A cytochrome P4502E1 genetic polymorphism and tobacco smoking in breast cancer

Functional Interaction between Cytochrome P450 and UDP-Glucuronosyltransferase on the Endoplasmic Reticulum Membrane: One of Post-translational Factors Which Possibly Contributes to Their Inter-Individual Differences

Cytochrome P450 (P450) and uridine 5'-diphosphate (UDP)-glucuronosyltransferase (UGT) catalyze oxidation and glucuronidation in drug metabolism, respectively. It is believed that P450 and UGT work separately because they perform distinct reactions and exhibit opposite membrane topologies on the endoplasmic reticulum (ER). However, given that some chemicals are sequentially metabolized by P450 and UGT, it is reasonable to consider that the enzymes may interact and work cooperatively. Previous research by our team detected protein-protein interactions between P450 and UGT by analyzing solubilized rat liver microsomes with P450-immobilized affinity column chromatography. Although P450 and UGT have been known to form homo- and hetero-oligomers, this is the first report indicating a P450-UGT association. Based on our previous study, we focused on the P450-UGT interaction and reported lines of evidence that the P450-UGT association is a functional protein-protein interaction that can alter the enzymatic capabilities, including enhancement or suppression of the activities of P450 and UGT, helping UGT to acquire novel regioselectivity, and inhibiting substrate binding to P450. Biochemical and molecular bioscientific approaches suggested that P450 and UGT interact with each other at their internal hydrophobic domains in the ER membrane. Furthermore, several in vivo studies have reported the presence of a functional P450-UGT association under physiological conditions. The P450-UGT interaction is expected to function as a novel post-translational factor for inter-individual differences in the drug-metabolizing enzymes.

Role of CYP2E1 polymorphisms in breast cancer: a systematic review and meta-analysis

BACKGROUND

CYP2E1 polymorphisms have been reported to influence individual's breast cancer susceptibility as a phase I enzyme, but the results of these previous studies remain controversial. We performed a comprehensive meta-analysis to assess their association.

METHODS

A comprehensive search of literature included in various databases (PubMed, Web of Science and Google scholar), published before August 2016, was performed. Odds ratios (ORs) with 95% confidence intervals (CIs) calculated in fixed or random-effects models were used to estimate the strength of the associations between three polymorphisms of CYP2E1 and breast cancer susceptibility. Subgroup analysis, sensitivity analysis and test for publication bias were also performed. A total of 11 separate comparisons involving 4311 cases and 4407 controls were included in the meta-analysis.

RESULTS

Our result showed that there was no significant association between the two common polymorphisms CYP2E1 rs2031920 C>T, CYP2E1*5 Rsa I/Rst I (c1/c2) and BC risk. For CYP2E1*6 Dra I (D/C) polymorphism, a significantly increased BC risk in the overall population was found in genetic model D/C vs. D/D (OR = 1.29, 95% CI = 1.04-1.61, P = 0.023) and C/C + D/C vs. D/D (OR = 1.25, 95% CI = 1.04-1.51, P = 0.019), together with subjects who have at least one C allele (C vs. D: OR = 1.46, 95% CI = 1.20-1.79, P < 0.001). Similar results were also found in subgroup analyses in Caucasians of these three comparison models.

CONCLUSIONS

The present meta-analysis suggests that CYP2E1*6 Dra I (D/C) variation significantly associated with the risk of BC. Individuals with D/C and C/C + D/C genotypes or carried at least one C allele of CYP2E1*6 Dra I (D/C) polymorphism had a significant higher susceptibility to develop BC.

The genetic profiles of CYP1A1, CYP1A2 and CYP2E1 enzymes as susceptibility factor in xenobiotic toxicity in Turkish population

Evaluation and sequencing of heritable alterations in the human genome and the large-scale identification of gene polymorphism for understanding the genetic background of individuals in response to potential toxicants are provided by toxicogenetics. Cytochrome P450 (CYP) enzymes play role not only phase I-dependent metabolism of xenobiotics but also metabolism of endogenous compounds. CYP1A1, CYP1A2 and CYP2E1 enzymes, which are in phase I enzymes, are responsible for metabolic activation and detoxification of several chemical compounds. In the present study, it was determined the genotype and allele frequency of CYP1A1∗2A, CYP1A2∗1C, CYP1A2∗1F, CYP2E1 and CYP2E1∗6, very common and functional single-nucleotide polymorphisms (SNPs), in Turkish healthy volunteers. It is believed that the determination of polymorphisms in the enzymes may be beneficial to prevent and reduce and adverse effects and death in response to drugs. The allele frequencies of these genes were 24%, 9%, 33%, 42%, and 12%, respectively. In the present study, the genotype profile of Turkish population was determined about critical enzymes for xenobiotic metabolism. It is suggested that the obtained results might be beneficial in order to dose adjustment of drugs and prevention of adverse reactions, and further investigation about mentioned enzymes and their polymorphisms.

Human cytochrome P450 2E1 mutations that alter mitochondrial targeting efficiency and susceptibility to ethanol-induced toxicity in cellular models

Human polymorphisms in the 5'-upstream regulatory regions and also protein coding regions of cytochrome P450 2E1 (CYP2E1) are known to be associated with several diseases, including cancer and alcohol liver toxicity. In this study, we report novel mutations in the N-terminal protein targeting regions of CYP2E1 that markedly affect subcellular localization of the protein. Variant W23R/W30R protein (termed W23/30R) is preferentially targeted to mitochondria but very poorly to the endoplasmic reticulum, whereas the L32N protein is preferentially targeted to the endoplasmic reticulum and poorly to mitochondria. These results explain the physiological significance of bimodal CYP targeting to the endoplasmic reticulum and mitochondria previously described. COS-7 cells and HepG2 cells stably expressing W23/30R mutations showed markedly increased alcohol toxicity in terms of increased production of reactive oxygen species, respiratory dysfunction, and loss of cytochrome c oxidase subunits and activity. Stable cells expressing the L32N variant, on the other hand, were relatively less responsive to alcohol-induced toxicity and mitochondrial dysfunction. These results further support our previous data, based on mutational studies involving altered targeting, indicating that mitochondria-targeted CYP2E1 plays an important role in alcohol liver toxicity. The results also provide an interesting new link to genetic variations affecting subcellular distribution of CYP2E1 with alcohol-induced toxicity.

Genetic polymorphism in CYP2E1: Population distribution of CYP2E1 activity

Cytochrome P-450 2E1 (CYP2E1) is a key enzyme in the metabolic activation of a variety of toxicants including nitrosamines, benzene, vinyl chloride, and halogenated solvents such as trichloroethylene. CYP2E1 is also one of the enzymes that metabolizes ethanol to acetaldehyde, and is induced by recent ethanol ingestion. There is evidence that interindividual variability in the expression and functional activity of this cytochrome (CYP) may be considerable. Genetic polymorphisms in CYP2E1 were identified and linked to altered susceptibility to hepatic cirrhosis induced by ethanol and esophageal and other cancers in some epidemiological studies. Therefore, it is important to evaluate how such polymorphisms affect CYP2E1 function and whether it is possible to construct a population distribution of CYP2E1 activity based upon the known effects of these polymorphisms and their frequency in the population. This analysis is part of the genetic polymorphism database project described in the lead article in this series and followed the approach described in that article (Ginsberg et al., 2009, this issue). Review of the literature found that there are a variety of CYP2E1 variant alleles but the functional significance of these variants is still unclear. Some, but not all, studies suggest that several upstream 5' flanking mutations affect gene expression and response to inducers such as ethanol or obesity. None of the coding-region variants consistently affects enzyme function. Part of the reason for conflicting evidence regarding genotype effect on phenotype may be due to the wide variety of exposures such as ethanol or dietary factors and physiological factors including body weight or diabetes that modulate CYP2E1 expression. In conclusion, evidence is too limited to support the development of a population distribution of CYP2E1 enzyme activity based upon genotypes. Health risk assessments may best rely upon data reporting interindividual variability in CYP2E1 function for input into physiologically based pharmacokinetic (PBPK) models involving CYP2E1 substrates.

Is the association between cigarette smoking and breast cancer modified by genotype? A review of epidemiologic studies and meta-analysis

Epidemiologic studies have examined the association between cigarette smoking and breast cancer risk according to genotype with increasing frequency, commensurate with the growing awareness of the roles genes play in detoxifying or activating chemicals found in cigarette smoke and in preventing or repairing the damage caused by those compounds. To date, approximately 50 epidemiologic studies have examined the association between smoking and breast cancer risk according to variation in genes related to carcinogen metabolism, modulation of oxidative damage, and DNA repair. Some of the findings presented here suggest possible effect modification by genotype. In particular, 14 epidemiologic studies have tended to show positive associations with long-term smoking among NAT2 slow acetylators, especially among postmenopausal women. Summary analyses produced overall meta-relative risk (RR) estimates for smoking of 1.2 [95% confidence interval (95% CI), 1.0-1.5] for rapid acetylators and 1.5 (95% CI, 1.2-1.8) for slow acetylators. After stratification by menopausal status, the meta-RR for postmenopausal slow acetylators was 2.4 (95% CI, 1.7-3.3), whereas similar analyses for the other categories showed no association. In addition, summary analyses produced meta-RRs for smoking of 1.1 (95% CI, 0.8-1.4) when GSTM1 was present and 1.5 (95% CI, 1.1-2.1) when the gene was deleted. Overall, however, interpretation of the available literature is complicated by methodologic limitations, including small sample sizes, varying definitions of smoking, and difficulties involving single nucleotide polymorphism selection, which likely have contributed to the inconsistent findings. These methodologic issues should be addressed in future studies to help clarify the association between smoking and breast cancer.

Polymorphism of CYPIA1 and GSTM1 genes associated with susceptibility of gastric cancer in Shandong Province of China

AIM: To explore whether polymorphisms of the CYPIA1 and GSTM1 genes are associated with susceptibility of stomach cancer.

METHODS: A total of 102 stomach cancer cases and 62 healthy persons were diagnosed by pathology in 1998-2000 in the Qilu Hospital of Shandong University. Gene polymorphisms were detected by the PCR using sequence-specific primers. Data analysis of the case-control study was carried out using the unconditional logistic method.

RESULTS: After adjustment for age, sex, educational levels, and occupation, the risk factors for stomach cancer were shown to be smoking, Helicobacter pylori (H pylori), and presence of the CYPIM G/G and GSTM1 O/O genotypes. Interaction was observed between the combined genotypes of either CYPIA1 G/G and GSTM1 O/O or H pylori infection, or GSTM1 O/O and H pylori infection or smoking.

CONCLUSION: Polymorphisms of the CYPIA1 and GSTM1 genes, H pylori infection and smoking are related to susce-ptibility to stomach cancer.

Association of cytochrome P450 2E1 genetic polymorphisms with squamous cell carcinoma of the oesophagus

Squamous cell carcinoma of the oesophagus is one of the most common cancers among black males in South Africa. Genetic polymorphism in the cytochrome P450 2E1 (CYP2E1) gene, coding for one of the main enzymes involved in the bioactivation of tobacco- and alcohol-related substances, was investigated for its role in the development of oesophageal cancer. Three single nucleotide polymorphisms -1053C--> T, -1293G--> A (both give rise to CYP2E1*5 ) and 7632T--> A ( CYP2E1*6 ) in the 5'-untranslated region of CYP2E1 were investigated in 189 patients and 198 control individuals in South Africa. The mutant variants occurred between patients and controls at frequencies of 1% and 2% (-1053C--> T), 1% and 3% (-1293G--> A) and 18% and 7% (7632T--> A), respectively. In comparing patients with controls, the heterozygous CYP2E1*6 genotype was associated with increased risk of the development of squamous cell carcinoma of the oesophagus (odds ratio, 5.90; p < 0.001) after adjusting for age, sex, smoking and alcohol consumption. In contrast, we did not find a significant association between CYP2E1*5 and oesophageal cancer. Six novel mutations, -1371G--> A, -1359C--> G, -1342C--> G, -1261T--> del, -1189T--> C and -1103C--> G, were identified by DNA sequence analysis of the CYP2E1 promoter region. In summary, our case-control study of oesophageal cancer revealed an elevated risk associated with the CYP2E1*6 allele in South Africans.

Association of cytochrome P450 2E1 polymorphisms and head and neck squamous cell cancer

The development of head and neck squamous cell cancer (HNSCC) is known to be strongly associated with tobacco use. One of the main enzymes for bioactivation of tobacco-related substances is the cytochrome 450 (CYP)2E1, of which different genetic variants are described. Analyzing a correlation between certain neoplasia and alteration of the CYP2E1 gene, most studies focus on the polymorphisms -1053C>T and 7632T>A, but recently another polymorphism, named -71G>T, with enhanced transcriptional activity, has been identified. In the current case-control study we investigate the putative association of the mentioned CYP2E1 polymorphisms on the risk of HNSCC. Comparing 312 German individuals with HNSCC to 299 controls we found a significantly enhanced risk for the development of that neoplasia in smoking carriers of -71G>T heterozygosity, while in -1053C>T and 7632T>A polymorphisms a corresponding correlation was absent. Since a coincidence of an aberrant p53 gene and CYP2E1 mutations has been described, we choose a subgroup of 140 patients with HNSCC for analyzing an association of mutations in these two genes. However, no such association could be found in either of the mentioned polymorphisms. Further studies have to focus on the -71G>T polymorphism and its possible linkage to cancers, in which smoking is a known risk-factor, as well as its functional relevance concerning the bioactivation of tobacco-related substances.

Active smoking, household passive smoking, and breast cancer: evidence from the California Teachers Study

BACKGROUND

There is great interest in whether exposure to tobacco smoke, a substance containing human carcinogens, may contribute to a woman's risk of developing breast cancer. To date, literature addressing this question has been mixed, and the question has seldom been examined in large prospective study designs.

METHODS

In a 1995 baseline survey, 116 544 members of the California Teachers Study (CTS) cohort, with no previous breast cancer diagnosis and living in the state at initial contact, reported their smoking status. From entry into the cohort through 2000, 2005 study participants were newly diagnosed with invasive breast cancer. We estimated hazard ratios (HRs) for breast cancer associated with several active smoking and household passive smoking variables using Cox proportional hazards models.

RESULTS

Irrespective of whether we included passive smokers in the reference category, the incidence of breast cancer among current smokers was higher than that among never smokers (HR = 1.32, 95% confidence interval [CI] = 1.10 to 1.57 relative to all never smokers; HR = 1.25, 95% CI = 1.02 to 1.53 relative to only those never smokers who were unexposed to household passive smoking). Among active smokers, breast cancer risks were statistically significantly increased, compared with all never smokers, among women who started smoking at a younger age, who began smoking at least 5 years before their first full-term pregnancy, or who had longer duration or greater intensity of smoking. Current smoking was associated with increased breast cancer risk relative to all nonsmokers in women without a family history of breast cancer but not among women with such a family history. Breast cancer risks among never smokers reporting household passive smoking exposure were not greater than those among never smokers reporting no such exposure.

CONCLUSION

Our study provides evidence that active smoking may play a role in breast cancer etiology and suggests that further research into the connection is warranted, especially with respect to genetic susceptibilities.

Genetic polymorphisms and susceptibility to childhood acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) is the most common form of pediatric cancer. Although exposure to environmental agents appears to predispose individuals to this disease, little attention has been paid to the role of genetic susceptibility to environmental exposures in the etiology of childhood ALL. The enzymes GSTM1, GSTT1, GSTP1, CYP1A1, and CYP2E1 are involved in the bioactivation and detoxification of a variety of xenobiotics present in food, organic solvents, tobacco smoke, drugs, alcoholic drinks, pesticides, and environmental pollutants. Polymorphisms in the genes coding for these enzymes have been associated with increased susceptibility to different cancers, including hematologic malignancies. To investigate whether these polymorphisms represent risk-modifying factors for childhood ALL, a study was conducted involving 113 Brazilian patients of childhood ALL and 221 controls with similar ethnic backgrounds. The data revealed that carriers of the rare GSTP1 Val allele were at higher risk of ALL (odds ratio [OR] = 2.7; 95% confidence interval [CI] = 1.1-6.8; P = 0.04). No difference was found in the prevalence of the GSTM1 and GSTT1 null genotypes between ALL patients and the controls, and no association was found between CYP1A1*2 and CYP2E1*3 variants and ALL. However, when the mutant CYP1A1 and CYP2E1 alleles were considered together with the GSTM1 and GSTP1 risk-elevating genotypes, the risk of ALL was increased further (OR = 10.3; 95% CI = 1.0-111.8; P = 0.05), suggesting a combined effect. These results imply that genetic variants of xenobiotic metabolizing genes influence the risk of developing childhood ALL.

Role of alcohol and genetic polymorphisms of CYP2E1 and ALDH2 in breast cancer development

OBJECTIVE

We examined the potential association between alcohol consumption and genetic polymorphisms in the alcohol metabolizing enzymes, CYP2E1 and ALDH2, in individual susceptibility to breast cancer in a Korean study population.

METHODS

Three hundred and forty-six histologically confirmed breast cancer patients and 377 controls with no present or previous history of cancer were recruited from several teaching hospitals in Seoul during 1995-2001. The CYP2E1 RsaI polymorphism was determined by a real time PCR method, and the ALDH2 Glu487 Lys polymorphism was determined by a PCR method with confronting two-pair primers (PCR-CTPP).

RESULTS

The drinking women had a 1.4-fold risk for breast cancer (95% CI = 0.99-2.11) compared to never drinkers after adjustment for age and family history of breast cancer. No statistically significant overall differences were seen in the genotype frequencies between breast cancer cases and controls. However, the "ever"-drinking women with the CYP2E1 c2 allele containing genotypes had a 1.9-fold risk (95% CI = 0.99-3.83) for developing breast cancer compared to non-drinkers with the CYP2E1 c1/c1 genotype (P for interaction = 0.043).

CONCLUSION

This study therefore suggests that the CYP2E1 c2 allele may influence the individual susceptibility to breast cancer in alcohol-consuming women.

Parental genotypes in the risk of a complex disease

Our understanding of the genetic etiology of complex disorders is still elusive. According to the common-variant/common-disease hypothesis, frequent functional polymorphisms are the best candidates for disease-susceptibility alleles. Implicitly, we also assume that disease-susceptibility alleles are preferentially transmitted from parents to the affected offspring and that this effect can be captured by the transmission/disequilibrium test (TDT). However, our study of genetic predisposition to childhood acute lymphoblastic leukemia suggests that a focus on the patient's genotype might, in certain instances, be misleading. Our results indicate that, at least at some loci, parental genetics might be of primary importance in predicting the risk of cancer in this pediatric model of a complex disease. Consequently, in addition to TDT, other complementary strategies will need to be simultaneously applied to dissect genetic predisposition to complex disorders.

Role of NQO1, MPO and CYP2E1 genetic polymorphisms in the susceptibility to childhood acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) is the most common pediatric cancer. The genetic factors underlying the susceptibility to this disease remain elusive. The enzymes CYP2E1, MPO and NQO1 are involved in the biotransformation of a variety of xenobiotics present in organic solvents, tobacco smoke, drugs, plastic derivatives and pesticides. They also control the level of the oxidative stress by catalyzing the formation of free radicals or by protecting cells from their deleterious effect. DNA variants in the corresponding genes have been associated with an increased susceptibility to different adult cancers, including hematologic malignancies. To investigate whether they represent risk-modifying factors in childhood ALL, we conducted a case-control study involving 174 patients and 337 controls, both of French-Canadian origin. We found that carriers of the CYP2E1*5 variant were at 2.8-fold higher risk of ALL (95%CI, 1.2-6.4) and that NQO1 alleles *2 and *3 contributed to the risk of ALL as well (OR = 1.7, 95%CI, 1.2-2.4). No such association was found with MPO alone. However, when the wild-type MPO allele was considered together with the CYP2E1 and NQO1 risk-elevating genotypes, the risk of ALL was increased further (OR = 5.4, 95%CI, 1.2-23.4) suggesting a combined effect. We also found a gene-gene interaction between the GSTM1 null genotype and NQO1 mutant alleles. It is therefore plausible that exposure to xenobiotics metabolized by these enzymes play a role in the etiology of childhood ALL.

Dynamics of cytochrome P4502E1 activity in man: induction by ethanol and disappearance during withdrawal phase

BACKGROUND/AIMS

Chronic ethanol consumption results in the induction of hepatic cytochrome P4502E1 (CYP2E1) in man, which is believed to play an important role in the pathogenesis of alcoholic liver disease. However, the amount and duration of alcohol intake associated with CYP2E1 induction is not known but limited information is available on the disappearance of CYP2E1 following alcohol withdrawal.

METHODS

To study these questions, five healthy male volunteers received ethanol daily (40 g/day) over 4 weeks. CYP2E1 induction was monitored by using the chlorzoxazone test before and every week following the start of alcohol ingestion. In addition, CYP2E1 was also determined in five alcoholics 1, 3, 8 and 15 days following ethanol withdrawal and in five patients with non-alcoholic liver disease.

RESULTS

A significant CYP2E1 induction occurred 1 week following the ingestion of 40 g ethanol per day and increased further after 4 weeks. The disappearance of CYP2E1 was found to be significant 3 days following ethanol withdrawal and further decreased up to day 8. Thereafter, no significant change occurred and CYP2E1 activities were comparable with those in patients with non-alcoholic liver disease.

CONCLUSIONS

These data show a significant and quick induction of CYP2E1 activity, already at moderate alcohol consumption, which may be of importance in the pathogenesis of alcoholic liver disease, of ethanol, drug and vitamin A interactions and in alcohol associated carcinogenesis.

Childhood acute lymphoblastic leukemia: genetic determinants of susceptibility and disease outcome

The origin of acute lymphoblastic leukemia (ALL), the most common pediatric cancer, can be explained by a combination of genetic factors and environmental exposure. The environmental toxicants to which an individual is exposed are biotransformed and eliminated from the body after metabolic conversion mediated by Phase I and Phase II xenobiotic-metabolizing enzymes. Phase I enzymes catalyze hydroxylation, reduction and oxidation reactions of xenobiotics (carcinogens/drugs), often converting them into more active or toxic compounds. Phase II enzymes catalyze conjugation reactions (glucuronidation, acetylation, methylation), thereby converting the metabolites into non-reactive, water-soluble products that are eliminated from the organism. The genetic polymorphism underlying the variation in enzyme activity can modify susceptibility to diverse adult cancers, probably by influencing the activation and removal of toxicants or drugs. Here we present an overview of the role of genetic variants of certain Phase I and Phase II enzymes in the development of childhood ALL, a good model for such studies because of its short latency period. The genetic contribution to the development of ALL is examined by association studies that analyze the loci of Phase I enzymes (cytochrome P-450, myeloperoxidase) and Phase II enzymes (quinone-oxidoreductase, glutathione-S-transferase, N-acetyltransferase). The loci of the enzyme variants CYPlA1, CYP2E1, NQO1, GSTM1, GSTP1, NAT2 are associated with disease development, and evidence of gene-gene interactions has emerged as well. Despite the improvements in treatment, resistant cases of ALL remain a leading cause of cancer-related death in children. Although the underlying mechanism of drug resistance is not well understood, differences in the capacity of ALL patients to process drugs and environmental carcinogens could play a role by modifying the risk of recurrent malignancy, as well as the response to therapy. Therefore, polymorphic genes encoding carcinogen- and drug-metabolizing enzymes may not only increase the risk of ALL but also influence the risk of relapse in patients. We found that the prognosis of patients with CYPlA1 and NQO1 variants was worse than that of patients who lack these variants. We conclude that genotyping ALL patients for functional polymorphisms of candidate genes can become an important tool in predicting disease outcome.

Inherited genetic predisposition in breast cancer. A population-based perspective

Two classes of inherited susceptibility genes may be considered in the etiology of breast and other common cancers. First, genes have been identified that confer a high degree of breast cancer (BC) risk, usually associated with hereditary syndromes, but disease-associated germline variants in these genes are relatively rare in the general population. These include BRCA1, BRCA2, and TP53. The proportion of BC in the general population that can be explained by these genes is relatively small. Second, variant genotypes at other loci may confer a relatively smaller degree of cancer risk, but they are carried by a larger proportion of the general population. As a result, the proportion of BC that could be explained by these genes may be relatively large. To understand the genetic basis for BCs in the general population, both of these classes of genes may need to be considered. This paper presents an overview of genes thought to be involved in BC susceptibility. Genes that confer a high degree of risk are more likely to result in hereditary patterns of cancer that are amenable to identification by genetic epidemiologic methods using pedigree data. More common (e.g., nonhereditary) forms of BC may be optimally analyzed by molecular epidemiologic studies using case-case, case-control, or cohort designs. The use of an appropriate study design is crucial to the identification of genes with relatively small effects on BC risk. To understand the inherited factors that explain BC in the general population, consideration should be given to genes with different allele frequencies and magnitudes of effect, using appropriate analytical approaches. By understanding the complex interactions of these genes with one another and with exposures, improved risk assessment and potential for targeted cancer prevention strategies may be possible.

Impact of CYP2E1 genotype in renal cell and urothelial cancer patients

Genetic polymorphisms of enzymes involved in carcinogen metabolism have been found to influence susceptibility to cancer. Ethanol-inducible CYP2E1 is an enzyme of major toxicological interest because it metabolizes several drugs, precarcinogens and solvents to reactive metabolites. In the present study, we investigated the cytochrome P450 2E1 genetic polymorphism in renal cell/urothelial cancer patients from two German regions, Jena and Halle, different with respect to their environmental pollution degree in comparison with healthy controls from the same regions. DNA of peripheral white blood cells was isolated both from 224 renal cell/urothelial cancer patients and 304 controls. We focussed on polymorphisms in the promoter region and intron 6 of the CYP2E1 gene. The polymorphisms were identified as RFLP's by amplification of the appropriate DNA fragment and subsequent digestion with the restriction enzymes PstI, RsaI and DraI. In Jena as well as in Halle, the frequency distributions of the PstI/RsaI, DraI and combined DraI + PstI/RsaI genotypes showed no significant differences between controls and renal cell/urothelial cancer patients. We did not find significant differences between Jena and Halle. 86.2% of all subjects with a homozygote PstI/RsaI genotype also carried a heterozygote DraI genotype, whereas 5.1% of the subjects with a heterozygote PstI/RsaI genotype also carried a heterozygote DraI genotype. Renal cell cancer as well as urothelial cancer risk was not elevated in patients with heterozygote DraI, PstI/RsaI and combined DraI + PstI/RsaI genotypes (odds ratios slightly insignificantly increased). Interestingly enough, an association between these polymorphisms and renal cell cancer risk was found in the female subgroup but not in the male subgroup. The basis of these sex-specifically increased risks are different frequencies concerning heterozygote and homozygote genotypes in controls and cancer patients. In controls, the heterozygote genotype frequency was lower in females than in males. In renal cell cancer patients, the results were quite the contrary. Summing up, our results demonstrate an lack between CYP2E1 genetic polymorphism and renal cell/urothelial cancer risk.