Human Platelet Aggregation Research Articles

Brain-derived gangliosides prime human platelet aggregation and induce platelet-leukocyte aggregate formation

BackgroundPlatelet activation and interaction with leukocytes are crucial in inflammation. Gangliosides, sialic acid–containing glycosphingolipids, have been linked to different inflammatory conditions related to cardio- and neurodegenerative disorders. The role of gangliosides in platelet and leukocyte function, although reported, still needs further investigation. ObjectivesWe aimed to study the role of gangliosides in platelet activation and platelet-leukocyte interaction in vitro. MethodsPlatelet activation was studied through aggregometry in platelet-rich plasma from apparently healthy human volunteers. Signaling protein phosphorylation was analyzed by immunoblotting. Platelet P-selectin expression and platelet-leukocyte aggregate formation were measured by flow cytometry. ResultsThe gangliosides monosialoganglioside GM1, disialoganglioside GD1a, and trisialoganglioside GT1b did not induce by themselves any platelet aggregation. Conversely, when preincubated with platelets, they potentiate platelet aggregation induced by submaximal adenosine diphosphate and collagen concentrations and increased P-selectin expression. Incubation of platelets with free sialic acid and the soluble part of monosialoganglioside GM1 induced a similar potentiating effect on platelet aggregation but not on platelet P-selectin expression. Consistently, analyzing the signaling protein phosphorylation, only the entire gangliosides activated extracellular stimuli–responsive kinase 1/2 suggesting that a complete ganglioside is crucial for its action on platelets. Both the priming effect on platelet aggregation and ERK1/2 activation were prevented by aspirin. Moreover, incubation of citrated whole blood with gangliosides induced platelet-leukocyte aggregate formation accompanied by increased expression of granulocyte and monocyte CD11b compared with untreated blood, suggesting a primary leukocyte activation. ConclusionGangliosides may act in vitro both on platelet and leukocyte activation and on their interaction. The observed effects might contribute to inflammatory processes in clinical conditions.

Epigenetic Targeting of Heparan Sulfate 3-O- and 6-O-Sulfation in Breast Cancer Cells: Prospects for Attenuating Prothrombotic Tumor Cell Activities.

The deregulation of cell surface heparan sulfate proteoglycans (HSPGs) is a main issue of cancer cells for increasing their malignancy. In these terms, the sulfation pattern of HS, created by an orchestrated activity of enzymes balancing a site-specific sulfation, is of key importance. These enzymes are often deregulated by epigenetic processes in cancer, e.g., being silenced by DNA hypermethylation. Here, we address this issue in human breast cancer cell lines aiming to target epigenetic processes to reactivate HS sulfation, shifting HS into an antithrombotic phenotype for which 3-O-sulfation is particularly important. Treatment of MCF-7 and MDA-MB-231 cells with nontoxic concentrations of 5-azacytidine (azacytidine) and 5-fluoro-2'-deoxycytidine (FdCyd) as DNMT inhibitors or vorinostat for targeting HDAC increased HS3-O-sulfation remarkably, as confirmed by fluorescence microscopy, by upregulating HS3-O-sulfotransferases, detected by quantitative real-time polymerase chain reaction and Western blot. Flow cytometry and microscopic approaches confirm that upon inhibitor treatment, increased HS3-O-sulfation improves cell binding to antithrombin, leading to an antithrombotic activity. Nevertheless, only azacytidine- and vorinostat-treated cells display anticoagulative properties, represented by attenuated thrombin formation, a lower activation of human platelet aggregation, or ATP release. In contrast, FdCyd additionally upregulated tissue factor expression in both cell lines, overshadowing the anticoagulant effects of HS, leading to an overall prothrombotic phenotype. Our data provide evidence for the first time that targeting epigenetic processes in HS sulfation is a valuable means to foster anticoagulative cell properties for decreasing malignancy and metastatic potency. These data warrant further investigations to fine-tune epigenetic targeting and to search for potential biomarkers attributed to these activities.

Potent inhibitory effect on human platelet aggregation of the aerial part of Canna edulis

Canna edulis Ker Gawl has been used in Vietnamese Traditional Medicine for the treatment of heart diseases with very limited scientific evidence. This study aimed to evaluate the inhibitory effect on human platelet aggregation of the aerial part of C. edulis. Aerial C. edulis was firstly macerated with methanol, and then fractionated with different solvents to obtain 3 fractions: n-hexane, ethyl acetate and aqueous extracts. The inhibitory effects on human platelet aggregation of extracts were evaluated via three parameters: percentage inhibition of platelet aggregation (%I), area under the aggregation curve (AUC) and aggregation slope, using two agonists adenosine diphosphate (ADP) and collagen. The results showed that all extracts significantly inhibited platelet aggregation in a dose-dependent manner for both agonists. Moreover, all extracts significantly decreased AUC and slope, indicating their antiaggregatory effects on both general aggregation and aggregation velocity. Among extracts, the ethyl acetate fraction exhibited the strongest effect regardless of agonists used (%I at 4 mg/mL, 99.2% for both ADP and collagen). The n-hexane fraction also had significant inhibitory effect but it was weaker than the others (p < 0.05). This is the first study to demonstrate the potent antiplatelet effect of the aerial part of C. edulis. This plant could be a potential natural source for searching novel antiplatelet agents and developing dietary supplements for management of cardiovascular diseases.

Small-Molecule Disruptors of the Interaction between Calcium- and Integrin-Binding Protein 1 and Integrin αIIbβ3 as Novel Antiplatelet Agents.

Thrombosis, a key factor in most cardiovascular diseases, is a major contributor to human mortality. Existing antithrombotic agents carry a risk of bleeding. Consequently, there is a keen interest in discovering innovative antithrombotic agents that can prevent thrombosis without negatively impacting hemostasis. Platelets play crucial roles in both hemostasis and thrombosis. We have previously characterized calcium- and integrin-binding protein 1 (CIB1) as a key regulatory molecule that regulates platelet function. CIB1 interacts with several platelet proteins including integrin αIIbβ3, the major glycoprotein receptor for fibrinogen on platelets. Given that CIB1 regulates platelet function through its interaction with αIIbβ3, we developed a fluorescence polarization (FP) assay to screen for potential inhibitors. The assay was miniaturized to 1536-well and screened in quantitative high-throughput screening (qHTS) format against a diverse compound library of 14,782 compounds. After validation and selectivity testing using the FP assay, we identified 19 candidate inhibitors and validated them using an in-gel binding assay that monitors the interaction of CIB1 with αIIb cytoplasmic tail peptide, followed by testing of top hits by intrinsic tryptophan fluorescence (ITF) and microscale thermophoresis (MST) to ascertain their interaction with CIB1. Two of the validated hits shared similar chemical structures, suggesting a common mechanism of action. Docking studies further revealed promising interactions within the hydrophobic binding pocket of the target protein, particularly forming key hydrogen bonds with Ser180. The compounds exhibited a potent antiplatelet activity based on their inhibition of thrombin-induced human platelet aggregation, thus indicating that disruptors of the CIB1- αIIbβ3 interaction could carry a translational potential as antithrombotic agents.

Investigating the role of rotenone on human blood platelets: Molecular insights into abnormal platelet functions in Parkinson's disease.

Parkinson's disease (PD) is a predominant neuromotor disorder characterized by the selective death of dopaminergic neurons in the midbrain. The majority of PD cases are sporadic or idiopathic, with environmental toxins and pollutants potentially contributing to its development or exacerbation. However, clinical PD patients are often associated with a reduced stroke frequency, where circulating blood platelets are indispensable. Although platelet structural impairment is evident in PD, the platelet functional alterations and their underlying molecular mechanisms are still obscure. Therefore, we investigated rotenone (ROT), an environmental neurotoxin that selectively destroys dopaminergic neurons mimicking PD, on human blood platelets to explore its impact on platelet functions, thus replicating PD conditions in vitro. Our study deciphered that ROT decreased thrombin-induced platelet functions, including adhesion, activation, secretion, and aggregation in human blood platelets. As ROT is primarily responsible for generating intracellular reactive oxygen species (ROS), and ROS is a key player regulating the platelet functional parameters, we went on to check the effect of ROT on platelet ROS production. In our investigation, it became evident that ROT treatment resulted in the stimulation of ROS production in human blood platelets. Additionally, we discovered that ROT induced ROS production by augmenting Ca2+ mobilization from inositol 1,4,5-trisphosphate receptor. Apart from this, the treatment of ROT triggers protein kinase C associated NADPH oxidase-mediated ROS production in platelets. In summary, this research, for the first time, highlights ROT-induced abnormal platelet functions and may provide a mechanistic insight into the altered platelet activities observed in PD patients.

Hemostatic activity <i>in vitro</i> of lectin-containing substances of bryathypes on the example of some Antarctic and Belarus representatives

BACKGROUND: The modern market of medical devices in Belarus and Russia is represented by a wide range of hemostatic agents, of which the most popular are local hemostatics of plant origin possessing the significant technological potential for renewal and improvement. A promising reserve for this may be biologically active compounds of mosses, which are characterized by anti-inflammatory, antibacterial and antifungal effects. However, their hemostatic effect is almost not studied, which determines the relevance of this work.
 AIM: The aim of this work is to study the effect of lectin-containing substances from mosses of three species collected in East Antarctica and Belarus on the parameters of human blood hemostasis in vitro.
 MATERIALS AND METHODS: We studied mosses of the genera Bryum, Ceratodon, and Coscinodon, collected in the area of the Belarusian Antarctic station Gora Vechernyaya in East Antarctica and in Belarus. Lectin-containing substances of mosses were obtained by extracting shoots in 0.05 M tris-HCl buffer (pH 8.0), centrifugation, filtration. The assessment of the biological activity of lectin-containing substances in mosses was carried out by the agglutination reaction of rabbit erythrocytes, as well as the effect on human platelet aggregation and in the test for activated partial thromboplastin time.
 RESULTS: It was established that lectin-containing substances of the studied moss species had agglutinating activity against erythrocytes in the range from 11708.28 (Belarusian samples) to 1333979.59 U/mg of protein (Antarctic samples) depending on the species and localization; initiated the aggregation of human platelets (25–80% of the effect of thrombin) regardless of blood group, Rh and gender of donors; influenced the plasma link of hemostasis, reducing activated partial thromboplastin time (by 15–18%).
 CONCLUSIONS: It was found that some species of mosses of the genera Bryum, Ceratodon and Coscinodon of Antarctica and Belarus had an agglutinating and hemostatic effect on erythrocytes and platelets, with the greatest activity noted for Antarctic species. A hypothesis has been put forward that the observed phenomenon is due to the structural features of proteins, including lectins. It is assumed that lectins are possible inducers of erythrocyte agglutination and platelet aggregation in mosses. It is shown that the moss species Bryum pseudotriquetrum and Ceratodon purpureus have a certain resource potential in Belarus for their annual harvest. The results obtained expand the list of moss species with hemostatic activity, and can be used to develop new hemostatics of plant origin for local use from Belarusian plant materials.

Potential Inhibitory Effects on Human Platelet Aggregation and blood Coagulation of the Aerial Part of Portulaca oleracea L

Potential Inhibitory Effects on Human Platelet Aggregation and blood Coagulation of the Aerial Part of Portulaca oleracea L

Gestodene, a novel positive allosteric modulator of PAR1, enhances PAR1-mediated human platelet aggregation.

Background: Protease-activated receptor 1 (PAR1) is expressed in human platelets and can be activated by low concentrations of thrombin. Vorapaxar, a selective antagonist of PAR1, inhibits thrombin-induced calcium mobilization in human platelet, which is associated with an increased risk of bleeding. Conversely, the administration of a positive allosteric modulator (PAM) of PAR1 may pose a substantial risk of thrombosis due to inducing excessive platelet activation. In this study, we discovered a novel PAM of PAR1 and investigated the effect of enhanced PAR1 activation by PAM of PAR1 on platelet activation. Methods: To find PAMs of PAR1, a cell-based screen was performed in HT29 cells, and finally, gestodene, an oral contraceptive drug (OC), was identified as a novel PAM of PAR1. The mechanism of action of gestodene and its effects on platelet activation were investigated in human megakaryocytic leukemia cell line MEG-01 cells and human platelet. Results: Gestodene enhanced both thrombin- and PAR1-activating peptide (AP)-induced intracellular calcium levels in a dose-dependent manner without altering PAR2 and PAR4 activity. Gestodene significantly increased PAR1-AP-induced internalization of PAR1 and phosphorylation of ERK1/2, and the enhancing effects were significantly blocked by vorapaxar. Furthermore, gestodene potently increased PAR1-AP induced morphological changes in MEG-01 cells. Remarkably, in human blood, gestodene exerted a robust augmentation of PAR1-AP-induced platelet aggregation, and vorapaxar effectively attenuated the gestodene-induced enhancement of platelet aggregation mediated by PAR1. Conclusion: Gestodene is a selective PAM of PAR1 and suggest one possible mechanism for the increased risk of venous thromboembolism associated with OCs containing gestodene.

Diphenyl-tetrazol-propanamide Derivatives Act as Dual-Specific Antagonists of Platelet CLEC-2 and Glycoprotein VI.

Platelet C-type lectin-like receptor 2 (CLEC-2) induces platelet activation and aggregation after clustering by its ligand podoplanin (PDPN). PDPN, which is not normally expressed in cells in contact with blood flow, is induced in inflammatory immune cells and some malignant tumor cells, thereby increasing the risk of venous thromboembolism (VTE) and tumor metastasis. Therefore, small-molecule compounds that can interfere with the PDPN-CLEC-2 axis have the potential to become selective antiplatelet agents. Using molecular docking analysis of CLEC-2 and a PDPN-CLEC-2 binding-inhibition assay, we identified a group of diphenyl-tetrazol-propanamide derivatives as novel CLEC-2 inhibitors. A total of 12 hit compounds also inhibited PDPN-induced platelet aggregation in humans and mice. Unexpectedly, these compounds also fit the collagen-binding pocket of the glycoprotein VI molecule, thereby inhibiting collagen interaction. These compounds also inhibited collagen-induced platelet aggregation, and one compound ameliorated collagen-induced thrombocytopenia in mice. For clinical use, these compounds will require a degree of chemical modification to decrease albumin binding. Nonetheless, as dual activation of platelets by collagen and PDPN-positive cells is expected to occur after the rupture of atherosclerotic plaques, these dual antagonists could represent a promising pharmacophore, particularly for arterial thrombosis, in addition to VTE and metastasis.

GDF-15 Inhibits ADP-Induced Human Platelet Aggregation through the GFRAL/RET Signaling Complex.

Growth differentiation factor-15 (GDF-15) is proposed to be strongly associated with several cardiovascular diseases, such as heart failure and atherosclerosis. Moreover, some recent studies have reported an association between GDF-15 and platelet activation. In this study, we isolated peripheral blood platelets from healthy volunteers and evaluated the effect of GDF-15 on adenosine diphosphate (ADP)-induced platelet activation using the platelet aggregation assay. Subsequently, we detected the expression of GDF-15-related receptors on platelets, including the epidermal growth factor receptor (EGFR), human epidermal growth factor receptor 2 (HER2), human epidermal growth factor receptor 3 (HER3), transforming growth factor-beta receptor I (TGF-βRI), transforming growth factor-beta receptor II (TGF-βRII), glial-cell-line-derived neurotrophic factor family receptor α-like (GFRAL), and those rearranged during transfection (RET). Then, we screened for GDF-15 receptors using the GDF-15-related receptor microarray comprising these recombinant proteins. We also performed the immunoprecipitation assay to investigate the interaction between GDF-15 and the receptors on platelets. For the further exploration of signaling pathways, we investigated the effects of GDF-15 on the extracellular signal-regulated kinase (ERK), protein kinase B (AKT), and Janus kinase 2 (JAK2) pathways. We also investigated the effects of GDF-15 on the ERK and AKT pathways and platelet aggregation in the presence or absence of RET agonists or inhibition. Our study revealed that GDF-15 can dose-independently inhibit ADP-induced human platelet aggregation and that the binding partner of GDF-15 on platelets is GFRAL. We also found that GDF-15 inhibits ADP-induced AKT and ERK activation in platelets. Meanwhile, our results revealed that the inhibitory effects of GDF-15 can be mediated by the GFRAL/RET complex. These findings reveal the novel inhibitory mechanism of ADP-induced platelet activation by GDF-15.

The inhibitory effects of glabridin on human platelet aggregation and thrombus formation

The inhibitory effects of glabridin on human platelet aggregation and thrombus formation

Influence of titanium nanoscale surface roughness on fibrinogen and albumin protein adsorption kinetics and platelet responses.

Biomaterials with nanoscale topography have been increasingly investigated for medical device applications to improve tissue-material interactions. This study assessed the impact of nanoengineered titanium surface domain sizes on early biological responses that can significantly affect tissue interactions. Nanostructured titanium coatings with distinct nanoscale surface roughness were deposited on quartz crystal microbalance with dissipation (QCM-D) sensors by physical vapor deposition. Physico-chemical characterization was conducted to assess nanoscale surface roughness, nano-topographical morphology, wettability, and atomic composition. The results demonstrated increased projected surface area and hydrophilicity with increasing nanoscale surface roughness. The adsorption properties of albumin and fibrinogen, two major plasma proteins that readily encounter implanted surfaces, on the nanostructured surfaces were measured using QCM-D. Significant differences in the amounts and viscoelastic properties of adsorbed proteins were observed, dependent on the surface roughness, protein type, protein concentration, and protein binding affinity. The impact of protein adsorption on subsequent biological responses was also examined using qualitative and quantitative in vitro evaluation of human platelet adhesion, aggregation, and activation. Qualitative platelet morphology assessment indicated increased platelet activation/aggregation on titanium surfaces with increased roughness. These data suggest that nanoscale differences in titanium surface roughness influence biological responses that may affect implant integration.

Extracts of tamarillo, horned melon, and raspberry, but not extract of pear, inhibit human blood platelet aggregation: Investigating the underlying factors for their differential mechanisms

In addition to their roles in thrombosis, hyperactive platelets contribute to atherosclerosis.Since anti-platelet drugs are not recommended for the vulnerable population with hyperactive platelets to reduce the risk of cardiovascular disease, a search is on to find alternative dietary antiplatelets that can be safely used.We here describe that in a dose-dependent manner, sugar-free extracts of tamarillo, horned melon (kiwano), and raspberryinhibited ADP-induced platelet aggregation in platelet-rich plasma, whereas pear extract had no effects.Furthermore, analysisof untargeted metabolites revealed the presence of platelet inhibitory components such as benzoic acid, caffeic acid, and gallic acid in the sugar-free extracts of tamarillo, raspberry, and kiwano but absent in pear extract.All these three fruit extracts inhibited the platelet production of TxB2and the release of platelet factor 4. Our work suggeststhat these fruitsinhibitplatelet aggregation partly due to anti-platelet compounds such asbenzoic, caffeic, and gallic acids.

Zingiber mioga: a perspective of its botany, uses, chemical constituents and health benefits

In this review, the botany, uses, bioactive metabolites and health benefits of Zingiber mioga or myoga (Zingiberaceae), a popular edible ginger in Japan, Korea and China, are highlighted. Myoga is endemic to Japan, occurring naturally in Honshu, Shikoku and Kyushu. Available during summer, Z. mioga flower buds (ZMB) are consumed fresh or pickled. Major production areas in Japan are Gumma and Kanto, where Z. mioga is widely planted in home gardens. The plant is deeply enshrined in Japanese culture and tradition with annual festivals held to celebrate its mythology and folklore. Major pungent principles are labdane-type diterpene aldehydes identified as galanal A, galanal B, miogadial, miogatrial and mioganal. Health benefits of ZMB include anti-inflammation, anti-obesity, hypolipidemic, anti-diabetic, antioxidant, acetylcholinesterase inhibition, memory improvement and skin nourishment. Bioactive compounds from ZMB display antimicrobial, antioxidant, anti-inflammatory, anti-cancer, human platelet aggregation, 5- lipoxygenase inhibitory, and indoleamine 2,3-dioxygenase 1 inhibitory activities. Bioactive compounds from the rhizomes have antibacterial and cytotoxic properties. Studies on allergic dermatitis due to regular contact with Z. mioga have been conducted. Some areas for future research on Z. mioga are suggested. Sources of information referred were from Google Scholar, PubMed, PubMed Central, Science Direct, J-Stage and PubChem

Campomanesia guazumifolia infusion decreases human platelet aggregation by reducing cyclooxygenase 1 activity and its underlying mechanisms

Campomanesia guazumifolia is a species from the Brazilian Cerrado, and its leaves are used by traditional medicine in the preparation of infusion. Its popular uses include antidiarrheal, hypocholesterolemic, and anti-inflammatory purposes. Here we studied the leaf infusion of Campomanesia guazumifolia (LICG) on platelet activity, investigating its role in the cyclooxygenase (COX) pathway. For this, the phytochemical composition, in vivo toxicity (using zebrafish) were evaluated and their effects were investigated on platelet reactivity using different agonists. To elucidate the possible mechanisms involved, we studied the impact of LICG on calcium mobilization, cyclic nucleotides and thromboxane levels, PKCβ2 phosphorylation, and COX inhibition. Furthermore, in silico studies showed the interactions of COX-1 with the compounds identified in LICG by molecular modeling. We describe for the first time that LICG acts by inhibiting platelet aggregation evoked by different physiological agonists, which results in a drastic reduction in intracellular calcium discharge without the involvement of cyclic nucleotide pathways. Furthermore, we showed that LICG appears to inhibit cyclooxygenase 1, reducing thromboxane A2 levels and PKCβ2 phosphorylation in human platelets, reinforced by similar interactions compared to a reference inhibitor at the catalytic site. This study demonstrates the antiplatelet effects of LICG via COX-1 and suggests that these agents may be therapeutic for preventing platelet-associated cardiovascular disease.

Repurposing of rilpivirine for preventing platelet β3 integrin-dependent thrombosis by targeting c-Src active autophosphorylation

BackgroundHIV-infected individuals are known to be at higher risk for thrombotic cardiovascular disease (CVD), which may also be differentially affected by components of anti-HIV drugs. To identify the effects of a series of FDA-approved anti-HIV drugs on platelet aggregation in humans, focusing on the novel pharmacological effects of rilpivirine (RPV), a reverse transcriptase inhibitor, on platelet function both in vitro and in vivo and the mechanisms involved. Methods and resultsIn vitro studies showed that RPV was the only anti-HIV reagent that consistently and efficiently inhibited aggregation elicited by different agonists, exocytosis, morphological extension on fibrinogen, and clot retraction. Treatment of mice with RPV significantly prevented thrombus formation in FeCl3-injured mesenteric vessels, postcava with stenosis surgery, and ADP -induced pulmonary embolism models without defects in platelet viability, tail bleeding, and coagulation activities. RPV also improved cardiac performance in mice with post-ischemic reperfusion. A mechanistic study revealed that RPV preferentially attenuated fibrinogen-stimulated Tyr773 phosphorylation of β3-integrin by inhibiting Tyr419 autophosphorylation of c-Src. Molecular docking and surface plasmon resonance analyses showed that RPV can bind directly to c-Src. Further mutational analysis showed that the Phe427 residue of c-Src is critical for RPV interaction, suggesting a novel interaction site for targeting c-Src to block β3-integrin outside-in signaling. ConclusionThese results demonstrated that RPV was able to prevent the progression of thrombotic CVDs by interrupting β3-integrin-mediated outside-in signaling via inhibiting c-Src activation without hemorrhagic side effects, highlighting RPV as a promising reagent for the prevention and therapy of thrombotic CVDs.

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

AimsMelatonin 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 methodsHuman 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 findingsOur 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. SignificanceThe 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.

Aqueous Extract of Malus domestica Inhibits Human Platelet Aggregation Induced by Multiple Agonists

Cardiovascular diseases such as hypertension, myocardial infarction, and atherosclerosis are the major cause of morbidity and mortality in humankind and not only afflict industrialized nations but also affect developing countries such as Pakistan. We attempted to screen one of the most common fruits, Malus domestica (MD or apple), used in Pakistan for its potential cardio-protective effects. The crude aqueous extract (MD-Aq) was prepared and investigated for inhibitory activity against several important cardiovascular drug targets. Activities of antioxidant enzymes such as glutathione peroxidase (GPx) and superoxide dismutase (SOD) were studied, as well as total antioxidant status (TAS). Calcium channel blocking activity was measured using guinea pig ileum in an isolated tissue bath setup. Platelet aggregation studies were carried out using a dual-channel aggregometer. MD-Aq showed dose-dependent improvement in the GPX activity. The highest SOD levels were observed with 10 mg/ml and were 185 U/L compared to 174 U/L for saline, which means no significant effect by MD-Aq. TAS levels were highest at 10 mg/ml of MD-Aq, reaching 1.75 mmol/L of plasma. At 10 mg/ml, close to 90% inhibition of KCl-induced opening of calcium channels was observed, compared with the effect of 1mM Verapamil. At each dose of 1, 5, and 10 mg/ml, a significantly higher arachidonic acid-induced inhibition of platelet aggregation was observed as compared to the saline effect. MD-Aq effects on platelet-activating factor-induced platelet aggregation were less potent. We concluded that MD-Aq could elevate GPX and TAS levels, is inactive at SOD, and is excellent as a calcium channel blocker, a more potent blocker of arachidonic acid-induced aggregation than platelet-activating factor-induced aggregation. These activities can help treat various cardiovascular diseases.

Ginsenoside Rk3 suppresses U46619-induced human platelets aggregation through regulation of cAMP and PI3K/Akt pathway

Ginsenoside Rk3 suppresses U46619-induced human platelets aggregation through regulation of cAMP and PI3K/Akt pathway

Divalent nanobodies to platelet CLEC-2 can serve as agonists or antagonists

CLEC-2 is a target for a new class of antiplatelet agent. Clustering of CLEC-2 leads to phosphorylation of a cytosolic YxxL and binding of the tandem SH2 domains in Syk, crosslinking two receptors. We have raised 48 nanobodies to CLEC-2 and crosslinked the most potent of these to generate divalent and tetravalent nanobody ligands. Fluorescence correlation spectroscopy (FCS) was used to show that the multivalent nanobodies cluster CLEC-2 in the membrane and that clustering is reduced by inhibition of Syk. Strikingly, the tetravalent nanobody stimulated aggregation of human platelets, whereas the divalent nanobody was an antagonist. In contrast, in human CLEC-2 knock-in mouse platelets, the divalent nanobody stimulated aggregation. Mouse platelets express a higher level of CLEC-2 than human platelets. In line with this, the divalent nanobody was an agonist in high-expressing transfected DT40 cells and an antagonist in low-expressing cells. FCS, stepwise photobleaching and non-detergent membrane extraction show that CLEC-2 is a mixture of monomers and dimers, with the degree of dimerisation increasing with expression thereby favouring crosslinking of CLEC-2 dimers. These results identify ligand valency, receptor expression/dimerisation and Syk as variables that govern activation of CLEC-2 and suggest that divalent ligands should be considered as partial agonists.