Effect of low concentrations of prostacyclin on platelet function in vitro

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

BACKGROUND

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSION

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

Prostacyclin Analogues Inhibit Platelet Reactivity, Extracellular Vesicle Release and Thrombus Formation in Patients with Pulmonary Arterial Hypertension

(1) Background: Prostacyclin analogues (epoprostenol, treprostinil, and iloprost) induce vasodilation in pulmonary arterial hypertension (PAH) but also inhibit platelet function. (2) Objectives: We assessed platelet function in PAH patients treated with prostacyclin analogues and not receiving prostacyclin analogues. (3) Methods: Venous blood was collected from 42 patients treated with prostacyclin analogues (49.5 ± 15.9 years, 81% female) and 38 patients not receiving prostacyclin analogues (55.5 ± 15.6 years, 74% female). Platelet reactivity was analyzed by impedance aggregometry using arachidonic acid (AA; 0.5 mM), adenosine diphosphate (ADP; 6.5 µM), and thrombin receptor-activating peptide (TRAP; 32 µM) as agonists. In a subset of patients, concentrations of extracellular vesicles (EVs) from all platelets (CD61⁺), activated platelets (CD61⁺/CD62P⁺), leukocytes (CD45⁺), and endothelial cells (CD146⁺) were analyzed by flow cytometry. Platelet-rich thrombus formation was measured using a whole blood perfusion system. (4) Results: Compared to controls, PAH patients treated with prostacyclin analogues had lower platelet reactivity in response to AA and ADP (p = 0.01 for both), lower concentrations of platelet and leukocyte EVs (p ≤ 0.04), delayed thrombus formation (p ≤ 0.003), and decreased thrombus size (p = 0.008). Epoprostenol did not affect platelet reactivity but decreased the concentrations of platelet and leukocyte EVs (p ≤ 0.04). Treprostinil decreased platelet reactivity in response to AA and ADP (p ≤ 0.02) but had no effect on the concentrations of EVs. All prostacyclin analogues delayed thrombus formation and decreased thrombus size (p ≤ 0.04). (5) Conclusions: PAH patients treated with prostacyclin analogues had impaired platelet reactivity, EV release, and thrombus formation, compared to patients not receiving prostacyclin analogues.

Molecular adsorbent recirculating system and hemostasis in patients at high risk of bleeding: an observational study

Introduction

Liver failure is associated with reduced synthesis of clotting factors, consumptive coagulopathy, and platelet dysfunction. The aim of the study was to evaluate the effects of liver support using a molecular adsorbent recirculating system (MARS) on the coagulation system in patients at high risk of bleeding.

Methods

We studied 61 MARS treatments in 33 patients with acute liver failure (n = 15), acute-on-chronic liver failure (n = 8), sepsis (n = 5), liver graft dysfunction (n = 3), and cholestasis (n = 2). Standard coagulation tests, standard thromboelastography (TEG), and heparinase-modified and abciximab-fab-modified TEG were performed immediately before and 30 minutes after commencement of MARS, and after the end of MARS treatment. Prostaglandin I₂ was administered extracorporeally to all patients; 17 patients additionally received unfractioned heparin.

Results

Three moderate bleeding complications in three patients, requiring three to four units of packed red blood cells, were observed. All were sufficiently managed without interrupting MARS treatment. Although there was a significant decrease in platelet counts (median, 9 G/l; range, -40 to 145 G/l) and fibrinogen concentration (median, 15 mg/dl; range, -119 to 185 mg/dl) with a consecutive increase in thrombin time, the platelet function, as assessed by abciximab-fab-modified TEG, remained stable. MARS did not enhance fibrinolysis.

Conclusion

MARS treatment appears to be well tolerated during marked coagulopathy due to liver failure. Although MARS leads to a further decrease in platelet count and fibrinogen concentration, platelet function, measured as the contribution of the platelets to the clot firmness in TEG, remains stable. According to TEG-based results, MARS does not enhance fibrinolysis.

Thrombelastography/thromboelastometry

The term thrombelastograph (TEG) was used to describe the trace produced from the measurement of the viscoelastic changes associated with fibrin polymerization. Recently the term rotational thromboelastometry has been applied to the output of the ROTEM instrument. Since its first description in 1948, the TEG/ROTEM has been successfully used in the near patient assessment of haemostasis. The greatest use has been the application of TEG-guided transfusion of blood components in hepatic and more widely in cardiac surgery. Recent years have seen a renewed interest in the technology with applications for both pharmaceutical monitoring and patient screening being described. The present review gives a broad overview of the developments and applications related to thrombelastography/thromboelastometry.

Vasopressin During Spinal Anesthesia in a Patient with Primary Pulmonary Hypertension Treated with Intravenous Epoprostenol

Primary pulmonary hypertension (PPH) is a progressive disease with frequent morbidity and mortality, including the risk of cardiac decompensation and death, during general anesthesia. Administration of IV epoprostenol (Flolan) improves symptoms and survival of patients with PPH and thus is an increasingly used long-term treatment for this condition. This therapy is associated with impaired platelet aggregation, which may complicate the perioperative management of patients with PPH. We present a case report of a patient with severe PPH receiving a continuous epoprostenol infusion undergoing skin grafting for a leg ulcer under spinal anesthesia. An IV infusion of vasopressin was given to prevent systemic hypotension resulting from sympathetic blockade while avoiding increases in pulmonary vascular resistance that may have resulted from catecholamine usage.

Inhaled prostacyclin is safe, effective, and affordable in patients with pulmonary hypertension, right heart dysfunction, and refractory hypoxemia after cardiothoracic surgery

BACKGROUND

The purpose of this study was to describe our institutional experience in using inhaled prostacyclin as a selective pulmonary vasodilator in patients with pulmonary hypertension, refractory hypoxemia, and right heart dysfunction after cardiothoracic surgery.

METHODS

Between February 2001 and March 2003, cardiothoracic surgical patients with pulmonary hypertension (mean pulmonary artery pressure >30 mm Hg or systolic pulmonary artery pressure >40 mm Hg), hypoxemia (PaO(2)/fraction of inspired oxygen <150 mm Hg), or right heart dysfunction (central venous pressure >16 mm Hg and cardiac index <2.2 L.min(-1).m(-2)) were prospectively administered inhaled prostacyclin at an initial concentration of 20,000 ng/mL and then weaned per protocol. Hemodynamic variables were measured before the initiation of inhaled prostacyclin, 30 to 60 minutes after initiation, and again 4 to 6 hours later.

RESULTS

One hundred twenty-six patients were enrolled during the study period. At both time points, inhaled prostacyclin significantly decreased the mean pulmonary artery pressure without altering the mean arterial pressure. The average length of time on inhaled prostacyclin was 45.6 hours. There were no adverse events attributable to inhaled prostacyclin. The average cost for inhaled prostacyclin was 150 US dollars per day. Compared with nitric oxide, which costs 3000 US dollars per day, the potential cost savings over this period were 681,686 US dollars.

CONCLUSIONS

Inhaled prostacyclin seems to be a safe and effective pulmonary vasodilator for cardiothoracic surgical patients with pulmonary hypertension, refractory hypoxemia, or right heart dysfunction. Overall, inhaled prostacyclin significantly decreases mean pulmonary artery pressures without altering the mean arterial pressure. Compared with nitric oxide, there is no special equipment required for administration or toxicity monitoring, and the cost savings are substantial.

Randomized controlled trial of aerosolized prostacyclin therapy in children with acute lung injury

OBJECTIVES

To investigate whether aerosolized prostacyclin improves oxygenation in children with acute lung injury.

DESIGN

Double-blind, randomized, and placebo-controlled trial.

SETTING

Pediatric intensive care unit at a university hospital.

PATIENTS

Fourteen children with acute lung injury defined by the criteria of an American-European Consensus Conference.

INTERVENTIONS

Aerosolized prostacyclin (epoprostenol sodium) by stepwise increments of different doses (10, 20, 30, 40, and 50 ng x kg x min) vs. aerosolized normal saline (placebo).

MEASUREMENTS AND MAIN RESULTS

Before the start of the study, and before and after each dose of prostacyclin/placebo, the following variables were measured: arterial blood gases, heart rate, mean arterial blood pressure, and ventilator settings required. Changes in oxygenation were measured by calculation of the oxygenation index (mean airway pressure x 100 x Pao2/Fio2). After treatment with aerosolized prostacyclin, there was a significant 26% (interquartile range, 3%, 35%) improvement in oxygenation index at 30 ng x kg x min compared with placebo (p =.001). The response to prostacyclin was not the same in all children. We saw an improvement of > or = 20% in eight of 14 children (i.e., responders), and the number needed to treat was 1.8 (95% confidence interval, 1.2-3.2). No adverse effects were observed.

CONCLUSIONS

Aerosolized prostacyclin improves oxygenation in children with acute lung injury. Future trials should investigate whether this treatment will positively affect outcome.

Inhaled epoprostenol (prostacyclin) and pulmonary hypertension before cardiac surgery

OBJECTIVE

Pulmonary hypertension is commonly found in patients undergoing valvular surgery and can be worsened by cardiopulmonary bypass. Inhaled epoprostenol (prostacyclin) has been used for the treatment of pulmonary hypertension, but its effects compared with those of placebo on hemodynamics, oxygenation, echocardiographic examination, and platelet function have not been studied during cardiac surgery.

METHODS

Twenty patients with pulmonary hypertension undergoing cardiac surgery were randomized in a double-blind study to receive inhaled epoprostenol (60 microg) or placebo. The inhalation occurred after induction of anesthesia and before surgical incision. The effects on left and right systolic and diastolic cardiac functions evaluated by means of pulmonary artery catheterization and transesophageal echocardiography, as well as oxygenation and platelet aggregation, were studied.

RESULTS

Inhalation of epoprostenol significantly reduced indexed right ventricular stroke work from 10.7 +/- 4.57 g. m. m(-2) to 7.8 +/- 3.94 g. m. m(-2) (P =.003) and systolic pulmonary artery pressure from 48.4 +/- 18 mm Hg to 38.9 +/- 11.9 mm Hg (P =.002). The effect was correlated with the severity of pulmonary hypertension (r = 0.76, P =.01) and was no longer apparent after 25 minutes. There was no significant effect on systemic arterial pressures, left ventricular function, arterial oxygenation, platelet aggregation, and surgical blood loss.

CONCLUSION

Inhaled epoprostenol reduces pulmonary pressure and improves right ventricular stroke work in patients with pulmonary hypertension undergoing cardiac surgery. A dose of 60 microg is hemodynamically safe, and its effect is completely reversed after 25 minutes. We did not observe any evidence of platelet dysfunction or an increase in surgical bleeding after administration of inhaled epoprostenol.

Inhaled prostacyclin (PGI2) is an effective addition to the treatment of pulmonary hypertension and hypoxia in the operating room and intensive care unit

PURPOSE

There is a growing interest in the intraoperative and intensive care use of inhaled epoprostenol (PGI2) for the treatment of pulmonary hypertension (PHT) and hypoxia of cardiac or non-cardiac origin. We report our experience with this form of therapy.

METHODS

A retrospective chart review of all patients who received inhaled PGI2 over a one-year period was undertaken. Demographic, hemodynamic, oxygenation status, mode of administration, side effects, duration of hospital stay, and mortality were noted.

RESULTS

Thirty-five patients, of which 33 (92%) were in the intensive care unit, received inhaled PGI2. Of the 27 patients whose pulmonary artery pressure (PAP) was monitored, a significant decrease in mean PAP from 34.8 +/- 11.8 mmHg to 32.1 +/- 11.8 mmHg was observed within one hour after the start of therapy (P=0.0017). Selective pulmonary vasodilatation occurred in 77.8% of the patients. Thirty-three patients had arterial blood gases before and after therapy. There was an improvement in the PaO2/FIO2 ratio in 88% of these with a 175% improvement on average. The ratio of PaO2/FIO2 improved from 108 +/- 8 to 138 +/- 105 (P=0.001). Six patients (17%) presented hypotension, two had subsequent pneumothorax, one had bronchospasm and in one patient PGI2 inhalation was stopped because of increasing peak pulmonary pressures from the secondary flow coming from the nebulizer. Mortality of the cohort was 54%.

CONCLUSION

Inhaled PGI2 can be useful in the treatment of patients with PHT and severe hypoxia. It can however be associated with systemic side effects.

Use of aerosolized inhaled epoprostenol in the treatment of portopulmonary hypertension

BACKGROUND

Portopulmonary hypertension is a known complication in the liver transplant candidate. Intravenous epoprostenol has been demonstrated to decrease pulmonary artery pressures and possibly remodel right ventricle geometry.

METHODS

In this report, we document the efficacy of inhaled aerosolized epoprostenol in a patient with portopulmonary hypertension. The effect was of rapid onset and offset.

RESULTS

After 10 min of delivery, mean pulmonary artery pressure decreased 26%; cardiac output increased by 22%; pulmonary vascular resistance decreased by 42%; and the transpulmonary gradient decreased by 29%. There were no untoward side effects.

CONCLUSION

The inhaled route of delivery of epoprostenol is potential alternative for the acute therapy of portpulmonary hypertension.

Dose-response to inhaled aerosolized prostacyclin for hypoxemia due to ARDS

STUDY OBJECTIVES

This study was carried out to determine the efficacy of and dose-response relationships to inhaled aerosolized prostacyclin (IAP), when used as a selective pulmonary vasodilator (SPV) in patients with severe hypoxemia due to ARDS.

DESIGN

Unblinded, interventional, prospective clinical study.

SETTING

A general ICU in a university-affiliated, tertiary referral center.

PATIENTS

Nine adult patients with severe ARDS (lung injury score, > or = 2.5).

INTERVENTIONS

All patients received IAP over the dose range 0 to 50 ng/kg/min. The IAP was delivered via a jet nebulizer placed in the ventilator circuit. Dose increments were 10 ng/kg/min every 30 min.

MEASUREMENTS AND RESULTS

Cardiovascular parameters (cardiac index and mean pulmonary and systemic pressures), indexes of oxygenation (PaO(2)/fraction of inspired oxygen [FIO(2)] ratio and alveolar-arterial oxygen partial pressure difference [P(A-a)O(2)]) and shunt fraction were measured or calculated at each dose interval, as were platelet aggregation and systemic levels of prostacyclin metabolite (6-keto prostaglandin F1(alpha)). A generalized linear regression model was used to determine a dose effect of IAP on these parameters. The Wilcoxon rank sum test for related measures was used to compare the effects of various doses of IAP. IAP acted as an SPV, with a statistically significant dose-related improvement in PaO(2)/FIO(2) ratio (p = 0.003) and P(A-a)O(2) (p = 0.01). Systemic prostacyclin metabolite levels increased significantly in response to delivered IAP (p = 0.001). There was no significant dose effect on systemic or pulmonary arterial pressures, or on platelet function, as determined by platelet aggregation in response to challenge with adenosine diphosphate.

CONCLUSIONS

IAP is an efficacious SPV, with marked dose-related improvement in oxygenation and with no demonstrable effect on systemic arterial pressures over the dose range 0 to 50 ng/kg/min. Despite significant systemic levels of prostacyclin metabolite, there was no demonstrable platelet function defect.

Systemic levels of 6-keto-prostaglandin F1 alpha following administration of inhaled aerosolized prostacyclin

A case is described where systemic levels of prostacyclin metabolite were measured during inhaled aerosolized prostacyclin (IAP) therapy for severe hypoxaemia in a patient with the acute respiratory distress syndrome. Comparable levels of prostacyclin metabolite have been associated with a marked platelet aggregation defect in vitro. A platelet aggregation defect was also demonstrated in vivo in this patient. Haemodynamic and gas exchange data during the IAP therapy are described.