Association of poor metabolizers of cytochrome P450 2C19 with head and neck cancer and poor treatment response

A case-control study consisting of 300 patients and an equal number of healthy controls was carried out to investigate the association of polymorphism in cytochrome P450 2C19 (CYP2C19), which results in poor and extensive metabolizers (PMs and EMs) genotypes, with squamous cell carcinoma of head and neck (HNSCC) and treatment response in patients receiving combination of chemo-radiotherapy. A higher frequency of CYP2C19*2 variants was observed in the cases resulting in significantly higher risk to HNSCC (Ad OR 3.36, 95% CI 1.94-5.82, p-value<0.05). The PM genotype of CYP2C19*3 was also found to be slightly increased in the cases, though the increase in risk was not significant when analyzed by multivariate logistic regression model. Tobacco chewing amongst the cases resulted in almost 13-fold increase in the risk with CYP2C19*2 (OR: 12.39) and 3-fold with CYP2C19*3 genotype (OR: 2.90) when compared to the tobacco chewers amongst the controls. Likewise, cigarette smoking in the cases increased the risk approximately 9-fold and 3-fold with CYP2C19*2 (OR: 8.93) and CYP2C19*3 (OR: 2.18) genotypes respectively when compared to smokers amongst the controls. Similar increase in risk was associated with alcohol use amongst the cases carrying variant genotypes of CYP2C19*2 (OR: 7.75) or CYP2C19*3 (OR: 2.60), demonstrating the importance of gene-environment interaction in modifying susceptibility to HNSCC. Interestingly, patients with PMs of CYP2C19 (CYP2C19*2 and CYP2C19*3) exhibited little response to the respective chemotherapy than the patients carrying wild-type genotype demonstrating that functional enzyme deficiencies due to polymorphism in CYPs may not only be important in modifying the susceptibility to HNSCC but also in determining chemotherapeutic response.     

Genetic polymorphisms in cytochrome P4501B1 and susceptibility to head and neck cancer

Cytochrome P4501B1 (CYP1B1), a polycyclic aromatic hydrocarbon (PAH) metabolizing CYP, is genetically polymorphic in humans and may be involved in the individual susceptibility to chemical-induced cancer. In the present study, genotype and haplotype frequencies of four single nucleotide polymorphisms (SNPs) in CYP1B1 that cause amino acid changes (Arg-Gly at codon 48, Ala-Ser at codon 119, Leu-Val at codon 432 and Asn-Ser at codon 453) were studied in 150 cases suffering from head and neck squamous cell carcinoma (HNSCC) and in an equal number of controls. A significant difference was observed for the distribution of variant genotypes of Arg48Gly (CYP1B1*2) and Ala119Ser (CYP1B1*2) polymorphisms of CYP1B1 in cases versus controls. No significant differences were observed for the distribution of variant genotypes-Leu432Val (CYP1B1*3) and Asn453Ser (CYP1B1*4), respectively. When the four SNPs were analyzed using a haplotype approach, SNPs at codon 48 (Arg48Gly) and codon 119 (Ala119Ser) exhibited complete linkage disequilibrium (LD) in all the cases and controls. Significant differences in the distribution of the two haplotypes (G-T-C-A and G-T-G-A) were observed both in the cases and in controls. Furthermore, our data indicates a several fold increase in risk in the cases who use tobacco (cigarette smoking or tobacco chewing) or alcohol with the variant genotypes of CYP1B1 (CYP1B1*2 and CYP1B1*3) suggesting the role of gene-environment interaction in the susceptibility to HNSCC.     

Polymorphism in environment responsive genes and association with Parkinson disease

Attempts were made in the present case-control study to investigate the association of polymorphism in the genes encoding proteins involved in toxication–detoxication and dopaminergic pathways and susceptibility to Parkinson’s disease (PD). Seventy patients suffering from PD and one hundred healthy controls belonging to the same geographical location and same ethnicity were included in the study. PCR-RFLP and allele-specific PCR-based methodology were used to identify the genotypes. Multivariate logistic regression analysis revealed that heterozygous genotypes of cytochrome P4502D6*4(CYP2D6*4), CYP2E1*5B (RsaI) polymorphism and homozygous mutant genotypes of CYP2E1*6 (Dra1) were found to be overrepresented in PD cases when compared to the controls. Risk was also found to be increased in patients carrying glutathione S-transferase T1 (GSTT1) null or homozygous variant genotypes of GSTP1. Significant association was observed for monoamine oxidase-B(MAO-B) variant allele G and PD, whereas no difference in genotype and allele frequencies was observed for manganese-superoxide dismutase (MnSOD), dopamine receptor-D2(DRD2), and dopamine transporter (DAT) genes between controls and PD cases. Genotype combinations characterized by the presence of two variant genotypes on their corresponding loci revealed that four combinations of GSTT1 null and MnSOD(-9Val) or GST null and MAOB-G or CYP2E1*5B and MAO-B-AG or CYP2E1*5B and DRD2 (Taq1A-het) genotypes in the patients exhibited severalfold higher and significant association with risk to PD. Our data suggest that polymorphism in the genes involved in detoxification and dopamine regulation may modulate the susceptibility to PD and could be important risk factors in the pathogenesis of PD.     

Association of genetic polymorphisms in glutathione S-transferases and susceptibility to head and neck cancer

Polymorphism in glutathione S-transferase (GST) genes (GSTM1, GSTT1 and GSTP1) and interaction with environmental factors such as tobacco (smoking or chewing) and alcohol on susceptibility to head and neck squamous cell carcinoma (HNSCC) was studied in a case-control study. The study group consisted of 175 patients suffering from HNSCC and 200 age matched healthy controls. Statistical analysis showed an increase in risk to HNSCC in the patients with null genotype of GSTM1 (OR: 2.02; 95% CI: 1.32-3.10; P=0.001) or GSTT1 (OR: 1.66; 95% CI: 1.02-2.69; P=0.04), though the risk was not found to be significant when adjusted for age, sex, smoking, tobacco chewing or alcohol use by multivariate logistic regression model. Our data further showed that combination of deletion genotypes of GST (GSTM1 and GSTT1) confer an even higher risk of HNSCC. Interestingly, GSTP1 wild type genotype in combination with GSTM1 null or GSTT1 null genotype increased susceptibility for HNSCC (OR: 2.49 and 2.75, respectively). Likewise a much greater risk for HNSCC was observed in the patients carrying a genotype combination of GSTM1 null, GSTT1 null and GSTP1 (Ile/Ile) (OR: 4.47; 95% CI: 1.62-12.31; P=0.002). Our data have further provided evidence that tobacco chewing and alcohol consumption are the important risk factors for HNSCC. The interaction between tobacco chewing and null genotype of GSTM1 or GSTT1 resulted in about 3.5- and 2.2-fold increase in the risk respectively in the patients when compared to those not chewing tobacco. Alcohol use resulted in more than 4-fold increase in the risk in the patients with null genotype of GSTM1 as compared to those who are non-drinkers. Alcohol consumption also increased the risk (approx. 3-fold) in the cases with null genotype of GSTT1, though the association was not found to be significant when compared to non-drinkers. Our data have provided evidence that GST polymorphism modifies the susceptibility to HNSCC and have further demonstrated importance of gene-environment interaction in modulating the risk to HNSCC.     

Impact of genetic variations of the CYP1A1, GSTT1, and GSTM1 genes on the risk of coronary artery disease

Carcinogenic and toxic molecules produce DNA adducts that contribute to the development of atherosclerosis. Genetic polymorphisms of xenobiotic-detoxified enzymes, which control the level of DNA adducts, may affect both enzymatic activity and individual susceptibility to coronary artery disease (CAD). In this study we investigated the effects of genetic polymorphisms of the CYP1A1*2C, GSTT1, and GSTM1 enzymes on CAD risk in a Turkish population. Genotypes were determined for 132 CAD patients and 151 healthy controls by the polymerase chain reaction/restriction fragment length polymorphism method. There were no significant differences between patients and controls in terms of CYP1A1, GSTT1, and GSTM1 genotypes. Analysis of the possible interactions between the genotypes, after adjustment for the risk factors, demonstrated that individuals carrying CYP1A1 variant GSTT1 null genotypes had an 8.907-fold increased CAD risk compared to their wild status (p<0.05). We suggest that genetic polymorphisms of xenobiotic-metabolizing enzymes could play an important role in CAD. Therefore, CYP1A1 and GSTM1 polymorphisms should be considered as important parameters for the prediction of CAD.     

CYP1A1, CYP2D6, CYP2E1, NAT2, GSTM1 and GSTT1 polymorphisms or their combinations are associated with the increased risk of the laryngeal squamous cell carcinoma

Polymorphisms in the selected genes controlling carcinogen metabolism (CYP1A1, CYP2D6, CYP2E1, NAT2, GSTM1, GSTT1) considered separately or in different combinations, were investigated for an association with tobacco smoke-associated squamous cell carcinoma (SCC) of the larynx. The case-control study was performed in 289 patients with laryngeal SCC and in 316 cancer-free controls; all were Caucasian males from the same region of Poland and current tobacco smokers. The DNA samples were genotyped using PCR-RFLP and multiplex PCR. The variants' frequencies in both groups were compared; odds ratios and their 95% confidence intervals were calculated by logistic regression analyses. The CYP1A1*1/*4, CYP2D6*4/*4, NAT2*4/*6A genotypes, as well as the CYP1A1*4, CYP2D6*4 and NAT2*4 alleles, were found at significantly higher frequencies in cases than in controls indicating their role as "risk-elevating" factors in laryngeal SCC. Combined genotypes, characterized by the presence of the "risk-elevating" variants at more than one locus, often occurred together with the null variant of the GSTM1 gene and homozygous XPD A/A (Lys751Gln, A35931C) genotype. Furthermore, we identified some "protective" variants, found more frequently in controls than in cases, i.e. the NAT2*6A/*6A and NAT2*5B/*6A genotypes. A distribution of "risk" or "protection" genotypes/alleles seems to be connected with age as an occurrence or risk genes was more frequent in the group of "young" cases (< or = 49 years). Accumulation of certain alleles or genotypes of the CYP1A1, NAT2, GSTM1 and XPD seems to be associated with either increased or decreased risk to develop laryngeal SCC. Therefore, polymorphisms in these genes may play a role in the laryngeal cancer etiology.     

Gene–gene interactions of drug metabolizing enzymes and transporter protein in the risk of upper aerodigestive tract cancers among Indians

Background: The combined genetic effects of single nucleotide polymorphisms may additively or synergistically contribute to the increased cancer risk. The interactions associated with xenobiotic metabolizing enzymes and transporter protein involved in the biotransformation and transport of xenobiotics could determine the functional outcomes over the independent effects of a single susceptibility gene in the risk of upper aerodigestive tract cancers. Methods: The hospital-based case–control study evaluated CYP1A1 (*2A and *2C), CYP2E1 (*1B, *5B, and *6), GST (M1, T1, and P1) and ABCB1 3435C>T polymorphisms among 408 histopathologically confirmed cases and 220 controls using polymerase chain reaction based methods in an Indian population. Results: The multivariate logistic regression analyses demonstrated potentially high risk gene–gene interactions with the concurrent deletions of the GSTT1 and GSTM1 genes and GSTP1 variant genotypes (OR 5.81; 95% CI 1.01–40.28), the deletions of GSTT1 and GSTM1 genotypes with variant genotypes of CYP1A1*2A (OR 8.21; 95% CI 1.91–49.48), GSTT1 and GSTM1 deficient genotypes along with CYP2E1*1B variant genotypes (OR 6.73; 95% CI 1.32–22.81), the polymorphic genotypes of ABCB1 and deficient GSTT1 (OR 6.08; 95% CI 2.21–16.76) and an enhanced risk with the combined variant genotypes of CYP1A1*2A, GSTT1 and ABCB1 (OR 11.14; 95% CI 2.70–46.02). Conclusion: The findings indicate that the interactions associated with various drug metabolizing enzymes and transporter protein exhibit high risk for UADT cancers than that ascribed to a single susceptible gene. This was particularly established among the polymorphic carriers of CYP1A1*2A, GSTT1 and ABCB1 genes in the population investigated.     

Study of the association between glutathione S-transferase (GSTM1, GSTT1, GSTP1) polymorphisms with type II diabetes mellitus in southern of Iran

Diabetes Mellitus is characterized by chronic hyperglycemia and associated with an increased production of reactive oxygen species (ROS). Oxidative stress is the result of accumulation of free radicals in tissues which specially affects beta cells in pancreas. Glutathione S-transferases (GSTs) are a family of antioxidant enzymes that include several classes of GSTs. These enzymes have important roles in decreasing of ROS species and act as a kind of antioxidant defense. To investigate the association between GSTs polymorphism with type 2 diabetes mellitus (T2DM), we investigated the frequency of GSTM1, T1 and P1 genotypes in patients with T2DM and controls. The genotypes of GSTT1, M1 and P1 were determined in 171 clinically documented T2DM patients and 169 normal cases (as controls) by multiplex polymerase chain reaction and PCR–RFLP. In diabetic patients, the frequency of GSTM1-null genotype was significantly (OR?=?1.74; 95?% CI?=?1.13–2.69, P?=?0.016) higher than that in control. However, the frequency of GSTT1 (OR?=?1.29; 95?% CI?=?0.07–2.14, P?=?0.367) and GSTP1 (OR?=?0.83; 95?% CI?=?0.53–1.30, P?=?0.389) genotypes were not significantly different comparing both groups. Also, the frequency of both GSTT1-null and GSTM1-null genotypes in patients (19.88?%) was significantly higher compared to controls with the same genotypes (11.83?%, P?=?0.022). Our results indicated that GSTM1 and GSTT1 genotypes might be involved in the pathogenesis of T2DM in south Iranian population.     

Interaction between the functional polymorphisms of the alcohol-metabolism genes in protection against alcoholism.

The genes that encode the major enzymes of alcohol metabolism, alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH), exhibit functional polymorphism. The variant alleles ADH2*2 and ADH3*1, which encode high-activity ADH isoforms, and the ALDH2*2 allele, which encodes the low-activity form of ALDH2, protect against alcoholism in East Asians. To investigate possible interactions among these protective genes, we genotyped 340 alcoholic and 545 control Han Chinese living in Taiwan at the ADH2, ADH3, and ALDH2 loci. After the influence of ALDH2*2 was controlled for, multiple logistic regression analysis indicated that allelic variation at ADH3 exerts no significant effect on the risk of alcoholism. This can be accounted for by linkage disequlibrium between ADH3*1 and ADH2*2 ALDH2*2 homozygosity, regardless of the ADH2 genotypes, was fully protective against alcoholism; no individual showing such homozygosity was found among the alcoholics. Logistic regression analyses of the remaining six combinatorial genotypes of the polymorphic ADH2 and ALDH2 loci indicated that individuals carrying one or two copies of ADH2*2 and a single copy of ALDH2*2 had the lowest risk (ORs 0.04-0.05) for alcoholism, as compared with the ADH2*1/*1 and ALDH2*1/*1 genotype. The disease risk associated with the ADH2*2/*2-ALDH2*1/*1 genotype appeared to be about half of that associated with the ADH2*1/*2-ALDH2*1/*1 genotype. The results suggest that protection afforded by the ADH2*2 allele may be independent of that afforded by ALDH2*2.     

Influence of glutathione S-transferase polymorphisms on genotoxic effects induced by tobacco smoke

Genotoxicity of tobacco smoke has long been investigated and tobacco smoke is considered to be one of the principal human carcinogens. Although its role in DNA-damage induction and cancer development has been documented, the mechanisms by which this happens are not well understood. Many chemical constituents of tobacco smoke are enzymatically metabolized by phase-I and phase-II enzymes, but modifications in coding and regulating sequences of these genes could influence their ability to detoxify these compounds. In this work, we studied several enzymes involved in the metabolism of xenobiotics, viz. the glutathione S-transferases (GST) M1, T1, P1 and A1, with respect to their influence on the genotoxic effects induced by cigarette smoking. We assessed the genotoxic effects of tobacco smoke on peripheral blood lymphocytes of 72 healthy caucasians by use of the chromosomal aberration (CA) assay and the micronucleus (MN) test. Genotypes of GST M1, T1, P1 and A1 were determined by means of the polymerase chain reaction and methods based on restriction fragment length polymorphism (RFLP). We found that smoke and gender are the two variables that most influence the DNA damage. In particular, we observed that female smokers seem to be more sensitive than male smokers, having a significantly higher frequency of CAs. Moreover, a significant increase in frequency of micronuclei in bi-nucleated cells (BNMN) was found in smokers, but not in non-smokers. This increase seems to be influenced not only by age and gender, but also by genetic constitution. Subjects carrying GSTM1-null genotype seemed to have an higher susceptibility to DNA damage induced by tobacco smoke than GSTM1-positive ones. When considering a combination of GST genotypes, we found a lower BNMN frequency in subjects with GSTP1 variant allele plus GSTM1-positive genotypes, while the most damaged cells are found in subjects bearing GSTM1-null plus GSTP1-wild type. Our results suggest that investigation of the association between several gene polymorphisms and important endpoints of DNA damage could contribute to better understanding the role of gene-gene interaction.     

Trimodal GSTT1 and GSTM1 genotyping assay by real-time PCR

The GSTT1 and GSTM1 genes are characterized by the existence of a GST*0 null allele responsible for a lack of enzyme activity, with the respective null genotypes GSTT1*0/0 and GSTM1*0/0. The three resulting genotypes (GSTs*1/1, *1/0 and *0/0) are associated with a trimodal distribution of glutathione-conjugator activity. Previous epidemiological studies have only evaluated the cancer risk associated with the GST null genotype relative to the two GST carrier genotypes (GSTs1*1/1 and *1/0). We developed GSTT1 and GSTM1 TaqMan real-time quantitative PCR assays to discriminate each of the three genotypes, with the albumin gene (ALB) as reference. The mean N(GSTT1*1/1) value was 1.0 (95% confidence interval 0.80-1.20). The mean N(GSTT1*1/0) value was 0.48 (95% CI 0.36-0.60). One (3.4%) of the 29 DNA samples yielded the GSTM1*1/1 genotype (N(GSTM1*1/1) = 1), a frequency in keeping with the Hardy-Weinberg distribution. The mean N(GSTM1*1/0) value was 0.50 (95% CI 0.42-0.58). All GSTT1*0/0 and GSTM1*0/0 samples yielded N(GST) values of 0 (Ct = 40); the frequencies of these genotypes (27.6% and 55.2%, respectively) were in keeping with published data. The GSTT1 and GSTM1 real-time PCR assays described here unambiguously discriminate each of the three existing genotypes which should be valuable for assessing the relative risk of cancer associated with each of the three GST genotypes.     

MTHFD1 G1958A, BHMT G742A, TC2 C776G and TC2 A67G polymorphisms and head and neck squamous cell carcinoma risk

Alterations in folate metabolism may contribute to the process of carcinogenesis by influencing DNA methylation and genomic stability. Polymorphisms in genes encoding enzymes involved in this pathway may alter enzyme activity and consequently interfere in concentrations of homocysteine and S-adenosylmethionine that are important for DNA synthesis and cellular methylation reactions. The objectives were to investigate MTHFD1 G1958A, BHMT G742A, TC2 C776G and TC2 A67G polymorphisms involved in folate metabolism on head and neck cancer risk and the association between these polymorphisms with risk factors. Polymorphisms were investigated in 762 individuals (272 patients and 490 controls) by polymerase chain reaction–restriction fragment length polymorphism (PCR–RFLP) and Real Time-PCR. Chi-square and Multiple logistic regression were used for the statistical analysis. Multiple logistic regression showed that tobacco and male gender were predictors for the disease (P < 0.05). Hardy–Weinberg equilibrium showed that the genotypic distributions were in equilibrium for both groups in all polymorphisms studied. The BHMT 742GA or AA genotypes associated with tobacco consumption (P = 0.016) increase the risk for head and neck squamous cell carcinoma (HNSCC). The present study suggests that BHMT 742GA polymorphism associated to tobacco modulate HNSCC risk. However, further investigation of gene–gene interactions in folate metabolism and studies in different populations are needed to investigate polymorphisms and HNSCC risk.     

The Incidence of Liver Injury in Uyghur Patients Treated for TB in Xinjiang Uyghur Autonomous Region,China, and Its Association with Hepatic Enzyme Polymorphisms NAT2, CYP2E1, GSTM1 and GSTT1

Background and Objective

Of three first-line anti-tuberculosis (anti-TB) drugs, isoniazid is most commonly associated with hepatotoxicity. Differences in INH-induced toxicity have been attributed to genetic variability at several loci, NAT2, CYP2E1, GSTM1and GSTT1, that code for drug-metabolizing enzymes. This study evaluated whether the polymorphisms in these enzymes were associated with an increased risk of anti-TB drug-induced hepatitis in patients and could potentially be used to identify patients at risk of liver injury.

Methods and Design

In a cross-sectional study, 2244 tuberculosis patients were assessed two months after the start of treatment. Anti-TB drug-induced liver injury (ATLI) was defined as an ALT, AST or bilirubin value more than twice the upper limit of normal. NAT2, CYP2E1, GSTM1 and GSTT1 genotypes were determined using the PCR/ligase detection reaction assays.

Results

2244 patients were evaluated, there were 89 cases of ATLI, a prevalence of 4% 9 patients (0.4%) had ALT levels more than 5 times the upper limit of normal. The prevalence of ATLI was greater among men than women, and there was a weak association with NAT2*5 genotypes, with ATLI more common among patients with the NAT2*5*CT genotype. The sensitivity of the CT genotype for identifying patients with ATLI was 42% and the positive predictive value 5.9%. CT ATLI was more common among slow acetylators (prevalence ratio 2.0 (95% CI 0.95,4.20) )compared to rapid acetylators. There was no evidence that ATLI was associated with CYP2E1 RsaIc1/c1genotype, CYP2E1 RsaIc1/c2 or c2/c2 genotypes, or GSTM1/GSTT1 null genotypes.

Conclusions

In Xinjiang Uyghur TB patients, liver injury was associated with the genetic variant NAT2*5, however the genetic markers studied are unlikely to be useful for screening patients due to the low sensitivity and low positive predictive values for identifying persons at risk of liver injury.     

The role of human glutathione S-transferases (hGSTs) in the detoxification of the food-derived carcinogen metabolite N-acetoxy-PhIP, and the effect of a polymorphism in hGSTA1 on colorectal cancer risk

Food-derived heterocyclic amines (HCAs), particularly 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), are implicated in the etiology of human colorectal cancer (CRC) via a process of N-oxidation followed by O-acetylation or O-sulfation to form electrophilic metabolites that react with DNA. Glutathione S-transferases (GSTs) detoxify activated carcinogen metabolites by catalysis of their reaction with GSH. However, among HCAs, only N-acetoxy-PhIP has been shown to be a substrate for the GSTs. By using a competitive DNA-binding assay, we confirm that hGSTA1-1 is an efficient catalyst of the detoxification of N-acetoxy-PhIP. Further, we show that hGSTs A2-2, P1-1, M1-1, T1-1 and T2-2 appear to have low activity towards N-acetoxy-PhIP, and that hGSTs A4-4, M2-2, M4-4 and Z1-1 appear to have no activity towards N-acetoxy-PhIP. A genetic polymorphism in the 5'-regulatory sequence of hGSTA1 has been shown to correlate with the relative and absolute levels of expression of GSTA1/GSTA2 in human liver. Examination of hGSTA1 allele frequency in 100 Caucasian CRC patients and 226 Caucasian controls demonstrated a significant over-representation of the homozygous hGSTA1*B genotype among cases compared to controls (24.0 and 13.7%, respectively, P=0.04). This corresponds to an odds ratio for risk of CRC of 2.0 (95% CI 1.0-3.7) when comparing homozygous hGSTA1*B individuals with all other genotypes. Thus, individuals who are homozygous hGSTA1*B, and who would be predicted to have the lowest levels of hGSTA1 expression in their livers, appear to be at risk of developing CRC, possibly as a result of inefficient hepatic detoxification of N-acetoxy-PhIP.     

Influence of the genetic polymorphism in the 5'-noncoding region of the CYP1A2 gene on CYP1A2 phenotype and urinary mutagenicity in smokers

The functional significance of genetic polymorphisms on tobacco smoke-induced CYP1A2 activity was examined. The influence of three polymorphisms of the cytochrome P450 1A2 gene (CYP1A2) (-3860 G-->A (allele *1C), -2467 T-->delT (allele *1D), -163C-->A (allele *1F)), located in the 5'-noncoding promoter region of the gene, on CYP1A2 activity (measured as caffeine metabolic ratio, CMR), was studied in Caucasian current smokers (n=95). Tobacco smoke intake was calculated from the number of cigarettes/day. Also, studied was the influence of these CYP1A2 genotypes on smoking-associated urinary mutagenicity, detected in Salmonella typhimurium strain YG1024 with S9 mix, considering the urinary excretion of nicotine plus its metabolites as an internal indicator of tobacco smoke exposure. Smokers with at least one of the variant alleles CYP1A2 -3860A and -2467 delT showed a significantly increased CYP1A2 CMR (-3860 G/A versus G/G, p<0.05; -2467 delT/delT versus T/delT and T/T, p<0.01). Multiple regression analysis showed that the increase in CYP1A2 CMR (ln values) was again significantly related to the presence of CYP1A2 variants -2467delT and also to variant -163A (p<0.05), but moderately to -3860A (p=0.084). No influence of the number of cigarettes smoked per day by each subject was found. Heavy smokers (n=48, with urinary nicotine plus its metabolites>or=0.69 mg/mmol creatinine) with variant allele -2467delT or -163A had significantly increased urinary mutagenicity (p<0.01 and <0.05). CYP1A2 genetic polymorphisms are shown to influence the CYP1A2 phenotype in smokers, -2467 T-->delT having the main effect. This information is of interest for future studies assessing the possible role of tobacco smoke-inducible CYP1A2 genotypes as individual susceptibility factors in exposure to carcinogens.     

Association of glutathione S-transferase omega gene polymorphisms with progression of head and neck cancer

This study investigated the influence of glutathione S-transferase omega 1 (GSTO1) and GSTO2 gene polymorphisms on susceptibility and aggressiveness of head and neck squamous cell carcinoma (HNSCC). A case–control study consisting of 300 HNSCC cases and 299 age and sex- matched normal control was performed. Genotyping of GSTO1*A140D and GSTO2*N142D polymorphisms was determined using the polymerase chain reaction—restriction fragment length polymorphism method. Our results revealed that the frequencies of GSTO1 and GSTO2 genotypes were not significantly different between HNSCC cases and controls. No significant differences were found in smoking or drinking status between cases and controls. However, HNSCC individuals with the GSTO1*D140 varient were significantly associated with nodal metastasis (OR?=?0.53, 95?%CI?=?0.31–0.91, P?=?0.020) and advanced pathological stage (OR?=?0.33,95?%CI?=?0.15–0.70, P?=?0.032), while no significant association was observed between GSTO2 genotype and clinicopathological features. Therefore, our findings suggest that the GSTO1*D140 variant genotype in individuals might play a protective role against the aggressiveness of HNSCC.     

Studies on the glutathione S-transferase proteome of adult Drosophila melanogaster: responsiveness to chemical challenge

GSTs from adult Drosophila melanogaster have been partially purified using three different affinity chromatography media and separated by 2-DE. Nine GSTs have been identified by MALDI-TOF MS. In the absence of special treatments, eight GSTs could be positively identified. These were DmGSTs D1 (the dominant Delta isoform which was present in five protein zones of differing pI) and D3 (and possibly also D5); the Epsilon-class GSTs E3, 6, 7 and 9 and a previously uncharacterised, probable member of the class, CG16936. The Sigma-class DmGSTS1 was prominent. DmGSTD2 was detected only after pretreatment of the flies with Phenobarbital (PhB). Treatment with Paraquat (PQ) led to an increase in the total GST activity, as measured with the substrates 1-chloro-2,4-dinitrobenzene (CDNB) and 3,4-dichloro-nitrobenzene (DCNB) and an increase in the relative amounts of the D1, D3, E6 and E7 isoforms. PhB treatment led to increases in the relative amounts of the D1, D2, E3, E6, E7 and E9 isoforms detected with a possible depression in the relative amount of GSTS1. CG16936 was unaffected by either pretreatment.     

CYP1A1 and CYP2D6 polymorphism and risk of lung cancer in a North Indian population.

This case-control study was conducted to examine the association between the CYP1A1 and CYP2D6 genotypes and lung cancer risk among North Indians. The estimated relative risk for lung cancer associated with the CYP1A1 Val/Val allele was 2.68, and was four-fold when cases with small cell lung cancer (SCLC) were considered alone. With regard to the metabolism of debrisoquine, no poor metabolizers were found amongst the subjects. The odds ratio of risk with the heterozygous extensive metabolizer (HEM) genotype was 1.5. However, in the presence of at least a single copy of the variant CYP1A1 MspI allele and the CYP2D6 HEM genotype, the risk was two-fold for squamous cell carcinoma (SQCC). When the CYP1A1 Val/Val and CYP2D6 HEM genotypes were taken together, the risk for SCLC was four-fold. Stratified analysis indicated an interaction between bidi smoking and variant CYP1A1 genotypes on the risk for SQCC and SCLC. Heavy smokers (Brinkman index>400) with Val/Val genotypes were at a very high risk of developing lung cancer (odds ratio 29.30, 95% confidence interval 2.42-355, p=0.008). Heavy smokers with CYP1A1 MspI (CYP1A1*1/2A or CYP1A1*2A/*2A) genotype had a seven-fold risk for SCLC compared with non-smokers. This study is the first to be carried out on a North Indian population, and, although small, suggests that CYP1A1 and CYP2D6 polymorphisms might have a role in determining the risk for lung cancer and should be investigated further.     

Molecular genetics and epigenetics of the cytochrome P450 gene family and its relevance for cancer risk and treatment

The cytochromes P450 (CYPs) are very efficient catalysts of foreign compound metabolism and are responsible for the major part of metabolism of clinically important drugs. The enzymes are important in cancer since they (a) activate dietary and environmental components to ultimate carcinogens, (b) activate or inactivate drugs used for cancer treatment, and (c) are potential targets for anticancer therapy. The genes encoding the CYP enzymes active in drug metabolism are highly polymorphic, whereas those encoding metabolism of precarcinogens are relatively conserved. A vast amount of literature is present where investigators have tried to link genetic polymorphism in CYPs to cancer susceptibility, although not much conclusive data have hitherto been obtained, with exception of CYP2A6 polymorphism and tobacco induced cancer, to a great extent because of lack of important functional polymorphisms in the genes studied. With respect to anticancer treatment, the genetic CYP polymorphism is of greater importance, where treatment with tamoxifen, but also with cyclophosphamide and maybe thalidomide is influenced by CYP genetic variants. In the present review we present updates on CYP genetics, cancer risk and treatment and also epigenetic aspects of interindividual variability in CYP expression and the use of these enzymes as targets for cancer therapy. We conclude that the CYP polymorphism does not predict cancer susceptibility to any large extent but that this polymorphism might be an important factor for optimal cancer therapy using selected anticancer agents.