Genetic analysis of microsomal epoxide hydrolase gene and its association with lung cancer risk

A Bibliometric Analysis of Comorbidity of COPD and Lung Cancer: Research Status and Future Directions

Objective

Although studies on the association between COPD and lung cancer are of great significance, no bibliometric analysis has been conducted in the field of their comorbidity. This bibliometric analysis explores the current situation and frontier trends in the field of COPD and lung cancer comorbidity, and to lay a new direction for subsequent research.

Methods

Articles in the field of COPD and cancer comorbidity were retrieved from Web of Science Core Collections (WoSCC) from 2004 to 2023, and analyzed by VOSviewer, CiteSpace, Biblimatrix and WPS Office.

Results

In total, 3330 publications were included. The USA was the leading country with the most publications and great influence. The University of Groningen was the most productive institution. Edwin Kepner Silverman was the most influential scholar in this field. PLOS One was found to be the most prolific journal. Mechanisms and risk factors were of vital importance in this research field. Environmental pollution and pulmonary fibrosis may be future research prospects.

Conclusion

This bibliometric analysis provided new guidance for the development of the field of COPD and lung cancer comorbidity by visualizing current research hotspots, and predicting possible hot research directions in the future.

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.

Regulation of cardiovascular biology by microsomal epoxide hydrolase

Microsomal epoxide hydrolase/epoxide hydrolase 1 (mEH/EPHX1) works in conjunction with cytochromes P450 to metabolize a variety of compounds, including xenobiotics, pharmaceuticals and endogenous lipids. mEH has been most widely studied for its role in metabolism of xenobiotic and pharmaceutical compounds where it converts hydrophobic and reactive epoxides to hydrophilic diols that are more readily excreted. Inhibition or genetic disruption of mEH can be deleterious in the face of many industrial, environmental or pharmaceutical exposures and EPHX1 polymorphisms are associated with the development of exposure-related cancers. The role of mEH in endogenous epoxy-fatty acid (EpFA) metabolism has been less well studied. In vitro, mEH metabolizes most EpFAs at a far slower rate than soluble epoxide hydrolase (sEH) and has thus been generally considered to exert a minor role in EpFA metabolism in vivo. Indeed, sEH inhibitors or sEH-deficiency increase EpFA levels and are protective in animal models of cardiovascular disease. Recently, however, mEH was found to have a previously unrecognized and substantial role in EpFA metabolism in vivo. While few studies have examined the role of mEH in cardiovascular homeostasis, there is now substantial evidence that mEH can regulate cardiovascular function through regulation of EpFA metabolism. The discovery of a prominent role for mEH in epoxyeicosatrienoic acid (EET) metabolism, in particular, suggests that additional studies on the role of mEH in cardiovascular biology are warranted.

Genetic Determinants of 1,3-Butadiene Metabolism and Detoxification in Three Populations of Smokers with Different Risks of Lung Cancer

Background: 1,3-Butadiene (BD) is an important carcinogen in tobacco smoke that undergoes metabolic activation to DNA-reactive epoxides. These species can be detoxified via glutathione conjugation and excreted in urine as the corresponding N-acetylcysteine conjugates. We hypothesize that single nucleotide polymorphisms (SNPs) in BD-metabolizing genes may change the balance of BD bioactivation and detoxification in White, Japanese American, and African American smokers, potentially contributing to ethnic differences in lung cancer risk.Methods: We measured the levels of BD metabolites, 1- and 2-(N-acetyl-L-cysteine-S-yl)-1-hydroxybut-3-ene (MHBMA) and N-acetyl-S-(3,4-dihydroxybutyl)-L-cysteine (DHBMA), in urine samples from a total of 1,072 White, Japanese American, and African American smokers and adjusted these values for body mass index, age, batch, and total nicotine equivalents. We also conducted a genome-wide association study to identify genetic determinants of BD metabolism.Results: We found that mean urinary MHBMA concentrations differed significantly by ethnicity (P = 4.0 × 10-25). African Americans excreted the highest levels of MHBMA followed by Whites and Japanese Americans. MHBMA levels were affected by GSTT1 gene copy number (P < 0.0001); conditional on GSTT1, no other polymorphisms showed a significant association. Urinary DHBMA levels also differed between ethnic groups (P = 3.3 × 10-4), but were not affected by GSTT1 copy number (P = 0.226).Conclusions:GSTT1 gene deletion has a strong effect on urinary MHBMA levels, and therefore BD metabolism, in smokers.Impact: Our results show that the order of MHBMA levels among ethnic groups is consistent with their respective lung cancer risk and can be partially explained by GSTT1 genotype. Cancer Epidemiol Biomarkers Prev; 26(7); 1034-42. ©2017 AACR.

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.

Microsomal epoxide hydrolase (EPHX1) polymorphisms are associated with aberrant promoter methylation of ERCC3 and hematotoxicity in benzene-exposed workers

Benzene is an important industrial chemical and widespread environmental pollutant known to induce leukemia and other blood disorders. To be carcinogenic, benzene must be metabolized to produce toxic metabolites. To investigate whether single nucleotide polymorphisms (SNPs) in the metabolic enzyme genes are associated with benzene-induced alterations in DNA methylation and hematotoxicity, we genotyped four commonly studied SNPs in three metabolic enzymes genes CYP1A1, EPHX1 and NQO1; and analyzed promoter DNA methylation status in 11 genes which have been reported to be associated with benzene-induced hematotoxicity (BLM, CYP1A1, EPHX1, ERCC3, NQO1, NUDT1, p15, p16, RAD51, TP53 and WRAP53) in 77 benzene-exposed workers and 25 unexposed controls in China. ERCC3, a DNA repair gene, showed a small but statistically significant increase of promoter DNA methylation in the exposed group compared with the unexposed group (mean ± SD: 4.73 ± 3.46% vs. 3.63 ± 1.96%, P = 0.048). We also observed that an increased number of C allele for rs1051740 in EPHX1 was associated with decreased ERCC3 methylation levels in benzene-exposed workers (P(trend)  = 0.001), but not in unexposed controls (P(trend)  = 0.379). Interestingly, another EPHX1 SNP (rs2234922) was associated with lower white blood cell (WBC) counts (P(trend)  = 0.044) in benzene-exposed workers. These associations remained the same when ERCC3 promoter methylation and WBCs were dichotomized according to the 90th percentile (≥6%) of methylation levels in controls and a leucopenia cutoff (<4 × 10(9) /L), respectively. Our findings suggest that benzene exposure may be associated with hypermethylation in ERCC3, and that genetic variants in EPHX1 may play an important role in epigenetic changes and hematotoxicity among benzene-exposed workers.

Association between microsomal epoxide hydrolase 1 T113C polymorphism and susceptibility to lung cancer

Previous case-control studies assessing the association between microsomal epoxide hydrolase 1 (EPHX1) T113C and susceptibility to lung cancer reported conflicting results. Thus, a systemic review and meta-analysis of published studies were performed to assess the possible association. PubMed and Embase databases were searched for all eligible studies. The strength of the association between EPHX1 T113C polymorphism and lung cancer risk was estimated by the pooled odds ratios (ORs) with its 95 % confidence interval. Twenty-four individual case-control studies involving a total of 4,970 lung cancer cases and 8,917 controls were finally included into the meta-analysis. When all 24 studies were included into the meta-analysis, the pooled results suggested that there was no association between EPHX1 T113C polymorphism and lung cancer risk under all four comparison models, and all P values for the pooled ORs were more than 0.05. In the subgroup analysis of Caucasians, the pooled results suggested that EPHX1 T113C polymorphism was associated with decreased risk of lung cancer under all four comparison models, and all P values for the pooled ORs were less than 0.05. However, in the subgroup analysis of Asians, the pooled results suggested that EPHX1 T113C polymorphism was associated with increased risk of lung cancer under three comparison models, and all P values for the pooled ORs were less than 0.05. There was no risk of publication bias. This current meta-analysis suggests that EPHX1 T113C polymorphism is associated with lung cancer risk, and there is an obvious race-specific effect in the association.

Genetic susceptibility to lung cancer--light at the end of the tunnel?

Lung cancer is one of the most common and deadliest cancers in the world. The major socio-environmental risk factor involved in the development of lung cancer is cigarette smoking. Additionally, there are multiple genetic factors, which may also play a role in lung cancer risk. Early work focused on the presence of relatively prevalent but low-penetrance alterations in candidate genes leading to increased risk of lung cancer. Development of new technologies such as genomic profiling and genome-wide association studies has been helpful in the detection of new genetic variants likely involved in lung cancer risk. In this review, we discuss the role of multiple genetic variants and review their putative role in the risk of lung cancer. Identifying genetic biomarkers and patterns of genetic risk may be useful in the earlier detection and treatment of lung cancer patients.

Microsomal epoxide hydrolase polymorphisms, cigarette smoking, and risk of colorectal cancer: the Fukuoka Colorectal Cancer Study

Microsomal epoxide hydrolase (EPHX1) plays an important role in the activation and detoxification of polycyclic aromatic hydrocarbons, carcinogens found in cigarette smoke. Polymorphisms in exon 3 (Y113H) and exon 4 (H139R) of the EPHX1 have been associated with enzyme activity. We investigated the risk of colorectal cancer in relation to the EPHX1 Y113H and H139R polymorphisms and assessed effect modifications of cigarette smoking and the other covariates. The interaction between the EPHX1 polymorphisms and selected genetic polymorphisms was also examined. We used data from Fukuoka Colorectal Cancer Study, a community-based case-control study, including 685 cases and 778 controls. In-person interviews were conducted to assess lifestyle factors. The EPHX1 Y113H and H139R polymorphisms were determined by the TaqMan assay and the polymerase chain reaction-restriction fragment length polymorphism, respectively. Neither of the two polymorphisms nor the imputed EPHX1 phenotype was associated with colorectal cancer risk. Cigarette smoking and alcohol intake showed no effect modification on the association with the EPHX1 polymorphisms or the imputed EPHX1 phenotype. Increased risks of colorectal cancer associated with the 113Y allele and imputed EPHX1 phenotype were observed among individuals with high body mass index (BMI; ≥25.0 kg/m(2)), but not among those with low BMI (<25.0 kg/m(2)). The risk decreased with an increasing number of the 139R allele in the null genotypes of GSTM1/GSTT1. It is unlikely that the EPHX1 polymorphisms play an important role in colorectal carcinogenesis. The observed interactions of the EPHX1 polymorphisms with BMI and the GSTM1/GSTT1 genotypes warrant further investigation.

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.

Genetic polymorphism in metabolism and host defense enzymes: implications for human health risk assessment

Genetic polymorphisms in xenobiotic metabolizing enzymes can have profound influence on enzyme function, with implications for chemical clearance and internal dose. The effects of polymorphisms have been evaluated for certain therapeutic drugs but there has been relatively little investigation with environmental toxicants. Polymorphisms can also affect the function of host defense mechanisms and thus modify the pharmacodynamic response. This review and analysis explores the feasibility of using polymorphism data in human health risk assessment for four enzymes, two involved in conjugation (uridine diphosphoglucuronosyltransferases [UGTs], sulfotransferases [SULTs]), and two involved in detoxification (microsomal epoxide hydrolase [EPHX1], NADPH quinone oxidoreductase I [NQO1]). This set of evaluations complements our previous analyses with oxidative and conjugating enzymes. Of the numerous UGT and SULT enzymes, the greatest likelihood for polymorphism effect on conjugation function are for SULT1A1 (*2 polymorphism), UGT1A1 (*6, *7, *28 polymorphisms), UGT1A7 (*3 polymorphism), UGT2B15 (*2 polymorphism), and UGT2B17 (null polymorphism). The null polymorphism in NQO1 has the potential to impair host defense. These highlighted polymorphisms are of sufficient frequency to be prioritized for consideration in chemical risk assessments. In contrast, SNPs in EPHX1 are not sufficiently influential or defined for inclusion in risk models. The current analysis is an important first step in bringing the highlighted polymorphisms into a physiologically based pharmacokinetic (PBPK) modeling framework.

Review of studies on metabolic genes and cancer in populations of African descent

Genetic polymorphisms described for a number of enzymes involved in the metabolism of tobacco carcinogens and alcohol have been linked to increase cancer risk. Racial disparities in cancer between whites and populations of African descent are well documented. In addition to differences in access to health care, both environment and genetic factors and their interaction may contribute to the increased cancer risk in minority populations. We reviewed the literature to identify case-control studies that included subjects of African descent. Meta-analyses investigating the association of genetic polymorphisms in tobacco metabolic genes and cancer were performed. Although several genes and cancers have been studied, only one or two studies per gene for each cancer site have been published, with the exception of breast (CYP1A1 and CYP1B1), lung (GSTM1, CYP1A1, and NQO1), and prostate (CYP3A4 A293G and CYP17). Marginal statistically significant associations were observed for CYP3A4 A293G and CYP17 5'UTR polymorphisms and prostate cancer. Our findings support the need for additional genetic association studies of breast, prostate, and lung cancers that include a larger number of minority participants. Because incidence and mortality rates for these cancers rank highest among populations of African descent, concentrated research in these areas are warranted.

Tobacco, Genetic Susceptibility and Lung cancer

Exposure to tobacco smoke is an established risk factor for lung cancer, although a possible role for genetic susceptibility in the development of lung cancer has been inferred from familial clustering of the disease and segregation analysis. Findings of familial aggregation and statistical evidence for a major susceptibility gene have led to the search for high penetrant, rare, single genes and low penetrant, high frequency susceptibility genes for lung cancer. The relatively small number of linkage studies conducted to date, have identified potential lung cancer susceptibility loci on chromosomes 6q, 12p, and 19q. A variety of studies have examined single nucleotide polymorphisms of several low penetrant, high frequency genes encoding for enzymes involved in the metabolism of carcinogens and DNA damage repair, as likely candidate susceptibility genes. These studies have produced somewhat conflicting findings and, when significant, only modest associations have been reported. Relatively few studies have looked for potential gene-environment interactions, explored associations between two or more genetic polymorphisms or evaluated interactions between genetic polymorphisms and endogenous risk factors. Few large scale genome wide association studies conducted recently have provided evidence that common variation on chromosome 15q25.1, 5p15.33 and 6p21.33 influences lung cancer risk and cancer types with strong environmental risk factors. It is hoped that newer research strategies, selecting candidate genes within pathways and genotype at multiple markers within a gene, employing new technologies, may allow complete coverage of the variation within candidate genes in multiple pathways and to unravel the genetic susceptibility to lung cancer. This knowledge could, in turn, be used to identify persons at risk, to individualize treatments such as chemoprevention, to personalize harms of smoking and to motivate cessation.

Association between polymorphisms of microsomal epoxide hydrolase and COPD: results from meta-analyses

BACKGROUND AND OBJECTIVE

COPD is a complex polygenic disease in which gene-environment interactions are very important. The gene encoding microsomal epoxide hydrolase (EPHX1) is one of several candidate loci for COPD pathogenesis and is highly polymorphic. Based chi on the polymorphisms of EPHX1 gene (tyrosine/histidine 113, histidine/arginine 139), the population can be classified into four groups of putative EPHX1 phenotypes (fast, normal, slow and very slow). A number of studies have investigated the association between the genotypes and phenotypes of EPHX1 and COPD susceptibility in different populations, with inconsistent results. A systematic review and meta-analysis of the published data was performed to gain a clearer understanding of this association.

METHODS

The MEDLINE database was searched for case-control studies published from 1966 to August 2007. Data were extracted and pooled odds ratios (OR) with 95% confidence intervals (CI) were calculated.

RESULTS

Sixteen eligible studies, comprising 1847 patients with COPD and 2455 controls, were included in the meta-analysis. The pooled result showed that the EPHX1 113 mutant homozygote was significantly associated with an increased risk of COPD (OR 1.59, 95% CI: 1.14-2.21). Subgroup analysis supported the result in the Asian population, but not in the Caucasian population. When the analysis was limited to only the larger-sample-size studies, studies in which controls were in Hardy-Weinberg equilibrium and studies in which controls were smokers/ex-smokers, the pooled results supported the conclusion. The EPHX1 139 heterozygote protected against the development of COPD in the Asian population, but not in the Caucasian population. The other gene types of EPHX1 113 and EPHX1 139 were not associated with an increased risk of COPD. The slow activity phenotype of EPHX1 was associated with an increased risk of COPD. The fast activity phenotype of EPHX1 was a protective factor for developing COPD in the Asian population, but not in the Caucasian population. However, the very slow activity phenotype of EPHX1 was a risk for developing COPD in the Caucasian population, but not in the Asian population.

CONCLUSIONS

The polymorphisms of EPHX1 113 and EPHX1 139 are genetic contributors to COPD susceptibility in Asian populations. The phenotypes of EPHX1 were contributors to overall COPD susceptibility.

Polymorphism of selected enzymes involved in detoxification and biotransformation in relation to lung cancer

Available data indicate that there are significant differences in individual susceptibility to lung cancer within the human population. It is believed to be underlie by inherited genetic predispositions related to the genetic polymorphism of several enzymes involved in the detoxification and xenobiotic metabolism. In this review, we collect and discuss the evidence reported up to date on the association between lung cancer and genetic polymorphism of cytochromes P450, N-acetyltransferase, glutathione S-transferases, microsomal epoxide hydrolase, NAD(P)H:quinone oxidoreductase, myeloperoxidase and glutathione peroxidase. All these genes might appear to be candidates for lung cancer susceptibility genes, nevertheless, the present state of the art still offers only a limited explanation of the link between such polymorphisms and increased risk of lung cancer.

Lung carcinoma in African Americans

Lung carcinoma is the most commonly diagnosed cancer and the leading cause of cancer deaths in the US. It accounts for 12% of all cancers diagnosed worldwide, making it the most common malignancy, other than nonmelanoma skin cancer. A new focus has emerged involving the role of race and ethnicity in lung carcinoma. Current health statistics data demonstrate striking disparities, which are most evident between African American patients and their white counterparts. This disparity is greatest among male patients, where statistically significant differences are seen not only in lung cancer incidence and risk, but also in survival and treatment outcomes. Several hypotheses that attempt to explain this disparity include genetic, cultural and socioeconomic differences, in addition to differences in tobacco use and exposure. Current evidence does not clearly identify the reasons for this observed disparity, or the role the aforementioned factors play in the development and overall outcomes of people with lung cancer in these populations. This disease continues to pose a considerable public health burden and more research is needed to improve understanding of the disparity of lung carcinoma statistics among African Americans. This review summarizes the existing body of knowledge regarding lung carcinoma in African Americans and attempts to identify promising areas for future investigation and intervention.

Xenobiotic-metabolizing enzymes involved in activation and detoxification of carcinogenic polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental carcinogens and metabolized by a variety of xenobiotic-metabolizing enzymes such as cytochrome P450 (P450 or CYP), epoxide hydrolase, glutathione transferase, UDP-glucuronosyltransferase, sulfotransferase, NAD(P)H quinone oxidoreductase 1, and aldo-keto reductase. These enzymes mainly participate in the conversion of PAHs to more polar and water-soluble metabolites, and the resultant metabolites are readily excreted from the body. However, during the course of metabolism, a variety of unstable and reactive intermediates of PAHs are formed, and these metabolites attack DNA, causing cell toxicity and transformation. P450s and epoxide hydrolase convert PAHs to proximate carcinogenic metabolites, PAH-diols, and these products are further metabolized by P450s to ultimate carcinogenic metabolites, PAH diol-epoxides, or by aldo-keto reductase to reactive PAH o-quinones. PAHs are also activated by P450 and peroxidases to reactive radical cations that bind covalently to DNA. The oxygenated and reactive metabolites of PAHs are usually converted to more polar and detoxified products by phase II enzymes. Inter-individual differences exist in levels of expression and catalytic activities of a variety of enzymes that activate and/or detoxify PAHs in various organs of humans and these phenomena are thought to be critical in understanding the basis of individual differences in response to PAHs. Factors affecting such variations include induction and inhibition of enzymes by diverse chemicals and, more importantly, genetic polymorphisms of enzymes in humans.

Familial lung cancer: genetic susceptibility and relationship to chronic obstructive pulmonary disease

Lung cancer continues to be the leading cause of cancer death, and although most lung cancer is attributable to cigarette smoking, underlying genetic susceptibility is suggested by studies demonstrating familial aggregation. The first family linkage study of lung cancer has identified linkage of lung, laryngeal, and pharyngeal cancer in families to a region on chromosome 6q23-25. Because lung cancer and chronic obstructive pulmonary disease (COPD) are known to aggregate in families beyond shared risk associated with smoking, the linkage results are compared and contrasted with results from genomewide linkage and association studies and candidate gene studies searching for genes for lung cancer, lung function, and COPD. Linkage on chromosome 6q to both lung cancer and lung function, and on 12 to lung cancer, COPD, and lung function, together with overlap in candidate genes for these outcomes, suggests that future research into underlying genetic mechanisms of lung disease would benefit from broadening the collection of family history data and better defining the "high risk" population. As familial risk of lung disease is better defined, referral into screening programs and prevention trials can be better targeted to reach families with both a history of lung cancer and COPD.

Polymorphisms for microsomal epoxide hydrolase and genetic susceptibility to COPD

Although smoking is the major causal factor in the development of chronic obstructive pulmonary disease (COPD), only 10-20% of chronic heavy cigarette smokers develop symptomatic COPD, which suggests the presence of genetic susceptibility. The human microsomal epoxide hydrolase (EH) is a metabolizing enzyme which involves the process of numerous reactive epoxide intermediates and contains polymorphic alleles which are associated with altered EH activity and may be linked to increased risk for COPD. To determine whether the EH polymorphisms contributed to increased risk for COPD, prevalence of the EH codons 113 and 139 polymorphisms were compared between COPD patients and controls by a PCR-RFLP analysis using genomic DNA isolated from 131 COPD patients and 262 individually matched controls by age (+/-5 years) among Caucasians with 2:1 ratio. Significantly increased risk for COPD was observed for subjects with the EH(113His/His) genotypes (OR=2.4, 95% CI=1.1-5.1). These results were consistent with the fact that a significant trend towards increased risk was observed with predicted less protective EH codon 113 genotypes (p=0.03, trend test). A similar association was not observed for EH codon 139 polymorphism. As expected, a significant correlation between smoking dose and severity of COPD was observed (p<0.001). These results suggest that EH codon 113 polymorphism may modify risk for COPD.