Boosting the coagulation restores haemostasis in ticagrelor-treated mice

How to undertake procedures while on antiplatelet agents: a hematologist's view

Cardiovascular diseases (CVDs) are the leading cause of mortality globally while also contributing to excess health system costs. Significant advancements have been made in the understanding and prevention of deaths from CVD. In addition to risk factor modifications, one of the key developments in this area is the appropriate prescribing of antiplatelet medications for secondary prevention of CVD. With the advent of vascular devices, there has been an increased use of potent antiplatelet agents to mitigate thrombosis risk. A well-recognized, albeit rare complication of antiplatelet drugs is the heightened risk of bleeding. This adverse effect is particularly relevant when a patient receiving these medications may require an urgent surgery. In addition, for elective surgeries, although these drugs can be withheld, there may be some situations when interruption of antiplatelet agents, even for short duration, may lead to thrombotic events. There are no robust guidelines on how to manage these clinical scenarios, although there have been some important studies published recently in this area. In this review, we provide our approach to patients on antiplatelet drugs who may require urgent surgeries or surgical interventions.

Management of Bleeding Events Associated with Antiplatelet Therapy: Evidence, Uncertainties and Pitfalls

Bleeding complications are common in patients treated with antiplatelet agents (APA), but their management relies on poor evidence. Therefore, practical guidelines and guidance documents are mainly based on expert opinion. The French Working Group on Perioperative Haemostasis provided proposals in 2018 to enhance clinical decisions regarding the management of APA-treated patients with a bleeding event. In light of these proposals, this review discusses the evidence and uncertainties of the management of patients with a bleeding event while on antiplatelet therapy. Platelet transfusion is the main option as an attempt to neutralise the effect of APA on primary haemostasis. Nevertheless, efficacy of platelet transfusion to mitigate clinical consequences of bleeding in patients treated with APA depends on the type of antiplatelet therapy, the time from the last intake, the mechanism (spontaneous versus traumatic) and site of bleeding and the criteria of efficacy (in vitro, in vivo). Specific antidotes for APA neutralisation are needed, especially for ticagrelor, but are not available yet. Despite the amount of information that platelet function tests are expected to give, little data support the clinical benefit of using such tests for the management of bleeding events in patients treated or potentially treated with APA.

Comparative In Vitro Study of Various α2-Adrenoreceptor Agonist Drugs for Ticagrelor Reversal

Ticagrelor, an antiplatelet adenosine diphosphate (ADP)-P2Y₁₂ receptor antagonist, increases the risk of bleeding. Its management is challenging because platelet transfusion is ineffective and no specific antidote is currently available. Epinephrine, a vasopressor catecholamine prescribed during shock, restores platelet functions inhibited by ticagrelor through stimulation of α_2A-adrenoreceptors. It subsequently inhibits cyclic adenosine monophosphate (cAMP) pathway and PI3K signaling. However, since epinephrine may expose a patient to deleterious hemodynamic effects, we hypothesized that other α₂-adrenoreceptor agonist drugs used in clinical practice with fewer side effects could reverse the antiplatelet effects of ticagrelor. We compared in vitro the efficacy of clonidine, dexmedetomidine, brimonidine, and norepinephrine with epinephrine to restore ADP- and PAR-1-AP-induced washed platelet aggregation inhibited by ticagrelor, as well as resulting platelet cAMP levels. In ticagrelor-free samples, none of the α₂-adrenoreceptor agonists induced aggregation by itself but all of them potentiated ADP-induced aggregation. Compared with epinephrine, norepinephrine, and brimonidine partially restored ADP- and fully restored PAR-1-AP-induced aggregation inhibited by ticagrelor while clonidine and dexmedetomidine were ineffective. Indeed, this lack of effect resulted from a lower decrease in cAMP concentration elicited by these partial α₂-adrenoreceptor agonists, clonidine, and dexmedetomidine, compared with full α₂-agonists. Our results support the development of specific full and systemic α₂-adrenoreceptor agonists for ticagrelor reversal.

Epinephrine restores platelet functions inhibited by ticagrelor: A mechanistic approach

Ticagrelor, an antagonist of the platelet adenosine diphosphate (ADP)-P2Y₁₂ receptor is recommended for patients with acute coronary syndromes. However, ticagrelor exposes to a risk of bleeding, the management of which is challenging because platelet transfusion is ineffective, and no antidote is yet available. We hypothesized that the vasopressor drug epinephrine could counter the antiplatelet effects of ticagrelor and restore platelet functions. We assessed in vitro the efficiency of epinephrine in restoring platelet aggregation inhibited by ticagrelor and investigated the underlying mechanisms. Washed platelet aggregation and secretion were measured upon stimulation by epinephrine alone or in combination with ADP, in the presence or absence of ticagrelor. Mechanistic investigations used P2Y₁ and phosphoinositide 3-kinase (PI3K) inhibitors and included vasodilator-stimulated phosphoprotein (VASP) and Akt phosphorylation assays as well as measurement of Ca²⁺ mobilisation. We found that epinephrine restored ADP-induced platelet aggregation, but not dense granule release. Epinephrine alone failed to induce aggregation whereas it fully induced VASP dephosphorylation and Akt phosphorylation regardless of the presence of ticagrelor. In the presence of ticagrelor, blockage of the P2Y₁ receptor prevented restoration of platelet aggregation by the combination of epinephrine and ADP, as well as intracellular Ca²⁺ mobilisation. In combination with ADP, epinephrine induced platelet aggregation of ticagrelor-treated platelets through inhibition of the cAMP pathway and activation of the PI3K pathway, thus enabling the P2Y₁ receptor signalling and subsequent Ca²⁺ mobilisation. This proof-of-concept study needs to be challenged in vivo for the management of bleeding in ticagrelor-treated patients.

Platelet CD40 ligand and bleeding during P2Y12 inhibitor treatment in acute coronary syndrome

Antiplatelet therapy through inhibition of the adenosine diphosphate (ADP)/P2Y12 pathway is commonly used in the treatment of acute coronary syndrome (ACS). Although efficient in preventing platelet activation and thrombus formation, it increases the risk of bleeding complications. In patients with ACS receiving platelet aggregation inhibitors, that is, P2Y12 blockers (n = 923), we investigated the relationship between plasma and platelet-associated CD40L levels and bleeding events (n = 71). Treatment with P2Y12 inhibitors in patients with ACS did not affect plasma-soluble CD40L levels, but decreased platelet CD40L surface expression (pCD40L) and platelet-released CD40L (rCD40L) levels in response to stimulation as compared to healthy controls. In vitro inhibition of the ADP pathway in healthy control platelets reduced both pCD40L and rCD40L levels. In a multivariable analysis, the reduced pCD40L level observed in ACS patients was significantly associated with the risk of bleeding occurrence (adjusted odds ratio = 0.15; 95% confidence interval = 0.034-0.67). P2Y12 inhibitor-treated (ticagrelor) mice exhibited a 2.5-fold increase in tail bleeding duration compared with controls. A significant reduction in bleeding duration was observed on CD40L+/+ but not CD40L-/- platelet infusion. In addition, CD40L blockade in P2Y12 inhibitor-treated blood samples from a healthy human reduced thrombus growth over immobilized collagen under arterial flow. In conclusion, measurement of pCD40L may offer a novel approach to assessing bleeding risk in patients with ACS who are being treated with P2Y12 inhibitors.

Successful Use of Recombinant Activated Factor VII to Reverse Ticagrelor-Induced Bleeding Risk: A Case Report

Management of ticagrelor-associated bleeding is challenging, especially in neurosurgery. Platelet transfusion is inefficient and no antidote is currently available. We report here the first case of recombinant activated factor VII (rFVIIa) use to bypass ticagrelor-induced platelet inhibition. A woman treated with ticagrelor and requiring emergent neurosurgery for an intracranial hematoma received preoperative high-dose platelet transfusion and 60 μg/kg rFVIIa. Laboratory monitoring demonstrated that platelet transfusion failed to reverse ticagrelor-induced platelet inhibition while rFVIIa improved hemostasis by shortening the thromboelastometric clotting time. Neurosurgery occurred without any bleeding event but the patient presented with a postoperative pulmonary embolism. In conclusion, rFVIIa may decrease ticagrelor-induced bleeding risk but careful assessment of the benefit-risk balance is warranted before using rFVIIa to reverse ticagrelor effects.

[Management of the bleeding risk associated with antiplatelet agents]

Like all antithrombotic drugs, antiplatelet agents expose to a risk of bleeding complications. Clinical research has extensively focused on the efficacy of these drugs to reduce ischemic events. The bleeding risk associated with them was solely considered as an inevitable and acceptable complication. When two new potent P2Y12-receptor inhibitors, prasugrel and ticagrelor, were marketed, the risk of major bleeding increased. These new agents have modified the balance between the absolute risk reduction in ischemic events and the absolute risk increase in bleeding events. This paper is an update on the bleeding risk assessment associated with antiplatelet agents. It discusses the place of platelet function monitoring, and the optimal management of bleeding complications. It addresses the challenging issue of reversal of antiplatelet therapy, focusing especially on ticagrelor, which pharmacodynamics complicate bleeding management.

Ticagrelor reversal: in vitro assessment of four haemostatic agents

AIM

Management of ticagrelor-induced bleeding is challenging as platelet transfusion is ineffective. An effective strategy is needed. This study aimed to investigate in vitro the efficacy of four haemostatic drugs (HDs), namely recombinant activated factor VII (rFVIIa), fibrinogen concentrate (Fib), tranexamic acid (TXA) and factor XIII concentrate (FXIII) to improve the haemostatic capacity in the presence of ticagrelor.

METHODS

Blood was spiked with ticagrelor then supplemented by either HD or control. Several assays were performed: ADP-induced platelet aggregation measured by impedance aggregometry, light transmission and two global assays, thrombolastography with the platelet mapping device (TEG-PM) and a platelet-dependent thrombin generation assay (TGA).

RESULTS

Ticagrelor inhibited ADP-induced platelet aggregation and decreased the clot strength maximum amplitude (MA) in TEG-PM_ADP. None of the HDs corrected these parameters. However, rFVIIa shortened the coagulation time R using TEG-PM_thrombin and the time to peak prolonged by ticagrelor in TGA. Fib increased MA_thrombin and FXIII decreased LY30. TXA had no effects.

CONCLUSIONS

Whereas none of the HDs corrected ticagrelor-induced platelet inhibition, rFVIIa shortened coagulation times, Fib increased clot firmness and FXIII decreased fibrinolysis. Consequently, they may bypass ticagrelor effects by acting on fibrin formation or fibrinolysis. Further studies are needed to confirm these data in vivo.

Effects of autologous platelet transfusion on platelet inhibition in ticagrelor-treated and clopidogrel-treated subjects

Essentials Limited data on hemostatic benefits of platelet transfusion (PT) exist. 44 healthy subjects had a single dose of ticagrelor or clopidogrel ± autologous PT post-dosing. PT did not reverse ticagrelor's antiplatelet effects and had minimal impact post clopidogrel. Post-ticagrelor, PT is unlikely to be beneficial, and the benefits post-clopidogrel are unknown.

SUMMARY

Background Antiplatelet agents increase bleeding risk. Few data on hemostatic benefits of platelet transfusion exist. Objective To assess the effect of autologous platelet transfusion on ticagrelor-mediated and clopidogrel-mediated platelet inhibition in a single-center, open-label, randomized, cross-over study (NCT01744288). Methods Forty-four healthy subjects received ticagrelor (180 mg) or clopidogrel (600 mg; two functional CYP2C19 alleles [*1 or *17] required) with or without platelet transfusion (14-day washout). Subjects received one autologous platelet apheresis unit (approximately six pooled donor platelet units) 24 h (n = 15) or 48 h (n = 13) after ticagrelor or 48 h after clopidogrel (n = 16). Platelet apheresis was conducted 72 h before transfusion. Aspirin (81 mg per day) was taken from after apheresis until 24 h before transfusion. P2Y12 reaction units (PRUs) and inhibition of platelet aggregation (IPA) induced by ADP were measured. Results Mean age and body mass index were 30 years (standard deviation [SD] 6 years) and 26.9 kg m-2 (SD 4.0 kg m-2 ), respectively; 98% of subjects were men, and 39 of 44 completed treatment. Platelet transfusion 24 h after ticagrelor had minimal effects on IPA or PRU values within 48 h after transfusion. Platelet transfusion 48 h after ticagrelor also had minimal effects on IPA or PRU values at most post-transfusion times. Platelet transfusion 48 h after clopidogrel, versus no transfusion, had a small reversing effect on IPA (24 h, 36 h, and 48 h) and PRU values (12 h, 24 h, and 36 h) after transfusion. Conclusions Autologous platelet transfusion is unlikely to be of clinical benefit in reversing the antiplatelet effects of ticagrelor. The clinical relevance of the small effects seen with clopidogrel is unknown.