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

Gastric mucosal defense and cytoprotection: bench to bedside

The gastric mucosa maintains structural integrity and function despite continuous exposure to noxious factors, including 0.1 mol/L HCl and pepsin, that are capable of digesting tissue. Under normal conditions, mucosal integrity is maintained by defense mechanisms, which include preepithelial factors (mucus-bicarbonate-phospholipid "barrier"), an epithelial "barrier" (surface epithelial cells connected by tight junctions and generating bicarbonate, mucus, phospholipids, trefoil peptides, prostaglandins (PGs), and heat shock proteins), continuous cell renewal accomplished by proliferation of progenitor cells (regulated by growth factors, PGE(2) and survivin), continuous blood flow through mucosal microvessels, an endothelial "barrier," sensory innervation, and generation of PGs and nitric oxide. Mucosal injury may occur when noxious factors "overwhelm" an intact mucosal defense or when the mucosal defense is impaired. We review basic components of gastric mucosal defense and discuss conditions in which mucosal injury is directly related to impairment in mucosal defense, focusing on disorders with important clinical sequelae: nonsteroidal anti-inflammatory drug (NSAID)-associated injury, which is primarily related to inhibition of cyclooxygenase (COX)-mediated PG synthesis, and stress-related mucosal disease (SRMD), which occurs with local ischemia. The annual incidence of NSAID-associated upper gastrointestinal (GI) complications such as bleeding is approximately 1%-1.5%; and reductions in these complications have been demonstrated with misoprostol, proton pump inhibitors (PPIs) (only documented in high-risk patients), and COX-2 selective inhibitors. Clinically significant bleeding from SRMD is relatively uncommon with modern intensive care. Pharmacologic therapy with antisecretory drugs may be used in high-risk patients (eg, mechanical ventilation >or=48 hours), although the absolute risk reduction is small, and a decrease in mortality is not documented.

Cyclooxygenase expression and prostanoid production in pyloric and duodenal mucosae in dogs after administration of nonsteroidal anti-inflammatory drugs

OBJECTIVE

To assess cyclooxygenase (COX) expression and prostanoid concentrations in pyloric and duodenal mucosae of dogs after administration of nonsteroidal anti-inflammatory drugs (NSAIDs).

ANIMALS

8 healthy dogs.

PROCEDURES

Each dog received carprofen (4.4 mg/kg, q 24 h), deracoxib (2 mg/kg, q 24 h), aspirin (10 mg/kg, q 12 h), and placebo (1 dog treat, q 24 h) orally for 3 days (4-week interval between treatments). Before study commencement (baseline) and on day 3 of each treatment, pyloric and duodenal mucosal appearance was assessed endoscopically and biopsy specimens were obtained for histologic examination. Cyclooxygenase-1 and COX-2 protein expressions were assessed via western blotting, and prostanoid concentrations were measured via ELISAs. An ANOVA was used to analyze data.

RESULTS

Treatments had no effect on mucosal appearance and ulceration was not evident histologically. In pyloric and duodenal mucosae, COX-1 expression was unaffected by treatments. Cyclooxygenase-2 expression remained unchanged in pyloric mucosa; in duodenal mucosa, aspirin significantly increased COX-2 expression, compared with effects of deracoxib and carprofen. At baseline, total prostaglandin and thromboxane B2 concentrations in pyloric mucosa were significantly greater than those in duodenal mucosa. Aspirin significantly decreased both prostanoid concentrations in both mucosal tissues, compared with other treatments. In pyloric mucosa, carprofen administration significantly decreased total prostaglandin and thromboxane B2 concentrations, compared with deracoxib administration.

CONCLUSIONS AND CLINICAL RELEVANCE

In dogs, prostanoid synthesis was greater in pyloric mucosa than it was in duodenal mucosa. Nonselective NSAIDs significantly decreased prostanoid concentrations in these mucosae, compared with the effects of a selective COX-2 NSAID.

Cyclooxygenase-2 in cancer and angiogenesis

Tumor angiogenesis is a process where new blood vessels are formed from preexisting ones, resulting in several pathologies. Solid tumors induce angiogenesis to obtain the required nutrients and oxygen. Otherwise, tumors do not grow beyond 2 to 3 mm in diameter. Cyclooxygenase-2, an inducible enzyme important in inflammation, catalyzes the production of prostanoids from arachidonic acid. Cyclooxygenase-2 plays an important role in several cancer types, including colorectal, gastric, prostate, breast, lung, and endometrial cancer. Besides, cyclooxygenase-2 has been implicated in the progression and angiogenesis of cancers. Cyclooxygenase-2 inhibitors have been used to block angiogenesis and tumor proliferation. In this review, the recent studies related to the role of cyclooxygenase-2 in several cancer types and tumor-induced angiogenesis were compiled.

Multi-Target Approaches in Colon Cancer Chemoprevention Based on Systems Biology of Tumor Cell-Signaling

Colorectal cancer is the leading cause of cancer related deaths in the United States. Although it is preventable, thousands of lives are lost each year in the U.S. to colorectal cancer than to breast cancer and AIDS combined. In colon cancer, the formation and progression of precancerous lesions like aberrant crypt foci and polyps is associated with the up-regulation of cycloxygenase-2 (COX-2), inducible nitric oxide synthase (iNOS) and hydroxy methyl glutaryl CoA reductase (HMG-CoA reductase). The current review will focus on the signaling pathway involving COX-2 and HMG-CoA reductase enzymes and their downstream effectors in signaling mechanism. Cancer cells need huge pools of both cholesterol and isoprenoids to sustain their unlimited growth potential. Cholesterol by modulating caveolae formation regulates several signaling molecules like AKT, IGFR, EGFR and Rho which are involved in cell growth and survival. Cholesterol is also essential for lipid body formation which serves as storage sites for COX-2, eicosanoids and caveolin-1. Experimental studies have identified important mechanisms showing that COX-2, caveolin-1, lipid bodies and prenylated proteins is involved in carcinogenesis. Therefore multi-target, multi-drug approach is the ideal choice for effective colon cancer chemoprevention. This review will give an overview of the two pathways, their signaling networks, and the interactions between the components of the two networks in the activation and regulation of cell signaling involving growth/survival and explain the rationale for colon cancer chemoprevention using COX-2 inhibitors and statins.

Morphological features and molecular markers in rectal cancer from 95 patients included in the European Organisation for Research and Treatment of Cancer 22921 trial: prognostic value and effects of preoperative radio (chemo) therapy

In this study, the prognostic and/or predictive value of different proteins (cyclo-oxygenase 2 (COX-2), Ki67 and cleaved cytokeratin (CK) 18) and fibro-inflammatory changes which might be of importance for the response to treatment were evaluated using tissue micro arrays. Samples were obtained from a subset of 95 patients included in the European Organisation for Research and Treatment of Cancer 22921 clinical trial, which randomised patients with rectal cancer to one of four arms treated with preoperative radiotherapy with or without pre- and/or postoperative chemotherapy. From our results, we can conclude that the addition of preoperative chemotherapy to radiotherapy led to significantly less COX-2 upregulation, less proliferation and more inflammation, as was seen in the resection specimen as well as less invasion and metastasis. For COX-2, Ki67 or cleaved CK18, no predictive or prognostic value could be identified. However, the fibro-inflammatory reaction after preoperative radiochemotherapy correlated with T-downstaging and seems to be an important factor for response.

Cyclooxygenase-1-selective inhibitors are attractive candidates for analgesics that do not cause gastric damage. design and in vitro/in vivo evaluation of a benzamide-type cyclooxygenase-1 selective inhibitor

Although cyclooxygenase-1 (COX-1) inhibition is thought to be a major mechanism of gastric damage by nonsteroidal anti-inflammatory drugs (NSAIDs), some COX-1-selective inhibitors exhibit strong analgesic effects without causing gastric damage. However, it is not clear whether their analgesic effects are attributable to COX-1-inhibitory activity or other bioactivities. Here, we report that N-(5-amino-2-pyridinyl)-4-(trifluoromethyl)benzamide ( 18f, TFAP), which has a structure clearly different from those of currently available COX-1-selective inhibitors, is a potent COX-1-selective inhibitor (COX-1 IC 50 = 0.80 +/- 0.05 microM, COX-2 IC 50 = 210 +/- 10 microM). This compound causes little gastric damage in rats even at an oral dose of 300 mg/kg, though it has an analgesic effect at as low a dose as 10 mg/kg. Our results show that COX-1-selective inhibitors can be analgesic agents without causing gastric damage.

Genetically determined susceptibility to COX-2 inhibitors: a report of exaggerated responders to diclofenac 3% gel in the treatment of actinic keratoses

Diclofenac 3% gel is an effective treatment for actinic keratoses (AKs) and is reported to be generally well tolerated with only mild local reactions. However, there is a subset of patients that seem to be susceptible to developing severe local reactions following application of diclofenac 3% gel. Although some of these reactions can be explained as being allergic contact dermatitis and/or photoallergic contact dermatitis, others cannot. We report a series of 10 patients who all developed severe local reactions following application of diclofenac 3% gel, despite negative diclofenac patch testing. This raises the question as to whether there is a subset of patients with skin cancer or AK lesions that are highly/more susceptible to local reactions caused by cyclo-oxygenase-2 (COX-2) inhibitors and peroxisome proliferator-activated receptor (PPAR) agonists? We speculate that underlying molecular differences exist in these patients that make the skin more susceptible to COX-2 inhibitors.

Cyclooxygenase-2/prostaglandin E2 accelerates the healing of gastric ulcers via EP4 receptors

We examined the involvement of cyclooxygenase (COX)-1 as well as COX-2 in the healing of gastric ulcers and investigated which prostaglandin (PG) EP receptor subtype is responsible for the healing-promoting action of PGE2. Male SD rats and C57BL/6 mice, including wild-type, COX-1(-/-), and COX-2(-/-), were used. Gastric ulcers were produced by thermocauterization under ether anesthesia. Gastric ulcer healing was significantly delayed in both rats and mice by indomethacin and rofecoxib but not SC-560 given for 14 days after ulceration. The impaired healing was also observed in COX-2(-/-) but not COX-1(-/-) mice. Mucosal PGE2 content increased after ulceration, and this response was significantly suppressed by indomethacin and rofecoxib but not SC-560. The delayed healing in mice caused by indomethacin was significantly reversed by the coadministration of 11-deoxy-PGE1 (EP3/EP4 agonist) but not other prostanoids, including the EP1, EP2, and EP3 agonists. By contrast, CJ-42794 (selective EP(4) antagonist) significantly delayed the ulcer healing in rats and mice. VEGF expression and angiogenesis were both upregulated in the ulcerated mucosa, and these responses were suppressed by indomethacin, rofocoxib, and CJ-42794. The expression of VEGF in primary rat gastric fibroblasts was increased by PGE2 or AE1-329 (EP4 agonist), and these responses were both attenuated by coadministration of CJ-42794. These results confirmed the importance of COX-2/PGE2 in the healing mechanism of gastric ulcers and further suggested that the healing-promoting action of PGE2 is mediated by the activation of EP4 receptors and is associated with VEGF expression.

Cyclooxygenase-2 expression in chronic hepatitis C and the effect of interferon alpha treatment

BACKGROUND AND AIM

Cyclooxygenase-2 (COX-2), a target of aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs), is upregulated in chronic hepatitis B and may have a role in hepatocellular carcinoma. Little is known about the expression of COX-2 in chronic hepatitis C (HCV) infection. The aim the present study was to evaluate the extent of COX-2 expression in liver biopsies in patients with HCV infection and to determine the effect of treatment with interferon alpha (IFN).

METHODS

Percutaneous liver biopsy specimens were retrieved. Following formalin fixation and paraffin embedding, the biopsies were histologically evaluated for inflammation and fibrosis. The extent of COX-2 expression was measured by the avidin biotin immunohistochemical technique using a monoclonal COX-2 antibody. The extent of COX-2 expression was graded according to the number of hepatocytes expressing COX-2. Data were analyzed using Student's t-test.

RESULTS

Liver biopsies from 10 patients before and after treatment with IFN were obtained and compared with nine normal liver biopsies. All of the liver biopsies showed some COX-2 expression. COX-2 expression was confined to hepatocytes and bile duct epithelium and was not detected in vascular endothelium or inflammatory cells. The extent of COX-2 expression was greater in hepatitis C infected liver biopsies than in normal biopsies. Following treatment with IFN, there was a greater than threefold reduction in COX-2 expression (P < 0.01). This result was independent of the sustained virological response.

CONCLUSION

In this small pilot study we have shown that COX-2 is overexpressed in liver biopsies infected with HCV and COX-2 expression is reduced following treatment with IFN.

Aggravation by selective COX-1 and COX-2 inhibitors of dextran sulfate sodium (DSS)-induced colon lesions in rats

We examined the effect of cyclooxygenase (COX) inhibitors on dextran sulfate sodium (DSS)-induced ulcerative colitis in rats and investigated the role of COX isozymes in the pathogenesis of this model. Experimental colitis was induced by treatment with 2.5% DSS in drinking water for 6 days. Indomethacin (a nonselective COX inhibitor), SC-560 (a selective COX-1 inhibitor), or celecoxib (a selective COX-2 inhibitor) was given PO twice daily for 6 days, during the first 3 or last 3 days of the experimental period. Daily treatment with 2.5% DSS for 6 days caused damage to the colon, with a decrease in body weight gain and colon length as well as an increase of myeloperoxidase (MPO) activity. All COX inhibitors given for 6 days significantly worsened the severity of DSS-induced colonic damage with increased MPO activity. The aggravation was also observed by SC-560 given for the first 3 days or by celecoxib given for the last 3 days. The expression of COX-2 mRNA in the colon was upregulated on day 3 during DSS treatment, with significant increase of prostaglandin E(2) PGE(2) production. The PGE(2) content on day 3 during DSS treatment was inhibited by both indomethacin and SC-560, but not by celecoxib; on day 6 it was suppressed by both indomethacin and celecoxib, but not SC-560. These results suggest that endogenous prostaglandins (PGs) afford protection against colonic ulceration, yet the COX isozyme responsible for the production of PGs differs depending on the stage of ulceration; COX-1 in the early stage and COX-2 in the late stage.

Toward the development of chemoprevention agents. Part II: Chemo-enzymatic synthesis and anti-inflammatory activities of a new class of 5-amino-2-substitutedphenyl-1,3-dioxacycloalkanes

A new series of optically pure 5-amino-2-substitutedphenyl-1,3-dioxacycloalkanes were designed and synthesized via a chemo-enzymatic combined method to develop new chemoprevention agents. Twenty-four of newly synthesized compounds significantly inhibited xylene-induced rat ear edema and exhibited comparable or better anti-inflammatory activities than the reference drug aspirin. Treatment of these anti-inflammatory agents did not prolong the tail bleeding time in rat. In addition, 5-amino-2-substitutedphenyl-1,3-dioxacycloalkanes exhibited good membrane permeability based on in vitro Caco-2 cell monolayer permeability assay. Furthermore, some preliminary structure-activity relationships were further analyzed among these compounds. Taken together, 5-amino-2-substitutedphenyl-1,3-dioxacycloalkanes may represent a new class of anti-inflammatory drugs with safer pharmacological profile.

Geranylgeranylacetone induces cyclooxygenase-2 expression in cultured rat gastric epithelial cells through NF-kappaB

Geranylgeranylacetone (GGA) effectively protects the gastric mucosa against noxious agents. The precise mechanisms underlying the gastroprotective actions of GGA are not known. To elucidate the precise mechanism of GGA, the effect of GGA treatment on COX-2 expression in rat gastric epithelial (RGM1) cells was investigated. We used a prostaglandin E2 (PGE2) enzyme-linked immunoassay kit and Western blot analysis to measure PGE2 production and COX-2 induction by GGA treatment in serum-starved RGM1 cells. Gel-shift assay, Western blot analysis, and a reporter assay were performed to determine which COX-2 promoter was involved in GGA-induced COX-2 expression. GGA treatment dose dependently increased COX-2 expression and PGE2 production. The nuclear factor (NF)-kappaB sites of the COX-2 gene promoter were critical for GGA-mediated COX-2 expression. GGA induces COX-2 expression and increases PGE2 production in serum-starved RGM1 cells via activation of the NF-kappaB sites of COX-2 gene promoters.

Inhibition of angiogenic tubule formation and induction of apoptosis in human endothelial cells by the selective cyclooxygenase-2 inhibitor 5-bromo-2-(4-fluorophenyl)-3-(methylsulfonyl) thiophene (DuP-697)

There are indications that inhibitors of the cyclooxygenase-2 (COX-2) enzyme may cause inhibition of angiogenesis, proliferation of endothelial cells and induce apoptosis in cell systems. The concentrations of inhibitors required for such effects are however much higher than those needed to inhibit COX-2, suggesting that the latter may not be involved in these actions of the drugs. We have however generated data that strongly indicates a critical role for COX-2 suppression in the inhibition of angiogenesis and induction of apoptosis in human cultured umbilical vein endothelial cells (HUVECs) by the selective cyclooxygenase-2 (COX-2) inhibitor 5-bromo-2-(4-fluorophenyl)-3-(methylsulfonyl) thiophene (DuP-697). DuP-697 concentration-dependently inhibited prostaglandin E(2) (PGE(2)) production by HUVECs and at its known IC(50) for COX-2 inhibition of 10 nM inhibited basal and vascular endothelial cell growth factor (VEGF)-induced PGE(2) production by 80% and 85% respectively. DuP-697 also induced apoptosis as shown by FACs analysis, an increase in chromatin condensation and DNA laddering in HUVECS treated with the drug. Moreover, these effects were reversed by PGE(2) and by VEGF. In parallel studies, DuP-697 induced caspases 3, 8 and 9, with the caspase-3 specific inhibitor N-Acetyl-Asp-Glu-Val-Asp-al (DEVD-CHO) blocking the induction of apoptosis. Capillary-like tubule formation by HUVECs cultured on Matrigel was inhibited by DuP-697 and this inhibition was prevented by PGE(2) but not by DEVD-CHO. These results indicate that the induction of apoptosis and inhibition of tubule formation by DuP-697 involves the inhibition of COX-2 and that whereas the induction of apoptosis is caspase-dependent, the inhibition of tubule formation occurs through a caspase-independent mechanism.

Toward the development of chemoprevention agents. Part 1: Design, synthesis, and anti-inflammatory activities of a new class of 2,5-disubstituted-dioxacycloalkanes

A new class of 2,5-disubstituted-dioxacycloalkanes were designed and synthesized via stereoselective synthetic method as cancer chemoprevention agents. The anti-inflammatory activities of these compounds were tested using the xylene-induced mouse ear edema model. Some of these compounds exhibited comparable or better anti-inflammatory activities than that of aspirin suggesting that they can be further developed as potential anti-inflammatory drug lead compounds. In addition, treatment of these anti-inflammatory agents did not prolong tail bleeding time in mice. The structure/activity relationships were also analyzed among these compounds.

Cyclooxygenase 2 expression in cervical intraepithelial neoplasia and vulvar cancer

OBJECTIVE

The purpose of this study is to describe the expression of cyclooxygenase (COX) 2 cervical intraepithelial neoplasia (CIN) and vulvar cancer specimens.

MATERIALS AND METHODS

Archived tissues from 21 cases including 6 cases negative for CIN (no CIN), 71 low-grade (CIN 1) diseases, 8 high-grade (CIN 2, 3) diseases, and 14 vulvar cancer cases were examined. Immunohistochemistry was evaluated in COX-2 expression in tissue using an isoform-specific COX-2 polyclonal antibody. Specimens were assigned an immunohistochemical score for intensity of staining and the percent of cells stained. The slides were scored by 2 independent pathologists and compared across histological categories.

RESULTS

A greater proportion of cells were stained in specimens with high-grade CIN (p = 0.01). Staining intensity was not statistically different among the 3 groups. Higher scores were found for vulvar cancer as compared with normal vulva (p = 0.01).

CONCLUSIONS

The increase in COX-2 in cervical cancer precursors may provide a potential target for prevention studies.

Potential antioxidant activity of celecoxib and amtolmetin guacyl: in vitro studies

1. In vitro studies of the potential antioxidant activity of the selective cyclo-oxygenase-2 inhibitor celecoxib and the non-steroid anti-inflammatory drug amtolmetin guacyl (AMG) were carried out. The study included experiments on the ability of these drugs to affect some indices of the oxidative stress [lipid peroxidation (LP), activity of antioxidant enzymes, glutathione (GSH) level] in rat stomach and colon mucosa and in liver. 2. Celecoxib and AMG did not change the activity of the enzymes GSH-peroxidase, oxidased glutathione (GSSG)-reductase and glucose-6-phosphate-dehydrogenase, as well as the GSH level in all tissue preparations. An increased superoxide dismutase (SOD) activity and a tendency to a decreased Fe/ascorbic acid-induced LP in stomach and colon mucosa were found, but only in the presence of AMG. 3. In the liver, both celecoxib and AMG decreased spontaneous and Fe/ascorbic acid-induced LP. SOD activity was enhanced only in the presence of AMG. 4. Experiments aimed at studying celecoxib and AMG in free oxygen radical-generating systems were also carried out. AMG and tolmetin (the main metabolite of AMG) inhibited OH*-provoked deoxyribose degradation in a Fenton system. Celecoxib had no effect on free radicals when tested in the same system. 5. In conclusion, the results of the present in vitro studies suggest that AMG and celecoxib possess antioxidant and metal-chelating abilities, which might contribute to their beneficial effects.

Indirect role of α2-adrenoreceptors in anti-ulcer effect mechanism of nimesulide in rats

Nimesulide, a non-steroidal, anti-inflammatory drug, produces ulcerogenic effects in adrenalectomized rats but is gastro-protective in intact rats. The objective of this study was to determine whether adrenal gland hormones are involved in the anti-ulcer effects of nimesulide. The results revealed that 100 mg/kg nimesulide produces gastric ulceration in adrenalectomized rats, which is prevented by prednisolone and adrenaline. The anti-ulcer effects of adrenaline and prednisolone in adrenalectomized rats were in turn antagonized by yohimbine, a selective alpha(2)-receptor blocker, but not by doxazosine (alpha(1)-receptor blocker) or propranolol (beta-blocker). Adrenaline prevented the formation of indomethacin-induced ulcers in both adrenalectomized and intact rats, but prednisolone increased the indomethacin-induced ulcerous area in intact rats, whereas it decreased the size of the ulcers in adrenalectomized rats. In addition, prednisolone prevented ulcer formation in intact rats in which the adrenaline concentration had been decreased by metyrosine. These results suggest that glucocorticoids are anti-ulcerogenic in not only adrenalectomized rats but also in intact rats with diminished circulating levels of adrenaline. In the light of these data, the effect of nimesulide on plasma adrenaline concentrations was studied. In comparison to the adrenaline levels found in intact control rats, the administration of nimesulide at doses of 10, 20, 40 and 100 mg/kg decreased adrenaline concentrations by 12.8, 22.6, 30.4, and 58.2%, respectively, without affecting blood corticosterone concentrations. The anti-ulcer effect of nimesulide was observed to be dose-dependent, and the strength of this effect was directly correlated the decreasing concentration of adrenaline. The concentration of adrenaline was decreased by 60.9% in rats treated with 300 mg/kg metyrosine in which prednisolone produced anti-ulcer effects. In summary, we have shown that nimesulide produces its anti-ulcer effect by decreasing endogenous adrenaline concentrations and that glucocorticoids may induce anti-ulcer effects via alpha(2)-adrenoreceptors, but not via their own receptors.

A robustness-based approach to systems-oriented drug design

Many potential drugs that specifically target a particular protein considered to underlie a given disease have been found to be less effective than hoped, or to cause significant side effects. The intrinsic robustness of living systems against various perturbations is a key factor that prevents such compounds from being successful. By studying complex network systems and reformulating control and communication theories that are well established in engineering, a theoretical foundation for a systems-oriented approach to more effectively control the robustness of living systems, particularly at the cellular level, could be developed. Here, I use examples that are based on existing drugs to illustrate the concept of robustness, and then discuss how a greater consideration of the importance of robustness could influence the design of new drugs that will be intended to control complex systems.

Preconditioning stress prevents cold restraint stress-induced gastric lesions in rats: roles of COX-1, COX-2, and PLA2

We investigated the protective effect of mild stress on gastric lesions induced by cold-restraint stress, especially concerning prostaglandins (PGs)/cyclo-oxygenase (COX) isozymes. Rats were exposed to severe stress (cold-restraint stress at 10 degrees C for 6 hr) or mild stress (cold-restraint stress at 10 degrees C for 30 min and kept at room temperature for 60 min) followed by severe stress. Severe stress induced gastric lesions, with a concomitant decrease in body temperature (BT). The ulcerogenic response was inhibited by atropine but worsened by indomethacin and SC-560 but not rofecoxib, although none of these agents had any effect on the change in BT. Mild stress suppressed the gastric ulceration and the decrease in BT induced by severe stress, and these effects were reversed by both COX-1 and COX-2 inhibitors. The expression of COX-2 in the stomach was up-regulated from 4 hr after severe stress and this response was slightly expedited by mild stress. COX-2 was also expressed in the hypothalamus under normal and stressed conditions. Quinacrine (phospholipase A(2) inhibitor) attenuated the protective effect of mild stress on the ulceration and decrease in BT caused by severe stress. TA-0910 (TRH analogue) at a low dose also prevented the gastric ulceration and the decrease in BT induced by severe stress. These results suggest that mild stress protects against cold-restraint stress-induced gastric ulceration, and the effect is peripherally and centrally mediated by PGs derived from both COX-1 and COX-2 through the activation of phospholipase A(2). TRH may also be involved in the protective effect of mild stress, probably through regulation of the thermogenic system.

Intestinal effects of nonselective and selective cyclooxygenase inhibitors in the rat

It is now widely recognized that nonsteroidal anti-inflammatory drugs (NSAIDs) may cause extensive damage to the intestine. The pathogenesis of NSAID-induced intestinal injury, however, is still controversial and both local irritant actions and cyclooxygenase (COX) inhibition have been proposed as underlying mechanisms. In this study we investigated further on NSAID-induced intestinal damage by using nonselective (indomethacin and ibuprofen), COX-1 selective (SC-560) or COX-2 selective (celecoxib) inhibitors. NSAIDs were administered orally to conscious rats and small intestinal injury was evaluated 24 h afterwards in terms of macroscopic and microscopic alterations, myeloperoxidase activity, lipid peroxidation, number of enterobacteria in the mucosa and epithelial mucin content. Oral administration of indomethacin (20 mg/kg) induced macroscopic and microscopic damage to the small intestine, increased translocation of enterobacteria from lumen into the mucosa, myeloperoxidase activity and lipid peroxidation. Ibuprofen (120 mg/kg), SC-560 (20 mg/kg), celecoxib (60 mg/kg) or the combination of SC-560 plus celecoxib did not cause any intestinal injury nor modified the number of bacteria in mucosal homogenates. SC-560 significantly increased both myeloperoxidase activity and lipid peroxidation, whereas celecoxib significantly reduced myeloperoxidase levels, while leaving unaltered lipid peroxidation. Finally, all NSAIDs, mostly indomethacin, increased neutral mucins and decreased acidic mucins in the intestinal goblet cells. These results indicate that inhibition of cyclooxygenase, although variably influencing mucosal integrity homeostasis, is not sufficient to initiate acute intestinal damage in rats. Moreover, topical mucosal injury induced by the NSAID molecule seems to be a critical factor in the development of intestinal injury.

Prostaglandin E2release in gastric antral mucosa of guinea-pigs: basal PGE2release by cyclo-oxygenase 2 and ACh-stimulated PGE2release by cyclo-oxygenase 1

Prostaglandin E(2) (PGE(2)), which is generated by two isoforms of cyclo-oxygenase (COX(1) and COX(2)), is a key mediator in gastric mucosal defense. In the present study, antral mucosa of guinea-pigs was incubated with various agonists or antagonists in a medium, the PGE(2) concentration of which was measured using a PGE(2) EIA kit. Prostaglandin E(2) was released from the antral mucosa spontaneously (basal PGE(2) release) and acetylcholine (ACh, 10 microM) enhanced the PGE(2) release (ACh-stimulated PGE(2) release) was mediated via intracellular Ca(2+) concentration ([Ca(2+)](i)). Arachidonic acid enhanced both forms of PGE(2) release, and a phospholipase A(2) inhibitor (amylcinnamoyl anthranilic acid) and COX inhibitors (acetylsalicylic acid and indomethacin) decreased them. 5-(4-Chlorophenyl)-1-(4-methoxyphenyl)-3-trifluoromethylpyrazol (SC560, 100 nm, a COX(1)-selective inhibitor) inhibited ACh-stimulated PGE(2) release without any decrease in basal PGE(2) release. N-(2-Cyclohexyloxy-4-nitrophenyl) methanesulphonamide (NS398, 20 microM, a COX(2)-selective inhibitor) decreased basal PGE(2) release without any reduction of ACh-stimulated PGE(2) release. However, ionomycin (a Ca(2+) ionophore) increased PGE(2) release from antral mucosa in the presence of SC560 or NS398, suggesting that COX(1) and COX(2) are regulated by [Ca(2+)](i). These findings indicate that COX(1)-containing cells have ACh receptors but COX(2)-containing cells do not. Moreover, in isolated antral epithelial cells, SC560 decreased basal and ACh-stimulated PGE(2) release, but NS398 did not. In conclusion, in antral mucosa, basal PGE(2) release is mainly maintained by COX(2) of non-epithelial cells, and ACh-stimulated PGE(2) release is maintained by COX(1) of epithelial cells.

Effects of cyclooxygenase inhibition on the gastrointestinal tract

Cyclooxygenase (COX) is a rate-limiting enzyme that catalyzes the conversion of arachidonic acid, an essential fatty acid present in cell membrane phospholipids and liberated by phospholipase, into prostaglandins (PGs) and prostanoids. COX has two distinct membrane-anchored isoenzymes; COX-1 and COX-2. COX-1 is a constitutively expressed and found in most normal body tissues; COX-2 is expressed in normal tissues at low levels and is highly induced by pro-inflammatory mediators in the setting of inflammation, injury, and pain. Inhibitors of COX activity include: (1) conventional non-selective non-steroidal anti-inflammatory drugs (ns-NSAIDs); (2) selective COX-2 inhibitors (COXIBs); and (3) COX-1 inhibitors. Non-selective NSAIDs, at therapeutic doses, inhibit both COX-1 and COX-2. The anti-inflammatory benefits of these drugs are primarily derived from COX-2 inhibition, while inhibition of COX-1 often elicits gastrointestinal (GI) toxicity. Therefore, COXIBs were developed to provide a selective COX-2 agent, i.e., one, that at fully therapeutic doses demonstrated comparable therapeutic benefit to non-selective NSAIDs, without the attendant COX-1-mediated GI toxicities. In this review, we evaluate available literature describing the pathophysiologic role of cyclooxygenases and the effects of their inhibition in GI system in experimental and domestic animal species.

Bacteroides fragilis enterotoxin induces cyclooxygenase-2 and fluid secretion in intestinal epithelial cells through NF-kappaB activation

Bacteroides fragilis produces an approximately 20-kDa heat-labile toxin (B. fragilis enterotoxin, BFT) which is known to be associated with diarrhea. To determine whether cyclooxygenase (COX)-2, via NF-kappaB activation, can contribute to BFT-induced diarrhea, the relationship between COX-2 expression and fluid secretion in BFT-stimulated human intestinal epithelial cells was examined. BFT stimulation increased the expression of COX-2, but not COX-1, in human intestinal epithelial cells. Suppression of the NF-kappaB signal significantly decreased COX-2 expression in response to BFT stimulation. Prostaglandin E2 (PGE2) levels were increased in parallel with COX-2 expression, and, conversely, PGE2 production was significantly inhibited when COX-2 or NF-kappaB activities were suppressed using COX-2 small interfering RNA (siRNA), p65 NF-kappaB subunit siRNA, or a retrovirus encoding the IkappaBalpha superrepressor. In addition, a selective COX-2 inhibitor, NS-398, significantly inhibited the increased cAMP level induced by BFT stimulation. Furthermore, a selective COX-2 inhibitor prevented BFT-induced PGE2 production and ileal fluid secretion in a mouse ileal loop model. These results suggest that the secretory response to BFT stimulation may be mediated by the production of PGE2, through NF-kappaB activation and the up-regulation of COX-2 in intestinal epithelial cells.

Prostanoid transport by multidrug resistance protein 4 (MRP4/ABCC4) localized in tissues of the human urogenital tract

PURPOSE

The seminal vesicles are the major source of prostaglandins in seminal fluid. For prostanoid action on cell surfaces they must be released from synthesizing cells. MRP4/ABCC4 (multidrug resistance protein 4 adenosine triphosphate-binding cassette, subfamily C, member 4) is an adenosine triphosphate dependent export pump for organic anions that may mediate prostanoid transport across the plasma membranes. Therefore, we analyzed whether MRP4 is expressed in the seminal vesicles and other tissues of the human urogenital tract, whether MRP4 and prostanoid synthesizing enzymes are co-expressed in the same cell type and whether MRP4 functions as a prostanoid export pump.

MATERIALS AND METHODS

The expression and localization of MRP4 and prostanoid synthesizing enzymes were investigated in several tissues of the male human urogenital tract by immunoblot and immunofluorescence analyses. Prostanoid transport was measured into inside-out membrane vesicles from cells expressing recombinant human MRP4.

RESULTS

MRP4 and prostanoid synthesizing enzymes were co-expressed in the epithelial cells of human seminal vesicles. Moreover, MRP4 was localized in the plasma membrane of epithelial cells of the ureter, in the basolateral membrane of glandular epithelial cells of the prostate, and in smooth muscle cells of the bladder and corpus cavernosum. Transport studies established MRP4 as an efflux pump for prostaglandin E2 (Michaelis constant [Km] 3.5 muM), thromboxane B2 (Km 9.9 muM) and prostaglandin F2alpha (Km 12.6 muM).

CONCLUSIONS

The co-expression of prostanoid synthesizing enzymes and MRP4 in epithelial cells of the human seminal vesicles and the function of MRP4 as a prostanoid efflux pump indicate that MRP4 mediates prostanoid transport from these cells, which are the main prostanoid synthesizing cells in the male urogenital tract.

ω-3 Polyunsaturated fatty acids and ionizing radiation: Combined cytotoxicity on human colorectal adenocarcinoma cells

OBJECTIVE

This study evaluated whether omega-3 polyunsaturated fatty acids (PUFAs) could enhance the radiosensitivity of three different human colorectal adenocarcinoma cell lines. To understand the underlying mechanisms, the effects of omega-3 PUFAs on the cell growth, survival, and apoptosis were evaluated alone or in combination with an antioxidant (vitamin E) and compared with the effects of omega-6 PUFAs.

METHODS

LS174T, CO112, and Caco-2 cell survival was assessed by clonogenic assay after a 3-d pretreatment with omega-3/omega-6 PUFAs and/or vitamin E before a single X-ray exposure to 4 Gy. Cell growth and viability were measured by double fluorescence-activated cell sorter analyses using propidium iodide and fluorescein isothiocyanate-conjugated annexin V. Student's t test or multivariable linear regression analyses were used for comparison.

RESULTS

Preincubation with 30 to 100 micromol/L of omega-3 PUFAs induced a dose-dependent additive decrease in cell survival after irradiation (P < 0.05). Evaluation of the underlying mechanisms indicated that omega-3 PUFAs mainly decreased the cell number via apoptosis induction. Moreover, formation of lipid peroxidation products and modulation of cyclooxygenase II activity seemed to be involved, because coincubation with 10 micromol/L vitamin E abolished the effect of 50 micromol/L of omega-3 PUFAs (P < 0.05), whereas omega-6 PUFAs could partly mimic omega-3 PUFA effects.

CONCLUSION

These observations suggest that omega-3 PUFAs may be potential candidates as nutritional adjuvants to enhance the efficacy of human colorectal cancer radiotherapy.

Roles of endogenous prostaglandins and cyclooxygenase isozymes in healing of indomethacin-induced small intestinal lesions in rats

The role of prostaglandins (PGs)/cyclooxygenase (COX) in the healing of indomethacin-induced small intestinal ulcers was examined in rats. Animals were given indomethacin (10 mg/kg s.c.) and killed 1, 2, 3, 5, and 7 days later. Indomethacin (2 mg/kg), 5-(4-chlorophenyl)-1-(4-methoxyphenyl)-3-trifluoromethylpyrazole (SC560; COX-1 inhibitor; 3 mg/kg), and rofecoxib (COX-2 inhibitor; 3 mg/kg) were given p.o. once daily for 6 days, during the first 3 days or last 3 days of the experimental period. All COX inhibitors given for 6 days significantly impaired the healing of these ulcers. Healing was also impaired by rofecoxib given for the first 3 days or by SC560 given for the last 3 days. The expression of COX-2 mRNA in the intestine was up-regulated after ulceration, persisting for 3 days and dissipating thereafter. Mucosal PGE2 contents decreased within 3 h after ulceration, recovered 24 h later, and increased above normal 1 approximately 3 days later. The PGE2 content at 4 days after ulceration was decreased by rofecoxib but not SC560, whereas that at 7 days was suppressed by SC560 but not rofecoxib. Vascular content in the ulcerated mucosa decreased when the healing was impaired by COX inhibitors. The deleterious effect of indomethacin on healing was mimicked by a prostacyclin E receptor (EP) 4 antagonist and reversed by coadministration of PGE2 as well as an EP4 agonist. In conclusion, endogenous PGs play a role in the healing of intestinal ulcers through EP4 receptors, yet the COX isozyme involved differs depending on the stage of healing; COX-2 in the early stage and COX-1 in the late stage.

Immunohistochemical study of cyclooxygenase-2 and p53 expression in skin tumors

Overexpression of cyclooxygenase-2 (COX-2) has been demonstrated in various cancers, including experimentally promoted tumors, gastrointestinal cancers, breast tumors and skin tumors. The mechanism that controls COX-2 expression is not yet clear. Currently, it is reported that COX-2 expression is frequently associated with mutated p53 genes. The goal of this study was to evaluate the expression patterns of COX-2 and p53 in several skin tumors and their correlation. An immunohistochemical method was used to investigate the expression of COX-2 and p53 proteins on formalin-fixed, paraffin-embedded tissue specimens of squamous cell carcinomas (SCC), basal cell carcinomas (BCC), Bowen's disease (BD), actinic keratosis (AK) and porokeratosis. The expression of COX-2 increased in 50% (5/10) of SCC, 80% (8/10) of BCC, 40% (4/10) of BD, 50% (5/10) of AK, and 20% (2/10) of porokeratosis cases. The expression of p53 increased in 90% (9/10) of SCC, 70% (7/10) of BCC, 70% (7/10) of BD, 50% (5/10) of AK, and 40% (4/10) of porokeratosis cases. COX-2 positivity rates of the p53-positive skin tumors were 56%, 100%, 57%, 80% and 25% in SCC, BCC, BD, AK and porokeratosis, respectively. However, the correlation between p53 and COX-2 expression in skin tumors was not statistically significant (P > 0.05). Our results indicate that skin COX-2 and p53 may play roles in skin tumors, but that there is no apparent correlation between the two markers.

Dexamethasone Impairs the Gastric Mucosal Integrity in Rats Treated with a Cyclooxygenase-1 but Not with a Cyclooxygenase-2 Inhibitor

In rats, neither the cyclooxygenase-1 inhibitor SC-560 nor the cyclooxygenase-2 inhibitor rofecoxib damages the gastric mucosa. Coadministration of dexamethasone induced injury in SC-560- but not in rofecoxib-treated rats. High levels of cyclooxygenase-1 protein occurred in the gastric mucosa of control rats, with no change after administration of SC-560. In contrast, the gastric cyclooxygenase-2 protein levels were low in control rats, but increased in a time-dependent manner after administration of SC-560. Dexamethasone prevented the increase in cyclooxygenase-2 protein levels. Our findings show that inhibition of cyclooxygenase-1 upregulates cyclooxygenase-2. When the upregulation is prevented by dexamethasone, gastric damage develops, suggesting that induction of cyclooxygenase-2 represents a compensatory mechanism that counteracts the injurious effect of cyclooxygenase-1 inhibition.

Products of cyclooxygenase-2 depress duodenal function in rats subjected to abdominal surgery

AIM

Abdominal surgery evokes powerful biological responses that affect gastrointestinal functions. Here we investigate the role of the cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2) isoforms in post-operative duodenal ileus.

METHODS

Proximal duodenum of anesthetized rats was perfused in situ with isotonic or hypotonic (50 mM) NaCl. Mucosal bicarbonate secretion, motility, mucosal permeability and effluent osmolality were determined in the absence and presence of different COX inhibitors.

RESULTS

The majority of control animals had no or few duodenal contractions and bicarbonate secretion averaged 10.9 +/- 1.4 micromol cm(-1) h(-1). These 'paralytic' controls responded to hypotonic NaCl with a small increase in mucosal permeability. In control animals exhibiting spontaneous duodenal contractions, the bicarbonate secretion was 50% higher and the hypotonicity-induced net increase in mucosal permeability sevenfold higher than in 'paralytic' controls. Treatment with the selective COX-2 inhibitors rofecoxib or parecoxib induced duodenal motility, increased bicarbonate secretion and potentiated the hypotonicity-induced increase in mucosal permeability. COX-2-inhibited animals had a twofold greater capacity to adjust luminal osmolality than 'paralytic' controls. The selective COX-1 inhibitor SC-560 only transiently stimulated motility and bicarbonate secretion and the hypotonicity-induced increase in mucosal permeability was smaller than in COX-2-inhibited animals.

CONCLUSIONS

Abdominal surgery increases the synthesis of prostanoids, particularly via the COX-2 isoform. This compromises the ability of the duodenum to contract and to secrete HCO and to adjust luminal osmolality possibly via altered mucosal permeability. It is proposed that studies of gastrointestinal functions in animals subjected to abdominal surgery should include animals pre-treated with a COX-2 inhibitor.

Influences of Helicobacter pylori on cyclooxygenase-2 expression and prostaglandinE2 synthesis in rat gastric epithelial cells in vitro

BACKGROUND AND AIM

It is known that cyclooxygenase (COX)-2 is over expressed in gastrointestinal neoplasia and Helicobacter pylori (H. pylori) infection is causally linked to gastric cancer. The present study aimed to elucidate the effects of H. pylori on COX-2 expression and prostaglandinE(2) (PGE(2)) production in a gastric epithelial cell line derived from normal rat gastric mucosa (RGM1).

METHOD

H. pylori water extracts were prepared from a supernatant of the H. pylori suspension in distilled water. RGM1 cells were cultured with H. pylori water extracts at the final concentration of 2.5, 5, 10 microg/mL for 24 h. For the time sequence study, RGM1 cells were cultured with 10 microg/mL H. pylori water extracts for 0, 6, 12, 24 and 48 h. COX-1 and COX-2 expression in the RGM1 cells was analyzed by western blotting. The levels of PGE(2) in the cultured media were measured by enzyme immunoassay.

RESULTS

H. pylori did not affect COX-1 expression; whereas COX-2 expression increased by six-fold at 24 h after incubation of RGM1 cells with 10 microg/mL H. pylori water extracts. The increase in COX-2 expression was evident after 12 h of incubation; reached a peak at 24 h and declined at 48 h. H. pylori dose dependently increased COX-2 expression and PGE(2) synthesis in RGM1 cells.

CONCLUSION

H. pylori induces COX-2 expression and increases PGE(2) synthesis in RGM1 cells in vitro. These results indicate that H. pylori-associated gastric carcinogenesis may depend on COX-2 expression.

Involvement of cyclooxygenase-2 in gastric mucosal hypertrophy in gastrin transgenic mice

Gastrin promotes gastric mucosal growth, and hypergastrinemia induces gastric mucosal hypertrophy. Recently, it has been reported that gastrin induces cyclooxygenase-2 (COX-2) in human gastric and colorectal cancer cell lines. However, whether COX-2 is involved in gastrin-induced gastric mucosal growth in vivo is unknown. We investigated the role of COX-2 in gastrin-induced gastric mucosal hypertrophy using gastrin transgenic mice. Hypergastrinemic mice [mice with mutated gastrin under the control of the beta-actin promoter (ACT-GAS mice)] received the COX-2 inhibitor celecoxib (0, 200, or 500 mg/kg of diet) from 5 wk of age and were killed at 16 or 24 wk. Some ACT-GAS mice received celecoxib from 16 wk and were killed at 24 wk. Eighty-week-old ACT-GAS mice without celecoxib treatment were also examined. The thickness of the gastric mucosa, cell populations, COX-2 expression, and PGE(2) levels were evaluated. All ACT-GAS mice showed gastric mucosal hypertrophy, and four of six 80-wk-old ACT-GAS mice developed gastric cancer. COX-2 was expressed in interstitial cells of the hypertrophic gastric mucosa and gastric cancers. Moreover, PGE(2) levels in the gastric mucosa of ACT-GAS mice were significantly higher than those of normal mice. With treatment with celecoxib, PGE(2) levels, the gastric mucosal thickness, and the number of total gastric cells per gastric gland of ACT-GAS mice were significantly decreased. The decrease in gastric mucosal thickness was caused by a reduction of foveolar hyperplasia. The thickness of glandules and the number of Ki67-positive cells were not significantly changed. In conclusion, COX-2 contributes to gastrin-induced mucosal hypertrophy of the stomach.

Preferential expression of cyclooxygenase-2 in colonic-phenotype of gastric intestinal metaplasia: association with helicobacter pylori and gastric carcinoma

OBJECTIVES

Gastric intestinal metaplasia (GIM) associated with H. pylori (HP) has been considered a premalignant lesion. However, GIM phenotype associated with HP infection and gastric cancer is unclear. The expression of COX-2 in relation to GIM phenotype is also unknown.

METHODS

We evaluated cellular phenotype and COX-2 expression in the GIM from HP-positive and -negative patients from Japan in the absence of gastric cancer (n = 31) by using a colon epithelium specific monoclonal antibody (mAb Das-1) and anti-COX-2 antibody. COX-2 expression was also examined in patients with gastric cancer (n = 34), both in the cancer and in the GIM areas away from the cancer field.

RESULTS

Sixty-eight percent of HP-positive GIM reacted with mAb Das-1, whereas the reactivity in the HP-negative GIM was only 25% (P < 0.001). The COX-2 expression was present in 32% of HP-positive GIM and in only 9% of HP-negative GIM (P < 0.001). In the cancer group, COX-2 expression was localized both in the cancer area (94%) and in the GIM (82%) away from the cancer. Each of the COX-2-positive tissue was also positive to mAb Das-1.

CONCLUSION

HP infection is highly associated with the development of colonic-phenotype of GIM, and about half of them expressed COX-2. COX-2 expression was frequent in both gastric cancer and the GIM adjacent to the cancer. The results suggest that the presence of mAb Das-1 and COX-2 reactivity in the GIM identify the subgroup of patients who may be at risk for gastric cancer and may need close surveillance.

Emerging roles for cyclooxygenase-2 in gastrointestinal mucosal defense

The development of selective inhibitors of cyclooxygenase-2 (COX-2) was based on the concept that this enzyme played little, if any, role in modulating the ability of the gastrointestinal (GI) tract to resist and respond to injury. There is now overwhelming evidence that this is far from true. Indeed, COX-2 mediates several of the most important components of 'mucosal defense', contributes significantly to the resolution of GI inflammation and plays a crucial role in regulating ulcer healing. COX-2 also contributes to long-term changes in GI function after bouts of inflammation.

Worsening effect of partial sleep deprivation on indomethacin-induced gastric mucosal damage

The present study was to investigate the roles of cyclooxygenase-1 and -2 (COX-1 and COX-2) and prostaglandin (PG) on gastric mucosal integrity of partially sleep deprived (PSD) rats. A slowly moving drum was used to induce PSD. The PG levels in the gastric mucosa of PSD rats, with or without indomethacin or rofecoxib treatment, were determined. Exogenous prostaglandin E (PGE) analog, misoprostol, was administered to PSD rats to investigate the modulating effect of PG in indomethacin-induced gastric damage. It was observed that COX-1 mRNA and protein were up-regulated in the gastric mucosa of PSD rats. Selective COX-2 inhibition by rofecoxib failed to decrease mucosal PGE2 levels nor to affect mucosal integrity in both PSD and sleep undisturbed rats. However, indomethacin, a COX-1 preferential non-selective COX inhibitor, significantly reduced mucosal PGE2 content and produced more severe mucosal damage in PSD rats than in the controls. The deleterious effect of indomethacin on gastric mucosal integrity of PSD rats was significantly attenuated with the administration of misoprostol. These results suggest that PSD enhances COX-1 biosynthesis of gastroprotective PGE2 as an adaptive response of the stomach to stress. The administration of non-selective COX inhibitors to subjects with chronic sleep deprivation may induce more gastric damages.

Fishing for prostanoids: deciphering the developmental functions of cyclooxygenase-derived prostaglandins

Prostaglandin G/H synthases (PGHS), commonly referred to as cyclooxygenases (COX-1 and COX-2), catalyze a key step in the synthesis of biologically active prostaglandins (PGs), the conversion of arachidonic acid (AA) into prostaglandin H(2) (PGH(2)). PGs have important functions in a variety of physiologic and pathologic settings, including inflammation, cardiovascular homeostasis, reproduction, and carcinogenesis. However, an evaluation of prostaglandin function in early development has been difficult due to the maternal contribution of prostaglandins from the uterus. The emergence of zebrafish as a model system has begun to provide some insights into the roles of this signaling cascade during vertebrate development. In zebrafish, COX-1 derived prostaglandins are required for two distinct stages of development, namely during gastrulation and segmentation. During gastrulation, PGE(2) signaling promotes cell motility, without altering the cell shape or directional migration of gastrulating cells. During segmentation, COX-1 signaling is also required for posterior mesoderm development, including the formation of vascular tube structures, angiogenesis of intersomitic vessels, and pronephros morphogenesis. We propose that deciphering the role for prostaglandin signaling in zebrafish development could yield insight and ultimately address the mechanistic details underlying various disease processes that result from perturbation of this pathway.

Expression of cyclooxygenase-2 and matrix metalloproteinase-9 in gastric carcinoma and its correlation with angiogenesis

OBJECTIVE

To investigate the expression of cyclooxygenase (COX)-2 and matrix metalloproteinase (MMP)-9 in gastric carcinomas, and to correlate this expression with clinicopathological parameters and angiogenesis.

METHODS

Ninety-six resected tumor specimens from patients with gastric carcinoma were obtained, and 30 corresponding paracancerous normal tissues were randomly selected as a control. Immunohistochemical staining was used for detecting the expression of COX-2 and MMP-9. Monoclonal antibody against CD34 was used for displaying vascular endothelial cells, and microvascular density (MVD) was calculated by counting of CD34-positive vascular endothelial cells.

RESULTS

The positive expression rates of COX-2, MMP-9 and MVD in the cancerous tissue were 80.2%, 74.0%, and 32.5 +/- 8.3, respectively, which were significantly higher than those in the normal tissue (P < 0.01). COX-2, MMP-9 expression rates and MVD in the patients with stages III and IV were 91.4%, 84.5% and 34.9 +/- 8.7, respectively, which were significantly higher than those in the patients with stages I and II (P < 0.01). In addition, the Spearman rank correlation test showed that tumor MVD was closely associated with COX-2 (r = 0.311, P < 0.01) and MMP-9 (r = 0.349, P < 0.01) expressions.

CONCLUSIONS

Overexpression of COX-2 and MMP-9 is related to tumor invasion and lymph node metastasis in the gastric carcinoma. These results provide evidence that COX-2 contribute to gastric cancer development by promoting MMP-9 expression and angiogenesis.

Effects of cyclooxygenase-1 and -2 inhibition on gastric acid secretion and cardiovascular functions in rats

The discovery of a second isoform of cyclooxygenase has led to a re-evaluation of the mechanisms underlying the adverse effects of nonsteroidal anti-inflammatory drugs, focusing in particular on the gastrointestinal system. We investigated the involvement of cyclooxygenase-1 and -2 in the regulation of gastric acid secretion and cardiovascular functions in anesthetized rats, after acute intravenous administration of the selective cyclooxygenase-1 inhibitor SC-560, the selective cyclooxygenase-2 inhibitor celecoxib and the nonselective inhibitor indomethacin. Indomethacin, celecoxib and SC-560 did not significantly modify basal acid secretion. Indomethacin and celecoxib were also ineffective on the acid secretion stimulated by pentagastrin; by contrast, SC-560 significantly enhanced the acid secretion stimulated by pentagastrin, electrical vagal stimulation or histamine. The stimulatory effects of SC-560 were prevented by cervical vagotomy, atropine and famotidine. Indomethacin caused either no change, increasing or decreasing effects on mean arterial pressure and heart rate. By contrast, SC-560 was unable to change cardiovascular parameters at 5 mg/kg, while inducing a marked bradycardia at 10 mg/kg. Celecoxib was ineffective. Our findings indicate that cyclooxygenase-1-derived prostaglandins are involved in the regulation of stimulated acid secretion and of basal heart rate; the role of prostaglandins in the acute control of systemic blood pressure under resting conditions seems to be negligible.

Expression of COX-2 and P16 protein and their correlations in various types of gastric polyps and gastric cancer cell

AIM: To explore the expression of COX-2 and P16 in various types of gastric polyps and gastric cancer cell, and to investigate the relationship between COX-2 and P16 protein in the process of gastric cancer.

METHODS: The expression of COX-2 and P16 proteins were detected in normal gastric mucosa (n = 10), non-tumor gastric polyps (n = 30, inflammatory polyps and hyperplastic polyps), tumor gastric polyps (n = 20, adenomatous polyps), and gastric cancer (n = 40) by S-P immunohistochemical staining.

RESULTS: In the normal gastric mucosa, non-tumor gastric polyps, tumor gastric polyps, and gastric cancer cell, the expression rate of the COX-2 was 10%, 13.33%, 45%, and 75%, respectively; and the rate of P16 protein expression in those tissues was 90%, 86.67%, 60%, and 32.5%, respectively. The positive rates of COX-2 and P16 protein were both significantly different between gastric cancer and other tissues (P <0.05). The expression of COX-2 and P16 were associated with the differentiation degree of gastric cancer and lymph node metastasis. COX-2 expression was negatively related to P16 expression in gastric cancer (P <0.05).

CONCLUSION: COX-2 and P16 protein play key roles in the development of gastric cancer, and can be used as important indexes in the research of the biological behavior of gastric cancer.

(2E,6Z,10E)-7-hydroxymethyl-3,11,15-trimethyl-2,6,10,14-hexadecatetraen-1-ol (Plaunotol) increases cyclooxygenase-2 expression via nuclear factor kappaB and cyclic AMP response element in rat gastric epithelial cells

Plaunotol, [(2E,6Z,10E)-7-hydroxymethyl-3,11,15-trimethyl-2,6,10,14-hexadecatetraen-1-ol], a gastroprotective agent, increases the prostaglandin production in the gastric mucosa and accelerates ulcer healing. The precise mechanisms underlying the gastroprotective actions by plaunotol are not known. On the other hand, cyclooxygenase (COX)-2 is a key enzyme in PGE(2) production and its induction is thought to have an important role in ulcer healing. We investigated the mechanism of plaunotol-mediated COX-2 induction in rat gastric epithelial (RGM1) cells. We used a PGE(2) enzyme-linked immunoassay kit and Western blot analysis to measure PGE(2) production and COX-2 induction with plaunotol treatment in serum-starved RGM1 cells. In addition, gel-shift assay, Western blot analysis and a reporter assay were performed to observe which Cox-2 promoter was involved in plaunotol-induced Cox-2 expression. The findings indicated that plaunotol treatment dose-dependently increased COX-2 expression and PGE(2) production. The nuclear factor kappaB (NF-kappaB) and cyclic AMP response element (CRE) sites of the COX-2 gene promoter were critical to plaunotol-mediated COX-2 expression. In conclusion, plaunotol induced COX-2 expression and increased PGE(2) production in serum-starved RGM1 cells via activation of the NF-kappaB and CRE sites of Cox-2 gene promoters.

COX-1 and COX-2 conversely promote and suppress ischemia-reperfusion gastric injury in mice

OBJECTIVE

Neutrophil activation followed by free radical production is a feature that is common to the various forms of gastric injury. However, the roles of cyclooxygenase (COX)-1 and -2 in neutrophil activation have yet to be clarified in the gastric mucosa. We examined the roles of both COX-1 and COX-2 in neutrophil activation and free radical production in ischemia-reperfusion (IR) injury in the gastric mucosa of mice.

MATERIAL AND METHODS

Ischemia was induced by clamping the celiac artery for 30 min, then removing the clamp for 90 min. SC-560, a selective COX-1 inhibitor; NS-398, a selective COX-2 inhibitor; or rebamipide, a mucoprotective agent, was administered to mice 60 min before ischemia. Gastric damage was evaluated histologically and by measuring myeloperoxidase (MPO) activity. Expressions of COX protein and intercellular adhesion molecule (ICAM)-1 were evaluated by Western blot analysis and ELISA, respectively. Effects of these drugs on thiobarbituric acid reactive substances (TBARS) and gastric blood flow were also evaluated.

RESULTS

COX-2 expression was induced in gastric mucosa 60 min after reperfusion, whereas COX-1 expression remained unaltered. Localization of COX-1 and ICAM-1 in IR-injured mucosa was observed mainly in endothelial cells, while COX-2 expression was detected in mesenchymal cells such as mononuclear cells, spindle-like cells and endothelial cells. SC-560 significantly decreased gastric blood flow at the reperfusion point and reduced gastric mucosal injury in IR mice. Furthermore, SC-560 pretreatment significantly reduced MPO activity, TBARS levels and ICAM-1 expression. In contrast, NS-398 significantly increased ICAM-1 expression, MPO activity and TBARS levels, and aggravated gastric damage in IR mice. Rebamipide pretreatment reduced both COX-2 expression and IR injury.

CONCLUSIONS

In IR mice, COX-2 protects the gastric mucosa by down-regulating ICAM-1 expression, whereas COX-1 is involved in up-regulating reperfusion flow, thereby aggravating the mucosa.

Role of cyclooxygenase isoforms in gastric mucosal defense and ulcer healing

The rationale for the development of selective inhibitors of cyclooxygenase-2 (COX-2) was the proposal that this enzyme plays an important role in inflammation but does not contribute to the resistance of the gastrointestinal mucosa against injury. However, studies from several groups have established that both COX-1 and COX-2 have important functions in the maintenance of gastrointestinal mucosal integrity. Thus, in the normal rat stomach lesions only develop when both COX-1 and COX-2 are inhibited. On the other hand, in specific pathophysiological situations the isolated inhibition of either COX-1 or COX-2 without simultaneous suppression of the other COX isoenzyme is ulcerogenic. Furthermore, COX-2 plays an important role in the healing of gastric ulcers and inhibition of COX-2 delays ulcer healing. From these findings the initial concept that only inhibition of COX-1 interferes with gastrointestinal defense has to be re-evaluated.

In vivo effects of tepoxalin, an inhibitor of cyclooxygenase and lipoxygenase, on prostanoid and leukotriene production in dogs with chronic osteoarthritis

OBJECTIVE

To evaluate in vivo effects of tepoxalin, an inhibitor of cyclooxygenase (COX) and lipoxygenase (LOX), on prostaglandin (PG) and leukotriene production in osteoarthritic dogs.

ANIMALS

7 mixed-breed adult dogs with chronic unilateral arthritis of a stifle joint.

PROCEDURE

Dogs were treated in accordance with a randomized 3-way crossover design. Each dog received an inert substance, meloxicam, or tepoxalin for 10 days. On day 0 (baseline), 3, and 10, dogs were anesthetized and samples of blood, stifle joint synovial fluid, and gastric mucosa were collected. Concentrations of PGE2 were measured in synovial fluid and after lipopolysaccharide stimulation of whole blood; PGE1 and PGE2 synthesis was measured in gastric mucosa. Thromboxane B2 (TxB2) concentration was measured in whole blood. Leukotriene B4 (LTB4) concentration was determined in gastric mucosa and in whole blood after ex vivo stimulation with a calcium ionophore.

RESULTS

Tepoxalin significantly decreased LTB4 concentrations in the blood and gastric mucosa at day 10 and TxB2 concentrations in the blood and PGE2 in the gastric mucosa and synovial fluid at days 3 and 10, compared with baseline values. Meloxicam significantly decreased PGE2 concentrations in the blood at days 3 and 10 and synovial fluid at day 3. Meloxicam also decreased PGE1 and PGE2 synthesis in the gastric mucosa at day 3. Meloxicam did not affect LTB4 synthesis in the blood or LTB4 concentrations in the gastric mucosa.

CONCLUSIONS AND CLINICAL RELEVANCE

Tepoxalin has in vivo inhibitory activity against COX-1, COX-2, and 5-LOX in dogs at the current approved recommended dosage.

In vivo effects of carprofen, deracoxib, and etodolac on prostanoid production in blood, gastric mucosa, and synovial fluid in dogs with chronic osteoarthritis

OBJECTIVE

To evaluate in vivo activity of carprofen, deracoxib, and etodolac on prostanoid production in several target tissues in dogs with chronic osteoarthritis.

ANIMALS

8 dogs with chronic unilateral osteoarthritis of the stifle joint.

PROCEDURE

Each dog received carprofen, deracoxib, or etodolac for 10 days with a 30- to 60-day washout period between treatments. On days 0, 3, and 10, prostaglandin (PG) E2 concentrations were measured in lipopolysaccharide-stimulated blood, synovial fluid, and gastric mucosal biopsy specimens; PGE1 concentrations were measured in gastric mucosal biopsy specimens; and thromboxane B2 (TXB2) was evaluated in blood.

RESULTS

Carprofen and deracoxib significantly suppressed PGE2 concentrations in blood at days 3 and 10, compared with baseline, whereas etodolac did not. None of the drugs significantly suppressed TXB2 concentrations in blood or gastric PGE1 synthesis at any time point. All 3 drugs significantly decreased gastric synthesis of PGE2 at day 3 but not day 10 of each treatment period. All 3 drugs decreased synovial fluid PGE2 concentrations in the affected and unaffected stifle joints at days 3 and 10.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicate that carprofen and deracoxib act in vivo on target tissues as COX-1-sparing drugs by sparing gastric PGE1 and PGE2 synthesis and production of TXB2 by platelets. Etodolac also appears to be COX-1 sparing but may have variable effects on COX-2 depending on the tissue. In gastric mucosa and synovial fluid, there were no significant differences in PG production between compounds at recommended concentrations.