Acetazolamide Interferes with the Protective Effect of Prostaglandin E2 in the Rat Gastric Mucosa

Oral prostaglandin E₂ protected the gastric mucosa against the damage induced by intraperitoneal indomethacin in the rat. Blocking of the gastric alkaline secretion by subcutaneous acetazolamide potentiated the ulcerogenic action of indomethacin and reduced or abolished the protective effect of a submaximal dose prostaglandin E₂. The results are compatible with the hypothesis that stimulation of the alkaline secretion is one of the mechanisms by which prostaglandin E₂ protects the gastric mucosa.     

Gastrointestinal Protection by Low-Dose Oral Prostaglandin E2 in Rheumatic Diseases

In a previous study oral prostaglandin E₂ (PGE₂) was shown to protect against indomethacin-induced gastrointestinal bleeding in patients with rheumatic diseases. This study examined whether a lower oral dose of PGE₂, without acid antisecretory effect, is protective. Its methylated analogue 15(R)15 Me PGE₂, which has effect on the acid secretion given orally, was also tested. Indomethacin, 50 mg three times daily, induced an increase in gastrointestinal bleeding measured by the ⁵¹Cr technique. PGE₂, 0.33 mg three times daily, taken concomitantly significantly reduced fecal blood loss. 15(R)15 Me PGE₂, 40 μg three times daily, was also effective. The prostaglandins did not increase joint symptoms and had no significant side effects. It is suggested that the combination of nonsteroidal anti-inflammatory drugs with a low oral dose of E₂ prostaglandins could be used clinically, especially in patients with rheumatic diseases.     

The Helicobacter felis Mouse Model in Assessing Anti-Helicobacter Therapies and Gastric Mucosal Prostaglandin E2 Levels

Background: The aims of the present study were to assess the usefulness of the Helicobacter felis mouse model in the evaluation of antimicrobial therapies and the effect of Helicobacter infection on gastric mucosal prostaglandin E₂ release. Methods: Barrier-maintained BALB/c mice were infected with H. felis and treated with different antibacterial therapies. H. felis status was determined by bacterial culture, urease test, and bacterial and histologic stainings. Release of prostaglandin E₂ from the gastric mucosa was measured by radioimmunoassay. Results: All triple-treated mice were cleared of bacteria both 24 h and 1 month after treatment. However, tinidazole alone also resulted in 100% eradication. Monotherapies with erythromycin acistrate, tetracycline, colloidal bismuth subcitrate, and nitecapone failed to eradicate the bacteria. The release of gastric prostaglandin E₂ was doubled in the infected mice (554 ± 39, mean ± SE) compared with the noninfected mice (270 ± 35) (p < 0.01). Conclusions: The H. felis mouse model proved satisfactory for assessing both anti-Helicobacter therapies and the prostaglandin E₂ release. The reliability of this method was improved when several methods to assess the H. felis status were used in parallel.     

Low Endogenous Prostaglandin E2 Predisposes to Relapsing Inflammation in Experimental Rat Enterocolitis

Intramural injection of peptidoglycan-polysaccharide (PG-PS) induces acute enterocolitis that spontaneously relapses in Lewis but not Fischer rats. Interleukin-1 (IL-1) and tumor necrosis factor- (TNF-) induce prostaglandin E₂ (PGE₂) secretion, which inhibits secretion of these cytokines by macrophages, suggesting an inhibitory feedback mechanism. We postulate that Lewis rat susceptibility to relapse is due to an imbalance between protective prostaglandins and cytokines. Female Fischer and Lewis rats were injected with PG-PS (37.5 g/g) or human serum albumin intramurally. Tissue IL-1 and PGE₂ immunoreactivities and myeloperoxidase (MPO) activity were determined. Relapsing rats had lower PGE₂ and PGE₂/IL-1 ratios than nonrelapsing rats (P < 0.05). In Fischer rats, 2 mg/kg/day of indomethacin potentiated cecal MPO and IL-1 concentrations above PG-PS alone (P < 0.05). Misoprostol treatment blocked PG-PS induced IL-1 and MPO and inhibited the potentiating effect of indomethacin on MPO and IL-1 (P < 0.05). In conclusion, increased endogenous PG may be protective against relapsing inflammation in PG-PS induced enterocolitis, at least partially via inhibition of proinflammatory cytokines. Imbalance between protective prostaglandins and proinflammatory cytokines may be involved in the pathogenesis of chronic relapsing inflammation in genetically susceptible hosts.     

Acid Instillation Increases Gastric Luminal Prostaglandin E2 Output in Man

ABSTRACT. The capacity of the gastroduodenal mucosa to maintain integrity when exposed to acid and pepsin may require formation of endogenous prostaglandins (PG). The gastric mucosa is capable of PG biosynthesis, and PGE₂ is present in the gastric contents of man. The purpose of this study was to examine if acidification of the human stomach affects the output of PGE₂. Gastric perfusion was made with 150 mM HC1 in seven healthy subjects pretreated with a histamine-2-receptor blocker (ranitidine). Gastric luminal PGE₂ was measured by gas chromatography-mass spectrometry. Basal output of PGE₂ was 1.42 ± 0.24 pmol/min (mean+SEM), which increased to 5.37 ± 0.91 pmol/min (p < 0.02) during acid perfusion. Gastric acidification did not cause mucosal damage as judged by luminal DNA. We conclude that PGE₂ is synthesized in the gastric mucosa even during nearly complete inhibition of parietal cell secretion. Luminal acid, a likely physiological stimulator of mucosal defense, induces a fivefold increase in PGE₂ output from the intact mucosa.     

Prostaglandin E2 stimulates ion transport in prairie dog gallbladder

The effects of prostaglandins, and specifically prostaglandin E₂, on gallbladder ion transport were examined in the prairie dog. Gallbladders were mounted in an Ussing chamber and baseline short-circuit current, potential difference, and tissue resistance were measured. Addition of arachidonic acid (10^–4 M, mucosal surface) produced sustained elevations in short-circuit current and potential difference (P<0.05), with mild reductions in resistance. In a second set of tissues, indomethacin exposure (10^–6 M) resulted in a significant (P<0.02) decrease in short-circuit current and potential difference, with an increase in resistance. Subsequent addition of prostaglandin E₂ (10^–7 M, serosal surface) fully reversed these changes and led to a significant increase in short-circuit current and potential difference (P<0.001) with a return of resistance to baseline values. These findings suggest that endogenous prostaglandins mediate gallbladder ion transport.Financial support received from the Veterans Administration. Dr. Saunders-Kirkwood was supported by the Claude E. Welch Research Fellowship, Department of Surgery, Massachusetts General Hospital.     

Effect of acute and chronic alcohol feeding on prostaglandin E2 biosynthesis in rat stomach

The effect of acute and chronic alcohol ingestion on gastric prostaglandin E₂ synthesis and the PGE₂ content in the stomach was studied in rats. Up to 8 hr following a single oral load of 20% alcohol (v/v; 4 g/kg body weight), the PGE₂ synthesis in isolated microsomes from rat stomach remained unchanged as compared with control values. Feeding a liquid alcohol-containing diet (37% of total Joules) for 1,6, or 12 weeks significantly decreased the rate of PGE₂ synthesis (percentage inhibition as compared with control values 39, 27, and 57, respectively). In addition, chronic alcohol feeding led to a drop in the tissue content of PGE₂, the decrease being more pronounced after 6 (–49%) and 12 (–58%) weeks than after 1 week (–24%). The results suggest that the inhibition of endogenous PGE₂ synthesis in the stomach following ingestion of appreciable quantities of alcohol might play a role in the pathogenesis of alcohol-induced injury of the gastric mucosa.     

Repair of Rat Gastric Mucosa (Effect of 16,16-Dimethyl Prostaglandin E2)

Prostaglandins protect the gastric mucosaagainst a variety of injurious agents and may acceleratethe recovery of the gastric mucosa following damage. Inprevious studies prostaglandins were given prior to the injurious agent, so it was not possibleto distinguish their potential effects on acceleratingrepair or reducing initial damage. We have investigatedthe effect of 16,16-dimethyl prostaglandin E₂ (dmPGE₂) on the repair of thegastric muscosa after injury induced by severalinjurious agents. dmPGE₂ was given orally 15min prior to aspirin or sodium salicylate, or 30 minafter aspirin, sodium salicylate, or ethanol. dmPGE₂ delivered priorto injury reduced the aspirin-induced fall in mucosalpotential difference (PD), but had no effect on thatinduced by sodium salicylate. dmPGE₂administered after ASA injury significantly increased recovery of PD (P <0.05), but did not alter the rate of recovery of PD withother damaging agents. Histological damage was decreasedin rats treated with dmPGE₂ after aspirincompared to aspirin-only-treated rats (P < 0.02).Exogenous dmPGE₂ protects and restoresgastric mucosal integrity after aspirin damage but hasno effect on the repair of sodium salicylate and ethanolinjured mucosa, suggesting that repair of the gastric mucosaafter aspirin damage is enhanced by dmPGE₂due to its ability to prevent ongoing damage, ratherthan directly enhancing repair processes.     

Low Endogenous Prostaglandin E2 Predisposes to Relapsing Inflammation in Experimental Rat Enterocolitis

Intramural injection ofpeptidoglycan-polysaccharide (PG-PS) induces acuteenterocolitis that spontaneously relapses in Lewis butnot Fischer rats. Interleukin-1 (IL-1) and tumornecrosisfactor- (TNF-) induce prostaglandin E₂(PGE₂) secretion, which inhibits secretion ofthese cytokines by macrophages, suggesting an inhibitoryfeedback mechanism. We postulate that Lewis ratsusceptibility to relapse is due to an imbalance betweenprotective prostaglandins and cytokines. Female Fischerand Lewis rats were injected with PG-PS (37.5 g/g)or human serum albumin intramurally. Tissue IL-1 and PGE₂ immunoreactivities andmyeloperoxidase (MPO) activity were determined.Relapsing rats had lower PGE₂ andPGE₂:IL-1 ratios than nonrelapsingrats (P < 0.05). In Fischer rats, 2 mg/kg/day indomethacinpotentiated cecal MPO and IL-1 concentrationsabove PG-PS alone (P < 0.05). Misoprostol treatmentblocked PG-PS-induced IL-1 and MPO and inhibited the potentiating effect of indomethacin on MPOand IL-1 (P < 0.05). In conclusion, increasedendogenous PG may be protective against relapsinginflammation in PG-PS induced enterocolitis, at least partially via inhibition of proinflammatorycytokines. An imbalance between protectiveprostaglandins and proinflammatory cytokines may beinvolved in the pathogenesis of chronic relapsinginflammation in genetically susceptible hosts.     

Cyclooxygenase-2 and prostaglandins in articular tissues

OBJECTIVES: To provide an overview on: 1) the expression of cyclooxygenase (COX)-2 in articular tissues; 2) the role of prostaglandin E2 (PGE2) in these tissue functions; and 3) clinical trials with COX-2-selective nonsteroidal anti-inflammatory drugs (NSAIDs) (coxibs). METHODS: MEDLINE search was performed using the key words "cyclooxygenase," "prostaglandin," "osteoarthritis" (OA), and "rheumatoid arthritis" (RA). Selected publications related to clinical trials with coxibs also are included. RESULTS: COX-2 is upregulated in inflamed joint tissues and is responsible for elevated PGE2 production. The overexpression of COX-2 is likely induced by proinflammatory mediators such as interleukin-1beta (IL-1beta) and tumor necrosis factor (TNF) alpha. However, the exact molecular mechanisms through which the expression of COX-2 is regulated remain to be elucidated. Several studies suggest that PGE2 is involved in inflammation, apoptosis, angiogenesis, and possibly structural changes that characterize arthritic diseases. NSAIDs are prescribed for the treatment of OA and RA and provide effective relief from symptoms; however, serious gastrointestinal complications occur with their use. The clinical efficacy of NSAIDs is primarily related to the inhibition of COX-2, whereas much of the toxicity is related to COX-1 inhibition. Selective COX-2 inhibitors (coxibs) that spare COX-1 at therapeutic doses are more effective than placebo and as effective as other NSAIDs for relief of symptoms of OA and RA, and have significantly improved gastrointestinal safety and tolerability. However, some studies showed that COX-2-selective inhibitors still have classic NSAID complications. CONCLUSIONS: Overexpression of COX-2 protein in articular tissues is a characteristic feature of arthritic diseases. However, the molecular mechanisms involved in the regulation of COX-2 expression and activity are still unclear. Elucidating the mechanisms of COX-2 expression and PGE2 production and action will help identify novel and more selective potential drug targets in the treatment of arthritic diseases.     

Upregulated Cyclooxygenase-2 Inhibits Apoptosis of Human Gastric Epithelial Cells Infected with Helicobacter pylori

Helicobacter pylori induces apoptosis and alters the proliferation of gastric mucosal epithelial cells. Cyclooxygenase-2 (COX-2), the inducible form of prostaglandin (PG) synthesis, is known to cause alteration in epithelial cell growth. The goal of this study was to determine whether COX-2 gene expression by H. pylori infection could influence gastric epithelial cell apoptosis. Expression of COX-2 mRNA and proteins was up-regulated in Hs746T gastric epithelial cell lines infected with H. pylori, when assessed by quantitative RT-PCR and western blot. Inhibition of COX-2 expression using NS-398, a specific COX-2 inhibitor, showed a significant increase of gastric epithelial cell apoptosis and caspase-3 activation in Hs746T cells infected with H. pylori. Moreover, the effect of NS-398 on H. pylori-induced apoptosis was reversed by the addition of PGE₂. These results suggest that up-regulated COX-2 expression by H. pylori infection can inhibit apoptosis of gastric epithelial cells.     

Effects of induced mast cell activation on prostaglandin E and metalloproteinase production by rheumatoid synovial tissue in vitro

OBJECTIVE—To determine whether induced mast cell activation/degranulation in rheumatoid synovial explants modulates the production of prostaglandin E (PGE₂), and the matrix metalloproteinases (MMPs) collagenase 1, gelatinase A, and stromelysin 1.
METHODS—Synovial explant cultures were treated either with rabbit IgG anti-human IgE as a mast cell (MC) secretagogue or with non-immune rabbit IgG as controls. After 20 hours conditioned medium was assayed for the release of MC tryptase, PGE₂, collagenase 1, gelatinase A, and stromelysin 1 using radioimmunoassay, enzyme linked immunosorbent assay, western blot, and zymogram techniques; tissue explants were examined immunohistologically for the relative distributions of MC tryptase, collagenase 1, and stromelysin 1.
RESULTS—Over a 20 hour incubation period the MC secretagogue treated explants showed a significant increase in the quantities of released tryptase and PGE₂ compared with controls. By contrast, the three MMPs showed variable values between experiments in response to MC activation; no reproducible trend of either an increased or decreased production of each MMP over control values was evident. Each MMP initially appeared as an inactive precursor form; collagenase 1 and stromelysin 1 were more effectively processed to active forms in the MC activated cultures. Immunolocalisation studies of MC activated explants showed that areas of extracellular tryptase were commonly associated with the local production of both collagenase 1 and stromelysin 1.
CONCLUSION—MC degranulation induced artificially in rheumatoid synovial explant cultures consistently resulted in an increased production of PGE₂ but had variable effects on the quantification of released collagenase 1, gelatinase A, and stromelysin 1. Such observations support the concept that activated synovial MCs within their native environment stimulate the production of non-MC derived PGE₂ and may contribute to the regulation and processing of specific MMPs; both aspects represent important components of the inflammatory and degradative processes of the rheumatoid lesion.

Keywords: mast cells; matrix metalloproteinases; prostaglandin E₂; rheumatoid synovium     

Role of prostaglandin E2 in cholinergic-mediated glycoprotein synthesis in canine antrum

We studied the mechanism of cholinergic stimulation of mucin synthesis in canine antral explants, including the role of PGE₂ as an intermediate messenger. Isolated antral mucosa was incubated with 10^–5 M carbachol (Cb), 10^–5 M indomethacin (IND), 10^–5 M pirenzepine (PZ), 10^–5 M Cb+10^–5 M PZ, 10^–5 M Cb+10^–5 M IND, and 10^–5 M IND +PGE₂ (10^–8, 10^–7 and 10^–6 M) in the presence or absence of [³H]glucosamine. After 24 hr, total glycoprotein synthesis was quantitated by Sepharose-4B chromatography and by 10% TCA/1%PTA precipitation with lipid extraction. PGE₂ released into the media was measured by radioimmunoassay (RIA). Cb significantly increased total glycoprotein synthesis and produced a significant increase in PGE₂ release. The increase in glycoprotein synthesis and the release of PGE₂ was blocked by the addition of muscarinic antagonist PZ. The addition of IND significantly inhibited glycoprotein synthesis and almost entirely suppressed PGE₂ secretion. IND also inhibited the effect of Cb on glycoprotein synthesis and PGE₂ release. Moreover, PGE₂ (10^–6 and 10^–7 M) significantly increased the glycoprotein synthesis in the canine stomach. This suggests the coordinate participation of PGE₂-releasing cell population in modulation of glycoprotein synthesis in gastric mucosa.Supported in part by the Research Service of the Veterans Administration and grant R01-DK37989 and Michigan Gastrointestinal Peptide Research Center, 5P30-DK34933 awarded by the PHS, DHHS.Presented in part at the annual meeting of American Gastroenterological Association in 1990 (Gastroenterology 98: A153).     

Effect of Different Cyclooxygenase Inhibitors on Gastric Adaptive Cytoprotection Induced by 20% Ethanol

In this study, we evaluated the effect of two different dosages of therapeutically prescribed nonsteroidal anti-inflammatory drugs (NSAIDs), ibuprofen, diclofenac, nimesulide, meloxicam, and celecoxib (ED80 for COX-1 and COX-2) on normal gastric mucosa and mucosa, previously exposed to 20% ethanol. At COX-2-inhibiting dosages, the NSAIDs tested were nonulcerogenic, and the same response profile was observed in “adapted” stomachs. Interestingly, low doses of nimesulide and celecoxib increase the levels of Prostaglandin E₂ and COX-2, and protect against subsequent 100% ethanol exposition, suggesting that these drugs may act as “mild irritants” to gastric mucosa. The ulcerogenic response to NSAIDs was prevented by the previous 20% ethanol exposition, probably the result of nitric oxide synthesis, because PGE₂ levels in gastric mucosa were reduced by these agents and a concomitant nitric oxide blockade reversed this protection. Supported by FAPESP, Brazil.     

Prostaglandin E2 and cyclic AMP in tumor and plasma of breast cancer patients

Summary Prostaglandin E₂ and cyclic AMP (cAMP) levels were measured in tumors and plasma of 78 patients with benign and malignant breast tumors. Two groups of malignant tissues were found, one with a high level of PGE₂ M=55.4 pg/mg and one with a low level M=10.7pg/mg. The low level did not differ significantly from the benign tissue level (M=8.7 pg/mg). Two malignant groups could not be detected in the plasma levels. Plasma PGE₂ concentration (in form of the 13,14-dihydro-15-Keto metabolite) did not reflect the tissue levels, and no difference was found between the benign (M=59.9 pg/ml) and the malignant (M=62.3 pg/ml) patients, but both concentrations were higher than those of healthy controls (M=34.4 pg/ml).The stage of the cancer, the histological classification and, most important, the period of survival, could not be related to the differences in the PGE₂ tissue levels. Neither could plasma cAMP be nominated as a breast cancer marker because no difference was found between the cAMP levels of benign tumor patients (M=16.48 pmol/ml), of malignant tumor patients (M=21.24 pmol/ml) and of healthy controls (M=19.07 pmol/ml). The conclusion is that although high amounts of PGE₂ appear in some malignant breast tumors, they do not affect the clinical situation. These results may explain the failure to treat human breast cancer patients with prostaglandin synthetase inhibitors.Abbreviations PGE₂ prostaglandin E₂ - cyclic AMP (cAMP) cyclic adenosine 35-monophosphate - BSA bovine serum albumin - SD standard deviation - SE standard error - M mean     

Attenuation of acetaminophen hepatitis by prostaglandin E2

Acute acetaminophen hepatitis was produced in three groups of five rats given 1600 mg/kg by gavage. The protective effect of 16,16-dimethyl prostaglandin E₂, 200 µg/kg administered subcutaneously 30 min later, was compared to the protective effect ofN-acetylcysteine 1 g/kg similarly administered. All animals were killed at 24 hr, and liver tissues were compared histologically to the damage found in acetaminophen-treated controls and untreated anatomic controls. Serum transaminase values at 24 hr exceeded 1000 units in the acetaminophen control group, averaged 658 units in the acetylcysteine treated group, and were near normal (75 units) in the prostaglandin treated group (P<0.02). Liver samples (1 cm³) were removed terminally at 24 hr. Liver damage was assessed without reference to precedent history. Histopathologically, damage was most severe in the acetaminophen control group, mainly in pericentral lobular zones. The prostaglandin-treated group showed considerably less damage, which was confined to the hepatic vein area. The acetylcysteine-treated group showed an intermediate degree of damage. We conclude that dmPGE₂, given 30 min after ingestion of acetaminophen was found to be more effective in limiting liver damage than NAC in this rat model.     

Prostaglandin E2 and cyclic AMP levels in human breast tumors

Summary Prostaglandin E₂ (PGE₂) and cyclic adenosine-3, 5-monophosphate (cAMP) concentrations were measured in human benign and malignant breast tumors by radioimmunoassay. Two groups were found among the malignant tissues, one with high PGE₂ ( =65.89 pg/mg) and high cAMP ( =0.704 pmole/mg) concentrations and one with low concentrations ( =9.24 pg/mg and =0.299 pmole/mg, respectively). The low PGE₂ levels in the malignant tumors did not differ significantly from the levels found in benign tumors ( =8.06 pg/mg). cAMP levels were positively and highly correlated (r=+0.81) with PGE₂ levels. No bone osteolysis could be discovered in any of the patients a few weeks after mastectomy operation, but PGE₂ analysis of breast tumors may have prognostic value for the future.Abbreviations used PGE₂ prostaglandin E₂ - cAMP cyclic adenosine 3, 5-monophosphate - EDTA ethylenediaminetetraacetic acid - BSA bovine serum albumine - mean - SD standard deviation - SE standard error We thank Mrs. Judith Grienberg for her excellent technical assistance     

Prostaglandin E2 and cyclic nucleotides in plasma and urine of colonic cancer patients

Summary Prostaglandin E₂ and cyclic nucleotide levels were measured in plasma and urine of 14 patients with colonic cancer. The measurements were performed 1 day before and 8 days after the removal of the tumor by operation. There was no difference between the plasma PGE₂ levels (in form of the 13, 14-dihydro-15-keto metabolite) before and after the operation, but they were significantly higher than the level of a control group. No differences before and after operation were found between plasma cyclic AMP (cAMP) levels, plasma cyclic GMP (cGMP) levels, urinary cAMP levels and urinary cGMP levels. All the cyclic nucleotide concentrations were within the normal range. No correlation could be found between the stage of the tumor spread and any of the substances analyzed. The conclusions are that plasma PGE₂ and plasma and urinary cyclic nucleotides do not originate from the colonic tumor tissue, and that these substances cannot be used as tumor markers.