define the extent of chemical depurination versus removal by DNA repair proteins. Interestingly, N7-guanine adducts are clearly present as endogenous background adducts and the endogenous background amounts appear to increase with age. Furthermore, the N7-guanine adducts have been shown to convert to ring opened lesions (FAPy), which are much more persistent and have higher mutagenic potency. Studies in humans are limited in sample size and differences between controls and study groups are small. Future investigations should involve human studies with larger numbers of individuals and analysis should include the corresponding ring opened FAPy derivatives.

Biomarkers of induced active and passive smoking damage

In addition to the well-known link between smoking and lung cancer, large epidemiological studies have shown a relationship between smoking and cancers of the nose, oral cavity, oropharynx, larynx, esophagus, pancreas, bladder, kidney, stomach, liver, colon and cervix, as well as myeloid leukemia. Epidemiological evidence has reported a direct link between exposure of non-smokers to environmental tobacco smoke and disease, most notably, lung cancer. Much evidence demonstrates that carcinogenic-DNA adducts are useful markers of tobacco smoke exposure, providing an integrated measurement of carcinogen intake, metabolic activation, and delivery to the DNA in target tissues. Monitoring accessible surrogate tissues, such as white blood cells or bronchoalveolar lavage (BAL) cells, also provides a means of investigating passive and active tobacco exposure in healthy individuals and cancer patients. Levels of DNA adducts measured in many tissues of smokers are significantly higher than in non-smokers. While some studies have demonstrated an association between carcinogenic DNA adducts and cancer in current smokers, no association has been observed in ex or never smokers. The role of genetic susceptibility in the development of smoking related-cancer is essential. In order to establish whether smoking-related DNA adducts are biomarkers of tobacco smoke exposure and/or its carcinogenic activity we summarized all data that associated tobacco smoke exposure and smoking-related DNA adducts both in controls and/or in cancer cases and studies where the effect of genetic polymorphisms involved in the activation and deactivation of carcinogens were also evaluated. In the future we hope we will be able to screen for lung cancer susceptibility by using specific biomarkers and that subjects of compared groups can be stratified for multiple potential modulators of biomarkers, taking into account various confounding factors.

Gene-environment interaction in tobacco-related cancers

This review summarizes the carcinogenic effects of tobacco smoke and the basis for interaction between tobacco smoke and genetic factors. Examples of published papers on gene-tobacco interaction and cancer risk are presented. The assessment of gene-environment interaction in tobacco-related cancers has been more complex than originally expected for several reasons, including the multiplicity of genes involved in tobacco metabolism, the numerous substrates metabolized by the relevant genes and the interaction of smoking with other metabolic pathways. Future studies on gene-environment interaction and cancer risk should include biomarkers of smoking dose, along with markers of quantitative historical exposure to tobacco. Epigenetic studies should be added to classic genetic analyses, in order to better understand gene-environmental interaction and individual susceptibility. Other metabolic pathways in competition with tobacco genetic metabolism/repair should be incorporated in epidemiological studies to generate a more complete picture of individual cancer risk associated with environmental exposure to carcinogens.

Lung cancer risk and variation in MGMT activity and sequence

O(6)-Alkylguanine-DNA alkyltransferase (MGMT) repairs DNA adducts that result from alkylation at the O(6) position of guanine. These lesions are mutagenic and toxic and can be produced by a variety of agents including the tobacco-specific nitrosamines, carcinogens present in cigarette smoke. Here, we review some of our work in the context of inter-individual differences in MGMT expression and their potential influence on lung cancer risk. In humans there are marked inter-individual differences in not only levels of DNA damage in the lung (N7-methylguanine) that can arise from exposure to methylating agents but also in MGMT activity in lung tissues. In the presence of such exposure, this variability in MGMT activity may alter cancer susceptibility, particularly as animal models have demonstrated that the complete absence of MGMT activity predisposes to alkylating-agent induced cancer while overexpression is protective. Recent studies have uncovered a series of polymorphisms that affect protein activity or are associated with differences in expression levels. The associations between these (and other) polymorphisms and cancer risk are inconsistent, possibly because of small sample sizes and inter-study differences in lung cancer histology. We have recently analysed a consecutive series of case-control studies and found evidence that lung cancer risk was lower in subjects with the R178 allele.

Effects of metabolic genotypes on intermediary biomarkers in subjects exposed to PAHS: results from the EXPAH study

Data from the EXPAH project on PAH exposure and intermediary biomarkers were analyzed with respect to individual genotypes at seven metabolic gene loci. The GSTM1 null allele was associated with significantly higher levels of two biomarkers, malondialdehyde-2'-deoxyguanosine and benzo[a]pyrene DNA adducts in the total population from three Central and Eastern European countries. The CYP1B1 Leu/Val variant demonstrated effects on both markers of oxidative DNA damage in opposite directions, producing a higher level of M(1)dG with a trend from wild type (Leu/Leu) to heterozygotes to homozygous (Val/Val) variants, whereas the effects of these variants were reversed for 8-oxodG. Cluster Analysis was used to group composite genotypes in order to determine if combined genotypes of multiple loci could explain some of the variation seen with the biomarkers, expressed per unit of exposure, referred to as a sensitivity index. This analysis revealed two closely related genotypes each involving four of the loci (GSTM1*0/*0, CYP1A1*1*1, CYP1B1*1/*2, GSTP1*1/*1 and GSTT1*0/*0, CYP1A1*1*1, CYP1B1*1/*2, GSTP1*1/*1.) that conferred significant resistance to the DNA damaging effects of benzo[a]pyrene, measured as the level of a benzo[a]pyrene-like adduct per unit of benzo[a]pyrene exposed.

Prospective study of urinary excretion of 7-methylguanine and the risk of lung cancer: Effect modification bymu class glutathione-S-transferases

Nitrosamines are mainly mutagenic through methylation of DNA. 7-Methylguanine (m(7)Gua) is a product of base excision repair and spontaneous depurination of such lesions in DNA and a metabolite from RNA. Associations between urinary excretion of m(7)Gua and risk of lung cancer were examined in a population-based cohort of 25,717 men and 27,972 women aged 50-64 years. During 3-7 years follow-up 260 cases with lung cancer were identified and a subcohort of 263 individuals matched on sex, age and smoking duration was selected for comparison. Urine collected at entry was analyzed for m(7)Gua by HPLC. Effect modification by glutathione-S-transferases GSTM1, GSTM3, GSTT1 and GSTP1 was investigated. We found higher excretion of m(7)Gua among current smokers than among former smokers. The IRR (incidence rate ratio) of lung cancer was 1.20 (95% CI: 1.00-1.43) per doubling of m(7)Gua excretion in unadjusted analysis and 1.12 (95% CI: 0.93-1.35) after adjustment for smoking status, intensity and duration at entry. This association was mainly present among current smokers. Comparing the highest with the lowest tertile of m(7)Gua excretion the IRR of lung cancer was 1.75 (95% CI: 1.04-2.95) irrespective of genotype and 2.75 (95% CI: 1.33-5.81) in subjects with GSTM1 null genotype. If not caused by residual confounding by smoking a possible association between m(7)Gua excretion and lung cancer supports the importance of methylation of guanine. The finding of an association between m(7)Gua excretion and lung cancer risk mainly among current smokers and subjects with GSTM1 null genotype supports causality in this respect.

Polymorphisms of phase II xenobiotic-metabolizing and DNA repair genes and in vitro N-ethyl-N-nitrosourea-induced O6-ethylguanine levels in human lymphocytes

This study tested the hypothesis that genetic variants of phase II detoxification enzymes and DNA repair proteins affect individual response to DNA damage from alkylating agents. In 171 healthy individuals, an immunoslot blot assay was used to measure O6-ethylguanosine (O6-EtGua) adduct levels in peripheral blood lymphocytes treated with N-ethyl-N-nitrosourea (ENU) in vitro. The genotypes of GSTM1, GSTT1, GSTP1 I(105)V and A(114)V, MGMT L(84)F and I(143)V, XPD D(312)N and K(751)Q, and XRCC3 T(241)M were determined. Demographic and exposure information was collected by in-person interview. Student's t-test, analysis of (co)variance, and multiple linear regression models were used in statistical analyses. The mean and median (range) O6-EtGua levels were 94.6 and 84.8 (3.2-508.1)fmol/g DNA, respectively. The adduct level was significantly lower in people who smoked >or=25 years than that in never-smokers (square-root transformed mean values 8.20 versus 9.37, P=0.03). Multiple linear regression models revealed that GSTT1 (beta=-2.36, P=0.009) polymorphism was a significant predictor of the level of adducts in 82 never-smokers, whereas the number of years smoked (beta=-0.08, P=0.005) and XRCC3 T(241)M (beta=2.22, P=0.007) in 89 ever-smokers. The association between GSTP1 I(105)V, MGMT I(143)V, and XPD D(312)N with the level of adducts was not conclusive. Each polymorphism could explain 2-10% of the variation of the adduct level. These observations suggest that GSTT1 null and XRCC3 T(241)M polymorphism may have some functional significance in modulating the level of ENU-induced DNA damage and these effects are smoking-dependent. Results from this exploratory study need to be confirmed in other experimental systems.

De minimus non curat lex--virtual thresholds for cancer initiation by tobacco specific nitrosamines--prospects for harm reduction by smokeless tobacco

Whereas the impact of tobacco specific nitrosamines in smokers is obscured by the presence of numerous other carcinogens and promoters, for smokeless tobacco virtually all the carcinogenic potential is associated with 4-(nitrosomethylamino)-1-(3-pyridyl)-1-butanone (NNK) and N'-nitrosonornicotine (NNN). In some countries exposure to smokeless tobacco with extremely high nitrosamine concentrations have been found to induce cancers in the head-neck region, whereas three recent large epidemiological studies failed to detect any such risk with respect to Swedish low-nitrosamine snuff. This review deals with quantitative aspects of DNA adduct formation from NNN and NNK in relation to the background levels ubiquitously found in healthy humans without known exposures to either tobacco or alkylating agents. The lack of significant increases of pro-mutagenic O6-methylations and DNA pyridyloxobutylations seen in smokers, as well as the negative outcome of the Swedish epidemiological studies, can be expected on basis of extrapolation of the dose response relationships found in rodents to actual exposures to NNK and NNN in Swedish snuff or from smoking. Sweden has the lowest prevalence of male smokers and smoking related diseases in the Western World, which has been ascribed to the fact that more than 20% of the grown up male population uses snuff. Smokeless tobacco represents an inexpensive and effective alternative to nicotine delivering products like nicotine patch, spray or gum. Considering that all other tobacco products are freely marketed, the ban on low-nitrosamine snuff in all countries in EU except Sweden is difficult to defend on either medical or ethical grounds.

No association between N7-methyldeoxyguanosine and 8-oxodeoxyguanosine levels in human lymphocyte DNA

To examine associations between two different classes of DNA damage that can occur through endogenous processes or exogenous exposures such as smoking, N7-methyldeoxyguanosine (N7-MedG) and 8-oxodeoxyguanosine (8-oxodG) levels were measured in lymphocyte DNA from 22 bronchoscopy patients. 8-OxodG and N7-MedG was detected in 100% and 91% of samples, respectively with 8-oxodG levels being approx 20 times higher (mean 8.39+/-3.578-oxodG/10(6)dG versus 0.41+/-0.33 N7-MedG/10(6) dG) which provides an indication of the relative importance of the agents that induce oxidative DNA damage or alkylation damage. The sources of these genotoxic lesions remain to be established but N7-MedG and 8-oxodG levels were not correlated (r(2)<0.01) suggesting that there is no association between alkylating agent and reactive oxygen species exposure, their metabolism and/or the DNA repair processes that can remove this DNA damage.

Glutathione S-transferase M1 and P1 genotype, passive smoking, and peak expiratory flow in asthma

OBJECTIVES

Our purpose with this work was to assess the contribution of glutathione S-transferase gene variants to asthma susceptibility and pulmonary function in relation to tobacco smoke exposure in the home.

METHODS

Young individuals with asthma (age: 3-21 years; n = 504) were recruited through primary and secondary care throughout Tayside, Scotland (BREATHE Study). Spirometry was obtained on 407 individuals. Binary logistic regression and general linear modeling were used to explore phenotypic characteristics by genotype and tobacco smoke exposure status in younger children (3-12 years; n = 384) and teenagers and young adults (13-21 years; n = 120).

RESULTS

Three- to 12-year-olds with asthma, null for the GSTM1 gene or homozygous for the GSTP1Val105 allele, were overrepresented in the group exposed to environmental tobacco smoke. No differences in lung function values could be detected in this group. In contrast, 13- to 21-year-olds with the GSTM1-null genotype or homozygous for the GSTP1Val105 allele from smoking households were more likely to have a substantially lower percentage of predicted peak expiratory flow rates than those from nonsmoking households (83% vs 98%).

CONCLUSIONS

Three- to 12-year-olds who are null for GSTM1 or homozygous for the GSTP1Val105 allele are more susceptible to asthma associated with environmental tobacco smoke exposure than those with more intact glutathione S-transferase status. In the 13- to 21-year-olds, GSTM1-null status interacts with environmental tobacco smoke exposure to substantially reduce peak expiratory flow rate. The environmental tobacco smoke effect in GSTM1-null children with asthma could be cumulative over time, resulting in detrimental effects on peak expiratory flow rate in 13- to 21-year-olds with asthma.

Rapid and sensitive quantification of urinary N7-methylguanine by isotope-dilution liquid chromatography/electrospray ionization tandem mass spectrometry with on-line solid-phase extraction

A rapid, highly specific and sensitive isotope-dilution liquid chromatography/tandem mass spectrometry (LC/MS/MS) method coupled with an on-line solid-phase extraction (SPE) system was developed to measure N7-methylguanine (N7-MeG) in urine. 15N5-Labeled N7-MeG was synthesized to serve as an internal standard, and an on-line SPE cartridge was used for on-line sample cleanup and enrichment. The urine sample can be directly analyzed within 15 min without prior sample purification. The detection limit for this method was estimated as 8.0 pg/mL (4.8 pmol) on-column. This method was further applied to study exposure to methylating agents arising from cigarette smoke. Sixty-seven volunteers were recruited, including 32 regular smokers and 35 nonsmokers. Urinary cotinine, a major metabolite of nicotine, was also determined using an isotope-dilution LC/MS/MS method. The results showed that urinary levels of N7-MeG observed in smokers (4215 +/- 1739 ng/mg creatinine) were significantly (P < 0.01) higher than those in nonsmokers (3035 +/- 720 ng/mg creatinine). It was further noted that the urinary level of N7-MeG was found to be correlated with that of cotinine for smokers, implying that cigarette smoking resulted in increased DNA methylation, followed by depurination and excretion of N7-MeG in urine. As a result of the on-line extraction system, this method is capable of routine high-throughput analysis and accurate quantitation of N7-MeG, and could be a useful tool for health surveillance of methylating agent exposure.