Contemporary use of glycoprotein IIb/IIIa inhibitors

An Updated Review on Glycoprotein IIb/IIIa Inhibitors as Antiplatelet Agents: Basic and Clinical Perspectives

The glycoprotein (GP) IIb/IIIa receptor is found integrin present in platelet aggregations. GP IIb/IIIa antagonists interfere with platelet cross-linking and platelet-derived thrombus formation through the competition with fibrinogen and von Willebrand factor. Currently, three parenteral GP IIb/IIIa competitors (tirofiban, eptifibatide, and abciximab) are approved for clinical use in patients affected by percutaneous coronary interventions (PCI) in the location of acute coronary syndrome (ACS). GP IIb/IIIa antagonists have their mechanism of action in platelet aggregation prevention, distal thromboembolism, and thrombus formation, whereas the initial platelet binding to damage vascular areas is preserved. This work is aimed to provide a comprehensive review of the significance of GP IIb/IIIa inhibitors as a sort of antiplatelet agent. Their mechanism of action is based on factors that affect their efficacy. On the other hand, drugs that inhibit GP IIb/IIIa already approved by the FDA were reviewed in detail. Results from major clinical trials and regulatory practices and guidelines to deal with GP IIb/IIIa inhibitors were deeply investigated. The cardiovascular pathology and neuro-interventional surgical application of GP IIb/IIIa inhibitors as a class of antiplatelet agents were developed in detail. The therapeutic risk/benefit balance of currently available GP IIb/IIa receptor antagonists is not yet well elucidated in patients with ACS who are not clinically evaluated regularly for early cardiovascular revascularization. On the other hand, in patients who have benefited from PCI, the antiplatelet therapy intensification by the addition of a GP IIb/IIIa receptor antagonist (intravenously) may be an appropriate therapeutic strategy in reducing the occurrence of risks of thrombotic complications related to the intervention. Development of GP IIb/IIIa inhibitors with oral administration has the potential to include short-term antiplatelet benefits compared with intravenous GP IIb/IIIa inhibitors for long-term secondary preventive therapy in cardiovascular disease. But studies showed that long-term oral administration of GP IIb/IIIa receptor inhibitors has been ineffective in preventing ischemic events. Paradoxically, they have been linked to a high risk of side effects by producing prothrombotic and pro-inflammatory events.

The Effects of Ticagrelor Combined with Tirofiban on Coagulation Function, Serum Myocardial Injury Markers, and Inflammatory Factor Levels in Patients with Acute Myocardial Infarction after Percutaneous Coronary Intervention

Background

Acute myocardial infarction (AMI) refers to the acute necrosis of part of the myocardium caused by persistent and severe myocardial ischemia. This study is aimed at investigating the efficacy of tirofiban combined with ticagrelor in AMI patients after percutaneous coronary intervention (PCI) and its effects on plasma activated partial thromboplastin time (APTT), fibrinogen (FIB), D-dimer (D-D) levels, myocardial injury markers, and inflammatory factors.

Methods

68 AMI patients with AMI who received PCI were divided into control group and observation group (n =34) according to postoperative treatment methods. Both groups received ticagrelor tablets (90 mg). The observation group was additionally given tirofiban (10 μg/kg). APTT, FIB, D-D, serum myoglobin (MB), cardiac troponin I (cTnI), serum C-reactive protein (CRP), tumor necrosis factor-α (TNF-α), and IL-6, myeloperoxidase (MPO) levels and the peak time in both groups were detected. The incidence of cardiovascular events and drug safety were compared.

Results

After treatment, APTT was increased, and FIB and D-D levels were decreased in both groups. After treatment, the APTT in the observation group was longer, and FIB and D-D levels were lower than those in the control group. The peak time of serum MB and cTnI in the observation group was earlier than that in the control group. The levels of serum MB and cTnI in the observation group were lower than those in the control group. After treatment, serum CRP, TNF-α, IL-6, and MPO levels were decreased. And the incidence of cardiovascular events was reduced.

Conclusion

Tirofiban combined with ticagrelor can improve coagulation function, protect myocardium, relieve inflammation, and reduce the risk of cardiovascular events in patients with AMI after PCI.

Introduction of BD Vacutainer® Barricor™ tubes in clinical biobanking and application of amino acid and cytokine quality indicators to Barricor plasma

OBJECTIVES

The use of BD Vacutainer® Barricor™ tubes (BAR) can reduce turnaround time (TAT) and improve separation of plasma from cellular components using a specific mechanical separator. Concentrations of amino acids (AAs) and cytokines, known to be labile during pre-analytical time delays, were compared in heparin (BAR, BD Heparin standard tube [PST]), EDTA and serum gel tubes (SER) to validate previously identified quality indicators (QIs) in BAR.

METHODS

Samples of healthy individuals (n=10) were collected in heparin, EDTA and SER tubes and exposed to varying pre- and post-centrifugation delays at room temperature (RT). Cytokines (interleukin [IL]-8, IL-16 and sCD40L) were analyzed by enzyme-linked immunosorbent assay (ELISA) and AAs were characterized by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS).

RESULTS

All QIs, AAs/AA ratio and cytokines increased during prolonged blood storage in heparin plasma (PST, BAR) and SER tubes. Comparison of 53 h/1 h pre-centrifugation delay resulted in an increase in taurine (Tau) and glutamic acid (Glu) concentrations by more than three times, soluble CD40L increased by 13.6, 9.2 and 4.3 fold in PST, BAR-CTRL and BAR-FAST, and IL-8 increased even more by 112.8 (PST), 266.1 (BAR-CTRL), 268.1 (BAR-FAST) and 70.0 (SER) fold, respectively. Overall, compared to prolonged blood storage, effects of post-centrifugation delays were less pronounced in all tested materials.

CONCLUSIONS

BAR tubes are compatible with the use of several established QIs and can therefore be used in clinical biobanking to reduce pre-analytical TAT without compromising QIs and thus pre-analytical sample quality analysis.

Thrombin-like serine protease, antiquorin from Euphorbia antiquorum latex induces platelet aggregation via PAR1-Akt/p38 signaling axis

Plant latex proteases (PLPs) are pharmacologically essential and are integral components of traditional medicine in the management of bleeding wounds. PLPs are known to promote blood coagulation and stop bleeding by interfering at various stages of hemostasis. There are a handful of scientific reports on thrombin-like enzymes characterized from plant latices. However, the role of plant latex thrombin-like enzymes in platelet aggregation is not well known. In the present study, we attempted to purify and characterize thrombin-like protease responsible for platelet aggregation. Among tested plant latices, Euphorbia genus latex protease fractions (LPFs) induced platelet aggregation. In Euphorbia genus, E. antiquorum LPF (EaLPF) strongly induced platelet aggregation and attenuated bleeding in mice. The purified thrombin-like serine protease, antiquorin (Aqn) is a glycoprotein with platelet aggregating activities that interfere in intrinsic and common pathways of blood coagulation cascade and alleviates bleeding and enhanced excision wound healing in mice. In continuation, the pharmacological inhibitor of PAR1 inhibited Aqn-induced phosphorylation of cPLA₂, Akt, and P38 in human platelets. Moreover, Aqn-induced platelet aggregation was inhibited by pharmacological inhibitors of PAR1, PI3K, and P38. These data indicate that PAR1-Akt/P38 signaling pathways are involved in Aqn-induced platelet aggregation. The findings of the present study may open up a new avenue for exploiting Aqn in the treatment of bleeding wounds.

Sushi Domain Containing 2 (SUSD2) inhibits platelet activation and binding to high-grade serous ovarian carcinoma cells

Platelets play a central role in primary hemostasis affecting tumor survival and metastases. Tumors induce platelets to aggregate and bind to the cancer cells, resulting in protection from immune surveillance and often leading to thrombocytosis. In ovarian cancer (OvCa), one-third of patients present with thrombocytosis, a diagnosis that correlates with shorter survival. SUSD2 (SUShi Domain containing 2), a type I transmembrane protein, shown to inhibit metastatic processes in high-grade serous ovarian carcinoma (HGSOC), is expressed on endothelial cells and thus may influence platelet reactivity. As such, we hypothesized that SUSD2 levels in ovarian cancer-derived cell lines influence platelet activation. We incubated OvCa non-targeting (NT) and SUSD2 knockdown (KD) cell lines with labeled platelets and quantified platelet binding, as well as GPIIb/IIIa integrin activation. The role of GPIIb/IIIa in tumor cell/platelet interaction was also examined by measuring cell-cell adhesion in the presence of eptifibatide. We found that platelets exposed to OvCa cells with low SUSD2 expression display increased tumor cell-platelet binding along with an increase in GPIIb/IIIa receptor activation. As such, platelet activation and binding to HGSOC cells was inversely correlated with the presence of SUSD2. This represents one of the first tumor proteins known to provide differential platelet interaction based on protein status.

Novel aspects of antiplatelet therapy in cardiovascular disease

Antiplatelet therapy is a cornerstone in the secondary prophylaxis of adverse cardiovascular events such as myocardial infarction and stroke. The cyclooxygenase inhibitor aspirin remains the most frequently prescribed antiplatelet drug, followed by adenosine diphosphate P2Y12 receptor blockers. Glycoprotein IIb-IIIa antagonists are intravenously available antiplatelet agents preventing platelet-to-platelet aggregation via the fibrinogen receptor. The thrombin receptor inhibitor vorapaxar allows the targeting of yet a third pathway of platelet activation. Despite the advent of novel agents and major advances in antiplatelet treatment over the last decade, atherothrombotic events still impair the prognosis of many patients with cardiovascular disease. Consequently, antiplatelet therapy remains a field of intense research and a large number of studies on its various aspects are published each year. This review article summarizes recent developments in antiplatelet therapy in cardiovascular disease focusing particularly on the duration of dual antiplatelet therapy, new treatment regimens, the role of platelet function testing, and potential future targets of antiplatelet agents.

rLj-RGD3, a novel recombinant toxin protein from Lampetra japonica, prevents coronary thrombosis-induced acute myocardial infarction by inhibiting platelet functions in rats

Recombinant Lampetra japonica RGD-peptide (rLj-RGD3), a soluble protein containing three RGD sequences, was acquired from the oral salivary glands of Lampetra japonica using recombinant DNA technology. The aim of this study was to investigate the protective effects of rLj-RGD3 against acute myocardial infarction (AMI) induced by coronary artery thrombosis, as well as the underlying mechanisms. A rat model of AMI caused by ferric chloride-induced thrombosis on the surface of the left anterior descending (LAD) coronary artery was successfully established. Rats were given various doses of rLj-RGD3 (12 μg/kg, 24 μg/kg and 48 μg/kg) via sublingual intravenous delivery 10 min before AMI. ST segment elevation was recorded by electrocardiogram (ECG) until the end of the model. Left ventricular Evans blue content and histopathological changes were examined. Blood samples were collected to determine 5-hydroxytryptamine (5-HT), β-thromboglobulin (β-TG), platelet factor 4 (PF4) and cAMP levels. The effects of rLj-RGD3 on platelet aggregation, adhesion and intracellular calcium concentrations were also measured. rLj-RGD3 significantly reduced ST segment elevation, prevented thrombus formation in the coronary artery and decreased Evans blue content in the left ventricular myocardium. Meanwhile, rLj-RGD3 exerted an inhibitory effect on adenosine diphosphate (ADP)-induced platelet aggregation and blocked platelet adhesion to collagen. Treatment with rLj-RGD3 prevented 5-HT, β-TG and PF4 release and significantly elevated intracellular cAMP levels in a dose-dependent manner but decreased the level of cytosolic-free Ca²⁺, an aggregation-inducing molecule. These results show that rLj-RGD3 can effectively reduce coronary thrombosis in AMI rats by strongly inhibiting platelet function, indicating that the recombinant RGD toxin protein rLj-RGD3 may serve as a potent clinical therapeutic agent for AMI.

GPIIb/IIIa inhibitors: From bench to bedside and back to bench again

From the discovery of the platelet glycoprotein (GP) IIb/IIIa and identification of its central role in haemostasis, the integrin GPIIb/IIIa (αIIbβ3, CD41/CD61) was destined to be an anti-thrombotic target. The subsequent successful development of intravenous ligand-mimetic inhibitors occurred during a time of limited understanding of integrin physiology. Although efficient inhibitors of ligand binding, they also mimic ligand function. In the case of GPIIb/IIIa inhibitors, despite strongly inhibiting platelet aggregation, paradoxical fibrinogen binding and platelet activation can occur. The quick progression to development of small-molecule orally available inhibitors meant that this approach inherited many potential flaws, which together with a short half-life resulted in an increase in mortality and a halt to the numerous pharmaceutical development programs. Limited clinical benefits, together with the success of other anti-thrombotic drugs, in particular P2Y12 ADP receptor blockers, have also led to a restrictive use of intravenous GPIIb/ IIIa inhibitors. However, with a greater understanding of this key platelet-specific integrin, GPIIb/IIIa remains a potentially attractive target and future drug developments will be better informed by the lessons learnt from taking the current inhibitors back to the bench. This overview will review the physiology behind the inherent problems of a ligand-based integrin inhibitor design and discuss novel promising approaches for GPIIb/IIIa inhibition.

Platelet function testing and prediction of procedural bleeding risk

The essential role of platelets in haemostasis underlies the relationship between platelet function and spontaneous or procedure-related bleeding, which has important prognostic implications. Although not routinely undertaken, platelet function testing offers the potential to tailor antiplatelet therapy for individual patients. However, uncertainties remain about how well platelet function testing may predict haemostasis and guide management of bleeding risk. Studies of aspirin, P2Y12 inhibitors and other antiplatelet drugs clearly demonstrate how inhibition of platelet function increases bleeding risk. More potent antiplatelet drugs are associated with higher bleeding rates, consistent with the levels of platelet inhibition achieved by these drugs. Studies of patients treated with clopidogrel, which is associated with wide inter-individual variation in antiplatelet effect, suggest that platelet function testing may predict bleeding risk related to coronary artery bypass grafting (CABG) surgery and potentially guide the timing of surgery following discontinuation of clopidogrel. Similarly, some studies have demonstrated a relationship between clopidogrel response and bleeding in patients undergoing percutaneous coronary intervention (PCI), although other studies have not supported this. Carriage of the *17 allele of cytochrome P450 2C19, which is associated with gain of function and enhanced response to clopidogrel, seems to be associated with increased bleeding risk, although studies showing lack of apparent effect of loss-of-function alleles provide contradictory evidence. Further large studies are needed to guide best practice in the application of platelet function testing in the clinical management of patients treated with antiplatelet drugs in order to optimise individual care.

Diagnostic and Therapeutic Strategies for Acute Intracranial Atherosclerosis-related Occlusions

Intracranial atherosclerosis-related occlusion (ICAS-O) is frequently encountered at the time of endovascular revascularization treatment (ERT), especially in Asian countries. However, because baseline angiographic findings are similar between ICAS-O and embolism-related occlusion (EMB-O), it is difficult to differentiate the etiologies before the ERT procedure. Moreover, despite successful randomized trials on ERT, results from studies examining the optimal treatment protocol in ICAS-O patients remain unclear. In this review, we describe the clinical and imaging factors that may possibly differentiate ICAS-O from EMB-O. We will also discuss some current hurdles for treating ICAS-O in the hyperacute period and suggest the optimal ERT strategy for ICAS-O patients.

The role of Glycoprotein IIb/IIIa inhibitors in acute coronary syndromes and the interference with anemia

The role played by glycoprotein (GP) IIb/IIIa inhibitors (GPI) has continuously evolved until the most recent Guidelines whereby they were stepped down from class I to class II recommendation for treating acute coronary syndromes (ACS). GPI compete with a wider use of ADP inhibitors and novel anticoagulant drugs although GPI use has greatly narrowed. However, GPI may still have a role. Several criteria were proposed to define post-PCI anemia which is strictly related to bleeding and transfusion. In ACS, it should be important to define anemia in comparative terms versus baseline levels: ≥ 15% of red blood cell decrease should be a practical cut-off value. If one wishes to concentrate on hemoglobin (Hb), a≥2g/dl Hb decrease from baseline should be considered. It is important to recognize post-PCI anemia in the setting of ACS. There are sub-populations exposed to short-term hemorrhagic and/or long-term ischemic risks. Ischemic and hemorrhagic risks need to be carefully evaluated along with thrombocytopenia and its prognostic significance in order to put all these blood and rheological parameters into a clinically oriented perspective on which therapeutical decisions should be based. Definition of high risk procedures (complexity, angiographic characteristics and patient's risk profile, regardless whether STEMI or NSTEMI) may help selecting GPI. There are positive elements in GPI use: efficacy, rapid onset and reversibility of action, absence of pharmacogenomic variability, pharmacoeconomic considerations and the possibility of intracoronary administration. All these elements should be evaluated when selecting these agents for therapeutics.

Integrin-based therapeutics: biological basis, clinical use and new drugs

Integrins are activatable molecules that are involved in adhesion and signalling. Of the 24 known human integrins, 3 are currently targeted therapeutically by monoclonal antibodies, peptides or small molecules: drugs targeting the platelet αIIbβ3 integrin are used to prevent thrombotic complications after percutaneous coronary interventions, and compounds targeting the lymphocyte α4β1 and α4β7 integrins have indications in multiple sclerosis and inflammatory bowel disease. New antibodies and small molecules targeting β7 integrins (α4β7 and αEβ7 integrins) and their ligands are in clinical development for the treatment of inflammatory bowel diseases. Integrin-based therapeutics have shown clinically significant benefits in many patients, leading to continued medical interest in the further development of novel integrin inhibitors. Of note, almost all integrin antagonists in use or in late-stage clinical trials target either the ligand-binding site or the ligand itself.

Tibial bypass salvage with eptifibatide in a patient with thrombocythemia

Early graft failure is a complex and challenging clinical condition faced by vascular surgeons performing infrainguinal bypass surgery. This case describes a patient with undiagnosed thrombocytosis undergoing urgent open revascularization for critical limb ischemia. The operative case was complicated by recurrent on-table acute thrombosis that was successfully managed with intravenous glycoprotein IIb/IIIa antagonism with eptifibatide. This is a novel case of its use for on-table salvage of an infrainguinal bypass graft. This case report outlines this challenging clinical problem and a novel use for glycoprotein IIb/IIIa antagonists.

Current antiplatelet treatment strategy in patients with diabetes mellitus

Patients with diabetes mellitus (DM) have accelerated atherosclerosis with an increased risk for atherothrombotic cardiovascular complications. A state of high platelet reactivity and activation, hypercoagulability (prothrombotic state) and a subdued response to standard antiplatelet agents may explain high rate of adverse cardiovascular events in patients with DM. Several antithrombotic treatment strategies have been developed to control the prothrombotic state in patients with DM: dose modification of commonly used agents; use of potent agents; and addition of a third antithrombotic drug (triple therapy) to commonly prescribed dual antiplatelet therapy of aspirin and a P2Y12 inhibitor. The present review aims to provide an overview of the current knowledge on platelet abnormalities in patients with DM, focusing on the challenges and perspectives of antiplatelet treatment strategies in this population.

Clinical and economic studies of eptifibatide in coronary stenting

Platelet adhesion and aggregation at the site of coronary stenting can have catastrophic clinical and economic consequences. Therefore, effective platelet inhibition is vital during and after percutaneous coronary intervention. Eptifibatide is an intravenous antiplatelet agent that blocks the final common pathway of platelet aggregation and thrombus formation by binding to glycoprotein IIb/IIIa receptors on the surface of platelets. In clinical studies, eptifibatide was associated with a significant reduction of mortality, myocardial infarction, or target vessel revascularization in patients with acute coronary syndrome undergoing percutaneous coronary intervention. However, recent trials conducted in the era of dual antiplatelet therapy and newer anticoagulants failed to demonstrate similar results. The previously seen favorable benefit of eptifibatide was mainly offset by the increased risk of bleeding. Current American College of Cardiology/American Heart Association guidelines recommend its use as an adjunct in high-risk patients who are undergoing percutaneous coronary intervention with traditional anticoagulants (heparin or enoxaparin), who are not otherwise at high risk of bleeding. In patients receiving bivalirudin (a newer safer anticoagulant), routine use of eptifibatide is discouraged except in select situations (eg, angiographic complications). Although older pharmacoeconomic studies favor eptifibatide, in the current era of P2Y12 inhibitors and newer safer anticoagulants, the increased costs associated with bleeding make the routine use of eptifibatide an economically nonviable option. The cost-effectiveness of eptifibatide with the use of strategies that decrease the bleeding risk (eg, transradial access) is unknown. This review provides an overview of key clinical and economic studies of eptifibatide well into the current era of potent antiplatelet agents, novel safer anticoagulants, and contemporary percutaneous coronary intervention.

The integrin adhesome: from genes and proteins to human disease

The adhesive interactions of cells with their environment through the integrin family of transmembrane receptors have key roles in regulating multiple aspects of cellular physiology, including cell proliferation, viability, differentiation and migration. Consequently, failure to establish functional cell adhesions, and thus the assembly of associated cytoplasmic scaffolding and signalling networks, can have severe pathological effects. The roles of specific constituents of integrin-mediated adhesions, which are collectively known as the 'integrin adhesome', in diverse pathological states are becoming clear. Indeed, the prominence of mutations in specific adhesome molecules in various human diseases is now appreciated, and experimental as well as in silico approaches provide insights into the molecular mechanisms underlying these pathological conditions.

Atherosclerosis, platelets and thrombosis in acute ischaemic heart disease

Atherosclerosis is the underlying reason for nearly all causes of coronary artery disease and peripheral arterial disease and many cases of stroke. Atherosclerosis is a systemic inflammatory process characterised by the accumulation of lipids and macrophages/lymphocytes within the intima of large arteries. The deposition of these blood borne materials and the subsequent thickening of the wall often significantly compromise the residual lumen leading to ischaemic events distal to the arterial stenosis. However, these initial fatty streak lesions may also evolve into vulnerable plaques susceptible to rupture or erosion. Plaque disruption initiates both platelet adhesion and aggregation on the exposed vascular surface and the activation of the clotting cascade leading to the so-called atherothrombotic process. Yet, platelets have also been shown to be transporters of regulatory molecules (micro-RNA), to drive the inflammatory response and mediate atherosclerosis progression. Here we discuss our current understanding of the pathophysiological mechanisms involved in atherogenesis - from fatty streaks to complex and vulnerable atheromas - and highlight the molecular machinery used by platelets to regulate the atherogenic process, thrombosis and its clinical implications.

Thrombodynamics of microvascular repairs: effects of antithrombotic therapy on platelets and fibrin

PURPOSE

To evaluate the hypothesis that platelets and fibrin differentially accrue at microvascular anastomoses in arteries versus veins and under different pharmacologic conditions.

METHODS

We evaluated mouse arterial and venous anastomoses with intravital fluorescence imaging, using fluorophore-labeled platelets and anti-fibrin antibodies to measure the extent of thrombus component development in the intraluminal anastomotic site. We evaluated systemic heparin or eptifibatide (platelet aggregation inhibitor) to determine their relative influences on thrombus composition.

RESULTS

Platelets accumulated rapidly in both arterial and venous repairs, and then fell in number after 10 to 30 minutes of reflow. Fibrin had a relatively steady development over 60 minutes in veins, with a more variable increase in arteries. Heparin reduced platelet accumulation in arteries and fibrin development in veins. Eptifibatide reduced platelets in both arteries and veins and had an apparent effect on lowering the amount of fibrin in veins.

CONCLUSIONS

These findings show that platelets have a rapid, transient response, whereas fibrin has a slower, more sustained accrual in both arterial and venous anastomoses. Furthermore, inhibition of either coagulation or platelet aggregation can influence presumably non-targeted components of thrombosis in vascular repairs of both arteries and veins.

CLINICAL RELEVANCE

Preventing replantation failure using antithrombotic therapies requires a better understanding of the effect of each pharmacologic compound on the various aspects of thrombogenesis.

P2Y12 receptor blockade augments glycoprotein IIb-IIIa antagonist inhibition of platelet activation, aggregation, and procoagulant activity

Background

New antiplatelet agents that provide greater, more consistent inhibition of the platelet ADP receptor P2Y₁₂ may be used in combination with glycoprotein (GP) IIb‐IIIa antagonists, but their combined effect on platelet function and procoagulant activity is not well studied. Therefore, the objective of this study was to evaluate the independent and complementary effects of P2Y₁₂ and GPIIb‐IIIa inhibition on platelet function and procoagulant activity.

Methods and Results

Healthy donor blood was treated with the active metabolite of prasugrel (R‐138727 5 μmol/L), GPIIb‐IIIa antagonists (abciximab 3 μg/mL or eptifibatide 0.9 μg/mL), and combinations thereof, exposed to physiologically relevant agonists (collagen and ADP) and then evaluated for markers of platelet activation and procoagulant activity. Significant interactions between R‐138727 and GPIIb‐IIIa antagonists were observed. R‐138727 and the GPIIb‐IIIa antagonists had additive inhibitory effects on collagen‐stimulated platelet aggregation and on the collagen plus ADP–stimulated level of activated platelet surface GPIIb‐IIIa. R‐138727 and abciximab each inhibited collagen plus ADP–stimulated platelet phosphatidylserine expression and prothrombin cleavage, and the combination produced greater inhibition than achieved with abciximab alone. In contrast, eptifibatide did not inhibit, but instead enhanced, collagen plus ADP–stimulated prothrombin cleavage. Addition of R‐138727 reduced prothrombin cleavage in eptifibatide‐treated samples, suggesting a novel mechanism for potential benefit from combined prasugrel and eptifibatide treatment.

Conclusions

The complementary effects of abciximab and R‐138727 on platelet activation, aggregation, and procoagulant activity suggest their combined use may, to a greater degree than with either agent alone, reduce thrombus formation in vivo.

GDF-15 prevents platelet integrin activation and thrombus formation

BACKGROUND

Integrin-mediated platelet function plays an important role in primary hemostasis. Growth-differentiation factor 15 (GDF-15) has been shown to inhibit β(2) -integrin activation in leukocytes.

METHODS

We investigated the effect of GDF-15 on platelet integrin activation in vitro and in different in vivo models of thrombus formation.

RESULTS

GDF-15(-/-) mice showed an accelerated thrombus formation and a reduced survival rate after collagen-induced pulmonary thromboembolism. In reconstitution experiments, recombinant GDF-15 decelerated thrombus formation and prolonged the bleeding time. In vitro experiments demonstrated that GDF-15 pretreated, agonist-stimulated platelets showed decreased binding to fibrinogen in flow chamber assays and reduced activation of β(1) - and β(3) -integrins in flow cytometry experiments. Pretreating human and mouse platelets with GDF-15 reduced platelet aggregation. Mechanistically, GDF-15 prevents agonist-induced Rap1- dependent α(II) (b) β(3) activation by activating PKA. Platelet P-selectin expression and dense granule secretion after stimulation were unaffected by GDF-15, indicating a specific effect of GDF-15 on integrin activation.

CONCLUSION

GDF-15 specifically inhibits platelet integrin activation. These findings may have profound clinical implications for the treatment of hemostatic conditions involving platelets.

Is There Still a Role for Glycoprotein IIb/IIIa Antagonists in Acute Coronary Syndromes?

The role played by glycoprotein (GP) IIb/IIIa inhibitors has continuously evolved from the initial introduction in mid 90 s until the most recent guidelines for treating acute coronary syndromes, and competed with a wider use of ADP inhibitors and novel anticoagulant drugs, to the extent that they stepped down from class I to class II recommendation in the routine setting of acute coronary syndromes. As a consequence, GP IIb/IIIa use was greatly narrowed. The purpose of this review is to define the roles that GP IIb/IIIa inhibitors may still have in acute ischemic settings by explaining why in high risk patients they might be preferable and/or whether they might be added to ADP inhibitors also emphasizing the underlying mechanistic actions. It is concluded that there might be a more extensive use of GP IIb/IIIa inhibitors in patients presenting with acute coronary syndromes, strictly based on the definition for a high risk procedure: complexity, angiographic characteristics and patient's risk profile, regardless whether STEMI or NSTEMI. The positive elements one should appreciate in GP IIb/IIIa inhibitors are: efficacy, rapid onset and reversibility of action, absence of pharmacogenomic variability, pharmacoeconomic considerations and the possibility of intracoronary administration.

Novel antiplatelet agents: ALX-0081, a Nanobody directed towards von Willebrand factor

This manuscript reviews the studies performed with ALX-0081 (INN: caplacizumab), a Nanobody targeting von Willebrand factor, in the context of current antithrombotic therapy in coronary artery disease. ALX-0081 specifically inhibits platelet adhesion to the vessel wall, and may control platelet aggregation and subsequent clot formation without increasing bleeding risk. A substantial number of antithrombotics are aimed at this cascade; however, their generally indiscriminative mode of action can result in a narrow therapeutic window, defined by the risk for bleeding complications, and thrombotic events. Nonclinically, ALX-0081 compared favorably to several antithrombotics. In Phase I studies in healthy subjects and stable angina patients undergoing percutaneous coronary intervention (PCI), ALX-0081 was well tolerated, and effectively inhibited pharmacodynamic markers. Following these results, a phase II study was initiated in high-risk acute coronary syndrome patients undergoing PCI. Based on its mechanism of action, ALX-0081 is also being developed for acquired thrombotic thrombocytopenic purpura.

cDNA cloning of a snake venom metalloproteinase from the eastern diamondback rattlesnake (Crotalus adamanteus), and the expression of its disintegrin domain with anti-platelet effects

A 5' truncated snake venom metalloproteinase was identified from a cDNA library constructed from venom glands of an eastern diamondback rattlesnake (Crotalus adamanteus). The 5'-rapid amplification of cDNA ends (RACE) was used to obtain the 1865 bp full-length cDNA sequence of a snake venom metalloproteinase (CamVMPII). CamVMPII encodes an open reading frame of 488 amino acids, which includes a signal peptide, a pro-domain, a metalloproteinase domain, a spacer, and an RGD-disintegrin domain. The predicted amino acid sequence of CamVMPII showed a 91%, 90%, 83%, and 82% sequence homology to the P-II class enzymes of C. adamanteus metalloproteinase 2, Crotalus atrox CaVMP-II, Gloydius halys agkistin, and Protobothrops jerdonii jerdonitin, respectively. Disintegrins are potent inhibitors of both platelet aggregation and integrin-dependent cell adhesion. Therefore, the disintegrin domain (Cam-dis) of CamVMPII was amplified by PCR, cloned into a pET-43.1a vector, and expressed in Escherichia coli BL21. Affinity purified recombinantly modified Cam-dis (r-Cam-dis) with a yield of 8.5 mg/L culture medium was cleaved from the fusion tags by enterokinase cleavage. r-Cam-dis was further purified by two-step chromatography consisting of HiTrap™ Benzamidine FF column, followed by Talon Metal affinity column with a final yield of 1 mg/L culture. r-Cam-dis was able to inhibit all three processes of platelet thrombus formation including platelet adhesion with an estimated IC(50) of 1 nM, collagen- and ADP-induced platelet aggregation with the estimated IC(50)s of 18 and 6 nM, respectively, and platelet function on clot retraction. It is a potent anti-platelet inhibitor, which should be further investigated for drug discovery to treat stroke patients or patients with thrombotic disorders.

Newer agents in antiplatelet therapy: a review

Antiplatelet therapy remains the mainstay in preventing aberrant platelet activation in pathophysiological conditions such as myocardial infarction, ischemia, and stroke. Although there has been significant advancement in antiplatelet therapeutic approaches, aspirin still remains the gold standard treatment in the clinical setting. Limitations in safety, efficacy, and tolerability have precluded many of the antiplatelet inhibitors from use in patients. Unforeseen incidences of increased bleeding risk and recurrent arterial thrombosis observed in patients have hampered the development of superior next generation antiplatelet therapies. The pharmacokinetic and pharmacodynamic profiles have also limited the effectiveness of a number of antiplatelet inhibitors currently in use due to variability in metabolism, time to onset, and reversibility. A focused effort in the development of newer antiplatelet therapies to address some of these shortcomings has resulted in a significant number of potential antiplatelet drugs which target enzymes (phosphodiesterase, cyclooxygenase), receptors (purinergic, prostaglandins, protease-activated receptors, thromboxane), and glycoproteins (αIIbβ3, GPVI, vWF, GPIb) in the platelet. The validation and search for newer antiplatelet therapeutic approaches proven to be superior to aspirin is still ongoing and should yield a better pharmacodynamic profile with fewer untoward side-effects to what is currently in use today.

Conotoxin engineering: dual pharmacophoric noradrenaline transport inhibitor/integrin binding peptide with improved stability

A dual-pharmacophoric peptide was engineered by grafting the integrin binding RGD motif between the C- and N-termini of a disulfide-rich noradrenaline transporter inhibiting χ-conotoxin resulting in a stable backbone cyclized peptide. The construct maintained two independent biological activities and showed increased plasma stability with no adverse effects observed following administration to rats, highlighting the potential value of pharmacophore grafting into constrained peptide scaffolds.