Activation of prostaglandin E2 EP1 receptor increases arteriolar tone and blood pressure in mice with type 2 diabetes

Prostaglandin E2 in the Tumor Microenvironment, a Convoluted Affair Mediated by EP Receptors 2 and 4

The involvement of the prostaglandin E2 (PGE2) system in cancer progression has long been recognized. PGE2 functions as an autocrine and paracrine signaling molecule with pleiotropic effects in the human body. High levels of intratumoral PGE2 and overexpression of the key metabolic enzymes of PGE2 have been observed and suggested to contribute to tumor progression. This has been claimed for different types of solid tumors, including, but not limited to, lung, breast, and colon cancer. PGE2 has direct effects on tumor cells and angiogenesis that are known to promote tumor development. However, one of the main mechanisms behind PGE2 driving cancerogenesis is currently thought to be anchored in suppressed antitumor immunity, thus providing possible therapeutic targets to be used in cancer immunotherapies. EP2 and EP4, two receptors for PGE2, are emerging as being the most relevant for this purpose. This review aims to summarize the known roles of PGE2 in the immune system and its functions within the tumor microenvironment. SIGNIFICANCE STATEMENT: Prostaglandin E2 (PGE2) has long been known to be a signaling molecule in cancer. Its presence in tumors has been repeatedly associated with disease progression. Elucidation of its effects on immunological components of the tumor microenvironment has highlighted the potential of PGE2 receptor antagonists in cancer treatment, particularly in combination with immune checkpoint inhibitor therapeutics. Adjuvant treatment could increase the response rates and the efficacy of immune-based therapies.

EP1 receptor: Devil in emperors coat

EP1 receptor belongs to prostanoid receptors and is activated by prostaglandin E2. The receptor performs contrasting functions in central nervous system (CNS) and other tissues. Although the receptor is neurotoxic and proapoptotic in CNS, it has also been reported to act in an antiapoptotic manner by modulating cell survival, proliferation, invasion, and migration in different types of cancers. The receptor mediates its neurotoxic effects by increasing cytosolic Ca2+ levels, leading to the activation of its downstream target, protein kinase C, in different neurological disorders including Alzheimer's disease, Parkinson's disease, stroke, amyotrophic lateral sclerosis, and epilepsy. Antagonists ONO-8713, SC51089, and SC51322 against EP1 receptor ameliorate the neurotoxic effect by attenuating the neuroinflammation. The receptor also shows increased expression in different types of cancers and has been found to activate different signaling pathways, which lead to the development, progression, and metastasis of different cancers. The receptor stimulates the cell survival pathway by phosphorylating the AKT and PTEN (phosphatase and tensin homolog deleted on chromosome 10) signaling pathways. Although there are limited studies about this receptor and not a single clinical trial has been targeting the EP1 receptor for different neurological disorders or cancer, the receptor is appearing as a potential candidate for therapeutic targets. The aim of this article is to review the recent progress in understanding the pathogenic roles of EP1 receptors in different pathological conditions.

The Link between Prostanoids and Cardiovascular Diseases

Cardiovascular diseases are the leading cause of global deaths, and many risk factors contribute to their pathogenesis. In this context, prostanoids, which derive from arachidonic acid, have attracted attention for their involvement in cardiovascular homeostasis and inflammatory processes. Prostanoids are the target of several drugs, but it has been shown that some of them increase the risk of thrombosis. Overall, many studies have shown that prostanoids are tightly associated with cardiovascular diseases and that several polymorphisms in genes involved in their synthesis and function increase the risk of developing these pathologies. In this review, we focus on molecular mechanisms linking prostanoids to cardiovascular diseases and we provide an overview of genetic polymorphisms that increase the risk for cardiovascular disease.

PhenoGeneRanker: Gene and Phenotype Prioritization Using Multiplex Heterogeneous Networks

Uncovering genotype-phenotype relationships is a fundamental challenge in genomics. Gene prioritization is an important step for this endeavor to make a short manageable list from a list of thousands of genes coming from high-throughput studies. Network propagation methods are promising and state of the art methods for gene prioritization based on the premise that functionally related genes tend to be close to each other in the biological networks. Recently, we introduced PhenoGeneRanker, a network-propagation algorithm for multiplex heterogeneous networks. PhenoGeneRanker allows multi-layer gene and phenotype networks. It also calculates empirical p values of gene and phenotype ranks using random stratified sampling of seeds of genes and phenotypes based on their connectivity degree in the network. In this study, we introduce the PhenoGeneRanker Bioconductor package and its application to multi-omics rat genome datasets to rank hypertension disease-related genes and strains. We showed that PhenoGeneRanker performed better to rank hypertension disease-related genes using multiplex gene networks than aggregated gene networks. We also showed that PhenoGeneRanker performed better to rank hypertension disease-related strains using multiplex phenotype network than single or aggregated phenotype networks. We performed a rigorous hyperparameter analysis and, finally showed that Gene Ontology (GO) enrichment of statistically significant top-ranked genes resulted in hypertension disease-related GO terms.

Immune Function of Endothelial Cells: Evolutionary Aspects, Molecular Biology and Role in Atherogenesis

Atherosclerosis is one of the key problems of modern medicine, which is due to the high prevalence of atherosclerotic cardiovascular diseases and their significant share in the structure of morbidity and mortality in many countries. Atherogenesis is a complex chain of events that proceeds over many years in the vascular wall with the participation of various cells. Endothelial cells are key participants in vascular function. They demonstrate involvement in the regulation of vascular hemodynamics, metabolism, and innate immunity, which act as leading links in the pathogenesis of atherosclerosis. These endothelial functions have close connections and deep evolutionary roots, a better understanding of which will improve the prospects of early diagnosis and effective treatment.

Involvement of Fatty Acids and Their Metabolites in the Development of Inflammation in Atherosclerosis

Despite all the advances of modern medicine, atherosclerosis continues to be one of the most important medical and social problems. Atherosclerosis is the cause of several cardiovascular diseases, which are associated with high rates of disability and mortality. The development of atherosclerosis is associated with the accumulation of lipids in the arterial intima and the disruption of mechanisms that maintain the balance between the development and resolution of inflammation. Fatty acids are involved in many mechanisms of inflammation development and maintenance. Endothelial cells demonstrate multiple cross-linkages between lipid metabolism and innate immunity. In addition, these processes are linked to hemodynamics and the function of other cells in the vascular wall, highlighting the central role of the endothelium in vascular biology.

Roles of EP Receptors in the Regulation of Fluid Balance and Blood Pressure

Prostaglandin E2 (PGE2) is an important prostanoid expressing throughout the kidney and cardiovascular system. Despite the diverse effects on fluid metabolism and blood pressure, PGE2 is implicated in sustaining volume and hemodynamics homeostasis. PGE2 works through four distinct E-prostanoid (EP) receptors which are G protein-coupled receptors. To date, pharmacological specific antagonists and agonists of all four subtypes of EP receptors and genetic targeting knockout mice for each subtype have helped in uncoupling the diverse functions of PGE2 and discriminating the respective characteristics of each receptor. In this review, we summarized the functions of individual EP receptor subtypes in the renal and blood vessels and the molecular mechanism of PGE2-induced fluid metabolism and blood pressure homeostasis.

Effects of Arachidonic Acid Metabolites on Cardiovascular Health and Disease

Arachidonic acid (AA) is an essential fatty acid that is released by phospholipids in cell membranes and metabolized by cyclooxygenase (COX), cytochrome P450 (CYP) enzymes, and lipid oxygenase (LOX) pathways to regulate complex cardiovascular function under physiological and pathological conditions. Various AA metabolites include prostaglandins, prostacyclin, thromboxanes, hydroxyeicosatetraenoic acids, leukotrienes, lipoxins, and epoxyeicosatrienoic acids. The AA metabolites play important and differential roles in the modulation of vascular tone, and cardiovascular complications including atherosclerosis, hypertension, and myocardial infarction upon actions to different receptors and vascular beds. This article reviews the roles of AA metabolism in cardiovascular health and disease as well as their potential therapeutic implication.

Untapped Potential: Therapeutically Targeting Eicosanoids and Endocannabinoids in the Lung

Inflammation of the airway involves the recruitment of highly active immune cells to combat and clear microbes and toxic factors; however, this inflammatory response can result in unintended damage to lung tissue. Tissue damage resulting from inflammation is often mitigated by resolving factors that limit the scope and duration of the inflammatory response. Both inflammatory and resolving processes require the actions of a vast array of lipid mediators that can be rapidly synthesized through a variety of airway resident and infiltrating immune cells. Eicosanoids and endocannabinoids represent two major classes of lipid mediators that share synthetic enzymes and have diverse and overlapping functions. This review seeks to provide a summary of the major bioactive eicosanoids and endocannabinoids, challenges facing researchers that study them, and their roles in modulating inflammation and resolution. With a special emphasis on cystic fibrosis, a variety of therapeutics are discussed that have been explored for their potential anti-inflammatory or proresolving impact toward alleviating excessive airway inflammation and improving lung function.

International Union of Basic and Clinical Pharmacology. CIX. Differences and Similarities between Human and Rodent Prostaglandin E2 Receptors (EP1-4) and Prostacyclin Receptor (IP): Specific Roles in Pathophysiologic Conditions

Prostaglandins are derived from arachidonic acid metabolism through cyclooxygenase activities. Among prostaglandins (PGs), prostacyclin (PGI2) and PGE2 are strongly involved in the regulation of homeostasis and main physiologic functions. In addition, the synthesis of these two prostaglandins is significantly increased during inflammation. PGI2 and PGE2 exert their biologic actions by binding to their respective receptors, namely prostacyclin receptor (IP) and prostaglandin E2 receptor (EP) 1-4, which belong to the family of G-protein-coupled receptors. IP and EP1-4 receptors are widely distributed in the body and thus play various physiologic and pathophysiologic roles. In this review, we discuss the recent advances in studies using pharmacological approaches, genetically modified animals, and genome-wide association studies regarding the roles of IP and EP1-4 receptors in the immune, cardiovascular, nervous, gastrointestinal, respiratory, genitourinary, and musculoskeletal systems. In particular, we highlight similarities and differences between human and rodents in terms of the specific roles of IP and EP1-4 receptors and their downstream signaling pathways, functions, and activities for each biologic system. We also highlight the potential novel therapeutic benefit of targeting IP and EP1-4 receptors in several diseases based on the scientific advances, animal models, and human studies. SIGNIFICANCE STATEMENT: In this review, we present an update of the pathophysiologic role of the prostacyclin receptor, prostaglandin E2 receptor (EP) 1, EP2, EP3, and EP4 receptors when activated by the two main prostaglandins, namely prostacyclin and prostaglandin E2, produced during inflammatory conditions in human and rodents. In addition, this comparison of the published results in each tissue and/or pathology should facilitate the choice of the most appropriate model for the future studies.

Prostaglandin E2 receptor EP1 (PGE2/EP1) deletion promotes glomerular podocyte and endothelial cell injury in hypertensive TTRhRen mice

Prostaglandin E2 receptor EP1 (PGE₂/EP₁) promotes diabetic renal injury, and EP₁ receptor deletion improves hyperfiltration, albuminuria, and fibrosis. The role of EP₁ receptors in hypertensive kidney disease (HKD) remains controversial. We examined the contribution of EP₁ receptors to HKD. EP₁ null (EP₁^-/-) mice were bred with hypertensive TTRhRen mice (Htn) to evaluate kidney function and injury at 24 weeks. EP₁ deletion had no effect on elevation of systolic blood pressure in Htn mice (HtnEP₁^-/-) but resulted in pronounced albuminuria and reduced FITC-inulin clearance, compared with Htn or wild-type (WT) mice. Ultrastructural injury to podocytes and glomerular endothelium was prominent in HtnEP₁^-/- mice; including widened subendothelial space, subendothelial lucent zones and focal lifting of endothelium from basement membrane, with focal subendothelial cell debris. Cortex COX2 mRNA was increased by EP₁ deletion. Glomerular EP₃ mRNA was reduced by EP₁ deletion, and EP₄ by Htn and EP₁ deletion. In WT mice, PGE₂ increased chloride reabsorption via EP₁ in isolated perfused thick ascending limb (TAL), but PGE₂ or EP₁ deletion did not affect vasopressin-mediated chloride reabsorption. In WT and Htn mouse inner medullary collecting duct (IMCD), PGE₂ inhibited vasopressin-water transport, but not in EP₁^-/- or HtnEP₁^-/- mice. Overall, EP₁ mediated TAL and IMCD transport in response to PGE₂ is unaltered in Htn, and EP₁ is protective in HKD.

Regulation of YAP by Mammalian Target of Rapamycin Complex 1 in Endothelial Cells Controls Blood Pressure Through COX-2/mPGES-1/PGE2 Cascade

Endothelial cells regulate vascular tone by producing both relaxing and contracting factors to control the local blood flow. Hypertension is a common side effect of mTORC1 (mammalian target of rapamycin complex 1) inhibitors. However, the role of endothelial mTORC1 in hypertension remains elusive. The present study aimed to determine the role of endothelial mTORC1 in Ang II (angiotensin II)-induced hypertension and the underlying mechanism. Endothelial mTORC1 activity was increased by Ang II both in vitro and in vivo. Blood pressure was higher in Tie-2-Cre-mediated regulatory associated protein of mTOR (mammalian target of rapamycin; Raptor) heterozygous-deficient (Tie2Cre-Raptor^KD) mice than control mice both before and after Ang II infusion. Acetylcholine-evoked endothelium-dependent relaxation of mesenteric arteries was impaired in Tie2Cre-Raptor^KD mice. Treatment with indomethacin or a specific COX (cyclooxygenase)-2 inhibitor, NS-398, but not L-NG-nitroarginine methyl ester reduced endothelium-dependent relaxation in Raptor^flox/- mice to a similar extent as in Tie2Cre-Raptor^KD mice. Metabolomic profiling revealed that the plasma content of prostaglandin E₂ was reduced in Tie2Cre-Raptor^KD mice with or without Ang II infusion. In endothelial cells, reduction of the protein level of YAP (yes-associated protein) with siRNA-mediated RPTOR deficiency was autophagy dependent and transcriptionally regulated the expression of COX-2 and mPGES-1 (microsomal prostaglandin E synthase-1). Hence, overexpression of YAP in endothelial cells enhanced the mRNA and protein levels of COX-2 and mPGES-1 and reversed the endothelial dysfunction and hypertension in Tie2Cre-Raptor^KD mice. The present results demonstrate that suppression of mTORC1 activity in endothelial cells reduces prostaglandin E₂ production and causes hypertension by reducing YAP-mediated COX-2/mPGES-1 expression.

Vascular Smooth Muscle-Specific EP4 Receptor Deletion in Mice Exacerbates Angiotensin II-Induced Renal Injury

AIMS

Cyclooxygenase inhibition by non-steroidal anti-inflammatory drugs is contraindicated in hypertension, as it may reduce glomerular filtration rate (GFR) and renal blood flow. However, the identity of the specific eicosanoid and receptor underlying these effects is not known. We hypothesized that vascular smooth muscle prostaglandin E2 (PGE2) E-prostanoid 4 (EP4) receptor deletion predisposes to renal injury via unchecked vasoconstrictive actions of angiotensin II (AngII) in a hypertension model. Mice with inducible vascular smooth muscle cell (VSMC)-specific EP4 receptor deletion were generated and subjected to AngII-induced hypertension.

RESULTS

EP4 deletion was verified by PCR of aorta and renal vessels, as well as functionally by loss of PGE2-mediated mesenteric artery relaxation. Both AngII-treated groups became similarly hypertensive, whereas albuminuria, foot process effacement, and renal hypertrophy were exacerbated in AngII-treated EP4^VSMC-/- but not in EP4^VSMC+/+ mice and were associated with glomerular scarring, tubulointerstitial injury, and reduced GFR. AngII-treated EP4^VSMC-/- mice exhibited capillary damage and reduced renal perfusion as measured by fluorescent bead microangiography and magnetic resonance imaging, respectively. NADPH oxidase 2 (Nox2) expression was significantly elevated in AngII-treated EP4^-/- mice. EP4-receptor silencing in primary VSMCs abolished PGE2 inhibition of AngII-induced Nox2 mRNA and superoxide production.

INNOVATION

These data suggest that vascular EP4 receptors buffer the actions of AngII on renal hemodynamics and oxidative injury.

CONCLUSION

EP4 agonists may, therefore, protect against hypertension-associated kidney damage. Antioxid. Redox Signal. 25, 642-656.

The EP1/EP3 receptor agonist 17-pt-PGE2 acts as an EP4 receptor agonist on endothelial barrier function and in a model of LPS-induced pulmonary inflammation

Endothelial dysfunction is a hallmark of inflammatory conditions. We recently demonstrated that prostaglandin (PG)E₂ enhances the resistance of pulmonary endothelium in vitro and counteracts lipopolysaccharide (LPS)-induced pulmonary inflammation in vivo via EP4 receptors. The aim of this study was to investigate the role of the EP1/EP3 receptor agonist 17-phenyl-trinor-(pt)-PGE₂ on acute lung inflammation in a mouse model. In LPS-induced pulmonary inflammation in mice, 17-pt-PGE₂ reduced neutrophil infiltration and inhibited vascular leakage. These effects were unaltered by an EP1 antagonist, but reversed by EP4 receptor antagonists. 17-pt-PGE₂ increased the resistance of pulmonary microvascular endothelial cells and prevented thrombin-induced disruption of endothelial junctions. Again, these effects were not mediated via EP1 or EP3 but through activation of the EP4 receptor, as demonstrated by the lack of effect of more selective EP1 and EP3 receptor agonists, prevention of these effects by EP4 antagonists and EP4 receptor knock-down by siRNA. In contrast, the aggregation enhancing effect of 17-pt-PGE₂ in human platelets was mediated via EP3 receptors. Our results demonstrate that 17-pt-PGE₂ enhances the endothelial barrier in vitro on pulmonary microvascular endothelial cells, and accordingly ameliorates the recruitment of neutrophils, via EP4 receptors in vivo. This suggests a beneficial effect of 17-pt-PGE₂ on pulmonary inflammatory diseases.

An Update of Microsomal Prostaglandin E Synthase-1 and PGE2 Receptors in Cardiovascular Health and Diseases

Nonsteroidal anti-inflammatory drugs (NSAIDs), especially cyclooxygenase-2 (COX-2) selective inhibitors, are among the most widely used drugs to treat pain and inflammation. However, clinical trials have revealed that these inhibitors predisposed patients to a significantly increased cardiovascular risk, consisting of thrombosis, hypertension, myocardial infarction, heart failure, and sudden cardiac death. Thus, microsomal prostaglandin E (PGE) synthase-1 (mPGES-1), the key terminal enzyme involved in the synthesis of inflammatory prostaglandin E2 (PGE2), and the four PGE2 receptors (EP1-4) have gained much attention as alternative targets for the development of novel analgesics. The cardiovascular consequences of targeting mPGES-1 and the PGE2 receptors are substantially studied. Inhibition of mPGES-1 has displayed a relatively innocuous or preferable cardiovascular profile. The modulation of the four EP receptors in cardiovascular system is diversely reported as well. In this review, we highlight the most recent advances from our and other studies on the regulation of PGE2, particularly mPGES-1 and the four PGE2 receptors, in cardiovascular function, with a particular emphasis on blood pressure regulation, atherosclerosis, thrombosis, and myocardial infarction. This might lead to new avenues to improve cardiovascular disease management strategies and to seek optimized anti-inflammatory therapeutic options.

The effect of green tea on blood pressure and lipid profile: a systematic review and meta-analysis of randomized clinical trials

INTRODUCTION

Many different dietary supplements are currently marketed for the management of hypertension, but the evidence for effectiveness is mixed. The aim of this systematic review was to evaluate the evidence for or against the effectiveness of green tea (Camellia sinensis) on blood pressure and lipid parameters.

METHODS AND RESULTS

Electronic searches were conducted in Medline, Embase, Amed, Cinahl and the Cochrane Library to identify relevant human randomized clinical trials (RCTs). Hand searches of bibliographies were also conducted. The reporting quality of included studies was assessed using a checklist adapted from the CONSORT Statement. Two reviewers independently determined eligibility, assessed the reporting quality of the included studies, and extracted the data. As many as 474 citations were identified and 20 RCTs comprising 1536 participants were included. There were variations in the designs of the RCTs. A meta-analysis revealed a significant reduction in systolic blood pressure favouring green tea (MD: -1.94 mmHg; 95% CI: -2.95 to -0.93; I(2) = 8%; p = 0.0002). Similar results were also observed for total cholesterol (MD: -0.13 mmol/l; 95% CI: -0.2 to -0.07; I(2) = 8%; p < 0.0001) and LDL cholesterol (MD: -0.19 mmol/l; 95% CI: -0.3 to -0.09; I(2) = 70%; p = 0.0004). Adverse events included rash, elevated blood pressure, and abdominal discomfort.

CONCLUSION

Green tea intake results in significant reductions in systolic blood pressure, total cholesterol, and LDL cholesterol. The effect size on systolic blood pressure is small, but the effects on total and LDL cholesterol appear moderate. Longer-term independent clinical trials evaluating the effects of green tea are warranted.

Chronic kidney disease: targeting prostaglandin E2 receptors

Chronic kidney disease is a leading cause of morbidity and mortality in the world. A better understanding of disease mechanisms has been gained in recent years, but the current management strategies are ineffective at preventing disease progression. A widespread focus of research is placed on elucidating the specific processes implicated to find more effective therapeutic options. PGE2, acting on its four EP receptors, regulates many renal disease processes; thus EP receptors could prove to be important targets for kidney disease intervention strategies. This review summarizes the major pathogenic mechanisms contributing to initiation and progression of chronic kidney disease, emphasizing the role of hyperglycemia, hypertension, inflammation, and oxidative stress. We have long recognized the multifaceted role of PGs in both the initiation and progression of chronic kidney disease, yet studies are only now seriously contemplating specific EP receptors as targets for therapy. Given the plethora of renal complications attributed to PG involvement in the kidney, this review highlights these pathogenic events and emphasizes the PGE2 receptor targets as options available to complement current therapeutic strategies.

H2O2 stimulates cystic fibrosis transmembrane conductance regulator through an autocrine prostaglandin pathway, using multidrug-resistant protein-4

Cystic fibrosis transmembrane conductance regulator (CFTR) activity is essential for the maintenance of airway surface liquid depth, and therefore mucociliary clearance. Reactive oxygen species, increased during inflammatory airway diseases, alter CFTR activity. Here, H2O2 levels in the surface liquid of normal human bronchial epithelial cultures differentiated at the air-liquid interface were estimated, and H2O2-mediated changes in CFTR activity were examined. In Ussing chambers, H2O2-induced anion currents were sensitive to the CFTR inhibitors CFTRinh172 and GlyH-101. These currents were absent in cells from patients with cystic fibrosis. Responses to greater than 500 μM H2O2 were transient. Cyclooxygenase inhibitors blocked the H2O2 response, as did EP1 and EP4 receptor antagonists. A multidrug-resistant protein (MRP) inhibitor and short hairpin RNA directed against MRP4 blocked H2O2 responses. EP1 and EP4 agonists mimicked H2O2 in both control and MRP4 knockdown cells. Thus, H2O2 activates the synthesis, export, and binding of prostanoids via EP4 and, interestingly, EP1 receptors in normal, differentiated human airway epithelial cells to activate cyclic adenosine monophosphate pathways that in turn activate CFTR channels in the apical membrane.

PTGER1 deletion attenuates renal injury in diabetic mouse models

We hypothesized that the EP1 receptor promotes renal damage in diabetic nephropathy. We rendered EP1 (PTGER1, official symbol) knockout mice (EP1(-/-)) diabetic using the streptozotocin and OVE26 models. Albuminuria, mesangial matrix expansion, and glomerular hypertrophy were each blunted in EP1(-/-) streptozotocin and OVE26 cohorts compared with wild-type counterparts. Although diabetes-associated podocyte depletion was unaffected by EP1 deletion, EP1 antagonism with ONO-8711 in cultured podocytes decreased angiotensin II-mediated superoxide generation, suggesting that EP1-associated injury of remaining podocytes in vivo could contribute to filtration barrier dysfunction. Accordingly, EP1 deletion in OVE26 mice prevented nephrin mRNA expression down-regulation and ameliorated glomerular basement membrane thickening and foot process effacement. Moreover, EP1 deletion reduced diabetes-induced expression of fibrotic markers fibronectin and α-actin, whereas EP1 antagonism decreased fibronectin in cultured proximal tubule cells. Similarly, proximal tubule megalin expression was reduced by diabetes but was preserved in EP1(-/-) mice. Finally, the diabetes-associated increase in angiotensin II-mediated constriction of isolated mesenteric arteries was blunted in OVE26EP1(-/-) mice, demonstrating a role for EP1 receptors in the diabetic vasculature. These data suggest that EP1 activation contributes to diabetic nephropathy progression at several locations, including podocytes, proximal tubule, and the vasculature. The EP1 receptor facilitates the actions of angiotensin II, thereby suggesting that targeting of both the renin-angiotensin system and the EP1 receptor could be beneficial in diabetic nephropathy.

Development of an in vivo active, dual EP1 and EP3 selective antagonist based on a novel acyl sulfonamide bioisostere

Recent preclinical studies demonstrate a role for the prostaglandin E(2) (PGE(2)) subtype 1 (EP1) receptor in mediating, at least in part, the pathophysiology of hypertension and diabetes mellitus. A series of amide and N-acylsulfonamide analogs of a previously described picolinic acid-based human EP1 receptor antagonist (7) were prepared. Each analog had improved selectivity at the mouse EP1 receptor over the mouse thromboxane receptor (TP). A subset of analogs gained affinity for the mouse PGE(2) subtype 3 (EP3) receptor, another potential therapeutic target. One analog (17) possessed equal selectivity for EP1 and EP3, displayed a sufficient in vivo residence time in mice, and lacked the potential for acyl glucuronide formation common to compound 7. Treatment of mice with 17 significantly attenuated the vasopressor activity resulting from an acute infusion of EP1 and EP3 receptor agonists. Compound 17 represents a potentially novel therapeutic in the treatment of hypertension and diabetes mellitus.

Increased cyclooxygenase-2-derived prostanoids contributes to the hyperreactivity to noradrenaline in mesenteric resistance arteries from offspring of diabetic rats

This study analyzed the effect of in utero exposure to maternal diabetes on contraction to noradrenaline in mesenteric resistance arteries (MRA) from adult offspring, focusing on the role of cyclooxygenase (COX)-derived prostanoids. Diabetes in the maternal rat was induced by a single injection of streptozotocin (50 mg/kg body weight) on day 7 of pregnancy. Contraction to noradrenaline was analyzed in isolated MRA from offspring of diabetic (O-DR) and non-diabetic (O-CR) rats at 3, 6 and 12 months of age. Release of thromboxane A₂ (TxA₂) and prostaglandins E₂ (PGE₂) and F_2α (PGF_2α), was measured by specific enzyme immunoassay kits. O-DR developed hypertension from 6 months of age compared with O-CR. Arteries from O-DR were hyperactive to noradrenaline only at 6 and 12 months of age. Endothelial removal abolished this hyperreactivity to noradrenaline between O-CR and O-DR. Preincubation with either the COX-1/2 (indomethacin) or COX-2 inhibitor (NS-398) decreased noradrenaline contraction only in 6- and 12-month-old O-DR, while it remained unmodified by COX-1 inhibitor SC-560. In vessels from 6-month-old O-DR, a similar reduction in the contraction to noradrenaline produced by NS-398 was observed when TP and EP receptors were blocked (SQ29548+AH6809). In 12-month-old O-DR, this effect was only achieved when TP, EP and FP were blocked (SQ29548+AH6809+AL8810). Noradrenaline-stimulated TxB₂ and PGE₂ release was higher in 6- and 12-month-old O-DR, whereas PGF_2α was increased only in 12-month-old O-DR. Our results demonstrated that in utero exposure to maternal hyperglycaemia in rats increases the participation of COX-2-derived prostanoids on contraction to noradrenaline, which might help to explain the greater response to this agonist in MRA from 6- and 12-month-old offspring. As increased contractile response in resistance vessels may contribute to hypertension, our results suggest a role for these COX-2-derived prostanoids in elevating vascular resistance and blood pressure in offspring of diabetic rats.

Signal transduction and modulating pathways in tryptamine-evoked vasopressor responses of the rat isolated perfused mesenteric bed

Tryptamine is an endogenous and dietary indoleamine-based trace amine implicated in cardiovascular pathologies, including hypertension, migraine and myocardial infarction. This study aimed at identifying the signalling pathways for the vasoconstrictor response to tryptamine in rat isolated perfused mesenteric arterial beds and co-released vasodilator modulators of tryptamine-mediated vasoconstriction. Tryptamine caused concentration-dependent vasoconstriction of the mesenteric bed, measured as increases in perfusion pressure. These were inhibited by the 5-HT_2A receptor antagonist, ritanserin, indicating mediation via 5-HT_2A receptors. The response was inhibited by the phospholipase C (PLC) and phospholipase A₂ (iPLA₂) inhibitors, U-73122 and PACOCF₃, suggesting involvement of phospholipase pathways. Activation of these pathways by tryptamine releases cyclooxygenase (COX) products since indomethacin (non-selective inhibitor of COX-1/2) and nimesulide (selective COX-2 inhibitor) reduced the vasoconstriction. The most likely COX vasoconstrictor product was prostaglandin PGE₂ since the responses to tryptamine were reduced by AH-6809, a non-selective EP₁ receptor antagonist. Involvement of the Rho-kinase pathway in the tryptamine-evoked vasoconstriction was also indicated by its reduction by the Rho-kinase inhibitors, Y-27,632 and fasudil. The tryptamine vasoconstriction is modulated by the co-released endothelial vasodilator, nitric oxide. Thus, circulating tryptamine can regulate mesenteric blood flow through a cascade of signalling pathways secondary to stimulation of 5-HT_2A receptors.

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.

Phosphatidylinositol 3-kinase/Akt signaling pathway activates the WNK-OSR1/SPAK-NCC phosphorylation cascade in hyperinsulinemic db/db mice

Metabolic syndrome patients have insulin resistance, which causes hyperinsulinemia, which in turn causes aberrant increased renal sodium reabsorption. The precise mechanisms underlying this greater salt sensitivity of hyperinsulinemic patients remain unclear. Abnormal activation of the recently identified with-no-lysine kinase (WNK)-oxidative stress-responsive kinase 1 (OSR1)/STE20/SPS1-related proline/alanine-rich kinase (SPAK)-NaCl cotransporter (NCC) phosphorylation cascade results in the salt-sensitive hypertension of pseudohypoaldosteronism type II. Here, we report a study of renal WNK-OSR1/SPAK-NCC cascade activation in the db/db mouse model of hyperinsulinemic metabolic syndrome. Thiazide sensitivity was increased, suggesting greater activity of NCC in db/db mice. In fact, increased phosphorylation of OSR1/SPAK and NCC was observed. In both SpakT243A/+ and Osr1T185A/+ knock-in db/db mice, which carry mutations that disrupt the signal from WNK kinases, increased phosphorylation of NCC and elevated blood pressure were completely corrected, indicating that phosphorylation of SPAK and OSR1 by WNK kinases is required for the increased activation and phosphorylation of NCC in this model. Renal phosphorylated Akt was increased in db/db mice, suggesting that increased NCC phosphorylation is regulated by the phosphatidylinositol 3-kinase/Akt signaling cascade in the kidney in response to hyperinsulinemia. A phosphatidylinositol 3-kinase inhibitor (NVP-BEZ235) corrected the increased OSR1/SPAK-NCC phosphorylation. Another more specific phosphatidylinositol 3-kinase inhibitor (GDC-0941) and an Akt inhibitor (MK-2206) also inhibited increased NCC phosphorylation. These results indicate that the phosphatidylinositol 3-kinase/Akt signaling pathway activates the WNK-OSR1/SPAK-NCC phosphorylation cascade in db/db mice. This mechanism may play a role in the pathogenesis of salt-sensitive hypertension in human hyperinsulinemic conditions, such as the metabolic syndrome.

Angiotensin II-dependent hypertension requires cyclooxygenase 1-derived prostaglandin E2 and EP1 receptor signaling in the subfornical organ of the brain

Cyclooxygenase (COX)-derived prostanoids have long been implicated in blood pressure (BP) regulation. Recently prostaglandin E(2) (PGE(2)) and its receptor EP(1) (EP(1)R) have emerged as key players in angiotensin II (Ang II)-dependent hypertension (HTN) and related end-organ damage. However, the enzymatic source of PGE(2,) that is, COX-1 or COX-2, and its site(s) of action are not known. The subfornical organ (SFO) is a key forebrain region that mediates systemic Ang II-dependent HTN via reactive oxygen species (ROS). We tested the hypothesis that cross-talk between PGE(2)/EP(1)R and ROS signaling in the SFO is required for Ang II HTN. Radiotelemetric assessment of blood pressure revealed that HTN induced by infusion of systemic "slow-pressor" doses of Ang II was abolished in mice with null mutations in EP(1)R or COX-1 but not COX-2. Slow-pressor Ang II-evoked HTN and ROS formation in the SFO were prevented when the EP(1)R antagonist SC-51089 was infused directly into brains of wild-type mice, and Ang-II-induced ROS production was blunted in cells dissociated from SFO of EP(1)R(-/-) and COX-1(-/-) but not COX-2(-/-) mice. In addition, slow-pressor Ang II infusion caused a ≈3-fold increase in PGE(2) levels in the SFO but not in other brain regions. Finally, genetic reconstitution of EP(1)R selectively in the SFO of EP(1)R-null mice was sufficient to rescue slow-pressor Ang II-elicited HTN and ROS formation in the SFO of this model. Thus, COX 1-derived PGE(2) signaling through EP(1)R in the SFO is required for the ROS-mediated HTN induced by systemic infusion of Ang II and suggests that EP(1)R in the SFO may provide a novel target for antihypertensive therapy.

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.

Impaired blood pressure recovery to hemorrhage in obese Zucker rats with orthopedic trauma

We have shown that obese Zucker rats with orthopedic trauma (OZT) exhibit a loss of arteriolar tone in skeletal muscle. We hypothesize that the loss of arteriolar tone in OZT blunts vasoconstrictor responses to hemorrhage, resulting in an impaired blood pressure recovery. Orthopedic trauma was induced with soft tissue injury and local injection of bone components in both hindlimbs in lean (LZT) and OZT (11-13 wk). One day after the orthopedic trauma, blood pressure responses following hemorrhage were measured in conscious control lean, control obese, LZT, and OZT. In another set of experiments, the spinotrapezius muscle of control and trauma animals was prepared for microcirculatory observation. Arteriolar responses to phenylephrine (PE) or hemorrhage were determined. Hemorrhage resulted in similar blood pressure responses in control animals and LZT, but the blood pressure recovery following hemorrhage was blunted in the OZT. In the spinotrapezius, OZT exhibited decreased arteriolar tone and blunted vasoconstrictor responses to PE and hemorrhage. Treatment with glibenclamide improved the blood pressure recovery in the conscious OZT and improved the arteriolar tone, and PE induced vasoconstriction in the spinotrapezius of the OZT. Thus, ATP-dependent K(+) channel-mediated loss of arteriolar tone in OZT blunts the arteriolar constriction to hemorrhage, resulting in impaired blood pressure recovery.

Protection of protease-activated receptor 2 mediated vasodilatation against angiotensin II-induced vascular dysfunction in mice

Background

Under conditions of cardiovascular dysfunction, protease-activated receptor 2 (PAR2) agonists maintain vasodilatation activity, which has been attributed to increased cyclooxygenase-2, nitric oxide synthase and calcium-activated potassium channel (SK3.1) activities. Protease-activated receptor 2 agonist mediated vasodilatation is unknown under conditions of dysfunction caused by angiotensin II. The main purpose of our study was to determine whether PAR2-induced vasodilatation of resistance arteries was attenuated by prolonged angiotensin II treatment in mice. We compared the vasodilatation of resistance-type arteries (mesenteric) from angiotensin II-treated PAR2 wild-type mice (WT) induced by PAR2 agonist 2-furoyl-LIGRLO-amide (2fly) to the responses obtained in controls (saline treatment). We also investigated arterial vasodilatation in angiotensin II-treated PAR2 deficient (PAR2^-/-) mice.

Results

2fly-induced relaxations of untreated arteries from angiotensin II-treated WT were not different than saline-treated WT. Treatment of arteries with nitric oxide synthase inhibitor and SK3.1 inhibitor (L-NAME + TRAM-34) blocked 2fly in angiotensin II-treated WT. Protein and mRNA expression of cyclooxygenase-1 and -2 were increased, and cyclooxygenase activity increased the sensitivity of arteries to 2fly in only angiotensin II-treated WT. These protective vasodilatation mechanisms were selective for 2fly compared with acetylcholine- and nitroprusside-induced relaxations which were attenuated by angiotensin II; PAR2^-/- were protected against this attenuation of nitroprusside.

Conclusions

PAR2-mediated vasodilatation of resistance type arteries is protected against the negative effects of angiotensin II-induced vascular dysfunction in mice. In conditions of endothelial dysfunction, angiotensin II induction of cyclooxygenases increases sensitivity to PAR2 agonist and the preserved vasodilatation mechanism involves activation of SK3.1.

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.

CD36 protein is involved in store-operated calcium flux, phospholipase A2 activation, and production of prostaglandin E2

The scavenger receptor FAT/CD36 contributes to the inflammation associated with diabetes, atherosclerosis, thrombosis, and Alzheimer disease. Underlying mechanisms include CD36 promotion of oxidative stress and its signaling to stress kinases. Here we document an additional mechanism for the role of CD36 in inflammation. CD36 regulates membrane calcium influx in response to endoplasmic reticulum (ER) stress, release of arachidonic acid (AA) from cellular membranes by cytoplasmic phospholipase A(2)α (cPLA(2)α) and contributes to the generation of proinflammatory eicosanoids. CHO cells stably expressing human CD36 released severalfold more AA and prostaglandin E(2) (PGE(2)), a major product of AA metabolism by cyclooxygenases, in response to thapsigargin-induced ER stress as compared with control cells. Calcium influx after ER calcium release resulted in phosphorylation of cPLA(2) and its translocation to membranes in a CD36-dependent manner. Peritoneal macrophages from CD36(-/-) mice exhibited diminished calcium transients and reduced AA release after thapsigargin or UTP treatment with decreased ERK1/2 and cPLA(2) phosphorylation. However, PGE(2) production was unexpectedly enhanced in CD36(-/-) macrophages, which probably resulted from a large induction of cyclooxygenase 2 mRNA and protein. The data demonstrate participation of CD36 in membrane calcium influx in response to ER stress or purinergic receptor stimulation resulting in AA liberation for PGE(2) formation. Collectively, these results identify a mechanism contributing to the pleiotropic proinflammatory effects of CD36 and suggest that its targeted inhibition may reduce the acute inflammatory response.

Mechanisms underlying the losartan treatment-induced improvement in the endothelial dysfunction seen in mesenteric arteries from type 2 diabetic rats

It is well known that type 2 diabetes mellitus is frequently associated with vascular dysfunction and an elevated systemic blood pressure, yet the underlying mechanisms are not completely understood. We previously reported that in mesenteric arteries from established type 2 diabetic Otsuka Long-Evans Tokushima fatty (OLETF) rats, which exhibit endothelial dysfunction, there is an imbalance between endothelium-derived vasodilators [namely, nitric oxide (NO) and hyperpolarizing factor (EDHF)] and vasoconstrictors [contracting factors (EDCFs) such as cyclooxygenase (COX)-derived prostanoids]. Here, we investigated whether the angiotensin II receptor antagonist losartan might improve endothelial dysfunction in OLETF rats at the established stage of diabetes. In mesenteric arteries isolated from OLETF rats [vs. those from age-matched control Long-Evans Tokushima Otsuka (LETO) rats]: (1) the acetylcholine (ACh)-induced relaxation was impaired, (2) the NO- and EDHF-mediated relaxations were reduced, (3) the ACh-induced EDCF-mediated contraction and the production of prostanoids were increased, and (4) superoxide generation was increased. After such OLETF rats had received losartan (25 mg/kg/day p.o. for 4 weeks), their isolated mesenteric arteries exhibited: (1) improvements in ACh-induced NO- and EDHF-mediated relaxations, (2) reduced EDCF- and arachidonic acid-induced contractions, (3) suppressed production of prostanoids, (4) reduced PGE(2)-mediated contraction, and (5) reduced superoxide generation. Within the timescale studied here, losartan did not change the protein expressions of endothelial NO synthase, COX1, or COX2 in mesenteric arteries from either OLETF or LETO rats. Losartan thus normalizes vascular dysfunction in this type 2 diabetic model, and the above effects may contribute to the reduction of adverse cardiovascular events seen in diabetic patients treated with angiotensin II receptor blockers.

Cyclooxygenase 1-derived prostaglandin E2 and EP1 receptors are required for the cerebrovascular dysfunction induced by angiotensin II

Prostaglandin E(2) (PGE(2)) EP1 receptors (EP1Rs) may contribute to hypertension and related end-organ damage. Because of the key role of angiotensin II (Ang II) in hypertension, we investigated the role of EP1R in the cerebrovascular alterations induced by Ang II. Mice were equipped with a cranial window, and cerebral blood flow was monitored by laser-Doppler flowmetry. The attenuation in cerebral blood flow responses to whisker stimulation (-46+/-4%) and the endothelium-dependent vasodilator acetylcholine (-40+/-4%) induced by acute administration of Ang II (250 ng/kg per minute; IV for 30 to 40 minutes) were not observed after cyclooxygenase 1 or EP1R inhibition or in cyclooxygenase 1 or EP1-null mice. In contrast, cyclooxygenase 2 inhibition or genetic inactivation did not prevent the attenuation. Ang II-induced oxidative stress was not observed after cyclooxygenase 1 or EP1R inhibition or in EP1R-null mice. Prostaglandin E(2) reinstated the Ang II-induced cerebrovascular dysfunction and oxidative stress after cyclooxygenase 1 inhibition. Brain prostaglandin E(2) levels were not increased by Ang II but were attenuated by cyclooxygenase 1 and not cyclooxygenase 2 inhibition. The cerebrovascular dysfunction induced by 14-day administration of "slow-pressor" doses of Ang II (600 ng/kg per minute) was attenuated by neocortical application of SC51089. Cyclooxygenase 1 immunoreactivity was observed in microglia and EP1R in endothelial cells. We conclude that the cerebrovascular dysfunction induced by Ang II requires activation of EP1R by constitutive production of prostaglandin E(2) derived from cyclooxygenase 1. The findings provide the first evidence that EP1Rs are involved in the deleterious cerebrovascular effects of Ang II and suggest new therapeutic approaches to counteract them.

Prostaglandins in action indispensable roles of cyclooxygenase-1 and -2 in endothelium-dependent contractions

Endothelium regulates local vascular tone by means of releasing relaxing and contracting factors, of which the latter have been found to be elevated in vascular pathogenesis of hypertension, diabetes, hypercholesterolemia, and aging. Endothelium-derived contracting factors (EDCFs) are mainly metabolites of arachidonic acid generated by cyclooxygenase (COX), as vasodilatations in patients with hypertension, metabolic diseases, or advancing age are improved by acute treatment with COX inhibitor indomethacin. COX is presented in two isoforms, COX-1 and COX-2, with the former regarded as constitutive and the latter mainly expressed upon induction. Experiments with animal models of vascular dysfunctions, however, reveal that both isoforms have similar capacity to participate in endothelium-dependent contractions, with augmented expression and activity. COX-derived prostaglandin (PG) H(2), PGF(2α), PGE(2), prostacyclin (PGI(2)), and thromboxane A(2) (TxA(2)) are the proposed EDCFs that mediate endothelium-dependent contractions via the activation of thromboxane-prostanoid (TP) receptor in various vascular beds from different species. Although COX inhibition seems to be a possible strategy in combating COX-associated vascular complications, the incidence of adverse cardiovascular effects of Vioxx has greatly antagonized this concept. Further review of COX inhibitors is required, especially toward the selectivity of coxibs and whether it directly inhibits prostacyclin synthase activity. Meanwhile, TP receptor antagonism may emerge as a therapeutic alternative to reverse prostanoid-mediated vascular dysregulations.