The anti-inflammatory mechanism of prostaglandin e2 receptor 4 activation in rat experimental autoimmune myocarditis

Prostanoids in Cardiac and Vascular Remodeling

Prostanoids are biologically active lipids generated from arachidonic acid by the action of the COX (cyclooxygenase) isozymes. NSAIDs, which reduce the biosynthesis of prostanoids by inhibiting COX activity, are effective anti-inflammatory, antipyretic, and analgesic drugs. However, their use is limited by cardiovascular adverse effects, including myocardial infarction, stroke, hypertension, and heart failure. While it is well established that NSAIDs increase the risk of atherothrombotic events and hypertension by suppressing vasoprotective prostanoids, less is known about the link between NSAIDs and heart failure risk. Current evidence indicates that NSAIDs may increase the risk for heart failure by promoting adverse myocardial and vascular remodeling. Indeed, prostanoids play an important role in modulating structural and functional changes occurring in the myocardium and in the vasculature in response to physiological and pathological stimuli. This review will summarize current knowledge of the role of the different prostanoids in myocardial and vascular remodeling and explore how maladaptive remodeling can be counteracted by targeting specific prostanoids.

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.

Prostaglandin E2 EP receptors in cardiovascular disease: An update

This review article provides an update for the role of prostaglandin E2 receptors (EP1, EP2, EP3 and EP4) in cardiovascular disease. Where possible we have reported citations from the last decade although this was not possible for all of the topics covered due to the paucity of publications. The authors have attempted to cover the subjects of ischemia-reperfusion injury, arrhythmias, hypertension, novel protein binding partners of the EP receptors and their pathophysiological significance, and cardiac regeneration. These latter two topics bring studies of the EP receptors into new and exciting areas of research that are just beginning to be explored. Where there is peer-reviewed literature, the authors have placed particular emphasis on clinical studies although these are limited in number.

Prostaglandin-E2 receptor-4 stimulant rescues cardiac malfunction during myocarditis and protects the heart from adverse ventricular remodeling after myocarditis

Cardioprotective effect of prostaglandin-E2 receptor-4 (EP4) stimulation on the ischemic heart has been demonstrated. Its effect on the heart affected by myocarditis, however, remains uncertain. In this study, we investigated therapeutic effect of EP4 stimulant using a mouse model of autoimmune myocarditis (EAM) that progresses to dilated cardiomyopathy (DCM). EP4 was present in the hearts of EAM mice. Treatment with EP4 agonist (ONO-0260164: 20 mg/kg/day) improved an impaired left ventricular (LV) contractility and reduction of blood pressure on day 21, a peak myocardial inflammation. Alternatively, DCM phenotype, characterized by LV dilation, LV systolic dysfunction, and collagen deposition, was observed on day 56, along with activation of matrix metalloproteinase (MMP)-2 critical for myocardial extracellular matrix disruption, indicating an important molecular mechanism underlying adverse ventricular remodeling after myocarditis. Continued treatment with ONO-0260164 alleviated the DCM phenotype, but this effect was counteracted by its combination with a EP4 antagonist. Moreover, ONO-0260164 inhibited in vivo proteolytic activity of MMP-2 in association with up-regulation of tissue inhibitor of metalloproteinase (TIMP)-3. EP4 stimulant may be a promising and novel therapeutic agent that rescues cardiac malfunction during myocarditis and prevents adverse ventricular remodeling after myocarditis by promoting the TIMP-3/MMP-2 axis.

Deficiency of Phospholipase A2 Receptor Exacerbates Autoimmune Myocarditis in Mice

Secretory phospholipase A₂ (sPLA₂) plays a critical role in the pathogenesis of various inflammatory diseases through production of pro-inflammatory eicosanoids. PLA₂ receptor 1 (PLA₂R) acts as a clearance receptor for sPLA₂s. This study examined whether PLA₂R plays a role in the pathogenesis of experimental autoimmune myocarditis using PLA₂R-deficient (PLA₂R KO) mice on a BALB/c background. Autoimmune myocarditis was induced by immunization with murine α-myosin heavy chain. In the immunostaining of PLA₂R wild-type (WT) myocardium, PLA₂R and sPLA₂s were expressed in α-SMA⁺ cells and neutrophils, respectively. In immunoblot analyses, tissue from PLA₂R KO myocardium after immunization had five to tenfold increases in the protein level of sPLA₂-IB and sPLA₂-IIA compared with PLA₂R WT myocardium. However, the mRNA expression levels of these sPLA₂s were similar in PLA₂R KO and WT myocardium. Compared with PLA₂R WT myocardium, PLA₂R KO myocardium after immunization showed 40% increase in areas affected by infiltration of inflammatory cells, eight to tenfold increase in levels of PGE₂ and TXB₂, and a threefold increase in number of Th17 cells in heart infiltrates assessed by flow cytometric analysis. Finally, PGE₂ promoted IL-23-induced expansion of Th17 cells in vitro. In conclusion, PLA₂R-deficiency increased sPLA₂-IB and sPLA₂-IIA levels in the myocardium after immunization probably through impaired clearance, leading to increased levels of PGE₂ in the myocardium. Elevated PGE₂ induced Th17 cell expansion, exacerbating myocarditis in PLA₂R KO mice. Thus, PLA₂R plays an important role in pathogenesis of experimental autoimmune myocarditis.

Prostaglandin E2 and an EP4 receptor agonist inhibit LPS-Induced monocyte chemotactic protein 5 production and secretion in mouse cardiac fibroblasts via Akt and NF-κB signaling

BACKGROUND

Prostaglandin E2 (PGE₂) signals through 4 separate G-protein coupled receptor sub-types to elicit a variety of physiologic and pathophysiological effects. We have previously reported that mice lacking the EP4 receptor in the cardiomyocytes develop heart failure with a phenotype of dilated cardiomyopathy. Also, these mice have increased levels of chemokines, like MCP-5, in their left ventricles. We have recently reported that overexpression of the EP4 receptor could improve cardiac function in the myocardial infarction model. Furthermore, we showed that overexpression of EP4 had an anti-inflammatory effect in the whole left ventricle. It has also been shown that PGE₂ can antagonize lipopolysaccharide-induced secretion of chemokines/cytokines in various cell types. We therefore hypothesized that PGE₂ inhibits lipopolysaccharide (LPS)-induced MCP-5 secretion in adult mouse cardiac fibroblasts via its EP4 receptor.

METHODS AND RESULTS

Our hypothesis was tested using isolated mouse adult ventricular fibroblasts (AVF) treated with LPS. Pre-treatment of the cells with PGE₂ and the EP4 agonist CAY10598 resulted in reductions of the pro-inflammatory response induced by LPS. Specifically, we observed reductions in MCP-5 secretion. Western blot analysis showed reductions in phosphorylated Akt and IκBα indicating reduced NF-κB activation. The anti-inflammatory effects of PGE₂ and EP4 agonist signaling appeared to be independent of cAMP, p-44/42, or p38 pathways.

CONCLUSION

Exogenous treatment of PGE₂ and the EP4 receptor agonist blocked the pro-inflammatory actions of LPS. Mechanistically, this was mediated via reduced Akt phosphorylation and inhibition of NF-κB.

Overexpression of prostaglandin E2 EP4 receptor improves cardiac function after myocardial infarction

BACKGROUND

Prostaglandin E2 (PGE₂) signals through 4 separate G-protein coupled receptor sub-types to elicit a variety of physiologic and pathophysiological effects. We recently reported that PGE₂ via its EP3 receptor could reduce cardiac contractility of isolated myocytes and the working heart preparation. We thus hypothesized that there is an imbalance in the EP3/EP4 ratio towards EP3 in the failing heart and that overexpression of EP4 in a mouse model of heart failure would improve cardiac function.

METHODS AND RESULTS

Our hypothesis was tested in a mouse model of myocardial infarction (MI) with the use of AAV9-EP4 driven by the myosin heavy chain promoter to overexpress EP4 in the cardiac myocytes. Echocardiography was performed to assess cardiac function. We found that overexpression of EP4 improved shortening fraction (p = 0.0025), ejection fraction (p = 0.0003), and reduced left ventricular dimension at systole (p = 0.0013). Overexpression of EP4 also significantly reduced indices of cardiac hypertrophy and interstitial collagen fraction. Animals treated with AAV9-EP4 also had a significant decrease in TNFα mRNA expression and in the number of macrophages and T cells migrated post MI coupled with a reduction in the expression of iNOS.

CONCLUSION

Overexpression of EP4 improves cardiac function post MI. This may be mediated through reductions in adverse cardiac remodeling or via inhibition of cytokine/chemokine production.

A peptide vaccine targeting angiotensin II attenuates the cardiac dysfunction induced by myocardial infarction

A peptide vaccine targeting angiotensin II (Ang II) was recently developed as a novel treatment for hypertension to resolve the problem of noncompliance with pharmacotherapy. Ang II plays a crucial role in the pathogenesis of cardiac remodeling after myocardial infarction (MI), which causes heart failure. In the present study, we examined whether the Ang II vaccine is effective in preventing heart failure. The injection of the Ang II vaccine in a rat model of MI attenuated cardiac dysfunction in association with an elevation in the serum anti-Ang II antibody titer. Furthermore, any detrimental effects of the Ang II vaccine were not observed in the rats that underwent sham operations. Treatment with immunized serum from Ang II vaccine-injected rats significantly suppressed post-MI cardiac dysfunction in MI rats and Ang II-induced remodeling-associated signaling in cardiac fibroblasts. Thus, our present study demonstrates that the Ang II vaccine may provide a promising novel therapeutic strategy for preventing heart failure.

A sustained-release drug-delivery system of synthetic prostacyclin agonist, ONO-1301SR: a new reagent to enhance cardiac tissue salvage and/or regeneration in the damaged heart

Cardiac failure is a major cause of mortality and morbidity worldwide, since the standard treatment for cardiac failure in the clinical practice is chiefly to focus on removal of insults against the heart or minimisation of additional factors to exacerbate cardiac failure, but not on regeneration of the damaged cardiac tissue. A synthetic prostacyclin agonist, ONO-1301, has been developed as a long-acting drug for acute and chronic pathologies related to regional ischaemia, inflammation and/or interstitial fibrosis by pre-clinical studies. In addition, poly-lactic co-glycolic acid-polymerised form of ONO-1301, ONO-1301SR, was generated to achieve a further sustained release of this drug into the targeted region. This unique reagent has been shown to act on fibroblasts, vascular smooth muscle cells and endothelial cells in the tissue via the prostaglandin IP receptor to exert paracrinal release of multiple protective factors, such as hepatocyte growth factor, vascular endothelial growth factor or stromal cell-derived factor-1, into the adjacent damaged tissue, which is salvaged and/or regenerated as a result. Our laboratory developed a new surgical approach to treat acute and chronic cardiac failure using a variety of animal models, in which ONO-1301SR is directly placed over the cardiac surface to maximise the therapeutic effects and minimise the systemic complications. This review summarises basic and pre-clinical information of ONO-1301 and ONO-1301SR as a new reagent to enhance tissue salvage and/or regeneration, with a particular focus on the therapeutic effects on acute and chronic cardiac failure and underlying mechanisms, to explore a potential in launching the clinical study.

Inhibition of NF-κB activation by a novel IKK inhibitor reduces the severity of experimental autoimmune myocarditis via suppression of T-cell activation

NF-κB, which is activated by the inhibitor of NF-κB kinase (IKK), is involved in the progression of inflammatory disease. However, the effect of IKK inhibition on the progression of myocarditis is unknown. We examined the effect of IKK inhibition on the progression of myocarditis. Lewis rats were immunized with porcine cardiac myosin to induce experimental autoimmune myocarditis (EAM). We administered the IKK inhibitor (IMD-0354; 15 mg·kg(-1)·day(-1)) or vehicle to EAM rats daily. Hearts were harvested 21 days after immunization. Although the untreated EAM group showed increased heart weight-to-body weight ratio, and severe myocardial damage, these changes were attenuated in the IKK inhibitor-treated group. Moreover, IKK inhibitor administration significantly reduced NF-κB activation and mRNA expression of IFN-γ, IL-2, and monocyte chemoattractant protein-1 in myocardium compared with vehicle administration. In vitro study showed that the IKK inhibitor treatment inhibited T-cell proliferation and Th1 cytokines production induced by myosin stimulation. The IKK inhibitor ameliorated EAM by suppressing inflammatory reactions via suppression of T-cell activation.

The prostanoid EP4 receptor and its signaling pathway

The EP4 prostanoid receptor is one of four receptor subtypes for prostaglandin E2. It belongs to the family of G protein-coupled receptors. It was originally identified, similar to the EP2 receptor as a G(s)α-coupled, adenylyl cyclase-stimulating receptor. EP4 signaling plays a variety of roles through cAMP effectors, i.e., protein kinase A and exchange protein activated by cAMP. However, emerging evidence from studies using pharmacological approaches and genetically modified mice suggests that EP4, unlike EP2, can also be coupled to G(i)α, phosphatidylinositol 3-kinase, β-arrestin, or β-catenin. These signaling pathways constitute unique roles for the EP4 receptor. EP4 is widely distributed in the body and thus plays various physiologic and pathophysiologic roles. In particular, EP4 signaling is closely related to carcinogenesis, cardiac hypertrophy, vasodilation, vascular remodeling, bone remodeling, gastrointestinal homeostasis, renal function, and female reproductive function. In addition to the classic anti-inflammatory action of EP4 on mononuclear cells and T cells, recent evidence has shown that EP4 signaling contributes to proinflammatory action as well. The aim of this review is to present current findings on the biologic functions of the EP4 receptor. In particular, we will discuss its diversity from the standpoint of EP4-mediated signaling.

E-type prostanoid receptor 4 (EP4) in disease and therapy

The large variety of biological functions governed by prostaglandin (PG) E2 is mediated by signaling through four distinct E-type prostanoid (EP) receptors. The availability of mouse strains with genetic ablation of each EP receptor subtype and the development of selective EP agonists and antagonists have tremendously advanced our understanding of PGE2 as a physiologically and clinically relevant mediator. Moreover, studies using disease models revealed numerous conditions in which distinct EP receptors might be exploited therapeutically. In this context, the EP4 receptor is currently emerging as most versatile and promising among PGE2 receptors. Anti-inflammatory, anti-thrombotic and vasoprotective effects have been proposed for the EP4 receptor, along with its recently described unfavorable tumor-promoting and pro-angiogenic roles. A possible explanation for the diverse biological functions of EP4 might be the multiple signaling pathways switched on upon EP4 activation. The present review attempts to summarize the EP4 receptor-triggered signaling modules and the possible therapeutic applications of EP4-selective agonists and antagonists.

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.

Autoimmune giant cell myocarditis: clinical characteristics, experimental models and future treatments

INTRODUCTION

Although prognosis in acute myocarditis is generally moderate, giant cell myocarditis shows poor prognosis. Giant cell myocarditis is considered to be an autoimmune disease, however, its pathophysiology and specific treatment is yet to be elucidated.

AREAS COVERED

This article reviews the clinical characteristics of autoimmune myocarditis and its possible future treatments. An animal model of experimental autoimmune myocarditis (EAM) is characterized by severe myocardial damage and multinucleated giant cell infiltration, and this has been used as a disease model for human acute giant cell myocarditis. Using experimental models, we reported that NF-κB, cytokines, adhesion molecules and other factors play a critical role in the development of autoimmune myocarditis.

EXPERT OPINION

Giant cell myocarditis, an autoimmune form of myocarditis, has a high mortality rate unless mechanical support or cardiac transplantation is performed. Therefore, further therapeutic applications of novel methodologies are needed to expand the number of alternative choices for treating autoimmune myocarditis.