Low Virulence of Helicobacter Pylori and Gastric Cancer: the Contribution of Polymorphisms of iNOS and DNA Repair Enzymes in this Process

Special Article- Stomach cancer

Austin J Gastroenterol. 2014;1(4): 1019.

Low Virulence of Helicobacter Pylori and Gastric Cancer: the Contribution of Polymorphisms of iNOS and DNA Repair Enzymes in this Process

Isabelle Joyce de Lima Silva-Fernandes, Ana Paula Santos do Carmo, Débora Menezes da Costa, Emanuele Silva de Oliveira, Eliane dos Santos Pereira and Silvia Helena Barem Rabenhorst*

Department of Pathology and Forensic Medicine, Federal University of Ceará, Brazil

*Corresponding author: : Rabenhorst SHB, Department of Pathology and Forensic Medicine, School of Medicine, Federal University of Ceará, Coronel Nunes de Melo, 1315, Rodolfo Teófilo, Fortaleza, CE CEP 60430-270, Brazil

Received: August 06, 2014; Accepted: September 08, 2014; Published: September 10, 2014

Abstract

This study aimed to investigate the interaction between the iNOS C >T polymorphism, the genotype of H. pylori strains and polymorphisms in DNA repair genes (OGG-1, APE-1 and PARP-1) in a set of gastric cancer patients. In our methods, polymorphism was assessed by polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP) and H. pylori detection/ genotyping by PCR. A significant result shows this iNOS polymorphism more frequent among young gastric cancer patients than older patients (p= 0.020). Host genetic features, such as DNA repair enzymes (OGG-1, APE-1, PARP- 1), are also important in preventing the malignancy process. Polymorphisms present in these enzymes associated with iNOS activity could lead to gastric cancer even in the presence of low virulent H. pylori strains. Within our results, iNOS homozygous wild-type (CC) genotype and APE-1 polymorphic allele (TG+GG) group were more infected by H. pylori low-virulent strains (p=0.021). In Conclusion, our study indicates the importance of H. pylori and host DNA repair enzymes genotypes in gastric carcinogenesis in interection with this specific iNOS polymorphism.

Keywords: Gastric cancer; Helicobacter pylori; PARP-1; APE-1; OGG-1

Introduction

Gastric cancer is the fifth most common cancer and the second leading cause of cancer-related mortality in the world [1]. In Brazil, it is an important cause of cancer-related death in patients, with a high prevalence in the Northeast region [2]. According to Lauren’s classification, the histological subtypes, intestinal and diffuse, show distinct histological and epidemiological features, as well as a different prognosis [3,4]. Furthermore, this tumor can be located in the proximal stomach (cardia), or distal (antrum, non-cardia). Differences between tumors located in the cardia or non-cardia region, as well as intestinal or diffuse subtypes, suggests that they represent distinct diseases with different etiologies. Gastric carcinogenesis is a multifactorial process, and Helicobacter pylorus (H. pylori) is the main initiator of inflammation and atrophic changes in the gastric mucosa [5]. The association between chronic H. pylori infection and the development of gastric cancer is well established [6]. It is known that both bacterial virulence and host genetic susceptibility are associated with cancer risk [7].

H. pylori has a great genetic diversity, and virulence factors play important roles in mucosal injury, especially the genes cagA (cytotoxin associated gene A) and vacA, (vacuolating cytotoxin A), more specifically vacAs1m1. cagA is involved in many host cell alterations and tightly associated with gastric cancer risk [8,9]. The vacA gene is present in essentially all H. pylori strains. VacA is a potent toxin, where it induces the formation of vacuoles in host cells. Additionally, the cagE and virB11 genes have been found at a relevant frequency in gastric cancer patients [10]. The chronic inflammatory process in the presence of H. pylori increases the expression of iNOS which could lead to cell injury, with large amounts of NO leading to DNA lesions [11,12]. The DNA damage caused by ROS can lead to gene alterations and, therefore, requires continuous DNA repair.

Polymorphism in the iNOS gene that leads to increased expression or altered function of the enzyme could affect the level of the DNA lesions and therefore increase DNA damage. In this context, Daff et al. [13], using a bacterial culture, found a deletion located six amino acids from the currently studied C>T polymorphism in exon 16. The proximity between this deletion and C>T polymorphism has been suggested by Jing Shen et al. [14] and Jesper Johannesen et al. [15] to account for the increase in iNOS activity. The increased activity is associated with several types of diseases, such as bladder cancer [16,17], and diabetes [18], besides gastric cancer [14].

Recently, host genetic susceptibility to cancer related to polymorphisms in DNA repair enzymes has been investigated [19,20]. In gastric cancer, our team observed and reported before [21] that polymorphisms in some enzymes of the base excision repair (BER) system, responsible for recognizing and removing the damaged base, should be investigated such as the following: OGG-1 Ser326Cys [22,23], associated with reduced DNA repair capacity [24]; APE-1 Asn148Glu [25,26], associated with increased sensitivity to ionizing radiation in homozygosis [26]; and PARP-1 Val762Ala, associated with gastric cancer risk besides cag(+) H. pylori infection [27].

Therefore, this study aimed to investigate the interaction between the iNOS C >T polymorphism, the genotype of H. pylori strains and polymorphisms in DNA repair genes (OGG-1, APE-1 and PARP-1) in a set of gastric cancer patients.

Materials and Methods

Patients and specimens

This study was approved by the ethics committee of the Federal University of Ceará. A total of 109 adenocarcinoma specimens, surgically resected, were obtained from three public hospitals in Fortaleza, Ceará State, Brazil: Walter Cantideo Hospital at Federal University of Ceará, Santa Casa de Misericórdia Hospital and Cesar Cals General Hospital. Fragments of tumor were collected during gastrectomy and frozen at -80°C. Histological diagnosis and tumor classification was based on Lauren’s criteria.

DNA extraction, H. pylori detection and genotyping

Genomic DNA was extracted from frozen tumor tissue samples consisting mainly of tumor cells (>80%), using the cetyltrimethyl ammonium bromide (CTAB) method adapted from Foster and Twell [28]. H. pylori infection was detected by amplification of the urease C gene, and virulence genes were identified using specific primers and conditions, as previously described by Lage et al. [29] and Domingo et al. [30], Atherton et al. [31] and Sozzi et al. [32]. Negative (water) and positive controls were assayed in each run. PCR products were separated on 6% polyacrylamide electrophoretic gels, which were then silver stained.

DNA repair polymorphism

Single nucleotide polymorphisms (SNPs) for DNA repair genes were determined by a PCR-RFLP based method as described by Vodicka et al. [33] and Shen et al. [14]. Negative (water) and positive (DNA containing known DNA repair genes) controls were assayed in each run. The amplified fragments were visualized in 2% agarose gels containing ethidium bromide under UV light and were digested with appropriate restriction endonucleases. The fragments were resolved by 8% polyacrylamide gel electrophoresis under non-denaturing conditions and silver staining. Randomly selected samples were re-genotyped (10% of samples).

Statistical analysis

All statistical analyses were conducted with the SPSS® 15.0 version statistical software program (SPSS, Chicago, IL, USA), using the χ2 and Fisher exact tests, and p<0.05 was considered statistically significant.

Results

In this study, the intestinal type was slightly more frequent than the diffuse (60/109 or 55.0% versus 49/109 or 45.0%), and most of the tumors were located in the non-cardia region of stomach (75.2%; 82/109). The genotype distributions were as follows: iNOS 78.0% CC (85/109), 21.1% CT (23/109) and 0.9% TT (1/109); APE-1 38.5% TT (42/109), 47.7% TG (52/109) and 13.8% GG (15/109); PARP-1 69.7% AA (76/109), 26.6% AG (29/109) and 3.7% GG (4/109); OGG-1 56% CC (61/109), 39.4% CG (43/109) and 4.6% GG (5/109).

With regard to the iNOS genotype distribution, no statistical difference was observed between histological characteristics or tumor localization (Table 1). However, considering 55 years old as the patients’ age cutoff, the iNOS wild-type (CC) was significantly (p= 0.020) more frequent in patients aged ≥ 55 years than those <55 years old (83.1% versus 16.8%, respectively), as shown in Table 1.

Table 1: iNOS genotype frequency considering tumor’s stomach location, histopathological characteristics and patients’ age.




  

    
 

    
CC

      
(n=85)

    
CT    or TT

      
(n=24)

    
p-value 

  

  

    
 

      
Cardia 

    
21

      
(24.7%)

    
6

      
(25.0%)

    
0.81

  

  

    
Non-cardia 

    
64

      
(75.3%)

    
18

      
(75.0%)

  

  

    
Diffuse 

    
38

      
(44.7%)

    
11

      
(45.8%)

    
0.89

  

  

    
Intestinal 

    
47

      
(55.3%)

    
13

      
(54.2%)

  

  

    
<    55 years 

    
16

      
(61.5%)

    
10

      
(38.4%)

    
0.02* 

  

  

    
≥ 55 years 

    
69

      
(83.1%)

    
14

      
(16.8%)

  









Table 1:  iNOS genotype frequency considering tumor’s stomach location, histopathological characteristics and patients’ age.

Among the samples, 92.7% (101/109) were H. pylori positive; of these, 65.3% (66/101) were cagA(+), 50.5% (51/101) were cagE(+), 60.4% (61/101) were virB11(+), 72.3% (73/101) were vacA s1m1, 17.8% (18/101) were vacA s1m2, 3.9% (4/101) were vacA s2m1 and 7.9% (8/101) were vacA s2m2.

The H. pylori strains were placed in group A, B or C, according to the vacA genotype as suggested by Lima et al. [10]. Group A was s1/ m1, B was s1/m2 or s2/m1 and C was s2/m2. The number that comes with the specific vacA group letter indicates the combination of cagA, cagE and virB11 genes. Number 1 indicates triple-positive strains and number 4 means triple-negative. Considering H. pylori as high (A1->B2) or low virulence (B3->C4) strains, a similar distribution of iNOS genotypes (p=0.086) was observed between these groups.

Considering the context of H. pylori virulence and polymorphism of iNOS and repair enzyme genes, the iNOS genotypes were combined with the genotypes of each repair enzyme as shown in Table 2. In this table, it is seen that patients carrying the iNOS homozygous wild-type genotype (CC) + APE-1 polymorphic allele (TG+GG) where were statically more frequently infected by low-virulent strains (B3- >C4 [88.2% (15/17); p=0.021] compared with carriers of both wild-type genotypes (iNOS-CC + APE-1-TT) (11.8%; 2/17). The opposite was observed considering the association with PARP-1, where patients carrying both homozygous wild-type genotypes (CC+AA, iNOS and PARP-1, respectively) were more frequently infected by low virulent strains compared with patients carrying CC+AG\GG genotypes (88.2% versus 11.8%, respectively). No difference was observed considering the association with OGG-1 genotypes or the polymorphic allele of iNOS (CT+TT) with the repair enzyme genotypes. Those data are shown in Table 2.

Table 2: H. pylori´s strains vs APE-1, OGG-1, PARP-1 in genotyped patients for iNOS.




  

    
Repair enzymes genotypes 

    
iNOS    genotype 

    
A1 -> B2

    
B3 -> C4

    
p-value 

  

  

    
APE-1 

    
TT

    
CC

    
26

      
(41.9%)

    
2

      
(11.8%)

    
0.021*

  

  

    
TG or GG

    
36

      
(58.1%)

    
15

      
(88.2%)

  

  

    
TT

    
CT or TT

    
7

      
(41.2%)

    
2

      
(40.0%)

    
0.68

      
 

      
 

  

  

    
TG or GG

    
10

      
(58.8%)

    
3

      
(60.0%)

  

  

    
OGG-1 

    
CC

    
CC

    
36

      
(58.1%)

    
10

      
(58.8%)

    
0.82

  

  

    
CG or GG

    
26

      
(41.9%)

    
7

      
(41.2%)

  

  

    
CC

    
CT or TT

    
8

      
(47.0%)

    
4

      
(80.0%)

    
 

      
0.21

  

  

    
CG or GG

    
9

      
(53.0%)

    
1

      
(20.0%)

  

  

    
PARP-1 

    
AA

    
CC

    
39

      
(63.0%)

    
15

      
(88.2%)

    
0.043* 

  

  

    
AG or GG

    
23

      
(37.0%)

    
2

      
(11.8%)

  

  

    
AA

    
CT or TT

    
11

      
(64.7%)

    
4

      
(80.0%)

    
0.47

  

  

    
AG or GG

    
6

      
(35.3%)

    
1

      
(20.0%)

  









Table 2:  H. pylori´s strains vs APE-1, OGG-1, PARP-1 in genotyped patients for iNOS.

Discussion

It is known that the inflammatory response with high NO production contributes to tissue damage, suggesting it as a possible role in the carcinogenesis process [14]. Additionally, a deficiency in DNA repair also contributes to the malignant changes in gastric cells [34]. In this way, polymorphisms that foster increased DNA damage may contribute to gastric cancer development, such as the iNOS Ser608Leu polymorphism and DNA repair enzyme polymorphism (OGG-1 Ser326Cys, APE-1 Asp148Glu and PARP-1 Val762Ala) [14,34,35]. Because polymorphism can detected from any biological sample, including peripheral blood, they are promising predictive molecular markers for disease susceptibility which make them a tool for clinic use. However polymorphism susceptibility depend on the multiple allelic variation, as well as environment factors. Since in gastric cancer the inflammatory process depends on H. pylori virulence, the bacterial genotype must be considered.

Concerning the frequency of the iNOS genotypes, the present study found a high polymorphic allele frequency, as found by Shen et al. [36] in a study of a Chinese population with gastric cancer (24.4%). The low frequency of the iNOS homozygous genotype (TT) identified in the present study, was similar to the value of 3.4% reported by Fermin- Mearin et al. [37] in a study conducted in Spain with esophageal achalasia.

The association observed in the present study between iNOS wild-type genotype and older patients could be explained when iNOS activity is taken into account. It is interesting to note that Escames et al. [38], using an animal model, showed a natural increase in iNOS activity and NO production in the aging process. When the gene polymorphisms of the repair enzymes were associated with the iNOS polymorphism, our data indicated that the high iNOS activity produced by the Ser608Leu polymorphism of iNOS is probably connected with the early development of gastric cancer, since the frequency of patients carrying the iNOS polymorphic allele (CT+TT) was higher in patients <55 years old than ≥ 55 years (38.4% versus 16.8%, respectively). On the other hand, since there is a natural increase in iNOS activity with aging, this polymorphism may not have an influence in older patients [38].

In this study, a high percentage of the tumor samples were H. pylori positive, which is in line with the finding of a high rate of infection with H. pylori in the Brazilian population [39].

Several polymorphisms in DNA repair enzymes, including OGG- 1, APE-1 and PARP-1, have been studied in many types of cancer, because of their role in maintaining genome integrity [19,22,40]. OGG1-mediated removal of 8-oxoguanine from DNA, which is a major base damage produced by ROS, may be affected by the presence of the Ser326Cys polymorphism. This polymorphism may decrease OGG-1 substrate specificity and capacity to excise 8-oxoguanine due to remodeling of its phosphorylation status and cellular localization [34]. The frequency of the OGG-1 polymorphic genotype (GG) was similar to that found by Hanaoka et al. [41] in studying Brazilian patients with gastric cancer. Despite the large number of studies showing OGG-1 as an important DNA-repair enzyme, no substantial results were obtained in the present study. Thus, there is a need for further studies analyzing the polymorphism of OGG-1 associated with those of other enzymes of the BER pathway to find a possible relevant association.

In the analysis involving iNOS and the repair enzyme genotypes, the patients carrying the iNOS wild-type genotype (CC) who had the polymorphic allele (TG/GG) of APE-1 as well as the PARP- 1 wild-type allele, were more infected by low-virulence H. pylori strains. It is known that APE-1 is a multifunctional enzyme, which is responsible for DNA repair of apurinic/apyrimidinic sites. However, the polymorphism Asp148Glu described in this gene can affect repair efficiency, as observed by Hu et al. [42] using cell culture. Additionally, it was shown that this polymorphism leads to greater sensitivity to ionizing radiation. Thus, our data suggest that APE-1 polymorphism contributes to gastric carcinogenesis associated with low-virulence strains, possibly due to the inability of the polymorphic enzyme to communicate with other repair enzymes [25]. Concerning PARP-1 wild-type association with these strains, it is important to note that 15 of the 19 samples showing PARP-1 (AA) associated with low-virulence H. pylori strains (78.9%) were carriers of the APE-1 polymorphic allele, highlighting the relevance of the APE-1 polymorphism. Another explanation for this apparently controversial result is that PARP-1 normal activity consumes a large amount of NAD+ and, therefore, cell energy. Even though PARP- 1 has an important role in DNA repair, its activation may cause necrosis and inflammation due to this energy depletion contributing to the carcinogenic process [43].

The results of this study of the polymorphic allele of iNOS considering 55 years as a cutoff, suggest the involvement of the Ser608Leu polymorphism in the process of gastric carcinogenesis among young patients. Moreover, low-virulence strains of H. pylori appear to act in gastric carcinogenesis when associated with the presence of the polymorphic allele of APE-1 or wild-type of PARP- 1. These data of this study point these polymorphisms as potential marker for future use in clinical screening considering the age and H. pylori virulence.

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Citation: de Lima Silva-Fernandes IJ, do Carmo APS, da Costa DM, de Oliveira ES, dos Santos Pereira E and Rabenhorst SHB. Low Virulence of Helicobacter Pylori and Gastric Cancer: the Contribution of Polymorphisms of iNOS and DNA Repair Enzymes in this Process. Austin J Gastroenterol. 2014;1(4): 1019. ISSN:2381-9219