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

Tirofiban potentiates agonist-induced platelet activation and degranulation, despite effectively inhibiting aggregation

We aimed to investigate the effects of integrin αIIbβ3 inhibitor tirofiban on hallmarks of platelet activation, degranulation, and aggregation during its use to analyze activated but non-complexed platelets via flow cytometry. To do so, we used washed platelets from healthy human donors. We combined aggregometry, an assay of platelet functionality, with flow cytometry and ELISA to detect and correlate, respectively, platelet aggregation, activation, and granule release. While tirofiban effectively inhibited agonist-induced platelet aggregation (thrombin receptor-activating peptide 6 (TRAP), convulxin (CVX), U46619 and IV.3), the surface expression of P-selectin and CD63 and granule release of RANTES were significantly increased, indicating that tirofiban enhances degranulation, uncoupled from aggregation. The results show that tirofiban alters the activation phenotype of platelets, something that should be considered when using tirofiban to enable flow cytometric analysis of activated but unaggregated platelet suspensions.

In Vitro Thrombogenicity Testing of Biomaterials

The short- and long-term thrombogenicity of implant materials is still unpredictable, which is a significant challenge for the treatment of cardiovascular diseases. A knowledge-based approach for implementing biofunctions in materials requires a detailed understanding of the medical device in the biological system. In particular, the interplay between material and blood components/cells as well as standardized and commonly acknowledged in vitro test methods allowing a reproducible categorization of the material thrombogenicity requires further attention. Here, the status of in vitro thrombogenicity testing methods for biomaterials is reviewed, particularly taking in view the preparation of test materials and references, the selection and characterization of donors and blood samples, the prerequisites for reproducible approaches and applied test systems. Recent joint approaches in finding common standards for a reproducible testing are summarized and perspectives for a more disease oriented in vitro thrombogenicity testing are discussed.

Perioperative blood product transfusion of two different perfusion strategies on pediatric patients undergoing aortic arch surgery

Simple regional cerebral perfusion (SRCP) or cerebro-myocardial perfusion (CMP) is selectively used in one-stage complex aortic arch malformation repair. This analysis was performed to investigate the effect of CMP and SRCP on perioperative blood product consumption, and to evaluate whether these two strategies have different effects on the clinical outcomes. A retrospective analysis of 284 children with complicated aortic malformation from January 2010 to June 2018 was performed. The overall cohort was divided into SRCP group (n = 202) and CMP group (n = 82). A comprehensive comparison of perioperative blood product consumption-related indexes was performed. Cardiopulmonary bypass time, cardiac arrest time, cooling, and rewarming time in the CMP group were significantly shorter than those in the SRCP group (P < .05). Chest tube time was 3.82 ± 1.33 days in the SRCP group compared to 3.42 ± 0.97 days in the CMP group (P = .005). Moreover, intraoperative platelet (PLT) transfusion volume (mL/kg) and rate (%) were significantly lower in the CMP group (P < .001). Multivariate regression analysis found that intraoperative PLT transfusion was significantly negatively correlated with CMP management [OR = 0.237 (0.110-0.507), P < .001] and CPB time was independently associated with delayed chest tube removal (>3 days) [OR = 1.010 (1.001-1.020), P = .031]. In-hospital mortality and early postoperative adverse events were not significantly different between the two groups. In children with on-pump complex aortic arch surgeries, CMP is more preferable than SRCP in blood protection. However, overall prognosis was not remarkably different between these two perfusion groups. They are both safe and feasible.

Adhesion and activation of platelets from subjects with coronary artery disease and apparently healthy individuals on biomaterials

On the basis of the clinical studies in patients with coronary artery disease (CAD) presenting an increased percentage of activated platelets, we hypothesized that hemocompatibility testing utilizing platelets from healthy individuals may result in an underestimation of the materials' thrombogenicity. Therefore, we investigated the interaction of polymer-based biomaterials with platelets from CAD patients in comparison to platelets from apparently healthy individuals. In vitro static thrombogenicity tests revealed that adherent platelet densities and total platelet covered areas were significantly increased for the low (polydimethylsiloxane, PDMS) and medium (Collagen) thrombogenic surfaces in the CAD group compared to the healthy subjects group. The area per single platelet-indicating the spreading and activation of the platelets-was markedly increased on PDMS treated with PRP from CAD subjects. This could not be observed for collagen or polytetrafluoroethylene (PTFE). For the latter material, platelet adhesion and surface coverage did not differ between the two groups. Irrespective of the substrate, the variability of these parameters was increased for CAD patients compared to healthy subjects. This indicates a higher reactivity of platelets from CAD patients compared to the healthy individuals. Our results revealed, for the first time, that utilizing platelets from apparently healthy donors bears the risk of underestimating the thrombogenicity of polymer-based biomaterials.

Expression of CD11b (MAC-1) and CD162 (PSGL-1) on monocytes is decreased under conditions of deep hypothermic circulatory arrest

Deep hypothermic circulatory arrest (DHCA) is a common technique used to protect vital organs during surgical interventions on the thoracic aorta or during surgery for complex congenital heart disease. Activated leukocytes are key mediators of inflammatory responses during ischemia. Intercellular crosstalk between leukocytes, platelets and endothelial cells is mediated by cell adhesion molecules. These molecules trigger complex cell-cell interaction mechanisms and initiate the release of proinflammatory molecules. One parameter that is known to have a significant impact on inflammatory cell activation and the production of proinflammatory markers is temperature. However, to the best of our knowledge, no data have yet been published on the effect of hypothermia on leukocyte surface markers during DHCA. Thus, the aim of the present study was to investigate the effect of hypothermia on the expression of cell adhesion molecules on monocytes under DHCA conditions in vitro. Blood samples collected from 11 healthy volunteers were incubated in a well-established model simulating circulatory arrest at 36°C and 18°C for 30 min. The expression of cluster of differentiation (CD) molecule 11B (CD11b), CD54 and CD162 on monocytes was measured as the mean fluorescence intensity (MFI) using flow cytometry. The expression level of CD11b on monocytes was significantly decreased following the incubation of the blood samples at 18°C compared with the level in blood samples incubated at 36°C (P<0.001). After 30 min of blood stasis in the circulatory arrest model, the expression level of CD162 on monocytes was significantly lower in the blood samples incubated at 18°C than in those incubated at 36°C (P<0.001). No association was identified between temperature and the surface expression of CD54 on monocytes following 30 min of stasis. These findings demonstrate that deep hypothermia decreases the expression of CD11b and CD162 on monocytes in an experimental setup simulating the conditions of DHCA. This may be the result of the inhibition of leukocyte-endothelial and leukocyte-platelet interactions, which may be a beneficial aspect of deep hypothermia that affects the inflammatory response and tissue damage during DHCA.

Progress in platelet blockers: the target is the P2Y12 receptor

The considerable progress in P2Y12-platelet blockers has important perioperative implications due to a family of novel agents beyond clopidogrel. Although prasugrel is more potent than clopidogrel due to more efficient hepatic metabolism, it is limited clinically by its irreversibility and bleeding risks. Ticagrelor, as the first approved direct and reversible oral P2Y12 blocker, still is limited clinically by its novel side-effect profile. Intravenous reversible P2Y12 blockade is possible now with both cangrelor and elinogrel, although both agents are still in clinical development. Furthermore, elinogrel offers the possibility of both oral and parenteral P2Y12 blockade with a single agent. Future trials likely will continue to evaluate and compare the safety and efficacy of these agents in multiple clinical settings, including the perioperative period.

Combined blockade of ADP receptors and PI3-kinase p110β fully prevents platelet and leukocyte activation during hypothermic extracorporeal circulation

Extracorporeal circulation (ECC) and hypothermia are used to maintain stable circulatory parameters and improve the ischemia tolerance of patients in cardiac surgery. However, ECC and hypothermia induce activation mechanisms in platelets and leukocytes, which are mediated by the platelet agonist ADP and the phosphoinositide-3-kinase (PI3K) p110β. Under clinical conditions these processes are associated with life-threatening complications including thromboembolism and inflammation. This study analyzes effects of ADP receptor P₂Y₁₂ and P₂Y₁ blockade and PI3K p110β inhibition on platelets and granulocytes during hypothermic ECC. Human blood was treated with the P₂Y₁₂ antagonist 2-MeSAMP, the P₂Y₁ antagonist MRS2179, the PI3K p110β inhibitor TGX-221, combinations thereof, or PBS and propylene glycol (controls). Under static in vitro conditions a concentration-dependent effect regarding the inhibition of ADP-induced platelet activation was found using 2-MeSAMP or TGX-221. Further inhibition of ADP-mediated effects was achieved with MRS2179. Next, blood was circulated in an ex vivo ECC model at 28°C for 30 minutes and various platelet and granulocyte markers were investigated using flow cytometry, ELISA and platelet count analysis. GPIIb/IIIa activation induced by hypothermic ECC was inhibited using TGX-221 alone or in combination with P₂Y blockers (p<0.05), while no effect of hypothermic ECC or antiplatelet agents on GPIIb/IIIa and GPIbα expression and von Willebrand factor binding was observed. Sole P₂Y and PI3K blockade or a combination thereof inhibited P-selectin expression on platelets and platelet-derived microparticles during hypothermic ECC (p<0.05). P₂Y blockade alone or combined with TGX-221 prevented ECC-induced platelet-granulocyte aggregate formation (p<0.05). Platelet adhesion to the ECC surface, platelet loss and Mac-1 expression on granulocytes were inhibited by combined P₂Y and PI3K blockade (p<0.05). Combined blockade of P₂Y₁₂, P₂Y₁ and PI3K p110β completely inhibits hypothermic ECC-induced activation processes. This novel finding warrants further studies and the development of suitable pharmacological agents to decrease ECC- and hypothermia-associated complications in clinical applications.

Short-acting P2Y12 blockade to reduce platelet dysfunction and coagulopathy during experimental extracorporeal circulation and hypothermia

BACKGROUND

Extracorporeal circulation (ECC) and hypothermia are routinely used in cardiac surgery to maintain stable circulatory parameters and to increase the ischaemic tolerance of the patient. However, ECC and hypothermia cause platelet activation and dysfunction possibly followed by a devastating coagulopathy. Stimulation of the adenosinediphosphate (ADP) receptor P(2)Y(12) plays a pivotal role in platelet activation. This experimental study tested P(2)Y(12) receptor blockade as an approach to protect platelets during ECC.

METHODS

Human blood was treated with the short-acting P(2)Y(12) blocker cangrelor (1 µM, t(1/2)<5 min) or the P(2)Y(12) inhibitor 2-MeSAMP (100 µM) and circulated in an ex vivo ECC model at normothermia (37°C) and hypothermia (28°C). Before and after circulation, markers of platelet activation and of coagulation (thrombin-antithrombin complex generation) were analysed. During hypothermic ECC in pigs, the effect of reversible P(2)Y(12) blockade on platelet function was evaluated by cangrelor infusion (0.075 µg kg(-1) min(-1)).

RESULTS

During ex vivo hypothermic ECC, P(2)Y(12) blockade inhibited platelet granule release (P<0.01), platelet-granulocyte binding (P<0.05), and platelet loss (P<0.001), whereas no effects on platelet-ECC binding, platelet CD42bα expression, glycoprotein IIb/IIIa activation, or thrombin-antithrombin complex generation were observed. During hypothermic ECC in pigs, cangrelor inhibited platelet-fibrinogen binding (P<0.05) and ADP-induced platelet aggregation (P<0.001). Platelet function was rapidly restored after termination of cangrelor infusion.

CONCLUSIONS

P(2)Y(12) blockade by cangrelor prevents platelet activation during ECC and hypothermia. Owing to its short half-life, platelet inhibition can be well controlled, thus potentially reducing bleeding complications. This novel pharmacological strategy has the potential to reduce complications associated with ECC and hypothermia.

Platelet aggregation monitoring with a newly developed quartz crystal microbalance system as an alternative to optical platelet aggregometry

The objective of this study was to establish a new test system for the monitoring of platelet aggregation during extracorporeal circulation (ECC) procedures. Even though extensive progress has been made in improving the haemocompatibility of extracorporeal circulation devices, activation of blood coagulation, blood platelets and inflammatory responses are still undesired outcomes of cardiopulmonary bypass. This study deals with an approach towards a platelet aggregation measuring system using a newly developed quartz crystal microbalance (QCM) system. Since QCM is a rarely used technique in the field of blood analytics, the challenge was to transfer the well established methods of aggregometry to the new test system. In a QCM system, either bare gold or fibrinogen-coated sensors were incubated with ADP or arachidonic acid (AA) stimulated platelet rich plasma. For negative controls the GPIIb/IIIa inhibitory antibody abciximab (Reopro®) was used as an inhibitor of platelet aggregation. During incubation, the frequency shifts of the sensors were recorded. The results gained from the QCM system were compared to results gained by optical platelet aggregometry (born aggregometry). For additional visualization of platelet adhesion to the sensor surfaces, fluorescent microscopy and scanning electron microscopy were used. The QCM sensor was able to detect platelet aggregation in both uncoated and fibrinogen coated sensors. The measuring curves of aggregation measurements and controls were clearly distinguishable from each other in terms of frequency shifts and kinetics. For aggregation measurements and inhibited controls the therapeutic diagnosis of platelet function is identical between aggregometer and QCM data. In future, QCM based measuring devices may become an alternative to established point of care methods for rapid bedside testing of platelet aggregation.

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.