Role of gastrin in gastric cancerogenesis in Helicobacter pylori infected humans

Numerous epidemiological studies demonstrated the association between Helicobacter pylori (H. pylori) infection and gastric cancer but the mechanism of the involvement of H. pylori in gastric cancerogenesis remains virtually unknown. This study was designed to determine the seropositivity of H. pylori and cytotoxin associated gene A (CagA), serum gastrin and gastric lumen gastrin levels under basal conditions and following stimulation with histamine in gastric cancer patients and controls. 100 gastric cancer patients aging from 21 to 60 years and 300 gender- and age-adjusted controls hospitalized with non-ulcer dyspepsia (NUD) entered this study. C-13-urea Breath Test (UBT), serum immunoglobulin (IgG) antibodies to H. pylori and CagA were used to assess the H. pylori infection and serum levels of IL-1 beta, IL-8 and TNF alpha were measured by enzyme-linked immunosorbent assay (ELISA) to evaluate the degree of gastric inflammation by H. pylori. Gastrin-17 mRNA and gastrin receptors (CCKB) mRNA expression in gastric mucosal samples taken by biopsy from the macroscopically intact fundic and antral mucosa as well as from the gastric tumor was determined using RT-PCR. The overall H. pylori seropositivity in gastric cancer patients at age 21-60 years was about 92%, compared, respectively, to 68%, in controls. A summary odds ratio (OR) for gastric cancer in H. pylori infected patients was about 5.0 The H. pylori CagA seropositivity in gastric cancer patients was about 58.5% compared to 32.4% in controls, giving the summary OR for gastric cancer in CagA positive patients about 8.0. The prevalence of H. pylori- and N. pylori CagA-seropositivity was significantly higher in cancers than in controls, irrespective of the histology of gastric tumor (intestinal, diffuse or mixed type). Median IL-1 beta and IL-8 reached significantly higher values in gastric cancer patients (9.31 and 30.8 pg/ml) than in controls (0.21 and 3.12, respectively). In contrast, median serum gastrin in cancers las total group) was several folds higher (62.6 pM) than in controls (19.3 pM). Also median luminal gastrin concentration in gastric cancer patients was many folds higher (310 pM) than in controls (20 pM). This study shows for the first time that cancer patients are capable of releasing large amounts of gastrin into the gastric lumen to increase luminal hormone concentration to the level that was recently reported to stimulate the growth of H. pylori. There was no any correlation between plasma gastrin levels and gastric luminal concentration of gastrin suggesting that: 1) luminal gastrin originates from different source than plasma hormone, most probably from the cancer cells, 2) cancer cells are capable of expressing gastrin and releasing it mainly into the gastric juice and 3) the gastric cancer cells are equipped with gastrin-specific (CCKB) receptor so they exhibit the self-growth promoting activity in autocrine fashion. This notion is supported by direct detection of gastrin mRNA and gastrin receptor (CCKB-receptors) mRNA using RT-PCR in cancer tissue. To our knowledge this is the first study showing an important role of gastrin as self-stimulant of cancer cells in patients infected with H. pylori. Basal and histamine maximally stimulated acid outputs were significantly lower in gastric cancer patients than in controls despite of enhanced gastrin release, particularly in cancer patients and this might reflect the mucosal inflammatory changes (increased serum levels of proinflammtory interleukins - IL-1 beta and IL-8), that are known to increase gastrin release. We conclude that: 1. N. pylori infected patients, particularly those showing CagA-seropositivity, are at greatly increased risk of development of gastric cancer, 2. H. pylori-infected cancer patients produce significantly more IL-1 beta and IL-8 that might reflect an H. pylori-associated chronic active gastritis in these patients, 3. Very high gastrin release, particularly into gastric lumen, as well as marked gene expression for gastrin and gastrin receptor In tumor tissue provide an evidence that gastrin plays an important role in development of gastric cancer in H. pylori-infected patients and 4. Gastrin in gastric cancer originates not from the G-cells but from the cancer cells that appear to stimulate themselves in autocrine fashion to grow in uncontrollable way, therefore, examination of gastrin release may be an useful marker of malignancy in H. pylori-infected patients.