Platelet activating factor: the good and the bad in the ischemic/reperfused heart

Qilong capsule prevents myocardial ischemia/reperfusion injury by inhibiting platelet activation via the platelet CD36 signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Qilong capsule (QC) is developed from the traditional Chinese medicine formula Buyang Huanwu Decoction, which has been clinically used to invigorate Qi and promote blood circulation to eliminate blood stasis. Myocardial ischemia‒reperfusion injury (MIRI) can be attributed to Qi deficiency and blood stasis. However, the effects of QC on MIRI remain unclear.

AIM OF THE STUDY

This study aimed to investigate the protective effect and possible mechanism of QC on platelet function in MIRI rats.

MATERIALS AND METHODS

The left anterior descending artery of adult Sprague‒Dawley rats was ligated for 30 min and then reperfused for 120 min with or without QC treatment. Then, the whole blood viscosity, plasma viscosity, coagulation, platelet adhesion rate, platelet aggregation, and platelet release factors were evaluated. Platelet CD36 and its downstream signaling pathway-related proteins were detected by western blotting. Furthermore, the active components of QC and the molecular mechanism by which QC regulates platelet function were assessed via molecular docking, platelet aggregation tests in vitro and BLI analysis.

RESULTS

We found that QC significantly reduced the whole blood viscosity, plasma viscosity, platelet adhesion rate, and platelet aggregation induced by ADP or AA in rats with MIRI. The inhibition of platelet activation by QC was associated with reduced levels of β-TG, PF-4, P-selectin and PAF. Mechanistically, QC effectively attenuated the expression of platelet CD36 and thus inhibited the activation of Src, ERK5, and p38. The active components of QC apparently suppressed platelet aggregation in vitro and regulated the CD36 signaling pathway.

CONCLUSIONS

QC improves MIRI-induced hemorheological disorders, which might be partly attributed to the inhibition of platelet activation via CD36-mediated platelet signaling pathways.

Role of Platelet Activating Factor as a Mediator of Inflammatory Diseases and Preterm Delivery

Nearly 70% of preterm deliveries occur spontaneously, and the clinical pathways involved include preterm labor and preterm premature rupture of membranes. Prediction of preterm delivery is considered crucial due to the significant effects of preterm birth on health and the economy at both the personal and community levels. Although similar inflammatory processes occur in both term and preterm delivery, the premature activation of these processes or exaggerated inflammatory response triggered by infection or sterile factors leads to preterm delivery. Platelet activating factor (PAF) is a phosphoglycerylether lipid mediator of inflammation that is implicated in infections, cancers, and various chronic diseases and disorders including cardiovascular, renal, cerebrovascular, and central nervous system diseases. In gestational tissues, PAF mediates the inflammatory pathways that stimulate the effector mechanisms of labor, including myometrial contraction, cervical dilation, and fetal membrane rupture. Women with preterm labor and preterm premature rupture of membranes have increased levels of PAF in their amniotic fluid. In mice, the intrauterine or intraperitoneal administration of carbamyl PAF activates inflammation in gestational tissues, thereby eliciting preterm delivery. This review summarizes recent research on PAF as an important inflammatory mediator in preterm delivery and in other inflammatory disorders, highlighting its potential value for prediction, intervention, and prevention of these diseases.

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.

Platelets and Cardioprotection: The Role of Nitric Oxide and Carbon Oxide

Nitric oxide (NO) and carbon monoxide (CO) represent a pair of biologically active gases with an increasingly well-defined range of effects on circulating platelets. These gases interact with platelets and cells in the vessels and heart and exert fundamentally similar biological effects, albeit through different mechanisms and with some peculiarity. Within the cardiovascular system, for example, the gases are predominantly vasodilators and exert antiaggregatory effects, and are protective against damage in myocardial ischemia-reperfusion injury. Indeed, NO is an important vasodilator acting on vascular smooth muscle and is able to inhibit platelet activation. NO reacts with superoxide anion (O₂(^-•)) to form peroxynitrite (ONOO(^-)), a nitrosating agent capable of inducing oxidative/nitrative signaling and stress both at cardiovascular, platelet, and plasma levels. CO reduces platelet reactivity, therefore it is an anticoagulant, but it also has some cardioprotective and procoagulant properties. This review article summarizes current knowledge on the platelets and roles of gas mediators (NO, and CO) in cardioprotection. In particular, we aim to examine the link and interactions between platelets, NO, and CO and cardioprotective pathways.

Myocardial ischemia-reperfusion injury is probably due to the excessive production of mitochondrial ROS caused by the activation of 5-HT degradation system mediated by PAF receptor

AIM

Previously, we revealed a crucial role of 5-HT degradation system (5DS), consisting of 5-HT2A receptor (5-HT2AR), 5-HT synthases and monoamine oxidase A (MAO-A), in ischemia-reperfusion (IR)-caused organ injury. Whereas, platelet activating factor receptor (PAFR) also mediates myocardial ischemia-reperfusion injury (MIRI). Here, we try to clarify the relationship between 5DS and PAFR in mediating MIRI.

METHODS

H9c2 cell injury and rat MIRI were caused by hypoxia/reoxygenation (H/R) or PAF, and by ligating the left anterior descending coronary artery then untying, respectively. 5-HT_2AR and PAFR antagonists [sarpogrelate hydrochloride (SH) and BN52021], MAO-A, AKT, mTOR and 5-HT synthase inhibitors (clorgyline, perifosine, rapamycin and carbidopa), and gene-silencing PKCε were used in experiments RESULTS: The mitochondrial ROS production, respiratory chain damage, inflammation, apoptosis and myocardial infarction were significantly prevented by BN52021, SH and clorgyline in H/R and PAF-treated cells and in IR myocardium. BN52021 also significantly suppressed the upregulation of PAFR, 5-HT_2AR, 5-HT synthases and MAO-A expression (mRNA and protein), and Gα_q and PKCε (in plasmalemma) expression induced by H/R, PAF or IR; the effects of SH were similar to that of BN52021 except for no affecting the expression of PAFR and 5-HT_2AR. Gene-silencing PKCε suppressed H/R and PAF-induced upregulation of 5-HT synthases and MAO-A expression in cells; perifosine and rapamycin had not such effects; however, clorgyline suppressed H/R and PAF-induced phosphorylation of AKT and mTOR.

CONCLUSION

MIRI is probably due to PAFR-mediated 5-HT_2AR activation, which further activates PKCε-mediated 5-HT synthesis and degradation, leading to mitochondrial ROS production.

Critical role of PAFR/YAP1 positive feedback loop in cardiac fibrosis

Aberrant activation of cardiac fibroblasts is the main cause and character of cardiac fibrosis, and inhibition of cardiac fibrosis becomes a promising treatment for cardiac diseases. Platelet-activating factor (PAF) and Hippo pathway is recently recognized as key signaling mechanisms in cardiovascular diseases. In this study we explored the potential roles of PAF and Hippo signaling pathway in cardiac fibrosis. Myocardial infarction (MI) was induced in mice by left anterior descending artery ligation. After 28 days, the mice were sacrificed, and the hearts were collected for analyses. We showed that PAF receptor (PAFR) and yes-associated protein 1 (YAP1, a key effector in the Hippo pathway) were significantly increased in the heart of MI mice. Increased expression of PAFR and YAP1 was also observed in angiotensin II (Ang II)-treated mouse cardiac fibroblasts. In mouse cardiac fibroblasts, forced expression of YAP1 increased cell viability, resulted in collagen deposition and promoted fibroblast-myofibroblast transition. We showed that PAF induced fibrogenesis through activation of YAP1 and promoted its nuclear translocation via interacting with PAFR, while YAP1 promoted the expression of PAFR by binding to and activating transcription factor TEAD1. More importantly, silencing PAFR or YAP1 by shRNA, or using transgenic mice to induce the conditional deletion of YAP1 in cardiac fibroblasts, impeded cardiac fibrosis and improved cardiac function in MI mice. Taken together, this study elucidates the role and mechanisms of PAFR/YAP1 positive feedback loop in cardiac fibrosis, suggesting a potential role of this pathway as novel therapeutic targets in cardiac fibrosis.

Platelets in Myocardial Ischemia/Reperfusion Injury

Coronary artery disease, including myocardial infarction (MI), remains a leading cause of global mortality. Rapid reperfusion therapy is key to the improvement of patient outcome but contributes substantially to the final cardiac damage. This phenomenon is called "ischemia/reperfusion injury (IRI)." The underlying mechanisms of IRI are complex and not fully understood. Contributing cellular and molecular mechanisms involve the formation of microthrombi, alterations in ion concentrations, pH shifts, dysregulation of osmolality, and, importantly, inflammation. Beyond their known action as drivers of the development of coronary plaques leading to MI, platelets have been identified as important mediators in myocardial IRI. Circulating platelets are activated by the IRI-provoked damages in the vascular endothelium. This leads to platelet adherence to the reperfused endothelium, aggregation, and the formation of microthrombi. Furthermore, activated platelets release vasoconstrictive substances, act via surface molecules, and enhance leukocyte infiltration into post-IR tissue, that is, via platelet-leukocyte complexes. A better understanding of platelet contributions to myocardial IRI, including their interaction with other lesion-associated cells, is necessary to develop effective treatment strategies to prevent IRI and further improve the condition of the reperfused myocardium. In this review, we briefly summarize platelet properties that modulate IRI. We also describe the beneficial impacts of antiplatelet agents as well as their mechanisms of action in IRI beyond classic effects.

Cardiac gene activation varies between young and adult cats and in the presence of hypertrophic cardiomyopathy

Little is known about the difference of myocardial gene transcription in young and adult cats and how transcription is further modified in cats with hypertrophic cardiomyopathy (HCM) and with left atrial (LA) thrombus formation. We hypothesized that selected factors for coagulation, endothelial activation, inflammation, and remodelling are modified with age and are activated in the hearts of cats with HCM. Left atrial and ventricular (LV) samples from 12 cats with HCM (seven without (HCMwoAT] and five with LA thrombi [HCMwAT]), and six young (YC) and six adult (AC) control cats without cardiac disease were investigated for relative expression of the following genes using quantitative polymerase chain reaction: von Willebrand factor, a disintegrin and metalloproteinase with a thrombospondin type 1 motif member 13, platelet activating factor, E- and P-selectin, intercellular and vascular adhesion molecules-1, ß2-integrin, vascular endothelial growth factor, interleukin-6 (IL-6), monocyte chemoattractant protein-1 (MCP-1), heat shock protein-70, and myocyte-specific enhancer factor 2C. Significant differences in gene activation were found between YC and AC, and YC and cats with HCM. Compared to AC, MCP-1 and IL-6 were significantly higher in cats with HCM. The presence of an LA thrombus was associated with higher IL-6 expression. These results illustrate the relevance of age and/or lifestyle on gene expression in the feline heart. The gene transcription pattern found in AC hearts might predispose cats to their characteristic cardiac remodelling processes and thrombus formation if disease occurs. It further supports the involvement of inflammation, but not coagulation and endothelial activation, in HCM.

PAF Physiology in Target Organ Systems—A Deep Dive to Understand the PAF Mystery in Pathogenesis of Disease

The purpose of this literature review is to gain an overview of the role of platelet-activating factor (PAF) within each of the body systems and how it contributes to normal and pathophysiological states. The review showed that there are multiple functions of PAF that are common to several body systems; however, there is little evidence to explain why PAF has this affect across multiple systems. Interestingly, there seems to be conflicting research as to whether PAF is an overall protective or pathogenic pathway. Within this research, it was found that there are different pathways depending on the specific body system, as well as between body systems. However, one universal function reported in the literature is of PAF as a pro-inflammatory molecule. Overall, this review identified five major functions of PAF: vasoconstriction, increased inflammation, vascular remodeling, increased edema, and endothelial permeability.

Protective Role of Platelets in Myocardial Infarction and Ischemia/Reperfusion Injury

Thrombotic occlusion of the coronary artery is a key component in the pathogenesis of myocardial ischemia and myocardial infarction (MI). The standard therapy for ischemia is revascularization and restoration of blood flow to previously ischemic myocardium. Paradoxically, reperfusion may result in further tissue damage called ischemia/reperfusion injury (IRI). Platelets play a major role in the pathogenesis of MI and IRI, since they contribute to the thrombus and microthrombi formation, inflammation, release of immunomodulatory mediators, and vasoconstrictive molecules. Antiplatelet therapies have proven efficacy in the prevention of thrombosis and play a protective role in cardiac IRI. Beyond the deterioration effect of platelets in MI and IRI, in the 90s the first reports on a protective effect of molecules released from platelets during MI appeared. However, the role of platelets in cardioprotection is still poorly understood. This review describes the involvement of platelets in MI, IRI, and inflammation. It mainly focuses on the protective role of platelets in MI and IRI. Platelets are involved in cardioprotection based on platelet-releasing molecules and antiplatelet therapy, apart from antiaggregatory effects. Additionally, the use of platelet-derived microparticles as possible markers of MI, with and without comorbidities, and their role in cardioprotection are discussed. This review is aimed at illustrating the present knowledge on the role of platelets in MI and IRI, especially in a context of cardioprotection.

A novel Danshensu/tetramethylpyrazine protects against Myocardial Ischemia Reperfusion Injury in rats

A new Danshensu/tetramethylpyrazine derivative (ADTM) with cardio-protection effects such as antioxidant, arterial relaxation, pro-angiogenesis and antiplatelet activities. Platelet activating factor receptor (PAFR) plays a key role in myocardial ischemia reperfusion (MIR) injury. This study aims to investigate the protective role of ADTM in MIR injury and clarify the potential role of PAFR. We measured the effects of ADTM on MIR injury in rats in vivo and hypoxia re-oxygenation (HR) injury in neonatal rat ventricular myocytes (NRVMs) in vitro. The results show that ADTM can significantly improve the IR-induced decline in heart function as increasing EF and FS, and restore the decreased cardiac hemodynamic parameters (LVSP, ± dp/dt max) and increased the level of LVEDP, decrease the infarct size of damaged myocardium and lactate dehydrogenase (LDH) activity in serum. Additionally, ADTM inhibits cardiomyocytes apoptosis, caspase-3 activity, and inflammatory response as well as down-regulates the MIR-induced IL-1β and TNFα production. Next, PAFR expression was significantly down-regulated in cardiomyocytes of MIR model in vivo and in vitro after treated with ADTM compare to IR group. At the same time, ADTM and PAFR small interfering RNA (siRNA) could inhibit cardiomyocytes apoptosis and inflammation during HR, while PAF presents the opposite effect. Furthermore, the above effects of PAF in HR induced cardiomyocytes were reversed by co-treatment of ADTM. Our findings demonstrate for the first time that ADTM protects against MIR injury through inhibition of PAFR signaling, which provides a new treatment for MIR.

Circulating blood cells and extracellular vesicles in acute cardioprotection

During an ST-elevation myocardial infarction (STEMI), the myocardium undergoes a prolonged period of ischaemia. Reperfusion therapy is essential to minimize cardiac injury but can paradoxically cause further damage. Experimental procedures to limit ischaemia and reperfusion (IR) injury have tended to focus on the cardiomyocytes since they are crucial for cardiac function. However, there is increasing evidence that non-cardiomyocyte resident cells in the heart (as discussed in a separate review in this Spotlight series) as well as circulating cells and factors play important roles in this pathology. For example, erythrocytes, in addition to their main oxygen-ferrying role, can protect the heart from IR injury via the export of nitric oxide bioactivity. Platelets are well-known to be involved in haemostasis and thrombosis, but beyond these roles, they secrete numerous factors including sphingosine-1 phosphate (S1P), platelet activating factor, and cytokines that can all strongly influence the development of IR injury. This is particularly relevant given that most STEMI patients receive at least one type of platelet inhibitor. Moreover, there are large numbers of circulating vesicles in the blood, including microvesicles and exosomes, which can exert both beneficial and detrimental effects on IR injury. Some of these effects are mediated by the transfer of microRNA (miRNA) to the heart. Synthetic miRNA molecules may offer an alternative approach to limiting the response to IR injury. We discuss these and other circulating factors, focussing on potential therapeutic targets relevant to IR injury. Given the prevalence of comorbidities such as diabetes in the target patient population, their influence will also be discussed. This article is part of a Cardiovascular Research Spotlight Issue entitled 'Cardioprotection Beyond the Cardiomyocyte', and emerged as part of the discussions of the European Union (EU)-CARDIOPROTECTION Cooperation in Science and Technology (COST) Action, CA16225.

Mechanisms Involved in Cardioprotection Induced by Physical Exercise

Significance: Regular exercise training can reduce myocardial damage caused by acute ischemia/reperfusion (I/R). Exercise can reproduce the phenomenon of ischemic preconditioning, due to the capacity of brief periods of ischemia to reduce myocardial damage caused by acute I/R. In addition, exercise may also activate the multiple kinase cascade responsible for cardioprotection even in the absence of ischemia. Recent Advances: Animal and human studies highlighted the fact that, besides to reduce risk factors related to cardiovascular disease, the beneficial effects of exercise are also due to its ability to induce conditioning of the heart. Exercise behaves as a physiological stress that triggers beneficial adaptive cellular responses, inducing a protective phenotype in the heart. The factors contributing to the exercise-induced heart preconditioning include stimulation of the anti-radical defense system and nitric oxide production, opioids, myokines, and adenosine-5'-triphosphate (ATP) dependent potassium channels. They appear to be also involved in the protective effect exerted by exercise against cardiotoxicity related to chemotherapy. Critical Issues and Future Directions: Although several experimental evidences on the protective effect of exercise have been obtained, the mechanisms underlying this phenomenon have not yet been fully clarified. Further studies are warranted to define precise exercise prescriptions in patients at risk of myocardial infarction or undergoing chemotherapy.

Platelet Contributions to Myocardial Ischemia/Reperfusion Injury

Obstruction of a coronary artery causes ischemia of heart tissue leading to myocardial infarction. Prolonged oxygen deficiency provokes tissue necrosis, which can result in heart failure and death of the patient. Therefore, restoration of coronary blood flow (reperfusion of the ischemic area) by re-canalizing the affected vessel is essential for a better patient outcome. Paradoxically, sudden reperfusion also causes tissue injury, thereby increasing the initial ischemic damage despite restoration of blood flow (=ischemia/reperfusion injury, IRI). Myocardial IRI is a complex event that involves various harmful mechanisms (e.g., production of reactive oxygen species and local increase in calcium ions) as well as inflammatory cells and signals like chemokines and cytokines. An involvement of platelets in the inflammatory reaction associated with IRI was discovered several years ago, but the underlying mechanisms are not yet fully understood. This mini review focusses on platelet contributions to the intricate picture of myocardial IRI. We summarize how upregulation of platelet surface receptors and release of immunomodulatory mediators lead to aggravation of myocardial IRI and subsequent cardiac damage by different mechanisms such as recruitment and activation of immune cells or modification of the cardiac vascular endothelium. In addition, evidence for cardioprotective roles of distinct platelet factors during IRI will be discussed.

The coronary circulation in acute myocardial ischaemia/reperfusion injury: a target for cardioprotection

The coronary circulation is both culprit and victim of acute myocardial infarction. The rupture of an epicardial atherosclerotic plaque with superimposed thrombosis causes coronary occlusion, and this occlusion must be removed to induce reperfusion. However, ischaemia and reperfusion cause damage not only in cardiomyocytes but also in the coronary circulation, including microembolization of debris and release of soluble factors from the culprit lesion, impairment of endothelial integrity with subsequently increased permeability and oedema formation, platelet activation and leucocyte adherence, erythrocyte stasis, a shift from vasodilation to vasoconstriction, and ultimately structural damage to the capillaries with eventual no-reflow, microvascular obstruction (MVO), and intramyocardial haemorrhage (IMH). Therefore, the coronary circulation is a valid target for cardioprotection, beyond protection of the cardiomyocyte. Virtually all of the above deleterious endpoints have been demonstrated to be favourably influenced by one or the other mechanical or pharmacological cardioprotective intervention. However, no-reflow is still a serious complication of reperfused myocardial infarction and carries, independently from infarct size, an unfavourable prognosis. MVO and IMH can be diagnosed by modern imaging technologies, but still await an effective therapy. The current review provides an overview of strategies to protect the coronary circulation from acute myocardial ischaemia/reperfusion injury. This article is part of a Cardiovascular Research Spotlight Issue entitled 'Cardioprotection Beyond the Cardiomyocyte', and emerged as part of the discussions of the European Union (EU)-CARDIOPROTECTION Cooperation in Science and Technology (COST) Action, CA16225.

α-Cyclodextrin and α-Cyclodextrin Polymers as Oxygen Nanocarriers to Limit Hypoxia/Reoxygenation Injury: Implications from an In Vitro Model

The incidence of heart failure (HF) is increasing worldwide and myocardial infarction (MI), which follows ischemia and reperfusion (I/R), is often at the basis of HF development. Nanocarriers are interesting particles for their potential application in cardiovascular disease. Impaired drug delivery in ischemic disease is challenging. Cyclodextrin nanosponges (NS) can be considered innovative tools for improving oxygen delivery in a controlled manner. This study has developed new α-cyclodextrin-based formulations as oxygen nanocarriers such as native α-cyclodextrin (α-CD), branched α-cyclodextrin polymer (α-CD POLY), and α-cyclodextrin nanosponges (α-CD NS). The three different α-CD-based formulations were tested at 0.2, 2, and 20 µg/mL to ascertain their capability to reduce cell mortality during hypoxia and reoxygenation (H/R) in vitro protocols. H9c2, a cardiomyoblast cell line, was exposed to normoxia (20% oxygen) or hypoxia (5% CO₂ and 95% N₂). The different formulations, applied before hypoxia, induced a significant reduction in cell mortality (in a range of 15% to 30%) when compared to samples devoid of oxygen. Moreover, their application at the beginning of reoxygenation induced a considerable reduction in cell death (12% to 20%). α-CD NS showed a marked efficacy in controlled oxygenation, which suggests an interesting potential for future medical application of polymer systems for MI treatment.

Platelets, diabetes and myocardial ischemia/reperfusion injury

Mechanisms underlying the pathogenesis of ischemia/reperfusion injury are particularly complex, multifactorial and highly interconnected. A complex and entangled interaction is also emerging between platelet function, antiplatelet drugs, coronary diseases and ischemia/reperfusion injury, especially in diabetic conditions. Here we briefly summarize features of antiplatelet therapy in type 2 diabetes (T2DM). We also treat the influence of T2DM on ischemia/reperfusion injury and how anti-platelet therapies affect post-ischemic myocardial damage through pleiotropic properties not related to their anti-aggregating effects. miRNA-based signature associated with T2DM and its cardiovascular disease complications are also briefly considered. Influence of anti-platelet therapies and different effects of healthy and diabetic platelets on ischemia/reperfusion injury need to be further clarified in order to enhance patient benefits from antiplatelet therapy and revascularization. Here we provide insight on the difficulty to reduce the cardiovascular risk in diabetic patients and report novel information on the cardioprotective role of widely used anti-aggregant drugs.

Protein S-nitrosylation in preconditioning and postconditioning

The coronary artery disease is a leading cause of death and morbidity worldwide. This disease has a complex pathophysiology that includes multiple mechanisms. Among these is the oxidative/nitrosative stress. Paradoxically, oxidative/nitrosative signaling plays a major role in cardioprotection against ischemia/reperfusion injury. In this context, the gas transmitter nitric oxide may act through several mechanisms, such as guanylyl cyclase activation and via S-nitrosylation of proteins. The latter is a covalent modification of a protein cysteine thiol by a nitric oxide-group that generates an S-nitrosothiol. Here, we report data showing that nitric oxide and S-nitrosylation of proteins play a pivotal role not only in preconditioning but also in postconditioning cardioprotection.

Signalling pathways and mechanisms of protection in pre- and postconditioning: historical perspective and lessons for the future

Ischaemic pre- and postconditioning are potent cardioprotective interventions that spare ischaemic myocardium and decrease infarct size after periods of myocardial ischaemia/reperfusion. They are dependent on complex signalling pathways involving ligands released from ischaemic myocardium, G-protein-linked receptors, membrane growth factor receptors, phospholipids, signalling kinases, NO, PKC and PKG, mitochondrial ATP-sensitive potassium channels, reactive oxygen species, TNF-α and sphingosine-1-phosphate. The final effector is probably the mitochondrial permeability transition pore and the signalling produces protection by preventing pore formation. Many investigators have worked to produce a roadmap of this signalling with the hope that it would reveal where one could intervene to therapeutically protect patients with acute myocardial infarction whose hearts are being reperfused. However, attempts to date to show efficacy of such an intervention in large clinical trials have been unsuccessful. Reasons for this inability to translate successes in the experimental laboratory to the clinical arena are evaluated in this review. It is suggested that all patients with acute coronary syndromes currently presenting to the hospital and being treated with platelet P2Y12 receptor antagonists, the current standard of care, are indeed already benefiting from protection from the conditioning pathways outlined earlier. If that proves to be the case, then future attempts to further decrease infarction will have to rely on interventions which protect by a different mechanism.

Redox signalling and cardioprotection: translatability and mechanism

The morbidity and mortality from coronary artery disease (CAD) remain significant worldwide. The treatment for acute myocardial infarction has improved over the past decades, including early reperfusion of culprit coronary arteries. Although it is mandatory to reperfuse the ischaemic territory as soon as possible, paradoxically this leads to additional myocardial injury, namely ischaemia/reperfusion (I/R) injury, in which redox stress plays a pivotal role and for which no effective therapy is currently available. In this review, we report evidence that the redox environment plays a pivotal role not only in I/R injury but also in cardioprotection. In fact, cardioprotective strategies, such as pre- and post-conditioning, result in a robust reduction in infarct size in animals and the role of redox signalling is of paramount importance in these conditioning strategies. Nitrosative signalling and cysteine redox modifications, such as S-nitrosation/S-nitrosylation, are also emerging as very important mechanisms in conditioning cardioprotection. The reasons for the switch from protective oxidative/nitrosative signalling to deleterious oxidative/nitrosative/nitrative stress are not fully understood. The complex regulation of this switch is, at least in part, responsible for the diminished or lack of cardioprotection induced by conditioning protocols observed in ageing animals and with co-morbidities as well as in humans. Therefore, it is important to understand at a mechanistic level the reasons for these differences before proposing a safe and useful transition of ischaemic or pharmacological conditioning. Indeed, more mechanistic novel therapeutic strategies are required to protect the heart from I/R injury and to improve clinical outcomes in patients with CAD.

Systemic protection through remote ischemic preconditioning is spread by platelet-dependent signaling in mice

Remote ischemic preconditioning (RIPC), the repetitive transient mechanical obstruction of vessels at a limb remote to the operative site, is a novel strategy to mitigate distant organ injury associated with surgery. In the clinic, RIPC has demonstrated efficacy in protecting various organs against ischemia reperfusion (IR), but a common mechanism underlying the systemic protection has not been identified. Here, we reasoned that protection may rely on adaptive physiological responses toward local stress, as is incurred through RIPC. Standardized mouse models of partial hepatic IR and of RIPC to the femoral vascular bundle were applied. The roles of platelets, peripheral serotonin, and circulating vascular endothelial growth factor (Vegf) were studied in thrombocytopenic mice, Tph1(-) (/) (-) mice, and through neutralizing antibodies, respectively. Models of interleukin-10 (Il10) and matrix metalloproteinase 8 (Mmp8) deficiency were used to assess downstream effectors of organ protection. The protection against hepatic IR through RIPC was dependent on platelet-derived serotonin. Downstream of serotonin, systemic protection was spread through up-regulation of circulating Vegf. Both RIPC and serotonin-Vegf induced differential gene expression in target organs, with Il10 and Mmp8 displaying consistent up-regulation across all organs investigated. Concerted inhibition of both molecules abolished the protective effects of RIPC. RIPC was able to mitigate pancreatitis, indicating that it can protect beyond ischemic insults.

CONCLUSIONS

We have identified a platelet-serotonin-Vegf-Il10/Mmp8 axis that mediates the protective effects of RIPC. The systemic action, the conservation of RIPC effects among mice and humans, and the protection beyond ischemic insults suggest that the platelet-dependent axis has evolved as a preemptive response to local stress, priming the body against impending harm.

Nitroglycerine and sodium trioxodinitrate: from the discovery to the preconditioning effect

The history began in the 19th century with Ascanio Sobrero (1812-1888), the discoverer of glycerol trinitrate (nitroglycerine, NTG), and with Angelo Angeli (1864-1931), the discoverer of sodium trioxodinitrate (Angeli's salt). It is likely that Angeli and Sobrero never met, but their two histories will join each other more than a century later. In fact, it has been discovered that both NTG and Angeli's salt are able to induce a preconditioning effect. As NTG has a long history as an antianginal drug its newly discovered property as a preconditioning agent has also been tested in humans. Angeli's salt properties as a preconditioning and inotropic agent have only been tested in animals so far.

Enhanced NO signaling in patients with Takotsubo cardiomyopathy: short-term pain, long-term gain?

PURPOSE

Little information is available concerning the mechanism(s) underlying Takotsubo cardiomyopathy (TTC), other than evidence of associated catecholamine secretion. Given the known effects of catecholamines on endothelial function, we tested the hypothesis that TTC might also be associated with impairment of nitric oxide (NO) signaling. We now report an evaluation of NO signaling in TTC patients (vs. aged-matched controls) in relation to (a) severity of the acute attack and (b) rate of recovery.

METHODS

In 56 patients with TTC, we utilized (1) platelet responsiveness to NO and (2) plasma levels of asymmetric dimethylarginine (ADMA) as indices of integrity of the cyclic guanosine monophosphate (cGMP) pathway. Additionally, endothelial progenitor cell (EPC) counts, which are partially NO-dependent, were evaluated. These parameters were measured at the time of diagnosis and 3 months thereafter, and compared with an aging female cohort (n = 81).

RESULTS

The data suggested that both NO generation and effect were accentuated in TTC patients: ADMA concentrations were lower (p = 0.003), and responsiveness to NO substantially greater (p = 0.0001) than in controls both acutely and after 3 months. Markers of severity of TTC attacks directly correlated with NO responsiveness, while extent of recovery at 3 months varied inversely with ADMA concentrations.

CONCLUSION

TTC is associated with intensification of NO signaling relative to that in normal age-matched females. Our data are consistent with this intensified signal's potential contribution to the extent of initial myocardial injury, but conversely to accelerated recovery.

Platelet-activating factor downregulates the expression of liver X receptor-α and its target genes in human neutrophils

Liver X receptors (LXRs) are ligand-activated members of the nuclear receptor superfamily that regulate the expression of genes involved in lipid metabolism and inflammation, although their role in inflammation and immunity is less well known. It has been reported that oxysterols/LXRs may act as anti-inflammatory molecules, although opposite actions have also been reported. In this study, we investigated the effect of platelet-activating factor (PAF), a proinflammatory molecule, on LXRα signalling in human neutrophils. We found that PAF exerted an inhibitory effect on mRNA expression of TO901317-induced LXRα, ATP-binding cassette transporter A1, ATP-binding cassette transporter G1, and sterol response element binding protein 1c. This negative action was mediated by the PAF receptor, and was dependent on the release of reactive oxygen species elicited by PAF, as it was enhanced by pro-oxidant treatment and reversed by antioxidants. Current data also support the idea that PAF induces phosphorylation of the LXRα molecule in an extracellular signal-regulated kinase 1/2-mediated fashion. These results suggest that a possible mechanism by which PAF exerts its proinflammatory effect is through the downregulation of LXRα and its related genes, which supports the notion that LXRα ligands exert a modulatory role in the neutrophil-mediated inflammatory response.

Platelet activating factor in heart failure: potential role in disease progression and novel target for therapy

Heart failure (HF) is a complex syndrome with cardiac, renal, neurohormonal and sympathetic nervous system's manifestations, the pathogenesis of which among others is connected to inflammation. PAF has local and systemic effects pertaining to HF progression since it causes a negative inotropic effect, it induces arrhythmias, it induces apoptosis and it is involved in inflammation and atherosclerosis. In the present review the role of PAF in HF will be thoroughly presented along with the relevant data on PAF enzymes and the potential role of PAF metabolic circuit as a novel pharmacological target.

Cooperative role of endogenous leucotrienes and platelet-activating factor in ischaemia-reperfusion-mediated tissue injury

Insufficient oxygen delivery to organs leads to tissue dysfunction and cell death. Reperfusion, although vital to organ survival, initiates an inflammatory response that may both aggravate local tissue injury and elicit remote organ damage. Polymorphonuclear neutrophil (PMN) trafficking to remote organs following ischaemia/reperfusion (I/R) is associated with the release of lipid mediators, including leucotriene (LT) B₄, cysteinyl-LTs (CysLTs) and platelet-activating factor (PAF). Yet, their potentially cooperative role in regulating I/R-mediated inflammation has not been thoroughly assessed. The present study aimed to determine the cooperative role of lipid mediators in regulating PMN migration, tissue oedema and injury using selective receptor antagonists in selected models of I/R and dermal inflammation. Our results show that rabbits, pre-treated orally with BIIL 284 and/or WEB 2086 and MK-0571, were protected from remote tissue injury following I/R or dermal inflammation in an additive or synergistic manner when the animals were pre-treated with two drugs concomitantly. The functional selectivity of the antagonists towards their respective agonists was assessed in vitro, showing that neither BIIL 284 nor WEB 2086 prevented the inflammatory response to IL-8, C5a and zymosan-activated plasma stimulation. However, these agonists elicited LTB₄ biosynthesis in isolated rabbit PMNs. Similarly, a cardioprotective effect of PAF and LTB₄ receptor antagonists was shown following myocardial I/R in mice. Taken together, these results underscore the intricate involvement of LTB₄ and PAF in each other’s responses and provide further evidence that targeting both LTs and PAF receptors provides a much stronger anti-inflammatory effect, regulating PMN migration and oedema formation.

Evaluation of the in vitro anti-atherogenic properties of lipid fractions of olive pomace, olive pomace enriched fish feed and gilthead sea bream (Sparus aurata) fed with olive pomace enriched fish feed

Given the pivotal role of Platelet-Activating-Factor (PAF) in atherosclerosis and the cardio-protective role of PAF-inhibitors derived from olive pomace, the inclusion of olive pomace in fish feed has been studied for gilthead sea bream (Sparus aurata). The aim of the current research was to elucidate the anti-atherogenic properties of specific HPLC lipid fractions obtained from olive pomace, olive pomace enriched fish feed and fish fed with the olive pomace enriched fish feed, by evaluating their in vitro biological activity against washed rabbit platelets. This in vitro study underlines that olive pomace inclusion in fish feed improves the nutritional value of both fish feed and fish possibly by enriching the marine lipid profile of gilthead sea bream (Sparus aurata) with specific bioactive lipid compounds of plant origin.

Platelet activating factors in depression and coronary artery disease: a potential biomarker related to inflammatory mechanisms and neurodegeneration

The persistence of a depressive episode in coronary artery disease (CAD) patients not only heightens the risk of acute ischemic events, but it is also associated with accelerated cognitive decline. Antidepressant interventions for depression in CAD have only modest effects and novel approaches are limited by a poor understanding of etiological mechanisms. This review proposes that the platelet activating factor (PAF) family of lipids might be associated with the persistence of a depressive episode and related neurodegenerative pathology in CAD due to their association with leading etiological mechanisms for depression in CAD such as inflammation, oxidative and nitrosative stress, vascular endothelial dysfunction, and platelet reactivity. The evidence implicating PAFs in CAD, vascular pathology, and neurodegenerative processes is also presented. We also propose future directions for the investigation of PAFs as mediators of persistent depression. In summary, PAFs are implicated in leading mechanisms associated with depression in CAD. PAFs may therefore be associated with the persistence of depression in CAD and related to neurodegenerative and cognitive sequelae.

Catestatin reduces myocardial ischaemia/reperfusion injury: involvement of PI3K/Akt, PKCs, mitochondrial KATP channels and ROS signalling

Catestatin (CST) limits myocardial ischaemia/reperfusion (I/R) injury with unknown mechanisms. Clearly phosphoinositide-3-kinase (PI3K), protein kinase C (PKC) isoforms, including intra-mitochondrial PKCε, mitochondrial KATP (mitoKATP) channels and subsequent reactive oxygen species (ROS)-signalling play important roles in postconditioning cardioprotection, preventing mitochondrial permeability transition pore (mPTP) opening. Therefore, we studied the role of these extra- and intra-mitochondrial factors in CST-induced protection. Isolated rat hearts and H9c2 cells underwent I/R and oxidative stress, respectively. In isolated hearts CST (75nM, CST-Post) given in early-reperfusion significantly reduced infarct size, limited post-ischaemic contracture, and improved recovery of developed left ventricular pressure. PI3K inhibitor, LY-294002 (LY), large spectrum PKC inhibitor, Chelerythrine (CHE), specific PKCε inhibitor (εV1-2), mitoKATP channel blocker, 5-Hydroxydecanoate (5HD) or ROS scavenger, 2-mercaptopropionylglycine (MPG) abolished the infarct-sparing effect of CST. Notably the CST-induced contracture limitation was maintained during co-infusion of 5HD, MPG or εV1-2, but it was lost during co-infusion of LY or CHE. In H9c2 cells challenged with H2O2, mitochondrial depolarization (an index of mPTP opening studied with JC1-probe) was drastically limited by CST (75nM). Our results suggest that the protective signalling pathway activated by CST includes mitoKATP channels, ROS signalling and prevention of mPTP opening, with a central role for upstream PI3K/Akt and PKCs. In fact, all inhibitors completely abolished CST-infarct-sparing effect. Since CST-anti-contracture effect cannot be explained by intra-mitochondrial mechanisms (PKCε activation and mitoKATP channel opening) or ROS signalling, it is proposed that these downstream signals are part of a reverberant loop which re-activates upstream PKCs, which therefore play a pivotal role in CST-induced protection.

Baseline and 6-Week follow-up levels of PAF and activity of its metabolic enzymes in patients with heart failure and healthy volunteers--a pilot study

This study aimed at evaluating the changes in platelet-activating factor (PAF) and its metabolic enzymes over a 6-week follow-up period in patients with newly diagnosed heart failure ([HF] n = 12) compared with age-, sex-, and BMI-matched apparently healthy volunteers (n = 10). The PAF, its key biosynthetic enzymes (lyso-PAF acetyltransferase [lyso-PAF-AT] and dithiothreitol [DTT]-insensitive CDP choline: 1-alkyl-2-acetyl-sn-glycerol cholinephosphotransferase [PAF-CPT]), and its catabolic isoenzymes (PAF-acetylhydrolase [PAF-AH] and lipoprotein-associated phospholipase A2 [Lp-PLA2]) were measured in serum and leukocytes of participants. At baseline, patients with HF had lower median activities of lyso-PAF-AT (P < .001) and PAF-CPT (P = .07) in parallel with PAF levels (P = .05) and higher activities of PAF-AH (P = .02) and Lp-PLA2 (P < .001) than controls. At follow-up, PAF-CPT and PAF levels marginally increased (P = .1), lyso-PAF-AT (P < .001) remained downregulated, while PAF-AH (P = .004) and Lp-PLA2 (P < .001) remained elevated compared with the controls. Newly diagnosed patients with HF under drug treatment have an affected profile of PAF biosynthetic enzymes and especially lyso-PAF-AT.

High-density lipoprotein and atherosclerosis: the role of antioxidant activity

Levels of high-density lipoprotein (HDL) cholesterol are generally inversely associated with the risk for the development of atherosclerosis. The mechanism by which HDL imparts protection from the initiation and progression of occlusive vascular disease is complex and multifactorial. The major anti-atherosclerotic effect of HDL is felt to be reverse cholesterol transport. HDL has been demonstrated to scavenge cholesterol from the peripheral vasculature with transport to the liver, where is it excreted in the biliary system. However, HDL exhibits multiple other physiologic effects that may play a role in the reduced risk for atherosclerosis. HDL has been demonstrated to exhibit beneficial effects on platelet function, endothelial function, coagulation parameters, inflammation, and interactions with triglyceride-rich lipoproteins. Increasing amounts of clinical and experimental data have shown that HDL cholesterol has significant antioxidant effect that may significantly contribute to protection from atherosclerosis.

A review of experimental evidence linking neurotoxic organophosphorus compounds and inflammation

Organophosphorus (OP) nerve agents and pesticides inhibit acetylcholinesterase (AChE), and this is thought to be a primary mechanism mediating the neurotoxicity of these compounds. However, a number of observations suggest that mechanisms other than or in addition to AChE inhibition contribute to OP neurotoxicity. There is significant experimental evidence that acute OP intoxication elicits a robust inflammatory response, and emerging evidence suggests that chronic repeated low-level OP exposure also upregulates inflammatory mediators. A critical question that is just beginning to be addressed experimentally is the pathophysiologic relevance of inflammation in either acute or chronic OP intoxication. The goal of this article is to provide a brief review of the current status of our knowledge linking inflammation to OP intoxication, and to discuss the implications of these findings in the context of therapeutic and diagnostic approaches to OP neurotoxicity.

Platelet-activating factor stimulates sodium-hydrogen exchange in ventricular myocytes

Sodium-hydrogen exchanger (NHE), the principal sarcolemmal acid extruder in ventricular myocytes, is stimulated by a variety of autocrine/paracrine factors and contributes to myocardial injury and arrhythmias during ischemia-reperfusion. Platelet-activating factor (PAF; 1-o-alkyl-2-acetyl-sn-glycero-3-phosphocholine) is a potent proinflammatory phospholipid that is released in the heart in response to oxidative stress and promotes myocardial ischemia-reperfusion injury. PAF stimulates NHE in neutrophils and platelets, but its effect on cardiac NHE (NHE1) is unresolved. We utilized quiescent guinea pig ventricular myocytes bathed in bicarbonate-free solutions and epifluorescence to measure intracellular pH (pH(i)). Methylcarbamyl-PAF (C-PAF; 200 nM), a metabolically stable analog of PAF, significantly increased steady-state pH(i). The alkalosis was completely blocked by the NHE inhibitor, cariporide, and by sodium-free bathing solutions, indicating it was mediated by NHE activation. C-PAF also significantly increased the rate of acid extrusion induced by intracellular acidosis. The ability of C-PAF to increase steady-state pH(i) was completely blocked by the PAF receptor inhibitor WEB 2086 (10 μM), indicating the PAF receptor is required. A MEK inhibitor (PD98059; 25 μM) also completely blocked the rise in pH(i) induced by C-PAF, suggesting participation of the MAP kinase signaling cascade downstream of the PAF receptor. Inhibition of PKC with GF109203X (1 μM) and chelerythrine (2 μM) did not significantly affect the alkalosis induced by C-PAF. In summary, these results provide evidence that PAF stimulates cardiac NHE1, the effect occurs via the PAF receptor, and signal relay requires participation of the MAP kinase cascade.