Influence of cigarette smoking on the levels of DNA adducts in human bronchial epithelium and white blood cells

High-Risk Human Papillomavirus and Tobacco Smoke Interactions in Epithelial Carcinogenesis

Cervical, anogenital, and some head and neck cancers (HNC) are etiologically associated with high-risk human papillomavirus (HR-HPV) infection, even though additional cofactors are necessary. Epidemiological studies have established that tobacco smoke (TS) is a cofactor for cervical carcinogenesis because women who smoke are more susceptible to cervical cancer when compared to non-smokers. Even though such a relationship has not been established in HPV-related HNC, a group of HPV positive patients with this malignancy are smokers. TS is a complex mixture of more than 4500 chemical compounds and approximately 60 of them show oncogenic properties such as benzo[α]pyrene (BaP) and nitrosamines, among others. Some of these compounds have been evaluated for carcinogenesis through experimental settings in collaboration with HR-HPV. Here, we conducted a comprehensive review of the suggested molecular mechanisms involved in cooperation with both HR-HPV and TS for epithelial carcinogenesis. Furthermore, we propose interaction models in which TS collaborates with HR-HPV to promote epithelial cancer initiation, promotion, and progression. More studies are warranted to clarify interactions between oncogenic viruses and chemical or physical environmental factors for epithelial carcinogenesis.

Quantification of DNA damage products by gas chromatography tandem mass spectrometry in lung cell lines and prevention effect of thyme antioxidants on oxidative induced DNA damage

Lung cancer has a high treatment cost and poor prognosis in comparison to other types of cancers. This work was involved in studying oxidative DNA base damage inhibition. Accordingly, standard carvacrol, thymol, thymoquinone with water and water-methanol extract of thyme (Origanum vulgare L. subsp. hirtum (link.) Ietswaart), thyme oil and thyme water were prepared and investigated for their efficacy to inhibit DNA oxidative damage formed by H₂O₂ in malignant lung cells (A549). The antioxidant capacity by ABTS assay was 271.73 ± 11.45 mg trolox equivalent/mL for thyme oil. HPLC analysis was carried out to determine the contents of different thyme extracts, results showing the presence of carvacrol, thymol, protocatechuic acid, caffeic acid, epicatechin and rosmarinic acid in water and water-methanol extracts while only carvacrol and thymol were found in thyme oil and thyme water. After DNA isolation from the cultured cells, the formed oxidative induced DNA damage products were analysed using GC-MS/MS. It was proven that the antioxidants in the cell culture media have succeeded to inhibit oxidative DNA base damage. Thymoquinone was shown to be the best protectant antioxidant among other antioxidants against the formation of oxidative DNA damage, whereas water-methanol extract of thyme was the best among the plant-sourced samples. Thymoquinone and thyme water-methanol extract were investigated for their efficacy on cultured healthy lung cells (BEAS-2B), and it was proven that they are efficient in protection against the oxidation of DNA of healthy lung cells too.

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.

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

The generation of bulky DNA adducts consists of conjugates formed between large reactive electrophiles and DNA-binding sites. The term "bulky DNA adducts" comes from early experiments that employed a ³²P-DNA postlabeling approach. This technique has long been used to elucidate the association between adducts and carcinogen exposure in tobacco smoke studies and assess the predictive value of adducts in cancer risk. Molecular data showed increased DNA adducts in respiratory tracts of smokers vs nonsmokers. Experimental studies and meta-analysis demonstrated that the relationship between adducts and carcinogens was linear at low doses, but reached steady state at high exposure, possibly due to metabolic and DNA repair pathway saturation and increased apoptosis. Polymorphisms of metabolic and DNA repair genes can increase the effects of environmental factors and confer greater likelihood of adduct formation. Nevertheless, the central question remains as to whether bulky adducts cause human cancer. If so, lowering them would reduce cancer incidence. Pooled and meta-analysis has shown that smokers with increased adducts have increased risk of lung cancer. Adduct excess in smokers, especially in prospective longitudinal studies, supports their use as biomarkers predictive of lung cancer.

Genetic polymorphisms of human cytochrome P450 CYP1A1 in an Egyptian population and tobacco-induced lung cancer

Background

Cytochrome P450 CYP1A1 helps detoxify the potential carcinogens in tobacco smoke, it was reported that polymorphisms in the coding gene result in variation in the expression and activity levels which alter metabolism and clearance of carcinogens and therefore modify cancer risk. In this work, we aimed to identify CYP1A1 gene polymorphisms associated with lung cancer in Egyptian population and to examine the interaction effect with Tobacco smoking in modulating disease risk.

Methods

A case–control study was conducted on 150 unrelated lung cancer patients and 150 unrelated control subjects. Genomic DNA was extracted and sequencing analysis of CYP1A1 gene was performed on ABI PRISM 3100 genetic analyzer.

Results

Three variants in CYP1A1 gene were identified in heterozygous forms in lung cancer patients I462V, T461N and I286T. A combined variant T461N/ I462V associated with lung cancer and those who carried this variant were 2-times more likely to develop lung cancer (OR = 2.03, 95% CI = 1.81-2.29, P = 0.04), specially the non-small cell type (NSCLC) (OR = 2.20, 95% CI = 1.93–2.50, P = 0.02). Wild type was more frequent among smoker controls (83.3%) compared to smoker lung cancer patients (54.8%), P = 0.03. Association studies to examine the interaction effect of identified variants with Tobacco smoking in modulating disease risk showed no significant associations. Identified polymorphisms showed no significant implication on the stage or the prognosis of the disease.

Conclusion

Our findings support that CYP1A1 polymorphisms play a role in the pathogenesis of lung cancer. In Egyptian population, CYP1A1 I462V, T461N and I286T variants were identified among lung cancer patients and combined T461N/ I462V was a risk variant for NSCLC in non smokers.

Complex relationships between occupation, environment, DNA adducts, genetic polymorphisms and bladder cancer in a case-control study using a structural equation modeling

DNA adducts are considered an integrate measure of carcinogen exposure and the initial step of carcinogenesis. Their levels in more accessible peripheral blood lymphocytes (PBLs) mirror that in the bladder tissue. In this study we explore whether the formation of PBL DNA adducts may be associated with bladder cancer (BC) risk, and how this relationship is modulated by genetic polymorphisms, environmental and occupational risk factors for BC. These complex interrelationships, including direct and indirect effects of each variable, were appraised using the structural equation modeling (SEM) analysis. Within the framework of a hospital-based case/control study, study population included 199 BC cases and 213 non-cancer controls, all Caucasian males. Data were collected on lifetime smoking, coffee drinking, dietary habits and lifetime occupation, with particular reference to exposure to aromatic amines (AAs) and polycyclic aromatic hydrocarbons (PAHs). No indirect paths were found, disproving hypothesis on association between PBL DNA adducts and BC risk. DNA adducts were instead positively associated with occupational cumulative exposure to AAs (p = 0.028), whereas XRCC1 Arg 399 (p<0.006) was related with a decreased adduct levels, but with no impact on BC risk. Previous findings on increased BC risk by packyears (p<0.001), coffee (p<0.001), cumulative AAs exposure (p = 0.041) and MnSOD (p = 0.009) and a decreased risk by MPO (p<0.008) were also confirmed by SEM analysis. Our results for the first time make evident an association between occupational cumulative exposure to AAs with DNA adducts and BC risk, strengthening the central role of AAs in bladder carcinogenesis. However the lack of an association between PBL DNA adducts and BC risk advises that these snapshot measurements are not representative of relevant exposures. This would envisage new scenarios for biomarker discovery and new challenges such as repeated measurements at different critical life stages.

Systems approaches evaluating the perturbation of xenobiotic metabolism in response to cigarette smoke exposure in nasal and bronchial tissues

Capturing the effects of exposure in a specific target organ is a major challenge in risk assessment. Exposure to cigarette smoke (CS) implicates the field of tissue injury in the lung as well as nasal and airway epithelia. Xenobiotic metabolism in particular becomes an attractive tool for chemical risk assessment because of its responsiveness against toxic compounds, including those present in CS. This study describes an efficient integration from transcriptomic data to quantitative measures, which reflect the responses against xenobiotics that are captured in a biological network model. We show here that our novel systems approach can quantify the perturbation in the network model of xenobiotic metabolism. We further show that this approach efficiently compares the perturbation upon CS exposure in bronchial and nasal epithelial cells in vivo samples obtained from smokers. Our observation suggests the xenobiotic responses in the bronchial and nasal epithelial cells of smokers were similar to those observed in their respective organotypic models exposed to CS. Furthermore, the results suggest that nasal tissue is a reliable surrogate to measure xenobiotic responses in bronchial tissue.

Case study: the role of mechanistic network models in systems toxicology

Twenty first century systems toxicology approaches enable the discovery of biological pathways affected in response to active substances. Here, we briefly summarize current network approaches that facilitate the detailed mechanistic understanding of the impact of a given stimulus on a biological system. We also introduce our network-based method with two use cases and show how causal biological network models combined with computational methods provide quantitative mechanistic insights. Our approach provides a robust comparison of the transcriptional responses in different experimental systems and enables the identification of network-based biomarkers modulated in response to exposure. These advances can also be applied to pharmacology, where the understanding of disease mechanisms and adverse drug effects is imperative for the development of efficient and safe treatment options.

A romatic DNA adduct levels in human peripheral blood lymphocytes and total white blood cells by 32P postlabelling: need for validation

Long lived lymphocytes tend to have higher 32P postlabelling measured levels of adducts than short lived granulocytes in environmental and life style associated i.e. smoking exposures. With the aim of investigating this issue for occupational exposure to PAH and contributing to further validation of some technical aspects of the 32P postlabelling assay, two Italian laboratories analysed PAH-DNA adducts from lymphocytes and total white blood cells WBC. Seventy seven blood samples from coke oven workers employed at a steel plant located in Taranto, Southern Italy, and 14 samples from control subjects were collected. At the University of Padua, DNA was purified from peripheral blood lymphocytes PBL. Two years later, at the University of Bari, white blood cells WBC were isolated from replicate blood samples stored at- 80 C and DNA purified by the same method. In both cases, the nuclease P1 modified postlabelling assay was used to determine aromatic DNA adduct levels. The mean adduct levels were 5.13 3.37 Padua and 2.48 1.27 Bari per 108 nucleotides. Both laboratories observed large inter individual variations of adduct levels ranging from 0.09 to 18.93 per 108 nucleotides. Both the correlation and the agreement of the two sets of data were assessed. Slight correlation r = 0.39; p 0.01 and a poor level of agreement were found, the intra class correlation coefficient being equal to 0.05. Better correlation coefficient r = 0.54, p 0.01 and intra class correlation coefficient r = 0.50 were observed comparing only the adduct levels determined on the diagonal zone DRZ. Our findings seem to confirm the same divergence reported in the literature on DNA adduct levels between lymphocytes and granulocytes.

The analysis of DNA adducts: the transition from (32)P-postlabeling to mass spectrometry

The technique of (32)P-postlabeling, which was introduced in 1982 for the analysis of DNA adducts, has long been the method of choice for in vivo studies because of its high sensitivity as it requires only <10μg DNA to achieve the detection of 1 adduct in 10(10) normal bases. (32)P-postlabeling has therefore been utilized in numerous human and animal studies of DNA adduct formation. Like all techniques (32)P-postlabeling does have several disadvantages including the use of radioactive phosphorus, lack of internal standards, and perhaps most significantly does not provide any structural information for positive identification of unknown adducts, a shortcoming that could significantly hamper progress in the field. Structural methods have since been developed to allow for positive identification of DNA adducts, but to this day, the same level of sensitivity and low sample requirements provided by (32)P-postlabeling have not been matched. In this mini review we will discuss the (32)P-postlabeling method and chronicle the transition to mass spectrometry via the hyphenation of gas chromatography, capillary electrophoresis, and ultimately liquid chromatography which, some 30years later, is only just starting to approach the sensitivity and low sample requirements of (32)P-postlabeling. This paper focuses on the detection of bulky carcinogen-DNA adducts, with no mention of oxidative damage or small alkylating agents. This is because the (32)P-postlabeling assay is most compatible with bulky DNA adducts. This will also allow a more comprehensive focus on a subject that has been our particular interest since 1990.

Biotransformation of benzo[a]pyrene in Ahr knockout mice is dependent on time and route of exposure

Benzo[a]pyrene (BP) is an ubiquitous environmental pollutant with potent mutagenic and carcinogenic properties. The Ah receptor (Ahr) is important in the metabolic activation of BP and is therefore central to BP-induced carcinogenesis. Although Ahr(-/-) mice are refractory to BP-induced carcinogenesis, higher levels of BP-DNA and -protein adducts were formed in them than in wild-type mice. These results indicated the presence of an Ahr-independent and/or a slower biotransformation of BP in Ahr knockout mice. To address this issue further, we have now performed a time-course experiment, with mice receiving a single oral dose of BP (100 mg/kg). Wild-type mice have an effective clearance of BP metabolites, mainly through 3-hydroxybenzo[a]pyrene and 9-hydroxybenzo[a]pyrene in the feces with reduced levels of DNA and protein adducts in the examined tissues. On the other hand, the Ahr(-/-) mice appear to have a lower metabolic clearance of BP resulting in increased levels of DNA and protein adducts and of unmetabolized BP. In addition, we have performed an administration route experiment and found that skin-exposed Ahr(-/-) mice showed lower levels of protein adducts along with markedly reduced P450 1B1 expression, but only in the exposed area, as compared with the wild-type mice. In addition, the systemic uptake of BP is increased in the Ahr(-/-) mice as compared with the wild-type mice. Hence, the lack of a functional Ah receptor results in an Ahr-independent biotransformation of BP with a slower clearance of BP and higher levels of DNA and protein adducts, but the distribution and levels of BP and BP-protein adducts are clearly dependent on the route of exposure.

CYP1A1 gene polymorphisms increase lung cancer risk in a high-incidence region of Spain: a case control study

Background

A rural region in south-west Spain has one of the highest lung cancer incidence rates of the country, as revealed by a previous epidemiological 10-year follow-up study. The present work was undertaken to ascertain the role of CYP1A1 gene polymorphisms and their interaction with tobacco smoking in the development of the disease in this location.

Methods

One-hundred-and-three cases of lung cancer and 265 controls participated in the study. The participants were screened for the presence of four CYP1A1 polymorphisms, namely MspI, Ile462Val, T3205C, and Thr461Asn. Lung cancer risk was estimated as odds ratios (OR) and 95% confidence intervals (CI) using unconditional logistic regression models adjusting for age, sex, and smoking.

Results

The distribution of the variant CYP1A1 alleles was different from that described for other Caucasian populations, with CYP1A1*2A showing an uncommonly high frequency (p < 0.01). The CYP1A1*2B allele (carrying MspI and Ile462Val mutations) was strongly associated with high lung cancer risk (OR = 4.59, CI:1.4-12.6, p <0.01). The Ile462Val polymorphism was also shown to increase the risk for the disease (OR = 4.51, CI:1.8-11.9; p <0.01) and particularly for squamous-cell (OR = 5.01; CI: 1.6-14.3, p < 0.01) and small-cell lung carcinoma (SCLC) (OR = 6.97, CI: 1.2-81.3; p = 0.04). Moreover, the Thr461Asn polymorphism was found to be associated with SCLC in a Caucasian population for the first time to our knowledge (OR = 8.33, CI: 1.3-15.2, p = 0.04).

Conclusion

The results suggest that CYP1A1 polymorphisms contribute to increase lung cancer susceptibility in an area with an uncommon high incidence rate.

Lifestyle, environmental, and genetic predictors of bulky DNA adducts in a study population nested within a prospective Danish cohort

Bulky DNA adducts are considered a potential biomarker of cancer risk. In this study, the association between various lifestyle, environmental, and genetic factors and the levels of bulky DNA adducts in peripheral leukocytes was examined in a study group nested within a population-based prospective Danish cohort. At enrollment, blood samples were collected and information on lifestyle, including dietary and smoking habits, obtained. Previously, bulky DNA adducts were measured in 245 individuals who developed lung cancer and 255 control members of the cohort. Of these 500 individuals, data on 375 individuals were included in this study, excluding 125 cases, which developed lung cancer within the first 3 yr after blood sampling. Bulky DNA adduct levels were measured by 32P-postlabeling technique and polymorphisms in carcinogen metabolism and DNA repair genes were determined. Potential predictors of bulky DNA adduct levels were analyzed by univariate and multivariate regression analyses. Women tended to have higher adduct levels than men. Living in central Copenhagen and surface darkness of fried meat and fish were associated with quantitative higher adduct levels. No significant associations were found between dietary factors or smoking and DNA adduct levels. Further, the results showed no prominent associations between any of 12 genetic polymorphisms and adduct levels. Overall, our study showed only few associations between dietary, environmental, and genetic factors and levels of bulky DNA adducts measured in peripheral leukocytes in a general Danish population.

PAH biomarkers for human health risk assessment: a review of the state-of-the-art

Polycyclic aromatic hydrocarbons (PAH) are widely distributed in the environment, and some are carcinogenic to human beings. The study of biomarkers has helped clarify the nature and magnitude of the human health risks posed by such substances. This article provides a review of the state-of-the-art on PAH biomarkers for human health risk assessment and also discusses their applicability within the context of environmental management in Brazil. The article discusses the methodologies for determination of some biomarkers such as 1-hydroxypyrene and PAH-DNA adducts. Cytogenetic markers, frequency of chromosomal aberrations, and micronucleus induction were considered for the evaluation of cancer risk. The current stage of studies on validation of such biomarkers was also approached.

Effect of active smoking on the human bronchial epithelium transcriptome

Background

Lung cancer is the most common cause of cancer-related deaths. Tobacco smoke exposure is the strongest aetiological factor associated with lung cancer. In this study, using serial analysis of gene expression (SAGE), we comprehensively examined the effect of active smoking by comparing the transcriptomes of clinical specimens obtained from current, former and never smokers, and identified genes showing both reversible and irreversible expression changes upon smoking cessation.

Results

Twenty-four SAGE profiles of the bronchial epithelium of eight current, twelve former and four never smokers were generated and analyzed. In total, 3,111,471 SAGE tags representing over 110 thousand potentially unique transcripts were generated, comprising the largest human SAGE study to date. We identified 1,733 constitutively expressed genes in current, former and never smoker transcriptomes. We have also identified both reversible and irreversible gene expression changes upon cessation of smoking; reversible changes were frequently associated with either xenobiotic metabolism, nucleotide metabolism or mucus secretion. Increased expression of TFF3, CABYR, and ENTPD8 were found to be reversible upon smoking cessation. Expression of GSK3B, which regulates COX2 expression, was irreversibly decreased. MUC5AC expression was only partially reversed. Validation of select genes was performed using quantitative RT-PCR on a secondary cohort of nine current smokers, seven former smokers and six never smokers.

Conclusion

Expression levels of some of the genes related to tobacco smoking return to levels similar to never smokers upon cessation of smoking, while expression of others appears to be permanently altered despite prolonged smoking cessation. These irreversible changes may account for the persistent lung cancer risk despite smoking cessation.

DNA adduct formation of benzo[a]pyrene in white blood cells of workers exposed to polycyclic aromatic hydrocarbons

The major DNA adducts of anti-benzo[a]pyrene diolepoxide (BPDE) were determined by high performance liquid chromatography with fluorescence detection (HPLC-FLD) in white blood cells (WBC) of workers exposed to benzo[a]pyrene (B[a]P). In addition, ambient concentrations of B[a]P at the workplace were determined by personal air sampling. Workers in a refractory setting were examined before (n=26) and 3 months after (n = 33) changing the production material (binding pitch). Furthermore, 9 coke oven workers were examined. The change in the production process in the refractory setting led to a decrease in the median of ambient B[a]P concentrations (0.14 to <0.07 microg/m3). The median of BPDE-DNA adduct levels in WBC also decreased from 0.9 adducts/10(8) nucleotides before changing the production material to <0.5 adducts/10(8) nucleotides 3 months afterwards. The B[a]P concentrations at the workplace for the coke oven workers were found to be significantly higher than in the refractory setting. However, BPDE-DNA adduct concentrations in coke oven workers and refractory setting workers showed no significant difference, which was probably due to the low number of studied subjects in the coke-oven setting. No significant differences could be observed for BPDE-DNA adduct levels between current smokers (n=21) and non-smokers (n=14; p = 0.93) from both plants. In addition, no correlation between B[a]P concentrations in the air and DNA adduct levels in refractory workers and in coke oven workers could be found (r = -0.03, p = 0.87). Because of the missing correlation between personal air sampling and BPDE-DNA adduct levels in WBC, the results may indicate that their formation is either influenced by other routes of exposure to B[a]P (e.g., skin absorption, dietary habits) or interindividual differences in their formation and repair.

Safety and efficacy of weekly oral oltipraz in chronic smokers

Cigarette smoking is thought to contribute to carcinogenesis by formation of DNA adducts of tobacco smoke constituents leading to genotoxic damage. The dithiolethione, oltipraz, is a putative cancer chemopreventive agent that induces phase II detoxifying enzymes in preclinical models and reduces aflatoxin adducts in humans living in areas with high dietary levels. To determine if oltipraz could reduce adduct levels of tobacco smoke constituents in the lungs and other target organs, chronic smokers were enrolled to one of three arms: 400 or 200 mg/wk oral oltipraz or placebo. Endobronchial tissue and bronchoalveolar lavage were done before and after 12 weeks of drug treatment; peripheral blood, urine, and oral saline rinse were also collected. Toxicity was assessed every 4 weeks. Fifty-nine of the 77 enrolled subjects completed the study. Of those receiving oltipraz, 15% experienced grade 2/3 toxicity, which was predominantly gastrointestinal. All subject withdrawals occurred in the oltipraz groups. There was no significant difference between pre- and post-polycyclic aromatic hydrocarbon-DNA adduct levels in lung epithelial cells measured by immunoperoxidase staining between treatment and placebo groups. Likewise, no significant differences were found in polycyclic aromatic hydrocarbon or benzo(a)pyrene-7,8-diol-9,10-epoxide adducts measured in blood, oral lining cells, or bladder lining cells. There was also no increase in mRNA or enzymatic activity of phase II enzymes and no change in glutathione levels. Thus, despite moderate drug-related toxicity, there was no significant effect on pharmacodynamic or surrogate risk biomarkers. Other agents with lower toxicity and greater activity to induce phase II enzymes are needed to definitively test the detoxification-induction paradigm in smokers.

Exocyclic malondialdehyde and aromatic DNA adducts in larynx tissues

Cigarette smoking and alcohol consumption, known to cause free radical generation and lipid peroxidation, are established risk factors for larynx cancer. Malondialdehyde (MDA) is a naturally occurring product of lipid peroxidation, capable of interacting with DNA to form exocyclic MDA-DNA adducts. In the present study, we investigated if the production of MDA-DNA adducts was increased in larynx cancer patients with respect to controls using (32)P-DNA postlabeling techniques. Moreover, we examined the potential effects of cigarette smoking and alcohol consumption on endogenous DNA adducts. We then analyzed the same set of larynx tissues for the presence of (32)P-postlabeled aromatic DNA adducts to determine more about the levels and types of adducts formed in the larynx. We observed that cancer patients tended to have increased levels of MDA and aromatic DNA adducts with respect to controls. In addition, smoking and alcohol were found to influence the formation of endogenous adducts in the larynx tissues. Finally, the amounts of endogenous adducts were found to be comparable to those observed for aromatic DNA adducts in the same set of larynx tissues. These findings imply that endogenous lesions, if not repaired, may contribute to larynx cancer development.

Role of estrogen receptor in regulation of polycyclic aromatic hydrocarbon metabolic activation in lung

Epidemiological and biochemical studies have indicated that females may be at greater risk of smoking associated lung cancer compared with males. Among lung cancer patients, female smokers have been found to have higher levels of PAH-related DNA adducts and CYP1A1 gene expression in their normal lung tissue compared to male smokers. A possible role of steroid hormones in these sex differences via interactions between aryl hydrocarbon receptor and estrogen receptor mediated cellular effects has been suggested. In the present study the impact of the estrogen receptor (ERalpha) on CYP1A1 and CYP1B1 gene expression was studied in vitro in human bronchial epithelial cells. Transient transfection of the BEP2D cell line with ERalpha influenced neither constitutive expression of CYP1A1 or CYP1B1 nor induction of these genes by TCDD as measured by real-time RT-PCR. ERalpha had no effect on the constitutive or TCDD-induced enzymatic activity of CYP1A1 (EROD). We also studied the effect of steroid hormones on lung PAH metabolic activation in A/J mice. Intact and ovariectomized female mice were orally exposed to a single dose of benzo[a]pyrene. Ovariectomy did not influence the levels of either benzo[a]pyrene-derived protein or DNA adducts in the lung tissue measured by HPLC and 32P-postlabeling, respectively. In conclusion, the present data do not support the hypothesis of a role of estrogen or the ERalpha in regulating the metabolic activation of polycyclic aromatic hydrocarbons in lung.

Genetic susceptibility to tobacco-related cancer

Although cigarette smoking is the dominant risk factor for several epithelial cancers, only a small fraction of individuals with tobacco exposure develop cancer. The underlying hypothesis is that genetic factors may render certain smokers more susceptible to cancer than others. Genetic alterations in critical regulatory pathways may predispose cells to carcinogenesis. These pathways include regulation of xenobiotic metabolism; control of genomic stability, including DNA repair mechanisms, cell-cycle checkpoints, apoptosis and telomere length; and control of microenvironmental factors, such as matrix metalloproteinases, inflammation and growth factors. In addition, epigenetic events, such as promoter hypermethylation and loss of imprinting, are also involved in carcinogenesis. In this review, we will summarize recent advances in genetic susceptibility to tobacco-related cancer. Emphasizing on risk assessment, we will describe how genetic variations in the above-mentioned genetic pathways modify the tobacco-related cancer risk. In addition, we will discuss how genetic variations may assist in predicting clinical outcome, such as the natural history of cancer and treatment response. The measurements of genetic susceptibility by both genotypic and phenotypic assays are covered in the text. Finally, we present a number of current concerns that need to be addressed as the exciting field of molecular cancer epidemiology advances rapidly.

Smoking-related DNA adducts in anal epithelium

Several studies have identified tobacco smoking as a risk factor for anal cancer in both women and men. Samples of anal epithelium from haemorrhoidectomy specimens from current smokers (n = 20) and age-matched life-long non-smokers (n = 16) were analysed for DNA adducts by the nuclease P(1) digestion enhancement procedure of 32P-postlabelling analysis. The study included 14 men and 22 women. Both qualitative and quantitative differences in the adduct profiles were observed between the smokers and non-smokers. The mean adduct level was significantly higher in the smokers than in the non-smokers (1.88 +/- 0.71) (S.D.) versus 1.36 +/- 0.60 adducts per 10(8) nucleotides, P = 0.02, two-tailed unpaired t-test with Welch's correction); furthermore, the adduct pattern seen in two-dimensional chromatograms revealed the smoking-related diagonal radioactive zone in 17/20 smokers, but not in any of the non-smokers (P < 0.00001, Fisher's exact test). These results indicate that components of tobacco smoke inflict genotoxic damage in the anal epithelium of smokers and provide a plausible mechanism for a causal association between smoking and anal cancer.

Resveratrol inhibits benzo[a]pyrene-DNA adduct formation in human bronchial epithelial cells

Resveratrol (trans-3,4′,5-trihydroxystilbene), a phytoalexin present in various plants and foods, has in several in vitro and in vivo studies demonstrated cancer chemopreventive and chemotherapeutic potential. We investigated the in vitro effect of resveratrol on benzo[a]pyrene (B[a]P) -induced DNA adducts in human bronchial epithelial cells. This was compared to the effect of resveratrol on the expression of the cytochrome P450 (CYP) genes CYP1A1 and CYP1B1 and the formation of B[a]P metabolites. Exposure of BEAS-2B and BEP2D cells to B[a]P and increasing concentrations of resveratrol resulted in a dose- and time-dependent inhibition of DNA adduct formation quantified by ³²P-postlabelling. Supporting this result, resveratrol was shown to inhibit CYP1A1 and CYP1B1 gene expression, as measured by real-time reverse transcriptase—polymerase chain reaction. Also, a significant correlation was found between the number of DNA adducts and the mRNA levels of these genes. Using HPLC analysis, a concomitant decrease in the formation of B[a]P-derived metabolic products was detected. In conclusion, these data lend support to a chemopreventive role of resveratrol in polycyclic aromatic hydrocarbon-induced carcinogenesis.

Environmental exposure and lung cancer among nonsmokers: an example of Taiwanese female lung cancer

Lung cancer is the leading cause of cancer death worldwide and in Taiwan. Cigarette smoking is considered to be the most important risk factor, since about 90% of lung cancer can be related to cigarette smoking. Despite the recent decrease of cigarette smoking, lung cancer is still the leading cause of cancer death in the United States. In Taiwan, only around 50% of lung cancer incidence could be associated with cigarette smoking, particularly less than 10% of Taiwanese women are smokers. Thus, the aetiology of lung cancer for nonsmokers remains unknown. DNA damages including bulky and oxidative damage may be related with mutation of tumor suppressor genes, such as p53 gene. The high DNA adduct levels in female may be associated with frequent exposure to indoor cooking oil fumes (COF) and outdoor heavy air pollution. Oxidative stress induced by COF was also discussed. Different p53 mutation spectra and mutation frequency between genders reflected that different environmental factors may be involved in nonsmoking male and female lung cancer development. Most importantly, our recent report has demonstrated that human papillomavirus (HPV) infection was associated with nonsmoking female lung cancer. Based on our studies with Taiwanese nonsmoking lung cancer as the model, the possible aetiological factors of lung cancer incidence in Taiwanese nonsmokers were elucidated.

A critical evaluation of DNA adducts as biological markers for human exposure to polycyclic aromatic compounds

The causative role of polycyclic aromatic hydrocarbons (PAH) in human carcinogenesis is undisputed. Measurements of PAH-DNA adduct levels in easily accessible white blood cells therefore represent useful early endpoints in exposure intervention or chemoprevention studies. The successful applicability of DNA adducts as early endpoints depends on several criteria: i. adduct levels in easily accessible surrogate tissues should reflect adduct levels in target-tissues, ii. toxicokinetics and the temporal relevance should be properly defined. iii. sources of interand intra-individual variability must be known and controllable, and finally iv. adduct analyses must have advantages as compared to other markers of PAHexposure. In general, higher DNA adduct levels or a higher proportion of subjects with detectable DNA adduct levels were found in exposed individuals as compared with nonexposed subjects, but saturation may occur at high exposures. Furthermore, DNA adduct levels varied according to changes in exposure, for example smoking cessation resulted in lower DNA adduct levels and adduct levels paralleled seasonal variations of air-pollution. Intraindividual variation during continuous exposure was low over a short period of time (weeks), but varied significantly when longer time periods (months) were investigated. Inter-individual variation is currently only partly explained by genetic polymorphisms in genes involved in PAH-metabolism and deserves further investigation. DNA adduct measurements may have three advantages over traditional exposure assessment: i. they can smooth the extreme variability in exposure which is typical for environmental toxicants and may integrate exposure over a longer period of time. Therefore, DNA adduct assessment may reduce the monitoring effort. ii. biological monitoring of DNA adducts accounts for all exposure routes. iii. DNA adducts may account for inter-individual differences in uptake, elimination, distribution, metabolism and repair amongst exposed individuals. In conclusion, there is now a sufficiently large scientific basis to justify the application of DNA adduct measurements as biomarkers in exposure assessment and intervention studies. Their use in risk-assessment, however, requires further investigation.

Induction and regulation of the carcinogen-metabolizing enzyme CYP1A1 by marijuana smoke and delta (9)-tetrahydrocannabinol

Induction of the carcinogen-metabolizing enzyme cytochrome P4501A1 (CYP1A1) is a key step in the development of tobacco-related cancers. To determine if marijuana smoke activates CYP1A1, a murine hepatoma cell line expressing an inducible CYP1A1 gene (Hepa-1) was exposed in vitro to tar extracts prepared from either tobacco, marijuana, or placebo marijuana cigarettes. Marijuana tar induced higher levels of CYP1A1 messenger RNA (mRNA) than did tobacco tar, yet resulted in much lower CYP1A1 enzyme activity. These differences between marijuana and tobacco were primarily due to Delta(9)-tetrahydrocannabinol (Delta(9)-THC), the psychoactive component of marijuana. Here we show that Delta(9)-THC acts through the aryl hydrocarbon receptor complex to activate transcription of CYP1A1. A 2-microg/ml concentration of Delta(9)-THC produced an average 2.5-fold induction of CYP1A1 mRNA, whereas a 10- microg/ml concentration of Delta(9)-THC produced a 4.3-fold induction. No induction was observed in Hepa-1 mutants lacking functional aryl-hydrocarbon receptor or aryl-hydrocarbon receptor nuclear translocator genes. At the same time, Delta(9)-THC competitively inhibited the CYP1A1 enzyme, reducing its ability to metabolize other substrates. Spiking tobacco tar with Delta(9)-THC resulted in a dose-dependent decrease in the ability to generate CYP1A1 enzyme activity as measured by the ethoxyresorufin-o-deethylase (EROD) assay. This inhibitory effect was confirmed by Michaelis-Menton kinetic analyses using recombinant human CYP1A1 enzyme expressed in insect microsomes. This complex regulation of CYP1A1 by marijuana smoke and the Delta(9)-THC that it contains has implications for the role of marijuana as a cancer risk factor.

Detection and quantification of depurinated benzo[a]pyrene-adducted DNA bases in the urine of cigarette smokers and women exposed to household coal smoke

Polycyclic aromatic hydrocarbons (PAH) are metabolized to electrophiles that can bind to DNA bases and destabilize the N-glycosyl bond, causing rapid depurination of the adducted bases. Recent studies support depurination of DNA as a mechanism central to the genesis of H-ras mutations in PAH-treated mouse skin. Depurinating adducts account for 71% of all DNA adducts formed in mouse skin treated with benzo[a]pyrene (BP). This study analyzed urine of cigarette smokers, coal smoke-exposed women, and nonexposed controls for the presence and quantities of the depurinated BP-adducted DNA bases, 7-(benzo[a]pyren-6-yl)guanine (BP-6-N7Gua) and 7-(benzo[a]pyren-6-yl)adenine (BP-6-N7Ade). Since these adducted bases originate from reaction of the BP radical cation with double-stranded DNA and not with RNA or denatured DNA, their presence in urine is indicative of DNA damage. Urine samples were fractionated by a combination of SepPak extraction and reverse-phase HPLC, and then analyzed by tandem mass spectrometry and capillary electrophoresis with laser-induced fluorescence. BP-adducted bases were detected in the urine from three of seven cigarette smokers and three of seven women exposed to coal smoke, but were not detected in urine from the 13 control subjects. Concentrations were estimated to be 60-340 and 0.1-0.6 fmol/mg of creatinine equivalent of urine for coal smoke-exposed women (maximum possible BP intake of ca. 23 000 ng/day) and cigarette smokers (BP intake of ca. 800 ng/day), respectively, exhibiting a sensitive response to BP exposures. BP-6-N7Gua was present at ca. 20-300 times the concentration of BP-6-N7Ade in the urine of coal smoke-exposed women, but was not detected in the urine of cigarette smokers. This difference may be due to the remarkably different BP exposures experienced by the two groups of PAH-exposed individuals. These results justify more extensive studies of depurinated BP-adducted DNA bases as potential biomarkers of PAH-associated cancer risk.

HPTLC screening assay for urinary cotinine as biomarker of environmental tobacco smoke exposure among male adolescents

For selective screening determination of urinary cotinine, i.e. (S)-1-methyl-5-(3-pyridyl)-2-pyrrolidinone, the major metabolite of nicotine, the high-performance thin-layer chromatographic (HPTLC) method have been proposed. Prior the final HPTLC analysis the procedure required a solid-phase extraction (SPE) of cotinine from collected urine samples with 1-methyl-2-pyrrolidinone as an internal standard. Densitometrical quantitation of cotinine on the chromatograms have been performed with a 16-grayscale scanner using the specialized software implemented on a desktop microcomputer. The lower detection limit of cotinine was 6 microg/l allowing the method to be applied for the measurement a concentration of this compound in urine samples collected from 35 elementary schoolboys exposed on both moderate and/or significant ETS. The mean recovery of cotinine from urine samples was 93%. The mean intra-day accuracy for the analysis of cotinine in range 6-750 microg/l. including four paralell measurements, was 2.9 %. The results of cotinine measurements by proposed SPE-HPTLC procedure were used in the pilot studies for assessment of hazard from home ETS on the health status of elementary schoolboys, especially an increased risk for infectious respiratory track diseases.

DNA adduct level in lung tissue may act as a risk biomarker of lung cancer

Lung cancer is a leading cause of mortality in Taiwan. We hypothesised that high susceptibility to DNA damage in the target organ acts as a risk biomarker for the development of lung cancer. To verify this hypothesis, the aromatic/hydrophobic DNA adduct levels of non-tumorous adjacent lung tissues from 73 primary lung cancer patients and 33 non-cancer controls were evaluated by 32P-postlabelling assay. Wilcoxon rank sum test showed that DNA adduct levels in lung cancer patients (49.58+/-33.39 adducts/10(8) nucleotides) were significantly higher than those in non-cancer controls (18.00+/-15.33 adducts/10(8) nucleotides, P<0.001). The DNA adduct levels among lung cancer and non-cancer samples were not influenced by smoking behaviour and cigarette consumption. Our data also showed that the polymorphisms of cytochrome P4501A1 (CYP1A1) Msp1, glutathione S-transferase M1 (GSTM1) and the combination of both genetic polymorphisms were not related to the DNA adduct levels. Interestingly, positive association between CYP1A1 protein expression and DNA adduct levels was found when CYP1A1 protein expression in lung specimens from lung cancer patients was examined by immunohistochemistry. Multivariate linear regression analysis indicated that the DNA adduct level was not associated with gender, smoking behaviour, or genetic polymorphisms of CYP1A1 and GSTM1. Moreover, multivariate logistic regression analysis showed that persons with high DNA adduct levels (>48.66 adducts/10(8) nucleotides) had an approximately 25-fold risk of lung cancer compared with persons with low DNA adduct levels (</=48.66 adducts/10(8) nucleotides). In conclusion, DNA adduct levels in lung tissue may be a more reliable lung cancer susceptibility biomarker than DNA adduct levels in leucocytes. In addition, higher susceptibility to DNA damage in lung cancer patients may partly play a role in the development of lung cancer.

Expression of CYP1A1, CYP1B1 and CYP3A, and polycyclic aromatic hydrocarbon-DNA adduct formation in bronchoalveolar macrophages of smokers and non-smokers

Variability in the expression of enzymes metabolizing carcinogens derived from cigarette smoke may contribute to individual susceptibility to pulmonary carcinogenesis. This study was designed to determine the effects of smoking and 3 major cytochrome P450 (CYP) enzymes, i.e., CYP1A1, CYP1B1 and CYP3A, which metabolize polycyclic aromatic hydrocarbons (PAH) on PAH-DNA adduct formation in the bronchoalveolar macrophages (BAM) of 31 smokers and 16 non-smokers. CYP protein levels were determined by immunoblotting and PAH-DNA adduct levels by the nuclease P1 enhanced (32)P-postlabeling method. The expression of specific CYP forms was confirmed by reverse transcriptase-polymerase chain reaction (RT-PCR) from 10 additional samples. CYP3A protein, CYP3A5 by RT-PCR, was detected in the majority of samples from smokers and non-smokers. The levels of CYP3A appeared to be lower in active smokers than in ex-smokers (p = 0.10) or never smokers (p = 0.02). CYP1A1 was not detectable by either immunoblotting or RT-PCR. The expression of CYP1B1 was low or undetectable in most samples. The PAH-DNA adduct levels were higher (mean 1.57/10(8) nucleotides) in samples from smokers compared with non-smokers (mean 0.42/10(8) nucleotides, p < 0.001) and the number of adducts correlated with the number of cigarettes smoked daily (regression analysis, p < 0. 001). Higher levels of adducts were detected in samples from smokers with a high level of CYP3A compared with those with a low level (regression analysis, p = 0.002). As CYP3A5 is abundant in both lung epithelial cells and BAM, its association with adduct formation suggests that this CYP form may be important in the activation of cigarette smoke procarcinogens.

DNA adducts: endogenous and induced

Human exposure to DNA damaging agents can arise from exogenous sources or endogenous processes that occur normally or in pathological states. DNA isolated from human tissues, obtained from the very young to the old, contains detectable amounts of a number of different types of DNA adducts that reflect exposure to both known carcinogens and as yet unidentified genotoxic agents. The levels of DNA damage observed in human studies as a result of exogenous exposures (noniatrogenic) is of the order of 1 adduct per 10(7)-10(9) normal DNA bases, whereas that arising from endogenous exposures may potentially be several orders of magnitude higher. Large interindividual variations in DNA adduct levels have been reported, and these are probably the result of host and environmental factors, although variation in analytical and sampling procedures may also play a role. It is important to recognize that the presence of DNA adducts in a tissue does not necessarily indicate a specific tumorigenic risk for that tissue, as other factors downstream of DNA adduct formation (including DNA repair and cell proliferation) play an important role in determining overall risk.

Biomonitoring the human population exposed to pollution from the oil fires in Kuwait: analysis of placental tissue using (32)P-postlabeling

The placenta is a readily available source of material for molecular epidemiological investigations. As such, DNA damage in this tissue can be indicative of maternal exposure to environmental pollutants such as polycyclic aromatic hydrocarbons (PAHs). Previous reports have demonstrated that (32)P-postlabeling (PPL) is able to detect the presence of aromatic adducts in human placenta that are associated with maternal smoking during pregnancy. Using PPL we have assayed the DNA damage in placental samples from Kuwaiti mothers who were exposed to environmental pollution during pregnancy. This pollution arose in the aftermath of the Iraqi invasion of Kuwait, which left hundreds of oil wells burning. For comparison, further Kuwaiti samples were obtained approximately 1 year after the oil well fires and, as such, are from individuals unexposed to the airborne pollution from the oil well fires during pregnancy. In addition, placental samples were obtained from subjects in the United Kingdom. Adduct levels were measured in all samples using both the nuclease P1 and butanol extraction enhancement procedures. No elevation of adduct levels was observed in the placenta of mothers exposed to the oil well fires (n = 40) with either procedure (144 +/- 30 attomol/microg DNA for nuclease P1 enrichment, 245 +/- 50 attomol/microg DNA for butanol extraction), when compared with the nonexposed Kuwaiti mothers (180 +/- 32 and 281 +/- 39 attomol/microg DNA, respectively, n = 24). Similar adduct levels were observed in UK mothers who smoked cigarettes (178 +/- 30 and 284 +/- 52 attomol/microg DNA, n = 30), which in turn were approximately twice those observed in nonsmoking mothers (90 +/- 14 and 141 +/- 15 attomol/microg DNA, n = 12), although there is no significant difference in the distribution of adduct levels when statistical analysis is performed. Comprehensive interpretation of the Kuwaiti data is difficult as precise information on PAH levels is unavailable, although the data do seem to indicate that exposure to PAHs was not biologically significant.

Molecular and cellular alterations in tobacco smoke-associated larynx cancer

Tumours of head and neck belong to the most frequent types of cancer world-wide. In Poland, mortality from larynx cancer among males has been continuously increasing during the last decades up to 8.4 deaths per 100,000 men in 1993, which exceeds epidemiological records from other countries. The aetiology of laryngeal cancer is strongly associated with exposure to carcinogens present in tobacco smoke. The review describes a sequence of molecular and cellular events from carcinogenic exposure, DNA adduct formation, detection of mutations in the p53 gene, loss of heterozygosity (LOH) in chromosomal loci encoding the p53 and p16 genes, and loss of control of the cell cycle. The section concerning DNA adducts includes a discussion of the role of such confounders as exogenous exposure, the age and sex of the subject, and disease progression. The significance of genetic factors as individual risk determinants is discussed in relation to bleomycin-induced chromosome instability and in connection with the occurrence of defects in genes encoding detoxifying enzymes. The question concerning the substantial difference between men and women in larynx cancer morbidity and mortality remains open, even when the significantly higher adduct formation in male DNA compared with female material was taken into account. Preliminary experiments suggest a role of the frequently observed loss of the Y-chromosome.

Molecular epidemiological approaches to the study of the genotoxic effects of urban air pollution

Direct epidemiological observations suggest that exposure to high levels of urban air pollution may result in increased risk of lung cancer, sufficient to account for a few (approximately 1-3) percent of total lung cancer incidence. Extrapolation from occupational exposure and risk data suggests that among potential carcinogens present in polluted urban air, polycyclic aromatic hydrocarbons (PAHs) may make a major contribution to air pollution-associated lung cancer risks. The use of biomarkers of genotoxocity in large-scale population studies may help to reduce the uncertainty involved in the assessment of such risks, especially those associated with relatively low pollution levels such as nowadays found in many Western cities. Increases in biomarkers of exposure to urban air PAHs as well as biomarkers of early effects have been detected in situations of relatively high levels of air pollution (e. g., ambient PAH concentrations of the order of a few tens of micrograms per cubic meter). Evidence has also been found about the modulation genetic damage accumulation in different individuals by polymorphisms in genes involved in the activation or detoxification of PAHs, especially of polymorphisms GSTM1 and CYP1A1 genes. However, the inconsistencies in the currently reported effects of genetic polymorphisms suggest that additional factors may also be important in the modulation of individual susceptibility to the accumulation of PAH-derived genetic damage. Biomarkers studies in populations exposed to relatively low ambient PAH concentrations (below 20 microg/m(3)) have not demonstrated clear dose-related effects (e.g., on DNA adduct levels), possibly because of the existence of multiple sources and routes of human exposure to PAHs in addition to inhalation of urban air (including, for example, home heating, environmental tobacco smoke and diet), and the consequent difficulty of adequately and specifically assessing atmospheric air-related exposure. This makes it imperative that molecular epidemiology studies be designed in such a way as to allow adequate assessment of exposure to urban air PAHs at the individual level and over short-, medium- and long-term time periods which correspond to the expression times of different biomarkers.

Early age at smoking initiation and tobacco carcinogen DNA damage in the lung

BACKGROUND

DNA adducts formed as a consequence of exposure to tobacco smoke may be involved in carcinogenesis, and their presence may indicate a high risk of lung cancer. To determine whether DNA adducts can be used as a "dosimeter" for cancer risk, we measured the adduct levels in nontumorous lung tissue and blood mononuclear cells from patients with lung cancer, and we collected data from the patients on their history of smoking.

METHODS

We used the 32P-postlabeling assay to measure aromatic hydrophobic DNA adducts in nontumorous lung tissue from 143 patients and in blood mononuclear cells from 54 of these patients. From the smoking histories, we identified exposure variables associated with increased DNA adduct levels by use of multivariate analyses with negative binomial regression models. RESULTS/ CONCLUSIONS: We found statistically significant interactions for variables of current and former smoking and for other smoking variables (e.g., pack-years [number of packs smoked per day x years of smoking] or years smoked), indicating that the impact of smoking variables on DNA adduct levels may be different in current and former smokers. Consequently, our analyses indicate that models for current and former smokers should be considered separately. In current smokers, recent smoking intensity (cigarettes smoked per day) was the most important variable. In former smokers, age at smoking initiation was inversely associated with DNA adduct levels. A highly statistically significant correlation (r=.77 [Spearman's correlation]; two sided P<.001) was observed between DNA adduct levels in blood mononuclear cells and lung tissue.

IMPLICATIONS

Our results in former smokers suggest that smoking during adolescence may produce physiologic changes that lead to increased DNA adduct persistence or that young smokers may be markedly susceptible to DNA adduct formation and have higher adduct burdens after they quit smoking than those who started smoking later in life.

Association of benzo[a]pyrene-diol-epoxide-deoxyribonucleic acid (BPDE-DNA) adduct level with aging in male smokers and nonsmokers

We used our new flow cytometric method to measure benzo[a]pyrene-diolepoxide-deoxyribonucleic acid adduct levels in peripheral lymphocytes from healthy male smokers and nonsmokers. Smokers who had pack-years of 20 or more had significantly higher mean benzo[a]pyrene-diol-epoxide-deoxyribonucleic acid adduct levels than nonsmokers. In smokers, the adduct levels were correlated significantly with age, years of smoking, and pack-years, whereas daily tobacco consumption was not correlated with adduct levels. We also found a positive relationship between age and benzo[a]pyrene-diol-epoxide-deoxyribonucleic acid adduct levels in nonsmokers. Passive exposure to tobacco smoke was not associated with adduct levels. The results of our study indicate that benzo[a]pyrene-diol-epoxide-deoxyribonucleic acid adduct levels may be closely related to aging and that tobacco smoking-as well as other environmental factors-may play a role in the benzo[a]pyrene-diol-epoxide-deoxyribonucleic acid adduct formation.

HPLC/fluorescence determination of anti-BPDE-DNA adducts in mononuclear white blood cells from PAH-exposed humans

The aim of this study was to compare (+/-)-r-7,t-8-dihydroxy-t-9,10-oxy-7,8,9,10-tetrahydrobenzo[a]pyrene (anti-BPDE)-DNA adduct levels in groups of humans subjected to various levels of polycyclic aromatic hydrocarbon (PAH) (benzo[a]pyrene) exposure. An HPLC/fluorescence method was applied to detect specifically anti-BPDE-DNA adducts in mononuclear white blood cells [lymphocyte plus monocyte fraction (LMF)] from humans exposed to PAHs. A total of 130 subjects comprised the sample population: 26 psoriatic patients (3 days after clinical coal tar treatment of the skin), 15 coke oven workers, 19 chimney sweeps, 36 aluminium anode plant workers and 34 non-occupationally PAH-exposed subjects (controls). PAH exposure was assessed in each group by means of the urinary excretion of 1-pyrenol (mean group levels: 1.2, 0.7, 0.3, 65.0 and 0.1 micromol/mol creatinine in coke oven workers, chimney sweeps, aluminium plant anode workers, psoriatic patients and non-occupationally PAH-exposed subjects, respectively). HPLC/fluorescence analysis of BPDE-DNA adducts showed that the percentage of subjects with adduct levels exceeding the 95 percentile control subject value (8.9 adducts/10(8) nucleotides) was significantly high in coke oven workers (46.7%) and chimney sweeps (21.0%) (chi2 test, P < 0.01 and P < 0.05, respectively) but not in aluminium plant workers (11.1%) and psoriatic patients (0%). The increase in BPDE-DNA adduct levels in LMF (Ln values) was significantly related to chronic inhalatory and high PAH exposure (linear multiple regression analysis, F = 6.37, P < 0.01; t = 4.2, P < 0.001). Skin acute (or short-term) and high PAH exposure, charcoal-grilled meat consumption and smoking habit did not seem to influence BPDE-DNA adduct formation in LMF.

Biomonitoring using accessible human cells for exposure and health risk assessment

A major goal for genetic toxicologist is to provide precise information on exposure and health risk assessment for effective prevention of health problems. A frequently used approach for population study has been to utilize readily available blood cells (lymphocytes and red blood cells) as sentinel cell types to detect biological effects from exposure and to provide early warning signals for health risk. However, such approach still cannot be used reliably for developing strategies in risk assessment and disease prevention. It is possible that other available cell types which are more representative of the target cells for disease may be used to overcome the deficiency. In this report, the use of non-blood cells for biomonitoring is briefly reviewed. Their usefulness in certain exposure condition is highlighted and their effectiveness in documenting exposure compared with other cell types such as the traditional blood cells is presented. It is obvious that the decision in using these non-blood cells in biomonitoring is based on the exposure condition and the experimental design. Nevertheless, monitoring studies using non-blood cells should be encouraged with emphasis on providing dose-response information, comparative response with other cell types and effectiveness for health risk assessment.

Benzo[a]pyrene diol-epoxide DNA adducts and levels of polycyclic aromatic hydrocarbons in autoptic samples from human lungs

Benzo[a]pyrene (BaP) and other polycyclic aromatic hydrocarbons (PAHs) which are present in cigarette smoke, are common air and food genotoxic contaminants and possible human carcinogens. We measured the following PAH levels: benzo[a]anthracene, benzo[b]fluoranthene, benzo[k]fluoranthene, BaP, dibenzo[a,h]anthracene, benzo[g,h,i]perylene as well as (+/-) syn and anti BaP diol-epoxide (BPDE) DNA adducts in autopsy samples from the lungs of non-smokers, ex-smokers and smokers who had lived in Florence, Italy. PAH levels in lung tissue were similar in all groups, with the exception of dibenzo[a,h]anthracene (DBA), which was higher in lung samples from smokers (n = 10, 0.18+/-0.17 ng/g d.w, mean +/- S.D.) compared to non-smokers (n = 15, 0.046+/-0.025 ng/g d.w) (P < 0.05), whereas ex-smokers (n = 5), had intermediate levels (0.07+/-0.03 ng/g d.w). The average level of total BPDE-DNA adducts was 4.46+/-5.76 per 10(8) bases in smokers, 4.04+/-2.37 per 10(8) in ex-smokers and 1.76+/-1.69 per 10(8) in non-smokers. The levels of non-smokers were significantly different (P < 0.05) from the levels of the smokers and ex-smokers combined. Total BPDE-DNA adducts were correlated with BaP levels in the lung samples in which both determinations were obtained (r = 0.63). Our results demonstrate that the biological load of PAHs due to environmental pollution is similar in individuals who smoke and those who do not, but BPDE-DNA adducts are higher in smokers and ex-smokers compared to non-smokers. This study further confirms the usefulness of BPDE-DNA adduct levels determination in the lungs from autopsy samples for monitoring long-term human exposure to BaP, a representative PAH.

Putative susceptibility markers of coronary artery disease: association between VDR genotype, smoking, and aromatic DNA adduct levels in human right atrial tissue

Cancer and cardiovascular diseases share risk factors such as smoking, and the onset of both diseases have been suggested to have a common mechanistic basis. The binding of carcinogens to DNA (carcinogen-DNA adducts), genetic polymorphisms in carcinogen-detoxifying enzymes glutathione S-transferases (GSTs), and genetic polymorphisms in the vitamin D receptor (VDR) are among the candidates for modifiers of cancer risk. We determined whether these biomarkers could be related to individual characteristics of patients suffering from cardiovascular diseases. For that purpose, DNA from the right atrial appendage of 41 patients who underwent open heart surgery was analyzed for smoking-related DNA adducts and polymorphisms in GSTM1, GSTT1, and VDR genes. Statistical analysis was used to identify any patient's characteristics associated with these molecular markers. Our results showed that heart tissue of cigarette smokers contained a variety of aromatic DNA adducts in significantly elevated levels compared to ex-smokers (P<0.01) or nonsmokers (P<0.001). A linear relationship was observed between DNA adduct levels and daily cigarette smoking (rs=0.73; P=0.0003). Since cardiac myocytes are terminally differentiated cells that have lost their ability to divide and seemingly have limited DNA repair capacities, their levels might accumulate with time and thereby affect heart cell function or viability. Substantial interindividual differences between DNA adduct levels were observed, and persons with severe coronary artery disease (CAD), as assessed by coronary angiography, had higher DNA adduct levels than persons with no or mild CAD (P=0.04). As polymorphisms in GST genes have been shown to modulate DNA adduct levels and risk for lung cancer in smokers, we explored for the first time whether the GST polymorphisms could also explain deviating heart DNA adduct levels and CAD risk. However, no relation could be found between these covariants. In contrast, a VDR genotype, which has been associated with decreased serum levels of the active hormonal form of vitamin D and increased risk for certain cancers, seemed to be related to severity of CAD (P=0.025). Our findings support the hypothesis that smoking-related DNA damage may be involved in the onset of cardiovascular diseases and suggest that VDR genotype may be a useful susceptibility marker of CAD.

The role of DNA adducts in chemical carcinogenesis

The reaction of chemical carcinogens with DNA appears to be one of the earliest events in the initiation phase of cancer. These DNA reactions can be base- and position-specific, are affected by sequence context, and are repaired at different rates depending on whether or not they are on the transcribed or nontranscribed strand of DNA and which nucleotide sequence is modified. Thus, measurement of total genomic DNA reaction of carcinogens is only a crude first step in dissecting out which are the critical lesions for cancer initiation. On the other hand, we know that DNA adducts, which have been primarily characterised in experimental studies, appear to have similar structures in human DNA arising from occupational or environmental exposures. A number of different methods have been developed to detect and measure DNA adducts in man. These include physico-chemical methods such as mass spectrometry, 32P-postlabelling, fluorescence and accelerator mass spectrometry (AMS) and biological methods such as immunoassay. All these methods have their strengths and weaknesses. Human studies, using 32P-postlabelling, demonstrate that this method can be used to examine the effect of potential chemoprotective agents on DNA adduct level. AMS has been used to measure DNA adducts in human tissue after patients have ingested trace quantities of the food mutagens 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline, a heterocyclic amine formed during the cooking of meat and the naturally occurring mycotoxin, aflatoxin B1. These studies can assist in assessing the risks associated with low-level exposure to food genotoxins.

Low response in white blood cell DNA adducts among workers in a highly polluted cokery environment

Coke oven workers are often heavily exposed to polynuclear aromatic hydrocarbons (PAHs); this exposure has been associated with higher cancer rates among these workers. We assessed the exposure of cokery workers in an oil shale processing plant. Personal hygienic monitoring, measurement of urinary 1-hydroxypyrene (1-OHP), and analysis of PAH-DNA adducts in white blood cells (WBCs) were performed. The 32P-postlabeling method was used for adduct measurement. The mean adduct value, 1.6 adducts per 10(8) nucleotides, did not differ significantly from the control value (P = 0.098). Smokers had significantly higher adduct levels than non-smoking workers (P = 0.002). 1-OHP levels measured in post-shift samples correlated with DNA adducts found in white blood cells (WBCs). We conclude that hygienic monitoring and measurement of urinary metabolites are essential background exposure data when the biologically effective dose of chemical carcinogens is assessed.

Glutathione S-transferase Mu (GST Mu) deficiency and DNA adducts in lymphocytes of smokers

The effect of smoking on DNA adduct formation in lymphocytes was analysed in individuals with low (deficient) and high (non-deficient) glutathione S-transferase (class Mu) activity. DNA adduct levels in lymphocytes were determined by the highly sensitive nuclease P1-enhanced 32P-postlabeling assay. The lymphocyte DNA adducts/10(8) nucleotides of smokers deficient in glutathione S-transferase Mu activity (n = 12) were significantly higher than those of smokers non-deficient (n = 9) in glutathione S-transferase Mu activity. The DNA adduct levels of the lymphocytes inversely correlated with glutathione S-transferase Mu activity. A correlation was found between DNA adduct levels and daily cigarette consumption. Results of the present study suggest that individuals deficient in glutathione S-transferase Mu activity may be at greater risk of DNA damage.

Variability in PAH-DNA adduct measurements in peripheral mononuclear cells: implications for quantitative cancer risk assessment

Biomarkers such as DNA adducts have significant potential to improve quantitative risk assessment by characterizing individual differences in metabolism of genotoxins and DNA repair and accounting for some of the factors that could affect interindividual variation in cancer risk. Inherent uncertainty in laboratory measurements and within-person variability of DNA adduct levels over time are putatively unrelated to cancer risk and should be subtracted from observed variation to better estimate interindividual variability of response to carcinogen exposure. A total of 41 volunteers, both smokers and nonsmokers, were asked to provide a peripheral blood sample every 3 weeks for several months in order to specifically assess intraindividual variability of polycyclic aromatic hydrocarbon (PAH)-DNA adduct levels. The intraindividual variance in PAH-DNA adduct levels, together with measurement uncertainty (laboratory variability and unaccounted for differences in exposure), constituted roughly 30% of the overall variance. An estimated 70% of the total variance was contributed by interindividual variability and is probably representative of the true biologic variability of response to carcinogenic exposure in lymphocytes. The estimated interindividual variability in DNA damage after subtracting intraindividual variability and measurement uncertainty was 24-fold. Inter-individual variance was higher (52-fold) in persons who constitutively lack the Glutathione S-Transferase M1 (GSTM1) gene which is important in the detoxification pathway of PAH. Risk assessment models that do not consider the variability of susceptibility to DNA damage following carcinogen exposure may underestimate risks to the general population, especially for those people who are most vulnerable.