Platelet collagen receptors, signaling and antagonism: Emerging approaches for the prevention of intravascular thrombosis

Use of clinical biological tests of haemostasis to evaluate topical haemostatics

INTRODUCTION

In addition to traditional means, topical haemostatics are currently used to avoid haemorrhage during surgery. Although they have been reported to be effective, there is a low level of proof of their clinical efficacy, which is at odds with their levels of use. This study used two methods to better understand their in vitro mechanism of action.

METHODS

Two clinical biology assays were used to measure the action of topical haemostatics on primary and secondary haemostasis. Calibrated samples of collagen sponges and polypropylene non-woven gauze were tested. Platelet aggregation was assessed using a multichannel aggregometer. A thrombin generation assay (TGA) was used with a fluorogenic readout. Tissue factor solutions were used to activate coagulation.

RESULTS

In terms of primary haemostasis, collagen sponges stimulated platelet aggregation, in particular between 2 and 5 min after incubation with platelet-rich plasma and with no dose effect. In regard to coagulation, the kinetics of thrombin generation was enhanced. Polypropylene non-woven gauze did not exhibit any effect on platelet aggregation, although it did have a weak effect on the kinetics of thrombin generation.

CONCLUSION

Collagen is well known to exert a haemostatic effect due to its action on platelet aggregation. By contrast, polypropylene non-woven gauze has not been shown to have any effect on platelet aggregation other than a minor impact on thrombin generation. The results obtained with the devices tested are in agreement with the literature. Platelet aggregation biological assays and TGA measurements appear to be suitable for evaluation of these medical products.

Mouse skin peptidomic analysis of the hemorrhage induced by a snake venom metalloprotease

Hemorrhage induced by snake venom metalloproteases (SVMPs) results from proteolysis, capillary disruption, and blood extravasation. HF3, a potent SVMP of Bothrops jararaca, induces hemorrhage at pmol doses in the mouse skin. To gain insight into the hemorrhagic process, the main goal of this study was to analyze changes in the skin peptidome generated by injection of HF3, using approaches of mass spectrometry-based untargeted peptidomics. The results revealed that the sets of peptides found in the control and HF3-treated skin samples were distinct and derived from the cleavage of different proteins. Peptide bond cleavage site identification in the HF3-treated skin showed compatibility with trypsin-like serine proteases and cathepsins, suggesting the activation of host proteinases. Acetylated peptides, which originated from the cleavage at positions in the N-terminal region of proteins in both samples, were identified for the first time in the mouse skin peptidome. The number of peptides acetylated at the residue after the first Met residue, mostly Ser and Ala, was higher than that of peptides acetylated at the initial Met. Proteins cleaved in the hemorrhagic skin participate in cholesterol metabolism, PPAR signaling, and in the complement and coagulation cascades, indicating the impairment of these biological processes. The peptidomic analysis also indicated the emergence of peptides with potential biological activities, including pheromone, cell penetrating, quorum sensing, defense, and cell-cell communication in the mouse skin. Interestingly, peptides generated in the hemorrhagic skin promoted the inhibition of collagen-induced platelet aggregation and could act synergistically in the local tissue damage induced by HF3.

Agomelatine inhibits platelet aggregation through melatonin receptor-dependent and independent mechanisms

AIMS

Melatonin is known to inhibit platelet aggregation induced by arachidonic acid (AA). In the present study we investigated whether agomelatine (Ago), an antidepressant with agonist activity at melatonin receptor 1 (MT1) and MT2 could reduce platelets aggregation and adhesion.

MAIN METHODS

Human platelets from healthy donors were used to test the in vitro effects of Ago in the presence of different platelet activators. We performed aggregation and adhesion assays, thromboxane B₂ (TxB₂), cAMP and cGMP measurements, intra-platelet calcium registration and flow cytometry assays.

KEY FINDINGS

Our data revealed that different concentrations of Ago reduced AA- and collagen-induced human platelet aggregation in vitro. Ago also reduced AA-induced increase in thromboxane B₂ (TxB₂) production, intracellular calcium levels and P-selectin expression at plasma membrane. The effects of Ago in AA-activated platelets were likely dependent on MT1 as they were blocked by luzindole (a MT1/MT2 antagonist) and mimicked by the MT1 agonist UCM871 in a luzindole-sensitive manner. The MT2 agonist UCM924 was also able to inhibit platelet aggregation, but this response was not affected by luzindole. On the other hand, although UCM871 and UCM924 reduced collagen-induced platelet aggregation and adhesion, inhibition of collagen-induced platelet aggregation by Ago was not mediated by melatonin receptors because it was not affected by luzindole.

SIGNIFICANCE

The present data show that Ago suppresses human platelet aggregation and suggest that this antidepressant may have the potential to prevent atherothrombotic ischemic events by reducing thrombus formation and vessel occlusion.

Sulforaphane attenuates glycoprotein VI-mediated platelet mitochondrial dysfunction through up-regulating the cAMP/PKA signaling pathway in vitro and in vivo

Platelet mitochondrial dysfunction is crucial for platelet activation, atherosclerosis and thrombosis. Sulforaphane (SFN) is a dietary isothiocyanate enriched in cruciferous vegetables and possesses multiple health benefits including cardiovascular protection. This study aims to investigate whether and how SFN modulates platelet mitochondrial dysfunction and hyperactivity in vitro and in vivo. Using a series of platelet functional assays in human platelets in vitro, we found that SFN at physiological concentrations attenuated oxidative stress-dependent platelet mitochondrial dysfunction (loss of mitochondrial membrane potential), apoptosis (cytochrome c release, caspase 3 activation and phosphatidylserine exposure) and activation induced by glycoprotein VI (GPVI) agonists (e.g., collagen and convulxin). Moreover, 12-week supplementation of SFN-enriched broccoli sprout extract (BSE, 0.06% diet) in C57BL/6J mice also attenuated GPVI-induced platelet mitochondrial dysfunction, apoptosis and hyperreactivity in vivo. Mechanistically, these inhibitory effects of SFN treatment and BSE supplementation were mainly mediated by up-regulating the cAMP/PKA pathway though decreasing phosphodiesterase 3A (PDE3A) activity. Thus, through modulating the PDE3A/cAMP/PKA signaling pathway, and attenuating platelet mitochondrial dysfunction and hyperreactivity, SFN may be a potent cardioprotective agent.

Canine Cancer Cells Activate Platelets via the Platelet P2Y12 Receptor

In addition to their well-known functions in haemostasis, anucleated platelets have a critical role in cancer biology. Many human and non-human cancer types can directly interact with and activate platelets, promoting cancer malignancy and progression. Although naturally occurring canine neoplastic diseases mimic the biologically complex conditions of human cancers more closely than laboratory-bred mice, studies evaluating the relationship between cancer cells and platelets in dogs are scarce, and the effects of tumour cells on platelets in these animals are unknown. To evaluate whether cancer cells could activate canine platelets, we assessed the response of platelet-rich plasma to cultured canine cancer cells using light transmittance aggregometry. Similar to human and murine cancer cell research, we demonstrated that both canine osteosarcoma and mammary carcinoma cells activated canine platelets in vitro, resulting in platelet aggregation. The degree of aggregation was most pronounced at a cancer cell to platelet ratio of 1:200 for most cell lines. Mechanistic studies revealed that the platelet adenosine diphosphate (ADP) receptor P2Y12 is essential for canine platelet aggregation induced by canine cancer. ADP receptor blockage on platelets inhibited >50% of cancer cell-induced maximum platelet aggregation in all cell lines evaluated. As in other species, our results suggest that canine cancers may activate canine platelets in vivo. This mechanism is likely relevant for the biology and progression of cancer in the dog.

Possible Risk of Thrombotic Events following Oxford-AstraZeneca COVID-19 Vaccination in Women Receiving Estrogen

People who receive the ChAdOx1 nCoV-19 vaccine, particularly perimenopausal women who are on birth control or postmenopausal women who take estrogen supplements, may experience thrombosis and thrombocytopenia. Estrogen and the ChAdOx1 nCoV-19 vaccine both have the potential to cause thrombus in different ways. Some postmenopausal women who are also taking estrogens may develop thrombosis and thrombocytopenia after receiving the ChAdOx1 nCoV-19 vaccine. Therefore, women are encouraged to stop taking drugs containing estrogen before receiving this vaccine. Furthermore, consuming fish oil can help reduce the risk of developing blood clots among women who are in the luteal phase and, thus, have high estrogen levels. In addition, ChAdOx1 nCoV-19's side effects in young women could be mitigated by administering it during the follicular phase.

Water-Soluble Tomato Extract Fruitflow Alters the Phosphoproteomic Profile of Collagen-Stimulated Platelets

Platelet hyperactivity is a risk factor for cardiovascular disease and thrombosis. Recent studies reported that the tomato extract Fruitflow inhibited platelet function, but the molecular mechanism is still unclear. The present study used proteomics to quantitatively analyze the effect of fruitflow on the inhibition of collagen-stimulated platelets and validated the involvement of several signaling molecules. Fruitflow significantly inhibited human platelet aggregation and P-selectin expression that were induced by collagen. Proteomics analysis revealed that compared fruitflow-treated collagen-stimulated platelets with only collagen-stimulated platelets, 60 proteins were upregulated and 10 proteins were downregulated. Additionally, 66 phosphorylated peptides were upregulated, whereas 37 phosphorylated peptides were downregulated. Gene Ontology analysis indicated that fruitflow treatment downregulated phosphoinositide 3-kinase (PI3K)/protein kinase B and guanosine triphosphatase-mediated signal transduction in collagen-activated platelets. Biological validation indicated that fruitflow decreased Akt, glycogen synthase kinase 3β, p38 mitogen-activated protein kinase (MAPK), and heat shock protein (Hsp27) phosphorylation in collagen-stimulated platelets. Fruitflow recovered cyclic adenosine monophosphate levels in collagen-activated platelets and reduced protein kinase A substrate phosphorylation that was induced by collagen. These findings suggest that fruitflow is a functional food that can inhibit platelet function, conferring beneficial effects for people who are at risk for platelet hyperactivity-associated thrombosis.

A tailored extracellular matrix (ECM) - Mimetic coating for cardiovascular stents by stepwise assembly of hyaluronic acid and recombinant human type III collagen

Collagen, a central component of the extracellular matrix (ECM), has been widely applied in tissue engineering, among others, for wound healing or bone and nerve regeneration. However, the inherent thrombogenic properties of collagen hinder the application in blood-contacting devices. Herein, a brand-new recombinant human type III collagen (hCOLIII) was explored that does not present binding sites for platelets while retaining the affinity for endothelial cells. The hCOLIII together with hyaluronic acid (HA) were deposited on the substrates via layer-by-layer assembly to form an ECM-mimetic multilayer coating. In vitro platelet adhesion and ex vivo blood circulation tests demonstrated prominent thromboprotective properties for the hCOLIII-based ECM-mimetic coating. In addition, the coating effectively guided the vascular cell fate by supporting the proliferation of endothelial cells and inhibiting the proliferation of smooth muscle cells by differentiating them to a more contractile phenotype. A polylactic acid (PLA) stent coated with hCOLIII-based ECM-mimetic coating was implanted in the abdominal aorta of rabbits to investigate the healing of the neointima. The enhanced endothelialization, suppressed inflammatory response, inhibition of excessive neointimal hyperplasia, and the superior thromboprotection strongly indicated the prospect of the hCOLIII-based ECM-mimetic coating as a tailored blood-contacting material for cardiovascular stents.

The Dual Role of Platelets in the Cardiovascular Risk of Chronic Inflammation

Patients with chronic inflammatory diseases often exhibit cardiovascular risk. This risk is associated with the systemic inflammation that persists in these patients, causing a sustained endothelial activation. Different mechanisms have been considered responsible for this systemic inflammation, among which activated platelets have been regarded as a major player. However, in recent years, the role of platelets has become controversial. Not only can this subcellular component release pro- and anti-inflammatory mediators, but it can also bind to different subsets of circulating lymphocytes, monocytes and neutrophils modulating their function in either direction. How platelets exert this dual role is not yet fully understood.

From Snake Venom's Disintegrins and C-Type Lectins to Anti-Platelet Drugs

Snake venoms are attractive natural sources for drug discovery and development, with a number of substances either in clinical use or in research and development. These drugs were developed based on RGD-containing snake venom disintegrins, which efficiently antagonize fibrinogen activation of αIIbβ3 integrin (glycoprotein GP IIb/IIIa). Typical examples of anti-platelet drugs found in clinics are Integrilin (Eptifibatide), a heptapeptide derived from Barbourin, a protein found in the venom of the American Southeastern pygmy rattlesnake and Aggrastat (Tirofiban), a small molecule based on the structure of Echistatin, and a protein found in the venom of the saw-scaled viper. Using a similar drug discovery approach, linear and cyclic peptides containing the sequence K(R)TS derived from VP12, a C-type lectin protein found in the venom of Israeli viper venom, were used as a template to synthesize Vipegitide, a novel peptidomimetic antagonist of α2β1 integrin, with anti-platelet activity. This review focus on drug discovery of these anti-platelet agents, their indications for clinical use in acute coronary syndromes and percutaneous coronary intervention based on several clinical trials, as well as their adverse effects.

Mirabegron, a β3-adrenoceptor agonist reduced platelet aggregation through cyclic adenosine monophosphate accumulation

Mirabegron is a β₃-adrenoceptor agonist and released on the marked for the treatment of overactive bladder. Because mirabegron is the only β₃-adrenoceptor agonist available and substances that increase the levels of cyclic adenosine monophosphate (cAMP) inhibit platelet activity, we tested the hypothesis that mirabegron could have antiplatelet activity. Collagen- and thrombin induced platelet aggregation, thromboxane B2 (TXB₂) and cyclic nucleotides quantification and calcium (Ca²⁺) mobilization were determined in the absence and presence of mirabegron in human washed platelets. Our results revealed that mirabegron (10-300 µM) produced significant inhibitions on platelet aggregation induced by collagen- or thrombin, accompanied by greater intracellular levels of cAMP. The β₃-adrenoceptor antagonist L 748,337 (1 µM) and the adenylate cyclase inhibitor, SQ 22,536 (100 µM) reversed the inhibition induced by mirabegron in thrombin-stimulated platelets. The selective antagonists for β₁-and β₂-adrenoceptors, atenolol and ICI 117,551 (3 µM), respectively did not interfere on the inhibition induced by mirabegron. In Fluo-4 loaded platelets, mirabegron reduced the total and intracellular Ca²⁺ levels. Pre-incubation with mirabegron almost abolished the levels of TXB2. Mirabegron did not augment the intracellular levels of cyclic guanosine monophosphate. In conclusion, mirabegron inhibited human platelet aggregation through cAMP accumulation, thus suggesting that substances that activate β₃-adrenoceptor could be beneficial as adjuvant antiplatelet therapy.

Does pathology of small venules contribute to cerebral microinfarcts and dementia?

Microinfarcts are small, but strikingly common, ischemic brain lesions in the aging human brain. There is mounting evidence that microinfarcts contribute to vascular cognitive impairment and dementia, but the origins of microinfarcts are unclear. Understanding the vascular pathologies that cause microinfarcts may yield strategies to prevent their occurrence and reduce their deleterious effects on brain function. Current thinking suggests that cortical microinfarcts arise from the occlusion of penetrating arterioles, which are responsible for delivering oxygenated blood to small volumes of tissue. Unexpectedly, pre-clinical studies have shown that the occlusion of penetrating venules, which drain deoxygenated blood from cortex, lead to microinfarcts that appear identical to those resulting from arteriole occlusion. Here we discuss the idea that cerebral venule pathology could be an overlooked source for brain microinfarcts in humans. This article is part of the Special Issue "Vascular Dementia". Cover Image for this Issue: doi: 10.1111/jnc.14167.

Licochalcones extracted from Glycyrrhiza inflata inhibit platelet aggregation accompanied by inhibition of COX-1 activity

Licochalcones extracted from Glycyrrhiza inflata are known to have a variety of biological properties such as anti-inflammatory, anti-bacterial, and anti-tumor activities, but their action on platelet aggregation has not yet been reported. Therefore, in this study we investigated the effects of licochalcones on platelet aggregation. Collagen and U46619, a thromboxane A₂ receptor agonist, caused rabbit platelet aggregation, which was reversed by pretreatment with licochalcones A, C and D in concentration-dependent manners. Among these compounds, licochalcone A caused the most potent inhibitory effect on collagen-induced platelet aggregation. However, the licochalcones showed marginal inhibitory effects on thrombin or ADP-induced platelet aggregation. In addition to rabbit platelets, licochalcone A attenuated collagen-induced aggregation in human platelets. Because licochalcone A also inhibited arachidonic acid-induced platelet aggregation and production of thromboxane A₂ induced by collagen in intact platelets, we further examined the direct interaction of licochalcone A with cyclooxygenase (COX)-1. As expected, licochalcone A caused an inhibitory effect on both COX-1 and COX-2 in vitro. Regarding the effect of licochalcone A on COX-1 enzyme reaction kinetics, although licochalcone A showed a stronger inhibition of prostaglandin E₂ synthesis induced by lower concentrations of arachidonic acid, Vmax values in the presence or absence of licochalcone A were comparable, suggesting that it competes with arachidonic acid at the same binding site on COX-1. These results suggest that licochalcones inhibit collagen-induced platelet aggregation accompanied by inhibition of COX-1 activity.

Inhibitory effect of hydrogen sulfide on platelet aggregation and the underlying mechanisms

H2S (hydrogen sulfide) possesses anti-inflammatory and antioxidant capabilities and offers cardiovascular protection. The effect of H2S on platelet function, however, has been less clear. Platelet activation is a key step in the initiation and development of atherothrombotic diseases. This study explored the effects and mechanisms of H2S on human platelet in vitro and under dyslipidemia conditions. This study indicated that the collagen-induced aggregation of washed human platelets, adenosine triphosphate release, and TXA2 formation were inhibited by NaHS incubation. Furthermore, NaHS significantly decreased intracellular calcium concentration in washed human platelets stimulated with collagen and inhibited collagen-induced c-PLA2, p38 MAPK, ERK, JNK, PLC-γ2, and Akt phosphorylation. Finally, NaHS inhibited the aggregation of washed human platelets induced by oxidized low-density lipoprotein plus collagen. The level of plasma lipids and the collagen-induced rapid platelet aggregation in ApoE knockout mice were also significantly decreased by NaHS treatment. Our study shows that NaHS is able to inhibit platelet aggregation induced by collagen. The underlying mechanisms are related to NaHS-induced changes in various signaling pathways and [Ca]i in the platelets. The interaction of NaHS and platelets is also affected by lipid metabolism.

Quantification of platelet-surface interactions in real-time using intracellular calcium signaling

Platelets get easily activated when in contact with a surface. Therefore in the design of microfluidic blood analysis devices surface activation effects have to be taken into account. So far, platelet-surface interactions have been quantified by morphology changes, membrane marker expression or secretion marker release. In this paper we present a simple and effective method that allows quantification of platelet-surface interactions in real-time. A calcium indicator was used to visualize intracellular calcium variations during platelet adhesion. We designated cells that showed a significant increase in cytosolic calcium as responding cells. The fraction of responding cells upon binding was analyzed for different types of surfaces. Thereafter, the immobilized platelets were chemically stimulated and the fraction of responding cells was analyzed. Furthermore, the time between the binding or chemical stimulation and the increased cytosolic calcium level (i.e. the response delay time) was measured. We used surface coatings relevant for platelet-function testing including Poly-L-lysine (PLL), anti-GPIb and collagen as well as control coatings such as Bovine Serum Albumin (BSA) and mouse immunoglobulin (IgG). We found that a lower percentage of responding cells upon binding, results in a higher percentage of responding cells upon chemical stimulation after binding. The measured delay time between platelet binding under sedimentation and calcium response was the lowest on a PLL-coated surface, followed by an anti-GPIb and collagen-coated surface and IgG-coated surface. The presented method provides real-time information of platelet-surface interactions on a single cell as well as on a cell ensemble level. For future in-vitro diagnostic tests, this real-time single-cell function analysis can reveal heterogeneities in the biological processes of a cell population.

Antiplatelet and anticoagulant effects of diterpenes isolated from the marine alga, Dictyota menstrualis

Cardiovascular diseases represent a major cause of disability and death worldwide. Therapeutics are available, but they often have unsatisfactory results and may produce side effects. Alternative treatments based on the use of natural products have been extensively investigated, because of their low toxicity and side effects. Marine organisms are prime candidates for such products, as they are sources of numerous and complex substances with ecological and pharmacological effects. In this work, we investigated, through in vitro experiments, the effects of three diterpenes (pachydictyol A, isopachydictyol A and dichotomanol) from the Brazilian marine alga, Dictyota menstrualis, on platelet aggregation and plasma coagulation. Results showed that dichotomanol inhibited ADP- or collagen-induced aggregation of platelet-rich plasma (PRP), but failed to inhibit washed platelets (WP). In contrast, pachydictyol A and isopachydictyol A failed to inhibit the aggregation of PRP, but inhibited WP aggregation induced by collagen or thrombin. These diterpenes also inhibited coagulation analyzed by the prothrombin time and activated partial thromboplastin time and on commercial fibrinogen. Moreover, diterpenes inhibited the catalytic activity of thrombin. Theoretical studies using the Osiris Property Explorer software showed that diterpenes have low theoretical toxicity profiles and a drug-score similar to commercial anticoagulant drugs. In conclusion, these diterpenes are promising candidates for use in anticoagulant therapy, and this study also highlights the biotechnological potential of oceans and the importance of bioprospecting to develop medicines.

Density functional theory based study on cis-trans isomerism of the amide bond in homodimers of β(2,3)- and β(3)-substituted homoproline

Preference for a cis/trans peptide bond between residues of dipeptides formed by substituted β(2,3) (I) and β(3) (II) homoproline is investigated using density functional theory (DFT). Potential energy surfaces for monomer and linear dimers are explored at the B3LYP/6-31G(d,p) level of theory. Minimum energy conformations of the dipeptides are optimized using B3LYP, PBE1PBE, B97D, and M06-2X functionals at the 6-31G(d,p) level of basis set in both the gas phase and solvent phase. The relative free energy difference between the selected conformations is marginal. Results obtained using the functionals M06-2X and B97D on dimers of I and II, respectively, agree with experimental results. The lowest energy conformations predicted by B97D/6-31G(d,p) and M06-2X/6-31G(d,p) levels of theory show greater relative MP2 correlation energy. Dipeptides of I with hydrophilic substituents show preference for a trans peptide bond. Support for cis/trans isomerism in dimers of I with hydrophobic substituents comes from potential energy surfaces and free energy data. Although dipeptides of II with hydrophilic substituents show preference for cis peptide bond, the dipeptides with hydrophobic substituent prefer trans bond.

Thrombodynamics of microvascular repairs: effects of antithrombotic therapy on platelets and fibrin

PURPOSE

To evaluate the hypothesis that platelets and fibrin differentially accrue at microvascular anastomoses in arteries versus veins and under different pharmacologic conditions.

METHODS

We evaluated mouse arterial and venous anastomoses with intravital fluorescence imaging, using fluorophore-labeled platelets and anti-fibrin antibodies to measure the extent of thrombus component development in the intraluminal anastomotic site. We evaluated systemic heparin or eptifibatide (platelet aggregation inhibitor) to determine their relative influences on thrombus composition.

RESULTS

Platelets accumulated rapidly in both arterial and venous repairs, and then fell in number after 10 to 30 minutes of reflow. Fibrin had a relatively steady development over 60 minutes in veins, with a more variable increase in arteries. Heparin reduced platelet accumulation in arteries and fibrin development in veins. Eptifibatide reduced platelets in both arteries and veins and had an apparent effect on lowering the amount of fibrin in veins.

CONCLUSIONS

These findings show that platelets have a rapid, transient response, whereas fibrin has a slower, more sustained accrual in both arterial and venous anastomoses. Furthermore, inhibition of either coagulation or platelet aggregation can influence presumably non-targeted components of thrombosis in vascular repairs of both arteries and veins.

CLINICAL RELEVANCE

Preventing replantation failure using antithrombotic therapies requires a better understanding of the effect of each pharmacologic compound on the various aspects of thrombogenesis.

Identification of susceptibility modules for coronary artery disease using a genome wide integrated network analysis

Although recent genome-wide association studies (GWAS) have identified a handful of variants with best significance for coronary artery disease (CAD), it remains a challenge to summarize the underlying biological information from the abundant genotyping data. Here, we propose an integrated network analysis that effectively combines GWAS genotyping dataset, protein-protein interaction (PPI) database, literature and pathway annotation information. This three-step approach was illustrated for a comprehensive network analysis of CAD as the following. First, a network was constructed from PPI database and CAD seed genes mined from the available literatures. Then, susceptibility network modules were captured from the results of gene-based association tests. Finally, susceptibility modules were annotated with potential mechanisms for CAD via the KEGG pathway database. Our network analysis identified four susceptibility modules for CAD including a complex module that consisted of 15 functional inter-connected sub-modules, AGPAT3-AGPAT4-PPAP2B module, ITGA11-ITGB1 module and EMCN-SELL module. MAPK10 and COL4A2 among the top-scored focal adhesion pathway related module were the most significant genes (MAPK10: OR=32.5, P=3.5 × 10(-11); COL4A2: OR=2.7, P=2.8 × 10(-10)). The significance of the two genes were further validated by other two gene-based association tests (MAPK10: P=0.009 and 0.007; COL4A2: P=0.001 and 0.023) and another independent GWAS dataset (MAPK10: P=0.001; COL4A2: P=0.0004). Furthermore, 34 out of 44 previously reported CAD susceptibility genes were captured by our CAD PPI network and 17 of them were also significant genes. The susceptibility modules identified in our study might provide novel clues for the clarification of CAD pathogenesis in the future.

New analogues of 13-hydroxyocatdecadienoic acid and 12-hydroxyeicosatetraenoic acid block human blood platelet aggregation and cyclooxygenase-1 activity

Background

Thromboxane A₂ is derived from arachidonic acid through the action of cyclooxygenases and thromboxane synthase. It is mainly formed in blood platelets upon activation and plays an important role in aggregation. Aspirin is effective in reducing the incidence of complications following acute coronary syndrome and stroke. The anti-thrombotic effect of aspirin is obtained through the irreversible inhibition of cyclooxygenases. Analogues of 12-hydroxyeicosatetraenoic acid and 13-hydroxyocatdecadienoic acid were shown previously to modulate platelet activation and to block thromboxane receptors.

Results and discussion

We synthesized 10 compounds based on the structures of analogues of 12-hydroxyeicosatetraenoic acid and 13-hydroxyocatdecadienoic acid and evaluated their effect on platelet aggregation triggered by arachidonic acid. The structure activity relationship was evaluated. Five compounds showed a significant inhibition of platelet aggregation and highlighted the importance of the lipidic hydrophobic hydrocarbon chain and the phenol group. Their IC₅₀ ranged from 7.5 ± 0.8 to 14.2 ± 5.7 μM (Mean ± S.E.M.). All five compounds decreased platelet aggregation and thromboxane synthesis in response to collagen whereas no modification of platelet aggregation in response to thromboxane receptor agonist, U46619, was observed. Using COS-7 cells overexpressing human cyclooxygenase-1, we showed that these compounds are specific inhibitors of cyclooxygenase-1 with IC₅₀ ranging from 1.3 to 12 μM. Docking observation of human recombinant cyclooxygenase-1 supported a role of the phenol group in the fitting of cyclooxygenase-1, most likely related to hydrogen bonding with the Tyr 355 of cyclooxygenase-1.

Conclusions

In conclusion, the compounds we synthesized at first based on the structures of analogues of 12 lipoxygenase metabolites showed a role of the phenol group in the anti-platelet and anti-cyclooxygenase-1 activities. These compounds mediate their effects via blockade of cyclooxygenase-1.

Activation of haem-oxidized soluble guanylyl cyclase with BAY 60-2770 in human platelets lead to overstimulation of the cyclic GMP signaling pathway

BACKGROUND AND AIMS

Nitric oxide-independent soluble guanylyl cyclase (sGC) activators reactivate the haem-oxidized enzyme in vascular diseases. This study was undertaken to investigate the anti-platelet mechanisms of the haem-independent sGC activator BAY 60-2770 in human washed platelets. The hypothesis that sGC oxidation potentiates the anti-platelet activities of BAY 60-2770 has been tested.

METHODS

Human washed platelet aggregation and adhesion assays, as well as flow cytometry for α(IIb)β(3) integrin activation and Western blot for α1 and β1 sGC subunits were performed. Intracellular calcium levels were monitored in platelets loaded with a fluorogenic calcium-binding dye (FluoForte).

RESULTS

BAY 60-2770 (0.001-10 µM) produced significant inhibition of collagen (2 µg/ml)- and thrombin (0.1 U/ml)-induced platelet aggregation that was markedly potentiated by the sGC inhibitor ODQ (10 µM). In fibrinogen-coated plates, BAY 60-2770 significantly inhibited platelet adhesion, an effect potentiated by ODQ. BAY 60-2770 increased the cGMP levels and reduced the intracellular Ca(2+) levels, both of which were potentiated by ODQ. The cell-permeable cGMP analogue 8-Br-cGMP (100 µM) inhibited platelet aggregation and Ca(2+) levels in an ODQ-insensitive manner. The cAMP levels remained unchanged by BAY 60-2770. Collagen- and thrombin-induced α(IIb)β(3) activation was markedly inhibited by BAY 60-2770 that was further inhibited by ODQ. The effects of sodium nitroprusside (3 µM) were all prevented by ODQ. Incubation with ODQ (10 µM) significantly reduced the protein levels of α1 and β1 sGC subunits, which were prevented by BAY 60-2770.

CONCLUSION

The inhibitory effects of BAY 60-2770 on aggregation, adhesion, intracellular Ca(2+) levels and α(IIb)β(3) activation are all potentiated in haem-oxidizing conditions. BAY 60-2770 prevents ODQ-induced decrease in sGC protein levels. BAY 60-2770 could be of therapeutic interest in cardiovascular diseases associated with thrombotic complications.

Bioengineered vascular access maintains structural integrity in response to arteriovenous flow and repeated needle puncture

OBJECTIVE

Tissue-engineered blood vessels (TEBV) have been proposed as an alternative to prosthetic grafts for dialysis access. However, arteriovenous (AV) grafts must withstand extreme flow rates and frequent needle trauma. In a proof-of-concept study, we sought to determine whether scaffold-based TEBV could withstand the hemodynamic and mechanical challenges of chronic dialysis access.

METHODS

TEBV were constructed using decellularized arterial scaffolds seeded with autologous ovine endothelial cells (EC) derived from circulating endothelial progenitor cells (EPC) using a novel high-affinity capture approach. Seeded scaffolds were preconditioned to arterial pressure and flow in a bioreactor for 2 weeks prior to implantation to create carotid artery to jugular vein AV grafts in each animal. TEBV were healed for 1 month before initiating percutaneous needle puncture 3 days/week. TEBV wall geometry and patency were monitored using duplex imaging and were either explanted for histologic analysis at 2 months (n = 5) or followed for up to 6 months until venous outflow stenosis threatened AV graft patency (n = 6).

RESULTS

Despite high flow, TEBV maintained stable geometry with only modest wall dilation (under 6%) by 4 months after implantation. Needle access was well tolerated with a single puncture site complication, a small pseudoaneurysm, occurring in the late group. Time-to-hemostasis at puncture sites averaged 4 ± 2 minutes. Histologic analysis at 2 months demonstrated repopulation of the outer TEBV wall by host cells and healing of needle punctures by cellular ingrowth and new matrix deposition along the tract. TEBV followed beyond 2 months showed stable wall geometry but, consistent with the primary mode of clinical AV graft failure, all TEBV eventually developed venous anastomotic stenosis (mean, 4.4 ± 0.9 months; range, 3.3-5.6 months postimplantation; n = 6).

CONCLUSIONS

This pilot study supports the concept of creating dialysis access from scaffold-based autologous TEBV. Engineered AV grafts were created within a clinically relevant time frame and demonstrated stable wall geometry despite high flow and repeated puncture. Cellular ingrowth and puncture site healing may improve wall durability, but venous outflow stenosis remains the primary mode of TEBV graft failure in the ovine model.

In vitro platelet antiaggregatory properties of 4-methylcoumarins

Platelets play a crucial role in physiological haemostasis. However, in coronary arteries damaged by atherosclerosis, enhanced platelet aggregation, with subsequent thrombus formation, is a precipitating factor in acute myocardial infarction. Current therapeutic approaches are able to reduce approximately one quarter of cardiovascular events, but they are associated with an increased risk of bleeding and in some resistant patients are not efficient. Some coumarins possess antiplatelet activity and, due to their additional antioxidant effects, may be promising drugs for use in combination with the present therapeutic agents. The aim of this study was to analyse a series of simple 4-methylcoumarins for their antiplatelet activity. Human plasma platelet suspensions were treated with different aggregation inducers [arachidonic acid (AA), collagen and ADP] in the presence of the 4-methylcoumarins. Complementary experiments were performed to explain the mechanism of action. 5,7-Dihydroxy-4-methylcoumarins, in particular those containing a lipophilic side chain at C-3, reached the activity of acetylsalicylic acid on AA-induced aggregation. Other tested coumarins were less active. Some of the tested compounds mildly inhibited either collagen- or ADP-induced aggregation. 5,7-Dihydroxy-4-methylcoumarins did not interfere with the function of thromboxane synthase, but were competitive antagonists of thromboxane A(2) receptors and inhibited cyclooxygenase-1 as well. 5,7-Dihydroxy-4-methylcoumarins appear to be promising candidates for the extension of the current spectrum of antiplatelet drugs.

Wnt5a potentiates U46619-induced platelet aggregation via the PI3K/Akt pathway

Platelet aggregation plays crucial roles in the formation of hemostatic plugs and thrombosis. Although it was recently shown that canonical Wnt signaling negatively regulates platelet aggregation, the role of non-canonical Wnt signaling remains unknown. Here, we observed that Wnt5a, one of the non-canonical Wnts, positively regulated platelet aggregation. Platelet aggregation was potentiated by the addition of Wnt5a to collagen-or U46619-induced rat platelet rich plasma (PRP). Treatment with Wnt5a to U46619-stimulated PRP resulted in an increase in the level of phosphorylated Akt, whereas phosphorylation of PKCδ and JNK1 was unaffected. In addition, inhibition of PI3K blocked the potentiating effect of Wnt5a. Taken together, these results suggest that Wnt5a potentiates U46619-induced platelet aggregation via the PI3K/Akt pathway.

Evaluation of Marine Brown Algae and Sponges from Brazil as Anticoagulant and Antiplatelet Products

The ischemic disorders, in which platelet aggregation and blood coagulation are involved, represent a major cause of disability and death worldwide. The antithrombotic therapy has unsatisfactory performance and may produce side effects. So, there is a need to seek molecules with antithrombotic properties. Marine organisms produce substances with different well defined ecological functions. Moreover, some of these molecules also exhibit pharmacological properties such as antiviral, anticancer, antiophidic and anticoagulant properties. The aim of this study was to evaluate, through in vitro tests, the effect of two extracts of brown algae and ten marine sponges from Brazil on platelet aggregation and blood coagulation. Our results revealed that most of the extracts were capable of inhibiting platelet aggregation and clotting measured by plasma recalcification tests, prothrombin time, activated partial thromboplastin time, and fibrinogenolytic activity. On the other hand, five of ten species of sponges induced platelet aggregation. Thus, the marine organisms studied here may have molecules with antithrombotic properties, presenting biotechnological potential to antithrombotic therapy. Further chemical investigation should be conducted on the active species to discover useful molecules for the development of new drugs to treat clotting disorders.

Coagulopathy during cardiac arrest and resuscitation in a swine model of electrically induced ventricular fibrillation

AIMS

Coagulopathy is often present after resuscitation from cardiac arrest but plays an undefined role in the post cardiac arrest syndrome. The aim of this study was to characterize coagulation changes during cardiac arrest and post-resuscitation care in order to direct further focused study.

METHODS

Ventricular fibrillation (VF) was induced electrically in immature male swine, followed by normothermic American Heart Association Advanced Cardiac Life Support and a uniform post-resuscitation goal-directed resuscitation protocol. PT, aPTT, fibrinogen, Thrombelastography (TEG), platelet contractile force (PCF), clot elastic modulus (CEM), and collagen-induced platelet aggregation were compared at baseline, at 8 min of VF, during the 3rd round of chest compressions (CPR), and at 15, 90, 180, and 360 min after return of circulation using repeated measures ANOVA.

RESULTS

8/18 (44%) animals were resuscitated after 10.9 ± 0.9 min of VF and 7.6 ± 3.4 min of CPR. TEG revealed a significant impairment in clot strength (MA) and clot formation kinetics (K, alpha angle) arising during CPR, followed by a brief prolongation of clot onset times (R) after return of circulation. Both PCF and CEM fell significantly during CPR (PCF by 50%, CEM by 47% of baseline) and platelet aggregation was significantly decreased during CPR. Coagulation changes were partially recovered by 3h of post-resuscitation care.

CONCLUSION

Whole blood coagulation was rapidly impaired during CPR after electrically induced VF in this swine model by impaired platelet aggregation/contractile function and clotting kinetics. Further platelet-specific study is indicated.

Anti-platelet effects of Curcuma oil in experimental models of myocardial ischemia-reperfusion and thrombosis

Extensive research on the mechanism of action and medicinal importance of curcumin obtained from turmeric (Curcuma longa) has unfolded its potential therapeutic value against many chronic ailments. Curcuma oil (C.oil), the highly lipophilic component from Curcuma longa has been documented for its neuroprotective efficacy against rat cerebral ischemia-reperfusion injury; however its effect on myocardial reperfusion injury remains unexplored. In the present study, effect of C.oil (500 mg/kg, po) was evaluated against myocardial ischemia-reperfusion induced injury in the rat model. C.oil failed to confer protection against cardiac injury, however significant reversal of ADP induced platelet aggregation (p<0.05) was evident in the same animals. Moreover, collagen and thrombin induced platelet aggregation (p<0.001) as well as tyrosine phosphorylation of various proteins in activated platelets was also suppressed. C.oil also offered significant protection against collagen-epinephrine induced thromboembolism in mice as well as augmented total time to occlusion against FeCl(3) induced arterial thrombosis in rats. C.oil however had no effect on coagulation parameters (TT, PT and aPTT) and exerted a mild effect on the bleeding time. Bioavailability of C.oil, as assessed by monitoring ar-turmerone, α,β-turmerone and curlone, was 13%, 11% and 7% respectively, indicating high systemic exposure. Moreover, longer mean residence time (MRT) of ar-turmerone (13.2h), α,β-turmerone (11.6h) and Curlone (14.0 h) and plasma elimination half lives in the range of 5.5 to 7.2h correlated with single 500 mg/kg dose regimen of C.oil. In the present study, C.oil thus seems to be an efficacious and safe anti-platelet agent which was protective against intravascular thrombosis.

Inhibitory effect of hericenone B from Hericium erinaceus on collagen-induced platelet aggregation

Platelet aggregation in the blood vessel causes thrombosis. Therefore, inhibitors of platelet aggregation promise to be preventive or therapeutic agents of various vascular diseases, including myocardial infarction and stroke. In the present study, we found that hericenone B had a strong anti-platelet activity and it might be a novel compound for antithrombotic therapy possessing a novel mechanism. Prior to this study, we examined anti-platelet aggregation activity of ethanol extracts of several species of mushrooms, and found that extract of Hericium erinaceus potently inhibited platelet aggregation induced by collagen. Therefore, we first fractionated the ethanol extract of H. erinaceus to identify the active substances. The anti-platelet activity of each fraction was determined using washed rabbit platelets. As a result, an active component was isolated and identified as hericenone B. Hericenone B selectively inhibited collagen-induced platelet aggregation, but it did not suppress the aggregation induced by U46619 (TXA₂ analogue), ADP, thrombin, or adrenaline. Furthermore, hericenone B did not inhibit arachidonic acid- or convulxin (GPVI agonist)-induced platelet aggregation. Therefore, hericenone B was considered to block collagen signaling from integrin α2/β1 to arachidonic acid release. Moreover, we found that collagen-induced aggregation was inhibited by hericenone B in human platelets, similar to in rabbit platelets.

The function and three-dimensional structure of a thromboxane A2/cysteinyl leukotriene-binding protein from the saliva of a mosquito vector of the malaria parasite

A salivary protein from a malaria-transmitting mosquito uses a single domain to bind to thromboxane A₂ and cysteinyl leukotrienes and prevent blood clotting and inflammation in the host on which it feeds.

The highly expressed D7 protein family of mosquito saliva has previously been shown to act as an anti-inflammatory mediator by binding host biogenic amines and cysteinyl leukotrienes (CysLTs). In this study we demonstrate that AnSt-D7L1, a two-domain member of this group from Anopheles stephensi, retains the CysLT binding function seen in the homolog AeD7 from Aedes aegypti but has lost the ability to bind biogenic amines. Unlike any previously characterized members of the D7 family, AnSt-D7L1 has acquired the important function of binding thromboxane A₂ (TXA₂) and its analogs with high affinity. When administered to tissue preparations, AnSt-D7L1 abrogated Leukotriene C₄ (LTC₄)-induced contraction of guinea pig ileum and contraction of rat aorta by the TXA₂ analog U46619. The protein also inhibited platelet aggregation induced by both collagen and U46619 when administered to stirred platelets. The crystal structure of AnSt-D7L1 contains two OBP-like domains and has a structure similar to AeD7. In AnSt-D7L1, the binding pocket of the C-terminal domain has been rearranged relative to AeD7, making the protein unable to bind biogenic amines. Structures of the ligand complexes show that CysLTs and TXA₂ analogs both bind in the same hydrophobic pocket of the N-terminal domain. The TXA₂ analog U46619 is stabilized by hydrogen bonding interactions of the ω-5 hydroxyl group with the phenolic hydroxyl group of Tyr 52. LTC₄ and occupies a very similar position to LTE₄ in the previously determined structure of its complex with AeD7. As yet, it is not known what, if any, new function has been acquired by the rearranged C-terminal domain. This article presents, to our knowledge, the first structural characterization of a protein from mosquito saliva that inhibits collagen mediated platelet activation.

When feeding, a female mosquito must inhibit the blood clotting and inflammatory responses of the host. To do this, the insect produces salivary proteins that neutralize key host molecules participating in clotting and inflammation. Here, we describe a salivary protein AnSt-D7L1 that scavenges both thomboxane A₂ and cysteinyl leukotrienes, two substances involved in blood vessel constriction, platelet aggregation, and inflammatory responses to an insect bite. We produced this protein in bacteria and showed that it tightly binds both these molecules, inhibiting the processes in which they are involved. We then determined its structure using X-ray crystallography and showed that there is a single binding site in one domain of the protein, accommodating both thromboxane A₂ and cysteinyl leukotrienes, and that this site is responsible for the scavenging effect of the protein. These studies reveal the structural features of proteins needed to bind to key molecules of potential pharmacological importance and add to our understanding of the process of mosquito blood feeding, which is essential for transmission of the malaria parasite.

A selective serotonin reuptake inhibitor, citalopram, inhibits collagen-induced platelet aggregation and activation

Clinical depression is a significant risk factor for cardiovascular diseases and confers an increased risk of mortality. Increased platelet reactivity may predispose depressed patients to cardiovascular diseases. The antidepressants selective serotonin reuptake inhibitors (SSRIs) have been found to have cardioprotective effects probably via the attenuation of platelet activation independently in addition to treatment of depression itself. However, the characters of the inhibitory effect of SSRIs on platelets remain largely unknown. Here we show that an SSRI, citalopram, specifically inhibited collagen-induced platelet aggregation. Citalopram, however, revealed only little inhibitory effect on platelet aggregation induced by thrombin, U46619, and ionomycin, and failed to inhibit reversible platelet aggregation induced by adenosine diphosphate with fibrinogen. Collagen-induced of αIIbβ3 integrin activation in platelets under a static condition was not influenced by citalopram. Citalopram inhibited convulxin-induced platelet aggregation and αIIbβ3 integrin activation. In the experiments with fibrinogen-induced aggregation in elastase-treated platelets, citalopram inhibited only collagen-induced αIIbβ3 activation but not the binding activities between activated αIIbβ3 integrin and fibrinogen. Moreover, citalopram inhibited α-granule and dense granule secretion from platelets in response to collagen, as determined by a reduced expression of P-selectin and adenosine triphosphate release, respectively. In addition, collagen-induced thromboxane A2 release in platelets was attenuated by citalopram pretreatment. These findings might specify the mechanisms of inhibitory effects of citalopram on collagen mediated platelet activation and aggregation, and further support the cardioprotective effect of SSRIs.

A class of 3S-2-aminoacyltetrahydro-beta-carboline-3-carboxylic acids: their facile synthesis, inhibition for platelet activation, and high in vivo anti-thrombotic potency

3S-Tetrahydro-beta-carboline-3-carboxylic acid (TCCA) effectively inhibits ADP-induced platelet activation. This paper used TCCA as a lead, modified its 2-position with amino acids, and provided 20 novel 3S-2-aminoacyl-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acids (5a-t). With the in vitro assay, it was demonstrated that this modification diminished the IC(50) values from 701 nM of TCCA to 10 nM of 5a-t. With the in vivo assay, it was demonstrated that this modification reduced the efficacious dose from 5.0 micromol/kg of TCCA to 0.1 micromol/kg of 5a-t. Comparing the Cerius based conformation of them with that of their analogues, the 3-position modified TCCA, it was suggested that the comparatively unfolded conformation was one of the important factors of enhancing the in vivo antithrombotic potency.

Cyclic nucleotides inhibit MAP kinase activity in low-dose collagen-stimulated platelets

Collagen-induced platelet activation is a complex process involving multiple signaling pathways. The role(s) of MAP kinases (ERKs and p38(MAPK)) are unclear, although at high, but not low, collagen concentrations p38(MAPK) is involved in cPLA(2)-mediated arachidonic acid release, prior to thromboxane generation. Cyclic nucleotides are conventionally regarded as mediators of platelet inhibition. However recent studies suggested a role for cGMP early in a MAP kinase pathway in platelet activation. In the current study the roles and relationships of MAP kinases, cyclic nucleotides and cPLA(2) in platelet activation by low-dose collagen and a thromboxane analogue (U46619) have been evaluated. Stimulants of neither adenylate cyclase (PGI(2)) nor guanylate cyclase (NaNP) alone had any effect on the basal phosphorylation of either MAP kinase. PGI(2) inhibited ERK/p38(MAPK) phosphorylation in response to both agonists which was unaffected by a cPLA(2) inhibitor (AACOCF(3)). NaNP inhibited collagen-induced ERK/p38(MAPK) phosphorylation, which was enhanced by AACOCF(3) and reversed by a guanylate cyclase inhibitor (ODQ). However NaNP had no effect on U46619-induced p38(MAPK) phosphorylation. Thus adenylate cyclase activation inhibits low-dose collagen-induced MAP kinase phosphorylation both prior, and distal, to thromboxane release. The study also supports an inhibitory, rather than stimulatory, role for guanylate cyclase in platelet signaling.

C1q induces a rapid up-regulation of P-selectin and modulates collagen- and collagen-related peptide-triggered activation in human platelets

Blood platelets are emerging as important immunomodulatory cells, but complement interaction with platelets is not well understood. Several platelet structures have been described as complement protein 1q (C1q) binding receptors, such as C1qRp/CD93 and gC1qR. However, there are conflicting results whether these receptors are C1q binding structures, or even at all expressed on the cell surface. Recently, the collagen-binding integrin αIIβI was reported to bind C1q on mast cells, and this receptor is also present on platelets. The aim of this study was to further characterize the effects of C1q on platelets, by quantifying the platelet surface expression of P-selectin (CD62P) and monitoring the formation of platelet-neutrophil aggregates. Using flow cytometry, we found that C1q dose-dependently triggered a rapid but moderate and transient up-regulation of P-selectin already within 5s of C1q exposure. Pre-incubation with an antibody directed against gC1qR significantly inhibited (with 57% compared to control) the up-regulation, whereas an antibody towards the αIIβI-integrin showed no effect. Stimulation with C1q did not change the cytosolic calcium-levels, as measured with the fluorescent ratiometric probe Fura-2, however, a protein kinase C inhibitor (GF109203x) blocked the C1q-induced P-selectin expression. Furthermore, pre-incubation of platelets with C1q diminished both the collagen as well as the collagen-related peptide-induced up-regulation of P-selectin, most evident after 90s of stimulation. This indicates that C1q may regulate platelet activation via the GPVI receptor, which is a novel finding. Moreover, C1q antagonized the collagen-induced formation of platelet-neutrophil aggregates, indicating a reduced interaction between platelet P-selectin and neutrophil P-selectin glycoprotein ligand-1(PSGL-1/CD162). In summary, C1q induces a moderate rapid platelet P-selectin expression, modulates subsequent collagen and collagen-related peptide stimulation of platelets, and inhibits the formation of platelet-neutrophil aggregates. These immuno-regulatory effects of C1q may have a crucial role in innate immunity and inflammation.