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

Abstract

The present study was conducted to elucidate the mechanisms by which Helicobacter pylori (HP)-derived ammonia causes gastric mucosal injury. Intact sheets of guinea pig gastric fundic mucosae were incubated in Ussing chambers. Both the luminal and the serosal pH were kept at 7.4. Transmucosal potential difference (PD) and electrical resistance (R) were monitored as indices of mucosal integrity. Restitution was evaluated by recovery of PD, R, and transmucosal [(3)H]mannitol flux after Triton X-100-induced mucosal injury. The effects of luminal or serosal NH(4)Cl on function and morphology of uninjured or injured mucosae were examined. In uninjured mucosae, serosal NH(4)Cl induced more profound decreases in PD and R and more prominent vacuolation in gastric epithelial cells than did luminal NH(4)Cl. In contrast, luminal NH(4)Cl markedly inhibited restitution in injured mucosae and caused an extensive vacuolation in gastric epithelial cells, as did serosal NH(4)Cl. Transmucosal ammonia flux was greater in the injured than in the uninjured mucosae. These results suggest that 1) basolateral membrane of gastric epithelial cells is more permeable to ammonia than apical membrane and 2) luminal ammonia, at concentrations detected in HP-infected gastric lumen, retards restitution in injured mucosae.

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

“…Animal models of gastrointestinal barrier function and various studies on epithelial cells confirm that ammonium exerts cytotoxic effects and induces apoptotic cell death in gastric mucosa (Suzuki et al, 2000(Suzuki et al, , 2002Smoot et al, 1990;Hagen et al, 2000). As an uncharged small molecule, ammonia (NH 3 ) permeates the luminal side of membranes (Suzuki et al, 2000;Lichtenberger & Romero, 1994;Kleiner, 1981), and the charged ammonium ion (NH et al, 2002;Sidebotham et al, 2003). The local elevation of mucosal surface pH during H. pylori infection can lead to ammonium-induced gastric injury, which may contribute to the opening of tight junctions that has been ascribed to virulence factors such as the vacuolating cytotoxin VacA and the cytotoxin-associated antigen CagA (Papini et al, 1998;Amieva et al, 2003;Blaser & Atherton, 2004).…”

“…Animal models of gastrointestinal barrier function and various studies on epithelial cells confirm that ammonium exerts cytotoxic effects and induces apoptotic cell death in gastric mucosa (Suzuki et al, 2000(Suzuki et al, , 2002Smoot et al, 1990;Hagen et al, 2000). As an uncharged small molecule, ammonia (NH 3 ) permeates the luminal side of membranes (Suzuki et al, 2000;Lichtenberger & Romero, 1994;Kleiner, 1981), and the charged ammonium ion (NH et al, 2002;Sidebotham et al, 2003).…”

Isothiocyanate Inhibits Restitution and Wound Repair after Injury in the Stomach: Ex Vivo and in Vitro Studies

“…5). ATP and nonhydrolyzable analogs of ATP, such as ␣,␤-methyl-ATP and 2-methylthio-ATP would be expected to bind P2-type purinoreceptors on the cell surface (Bü ltmann and Starke, 1994;Suzuki et al, 2000) and to accelerate the rate of wound repair (Dignass et al, 1998;Chen et al, 2006). Figure 5A shows that wound repair in RGM1 cells is unaffected by ATP.…”

New Frontiers in Gut Nutrient Sensor Research: Prophylactic Effect of Glutamine Against Helicobacter pylori–Induced Gastric Diseases in Mongolian Gerbils

“…These results suggest the pathogenic importance of urease-derived ammonia, rather than that of VacA or gene product of Cag PAI, in the formation of gastritis induced by H. pylori. Indeed, a number of studies showed that ammonia, at a concentration detectable in the gastric juice of H. pylori-infected patients, in hibits gastric epithelial proliferation (12), retards restitution (13), and induces mucosal cell death (14 -17) and by so, doing impairs the gastric mucosal barrier function.…”