Effects of vorapaxar on clot characteristics, coagulation, inflammation, and platelet and endothelial function in patients treated with mono- and dual-antiplatelet therapy

Suppression of Heart Failure With PAR1 Pepducin Technology in a Pressure Overload Model in Mice

BACKGROUND

PAR1 (protease-activated receptor-1) contributes to acute thrombosis, but it is not clear whether the receptor is involved in deleterious inflammatory and profibrotic processes in heart failure. Here, we employ the pepducin technology to determine the effects of targeting PAR1 in a mouse heart failure with reduced ejection fraction model.

METHODS

After undergoing transverse aortic constriction pressure overload or sham surgery, C57BL/6J mice were randomized to daily sc PZ-128 pepducin or vehicle, and cardiac function, inflammation, fibrosis, and molecular analyses conducted at 7 weeks RESULTS: After 7 weeks of transverse aortic constriction, vehicle mice had marked increases in macrophage/monocyte infiltration and fibrosis of the left ventricle as compared with Sham mice. PZ-128 treatment significantly suppressed the inflammatory cell infiltration and cardiac fibrosis. Despite no effect on myocyte cell hypertrophy, PZ-128 afforded a significant reduction in overall left ventricle weight and completely protected against the transverse aortic constriction-induced impairments in left ventricle ejection fraction. PZ-128 significantly suppressed transverse aortic constriction-induced increases in an array of genes involved in myocardial stress, fibrosis, and inflammation.

CONCLUSIONS

The PZ-128 pepducin is highly effective in protecting against cardiac inflammation, fibrosis, and loss of left ventricle function in a mouse model.

Protease-activated receptors and glycoprotein VI cooperatively drive the platelet component in thromboelastography

BACKGROUND

Thromboelastography (TEG) is used for real-time determination of hemostatic status in patients with acute risk of bleeding. Thrombin is thought to drive clotting in TEG through generation of polymerized fibrin and activation of platelets through protease-activated receptors (PARs). However, the specific role of platelet agonist receptors and signaling in TEG has not been reported.

OBJECTIVES

Here, we investigated the specific receptors and signaling pathways required for platelet function in TEG using genetic and pharmacologic inhibition of platelet proteins in mouse and human blood samples.

METHODS

Clotting parameters (R time, α-angle [α], and maximum amplitude [MA]), were determined in recalcified, kaolin-triggered citrated blood samples using a TEG 5000 analyzer.

RESULTS

We confirmed the requirement of platelets, platelet contraction, and αIIbβ3 integrin function for normal α and MA. Loss of the integrin adaptor Talin1 in megakaryocytes/platelets (Talin1mKO) also reduced α and MA, but only minimal defects were observed in samples from mice lacking Rap1 GTPase signaling. PAR4mKO samples showed impaired α but normal MA. However, impaired TEG traces similar to those in platelet-depleted samples were observed with samples from PAR4mKO mice depleted of glycoprotein VI on platelets or with addition of a Syk inhibitor. We reproduced these results in human blood with combined inhibition of PAR1, PAR4, and Syk.

CONCLUSION

Our results demonstrate that standard TEG is not sensitive to platelet signaling pathways critical for integrin inside-out activation and platelet hemostatic function. Furthermore, we provide the first evidence that PARs and glycoprotein VI play redundant roles in platelet-mediated clot contraction in TEG.

Species Differences in Platelet Protease-Activated Receptors

Protease-activated receptors (PARs) are a class of integral membrane proteins that are cleaved by a variety of proteases, most notably thrombin, to reveal a tethered ligand and promote activation. PARs are critical mediators of platelet function in hemostasis and thrombosis, and therefore are attractive targets for anti-platelet therapies. Animal models studying platelet PAR physiology have relied heavily on genetically modified mouse strains, which have provided ample insight but have some inherent limitations. The current review aims to summarize the notable PAR expression and functional differences between the mouse and human, in addition to highlighting some recently developed tools to further study human physiology in mouse models.

Efficacy of medical treatment and balloon angioplasty for severe intracranial atherosclerosis: a high-resolution MR vessel wall imaging

OBJECTIVES

To investigate the efficacy of medical treatment and balloon angioplasty for intracranial atherosclerosis using high-resolution MR vessel wall imaging (HR-MRI).

METHODS

In this prospective study, patients with symptomatic severe stenosis from January 2018 to August 2021 were treated with medical treatment or balloon angioplasty. The patients underwent HR-MRI at baseline and at 3, 6, and 12 months. Plaque characteristics at follow-up were compared with those at baseline using paired sample T-test or Wilcoxon rank sum test. The difference in the recurrence of ischemic events between two groups was compared.

RESULTS

A total of 37 patients (26 males; mean age = 60.5 ± 11.6 years) were evaluated. Of 68 plaques, 42 (61.8%) were treated with medication only. At 12 months of medical treatment, maximum plaque length (p = 0.004), maximum wall thickness (p = 0.036), and plaque enhancement (p = 0.001) were significantly reduced than baseline. At 3 months after balloon angioplasty, luminal stenosis (p = 0.048) was significantly reduced compared to baseline. At 6 months after balloon angioplasty, maximum plaque length (p = 0.011), maximum wall thickness (p = 0.003), and luminal stenosis (p = 0.001) were significantly reduced than baseline. No difference was found in the recurrence of ischemic events between two groups (p = 0.458).

CONCLUSION

Intracranial atherosclerotic plaque shrank and tended to be stable at 12 months of medical treatment. Plaque burden was significantly reduced 6 months after balloon angioplasty. This may provide evidence for the application and selection of treatment strategies for intracranial atherosclerotic disease.

KEY POINTS

• Plaque burden and plaque enhancement were significantly reduced at 12 months of medical treatment compared to baseline. • Plaque burden was significantly reduced at 6 months after balloon angioplasty compared with baseline. • No significant difference in the recurrence rate of ischemic stroke between patients treated with medication and balloon angioplasty.

Clinical pharmacology of antiplatelet drugs

INTRODUCTION

Platelets play a key role in arterial thrombosis and antiplatelet therapy is pivotal in the treatment of cardiovascular disease. Current antiplatelet drugs target different pathways of platelet activation and show specific pharmacodynamic and pharmacokinetic characteristics, implicating clinically relevant drug-drug interactions.

AREAS COVERED

This article reviews the role of platelets in hemostasis and cardiovascular thrombosis, and discusses the key pharmacodynamics, drug-drug interactions and reversal strategies of clinically used antiplatelet drugs.

EXPERT OPINION

Antiplatelet therapies target distinct pathways of platelet activation: thromboxane A₂ synthesis, adenosine diphosphate-mediated signaling, integrin α_IIbβ₃ (GPIIb/IIIa), thrombin-mediated platelet activation via the PAR1 receptor and phosphodiesterases. Key clinical drug-drug interactions of antiplatelet agents involve acetylsalicylic acid - ibuprofen, clopidogrel - omeprazole, and morphine - oral P2Y₁₂ inhibitors, all of which lead to an attenuated antiplatelet effect. Platelet function and genetic testing and the use of scores (ARC-HBR, PRECISE-DAPT, ESC ischemic risk definition) may contribute to a more tailored antiplatelet therapy. High on-treatment platelet reactivity presents a key problem in the acute management of ST-elevation myocardial infarction (STEMI). A treatment strategy involving early initiation of an intravenous antiplatelet agent may be able to bridge the gap of insufficient platelet inhibition in high ischemic risk patients with STEMI.

Thromboprophylaxis with argatroban in critically ill patients with sepsis: a review

During sepsis, an initial prothrombotic shift takes place, in which coagulatory acute-phase proteins are increased, while anticoagulatory factors and platelet count decrease. Further on, the fibrinolytic system becomes impaired, which contributes to disease severity. At a later stage in sepsis, coagulation factors may become depleted, and sepsis patients may shift into a hypo-coagulable state with an increased bleeding risk. During the pro-coagulatory shift, critically ill patients have an increased thrombosis risk that ranges from developing micro-thromboses that impair organ function to life-threatening thromboembolic events. Here, thrombin plays a key role in coagulation as well as in inflammation. For thromboprophylaxis, low molecular weight heparins (LMWH) and unfractionated heparins (UFHs) are recommended. Nevertheless, there are conditions such as heparin resistance or heparin-induced thrombocytopenia (HIT), wherein heparin becomes ineffective or even puts the patient at an increased prothrombotic risk. In these cases, argatroban, a direct thrombin inhibitor (DTI), might be a potential alternative anticoagulatory strategy. Yet, caution is advised with regard to dosing of argatroban especially in sepsis. Therefore, the starting dose of argatroban is recommended to be low and should be titrated to the targeted anticoagulation level and be closely monitored in the further course of treatment. The authors of this review recommend using DTIs such as argatroban as an alternative anticoagulant in critically ill patients suffering from sepsis or COVID-19 with suspected or confirmed HIT, HIT-like conditions, impaired fibrinolysis, in patients on extracorporeal circuits and patients with heparin resistance, when closely monitored.

Which proteinase-activated receptor-1 antagonist is better?: Evaluation of vorapaxar and parmodulin-2 effects on human left internal mammary artery endothelial function

OBJECTIVE

Endothelial dysfunction occurs as an early event in cardiovascular disease. Previously, vorapaxar, a proteinase-activated receptor-1 antagonist, was shown to cause endothelial damage in a cell culture study. Therefore, our study aimed to compare the effects of vorapaxar and parmodulin-2, proteinase-activated receptor-1 biased agonist, on human left internal mammary artery endothelial function in vitro.

METHOD

Isolated arteries were hung in the organ baths. Acetylcholine responses (10^-11-10^-6 M) were obtained in endothelium-intact tissues the following incubation with vorapaxar/parmodulin-2 (10^-6 M) to determine the effects of these molecules on the endothelium-dependent relaxation. Subsequently, endothelium-dependent relaxation responses of tissues were investigated in the presence of L-NAME (10^-4 M), L-arginine (10^-5 M), indomethacin (10^-5 M), and charybdotoxin-apamin (10^-7 M) in addition to vorapaxar/parmodulin-2 incubation. Besides, the effect of these molecules on endothelium-independent relaxation response was evaluated with sodium nitroprusside (10^-11-10^-6 M). Finally, the sections of human arteries were imaged using a transmission electron microscope, and the integrity of the endothelial layer was evaluated.

RESULTS

We found that vorapaxar caused significant endothelial dysfunction by disrupting nitric oxide and endothelium-derived hyperpolarizing factor-dependent relaxation mechanisms. Parmodulin-2 did not cause endothelial damage. Neither vorapaxar nor parmodulin-2 disrupted endothelium-independent relaxation responses. The effect of vorapaxar on the endothelial layer was supported by the transmission electron microscope images.

CONCLUSION

Parmodulin-2 may be a better option than vorapaxar in treating cardiovascular diseases since it can inhibit PAR-1 without caused endothelial dysfunction.

Improving Outcomes in Cardiovascular Diseases: A Review on Vorapaxar

Antiplatelet agents are the standard of practice in the management of atherosclerosis and acute coronary syndrome (ACS). In contrast to the available antiplatelet agents, vorapaxar represents a novel mechanism of action. It is an antagonist of the platelet protease-activated receptor-1 (PAR-1) and inhibits thrombin-induced and thrombin receptor agonist peptide (TRAP)- induced platelet aggregation. The TRA2○P-TIMI 50 trial led to the approval of vorapaxar by the Food and Drug Administration and European Medicines Agency for the reduction of thrombotic cardiovascular events in patients with a history of myocardial infarction (MI) or peripheral arterial disease. TRA2○P-TIMI 50 trial showed that the use of vorapaxar (2.5 mg once/daily) in addition to standard dual antiplatelet therapy (DAPT) with aspirin and a P2Y12 receptor inhibitor, was effective in the secondary prevention of recurrent thrombotic events among patients with previous atherothrombosis, particularly in patients with prior MI; at the expense of an increase in major bleeding. Another recently published VORA-PRATIC (Vorapaxar in Patients with Prior Myocardial Infarction Treated with prasugrel and ticagrelor) study showed that among post-MI patients treated with potent P2Y12 inhibitors (prasugrel or ticagrelor), vorapaxar reduced platelet-driven global thrombogenicity, an effect that persisted, albeit attenuated, in the absence of aspirin. The current review summarizes an up to date literature on pharmacokinetics, pharmacodynamics, and clinical efficacy of vorapaxar and proposes future directions of research.

Lipid Receptor GPR31 (G-Protein-Coupled Receptor 31) Regulates Platelet Reactivity and Thrombosis Without Affecting Hemostasis

OBJECTIVE

12-LOX (12-lipoxygenase) produces a number of bioactive lipids including 12(S)-HETE that are involved in inflammation and platelet reactivity. The GPR31 (G-protein-coupled receptor 31) is the proposed receptor of 12(S)-HETE; however, it is not known whether the 12(S)-HETE-GPR31 signaling axis serves to enhance or inhibit platelet activity. Approach and Results: Using pepducin technology and biochemical approaches, we provide evidence that 12(S)-HETE-GPR31 signals through Gi to enhance PAR (protease-activated receptor)-4-mediated platelet activation and arterial thrombosis using both human platelets and mouse carotid artery injury models. 12(S)-HETE suppressed AC (adenylyl cyclase) activity through GPR31 and resulted in Rap1 (Ras-related protein 1) and p38 activation and low but detectable calcium flux but did not induce platelet aggregation. A GPR31 third intracellular (i3) loop-derived pepducin, GPR310 (G-protein-coupled receptor 310), significantly inhibited platelet aggregation in response to thrombin, collagen, and PAR4 agonist, AYPGKF, in human and mouse platelets but relative sparing of PAR1 agonist SFLLRN in human platelets. GPR310 treatment gave a highly significant 80% protection (P=0.0018) against ferric chloride-induced carotid artery injury in mice by extending occlusion time, without any effect on tail bleeding. PAR4-mediated dense granule secretion and calcium flux were both attenuated by GPR310. Consistent with these results, GPR310 inhibited 12(S)-HETE-mediated and PAR4-mediated Rap1-GTP and RASA3 translocation to the plasma membrane and attenuated PAR4-Akt and ERK activation. GPR310 caused a right shift in thrombin-mediated human platelet aggregation, comparable to the effects of inhibition of the Gi-coupled P2Y12 receptor. Co-immunoprecipitation studies revealed that GPR31 and PAR4 form a heterodimeric complex in recombinant systems.

CONCLUSIONS

The 12-LOX product 12(S)-HETE stimulates GPR31-Gi-signaling pathways, which enhance thrombin-PAR4 platelet activation and arterial thrombosis in human platelets and mouse models. Suppression of this bioactive lipid pathway, as exemplified by a GPR31 pepducin antagonist, may provide beneficial protective effects against platelet aggregation and arterial thrombosis with minimal effect on hemostasis.

PAR1 (Protease-Activated Receptor 1) Pepducin Therapy Targeting Myocardial Necrosis in Coronary Artery Disease and Acute Coronary Syndrome Patients Undergoing Cardiac Catheterization: A Randomized, Placebo-Controlled, Phase 2 Study

OBJECTIVE

Arterial thrombosis leading to ischemic injury worsens the prognosis of many patients with cardiovascular disease. PZ-128 is a first-in-class pepducin that reversibly inhibits PAR1 (protease-activated receptor 1) on platelets and other vascular cells by targeting the intracellular surface of the receptor. The TRIP-PCI (Thrombin Receptor Inhibitory Pepducin in Percutaneous Coronary Intervention) trial was conducted to assess the safety and efficacy of PZ-128 in patients undergoing cardiac catheterization with intent to perform percutaneous coronary intervention. Approach and Results: In this randomized, double-blind, placebo-controlled, phase 2 trial, 100 patients were randomly assigned (2:1) to receive PZ-128 (0.3 or 0.5 mg/kg), or placebo in a 2-hour infusion initiated just before the start of cardiac catheterization, on top of standard oral antiplatelet therapy. Rates of the primary end point of bleeding were not different between the combined PZ-128 doses (1.6%, 1/62) and placebo group (0%, 0/35). The secondary end points of major adverse coronary events at 30 and 90 days did not significantly differ but were numerically lower in the PZ-128 groups (0% and 2% in the PZ-128 groups, 6% and 6% with placebo, p=0.13, p=0.29, respectively). In the subgroup of patients with elevated baseline cardiac troponin I, the exploratory end point of 30-day major adverse coronary events + myocardial injury showed 83% events in the placebo group versus 31% events in the combined PZ-128 drug groups, an adjusted relative risk of 0.14 (95% CI, 0.02-0.75); P=0.02.

CONCLUSIONS

In this first-in-patient experience, PZ-128 added to standard antiplatelet therapy appeared to be safe, well tolerated, and potentially reduced periprocedural myonecrosis, thus providing the basis for further clinical trials. Registration: URL: https://www.clinicaltrials.gov. Unique identifier: NCT02561000.

Vorapaxar in the treatment of cardiovascular diseases

Vorapaxar specifically and effectively inhibits protease activated receptor-1 and may reduce thrombin-mediated ischemic events without interfering primary hemostasis. In the TRA-2P-TIMI 50 trial, vorapaxar reduced the risk of primary ischemic outcome but with increased bleeding risk. In the post hoc analysis, in patients with a history of myocardial infarction, peripheral artery disease, the net clinical outcome favored vorapaxar therapy with 10% reduction in cardiovascular death, myocardial infarction, stroke, urgent coronary revascularization and moderate or severe bleeding. Based on these favorable results, vorapaxar was approved for the reduction of thrombotic cardiovascular events in patients with prior myocardial infarction or with peripheral artery disease on top of standard antiplatelet therapy. A careful patient selection is needed to balance efficacy versus safety.

Platelet activation and prothrombotic mediators at the nexus of inflammation and atherosclerosis: Potential role of antiplatelet agents

Platelets are central to inflammation-related manifestations of cardiovascular diseases (CVD) such as atherosclerosis. Platelet-activating factor (PAF), thrombin, thromboxane A₂ (TxA₂), and adenosine diphosphate (ADP) are some of the key agonists of platelet activation that are at the intersection between a plethora of inflammatory pathways that modulate pro-inflammatory and coagulation processes. The aim of this article is to review the role of platelets and the relationship between their structure, function, and the interactions of their constituents in systemic inflammation and atherosclerosis. Antiplatelet therapies are discussed with a view to primary prevention of CVD by the clinical reduction of platelet reactivity and inflammation. Current antiplatelet therapies are effective in reducing cardiovascular risk but increase bleeding risk. Novel therapeutic antiplatelet approaches beyond current pharmacological modalities that do not increase the risk of bleeding require further investigation. There is potential for specifically designed nutraceuticals that may become safer alternatives to pharmacological antiplatelet agents for the primary prevention of CVD but there is serious concern over their efficacy and regulation, which requires considerably more research.

Using PAR4 Inhibition as an Anti-Thrombotic Approach: Why, How, and When?

Protease-activated receptors (PARs) are a family of four GPCRs with a variety of cellular functions, yet the only advanced clinical endeavours to target these receptors for therapeutic gain to date relates to the impairment of platelet function for anti-thrombotic therapy. The only approved PAR antagonist is the PAR1 inhibitor, vorapaxar—the sole anti-platelet drug against a new target approved in the past 20 years. However, there are two PARs on human platelets, PAR1 and PAR4, and more recent efforts have focused on the development of the first PAR4 antagonists, with first-in-class agents recently beginning clinical trial. Here, we review the rationale for this approach, outline the various modes of PAR4 inhibition, and speculate on the specific therapeutic potential of targeting PAR4 for the prevention of thrombotic conditions.