Determination of strains of Helicobacter pylori and of polymorphism in the interleukin-8 gene in patients with stomach cancer.

CONTEXT

Gastric neoplasia is the second most common cause of death by cancer in the world and H. pylori is classified as a type I human carcinogen by the World Health Organization. However, despite the high prevalence of infection by H. pylori around the world, less than 3% of individuals carrying the bacteria develop gastric neoplasias. Such a fact indicates that evolution towards malignancy may be associated with bacterial factors in the host and the environment.

OBJECTIVES

To investigate the association between polymorphism in the region promoting the IL-8 (-251) gene and the H. pylori genotype, based on the vacA alleles and the presence of the cagA gene, using clinical and histopathological data.

METHODS

In a prospective study, a total of 102 patients with stomach cancer and 103 healthy volunteers were analysed. Polymorphism in interleukin 8 (-251) was determined by the PCR-restriction fragment length polymorphism reaction and sequencing. PCR was used for genotyping the vacA alleles and the cagA in the bacterial strains PCR. Gastric biopsies were histologically assessed.

RESULTS

The H. pylori serology was positive for 101 (99%) of all patients analysed, and 98 (97%) of them were colonized by only one strain. In patients with monoinfection, 82 (84%) of the bacterial strains observed had the s1b/m1 genotype. The cagA gene was detected in 74 (73%) of patients infected by H. pylori. The presence of the cagA gene was demonstrated as associated with the presence of the s1b/m1 genotype of the vacA gene (P = 0.002). As for polymorphism in the interleukin 8 (-251) gene we observed that the AA (P = 0.026) and AT (P = 0.005) genotypes were most frequent in the group of patients with gastric adenocarcinoma. By comparing the different types of isolated bacterial strains with the interleukin -8 (-251) and the histopathological data we observed that carriers of the A allele (AT and AA) infected by virulent strains (m1s1 cagA+) demonstrated a greater risk of presenting a degree of inflammation (OR = 24.75 CI 95% 2.29-267.20 P = 0.004) and increased neutrophilic activity (OR = 28.71 CI 95% 2.62-314 P = 0.002) in the gastric mucosa.

CONCLUSION

Our results demonstrate that the interaction between polymorphism in the interleukin -8 (-251) gene, particularly with carriers of the A allele and the infecting type of H. pylori strain (s1m1 cagA positive) performs an important function in development of gastric adenocarcinoma.