Review article: new insights into prostaglandins and mucosal defence

Selective striatal cell loss is ameliorated by regulated autophagy of the cortex

AIMS

The harmful cellular environment leads to brain damage, and each brain subregion exhibits a differential vulnerability to its effects. This study investigated the causes of selectively striatal cell loss in systemic 3-nitropropionic acid (3-NP) infused mice.

MAIN METHODS

This study was performed in the neuronal cell line, primary neuron, cultured mouse brain, and mice brain tissues. The 3-NP solution was delivered using an osmotic mini-pump system for 7 days. ROS in brain tissue were detected and evaluated with the signals of CM-H2DCFDA for total cellular ROS and MitoSOX Red for mitochondrial ROS. Cellular ROS and the functional status of mitochondria were assessed with a detection kit and analyzed using flow cytometry. To quantify oxidative damaged DNA, apurinic/apyrimidinic (AP) site numbers in DNA were measured. The protein expression level was assessed using Western blotting, and immunohistochemistry was performed. Cleaved caspase-3 activities were measured by using an enzyme-linked immunosorbent assay (ELISA) kit.

KEY FINDINGS

By 3-NP, mitochondrial dysfunction was higher in the striatum than in the cortex, and mitochondria-derived ROS levels were higher in the striatum than in the cortex. However, autophagy that may restore the energy depletion resulting from mitochondrial dysfunction occurred comparably less in the striatum than in the cortex. Inhibition of ASK1 by NQDI1 regulates MAPK signaling, apoptosis, and autophagy. Regulated autophagy of the cortex improved non-cell autonomously striatal damaged condition.

SIGNIFICANCE

This study illustrated that the different vulnerabilities of the brain subregions, striatum or cortex, against 3-NP are rooted in different mitochondria-derived ROS amounts and autophagic capacity.

Antiulcer Effect of Honey in Nonsteroidal Anti-Inflammatory Drugs Induced Gastric Ulcer Model in Rats: A Systematic Review

Background

Peptic ulcer is a basic term for ulcers on the lower oesophagus, stomach, or jejunum. The specific term for ulcer in the stomach is gastric ulcer. The extensive use of honey around the globe helps researchers to study the usefulness of honey. Many studies had already been conducted and proved the effectiveness of honey in treating gastric ulcer.

Methods

A systematic review of the literature was conducted to identify relevant studies on honey used as an alternative treatment of gastric ulcer cause by NSAIDs. A comprehensive search was conducted in Medline, SCOPUS, and Ebscohost. The main criteria used were articles published in English and using NSAIDs-induced gastric ulcer in rat's model and those reporting the effectiveness of honey.

Results

Articles published between 2001 and 2014 were identified to be relevant in studies related to the inclusion criteria. The literature search found 30 potential and closely related articles in this review, but only 5 articles were taken which meet the criteria needed to be fulfilled.

Conclusions

All studies in this review reported the efficacy of honey for gastric ulcer based on its antioxidant and cytoprotective activities. Most of the studies conducted used different types of honey at various doses on rats. Future studies should be conducted to identify the appropriate dose for humans to achieve similar gastroprotective effects.

Effect of Aspirin and ibuprofen either alone or in combination on gastric mucosa and bleeding time and on serum prostaglandin E2 and thromboxane A2 levels in the anaesthetized rats in vivo

There is much evidence that a combination of ibuprofen (IBU) and Aspirin (ASA) can antagonize the irreversible inhibition of platelet function. This study was designed to investigate the degree of gastric damage, bleeding time (BT) and fluctuations in the serum levels of prostaglandin E₂ (PGE₂) and thromboxane A₂ (TXA₂) after oral administration of ASA (200 mg/kg) and IBU (50 mg/kg) either alone or in combination in rats in vivo. The stomach was assessed for any damage either after 6 h, 18 h or 6 days and carboxymethylcellulose (1% CMC) served as a vehicle and control. ELISA was used to measure TXA₂ and PGE₂ in serum. Bleeding time was assessed using tail blood. The results show that ASA and IBU either alone or in combination can cause gastric ulceration in 25-100% of the rats at 6 and 18 h. In contrast, gastric ulceration was seen in 50% of rats with a combination of ASA given before IBU only after 6 days of oral administration. BT was unaffected either by ASA or IBU when administered alone except after 18 h for IBU. In contrast, BT was significantly reduced when IBU was administered before ASA after 18 h and 6 days (P < 0.001). Serum PGE₂ levels decreased significantly after ASA administered either alone or in combination with IBU for 6 h, 18 h and 6 days (P < 0.05). Serum TXA₂ levels were significantly reduced after 6 h, 18 h and 6 days following ASA and IBU administration except for IBU alone which caused a significant increase in serum TXA₂ 6 days after its administration (P < 0.01). It can be concluded that ASA and IBU administered either alone or in combination can cause gastric ulcers in the rat stomach after 6 h and 18 h, but less severe after 6 days. IBU either alone or in combination with ASA reduced BT only after 18 h and 6 days of administration. Together, the results show that gastric ulceration correlated well with the inhibition of serum PGE₂ and TXA₂ levels.

Should patients prescribed long-term low-dose aspirin receive proton pump inhibitors? A systematic review and meta-analysis

BACKGROUND

Several clinical guidelines recommend the use of proton pump inhibitors (PPIs) in patients taking low-dose aspirin but report no or limited supporting data. We conducted a systematic review and meta-analysis to examine the effects of co-administration of PPIs in patients taking low-dose aspirin on the risks of adverse gastrointestinal (GI) and cardiovascular (CV) events, and on patient adherence to aspirin.

METHODS

We searched PUBMED, EMBASE and Cochrane Central Register of Controlled Trials databases for relevant articles published through November 2013. We included randomised controlled trials (RCTs) and observational studies in patients taking low-dose aspirin with and without PPIs. Risk of bias was assessed using the Cochrane Collaboration's tool (for RCTs) and the Newcastle-Ottawa Scale (for observational studies). Pooled risk ratios (RRs) were computed using a random-effects model.

RESULTS

We included 13 studies, of which 12 (2 RCTs and 10 observational studies) reported on GI events, and one (cohort study) on both GI bleeding and CV events. No study reported on adherence to aspirin. Co-administration of PPIs in patients receiving low-dose aspirin was associated with risk reductions of 73% (RR 0.27, 95% CI 0.17-0.42) and 50% (RR 0.50, 95% CI 0.32-0.80) in the occurrence of peptic ulcer and GI bleeding respectively. There was evidence of bias in publications reporting on the GI events.

CONCLUSIONS

The practice of co-prescribing PPIs in patients taking low-dose aspirin is supported by some data, but the evidence is rather weak. It currently remains unclear whether the benefits of co-administration of PPIs in users of low-dose aspirin outweigh their potential harms.

Gastric mucosal protection by aegle marmelos against gastric mucosal damage: role of enterochromaffin cell and serotonin

BACKGROUND/AIMS

Serotonin (5-hydroxytryptamine; 5-HT) released from enterochromaffin (EC) cells in gastric mucosa inhibits gastric acidity by increasing the gastric mucus secretion. In the present study, we evaluated the effect of aqueous extract of Aegle marmelos (AM) ripe fruit pulp (250 mg/kg body weight) on mean ulcer index (MUI), EC cells, 5-HT content, and adherent mucosal thickness of ulcerated gastric tissue in adult albino rats.

MATERIAL AND METHODS

Ulceration was induced by using aspirin (500 mg/kg, p.o.), cerebellar nodular lesion and applying cold-restraint stress.

RESULTS

In all cases increased MUI in gastric tissue along with decreased EC cell count was observed with concomitant decrease of 5-HT content and adherent mucosal thickness (P < 0.05). Pretreatment with AM for 14 days decreased MUI, increased EC cell count, and 5-HT content as well as adherent mucosal thickness in all ulcerated group (P < 0.05).

CONCLUSION

AM produces gastric mucosal protection mediated by increased EC cell count and 5-HT levels.

Yu Ping Feng San, an ancient Chinese herbal decoction, regulates the expression of inducible nitric oxide synthase and cyclooxygenase-2 and the activity of intestinal alkaline phosphatase in cultures

Yu Ping Feng San (YPFS), a Chinese herbal decoction comprising Astragali Radix (AR; Huangqi), Atractylodis Macrocephalae Rhizoma (AMR; Baizhu), and Saposhnikoviae Radix (SR; Fangfeng), has been used clinically to treat inflammatory bowel diseases (IBD). Previously, we demonstrated a dual role of YPFS in regulating cytokine release in cultured macrophages. In this study, we elucidated the anti-inflammatory effect of YPFS that is mediated through modulating the expression of three key enzymes involved in IBD: inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), and intestinal alkaline phosphatase (IALP). In a lipopolysaccharide (LPS)-induced chronic-inflammation model of cultured murine macrophages, YPFS treatment suppressed the activation of iNOS and COX-2 expression in a dose-dependent manner. Conversely, application of YPFS in cultured small intestinal enterocytes markedly induced the expression of IALP in a time-dependent manner, which might strengthen the intestinal detoxification system. A duality of YPFS in modulating the expression of iNOS and COX-2 was determined here. The expression of iNOS and COX-2 in macrophages was induced by YPFS, and this activation was partially blocked by the NF-κB-specific inhibitor BAY 11-7082, indicating a role of NF-κB signaling. These YPFS-induced changes in gene regulation strongly suggest that the anti-inflammatory effects of YPFS are mediated through the regulation of inflammatory enzymes.

Brainstem neuropeptides and vagal protection of the gastric mucosal against injury: role of prostaglandins, nitric oxide and calcitonin-gene related peptide in capsaicin afferents

Earlier experimental studies indicated that the integrity of vagal pathway was required to confer gastric protection against damaging agents. Several peptides located in the brainstem initially identified to influence vagal outflow to the stomach, as assessed by electrophysiological approach or by vagal dependent alterations of gastric secretory and motor function, were investigated for their influence in the vagal regulation of the resistance of the gastric mucosa to injury. Thyrotropin releasing hormone (TRH), or its stable TRH analog, RX-77368, injected at low doses into the cisterna magna or the dorsal motor nucleus (DMN) was the first peptide reported to protect the gastric mucosa against ethanol injury through stimulation of vagal cholinergic pathways, inducing the release of gastric prostaglandins/nitric oxide (NO) and the recruitment of efferent function of capsaicin sensitive afferent fibers containing calcitonin-gene related peptide (CGRP). Activation of endogenous TRH-TRH1 receptor signaling located in the brainstem plays a role in adaptive gastric protection against damaging agents. Since then, an expanding number of peptides, namely peptide YY, CGRP, adrenomedullin, amylin, glugacon-like peptide, opioid peptides acting on µ, δ1 or δ2 receptors, nocicpetin, nocistatin, ghrelin, leptin and TLQP-21, a peptide derived from VGF prohormone, have been reported to act in the brainstem to afford gastric protection against ethanol injury largely through similar peripheral effectors mechanisms than TRH. Therefore gastric prostaglandins and CGRP/NO pathways represent a common final mechanism through which brain peptides confer vagally mediated gastroprotection against injury. A better understanding of brain circuitries through which these peptides are released will provide new strategies to recruit integrated and multifaceted gastroprotective mechanisms.

Attenuation of stress-induced gastric lesions by lansoprazole, PD-136450 and ranitidine in rats

Combining restraint with cold temperature (4°C) consistently induces gastric ulceration in rats after 3.5 h. The cold restraint-stress (CRS) method provides a suitable model for acute ulcer investigations. This study compares the antiulcer activities of lansoprazole (a proton pump inhibitor), PD-136450 (CCK(2)/gastrin receptor antagonist) and ranitidine (histamine H(2) receptor antagonist) on CRS-induced gastric ulcers in rats. The results have shown that lansoprazole, which is a potent anti-secretory agent, provides complete protection in this model of ulcer formation. The use of indomethacin pretreatment to inhibit the prostaglandin (PG) synthesis and N(G)-nitro L-arginine methyl ester (L-NAME) pretreatment to inhibit nitric oxide synthase did not alter the lansoprazole-induced inhibition of ulcer index obtained in the untreated Wistar rats indicating that these two systems were not involved in the activation of lansoprazole. PD-136450, an effective anti-secretory agent against gastrin- but not dimaprit-induced stimulation, evoked a dose-dependent inhibition of CRS-induced gastric ulcers. The results show that both PG and nitric oxide pathways can influence the inhibitory effect of PD-136450 against CRS-induced gastric ulcer. The antiulcer activities of both lansoprazole and PD-136450 were compared to that of ranitidine. The results showed that ranitidine was more potent than lansoprazole and PD-136450 in inhibiting CRS-induced gastric ulcers and its effect was shown to be influenced by PG as well as nitric oxide synthase. The results of this study have demonstrated that although lansoprazole, PD-136450 and ranitidine were protective against CRS-induced gastric ulcers, the antiulcer activities of PD-136450 and ranitidine involved both PG and nitric oxide pathways, while lansoprazole acted independently of these two systems during CRS.

Role of cyclooxygenase isoforms in prostacyclin biosynthesis and murine prehepatic portal hypertension

Portal hypertension (PHT) is a common complication of liver cirrhosis and significantly increases morbidity and mortality. Abrogation of PHT using NSAIDs has demonstrated that prostacyclin (PGI(2)), a direct downstream metabolic product of cyclooxygenase (COX) activity, is an important mediator in the development of experimental and clinical PHT. However, the role of COX isoforms in PGI(2) biosynthesis and PHT is not fully understood. Prehepatic PHT was induced by portal vein ligation (PVL) in wild-type, COX-1(-/-), and COX-2(-/-) mice treated with and without COX-2 (NS398) or COX-1 (SC560) inhibitors. Hemodynamic measurements and PGI(2) biosynthesis were determined 1-7 days after PVL or sham surgery. Gene deletion or pharmacological inhibition of COX-1 or COX-2 attenuated but did not ameliorate PGI(2) biosynthesis after PVL or prevent PHT. In contrast, treatment of COX-1(-/-) mice with NS398 or COX-2(-/-) mice with SC560 restricted PGI(2) biosynthesis and abrogated the development of PHT following PVL. In conclusion, either COX-1 or COX-2 can mediate elevated PGI(2) biosynthesis and the development of experimental prehepatic PHT. Consequently, PGI(2) rather then COX-selective drugs are indicated in the treatment of PHT. Identification of additional target sites downstream of COX may benefit the >27,000 patients whom die annually from cirrhosis in the United States alone.

Role of nitric oxide in the gastrointestinal tract

Worldwide osteoarthritis (OA) affects more than 9.6% of men and 18% of women older that 60 years. Treatment for OA often requires chronic use of selective or nonselective nonsteroidal anti-inflammatory drugs (NSAIDs), which have been associated with gastrointestinal and cardiovascular complications. An increased risk for upper gastrointestinal bleeding with NSAIDs alone and when combined with low-dose aspirin has been described in numerous studies. Although cyclo-oxygenase-2 inhibitors have been shown to carry a lower risk for gastrointestinal injury than nonselective NSAIDs, research continues to identify new treatments that not only are effective but also provide an improved benefit/risk profile, including better gastrointestinal tolerability. Nitric oxide (NO) is known to have a protective effect on the gastrointestinal tract. In preclinical studies NO was shown to help maintain gastric mucosal integrity, to inhibit leukocyte adherence to the endothelium, and to repair NSAID-induced damage. In addition, epidemiologic studies have shown that the use of NO-donating agents with NSAIDs or aspirin resulted in reduced risk for gastrointestinal bleeding. Recent studies have shown that cyclo-oxygenase inhibiting NO-donating drugs (CINODs), in which a NO molecule is chemically linked to an NSAID, are effective anti-inflammatory agents and may result in less gastrointestinal damage than is associated with NSAID use. Therefore, these agents provide a potential therapeutic option for patients with arthritis who require long-term NSAID therapy.

Lack of effects of acemetacin on signalling pathways for leukocyte adherence may explain its gastrointestinal safety

BACKGROUND AND PURPOSE

Acemetacin is a non-steroidal anti-inflammatory drug which is rapidly bioconverted to indomethacin, but produces significantly less gastric damage than indomethacin. This study was performed to investigate several possible mechanisms that could account for the gastrointestinal tolerability of acemetacin.

EXPERIMENTAL APPROACH

The gastric and intestinal damaging effects of acemetacin and indomethacin were examined in the rat. Effects of the drugs on blood levels of leukotriene B(4) and thromboxane B(2), on leukocyte-endothelial adherence in post-capillary mesenteric venules, and on gastric expression of tumour necrosis factor-alpha (TNF-alpha) were determined. The two drugs were also compared for gastric toxicity in rats pretreated with inhibitors of COX-2 and NOS.

KEY RESULTS

Acemetacin induced significantly less gastric and intestinal damage than indomethacin, despite markedly suppressing COX activity. Indomethacin, but not acemetacin, significantly increased leukocyte adherence within mesenteric venules, and gastric expression of TNF-alpha. Pretreatment with L-nitro-arginine methyl ester or lumiracoxib increased the severity of indomethacin-induced gastric damage, but this was not the case with acemetacin.

CONCLUSIONS AND IMPLICATIONS

The increased gastric and intestinal tolerability of acemetacin may be related to the lack of induction of leukocyte-endothelial adherence. This may be attributable to the reduced ability of acemetacin to elevate leukotriene-B(4) synthesis and TNF-alpha expression, compared to indomethacin, despite the fact that acemetacin is rapidly bioconverted to indomethacin after its absorption.

The anti-apoptosis protein, survivin, mediates gastric epithelial cell cytoprotection against ethanol-induced injury via activation of the p34(cdc2) cyclin-dependent kinase

The anti-apoptosis protein, survivin, promotes cell survival and mitosis. Recent studies have demonstrated that survivin is expressed in normal gastric mucosa. Using an in vitro model, we examined whether survivin plays a role in the cytoprotection produced in gastric mucosa by mild irritant ethanol (ETOH) against subsequent exposure to concentrated ETOH. Pre-treatment of rat gastric epithelial cells with 1% ETOH reduced cell death, in response to subsequent incubation with 5% ETOH, by 94% (P < 0.005). This pre-treatment also resulted in increased total and phosphorylated survivin protein levels by 180% (P < 0.0001) and 540% (P < 0.0002), respectively, which required the p34(cdc2) cell cycle-dependent kinase. The cytoprotective effect was abrogated upon siRNA knockdown of survivin protein levels. Further, overexpression of exogenous survivin resulted in significant cytoprotection by 62% (P < 0.02) in the absence of any pre-treatment. We further examined the in vivo relevance of these findings. In fasted rats, administration of 20% ETOH, which we found to be 93% (P < 0.0001) cytoprotective against 50% ETOH challenge, resulted in increased total and phosphorylated survivin protein levels by 234% (P < 0.001) and 214% (P < 0.02), respectively. Administration of 20% ETOH resulted in increased gastric p34(cdc2) activity by 146% (P < 0.01). Inhibition of p34(cdc2) by the potent inhibitor, roscovitine, abolished the increased survivin levels in response to pre-administration of 20% ETOH and reduced the cytoprotection against 50% ETOH challenge by 59% (P < 0.01). These results indicate that survivin is a key mediator of cytoprotection against ETOH-induced gastric injury, acting at the epithelial cell level, by a mechanism that is dependent, in part, on p34(cdc2).

The anti-secretory and anti-ulcer activities of esomeprazole in comparison with omeprazole in the stomach of rats and rabbits

Proton pump inhibitors (PPIs) are widely used to treat hyperacid secretion and stomach ulcers. The study investigated the anti-secretory and anti-ulcer effects of esomeprazole, the S-isomer of omeprazole on dimaprit, histamine and dibutyryl adenosine 3, 5 cyclic monophosphate (dbcAMP)-evoked gastric acid secretion, acidified ethanol (AE) and indomethacin (INDO)-induced haemorrhagic lesions and on prostaglandin E2 (PGE2) level in the rat in vivo and rabbit in vitro preparations. The effect of omeprazole was also investigated for comparison. Dimaprit-induced acid secretion was significantly (P < 0.05) inhibited by both PPIs in a dose-dependent manner. In the isolated rabbit gastric glands, both PPIs elicited marked reductions in histamine- and dbcAMP-evoked acid secretion with similar potency. The lesions induced by either AE or INDO were significantly (P < 0.05) reduced in the presence of either esomeprazole or omeprazole compared to control values. Increasing doses of esomeprazole before AE treatment resulted in a marked degree of cytoprotection and an elevation in the concentration of bound PGE2 in the stomach tissue homogenate. The results show that esomeprazole and omeprazole were equally effective against gastric haemorrhagic lesions induced by either AE or INDO and in inhibiting dimaprit-, dbcAMP- and histamine-induced gastric acid secretion in the rat and rabbit stomach both in vivo and in vitro. The gastro-protective effect of esomeprazole was found to be proportional to the bound PGE2 levels in the glandular area of the stomach.

Antiinflammatory and antiulcer properties of tannins fromMyracrodruon urundeuva Allemão (Anacardiaceae) in Rodents

Myracrodruon urundeuva Allemão is a plant utilized in Northeast Brazil as an antiinflammatory, wound healing and in gynecological illnesses. The objectives of the present study were to evaluate the antiinflammatory and antiulcer properties of the tannin-enriched fraction (TEF) isolated from the stem bark of M. urundeuva, in the formalin test, in mice, and in carrageenan-induced paw edema and gastric ulcer models, in rats. The results showed that TEF dose-dependently inhibited both phases of the formalin test. However, the effect was predominant in the 2nd phase of the response where inhibitions of 47%, 76% and 85% were observed, with doses of 5, 10 and 50 mg/kg, i.p. In the carrageenan-induced paw edema, significant inhibitions were observed at 3 h (44%) and 4 h (28%), with a dose of 10 mg/kg, i.p. TEF also significantly decreased by 37%, 43% and 57% gastric ulceration induced by indomethacin, at doses of 10, 20 and 50 mg/kg p.o. In the ethanol-induced gastric ulcer model, TEF was less effective, and significant inhibitions (42% to 46%) were observed only with doses of 100 and 200 mg/kg, p.o., respectively. In conclusion, it was shown that TEF presents antiinflammatory and antiulcer effects, partly due to its antioxidant action, known to be present in polyphenols, including tannins.

Mechanisms of action of leptin in preventing gastric ulcer

AIM: To investigate the effects of leptin (1-20 μg/kg) on acidified ethanol (AE)- and indomethacin (Indo)-induced gastric lesions in rats and compare it with ranitidine, lanso-prazole, and omeprazole and to determine its mechanisms of actions.

METHODS: Gastric ulcers, which were approximately 1 mm in width, formed in the glandular portion of the gastric mucosa produced by oral administration of either AE or Indo were taken as ulcer index. The inhibitory effect of subcutaneous administration of leptin, two proton pump inhibitors (PPIs) lansoprazole and omeprazole, or H₂-receptor antagonist ranitidine 30 min before AE or Indo was evaluated. A radioimmunoassay was used to determine the PGE₂ concentration in the homogenate of the glandular portion of the stomach. We performed histological study of the glandular stomach for the evaluation of total, acidic, and sulfated mucus content.

RESULTS: Subcutaneous administration of leptin, two PPIs lansoprazole and omeprazole or H₂-receptor antagonist ranitidine 30 min before AE or Indo produced a dose-dependent and reproducible inhibition of gastric ulcers (GUs). This inhibition was found to be more potent than other antagonists used. In N^G-nitro L-arginine methyl ester (L-NAME)-pretreated animals, the ulcer prevention ability of leptin in AE-induced ulcer was significantly reduced, compared to rats without L-NAME pretreatment. However, the ulcer prevention ability of leptin was not altered by L-NAME treatment in Indo-induced ulcers. Leptin produced a dose-dependent increase in PGE₂ level in the gastric glandular tissues. Leptin also increased mucus secretion.

CONCLUSION: The results of the present study show that leptin inhibits GU formation by AE or Indo in a dose-dependent and reproducible manner in rats. The results also suggest that leptin prevents ulcer formation by increasing the activities of the cyclo-oxygenase and/or nitric oxide pathways and by increasing mucus secretion.

The role of arachidonic acid regulatory enzymes in colorectal disease

PURPOSE

Nonsteroidal anti-inflammatory drugs have a wide ranging effect on diseases of the colon and rectum. Interestingly, nonsteroidal anti-inflammatory drugs seem to play a beneficial role in colorectal cancer chemoprevention and adenoma regression, but may have a deleterious effect in inflammatory bowel disease. Prostaglandin inhibition is central to both the beneficial and toxic effects of this class of drugs. Arachidonic acid metabolism is essential to prostaglandin synthesis.

METHODS

A Medline search using "nonsteroidal anti-inflammatory drugs," "colon cancer," "inflammatory bowel disease," "colitis," "COX inhibitors," "arachidonic acid," and "chemoprevention" as key words was performed for English-language articles. Further references were obtained through cross-referencing the bibliography cited in each work.

RESULTS

Based on numerous studies, nonsteroidal anti-inflammatory drugs have a beneficial role in colon cancer and colonic adenomas. However, they have been reported to have a deleterious effect on the colon in inflammatory bowel disease and have been shown to cause colitis. Nonsteroidal anti-inflammatory drugs work via multiple pathways, some well defined, and others unknown.

CONCLUSIONS

In the new millennium, nonsteroidal anti-inflammatory drugs may be used for chemoprevention of colorectal and other cancers. In addition, they may be used in combination with surgery and chemotherapy to primarily treat colorectal carcinoma. Undoubtedly, the use of novel cyclooxygenase inhibitors with less of a toxicity profile will allow more widespread use of nonsteroidal anti-inflammatory drugs for a variety of diseases. The future of this class of drugs is promising.

NSAID-induced peptic ulcers and Helicobacter pylori infection: implications for patient management

The conflicting data about the influence of Helicobacter pylori infection on the ulcer risk in patients receiving NSAIDs can be accounted for by the heterogeneity of study designs and the diversified host response to H. pylori. Factors that will affect the outcome include the choice of H. pylori diagnostic tests, previous ulcer complications, concurrent use of acid suppressants, NSAID-naive versus long-term users, low-dose aspirin (acetylsalicylic acid) versus non-aspirin NSAIDs and whether the result was derived from a pre-specified endpoint or post hoc subgroup analysis. Current evidence suggests that H. pylori eradication reduces the ulcer risk for patients who are about to start receiving NSAIDs but not for those who are already on long-term NSAID therapy. Since treatment with a proton pump inhibitor (PPI) worsens H. pylori-associated corpus gastritis, H. pylori should be tested for, and eradicated if present, before starting long-term prophylaxis with PPIs. Patients with H. pylori infection and a history of ulcer complications who require NSAIDs should receive concomitant PPIs or misoprostol after curing the infection. Among patients receiving low-dose aspirin, who have H. pylori infection and previous ulcer complications, long-term treatment with a PPI further reduces the risk of complicated ulcers if H. pylori eradication fails or if patients use concomitant non-aspirin NSAIDs. Current data on the gastric safety of COX-2 selective NSAIDs in H. pylori-infected patients are conflicting. Limited data suggest that the gastroduodenal sparing effect of rofecoxib is negated by H. pylori infection in patients who have had prior upper gastrointestinal events. In light of potential cardiovascular risk with COX-2 selective NSAIDs, it is important to weigh the potential adverse effects against the benefits for an individual patient.

Plaunotol prevents the progression of acute gastric mucosal lesions induced by compound 48/80, a mast cell degranulator, in rats

We examined the preventive effect of plaunotol, an antiulcer drug, on acute gastric mucosal lesion progression in rats treated once with compound 48/80 (C48/80). Rats treated with C48/80 (0.75 mg/kg BW, i.p.) received plaunotol (10, 25 or 50 mg/kg BW, p.o.) 0.5 h after the treatment at which time gastric mucosal lesions appeared. The gastric mucosa of C48/80-treated rats showed progressed lesions and had increased myeloperoxidase (an index of neutrophil infiltration) activity and thiobarbituric acid reactive substances (an index of lipid peroxidation) content and decreased ascorbic acid and adherent mucus contents and Se-glutathione peroxidase activity at 3 h after C48/80 treatment. Postadministered plaunotol attenuated all these changes dose-dependently. These attenuating effects of plaunotol were not counteracted by pretreatment with indomethacin (5 mg/kg BW, i.p.), a prostaglandin synthesis inhibitor. These results indicate that plaunotol prevents the progression of C48/80-induced acute gastric mucosal lesions in rats possibly by its anti-inflammatory and antioxidant actions, but not by affecting gastric mucosal prostaglandin levels.

The effects of selective cyclooxygenase-2 inhibitors, celecoxib and rofecoxib, on experimental colitis induced by acetic acid in rats

Several mediators may be involved in the pathogenesis of inflammatory bowel disease, as well as in experimental colitis. The present work was conducted to investigate the effects of the two selective cyclooxygenase-2 inhibitors, celecoxib and rofecoxib, on experimentally induced colitis in rats. Rectal instillation of acetic acid was used to induce the colitis. Acetic acid treatment caused haemorrhagic diarrhoea and weight loss in rats. Celecoxib (5 mg/kg) or rofecoxib (2.5 mg/kg), when given twice daily by the oral route, reduced the degree of haemorrhagic diarrhoea and the weight loss produced. In addition, they produced a significant reduction in the degree of colonic injury, the rise in myeloperoxidase (MPO) levels, total nitric oxide synthetase (NOS) activity, platelet-activating factor (PAF), histamine levels and prostaglandin E2 levels. In contrast, there was a significant increase in the levels of reduced glutathione (GSH). Thus, the findings of the present study provide evidence that selective cyclooxygenase-2 inhibitors may be beneficial in patients with inflammatory bowel disease.

Nitrite in saliva increases gastric mucosal blood flow and mucus thickness

Salivary nitrate from dietary or endogenous sources is reduced to nitrite by oral bacteria. In the acidic stomach, nitrite is further reduced to NO and related compounds, which have potential biological activity. We used an in vivo rat model as a bioassay to test effects of human saliva on gastric mucosal blood flow and mucus thickness. Gastric mucosal blood flow and mucus thickness were measured after topical administration of human saliva in HCl. The saliva was collected either after fasting (low in nitrite) or after ingestion of sodium nitrate (high in nitrite). In additional experiments, saliva was exchanged for sodium nitrite at different doses. Mucosal blood flow was increased after luminal application of nitrite-rich saliva, whereas fasting saliva had no effects. Also, mucus thickness increased in response to nitrite-rich saliva. The effects of nitrite-rich saliva were similar to those of topically applied sodium nitrite. Nitrite-mediated effects were associated with generation of NO and S-nitrosothiols. In addition, pretreatment with an inhibitor of guanylyl cyclase markedly inhibited nitrite-mediated effects on blood flow. We conclude that nitrite-containing human saliva given luminally increases gastric mucosal blood flow and mucus thickness in the rat. These effects are likely mediated through nonenzymatic generation of NO via activation of guanylyl cyclase. This supports a gastroprotective role of salivary nitrate/nitrite.

Nitrite in saliva increases gastric mucosal blood flow and mucus thickness

Salivary nitrate from dietary or endogenous sources is reduced to nitrite by oral bacteria. In the acidic stomach, nitrite is further reduced to NO and related compounds, which have potential biological activity. We used an in vivo rat model as a bioassay to test effects of human saliva on gastric mucosal blood flow and mucus thickness. Gastric mucosal blood flow and mucus thickness were measured after topical administration of human saliva in HCl. The saliva was collected either after fasting (low in nitrite) or after ingestion of sodium nitrate (high in nitrite). In additional experiments, saliva was exchanged for sodium nitrite at different doses. Mucosal blood flow was increased after luminal application of nitrite-rich saliva, whereas fasting saliva had no effects. Also, mucus thickness increased in response to nitrite-rich saliva. The effects of nitrite-rich saliva were similar to those of topically applied sodium nitrite. Nitrite-mediated effects were associated with generation of NO and S-nitrosothiols. In addition, pretreatment with an inhibitor of guanylyl cyclase markedly inhibited nitrite-mediated effects on blood flow. We conclude that nitrite-containing human saliva given luminally increases gastric mucosal blood flow and mucus thickness in the rat. These effects are likely mediated through nonenzymatic generation of NO via activation of guanylyl cyclase. This supports a gastroprotective role of salivary nitrate/nitrite.

Effects of Ginkgo biloba extract on cytoprotective factors in rats with duodenal ulcer

AIM: To investigate the effects of Ginkgo biloba extract on cytoprotective factors in rats with duodenal ulcer.

METHODS: Sprague-Dawley rats were randomly divided into four groups: sham operation without ginkgo, sham operation with ginkgo, duodenal ulcer without ginkgo, and duodenal ulcer with ginkgo. Rats with duodenal ulcer were induced by 500 mL/L acetic acid. Rats with ginkgo were intravenously injected with Ginkgo biloba extract from the tail at a dose of 0.5 mg/(kg·d) for 7 and 14 days.

RESULTS: Pathological result showed that duodenal ulcer rats with ginkgo improved mucosal healing and inflammation compared with those without ginkgo after 7 d treatment. After 14 d treatment, duodenal ulcer rats with ginkgo significantly increased weight gain (34.0 ± 4.5 g versus 24.5 ± 9.5 g, P < 0.05) compared with those without ginkgo. Duodenal ulcer rats significantly increased cell proliferation (27.4 ± 4.0 and 27.8 ± 2.3 BrdU-labeled cells in duodenal ulcer rats with and without ginkgo versus 22.4 ± 3.5 and 20.8 ± 0.5 BrdU-labeled cells in sham operation rats with and without ginkgo, P < 0.05) compared with sham operation rats. Mucosal prostaglandin E₂ concentration significantly increased by 129% (P < 0.05) in duodenal ulcer rats with ginkgo compared with that in those without ginkgo. Duodenal ulcer rats without ginkgo significantly decreased superoxide dismutase activity in the duodenal mucosa and erythrocytes (19.4 ± 6.7 U/mg protein versus 38.1 ± 18.9 U/mg protein in the duodenal mucosa, and 4.87 ± 1.49 U/mg protein versus 7.78 ± 2.16 U/mg protein in erythrocytes, P < 0.05) compared with sham operation rats without ginkgo. However, duodenal ulcer rats with ginkgo significantly increased erythrocyte superoxide dismutase activity (8.22 ± 1.92 U/mg protein versus 4.87 ± 1.49 U/mg protein, P < 0.05) compared with those without ginkgo. Duodenal ulcer rats without ginkgo significantly increased plasma lipid peroxides (4.18 ± 1.12 μmol/mL versus 1.60 ± 1.10 μmol/mL and 1.80 ± 0.73 μmol/mL, P < 0.05) compared with sham operation rats without ginkgo and duodenal ulcer rats with ginkgo during the experimental period.

CONCLUSION: Ginkgo biloba extract can improve weight gain and mucosal healing in duodenal ulcer rats by the actions of cytoprotection and antioxidation.

Treatment of acute and chronic gastrointestinal inflammation

Treating inflammation in the equine gastrointestinal tract remains a challenge. Our most potent anti-inflammatory drugs, COX inhibitors and glucocorticoids, have unwanted effects on the gastrointestinal tract and host defense that often limit their use. Newer strategies targeting specific cells and molecules that regulate a subset of the events occurring during inflammation are rapidly becoming available and should allow clinicians to reduce the detrimental effects of inflammation without inhibiting the beneficial aspects.

The CINOD, AZD3582, exhibits an improved gastrointestinal safety profile compared with naproxen in healthy volunteers

COX-inhibiting nitric oxide donators (CINODs) are a new class of drugs in development for the treatment of acute and chronic pain. They comprise a COX-inhibiting moiety linked to a nitric-oxide-donating component and are designed to provide an innovative mechanism of action of balanced COX inhibition and controlled nitric oxide donation. Through these pathways, CINODs should provide analgesic and anti-inflammatory efficacy, while offering gastrointestinal safety through the tissue-protective effects of nitric oxide donation. AZD3582 [4-(nitrooxy)butyl-(2S)-2-(6-methoxy-2-naphthyl)propanoate] is the first agent in the CINOD class to enter extensive clinical development. Pre-clinical studies demonstrate that AZD3582 has a superior gastrointestinal safety profile to naproxen, while demonstrating analgesic and anti-inflammatory efficacy. In healthy human volunteers, AZD3582 caused little gastrointestinal damage compared with equimolar doses of naproxen. Studies to evaluate the longer-term gastrointestinal safety of AZD3582, alongside its efficacy in alleviating chronic and acute pain, are ongoing.

Nitric oxide releasing drugs: from bench to bedside

NO biology has had an enormous boost and several aspects of its role in physiology and pathology has been extensively studied. NO acts as a double edge sword mediator that has beneficial physiological effects as well as detrimental pathological effects making very difficult to develop drugs. Studies on nitric oxide therapeutic approach can be divided into two simple approaches: one directed to increase the NO release and another to inhibit NO release. Gene therapy approach have been also developed and pre-clinical data on iNOS and eNOS have shown promising results in post-angioplasty restenosis. The major limitation to the use of NSAID is represented by their ability to cause ulceration and bleeding in the gastrointestinal tract NO plays an important role in GI integrity. NO releasing NSAID have higher GI tolerability and retain their anti-inflammatory activity as well as the ability to inhibit platelet aggregation. NO-NSAIDs not only represents a new class of drugs but they represent the first "proof of concept" on the key role of NO in the gastrointestinal homeostasis.

Effect of H. pylori infection on the expression of cyclooxygenase-2 in human gastric mucosa

Cyclooxygenase-1 is the primary isoform responsible for the production of cytoprotective prostaglandins (PGE(2) and PGI(2)) in the stomach. In contrast COX-2 is induced at the sites of inflammation. Using Helicobacter pylori infection as a model of inflammation, this study was designed to evaluate the effects of H. pylori infection on prostanoid synthesis and expression of COX-2 in human gastric mucosa. Prostaglandin (PGE(2)) and prostacyclin (PGI(2)) synthesis in gastric biopsies obtained from 21 patients undergoing diagnostic endoscopy, were determined. H. pylori was detected by CLO test, histology and culture. Biopsy samples were incubated either with NS-398, selective COX-2 inhibitor or aspirin. Samples were also treated with endotoxin (LPS) in order to induce COX-2 expression. Tissue was also analysed for COX-2 expression in vivo by immunohistochemistry. In 15 out of 21 patients, H. pylori was detected by at least two of the three methods. Higher levels of PGE(2) and PGI(2) were seen in patients infected with H. pylori (191+/-30 and 245+/-88ng/mg protein, respectively) compared with non-infected patients (77+/-17 and 120+/-36ng/mg protein, respectively). There was significant inhibition of PGE(2) and PGI(2) with aspirin in both H. pylori infected (28+/-6.6 and 53+/-43ng/mg, respectively) and in non-infected patients (16+/-7 and 12.5+/-3.5ng/mg protein, respectively). However, NS-398 and LPS did not alter prostaglandin function significantly. Immunohistochemistry in all patients irrespective of Hp status demonstrated expression of COX-2.Lower concentration of constitutive expression of COX-2 was detected in human gastric mucosa by immunohistochemistry, however, H. pylori infection failed to induce COX-2 protein. In addition, increased prostaglandin synthesis in Hp-infected patients appears to be COX-1 mediated rather than COX-2. Furthermore, failure of endotoxaemia-treated sample to produce more PGE(2) in the face of enhanced COX-2 expression in gastric mucosa further suggests that increased prostanoids in human gastric stomach are COX-1 mediated.

Cellular localization of cyclooxygenase-1 and cyclooxygenase-2 in the normal mouse, rat, and human retina

Prostaglandins, synthesized by cyclooxygenase (COX), regulate diverse neurophysiological actions such as regulation of autonomic responses, transmission of pain, generation of fever, control of sleep-wake cycle, synaptic signaling, and cross-talk between neurons and glia in the central nervous system. Although prostaglandins have been widely studied in the anterior segment tissues of the eye, relatively little is known about prostaglandins in the neural retina. By using immunohistochemistry, we have compared the cellular expression and localization of COX-1 and COX-2 in the normal mouse, rat, and human retina. In the normal mouse retina, COX-1 immunoreactivity is present in the outer segments of photoreceptor cells, horizontal cells, microglia, retinal ganglion cells, and displaced amacrine cells. In the normal rat retina, COX-1 immunoreactivity is present in microglia, retinal ganglion cells, and displaced amacrine cells. In the normal human retina, COX-1 immunoreactivity is present in microglia, astrocytes, retinal ganglion cells, and displaced amacrine cells. In the normal mouse and rat retina, COX-2 immunoreactivity is present in processes of the outer plexiform layer and in certain amacrine cells and retinal ganglion cells. In the normal human retina, COX-2 immunoreactivity is only present in processes of the outer plexiform layer. These results suggest that prostaglandins, synthesized by COX-1 or COX-2, may contribute to normal physiological and homeostatic functions in the retina.

Impact of Helicobacter pylori and nonsteroidal anti-inflammatory drugs on gastric ulcerogenesis in experimental animals and in humans

Helicobacter pylori (H. pylori) and nonsteroidal anti-inflammatory drugs (NSAID) are the most common pathogens in the gastroduodenal mucosa in animals and humans, but their relationship in ulcerogenesis has been little studied. According to some authors, H. pylori infection in humans does not act synergistically with NSAID on ulcer healing, therefore, there is no need to eradicate the germ. This notion is supported by the finding that the eradication of H. pylori does not affect NSAID-induced gastropathy treated with omeprazole and that H. pylori infection induces a strong cyclooxygenase-2 expression resulting in excessive biosynthesis of gastroprotective prostaglandins, which should in turn counteract NSAID-induced gastropathy and heal the existing ulcer. Other investigators claim that H. pylori infection acts synergistically with NSAID on ulcer development, therefore, H. pylori should be eradicated, particularly at the start of long-term NSAID therapy. Maastricht 2-2000 consensus also recommends eradication prior to NSAID treatment, but this eradication does not appear to accelerate ulcer healing or to prevent the recurrent ulcers in NSAID users. Our studies in almost 6,000 dyspeptic patients undergoing upper endoscopy and [(13)C]-urea breath test (UBT) revealed that about 70% of these patients are H. pylori (+) and about 30.6% of these develop gastroduodenal ulcers. Of these ulcers, over 70% were H. pylori (+) positive, 12% NSAID (+), 8% were both H. pylori (+) and NSAID (+), while 22% ulcers were H. pylori (-) and NSAID (-) or "idiopathic" ulcers. Basically, our results support Hawkey's concept and this also agrees with our findings in the rat model showing that: (1) there is no synergistic interaction between H. pylori infection and NSAID on gastric ulcer development, (2) H. pylori and NSAID are independent risk factors for peptic ulceration, and (3) NSAID therapy in H. pylori positive patients attenuates the ulcer development possibly due to direct inhibitory action of these drugs on H. pylori.

Phenotypes of the COX-deficient mice indicate physiological and pathophysiological roles for COX-1 and COX-2

The development of mice deficient in either cyclooxygenase-1 (COX-1) or COX-2, as well as mice deficient in both COX isoforms, has provided models to elucidate the physiological and pathophysiological roles of these enzymes. The findings obtained with the COX-deficient mice suggest that COX-2 may be more important than COX-1 for supplying prostaglandins (PGs) to maintain tissue homeostasis. Furthermore, both isoforms may be involved in the development of diseases, such as inflammation and cancer. Therefore, the contribution of each isoform to the prevention or development of disease is more complex than originally described. Studies with the COX-deficient mice suggest that in addition to COX-2-selective inhibition, therapeutic advances may also be achieved with COX-1-selective inhibitors which lack gastrointestinal side effects.

Helicobacter pylori and nonsteroidal anti-inflammatory drugs

The complex interaction between H. pylori and NSAIDs implies that it is over simplistic to conclude that their relationship is independent, synergistic, or antagonistic without considering the influence of other factors. Factors such as previous exposure to NSAIDs, a history of ulcer complication, concurrent use of acid-suppressant therapy, and the difference between NSAIDs and low-dose aspirin all affect the outcome. Several recommendations can be made with regard to the indications of H. pylori eradication for patients requiring NSAIDs. First, patients taking NSAIDs who have ulcers or previous ulcer disease should be tested for the bacterium, and it should be eradicated if present because it is impossible to determine whether the ulcers are caused by H. pylori or NSAIDs or both. Antiulcer drugs should be prescribed to prevent ulcer recurrence for patients who continue to require NSAIDs. Although the efficacy of omeprazole is enhanced by H. pylori infection, it is not justified to leave a pathogen in the stomach in exchange for a modest therapeutic gain. Second, for patients who take low-dose aspirin, eradication of H. pylori substantially reduces the risk of ulcer bleeding. It is advisable that patients taking low-dose aspirin who are at risk of ulcer bleeding should be tested for H. pylori and treated for it if the infection is found. Third, for patients who are about to start NSAIDs, screen-and-treat H. pylori has the potential of reducing the ulcer risk at an affordable incremental cost. It might be argued that any interaction between H. pylori and NSAIDs would become irrelevant in the era of COX-2-selective NSAIDs. Even among patients who are receiving a COX-2-selective NSAID, however, a large-scale study showed that the ulcer risk is significantly higher in H. pylori-positive patients than in uninfected patients. This finding suggests that the relative importance of H. pylori in ulcer development might increase with a reduced toxicity of COX-2-selective NSAIDs. With an increasing use of low-dose aspirin for cardiovascular prophylaxis, the problem of aspirin-related ulcer disease is expected to rise. Given the significant role of H. pylori in the latter condition, screen-and-treat H. pylori might be a useful strategy for the prevention of ulcer complications in high-risk patients receiving low-dose aspirin in the future.

Soluble products from Eikenella corrodens stimulate oral epithelial cells to induce inflammatory mediators

In the inflammatory response elicited by bacterial colonization in periodontal pockets, pocket epithelial cells not only serve as a barrier to isolate the pocket microenvironment from external stimuli but also regulate the functions of neighboring cells including fibroblasts and inflammatory cells. To elucidate this mechanism, we characterized the effects of periodontopathic bacterium Eikenella corrodens 1073 components on the production of some inflammatory mediators in a human oral epithelial cell line (KB). In enzyme-linked immunosorbent assay (ELISA), the E. corrodens supernatant induced interleukin-6 (IL-6), IL-8 and prostaglandin E2 but not interferon-gamma (IFN-gamma) production by KB cells. After incubation with E. corrodens supernatant, KB cells showed a marked increase in the levels of IL-6, IL-8 and PG G/H synthase (cyclooxygenase)-2, but not IFN-gamma, gene expression by reverse-transcriptase polymerase chain reaction. All these E. corrodens products responsible for production of these inflammatory mediators resisted freezing and boiling and were present in a 10-kDa filtrate. These results imply that these soluble small-molecular-mass products from E. corrodens stimulate various inflammatory mediator productions by human oral epithelial cells and may play a role in the initiation of periodontal inflammation and subsequently perpetuate the inflammatory response during chronic infection.

Ridogrel enemas in distal ulcerative colitis

OBJECTIVE

To evaluate the effect of Ridogrel enemas (Janssen Research Foundation, Beerse, Belgium) on disease activity and mucosal inflammatory mediators in patients with active left-sided ulcerative colitis.

DESIGN AND METHODS

Eleven patients with active left-sided ulcerative colitis were evaluated in an open non-placebo-controlled pilot study. All patients were treated with Ridogrel enemas (300 mg/40 ml once daily) over four weeks. A disease activity score based on clinical, endoscopic and histological criteria was obtained before and after treatment with Ridogrel. The concentrations of thromboxane B2 (TxB2), prostaglandin E2 (PGE2), interleukin-6 (IL-6) and tumour necrosis factor alpha (TNF-alpha) were measured in mucosal biopsies before and after treatment.

RESULTS

One patient discontinued treatment because of progression of disease, the other ten patients tolerated the Ridogrel enemas well. Mucosal TxB2 concentration decreased significantly in all patients. The mucosal concentrations of the other inflammatory mediators (PGE2, IL-6 and TNF-alpha) were unaltered. The disease score decreased in five patients. However, clinical improvement was not always associated with a decrease in endoscopic and/or histological scores.

CONCLUSIONS

This pilot study shows that Ridogrel enemas selectively reduce mucosal TxB2 concentration.

Helicobacter pylori-induced prostaglandin E(2) synthesis involves activation of cytosolic phospholipase A(2) in epithelial cells

Helicobacter pylori initiates an inflammatory response and gastric diseases, which are more common in patients infected with H. pylori strains carrying the pathogenicity island, by colonizing the gastric epithelium. In the present study we investigated the mechanism of prostaglandin E(2) (PGE(2)) synthesis in response to H. pylori infection. We demonstrate that H. pylori induces the synthesis of PGE(2) via release of arachidonic acid predominately from phosphatidylinositol. In contrast to H. pylori wild type, an isogenic H. pylori strain with a mutation in the pathogenicity island exerts only weak arachidonic acid and PGE(2) synthesis. The H. pylori-induced arachidonic acid release was abolished by phospholipase A(2) (PLA(2)) inhibitors and by pertussis toxin (affects the activity of G alpha(i)/G alpha(o)). The role of phospholipase C, diacylglycerol lipase, or phospholipase D was excluded by using specific inhibitors. An inhibitor of the stress-activated p38 kinase (SB202190), but neither inhibitors of protein kinase C nor an inhibitor of the extracellular-regulated kinase pathway (PD98059), decreased the H. pylori-induced arachidonic acid release. H. pylori-induced phosphorylation of p38 kinase and cytosolic PLA(2) was blocked by SB202190. These results indicate that H. pylori induces the release of PGE(2) from epithelial cells by cytosolic PLA(2) activation via G alpha(i)/G alpha(o) proteins and the p38 kinase pathway.

Group I secreted PLA2 in the maintenance of human lower esophageal sphincter tone

BACKGROUND & AIMS

In cat spontaneous lower esophageal sphincter (LES), tone is maintained by the activity of group I secreted phospholipase A2 (sPLA2-I) that produces arachidonic acid. Arachidonic acid metabolites activate G proteins linked to phospholipases, producing second messengers and activation of a protein kinase C-dependent pathway to maintain tone. We examined the role of sPLA2-I in the maintenance of tone in human LES samples obtained from organ donors.

METHODS

In vitro LES tone and sPLA2-I-induced contraction of enzymatically isolated LES smooth muscle cells were measured in the absence or presence of inhibitors. Cell permeabilization by saponin allowed use of G-protein antibodies.

RESULTS

In vitro LES tone was reduced by inhibitors of sPLA2-I, by indomethacin, by the phosphatidylcholine-specific phospholipase C inhibitor D609, and by the protein kinase C inhibitor chelerythrine. sPLA2-I-induced contraction of isolated LES smooth muscle cells was reduced by indomethacin, pertussis toxin, Gi3 antibodies, D609, and by chelerythrine.

CONCLUSIONS

Human LES tone is maintained by the activity of sPLA2-I that produces arachidonic acid and metabolites and activation of Gi3-linked receptors and of phosphatidylcholine-specific phospholipase C, resulting in production of diacylglycerol, activation of PKC, and maintenance of tone through a protein kinase C-dependent contractile pathway.

Comparison of the intestinal toxicity of celecoxib, a selective COX-2 inhibitor, and indomethacin in the experimental rat

BACKGROUND

It is suggested that the gastrointestinal toxicity of conventional non-steroid anti-inflammatory drugs (NSAIDs) is due to a 'topical' effect in addition to inhibition of the mucosal constitutive cyclo-oxygenase-1 (COX-1) enzyme. COX-2 selective inhibitors have been shown to have excellent gastrointestinal tolerability, but it is not known whether this is due to their selectivity and/or a lack of a 'topical' effect. We assessed the effects of celecoxib (a highly selective COX-2 inhibitor) on key pathophysiologic events in NSAID enteropathy.

METHODS

The 'topical' effects of indomethacin and celecoxib were assessed in vitro (coupled mitochondrial respiration) and in vivo (mitochondrial electron microscopy) and the consequences by study of intestinal permeability (51-Cr-labelled ethylenediamine-tetraacetic acid urinary excretion) and inflammation. We also assessed intestinal prostanoid levels (prostaglandin E, PGE) and the propensity of the drugs to induce intestinal ulcers.

RESULTS

Indomethacin uncoupled mitochondrial oxidative phosphorylation in vitro and in vivo, caused a significant (P < 0.0001) increase in intestinal permeability, caused mucosal inflammation and a 90% decline in intestinal PGE levels, and was associated with multiple small intestinal ulcers. Celecoxib caused no significant increase in any of these parameters, did not decrease intestinal PGE levels, and caused no intestinal ulcers.

CONCLUSIONS

The intestinal tolerability of celecoxib appears to be due to a combination of the absence of a 'topical' damaging effect and selective COX inhibition.

Mechanism of action of nonsteroidal anti-inflammatory drugs

After more than a century of use, pharmacologists thought they had discovered the mechanism of action of nonsteroidal anti-inflammatory drugs (NSAIDs) when their inhibitory action on the production of prostaglandins was described. This action was located at the inhibition of the enzyme responsible for the conversion of arachidonic acid to prostaglandins, namely cyclo-oxygenase. More recently, it has been recognized that more than one isoform of the enzyme exists. The two forms of cyclo-oxygenase described are widely different in their location, activity, and role, especially because the COX-1 isoenzyme seems to be mainly a constitutive enzyme whereas the COX-2 isoenzyme is inducible. This separation of activity appears to be correlated with the separation of function of the various prostaglandins, whereas the constitutive form is associated with "physiologic" functions and the inducible form with inflammatory responses. Recent advances have included the development of drugs with a high specificity toward the inducible enzyme (COX-2) to focus on the anti-inflammatory actions, because many of the unwanted side effects of NSAIDs have been associated with inhibition of the constitutive isoform (COX-1). Other recent developments in studies of the NSAIDs have included potential therapeutic actions in other degenerative conditions.

Non-steroidal anti-inflammatory drugs and apoptosis in the gastrointestinal tract: potential role of the pentose phosphate pathways

Non-steroidal anti-inflammatory drugs (NSAIDs) are among the most widely prescribed drugs, primarily for treatment of arthritis. NSAIDs can have two effects independent of their anti-inflammatory action. In the stomach and small bowel long term NSAID consumption can lead to ulceration, whereas in the colon NSAID use can regress existing tumours. In this review, we hypothesise that NSAID-induced damage occurs predominantly by promoting apoptosis, involving a number of mechanisms depending on the type and the redox state of the cell. In addition to inhibiting cyclooxygenase (COX) activity, this includes interfering with glucose metabolism through both arms of the pentose phosphate pathways and energy production via glycolysis and oxidative phosphorylation. Shifting the cellular balance from proliferation to apoptosis is probably the most important outcome by which NSAIDs exhibit their differing actions. Understanding how these different pathways can be reconciled and their contribution to the balance between cell birth and cell death is the challenge for the future. The pentose phosphate pathways may provide a pivotal point for understanding links between factors which alter proliferative activity (e.g. COXs), provide energy metabolism (particularly aerobic and anaerobic metabolism of glucose), and change the redox state of the cell leading to apoptosis.

How do NSAIDs cause ulcer disease?

Gastroduodenal ulceration and bleeding are the major limitations to the use of non-steroidal anti-inflammatory drugs (NSAIDs). The development of safer NSAIDs or of effective therapies for the prevention of the adverse effects of existing NSAIDs requires a better understanding of the pathogenesis of NSAID-induced ulcer disease. NSAIDs can cause damage to the gastroduodenal mucosa via several mechanisms, including the topical irritant effect of these drugs on the epithelium, impairment of the barrier properties of the mucosa, suppression of gastric prostaglandin synthesis, reduction of gastric mucosal blood flow and interference with the repair of superficial injury. The presence of acid in the lumen of the stomach also contributes to the pathogenesis of NSAID-induced ulcers and bleeding, by impairing the restitution process, interfering with haemostasis and inactivating several growth factors that are important in mucosal defence and repair. In recent years, a fuller understanding of the pathogenesis of NSAID-induced ulcer disease has facilitated some new, very promising approaches to the development of stomach-sparing NSAIDs.

Non-steroidal anti-inflammatory drugs (NSAIDs) and gastro-intestinal toxicity: current issues

Non-steroidal anti-inflammatory drugs (NSAIDs) are among the most widely used drugs and their widespread use is associated with increased gastro-intestinal toxic effects such as ulceration, haemorrhage, perforation and death. They result in these complications mainly by reducing cytoprotective prostaglandins (PGE2 and PGI2) in the stomach, through the inhibition of cyclo-oxygenase (COX) enzyme. The increased morbidity and mortality, in addition to enormous cost, associated with NSAID-associated side effects, necessitates a need for safer GI-friendly NSAID. Various approaches have been used to counteract NSAID associated side effects with varying degrees of success and acceptance. These include the use of alternative analgesia, anti-acid secretory agents like proton pump inhibitors, sucralfate and prostaglandin analogues. In addition, new types of NSAIDs are being developed, based on new understanding of their mechanism of action and the pathogenesis of inflammation. These include a new class of NSAIDs called "selective Cox-2 inhibitors". These agents preserve the COX-1 that is responsible for the production of cytoprotective prostaglandins in the stomach and selectively inhibit COX-2 induced at the sites of inflammation. Selective COX-2 inhibitors exert the same analgesic and anti-inflammatory effects as the existing NSAIDs but may be less toxic to the stomach. In this review the background development and well-structured clinical trials on this new generation NSAIDs are discussed.

Central and peripheral vagal mechanisms involved in gastric protection against ethanol injury

Activation of medullary thyrotropin-releasing hormone (TRH), at a dose subthreshold to increase gastric acid secretion, protects the gastric mucosa against ethanol injury through vagal cholinergic pathways in urethane-anaesthetized rats. Peripheral mediators involve the efferent function of capsaicin-sensitive splanchnic afferents leading to calcitonin gene-related peptide (CGRP)- and nitric oxide (NO)-dependent gastric vasodilatory mechanisms. In addition, gastric prostaglandins participate in gastric protection through mechanisms independent of the stimulation of gastric mucosal blood flow and mucus secretion. Medullary TRH has physiological relevance in the vagal-dependent adaptive gastric protection induced by mild (acid or ethanol), followed by strong, irritants. Additional neuropeptides, namely peptide YY (PYY), somatostatin analogues, CGRP and adrenomedullin, also act in the brainstem to induce a vagal-dependent gastric protection against ethanol through interactions with their specific receptors in the medulla. Central PYY and adrenomedullin act through vagal cholinergic prostaglandins and NO pathways, while somatostatin analogue acts through vagal non-adrenergic, non-cholinergic vasoactive intestinal peptide and NO mechanisms. Although their biological relevance is still to be established, these peptides provide additional tools to investigate the multiple vagal-dependent mechanisms which increase the resistance of the gastric mucosa to injury.

Expression of nitric oxide synthase in inflammatory bowel disease is not affected by corticosteroid treatment

AIM

To examine the effect of corticosteroid treatment on the expression of inducible nitric oxide synthase (iNOS) in the colon of patients with inflammatory bowel disease.

METHODS

Four groups of patients were studied: (1) ulcerative colitis treated with high dose corticosteroids (six patients, 10 blocks); (2) ulcerative colitis patients who had never received corticosteroids (10 patients, 16 blocks); (3) Crohn's disease treated with high dose corticosteroids (12 patients, 24 blocks); (4) Non-inflammatory, non-neoplastic controls (four patients, six blocks). Full thickness paraffin sections of colons removed at surgery were immunostained with an antibody raised against the C terminal end of iNOS. Sections were assessed semiquantitatively for the presence and degree of inflammation and immunoreactivity for nitric oxide synthase.

RESULTS

Cases of ulcerative colitis and Crohn's disease with active inflammation showed strong staining for nitric oxide synthase. The staining was diffuse in ulcerative colitis and patchy in Crohn's disease, in accordance with the distribution of active inflammation. Staining was seen in epithelial cells and was most intense near areas of inflammation such as crypt abscesses. Non-inflamed epithelium showed no immunoreactivity. Treatment with corticosteroids made no difference to the amount of nitric oxide synthase.

CONCLUSIONS

Expression of nitric oxide synthase is increased in both ulcerative colitis and Crohn's disease and appears to be unaffected by treatment with corticosteroids. Disease severity necessitated surgery in all the cases included in this study, regardless of whether or not the patients had received long term corticosteroid treatment. It seems therefore that a high level of iNOS expression and, presumably, production of nitric oxide characterise cases which are refractory to clinical treatment; this suggests that specific inhibition of the enzyme may be a useful therapeutic adjunct.

Effect of a nitric oxide-releasing naproxen derivative on hypertension and gastric damage induced by chronic nitric oxide inhibition in the rat

NSAIDs can elevate blood pressure through mechanisms such as renal vasoconstriction and sodium retention. These effects are particularly evident in hypertensive individuals. Nitric oxide-releasing NSAID derivatives have been shown to have greatly reduced toxicity in the gastrointestinal tract and kidney. We therefore evaluated the effects of a 4 week treatment with either naproxen or its nitric oxide-releasing derivative (NO-naproxen) on systemic arterial blood pressure and gastric damage in rats in which hypertension was induced by L-NAME. Rats received either L-NAME dissolved in the drinking water (400 mg/L) or tap water (control). Vehicle, naproxen (10 mg/kg) or an equimolar dose of NO-naproxen (14.5 mg/kg) were administered orally each day. After 4 weeks, blood pressure was measured, blood samples were taken for measurement of thromboxane synthesis, and gastric damage was evaluated by blind, macroscopic scoring. Both naproxen and NO-naproxen inhibited systemic cyclooxygenase activity by >90%. NO-naproxen-treated rats exhibited no significant gastric damage. The gastric damage produced by L-NAME alone was potentiated by naproxen but prevented by NO-naproxen. L-NAME treatment significantly increased blood pressure. In the absence of L-NAME, the naproxen group had significantly higher blood pressure than both the control and NO-naproxen groups. In rats receiving L-NAME, the same conclusions apply, but the concomitant administration of NO-naproxen was able to significantly reduce the blood pressure compared to L-NAME alone. Based on these results, we conclude that NO-naproxen may represent a safer alternative to standard NSAIDs in the treatment of inflammatory conditions in hypertensive patients.

A chelate theory for the mechanism of action of aspirin-like drugs

Two hundred years after the discovery of the pharmaceutical usefulness of aspirin, it and aspirin-like drugs, a family with an ever-increasing number of members, are an indispensable part of modern life. However, the question as to how these drugs work in the body has remained unsettled. It is postulated here that this group of drugs may exert their therapeutic (and adverse) effects by chelating various physiologically important metallic cations in the body. The chelate theory is supported by the vast majority, if not all, of the observations on these drugs made in the past.