CYP1A1 Ile462Val Research Articles

CYP1A1 Ile462Val and MPO G-463A interact to increase risk of adenocarcinoma but not squamous cell carcinoma of the lung

Common polymorphisms in genes encoding phase I and phase II enzymes are considered to modify lung cancer risk due to changes in enzyme activity. Candidates include genetic variants of glutathione S-transferases (GSTM1, GSTT1 and GSTP1) and myeloperoxidase (MPO). We performed a large case-control study of these candidate genes in 1103 patients with non-small cell lung cancer (NSCLC) and 627 controls without NSCLC. Associations between deletion genotypes of GSTM1 and GSTT1 and between single nucleotide polymorphisms (SNPs) of GSTP1 Ile105Val and MPO G-463A were first tested by adjusted logistic regression. Then we analysed gene-gene interactions, also incorporating our published data on the Ile462Val SNP in the phase I enzyme, cytochrome P450 CYP1A1. The homozygous GSTP1 105Val genotype was significantly under-represented in NSCLC compared with controls (OR = 0.73; 95%CI 0.53-1.00; P = 0.050), especially in females (OR = 0.57; 95%CI 0.34-0.98; P = 0.04). The GSTT1-null genotype was significantly over-represented in adenocarcinomas (OR = 1.41; 95%CI 1.06-1.90; P = 0.02) but not in squamous cell carcinomas (OR = 1.03; 95%CI 0.76-1.41; P = 0.84). There was weak risk reduction associated with GSTM1 null in heavy smokers (OR = 0.71; 95%CI 0.54-0.94; P = 0.02), but neither GSTM1 nor MPO genotypes affected the overall risk of NSCLC. The MPO and CYP1A1 risk genotypes interacted to increase the overall risk of NSCLC (OR = 2.88; 95%CI 1.70-5.00; P < 0.001). The data are consistent with the concept that multiple genes of modest effect interact to confer genomic-based susceptibility to lung cancer.

Genetic polymorphisms and the effect of cigarette smoking in the comet assay

A potential genotoxic effect of cigarette smoking has repeatedly been investigated with the comet assay (alkaline single cell gel electrophoresis) and conflicting results have been reported. Besides differences in the methodology and the study design used, genetic differences between the subjects investigated might contribute to the variability of test results. Considering genetic polymorphisms of genes involved in metabolism or DNA repair has led to a better discrimination of smoking-related genotoxic effects in some cases but also led to discrepant results. We therefore evaluated our baseline comet assay effects obtained for nonsmokers and smokers in relation to selected genetic polymorphisms. Our study group comprised 52 nonsmokers and 51 smokers who were strictly selected to exclude potential confounding factors. We chose polymorphisms in the genes GSTM1 and CYP1A1 (Ile462Val) because they take part in the metabolism of genotoxins contained in tobacco smoke. In a subgroup of 32 nonsmokers and 31 smokers we also studied polymorphisms in XPD (Lys751Gln), XRCC1 (Arg399Gln) and XRCC3 (Thr241Val) because they are part of DNA repair pathways involved in the repair of tobacco-related DNA damage. Freshly collected peripheral whole blood samples were tested in the alkaline (pH > 13) comet assay. In all experiments a reference standard (untreated V79 cells) was included to correct for assay variability. An independent second evaluation was carried out for all experiments. None of these approaches revealed a significant difference between nonsmokers and smokers.

Risk of non-small cell lung cancer and the cytochrome P4501A1 Ile462Val polymorphism

The Ile462Val substitution in the cytochrome P450 1A1 gene (CYP1A1) results in increased enzymatic activity. Preliminary data suggesting a link between this polymorphism and lung cancer risk in Caucasians are inconsistent, reflecting small sample sizes and the relatively low frequency of the variant. The data set consisted of 1050 primary non-small cell lung cancer cases and 581 controls, a large homogenous population designed specifically to address previous inconsistencies. Patients were genotyped using a PCR-RFLP technique. Carriers of the valine allele, CYP1A1*2C, (Ile/Val or Val/Val genotypes) were significantly over-represented in non-small cell lung cancer compared to controls (OR=1.9; 95% CI=1.2-2.9; p=0.005) when adjusted for confounders, particularly in women (OR=4.6; 95% CI=1.7-12.4; p=0.003). The valine variant was statistically significantly over-represented in cases of lung cancer younger than the median age (64 years) (OR=2.5; 95% CI=1.3-4.8; p=0.005) and cases with less than the median cumulative tobacco-smoke exposure (46 pack-years) (OR=2.4; 95% CI=1.3-4.7; p=0.007). These new data establish an association between the CYP1A1 Ile462Val polymorphism and the risk of developing non-small cell lung cancer, especially among women.

An investigation of mammographic density and gene variants in healthy women.

This cross-sectional study examined if polymorphisms in genes that code for enzymes involved in the production and metabolism of estrogens are associated with mammographic density, a strong predictor of breast cancer risk. The study included 328 healthy women of different ethnicities who underwent mammographic screening and donated a blood or mouthwash sample for DNA analysis. After digitizing cranio-caudal views of the mammograms, we performed computer-assisted mammographic density assessment. Following DNA extraction, samples were analyzed for polymorphisms in the COMT (Val158Met), CYP1A1 (Ile462Val), CYP1B1 (Val432Leu), CYP1A2 (*1F) and CYP17 (T27C) genes using PCR-RFLP. Breast density was lower in Caucasians than in Asians. Caucasian women were less likely to carry the CYP1A1 variant allele and more likely to carry the variant alleles for CYP1B1 and COMT than women with Asian or Hawaiian ancestry. The low-activity COMT and CYP1A2 variant alleles were weakly related to lower percent mammographic density after adjustment for age, ethnicity, body mass index and reproductive variables (p for gene-dosage =0.08 and 0.05, respectively). These relations were observed in premenopausal women only and were similar in direction and magnitude after stratification by ethnicity. We found no significant associations between breast density and the variant alleles for CYP1A1, CYP1B1 and CYP17. Our data suggest lower mammographic density for women carrying the COMT and CYP1A2 variant alleles than for women carrying the common alleles, though this is the opposite of what is commonly hypothesized from the enzyme function.

Impact of metabolic genotypes on levels of biomarkers of genotoxic exposure

Phase I and Phase II xenobiotic-metabolising enzyme families are involved in the metabolic activation and detoxification of various classes of environmental carcinogens. Particular genetic polymorphisms of these enzymes have been shown to influence individual cancer risk. A brief overview is presented about recent research of the relationship between metabolic genotypes and internal dose, biologically effective dose and cytogenetic effects of complex and specific genotoxic exposures of human study populations, and we report our new results from two molecular epidemiological studies. We investigated the effects of multiple interactions among CYP1A1 Ile462Val, CYP1A1 MspI, CYP1B1 Leu432Val, CYP2C9 Arg144Cys, CYP2C9 Ile359Leu, NQO1 Pro189Ser, GSTM1 gene deletion and GSTP1 Ile105Val genotypes on the levels of carcinogen–DNA adducts determined by 32 P -postlabelling and PAH–DNA immunoassay in peripheral blood lymphocytes from workers occupationally exposed to polycyclic aromatic hydrocarbons in aluminium plants, and in bronchial tissue from smoking lung patients. A statistically significant positive linear correlation was observed between white blood cell aromatic DNA adduct and urinary 1-hydroxypyrene (1-OHPY) levels from potroom workers with GSTM1 null genotype ( P=0.011). Our results suggest interactions between GSTM1 and GSTP1 alleles in modulation of urinary 1-OHPY levels and white blood cell DNA adduct levels in the PAH-exposed workers. Interactions between GSTM1 and GSTP1 alleles, in association with particular genotype combinations of CYPs, were also recognised in bronchial aromatic DNA adduct levels of smoking lung patients. The impact of single metabolic genotypes and their combinations on biomarkers of exposure was usually weak, if any, in both our studies and reports of the literature. The effect of special metabolic gene interactions may be better recognised if the compared groups of individuals are stratified for multiple potential modulators of the observable biomarker end-point, and/or if chemical structure-specific biomarker methods are applied.

Genetic polymorphisms in head and neck cancer risk.

To assess whether genetic polymorphisms implicated as risk factors for other tobacco-associated malignancies are associated with altered risk of head and neck squamous cell carcinoma. Case-control study. One hundred sixty patients with head and neck squamous cell carcinoma recruited from a university-based head and neck oncology clinic and 149 population-based controls. Genotyping of the CYP1A1 (Ile462Val), GSTM1 (null), GSTP1 (Ile105Val), GSTT1 (null), and P53 (Arg72Pro) genes was performed by polymerase chain reaction-based techniques on DNA prepared from peripheral blood. In addition, a questionnaire was used to collect demographic information from each subject. Cases were significantly older (p <.0001) and had significantly greater tobacco use (p <.0001) and were more likely to be male (p <.0001) than were control subjects, thus confirming known risk factors for this disease. When cases and controls were compared by simple chi-square analysis, only the frequency of CYP1A1 (Ile462Val) polymorphism was significantly different between cases and controls (OR =.42; 95% CI =.18-.99; p <.04). However, with a logistic regression model to control for known risk factors, we were unable to demonstrate a significant association with head and neck cancer for any of the polymorphisms tested, including CYP1A1. This population fails to identify a relationship between the above-mentioned polymorphisms and head and neck cancer.