Published online Nov 15, 2019. doi: 10.4251/wjgo.v11.i11.998
Peer-review started: March 14, 2019
First decision: May 9, 2019
Revised: July 26, 2019
Accepted: August 27, 2019
Article in press: August 27, 2019
Published online: November 15, 2019
Gastric cancer (GC) is one of the most prevalent cancers worldwide, with high rates of incidence and death. It ranks sixth in the world and is the fifth leading cause of cancer-related deaths worldwide. In Brazil, GC is the fourth most frequent type of cancer in men, and the sixth in women, with an estimated incidence of 21,290 new cases in 2018. The main risk factor associated with this type of cancer is the infection by the bacterium Helicobacter pylori (H. pylori). Toll-like receptors are the first line of host defense, and are involved in H. pylori recognition and activation of the inflammatory and carcinogenic process. The presence of single nucleotide polymorphisms (SNPs) in genes that activate the immune response may modulate the risk of precancerous lesions and GC, among them of which is TLR9 polymorphisms.
Polymorphisms in toll-like receptors genes have emerged with a risk factor of infectious diseases and cancer. However, the literature presents conflicting results. Therefore, several studies are needed to assess and confirm the real role among factors that influence changes in immune inflammatory processes related to GC, especially when it is a mixed population such as the Brazilian population.
Considering the inconsistent results and the importance of these receptors in the immune response and to susceptibility to inflammatory diseases and cancer, new studies are needed. Thus, the aim of this study was to evaluate whether the TLR9-1237 TC (rs5743836) and TLR9-1486 CT (rs187084) polymorphisms (alone and in combination) are associated with a risk of chronic gastritis (CG) and GC. In addition, we also evaluate the influence of both polymorphisms and H. pylori infection on TLR9 mRNA expression. The results may highlight important polymorphisms that act on gastric carcinogenesis.
A case-control study was conducted to evaluate two TLR9 SNPs (TLR9-1237 TC-rs5743836 and TLR9-1486 CT-rs187084) in CG and GC patients. A total of 609 DNA samples of peripheral blood [248 CG, 161 GC, and 200 samples from healthy individuals (C)] were genotyped by polymerase chain reaction-restriction fragment length polymorphism. All samples were tested for the H. pylori infection using Hpx1 and Hpx2 primers. Quantitative polymerase chain reaction by TaqMan® assay was used to quantify TLR9 mRNA from fresh gastric tissues (48 GC, 26 CG, and 14 C).
The data showed that for TLR9-1237, the TC + CC or CC genotypes were associated with a higher risk of GC than the C and CG groups. For TLR9-1486, an association between the CT + TT genotypes and increased risk of both GC and CG was observed when compared to the C group. Moreover, the presence of TLR9-1237 TC/CC + TLR9-1486 CC genotypes potentiates the risk for this neoplasm. The TLR9 mRNA level was significantly higher in the GC group in relation to the CG group and normal mucosa. When the samples were grouped according to the polymorphic genotypes and the presence of H. pylori infection, an influence of TLR9-1237 TC + CC polymorphic genotypes and H. pylori infection was observed on the upregulation of mRNA expression.
Our findings highlight that the functional polymorphisms of the TLR9-1237 T/C (rs5743836) and TLR9-1486 C/T (rs187084) receptors are associated with an increased risk of developing premalignant and malignant gastric diseases in this Brazilian population, and therefore may act as a potential factor in the progression of gastric carcinogenesis. TLR9 mRNA expression levels are upregulated in GC tissues and are modulated by both H. pylori infection and the presence of TLR9-1237 TC + CC-variant genotypes. The pattern of the host’s immune response, along with genetic and environmental factors, are essential for understanding the pathology of GC. Thus, polymorphisms in genes that affect its expression, such as TLR9, could have an effect on the development and clinical manifestation of disease.
Considering that most cases of GC have a good prognosis and are treatable when diagnosed at an early stage, it is of the utmost importance to establish molecular markers capable of identifying risk groups and providing early diagnosis in individuals with increased risk of developing this neoplasm. Overall, our results indicate that the TLR9 gene plays an important role in gastric carcinogenesis, highlighting the importance of the TLR9-1237 T/C (rs5743836) polymorphism in increasing gene expression and H. pylori infection, possibly triggering a stronger inflammatory response, which in turn enhances the risk of tumor progression. In the future, it would be important to investigate another polymorphism in the TLR9 gene [TLR9-2848 C/T (rs352140)], described in the literature as associated with cancer, but not yet analyzed in our Brazilian population.