A sensitive color ELISA for detecting polycyclic aromatic hydrocarbon-DNA adducts in human tissues

Polycyclic aromatic hydrocarbons residues and the carcinogenic risk assessment to pregnant women in Nantong, China using QuEChERS method and HPLC-A pilot case study

A high-performance liquid chromatographic method with a modified QuEChERS extraction for the determination of polycyclic aromatic hydrocarbons (PAHs) in blood serum was developed to investigate the internal exposure level and the carcinogentic toxicity contribution rate of PAHs for pregnant women in Nantong, China. Venous blood (n = 48) was collected in the local hospital and the internal exposure level of 16 PAHs and the contribution rate of carcinogenicity to pregnant women were analyzed. Among all of the detected PAHs, the detection rate of pyrene (77.08%) was the highest, followed by naphthalene (64.58%) and benzo[a]anthracene (BaA, 45.83%). The carcinogenicity contribution rate of BaA (37.37%) was the highest, followed by fluorene (32.96%) and acenaphthylene (22.01%). The results showed that many kinds of carcinogenic PAHs can be detected in the serum of pregnant women in Nantong city, among which BaA should be paid most attention because of its high internal exposure level and carcinogenic risk. Meanwhile, the origins of general PAHs in serum samples were analyzed using the characteristic ratio analysis method. The PAH pollution level of air samples (n = 42) during the collection time of blood samples was also analyzed to compare the possible correlations between the two different results.

DNA adducts: Formation, biological effects, and new biospecimens for mass spectrometric measurements in humans

Hazardous chemicals in the environment and diet or their electrophilic metabolites can form adducts with genomic DNA, which can lead to mutations and the initiation of cancer. In addition, reactive intermediates can be generated in the body through oxidative stress and damage the genome. The identification and measurement of DNA adducts are required for understanding exposure and the causal role of a genotoxic chemical in cancer risk. Over the past three decades, 32 P-postlabeling, immunoassays, gas chromatography/mass spectrometry, and liquid chromatography/mass spectrometry (LC/MS) methods have been established to assess exposures to chemicals through measurements of DNA adducts. It is now possible to measure some DNA adducts in human biopsy samples, by LC/MS, with as little as several milligrams of tissue. In this review article, we highlight the formation and biological effects of DNA adducts, and highlight our advances in human biomonitoring by mass spectrometric analysis of formalin-fixed paraffin-embedded tissues, untapped biospecimens for carcinogen DNA adduct biomarker research.

Formalin-Fixed Paraffin-Embedded Tissues-An Untapped Biospecimen for Biomonitoring DNA Adducts by Mass Spectrometry

The measurement of DNA adducts provides important information about human exposure to genotoxic chemicals and can be employed to elucidate mechanisms of DNA damage and repair. DNA adducts can serve as biomarkers for interspecies comparisons of the biologically effective dose of procarcinogens and permit extrapolation of genotoxicity data from animal studies for human risk assessment. One major challenge in DNA adduct biomarker research is the paucity of fresh frozen biopsy samples available for study. However, archived formalin-fixed paraffin-embedded (FFPE) tissues with clinical diagnosis of disease are often available. We have established robust methods to recover DNA free of crosslinks from FFPE tissues under mild conditions which permit quantitative measurements of DNA adducts by liquid chromatography-mass spectrometry. The technology is versatile and can be employed to screen for DNA adducts formed with a wide range of environmental and dietary carcinogens, some of which were retrieved from section-cuts of FFPE blocks stored at ambient temperature for up to nine years. The ability to retrospectively analyze FFPE tissues for DNA adducts for which there is clinical diagnosis of disease opens a previously untapped source of biospecimens for molecular epidemiology studies that seek to assess the causal role of environmental chemicals in cancer etiology.

Obesity mediated the association of exposure to polycyclic aromatic hydrocarbon with risk of cardiovascular events

Exposure to polycyclic aromatic hydrocarbons (PAHs) could cause high blood pressure (BP) and increased risk for atherosclerotic cardiovascular disease (ASCVD). However, the mechanisms underlying the relationship between them were unclear. We investigated potential mediation effect of obesity on the association of exposure to PAHs with high BP and increased risk for ASCVD. In the repeated measures study, 106 community-dwelling residents in Wuhan, China finished the physical examination in the winter and summer seasons, eight urinary PAHs metabolites were measured. Associations of urinary PAHs with high BP and increased risk for ASCVD were assessed using either linear mixed effect models or generalized estimating equations models. Mediation analysis was performed to evaluate the mediating effect of obesity on the association of urinary PAHs metabolites with high BP or increased risk of ASCVD. We observed the positive association between urinary PAHs metabolites and BP or the odds ratios for high BP (all P<0.05). Additionally, each one-unit increase in ln-transformed urinary levels of 4-hydroxyphenanthrene or the total of PAH metabolites was associated with a 12.63% or 11.91% increase in the estimated 10-year ASCVD risk (both P<0.05). The waist-to-height ratio mediated 29.0% of the association of urinary 4-hydroxyphenanthrene with increased risk of ASCVD (P<0.05). The findings suggest that PAHs exposure may be associated with elevated BP and an increased risk of ASCVD. Obesity may partially mediate the association between PAHs exposure and higher BP or increased risk of ASCVD.

Cadmium alters the formation of benzo[a]pyrene DNA adducts in the RPTEC/TERT1 human renal proximal tubule epithelial cell line

Previously, we demonstrated the sensitivity of RPTEC/TERT1 cells, an immortalized human renal proximal tubule epithelial cell line, to two common environmental carcinogens, cadmium (Cd) and benzo[a]pyrene (B[a]P). Here, we measured BPDE-DNA adducts using a competitive ELISA method after cells were exposed to 0.01, 0.1, and 1 μM B[a]P to determine if these cells, which appear metabolically competent, produce BPDE metabolites that react with DNA. BPDE-DNA adducts were most significantly elevated at 1 μM B[a]P after 18 and 24 h with 36.34 ± 9.14 (n = 3) and 59.75 ± 17.03 (n = 3) adducts/10⁸ nucleotides respectively. For mixture studies, cells were exposed to a non-cytotoxic concentration of Cd, 1 μM, for 24 h and subsequently exposed to concentrations of B[a]P for 24 h. Under these conditions, adducts detected at 1 μM B[a]P after 24 h were significantly reduced, 17.28 ± 1.30 (n = 3) adducts/10⁸ nucleotides, in comparison to the same concentration at previous time points without Cd pre-treatment. We explored the NRF2 antioxidant pathway and total glutathione levels in cells as possible mechanisms reducing adduct formation under co-exposure. Results showed a significant increase in the expression of NRF2-responsive genes, GCLC, HMOX1, NQO1, after 1 μM Cd × 1 μM B[a]P co-exposure. Additionally, total glutathione levels were significantly increased in cells exposed to 1 μM Cd alone and 1 μM Cd × 1 μM B[a]P. Together, these results suggest that Cd may antagonize the formation of BPDE-DNA adducts in the RPTEC/TERT1 cell line under these conditions. We hypothesize that this occurs through priming of the antioxidant response pathway resulting in an increased capacity to detoxify BPDE prior to BPDE-DNA adduct formation.

BPDE-like DNA adduct level in oral tissue may act as a risk biomarker of oral cancer

OBJECTIVE

Most reports have shown that PAH-related DNA adducts are positively correlated with the smoking status of oral cancer patients. However, these reports did not focus on a specific carcinogen in cigarette smoke. The purpose of this study was to elucidate the role of the BPDE (7,8-dihydroxy-anti-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene)-DNA adduct in the development of oral cancer in Taiwanese patients.

DESIGN

We enrolled 158 oral cancer patients and 64 non-cancer controls to investigate whether there were differences in susceptibility to cigarette smoke exposure in the formation of DNA adducts between cancer patients and controls. Immunohistochemistry and ELISA (enzyme-linked immunosorbent assay) were used to evaluate BPDE-DNA adduct levels in this study.

RESULTS

Our data showed that the BPDE-DNA adduct levels were positively correlated with gender, smoking status, betel nut chewing and alcohol consumption. The difference in DNA adduct levels could be explained by genetic polymorphisms of glutathione S-transferase M1 (GSTM1), but not by cytochrome P-4501A1 (CYP1A1). Patients with high DNA adduct levels (≧34.03 adducts/10(8) nucleotides) had an approximately 9.936-fold risk of oral cancer compared with those with low DNA adduct levels (<34.03 adducts/10(8) nucleotides) (p<0.001).

CONCLUSIONS

We suggest that genetic background and carcinogen exposure may increase the risk of developing oral cancer.

Elevated polycyclic aromatic hydrocarbon-DNA adducts in benign prostate and risk of prostate cancer in African Americans

Carcinogen-DNA adducts, a marker of DNA damage, are capable of inducing mutations in oncogenes and tumor suppressor genes, resulting in carcinogenesis. We have shown previously that polycyclic aromatic hydrocarbon (PAH)-DNA adduct levels in prostate cancer cases vary by cellular histology and that higher adduct levels are associated with biochemical recurrence. A nested case-control study was conducted in a historical cohort of 6692 men with histopathologically benign prostate specimens. PAH-DNA adduct levels were determined by immunohistochemistry in benign prostate specimens from 536 prostate cancer case-control pairs (59% White and 41% African American). We estimated the overall and race-stratified risk of subsequent prostate cancer associated with higher adduct levels. Prostate cancer risk for men with elevated adduct levels (defined as greater than control group median) was slightly increased [odds ratio (OR) = 1.28, 95% confidence interval (CI) = 0.98-1.67, P = 0.07]. After race stratification, elevated adduct levels were significantly associated with increased risk in African American men (OR = 1.56, CI = 1.00-2.44, *P = 0.05) but not White men (OR = 1.14, CI = 0.82-1.59, P = 0.45). Elevated PAH-DNA adduct levels were significantly associated with 60% increased risk of prostate cancer among cases diagnosed 1-4 years after cohort entry (OR = 1.60, CI = 1.07-2.41) with a greater risk observed in African Americans within the first 4 years of follow-up (OR = 4.71, CI = 1.97-11.26, ***P = 0.0005). Analyses stratified by age or tumor grade revealed no additional significant heterogeneity in risk. Increased prostate cancer risk associated with high PAH-DNA adduct levels in benign prostate was found only in African Americans; risk was greatest within 4 years of follow-up, possibly reflecting a carcinogenic process not yet histologically detectable.

Methods for the detection of DNA adducts

The detection and characterisation of DNA adducts can provide mechanistic information on mode of action for genotoxic chemicals and in this context is vital for human risk assessments. Adducts are measured extensively in biomonitoring studies to examine exposure to environmental, dietary, and occupational chemicals and as biomarkers of efficacy for cancer chemotherapeutic drugs and chemopreventive agents. Methods used for adduct analysis must possess a certain degree of specificity and be sufficiently sensitive to detect lesions in the model system under investigation. A variety of techniques have been established for this purpose, which are capable of detecting and quantifying adducts in DNA isolated from animal or human tissues, cells, and biofluids as well as naked DNA from in vitro studies. These can be grouped as those involving (32)P-post-labelling, mass spectrometry, physical detection methods, immunological assays and radiolabelled compounds. Each approach presents different advantages and limitations and the most appropriate method depends on the type of sample, level of damage, and nature of the investigation as well as practical considerations. In this chapter, the basic principles of the most commonly used quantitative methods are described and their strengths and weaknesses discussed.

A sandwich enzyme-linked immunosorbent assay for adducts of polycyclic aromatic hydrocarbons with human serum albumin

Adducts of benzo[a]pyrene-diolepoxide (BPDE) with blood nucleophiles have been used as biomarkers of exposure to polycyclic aromatic hydrocarbons (PAHs). The most popular such assay is a competitive enzyme-linked immunosorbent assay (ELISA) that employs monoclonal antibody 8E11 to detect benzo[a]pyrene tetrols following hydrolysis of BPDE adducts from lymphocyte DNA or human serum albumin (HSA). Here we used 8E11 as the capture antibody in a sandwich ELISA to detect BPDE-HSA adducts directly in 1-mg samples of HSA or 20 microl of serum/plasma. The assay employs an anti-HSA antibody for detection, and this is amplified by an avidin/biotinylated horseradish peroxidase complex. The sandwich ELISA has advantages of specificity and simplicity and is approximately 10 times more sensitive than the competitive ELISA. To validate the assay, HSA samples were assayed from three populations with known high PAH exposures (coke oven workers), medium PAH exposures (steel factory control workers), and low PAH exposures (volunteer subjects) (n=30). The respective geometric mean levels of BPDE-HSA adducts--67.8, 14.7, and 1.93 ng/mg HSA (1010, 220, and 28.9 fmol BPDE equiv/mg HSA)--were significantly different (P<0.05). The sandwich ELISA will be useful for screening PAH exposures in large epidemiologic studies and can be extended to other adducts for which capture antibodies are available.

A possible role for dihydrodiol dehydrogenase in the formation of benzo[a]pyrene-DNA adducts in lung cancer cells and tumor tissues

Epidemiological studies indicate that there is a gender difference in the susceptibility to tobacco and environmental carcinogens, and this gender difference is suspected to result in a higher risk for lung cancer among women. However, the molecular mechanisms underlying this sexual dimorphism remain unclear. In the present study, we have evaluated the roles of CYP1A1 and dihydrodiol dehydrogenase (DDH) in the formation of benzo[a]pyrene (BaP) DNA adducts in various lung cancer cell lines. Among six lung cancer cell lines tested, higher adduct levels were observed in CL-3 and CL1-1 cells, which had relatively high expression of both CYP1A1 and DDH isoform 1 (DHH1). To determine whether a reduction in DDH expression changed the adduct levels, an siRNA was used to knock down DDH1 expression in CL-3 cells. The BaP adduct levels in siDDH-CL-3 cells increased 1.4-2.2-fold relative to that of the parental CL-3 cells. We also examined BaP-like DNA adducts, and CYP1A1 and DDH1 expression by immunohistochemistry in 120 lung tumors. Detection of DNA adducts correlated with CYP1A1-positive tumors (P = 0.023), but not with DDH1-positive tumors. In addition, 28 of 33 tumors (85%) that were CYP1A1-positive and DDH1-negative contained detectable levels of DNA adducts, a proportion that was higher than for tumors from the other three categories of CYP1A1 and DDH1 expression (P = 0.012). Finally, a greater proportion of adduct-positive tumors from females were CYP1A1-positive/DDH1-negative (45.3%) than were tumors from males (27.3%). These results suggest that the reduction of DDH expression in lung tumors may contribute to an increase in DNA adduct levels, which may be partly responsible for the higher susceptibility of female lung cancer patients to DNA damage.

Selective immunoclean-up followed by liquid chromatography for the monitoring of a biomarker of exposure to polycyclic aromatic hydrocarbons in urine at the ngl−1 level

A selective clean-up procedure using an immunosorbent (IS) was developed for the trace-level determination, in water and urine samples, of 3-benzo(a)pyrene-glucuronide (3-BP-G), a biomarker of exposure to carcinogenic polycyclic aromatic hydrocarbons (PAHs). First, three sorbents used for the immobilization of antibodies were evaluated for their ability to limit the risk of non-specific interactions and to provide a high bonding density. The best sorbent, i.e. sepharose, was used for the immobilization of two different monoclonal antibodies. The most specific antibody for 3-BP-G was applied to the selective extraction from urine providing a clean extract, an easy and reliable quantification by comparison with a classical SPE process. The sensitivity of the fluorescence associated with the selectivity of the IS provides a limit of detection up to 1.2 ng l(-1) in urine for 3-BP-G.

GSTM1 [corrected] deletion modifies the levels of polycyclic aromatic hydrocarbon-DNA adducts in human sperm

DNA adducts measured in tissues are promising markers for identifying damage in organs that could be a target for carcinogens. Polymorphisms in genes involved in polycyclic aromatic hydrocarbons (PAHs) metabolism have been shown to modify the levels of PAH-DNA adducts in target tissues. In order to study the role of metabolic gene polymorphisms on DNA-adduct formation in sperm, we determined the GSTM1 genotype in a group of men in whom PAH-DNA adducts in sperm had been previously measured by immunofluorescence. The mean level of adducts in sperm was significantly higher in subjects carrying the homozygous deletion variant of GSTM1 than in subjects with a functional GSTM1 (mean fluorescence staining intensity: 1.62+/-0.62 versus 1.33+/-0.55; p=0.02). With respect to environmental factors, subjects who reported occupational exposure to PAHs and who carried the GSTM1 deletion had a significant increase in PAH-DNA adducts in sperm in comparison with subjects who were not exposed and had a functional GSTM1 (mean staining intensity: 1.83+/-0.67 versus 1.30+/-0.53; p=0.05), although among GSTM1-null subjects there was no significant difference with or without occupational exposure. This study presents for the first time the effect of a common polymorphism in a gene that metabolizes PAHs on DNA-adduct levels in sperm.

Age-related changes in oxidative DNA damage and benzo(a)pyrene diolepoxide-I (BPDE-I)-DNA adduct levels in human stomach

This study was conducted in order to obtain information on the association between age and oxidative DNA damage and benzo[a]pyrene diolepoxide-I (BPDE-I)-DNA adduct levels in the stomach tissues of normal subjects (n = 113). Subjects ranged from 17 to 75 yr. The levels of 8-hydroxy-2'-deoxyguanosine (8-OHdG), a biomarker of oxidative DNA damage, were measured by high-performance liquid chromatography-electrochemical detector (HPLC-ECD). BPDE-I-DNA adduct levels were quantitatively measured by enzyme-linked immunosorbent assay (ELISA) using the monoclonal antibody 8E11. Increase in 8-OHdG levels was observed in subjects from 31 to 60 yr of age. Higher levels of 8-OHdG were observed in the stomach tissues of those in the 51-60 yr old group. Although Helicobacter. Pylori-positive group subjects had higher 8-OHdG levels than those in the H. pylori-negative group, no age-related changes in 8-OHdG levels were observed in these groups. The levels of BPDE-I-DNA adduct also markedly increased with age. Higher levels of BPDE-I-DNA adduct were observed in subjects aged 61-70 yr, but this difference was not significant from other age groups. These results provide evidence that there is a progressive age-dependent accumulation of oxidative DNA damage and of BPDE-I-DNA adducts in human stomach tissues. It is possible that such damage contributes to the known increased incidence of gastric tumor with aging.

An approach to investigating the importance of high potency polycyclic aromatic hydrocarbons (PAHs) in the induction of lung cancer by air pollution

Evidence suggests that people living in urban areas have an increased risk of lung cancer due to higher levels of air pollution in these areas. Benzo[a]pyrene (B[a]P) is currently used as the main indicator of carcinogenic polycyclic aromatic hydrocarbons (PAHs) in air pollution, but there is concern that B[a]P may not be the ideal surrogate of choice for PAH mixtures since higher potency PAHs have recently been identified which could potentially contribute more and variably to the overall carcinogenicity. Dibenzo[a,h]anthracene (DBA) and dibenzo[a,l]pyrene (DB[a,l]P) are estimated to have carcinogenic potencies 10 or more times greater than B[a]P but data on their presence and formation in the environment are limited. Several occupational and environmental PAH biomonitoring studies are reviewed here, with particular focus on the specific exposure groups, study design, sample tissue, in particular the use of nasal tissues, and biomarkers used in each study. Consideration of these data is then used to propose a novel biomonitoring approach to evaluate exposure, uptake and the role of high potency PAHs in air pollution-related lung cancer. This is based upon an occupational study examining specific DNA adducts for DBA and DB[a,l]P in nasal cells to evaluate the extent to which these high potency PAHs might contribute to the increased risk of developing lung cancer from air pollution.

Immunofluorescent detection of 8-oxo-dG and PAH bulky adducts in fish liver and mussel digestive gland

Development of methodologies to detect DNA damage induced by pollutants is of increasing concern in marine ecotoxicology. We previously described an immunoperoxidase method for revealing 7,8-dihydro-8-oxodeoxyguanosine (8-oxo-dG) in marine organisms. In this work, the approach was extended to immunofluorescence detection and to the use of another antibody for polycyclic aromatic hydrocarbon (PAH)-DNA adducts. Specimens of European eel (Anguilla anguilla) and Mediterranean mussel (Mytilus galloprovincialis) were exposed to benzo(a)pyrene (B[a]P), as model chemical carcinogen to induce both oxidized bases and B[a]P diol-epoxide-deoxyguanosine adducts. Cryostat sections of liver and digestive gland from both species were immunostained, and DNA damage was semiquantitatively evaluated by an image analysis system. Compared to untreated organisms, B[a]P-exposed organisms exhibited increased levels of oxidative DNA damage; in eels, which rapidly metabolize PAHs, the occurrence of B[a]P-DNA adducts was also detected. The immunofluorescent assay maintained all the advantages previously reported for the immunoperoxidase protocol. Both methods were tested on the same eel specimens and the immunofluorescence method showed a greater extent of relative DNA damage and a higher sensitivity. Although field validation is being carried out, our results indicate the utility of antibodies to rapidly detect DNA alterations in aquatic organisms, and to investigate the risk associated with genotoxins in marine environment.

Biomarkers of exposure in community settings

Biomonitoring is a valuable tool for assessing human exposures to chemical contaminants in the environment. Biomonitoring tests can be divided into biomarkers of exposure, effect, and susceptibility. In studies of community exposure to an environmental contaminant, biomarkers of exposure are most often used. The ideal biomarker should be sensitive, specific, biologically relevant, practical, inexpensive, and available. Seldom does a biomarker meet all of these criteria--most biomarkers represent a compromise of these criteria. In designing a community exposure study, consideration should also be given to the selection of the test population, the practicality of collecting biological samples, temporal or seasonal variations in exposure, the availability of background comparison ranges, and interpretation of the test results. Biomonitoring tests provide unequivocal evidence of exposure, but they do not typically identify the source of exposure. Furthermore, rarely do the test results predict a health outcome. For many chemicals, testing must be conducted soon after exposure has occurred. In spite of these limitations, the use of biomonitoring is finding wider application in many scientific disciplines. Recent advances in analytical techniques are expanding the utility of biomarker testing in public health investigations.

Polycyclic aromatic hydrocarbon-DNA adducts in human sperm as a marker of DNA damage and infertility

Severe DNA damage, which might prevent egg fertilization or the development of the embryo, could be a cause of infertility. In order to assess whether polycyclic aromatic hydrocarbon (PAH)-DNA adducts are an early marker of sperm genotoxicity and infertility, we studied 205 men consecutively recruited from 1 January to 30 May 2001 through the Infertility Clinic of the University of Milan (Italy), with morphological abnormalities in the sperm. No known causes of infertility were present in their female partners. Sperm were collected after 3-5 days of abstinence, fixed on polylysine slides, and frozen at -20 degrees C. PAH-DNA adducts were measured by immunofluorescence using a polyclonal antiserum. A questionnaire was filled out at the time of the visit, with demographic information, smoking and drinking habits, and occupational history. Data on PAH-DNA adducts were available for 182 men. The mean age of the subjects was 35.5+/-5.0 years; 38.6% of them were current smokers. PAH-DNA adducts were negatively correlated with the percentage of physiologic forms (r=-0.18; P=0.016) and with abnormalities of the neck of the sperm cell (r=-0.21; P>/=0.009), while they were positively correlated with morphological abnormalities of the head (r=0.30; P>0.0001). Occupational exposure to PAH, but not smoking, was significantly associated with higher levels of PAH-DNA adducts. A significant negative association was observed between daily alcohol consumption and PAH-DNA adducts in sperm (P=0.01). PAH-DNA adducts levels were significantly higher in infertile versus fertile men (P=0.04). These results suggest a role for DNA damage in infertility.

Methodologies for bulky DNA adduct analysis and biomonitoring of environmental and occupational exposures

It is undisputed that DNA adduct formation is one of the key processes in early carcinogenesis. Therefore, analysis of DNA adduct levels may be one of the best tools available to characterize exposure to complex mixtures of genotoxic chemicals as occurring in different environmental and occupational exposure settings. However, from an analytical point of view the detection and quantification of DNA adducts is a challenging enterprise as extremely high sensitivity and selectivity are required. The entire spectrum of chromatographic techniques, including thin-layer chromatography (TLC), gas and liquid chromatography as well as capillary electrophoresis has been used in combination with different detection systems, all with their own specific characteristics. Among the various combinations of techniques, the TLC-(32)P-postlabeling combination appears to meet best with criteria of sensitivity and requirements of minimal amounts of material. Recent developments in the application of capillary electrophoresis in combination with either immunochemical or mass spectrometric detection techniques may offer new and promising approaches, with higher selectivity as compared to TLC-(32)P postlabeling. The applicability of these new techniques in biomonitoring studies aiming at the exposure and risk assessment of low and chronic exposures remains to be determined. In this paper we compare and discuss the advantages and limitations of different techniques used in DNA adduct analysis, with specific emphasis on those adducts formed by the polycyclic aromatic hydrocarbons and heterocyclic aromatic amines.

Polycyclic aromatic hydrocarbon-DNA adducts in liver tissues of hepatocellular carcinoma patients and controls

HCC is a common cancer and HBV and AFB(1) are well-documented, major risk factors. Epidemiologic studies have documented that cigarette smoking also contributes to the development of HCC. PAHs are ubiquitous environmental pollutants and products of incomplete combustion. They are present in both mainstream and sidestream cigarette smoke. PAHs are metabolically activated by phase I enzymes, including CYP1A1, into electrophilic reactants (diol epoxides), which covalently bind to DNA to form adducts. Diol epoxides are also substrates for phase II detoxifying enzymes, including GSTM and GSTP. To examine the association between PAH-DNA adducts and HCC, adduct levels were determined in liver tissue by relative staining intensity with an immunoperoxidase method using a polyclonal antiserum against BPDE-modified DNA. Subjects were also genotyped for polymorphism in several genes involved in the metabolism of PAH, including GSTM1 and GSTP1. Liver tissue was collected from patients with histologically confirmed HCC (n = 105) and from non-HCC controls (n = 37). There was a significant positive correlation (r = 0.3, p < 0.01) between adducts in tumor and adjacent nontumor tissues among HCC cases. The risk of HCC was higher after adjustment for age, sex and HBsAg in the group with the highest tertile tissue levels of PAH-DNA adducts (mean relative nuclear staining intensity of tumor and nontumor tissue > 344) than in the group with the lowest tertile (staining < 241, OR = 3.9, 95% CI = 1.0-14.9). Among non-HCC controls, there were no significant associations between adduct levels and cigarette smoking, GSTM1 null genotype and HBsAg positivity. A strikingly increased HCC risk was observed (OR = 20.3, 95% CI = 5.0-81.8) among HBsAg-positive subjects whose PAH-DNA adduct levels were high (mean relative nuclear staining intensity of tumor and nontumor tissue > 301, median of control tissues) compared to HBsAg-negative subjects who had low PAH-DNA adduct levels. 4-ABP- and AFB(1)-DNA adducts had been measured previously in these same tissues. Subjects with elevated DNA adduct levels of PAH, 4-ABP and AFB(1) had a significantly higher HCC risk with an OR of 36.7 (95% CI 7.2-187.2) compared to those who had low DNA adduct levels. These results suggest that PAHs may play a role in human hepatocarcinogenesis in conjunction with HBsAg carrier status, GSTM1 and GSTP1 genotypes and exposure to 4-ABP and AFB(1).

Removal of benzo(a)pyrene diol epoxide (BPDE)-DNA adducts as a measure of DNA repair capacity in lymphoblastoid cell lines from sisters discordant for breast cancer

The mutagen sensitivity assay is one of the approaches used to investigate individual DNA repair capacity. This method is based on the premise that after in vitro treatment with a test mutagen, DNA from subjects with defective repair will be more damaged than DNA from those with an efficient repair system. However, very little is known about unmeasured processes that occur between cell treatment and final assessment of DNA damage. To develop a more precise assay, we modified the traditional mutagen sensitivity assay to also include measurement of DNA damage after culturing cells in the absence of mutagen. First, we treated apparently normal and xeroderma pigmentosum lymphoblastoid cell lines with various doses of benzo(a)pyrene diol epoxide (BPDE) and harvested cells at different time points. A polyclonal antiserum against BPDE-DNA was used to quantitate levels of adducts by immunoslot-blot and immunohistochemistry. Selected conditions included treatment with 10 microM BPDE, a 4-hr culture in mutagen-free medium, and immunohistochemical measurement of BPDE-DNA adducts. The method was then applied in a pilot study to 50 lymphoblastoid lines from sisters discordant for breast cancer. There was no significant difference between cases and controls in the level of BPDE-DNA adducts in lymphoblasts harvested immediately after BPDE treatment. However, after a 4-hr culture in mutagen-free medium, the level of adducts was significantly higher (P = 0.006) among cases than in controls. There was a two-fold increase in mean adduct removal in lines from nonaffected as compared to affected sisters (44% and 22% decrease, respectively). DNA repair capacity was predictive of case status (P = 0.04) in logistic regression analysis. This method, which can be easily applied to large numbers of samples, should be useful in studies to investigate the role of DNA repair in cancer risk.

Gender difference in DNA adduct levels among nonsmoking lung cancer patients

Lung cancer is the leading cause of cancer mortality in Taiwanese women. Cigarette smoking cannot explain the high lung cancer mortality in this population because less than 10% of women in Taiwan are smokers. Therefore, environmental factors other than smoking may play an important role in lung cancer development in female nonsmokers. The purpose of this study was to elucidate the role of environmental carcinogen exposure in lung cancer development in Taiwanese female nonsmokers, based on DNA adduct formation. We collected nontumorous lung tissues resected from 62 nonsmoking lung cancer patients and 20 noncancer controls to investigate whether differences in susceptibility to DNA adduct formation exist between men and women. (32)P-postlabeling and ELISA (enzyme-linked immunosorbent assay) with polyclonal antibody against BPDE (7,8-dihydroxy-anti-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene)-DNA adduct were used to evaluate DNA adduct levels in lung tissues of study subjects. Our data showed that the DNA adduct levels of lung cancer patients determined by both assays were significantly higher than those of noncancer controls (P = 0.0001 for (32)P-postlabeling; P = 0.01 for ELISA). Moreover, DNA adduct levels in females were markedly greater than those in males (P = 0.014 for (32)P-postlabeling; P = 0.001 for ELISA). The difference in DNA adduct levels could not be explained by genetic polymorphisms of cytochrome P-4501A1 (CYP1A1) or glutathione S-transferase (GSTM1), as determined by polymerase chain reaction and restriction fragment length polymorphism. These results demonstrate that lung cancer patients have a higher susceptibility to DNA damage than that of noncancer controls. In addition, differences in susceptibility to DNA damage derived from environmental carcinogen exposure were observed between male and female nonsmokers. In conclusion, high susceptibility to DNA damage in females may partially explain the high mortality rate of lung cancer in nonsmoking Taiwanese women.

Immunohistochemical analysis of polycyclic aromatic hydrocarbon-DNA adducts in breast tumor tissue

Environmental carcinogens may play a role in the etiology of breast cancer, but the extent of their contribution is not yet defined. The aims of this study were to determine whether polycyclic aromatic hydrocarbon (PAH)-DNA adducts could be detected in stored paraffin blocks of breast tumor tissue (n=147) with an immunoperoxidase technique and whether they correlated with smoking history and/or mutant p53 protein expression. There was no significant difference in mean relative nuclear staining intensity in non-smokers (444+/-90, n=75), ever smokers (435+/-91, n=72), and current smokers (456+/-98, n=35). In either current or ever smokers, PAH-DNA adducts were non-significantly elevated in those with greater compared with lower exposure in relation to age at started smoking, years of smoking, cigarettes per day, and pack years. DNA damage levels were not elevated in tissues with compared with those without mutant p53 protein expression. These data demonstrate that immunohistochemical methods can be used to monitor DNA damage levels in archived breast tissues.

Polycyclic aromatic hydrocarbon-DNA adducts in cervical smears of smokers and nonsmokers

OBJECTIVES

The aim of this study was to detect polycyclic aromatic hydrocarbon-DNA (PAH-DNA) adducts in single cervical cells collected during a routine Papanicolaou smear and to relate this carcinogen exposure dose marker to smoking habit.

METHODS

An immunohistochemical assay, using a polyclonal antiserum raised against benzo[a]pyrene diol epoxide-DNA adducts, was performed to evaluate PAH-DNA adducts in cervical cells collected from 16 volunteers who smoked at least 20 cigarettes/day and 16 nonsmokers.

RESULTS

The mean adduct level, determined as relative staining intensity by an optical density image analyzer, was significantly higher in smokers compared to nonsmokers (AOD x 1000 +/- SD = 98 +/- 32 and 73 +/- 25, respectively) (P = 0.04).

CONCLUSIONS

These results demonstrate that this immunohistochemical assay, much simpler than other methodologies used to evaluate PAH-DNA adducts in cervical tissue, is sufficiently sensitive for quantitative adduct evaluation in single epithelial cervical cells, as already verified for other exfoliated material. This work thus confirms that tobacco smoke is a risk factor for genotoxic damage generation in cervical cells and indicates a procedure likely adaptable to a large population screening.

Biological monitoring exposure of workers from plant producing carbon electrodes: quantification of benzo[a]pyrene DNA-adducts in leukocytes, by a 32P-postlabelling method and an immunoassay

The levels of benzo[a]pyrene were monitored for blood DNA-benzo[a]pyrene adducts in 17 workers from a plant producing carbon electrodes, with high exposure to benzo[a]pyrene (575-902-1149 ng m(-3)). Two different techniques, a 32P-postlabelling method and a competitive immunoassay using polyclonal antibodies obtained from rabbits immunised with DNA modified by benzo[a]pyrene-trans-7,8-dihydrodiol-9,10-epoxide were used. For each worker, urinary 1-hydroxypyrene, a potential indicator of exposure to polycyclic aromatic hydrocarbons, was measured. The effect of tobacco by urinary cotinine measurement was also considered. The postlabelling and immunoassay detection limits for DNA-benzo[a]pyrene adducts were respectively 0.15 and 10 fmol 50 microg(-1) of DNA. The results obtained by the two methods demonstrated a good detection of DNA-benzo[a]pyrene adducts, but no direct relationship between the quantity of adducts and the concentration of benzo[a]pyrene in air-borne was noted in the studied plant. The levels of DNA-benzo[a]pyrene adducts obtained by immunoassay were significantly higher than those obtained by the 32P-postlabelling (P < 0.001). For several workers, variations due to professional or non professional factors must be taken into account in interpreting the results. In conclusion, the two methods used proved very efficient in determining DNA-benzo[a]pyrene adducts, and may be useful in monitoring human exposure to known and previously unidentified environmental genotoxic agents.

Polycyclic aromatic hydrocarbon-DNA adducts in humans: relevance as biomarkers for exposure and cancer risk

The methodology applied for DNA adducts in humans has become more reliable in recent years, allowing to detect even background carcinogenic adduct levels in environmentally exposed persons. Particularly, combinations of the various methods now allow the elucidation of specific adduct structures with detection limits of 1 adduct in 108 unmodified nucleotides or even lower. The quantification of polycyclic aromatic hydrocarbon-DNA (PAH-DNA) adducts in human tissues and cells has been achieved with a number of highly sensitive techniques: immunoassays and immunocytochemistry using polyclonal or monoclonal antisera specific for DNA adducts or modified DNA, the assay, and adduct identification using physicochemical instrumentation. The results summarized in this review show that PAH-DNA adducts have been detected in a variety of human tissues, including target organs of PAH- and tobacco-associated cancers. Although dosimetry has not always been precise, a large number of data now clearly show that lowering exposure to carcinogenic PAH results in decreasing PAH-DNA adduct levels. In most studies, however, bulk DNA of a certain tissue or cell type has been examined, and there were relatively few studies in which mutations as a consequence of DNA damage at specific genes have been investigated. Promising as these biomarker studies seem for epidemiology and health surveillance, future biomonitoring and molecular epidemiological studies should be directed to combine several endpoint measurements: i.e., adduct formation (preferably at specific sites), mutational spectra in cancer-relevant genes, and genetic markers of (cancer) susceptibility in a number of cancer-predisposing genes.

Detection of benzo[a]pyrene-DNA adducts in human placenta and umbilical cord blood

Placenta constitutes a vital organ of exchange between mother and foetus. In addition to this favourable effect for foetal development, placenta indirectly may allow transfer of several maternal blood xenobiotics. Human placenta and umbilical cord blood are interesting models for investigating maternal environment and the metabolism, the bioactivation and the transfer of carcinogens such as polycyclic aromatic hydrocarbons. We used them to assess the effect of a woman's smoking on the foetus. Few studies cover this subject. In pregnant women who have continued to smoke, benzo[a]pyrene compound of cigarette smoke is metabolically activated to diol-epoxide derivative: benzo[a]pyrene-trans-7,8-dihydrodiol-9,10-epoxide, ultimate carcinogen (BPDE-I). This derivative is covalently fixed on DNA and gives BPDE-I-DNA adducts. By a competitive immunoassay technique, we determined BDPE-I-DNA adducts in 20 samples of placenta and umbilical cord blood from women who smoked (n = 15) and who did not (n = 10). Tobacco consumption was checked by urinary cotinine determination. In the group of smokers levels of adducts were found in 13 specimens of placenta (from 10 to 60 fmol/50 micrograms of DNA) and 12 umbilical cord blood (from 10 to 22.15 fmol/50 micrograms of DNA) samples. These results indicate that a mother's tobacco consumption is linked to the accumulation of BPDE-I-DNA adducts in the placenta, which are seen in smaller quantities in the umbilical cord blood, probably because of the metabolic capacity of the placenta and the transfer of B[a]P from the mother to the foetus.