Genetic-environmental interactions and low-level exposure to carcinogens

Glutathione S-transferase M1 null genotype, household pesticides exposure and cutaneous melanoma

Glutathione S-transferase (GST) activity is believed to play a critical role in cellular protection against toxic chemicals. We evaluated the role of GSTM1 polymorphisms in modifying the association between indoor pesticide exposure and cutaneous melanoma. Peripheral blood samples were collected from 325 individuals (177 patients with cutaneous melanoma and 148 controls). Genotyping was performed using the PCR method. Participants were interviewed to collect data on pesticides used indoors, sociodemographic characteristics, medical history, sun exposure and pigmented characteristics. Odds ratio and 95% confidence intervals (CIs) were calculated by unconditional logistic regression. After adjustment for sex, age, education, hair colour, skin photo-type, solar lentigines, number of nevi and sunburns episodes in childhood, a 2.76-fold (95% CI: 1.08-7.08) increase in the risk of cutaneous melanoma was observed for GSTM1 null individuals highly exposed to indoor pesticides (≥2 times/year) in comparison with GSTM1 active individuals who received low exposure (<2 times/year). Participants exposed to these products for 10 years or more and with GSTM1 null genotype also had an increased risk of cutaneous melanoma (odds ratio: 2.78; 95% CI: 1.01-7.66) in comparison with participants with a low duration of exposure (<10 years) and active GSTM1. These findings suggest that the GSTM1 null genotype is a risk modifier for cutaneous melanoma.

UGT1A1 and UGT1A9 functional variants, meat intake, and colon cancer, among Caucasians and African-Americans

Glucuronidation by the UDP-glucuronosyltransferase enzymes (UGTs) is one of the primary detoxification pathways of dietary heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs). In a population-based case-control study of 537 cases and 866 controls, we investigated whether colon cancer was associated with genetic variations in UGT1A1 and UGT1A9 genes and we determined if those variations modify the association between colon cancer and dietary HCA and PAH exposure. We measured functional UGT1A1 polymorphisms at positions -53 (28; A(TA)6TAA to A(TA)7TAA), -3156 (G>A), -3279 (T>G) and the UGT1A9-275(T>A) polymorphism, and found no association with colon cancer overall. However, when stratified by race, the UGT1A1-3279 GG/TG intermediate/low activity genotypes were associated with an increased risk of colon cancer (odds ratio (OR)=1.5, 95% confidence interval (CI)=1.1-2.0) in Caucasians. This finding is also supported by haplotype analyses where the UGT1A1-3279G-allele-bearing haplotype is overrepresented in case group. Overall, UGT1A1-53 and -3156 genotypes modified the association between dietary benzo(a)pyrene (BaP) and colon cancer (P for interaction=0.02 and 0.03, respectively). The strongest association was observed for those with <7.7 ng/day BaP exposure and the low activity genotypes, for both UGT1A1 28/28 (OR=1.8, 95% CI=1.1-2.9) and -3156AA (OR=1.7, 95% CI=1.0-3.0), compared to >or=7.7 ng/day and combined high/intermediate genotypes. These data support a hypothesis that UGTs modify the association between meat-derived PAH exposure and colon cancer by their role in the elimination of dietary carcinogens.

Association of genetic polymorphisms in glutathione S-transferases and susceptibility to head and neck cancer

Polymorphism in glutathione S-transferase (GST) genes (GSTM1, GSTT1 and GSTP1) and interaction with environmental factors such as tobacco (smoking or chewing) and alcohol on susceptibility to head and neck squamous cell carcinoma (HNSCC) was studied in a case-control study. The study group consisted of 175 patients suffering from HNSCC and 200 age matched healthy controls. Statistical analysis showed an increase in risk to HNSCC in the patients with null genotype of GSTM1 (OR: 2.02; 95% CI: 1.32-3.10; P=0.001) or GSTT1 (OR: 1.66; 95% CI: 1.02-2.69; P=0.04), though the risk was not found to be significant when adjusted for age, sex, smoking, tobacco chewing or alcohol use by multivariate logistic regression model. Our data further showed that combination of deletion genotypes of GST (GSTM1 and GSTT1) confer an even higher risk of HNSCC. Interestingly, GSTP1 wild type genotype in combination with GSTM1 null or GSTT1 null genotype increased susceptibility for HNSCC (OR: 2.49 and 2.75, respectively). Likewise a much greater risk for HNSCC was observed in the patients carrying a genotype combination of GSTM1 null, GSTT1 null and GSTP1 (Ile/Ile) (OR: 4.47; 95% CI: 1.62-12.31; P=0.002). Our data have further provided evidence that tobacco chewing and alcohol consumption are the important risk factors for HNSCC. The interaction between tobacco chewing and null genotype of GSTM1 or GSTT1 resulted in about 3.5- and 2.2-fold increase in the risk respectively in the patients when compared to those not chewing tobacco. Alcohol use resulted in more than 4-fold increase in the risk in the patients with null genotype of GSTM1 as compared to those who are non-drinkers. Alcohol consumption also increased the risk (approx. 3-fold) in the cases with null genotype of GSTT1, though the association was not found to be significant when compared to non-drinkers. Our data have provided evidence that GST polymorphism modifies the susceptibility to HNSCC and have further demonstrated importance of gene-environment interaction in modulating the risk to HNSCC.

Influence of polymorphism in DNA repair and defence genes on p53 mutations in bladder tumours

We studied the effects of polymorphisms in nine genes involved in DNA repair and detoxification on occurrence and type of p53 mutation in 327 bladder cancer patients. The included polymorphisms are XPC(Lys939Gln), XPD(Lys751Gln), XPG(Asp1104His), XRCC1(Arg3999Gln), XRCC3(Thr241Met), NBS1(Glu185Gln), cyclin D1(Pro241Pro), MTHFR(Ala222Val and Glu429Ala) and NQO1(Arg139Trp and Pro187Ser). We found increased risk for p53 mutation among cyclin D1 variant allele homozygotes (OR 2.4 CI 0.8-6.7). Among non-smokers, 75% (3/4) with p53 mutation but only 12.5% (3/24) without p53 mutations were XRCC3 241Met homozygotes (P=0.03). Among smokers, all p53 transversions (3/3), but only 41.7% (5/12) of p53 transitions were found among carriers of the XPC 939Gln allele. Individuals carrying the NQO1 187Ser allele showed increased risk for p53 transversions (OR 4.7, CI 0.9-26.1). All (2/2) NQO1 139Trp allele carriers but only 17.5% (7/40) of the Arg139 homozygotes had p53 transversions. Our findings suggest that altered repair and detoxification due to genetic polymorphism may influence the occurrence of p53 mutations in bladder cancer.

Joint Effects between UDP-Glucuronosyltransferase 1A7 Genotype and Dietary Carcinogen Exposure on Risk of Colon Cancer

The UDP-glucuronosyltransferase 1A7 (UGT1A7) gene is polymorphic and encodes an enzyme involved in the detoxification of heterocyclic amines (HCA) and polycyclic aromatic hydrocarbons (PAH). Consumption of pan-fried and well-done meat are surrogates for HCA and PAH exposure and are possibly associated with colon cancer. We have evaluated whether UGT1A7 allelic variations are associated with colon cancer and whether UGT1A7 genotype modified associations among meat intake, exposure to HCAs and PAHs, and colon cancer in a population-based case-control study of African Americans (197 cases and 202 controls) and whites (203 cases and 210 controls). As part of a 150-item food frequency questionnaire, meat intake was assessed by cooking method and doneness and used to estimate individual HCA and PAH exposure. UGT1A7 alleles (UGT1A7*1, UGT1A7*2, UGT1A7*3, and UGT1A7*4) were measured and genotypes were categorized into predicted activity groups (high: *1/*1, *1/*2, *2/*2; intermediate: *1/*3, *1/*4, *2/*3; low: *3/*3, *3/*4, *4/*4). There was no association with UGT1A7 low versus high/intermediate genotype [odds ratio (OR), 1.1; 95% confidence interval (95% CI), 0.7-1.8], regardless of race. Greater than additive joint effects were observed for UGT1A7 low genotype and HCA-related factors. For example, equal to or greater than the median daily intake of the HCA, 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (DiMeIQx) and having UGT1A7 low genotype was positively associated with colon cancer (OR, 2.4; 95% CI, 1.2-4.8), compared with less than the median daily intake and UGT1A7 high/intermediate genotypes. These data suggest that the associations among cooked meat-derived compound exposure, and colon cancer are modified by the UGT1A7 genotype.

Interspecies metabolism of heterocyclic aromatic amines and the uncertainties in extrapolation of animal toxicity data for human risk assessment

Heterocyclic aromatic amines (HAAs) are potent bacterial mutagens that are formed in cooked meats, tobacco smokes condensate, and diesel exhaust. Many HAAs are carcinogenic in experimental animal models. Because of their wide-spread occurrence in the diet and environment, HAAs may contribute to some common types of human cancers. The extrapolation of animal toxicity data on HAAs to asses human health risk has many uncertainties, which can lead to tenuous risk assessment estimates. Perhaps the most critical and variable parameters in interspecies extrapolation are the effects of dose, species differences in catalytic activities of xenobiotic metabolism enzymes (XMEs), human XME polymorphisms that lead to interindividual differences in carcinogen metabolism and dietary constituents that may either augment or diminish the carcinogenic potency of these genotoxins. The impact of these parameters on the metabolism and toxicological properties of HAAS and uncertainties in extrapolation of animal toxicity data for human risk assessment are presented in this article.

N-Nitrosodiethylamine mutagenicity at low concentrations

N-Nitrosodiethylamine (NDEA) requires metabolic activation by cytochrome P450 enzymes, leading to electrophile species that react in DNA. Although, carcinogenicity is not an end point in genotoxicity assays, NDEA has been considered a weak carcinogen. In this study, we carried out an analysis of the mutagenicity at low concentrations of NDEA. Using SOS chromotest in the presence of metabolic activation, we detected positive mutagenicity response for NDEA doses between 0.75 and 36.46 microg/ml. In Ames test, using more sensitive strains in the presence of S9 metabolic activation mixture (S9 mix), positive results were also detected for NDEA doses between 1.01 x 10(-3) and 50.64 x 10(-3 microg per plate. Our results indicate that NDEA mutagenicity can be detected at low concentrations when more sensitive conditions are used.

Smoking, DNA repair capacity and risk of nonsmall cell lung cancer

Tobacco-related carcinogens cause a variety of DNA damage that is repaired by different enzymatic pathways, suggesting that DNA repair plays an important role in tobacco-induced carcinogenesis. In a large hospital-based case-control study, we investigated DNA repair capacity (DRC) as a biomarker for susceptibility to nonsmall cell lung cancer (NSCLC) and evaluated the possible interaction between DRC and tobacco smoke in 467 newly diagnosed NSCLC patients and 488 cancer-free controls. We measured DRC in cultured peripheral lymphocytes using the host-cell reactivation assay with a reporter gene damaged by an activated tobacco carcinogen, benzo[a]pyrene diol epoxide. The results showed that current smokers exhibited the highest DRCs as compared to former and nonsmokers both among patients and control subjects. There were no differences of DRC among 3 different histopathologic types of NSCLC. Logistic regression analysis revealed that suboptimal DRC and pack-years smoked were independent predictors of NSCLC risk. The overall 15.5% reduction in DRC observed in the cases (7.84%) compared to the controls (9.28%) (p<0.001) was associated with an approximately 2-fold increased risk of NSCLC (adjusted odds ratio (OR) = 1.85, 95% confidence interval (CI) 1.42-2.42). There was a significant dose-response association between decreased DRC and increased risk of lung cancer. Furthermore, we observed a nonstatistically significant additive but not multiplicative interaction between DRC and pack-years smoked on lung cancer risk, particularly in the histopathologic types of NSCLC other than adenocarcinoma. The results suggest that suboptimal DRC is associated with increased risk of NSCLC and DRC may modulate the risk of lung cancer associated with smoking but the latter needs to be verified in larger studies.

Biological indicators of genotoxic risk and metabolic polymorphisms

International scientific publications on the influence of metabolic genotypes on biological indicators of genotoxic risk in environmental or occupational exposure are reviewed. Biomarkers of exposure (substance or its metabolites in biological fluids, urinary mutagenicity, protein and DNA adducts) and of effects (chromosome aberrations (CAs), sister chromatid exchanges (SCEs), micronuclei (Mn), COMET assay, HPRT mutants) have been evaluated according to different genotypes (or phenotypes) of several activating/detoxifying metabolic activities. In less than half the studies (43 out of 95), the influence of genotype on the examined biological indicator was found, of which four report poorly reliable results (i.e., with scarce biological plausibility, because of the inconsistency of modulated effect with the type of enzymatic activity expressed). As regards urinary metabolites, the excretion of mercapturic acids (MA) is greater in subjects with high GST activity, that of 1-pyrenol and other PAH metabolites turns out to be significantly influenced by genotypes CYP1A1 or GSTM1 null, and that of exposure indicators to aromatic amines (AA) (acetylated and non-acetylated metabolites) is modulated by NAT2. In benzene exposure, preliminary results suggest an increase in urinary t, t-muconic acid (t,t-MA) in subjects with some genotypes. On urinary mutagenicity of PAH-exposed subjects, the effects of genotype GSTM1 null, alone or combined with NAT2 slow are reported. When DNA adduct levels are clearly increased in PAH-exposed group (18 out of 22), 7 out of 18 studies report the influence of GSTM1 null on this biomarker, and of the five studies which also examined genotype CYP1A1, four report the influence of genotype CYP1A1, alone or in combination with GSTM1 null. A total of 25 out of 41 publications (61%) evaluating the influence of metabolic polymorphisms on biomarkers of effect (cytogenetic markers, COMET assay, HPRT mutants) do not record any increase in the indicator due to exposure to the genotoxic agents studied, confirming the scarce sensitivity of these indicators (mainly HPRT mutants, Mn, COMET assay) for assessing environmental or occupational exposure to genotoxic substances. Concluding, in determining urinary metabolites for monitoring exposure to genotoxic substances, there is sufficient evidence that genetically-based metabolic polymorphisms must be taken into account in the future. The unfavourable association for the activating/detoxifying metabolism of PAH is also confirmed as a risk factor due to the formation of PAH-DNA adducts. The clearly protective role played by GSTT1 on DEB (and/or related compound)-induced sister chromatid exchanges (SCEs) should be noted. The modulating effects of genotypes on protein adduct levels in environmental and occupational exposure have not yet been documented, and most studies on the influence of genotype on biological indicators of early genotoxic effects report negative results.

Increased cancer risk among relatives of nonsmoking lung cancer cases

Lung cancer has been shown to aggregate in families of nonsmoking lung cancer cases with an earlier age at onset. The current study evaluates whether relatives of nonsmoking lung cancer cases are at increased risk of cancers at sites other than lung. Families were identified through 257 population-based, nonsmoking lung cancer cases and 277 population-based, nonsmoking controls residing in metropolitan Detroit. Data were collected for 2,252 relatives of cases and 2,408 relatives of controls. First-degree relatives of nonsmoking lung cancer cases were at 1.52-fold (95% CI, 1.02-2.27) increased risk of cancer of the digestive system after adjustment for each relative's age, race, sex, and smoking status. Relative risk estimates also were elevated, but not significantly, for tobacco-related cancers (RR = 1.39) and breast cancer (RR = 1.72). Among first-degree relatives of younger probands (age 40-59), risk was non-significantly increased 72% (95% CI 0.95-3.10) for all cancers combined and 3.14-fold for cancers of the digestive system (95% CI 0.76-12.9). Nonsmoking relatives of cases were at increased risk of all cancer sites combined (RR = 1.32; 95% CI 1.003-1.73), cancers other than lung (RR = 1.37; 95% CI 1.03-1.82), and digestive system cancers (RR = 2.01; 95% CI 1.20-3.37). These findings of moderate familial aggregation for cancers of the lung, digestive system, breast, and tobacco-related sites suggest that common susceptibility genes may act to increase risk for a variety of cancers in families.

DNA adducts in human placenta as related to air pollution and to GSTM1 genotype

DNA adducts in human placenta have been studied in relation to metabolic genotype for glutathione S-transferase M1 (GSTM1) in 98 mothers living in two regions with a different annual average air pollution levels: Northern Bohemia-the district of Teplice as polluted industrial area (mines, brown coal power plants) and Southern Bohemia-the district of Prachatice as agricultural area without heavy industry. Forty-nine placenta samples (25 from the Teplice district and 24 from the Prachatice district) from non-smoking mothers with the date of delivery in the summer period and 49 placenta samples (25 from the Teplice district and 24 from Prachatice district) from mothers with the date of delivery in the winter period were analysed. The total DNA adduct levels were calculated as the sum of adducts in the diagnoal radioactive zone (DRZ) and one distinct spot outside of the DRZ (termed X), which was detected in almost all placenta samples. We found total DNA adduct levels of 1.40 +/- 0.87 (0.04-3.65) and 1.04 +/- 0.63 (0.11-3.08) adducts per 10(8) nucleotides for the Teplice and Prachatice districts, respectively. The significant difference between both districts in placental DNA adduct levels was found for the winter sampling period only (1.49 vs. 0.96 adducts per 10(8) nucleotides; p = 0.023). No seasonal variation was observed for DNA adduct levels in the overall population studied. A positive GSTM1 genotype was detected in 51 subjects, while GSTM1-null genotype was found in 47 subjects. Higher DNA adduct levels were detected in a group with GSTM1-null genotype (p = 0.009). This finding seems more significant for subjects in the Teplice district (p = 0.047) than for those in the Prachatice district (p = 0.092). Significant district and seasonal differences were found in subgroups carrying the GSTM1-null genotype. DNA adduct levels in placentas of mothers with GSTM1-null genotype living in the polluted district of Teplice were higher than those in Prachatice (p = 0.050); also the adduct levels in placentas sampled in the summer period were higher than those sampled in the winter period (p = 0.011). Our results indicate that simultaneous analysis of DNA adducts and metabolic genotypes could emphasize the use of DNA adduct measurements, particularly in the case of the environmental exposure when the total doses of genotoxic pollutants are very low.

Influence of GSTM1 and NAT2 genotypes on placental DNA adducts in an environmentally exposed population

The placenta bulky DNA adducts have been studied in relation to metabolic genotypes for glutathione S-transferase M1 (GSTM1) and N-acetyl transferase 2 (NAT2) in 158 mothers (113 nonsmokers and 45 smokers) living in two regions with different annual average air pollution levels of sulphur dioxide, nitrogen oxides, particulate matter < 10 microns, and polycyclic aromatic hydrocarbons. One region was the district of Teplice as the polluted industrial region with mines and brown coal power plants, and the other was the district of Prachatice, an agricultural region without heavy industry. DNA adduct levels were determined by using a butanol extraction enrichment procedure of 32P-postlabeling. GSTM1 and NAT2 genotypes were studied by using polymerase chain reaction. The total DNA adduct levels included a diagonal radioactive zone (DRZ) and one distinct spot outside DRZ (termed X), which was detected in almost all placenta samples and correlated with DRZ (r = .682; P < .001). We found the total DNA adduct levels 2.12 +/- 1.46 (0.04-7.70) and 1.48 +/- 1.09 (0.11-4.98) adducts per 10(8) nucleotides for Teplice and Prachatice districts, respectively, indicating significant differences between both regions studied (P = .004). Elevated DNA adduct levels were found in smoking mothers (10 or more cigarettes per day) by comparison with nonsmoking mothers (3.21 +/- 1.39 versus 1.32 +/- 0.88 adducts per 10(8) nucleotides; P < .001). Placental DNA adduct levels in smokers correlated with cotinine measured in plasma (r = .432; P = .003). This relation indicates that cigarette smoking could be predominantly responsible for DNA adduct formation in placentas of smoking mothers. DNA adduct levels were evaluated separately for non-smokers (1.50 +/- 1.00 vs. 1.09 +/- 0.66 adducts/10(8) nucleotides for the Teplice and Prachatice districts, respectively; P = .046) and smokers (3.35 +/- 1.47 vs. 2.91 +/- 1.20 adducts/10(8) nucleotides for Teplice and Prachatice districts, respectively; P = .384) to exclude the effect of active cigarette smoking on the district variation. These findings indicate that the effect of the environmental pollution in cigarette smokers is practically overlapped by tobacco exposure. No seasonal variation was observed for DNA adduct levels in the overall population studied and no relation between total DNA adduct levels in placenta and levels of vitamins A, C, and E in venous and cord blood was found. A positive GSTM1 genotype was detected in 78 subjects, while negative GSTM1 genotype was found in 80 subjects. Higher DNA adduct levels were detected in the group with GSTM1-negative genotype by comparison with GSTM1-positive genotype (2.05 +/- 1.30 vs. 1.66 +/- 1.39 adducts/10(8) nucleotides; P = .018). This finding is more pronounced in the Teplice district (2.33 +/- 1.36 vs. 1.88 +/- 1.56 adducts/10(8) nucleotides; P = .053) than for the Prachatice district (1.61 +/- 1.09 vs. 1.36 +/- 1.10 adducts/10(8) nucleotides; P = .248) and for nonsmokers (1.45 +/- 0.82 vs. 1.18 +/- 0.93 adducts/10(8) nucleotides; P = .029) more than for smokers (3.45 +/- 1.14 vs. 2.95 +/- 1.62 adducts/10(8) nucleotides; P = .085). Significant district and seasonal differences were found in subgroups with GSTM1-negative genotype. DNA adduct levels in placentas of the GSTM1-negative subgroup were higher in mothers living in the polluted district of Teplice than in Prachatice (P = .012). The adduct levels in placentas sampled in the summer period were higher than in the winter period in the GSTM1-negative population (P = .006). No effect of the NAT2 genotype on DNA adduct levels was observed.