Non-steroidal anti-inflammatory drugs and prostaglandin effects on pepsinogen secretion by dispersed human peptic cells

Inhibition of acid secretion by the nonsteroidal anti-inflammatory drugs diclofenac and piroxicam in isolated gastric glands: analysis of a multifocal mechanism

In nonstimulated rabbit gastric glands, acetylsalicylic acid (10-500 microM) and indomethacin (3-300 microM) did not significantly modify the basal rate of acid secretion, whereas diclofenac and piroxicam (10-1,000 microM each) caused a marked and dose-dependent inhibitory effect (EC(50) = 138 and 280 microM, respectively). In gastric glands stimulated by histamine (100 microM), diclofenac also reduced the rate of acid formation in a dose-dependent manner. In contrast, acetylsalicylic acid, indomethacin, and piroxicam exerted a biphasic effect; thus low concentrations (3-100 microM) of these three agents significantly increased the rate of histamine-stimulated acid secretion (10-20% over the corresponding control value) by a cAMP-independent mechanism, whereas higher concentrations reduced the rate of acid formation. With respect to underlying biochemical mechanisms that could mediate inhibitory effects of NSAIDs on gastric acid formation, it was observed that both diclofenac and piroxicam, but not acetylsalicylic acid or indomethacin, decreased the glandular content of ATP, inhibited hydrolytic activity of gastric gland microsomal H(+)-K(+)-ATPase, and reduced the rate of H(+)-K(+)-ATPase-dependent proton transport across microsomal membranes in a dose-dependent manner. Furthermore, diclofenac and piroxicam also significantly increased passive permeability of microsomal membranes to protons. In conclusion, our work shows that diclofenac and piroxicam cause a significant reduction in the rate of basal and histamine-stimulated acid formation in isolated rabbit gastric glands at concentrations that can be attained in the gastric lumen of patients treated with these drugs. Mechanisms involved in these inhibitory effects appear to be multifocal and include different steps of stimulus-secretion coupling.

Helicobacter pylori stimulates pepsinogen secretion from isolated human peptic cells

BACKGROUND

Different acid and peptic related gastroduodenal diseases are associated with both increased gastric secretion and Helicobacter pylori infection. Patients with H pylori associated gastritis or duodenal ulcer have increased serum pepsinogen levels which decrease after eradication. The mechanisms of H pylori induced gastric mucosal damage are not completely understood.

AIM

To determine the effects of H pylori on pepsinogen secretion from isolated human peptic cells.

METHODS

Dispersed human peptic cells were prepared from endoscopically obtained biopsy specimens after collagenase digestion, mechanical disruption, and density gradient centrifugation. H pylori was obtained from gastric biopsies (antrum and body), and cultured in non-selective and selective media. Isolates of H pylori were used at different concentrations (1 - 20 x 10(6) colony forming units (cfu)).

RESULTS

H pylori (10(6) - 2 x 10(7) cfu) increased basal pepsinogen secretion in a concentration dependent manner. This stimulus was not observed with Escherichia coli. The increased secretion was in addition to that observed with 0.1 mM histamine and 0.1 mM dibutyryl-cyclic adenosine monophosphate. However, H pylori did not affect either carbamylcholine (0.1-10 microM) or cholecystokinin (1 microM) stimulated pepsinogen secretion. Addition of the nitric oxide synthase inhibitor N(w)-monomethyl-L-arginine (1 mM) inhibited H pylori induced cGMP generation and pepsinogen secretion, which were also reduced in the absence of extracellular calcium. H pylori induced pepsinogen secretion was not affected by the absence/presence of the cagA gene.

CONCLUSIONS

H pylori increases pepsinogen secretion from human peptic cells through a calcium and nitric oxide mediated intracellular pathway. This effect is independent of the H pylori virulent cagA gene, and may be a mechanism of H pylori induced gastric mucosal damage.

Mucosal defense and repair. Role of prostaglandins in the stomach and duodenum

When considering the diseases of the stomach and duodenum, peptic ulcer disease has been the one of greatest clinical impact. Although there are several components that contribute mechanistically to ulcer disease, it is recognized that gastroduodenal mucosal prostaglandins play a central pathogenic role, especially in ulcers related to the use of NSAIDs. As a result of understanding the mechanisms of NSAID-induced ulceration, the crucial function that gastroduodenal mucosal prostaglandins have in mucosal defense and repair is appreciated. It now is held widely that mucosal prostaglandin deficiency increases susceptibility to ulcer formation and that exogenous administration of supplemental prostaglandins reduces ulcer risk. This article reviews the role that mucosal prostaglandins play in defense of the gastric and duodenal mucosa against injury and ulceration.

Distribution of prostaglandin E receptors in the rat gastrointestinal tract

AIMS

In order to study the role of prostaglandin in the regulation of the gastrointestinal functions, gene expression of prostaglandin receptors along the rat gastrointestinal tracts were investigated.

METHODS

Rats were used for the study. The combination of counterflow elutriation separation of mucosal cells and Northern blot analysis was used to detect the gene expression of prostaglandin receptors in gastrointestinal tracts.

RESULTS

In small intestine and colon, prostaglandin E2 EP1 and EP3 receptor mRNAs were mainly localized in the deeper intestinal wall containing muscle layers. EP4 receptor gene expression, on the other hand, was detected in the intestinal mucosal layer. In the stomach, EP1 mRNA was detected in gastric muscle layers, whereas EP3 and EP4 receptor gene expression was mainly present in the gastric mucosal layer containing epithelial cells. In gastric epithelial cells, parietal cells were found to have both EP3 and EP4 receptors. At lower concentrations, prostaglandin E2 inhibited gastric acid secretion by parietal cells probably through EP4 receptors. At higher concentrations, however, it stimulated it. On the other hand, mucous cells possessed only EP4 receptor mRNA.

CONCLUSIONS

Thus, it is suggested that prostaglandin E2 modulates gastrointestinal functions through at least three different prostaglandin receptors (EP1, EP3, and EP4), each of which has a distinct contribution in the gastrointestinal tract.

Superoxide anions produced by inflammatory cells play an important part in the pathogenesis of acid and pepsin induced oesophagitis in rabbits

BACKGROUND

Reactive oxygen metabolites have been associated with gastrointestinal injury.

OBJECTIVE

To investigate whether mucosal reactive oxygen metabolites are involved in acid and pepsin induced oesophagitis, and if so, which specific metabolites.

METHODS

The effects of free radical scavengers and the anti-inflammatory drug ketotifen on rabbit oesophagitis induced by acidified pepsin were studied. Isolated oesophageal cells were obtained before and after oesophageal injury and the generation of superoxide anion and hydrogen peroxide was analysed by flow cytometry. The presence of inflammatory cells was determined by indirect immunofluorescence with a mouse antirabbit CD11b antibody.

RESULTS

Of the free radical scavengers tested, superoxide dismutase, which reacts with the superoxide anion, significantly reduced oesophagitis, whereas catalase, which reacts with hydrogen peroxide, had only a mild effect and dimethylsulphoxide had no effect. Ketotifen significantly reduced the inflammation and also prevented the induction of oesophagitis. Isolated cells obtained from the oesophageal mucosa after acidified pepsin exposure generated increased amounts of superoxide anions, which were mainly produced by CD11b positive cells.

CONCLUSIONS

Reactive oxygen metabolites, especially superoxide anion, produced by inflammatory cells play a significant part in the genesis of oesophagitis induced by acid and pepsin in rabbits and might be a target for future medical therapy.

Cytokine effects on pepsinogen secretion from human peptic cells

BACKGROUND

Different cytokines, including epidermal growth factor (EGF) and interleukin 1 beta (IL 1 beta), participate in the pathogenesis of gastric mucosal damage and repair by means of different mechanisms that are either paracrine or autocrine in nature.

AIMS

To study whether EGF and IL 1 beta affect pepsinogen secretion in vitro.

METHODS

Dispersed human peptic cells were prepared from endoscopically obtained biopsy specimens after collagenase digestion, mechanical disruption, and density gradient centrifugation.

RESULTS

EGF dose dependently increased basal pepsinogen secretion and mitogenic concentrations (0.1 nM) of EGF induced submaximal stimulation. Similar effects were observed with transforming growth factor alpha. EGF effects on pepsinogen secretion were in addition to that induced by CCK-OP and db-cAMP stimulated pepsinogen secretion. EGF stimulated pepsinogen secretion was completely inhibited by a human immunospecific EGF receptor antibody and reduced by both genistein and tyrphostin-25, two different tyrosine kinase inhibitors. IL 1 beta does not affect basal, CCK-OP or acetylcholine stimulated pepsinogen secretion. However, IL 1 beta dose dependently inhibited db-cAMP and histamine stimulated pepsinogen secretion.

CONCLUSIONS

These results show that both EGF and IL 1 beta modulate human pepsinogen secretion in vitro and suggest that the paracrine effects of these cytokines on pepsinogen secretion might be involved in some pathological conditions of damage and inflammation of the gastric mucosa.