Pharmacologic platelet anesthesia by glycoprotein IIb/IIIa complex antagonist and argatroban during in vitro extracorporeal circulation

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

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

Preparation and characterization of a thrombin inhibitor grafted polyethersulfone blending membrane with improved antithrombotic property

A thrombin inhibitor grafted polyethersulfone membrane with improved antithrombotic property.

The effect of a polyurethane coating incorporating both a thrombin inhibitor and nitric oxide on hemocompatibility in extracorporeal circulation

Nitric oxide (NO) releasing (NORel) materials have been extensively investigated to create localized increases in NO concentration by the proton driven diazeniumdiolate-containing polymer coatings and demonstrated to improve extracorporeal circulation (ECC) hemocompatibility. In this work, the NORel polymeric coating composed of a diazeniumdiolated dibutylhexanediamine (DBHD-N2O2)-containing hydrophobic Elast-eon™ (E2As) polyurethane was combined with a direct thrombin inhibitor, argatroban (AG), and evaluated in a 4 h rabbit thrombogenicity model without systemic anticoagulation. In addition, the immobilizing of argatroban to E2As polymer was achieved by either a polyethylene glycol-containing (PEGDI) or hexane methylene (HMDI) diisocyanate linker. The combined polymer film was coated on the inner walls of ECC circuits to yield significantly reduced ECC thrombus formation compared to argatroban alone ECC control after 4 h blood exposure (0.6 ± 0.1 AG/HMDI/NORel vs 1.7 ± 0.2 cm(2) AG/HMDI control). Platelet count (2.8 ± 0.3 AG/HMDI/NORel vs 1.9 ± 0.1 × 10(8)/ml AG/HMDI control) and plasma fibrinogen levels were preserved after 4 h blood exposure with both the NORel/argatroban combination and the AG/HMDI control group compared to baseline. Platelet function as measured by aggregometry remained near normal in both the AG/HMDI/NORel (63 ± 5%) and AG/HMDI control (58 ± 7%) groups after 3 h compared to baseline (77 ± 1%). Platelet P-selectin mean fluorescence intensity (MFI) as measured by flow cytometry also remained near baseline levels after 4 h on ECC to ex vivo collagen stimulation (16 ± 3 AG/HMDI/NORel vs 11 ± 2 MFI baseline). These results suggest that the combined AG/HMDI/NORel polymer coating preserves platelets in blood exposure to ECCs to a better degree than AG/PEGDI/NORel, NORel alone or AG alone. These combined antithrombin, NO-mediated antiplatelet effects were shown to improve thromboresistance of the AG/HMDI/NORel polymer-coated ECCs and move potential nonthrombogenic polymers closer to mimicking vascular endothelium.

Does tirofiban prevent platelet loss in patients after cardiogenic shock during continuous renal replacement therapy?

Link and colleagues present a pilot study investigating platelet function and platelet numbers in patients with cardiogenic shock and acute kidney failure undergoing continuous venovenous haemodialysis. Their data indicate a significantly reduced platelet loss with combined therapy of unfractionated heparin plus tirofiban, the glycoprotein IIb/IIIa antagonist, compared with unfractionated heparin therapy alone. Owing to the small sample size, however, the potential impact of additional treatment variables (antiplatelet agents, intraaortic counterpulsation) could not be clarified. A substantially larger, adequately powered study is therefore called for to establish the potential clinical relevance of these findings.

Platelet anaesthesia during extracorporeal circulation: differential effects of GP IIb/IIIa blockers on platelet activation marker P-selectin expression at hypothermia

INTRODUCTION

Blood contact with artificial surfaces of extracorporeal circulation (ECC) and hypothermia as applied in cardiac surgery cause platelet dysfunction possibly followed by bleeding complications. "Platelet anaesthesia" is a pharmacological strategy to protect platelets against ECC-induced damage using a GP IIb/IIIa blocker, which should be short acting to achieve maximal therapy control thereby avoiding post-ECC haemorrhage. However, GP IIb/IIIa blockers can paradoxically induce platelet activation, which may limit their efficiency as anti-platelet drugs. This in-vitro study investigated potentially platelet-activating effects of short-acting GP IIb/IIIa blockers during normothermic and hypothermic ECC.

MATERIALS AND METHODS

Control (untreated) and treated (using either FK633 [half-life: 0.52 h], tirofiban [half-life: 1.5-2 h], or eptifibatide [half-life: 1.5 h]) heparinized blood was circulated in an ECC-model at normothermia (37 degrees C) and hypothermia (18 degrees C). Percentages of platelet aggregates and P-selectin-expressing (activated) platelets, platelet-counts and Thrombin-Antithrombin (TAT) complex formation were determined before (baseline) and after ECC. Statistical analysis was performed using multifactorial ANOVA after log-transforming the data.

RESULTS

GP IIb/IIIa blockade inhibited ECC-induced platelet aggregation and platelet loss and decreased P-selectin expression at normothermia. During hypothermic ECC P-selectin was decreased by tirofiban but augmented by FK633 and eptifibatide. TAT formation was only decreased by FK633.

CONCLUSIONS

Especially regarding its ultra-short half-life FK633 has the best properties for platelet protection during normothermic ECC. However, at hypothermia FK633 and eptifibatide induce platelet activation. In relation with "platelet anaesthesia" possible hypothermia-associated prothrombotic side effects of GP IIb/IIIa blockers should be considered.

Concentration-dependent effect of abciximab on platelets and neutrophils in a model of cardiopulmonary bypass

Abciximab is a GPIIb/IIIa antagonist used in percutaneous coronary interventions to avoid platelet activation, thrombosis and inflammation. We investigated whether abciximab influenced platelet activation and platelet interaction with neutrophils and polyvinyl chloride (PVC) in a cardiopulmonary bypass (CPB) model. Isolated platelets, preincubated with and without 0.1-20 μg/mL of abciximab, were resuspended with neutrophils in plasma and recirculated by a roller pump. Platelet, but not neutrophil adhesion to PVC was inhibited by abciximab. Only high doses of abciximab reduced platelet aggregation size, but simultaneously increased platelet-neutrophil aggregation. Abciximab had no effect on platelet CD62P expression or degranulation, but platelet activation on platelet-neutrophil aggregates increased with high doses. Only low doses inhibited neutrophil degranulation. The concentration-dependent effect of abciximab on platelet-neutrophil interaction reduces its usefulness and stresses the dependency on experimental design in the evaluation of abciximab. Our study does not support the use of abciximab alone in CPB. However, incorporation of surface-coating the biomaterial with abciximab may be an interesting option.

The effect of intraportal prostaglandin E1 on adhesion molecule expression, inflammatory modulator function, and histology in canine hepatic ischemia/reperfusion injury

BACKGROUND

Prostaglandin E1 (PGE1) is known to protect the liver from I/R, however, the mechanism of cytoprotection is not well understood. This study investigates the effect of intraportal infusion of PGE1 in a warm liver ischemia/reperfusion (I/R) model on cytokines, adhesion molecules and liver structure.

MATERIALS AND METHODS

Twenty dogs underwent laparotomy under general anesthesia. PGE1 (0.02 microg\kg\min) was perfused through the portal vein in the PGE1 group (n = 10), or a similar volume of Ringer's solution in the control group (n = 10) for 15 min. Liver ischemia was induced by hepatic artery and portal vein occlusion and PGE1 was infused via the portal vein for 60 min. The occlusion was released and PGE1 infusion recommenced for 30 min. Blood and liver biopsies were sampled at baseline, 60 min ischemia, and 30 min reperfusion and assessed for transaminases, cytokines, adhesion molecules, and electron microscopy.

RESULTS

PGE1 infusion significantly reduced transaminases TNF-alpha, sICAM-1, sP-selectin, and sE-selectin on ischemia and reperfusion. PGE1 reduced hepatocytic degeneration, portal and central ICAM-1 expression, central and sinusoidal VCAM-1 expression, portal and central P-selectin expression, and portal and sinusoidal E-selectin expression on reperfusion.

CONCLUSION

Intraportal PGE1 infusion reduced I/R injury and was associated with down-regulation of ICAM-1, VCAM-1, P-selectin, and E-selectin on reperfusion.

Tissue factor upregulation drives a thrombosis-inflammation circuit in relation to cardiovascular complications

The extrinsic coagulation is recognized as an 'inducible' signalling cascade resulting from tissue factor (TF) upregulation by exposure to clotting zymogen FVII upon inflammation or tissue injury. Following the substantial initiation, an array of proteolytic activation generates mediating signals (active serine proteases: FVIIa, FXa and FIIa) that lead to hypercoagulation with fibrin overproduction manifesting thrombosis. In addition, TF upregulation plays a central role in driving a thrombosis-inflammation circuit. Coagulant mediators (FVIIa, FXa and FIIa) and endproduct (fibrin) are proinflammatory, eliciting tissue necrosis factor, interleukins, adhesion molecules and many other intracellular signals in different cell types. Such resulting inflammation could ensure 'fibrin' thrombosis via feedback upregulation of TF. Alternatively, the resulting inflammation triggers platelet/leukocyte/polymononuclear cell activation thus contributing to 'cellular' thrombosis. TF is very vulnerable to upregulation resulting in hypercoagulability and subsequent thrombosis and inflammation, either of which presents cardiovascular risks. The prevention and intervention of TF hypercoagulability are of importance in cardioprotection. Blockade of inflammation reception and its intracellular signalling prevents TF expression from upregulation. Natural (activated protein C, tissue factor pathway inhibitor, or antithrombin III) or pharmacological anticoagulants readily offset the extrinsic hypercoagulation mainly through FVIIa, FXa or FIIa inhibition. Therefore, anticoagulants turn off the thrombosis-inflammation circuit, offering not only antithrombotic but anti-inflammatory significance in the prevention of cardiovascular complications.

Platelet Preservation With a Glycoprotein IIb/IIIa Inhibitor in a Porcine Cardiopulmonary Bypass Model

BACKGROUND

We tested whether administration of FK633, a short-acting glycoprotein IIb/IIIa inhibitor, before median sternotomy and cardiopulmonary bypass was able to interrupt the platelet activation loop and thereby preserve platelet number and function.

METHODS

This study investigated 16 pigs that underwent median sternotomy and 120 minutes of normothermic cardiopulmonary bypass (100 mL/kg) adding pericardial blood to the perfusate. FK633 was administered with heparin to one group (group F, n = 8), whereas only heparin was administered to the control group (group C, n = 8). Blood samples were obtained at several times, and complete blood count, platelet aggregation to adenosine diphosphate, thrombin-antithrombin complex, and bradykinin were evaluated. P-selectin expression and fibrinogen binding on platelet surfaces were measured by flow cytometry. Template bleeding times were measured before and after cardiopulmonary bypass. Chest tube drainage and hematocrit were determined at 2 and 6 hours after cardiopulmonary bypass.

RESULTS

In group F, platelet counts were preserved from 90 minutes of cardiopulmonary bypass. Platelet aggregation was inhibited at the beginning of cardiopulmonary bypass and showed no change at wound closure, and bleeding times were shortened at 2 hours after cardiopulmonary bypass. There were significant reductions in hematocrit of drainage. Flow cytometry showed no changes in P-selectin expression and fibrinogen binding in group F, whereas P-selectin expression and fibrinogen binding were elevated in group C.

CONCLUSIONS

Platelet inhibition with FK633 before invasive surgical procedure preserved platelet counts during and after cardiopulmonary bypass, and produced normal or near-normal bleeding times in the immediate postoperative period.