Adenosine Diphosphate Activation Research Articles

DNAse-dependent, NET-independent pathway of thrombus formation in vivo

The contribution of NETs (neutrophil extracellular traps) to thrombus formation has been intensively documented in both arterial and venous thrombosis in mice. We previously demonstrated that adenosine triphosphate (ATP)-activated neutrophils play a key role in initiating the tissue factor-dependent activation of the coagulation cascade, leading to thrombus formation following laser-induced injury. Here, we investigated the contribution of NETs to thrombus formation in a laser-induced injury model. In vivo, treatment of mice with DNase-I significantly inhibited the accumulation of polymorphonuclear neutrophils at the site of injury, neutrophil elastase secretion, and platelet thrombus formation within seconds following injury. Surprisingly, electron microscopy of the thrombus revealed that neutrophils present at the site of laser-induced injury did not form NETs. In vitro, ATP, the main neutrophil agonist present at the site of laser-induced injury, induced the overexpression of PAD4 and CitH3 but not NETosis. However, compared to no treatment, the addition of DNase-I was sufficient to cleave ATP and adenosine diphosphate (ADP) in adenosine. Human and mouse platelet aggregation by ADP and neutrophil activation by ATP were also significantly reduced in the presence of DNase-I. We conclude that following laser-induced injury, neutrophils but not NETs are involved in thrombus formation. Treatment with DNase-I induces the hydrolysis of ATP and ADP, leading to the generation of adenosine and the inhibition of thrombus formation in vivo.

The TICONC (Ticagrelor-Oncology) Study: Implications of P2Y12 Inhibition for Metastasis and Cancer-Associated Thrombosis

BackgroundIn cancer, platelets may facilitate metastatic spread by a number of mechanisms as well as contribute to thrombotic complications. Ticagrelor, a platelet antagonist- that blocks adenosine diphosphate activation of platelet P2Y12 receptors, is widely used in the treatment of cardiovascular disease, but its efficacy in cancer remains unknown. ObjectivesThis study sought to evaluate the effect of aspirin and ticagrelor monotherapy, as well as dual antiplatelet therapy, on platelet activation in cancer. MethodsThis study consisted of 2 phases: first, an in vitro study of human platelet−tumor cell interaction; and second, a randomized crossover clinical trial of 22 healthy donors and 16 patients with metastatic breast or colorectal cancer. Platelet activation and inhibition were measured by aggregometry and flow cytometry. ResultsIn vitro, tumor cells induced cellular clusters that were predominantly platelet−platelet aggregates. Ticagrelor significantly inhibited formation of large tumor cell-induced platelet−platelet aggregates: 65.4 ± 4.8% to 50.9 ± 5.9% (p = 0.002) and 62.3 ± 3.1% to 48.3 ± 7.3% (p = 0.014) for MCF-7 and HT-29-induced aggregation, respectively. Supporting this finding, cancer patients on ticagrelor had significantly reduced levels of spontaneous platelet aggregation and activation compared with baseline; 14.8 ± 2.7% at baseline to 7.8 ± 2.3% with ticagrelor (p = 0.012). ConclusionsOur findings suggested that P2Y12 inhibition with ticagrelor might reduce spontaneous platelet aggregation and activation in patients with metastatic cancer and merits further investigation in patients at high risk of cancer-associated thrombosis. (Ticagrelor-Oncology [TICONC] Study; EudraCT: 2014-004049-29)

Laboratory assessments of therapeutic platelet inhibition in endovascular neurosurgery: complication prediction using the VerifyNow P2Y12 assay and thromboelastography with platelet mapping.

Inhibition of platelet aggregation is universally used to prevent thromboembolic complications related to stent placement in endovascular neurosurgery, but excessive inhibition potentiates hemorrhagic complications. Previously, the authors demonstrated that two different commercially available measures of adenosine diphosphate (ADP)-dependent platelet inhibition-the VerifyNow P2Y12 clopidogrel assay (measured in platelet reactivity units [PRU]) and maximal amplitude (MA) attributable to ADP activity (MA-ADP) derived from thromboelastography (TEG) with platelet mapping (PM)-yielded wildly different results. This study sought to analyze observed complications to quantify the ideal therapeutic windows for both tests. Ninety-one patients with simultaneous or near-simultaneous PRU and TEG-PM results who underwent craniocervical endovascular stenting at the authors' institution between September 2015 and November 2017 were identified and retrospectively enrolled. From November 2017 until June 2019, 109 additional patients were prospectively enrolled. For this study, in-hospital thrombotic and hemorrhagic complications (both CNS and non-CNS) were tabulated, and receiver operating characteristic (ROC) curve analysis was used to identify threshold values of the PRU and MA-ADP for predicting each type of complication. Of the 200 patients enrolled, 7 were excluded because of anemia or thrombocytopenia outside of the test manufacturer's specified ranges and 1 was excluded because they did not have a TEG-PM result. Including complications of all severities, there were a total of 15 CNS thrombotic complications, 1 access-site thrombotic complication, 3 CNS hemorrhages, 8 access-site hemorrhagic complications, and 3 hemorrhagic complications not affecting either the CNS or the access site. ROC curve analysis yielded therapeutic threshold values of 118-144 PRU. The results demonstrated PRU has a significant dose-dependent effect on the rates of thrombosis and hemorrhage. Logistic regression models did not demonstrate statistically significant relationships between the MA-ADP and either thrombosis or hemorrhage. ROC analysis based on these models is of little value and did not identify significant threshold values for MA-ADP. There continues to be poor correlation between the results of TEG-PM and PRU. PRU accurately predicted complications, with a relatively narrow ideal value range of 118-144. The MA-ADP alone does not appear able to accurately predict either hemorrhagic or thrombotic complications in this group.

Predictive Effect of Platelet Activation Index Expression before and after Adenosine Bisphosphate Activation on Bleeding Risk in ITP Patients

To investigate the predictive effect of platelet activation index expression before and after adenosine bisphosphate activation on bleeding risk in patients with primary immune thrombocytopenia (ITP). Eighty-nine patients with ITP admitted in our hospital from January 2017 to October 2018 were selected and inrolled in ITP group, the bleeding scoreing and grading were performed by using the ITP-BAT for ITP patients, then 89 ITP patients were divided into 4 subgroups: nothing bleeding symptom group, mild bleeding symprom group, mode rate bleeding symptom group and severe bleeding symptom group according to bleeding scores and grades obtained from ITP-BAT detection. At the same time, 22 persons underwent the health physical examination were selected and enrolled in control group. The adenosine diphosphate (ADP) was used as activator for all patients and controls. The flow cytonetry was used to analyze the expression of platelet membranc glyco protein (GPⅠb, GPⅡb /Ⅲ a) and P-selectin before and after ADP activation, the multiple linear person's correlation analysis was used to analyze the correlation of bleeding degree of ITP patients before and after ADP acbivation with the expression levels of GPⅠb, GPⅡb/Ⅲa and P-selectin. After the ADP activation, the expression level of GPⅠb significantly decreased, while the expression levels of GPⅠb, GPⅡb/Ⅲ a and P-selectin significantly increased in control group, nothing bleeding symptom group and mild bleeding symptom group; but the expression level of GPⅠb significantly increased, while the expression level of GPⅡb/Ⅲ a significantly decreased in moderate and severe bleeding symptom group, the both differences were statistically significant (P＜0.05). however, the expression level of P-selectin in moderate and severe bleeding symptom groups before and after ADP activation was not statistivally significant (P＞0.05). Before ADP activation, the expression level of GPⅠb in ITP subgroups was lower than that in control group, the expression level of GPⅡb/Ⅲ a in ITP subgroups was higher than that in control group, the expression level of P-selectin in moderate and severe bleeding symptom groups was higher than that in control group (P＜0.05). After ADP activation, the expression levels of GPⅠb and P-selectin in ITP subgroups both were lower than those in control group, the expression level of GPⅡb/Ⅲa in ITP subgroups was higher than that in control group (P＜0.05). The comparison among ITP subgroups showed that before ADP activation, the expression level of GPⅠb in moderate and severe bleeding symptom groups was lower than that in nothing bleeding symotom and mild bleeding symptom groups, while the expression levels of GPⅡb/Ⅲa and P-selectin were higher than those in nothing bleeding symptom and mild bleeding symptom groups (P＜0.05), however, after ADP activation, the expression level of GPⅠb in moderate and severe bleeding symptom groups was higher than that in nothing bleeding symptom and mild bleeding symptom groups, while the expression levels of GPⅡb/Ⅲ a and P-selection in moderate and severe bleeding symptom groups were lower than those in nothing and mild bleeding symptom groups (P＜0.05). The correlation analysis showed that before ADP activation, the expression levels of GPⅠb and GPⅡb/Ⅲa positivdy correlated with the bleeding risk (r=0.483, 0.504), and the P-selectin not correlated with the bleeding risk (r=0.000); however, after ADP activation, the expression level of GPⅠb and GPⅡb/Ⅲ a negatively correlated with the bleeding risk (r=-0.627, -0.406, -0.108). The expression level of platelet activation indicators before and after ADP activation is of certain value for prevention of bleeding risk in ITP patients and can be used as a reference indicator for the treatment and efficacy evaluation.

Ebselen Reversibly Inhibits Human Glutamate Dehydrogenase at the Catalytic Site.

Human glutamate dehydrogenase (GDH) plays an important role in neurological diseases, tumor metabolism, and hyperinsulinism-hyperammonemia syndrome (HHS). However, there are very few inhibitors known for human GDH. Recently, Ebselen was reported to crosslink with Escherichia coli GDH at the active site cysteine residue (Cys321), but the sequence alignment showed that the corresponding residue is Ala329 in human GDH. To investigate whether Ebselen could be an inhibitor for human GDH, we cloned and expressed an N-terminal His-tagged human GDH in E. coli. The recombinant human GDH enzyme showed expected properties such as adenosine diphosphate activation and nicotinamide adenine dinucleotide/nicotinamide adenine dinucleotide phosphate dual recognition. Further, we developed a 2-(3-(2-methoxy-4-nitrophenyl)-2-(4-nitrophenyl)-2H-tetrazol-3-ium-5-yl) benzenesulfonate sodium salt (EZMTT)-based assay for human GDH, which was highly sensitive and is suitable for high-throughput screening for potent GDH inhibitors. In addition, ForteBio binding assays demonstrated that Ebselen is a reversible active site inhibitor for human GDH. Since Ebselen is a multifunctional organoselenium compound in Phase III clinical trials for inflammation, an Ebselen-based GDH inhibitor might be valuable for future drug discovery for HHS patients.

Antiplatelet regimen following stent-assisted embolization for intracranial aneurysms

Objective To investigate the efficacy and safety of one antiplatelet regimen following stent-assisted embolization for intracranial aneurysms. Methods Clinical data were analyzed retrospectively in 684 patients with intracranial aneurysms who underwent stent-assisted embolization from July 2014 to July 2016 at Wuhan General Hospital of the Chinese Liberation Army. Tirofiban hydrochloride was injected immediately after stent deploying and infused continuously by micro-pump for 24 hours. Dual antiplatelet therapy (aspirin 100 mg/d + clopidogrel 75 mg/d) started on the second day. Postoperatively, the platelet activation function was dynamically monitored by flow cytometry. The dose adjustment criteria of antiplatelet drugs were based on the platelet inhibition status (the positive rate of CD62P after adenosine diphosphate activation was below 20%) and specific postoperative conditions such as hemorrhage or ischemia for 486 cases (passive adjustment group) before June 2015, and those for 198 cases (active adjustment group) after June 2015 were only according to the platelet inhibition status regardless of hemorrhage or ischemia. Results Complications were reported in 67 out of 684 (9.8%) cases and included aneurysm rerupture (n=23, 3.4%), hydrocephalus requiring ventriculoperitoneal shunting (n=13, 1.9%), stent thrombosis (n=9, 1.3%), cerebral infarction (n=6, 0.9%), intracranial hemorrhage in remote areas (n=4, 0.6%), plaque shedding (n=2, 0.3%) cases, aneurysm recurrence (n=3, 0.4%) and death (n=26, 3.8%). The medication regimen was adjusted in a total of 221 (32.3%) patients including 147 (30.2%, 147/486) cases in the passive adjustment group and 74 (37.4%, 74/198) cases in the active adjustment group. There was significant difference in the complication rate of hemorrhage between passive and active adjustment groups (9.1% [44/486] vs. 3.5% [7/198], P<0.05). No significant difference was identified in the complication rate of ischemia between the two groups (0.2% [1/462] vs. 1.0% [2/196], P=0.19). Transient ischemic attack occurred in 3 (0.4%) cases during the process of dose reduction of clopidogrel which remitted following the dose increase. No case of resistance to antiplatelet therapy was found. Conclusion Antiplatelet therapy regimen guided by platelet activation assay could be useful for preventing thrombosis and hemorrhagic events following stent-assisted embolization for intracranial aneurysms. Key words: Intracranial aneurysm; Aneurysm, ruptured; Embolization, therapeutic; Stents; Platelet aggregation inhibitors; Coil

Ovine platelet function is unaffected by extracorporeal membrane oxygenation within the first 24 h.

This study investigated platelet dysfunction during short-term extracorporeal membrane oxygenation (ECMO) and secondarily to determine if hyperoxaemia contributes to this dysfunction. Healthy sheep were anaesthetized and maintained on ECMO for either 2 or 24 h, with or without induction of smoke inhalation acute lung injury. A specialized animal-operating theatre was used to conduct the experimentation. Forty-three healthy female sheep were randomized into either a test or a control group. Following anaesthesia, test groups received ECMO ± smoke inhalation acute lung injury (SALI), whereas control groups were maintained with ventilation only ± SALI. Physiological, biochemical and coagulation data were obtained throughout via continuous monitoring and blood sampling. Platelet function was quantified through whole blood impedance aggregometry using Multiplate. Ovine platelet activity induced by adenosine diphosphate (ADP) and collagen was unaffected during the first 24 h of ECMO. However, progressive divergence of ADP-induced platelet activity was noted at cessation of the experiment. PaO2 was inversely related to ADP-dependent platelet activity in the ECMO groups--a relationship not identified in the control groups. ADP and collagen-dependent platelet activity are not significantly affected within the first 24 h of ECMO in sheep. However, dysfunction in ADP-dependent platelet activity may have continued to develop if observed beyond 24 h. Hyperoxaemia during ECMO does appear to affect how platelets react to ADP and may contribute to this developing dysfunction. Long-term animal models and investigation in clinical animals are warranted to fully investigate platelet function during ECMO.

Signaling via P2Y12 May Be Critical for Early Stabilization of Platelet Aggregates

P2Y(12) receptor antagonism inhibits platelet aggregation by preventing adenosine diphosphate (ADP)-mediated amplification of activation pathways downstream of primary agonists, such as thrombin and collagen. However, the role of ADP signaling in maintaining aggregate stability and the effects of P2Y(12) antagonists on preestablished aggregates in vitro and arterial thrombus in vivo are not well understood. This study evaluated the impact of P2Y(12) signaling on platelet aggregate stability and early thrombotic occlusion using a reversible P2Y(12) antagonist, ticagrelor. There were 2 study objectives: (1) to determine if there was a time-dependent factor on the capacity of a P2Y(12) antagonist to affect human platelet aggregate stability in vitro using light transmission aggregometry and (2) to evaluate the extent of arterial thrombus reversal in a preclinical model upon administration of ticagrelor in vivo. Platelet aggregates were exposed to ticagrelor after ADP or collagen activation, monitored for stability by aggregometry, and visualized by microscopy. Freshly formed ADP- and collagen-induced platelet aggregates were more rapidly dispersed by a P2Y(12) antagonist than drug carrier control at clinically relevant concentrations (P < 0.05). However, stable aggregates were not noticeably affected. A murine arterial thrombosis model was used to evaluate thrombus stability in an in vivo mouse model. Thrombotic occlusion was induced by FeCl(3), followed by a bolus intravenous administration of ticagrelor or vehicle control. Doppler blood flow was monitored before injury and 30 minutes after bolus administration. Arteries were retrieved for inspection for residual thrombus. Early arterial thrombotic occlusion in vivo was partially reversed by ticagrelor administration. Blood flow through the injured artery increased, and thrombus size within the artery decreased (P < 0.05, n = 3). In conclusion, P2Y(12) antagonism disrupts the stability of newly formed platelet aggregates, promoting disaggregation, and reverses thrombotic vascular occlusion. Thus, in addition to activating platelets, signaling via P2Y(12) seems to be required for stabilizing platelet thrombi.

Adverse Effects of Hemorrhagic Shock Resuscitation With Stored Blood Are Ameliorated by Inhaled Nitric Oxide in Lambs*

Transfusion of stored RBCs is associated with increased morbidity and mortality in trauma patients. Plasma hemoglobin scavenges nitric oxide, which can cause vasoconstriction, induce inflammation, and activate platelets. We hypothesized that transfusion of RBCs stored for prolonged periods would induce adverse effects (pulmonary vasoconstriction, tissue injury, inflammation, and platelet activation) in lambs subjected to severe hemorrhagic shock and that concurrent inhalation of nitric oxide would prevent these adverse effects. Animal study. Research laboratory at the Massachusetts General Hospital, Boston, MA. Seventeen awake Polypay-breed lambs. Lambs were subjected to 2 hours of hemorrhagic shock by acutely withdrawing 50% of their blood volume. Lambs were resuscitated with autologous RBCs stored for 2 hours or less (fresh) or 39 ± 2 (mean ± SD) days (stored). Stored RBCs were administered with or without breathing nitric oxide (80 ppm) during resuscitation and for 21 hours thereafter. We measured hemodynamic and oxygenation variables, markers of tissue injury and inflammation, plasma hemoglobin concentrations, and platelet activation. Peak pulmonary arterial pressure was higher after resuscitation with stored than with fresh RBCs (24 ± 4 vs 14 ± 2 mm Hg, p < 0.001) and correlated with peak plasma hemoglobin concentrations (R = 0.56, p = 0.003). At 21 hours after resuscitation, pulmonary myeloperoxidase activity was higher in lambs resuscitated with stored than with fresh RBCs (11 ± 2 vs 4 ± 1 U/g, p = 0.007). Furthermore, transfusion of stored RBCs increased plasma markers of tissue injury and sensitized platelets to adenosine diphosphate activation. Breathing nitric oxide prevented the pulmonary hypertension and attenuated the pulmonary myeloperoxidase activity, as well as tissue injury and sensitization of platelets to adenosine diphosphate. Our data suggest that resuscitation of lambs from hemorrhagic shock with autologous stored RBCs induces pulmonary hypertension and inflammation, which can be ameliorated by breathing nitric oxide.

The P2Y(12) receptor as a target of antithrombotic drugs.

The P2Y(12) receptor as a target of antithrombotic drugs.

The impact of bleeding history, von Willebrand factor and PFA–100® on the diagnosis of type 1 von Willebrand disease: results from the European study MCMDM‐1VWD

The relationships between the Platelet Function Analyzer (PFA)-100 and von Willebrand factor (VWF) levels and bleeding score (BS) were evaluated within a multicentre project on Molecular and Clinical Markers for the Diagnosis and Management of type 1 von Willebrand disease (MCMDM-1VWD). PFA-100 closure time, either with epinephrine (EPI) or adenosine diphosphate (ADP)-cartridges, was measured in 107 index cases, 105 affected and 71 unaffected family members, and 79 healthy controls. By regression analysis VWF levels were strongly related to both closure times, with a non-linear progression. In a multiple stepwise regression model, age- and sex-adjusted PFA-100 ADP and VWF ristocetin cofactor activity (VWF:RCo) were independently associated with BS. Most of the variation of BS was predicted by PFA-100 ADP and VWF:RCo alone. In the subgroup of patients with subtle abnormalities of the multimeric pattern, VWF was invariably reduced and closure time prolonged in almost all of them. Neither PFA-100 ADP nor EPI closure times appeared to significantly improve the diagnostic capability of VWF antigen (VWF:Ag) measurement. Thus, in an unselected population a normal PFA-100 would be useful to exclude VWD, but whether it could replace the more specific VWF assay in patients with significant mucocutaneous bleeding symptoms remains to be investigated prospectively.

Resolvin E1 Regulates Adenosine Diphosphate Activation of Human Platelets

To investigate the ability of resolvin E1 (RvE1) to regulate adenosine diphosphate (ADP) activation of platelets via specific receptors because RvE1 reduces platelet aggregation with certain agonists, including ADP. RvE1 is an eicosapentaenoic acid-derived specialized proresolving mediator generated during the resolution of acute inflammation. RvE1 exhibits potent organ-protective actions in vivo and acts on specific cell types, including platelets. RvE1, 0.1 to 100 nmol/L, incubated with platelets gave reduced ADP-stimulated P-selectin mobilization (IC(50), approximately 1.6×10(-12) mol/L) and polymerized actin content compared with control platelets. RvE1, 1 to 100 nmol/L, did not stimulate or block intracellular Ca(2+) mobilization. By using a new P2Y(12)-β-arrestin-coupled cell system, ADP-activated P2Y(12) with an EC(50) of 5×10(-6) mol/L and RvE1 did not directly stimulate P2Y(12) or block the ADP-P2Y(12) signals. In this system, another eicosanoid, leukotriene E(4) (LTE(4)) (EC(50), 1.3×10(-11) mol/L), dose dependently activated P2Y(12). When recombinant P2Y(12)-expressing cells were transiently transfected with an RvE1 receptor, human ChemR23 (present on human platelets), with the addition of RvE1 (0.1-10.0 nmol/L), blocked ADP signals (IC(50), approximately 1.6×10(-11) mol/L) in P2Y(12)-ChemR23-expressing cells compared with mock transfections. RvE1's regulatory actions (ie, reducing ADP-stimulated P-selectin mobilization and actin polymerization) are human (h)ChemR23-dependent. Moreover, specific platelet actions of RvE1 selectively engaged with ADP-activated platelets that illuminate a new cellular mechanism and affect ω-3 eicosapentaenoic acid, which may contribute to both resolution of vascular inflammation and ADP-dependent platelet activation relevant in pathological cardiovascular events.

ACCF/AHA Clopidogrel Clinical Alert: Approaches to the FDA “Boxed Warning”

The recent US Food and Drug Administration (FDA) “boxed warning” on clopidogrel raises important questions for practitioners and patients. The warning addresses the need for pharmacogenomic testing to identify patients’ altered clopidogrel metabolism and thus their risk for a suboptimal clinical response to clopidogrel. Although there is an expanding database on genetic polymorphisms that may affect clopidogrel metabolism and thus clinical outcomes, there are no evidence-based data upon which todevelop specific recommendations on the role of genetic testing in routine care nor strategies proven to improve the safety/efficacy of specific pharmacologic approaches. To provide guidance on this issue, the American College of Cardiology Foundation (ACCF) and the American Heart Association (AHA) convened a writing committee. The ACCF and AHA adhere to a rigorous policy regarding relationships with industry and other entities (RWI) of authors and peer reviewers for clinical document development (see http://www.cardiosource.org/Science-And-Quality/Practice-Guidelines-and-Quality-Standards/Relationships-With-Industry-Policy.aspx). This policy requires that a majority of writing committee members have no relevant relationships with industry to this topic, a standard that has been achieved for this document as indicated in Appendix 1. In the spirit of full disclosure, comprehensive RWI (RWI not relevant to this document) for all authors is available online for public view. RWI …

The effect of P2Y-mediated platelet activation on the release of VEGF and endostatin from platelets

Vascular endothelial growth factor (VEGF) and endostatin are key protein modulators of angiogenesis found within platelets. The platelet activation pathways that control angiogenic protein release are incompletely elucidated. The differential release of pro-angiogenic and anti-angiogenic proteins from the platelet has been demonstrated for proteinase activated receptors (PARs). Given the ability of tumors to secrete ADP and the availability of ADP receptor antagonists clinically, we determined the influence of adenosine diphosphate (ADP) and the ADP receptors, P2Y1 and P2Y12, on platelet release of the angiogenic stimulator protein, VEGF, and the angiogenic inhibitor protein, endostatin. Minimally altered whole blood (WB) and platelet rich plasma (PRP) from healthy volunteers was stimulated with ADP alone (12.5 uM), in combination with a P2Y1 antagonist (MRS2179) or a P2Y12 antagonist (cangrelor). VEGF and endostatin protein concentrations were assessed by an ELISA assay. We report that maximally stimulating concentrations of ADP significantly increased VEGF release from platelets in both PRP and WB by 36+/−12% 36+/−12% 54+/−18% 36 ± 12% (p < 0.05) respectively as compared to control. Both P2Y1 and P2Y12 receptor antagonism inhibited this release. Conversely, endostatin levels did not change following ADP stimulation in PRP, while a 4.7% (p = 0.03) increase was observed in WB. As compared to thrombin receptor activation, ADP activation was a weaker stimulus for VEGF release. We found that activation of platelets by ADP results in an increase in soluble VEGF concentrations with minimal effects on endostatin concentrations, suggesting ADP release in the tumor microenvironment may be, on balance, proangiogenic. P2Y receptor antagonism abrogates ADP mediated proangiogenic protein release and thus may represent a potential pharmacologic strategy for regulating platelet mediated angiogenesis.

A functional genomics approach reveals novel quantitative trait loci associated with platelet signaling pathways

AbstractPlatelet response to activation varies widely between individuals but shows interindividual consistency and strong heritability. The genetic basis of this variation has not been properly explored. We therefore systematically measured the effect on function of sequence variation in 97 candidate genes in the collagen and adenosine-diphosphate (ADP) signaling pathways. Resequencing of the genes in 48 European DNA samples nearly doubled the number of known single nucleotide polymorphisms (SNPs) and informed the selection of 1327 SNPs for genotyping in 500 healthy Northern European subjects with known platelet responses to collagen-related peptide (CRP-XL) and ADP. This identified 17 novel associations with platelet function (P < .005) accounting for approximately 46% of the variation in response. Further investigations with platelets of known genotype explored the mechanisms behind some of the associations. SNPs in PEAR1 associated with increased platelet response to CRP-XL and increased PEAR1 protein expression after platelet degranulation. The minor allele of a 3′ untranslated region (UTR) SNP (rs2769668) in VAV3 was associated with higher protein expression (P = .03) and increased P-selectin exposure after ADP activation (P = .004). Furthermore the minor allele of the intronic SNP rs17786144 in ITPR1 modified Ca2+ levels after activation with ADP (P < .004). These data provide novel insights into key hubs within platelet signaling networks.

The Effect of Milrinone on Platelet Activation as Determined by TEG® Platelet Mapping™

Milrinone is a phosphodiesterase III inhibitor that increases intracellular cyclic adenosine monophosphate resulting in improved ventricular function and vasodilation. Increased intracellular levels of cyclic adenosine monophosphate also inhibit adenosine diphosphate (ADP) and arachidonic acid (AA)-induced platelet aggregation. We hypothesized that inhibition of ADP and AA-induced platelet activation by therapeutic blood concentrations of milrinone could be quantified using TEG Platelet Mapping. Blood was taken from 15 healthy adults who had not been taking antiplatelet medications. Milrinone was added to whole blood in three clinically relevant concentrations (30, 100, and 300 ng/mL). Conventional thromboelastography (TEG) and TEG Platelet Mapping were performed on whole blood without milrinone and at each of these three concentrations. Increased blood concentrations of milrinone were associated with increased inhibition of ADP and AA-induced platelet activation (P < 0.0001). Milrinone at a blood concentration of 300 ng/mL markedly impaired the platelet activation response to ADP and AA. Therapeutic blood concentrations of milrinone exhibit a significant inhibitory effect on ADP and AA-induced platelet activation as determined by TEG Platelet Mapping, without affecting the conventional kaolin-activated TEG. We suggest that TEG Platelet Mapping results be interpreted with caution in patients being treated with milrinone, and other drugs that modify platelet cyclic nucleotide concentrations.

Comparison of the effects of unfractionated heparin and the low molecular weight heparins, dalteparin and enoxaparin, on spontaneous platelet aggregation and adenosine diphosphate activity in platelets during the third trimester of pregnancy

Low-molecular-weight heparins (LMWHs) have demonstrable pharmacokinetic, pharmacodynamic and safety advantages over unfractionated heparin (UH) in routine clinical use and are now the preferred agents in routine anticoagulant therapy. However, the utility and impact of the LMWH compared with that of UH has not been studied extensively in human pregnancy, wherein the prophylaxis against venous thromboembolism is imperative. Human pregnancy is a hypercoagulable state with an increase in spontaneous platelet aggregation (SPA) in vivo. We evaluated and compared the effects of UH and the LMWHs dalteparin and enoxaparin (10 U/ml) on SPA in citrated whole blood with an ultraflow platelet counter in pregnancy and also investigated the role of adenosine diphosphate (ADP) in heparin-induced platelet aggregation in the third trimester of pregnant women (aged 28 +/- 3 years, gestational age 34 +/- 5 weeks) and in healthy, age-matched nonpregnant women. Pregnant women showed a significantly increased SPA of 37% 6 5% compared with 16% 6 3% in nonpregnant women (p < 0.01). UH exerted a significantly greater proaggregatory effect on SPA compared with that of LMWHs or saline (p < 0.0002; ANOVA). The maximum values of SPA were as follows: UH, 69% +/- 5%; dalteparin, 46% +/- 5%; and enoxaparin, 54% +/- 3%. There was no difference between SPA induced by LMWHs and saline or between enoxaparin and dalteparin. At 480 s, there was no difference in SPA induced by LMWH between pregnant and nonpregnant women, but UH substantially and specifically increased SPA in pregnant women compared with that in nonpregnant women (p < 0.01). This heparin-induced platelet activation and thrombocytopenic response was reversed by apyrase grade II (ADP scavenger) that also inhibited SPA in pregnancy to a level similar to that of nonpregnant women (p < 0.0002; ANOVA). These results indicate that the LMWHs dalteparin and enoxaparin cause significantly less platelet aggregation in whole blood in pregnancy and in the nonpregnant state when compared with UH. The proaggregatory platelet effects of UH is substantially enhanced in pregnancy, a property not shared by LMWHs. The reversal of the heparin-induced platelet activation by apyrase grade II suggests that the mechanism is, at least in part, mediated by copious ADP release from platelets or red cells by heparin but not LMWHs.

Comparison of modified Thrombelastograph and Plateletworks whole blood assays to optical platelet aggregation for monitoring reversal of clopidogrel inhibition in elective surgery patients

Clinically monitoring recovery from clopidogrel and nonsteroidal anti-inflammatory drug (NSAID) inhibition requires whole blood assays corresponding to a standard methodology such as platelet-rich plasma aggregation monitored optically (OPA). We compared OPA, using an ED 50 dose of adenosine diphosphate activation, with 2 whole blood assays, Plateletworks (PWA) and modified Thrombelastograph (TEG). Two sets of assays were performed on 43 surgery patients while on clopidogrel and off clopidogrel to determine the reversal of absolute and relative inhibition. The modified TEG had Spearman correlations with OPA for absolute (rho = .424; P = .006) and relative inhibition (rho = .742; P < .0001). PWA correlations with OPA gave absolute (rho = .28; P = .08) and relative inhibition (rho = .46; P = .004) values. Bland-Altman analysis indicated agreement of both tests with OPA, showing constant biases of about 18% and some dependency on mean magnitude error. Cohen effect size thresholds defined nonresponders as < 7.7% clopidogrel inhibition relative to baseline recovery of full platelet function. Apparent nonresponse to clopidogrel or lack of platelet recovery did not correlate with statin or NSAID therapies. These PWA and modified TEG whole blood assays could prove useful for monitoring the reversal of clopidogrel and NSAID inhibition before surgery. More important, these assays done at baseline and after beginning clopidogrel therapy could monitor the effectiveness for the individual patients with cardiovascular disease and help identify the need for alternative therapies.

Effects of cytochalasin H, a potent inhibitor of cytoskeletal reorganisation, on platelet function

Platelets contain a well-developed and dynamic cytoskeleton composed mainly of actin and actin-associated proteins. Upon platelet activation there is rapid polymerisation of actin and a marked reorganisation of the platelet cytoskeleton. Cytochalasins are agents that interfere with the polymerisation of actin, and it has recently been discovered that cytochalasin H (CyH) is particularly effective as an inhibitor of the cytoskeletal reorganisation that occurs in platelets following activation by adenosine diphosphate (ADP). Here we have used CyH to inhibit platelet cytoskeletal reorganisation and to determine its effects on various aspects of platelet function. Experiments were performed in hirudinized platelet-rich plasma (PRP) or whole blood obtained from human volunteers. PRP was treated with 10 w M CyH or vehicle, then activated by ADP. The effect of CyH on cytoskeletal reorganisation was determined by SDS-PAGE of the Triton X-100 insoluble cytoskeletons and quantitated by densitometry. Platelet aggregation and aggregate stability in PRP were measured by monitoring changes in light absorbance; aggregation was measured in whole blood via platelet counting. Shape change, P-selectin expression and changes in intracellular calcium were measured using flow cytometry. CyH prevented the normal incorporation of actin, f -actinin and actin-binding protein into the cytoskeleton that occurred following ADP activation, and incorporation of myosin was markedly reduced. Aggregation was only partially inhibited but, more dramatically, the rate of disaggregation following addition of certain agents that interfere with fibrinogen binding to glycoprotein IIb/IIIa on the surface of platelets was markedly increased. The ADP-induced shape change was also inhibited. CyH had no effect on calcium mobilisation. Curiously, expression of P-selectin was potentiated by CyH, suggesting a modulatory role of the cytoskeleton in platelet secretory activity. The results suggest that cytoskeletal reorganisation plays an important role in platelet shape change and aggregation and contributes in a major way to the stability of the aggregates that form.

Characterization of a new hereditary thrombopathy in a closed colony of Wistar rats

A new hereditary thrombopathy has been identified in a closed colony of Wistar rats. A simple and reproducible cuticle bleeding time test was developed as a rapid screening procedure for the bleeding diathesis. Affected animals exhibit markedly prolonged bleeding times and complete absence of platelet aggregation either with adenosine diphosphate (ADP) or with thrombin. Inheritance data suggest an autosomal dominant inheritance pattern with variable penetrance. Coagulation tests, platelet counts, plasma von Willebrand factor (vWF) activity, and clot retraction are within normal limits in thrombopathic animals. GPlb-dependent botrocetininduced platelet agglutination was present in washed thrombopathic rat platelets. No discernible abnormality of intraplatelet organelles or granules was seen by transmission electron microscopy of thrombopathic platelets. A qualitative morphologic assessment of intraplatelet fibrinogen in thrombopathic rat platelets showed no discernible difference as compared with control rat platelets. Thrombopathic rat platelets exhibit decreased glycoprotein IIb/Illa (GPIIb/IIIa) antigen by flow cytometric analysis and markedly decreased iodine 125-labeled fibrinogen binding to platelet GPIIb/IIIa after ADP activation. This rat colony demonstrates a unique thrombopathy, distinct from previously described animal thrombopathies, with some characteristics of variant Glanzmann's thrombasthenia. This animal model may provide further insight into the regulatory mechanisms and pathophysiology of platelet GPIIb/IIIa.