Helicobacter pylori induces apoptosis in Barrett's-derived esophageal adenocarcinoma cells

Prevalence of Helicobacter pylori infection among patients with esophageal carcinoma

BACKGROUND

Helicobacter pylori (H. pylori) is a widespread microorganism related to gastric adenocarcinoma (AC). In contrast, it has been reported that an inverse association exists between H. pylori infection and esophageal carcinoma. The mechanisms underlying this supposedly protective effect remain controversial.

AIM

To determine the prevalence of H. pylori infection in esophageal carcinoma patients, we performed a retrospective observational study of esophageal tumors diagnosed in our hospital.

METHODS

We retrospectively reviewed the prevalence of H. pylori infection in a cohort of patients diagnosed with esophageal carcinoma. Concomitant or previous proton pump inhibitor (PPI) usage was also recorded.

RESULTS

A total of 89 patients with esophageal carcinoma (69 males, 77.5%), with a mean age of 66 years (range, 26-93 years) were included. AC was the most frequent pathological variant (n = 47, 52.8%), followed by squamous cell carcinoma (n = 37, 41.6%). Fourteen ACs (29.8%) originated in the gastroesophageal junction and 33 (70.2%) in the esophageal body. Overall, 54 patients (60.7%) presented at stages III and IV. Previous H. pylori infection occurred only in 4 patients (4.5%), 3 with AC (6.3% of all ACs) and 1 with squamous cell carcinoma (2.7% of all squamous cell tumors). All patients with previous H. pylori infection had stage III-IV. Only one patient had received prior H. pylori eradication therapy, whereas 86 (96.6%) had received previous or concomitant PPI treatment.

CONCLUSION

In our cohort of patients, and after histologic evaluation of paraffin-embedded primary tumors, we found a very low prevalence of previous H. pylori infection. We also reviewed the medical history of the patients, concluding that the majority had received or were on PPI treatment. The minimal prevalence of H. pylori infection found in this cohort of patients with esophageal carcinoma suggests a protective role.

Relationship between pathogenic microorganisms and the occurrence of esophageal carcinoma based on pathological type: a narrative review

INTRODUCTION

Esophageal cancer (EC) is one of the most common malignant tumors of the upper gastrointestinal tract. The etiology of EC is complicated and increasing evidence has shown that microbial infection is closely related to the occurrence of various malignant tumors. Though many studies have been focused on this subject in recent years, the exact relationship between microbial infection and the occurrence of EC remains unclear.

AREAS COVERED

In this review, we searched all eligible literature reports, summarized the most recent studies in this research field, and analyzed the pathogenic microorganisms associated with EC, providing the latest evidence and references for the prevention of pathogenic microorganism-related EC.

EXPERT OPINION

In recent years, increasing evidence has shown that pathogenic microbial infections are closely associated with the development of EC. Therefore, it is necessary to describe in detail the relationship between microbial infection and EC and clarify its possible pathogenic mechanism, which will shed a light on clinical prevention and treatment of cancer caused by pathogenic microbial infection.

Association Between Helicobacter pylori Infection and Short-segment/Long-segment Barrett's Esophagus in a Japanese Population: A Large Cross-Sectional Study

GOAL

The goal of this study was to investigate the relationship between Helicobacter pylori (H. pylori) infection and short-segment and long-segment Barrett's esophagus (SSBE and LSBE).

BACKGROUND

H. pylori infection is reported to be inversely associated with Barrett's esophagus (BE) in western countries. However, the impact of BE segment length on the association between BE and H. pylori infection has scarcely been investigated.

MATERIALS AND METHODS

The study subjects were 41,065 asymptomatic Japanese individuals who took medical surveys between October 2010 and September 2017. Using this large database of healthy Japanese subjects, we investigated the association between H. pylori infection and SSBE/LSBE. We used multivariable logistic regression analysis to estimate odds ratios (ORs) and 95% confidence intervals (CIs).

RESULTS

Among the study subjects, 36,615 were eligible for the analysis. H. pylori seropositivity was significantly associated with a lower rate of LSBE (OR: 0.42; 95% CI: 0.16-0.91) and a higher rate of SSBE (OR: 1.66; 95% CI: 1.56-1.78) after multivariate adjustment. In the subgroup analysis, H. pylori seropositivity was significantly associated with a high rate of SSBE in subjects without reflux esophagitis (RE) (OR: 1.73; 95% CI: 1.61-1.85). However, H. pylori seropositivity was not associated with SSBE in subjects with RE (OR: 1.07; 95% CI: 0.84-1.37).

CONCLUSION

In a Japanese population, H. pylori infection was inversely associated with LSBE but significantly associated with SSBE only in subjects without RE. H. pylori may be a risk factor for SSBE, especially in individuals without RE.

Systematic Review with Meta-analysis: Association of Helicobacter pylori Infection with Esophageal Cancer

Background

Helicobacter pylori is an important carcinogenic factor in gastric cancer. Studies have shown that Helicobacter pylori infection is inversely associated with certain diseases such as esophageal cancer and whose infection appears to have a “protective effect.” At present, the relationship between Helicobacter pylori infection and esophageal cancer remains controversial. This study was designed to investigate the relationship between Helicobacter pylori infection and the risk of esophageal cancer in different regions and ethnicities.

Methods

Systematic search of the articles on the relationship between Helicobacter pylori infection and esophageal cancer from the database with the duration time up to December 2018. This systematic review was performed under the MOOSE guidelines.

Results

This meta-analysis included 35 studies with 345,886 patients enrolled. There was no significant correlation between Helicobacter pylori infection and esophageal squamous cell carcinoma in the general population (OR: 0.84; 95% CI: 0.64-1.09/OR: 0.74; 95% CI: 0.54-0.97). However, a significant correlation was found in the Middle East (OR: 0.34; 95% CI: 0.22-0.52/95% CI: 0.26-0.44). There was no significant difference in the prevalence of Helicobacter pylori between the case group and the control group in esophageal adenocarcinoma (8.87% vs. 9.67%). The pooled OR was 0.55 (95% CI: 0.43-0.70) or 0.23 (95% CI: 0.15-0.36). When grouped by match or not, the pooled OR of the nonmatching group and the matching group was 0.48/0.21 (95% CI: 0.36-0.65/95% CI: 0.13-0.36) and 0.73/0.71 (95% CI: 0.57-0.92/95% CI: 0.60-0.84), respectively.

Conclusion

In the general populations, no significant association was found between Helicobacter pylori infection and the risk of esophageal squamous cell carcinoma. However, lower risk was found in the Middle East. Helicobacter pylori infection may reduce the risk of esophageal adenocarcinoma, but such “protection effect” may be overestimated.

Bacterial Composition of the Human Upper Gastrointestinal Tract Microbiome Is Dynamic and Associated with Genomic Instability in a Barrett's Esophagus Cohort

Background

The incidence of esophageal adenocarcinoma (EAC) has increased nearly five-fold over the last four decades in the United States. Barrett’s esophagus, the replacement of the normal squamous epithelial lining with a mucus-secreting columnar epithelium, is the only known precursor to EAC. Like other parts of the gastrointestinal (GI) tract, the esophagus hosts a variety of bacteria and comparisons among published studies suggest bacterial communities in the stomach and esophagus differ. Chronic infection with Helicobacter pylori in the stomach has been inversely associated with development of EAC, but the mechanisms underlying this association remain unclear.

Methodology

The bacterial composition in the upper GI tract was characterized in a subset of participants (n=12) of the Seattle Barrett’s Esophagus Research cohort using broad-range 16S PCR and pyrosequencing of biopsy and brush samples collected from squamous esophagus, Barrett’s esophagus, stomach corpus and stomach antrum. Three of the individuals were sampled at two separate time points. Prevalence of H. pylori infection and subsequent development of aneuploidy (n=339) and EAC (n=433) was examined in a larger subset of this cohort.

Results/Significance

Within individuals, bacterial communities of the stomach and esophagus showed overlapping community membership. Despite closer proximity, the stomach antrum and corpus communities were less similar than the antrum and esophageal samples. Re-sampling of study participants revealed similar upper GI community membership in two of three cases. In this Barrett’s esophagus cohort, Streptococcus and Prevotella species dominate the upper GI and the ratio of these two species is associated with waist-to-hip ratio and hiatal hernia length, two known EAC risk factors in Barrett’s esophagus. H. pylori-positive individuals had a significantly decreased incidence of aneuploidy and a non-significant trend toward lower incidence of EAC.

Chemoprevention in Barrett's oesophagus

Increasing incidence of oesophageal adenocarcinoma along with poor survival entails novel preventive strategies. Agents that target pro-oncogenic pathways in Barrett's mucosa could halt this neoplastic transformation. In this review, we will use epidemiological associations and molecular mechanisms to identify novel chemoprevention targets in Barrett's oesophagus. We will also discuss recent chemoprevention trials.

Association of Helicobacter pylori infection with esophageal adenocarcinoma and squamous cell carcinoma: a meta-analysis

To evaluate the relationship of Helicobacter pylori and cytotoxin-associated gene A (CagA) positive strains with esophageal neoplasm, including esophageal adenocarcinoma (EAC) and esophageal squamous cell carcinoma (ESCC), the authors conducted a meta-analysis using a predefined protocol. PubMed, Web of Science, China biology medical literature database, Wanfang, and China National Knowledge Infrastructure were searched for relevant articles from the first available year to April 8, 2013. The fixed or random effect pooled measure was selected based on heterogeneity among studies, which was evaluated using Q test and the I(2) of Higgins and Thompson. Metaregression was used to explore the sources of between-study heterogeneity. Publication bias was analyzed by Begg's funnel plot and Egger's regression test. The association was assessed by odds ratio (OR) with 95% confidence interval (CI). A total of 28 eligible studies were included in the meta-analysis. There was a significant inverse association between H. pylori infection (pooled OR, 0.57; 95% CI, 0.44-0.73) and EAC; CagA-positive H. pylori strains were less likely to be associated with EAC compared with CagA-negative strains (pooled OR, 0.64; 95% CI, 0.52-0.79). However, there was no statistically significant association between H. pylori/CagA-positive H. pylori strains infection and ESCC, and the pooled ORs were 1.16 (95% CI, 0.83-1.60) and 0.97 (95% CI, 0.79-1.19). But significant associations between CagA-positive H. pylori strains infection and ESCC risk were found in the stratified analysis of the study location (Asian and non-Asian), and the summary ORs were 0.74 (95% CI, 0.57-0.97) and 1.41 (95% CI, 1.02-1.94). H. pylori infection and CagA-positive strains are associated with decreased risk of EAC in the overall population. No significant association was found between H. pylori infection/CagA-positive strains and ESCC. But CagA-positive strains might have a positive association with ESCC in non-Asian population and an inverse association in Asian population.

Effect of Helicobacter pylori infection on esophageal epithelial cells in vitro

AIM: To investigate the effect of Helicobacter pylori (H. pylori) exposure on esophageal cell line OE33 in vitro.

METHODS: Human esophageal adenocarcinoma cell line OE33 was cultured and treated with 200 mmol/L acidified deoxycholic acid (pH 6.0) or infected with H. pylori 26695. After treatment or infection, cell viability was tested by CCK-8 assay; cell apoptosis was determined by flow cytometric analysis with Annexin V-FITC/7-AAD; the mRNA expression of CDX2 and MUC2 was assessed by real time-PCR; nuclear factor-kB (NF-kB)-associated proteins were examined by Western blot; and the DNA binding activity of NF-kB was evaluated by electrophoretic mobility shift assay (EMSA).

RESULTS: The viability of OE33 cells was reduced significantly after treatment with acidified deoxycholic acid or infection with H. pylori compared with negative controls (both P < 0.01). Treatment with acidified deoxycholic acid or infection with H. pylori induced apoptosis and increased the mRNA expression of CDX2 and MUC2 (all P < 0.01). Both H. pylori infection and treatment with acidified deoxycholic acid enhanced the DNA binding activity of NF-kB and the protein expression of phosphorylated IkBa and P65 in esophageal epithelial cells.

CONCLUSION: H. pylori infection reduces cell viability, induces apoptosis, and increases the expression of CDX2 and MUC2 and the activation of NF-kB in esophageal epithelial cells.

Helicobacter pylori infection and the risks of Barrett's oesophagus: a population-based case-control study

Infection with Helicobacter pylori is associated with significantly reduced risks of oesophageal adenocarcinoma; however, few studies have examined the association between H. pylori and Barrett's oesophagus (BO), the precursor lesion. We explored the relationship between H. pylori infection and BO and sought to identify potential modifiers. We compared the prevalence of positive H. pylori serology among 217 adults with simple BO (without dysplasia), 95 with dysplastic BO and 398 population controls sourced from the metropolitan Brisbane area. We determined H. pylori serostatus using enzyme-linked immunosorbent assay. To estimate relative risks, we calculated odds ratios (OR) and 95% confidence intervals (CI) using multivariable logistic regression in the entire sample and stratified by factors known to cause BO. The prevalence of H. pylori seropositivity was 12%, 3%, and 18%, respectively, among patients with simple BO, dysplastic BO and population controls. BO patients were significantly less likely to have antibodies for H. pylori (Simple BO: OR = 0.51, 95% CI: 0.30-0.86; Dysplastic BO: OR = 0.10, 95% CI: 0.03-0.33) than population controls. For simple BO, the association was diminished after adjustment for frequency of gastro-oesophageal reflux (GOR) symptoms. Adjustment for frequency of GOR symptoms did not substantially alter the observed effect for dysplastic BO. Although there was some variation in the magnitude of risk estimates across strata of age, sex, GOR symptoms and use of proton pump inhibitors or H2-receptor antagonists, the differences were uniformly nonsignificant. Helicobacter pylori infection is inversely associated with BO, and our findings suggest that decreased acid load is not the only mechanism underlying the H. pylori protective effect.

Association between Helicobacter pylori seropositivity and digestive tract cancers

AIM: To explore the role of Helicobacter pylori (H pylori) infection on the risk of digestive tract cancers.

METHODS: In total, 199 oral squamous-cell carcinoma (SCC), 317 esophageal SCC, 196 gastric cardia and non-cardia adenocarcinoma and 240 colon adenocarcinoma patients were recruited for serum tests of H pylori infection. Two hospital- and one community-based control groups were used for the comparisons. H pylori seropositivity was determined by an enzyme linked immunosorbent assay method against H pylori IgG.

RESULTS: Presence of H pylori infection was significantly inversely associated with esophageal SCC [adjusted odds ratio (AOR): 0.315-0.472, all P-value < 0.05] but positively associated with gastric adenocarcinoma (both cardia and non-cardia) (AOR: 1.636-3.060, all P-value < 0.05) in comparison to the three control groups. Similar results were not found in cancers of the oral cavity and colon.

CONCLUSION: Our findings support the finding that H pylori seropositivity is inversely associated with esophageal SCC risk, but increases the risk of gastric cardia adenocarcinoma.

Apoptotic effect of Helicobacter pylori on oesophageal squamous-cell carcinoma cells in vitro

BACKGROUND

The relationship between Helicobacter pylori (Hp) infection and oesophageal squamous-cell carcinoma (ESCC) risk is still inconclusive. Our previous study found an inverse association between the two, but its mechanism is still unknown. Thus, we conducted in vitro studies to clarify the issue.

MATERIALS AND METHODS

One ESCC (CE 81T/VGH) cell line was co-cultured with Hp, using one gastric adenocarcinoma (AGS) cell line as the control. Hp-induced cell apoptosis was determined by flow cytometry, terminal transferase-mediated dUTP nick end labelling (TUNEL) assay and staining; caspase-3 protein expressions in cell lysates were detected by Western immunoblot.

RESULTS

Increased apoptosis was found in CE 81T/VGH, but not in AGS cells, by flow cytometry and TUNEL assay after being co-cultured with Hp at the multiplicity of infection of 1/100 (but not at 1/400) for 36 h. The amount of activated caspase-3 (17/19 kDa) also increased in CE 81T/VGH, but not in AGS cells, after co-culturing with Hp at MOI of 1/100 for 36 h. The results were confirmed by triplicate experiments in which the different apoptotic assays remained consistent.

CONCLUSIONS

Our study provides indirect evidence of the inverse association between Hp infection and ESCC risk, which is possibly due to Hp-induced apoptosis in ESCC cells. A further in vivo study is necessary to confirm our findings.

Hyperosmotic stress enhances interleukin-1beta expression in Helicobacter pylori-infected murine gastric epithelial cells in vitro

BACKGROUND AND AIM

Gastric cancer is associated not only with Helicobacter pylori (H. pylori) infection, but also with the intake of a high salt diet. Interleukin-1beta (IL-1beta) is highly expressed in H. pylori-infected gastric mucosa. The aim of the present study was to determine if hyperosmotic stress induces IL-1beta expression in gastric epithelial cells in vitro.

METHOD

Murine gastric epithelial cells, GSM06, were cultured with or without H. pylori (Sydney strain-1) at different osmolarities in the range of 300-450 mOsM. Expressions of IL-1beta mRNA and mature IL-1beta protein were evaluated by reverse transcription-polymerase chain reaction (RT-PCR) and an IL-1beta enzyme-linked immunosorbent assay (ELISA), respectively. IL-1beta converting enzyme (ICE) activity was measured by an ICE colorimetric assay. Apoptosis was evaluated by a single stranded-DNA assay.

RESULTS

Addition of H. pylori at 300 mosM caused significant increases in IL-1beta mRNA, IL-1beta protein, ICE activity and apoptosis. Hyperosmotic stress alone also caused upregulation of IL-1beta mRNA and IL-1beta protein, enhanced ICE activity and accelerated apoptosis. Hyperosmotic stress accentuated the increases in IL-1beta mRNA, IL-1beta protein, ICE activity and apoptosis induced by H. pylori alone. Enhancement of IL-1beta protein release induced by hyperosmotic stress was significantly attenuated by an ICE inhibitor, Z-YVAD-FMK.

CONCLUSIONS

Hyperosmotic stress enhances the release of bioactive mature IL-1beta protein in H. pylori-infected gastric epithelial cells, in part by upregulating IL-1beta mRNA expression, and in part by enhancing ICE activity. These results may explain the mechanisms by which chronic intake of a high salt diet increases the risk of gastric cancer among H. pylori-infected human subjects.

Helicobacter pylori extract induces nuclear factor-kappa B, activator protein-1, and cyclooxygenase-2 in esophageal epithelial cells

Helicobacter pylori infection is recognized as the major cause of gastritis and gastric cancer; however, its role in the development of gastroesophageal reflux disease and Barrett's adenocarcinoma is unclear. The expression of NF-kappaB, AP-1, and COX-2 may be important in inflammation and tumorigenesis in the esophagus. The aim of this study was to examine the effect of live H pylori or H pylori extract (HPE) on these factors in the esophageal epithelial cell lines SKGT-4 and OE33. NF-kappaB and AP-1 activity were assessed by gel shift assay and COX-2 by Western blotting. Coculture of SKGT-4 and OE33 with live H pylori and HPE induced NF-kappaB and AP-1 DNA-binding activity, and also decreased IkappaB-alpha levels. Treatment with the specific MEK1/2 MAPK inhibitor PD98059, but not the p38 MAPK inhibitor SB203580, inhibited NF-kappaB and AP-1 activity. The antioxidant vitamin C inhibited H pylori-induced NF-kappaB activation, but increased AP-1 expression. Moreover, HPE induced COX-2 expression and IL-8 production, and PD98059 inhibited COX-2 expression, ERK1/2 phosphorylation, and IL-8 production. These data demonstrate that both live H pylori and HPE induce NF-kappaB and AP-1 expression in esophageal epithelial cells. The induction of such transcription factors may play a role in the specific immune response within Barrett's mucosa and may indirectly cause inflammation of the gastric cardia and the distal esophagus.

Mechanisms of disease: Carcinogenesis in Barrett's esophagus

The pathogenesis of cancer in Barrett's esophagus is multifactorial. Gastroesophageal reflux seems to be important in the initiation of Barrett's esophagus, but its role in promoting carcinogenesis has yet to be established. Diet, lifestyle and carcinogens, especially the nitrates, may be important in the development of carcinogenesis, and require further investigation. Inhibition of reflux-stimulated inflammatory changes, for example by inhibiting cyclooxygenase, holds promise for decreasing cancer progression. Similarly, dietary and lifestyle modification used in the management of reflux may also help to prevent the development of esophageal cancer. The molecular changes that are associated with the development of cancer in Barrett's esophagus offer several potential areas of intervention to prevent and manage esophageal cancer. Limiting cell growth, increasing apoptosis of damaged cells, limiting cell invasion and angiogenesis factors could be useful to accomplish this goal. Having a greater understanding of the pathogenesis of this condition can only help to develop more management options in the future.

New Molecular Concepts of Barrett’s Esophagus: Clinical Implications and Biomarkers

Barrett's esophagus (BE) represents the most serious histological consequence of gastroesophageal reflux disease (GERD) that develops in 5-10% of patients with GERD. Given that BE is the only known precursor to esophageal adenocarcinoma (EA), a systematic endoscopic biopsy protocol can detect EAs at an early stage. However, endoscopic and histopathological evaluation of BE are not adequate for effective screening of high risk patients. Therefore, molecular abnormalities associated with BE have been considered as surrogate markers and their use as such is proposed. Flow cytometry is the most useful adjunct to histology, and ploidy status of BE is an independent risk factor. Cyclin D1 overexpression is inversely correlated with survival in EA. C-erbB2 (+) patients have poorer prognosis. High plasma adenomatous polyposis coli levels correlate with reduced patient survival. p53 expression allows patient risk for EA stratification. Nuclear factor-kappaB overexpression inversely correlates with good response to adjuvant chemotherapy and radiotherapy in EA. Patients with cyclooxygenase-2 overexpression have reduced survival rates. Increased E-cadherin staining is associated with shorter survival in EA patients who received chemoradiotherapy. Finally, existing data cannot rule out a correlation between EA and colorectal tumors. Seventeen BE molecular alterations yielded noteworthy clinical implications. Apart from endoscopy and histology, these data allow for better risk stratification for patients with BE and for more efficient and timely therapeutic approaches.

Helicobacter pylori infection: a protective factor for esophageal squamous cell carcinoma in a Taiwanese population

AIM

Many researchers have reported the inverse relationship between Helicobacter pylori (H. pylori) infection and esophageal adenocarcinoma risk, but very few studies have examined the association between H. pylori infection and the development of esophageal squamous-cell carcinoma (ESCC). Therefore, the aim of this study is to evaluate the relationship between H. pylori infection and ESCC risk.

METHOD

Subjects were cancer cases, pathologically proven to have ESCC, in two large medical centers in Kaohsiung metropolitan of southern Taiwan between August 2000 and May 2003. Controls were from the healthy subjects who lived in Kaohsiung metropolitan and voluntarily participated in one large multiyear of gene-environmental study. In total, 127 cases (116 males and 11 females) and 171 controls (161 males and 10 females) were recruited in the same period of time for interviews. H. pylori seropositivity was determined by an enzyme-linked immunosorbant assay measuring IgG.

RESULTS

A total of 28 (22.1%) and 74 (43.3%) out of 127 cases and 171 controls, respectively, had positive H. pylori infection. After adjusting for other covariates, subjects with positive H. pylori infections had a significantly reduced risk (adjusted odds ratio (AOR) = 0.51; 95% CI = 0.27-0.96; p= 0.037) of developing ESCC than those without. This result was even more pronounced in the groups of younger subjects, nonsmokers, or nondrinkers. In addition, among the 117 cancer patients who provided information about site of cancer lesion, the present study found that subjects with cancer lesions in the lower third of the esophagus had significantly fewer positive H. pylori infections (AOR = 0.34; 95% CI = 0.14-0.80; p= 0.013) than controls.

CONCLUSION

Our findings suggest that H. pylori infection may protect against the development of ESCC. Additional studies are needed to confirm these findings.

Cellular vacuolation and mitochondrial cytochrome c release are independent outcomes of Helicobacter pylori vacuolating cytotoxin activity that are each dependent on membrane channel formation

Helicobacter pylori vacuolating toxin (VacA) is a secreted toxin that is reported to produce multiple effects on mammalian cells. In this study, we explored the relationship between VacA-induced cellular vacuolation and VacA-induced cytochrome c release from mitochondria. Within intoxicated cells, vacuolation precedes cytochrome c release and occurs at lower VacA concentrations, indicating that cellular vacuolation is not a downstream consequence of cytochrome c release. Conversely, bafilomycin A1 blocks VacA-induced vacuolation but not VacA-induced cytochrome c release, which indicates that cytochrome c release is not a downstream consequence of cellular vacuolation. Acid activation of purified VacA is required for entry of VacA into cells, and correspondingly, acid activation of the toxin is required for both vacuolation and cytochrome c release, which suggests that VacA must enter cells to produce these two effects. Single amino acid substitutions (P9A and G14A) that ablate vacuolating activity and membrane channel-forming activity render VacA unable to induce cytochrome c release. Channel blockers known to inhibit cellular vacuolation and VacA membrane channel activity also inhibit cytochrome c release. These data indicate that cellular vacuolation and mitochondrial cytochrome c release are two independent outcomes of VacA intoxication and that both effects are dependent on the formation of anion-selective membrane channels.