Comparison of a new ELISA-based with the flow cytometric assay for vasodilator-associated stimulated phosphoprotein (VASP) phosphorylation to assess P2Y12 -inhibition after ticagrelor intake

Advanced pharmacodynamics of cangrelor in healthy volunteers: a dose-finding, open-label, pilot trial

Background

High on-treatment platelet reactivity (HTPR) remains a major problem in the acute management of ST-elevation myocardial infarction (STEMI), leading to higher rates of stent thrombosis and mortality. We aimed to investigate a novel, prehospital treatment strategy using cangrelor and tested its pharmacodynamic effects in a model using healthy volunteers.

Methods

We conducted a dose-finding, open-label, pilot trial including 12 healthy volunteers and tested three ascending bolus infusions of cangrelor (5 mg, 10 mg and 20 mg) and a bolus infusion followed by a continuous infusion via an intravenous (IV) flow regulator. Platelet function was assessed using multiple electrode aggregometry (MEA), vasodilator-stimulated phosphoprotein phosphorylation assay (VASP-P) and the platelet function analyzer. In an ex vivo experiment, epinephrine was used to counteract the antiplatelet effect of cangrelor.

Results

All cangrelor bolus infusions resulted in immediate and pronounced platelet inhibition. Bolus infusions of cangrelor 20 mg resulted in sufficient platelet inhibition assessed by MEA for 20 min in 90% of subjects. Infusion of cangrelor via the IV flow regulator resulted in sufficient platelet inhibition throughout the course of administration. Ex vivo epinephrine, in concentrations of 200 and 500 ng/mL was able to partially reverse the antiplatelet effect of cangrelor in a dose-dependent manner.

Conclusions

Weight-adapted bolus infusions followed by a continuous infusion of cangrelor via IV flow regulator result in immediate and pronounced platelet inhibition in healthy subjects. Cangrelor given as weight-adapted bolus infusion followed by a continuous infusion using an IV flow regulator may be a viable treatment approach for effective and well controllable prehospital platelet inhibition.

Trial registration

EC (Medical University of Vienna) 1835/2019 and EudraCT 2019-002792-34.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12959-022-00377-z.

Head-to-Head Comparison of Consensus-Recommended Platelet Function Tests to Assess P2Y12 Inhibition-Insights for Multi-Center Trials

The vasodilator-associated stimulated phosphoprotein (VASP) phosphorylation level is a highly specific method to assess P2Y12 receptor inhibition. Traditionally, VASP phosphorylation is analyzed by flow cytometry, which is laborious and restricted to specialized laboratories. Recently, a simple ELISA kit has been commercialized. The primary objective of this study was to compare the performance of VASP assessment by ELISA and flow cytometry in relation to functional platelet aggregation testing by Multiplate^® whole-blood aggregometry. Blood from 24 healthy volunteers was incubated with increasing concentration of a P2Y12 receptor inhibitor (AR-C 66096). Platelet function testing was carried out simultaneously by Multiplate^® aggregometry and by VASP assessment through ELISA and flow cytometry. As expected, increasing concentrations of the P2Y12 receptor inhibitor induced a proportional inhibition of platelet aggregation and P2Y12 receptor activation across the modalities. Platelet reactivity index values of both ELISA- and flow cytometry-based VASP assessment methods correlated strongly (r = 0.87, p < 0.0001) and showed minimal bias (1.05%). Correlation with Multiplate^® was slightly higher for the flow cytometry-based VASP assay (r = 0.79, p < 0.0001) than for the ELISA-based assay (r = 0.69, p < 0.0001). Intraclass correlation (ICC) was moderate for all the assays tested (ICC between 0.62 and 0.84). However, categorization into low, optimal, or high platelet reactivity based on these assays was strongly concordant (κ between 0.86 and 0.92). In conclusion, the consensus-recommended assays with their standardized cut-offs should not be used interchangeably in multi-center clinical studies but, rather, they should be standardized throughout sites.

Clopidogrel in Critically Ill Patients

Only limited data are available regarding the treatment of critically ill patients with clopidogrel. This trial investigated the effects and the drug concentrations of the cytochrome P450 (CYP450) activated prodrug clopidogrel (n = 43) and the half‐life of the similarly metabolized pantoprazole (n = 16) in critically ill patients. ADP‐induced aggregometry in whole blood classified 74% (95% confidence intervals 59–87%) of critically ill patients as poor responders (n = 43), and 65% (49–79%) responded poorly according to the vasodilator‐stimulated phosphoprotein phosphorylation (VASP‐P) assay. Although the plasma levels of clopidogrel active metabolite normally exceed the inactive prodrug ∼30‐fold, the parent drug levels even exceeded those of the metabolite 2‐fold in critically ill patients. The half‐life of pantoprazole was several‐fold longer in these patients compared with reference populations. The inverse ratio of prodrug/active metabolite indicates insufficient metabolization of clopidogrel, which is independently confirmed by the ∼5‐fold increase in half‐life of pantoprazole. Thus, high‐risk patients may benefit from treatment with alternative platelet inhibitors.

Reversal strategy in antagonizing the P2Y12 -inhibitor ticagrelor

BACKGROUND

Patients on antiplatelet therapy have a higher incidence of bleeding complications. Reversal of antiplatelet drug effects is an important issue at trauma or emergency departments. For old and conventional anticoagulants, reversal strategies are established. While the effects of ticagrelor are reversible, developing a method to restore platelet function in patients is of importance due to its longer half-life (approximately 8 h), compared with other P2Y12 -inhibitors.

MATERIALS AND METHODS

We report an ex vivo model to reverse the effects of the novel and highly effective P2Y12 -inhibitor ticagrelor in 20 healthy volunteers. To normalize platelet reactivity, we added increasing amounts of autologous platelet-rich plasma (PRP) to whole blood which was obtained 3 h after the intake of 180 mg of ticagrelor. Platelet aggregation was assessed by whole blood multiple electrode aggregometry (MEA), which is based on impedance aggregometry.

RESULTS

The basal ADP-induced platelet aggregation averaged 71 ± 16 U (Units). Ticagrelor decreased ADP-induced platelet aggregation to 16 ± 8 U. A clear dose-response was obtained after spiking whole blood with increasing amounts of PRP. It is estimated that ≥2 units of apheresis platelet concentrates will be necessary to completely restore baseline platelet aggregation in the majority of patients after ticagrelor.

CONCLUSIONS

Platelets dose dependently improve ex vivo platelet aggregation of subjects after a loading dose of 180 mg of ticagrelor, making transfusion of platelet concentrates potentially useful in bleeding patients and those who need to undergo emergency surgery.

'VASPFix' for measurement of VASP phosphorylation in platelets and for monitoring effects of P2Y12 antagonists

Vasodilator-stimulated phosphoprotein (VASP) is phosphorylated and dephosphorylated consequent to increases and decreases in cyclic nucleotide levels. Monitoring changes in VASP phosphorylation is an established method for indirect measurement of cyclic nucleotides. Here we describe the use of an innovative cocktail, VASPFix, which allows sensitive and reproducible measurement of phosphorylated VASP (VASP-P) in a simple, single-step procedure using cytometric bead technology. Frozen VASPFix-treated samples are stable for at least six months prior to analysis. We successfully used VASPFix to measure VASP-P in platelets in both platelet-rich plasma and blood in response to compounds that increase (dibutyryl cAMP, adenosine, iloprost, PGE1) and decrease (ADP, PGE1) cAMP, and to determine the effects of certain receptor antagonists on the results obtained. The change in VASP-P brought about by adding ADP to PGE1-stimulated platelets is a combination of the effect of ADP at the P2Y12 receptor and of PGE1 at both IP and EP3 receptors. For iloprost-stimulated platelets EP3 receptors are not involved. A procedure in which iloprost, ADP and VASPFix were used to determine effectiveness of clopidogrel and prasugrel in patients was compared with an established commercial procedure that uses PGE1 and ADP; the latter produced higher platelet reactivity values that were the result of PGE1 interacting with platelet EP3 receptors. We conclude that VASPFix can be used both as a research tool and for clinical investigations and provides better specificity for P2Y12 receptor inhibition. The latter confers a distinct advantage over existing methods used to monitor effects of P2Y12 antagonists on platelet function.