Phosphorylation of vasodilator-stimulated phosphoprotein prevents platelet-neutrophil complex formation and dampens myocardial ischemia-reperfusion injury

Targeting Gαi2 in neutrophils protects from myocardial ischemia reperfusion injury

Neutrophils are not only involved in immune defense against infection but also contribute to the exacerbation of tissue damage after ischemia and reperfusion. We have previously shown that genetic ablation of regulatory Gαi proteins in mice has both protective and deleterious effects on myocardial ischemia reperfusion injury (mIRI), depending on which isoform is deleted. To deepen and analyze these findings in more detail the contribution of Gαi2 proteins in resident cardiac vs circulating blood cells for mIRI was first studied in bone marrow chimeras. In fact, the absence of Gαi2 in all blood cells reduced the extent of mIRI (22,9% infarct size of area at risk (AAR) Gnai2-/- → wt vs 44.0% wt → wt; p < 0.001) whereas the absence of Gαi2 in non-hematopoietic cells increased the infarct damage (66.5% wt → Gnai2-/- vs 44.0% wt → wt; p < 0.001). Previously we have reported the impact of platelet Gαi2 for mIRI. Here, we show that infarct size was substantially reduced when Gαi2 signaling was either genetically ablated in neutrophils/macrophages using LysM-driven Cre recombinase (AAR: 17.9% Gnai2fl/fl LysM-Cre+/tg vs 42.0% Gnai2fl/fl; p < 0.01) or selectively blocked with specific antibodies directed against Gαi2 (AAR: 19.0% (anti-Gαi2) vs 49.0% (IgG); p < 0.001). In addition, the number of platelet-neutrophil complexes (PNCs) in the infarcted area were reduced in both, genetically modified (PNCs: 18 (Gnai2fl/fl; LysM-Cre+/tg) vs 31 (Gnai2fl/fl); p < 0.001) and in anti-Gαi2 antibody-treated (PNCs: 9 (anti-Gαi2) vs 33 (IgG); p < 0.001) mice. Of note, significant infarct-limiting effects were achieved with a single anti-Gαi2 antibody challenge immediately prior to vessel reperfusion without affecting bleeding time, heart rate or cellular distribution of neutrophils. Finally, anti-Gαi2 antibody treatment also inhibited transendothelial migration of human neutrophils (25,885 (IgG) vs 13,225 (anti-Gαi2) neutrophils; p < 0.001), collectively suggesting that a therapeutic concept of functional Gαi2 inhibition during thrombolysis and reperfusion in patients with myocardial infarction should be further considered.

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.

Cardiovascular Functions of Ena/VASP Proteins: Past, Present and Beyond

Actin binding proteins are of crucial importance for the spatiotemporal regulation of actin cytoskeletal dynamics, thereby mediating a tremendous range of cellular processes. Since their initial discovery more than 30 years ago, the enabled/vasodilator-stimulated phosphoprotein (Ena/VASP) family has evolved as one of the most fascinating and versatile family of actin regulating proteins. The proteins directly enhance actin filament assembly, but they also organize higher order actin networks and link kinase signaling pathways to actin filament assembly. Thereby, Ena/VASP proteins regulate dynamic cellular processes ranging from membrane protrusions and trafficking, and cell-cell and cell-matrix adhesions, to the generation of mechanical tension and contractile force. Important insights have been gained into the physiological functions of Ena/VASP proteins in platelets, leukocytes, endothelial cells, smooth muscle cells and cardiomyocytes. In this review, we summarize the unique and redundant functions of Ena/VASP proteins in cardiovascular cells and discuss the underlying molecular mechanisms.

The NO-cGMP-PKG Axis in HFpEF: From Pathological Mechanisms to Potential Therapies

Heart failure with preserved ejection fraction (HFpEF) accounts for almost half of all heart failure (HF) cases worldwide. Unfortunately, its incidence is expected to continue to rise, and effective therapy to improve clinical outcomes is lacking. Numerous efforts currently directed towards the pathophysiology of human HFpEF are uncovering signal transduction pathways and novel therapeutic targets. The nitric oxide-cyclic guanosine phosphate-protein kinase G (NO-cGMP-PKG) axis has been described as an important regulator of cardiac function. Suppression of the NO-cGMP-PKG signalling pathway is involved in the progression of HFpEF. Therefore, the NO-cGMP-PKG signalling pathway is a potential therapeutic target for HFpEF. In this review, we aim to explore the mechanism of NO-cGMP-PKG in the progression of HFpEF and to summarize potential therapeutic drugs that target this signalling pathway.

Cardiac repair after myocardial infarction: A two-sided role of inflammation-mediated

Myocardial infarction is the leading cause of death and disability worldwide, and the development of new treatments can help reduce the size of myocardial infarction and prevent adverse cardiovascular events. Cardiac repair after myocardial infarction can effectively remove necrotic tissue, induce neovascularization, and ultimately replace granulation tissue. Cardiac inflammation is the primary determinant of whether beneficial cardiac repair occurs after myocardial infarction. Immune cells mediate inflammatory responses and play a dual role in injury and protection during cardiac repair. After myocardial infarction, genetic ablation or blocking of anti-inflammatory pathways is often harmful. However, enhancing endogenous anti-inflammatory pathways or blocking endogenous pro-inflammatory pathways may improve cardiac repair after myocardial infarction. A deficiency of neutrophils or monocytes does not improve overall cardiac function after myocardial infarction but worsens it and aggravates cardiac fibrosis. Several factors are critical in regulating inflammatory genes and immune cells' phenotypes, including DNA methylation, histone modifications, and non-coding RNAs. Therefore, strict control and timely suppression of the inflammatory response, finding a balance between inflammatory cells, preventing excessive tissue degradation, and avoiding infarct expansion can effectively reduce the occurrence of adverse cardiovascular events after myocardial infarction. This article reviews the involvement of neutrophils, monocytes, macrophages, and regulatory T cells in cardiac repair after myocardial infarction. After myocardial infarction, neutrophils are the first to be recruited to the damaged site to engulf necrotic cell debris and secrete chemokines that enhance monocyte recruitment. Monocytes then infiltrate the infarct site and differentiate into macrophages and they release proteases and cytokines that are harmful to surviving myocardial cells in the pre-infarct period. As time progresses, apoptotic neutrophils are cleared, the recruitment of anti-inflammatory monocyte subsets, the polarization of macrophages toward the repair phenotype, and infiltration of regulatory T cells, which secrete anti-inflammatory factors that stimulate angiogenesis and granulation tissue formation for cardiac repair. We also explored how epigenetic modifications regulate the phenotype of inflammatory genes and immune cells to promote cardiac repair after myocardial infarction. This paper also elucidates the roles of alarmin S100A8/A9, secreted frizzled-related protein 1, and podoplanin in the inflammatory response and cardiac repair after myocardial infarction.

Platelets and the Cybernetic Regulation of Ischemic Inflammatory Responses through PNC Formation Regulated by Extracellular Nucleotide Metabolism and Signaling

Ischemic events are associated with severe inflammation and are here referred to as ischemic inflammatory response (IIR). Recent studies identified the formation of platelet–neutrophil complexes (PNC) as key players in IIR. We investigated the role of extracellular platelet nucleotide signaling in the context of IIR and defined a cybernetic circle, including description of feedback loops. Cybernetic circles seek to integrate different levels of information to understand how biological systems function. Our study specifies the components of the cybernetic system of platelets in IIR and describes the theoretical progression of IIR passing the cybernetic cycle with positive and negative feedback loops based on nucleotide-dependent signaling and functional regulation. The cybernetic components and feedback loops were explored by cytometry, immunohistological staining, functional blocking antibodies, and ADP/ATP measurements. Using several ex vivo and in vivo approaches we confirmed cybernetic parameters, such as controller, sensor, and effector (VASP phosphorylation, P2Y₁₂, ADORAs and GPIIb/IIIa activity), as well as set points (ADP, adenosine) and interfering control and disturbance variables (ischemia). We demonstrate the impact of the regulated platelet–neutrophil complex (PNC) formation in blood and the resulting damage to the affected inflamed tissue. Taken together, extracellular nucleotide signaling, PNC formation, and tissue damage in IIR can be integrated in a controlled cybernetic circle of platelet function, as introduced through this study.

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.

Elevated platelet-leukocyte complexes are associated with, but dispensable for myocardial ischemia-reperfusion injury

AIMS

P-selectin is an activatable adhesion molecule on platelets promoting platelet aggregation, and platelet-leukocyte complex (PLC) formation. Increased numbers of PLC are circulating in the blood of patients shortly after acute myocardial infarction and predict adverse outcomes. These correlations led to speculations about whether PLC may represent novel therapeutic targets. We therefore set out to elucidate the pathomechanistic relevance of PLC in myocardial ischemia and reperfusion injury.

METHODS AND RESULTS

By generating P-selectin deficient bone marrow chimeric mice, the post-myocardial infarction surge in PLC numbers in blood was prevented. Yet, intravital microscopy, flow cytometry and immunohistochemical staining, echocardiography, and gene expression profiling showed unequivocally that leukocyte adhesion to the vessel wall, leukocyte infiltration, and myocardial damage post-infarction were not altered in response to the lack in PLC.

CONCLUSION

We conclude that myocardial infarction associated sterile inflammation triggers PLC formation, reminiscent of conserved immunothrombotic responses, but without PLC influencing myocardial ischemia and reperfusion injury in return. Our experimental data do not support a therapeutic concept of selectively targeting PLC formation in myocardial infarction.

Cellular mechanisms and pathways in myocardial reperfusion injury

Despite the progress of cardiovascular medicine, ischemia-reperfusion injury can contribute to increased mortality and prolonged hospitalization after myocardial infarction. Ischemia-reperfusion injury pathophysiology encompasses many cells including cardiomyocytes, fibroblasts, mesenchymal stromal cells, vascular endothelial and smooth muscle cells, platelets, polymorphonuclear cells, macrophages, and T lymphocytes. However, specific mechanisms for all contributing cells and molecular pathways are still under investigation. What is definitely known is that endothelial dysfunction, immunity activation and inflammatory response are crucial events during ischemia-reperfusion injury while toll-like receptors, inflammasomes, reactive oxygen species, intracellular calcium overload and mitochondrial permeability transition pore opening consist of key molecular mediators. Indicatively, cardiac fibroblasts through inflammasome activation mediate the initial inflammatory response. Cardiac mesenchymal stromal cells can respond to myocardial injury by pro-inflammatory activation. Endothelial cell activation contributes to the impaired vasomotion, inflammation and thrombotic events and together with platelet activation leads to microcirculation dysfunction and polymorphonuclear cells recruitment promoting inflammation. Polymorphonuclear cells and monocytes/macrophages subsets are critically involved in the inflammation process by producing toxic proteolytic enzymes and reactive oxygen species. T cells subsets are also involved in several stages of ischemia-reperfusion injury. In this review, we summarize the specific contribution of each of the above cells and the related molecular pathways in the pathophysiology of ischemia-reperfusion injury.

Antiplatelet Therapy with Integrated Traditional Chinese and Western Medicine for Use in Myocardial Ischemia-Reperfusion Injury: A Review of Clinical Applications and Mechanisms

Myocardial ischemia-reperfusion injury (MIRI) is common in patients with acute coronary syndrome (ACS) after PCI treatment, which seriously affects the efficacy of revascularization and hinders the postoperative recovery of patients; therefore, the current study is focused on determining effective methods in the treatment of MIRI. Antiplatelet therapy is a routine treatment for ACS, and its benefits for treating MIRI have been previously verified. With the development of traditional Chinese medicine (TCM), many TCM preparations are widely used in the clinic. Many basic and clinical studies have shown that TCM can be used together with antiplatelet drugs, and the safety and efficacy when TCM is included in the treatment are better than when antiplatelet drugs are used alone. This paper summarizes the current research progress of traditional Chinese medicine and Western medicine in the treatment of MIRI to provide a theoretical basis for further research and clinical treatment.

Platelets as drivers of ischemia/reperfusion injury after stroke

Ischemic stroke is a leading cause of morbidity and mortality worldwide and, despite reperfusion either via thrombolysis or thrombectomy, stroke patients often suffer from lifelong disabilities. These persistent neurological deficits may be improved by treating the ischemia/reperfusion (I/R) injury that occurs following ischemic stroke. There are currently no approved therapies to treat I/R injury, and thus it is imperative to find new targets to decrease the burden of ischemic stroke and related diseases. Platelets, cell fragments from megakaryocytes, are primarily known for their role in hemostasis. More recently, investigators have studied the nonhemostatic role of platelets in inflammatory pathologies, such as I/R injury after ischemic stroke. In this review, we seek to provide an overview of how I/R can lead to platelet activation and how activated platelets, in turn, can exacerbate I/R injury after stroke. We will also discuss potential mechanisms by which platelets may ameliorate I/R injury.

Left ventricular assist device implantation causes platelet dysfunction and proinflammatory platelet-neutrophil interaction

Blood flow through left ventricular assist devices (LVAD) may induce activation and dysfunction of platelets. Dysfunctional platelets cause coagulation disturbances and form platelet-neutrophil conjugates (PNC), which contribute to inflammatory tissue damage. This prospective observational cohort study investigated patients, who underwent implantation of a LVAD (either HeartMate II (HM II) (n = 7) or HeartMate 3 (HM 3) (n = 6)) and as control patients undergoing coronary artery bypass grafting (CABG) and/or aortic valve replacement (AVR) (n = 10). We performed platelet and leukocyte flow cytometry, analysis of platelet activation markers, and platelet aggregometry. Platelet CD42b expression was reduced at baseline and perioperatively in HM II/3 compared to CABG/AVR patients. After surgery the platelet activation marker β-thromboglobulin and platelet microparticles increased in all groups while platelet aggregation decreased. Platelet aggregation was more significantly impaired in LVAD compared to CABG/AVR patients. PNC were higher in HM II compared to HM 3 patients. We conclude that LVAD implantation is associated with platelet dysfunction and proinflammatory platelet-leukocyte binding. These changes are less pronounced in patients treated with the newer generation LVAD HM 3. Future research should identify device-specific LVAD features, which are associated with the least amount of platelet activation to further improve LVAD therapy.

Platelets in cardiac ischaemia/reperfusion injury: a promising therapeutic target

Acute myocardial infarction (AMI) is the single leading cause of mortality and morbidity worldwide. A key component of AMI therapy is the timely reopening of occluded vessels to prevent further ischaemic damage to the myocardium. However, reperfusion of the ischaemic myocardium can itself trigger reperfusion injury causing up to 50% of the overall infarct size. In recent years, considerable research has been devoted to understanding the pathogenesis of ischaemia/reperfusion (I/R) injury and platelets have emerged as a major contributing factor. This review summarizes the role of platelets in the pathogenesis of I/R injury and highlights the potential of platelet-directed therapeutics to minimize cardiac I/R injury. Activated platelets infiltrate specifically into the ischaemic/reperfused myocardium and contribute to I/R injury by the formation of microthrombi, enhanced platelet–leucocyte aggregation, and the release of potent vasoconstrictor and pro-inflammatory molecules. This review demonstrates the benefits of platelet inhibition beyond their well-described anti-thrombotic effect and highlights the direct cardioprotective role of anti-platelet drugs. In particular, the inhibition of COX, the P2Y12 receptor and the GPIIb/IIIa receptor has demonstrated the potential to attenuate I/R injury. Moreover, targeting of drug candidates or regenerative cells to the activated platelets accumulated within the ischaemic/reperfused myocardium shows remarkable potential to protect the myocardium from I/R injury. Overall, activated platelets play a key role in the pathogenesis of I/R injury. Their direct inhibition as well as their use as epitopes for site-directed therapy is a unique and promising therapeutic approach for the prevention of I/R injury and ultimately the preservation of cardiac function.

Red blood cell-derived semaphorin 7A promotes thrombo-inflammation in myocardial ischemia-reperfusion injury through platelet GPIb

Myocardial ischemia is one of the leading health problems worldwide. Therapy consists of the restitution of coronary perfusion which is followed by myocardial inflammation. Platelet–neutrophil interaction is a crucial process during inflammation, yet its consequences are not fully understood. Here, we show that platelet–neutrophil complexes (PNCs) are increased in patients with acute myocardial infarction and that this is associated with increased levels of neuronal guidance protein semaphorin 7A (SEMA7A). To investigate this further, we injected WT animals with Sema7a and found increased infarct size with increased numbers of PNCs. Experiments in genetically modified animals identify Sema7a on red blood cells to be crucial for this condition. Further studies revealed that Sema7a interacts with the platelet receptor glycoprotein Ib (GPIb). Treatment with anti-Sema7a antibody protected from myocardial tissue injury. In summary, we show that Sema7a binds to platelet GPIb and enhances platelet thrombo-inflammatory activity, aggravating post-ischemic myocardial tissue injury.

Reperfusion injury following myocardial ischemia is aggravated by inflammation and platelet–neutrophil complex formation. Here the authors show that semaphorin 7A binds to platelet GPIb, enhancing platelet–neutrophil interaction and increasing post-ischemic myocardial tissue injury, and that blockage of semaphorin 7A is protective.

Targeting CD39 Toward Activated Platelets Reduces Systemic Inflammation and Improves Survival in Sepsis: A Preclinical Pilot Study

OBJECTIVES

Sepsis is associated with a systemic inflammatory reaction, which can result in a life-endangering organ dysfunction. Pro-inflammatory responses during sepsis are characterized by increased activation of leukocytes and platelets, formation of platelet-neutrophil aggregates, and cytokine production. Sequestration of platelet-neutrophil aggregates in the microvasculature contributes to tissue damage during sepsis. At present no effective therapeutic strategy to ameliorate these events is available. In this preclinical pilot study, a novel anti-inflammatory approach was evaluated, which targets nucleoside triphosphate hydrolase activity toward activated platelets via a recombinant fusion protein combining a single-chain antibody against activated glycoprotein IIb/IIIa and the extracellular domain of CD39 (targ-CD39).

DESIGN

Experimental animal study and cell culture study.

SETTING

University-based experimental laboratory.

SUBJECTS

Human dermal microvascular endothelial cells 1, human platelets and neutrophils, and C57BL/6NCrl mice.

INTERVENTIONS

Platelet-leukocyte-endothelium interactions were evaluated under inflammatory conditions in vitro and in a murine lipopolysaccharide-induced sepsis model in vivo. The outcome of polymicrobial sepsis was evaluated in a murine cecal ligation and puncture model. To evaluate the anti-inflammatory potential of activated platelet targeted nucleoside triphosphate hydrolase activity, we employed a potato apyrase in vitro and in vivo, as well as targ-CD39 and as a control, nontarg-CD39 in vivo.

MEASUREMENTS AND MAIN RESULTS

Under conditions of sepsis, agents with nucleoside triphosphate hydrolase activity decreased platelet-leukocyte-endothelium interaction, transcription of pro-inflammatory cytokines, microvascular platelet-neutrophil aggregate sequestration, activation marker expression on platelets and neutrophils contained in these aggregates, leukocyte extravasation, and organ damage. Targ-CD39 had the strongest effect on these variables and retained hemostasis in contrast to nontarg-CD39 and potato apyrase. Most importantly, targ-CD39 improved survival in the cecal ligation and puncture model to a stronger extent then nontarg-CD39 and potato apyrase.

CONCLUSIONS

Targeting nucleoside triphosphate hydrolase activity (CD39) toward activated platelets is a promising new treatment concept to decrease systemic inflammation and mortality of sepsis. This innovative therapeutic approach warrants further development toward clinical application.

Neutrophil Recruitment: From Model Systems to Tissue-Specific Patterns

Neutrophil recruitment is not only vital for host defense, but also relevant in pathological inflammatory reactions, such as sepsis. Model systems have been established to examine different steps of the leukocyte recruitment cascade in vivo and in vitro under inflammatory conditions. Recently, tissue-specific recruitment patterns have come into focus, requiring modification of formerly generalized assumptions. Here, we summarize existing models of neutrophil recruitment and highlight recent discoveries in organ-specific recruitment patterns. New techniques show that previously stated assumptions of integrin activation and tissue invasion may need revision. Similarly, neutrophil recruitment to specific organs can rely on different organ properties, adhesion molecules, and chemokines. To advance our understanding of neutrophil recruitment, organ-specific intravital microscopy methods are needed.

Circulating platelet-neutrophil aggregates as risk factor for deep venous thrombosis

Background

Platelet-neutrophil aggregates (PNAs) are fundamental mechanisms linking hemostasis and inflammatory processes. Elevated level of PNAs have been reported in inflammatory diseases and coronary artery diseases. However, studies on the correlation between PNAs formation and deep venous thrombosis (DVT) are not available.

Methods

A total of 92 participants were involved in this study, including 32 cases with DVT and 60 cases without DVT. Blood samples coagulated by K2-EDTA or sodium citrate were prepared for blood cell count and blood smears. PNAs and platelet activation were measured using flow cytometry. The correlation between platelet activation level and PNAs level was analyzed by linear regression. Receiver operating characteristic (ROC) analysis was performed, assessing the prognostic performance of PNAs to predict potential risk of DVT occurrence.

Results

PNAs was found in the blood smears of patients with DVT. Significant increased level of PNAs was identified in DVT group (medium 8.43%, interquartile range [IQR] 4.11%–15.69%), compared with that in control group (5.16%, IQR 2.40–9.60, p<0.01). The DVT group also showed a dramatic elevated level of total platelet activation (medium 16.06%, IQR 6.04–22.05) vs. control group (11.26%, IQR 5.54–19.99, p<0.05). The PNAs level was correlated with total platelet activation (r2=0.58, p<0.0001). A significantly high odds ratio (OR) of DVT occurrence was identified when the level of PNAs was higher than 7.4% (OR 3.60, 95% confidence interval [CI] 1.463–8.838, p<0.01).

Conclusions

An elevated level of PNAs was associated with risk of DVT occurrence, which might be a suitable marker predicting DVT development.

Rosuvastatin Alleviates Ischemia/Reperfusion Injury in Cardiomyocytes by Downregulating Hsa-miR-24-3p to Target Upregulated Uncoupling Protein 2

Statins could reduce the risks of coronary heart disease death and ischemic cardiovascular events. In this study, we aim to explore the role of rosuvastatin in ischemia/reperfusion (I/R)-injured cardiomyocytes and the possible mechanism. An I/R model was established by oxygen-glucose deprivation/reperfusion (OGD/R). The protective effects of rosuvastatin pretreatment on OGD/R-injured cardiomyocytes were performed using MTT assay, lactate dehydrogenase (LDH) release assay, and quantitative real-time polymerase chain reaction (qRT-PCR). Bioinformatics software TargetScan and miRTarBase were used to predict the targeted miRNAs with uncoupling protein (UCP)2. Furthermore, verify the binding capacity of hsa-miR-24-3p and UCP2 with qRT-PCR and dual-luciferase reporter assay. The expression of UCP2, cell viability, LDH level, and apoptosis level affected by downregulated hsa-miR-24-3p were assessed using qRT-PCR, western blotting, MTT, the LDH kit, and flow cytometry. Pretreatment with rosuvastatin could significantly augment cell viability, reduce LDH level, increase the expression of UCP2, and downregulate hsa-miR-24-3p in OGD/R-injured H9c2 cells. miR-24-3p was closely connected with UCP2, and downregulated miR-24-3p could promote UCP2 expression, which presented cell viability increasing, LDH release and cell apoptosis inhibition in OGD/R condition. Moreover, it decreased the protein expression of Cleaved-Caspase-9 and Cyto C. This is the first time our study suggests that rosuvastatin pretreatment protects cardiomyocytes from OGD/R through upregulating UCP2 through downregulation of hsa-miR-24-3p.

Do platelets promote cardiac recovery after myocardial infarction: roles beyond occlusive ischemic damage

Our understanding of platelet function has traditionally focused on their roles in physiological hemostasis and pathological thrombosis, with the latter being causative of vessel occlusion and subsequent ischemic damage to various tissues. In particular, numerous in vivo studies have implicated causative roles for platelets in the pathogenesis of ischemia-reperfusion (I/R) injury to the myocardium. However, platelets clearly have more complex pathophysiological roles, particularly as a result of the heterogeneous nature of biologically active cargo secreted from their granules or contained within released microparticles or exosomes. While some of these released mediators amplify platelet activation and thrombosis through autocrine or paracrine amplification pathways, they can also regulate diverse cellular functions within the localized microenvironment and recruit progenitor cells to the damage site to facilitate repair processes. Notably, there is evidence to support cardioprotective roles for platelet mediators during I/R injury. As such, it is becoming more widely appreciated that platelets fulfill a host of physiological and pathological roles beyond our basic understanding. Therefore, the purpose of this perspective is to consider whether platelets, through their released mediators, can assume a paradoxically beneficial role to promote cardiac recovery after I/R injury.

Phosphorylation of vasodilator-stimulated phosphoprotein contributes to myocardial ischemic preconditioning

Ischemic preconditioning (IP) is a well-known strategy to protect organs against cell death following ischemia. The previous work has shown that vasodilator-stimulated phosphoprotein (VASP) is involved in cytoskeletal reorganization and that it holds significant importance for the extent of myocardial ischemia reperfusion injury. Yet, the role of VASP during myocardial IP is, to date, not known. We report here that VASP phosphorylation at serine¹⁵⁷ and serine²³⁹ is induced during hypoxia in vitro and during IP in vivo. The preconditioning-induced VASP phosphorylation inactivates the GP IIb/IIIa integrin receptor on platelets, which results in the reduced formation of organ compromising platelet neutrophil complexes. Experiments in chimeric mice confirmed the importance of VASP phosphorylation during myocardial IP. When studying this in VASP^-/- animals and in an isolated heart model, we were able to confirm the important role of VASP on myocardial IP. In conclusion, we were able to show that IP-induced VASP phosphorylation in platelets is a protective mechanism against the deleterious effects of ischemia.

Melatonin suppresses platelet activation and function against cardiac ischemia/reperfusion injury via PPARγ/FUNDC1/mitophagy pathways

Platelet activation is a major (patho-) physiological mechanism that underlies ischemia/reperfusion (I/R) injury. In this study, we explored the molecular signals for platelet hyperactivity and investigated the beneficial effects of melatonin on platelet reactivity in response to I/R injury. After reperfusion, peroxisome proliferator-activated receptor γ (PPARγ) was progressively downregulated in patients with acute myocardial infarction undergoing coronary artery bypass grafting (CABG) surgery and in mice with I/R injury model. Loss of PPARγ was closely associated with FUN14 domain containing 1 (FUNDC1) dephosphorylation and mitophagy activation, leading to increased mitochondrial electron transport chain complex (ETC.) activity, enhanced mitochondrial respiratory function, and elevated ATP production. The improved mitochondrial function strongly contributed to platelet aggregation, spreading, expression of P-selectin, and final formation of micro-thromboses, eventually resulting in myocardial dysfunction and microvascular structural destruction. However, melatonin powerfully suppressed platelet activation via restoration of the PPARγ content in platelets, which subsequently blocked FUNDC1-required mitophagy, mitochondrial energy production, platelet hyperactivity, and cardiac I/R injury. In contrast, genetic ablation of PPARγ in platelet abolished the beneficial effects of melatonin on mitophagy, mitochondrial ATP supply, and platelet activation. Our results lay the foundation for the molecular mechanism of platelet activation in response to I/R injury and highlight that the manipulation of the PPARγ/FUNDC1/mitophagy pathway by melatonin could be a novel strategy for cardioprotection in the setting of cardiac I/R injury.

Discordance Between VASP Phosphorylation and Platelet Aggregation in Defining High On-Clopidogrel Platelet Reactivity After ST-Segment Elevation Myocardial Infarction

To investigate potential clinical characteristics associated with discordance between platelet vasodilator-stimulated phosphoprotein phosphorylation (VASP-P) flow cytometry (FCM) assay and light transmission aggregometry (LTA) in defining high on-clopidogrel platelet reactivity (HPR) after ST-segment elevation myocardial infarction (STEMI). In this study, platelet responsiveness was measured by the above 2 methods simultaneously on day 1 and on day 6 of STEMI onset in 90 consecutive patients who underwent primary percutaneous coronary intervention. The FCM-derived platelet reactivity index and LTA-derived platelet aggregation rate were both significantly reduced after dual antiplatelet therapy on day 6. Multiple variable-adjusted logistic regression analysis revealed that smoking (odds ratio [OR]: 4.507, 95% confidence interval [CI]: 1.123-18.09, P = .034) and onset-to-admission time (per 1 hour increase, OR: 1.196, 95% CI: 1.023-1.398, P = .025) both were independent predictors for the discordance between the 2 methods. Additionally, improved correlation and concordance was observed in nonsmokers compared with smokers. Our data show that smoking and prolonged onset-to-admission time are associated with discordance between platelet VASP-P and LTA in defining HPR after STEMI, which should be considered when planning personalized antiplatelet therapy.

HSPA12B Attenuated Acute Myocardial Ischemia/reperfusion Injury via Maintaining Endothelial Integrity in a PI3K/Akt/mTOR-dependent Mechanism

Endothelial damage is a critical mediator of myocardial ischemia/reperfusion (I/R) injury. HSPA12B is an endothelial-cell-specifically expressed heat shock protein. However, the roles of HSPA12B in acute myocardial I/R injury is unknown. Here we reported that myocardial I/R upregulated HSPA12B expression in ventricular tissues, and endothelial overexpression of HSPA12B in transgenic mice (Tg) limited infarct size, attenuated cardiac dysfunction and improved cardiomyocyte survival compared with their wild type littermates. These improvements were accompanied with the diminished myocardial no-reflow phenomenon, decreased microvascular leakage, and better maintained endothelial tight junctions. The I/R-evoked neutrophil infiltration was also suppressed in Tg hearts compared with its wild type (WT) littermates. Moreover, Tg hearts exhibited the enhanced activation of PI3K/Akt//mTOR signaling following I/R challenge. However, pharmacological inhibition of PI3K abolished the HSPA12B-induced cardioprotection against myocardial I/R injury. The data demonstrate for the first time that the endothelial HSPA12B protected hearts against myocardial I/R injury. This cardioprotective action of HSPA12B was mediated, at least in part, by improving endothelial integrity in a PI3K/Akt/mTOR-dependent mechanism. Our study suggests that targeting endothelial HSPA12B could be an alternative approach for the management of patients with myocardial I/R injury.

Adenosine Receptor Adora2b Plays a Mechanistic Role in the Protective Effect of the Volatile Anesthetic Sevoflurane during Liver Ischemia/Reperfusion

Background

Liver ischemia/reperfusion (IR) injury is characterized by hepatic tissue damage and an inflammatory response. This is accompanied by the formation and vascular sequestration of platelet–neutrophil conjugates (PNCs). Signaling through Adora2b adenosine receptors can provide liver protection. Volatile anesthetics may interact with adenosine receptors. This study investigates potential antiinflammatory effects of the volatile anesthetic sevoflurane during liver IR.

Methods

Experiments were performed ex vivo with human blood and in a liver IR model with wild-type, Adora2a−/−, and Adora2b−/− mice. The effect of sevoflurane on platelet activation, PNC formation and sequestration, cytokine release, and liver damage (alanine aminotransferase release) was analyzed using flow cytometry, luminometry, and immunofluorescence. Adenosine receptor expression in liver tissue was analyzed using immunohistochemistry and real-time polymerase chain reaction.

Results

Ex vivo experiments indicate that sevoflurane inhibits platelet and leukocyte activation (n = 5). During liver IR, sevoflurane (2 Vol%) decreased PNC formation 2.4-fold in wild-type (P &lt; 0.05) but not in Adora2b−/− mice (n ≥ 5). Sevoflurane reduced PNC sequestration 1.9-fold (P &lt; 0.05) and alanine aminotransferase release 3.5-fold (P &lt; 0.05) in wild-type but not in Adora2b−/− mice (n = 5). In Adora2a−/− mice, sevoflurane also inhibited PNC formation and cytokine release. Sevoflurane diminished cytokine release (n ≥ 3) and increased Adora2b transcription and expression in liver tissue of wild-types (n = 4).

Conclusions

Our experiments highlight antiinflammatory and tissue-protective properties of sevoflurane during liver IR and reveal a mechanistic role of Adora2b in sevoflurane-associated effects. The targeted use of sevoflurane not only as an anesthetic but also to prevent IR damage is a promising approach in the treatment of critically ill patients.

Perivascular Mast Cells Govern Shear Stress-Induced Arteriogenesis by Orchestrating Leukocyte Function

The body has the capacity to compensate for an occluded artery by creating a natural bypass upon increased fluid shear stress. How this mechanical force is translated into collateral artery growth (arteriogenesis) is unresolved. We show that extravasation of neutrophils mediated by the platelet receptor GPIbα and uPA results in Nox2-derived reactive oxygen radicals, which activate perivascular mast cells. These c-kit(+)/CXCR-4(+) cells stimulate arteriogenesis by recruiting additional neutrophils as well as growth-promoting monocytes and T cells. Additionally, mast cells may directly contribute to vascular remodeling and vascular cell proliferation through increased MMP activity and by supplying growth-promoting factors. Boosting mast cell recruitment and activation effectively promotes arteriogenesis, thereby protecting tissue from severe ischemic damage. We thus find that perivascular mast cells are central regulators of shear stress-induced arteriogenesis by orchestrating leukocyte function and growth factor/cytokine release, thus providing a therapeutic target for treatment of vascular occlusive diseases.

Inhibition of Adenosine Kinase Attenuates Acute Lung Injury

OBJECTIVES

Extracellular adenosine has tissue-protective potential in several conditions. Adenosine levels are regulated by a close interplay between nucleoside transporters and adenosine kinase. On the basis of the evidence of the role of adenosine kinase in regulating adenosine levels during hypoxia, we evaluated the effect of adenosine kinase on lung injury. Furthermore, we tested the influence of a pharmacologic approach to blocking adenosine kinase on the extent of lung injury.

DESIGN

Prospective experimental animal study.

SETTING

University-based research laboratory.

SUBJECTS

In vitro cell lines, wild-type and adenosine kinase+/- mice.

INTERVENTIONS

We tested the expression of adenosine kinase during inflammatory stimulation in vitro and in a model of lipopolysaccharide inhalation in vivo. Studies using the adenosine kinase promoter were performed in vitro. Wild-type and adenosine kinase+/- mice were subjected to lipopolysaccharide inhalation. Pharmacologic inhibition of adenosine kinase was performed in vitro, and its effect on adenosine uptake was evaluated. The pharmacologic inhibition was also performed in vivo, and the effect on lung injury was assessed.

MEASUREMENTS AND MAIN RESULTS

We observed the repression of adenosine kinase by proinflammatory cytokines and found a significant influence of nuclear factor kappa-light-chain-enhancer of activated B-cells on regulation of the adenosine kinase promoter. Mice with endogenous adenosine kinase repression (adenosine kinase+/-) showed reduced infiltration of leukocytes into the alveolar space, decreased total protein and myeloperoxidase levels, and lower cytokine levels in the alveolar lavage fluid. The inhibition of adenosine kinase by 5-iodotubercidin increased the extracellular adenosine levels in vitro, diminished the transmigration of neutrophils, and improved the epithelial barrier function. The inhibition of adenosine kinase in vivo showed protective properties, reducing the extent of pulmonary inflammation during lung injury.

CONCLUSIONS

Taken together, these data show that adenosine kinase is a valuable target for reducing the inflammatory changes associated with lung injury and should be pursued as a therapeutic option.

Platelet-neutrophil complex formation-a detailed in vitro analysis of murine and human blood samples

Platelets form complexes with neutrophils during inflammatory processes. These aggregates migrate into affected tissues and also circulate within the organism. Several studies have evaluated platelet-neutrophil complexes as a marker of cardiovascular diseases in human and mouse. Although multiple publications have reported platelet-neutrophil complex counts, we noticed that different methods were used to analyze platelet-neutrophil complex formation, resulting in significant differences, even in baseline values. We established a protocol for platelet-neutrophil complex measurement with flow cytometry in murine and human whole blood samples. In vitro platelet-neutrophil complex formation was stimulated with ADP or PMA. We tested the effect of different sample preparation steps and cytometer settings on platelet-neutrophil complex detection and noticed false-positive counts with increasing acquisition speed. Platelet-neutrophil complex formation depends on platelet P-selectin expression, and antibody blocking of P-selectin consequently prevented ADP-induced platelet-neutrophil complex formation. These findings may help generating more comparable data among different research groups that examine platelet-neutrophil complexes as a marker for cardiovascular disease and novel therapeutic interventions.

Scutellarin's Cardiovascular Endothelium Protective Mechanism: Important Role of PKG-Iα

Scutellarin (SCU), a flavonoid glycoside compound, has been successfully used in clinic for treatment of ischemic diseases in China. In this report, we checked the effects of SCU on endothelium dysfunction (ED) of coronary artery (CA) against myocardial ischemia reperfusion (MIR) injury in vivo. The involvement of PKG-Iα was further studied using cultured endothelial cells subjected to hypoxia reoxygenation (HR) injury in vitro. In rat MIR model, SCU (45 and 90 mg/kg, iv) significantly reduced ischemic size and restored the endothelium-dependent vasodilation of isolated CA rings. PKG inhibitor Rp-8-Br-cGMP (50 μg/kg, iv) could ameliorate the protective effects of SCU. Increase in phosphorylation of vasodilator-stimulated phosphoprotein (VASP), a main substrate of PKG, at Ser 239 was observed in both heart tissue and serum of SCU-treated animals. In cultured human cardiac microvascular endothelial cells (HCMECs), SCU (1 and 10 μM) dose-dependently protected cell viability and increased the mRNA and protein level of PKG-Iα against HR injury. The activity of PKG was also increased by SCU treatment. The activation of PKG–1α was then studied using targeted proteomic analysis (MRM-MS) checking the phosphorylation state of the autophosphorylation domain (aa42-94). Significant decrease in phosphorylation of PKG-Iα at Ser50, Ser72, Ser89 was induced by HR injury while SCU treatment significantly increased the phosphorylation of PKG-Iα, not only at Ser50, Ser72 and Ser89, but also at Ser44 and Thr58 (two novel phosphorylation domains). Our results demonstrate PKG-Iα might play an important role in the protective effects of SCU on ED against MIR injury.

Platelet Gi protein Gαi2 is an essential mediator of thrombo-inflammatory organ damage in mice

Platelets are crucial for hemostasis and thrombosis and exacerbate tissue injury following ischemia and reperfusion. Important regulators of platelet function are G proteins controlled by seven transmembrane receptors. The Gi protein Gα(i2) mediates platelet activation in vitro, but its in vivo role in hemostasis, arterial thrombosis, and postischemic infarct progression remains to be determined. Here we show that mice lacking Gα(i2) exhibit prolonged tail-bleeding times and markedly impaired thrombus formation and stability in different models of arterial thrombosis. We thus generated mice selectively lacking Gα(i2) in megakaryocytes and platelets (Gna(i2)(fl/fl)/PF4-Cre mice) and found bleeding defects comparable to those in global Gα(i2)-deficient mice. To examine the impact of platelet Gα(i2) in postischemic thrombo-inflammatory infarct progression, Gna(i2)(fl/fl)/PF4-Cre mice were subjected to experimental models of cerebral and myocardial ischemia/reperfusion injury. In the model of transient middle cerebral artery occlusion stroke Gna(i2)(fl/fl)/PF4-Cre mice developed significantly smaller brain infarcts and fewer neurological deficits than littermate controls. Following myocardial ischemia, Gna(i2)(fl/fl)/PF4-Cre mice showed dramatically reduced reperfusion injury which correlated with diminished formation of the ADP-dependent platelet neutrophil complex. In conclusion, our data provide definitive evidence that platelet Gα(i2) not only controls hemostatic and thrombotic responses but also is critical for the development of ischemia/reperfusion injury in vivo.

TM-1-1DP exerts protective effect against myocardial ischemia reperfusion injury via AKT-eNOS pathway

Coronary heart disease remains a leading cause of death in the world. The demand on targeting therapy to reduce myocardial ischemia/reperfusion (I/R) injury is still urgent. The pathogenesis of I/R-induced myocardial injury is complicated. Reactive oxygen species (ROS) generation and inflammatory response activation participate in the development of I/R injury. Cell death occurs and finally leads to myocardial infarction. A newly phenolic aporphine alkaloid derivative, TM-1-1DP, was synthesized in our team. We aimed to investigate the effect of novel compound on myocardial I/R injury. Rats were subjected to 1-h coronary artery occlusion and followed by 2-h reperfusion. Adult rat cardimoycyte was isolated for the cell study, and H2O2 was added into culture medium to induce ROS stress. As compared to the sham group, TM-1-1DP-treated rats had better cardiac performance in association with less infarct size and cardiac injury markers after myocardial I/R. The protective effect is associated with the inhibition of inflammatory response, cell death-related pathway (caspase-3 and TNF-α), and the activation of AKT-eNOS pathway. The finding was further coincided with the cell study. TM-1-1DP treatment significantly alleviated ROS production and improved cell viability in cardiomyocyte after H2O2 exposure. The action of TM-1-1DP is via a nitric oxide (NO)-dependent manner, since NOS inhibitor, L-NAME, abolished the protective effect. We provide a new insight into this therapeutic potential for phenolic aporphine alkaloid in myocardial I/R.

Neutrophil extracellular traps in ischemia-reperfusion injury-induced myocardial no-reflow: therapeutic potential of DNase-based reperfusion strategy

Emerging evidence suggests a potential role of neutrophil extracellular traps (NETs) in linking sterile inflammation and thrombosis. We hypothesized that NETs would be induced during myocardial ischemia-reperfusion (I/R), and NET-mediated microthrombosis may contribute to myocardial "no-reflow". Male Wistar rats were randomly divided into I/R control, DNase (DNase I, 20 μg/rat), recombinant tissue-type plasminogen activator (rt-PA, 420 μg/rat), DNase + rt-PA, and sham control groups after 45-min myocardial ischemia. In situ NET formation, the anatomic "no re-flow" area, and infarct size were evaluated immediately after 3 h of reperfusion. Long-term left ventricular (LV) functional and histological analyses were performed 45 days after operation. Compared with the I/R controls, the DNase + rt-PA group exhibited reduced NET density [8.38 ± 1.98 vs. 26.86 ± 3.07 (per 200 × field), P < 0.001] and "no-flow" area (15.22 ± 0.06 vs. 34.6 ± 0.05%, P < 0.05) in the ischemic region, as well as reduced infarct size (38.39 ± 0.05 vs. 71.00 ± 0.03%, P < 0.001). Additionally, compared with the I/R controls, DNase + rt-PA treatment significantly ameliorated I/R injury-induced LV remodeling (LV ejection fraction: 64.22 ± 3.37 vs. 33.81 ± 2.98%, P < 0.05; LV maximal slope of the LV systolic pressure increment: 3,785 ± 216 vs. 2,596 ± 299 mmHg/s, P < 0.05). The beneficial effect was not observed in rats treated with DNase I or rt-PA alone. Our study provides evidence for the existence of NETs in I/R-challenged myocardium and confirms the long-term benefit of a novel DNase-based reperfusion strategy (DNase I + rt-PA), which might be a promising option for the treatment of myocardial I/R injury and coronary no-reflow.

Immune functions of platelets

This review collects evidence about immune and inflammatory functions of platelets from a clinician's point of view. A focus on clinically relevant immune functions aims at stimulating further research, because the complexity of platelet immunity is incompletely understood and not yet translated into patient care. Platelets promote chronic inflammatory reactions (e.g. in atherosclerosis), modulate acute inflammatory disorders such as sepsis and other infections (participating in the host defense against pathogens), and contribute to exacerbations of autoimmune conditions (like asthma or arthritis). It would hence be obsolete to restrict a description of platelet functions to thrombosis and haemostasis--platelets clearly are the most abundant cells with immune functions in the circulation.

Dual-contrast molecular imaging allows noninvasive characterization of myocardial ischemia/reperfusion injury after coronary vessel occlusion in mice by magnetic resonance imaging

BACKGROUND

Inflammation and myocardial necrosis play important roles in ischemia/reperfusion injury after coronary artery occlusion and recanalization. The detection of inflammatory activity and the extent of myocardial necrosis itself are of great clinical and prognostic interest. We developed a dual, noninvasive imaging approach using molecular magnetic resonance imaging in an in vivo mouse model of myocardial ischemia and reperfusion.

METHODS AND RESULTS

Ischemia/reperfusion injury was induced in 10-week-old C57BL/6N mice by temporary ligation of the left anterior descending coronary artery. Activated platelets were targeted with a contrast agent consisting of microparticles of iron oxide (MPIOs) conjugated to a single-chain antibody directed against a ligand-induced binding site (LIBS) on activated glycoprotein IIb/IIIa (LIBS-MPIOs). After injection and imaging of LIBS-MPIOs, late gadolinium enhancement was used to depict myocardial necrosis; these imaging experiments were also performed in P2Y12 (-/-) mice. All imaging results were correlated to immunohistochemistry findings. Activated platelets were detectable by magnetic resonance imaging via a significant signal effect caused by LIBS-MPIOs in the area of left anterior descending coronary artery occlusion 2 hours after reperfusion. In parallel, late gadolinium enhancement identified the extent of myocardial necrosis. Immunohistochemistry confirmed that LIBS-MPIOs bound significantly to microthrombi in reperfused myocardium. Only background binding was found in P2Y12 (-/-) mice.

CONCLUSIONS

Dual molecular imaging of myocardial ischemia/reperfusion injury allows characterization of platelet-driven inflammation by LIBS-MPIOs and myocardial necrosis by late gadolinium enhancement. This noninvasive imaging strategy is of clinical interest for both diagnostic and prognostic purposes and highlights the potential of molecular magnetic resonance imaging for characterizing ischemia/reperfusion injury.

The CXCR1/2 ligand NAP-2 promotes directed intravascular leukocyte migration through platelet thrombi

Thrombosis promotes leukocyte infiltration into inflamed tissues, leading to organ injury in a broad range of diseases; however, the mechanisms by which thrombi guide leukocytes to sites of vascular injury remain ill-defined. Using mouse models of endothelial injury (traumatic or ischemia reperfusion), we demonstrate a distinct process of leukocyte recruitment, termed "directed intravascular migration," specifically mediated by platelet thrombi. Single adherent platelets and platelet aggregates stimulated leukocyte shape change at sites of endothelial injury; however, only thrombi were capable of inducing directed intravascular leukocyte migration. Leukocyte recruitment and migration induced by platelet thrombi occurred most prominently in veins but could also occur in arteries following ischemia-reperfusion injury. In vitro studies demonstrated a major role for platelet-derived NAP-2 (CXCL-7) and its CXCR1/2 receptor in regulating leukocyte polarization and motility. In vivo studies demonstrated the presence of an NAP-2 chemotactic gradient within the thrombus body. Pharmacologic blockade of CXCR1/2 as well as genetic deletion of NAP-2 markedly reduced leukocyte shape change and intrathrombus migration. These studies define a distinct process of leukocyte migration that is initiated by homotypic adhesive interactions between platelets, leading to the development of an NAP-2 chemotactic gradient within the thrombus body that guides leukocytes to sites of vascular injury.

Prasugrel metabolites inhibit neutrophil functions

Clopidogrel and prasugrel belong to a thienopyridine class of oral antiplatelet drugs that, after having been metabolized in the liver, can inhibit platelet function by irreversibly antagonizing the P2Y(12) receptor. Furthermore, thienopyridines influence numerous inflammatory conditions, but their effects on neutrophils have not been evaluated, despite the important role of these cells in inflammation. Therefore, we investigated the effect of prasugrel metabolites on neutrophils to further clarify the role of thienopyridines in inflammation. Interestingly, a prasugrel metabolite mixture, produced in vitro using rat liver microsomes, significantly inhibited N-formyl-methionyl-leucyl-phenylalanine (fMLP)- and platelet-activating factor (PAF)-induced neutrophil activation. More specifically, prasugrel metabolites inhibited neutrophil transmigration, CD16 surface expression, and neutrophil-platelet aggregation. Moreover, prasugrel metabolite pretreatment also significantly decreased fMLP- or PAF-induced extracellular-signal-regulated kinase phosphorylation as well as calcium mobilization. To determine the target of prasugrel in neutrophils, the role of both P2Y(12) and P2Y(13) receptors was studied using specific reversible antagonists, AR-C69931MX and MRS2211, respectively. Neither antagonist had any direct effect on the agonist-induced neutrophil functional responses. Our findings indicate that prasugrel metabolites may directly target neutrophils and inhibit their activation, suggesting a possible explanation for their anti-inflammatory effects previously observed. However, these metabolites do not act through either the P2Y(12) or P2Y(13) receptor in neutrophils.

Secretome of apoptotic peripheral blood cells (APOSEC) attenuates microvascular obstruction in a porcine closed chest reperfused acute myocardial infarction model: role of platelet aggregation and vasodilation

Although epicardial blood flow can be restored by an early intervention in most cases, a lack of adequate reperfusion at the microvascular level is often a limiting prognostic factor of acute myocardial infarction (AMI). Our group has recently found that paracrine factors secreted from apoptotic peripheral blood mononuclear cells (APOSEC) attenuate the extent of myocardial injury. The aim of this study was to determine the influence of APOSEC on microvascular obstruction (MVO) in a porcine AMI model. A single dose of APOSEC was intravenously injected in a closed chest reperfused infarction model. MVO was determined by magnetic resonance imaging and cardiac catheterization. Role of platelet function and vasodilation were monitored by means of ELISA, flow cytometry, aggregometry, western blot and myographic experiments in vitro and in vivo. Treatment of AMI with APOSEC resulted in a significant reduction of MVO. Platelet activation markers were reduced in plasma samples obtained during AMI, suggesting an anti-aggregatory capacity of APOSEC. This finding was confirmed by in vitro tests showing that activation and aggregation of both porcine and human platelets were significantly impaired by co-incubation with APOSEC, paralleled by vasodilator-stimulated phosphoprotein (VASP)-mediated inhibition of platelets. In addition, APOSEC evidenced a significant vasodilatory capacity on coronary arteries via p-eNOS and iNOS activation. Our data give first evidence that APOSEC reduces the extent of MVO during AMI, and suggest that modulation of platelet activation and vasodilation in the initial phase after myocardial infarction contributes to the improved long-term outcome in APOSEC treated animals.

Laropiprant attenuates EP3 and TP prostanoid receptor-mediated thrombus formation

The use of the lipid lowering agent niacin is hampered by a frequent flush response which is largely mediated by prostaglandin (PG) D₂. Therefore, concomitant administration of the D-type prostanoid (DP) receptor antagonist laropiprant has been proposed to be a useful approach in preventing niacin-induced flush. However, antagonizing PGD₂, which is a potent inhibitor of platelet aggregation, might pose the risk of atherothrombotic events in cardiovascular disease. In fact, we found that in vitro treatment of platelets with laropiprant prevented the inhibitory effects of PGD₂ on platelet function, i.e. platelet aggregation, Ca²⁺ flux, P-selectin expression, activation of glycoprotein IIb/IIIa and thrombus formation. In contrast, laropiprant did not prevent the inhibitory effects of acetylsalicylic acid or niacin on thrombus formation. At higher concentrations, laropiprant by itself attenuated platelet activation induced by thromboxane (TP) and E-type prostanoid (EP)-3 receptor stimulation, as demonstrated in assays of platelet aggregation, Ca²⁺ flux, P-selectin expression, and activation of glycoprotein IIb/IIIa. Inhibition of platelet function exerted by EP4 or I-type prostanoid (IP) receptors was not affected by laropiprant. These in vitro data suggest that niacin/laropiprant for the treatment of dyslipidemias might have a beneficial profile with respect to platelet function and thrombotic events in vascular disease.

Behcet's Disease: New Concepts in Cardiovascular Involvements and Future Direction for Treatment

Behcet's disease (BD) is the only systemic vasculitis involving both arteries and vein in any sizes. It frequently encounters in rheumatology clinics. It has some major morbidities and even fatal outcomes in some cases. The aim of this paper is to analyze the main concepts on pathophysiology and treatment options in BD, focusing on cardiovascular aspects, thrombosis, and potential future treatment.

Phosphorylation of vasodilator-stimulated phosphoprotein (VASP) dampens hepatic ischemia-reperfusion injury

Recent work has demonstrated that the formation of platelet neutrophil complexes (PNCs) affects inflammatory tissue injury. Vasodilator-stimulated phosphoprotein (VASP) is crucially involved into the control of PNC formation and myocardial reperfusion injury. Given the clinical importance of hepatic IR injury we pursued the role of VASP during hepatic ischemia followed by reperfusion. We report here that VASP^−/− animals demonstrate reduced hepatic IR injury compared to wildtype (WT) controls. This correlated with serum levels of lactate dehydrogenase (LDH), aspartate (AST) and alanine (ALT) aminotransferase and the presence of PNCs within ischemic hepatic tissue and could be confirmed using repression of VASP through siRNA. In studies employing bone marrow chimeric mice we identified hematopoietic VASP to be of crucial importance for the extent of hepatic injury. Phosphorylation of VASP on Ser¹⁵³ through Prostaglandin E1 or on Ser²³⁵ through atrial natriuretic peptide resulted in a significant reduction of hepatic IR injury. This was associated with a reduced presence of PNCs in ischemic hepatic tissue. Taken together, these studies identified VASP and VASP phosphorylation as crucial target for future hepatoprotective strategies.