Genetic polymorphisms and metabolism of endocrine disruptors in cancer susceptibility

Environmental exposure to benzene: evaluation of urinary S-PMA and polymorphism (CYP2E1-1293G>C and NQO1 609C>T) in Campos Elíseos residents, Duque de Caxias, Rio de Janeiro State, Brazil

Benzene is one of the most important substances for assessment, due to its significant use, the environmental contamination resulting from its emission and the effects on human health. It is classified by the International Agency for Research on Cancer (IARC) as a known carcinogen to humans (group 1) and associated with the development of leukemia. In general, the population is exposed to this substance by inhaling contaminated air, which varies according to the location and intensity of its potential sources. The petrochemical industry is one of the most important sources of this compound. The municipality of Duque de Caxias, specifically the Campos Elíseos district, in Rio de Janeiro State, Brazil, houses the Industrial Complex of Campos Elíseos (PICE), a grouping of over 25 industries, which includes the second largest oil refinery in Brazil. Environmental contamination from the PICE has been recognized, but there is a lack of studies concerning its impact on the health of the surrounding population. S-phenylmercapturic acid (S-PMA) concentrations ranging from 0.80 to 8.01μg.g-1 creatinine were observed in the local population, apparently related to hematological changes also observed in exposed population. The quantifiable presence of urinary S-PMA from the benzene metabolism is associated with the fact that 60% of the participants present specific hematological changes, which may be due to the environmental benzene exposure. The allele and genotype frequencies of the CYP2E1 and NQO1 enzymes observed in the study population were similar to those reported in other studies. The presence of the variant allele in the NQO1 genotype may be a risk factor for the observed hematological changes.

Association of CYP3A5*3 and CYP1A1*2C Polymorphism with Development of Acute Myeloid Leukemia in Egyptian Patients

Aim: Cytochrome P450 (CYP) enzyme catalyzes the phase I metabolism reaction which metabolize endogenous and exogenous DNA-reactive chemical compounds and xenobiotics which could induce genotoxicity and increase the risk for leukemia. We aimed to detect frequency of CYP3A5*3 and CYP1A1*2C polymorphisms in Egyptian acute myeloid leukemia (AML) patients and to determine role of allele’s variants as a risk factor for developing leukemia. Patients and Methods: A case-control study was conducted on seventy acute myeloid leukemia patients and thirty control subjects. Samples were analyzed for prevalence of CYP3A5*3 and CYP1A1*2C polymorphisms using PCR - restriction fragment length polymorphism method. Results: CYP3A5*3 polymorphism (3/3) and (1/3) genotype were significantly elevated in AML group compared to control group (p=0.002). However, no statistical significant differences were found between patients and control group as regard CYP1A1*2C polymorphism. Conclusion: Our results suggest that Egyptians carrying CYP3A5*3 polymorphism might have an increased risk of AML emphasizing the significance of effective phase I detoxification in carcinogenesis.

Association of CYP1A1 and GSTM1 Polymorphisms With Oral Cancer Susceptibility: A Meta-Analysis

Our meta-analysis was aimed to evaluate the association of CYP1A1 and glutathione-S-transferase M1 (GSTM1) polymorphisms with oral cancer susceptibility.The related articles were searched in PubMed, Embase, and CNKI databases. Fifty eligible studies were included in our meta-analysis. Odds ratios (ORs) with 95% confidence intervals (CIs) were used to evaluate the relationship of CYP1A1 (rs4646903 and rs1048943) and GSTM1 polymorphisms with oral cancer risk. A random-effects model or fixed-effects model was employed depending on the heterogeneity.In overall analysis, CYP1A1 rs4646903 polymorphism was associated with the risk of oral cancer (CC vs TT: OR 1.65, 95% CI 1.33-2.05; CC vs TC+TT: OR 1.77, 95% CI 1.48-2.11; C vs T: OR 1.17, 95% CI 1.07-1.28), whereas rs1048943 showed no obvious association with oral cancer susceptibility. Moreover, subgroup analysis by ethnicity demonstrated that rs4646903 and rs1048943 both related with increased risk of oral cancer in Asians. Moreover, the analysis based on source of control suggested that rs4646903 could increase the risk for oral cancer in both population- and hospital-based populations, whereas no remarkable relationship of rs1048943 with oral cancer susceptibility was observed. For GSTM1 gene, null genotype appeared to be a risk factor for oral cancer (null vs present: OR 1.23, 95% CI 1.12-1.34), which was also proved in the subgroup analysis.The results demonstrated that CYP1A1 rs4646903 and null genotype of GSTM1 polymorphisms might serve as risk factors for oral cancer.

Human glutathione S-transferase polymorphisms associated with prostate cancer in the Brazilian population

OBJECTIVE

To evaluate the influence of polymorphisms in GSTA1, GSTM1, GSTT1, and GSTP1 in the risk of developing Prostate Cancer (PCa) in a population of Rio de Janeiro and compare the distribution of allele and genotype frequencies of the polymorphisms analyzed in the present study population with other regions in the country and different ethnic groups.

MATERIALS AND METHODS

We analyzed a sample of the Brazilian population, comprising 196 patients with PCa treated by the urology services of the Brazilian National Cancer Institute (INCA) and Mario Kroeff Hospital (HMK), and 208 male blood donors from the Clementino Fraga Filho Hospital, Federal University of Rio de Janeiro (UFRJ). The polymorphisms were determined in DNA, extracted from peripheral blood leucocytes using the Polymerase Chain Reaction and Restriction Fragment Length Polymorphism (PCR-RFLP).

RESULTS

Our results showed that the distribution of polymorphisms can vary significantly according to the Brazilian region and ethnic groups. The distribution of allele and genotype frequencies of the polymorphism GSTA1 was statistically different between cases and controls. Genotypes (A / B + B / B) were associated with protection (OR = 0.61, 95% CI = 0.40-0.92) for PCa in comparison to genotype A / A.

CONCLUSION

The distribution of genotype frequencies of the polymorphism GSTA1 was statistically different between the case and control groups (p = 0.023), and the presence of genotypes A / B and B / B suggests a protective role against the risk of PCa compared to genotype A / A. This is the first study that reports the genotypic frequency of this polymorphism and its association with PCa in a Brazilian population sample.

Glutathione S-transferase Mu-1 gene polymorphism in Egyptian patients with idiopathic male infertility

The aim of this study was to examine whether an association exists between glutathione S-transferase Mu-1 (GSTM1) gene polymorphism and idiopathic male infertility. Sixty men with primary idiopathic infertility and 60 fertile men, serving as controls, were recruited for the study. The polymorphism was analysed using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique. The frequency of GSTM1 null genotype was observed to be higher in infertile men 40% in comparison with 33.3% in the fertile men, but this difference was not statistically significant. There was statistically significant difference between cases and controls as regards GSTM1 genotype distribution ((MC) P = 0.006*) in GSTM1-positive men. Patients with the GSTM1 null genotype had significantly lower sperm concentrations and total sperm count when compared with patients with GSTM1-positive genotype. In the control group, men with GSTM1 null genotype had significantly lower sperm concentrations but not total sperm count when compared with men with GSTM1-positive genotype. The results of this study suggest a possible negative effect of GSTM1 null genotype on the spermatogenic potential of the testis.

Polymorphisms of catechol estrogens metabolism pathway genes and breast cancer risk in Mexican women

Breast cancer is associated to estrogen exposure. Allelic variants involved in estrogen metabolism might change the risk of developing this neoplasia. We examined the potential association of breast cancer risk in Mexican women with the polymorphisms CYP1A1 rs1048943, CYP1B1 rs1056836, COMT rs4680, GSTP1 rs1695, GSTT1 null and GSTM1 null which are involved in estrogen metabolism pathway. This study included 150 cases and 150 controls. A significant association was observed between, CYP1A1 rs1048943 (OR = 1.95, C.I. 1.13-3.36) and GSTP1 rs1695 (OR = 2.39, C.I. 1.24-4.24) polymorphisms with the risk of breast cancer. This risk was increased when the women were stratified according to their menopausal status. The results show that breast cancer risk significantly increases in women with 3-6 risk polymorphisms (OR = 3.75, C.I. 1.44-9.74).

Dietary benzo(a)pyrene and fetal growth: effect modification by vitamin C intake and glutathione S-transferase P1 polymorphism

BACKGROUND

Previous studies have reported maternal exposure to airborne polycyclic aromatic hydrocarbons (PAH), as well as DNA adducts reflecting total PAH exposure, to be associated with reduced fetal growth. The role of diet, the main source of PAH exposure among non-smokers, remains uncertain.

OBJECTIVE

To assess associations between birth weight, length and small size for gestational age (SGA) with maternal intakes of the genotoxic PAH benzo(a)pyrene [B(a)P] during pregnancy, exploring potential effect modification by dietary intakes of vitamin C, vitamin E, alpha- and beta-carotene, as well as glutathione S-transferase P1 (GSTP1) polymorphisms, hypothesized to influence PAH metabolism.

METHODS

657 women in the INMA (Environment and Childhood) Project from Sabadell (Barcelona) were recruited during the first trimester of pregnancy. Dietary B(a)P and nutrient intakes were estimated from food consumption data. Genotyping was conducted for the Ile105Val variant of GSTP1. Multivariable models were used to assess associations between size at birth and dietary B(a)P, evaluating potential interactions with candidate nutrients and GSTP1 variants.

RESULTS

There were significant interactions between elevated intakes of vitamin C (above the mean of 189.41 mg/day) and dietary B(a)P during the first trimester of pregnancy in models for birth weight and length (P<0.05), but no interactions were found with other nutrients. B(a)P intakes were associated with significant reductions in birth weight and length (coefficient±SE for a 1-SD increase in B(a)P: -101.63±34.62 g and -0.38±0.16 cm, respectively) among women with low, but not high, vitamin C intakes. Elevated dietary B(a)P was also associated with increased risk of SGA births among women with low dietary vitamin C. Among these women, associations were strongest in those carrying the GSTP1 Val allele, associated with lower contaminant detoxification activity.

CONCLUSION

Results suggest that dietary B(a)P exposure may impair fetal growth, particularly in genetically susceptible populations, and that increasing maternal intakes of vitamin C may help to reduce any adverse effects.

Polymorphisms of CYP1A1, GSTM1 and GSTT1 Loci as the Genetic Predispositions of Oral Cancers and Other Oral Pathologies: Tobacco and Alcohol as Risk Modifiers

Polycyclic aromatic hydrocarbons of tobacco require activation by phase I enzymes, such as cytochrome-P4501A1 (CYP1A1) to become an ultimate carcinogen, which are subjected to detoxification by phase II enzymes, especially glutathione S-transferases (GSTs). A study was designed to find whether genetic predisposition are risk modifiers of oral pathologies. The study included 102 cases with Oral Cancers (OCs), 68 cases with nonmalignant pathologies, 100 cases as control group. GSTM1 null genotype was associated with increased risk of OCs but not with benign pathologies. Deleted GSTT1 was associated with all pathologies. Both m1m2 and m2m2 polymorphisms of CYP1A1 were associated with oral pathologies.

Just who is at risk? The ethics of environmental regulation

The willingness to view risk as part of daily life has vanished. A risk-averse mindset among environmental regulators engenders confusion between the ethics of intention and the ethics of consequence, leading to the elevation of the precautionary principle with unintended and often unfortunate outcomes. Environmental risk assessment is conservative, but the actual level of conservatism cannot be determined. High-end exposure assumptions and current toxicity criteria from the USEPA, based on linear extrapolation for carcinogens and default uncertainty factors for systemic toxicants, obscure the degree of conservatism in risk assessments. Ideally, one could choose a percentile of the target population to include within environmental standards, but this choice is complicated by the food, pharmaceutical and advertising industries, whose activities, inadvertent or not, often promote maladaptive and unhealthy lifestyle choices. There has lately been much discussion about background exposures and disease processes and their potential to increase the risk from environmental chemicals. Should these background exposures or disease processes, especially those associated with maladaptive individual choices, be included as part of a regulatory risk evaluation? A significant ethical question is whether environmental regulation should protect those pursuing a self-destructive lifestyle that may add to or synergize with otherwise innocuous environmental exposures. Choosing a target percentile of protection would provide an increased level of transparency and the flexibility to choose a higher or lower percentile if such a choice is warranted. Transparency and flexibility will lead to more responsive environmental regulation that balances protection of public health and the stewardship of societal resources.

Genetic polymorphisms of metabolic enzymes CYP1A1, CYP2D6, GSTM1 and GSTT1 and leukemia susceptibility

The genetic polymorphisms of biotransformation phase I enzymes, cytochrome P450 (CYP1A1 and CYP2D6), and phase II enzymes, glutathione S-transferase (GSTM1 and GSTT1), were analyzed in 204 healthy persons and 348 leukemia patients, who suffered from also acute lymphoblastic leukemia (ALL), acute nonlymphoblastic leukemia (ANLL) chronic myelogenous leukemia (CML), from the Han ethnic group in Changsha City of Hunan Province of China. Our results showed that the frequencies of polymorphisms of CYP1A1, CYP2D6 and GSTT1 among the groups including acute lymphoblastic leukemia, ANLL, chronic myelogenous leukemia and healthy control have no significant differences. The variation of GSTM1-null genotype alone correlated with the development of ANLL. The combined genotypes of GSTM1-null with GSTT1-null, or GSTM1-null with CYP1A1 heterozygous mutant, or GSTM1-null with CYP1A1 heterozygous mutant and CYP2D6 heterozygous mutant, or GSTM1-null with CYP1A1 heterozygous mutant, CYP2D6 heterozygous mutant and GSTT1-null were found in individuals with high risk of ANLL. All these findings suggest that GSTM1-null genotype alone or in coordination with the relevant genotypes of other metabolic enzymes might be susceptibility factors in the etiology of ANLL.

Past and future applications of CYP450-genetic polymorphisms for biomonitoring of environmental toxicants

Cytochrome P450s (CYPs) are a huge gene superfamily of heme enzymes involved in xenobioitc as well as endobiotic metabolism. They play a critical role in adaptation to environmental changes for survival of living organisms. In addition, the huge environmental loads of human-made chemicals are biotransformed into bioactive or detoxified forms by CYPs. Thus, CYPs have been used for biomonitoring of environmental pollutants, screening of their metabolisms and exploring remedy. In particular, the induction or inhibition of CYPs has been applied to exposure monitoring of environmental toxicants, which are biotransformed by CYPs. This review considers past and future applications of CYP-genetic polymorphisms as susceptibility biomarkers for biomonitoring. Furthermore, we suggest the needs for further understanding of the characteristics of each CYP isozyme, consideration of real-life exposures such as mixed contamination with various chemicals, and incorporation of the presence of other phase I and phase II enzymes, for proper applications of CYP polymorphisms on biomonitoring.

Stem cell fusion as an ultimate line of defense against xenobiotics

There are several indications that the potential of stem cells to fuse with somatic cells is extremely high and, what's more exciting, in some instances goes as far as reprogramming and/or rescuing altered cells. It remains unclear, however, how frequent this mechanism is and what patho-physiological role it might play in nature. A plausible hypothesis, discussed in this paper, suggests that stem cell niches might provide a safeguard for the intact genome and epigenome. By fusing with somatic de-differentiated cells, stem cells might consent epigenetic reprogramming and/or genetic recovery of genes which otherwise could drive altered cells to malignancy. If the many sophisticated mechanisms of metabolism, cell repair, programmed cell death and tissue regeneration should fail, stem cells might represent a final attempt to recover dedifferentiated cells to avoid inflowing in cancer. In the current reappraisal of the different mechanisms of defense against xenobiotics, even the incidence of cancer itself is considered an evolving mechanism which, through a kind of programmed death of individuals exhibiting defective mutations, favors advancement of the phenotypes which adapt best. Additionally, with regard to the mechanisms of transmitting somatic mutations, based on stem cells' capacity to migrate and to fuse, here it is speculated that stem cells might be capable of carrying acquired somatic mutations from peripheral tissues to the gonads, and transmit that information into the germinal line. If appropriately demonstrated, these mechanisms might delineate a novel therapeutic area to be explored. The use of stem cells to reprogram/recover irreversibly damaged cells or to transmit beneficial mutations might be a valuable therapeutic approach in the future.

Influence of CYP1A1, CYP2E1, GSTM3 and NAT2 genetic polymorphisms in oral cancer susceptibility: results from a case-control study in Rio de Janeiro

Xenobiotic metabolizing enzymes are involved in the detoxification of many carcinogens and may be important in modulating cancer susceptibility. CYP1A1, CYP2E1, GSTM3, and NAT2 polymorphisms were determined in peripheral blood DNA of 231 oral cancer patients and 212 hospital controls in Rio de Janeiro, Brazil, using the PCR-RFLP technique. NAT2 polymorphism distribution was different between cases and controls (P=0.035), with an overrepresentation of NAT2( *)11 mutant allele in controls. Risk analysis showed that NAT2 4/4 individuals (OR=1.95, 95% CI=1.05-3.60) and combined GSTM3 and NAT2 heterozygotes (OR=1.94, 95% CI=1.04-3.66) were at increased oral cancer risk. No statistically significant association was observed for CYP1A1 and CYP2E1 polymorphisms. Our results suggest that NAT2 polymorphism, alone or combined with GSTM3, may modulate susceptibility to oral cancer in Rio de Janeiro.

Is GST gene polymorphism a risk factor in developing exfoliation syndrome?

PURPOSE

To evaluate the distribution of GSTM1, GSTP1, and GSTT1 gene polymorphisms in exfoliation syndrome (XFS) and the possible associations between the presence of exfoliation syndrome and glutathione S-transferase (GST) gene polymorphisms.

METHODS

Using a real-time polymerase chain reaction, GSTM1, GSTP1, and GSTT1 gene polymorphisms were detected in 60 patients with exfoliation syndrome, among which 71.7% had exfoliative glaucoma (43 patients), 16.7% had XFS with elevated intraocular pressure (IOP) (10 patients), and 11.7% had XFS only (7 cases), and in 65 otherwise healthy control group of similar age.

RESULTS

Although the exfoliation syndrome group presented a higher prevalence of the GSTM1 null and GSTP1 Ile/Val genotypes than the control group, this increase was not statistically significant. GSTT1 null and GSTP1 Val/Val polymorphisms were also not different among groups. The risk of exfoliation syndrome was not increased as the number of putative high-risk genotypes increase (p = 0.73).

CONCLUSIONS

GSTM1, GSTP1, and GSTT1 gene polymorphisms were not different among exfoliation syndrome patients, with or without glaucoma, and the controls therefore GSTM1, GSTP1, and GSTT1 gene polymorphisms did not seem to be associated with the risk of development of exfoliation syndrome.

Modern cancer epidemiological research: genetic polymorphisms and environment

Individual cancer susceptibility seems to be related to factors such as changes in oncogenes and tumor suppressor genes expression, and differences in the action of metabolic enzymes and DNA repair regulated by specific genes. Epidemiological studies on genetic polymorphisms of human xenobiotics metabolizing enzymes and cancer have revealed low relative risks. Research considering genetic polymorphisms prevalence jointly with environmental exposures could be relevant for a better understanding of cancer etiology and the mechanisms of carcinogenesis and also for new insights on cancer prognosis. This study reviews the approaches of molecular epidemiology in cancer research, stressing case-control and cohort designs involving genetic polymorphisms, and factors that could introduce bias and confounding in these studies. Similarly to classical epidemiological research, genetic polymorphisms requires considering aspects of precision and accuracy in the study design.

The case for taking account of metabolism when testing for potential endocrine disruptors in vitro

Legislation in the USA, Europe and Japan will require that chemicals are tested for their ability to disrupt the hormonal systems of mammals. Such chemicals are known as endocrine disruptors (EDs), and will require extensive testing as part of the new European Union Registration, Evaluation and Authorisation of Chemicals (REACH) system for the risk assessment of chemicals. Both in vivo and in vitro tests are proposed for this purpose, and there has been much discussion and action concerning the development and validation of such tests. However, to date, little interest has been shown in incorporating metabolism into in vitro tests for EDs, in sharp contrast to other areas of toxicity testing, such as genotoxicity, and, ironically, such in vitro tests are criticised for not modelling in vivo metabolism. This is despite the existence of much information showing that endogenous and exogenous steroids are extensively metabolised by Phase I and Phase II enzymes both in the liver and in hormonally active tissues. Such metabolism can lead to the activation or detoxification of steroids and EDs. The absence of metabolism from these tests could give rise to false-positive data (due to lack of detoxification) or false-negative data (lack of activation). This paper aims to explain why in vitro assays for EDs should incorporate mammalian metabolising systems. The background to ED testing, the test methods available, and the role of mammalian metabolism in the activation and detoxification of both endogenous and exogenous steroids, are described. The available types of metabolising systems are compared, and the potential problems in incorporating metabolising systems into in vitro tests for EDs, and how these might be overcome, are discussed. It is recommended that there should be: a) an assessment of the intrinsic metabolising capacity of cell systems used in tests for EDs; b) an investigation into the relevance of using the prostaglandin H synthase system for metabolising EDs; and c) a feasibility study into the generation of genetically engineered mammalian cell lines expressing specific metabolising enzymes, which could also be used to detect EDs.