COXIBs and 2,5-dimethylcelecoxib counteract the hyperactivated Wnt/ß-catenin pathway and COX-2/PGE2/EP4 signaling in glioblastoma cells.

BACKGROUND: Glioblastoma (GBM) is the deadliest and the most common primary brain tumor in adults. The invasiveness and proliferation of GBM cells can be decreased through the inhibition of Wnt/ß-catenin pathway. In this regard, celecoxib is a promising agent, but other COXIBs and 2,5-dimethylcelecoxib (2,5-DMC) await elucidation. Thus, the aim of this study was to analyze the impact of celecoxib, 2,5-DMC, etori-, rofe-, and valdecoxib on GBM cell viability and the activity of Wnt/ß-catenin pathway. In addition, the combination of the compounds with temozolomide (TMZ) was also evaluated. Cell cycle distribution and apoptosis, MGMT methylation level, COX-2 and PGE2 EP4 protein levels were also determined in order to better understand the molecular mechanisms exerted by these compounds and to find out which of them can serve best in GBM therapy. METHODS: Celecoxib, 2,5-DMC, etori-, rofe- and valdecoxib were evaluated using three commercially available and two patient-derived GBM cell lines. Cell viability was analyzed using MTT assay, whereas alterations in MGMT methylation level were determined using MS-HRM method. The impact of COXIBs, in the presence and absence of TMZ, on Wnt pathway was measured on the basis of the expression of ß-catenin target genes. Cell cycle distribution and apoptosis analysis were performed using flow cytometry. COX-2 and PGE2 EP4 receptor expression were evaluated using Western blot analysis. RESULTS: Wnt/ß-catenin pathway was attenuated by COXIBs and 2,5-DMC irrespective of the COX-2 expression profile of the treated cells, their MGMT methylation status, or radio/chemoresistance. Celecoxib and 2,5-DMC were the most cytotoxic. Cell cycle distribution was altered, and apoptosis was induced after the treatment with celecoxib, 2,5-DMC, etori- and valdecoxib in T98G cell line. COXIBs and 2,5-DMC did not influence MGMT methylation status, but inhibited COX-2/PGE2/EP4 pathway. CONCLUSIONS: Not only celecoxib, but also 2,5-DMC, etori-, rofe- and valdecoxib should be further investigated as potential good anti-GBM therapeutics.

Role of cyclooxygenase-2-mediated prostaglandin E2-prostaglandin E receptor 4 signaling in cardiac reprogramming.

Direct cardiac reprogramming from fibroblasts can be a promising approach for disease modeling, drug screening, and cardiac regeneration in pediatric and adult patients. However, postnatal and adult fibroblasts are less efficient for reprogramming compared with embryonic fibroblasts, and barriers to cardiac reprogramming associated with aging remain undetermined. In this study, we screened 8400 chemical compounds and found that diclofenac sodium (diclofenac), a non-steroidal anti-inflammatory drug, greatly enhanced cardiac reprogramming in combination with Gata4, Mef2c, and Tbx5 (GMT) or GMT plus Hand2. Intriguingly, diclofenac promoted cardiac reprogramming in mouse postnatal and adult tail-tip fibroblasts (TTFs), but not in mouse embryonic fibroblasts (MEFs). Mechanistically, diclofenac enhanced cardiac reprogramming by inhibiting cyclooxygenase-2, prostaglandin E2/prostaglandin E receptor 4, cyclic AMP/protein kinase A, and interleukin 1ß signaling and by silencing inflammatory and fibroblast programs, which were activated in postnatal and adult TTFs. Thus, anti-inflammation represents a new target for cardiac reprogramming associated with aging.

COX-2/EP2-EP4/ß-catenin signaling regulates patulin-induced intestinal cell proliferation and inflammation.

Patulin (PAT), a mycotoxin, is a natural contaminant that is produced by certain species of Penicillium, Aspergillus and Byssochlamys. The major contamination of PAT is in apple and apple based products. PAT is known to cause glutathione depletion, oxidative DNA damage and cell proliferation. Recently, in vitro studies have indicated that PAT can also increase the intestinal epithelial permeability, modulate tight junctions and decrease transepithelial electrical resistance. Nonetheless, no previous study has evaluated the mechanisms responsible for PAT-induced intestinal toxicity or its relevance to the in vivo situation. Here, Wistar rats were orally treated with 100 µg/kg body weight (b.wt.) of PAT, either alone or along with 100 mg/kg b. wt. of celecoxib for 3 days. We found that PAT exposure led to significantly higher levels of PGE2 in serum and intestinal tissue and high expression of COX-2 and Ki-67 compared to controls. Interestingly, our results showed that celecoxib treatment could decrease the PAT-induced PGE2 and reduce the PAT-induced intestinal damage. To study the mechanistic aspect, normal rat intestinal epithelial cells (IEC-6) were treated with non-toxic concentrations (100 nM, 250 nM and 500 nM) of PAT for 6 h. It was observed that PAT exposure caused enhanced proliferation, higher expression of COX-2, and EP2 and EP4 receptors, along with increased PGE2 secretion. Additionally, PAT exposure caused enhanced Akt expression, which in turn inhibits GSK-3ß and stabilizes ß-catenin. Overall, our study suggests that the COX-2/EP2-EP4/ß-catenin signaling cascades are involved in the regulation of PAT-induced intestinal cell proliferation and inflammation.

Discovery of 2-Piperidinyl Phenyl Benzamides and Trisubstituted Pyrimidines as Positive Allosteric Modulators of the Prostaglandin Receptor EP2.

Prostaglandin E2 (PGE2) via its Gαs-coupled EP2 receptor protects cerebral cortical neurons from excitotoxic and anoxic injury, though EP2 receptor activation can also cause secondary neurotoxicity in chronic inflammation. We performed a high-throughput screen of a library of 292 000 small molecules and identified several compounds that have a 2-piperidinyl phenyl benzamide or trisubstituted pyrimidine core as positive modulators for human EP2 receptor. The most active compounds increased the potency of PGE2 on EP2 receptor 4-5-fold at 20 µM without altering efficacy, indicative of an allosteric mechanism. These compounds did not augment the activity of the other Gαs-coupled PGE2 receptor subtype EP4 and showed neuroprotection against N-methyl-d-aspartate (NMDA)-induced excitotoxicity. These newly developed compounds represent second-generation allosteric potentiators for EP2 receptor and shed light on a promising neuroprotective strategy. They should prove valuable as molecular tools to achieve a better understanding of the dichotomous action of brain EP2 receptor activation.

Direct growth-inhibitory effects of prostaglandin E2 in pancreatic cancer cells in vitro through an EP4/PKA-mediated mechanism.

BACKGROUND: There is strong evidence linking inflammation and the development of pancreatic ductal adenocarcinoma. Cyclooxygenase-2 (COX-2) and COX-2-derived PGE2 are overexpressed in human and murine pancreatic ductal adenocarcinoma. Several studies have demonstrated an important role of COX-2-derived PGE2 in tumor-stroma interactions; however, the direct growth effects of prostaglandin E2 (PGE2) on pancreatic ductal adenocarcinoma cells is less well defined. Our aim was to investigate the effects of PGE2 on pancreatic ductal adenocarcinoma cell growth and to characterize the underlying mechanisms. METHODS: Human pancreatic ductal adenocarcinoma cell lines, Panc-1 and MIA PaCa-2, were treated with PGE2 in varying doses (0-10 µM). Effects on the phosphorylation of ERK1/2 were evaluated by Western blot. Colony formation was observed for cells treated with PGE2 for 11 days. DNA synthesis was determined by (3H)-thymidine incorporation assay. Gene expression of E-type prostaglandin (EP)2/EP4 receptors and their correlation with survival in patients with pancreatic ductal adenocarcinoma were assessed using the RNA-Seq data set from The Cancer Genome Atlas Research Network. RESULTS: PGE2 decreased the size and number of colonies in Panc-1 but not MIA PaCa-2 cells. In the Panc-1 cells, PGE2 activated PKA/CREB and decreased phosphorylation of ERK1/2, which was reversed by an EP4 receptor antagonist, while an EP2 receptor antagonist had no effect. In contrast, in MIA PaCa-2 cells, PGE2 had no effect on ERK1/2 phosphorylation. Treatment of both Panc-1 and MIA PaCa-2 cells with forskolin/IBMX decreased ERK1/2 phosphorylation. Finally, PGE2 decreased DNA synthesis only in Panc-1 cells, which was reversed by an EP4 receptor antagonist. In human pancreatic ductal adenocarcinoma, high EP2 and low EP4 gene expression was correlated to worse median overall survival (15.6 vs 20.8 months, log-rank P = .017). CONCLUSION: Our study provides evidence that PGE2 can inhibit directly pancreatic ductal adenocarcinoma cell growth through an EP4-mediated mechanism. Together with our gene expression and survival analysis, this observation suggests a protective role of EP4 receptors in human pancreatic ductal adenocarcinoma that expresses E-type prostaglandin receptors.

Pharmacology of grapiprant, a novel EP4 antagonist: receptor binding, efficacy in a rodent postoperative pain model, and a dose estimation for controlling pain in dogs.

Grapiprant is an analgesic and anti-inflammatory drug in the piprant class that was approved in March 2016 by FDA's Center for Veterinary Medicine for the control of pain and inflammation associated with osteoarthritis (OA) in dogs. Grapiprant functions as a selective antagonist of the EP4 receptor, one of the four prostaglandin E2 (PGE2 ) receptor subtypes. The EP4 receptor mediates PGE2 -elicited nociception, and grapiprant has been shown to decrease pain in several rat inflammatory pain models. It was also effective in reducing pain associated with OA in humans, providing evidence for its mechanism of action in these species. The estimated canine efficacy dose of between 1.3 and 1.7 mg/kg, p.o. with a methylcellulose suspension, once a day, was predicted based on calculations from comparative affinity of grapiprant to the dog, rat, and human EP4 receptors, serum protein binding, effective doses defined in rat models of pain and inflammation, and human clinical studies. The results of this study guided the doses to be tested in the pilot study and demonstrated the usefulness of the efficacy dose prediction method. The approved commercial tablet dose of grapiprant is 2 mg/kg once a day for the control of pain and inflammation associated with OA in dogs.

Opposing roles of LTB4 and PGE2 in regulating the inflammasome-dependent scorpion venom-induced mortality.

Tityus serrulatus sting causes thousands of deaths annually worldwide. T. serrulatus-envenomed victims exhibit local or systemic reaction that culminates in pulmonary oedema, potentially leading to death. However, the molecular mechanisms underlying T. serrulatus venom (TsV) activity remain unknown. Here we show that TsV triggers NLRP3 inflammasome activation via K(+) efflux. Mechanistically, TsV triggers lung-resident cells to release PGE2, which induces IL-1ß production via E prostanoid receptor 2/4-cAMP-PKA-NFκB-dependent mechanisms. IL-1ß/IL-1R actions account for oedema and neutrophil recruitment to the lungs, leading to TsV-induced mortality. Inflammasome activation triggers LTB4 production and further PGE2 via IL-1ß/IL-1R signalling. Activation of LTB4-BLT1/2 pathway decreases cAMP generation, controlling TsV-induced inflammation. Exogenous administration confirms LTB4 anti-inflammatory activity and abrogates TsV-induced mortality. These results suggest that the balance between LTB4 and PGE2 determines the amount of IL-1ß inflammasome-dependent release and the outcome of envenomation. We suggest COX1/2 inhibition as an effective therapeutic intervention for scorpion envenomation.

Prostaglandin E2 stimulates normal bronchial epithelial cell growth through induction of c-Jun and PDK1, a kinase implicated in oncogenesis.

BACKGROUND: Cyclooxygenase-2-derived prostaglandin E2 (PGE2), a bioactive eicosanoid, has been implicated in many biological processes including reproduction, inflammation and tumor growth. We previously showed that PGE2 stimulated lung cancer cell growth and progression through PGE2 receptor EP2/EP4-mediated kinase signaling pathways. However, the role of PGE2 in controlling lung airway epithelial cell phenotype remains unknown. We evaluated the effects of c-Jun and 3-phosphoinositede dependent protein kinase-1 (PDK1) in mediating epithelial cell hyperplasia induced by PGE2. METHOD: The bronchial epithelial cell lines BEAS-2B and HBEc14-KT were cultured and then treated with PGE2. PDK1 small interfering RNA (siRNA) and a PDK1 inhibitor, an antagonist of the PGE2 receptor subtype EP4 and EP4 siRNA, c-Jun siRNA, and overexpressions of c-Jun and PDK1 have been used to evaluate the effects on cell proliferation. RESULTS: We demonstrated that PGE2 increased normal bronchial epithelial cell proliferation through induction of PDK1, an ankyrin repeat-containing Ser/Thr kinase implicated in the induction of apoptosis and the suppression of tumor growth. PDK1 siRNA and a PDK1 inhibitor blocked the effects of PGE2 on normal cell growth. The PGE2-induced PDK1 expression was blocked by an antagonist of the PGE2 receptor subtype EP4 and by EP4 siRNA. In addition, we showed that induction of PDK1 by PGE2 was associated with induction of the transcription factor, c-Jun protein. Silencing of c-Jun using siRNA and point mutations of c-Jun sites in the PDK1 gene promoter resulted in blockade of PDK1 expression and promoter activity induced by PGE2. In contrast, overexpression of c-Jun induced PDK1 gene promoter activity and expression followed increased cell proliferation. CONCLUSION: PGE2 increases normal bronchial epithelial cell proliferation through increased PDK1 gene expression that is dependent on EP4 and induction of c-Jun. Therewith, our data suggest a new role of c-Jun and PDK1 in mediating epithelial cell hyperplasia induced by PGE2.

Doxycycline Attenuates Endotoxin-Induced Uveitis by Prostaglandin E2-EP4 Signaling.

PURPOSE: We explored the anti-inflammatory effects of doxycycline in experimental uveitis and the underlying mechanisms. METHODS: Rats with endotoxin-induced uveitis (EIU) received doxycycline (1.5 mg/kg) or the control vehicle via intraperitoneal injection. Clinical scores were graded under a slit lamp. Rat peritoneal macrophages were used in vitro to further explore the anti-inflammatory mechanisms of doxycycline. The levels of nitric oxide (NO), TNF-α, IL-1ß, prostaglandin E2 (PGE2), cyclooxygenase (COX)-2, I kappa B-α (IκB-α), inducible nitric oxide synthase (iNOS), Akt, caspase-3, and nuclear factor-kappa B (NF-κB) were analyzed. RESULTS: Treatment with doxycycline dramatically reduced the clinical scores of EIU (P < 0.001), with significant decreases in inflammatory cell infiltration, protein concentrations, and the production of NO, TNF-α, and IL-1ß in the aqueous humor (AqH). In vitro, doxycycline significantly inhibited the production of NO, IL-1ß, and TNF-α in peritoneal macrophages by modulating the PI3K/Akt/IκB-α/NF-κB pathway. Importantly, we found that doxycycline significantly enhanced COX2 expression and PGE2 production both in vivo and in vitro. More importantly, blockade of the EP4 receptor of PGE2 significantly reversed the doxycycline-mediated inhibition of macrophages and the PI3K/Akt pathway in vitro. Furthermore, simultaneous injection of an EP4 antagonist and doxycycline significantly blocked the doxycycline-mediated attenuation of EIU. CONCLUSIONS: Doxycycline can ameliorate EIU, and PGE2-EP4 signaling is essential for the anti-inflammatory effects of doxycycline in vitro and in vivo.

Cardiohemodynamic and electrophysiological effects of a selective EP4 receptor agonist ONO--AE1--329 in the halothane-anesthetized dogs.

Cardiovascular effects of a highly selective prostaglandin E2 type 4 (EP4) receptor agonist ONO-AE1-329 were assessed with the halothane-anesthetized dogs (n=6). ONO-AE1-329 was intravenously infused in three escalating doses of 0.3, 1 and 3ng/kg/min for 10min with a pause of 20min between the doses. The low dose of 0.3ng/kg/min significantly increased maximum upstroke velocity of left ventricular pressure by 18% at 20min, indicating increase of ventricular contractility. The middle dose of 1ng/kg/min significantly decreased total peripheral resistance by 24% and left ventricular end-diastolic pressure by 32% at 10min, indicating dilation of arteriolar resistance vessels and venous capacitance ones, respectively; and increased cardiac output by 25% at 10min in addition to the change induced by the low dose. The high dose of 3ng/kg/min increased heart rate by 34% at 10min; decreased mean blood pressure by 14% at 10min and atrioventricular nodal conduction time by 13% at 5min; and shortened left ventricular systolic period by 8% at 10min and electromechanical coupling defined as an interval from completion of repolarization to the start of ventricular diastole by 39% at 10min in addition to the changes induced by the middle dose. No significant change was detected in a ventricular repolarization period. These results indicate that ONO-AE1-329 may possess a similar cardiovascular profile to typical phosphodiesterase 3 inhibitors as an inodilator, and suggest that EP4 receptor stimulation can become an alternative strategy for the treatment of congestive heart failure.

Prostaglandin I2 and prostaglandin E2 modulate human intrarenal artery contractility through prostaglandin E2-EP4, prostacyclin-IP, and thromboxane A2-TP receptors.

Cyclooxygenase inhibitors decrease renal blood flow in settings with decreased effective circulating volume. The present study examined the hypothesis that prostaglandins, prostaglandin E2 (PGE2) and prostacyclin (PGI2), induce relaxation of human intrarenal arteries through PGE2-EP and PGI2-IP receptors. Intrarenal arteries were microdissected from human nephrectomy samples (n=53, median diameter ≈362 µm, 88% viable, 76% relaxed in response to acetylcholine). Rings were suspended in myographs to record force development. In vessels with K(+)-induced tension (EC70: -log [mol/L]=1.36±0.03), PGE2 and PGI2 induced concentration-dependent relaxation (-log EC50: PGE2=7.1±0.3 and PGI2=7.7). The response to PGE2 displayed endothelium dependence and desensitization. Relaxation by PGE2 was mimicked by an EP4 receptor agonist (CAY10598, EC50=6.7±0.2). The relaxation after PGI2 was abolished by an IP receptor antagonist (BR5064, 10(-8) mol/L). Pretreatment of quiescent arteries with PGE2 for 5 minutes (10(-6) mol/L) led to a significant right shift of the concentration-response to norepinephrine (EC50 from 6.6±0.1-5.9±0.1). In intrarenal arteries with K(+)-induced tone, PGE2 and PGI2 at 10(-5) mol/L elicited increased tension. This was abolished by thromboxane receptor (TP) antagonist (S18886, 10(-6) mol/L). A TP agonist (U46619, n=6) evoked tension (EC50=8.1±0.2) that was inhibited by S18886. Polymerase chain reaction and immunoblotting showed EP4, IP, and TP receptors in intrarenal arteries. In conclusion, PGE2 and PGI2 may protect renal perfusion by activating cognate IP and EP4 receptors associated with smooth muscle cells and endothelium in human intrarenal arteries and contribute to increased renal vascular resistance at high pathological concentrations mediated by noncognate TP receptor.

G-protein-coupled receptor 91 and succinate are key contributors in neonatal postcerebral hypoxia-ischemia recovery.

OBJECTIVE: Prompt post-hypoxia-ischemia (HI) revascularization has been suggested to improve outcome in adults and newborn subjects. Other than hypoxia-inducible factor, sensors of metabolic demand remain largely unknown. During HI, anaerobic respiration is arrested resulting in accumulation of carbohydrate metabolic intermediates. As such succinate readily increases, exerting its biological effects via a specific receptor, G-protein-coupled receptor (GPR) 91. We postulate that succinate/GPR91 enhances post-HI vascularization and reduces infarct size in a model of newborn HI brain injury. APPROACH AND RESULTS: The Rice-Vannucci model of neonatal HI was used. Succinate was measured by mass spectrometry, and microvascular density was evaluated by quantification of lectin-stained cryosection. Gene expression was evaluated by real-time polymerase chain reaction. Succinate levels rapidly increased in the penumbral region of brain infarcts. GPR91 was foremost localized not only in neurons but also in astrocytes. Microvascular density increased at 96 hours after injury in wild-type animals; it was diminished in GPR91-null mice leading to an increased infarct size. Stimulation with succinate led to an increase in growth factors implicated in angiogenesis only in wild-type mice. To explain the mode of action of succinate/GPR91, we investigated the role of prostaglandin E2-prostaglandin E receptor 4, previously proposed in neural angiogenesis. Succinate-induced vascular endothelial growth factor expression was abrogated by a cyclooxygenase inhibitor and a selective prostaglandin E receptor 4 antagonist. This antagonist also abolished succinate-induced neovascularization. CONCLUSIONS: We uncover a dominant metabolic sensor responsible for post-HI neurovascular adaptation, notably succinate/GPR91, acting via prostaglandin E2-prostaglandin E receptor 4 to govern expression of major angiogenic factors. We propose that pharmacological intervention targeting GPR91 could improve post-HI brain recovery.

Lipopolysaccharide of Aggregatibacter actinomycetemcomitans up-regulates inflammatory cytokines, prostaglandin E2 synthesis and osteoclast formation in interleukin-1 receptor antagonist-deficient mice.

BACKGROUND AND OBJECTIVE: The interleukin (IL)-1 receptor antagonist (Ra) binds to IL-1 receptors and inhibits IL-1 activity. However, it is unclear whether the IL-1Ra plays a protective role in periodontal disease. The purpose of this study was to compare IL-1Ra knockout (KO) and wild-type (WT) mice in regard to proinflammatory cytokine production, osteoclast formation and bone resorption in response to periodontal bacterial lipopolysaccharide (LPS). MATERIAL AND METHODS: Peritoneal macrophages (Mφs) were obtained from 13-wk-old IL-1Ra KO and WT mice. Peritoneal Mφs were cultured with or without 10 µg/mL of Aggregatibacter actinomycetemcomitans LPS for 24 h. The levels of IL-1alpha (IL-1α), IL-1beta (IL-1ß), tumor necrosis factor-α (TNF-α) and IL-6 were measured in periotoneal Mφs supernatant fluid (PM-SF) using an ELISA. Bone marrow cells were obtained from the mice and stimulated with PM-SF for 9 d, then stained with TRAP. The frequency of TRAP-positive multinucleated giant cell formation was calculated based on a fusion index. PM-SF-stimulated calvarial bone resorption was analyzed using micro-computed tomography, and calvarial histological analysis was performed using hematoxylin and eosin and TRAP staining. The expression of cyclooxygenase-2 (Cox2), prostanoid receptor EP4 (Ep4) and Rank mRNAs in bone marrow cells were measured using real-time quantitative PCR, while prostaglandin E2 (PGE2 ) production was determined by ELISA. RESULTS: The levels of IL-1α, IL-1ß, TNF-α and IL-6 in IL-1Ra KO mice PM-SF stimulated with A. actinomycetemcomitans LPS were significantly increased by approximately 4- (p < 0.05), 5- (p < 0.05), 1.3- (p < 0.05) and 6- (p < 0.05) fold, respectively, compared with the levels in WT mice. Moreover, osteoclast formation, expression of Rank, Ep4 and Cox2 mRNAs and production of PGE2 were significantly increased by approximately 2- (p < 0.05), 1.6- (p < 0.05), 2.5- (p < 0.05), 1.6- (p < 0.05) and 1.9- (p < 0.05) fold, respectively, in IL-1Ra KO mice stimulated with A. actinomycetemcomitans LPS compared with WT mice. CONCLUSION: IL-1Ra regulates IL-1 activity and appears to reduce the levels of other inflammatory cytokines, including TNF-α and IL-6, while it also reduces expression of the EP4 receptor related to prostanoid sensitivity and osteoclast formation. These results suggest that IL-1Ra is an important molecule for inhibition of inflammatory periodontal bone resorption.

Novel prostaglandin receptor modulators--part II: EP receptor modulators; a patent review (2002 - 2012).

INTRODUCTION: Prostaglandins and their G-protein-coupled receptors play numerous physiological and pathophysiological roles, especially in inflammation and its resolution. The variety of effects mediated by prostanoids makes prostanoid receptors valuable drug targets and the research on prostaglandin receptor modulators is intensive. The physiological and pathophysiological effects of prostaglandin E(2) are especially complex and numerous. The four subtypes of EP receptor have gained a lot of industrial and academic interest, in particular EP(2) and EP(4) for various indications. AREAS COVERED: Evaluation of the patent activity over the last decade (2002 - 2012) illustrates several potent compounds targeting the distinct prostaglandin E(2) receptors. Many novel methods for the use of EP receptor modulators have been developed, in addition to the classical indications for agents modulating the arachidonic acid cascade such as pain and inflammation. EXPERT OPINION: Several EP targeting agents with good potency and selectivity have been developed but their pharmacological use and utility has not yet been satisfactorily investigated. More research is necessary, and clinical use of these agents might therefore take some more time.

Cancer-induced anorexia in tumor-bearing mice is dependent on cyclooxygenase-1.

It is well-established that prostaglandins (PGs) affect tumorigenesis, and evidence indicates that PGs also are important for the reduced food intake and body weight loss, the anorexia-cachexia syndrome, in malignant cancer. However, the identity of the PGs and the PG producing cyclooxygenase (COX) species responsible for cancer anorexia-cachexia is unknown. Here, we addressed this issue by transplanting mice with a tumor that elicits anorexia. Meal pattern analysis revealed that the anorexia in the tumor-bearing mice was due to decreased meal frequency. Treatment with a non-selective COX inhibitor attenuated the anorexia, and also tumor growth. When given at manifest anorexia, non-selective COX-inhibitors restored appetite and prevented body weight loss without affecting tumor size. Despite COX-2 induction in the cerebral blood vessels of tumor-bearing mice, a selective COX-2 inhibitor had no effect on the anorexia, whereas selective COX-1 inhibition delayed its onset. Tumor growth was associated with robust increase of PGE(2) levels in plasma - a response blocked both by non-selective COX-inhibition and by selective COX-1 inhibition, but not by COX-2 inhibition. However, there was no increase in PGE(2)-levels in the cerebrospinal fluid. Neutralization of plasma PGE(2) with specific antibodies did not ameliorate the anorexia, and genetic deletion of microsomal PGE synthase-1 (mPGES-1) affected neither anorexia nor tumor growth. Furthermore, tumor-bearing mice lacking EP(4) receptors selectively in the nervous system developed anorexia. These observations suggest that COX-enzymes, most likely COX-1, are involved in cancer-elicited anorexia and weight loss, but that these phenomena occur independently of host mPGES-1, PGE(2) and neuronal EP(4) signaling.

Potential therapeutic interventions via EP2/EP4 prostaglandin receptors.

Prevention and treatment of pathological inflammatory processes requires application of various classes of immune suppressors, such as calcineurin inhibitors, steroids and non-steroid inhibitors of prostaglandin synthesis. However, each type of these immune suppressors causes less or more serious adverse side-effects. Exploration of the role played by prostanoids in the immune response and identification of functionally distinct prostaglandin E receptors (EP1-EP4) opened new perspectives in therapy of inflammation, autoimmunity and prevention of graft rejection. The EP4 receptor appeared to be an attractive target to affect manifestations of various pathological states by application of either agonists or antagonists of the receptor. This article presents a short overview of experimental approaches aimed at manipulation of signaling via EP2 and EP4 receptors that could have therapeutic utility.

Distinct roles of central and peripheral prostaglandin E2 and EP subtypes in blood pressure regulation.

Prostaglandin E(2) (PGE(2)) is a major prostanoid with a wide variety of biological activities. PGE(2) can influence blood pressure (BP) both positively and negatively. In particular, centrally administered PGE(2) induces hypertension whereas systemic administration of PGE(2) produces a hypotensive effect. These physiologically opposing effects are generated by the existence of multiple EP receptors, namely EP(1-4), which are G protein-coupled receptors with distinct signaling properties. This review highlights the distinct roles of PGE(2) in BP regulation and the involvement of specific EP receptor subtypes.

Prostaglandin E2 represses interleukin 1 beta-induced inflammatory mediator output from pregnant human myometrial cells through the EP2 and EP4 receptors.

Inflammatory mediators, including prostaglandins, cytokines, and chemokines, are strongly implicated in the mechanism of human labor, though their precise roles remain unknown. Here we demonstrate that interleukin 1 beta (IL-1beta) significantly increased the expression and release of interleukin-8 (CXCL8), monocyte chemotactic protein-1 (CCL2), and granulocyte macrophage colony-stimulating factor (CSF2) by primary human myometrial cells. However, this effect was repressed by prostaglandin E(2) (PGE(2)). As PGE(2) can activate four distinct PGE(2) receptors (EP(1), EP(2), EP(3), and EP(4)) to elicit various responses, we sought to define the EP receptor(s) responsible for this repression. Using selective EP receptor agonists and a selective EP(4) antagonist, we show that PGE(2) mediates the repression of IL-1beta-induced release of CXCL8, CCL2, and CSF2 via activation of the EP(2) and EP(4) receptors. The use of siRNA gene-specific knockdown further confirmed a role for both receptors. Real-time RT-PCR demonstrated that EP(2) was the most highly expressed of all four EP receptors at the mRNA level in human myometrial cells, and immunocytochemistry showed that EP(2) protein is abundantly present throughout the cells. Interestingly, PGE(2) does not appear to reduce mRNA expression of CXCL8, CCL2, and CSF2. Our results demonstrate that PGE(2) can elicit anti-inflammatory responses via activation of the EP(2) and EP(4) receptors in lower segment term pregnant human myometrial cells. Further elucidation of the EP receptor-mediated signaling pathways in the pregnant human uterus may be beneficial for optimizing the maintenance of pregnancy, induction of labor or indeed treatment of preterm labor.

EP2 and EP4 receptors on muscularis resident macrophages mediate LPS-induced intestinal dysmotility via iNOS upregulation through cAMP/ERK signals.

Intestinal resident macrophages play an important role in gastrointestinal dysmotility by producing prostaglandins (PGs) and nitric oxide (NO) in inflammatory conditions. The causal correlation between PGs and NO in gastrointestinal inflammation has not been elucidated. In this study, we examined the possible role of PGE(2) in the LPS-inducible inducible NO synthase (iNOS) gene expression in murine distal ileal tissue and macrophages. Treatment of ileal tissue with LPS increased the iNOS and cyclooxygenase (COX)-2 gene expression, which lead to intestinal dysmotility. However, LPS did not induce the expression of iNOS and COX-2 in tissue from macrophage colony-stimulating factor-deficient op/op mice, indicating that these genes are expressed in intestinal resident macrophages. iNOS and COX-2 protein were also expressed in dextran-phagocytized macrophages in the muscle layer. CAY10404, a COX-2 inhibitor, diminished LPS-dependent iNOS gene upregulation in wild-type mouse ileal tissue and also in RAW264.7 macrophages, indicating that PGs upregulate iNOS gene expression. EP(2) and EP(4) agonists upregulated iNOS gene expression in ileal tissue and isolated resident macrophages. iNOS mRNA induction mediated by LPS was decreased in the ileum isolated from EP(2) or EP(4) knockout mice. In addition, LPS failed to decrease the motility of EP(2) and EP(4) knockout mice ileum. EP(2)- or EP(4)-mediated iNOS expression was attenuated by KT-5720, a PKA inhibitor and PD-98059, an ERK inhibitor. Forskolin or dibutyryl-cAMP mimics upregulation of iNOS gene expression in macrophages. In conclusion, COX-2-derived PGE(2) induces iNOS expression through cAMP/ERK pathways by activating EP(2) and EP(4) receptors in muscularis macrophages. NO produced in muscularis macrophages induces dysmotility during gastrointestinal inflammation.

Towards developing new strategies to reduce the adverse side-effects of nonsteroidal anti-inflammatory drugs.

The antipyretic and analgesic actions of nonsteroidal anti-inflammatory drugs (NSAIDs) are caused by the inhibition of prostaglandin E(2) (PGE(2)), thromboxane A(2) and prostacyclin (PGI(2)) production. Accumulating evidence suggests that the inhibition of PGE(2) production can cause adverse side-effects of NSAIDs on fluid and blood pressure regulation, such as hypertension and edema formation. Since both cyclooxygenase (COX)-1 and COX-2 isoforms contribute to the production of PGE(2), selective COX-2 inhibitors are not free of these adverse side-effects although they may be less severe. Four subtypes of PGE(2) receptors have been identified. The antipyretic action of blunted PGE(2) production is mediated predominantly by a reduced input to the prostaglandin E receptor 3 (EP(3)) pathway, whereas the analgesic action is mediated predominantly by a reduced input to the EP(1) pathway and perhaps by contributions from the other EP receptors. Accordingly, some of the adverse side-effects might be moderated by combined use of NSAIDs with selective EP(2) or EP(4) agonists that do not block the antipyretic or analgesic actions of NSAIDs that are mediated by reduced activation of EP(1) or EP(3) receptors. Moreover, EP(2) receptor-deficient mice had salt-sensitive hypertension and EP(4) receptor blockade moderated salt and water excretion and both EP(2) and EP(4) agonists had renoprotective effects. This suggests that strategies to maintain activation of EP(2) and EP(4) receptors during NSAID administration may not only reduce adverse effects but might confer additional benefits. In conclusion, enhancing EP(2) and EP(4) receptor activity by administration of selective agonists during the administration of NSAIDs has the potential to permit treating fever, inflammation and pain but with marginal adverse effects on fluid or blood pressure regulation.