Background & Aims Infection with the gastric mucosal pathogen Helicobacter pylori is the strongest identified risk factor for distal gastric cancer. These bacteria colonize a significant part of the ...world's population. We investigated the molecular mechanisms of p53 regulation in H pylori –infected cells. Methods Mongolian gerbils were challenged with H pylori and their gastric tissues were analyzed by immunohistochemistry and immunoblotting with p53 antibodies. Gastric epithelial cells were co-cultured with H pylori and the regulation of p53 was assessed by real-time polymerase chain reaction, immunoblotting, immunofluorescence, and cell survival assays. Short hairpin RNA and dominant-negative mutants were used to inhibit activities of Human Double Minute 2 (HDM2) and AKT1 proteins. Results We found that in addition to previously reported up-regulation of p53, H pylori can also negatively regulate p53 by increasing ubiquitination and proteasomal degradation via activation of the serine/threonine kinase AKT1, which phosphorylates and activates the ubiquitin ligase HDM2. These effects were mediated by the bacterial virulence factor CagA; ectopic expression of CagA in gastric epithelial cells increased phosphorylation of HDM2 along with the ubiquitination and proteasomal degradation of p53. The decrease in p53 levels increased survival of gastric epithelial cells that had sustained DNA damage. Conclusions H pylori is able to inhibit the tumor suppressor p53. H pylori activates AKT1, resulting in phosphorylation and activation of HDM2 and subsequent degradation of p53 in gastric epithelial cells. H pylori –induced dysregulation of p53 is a potential mechanism by which the microorganism increases the risk of gastric cancer in infected individuals.
Background & Aims The Helicobacter pylori toxin vacuolating cytotoxin (VacA) promotes gastric colonization, and its presence (VacA+ ) is associated with more-severe disease. The exact mechanisms by ...which VacA contributes to infection are unclear. We previously found that limited exposure to VacA induces autophagy of gastric cells, which eliminates the toxin; we investigated whether autophagy serves as a defense mechanism against H pylori infection. Methods We investigated the effect of VacA on autophagy in human gastric epithelial cells and primary gastric cells from mice. Expression of p62, a marker of autophagy, was also assessed in gastric tissues from patients infected with toxigenic (VacA+ ) or nontoxigenic strains. We analyzed the effect of VacA on autophagy in peripheral blood monocytes obtained from subjects with different genotypes of ATG16L1 , which regulates autophagy. We performed genotyping for ATG16L1 in 2 cohorts of infected and uninfected subjects. Results Prolonged exposure of human gastric epithelial cells and mouse gastric cells to VacA disrupted induction of autophagy in response to the toxin, because the cells lacked cathepsin D in autophagosomes. Loss of autophagy resulted in the accumulation of p62 and reactive oxygen species. Gastric biopsy samples from patients infected with VacA+ , but not nontoxigenic strains of H pylori , had increased levels of p62. Peripheral blood monocytes isolated from individuals with polymorphisms in ATG16L1 that increase susceptibility to Crohn's disease had reduced induction of autophagy in response to VacA+ compared to cells from individuals that did not have these polymorphisms. The presence of the ATG16L1 Crohn's disease risk variant increased susceptibility to H pylori infection in 2 separate cohorts. Conclusions Autophagy protects against infection with H pylori ; the toxin VacA disrupts autophagy to promote infection, which could contribute to inflammation and eventual carcinogenesis.
Background & Aims Helicobacter pylori -induced gastritis predisposes to the development of gastric cancer. Increased epithelial tight junction permeability and alterations in apical-junctional ...complexes are also associated with an increased risk of carcinogenesis. Phosphorylation of myosin regulatory light chain (MLC) by MLC kinase (MLCK) regulates tight junction function. We determined whether MLCK was activated by H pylori and defined the mechanisms through which such activation dysregulates gastric epithelial barrier function. Methods MKN28 gastric epithelial cells were cocultured with the H pylori cag+ strain 60190 or cagA− , cagE− , ureB− , or vacA− mutants. MLC phosphorylation and barrier integrity were determined by immunoblot analysis and transepithelial electrical resistance measurements, respectively. Localization of the tight junction protein occludin was determined by immunocytochemistry in MKN28 cells and INS-GAS mice. Results H pylori induced a progressive loss of barrier function that was attenuated by inactivation of ureB , but not cagA, cagE , or vacA . Reductions in transepithelial electrical resistance were also dependent on functional urease activity. H pylori increased MLC phosphorylation in epithelial monolayers; this was significantly decreased by inhibition of MLCK or Rho kinase or by loss of UreB. H pylori infection of either cultured monolayers or hypergastrinemic INS-GAS mice induced occludin endocytosis, reflecting cytoskeletally mediated disruption of tight junctions. Conclusions H pylori increases MLC phosphorylation, occludin internalization and barrier dysfunction in gastric epithelial cells. This process requires functional urease activity and is independent of the cag pathogenicity island or VacA. These data provide new insights into the mechanisms by which H pylori disrupts gastric barrier function.
Background & Aims Gastric cancer evolves in the setting of a pathologic mucosal milieu characterized by both loss of acid-secreting parietal cells and mucous cell metaplasias. Indeed, mucous cell ...metaplasia is considered the critical preneoplastic lesion for gastric cancer. Previous investigations have shown that infection of mice with Helicobacter felis or induction of acute parietal cell loss with the drug DMP-777 leads to the emergence of a type of metaplasia designated spasmolytic polypeptide-expressing metaplasia (SPEM). We have hypothesized that SPEM arises from proliferating cells in gland bases, either from a cryptic progenitor cell or by transdifferentiation of mature chief cells. Methods Taking advantage of the chief cell-restricted expression of Mist1-Cre-ERT2 , we used lineage mapping to examine whether SPEM lineages were derived from chief cells in 3 independent models of induction by DMP-777 treatment, L-635 treatment, or H felis infection. Results Treatment of mice with L-635 for 3 days led to rapid parietal cell loss, induction of a prominent inflammatory infiltrate, and emergence of SPEM. In all 3 models, SPEM developed, at least in part, from transdifferentiation of chief cells. We further found that acute parietal cell loss in the setting of inflammation (L-635 treatment) led to more rapid induction and expansion of SPEM derived from transdifferentiation of chief cells. Conclusions These studies provide direct evidence by lineage tracing that SPEM evolves from differentiated chief cells. Thus, mature gastric chief cells have the ability to act as cryptic progenitors and reacquire proliferative capacity within the context of mucosal injury and inflammation.
Background
Antimicrobial resistance is a global public health problem, particularly in low‐ and middle‐income countries (LMICs), where antibiotics are often obtained without a prescription. H. pylori ...antimicrobial resistance patterns are informative for patient care and gastric cancer prevention programs, have been shown to correlate with general antimicrobial consumption, and may guide antimicrobial stewardship programs in LMICs. We report H. pylori resistance and antimicrobial utilization patterns for western Honduras, representative of rural Central America.
Methods
In the context of the western Honduras gastric cancer epidemiology initiative, gastric biopsies from 189 patients were studied for culture and resistance patterns. Antimicrobial utilization was investigated for common H. pylori treatment regimens from regional public (7 antimicrobials) and national private (4 antimicrobials) data, analyzed in accordance with WHO anatomical therapeutic chemical defined daily doses (DDD) method and expressed as DDD/1000 inhabitants per day (DID) and per year (DIY).
Results
H. pylori was successfully cultured from 116 patients (56% males, mean age: 54), and nearly all strains were cagA+ and vacAs1m1+ positive (99% and 90.4%, respectively). Unexpectedly, high resistance was noted for levofloxacin (20.9%) and amoxicillin (10.7%), while metronidazole (67.9%) and clarithromycin (11.2%) were similar to data from Latin America. Significant associations with age, gender, or histology were not noted, with the exception of levofloxacin (28%, P = 0.01) in those with histology limited to non‐atrophic gastritis. Total antimicrobial usage in western Honduras of amoxicillin (17.3 DID) and the quinolones had the highest relative utilizations compared with other representative nations.
Conclusions
We observed significant H. pylori resistance to amoxicillin and levofloxacin in the context of high community antimicrobial utilization. This has implications in Central America for H. pylori treatment guidelines as well as antimicrobial stewardship programs.
Background & Aims Helicobacter pylori –induced gastric carcinogenesis has been linked to the microbial oncoprotein cytotoxin-associated gene A (CagA). Spermine oxidase (SMO) metabolizes the polyamine ...spermine into spermidine and generates H2 O2 , which causes apoptosis and DNA damage. We determined if pathogenic effects of CagA are attributable to SMO. Methods Levels of SMO, apoptosis, and DNA damage (8-oxoguanosine) were measured in gastric epithelial cell lines infected with cagA+ or cagA− H pylori strains, or transfected with a CagA expression plasmid, in the absence or presence of SMO small interfering RNA, or an SMO inhibitor. The role of CagA in induction of SMO and DNA damage was assessed in H pylori –infected gastritis tissues from humans, gerbils, and both wild-type and hypergastrinemic insulin-gastrin mice, using immunohistochemistry and flow cytometry. Results cagA+ strains or ectopic expression of CagA, but not cagA− strains, led to increased levels of SMO, apoptosis, and DNA damage in gastric epithelial cells, and knockdown or inhibition of SMO blocked apoptosis and DNA damage. There was increased SMO expression, apoptosis, and DNA damage in gastric tissues from humans infected with cagA+ , but not cagA− strains. In gerbils and mice, DNA damage was CagA-dependent and present in cells that expressed SMO. Gastric epithelial cells with DNA damage that were negative for markers of apoptosis accounted for 42%–69% of cells in gerbils and insulin-gastrin mice with dysplasia and carcinoma. Conclusions By inducing SMO, H pylori CagA generates cells with oxidative DNA damage, and a subpopulation of these cells are resistant to apoptosis and thus at high risk for malignant transformation.
To evaluate the long-term effect of cumulative time exposed to
infection on the progression of gastric lesions.
795 adults with precancerous gastric lesions were randomised to receive anti-
treatment ...at baseline. Gastric biopsies were obtained at baseline and at 3, 6, 12 and 16 years. A total of 456 individuals attended the 16-year visit. Cumulative time of
exposure was calculated as the number of years infected during follow-up. Multivariable logistic regression models were used to estimate the risk of progression to a more advanced diagnosis (versus no change/regression) as well as gastric cancer risk by intestinal metaplasia (IM) subtype. For a more detailed analysis of progression, we also used a histopathology score assessing both severity and extension of the gastric lesions (range 1-6). The score difference between baseline and 16 years was modelled by generalised linear models.
Individuals who were continuously infected with
for 16 years had a higher probability of progression to a more advanced diagnosis than those who cleared the infection and remained negative after baseline (p=0.001). Incomplete-type IM was associated with higher risk of progression to cancer than complete-type (OR, 11.3; 95% CI 1.4 to 91.4). The average histopathology score increased by 0.20 units/year (95% CI 0.12 to 0.28) among individuals continuously infected with
. The effect of cumulative time of infection on progression in the histopathology score was significantly higher for individuals with atrophy (without IM) than for individuals with IM (p<0.001).
Long-term exposure to
infection was associated with progression of precancerous lesions. Individuals infected with
with these lesions may benefit from eradication, particularly those with atrophic gastritis without IM. Incomplete-type IM may be a useful marker for the identification of individuals at higher risk for cancer.
Helicobacter pylori is the principal cause of gastric cancer, the second leading cause of cancer mortality worldwide. However, H. pylori prevalence generally does not predict cancer incidence. To ...determine whether coevolution between host and pathogen influences disease risk, we examined the association between the severity of gastric lesions and patterns of genomic variation in matched human and H. pylori samples. Patients were recruited from two geographically distinct Colombian populations with significantly different incidences of gastric cancer, but virtually identical prevalence of H. pylori infection. All H. pylori isolates contained the genetic signatures of multiple ancestries, with an ancestral African cluster predominating in a low-risk, coastal population and a European cluster in a high-risk, mountain population. The human ancestry of the biopsied individuals also varied with geography, with mostly African ancestry in the coastal region (58%), and mostly Amerindian ancestry in the mountain region (67%). The interaction between the host and pathogen ancestries completely accounted for the difference in the severity of gastric lesions in the two regions of Colombia. In particular, African H. pylori ancestry was relatively benign in humans of African ancestry but was deleterious in individuals with substantial Amerindian ancestry. Thus, coevolution likely modulated disease risk, and the disruption of coevolved human and H. pylori genomes can explain the high incidence of gastric disease in the mountain population.
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