The effect of genetic admixture in an association study: genetic polymorphisms and chromosome aberrations in a Colombian population exposed to organic solvents.

The human population is heterogeneous in genetic susceptibility, chromosomal instability and disease risk; all factors which depend on inherited genetic constitution and acquired nongenetic environmental and occupational factors. Recently, special attention has been directed to the identification of sources of potential bias in population studies of gene-environment interactions including genetic admixture. The aim of this study was to evaluate the effect of genetic admixture in the association of genetic polymorphisms and chromosome aberrations (CA) in a population exposed to organic solvents. We assessed genetic admixture via 34 genetic ancestry informative markers (AIMs) in 398 Colombian individuals. We report a statistically significant difference of higher CA frequency in individuals' below-average European component, and in individuals' above-average Native American component after adjusting for covariates. In addition, the confounding risk ratio values are ≥10% than the adjusted risk ratio, suggesting that population stratification is a confounding factor in this gene-environment association study. Furthermore, after adjusting for individual admixture proportions and covariates, the results demonstrate that glutathione-S-transferase M1 (GSTM1)-null is associated with CA frequency increase. These results suggest that gene-environment association studies that involve recently admixed populations should take into consideration population stratification as a confounding factor and suggest GSTM1-null as a genetic marker associated with CA frequency increase.

Chromosome aberrations in workers exposed to organic solvents: Influence of polymorphisms in xenobiotic-metabolism and DNA repair genes.

Organic solvents are widely used as diluents or thinners for oil-paints, gasoline and other organic mixtures. We evaluated chromosome aberrations (CAs) in lymphocytes of 200 workers exposed to organic solvents and 200 referents and the influence of polymorphisms in xenobiotic-metabolism (CYP2E1, GSTM1 and GSTT1) and in DNA repair genes (XRCC1(194) Arg/Trp, XRCC1(280) Arg/His, XRCC1(399) Arg/Gln and XRCC3(241) Thr/Met). Polymorphisms were determined by PCR-RFLP. Poisson regression analysis indicates a significant CA frequency increase in exposed workers, representing a higher risk in relation to the matched referent (RR 2.15, 95% CI 1.21-1.53, p<0.001). The CA frequency in exposed workers was influenced by the polymorphic genotypes: GSTM1 null (RR 1.33, 95% CI 1.31-1.69, p<0.001), XRCC1(194) Arg/Trp, Trp/Trp (RR 1.23, 95% CI 1.08-1.40, p<0.001) and by the wild genotypes CYP2E1 C1/C1 (RR 1.20, 95% CI 1.05-1.37, p<0.001), GSTT1 positive (RR 1.49, 95% CI 1.31-1.69, p<0.001), XRCC1(280) Arg/Arg (RR 1.44, 95% CI 1.26-1.64, p<0.001) and XRCC1(241) Thr/Thr (RR 1.54, 95% CI 1.34-1.76, p=0.001). We contribute to the follow-up predictive value of individual susceptibility biomarkers and their CA frequency influence during occupational organic solvent exposure. We provide tools for surveillance and prevention strategies to reduce potential health risks in countries with a large population of car painters not using protection devices and limited organic solvents use control.

Myeloperoxidase G-463A polymorphism and lung cancer: a HuGE genetic susceptibility to environmental carcinogens pooled analysis.

Myeloperoxidase is a phase I metabolic enzyme that converts the metabolites of benzo[a]pyrene from tobacco smoke into highly reactive epoxides. A polymorphism in the promoter region of myeloperoxidase (463G-->A) has been found to be inversely associated with lung cancer; differences in the association with age and gender have been suggested. We conducted a pooled analysis of individual data from 10 studies (3688 cases and 3874 controls) from the Genetic Susceptibility to Environmental Carcinogens database. The odds ratio for lung cancer was 0.88 (95% confidence interval: 0.80-0.97) for the AG variant of myeloperoxidase G-463A polymorphism, and 0.71 (95% confidence interval: 0.57-0.88) for the AA variant after adjusting for smoking, age, gender, and ethnicity. The inverse association between lung cancer and myeloperoxidase G-463A polymorphism was equally found in males and females (odds ratio for the AA genotype 0.73 [95% confidence interval: 0.56-0.96] and 0.67 [95% confidence interval: 0.46-0.98], respectively), without differences in the association according to age in the two genders. The myeloperoxidase G-463A polymorphism was significantly protective in "ever" smokers but not in "never" smokers. Myeloperoxidase is a key enzyme in tobacco-induced carcinogenesis.

CYP2E1 polymorphism, cigarette smoking, p53 expression, and survival in non-small cell lung cancer: a long term follow-up study.

The expression of selected gene products involved in cell differentiation and cell growth and genetic polymorphism of detoxifying genes was examined in 105 surgically resected nonsmall cell lung cancer (NSCLC) patients, and the relationship of these factors was correlated with cigarette smoking and patient survival. Genotyping of peripheral blood lymphocytes from 87 patients was performed for CYP2E1, GSTM1, GSTT1, mEH, and MPO detoxifying genes using polymerase chain reaction. Formalin-fixed, paraffin-embedded tissue was immunostained with antibodies to p53, p27, phospho-AKT, and bcl-2 using the avidin-biotin-peroxidase method and tissue microarray technique. Tumors were assigned a positive or negative score based on more than 10% of tumor cells staining positive with the antibody. The subtypes of NSCLC included 48 adenocarcinomas, 47 squamous cell carcinomas, and 10 large cell undifferentiated carcinomas. A total of 54 tumors were pathologic stage I, 23 were stage II, and 26 were stage III. All subjects smoked (range, 10-175 pack-years; mean, 60 pack-years). The mean overall survival was 112 weeks (median, 129 weeks). Patients with p53-positive tumors had significantly fewer pack-years of smoking (52 pack-years vs 72 pack-years; P = 0.021), smoked fewer years (34 years vs 40 years; P = 0.018), and had significantly better survival compared with those with p53-negative tumors (P = 0.045). When smoking history was further analyzed, the authors found that p53 expression was associated with the number of years smoked and not the number of packs smoked per day. Patients with squamous cell carcinoma had smoked longer compared with those with adenocarcinoma (P = 0.011). Significant association was seen between the CYP2E1 wild-type allele and better survival (P = 0.016). Patients with stage I tumors had better survival compared with stages II and III (P = 0.032). No association was found between survival and tumor type; tumor differentiation; expression of phospho-AKT, p27, and bcl-2; and polymorphic metabolizing genes other than CYP2E1. The significant association of long duration of smoking (>40 years) with loss of p53 expression and poor survival suggests inactivation of the protective p53 pathway in those who had a history of more than 40 years of smoking.

Polymorphisms in DNA repair genes, chromosome aberrations, and lung cancer.

We have previously investigated the role of polymorphic chemical metabolizing genes in the susceptibility to the development of lung cancer using 110 primary lung cancer patients and 119 matched smoker controls. Together with data from the present study on DNA repair genes, we did not observe significant associations between any single variant genotype for several DNA-repair and chemical-metabolizing genes (XPD [or ERCC2], XRCC1, XRCC3, GSTM1, GSTT1, MPO, and mEH [or EPHX1]) and lung cancer. In the present study, we have further evaluated a nested group of 79 patients and 69 matched controls, and observed that increased chromosome aberrations (CAs) were associated with variant DNA-repair genotypes among both the patient and the control groups, with a significant increase for individuals having the XPD Lys/Gln + Gln/Gln genotypes (P = 0.046). Patients often had significantly increased CAs compared with controls with the same DNA-repair genotype and with similar cigarette smoking habits (< or =40 pack-years or >40 pack-years). Analyses of interactions between the DNA-repair and chemical-metabolizing genes indicated that the most significant interactions were between the repair genotypes and the GSTM1/T1 null genotypes. Significant increases in CA from the interactions were often observed among patients with < or =40 pack-years, but not among those with >40 pack-years. Since some variant DNA-repair genotypes have functional deficits for DNA repair, the association between variant DNA-repair genotypes and increased CAs suggests a risk mechanism for the development of lung cancer, with the DNA-repair genotypes interacting with variant chemical metabolizing genotypes to further increase the risk. The observation that patients had significantly increased CA frequencies compared with controls, irrespective of genotype, suggests that patients have additional factors that contribute to the development of lung cancer.

Combined effect of MPO, GSTM1 and GSTT1 polymorphisms on chromosome aberrations and lung cancer risk.

The role of myeloperoxidase (MPO), and glutathione S-transferase mu and theta (GSTM1 and GSTT1) genetic polymorphisms on lung cancer risk was investigated in 110 Caucasian patients and 119 matched controls. Single genotype variants were not significantly associated with lung cancer risk. However, inheritance of the combined GSTM1 and GSTT1 null genotypes showed a significant increase in risk (crude OR = 2.32, 95% CI = 1.01-6.04). Based on adjustment by age, gender and smoking history, the MPO GA interacted with the presence of GSTM1 and GSTT1 genotypes to significantly reduce the risk (OR = 0.17, 95% CI = 0.03-0.98). From the chromosome aberration (CA) study in a subgroup of 79 patients and 69 matched controls, patients had significantly more CA than the controls. Among the patients, GSTM1 null was associated with a significant increase of CA and MPO AA was associated with a significant decrease of CA compared to their respective wild-type genotypes. After stratifying by smoking history (< or = and > 40 pack-years) and genotype, patients still had significantly more CA than the respective controls in most genotype categories. This indicates that the patients had additional contributing factors such as other susceptibility genes and/or different styles of smoking compared with the controls. In conclusion, our study indicates that CA is a useful biomarker to show the functional characteristics of genotypes and the interactive effects from combined genotypes. Therefore, our study strengthens the combined use of genotype and biomarkers for genetic susceptibility to environmental cancer.

Effect of epoxide hydrolase polymorphisms on chromosome aberrations and risk for lung cancer.

Microsomal epoxide hydrolase (mEH) gene is polymorphic and its enzyme is involved in the activation and subsequent detoxification of several tobacco carcinogens, for example polycyclic aromatic hydrocarbons. Therefore, we have investigated the association of two polymorphisms at exons 3 and 4 of the mEH gene with the development of lung cancer in 110 patients and 119 matched controls. In addition, we have investigated the relationship between the different mEH alleles and the frequency of chromosome aberrations (CA), as an approach to understand the role of genetic susceptibility on cancer risk. Our results show that only the homozygous exon 4 fast genotype is significantly associated with increased risk for lung cancer (odds ratio [OR]=6.26; 95% confidence interval [CI]=1.02-38.3). When the exons 3 and 4 polymorphisms are considered together, patients carrying the high enzyme activity genotype have a significantly increased risk for lung cancer (OR=2.46; 95% CI=1.06-5.68). More importantly, the increased risk for this group is confirmed by their having the highest frequency of CA compared to any other genotype groups. In addition, genotypes with higher risk had consistently more CA than those with lower risk. Our CA data also indicates that the low activity genotype may exert a protective role in cigarette smokers, as it was associated with a significant decrease in CA compared to the high and intermediate activity genotypes. In conclusion, the CA data provides evidence to support that susceptibility mEH alleles are significantly involved with the development of lung cancer from cigarette smoking.

Polymorphisms for chemical metabolizing genes and risk for cervical neoplasia.

Infection with high-risk human papillomavirus (HPV) plays a major role in the etiology of cervical cancer (CC). However, most infected women do not develop cancer. Therefore, exposure to other carcinogenic agents may be a contributing risk factor for CC. We investigated the hypothesis that environmental exposure to cigarette smoke and inheritance of polymorphic chemical metabolizing genes (CYP2E1, GSTM1, and mEH) significantly increase the risk for neoplasia. We selected 76 cases with high-grade cervical neoplasia or with invasive CC and 75 matched healthy controls. The collected data support the well-established observation that infection with high-risk HPV is the major risk factor for CC (OR = 75; 95% CI = 26-220). In addition, our data show that women who smoked more than 15 "pack-year" had a significant 6.9-fold increase in risk (95% CI = 1.2-40.3) after adjustment for HPV infection. The CYP2E1 variant genotype did not significantly increase the risk for neoplasia. A significant increase in risk for neoplasia was observed for the low-activity mEH 113 His allele after adjustment for smoking (OR = 3.0; 95% CI = 1.4-6.3). The GSTM1 null genotype was associated with a significant 3.3-fold increased risk for neoplasia (95% CI = 1.0-11.8) compared to women who were GSTM1-positive after adjustment for smoking and HPV infection. Our study suggests that genetic differences in the metabolism of cigarette smoke, particularly GSTM1, may confer susceptibility to CC. Further studies using larger populations will be needed to confirm our observations and to validate data for disease prevention.