ABSTRACT
TLR4, a member of pattern recognition receptors, is the main receptor of LPS. MD-2 physically associates with TLR4 on the cell surface and confers LPS responsiveness. Helicobacter pylori LPS is one of the major virulence factors for induction of gastritis. We demonstrated in this study the role of MD-2 in TLR4-dependent signaling in H. pylori-associated gastritis. Gastric biopsy samples collected from patients with and without H. pylori infection and four gastric cancer cell lines were used for this study. TLR-4 and MD-2 expression in biopsy specimens and the cell lines was examined by using RT-PCR. Localization of TLR-4 in histological sections was evaluated by immunohistochemistry. For in vitro functional assays, we established stable transfectants of AGS cells expressing TLR4 and MD-2. Cellular distribution of TLR4 was examined by flow cytometry. NF-kappaB activation and activation of IL-8 and MD-2 promoters were assessed by reporter gene assay. H. pylori infection up-regulated the TLR4 and MD-2 expression in gastric mucosa. TLR4 staining was observed predominantly in epithelial cells, located in both the cytoplasm and at the apical surface. MD-2 transfection in AGS cells markedly increased cell surface expression of TLR4 and augmented the activation of NF-kappaB and IL-8 promoter upon stimulation with H. pylori LPS. Live H. pylori also stimulated transcriptional activation of MD-2. This study revealed that MD-2 expression is elevated in gastric epithelial cells during H. pylori infection, suggesting that the TLR4/MD-2 system is a potent receptor complex involved in the response to H. pylori LPS in the stomach.
Subject(s)
Antigens, Surface/metabolism , Gastritis/metabolism , Helicobacter Infections/immunology , Membrane Glycoproteins/metabolism , Receptors, Cell Surface/metabolism , Signal Transduction/physiology , Adult , Antigens, Surface/genetics , Female , Gastritis/immunology , Gastritis/microbiology , Genes, Reporter , Helicobacter Infections/metabolism , Helicobacter pylori/immunology , Helicobacter pylori/metabolism , Humans , Interleukin-8/genetics , Lipopolysaccharides/metabolism , Lymphocyte Antigen 96 , Male , Membrane Glycoproteins/genetics , Middle Aged , NF-kappa B/metabolism , Promoter Regions, Genetic , RNA, Messenger/metabolism , Receptors, Cell Surface/genetics , Toll-Like Receptor 4 , Toll-Like ReceptorsABSTRACT
Lafutidine is a novel histamine H(2)-receptor antagonist with a potent and long-lasting anti-acid secretory effect that has also been found to have a potent gastroprotective effect. We investigated the effect of lafutidine on gastric mucosal injury induced in rats with the use of water-immersion restraint stress (WRS) by examining serum calcitonin gene-related peptide (CGRP) concentrations, which we measured with the use of an enzyme immunometric assay. WRS-induced mucosal erosive injury in the stomach was reduced significantly by both lafutidine and famotidine pretreatment (from 7.79 +/- 2.02 mm(2) to 3.09 +/- 0.74 mm(2) and 4.05 +/- 1.18 mm(2), respectively). A single administration of lafutidine or famotidine did not change the serum CGRP concentration from the control value when these drugs were administered without WRS. Lafutidine pretreatment before WRS caused a significant increase in serum CGRP concentration compared with famotidine (lafutidine, 86.64 +/- 9.52 pg/mL; famotidine, 47.55 +/- 4.35 pg/mL; control, 58.43 +/- 6.07 pg/mL). Our results suggest that lafutidine augments CGRP release from the rat stomach when administered before the induction of WRS.
Subject(s)
Acetamides/pharmacology , Calcitonin Gene-Related Peptide/blood , Histamine H2 Antagonists/pharmacology , Immersion , Piperidines/pharmacology , Pyridines/pharmacology , Restraint, Physical , Stress, Physiological/blood , Animals , Famotidine/pharmacology , Male , Rats , Rats, Sprague-Dawley , Stomach Ulcer/etiology , Stomach Ulcer/prevention & control , Stress, Physiological/complications , WaterABSTRACT
Hypergastrinemia is known to cause hyperplasia of the gastric mucosa, especially in gastric enterochromaffinlike (ECL) cells. In some clinical conditions causing hypergastrinemia, such as long-term gastric-acid inhibition and gastric-mucosa atrophy, hyperplastic ECL cells may develop into gastric carcinoid tumors. A newly developed gastrin-receptor antagonist, S-0509, has been reported to block gastrin-induced stimulation of gastric-acid secretion. We therefore investigated whether S-0509 inhibits the omeprazole- and gastrin-stimulated hyperproliferation of gastric mucosa, especially of ECL cells. Daily administration of omeprazole and gastrin in male Sprague-Dawley rats induced marked hypergastrinemia and increased proliferation of gastric-mucosa cells. The numbers of ECL cells and of ECL cells producing messenger RNA for regenerating gene, a potent growth factor for gastric-mucosa cells, were also augmented by long-term administration of omeprazole and gastrin. Coadministration of S-0509 with omeprazole or gastrin almost completely inhibited the omeprazole- and gastrin-induced changes in gastric mucosa, including mucosal thickening and ECL hyperplasia. S-0509 did not induce gastric-mucosa atrophy, even when administered for as long as 4 weeks. In summary, we have found that a newly developed gastrin receptor antagonist, S-0509, inhibits omeprazole- and gastrin-induced mucosal hyperplasia, especially ECL-cell hyperplasia, in rats.
