Association between glutathione S-transferase M1 and T1 polymorphisms and increased risk for bladder cancer in Korean smokers

Association of Glutathione S-transferase gene polymorphism with bladder Cancer susceptibility

BACKGROUND

We conducted a meta-analysis to evaluate the relationship between the glutathione S-transferase μ1 (GSTM1)- and glutathione S-transferase θ1 (GSTT1)- null genotypes and susceptibility to bladder cancer.

METHODS

We identified association reports from the databases of PubMed, Embase, the Cochrane Library and the China Biological Medicine Database (CBM disc) on July 1, 2017 and synthesized eligible investigations. Results were expressed using odds ratios (ORs) for dichotomous data, and we also calculated 95% confidence intervals (CIs).

RESULTS

In this meta-analysis, we found that the GSTM1-null genotype was associated with bladder cancer risk in the overall population, and individually in whites, Africans and Asians (overall population: OR = 1.40, 95% CI: 1.31-1.48, P<0.00001; whites: OR = 1.39, 95% CI: 1.26-1.54, P<0.00001; Africans: OR = 1.54, 95% CI: 1.16-2.05, P = 0.003; Asians: OR = 1.45, 95% CI: 1.33-1.59, P<0.00001). The GSTT1-null genotype was associated with bladder cancer risk in the overall population, but not in whites, in Africans or Asians (overall population: OR = 1.11, 95% CI: 1.01-1.22, P = 0.03; whites: OR = 1.16, 95% CI: 0.99-1.36, P = 0.07; Africans: OR = 1.07, 95% CI: 0.65-1.76, P = 0.79; Asians: OR = 1.05, 95% CI: 0.91-1.22, P = 0.51). Interestingly, a dual-null GSTM1-GSTT1 genotype was associated with bladder cancer risk in the overall population and in Asians (overall population: OR = 1.48, 95% CI: 1.15-1.92, P = 0.002; Asians: OR = 1.62, 95% CI: 1.15-2.28, P = 0.006). In conclusion, the GSTM1-null, GSTT1-null and dual-null GSTM1-GSTT1 genotypes might be associated with the onset of bladder cancer, but additional genetic-epidemiological studies should be conducted to explore this association further.

GSTM1 and GSTT1 polymorphisms are associated with increased bladder cancer risk: Evidence from updated meta-analysis

BACKGROUND

Previous studies have indicated association between GSTM1 and GSTT1 gene polymorphisms and bladder cancer susceptibility, but the results have been inconclusive. Here, we performed a meta-analysis to investigate the association between GSTM1/GSTT1 deletion polymorphisms and bladder cancer susceptibility.

METHODS

We searched for all studies investigating the association between GSTM1 or GSTT1 polymorphism and bladder cancer susceptibility in Pubmed, Web of Knowledge, and the Cochrane Central Search Library. A systematic review and meta-analysis were performed. Subgroup analyses were performed on different ethnicity, population-based and smoking status.

RESULTS

Our search identified 63 studies. GSTM1 null, GSTT1 null and GSTM1/GSTT1 double-null genotypes were associated with increased risk of bladder cancer (OR: 1.36 95% CI: 1.25-1.47, P<0.01; OR: 1.13 95% CI: 1.02-1.25, P<0.01; OR: 1.84 95% CI: 1.50-2.26, P<0.01). Subgroup analyses indicated that the GSTM1-null genotype was associated with increased risk of bladder cancer in Caucasians and Asians, while the GSTT1-null genotype was associated with increased risk of bladder cancer in Caucasians. The GSTM1/GSTT1 double-null genotype was associated with increased risk of bladder cancer in Caucasians, Asians, and Africans. Stratified analyses of population-based associations indicated increased bladder cancer risk associated with GSTM1-null and GSTM1/GSTT1 double-null genotypes in hospital-based and population-based studies. GSTM1 deletion was associated with increased bladder cancer risk in both smokers and nonsmokers. Non-smokers with the GSTM1/GSTT1 double-null genotype had an increased bladder cancer risk.

CONCLUSION

This meta-analysis demonstrates that the GSTM1-null, GSTT1-null, and GSTM1/GSTT1 double-null genotypes are associated with increased bladder cancer risk.

The relationship between GSTA1, GSTM1, GSTP1, and GSTT1 genetic polymorphisms and bladder cancer susceptibility: A meta-analysis

BACKGROUND

Previous studies have investigated the relationship between GSTA1, GSTM1, GSTP1, and GSTT1 polymorphisms and bladder cancer (BCa) susceptibility, respectively, but the results remain inconsistent. So, we conducted this meta-analysis including 79 case-control studies to explore such relationships.

METHODS

We searched PubMed, EMBASE, Cochrane library, Web of Science, and CNKI for relevant available studies. The pooled odds ratios (ORs) with 95% confidence intervals (CIs) were implemented to evaluate the intensity of associations. Publication bias was estimated using Begg funnel plots and Egger regression test. To assess the stability of the results, we used sensitivity analysis with the method of calculating the results again by omitting 1 single study each time. Between-study heterogeneity was tested using the I statistic.

RESULTS

No significant association between GSTA1 polymorphism and BCa susceptibility (OR = 1.05, 95% CI 0.83-1.33) was noted. Besides, meaningful association between individuals who carried the GSTM1 null genotype and increased BCa risk was detected (OR = 1.39, 95%CI 1.28-1.51). When stratified by ethnicity, significant difference was found in both Caucasian (OR = 1.39, 95% CI 1.23-1.58) and Asian populations (OR = 1.45, 95% CI 1.31-1.61). Moreover, in the subgroup analysis by source of controls (SOC), the results were significant in both hospital-based control groups (OR = 1.49, 95% CI 1.35-1.64) and population-based control groups (OR = 1.21, 95% CI = 1.07-1.37). Additionally, the analysis revealed no significant association between GSTP1 polymorphism and BCa risk (OR = 1.07, 95% CI 0.96-1.20). What is more, significant associations between GSTT1 polymorphism and BCa susceptibility were discovered (OR = 1.11, 95% CI 1.00-1.22). In the subgroup analysis by ethnicity, significant associations between GSTT1 null genotype and BCa risk were observed only in Caucasians (OR = 1.25, 95% CI 1.09-1.44). Furthermore, when stratified by SOC, no obvious relationship was found between the GSTT1 null genotype polymorphism with hospital-based population (OR = 1.11, 95% CI 0.97-1.28) or population-based population (OR = 1.10, 95% CI 0.96-1.27).

CONCLUSION

This study suggested that GSTM1 null genotype and GSTT1 null genotype might be related to higher BCa risk, respectively. However, no associations were observed between GSTA1 or GSTP1 polymorphisms and BCa susceptibility.

GSTT1 Null Genotype Significantly Increases the Susceptibility to Urinary System Cancer: Evidences from 63,876 Subjects

GSTT1 gene plays an important role in detoxification and clearance of reactive oxygen species(ROS). A null variant in this gene has been demonstrated to confer cancer susceptibility. Although many studies have demonstrated the association between GSTT1 null polymorphism and urinary system cancer susceptibility, several publications reported opposite conclusions. For better understanding the effects of this polymorphism on the risk of urinary system cancer, a updated meta-analysis was performed with a total of 26,666 cases and 37,210 controls extracted from 117 studies, by following the latest meta-analysis guidelines (PRISMA). The results suggested that the GSTT1 null genotype was significantly associated with an increased risk of urinary system cancer (OR=1.13, 95%CI=1.05-1.22). Furthermore, stratified analyses by the type of cancer, ethnicity, source of control and quality score presented a significantly increased risk associated with GSTT1 null genotype in bladder and prostate cancer subgroup, Caucasians and Indians subgroup, population-based(PB) subgroup, medium quality and low quality subgroup. Overall, our meta-analysis suggested that GSTT1 null genotype is a potential cancer susceptibility variant. Well-designed and large-cohort studies are needed to confirm the association between GSTT1 null genotype and urinary system cancer risk.

A common carcinogen benzo[a]pyrene causes p53 overexpression in mouse cervix via DNA damage

Benzo[a]pyrene (BaP) is cytotoxic and/or genotoxic to lung, stomach and skin tissue in the body. However, the effect of BaP on cervical tissue remains unclear. The present study detected DNA damage and the expression of the p53 gene in BaP-induced cervical tissue in female mice. Animals were intraperitoneally injected and orally gavaged with BaP at the doses of 2.5, 5, and 10mg/kg twice a week for 14 weeks. The single-cell gel electrophoresis (SCGE) assay was used to detect the DNA damage. Immunohistochemistry (IHC) and in situ hybridization (ISH) were used to detect the expression of p53 protein and p53 mRNA, respectively. The results showed that BaP induced a significant and dose-dependent increase of the number of cells with DNA damaged and the tail length as well as Comet tail moment in cervical tissue. The expression level of p53 protein and mRNA was increased. The results demonstrate that BaP may show toxic effect on the cervix by increasing DNA damage and the expression of the p53 gene.

Glutathione S-transferase M1 polymorphism and bladder cancer risk: a meta-analysis involving 33 studies

Glutathione S-transferase M1 ( GSTM1) might be involved in inactivation of procarcinogens that contribute to the genesis and progression of cancers. GSTM1 null status has been extensively studied as a risk factor in bladder cancer susceptibility. The aim of this study is to evaluate the role of GSTM1 null genotype in bladder cancer risk. All available studies were considered in this meta-analysis, including 7301 cases and 9405 controls from 33 studies. Significantly increased risk was detected between GSTM1 deletion and bladder cancer susceptibility in all subjects (odds ratio [OR] = 1.409 [1.267–1.568], P < 0.001). The same patterns were observed in Caucasians (OR = 1.434 [1.212–1.697], P < 0.001) and Asians (OR = 1.485 [1.295–1.704], P < 0.001). When stratified with study design, a positive association was also found in hospital-based studies (OR = 1.552 [1.382–1.744], P < 0.001), but no association in population-based ones (OR = 1.088 [0.970–1.221], P = 0.151). In summary, our meta-analysis suggested that GSTM1 null status is associated with a high increase in the risk of bladder cancer, and further studies based on population design are necessary to confirm our conclusion.

Functional glutathione S-transferase genotypes among testicular germ cell tumor survivors: associations with primary and post-chemotherapy tumor histology

PURPOSE

The pathogenesis of testicular germ cell tumor (TGCT) remains unknown. The aim of this study was to evaluate the pathogenic role of functional polymorphisms in detoxification enzymes among TGCT patients, through association studies of constitutive genotypes and medical parameters before and after chemotherapy.

EXPERIMENTAL DESIGN

Germline deletion polymorphisms in the glutathione S-transferase mu 1 (GSTM1) and the GST theta 1 (GSTT1), and a functional single nucleotide polymorphism in GST pi 1 (GSTP1, Ile105Val), were analyzed in TGCT survivors (TCSs) (n = 675) and controls (n = 189). Statistical analyses were performed for the genotype distributions between the TCSs and control populations, and between the genotypes and clinicopathological parameters of the TCSs.

RESULTS

The GST genotypes showed comparable distributions among the TCSs and the control population. However, the genotype combination GSTT1positive/GSTP1-GG or GSTP1-AG/GSTM1positive was more frequent among the TCSs [P = 0.050, odds ratio (OR): 1.47, 95% confidence interval (CI): 0.998-2.165]. The combined genotype GSTT1positive/GSTP1AA/GSTM1positive was associated with decreased risk of development of pure embryonal carcinoma (P = 0.009, OR: 0.309, 95% CI: 0.122-0.784) and the GSTP1-A-allele (i.e. genotypes GSTP-AA or GSTP-AG) was also associated with decreased risk for development of pure teratoma (P = 0.032, OR: 0.326, 95% CI: 0.122-0.873). Furthermore, the GSTP1-A-allele was overrepresented within the 'good prognosis group' (P = 0.032, OR: 2.407, 95% CI: 1.060-5.469), whereas the GSTM1nulltype was associated with the extent of TC qualifying as 'poor prognosis group' (P = 0.025, OR: 2.839, 95% CI: 1.104-7.301). The GSTP1-AG genotype was associated with necrosis in the tumor's post-chemotherapy histology (P = 0.001, OR: 16.087, 95% CI: 1.930-134.087). Failure, after platinum-based chemotherapy, was associated with the GSTT1positive/GSTP-AA or GSTP-GG/GSTM1-positive genotype (P = 0.019, OR: 2.168, 95% CI: 1.130-4.160).

CONCLUSION

This study confirms an association between the GSTP1-G-allele and TGCT. Combinations of GST genotypes were associated with primary and post-chemotherapy tumor histology, and prognostic group presentation.

Genetic epidemiology of bladder cancer: scaling up in the identification of low-penetrance genetic markers of bladder cancer risk and progression

Bladder cancer is an increasingly important international public health problem. As a multifactorial disease, both environmental and genetic factors are involved in its development and progression. This neoplasm is a paradigm for the participation of low-penetrance genetic variants (GSTM1-null and NAT2-slow) and provides the best established gene-environment interaction in cancer (NAT2-slow * tobacco). Genetic variants in nucleotide excision and double strand break DNA repair pathways have provided promising results, ERCC2-XPD rs238406 being the most consistent variant associated with an increased of bladder cancer risk, by itself and by interacting with tobacco. Variants in other pathways such as cell-cycle control, 1-C metabolism and inflammation have been studied, although the results are inconsistent. Three very large whole genome association studies are being undertaken using the same genotyping platform. Their results will be available soon. Genetic variants have seldom been considered as markers of prognosis or response to therapy in this tumour. The results of these studies are inconclusive. Other issues that need to be addressed are the role of genetic variants in different population subgroups--defined by ethnicity, gender and age, among others--and the association with bladder cancer subphenotypes according to clinical, pathological and molecular characteristics of the tumour. This endeavour can only be achieved by integrating multidisciplinary tools and information. Can this information be applied better to identify high-risk populations? Can the information be used to better assess prognosis or predict response to therapy? These questions require large, well-designed, multicentre studies to be conducted. Funding agencies should be aware of these needs.

The effect of smoking on the male excess of bladder cancer: a meta-analysis and geographical analyses

Smoking is considered the primary risk factor for bladder cancer. Although smoking prevalence and bladder cancer incidence vary around the world, bladder cancer is on average 4 times more common in males than in females. This article describes the observed male-female incidence ratio of bladder cancer for 21 world regions in 2002 and 11 geographical areas during the time period 1970-1997. A meta-analysis, including 34 studies, was performed to ascertain the increased risk for bladder cancer in males and females when smoking. The summary odds ratios (SORs) calculated in the meta-analysis were used to estimate the male-female incidence ratio of bladder cancer that would be expected for hypothetical smoking prevalence scenarios. These expected male-female incidence ratios were compared with the observed ratios to evaluate the role of smoking on the male excess of bladder cancer. The male-female incidence ratio of bladder cancer was higher than expected worldwide and over time, based on a smoking prevalence of 75% in males, 10% in females and an increased risk (SOR) of bladder cancer associated with smoking of 4.23 for males and 1.35 for females, respectively. This implied that, at least in the Western world, smoking can only partially explain the difference in bladder cancer incidence. Consequently, other factors are responsible for the difference in bladder cancer incidence.

GENOTYPE AND ALLELE FREQUENCIES OF N-ACETYLTRANSFERASE 2 AND GLUTATHIONE S-TRANSFERASE IN THE IRANIAN POPULATION

1. Xenobiotic-metabolizing enzymes constitute an important line of defence against a variety of carcinogens. Many are polymorphic, constituting the basis for the wide interindividual variation in metabolic capacity and possibly a source of variation in the susceptibility to chemical-induced carcinogenesis. The aim of the present study was to determine the frequencies of important allelic variants in the N-acetyltransferase 2 (NAT2) and glutathione S-transferase (GST) genes in the Iranian population and compare them with frequencies in other ethnic populations. 2. Genotyping was performed in a total of 229 unrelated healthy subjects (119 men, 110 women) for NAT2 and 170 unrelated healthy subjects (89 men, 81 women) for GST from the general Tehran population. A combination of polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) was applied for typing of NAT2 polymorphisms. Detection of GSTM1 and GSTT1 null alleles was performed simultaneously using a multiplex PCR assay. 3. The frequencies of specific NAT2 alleles were 0.299, 0.314, 0.380, 0.007 and 0.000 for 4 (wild-type), 5 (C481T, M1), 6 (G590A, M2), 7 (G857A, M3) and 14 (G191A, M4), respectively. The most prevalent genotypes were NAT2 5/6 (29.70%) and 4/6 (21.40%). The GSTM1- and GSTT1-null alleles were detected in 44.7 and 21.2% of subjects, respectively. 4. We found that Iranians resemble Indians with regard to allelic frequencies of the tested variants of NAT2. The predominance of slow (49.36%) and intermediate (41.47%) acetylation status compared with wild-type rapid acetylation status (9.17%) in the study group suggests the significant prevalence of the slow acetylator (SA) phenotypes in the Iranian population. Our data confirmed that Iranians are similar to other Caucasian populations in the frequency of both GSTM1- and GSTT1-null alleles.

Epidemiology of urinary bladder cancer: from tumor development to patient’s death

Urinary bladder cancer (UBC) ranks ninth in worldwide cancer incidence. It is more frequent in men than in women. We review the main established/proposed factors, both environmental and genetic, associated with bladder cancer etiology and prognosis. Data were extracted from previous reviews and original articles identified from PubMed searches, reference lists, and book chapters dealing with the reviewed topics. Evaluation and consensus of both the contribution of each factor in bladder cancer burden and the appropriateness of the available evidences was done during an ad hoc meeting held during the 18th Congress of the European Society for Urological Research. Cigarette smoking and specific occupational exposures are the main known causes of UBC. Phenacetin, chlornaphazine and cyclophosphamide also increase the risk of bladder cancer. Chronic infection by Schistosoma haematobium is a cause of squamous cell carcinoma of the bladder. NAT2 slow acetylator and GSTM1 null genotypes are associated with an increased risk of this cancer. Vegetables and fresh fruits protect against this tumor. Regarding prognosis, there is little knowledge on the predictive role of environmental exposures and genetic polymorphisms on tumor recurrence and progression and patient's death. Although active tobacco smoking is the most commonly studied factor, no definitive conclusion can be drawn from the literature. More research is needed regarding the effect of complex etiological factors in bladder carcinogenesis. Subgroup analysis according to stage, grade, and molecular features may help in identifying specific etiological and prognostic factors involved in different bladder cancer progression pathways.

Glutathione-S-transferase M1 polymorphisms on the susceptibility to esophageal cancer among three Chinese minorities: Kazakh, Tajik and Uygur

AIM: To investigate the glutathione-S-transferase M1 (GSTM1) polymorphisms in three Chinese minorities, Kazakh, Uygur, and Tajik; and the pathological significance of GSTM1 polymorphisms in esophageal carcinogenesis in Kazakh.

METHODS: A total of 1121 blood samples (442 males and 679 females) were obtained from healthy Kazakh (654), Uygur (412) and Tajik (55). Primary esophageal squamous cell cancer (ESCC) tissues from Kazakh were obtained from 116 patients who underwent surgery. GSTM1 polymorphisms were analyzed by a combined approach of PCR and electrophoresis techniques.

RESULTS: GSTM1 null genotype was found in 62.63% Uygur, 50.91% Tajik and 47.40% Kazakh. A significantly higher frequency of GSTM1 null genotype in Uygur was observed compared with Kazakh (OR: 1.859, 95% CI: 1.445 -2.391, χ² = 23.71, P = 0.000). In addition, GSTM1 null genotype was found in 23.53% of well-differentiated ESCC in Kazakh, in 49.23% of poorly differentiated ESCC, with a significant difference (OR: 3.152, 95% CI: 1.403-7.080, χ² = 8.018, P = 0.007).

CONCLUSION: There is a marked difference in the frequency of common GSTM1 null genotype between Uygur and Kazakh. GSTM1 null genotype is associated with differentiation of ESCC in Kazakh.

NAT2 slow acetylation, GSTM1 null genotype, and risk of bladder cancer: results from the Spanish Bladder Cancer Study and meta-analyses

BACKGROUND

Many reported associations between common genetic polymorphisms and complex diseases have not been confirmed in subsequent studies. An exception could be the association between NAT2 slow acetylation, GSTM1 null genotype, and bladder-cancer risk. However, current evidence is based on meta-analyses of relatively small studies (range 23-374 cases) with some evidence of publication bias and study heterogeneity. Associations between polymorphisms in other NAT and GST genes and bladder-cancer risk have been inconsistent.

METHODS

We investigated polymorphisms in NAT2, GSTM1, NAT1, GSTT1, GSTM3, and GSTP1 in 1150 patients with transitional-cell carcinoma of the urinary bladder and 1149 controls in Spain; all the participants were white. We also carried out meta-analyses of NAT2, GSTM1, and bladder cancer that included more than twice as many cases as in previous reports.

FINDINGS

In our study, the odds ratios for bladder cancer for individuals with deletion of one or two copies of the GSTM1 gene were 1.2 (95% CI 0.8-1.7) and 1.9 (1.4-2.7) respectively (p for trend <0.0001). Compared with NAT2 rapid or intermediate acetylators, NAT2 slow acetylators had an increased overall risk of bladder cancer (1.4 [1.2-1.7]) that was stronger for cigarette smokers than for never smokers (p for interaction 0.008). No significant associations were found with the other polymorphisms. Meta-analyses showed that the overall association for NAT2 was robust (p<0.0001), and case-only meta-analyses provided support for an interaction between NAT2 and smoking (p for interaction 0.009). The overall association for GSTM1 was also robust (p<0.0001) and was not modified by smoking status (p=0.86).

INTERPRETATION

The GSTM1 null genotype increases the overall risk of bladder cancer, and the NAT2 slow-acetylator genotype increases risk particularly among cigarette smokers. These findings provide compelling evidence for the role of common polymorphisms in the aetiology of cancer.

RELEVANCE TO PRACTICE

Although the relative risks are modest, these polymorphisms could account for up to 31% of bladder cancers because of their high prevalence.

Genetic and epigenetic aspects of bladder cancer

Transitional cell carcinoma of the urinary bladder has a diverse collection of biologic and functional characteristics. This is reflected in differing clinical courses. The diagnosis of bladder cancer is based on the information provided by cystoscopy, the gold standard in combination with urinary cytology findings. Many tumor markers have been evaluated for detecting and monitoring the disease in serum, bladder washes, and urinary specimens. However, none of these biomarkers reported to date has shown sufficient sensitivity and specificity for the detection of the whole spectrum of bladder cancer diseases in routine clinical practice. The limited value of established prognostic markers requires the analysis of new molecular parameters of interest in predicting the prognosis of bladder cancer patients; in particular, the high-risk patient groups at risk of progression and recurrence. Over the past decade, there has been major progress elucidating of the molecular genetic and epigenetic changes leading to the development of transitional cell carcinoma. This review focuses on the recent advances of genetic and epigenetic aspects in bladder cancer, and emphasizes how molecular biology would be likely to affect the future therapies.

Diverse expression profiles of glutathione-S-transferase subunits in mammalian urinary bladders

The hGSTM1 null genotype has been associated with increased susceptibility to urinary bladder cancer. However, the extent to which the GSTM1 subunit actually contributes to GST activities in mammalian urinary bladders is not clear. For adult mice, urinary bladders exhibited GST activity which was among the highest observed in the tissues tested. The mouse bladder GST activity with the 1-chloro 2,4-dinitrobenzene substrate was also more than 10-fold greater than that of rat and human bladders. A large increase in mouse bladder GST activity occurs during early development with the sharpest increase between 7 and 17 days of age. Subunit compositions of GSTs in adult mouse, human, and rat bladders are also markedly different. The mGSTM1 subunit is by far the predominant GST in mouse bladder, with increases in mGSTM1 between 7 and 17 days accounting for the sharp rise in GST activity during maturation. By contrast, Pi class GSTs predominate in both human and rat bladders. Investigators seeking to establish direct connections between susceptibility to bladder cancer and the hGSTM1 gene deletion should take into account the fact that the hGSTM1 subunit, even when present, represents a very minor fraction of the GST protein in human bladder.

Polymorphisms of glutathione S-transferase M1 and T1 modulate blood pressure of individuals chronically exposed to natural sour gas containing sulfur compounds

In order to find the effect of genetic polymorphisms of GSTM1 and GSTT1 on blood pressure of individuals chronically exposed to sulfur compounds, the present study was done. Study subjects (38 males, 38 females) were residents of contaminated areas of Masjid-i-Sulaiman (southwest of Iran). The GSTM1 and GSTT1 genotypes were determined using a polymerase chain reaction (PCR)-based method. The non-parametric Sign test was applied in order to detect differences between the GSTs genotypes of study subjects and the normal mean values according to the sex and age of subjects. From four combination of genotypes, systolic blood pressure significantly decreased in combination of null-GSTM1 and present-GSTT1 (Z=-2.41; P=0.016), and diastolic blood pressure significantly increased in combination of present-GSTM1 and null-GSTT1 (Z=+2.14; P=0.032). It is speculated about polymorphisms of GSTs in individuals chronically exposed to natural sour gas, which contains H2S, fulfilling a physiological role(s) in regulating blood pressure.