Relationship between GSTM1/GSTT1 Null Genotypes and Renal Cell Carcinoma Risk: A Meta-Analysis

Abstract

The results from the published studies on the relationship between GSTM1/GSTT1 null genotypes and renal cell carcinoma (RCC) risk are still conflicting. This meta-analysis was performed to evaluate the relationship between GSTM1/GSTT1 null genotypes and RCC susceptibility. Association studies were identified from the databases of PubMed, Embase, Cochrane Library, and CBM-disc (China Biological Medicine Database) on 1 February 2012, and eligible investigations from 1950 to 2012 were synthesized using meta-analysis method. Results were expressed as odds ratios (ORs) for dichotomous data, and 95% confidence intervals (CIs) were also calculated. Six studies were identified for the analysis of association between polymorphic deletion of GSTM1/GSTT1 and RCC risk. There was no association between GSTM1/GSTT1 null genotype and RCC susceptibility (GSTM1: N = 6, p-heterogeneity = 0.07, OR = 1.07, 95% CI: 0.85–1.35, p = 0.57; GSTT1: N = 6, p-heterogeneity < 0.00001, OR = 0.98, 95% CI: 0.58–1.65, p = 0.94). Interestingly, null genotype of GSTT1 was associated with RCC risk in Caucasians and Asians (Caucasians: N = 4, p-heterogeneity = 0.38, OR = 0.76, 95% CI: 0.61–0.95, p = 0.01; Asians: N = 1, OR = 2.39, 95% CI: 1.63–3.51, p < 0.00001). For the GSTM1–GSTT1 interaction analysis, the dual null genotype of GSTM1/GSTT1 was not significantly associated with RCC susceptibility (N = 4, p-heterogeneity = 0.006, OR = 1.17, 95% CI: 0.98–1.39, p = 0.09). However, the dual null genotype of GSTM1–GSTT1 was associated with RCC risk in Asians (N = 1, OR = 2.06, 95% CI: 1.36–3.13, p = 0.007). In conclusion, our study results suggest that GSTT1 null genotype is associated with the RCC susceptibility in Caucasians and Asians, and the dual null genotype of GSTM1–GSTT1 is associated with RCC risk in Asians. However, more genetic epidemiological investigations are required to further explore this relationship.

• renal cell carcinoma
• gene polymorphism
• GSTM1
• GSTT1
• meta-analysis

INTRODUCTION

Renal cell carcinoma (RCC) is one of the most lethal urologic cancers and is highly resistant to both radiotherapy and chemotherapy.¹ Its survival rates are very low since most of patients develop metastases beyond the kidney at the time of diagnosis.² Early diagnosis for RCC is very difficult, and the etiology of RCC is unclear. Current evidence indicates that the gene polymorphism is associated with the RCC susceptibility.^3–5

Glutathione S-transferases (GSTs) are phase II enzymes that facilitate the detoxification of xenobiotics and also play important roles in antioxidant defense.^6,7 Genetic polymorphisms in GST genes might influence the detoxification activities of the enzymes predisposing individuals to cancer risk.⁸ GSTM1 and GSTT1 gene deletions are the most commonly studied GST variants.⁹ There were some investigations reporting that GSTM1 and GSTT1 gene deletions were associated with cancer risk.^10–12

Gene polymorphism has been reported to be an important factor that increases the risk of RCC. Phase II enzymes such as GSTM1 and GSTT1 play important roles in protecting cells against damage induced by carcinogens.¹³ In the past decades, most of the epidemiological studies investigating the association of null genotype of GSTM1/GSTT1 with RCC susceptibility were conducted. However, the available evidences are weak at present, due to the sparseness of data or disagreements among the reported studies. The evidence from meta-analysis might be powerful compared with the individual investigation. This meta-analysis was performed to investigate whether null genotype of GSTM1/GSTT1 was associated with the onset of RCC, by widely collecting the reported investigations.

MATERIALS AND METHODS

Search Strategy for the Association of Null Genotype of GSTM1/GSTT1 with RCC Susceptibility

The relevant studies were searched from the electronic databases of PubMed, Embase, Cochrane Library, and CBM-disc (China Biological Medicine Database) on 1 February 2012, and eligible original articles published from 1950 to 2012 were selected for our study. The retrieval strategy of ‘glutathione S-transferases or GSTs or GSTM1 or GSTT1’ and ‘renal cell carcinoma or renal cancer or RCC’ was entered into the above-mentioned databases for search. The searches in PubMed and Embase were limited to human. Additional articles were identified through references cited in retrieved articles.

Inclusion and Exclusion Criteria

Inclusion Criteria

The inclusion criteria are as follows:

1.	The outcome had to be RCC.
2.	There had to be at least two comparison groups (RCC group vs. control group).
3.	Investigation should provide the data of GSTM1/GSTT1 genotype distribution.

Exclusion Criteria

The exclusion criteria are as follows:

1.	Review articles and editorials
2.	Case reports
3.	Preliminary result not on GSTM1/GSTT1 or outcome
4.	Investigating the role of GST gene expression in disease
5.	If multiple publications from the same study group occurred, we selected only the most complete paper for our final analysis.

Data Extraction and Synthesis

Two investigators independently extracted the following information from each eligible study: first author’s surname, year of publication, and the number of cases and controls for GSTM1/GSTT1 genotypes. Frequencies of null genotype of GSTM1 and GSTT1 were calculated for the case and the control groups, from the corresponding genotype distribution. The results were compared and the disagreement was resolved by discussion.

Statistical Analysis

Cochrane Review Manager Version 5 (Cochrane Library, Oxford, UK) was used to calculate the available data from each investigation. The pooled statistic was counted using the fixed effects model, but a random effects model was conducted when the p-value of heterogeneity test was 0.1.^14,15 Results were expressed as odds ratios (ORs) for dichotomous data, and 95% confidence intervals (CIs) were also calculated.^16,17 A p-value <0.05 was required for the pooled OR to be statistically significant.^18,19 I² was used to test the heterogeneity among the included studies.^20–23 The Begg adjusted rank correlation test²⁴ and the Egger regression asymmetry test²⁵ were used for exploring publication bias (p < 0.1 was considered significant), when the number of the included studies was more than six.

RESULTS

Study Characteristics

The studies reporting the relationship between GST gene polymorphism and RCC risk were identified from the databases, and six articles^26–31 were selected for this meta-analysis (Figure 1).

Figure 1.  Flow chart of our meta-analysis.

Study Characteristics for GSTM1 Null Genotype with RCC Risk

Six studies^26–31 were selected for our investigation to study the relationship between GSTM1 null genotype and RCC susceptibility (Table 1). The data of our interest were extracted: first author’s surname, year of publication, and the number of cases and controls for GSTM1 genotype (Table 1). Those six investigations contained 1311 case series and 2013 controls. The average distribution frequency of GSTM1 null genotype in RCC cases was 46.62% and the average frequency in controls was 47.46%. The average distribution frequency of GSTM1 null genotype in cases was similar to that in controls (RCC/control = 0.98).

Table 1.  Characteristics of the studies evaluating the effects of null genotypes of GSTM1 and GSTT1 on RCC risk.

		Cases			Controls			Null allele (%)
First author, year	Ethnicity	−	+	Total	−	+	Total	Cases	Controls
GSTM1
Bruning, 1997	Caucasian	18	27	45	31	17	48	40.00	64.58
Longuemaux, 1999	Caucasian	60	113	173	57	154	211	34.68	27.01
Sweeney, 2000	Mix	63	63	126	255	250	505	50.00	50.50
Karami, 2008	Caucasian	303	321	624	433	454	887	48.56	48.82
Martino, 2010	Caucasian	80	67	147	53	59	112	54.42	47.73
Ahmad, 2011	Asian	102	94	196	116	134	250	52.04	46.40
GSTT1
Bruning, 1997	Caucasian	3	42	45	11	37	48	6.67	22.92
Longuemaux, 1999	Caucasian	25	148	173	40	171	211	14.45	18.96
Sweeney, 2000	Mix	36	90	126	93	411	504	28.57	18.45
Karami, 2008	Caucasian	129	499	628	161	499	660	20.54	24.39
Martino, 2010	Caucasian	27	120	147	28	84	112	18.37	25.42
Ahmad, 2011	Asian	125	71	196	106	144	250	63.78	42.40

Note: “−”, null; “+”, present.

Study Characteristics for GSTT1 Null Genotype with RCC Risk

Six studies^26–31 were selected for our investigation to study the relationship between GSTT1 null genotype and RCC risk (Table 1). The average distribution frequency of GSTM1 null genotype in RCC cases was 25.40% and the average frequency in controls was 25.42%. The average distribution frequency of GSTT1 null genotype in cases was similar to that in controls (RCC/control = 1.00).

Study Characteristics for Dual Null Genotype of GSTM1–GSTT1 with RCC Risk

Four studies^26,27,29,31 were selected for our investigation to study the relationship between dual null genotype of GSTM1–GSTT1 and RCC susceptibility. The average distribution frequency of the dual null genotype of GSTM1–GSTT1 in RCC cases was 27.55% and the average frequency in controls was 25.46%. The average distribution frequency of the dual null genotype of GSTM1–GSTT1 in cases was slightly increased compared to that in controls (RCC/control = 1.08).

Association of GSTM1 Null Genotype with RCC Risk

In this meta-analysis, we found that GSTM1 null genotype was not associated with RCC risk in overall populations, Caucasians, and Asians (Figure 2 for overall populations; Table 2).

Figure 2.  Association between GSTM1 null genotype and RCC susceptibility.

Figure 3.  Association between GSTT1 null genotype and RCC susceptibility.

Table 2.  Meta-analysis of the association of null genotypes of GSTM1 and GSTT1 with RCC risk.

			Q test
Genetic contrasts	Group and subgroups	Number of studies	p-Value	Model selected	OR (95% CI)	p
GSTM1
− vs. +	Overall	6	0.07	Random	1.07 (0.85–1.35)	0.57
	Caucasian	4	0.03	Random	1.02 (0.70–1.50)	0.91
	Asian	1	–	Fixed	1.25 (0.86–1.82)	0.24
GSTT1
− vs. +	Overall	6	<0.00001	Random	0.98 (0.58–1.65)	0.94
	Caucasian	4	0.38	Fixed	0.76 (0.61–0.95)	0.01
	Asian	1	–	Fixed	2.39 (1.63–3.51)	<0.00001
Dual null genotype of GSTM1/GSTT1
− vs. +	Overall	4	0.006	Random	1.17 (0.98–1.39)	0.09
	Caucasian	2	0.09	Random	1.00 (0.81–1.22)	0.96
	Asian	1	–	Fixed	2.06 (1.36–3.13)	0.0007

Note: “−”, null; “+”, present.

Association of GSTT1 Null Genotype with RCC Risk

In this meta-analysis, we found that GSTT1 null genotype was not associated with RCC risk in overall populations (Figure 3 for overall populations; Table 2). Subgroup analysis according to different races was also performed, and we found that the GSTT1 null genotype was associated with the onset of RCC in Caucasians and Asians (Table 2).

Association of Dual Null Genotype of GSTM1–GSTT1 with RCC Risk

No association of the dual null genotype of GSTM1–GSTT1 with RCC risk was observed in overall populations (Table 2). Subgroup analysis according to different races was also performed, and we found that the GSTT1 null genotype was associated with the onset of RCC in Asians, but the association was not observed in Caucasians (Table 2).

Evaluation of Publication Bias

Publication bias test for the association of GSTM1 null genotype or GSTT1 null genotype with RCC risk in overall populations was performed. There were no publication bias for the association of GSTM1 null genotype or GSTT1 null genotype with RCC risk in overall populations (GSTM1: Begg p = 1.000, Egger p = 0.926; GSTT1: Begg p = 0.452, Egger p = 0.475).

DISCUSSION

The etiology of RCC was not elucidated and the genetic origin of RCC had been a focus of research in the past decades, and some investigations found that the genetic alteration could become an early diagnosis indicator to predict the onset of some cancers.^32–34 GSTs are implicated in the inactivation of procarcinogens that contribute to cancer progression.³⁵ There were a lot of significant evidences showing that the GSTs had taken part in the onset of RCC, and some studies found that some mutant sites of the GST genes might affect the activation of GSTs to play the multifunctional physiological processes. However, findings on the association of GSTM1/GSTT1 null genotype with RCC susceptibility have been controversial since the first investigation was reported. Most of the studies were performed in Caucasians. In this meta-analysis, we investigated whether the GSTM1/GSTT1 null genotype could become a valuable indicator to predict the risk of RCC and tried to draw a more robust conclusion.

In the analysis of null genotype of GSTM1 with RCC risk, our results indicated that GSTM1 null genotype did not predict the risk of RCC in overall populations, Caucasians, and Asians. Zhang et al.³⁶ performed a meta-analysis for the relationship of GSTT1 null genotype and oral cancer, and the results were not supportive for the association of GSTT1 null genotype with oral cancer risk. Chen et al.³⁷ conducted a meta-analysis to investigate the association between GSTT1 null genotype and gastric cancer risk, and the results were not supportive for the association of GSTT1 gene polymorphism with gastric cancer risk among Europeans, Americans, and East Asians. GSTM1 null genotype might not be associated with the onset of RCC. However, more studies should be performed in the future.

For the analysis of GSTT1 null genotype with RCC risk in Asians, our results indicated that GSTT1 null genotype could predict the susceptibility of RCC. In this study, we found that the GSTT1 null genotype was not associated with RCC susceptibility in overall populations, but the association was observed in Caucasians and Asians. Gao et al.³⁸ conducted a meta-analysis and reported that the null genotype of GSTT1 was associated with a significantly increased risk of cervical neoplasia in Asians. Some other investigations^39,40 also found that GSTT1 gene polymorphism was a risk factor for cancer in Asians using meta-analysis method. Liao et al.⁴¹ conducted a meta-analysis and found that null genotype of GSTT1 was associated with the risk of colorectal cancer, especially in Caucasian and Asian population. GSTT1 null genotype might be a risk factor for cancer morbidity in Caucasians and Asians.

Among the included studies, the study of De Martino et al.³⁰ did not provide the detailed genotype distributions for GSTM1 and GSTT1 for the control group, and we calculated the null genotype of the controls using the average distribution frequency of GSTM1/GSTT1 null genotype. Furthermore, we also excluded the study of De Martino et al.³⁰ for meta-analysis and found that the results were similar to those in the meta-analysis including the study of De Martino et al.³⁰ (data not shown).

We also tested the association between dual null genotype of GSTM1–GSTT1 and RCC risk. The results showed that the dual null genotype of GSTM1–GSTT1 could predict the risk of RCC in Asians, but this association was not observed in overall populations and Caucasians. The dual null genotype of GSTM1–GSTT1 might be a risk factor for RCC in Asians. However, more investigations are still required to further evaluate the interaction of GSTT1 gene polymorphism with RCC risk.

Our results indicated that GSTM1/GSTT1 null genotype was associated with the RCC susceptibility in Caucasians and Asians, and the dual null genotype of GSTM1–GSTT1 was associated with RCC risk in Asians. However, more genetic epidemiological investigations are required to further explore this relationship. However, those findings should be regarded cautiously because many other ingredients, such as language bias, small sample size of the included report, limited statistical power, heterogeneity of enrolled cases, variable study designs, and different interventions, were closely related to affect the results.

In this meta-analysis, publication bias test was performed when the number of included studies was not less than six. In our publication bias test, we found that there was no publication bias for the association of GSTM1 or GSTT1 null genotype with RCC risk in overall populations. The results for the association of GSTM1 or GSTT1 null genotype with RCC risk in overall populations might be robust to some extent. However, the number of included studies was also a little small (only six), and more studies should be performed in the future.

In conclusion, the results from our study support that the null genotype of GSTM1/GSTT1 is associated with the risk of RCC in Caucasians and Asians, and there is an association between the dual null genotype of GSTM1–GSTT1 and the risk of RCC in Asians. However, more association investigations are required to further clarify the role of the null genotype of GSTM1/GSTT1 in predicting the risk of RCC.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this article.