Characterization of a human glutathione S-transferase mu cluster containing a duplicated GSTM1 gene that causes ultrarapid enzyme activity

Kinetic Behavior of Glutathione Transferases: Understanding Cellular Protection from Reactive Intermediates

Glutathione transferases (GSTs) are the primary catalysts protecting from reactive electrophile attack. In this review, the quantitative levels and distribution of glutathione transferases in relation to physiological function are discussed. The catalytic properties (random sequential) tell us that these enzymes have evolved to intercept reactive intermediates. High concentrations of enzymes (up to several hundred micromolar) ensure efficient protection. Individual enzyme molecules, however, turn over only rarely (estimated as low as once daily). The protection of intracellular protein and DNA targets is linearly proportional to enzyme levels. Any lowering of enzyme concentration, or inhibition, would thus result in diminished protection. It is well established that GSTs also function as binding proteins, potentially resulting in enzyme inhibition. Here the relevance of ligand inhibition and catalytic mechanisms, such as negative co-operativity, is discussed. There is a lack of knowledge pertaining to relevant ligand levels in vivo, be they exogenous or endogenous (e.g., bile acids and bilirubin). The stoichiometry of active sites in GSTs is well established, cytosolic enzyme dimers have two sites. It is puzzling that a third of the site's reactivity is observed in trimeric microsomal glutathione transferases (MGSTs). From a physiological point of view, such sub-stoichiometric behavior would appear to be wasteful. Over the years, a substantial amount of detailed knowledge on the structure, distribution, and mechanism of purified GSTs has been gathered. We still lack knowledge on exact cell type distribution and levels in vivo however, especially in relation to ligand levels, which need to be determined. Such knowledge must be gathered in order to allow mathematical modeling to be employed in the future, to generate a holistic understanding of reactive intermediate protection.

Many hands make light work: CNV of GSTM1 effect on the oral carcinoma risk

BACKGROUND

Genetic alterations of oral squamous cell carcinoma (OSCC) allow the understanding of the oral carcinogenesis and the identification of molecular biomarkers that aid the early diagnosis of the disease. The copy number variation (CNV) of GSTM1 and GSTT1 are promising targets because these two genes codify enzymes that perform the inactivation of tobacco carcinogens, which are the main risk factor of OSCC. However, the different levels of - detoxification mechanism in relation to each copy of the genes are unknown. Therefore, this study aimed to investigate the possible association of the CNV of GSTM1 and GSTT1 with the risk of development of OSCC.

METHODS

A total of 234 OSCC patients and 422 patients without any cancer diagnoses were recruited from Heliópolis Hospital from 2000 to 2011. The CNV was determined by TaqMan real-time PCR and the CopyCaller software. Odds ratio (OR) and 95% confidence interval (95% CI) values were calculated by Multiple Logistic Regression.

RESULTS

Most OSCC patients reported they continued smoking high amounts of cigarettes despite the tumor diagnosis. The CNV of GSTM1 varied from zero to two copies and the analysis revealed that two copies of GSTM1 decreased by 53% the OSCC risk (OR 0.47; 95% CI 0.24-0.92) and the risk of the tumor was modified according to the interaction of the CNV of GSTM1 and the cigarette smoking consumption, which for the amount of 40 packs-year of cigarettes the OSCC risk diminished progressively according to the increase of copies of GSTM1. Although the GSTT1 gene varied from zero to three copies, none of them were associated with the tumor risk.

CONCLUSION

The findings suggest that the CNV of GSTM1 might be applied as a tool for the surveillance of patients and the early detection of OSCC.

Influence of genetic polymorphisms in glutathione-S-transferases gene in response to imatinib among Brazilian patients with chronic myeloid leukemia

Polymorphism in metabolizing enzymes can influence drug response as well as the risk for adverse drug reactions. Nevertheless, there are still few studies analyzing the consequence of polymorphisms for the Glutathione-S-transferases (GST) gene to drug response in chronic myeloid leukemia (CML). This study reports, the influence of GSTP1*B and GSTT1/GSTM1null polymorphisms in response to imatinib in CML patients in a Brazilian population. One hundred thirty-nine CML patients from the Clinical Hospital of Goiânia, Goiás, Brazil, treated with imatinib were enrolled in this study. Genotyping of GSTT1 and GSTM1 genes deletions were performed by qPCR and of GSTP1 gene was performed by RFLP-PCR. The frequency of GSTP1*1B, GSTT1 and GSTM1null polymorphisms were determined for all patients. The influence of each patient's genotypes was analyzed with the patient's response to imatinib treatment. Brazilian CML patients revealed GSTT1 and GSTM1 genes deletions. GSTT1 deletion was found in 19.3% of patients and GSTM1 deletion in 48.7% of patients with CML. GSTT1/GSTM1 deletion was found in 11.7% in Brazilian CML patients. The "G allele" of GSTP1*B, is associated with later cytogenetic response in imatinib therapy. While, the gene presence combined with GG genotype (GSTM1 present/GSTPI-GG) conferred a tend to a later cytogenetic response to patients. GSTP1*B and GSTT1/GSTM1null polymorphisms influence treatment response in CML. Brazilian CML patients presenting GSTP1 AA/AG genotypes alone and in combination with GSTT1 null reach the cytogenetic response faster, while patients presenting GSTP1-GG and GSTMI positive genotypes may take longer to achieve cytogenetic response. As a result, it allows a better prognosis, with the use of an alternative therapy, other than reducing treatment cost.

Role of GSTM1 and GSTT1 genotypes in differentiated thyroid cancer and interaction with lifestyle factors: Results from case-control studies in France and New Caledonia

Background

GSTM1 and GSTT1 are involved in detoxification of xenobiotics, products of oxidative stress and in steroid hormones metabolism. We investigated whether GSTM1 and GSTT1 gene deletion was associated with DTC risk and explored interaction with non-genetic risk factors of DTC.

Methods

The study included 661 DTC cases and 736 controls from two case-control studies conducted in France and New Caledonia. Odds ratios (OR) and their confidence interval (CI) for DTC associated with GST genotypes, alcohol drinking, tobacco smoking, body mass index and hormonal factors were calculated using logistic regression models.

Results

Results are presented for Europeans and Melanesians combined, as no heterogeneity between groups was detected. We found that DTC risk increased with obesity and decrease with alcohol drinking. After stratification by gene deletion status, the OR for obesity was 5.75, (95%CI 2.25–14.7) among individuals with GSTT1 and GSTM1-deleted genotype, and 1.26, (95%CI 0.89–1.77) in carriers of both genes (p-interaction = 0.02). The OR for drinking ≥1 glass/week was 0.33 (95%CI 0.15–0.74) in GSTT1-null individuals while it was 1.01 (95%CI 0.67–1.52) in non-null carriers of the gene (p-interaction = 0.01). No interaction between GST genotypes and other non-genetic risk factors was detected.

Conclusion

GSTM1 and GSTT1 genotypes may modulate the DTC risk associated with BMI and alcohol consumption.

How many copies of GSTM1 and GSTT1 are associated with head and neck cancer risk?

Purpose: GSTM1 and GSTT1 present a polymorphism that can drive complete gene deletions. The current methodology can powerfully determine GSTM1 and GSTT1 copy number variations (CNVs), which may clarify the real contribution of each gene copies to the cellular detoxification process and tumour risk. However, only analysing the presence/absence of these genes yielded controversial results for several disorders, including cancer. Because head and neck cancer (HNC) is becoming a serious global health problem, this study determined the CNVs of GSTM1 and GSTT1 in an HNC case-control population and investigated the possible association between gene copy numbers and tumour risk. Methods: CNV was evaluated by (Ct) 2^-ΔΔCt qPCR methodology in 619 HNC patients and 448 patients with no tumour diagnosis. Results: The genes copy number range was 0-3. The CNV of GSTM1 and GSTT1 frequencies were similar between the cases and control. Thus, none copy of GSTM1 and GSTT1 were associated with HNC risk. Notwithstanding, one copy of both genes had higher frequencies among individuals who carried GSTM1 and GSTT1. Conclusions: One copy number of GSTM1 and GSTT1 presented a higher frequency among carrier genes, but the CNV of GSTM1 and GSTT1 was not associated with HNC risk.

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 geno-® types (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 NGSTT1*1/1 value was 1.0 (95% confidence interval 0.80–1.20). The mean NGSTT1*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 (NGSTM1*1/1 = 1), a frequency in keeping with the Hardy-Weinberg distribution. The mean NGSTM1*1/0 value was 0.50 (95% CI 0.42–0.58). All GSTT1*0/0 and GSTM1*0/0 samples yielded NGST 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.

Characterization of ADME gene variation in 21 populations by exome sequencing

OBJECTIVE

Proteins involving absorption, distribution, metabolism, and excretion (ADME) play a critical role in drug pharmacokinetics. The type and frequency of genetic variation in the ADME genes differ among populations. The aim of this study was to systematically investigate common and rare ADME coding variation in diverse ethnic populations by exome sequencing.

MATERIALS AND METHODS

Data derived from commercial exome capture arrays and next-generation sequencing were used to characterize coding variation in 298 ADME genes in 251 Northeast Asians and 1181 individuals from the 1000 Genomes Project.

RESULTS

Approximately 75% of the ADME coding sequence was captured at high quality across the joint samples harboring more than 8000 variants, with 49% of individuals carrying at least one 'knockout' allele. ADME genes carried 50% more nonsynonymous variation than non-ADME genes (P=8.2×10) and showed significantly greater levels of population differentiation (P=7.6×10). Out of the 2135 variants identified that were predicted to be deleterious, 633 were not on commercially available ADME or general-purpose genotyping arrays. Forty deleterious variants within important ADME genes, with frequencies of at least 2% in at least one population, were identified as candidates for future pharmacogenetic studies.

CONCLUSION

Exome sequencing was effective in accurately genotyping most ADME variants important for pharmacogenetic research, in addition to identifying rare or potentially de novo coding variants that may be clinically meaningful. Furthermore, as a class, ADME genes are more variable and less sensitive to purifying selection than non-ADME genes.

Droplet Digital PCR Analysis of GSTM1 Deletion Polymorphism in Psoriatic Subjects Treated with Goeckerman Therapy

Goeckerman therapy (GT) represents an effective treatment of psoriasis including a combination of pharmaceutical grade crude coal tar (CCT) and ultraviolet irradiation (UV-R). Coal tar contains a mixture of polycyclic aromatic hydrocarbons. The best known carcinogenic polyaromate - benzo[a]pyrene is metabolized into a highly reactive benzo[a]pyrene-7,8-diol-9,10-epoxide (BPDE). Glutathione S-transferase M1 (GSTM1) catalyses the conjugation of drugs, toxins and products of oxidative stress with glutathione. The aim of the study is to found possible associations between GSTM1 genotypes and the level of BPDE-DNA adducts in 46 psoriatic patients treated with GT. For genotyping, droplet digital PCR was applied. The GSTM1 copy number was normalized to β-globin reference gene. In five GSTM1*1/*1 subjects, the GSTM1 to β-globin ratio moved from 0.99 to 1.03 with a median of 1.01. GSTM1*0/*1 heterozygotes (n = 20) contained only one GSTM1 function allele which conditioned the ratio 0.47-0.53 (median 0.50). GSTM1*0/*0 individuals (n = 21) showed no amplification of the null variants because of the large deletion in GSTM1. BPDE-DNA concentrations ranged from 1.8 to 66.3 ng/µg with a median of 12.3 ng/µg. GSTM1*0/*0 and GSTM1*0/*1 genotypes showed non-significantly higher concentrations of BPDE-DNA adducts than the GSTM1*1/*1 one (12.3 and 12.4 vs 7.8 ng/µg). The non-significant relationship between BPDE-DNA adducts and GSTM1 genotypes in psoriatic patients could be associated with relatively low doses of CCT and short-term UV-R exposures used in GT.

GSTM1 and GSTP1 Genetic Polymorphisms and Their Associations With Acute Lymphoblastic Leukemia Susceptibility in a Jordanian Population

The genetic variations between different individuals in the xenobiotic detoxifying enzyme activity were shown to change susceptibility to acute lymphoblastic leukemia (ALL). The current study aimed to assess the association of GSTM1 and GSTP1 genetic polymorphisms with the susceptibility of ALL. This case-control study (N=264) involved 88 Jordanian ALL children and 176 healthy controls from an ethnically homogenous Jordanian children population. The polymerase chain reaction assay was used to genotype GSTM1 (null/present) and the polymerase chain reaction-restriction fragment length polymorphism technique was also applied to detect the genetic polymorphisms of GSTP1 (Ile105Val) at the rs1695 position. The biallelic analysis revealed that there was no association between GSTM1 double-null genotype and ALL (P=0.57). However, there was a strong association between GSTP1 (Ile105Val) polymorphism genotypes and alleles within GSTP1 gene and ALL (P=0.00049 and 0.000044, respectively). A combination between GSTM1 double-null genotype and rs1695 also showed an association with ALL (P=0.042). This study showed that the rs1695 single nucleotide polymorphism within the GSTP1 gene is strongly implicated in ALL among Jordanian children with ALL. These results indicate that genetic variants of GSTP1 gene influence the risk of developing ALL in the Jordanian children of Arab ancestry.

Glutathione Transferase Gene Variants Influence Busulfan Pharmacokinetics and Outcome After Myeloablative Conditioning

Supplemental Digital Content is Available in the Text.

Background:

Busulfan (Bu) and cyclophosphamide (Cy) are frequently included in conditioning regimens before hematopoietic stem cell transplantation (HSCT). Both drugs are detoxified by glutathione transferases (GST), and GST gene variants may explain some of the interindividual variability in pharmacokinetics and drug toxicity.

Methods:

The study investigated adult patients (n = 114) receiving oral Bu pre-HSCT. Bu doses were adjusted to obtain an average steady-state concentration (C_ss) of 900 mcg/L.

Results:

Median first dose Bu C_ss was 1000 mcg/L (600–1780 mcg/L). Patients carrying 1 and 2 GSTA1*B (rs3957357) alleles demonstrated median 12% and 16% higher Bu C_ss (P ≤ 0.05). Bu exposure (average C_ss; odds ratio = 1.009, 95% confidence interval = 1.002–1.017, P = 0.013) and GSTM1 gene copy number (odds ratio = 17.1, 95% confidence interval = 1.46–201, P = 0.024) were significant predictors of mortality ≤30 days. The mortality was 25% versus 2% among carriers of 2 versus no GSTM1 copies (P = 0.021). Mortality ≤3 months was associated with higher first dose Bu exposure (1090 versus 980 mcg/L, P = 0.021). GSTM1 expression and high Bu exposure may increase Cy toxicity by reducing intracellular glutathione.

Conclusions:

GST genotyping before HSCT may allow better prediction of Bu pharmacokinetics and drug toxicity, and thereby improve outcome after BuCy conditioning.

Analyses of Genetic Variations of Glutathione S-Transferase Mu1 and Theta1 Genes in Bangladeshi Tannery Workers and Healthy Controls

Glutathione S-transferases (GSTs) belong to a group of multigene detoxification enzymes, which defend cells against oxidative stress. Tannery workers are at risk of oxidative damage that is usually detoxified by GSTs. This study investigated the genotypic frequencies of GST Mu1 (GSTM1) and GST Theta1 (GSTT1) in Bangladeshi tannery workers and healthy controls followed by their status of oxidative stress and total GST activity. Of the 188 individuals, 50.0% had both GSTM1 and GSTT1 (+/+), 12.2% had GSTM1 (+/-), 31.4% had GSTT1 (-/+) alleles, and 6.4% had null genotypes (-/-) with respect to both GSTM1 and GSTT1 alleles. Among 109 healthy controls, 54.1% were double positive, 9.2% had GSTM1 allele, 32.1% had GSTT1 allele, and 4.6% had null genotypes. Out of 79 tannery workers, 44.3% were +/+, 16.8% were +/-, 30.5% were -/+, and 8.4% were -/-. Though the polymorphic genotypes or allelic variants of GSTM1 and GSTT1 were distributed among the study subjects with different frequencies, the differences between the study groups were not statistically significant. GST activity did not vary significantly between the two groups and also among different genotypes while level of lipid peroxidation was significantly higher in tannery workers compared to controls irrespective of their GST genotypes.

Copy number variation of GSTT1 and GSTM1 and the risk of prostate cancer in a Caribbean population of African descent

Background

Deletions of the glutathione S-transferase genes M1 and T1 (GSTM1 and GSTT1) have been studied as potential risk factors for prostate cancer. Conflicting results have been obtained. Moreover, most such studies could not discriminate heterozygous from homozygous carriers of the non-deleted alleles.

Objective

We investigated whether copy number variation (CNV) of the GSTM1 and/or GSTT1 genes contribute to the risk of prostate cancer in the Caribbean population of African descent of Guadeloupe.

Methods

In a population-based case-control study, we compared 629 prostate cancer patients and 622 control subjects. Logistic regression was used to estimate adjusted odds ratios (OR) and 95% confidence intervals (CI). Exact copy numbers of GSTM1 and GSTT1 were determined by real-time PCR.

Results

A higher copy number of GSTM1 was marginally associated with prostate cancer risk. Men with 2 and 3 or more GSTT1 genes were at higher risk of prostate cancer (OR: 1.55, 95% CI: 1.11–2.16 and OR: 4.89, 95% CI: 1.71–13.99, respectively; P_trend<0.001). Men with 3, 4 and 5 or more copies of both GSTM1 and GSTT1 genes were at higher risk of prostate cancer (OR: 2.18, 95% CI: 1.21–3.91, OR: 3.24, 95% CI: 1.63–6.46, and OR: 5.77, 95% CI: 1.40–23.84, respectively; P_trend<0.001).

Conclusions

Copy number of GSTT1 and combined GSTM1/GSTT1 appear to be associated with prostate cancer risk in our population study with gene dose relationship. Our results support the hypothesis that variations in copy number of GSTT1 modulate the risk of prostate cancer.

Functional compensation of glutathione S-transferase M1 (GSTM1) null by another GST superfamily member, GSTM2

The gene for glutathione-S-transferase (GST) M1 (GSTM1), a member of the GST-superfamily, is widely studied in cancer risk with regard to the homozygous deletion of the gene (GSTM1 null), leading to a lack of corresponding enzymatic activity. Many of these studies have reported inconsistent findings regarding its association with cancer risk. Therefore, we employed in silico, in vitro, and in vivo approaches to investigate whether the absence of a functional GSTM1 enzyme in a null variant can be compensated for by other family members. Through the in silico approach, we identified maximum structural homology between GSTM1 and GSTM2. Total plasma GST enzymatic activity was similar in recruited individuals, irrespective of their GSTM1 genotype (positive/null). Furthermore, expression profiling using real-time PCR, western blotting, and GSTM2 overexpression following transient knockdown of GSTM1 in HeLa cells confirmed that the absence of GSTM1 activity can be compensated for by the overexpression of GSTM2.

GSTM1 copy number and promoter haplotype as predictors for risk of recurrence and/or second primary tumor in patients with head and neck cancer

The objective of this study was to determine copy number variant (CNV) and promoter genetic variants in glutathione S-transferase Mu class 1 (GSTM1) and the risk of recurrence (REC)/second primary tumor (SPT) in patients with previously diagnosed early stage head and neck cancer. Among 441 subjects, 133 experienced REC and/or an SPT, while 308 had single primary disease. TaqMan real-time polymerase chain reaction was used to measure the exact copy number of GSTM1 and direct sequencing was used to determine genetic variants in the GSTM1 promoter region. Multivariate Cox regression analysis was performed to estimate hazard ratios (HRs) and 95% confidence intervals (95% CIs) associated with copy number and genetic variants. REC/SPT-free survival times were compared by constructing Kaplan–Meier curves and differences between curves were tested by logrank test. Results showed a significantly decreased REC/SPT (HR = 0.57; 95% CI = 0.35–0.95) and longer REC/SPT-free survival in subjects with at least two copies of GSTM1 compared with the GSTM1 homozygous deletion, but not in those with one copy of GSTM1. The −498G, −426G, and −339T alleles were significantly associated with REC/SPT, with HRs of 0.11 (0.02–0.85), 0.28 (0.11–0.74) and 2.02 (1.07–3.82), respectively. Kaplan–Meier survival analysis showed that the −498G, −426G, and −339C alleles were also significantly associated with increased REC/SPT-free survival. Further haplotype analysis showed the haplotype P^{−498G-−426G-−339C} carriers had decreased REC/SPT with a HR of 0.09 (95% CI 0.01–0.71) and increased REC/SPT-free survival compared with those with haplotype P^{−498C-−426A-−339T}. The P^{−498C-−426A-−339T}-containing reporter construct had significantly increased luciferase expression. These results suggest that the GSTM1 CNV and promoter haplotype are better predictors of REC/SPTs of head and neck cancer than just measuring the presence/absence of GSTM1.

Birth weight of Korean infants is affected by the interaction of maternal iron intake and GSTM1 polymorphism

Excessive iron consumption during pregnancy can lead to increased oxidative stress in the maternal body, which may result in adverse pregnancy outcomes. Glutathione S-transferases (GSTs) originate from a superfamily of detoxifying enzymes that play a role in reducing xenobiotic compounds and oxidative stress. The aim of this study was to determine the relationship among GST gene expression, maternal iron intake during pregnancy, and neonatal birth weight. The study participants were 1087 Korean gravidas and their newborns recruited for the Mothers and Children's Environmental Health study between 2006 and 2010. A 24-h dietary recall interview was conducted to estimate iron intake; additional intake through nutritional supplements was thoroughly investigated. Deletion polymorphisms of GSTM1 and GSTT1 were genotyped using PCR. Dietary iron consumption during pregnancy was positively associated with birth weight in pregnant women who were GSTM1-present after adjustment for the following covariates: maternal age, prepregnancy BMI, mother's education level, log-transformed urinary cotinine level, infant gender, gestational age at term, log-transformed energy intake, parity, and the use of folic acid supplements (P < 0.05). There were interactions between the GSTM1 genotype and iron intakes from animal foods (P < 0.05), diet (P < 0.05), and diet with supplements (P < 0.05). No relationship was found between maternal iron intake and birth weight for the GSTT1 polymorphism. This study demonstrates that increased iron consumption during pregnancy may improve infant birth weight for mothers who are GSTM1-present, but it might not be beneficial for mothers with the GSTM1-null genotype.

Glutathione transferases, regulators of cellular metabolism and physiology

BACKGROUND

The cytosolic glutathione transferases (GSTs) comprise a super family of proteins that can be categorized into multiple classes with a mixture of highly specific and overlapping functions.

SCOPE OF REVIEW

The review covers the genetics, structure and function of the human cytosolic GSTs with particular attention to their emerging roles in cellular metabolism.

MAJOR CONCLUSIONS

All the catalytically active GSTs contribute to the glutathione conjugation or glutathione dependant-biotransformation of xenobiotics and many catalyze glutathione peroxidase or thiol transferase reactions. GSTs also catalyze glutathione dependent isomerization reactions required for the synthesis of several prostaglandins and steroid hormones and the catabolism of tyrosine. An increasing body of work has implicated several GSTs in the regulation of cell signaling pathways mediated by stress-activated kinases like Jun N-terminal kinase. In addition, some members of the cytosolic GST family have been shown to form ion channels in intracellular membranes and to modulate ryanodine receptor Ca(2+) channels in skeletal and cardiac muscle.

GENERAL SIGNIFICANCE

In addition to their well established roles in the conjugation and biotransformation of xenobiotics, GSTs have emerged as significant regulators of pathways determining cell proliferation and survival and as regulators of ryanodine receptors that are essential for muscle function. This article is part of a Special Issue entitled Cellular functions of glutathione.

Polymorphic variation in glutathione-S-transferase genes and risk of chronic myeloid leukaemia in the Kashmiri population

Cancer is a complex disease and the genetic susceptibility to it could be an outcome of the inherited difference in the capacity of xenobiotic metabolizing enzymes. Glutathione-S-transferases (GSTs) are phase II metabolizing enzymes whose various genotypes have been associated with increased risk of different types of cancer. Null mutations caused by the deletion of the entire gene result in the absence of the enzymatic activity and increase in the risk of developing cancer including chronic myeloid leukaemia (CML). In the present case-control study we evaluated the effect of null mutations in GSTM1 and GSTT1 genes on the risk of developing CML. The study included 75 CML patients (43 males and 32 females; age (mean ± S.D) 42.3 ± 13.4 years) and unrelated non-malignant controls (76 male and 48 females; age (mean ± S.D) 41.5 ± 12.9). The distribution of GSTM1 and GSTT1 genotypes in CML patients and controls was assessed by multiplex-PCR method. Logistic regression was used to assess the relationship between GSTM1 and GSTT1 genotypes and risk of CML. Chi-square test was used to evaluate the trend in modulating the risk to CML by one or more potential high risk genotype. Although GSTM1 null genotype frequency was higher in CML patients (41%) than in the controls (35%), it did not reached a statistical significance (OD = 1.32, 95% CI: 0.73-2.40; P value = 0.4295). The frequency of GSTT1 null genotypes was higher in the CML patients (36%) than in the controls (21%) and the difference was found to be statistically significant (OD = 2.12, 95% CI: 1.12-4.02; P value = 0.0308). This suggests that the presence of GSTT1 genotype may have protective role against the CML. We found a statistically significant (OD = 3.09, 95% CI: 1.122-8.528; P value = 0.0472) interaction between the GSTM1 and GSTT1 null genotypes and thus individuals carrying null genotypes of both GSTM1 and GSTT1 genes are at elevated risk of CML.

Genetic variants in carcinogen-metabolizing enzymes, cigarette smoking and pancreatic cancer risk

Individual susceptibility to the toxic effects of cigarette smoke may be modified by inherited variability in carcinogen metabolism. The purpose of the present study was to investigate pancreatic cancer risk associated with cigarette smoking and 33 variants within carcinogen metabolism genes and examine whether these variants modify the association between smoking and pancreatic cancer. A population-based study was conducted with 455 pancreatic cancer cases and 893 controls. Epidemiological and smoking data were collected from questionnaires and variants were genotyped by mass spectrometry. Age- and sex-adjusted odds ratio (ASOR) and multivariate-adjusted odds ratio (MVOR) estimates were obtained using multivariate logistic regression, and interactions between each variant and smoking were investigated. Current smoker status [MVOR = 2.29, 95% confidence interval (95% CI): 1.62, 3.22], 10-27 pack-years (MVOR = 1.57, 95% CI: 1.13, 2.18), >27 pack-years (MVOR = 1.77, 95% CI: 1.27, 2.46) and longer durations of smoking (19-32 years: MVOR = 1.46, 95% CI: 1.05, 2.05; >32 years: MVOR = 1.78, 95% CI: 1.30, 2.45) were associated with increased pancreatic cancer risk. CYP1B1-4390-GG (ASOR = 0.36, 95% CI: 0.15, 0.86) and Uridine 5'-diphospho glucuronosyltransferase 1 family, polypeptide A7-622-CT (ASOR = 0.77, 95% CI: 0.60, 0.99) were associated with reduced risk. N-acetyltransferase 1-640-GT/GG (ASOR = 1.75, 95% CI: 1.00, 3.05), GSTM1 (rs737497)-GG (ASOR = 1.41, 95% CI: 1.02, 1.95), GSTM1 gene deletion (ASOR = 4.89, 95% CI: 3.52, 6.79) and glutathione S-transferase theta-1 gene deletion (ASOR = 4.41, 95% CI: 2.67, 7.29) were associated with increased risk. Significant interactions were observed between pack-years and EPHX1-415 (P = 0.04) and smoking status and N-acetyltransferase 2-857 (P = 0.03). Variants of carcinogen metabolism genes are independently associated with pancreatic cancer risk and may modify the risk posed by smoking.

Copy Number Variation in Glutathione S-Transferases M1 and T1 and Ischemic Vascular Disease

Background—

Glutathione S-transferases (GSTs) M1 and T1 detoxify products of oxidative stress and may protect against atherosclerosis and ischemic vascular disease (IVD). We tested the hypothesis that copy number variation (CNV) in GSTM1 and GSTT1 genes, known to be associated with stepwise decreases in catalytic activity, predict risk of IVD.

Methods and Results—

We included 23 059 Danes from 2 general population studies and 2 case-control studies, of whom 4930 had ischemic heart disease (IHD) and 2086 had ischemic cerebrovascular disease. A real-time polymerase chain reaction method genotyped for the exact number of GSTM1 and GST T1 gene copies. We also performed meta-analyses, including our own and former studies, totaling 13 196 IHD cases and 33 228 controls. CNV in GSTM1 or GSTT1 or genotype combinations were not associated with an increased risk of IHD, myocardial infarction, ischemic cerebrovascular disease, ischemic stroke, or any ischemic vascular event in studies individually or combined or in the meta-analyses. Furthermore, genotypes did not interact with smoking on risk of disease end points. Finally, GST genotypes did not associate with markers of inflammation and oxidation or interact with smoking on markers of inflammation in the general population. In contrast, we observed the well-established association between CNV in GSTM1 and risk of bladder cancer.

Conclusions—

In studies including 6557 IVD cases and 16 502 controls and in meta-analyses of 13 196 cases and 33 228 controls, CNV in GSTM1 and GST T1 genes did not associate with risk of IVD or with markers of inflammation. These observations were independent of smoking exposure.

Pharmacogenomics of cisplatin-induced ototoxicity

Cisplatin ototoxicity affects different individuals in a widely variable manner. These variations are likely to be explained by genetic differences among those affected. It would be highly advantageous to identify genetic variants that predispose to cisplatin ototoxicity in order to minimize the risk to susceptible subgroups. Although this area of research is very important, only a few studies have rigorously examined the genetic basis for cisplatin-induced susceptibility to hearing loss. This article addresses recent progress in clarifying the incidence of cisplatin ototoxicity and the risk factors and controversies regarding the identification of genetic variants associated with cisplatin-induced hearing loss.

GSTM1 and GSTT1 copy number variation in population-based studies of endometrial cancer risk

BACKGROUND

Glutathione S-transferases (GST) detoxify a broad range of carcinogenic metabolites and lack of GSTM1 and GSTT1 activity due to gene deletions are prevalent. The associations of GSTM1 and GSTT1 polymorphisms with endometrial cancer risk have been inconsistent.

METHODS

We investigated gene dosage effects of GSTM1 and GSTT1 copy number in 441 endometrial cancer cases and 1,237 matched controls selected from the Nurses' Health Study and Women's Health Study, as well as gene-environment interactions.

RESULTS

Carriers of at least 2 GSTT1 genes had an increased risk of endometrial cancer (OR = 1.51, 95% CI = 1.04-2.19; P(trend) = 0.04) compared with women who were GSTT1 null. GSTM1 was not associated with endometrial cancer risk (OR(2/3 vs. 0 copies) = 0.82, 95% CI = 0.52-1.27; P(trend) = 0.41). We did not observe effect modification of either the GSTM1 or GSTT1 association with cancer risk by smoking status, postmenopausal hormone use, or body mass index.

CONCLUSIONS

Our results suggested GSTM1 copy number does not influence endometrial cancer risk, whereas higher GSTT1 copy number may be associated with increased risk. Our findings supported that GSTT1 differs in its substrate specificity from GSTM1 and may generate intermediates more genotoxic to endometrial cells than the parent chemical. Future studies are needed to clarify this relationship.

IMPACT

We hypothesized risk associated with GST enzymes may differ depending on environmental and/or occupational exposures. Our assessment of gene-environment interactions suggested GSTM1 and GSTT1 are not involved in the in vivo human metabolism of estrogen and its metabolites.

Effects of GSTM1 in rheumatoid arthritis; results from the Swedish EIRA study

Objective

Glutathione-S-transferases (GSTs) play an important role in tobacco smoke detoxification, interestingly approximately 50% of individuals in most human populations lack the gene GSTM1 due to copy number variation (CNV). We aimed to investigate GSTM1 CNV in Rheumatoid Arthritis (RA) in relation to smoking and HLA-DRB1 shared epitope; the two best known risk factors for RA and in addition, to perform subanalyses in patients where relations between variations in GSTM1 and RA have previously been described.

Methods

qPCR was performed using TaqMan Copy Number assays (Applied Biosystems) for 2426 incident RA cases and 1257 controls from the Swedish EIRA. Odds ratio (OR) together with 95% confidence intervals (CI) was calculated and used as a measure of the relative risk of developing RA.

Results

No association between RA and GSTM1 CNV was observed when analyzing whole EIRA. However, ≥1 copy of GSTM1 appears to be a significant risk factor for autoantibody positive RA in non-smoking females ≥60 years (OR: 2.00 95% CI: 1.07–3.74), a population where such relationships have previously been described. Our data further suggest a protective effect of GSTM1 in ACPA-negative smoking men (OR: 0.56 95% CI: 0.35–0.90).

Conclusion

We assessed the exact number of GSTM1 gene copies in relation to development and severity of RA. Our data provide support for the notion that variations in copy numbers of GSTM1 may influence risk in certain subsets of RA, but do not support a role for GSTM1 CNV as a factor that more generally modifies the influence of smoking on RA.

Glutathione S-transferase copy number variation alters lung gene expression

The glutathione S-transferase (GST) enzymes catalyse the conjugation of xenobiotics to glutathione. Based on reports that inherited copy number variations (CNVs) modulate some GST gene expression levels, and that the small airway epithelium (SAE) and alveolar macrophages (AMs) are involved early in the pathogenesis of smoking-induced lung disease, we asked: do germline CNVs modulate GST expression levels in SAE and AMs? Microarrays were used to survey GST gene expression and determine CNVs genotypes in SAE and AMs obtained by bronchoscopy from current smokers and nonsmokers. 26% of subjects were null for both GSTM1 alleles, with reduced GSTM1 mRNA levels seen in both SAE and AMs. 30% of subjects had homozygous deletions of GSTT1, with reduced mRNA levels in both tissues. Interestingly, GSTT2B exhibited homozygous deletion in the blood of 27% of subjects and was not expressed in SAE in the remainder of subjects, but was expressed in AMs of heterozygotes and wild-type subjects, proportionate to genotype. These data show a germline CNV-mediated linear relationship of genotype with expression level, suggesting minimal compensation of gene expression levels in heterozygotes, consistent with GST polymorphisms playing a role in the risk of smoking-associated, xenobiotic-induced lung disease.

Genetic variations in human glutathione transferase enzymes: significance for pharmacology and toxicology

Glutathione transferase enzymes (GSTs) catalyze reactions in which electrophiles are conjugated to the tripeptide thiol glutathione. While many GST-catalyzed transformations result in the detoxication of xenobiotics, a few substrates, such as dihaloalkanes, undergo bioactivation to reactive intermediates. Many molecular epidemiological studies have tested associations between polymorphisms (especially, deletions) of human GST genes and disease susceptibility or response to therapy. This review presents a discussion of the biochemistry of GSTs, the sources-both genetic and environmental-of interindividual variation in GST activities, and their implications for pharmaco- and toxicogenetics; particular attention is paid to the Theta class GSTs.

Copy number variation in glutathione-S-transferase T1 and M1 predicts incidence and 5-year survival from prostate and bladder cancer, and incidence of corpus uteri cancer in the general population

Glutathione-S-transferase T1 (GSTT1) and GSTM1 detoxify carcinogens and thus potentially contribute to inter-individual susceptibility to cancer. We determined the ability of GST copy number variation (CNV) to predict the risk of cancer in the general population. Exact copy numbers of GSTT1 and GSTM1 were measured by real-time PCR in 10 247 individuals, of whom 2090 had cancer. In men, the cumulative incidence of prostate cancer increased and the cumulative 5-year survival decreased with decreasing GSTT1 copy numbers (trends=0.02). The hazard ratios (HRs) (95% CIs) for prostate cancer and for death after prostate cancer diagnosis were, respectively, 1.2 (0.8-1.8) and 1.2 (0.6-2.1) for GSTT1*1/0, and 1.8 (1.1-3.0) and 2.2 (1.1-4.4) for GSTT1*0/0 versus GSTT1*1/1. In women, the cumulative incidence of corpus uteri cancer increased with decreasing GSTT1 copy numbers (trend=0.04). The HRs for corpus uteri cancer were, respectively, 1.8 (1.0-3.2) and 2.2 (1.0-4.6) for GSTT1*1/0 and GSTT1*0/0 versus GSTT1*1/1. Finally, the cumulative incidence of bladder cancer increased, and the cumulative 5-year survival decreased, with decreasing GSTM1 copy numbers (P=0.03-0.05). The HRs for bladder cancer were, respectively, 1.5 (0.7-3.2) and 2.0 (0.9-4.3) for GSTM1*1/0 and GSTM1*0/0 versus GSTM1*1/1. The HR for death after bladder cancer diagnosis was 1.9 (1.0-3.7) for GSTM1*0/0 versus GSTM1*1/0. In conclusion, exact CNV in GSTT1 and GSTM1 predict incidence and 5-year survival from prostate and bladder cancer, and incidence of corpus uteri cancer.

Glutathione-S-transferase genes and asthma phenotypes: a Human Genome Epidemiology (HuGE) systematic review and meta-analysis including unpublished data

BACKGROUND

Oxidative stress is thought to be involved in the pathogenesis of asthma. Glutathione-S-transferase (GST) enzymes, which play an important role in antioxidant defences, may therefore influence asthma risk. Two common deletion polymorphisms of GSTM1 and GSTT1 genes and the GSTP1 Ile105Val polymorphism have been associated with asthma in children and adults, but results are inconsistent across studies.

METHODS

Systematic review and meta-analysis of the effects of GST genes on asthma, wheezing and bronchial hyper-responsiveness (BHR), with inclusion of unpublished data from three studies, including the large Avon Longitudinal Study of Parents and Children (ALSPAC). Random effect or fixed effect models were used as appropriate, and sensitivity analyses were performed to assess the impact of study characteristics and quality on pooled results.

RESULTS

The meta-analyses of GSTM1 (n = 22 studies) and GSTT1 (n = 19) showed increased asthma risk associated with the null genotype, but there was extreme between-study heterogeneity and publication bias and the association disappeared when meta-analysis was restricted to the largest studies. Meta-analysis of GSTP1 Ile105Val (n = 17) and asthma suggested a possible protective effect of the Val allele, but heterogeneity was extreme. Few studies evaluated wheezing and BHR and most reported no associations, although weak evidence was found for positive associations of GSTM1 null and GSTP1 Val allele with wheezing and a negative association of GSTP1 Val allele with BHR.

CONCLUSIONS

Our findings do not support a substantial role of GST genes alone in the development of asthma. Future studies of large size should focus on interactions of GST genes with environmental oxidative exposures and with other genes involved in antioxidant pathways. Quality of study conduct and reporting needs to be improved to increase credibility of the evidence accumulating over time.

Residue 234 is a master switch of the alternative-substrate activity profile of human and rodent theta class glutathione transferase T1-1

BACKGROUND

The Theta class glutathione transferase GST T1-1 is a ubiquitously occurring detoxication enzyme. The rat and mouse enzymes have high catalytic activities with numerous electrophilic compounds, but the homologous human GST T1-1 has comparatively low activity with the same substrates. A major structural determinant of substrate recognition is the H-site, which binds the electrophile in proximity to the nucleophilic sulfur of the second substrate glutathione. The H-site is formed by several segments of amino acid residues located in separate regions of the primary structure. The C-terminal helix of the protein serves as a lid over the active site, and contributes several residues to the H-site.

METHODS

Site-directed mutagenesis of the H-site in GST T1-1 was used to create the mouse Arg234Trp for comparison with the human Trp234Arg mutant and the wild-type rat, mouse, and human enzymes. The kinetic properties were investigated with an array of alternative electrophilic substrates to establish substrate selectivity profiles for the different GST T1-1 variants.

RESULTS

The characteristic activity profile of the rat and mouse enzymes is dependent on Arg in position 234, whereas the human enzyme features Trp. Reciprocal mutations of residue 234 between the rodent and human enzymes transform the substrate-selectivity profiles from one to the other.

CONCLUSIONS

H-site residue 234 has a key role in governing the activity and substrate selectivity profile of GST T1-1.

GENERAL SIGNIFICANCE

The functional divergence between human and rodent Theta class GST demonstrates that a single point mutation can enable or suppress enzyme activities with different substrates.

Genetic association studies of methamphetamine use disorders: A systematic review and synthesis

Efforts to understand the biological processes that increase susceptibility to methamphetamine (METH) use disorders (i.e., abuse, dependence, and psychosis) have uncovered several putative genotypic variants. However, to date a synthesis of this information has not been conducted. Thus, systematic searches of the current literature were undertaken for genetic-association studies of METH use disorders. Each gene's chromosomal location, function, and examined polymorphic markers were extracted. Frequencies, odds ratios and 95% confidence intervals for risk alleles, as well as sample size and power, were calculated. We uncovered 38 studies examining 39 genes, of which 18 were found to have a significant genotypic, allelic, and/or haplotypic association with METH use disorders. Three genes (COMT, DRD4, and GABRA1) were associated with METH abuse, nine (ARRB2, BDNF, CYP2D6, GLYT1, GSTM1, GSTP1, PDYN, PICK1, and SLC22A3) with METH dependence, two (AKT1 and GABRG2) with METH abuse/dependence, and four (DTNBP1, OPRM1, SNCA, and SOD2) with METH psychosis. Limitations related to phenotypic classification, statistical power, and potential publication bias in the current literature were noted. Similar to other behavioral, psychiatric, and substance use disorders, the genetic epidemiology of METH use disorders is complex and likely polygenic. National and international collaborative efforts are needed to increase the availability of large population-based samples and improve upon the power to detect genetic associations of small magnitude. Further, replication of the findings reviewed here along with further development of more rigorous methodologies and reporting protocols will aid in delineating the complex genetic epidemiology of METH use disorders.

Residue 234 in glutathione transferase T1-1 plays a pivotal role in the catalytic activity and the selectivity against alternative substrates

GST (glutathione transferase) T1-1 plays an important role in the biotransformation of halogenated alkanes, which are used in large quantities as solvents and occur as environmental pollutants. Many reactions that are catalysed by GST T1-1 qualify as detoxification processes, but some reactions with dihalogenated alkanes lead to reactive products more toxic than the substrates. Murine GST T1-1 is particularly active with dichloromethane, which may explain the high carcinogenicity of dichloromethane in the mouse. Human GST T1-1 activity is considerably lower with halogenated hydrocarbons and some related substrates. Human GST T1-1 is polymorphic with a frequent null phenotype, suggesting that it is advantageous, under some circumstances, to lack the functional enzyme, which catalyses GSH conjugations that may cause bioactivation. The present study shows that amino acid residue 234 is a determinant of the differences in catalytic efficiency between the human and the rodent enzymes. The replacement of Trp234 in human GST T1-1 by arginine, found in the rodent enzyme, enhanced the alkyltransferase activity by an order of magnitude with a series of homologous iodoalkanes and some typical GST substrates. The specific activity of the alternative mutant Trp234-->Lys was lower than for the parental human GST T1-1 with many substrates, showing that a positive charge is not sufficient for increased activity. The enhanced activity of Trp234-->Arg with alkylating agents was dependent on the substrate tested, whereas no increase of the peroxidase activity with cumene hydroperoxide was noted. Residue 234 therefore is also involved in the control of the substrate selectivity of GST T1-1.

Copy-number variation genotyping of GSTT1 and GSTM1 gene deletions by real-time PCR

BACKGROUND

Structural variation in the human genome is increasingly recognized as being highly prevalent and having relevance to common human diseases. Array-based comparative genome-hybridization technology can be used to determine copy-number variation (CNV) across entire genomes, and quantitative PCR (qPCR) can be used to validate de novo variation or assays of common CNV in disease-association studies. Analysis of large qPCR data sets can be complicated and time-consuming, however.

METHODS

We describe qPCR assays for GSTM1 (glutathione S-transferase mu 1) and GSTT1 (glutathione S-transferase theta 1) gene deletions that can genotype up to 192 samples in duplicate 5-microL reaction volumes in <2 h on the ABI Prism 7900HT Sequence Detection System. To streamline data handling and analysis of these CNVs by qPCR, we developed a novel interactive, macro-driven Microsoft Excel(R) spreadsheet. As proof of principle, we used our software to analyze CNV data for 1478 DNA samples from a family-based cohort.

RESULTS

With only 8 ng of DNA template, we assigned CNV genotypes (i.e., 2, 1, or 0 copies) to either 96% (GSTM1) or 91% (GSTT1) of all DNA samples in a single round of PCR amplification. Genotyping accuracy, as ascertained by familial inheritance, was >99.5%, and independent genotype assignments with replicate real-time PCR runs were 100% concordant.

CONCLUSIONS

The genotyping assay for GSTM1 and GSTT1 gene deletion is suitable for large genetic epidemiologic studies and is a highly effective analysis system that is readily adaptable to analysis of other CNVs. .

Expression quantitative trait loci mapping identifies new genetic models of glutathione S-transferase variation

Expression quantitative trait loci (eQTL) mapping can be used to identify the genetic variations that underlie inherited differences in gene transcription. We performed eQTL mapping by combining whole genome transcriptional data from the hypothalami of 33 strains of inbred mice with a detailed haplotype map of those same strains, revealing 10,655 trans associations and 31 cis eQTLs. One of the cis associations was found to be driven by strain-specific variation in the expression of Glutathione S-transferase, mu 5 (Gstm5). Gstm5 is one of seven members of the glutathione S-transferase, Mu family of genes. The glutathione S-transferases are phase II metabolic enzymes and are key regulators of drug and toxin clearance. In mouse, all seven family members are tightly clustered on mouse chromosome 3. Investigation of the Gstm5 cis association in multiple tissues types revealed that an 84-kilobase region on MMU3 acts as a haplotype-specific locus control region for the glutathione S-transferase, Mu cluster. In the strains that share the minor haplotype, drastic reductions in mRNA levels in multiple members of the Gst Mu family were observed. The strain-specific differences in Gst Mu transcription characterized here accurately model the human population, in which extreme variations in expression of GST Mu family members have been observed. Furthermore, the reduction in Gst Mu levels has important relevance for pharmacology and toxicology studies conducted in these strains. For instance, the reduced levels of Gst Mu in general and Gstm5 in particular have implications in models of dopamine metabolism, Parkinson's disease, and chemical neurotoxicity.

Acquisition of inverted GSTM exons by an intron of primate GSTM5 gene

The human GSTM gene family is composed of five gene members, GSTM1-5, and plays an important role in detoxification. In this study, the human GSTM5 gene was found to have a long inverted repeat (LIR) in intron 5. The LIR is able to form a stem-loop structure with a 31-bp stem and a 9-nt loop. The intronic LIR was also identified in other primates but not in non-primates. The human and chimpanzee LIRs had undergone compensating mutations that make the stem loop more stable, suggesting a functional role for the LIR. Sequence homology showed that the LIR was actually a part of inverted exons acquired by the intron. Results of phylogenetic analysis indicate that the inverted exons were derived from exon 5 of GSTM4 and exon 5 of GSTM1. The intronic LIR and inverted GSTM exons can probably introduce complexity in the expression of GSTM gene family.

Human genes involved in copy number variation: mechanisms of origin, functional effects and implications for disease

Copy number variants (CNVs) overlap over 7000 genes, many of which are pivotal in biological pathways. The implications of this are profound, with consequences for evolutionary studies, population genetics, gene function and human phenotype, including elucidation of genetic susceptibility to major common diseases, the heritability of which has thus far defied full explanation. Even though this research is still in its infancy, CNVs have already been associated with a number of monogenic, syndromic and complex diseases: the development of high throughput and high resolution techniques for CNV screening is likely to bring further new insights into the contribution of copy number variation to common diseases. Amongst genes overlapped by CNVs, significant enrichments for certain gene ontology categories have been identified, including those related to immune responses and interactions with the environment. Genes in both of these categories are thought to be important in evolutionary adaptation and to be particular targets of natural selection. Thus, a full appreciation of copy number variation may be important for our understanding of human evolution.

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.

The influence of genetic polymorphisms on population variability in six xenobiotic-metabolizing enzymes

This review provides variability statistics for polymorphic enzymes that are involved in the metabolism of xenobiotics. Six enzymes were evaluated: cytochrome P-450 (CYP) 2D6, CYP2E1, aldehyde dehydrogenase-2 (ALDH2), paraoxonase (PON1), glutathione transferases (GSTM1, GSTT1, and GSTP1), and N-acetyltransferases (NAT1 and NAT2). The polymorphisms were characterized with respect to (1) number and type of variants, (2) effects of polymorphisms on enzyme function, and (3) frequency of genotypes within specified human populations. This information was incorporated into Monte Carlo simulations to predict the population distribution and describe interindividual variability in enzyme activity. The results were assessed in terms of (1) role of these enzymes in toxicant activation and clearance, (2) molecular epidemiology evidence of health risk, and (3) comparing enzyme variability to that commonly assumed for pharmacokinetics. Overall, the Monte Carlo simulations indicated a large degree of interindividual variability in enzyme function, in some cases characterized by multimodal distributions. This study illustrates that polymorphic metabolizing systems are potentially important sources of pharmacokinetic variability, but there are a number of other factors including blood flow to liver and compensating pathways for clearance that affect how a specific polymorphism will alter internal dose and toxicity. This is best evaluated with the aid of physiologically based pharmacokinetic (PBPK) modeling. The population distribution of enzyme activity presented in this series of articles serves as inputs to such PBPK modeling analyses.

High-throughput genotyping of copy number variation in glutathione S-transferases M1 and T1 using real-time PCR in 20,687 individuals

OBJECTIVES

Characteristic for the genes encoding glutathione S-transferase (GST) M1 and GSTT1 is a null allele, suggested to increase susceptibility to chronic diseases. We report an optimized method for the determination of copy number variation (CNV) in GST genes.

DESIGN AND METHODS

Real-time multiplex PCR reactions were optimized for quantification of GSTM1 and GSTT1 CNV using the DeltaCt method, a fixed volume of diluted DNA, a total volume of 10 microL, 384-well formats, and single determinations of each sample.

RESULTS

Consistent genotyping was obtained using DNA in a range of 0.41 ng to 100 ng. In a general population sample of 20,687 individuals the genotype frequencies were concordant with other methods used as standards. Throughput was 4600 genotypes per day at a reagent price of 0.5 euros per sample.

CONCLUSIONS

This high-throughput, low cost method accurately determines CNV in the GST genes enabling reliable estimates of disease prediction in large epidemiological samples.

Population-specific GSTM1 copy number variation

As one of the major glutathione conjugation enzymes, GSTM1 detoxifies a number of drugs and xenobiotics. Its expression and activity have been shown to correlate both with cancer risks and drug resistance. Through a genome-wide association study, we identified a significant association between HapMap SNP rs366631 and GSTM1 expression. In this study, utilizing lymphoblastoid cell lines derived from International HapMap Consortium CEU and YRI populations, we designed and performed site-specific genotyping assays for both rs366631 and a highly homologous GSTM1 upstream site. Copy number variation (CNV) assays were performed for three different regions of the GSTM1 gene. We demonstrated that HapMap SNP rs366631 is a non-polymorphic site. The false genotyping call arises from sequence homology, a common GSTM1 region deletion and a non-specific genotyping platform used to identify the SNP. However, the HapMap call for rs366631 genotype is an indicator of GSTM1 upstream region deletion. Furthermore, this upstream deletion can be used as a marker of GSTM1 gene deletion. Using a novel GSTM1 CNV assay, we showed a population-specific CNV in this region upstream of the gene. More than 75% of the Caucasian (CEU) samples exhibit GSTM1 deletion and none contain two copies of GSTM1. In contrast, up to 25% of African (YRI) samples were found to have two copies of GSTM1. In conclusion, HapMap rs366631 is a pseudo-SNP that can be used as a GSTM1 deletion marker. Both the pseudo-SNP allele frequency and GSTM1 upstream region CNV show population-specific patterns between CEU and YRI samples.

Association study between polymorphisms in glutathione-related genes and methamphetamine use disorder in a Japanese population

Accumulating evidence suggests that oxidative stress plays a role in the mechanisms of action of methamphetamine (METH) in the brain. In the present study, we investigated the association between the genetic polymorphisms among glutathione (GSH)-related enzymes; glutathione S-transferases (GSTs) such as GSTT1 (Non-deletion/Null), GSTT2 (Met139Ile), GSTA1 (-69C/T), and GSTO1 (Ala140Asp); glutathione peroxidase 1 (GPX1) (Pro198Leu); and glutamate-cysteine ligase modifier (GCLM) subunit and METH use disorder in a Japanese population. Two hundred eighteen METH abusers and 233 healthy controls were enrolled in the study. There was a significant difference in GSTT1 genotype frequency between patients with METH psychosis and controls (P = 0.039, odds ratio: 1.52, 95% CI 1.03-2.24). Furthermore, the frequency (66.0%) of the GSTT1 null genotype among prolonged-type METH psychotic patients with spontaneous relapse was significantly higher (P = 0.025, odds ratio: 2.43, 95% CI 1.13-5.23) than that (44.4%) of transient-type METH psychotic patients without spontaneous relapse. However, there were no associations between the polymorphisms of other genes and METH abuse. The present study suggests that the polymorphism of the GSTT1 gene might be a genetic risk factor of the development of METH psychosis in a Japanese population.

Defining drug disposition determinants: a pharmacogenetic-pharmacokinetic strategy

In preclinical and early clinical drug development, information about the factors influencing drug disposition is used to predict drug interaction potential, estimate and understand population pharmacokinetic variability, and select doses for clinical trials. However, both in vitro drug metabolism studies and pharmacogenetic association studies on human pharmacokinetic parameters have focused on a limited subset of the proteins involved in drug disposition. Furthermore, there has been a one-way information flow, solely using results of in vitro studies to select candidate genes for pharmacogenetic studies. Here, we propose a two-way pharmacogenetic-pharmacokinetic strategy that exploits the dramatic recent expansion in knowledge of functional genetic variation in proteins that influence drug disposition, and discuss how it could improve drug development.

Structural variation of the human genome

There is growing appreciation that the human genome contains significant numbers of structural rearrangements, such as insertions, deletions, inversions, and large tandem repeats. Recent studies have defined approximately 5% of the human genome as structurally variant in the normal population, involving more than 800 independent genes. We present a detailed review of the various structural rearrangements identified to date in humans, with particular reference to their influence on human phenotypic variation. Our current knowledge of the extent of human structural variation shows that the human genome is a highly dynamic structure that shows significant large-scale variation from the currently published genome reference sequence.

Glutathione S-transferase T1 and M1: gene sequence variation and functional genomics

PURPOSE

The glutathione S-transferases (GSTs) catalyze the glutathione conjugation of reactive electrophiles, including carcinogens and many antineoplastic drugs. GSTT1 and GSTM1 are polymorphically deleted, but the full range of genetic variation in these two genes has not yet been explored. We set out to systematically identify common polymorphisms in GSTT1 and GSTM1, followed by functional genomic studies.

EXPERIMENTAL DESIGN

First, multiplex PCR was used to determine GSTT1 and GSTM1 copy number in 400 DNA samples (100 each from 4 ethnic groups). Exons, splice junctions, and 5'-flanking regions (5'-FR) were then resequenced using DNA samples that contained at least one copy of GSTT1 or GSTM1.

RESULTS

Gene deletion frequencies among ethnic groups were from 33.5% to 73.5% for GSTT1 and from 50.5% to 78.0% for GSTM1. GSTT1 deletion data correlated with the results of mRNA microarray expression studies. The 18 single nucleotide polymorphisms (SNP) observed in GSTT1 included three nonsynonymous coding SNPs (cSNPs) and one single-nucleotide deletion, whereas the 51 GSTM1 SNPs included two nonsynonymous cSNPs. Two of the GSTT1 nonsynonymous cSNPs resulted in decreases in levels of immunoreactive protein to 56% and 12% of wild type (WT), whereas those in GSTM1 resulted in modest increases in protein levels. Reporter gene assays showed that one GSTT1 5'-FR haplotype, with a frequency of 32% in African-American subjects, resulted in an increase in transcription in JEG-3 cells to 351% of that for the WT sequence, and one GSTM1 5'-FR haplotype resulted in an increase in transcription in JEG-3 cells to 129% of WT.

CONCLUSIONS

These observations suggest that functionally significant pharmacogenomic variation beyond GSTT1 and GSTM1 gene deletion may contribute to carcinogenesis or individual variation in antineoplastic drug therapy response.

Genetic polymorphism and function of glutathione S-transferases in tumor drug resistance

The human glutathione S-transferase, GSTs, possess both enzymatic and non-enzymatic functions and are involved in many important cellular processes, such as, phase II metabolism, stress response, cell proliferation, apoptosis, oncogenesis, tumor progression and drug resistance. The non-enzymatic functions of GSTs involve their interactions with cellular proteins, such as, JNK, TRAF, ASK, PKC, and TGM2, during which, either the interacting protein partner undergoes functional alteration or the GST protein itself is post-translationally modified and/or functionally altered. The majority of GST genes harbor polymorphisms that influence their transcription and/or function of their encoded proteins. This overview focuses on recent insights into the biology and pharmacogenetics of GSTs as a determinant of cancer drug resistance and response of cancer patients to therapy.