Variability of platelet aggregate dispersal with glycoprotein IIb-IIIa antagonists eptifibatide and abciximab

Translating proof-of-concept for platelet slip into improved antithrombotic therapeutic regimens

Platelets are central to thrombosis. Research at the intersection of biological and physical sciences provides proof-of-concept for shear rate-dependent platelet slip at vascular stenosis and near device surfaces. Platelet slip extends the observed biological "slip-bonds" to the boundary of functional gliding without contact. As a result, there is diminished engagement of the coagulation cascade by platelets at these surfaces. Comprehending platelet slip would more precisely direct antithrombotic regimens for different shear environments, including for percutaneous coronary intervention (PCI). In this brief report we promote translation of the proof-of-concept for platelet slip into improved antithrombotic regimens by: (1) reviewing new supporting basic biological science and clinical research for platelet slip; (2) hypothesizing the principal variables that affect platelet slip; (3) applying the consequent construct model in support of-and in some cases to challenge-relevant contemporary guidelines and their foundations (including for urgent, higher-risk PCI); and (4) suggesting future research pathways (both basic and clinical). Should future research demonstrate, explain and control platelet slip, then a paradigm shift for choosing and recommending antithrombotic regimens based on predicted shear rate should follow. Improved clinical outcomes with decreased complications accompanying this paradigm shift for higher-risk PCI would also result in substantive cost savings.

Amplified inhibition of atherosclerotic plaque-induced platelet activation by glenzocimab with dual antiplatelet therapy

BACKGROUND

Aspirin and platelet P2Y12 inhibitors, such as ticagrelor, suboptimally inhibit microvascular thrombosis during ST-elevation myocardial infarction. Glycoprotein (GP) IIb/IIIa inhibitors may further inhibit this but cause excessive bleeding.

OBJECTIVES

We investigated whether combination of glenzocimab, a GPVI inhibitor, with aspirin and ticagrelor provides additional antithrombotic effects, as GPVI has a critical role in atherothrombosis but minimal involvement in hemostasis.

METHODS

We investigated the effects of glenzocimab (monoclonal antibody Fab fragment) using blood from healthy donors and patients with acute coronary syndrome treated with aspirin and ticagrelor. Platelets were stimulated with multiple agonists, including atherosclerotic plaque, from patients undergoing carotid endarterectomy.

RESULTS

Aspirin and ticagrelor partially inhibited atherosclerotic plaque-induced platelet aggregation by 48% compared with control (34 ± 3 vs 65 ± 4 U; P < .001). Plaque-induced platelet aggregation, adhesion, secretion, and activation were critically dependent on GPVI activation. Glenzocimab alone reduced plaque-induced aggregation by 75% compared with control (16 ± 4 vs 65 ± 4 U; P < .001) and by >95% when combined with aspirin and ticagrelor (3 ± 1 vs 65 ± 4 U; P < .001). Glenzocimab reduced platelet aggregation, adhesion, and thrombin generation when added to blood of aspirin- and ticagrelor-treated patients with acute coronary syndrome. Glenzocimab shared several antithrombotic effects with the GPIIb/IIIa inhibitor eptifibatide with less effect on general hemostasis assessed by rotational thromboelastometry. In a murine intravital model of ST-elevation myocardial infarction, genetic depletion of GPVI reduced microvascular thrombosis.

CONCLUSION

Addition of glenzocimab to aspirin and ticagrelor enhances platelet inhibition via multiple mechanisms of atherothrombosis. Compared with a GPIIb/IIIa inhibitor, glenzocimab shares multiple antithrombotic effects, with less inhibition of mechanisms involved in general hemostasis.

Novel function of transglutaminase 2 in extracellular histone-induced acute lung injury

Extracellular histones induce endothelial damage, resulting in lung haemorrhage; however, the underlying mechanism remains unclear. Factor XIII, as a Ca2+-dependent cross-linking enzyme in blood, mediates fibrin deposition. As another isozyme, transglutaminase 2 (TG2) has a catalytic activity distributing in most tissues. Herein, we investigated whether TG2 promotes fibrin deposition and mediates the adhesion of platelets to ECs in histone-induced acute lung injury (ALI). We evaluated the lung histology and the adhesion of platelets to endothelial cells (ECs) after injecting histones to wild-type (WT) C57BL/6J and TG2 knockout (TG2-/-) mice, and administered a TG2 inhibitor (NC9) to WT mice. Pulmonary haemorrhage was more severe in TG2-/- mice than that in WT mice. The area of fibrin deposition and the proportion of CD41+CD31+ cells were lower in TG2-/- mice than in WT mice. Pre-treatment of NC9 decreased the area of fibrin deposition and the proportion of CD41+CD31+ cells in WT mice. These results suggest that TG2 prevents from pulmonary haemorrhage in ALI by promoting the adhesion of platelets to ECs and the fibrin deposition.

Intracoronary versus intravenous glycoprotein IIb/IIIa inhibitors during primary percutaneous coronary intervention in patients with STEMI: a systematic review and meta-analysis

BACKGROUND

Intracoronary (IC) administration of glycoprotein IIb/IIIa inhibitors (GPIs) has been studied as an adjunctive therapy to improve outcomes in patients with ST-segment elevation myocardial infarction (STEMI) undergoing percutaneous coronary intervention. In this systematic review and meta-analysis, we aimed to evaluate the efficacy and safety of IC administration of GPIs compared with those of intravenous (IV) administration in patients with STEMI.

METHODS

We searched the MEDLINE, Embase, and Cochrane CENTRAL databases for relevant studies published before September 21, 2022. In total, 22 randomized controlled trials involving 7,699 patients were included.

RESULTS

The proportions of patients achieving thrombolysis in myocardial infarction grade 3 flow, myocardial blush grade 2/3, and complete ST-segment resolution were significantly higher in the IC group than in the IV group. Major adverse cardiac events (MACE) (RR: 0.54, 95% CI: 0.37-0.80) and heart failure (RR: 0.48, 95% CI: 0.25-0.91) within 1 month were significantly lower in the IC group than in the IV group; however, after 6 months, no difference was observed in MACE risk. Additionally, the risks of death and bleeding did not differ between the two routes of administration.

CONCLUSIONS

When considering adjunctive GPI administration for patients with STEMI, the IC route may offer greater benefits than the IV route in terms of myocardial reperfusion and reduced occurrence of MACE and heart failure within 1 month. Nonetheless, when making decisions for IC administration of GPIs, the absence of a benefit for bleeding risk and difficulty accessing the administration route should be considered.

Tirofiban for Stroke without Large or Medium-Sized Vessel Occlusion

BACKGROUND

The effects of the glycoprotein IIb/IIIa receptor inhibitor tirofiban in patients with acute ischemic stroke but who have no evidence of complete occlusion of large or medium-sized vessels have not been extensively studied.

METHODS

In a multicenter trial in China, we enrolled patients with ischemic stroke without occlusion of large or medium-sized vessels and with a National Institutes of Health Stroke Scale score of 5 or more and at least one moderately to severely weak limb. Eligible patients had any of four clinical presentations: ineligible for thrombolysis or thrombectomy and within 24 hours after the patient was last known to be well; progression of stroke symptoms 24 to 96 hours after onset; early neurologic deterioration after thrombolysis; or thrombolysis with no improvement at 4 to 24 hours. Patients were assigned to receive intravenous tirofiban (plus oral placebo) or oral aspirin (100 mg per day, plus intravenous placebo) for 2 days; all patients then received oral aspirin until day 90. The primary efficacy end point was an excellent outcome, defined as a score of 0 or 1 on the modified Rankin scale (range, 0 [no symptoms] to 6 [death]) at 90 days. Secondary end points included functional independence at 90 days and a quality-of-life score. The primary safety end points were death and symptomatic intracranial hemorrhage.

RESULTS

A total of 606 patients were assigned to the tirofiban group and 571 to the aspirin group. Most patients had small infarctions that were presumed to be atherosclerotic. The percentage of patients with a score of 0 or 1 on the modified Rankin scale at 90 days was 29.1% with tirofiban and 22.2% with aspirin (adjusted risk ratio, 1.26; 95% confidence interval, 1.04 to 1.53, P = 0.02). Results for secondary end points were generally not consistent with the results of the primary analysis. Mortality was similar in the two groups. The incidence of symptomatic intracranial hemorrhage was 1.0% in the tirofiban group and 0% in the aspirin group.

CONCLUSIONS

In this trial involving heterogeneous groups of patients with stroke of recent onset or progression of stroke symptoms and nonoccluded large and medium-sized cerebral vessels, intravenous tirofiban was associated with a greater likelihood of an excellent outcome than low-dose aspirin. Incidences of intracranial hemorrhages were low but slightly higher with tirofiban. (Funded by the National Natural Science Foundation of China; RESCUE BT2 Chinese Clinical Trial Registry number, ChiCTR2000029502.).

Inhibition of Src but not Syk causes weak reversal of GPVI-mediated platelet aggregation measured by light transmission aggregometry

Src tyrosine kinases and spleen tyrosine kinase (Syk) have recently been shown to contribute to sustained platelet aggregation on collagen under arterial shear. In the present study, we have investigated whether Src and Syk are required for aggregation under minimal shear following activation of glycoprotein VI (GPVI) and have extended this to C-type lectin-like receptor-2 (CLEC-2) which signals through the same pathway. Aggregation was induced by the GPVI ligand collagen-related peptide (CRP) and the CLEC-2 ligand rhodocytin and monitored by light transmission aggregometry (LTA). Aggregation and tyrosine phosphorylation by both receptors were sustained for up to 50 min. The addition of inhibitors of Src, Syk or Bruton's tyrosine kinase (Btk) at 150 sec, by which time aggregation was maximal, induced rapid loss of tyrosine phosphorylation of their downstream proteins, but only Src kinase inhibition caused a weak (~10%) reversal in light transmission. A similar effect was observed when the inhibitors were combined with apyrase and indomethacin or glycoprotein IIb-IIIa (GPIIb-IIIa) antagonist, eptifibatide. On the other hand, activation of GPIIb-IIIa by GPVI in a diluted platelet suspension, as measured by binding of fluorescein isothiocyanate-labeled antibody specific for the activated GPIIb-IIIa (FITC-PAC1), was reversed on the addition of Src and Syk inhibitors showing that integrin activation is rapidly reversible in the absence of outside-in signals. The results demonstrate that Src but not Syk and Btk contribute to sustained aggregation as monitored by LTA, possibly as a result of inhibition of outside-in signaling from GPIIb-IIIa to the cytoskeleton through a Syk-independent pathway. This is in contrast to the role of Syk in supporting sustained aggregation on collagen under arterial shear.

Impaired Spontaneous/Endogenous Fibrinolytic Status as New Cardiovascular Risk Factor?: JACC Review Topic of the Week

Endogenous fibrinolysis is a powerful natural defense mechanism against lasting arterial thrombotic occlusion. Recent prospective studies have shown that impaired endogenous fibrinolysis (or hypofibrinolysis) can be detected in a significant number of patients with acute coronary syndrome (ACS) using global assays and is a strong marker of future cardiovascular risk. This novel risk biomarker is independent of traditional cardiovascular risk factors and unaffected by antiplatelet therapy. Most prospective prognostic data have been obtained using a global assay using native whole blood at high shear or plasma turbidimetric assays, which are described herein. Tests of endogenous fibrinolysis could be used to identify patients with ACS who, despite antiplatelet therapy, remain at high cardiovascular risk. This review discusses the impact of currently available medications and those in development that favorably modulate fibrinolytic status and may offer a potential new avenue to improve outcomes in ACS.

Microvascular obstruction in acute myocardial infarction: an old and unsolved mystery

In the setting of acute myocardial infarction, flow restoration in the culprit epicardial coronary artery is not synonymous with efficient reperfusion. Microvascular obstruction occurs in 50% of cases and represents a predictor of a long-term unfavorable outcome. Its prevalence has remained constant in recent years despite various treatment attempts. However, the success of targeted therapies could be mainly a problem of timing. Recent data bring evidence with regard to the role of pre-procedural distal embolization and highlight the relation between distal embolism, microvascular obstruction and intramyocardial inflammation. As a result, early detection of microvascular injury represents the first step in the development of targeted, individualized therapeutic approaches. In this context, the identification of new invasive surrogate parameters for the timely assessment and quantification of microvascular obstruction in the catheterization laboratory has become an important subject of current research. Among these, coronary wedge pressure is the most practical and revealing in the setting of primary percutaneous coronary intervention. It may offer comprehensive details on the mechanisms of microvascular injury and may therefore offer guidance for appropriate treatment selection.

Potentiation of thrombus instability: a contributory mechanism to the effectiveness of antithrombotic medications

The stability of an arterial thrombus, determined by its structure and ability to resist endogenous fibrinolysis, is a major determinant of the extent of infarction that results from coronary or cerebrovascular thrombosis. There is ample evidence from both laboratory and clinical studies to suggest that in addition to inhibiting platelet aggregation, antithrombotic medications have shear-dependent effects, potentiating thrombus fragility and/or enhancing endogenous fibrinolysis. Such shear-dependent effects, potentiating the fragility of the growing thrombus and/or enhancing endogenous thrombolytic activity, likely contribute to the clinical effectiveness of such medications. It is not clear how much these effects relate to the measured inhibition of platelet aggregation in response to specific agonists. These effects are observable only with techniques that subject the growing thrombus to arterial flow and shear conditions. The effects of antithrombotic medications on thrombus stability and ways of assessing this are reviewed herein, and it is proposed that thrombus stability could become a new target for pharmacological intervention.

Intracoronary Eptifibatide During Primary Percutaneous Coronary Intervention in Early Versus Late Presenters with ST Segment Elevation Myocardial Infarction: A Randomized Trial

Introduction

The role of intracoronary (IC) eptifibatide in primary percutaneous coronary intervention (PPCI) for ST segment elevation myocardial infarction (STEMI) and whether time of patient presentation affects this role are unclear. We sought to evaluate the benefit of IC eptifibatide use during primary PCI in early STEMI presenters compared to late STEMI presenters.

Methods

We included 70 patients who presented with STEMI and were eligible for PPCI. On the basis of symptom-to-door time, patients were classified into two arms: early (<3 h, n = 34) vs late (≥3 h, n = 36) presenters. They were then randomized to local IC eptifibatide infusion vs standard care (control group). The primary end point was post-PCI myocardial blush grade (MBG) in the culprit vessel. Other end points included corrected TIMI frame count (cTFC), ST segment resolution (STR) ≥70%, and peak CKMB.

Results

In the early presenters arm, no difference was observed in MBG results ≥2 in the IC eptifibatide and control groups (100% vs 82%; p = 0.23). In the late presenters arm, the eptifibatide subgroup was associated with improved MBG ≥2 (100% vs 50%; p = 0.001). IC eptifibatide in both early and late presenters was associated with less cTFC (early presenters 19 vs. 25.6, p = 0.001; late presenters 20 vs. 31.5, p < 0.001) and less peak CKMB (early presenters 210 vs 260 IU/L, p = 0.006; late presenters 228 vs 318 IU/L, p = 0.005) compared with the control group. No difference existed between both groups in STR index in early and late presenters.

Conclusion

IC eptifibatide might improve the reperfusion markers during PPCI for STEMI patients presenting after 3 h from onset of symptoms. A large randomized study is recommended to ascertain the benefits of IC eptifibatide in late presenters on clinical outcomes.

Antiplatelet activity of flavonoid and coumarin drugs

Polyphenols are used as phlebotonic drugs, but their mechanism of action remains unknown. Since platelet activity and platelet-endothelial cell interactions are involved in the pathogenesis of cardiovascular disease, this work examines whether different flavonoid and coumarin drugs are able to inhibit platelet aggregation. This specific case of coumarins, the antiplatelet effect is not linked with a possible interaction over blood coagulation since this effect only dicoumarols have it. The antiplatelet capacity of polyphenols was assayed using peripheral blood platelets from healthy controls. The distribution of the different platelets subsets was quantified by flow cytometry, using the calcium ionophore as a pro-aggregant. The number of GPIIb/IIIa receptors occupied by the drugs was assayed by flow cytometry using two CD61 surface fluorescein antibodies. All the polyphenols tested inhibited platelet aggregation. A percentage antiplatelet activity of 88.91±7.98% was recorded for naringin, 48.43±8.84% for naringenin, 53.83±7.87% for esculetin, 54.65±6.91% for fraxetin, and 25.75±4.12% for coumarin. Naringin showed significantly greater percentage occupation of GPIIb/IIIa receptors than did naringenin (14.82±0.81% vs. 3.90±0.55%), and esculetin returned significantly higher values than fraxetin and coumarin (12.47±0.97 vs. 7.53±0.49 and 7.90±0.69 respectively). All drugs show important antiplatelet activity. Naringin was the best antiplatelet compound, showing the greatest antiplatelet activity and the highest percentage binding of GPIIb/IIIa receptors. However, any of the compounds used could be used in the prevention of cardiovascular disease.

Signaling via P2Y12 may be critical for early stabilization of platelet aggregates

P2Y(12) receptor antagonism inhibits platelet aggregation by preventing adenosine diphosphate (ADP)-mediated amplification of activation pathways downstream of primary agonists, such as thrombin and collagen. However, the role of ADP signaling in maintaining aggregate stability and the effects of P2Y(12) antagonists on preestablished aggregates in vitro and arterial thrombus in vivo are not well understood. This study evaluated the impact of P2Y(12) signaling on platelet aggregate stability and early thrombotic occlusion using a reversible P2Y(12) antagonist, ticagrelor. There were 2 study objectives: (1) to determine if there was a time-dependent factor on the capacity of a P2Y(12) antagonist to affect human platelet aggregate stability in vitro using light transmission aggregometry and (2) to evaluate the extent of arterial thrombus reversal in a preclinical model upon administration of ticagrelor in vivo. Platelet aggregates were exposed to ticagrelor after ADP or collagen activation, monitored for stability by aggregometry, and visualized by microscopy. Freshly formed ADP- and collagen-induced platelet aggregates were more rapidly dispersed by a P2Y(12) antagonist than drug carrier control at clinically relevant concentrations (P < 0.05). However, stable aggregates were not noticeably affected. A murine arterial thrombosis model was used to evaluate thrombus stability in an in vivo mouse model. Thrombotic occlusion was induced by FeCl(3), followed by a bolus intravenous administration of ticagrelor or vehicle control. Doppler blood flow was monitored before injury and 30 minutes after bolus administration. Arteries were retrieved for inspection for residual thrombus. Early arterial thrombotic occlusion in vivo was partially reversed by ticagrelor administration. Blood flow through the injured artery increased, and thrombus size within the artery decreased (P < 0.05, n = 3). In conclusion, P2Y(12) antagonism disrupts the stability of newly formed platelet aggregates, promoting disaggregation, and reverses thrombotic vascular occlusion. Thus, in addition to activating platelets, signaling via P2Y(12) seems to be required for stabilizing platelet thrombi.

Synergistic effect of signaling from receptors of soluble platelet agonists and outside-in signaling in formation of a stable fibrinogen-integrin αIIbβ3-actin cytoskeleton complex

INTRODUCTION

Thrombus formation in the injured vessel wall is a highly complex process involving various blood-born components that go through specific temporal and spatial changes as observed by intravital videomicroscopy. Platelets bind transiently to the developing thrombus and may either become stably incorporated into or disengage from the thrombus. The aim of the present study was to reveal the processes involved in the formation of a stable thrombus.

METHODS

Platelet-rich plasma and washed platelets were studied by the aggregometer. The aggregate stability was challenged by eptifibatide. Platelet Triton-insoluble fraction was prepared and the actin and αIIb content in the cytoskeleton was analyzed by western blot.

RESULTS

Maximal actin polymerization is achieved 1min after platelet activation while maximal αIIbβ3-actin cytoskeleton association requires 5 to 10min of activation and fibrinogen-mediated platelet-to-platelet bridging. Thus, actin polymerization is dependent on platelet activation and requires neither αIIbβ3 integrin occupation nor platelet aggregation. Formation of a stable aggregate requires platelet activation for more than 1min, complete increase in actin cytoskeleton fraction and partial association of αIIbβ3 with the actin cytoskeleton. However, direct αIIbβ3 activation is not sufficient for cytoskeleton complex formation. Thus, stable αIIbβ3-fibrinogen interaction, representing stable aggregate, is achieved after more than 1min agonist activation, involving inside-out and outside-in signaling but not after direct integrin activation, involving only outside-in signaling.

CONCLUSIONS

Formation of a stable fibrinogen-αIIbβ3-actin cytoskeleton complex is the result of the combined effect of platelet stimulation by soluble agonists, activation of αIIbβ3, fibrinogen binding and platelet-to-platelet bridging.

Antithrombotic effect of Z4A5 on coronary thrombosis in a canine model of acute unstable angina

BACKGROUND AND PURPOSE

The glycoprotein IIb/IIIa receptor is the final common pathway of platelet aggregation, regardless of the agonist, and thus represents an ideal therapeutic target for blocking coronary thrombosis. In this study, the anti-platelet and antithrombotic actions of Z4A5, a new glycoprotein IIb/IIIa receptor inhibitor, were evaluated in a canine model of acute unstable angina.

EXPERIMENTAL APPROACH

Z4A5 was given i.v. as a bolus followed by 60 min of continuous infusion at doses of 30 μg·kg⁻¹ + 1 μg·kg⁻¹·min⁻¹, 30 μg·kg⁻¹ + 5 μg·kg⁻¹·min⁻¹ or 300 μg·kg⁻¹ + 5 μg·kg⁻¹·min⁻¹. Its antithrombotic effect was evaluated in a model of coronary thrombosis, the injured, stenosed left circumflex coronary artery, in which platelet-dependent cyclic flow reductions (CFRs) were induced by vascular compression and constriction to simulate clinical acute unstable angina. Platelet aggregation and coagulation parameters were determined in platelet-rich plasma and platelet poor plasma respectively.

KEY RESULTS

The Z4A5 infusion induced a dose-dependent reduction in CFR frequency, which returned to baseline levels after the termination of the infusion at low doses. At medium dose that inhibited most part of platelet aggregation, it increased tongue bleeding time marginally with no dramatic changes in haemodynamic and coagulation parameters. Furthermore, the inhibition of ADP-induced platelet aggregation and prolonged bleeding time observed during Z4A5 infusion reverted to baseline levels after the termination of the infusion.

CONCLUSIONS AND IMPLICATIONS

Z4A5 is an effective antithrombotic agent for coronary artery thrombosis with a rapid-on and rapid-off pharmacological profile, and could be used as an alternative treatment of coronary artery ischaemic syndromes.

Naringin administration inhibits platelet aggregation and release by reducing blood cholesterol levels and the cytosolic free calcium concentration in hyperlipidemic rabbits

This study investigated the effects of naringin on platelet aggregation and release in hyperlipidemic rabbits, and the underlying mechanisms. The safety of naringin was also investigated. The rabbits were orally administered 60, 30 or 15 mg/kg of naringin once a day for 14 days after being fed a high fat/cholesterol diet for four weeks. Following the two weeks of drug administration, the degree of platelet aggregation induced by arachidonic acid, adenosine diphosphate and collagen was significantly reduced by naringin at certain doses compared with those in the rabbits of the model group (P<0.01). The levels of P-selectin and platelet factor 4 (PF4) also decreased following treatment with naringin compared with those of the model group. Certain doses of naringin significantly reduced the total cholesterol (TC) levels and elevated the ratio of high-density lipoprotein cholesterol to TC compared with those in the model group, and significantly decreased the cytosolic free calcium concentration ([Ca²⁺]_i). No significant difference in the coagulation function was observed between the control and drug-treatment groups. These results indicate that naringin improved platelet aggregation and inhibited the excessive release of P-selectin and PF4 in hyperlipidemic rabbits. This study suggests that the antiplatelet effect of naringin may be due to its ability to regulate the levels of blood cholesterol and [Ca²⁺]_i in platelets. Naringin also did not cause bleeding in the hyperlipidemic rabbits.

Local Intracoronary Eptifibatide versus Mechanical Aspiration in Patients with Acute ST-Elevation Myocardial Infarction

Objectives. We compared local delivery of intracoronary eptifibatide via perfusion catheter to thrombus aspiration in primary PCI. Background. Perfusion catheter increases local concentration of the drugs at the culprit site and prolongs their residency time. Methods. 75 patients with acute STEMI were randomized to three groups: 25 received local intracoronary eptifibatide and verapamil via perfusion catheter; 25 patients were managed by Diver CE thrombectomy device and 25 patients by primary PCI without thrombus aspiration. Primary end point was assessment of postprocedural TIMI flow, MPG, and corrected TIMI frame count (cTFC) in the culprit vessel. Results. Perfusion catheter was superior to thrombus aspiration and conventional PCI as regards MBG (68% versus 36% in Diver CE and 20% in the control arm; P value = 0.002), with shorter cTFC rates than thrombectomy and control groups (20.76 ± 4.44 versus 26.68 ± 8.40 and 28.16 ± 5.96, resp.; P = 0.001). TIMI flow was not different between the 3 groups. Eptifibatide led to less time to peak CK (13.12 hours versus 16.5 and 19.5 hours, respectively, P value = 0.001). Conclusion. Local intracoronary eptifibatide by perfusion catheter reduces thrombus burden with better results in microvascular perfusion assessed by cTFC and MBG compared to aspiration device or conventional PCI.

Rapid purification of a new P-I class metalloproteinase from Bothrops moojeni venom with antiplatelet activity

The present study aimed to evaluate the proteolytic and biological activities of a new metalloproteinase from B. moojeni venom. The purification of BmooMPα-II was carried out through two chromatographic steps (ion-exchange and affinity). BmooMPα-II is a monomeric protein with an apparent molecular mass of 22.5 kDa on SDS-PAGE 14% under nonreducing conditions. The N-terminal sequence (FSPRYIELVVVADHGMFTKYKSNLN) revealed homology with other snake venom metalloproteinases, mainly among P-I class. BmooMPα-II cleaves Aα-chain of fibrinogen followed by Bβ-chain, and does not show any effect on the γ-chain. Its optimum temperature and pH for the fibrinogenolytic activity were 30–50°C and pH 8, respectively. The inhibitory effects of EDTA and 1,10-phenantroline on the fibrinogenolytic activity suggest that BmooMPα-II is a metalloproteinase. This proteinase was devoid of haemorrhagic, coagulant, or anticoagulant activities. BmooMPα-II caused morphological alterations in liver, lung, kidney, and muscle of Swiss mice. The enzymatically active protein yet inhibited collagen, ADP, and ristocetin-induced platelet aggregation in a concentration-dependent manner. Our results suggest that BmooMPα-II contributes to the toxic effect of the envenomation and that more investigations to elucidate the mechanisms of inhibition of platelet aggregation may contribute to the studies of snake venom on thrombotic disorders.

Purification and characterization of BmooAi: a new toxin from Bothrops moojeni snake venom that inhibits platelet aggregation

In this paper, we describe the purification/characterization of BmooAi, a new toxin from Bothrops moojeni that inhibits platelet aggregation. The purification of BmooAi was carried out through three chromatographic steps (ion-exchange on a DEAE-Sephacel column, molecular exclusion on a Sephadex G-75 column, and reverse-phase HPLC chromatography on a C2/C18 column). BmooAi was homogeneous by SDS-PAGE and shown to be a single-chain protein of 15,000 Da. BmooAi was analysed by MALDI-TOF Spectrometry and revealed two major components with molecular masses 7824.4 and 7409.2 as well as a trace of protein with a molecular mass of 15,237.4 Da. Sequencing of BmooAi by Edman degradation showed two amino acid sequences: IRDFDPLTNAPENTA and ETEEGAEEGTQ, which revealed no homology to any known toxin from snake venom. BmooAi showed a rather specific inhibitory effect on platelet aggregation induced by collagen, adenosine diphosphate, or epinephrine in human platelet-rich plasma in a dose-dependent manner, whereas it had little or no effect on platelet aggregation induced by ristocetin. The effect on platelet aggregation induced by BmooAi remained active even when heated to 100°C. BmooAi could be of medical interest as a new tool for the development of novel therapeutic agents for the prevention and treatment of thrombotic disorders.

Elevating local concentrations of GPIIb-IIIa antagonists counteracts platelet thrombus stability

Glycoprotein IIb-IIIa (GPIIb-IIIa) antagonists have the capacity to destabilize coronary thrombi and restore vessel patency. Antagonist concentration and residence time, which can be increased by local intracoronary (LIC) administration, and thrombus age may be key factors that influence thrombus stability. Light transmission aggregometry was used to examine the effects of exposing human platelet aggregates to extremely high local levels of GPIIb-IIIa antagonists versus conventional therapeutic levels in vitro. Freshly-formed or aged platelet aggregates were subjected to GPIIb-IIIa antagonists (abciximab, eptifibatide) or direct thrombin inhibitor bivalirudin at concentrations simulating either conventional intravenous (IV) or LIC administration. The degree of antagonist-induced disaggregation was significantly higher using elevated (LIC) doses versus conventional (IV) doses (60.1 % vs. 7.4 % for abciximab, 41.6 % or 45.3 % vs. 17.6 % for eptifibatide, p < 0.01). Bivalirudin did not promote disaggregation. Microscopy confirmed noticeably smaller, more dispersed aggregates for antagonist LIC treatments. Dosing at LIC levels also induced more disaggregation than IV levels when aggregates were aged for 30 min prior to exposure. An in vitro perfusion model was used to simulate the fluid dynamics of IV or LIC administration of abciximab using a microporous local drug delivery balloon catheter such as the Atrium ClearWay™ RX. The perfusion model resulted in more rapid thrombus clearance with LIC dosing levels compared to IV. In summary, boosting the concentration of GPIIb-IIIa antagonists enhances dispersal of human platelet aggregates in vitro. These data provide a foundation for investigating increased local concentrations of GPIIb-IIIa antagonists in patients, as with LIC administration.

Construction and characterization of a novel chimeric antibody c3C7 specific for the integrin αIIbβ3 complex

A murine monoclonal antibody (mAb) 3C7 against integrin αIIbβ3 was previously obtained as a potential antithrombotic agent in our laboratory. The epitope of 3C7 is a specific conformation of the αIIbβ3 complex, but not either of the two subunits, which makes it different from abciximab, a supplementary antibody drug used in percutaneous coronary intervention which has a cross-reaction with other integrins sharing the β3 subunit. To reduce the human anti-mouse antibody reactions of 3C7, the variable regions of this antibody were cloned and fused with the constant counterparts of human IgG1. Two vectors of light and heavy chains were constructed and co-transfected into CHO-dhfr(-) cells. The chimeric antibody c3C7 was purified and the properties of c3C7 were compared with 3C7. Identical to its parent antibody 3C7, c3C7 binds to the αIIbβ3 complex, but not to either of the subunits. The K(d) value of c3C7 was in the same order of magnitude as 3C7 (1.570 ± 0.326 vs 0.780 ± 0.182 nmol/L). Human platelet aggregation induced by adenosine diphosphate was effectively inhibited by c3C7 in a dose-dependent manner. In conclusion, after the modification, c3C7 retained the properties of its parent mAb with no loss of its biological activity. Therefore, c3C7 has the potential to become a novel agent for the treatment of thrombosis.

Intracoronary glycoprotein IIb/IIIa inhibitor infusion via a perfusion coronary catheter to decrease thrombus burden: results from the ClearWay™ Multicenter Registry

OBJECTIVES

This multicenter registry aimed to assess the ClearWay™ (CW) perfusion catheter in reduction of thrombus burden and improvement of the coronary flow during percutaneous coronary intervention (PCI).

BACKGROUND

The presence or development of thrombus during PCI is associated with poor prognosis.

METHODS

The utility of the CW perfusion catheter was assessed in patients who presented with intracoronary thrombus and were subjected to PCI. Data were collected by online survey from 15 US sites. Angiographic assessment of the coronary thrombus burden and the coronary flow after intracoronary infusion of glycoprotein (GP) IIb/IIIa inhibitors via the CW catheter was evaluated at baseline, immediately after infusion, and at the end of the procedure. The cohort included 102 patients; 71.6% presented with ST-elevation myocardial infarction (MI), 21.6% with non-ST-elevation MI, 5.9% with stable angina pectoris, and 2.9% with silent ischemia. The mean cohort age was 59.9±14.5years and comprised mostly of men (72.5%).

RESULTS

GP IIb/IIIa inhibitors were infused via the CW catheter on average 1.1±0.3 times, with a mean pressure of 4.2±2.7atm and a mean infusion time of 55±55s. Following the infusion, Thrombolysis In Myocardial Infarction (TIMI) flow improved by 1° in 71 patients (69.6%) and by 2° in 51 patients (50%), while visible thrombus was reduced by 52% (p<0.001). In the final angiogram, TIMI flow was restored in 90.2% and clearance of a visible thrombus was obtained in 91.8% of the lesions.

CONCLUSION

Intracoronary infusion of GP IIb/IIIa inhibitors via the perfusion CW catheter is associated with significant reduction in thrombus burden and with improvement of the coronary flow in patients presenting or developing thrombus burden during PCI.

Microvascular effect of intracoronary eptifibatide in acute myocardial infarction

OBJECTIVES

In this prospective, randomized trial in patients with acute myocardial infarction (AMI) admitted for primary percutaneous coronary intervention (PPCI), loaded with 600 mg clopidogrel, we hypothesized that eptifibatide administered downstream of the coronary occlusion leads to a lower degree of microvascular obstruction compared with no additional eptifibatide.

METHODS

Fifty patients with AMI, loaded with 600 mg of clopidogrel at the first hospital contact, with occlusion of the left anterior descending artery (LAD), were randomized to an eptifibatide group (EG) or a control group (CG). In both groups, stenting was performed after thrombus aspiration. Microvascular reperfusion was assessed by angiography, electrocardiography, and transthoracic Doppler ultrasonography of the LAD.

RESULTS

TIMI myocardial perfusion grade 2-3 was not different between the EG (72%) and the CG (84%) (p = 0.31). ST segment resolution >70% was similarly detected in both groups (32 vs. 40%; p = 0.56). The mean diastolic deceleration time did not differ significantly between the CG (856.36 ± 397.88 ms) and the EG (935.72 ± 252.22 ms) (p = 0.41). Multivariate logistic regression revealed no significant influence of the treatment with eptifibatide on ST segment resolution (OR 0.47; 95% CI 0.11-2.10, p = 0.32), TIMI myocardial perfusion (OR 0.52; 95% CI 0.10-2.59, p = 0.42), and diastolic deceleration time (OR 0.21; 95% CI 0.03-1.51, p = 0.12).

CONCLUSIONS

In AMI patients loaded with 600 mg of clopidogrel undergoing PPCI, intracoronary administration of eptifibatide does not clearly improve microvascular obstruction.

Antiplatelet effects of qishen yiqi dropping pill in platelets aggregation in hyperlipidemic rabbits

We investigated the effects of Qishen Yiqi Dropping Pill (QSYQ) on platelets aggregation and its possible mechanisms. Hyperlipidemic model in rabbits was produced by a high fat/cholesterol diet for 6 weeks, the therapeutic effect of QSYQ with 2.0 g/kg, 1.0 g/kg, and 0.5 g/kg was observed. Fourteen days after drug treatment, platelet aggregation induced by adenosine diphosphate (ADP), arachidonic acid (AA), and collagen (COLL) was significantly reduced in rabbits of model group. Moreover, β-thromboglobulin (β-TG) level decreased obviously but no significant change in P-selectin and platelet factor 4 (PF4) level, while QSYQ significantly decreased the ratio of thromboxane B2 (TXB(2)) to 6-keto-prostaglandin F(1α) (6-Keto-PGF(1α)) and increased cyclic adenosine monophosphate (cAMP) level in rabbits. In summary, QSYQ can improve platelets aggregation and inhibit the over-release of β-TG in hyperlipidemic rabbits; and the increased cAMP level may be involved in this process. These results suggest that the antiplatelet aggregation effect of QSYQ may be due to its ability to increase cAMP level for improving cAMP metabolism.

Ent-16β,17-dihydroxy-kauran-19-oic acid, a kaurane diterpene acid from Siegesbeckia pubescens, presents antiplatelet and antithrombotic effects in rats

The antiplatelet and antithrombotic effects of ent-16β,17-dihydroxy-kauran-19-oic acid (DDKA) isolated from Siegesbeckia pubescens were investigated with different methods both in vitro and in vivo. We tested the antithrombotic activity of DDKA in arterio-venous shunt model. The effects of DDKA on adenosine diphosphate (ADP)-, Thrombin-, Arachidonic acid-induced rat platelets aggregation were tested in vitro. We also assessed its bleeding side effect by measuring coagulation parameters after intravenous administration for 5 days and investigated the potential mechanisms underlying such activities. In vivo, DDKA significantly reduced thrombus weight in the model of arterio-venous shunt. Meanwhile, DDKA increased plasma cAMP level determined by radioimmunoassay in the same model. Notably, DDKA prolonged PT and APTT in rats after intravenous administration DDKA for successive 5 days. In vitro, pretreatment with DDKA on washed rat platelets significantly inhibited various agonists stimulated platelet aggregation and caused an increase in cAMP level in platelets activated by ADP. These findings support our hypothesis that DDKA possesses antiplatelet and antithrombotic activities. The mechanisms underlying such activities may involve the anticoagulatory effect and cAMP induction.

Efficacy and safety of abciximab in diabetic patients who underwent percutaneous coronary intervention with thienopyridines loading: a meta-analysis

BACKGROUND

It has been controversial whether abciximab offered additional benefits for diabetic patients who underwent percutaneous coronary intervention (PCI) with thienopyridines loading.

METHODS

MEDLINE, EMBASE, the Cochrane library clinical trials registry, ISI Science Citation Index, ISI Web of Knowledge and China National Knowledge Infrastructure (CNKI) were searched, supplemented with manual-screening for relevant publications. Quantitative meta-analyses were performed to assess differences between abciximab groups and controls with respect to post-PCI risk of major cardiac events (MACEs), angiographic restenosis and bleeding complications.

RESULTS

9 trials were identified, involving 2,607 diabetic patients receiving PCI for coronary artery diseases. Among those patients who underwent elective PCI or primary PCI, pooling results showed that abciximab did not significantly reduce risks of MACEs (for elective-PCI patients: RR(1-month): 0.93, 95% CI: 0.60-1.44; RR(1-year): 0.95, 95% CI: 0.81-1.11; for primary-PCI patients: RR(1-month): 1.05, 95% CI: 0.70-1.57; RR(1-year): 0.98, 95% CI: 0.80-1.21), nor all-cause mortality, re-infarction and angiographic restenosis in either group. The only beneficial effect by abciximab appeared to be a decrease 1-year TLR (target lesion revascularization) risk in elective-PCI patients (RR1-year: 0.83, 95% CI: 0.70-0.99). Moreover, occurrence of minor bleeding complications increased in elective-PCI patients treated with abciximab (RR: 2.94, 95% CI: 1.68-5.13, P<0.001), whereas major bleedings rate was similar (RR: 0.83, 95% CI: 0.27-2.57).

CONCLUSIONS

Concomitant dosing of abciximab and thienopyridines provides no additional benefit among diabetic patients who underwent PCI; this conclusion, though, needs further confirmation in larger studies.

Intracoronary versus intravenous bolus abciximab application in patients with ST-elevation myocardial infarction undergoing primary percutaneous coronary intervention: 6-month effects on infarct size and left ventricular function. The randomised Leipzig Immediate PercutaneouS Coronary Intervention Abciximab i.v. versus i.c. in ST-Elevation Myocardial Infarction Trial (LIPSIAbciximab-STEMI)

BACKGROUND

Administration of abciximab during primary percutaneous coronary intervention (PCI) reduces major adverse cardiac events (MACE) in patients with ST-elevation myocardial infarction (STEMI). Intracoronary (IC) abciximab bolus application during PCI results in high local drug concentration, improved perfusion, reduction of infarct size, and less microvascular obstruction early after infarction. Aim of this study was to investigate whether the early benefits of an IC abciximab administration in STEMI patients undergoing PCI are sustained at 6 months.

METHODS

We performed 6-month follow-up of 154 STEMI patients undergoing PCI, who were randomised to either IC (n = 77) or intravenous (IV) (n = 77) bolus abciximab administration with subsequent 12-h intravenous infusion. The primary endpoint was infarct size at 6-month follow-up as assessed by delayed enhancement magnetic resonance imaging. Clinical end points were MACEs within 6 months after infarction.

RESULTS

The median infarct size after 6 months was significantly reduced in the IC abciximab group (16.7 vs. 24.1%, p = 0.002). A significant recovery of LV function was only observed in the IC abciximab group (p < 0.001), and IC abciximab group patients had significantly less adverse remodelling as compared to standard IV abciximab treatment (p = 0.03). These beneficial effects also translated into a strong trend towards a reduced MACE rate in the IC abciximab group at 6-month follow-up (10 vs. 21%, p = 0.07).

CONCLUSIONS

Intracoronary abciximab application in STEMI patients undergoing PCI is superior to standard IV treatment with respect to infarct size, recovery of LV function and reverse remodelling 6 months after infarction.

Intracoronary Eptifibatide Bolus Administration During Percutaneous Coronary Revascularization for Acute Coronary Syndromes With Evaluation of Platelet Glycoprotein IIb/IIIa Receptor Occupancy and Platelet Function

Background— Eptifibatide reduces major adverse cardiac events in patients with acute coronary syndromes undergoing percutaneous coronary intervention (PCI). Intracoronary bolus administration of eptifibatide may result in higher levels of platelet glycoprotein IIb/IIIa receptor occupancy in the local coronary bed, disaggregate thrombus in the epicardial artery and microvasculature, and thereby improve coronary flow.

Methods and Results— Patients undergoing PCI for an acute coronary syndrome were randomized to either intracoronary or intravenous bolus administration of eptifibatide. The primary end point was the local glycoprotein IIb/IIIa receptor occupancy measured in the coronary sinus. There were no angiographic, electrophysiological, or other adverse findings attributable to intracoronary eptifibatide. Platelet glycoprotein IIb/IIIa receptor occupancy was significantly greater with intracoronary versus intravenous administration: first bolus, 94±9% versus 51±15% ( P <0.001); and second bolus, 99±2% versus 91±4% ( P =0.001), respectively. Microvascular perfusion was significantly improved as measured by the corrected thrombolysis in myocardial infarction frame count (cTFC) with intracoronary versus intravenous administration: pre-PCI, 36 (median) (25th and 75th percentiles, 16 and 64) versus 31 (25th and 75th percentiles, 23 and 45; P =0.8); and post-PCI, 18 (25th and 75th percentiles, 10 and 22) versus 25 (25th and 75th percentiles, 22 and 35; P =0.007), respectively. The only multivariate predictor associated with a post-PCI cTFC rank score was the first bolus glycoprotein IIb/IIIa receptor occupancy ( P <0.001).

Conclusions— Intracoronary bolus administration of eptifibatide during PCI in patients with acute coronary syndromes results in higher local platelet glycoprotein IIb/IIIa receptor occupancy, which is associated with improved microvascular perfusion demonstrated by an improved cTFC.