Mast cells are involved in the gastric hyperemic response to acid back diffusion via release of histamine

Histamine stimulation of MMP-1(collagenase-1) secretion and gene expression in gastric epithelial cells: role of EGFR transactivation and the MAP kinase pathway

BACKGROUND AND AIMS

GPCR stimulation by various ligands including histamine has been shown to transactivate the epidermal growth factor receptor (EGFR). This study examines the functional interactions between the H2 receptor and the EGFR in the regulation of matrix metalloproteinase-1 (MMP-1) secretion and gene expressions in cultured gastric epithelial cells.

METHODS

AGS cells were incubated for up to 24 h with either histamine or heparin binding-epidermal growth factor (HB-EGF) and MMP-1 release was determined by immunoassay. MMP-1 responses to histamine and HB-EGF were further tested by the use of H2 receptor antagonist, EGFR inhibitor and mitogen activator protein kinase (MAPK) inhibitor. The role of EGFR in MMP-1 release was further tested in cells transfected with specific EGFR siRNA. EGFR and ERK1/2 phosphorylation was determined by Western blot analysis. MMP-1 gene expression was determined by RNase protection assay (RPA).

RESULTS

Histamine and HB-EGF caused a dose-dependent release of MMP-1 with maximal responses that were 2.7- and 4.5-fold greater, respectively, than control, P<0.001. Famotidine prevented histamine-mediated MMP-1 release and AG1478 and EGFR siRNA completely inhibited MMP-1 secretion stimulated by both histamine and HB-EGF. Both histamine and HB-EGF stimulation of MMP-1 release was associated with activation of ERK1/2. MAPK inhibition also prevented histamine-and HB-EGF-induced MMP-1 secretion. Results of MMP-1 gene expression, either stimulatory or inhibitory, paralleled responses to MMP-1 secretion.

CONCLUSION

Histamine stimulation of the H2 receptor on AGS cells evoked MMP-1 secretion and gene up regulation that was dependent on transactivation of the EGFR and downstream activation of MAPK.

Role of bradykinin in gastric vasodilation caused by hypertonic saline and acid back diffusion

Protective vasodilation in response to tissue injury and acid back diffusion is associated with release of bradykinin in the rat stomach. We hypothesized that bradykinin might be involved in mechanisms behind such vasodilation via influence on mast cells and sensory neurons. Acid back diffusion after mucosal barrier disruption with hypertonic saline evoked degranulation of mast cells in the rat stomach wall. Acid back diffusion was also associated with increased luminal release of histamine and gastric blood flow in normal rats, but not in mast cell-deficient rats. Bradykinin (BK(2)) receptor blockade inhibited degranulation of submucosal mast cells in the stomach and attenuated gastric vasodilation both in response to acid back diffusion and after stimulation of sensory neurons with capsaicin. Gastric vasodilation caused by mucosal injury with hypertonic saline alone was associated with degranulation of mucosal mast cells. These events were unaffected by inhibition of prostaglandin synthesis, whereas bradykinin (BK(2)) receptor blockade was associated with abolished vasodilation and inhibition of mucosal mast cell degranulation. We conclude that bradykinin is involved in gastric vasodilation caused by hypertonic injury alone via influence on mast cells, and by acid back diffusion via influence on both sensory neurons and mast cells.

Gastroprotective effect of leptin on gastric mucosal injury induced by ischemia-reperfusion is related to gastric histamine content in rats

Leptin has cytoprotective effect to gastric mucosal injury in rats. We aimed to test the hypothesis that leptin induced histamine is involved in the prevention of ischemia-reperfusion (I/R) induced gastric mucosal injury in rats. At the end of the 30 min celiac artery occlusion and 12h reperfusion process, serum and gastric tissue samples were taken from three group of rats to measure oxidative status, histamine levels and for histological examinations. Leptin decreased ulcer and polymorphonuclear leukocyte (PMNL) index, and serum malondialdehyde (MDA) and protein carbonyl content but increased gastric tissue histamine levels. We concluded that leptin exerts a protective effect on gastric mucosa to I/R induced gastric injury probably through increasing tissue histamine content which, in turn, maintain the gastric mucosal blood flow.

Gastroduodenal mucosal defense: an integrated protective response

The mechanisms by which the gastroduodenal mucosa maintains viability and normal functioning despite its intensely caustic environment have puzzled clinicians and investigators alike for at least 150 years. Protective mechanisms have been divided into three main categories: preepithelial (mucus and bicarbonate secretion), epithelial (cellular buffering, mucosal architecture and permeability), and postepithelial mechanisms (mucosal blood flow). Within each category are many other factors that bear on the ability of the mucosa to withstand constant changes of luminal pH. We will summarize some of the recent findings that pertain to the nature and regulation of these defense mechanisms in the context of a historical overview. Therapeutic implications of these findings will also be presented in the discussion of novel antiinflammatory compounds designed to upregulate simultaneously several defensive mechanisms, with the expectation that gastroduodenal damage will be minimized.

Histamine is involved in gastric vasodilation during acid back diffusion via activation of sensory neurons

Protective vasodilation during acid back diffusion into the rat gastric mucosa depends on activation of sensory neurons and mast cell degranulation with histamine release. We hypothesized that these two mediator systems interact and that histamine partly exerts its effect via sensory nerves. Gastric blood flow (GBF) and luminal histamine were measured in chambered stomachs, and mast cell numbers were assessed by morphometry. Ablation of sensory neurons and depletion of mast cells were produced by pretreatment with capsaicin or dexamethasone, respectively. Mucosal exposure to 1.5 M NaCl and then to pH 1.0 saline in ablated and control rats caused increased luminal histamine and reduced numbers of mast cells. Enterochromaffin-like cell marker pancreastatin remained unchanged. Only control rats responded with an increase in GBF. Capsaicin stimulation (640 microM) of the undamaged mucosa induced identical increase in GBF and unchanged mast cell mass in normal and dexamethasone-treated rats. Increase in GBF after topical exposure to histamine (30 mM) in rats pretreated with capsaicin or a calcitonin gene-related peptide (CGRP)(1) antagonist human CGRP(8-37) or exposed to the calcium pore blocker ruthenium red was less than one-half of that in control rats. These data suggest that mast cell-derived histamine is involved in gastric vasodilatation during acid back diffusion partly via sensory neurons.