Combined genetic polymorphism and risk for development of lung cancer

Combined effects of glutathione S-transferase M1 and T1 polymorphisms on risk of lung cancer: Evidence from a meta-analysis

Many studies have reported an association between the glutathione S-transferase M1 null and T1 null polymorphisms and lung cancer risk. However, the combined effects of GSTM1 null and GSTT1 null polymorphisms have not been reported previously. We, therefore, performed a meta-analysis to investigate the combined effects. 40 publications with 44 case–control studies were selected in the meta-analysis, including 13,706 cases and 13,093 controls. Significant association was observed between the combined effects of GSTM1 and GSTT1 polymorphisms and lung cancer risk when all the eligible studies were pooled into the meta-analysis. When we performed subgroup analysis, significantly increased lung cancer risk was observed in Caucasians (− − vs. + +: OR = 1.23, 95% CI: 1.07 to 1.41), Asians (− − vs.− +: OR = 1.24, 95% CI: 1.10 to 1.41; recessive model: OR = 1.45, 95% CI: 1.19 to 1.77; dominant model: OR = 1.53, 95% CI: 1.24 to 1.90), Indians (− − vs. + +: OR = 2.53, 95% CI: 1.61 to 3.98; recessive model: OR = 1.69, 95% CI: 1.07 to 2.67; dominant model: OR = 2.11, 95% CI: 1.36 to 3.28), hospital-based studies, and population-based studies. In summary, this meta-analysis indicates that the combined effects of the GSTM1 and GSTT1 polymorphisms are associated with increased lung cancer risk in Asians, Caucasians, and Indians.

Will Genetic Testing for Complex Diseases Increase Motivation to Quit Smoking? Anticipated Reactions in a Survey of Smokers

The aim of this study was to improve understanding of smokers’ potential reactions to genetic testing for smoking-related diseases. One thousand twenty-four respondents completed a postal survey; 186were smokers. Questions addressed anticipated psychological and behavioral reactions to genetic test results using hypothetical scenarios. Of smokers, 65% anticipated being motivated to quit smoking upon receiving a positive genetic test result; 39% anticipated being demotivated by a negative result. More smokers anticipated being depressed in response to receiving a positive result for cancer than for heart disease (40% vs. 24%). Anticipated motivation was associated with higher desire to quit and lower nicotine addiction, anticipated depression with poorer understanding of genetic testing, and anticipated demotivation with lower education. Smokers who have a high desire to quit may use genetic testing as a motivational tool. Understanding of genetics may be important in determining how individuals respond to genetic tests for complex diseases.

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

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

Association between GSTM1, GSTT1, and GSTP1 polymorphisms and lung cancer risk in a Turkish population

Several studies focused on investigating genetic polymorphisms in order to estimate genetic contribution to lung cancer often showed conflicting results. In this study, we investigated the role of GSTM1, GSTT1, GSTP1 exon 5 and exon 6 polymorphisms on developing lung cancer and histological subtypes in 213 lung cancer patients and 231 controls. GSTM1 null, GSTT1 null, and GSTP1 exon 5 variant genotypes did not show a significant risk for developing lung cancer overall. Significant association was noted between GSTP1 exon 6 variant genotypes and overall lung cancer risk (OR 2.17, 95% CI 1.25-3.78; P = 0.006). These results show that GSTP1 exon 6 polymorphism might be an important factor in determining lung cancer susceptibility in a Turkish population.

Common polymorphisms in CYP1A1, GSTM1, GSTT1, GSTP1 and XPD genes and endogenous DNA damage

Endogenous DNA damage levels were analyzed in relation to polymorphisms in genes encoding phase I detoxifying enzyme-CYP1A1, phase II detoxifying enzymes-GSTM1, GSTT1, GSTP1 and enzyme involved in nucleotide excision repair-XPD. The study group consisted of 220 healthy non-smoking volunteers; 90 men and 130 woman, 25-60 years old (44 ± 10 years). The level of DNA damage (% DNA in tail) was evaluated by alkaline comet assay. The genetic variants were determined by restriction fragment length polymorphism PCR. The highest level of DNA damage (6.7%) was found in carriers of both: AA variant of XPD gene and M1 null variant of GSTM1 gene. The lowest level of DNA breaks (3.7%) was associated with the genotype GSTP1-AA/GSTM1 (+).

Interaction between glutathione-S-transferase polymorphisms, smoking habit, and HPV infection in cervical cancer risk

PURPOSE

Human papillomavirus (HPV) infection is considered the major cause of cervical cancer (CC), but a number of infected women do not develop invasive lesions, suggesting the role of genetic susceptibility and environmental co-factors for cancer outbreak. The aim of this study was to investigate whether some GST polymorphisms could influence the risk to develop CC, either by themselves or in combination with smoking habit, in a cohort of high-risk HPV (HR-HPV) infected Italian women.

METHODS

The study population comprises 192 Italian women including 81 HR-HPV infected women bearing cervical lesions and 111 healthy controls. The cases include: 26 low-grade squamous intraepithelial lesions (LSILs), 30 high-grade-SIL, and 25 CCs, while controls were all negative for HPV. DNA was extracted from peripheral blood samples or cytobrush and individuals were genotyped for GSTM1, GSTT1, and GSTP1 polymorphisms using PCR and PCR/RFLP techniques.

RESULTS

On studying the association of GSTs gene polymorphisms with cervical cancer lesions, the combination of GSTM1 null, GSTT1 null and GSTP1 AA genotypes, independently on smoking habit, seems to be related to a 5.7-fold increased risk of developing CLs with a considerable statistical significance (P = 0.0091).

CONCLUSIONS

We suggest that the investigation of multiple gene polymorphisms, versus single genes, could contribute to a better understanding of the effect of susceptibility genes on cancer risk.

Genetic Polymorphism in Glutathione Transferases (GST): Population distribution of GSTM1, T1, and P1 conjugating activity

Glutathione transferases (GST) catalyze the conjugation of glutathione (GSH) with electrophiles, many of which may otherwise interact with protein or DNA. In select cases such as halogenated solvents, GST-mediated conjugation may lead to a more toxic or mutagenic metabolite. Polymorphisms that exert substantial effects on GST function were noted in human populations for several isozymes. This analysis focuses on three well-characterized isozymes, GSTM1, T1, and P1, in which polymorphisms were extensively studied with respect to DNA adducts and cancer in molecular epidemiologic studies. The current review and analysis focused upon how polymorphisms in these GST contributed to population variability in GST function. The first step in developing this review was to characterize the influence of genotype on phenotype (enzyme function) and the frequency of the polymorphisms across major population groups for all three GST. This information was then incorporated into Monte Carlo simulations to develop population distributions of enzyme function. These simulations were run separately for GSTM1, T1, and P1, and also for the combination of these isozymes, to assess the possibility of overlapping substrate specificity. Monte Carlo simulations indicated large interindividual variability for GSTM1 and T1 due to the presence of the null (zero activity) genotype, which is common in all populations studied. Even for GSTM1 or T1 non-null individuals, there was considerable interindividual variability with a bimodal distribution of enzyme activity evident. GSTP1 polymorphisms are associated with somewhat less variability due to the absence of null genotypes. However, in all cases simulated, the estimated variability is sufficiently large to warrant consideration of GST function distributions in assessments involving GST-mediated activation or detoxification of xenobiotics. Ideally, such assessments would involve physiologically based toxicokinetic (PBTK) modeling to assess population variability in internal dose.

Genotype and allele frequencies of polymorphic CYP2E1 in the Turkish population

Cytochrome P4502E1 (CYP2E1) gene shows genetic polymorphisms that vary markedly in frequency among different ethnic and racial groups. We studied the genotype distributions and allele frequencies of three CYP2E1 polymorphisms: CYP2E1*5B (RsaI/PstI RFLP, C-1053T/G-1293C SNP, rs2031920 /rs3813867), CYP2E1*6 (DraI RFLP, T7632A SNP, rs6413432), and CYP2E1*7B (DdeI RFLP, G-71T SNP, rs6413420) by PCR/RFLP technique in a sample of 206 healthy subjects representing Turkish population. CYP2E1*5B polymorphism analysis yielded the genotype distribution as 96.12% for *1A/*1A (c1/c1), and 3.88% for *1A/*5B (c1/c2). The genotype frequencies for CYP2E1*6 polymorphism were found as 83.98% for *1A/*1A (T/T), 15.53% for *1A/*6 (T/A) and 0.49% for *6/*6 (A/A). For CYP2E1*7B (G-71T) polymorphism, the genotype frequencies were determined to be 86.89% for *1A/*1A (G/G), 12.62% for *1A/*7B (G/T) and 0.49% for *7B/*7B (T/T). Accordingly, the allele frequencies for *5B, *6 and *7B were 1.94, 8.25, and 6.80%, respectively. The genotype distributions of CYP2E1*5B and *6 in Turkish population were similar to those in other Caucasian populations, while differed significantly from East Asian populations. Recently, a novel and functionally important CYP2E1*7B polymorphism was identified in the promoter region. There have been few studies and limited data on CYP2E1*7B polymorphism frequency in the world and, so far, no information has been available for Turkish population. The genotype frequencies of CYP2E1*7B in Turkish population were found to be similar to those of other Caucasian populations. Population studies like this could be useful in assessing the susceptibility of different populations to chemical-induced diseases, including several types of cancer.

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.

PROBLEMS OF POSITIVE LIST SYSTEM REVEALED BY SURVEY OF PESTICIDE RESIDUE IN FOOD

The positive list system became effective from May 29, 2006 to improve the regulation of residual agricultural chemicals (pesticides, feed additives and veterinary drugs) in foods. In accordance with the system, we investigated pesticide residues in 50 agricultural products purchased in Morioka city from March to November 2006. Analyses were performed according to the "Multiresidue Method for Agricultural Chemicals by GC/MS", the Notice of the Ministry of Health, Labour and Welfare. Five pesticides and two non-agricultural chemicals were detected from 16 samples. Ortho-phenylphenol (OPP) was detected from 8 samples: immature pea, snap bean, kiwi, plain-boiled bamboo shoot, mango, white asparagus, lemon and domestic shiitake mushroom. Maximum residue limits (MRLs) have not been established for these products, and they exceeded the uniform level of 0.01 ppm. DDT was detected from Philippines banana (0.30 ppm) and Korean paprika (0.45 ppm). The residual level in Philippines banana was lower than the MRL, but Korean paprika exceeded its MRL. Chlorpyrifos, Thiabendazole and Imazaril were detected from citrus imported from the U.S.A., but their residue levels were lower than the respective MRLs. Aniline and 2-pyrrolidone were detected from several imported products. These two may not be regulated by the positive list system because they are not agricultural chemicals, although their derivatives are used as pesticides or veterinary drugs. Three problems have been revealed from this survey: 1) application of the uniform level to minor agricultural products, 2) residues of non-agricultural chemicals whose toxicity is uncertain, 3) metabolites of agricultural chemicals, which are also regulated by the positive list system, have not been clearly defined.

Single nucleotide polymorphisms: early diagnosis and risk assessment in genitourinary malignancy

Genetic screening for malignancy has been limited to high-risk individuals with a strong hereditary predisposition to cancer. With the cloning of the human genome, it has become apparent that genetic anomalies are not limited to high-risk individuals; more than 10 million genetic variants exist. Because the vast majority of these genetic variants have no functional significance, current efforts are focused on identification of which impact cancer development and/or progression. Here, we review the rationale for studying polymorphic variants in urologic malignancies, prior studies in the field, and future avenues of research.

Glucoraphanin, the bioprecursor of the widely extolled chemopreventive agent sulforaphane found in broccoli, induces phase-I xenobiotic metabolizing enzymes and increases free radical generation in rat liver

Epidemiological and animal studies linking high fruit and vegetable consumption to lower cancer risk have strengthened the belief that long-term administration of isolated naturally occurring dietary constituents could reduce the risk of cancer. In recent years, metabolites derived from phytoalexins, such as glucoraphanin found in broccoli and other cruciferous vegetables (Brassicaceae), have gained much attention as potential cancer chemopreventive agents. The protective effect of these micronutrients is assumed to be due to the inhibition of Phase-I carcinogen-bioactivating enzymes and/or induction of Phase-II detoxifying enzymes, an assumption that still remains uncertain. The protective effect of glucoraphanin is thought to be due to sulforaphane, an isothiocyanate metabolite produced from glucoraphanin by myrosinase. Here we show, in rat liver, that while glucoraphanin slightly induces Phase-II enzymes, it powerfully boosts Phase-I enzymes, including activators of polycyclic aromatic hydrocarbons (PAHs), nitrosamines and olefins. Induction of the cytochrome P450 (CYP) isoforms CYP1A1/2, CYP3A1/2 and CYP2E1 was confirmed by Western immunoblotting. CYP induction was paralleled by an increase in the corresponding mRNA levels. Concomitant with this Phase-I induction, we also found that glucoraphanin generated large amount of various reactive radical species, as determined by electron paramagnetic resonance (EPR) spectrometry coupled to a radical-probe technique. This suggests that long-term uncontrolled administration of glucoraphanin could actually pose a potential health hazard.

Five glutathione s-transferase gene variants in 23,452 cases of lung cancer and 30,397 controls: meta-analysis of 130 studies

BACKGROUND

Glutathione S-transferases (GSTs) are known to abolish or reduce the activities of intracellular enzymes that help detoxify environmental carcinogens, such as those found in tobacco smoke. It has been suggested that polymorphisms in the GST genes are risk factors for lung cancer, but a large number of studies have reported apparently conflicting results.

METHODS AND FINDINGS

Literature-based meta-analysis was supplemented by tabular data from investigators of all relevant studies of five GST polymorphisms (GSTM1 null, GSTT1 null, I105V, and A114V polymorphisms in the GSTP1 genes, and GSTM3 intron 6 polymorphism) available before August, 2005, with investigation of potential sources of heterogeneity. Included in the present meta-analysis were 130 studies, involving a total of 23,452 lung cancer cases and 30,397 controls. In a combined analysis, the relative risks for lung cancer of the GSTM1 null and GSTT1 null polymorphisms were 1.18 (95% confidence interval [CI]: 1.14-1.23) and 1.09 (95% CI: 1.02-1.16), respectively, but in the larger studies they were only 1.04 (95% CI: 0.95-1.14) and 0.99 (95% CI: 0.86-1.11), respectively. In addition to size of study, ethnic background was a significant source of heterogeneity among studies of the GSTM1 null genotype, with possibly weaker associations in studies of individuals of European continental ancestry. Combined analyses of studies of the 105V, 114V, and GSTM3*B variants showed no significant overall associations with lung cancer, yielding per-allele relative risks of 1.04 (95% CI: 0.99-1.09), 1.15 (95% CI: 0.95-1.39), and 1.05 (95% CI: 0.89-1.23), respectively.

CONCLUSIONS

The risk of lung cancer is not strongly associated with the I105V and A114V polymorphisms in the GSTP1 gene or with GSTM3 intron 6 polymorphism. Given the non-significant associations in the larger studies, the relevance of the weakly positive overall associations with the GSTM1 null and the GSTT1 null polymorphisms is uncertain. As lung cancer has important environmental causes, understanding any genetic contribution to it in general populations will require the conduct of particularly large and comprehensive studies.

Metabolic gene polymorphisms and lung cancer risk in non-smokers. An update of the GSEC study

BACKGROUND

Since genetic factors may play an important role in lung cancer development at low dose carcinogen exposure, non-smokers are a good model to study genetic susceptibility and its interaction with environmental factors.

MATERIALS AND METHODS

We evaluated the role of the metabolic gene polymorphisms CYP1A1MspI, CYP1A1Ile462Val, GSTM1, and GSTT1 in non-smoker lung cancer patients from the International Collaborative Study on Genetic Susceptibility to Environmental Carcinogens (GSEC). Non-smokers (defined as subjects who never smoked on a regular basis) were selected from the GSEC database. We pooled the raw data from 21 case-control studies for a total of 2764 Caucasians (555 cases and 2209 controls) and 383 Asians (113 cases and 270 controls). Tests of heterogeneity and of inclusion bias were performed.

RESULTS

A significant association between lung cancer and CYP1A1Ile462Val polymorphism was observed in Caucasians (adjusted OR=2.04, 95% CI 1.17-3.54). GSTT1 deletion seems to be a risk factor for lung cancer in Caucasian non smokers only when the analysis was restricted to studies including healthy controls (adjusted OR=1.66, 95% CI 1.12-2.46). A protective effect on lung cancer was observed with the combination of CYP1A1 wild type, GSTM1 null, and GSTT1 non-null genotypes. None of the analysed polymorphisms were associated with lung cancer in Asian non-smokers.

DISCUSSION

Our analysis confirms previous findings that CYP1A1Ile462Val polymorphism may play a role in lung carcinogenesis in Caucasian non-smokers.

Genetic polymorphisms and possible gene-gene interactions in metabolic and DNA repair genes: effects on DNA damage

We investigated in a central European population, the association between genetic polymorphisms in several genes coding for xenobiotic metabolizing enzymes (CYP1A1, CYP2E1, EPHX1, GSTP1, GSTM1 and GSTT1) and in DNA repair genes (XPD, XPG, XPC and XRCC1) and the levels of single-strand breaks (SSBs) and SSB endonuclease III sensitive sites (endoIII sites) in peripheral blood lymphocytes. No significant differences in the mean levels of SSBs and endoIII sites after stratification for main confounders and occupational exposure were observed in the studied population. Significantly higher levels of SSBs were observed in individuals bearing the wild-type alleles (AA) (0.75+/-0.51SSB/10(9)Da) and heterozygous (AC) genotypes (0.67+/-0.49SSB/10(9)Da) compared to those with homozygous XPD (CC) genotype (0.43+/-0.28SSB/10(9)Da, P=0.033). A moderate increase in the levels of SSBs was also found in individuals with the homozygous XPG exon 15 wild type (GG) and heterozygous (GC) genotypes in comparison to those with the homozygous (CC) genotype (P=0.066) and in individuals with low activity EPHX1 genotype in comparison to those with high activity genotype. Nevertheless, these differences were not statistically significant. No other significant association was found. When gene-gene interactions were evaluated, a combination of EPHX1 activity genotypes with that of either XPD or XPG significantly (P=0.003 and 0.016, respectively) modulated SSB levels resulting in a three-fold difference between the "protective" and the "adverse" genotype-combinations. Almost three-fold differences in SSB levels were found between the "protective" and the "adverse" genotype-combinations of EPHX1 activity genotype and GSTM1 or GSTT1 genotypes, respectively. In conclusion, our results suggest a relation between markers of genotoxicity and polymorphisms in genes coding for xenobiotic metabolizing and DNA repair enzymes as well as a modulating effect of combinations of these polymorphisms.

Polymorphisms in genes involved in xenobiotic metabolism and lung cancer risk under the age of 60 years

The genetic susceptibility hypothesis has been used to explain why only a minority of smokers develop lung cancer. Only few studies have studied the role of polymorphisms in phase-I and II metabolizing genes, among young lung cancer patients. We have pooled the individual data of three studies from Denmark and Norway, including 320 patients diagnosed with non-small cell lung cancer at age 59 or below, and 618 age and gender matched controls. A questionnaire was used to determine relevant demographic and lifestyle characteristics, and polymorphisms in following genotypes were determined GSTM1, GSTM3, GSTP1, GSTT1, GPX1, MPO, NQO1 and NAT2. Based on the literature, the alleles of the genotypes were categorised as high- or low-risk alleles. No individual effect of the genotypes was found on the risk of lung cancer. Given a smoking exposure, the presence of high-risk alleles (or phenotypes) was generally found to increase the risk of lung cancer, although the effect modification did not reach statistical significance. A pattern of stronger protective effect was observed in carriers of more than one allele associated with lower risk of lung cancer, and a higher risk of lung cancer in carriers of one or more alleles associated with higher risk of lung cancer, but the results did not reach statistical significance. The effect modification was generally strongest at lower levels of smoking.

Integrative epidemiology: from risk assessment to outcome prediction

In this paper, we advance the concept of integrative epidemiology. Our unifying premise is that the same genes that are implicated in cancer risk may also be involved in a person's propensity to carcinogenic exposure and/or to modulation of therapeutic outcome. In the coming years, molecular epidemiology will play an increasingly prominent role in early detection of cancer and in identifying genetically high-risk subgroups that might benefit disproportionately from more intensive screening or chemoprevention interventions. Molecular epidemiology is also integral to pharmacogenetic research, by constructing genetic profiles that could be used to individualize therapy and to understand the functional consequences of chemoprevention, chemotherapy, or radiotherapy response. At the level of risk assessment, the focus might be on germline polymorphisms in candidate genes; for early detection, epigenetic events in these same or other genes may be relevant; and tumor tissue expression levels, loss of heterozygosity, genomic amplification, rearrangements, or somatic mutations in the same classes of genes may determine outcome. We will provide examples of how changes in the function of a single gene can contribute to susceptibility to carcinogenic exposure, predisposition to cancer development, patient prognosis, and prediction of outcome.

A review of selected anti-tumour therapeutic agents and reasons for multidrug resistance occurrence

It is assumed that proteins from the ABC family (i.e., glycoprotein P (Pgp)) and a multidrug resistance associated protein (MRP) play a main role in the occurrence of multidrug resistance (MDR) in tumour cells. Other factors that influence the rise of MDR are mechanisms connected with change in the effectiveness of the glutathione cycle and with decrease in expression of topoisomerases I and II. The aim of this review is to characterize drugs applied in anti-tumour therapy and to describe the present state of knowledge concerning the mechanisms of MDR occurrence, as well as the pharmacological agents applied in reducing this phenomenon.

Lung cancer susceptibility and polymorphisms of glutathione-S-transferase genes in Hong Kong

OBJECTIVE

To study the potential role of genetic polymorphisms of glutathione-S-transferases GSTM1, GSTT1 and GSTP1 in susceptibility to lung cancer in Hong Kong Chinese.

METHODS

229 consecutive incident patients with a histological diagnosis of lung cancer from a regional hospital and 197 healthy population-based controls were recruited for this study between July 1999 and June 2001. Genetic polymorphisms of GSTT1 and GSTM1 were determined using PCR-based technique.

RESULTS

The frequencies of GSTT1 and GSTM1 null genotypes were 51.8 and 59.4% in healthy controls and 63 and 54.7%, respectively, in lung cancer patients. GSTP1 Val105/Val105 genotype was found in only 1% of healthy controls. The risk for lung cancer with GSTT1 null genotype was significantly higher, adjusted odds ratio (OR) 1.69, 95% confidence interval (CI) 1.12-2.56, compared with those with the GSTT1 genotype; the increase in risk was found only in non-smokers. GSTM1 null genotype, combined GSTT1 and GSTM1 null genotype and GSTP1 Val105/Val105 genotype did not confer any increase risk for lung cancer.

CONCLUSION

GSTT1 null genotype is associated with an increased risk for lung cancer in non-smoking Chinese in Hong Kong.

Chromosome aberrations among cigarette smokers in Colombia

Worldwide, the annual morbimortality caused by cigarette smoking is a major public health concern. In Colombia, up to 33% of the adult population has smoked at some point in life, raising important national issues on the disease burden from tobacco. The aim of this study was to establish whether cigarette smoking increases the frequency of chromosome aberrations (CA) in peripheral blood lymphocytes of smokers (n = 52) compared with non-smokers (n = 52) in Popayán, Colombia. After signing a consent form, volunteers provided a blood sample (20 ml) to establish cell cultures at 52 h. For CA analysis, 100 complete metaphase cells from each subject were evaluated. The CA frequency was significantly higher in smokers (8.38 +/- 0.61) than in non-smokers (3.13 +/- 0.29), showing the highest number of CA (14.83 +/- 1.01) among heavy smokers (>20 pack-years). Interestingly, light smokers (< or =10 pack-years) also showed a significant increase in CA when compared to non-smokers (6.62 +/- 0.53 versus 3.13 +/- 0.29, P < 0.01, respectively). In addition, a significant positive correlation was found between the frequency of CA and the intensity of smoking in pack-years (R2 = 0.60). Our study indicates that the genotoxic effects in lymphocytes from smokers are most likely caused by cigarette smoke constituents, providing scientific evidence to encourage national campaigns to prevent tobacco consumption.

Glutathione S-transferase T1 null-genotype is associated with an increased risk of lung cancer

Glutathione S-transferases (GSTs) are involved in detoxification of carcinogens, e.g., from tobacco smoke. Therefore, polymorphisms in the GST genes have been considered as potential modifiers of individual cancer risk. In a population-based case-cohort study where cases and the subcohort sample were matched on duration of smoking, we investigated the occurrence of lung cancer and histological subtypes of lung cancer in relation to deletion polymorphism in both GSTM1 and GSTT1, single nucleotide polymorphisms (SNPs) in GSTP1 (Ile105Val and Ala114Val) and a 3 base pair deletion polymorphism in GSTM3. We further investigated the effects of the GST polymorphisms on lung cancer risk within subgroups of subjects defined by gender and age. The results showed a 2.4-fold (CI = 1.31-4.41) increased risk of lung cancer in GSTT1 null-genotype carriers but no significant effects of the polymorphisms in GSTM1, GSTM3, GSTP1-105 or GSTP1-114. The association was strongest in lower age groups, with a 9.6-fold increase in risk for subjects with the GSTT1 null-genotype in the 50-55 years age interval (CI = 3.03-30.59). Positive associations were found for GSTT1 within all major histological subtypes. Squamous cell carcinoma was the histological type most strongly associated with the GSTT1 genotype, with a 5.0-fold (CI = 2.26-11.18) increase in risk for subjects carrying the GSTT1 null-genotype. The effects of the GSTT1 null-genotype seemed stronger in the presence of the GSTM1 null-genotype or the GSTP1-105 variant allele. These results suggest that the GSTT1 null-genotype is associated with an increased risk of lung cancer, especially in younger individuals.

Effect of a 4-Month Tea Intervention on Oxidative DNA Damage among Heavy Smokers

Glutathione S-transferase (GST), a member of the phase II group of xenobiotic metabolizing enzymes, has been intensively studied at the levels of phenotype and genotype. The GST mu 1 (GSTM1) and GST theta 1 (GSTT1) genes have a null-allele variant in which the entire gene is absent. The null genotype for both enzymes has been associated with many different types of tumors. The aim of this study was to determine the possible differences in increased oxidative stress susceptibility to smoking within the GSTM1 and GSTT1 genotypes and the impact of high tea drinking on this. We designed a Phase II randomized, controlled, three-arm tea intervention trial to study the effect of high consumption (4 cups/day) of decaffeinated green or black tea, or water on oxidative DNA damage, as measured by urinary 8-hydroxydeoxyguanosine (8-OHdG), among heavy smokers over a 4-month period and to evaluate the roles of GSTM1 and GSTT1 genotypes as effect modifiers. A total of 133 heavy smokers (100 females and 33 males) completed the intervention. GSTM1 and GSTT1 genotype statuses were determined with a PCR-based approach. Multiple linear regression models were used to estimate the main effects and interaction effect of green and black tea consumption on creatinine-adjusted urinary 8-OHdG, with or without adjustment for potential confounders. Finally, we studied whether the effect of treatment varied by GSTM1 and GSTT1 status of the individual. Although there were no differences in urinary 8-OHdG between the groups at baseline, the between-group 8-OHdG levels at month 4 were statistically significant for GSTM1-positive smokers (P = 0.05) and GSTT1-positive smokers (P = 0.02). GSTM1-positive and GSTT1-positive smokers consuming green tea showed a decrease in urinary 8-OHdG levels after 4 months. Assessment of urinary 8-OHdG after adjustment for baseline measurements and other potential confounders revealed significant effect for green tea consumption (P = 0.001). The change from baseline was significant in both GSTM1-positive (t = -2.99; P = 0.006) and GSTT1-positive (P = 0.004) green tea groups, but not in the GSTM1-negative (P = 0.07) or GSTT1-negative (P = 0.909) green tea groups. Decaffeinated black tea consumption had no effect on urinary 8-OHdG levels among heavy smokers. Our data show that consumption of 4 cups of tea/day is a feasible and safe approach and is associated with a significant decrease in urinary 8-OHdG among green tea consumers after 4 months of consumption. This finding also suggests that green tea intervention may be effective in the subgroup of smokers who are GSTM1 and/or GSTT1 positive.

Combined effect of MPO, GSTM1 and GSTT1 polymorphisms on chromosome aberrations and lung cancer risk

The role of myeloperoxidase (MPO), and glutathione S-transferase mu and theta (GSTM1 and GSTT1) genetic polymorphisms on lung cancer risk was investigated in 110 Caucasian patients and 119 matched controls. Single genotype variants were not significantly associated with lung cancer risk. However, inheritance of the combined GSTM1 and GSTT1 null genotypes showed a significant increase in risk (crude OR = 2.32, 95% CI = 1.01-6.04). Based on adjustment by age, gender and smoking history, the MPO GA interacted with the presence of GSTM1 and GSTT1 genotypes to significantly reduce the risk (OR = 0.17, 95% CI = 0.03-0.98). From the chromosome aberration (CA) study in a subgroup of 79 patients and 69 matched controls, patients had significantly more CA than the controls. Among the patients, GSTM1 null was associated with a significant increase of CA and MPO AA was associated with a significant decrease of CA compared to their respective wild-type genotypes. After stratifying by smoking history (< or = and > 40 pack-years) and genotype, patients still had significantly more CA than the respective controls in most genotype categories. This indicates that the patients had additional contributing factors such as other susceptibility genes and/or different styles of smoking compared with the controls. In conclusion, our study indicates that CA is a useful biomarker to show the functional characteristics of genotypes and the interactive effects from combined genotypes. Therefore, our study strengthens the combined use of genotype and biomarkers for genetic susceptibility to environmental cancer.

GST genetic polymorphisms and lung adenocarcinoma susceptibility in a Chinese population

Lung adenocarcinoma (AC) has been increasing over the last several decades in many countries, including China. Some of the glutathione S-transferases (GSTs) demonstrate polymorphisms which may play a role in lung AC susceptibility. Our previous study of a Chinese population found the GSTM1 null genotype to be associated with an increased risk of lung AC, and the combination of GSTM1 null genotype and CYP2E1 wild type conferred a significantly elevated risk. Here, we extended the study to investigate the potential role of GSTT1 and GSTP1 polymorphisms in likelihood of development of lung AC, either separately or in combination. This case-control study encompassed 112 cases with lung ACs and 119 age- and gender-matched cancer-free controls from Beijing. The frequencies for the GSTM1 null genotype were 61.6 and 50.4% among cases and controls, and for the GSTT1 null genotype 47.3 and 45.4%, respectively. The distribution of the GSTP1 Ile/Ile, Ile/Val and Val/Val genotypes was 59.8, 39.3 and 0.9% in cases, and 70.6, 28.6 and 0.8% in controls, respectively. No relationship between lung AC and the GSTT1 genotype was observed in the present study, either separately or in combination with the GSTM1 or GSTP1 genotypes. Although separate GSTM1 and GSTP1 polymorphisms were not statistically related to lung AC, the combination of GSTM1 null and GSTP1 Val was significantly associated with an elevated lung AC risk (OR=2.4, 95% CI 1.1-5.1).

Markers of individual susceptibility and DNA repair rate in workers exposed to xenobiotics in a tire plant

Workers employed in tire plants are exposed to a variety of xenobiotics, such as 1,3-butadiene (BD), soots containing polycyclic aromatic hydrocarbons, and other organic chemicals (e.g., styrene). In the present study, we investigated markers of genotoxicity [chromosomal aberrations (CAs) and single-strand breaks (SSBs)] in a cohort of 110 tire plant workers engaged in jobs with different levels of xenobiotic exposure in relation to various polymorphisms in genes coding for biotransformation enzymes (CYP1A1, CYP2E1, EPHX1, GSTM1, GSTP1, and GSTT1) and in genes involved in DNA repair (XPD exon 23, XPG exon 15, XPC exon 15, XRCC1 exon 10, and XRCC3 exon 7). In addition, the expression of CYP2E1, a gene playing a key role in BD metabolism, was determined by real-time PCR in peripheral blood lymphocytes, and the capacity of lymphocytes to repair gamma-ray-induced SSBs and to convert 8-oxoguanine in HeLa cell DNA into SSBs was assessed using in vitro assays. No positive associations were detected between the CA frequency or SSB induction and levels of workplace exposure; however, a nonsignificant twofold higher irradiation-specific DNA repair rate was found among highly exposed workers. In evaluations conducted with the markers of individual susceptibility, workers with low-EPHX1-activity genotypes exhibited a significantly higher CA frequency as compared to those with medium and high-EPHX1-activity genotypes (P = 0.050). CA frequencies were significantly lower in individuals homozygous for the XPD exon 23 variant allele in comparison to those with the wild-type CC genotype (P = 0.003). Interestingly, CAs were higher in individuals with higher CYP2E1 expression levels, but the association was nonsignificant (P = 0.097). The results from this study suggest the importance of evaluating markers of individual susceptibility, since they may modulate genotoxic effects induced by occupational exposure to xenobiotics.

Catalog of 680 variations among eight cytochrome p450 ( CYP) genes, nine esterase genes, and two other genes in the Japanese population

We screened DNAs from 48 Japanese individuals for single-nucleotide polymorphisms (SNPs) in eight cytochrome p450 ( CYP) genes, nine esterase genes, and two other genes by directly sequencing the relevant genomic regions in their entirety except for repetitive elements. This approach identified 607 SNPs and 73 insertion/deletion polymorphisms among the 19 genes examined. Of the 607 SNPs, 284 were identified in CYP genes, 302 in esterase genes, and 21 in the other two genes ( GGT1, and TGM1); overall, 37 SNPs were located in 5' flanking regions, 496 in introns, 55 in exons, and 19 in 3' flanking regions. These variants should contribute to studies designed to investigate possible correlations between genotypes and phenotypes of disease susceptibility or responsiveness to drug therapy.

A population-based study of glutathione S-transferase M1, T1 and P1 genotypes and risk for lung cancer

A deletion polymorphism for glutathione S-transferase M1 (GSTM1) has been related to risk for lung cancer among smokers in some studies but not in others. We examined GSTM1, a GSTT1 deletion polymorphism and a common GSTP1 gene variant (iso-->val), as risk factors for lung cancer in a population-based case-control study of men. Cases (N=274) were males identified from 1993 to 1996 through the Fred Hutchinson Cancer Research Center Cancer Surveillance System registry for western Washington State. Male age-matched controls (N=501) were selected by random-digit dialing. Subjects participated in a telephone interview and blood draw. GSTM1 and GSTT1 were genotyped with a multiplex PCR assay using beta-globin as a positive control, and GSTP1 single nucleotide variant determined with PCR-based oligonucleotide ligation assays. GSTM1 absence was associated with a modest elevation in risk among all cases (odds ratio=1.27, 95% CI 0.91-1.77) and among non-small cell cancers (adenocarcinoma OR=1.58, 95% CI 0.99-2.52; squamous cell OR=1.40, 95% CI 0.83-2.34). Risk associated with GSTM1 null was increased two to sixfold among heavy smokers. GSTT1 was not associated with lung cancer risk and GSTP1 val was non-significantly associated with a modest reduction in risk, particularly among heavy smokers. No specific combination of GST genotypes was particularly associated with risk. These results support previous reports that the GSTM1 null genotype is associated with a modest increase in risk for lung cancer, particularly among heavy smokers, suggest no role for GSTT1 and the need for further study of GSTP1.

Polymorphisms for chemical metabolizing genes and risk for cervical neoplasia

Infection with high-risk human papillomavirus (HPV) plays a major role in the etiology of cervical cancer (CC). However, most infected women do not develop cancer. Therefore, exposure to other carcinogenic agents may be a contributing risk factor for CC. We investigated the hypothesis that environmental exposure to cigarette smoke and inheritance of polymorphic chemical metabolizing genes (CYP2E1, GSTM1, and mEH) significantly increase the risk for neoplasia. We selected 76 cases with high-grade cervical neoplasia or with invasive CC and 75 matched healthy controls. The collected data support the well-established observation that infection with high-risk HPV is the major risk factor for CC (OR = 75; 95% CI = 26-220). In addition, our data show that women who smoked more than 15 "pack-year" had a significant 6.9-fold increase in risk (95% CI = 1.2-40.3) after adjustment for HPV infection. The CYP2E1 variant genotype did not significantly increase the risk for neoplasia. A significant increase in risk for neoplasia was observed for the low-activity mEH 113 His allele after adjustment for smoking (OR = 3.0; 95% CI = 1.4-6.3). The GSTM1 null genotype was associated with a significant 3.3-fold increased risk for neoplasia (95% CI = 1.0-11.8) compared to women who were GSTM1-positive after adjustment for smoking and HPV infection. Our study suggests that genetic differences in the metabolism of cigarette smoke, particularly GSTM1, may confer susceptibility to CC. Further studies using larger populations will be needed to confirm our observations and to validate data for disease prevention.

Meta- and pooled analyses of the effects of glutathione S-transferase M1 polymorphisms and smoking on lung cancer risk

Susceptibility to lung cancer may in part be attributable to inter-individual variability in metabolic activation or detoxification of tobacco carcinogens. The glutathione S-transferase M1 (GSTM1) genetic polymorphism has been extensively studied in this context; two recent meta-analyses of case-control studies suggested an association between GSTM1 deletion and lung cancer. At least 15 studies have been published after these overviews. We undertook a new meta-analysis to summarize the results of 43 published case-control studies including >18 000 individuals. A slight excess of risk of lung cancer for individuals with the GSTM1 null genotype was found (odds ratio (OR) = 1.17, 95% confidence interval (CI) 1.07-1.27). No evidence of publication bias was found (P = 0.4), however, it is not easy to estimate the extent of such bias and we cannot rule out some degree of publication bias in our results. A pooled analysis of the original data of about 9500 subjects involved in 21 case-control studies from the International Collaborative Study on Genetic Susceptibility to Environmental Carcinogens (GSEC) data set was performed to assess the role of GSTM1 genotype as a modifier of the effect of smoking on lung cancer risk with adequate power. Analyses revealed no evidence of increased risk of lung cancer among carriers of the GSTM1 null genotype (age-, gender- and center-adjusted OR = 1.08, 95% CI 0.98-1.18) and no evidence of interaction between GSTM1 genotype and either smoking status or cumulative tobacco consumption.

Discovery in toxicology: mediation by gene expression array technology

Toxicogenomics is a term that represents the merging of toxicology with novel genomics techniques. Data generated in the new-age era of toxicology is relatively complex, requires new bioinformatics tools for adequate interpretation, and allows for the rapid generation of testable hypotheses. Hazard identification and risk assessment processes will advance from the use of genomics techniques, which will lead to greater understanding of mechanism(s) of action of toxicants, development of novel biomarkers of exposure and effect, and better identification of sensitive subpopulations.

Genetic polymorphisms and metabolism of endocrine disruptors in cancer susceptibility

Epidemiological studies have estimated that approximately 80% of all cancers are related to environmental factors. Individual cancer susceptibility can be the result of several host factors, including differences in metabolism, DNA repair, altered expression of tumor suppressor genes and proto-oncogenes, and nutritional status. Xenobiotic metabolism is the principal mechanism for maintaining homeostasis during the body's exposure to xenobiotics. The balance of xenobiotic absorption and elimination rates in metabolism can be important in the prevention of DNA damage by chemical carcinogens. Thus the ability to metabolize and eliminate xenobiotics can be considered one of the body's first protective mechanisms. Variability in individual metabolism has been related to the enzymatic polymorphisms involved in activation and detoxification of chemical carcinogens. This paper is a contemporary literature review on genetic polymorphisms involved in the metabolism of endocrine disruptors potentially related to cancer development.

Genetic variation in CYP2A6-mediated nicotine metabolism alters smoking behavior

Approximately 50% of the initiation of tobacco dependence is genetically influenced, whereas maintenance of dependent smoking behavior and amount smoked have approximately 70% genetic contribution (1-5). Determining the variation in nicotine's inactivation is important because of nicotine's role in producing tobacco dependence and regulating smoking patterns (6-11). The genetically polymorphic CYP2A6 enzyme is responsible for the majority of the metabolic inactivation of nicotine to cotinine (12-14). Both in vitro and in vivo studies have demonstrated considerable interindividual variation in CYP2A6 activity (15-17). CYP2A6 is genetically polymorphic, individuals carrying inactive CYP2A6 alleles have decreased nicotine metabolism, are less likely to become smokers and if they do, they smoke fewer cigarettes per day (13,18,19). The decrease in smoking behavior was confirmed by measuring carbon monoxide (CO, a measure of smoke inhalation) levels, plasma and urine nicotine and cotinine levels, and cigarette counts (13,18,19). A duplication variant in the CYP2A6 gene locus has been identified which increases nicotine inactivation and increases smoking (19). CYP2A6 can also activate tobacco smoke procarcinogens (e.g. NNK, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone); current studies are investigating the role of CYP2A6 in risk for lung cancer. Based on these epidemiologic data it was postulated that inhibition of CYP2A6 activity might be useful in a therapeutic context. Kinetic studies in humans indicated that selective CYP2A6 inhibitors decrease the metabolic removal of nicotine. It was also shown that inhibiting CYP2A6 in vivo (phenocopying, or mimicking the genetic defect) in smokers results in decreased smoking, making nicotine orally bioavailable, and the rerouting of procarcinogens to detoxifying pathways (20-22).

Effect of genotoxic exposure to chromium among electroplating workers in Taiwan

The objective of this study was to investigate the association between chromium (Cr) concentrations and sister chromatid exchanges (SCE) formation in Cr workers and to assess the effects of susceptible genes (glutathione S-transferase M1 and T1) on the frequency of deletion and SCE/cell. Urinary Cr concentration was significantly elevated in Cr workers (3.67 +/- 3.89 microg/g creatinine) compared to control group (1.21 +/- 1.16 microg/g creatinine, P < 0.01). There was also a significant difference of superoxide dismutase (SOD) levels between Cr workers (6.86 +/- 0.80 U/mg Hb) and controls (7.16 +/- 0.53 U/mg Hb, P < 0.01). The frequencies of SCE and high frequency cells (HFC) were significantly correlated with smoking habits and with duration of exposure to Cr. A significantly higher percentage (50%) of Cr workers had both the null GSTM1 and GSTT1 genotype as compared to 10% of the controls (P < 0.01). However, the chromosomal DNA damage effect of GSTM1 and GSTT1 genotypes, individually or in combination, was not revealed in Cr exposed workers.

Association between genetic polymorphisms and biomarkers in styrene-exposed workers

A comprehensive approach to evaluate genotoxic effects induced by styrene exposure was employed in 44 hand-lamination workers in comparison with 18 unexposed controls. The acquired data on single-strand breaks in DNA (SSBs), frequency of chromosomal aberrations and HPRT mutant frequency in peripheral blood lymphocytes were compared to the results on genotyping of some of the xenobiotic-metabolising enzymes (CYP1A1, CYP2E1, epoxide hydrolase and GSTM1, GSTP1 and GSTT1). Multifactorial regression analysis indicated that SSB in DNA were significantly associated with styrene exposure and with heterozygosity in CYP2E1 (5'-flanking region and intron 6; r(2)=0.614). The frequency of chromosomal aberrations (CA), as analysed by linear multiple regression analysis, significantly correlated with years of employment (P=0.004) and with combinations of epoxide hydrolase (EPHX) genotypes (exon 3, Tyr/His and exon 4, His/Arg), where individuals with low and medium activity EPHX genotypes exhibited higher frequencies of CA than those with high activity genotypes (P=0.044, r(2)=0.563). Moderately higher HPRT mutant frequencies were detected in styrene-exposed individuals (20.2 +/- 25.8 x 10(-6)) as compared to controls (13.3 +/- 6.3 x 10(-6)), but this difference was not significant. ANOVA (in the whole set of data) revealed that mutant frequencies at the HPRT gene were significantly associated with years of employment (F=6.9, P=0.0001), styrene in blood (F=10.1, P=0.0001), and heterozygosity in CYP2E1 (intron 6; F=13.5, P=0.0008) and GSTP1 (exon 5; F=3.6, P=0.038). In conclusion, our present data suggest that analysed biomarkers of DNA damage may be modulated by polymorphic CYP2E1, EPHX and GSTP1. In our study, styrene-specific DNA and haemoglobin adducts are under investigation. Completing these data with the results of genotyping of metabolising enzymes may provide a useful tool for individual genotoxic risk assessment.

Usefulness of genetic susceptibility and biomarkers for evaluation of environmental health risk

Recent attention is focused on understanding the genetic basis for individual susceptibility to the development of chronic disease. An emphasis is concentrated on establishing an association between inheritance of polymorphic chemical metabolizing genes and development of environmental cancer (e.g., lung cancer among cigarette smokers). The early reports of such associations have been very encouraging. However, some reported positive associations were not substantiated in subsequent studies using larger sample sizes and different ethnic populations. In this review, some confounding factors that contribute to the discrepancies are presented (e.g., ethnic-dependent distribution of variant gene alleles, differential expression of metabolizing genes, and inadequate study design). It is possible that the precision of the association can be improved if the mentioned investigations are complemented with concurrent studies of biological activities/effects. The usefulness of integrating metabolic susceptibility with biomarker measurement for understanding the development of lung cancers is presented. The importance of using adequate sample size and experimental design is emphasized. Development of a reliable approach for prediction of environmental disease not only will provide fundamental information regarding the genetic basis of human disease but will be useful for reducing disease burden in the population and for advancing patient care. Environ. Mol. Mutagen. 37:215-225, 2001. &copy 2001 Wiley-Liss, Inc.

Variant metabolizing gene alleles determine the genotoxicity of benzo[a]pyrene

Understanding the mechanisms involved with genetic susceptibility to environmental disease is of major interest to the scientific community. We have conducted an in vitro study to elucidate the involvement of polymorphic metabolizing genes on the genotoxicity of benzo[a]pyrene (BP). Blood samples from 38 donors were treated with BP and the induction of sister chromatid exchanges (SCE) and chromosome aberrations (CA) were evaluated. The latter is based on the tandem-probe fluorescence in situ hybridization (FISH) assay. The data indicate that the induction of genotoxicity was clearly determined by the inherited variant genotypes for glutathione-S-transferase (GSTM1) and microsomal epoxide hydrolase (EH). In a comparison of the two biomarkers, the CA biomarker shows a more definite association with the genotypes than does SCE. For example, the presence of the GSTM1 null genotype (GSTM1 0/0) is responsible for the highest level and significant induction of CA, irrespective of the presence of other genotypes in the different donors. This effect is further enhanced significantly by the presence of the excessive activation EH gene allele (EH4*) and decreased by the reduced activation EH gene allele (EH3*). Overall, the modulation of genotoxicity by the susceptibility genotypes provides support of their potential involvement in environmental cancer. Furthermore, the data indicate that the variant enzymes function independently by contributing their metabolic capability toward the expression of biologic activities. Therefore, studies like this one can be used to resolve the complexity of genetic susceptibility to environmental disease in human.

Genetic and environmental interactions on oral cancer in Southern Thailand

Many countries are interested in understanding the relationship between genetic susceptibility and their prevalent environmental cancers for disease prevention. In Thailand we conducted a population-based case-control study of 53 matched pairs to assess the risk of oral cancer in relation to genetic polymorphism of the glutathione-S-transferase genes (GSTM1 and GSTT1) in cigarette smokers, alcohol drinkers, and betel quid chewers. Interaction of the genes with other potential risk factors such as local bean consumption were also elucidated. Homozygous deletion of GSTM1 has a frequency of 56.6% (n = 30 over 53) among the patients and 30.2% (16/53) among the controls. This gene is associated with a 2.6-fold higher risk for development of oral cancer (95% CI 1.04-6.5). Among the null GSTM1 individuals, those who smoke, consume alcohol, and/or chew betel quid have a significantly increased risk for oral cancer with an odd ratio (OR) = 4.0 (95% CI = 1.2-13.7), OR = 7.2 (95% CI = 1.5-33.8), and OR = 4.4 (95% CI = 1.1-17.8), respectively. Interactions between any two of the lifestyle habits for oral cancer risk, however, are not found. The frequency of the GSTT1 null genotype is 34.0% (18/53) among the patients and 47.2% (25/53) among our controls. There is no association between the GSTT1 null allele and oral cancer risk. In conclusion, our study provides data to indicate that individuals who have homozygous deletion of the GSTM1 gene have increased risk for oral cancer. The risk increases further when these individuals are exposed to environmental toxicants such as chemicals in cigarette smoke, alcohol, and betel quid. These baseline data can be applied to a larger population-based study, both to verify the observation and to conduct mechanistic investigations.

Genetic polymorphisms of biotransformation enzymes: allele frequencies in the population of the Czech Republic

Polymerase chain reaction-restriction fragment length polymorphism based genotyping assays were used to determine the frequency of polymorphisms in CYP1A1 (3'-flanking region), CYP2E1 (5'-flanking region and intron 6), EPHX (exon 3 and exon 4), GSTM1 (deletion), GSTP1 (exon 5) and GSTT1 (deletion) in a group of 416 Czech individuals. A comprehensive overview of the methodology is also presented. We have found the following frequencies of mutated alleles: CYP1A1-m2, 0.097; CYP2E1-C, 0.077; CYP2E1-c2, 0.023; EPHX(exon 3)-His, 0.381; EPHX(exon 4)-Arg, 0.198; GSTM1-null, 0.51; GSTP1-Val, 0.3; GSTT1-null, 0.164. These values are similar to those presented in the majority of studies on European Caucasians, although a few cases of significant differences in the distribution of genotypes were found. These differences were most probably caused by methodological variations or statistical bias in the analyses of low numbers of samples in the control groups of some authors. Based on the results of EPHX genotyping, the activity of its protein product was deduced and the Czech population was divided into three subgroups with low, medium and high EPHX activity. We found that 43% of the Czech population would fall into the low, 44% into the medium and 13% into the high EPHX activity group. The data obtained may prove to be very useful for epidemiological studies on the influence of genetic polymorphisms of biotransformation enzymes on carcinogenesis or other environment-related diseases.

Mammalian class theta GST and differential susceptibility to carcinogens: a review

Glutathione S-transferases (GSTs) are an important part of the cellular detoxification system and, perhaps, evolved to protect cells against reactive oxygen metabolites. Theta is considered the most ancient among the GSTs and theta-like GSTs are found in mammals, fish, insects, plants, unicellular algae, and bacteria. It is thought that an ancestral theta-gene underwent an early duplication before the divergence of fungi and animals and further duplications generated the variety of the other classes of GSTs (alpha, mu, phi, etc.). The comparison of the aminoacidic homologies among mammals suggests that a duplication of an ancient GST theta occurred before the speciation of mammals and resulted in the subunits GSTT1 and GSTT2. The ancestral GST theta has a dehalogenase activity towards several halogenated compounds, such as the dichloromethane. In fact, some aerobic and anaerobic methylotrophic bacteria can use these molecules as the sole carbon and energy source. The mammalian GST theta cannot sustain the growth of bacteria but still retains the dehalogenating activity. Therefore, although mammalian GST theta behaves as a scavenger towards electrophiles, such as epoxides, it acts also as metabolic activator for halogenated compounds, producing a variety of intermediates potentially dangerous for DNA and cells. For example, mice exposed to dichloromethane show a dose-dependent incidence of cancer via the GSTT1-1 pathway. Because GSTT1-1 is polymorphic in humans, with about 20% of Caucasians and 80% of Asians lacking the enzyme, the relationship between the phenotype and the incidence of cancer has been investigated extensively in order to detect GSTT1-1-associated differential susceptibility towards endogenous or exogenous carcinogens. The lack of the enzyme is related to a slightly increased risk of cancer of the bladder, gastro-intestinal tract, and for tobacco-related tumors (lung or oral cavity). More pronounced risks were found in males with the GSTT1-null genotype for brain diseases and skin basal cell carcinomas not related to sunlight exposures. Moreover, there was an increased risk of kidney and liver tumors in humans with the GSTT1-1 positive genotype following exposures to halogenated solvents. Interestingly, the liver and kidney are two organs that express the highest level of GST theta in the human body. Thus, the GSTT1-1 genotype is suspected to confer decreased or increased risk of cancer in relation to the source of exposure; in vitro studies, mostly conducted on metabolites of butadiene, confirm the protective action of GSTT1-1, whereas, thus far, experimental studies prove that the increasing risk is limited.

Characterization of Cyp2d22, a novel cytochrome P450 expressed in mouse mammary cells

Endogenous steroids and numerous environmental agents have potent effects on mammary development and carcinogenesis. Locally produced cytochrome P450 enzymes that modify such molecules are therefore likely to be important regulators of these processes. Here we describe the characterization of a novel mouse gene, termed Cyp2d22, that is highly expressed in the mammary tumor derived cell line RIII/Prl. Cyp2d22 is expressed at intermediate levels in the weakly tumorigenic cell line RIII/MG, whereas expression is low or absent in all normal mouse mammary epithelial cell lines tested and three C3H mammary tumor derived cell lines. Immunoblot analysis of mouse tissues with highly specific antisera indicates that 2D22 protein levels are most abundant in liver, while intermediate levels of expression are seen in adrenal, ovary, and mammary gland. Immunohistochemical staining of liver sections with these antisera demonstrates that 2D22 is most abundant in the first layer or two of parenchymal cells surrounding the central vein, with virtually no expression detected in periportal cells. Interestingly, sequence similarity and functional data suggest that Cyp2d22 may be the mouse ortholog of human CYP2D6. These observations support the hypothesis that 2D22 mediates a distinct, biologically significant activity in relation to other mouse 2D family members.

Genetic polymorphisms in head and neck cancer risk

OBJECTIVE

To assess whether genetic polymorphisms implicated as risk factors for other tobacco-associated malignancies are associated with altered risk of head and neck squamous cell carcinoma.

DESIGN

Case-control study.

SUBJECTS

One hundred sixty patients with head and neck squamous cell carcinoma recruited from a university-based head and neck oncology clinic and 149 population-based controls.

METHODS

Genotyping of the CYP1A1 (Ile462Val), GSTM1 (null), GSTP1 (Ile105Val), GSTT1 (null), and P53 (Arg72Pro) genes was performed by polymerase chain reaction-based techniques on DNA prepared from peripheral blood. In addition, a questionnaire was used to collect demographic information from each subject.

RESULTS

Cases were significantly older (p <.0001) and had significantly greater tobacco use (p <.0001) and were more likely to be male (p <.0001) than were control subjects, thus confirming known risk factors for this disease. When cases and controls were compared by simple chi-square analysis, only the frequency of CYP1A1 (Ile462Val) polymorphism was significantly different between cases and controls (OR =.42; 95% CI =.18-.99; p <.04). However, with a logistic regression model to control for known risk factors, we were unable to demonstrate a significant association with head and neck cancer for any of the polymorphisms tested, including CYP1A1.

CONCLUSIONS

This population fails to identify a relationship between the above-mentioned polymorphisms and head and neck cancer.

Role of polymorphic CYP2E1 and CYP2D6 genes in NNK-induced chromosome aberrations in cultured human lymphocytes

Polymorphisms in genes of xenobiotic-metabolizing enzymes are largely responsible for interindividual differences in ability to activate and detoxify genotoxic agents and therefore may influence individual susceptibility to environmental cancer. The tobacco-specific nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), requires metabolic activation by cytochrome P450 (CYP) enzymes to generate DNA-reactive intermediates that induce mutations and cancer. In the current study, we investigated the role of the polymorphic CYP2E1 and CYP2D6 genes in the genotoxicity of NNK using the tandem-probe fluorescence in-situ hybridization (FISH) chromosome aberration assay as a marker. Our results, using whole blood cultures from 39 volunteers, indicated that NNK (0.12, 0.24 or 0.72 mM) induced a concentration-dependent increase in the frequency of chromosome aberration. The potential role of CYP2E1 and CYP2D6 in NNK-induced genetic damage in cultured human lymphocytes was characterized using specific CYP inhibitors. Treatment of blood cultures with 25 microM diethyldithiocarbamate (DDC), a specific CYP2E1 inhibitor, or 0.5 microM quinidine, a specific CYP2D6 inhibitor, simultaneously with NNK, significantly decreased NNK-induced chromosome aberration. We also studied the role of CYP2E1 and CYP2D6 allelic variants on NNK-induced chromosome aberration. Our results indicate that NNK induced a significantly higher level of chromosome aberration in cells with the CYP2E1 WT/*5B genotype compared to cells with the CYP2E1 WT/WT. In contrast, no difference in NNK-induced chromosome aberration was observed between cells with the CYP2D6 extensive metabolizers compared to cells with the CYP2D6 poor metabolizer genotypes. These results underscore the important role of polymorphic metabolizing genes in influencing the genotoxic responses to environmental mutagens and provide support to the reported findings linking CYP2E1 polymorphism to smoking-related lung cancer.

A patient with genetic deletion of glutathione-S-transferase T1 and M1 who developed non-small-cell lung cancer and myelodysplastic syndromes

Glutathione S-transferase (GST) M1 polymorphism is a marker for susceptibility to smoking-related neoplasms, such as lung and bladder cancer. Recently, a genetic deletion of GSTT1, an isoenzyme of GST, has been reported to be associated with myelodysplastic syndromes (MDS). A 59-year-old man with a long-term smoking habit was treated successfully for non-small-cell lung cancer. Four years after the surgical removal of his lung cancer, he developed MDS and died. Using a polymerase chain reaction-based genotyping method, he was found to have a deletion of both the GSTM1 and GSTT1 genes. Screening for the deletion of the GSTM1 and GSTT1 genes may be useful for assessing individual genetic susceptibility to smoking-related lung cancer and MDS.

Tobacco smoke carcinogens and lung cancer

The complexity of tobacco smoke leads to some confusion about the mechanisms by which it causes lung cancer. Among the multiple components of tobacco smoke, 20 carcinogens convincingly cause lung tumors in laboratory animals or humans and are, therefore, likely to be involved in lung cancer induction. Of these, polycyclic aromatic hydrocarbons and the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone are likely to play major roles. This review focuses on carcinogens in tobacco smoke as a means of simplifying and clarifying the relevant information that provides a mechanistic framework linking nicotine addiction with lung cancer through exposure to such compounds. Included is a discussion of the mechanisms by which tobacco smoke carcinogens interact with DNA and cause genetic changes--mechanisms that are reasonably well understood--and the less well defined relationship between exposure to specific tobacco smoke carcinogens and mutations in oncogenes and tumor suppressor genes. Molecular epidemiologic studies of gene-carcinogen interactions and lung cancer--an approach that has not yet reached its full potential--are also discussed, as are inhalation studies of tobacco smoke in laboratory animals and the potential role of free radicals and oxidative damage in tobacco-associated carcinogenesis. By focusing in this review on several important carcinogens in tobacco smoke, the complexities in understanding tobacco-induced cancer can be reduced, and new approaches for lung cancer prevention can be envisioned.

Polymorphism of glutathione S-transferase loci GSTM1 and GSTT1 and susceptibility to colorectal cancer in Egypt

Egypt has an unusually high proportion of early-onset colorectal cancer under age 40 years. Environmental exposures and low DNA repair capacity are among the risk factors. Because GSTM1 and GSTT1 gene deficiencies may act as risk modifiers for colorectal cancer risk, we investigated the relationship between genetic polymorphism in these genes and colorectal cancer risk in Egyptians. Sixty-six patients and 55 controls were included. Genotyping for GSTM1 and GSTT1 was conducted using PCR techniques and the results were related to epidemiologic and clinical information. No overall association was observed between GSTM1 or GSTT1 null genotypes and colorectal cancer risk. However, the data suggest a possible role for GSTM1 genotype in influencing tumor site. Furthermore, GSTM1 and GSTT1 genotypes, in conjunction with gender and place of residence, may play a role in modifying disease risk. Further studies on a larger population in Egypt are needed to generalize the results of this study.