Glutathione S-transferase: genetics and role in toxicology

Synthesis and biological evaluation of potential modulators of malarial glutathione-S-transferase(s)

Glutathione-S-transferase(s) (E.C.2.5.1.18, GSTs) have been investigated in parasitic protozoans with respect to their biochemistry and they have been identified as potential vaccine candidates in protozoan parasites and as a target in the synthesis of new antiparasitic agents. In a search towards the identification of novel biochemical targets for antimalarial drug design, the area of Plasmodium glutathione metabolism provides a number of promising chemotherapeutic targets. GST activity was determined in various subcellular fractions of malarial parasites Plasmodium yoelii and was found to be localized mainly in the cytosolic fraction (specific activity, c. 0.058 +/- 0.016 micromol/min/mg protein). Hemin, a known inhibitor of mammalian GST(s), maximally inhibited this enzyme from P. yoelii to nearly 86%. In a search towards synthetic modulators of malarial GST(s), 575 compounds belonging to various chemical classes were screened for their effect on crude GST from P. yoelii and 92 compounds belonging to various chemical classes were studied on recombinant GST from P. falciparum. Among all the compounds screened, 83 compounds inhibited/stimulated the enzyme from P. yoelii/P. falciparum to the extent of 40% or more.

Diversity of glutathione s-transferase omega 1 (a140d) and 2 (n142d) gene polymorphisms in worldwide populations

1. Glutathione S-transferase class omega (GSTO) 1 and 2 are members of the glutathione-S-transferase family, which uses glutathione in the process of the biotransformation of drugs, xenobiotics and oxidative stress. Associations with the age-at-onset of Alzheimer's and Parkinson's diseases have been shown in the genetic polymorphism of GSTO1 and GSTO2. 2. In the present study, the frequencies of GSTO1*A140D and GSTO2*N142D in Ovambos (n = 163), Turks (n = 194), Mongolians (n = 243) and Japanese (n = 102) were investigated and compared with findings from other studies. Detection of these single nucleotide polymorphisms was performed by polymerase chain reaction-restriction fragment length polymorphism analysis. 3. The allele frequencies of these polymorphisms in Ovambos, Turks, Mongolians and Japanese were 0.040, 0.085, 0.128 and 0.108, respectively, for GSTO1*A140D and 0.583, 0.219, 0.173 and 0.216, respectively, for GSTO2*N142D. Ovambos showed the lowest allele frequency of GSTO1*A140D. Conversely, Africans, including Ovambos, showed higher allele frequencies of GSTO2*N142D than Caucasians and Asians. 4. The existence of a certain genetic heterogeneity in the worldwide distribution of these two polymorphisms is revealed in the present study.

Metabolic control of transcription: paradigms and lessons from Saccharomyces cerevisiae

The comparatively simple eukaryote Saccharomyces cerevisiae is composed of some 6000 individual genes. Specific sets of these genes can be transcribed co-ordinately in response to particular metabolic signals. The resultant integrated response to nutrient challenge allows the organism to survive and flourish in a variety of environmental conditions while minimal energy is expended upon the production of unnecessary proteins. The Zn(II)2Cys6 family of transcriptional regulators is composed of some 46 members in S. cerevisiae and many of these have been implicated in mediating transcriptional responses to specific nutrients. Gal4p, the archetypical member of this family, is responsible for the expression of the GAL genes when galactose is utilized as a carbon source. The regulation of Gal4p activity has been studied for many years, but we are still uncovering both nuances and fundamental control mechanisms that impinge on its function. In the present review, we describe the latest developments in the regulation of GAL gene expression and compare the mechanisms employed here with the molecular control of other Zn(II)2Cys6 transcriptional regulators. This reveals a wide array of protein-protein, protein-DNA and protein-nutrient interactions that are employed by this family of regulators.

Polymorphisms of selected xenobiotic genes contribute to the development of papillary thyroid cancer susceptibility in Middle Eastern population

Background

The xenobiotic enzyme system that enables us to detoxify carcinogens exhibits identifiable genetic polymorphisms that are highly race specific. We hypothesized that polymorphisms of these genes may be associated with risk of thyroid cancer. To evaluate the role of genetic polymorphisms of xenobiotic genes in thyroid cancer, we conducted a hospital-based case-control study in Saudi population.

Methods

223 incident papillary thyroid cancer cases and 513 controls recruited from Saudi Arabian population were analyzed for the association between polymorphisms in genes encoding folic acid metabolizing enzymes MTHFR and six xenobiotics-metabolizing enzymes including CYP1A1 T3801C, C4887A, GSTP1 A1578G, C2293T, GSTM1, GSTT1, NAT2 G590A, NQO*1 C609T, using PCR-RELP.

Results

Among selected genes, CYP1A1 C4887A genotypes CA, AA and variant allele A demonstrated significant differences and greater risk of developing thyroid cancer comparing to wild type genotype CC (CA vs. CC; p < 0.0001, OR = 1.91, 95% CI = 1.36–2.70, AA vs. CC; p < 0.001, OR = 3.48, 95% CI = 1.74–6.96 and CA+AA vs. CC; p < 0.0001, OR = 2.07, 95% CI = 1.49–2.88). GSTT1 null showed 3.48 times higher risk of developing thyroid cancer (p < 0.0001, 95% CI = 2.48–4.88) while GSTM1 null showed protective effect (p < 0.05, OR = 0.72, 95% CI = 0.52–0.99). Remaining loci demonstrated no significance with risk.

Conclusion

Of the 9 polymorphisms screened, we identified GST, GSTM1 and CYP1A1 C4887A, may be of importance to disease process and may be associated with papillary thyroid cancer risk in Saudi Arabian population.

Genetic polymorphisms associated with cigarette smoking and the risk of Graves' disease

OBJECTIVE

Cigarette smoking is a well-recognized risk factor of Graves' disease and, particularly, Graves' ophthalmopathy. Hence, germline polymorphisms of detoxification genes and genes belonging to the major DNA repair-apoptosis pathways might have an important role in disease susceptibility. In addition, as some of these genes are regulated by thyroid hormones, they may affect the patients' outcomes. We aimed to assess the influence of the GST, CYP and TP53 gene polymorphisms in the risk of Graves' disease and its outcome.

DESIGN

Prospective case-control study.

PATIENTS

A PCR-based strategy was used for GSTT1, GSTM1, GSTP1, CYP1A1 and TP53 codon 72 genotypes in a group of 400 Graves' disease patients, and to compare them to 574 control individuals with similar environmental exposure features.

RESULTS

GSTM1 and GSTT1 genotypes were equally distributed in cases and controls, respectively. However, GSTP1 (P < 0.0001), CYP1A1 (P < 0.0033) and Pro/ProTP53 (P < 0.0035) variants appeared more frequently in Graves' disease patients than in controls. A multivariate analysis indicated that cigarette smoking and inheritance of GSTP1, CYP1A1 and Pro/ProTP53 variants were important risk factors for Graves' disease, but only smoking appeared as an independent risk factor for Graves' ophthalmopathy. There was no association between clinical features, including ophthalmopathy or treatment outcome, and the studied genotypes.

CONCLUSION

We concluded that GSTP1, CYP1A1 and TP53, but not GSTT1 and GSTM1 germline polymorphisms, may be associated with smoking-related Graves' disease susceptibility and configure a risk profile for the disease. However, these polymorphisms do not influence the patients' response to treatment.

Expression of placental glutathione S-transferase in rat tongue mucosa exposed to cigarette smoke

Glutatione S-transferases (GSTs) are a family of enzymes involved in detoxification of xenobiotics. Placental GST, known as GST-P, has been detected in tissues following exposure to carcinogenic agents being regarded a reliable biomarker of exposure and susceptibility in early phases of carcinogenesis. The aim of this study was to investigate the expressivity of GST-P positive foci in the rat tongue mucosa exposed to cigarette smoke by means of immunohistochemistry. A total of twelve male Wistar rats were distributed into two groups: negative control and experimental group exposed to cigarette smoke during 75 days. After experimental period, no histopathological changes in the tongue mucosa were evidenced in the negative control and the experimental group. However, a total of five GST-P positive foci were detected in two out of six animals exposed to cigarrette smoke. None control animals were noticed GST-P positive foci. These data indicate that expression of GST-P may reflect the carcinogenic effect of cigarette smoke as well as the genetic susceptibility of animals in relation to continuous carcinogens exposure.

Placental glutathione S-transferase correlates with cellular proliferation during rat tongue carcinogenesis induced by 4-nitroquinoline 1-oxide

Taking into consideration that glutatione S-transferase (GST) and cellular proliferation play a crucial role during carcinogenesis, the goal of this study was to investigate the expression of placental GST, called GST-P, and proliferating cellular nuclear antigen (PCNA) by means of immunohistochemistry during rat tongue carcinogenesis induced by 4-nitroquinoline 1-oxide (4NQO). This is a useful model for studying oral squamous cell carcinoma phase by phase. Male Wistar rats were distributed into three groups of 10 animals each and treated with 50 ppm 4NQO solution by drinking water for 4, 12 or 20 weeks. Ten animals were used as negative control. GST-P positive foci were detected in non-neoplastic oral cells at 4 weeks of 4NQO administration. In the same way, GST-P positive cells were detected in pre-neoplastic lesions and squamous cell carcinomas induced after 12 and 20 weeks-treatment, respectively. None of the control animals expressed GST-P positive cells. Regarding cellular proliferation, PCNA positive nuclei were higher at 12 and 20 weeks following 4NQO exposure (p<0.05) when compared to negative control. These results suggest that the expression of GST-P is correlated with cellular proliferation, in which GST-P is associated with risk and progression of oral cancer, whereas PCNA is closely involved during neoplastic conversion.

Nitro-fatty acid reaction with glutathione and cysteine. Kinetic analysis of thiol alkylation by a Michael addition reaction

Fatty acid nitration by nitric oxide-derived species yields electrophilic products that adduct protein thiols, inducing changes in protein function and distribution. Nitro-fatty acid adducts of protein and reduced glutathione (GSH) are detected in healthy human blood. Kinetic and mass spectrometric analyses reveal that nitroalkene derivatives of oleic acid (OA-NO2) and linoleic acid (LNO2) rapidly react with GSH and Cys via Michael addition reaction. Rates of OA-NO2 and LNO2 reaction with GSH, determined via stopped flow spectrophotometry, displayed second-order rate constants of 183 M(-1)S(-1) and 355 M(-1)S(-1), respectively, at pH 7.4 and 37 degrees C. These reaction rates are significantly greater than those for GSH reaction with hydrogen peroxide and non-nitrated electrophilic fatty acids including 8-iso-prostaglandin A2 and 15-deoxy-Delta(12,14)-prostaglandin J2. Increasing reaction pH from 7.4 to 8.9 enhanced apparent second-order rate constants for the thiol reaction with OA-NO2 and LNO2, showing dependence on the thiolate anion of GSH for reactivity. Rates of nitroalkene reaction with thiols decreased as the pKa of target thiols increased. Increasing concentrations of the detergent octyl-beta-d-glucopyranoside decreased rates of nitroalkene reaction with GSH, indicating that the organization of nitro-fatty acids into micellar or membrane structures can limit Michael reactivity with more polar nucleophilic targets. In aggregate, these results reveal that the reversible adduction of thiols by nitro-fatty acids is a mechanism for reversible post-translational regulation of protein function by nitro-fatty acids.

Genetic polymorphisms of manganese superoxide dismutase, NAD(P)H:quinone oxidoreductase, glutathione S-transferase M1 and T1, and the susceptibility to drug-induced liver injury

BACKGROUND/AIMS

Drug metabolizing enzymes may be related to drug-induced liver injury (DILI). Manganese superoxide dismutase (MnSOD), NAD(P)H:quinone oxidoreductase (NQO1), and glutathione S-transferase (GST) are important drug metabolizing enzymes. We aimed to elucidate the relationship between genetic polymorphisms of these enzymes and the susceptibility to DILI.

METHODS

A total of 115 patients with DILI and 115 drug-, sex-, and age-matched controls were enrolled. Their genetic polymorphisms of MnSOD, NQO1, GSTM1, and GSTT1 were assayed.

RESULTS

Sixty-three (54.8%) of DILI patients were incriminated to anti-tuberculosis drugs. Subjects with a mutant C allele (T/C or C/C genotype) of MnSOD had a higher risk of DILI than those with MnSOD T/T genotype, both in overall drugs studied (adjusted OR: 2.44, 95% C.I.: 1.38-4.30, P=0.002), and in sub-category of anti-tuberculosis drugs (adjusted OR: 2.47, 95% C.I.: 1.13-5.39, P=0.02). In addition, subjects carrying GSTM1 null genotype had increased risk of anti-tuberculosis DILI (adjusted OR: 2.23, 95% C.I.: 1.07-4.67, P=0.03).

CONCLUSIONS

The MnSOD mutant C allele may increase the susceptibility to DILI, and GSTM1 null genotype may be related to anti-tuberculosis drug-induced hepatotoxicity. Determination of the MnSOD and GSTM1 genotypes may help identify patients at high risk for DILI.

Genetic polymorphisms of drug-metabolizing enzymes and the susceptibility to antituberculosis drug-induced liver injury

Three first-line antituberculosis drugs, isoniazid, rifampicin and pyrazinamide, may induce liver injury, especially isoniazid. This antituberculosis drug-induced liver injury ranges from a mild to severe form, and the associated mortality cases are not rare. The major drug-metabolizing enzyme of isoniazid is N-acetyltransferase. Other possible enzymes are CYP2E1 and glutathione S-transferase. There is evidence that polymorphisms of the genes that encode these enzymes may influence the activity of the corresponding drug-metabolizing enzymes. Recent studies demonstrated that these genetic polymorphisms may be associated with the susceptibility to antituberculosis drug-induced liver injury. The proposed risk-associated genotypes are NAT2 slow acetylator (without wild-type NAT2*4 allele), CYP2E1 *1A/*1A (homozygous wild type) and homozygous null GSTM1 genotype. Although the available data in the field are still limited and warrants further confirmation in different ethnic populations with larger sample sizes, it still cast some light on the application of these pharmacogenetic or pharmacogenomic approaches to prevent grave antituberculosis drug-induced liver injury in the near future.

Exposure to ethylene oxide in hospitals: biological monitoring and influence of glutathione S-transferase and epoxide hydrolase polymorphisms

Ethylene oxide is considered as a human carcinogen. A biomarker of exposure would be a useful instrument to assess the risk in occupationally exposed workers. This cross-sectional study aimed at examining (a) whether the urinary excretion of a metabolite of ethylene oxide, 2-hydroxyethyl mercapturic acid (HEMA), could be used for monitoring occupational exposure and (b) whether glutathione S-transferase (GST) and epoxide hydrolase genotypes influenced biological monitoring. Exposure to ethylene oxide was measured by personal sampling in 80 hospital workers (95% of those eligible). HEMA concentrations were determined in three urine samples (baseline, end of shift, and next morning) by liquid chromatography with tandem mass spectrometry. GSTs (GSTT1, GSTM1, and GSTP1) and epoxide hydrolase (EPHX1) were also genotyped. The influence of exposure, genotypes, and several other factors was examined in multiple regression analyses. Exposure was always <1 parts per million. On a group basis, exposure and a non-null GSTT1 genotype increased the HEMA concentrations in the urine sample collected at the end of the shift and these factors remained statistically significant after considering possible confounding or modifying factors.

Association of glutathione S-transferase gene polymorphisms (GSTM1 and GSTT1) of vitiligo in Korean population

Vitiligo is an acquired pigmentary disorder of the skin involving melanocyte dysfunction. It has been reported that melanocyte impairment could be related to increased oxidative stress. The glutathione S-transferases (GSTs) are group of polymorphic enzymes that are important in protection against oxidative stress. To find the relationship between GSTM1 and GSTT1 polymorphisms with vitiligo susceptibility, GSTM1 and GSTT1 (homozygous deletion vs. non-deleted) polymorphisms between vitiligo patients (n=310) and healthy controls (n=549) were analyzed. We observed significant association in null alleles of the GSTM1 (P<0.001, OR=2.048, 95% CI=1.529-2.743). GSTM1 null type was also statistically different between two vitiligo subtypes and controls (Focal P<0.001, OR=2.224, 95% CI=1.499-3.298; Generalized P=0.001, OR=1.974, 95% CI=1.342-2.904). However, no significant association in GSTT1 (P=0.869, OR=1.024, 95% CI=0.775-1.353) was observed with vitiligo. In combined analysis of GSTM1 and GSTT1, both null type and GSTM1/GSTT1 (null/present) group showed significant differences between controls and vitiligo patients. These results suggest that GSTM1 null type might be associated with vitiligo susceptibility in Korean population.

Relationship of glutathione S-transferase genotypes with side-effects of pulsed cyclophosphamide therapy in patients with systemic lupus erythematosus

AIMS

Cyclophosphamide (CTX) is an established treatment of severe systemic lupus erythematosus (SLE). Cytotoxic CTX metabolites are mainly detoxified by multiple glutathione S-transferases (GSTs). However, data are lacking on the relationship between the short-term side-effects of CTX therapy and GST genotypes. In the present study, the effects of common GSTM1, GSTT1, and GSTP1 genetic mutations on the severity of myelosuppression, gastrointestinal (GI) toxicity, and infection incidences induced by pulsed CTX therapy were evaluated in patients SLE.

METHODS

DNA was extracted from peripheral leucocytes in patients with confirmed SLE diagnosis (n = 102). GSTM1 and GSTT1 null mutations were analyzed by a polymerase chain reaction (PCR)-multiplex procedure, whereas the GSTP1 codon 105 polymorphism (Ile-->Val) was analyzed by a PCR-restriction fragment length polymorphism (RFLP) assay.

RESULTS

Our study demonstrated that SLE patients carrying the genotypes with GSTP1 codon 105 mutation [GSTP1*-105I/V (heterozygote) and GSTP1*-105 V/V (homozygote)] had an increased risk of myelotoxicity when treated with pulsed high-dose CTX therapy (Odds ratio (OR) 5.00, 95% confidence interval (CI) 1.96, 12.76); especially in patients younger than 30 years (OR 7.50, 95% CI 2.14, 26.24), or in patients treated with a total CTX dose greater than 1.0 g (OR 12.88, 95% CI 3.16, 52.57). Similarly, patients with these genotypes (GSTP1*I/V and GSTP1*V/V) also had an increased risk of GI toxicity when treated with an initial pulsed high-dose CTX regimen (OR 3.33, 95% CI 1.03, 10.79). However, GSTM1 and GSTT1 null mutations did not significantly alter the risks of these short-term side-effects of pulsed high-dose CTX therapy in SLE patients.

CONCLUSIONS

The GSTP1 codon 105 polymorphism, but not GSTM1 or GSTT1 null mutations, significantly increased the risks of short-term side-effects of pulsed high-dose CTX therapy in SLE patients. Because of the lack of selective substrates for a GST enzyme phenotyping study, timely detection of this mutation on codon 105 may assist in optimizing pulsed high-dose CTX therapy in SLE patients.

Association of GST genes polymorphisms with asthma in Tunisian children

Background. A positive association between genetic polymorphism and asthma may not be extrapolated from one ethnic group to another based on intra- and interethnic allelic and genotype frequencies differences. Objective. We assessed whether polymorphisms of GST genes (GSTM1, GSTT1, and GSTP1) are associated with asthma and atopy among Tunisian children. Methods. 112 unrelated healthy individuals and 105 asthmatic (73 atopic and 32 nonatopic) children were studied. Genotyping the polymorphisms in the GSTT1 and GSTM1 genes was performed using the multiplex PCR. The GSTP1 ILe105Val polymorphism was determined using PCR-RFLP. Results. GSTM1 null genotype was significantly associated with the increased risk of asthma (P = .002). Asthmatic children had a higher prevalence of the GSTP1Ile105 allele than the control group (43.8% and 33.5%, respectively; P = .002). Also, the presence of the GSTP1 homozygote Val/Val was less common in subjects with asthma than in control group. We have found that GSTT1 null genotype (GSTT1 *0/*0) was significantly associated with atopy (P = .008). Conclusion. Polymorphisms within genes of the GST superfamily were associated with risk of asthma and atopy in Tunisia.

Arsenic methylation, GSTT1, GSTM1, GSTP1 polymorphisms, and skin lesions

OBJECTIVE

We investigated whether primary and secondary arsenic methylation ratios were associated with skin lesions and whether GSTT1, GSTP1, and GSTM1 polymorphisms modify these relationships.

METHODS

A case-control study of 600 cases and 600 controls that were frequency matched on age and sex was conducted in Pabna, Bangladesh, in 2001-2002. Individual well water, urine, and blood samples were collected. Water arsenic concentration was determined using inductively coupled plasma mass spectrometry (ICP-MS). Urinary arsenic speciation was determined using high performance liquid chromatography hydride with generator atomic absorption spectrometry and ICP-MS. Genotyping was conducted using multiplex polymerase chain reaction and TaqMan.

RESULTS

A 10-fold increase in primary methylation ratio [monomethylarsonic acid (MMA)/(arsenite + arsenate] was associated with a 1.50-fold increased risk of skin lesions (multivariate odds ratio = 1.50; 95% confidence interval, 1.00-2.26). We observed significant interaction on the multiplicative scale between GSTT1 wildtype and secondary methylation ratio [dimethylarsinic acid/MMA; likelihood ratio test (LRT), p = 0.01]. No significant interactions were observed for GSTM1 or GSTP1 or for primary methylation ratios.

CONCLUSION

Our findings suggest that increasing primary methylation ratios are associated with an increase in risk of arsenic-related skin lesions. The interaction between GSTT1 wildtype and secondary methylation ratio modifies risk of skin lesions among arsenic-exposed individuals.

Effect of glutathione S-transferase polymorphisms and proximity to hazardous waste sites on time to systemic lupus erythematosus diagnosis: results from the Roxbury lupus project

OBJECTIVE

The high prevalence of systemic lupus erythematosus (SLE) among African American women may be due to environmental exposures, genetic factors, or a combination of factors. Our goal was to assess association of residential proximity to hazardous waste sites and genetic variation in 3 glutathione Stransferase (GST) genes (GSTM1, GSTT1, and GSTP1) with age at diagnosis of SLE.

METHODS

Residential histories were obtained by interviewing 93 SLE patients from 3 predominantly African American neighborhoods in Boston. Residential addresses and locations of 416 hazardous waste sites in the study area were geocoded using ArcView software. Time-varying Cox models were used to study the effect of residential proximity to hazardous sites, GST genotype, and interaction between genotype and exposure in determining age at diagnosis.

RESULTS

The prevalence of SLE among African American women in these neighborhoods was 3.56 SLE cases per 1,000. Homozygosity for GSTM1-null and GSTP1 Ile105Val in combination was associated with earlier SLE diagnosis (P = 0.03), but there was no association with proximity to 416 hazardous sites. Available data on specific site contaminants suggested that, at a subset of 67 sites, there was higher potential risk for exposure to volatile organic compounds (P < 0.05 with Bonferroni correction). GST genotypes had a significant interaction with proximity (P = 0.03) in analyses limited to these sites.

CONCLUSION

There was no independent association between residential proximity to hazardous waste sites and the risk of earlier SLE diagnosis in this urban population. However, analysis of a limited number of sites indicated that the risk of earlier SLE associated with proximity to hazardous sites might be modulated by GST polymorphisms.

A case-control study of GST polymorphisms and arsenic related skin lesions

BACKGROUND

Polymorphisms in GSTT1, GSTM1 and GSTP1 impact detoxification of carcinogens by GSTs and have been reported to increase susceptibility to environmentally related health outcomes. Individual factors in arsenic biotransformation may influence disease susceptibility. GST activity is involved in the metabolism of endogenous and exogenous compounds, including catalyzing the formation of arsenic-GSH conjugates.

METHODS

We investigated whether polymorphisms in GSTT1, GSTP1 and GSTM1 were associated with risk of skin lesions and whether these polymorphisms modify the relationship between drinking water arsenic exposure and skin lesions in a case control study of 1200 subjects frequency matched on age and gender in community clinics in Pabna, Bangladesh in 2001-2002.

RESULTS AND DISCUSSION

GSTT1 homozygous wildtype status was associated with increased odds of skin lesions compared to the null status (OR1.56 95% CI 1.10-2.19). The GSTP1 GG polymorphism was associated with greater odds of skin lesions compared to GSTP1 AA, (OR 1.86 (95%CI 1.15-3.00). No evidence of effect modification by GSTT1, GSTM1 or GSTP1 polymorphisms on the association between arsenic exposure and skin lesions was detected.

CONCLUSION

GSTT1 wildtype and GSTP1 GG are associated with increased risk of skin lesions.

Direct evidence for the covalent modification of glutathione-S-transferase P1-1 by electrophilic prostaglandins: Implications for enzyme inactivation and cell survival

Glutathione-S-transferases (GST) catalyze the conjugation of electrophilic compounds to glutathione, thus playing a key role in cell survival and tumor chemoresistance. Cyclopentenone prostaglandins (cyPG) are electrophilic eicosanoids that display potent antiproliferative properties, through multiple mechanisms not completely elucidated. Here we show that the cyPG 15-deoxy-Delta(12,14)-PGJ2 (15d-PGJ2) binds to GSTP1-1 covalently, as demonstrated by mass spectrometry and by the use of biotinylated 15d-PGJ2. Moreover, cyPG inactivate GSTP1-1 irreversibly. The presence of the cyclopentenone moiety is important for these effects. Covalent interactions also occur in cells, in which 15d-PGJ2 binds to endogenous GSTP1-1, irreversibly reduces GST free-thiol content and inhibits GST activity. Protein delivery of GSTP1-1 improves cell survival upon serum deprivation whereas 15d-PGJ2-treated GSTP1-1 displays a reduced protective effect. These results show the first evidence for the formation of stable adducts between cyPG and GSTP1-1 and may offer new perspectives for the development of irreversible GST inhibitors as anticancer agents.

Glutathione s-transferases M1 and P1 prevent aggravation of allergic responses by secondhand smoke

RATIONALE

Secondhand tobacco smoke (SHS) and traffic-related air pollutants are associated with asthma and allergy. Diesel exhaust particles (DEPs) and SHS can interact with allergens in exacerbating allergic airway diseases through generation of reactive oxygen species. Glutathione S-transferases (GSTs) metabolize reactive oxygen species and detoxify electrophilic xenobiotics present in SHS and DEPs.

OBJECTIVES

We tested the hypotheses that functional GSTM1-null genotype and GSTP1 codon 105 variants (Ile105 and Val105) are determinants of allergic responses to SHS, and that responses to SHS and DEPs are correlated.

METHODS AND MEASUREMENTS

In a randomized, placebo-controlled crossover trial, 19 ragweed allergen-sensitive subjects who had previously participated in a DEP trial were challenged intranasally with allergen after having been exposed to either clean air or SHS at separate visits. Nasal allergen-specific IgE, histamine, IL-4, and IFN-gamma levels were measured before and after allergen challenge.

MAIN RESULTS

Individuals with GSTM1-null or GSTP1 Ile105 genotypes showed larger nasal responses to allergens with SHS compared with clean air. GSTM1-null subjects had a larger increase in IgE than GSTM1-present subjects (median, 173.3 vs. 46.7 U/ml; p = 0.03), and the Ile105 GSTP1 genotype subjects had increased histamine (median, 10.2 vs. 4.6 nM; p = 0.01) after SHS plus allergen challenge. Responses to SHS and DEPs were correlated. Enhancement of IgE and histamine was greatest in the subjects with both the GSTM1-null and GSTP1 Ile/Ile genotypes.

CONCLUSIONS

GSTM1 and GSTP1 are important cytoprotective factors that reduce SHS and DEP exacerbation of allergic responses.

Effects of arsenic exposure and genetic polymorphisms of p53, glutathione S-transferase M1, T1, and P1 on the risk of carotid atherosclerosis in Taiwan

To evaluate the joint effects between genetic polymorphisms of glutathione S-transferase M1, T1, P1, and p53, and arsenic exposure through drinking well water on the risk of carotid atherosclerosis, 605 residents including 289 men and 316 women were recruited from a northeastern area of Taiwan. Carotid atherosclerosis was diagnosed by either a carotid artery intima-media thickness (IMT) of >1.0 mm, a plaque score of > or =1, or stenosis of >50%. A significant age- and gender-adjusted odds ratio of 3.3 for the development of carotid atherosclerosis was observed among the high-arsenic exposure group who drank well water containing arsenic at levels >50 microg/L. The high-arsenic exposure group with GSTP1 variant genotypes of Ile/Val and Val/Val, and with the p53 variant genotypes of Arg/Pro and Pro/Pro had 6.0- and 3.1-fold higher risks of carotid atherosclerosis, respectively. In addition, the high-arsenic exposure group with one or two variant genotypes of GSTP1 and p53 had 2.8- and 6.1-fold higher risks of carotid atherosclerosis, respectively, and showed a dose-dependent relationship. A multivariate-adjusted odds ratio of 3.4 for the risk of carotid atherosclerosis among study subjects with the two variant genotypes of GSTP1 and p53 was also found. Our study showed the joint effects on the risk of carotid atherosclerosis between the genetic polymorphisms of GSTP1 and p53, and arsenic exposure.

GSTT1 and M1 polymorphisms in Hürthle thyroid cancer patients

Glutathione S-transferases (GST) are an important part of cell defense against numerous genotoxic compounds and ROS. In order to test the possibility of association between the GSTT1 and M1 null allele variant, and the risk of TCO (thyroid carcinoma with cell oxyphilia), a case-control study was carried out. The rationale for our study was that according to the important roles of GST enzymes in cells and association of GST null genotypes with many types of tumors, inactivating polymorphisms may be genetic susceptibility factors in the etiology of oxyphilic thyroid tumors characterized by mitochondrial dysfunction, increased ROS production and resistance to chemio- and radio-therapy. We found the frequency of GSTT1 null genotype of 19.2% in cases and 15.7% in controls, with an adjusted odds ratio (OR) of 1.4 (95% confidence interval (CI), 0.70-2.81), and a frequency of GSTM1 null genotype of 59% in cases with oxyphilic tumors and of 55.6% in controls (OR 1.24; 95% CI, 0.62-2.48), indicating that the GSTT1 and M1 null genotypes do not increase the risk of development of oxyphilic tumors.

Evaluation of glutathione S-transferase polymorphisms and mutagen sensitivity as risk factors for the development of second primary tumors in patients previously diagnosed with early-stage head and neck cancer

BACKGROUND

The objective of this study was to evaluate the effects of polymorphisms in 2 genes in the glutathione S-transferase (GST) family and the mutagen-sensitivity phenotype on the risk of second primary tumors (SPTs) in patients with previously diagnosed early-stage head and neck squamous cell carcinoma. Data were available for 303 patients who were enrolled in a placebo-controlled chemoprevention trial of low-dose 13-cis-retinoic acid to reduce the occurrence of SPTs.

METHODS

A Cox proportional hazards model and survival tree analysis were used to evaluate the association between specified genetic variations and the development of SPTs. The average number of bleomycin-induced chromatid breaks per cell was used to quantify mutagen sensitivity as an individual patient's degree of sensitivity to genotoxicity.

RESULTS

The GST-M1 null genotype was associated with an increased risk for any SPTs (hazard ratio [HR], 1.99; 95% confidence interval [95% CI], 1.11-3.56) and for tobacco-related SPTs (HR, 2.16; 95% CI, 1.01-4.62) after adjusting for covariates. The GST-T1 null genotype and bleomycin-induced chromatid breaks were not associated with a statistically significant increased risk for SPTs or tobacco-related SPTs after similar adjustment. Simultaneous nonnull status for both GST genotypes was associated with a decreased risk for any SPTs (HR, 0.52; 95% CI, 0.28-0.96) and tobacco-related SPTs (HR, 0.50; 95% CI, 0.22-1.11) compared with null status for GST-M1 accompanied by nonnull status for GST-T1.

CONCLUSIONS

An association was observed between the development of SPTs and the GST-M1 null genotype after successful treatment for early-stage head and neck squamous cell carcinoma. The GST-T1 null genotype and bleomycin-induced chromatid breaks were not associated with an increased risk, and no significant interactions were identified.

Characterization of phenotypes in Gstm1-null mice by cytosolic and in vivo metabolic studies using 1,2-dichloro-4-nitrobenzene

Glutathione S-transferase Mu 1 (GSTM1) has been regarded as one of the key enzymes involved in phase II reactions in the liver, because of its high expression level. In this study, we generated mice with disrupted glutathione S-transferase Mu 1 gene (Gstm1-null mice) by gene targeting, and characterized the phenotypes by cytosolic and in vivo studies. The resulting Gstm1-null mice appeared to be normal and were fertile. Expression analyses for the Gstm1-null mice revealed a deletion of Gstm1 mRNA and a small decrease in glutathione S-transferase alpha 3 mRNA. In the enzymatic study, GST activities toward 1,2-dichloro-4-nitrobenzene (DCNB) and 1-chloro-2,4-dinitrobenzene (CDNB) in the liver and kidney cytosols were markedly lower in Gstm1-null mice than in the wild-type control. Gstm1-null mice had GST activities of only 6.1 to 21.0% of the wild-type control to DCNB and 26.0 to 78.6% of the wild-type control to CDNB. After a single oral administration of DCNB to Gstm1-null mice, the plasma concentration of DCNB showed larger AUC0-24 (5.1-5.3 times, versus the wild-type control) and higher Cmax (2.1-2.2 times, versus the wild-type control), with a correspondingly lower level of glutathione-related metabolite (AUC0-24, 9.4-17.9%; and Cmax, 9.7-15.6% of the wild-type control). In conclusion, Gstm1-null mice showed markedly low ability for glutathione conjugation to DCNB in the cytosol and in vivo and would be useful as a deficient model of GSTM1 for absorption, distribution, metabolism, and excretion/toxicology studies.

GLUTATHIONES-TRANSFERASE OMEGA 1 AND OMEGA 2 PHARMACOGENOMICS

Glutathione S-transferase omega 1 and omega 2 (GSTO1 and GSTO2) catalyze monomethyl arsenate reduction, the rate-limiting reaction in arsenic biotransformation. As a step toward pharmacogenomic studies of these phase II enzymes, we resequenced human GSTO1 and GSTO2 using DNA samples from four ethnic groups. We identified 31 and 66 polymorphisms in GSTO1 and GSTO2, respectively, with four nonsynonymous-coding single nucleotide polymorphisms (cSNPs) in each gene. There were striking variations among ethnic groups in polymorphism frequencies and types. Expression constructs were created for all eight nonsynonymous cSNPs, as well as a deletion of codon 155 in GSTO1, and those constructs were used to transfect COS-1 cells. Quantitative Western blot analysis, after correction for transfection efficiency, showed a reduction in protein level of greater than 50% for the GSTO1 Tyr32 variant allozyme compared with wild type (WT), whereas levels for the Asp140, Lys208, Val236, and codon 155 deletion variant constructs were similar to that of the WT. For GSTO2, the Tyr130 and Ile158 variant allozymes showed 50 and 84% reductions in levels of expression, respectively, compared with WT, whereas the Ile41 and Asp142 allozymes displayed levels similar to that of WT GSTO2. Rabbit reticulocyte lysate degradation studies showed that the GSTO1 Tyr32 and the GSTO2 Tyr130, Ile158, and Asp142/Ile158 variant allozymes were degraded more rapidly than were their respective WT allozymes. These observations raise the possibility of functionally significant pharmacogenomic variation in the expression and function of GSTO1 and GSTO2.

Role of the Glutathione Metabolic Pathway in Lung Cancer Treatment and Prognosis: A Review

Inherent and acquired drug resistance is a cause of chemotherapy failure, and pharmacogenomic studies have begun to define gene variations responsible for varied drug metabolism, which influences drug efficacy. Platinum-based compounds are the most commonly used chemotherapeutic agents in the treatment of advanced stage lung cancer patients, and the glutathione metabolic pathway is directly involved in the detoxification or inactivation of platinum drugs. Consequently, genotypes corresponding to higher drug inactivation enzyme activity may predict poor treatment outcome. Available evidence is consistent with this hypothesis, although a definitive role for glutathione system genes in lung cancer prognosis needs to be elucidated. We present evidence supporting a role of the glutathione system in acquired and inherited drug resistance and/or adverse effects through the impact of either drug detoxification or drug inactivation, thus adversely effecting lung cancer treatment outcome. The potential application of glutathione system polymorphic genetic markers in identifying patients who may respond favorably, selecting effective antitumor drugs, and balancing drug efficacy and toxicity are discussed.

Changes in hepatic cytosolic glutathione S-transferase activity and expression of its class-P during prenatal and postnatal period in rats treated with aflatoxin B1

The effect of aflatoxin B1 (AFB1) on the expression of glutathione S-transferase-P (GST-P) which is the major isoform of GST in developmental stages has been investigated in rat liver during prenatal and postnatal stages. Following administration of AFB1 (0, 0.5, 1.0, 2.0, 3.0 or 4.0 mg/kg bw) injected I.P on day 8.5 of gestation the number of dead or reabsorbed fetuses and malformed embryos were recorded. Then the fetal livers were processed for measurement of total GST and GST-P activities, using 1-chloro-2,4-dinitrobenzene (CDNB) and ethacrynic acid (ETA) as substrates respectively. RT-PCR using rat GST-P specific primers was performed on mRNA extracted from livers. Besides, the effects of AFB1 on hepatic GST and GST-P were assessed in groups of suckling rats directly injected with the toxin. The results show that a single dose of AFB1 (1.0 or 2.0 mg/kg bw) caused approximately 50-60% depletion in fetal liver GST towards CDNB. Postnatal experiments revealed that liver GST (using CDNB as substrate) was significantly induced (approximately 40%) in suckling rats injected with a single dose of AFB1 (3.0 mg AFB1/kg) 24 h before killing. Liver GST-P expression was unaffected due to AFB1 exposures of rats before and after the birth. This finding was substantiated by western blotting and RT-PCR techniques. These data suggest that AFB1-related induction in rat liver total GST after birth may be implicated in protective mechanisms against AFB1. In contrast, inhibition of this enzyme in fetal liver following placental transfer of the carcinogen may explain high susceptibility of fetal cells to trans-plancental aflatoxins. Furthermore, lack of influence of AFB1 on GST-P expression in developmental stages can role out the involvement of this class of GST in AFB1 biotransformation.

Associations of tumor necrosis factor G-308A with childhood asthma and wheezing

RATIONALE

Tumor necrosis factor (TNF) mediates a spectrum of airway inflammatory responses, including those to air pollutants, and is an asthma candidate gene. One TNF promoter variant (G-308A) affects expression of TNF and has been associated with inflammatory diseases; however, studies of asthma have been inconsistent. Because ozone produces oxidative stress, increased airway TNF, and inflammation, the associations of the -308 TNF polymorphism with asthma may vary by ozone exposure and variants of oxidant defense genes glutathione-S-transferase (GST) M1 and GSTP1.

OBJECTIVES

To investigate the association of TNF G-308A with asthma and wheezing and to determine whether these associations vary with ozone exposure and GSTM1 and GSTP1 genotype.

METHODS

We studied associations of TNF-308 genotype with lifetime and current wheezing and asthma among 3,699 children in the Children's Health Study. We examined differences in associations with community ozone and by GSTM1 null and GSTP1 105 Ile/Val (A105G) genotype.

RESULTS

Children with TNF-308 GG had decreased risk of asthma (odds ratio, 0.8; 95% confidence interval, 0.7-0.9) and lifetime wheezing (odds ratio, 0.8; 95% confidence interval, 0.7-0.9). The protective effects of GG genotype on wheezing outcomes were of greater magnitude in lower compared with higher ozone communities. These findings were replicated in the two cohorts of fourth-grade children recruited in 1993 and 1996. The reduction of the protective effect from the -308 GG genotype with higher ozone exposure was most marked in the GSTM1 null and GSTP1 Ile/Ile groups.

CONCLUSIONS

The TNF-308 GG genotype may have a protective role in asthma pathogenesis, depending on airway oxidative stress levels.

New evidence on variations of human body burden of methylmercury from fish consumption

Epidemiologic studies commonly use mercury (Hg) level in hair as a valid proxy to estimate human exposure to methylmercury (MeHg) through fish consumption. This study presents the results yielded by a complete data set on fish consumption habits, Hg levels in edible fish resources, and corresponding Hg accumulation in hair, gathered in three distinct communities of eastern Canada. For one of these communities, the average hair Hg concentration was 14 times less than the expected value based on calculated daily oral exposure and current knowledge of MeHg metabolism. This finding could be explained by differences in specific genetic characteristics and/or interactive effects of other dietary components.

Gene by environment interactions and the development of asthma and allergy

Asthma is the most common chronic disease during childhood in modern societies. Prevalence rates differ between countries, but on an average, 10-20% of the children in Western Europe and the US are affected. While the true cause of the disease is not yet known, it is common perception that genetic alterations and environmental factors act together in the development of atopic diseases such as asthma, allergic rhinitis and atopic eczema. Numerous studies have reported an association between environmental tobacco smoke (ETS) exposure and respiratory diseases: maternal smoking during pregnancy and early childhood is associated with impaired lung growth and diminished lung function, and in asthmatic children parental smoking increases symptoms and the frequency of asthma attacks. Recent studies have shown that the capability of ETS to induce asthma and asthma symptoms may be modified by genetics. Linkage studies, which took smoking and passive smoking status of study subjects into account, came to different results than those studies based on unstratified samples. These analyses indicated that some chromosomal regions (e.g. 5q) might harbor genes that exert their effects predominantly in combination with ETS exposure. Some of the genes modifying the effect of ETS and air pollution on the body may have been identified. When these detoxification enzymes are genetically defect or missing the capability of the lung to metabolize hazardous substances is dramatically diminished. As a consequence, pulmonary inflammation may occur and the barrier function of the lung may be compromised allowing allergens to penetrate and asthma to start. Knowledge of these interactions may be the key in understanding the complex nature of the disease. It may allow for prediction and an earlier diagnosis of the disease as well as better and more efficient prevention. In the long run, it may contribute significantly to the development of new and better-tailored drugs for one of the major diseases of the 21st century.

Chronic treatment with mood stabilizers lithium and valproate prevents excitotoxicity by inhibiting oxidative stress in rat cerebral cortical cells

BACKGROUND

Recent studies indicate that chronic treatment with the mood-stabilizing drugs lithium and valproate produces a neuroprotective effect against excitotoxicity. In this study, we aimed to determine whether inhibiting oxidative damage plays a role in a neuroprotective effect of lithium and valproate against excitotoxicity.

METHODS

Intracellular free calcium concentration was measured with the fluorescent calcium ion indicator fluo-3. Malondialdehyde, an end product derived from peroxidation of polyunsaturated fatty acid, and protein carbonyls were used to assess oxidative damage to lipid and protein. Excitotoxicity was assayed by measuring cell viability with the MTT [3-(4,5-dimethylthiazol-2yl)-2,5-diphenyl tetrazolium bromide] method and by measuring deoxyribonucleic acid (DNA) fragmentation with TUNEL (terminal deoxynucleotidyltransferase-mediated deoxyuridine triphosphate nick end labeling) staining.

RESULTS

We found that chronic treatment with lithium and valproate at their therapeutically relevant concentrations significantly inhibited the glutamate-induced increase of intracellular free calcium concentration, lipid peroxidation, protein oxidation, DNA fragmentation, and cell death in primary cultured rat cerebral cortical cells. This treatment had no effect on basal intracellular free calcium concentration, lipid peroxidation, protein oxidation, DNA fragmentation, and cell death.

CONCLUSIONS

Our results suggest that chronic treatment with lithium and valproate inhibits oxidative damage to lipid and protein and in turn produces a neuroprotective effect against excitotoxicity.

Evaluation of the association between null genotypes of glutathione-S-transferases and Behcet’s disease

Glutathione S-transferases (GST) play an important role in oxidative stress related syndromes. An imbalance of the oxidant and antioxidant systems is important in the pathogenesis of Behcet's disease (BD). The objective of this study was to evaluate the association of null genotypes of GST-M1 and GST-T1 with BD since some preliminary molecular genetic data were recently published. Ninety-four Turkish BD patients (42 male, 52 female, 37.1+/-10.4 years) and 140 healthy volunteers (70 male, 70 female, 36.8+/-11.7 years) matched for age and gender with the patients as the control group were included in the study. Distributions of GST-M1 and GST-T1 genotypes were determined by multiplexed PCR using three sets of primers for GST-M1, GST-T1, and beta-globulin genes. There was no association between BD and the frequencies of GST-M1 and GST-T1 null genotypes when compared to controls by separate analysis. However, by cross and pooled combination analysis there was a significant association between the frequencies of pooled GSTs with one or both null genotypes in BD and controls. This is the first evidence that the association between the frequencies of GST-M1 and GST-T1 null genotypes and BD might be dependent on the interaction of multiple null allele polymorphisms rather than a single null allele of GST-M1 and GST-T1.

Genetic analysis of glutathione S-transferase A1 polymorphism in the Chinese population and the influence of genotype on enzymatic properties

Genetic polymorphisms of human glutathione S-transferases (hGSTs) have important implications for drug efficacy and cancer susceptibility. hGSTA1 is the most abundant subfamily of hGSTs. The aim of this study was to investigate the distribution of hGSTA1 genetic polymorphism in the Chinese population and whether there exists the potential activity alterations caused by this polymorphism. Therefore, genomic DNA was extracted from peripheral blood of 140 healthy Chinese people and 11 normal liver tissues obtained from patients who had undergone liver surgery. Two variants in the promoter region of the hGSTA1 gene were identified by polymerase chain reaction-restricted fragment length polymorphism (PCR-RFLP). Activities toward selected substrates of the wild type (hGSTA1*A) and variant (hGSTA1*B) were measured spectrometrically using S-9 fractions from liver samples. Delta5-androstene-3,17-dione (AD), cumene hydroperoxide (CuOOH), and 1-chloro-2,4-dinitrobenzene (CDNB) were used as marker substrates toward hGSTA1, hGSTA, and hGST, respectively. The kinetic parameters (Km, Vmax, and Vmax/Km) of hGSTA1 were determined with different concentrations of AD. The results showed that, in the study population, the proportions of hGSTA1*A/*A, hGSTA1*A/*B, and hGSTA1*B/*B genotypes were 75.0, 24.3, and 0.7%, respectively, and the allele frequencies of hGSTA1*A and hGSTA1*B were detected to be 87.1 and 12.9%, respectively. The variant hGSTA1 showed a significantly decreased activity for AD isomerization as compared to the wild type. Kinetic analyses revealed that the V(max) value of the variant hGSTA1 was 48% of that of the wild type despite a Km value of 62% (p < 0.01). This means that the Vma)/Km) in the variant hGSTA1 was 76%. These data indicate that the distribution of hGSTA1 gene is polymorphic in Chinese and is different from those in other racial populations. The promoter sequence polymorphism of the hGSTA1 gene is associated with decreased Km and Vmax values of the enzyme in individuals with the variant allele. This variant is also associated with a decrease in hGSTA1 activity toward preferred substrates. This altered activity, however, is accompanied by significant individual variation in the variant population.

Glutathione S-transferase M1 and T1 null genotype frequency in chronic myeloid leukaemia

Polymorphisms associated with genes coding for glutathione S-transferase enzymes are known to influence metabolism of different carcinogens and have been associated with incidence of various types of cancer. We have determined the GST M1 and GST T1 'null' genotype frequency in 81 patients with chronic myeloid leukaemia (CML) and 123 racially and geographically matched control individuals by multiplex polymerase chain reaction (PCR). GST M1 null genotype frequencies in CML and controls were 28.4% and 27.7%, respectively. GST T1 null genotype frequencies in CML and controls were 19.8% and 7.3%, respectively. The GST T1 null genotype frequency in CML patients is significantly different from that in controls (odds ratio (OR) 3.12, 95% confidence interval (CI) 1.3-7.45, P=0.008).

Molecular Prognosticators and Genomic Instability in Papillary Thyroid Cancer

OBJECTIVES/HYPOTHESIS

Tumor progression has been attributed to the accumulation of DNA damage concurrent with selection of advantageous mutations; this DNA damage may result from failure to maintain genomic integrity or from susceptibility to carcinogens. Glutathione S-transferases (GSTs), enzymes that metabolize many carcinogens, may play a role in preserving genome integrity. The objectives of this study are to assess the relationship of GST genotypes with prognosis, clinicopathologic parameters, and genomic instability in papillary thyroid cancer.

STUDY DESIGN

Prospective analysis.

METHODS

GSTM1 and GSTT1 genotypes of 35 matched normal and papillary thyroid cancer specimens were determined by polymerase chain reaction (PCR) using primers specific for the coding sequences of each gene. Genomic instability was measured by intersimple sequence repeat PCR for each tumor/normal pair and compared with the GAMES prognostic scoring system and clinicopathologic parameters including age, extrathyroidal extension, tumor grade, size, stage metastasis, sex, and smoking history.

RESULTS

GSTM1 and GSTT1 null genotypes were found in the normal tissues of 46% and 45%, respectively. No gene losses were detected in the tumor specimens. A significant association between the GSTM1 null genotype and increased risk of recurrence and death was observed. Elevated GII correlated with smoking and tumor stage but not with GST genotype.

CONCLUSION

The association of GSTM1 null genotype with intermediate and high risk GAMES categories suggests that GSTM1 provides some protection against disease progression. However, this protection does not confer resistance to disease onset. GST genotyping may be a useful adjunct prognosticator with GAMES.

Glutathione S-transferase P1 genotype and prognosis in Hodgkin's lymphoma

PURPOSE

Glutathione S-transferase P1 (GSTP1) is a member of the GST enzyme superfamily that is important for the detoxification of several cytotoxic drugs and their by-products. A single nucleotide polymorphism results in the substitution of isoleucine (Ile) to valine (Val) at codon 105, causing a metabolically less active variant of the enzyme. We assessed the impact of the GSTP1 codon 105 genotype on treatment outcome in patients with Hodgkin's lymphoma.

EXPERIMENTAL DESIGN

The Ile(105)Val polymorphism in the GSTP1 gene was analyzed using a PCR-RFLP technique. Ninety-seven patients with Hodgkin's lymphoma were included and associations with patient characteristics and treatment outcome were analyzed.

RESULTS

The GSTP1 Ile(105)Val polymorphism was associated in a dose-dependent fashion with an improved failure-free survival in patients with Hodgkin's lymphoma (P = 0.02). The probability of 5-year survival for patients homozygous for the (105)Val/(105)Val GSTP1 genotype was 100%, for heterozygous patients 74% (95% confidence interval, 56-85), and for patients homozygous for the (105)Ile/(105)Ile genotype 43% (95% confidence interval, 23-61). The Cox multivariate analysis showed that GSTP1 codon 105 genotype was an independent prognostic factor.

CONCLUSIONS

The GSTP1 genotype predicts clinical outcome in patients with Hodgkin's lymphoma.

Functional polymorphism of human glutathione transferase A3: effects on xenobiotic metabolism and steroid biosynthesis

The alpha class glutathione transferase GSTA3-3 is involved in steroid biosynthesis and the metabolism of some xenobiotics. A bioinformatics approach was utilized to identify novel coding region polymorphisms in the glutathione transferase A3 gene (GSTA3). We describe an I71L polymorphism in GSTA3 that occurs at a low frequency in African populations. The activity of the leucine containing isoform was significantly reduced in a range of glutathione-conjugating reactions due to a diminished affinity for reduced glutathione, indicating that this allele could be implicated in disease caused by oxidative stress in steroidogenic tissue. By contrast, the delta(5)-androsten-3,17-dione isomerase activity of GSTA3-3 was not affected by this substitution, indicating that there is no direct effect on steroid synthesis. However, the L71 isoform displayed diminished stability at 45 degrees C. If this relative instability is mirrored in vivo, testosterone and progesterone synthesis may be affected in individuals carrying this allele.

Human glutamate cysteine ligase gene regulation through the electrophile response element

Glutathione (GSH) is the primary nonprotein thiol in the cell. It has many important roles in cell function, including regulating redox-dependent signal transduction pathways. The content of GSH within the cell varies with stress. In many cases, a process involving GSH synthesis results in adaptation to subsequent stressors. Sustained increases in GSH content are controlled primarily through induction of two genes, Gclc and Gclm, leading to the synthesis of the rate-limiting enzyme for GSH synthesis, glutamate cysteine ligase. Each of these genes in humans has a number of putative enhancer elements in their promoters. Overall, the most important element in both Gclc and Gclm expression is the electrophile response element. We review the evidence that has led to this conclusion and the implications for the redox-dependent regulation of this critical intracellular antioxidant.

Azathioprine acts upon rat hepatocyte mitochondria and stress-activated protein kinases leading to necrosis: protective role of N-acetyl-L-cysteine

Azathioprine is an immunosuppressant drug widely used. Our purpose was to 1) determine whether its associated hepatotoxicity could be attributable to the induction of a necrotic or apoptotic effect in hepatocytes, and 2) elucidate the mechanism involved. To evaluate cellular responses to azathioprine, we used primary culture of isolated rat hepatocytes. Cell metabolic activity, reduced glutathione, cell proliferation, and lactate dehydrogenase release were assessed. Mitochondria were isolated from rat livers, and swelling and oxygen consumption were measured. Mitogen-activated protein kinase pathways and proteins implicated in cell death were analyzed. Azathioprine decreased the viability of hepatocytes and induced the following events: intracellular reduced glutathione (GSH) depletion, metabolic activity reduction, and lactate dehydrogenase release. However, the cell death was not accompanied by DNA laddering, procaspase-3 cleavage, and cytochrome c release. The negative effects of azathioprine on the viability of hepatocytes were prevented by cotreatment with N-acetyl-L-cysteine. In contrast, 6-mercaptopurine showed no effects on GSH content and metabolic activity. Azathioprine effect on hepatocytes was associated with swelling and increased oxygen consumption of intact isolated rat liver mitochondria. Both effects were cyclosporine A-sensitive, suggesting an involvement of the mitochondrial permeability transition pore in the response to azathioprine. In addition, the drug's effects on hepatocyte viability were partially abrogated by c-Jun N-terminal kinase and p38 kinase inhibitors. In conclusion, our findings suggest that azathioprine effects correlate to mitochondrial dysfunction and activation of stress-activated protein kinase pathways leading to necrotic cell death. These negative effects of the drug could be prevented by coincubation with N-acetyl-L-cysteine.

Combined effects of glutathione S-transferase polymorphisms and thyroid cancer risk

Since exposure to ionizing radiation, a risk factor for thyroid cancer, may produce genotoxins potentially eliminated by glutathione-S-transferases, we conducted a case control study to evaluate the role of the GSTM1- and GSTT1-null genotypes and GSTP1 polymorphisms in thyroid cancer. The frequency of GSTP1 Ile/Ile, GSTM1-, and GSTT1-null genotypes was increased in cancer patients when compared with control population. Considering the genotypes over-represented in thyroid cancer patients as potential risk genotypes, we carried out an odds ratio (OR) analysis considering the presence of none, one, two, or three risk genotypes. The results obtained showed that the presence of three potentially risk alleles (GSTM1 null, GSTT1 null, and GSTP1 Ile/Ile) lead to a significant OR increase for all the cases, irrespective of the type of tumor (OR=2.91), for papillary (OR=3.64) but not for follicular tumors. The presence of GSTP1 Ile/Ile leads to a significant later age of tumor onset when compared with GSTP1 Ile/Val and Val/Val (P<0.05), suggesting a possible association between GSTP1 Ile/Ile and the age of disease manifestation. These results suggest that combined GST polymorphisms lead to a moderate increased risk for thyroid cancer, especially for the papillary type, and GSTP1 polymorphisms might modulate the age of onset of the disease.

Inhibition of tumor growth by replacing glutathione with N-acetyl-l-cysteine

There have been several attempts to prevent the tumor growth and the resulting death. However, almost none of the developed methods designed to inhibit tumor growth gives a satisfactorily result without deleterious side effects. Some of the existing methods employed on prevention of tumor growth and invasion target the metabolic differences between normal and tumor cells. The most pronounced metabolic differences between normal and tumor cells appear to be in the energy generating pathways. The energy generating pathways in normal cells are inter-regulated and the most developed pathway controls the activity of the least developed pathway. Cancer cells do not respond to these regulations and as a result energy generating pathways start to operate independently. Among the energy generating pathways, the least developed or the most primitive pathway is the non-phosphorylating glycolysis. The increased activity of this pathway has been suggested to provide the cells with sufficient mitotic activity. It has been suggested that in non-phosphorylating glycolysis, glucose is broken down to lactate in a manner that requires glutathione. Here, I hypothesize that manipulation of intracellular glutathione concentrations as protecting the cells form oxidative stress may efficiently inhibit tumor growth. Glutathione is a soluble antioxidant and its concentration is high in prenatal tissue and in cancer cells. Though its primary function seems to combat against oxidant injury and toxic xenobiotics, glutathione is implicated in many other different cellular processes including cell proliferation and DNA and RNA synthesis. Another function of glutathione relevant to the subject is its involvement in detoxification of methylglyoxal, a compound that is generated at high concentrations in rapidly proliferating cells possessing an inhibitory activity on cell proliferation. Therefore, inhibition of intracellular glutathione concentration may negatively impact the tumor cell growth by at least three ways. The first is through inhibition of non-phosphorylating glycolysis that provides mitotic energy for cells. The second is through the inhibition of methylglyoxal metabolism and the third is through the redox regulation of DNA and RNA synthesis.

GSTM1, GSTT1, and GSTP1 genotypes and the genotoxicity of hydroquinone in human lymphocytes

Hydroquinone is a myelotoxin that is found in many foods and is also formed through the metabolism of benzene. Human exposure to benzene is associated with the development of myelodysplastic syndrome and acute myelogenous leukemia. Hydroquinone is genotoxic in several in vitro and in vivo test systems, inducing micronuclei (MN), sister-chromatid exchange (SCE), and chromosomal aberrations. Glutathione S-transferases (GSTs) are a superfamily of polymorphic enzymes involved in the conjugation of reactive chemical intermediates to soluble forms. These enzymes play a key role in the detoxification of endogenous and exogenous compounds, and the polymorphic genes GSTM1, GSTT1, and GSTP1 have been associated with the differential metabolism of several genotoxicants. In the present study, we have evaluated the effect of GSTM1, GSTT1, and GSTP1 polymorphisms on the frequency of MN and SCE induced by hydroquinone in human lymphocytes. Lymphocytes were obtained from 15 healthy non-smoking donors, and their GSTM1, GSTT1, and GSTP1 genotypes determined. Treatment of cultures of the lymphocytes with hydroquinone significantly increased the overall frequencies of MN and SCE (P<0.0001). Individuals with the GSTM1 null genotype had a significantly higher frequency of MN compared with GSTM1-present individuals (P=0.013); in contrast, the GSTM1 genotype had no effect on hydroquinone-induced SCE frequency. The other polymorphisms did not significantly affect the frequencies of MN or SCE. These results suggest that GSTM1 is involved in the metabolic fate of hydroquinone and that polymorphisms in GSTM1 could be related to inter-individual differences in DNA damage arising from the exposure to this compound.

X-ray structure of glutathione S-transferase from the malarial parasite Plasmodium falciparum

GSTs catalyze the conjugation of glutathione with a wide variety of hydrophobic compounds, generally resulting in nontoxic products that can be readily eliminated. In contrast to many other organisms, the malarial parasite Plasmodium falciparum possesses only one GST isoenzyme (PfGST). This GST is highly abundant in the parasite, its activity was found to be increased in chloroquine-resistant cells, and it has been shown to act as a ligandin for parasitotoxic hemin. Thus, the enzyme represents a promising target for antimalarial drug development. We now have solved the crystal structure of PfGST at a resolution of 1.9 A. The homodimeric protein of 26 kDa per subunit represents a GST form that cannot be assigned to any of the known GST classes. In comparison to other GSTs, and, in particular, to the human isoforms, PfGST possesses a shorter C-terminal section resulting in a more solvent-accessible binding site for the hydrophobic and amphiphilic substrates. The structure furthermore reveals features in this region that could be exploited for the design of specific PfGST inhibitors.

Genetic susceptibility, biomarker respones, and cancer

A large number of studies have reported associations between polymorphisms of xenobiotic-metabolizing enzymes (XMEs) and various cancers. However, the carcinogenic exposures behind such findings have usually been unclear. Information on susceptibility to specific carcinogens could better be obtained by examining situations where the exposure and the endpoint studied are nearer in time, i.e., by studying biomarkers of carcinogen exposure and early (genotoxic) effect in exposed humans. For example, analyses of DNA adducts and cytogenetic endpoints have indicated an increased susceptibility of glutathione S-transferase M1 (GSTM1) null genotype to genotoxicity of tobacco smoking, supporting the view that the associations of the GSTM1 null genotype with bladder and lung cancer are partly related to smoking. In vitro genotoxicity studies with human cells offer an experimental tool that can be used, within the limits of the cell systems, to predict individual sensitivity and genotype-carcinogen interactions. In vitro sensitivity to the genotoxicity of 1,2:3,4-diepoxybutane, an epoxide metabolite of 1,3-butadiene has clearly been shown to depend on GSTT1 genotype, which has also been implicated to modify, along with GSTM1 genotype, the in vitro genotoxicity of 1,2-epoxy-3-butene, another epoxide metabolite of 1,3-butadiene. These genotypes appear to modulate the excretion of 1,3-butadiene-specific mercapturic acids, and influence genotoxicity biomarker levels in 1,3-butadiene-exposed workers. The excretion of specific mercapturic acids (PHEMA) in workers exposed to styrene has clearly been shown to depend on GSTM1 genotype, and GSTT1 genotype seems to modulate the excretion of one PHEMA diastereoisomer. These genotypes have also been implicated to modulate the in vitro genotoxicity of styrene. In general, the genetic polymorphisms potentially important for biomarker response largely depend on the exposing agent, biological material examined, and ethnicity of the population under study. Individual exposure level may vary a lot, and a reliable estimate of the exposure is essential for correct interpretation of genotype-exposure interaction. Besides XME polymorphisms, any polymorphisms that affect cellular response to DNA damage could, in principle, modify individual sensitivity to genotoxins. For instance, those concerning DNA repair proteins are presently being studied by many laboratories.

Molecular epidemiology of sporadic breast cancer. The role of polymorphic genes involved in oestrogen biosynthesis and metabolism

The major known risk factors for female breast cancer are associated with prolonged exposure to increased levels of oestrogen. The predominant theory relates to effects of oestrogen on cell growth. Enhanced cell proliferation, induced either by endogenous or exogenous oestrogens, increases the number of cell divisions and thereby the possibility for mutation. However, current evidence also supports a role for oxidative metabolites, in particular catechol oestrogens, in the initiation of breast cancer. As observed in drug and chemical metabolism, there is considerable interindividual variability (polymorphism) in the conjugation pathways of both oestrogen and catechol oestrogens. These person-to-person differences, which are attributed to polymorphisms in the genes encoding for the respective enzymes, might define subpopulations of women with higher lifetime exposure to hormone-dependent growth promotion, or to cellular damage from particular oestrogens and/or oestrogen metabolites. Such variation could explain a portion of the cancer susceptibility associated with reproductive effects and hormone exposure. In this paper the potential role of polymorphic genes encoding for enzymes involved in oestrogen biosynthesis (CYP17, CYP19, and 17beta-HSD) and conversion of the oestrogen metabolites and their by-products (COMT, CYP1A1, CYP1B1, GSTM1, GSTM3, GSTP1, GSTT1 and MnSOD) in modulating individual susceptibility to breast cancer are reviewed. Although some of these low-penetrance genes appeared as good candidates for risk factors in the etiology of sporadic breast cancer, better designed and considerably larger studies than the majority of the studies conducted so far are evidently needed before any firm conclusions can be drawn.

Relationship of tobacco smoking with GSTM1 gene polymorphism in laringeal cancer

This paper aimed to analyze the association of polymorphism of GSTM1 0/0 genotype with laryngeal cancer along a hospital based case-control study. Polymorphisms of GSTM1 0/0 of samples from 36 patients with laryngeal cancer and 35 healthy controls were detected by PCR method. The reaction used as GSTM1 primers, using the sequence sense: 5'-CTGCCCTACTTGGATTGATGGG-3' and antisense: 5'-TGGATTGTAGCAGATCATGC-3'. N Acetyl transferase 1 (NAT1) gene using the primers sense: 5'-TAAAAGTAAAATGATTTGCTTTCG-3' and antisense: 5'- GCTTTCTAGCATAAATCACCAA-3' was used as internal positive control. Two sided 2 and multivariation analysis were used to analyse the results. The proportions of GSTM1 deleted genotype in cases and controls were 47.2% and 54.3%, respectively. There was significant increment of GSTM 0/0 genotype frequency in moderate smokers group of patients compared to control (P=0.033, OR= 4.78, 95% CI = 1.30-7.13). We conclude that GSTM1 deleted genotype may be a genetic susceptibility marker for laryngeal cancer whose exposed to low doses carcinogens. The absence of this enzyme seems to have a role in the development of laryngeal cancer, in which the mechanism still needs further investigation.