|Year : 2016 | Volume
| Issue : 2 | Page : 65-69
Glutathione-S-transferase P1 as a risk factor for Egyptian patients with chronic myeloid leukemia
Nahla A. M. Hamed1, Omar Ghallab MD 1, Dalia El-Neily2
1 Department of Internal Medicine, Hematology Unit, Faculty of Medicine, Alexandria University, Alexandria, Egypt
2 Department of Clinical Pathology, Faculty of Medicine, Alexandria University, Alexandria, Egypt
|Date of Submission||25-Jun-2015|
|Date of Acceptance||30-Jul-2016|
|Date of Web Publication||15-Jul-2016|
Department of Internal Medicine, Hematology Unit, Faculty of Medicine, Alexandria University, Alexandria, 21526
Source of Support: None, Conflict of Interest: None
Background The interest in glutathione-S-transferase (GST) isoenzymes has increased because of their regulatory role in the interaction with critical kinases involved in controlling stress response, apoptosis, and proliferation. GSTP1 is of particular interest with regard to cancer, because many tumors are characterized by high GSTP1 expression.
Aim of the work We aimed at evaluating the role of GSTP1 genetic polymorphisms in chronic myeloid leukemia (CML) patients.
Patients and methods We genotyped 40 CML patients and 30 healthy individuals of matched age and sex.
Results Wild GSTP1 was found in 15/40 CML patients (37.5%) and in 21/30 (70%) controls, whereas mutant allele (homozygous and heterozygous) was present in 25/40 (62.5%) and 9/30 (30%) CML patients and controls, respectively. The odds ratio for GSTP1 was 3.889 (95% confidence interval, 1.417-10.674; P = 0.009*) with four-fold increased risk for CML. No significant difference in genotype frequency was present between wild and mutant genotypes when age of onset, sex, white blood cell count over 100×10 9 /l at presentation, or smoking status were considered.
Conclusion These data indicate that GSTP1 mutant allele may contribute significantly to the susceptibility to CML in a sample of the Egyptian patients. These results should be considered preliminary and must be confirmed in studies with larger sample sizes.
Keywords: chronic myeloid leukemia, Egyptian population, GSTP1, polymorphism
|How to cite this article:|
Hamed NA, Ghallab O, El-Neily D. Glutathione-S-transferase P1 as a risk factor for Egyptian patients with chronic myeloid leukemia. Egypt J Haematol 2016;41:65-9
|How to cite this URL:|
Hamed NA, Ghallab O, El-Neily D. Glutathione-S-transferase P1 as a risk factor for Egyptian patients with chronic myeloid leukemia. Egypt J Haematol [serial online] 2016 [cited 2019 Dec 11];41:65-9. Available from: http://www.ehj.eg.net/text.asp?2016/41/2/65/186408
| Introduction|| |
Chronic myeloid leukemia (CML) is a hematological stem cell malignancy characterized by the presence of the Philadelphia chromosome and the t(9;22)(q34;q11) translocation. The disease is characterized by high levels of leukocytes, splenomegaly, myeloid hyperplasia in bone marrow, and high levels of mature myeloid cells in peripheral blood .
Results of most epidemiological studies do not indicate a role of genetic factors or environmental exposures in the development of CML, with the notable exception of ionizing radiation, the procarcinogen benzene, and perhaps pesticide exposure. A recent report of an association between obesity and risk for CML, however, suggests that lifestyle factors may also play a role .
Polymorphisms of functional significance have been reported in genes that encode phase II drug metabolizing enzymes, including glutathione-S-transferases (GSTs). GSTs detoxify potentially mutagenic and cytotoxic DNA-reactive metabolites by conjugation to glutathione .
The interest in GST isoenzymes has further increased because of their regulatory role in the interaction with critical kinases involved in controlling stress response, apoptosis, and proliferation . Glutathione-S-transferase P1 (GSTP1) is of particular interest with regard to cancer, because many tumors and cancer cell lines are characterized by high GSTP expression. Further, increased expression of GSTP has also been linked to acquired resistance to cancer drugs .
GSTP (π) belongs to the pi class gene family, located on chromosome 11q13. It spans 2.48 kb of DNA and comprises seven exons that encode for cytosolic GST enzyme. GSTP1 is overexpressed in a variety of preneoplastic and neoplastic tissues .
Elevated levels of GSTP had been found in tumors of the stomach, colon, bladder, oral, breast, skin, and lung. In some cancer models, GSTP1 expression was considered as preneoplastic tumor marker. Increased levels of GSTP1 in tumors might account for part of the inherent drug resistance, which was observed in many tumors suggesting its role in cancer etiology and therapy .
| Aim of the work|| |
The aim of this work was to examine the frequency of genetic polymorphisms in the GSTP1 gene loci and its relationship with the development of CML.
| Patients and methods|| |
The study was conducted on 40 randomly selected Egyptian adult patients with newly diagnosed CML in chronic phase before receiving initial therapy [18 female (45%) and 22 male (55%)], with a mean age of 38.43 ± 12.03 years. All patients were presented to the Hematology Department of Alexandria Main University Hospital during the period from November 2013 to February 2014. Written consent was taken from all patients included in the study. Thirty normal individuals of matched age and sex with no cancer history were included in this study as the control group. Diagnosis was based on clinicohematological criteria, as well as the presence of BCR-ABL gene using RT-PCR. All patients were subjected to full history taking, complete clinical examination and routine investigations, including complete blood picture and liver and kidney function tests. Polymorphism in genes encoding GSTP1 was determined for patients and controls.
Smokers were defined as individuals who reported at the time of collection of blood samples as smoking at least one pack of cigarettes daily for 1 year at any time during their life; nonsmokers were defined as individuals who reported never to have smoked.
DNA isolation and genotyping of GSTP1 (Ile105Val) 
All PCR reagents were obtained from Fermentas, Burlington, Ontario, Canada, including the primers. Genomic DNA was extracted from EDTA whole-blood samples by means of column method using a DNA extraction kit (Gene JET Genomic DNA Purification, Thermo Scientific, MA, USA). GSTP1 (Ile105Val) gene polymorphism was detected with fragment length polymorphism of PCR amplified DNA sequences (PCR-RFLP) using the following primers: forward 5'-ACCCCAGGGCTCTATGGGAA-3'and reverse 5'-TGAGGGCACAAGAAGCCCCT-3'. PCR thermal profile included initial denaturation step at 94°C for 5 min, followed by 35 cycles of PCR. Each cycle was carried out at 94°C for 30 s, 55°C for 30 s, and 72°C for 30 s. Thereafter, the final extension step was carried out at 72°C for 10 min. Fast Digest Alw26 I restriction enzyme was used for digestion of the resulting amplicon. Digested PCR fragments were separated by means of electrophoresis on 4% agarose gel. The expected pattern after digestion using restriction endonuclease Alw26 I was one of the following: one uncut fragment of 176 bp for wild type Ile/Ile, two fragments of 91 and 85 bp for the Val/Val represented the homozygous mutated alleles, whereas the Ile/Val was represented by three distinct fragments of 176, 91, and 85 bp.
SPSS for Windows 15.0 was used for statistical analysis. Numerical data were recorded as mean ± SD, whereas qualitative data were expressed as frequency and percentage. The t-test was used to compare two means. The χ2 -test and Fischer's exact test were used to compare genotypes. Risk was estimated as odds ratio with 95% confidence interval. P values less than 0.05 were accepted as statistically significant.
| Results|| |
The characteristics of the study population are shown in [Table 1]. The age distribution was not different between patients and controls, with the mean age being 38.43 ± 12.03 and 36.6 ± 9.80 years for patients and controls, respectively (P = 0.205). However, within the CML group, leukocyte counts were significantly different from those of the control group (P = 0.000).
|Table 1 Clinical data of chronic myeloid leukemia patients and controls |
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The distribution of the GSTP1 genotype (wild and mutant) is shown in [Table 1] and [Figure 1]. The distribution of the GSTP1 homozygous wild-type allele (Ile/Ile) was higher among controls (70%) than among CML patients (37.5%). The frequency of the GSTP1 mutant heterozygous (Ile/Val) was higher in CML patients (52.5%) than in the controls (26.6%), whereas the frequency of homozygous mutant allele (Val/Val) was 10% in CML patients and only apparent in 3.33% (one person) of controls. The odds ratio for GSTP1 was 3.889 (95% confidence interval, 1.417-10.674; P = 0.009*) (data not shown). All mutants (Ile/Val and Val/Val) were present in 62.5% of CML patients and in 39.9% of controls.
|Figure 1 GSTP1 gene polymorphism in chronic myeloid leukemia (CML) patients and controls|
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[Table 2] shows the distribution of the genotype of GSTP1 in CML patients as regards sex, smoking status (passive and active), and white blood cell over 100 × 10 9 /l.
|Table 2 Odd ratios and 95% confidence intervals for sex, smoking status, and white blood cells in chronic myeloid leukemia patients in relation to GSTP1 genotype |
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| Discussion|| |
Human GSTs can be divided into membrane bound microsomal and cytosolic. Microsomal GST contains three isoforms (mGST 1, 2, and 3) and are involved in the endogenous metabolism of leukotrienes and prostaglandins. Cytosolic GST is divided into six classes in humans: alpha, mu, omega, pi, theta, and zeta. All have genetic polymorphisms in human populations .
GST isoenzymes, in particular the GSTP class, have been shown to be overexpressed in tumors. In contrast, reduced enzymatic activity may not only determine inefficient detoxification and increased activity of drugs but also prolonged damage to stem cells, leading to secondary tumorgenesis .
Several studies have investigated the relationship between GST polymorphisms and acute leukemia ,. However, there is very little information on the role of GST polymorphisms in CML development. Taspinar et al.  studied GSTM1 and GSTT1 polymorphisms, whereas in two other studies GSTP1 (Ile105Val) gene polymorphism was studied in CML patients ,.
In our study, the frequency of GSTP1 wild genotype was higher in controls (70%) than in CML patients (37.5%). The frequency of GSTP1 mutant heterozygous (Ile/Val) was higher in CML patients (52.5%) than in controls (26.6%), whereas the frequency of homozygous mutant allele (Val/Val) was 10% in CML patients and only apparent in 3.33% (one person) of controls. The odds ratio for GSTP1 was 3.889 (95% confidence interval, 1.417-10.674; P = 0.009*) with nearly four-fold increased risk for CML. All mutants (Ile/Val and Val/Val) were present in 62.5% of CML patients and in 39.9% of controls.
The frequency of GSTP1 (Ile105Val) allele was observed to be 22% in the CML patient group in Turkish population and 31% in the control group. Although its frequency was higher in the control group, no significant difference was observed between the two groups . Similar values were obtained by Sailaja et al. , with frequencies of 26% in the patient group and 24% in the control group.
In these two different studies, the frequency of GSTP1 mutant genotype did not reach statistical significance in CML patients.
The differences in the frequencies of polymorphism between our results and these studies in different population might be attributed to the different ethnic backgrounds, environment, and even lifestyle .
No significant difference was observed in the present study as regards the distribution of GST genotypes on the basis of age, sex, cigarette smoking status, and leukocytosis above 100 × 10 9 /l. In a recent Egyptian study conducted in 2014 by Elhoseiny et al. , the heterozygous mutant type was 50% in children compared with 45% in adults. It was reported that heterozygote mutant type Ile/Val was elevated in a group of patients below 20 years of age when compared with patients in higher age groups .
Authors suggested that the presence of valine allele confers increased risk to develop CML at an early age. Valine genotype has decreased enzyme activity, which might be due to altered catalytic activity and thermal stability of the enzyme. This could lead to less detoxifying efficiency for the ultimate carcinogens such as polycyclic aromatic hydrocarbons, which can induce DNA adducts and ultimately lead to carcinogenesis .
Systematic investigations have suggested that GSTP has a diversity of functions in cancer cells, some of which are unrelated to its capacity to detoxify chemicals or drugs. GSTP interacts with the mitogen-activated protein kinase JNK complex, which is subject to further regulation by changes in redox conditions. Oxidative stress can destabilize the GSTP-JNK complex and cause an activation of the kinase cascade. Thus, GSTP serves as a sensor of intracellular changes in redox potential and has the capacity to regulate kinase pathways. JNK phosphorylation and subsequent transactivation of c-Jun transcription factors has been linked to cell proliferation. GSTP also has a role in modulating ERK and p38 activation, and the possible involvement of GSTP in pathways relevant to myeloproliferation; the regulation of p38 is important in the maintenance of human stem cell self-renewal and hematopoiesis .
Information gained from studies conducted on this issue may guide us in the diagnosis and treatment of this disease, as well as protection against developing it. These data indicate that the GSTP1 mutant allele may contribute significantly to the susceptibility to CML in a sample of the Egyptian population and this effect was irrelevant to age, sex, smoking status, or white blood cell count. However, these results should be considered preliminary and must be confirmed in studies with larger sample sizes.
Written consent was taken from all patients. The study was approved by the local Ethics Committee.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2]