Flow cytometric detection of platelet activation in patients undergoing diagnostic and interventional coronary angiography

Platelet activation parameters and platelet-leucocyte-conjugate formation in glioblastoma multiforme patients

Patients with glioblastoma multiforme (GBM) suffer from an increased incidence of vascular thrombotic events. However, key influencing factors of the primary hemostasis have not been characterized in GBM patients to date. Thus, the present study determines the activation level of circulating platelets in GBM patients, in-vitro reactivity to agonist-induced platelet stimulation and the formation of circulating platelet-leucocyte conjugates as well as the plasma levels of the proinflammatory lipid mediator sphingosine-1-phosphate (S1P). The endogenous thrombin potential (ETP) was determined as global marker for hemostasis. The 21 GBM patients and 21 gender and age matched healthy individuals enrolled in this study did not differ in mean total platelet count. Basal surface expression of platelet CD63 determined by flow cytometry was significantly increased in GBM patients compared to controls as was observed for the concentration of soluble P-selectin in the plasma of GBM patients. While the ETP was not affected, the immunomodulatory lipid S1P was significantly decreased in peripheral blood in GBM. Interestingly, monocyte expression of PSGL-1 (CD162) was decreased in GBM patient blood, possibly explaining the rather decreased formation of platelet-monocyte conjugates. Our study reveals an increased CD63 expression and P-selectin expression/ secretion of circulating platelets in GBM patients. In parallel a down-modulated PSGL-1 expression in circulating monocytes and a trend towards a decreased formation of heterotypic platelet-monocyte conjugates in GBM patients was seen. Whether this and the observed decreased plasma level of the immunomodulatory S1P reflects a systemic anti-inflammatory status needs to be addressed in future studies.

Platelet growth factors suppress ex vivo expansion and enhance differentiation of umbilical cord blood CD133+ stem cells to megakaryocyte progenitor cells

BACKGROUND AND OBJECTIVES

Umbilical cord blood (UCB) is a rich source of hematopoietic cells. Here, for the first time, we surveyed the effects of different concentrations of platelet growth factors and cytokine cocktail (CC) on the expansion and differentiation of UCB CD133(+) stem cells into megakaryocyte progenitors.

MATERIALS AND METHODS

UCB CD133(+) cells were separated by magnetic cell sorting and cultured in different concentrations of platelet growth factors in combination with a CC containing interleukins 3 and 6, stem cell factor, and thrombopoietin. Cell expansion and differentiation were assessed using mononuclear cell count and flow cytometry.

RESULTS

The results show that either activated platelet-rich plasma or the platelet supernatant, when added in the first day of culture, significantly suppress the expansion of CD133(+) cells after 7 days in culture (p < 0.05). By contrast, the expression of CD41, CD61, and CD42b markers in the presence of all platelet growth factors increased compared with that of the control (p < 0.05).

CONCLUSION

Taken together, platelet growth factors in the presence of CC suppress ex vivo expansion of UCB CD133(+) cells and enhance their differentiation into megakaryocytic progenitor cells in a dose- and time-dependent manner.

Effects of cytarabine and various anthracyclins on platelet activation: characterization of in vitro effects and their possible clinical relevance in acute myelogenous leukemia

Previous in vitro studies have demonstrated that normal platelets and platelet-released mediators can alter in vitro characteristics of human acute myelogenous leukemia (AML) blasts. To further investigate whether platelets can be expected to adhere to and thereby affect AML blasts through their release of soluble mediators into a common microenvironment, we investigated (i) the effects on platelet activation by cytotoxic drugs commonly used in AML therapy; (ii) the occurrence of circulating activated platelets in acute leukemia patients; and (iii) the in vivo and in vitro adherence of platelets to AML blasts. The anthracyclins daunorubicin and idarubicin increased the expression of activation-associated membrane molecules (GPIIb/IIIa, CD62P, CD63) by normal platelets, daunorubicin then having the strongest effect. In contrast, cytarabine, epirubicin, doxorubicin and mitoxantrone had no significant effects. Although AML patients did not show increased levels of activated platelets in the circulation, adhesion of platelets to AML blasts was demonstrated both in vivo and in vitro. These results suggest that platelets and AML blasts may locate to common in vivo microenvironments, and platelet-derived soluble mediators may thereby affect the functional characteristics of the leukemia cells.

Peripheral blood progenitor cell grafts contain high levels of platelet-secreted mediators

BACKGROUND

The cytokine network in peripheral blood progenitor cell (PBPC) grafts may affect hematopoietic reconstitution or the risk of postransplant relapse of malignant disorders through effects on normal progenitor cells or contaminating malignant cells. Whether thrombopoietin (TPO), SCF, and platelet-secreted mediators are parts of this network was investigated.

STUDY DESIGN AND METHODS

Peripheral blood and PBPC plasma samples were collected consecutively from patients with malignant disorders who underwent PBPC harvest. Blood samples were collected immediately before and after apheresis. Patients underwent mobilization by chemotherapy plus G-CSF, except for one patient who received only G-CSF. Plasma levels were also determined for healthy controls.

RESULTS

PBPC grafts had greater levels of platelet-secreted platelet factor 4 (PF4), beta-thromboglobulin, and platelet-derived growth factor isoform AB, as compared with venous levels in patients and controls. Although platelet and PF4 levels in autografts were significantly correlated, the graft:blood ratio was higher for PF4 than for platelets. In both the patients' blood and the autografts, TPO levels were increased from the levels in normal controls. Blood and graft levels of SCF were within the normal range.

CONCLUSION

The cytokine network of PBPC autografts includes increased levels of TPO and several platelet-derived mediators.

Preanalytical requirements for flow cytometric evaluation of platelet activation: choice of anticoagulant

Accurate assessment of in vivo or in vitro platelet activation requires optimal preanalytical conditions to prevent artefactual in vitro activation of the platelets. The choice of anticoagulant is one of the critical preanalytical conditions as anticoagulants exert different effects on the activation of platelets ex vivo. We tested the effectiveness of Diatube-H (also known as CTAD; sodium citrate, theophylline, adenosine and dipyridamole) and citrate vacutainer tubes in preventing artefactual activation of platelets and preserving functional reserve. Platelet surface expression of the CD62P (reflecting alpha granule release), CD63 (reflecting lysosomal release) and modulation of normal platelet membrane glycoproteins CD41a and CD42b, were measured in whole blood and in isolated platelets immediately after collection and at 6, 24 and 48 h after venipuncture. Samples taken into Diatube-H showed less spontaneous platelet activation than did those taken into citrate. To measure in vitro platelet functional reserve, thrombin was added as agonist to blood stored for varying periods up to 48 h. Although Diatube-H suppressed in vitro platelet activation for up to 4 h, in samples kept for 6-24 h before thrombin addition, the inhibitory effect was lost and platelets responded fully to agonist activation. Hence, Diatube-H preserved platelets and allowed for measurement of in vivo platelet activation as well as thrombin-induced in vitro platelet activation after 6-24 h, in both whole blood and isolated platelets.