|Year : 2016 | Volume
| Issue : 2 | Page : 731-734
Association of GSTM1 and GSTT1 deletion with lung cancer development in Pakistani population
Nosheen Masood, Baseerat Taseer, Azra Yasmin
Department of Environmental Sciences, Fatima Jinnah Women University, Rawalpindi, Pakistan
|Date of Web Publication||25-Jul-2016|
Department of Environmental Sciences, Fatima Jinnah Women University, Rawalpindi
Source of Support: None, Conflict of Interest: None
Aim: Lung cancer has increased rapidly in the past few decades. Environmental and genetic factors are contributing toward its incidence. Several studies have been reported with conflicting results regarding polymorphism of GSTM1 and GSTT1 genes and their contribution in development of lung cancer. It has been observed that these genetic polymorphisms show geographical variations. Therefore, we conducted a case control study to find the association of various environmental factors as well as GSTM1 and GSTT1 deletion with susceptibility of lung cancer.
Patients and Methods: DNA of pathologically confirmed lung cancer patients and cancer-free controls were amplified using multiplex PCR to check the deletion of GSTM1 and GSTT1 genes.
Results: Demographic factors like age, gender, smoking, passive smoking, smoking duration, smoking dose and other addictions were found to be significantly related (P = 0.05) with incidence of lung cancer. Deletion of GSTM1 and GSTT1 showed non--significant results (P = 0.05) when comparing with development of lung cancer.
Conclusion: Results revealed that certain environmental factors may be considered as a risk factor but deletion of GSTM1 and GSTT1 are not associated with the development of lung cancer; however, studies including >500 patient samples is suggested.
Keywords: Deletions, GSTM1, GSTT1, lung cancer
|How to cite this article:|
Masood N, Taseer B, Yasmin A. Association of GSTM1 and GSTT1 deletion with lung cancer development in Pakistani population. J Can Res Ther 2016;12:731-4
| > Introduction|| |
Worldwide, lung cancer is the most common cancer and the primary cause of death in males and secondary in females. Worldwide, 1.6 million cases are registered for lung cancer and death figure has reached 1.4 million each year. Cigarette smoking is the main risk factor of lung cancer. In Western countries like United States, United Kingdom and Canada, trend of cigarette smoking has already been established many years ago but incidence of lung cancer has been declining. Whereas in countries like China and Korea, smoking trend has recently been established and lung cancer incidence has been increasing gradually. Histologically, lung cancer is a varied disease. Environmental as well as genetic factors are involved in its etiogenesis. Approximately 85% of lung cancer is caused by cigarette smoking. Risk of cancer is 10-fold higher in smokers as compared to non-smokers. Genetically enzymes metabolize the carcinogens present in cigarette smoke. Metabolization of carcinogens is affected by inherited or somatic polymorphism of these enzymes. In our body, a well-developed enzymatic and non-enzymatic antioxidant system is present, which protect our lungs against harmful carcinogens. Phase I enzymes activate and phase II enzymes detoxify the carcinogens. GST gene family is included in phase II enzymes and provides protection against carcinogens. These enzymes catalyze the reduced glutathione and electrophilic intermediates, which are metabolites of carcinogens and convert them into non-toxic water soluble compounds and excrete them from body. Two members of GST family, Glutathione S transferases Mu 1 (GSTM1) and Glutathione S transferases Theta 1 (GSTT1) are mainly linked to susceptibility of lung cancer. Any polymorphism or deletion of GSTM1 and GSTT1 increases the risk of lung cancer development.GSTM1 deletion was 45% in Southern Punjab of Pakistan and it was suggested that Pakistani population, including southern Punjab population is variant in activation and deactivation of carcinogens as compared to other populations of world. Current case control study was conducted to reveal the association of GSTM1 and GSTT1 deletion with risk of lung cancer development in Pakistani population along with different environmental factors.
| > Patients and Methods|| |
This study included 252 lung cancer cases and 270 age- and gender-matched controls. All individuals were interviewed by questionnaires to obtain information about lung cancer-related factors (like smoking, cancer family history, other addictions, lifestyle, habits etc.) Control group were individuals who were free from all types of cancer, and informed consents were signed from all individuals. Study was approved from the ethical committees of university and hospitals. Genomic DNA was extracted by phenol chloroform extraction and all samples were amplified by multiplex polymerase chain reaction (PCR). For GSTM1 amplification 5'-TCTGGGGAGGTTTGTTTTCA-3' and 5'-TGGACACAGAACATCATGGAA-3' and for GSTT1 5'-GGCGAGAGAGCAAGACTCAG-3' and 5'-GGCAGCATAAGCAGGACTTC-3' forward and reverse primers were used, respectively. CYP1A1 7th exon was used as housekeeping gene. The PCR products were separated by 2% agarose gel electrophoresis. Gels were visualized by gel documentation system (WEALTEC, Dolphin-ID, GMG96G, USA, Catalog # 1141004, gel analysis software, version 2.7) and evaluated by two independent researchers blindfolded to each other's assessments. Odds ratio (OR), 95% confidence interval (CI), Chi-square test and logistic regression were used to statistically evaluate the results.
| > Results|| |
Environmental factors associated with lung cancer
Mean age of the cases was 54 (±11.5) years and for controls it was 53 (±12.6) years. Incidence of lung cancer was found more in males (73%) as compared to females (27%). Epidemiological factors like smoking, passive smoking, residential area, chemotherapy and radiotherapy, smoking dose, smoking duration, other addictions, occupation, lung cancer stage and education were found to be significantly (P ≤ 0.05) associated with lung cancer [Table 1]. Other demographic factors like cancer family history, hooka smoking, chemical exposure, surgical history and metastasis were not significantly associated to the risk of lung cancer. Statistically non-significant association was obtained by correlating gender vs. metastasis (P = 0.1) and smoking vs. lung cancer stages (stage I, P = 0.4), (stage II, P = 0.7), (stage III, P = 0.5), (stage IV, P = 0.7) [Table 1].
Environmental factors associated with GSTM1 and GSTT1 deletions
Non-significant association was found in GSTM1 deletion among males (P = 0.9) and females (P = 0.9) [Table 2]. Result of GSTT1 deletion was found to be statistically non-significant in males (P = 0.6) and females (OR = P = 0.2). No significant difference was demonstrated (P = 0.6), (P = 0.2) by comparing both GSTM1 and GSTT1 deletion in males and females, respectively. In the current study, 52% cases and 29% controls were smokers and the risk of lung cancer was higher in smokers as compared to non-smokers. Statistically highly significant association (OR = 2.5, 95% CI = 1.1–5.3, P = 0.01) was found by comparing smoking status in patients and controls. Non-significant associations were demonstrated by comparing GSTM1 deletion (P = 0.8), GSTT1 deletion (P = 0.4) and both GSTM1 and GSTT1 deletion (P = 0.4) in smoker patients and smoker controls [Table 2].
|Table 2: GSTM1 deletion, GSTT1 deletion and both GSTM1 and GSTT1 deletion in cases and controls and the demographic factors associated with these deletions|
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Association of GSTM1 and GSTT1 deletions with lung cancer
GSTM1 deletion was found to be 21.1% in cases and 21.4% in controls [Figure 1]. Statistically non-significant differences (OR = 0.9, 95% CI = 0.4-2.3, P = 0.9) were obtained by comparing GSTM1 deletion in cases and controls. GSTT1 null deletion was observed in 8% of cases and 9% of controls. No significant association was obtained (OR = 0.8, 95% CI = 0.2-3.3, P = 0.8) by comparing GSTT1 deletion in cases and controls. Frequency of null deletion of both GSTM1 and GSTT1 genes was 8% in patients and 9% in controls. Deletion of both GSTM1 and GSTT1 genes was statistically non-significant (OR = 0.8, 95% CI = 0.2-3.3, P = 0.8) in patients and controls [Figure 1].
|Figure 1: 2% agarose gel showing deletion of GSTM1 and GSTT1 genes and the expression of CYP1A1 as housekeeping gene is shown in last picture|
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| > Discussion|| |
Various studies revealed that genetic changes may affect carcinogen detoxification that leads to lung cancer. This study was performed to find the association of GSTM1 and GSTT1 deletion in relation to lung cancer among Pakistani population. Lung cancer incidence was found more in individuals with age >40 years; this might be due to late diagnosis of lung cancer and ratio of smoking being the highest in patients of age group >40 years. Almost similar findings were reported in populations of Belarus, Austria and Brazil.,, Males were more affected from lung cancer than females in this study. Findings of other countries like Brazil, Austria, America, and China and North India also demonstrated that incidence of lung cancer was more in males than females.,,,,,, Higher ratio of lung cancer was found in patients and controls of open area as compared to patients and controls of congested areas. Similar results were found in China and North India., Few patients in the study had family history of different cancers and no patient had lung cancer in his/her family history. Therefore it was revealed that lung cancer is not hereditary. A study by López et al., found that most of the patients had no cancer in their family history. Statistically higher association was found (P ≤ 0.05) when comparing lung cancer incidence between smokers patients and controls. Findings of other countries like Turkey, North India, China, Belarus, Austria and Brazil also demonstrated the same results.,,,,,, Passive smoking was significantly associated (P ≤ 0.05) with lung cancer incidence. Similar results were demonstrated in a study by Chakova et al. Patients who smoked 10-20 cigarettes per day had the highest incidence (37%) of lung cancer and almost similar results were observed in Turkish and American studies.,, Maximum patients in this data were of stage III and stage IV lung cancer; a study by Cabral et al., found almost similar results. Incidence of lung cancer was maximum (60%) in employed persons. This might be due to the exposure of different carcinogenic chemicals and radiations during working hours. Contrasting result of a study by Lopez et al., demonstrated that lung cancer was found more in jobless patients; this might be due to increased cigarette addictions, indirect smoking exposure and mental stress as compared to employed individuals.
GSTM1 and GSTT1 deletion in current study was lower in patients (21.2%, 8%, respectively) compared with controls (21.4%, 9%, respectively) but the results were statistically non-significant (P ≥ 0.05). Similar findings were observed in Brazil and Turkey, where no significant association was detected between the GSTM1 null genotype and susceptibility to lung cancer.,, A study conducted by Altinisik et al., showed similar results. A study by Lopez et al., revealed that statistically non-significant difference was observed in GSTM1 and GSTT1 deletion and lung cancer. In the current study, ratio of GSTM1 or GSTT1 deletion was slightly higher in smokers than non-smokers but statistically no significant association (P ≥ 0.05) was found. This might be due to the small sample size. Similar findings by a study revealed that statistically non-significant association was found between GSTM1 and GSTT1 deletion with lung cancer in smokers. Contrasting results in some studies showed that smokers had increased GSTM1 null deletion. This might be due to the reason that impact of smoking on GSTM1 and GSTT1 deletion on lung cancer vary in different populations geographically.
When comparing simultaneous GSTM1 and GSTT1 deletion between patients and controls statistically, non-significant association (P ≥ 0.05) was found. In other studies minor ratio of GSTM1 and GSTT1 null deletion has been reported., No association was found in smoking status and other demographic factors with GSTM1 and GSTT1 deletion because deletion is not specifically found in lung cancer patients but also found in general population as well.
| > Conclusion|| |
From this study, it may be concluded that since the trend of cigarette smoking and other addictions is increasing in Pakistan especially in younger people; therefore, smoking (as demographic factor) may be a risk factor for lung cancer development. Deletions of GSTM1 and GSTT1 are not associated with increased risk of lung cancer in Pakistani population.
| > Acknowledgment|| |
All authors would like to thanks the individuals and hospitals who participated in this research. Acknowledgment also goes to the Fatima Jinnah Women University and Higher Education Commission of Pakistan for supporting this research.
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[Table 1], [Table 2]