Roles of prostaglandin I(2) and thromboxane A(2) in cardiac ischemia-reperfusion injury: a study using mice lacking their respective receptors

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.

Protective role of arachidonic acid against diabetic myocardial ischemic injury: a translational study of pigs, rats, and humans

AIM

Patients with diabetes mellitus have poor prognosis after myocardial ischemic injury. However, the mechanism is unclear and there are no related therapies. We aimed to identify regulators of diabetic myocardial ischemic injury.

METHODS AND RESULTS

Mass spectrometry-based, non-targeted metabolomic approach was used to profile coronary sinus blood from diabetic and non-diabetic Bama-mini pigs at 0.5-h post coronary artery ligation. Six metabolites had a |log2 (Fold Change)|> 1.3. Among them, the most changed is arachidonic acid (AA), levels of which were 32 times lower in diabetic pigs than in non-diabetic pigs. The AA-derived products, PGI2 and 6-keto-PGF1α, were also significantly reduced. AA treatment of cultured cardiomyocytes protected against cell death by 30% at 48 h of high glucose and oxygen deprivation, which coincided with increased mitophagic activity (as indicated by increased LC3II/LC3I, decreased p62 and increased parkin & PINK1), improved mitochondrial renewal (upregulation of Drp1 and FIS1), reduced ROS generation and increased ATP production. These cardioprotective effects were abolished by PINK1(a crucial mitophagy protein) knockdown or the autophagy inhibitor 3-Methyladenine. The protective effect of AA was also inhibited by indomethacin and Cay10441, a prostacyclin receptor antagonist. Furthermore, diabetic Sprague Dawley rats were subjected to coronary ligation for 40 min and AA treatment (10 mg/day per animal gavaged) decreased myocardial infarct size, cell apoptosis index, inflammatory cytokines and improved heart function. Scanning electron microscopy showed more intact mitochondria in the border zone of infarcted myocardium in AA treated rats. Lastly, diabetic patients after myocardial infarction had lower plasma levels of AA and 6-keto-PGF1α and reduced cardiac ejection fraction, compared with non-diabetic patients after myocardial infarction. Plasma AA level was inversely correlated with fasting blood glucose.

CONCLUSIONS

AA protects against diabetic ischemic myocardial damage by promoting mitochondrial autophagy and renewal, which is related to AA derived PGI2 signaling. AA may represent a new strategy to treat diabetic myocardial ischemic injury.

What do we know about platelets in myocardial ischemia-reperfusion injury and why is it important?

Myocardial ischemia-reperfusion injury (MIRI), the joint result of ischemic injury and reperfusion injury, is associated with poor outcomes in patients with acute myocardial infarction undergoing primary percutaneous coronary intervention. Accumulating evidence demonstrates that activated platelets directly contribute to the pathogenesis of MIRI through participating in the formation of microthrombi, interaction with leukocytes, secretion of active substances, constriction of microvasculature, and activation of spinal afferent nerves. The molecular mechanisms underlying the above detrimental effects of activated platelets include the homotypic and heterotypic interactions through surface receptors, transduction of intracellular signals, and secretion of active substances. Revealing the roles of platelet activation in MIRI and the associated mechanisms would provide potential targets/strategies for the clinical evaluation and treatment of MIRI. Further studies are needed to characterize the temporal (ischemia phase vs. reperfusion phase) and spatial (systemic vs. local) distributions of platelet activation in MIRI by multi-omics strategies. To improve the likelihood of translating novel cardioprotective interventions into clinical practice, basic researches maximally replicating the complexity of clinical scenarios would be necessary.

Preparing to strike: Acute events in signaling by the serpentine receptor for thromboxane A2

Over the last two decades, awareness of the (patho)physiological roles of thromboxane A₂ signaling has been greatly extended. From humble beginnings as a short-lived stimulus that activates platelets and causes vasoconstriction to a dichotomous receptor system involving multiple endogenous ligands capable of modifying tissue homeostasis and disease generation in almost every tissue of the body. Thromboxane A₂ receptor (TP) signal transduction is associated with the pathogenesis of cancer, atherosclerosis, heart disease, asthma, and host response to parasitic infection amongst others. The two receptors mediating these cellular responses (TPα and TPβ) are derived from a single gene (TBXA2R) through alternative splicing. Recently, knowledge about the mechanism(s) of signal propagation by the two receptors has undergone a revolution in understanding. Not only have the structural relationships associated with G-protein coupling been established but the modulation of that signaling by post-translational modification to the receptor has come sharply into focus. Moreover, the signaling of the receptor unrelated to G-protein coupling has become a burgeoning field of endeavor with over 70 interacting proteins currently identified. These data are reshaping the concept of TP signaling from a mere guanine nucleotide exchange factors for Gα activation to a nexus for the convergence of diverse and poorly characterized signaling pathways. This review summarizes the advances in understanding in TP signaling, and the potential for new growth in a field that after almost 50 years is finally coming of age.

Prostaglandin I2 suppresses the development of gut-brain axis disorder in irritable bowel syndrome in rats

In this study, we attempted to clarify a role of prostaglandin (PG) I₂ and its specific receptor, IP in the pathogenesis of irritable bowel syndrome (IBS) using a maternal separation (MS)-induced IBS model. Administration of beraprost (BPS), a specific IP agonist, improved visceral hypersensitivity and depressive state with decreased serum CRF level in the IBS rats. To clarify the mechanism of the effect of BPS, we performed serum metabolome analysis and 1-methylnicotinamide (1-MNA) was identified as a possible candidate for a clue metabolite of pathogenesis of IBS. The serum 1-MNA levels revealed inverse correlation to the level of visceral sensitivity, and positive correlation to a depression marker, immobilizing time. Administration of 1-MNA induced visceral hypersensitivity and depression with increased levels of serum CRF. Since fecal 1-MNA is known for a marker of dysbiosis, we examined the composition of fecal microbiota by T-RFLP analysis. The proportion of clostridium cluster XI, XIVa and XVIII was significantly changed in MS-induced IBS rats treated with BPS. Fecal microbiota transplant of BPS-treated rats improved visceral hypersensitivity and depression in IBS rats. These results suggest for the first time that PGI₂-IP signaling plays an important role in IBS phenotypes such as visceral hypersensitivity and depressive state. BPS modified microbiota, thereby inhibition of 1-MNA-CRF pathway, followed by improvement of MS-induced IBS phenotype. These results suggest that the PGI₂-IP signaling could be considered to be a therapeutic option for IBS.

Prostaglandin E2 mediates the late phase of ischemic preconditioning in the heart via its receptor subtype EP4

Ischemic preconditioning (IPC) describes a phenomenon wherein brief ischemia of the heart induces a potent cardioprotective mechanism against succeeding ischemic insult. Cyclooxygenase-2 (COX-2), a rate-limiting enzyme in prostanoid biosynthesis, is upregulated in the ischemic heart and contributes to IPC. Prostaglandin E₂ (PGE₂) protects the heart from ischemia-reperfusion (I/R) injury via its receptor subtype EP₄. We sought to clarify the role of the PGE₂/EP₄ system in the late phase of IPC. Mice were subjected to four IPC treatment cycles, consisting of 5 min of occlusion of the left anterior descending coronary artery (LAD). We found that COX-2 mRNA was significantly upregulated in wild-type hearts at 6 h after IPC treatment. Cardiac PGE₂ levels at 24 h after IPC treatment were significantly increased in both wild-type mice and mice lacking EP₄ (EP₄^-/-). At 24 h after IPC treatment, I/R injury was induced by 30 min of LAD occlusion followed by 2 h of reperfusion and the cardiac infarct size was determined. The infarct size was significantly reduced by IPC treatment in wild-type mice; a reduction was not observed in EP₄^-/- mice. AE1-329, an EP₄ agonist, significantly reduced infarct size and significantly ameliorated deterioration of cardiac function in wild-type mice subjected to I/R without IPC treatment. Furthermore, AE1-329 significantly enhanced the I/R-induced activation of Akt, a pro-survival kinase. We demonstrated that the PGE₂/EP₄ system in the heart plays a critical role in the late phase of IPC, partly by augmenting Akt-mediated signaling. These findings clarify the mechanism of IPC and may contribute to the development of therapeutic strategies for ischemic heart disease.

NO and Heme Proteins: Cross-Talk between Heme and Cysteine Residues

Heme proteins are a diverse group that includes several unrelated families. Their biological function is mainly associated with the reactivity of the heme group, which-among several other reactions-can bind to and react with nitric oxide (NO) and other nitrogen compounds for their production, scavenging, and transport. The S-nitrosylation of cysteine residues, which also results from the reaction with NO and other nitrogen compounds, is a post-translational modification regulating protein activity, with direct effects on a variety of signaling pathways. Heme proteins are unique in exhibiting this dual reactivity toward NO, with reported examples of cross-reactivity between the heme and cysteine residues within the same protein. In this work, we review the literature on this interplay, with particular emphasis on heme proteins in which heme-dependent nitrosylation has been reported and those for which both heme nitrosylation and S-nitrosylation have been associated with biological functions.

Qualitative and Quantitative Effects of Fatty Acids Involved in Heart Diseases

Fatty acids (FAs) have structural and functional diversity. FAs in the heart are closely associated with cardiac function, and their qualitative or quantitative abnormalities lead to the onset and progression of cardiac disease. FAs are important as an energy substrate for the heart, but when in excess, they exhibit cardio-lipotoxicity that causes cardiac dysfunction or heart failure with preserved ejection fraction. FAs also play a role as part of phospholipids that compose cell membranes, and the changes in mitochondrial phospholipid cardiolipin and the FA composition of plasma membrane phospholipids affect cardiomyocyte survival. In addition, FA metabolites exert a wide variety of bioactivities in the heart as lipid mediators. Recent advances in measurement using mass spectrometry have identified trace amounts of n-3 polyunsaturated fatty acids (PUFAs)-derived bioactive metabolites associated with heart disease. n-3 PUFAs have a variety of cardioprotective effects and have been shown in clinical trials to be effective in cardiovascular diseases, including heart failure. This review outlines the contributions of FAs to cardiac function and pathogenesis of heart diseases from the perspective of three major roles and proposes therapeutic applications and new medical perspectives of FAs represented by n-3 PUFAs.

MG53 E3 Ligase-Dead Mutant Protects Diabetic Hearts From Acute Ischemic/Reperfusion Injury and Ameliorates Diet-Induced Cardiometabolic Damage

Cardiometabolic diseases, including diabetes and its cardiovascular complications, are the global leading causes of death, highlighting a major unmet medical need. Over the past decade, mitsugumin 53 (MG53), also called TRIM72, has emerged as a powerful agent for myocardial membrane repair and cardioprotection, but its therapeutic value is complicated by its E3 ligase activity, which mediates metabolic disorders. Here, we show that an E3 ligase-dead mutant, MG53-C14A, retains its cardioprotective function without causing metabolic adverse effects. When administered in normal animals, both the recombinant human wild-type MG53 protein (rhMG53-WT) and its E3 ligase-dead mutant (rhMG53-C14A) protected the heart equally from myocardial infarction and ischemia/reperfusion (I/R) injury. However, in diabetic db/db mice, rhMG53-WT treatment markedly aggravated hyperglycemia, cardiac I/R injury, and mortality, whereas acute and chronic treatment with rhMG53-C14A still effectively ameliorated I/R-induced myocardial injury and mortality or diabetic cardiomyopathy, respectively, without metabolic adverse effects. Furthermore, knock-in of MG53-C14A protected the mice from high-fat diet-induced metabolic disorders and cardiac damage. Thus, the E3 ligase-dead mutant MG53-C14A not only protects the heart from acute myocardial injury but also counteracts metabolic stress, providing a potentially important therapy for the treatment of acute myocardial injury in metabolic disorders, including diabetes and obesity.

The role of thromboxane prostanoid receptor signaling in gastric ulcer healing

The process of gastric ulcer healing includes cell migration, proliferation, angiogenesis and re-epithelialization. Platelets contain angiogenesis stimulating factors that induce angiogenesis. Thromboxane A2 (TXA2 ) not only induces platelet activity but also angiogenesis. This study investigated the role of TXA2 in gastric ulcer healing using TXA2 receptor knockout (TPKO) mice. Gastric ulcer healing was suppressed by treatment with the TXA2 synthase inhibitor OKY-046 and the TXA2 receptor antagonist S-1452 compared with vehicle-treated mice. TPKO showed delayed gastric ulcer healing compared with wild-type mice (WT). The number of microvessels and CD31 expression were lower in TPKO than in WT mice, and TPKO suppressed the expression of transforming growth factor beta (TGF-β) and vascular endothelial growth factor A (VEGF-A) in areas around gastric ulcers. Immunofluorescence assays showed that TGF-β and VEGF-A co-localized with platelets. Gastric ulcer healing was significantly reduced in WT mice transplanted with TPKO compared with WT bone marrow. These results suggested that TP signalling on platelets facilitates gastric ulcer healing through TGF-β and VEGF-A.

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.

Thromboxane A2 is involved in the development of hypertension in chronic kidney disease rats

Hypertension is one of the most common complications of chronic kidney disease (CKD). Some research has indicated that changes in large artery function especially caused by thromboxane A2 (TXA2) may be a novel factor acting to induce hypertension in CKD. We studied the 5/6 nephrectomy rat model and measured serum levels of creatinine (Cr), calcium (Ca), phosphorus (P), TXA2-stable metabolites (thromboxane B2, TXB2), and caudal artery pressure after nephrectomy. The tension variations in thoracic aortas were measured after stimulating by vasoconstrictor/vasodilator using the cumulative concentration administration method and then tested the expression of TXA2 receptors in the thoracic aortas through western blots. The CKD rats developed uremia, electrolyte imbalances，and hypertension. They also exhibited a significant increase in TXB2 concentration. The aortic rings of CKD rats showed an increased contraction response to U46619 (a TXA2 analogue) and the expression of TXA2 receptors also enhanced. In the meanwhile, the diastolic function decreased in the CKD group. Our results demonstrate that the impairment of artery contractile function caused by the increase of TXA2 receptors on the wall of aortic rings may be involved in hypertension in CKD rats.

New horizons in the roles and associations of COX-2 and novel natural inhibitors in cardiovascular diseases

Age-related cardiovascular disease is the leading cause of death in elderly populations. Coxibs, including celecoxib, valdecoxib, etoricoxib, parecoxib, lumiracoxib, and rofecoxib, are selective cyclooxygenase-2 (COX-2) inhibitors used to treat osteoarthritis and rheumatoid arthritis. However, many coxibs have been discontinued due to adverse cardiovascular events. COX-2 contains cyclooxygenase (COX) and peroxidase (POX) sites. COX-2 inhibitors block COX activity without affecting POX activity. Recently, quercetin-like flavonoid compounds with OH groups in their B-rings have been found to serve as activators of COX-2 by binding the POX site. Galangin-like flavonol compounds serve as inhibitors of COX-2. Interestingly, nabumetone, flurbiprofen axetil, piketoprofen-amide, and nepafenac are ester prodrugs that inhibit COX-2. The combination of galangin-like flavonol compounds with these prodrug metabolites may lead to the development of novel COX-2 inhibitors. This review focuses on the most compelling evidence regarding the role and mechanism of COX-2 in cardiovascular diseases and demonstrates that quercetin-like compounds exert potential cardioprotective effects by serving as cofactors of COX-2.

The role of lipid-based signalling in wound healing and senescence

Lipid-based signalling modulates several cellular processes and intercellular communication during wound healing and tissue regeneration. Bioactive lipids include but are not limited to the diverse group of eicosanoids, phospholipids, and extracellular vesicles and mediate the attraction of immune cells, initiation of inflammatory responses, and their resolution. In aged individuals, wound healing and tissue regeneration are greatly impaired, resulting in a delayed healing process and non-healing wounds. Senescent cells accumulate with age in vivo, preferably at sites implicated in age-associated pathologies and their elimination was shown to alleviate many age-associated diseases and disorders. In contrast to these findings, the transient presence of senescent cells in the process of wound healing exerts beneficial effects and limits fibrosis. Hence, clearance of senescent cells during wound healing was repeatedly shown to delay wound closure in vivo. Recent findings established a dysregulated synthesis of eicosanoids, phospholipids and extracellular vesicles as part of the senescent phenotype. This intriguing connection between cellular senescence, lipid-based signalling, and the process of wound healing and tissue regeneration prompts us to compile the current knowledge in this review and propose future directions for investigation.

Roles of Thromboxane Receptor Signaling in Enhancement of Lipopolysaccharide-Induced Lymphangiogenesis and Lymphatic Drainage Function in Diaphragm

[Figure: see text].

Prostaglandin E2 Receptor 4 (EP4) as a Therapeutic Target to Impede Breast Cancer-Associated Angiogenesis and Lymphangiogenesis

The formation of new blood (angiogenesis) and lymphatic (lymphangiogenesis) vessels are major events associated with most epithelial malignancies, including breast cancer. Angiogenesis is essential for cancer cell survival. Lymphangiogenesis is critical in maintaining tumoral interstitial fluid balance and importing tumor-facilitatory immune cells. Both vascular routes also serve as conduits for cancer metastasis. Intratumoral hypoxia promotes both events by stimulating multiple angiogenic/lymphangiogenic growth factors. Studies on tumor-associated lymphangiogenesis and its exploitation for therapy have received less attention from the research community than those on angiogenesis. Inflammation is a key mediator of both processes, hijacked by many cancers by the aberrant expression of the inflammation-associated enzyme cyclo-oxygenase (COX)-2. In this review, we focus on breast cancer and showed that COX-2 is a major promoter of both events, primarily resulting from the activation of prostaglandin (PG) E receptor EP4 on tumor cells, tumor-infiltrating immune cells, and endothelial cells; and the induction of oncogenic microRNAs. The COX-2/EP4 pathway also promotes additional events in breast cancer progression, such as cancer cell migration, invasion, and the stimulation of stem-like cells. Based on a combination of studies using multiple breast cancer models, we show that EP4 antagonists hold a major promise in breast cancer therapy in combination with other modalities including immune check-point inhibitors.

Routine Intraoperative Inhaled Milrinone and Iloprost Reduces Inotrope Use in Patients Undergoing Cardiac Surgery: A Retrospective Cohort Pilot Study

BACKGROUND

Catecholamine inotropes are frequently used after cardiopulmonary bypass (CPB) but may have undesirable effects. The aim was to identify whether the routine use of inhaled pulmonary vasodilators might reduce the requirement for inotrope drugs after cardiac surgery.

METHODS

Retrospective cohort study of sequential patients undergoing cardiac surgery at the Royal Melbourne Hospital performed by a single surgeon and anesthesia care team, within 14 months before and after routine implementation of inhaled pulmonary vasodilators, August 2017. Milrinone 4 mg and iloprost 20 µg were inhaled using a vibrating mesh nebulizer (Aerogen) before initiation of CPB and at chest closure. Other aspects of clinical management were unaltered over the time period. Two investigators blinded to each other extracted data from electronic and written medical records. The primary outcome was any use of inotropes in the perioperative period; a Fisher exact test was used to analyze any differences between the 2 groups. Demographic data, hemodynamic data, and use of inotropes and vasopressors were collected from induction of anesthesia to 36 hours postoperative in the intensive care unit (ICU). Hospital and ICU length of stay, cost, and complications were collected.

RESULTS

Any use of inotropes was significantly lower with inhaled pulmonary dilators (62.5% vs 86.8%, odds ratio [95% confidence interval {CI}], 0.253 (0.083-0.764); P = .011), including intraoperative inotrope use (37.5% vs 86.8%, odds ratio [95% CI], 0.091 (0.03-0.275); P < .001). ICU length of stay was significantly lower with inhaled pulmonary dilators (45 hours, interquartile range [IQR], 27-65 vs 50 hours, IQR, 45-74; P = .026). There were no significant differences among major postoperative complications or costs between groups.

CONCLUSIONS

Routine use of inhaled milrinone 4 mg and iloprost 20 µg before and after CPB is associated with reduced postoperative inotrope use.

The Role of Arachidonic Acid Metabolism in Myocardial Ischemia-Reperfusion Injury

Patients with myocardial ischemic diseases or who are undergoing one of various heart treatments, such as open heart surgery, coronary artery bypass grafting, percutaneous coronary artery intervention or drug thrombolysis, face myocardial ischemia-reperfusion injury (MIRI). However, no effective treatment is currently available for MIRI. To improve the prognosis of people with cardiovascular disease, it is important to research the mechanism of MIRI. Arachidonic acid (AA) is one of the focuses of current research. The various metabolic pathways of AA are closely related to the development of cardiovascular disease, and the roles of various metabolites in ischemia-reperfusion injury have gradually been confirmed. AA is mainly metabolized in the cyclooxygenase (COX) pathway, lipoxygenase (LOX) pathway, and cytochrome P450 monooxygenase (CYP) pathway. This paper summarizes the progress of research on these three major AA metabolic pathways with respect to MIRI.

Cardiovascular Biology of Prostanoids and Drug Discovery

Prostanoids are a group of bioactive lipids that are synthesized de novo from membrane phospholipid-released arachidonic acid and have diverse functions in normal physiology and disease. NSAIDs (non-steroidal anti-inflammatory drugs), which are among the most commonly used medications, ameliorate pain, fever, and inflammation by inhibiting COX (cyclooxygenase), which is the rate-limiting enzyme in the biosynthetic cascade of prostanoids. The use of NSAIDs selective for COX-2 inhibition increases the risk of a thrombotic event (eg, myocardial infarction and stroke). All NSAIDs are associated with an increased risk of heart failure. Substantial variation in clinical responses to aspirin exists and is associated with cardiovascular risk. Limited clinical studies suggest the involvement of prostanoids in vascular restenosis in patients who received angioplasty intervention. mPGES (microsomal PG [prostaglandin] E synthase)-1, an alternative target downstream of COX, has the potential to be therapeutically targeted for inflammatory disease, with diminished thrombotic risk relative to selective COX-2 inhibitors. mPGES-1-derived PGE₂ critically regulates microcirculation via its receptor EP (receptor for prostanoid E) 4. This review summarizes the actions and associated mechanisms for modulating the biosynthesis of prostanoids in thrombosis, vascular remodeling, and ischemic heart disease as well as their therapeutic relevance.

Cyclo-Oxygenase (COX) Inhibitors and Cardiovascular Risk: Are Non-Steroidal Anti-Inflammatory Drugs Really Anti-Inflammatory?

Cyclo-oxygenase (COX) inhibitors are among the most commonly used drugs in the western world for their anti-inflammatory and analgesic effects. However, they are also well-known to increase the risk of coronary events. This area is of renewed significance given alarming new evidence suggesting this effect can occur even with acute usage. This contrasts with the well-established usage of aspirin as a mainstay for cardiovascular prophylaxis, as well as overwhelming evidence that COX inhibition induces vasodilation and is protective for vascular function. Here, we present an updated review of the preclinical and clinical literature regarding the cardiotoxicity of COX inhibitors. While studies to date have focussed on the role of COX in influencing renal and vascular function, we suggest an interaction between prostanoids and T cells may be a novel factor, mediating elevated cardiovascular disease risk with NSAID use.

Metabolomics profiling of haloperidol and validation of thromboxane-related signaling in the early development of zebrafish

Haloperidol is a common butyrophenone-derivative antipsychotic drug that is used clinically to treat schizophrenia and to control Tourette disorder. Haloperidol has been shown to be an embryonic toxicant and to cause a variety of adverse effects that affect human embryonic development. However, the pathway impaired by haloperidol during the developmental stages remains unclear. To elucidate the innate toxicological pathway of haloperidol, we investigated the lethality of haloperidol during the embryonic development of zebrafish. We observed that haloperidol caused serious morphological changes, with an LD₅₀ of 9.7 x 10^-6 ± 2.4 x 10^-6 μg/L. Next, we established a systematic approach to perform metabolite profiling in embryonic zebrafish with various concentrations of haloperidol and analyzed the metabolites using ultra-performance liquid chromatography quadrupole time-of-flight mass spectrometry (UPLC/Q-TOF MS). A total of 304 metabolites were identified and 86 metabolites were chosen to predict potential pathways. Among the metabolites, we found through prediction that numerous metabolomics-biological pathways are associated with haloperidol, including peroxisome-proliferator-activated receptor (ppar), thromboxane, and mTOR signaling. Quantitative real time-qPCR was then used to validate the gene expression potentially associated with the thromboxane, which is a metabolic product of arachidonic acid and considered to be important for cell proliferation and the inflammatory response. To sum up, analysis of metabolites in the zebrafish model provides a system for mining biomarkers that reflect biological significance and highlight the therapeutic potency in humans. In addition, it may show potential for application to other pharmaceuticals to identify their various activities and clarify functional mechanisms in the future.

The cyclooxygenase-1/mPGES-1/endothelial prostaglandin EP4 receptor pathway constrains myocardial ischemia-reperfusion injury

The use of nonsteroidal anti-inflammatory drugs that inhibit cyclooxygenase (COX)-1 and COX-2, increases heart failure risk. It is unknown whether microsomal (m) prostaglandin (PG) E synthase (S)-1, a target downstream of COX, regulates myocardial (M) ischemia/reperfusion (I/R) injury, a key determinant of heart failure. Here we report that COX-1 and mPGES-1 mediate production of substantial amounts of PGE₂ and confer cardiac protection in MI/R. Deletion of mPges-1 impairs cardiac microvascular perfusion and increases inflammatory cell infiltration in mouse MI/R. Consistently, mPges-1 deletion depresses the arteriolar dilatory response to I/R in vivo and to acetylcholine ex vivo, and enhances leukocyte-endothelial cell interaction, which is mediated via PGE receptor-4 (EP4). Furthermore, endothelium-restricted Ep4 deletion impairs microcirculation, and exacerbates MI/R injury, irrespective of EP4 agonism. Treatment with misoprostol, a clinically available PGE analogue, improves microcirculation and reduces MI/R injury. Thus, mPGES-1, a key microcirculation protector, constrains MI/R injury and this beneficial effect is partially mediated via endothelial EP4.

The use of nonsteroidal anti-inflammatory drugs inhibiting COX-1/2 is associated with an increased risk of heart failure. Here the authors show that mPGES-1, a therapeutic target downstream of COX enzymes, protects from cardiac ischemia/reperfusion injury, limiting leukocyte-endothelial interactions and preserving microvascular perfusion partly via the endothelial EP4 receptor.

Roles of prostaglandins in tumor-associated lymphangiogenesis with special reference to breast cancer

Lymphangiogenesis (formation of new lymphatic vessels), unlike angiogenesis, has been a lesser-focused field in cancer biology, because of earlier controversy regarding whether lymphatic metastasis occurs via pre-existing or newly formed lymphatics. Recent evidence reveals that peri-tumoral or intra-tumoral lymphangiogenesis is a precursor for lymphatic metastasis in most carcinomas and melanomas. Two major lymphangiogenic factors, vascular endothelial growth factor (VEGF)-C and VEGF-D, are produced by cancer cells or immune cells such as macrophages in the tumor-stroma to promote sprouting of lymphatics from lymphatic endothelial cells (LEC) or LEC precursors (LECP) by binding to their primary (high affinity) receptor VEGF-R3 or secondary receptors VEGF-R2, neuropilin (NRP)2 and α9/β1 integrin. Many other growth factors/receptors such as VEGF-A/VEGF-R2, fibroblast growth factor (FGF)2/FGF-R, platelet-derived growth factor (PDGF)/PDGF-R, hepatocyte growth factor (HGF)/C-Met, angiopoietins (Ang)1, 2/Tie2, and chemokines/ chemokine receptors (CCL21/CCR7, CCL12/CCR4) can also stimulate LEC sprouting directly or indirectly. This review deals with the roles of prostaglandins (PG), in particular PGE2, in cancer-associated lymphangiogenesis, with special emphasis on breast cancer. We show that cyclooxygenase (COX)-2 expression by breast cancer cells or tumor stroma leading to high PGE2 levels in the tumor milieu promotes lymphangiogenesis and lymphatic metastases, resulting from binding of PGE2 to PGE receptors (EP, in particular EP4) on multiple cell types: tumor cells, tumor-infiltrating immune cells, and LEC. EP4 activation on cancer cells and macrophages upregulated VEGF-C/D production to stimulate LEC sprouting. Furthermore, ligation of EP4 with PGE2 on cancer or host cells can initiate a new cascade of molecular events leading to cross-talk between cancer cells and LEC, facilitating lymphangiogenesis and lympho-vascular transport of cancer cells. We make a case for EP4 as a potential therapeutic target for breast cancer.

Lipid mediators in immune regulation and resolution

We are all too familiar with the events that follow a bee sting-heat, redness, swelling, and pain. These are Celsus' four cardinal signs of inflammation that are driven by very well-defined signals and hormones. In fact, targeting the factors that drive this onset phase is the basis upon which most current anti-inflammatory therapies were developed. We are also very well aware that within a few hours, these cardinal signs normally disappear. In other words, inflammation resolves. When it does not, inflammation persists, resulting in damaging chronic conditions. While inflammatory onset is actively driven, so also is its resolution-years of research have identified novel internal counter-regulatory signals that work together to switch off inflammation. Among these signals, lipids are potent signalling molecules that regulate an array of immune responses including vascular hyper reactivity and pain, as well as leukocyte trafficking and clearance, so-called resolution. Here, we collate bioactive lipid research to date and summarize the major pathways involved in their biosynthesis and their role in inflammation, as well as resolution. LINKED ARTICLES: This article is part of a themed section on Eicosanoids 35 years from the 1982 Nobel: where are we now? To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.8/issuetoc.

Complex Role for E-Prostanoid 4 Receptors in Hypertension

Background Prostaglandin E2 ( PGE 2) is a major prostanoid with multiple actions that potentially affect blood pressure ( BP ). PGE 2 acts through 4 distinct E-prostanoid ( EP ) receptor isoforms: EP 1 to EP 4. The EP 4 receptor ( EP 4R) promotes PGE 2-dependent vasodilation, but its role in the pathogenesis of hypertension is not clear. Methods and Results To address this issue, we studied mice after temporal- and cell-specific deletion of EP 4R. First, using a mouse line with loss of EP 4 expression induced universally after birth, we confirm that EP 4R mediates a major portion of the acute vasodilatory effects of infused PGE 2. In addition, EP 4 contributes to control of resting BP , which was increased by 5±1 mm Hg in animals with generalized deficiency of this receptor. We also show that EP 4 is critical for limiting elevations in BP caused by high salt feeding and long-term infusion of angiotensin II . To more precisely identify the mechanism for these actions, we generated mice in which EP 4R loss is induced after birth and is limited to smooth muscle. In these mice, acute PGE 2-dependent vasodilation was attenuated, indicating that this response is mediated by EP 4R in vascular smooth muscle cells. However, absence of EP 4R only in this vascular compartment had a paradoxical effect of lowering resting BP , whereas the protective effect of EP 4R on limiting angiotensin II-dependent hypertension was unaffected. Conclusions Taken together, our findings support a complex role for EP 4R in regulation of BP and in hypertension, which appears to involve actions of the EP 4R in tissues beyond vascular smooth muscle cells.

Perioperative urinary thromboxane metabolites and outcome of coronary artery bypass grafting: a nested case-control study

OBJECTIVE

As a marker of in vivo thromboxane generation, high-level urinary thromboxane metabolites (TXA-M) increase the occurrence of cardiovascular events in high-risk patients. To investigate whether perioperative urinary TXA-M level is associated with major adverse cardiac and cerebrovascular events (MACCE) after coronary artery bypass graft (CABG) surgery, we designed a nested case-control study.

DESIGN

Observational, nested case-control study.

SETTING

Single-centre outcomes research in Fuwai Hospital, Beijing, China.

PARTICIPANTS

One thousand six hundred and seventy Chinese patients undergoing CABG surgery from September 2011 to October 2013.

METHODS

We obtained urinary samples from 1670 Chinese patients undergoing CABG 1 hour before surgery (pre-CABG), and 6 hours (post-CABG 6 hours) and 24 hours after surgery (post-CABG 24 hours). Patients were followed up for 1 year, and we observed 56 patients had MACCE. For each patient with MACCE, we matched three control subjects. Perioperative urinary TXA-M of the three time spots was detected in these 224 patients.

RESULTS

Post-CABG 24 hours TXA-M is significantly higher than that of patients without MACCE (11 101vs8849 pg/mg creatine, P=0.007). In addition, patients in the intermediate tertile and upper tertile of post-CABG 24 hours urinary TXA-M have a 2.2 times higher (HR 2.22, 95% CI 1.04 to 4.71, P=0.038) and a 2.8 times higher (HR 2.81, 95% CI 1.35 to 5.85, P=0.006) risk of 1 year MACCE than those in the lower tertile, respectively.

CONCLUSIONS

In conclusion, post-CABG 24 hours urinary TXA-M elevation is associated with an increase of 1 year adverse events after CABG, indicating that the induction of cyclo-oxygenase-2 by surgery-related inflammatory stimuli or platelet turnover may be responsible for the high levels of post-CABG urinary TXA-M.

TRIAL REGISTRATION NUMBER

NCT01573143.

Investigating the possible mechanisms involved in adenosine preconditioning-induced cardioprotection in rats

BACKGROUND

Adenosine is a breakdown product of adenosine triphosphate and plays an important role in pharmacological preconditioning. The cardioprotective effects of adenosine preconditioning are well established. However, the possible mechanisms need to be explored.

AIM

This study was aimed to investigate the possible mechanisms involved in adenosine preconditioning-induced cardioprotection in rats.

METHODS

Rat heart was isolated and perfused on Langendorff apparatus. Global ischemia for 30 minutes followed by reperfusion for 120 minutes was employed to produce myocardial injury. Myocardial injury was assessed by measuring myocardial infarct size, release of lactate dehydrogenase (LDH) and creatine kinase (CK) in the coronary effluent and hemodynamic parameters including left ventricular developed pressure (LVDP), dp/dt_max, and dp/dt_min . Serum nitrite levels were measured as an index of nitric oxide release in blood.

RESULTS

Adenosine (4 mg/kg) preconditioning significantly decreased ischemia-reperfusion-induced increase in LDH, CK release, infarct size, improved LVDP, dp/dt_max and dp/dt_min, and increased serum nitrite levels. Pretreatment with L-NAME, a specific NOS inhibitor, (5 mg/kg) and montelukast, leukotriene receptor antagonist, (10 mg/kg) significantly abrogated the cardioprotective effect of adenosine preconditioning. However, seratrodast, thromboxane A₂ antagonist, (15 mg/kg) had no effect on adenosine-induced cardioprotection. Sodium nitroprusside (SNP) preconditioning also produced cardioprotective effects. However, caffeine (20 mg/kg) (adenosine receptor blocker) and seratrodast (15 mg/kg) had no effect on SNP-induced cardioprotection. Administration of montelukast abrogated the cardioprotective effects of SNP preconditioning-induced cardioprotection.

CONCLUSION

Adenosine preconditioning may increase the release of nitric oxide, which in turn may increase the release of cysteinyl leukotrienes to confer cardioprotection.

EP4 as a Therapeutic Target for Aggressive Human Breast Cancer

G-protein-coupled receptors (GPCRs, also called seven-transmembrane or heptahelical receptors) are a superfamily of cell surface receptor proteins that bind to many extracellular ligands and transmit signals to an intracellular guanine nucleotide-binding protein (G-protein). When a ligand binds, the receptor activates the attached G-protein by causing the exchange of Guanosine-5′-triphosphate (GTP) for guanosine diphosphate (GDP). They play a major role in many physiological functions, as well as in the pathology of many diseases, including cancer progression and metastasis. Only a few GPCR members have been exploited as targets for developing drugs with therapeutic benefit in cancer. Present review briefly summarizes the signaling pathways utilized by the EP (prostaglandin E receptor) family of GPCR, their physiological and pathological roles in carcinogenesis, with special emphasis on the roles of EP4 in breast cancer progression. We make a case for EP4 as a promising newer therapeutic target for treating breast cancer. We show that an aberrant over-expression of cyclooxygenase (COX)-2, which is an inflammation-associated enzyme, occurring in 40–50% of breast cancer patients leads to tumor progression and metastasis due to multiple cellular events resulting from an increased prostaglandin (PG) E2 production in the tumor milieu. They include inactivation of host anti-tumor immune cells, such as Natural Killer (NK) and T cells, increased immuno-suppressor function of tumor-associated macrophages, promotion of tumor cell migration, invasiveness and tumor-associated angiogenesis, due to upregulation of multiple angiogenic factors including Vascular Endothelial Growth Factor (VEGF)-A, increased lymphangiogenesis (due to upregulation of VEGF-C/D), and a stimulation of stem-like cell (SLC) phenotype in cancer cells. All of these events were primarily mediated by activation of the Prostaglandin (PG) E receptor EP4 on tumor or host cells. We show that selective EP4 antagonists (EP4A) could mitigate all of these events tested with cells in vitro as well as in vivo in syngeneic COX-2 expressing mammary cancer bearing mice or immune-deficient mice bearing COX-2 over-expressing human breast cancer xenografts. We suggest that EP4A can avoid thrombo-embolic side effects of long term use of COX-2 inhibitors by sparing cardio-protective roles of PGI2 via IP receptor activation or PGE2 via EP3 receptor activation. Furthermore, we identified two COX-2/EP4 induced oncogenic and SLC-stimulating microRNAs—miR526b and miR655, one of which (miR655) appears to be a potential blood biomarker in breast cancer patients for monitoring SLC-ablative therapies, such as with EP4A. We suggest that EP4A will likely produce the highest benefit in aggressive breast cancers, such as COX-2 expressing triple-negative breast cancers, when combined with other newer agents, such as inhibitors of programmed cell death (PD)-1 or PD-L1.

Prostaglandin I2 suppresses the development of diet-induced nonalcoholic steatohepatitis in mice

Nonalcoholic steatohepatitis (NASH) is a hepatic manifestation of metabolic syndrome. Although the prostaglandin (PG)I₂ receptor IP is expressed broadly in the liver, the role of PGI₂-IP signaling in the development of NASH remains to be determined. Here, we investigated the role of the PGI₂-IP system in the development of steatohepatitis using mice lacking the PGI₂ receptor IP [IP-knockout (IP-KO) mice] and beraprost (BPS), a specific IP agonist. IP-KO and wild-type (WT) mice were fed a methionine- and choline-deficient diet (MCDD) for 2, 5, or 10 wk. BPS was administered orally to mice every day during the experimental periods. The effect of BPS on the expression of chemokine and inflammatory cytokines was examined also in cultured Kupffer cells. WT mice fed MCDD developed steatohepatitis at 10 wk. IP-KO mice developed steatohepatitis at 5 wk with augmented histologic derangements accompanied by increased hepatic monocyte chemoattractant protein-1 (MCP-1) and TNF-α concentrations. After 10 wk of MCDD, IP-KO mice had greater hepatic iron deposition with prominent oxidative stress, resulting in hepatocyte damage. In WT mice, BPS improved histologic and biochemical parameters of steatohepatitis, accompanied by reduced hepatic concentration of MCP-1 and TNF-α. Accordingly, BPS suppressed the LPS-stimulated Mcp-1 and Tnf-α mRNA expression in cultured Kupffer cells prepared from WT mice. PGI₂-IP signaling plays a crucial role in the development and progression of steatohepatitis by modulating the inflammatory response, leading to augmented oxidative stress. We suggest that the PGI₂-IP system is an attractive therapeutic target for treating patients with NASH.-Kumei, S., Yuhki, K.-I., Kojima, F., Kashiwagi, H., Imamichi, Y., Okumura, T., Narumiya, S., Ushikubi, F. Prostaglandin I₂ suppresses the development of diet-induced nonalcoholic steatohepatitis in mice.

Misoprostol Reverse Hippocampal Neuron Cyclooxygenase-2 Downstream Signaling Imbalance in Aluminum-Overload Rats

Although COX-2 inhibition in animal models of neurodegenerative diseases has shown neuroprotection, recent studies have revealed some serious side effects (ulcers, bleeding, fatal cerebrovascular diseases etc.) and the limited benefits of COX-2 inhibitors. A more focused approach is necessary to explore the therapeutic effect of the COX downstream signaling pathway in neurological research. The aim of this study was to explore the alterations of the PGES-PGE2-EP signal pathway and the effect of misoprostol on neurodegeneration by chronic aluminum-overload in rats. Adult rats were treated by intragastric administration of aluminum gluconate. The PGE2 content and expression of PGES and EPs in the hippocampi of rats were detected using ELISA, q-PCR and Western blot analysis, respectively. The content of malondialdehyde (MDA) and the activity of superoxide dismutase (SOD) in the rat hippocampi were also detected. The misoprostol treatment dose-dependently improved spatial learning and memory function as well as healing after hippocampal neuron damage induced by chronic aluminum-overload in rats. Meanwhile, the administration of misoprostol resulted in a decrease in the PGE2 level and down-regulation of the mPGES-1, EP2 and EP4 expression levels, while there was a dosedependent up-regulation of EP3 expression. These results suggest that misoprostol possesses a neuroprotective property, and the mechanism involves affecting the EP3 level and reducing the endogenous production of PGE2 through a negative feedback mechanism, increasing the EP3 expression level, decreasing the EP2 and EP4 expression levels, and rebuilding the mPGES-1-PGE2-EP1-4 signal pathway balance. In this way, misoprostol has a counteractive effect on oxidant stress and inflammation in the central nervous system. The PGES-PGE2-EPs signaling pathway is a potential therapeutic strategy for treating neurodegeneration in patients.

Lipid Mediators in Inflammation

Lipids are potent signaling molecules that regulate a multitude of cellular responses, including cell growth and death and inflammation/infection, via receptor-mediated pathways. Derived from polyunsaturated fatty acids (PUFAs), such as arachidonic acid (AA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), each lipid displays unique properties, thus making their role in inflammation distinct from that of other lipids derived from the same PUFA. This diversity arises from their synthesis, which occurs via discrete enzymatic pathways and because they elicit responses via different receptors. This review will collate the bioactive lipid research to date and summarize the major pathways involved in their biosynthesis and role in inflammation. Specifically, lipids derived from AA (prostanoids, leukotrienes, 5-oxo-6,8,11,14-eicosatetraenoic acid, lipoxins, and epoxyeicosatrienoic acids), EPA (E-series resolvins), and DHA (D-series resolvins, protectins, and maresins) will be discussed herein.

Identification of α-helix 4 (α4) of Rab11a as a novel Rab11-binding domain (RBD): Interaction of Rab11a with the Prostacyclin Receptor

The cellular trafficking of numerous G protein-coupled receptors (GPCRs) is known to be regulated by Rab proteins that involves a direct protein:protein interaction between the receptor and the GTPase. In the case of the human prostacyclin receptor (hIP), it undergoes agonist-induced internalization and subsequent Rab11a-dependent recyclization involving an interaction between a Rab11-binding domain (RBD) localized within its carboxyl-tail domain with Rab11a. However, the GPCR-interacting domain on Rab11a itself is unknown. Hence, we sought to identify the region within Rab11a that mediates its interaction with the RBD of the hIP. The α4 helix region of Rab11 was identified as a novel binding domain for the hIP, a site entirely distinct from the Switch I/Switch II -regions that act as specific binding domain for most other Rab and Ras-like GTPase interactants. Specifically, Glu¹³⁸ within α4 helix of Rab11a appears to contact with key residues (e.g. Lys³⁰⁴) within the RBD of the hIP, where such contacts differ depending on the agonist-activated versus -inactive status of the hIP. Through mutational studies, supported by in silico homology modelling of the inactive and active hIP:Rab11a complexes, a mechanism is proposed to explain both the constitutive and agonist-induced binding of Rab11a to regulate intracellular trafficking of the hIP. Collectively, these studies are not only the first to identify α4 helix of Rab11a as a protein binding domain on the GTPase but also reveal novel mechanistic insights into the intracellular trafficking of the hIP, and potentially of other members of the GPCR superfamily, involving Rab11-dependent mechanisms.

Electroacupuncture prevents endothelial dysfunction induced by ischemia-reperfusion injury via a cyclooxygenase-2-dependent mechanism: A randomized controlled crossover trial

Objective

Exploring clinically effective methods to reduce ischemia-reperfusion (IR) injury in humans is critical. Several drugs have shown protective effects, but studies using other interventions have been rare. Electroacupuncture (EA) has induced similar protection in several animal studies but no study has investigated how the effects could be translated and reproduced in humans. This study aimed to explore the potential effect and mechanisms of EA in IR-induced endothelial dysfunction in humans.

Methods

This is a prospective, randomized, crossover, sham-controlled trial consisting of two protocols. Protocol 1 was a crossover study to investigate the effect of EA on IR-induced endothelial dysfunction. Twenty healthy volunteers were randomly assigned to EA or sham EA (sham). Flow mediated dilation (FMD) of the brachial artery (BA), nitroglycerin-mediated endothelial independent dilation, blood pressure before and after IR were measured. In protocol 2, seven volunteers were administered COX-2 inhibitor celecoxib (200 mg orally twice daily) for five days. After consumption, volunteers underwent FMD before and after IR identical to protocol 1.

Results

In protocol 1, baseline BA diameter, Pre-IR BA diameter and FMD were similar between the two groups (p = NS). After IR, sham group showed significantly blunted FMD (Pre-IR: 11.41 ± 3.10%, Post-IR: 4.49 ± 2.04%, p < 0.001). However, EA protected this blunted FMD (Pre-IR: 10.96 ± 5.30%, Post-IR: 9.47 ± 5.23%, p = NS, p < 0.05 compared with sham EA after IR). In protocol 2, this protective effect was completely abolished by pre-treatment with celecoxib (Pre-IR: 11.05 ± 3.27%; Post-IR: 4.20 ± 1.68%, p = 0.001).

Conclusion

EA may prevent IR-induced endothelial dysfunction via a COX-2 dependent mechanism.

Vascular hepoxilin and trioxilins mediate vasorelaxation through TP receptor inhibition in mouse arteries

AIM

12/15-lipoxygenase (12/15-LO) metabolizes arachidonic acid (AA) into several vasoactive eicosanoids. In mouse arteries, we previously characterized the enzyme's 15-LO metabolites 12(S)-hydroxyeicosatetraenoic acid (HETE), 15-HETE, hydroxyepoxyeicosatrienoic acids (HEETAs) and 11,12,15-trihydroxyeicosatrienoic acids (11,12,15-THETAs) as endothelium-derived relaxing factors. However, the observed 12-LO metabolites remained uncharacterized. The purpose of this study was to determine the structure and biological functions of eicosanoids generated by the enzyme's 12-LO activity.

METHODS

Metabolites extracted from aortas of C57BL/6 male mice were separated using a series of reverse and normal phase chromatographic steps and identified as hepoxilin A₃ , trioxilin A₃ and trioxilin C₃ by mass spectrometry. Activities of these natural compounds were tested on isometric tension and intracellular calcium release. The role of thromboxane (TP) receptor was determined in HEK293 cells overexpressing TPα receptor (TPα -HEK).

RESULTS

All identified vascular 12-LO metabolites were biologically active. In mouse mesenteric arteries, trioxilin A₃ , C₃ and hepoxilin A₃ (3 μm) relaxed arteries constricted with the thromboxane mimetic, U46619-constricted arteries (maximum relaxations of 78.9 ± 3.2, 29.7 ± 4.6, 82.2 ± 5.0 and 88.0 ± 2.4% respectively), but not phenylephrine-constricted arteries. In TPα-HEK cells, trioxilin A₃ , C₃ and hepoxilin A₃ (10 μm) inhibited U46619 (10 nM)-induced increases in intracellular calcium by 53.0 ± 7.2%, 32.8 ± 5.0% and 37.9 ± 13.5% respectively. In contrast, trioxilin B₃ and hepoxilin B₃ were not synthesized in arteries and exhibited little biological activity.

CONCLUSION

Trioxilin A₃ and C₃ and hepoxilin A₃ are endogenous vascular relaxing factors. They are not endothelium-derived hyperpolarizing factors but mediate vascular relaxation by inhibiting TP agonist-induced increases in intracellular calcium. Thus, they regulate vascular homeostasis by acting as endogenous TP antagonists.

Oxymatrine attenuated isoproterenol-induced heart failure in rats via regulation of COX-2/PGI2 pathway

Oxymatrine (OMT) is an active constituent of traditional Chinese herb Sophora japonica Ait which has been shown to exert potent anti-inflammatory,anti-oxidant and anti-fibrosis properties. Our previous studies have demonstrated that OMT has protective effects on isoproterenol-induced heart failure in rats through regulation of DDAH/ADMA metabolism pathway.In this study,we further investigated whether OMT could attenuate isoproterenol-induced heart failure through the regulation of COX-2/PGI₂ pathway. Heart failure was induced in Sprague-Dawley rats by 5mg/kg isoproterenol subcutaneous injection for 7days. The rats were maintained on normal diet and randomly divided into five groups: control, isoproterenol, isoproterenol with OMT (50, 100mg/kg), and OMT alone groups (n=12 in each group). Serum brain natruretic peptide (BNP, a heart failure biomarker), histopathological variables, expression of Cytosolic phospholipase A₂ (cPLA₂), cyclooxygenase-1 (COX-1), cyclooxygenase-2 (COX-2) and Prostacyclin synthase (PGIS) were analysed. Administration of OMT significantly reduced the increased BNP in plasm of isoproterenol-induced rats, attenuated cardiac fibrosis,suppressed overexpression of myocardial COX-1 expression, up-regulated COX-2 and PGIS expression, but had no effects on isoproterenol-induced elevated protein cPLA₂. And compared with control group, any indexes in sham rats treated with OMT (100mg/kg) alone were unaltered. These results demonstrated that OMT has cardioprotective effects on isoproterenol-induced heart failure in rats by regulating COX-2/PGI₂ pathway.

Influence of Thromboxane A2 on the Regulation of Adenosine Triphosphate-Sensitive Potassium Channels in Mouse Ventricular Myocytes

Background and Objectives

Adenosine triphosphate (ATP)-sensitive potassium (K_ATP) channels play an important role in myocardial protection. We examined the effects of thromboxane A₂ on the regulation of K_ATP channel activity in single ventricular myocytes.

Subjects and Methods

Single ventricular myocytes were isolated from the hearts of adult Institute of Cancer Research (ICR) mice by enzymatic digestion. Single channel activity was recorded by excised inside-out and cell-attached patch clamp configurations at −60 mV holding potential during the perfusion of an ATP-free K-5 solution.

Results

In the excised inside-out patches, the thromboxane A₂ analog, U46619, decreased the K_ATP channel activity in a dose-dependent manner; however, the thromboxane A₂ receptor antagonist, SQ29548, did not significantly attenuate the inhibitory effect of U46619. In the cell-attached patches, U46619 inhibited dinitrophenol (DNP)-induced K_ATP channel activity in a dose-dependent manner, and SQ29548 attenuated the inhibitory effects of U46619 on DNP-induced K_ATP channel activity.

Conclusion

Thromboxane A₂ may inhibit K_ATP channel activity, and may have a harmful effect on ischemic myocardium.

Prostaglandins in the eye: Function, expression, and roles in glaucoma

Prostaglandins are small pro-inflammatory molecules derived from arachidonic acid that play roles in a multitude of biological processes including, but not limited to, inflammation, pain modulation, allergies, and bone formation. Prostaglandin analogues are the front-line medications for the treatment of glaucoma, a condition resulting in blindness due to the death of retinal ganglion cells. These drugs act by lowering intraocular pressure (IOP), a major risk factor for glaucoma. The currently used prostaglandin analogues (latanoprost, bimatoprost, tafluprost, and travoprost) mimic PGF2 and target one of the prostaglandin receptors (FP), though research into harnessing the other receptors using compounds like Sulprostone (EP3 receptor), or Iloprost (IP receptor) are currently ongoing. In this review, we summarize the research into each of the prostaglandin molecules (PGD2, PGE2, PGF2, PGI2, TXA2) and their respective receptors (DP, EP1, 2, 3, 4, FP, IP). We examine the modes of action of each of these receptors, their expression, their role in aqueous humour production and outflow within the eye, as well as their roles as medications for the treatment of glaucoma.

Treprostinil indirectly regulates endothelial colony forming cell angiogenic properties by increasing VEGF-A produced by mesenchymal stem cells

Pulmonary vasodilators and prostacyclin therapy in particular, have markedly improved the outcome of patients with pulmonary hypertension (PH). Endothelial dysfunction is a key feature of PH, and we previously reported that treprostinil therapy increases number and proliferative potential of endothelial colony forming cells (ECFC) isolated from PH patients' blood. In the present study, the objective was to determine how treprostinil contributes to the proangiogenic functions of ECFC. We examined the effect of treprostinil on ECFC obtained from cord blood in terms of colony numbers, proliferative and clonogenic properties in vitro, as well as in vivo vasculogenic properties. Surprisingly, treprostinil inhibited viability of cultured ECFC but did not modify their clonogenic properties or the endothelial differentiation potential from cord blood stem cells. Treprostinil treatment significantly increased the vessel-forming ability of ECFC combined with mesenchymal stem cells (MSC) in Matrigel implanted in nude mice. In vitro, ECFC proliferation was stimulated by conditioned media from treprostinil-pretreated MSC, and this effect was inhibited either by the use of VEGF-A blocking antibodies or siRNA VEGF-A in MSC. Silencing VEGF-A gene in MSC also blocked the pro-angiogenic effect of treprostinil in vivo. In conclusion, increased VEGF-A produced by MSC can account for the increased vessel formation observed during treprostinil treatment. The clinical relevance of these data was confirmed by the high level of VEGF-A detected in plasma from patients with paediatric PH who had been treated with treprostinil. Moreover, our results suggest that VEGF-A level in patients could be a surrogate biomarker of treprostinil efficacy.

Expression of prostaglandin I2 (prostacyclin) receptor in blood of migraine patients: A potential biomarker

Background:

Migraine is the most common chronic neurological disorders that may be associated with vasodilatation. According to the role of prostaglandin I2 (prostacyclin) receptor (PTGIR) in migraine as a receptor, which acts in vasodilatation, we decided to study the changes of PTGIR expression in migraine patients in relation to a suitable control group.

Materials and Methods:

Extracted mRNA from lymphocytes of 50 cases and 50 controls was used to synthesize cDNA. Real-time polymerase chain reaction was performed, and the data were analyzed. Our results show that PTGIR mRNA expression in cases was significantly higher than the control group (P = 0.010).

Results:

In conclusion, mRNA expression of PTGIR in the blood of people with migraines could be considered as a biomarker.

Conclusion:

In addition, repression of PTGIR gene expression by methods such as using siRNA is probably suitable for therapy of migraine patients.

Cardioprotection of recombinant human MG53 protein in a porcine model of ischemia and reperfusion injury

Ischemic heart disease is a leading cause of death in human population and protection of myocardial infarction (MI) associated with ischemia-reperfusion (I/R) remains a challenge. MG53 is an essential component of the cell membrane repair machinery that protects injury to the myocardium. We investigated the therapeutic value of using the recombinant human MG53 (rhMG53) protein for treatment of MI. Using Langendorff perfusion of isolated mouse heart, we found that I/R caused injury to cardiomyocytes and release of endogenous MG53 into the extracellular solution. rhMG53 protein was applied to the perfusion solution concentrated at injury sites on cardiomyocytes to facilitate cardioprotection. With rodent models of I/R-induced MI, we established the in vivo dosing range for rhMG53 in cardioprotection. Using a porcine model of angioplasty-induced MI, the cardioprotective effect of rhMG53 was evaluated. Intravenous administration of rhMG53, either prior to or post-ischemia, reduced infarct size and troponin I release in the porcine model when examined at 24h post-reperfusion. Echocardiogram and histological analyses revealed that the protective effects of rhMG53 observed following acute MI led to long-term improvement in cardiac structure and function in the porcine model when examined at 4weeks post-operation. Our study supports the concept that rhMG53 could have potential therapeutic value for treatment of MI in human patients with ischemic heart diseases.

Time course change of COX2-PGI2/TXA2 following global cerebral ischemia reperfusion injury in rat hippocampus

BACKGROUND

Neuroinflammation plays pivotal roles in the progression of cerebral ischemia injury. Prostaglandins (PGs) as the major inflammatory mediators in the brain participate in the pathophysiological processes of cerebral ischemia injury. Cyclooxygenase-2 (COX2) is the rate-limiting enzyme of PGs, and thus it is necessary to characterize of the expression patterns of COX2 and its downstream products at the same time in a cerebral ischemia/reperfusion (I/R) model.

METHODS

The levels of prostacyclin (PGI2) and thromboxane (TXA2) and the expression of COX2 were detected in the rat hippocampus at different time points after reperfusion (30 min, 2 h, 6 h, 24 h, 48 h, 7 d, and 15 d).

RESULTS

The COX2 mRNA and protein expressions in hippocampus both remarkably increased at 30 min, and peaked at 7 d after global cerebral I/R compared with the sham-operated group. The level of PGI2 significantly increased at 2 h after reperfusion, with a peak at 48 h, but was still significantly higher than the sham-operated animals at 15 d. TXA2 level decreased at 30 min and 2 h after reperfusion, but significantly increased at 6 h and peaked at 48 h. PGI2/TXA2 ratio increased at 30 min after reperfusion, and peaked at 48 h compared with the sham-operated animals.

CONCLUSIONS

I/R injury significantly increased the COX2 expression, PGI2 and TXA2 levels, and the PGI2/TXA2 ratio in rat hippocampus in a time-dependent manner. As a consequence, the increased PGI2 level and PGI2/TXA2 ratio may represent a physiological mechanism to protect the brain against the neuronal damage produced by I/R injury.

Natakalim improves post-infarction left ventricular remodeling by restoring the coordinated balance between endothelial function and cardiac hypertrophy

Endothelial dysfunction can lead to congestive heart failure and the activation of endothelial ATP-sensitive potassium (K_ATP) channels may contribute to endothelial protection. Therefore, the present study was carried out to investigate the hypothesis that natakalim, a novel K_ATP channel opener, ameliorates post-infarction left ventricular remodeling and failure by correcting endothelial dysfunction. The effects of myocardial infarction were assessed 8 weeks following left anterior descending coronary artery occlusion in male Wistar rats. Depressed blood pressure, cardiac dysfunction, evidence of left ventricular remodeling and congestive heart failure were observed in the rats with myocardial infarction. Treatment with natakalim at daily oral doses of 1, 3 or 9 mg/kg/day for 8 weeks prevented these changes. Natakalim also prevented the progression to cardiac failure, which was demonstrated by the increase in right ventricular weight/body weight (RVW/BW) and relative lung weight, signs of cardiac dysfunction, as well as the overexpression of atrial and brain natriuretic peptide mRNAs. Our results also demonstrated that natakalim enhanced the downregulation of endothelium-derived nitric oxide, attenuated the upregulation of inducible nitric oxide synthase-derived nitric oxide (NO), inhibited the upregulated endothelin system and corrected the imbalance between prostacyclin and thromboxane A₂. Overall, our findings suggest that natakalim prevents post-infarction hypertrophy and cardiac failure by restoring the coordinated balance between endothelial function and cardiac hypertrophy.

Prostacyclin signaling boosts NADPH oxidase 4 in the endothelium promoting cytoprotection and angiogenesis

AIMS

Prostacyclin (PGI2) that is released from the vascular endothelium plays an important role in vasodilatation and thrombo-resistance, and it has long been suspected to protect cell survival. How it does so has never been clear. Recently, it has been shown that the NADPH oxidase 4 (Nox4) improves endothelial cell functions and promotes angiogenesis in vivo, but it was not known how to boost Nox4 therapeutically to exploit its protective functions in the vasculature. Here, we identified such a stimulus.

RESULTS

The selective and stable prostacyclin receptor (IP-R) agonist cicaprost increases the expression of Nox4 in human endothelial cells of several types, including endothelial progenitor cells. The elevation of cellular cyclic-AMP increased Nox4 expression and H2O2 production and prevented endothelial cell apoptosis. We delineate the intracellular signaling that promotes cytoprotection: Cicaprost acts via the IP-R/protein kinase A (PKA)/cyclic adenosine monophosphate (cAMP) response element binding (CREB) protein pathway. Importantly, the up-regulation of Nox4 by cicaprost also enhanced endothelial cell proliferation, migration, and angiogenesis, with all effects being substantially decreased by Nox4 gene silencing. Finally, cicaprost enhanced the growth of blood vessels into subcutaneous sponges implanted in mice, an effect that was also blocked by Nox4 gene silencing.

INNOVATION

The prostacyclin analogue cicaprost induces Nox4 via IP receptor-cAMP/PKA/CREB pathway. The activation of this pathway protects endothelial cells and enhances pro-angiogenic activity both in vitro and in vivo.

CONCLUSION

Prostacyclin promotes the up-regulation of Nox4 in endothelial cells, which opens up a novel strategy that protects and enhances endothelial cell functions in cardiovascular disease, such as repair after myocardial infarction or other ischemic conditions.