Characterization of Prostaglandin G/H Synthase 1 and 2 in rat, dog, monkey, and human gastrointestinal tracts

The role of prostaglandins and other eicosanoids in the gastrointestinal tract

Nonsteroidal anti-inflammatory drugs (NSAIDs) are generally prescribed to ameliorate symptoms associated with acute pain and chronic inflammatory diseases such as arthritis. Recent epidemiologic studies and clinical trials indicate that use of NSAIDs and cyclooxygenase (COX)-2 selective inhibitors are associated with a reduced risk of certain malignancies, especially gastrointestinal cancer. The cyclooxygenase enzymes are the best known targets of NSAIDs; this diverse class of compounds blocks conversion of arachidonic acid to prostanoids. Prostaglandins and other eicosanoids derived from COX-1 and COX-2 are involved in a variety of physiologic and pathologic processes in the gastrointestinal tract. Recent efforts to identify the molecular mechanisms by which COX-2-derived prostanoids exert their proneoplastic effects have provided a rationale for the possible use of NSAIDs alone or in a combination with conventional or experimental anticancer agents for the treatment or prevention of gastrointestinal cancers.

Modified Ant Colony Optimization Algorithm for Variable Selection in QSAR Modeling: QSAR Studies of Cyclooxygenase Inhibitors

A new version of an ant colony optimization (ACO) algorithm has been proposed. A modified ACO algorithm is proposed to select variables in QSAR modeling and to predict inhibiting action of some diarylimidazole derivatives on cyclooxygenase (COX) enzyme. As a comparison to this method, the evolution algorithm (EA) was also tested. Experimental results have demonstrated that the modified ACO is a useful tool for variable selection that needs few parameters to be adjusted and converges quickly toward the optimal position.

COX-2 inhibitor, NS398, enhances Fas-mediated apoptosis via modulation of the PTEN-Akt pathway in human gastric carcinoma cell lines

A variety of human cancer cells are resistant to Fas ligand and anti-Fas antibody induced apoptosis. Previously, we reported that human gastric carcinoma cell lines were resistant to the anti-Fas antibody, CH-11, without interferon-gamma pretreatment in vitro. Cyclooxygenase (COX)-2 is known to be expressed in many human malignancies, and is correlated with tumor progression and resistance to apoptosis. This study examined whether NS398, a COX-2 inhibitor, inhibited cell proliferation and increased Fas-mediated apoptosis in human gastric carcinoma cell lines. Treatment of NS398 inhibited cell proliferation in MKN-45, which expressed the highest level of COX-2 among seven human gastric carcinoma cell lines, in a dose- and time-dependent manner, in contrast to less prominent effects in KATO-III, which expresses no COX-2. Although the treatment of CH-11 induced apoptosis in both cells, the simultaneous treatment of NS398 and CH-11 remarkably induced apoptosis, as confirmed by Hoechst 33258 staining and the terminal deoxynucleotidyl transferase- mediated dUTP-digoxigenin nick-end labeling (TUNEL) method in MKN-45. Flow cytometric analysis also revealed the increased pre-G1 fraction by the simultaneous treatment. The treatment of NS398 induced upregulation of Bad and PTEN, and downregulation of phosphorylated Akt (Thr308). These findings suggest that COX-2 might inhibit Fas-mediated apoptosis in human gastric carcinoma cell lines, especially MKN-45, by modulating PTEN and Akt.

Significance of cyclooxygenase-2 induced via p38 mitogen-activated protein kinase in mechanical stimulus-induced peritoneal adhesion in mice

Postoperative peritoneal adhesion represents a major complication of surgery, but the molecular mechanism underlying pathogenesis of adhesion is not fully understood. The present study investigated the roles of cyclooxygenase (COX)-1 and COX-2 in peritoneal adhesion induced by scraping the surface of the cecum and abdominal wall in mice. Slight, but macroscopically observable, peritoneal adhesion was induced even on day 1, and the extent of adhesion reached a maximum on day 7 and beyond. COX-1 mRNA was constitutively expressed in the intact cecum, and its expression level was not altered after the mechanical stimulus. In contrast, expression of the COX-2 gene was markedly increased after the stimulus, and maximum expression was observed on days 3 to 7. Mofezolac, a specific COX-1 inhibitor, had no effect on peritoneal adhesion at 30 mg/kg and had only marginal effects on prostaglandin (PG)E2 levels in the cecum or peritoneal fluid. On the other hand, two highly selective inhibitors for COX-2, NS-398 (N-[2-(cyclohexyloxy)-4-nitrophenyl]-methanesulfonamide) and CAY10404 [3-(4-methylsulphonylphenyl)-4-phenyl-5-trifluoromethylisoxazole], dose-dependently inhibited both adhesion formation and the increase in PGE2 levels (3-30 mg/kg). The effects of NS-398 were eliminated when PGE2 or (R)-butaprost was administered exogenously. A COX-2 antisense oligonucleotide also attenuated adhesion formation. Activation of p38 mitogen-activated protein (MAP) kinase was observed in the traumatized cecum, and an MAP kinase inhibitor, SB202190 [4-(4-fluorophenyl)-2-(4-hydroxyphenyl)-5-(4-pyridyl)-1H-imidazole], inhibited adhesion formation (54% inhibition at 15 microM) and also reduced the COX-2 mRNA level and PGE2 levels. In conclusion, COX-2, but not COX-1, plays a significant role in mechanical stimulus-induced peritoneal formation in the mouse cecum.

Effect of Sodium Diclofenac on Microcirculation and Composition of the Lymph during Fever Reaction

Therapeutic effect of sodium diclofenac during fever reaction is associated not only with specific modulation of thermoregulation, but also with the increase in the count of lymphocytes transported with the lymph into systemic circulation, stimulation of lymph microcirculation, and improvement of metabolism in the interstitial space. This preparation inhibited kininogenesis and stimulated degradation of kinins. Sodium diclofenac serves as a universal inhibitor of the kallikrein-kinin system.

Cyclo-oxygenase-1 and -2 expression in human oral mucosa, dysplasias and squamous cell carcinomas and their pathological significance

Cyclo-oxygenase (COX) is a key enzyme in the conversion of arachidonic acid to prostanoids. The expression of its isoforms, COX-1 and -2 is found in many human malignancies. This study analyzed the correlation between COX expression and the pathobiological nature of human oral mucosa, dysplasias and squamous cell carcinomas (SCCs). We examined 9 specimens of normal oral epithelia, 65 lesions with dysplasias and 50 SCCs. Labeling indices (LIs) for COX-1, COX-2, Ki-67 and P53, microvessel density (MVD) and apoptotic index (AI) were evaluated using immunohistochemistry and TUNEL methods. Western blot analysis of COX-1 and -2 was performed on four human oral SCC cell lines, all of which showed expression. The LIs for COX-1 and -2 were higher for the dysplasias than the SCCs. LIs of COX-2 but not COX-1 correlated with the histological grade of dysplasia, being highest for the severe dysplasias (p < 0.05). In contrast, the COX-2 LIs as well as COX-1 were significantly (p < 0.05) inversely correlated with the histological differentiation of the SCCs. COX-2 expression was significantly correlated with LIs of COX-1 for dysplasia (p < 0.05), but not for the SCCs. In addition no significant relationship was noted between COX-2 expression and the Lis of Ki-67, P53, AI as well as MVD for the dysplasias and SCCs. The expression of COX-1 and -2 is correlated with early stage tumorigenesis and cellular differentiation of SCCs in the oral dysplasia-carcinoma sequence.

Gastrointestinal effects of COX-2 inhibitors

The developing popularity of non-steroidal anti-inflammatory drugs (NSAIDs) over the last 100 years has been paralleled by an increase in associated complications, particularly affecting the gastrointestinal (GI) tract [1]. Over this period, there have been several attempts to develop less toxic NSAIDs, most of which have been unsuccessful. Since the discovery that the enzyme cyclooxygenase (COX) exists as two isoforms, the largely constitutive COX-1 and the mainly inducible COX-2, much interest has centred on the development of drugs capable of selectively inhibiting COX-2. Early studies that investigated specific COX-2 inhibitors (with no effect on the COX-1 isoform over the whole range of concentrations achieved in clinical usage) are encouraging, as they demonstrate that these drugs have fewer effects on gastroduodenal mucosa than standard NSAIDs given at equivalent doses. Further clinical experience with these agents outside trial settings and additional studies to assess the role of COX-2 when induced in the GI tract are needed, before such agents can be safely recommended for widespread prescribing.

Cyclooxygenase-2 regulates the degree of apoptosis by modulating bcl-2 protein in pleomorphic adenoma and mucoepidermoid carcinoma of the parotid gland

CONCLUSION

These results suggest that COX-2 and bcl-2 protein were overexpressed and that apoptosis was reduced in MEC compared to PMA, and that COX-2 may regulate the degree of apoptosis by modulating bcl-2 protein in PMA and MEC.

OBJECTIVE

Cyclooxygenase (COX)-2 plays a crucial role in tumorigenesis and overexpression of COX-2 in vitro accompanied by overexpression of bcl-2 protein has been shown to reduce apoptosis. The purpose of this study was to verify that COX-2 regulates the degree of apoptosis by modulating bcl-2 protein in benign and malignant parotid gland tumors. : We examined archival formalin-fixed, paraffin-embedded tissue sections of 10 pleomorphic adenomas (PMAs) and 10 mucoepidermoid carcinomas (MECs) by immunostaining with anti-COX-2, anti-bcl-2 and anti-single-stranded DNA (ssDNA) antibodies. Labeling indices of the three antibodies were calculated using computer-assisted image analysis.

RESULTS

Labeling indices (mean+/-SD) of anti-COX-2 antibody in PMA and MEC were 2.05+/-1.30 and 11.2+/-2.95, respectively (p < 0.001), those of anti-bcl-2 antibody were 2.00+/-1.28 and 9.68+/-4.05, respectively (p < 0.001) and those of anti-ssDNA antibody were 8.06+/-2.54 and 2.08+/-1.47; respectively (p <0.001). Correlation coefficients between the labeling indices of anti-COX-2 antibody and anti-bcl-2 antibody, anti-bcl-2 antibody and anti-ssDNA antibody and anti-COX-2 antibody and anti-ssDNA antibody were 0.88, -0.75 and -0.76, respectively (p <0.001).

Video capsule endoscopy to prospectively assess small bowel injury with celecoxib, naproxen plus omeprazole, and placebo

BACKGROUND & AIMS

Data indicate that cyclooxygenase-2-specific inhibitors cause less gastroduodenal mucosal damage than nonspecific NSAIDS, but their effects on the small bowel mucosa are less well recognized. In a multicenter, double-blind, placebo-controlled trial with video capsule endoscopy (VCE) we prospectively evaluated the incidence of small bowel injury in healthy subjects treated with celecoxib compared to naproxen plus omeprazole.

METHODS

We randomly assigned subjects with normal baseline VCEs to celecoxib 200 mg twice daily (n = 120), naproxen 500 mg twice daily plus omeprazole 20 mg once daily (n = 118), or placebo (n = 118) for 2 weeks. The primary end point was the mean number of small bowel mucosal breaks per subject.

RESULTS

Baseline VCE found small bowel lesions in 13.8% (57/413) of screened subjects, who became ineligible for randomization. The mean number of small bowel mucosal breaks per subject and the percentage of subjects with these mucosal breaks were 2.99 +/- 0.51, 55% for naproxen/omeprazole compared to 0.32 +/- 0.10, 16% for celecoxib and 0.11 +/- 0.04, 7% for placebo (P < .001, both comparisons). The magnitude of the difference between celecoxib and placebo was small but statistically significant (P = .04).

CONCLUSIONS

Among healthy subjects with lesion-free baseline VCEs, celecoxib was associated with significantly fewer small bowel mucosal breaks than naproxen plus omeprazole. This study also showed that the background incidence of small bowel lesions in healthy adults is not insignificant and should be considered in future trials with VCE.

Induced microsomal PGE synthase-1 is involved in cyclooxygenase-2-dependent PGE2 production in gastric fibroblasts

We have previously shown that the cyclooxygenase (COX)-2/PGE2 pathway plays a key role in VEGF production in gastric fibroblasts. Recent studies have identified three PGE synthase (PGES) isozymes: cytosolic PGES (cPGES) and microsomal PGES (mPGES)-1 and -2, but little is known regarding the expression and roles of these enzymes in gastric fibroblasts. Thus we examined IL-1beta-stimulated mPGES-1 and cPGES mRNA and protein expression in gastric fibroblasts by quantitative PCR and Western blot analysis, respectively, and studied both their relationship to COX-1 and -2 and their roles in PGE2 and VEGF production in vitro. IL-1beta stimulated increases in both COX-2 and mPGES-1 mRNA and protein expression levels. However, COX-2 mRNA and protein expression were more rapidly induced than mPGES-1 mRNA and protein expression. Furthermore, MK-886, a nonselective mPGES-1 inhibitor, failed to inhibit IL-1beta-induced PGE2 release at the 8-h time point, while totally inhibiting PGE2 at the later stage. However, MK-886 did inhibit IL-1beta-stimulated PGES activity in vitro by 86.8%. N-(2-cyclohexyloxy-4-nitrophenyl)-methanesulfonamide (NS-398), a selective COX-2 inhibitor, totally inhibited PGE2 production at both the 8-h and 24-h time points, suggesting that COX-2-dependent PGE2 generation does not depend on mPGES-1 activity at the early stage. In contrast, NS-398 did not inhibit VEGF production at 8 h, and only partially at 24 h, whereas MK-886 totally inhibited VEGF production at each time point. These results suggest that IL-1beta-induced mPGES-1 protein expression preferentially coupled with COX-2 protein at late stages of PGE2 production and that IL-1beta-stimulated VEGF production was totally dependent on membrane-associated proteins involved in eicosanoid and glutathione metabolism (MAPEG) superfamily proteins, which includes mPGES-1, but was partially dependent on the COX-2/PGE2 pathway.

Toxic effects of nonsteroidal antiinflammatory drugs on the small bowel, colon, and rectum

The gastrointestinal toxicity of conventional nonsteroidal antiinflammatory drugs (NSAIDs) is not confined to the stomach and proximal duodenum but extends also to the rest of the small bowel, colon, and rectum. Long-term NSAID therapy usually induces clinically silent enteropathy characterized by increased intestinal permeability and inflammation. Chronic occult bleeding and protein loss may result in iron-deficiency anemia and hypoalbuminemia. NSAIDs can also induce small bowel ulcers that infrequently lead to acute bleeding, perforation, or chronic scarring responsible for diaphragm-like strictures. At the colon and rectum, NSAID use can result in de novo lesions such as nonspecific colitis and rectitis, ulcers, and diaphragm-like strictures. NSAIDs have been implicated in the development of segmental ischemic colitis. In patients with diverticular disease, NSAID use increases the risk of severe diverticular infection and perforation. NSAIDs can trigger exacerbations of ulcerative colitis or Crohn's disease. With selective COX-2 inhibitors, the risk of gastrointestinal toxicity is reduced as compared to conventional NSAIDs but is not completely eliminated. Experimental studies suggest that long-term COX-2 inhibitor therapy may cause damage to the previously healthy small bowel. Similar to conventional NSAIDs, COX-2 inhibitors may be capable of triggering exacerbations of inflammatory bowel disease.

Lessons from the withdrawal of rofecoxib

Patients would be safer if drug companies disclosed adverse events before licensing

Reduced incidence of upper gastrointestinal ulcer complications with the COX-2 selective inhibitor, valdecoxib

AIM

In a predefined analysis, data were pooled from eight blinded, randomized, controlled trials, and separately from three long-term, open-label trials to determine the rate of upper gastrointestinal ulcer complications with the cyclo-oxygenase-2 selective inhibitor, valdecoxib, vs. non-selective non-steroidal anti-inflammatory drugs.

METHODS

In randomized, controlled trials, 7434 osteoarthritis and rheumatoid arthritis patients received placebo (n = 973), valdecoxib 5-80 mg daily (n = 4362), or a non-selective non-steroidal anti-inflammatory drug (naproxen, ibuprofen or diclofenac; n = 2099) for 12-26 weeks. In long-term, open-label trials, 2871 patients received valdecoxib 10-80 mg daily for up to 1 year. All potential events were reviewed by a blinded, independent review committee based on a priori definitions of ulcer complications (perforations, obstructions, bleeds).

RESULTS

In randomized, controlled trials, 19 of 955 potential events were adjudicated to be ulcer complications. Valdecoxib was associated with a significantly lower ulcer complication rate than non-selective non-steroidal anti-inflammatory drugs (0.68% vs. 1.96%, all patients; 0.29% vs. 2.08%, non-aspirin users; P < 0.05). In long-term, open-label trials, seven of 310 potential events were adjudicated to be ulcer complications; the annualized incidence for valdecoxib was 0.39% (seven of 1791 patient-years) for all patients and 0.2% (three of 1472 patient-years) for non-aspirin users.

CONCLUSIONS

Valdecoxib, including above recommended doses, is associated with a significantly lower rate of upper gastrointestinal ulcer complications than therapeutic doses of non-selective non-steroidal anti-inflammatory drugs.

Cyclooxygenase-2-regulated vascular endothelial growth factor release in gastric fibroblasts

VEGF is a highly specific stimulator of endothelial cells and may play an important role in angiogenesis in the process of tissue regeneration. We previously showed that cyclooxygenase-2 (COX-2) expressed in mesenchymal cells of the ulcer bed is involved in the ulcer repair process. To clarify the role of COX-2 in angiogenesis during gastric ulcer healing, we investigated the relation between COX-2 expression and VEGF production in human gastric fibroblasts in vivo and in vitro. Gastric fibroblasts were cultured in RPMI 1640 with and without IL-1alpha or IL-1beta in the presence or absence of NS-398, a selective COX-2 inhibitor. Supernatant VEGF and PGE(2) concentrations were measured by enzyme-linked immunosorbent assay. COX-2 expression in fibroblasts was determined by Western blot analysis. VEGF and COX-2 expression in surgical resections of human gastric ulcer tissue was examined immunohistochemically. IL-1 dose dependently enhanced VEGF release in cultured gastric fibroblasts after a 24-h stimulation. IL-1 also stimulated PGE(2) production in gastric fibroblasts via COX-2 induction. NS-398 significantly suppressed VEGF and PGE(2) release from IL-1-stimulated gastric fibroblasts; concurrent addition of PGE(2) restored NS-398-inhibited VEGF release. COX-2 and VEGF immunoreactivity were colocalized in fibroblast-like cells in the ulcer bed of gastric tissues. These results suggest that COX-2 plays a key role in VEGF production in gastric fibroblasts stimulated by IL-1 in vitro and that angiogenesis induced by the COX-2-VEGF pathway might be involved in gastric ulcer healing.

QSAR analysis of cyclooxygenase inhibitor using particle swarm optimization and multiple linear regression

Quantitative structure-activity relationship (QSAR) models of inhibiting action of some diarylimidazole derivatives on cylcooxygenase (COX) enzyme were constructed using modified particle swarm optimization (PSO) method. As a comparison to this method, the genetic algorithm (GA) was also tested. It has been demonstrated that the modified PSO is a useful tool for variable selection comparable to GA and even superior to GA. QSAR models are constructed separately for COX-2 inhibitory activity and selectivity of COX-2 inhibition over COX-1. The spatial descriptors play a key role in the compounds' activity and selectivity to COX-2, especially Jurs descriptors. Polar interactions are the principal binding strength between compounds and COX-2 enzyme. In addition, the aqueous desolvation free energy (FH2O) value of substituent will affect the COX-2 inhibitory activity, while the charge distribution can affect the selectivity to COX-2.

[Pharmacology and classification of cyclooxygenase inhibitors]

The discovery of at least two cyclooxygenase (COX) isoenzymes had two major consequences: i) to give a new impetus to the research on lipid metabolism, giving rise to the crystallization of these peculiar membrane enzymes, the characterization of their active sites and their gene regulation, and the identification of new metabolic pathways; ii) the development of new NSAIDs aimed to have an improved safety profile, the coxibs. These drugs are defined by their COX-2 selectivity which is supported by a negligible inhibitory potency on platelet COX-1 in vitro and ex vivo after oral intake of maximal therapeutic doses. However, the coxibs marketed in France (celecoxib, rofecoxib, parecoxib) are not equivalent in terms of selectivity and some drugs developed by pharmaceutical companies (etoricoxib, lumiracoxib) will be even more selective for COX-2. These "new" coxibs are the final step in the theory of COX-2 selectivity and they will probably be helpful to better define the limitations of the therapeutic concept based on a selective inhibition of this iso-enzyme.

Gastric effects of the selective cyclooxygenase-2 inhibitor, celecoxib, in the rat

BACKGROUND

Recent studies have revealed that cyclooxygenase-2 is involved in the protection of the damaged gastric mucosa, mediating, in particular, the acceleration of ulcer healing and angiogenesis; therein, it has been suggested that selective cyclooxygenase-2 inhibitors, although safe in healthy stomach, may have deleterious effects on the injured gastric mucosa. Moreover, no information is available about direct effects of these drugs on gastric surface epithelium.

AIMS

To investigate the gastric effects of the selective cyclooxygenase-2 inhibitor, celecoxib, in healthy and damaged rat gastric mucosa.

METHODS

Gastric toxicity was studied in the rat by measuring gastric potential difference and mucosal lesions. Celecoxib was administered intragastrically, either in basal conditions or in combination with damaging (acetylsalicylic acid and ethanol) or protective (sodium nitroprusside and lipopolysaccharides from Escherichia coli) agents. The anti-inflammatory activity was evaluated in the carrageenan-induced paw oedema assay. The non-selective inhibitors indomethacin and acetylsalicylic acid were used for comparison.

RESULTS

In conscious rats celecoxib, indomethacin and acetylsalicylic acid significantly reduced the paw oedema induced by carrageenan. While acetylsalicylic acid and indomethacin significantly reduced basal gastric potential difference and caused gastric mucosal lesions, celecoxib was ineffective; moreover, it did not aggravate the direct damaging effect of intragastric ethanol or aspirin. Pretreatment with the non-selective nitric oxide synthase inhibitor N-nitro-L-argynine methyl ester did not significantly change the gastric effects of celecoxib. Both celecoxib and indomethacin prevented the gastroprotective effects induced by sodium nitroprusside (nitric oxide donor) or by bacterial lipopolysaccharides (inducer of nitric oxide synthesis). CONCLUSIONS. These data indicate that the selective cyclooxygenase-2 inhibitor celecoxib did not alter gastric mucosal barrier nor induced mucosal lesions in the healthy or nitric oxide-deficient rat gastric mucosa. However, cyclooxygenase-2 inhibition impaired nitric oxide-dependent gastroprotection, indicating that cyclooxygenase-2 derived prostaglandins may be involved in the gastric mucosal defence.

Role of prostaglandins in maintaining gastric mucus-cell permeability against acid exposure

Regulation of gastric epithelial permeability is important in the protection of the gastric mucosa from secreted acid. However, the mechanism(s) for this regulation in gastric mucus cells remains unknown. In this study, we evaluated gastric epithelial-cell permeability in response to acid exposure by monitoring trans-epithelial electrical resistance (TEER) and paracellular permeability with carbon 14-labeled mannitol. We also examined the role of prostaglandins on gastric epithelial permeability. Rat gastric epithelial cells (RGM-1) were plated on 8-microm-pore tissue-culture inserts. Cells were exposed to solutions of differing pH (3-7.4), with and without the nonsteroidal antiinflammatory drug (NSAID) indomethacin (10(-7) mol/L), for 60 to 120 minutes. Transepithelial permeability was measured on the basis of TEER and the diffusion rate of [(14)C]mannitol. Prostaglandin E(2) (PGE(2)) was administered in some experiments with NSAIDs. After acid exposure (pH 3.0-5.0), TEER rapidly and significantly increased, peaking in 5 minutes. Diffusion of [(14)C]mannitol was blocked during the period when TEER increased. Pretreatment with the cyclooxygenase (COX) inhibitor indomethacin blocked the rapid acid-induced increase in TEER. A specific COX-2 inhibitor had no effect on this rapid increase in TEER. The blockade by indomethacin was eliminated by the addition of PGE(2). These findings suggest that when gastric-surface mucus cells are exposed to acid, gastric epithelial permeability decreases rapidly to inhibit acid back-diffusion. Prostaglandins play an important role in this protective response to acid exposure. COX inhibitors such as indomethacin may inhibit the regulation of epithelial permeability by reducing the concentration of PGE(2).

Interaction of cyclooxygenase isoenzymes, nitric oxide, and afferent neurons in gastric mucosal defense in rats

The cyclooxygenase (COX)-2 inhibitors 5,5-dimethyl-3-(3-fluorophenyl)-4-(4-methylsulfonyl)phenyl-2(5II)-furanone (DFU) (0.02-2 mg/kg) and N-[2-(cyclohexyloxy)-4-nitrofenyl]-methanesulfonamide (NS-398) (0.01-1 mg/kg), the COX-1 inhibitor 5-(4-chlorophenyl)-1-(4-methoxyphenyl)-3-trifluoromethylpyrazole (SC-560) (0.05-5 mg/kg), and dexamethasone (1 mg/kg) were studied in rats challenged with intragastric acid (300 mM HCl). All compounds induced severe gastric damage when rats were treated concurrently with the inhibitor of constitutive and inducible nitric-oxide (NO) synthase N(G)-monomethyl-L-arginine methyl ester (L-NAME) (3 or 40 mg/kg). DFU and NS-398 caused significantly less damage in rats receiving the selective inhibitor of inducible NO synthase N-(3-(aminomethyl)benzyl)acetamidine (1400W) (0.3 mg/kg). The COX-1 inhibitor SC-560 induced moderate damage in the acid-challenged stomach even without suppression of NO, but damage was aggravated by L-NAME. The COX-3 inhibitor phenacetin (400 mg/kg) did not injure the gastric mucosa despite suppression of NO. Furthermore, DFU, NS-398, SC-560, and dexamethasone caused severe injury in the acid-challenged stomach of rats pretreated with capsaicin to ablate afferent neurons. The mucosal damage induced by the COX-1 inhibitor, the COX-2 inhibitors, and dexamethasone in L-NAME- or capsaicin-treated rats was reversed by coadministration of 16,16-dimethyl-prostaglandin E2 (2 x 8 ng/kg). Gross mucosal damage was paralleled by histology. Our results support the concept that endogenous NO, prostaglandins, and afferent neurons act in concert in the regulation of gastric mucosal integrity. The prostaglandins necessary for mucosal defense in the face of NO suppression, and afferent nerve ablation can be derived either from COX-1 or COX-2. The data do not propose a protective role for a phenacetin-sensitive COX-3. Our findings suggest that not only COX-1 but also COX-2 has important functions in the maintenance of gastric integrity.

Synthesis and COX-2 inhibitory properties of N-phenyl- and N-benzyl-substituted amides of 2-(4-methylsulfonylphenyl)cyclopent-1-ene-1-carboxylic acid and of their pyrazole, thiophene and isoxazole analogs

Some N-phenyl- (7a-10a) and N-benzyl-substituted (7b-10b) amido analogs of cyclooxygenase (COX-2) selective tricyclic non-steroidal anti-inflammatory drugs have been synthesized with the aim to obtain information on the structural requirements for the COX-inhibitory activity. Compounds 7-10 were tested in vitro for their inhibitory properties only towards COX-2 enzyme by measuring prostaglandin E2 (PGE2) production on activated J774.2 macrophages. Some of the new compounds (7a, 8a, 9a and 9b) showed a modest activity, with percentage inhibition values near 30% at a concentration of 10 microM. These data have been tentatively explained by a conformational study which indicates that at least the N-phenyl-substituted amides 7a-9a present steric hindrances which may prevent a good interaction with COX-2 active site.

Cyclooxygenase-2 and gastric carcinogenesis

Epidemiological studies have shown that the use of nonsteroid anti-inflammatory drugs (NSAIDs) is associated with reduced risk of gastric cancer. The best-known target of NSAIDs is the cyclooxygenase (Cox) enzyme. Two Cox genes have been cloned, of which Cox-2 has been connected with gastric carcinogenesis. Expression of Cox-2 is elevated in gastric adenocarcinomas, which correlates with several clinicopathological parameters, including depth of invasion and lymph node metastasis. This suggests that Cox-2-derived prostanoids promote aggressive behavior of adenocarcinomas of the stomach. Cox-2 expression is especially prominent in intestinal-type gastric carcinoma and it is already present in dysplastic precursor lesions of this disease, which suggests that Cox-2 contributes to gastric carcinogenesis already at the preinvasive stage. Our most recent data show that Cox-2 is expressed in gastric adenomas of trefoil factor 1 deficient mice. Treatment of these mice with a Cox-2 selective inhibitor, celecoxib, reduced the size of the adenomas. Taken together these data support efforts to initiate clinical studies to investigate the effect of Cox-2 inhibitors as chemotherapeutic agents and as adjuvant treatment modalities against gastric neoplasias.

Cyclooxygenase isozymes involved in adaptive functional responses in rat stomach after barrier disruption

We investigated the preferential role of cyclooxygenase (COX) isozymes in various functional changes of the rat stomach after exposure to taurocholate (TC) as a mild irritant. Under urethane anesthesia, a rat stomach mounted in an ex vivo chamber was perfused with saline or acid (50 mM HCl), and transmucosal potential difference (PD), gastric mucosal blood flow (GMBF), and acid secretion were measured before and after exposure of the stomach to 20 mM TC for 30 min. Indomethacin, 5-(4-chlorophenyl)-1-(4-methoxyphenyl)-3-trifluoromethylpyrazole (SC-560) (a selective COX-1 inhibitor), or rofecoxib (a selective COX-2 inhibitor) was given intraduodenally 30 min before the TC treatment. Mucosal application of TC caused a marked reduction in PD, followed by a decrease of acid secretion and an increase of GMBF. Previous administration of indomethacin did not affect the reduction in PD but significantly mitigated the two other responses induced by TC, resulting in a delay in the recovery in PD. These effects were mimicked by SC-560 but not rofecoxib, although neither of these drugs had any effect on the reduction in PD. Perfusion of TC-treated stomachs with 50 mM HCl caused only minimal damage, yet this treatment produced gross lesions in the presence of indomethacin or SC-560. Mucosal exposure to TC increased prostaglandin E2 production, but the response was inhibited by both indomethacin and SC-560 but not rofecoxib. These results suggested that COX-1 but not COX-2 is a key enzyme for regulating the functional alterations of the stomach and for maintaining the mucosal integrity after barrier disruption.

Expression of key prostaglandin synthases in equine endometrium during late diestrus and early pregnancy

Luteolysis in domestic species is mediated by the release of luteolytic pulses of prostaglandin (PG) F(2alpha) by the uterus at the end of diestrus, which must be suppressed by the conceptus to permit maternal recognition of pregnancy. In many species, including the horse, both the conceptus and the endometrium also synthesize PGE(2), which may antagonize PGF(2alpha) by playing a luteotropic and/or antiluteolytic role. While the release of PGE(2) and PGF(2alpha) by the equine endometrium in late diestrus and early pregnancy has been previously studied, the underlying prostaglandin synthase gene regulatory mechanisms remain poorly defined. To resolve this issue, cyclooxygenase-2 (COX-2), microsomal PGE(2) synthase (PGES), and PGF(2alpha) synthase (PGFS) expression were examined in a series of endometrial biopsies obtained from cycling mares on Days 10, 13, and 15 postovulation, as well as from pregnant mares on Day 15. Quantification of COX-2 expression revealed significant (P < 0.01) increases in both mRNA and protein levels at Day 15 in cycling endometrium relative to other timepoints. Importantly, the level of COX-2 expression in Day 15 pregnant endometrium was found to be comparable with that observed in Day 10 and Day 13 cycling animals, suggesting that the presence of the conceptus blocks the induction of COX-2. Immunohistochemistry demonstrated that the induction of COX-2 expression on Day 15 occurs specifically in surface epithelial cells in cycling animals only. As equine PGFS had not been previously characterized, a 1380-base pair (bp) cDNA transcript was cloned by a combination of reverse transcription-PCR techniques and found to be highly homologous to bovine liver-type PGFS. The pattern of expression observed for the terminal PG synthases was distinct from that of COX-2, as PGES and PGFS mRNA and protein levels were found to be invariant throughout the timecourse and unaffected by pregnancy. Similar to COX-2, however, the PGES and PGFS proteins were found to localize mainly to the surface epithelium. Thus, this study describes for the first time the regulation and spatial distribution of COX-2, PGES, and PGFS expression in equine endometrium in late diestrus, with a marked induction of COX-2 but not of PGES and PGFS expression in uterine epithelial cells at Day 15. Furthermore, the presence of the conceptus was shown to block the induction of COX-2 expression at Day 15, suggesting an important mechanism by which it may suppress uterine PGF(2alpha) release and prevent luteolysis during early pregnancy.

Helicobacter pylori induces cyclooxygenase-1 and cyclooxygenase-2 expression in vascular endothelial cells

BACKGROUND

Helicobacter pylori induces cyclooxygenase activity in the stomach, although the COX isoform and cellular source are unclear. A potential source is the vascular endothelial cell, which plays a role in regulating mucosal blood flow and inflammatory cell infiltration.

METHODS

We examined the effect of four strains (toxigenic and non-toxigenic) of H. pylori on COX isoform expression in vascular endothelial cells. Prostaglandin synthesis was measured by enzyme immunoassay and COX isozyme expression determined by Western blot and RT-PCR. Gene induction was examined using 5' deletion constructs of the COX-1 and COX-2 promoters coupled with luciferase.

RESULTS

All H. pylori strains induced prostaglandin generation and expression of both COX-1 and COX-2 in HUVEC, although this was most pronounced with the highly toxigenic strain H. pylori 60190. Treatment of the cells with selective COX inhibitors demonstrated that COX-1 was predominantly responsible for the enhanced generation of prostacyclin induced by H. pylori 60190. Similar results were seen with H. pylori broth culture filtrates, suggesting that a secreted product was responsible. Induction of COX-2 reflected both enhanced gene expression and stabilization of the mRNA.

CONCLUSIONS

H. pylori increased both COX-1 and COX-2 activity in vascular endothelial cells. This increased generation of endothelial cell prostacyclin may play a role in modulating mucosal blood flow, platelet function and inflammatory cell infiltration in response to H. pylori infection. The regulation of COX-1 at the transcriptional level by H. pylori described in this study is a novel finding and calls into question the traditional description of COX-1 as a purely constitutive, housekeeping gene.

Why cyclooxygenase-2 inhibition plus chemotherapy?

New approaches to treating cancers are needed. Preclinical studies have identified numerous candidate genes/proteins that promote the cancer process. Cyclooxygenase-2 (COX-2) is a reasonable "target" because it is found in many epithelial tumors, has been shown to portend a poor prognosis, and is involved in many processes that promote cancer progression and chemotherapy resistance. Inhibition of COX-2 also has the potential to provide supportive care to patients with cancer. This article describes the rationale for performing a phase II trial of specific COX-2 inhibition in combination with chemotherapy to define toxicity and efficacy. However, as with most new therapies, phase III trials will be needed to determine whether specific COX-2 therapy is able to improve patient outcome with a reasonable safety profile.

The metabolic effects of inhibitors of 5-lipoxygenase and of cyclooxygenase 1 and 2 are an advancement in the efficacy and safety of anti-inflammatory therapy

Chronic treatment of inflammatory diseases with non-steroidal anti-inflammatory drugs is effective but not always devoid of serious side effects. In particular, the use of traditional non-steroidal aspirin-like drugs has been associated with a high incidence of gastrointestinal bleedings. The development of a new class of drugs, the selective cyclooxygenase type 2 (COX-2) inhibitors, has generated much expectation on the possibility to have safer compounds. After the initial enthusiasm of the scientific community, a re-evaluation of some large, randomized double-blind clinical studies performed with two of these compounds, has disclosed that the late serious gastrointestinal complications are not significantly reduced in comparison with non-selective inhibitors and that cardiovascular concerns might arise particularly if theses drugs are utilized in patients with underlying heart diseases. A new promising class of drugs to control inflammatory diseases is in advanced clinical development. The balanced inhibitors of 5-lipoxygenase (5-LOX) and of cyclooxygenase (both types 1 and 2) block the formation of all the enzymatically arachidonic acid-derived metabolites, both prostaglandins (like COX inhibitors) and leukotrienes (LT); these drugs have been shown to possess a very good anti-inflammatory efficacy without serious side effects. Licofelone, previously known as ML3000, is the molecule in the most advanced phase of clinical development (phase III) among this class of compounds; it is a potent, competitive, and well balanced inhibitor of 5-LOX and COX pathways. The drug has been shown to possess analgesic, anti-inflammatory, antipyretic antibronchocostrictory and antiplatelet properties at doses which are safe for the gastrointestinal tract. Moreover, the newly performed preclinical studies, here briefly reviewed, appear to indicate that the compound seems particularly suitable to protect the articular cartilage and the synovial space in degenerative joint disease and to exert a relevant antithrombotic activity. Preliminary results of clinical studies of licofelone in osteoarthritis indicate that the drug has a comparable or slightly better efficacy than that of naproxen but possesses a much better gastrointestinal safety. This latter important aspect has been also evaluated by an endoscopic study in normal volunteers randomly assigned to a 4-week treatment with licofelone, placebo or naproxen. The results indicate that no ulcers occurred in either licofelone group or the placebo group, while ulcers with unequivocal depth were present in 20% of the naproxen-treated subjects.

Rofecoxib: an update on physicochemical, pharmaceutical, pharmacodynamic and pharmacokinetic aspects

Rofecoxib (MK-966) is a new generation non-steroidal anti-inflammatory agent (NSAID) that exhibits promising anti-inflammatory, analgesic and antipyretic activity. It selectively inhibits cyclooxygenase (COX)-2 isoenzyme in a dose-dependent manner in man. No significant inhibition of COX-1 is observed with rofecoxib up to doses of 1000 mg. The pharmacokinetics of rofecoxib has been found to be complex and variable. Mean oral bioavailability after single dose of rofecoxib (12.5, 25 or 50 mg) is 93% with t(max) varying widely between 2 and 9 h. It is highly plasma-protein bound and is metabolized primarily by cytosolic reductases to inactive metabolites. Rofecoxib is eliminated predominantly by hepatic metabolism with a terminal half-life of approximately 17 h during steady state. Various experimental models and clinical studies have demonstrated rofecoxib to be superior, or at least equivalent, in anti-inflammatory, analgesic and antipyretic efficacy to comparator nonselective NSAIDs in osteoarthritis, rheumatoid arthritis and other pain models. Emerging evidence suggests that rofecoxib may also find potential use as supportive therapy in various pathophysiologic conditions like Alzheimer's disease, and in various malignant tumours and polyps, where COX-2 is overly expressed. Rofecoxib is generally well-tolerated. Analysis of data pooled from several trials suggests that rofecoxib is associated with fewer incidences of clinically symptomatic gastrointestinal ulcers and ulcer complications vis-à-vis conventional NSAIDs. However, this gastropreserving effect may be negated by concurrent use of low-dose aspirin for cardiovascular risk reduction. Rofecoxib tends to show similar tolerability for renal and cardiothrombotic events as compared with nonnaproxen nonselective NSAIDs. No clinically significant drug interaction has been reported for rofecoxib except with diuretics, where it reverses their salt-wasting effect and thus can be clinically exploited in electrolyte-wasting disorders. There is only modest information about the physicochemical and pharmaceutical aspects of rofecoxib. Being poorly water soluble, its drug delivery has been improved using varied formulation approaches. Although it is stable in solid state, rofecoxib is photosensitive and base-sensitive in solution form with its degradation mechanistics elucidated. Analytical determinations of rofecoxib and its metabolites in biological fluids employing HPLC with varied types of detectors have been reported. Isolated studies have also been published on the chromatographic and spectrophotometric assay of rofecoxib and its degradants in bulk samples and pharmaceutical dosage forms. The current article provides an updated overview on the physicochemical, pharmaceutical, pharmacokinetic and pharmacodynamic vistas of rofecoxib.

A comparison of the upper gastrointestinal mucosal effects of valdecoxib, naproxen and placebo in healthy elderly subjects

BACKGROUND

In long-term outcomes studies, cyclooxygenase COX-2 specific inhibitors spare COX-1 at supratherapeutic doses and therefore demonstrate improved gastrointestinal safety over nonspecific nonsteroidal anti-inflammatory drugs (NSAIDs). However, in clinical practice, anti-inflammatory drugs are often used for short-term treatment of pain.

AIM

To compare the short-term upper gastrointestinal mucosal effects of naproxen with the new COX-2 specific inhibitor, valdecoxib, or placebo, in elderly subjects.

METHODS

In this multicentre, double-blind, randomized, study, elderly subjects (65-76 years old), with a normal baseline esophagogastroduodenoscopy (EGD), received oral valdecoxib (a supratherapeutic 40 mg b.d. dosage, n = 62), naproxen (500 mg b.d., n = 62), or placebo (n = 62) for 6.5 days. Upper gastrointestinal mucosal injury was evaluated post-treatment by EGD (day 7).

RESULTS

Subjects receiving naproxen (11/60, 18%) had significantly more gastroduodenal ulcers post-treatment than those receiving placebo (2/61, 3%; P < 0.01) or valdecoxib (0/60, 0%; P < 0.001). A similar significant finding was observed for gastric ulcer rates. All treatments had similar adverse event rates and clinical laboratory findings.

CONCLUSIONS

Valdecoxib, even at supratherapeutic doses, was associated with an ulcer rate significantly lower than naproxen but similar to placebo in healthy elderly subjects, despite the short duration of therapy (6.5 days). Naproxen and valdecoxib were as well tolerated as placebo.

Celecoxib and rofecoxib potentiate chronic colitis and premalignant changes in interleukin 10 knockout mice

Nonsteroidal anti-inflammatory drugs decrease sporadic colorectal carcinoma and adenomas in patients with familial adenomatous polyposis and in rodent models of sporadic colon cancer and familial adenomatous polyposis. Similarly, selective cyclooxygenase 2 inhibitors decrease adenomas in humans and rodents. However, their effects on chronic colitis and colitis-associated neoplasia are unknown. Interleukin 10-/- mice (C57/B6) were fed regular chow (n = 20) or chow with celecoxib (1,500 ppm, n = 18) or rofecoxib (75 ppm, n = 20) for 12 weeks. Twenty-eight percent of the celecoxib group died versus 5% of the control and rofecoxib groups (p < 0.05 compared with control). Celecoxib and rofecoxib increased the incidence of colitis (26% vs. 92% and 68%, p < 0.01), colitis score (0.4 +/- 0.2 vs. 2.5 +/- 0.3 and 2 +/- 0.4, p < 0.01), aberrant crypt foci (0.5 +/- 0.3 vs. 3.7 +/- 2.6 and 2.8 +/- 0.7, p < 0.01), aberrant crypts per mouse (4.11 +/- 2.1 vs. 41.2 +/- 9.7 and 27.1 +/- 7.5, p < 0.01) and dysplasia (11% vs. 54% and 42%, p < 0.01). Similarly, indomethacin (9 ppm, n = 15) increased colitis score, aberrant crypt foci, and dysplasia after 27 days of treatment. Two selective cyclooxygenase 2 inhibitors exacerbate colitis and premalignant changes in the interleukin 10-/- mouse model of chronic colitis and colitis-associated colon carcinoma.

An open-label trial of the selective cyclo-oxygenase-2 inhibitor, rofecoxib, in inflammatory bowel disease-associated peripheral arthritis and arthralgia

BACKGROUND

Conventional non-steroidal anti-inflammatory drugs have been associated with an increased risk of exacerbation of inflammatory bowel disease.

AIM

To evaluate, in a prospective, open-label study, the safety and efficacy of a 20-day regimen of the selective cyclo-oxygenase-2 inhibitor, rofecoxib, 12.5-25 mg/day, in inflammatory bowel disease patients with associated peripheral arthropathy and/or arthritis.

METHODS

Patients with clinically inactive to mild inflammatory bowel disease and a joint pain score of at least two points on a scale ranging from zero (none) to four (very poor) were eligible. Response was defined by a decrease of at least two points in the arthralgia score.

RESULTS

Of the 32 patients included, 26 (81%) were treated with rofecoxib, 25 mg/day, and six (19%) with rofecoxib, 12.5 mg/day. In three patients (9%), rofecoxib had to be withdrawn after a few days due to gastrointestinal complaints which ceased immediately after drug discontinuation. No flare of inflammatory bowel disease occurred. Thirteen of the 32 patients (41%) were responders and, overall, the arthralgia score decreased from two to one (P = 0.0001).

CONCLUSIONS

This is the first prospective study on the use of a selective cyclo-oxygenase-2 inhibitor in inflammatory bowel disease patients with peripheral arthropathy and/or arthralgia. The promising safety and efficacy profile warrants further evaluation in controlled trials.

Correlation between expression of cyclooxygenase-2 and angiogenesis in human gastric adenocarcinoma

AIM: To evaluate the expression of cyclooxygenase (COX-2) and the relationship with tumor angiogenesis and advancement in gastric adenocarcinoma.

METHODS: Immunohistochemical stain was used for detecting the expression of COX-2 in 45 resected specimens of gastric adenocarcinoma; the monoclonal antibody against CD34 was used for displaying vascular endothelial cells, and microvascular density (MVD) was detected by counting of CD34-positive vascular endothelial cells. Paracancerous tissues were examined as control.

RESULTS: Immunohistological staining with COX-2-specific polyclonal antibody showed cytoplasmic staining in the cancer cells, some atypical hyperplasia and intestinal metaplasia, as well as angiogenic vasculature present within the tumors and prexisting vasculature adjacent to cancer lesions. The rate of expression of COX-2 and MVD index in gastric cancers were significantly increased, compared with those in the paracancerous tissues (77.78 vs 33.33%, 58.13 ± 19.99 vs 24.02 ± 10.28, P < 0.01, P < 0.05, respectively). In 36 gastric carcinoma specimens with lymph node metastasis, the rate of COX-2 expression and MVD were higher than those in the specimens without metostasis (86.11 vs 44.44%, 58.60 ± 18.24 vs 43.54 ± 15.05, P < 0.05, P < 0.05, respectively). The rate of COX-2 expression and MVD in the specimens with invasive serosa were significantly higher than those in the specimens without invasion to serosa (87.88 vs 50.0%, 57.01 ± 18.79 vs 42.35 ± 14.65, P < 0.05, P < 0.05). Moreover, MVD in COX-2-positive specimens was higher than that in COX-2-negative specimens (61.29 ± 14.31 vs 45.38 ± 12.42, P < 0.05). COX-2 expression was positively correlated with MVD (r = 0.63, P < 0.05).

CONCLUSION: COX-2 expression might correlate with the occurance and advancement of gastric carcinoma and is involved in tumor angiogenesis in gastric carcinoma. It is likely that COX-2 by inducing angiogenesis can be one of mechanisms which promotes invasion and metastasis of gastric carcinoma. It may become a new therapeutic target for anti-angiogenesis.

The development of COX2 inhibitors

Aspirin, arguably the world's favourite drug, has been around since the late nineteenth century, but it wasn't until the late 1970s that its ability to inhibit prostaglandin production by the cyclooxygenase enzyme was identified as the basis of its therapeutic action. Early hints of a second form of the cyclooxygenase that was differentially sensitive to other aspirin-like drugs ultimately ushered in an exciting era of drug discovery, culminating in the introduction of an entirely new generation of anti-inflammatories. This article reviews the story of this discovery and looks at the future of cyclooxygenase pharmacology.

Gastrointestinal effects of NSAIDs and coxibs

Nonsteroidal anti-inflammatory drugs (NSAIDs) are among the most commonly used drugs in the world, but their use is limited because of their propensity to cause gastrointestinal (GI) injury. All patients are at risk of GI injury but certain risk factors increase the likelihood of adverse GI effects. The most important include a history of ulcer or GI complications, increasing age, concomitant anticoagulation, concomitant corticosteroid use, and high-dose NSAIDs or multiple NSAIDs (including an NSAID plus low-dose aspirin). Concurrent illness (e.g., severe rheumatoid arthritis, heart disease) has also been reported to increase the risk of GI events. NSAID-associated GI side effects markedly increase health care costs, with up to 31% of cost of managing arthritis patients accounted for through the management of GI side effects. The COX-2 specific inhibitors (coxibs) were developed with the aim of maintaining anti-inflammatory efficacy but improving gastrointestinal safety in comparison to non-selective NSAIDs. The use of COX-2 specific inhibitors significantly decreases the rate of endoscopic ulcers as compared to traditional NSAIDs. Prospective GI outcomes studies also indicate that these agents decrease clinical GI events as compared to non-selective NSAIDs. The number of patients needed to treat to avert one clinical event in one year is approximately 40-100. The cost-effectiveness of coxibs increases (the cost per GI event averted decreases) in patients with high-risk clinical features because they have higher rates of GI hospitalizations and greater use of expensive prophylactic co-therapy.

Advances in the pathophysiology of constitutive and inducible cyclooxygenases: two enzymes in the spotlight

The aim of this commentary is to discuss recent data on the role of prostaglandins generated by both constitutive and inducible cyclooxygenases (COXs). According to a popular hypothesis, COX-1 generates 'good' prostaglandins for physiological 'housekeeping' functions like gastrointestinal (GI) mucosal integrity and regulation of renal blood flow, while COX-2 forms the 'bad' prostaglandins responsible for inflammatory symptoms. However, recent data show that the biological functions of prostanoids formed by the two enzymes are much more complex and interrelated than previously appreciated. Experimental evidence indicates that a full inflammatory response is likely sustained by prostanoids generated by both enzymes, and an effective anti-inflammatory effect requires the inhibition of the two enzymes. Similarly, the selective inhibition of either COX-1 or COX-2 does not elicit GI damage, but inhibition of both enzymes is necessary for GI mucosal damage to develop. Prostaglandins generated by both enzymes contribute to normal renal function by regulating the vascular tone and the normal blood flow. The synthesis of endothelial prostacyclin is mainly driven by COX-2, so that the selective COX-2 inhibition may bias vascular prostaglandin synthesis in favour of COX-1-derived thromboxane A(2) in platelets, leading to a prothrombotic outcome. Moreover, prostaglandins formed by COX-2 appear to have a major role in myocardial protection. We propose that the complexity of the situation in the field of COX-derived mediators should be borne in mind when anti-inflammatory therapy is required.

Regional biosynthesis of prostaglandins and hydroxyeicosatetraenoic acids from arachidonic acid in the rat stomach tissue

The present study was conducted to determine regional differences in the biosynthesis of prostaglandins (PGs) and hydroxyeicosatetraenoic acids (HETEs) in the rat stomach tissue (fundus, corpus and pyloric antrum) from radioactive arachidonic acid (AA). The radioactive metabolites were validated by RP-HPLC using non-radioactive AA as substrate. PGE(2) was the major prostanoid in the tissue(.) The relative ratio of PGE(2):PGF(2)alpha:PGD(2) in the whole stomach was 1:0.5:0.1. Regionally, the fundus biosynthesized the largest amount of all three cyclo-oxygenase products. Among the lipoxygenase metabolites, 15S-HETE was the predominant product, while 12S-HETE was found to be the lowest. The relative ratio of 15S-HETE:5S-HETE:12S-HETE in the whole stomach was 1:0.6:0.4. Interestingly, the generation of lipoxygenase products was the highest in the pyloric antrum when compared to fundus or corpus. Thus, the regional differences in the biosyntheses of gastric PGs and monohydroxy fatty acids may be relevant to our understanding of corresponding differences in mucosal resistance or susceptibility to gastric disease.

Gastrin enhances gastric mucosal integrity through cyclooxygenase-2 upregulation in rats

Gastrin, PGs, and growth factors have important roles in maintaining gastrointestinal mucosal integrity. Cyclooxygenases (COX-1 and COX-2) are the key enzymes involved in PG synthesis. This study aimed to clarify the mechanisms of gastric mucosal protection by gastrin. Fasted rats were administered subcutaneous gastrin 17 with or without gastrin receptor antagonist YM022 pretreatment. Heparin-binding epidermal growth factor-like growth factor (HB-EGF) and COX-2 expression were examined using Western blot analysis. Another series of experiments investigated 1) PGE(2) levels in gastric mucosa, 2) the protective action of gastrin against gastric damage by acidified ethanol, 3) the effects of a specific HB-EGF-neutralizing antibody on gastrin-induced COX-2 expression, and 4) the effects of a specific COX-2 inhibitor NS-398 on PGE(2) synthesis and the mucosal protection afforded by gastrin. Gastrin dose-dependently increased HB-EGF, COX-2 expression, and PGE(2) levels and reduced gastric damage. However, pretreatment with YM022 dose-dependently abolished such effects of gastrin. A specific HB-EGF- neutralizing antibody and an EGF receptor inhibitor decreased gastrin-induced COX-2 expression. NS-398 blocked gastrin-induced PGE(2) synthesis and mucosal protection. In conclusion, this study demonstrates that gastrin enhances gastric mucosal integrity through COX-2, which is partially mediated by HB-EGF, and PGE(2) upregulation in rats.

Lansoprazole induces mucosal protection through gastrin receptor-dependent up-regulation of cyclooxygenase-2 in rats

Proton pump inhibitors (PPIs) are antiulcer agents that have both gastric antisecretory and mucosal protective actions. The mechanisms of PPI-induced gastric mucosal protection are not known. The present study was designed to examine the mechanism for lansoprazole-induced gastric mucosal protection in rats. Rats were given 0.5, 5, and 50 mg/kg/day lansoprazole alone or both lansoprazole (50 mg/kg/day) and a specific gastrin receptor antagonist 3R-1-(2,2-diethoxyethyl)-((4-methylphenyl)amino-carbonyl methyl)-3-((4-methylphenyl)ureidoindoline-2- one) (AG-041R) (3, 10, and 30 mg/kg/day) for 14 days. Serum gastrin concentrations were measured. The expression of cyclooxygenases (COX-1 and COX-2) in the gastric mucosa was analyzed using Western blotting and immunohistochemical staining. Another series of rats was used to examine the 1) levels of prostaglandin (PG) E2 in gastric mucosa, 2) influences of the drugs on gastric damage caused by absolute ethanol, and 3) effects of a COX-2-specific inhibitor on PGE2 in the gastric mucosa and the mucosal protection afforded by lansoprazole. Lansoprazole dose dependently increased the serum gastrin concentration and enhanced the mucosal expression of COX-2 but not that of COX-1. Lansoprazole increased gastric mucosal PGE2 and reduced gastric damage caused by ethanol. Concomitant administration of AG-041R abolished the lansoprazole-induced COX-2 expression, and increased mucosal PGE2 and mucosal protection. A specific COX-2 inhibitor blocked the lansoprazole-induced increase in mucosal PGE2 and mucosal protection. Activation of gastrin receptors by endogenous gastrin has a pivotal role in the effects of lansoprazole on COX-2 up-regulation and mucosal protection in the rat stomach.

Ulcerogenic influence of selective cyclooxygenase-2 inhibitors in the rat stomach with adjuvant-induced arthritis

Cyclooxygenase (COX)-2 inhibitors have been developed as new gastric sparing anti-inflammatory drugs. We previously reported that the ulcerogenic response to conventional nonselective COX inhibitors, such as indomethacin and aspirin, was markedly increased in arthritic rats. The ulcerogenic effect of selective COX-2 inhibitors in arthritic animals, however, remains unknown. The present study was designed to examine the influence of selective COX-2 inhibitors, such as rofecoxib and celecoxib, on gastric mucosal integrity in rats with adjuvant-induced arthritis. Arthritis was induced in male dark Agouti rats by injection of Freund's complete adjuvant into the right hind paw. Two weeks after the injection, the animals were fasted for 18 h, various COX inhibitors were administered orally, and the mucosa was examined for lesions 4 h later. Oral administration of indomethacin caused hemorrhagic gastric lesions in both normal and arthritic rats, although the severity of lesions was significantly greater in the latter group. In contrast, neither rofecoxib nor celecoxib caused any gastric damage in normal rats, but both drugs provoked hemorrhagic gastric lesions in arthritic rats. The expression of COX-2 mRNA and immuno-positive cells was observed in the gastric mucosa of arthritic but not normal rats. The gastric mucosal prostaglandin (PG) E(2) content was significantly elevated in arthritic rats in a rofecoxib-sensitive manner. In conclusion, COX-2 inhibitors produce gastric lesions in arthritic rats, similar to the nonselective COX-inhibitors. COX-2 is up-regulated in the stomach of arthritic rats, and PGs produced by COX-2 play a role in maintaining the integrity of the gastric mucosa.

In vivo effects of meloxicam and aspirin on blood, gastric mucosal, and synovial fluid prostanoid synthesis in dogs

OBJECTIVE

To evaluate in vivo activity in dogs of meloxicam or aspirin, previously shown in vitro to be a selective cyclooxygenase-2 (COX-2) inhibitor (COX-1 sparing drug), or a nonselective COX inhibitor, respectively.

ANIMALS

12 male dogs with unilateral osteoarthritis of the stifle joint.

PROCEDURE

Each dog was treated in a crossover design with aspirin or meloxicam for 21 days. Prostaglandin E2 (PGE2) concentrations were measured at days 0 (baseline), 7, and 21 of each treatment period in lipopolysaccharide (LPS)-stimulated blood, synovial fluid collected by arthrocentesis, and endoscopic gastric mucosal biopsy specimens. Thromboxane B2 (TXB2) was evaluated in blood on days 0, 7, and 21 of each treatment period.

RESULTS

Aspirin administration significantly suppressed PGE2 concentrations in blood, gastric mucosa, synovial fluid, and suppressed TXB2 concentration in blood at days 7 and 21. Meloxicam administration significantly suppressed PGE2 concentrations in blood and synovial fluid at days 7 and 21, but had no effect on concentrations of TXB2 in blood or PGE2 in gastric mucosa. Suppression of LPS-stimulated PGE2 concentrations in blood and synovial fluid by aspirin and meloxicam administration is consistent with activity against the COX-2 isoenzyme. Suppression of concentrations of PGE2 in the gastric mucosa and TXB2 in blood by aspirin administration is consistent with activity against COX-1. Meloxicam, in contrast, had a minimal effect on functions mediated by COX-1.

CONCLUSIONS AND CLINICAL RELEVANCE

Meloxicam acts in vivo in dogs as a COX-1 sparing drug on target tissues by sparing gastric PGE2 synthesis while retaining antiprostaglandin effects within inflamed joints.

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.

Rheumatoid arthritis: developing pharmacological therapies

Rheumatoid arthritis (RA) is a chronic inflammatory disease that, despite recent advances in therapy, still results in significant morbidity, mortality and disability. The aetiology remains unknown and past therapies, although helpful for the majority of patients, have been suboptimal. The recent introduction of newer agents has changed the treatment paradigm of RA. COX-2 inhibitors, anti-TNF agents and interleukin-1 antagonists have allowed us to treat RA more effectively with relatively low risk of side effects. Investigations of other possible treatment pathways, such as inhibition of angiogenesis, may produce still better treatment and rapid unraveling of the immune system and how it relates to RA greatly enhances the opportunities for improved therapeutics in RA.

Valdecoxib does not impair platelet function

The platelet effects of a supratherapeutic dose of the new cyclooxygenase (COX)-2 specific inhibitor, valdecoxib (40 mg twice a day), naproxen 500 mg twice a day, diclofenac 75 mg twice a day, and placebo were compared in 62 healthy adult subjects in this 7(1/2) day single-center, randomized, placebo-controlled trial. Platelet aggregation responses (to arachidonate [AA], collagen, and adenosine diphosphate [ADP]), bleeding time, and serum thromboxane B(2) (TxB(2)) concentrations were measured at baseline and at regular intervals on days 1 and 8. Valdecoxib had no effect on platelet function. Naproxen and diclofenac significantly reduced the platelet aggregation response to AA and to a lesser extent collagen and ADP at most assessments compared with placebo. Naproxen significantly lowered serum TxB(2) levels. In contrast to standard doses of 2 nonsteroidal antiinflammatory drugs (NSAIDs), a supratherapeutic valdecoxib dosage does not impair platelet function (COX-1). Valdecoxib may be a safer analgesic option than conventional NSAIDs in patients for whom bleeding complications are a concern. (Am J Emerg Med 2002;20:275-281.

Induction of cyclo-oxygenase-2 expression in naturally occurring gastric ulcers

Cyclo-oxygenase-2 (COX-2) is believed to participate in the repair of gastric ulcer. Like humans, pigs frequently develop gastric ulcers and thus represent an attractive animal model in which to study the repair process of naturally occurring gastric ulcers. However, expression of COX in the pig stomach has not been reported. The objectives of this study were to determine whether COX isoenzymes are expressed in porcine gastric ulcers and to characterize the porcine COX-2 cDNA. Normal stomachs (n=5) and those with gastric ulcers (n=35) were studied by immunohistochemistry and immunoblotting analysis. Reverse transcription-polymerase chain reaction (RT-PCR) was used to isolate the complete porcine COX-2 cDNA. COX-1 staining was present in normal stomach and in ulcerated areas. No COX-2 was detected in normal stomach, but COX-2 was strongly expressed in the ulcerated area in 28/35 (80%) gastric ulcers (p<0.01). Immunoblotting analysis confirmed the restricted expression of COX-2 in the ulcerated areas. The porcine COX-2 cDNA was shown to code for a 604 amino acid protein that is 89% identical to human COX-2. These results provide the complete primary structure of porcine COX-2 and demonstrate for the first time that the enzyme is induced in naturally occurring porcine gastric ulcers.

Examination of rofecoxib solution decomposition under alkaline and photolytic stress conditions

Rofecoxib is a highly active and selective cyclo-oxygenase II inhibitor. A stability-indicating method for the assay of rofecoxib has been developed using reverse-phase high-performance liquid chromatography (HPLC). Stress testing of rofecoxib was conducted during the method development and validation. HPLC analysis of rofecoxib solutions stressed under alkaline and photolytic conditions revealed the presence of several degradates. Two main degradates were determined to be the cyclization product formed by photo-cyclization and the dicarboxylate formed by ring opening in the presence of base and oxygen. The identities of these degradates were confirmed by comparison of UV spectra and HPLC retention time with the independently synthesized products. The mechanistic pathways for the formation of these degradates are discussed. Further improvement of the HPLC method's ruggedness has been made based on these studies.