Antibody-Based Ticagrelor Reversal Agent in Healthy Volunteers.

BACKGROUND: Ticagrelor is an oral P2Y12 inhibitor that is used with aspirin to reduce the risk of ischemic events among patients with acute coronary syndromes or previous myocardial infarction. Spontaneous major bleeding and bleeding associated with urgent invasive procedures are concerns with ticagrelor, as with other antiplatelet drugs. The antiplatelet effects of ticagrelor cannot be reversed with platelet transfusion. A rapid-acting reversal agent would be useful. METHODS: In this randomized, double-blind, placebo-controlled, phase 1 trial, we evaluated intravenous PB2452, a monoclonal antibody fragment that binds ticagrelor with high affinity, as a ticagrelor reversal agent. We assessed platelet function in healthy volunteers before and after 48 hours of ticagrelor pretreatment and again after the administration of PB2452 or placebo. Platelet function was assessed with the use of light transmission aggregometry, a point-of-care P2Y12 platelet-reactivity test, and a vasodilator-stimulated phosphoprotein assay. RESULTS: Of the 64 volunteers who underwent randomization, 48 were assigned to receive PB2452 and 16 to receive placebo. After 48 hours of ticagrelor pretreatment, platelet aggregation was suppressed by approximately 80%. PB2452 administered as an initial intravenous bolus followed by a prolonged infusion (8, 12, or 16 hours) was associated with a significantly greater increase in platelet function than placebo, as measured by multiple assays. Ticagrelor reversal occurred within 5 minutes after the initiation of PB2452 and was sustained for more than 20 hours (P\u3c0.001 after Bonferroni adjustment across all time points for all assays). There was no evidence of a rebound in platelet activity after drug cessation. Adverse events related to the trial drug were limited mainly to issues involving the infusion site. CONCLUSIONS: In healthy volunteers, the administration of PB2452, a specific reversal agent for ticagrelor, provided immediate and sustained reversal of the antiplatelet effects of ticagrelor, as measured by multiple assays. (Funded by PhaseBio Pharmaceuticals; ClinicalTrials.gov number, NCT03492385.)

Remote assessment of platelet function in patients with acute stroke or transient ischaemic attack

Background: Antiplatelets reduce recurrence after cerebral ischaemia. The international TARDIS trial assessed the safety and efficacy of intensive (combined aspirin, dipyridamole and clopidogrel) versus guideline (aspirin and dipyridamole, or clopidogrel alone) antiplatelet agents given for one month in patients with acute stroke or TIA. The aim of this substudy was to assess the effect of antiplatelet agents taken at baseline on platelet function reactivity and activation. Methods: In a substudy, platelet function, assessed by remotely measured surface expression of P-selectin (CD62P, Platelet Solutions Ltd), was assessed at baseline in patients who were and were not taking antiplatelet agents at the time of randomisation. Data are Median Fluorescence values (MF). Results: The aspirin P-selectin test demonstrated that platelet expression was lower in 485 patients taking aspirin than in 171 patients taking no aspirin: mean 209 (SD 188) vs. 552 (431), difference 343 (95% confidence intervals, CI 295.3, 390.7) (2p<0.001). Aspirin did not suppress P-selectin levels below 500 units in 22 (4.5%) patients. The clopidogrel P-selectin test showed that platelet reactivity was lower in 96 patients taking clopidogrel than in 586 patients taking no clopidogrel: 653 (297) vs. 969 (315), difference 316.1 (95% CI 248.6, 383.6) (2p<0.001). However, clopidogrel did not suppress P selectin level below 860 units in 24 (24.7%) patients. Conclusions: Aspirin and clopidogrel each suppress stimulated platelet P-selectin although one quarter of patients on clopidogrel have high on-treatment platelet reactivity. Platelet function testing, assessed as platelet P-selectin expression, may be performed remotely in the context of a large multicentre trial

Platelet Biochemistry and Morphology after Cryopreservation

Platelet cryopreservation has been investigated for several decades as an alternative to room temperature storage of platelet concentrates. The use of dimethylsulfoxide as a cryoprotectant has improved platelet storage and cryopreserved concentrates can be kept at −80 °C for two years. Cryopreserved platelets can serve as emergency backup to support stock crises or to disburden difficult logistic areas like rural or military regions. Cryopreservation significantly influences platelet morphology, decreases platelet activation and severely abrogates platelet aggregation. Recent data indicate that cryopreserved platelets have a procoagulant phenotype because thrombin and fibrin formation kicks in earlier compared to room temperature stored platelets. This happens both in static and hydrodynamic conditions. In a clinical setting, low 1-h post transfusion recoveries of cryopreserved platelets represent fast clearance from circulation which may be explained by changes to the platelet GPIbα receptor. Cryopreservation splits the concentrate in two platelet subpopulations depending on GPIbα expression levels. Further research is needed to unravel its physiological importance. Proving clinical efficacy of cryopreserved platelets is difficult because of the heterogeneity of indications and the ambiguity of outcome measures. The procoagulant character of cryopreserved platelets has increased interest for use in trauma stressing the need for double-blinded randomized clinical trials in actively bleeding patients

Effects of High Flavanol Dark Chocolate on Cardiovascular Function and Platelet Aggregation.

Regular consumption of chocolate and cocoa products has been linked to reduced cardiovascular mortality. This study compared the effects of high flavanol dark chocolate (HFDC; 1064mg flavanols/day for 6 weeks) and low flavanol dark chocolate (LFDC; 88mg flavanols/day for 6 weeks) on blood pressure, heart rate, vascular function and platelet aggregation in men with pre-hypertension or mild hypertension. Vascular function was assessed by pulse wave analysis using radial artery applanation tonometry in combination with inhaled salbutamol (0.4 mg) to assess changes due to endothelium-dependent vasodilatation. HFDC did not significantly reduce blood pressure compared to baseline or LFDC. Heart rate was increased by LFDC compared to baseline, but not by HFDC. Vascular responses to salbutamol tended to be greater after HFDC. Platelet aggregation induced by collagen or the thromboxane analogue U46619 was unchanged after LFDC or HFDC, whereas both chocolates reduced responses to ADP and the thrombin receptor activator peptide, SFLLRNamide (TRAP6), relative to baseline. Pre-incubation of platelets with theobromine also attenuated platelet aggregation induced by ADP or TRAP6. We conclude that consumption of HFDC confers modest improvements in cardiovascular function. Platelet aggregation is modulated by a flavanol-independent mechanism that is likely due to theobromine.This study was supported by a grant (to R. Corder) from Barry Callebaut Belgium N

BMQ

BMQ: Boston Medical Quarterly was published from 1950-1966 by the Boston University School of Medicine and the Massachusetts Memorial Hospitals

Myricetin, the main flavonoid in Syzygium cumini leaf, is a novel inhibitor of platelet thiol isomerases PDI and ERp5

Background: Flavonoids have been characterized as a prominent class of compounds to treat thrombotic diseases through the inhibition of thiol isomerases. Syzygium cumini is a flavonoid-rich medicinal plant that contains myricetin and gallic acid. Little is known about the potential anti-platelet properties of S. cumini and its constituent flavonoids. Objective To evaluate the anti-platelet effects and mechanism of action of a polyphenol-rich extract (PESc) from S. cumini leaf and its most prevalent polyphenols, myricetin and gallic acid. Methods PESc, myricetin and gallic acid were incubated with platelet-rich plasma and washed platelets to assess platelet aggregation and activation. In vitro platelet adhesion and thrombus formation as well as in vivo bleeding time were performed. Finally, myricetin was incubated with recombinant thiol isomerases to assess its potential to bind and inhibit these, whilst molecular docking studies predicted possible binding sites. Results: PESc decreased platelet activation and aggregation induced by different agonists. Myricetin exerted potent anti-platelet effects, whereas gallic acid did not. Myricetin reduced the ability of platelets to spread on collagen, form thrombi in vitro without affecting haemostasis in vivo. Fluorescence quenching studies suggested myricetin binds to different thiol isomerases with similar affinity, despite inhibiting only protein disulphide isomerase (PDI) and ERp5 reductase activities (IC50~3.5 μM). Finally, molecular docking studies suggested myricetin formed non-covalent bonds with PDI and ERp5. Conclusions: PESc and its most abundant flavonoid myricetin strongly inhibit platelet function. Additionally, myricetin is a novel inhibitor of ERp5 and PDI, unveiling a new therapeutic perspective for the treatment of thrombotic disorders

High Glucose, But Not Testosterone, Increases Platelet Aggregation Mediated by Endothelial Cells

Endothelial cells inhibit platelet aggregation by releasing thromboregulators, such as prostacyclin and nitric oxide. Male subject is a traditional risk factor for cardiovascular diseases. Platelet hyperreactivity has been frequently found in patient with diabetes mellitus. To examine whether testosterone and high glucose modify platelet aggregation through endothelial cells, we did an in vitro study using endothelial cells culture from human umbilical vein (HUVEC). Treatments were performed in HUVEC sub culture as either normoglucose (5.6 mM) or high glucose (22.4 mM) medium, with or without testosterone (0, 1, 10, 100 nM), for 24 hours. HUVEC were trypsinized, resuspended, and then incubated with platelet rich plasma from healthy male donors with ratio 1:104 for 3 minutes. Platelet aggregation measured by turbidimetry methode. This study showed that testosterone did not significantly influence platelet aggregation through endothelial cells in normoglucose (p = 0.144) or high glucose (p = 0.916) medium. There was no main effect of testosterone (p = 0.73) as well as no interaction between testosterone and glucose (p = 0.69), but there was a main effect of glucose (p = 0.004), to platelet aggregation through endothelial cells. In conclusion, high glucose, but not testosterone, inhibits platelet aggregation mediated by endothelial cells

Apixaban Enhances Endogenous Fibrinolysis in Patients with Atrial Fibrillation

© The Author(s) 2019. Published by Oxford University Press on behalf of the European Society of Cardiology.AIMS: Approximately 20% of ischaemic stroke patients exhibit spontaneous arterial recanalization, attributable to endogenous fibrinolysis, which strongly relates to improved functional outcome. The impact of oral anticoagulants on endogenous fibrinolysis is unknown. Our aim was to test the hypothesis that apixaban enhances endogenous fibrinolysis in non-valvular atrial fibrillation (NVAF). METHODS AND RESULTS: In a prospective cross-sectional analysis, we compared endogenous fibrinolysis in NVAF patients (n = 180) taking aspirin, warfarin, or apixaban. In a prospective longitudinal study, patients were tested before and after apixaban (n = 80). Endogenous fibrinolysis was assessed using the Global Thrombosis Test (GTT) and thromboelastography (TEG). Endogenous fibrinolysis [measured by GTT lysis time (LT)] was shorter on apixaban compared with warfarin or aspirin [median 1850 (IQR 1591-2300) vs. 2758 (2014-3502) vs. 2135 (1752-2463) s, P < 0.0001]. Among TEG indices, a small but significant difference in clot lysis time (CLT) was observed [apixaban 60.0 (45.0-61.0) vs. warfarin 61.0 (57.0-62.0) vs. aspirin 61.0 (59.0-61.0) min, P = 0.036]. Apixaban improved endogenous fibrinolysis measured using the GTT [LT pre-treatment 2204 (1779-2738) vs. on-treatment 1882 (1607-2374) s, P = 0.0003], but not by using TEG. Change in LT (ΔLT) with apixaban correlated with baseline LT (r = 0.77, P < 0.0001). There was weak correlation between ΔLT and ΔCLT in response to apixaban (r = 0.28, P = 0.02) and between on-apixaban LT and CLT (r = 0.25, P = 0.022). CONCLUSION: Apixaban enhances endogenous fibrinolysis, with maximal effect in those with impaired fibrinolysis pre-treatment. Apixaban-treated patients exhibit more favourable fibrinolysis profiles than those taking warfarin or aspirin. Whether apixaban may confer additional thrombotic risk reduction in NVAF patients with impaired fibrinolysis, compared to warfarin, merits further study.Peer reviewedFinal Accepted Versio