A PROSTAGLANDIN E2 RECEPTOR SUBTYPE EP4 AGONIST ATTENUATES CARDIOVASCULAR DEPRESSION IN ENDOTOXIN SHOCK BY INHIBITING INFLAMMATORY CYTOKINES AND NITRIC OXIDE PRODUCTION

Prostaglandin E2 and myocarditis; friend or foe?

This review article summarizes the role of prostaglandin E2 (PGE2) and its receptors (EP1-EP4) as it relates to the inflammatory cardiomyopathy, myocarditis. During the COVID-19 pandemic, the onset of myocarditis in a subset of patients prompted a debate on the use of nonsteroidal anti-inflammatory drugs (NSAIDs), like ibuprofen, which act to inhibit the actions of prostaglandins. This review aims to further understanding of the role of PGE2 in the pathogenesis or protection of the myocardium in myocarditis. Inflammatory cardiomyopathies encompass a broad spectrum of disorders, all characterized by cardiac inflammation. Therefore, for the purpose of this review, the authors have placed particular emphasis on etiologies of myocarditis where effects of PGE2 have been documented.

The molecular, functional and phylogenetic characterization of PGE2 receptors reveals their different roles in the immune response of the teleost fish gilthead seabream (Sparus aurata L.)

Prostaglandin E₂ (PGE₂) plays an important role in immune activities in teleost fish, including seabream. However, receptors involved in PGE₂ signaling, as well as the pathways activated downstream, are largely unknown. In this study, one ortholog of mammalian PTGER1, PTGER3 and PTGER4, and two of PTGER2 (Ptger2a and Ptger2b) were identified and characterized in gilthead seabream. In silico analysis showed that all these receptors possessed the organization domain of G protein-coupled receptors, with the exception of Ptger2b. The corresponding in vivo studies revealed that they were expressed in all the tissues examined, the highest mRNA levels of ptger1 and ptger3 being observed in the spleen and of ptger2a and ptger4 in the blood. Bacterial infection induced higher mRNA levels of ptger2a, ptger3 and ptger4 in peritoneal exudate (the site of bacterial injection). In addition, head kidney acidophilic granulocytes and macrophages displayed different ptger1, ptger2a, ptger3 and ptger4 expression profiles. Furthermore, in macrophages the expression of the receptors was weakly affected by stimulation with bacterial DNA or with PGE₂, while in acidophilic granulocytes stimulation resulted in the upregulation of ptger2a and ptger4. Taken together, these results suggest different roles for seabream PGE₂ receptors in the regulation of the immune responses.

Macrophages and the maintenance of homeostasis

There have been many chapters written about macrophage polarization. These chapters generally focus on the role of macrophages in orchestrating immune responses by highlighting the T-cell-derived cytokines that shape these polarizing responses. This bias toward immunity is understandable, given the importance of macrophages to host defense. However, macrophages are ubiquitous and are involved in many different cellular processes, and describing them as immune cells is undoubtedly an oversimplification. It disregards their important roles in development, tissue remodeling, wound healing, angiogenesis, and metabolism, to name just a few processes. In this chapter, we propose that macrophages function as transducers in the body. According to Wikipedia, “A transducer is a device that converts energy from one form to another.” The word transducer is a term used to describe both the “sensor,” which can interpret a wide range of energy forms, and the “actuator,” which can switch voltages or currents to affect the environment. Macrophages are able to sense a seemingly endless variety of inputs from their environment and transduce these inputs into a variety of different response outcomes. Thus, rather than functioning as immune cells, they should be considered more broadly as cellular transducers that interpret microenvironmental changes and actuate vital tissue responses. In this chapter, we will describe some of the sensory stimuli that macrophages perceive and the responses they make to these stimuli to achieve their prime directive, which is the maintenance of homeostasis.

Isolevuglandins and cardiovascular disease

Isolevuglandins are 4-ketoaldehydes formed by peroxidation of arachidonic acid. Isolevuglandins react rapidly with primary amines including the lysyl residues of proteins to form irreversible covalent modifications. This review highlights evidence for the potential role of isolevuglandin modification in the disease processes, especially atherosclerosis, and some of the tools including small molecule dicarbonyl scavengers utilized to assess their contributions to disease.

Macrophage responses to lipopolysaccharide are modulated by a feedback loop involving prostaglandin E2, dual specificity phosphatase 1 and tristetraprolin

In many different cell types, pro-inflammatory agonists induce the expression of cyclooxygenase 2 (COX-2), an enzyme that catalyzes rate-limiting steps in the conversion of arachidonic acid to a variety of lipid signaling molecules, including prostaglandin E₂ (PGE₂). PGE₂ has key roles in many early inflammatory events, such as the changes of vascular function that promote or facilitate leukocyte recruitment to sites of inflammation. Depending on context, it also exerts many important anti-inflammatory effects, for example increasing the expression of the anti-inflammatory cytokine interleukin 10 (IL-10), and decreasing that of the pro-inflammatory cytokine tumor necrosis factor (TNF). The tight control of both biosynthesis of, and cellular responses to, PGE₂ are critical for the precise orchestration of the initiation and resolution of inflammatory responses. Here we describe evidence of a negative feedback loop, in which PGE₂ augments the expression of dual specificity phosphatase 1, impairs the activity of mitogen-activated protein kinase p38, increases the activity of the mRNA-destabilizing factor tristetraprolin, and thereby inhibits the expression of COX-2. The same feedback mechanism contributes to PGE₂-mediated suppression of TNF release. Engagement of the DUSP1-TTP regulatory axis by PGE₂ is likely to contribute to the switch between initiation and resolution phases of inflammation.

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.

Mice lacking prostaglandin E receptor subtype 4 manifest disrupted lipid metabolism attributable to impaired triglyceride clearance

Upon high-fat feeding, prostaglandin E receptor subtype 4 (EP4)-knockout mice gain less body weight than their EP4(+/+) littermates. We investigated the cause of the lean phenotype. The mice showed a 68.8% reduction in weight gain with diminished fat mass that was not attributable to reduced food intake, fat malabsorption, or increased energy expenditure. Plasma triglycerides in the mice were elevated by 244.9%. The increase in plasma triglycerides was independent of changes in hepatic very low density lipoprotein (VLDL)-triglyceride production or intestinal chylomicron-triglyceride synthesis. However, VLDL-triglyceride clearance was drastically impaired in the EP4-knockout mice. The absence of EP4 in mice compromised the activation of lipoprotein lipase (LPL), the key enzyme responsible for trafficking of plasma triglycerides into peripheral tissues. Deficiency in EP4 reduced hepatic mRNA expression of the transcriptional factor cAMP response element binding protein H (by 36.8%) and LPL activators, including apolipoprotein (Apo)a5 (by 40.2%) and Apoc2 (by 61.3%). In summary, the lean phenotype of EP4-deficient mice resulted from reduction in adipose tissue and accretion of other peripheral organs caused by impaired triglyceride clearance. The findings identify a new metabolic dimension in the physiologic role played by endogenous EP4.

Platelets protect from septic shock by inhibiting macrophage-dependent inflammation via the cyclooxygenase 1 signalling pathway

Although it has long been known that patients with sepsis often have thrombocytopenia and that septic patients with severe thrombocytopenia have a poor prognosis and higher mortality, the role of platelets in the pathogenesis of sepsis is poorly understood. Here we report a protective role of platelets in septic shock. We show that experimental thrombocytopenia induced by intraperitoneal injection of an anti-glycoprotein Ibα monoclonal antibody increases mortality and aggravates organ failure, whereas transfusion of platelets reduces mortality in lipopolysaccharide-induced endotoxemia and a bacterial infusion mouse sepsis model. Plasma concentrations of proinflammatory cytokines TNF-α and IL-6 are elevated by thrombocytopenia and decreased by platelet transfusion in septic mice. Furthermore, we identify that platelets protect from septic shock by inhibiting macrophage-dependent inflammation via the COX1/PGE₂/EP4-dependent pathway. Thus, these findings demonstrate a previously unappreciated role for platelets in septic shock and suggest that platelet transfusion may be effective in treating severely septic patients.

Anti-inflammation therapy by activation of prostaglandin EP4 receptor in cardiovascular and other inflammatory diseases

Prostaglandin E2 constitutes a major cyclooxygenase-2-derived prostanoid produced at inflammatory sites. In vitro and in vivo data support its role as a modulator of inflammation. Prostaglandin E2 exerts anti-inflammatory effects by binding to one of its receptors, the prostaglandin E receptor 4 (EP4), thereby modulating macrophage and T lymphocyte functions that participate crucially in innate and adaptive immunity and tissue remodeling and repair. The activation of EP4 suppresses the release of cytokines and chemokines from macrophages and T cells, inhibits the proliferation and the activation of T cells, and induces T-cell apoptosis. Lack of EP4 in bone marrow-derived cells accelerates local inflammation in atherosclerotic and aneurysm lesions and increases the prevalence of aneurysm formation. An EP4 agonist promotes graft survival in allograft cardiac transplantation and dampens tissue damage after myocardial ischemia. Anti-inflammatory actions of EP4 agonism may benefit other inflammatory disorders, including colitis and gastric ulcers. By contrast, EP4 acts as a proinflammatory mediator in encephalomyelitis, skin inflammation, and arthritis by promoting T helper (Th) 1 differentiation and Th17 expansion. Overall, EP4 activation produces powerful anti-inflammatory responses in many experimental diseases, rendering EP4 agonists attractive agents to attenuate syndromes associated with inflammation.

Roles of prostaglandin E2 in cardiovascular diseases

Prostaglandin E2 (PGE(2)) is produced in inflammatory responses and regulates a variety of immunological reactions through 4 different receptor subtypes; EP1, 2, 3 and 4. However, the precise role of each receptor in cardiovascular disease has not yet been elucidated. Enhanced expression of some EPs has been observed in clinical and experimental cardiovascular diseases. EP agonists have been developed to clarify the role of each receptor. Recently, we developed a novel selective agonist to examine the effects of EP4 on cardiac transplantation, myocardial ischemia, and myocarditis. Of note, a selective EP4 agonist attenuated inflammatory cytokines and chemokines via attenuation of macrophage activation in inflammatory heart diseases. In this review article, we discuss the effects of PGE(2) receptor agonists on the development of cardiovascular diseases.

International Union of Basic and Clinical Pharmacology. LXXXIII: classification of prostanoid receptors, updating 15 years of progress

It is now more than 15 years since the molecular structures of the major prostanoid receptors were elucidated. Since then, substantial progress has been achieved with respect to distribution and function, signal transduction mechanisms, and the design of agonists and antagonists (http://www.iuphar-db.org/DATABASE/FamilyIntroductionForward?familyId=58). This review systematically details these advances. More recent developments in prostanoid receptor research are included. The DP(2) receptor, also termed CRTH2, has little structural resemblance to DP(1) and other receptors described in the original prostanoid receptor classification. DP(2) receptors are more closely related to chemoattractant receptors. Prostanoid receptors have also been found to heterodimerize with other prostanoid receptor subtypes and nonprostanoids. This may extend signal transduction pathways and create new ligand recognition sites: prostacyclin/thromboxane A(2) heterodimeric receptors for 8-epi-prostaglandin E(2), wild-type/alternative (alt4) heterodimers for the prostaglandin FP receptor for bimatoprost and the prostamides. It is anticipated that the 15 years of research progress described herein will lead to novel therapeutic entities.

Atrial natriuretic peptide alleviates cardiovascular and metabolic disorders in a rat endotoxemia model: a possible role for its anti-inflammatory properties

BACKGROUND

Atrial natriuretic peptide (ANP) plays important roles in the regulation of cardiovascular and renal homeostasis. Furthermore, several studies have shown that ANP may have anti-inflammatory activities. We hypothesized that ANP may alleviate cardiovascular and/or metabolic disorders in rats with lipopolysaccharide (LPS)-induced endotoxemia.

METHODS

In rats anesthetized with pentobarbital, LPS was injected and ANP was continuously infused at 0.15 µg/kg/min. Mean arterial pressure and pulse rate were monitored hourly, and arterial blood gases were analyzed before LPS injection and at 1, 4, and 6 hours after LPS injection. The expression in the rat left ventricle of mRNAs encoding nitric oxide synthase 2 and 3 (iNOS, eNOS), heme oxygenase 1 and 2 (HO-1, 2), tumor necrosis factor α (TNFα), and interleukin (IL)-1β was measured with the real-time reverse transcriptase-polymerase chain reaction.

RESULTS

LPS increased the expression of TNFα, IL-1β, iNOS, and HO-1, which was inhibited by infusion of ANP. Furthermore, the LPS-induced decrease in mean arterial pressure was attenuated, and the acid-base imbalance caused by increased lactate production was improved 6 hours after the administration of ANP.

CONCLUSIONS

Our results suggest that continuous infusion of ANP counteracts the cardiovascular and metabolic disorders associated with endotoxemia, possibly via anti-inflammatory mechanisms.

Prostaglandin E2 receptor EP2, EP3, and EP4 agonists inhibit antigen-induced mucus hypersecretion in the nasal epithelium of sensitized rats

OBJECTIVES

Prostaglandin (PG) E2 is a potential anti-inflammatory mediator that attenuates airway inflammation. To elucidate the functions of the PGE2 receptors (EP1, EP2, EP3, and EP4) in allergic inflammation, we examined the in vivo effects of EP agonists on mucus hypersecretion and eosinophil infiltration in rat nasal epithelium.

METHODS

We induced hypertrophic and metaplastic changes in goblet cells in nasal epithelium of ovalbumin-sensitized rats by intranasal challenge with ovalbumin. The effects of subcutaneous injections of EP agonists on mucus production and eosinophil infiltration were examined.

RESULTS

The EP4 agonist (1 to 100 microg/kg) dose-dependently inhibited ovalbumin-induced mucus production. The EP2 and EP3 agonists (100 microg/kg) also significantly inhibited mucus production. The EP3 agonist inhibited antigen-induced eosinophil infiltration, whereas the EP1 agonist showed no effect. This suppression of mucus production by the EP4 agonist was only effective when the EP4 agonist was given in the effector phase; administration in the induction phase resulted in no effect.

CONCLUSIONS

These results indicate that PGE2 acts as an anti-inflammatory mediator via the EP receptors of airways in allergic inflammation. Selective EP agonists may provide a new therapeutic strategy for airway mucus hypersecretion.

E-prostanoid 3 receptor deletion improves pulmonary host defense and protects mice from death in severe Streptococcus pneumoniae infection

Prostaglandins (PGs) are potent lipid mediators that are produced during infections and whose synthesis and signaling networks present potential pharmacologic targets for immunomodulation. PGE(2) acts through the ligation of four distinct G protein-coupled receptors, E-prostanoid (EP) 1-4. Previous in vitro and in vivo studies demonstrated that the activation of the G(alphas)-coupled EP2 and EP4 receptors suppresses inflammatory responses to microbial pathogens through cAMP-dependent signaling cascades. Although it is speculated that PGE(2) signaling via the G(alphai)-coupled EP3 receptor might counteract EP2/EP4 immunosuppression in the context of bacterial infection (or severe inflammation), this has not previously been tested in vivo. To address this, we infected wild-type (EP3(+/+)) and EP3(-/-) mice with the important respiratory pathogen Streptococcus pneumoniae or injected mice i.p. with LPS. Unexpectedly, we observed that EP3(-/-) mice were protected from mortality after infection or LPS. The enhanced survival observed in the infected EP3(-/-) mice correlated with enhanced pulmonary clearance of bacteria; reduced accumulation of lung neutrophils; lower numbers of circulating blood leukocytes; and an impaired febrile response to infection. In vitro studies revealed improved alveolar macrophage phagocytic and bactericidal capacities in EP3(-/-) cells that were associated with an increased capacity to generate NO in response to immune stimulation. Our studies underscore the complex nature of PGE(2) immunomodulation in the context of host-microbial interactions in the lung. Pharmacological targeting of the PGE(2)-EP3 axis represents a novel area warranting greater investigative interest in the prevention and/or treatment of infectious diseases.

Ocular pharmacokinetics and hypotensive activity of PF-04475270, an EP4 prostaglandin agonist in preclinical models

Prostaglandins are widely used to lower intraocular pressure (IOP) as part of the treatment regimen for glaucoma. While FP and EP2 agonists are known to lower IOP, we investigated the ocular hypotensive activity and ocular drug distribution of PF-04475270, a novel EP4 agonist following topical administration in normotensive Beagle dogs. PF-04475270 is a prodrug of CP-734432, which stimulated cAMP formation in HEK293 cells expressing EP4 receptor and beta-lactamase activity in human EP4 expressing CHO cells transfected with a cAMP response element (CRE) with an EC(50) of 1 nM. Prodrug conversion and transcorneal permeability were assessed in rabbit corneal homogenates and a human corneal epithelial cell (cHCE) model. The compound underwent rapid hydrolysis to CP-734432 in corneal homogenates, and exhibited good permeability in the cHCE model. The descending order of ocular exposure to CP-734432 after topical dosing of PF-04475270 in dogs was as follows: cornea > aqueous humor >or= iris/ciliary body. When administered q.d., PF-04475270 lowered IOP effectively in the dog IOP model both after single and multiple days of dosing. A maximum decrease in IOP with PF-04475270 was between 30 and 45% at 24h post-dose relative to that observed with vehicle. In conclusion, PF-04475270 is a novel ocular hypotensive compound which is bioavailable following topical dosing, effectively lowering IOP in dogs. EP4 agonists could be considered as potential targets for lowering IOP for the treatment of glaucoma and ocular hypertension.

Emerging roles of PGE2 receptors in models of neurological disease

This review presents an overview of the emerging field of prostaglandin signaling in neurological diseases, focusing on PGE(2) signaling through its four E-prostanoid (EP) receptors. A large number of studies have demonstrated a neurotoxic function of the inducible cyclooxygenase COX-2 in a broad spectrum of neurological disease models in the central nervous system (CNS), from models of cerebral ischemia to models of neurodegeneration and inflammation. Since COX-1 and COX-2 catalyze the first committed step in prostaglandin synthesis, an effort is underway to identify the downstream prostaglandin signaling pathways that mediate the toxic effect of COX-2. Recent epidemiologic studies demonstrate that chronic COX-2 inhibition can produce adverse cerebrovascular and cardiovascular effects, indicating that some prostaglandin signaling pathways are beneficial. Consistent with this concept, recent studies demonstrate that in the CNS, specific prostaglandin receptor signaling pathways mediate toxic effects in brain but a larger number appear to mediate paradoxically protective effects. Further complexity is emerging, as exemplified by the PGE(2) EP2 receptor, where cerebroprotective or toxic effects of a particular prostaglandin signaling pathway can differ depending on the context of cerebral injury, for example, in excitotoxicity/hypoxia paradigms versus inflammatory-mediated secondary neurotoxicity. The divergent effects of prostaglandin receptor signaling will likely depend on distinct patterns and dynamics of receptor expression in neurons, endothelial cells, and glia and the specific ways in which these cell types participate in particular models of neurological injury.

Cardioprotection by polysaccharide sulfate against ischemia/reperfusion injury in isolated rat hearts

AIM

Polysaccharide sulfate (PSS) is a new type of heparinoid synthesized with alginic acid as the basic material and then by chemical introduction of effective groups. Although PSS is successfully applied in ischemic cardio-cerebrovascular disease, its effect on cardiac function after ischemia/reperfusion (I/R) injury has previously not been investigated. The aim of the present study was to investigate whether PSS can protect the heart from I/R injury and the underlying mechanism of protection.

METHODS

Isolated rat hearts were perfused (Langendorff) and subjected to 20 min global ischemia followed by 60 min reperfusion with Kreb's Henseleit solution or PSS (0.3-100 mg/L). Myocardial contractile function was continuously recorded. Creatine kinase (CK) and lactate dehydrogenase (LDH) leakage were measured. Tumor necrosis factor-alpha (TNF-alpha) expression in cardiomyocytes was investigated. Western blot analysis for extracellular regulated kinases (ERKs), c-jun amino-terminal kinase (JNKs) and p38 mitogen-activated protein kinase (MAPK) activity was performed.

RESULTS

After I/R, cardiac contractility decreased, CK and LDH levels increased in the coronary effluent, and TNF-alpha expression increased in cardiomyocytes. PSS administration at concentrations of 1-30 mg/L improved cardiac contractility, reduced CK and LDH release and inhibited TNF-alpha production. Phosphorylated-p38MAPK (p-p38MAPK) and p-p54/p46-JNK increased in I/R rat hearts but diminished in PSS (1-30 mg/L) treated hearts. P-p44/p42-ERK levels were unchanged. In contrast, high concentrations of PSS (100 mg/L) had adverse effects that caused a worsening of heart function.

CONCLUSION

PSS has dose-dependent cardioprotective effects on the rat heart after I/R injury. The beneficial effects may be mediated through normalization of the activity of p38 MAPK and JNK pathways as well as controlling the level of TNF-alpha expression.

Direct hemoperfusion with polymyxin-B-immobilized fiber columns improves septic hypotension and reduces inflammatory mediators in septic patients with colorectal perforation

PURPOSE

Although some studies have reported favorable effects of direct hemoperfusion with polymyxin-B-immobilized fiber columns (PMX) for the treatment of septic shock, few studies have demonstrated the efficacy of PMX in studies with a uniform case definition and without any other blood purification techniques.

MATERIALS AND METHODS

Fifty-two patients with severe sepsis or septic shock secondary to colorectal perforation were treated with PMX. Hemodynamic alterations and plasma concentrations of endotoxin, interleukin (IL)-1beta, IL-1 receptor antagonist (IL-1Ra), IL-6, IL-8, and IL-10 were evaluated following PMX treatment.

RESULTS

We observed a significant reduction in plasma endotoxin in the nonsurvivors immediately after PMX treatment compared to before treatment. Systolic blood pressure was markedly increased and circulating levels of IL-1beta, IL-1Ra, and IL-8 were significantly reduced during a 2-h interval of PMX.

CONCLUSIONS

Our findings suggested that PMX treatment appears to adsorb endotoxin and also modulates circulating cytokine during a 2-h interval of direct hemoperfusion in septic patients with such condition.

The role of adenosine A2 receptors in the regulation of TNF-α production and PGE2 release in mouse peritoneal macrophages

The adenosine A(2) receptors are known to mediate most of the anti-inflammatory activities of adenosine. In lipopolysaccharides (LPS)-stimulated macrophages adenosine strongly inhibits TNF-alpha release, but may also enhance PGE(2) generation. The aims of this study were to determine the relative contributions of the A(2A) and A(2B) receptor subclasses in these two effects and to determine whether the enhanced release of PGE(2) contributes to the inhibition of TNF-alpha release. In LPS-stimulated mouse macrophages, adenosine potently inhibited TNF-alpha production and also potentiated PGE(2) release, though less potently (IC(50)=250 nM vs EC(50) approximately 8 microM, respectively). The non-selective adenosine receptor agonist NECA, and the selective A(2A) receptor agonist CGS21680 also inhibited TNF-alpha production even more potently (IC(50)=4.8 and 2.3 nM, respectively). NECA, but not CGS21680, also enhanced PGE(2) production. The selective A(2A) receptor antagonist ZM241385 (30 nM), but not the selective A(2B) receptor antagonist MRS1754 (30 nM), blocked the inhibitory effect of NECA and CGS21680 on TNF-alpha release. On the other hand, MRS1754, but not ZM241385, abolished the PGE(2) potentiating effect of NECA. Pre-treatment with indomethacin (1 microM) abolished adenosine-induced PGE(2) release enhancement but did not prevent the inhibition of TNF-alpha release. These results show that in this system, the inhibition of TNF-alpha release by adenosine is mediated by the A(2A) receptors whereas the enhancement of PGE(2) release appears to be mediated by the A(2B) receptors. The results also show that while exogenous PGE(2) is a potent inhibitor of TNF-alpha release, the enhanced PGE(2) release induced by adenosine does not appear to contribute to the inhibition of TNF-alpha release.

Fluid resuscitation with hemoglobin-vesicle solution does not increase hypoxia or inflammatory responses in moderate hemorrhagic shock

The aim of the present study was to compare the hypoxic and inflammatory effects of transfusing hemoglobin-vesicles (HbV) or lactated Ringer's (LR) solution on several organs in a hemorrhagic shock model. Hemorrhagic shock was induced in 48 anesthetized rats by withdrawing 28 mL/kg blood. The animals were resuscitated by replacing the blood with an equal volume of HbV solution or three times the volume of LR solution. The heart, lung, liver, kidney and spleen were extracted at different time points following resuscitation, and mRNA expression levels of hypoxia-induced factor 1-alpha (HIF-1alpha) and tumor necrosis factor-alpha (TNF-alpha) were determined. Blood lactate concentrations in the HbV group rapidly returned to baseline levels, whereas elevated lactate concentrations in the LR group were prolonged. There were no significant differences between the two resuscitation groups in terms of HIF-1alpha and TNF-alpha expression in the organs examined. HIF-1alpha and TNF-alpha expression in the lungs was significantly greater than in other organs. Our results suggest that resuscitation from hemorrhagic shock with HbV did not increase hypoxic or inflammatory effects in major organs, compared with resuscitation using LR solution, despite prolonged elevation of blood lactate.

Lipopolysaccharide-induced up-regulation of triggering receptor expressed on myeloid cells-1 expression on macrophages is regulated by endogenous prostaglandin E2

Triggering receptor expressed on myeloid cells-1 (TREM-1) is a recently identified cell surface molecule that is expressed by neutrophils and monocytes. TREM-1 expression is modulated by various ligands for TLRs in vitro and in vivo. However, the influence of PGE(2), a potential mediator of inflammation, on TREM-1 expression has not been elucidated. In this study, we examined the effects of PGE(2) on LPS-induced TREM-1 expression by resident murine peritoneal macrophages (RPM) and human PBMC. PGE(2) significantly induced murine TREM-1 (mTREM-1) expression by RPM. Up-regulation of TREM-1 expression was specific to PGE(2) among arachidonic acid metabolites, while ligands for chemoattractant receptor-homologous molecule expressed on Th2 cells and the thomboxane-like prostanoid receptor failed to induce mTREM-1 expression. PGE(2) also increased expression of the soluble form of TREM-1 by PBMC. LPS-induced TREM-1 expression was regulated by endogenous PGE(2) especially in late phase (>2 h after stimulation), because cyclooxygenase-1 and -2 inhibitors abolished this effect at that points. A synthetic EP4 agonist and 8-Br-cAMP also enhanced mTREM-1 expression by RPM. Furthermore, protein kinase A, PI3K, and p38 MAPK inhibitors prevented PGE(2)-induced mTREM-1 expression by RPM. Activation of TREM-1 expressed on PGE(2)-pretreated PBMC by an agonistic TREM-1 mAb significantly enhanced the production of IL-8 and TNF-alpha. These findings indicate that LPS-induced TREM-1 expression on macrophages is mediated, at least partly, by endogenous PGE(2) followed by EP4 and cAMP, protein kinase A, p38 MAPK, and PI3K-mediated signaling. Regulation of TREM-1 and the soluble form of TREM-1 expression by PGE(2) may modulate the inflammatory response to microbial pathogens.

Night eating and obesity in the EP3R-deficient mouse

Adult mice carrying a null mutation of the prostanoid receptor EP3R (EP3R(-/-) mice) exhibit increased frequency of feeding during the light cycle of the day and develop an obese phenotype under a normal fat diet fed ad libitum. EP3R(-/-) mice show increased motor activity, which is not sufficient to offset the increased feeding leading to increased body weight. Altered "nocturnal" activity and feeding behavior is present from a very early age and does not seem to require age-dependent factors for the development of obesity. Obesity in EP3R(-/-) mice is characterized by elevated leptin and insulin levels and >20% higher body weight compared with WT littermates. Abdominal and subcutaneous fat and increased liver weight account for the weight increase in EP3R(-/-) mice. These observations expand the roles of prostaglandin E(2) signaling in metabolic regulation beyond the reported stimulation of leptin release from adipose tissue to involve actions mediated by EP3R in the regulation of sleep architecture and feeding behavior. The findings add to the growing literature on links between inflammatory signaling and obesity.

Extracellular Signal-Regulated Kinase (ERK1/2) Contributes to Endotoxin-Induced Hyporeactivity via Nitric Oxide and Prostacyclin Production in Rat Aorta

This study was conducted to determine if mitogen-activated protein kinases (MAPKs) such as extracellular signal-regulated kinase (ERK1/2) contribute to endotoxin-induced vascular hyporeactivity via nitric oxide (NO) and/or prostacyclin (PGI(2)) production in the rat isolated thoracic aorta. Incubation of endothelium-intact rings with endotoxin (100 microg/ml) for 4 h decreased the E(max) value and increased the EC(50) value of norepinephrine. The endotoxin-induced increase in the EC(50) value of norepinephrine was decreased by phenylene-1,3-bis[ethane-2-isothiourea] dihydrobromide (1,3-PBIT), a selective inducible NO synthase inhibitor, and U0126, a selective inhibitor of ERK1/2 phosphorylation by MAPK kinase. The endotoxin-induced decrease in the E(max) value of norepinephrine was reversed by 1,3-PBIT and further decreased by U0126. 1,3-PBIT and U0126 decreased the endotoxin-induced increase in the tissue nitrite and 6-keto-PGF(1)(alpha) levels. These data suggest that events related to the activation of ERK1/2 contribute to the endotoxin-induced hyporeactivity by increasing NO and PGI(2) production.

Inhibited skeletal muscle healing in cyclooxygenase-2 gene-deficient mice: the role of PGE2 and PGF2alpha

Nonsteroidal anti-inflammatory drugs (NSAIDs) are commonly used to treat skeletal muscle injury. However, studies have shown that NSAIDs may be detrimental to the healing process. Mediated by prostaglandin F(2alpha) (PGF(2alpha)) and prostaglandin E(2) (PGE(2)), the cycloxygenase-2 (COX-2) pathway plays an important role in muscle healing. We hypothesize that the COX-2 pathway is important for the fusion of muscle cells and the regeneration of injured muscle. For the in vitro experiments, we isolated myogenic precursor cells from wild-type (Wt) and COX-2 gene-deficient (COX-2(-/-)) mice and examined the effect of PGE(2) and PGF(2alpha) on cell fusion. For the in vivo experiments, we created laceration injury on the tibialis anterior (TA) muscles of Wt and COX-2(-/-) mice. Five and 14 days after injury, we examined the TA muscles histologically and functionally. We found that the secondary fusion between nascent myotubes and myogenic precursor cells isolated from COX-2(-/-) mice was severely compromised compared with that of Wt controls but was restored by the addition of PGF(2alpha) or, to a lesser extent, PGE(2) to the culture. Histological and functional assessments of the TA muscles in COX-2(-/-) mice revealed decreased regeneration relative to that observed in the Wt mice. The findings reported here demonstrate that the COX-2 pathway plays an important role in muscle healing and that prostaglandins are key mediators of the COX-2 pathway. It suggests that the decision to use NSAIDs to treat muscle injuries warrants critical evaluation because NSAIDs might impair muscle healing by inhibiting the fusion of myogenic precursor cells.

Peroxynitrites and impaired modulation of nitric oxide concentrations in embryos from diabetic rats during early organogenesis

Maternal diabetes significantly increases the risk of congenital malformation, a syndrome known as diabetic embryopathy. Nitric oxide (NO), implicated in embryogenesis, has been found elevated in embryos from diabetic rats during organogenesis. The developmental signaling molecules endothelin-1 (ET-1) and 15-deoxy delta(12,14)prostaglandin J2 (15dPGJ2) downregulate embryonic NO levels. In the presence of NO and superoxide, formation of the potent oxidant peroxynitrite may occur. Therefore, we investigated peroxynitrite-induced damage, ET-1 and 15dPGJ2 concentrations, and the capability of ET-1, 15dPGJ2 and prostaglandin E2 (PGE2) to regulate NO production in embryos from severely diabetic rats (streptozotocin-induced before pregnancy). We found intense nitrotyrosine immunostaining (an index of peroxynitrite-induced damage) in neural folds, neural tube and developing heart of embryos from diabetic rats (P < 0.001 vs controls). We also found reduced ET-1 (P < 0.001) and 15dPGJ2 (P < 0.001) concentrations in embryos from diabetic rats when compared with controls. In addition, the inhibitory effect of ET-1, 15dPGJ2 and PGE2 on NO production found in control embryos was not observed in embryos from severely diabetic rats. In conclusion, both the demonstrated peroxynitrite-induced damage and the altered levels and function of multiple signaling molecules involved in the regulation of NO production provide supportive evidence of nitrosative stress in diabetic embryopathy.

Prostaglandin EP4 receptor agonist protects against acute neurotoxicity

Under various abnormal physiologic conditions, overactivation of glutamate-gated ion channel receptor family members, including NMDA receptors, causes increase in COX-2 expression and generation of prostaglandins. PGE(2) exerts its physiologic actions mainly through its PGE(2) prostanoid (EP) receptors. In the present study, the role of the EP4 receptor against NMDA-induced excitotoxicity was investigated. Using the EP4 receptor agonist ONO-AE1-329, which has relative selectivity toward murine EP receptors on the order of EP1:EP2:EP3:EP4 of >1000:210:120:1, respectively, we questioned whether activation of the EP4 receptors has the potential to attenuate injury in brain. Mice were pretreated by intracerebroventricular injection with different doses of ONO-AE1-329 (0.1, 1, and 10 nmol; n = 9/group) and, after 20 min, by a single unilateral intrastriatal injection of NMDA (15 nmol, n = 12). NMDA injection produced a significant lesion in the ipsilateral striatum. This lesion volume was significantly reduced in groups that were pretreated with ONO-AE1-329, with maximum protection of more than 32% at 10 nmol. This is the first study revealing the protective effect of ONO-AE1-329 in an acute model of excitotoxicity in brain, and it suggests that preferential stimulation of EP4 receptors attenuates excitotoxic brain injury.

SEX DIFFERENCES IN THE MYOCARDIAL INFLAMMATORY RESPONSE TO ACUTE INJURY

Hemorrhage, trauma, ischemia/reperfusion, burn, and sepsis each lead to cardiac dysfunction. These insults lead to an inflammatory cascade, which plays an important role in this process. Gender has been shown to influence the inflammatory response, as well as outcomes after acute injury. The mechanisms by which gender affects the inflammatory response to and the outcome of acute injury are being actively investigated. We searched PubMed for articles in the English language by using the search words sex, gender, estrogen, testosterone, inflammation, acute injury, ischemia reperfusion, sepsis, trauma, and burns. These were used in various combinations. We read the abstracts of the relevant titles to confirm their relevance, and the full articles were then extracted. References from extracted articles were checked for any additional relevant articles. This review will examine evidence for gender differences in the outcome to acute injury, explain the myocardial inflammatory response to acute injury, and elucidate the various mechanisms by which gender affects the myocardial response to acute injury.