Platelets in atherosclerosis

Oxidative Stress and Inflammation in Renal and Cardiovascular Complications of Diabetes

Simple Summary

The progressive nature of type 2 diabetes mellitus (T2DM) leads to micro- and macro-vascular complications, including renal and cardiovascular disease. These alone, or in combination, are a major cause of premature morbidity and mortality in diabetic patients. Despite advances in glucose lowering treatments, these diabetic complications are still inadequately prevented or reversed. This ongoing cardiovascular–renal burden in diabetes poses a heavy cost on the health care system. Therefore, there is an urgent need to develop more effective treatments. In this review, we discuss how oxidative stress and inflammation induce and perpetuate the renal and cardiovascular complications of diabetes. It is particularly important to understand these driving mechanisms in order to elucidate pharmacological targets and mechanism-based future drug therapies.

Abstract

Oxidative stress and inflammation are considered major drivers in the pathogenesis of diabetic complications, including renal and cardiovascular disease. A symbiotic relationship also appears to exist between oxidative stress and inflammation. Several emerging therapies target these crucial pathways, to alleviate the burden of the aforementioned diseases. Oxidative stress refers to an imbalance between reactive oxygen species (ROS) and antioxidant defenses, a pathological state which not only leads to direct cellular damage but also an inflammatory cascade that further perpetuates tissue injury. Emerging therapeutic strategies tackle these pathways in a variety of ways, from increasing antioxidant defenses (antioxidants and Nrf2 activators) to reducing ROS production (NADPH oxidase inhibitors and XO inhibitors) or inhibiting the associated inflammatory pathways (NLRP3 inflammasome inhibitors, lipoxins, GLP-1 receptor agonists, and AT-1 receptor antagonists). This review summarizes the mechanisms by which oxidative stress and inflammation contribute to and perpetuate diabetes associated renal and cardiovascular disease along with the therapeutic strategies which target these pathways to provide reno and cardiovascular protection in the setting of diabetes.

Targeting Platelet in Atherosclerosis Plaque Formation: Current Knowledge and Future Perspectives

Besides their role in hemostasis and thrombosis, it has become increasingly clear that platelets are also involved in many other pathological processes of the vascular system, such as atherosclerotic plaque formation. Atherosclerosis is a chronic vascular inflammatory disease, which preferentially develops at sites under disturbed blood flow with low speeds and chaotic directions. Hyperglycemia, hyperlipidemia, and hypertension are all risk factors for atherosclerosis. When the vascular microenvironment changes, platelets can respond quickly to interact with endothelial cells and leukocytes, participating in atherosclerosis. This review discusses the important roles of platelets in the plaque formation under pro-atherogenic factors. Specifically, we discussed the platelet behaviors under disturbed flow, hyperglycemia, and hyperlipidemia conditions. We also summarized the molecular mechanisms involved in vascular inflammation during atherogenesis based on platelet receptors and secretion of inflammatory factors. Finally, we highlighted the studies of platelet migration in atherogenesis. In general, we elaborated an atherogenic role of platelets and the aspects that should be further studied in the future.

Platelet activation contributes to hypoxia-induced inflammation

Inflammation is central to the pathogenesis of pulmonary vascular remodeling and pulmonary hypertension (PH). Inflammation precedes remodeling in preclinical models, thus supporting the concept that changes in immunity drive remodeling in PH. Platelets are recognized as mediators of inflammation, but whether platelets contribute to hypoxia-driven inflammation has not been studied. We utilized a murine hypoxia model to test the hypothesis that platelets drive hypoxia-induced inflammation. We evaluated male and female 9-wk-old normoxic and hypoxic mice and in selected experiments included hypoxic thrombocytopenic mice. Thrombocytopenic mice were generated with an anti-GP1bα rat IgG antibody. We also performed immunostaining of lung sections from failed donor controls and patients with idiopathic pulmonary arterial hypertension. We found that platelets are increased in the lungs of hypoxic mice and hypoxia induces platelet activation. Platelet depletion prevents hypoxia-driven increases in the proinflammatory chemokines CXCL4 and CCL5 and attenuates hypoxia-induced increase in plasma CSF-2. Pulmonary interstitial macrophages are increased in the lungs of hypoxic mice; this increase is prevented in thrombocytopenic mice. To determine the potential relevance to human disease, lung sections from donors and patients with advanced idiopathic pulmonary arterial hypertension (iPAH) were immunostained for the platelet-specific protein CD41. We observed iPAH lungs had a two-fold increase in CD41, compared with controls. Our data provide evidence that the platelet count is increased in the lungs and activated in mice with hypoxia-induced inflammation and provides rationale for the further study of the potential contribution of platelets to inflammatory mediated vascular remodeling and PH.

Platelet apelin receptor expression is reduced in patients with acute myocardial infarction

BACKGROUND

The G-protein-coupled apelin receptor and its apelin ligand are an emerging regulatory system of the vascular homeostasis. To date, the implications of the apelin/apelin receptor system in athero-thrombosis are not completely clarified yet. This study determines the expression of the apelin receptor on human platelets, the effect of different apelin isoforms on platelet aggregation and the potential role of the apelin/apelin receptor system in acute myocardial infarction.

METHODS

We applied immunofluorescence staining, Western Blot analysis, aggregometry, and flow cytometry to elucidate the role of the apelin receptor in activated platelets. Furthermore, in an observational pilot study, we assessed platelet apelin recpetor expression and apelin-17 plasma levels in patients with acute myocardial infarction (AMI, n = 27).

RESULTS

Immunofluorescence staining indicates that the apelin receptor is located at the cell membrane in resting platelets and diminishes upon activation with a selective thrombin receptor-activating peptide (AP1, 3 to 100 μM). Western Blot analyses of AP1-activated platelets and their supernatants suggest that the apelin receptor is not predominantly internalized but is released from activated platelets. The isoform apelin-17 attenuated AP-1-induced platelet activation in-vitro, presumably via a NO-dependent mechanism. Furthermore, platelet apelin receptor expression was significantly reduced in patients with AMI (n = 27) compared to age-matched controls (n = 14; p < 0.05) and inversely correlated with troponin I plasma levels (r = -0.46; p = 0.03). Besides that, circulating apelin-17 was significantly reduced in MI patients compared to the control group.

CONCLUSION

Taken together, our data support a crucial role of the platelet apelinergic system assuming an antithrombotic effect and therefore holding a potential diagnostic and therapeutic impact.

The association between carotid atherosclerosis and treatment with lithium and antipsychotics in patients with bipolar disorder

OBJECTIVES

Patients with bipolar disorder are at high risk of cardiovascular diseases. Among cardiovascular diseases, coronary heart disease and stroke are the leading causes of premature death and both share the pathogenesis of arterial atherosclerosis. Increased carotid intima-media thickness is sensitive for detecting early atherosclerosis and a practical index for predicting cardiovascular diseases. However, few studies investigated carotid intima-media thickness in adults with bipolar disorder. We attempted to determine the factors associated with carotid intima-media thickness in adults with bipolar disorder.

METHODS

The euthymic out-patients with bipolar I disorder aged over 20 years were recruited to measure the carotid intima-media thickness value through B-mode carotid ultrasound. Those with any psychiatric disorder, acute or life-threatening medical condition were excluded. All clinical information was obtained by reviewing medical records and directly interviewing patients with reliable others.

RESULTS

Of the 106 participants with a mean age of 44.5 years, 40.6% (N = 43) had concurrent cardiovascular/endocrine/metabolic diseases. A multivariate regression indicated that higher assumed daily lithium dosage was significantly associated with a decreased carotid intima-media thickness in the whole sample. In the young subgroup (⩽45 years old, N = 63), higher current daily lithium dosage and lower body mass index were associated with lower carotid intima-media thickness. In those without concurrent cardiovascular/endocrine/metabolic diseases, higher ratio of first-generation antipsychotics exposure in relation to illness chronicity was associated with higher carotid intima-media thickness, after controlling for body mass index or age.

CONCLUSION

Lithium treatment may be associated with less progression in carotid intima-media thickness and the reduced risk for atherosclerosis in adults with bipolar disorder, including those with high cardiovascular disease risk. In addition to age and body mass index, antipsychotics may increase carotid intima-media thickness even in the low cardiovascular disease-risk patients.

Drug Targeting via Platelet Membrane-Coated Nanoparticles

Platelets possess distinct surface moieties responsible for modulating their adhesion to various disease-relevant substrates involving vascular damage, immune evasion, and pathogen interactions. Such broad biointerfacing capabilities of platelets have inspired the development of platelet-mimicking drug carriers that preferentially target drug payloads to disease sites for enhanced therapeutic efficacy. Among these carriers, platelet membrane-coated nanoparticles (denoted 'PNPs') made by cloaking synthetic substrates with the plasma membrane of platelets have emerged recently. Their 'top-down' design combines the functionalities of natural platelet membrane and the engineering flexibility of synthetic nanomaterials, which together create synergy for effective drug delivery and novel therapeutics. Herein, we review the recent progress of engineering PNPs with different structures for targeted drug delivery, focusing on three areas, including targeting injured blood vessels to treat vascular diseases, targeting cancer cells for cancer treatment and detection, and targeting drug-resistant bacteria to treat infectious diseases. Overall, current studies have established PNPs as versatile nanotherapeutics for drug targeting with strong potentials to improve the treatment of various diseases.

Plasma sphingolipids and risk of cardiovascular diseases: a large-scale lipidomic analysis

INTRODUCTION

Sphingolipids are a diverse class of lipids with various roles in cell functions and subclasses such as ceramides have been associated with cardiovascular diseases (CVD) in previous studies.

OBJECTIVES

We aimed to measure molecularly-distinct sphingolipids via a large-scale lipidomic analysis and expand the literature to an Asian population.

METHODS

We performed a lipidomics evaluation of 79 molecularly distinct sphingolipids in the plasma of 2627 ethnically-Chinese Singaporeans.

RESULTS

During a mean follow-up of 12.9 years, we documented 152 cases of major CVD (non-fatal myocardial infarction, stroke and cardiovascular death). Total ceramide concentrations were not associated with CVD risk [hazard ratio (HR), 0.99; 95% CI 0.81-1.21], but higher circulating total monohexosylceramides (HR, 1.22; 95% CI 1.03, 1.45), total long-chain sphingolipids (C16-C18) (HR, 1.22; 95% CI 1.02, 1.45) and total 18:1 sphingolipids (HR, 1.21; 95% CI 1.01, 1.46) were associated with higher CVD risk after adjusting for conventional CVD risk factors.

CONCLUSIONS

Our results do not support the hypothesis that higher ceramide concentrations are linked to higher CVD risk, but suggest that other classes of sphingolipids may affect CVD risk.

The relationship between the platelet to leukocyte ratio and mechanical thrombectomy outcomes in acute ischemic stroke patients

BACKGROUND AND PURPOSE

The predictive effect of blood cell ratio on ischemic event has been widely confirmed. Whether PWR and PNR can assess the risk of endovascular treatment (EVT) is largely unclear. This study aimed to investigate the prognostic value of PNR and PWR in acute ischemic stroke patients treated with EVT.

METHODS

Poor functional outcome was defined as Modified Rankin Scale (mRS) of 3-6 at 3 months, Symptomatic intracranial hemorrhage (sICH) was diagnosed based on CT scan and classified according to the criterial of Heidelberg Bleeding Classification. Binary logistical regression was used to analyze the relationship of PWR, PNR with functional outcome and symptomatic intracranial hemorrhage (sICH).

RESULTS

Patients with good prognosis had higher PNR and PWR value (29 vs. 24, P=0.002) (22 vs. 19, P=0.009), a lower rate of sICH (2.9% vs. 24.9%, P<0.001). In model 1, the lower PNR significantly associated with poor functional outcome (OR, 0.48; 95% CI 0.26-0.88; P=0.018), and sICH (OR, 0.42; 95% CI 0.19-0.91; P=0.028). The lower PWR only significantly associated with poor prognosis (OR, 0.97; 95% CI 0.94-1.00; P=0.038), and had a trend relation with sICH (OR, 0.98; 95% CI 0.94-1.02; P=0.328). In model 2 lower PNR still significantly associated with poor functional outcome (OR, 0.53; 95% CI 0.29-0.99; P=0.047), but showed a trend for predicting sICH (OR, 0.56; 95% CI 0.25-1.25; P=0.158).

CONCLUSION

Platelet to leukocyte ratio may be use to assess the risk of functional outcome and sICH in patients with acute anterior circulation occlusion stroke undergoing endovascular treatment in real world China.

Prioritization of causal genes for coronary artery disease based on cumulative evidence from experimental and in silico studies

Genome-wide association studies have led to a significant progress in identification of genomic loci affecting coronary artery disease (CAD) risk. However, revealing the causal genes responsible for the observed associations is challenging. In the present study, we aimed to prioritize CAD-relevant genes based on cumulative evidence from the published studies and our own study of colocalization between eQTLs and loci associated with CAD using SMR/HEIDI approach. Prior knowledge of candidate genes was extracted from both experimental and in silico studies, employing different prioritization algorithms. Our review systematized information for a total of 51 CAD-associated loci. We pinpointed 37 genes in 36 loci. For 27 genes we infer they are causal for CAD, and for 10 further genes we judge them most likely causal. Colocalization analysis showed that for 18 out of these loci, association with CAD can be explained by changes in gene expression in one or more CAD-relevant tissues. Furthermore, for 8 out of 36 loci, existing evidence suggested additional CAD-associated genes. For the remaining 15 loci, we concluded that evidence for gene prioritization remains inconsistent, insufficient, or absent. Our results provide deeper insights into the genetic etiology of CAD and demonstrate knowledge gaps where further research is warranted.

Platelets in Healthy and Disease States: From Biomarkers Discovery to Drug Targets Identification by Proteomics

Platelets are a heterogeneous small anucleate blood cell population with a central role both in physiological haemostasis and in pathological states, spanning from thrombosis to inflammation, and cancer. Recent advances in proteomic studies provided additional important information concerning the platelet biology and the response of platelets to several pathophysiological pathways. Platelets circulate systemically and can be easily isolated from human samples, making proteomic application very interesting for characterizing the complexity of platelet functions in health and disease as well as for identifying and quantifying potential platelet proteins as biomarkers and novel antiplatelet therapeutic targets. To date, the highly dynamic protein content of platelets has been studied in resting and activated platelets, and several subproteomes have been characterized including platelet-derived microparticles, platelet granules, platelet releasates, platelet membrane proteins, and specific platelet post-translational modifications. In this review, a critical overview is provided on principal platelet proteomic studies focused on platelet biology from signaling to granules content, platelet proteome changes in several diseases, and the impact of drugs on platelet functions. Moreover, recent advances in quantitative platelet proteomics are discussed, emphasizing the importance of targeted quantification methods for more precise, robust and accurate quantification of selected proteins, which might be used as biomarkers for disease diagnosis, prognosis and therapy, and their strong clinical impact in the near future.

Intelligent classification of platelet aggregates by agonist type

Platelets are anucleate cells in blood whose principal function is to stop bleeding by forming aggregates for hemostatic reactions. In addition to their participation in physiological hemostasis, platelet aggregates are also involved in pathological thrombosis and play an important role in inflammation, atherosclerosis, and cancer metastasis. The aggregation of platelets is elicited by various agonists, but these platelet aggregates have long been considered indistinguishable and impossible to classify. Here we present an intelligent method for classifying them by agonist type. It is based on a convolutional neural network trained by high-throughput imaging flow cytometry of blood cells to identify and differentiate subtle yet appreciable morphological features of platelet aggregates activated by different types of agonists. The method is a powerful tool for studying the underlying mechanism of platelet aggregation and is expected to open a window on an entirely new class of clinical diagnostics, pharmacometrics, and therapeutics.

Platelets are small cells in the blood that primarily help stop bleeding after an injury by sticking together with other blood cells to form a clot that seals the broken blood vessel. Blood clots, however, can sometimes cause harm. For example, if a clot blocks the blood flow to the heart or the brain, it can result in a heart attack or stroke, respectively. Blood clots have also been linked to harmful inflammation and the spread of cancer, and there are now preliminary reports of remarkably high rates of clotting in COVID-19 patients in intensive care units.

A variety of chemicals can cause platelets to stick together. It has long been assumed that it would be impossible to tell apart the clots formed by different chemicals (which are also known as agonists). This is largely because these aggregates all look very similar under a microscope, making it incredibly time consuming for someone to look at enough microscopy images to reliably identify the subtle differences between them. However, finding a way to distinguish the different types of platelet aggregates could lead to better ways to diagnose or treat blood vessel-clogging diseases.

To make this possible, Zhou, Yasumoto et al. have developed a method called the “intelligent platelet aggregate classifier” or iPAC for short. First, numerous clot-causing chemicals were added to separate samples of platelets taken from healthy human blood. The method then involved using high-throughput techniques to take thousands of images of these samples. Then, a sophisticated computer algorithm called a deep learning model analyzed the resulting image dataset and “learned” to distinguish the chemical causes of the platelet aggregates based on subtle differences in their shapes. Finally, Zhou, Yasumoto et al. verified iPAC method’s accuracy using a new set of human platelet samples.

The iPAC method may help scientists studying the steps that lead to clot formation. It may also help clinicians distinguish which clot-causing chemical led to a patient’s heart attack or stroke. This could help them choose whether aspirin or another anti-platelet drug would be the best treatment. But first more studies are needed to confirm whether this method is a useful tool for drug selection or diagnosis.

Activated Platelets Induce Endothelial Cell Inflammatory Response in Psoriasis via COX-1

OBJECTIVE

Patients with psoriasis have impaired vascular health and increased cardiovascular disease (CVD). Platelets are key players in the pathogenesis of vascular dysfunction in cardiovascular disease and represent therapeutic targets in cardiovascular prevention. The object of this study was to define the platelet phenotype and effector cell properties on vascular health in psoriasis and evaluate whether aspirin modulates the platelet-induced phenotype. Approach and Results: Platelets from psoriasis patients (n=45) exhibited increased platelet activation (relative to age- and gender-matched controls, n=18), which correlated with psoriasis skin severity. Isolated platelets from psoriasis patients demonstrated a 2- to 3-fold (P<0.01) increased adhesion to human aortic endothelial cells and induced proinflammatory transcriptional changes, including upregulation of IL 8 (interleukin 8), IL1β, and Cox (cyclooxygenase)-2 Platelet RNA sequencing revealed an interferon signature and elevated expression of COX-1, which correlated with psoriasis disease severity (r=0.83, P=0.01). In a randomized trial of patients with psoriasis, 2 weeks of 81 mg low-dose aspirin, a COX-1 inhibitor, reduced serum thromboxane (Tx) B2 and reduced brachial vein endothelial proinflammatory transcript expression >70% compared with the no-treatment group (P<0.01). Improvement in brachial vein endothelial cell inflammation significantly correlated with change in serum TxB2 (r=0.48, P=0.02).

CONCLUSIONS

In patients with psoriasis, platelets are activated and induce endothelial cell inflammation. Low-dose aspirin improved endothelial cell health in psoriasis via platelet COX-1 inhibition. These data demonstrate a previously unappreciated role of platelets in psoriasis and endothelial cell inflammation and suggests that aspirin may be effective in improving vascular health in patients with psoriasis. Registration: URL: http://www.clinicaltrials.gov. Unique identifier: NCT03228017.

Platelet activation and prothrombotic mediators at the nexus of inflammation and atherosclerosis: Potential role of antiplatelet agents

Platelets are central to inflammation-related manifestations of cardiovascular diseases (CVD) such as atherosclerosis. Platelet-activating factor (PAF), thrombin, thromboxane A₂ (TxA₂), and adenosine diphosphate (ADP) are some of the key agonists of platelet activation that are at the intersection between a plethora of inflammatory pathways that modulate pro-inflammatory and coagulation processes. The aim of this article is to review the role of platelets and the relationship between their structure, function, and the interactions of their constituents in systemic inflammation and atherosclerosis. Antiplatelet therapies are discussed with a view to primary prevention of CVD by the clinical reduction of platelet reactivity and inflammation. Current antiplatelet therapies are effective in reducing cardiovascular risk but increase bleeding risk. Novel therapeutic antiplatelet approaches beyond current pharmacological modalities that do not increase the risk of bleeding require further investigation. There is potential for specifically designed nutraceuticals that may become safer alternatives to pharmacological antiplatelet agents for the primary prevention of CVD but there is serious concern over their efficacy and regulation, which requires considerably more research.

Platelet aggregation is not altered among men with diabetes mellitus

AIMS

Platelets are pivotal in arterial thrombosis, and platelet hyperresponsiveness may contribute to the increased incidence of cardiovascular events in diabetes mellitus. Consequently, we hypothesized that increased in vitro platelet aggregation responses exist in men with diabetes mellitus.

METHODS

The Danish Cardiovascular Screening Trial (DANCAVAS) is a community-based cardiovascular screening trial including men aged 65-74 years. Platelet aggregation was tested using 96-well light transmission aggregometry with thrombin receptor-activating peptide (TRAP), adenosine diphosphate, collagen type 1, arachidonic acid and protease-activated receptor-4 in three concentrations. Further, cardiovascular risk factors and coronary artery calcification (CAC), estimated by CT scans and ankle-brachial index, were obtained.

RESULTS

Included were 720 men aged 65-74 years, 110 with diabetes mellitus. Overall, there was no difference in platelet aggregation among men with versus without diabetes mellitus when adjusting for or excluding platelet inhibitor treatment and men with established cardiovascular disease (CVD). This was true for all agonists, e.g., 10 µM TRAP-induced platelet aggregation of median 69% (IQR 53-75) versus 70% (IQR 60-76) in men with versus without diabetes mellitus. Platelet aggregation did not correlate with HbA_1c or CAC. Men with diabetes mellitus displayed higher CAC, median 257 Agatston units (IQR 74-1141) versus median 111 Agatston units (IQR 6-420) in the remaining individuals, p < 0.0001.

CONCLUSIONS

Among outpatients with diabetes mellitus, but no CVD and no platelet inhibitor treatment, neither are platelets hyperresponsive in diabetes mellitus, nor is platelet aggregation associated with glycemic status or with the degree of coronary atherosclerosis.

TRIAL REGISTRATION

ISRCTN12157806.

Platelet activation in experimental murine neonatal pulmonary hypertension

Serotonin (5-HT) contributes to the pathogenesis of experimental neonatal pulmonary hypertension (PH) associated with bronchopulmonary dysplasia (BPD). Platelets are the primary source of circulating 5-HT and is released upon platelet activation. Platelet transfusions are associated with neonatal mortality and increased rates of BPD. As BPD is often complicated by PH, we tested the hypothesis that circulating platelets are activated and also increased in the lungs of neonatal mice with bleomycin-induced PH associated with BPD. Newborn wild-type mice received intraperitoneal bleomycin (3 units/kg) three times weekly for 3 weeks. Platelets from mice with experimental PH exhibited increased adhesion to collagen under flow (at 300 s-1 and 1,500 s-1 ) and increased expression of the αIIbβ3 integrin and phosphatidylserine, markers of platelet activation. Platelet-derived factors 5-HT and platelet factor 4 were increased in plasma from mice with experimental PH. Pharmacologic blockade of the 5-HT 2A receptor (5-HT 2A R) prevents bleomycin-induced PH and pulmonary vascular remodeling. Here, platelets from mice with bleomycin-induced PH demonstrate increased 5-HT 2A R expression providing further evidence of both platelet activation and increased 5-HT signaling in this model. In addition, bleomycin treatment increased lung platelet accumulation. In summary, platelets are activated, granule factors are released, and are increased in numbers in the lungs of mice with experimental neonatal PH. These results suggest platelet activation and release of platelet-derived factors may increase vascular tone, promote aberrant angiogenesis, and contribute to the development of neonatal PH.

Near-infrared -triggered release of tirofiban from nanocarriers for the inhibition of platelet integrin αIIbβ3 to decrease early-stage neointima formation

Platelets play an important role in the early stage of arterial remodeling after injury. Integrin GPIIb/IIIα (αIIbβ3) regulates platelet activation in the inside-out and outside-in signaling pathways. The use of tirofiban, an integrin αIIbβ3 inhibitor, in clinical therapy is limited by its short in vivo circulation time. Herein, a controlled drug-release system was formulated using CuS@mSiO2-PEG core-shell nanoparticles as near-infrared-triggered nanocarriers to release tirofiban on demand. The nanocarriers possessed good colloidal stability and very high loading efficiency for the integrin αIIbβ3 inhibitor (14.5 wt% for tirofiban). Local application of αIIbβ3 antagonist-tirofiban on an injured arterial wall inhibited platelet activation, which was accelerated by laser irradiation. Ex vivo platelet-promoted monocyte transmigration trans-well assays revealed decreased monocyte transmigration after platelet activation was inhibited by tirofiban. Two weeks after the wire-induced injury, the intimal area and cellular content were analyzed. The neointimal area was decreased in ApoE-/- mice with CuS@mSiO2-PEG/tirofiban and laser irradiation-promoted tirofiban release, which had limited the neointima formation. The lesions showed a decreased content of macrophages and smooth muscle cells compared with ApoE-/- mice without tirofiban inhibition. Therefore, the action of platelet-integrin αIIbβ3 in neointima formation after vascular injury was successfully inhibited in vivo through the controlled release of tirofiban using a near-infrared-triggered nanocarrier, leading to the decrease of early-stage neointima formation. This study also emphasizes the role of platelets in vascular remodeling and provides a new target, namely integrin αIIbβ3, for the inhibition of neointimal hyperplasia during vascular inflammation.

P2Y12 Inhibition beyond Thrombosis: Effects on Inflammation

The P2Y₁₂ receptor is a key player in platelet activation and a major target for antithrombotic drugs. The beneficial effects of P2Y₁₂ receptor antagonists might, however, not be restricted to the primary and secondary prevention of arterial thrombosis. Indeed, it has been established that platelet activation also has an essential role in inflammation. Additionally, nonplatelet P2Y₁₂ receptors present in immune cells and vascular smooth muscle cells might be effective players in the inflammatory response. This review will investigate the biological and clinical impact of P2Y₁₂ receptor inhibition beyond its platelet-driven antithrombotic effects, focusing on its anti-inflammatory role. We will discuss the potential molecular and cellular mechanisms of P2Y₁₂-mediated inflammation, including cytokine release, platelet–leukocyte interactions and neutrophil extracellular trap formation. Then we will summarize the current evidence on the beneficial effects of P2Y₁₂ antagonists during various clinical inflammatory diseases, especially during sepsis, acute lung injury, asthma, atherosclerosis, and cancer.

Diallyl Trisulfide Inhibits Platelet Aggregation through the Modification of Sulfhydryl Groups

Diallyl trisulfide (DATS) is a secondary metabolite of allicin, a volatile organosulfur flavoring compound generated by the crushing of garlic. These compounds have various medicinal effects such as antiplatelet activity. In this study, we demonstrated for the first time the cellular mechanism involved in the inhibition of platelet aggregation by DATS and dipropyl trisulfide (DPTS), which is a saturated analogue of DATS. Washed murine platelets were incubated with these sulfides, and platelet aggregation was evaluated by light transmission aggregometry. The amount of reaction products produced by DATS, DPTS, and glutathione (GSH) was measured using liquid chromatography-mass spectrometry. Compared with DPTS, DATS potently inhibited platelet aggregation induced by thrombin, U46619, and collagen. N-Ethylmaleimide (NEM), which is commonly used to modify sulfhydryl groups, also suppressed platelet aggregation. The reactivity of DATS with GSH was higher than that of DPTS. These data suggested that DATS inhibited platelet aggregation through the reaction of sulfhydryl groups.

Platelet to lymphocyte ratio predicting 6-month primary patency of drug-coated balloon for femoropopliteal disease

Background

Inflammatory reaction is an essential factor in the occurrence, development and prognosis of femoropopliteal disease (FPD). The ratio of platelets to lymphocytes (PLR) is a new indicator reflecting platelet aggregation and burden of systemic inflammation. Our study is to explore the association between preoperative platelet-to-lymphocyte ratio (pre-PLR) and 6-month primary patency (PP) after drug-coated balloon (DCB) in FPD.

Methods

There were 70 patients who underwent DCB for FPD contained in the study. According to 6-month PP, patients were divided into group A (PP ≥6 months, n = 54) and group B (PP < 6 months, n = 16). Logistic regression analysis was used to identify potential predictors for 6-month PP after DCB in FPD. A receiver operating characteristic (ROC) curve analysis was used to identify the cut-off value of pre-PLR to predict 6-month PP.

Results

Logistic regression analysis showed that pre-PLR (OR: 1.008, 95% CI: 1.001–1.016, P = 0.031) and lesion length > 10 cm (OR: 4.305, 95% CI: 1.061–17.465, P = 0.041) were independently predictive for 6-month PP. The cutoff value of pre-PLR obtained from the ROC analysis was 127.35 to determine 6-month PP with the area of 0.839. Subgroup analysis was conducted based on the cutoff value of pre-PLR. The 6-month PP in the group of pre-PLR < 127.35 was higher than that of pre-PLR ≥ 127.35 group (p < 0.001).

Conclusions

The present study indicated that an elevated pre-PLR was an effective additional indicator for predicting early PP in FPD after DCB.

Comprehensive analysis of circRNA expression pattern and circRNA-miRNA-mRNA network in the pathogenesis of atherosclerosis in rabbits

Atherosclerosis is a chronic and multifactorial inflammatory disease and is closely associated with cardiovascular and cerebrovascular diseases. circRNAs can act as competing endogenous RNAs to mRNAs and function in various diseases. However, there is little known about the function of circRNAs in atherosclerosis. In this study, three rabbits in the case group were fed a high-fat diet to induce atherosclerosis and another three rabbits were fed a normal diet. To explore the biological functions of circRNAs in atherosclerosis, we analyzed the circRNA, miRNA and mRNA expression profiles using RNA-seq. Many miRNAs, mRNAs and circRNAs were identified as significantly changed in atherosclerosis. We next predicted miRNA-target interactions with the miRanda tool and constructed a differentially expressed circRNA-miRNA-mRNA triple network. A gene ontology enrichment analysis showed that genes in the network were involved in cell adhesion, cell activation and the immune response. Furthermore, we generated a dysregulated circRNA-related ceRNAs network and found seven circRNAs (ocu-cirR-novel-18038, -18298, -15993, -17934, -17879, -18036 and -14389) were related to atherosclerosis. We found these circRNAs also functioned in cell adhesion, cell activation and the immune response. These results show that the crosstalk between circRNAs and their competing mRNAs might play crucial roles in the development of atherosclerosis.

Inflammation in acute coronary syndrome: Expression of TLR2 mRNA is increased in platelets of patients with ACS

Background

Platelets are key components in atherogenesis and determine the course of its clinical sequelae acute coronary syndrome (ACS). Components of the innate immune system—the superfamily of TLR receptors–are present in platelets and represent a link between atherothrombosis and inflammation. We hypothesize that alteration in platelet TLR mRNA expression is a result of inflammation driving coronary atherosclerosis and may represent an alternative platelet activation pathway in ACS.

TLR2-, TLR4- and TLR9- mRNA-expression was determined in ACS patients and compared to patients with invasive exclusion of atherosclerotic lesions of coronary arteries.

Methods

A total of fifty-four patients were enrolled in this clinical retrospective cohort single centre study. Total RNA from sepharose-filtered highly purified platelets was isolated using acid guanidinium thiocyanate-phenol-chloroform extraction and transcribed to cDNA using a first strand cDNA synthesis kit. To determine absolute copy numbers of TLR2, TLR4 and TLR9 we used plasmid based quantitative PCR with normalisation to an internal control.

Results

We found that mRNA expression levels of TLR2 but not TLR 4 and 9 are up-regulated in platelets of patients with ACS when compared to patients without coronary atherosclerosis.

Conclusion

Our results suggest elevated TLR2 mRNA expression in platelets as a biomarker reflecting the underlying inflammation in ACS and possibly severity of coronary atherosclerosis. Platelet TLR2 may represent a link between inflammation and atherothrombosis in ACS.

Oxidative pathways of arachidonic acid as targets for regulation of platelet activation

Platelet activation plays an important role in acute and chronic cardiovascular disease states. Multiple pathways contribute to platelet activation including those dependent upon arachidonic acid. Arachidonic acid is released from the platelet membrane by phospholipase A2 action and is then metabolized in the cytosol by specific arachidonic acid oxidation enzymes including prostaglandin H synthase, 12-lipoxygenase, and cytochrome P450 to produce pro- and anti-inflammatory eicosanoids. This review aims to analyze the role of arachidonic acid oxidation on platelet activation, the enzymes that use it as a substrate associated as novel therapeutics target for antiplatelet drugs.

Platelets and Hepatocellular Cancer: Bridging the Bench to the Clinics

Growing interest is recently being focused on the role played by the platelets in favoring hepatocellular cancer (HCC) growth and dissemination. The present review reports in detail both the experimental and clinical evidence published on this topic. Several growth factors and angiogenic molecules specifically secreted by platelets are directly connected with tumor progression and neo-angiogenesis. Among them, we can list the platelet-derived growth factor, the vascular endothelial growth factor, the endothelial growth factor, and serotonin. Platelets are also involved in tumor spread, favoring endothelium permeabilization and tumor cells’ extravasation and survival in the bloodstream. From the bench to the clinics, all of these aspects were also investigated in clinical series, showing an evident correlation between platelet count and size of HCC, tumor biological behavior, metastatic spread, and overall survival rates. Moreover, a better understanding of the mechanisms involved in the platelet–tumor axis represents a paramount aspect for optimizing both current tumor treatment and development of new therapeutic strategies against HCC.

Passing the Vascular Barrier: Endothelial Signaling Processes Controlling Extravasation

A central function of the vascular endothelium is to serve as a barrier between the blood and the surrounding tissue of the body. At the same time, solutes and cells have to pass the endothelium to leave or to enter the bloodstream to maintain homeostasis. Under pathological conditions, for example, inflammation, permeability for fluid and cells is largely increased in the affected area, thereby facilitating host defense. To appropriately function as a regulated permeability filter, the endothelium uses various mechanisms to allow solutes and cells to pass the endothelial layer. These include transcellular and paracellular pathways of which the latter requires remodeling of intercellular junctions for its regulation. This review provides an overview on endothelial barrier regulation and focuses on the endothelial signaling mechanisms controlling the opening and closing of paracellular pathways for solutes and cells such as leukocytes and metastasizing tumor cells.

Effects of high-intensity interval training on platelet function in cardiac rehabilitation: a randomised controlled trial

Objective

To compare effects of moderate-intensity continuous training (MICT) and high-intensity interval training (HIIT) on platelet function in patients undergoing cardiac rehabilitation, as hyper-reactive platelets are involved in atherogenesis and atherothrombosis.

Methods

In this single-centre parallel group randomised controlled trial, male patients after an acute coronary syndrome under dual antiplatelet therapy performed MICT or HIIT+MICT for 12 weeks. Main outcome was platelet reactivity measured by the half-maximal concentration (EC50) of platelet agonist thrombin receptor-activating peptide-6 (TRAP-6) in terms of P-selectin expression. EC50 was determined at baseline, after 6 and 12 weeks, each time at physical rest and on exertion.

Results

82 patients were randomised to MICT or HIIT+MICT. Mean (95% CI) baseline EC50values at physical rest were 6.7 µM (6.3 µM to 7.0 µM) TRAP-6. After 6/12 weeks, 36/33 MICT and 34/28 HIIT+MICT patients were examined. HIIT+MICT patients had 0.9 µM (0.4 µM to 1.4 µM)/0.5 µM (−0.1 µM to 1.0 µM) higher EC50values than MICT ones, and the propensity of their platelets to form aggregates with monocytes was significantly lower after 12 weeks. Short-term strenuous physical exertion was generally associated with platelet activation and an EC50reduction of 0.7 µM (0.6 µM to 0.8 µM). HIIT+MICT patients tended to be fitter after 12 weeks. No serious harms were observed.

Conclusions

Including HIIT in cardiac rehabilitation seems to confer additional benefits compared with MICT alone, which should be confirmed in clinical trials with hard endpoints. Exertion-induced platelet activation and hyper-reactivity occur despite dual antiplatelet therapy.

Trial registration number

NCT02930330; Results.

Contribution of the uremic milieu to an increased pro-inflammatory monocytic phenotype in chronic kidney disease

Intermediate (CD14⁺⁺CD16⁺) monocytes have important pro-inflammatory and atherogenic features and are increased in patients with chronic kidney disease (CKD). The present study aims to elucidate the role of the uremic milieu and of platelet activation in monocyte differentiation. Monocyte subtypes were analyzed in CKD patients (n = 193) and healthy controls (n = 27). Blood from healthy controls (Ctrl; n = 8) and hemodialysis patients (HD; n = 8) was centrifuged, and plasma (pl) was exchanged between Ctrl and HD (Ctrlcells/HDpl and HDcells/Ctrlpl) or reconstituted as original (Ctrlsham and HDsham) and incubated for 24 h (T24). Monocyte differentiation and platelet aggregation to monocytes (MPA) was assessed by flow cytometry. Especially, a higher proportion of CD14⁺⁺CD16⁺ monocytes was found in hemodialysis (HD) patients (p < 0.01). In plasma exchange experiments, Ctrl cells/HD pl T24 showed an increased percentage of CD14⁺⁺CD16⁺ monocytes versus Ctrl sham (33.7% ± 15 vs. 15.7% ± 9.6; P < 0.005), comparable to the level of CD14⁺⁺CD16⁺ monocytes in the HD sham condition. The percentage of CD14⁺⁺CD16⁺ monocytes was lowered by suspending HD cells in Ctrl pl (18.4% ± 7.8 vs. 36.7% ± 15 in HD sham; P < 0.005) reaching the level of the Ctrl sham condition (15.7% ± 9.6). A mixture of uremic sulfates increased CD14⁺⁺CD16⁺ monocytes compared to control (19.8 ± 9.6% vs. 15.8 ± 10.9%; P < 0.05), paralleled by a rise MPA. Blocking MPA by abciximab, a potential therapeutic strategy, or anti-CD62P did not inhibit differentiation towards the CD14⁺⁺CD16⁺ monocytes. In conclusion, in the present cohort, CD14⁺⁺CD16⁺ monocytes are especially increased in HD patients and this can at least in part be attributed to the presence of the uremic milieu, with uremic sulfates inducing a reversible shift towards pro-inflammatory CD14⁺⁺CD16⁺ monocytes.

Impaired frequencies and function of platelets and tissue remodeling in chronic Chagas disease

Chronic inflammation, as a consequence of the persistent infection with Trypanosoma cruzi, leads to continuous activation of the immune system in patients with chronic Chagas disease. We have previously shown that increased sera levels of soluble P-selectin are associated with the severity of the cardiomyopathy distinctive of chronic Chagas disease. In this study, we explored the expression of biomarkers of platelet and endothelial activation, tissue remodeling, and mediators of the coagulation cascade in patients at different clinical stages of chronic Chagas heart disease. The frequencies of activated platelets, measured by the expression of CD41a and CD62P were decreased in patients with chronic Chagas disease compared with those in uninfected subjects, with an inverse association with disease severity. Platelet activation in response to adenosine diphosphate was also decreased in T. cruzi-infected subjects. A major proportion of T. cruzi infected subjects showed increased serum levels of fibrinogen. Patients with severe cardiac dysfunction showed increased levels of endothelin-1 and normal values of procollagen I. In conclusion, chronic infection with T. cruzi induced hemostatic alterations, even in those patients who do not yet present cardiac symptoms.

Platelets of Healthy Origins Promote Functional Improvement of Atherosclerotic Endothelial Progenitor Cells

The purpose was to evaluate the effect of platelets on functional properties of late endothelial progenitor cells (EPCs), in the direct co-culture conditions, and to investigate the involved mediators, in experimental induced atherosclerosis. The late EPCs obtained from two animal groups, hypertensive-hyperlipidemic (HH) and control (C) hamsters, named late EPCs-HH and late EPCs-C, were co-incubated with or without platelets isolated from both groups. Our results have showed that exposure to platelets from control animals: (i) promoted the late EPCs-C capacity to form colonies and capillary-like structures, and also to proliferate and migrate; (ii) improved the functional properties of late EPCs-HH; (iii) strengthened the direct binding EPCs-platelets; (iv) increased SDF-1α,VEGF, PDGF, and reduced CD40L, IL-1β,-6,-8 levels; and (v) enhanced miR-223 and IGF-1R expressions. Platelets from HH group diminished functional abilities for both EPC types and had opposite effects on these pro-angiogenic and pro-inflammatory molecules. Furthermore, testing the direct effect of miR-223 and IGF-1R on late EPCs disclosed that these molecular factors improve late EPC functional properties in atherosclerosis in terms of stimulation of the proliferation and migration abilities. In conclusion, in vitro exposure to platelets of healthy origins had a positive effect on functional properties of atherosclerotic late EPCs. The most likely candidates mediating EPC-platelet interaction can be SDF-1α, VEGF, CD40L, PDGF, IL-1β,-6,-8, miR-223, and IGF-1R. The current study brings evidences that the presence of healthy origin platelets is of utmost importance on functional improvement of EPCs in atherosclerosis.

Anti-inflammatory therapy for cardiovascular disease

Chronic subclinical inflammation is a central process in the pathogenesis of cardiovascular disease (CVD) and it has been linked with both the initiation and progression of atherosclerosis. Several pro-inflammatory cytokines, such as the C-reactive protein (CRP), tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) have been described as independent risk factors for coronary heart disease and promoters of atherogenesis. Thus, extensive research is being conducted to assess the role of anti-inflammatory therapy in the primary and secondary prevention of CVD. Our review aims to provide the clinical and scientific data pertaining to the effects of different anti-inflammatory agents administered in patients with CVD.

Co-culture of Platelets with Monocytes Induced M2 Macrophage Polarization and Formation of Foam Cells: Shedding Light on the Crucial Role of Platelets in Monocyte Differentiation

Objective

Far beyond hemostasis and thrombosis, significant evidence has indicated the critical role of platelets in atherosclerosis. SDF-1 is among the pro-inflammatory chemokines that are increased in platelets of patients with coronary artery disease (CAD). The goal of the current work is to identify the in vitro effect of platelets from either CAD patients or healthy volunteers on the induction of macrophages and foam cells.

Materials and Methods

The expression of SDF-1 on platelet surfaces in CAD patients and healthy volunteers was investigated using flow cytometry. We also evaluated the CXCR4/CXCR7 expression on monocytes from buffy coats of healthy volunteers. The effect of platelets from CAD patients and healthy volunteers on differentiation of monocytes and foam cell formation was evaluated using Oil Red O (ORO) staining. Flow cytometry and real-time PCR were also employed to evaluate surface markers and mRNA expression of genes involved in this process after co-culture of platelets with monocytes.

Results

Monocytes in co-culture with platelets acquired a spindleshape appearance and ORO-positive lipid droplets. In addition, platelets could induce CD163 expression, as an important marker of M2 macrophage, and upregulate the mRNA expression of the SRB, CD36, ACAT, LXR-α, and ABCA1 genes in monocytes. Notably, platelets of CAD patients with higher expression of SDF-1, increased the expression of genes encoding SRB and CD36 as compared to platelets of healthy volunteers.

Conclusion

Our results indicate that platelets from CAD patients could provoke monocyte differentiation into macrophages with an M2 phenotype, which in turn may participate in an atheroprotective process.

Inflammasomes: a novel therapeutic target in pulmonary hypertension?

Pulmonary hypertension (PH) is a rare, progressive pulmonary vasculopathy characterized by increased mean pulmonary arterial pressure, pulmonary vascular remodelling and right ventricular failure. Current treatments are not curative, and new therapeutic strategies are urgently required. Clinical and preclinical evidence has established that inflammation plays a key role in PH pathogenesis, and recently, inflammasomes have been suggested to be central to this process. Inflammasomes are important regulators of inflammation, releasing the pro-inflammatory cytokines IL-1β and IL-18 in response to exogenous pathogen- and endogenous damage-associated molecular patterns. These cytokines are elevated in PH patients, but whether this is a consequence of inflammasome activation remains to be determined. This review will briefly summarize current PH therapies and their pitfalls, introduce inflammasomes and the mechanisms by which they promote inflammation and, finally, highlight the preclinical and clinical evidence for the potential involvement of inflammasomes in PH pathobiology and how they may be targeted therapeutically. LINKED ARTICLES: This article is part of a themed section on Immune Targets in Hypertension. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.12/issuetoc.

Platelet pathophysiology, pharmacology, and function in coronary artery disease

Platelets play a key role in the pathophysiology of coronary artery disease and acute coronary syndromes. Our understanding of platelet function in thrombus formation has increased considerably, resulting in the development of clinically effective treatment strategies and identification of new targets. An underappreciated platelet function is their contribution toward acute and chronic inflammatory processes including atherogenesis. In this review, we discuss the role of platelets in atherosclerosis and thrombosis, platelet function testing, and the pharmacology of currently available antiplatelet drugs.

Radiopaque nano and polymeric materials for atherosclerosis imaging, embolization and other catheterization procedures

A review of radiopaque nano and polymeric materials for atherosclerosis imaging and catheterization procedures is presented in this paper. Cardiovascular diseases (CVDs) are the leading cause of death in the US with atherosclerosis as a significant contributor for mortality and morbidity. In this review paper, we discussed the physics of radiopacity and X-ray/CT, clinically used contrast agents, and the recent progress in the development of radiopaque imaging agents and devices for the diagnosis and treatment of CVDs. We focused on radiopaque imaging agents for atherosclerosis, radiopaque embolic agents and drug eluting beads, and other radiopaque medical devices related to catheterization procedures to treat CVDs. Common strategies of introducing radiopacity in the polymers, together with examples of their applications in imaging and medical devices, are also presented.

Nitrated fatty acids in cardiovascular diseases

Cardiovascular disease (CVD) is the leading cause of death and accounts for one third of disease-related mortality worldwide. Dysregulated redox mechanisms, in particular the formation of reactive oxygen species (ROS) play a pivotal pathogenetic role in CVD. Nitro-fatty acids (NO2-FAs) are electrophilic molecules which have a NO2-group bound to one of their olefinic carbons. They are endogenously formed by the reaction of reactive nitrogen species with unsaturated fatty acids. Basal levels of NO2-FAs are in the low nanomolar range and higher concentrations can be encountered under acidic (stomach) and inflammatory (e.g. ischemia/reperfusion) conditions. Dietary intake of polyunsaturated fatty acids in combination with nitrites raises circulating NO2-FAs to a clinically relevant level in mice. NO2-FAs undergo reversible covalent binding to cysteine residues and by virtue of these posttranslational protein modifications act as potent anti-inflammatory signaling mediators via modulation of various critical pathways like nuclear factor E2-related factor 2 (Nrf2)- and peroxisome proliferator-activated receptor γ (PPARγ) activation, nuclear factor-kappa B (NF-κB) inhibition and hem oxygenase-1 (HO-1)- and heat shock protein (HSP) induction. In this review article, we summarize recent findings about the effects and underlying molecular mechanisms of NO2-FAs from a variety of pre-clinical cardiovascular disease models. The described findings suggest the potential of NO2-FAs to emerge as therapeutic agents with a broad range of potential clinical applications for CVD.

Nanoparticle Functionalization with Platelet Membrane Enables Multifactored Biological Targeting and Detection of Atherosclerosis

Cardiovascular disease represents one of the major causes of death across the global population. Atherosclerosis, one of its most common drivers, is characterized by the gradual buildup of arterial plaque over time, which can ultimately lead to life-threatening conditions. Given the impact of the disease on public health, there is a great need for effective and noninvasive imaging modalities that can provide valuable information on its biological underpinnings during development. Here, we leverage the role of platelets in atherogenesis to design nanocarriers capable of targeting multiple biological elements relevant to plaque development. Biomimetic nanoparticles are prepared by coating platelet membrane around a synthetic nanoparticulate core, the product of which is capable of interacting with activated endothelium, foam cells, and collagen. The effects are shown to be exclusive to platelet membrane-coated nanoparticles. These biomimetic nanocarriers are not only capable of efficiently localizing to well-developed atherosclerotic plaque, but can also target subclinical regions of arteries susceptible to plaque formation. Using a commonly employed magnetic resonance imaging contrast agent, live detection is demonstrated using an animal model of atherosclerosis. Ultimately, this strategy may be leveraged to better assess the development of atherosclerosis, offering additional information to help clinicians better manage the disease.

Patrolling Mechanics of Non-Classical Monocytes in Vascular Inflammation

Non-classical monocytes have emerged as the preeminent vascular housekeepers. Continuous intravascular screening is enabled by slow patrolling on the endothelium and allows a rapid response to local perturbations. Intravital imaging has been crucial to elucidate the molecular mechanisms and migratory phenotype of patrolling. In this review, we discuss technical requirements of intravital microscopy such as imaging modalities, labeling strategies, and data analysis. We further focus on patrolling kinetics and adhesion receptors in different organs and vascular beds including arteries during homeostasis and vascular inflammation and define pertinent questions in the field.

Platelet chemokines in health and disease

In recent years, it has become clear that platelets and platelet-derived chemokines, beyond their role in thrombosis and haemostasis, are important mediators affecting a broad spectrum of (patho)physiological conditions. These biologically active proteins are released from α-granules upon platelet activation, most probably even during physiological conditions. In this review, we give a concise overview and an update on the current understanding of platelet-derived chemokines in a context of health and disease.

Note: The review process for this manuscript was fully handled by G. Y. H. Lip, Editor in Chief.

Identification of CalDAG-GEFI as an intracellular target for the vicinal dithiol binding agent phenylarsine oxide in human platelets

CalDAG-GEFI, a guanine nucleotide exchange factor activating Rap1, is known to play a key role in Ca2+-dependent glycoprotein (GP)IIb/IIIa activation and platelet aggregation. Although inhibition of CalDAG-GEFI could be a potential strategy for antiplatelet therapy, no inhibitor of this protein has been identified. In the present study, phenylarsine oxide (PAO), a vicinal dithiol blocker, potently prevented Rap1 activation in thrombin-stimulated human platelets without significantly inhibiting intracellular Ca2+ mobilisation and protein kinase C activation. PAO also prevented the Ca2+ ionophore-induced Rap1 activation and platelet aggregation, which are dependent on CalDAG-GEFI. In the biotin-streptavidin pull-down assay, CalDAG-GEFI was efficiently pull-downed by streptavidin beads from the lysates of biotin-conjugated PAO-treated platelets, suggesting that PAO binds to intracellular CalDAG-GEFI with high affinity. The above effects of PAO were reversed by a vicinal dithiol compound 2,3-dimercaptopropanol. In addition, CalDAG-GEFI formed disulfide-linked oligomers in platelets treated with the thiol-oxidant diamide, indicating that CalDAG-GEFI contains redox-sensitive thiols. In a purified recombinant protein system, PAO directly inhibited CalDAG-GEFI-stimulated GTP binding to Rap1. Using CalDAG-GEFI and Rap1-overexpressed human embryonic kidney 293T cells, we further confirmed that PAO abolished Ca2+-mediated Rap1 activation. Taken together, these results have demonstrated that CalDAG-GEFI is one of the targets of action of PAO, and propose an important role of vicinal cysteines for the functions of CalDAG-GEFI.

Platelets directly enhance neutrophil transmigration in response to oxidised low-density lipoprotein

Beyond their primary role in haemostasis and tissue repair, platelets are causally involved in the onset of inflammatory reactions, cell proliferation and immune response. Platelet activation and platelet binding to the endothelium result in release of chemokines and increased expression of adhesion molecules, which promote the recruitment of leukocytes that will eventually migrate across the endothelium into the tissue. Here, we provide the first evidence that platelets stimulated with oxidised low-density lipoprotein (oxLDL) directly enhance recruitment and transmigration of neutrophils, via cell-cell interaction. OxLDL immediately activates platelets, which then rapidly bind to neutrophils, foster their activation and facilitate transmigration through an endothelial monolayer. The observed effects of oxLDL on platelet-neutrophil aggregate (PNA) formation depend on incubation time, lipoprotein concentration and the degree of oxidative modification of LDL. PNA form within minutes following stimulation by oxLDL and remain for up to 1 h post stimulation, while native LDL is unable to induce platelet-neutrophil interactions. In the presence of acetylsalicylic acid the formation of PNA in response to oxLDL is virtually absent, and platelets fail to further enhance oxLDL-induced neutrophil transmigration. P2Y1 and P2Y12 inhibitors have less pronounced effects on PNA formation in response to oxLDL. Furthermore, we demonstrate that the PI3K pathway is essential for efficient neutrophil transmigration induced by oxLDL. Consequently, platelets enhance neutrophil transmigration in response to oxLDL and might thereby contribute essentially to the amplification of inflammatory processes within the vessel wall, which fosters the development of atherosclerosis.

Circulating miRNAs: messengers on the move in cardiovascular disease

Note: The review process for this paper was fully handled by G. Y. H. Lip, Editor in Chief.

Platelet receptors as therapeutic targets: Past, present and future

Anti-platelet drugs reduce arterial thrombosis after plaque rupture and erosion, prevent stent thrombosis and are used to prevent and treat myocardial infarction and ischaemic stroke. Some of them may also be helpful in treating less frequent diseases such as thrombotic thrombocytopenic purpura. The present concise review aims to cover current and future developments of anti-platelet drugs interfering with the interaction of von Willebrand factor (VWF) with glycoprotein (GP) Ibα, and directed against GPVI, GPIIb/IIIa (integrin αIIbβ3), the thrombin receptor PAR-1, and the ADP receptor P2Y12. The high expectations of having novel antiplatelet drugs which selectively inhibit arterial thrombosis without interfering with normal haemostasis could possibly be met in the near future.

Fractalkine – a local inflammatory marker aggravating platelet activation at the vulnerable plaque

Chemokines play an important role in inducing chemotaxis of cells, piloting white blood cells in immune surveillance and are crucial parts in the development and progression of atherosclerosis. Platelets are mandatory players in the initiation of atherosclerotic lesion formation and are susceptible targets for and producers of chemokines. Several chemokine receptors on platelets have been described previously, amongst them CX3CR1, the receptor for fractalkine. The unique chemokine fractalkine (CX3CL1, FKN) exists as a soluble as well as a membrane-anchored glycoprotein. Its essential role in the formation of atherosclerotic lesions and atherosclerosis progression has been impressively described in mouse models. Moreover, fractalkine induces platelet activation and adhesion via a functional fractalkine receptor (CX3CR1) expressed on the platelet surface. Platelet activation via the FKN/CX3CR1-axis triggers leukocyte adhesion to activated endothelium, and fractalkine-induced platelet P-selectin is mandatory for leukocyte recruitment under arterial flow conditions. This review summarises the role of fractalkine as a potential local inflammatory mediator which influences platelet activation in the setting of atherosclerosis. Beyond that, aspects of a potential interaction between fractalkine and platelet responsiveness to antiplatelet drugs are described. Furthermore, the possible impact of high-density lipoprotein cholesterol (HDL-C) on atherosclerosis progression, platelet activation and fractalkine signalling are discussed.

CD4+ T cells in atherosclerosis: Regulation by platelets

Atherosclerosis is an inflammatory and thrombotic disease, in which both CD4+ T cells and platelets play important roles throughout all stages of atherogenesis. CD4+ T cells are the most abundant T cells present in atherosclerotic lesions. They are primarily seen as type 1 T helper (Th1) cells, while the other CD4+ T cell subsets Th2, Th17, and regulatory T (Treg) cells are also found in the lesions with lower frequencies. CD4+ T effector cells release various cytokines, which exert paracrine or autocrine effects among different CD4+ T cell subsets and other lesional cells and subsequently modulate inflammatory processes in the lesions. Platelets are instrumental in thrombosis and haemostasis, but also play important regulatory roles in immune response, inflammation, and angiogenesis. The present review summarises the current knowledge and/or understanding on how platelets regulate recruitment, activation, differentiation, and cytokine production of different CD4+ T cell subsets, as well as impacts of the platelet-CD4+ T cell interactions on atherogenesis. The research perspectives of platelet-CD4+ T cell interaction in atherosclerosis are also discussed.

Thymidine phosphorylase: A potential new target for treating cardiovascular disease

We recently found that thymidine phosphorylase (TYMP), also known as platelet-derived endothelial cell growth factor, plays an important role in platelet activation in vitro and thrombosis in vivo by participating in multiple signaling pathways. Platelets are a major source of TYMP. Since platelet-mediated clot formation is a key event in several fatal diseases, such as myocardial infarction, stroke and pulmonary embolism, understanding TYMP in depth may lead to uncovering novel mechanisms in the development of cardiovascular diseases. Targeting TYMP may become a novel therapeutic for cardiovascular disorders. In this review article, we summarize the discovery of TYMP and the potential molecular mechanisms of TYMP involved in the development of various diseases, especially cardiovascular diseases. We also offer insights regarding future studies exploring the role of TYMP in the development of cardiovascular disease as well as in therapy.

New Concepts and Mechanisms of Platelet Activation Signaling

Upon blood vessel injury, platelets are exposed to adhesive proteins in the vascular wall and soluble agonists, which initiate platelet activation, leading to formation of hemostatic thrombi. Pathological activation of platelets can induce occlusive thrombosis, resulting in ischemic events such as heart attack and stroke, which are leading causes of death globally. Platelet activation requires intracellular signal transduction initiated by platelet receptors for adhesion proteins and soluble agonists. Whereas many platelet activation signaling pathways have been established for many years, significant recent progress reveals much more complex and sophisticated signaling and amplification networks. With the discovery of new receptor signaling pathways and regulatory networks, some of the long-standing concepts of platelet signaling have been challenged. This review provides an overview of the new developments and concepts in platelet activation signaling.

New Insights into the Role of Inflammation in the Pathogenesis of Atherosclerosis

Atherosclerosis is a chronic inflammatory disease characterized by the accumulation of lipids, smooth muscle cell proliferation, cell apoptosis, necrosis, fibrosis, and local inflammation. Immune and inflammatory responses have significant effects on every phase of atherosclerosis, and increasing evidence shows that immunity plays a more important role in atherosclerosis by tightly regulating its progression. Therefore, understanding the relationship between immune responses and the atherosclerotic microenvironment is extremely important. This article reviews existing knowledge regarding the pathogenesis of immune responses in the atherosclerotic microenvironment, and the immune mechanisms involved in atherosclerosis formation and activation.

Relationship between monocyte-platelet aggregation and endothelial function in middle-aged and elderly adults

Low-grade inflammation, endothelial dysfunction, and platelet hyper-reactivity to agonists are associated with an increased risk of cardiovascular events. In vitro and animal studies infer an inverse mechanistic relationship between platelet activation and the production of endothelium-derived nitric oxide and prostacyclin. This concept is supported by evidence of an inverse relationship between endothelial function and platelet activation in high-risk cardiac patients. The aim of this study was to investigate what relationship, if any, exists between platelet and endothelial function in healthy, middle-aged, and elderly adults. In 51 participants (18 male, 33 post menopausal female), endothelial function was assessed by flow-mediated dilation (FMD). Platelet function was assessed by flow cytometric determination of glycoprotein IIb/IIIa activation (measured by PAC-1 binding), granule exocytosis (measured by surface P-selectin expression), and monocyte-platelet aggregates (MPAs), with and without stimulation by canonical platelet agonists adenosine diphosphate (ADP), arachidonic acid (AA), and collagen. Correlation analysis indicated there was no significant (all P => 0.05) relationship between FMD and any marker of in vivo platelet activation (MPAs R = 0.193, PAC-1 R = -0.113, anti-CD62P R = -0.078) or inducible platelet activation by ADP (MPA R = -0.128, anti-CD62P R = -0.237), AA (MPA R = -0.122, PAC-1 R = -0.045, anti-CD62P R = -0.142), or collagen (MPA R = 0.136, PAC-1 R = 0.174, anti-CD62P R = -0.077). Our findings contrast with two previous studies performed in high-risk cardiac patients, which reported inverse relationships between platelet activation and endothelial function, suggesting that some compensatory redundancy may exist in the relationship between platelet and endothelial function in preclinical populations.