An Rsa I polymorphism in the CYP2E1 gene does not affect lung cancer risk in a Japanese population

Alcoholic Liver Disease: Alcohol Metabolism, Cascade of Molecular Mechanisms, Cellular Targets, and Clinical Aspects

Alcoholic liver disease is the result of cascade events, which clinically first lead to alcoholic fatty liver, and then mostly via alcoholic steatohepatitis or alcoholic hepatitis potentially to cirrhosis and hepatocellular carcinoma. Pathogenetic events are linked to the metabolism of ethanol and acetaldehyde as its first oxidation product generated via hepatic alcohol dehydrogenase (ADH) and the microsomal ethanol-oxidizing system (MEOS), which depends on cytochrome P450 2E1 (CYP 2E1), and is inducible by chronic alcohol use. MEOS induction accelerates the metabolism of ethanol to acetaldehyde that facilitates organ injury including the liver, and it produces via CYP 2E1 many reactive oxygen species (ROS) such as ethoxy radical, hydroxyethyl radical, acetyl radical, singlet radical, superoxide radical, hydrogen peroxide, hydroxyl radical, alkoxyl radical, and peroxyl radical. These attack hepatocytes, Kupffer cells, stellate cells, and liver sinusoidal endothelial cells, and their signaling mediators such as interleukins, interferons, and growth factors, help to initiate liver injury including fibrosis and cirrhosis in susceptible individuals with specific risk factors. Through CYP 2E1-dependent ROS, more evidence is emerging that alcohol generates lipid peroxides and modifies the intestinal microbiome, thereby stimulating actions of endotoxins produced by intestinal bacteria; lipid peroxides and endotoxins are potential causes that are involved in alcoholic liver injury. Alcohol modifies SIRT1 (Sirtuin-1; derived from Silent mating type Information Regulation) and SIRT2, and most importantly, the innate and adapted immune systems, which may explain the individual differences of injury susceptibility. Metabolic pathways are also influenced by circadian rhythms, specific conditions known from living organisms including plants. Open for discussion is a 5-hit working hypothesis, attempting to define key elements involved in injury progression. In essence, although abundant biochemical mechanisms are proposed for the initiation and perpetuation of liver injury, patients with an alcohol problem benefit from permanent alcohol abstinence alone.

Cytochrome P450 in Cancer Susceptibility and Treatment

Cytochrome 450 (CYP450) designates a group of enzymes abundant in smooth endoplasmic reticulum of hepatocytes and epithelial cells of small intestines. The main function of CYP450 is oxidative catalysis of various endogenous and exogenous substances. CYP450 are implicated in phase I metabolism of 80% of drugs currently in use, including anticancer drugs. They are also involved in synthesis of various hormones and influence hormone-related cancers. CYP450 genes are highly polymorphic and their variants play an important role in cancer risk and treatment. Association studies and meta-analyses have been performed to decipher the role of CYP450 polymorphisms in cancer susceptibility. Cancer treatment involves multimodal therapies and evaluation of CYP450 polymorphisms is necessary for pharmacogenetic assessment of anticancer therapy outcomes. In addition, CYP450 inhibitors are being evaluated for improved pharmacokinetics and oral formulation of several anticancer drugs.

CYP2E1 Rsa Ι/Pst Ι polymorphism and lung cancer susceptibility: a meta-analysis involving 10,947 subjects

Many studies have examined the association between the CYP2E1 Rsa Ι/Pst Ι (rs3813867) polymorphism gene polymorphisms and lung cancer risk in various populations, but their results have been inconsistent. The PubMed and CNKI database was searched for case–control studies published up to October 2013. Data were extracted and pooled odds ratios (OR) with 95% confidence intervals (CI) were calculated. In this meta-analysis, we assessed 23 published studies involving comprising 4727 lung cancer cases and 6220 controls of the association between CYP2E1 Rsa Ι/Pst Ι polymorphism and lung cancer risk. For the homozygote c2/c2 and c2 allele carriers (c1/c2 + c2/c2), the pooled ORs for all studies were 0.73(95% CI = 0.62–0.84; P = 0.005 for heterogeneity) and 0.84 (95% CI = 0.77–0.92; P = 0.001 for heterogeneity) when compared with the homozygous wild-type genotype (c1/c1). In the stratified analysis by ethnicity, the same significantly risks were found among Asians and mixed population for both the c2 allele carriers and homozygote c2/c2. However, no significant associations were found in Caucasian population all genetic models. This updated meta-analysis suggests that CYP2E1 Rsa Ι/Pst Ι c2 allele is a decreased risk factor for the developing lung cancer among Asians and mixed population.

The polymorphism of CYP2E1 Rsa I/Pst I gene and susceptibility to respiratory system cancer: a systematic review and meta-analysis of 34 studies

The purpose of this articles is to determine whether the cytochrome P450 2E1 (CYP2E1) Rsa I/Pst I gene polymorphism is correlated with respiratory system cancers. Respiratory system cancers included lung cancer, laryngeal cancer, nasopharyngeal cancer, and cancers of other respiratory organs, which are the most common malignant tumors worldwide; the significant relationship between CYP2E1 Rsa I/Pst I gene polymorphism and some respiratory system cancer have been reported, but results of some other studies are controversial. The pooled odds ratio (OR) with 95% confidence interval (CI) was calculated to assess the association. PubMed, EMBASE, Cochrane Library Databases, China National Knowledge Infrastructure, and Wanfang Database (up to July 20, 2014) were searched for all case-control studies those mainly studied the relationship between CYP2E1 Rsa I/Pst I gene polymorphism and the susceptibility of respiratory system cancer. A total of 332 articles were collected, among which 34 studies that involved 7028 cases and 9822 controls fulfilled the inclusion criteria after being assessed by 2 reviewers. When stratified by cancer site, the C2/C2 polymorphism could increase the risk of nasopharyngeal cancer under the homozygote model (C2C2 vs C1C1: OR = 1.85, 95% CI = 1.20-2.85, P = 0.005) and recessive model (C2C2 vs C1C2/C1C1: OR = 1.89, 95% CI = 1.23-2.89, P = 0.003). Protection effect was found in lung cancer in heterozygote model (C1C2 vs C1C1: OR = 0.82, 95% CI = 0.74-0.91, P < 0.001), dominant model (C1C2/C2C2 vs C1C1: OR = 0.83, 95% CI = 0.76-0.90, P < 0.001), and allele contrast model (C2 vs C1: OR = 0.85, 95% CI = 0.73-1.00, P = 0.045). With regard to ethnicity subgroup analysis, there was significant association in Asian population in heterozygote model (C1C2 vs C1C1: OR = 0.85, 95% CI = 0.78-0.94, P = 0.001), dominant model (C1C2/C2C2 vs C1C1: OR = 0.88, 95% CI = 0.81-0.95, P = 0.001), and recessive model (C2C2 vs C1C2/C1C1: OR = 1.25, 95% CI = 1.01-1.53, P = 0.036). CYP2E1 Rsa I/Pst I gene polymorphism may reduce the risk of respiratory system cancer. Furthermore, significant association was also found in Asian populations.

Role and importance of polymorphisms with respect to DNA methylation for the expression of CYP2E1 enzyme

Different individuals possess slightly different genetic information and show genetically-determined differences in several enzyme activities due to genetic variability. Following an integrated approach, we studied the polymorphisms and methylation of sites contained in the 5' flanking region of the metabolizing enzyme CYP2E1 in correlation to its expression in both tumor and non-neoplastic liver cell lines, since to date little is known about the influence of these (epi)genetic elements in basal conditions and under induction by the specific inductor and a demethylating agent. In treated cells, reduced DNA methylation, assessed both at genomic and gene level, was not consistently associated with the increase of enzyme expression. Interestingly, the Rsa/Pst haplotype differentially influenced CYP2E1 enzyme expression. In addition, regarding the Variable Number of Tandem Repeats polymorphism, cells with A4/A4 genotype showed a greater expression inhibition (ranging from 20% to 30%) compared with others carrying the A2/A2 one, while those cells bringing A2/A3 genotype showed an increase of expression (of 25%, about). Finally, we demonstrated for the first time that the A2 and A3 CYP2E1 alleles play a more important role in the expression of the enzyme, compared with other (epi)genetic factors, since they are binding sites for trans-acting proteins.

CYP2E1 Rsa I/Pst I polymorphism is associated with lung cancer risk among Asians

The genetic polymorphism of CYP2E1 Rsa I/Pst I is thought to have significant effect on lung cancer risk, but the results are inconsistent. In this meta-analysis, we assessed 21 published studies involving 9380 subjects of the association between CYP2E1 Rsa I/Pst I polymorphism and lung cancer risk. For the homozygote c2/c2 and c2 allele carriers (c1/c2+c2/c2), the pooled ORs for all studies were 0.734 (95% CI=0.628-0.847; P=0.035 for heterogeneity) and 0.852 (95% CI=0.777-0.933; P=0.004 for heterogeneity) when compared with the homozygous wild-type genotype (c1/c1). In the stratified analysis by ethnicity, the same significant risks were found among Asians for both the c2 allele carriers and homozygote c2/c2. Among mixed populations, only significant risk was associated with c2 allele carriers. No significant associations were found in all Caucasians genetic models. In the subgroup analyses by pathological types, for lung SC the ORs of the c2 allele carriers and the homozygote c2/c2 were 0.749 (95% CI=0.683-0.813; P=0.247 for heterogeneity) and 0.726 (95% CI=0.662-0.847; P=0.006 for heterogeneity), respectively. In the subgroup analyses by smoking status, there were no significant associations among smokers or non-smokers subgroup. This meta-analysis suggests that CYP2E1 Rsa I/Pst I c2 allele is a decreased risk factor for the developing lung cancer among Asians and lung SC.

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.

Genetic polymorphisms of CYP2E1 and risk of colorectal adenomas in the Self Defense Forces Health Study

CYP2E1 is an enzyme involved in the metabolism of N-nitrosamines and other carcinogenic substances. Functional RsaI and 96-bp insertion polymorphisms in 5'-flanking region have drawn interest in relation to the risk of colorectal cancer. We investigated the relation of these genetic polymorphisms and colorectal adenoma, a well-established precursor lesion of colorectal cancer. Subjects were 455 cases of colorectal adenomas and 1,052 controls of normal colonoscopy among men receiving a preretirement health examination in the Self Defense Forces. Genotypes were determined by either PCR-RFLP or PCR method. Statistical adjustment was made for smoking, alcohol use, body mass index, physical activity, and others. Individuals with RsaI c2 allele showed a decreased risk of proximal colon adenomas; adjusted odds ratios (95% confidence interval) of proximal and distal adenomas for the c1/c2 or c2/c2 genotype versus c1/c1 was 0.61 (0.41-0.88) and 0.95 (0.71-1.27), respectively. CYP2E1 96-bp insertion allele was associated with an increased risk of large (> or = 5 mm) adenomas; adjusted odds ratios (95% confidence interval) of large and small adenomas for having at least one insertion allele were 1.41 (1.03-1.94) and 0.94 (0.71-1.25), respectively. A suggestive effect modification was noted for alcohol consumption on the association between RsaI polymorphism and proximal adenomas (P(interaction) = 0.09) as well as on the association between 96-bp insertion and large adenomas (P(interaction) = 0.05). These findings indicate that variation in activity and inducibility of CYP2E1 contribute to the development of colorectal carcinogenesis.

Susceptibility to lung cancer and genetic polymorphisms in the alcohol metabolite-related enzymes alcohol dehydrogenase 3, aldehyde dehydrogenase 2, and cytochrome P450 2E1 in the Japanese population

BACKGROUND

It is believed that acetaldehyde plays an important role in alcohol-related carcinogenesis; although current epidemiologic studies have provided inconsistent findings on the association between alcohol consumption and the risk of lung cancer.

METHODS

To clarify the hypothesis that genetic polymorphisms in alcohol-metabolizing enzymes may influence susceptibility to lung cancer, the authors conducted a hospital-based case-control study and examined genetic polymorphisms in the alcohol dehydrogenase 3, aldehyde dehydrogenase 2 (ALDH(2)), and cytochrome P450 2E1 genes in 505 patients with histologically confirmed lung cancer and in a group of 256 noncancer controls who provided complete cigarette and alcohol consumption histories. Genotyping was conducted by polymerase chain reaction-restriction fragment-length polymorphism assay.

RESULTS

A significant association was noted between alcohol consumption and lung cancer risk. Thus, using the median value for the controls as the cut-off point, the odds ratios (OR) for light and heavy drinkers were 1.76 and 1.95, respectively (P for trend = .012), compared with nondrinkers. In addition, there was a significant trend toward increased risk of lung cancer in drinkers with ALDH(2) variant alleles (P for trend <.0001). The adjusted OR for heavy drinkers was 6.15 compared with nondrinkers. Regarding associations between histologic type and genotypes, the ALDH(2) variant allele was significantly less common in patients who had adenocarcinoma compared with controls.

CONCLUSIONS

The current observations suggested a positive association between alcohol consumption and the risk of lung cancer: Drinking may increase the risk, especially among individuals who have the variant ALDH(2) alleles.

Gene-environmental interactions between alcohol-drinking behavior and ALDH2 and CYP2E1 polymorphisms and their impact on micronuclei frequency in human lymphocytes

Ethanol is converted to acetaldehyde by alcohol dehydrogenase (ADH), cytochrome p4502E1 (CYP2E1) and catalase. This metabolite is then detoxified by aldehyde dehydrogenase 2 (ALDH2), a key enzyme in the elimination of acetaldehyde, via further oxidation to acetic acid. The toxic effects of acetaldehyde are well documented and may be partially mediated by genotoxic damage. In the present study, we investigated the effects of alcohol-drinking behavior and genetic polymorphisms in two different genes (ALDH2 and CYP2E1) on the micronuclei (MN) frequency in 248 healthy Japanese men. Genotyping was performed by PCR-RFLP analysis. The ALDH2 variant (deficient type) was significantly associated with an increased MN frequency in subjects drinking more than three times/wk, while habitual drinkers with wild-type CYP2E1 also had a significantly increased MN frequency. Furthermore, when the subjects were divided into eight groups according to their drinking frequency and genotypes of ALDH2 and CYP2E1, we found that habitual drinkers with homozygous CYP2E1*1/*1 and heterozygous ALDH2*1/*2 or homozygous ALDH2*2/*2 showed the highest mean MN frequency. In the present study, we found clear associations among ALDH2 and CYP2E1 gene polymorphisms, alcohol-drinking behavior and genotoxic effects in a healthy Japanese population. Therefore, analysis of the polymorphisms of alcohol-metabolizing enzymes may lead to elucidation of the mechanism(s) for individual susceptibilities to the toxicity of ethanol metabolites.

Use of duplex PCR-CTPP methods for CYP2E1RsaI/IL-2 T-330G and IL-1B C-31T/TNF-A T-1031C polymorphisms

BACKGROUND

Two duplex polymerase chain reaction (PCR) with confronting two-pair primer (PCR-CTPP) methods were designed for cytochrome P450 (CYP) 2E1 RsaI and interleukin (IL-2) T-330G, and for IL-1B C-31T and tumor necrosis factor-alpha (TNF-A) T-1031C. The four polymorphisms are considered to be functional, and the three cytokines reportedly inhibit CYP2E1 expression. Many studies have reported associations between the above polymorphisms and risk of diseases including cancers and inflammatory diseases.

AIM

The main objective of this study was to examine the applicability of the established PCR conditions to a real situation.

PARTICIPANTS

Participants were female examinees aged from 35 to 85 years who attended health checks run by a local government in Japan.

RESULTS

The allele frequencies among 325 female health check examinees were 0.804 for CYP2E1 c1 allele, 0.668 for IL-2-330T allele, 0.554 for IL-1B-31T allele, and 0.822 for TNF-A-1031T allele. p-Values from a Hardy-Weinberg equilibrium test were 0.658, 0.955, 0.062, and 0.806, respectively.

DISCUSSION

Clear DNA bands observed with electrophoresis allowed us to genotype the four polymorphisms. The genotype frequencies were within the Hardy-Weinberg equilibrium test proportions, though the p-value for IL-1B C-31T was marginal.

CONCLUSIONS

Both duplex PCR-CTPP methods may be useful tools for studies on the association between these polymorphisms and disease risk.

The discovery of the microsomal ethanol oxidizing system and its physiologic and pathologic role

Oxidation of ethanol via alcohol dehydrogenase (ADH) explains various metabolic effects of ethanol but does not account for the tolerance. This fact, as well as the discovery of the proliferation of the smooth endoplasmic reticulum (SER) after chronic alcohol consumption, suggested the existence of an additional pathway which was then described by Lieber and DeCarli, namely the microsomal ethanol oxidizing system (MEOS), involving cytochrome P450. The existence of this system was initially challenged but the effect of ethanol on liver microsomes was confirmed by Remmer and his group. After chronic ethanol consumption, the activity of the MEOS increases, with an associated rise in cytochrome P450, especially CYP2E1, most conclusively shown in alcohol dehydrogenase negative deer mice. There is also cross-induction of the metabolism of other drugs, resulting in drug tolerance. Furthermore, the conversion of hepatotoxic agents to toxic metabolites increases, which explains the enhanced susceptibility of alcoholics to the adverse effects of various xenobiotics, including industrial solvents. CYP2E1 also activates some commonly used drugs (such as acetaminophen) to their toxic metabolites, and promotes carcinogenesis. In addition, catabolism of retinol is accelerated resulting in its depletion. Contrasting with the stimulating effects of chronic consumption, acute ethanol intake inhibits the metabolism of other drugs. Moreover, metabolism by CYP2E1 results in a significant release of free radicals which, in turn, diminishes reduced glutathione (GSH) and other defense systems against oxidative stress which plays a major pathogenic role in alcoholic liver disease. CYP1A2 and CYP3A4, two other perivenular P450s, also sustain the metabolism of ethanol, thereby contributing to MEOS activity and possibly liver injury. CYP2E1 has also a physiologic role which comprises gluconeogenesis from ketones, oxidation of fatty acids, and detoxification of xenobiotics other than ethanol. Excess of these physiological substrates (such as seen in obesity and diabetes) also leads to CYP2E1 induction and nonalcoholic fatty liver disease (NAFLD), which includes nonalcoholic fatty liver and nonalcoholic steatohepatitis (NASH), with pathological lesions similar to those observed in alcoholic steatohepatitis. Increases of CYP2E1 and its mRNA prevail in the perivenular zone, the area of maximal liver damage. CYP2E1 up-regulation was also demonstrated in obese patients as well as in rat models of obesity and NASH. Furthermore, NASH is increasingly recognized as a precursor to more severe liver disease, sometimes evolving into "cryptogenic" cirrhosis. The prevalence of NAFLD averages 20% and that of NASH 2% to 3% in the general population, making these conditions the most common liver diseases in the United States. Considering the pathogenic role that up-regulation of CYP2E1 also plays in alcoholic liver disease (vide supra), it is apparent that a major therapeutic challenge is now to find a way to control this toxic process. CYP2E1 inhibitors oppose alcohol-induced liver damage, but heretofore available compounds are too toxic for clinical use. Recently, however, polyenylphosphatidylcholine (PPC), an innocuous mixture of polyunsaturated phosphatidylcholines extracted from soybeans (and its active component dilinoleoylphosphatidylcholine), were discovered to decrease CYP2E1 activity. PPC also opposes hepatic oxidative stress and fibrosis. It is now being tested clinically.

Metabolism of alcohol

Most tissues of the body contain enzymes capable of ethanol oxidation or nonoxidative metabolism, but significant activity occurs only in the liver and, to a lesser extent, in the stomach. Hence, medical consequences are predominant in these organs. In the liver, ethanol oxidation generates an excess of reducing equivalents, primarily as NADH, causing hepatotoxicity. An additional system, containing cytochromes P-450 inducible by chronic alcohol feeding, was demonstrated in liver microsomes and found to be a major cause of hepatotoxicity.

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.

Association of GSTM1, CYP1A1 and CYP2E1 genetic polymorphisms with susceptibility to lung adenocarcinoma: a case-control study in Chinese population

A case-control study of 164 lung adenocarcinoma (AC) patients with 181 age- and gender-matched healthy controls was conducted in order to assess any associations between glutathione-S-transferase M1 (GSTM1), cytochrome P4501A1 (CYP1A1) and cytochrome P4502E1 (CYP2E1) polymorphisms and susceptibility to lung AC in Chinese. The presence of CYP2E1 variant allele was significantly less frequent in cases than in controls, while the distribution of GSTM1 null genotype and variant CYP1A1 Msp1 allele did not vary between cases and controls. After adjustment for age, gender, smoking and all other genotypes, the CYP2E1 Rsa1 variant allele was significantly associated with decreased risk of lung AC [odds ratio 0.534 (95% confidence interval, 0.340-0.837)]. Furthermore, 3.0-fold increased risk was found in individuals with combined GSTM1 null genotype and CYP2E1 Rsa1 wild type versus those with combined GSTM1 non-null type and CYP2E1 variant allele. Our results suggest that CYP2E1 Rsa1 variant allele is associated with a decreased risk of lung AC, and combined GSTM1 null genotype and CYP2E1 Rsa1 wild type has a promoting effect on susceptibility to lung AC.

Effects of cytochrome P450 (CYP) 2A6 gene deletion and CYP2E1 genotypes on gastric adenocarcinoma

Cytochrome P450 (CYP) 2A6 and CYP2E1 are enzymes with a high ability to activate a nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), to its potent and ultimate carcinogens. The polymorphic CYP2A6 and CYP2E1 have been implicated in increased susceptibility to certain malignancies. In our study, 120 Japanese patients with gastric adenocarcinoma and 158 healthy controls were compared for frequencies of CYP2A6 and CYP2E1 genotypes. The frequency with which the subjects carried homozygotes of the CYP2A6 gene deletion allele, which causes lack of the enzyme activity, was significantly higher in the gastric cancer patients than in the healthy control subjects (OR = 3.14, 95% confidence interval (95% CI) = 1.05-9.41). Subdividing gastric adenocarcinoma according to tumor differentiation, patients with the well-differentiated type were 4.9-fold more likely to have the CYP2A6 homozygote deletion genotype (OR = 4.91, 95% CI 1.17-20.52). Stratifying by smoking status, we did not find the risk of CYP2A6 gene deletion allele in gastric adenocarcinoma. The CYP2E1 polymorphism detected by RsaI was not significantly different between gastric adenocarcinoma patients (40.8%) and the control population (44.3%). No statistically significant changes were observed when the CYP2E1 genotype was examined relative to tumor differentiation and smoking status. These results suggest that the CTY2A6 deletion is associated with gastric adenocarcinoma among Japanese populations.

Genetic polymorphism of enzymes involved in xenobiotic metabolism and the risk of lung cancer

Chronic inhalation of cigarette smoke is a major risk factor for the development of lung cancer. It has been suggested that genetic susceptibility may contribute to the risk, because only a small portion of smokers develops the disease. Several polymorphisms that involve the metabolic activation or detoxification of carcinogens derived from cigarette smoke have been found to be associated with lung cancer risk. Many studies have focused on the relation between the distribution of polymorphic variants of different forms of the metabolic enzymes and lung cancer susceptibility. In this respect two groups of genetic polymorphisms of enzymes involved in xenobiotic metabolism, cytochrome P450 (CYP) and glutathione S-transferases (GSTs), have been discussed.CYP multigene superfamily consists of 10 subfamilies (CYP1-CYP10). A positive association between development of lung cancer and the mutant homozygous genotype ofCYP1A1 gene has been reported in several Japanese populations but such an association has not been observed in either Caucasians or African-Americans. The relation betweenCYP2D6 and lung cancer remains conflicting and inconclusive. Several polymorphisms have been identified at theCYP2E1 locus. No definitive link between the polymorphisms ofCYP2E1 and the risk of lung cancer has, however, been identified. The role of otherCYP2 isoforms in lung carcinogenesis has not been sufficiently investigated.GSTs form a superfamily of genes consisting of five distinct families, namedGSTA, GSTM, GSTP, GSTT andGSTS. The role ofGSTM, GSTT1 orGSTP1 polymorphism in modifying the lung cancer risk may be more limited than has been so far anticipated.Although some genetic polymorphisms discussed here have not shown significant increases/decreases in risk, individuals with differing genotypes may have different susceptibilities to lung cancer. Hopefully, in future studies it will be possible to screen for lung cancer using specific biomarkers.

Cytochrome CYP2E1 phenotyping and genotyping in the evaluation of health risks from exposure to polluted environments

Humans are exposed to over 70,000 man-made chemicals including drugs, food additives, herbicides, pesticides, and industrial agents. It is well established that environmental chemicals are the cause of numerous human diseases including cancer. In most cases, chemical carcinogens require metabolic activation, which is mainly achieved by P450s enzymes. CYP2E1 is of clinical relevance because it is inducible by ethanol, and it metabolizes many common organic solvents such as benzene, alcohols and halogenated solvents. Therefore, alteration in the level of CYP2E1 might influence the health effects of the environmental pollutants. This hypothesis needs to be validated by epidemiological studies and the objective of the "Biomed-2" project was to develop new tests to assess the individual metabolic capacity of workers exposed to volatile organic compounds in order to predict their occupational risk. In vivo chlorzoxazone 6-hydroxylation was validated as a non-invasive and selective test for the determination of liver CYP2E1 activity. Preliminary data in workers exposed to organic solvents indicated that chlorzoxazone metabolism may be a biomarker of occupational exposure to organic solvents. Other approaches, such as use of salicylate as catalytic probe or measurement of catalytic activity in lymphocytes, were not conclusive. Attempts to use CYP2E1 genotyping for estimating human risks from chemical exposure did not bring convincing data as genetic polymorphism of CYP2E1 could not be clearly related to its catalytic activity.

Elucidation of CYP2E1 5' regulatory RsaI/Pstl allelic variants and their role in risk for oral cancer

The CYP2E1 gene, whose protein product plays an important role in the metabolism of various carcinogens, exhibits two polymorphisms recognized by the restriction enzymes RsaI and PstI in its transcriptional regulatory region that have been previously implicated in cancer susceptibility. In this study, we have examined these polymorphisms to elucidate CYP2E1 allelic haplotype, examining the prevalence of these CYP2E1 alleles in Caucasians and African Americans and their potential role in risk for oral cancer. In addition to the c1 (RsaI[+]/PstI[-]) and c2 (RsaI[-]/PstI[+]) alleles reported in previous studies, we have identified two new alleles, c3 (RsaI[+]/PstI[+]) and c4 (RsaI[-]/PstI[-]). The prevalence of the c2 and c3 alleles differs between racial groups, with African Americans exhibiting a lower prevalence of the c2 allele (0.003) but a higher prevalence of the c3 allele (0.049) than Caucasians (0.031 for c2 and 0.004 for c3). Of the 570 subjects screened in this study, the c4 allele was observed in one subject, a Caucasian case with the (c4/c4) genotype. A significant increase in the CYP2E1 (c1/c1) genotype was observed in oral cancer cases as compared to frequency-matched controls in subjects who smoked < or =24 pack-years (P=0.033). No association was observed between CYP2E1 genotype and risk for oral cancer in the heavy-smoking group (i.e. > 24 pack-years). Similar trends were observed for both Caucasians and African Americans. These data suggest that the c1 allele may contribute to increased risk for oral cancer.

Human variability and susceptibility to trichloroethylene

Although humans vary in their response to chemicals, comprehensive measures of susceptibility have generally not been incorporated into human risk assessment. The U.S. EPA dose-response-based risk assessments for cancer and the RfD/RfC (reference dose-reference concentration) approach for noncancer risk assessments are assumed to protect vulnerable human subgroups. However, these approaches generally rely on default assumptions and do not consider the specific biological basis for potential susceptibility to a given toxicant. In an effort to focus more explicitly on this issue, this article addresses biological factors that may affect human variability and susceptibility to trichloroethylene (TCE), a widely used halogenated industrial solvent. In response to Executive Order 13045, which requires federal agencies to make protection of children a high priority in implementing their policies and to take special risks to children into account when developing standards, this article examines factors that may affect risk of exposure to TCE in children. The influence of genetics, sex, altered health state, coexposure to alcohol, and enzyme induction on TCE toxicity are also examined.

Smoking and the molecular epidemiology of lung cancer

Lung carcinogenesis in humans requires exposure to environmental agents, including the inhalation of tobacco smoke, radioactive compounds, asbestos, heavy metals, and petrochemicals. Tobacco smoking is the risk factor with the highest attributable lung cancer risk worldwide. This article discusses occupational carcinogen exposure and exposure from tobacco use, and the lung-cancer risk associated with these types of exposure.

Genetic susceptibility to tobacco carcinogenesis

Lung cancer risk is thus defined by the balance between metabolic activation and detoxification of xenobiotic compounds and by the efficiency of DNA repair. It is most likely that multiple susceptibility factors must be accounted for to represent the true dimensions of gene-environment interactions. The ability to identify smokers with the highest risks of developing cancer has substantial preventive implications. These subgroups could be targeted for the most intensive screening and smoking cessation interventions and could be enrolled into chemoprevention trials. Studying susceptibility to common cancers and widely prevalent exposures may provide further insights into the basic mechanisms of carcinogenesis. Issues that will need to be addressed in the very near future include risk communication to study subjects and the ethical, legal, and social consequences of such testing.

Influence of genetic admixture on polymorphisms of drug-metabolizing enzymes: analyses of mutations on NAT2 and C gamma P2E1 genes in a mixed Hispanic population

OBJECTIVES AND STUDY DESIGN

The genetic basis of two polymorphisms of drug- and carcinogen-metabolizing enzymes, NAT2 (arylamine N-acetyltransferase-2) and CYP2E1 (cytochrome P450 2E1), was studied in genomic deoxyribonucleic acid from 137 healthy, unrelated subjects from a mixed Nicaraguan population.

RESULTS

Six point mutations were identified at the coding region of the NAT2 gene, including the most common alleles NAT2*4 (41.6%), NAT2*5B (31.4%), and NAT2*6A (16.8%). The percentage of carriers of two defective genes was 49.6%. The Nicaraguan population studied was in Hardy-Weinberg's disequilibrium for the NAT2 genotype (p < 0.01) and the allele frequencies were significantly different from those of other populations, being intermediate between those of pure Central American Indians and Spanish persons. The frequency of CYP2E1 alleles mutated at the RsaI site (c2 allele; 16.5%) was intermediate between that of Spanish white and Asian subjects. About 5% of the subjects were homozygous for the c2 allele.

CONCLUSIONS

These findings indicate a high impact of genetic admixture of populations of Asian origin (Central American Indians) and white persons (Spaniards) on the genetic polymorphisms studied here and suggest that among mixed Hispanics a high heterogeneity of genotypes and phenotypes can be expected depending on the degree of genetic admixture of every subgroup. Therefore different subgroups of mixed Hispanic subjects can exhibit different results when treated with drugs that are inactivated through polymorphic enzymes.

Activation of procarcinogens by human cytochrome P450 enzymes

Enzymatic transformation of most chemical carcinogens is requisite to the formation of electrophiles that cause genotoxicity, and the cytochrome P450 (P450) enzymes are the most prominent enzymes involved in such activation reactions. During the past 15 years the human P450 enzymes have been extensively characterized. Considerable evidence exists that the variation in activity of these enzymes can have important consequences in the actions of drugs. Other studies have been concerned with the activation of procarcinogens by human P450s. Assignments of roles of particular P450s in the metabolism of chemical carcinogens are discussed, along with the current state of evidence for relationships of particular P450s with human cancer.

Genetic polymorphisms of tobacco- and alcohol-related metabolizing enzymes and human esophageal squamous cell carcinoma susceptibility

Many human cancers are caused by synthetic or natural chemical compounds in the environment. Esophageal squamous cell carcinoma has been reported to be epidemiologically associated with tobacco and alcohol consumption. We studied the association between genetic polymorphisms of tobacco- and alcohol-related metabolizing enzymes and esophageal squamous cell carcinoma susceptibility. We examined genetic polymorphisms of the CYPIA1, GSTM1, CYPIIE1, ADH2, and ALDH2 genes in 94 Japanese patients with esophageal squamous cell carcinoma and 70 unrelated healthy Japanese persons. There were no significant differences between healthy controls and patients with esophageal cancer in the polymorphisms of the CYPIA1, GSTM1, and CYPIIE1 genes. On the other hand, there were significant differences in the ADH2 and ALDH2 polymorphisms between healthy controls and esophageal cancer patients. The ADH2(1)/ADH2(1) and ALDH2(1)/ALDH2(2) genotypes were independently and significantly higher in esophageal cancer patients than in healthy controls. Furthermore, persons with the combined genotypes ADH2(1)/ADH2(1) and ALDH2(1)/ALDH2(2) were at extraordinarily high risk for esophageal squamous cell carcinoma, with an odds ratio of 17.9 (p < 0.001). Thus polymorphisms of alcohol-metabolizing enzymes, that is, ADH2 and ALDH2, may be useful for screening patients at high risk for esophageal cancer, which might facilitate clarification of esophageal tumorigenesis and prevention of esophageal cancer.