Duodenal mucosa synthesis of prostaglandins in duodenal ulcer disease

PGI2 Inhibits Intestinal Epithelial Permeability and Apoptosis to Alleviate Colitis

BACKGROUND & AIMS

Inflammatory bowel diseases (IBDs) that encompass both ulcerative colitis and Crohn's disease are a major public health problem with an etiology that has not been fully elucidated. There is a need to improve disease outcomes and preventive measures by developing new effective and lasting treatments. Although polyunsaturated fatty acid metabolites play an important role in the pathogenesis of several disorders, their contribution to IBD is yet to be understood.

METHODS

Polyunsaturated fatty acids metabolite profiles were established from biopsy samples obtained from Crohn's disease, ulcerative colitis, or control patients. The impact of a prostaglandin I₂ (PGI₂) analog on intestinal epithelial permeability was tested in vitro using Caco-2 cells and ex vivo using human or mouse explants. In addition, mice were treated with PGI₂ to observe dextran sulfate sodium (DSS)-induced colitis. Tight junction protein expression, subcellular location, and apoptosis were measured in the different models by immunohistochemistry and Western blotting.

RESULTS

A significant reduction of PGI₂ in IBD patient biopsies was identified. PGI₂ treatment reduced colonic inflammation, increased occludin expression, decreased caspase-3 cleavage and intestinal permeability, and prevented colitis development in DSS-induced mice. Using colonic explants from mouse and human control subjects, the staurosporine-induced increase in paracellular permeability was prevented by PGI₂. PGI₂ also induced the membrane location of occludin and reduced the permeability observed in colonic biopsies from IBD patients.

CONCLUSIONS

The present study identified a PGI₂ defect in the intestinal mucosa of IBD patients and demonstrated its protective role during colitis.

Oestrogen upregulates the expression levels and functional activities of duodenal mucosal CFTR and SLC26A6

NEW FINDINGS

What is the central question of this study? Duodenal ulcer is a common disease. A sex-based difference in the incidence of duodenal ulcer has long been observed clinically, but the cause is unclear. What is the main finding and its importance? Duodenal mucosal bicarbonate secretion is the most important protective factor in duodenal mucosa against acid-induced damage. The cystic fibrosis transmembrane conductance regulator (CFTR) and the solute-linked carrier 26 gene family A6 (SLC26A6) are two key bicarbonate transport proteins that mediate duodenal mucosal bicarbonate secretion. We demonstrate that endogenous oestrogen upregulates the expression levels and functional activities of duodenal mucosal CFTR and SLC26A6, which contributes to the sex difference in the prevalence of duodenal ulcer. The incidence of duodenal ulcer is markedly lower in women than men, but the cause of the sex difference is not clear. The cystic fibrosis transmembrane conductance regulator (CFTR) and the solute-linked carrier 26 gene family A6 (SLC26A6) are two key bicarbonate transport proteins that mediate duodenal mucosal bicarbonate secretion, which is an important protective factor against acid-induced duodenal injury. The aim of this study was to investigate the effect of oestrogen on the expressions and functional activities of CFTR and SLC26A6 in duodenal mucosa. We found that the expression levels of duodenal CFTR and SLC26A6 were markedly higher in young (20- to 30-year-old) women than in young men and old (60- to 70-year-old) women and men. The expression levels of CFTR and SLC26A6 in young women were markedly higher in preovulatory phases than in premenstrual phases, which was consistent with the changes of serum estradiol concentrations. Further results showed that duodenal CFTR and SLC26A6 expression levels in female mice were markedly decreased after ovariectomy, and supplementation with estradiol reversed the changes in CFTR and SLC26A6. 17β-Estradiol increased CFTR and SLC26A6 expression levels of human duodenocytes in experiments in vitro. Functional experiments showed that basal and forskolin- and prostaglandin E₂ -stimulated duodenal bicarbonate secretion in ovariectomized mice was markedly decreased and, likewise, supplementation with 17β-estradiol reversed the changes. In conclusion, endogenous oestrogen upregulates the expressions and functional activities of CFTR and SLC26A6 in duodenal mucosa, which could contribute to protection of the duodenum and explain the sex difference in the prevalence of duodenal ulcer.

Estrogen potentiates prostaglandin E₂-stimulated duodenal mucosal HCO₃⁻ secretion in mice

The cause of lower prevalence of duodenal ulcer in young women compared with men is largely unknown. We recently found that sex difference in duodenal mucosal HCO₃⁻ secretion existed in humans and mice, but the mechanisms are not clear. Prostaglandin E₂ (PGE₂) is an important endogenous mediator that plays an important role in the regulation of duodenal HCO₃⁻ secretion. Therefore, in the present study, we investigated the effect of estrogen on PGE₂-stimulated duodenal HCO₃⁻ secretion and the underlying mechanisms. The results showed that 17β-estradiol at the physiological concentration (1 nM) had no significant effects on duodenal mucosal HCO₃⁻ secretion or short-circuit current (I(sc)) in mice. However, the pretreatment of 17β-estradiol (1 nM) markedly potentiated PGE₂-stimulated duodenal HCO₃⁻ secretion and I(sc) (P < 0.01 and P < 0.05). Global estrogen receptor (ER) antagonist ICI-182,780 and ERα-specific antagonist MPP, but not the ERβ-specific antagonist PHTPP, abolished estrogen-potentiated PGE₂-stimulated duodenal HCO₃⁻ secretion and I(sc). 17β-Estradiol and PGE₂ additively increased phosphatidylinositol 3-kinase (PI3K) activity and Akt phosphorylation. Wortmannin, a specific PI3K inhibitor, inhibited estrogen-potentiated PGE₂-stimulated duodenal HCO₃⁻ secretion and I(sc). In conclusion, estrogen at the physiological concentration potentiates PGE₂-stimulated duodenal mucosal HCO₃⁻ secretion through the activation of ERα and the PI3K-dependent mechanism, which may contribute to the sex difference in duodenal mucosal HCO₃⁻ secretion and the lower prevalence of duodenal ulcer in young women.

What is new in the epidemiology and pathogenesis of peptic ulcer?

The old dictum 'no acid--no ulcer' is no longer a sufficient explanation of the pathogenesis of ulcer disease. The real question is 'if acid--why ulcer?' Although acid remains predominant, some of the other factors influencing ulcerogenesis are nocturnal acid secretion, pepsin enzyme subspecies, the mucus layer, bicarbonate levels, prostaglandins, Campylobacter pylori infection, consumption of non-steroidal anti-inflammatory drugs, and smoking habits. Although the ulcer burden has been greatly reduced by the introduction of H2-receptor antagonists, complications such as bleeding and perforation remain a problem, especially in the elderly. Medical treatment, in the form of H2-receptor antagonists, is effective for many patients.

Indomethacin treatment during initial period of acetic acid-induced rat gastric ulcer healing promotes persistent polymorphonuclear cell-infiltration and increases future ulcer recurrence. Possible mediation of prostaglandins

The study was performed to examine whether indomethacin administered during the initial period of acetic acid-induced gastric ulcer healing affects future ulcer recurrence. Gastric ulcers were produced in rats by subserosal injection of acetic acid. Indomethacin (1 mg/kg/day, orally) administered either alone or concomitant with ornoprostil (50 micrograms/kg/day, orally) was started on the fourth day and continued for 56 days. In rats whose ulcer healed at the 90th day after production of ulcer, endoscopy was done every 30 days to examine recurrence of ulcer. Gastric specimens were obtained 10, 30, 60, 90, and 240 days after ulcer production for histology, to quantitate the height of regenerated mucosa, thickness of fibrous tissue, degree of polymorphonuclear cell infiltration, and PAS-positive cells. Cumulative ulcer recurrence rate was significantly higher in rats initially treated with indomethacin than in controls. Increased polymorphonuclear cell infiltration was the major histologic abnormality persisting after cessation of indomethacin. Ornoprostil reversed these abnormalities caused by indomethacin. In conclusion, the administration of indomethacin during the initial period of the ulcer healing promoted persistent polymorphonuclear cell infiltration and increased ulcer recurrence rates, possibly via a prostaglandin-dependent mechanism.

The role of prostaglandins in gastric mucosal protection

Images

Gastric bicarbonate secretion and release of prostaglandin E2 are increased in duodenal ulcer patients but not in Helicobacter pylori-positive healthy subjects

BACKGROUND

Duodenal ulcer (DU) patients have impaired proximal duodenal mucosal bicarbonate secretion at rest and in response to luminal acid with higher acid-stimulated mucosal release of prostaglandin (PG) E2 than healthy subjects. Our purpose was to determine whether this abnormality was present also in the stomach of DU patients.

METHODS

Simultaneous determinations of gastric and duodenal bicarbonate secretion and luminal release of PGE2 were performed in 16 healthy volunteers (5 Helicobacter pylori-positive) and 8 inactive DU patients (all H. pylori-positive).

RESULTS

In healthy volunteers the rates of gastroduodenal bicarbonate secretion and the release of PGE2 were not influenced by H. pylori status. In inactive DU patients the rates of basal (704 +/- 84 versus 356 +/- 40 mumol/h; mean +/- SEM) and vagally stimulated (modified sham feeding) (1724 +/- 376 versus 592 +/- 52 mumol/h) gastric bicarbonate secretion were higher (p < 0.05) than in the health, whereas the corresponding rates (339 +/- 42 versus 591 +/- 51 mumol/h and 543 +/- 99 versus 778 +/- 69 mumol/h) in duodenal bicarbonate secretion were lower (p < 0.05). In addition, inactive DU patients had higher basal (148 +/- 32 versus 53 +/- 5 ng/h) and stimulated (291 +/- 84 versus 131 +/- 25 ng/h) gastric release of PGE2, but only the basal release of PGE2 into the duodenum was significantly increased (20 +/- 3 versus 5 +/- 1 ng/h; p < 0.05).

CONCLUSION

Increased mucosal production of PGE2 may be responsible for the abnormally high gastric secretion of bicarbonate in inactive DU patients. The defective duodenal secretion of bicarbonate observed in these patients may be a consequence of previous ulceration rather than the mere presence of H. pylori infection.

Rebamipide, novel prostaglandin-inducer accelerates healing and reduces relapse of acetic acid-induced rat gastric ulcer. Comparison with cimetidine

This study was done to elucidate whether rebamipide during the initial period of acetic acid-induced gastric ulcer affected healing and future ulcer relapse. The cumulative healing rate was higher in rats given rebamipide alone or those given rebamipide and cimetidine during and after administration, but not in rats given cimetidine alone, compared to control rats. Cumulative relapse rate was significantly lower in rats initially given rebamipide alone or those given rebamipide and cimetidine than in rats initially given cimetidine alone. These results suggest that rebamipide is beneficial for obtaining a better quality of ulcer healing and reduction of future ulcer relapse.

Misoprostol inhibits gastric mucosal release of endogenous prostaglandin E2 and thromboxane B2 in healthy volunteers

Prostaglandin analogues of the E-series theoretically offer the ideal antiulcer drugs. Peptic ulcer healing with prostaglandin analogues is, however, no better than would be predicted from their ability to inhibit gastric acid secretion and they are less effective than histamine H2 receptor antagonists in preventing ulcer relapse. It could be that prostaglandin analogues inhibit gastric mucosal synthesis or release of endogenous eicosanoids, thereby abrogating their own effects. This study, therefore, examined how a single therapeutic dose (200 micrograms) of misoprostol, a synthetic analogue of prostaglandin E1, influences gastric mucosal release of endogenous prostaglandin E2 (PGE2), thromboxane B2 (TXB2), and chemotactic leukotriene B4 (LTB4) during basal conditions and in response to gastric luminal acidification (0.1 M HCl; 5 ml/min for 10 minutes). Nine healthy volunteers were studied in a single blind, cross over design. In each subject misoprostol or placebo was instilled in randomised order into the stomach, which was subsequently perfused with isotonic mannitol. Misoprostol significantly decreased basal as well as acid stimulated output of PGE2 and TXB2, without affecting output of LTB4. These data show that misoprostol inhibits gastric mucosal synthesis of prostanoids. Decreased concentrations, or even a changed profile, of native eicosanoids modulating the release of inflammatory mediators from immune cells might explain why prostaglandin analogues have a comparatively poor clinical performance in ulcer healing and prevention.

Laboratory medicine in ulcer disease

The role of laboratory medicine in ulcer disease is poorly defined. However there is increasing evidence of the clinical usefulness of some laboratory tests that investigate secretory functions and defensive properties of the stomach, gastrointestinal hormones and Helicobacter pylori infection. These tests may modify the clinical management of patients with peptic ulcer by identifying H. pylori positive subjects, patients with high acid output, patients who do not respond to antisecretory therapy, and patients with high gastrin levels in whom Zollinger-Ellison syndrome may be suspected. Here we review the clinical value of laboratory tests in ulcer disease, particularly as concerns the cost/benefit ratio. The relative merits of these tests are described giving an indication of their possible role in the diagnostic algorithm.

Effect of nizatidine versus ranitidine on gastric intraluminal prostaglandin release in duodenal ulcer patients

The role of prostaglandins in peptic ulcer disease and their relation to Helicobacter pylori infection remain controversial. This study sought to compare the effects of oral nizatidine and ranitidine on the gastric mucosal release of prostanoids in duodenal ulcer (DU) patients and to correlate prostanoid concentrations with H. pylori status. Twenty-eight patients with DUs were randomized to receive either nizatidine or ranitidine. Nizatidine 300 mg at night elevated intraluminal PGE2 concentrations; 6-keto-PGF1 alpha concentrations also rose, but did not reach statistical significance. Ranitidine induced non-significant falls in PGE2 and 6-keto-PGE1 alpha concentrations. Patients with H. pylori infection had lower PGE2 and 6-keto-PGF1 alpha concentrations than non-infected patients, but nizatidine was equally effective in increasing prostanoid levels in both groups. These findings may be considered as favourable side effects of nizatidine with uncertain clinical significance. Further studies are needed to elucidate the synergism between prostanoids, eradication of H. pylori and nizatidine in the treatment of DU.

Effect of Helicobacter pylori colonisation on gastric mucosal eicosanoid synthesis in patients taking non-steroidal anti-inflammatory drugs

Colonisation with Helicobacter pylori may influence susceptibility to gastroduodenal injury and ulceration in patients taking non-steroidal anti-inflammatory drugs (NSAIDs). The aim of this study was to determine if Helicobacter pylori colonisation altered eicosanoid synthesis by gastric mucosa in these patients. Sixty five patients with long-standing NSAID intake and 23 control subjects underwent endoscopy. In vitro gastric antral biopsies were stimulated by vortex mixing and eicosanoid measurements determined by radioimmunoassay. Helicobacter pylori colonisation was determined by a CLO test (a gel based rapid urease test) and histological assessment. Median prostaglandin E2 synthesis by gastric mucosa was 61.0 (interquartile range: 19.2-73.1) pg/mg in control subjects colonised with Helicobacter pylori compared with 46.5 (23.3-65.5) pg/mg in Helicobacter pylori negative subjects. This was not significantly different. Treatment with NSAIDs was associated with a significant difference (p < 0.001) in prostaglandin E2 (PGE2) synthesis between those colonised with Helicobacter pylori (37.5(22.0-77.3) pg/mg) compared with patients not infected (12.6(7.0-19.3) pg/mg). Values in patients taking NSAIDs who were colonised were not different from control subjects. Synthesis of PGE2 was strongly associated with type B (chronic active), but not type C (chemical) gastritis. Dyspeptic symptoms were more common in subject colonised with Helicobacter pylori (p < 0.002) and were associated with higher PGE2 synthesis. In patients taking NSAIDs Helicobacter pylori colonisation removes rather then enhances depression of PGE2 synthesis associated with NSAIDs and may promote dyspepsia associated with ulcers and prevent superficial mucosal injury.

Eicosanoid synthesis in duodenal ulcer disease: decrease in leukotriene C4 by colloidal bismuth subcitrate

The release of immunoreactive prostaglandin E2 (PGE2) and leukotriene C4 (LTC4) from antral and duodenal mucosal biopsy specimens taken from 20 patients with duodenal ulcer disease was measured by radioimmunoassay before and four weeks after treatment with colloidal bismuth subcitrate. Gastroscopic and histological examination showed complete ulcer healing in 15/18 patients and duodenal histology looked normal (n = 15) or improved (n = 3): two patients failed to attend for a second endoscopy. Analysis of the supernatant from incubations of biopsy tissue in vitro showed that unstimulated antral release of PGE2 was significantly more than that from the duodenal mucosa (p less than 0.05), whereas basal release of LTC4 was significantly lower from antral biopsy specimens (p less than 0.05). Subsequent incubation of specimens with calcium ionophore A23187 caused an increase in LTC4 but not in PGE2 generation. The ability of antral and duodenal mucosa to form ionophore mediated LTC4 in patients with duodenal ulcer disease was significantly greater (p less than 0.05; p less than 0.01 respectively) than that of normal gastroduodenal mucosa. After colloidal bismuth subcitrate treatment, basal synthesis of PGE2 was unchanged in duodenal and antral specimens. In contrast, basal duodenal LTC4 was reduced (p less than 0.05), and the capacity for ionophore mediated duodenal LTC4 formation was substantially and significantly reduced after treatment (p less than 0.001). These results indicate that after therapeutic healing of duodenal ulcer (accompanied by clearance of inflammatory cell infiltrate), there is a reduced ability of duodenal mucosa to generate proinflammatory peptidoleukotrienes.

Prostaglandin protects against bile salt induced increases in proton permeation of duodenal brush border membrane

A direct protective action of prostaglandin on luminal cell membranes was investigated by preincubating rabbit duodenal brush border membrane vesicles with prostaglandin E2 (PGE2) before incubation with bile salts. Membrane perturbation was assessed by measuring the net proton permeability (Pnet). Bile salts (deoxycholate, glycodeoxycholate, and taurodeoxycholate; 0.1-1.0 mmol/l) resulted in concentration dependent increases in Pnet: from (mean (SE] 5.42 (0.17) (n = 20) to 8.44 (0.24) x 10(-4) (n = 13) cm/s with 0.5 mmol/l deoxycholate. PGE2, 10(-8)-10(-6) mol/l, when added alone had no effect on Pnet: 5.41 (0.21) x 10(-4) (n = 14) cm/s with 10(-6) M PGE2. When duodenal brush border membranes were preincubated with PGE2, 10(-7)-10(-6) mol/l, however, the bile salt induced increase in Pnet was significantly reduced: 7.22 (0.18) x 10(-4) (n = 13) cm/s with 10(-7) mol/l PGE2 and 0.5 mmol/l deoxycholate. These findings indicate that PGE2 exerts a direct protective action on duodenal luminal membranes.

Acid-induced increase in electrical conductance of guinea pig duodenal mucosa in vitro. Temporary protection by combined effects of bicarbonate and prostaglandin E2

Electrical conductance as a sensitive indicator of acid damage has been investigated in guinea pig duodenal mucosa using Ussing-chamber techniques. Reductions of luminal pH from 7.4 to 3.0, 2.3, or 2.0 caused concentration-dependent, progressive increases in conductance, accompanied (pH 2.0) by a continuous increase in hydrogen permeation as determined by pH-stat titration. Increases in conductance and hydrogen flux were related to base-line conductance, with higher values conditioning for a sooner onset and/or more marked elevation. Conductance increases were prevented by timely back titration. Recently, it has been shown that serosal HCO3 reduces conductance by actions dependent on prostaglandins and serosal Na and sensitive to loop diuretics. Here, serosal HCO3 delayed the onset of acid-induced conductance increase by approximately 8 minutes, an effect reduced by omission of serosal Na and during exposure to serosal furosemide (10(-3) mol/L). In the presence of serosal indomethacin (10(-4) mol/L) and HCO3, prostaglandin E2 (10(-6) mol/L serosal bath) delayed the conductance increase. Because HCO3 secretion is negligible in this model, these results indicate effects of HCO3/prostaglandin E2 beyond mere buffering of invading hydrogen. These results are consistent with intracellular actions that tighten the paracellular pathway against acid and thus provide temporary protection from acid injury. In agreement with this view, HCO3 also limited conductance increases after luminal alkalinization by a furosemide-sensitive action.

Proximal duodenal prostaglandin E2 release and mucosal bicarbonate secretion are altered in patients with duodenal ulcer

Proximal duodenal mucosal bicarbonate production is impaired in patients with duodenal ulcer disease. Because prostaglandins of the E class increase human proximal duodenal bicarbonate secretion, this study tested the hypothesis that endogenous prostaglandin E2 production is defective in patients with duodenal ulcer. Ten patients, five with active and five with inactive duodenal ulcer disease, were studied along with 10 normal volunteers. The proximal 4 cm of duodenum, the bulb, was isolated and continuously perfused with 154 mmol/L NaCl. Basal bicarbonate secretion was measured for 30 minutes. The test segment was then acidified with a physiological amount of HCl (2 mmol over 5 minutes), and acid-stimulated bicarbonate secretion was measured by pH/PCO2 and back-titration for 55 more minutes. Prostaglandin E2 was measured in the effluents by a radioimmunologic assay validated by gas chromatography-mass spectrometry. Compared with the normal subjects after luminal acidification, the duodenal ulcer patients had significantly greater PGE2 release and decreased total 1-hour bicarbonate output. The peak 5-minute acid-stimulated bicarbonate responses were not significantly different between the duodenal ulcer patients and normal subjects. After luminal acidification, PGE2 output remained elevated in the duodenal ulcer patients but returned promptly to basal in the normal subjects. Furthermore, the ratio of bicarbonate secreted to the amount of PGE2 released was significantly less in the ulcer patients. These findings suggest that patients with duodenal ulcer disease have an impaired mucosal bicarbonate response to endogenous PGE2. The increased acid-stimulated PGE2 response in duodenal ulcer patients suggests a compensatory phenomenon in response to the diminished mucosal bicarbonate production.

Mechanism of action of Roter (bismuth subnitrate) in patients with duodenal ulcer disease and healthy volunteers

The effects of Roter (compound bismuth subnitrate) on antacid activity and mucosal prostaglandin E2 (PGE2) synthesis were variously investigated in patients with duodenal ulcer disease and healthy volunteers. Roter had a significant but small antacid activity with a buffering capacity of 10.9 mmol per tablet. In healthy volunteers, this was assessed by 24 h gastric pH monitoring on matched days with and without Roter treatment. The percentage of time that gastric pH was above 3 and the time after a standard meal that the pH was above 3, were both significantly increased by treatment with Roter (II tds post-cibal) (P less than 0.01). Endogenous PGE2 synthesis was measured in endoscopic duodenal biopsies taken both before and after Roter treatment in patients with acute untreated duodenal ulceration. There was a significant deficiency of mucosal PGE2 synthesis in untreated patients compared with controls (P less than 0.005). However, following 4 weeks' treatment with Roter, there was a 90% rate of healing accompanied by a significant increase in PGE2 synthesis (P less than 0.05) up to control levels. These findings suggest that Roter heals by the combined effects of a modest antacid neutralizing capacity and the ability to restore mucosal prostaglandins to normal levels, thereby mediating prostaglandin-dependent defence mechanisms.

Effect on gastric and duodenal mucosal prostaglandins of repeated intake of therapeutic doses of naproxen and etodolac in rheumatoid arthritis

The synthesis of gastric and duodenal mucosal prostaglandin E2, prostaglandin I2, and thromboxane B2 during a 60 minute incubation of biopsy specimens, the degree of endoscopic and histological damage, and the anti-inflammatory response were all studied after a four week, double blind study of therapeutic doses of two non-steroidal anti-inflammatory drugs, naproxen and etodolac, received by 27 patients with active rheumatoid arthritis (13 receiving naproxen, 14 etodolac). Prostaglandin values after treatment did not differ from the baseline levels when all the patients were analysed as one group. Subgroup analysis showed that naproxen suppressed gastric prostaglandin E2 from a median of 29 to 9 ng/mg protein, duodenal prostaglandin E2 from 34 to 11 ng/mg, and duodenal prostaglandin I2 from 62 to 15 ng/mg protein. No overall suppression occurred with etodolac. Also, on the second assessment patients receiving naproxen had lower gastric and duodenal prostaglandin E2 and prostaglandin I2, but higher values of duodenal thromboxane B2, than patients receiving etodolac. Both drugs had comparable anti-arthritic activity and caused microscopic gastritis in similar proportions of patients. No correlation was detected between prostaglandin values and the mucosal damage which developed in seven patients receiving naproxen (54%) and three receiving etodolac (21%). These findings indicate that, unlike naproxen, etodolac does not seem to affect gastric or duodenal prostaglandin synthesis; other mechanisms of injury need to be considered.

Prostaglandins in the gut and their relationship to non-steroidal anti-inflammatory drugs

Prostaglandins are long-chain, saturated, oxygenated fatty acids. Relatively large quantities of prostaglandins have been found in gut mucosa, suggesting that these substances play an important role in gastrointestinal physiology. Non-steroidal anti-inflammatory drugs (NSAIDs) cause damage to the gastric, intestinal, and colonic mucosa in experimental animals and in humans. Prostaglandins protect the gastric mucosa against injury induced by NSAIDs, and this property has been labelled cytoprotection. The mechanisms of cytoprotection have been extensively evaluated and are probably multifactorial, including effects on the gastric mucosal barrier, gastric blood flow, mucus, bicarbonate, and fluid section, ionic transport, cyclic AMP, and surface-active phospholipids. Prostaglandins may also prevent NSAID-induced injury in the small intestine and colon. The mechanisms responsible for prostaglandin protection in the lower gut against injurious agents are unknown. Further studies of the role of prostaglandins in the gut and their relationship to the effects of NSAIDs are needed. The results of these investigations may lead to a better understanding of the importance of prostaglandins in the physiology of the gastrointestinal tract, and may provide information regarding actions of NSAIDs on the functional integrity of the gastric, intestinal, and colonic mucosa.

Duodenal and antral mucosal prostaglandin E2 synthesis in a study of normal subjects and all stages of duodenal ulcer disease treated by H2 receptor antagonists

We tested the hypothesis that the production of prostaglandin E2 (PGE2) is impaired in duodenal ulcer disease and affected by treatment and healing. This was investigated by a study of maximal PGE2 synthesis rates in duodenal and antral mucosal biopsies obtained at endoscopy. The patients were divided into three groups. Group (a): endoscopically normal controls (n = 56); group (b): treatment controls (non-DU disease: gastric ulcer or oesophagitis treated by histamine H2 receptor antagonists) (n = 41); and group (c): patients with DU disease (n = 183) further subdivided into group (c1) active ulcer not on treatment (n = 47), (c2) treated active ulcer (n = 35), (c3) healed ulcer on treatment (n = 86), and (c4) healed ulcer not on treatment (n = 15). Group (a) synthesised (mean (SD] 106.6 (39.0) pg PGE2/mg wt of tissue from the duodenal bulb and 129.9 (56.9) from the second part of the duodenum. No difference was found between group (a) and (b) at either site. Group (c1) ulcer rim made 49.8 (22.7) and at all stages ulcer rim and scar made less than the control duodenal bulb (p less than 0.02). Uninvolved duodenal bulb form groups (c1) (63.4 (31.0], (c2) (83.6 (38.5], and (c3) (81.5 (31.1], however, also made significantly less than controls (p less than 0.02) and a similar though non-significant trend was seen in group (c4). Biopsies from the second part of the duodenum did not synthesise significantly less than the control group but a similar trend was noticed at each stage of ulcer treatment. Biopsies of control antrum synthesised 124.5 (32.2) but only 93.7 (44.2) in group (cl) (p < 0.005). All stages of duodenal ulcer healing were associated with a decreased capacity to synthesise the major prostaglandin PGE2 at the ulcer site and the uninvolved duodenal bulb and, in acute untreated duodenal ulcer, the uninvolved antrum. This decreased capacity may be the consequence of the disease process itself and not secondary to the treatment, indicating a basic pathophysiological abnormality which may explain the characteristic tendency of the disease to relapse.

Gas chromatographic/mass spectrometric quantitative analysis of eicosanoids in human oesophageal mucosa

In order to investigate the contribution of eicosanoids to human oesophageal functions and disorders (gastrooesophageal reflux, GOR and reflux oesophagitis, RO), we have used a selected ion monitoring gas chromatographic/mass spectrometric methodology to quantify the cyclooxygenase and lipoxygenase products biosynthesized in vitro by endoscopic mucosal biopsy specimens. Prostaglandins (PGs) were quantified as MEMOTMS derivatives and HETEs, as hydrogenated methyl ester of tert-butyldimethylsilyl) ether derivatives. PGE2, PGF2 alpha appeared as the major prostanoids, whereas 12HETE seemed to be the major lipoxygenase product. In the case of GOR or RO, biosynthesis of PGE2 was dramatically increased, while no change could be detected for 12HETE. PGE2 increase seems to be related to inflammatory reaction, in which its exact role remains unclear. Moreover, it cannot be excluded that PGE2 is a side product which might be protective to the oesophageal mucosa.

Enprostil, a prostaglandin E2 analogue, in the treatment of duodenal ulcer; a multicentre comparison with cimetidine

In a multicentre trial, 120 patients with endoscopically diagnosed duodenal ulcer were randomly allocated to treatment with either 35 micrograms enprostil b.d. or 400 mg cimetidine b.d. for up to 6 weeks on a double-blind basis. After 6 weeks, 82% (42/51) of enprostil-treated patients and 92% (44/48) of cimetidine-treated patients were healed. Corresponding healing figures on an intention-to-treat basis were 70% and 76%. No significant differences were detected between treatments with respect to healing rates or symptom control at any time. Side-effects were reported by 14 patients taking enprostil and 17 patients taking cimetidine; none were serious but they resulted in withdrawal of one and two patients respectively. Enprostil was found to be similar in efficacy and tolerance to cimetidine.

Modification of upper gastrointestinal prostaglandin synthesis by dietary fatty acids

The effects of dietary oils on gastric, duodenal mucosa and liver were investigated in a rat model. Unsaturated fatty acid profiles and in vitro prostaglandin (PG) synthesis (PGE2, PGF2 alpha, 6-oxo-PGF1 alpha and thromboxane B2), were measured after 14 days of dietary oil supplements. There were no significant differences in prostanoid synthesis between rats fed coconut oil (high saturated fat content) and standard diet. After fish oil supplement, tissue eicosapentaenoic acid and docosahexaenoic acid levels were higher, arachidonic acid levels were lower, and prostanoid synthesis was reduced in both stomach and duodenum. After corn oil and evening primrose oil, linoleic acid levels were variably increased, but there were no significant differences in arachidonic acid or prostanoid synthesis. Dihomogamma-linolenic acid levels were slightly increased after evening primrose oil. Dietary incorporation of fatty acids into gastroduodenal tissue is not uniform. When incorporated, fatty acids can modify prostaglandin synthesis.

The pathophysiological and pharmacological basis of peptic ulcer therapy

Both genetic and nongenetic factors predispose to ulcer diathesis. At the mucosal level ulcers result from an imbalance between aggressive factors and mucosal defense. Ulcer therapy reduces aggressive forces, bolsters defense, or both. Gastric acid, the major aggressive factor, may have its secretion inhibited or it may be partially neutralized by antacids. H2 receptor antagonists competitively block histamine occupancy of H2 receptors on parietal cells, thereby preventing stimulation of adenylate cyclase, cAMP rises, and activation of protein kinase and H+/K+ATPase. Prostaglandins inhibit acid secretion largely by preventing histamine-induced cAMP rises. Proton pump inhibitors bind H+/K+ATPase. Antimuscarinics inhibit acetylcholine receptors on the parietal cell, thereby blocking Ca2+ entry and subsequent activation of protein kinase and the proton pump. Mucosal defense is enhanced by certain prostaglandins, colloidal bismuth subcitrate and sucralfate. Prostaglandins stimulate secretion of bicarbonate and mucus, among other effects. Colloidal bismuth and sucralfate bind to proteins in the ulcer base and stimulate bicarbonate and mucus secretion, partially, in the case of sucralfate, by increasing endogenous prostanoid synthesis. Sucralfate also binds pepsin and bile acids. Colloidal bismuth temporarily eradicates mucosal colonization by Campylobacter pylori, another putative agent in ulcer diathesis.

Peptic ulcer disease in the pediatric population

Peptic ulcer disease occurs in infants, children, and adolescents. Primary and stress ulcers pose a challenge to the pediatrician, who needs to arrange for appropriate diagnostic and therapeutic services. Highlights of our understanding of the pathophysiology, genetics, natural history, diagnosis, and therapy of peptic ulcer disease are presented.

[Risk of ulcer following conversion operations of Billroth I stomachs in restorative reflux-preventing procedures--an animal experiment]

In an experimental study on 74 rats the ulcer risk was analyzed after Billroth-I-resection changed into secondary Roux-Y-gastro-jejunostomy resp. jejunal interposition. The following results were obtained: 1) 10 months postoperatively stomal ulcers were found in up to 75%. 2) The gastric pH was comparable with the control and significantly lower than after Billroth-I-resection. 3) An additional vagotomy caused a reduction but not an elimination of the ulcer risk. We conclude from our results that there is a protective role of the postresectional intestino-gastric reflux on the gastrojejunal anastomosis. A reflux-preventive procedure is therefore heavily ulcer-prone.

Simultaneous measurement of in vitro gastroduodenal prostaglandin E2 synthesis and degradation in peptic ulcer disease

The ability of mucosal specimens from the stomach and duodenum to synthesize and degrade prostaglandin E2 has been determined in normal subjects and peptic ulcer patients. Significant reduction in fundic PGE2 synthesis capacity was observed in gastric ulcer patients. There was also significant reduction in the PGE2 degradation capacity of antral, fundic, and duodenal mucosal specimens in gastric ulcer patients. Patients with gastritis showed significant elevation of both antral and fundic PGE2 synthesis capacity compared with normal but no alteration in PGE2 degradation. No differences were observed in PGE2 synthesis and degradation rates in patients with duodenal ulcer. The results argue in favour of an association between impairment of PGE2 metabolism in the mucosa of patients with gastric but not duodenal ulceration.

Failure of a cytoprotective dose of arbaprostil to heal acute duodenal ulcers. Results of a multiclinic trial

Previous therapeutic trials with prostaglandins have shown them to be effective in healing duodenal ulcers when used at doses that are highly effective suppressors of gastric acid secretion. We undertook this trial to determine if a cytoprotective dose of arbaprostil (10 micrograms q.i.d. for 4 wk) would also be efficacious in this disease state. Eighty-two patients between the ages of 19 and 72 yr with endoscopically documented duodenal ulcers were entered into this randomized double-blind placebo-controlled trial. The patients were monitored with biweekly endoscopies and laboratory examinations, weekly interviews during the period when drug was administered, and a follow-up interview plus laboratory examinations 1 wk after drug administration was completed. No statistically significant differences between the arbaprostil and placebo treatment groups were found for ulcer healing rates, pain relief, antacid consumption, side effects, or laboratory examinations. It is presumed that this prostaglandin may not have sufficient duodenal cytoprotective capacity to effectively heal duodenal ulcers, or that some suppression of gastric acid secretion may be required to achieve significant clinical efficacy.

Impaired proximal duodenal mucosal bicarbonate secretion in patients with duodenal ulcer

The defensive factors that prevent the human duodenal mucosa from acidic and peptic damage have not been fully evaluated. To determine whether duodenal mucosal bicarbonate production was altered in patients with inactive duodenal ulcer, we measured basal and acid-stimulated bicarbonate output from the duodenal bulb and the distal duodenum in healthy subjects and patients with inactive duodenal ulcer. As compared with 16 normal subjects, the 12 patients had significantly less mean (+/- SE) basal proximal duodenal mucosal bicarbonate secretion (185 +/- 13 vs. 107 +/- 18 mumol per centimeter per hour; P less than 0.001). Moreover, in response to a physiologic amount of hydrochloric acid (2 mmol per five minutes) instilled directly into the duodenal bulb, peak proximal duodenal bicarbonate output in the patients was 41 percent of the normal response (263 +/- 65 vs. 642 +/- 77 mumol per centimeter per hour; P less than 0.01). There was little overlap between groups. In contrast, bicarbonate outputs in the distal duodenum were similar in the two groups. We conclude that most patients with duodenal ulcer disease have decreased proximal duodenal mucosal bicarbonate production at rest, in response to hydrochloric acid, and in relation to peak gastric acid secretion. Impaired proximal duodenal mucosal bicarbonate secretion may be an important factor in the development and natural history of duodenal ulcer.

Prostaglandin synthesis in the human gastrointestinal mucosa

Prostaglandins derive from polyunsaturated fatty acids, of which arachidonic acid is the most abundant. Arachidonic acid occurs in all cell membranes, where it is bound to phospholipids and can, once liberated by phospholipases, be metabolized by cyclooxygenase into prostaglandins and thromboxanes and by lipoxygenases into hydroxyacids, leukotrienes and lipoxins. In most studies on prostaglandin formation in the human gastrointestinal mucosa PGE2 and PGF2 alpha seem to be the regularly occurring products. Quantification of mucosal prostaglandin synthesis in vivo is problematic. Mechanical handling of tissues immediately activates arachidonic acid metabolism, and the determination of "tissue levels" of prostaglandins or prostaglandin biosynthesis in biopsy specimens ex vivo thus becomes unreliable as a measure of in vivo formation. A more reliable approach may be to measure prostaglandins in gastrointestinal luminal contents, which can be obtained atraumatically. Most measurements are made by radioimmunological methods, but the specificity of most assays has not been satisfactorily examined. More specific methods such as gas chromatography-mass spectrometry should be used to validate of a radioimmunoassays. Prostaglandin E2, which can be measured by gas chromatography-mass spectrometry, is regularly found in human gastroduodenal luminal contents. Exposure of the mucosa to hydrochloric acid increases the output of PGE2 to the lumen, indicating increased mucosal PGE2 formation during physiological activation of mucosal defense mechanisms.

Increased ex vivo synthesis of prostaglandin E2 by gastric tissue after hemorrhage in rats

Endogenously synthesized prostaglandins are potential mediators of gastrointestinal mucosal protection. Some data suggest that gastric ulceration caused by stressful stimuli is due to diminished mucosal synthesis of prostaglandins. To examine this hypothesis, we determined the effect of hemorrhage, an ulcerogenic stimulus, on ex vivo production of immunoreactive prostaglandin E2 by gastric tissue in the rat. Macroscopic gastric ulcers were reproducibly observed in Sprague-Dawley rats subjected to hemorrhage (3 ml/100 g body weight). The number of ulcers was linearly related to the duration of shock. Prostaglandin E2 synthesis was significantly increased during in vitro incubation of oxyntic and nonoxyntic stomach tissue excised from rats subjected to hemorrhage for 30 minutes (p less than 0.05). These results indicate that damage to the gastric mucosa in rats subjected to hemorrhage occurs despite augmented endogenous secretion of prostaglandin E2. Mechanisms other than impaired prostaglandin biosynthesis were probably responsible for mucosal injury in this model.

Kinetics of prostaglandin E2 and thromboxane A2 synthesis and suppression of PHA-stimulated peripheral blood mononuclear leucocytes

The immunomodulatory effects of thromboxane A2 and prostaglandin E2 on peripheral blood mononuclear leucocytes stimulated with PHA in vitro, and the relationship of this to the time-course of their synthesis in culture, were investigated using prostaglandin E2, a thromboxane A2 synthesis inhibitor (UK37248), a thromboxane A2 mimic (U46619) and a thromboxane A2 receptor blocker (EP045). The inhibitory effect of prostaglandin E2 on PHA-induced human peripheral blood mononuclear leucocyte proliferation diminishes if the addition of PGE2 is delayed. If added 4 hr after a maximum concentration of PHA (5 micrograms/ml), the effect of PGE2 was reduced by 60%. If a submaximal concentration of PHA (1 microgram/ml) was used, the effect of PGE2 was not reduced if added 4 hr later but fell by about 60% after 16 hr. UK37248 moderately inhibited PHA-induced activation while substantially inhibiting thromboxane A2 synthesis and simultaneously enhancing PGE2 synthesis. The enhanced accumulation of PGE2 occurs while sensitivity to PGE2 is dropping. U46619, exogenously applied as a thromboxane A2 mimic, inhibited PHA-induced activation at concentrations that did not significantly alter PGE2 synthesis. EP045, which may modulate the effects of endogenous thromboxane A2 by blocking receptors, did not alter PHA-induced activation. We conclude that thromboxane A2 may have a role in inhibiting PHA-induced activation on the basis of the effect of U46619. However, this study highlights difficulties in utilizing prostaglandin and thromboxane receptor and synthesis inhibitors to examine their endogenous role in the modulation of mitogen-induced activation in vitro. If sensitivity to the purported endogenous substance is limited to the early stages of culture and if only low levels are synthesized at this early stage, then blocking drugs would have little effect.

Prostaglandins for peptic ulcer: a promise unfulfilled

Prostaglandin analogues appear to heal peptic ulcers no better than would be predicted from their ability to inhibit acid secretion. This implies that their cytoprotective properties, which are so dramatic in acute animal experiments, play no part in ulcer healing. Ulcer healing involves mucosal repair, whereas cytoprotection concerns preservation of normal mucosa, the two processes being conceptually different. If any general benefits of prostaglandin cytoprotection are to be harnessed to clinical ends, drug delivery systems that ensure long-lasting contact with the gastroduodenal mucosa may be needed.

Prostaglandins in peptic ulcer disease. An overview of current status and future directions

Naturally occurring prostaglandins almost certainly play an important role in maintaining the integrity of the gastrointestinal mucosa. Clinical evidence available to date indicates that synthetic analogues of prostaglandins heal gastroduodenal ulcer only in doses that suppress gastric acid. However, non-antisecretory doses of prostaglandins may eventually have a role in the treatment of ulcer disease by maintaining ulcer healing and preventing recurrence. This possibility along with the potential of prostaglandins to prevent gastroduodenal mucosal injury caused by NSAIDs, alcohol, aspirin and stress, if supported by the results of ongoing clinical trials, may prove to be a major therapeutic advance for the treatment of acid peptic disease.

Prostaglandin metabolism in peptic ulcer disease

Over the past decade, the physiological role of prostaglandins synthesized by the gastroduodenal mucosa has been the subject of intense research. Unfortunately, progress has been slow. Methodological problems in the identification and measurement of different prostanoids, as well as technical difficulties in performing definitive experiments, are largely to blame. Prostaglandins are not stored in tissue, can be rapidly synthesized and metabolized during tissue analysis, and appear to have multiple and sometimes conflicting biological actions on the mucosal tissues. Given these challenging problems at the biochemical and cellular levels, it is not surprising that relatively few studies have addressed potential defects in prostaglandin synthesis in patients with ulcer disease. Furthermore, the results obtained by these human studies are not always comparable because of the diverse methodological approaches chosen by different investigators. The evidence so far obtained suggests, though not conclusively, that mucosal prostaglandins play a role in the pathogenesis of ulcer disease. The most plausible hypothesis holds that defects in prostaglandin synthesis, metabolism or action on target tissues either weaken mucosal resistance to luminal acid-peptic activity or impair mucosal repair, leading to the development of chronic peptic ulcer.

Prostaglandin biosynthesis in gastroduodenal mucosa: methodological difficulties and their implications

A deficiency of locally synthesized prostaglandins has been suggested to underly gastric and duodenal ulcer disease and to mediate the mucosal lesions induced by non-steroidal anti-inflammatory drugs. The exact definition of their role is hampered by various methodological problems. First, the mucosal content of prostaglandins is affected by mechanical manipulation and homogenization and does not correspond to the rate of synthesis. Secondly, the assay of this rate in mass terms is also susceptible to these artefacts, and a steady state of prostaglandin secretion in vitro is usually not achieved. Thirdly, if prostaglandin synthesis is measured in vitro by the incorporation of labelled arachidonic acid, the possibly rate-limiting role of substrate supply is not taken into account. Thus, it is likely that a part of the disagreement in the field stems from the problems in measuring the true rates of prostaglandin synthesis in vivo.

Prostaglandins and the gastrointestinal mucosa: are they important in its function, disease, or treatment?

In 1971 interest in the role of prostaglandins in the gastrointestinal tract was stimulated by the publication of two hypotheses--that aspirin damaged the gastric mucosa by inhibiting prostaglandin synthesis (1) and that cholera toxin caused diarrhea by stimulating it (2). Subsequent research into the gastrointestinal actions of prostaglandins has been considerable and now impinges on clinical practice. This paper reviews the involvement of prostaglandins and related compounds in mucosal protection, in ulcer healing, in diarrhea, and in gastrointestinal inflammation, with particular reference to the growing body of human data.