Cytochrome P4501A1 and Microsomal Epoxide Hydrolase Gene Polymorphisms: Gene–Environment Interaction and Risk of Prostate Cancer

Genetic polymorphisms in the mEH gene in relation to tobacco smoking: role in lung cancer susceptibility and survival in north Indian patients with lung cancer undergoing platinum-based chemotherapy

Aim: Epoxide hydrolase is involved in oxidative defenses and is responsible for the activation of carcinogens. The relationship between EPHX1 polymorphisms (Tyr¹¹³His and His¹³⁹Arg) and overall survival (OS) and lung cancer (LC) risk was investigated. Methods: The study comprised 550 cases and 550 controls. Genotyping and statistical analysis were applied. Results: The variant genotypes of EPHX1 polymorphisms exhibited no association with LC risk. The Tyr¹¹³His polymorphism exhibited twofold increased odds of lymph node invasion (p = 0.04). The Tyr/His genotype is a risk factor for smokers. Subjects carrying the combined genotype for His¹³⁹Arg showed better median survival time (MST) and the heterozygous genotype revealed better MST in the case of small-cell lung cancer (SCLC; 11.30 vs 6.73 months; log-rank test: p = 0.02). The heterozygous genotype (His139Arg) had longer MST in patients receiving cisplatin/carboplatin and irinotecan (11.30 vs 7.23; log-rank test: p = 0.007) Conclusion: The Tyr¹¹³His polymorphism is associated with LC risk in smokers and is a potential prognostic factor for OS in patients with SCLC after irinotecan.

Genetic susceptibility of CYP1A1 gene and risk of pesticide exposure in prostate cancer

BACKGROUND

The etiology of prostate cancer (PCa) is multi-factorial including environmental and genetic factors. Present study evaluates the association between level of pesticides, stress level and CYP1A1 gene polymorphism with PCa patients.

METHODS

A case control study was conducted with 102 PCa patients and age match symptomatic (n= 107) and asymptomatic benign prostatic hyperplasia (BPH, n= 70) patients. Pesticide level was characterized by Gas Chromatography. The oxidative stress and scavenging mechanisms were determined by biochemical method. Two polymorphisms of CYP1A1 gene, rs4646903 and rs1048943, were analyzed by polymerase chain reaction (PCR) followed by restriction fragment length polymorphism and allele specific PCR method.

RESULTS

Higher level of pesticide namely beta-hexachlorocyclohexane (β-HCH), Malathion, Chlorpyrifos and Fenvalerate were found in PCa group (all p value: < 0.05). Kruskal Wallis H test depicted that level of β-HCH and Malathion significantly correlated with higher grade of PCa (all p< 0.05). The PCa Patients with simultaneously low antioxidant activity and high stress level tended to suffer worst clinical outcomes. Dominant model of rs4646903 and rs1048943 suggested that substitution is associated with a higher risk of PCa (OR: 2.2, CI: 1.6-3.8, p: 0.009 and OR: 1.95, CI: 1.1-3.4, p: 0.026; respectively) and this risk was also influenced by smoking and pesticide exposure.

CONCLUSION

Environmental and genetic factors are reported to raise risk; person with high level of these pesticides especially in high risk genotype might be more susceptible to PCa.

Missense Genetic Polymorphisms of Microsomal (EPHX1) and Soluble Epoxide Hydrolase (EPHX2) and Their Relation to the Risk of Large Artery Atherosclerotic Ischemic Stroke in a Turkish Population

PURPOSE

Soluble epoxide hydrolase (sEH) and microsomal epoxide hydrolase (mEH) both catalyze the metabolism of epoxyeicosatrienoic acids (EETs), lipid signaling molecules that are protective against ischemic brain injury owing to their participation in the regulation of vascular tone and cerebral blood flow. In addition, mEH metabolizes polycyclic aromatic hydrocarbons, one of the causative factors of atherosclerotic lesion development. In this study, we aimed to investigate the association of enzyme activity-modifying missense single nucleotide polymorphisms (SNPs) of the sEH gene (EPHX2) and mEH gene (EPHX1) and ischemic stroke risk in a Turkish population.

PATIENTS AND METHODS

Genomic DNA of patients with large artery atherosclerotic ischemic stroke (n=237) and controls (n=120) was isolated from blood samples, and genotypes for Tyr113His (rs1051740) and His139Arg (rs2234922) SNPs of EPHX1 and Arg287Gln (rs751141) SNP of EPHX2 were attained by the PCR/RFLP method.

RESULTS

Minor allele frequency and genotype distributions for Arg287Gln, Tyr113His and His139Arg SNPs did not differ significantly between stroke patients and controls. However, hypertension- and diabetes-associated ischemic stroke risk was decreased by EPHX1 and increased by EPHX2 variants in stratification analyses.

CONCLUSION

This study has shown for the first time that the polymorphic alleles of EPHX1 were unlikely to be associated with large artery atherosclerotic ischemic stroke susceptibility; however, protective effects were evident within subgroups of hypertension and diabetes. In addition, EPHX2 Arg287Gln polymorphism, which has been studied for the first time in a Turkish population, was not significantly related to ischemic stroke, but increased the stroke risk in subgroup analysis.

Associations of CYP1 polymorphisms with risk of prostate cancer: an updated meta-analysis

Background. The results of previous studies on the association between polymorphisms of CYP1A1 and CYP1B1 and prostate cancer (PCa) susceptibility are inconsistent. The aim of the present study was to conduct a meta-analysis in order to better estimate this association. Methods. A systematic search was carried out on PubMed, Embase, Cochrane Library, and China National Knowledge Infrastructure (CNKI) databases for relevant articles published up to 15 August 2018. Pooled odds ratios (ORs) and 95% confidence intervals were obtained using fixed-effect or random-effect models. Results. A significant association was found between the CYP1A1 rs1048943 polymorphism and PCa in the overall population (B [the minor allele] vs. A [the major allele]: OR = 1.20, 95% confidence interval (CI) = 1.04–1.39, P=0.014; AB vs. AA: OR = 1.24, 95% CI = 1.02–1.51, P=0.029; BB + AB vs. AA: OR = 1.25, 95% CI = 1.04–1.50, P=0.018) and Asian population (B vs. A: OR = 1.32, 95% CI = 1.11–1.56, P=0.001; BB vs. AA: OR = 1.81, 95% CI = 1.20–2.72, P=0.005; AB vs. AA: OR = 1.30, 95% CI = 1.03–1.64, P=0.029; BB + AB vs. AA: OR = 1.38, 95% CI = 1.11–1.73, P=0.004; BB vs. AA + AB: OR = 1.58, 95% CI = 1.08–2.01, P=0.019), but not in the Caucasian population. Moreover, we found that the rs4646903 polymorphism was associated with a significant increase in the risk of PCa in the Asian population (AB vs. AA: OR = 1.43, 95% CI = 1.13–1.80, P=0.003) and Caucasian population (BB vs. AA: OR = 2.12, 95% CI = 1.29–3.49, P=0.003). Conclusion. This meta-analysis revealed a clear association between rs1048943 and rs4646903 polymorphisms of the CYP1A1 gene but not between CYP1B1 rs10012, rs162549, rs1800440, and rs2551188 polymorphisms and the risk of PCa.

EPHX1 rs1051740 T>C (Tyr113His) is strongly associated with acute myeloid leukemia and KMT2A rearrangements in early age

Experimental and epidemiological data have shown that acute myeloid leukemia in early-age (i-AML) originates prenatally. The risk association between transplacental exposure to benzene metabolites and i-AML might be influenced by genetic susceptibility. In this study, we investigated the relationship between genetic polymorphisms in CYP2E1, EPHX1, MPO, NQO1, GSTM1 and GSTT1 genes, and i-AML risk. The study included 101 i-AMLs and 416 healthy controls. Genomic DNA from study subjects was purified from bone marrow or peripheral blood aspirates and genotyped for genetic polymorphisms by real-time PCR allelic discrimination, Sanger sequencing and multiplex PCR. Crude and adjusted odds ratios (OR, _adjOR, respectively) with 95% confidence intervals (95% CI) were assessed using unconditional logistic regression to estimate the magnitude of risk associations. EPHX1 rs1051740 T>C was associated with i-AML risk under the co-dominant (_adjOR 3.04, P = 0.003) and recessive (_adjOR 2.99, P = 0.002) models. In stratified analysis, EPHX1 rs1051740 was associated with increased risk for i-AML with KMT2A rearrangement (_adjOR 3.06, P = 0.045), i-AML with megakaryocytic differentiation (_adjOR 5.10, P = 0.008), and i-AML with type I mutation (_adjOR 2.02, P = 0.037). EPHX1 rs1051740-rs2234922 C-G haplotype was also associated with increased risk for i-AML (_adjOR 2.55, P = 0.043), and for i-AML with KMT2A rearrangement (_adjOR 3.23, P = 0.034). Since EPHX1 enzyme is essential in cellular defense against epoxides, the diminished enzymatic activity conferred by the variant allele C could explain the risk associations found for i-AML. In conclusion, EPHX1 rs1051740 plays an important role in i-AML's genetic susceptibility by modulating the carcinogenic effects of epoxide exposures in the bone marrow.

CYP1A1 and GSTP1 gene variations in breast cancer: a systematic review and case-control study

In first part of this study, a systematic review was designed to explore the involvement of CYP1A1 and GSTP1 genes in breast cancerogenesis. Based on systematic review, we designed a study to screen CYP1A1 and GSTP1 genes for mutation and their possible association with breast carcinogenesis. A total of 400 individuals were collected and analyzed by PCR-SSCP. After sequence analysis of coding region of CYP1A1 we identified eleven mutations in different exons of respective gene. Among these eleven mutations, ~3 folds increased breast cancer risk was found associated with Asp82Glu mutation (OR 2.99; 95% CI 1.26-7.09), with Ser83Thr mutation (OR 2.99; 95% CI 1.26-7.09) and with Glu86Ala mutation (OR 3.18; 95% CI 1.27-7.93) in cancer patients compared to controls. Furthermore, ~4 folds increase in breast cancer risk was found associated with Asp347Glu, Phe398Tyr and 5178delT mutations (OR 3.92; 95% CI 1.35-11.3) in patients compared to controls. The sequence analysis of GSTP1 resulted in identification of total five mutations. Among these five mutations, ~3 folds increase in breast cancer risk was observed associated with 1860G>A mutation, with 1861-1876delCAGCCCTCTGGAGTGG mutation (OR 2.70; 95% CI 1.10-6.62) and with 1861C>A mutation (OR 2.97; 95% CI 1.01-8.45) in cancer patients compared to controls. Furthermore, ~5 folds increase in breast cancer risk was associated with 1883G>T mutation (OR 4.75; 95% CI 1.46-15.3) and ~6 folds increase in breast cancer risk was found associated with Iso105Val mutation (OR 6.43; 95% CI 1.41-29.3) in cancer patients compared to controls. Our finding, based on systematic review and experimental data suggest that the polymorphic CYP1A1 and GSTP1 genes may contribute to risk of developing breast cancer.

Quantitative assessment of the influence of EPHX1 gene polymorphisms and cancer risk: a meta-analysis with 94,213 subjects

Purpose

Previous studies investigating the association between EPHX1 polymorphisms (Tyr113His and His139Arg) and cancer risk have yielded inconsistent results. This meta-analysis was performed to derive a more precise estimation of relationship between two EPHX1 polymorphisms and risk of different types of cancer.

Methods

Data were extracted from relevant studies detected by a systematic literature search. Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated to assess the strength of the association between EPHX1 polymorphisms and cancer risk.

Results

This meta-analysis carefully collected 99 studies on these two polymorphisms and cancer risk published up to March 2014, consisting of 45 studies (20,091 cases and 27,396 controls) for Tyr113His and 54 studies (19,437 cases and 27,289 controls) for His139Arg. The results in overall population did not show any significant association between these two polymorphisms and cancer risk for all genetic models. However, EPHX1 Tyr113His homozygote individuals have a significantly increased risk of cancer among Asians (homozygote model: OR =1.46, 95% CI=1.05–2.03; recessive model: OR =1.39, 95% CI =1.10–1.76) and mixed population (homozygote model: OR =1.17, 95% CI =1.02–1.34; recessive model: OR =1.17, 95% CI =1.02–1.33), but not Caucasians.

Conclusion

His/His genotype of EPHX1 Tyr113His polymorphism is a risk factor for developing caner for Asian and mixed population, while no evidence was found for the association between the EPHX1 His139Arg polymorphism and increased cancer risk.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-014-0082-9) contains supplementary material, which is available to authorized users.

The role of epoxide hydrolases in health and disease

Epoxide hydrolases (EH) are ubiquitously expressed in all living organisms and in almost all organs and tissues. They are mainly subdivided into microsomal and soluble EH and catalyze the hydration of epoxides, three-membered-cyclic ethers, to their corresponding dihydrodiols. Owning to the high chemical reactivity of xenobiotic epoxides, microsomal EH is considered protective enzyme against mutagenic and carcinogenic initiation. Nevertheless, several endogenously produced epoxides of fatty acids function as important regulatory mediators. By mediating the formation of cytotoxic dihydrodiol fatty acids on the expense of cytoprotective epoxides of fatty acids, soluble EH is considered to have cytotoxic activity. Indeed, the attenuation of microsomal EH, achieved by chemical inhibitors or preexists due to specific genetic polymorphisms, is linked to the aggravation of the toxicity of xenobiotics, as well as the risk of cancer and inflammatory diseases, whereas soluble EH inhibition has been emerged as a promising intervention against several diseases, most importantly cardiovascular, lung and metabolic diseases. However, there is reportedly a significant overlap in substrate selectivity between microsomal and soluble EH. In addition, microsomal and soluble EH were found to have the same catalytic triad and identical molecular mechanism. Consequently, the physiological functions of microsomal and soluble EH are also overlapped. Thus, studying the biological effects of microsomal or soluble EH alterations needs to include the effects on both the metabolism of reactive metabolites, as well as epoxides of fatty acids. This review focuses on the multifaceted role of EH in the metabolism of xenobiotic and endogenous epoxides and the impact of EH modulations.

Association of CYP1A1 gene polymorphism with chronic kidney disease: a case control study

CYP1A1 is an important xenobiotic metabolizing enzyme, present in liver and kidney. Expression of CYP1A1 enzyme increases manifold when kidney cells are exposed to nephrotoxins/chemicals leading to oxidative stress-induced cell damage. To study the association of CYP1A1 gene polymorphism in patients of chronic kidney disease with unknown etiology (CKDU), we recruited 334 CKDU patients and 334 age and sex matched healthy controls. CYP1A1*2A and *2C polymorphisms were studied by PCR-RFLP and allele specific-PCR respectively. Subjects carrying at least one mutant allele of CYP1A1*2A (TC, CC) and *2C (AG, GG) were shown to be associated with 1.4-2-fold increased risk of CKDU. Also, genotypic combinations of hetero-/homozygous mutants of CYP1A1*2A (TC, CC) with hetero-/homozygous mutant genotypes of CYP1A1*2C (AG, GG) i.e. TC/AG (p<0.01), TC/GG (p<0.05), CC/AG (p<0.05) and CC/GG (p<0.01) were associated with CKDU with an odd ratio ranging 1.8-3.3 times approximately. This study demonstrates association of CYP1A1 polymorphisms with CKDU.

CYP1A1 MspI polymorphism is associated with prostate cancer susceptibility: evidence from a meta-analysis

Cytochrome P450 1A1 (CYP1A1), an important phase I xenobiotic metabolizing enzyme, is responsible for metabolizing numerous carcinogens, particularly polycyclic aromatic hydrocarbons. The genetic polymorphism of CYP1A1 at the site of MspI (CYP1A1 MspI) has been implicated in prostate cancer risk, but the results of individual studies remain conflicting and inconclusive. The aim of this meta-analysis was to investigate the association of CYP1A1 MspI polymorphism with prostate cancer risk more precisely. We performed a comprehensive search of the PubMed, Embase, Web of Science, and China National Knowledge Infrastructure databases from their inception up to September 20, 2012 for relevant publications. The pooled odds ratios with the corresponding 95% confidence intervals (95% CIs) were calculated to assess the association of CYP1A1 MspI polymorphism with prostate cancer risk. In addition, stratified analyses by ethnicity and sensitivity analyses were conducted for further estimation. Sixteen eligible publications with 6,411 subjects were finally included into the meta-analysis after checking the retrieved papers. Overall, meta-analysis of total studies suggested that individuals carrying the TC genotype and a combined C genotype (CC + TC) were more susceptible to prostate cancer (OR(TC vs. TT) = 1.33, 95% CI 1.10-1.61, P(OR) = 0.004; OR(CC+TC vs. TT) = 1.27, 95% CI 1.05-1.55, P(OR) = 0.016). Stratified analysis of high quality studies also confirmed the significant association (OR(TC vs. TT) = 1.32, 95% CI 1.04-1.67, P(OR) = 0.024; OR(CC+TC vs. TT) = 1.30, 95% CI 1.02-1.66, P(OR) = 0.035). In subgroup analyses by ethnicity, a significant association between the CYP1A1 MspI polymorphism and risk of prostate cancer was found among Asians (OR(TC vs. TT) = 1.44, 95% CI 1.20-1.72, P(OR) < 0.001; OR(CC+TC vs. TT) = 1.33, 95% CI 1.12-1.58, P(OR) = 0.001), but not in Caucasians or mixed populations. The meta-analysis suggests an important role of the CYP1A1 MspI polymorphism in the risk of developing prostate cancer, especially in Asians.

Polymorphisms in carcinogen metabolism enzymes, fish intake, and risk of prostate cancer

Cooking fish at high temperature can produce potent carcinogens such as heterocyclic amines and polycyclic aromatic hydrocarbons. The effects of these carcinogens may undergo modification by the enzymes responsible for their detoxification and/or activation. In this study, we investigated genetic polymorphisms in nine carcinogen metabolism enzymes and their modifying effects on the association between white or dark fish consumption and prostate cancer (PCA) risk. We genotyped 497 localized and 936 advanced PCA cases and 760 controls from the California Collaborative Case-Control Study of Prostate Cancer. Three polymorphisms, EPHX1 Tyr113His, CYP1B1 Leu432Val and GSTT1 null/present, were associated with localized PCA risk. The PTGS2 765 G/C polymorphism modified the association between white fish consumption and advanced PCA risk (interaction P 5 0.002), with high white fish consumption being positively associated with risk only among carriers of the C allele. This effect modification by PTGS2 genotype was stronger when restricted to consumption of well-done white fish (interaction P 5 0.021). These findings support the hypotheses that changes in white fish brought upon by high-temperature cooking methods, such as carcinogen accumulation and/or fatty acid composition changes, may contribute to prostate carcinogenesis. However, the gene-diet interactions should be interpreted with caution given the limited sample size. Thus, our findings require further validation with additional studies.

Putative EPHX1 enzyme activity is related with risk of lung and upper aerodigestive tract cancers: a comprehensive meta-analysis

Background

EPHX1 is a key enzyme in metabolizing some exogenous carcinogens such as products of cigarette-smoking. Two functional polymorphisms in the EPHX1 gene, Tyr113His and His139Arg can alter the enzyme activity, suggesting their possible association with carcinogenesis risk, particularly of some tobacco-related cancers.

Methodology/Principal Findings

A comprehensive systematic review and meta-analysis was performed of available studies on these two polymorphisms and cancer risk published up to November 2010, consisting of 84 studies (31144 cases and 42439 controls) for Tyr113His and 77 studies (28496 cases and 38506 controls) for His139Arg primarily focused on lung cancer, upper aerodigestive tract (UADT) cancers (including oral, pharynx, larynx and esophagus cancers), colorectal cancer or adenoma, bladder cancer and breast cancer. Results showed that Y113H low activity allele (H) was significantly associated with decreased risk of lung cancer (OR = 0.88, 95%CI = 0.80–0.96) and UADT cancers (OR = 0.86, 95%CI = 0.77–0.97) and H139R high activity allele (R) with increased risk of lung cancer (OR = 1.18, 95%CI = 1.04–1.33) but not of UADT cancers (OR = 1.05, 95%CI = 0.93–1.17). Pooled analysis of lung and UADT cancers revealed that low EPHX1 enzyme activity, predicted by the combination of Y113H and H139R showed decreased risk of these cancers (OR = 0.83, 95%CI = 0.75–0.93) whereas high EPHX1 activity increased risk of the cancers (OR = 1.20, 95%CI = 0.98–1.46). Furthermore, modest difference for the risk of lung and UADT cancers was found between cigarette smokers and nonsmokers both in single SNP analyses (low activity allele H: OR = 0.77/0.85 for smokers/nonsmokers; high activity allele R: OR = 1.20/1.09 for smokers/nonsmokers) and in combined double SNP analyses (putative low activity: OR = 0.73/0.88 for smokers/nonsmokers; putative high activity: OR = 1.02/0.93 for smokers/ nonsmokers).

Conclusions/Significance

Putative low EPHX1 enzyme activity may have a potential protective effect on tobacco-related carcinogenesis of lung and UADT cancers, whereas putative high EPHX1 activity may have a harmful effect. Moreover, cigarette-smoking status may influence the association of EPHX1 enzyme activity and the related cancer risk.

Metabolism and toxicity of styrene in microsomal epoxide hydrolase-deficient mice

Styrene, which is widely used in manufacturing, is both acutely and chronically toxic to mice. Styrene is metabolized by cytochromes P-450 to the toxic metabolite styrene oxide, which is detoxified via hydrolysis with microsomal epoxide hydrolase (mEH) playing a major role. The purpose of these studies was to characterize the importance of this pathway by determining the hepatotoxicity and pneumotoxicity of styrene in wild-type and mEH-deficient (mEH(-/-)) mice. While the mEH(-/-) mice metabolized styrene to styrene oxide at the same rate as the wild-type mice, as expected there was minimal metabolism of styrene oxide to glycol. mEH(-/-) mice were more susceptible to the lethal effects of styrene. Twenty-four hours following the administration of 200 mg/kg ip styrene, mice demonstrated a greater hepatotoxic response due to styrene, as measured by increased serum sorbitol dehydrogenase activity and greater pneumotoxicity as shown by increased protein levels, cell numbers, and lactate dehydrogenase activity in bronchioalveolar lavage fluid. mEH(-/-) mice were also more susceptible to styrene-induced oxidative stress, as indicated by greater decreases in hepatic glutathione levels 3 h after styrene. Styrene oxide at a dose of 150 mg/kg did not produce hepatotoxicity in either wild-type or mEH(-/-) mice. However, styrene oxide produced pneumotoxicity that was similar in the two strains. Thus, mEH plays an important role in the detoxification of styrene but not for exogenously administered styrene oxide.

Haplotypes of microsomal epoxide hydrolase and x-ray cross-complementing group 1 genes in Indian hepatocellular carcinoma patients

Hepatocellular carcinoma (HCC) is a life-threatening disease that is often associated with chronic infection by hepatitis B and C viruses. Genetic polymorphisms have been reported to alter the risk for HCC development. Genetic studies based on the haplotype have an increased power for detecting disease associations compared with single-nucleotide polymorphism-based analysis. There is sufficient epidemiological evidence suggesting a link between genetic polymorphism and haplotypes of microsomal epoxide hydrolase (mEPHX) and X-ray cross-complementing group 1 (XRCC1) with altered cancer risk. However, no report correlates the risk of HCC development with mEPHX and XRCC1 haplotypes. Genetic polymorphism of these genes was studied for haplotype construction in 169 control subjects, 174 hepatitis patients, and 63 HCC patients. 113Tyr-139Arg and 113His-139His haplotypes of mEPHX significantly elevated the risk for HCC by 1.4- and 1.5-folds, respectively. Arg-His-Arg haplotype of XRCC1 significantly enhanced the risk for hepatitis by 2.8-folds (p = 0.001), but not for HCC (odds ratio = 1.5; p = 0.28). mEPHX haplotypes shared a positive association with HCC risk in India.

Polymorphism of human cytochrome P450 enzymes and its clinical impact

Pharmacogenetics is the study of how interindividual variations in the DNA sequence of specific genes affect drug response. This article highlights current pharmacogenetic knowledge on important human drug-metabolizing cytochrome P450s (CYPs) to understand the large interindividual variability in drug clearance and responses in clinical practice. The human CYP superfamily contains 57 functional genes and 58 pseudogenes, with members of the 1, 2, and 3 families playing an important role in the metabolism of therapeutic drugs, other xenobiotics, and some endogenous compounds. Polymorphisms in the CYP family may have had the most impact on the fate of therapeutic drugs. CYP2D6, 2C19, and 2C9 polymorphisms account for the most frequent variations in phase I metabolism of drugs, since almost 80% of drugs in use today are metabolized by these enzymes. Approximately 5-14% of Caucasians, 0-5% Africans, and 0-1% of Asians lack CYP2D6 activity, and these individuals are known as poor metabolizers. CYP2C9 is another clinically significant enzyme that demonstrates multiple genetic variants with a potentially functional impact on the efficacy and adverse effects of drugs that are mainly eliminated by this enzyme. Studies into the CYP2C9 polymorphism have highlighted the importance of the CYP2C9*2 and *3 alleles. Extensive polymorphism also occurs in other CYP genes, such as CYP1A1, 2A6, 2A13, 2C8, 3A4, and 3A5. Since several of these CYPs (e.g., CYP1A1 and 1A2) play a role in the bioactivation of many procarcinogens, polymorphisms of these enzymes may contribute to the variable susceptibility to carcinogenesis. The distribution of the common variant alleles of CYP genes varies among different ethnic populations. Pharmacogenetics has the potential to achieve optimal quality use of medicines, and to improve the efficacy and safety of both prospective and currently available drugs. Further studies are warranted to explore the gene-dose, gene-concentration, and gene-response relationships for these important drug-metabolizing CYPs.

Mammalian epoxide hydrolases in xenobiotic metabolism and signalling

Epoxide hydrolases catalyse the hydrolysis of electrophilic--and therefore potentially genotoxic--epoxides to the corresponding less reactive vicinal diols, which explains the classification of epoxide hydrolases as typical detoxifying enzymes. The best example is mammalian microsomal epoxide hydrolase (mEH)-an enzyme prone to detoxification-due to a high expression level in the liver, a broad substrate selectivity, as well as inducibility by foreign compounds. The mEH is capable of inactivating a large number of structurally different, highly reactive epoxides and hence is an important part of the enzymatic defence of our organism against adverse effects of foreign compounds. Furthermore, evidence is accumulating that mammalian epoxide hydrolases play physiological roles other than detoxification, particularly through involvement in signalling processes. This certainly holds true for soluble epoxide hydrolase (sEH) whose main function seems to be the turnover of lipid derived epoxides, which are signalling lipids with diverse functions in regulatory processes, such as control of blood pressure, inflammatory processes, cell proliferation and nociception. In recent years, the sEH has attracted attention as a promising target for pharmacological inhibition to treat hypertension and possibly other diseases. Recently, new hitherto uncharacterised epoxide hydrolases could be identified in mammals by genome analysis. The expression pattern and substrate selectivity of these new epoxide hydrolases suggests their participation in signalling processes rather than a role in detoxification. Taken together, epoxide hydrolases (1) play a central role in the detoxification of genotoxic epoxides and (2) have an important function in the regulation of physiological processes by the control of signalling molecules with an epoxide structure.