Molecular epidemiology: low-dose carcinogens and genetic susceptibility

CYP1A1 *2B and *4 Polymorphisms are associated with Lung Cancer Susceptibility in Mexican Patients

Background

CYP1A1 is a gene involved in the high aryl hydrocarbon hydroxylase -inducible phenotype, which is a genetically-determined variation among individuals that has been associated with lung cancer risk. More specifically, CYP1A1*2B and *4 polymorphisms have been associated with high susceptibility to lung cancer among cigarette smokers. Materials and methods: DNA was obtained from blood samples and we studied by PCR-RFLP the distribution of CYP1A1*2B (n=248) and *4 (n=222) polymorphisms in healthy controls and 222 lung cancer patients from a Mexican population.

Results

Comparisons between groups showed an increased risk for lung cancer patients of *2B/*2B (18%; OR 7.6; 95% CI 3.0–19.2) and *4/*4 genotypes (15%; OR 11.45; 95% CI 2.19–59.85) compared to the control group (1% for *2B/*2B and 4.4% for *4/*4). A significant association between lung cancer and homozygous *2B/*2B passive smokers and *4/*4 ever (cigarettes) and passive smokers was also observed (p<0.05). Multivariate analysis revealed an increased risk for the *2B/2B genotype (OR 6.83), as well as for *4/*4 (OR 28.8).

Conclusion

The results of the study indicate a significant association between *2B/*2B and *4/*4 genotypes and the risk of developing lung cancer among Mexicans.

Self-reported smoking, serum cotinine, and blood DNA methylation

BACKGROUND

Epigenome-wide profiling of DNA methylation pattern with respect to tobacco smoking has given rise to a new measure of smoking exposure. We investigated the relationships of methylation markers with both cotinine, an established marker of internal smoking exposure, and self-reported smoking.

METHODS

Blood DNA methylation levels across the genome and serum cotinine were measured in 1000 older adults aged 50-75 years. Epigenome-wide scans were performed to identify methylation markers associated with cotinine. The inter-dose-response relationships between the number of cigarettes smoked per day, cotinine concentration, and DNA methylation were modeled by restricted cubic spline regression.

RESULTS

Of 61 CpGs that passed the genome-wide significance threshold (p<1.13×10(-7)), 40 CpGs in 25 chromosomal regions were successfully replicated, showing 0.2-3% demethylation per 10ng/ml increases in cotinine. The strongest associations were observed for several loci at AHRR, F2RL3, 2q37.1, 6p21.33, and GFI1 that were previously identified to be related to self-reported smoking. One locus at RAB34 was newly discovered. Both cotinine and methylation markers exhibited non-linear relationships with the number of cigarettes smoked per day, where the highest rates of increase in cotinine and decreases in methylation were observed at low smoking intensity (1-15 cigarettes/day) and plateaued at high smoking intensity (>15-20 cigarettes/day). A clear linear relationship was observed between cotinine concentration and methylation level. Both cotinine and methylation markers showed similar accuracy in distinguishing current from never smoker, but only methylation markers distinguished former from never smoker with high accuracy.

CONCLUSIONS

Our study corroborates and expands the list of smoking-associated DNA methylation markers. Methylation levels were linearly related to cotinine concentration and provided accurate measures for both current and past smoking exposure.

Risk of renal cell carcinoma and polymorphism in phase I xenobiotic metabolizing CYP1A1 and CYP2D6 enzymes

The progressive increase in sporadic renal cell carcinoma (RCC) observed in industrialized countries supports the opinion that certain carcinogens present in the environment (tobacco smoke, drugs, pollutants, and dietary constituents) may affect the occurrence and progression of this disease in developing countries like India. The polymorphism of the enzymes involved in metabolism of such environmental factors may, therefore, confer variable propensity to RCC. The possible association between RCC and a polymorphism of the CYP1A1 and CYP2D6 genes specific to the Indian population was examined using peripheral blood DNA from 196 RCC cases and 250 population controls with detailed data of clinicopathologic characteristics for the disease. The CYP1A1 (val) "variant" genotype, which contains at least 1 copy of the CYP1A1 variant alleles, was found to be associated with a 2.03-fold [GG ver. AA/AG, unadjusted OR = 2.03; 95%CI = 1.233-3.342; P = 0.005] increase in the risk of RCC. There was also a significant association (p(trend) = 0.034) between higher frequency of RCC subjects containing at least of copy of the CYP1A1 (val) "variant" genotype with III or IV Fuhrman's grade. Whereas, the CYP2D6 polymorphism did not show any association with RCC risk [TT ver. CT/CC, unadjusted OR = 95%CI = 1.233-3.342; P = 0.005]. There was a significant association (p(trend) = 0.001) between the poor metabolizer CYP2D6 (TT) and progression towards higher pathological stage of RCC. Our data demonstrate for the first time a significant association between pharmacogenetic polymorphisms of CYP1A1 and risk of RCC development in the Indian population. The findings suggest that inter-individual variation in the phase I metabolic enzymes involved in the fictionalization and detoxification of specific xenobiotics is an important susceptibility factor for development and progression of RCC in Indians.

ATM polymorphisms and risk of lung cancer among never smokers

The ataxia-telangiectasia mutated (ATM) gene, an important caretaker of overall genome stability, is thought to play a role in the development of human malignancy. Therefore, we hypothesized that sequence variants in ATM may influence the disposition to lung cancer. In this hospital-based matched case-control study, nine ATM single nucleotide polymorphisms (rs189037, rs228597, rs228592, rs664677, rs609261, rs599558, rs609429, rs227062, and rs664982) were genotyped in 730 lung cancer patients and 730 healthy controls. Pairwise linkage disequilibrium among nine polymorphisms in the ATM gene was very high. None of the main effects of any of the ATM polymorphisms were related to the risk of lung cancer. Interestingly, ATM polymorphisms were significantly associated with lung cancer among never smokers, and the association was modulated by low-level exposure to carcinogens such as environmental tobacco smoke. When the haplotypes of nine ATM polymorphism sites were studied, no overall association between ATM haplotypes and risk of lung cancer was found. However, the frequency distribution of haplotypes between lung cancer cases and controls was significant in the never smokers (P=0.009), demonstrating that haplotypes have a significant effect on the risk of lung cancer. In conclusion, we found that never smokers with sequence variants of the ATM gene may be at increased risk for lung cancer. Our data also suggest this association may be further modified by exposure to environmental tobacco smoke. This study suggests support to the literature that ATM polymorphisms and environmental tobacco smoke exposure have a role in lung carcinogenesis among never smokers.

Effects of cigarette smoking, XRCC1 genetic polymorphisms, and age on basal DNA damage in human blood mononuclear cells

The aim of this study was to investigate the effects of smoking, polymorphisms of XRCC1 codons 194 and 399, and age on levels of basal DNA damage (as measured by an alkaline comet assay) on mononuclear cells in 122 healthy Japanese workers. In the whole group of 122 individuals, the tail moment (TM) values of current smokers (P < 0.001) or former smokers (P = 0.03) were significantly higher than those of nonsmokers. Individuals bearing the XRCC1 399Gln variant allele showed significant increases in TM values in all subjects or in referent subgroups stratified by age or smoking status except in the current smokers group; in contrast, the TM values of individuals bearing the XRCC1 194Trp variant allele were significantly lower than those of individuals bearing wild-type Arg/Arg genotypes. Furthermore, older subjects (> or =47 years old) had significantly higher TM values than younger subjects (<47 years old) in all subjects (P = 0.008). Multiple regression analysis indicated that smoking habits, polymorphisms of XRCC1 codons 194 and 399, and age were important variables affecting individuals basal DNA damage.

CYP1A1/2 haplotypes and lung cancer and assessment of confounding by population stratification

Prior studies of lung cancer and CYP1A1/2 in African-American and Latino populations have shown inconsistent results and have not yet investigated the haplotype block structure of CYP1A1/2 or addressed potential population stratification. To investigate haplotypes in the CYP1A1/2 region and lung cancer in African-Americans and Latinos, we conducted a case-control study (1998-2003). African-Americans (n = 535) and Latinos (n = 412) were frequency matched on age, sex, and self-reported race/ethnicity. We used a custom genotyping panel containing 50 single nucleotide polymorphisms in the CYP1A1/2 region and 184 ancestry informative markers selected to have large allele frequency differences between Africans, Europeans, and Amerindians. Latinos exhibited significant haplotype main effects in two blocks even after adjusting for admixture [odds ratio (OR), 2.02; 95% confidence interval (95% CI), 1.28-3.19 and OR, 0.55; 95% CI, 0.36-0.83], but no main effects were found among African-Americans. Adjustment for admixture revealed substantial confounding by population stratification among Latinos but not African-Americans. Among Latinos and African-Americans, interactions between smoking level and haplotypes were not statistically significant. Evidence of population stratification among Latinos underscores the importance of adjusting for admixture in lung cancer association studies, particularly in Latino populations. These results suggest that a variant occurring within the CYP1A2 region may be conferring an increased risk of lung cancer in Latinos.

Polymorphisms of DNA repair genes: ADPRT, XRCC1, and XPD and cancer risk in genetic epidemiology

Many studies have suggested that adenosine diphosphate ribosyl transferase (ADPRT), X-ray repair cross-complementing 1 (XRCC1), and xeroderma pigmentosum complementary group D (XPD) are three major DNA base excision repair (BER) genes and that they act interactively in stimulating and executing BER processes. Polymorphisms of these genes may influence the rate of gene transcription, the stability of the messenger RNA, or the quantity and activity of the resulting protein. Thus, the susceptibility or severity of several disorders is influenced by possession of specific alleles of polymorphic genes. So, it is plausible that variations and mutations in these genes affect DNA repair capacity in normal populations, and thus facilitate cancer development in normal or exposed individuals. To promote translation of scientific findings for potential clinical application of DNA repair function, we have searched publications relevant to molecular epidemiology studies of associations between single-nucleotide polymorphisms (SNPs) in the genes, and several frequent human cancer. We have focused on five particular polymorphisms as our starting point: the T-->C polymorphism (Val762Ala) in exon 17 of ADPRT, the novel transition at the promoter region (-77T-->C) of XRCC1, two common nonsynonymous polymorphisms (Arg194Trp and Arg399Gln), and the C-->A silent polymorphism (Arg156Arg) in exon 6 of XPD. We review here the case-control studies examining whether these polymorphisms are correlated with reduced DNA repair efficiency, their influence on the development of different solid tumors, and their possible interactions with other genetic factors and environmental exposures.

Chromosomal aberrations in tire plant workers and interaction with polymorphisms of biotransformation and DNA repair genes

We evaluated chromosomal aberrations in lymphocytes of 177 workers exposed to xenobiotics in a tire plant and in 172 controls, in relation to their genetic background. Nine polymorphisms in genes encoding biotransformation enzymes and nine polymorphisms in genes involved in main DNA repair pathways were investigated for possible modulation of chromosomal damage. Chromosomal aberration frequencies were the highest among exposed smokers and the lowest in non-smoking unexposed individuals (2.5+/-1.8% vs. 1.7+/-1.2%, respectively). The differences between groups (ANOVA) were borderline significant (F=2.6, P=0.055). Chromosomal aberrations were higher in subjects with GSTT1-null (2.4+/-1.7%) than in those with GSTT1-plus genotype (1.8+/-1.4%; F=7.2, P=0.008). Considering individual groups, this association was significant in smoking exposed workers (F=4.4, P=0.040). Individuals with low activity EPHX1 genotype exhibited significantly higher chromosomal aberrations (2.3+/-1.6%) in comparison with those bearing medium (1.7+/-1.2%) and high activity genotype (1.5+/-1.2%; F=4.7, P=0.010). Both chromatid- and chromosome-type aberration frequencies were mainly affected by exposure and smoking status. Binary logistic regression analysis revealed that frequencies of chromatid-type aberrations were modulated by NBS1 Glu185Gln (OR 4.26, 95%CI 1.38-13.14, P=0.012), and to a moderate extent, by XPD Lys751Gln (OR 0.16, 95%CI 0.02-1.25, P=0.081) polymorphisms. Chromosome-type aberrations were lowest in individuals bearing the EPHX1 genotype conferring the high activity (OR 0.38, 95%CI 0.15-0.98, P=0.045). Present results show that exposed individuals in the tire production, who smoke, exhibit higher chromosomal aberrations frequencies, and the extent of chromosomal damage may additionally be modified by relevant polymorphisms.

Effect of the CYP2E1 genotype on vinyl chloride monomer-induced liver fibrosis among polyvinyl chloride workers

Although a relationship between vinyl chloride monomer (VCM) and liver cirrhosis has been reported, the underlying mechanisms are not clear. Cytochrome P450 2E1 (CYP2E1), aldehyde dehydrogenase 2 (ALDH2) and glutathione S-transferase theta 1 (GSTT1) enzymes are involved in activation and detoxification of VCM, and thus may be important determinants of interindividual susceptibility to VCM-induced liver damage, including liver cirrhosis. The objective of this study was to evaluate if metabolizing genetic polymorphisms could modify individual susceptibility to liver fibrosis of the VCM exposure. CYP2E1, ALDH2, and GSTT1 polymorphisms were determined by the PCR-RFLP method among 320 workers who were employed in five polyvinyl chloride manufacturing plants. Cumulative VCM exposure levels for study subjects were calculated using a job exposure matrix model. Thirteen workers were diagnosed as having liver fibrosis by using ultrasonography. We observed a dose-response trend between VCM exposure and liver fibrosis. Regarding the results on genetic polymorphisms, CYP2E1 c2c2 genotype showed a significant increase in the risk of liver fibrosis as compared to those with CYP2E1 c1c1 or c1c2 genotypes. No differences were observed between GSTT1 and ALDH2 genotypes and liver fibrosis. In summary, our result suggests that genetic polymorphism in CYP2E1 may be responsible for individual differences in susceptibility to liver fibrosis with regard to chronic VCM exposure. Thus, polymorphism analysis of metabolizing enzymes might be useful in the risk assessment of liver damage in workers with VCM exposure.

The risk of developing cervical cancer in Mexican women is associated to CYP1A1 MspI polymorphism

The aim of the study was to evaluate the association of two CYP1A1 polymorphisms (Msp1 and exon 7) with cervical cancer in Mexican women considering their smoking habit. The polymorphisms were determined in 310 individuals (155 with cervical cancer and 155 healthy controls). Women with MspI T/C or C/C showed increased risk of developing cervical cancer (3.7- and 8.3-fold increase, respectively) compared to women with T/T genotype. When smoking habit was considered, the risk for non-smokers with T/C and C/C genotypes was similar (5.2 and 4.1, respectively), whereas smoking women with C/C genotype showed a 19.4-fold increase of cervical cancer. Number of child births, number of sexual partners and marital status were strong risk factors for developing cervical cancer in women with T/T genotype; however, in women with T/C genotype, only the number of child births and sexual partners had a significant influence. These results suggest an important role of the CYP1A1 MspI polymorphism in the risk of developing cervical cancer.

Metformin does not prevent DNA damage in lymphocytes despite its antioxidant properties against cumene hydroperoxide-induced oxidative stress

Metformin (1-(diaminomethylidene)-3,3-dimethyl-guanidine), which is the most commonly prescribed oral antihyperglycaemic drug in the world, was reported to have several antioxidant properties such as the inhibition of advanced glycation end-products. In addition to its use in the treatment of diabetes, it has been suggested that metformin may be a promising anti-aging agent. The present work was aimed at assessing the possible protective effects of metformin against DNA-damage induction by oxidative stress in vitro. The effects of metformin were compared with those of N-acetylcysteine (NAC). For this purpose, peripheral blood lymphocytes from aged (n=10) and young (n=10) individuals were pre-incubated with various concentrations of metformin (10-50microM), followed by incubation with 15microM cumene hydroperoxide (CumOOH) for 48h, under conditions of low oxidant level, which do not induce cell death. Protection against oxidative DNA damage was evaluated by use of the Comet assay and the cytokinesis-block micronucleus technique. Changes in the levels of malondialdehyde+4-hydroxy-alkenals, an index of oxidative stress, were also measured in lymphocytes. At concentrations ranging from 10microM to 50microM, metformin did not protect the lymphocytes from DNA damage, while 50microM NAC possessed an effective protective effect against CumOOH-induced DNA damage. Furthermore, NAC, but not metformin, inhibited DNA fragmentation induced by CumOOH. In contrast to the lack of protection against oxidative damage in lymphocyte cultures, metformin significantly protected the cells from lipid peroxidation in both age groups, although not as effective as NAC in preventing the peroxidative damage at the highest doses. Within the limitations of this study, the results indicate that pharmacological concentrations of metformin are unable to protect against DNA damage induced by a pro-oxidant stimulus in cultured human lymphocytes, despite its antioxidant properties.

CYP1A1 and CYP1B1 genetic polymorphisms, smoking and breast cancer risk in a Finnish Caucasian population

We investigated the associations between two CYP1A1 polymorphisms (Ile462Val and Thr461Asn) and one CYP1B1 polymorphism (Leu432Val) and breast cancer risk. The study population consisted of 483 breast cancer patients and 482 healthy population controls, all of homogenous Finnish origin. No statistically significant overall associations were found between the CYP1A1 and CYP1B1 genotypes and breast cancer risk. However, a significant increase in the breast cancer risk was seen for women who had smoked 1-9 cigarettes/day and carried the CYP1B1 432Val allele; the OR was 2.6 (95% CI 1.07-6.46) for women carrying the Leu/Val genotype and 5.1 (95% CI 1.30-19.89, P for trend 0.005) for women with the Val/Val genotype compared to similarly smoking women homozygous for the 432Leu allele. Furthermore, when CYP1B1 genotypes were combined with the previously analyzed N-acetyl transferase (NAT2) genotypes, a significant increase in breast cancer risk was found among women who had at least one CYP1B1 432Val allele together with the NAT2 slow acetylator genotype (OR 1.52; 95% CI 1.03-2.24) compared to women carrying a combination of CYP1B1 Leu/Leu and NAT2 rapid acetylator genotypes. This risk was seen to be confined to ever smokers; the OR was 2.46 (95% CI 1.11-5.45) for ever smokers carrying at least one CYP1B1 432Val allele together with the NAT2 slow acetylator genotype compared to ever smokers with the CYP1B1 Leu/Leu and NAT2 rapid acetylator genotype combination. Our results suggest that the CYP1B1 polymorphism may be an important modifier of breast cancer risk in Finnish Caucasian women who have been exposed to tobacco smoke and/or carry the NAT2 slow acetylator genotype.

Association of genetic polymorphisms in the base excision repair pathway with lung cancer risk: a meta-analysis

Lung cancer is a major cause of cancer-related death in the developed countries and the overall survival rate has still an extremely poor. Although cigarette smoking is the main cause of lung cancer, not all smokers develop lung cancer, and a fraction of lifelong non-smokers will die from lung cancer. Genetic host factors have recently been implicated to account for some of the observed differences in lung cancer susceptibility. Various DNA alterations can be caused by exposure to environmental and endogenous carcinogens. Most of these alterations, if not repaired, may result in genetic instability, mutagenesis and cell death. DNA repair mechanisms are important for maintaining DNA integrity and preventing carcinogenesis. Recent genetic association studies on lung cancer risk have focused on identifying effects of single nucleotide polymorphisms (SNPs) in candidate genes, among which DNA repair genes are increasingly studied. Genetic variations in DNA repair genes are thought to modulate DNA repair capacity and are suggested to be related to lung cancer risk. We identified a sufficient number of epidemiologic studies on lung cancer to conduct a meta-analysis for genetic polymorphisms in nucleotide base repair (BER) pathway, focusing on 8-oxoguanine DNA glycosylase 1, X-ray cross-complementing group 1 (XRCC1) and apurinic/apyrimidinic endonuclease 1. The 399Gln/Gln genotype of the XRCC1 Arg399Gln polymorphism was associated with an increased risk of lung cancer among Asians (OR=1.34, 95% CI=1.16-1.54) but not among Caucasians. Little evidence of associations has been found between other BER genes and lung cancer risk. Considering the data available, it can be conjectured that if there is any risk association between single SNP and lung cancer, this risk increase/decrease will probably be minimal. Advances in identification of new polymorphisms and in high-throughput genotyping techniques will facilitate analysis of multiple genes in multiple DNA repair pathways. Therefore, it is likely that the defining feature of future epidemiologic studies will be the simultaneous analysis of large samples of cases and controls.

Polymorphisms of XRCC1 genes and risk of nasopharyngeal carcinoma in the Cantonese population

Background

Nasopharyngeal carcinoma (NPC) is one of the most common cancers in southern China. In addition to environmental factors such as Epstein-Barr virus infection and diet, genetic susceptibility has been reported to play a key role in the development of this disease. The x-ray repair cross-complementing group 1 (XRCC1) gene is important in DNA base excision repair. We hypothesized that two common single nucleotide polymorphisms of XRCC1 (codons 194 Arg→Trp and 399 Arg→Gln) are related to the risk of NPC and interact with tobacco smoking.

Methods

We sought to determine whether these genetic variants of the XRCC1 gene were associated with the risk of NPC among the Cantonese population in a hospital-based case control study using polymerase chain reaction-restriction fragment length polymorphism analysis. We conducted this study in 462 NPC patients and 511 healthy controls.

Results

After adjustment for sex and age, we found a reduced risk of developing NPC in individuals with the Trp194Trp genotype (OR = 0.48; 95% CI, 0.27–0.86) and the Arg194Trp genotype (OR = 0.79; 95% CI, 0.60–1.05) compared with those with the Arg194Arg genotype. Compared with those with the Arg399Arg genotype, the risk for NPC was not significantly different in individuals with the Arg399Gln genotype (OR = 0.82; 95% CI, 0.62–1.08) and the Gln399Gln genotype (OR = 1.20; 95% CI, 0.69–2.06). Further analyses stratified by gender and smoking status revealed a significantly reduced risk of NPC among males (OR = 0.32; 95% CI, 0.14–0.70) and smokers (OR = 0.34; 95% CI, 0.14–0.82) carrying the XRCC1 194Trp/Trp genotype compared with those carrying the Arg/Arg genotype. No association was observed between Arg399Gln variant genotypes and the risk of NPC combined with smoking and gender.

Conclusion

Our findings suggest that the XRCC1 Trp194Trp variant genotype is associated with a reduced risk of developing NPC in Cantonese population, particularly in males and smokers. Larger studies are needed to confirm our findings and unravel the underlying mechanisms.

APE1 genotype and risk of bladder cancer: evidence for effect modification by smoking

Apurinic/apyrimidinic (AP) sites are common mutagenic and cytotoxic DNA lesions that arise from the loss of normal bases. APE1, the major AP endonuclease of human cells, plays a central role in the repair of AP sites through both its endonuclease and phosphodiesterase activities. A common APE1 polymorphism, a T-->G transversion (Asp 148 Glu), was previously shown to be associated with risk of lung cancer, an association that was modified by cigarette smoking. To explore the association between APE1 genotype, smoking and bladder cancer risk, we examined data from an existing case-control study of bladder cancer patients (n = 239) and control individuals (n = 215) recruited from urology clinics at 2 hospitals in North Carolina. Genotype at the polymorphic site was determined using allele-specific primer extension reactions, followed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. We found no overall association between APE1 genotype and bladder cancer risk. In stratified analyses, however, a positive association with risk was observed with an increasing number of Glu alleles among never smokers, but not among smokers (p-value for interaction = 0.005). We can speculate that small allelic differences that are apparent in never smokers are obscured by the large amount of DNA damage found in smokers. Given the lack of established biological mechanisms, and suboptimal numbers of subjects in some exposure categories, our findings should be interpreted cautiously.

Caspase 9 promoter polymorphisms and risk of primary lung cancer

Caspase-9 (CASP-9) is an initiator CASP in the apoptosome-driven apoptosis pathway and plays an important role in the development and progression of cancer. Polymorphisms in the promoter region of the CASP-9 gene may influence the promoter activity of this gene, thereby modulating susceptibility to lung cancer. To test this hypothesis, we examined the association of four polymorphisms [-1263A>G, -905T>G, -712C>T and -293_-275delCGTGAGGTCAGTGCGGGGA (-293del)] in the CASP-9 promoter with the risk of lung cancer in a Korean population. The CASP-9 genotypes were determined in 432 lung cancer patients and 432 healthy controls that were frequency-matched for age and gender. The -1263 GG genotype was associated with a significantly decreased risk of lung cancer compared with the -1263 AA genotype or combined -1263 AA+AG genotype [adjusted odds ratio (OR)=0.64, 95% confidence interval (95% CI)=0.42-0.98, P=0.04 and adjusted OR=0.67, 95% CI=0.46-0.97, P=0.01, respectively]. For the -712C>T polymorphism, individuals with at least one -712T allele were at a significantly increased risk of lung cancer compared with those harboring the -712 CC genotype (adjusted OR=1.42, 95% CI=1.06-1.89, P=0.02). Consistent with the results of genotype analyses, the -1263G/-712C (G-C) haplotype was associated with a significantly decreased risk of lung cancer [adjusted OR=0.59, 95% CI=0.47-0.75, P and Bonferroni corrected P (Pc)<0.001]. Moreover, the risk of lung cancer decreased in a dose-dependent manner as the number of the G-C haplotypes increased (adjusted OR=0.60, 95% CI=0.45-0.81, P=0.0007 and Pc=0.0014 for the G-C heterozygotes and adjusted OR=0.34, 95% CI=0.17-0.68, P=0.0023 and Pc=0.0046 for the G-C homozygotes; P(trend)<0.001). The promoter assay revealed the G-C haplotype to have a significantly higher promoter activity than the -1263G/-712T and -1263A/-712C haplotypes. These results suggest that CASP-9 promoter polymorphisms affect CASP-9 expression and contribute to genetic susceptibility to lung cancer.

A novel T-77C polymorphism in DNA repair gene XRCC1 contributes to diminished promoter activity and increased risk of non-small cell lung cancer

X-ray repair cross-complementing 1 (XRCC1) plays a key role in DNA base excision repair and cells lacking its activity are hypersensitive to DNA damage. Recently, we reported a SNP (rs3213245, -77T>C) in the XRCC1 gene 5' untranslated region (UTR) was significantly associated with the risk of developing esophageal squamous-cell carcinoma. Computer analysis predicted that this SNP was in the core of Sp1-binding motif, which suggested its functional significance. Gel shift and super shift assays confirmed that -77T>C polymorphic site in the XRCC1 promoter was within the Sp1-binding motif and the T>C substitution greatly enhanced the binding affinity of Sp1 to this region. Luciferase assays indicated that the Sp1-high-affinity C-allelic XRCC1 promoter was associated with a reduced transcriptional activity. The association between -77T>C and three other amino-acid substitution-causing polymorphisms in XRCC1 and risk of lung cancer was examined in 1024 patients and 1118 controls and the results showed that only the -77T>C polymorphism was significantly associated with an increased risk of developing lung cancer. Multivariate logistic regression analysis found that an increased risk of lung cancer was associated with the variant XRCC1 -77 genotypes (TC and CC) compared with the TT genotype (OR=1.46, 95% CI=1.18-1.82; P=0.001) and the increased risk was more pronounced in smokers (OR=1.63, 95% CI=1.20-2.21) than in non-smokers (OR=1.28, 95% CI=0.94-1.76). Taken together, these results showed that the functional SNP -77T>C in XRCC1 5'UTR was associated with cancer development owing to the decreased transcriptional activity of C-allele-containing promoter with higher affinity to Sp1 binding.

Gene-gene, gene-environment & multiple interactions in colorectal cancer

This review comprehensively evaluates the influence of gene-gene, gene-environment and multiple interactions on the risk of colorectal cancer (CRC). Methods of studying these interactions and their limitations have been discussed herein. There is a need to develop biomarkers of exposure and of risk that are sensitive, specific, present in the pathway of the disease, and that have been clinically tested for routine use. The influence of inherited variation (polymorphism) in several genes has been discussed in this review; however, due to study limitations and confounders, it is difficult to conclude which ones are associated with the highest risk (either individually or in combination with environmental factors) to CRC. The majority of the sporadic cancer is believed to be due to modification of mutation risk by other genetic and/or environmental factors. Micronutrient deficiency may explain the association between low consumption of fruit/vegetables and CRC in human studies. Mitochondrial modulation by dietary factors influences the balance between cell renewal and death critical in colon mucosal homeostasis. Both genetic and epigenetic interactions are intricately dependent on each other, and collectively influence the process of colorectal tumorigenesis. The genetic and environmental interactions present a good prospect and a challenge for prevention strategies for CRC because they support the view that this highly prevalent cancer is preventable.

GSTM1 and CYP1A1 polymorphisms, tobacco, air pollution, and lung cancer: a study in rural Thailand

OBJECTIVES

The Lampang Province is situated in the northern region of Thailand. Incidence rates of lung cancer are high for Asian standards, particularly in women. This study was conducted to quantify the risk of lung cancer associated with exposures prevalent in the area and to investigate possible interactions with genetic susceptibility. The presence of several large open-cast coal mines from 1955 close to electricity-generating plants was a particular focus of concern.

METHODS

Two-hundred and eleven cases of primary lung cancers diagnosed in 1993 to 1995 and residents in the province were recruited at the Lampang Provincial Hospital (main referral center for treatment of the disease). Two sets of controls, frequency-matched to the cases by sex and age, were recruited (a) from the resident population (202 interviewed) and (b) from patients admitted to the hospital for diseases predominantly unrelated to tobacco smoking (211 interviewed). Sociodemographic information, complete residential history, and characteristics of the household (place of cooking, cooking fuel, and heating fuels), occupational history, and history of tobacco smoking were obtained by interview. Cases and controls ( approximately 50% of the population-based series) provided a blood sample. A point source air pollution exposure index was calculated for each village/township reported in residential histories based on the linear distance from the Mae Moh Center (the area of the electricity-generating plants), the year-specific gaseous (SO(2) and NO(2)) or total suspended particulate emissions from the Mae Moh Power Plant, and the percentage of wind from the center. Odds ratios (OR) for the disease associated with categorical variables were estimated within unconditional logistic regression. Extraction of genomic DNA and genotyping of variants in CYP1A1 and GSTM1 were conducted to assess the extent of modification of risk by these genes that are involved in the metabolism of polycyclic aromatic hydrocarbons, a common component of the exposures.

RESULTS

Overall, there was no evidence of relevant differences in the socioeconomic level of the three groups. The two control sets were similar with respect to lifelong tobacco habit and were subsequently pooled in analyses. Never-smokers were 7% of men and 33% of women. Smoking of local traditional products unfiltered and high in tar content is a common habit in the rural female population. ORs associated with smoking increased with duration of the habit and average daily amount, being 4.9 [95% confidence interval (95% CI), 2.5-9.7] for smokers of > or =7 cigarettes/d and 3.3 (95% CI, 1.7-6.2) for duration of 41 years or longer compared with nonsmokers. Smoking of local products was associated with an independent OR of 3.1 (95% CI, 1.7-5.6) adjusted for lifelong cumulative amount of tobacco smoked. Although most smokers had the habit for at least 16 years, the daily consumption was low compared with Western standards. Other potential sources of exposure to lung carcinogens (emission from the power-generating plants and domestic burning of coal and wood for cooking and heating) were not associated with increased risk of lung cancer. None of the three polymorphisms examined increased the risk of lung cancer or modified the risk associated with tobacco smoking.

CONCLUSION

In this rural population, 96% of male and 64% of female lung cancer incidence were explained by tobacco smoking. None of the potential sources of air pollution deriving from the combustion of coal and wood, or polymorphisms in the CYP1A1 gene or deletion of the GSTM1 had an effect on the risk of lung cancer, either together or separately.

EPHX1 polymorphisms and the risk of lung cancer: a HuGE review

BACKGROUND

Microsomal epoxide hydrolase 1 (EPHX1) plays an important role in both the activation and detoxification of tobacco-derived carcinogens. Polymorphisms at exons 3 and 4 of the EPHX1 gene have been reported to be associated with variations in EPHX1 activity. The aim of this study is to review and summarize the available molecular epidemiologic studies of lung cancer and EPHX1.

METHODS

We searched MEDLINE, Current Contents, and Web of Science databases for studies published before August 2004. We conducted a systematic review and meta-analysis of 13 case-control studies. Summary odds ratios and summary prevalence of the variant allele (genotype) of both polymorphisms in the EPHX1 gene were calculated using the DerSimonian and Laird method.

RESULTS

The low-activity (variant) genotype of EPHX1 polymorphism at exon 3 was associated with decreased risk of lung cancer (odds ratio = 0.65; 95% confidence interval = 0.44-0.96) in lung cancer risk among whites. In white populations, the high-activity (variant) genotype of EPHX1 polymorphism at exon 4 was associated with a modest increase in risk of lung cancer (1.22; 0.79-1.90) and the predicted low activity was associated with a modest decrease in risk (0.72; 0.43-1.22).

CONCLUSIONS

EPHX1 enzyme may act as a phase I enzyme in lung carcinogenesis. The low-activity genotype of EPHX1 gene is associated with decreased risk of lung cancer among whites.

MS-920: DNA repair gene polymorphisms, diet and colorectal cancer risk in Taiwan

This hospital-based case-control study examined whether polymorphic DNA repair genes: XRCC1 Arg399Gln, XRCC3 Thr241Met and XPD Lys751Gln, play a role in the susceptibility to colorectal cancer. We genotyped these polymorphisms for 727 newly diagnosed colorectal adenocarcinoma cases and 736 age and sex matched healthy controls in Taiwan. Although the colorectal cancer risk was not significantly associated with these genes, the risk was significantly elevated in younger subjects (< or =60 years) with the XRCC1 399Arg/Arg genotype compared to those with XRCC1 399Gln allele (OR=1.46, 95% CI=1.06-2.99, P=0.02). The stratified analysis showed that XRCC3 interacted with meat consumption (P for interaction=0.02), but was limited to the low meat consumption (OR=2.34, 95% CI=1.28-4.29). Our results suggest that the XRCC1 Arg399Gln polymorphism may contribute to the risk of early-onset colorectal cancer and the XRCC3 Thr241Met polymorphism may modify the risk for meat-associated colorectal cancer.

Enhanced Sensitivity to Oxidant-Induced Micronucleus Frequency in Elderly Individuals Is Not Associated with Glutathione S- Transferase M1 (GSTM1) Null Genotype in Lymphocytes

BACKGROUND

A large number of studies have demonstrated that various kinds of DNA damage accumulate during aging and that oxidative stress possibly contributes to this process. Glutathione S-transferase M1 (GSTM1) can prevent their possible effects on DNA via detoxification of reactive substances that induced oxidative stress.

OBJECTIVE

To investigate the relationship between GSTM1 polymorphism and DNA sensitivity to oxidative stress with age, we used micronucleus (MN) frequency as a marker of DNA damage in lymphocytes from young and elderly subjects.

METHODS

This study was performed in 30 young (age range 20-36 years) and 30 elderly (age range 66-87 years) healthy individuals who were chosen on the basis of their GSTM1 genotype (15 GSTM1 null and 15 GSTM1 positive for each group). Lymphocytes were cultured after Ficoll isolation and treated for 48 h with a 30-muM dose of cumene hydroperoxide (CumOOH), a dose that does not decrease cell viability.

RESULTS

There was no significant difference in the MN frequency observed in control cultures from young and elderly individuals. However, the MN frequency in CumOOH-treated cultures was significantly higher in the elderly group than the young group (p < 0.001). No association was found between the GSTM1 phenotype and CumOOH-induced MN frequency.

CONCLUSIONS

The results suggest that lymphocytes of elderly individuals are more susceptible to in vitro MN induction by CumOOH. However, this difference in susceptibility is not explained by the lack of GSTM1.

Genetic variation and exposure related risk estimation: will toxicology enter a new era? DNA repair and cancer as a paradigm

With the vast technological and informational resources increasingly available from investments in "genomics," toxicology and much of biological science, is faced with previously undreamed of opportunities and equally daunting challenges. The ability to generate the large quantities of data becoming routinely available could not be imagined a decade ago. The complexities of data analysis are increasingly the rate-limiting element in scientific advances. The expectations that these large scientific investments will reduce the incidence of human disease and improve health are very high. An emphasis on genetic variation and Toxicogenetics is expected to yield risk estimates for specific rather than average individuals and individuals with varied lifestyles and complex patterns of exposure. Examples from studies of polymorphic variation in DNA repair genes in the healthy population and cancer risk highlight the complexity and challenges of incorporating genetic variation into quantitative estimates of risk associated with environmentally relevant exposures. Similar issues exist in selecting the animal models most appropriate for predicting human risk from environmental exposures to toxic agents.

Risk modification by CYP1A1 and GSTM1 polymorphisms in the association of environmental tobacco smoke and lung cancer: a case-control study in Japanese nonsmoking women

Genetic backgrounds may modify the association of environmental tobacco smoke (ETS) with lung cancer risk. Polymorphisms of both the activating and detoxifying enzymes, cytochrome P4501A1 (CYP1A1) and glutathione-S-transferase M1 (GSTM1), may be important as genetic factors. We conducted a multicenter case-control study in Japanese nonsmoking women. Cases were women aged 30-89 years and newly diagnosed as having lung cancer from November 1997 to March 2001 in 4 study areas. We also recruited age-matched (5-year strata) and hospital-matched nonsmoking controls. A total of 158 cases and 259 hospital controls supplied blood for genotyping. Detailed information on ETS exposure from husbands and that in other situations and on potential confounders was collected by interview. Odds ratios (ORs) were estimated by using conditional logistic models. We found no increase in the risk of lung cancer for CYP1A1 Msp I genotypes. For the GSTM1 null genotype vs. nonnull genotype, the OR was 1.37 [95% confidence interval (CI) 0.90-2.09], which indicated a somewhat increased risk for the GSTM1 null genotype. A gene-environment interaction was suggested, with combined GSTM1 null genotype and high-dose ETS exposure (>/=40 pack-years by husbands) conferring significantly higher risk (OR = 2.27, 95% CI 1.13-4.57) compared to the GSTM1 nonnull genotype and low-dose ETS exposure (<40 pack-years). Our results do not support a major role of Msp I polymorphism of the CYP1A1 gene as a risk factor for lung cancer among nonsmoking women. In contrast, the GSTM1 null genotype posed an increased, although not significant, risk among them. Additional studies are warranted to confirm the ETS-GSTM1 polymorphism interaction suggested in our present study.

Relationship of tobacco smoking with GSTM1 gene polymorphism in laringeal cancer

This paper aimed to analyze the association of polymorphism of GSTM1 0/0 genotype with laryngeal cancer along a hospital based case-control study. Polymorphisms of GSTM1 0/0 of samples from 36 patients with laryngeal cancer and 35 healthy controls were detected by PCR method. The reaction used as GSTM1 primers, using the sequence sense: 5'-CTGCCCTACTTGGATTGATGGG-3' and antisense: 5'-TGGATTGTAGCAGATCATGC-3'. N Acetyl transferase 1 (NAT1) gene using the primers sense: 5'-TAAAAGTAAAATGATTTGCTTTCG-3' and antisense: 5'- GCTTTCTAGCATAAATCACCAA-3' was used as internal positive control. Two sided 2 and multivariation analysis were used to analyse the results. The proportions of GSTM1 deleted genotype in cases and controls were 47.2% and 54.3%, respectively. There was significant increment of GSTM 0/0 genotype frequency in moderate smokers group of patients compared to control (P=0.033, OR= 4.78, 95% CI = 1.30-7.13). We conclude that GSTM1 deleted genotype may be a genetic susceptibility marker for laryngeal cancer whose exposed to low doses carcinogens. The absence of this enzyme seems to have a role in the development of laryngeal cancer, in which the mechanism still needs further investigation.

Myeloperoxidase (MPO) genotype and lung cancer histologic types: the MPO -463 A allele is associated with reduced risk for small cell lung cancer in smokers

MPO participates in the metabolic activation of tobacco carcinogens such as PAHs. A frequent MPO -463 G-->A polymorphism in the promoter region reduces MPO transcription and has been correlated with >4-fold lower benzo[a]pyrene-DNA adduct levels in the skin of coal tar-treated patients. Four of 7 case-control studies found significantly reduced lung cancer risk associated with the A allele. Due to their different etiologies, we examined whether the MPO genotype affects histologic lung cancer types differentially. A case-control study was conducted in 625 ever-smoking lung cancer patients, including 228 adenocarcinomas, 224 SCCs, 135 SCLCs and 340 ever-smoking hospital controls. MPO genotyping was performed by capillary PCR followed by fluorescence-based melting curve analysis. Combining the MPO -463 (G/A+A/A) genotypes, a protective effect approaching significance (OR = 0.75, 95% CI 0.55-1.01) was observed when comparing all lung cancer cases to controls. Among histologic types of lung cancer, a weak protective effect was found for both adenocarcinoma (OR = 0.81, CI 0.55-1.19) and SCC (OR = 0.82, CI 0.56-1.21); a stronger and significant effect was found for SCLC (OR = 0.58, CI 0.36-0.95; p = 0.029). Our results also suggest that the MPO genotype varies among inflammatory nonmalignant lung diseases. In conclusion, our results emphasize the need for a separate analysis of lung cancer histologic types and an adjustment for inflammatory nonmalignant lung diseases in future MPO-related studies. We confirm that the MPO -463 A variant affords a protective effect against lung cancer risk in smokers, which was strongest for SCLC patients.

The effect of the genetic polymorphisms of CYP1A1,CYP2D6, GSTM1 and GSTP1 on aromatic DNA adduct levels in the population of healthy women

Aromatic DNA adduct levels and polymorphisms of two phase I enzymes - CYP1A1 and CYP2D6 and two phase II enzymes - GSTM1 and GSTP1 were analyzed in a group of 133 nonsmoking healthy women 35-45 years old and holding jobs not connected with the exposure to the combustion products of organic matter. They were office workers from the south and north-eastern parts of Poland. Blood samples were collected in winter and in summer. Aromatic DNA adduct levels were measured in all winter and summer samples. The frequencies of CYP1A1, CYP2D6, GSTM1 and GSTP1 polymorphisms in samples from the studied women did not show any differences when compared with other Caucasian populations and the Polish male population studied previously. The differences in the levels of DNA adducts among the carriers of different genotypes were statistically non-significant. Analysis of combined genotypes selected the groups of volunteers with the highest and the lowest DNA adduct levels. The highest levels of DNA adducts were observed in the carriers of GSTM1(null)/CYP1A1Ile/Val (8.00+/-13.00 adducts/10(8) nucleotides in summer samples) and GSTP1-AA/CYP1A1Ile/Val genotypes (7.00+/-4.32 in winter and 7.30+/-7. 27/10(8) nucleotides in summer). The lowest levels of DNA adducts (3. 00+/-2.30 in winter and 2.00+/-3.16/10(8) nucleotides in summer) were found in the carriers of the genotype GSTP1-AG+GG/CYP1A1Ile/Val. The levels of DNA adducts in these groups were determined by the polymorphisms of GSTM1 and GSTP1 phase II detoxifying enzymes.

Studies on biomarkers in cancer etiology and prevention: a summary and challenge of 20 years of interdisciplinary research

Sensitive, specific methods have been developed that allow quantitative measurements of the metabolites of carcinogen metabolites and of DNA and protein adducts in humans exposed occupationally, environmentally and endogenously to genotoxic agents. The interrelationship between exposure to carcinogens, host risk factors and the responses of biomarkers has been examined in cross-sectional, ecological and case-control studies which provided new insights into the causes of cancer and the mechanisms of carcinogenesis. The identification of hitherto unknown DNA-reactive chemicals formed in the human body from dietary precursors and of carcinogenic components of complex mixtures has increased the possibility of establishing causal relationships in etiology. The identification of individuals and subgroups heavily exposed to carcinogens has led to the development of measures for avoiding or decreasing exposure to carcinogenic risk factors. New, ultrasensitive methods for measuring DNA adducts allow the quantification and structural elucidation of specific DNA damage in humans arising from oxidative stress and lipid peroxidation (LPO), which have been found to be the driving forces in several human malignancies. Background DNA damage in "unexposed" individuals has been shown unequivocally to be due to LPO products, and a significant interindividual variation in adduct levels has been shown in individuals with comparable exposure to carcinogens. Thus, pharmacogenetic variants with higher susceptibility to carcinogenic insults, due to genetic polymorphism in xenobiotic-metabolizing enzymes, have been characterized by a combination of genotyping and measurements of macromolecular adducts. Dosimetry has been used in human studies to evaluate the efficacy of interventions with chemopreventive agents like ascorbic acid, dietary phenols and green tea. Advances in the application of selected biomarkers in human studies are reviewed and illustrated by examples from the author's research conducted during the past two decades.

Variability in nucleotide excision repair and cancer risk: a review

Cancer initiation is classically associated with the induction of mutations on specific oncogenes or tumor suppressor genes, due to the presence of unrepaired DNA lesions produced by endogenous or exogenous genotoxic agents. Among several DNA repair pathways, the nucleotide excision repair (NER) is the most important and versatile one in removing the bulky adducts induced by physical and chemical carcinogens. Xeroderma pigmentosum (XP), characterized by a deficiency in NER and an over 1000-fold increased risk of skin cancer, represents a paradigm to understand the role of unrepaired lesion in the development of cancer. We reviewed here several NER assays used in epidemiological studies investigating the association between DNA repair efficiency and cancer risk. Reduced DNA repair could contribute to the development of cutaneous basal cell carcinoma (BCC), although discordant results have been reported. More consistent findings were observed between cellular sensitivity towards genotoxic agents and smoking-related cancers.

The influence of GSTM1 and GSTT1 genotypes on the induction of sister chromatid exchanges and chromosome aberrations by 1,2:3,4-diepoxybutane

Cytogenetic tests - chromosome aberrations (CA), sister chromatid exchanges (SCE) and micronuclei (MN) - are most often applied in biomonitoring of the genotoxicity of potentially carcinogenic chemicals in human cells. One of the extensively studied genotoxins is diepoxybutane (DEB) - reactive biometabolite of butadiene (BD). Several studies showed a high SCE induction in human lymphocytes exposed in vitro to various concentrations of DEB. DEB also proved to be a potent inducer of chromosome aberrations and micronuclei. A bimodal distribution of SCE frequency after in vitro DEB treatment was observed. The aim of the present study was to examine the ability of DEB to induce different individual cytogenetic response measured by SCE and CA frequency. The possible influence of genetic polymorphism has also been taken into account, by including donors representing positive or null GSTM1 and GSTT1 genotypes. Our study supported the earlier results showing that DEB is an effective inducer of SCEs and CAs, causing also the decrease in replication index (RI). DEB bioactivity measured by SCE induction - but not by CA test - was significantly higher in GSTT1 negative than in GSTT1 positive donors. GSTM1 polymorphism had no influence on these endpoints. The donors GSTT1-/GSTM1+ were shown to be slightly more sensitive to DEB than GSTT1-/GSTM1- individuals. There was also observed a unimodal distribution of DEB-induced SCEs and CAs in the group, despite the fact that the experiment was performed on the lymphocytes obtained from both GSTT1 positive and negative donors.

Environmental tobacco smoke, genetic susceptibility, and risk of lung cancer in never-smoking women

BACKGROUND

Exposure to environmental tobacco smoke (ETS) is considered to be a major lung cancer risk factor for never smokers. We investigated the hypothesis that never-smoking women who are exposed to ETS and develop lung cancer are a genetically susceptible population.

METHODS

Archival tumor tissues were analyzed from 106 never-smoking women enrolled in a case-control study of ETS (and other personal and environmental factors) and lung cancer risk. We analyzed germline polymorphisms in genes that have been associated with cancer susceptibility and whose products activate (cytochrome P450 1A1 [CYP1A1]) and detoxify (glutathione S-transferases M1 [GSTM1] and T1 [GSTT1]) chemical carcinogens found in tobacco smoke.

RESULTS

When compared with never smokers who had no ETS exposure and developed lung cancer (n = 55), never smokers with exposure to ETS who developed lung cancer (n = 51) were more likely to be deficient in GSTM1 activity (i.e., were GSTM1 null) because of a genetic polymorphism in the GSTM1 gene (odds ratio = 2.6; 95% confidence interval = 1.1-6.1). A statistically significant rising trend in risk occurred with increasing ETS exposure (two-sided P =. 02), reaching a more than sixfold excess risk in those exposed to 55 pack-years of ETS (ETS pack-year = ETS produced by an active smoker, within a confined space such as a room, who smokes one pack of cigarettes a day for a year). No evidence was found of associations between GSTT1 deficiency or the CYP1A1 valine variant and lung cancer risk due to ETS exposure.

CONCLUSIONS

A common genetic polymorphism divides the population of never smokers into two groups of approximately equal size, one (homozygous carriers of the GSTM1 null allele) that has a statistically significant greater risk of lung cancer from ETS than the other (heterozygous or homozygous carriers of the wild-type GSTM1 allele).

Glutathione S-transferase GSTM1, GSTM3, GSTP1 and GSTT1 genotypes and the risk of smoking-related oral and pharyngeal cancers

Several polymorphic glutathione S-transferase enzymes are involved in the detoxification of active metabolites of many potential carcinogens from tobacco smoke and may therefore be important in modulating susceptibility to smoking-related cancers. As part of a hospital-based case-control study performed in France among Caucasian smokers, we studied GSTM1, GSTM3, GSTP1 and GSTT1 gene polymorphisms in 121 patients with oral cavity and pharyngeal cancers and 172 hospital controls using peripheral blood DNA. An increase in risk was found among carriers of the GSTP1 (AG or GG) genotype (OR 1.6, 95% CI 1.0-2.8, p = 0.07) or the GSTT1 null genotype (OR 2.0, 95% CI 1.0-4.0, p = 0.05). The effect of these at-risk genotypes was most marked in subjects with a history of more than 30 years of smoking, among whom the respective ORs were 2.0 (95% CI 1.0-3.9) and 3.3 (95% CI 1.3-8.1), though the interaction tests between these genotypes and duration of smoking were not significant. In contrast, neither the GSTM1 null genotype nor the GSTM3 AA genotype was associated with oropharyngeal cancer risk (OR 0.9, 95% CI 0.5-1.5 and OR = 1.3, 95% CI 0.7-2.3, respectively). Our results thus suggest that GSTP1 and GSTT1 gene polymorphisms modulate susceptibility to smoking-related cancers of the oral cavity and pharynx.

Impact of adduct determination on the assessment of cancer susceptibility

The characterization of genetic determinants for cancer susceptibility is important for understanding disease pathogenesis and for preventive measures. There is growing evidence that a group of predisposing polymorphic genes exists, such as those involved in carcinogen metabolism and repair, which may increase cancer in certain environmentally exposed subjects, even those exposed only to low levels of carcinogens. In developing preventive strategies, it is therefore necessary to identify these vulnerable members in our society, particularly those suffering from an unfortunate combination of high carcinogen exposure, cancer-predisposing genes and lack of protective (dietary) factors. Thus, molecular epidemiology faces the difficult task of analyzing carcinogen-exposed individuals for a combination of genotypes associated with cancer susceptibility. Once identified, combinations of cancer-predisposing genes can then be used as intermediate risk markers rather than taking cancer as an endpoint. In case-control studies, simultaneous measurements were carried out in each subject to determine exposure/early effect markers, e.g. polycyclic aromatic hydrocarbons (PAH)-DNA adducts, and susceptibility markers, e.g. genetic polymorphism, in drug-metabolizing enzymes related to cytochrome P450 1A1 (CYP1A1) and glutathione S-transferase (GSTM1) genes. The genotype dependence of human lung (+)-anti-benzo[a]pyrene diol-epoxide (BPDE)-DNA adducts in lung cancer patients was examined. BPDE-DNA adduct levels in bronchial tissue of smokers with high pulmonary CYP1A1 inducibility (by immunohistochemistry) and GSTM1 inactive were approximately 100-fold higher than in subjects with an active GSTM1 at similar smoking dose. Further genetic analyses confirmed that the combination of CYP1A1 homozygous mutants and GSTM1 inactive leads to high levels of BPDE-DNA adducts in human lung of smokers and white blood cells of PAH-exposed coke oven workers. Thus, BPDE-DNA adduct levels resulting from the "at risk" genotype combinations may serve as markers to identify high-risk subjects among smokers and individuals occupationally and/or environmentally exposed to PAH.

Study of the frequencies of CYP1A1 gene polymorphisms and glutathione S-transferase mu1 gene in primary breast cancers: an update with an additional 114 cases

We studied the polymorphisms m1 (Msp1 restriction site) and m2 (codon Val substitution) of CYP1A1 gene and the copy number of glutathione S-transferase mu1 (GSTM1) gene on 487 DNA of breast cancer primary tumours from Caucasian group. Tumours of patients aged 55 years and under at diagnosis presented a great proportion of wild m1 (-/-) genotype; 83.6% vs. 69.5% (p < 0.0006), and a higher percentage of copy number of GSTM1 equal or under one copy; 65.2% vs. 53.4% (p < 0.011) for older patients m1 and m2 variants are closely linked (p < 0.0000). Tumour with a low copy number of GSTM1 is correlated with high histological grading (p < 0.01) and high Cathepsin D concentrations (p < 0.02). The combinations of different genotypes showed that association wild m1 (-/-) genotype and copy number of GSTM1 inferior or equal to one copy is correlated with an early onset of breast cancer primary tumour 44% vs. 6.4% for m1 (-/+) or (+/+) genotype and copy number of GSTM1 superior to one (p < 0.0000). The CYP1A1 gene wild form seems to be associated with early cancer development in Caucasian patients.

Urinary excretion of 5-(hydroxymethyl) uracil in healthy volunteers: effect of active and passive tobacco smoke

The urinary excretion of 5-(hydroxymethyl)uracil (5-HMUra), one of the major oxidative modifications of thymine, was investigated in 134 healthy volunteers living in North Italy. Overnight urine was collected, and a questionnaire was completed on smoking habits and exposure to environmental tobacco smoke (ETS). 5-HMUra was analyzed by GC/MS, following urine purification by HPLC. 5-HMUra excretion showed an approximately normal distribution, ranging from 0.08 to 0.84 (mean 0.44) nmoles/kg/8 hr and from 3.2 to 18.7 (mean 8.5) nmoles/mmoles creatinine. 5-HMUra excretion was significantly higher in women than in men and in smokers than in non-smokers when results were expressed as the ratio to creatinine. Slightly higher levels of 5-HMUra excretion, expressed as nmoles/mmoles creatinine, were also found in subjects highly exposed to ETS, monitored either as the number of hours of exposure or as the number of smokers in the workplace and at home. Our results show that the urinary excretion of 5-HMUra is higher than that of other oxidized nucleobases, including 8-oxo-7,8-dihydroguanine, and can be slightly modified by environmental factors such as tobacco smoke. These findings suggest that measurement of urinary excretion of 5-HMUra could be useful as a biomarker of oxidative DNA damage and repair, though further research is needed to support these data.

Variation in DNA repair is a factor in cancer susceptibility: a paradigm for the promises and perils of individual and population risk estimation?

The repair of DNA damage protects the genome of the cell from the insults of cancer causing agents. This was originally demonstrated in individuals with the rare genetic disease, xeroderma pigmentosum, the prototype of cancer genes, and subsequently in the relationship of mismatch repair to colon cancer. Recent studies suggest that individuals with less dramatic reductions in the capacity to repair DNA damage are observed at polymorphic frequency and these individuals have an increased susceptibility to several types of cancer. Screening of individuals for DNA sequence variation in the exons of 9 DNA repair genes has resulted in identification of 15 different polymorphic amino acid substitution variants. Although the studies to relate these variants to reduced DNA repair capacity and cancer status have not been completed, the available information is sufficient to suggest that DNA repair genes should be incorporated into molecular epidemiology and cancer susceptibility studies. The availability of molecular epidemiology data presents exciting opportunities for refinement of risk estimation models and identification of individuals at increased risk of disease, with resultant opportunities for effective surveillance and early intervention and treatment. The opportunities to acquire susceptibility data are associated with possible perils for establishment of regulations for permissible exposures to carcinogenic agents and also stigmatization of 'at risk' individuals that may result in decreased access to employment opportunities and health care.