Tubulovascular protection from protease-activated receptor-1 depletion during AKI-to-CKD transition.

BACKGROUND: Thromboembolic events are prevalent in chronic kidney disease (CKD) patients due to increased thrombin generation leading to a hypercoagulable state. We previously demonstrated that inhibition of protease-activated receptor-1 (PAR-1) by vorapaxar reduces kidney fibrosis. METHODS: We used an animal model of unilateral ischemia-reperfusion injury-induced CKD to explore the tubulovascular crosstalk mechanisms of PAR-1 in acute kidney injury (AKI)-to-CKD transition. RESULTS: During the early phase of AKI, PAR-1-deficient mice exhibited reduced kidney inflammation, vascular injury, and preserved endothelial integrity and capillary permeability. During the transition phase to CKD, PAR-1 deficiency preserved kidney function and diminished tubulointerstitial fibrosis via downregulated transforming growth factor-ß/Smad signaling. Maladaptive repair in the microvasculature after AKI further exacerbated focal hypoxia with capillary rarefaction, which was rescued by stabilization of hypoxia-inducible factor and increased tubular vascular endothelial growth factor A in PAR-1-deficient mice. Chronic inflammation was also prevented with reduced kidney infiltration by both M1- and M2-polarized macrophages. In thrombin-induced human dermal microvascular endothelial cells (HDMECs), PAR-1 mediated vascular injury through activation of NF-κB and ERK MAPK pathways. Gene silencing of PAR-1 exerted microvascular protection via a tubulovascular crosstalk mechanism during hypoxia in HDMECs. Finally, pharmacologic blockade of PAR-1 with vorapaxar improved kidney morphology, promoted vascular regenerative capacity, and reduced inflammation and fibrosis depending on the time of initiation. CONCLUSIONS: Our findings elucidate a detrimental role of PAR-1 in vascular dysfunction and profibrotic responses upon tissue injury during AKI-to-CKD transition and provide an attractive therapeutic strategy for post-injury repair in AKI.

The Impact of Convertase Subtilisin/Kexin Type 9 Monoclonal Antibodies with and without Apheresis on Platelet Aggregation in Familial Hypercholesterolemia.

BACKGROUND AND AIMS: It is well known that elevated cholesterol is associated with enhanced platelet aggregation and patients suffering from familial hypercholesterolemia (FH) have a high risk of thrombotic cardiovascular events. Although decreasing cholesterol level is associated with attenuation of platelet hyperactivity, there are currently no data on the effect of convertase subtilisin/kexin type 9 monoclonal antibodies (PCSK9ab) on platelet reactivity in FH. The aim of the study was to analyse the impact of different therapies including PCSK9ab on platelet aggregation in FH. METHODS: This study enrolled all 15 patients treated in the University Hospital Hradec Králové for FH. PCSK9ab have been administered in 12 of 15 patients while 8 patients were also undergoing lipid apheresis. Blood samples from all patients including pre- and post-apheresis period were tested for platelet aggregation triggered by 7 inducers, and the effect of 3 clinically used drugs (acetylsalicylic acid, ticagrelor and vorapaxar) was compared as well. RESULTS: Although apheresis decreased the reactivity of platelets in general, platelet responses were not different between non-apheresis patients treated with PCSK9ab and apheresis patients (post-apheresis values) with the exception of ristocetin. However, when compared to age-matched healthy population, FH patients had significantly lower platelet aggregation responses to 4 out of 7 used inducers and higher profit from 2 out of 3 used antiplatelet drugs even after exclusion of FH patients regularly receiving conventional antiplatelet treatment. CONCLUSION: This study showed for the first time the suitability of PCSK9ab treatment for reduction of platelet reactivity in FH patients.

Factor Xa and thrombin induce endothelial progenitor cell activation. The effect of direct oral anticoagulants.

Factor Xa (FXa) and thrombin exert non-hemostatic cellular actions primarily mediated through protease-activated receptors (PARs). We investigated the effect of FXa and thrombin on human late-outgrowth endothelial cells (OECs), a type of endothelial progenitor cells (EPCs), and on human umbilical vein endothelial cells (HUVECs). The effect of direct oral anticoagulants (DOACs), rivaroxaban and dabigatran, was also studied. The membrane expression of intercellular adhesion molecule-1 (ICAM-1) and the secretion of monocyte chemoattractant protein-1 (MCP-1) were used as cell activation markers. FXa and thrombin increase the ICAM-1 expression and the MCP-1 secretion on both cells, being higher on OECs. Vorapaxar, a specific PAR-1 antagonist, completely inhibits FXa-induced activation of both cells and thrombin-induced HUVEC activation, but only partially thrombin-induced OEC activation. Furthermore, thrombin-receptor activating peptide; TRAP-6, only partially activates OECs. OECs do not membrane-express PAR-4, therefore it may not be involved on thrombin-induced OEC activation. Rivaroxaban and dabigatran inhibit OEC and HUVEC activation by FXa and thrombin, respectively. Rivaroxaban enhances thrombin-induced OEC and HUVEC activation, which is completely inhibited by vorapaxar. The inhibition of OEC and HUVEC activation by vorapaxar and DOACs may represent a new pleiotropic effect of these drugs. The pathophysiological and clinical significance of our findings need to be established.

Pharmacological PAR-1 inhibition reduces blood glucose levels but does not improve kidney function in experimental type 2 diabetic nephropathy.

Vorapaxar-dependent protease-activated receptor (PAR)-1 inhibition diminishes diabetic nephropathy in experimental type 1 diabetes. As most patients with diabetic nephropathy suffer from type 2 diabetes, the aim of this study was to investigate whether PAR-1 inhibition also limits diabetic nephropathy in experimental type 2 diabetes. Consequently, leptin-deficient black and tan brachyuric (BTBRob/ob) mice were randomly assigned to vorapaxar (1.75 mg/kg; twice weekly via oral gavage) or vehicle treatment, whereas matched wild-type (WT) BTBR (BTBRWT) mice served as nondiabetic controls. Weight and (nonfasting) blood glucose levels were monitored for up to 18 wk, after which kidney function and histologic damage was evaluated postmortem. We show that blood glucose levels and body weight increased in diabetic BTBRob/ob mice compared with nondiabetic BTBRWT controls. Vorapaxar-dependent PAR-1 inhibition reduced but did not normalize blood glucose levels in BTBRob/ob mice, whereas it potentiated the increase in body weight. Vorapaxar did not, however, preserve kidney function, whereas it only minimally reduced histopathological signs of kidney injury. Overall, we thus show that PAR-1 inhibition reduces blood glucose levels during the progression of diabetic nephropathy in experimental type 2 diabetes but does not improve renal function. This is in contrast to the therapeutic potential of vorapaxar in type 1 diabetes-induced nephropathy, highlighting the importance of disease-dependent treatment modalities.-Waasdorp, M., Florquin, S., Duitman, J., Spek, C. A. Pharmacological PAR-1 inhibition reduces blood glucose levels but does not improve kidney function in experimental type 2 diabetic nephropathy.

Design and synthesis of potent PAR-1 antagonists based on vorapaxar.

A series of novel vorapaxar analogues with different amino substitutes at the C-7, C-9a and aromatic substitutes at the C-4 position were designed, synthesized, and evaluated for their inhibitory activity to PAR-1. Several compounds showed good potency in antagonist activity based on the intracellular calcium mobilization assay and excellent pharmacokinetics profile in rats. Among these analogues, 3d exhibited excellent PAR-1 inhibitory activity (IC50 = 0.18 µM) and the lower ability to cross the blood-brain barrier compared with vorapaxar (IC50 = 0.25 µM). Compound 3d has the potential to be developed as a new generation of PAR-1 antagonists with a better therapeutic window.

Cholesterol-Rich Microdomains Contribute to PAR1 Signaling in Platelets Despite a Weak Localization of the Receptor in These Microdomains.

Platelet protease-activated receptor 1 (PAR1) is a cell surface G-protein-coupled receptor (GPCR) that acts as a thrombin receptor promoting platelet aggregation. Targeting the PAR1 pathway by vorapaxar, a PAR1 antagonist, leads to a reduction in ischemic events in cardiovascular patients with a history of myocardial infarction or with peripheral arterial disease. In platelets, specialized microdomains highly enriched in cholesterol act as modulators of the activity of several GPCRs and play a pivotal role in the signaling pathway. However, their involvement in platelet PAR1 function remains incompletely characterized. In this context, we aimed to investigate whether activation of PAR1 in human platelets requires its localization in the membrane cholesterol-rich microdomains. Using confocal microscopy, biochemical isolation, and proteomics approaches, we found that PAR1 was not localized in cholesterol-rich microdomains in resting platelets, and only a small fraction of the receptor relocated to the microdomains following its activation. Vorapaxar treatment increased the level of PAR1 at the platelet surface, possibly by reducing its endocytosis, while its colocalization with cholesterol-rich microdomains remained weak. Consistent with a cholesterol-dependent activation of Akt and p38 MAP kinase in thrombin receptor-activating peptide (TRAP)-activated platelets, the proteomic data of cholesterol-rich microdomains isolated from TRAP-activated platelets showed the recruitment of proteins contributing to these signaling pathways. In conclusion, contrary to endothelial cells, we found that PAR1 was only weakly present in cholesterol-rich microdomains in human platelets but used these microdomains for efficient activation of downstream signaling pathways following TRAP activation.

Frequency, Predictors, and Impact of Combined Antiplatelet Therapy on Venous Thromboembolism in Patients With Symptomatic Atherosclerosis.

BACKGROUND: Observational studies suggest that symptomatic atherosclerosis may be associated with risk of venous thromboembolism (VTE). Prior randomized studies have demonstrated a significant reduction in recurrent VTE with aspirin monotherapy. Whether VTE risk is associated with more severe symptomatic atherosclerosis and more intensive antiplatelet therapy reduces VTE risk beyond aspirin monotherapy is unknown. METHODS: TRA2P-TIMI 50 (Thrombin Receptor Antagonist in Secondary Prevention of Atherothrombotic Ischemic Events-Thrombolysis in Myocardial Infarction) (vorapaxar) and PEGASUS-TIMI 54 (Prevention of Cardiovascular Events in Patients With Prior Heart Attack Using Ticagrelor Compared to Placebo on a Background of Aspirin-Thrombolysis in Myocardial Infarction 54) (ticagrelor) were blinded, randomized placebo-controlled trials of antiplatelet therapy for the prevention of ischemic events in stable patients with symptomatic atherosclerosis. Two blinded vascular specialists systematically identified symptomatic venous thromboembolic events in both trials. RESULTS: Of 47 611 patients with stable vascular disease followed for 3 years in both studies there were 343 VTE events in 301 patients (Kaplan-Meier rate at 3 years, 0.9% for placebo). The risk of VTE was independently associated with age, body mass index, polyvascular disease, chronic obstructive pulmonary disease, and malignancy. The burden of atherosclerosis manifested as an increasing number of symptomatic vascular territories was associated with a graded increase in the 3-year rates of VTE (0.76% for 1, 1.53% for 2, and 2.45% for 3 territories). More intensive antiplatelet therapy (vorapaxar and ticagrelor pooled) significantly reduced the risk of VTE by 29% compared with background antiplatelet therapy, from 0.93% to 0.64% at 3 years (hazard ratio, 0.71; 95% confidence interval, 0.56-0.89; P=0.003). CONCLUSIONS: The rate of VTE in patients with atherosclerosis is ≈0.3% per year while on treatment with ≥1 antiplatelet agent, with increased risk independently associated with the number of symptomatic vascular territories. More intensive antiplatelet therapy reduces the risk of VTE. These data suggest a relationship between atherosclerosis burden and VTE risk, and they support inclusion of VTE as a prospective end point in long-term secondary prevention trials evaluating the risks and benefits of antiplatelet therapies in patients with atherosclerosis. CLINICAL TRIAL REGISTRATION: URL: https://www.clinicaltrials.gov. Unique identifier: NCT01225562.

Efficacy and safety of more potent antiplatelet therapy with vorapaxar in patients with impaired renal function.

Patients with renal disease are often undertreated with antiplatelet therapy due to concerns about bleeding. Vorapaxar blocks platelet activation via the PAR-1 receptor and reduces cardiovascular events in patients with stable atherosclerosis, but with increased bleeding. We examined the efficacy and safety of vorapaxar in patients with impaired renal function. TRA2°P-TIMI 50 randomized patients with stable atherosclerosis to vorapaxar or. We analyzed patients with eGFR assessed who qualified with a history of MI or PAD (without stroke or TIA) (n = 19,932). Cox models assessed the risk of CV events and bleeding by quartile of baseline eGFR in the placebo arm and then by randomized assignment. Net clinical outcome (NCO) was predefined as CV death, MI, stroke, or GUSTO severe bleeding. Patients with lower eGFR tended to be older, female, have hypertension, hyperlipidemia or prior PAD. In the placebo arm, baseline eGFR in the lowest quartile was associated with a 26% higher risk of CV death, MI or stroke (Q1:Q4 HRadj 1.26, 1.03-1.55) and 73% higher risk of GUSTO moderate or severe bleeding (HRadj 1.73, 1.12-2.65). Vorapaxar reduced the risk of MACE to a similar extent (14-26%) across quartiles of baseline eGFR (P interaction = 0.70) and increased the relative risk of GUSTO moderate or severe bleeding (P interaction = 0.54). NCO was similar across quartiles of eGFR (P interaction = 0.65). Intensification of antiplatelet therapy with vorapaxar offers comparable net clinical benefit regardless of baseline renal function. These data support the use of more potent antiplatelet regimens in patients with renal dysfunction.

Direct Oral Anticoagulants in Addition to Antiplatelet Therapy for Secondary Prevention after Acute Coronary Syndromes: a Review.

PURPOSE OF REVIEW: As the management of acute coronary syndrome (ACS) continues to evolve, many old practices proved to be of a little benefit and other approaches established the new pillars of modern medicine. Treating ACS patients with dual antiplatelet therapy (DAPT) for a year by combining aspirin and a P2Y12 inhibitor (clopidogrel, ticagrelor, or prasugrel) has resulted in better outcomes and is currently the standard of therapy. However, owing to the persistent activation of the coagulation cascade, patients may continue to experience recurrent ischemia and high mortality rates despite compliance with the dual antiplatelet therapy. Research is underway to establish new treatment modalities for secondary prevention post-ACS, including the use of the novel direct oral anticoagulants (DOACs). RECENT FINDINGS: Multiple trials have been conducted to evaluate the use of DOACs for the secondary prevention after ACS. Recent emerging data showed that the addition of rivaroxaban in a very low dose of 2.5 mg twice daily to the regular DAPT regimen after ACS is beneficial in the reduction of major cardiovascular events, including recurrent myocardial infarction (MI) and strokes. On the other hand, other DOACs, including apixaban, did not show similar efficacy and did not improve the cardiovascular outcomes. Patients who experience an ACS continue to suffer long-term consequences and thromboembolic complications. Many studies have shown that after the initial ACS event, patients remain in a hypercoagulable state and are more prone to recurrent ischemic attacks including stroke, recurrent MI, or unstable angina (UA). With the objective of seeking better outcomes, it is imperative to explore more aggressive anticoagulation strategies in ACS patients. In this article, we discuss the progress that was made and the limitations we face regarding the role of different anticoagulants in this setting.

Protease-activated receptor 1 activation enhances doxorubicin-induced cardiotoxicity.

OBJECTIVE: The anti-cancer anthracycline drug Doxorubicin (Dox) causes cardiotoxicity. We investigated the role of protease-activated receptor 1 (PAR-1) in Dox-induced cardiotoxicity. METHODS AND RESULTS: In vitro experiments revealed that PAR-1 enhanced Dox-induced mitochondrial dysfunction, reactive oxygen species and cell death of cardiac myocytes and cardiac fibroblasts. The contribution of PAR-1 to Dox-induced cardiotoxicity was investigated by subjecting PAR-1-/- mice and PAR-1+/+ mice to acute and chronic exposure to Dox. Heart function was measured by echocardiography. PAR-1-/- mice exhibited significant less cardiac injury and dysfunction compared to PAR-1+/+ mice after acute and chronic Dox administration. PAR-1-/- mice had reduced levels of nitrotyrosine, apoptosis and inflammation in their heart compared to PAR-1+/+ mice. Furthermore, inhibition of PAR-1 in wild-type mice with vorapaxar significantly reduced the acute Dox-induced cardiotoxicity. CONCLUSION: Our results indicate that activation of PAR-1 contributes to Dox-induced cardiotoxicity. Inhibition of PAR-1 may be a new approach to reduce Dox-induced cardiotoxicity in cancer patients.

Characterization of Protease-Activated Receptor (PAR) ligands: Parmodulins are reversible allosteric inhibitors of PAR1-driven calcium mobilization in endothelial cells.

Several classes of ligands for Protease-Activated Receptors (PARs) have shown impressive anti-inflammatory and cytoprotective activities, including PAR2 antagonists and the PAR1-targeting parmodulins. In order to support medicinal chemistry studies with hundreds of compounds and to perform detailed mode-of-action studies, it became important to develop a reliable PAR assay that is operational with endothelial cells, which mediate the cytoprotective effects of interest. We report a detailed protocol for an intracellular calcium mobilization assay with adherent endothelial cells in multiwell plates that was used to study a number of known and new PAR1 and PAR2 ligands, including an alkynylated version of the PAR1 antagonist RWJ-58259 that is suitable for the preparation of tagged or conjugate compounds. Using the cell line EA.hy926, it was necessary to perform media exchanges with automated liquid handling equipment in order to obtain optimal and reproducible antagonist concentration-response curves. The assay is also suitable for study of PAR2 ligands; a peptide antagonist reported by Fairlie was synthesized and found to inhibit PAR2 in a manner consistent with reports using epithelial cells. The assay was used to confirm that vorapaxar acts as an irreversible antagonist of PAR1 in endothelium, and parmodulin 2 (ML161) and the related parmodulin RR-90 were found to inhibit PAR1 reversibly, in a manner consistent with negative allosteric modulation.

Combination antiplatelet treatment in coronary artery disease patients: A necessary evil or an overzealous practice?

In seeking to improve care in coronary artery disease patients, further platelet inhibition has been occasionally applied beyond that provided by aspirin and a P2Y12 receptor antagonist. This review aims to offer insights about the rationale, the efficacy and safety of combination antiplatelet therapy, involving three or more agents. Overall, the use of glycoprotein (GP) IIb/IIIa inhibitors did not significantly modify the treatment effect of different antiplatelet strategies, including double vs standard clopidogrel, prasugrel vs clopidogrel, ticagrelor vs clopidogrel, cangrelor vs clopidogrel, and vorapaxar vs placebo. With the caveat that the use of GP IIb/IIIa inhibitor was not randomized, adding such an agent to aspirin and a P2Y12 receptor antagonist appears to carry a significantly increased bleeding potential. Moreover, adding vorapaxar to aspirin- and clopidogrel-treated patients is associated with more bleeding events, while the bleeding potential is further exacerbated in cases of quadruplicate antiplatelet treatment including aspirin, clopidogrel, vorapaxar, and a GP IIb/IIIa inhibitor. In ST-segment elevation, myocardial infarction patients' administration of an intravenous antiplatelet agent (GP IIb/IIIa inhibitor or cangrelor), in addition to aspirin and a P2Y12 receptor antagonist, efficiently bridges the pharmacodynamic gap of oral agents. Cilostazol on top of aspirin and clopidogrel appears to be safe, although of questionable clinical benefit. In conclusion, combination antiplatelet therapy should be reserved only for selected cases and following thoughtful consideration of the associated risk/benefit ratio.

Molecular requirements involving the human platelet protease-activated receptor-4 mechanism of activation by peptide analogues of its tethered-ligand.

Thrombin is the most potent agonist of human platelets and its effects are primarily mediated through the protease-activated receptors (PARs)-1 and -4. Although PAR-1 has higher affinity for thrombin than PAR-4, both receptors contribute to thrombin-mediated actions on platelets. Recently, a potent and selective PAR-1 antagonist (vorapaxar) was approved for clinical use in selected patients. In contrast, despite the fact that several PAR-4 antagonists have been developed, few of them have been tested in clinical trials. The aim of the present study was to elucidate the molecular requirements involving the PAR-4 mechanism of activation by peptide analogues of its tethered-ligand. Eight synthetic PAR-4 tethered-ligand peptide analogues were synthesized and studied for their agonistic/antagonistic potency and selectivity toward human washed platelet aggregation, using light transmittance aggregometry. In addition, in silico studies were conducted to describe the receptor-peptide interactions that are developed following PAR-4 exposure to the above analogues. To provide a first structure-activity relationship rationale on the bioactivity profiles recorded for the studied analogues, molecular docking was applied in a homology model of PAR-4, derived using the crystal structure of PAR-1. The following peptide analogues were synthesized: AYPGKF-NH2 (1), GYPGKF-NH2 (2), Ac-AYPGKF-NH2 (3), trans-cinnamoyl-AYPGKF-NH2 (4), YPGKF-NH2 (5), Ac-YPGKF-NH2 (6), trans-cinnamoyl-YPGKF-NH2 (7), and caffeoyl-YPGKF-NH2 (8). Peptide (1) is a selective PAR-4 agonist inducing platelet aggregation with an IC50 value of 26.2 µM. Substitution of Ala-1 with Gly-1 resulted in peptide (2), which significantly reduces the agonistic potency of peptide (1) by 25-fold. Importantly, substitution of Ala-1 with trans-cinnamoyl-1 resulted in peptide (7), which completely abolishes the agonistic activity of peptide (1) and renders it with a potent antagonistic activity toward peptide (1)-induced platelet aggregation. All other peptides tested were inactive. Tyr-2, residue, along with its neighboring environment was a key determinant in the PAR-4 recognition mode. When the neighboring residues to Tyr-2 provided an optimum spatial ability for the ligand to enter into the binding site of the transmembrane receptor, a biological response was propagated. These results were compared with the predicted binding poses of small molecule antagonists of PAR-4, denoted as YD-3, ML-354, and BMS-986120. π-π stacking interaction with Tyr-183 appears to be critical and common for both small molecules antagonists and the peptide trans-cinnamoyl-YPGKF-NH2. Conclusively, the lipophilicity, size, and aromatic nature of the residue preceding Tyr-2 are determining factors on whether a human platelet PAR-4 tethered-ligand peptide analogue will exert an agonistic or antagonistic activity.

Clinical pathways and management of antithrombotic therapy in patients with acute coronary syndrome (ACS): a Consensus Document from the Italian Association of Hospital Cardiologists (ANMCO), Italian Society of Cardiology (SIC), Italian Society of Emergency Medicine (SIMEU) and Italian Society of Interventional Cardiology (SICI-GISE).

Antiplatelet therapy is the cornerstone of the pharmacologic management of patients with acute coronary syndrome (ACS). Over the last years, several studies have evaluated old and new oral or intravenous antiplatelet agents in ACS patients. In particular, research was focused on assessing superiority of two novel platelet ADP P2Y12 receptor antagonists (i.e., prasugrel and ticagrelor) over clopidogrel. Several large randomized controlled trials have been undertaken in this setting and a wide variety of prespecified and post-hoc analyses are available that evaluated the potential benefits of novel antiplatelet therapies in different subsets of patients with ACS. The aim of this document is to review recent data on the use of current antiplatelet agents for in-hospital treatment of ACS patients. In addition, in order to overcome increasing clinical challenges and implement effective therapeutic interventions, this document identifies all potential specific care pathway for ACS patients and accordingly proposes individualized therapeutic options.

Vorapaxar in atherosclerotic disease management.

OBJECTIVE: To review the pharmacology, efficacy, and safety of vorapaxar, a protease activator receptor-1 (PAR-1) antagonist, in the management of atherosclerotic diseases. DATA SOURCES: Peer-reviewed clinical trials and review articles were identified from MEDLINE and Current Content database (both 1966 to December 31, 2014) using the search terms vorapaxar and protease activator receptor antagonist. STUDY SELECTION AND DATA EXTRACTION: A total of 30 clinical studies were identified (16 clinical trials, including subanalyses, 14 related to pharmacology, pharmacokinetics, and pharmacodynamics and drug interactions). DATA SYNTHESIS: Two phase III clinical trials with vorapaxar have been published. In patients with non-ST segment elevation myocardial infarction (MI), vorapaxar failed to significantly reduce the primary efficacy end point (composite of cardiovascular death, MI, stroke, recurrent ischemia with hospitalization, and urgent coronary revascularization). Conversely, in a study of secondary prevention for patients with cardiovascular disease, the composite end point of cardiovascular death, MI, or stroke was significantly reduced. In both trials, the safety end points of major/minor bleeding were increased compared with placebo. In the secondary prevention trial, an increased incidence of intracranial hemorrhage led to the exclusion of patients with a prior history of stroke. CONCLUSION: Vorapaxar is approved for use with aspirin and/or clopidogrel in the secondary prevention of cardiovascular events in stable patients with peripheral arterial disease or a history of MI. However, the addition of vorapaxar to other antiplatelets can significantly increase the risk of bleeding. It is, therefore, essential to balance the need for further reduction of risk of thrombotic event with patient's individual bleeding risk.

PAR1 antagonists inhibit thrombin-induced platelet activation whilst leaving the PAR4-mediated response intact.

Thrombin-induced platelet activation is initiated by PAR1 and PAR4 receptors. Vorapaxar, a PAR1 antagonist, has been assessed in patients with acute coronary syndromes (ACS) and stable atherosclerotic disease in addition to standard-of-care treatment. In clinical trials, vorapaxar has been observed to reduce the frequency of ischaemic events in some subgroups though in others has increased the frequency of bleeding events. Among patients undergoing CABG surgery, which is associated with excess thrombin generation, bleeding was not increased. The aim of these studies was to investigate the effects of selective PAR1 antagonism on thrombin-induced platelet activation in patients receiving vorapaxar or placebo in the TRACER trial and to explore the roles of PAR1 and PAR4 in thrombin-induced platelet activation in healthy volunteers. ACS patients receiving vorapaxar or placebo in the TRACER trial were studied at baseline and 4 hours, 1 and 4 months during drug administration. Thrombin-induced calcium mobilisation in platelet-rich plasma was assessed by flow cytometry. In vitro studies were performed in healthy volunteers using the PAR1 antagonist SCH79797 or PAR4 receptor desensitisation. Vorapaxar treatment significantly inhibited thrombin-induced calcium mobilisation, leaving a residual, delayed response. These findings were consistent with calcium mobilisation mediated via the PAR4 receptor and were reproduced in vitro using SCH79797. PAR4 receptor desensitization, in combination with SCH79797, completely inhibited thrombin-induced calcium mobilisation confirming that the residual calcium mobilisation was mediated via PAR4. In conclusion vorapaxar selectively antagonises the PAR1-mediated component of thrombin-induced platelet activation, leaving the PAR4-mediated response intact, which may explain why vorapaxar is well tolerated in patients undergoing CABG surgery since higher thrombin levels in this setting may override the effects of PAR1 antagonism through PAR4 activation, thus preserving haemostasis. Further assessment may be warranted.

[The multidirectional effects of thrombin and the possibility of their control in neurology]. / Raznonapravlennye effekty trombina na protsessy gemokoagulyatsii i vozmozhnost' ikh kontrolya v nevrologii.

The review presents the main physiological functions of thrombin. The procoagulant and anticoagulant activities of the key serine protease are discussed in both physiological and pathological conditions of hemostasis. The involvement of thrombin in atherogenesis, as well as its role as a mediator of vascular dysfunction and inflammation in both the peripheral and central nervous system, is highlighted. A pronounced imbalance between the pro- and anticoagulant systems leads to an increase in thrombin formation and creates conditions for the development of thrombosis. Tests that allow direct or indirect assessment of thrombin's functional activity are presented. The potential applications of direct thrombin inhibitors and direct blockers of thrombin PAR receptors in vascular neurology are also considered.

Vorapaxar proven to be a promising candidate for pulmonary fibrosis by intervening in the PAR1/JAK2/STAT1/3 signaling pathway-an experimental in vitro and vivo study.

Idiopathic pulmonary fibrosis (IPF) is a lethal lung disease, and its 5-year mortality rate is even higher than the mortality rate of some cancers. Fibrosis can cause irreversible damage to lung structure and function. Treatment options for IPF remain limited, and there is an urgent need to develop effective therapeutic drugs. Protease activated receptor-1 (PAR-1) is a G-protein-coupled receptor and is considered a potential target for the treatment of fibrotic diseases. Vorapaxar is a clinically approved PAR-1 antagonist for cardiovascular protection. The purpose of this study was to explore the potential effect and mechanism of Vorapaxar on pulmonary fibrosis in vivo and in vitro. In the experimental animal model, Vorapaxar can effectively alleviate bleomycin (BLM)-induced pulmonary fibrosis. Treatment with 2.5, 5 or 10 mg/kg Vorapaxar once a day reduced the degree of fibrosis in a dose-dependent manner. The expression of fibronectin, collagen and α smooth muscle actin decreased significantly at the messenger RNA (mRNA) and protein levels in treated mice. In vitro, our results showed that Vorapaxar could inhibit the activation of fibroblasts induced by thrombin in a dose-dependent manner. In terms of mechanism, Vorapaxar inhibits the signal transduction of JAK2/STAT1/3 by inhibiting the activation of protease activated receptor 1, which reduces the expression of HSP90ß and the interaction between HSP90ß and transforming growth factor-ß (TGFß) receptor II and inhibits the TGFß/Smad signaling pathway. In conclusion, Vorapaxar inhibits the activation of pulmonary fibroblasts induced by thrombin by targeting protease activated receptor 1 and alleviates BLM-induced pulmonary fibrosis in mice.

Epidemiology of heart failure hospitalization in patients with stable atherothrombotic disease: Insights from the TRA 2°P-TIMI 50 trial.

BACKGROUND: Heart failure (HF) is a growing public health problem and ischemic heart disease is an important risk factor. Understanding the epidemiology of HF in patients with atherosclerosis may help identify subgroups at greater risk who have the potential to derive greater benefit from preventive strategies. METHODS AND RESULTS: The TRA 2°P-TIMI 50 trial randomized 26,449 patients with stable atherosclerosis to the antiplatelet agent vorapaxar versus placebo. Hospitalization for HF (HHF) endpoints were adjudicated from serious adverse events by blinded structured review using established definitions. HHF incidence was estimated using Kaplan-Meier analysis. Independent predictors of HHF risk were identified using multivariable logistic regression. The effect of vorapaxar on HHF risk was explored using Cox regression. The estimated incidence of HHF at 3 years was 1.6%. Independent predictors of HHF included prior HF (adjusted odds ratio [adj-OR]: 8.31; 95% confidence interval [CI]: 6.56-10.54), age (adj-OR [per 10 years]: 1.67; 95% CI: 1.47-1.89), type 2 diabetes mellitus (T2DM; adj-OR: 2.55; 95% CI: 2.01-3.24), polyvascular disease (two-territory disease, adj-OR: 1.89; 95% CI: 1.46-2.44; three-territory disease, adj-OR: 2.68; 95% CI: 1.94-3.70), chronic kidney disease (CKD; adj-OR: 1.65; 95% CI: 1.30-2.11), body mass index (BMI; adj-OR [per 5 kg/m2 ]: 1.15; 95% CI: 1.03-1.27), prior myocardial infarction (MI) (adj-OR: 1.35; 95% CI: 1.03-1.78), and hypertension (adj-OR: 1.44; 95% CI: 1.02-2.04). Patients who experienced HHF during follow-up had higher rates of subsequent rehospitalization and death. Vorapaxar did not modify the risk of HHF. CONCLUSIONS: In patients with stable atherosclerosis, prior HF, age, T2DM, polyvascular disease, CKD, BMI, prior MI, and hypertension are important predictors of HHF risk.