Luminal ammonia retards restitution of guinea pig injured gastric mucosa in vitro

Helicobacter pylori Uses the TlpB Receptor To Sense Sites of Gastric Injury

Helicobacter pylori is a pathogen that chronically colonizes the stomachs of approximately half of the world's population and contributes to the development of gastric inflammation. We demonstrated previously in vivo that H. pylori uses motility to preferentially colonize injury sites in the mouse stomach. However, the chemoreceptor responsible for sensing gastric injury has not yet been identified. In this study, we utilized murine gastric organoids (gastroids) and mutant H. pylori strains to investigate the components necessary for H. pylori chemotaxis. High-intensity 730-nm light (two-photon photodamage) was used to cause single-cell damage in gastroids, and repair of the damage was monitored over time; complete repair occurred within ∼10 min in uninfected gastroids. Wild-type H. pylori accumulated at the damage site after gastric damage induction. In contrast, mutants lacking motility (ΔmotB) or chemotaxis (ΔcheY) did not accumulate at the injury site. Using mutants lacking individual chemoreceptors, we found that only TlpB was required for H. pylori accumulation, while TlpA, TlpC, and TlpD were dispensable. All strains that were able to accumulate at the damage site limited repair. When urea (an identified chemoattractant sensed by TlpB) was microinjected into the gastroid lumen, it prevented the accumulation of H. pylori at damage sites. Overall, our findings demonstrate that H. pylori colonizes and limits repair at damage sites via chemotactic motility that requires the TlpB chemoreceptor to sense signals generated by gastric epithelial cells.

Quantification of Mg2+, Ca2+ and H+ transport by the gastrointestinal tract of the goldfish, Carassius auratus, using the Scanning Ion-selective Electrode Technique (SIET)

An in vitro gut-sac technique and the scanning ion-selective electrode technique (SIET) were used to characterize Mg²⁺, Ca²⁺, and H⁺ transport at both the mucosal and serosal surfaces of non-everted and everted gastrointestinal tissues obtained from Carassius auratus. As part of the study, two magnesium ionophores were compared (II vs. VI). Unfed animals displayed uniform transport of all ions along the intestine. Feeding resulted in elevated Mg²⁺ and Ca²⁺ transport when the gut lumen contained chyme however, under symmetrical conditions this increased transport rate was absent. Furthermore, zonation of divalent cation transport was present for both Ca²⁺ and Mg²⁺ under non-symmetrical conditions while the zonation remained for Ca²⁺ alone under symmetrical conditions. High dietary Mg²⁺ decreased absorption and induced secretion of Mg²⁺ in the posterior intestine. Uptake kinetics in the esophagus suggest large diffusive and/or convective components based on a linear relationship between Mg²⁺ transport and concentration and lack of inhibition by ouabain, an inhibitor of Na⁺-K⁺-ATPase. In contrast, kinetics in the rectum were suggestive of a low affinity, saturable carrier-mediated pathway. A decrease in Mg²⁺ and Ca²⁺ transport was observed in the posterior intestine (both at the mucosal and serosal surfaces) in response to ouabain. This impact was greatest for Ca²⁺ transport and when applied to the mucosal fluid and measured in everted preparations. In contrast a putative Mg²⁺ transport inhibitor, cobalt(III)hexamine-chloride, did not affect Mg²⁺ transport. This is the first study to use SIET approaches to study ion transport in the gut of teleost fish. This is also the first study to provide characterization of Mg²⁺ transport in the gut of C. auratus. Due to the limited selectivity of Magnesium ionophore II, subsequent studies of tissues bathed in physiological saline should be made using Magnesium Ionophore VI.

New frontiers in gut nutrient sensor research: prophylactic effect of glutamine against Helicobacter pylori-induced gastric diseases in Mongolian gerbils

Ammonia is one of the important toxins produced by Helicobacter pylori (H. pylori), the major cause of peptic ulcer diseases. We examined whether glutamine or marzulene (a gastroprotective drug containing 1% sodium azulene and 99% glutamine) protects the gastric mucosa against H. pylori in vivo and investigated the mechanism underlying glutamine-induced mucosal protection against ammonia in gastric epithelial cells in vitro. Mongolian gerbils were fed for 3 months with a diet containing glutamine (2%-20%) or marzulene (20%) starting from 2 weeks or 2 years after H. pylori infection. Then, gastric mucosal changes were evaluated both macro- and microscopically. Cultured gastric epithelial cells were incubated in the presence of ammonia, with or without glutamine; and cell viability, ammonia accumulation, and chemokine production were determined. Gerbils exhibited edema, congestion, and erosion after 3-month infection; and after 2-year infection, they showed cancer-like changes in the gastric mucosa. Glutamine and marzulene significantly suppressed these pathological changes caused in the gastric mucosa by H. pylori infection. Ammonia was accumulated in the cells, resulting in an increase in chemokine production and a decrease in cell viability. These pathological responses were prevented by glutamine. In addition, glutamine decreased chemokine production and cell death through inhibition of cellular accumulation of ammonia, resulting in the prevention of H. pylori-induced gastric diseases in vivo. These results suggest that glutamine/marzulene would be useful for prophylactic treatment of H. pylori-induced gastric diseases in patients.

Inflammation and foveolar hyperplasia are reduced by supplemental dietary glutamine during Helicobacter pylori infection in mice

We recently showed that L-Gln protects cultured gastric cells from ammonia-induced cell death and predicted that Gln may also protect during Helicobacter pylori infection in vivo. Thus, the aim of this study was to test whether supplemental dietary Gln protects against H. pylori-associated pathology. For this, C57BL/6 mice were fed a purified diet consisting of 20.3% protein (1.9% Gln), 66% carbohydrate, and 5% fat or 25.3% protein (5% supplemental L-Gln; 6.9% total Gln), 61% carbohydrate, and 5% fat. After a 2-wk prefeeding period, mice were divided into sham-(uninfected) or H. pylori-infected groups. Body weight and food consumption were recorded weekly. Tissue histopathology, H. pylori colonization, serum IgG, and pro- and antiinflammatory cytokine mRNA expression were determined at 6, 12, and 20 wk postinfection (wkPI). Inflammation, antiinflammatory cytokine, and interleukin-1beta mRNA expression were significantly greater at 6 wkPI in H. pylori-infected mice fed supplemental Gln compared with those fed the control diet. At 20 wkPI, however, inflammation and foveolar hyperplasia were significantly lower in H. pylori-infected mice fed supplemental Gln compared with those fed the control diet. Body weight gain, food consumption, H. pylori colonization, and serum IgG did not differ in H. pylori-infected mice fed supplemental Gln compared with the control diet. Our data demonstrate that H. pylori-infected mice fed supplemental dietary Gln have reduced H. pylori-associated pathology in vivo that is accompanied by beneficial changes in the immune response to H. pylori early in infection. Thus, Gln supplementation may be an alternative therapy for reducing H. pylori-associated pathology.

Isothiocyanate inhibits restitution and wound repair after injury in the stomach: ex vivo and in vitro studies

The role of isothiocyanate (ITC) in blocking epithelial restitution after injury and in the recovery of round wounds was examined in the ex vivo guinea pig stomach and in rat gastric mucosal-1 (RGM1) cells, respectively. For this, recovery of transepithelial electrical resistance and morphology after injury or the closure of round wounds was evaluated in the presence of 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS) or 4,4-diisothiocyanatodihydrostilbene-2,2'-disulfonic acid (H2DIDS) (two ITC groups), 4-acetamido-4-isothiocyanatostilbene-2,2'-disulfonic acid (SITS) (one ITC group), or 4,4-diinitrostilbene-2,2'-disulfonic acid (DNDS) (no ITC groups). Wounded RGM1 cells were also incubated with bicarbonate-free buffer, ATP, barium, or phloretin to determine the mechanism of ITC inhibition. At 300 microM, DIDS or H2DIDS blocked restitution and wound repair by 100%, SITS blocked wound repair by 50%, and DNDS blocked wound repair by 2%. These results demonstrate the dependence of restitution and wound repair on ITC. ITC-binding purino (ATP) receptors and KATP channels were investigated as potential sites of inhibition, but they were found not to be the target of ITC in wound repair. Phloretin, blocking the monocarboxylate transporter (MCT), dose-dependently inhibited wound repair, and this result was exacerbated when the sodium bicarbonate cotransporter (NBC) was also blocked by bicarbonate-free conditions, resulting in 100% inhibition of wound repair with no reduction in viability when both transporters were blocked simultaneously. ITC potently inhibits both MCT and NBC, which may account for the inhibitory action of DIDS during restitution and wound repair. Reverse transcription-polymerase chain reaction data verified that MCT-1 is expressed in RGM1 cells. In conclusion, our results suggest that bicarbonate and monocarboxylate transport may work cooperatively to facilitate restitution of the gastric mucosa after injury.

Effects of Helicobacter pylori infection on gastric epithelial cell kinetics in patients with chronic renal failure

AIM

To evaluate the effects of Helicobacter pylori infection on gastric epithelial cell kinetics in patients with chronic renal failure (CRF).

METHODS

Forty-four patients were enrolled in this study and divided into four groups with respect to their Helicobacter pylori (H pylori) and CRF status. Groups were labeled as follows: 1a: normal renal function, H pylori negative (n = 12), 1b: normal renal function, H pylori positive (n = 11), 2a: CRF, H pylori negative (n = 10), 2b: CRF, H pylori positive (n = 11). Upper gastrointestinal endoscopy was done in all the patients involved in the study. During endoscopical investigation, antral biopsy specimens were taken from each patient. In order to evaluate the cell apoptosis and proliferation in gastric epithelial cells, Bax and proliferating cell nuclear antigen (PCNA) labeling indexes (LI) were assessed with immunohistochemical staining method.

RESULTS

For groups 1a, 1b, 2a, and 2b, mean Bax LI was identified as 34.4+/-13.7, 44.1+/-16.5, 46.3+/-20.5, 60.7+/-13.8, respectively and mean PCNA LI was identified as 36.2+/-17.2, 53.6+/-25.6, 59.5+/-25.6, 67.2+/-22, respectively. When the one-way ANOVA test was applied, statistically significant differences were detected between the groups for both Bax LI (P = 0.004 <0.01) and PCNA LI (P = 0.009 <0.01). When groups were compared further in terms of Bax LI and PCNA LI with Tukeyos HSD test for multiple pairwise comparisons, statistically significant difference was observed only between groups 1a and 2b (P = 0.006 <0.01).

CONCLUSION

In gastric epithelial cells, expression of both the pre-apoptotic protein Bax and the proliferation marker PCNA increase with H pylori infection. This increase is more evident in patients with uremia. These findings suggest that uremia accelerates apoptosis and proliferation in gastric epithelial cells.

Production of ammonium by Helicobacter pylori mediates occludin processing and disruption of tight junctions in Caco-2 cells

Tight junctions, paracellular permeability barriers that define epithelial cell polarity, play an essential role in transepithelial transport, cell-cell adhesion and lymphocyte transmigration. They are also important for the maintenance of innate immune defence and intestinal antigen uptake. Ammonium (NH4+) is elevated in the gastric aspirates of Helicobacter pylori-infected patients and has been implicated in the disruption of tight-junction functional integrity and the induction of gastric mucosal damage during H. pylori infection. The precise mechanism of the effect of ammonium and the molecular targets of ammonium in host tissue are not yet identified. To study the effects of ammonium on epithelial tight junctions, the human colon carcinoma cell line Caco-2 was cultured on permeable supports and the transepithelial resistance (TER) was measured at different time intervals following exposure to ammonium salts or H. pylori-derived ammonium. A biphasic response to treatment with ammonium was found. Acute exposure to ammonium salts or NH3/NH4+ derived from urea metabolism by wild-type H. pylori resulted in a 20-30 % decrease in TER. After 24 h, the NH4Cl-treated cells showed a partial recovery of TER. In contrast, the control culture, or cultures that were exposed to supernatants derived from urease-deficient H. pylori, showed no significant decrease in TER. Occludin-specific immunoblots revealed the expression of a low-molecular-weight form of occludin of 42 kDa upon NH3/NH4+ exposure. The results indicate that modulation of tight-junction function by H. pylori is ammonium-dependent and linked to the accumulation of a low-molecular-weight and detergent-soluble form of occludin.

Restitution of the bullfrog gastric mucosa is dependent on a DIDS-inhibitable pathway not related to HCO3- ion transport

This study was conducted to determine the contribution of ion transport to restitution after injury in the gastric mucosa. For this, intact sheets of stomach from the bullfrog, Rana catesbeiana, were mounted in Ussing chambers. Restitution was evaluated in the presence or absence of ion transport inhibitors amiloride, DIDS, and bumetanide to block Na(+)/H(+) exchange, Cl(-)/HCO(3)(-) exchange and Na(+)/HCO(3)(-) co-transport, and Na(+)-K(+)-2Cl(-) cotransport, respectively. Ion substitution experiments with Na(+)-free, Cl(-)-free, and HCO(3)(-)-free solutions were also performed. Injury to the mucosa was produced with 1 M NaCl, and restitution was evaluated by recovery of transepithelial resistance (TER), mannitol flux, and morphology. Amiloride, bumetanide, Cl(-)-free, or HCO(3)(-)-free solutions did not affect restitution. In Na(+)-free solutions, recovery of TER and mannitol flux did not occur because surface cells did not attach to the underlying basement membrane. In contrast, all aspects of restitution were inhibited by DIDS, a compound that inhibits Na(+)-dependent HCO(3)(-) transport. Because HCO(3)(-)-free solutions did not inhibit restitution, it was concluded that DIDS must block a yet undefined pathway not involved in HCO(3)(-) ion transport but essential for cell migration after injury and restitution in the gastric mucosa.

Blood-brain barrier permeability to ammonia in liver failure: a critical reappraisal

In patients with acute liver failure (ALF), hyperammonemia is related to development of cerebral edema and herniation. The present review discusses the mechanisms for the cerebral uptake of ammonia. A mathematical framework is provided to allow a quantitative examination of whether published studies can be explained by the conventional view that cerebral uptake of ammonia is restricted to diffusion of the unprotonated form (NH(3)) (the diffusion hypothesis). An increase in cerebral blood flow (CBF) enhanced ammonia uptake more than expected, possibly due to recruitment or heterogeneity of brain capillaries. Reported effects of pH on ammonia uptake were in the direction predicted by the diffusion hypothesis, but often less pronounced than expected. The published effects of mannitol, cooling, and indomethacin in experimental animals and patients were difficult to explain by the diffusion hypothesis alone, unless dramatic changes of capillary surface area or permeability for ammonia were induced. Therefore we considered the possible role of membrane protein mediated transport of NH(4)(+) across the blood-brain barrier (BBB). Early tracer studies in Rhesus monkeys suggested that NH(4)(+) is responsible for 20% or even more of the transport of ammonia from plasma to brain. In other locations, such as in the thick ascending limb of Hendle's loop and in isolated astrocytes, transport protein mediated translocation of NH(4)(+) is predominant. Many of the ion-transporters involved in renal NH(4)(+) reabsorbtion are also present in brain capillary membranes and could mediate uptake of NH(4)(+). Astrocytic uptake of NH(4)(+) is associated with increased extracellular K(+), which is a potent cerebral vasodilator. Such interference between transport of NH(4)(+) and other cations could be clinically important because increased cerebral blood flow often precedes cerebral herniation in acute liver failure. We suggest that protein mediated transport of NH(4)(+) through the brain capillary wall is a realistic possibility that should be more intensely studied.

Role of glutamine and arginase in protection against ammonia-induced cell death in gastric epithelial cells

Ammonia is a cytotoxic factor produced during Helicobacter pylori infection that may reduce the survival of surface epithelial cells. Here we examine whether ammonia kills cells and whether L-glutamine (L-Gln) protects against cell death by stimulating ammonia detoxification pathways. Cell viability and vacuolation were quantified in rat gastric epithelial (RGM1) cells incubated with ammonium chloride at pH 7.4 in the presence or absence of L-Gln. Incubation of RGM1 cells with ammonium chloride caused a dose-dependent increase in cell death and vacuolation, which were both inhibited by L-Gln. We show that RGM1 cells metabolize ammonia to urea via arginase, a process that is stimulated by L-Gln and results in reduced ammonia cytotoxicity. L-Gln also inhibits the uptake and facilitates the extrusion of ammonia from cells. Blockade of glutamine synthetase did not reduce the survival of RGM1 cells, demonstrating that the conversion of L-glutamate and ammonia to L-Gln is not involved in ammonia detoxification. Thus our data support a role for L-Gln and arginase in protection against ammonia-induced cell death in gastric epithelial cells.

Ammonia-induced apoptosis is accelerated at higher pH in gastric surface mucous cells

Gastric luminal ammonia produced by Helicobacter pylori has been shown to cause gastric mucosal injury. This study was conducted to examine the mechanisms by which gastric luminal ammonia causes apoptosis of gastric epithelial cells. Monolayers of GSM06 cells, developed from murine gastric surface mucous cells, were cultured in the absence or presence of 10-30 mM NH(4)Cl at ambient pH of 5.0, 6.0, and 7.0. In the presence of luminal NH(4)Cl, GSM06 cells showed 1) cell shrinkage and nuclear chromatin condensation, 2) DNA fragmentation into oligonucleosomes, 3) leakage of cytochrome c into cytosolic fraction without affecting bax expression, and 4) increases in activity of caspases-3 and -9. These changes were accentuated when the cells were cultured at pH 7.0. In the absence of NH(4)Cl, none of these changes was detected at any pH examined. These results suggest that gastric luminal ammonia, at concentrations detected in H. pylori-infected subjects, induces apoptosis of gastric epithelial cells by release of cytochrome c from mitochondria, followed by activation of caspases-9 and -3, especially at higher ambient pH.