Differential Expression of Platelet Activation Markers CD62P and CD63 Following Stimulation with PAF, Arachidonic Acid and Collagen

The Correlation Between Bronchopulmonary Dysplasia and Platelet Metabolism in Preterm Infants

Background: Platelets play an important role in the formation of pulmonary blood vessels, and thrombocytopenia is common in patients with pulmonary diseases. However, a few studies have reported on the role of platelets in bronchopulmonary dysplasia. Objective: The objective of the study was to explore the relationship between platelet metabolism and bronchopulmonary dysplasia in premature infants. Methods: A prospective case-control study was performed in a cohort of premature infants (born with a gestational age <32 weeks and a birth weight <1,500 g) from June 1, 2017 to June 1, 2018. Subjects were stratified into two groups according to the diagnostic of bronchopulmonary dysplasia: with bronchopulmonary dysplasia (BPD group) and without bronchopulmonary dysplasia (control group). Platelet count, circulating megakaryocyte count (MK), platelet-activating markers (CD62P and CD63), and thrombopoietin (TPO) were recorded and compared in two groups 28 days after birth; then serial thrombopoietin levels and concomitant platelet counts were measured in infants with BPD. Results: A total of 252 premature infants were included in this study. Forty-eight premature infants developed BPD, 48 premature infants without BPD in the control group who were matched against the study infants for gestational age, birth weight, and admission diagnosis at the age of postnatal day 28. Compared with the controls, infants with BPD had significantly lower peripheral platelet count [BPD vs. controls: 180.3 (24.2) × 10⁹/L vs. 345.6 (28.5) × 10⁹/L, p = 0.001]. Circulating MK count in the BPD group was significantly more abundant than that in the control group [BPD vs. controls: 30.7 (4.5)/ml vs. 13.3 (2.6)/ml, p = 0.025]. The level of CD62p, CD63, and TPO in BPD group was significantly higher than the control group [29.7 (3.1%) vs. 14.5 (2.5%), 15.4 (2.0%) vs. 5.8 (1.7%), 301.4 (25.9) pg/ml vs. 120.4 (14.2) pg/ml, all p < 0.05]. Furthermore, the concentration of TPO was negatively correlated with platelet count in BPD group with thrombocytopenia. Conclusions: Our findings suggest that platelet metabolism is involved in the development of BPD in preterm infants. The possible mechanism might be through increased platelet activation and promoted TPO production by feedback.

Platelet storage and functional integrity

Platelet transfusion is a topic of common interest for many specialists involved in patient care, from laboratory staff to clinical physicians. Various aspects make this type of transfusion different from those of other blood components. In this review, the challenges in platelet transfusion practice that are relevant for laboratory colleagues will be discussed, highlighting how the biochemical and structural characteristics of these blood elements directly affect their function and consequently the clinical outcome. More than 1,300 platelet concentrates are transfused in Germany every day, and several types are offered by their respective manufacturers. We describe the technological advances in platelet concentrate production, with a focus on how the storage conditions of platelets can be improved. Laboratory quality assessment procedures for a safe transfusion are discussed in detail. For this purpose, we will refer to the Hemotherapy Directives (Richtlinie Hämotherapie) of the German Medical Association.

Direct activation of platelets by addition of CaCl2 leads coagulation of platelet-rich plasma

Background

Based on the notion that full activation of platelets is required for a growth factor release, in regenerative dentistry, platelet-rich plasma (PRP) in liquid form is usually clotted by addition of CaCl₂ in glassware before topical implantation. However, there has been no evidence as to which is better, full or partial activation of platelets, for minimizing the loss of growth factors and improving the controlled release of growth factors from coagulated PRP. To address this matter, here, we primarily examined direct effects of CaCl₂ on platelets in PBS and on coagulation in citrated PRP.

Methods

PRP was prepared from healthy volunteers’ blood. Platelets’ actions were monitored by scanning electron microscopy, flow cytometry, digital holographic microscopy, and immunofluorescent staining. Clot formation was examined in plasma.

Results

In plasma-free PBS, 0.1% CaCl₂ immediately upregulated CD62P and CD63, causing a release of microparticles and fibrinogen/fibrin; consequently, platelets aggregated and adhered to polystyrene culture dishes with enlargement of their attachment area. In a clot formation assay in plasma, CaCl₂ initially induced platelet aggregation, which triggered loop-like matrix formation and subsequently induced coagulation on a watch glass. Such changes were not clearly observed either with PRP in a plastic dish or in platelet-poor plasma on a watch glass: coagulation was delayed in both conditions.

Conclusions

These findings indicate that besides the well-known coagulation pathway, which activates platelets via thrombin conversion in a coagulation cascade, CaCl₂ directly activates platelets, which then facilitate clot formation independently and in cooperation with the coagulation pathway.

Stapled peptides as a new technology to investigate protein-protein interactions in human platelets

We describe the first application of stapled peptides in human platelets. Bim BH3 stapled peptides are used to overcome the limitations of traditional methods and uncover a new role for Bim in platelet activation.

Platelets are blood cells with numerous crucial pathophysiological roles in hemostasis, cardiovascular thrombotic events and cancer metastasis. Platelet activation requires the engagement of intracellular signalling pathways that involve protein–protein interactions (PPIs). A better understanding of these pathways is therefore crucial for the development of selective anti-platelet drugs. New strategies for studying PPIs in human platelets are required to overcome limitations associated with conventional platelet research methods. For example, small molecule inhibitors can lack selectivity and are often difficult to design and synthesise. Additionally, development of transgenic animal models is costly and time-consuming and conventional recombinant techniques are ineffective due to the lack of a nucleus in platelets. Herein, we describe the generation of a library of novel, functionalised stapled peptides and their first application in the investigation of platelet PPIs. Moreover, the use of platelet-permeable stapled Bim BH3 peptides confirms the part of Bim in phosphatidyl-serine (PS) exposure and reveals a role for the Bim protein in platelet activatory processes. Our work demonstrates that functionalised stapled peptides are a complementary alternative to conventional platelet research methods, and could make a significant contribution to the understanding of platelet signalling pathways and hence to the development of anti-platelet drugs.

The effect of aspirin on thrombin stimulated platelet adhesion receptor expression and the role of neutrophils

AIMS

Aspirin has proven clinical efficacy in limiting the thrombotic complications of atherosclerotic vascular disease but its mechanism of action remains unclear. Recent evidence suggests the anti-platelet action of aspirin may be partly mediated by neutrophil derived nitric oxide (NO). The aim of the study was to determine the effects of aspirin on thrombin-induced platelet expression of the alpha-granule membrane protein, P-selectin, and the platelet surface glycoprotein required for aggregation, GPIIb-IIIa, and to assess whether this was enhanced by the presence of neutrophils.

METHODS

Platelet P-selectin and GPIIb-IIIa receptor expression were assessed by flow cytometric analysis of washed platelets stimulated with thrombin (0.025 iu ml(-1), sub aggregatory concentration) alone or after pre-incubation with aspirin (0.05, 0.1, 0.5, 1.0 mg m1(-1) either in the presence or absence of neutrophils (100 platelets per neutrophil). NO release was determined by assay of nitrite in the supernatants from parallel samples.

RESULTS

In preliminary aggregation studies, aspirin at all concentrations inhibited arachidonic acid but not thrombin-induced platelet aggregation. Similarly, aspirin at all concentrations failed to inhibit thrombin-induced platelet P-selectin or GPIIb-IIIa expression and this was not influenced by the presence of neutrophils. A reduction in P-selectin and GPIIb-IIIa receptor density on non-activated platelets co-incubated with unstimulated neutrophils was associated with NO release from neutrophils, but this was not enhanced by the addition of aspirin.

CONCLUSIONS

These results confirm that thrombin-induced platelet alpha-granule release, with consequent P-selectin expression, and platelet GPIIb-IIIa expression, are not affected by aspirin inhibition of cyclo-oxygenase and suggest that the anti-thrombotic efficacy of aspirin in vivo may partly depend on other mechanisms. This study did not demonstrate an effect of neutrophils or neutrophil derived NO on aspirin inhibition of platelet adhesion receptor expression.