Search

Coagulation factor XIII (FXIII) is a transglutaminase that catalyzes crosslink formation in fibrin clots. Endothelial cells (EC) were demonstrated to bind FXIII via their αvβ3 integrin receptor. FXIII was also shown to bind platelet glycoprotein IIb/IIIa receptor. In the present study, we analyzed if FXIII can mediate platelet–EC interaction. Both FXIII and activated FXIII (FXIIIa) bound to EC monolayers; this binding was enhanced by the addition of Mn2+ and was inihibited by the monoclonal antibody L609 against αvβ3 integrin. Normal washed platelets also bound surface-immobilized or soluble FXIII and FXIIIa, and the binding was GPIIb/IIIa dependent. The effect of FXIII concentrate (Fibrogammin-P) treatment on the interaction of ECs with platelets from six FXIII-deficient patients was studied. Patients'' platelets were radiolabeled with 3H-Adenine, washed, resuspended in autologous plasma and allowed to adhere to immortalized EC line EAhy926. Adhesion of platelets from FXIII-deficient patients to ECs increased 1.7±0.4-fold (P=.01) following intravenous infusion of FXIII concentrate. Similarly, addition of 1 U/ml of FXIII concentrate to the patients'' PRP in vitro increased the adhesion 1.8±0.5-fold (P=.008). Preincubation of the EC monolayers with increasing concentrations of either FXIII or FXIIIa augmented the adhesion of normal washed platelets to ECs in a dose-dependent manner. At 10 U/ml of EC-bound FXIII or FXIIIa, platelet adhesion enhanced 1.7±0.25-fold (P=.03) and 2.5±0.5-fold (P=.02), respectively. The increase in platelet adhesion was completely abolished by pretreatment of ECs with the anti-αvβ3 antibody L609 or by preincubation of the platelets with the GPIIb/IIIa inhibitor Abciximab. Taken together, our data indicate that FXIII mediates the interaction of platelets with ECs by bridging between endothelial αvβ3 and platelet GPIIb/IIIa integrins. This interaction may be relevant for tissue remodeling and wound repair after vascular injury in FXIII-deficient patients. [Copyright &y& Elsevier]

The effect of He-Ne laser irradiation on platelet adhesion, activation and aggregation was investigated. Citrated whole blood was irradiated in vitro by He-Ne laser (632.8 nm, 7 mW) and then subjected to shear stress (1300 s[sup -1]) on subendothelial extracellular matrix (ECM)-coated plates. Laser irradiation was followed by a decrease in platelet adhesion and aggregation on ECM under flow conditions in a time exposure-dependent manner (by 30-40%). The inhibiting effect of laser light on platelets was detectable up to 1 h after the termination of irradiation. Laser irradiation of either platelet-rich plasma, gel-filtered platelets, platelet-poor plasma, or packed blood cells followed by whole blood reconstitution revealed a marked decrease in platelet deposition on ECM only in the cases of platelet-rich plasma or gel filtered platelets. In conventional aggregometry, laser-treated platelet-rich plasma demonstrated a diminished platelet response to both thrombin receptor-activating peptide (TRAP), converting a two-wave aggregation curve to reversible, and to the protein kinase C activator PMA (by 45%). In flow cytometry analysis, irradiated platelets presented lower fibrinogen binding and P-selectin expression in response to TRAP. Laser irradiation had no additional inhibitory effect on dibutyryl cGMP- and dibutyryl cAMP-pretreated platelets. A 50% increase in cGMP level was observed in laser-treated gel filtered platelets, both in the presence and in absence of the phosphodiesterase inhibitor, isobuthylmethylxanthine. The results suggest that guanylate cyclase is one of the primary mediators of the laser effect on platelet function. [ABSTRACT FROM AUTHOR]

Extracellular matrix (ECM) derived from bovine corneal endothelial cells was used as a model to study the role of platelets in Staphylococcus aureus interaction with the vascular subendothelium. In whole blood, S. aureus activated platelets, as demonstrated by P-selectin expression on the platelet membrane. Subjecting platelet-rich plasma (PRP) to the ECM under oscillatory conditions resulted in platelet adhesion and aggregation. S. aureus increased platelet deposition on ECM depending on the bacterium-platelet ratio. Scanning electron microscopy revealed that S. aureus adhered to and formed clusters on ECM-bound platelets. These findings were confirmed by using [3H]thymidine-labeled bacteria that adhered to the surface more extensively after deposition of platelets on ECM. Platelet pre-treatment with prostaglandin E1 resulted in inhibition of bacterial adherence. Glycoprotein (GP)Ib was involved in the bacterium-platelet interaction, as indicated by the following: (i) S. aureus diminished the binding of GPIb but not of GPIX or GPIIb-IIIa monoclonal antibodies (Mab) to washed fixed platelets; (ii) GPIb Mab inhibited S. aureus -induced platelet aggregation in a dose-dependent fashion; (iii) blockade of von Willebrand factor (vWf) binding to GPIb by a recombinant vWf fragment reversed the enhanced platelet deposition on ECM in the presence of S. aureus but did not affect platelet deposition in the absence of bacteria. The results indicate that S. aureus activates platelets and promotes their deposition on ECM via GPIb-dependent mechanism and that adherent platelets mediate S. aureus deposition on the subendothelium. These interactions might play a role in the pathogenesis of bacterial endocarditis. [ABSTRACT FROM AUTHOR]

Severe protein C deficiency (SPCD) is a rare inherited thrombotic disease associated with high morbidity and mortality. In the current study, we established a viable murine model of SPCD, enabling preclinical gene therapy studies. By creating SPCD mice with severe hemophilia A (PROC -/- /F8 - ), the multi-month survival of SPCD mice enabled the exploration of recombinant adeno-associated viral vector-PC (rAAV8-PC) gene therapy (GT). rAAV8- PC (10 12 vg/kg of AAV8-PC) was injected via the tail vein into 6-8-week-old PROC -/- /F8 - mice. Their plasma PC antigen levels (median of 714 ng/mL, range 166-2488 ng/mL) and activity (303.5 ± 59%) significantly increased to the normal range after GT compared to untreated control animals. PC's presence in the liver after GT was also confirmed by immunofluorescence staining. Our translational research results provide the first proof of concept that an infusion of rAAV8-PC increases PC antigen and activity in mice and may contribute to future GT in SPCD. Further basic research of SPCD mice with prolonged survival due to the rebalancing of this disorder using severe hemophilia A may provide essential data regarding PC's contribution to specific tissues' development, local PC generation, and its regulation in inflammatory conditions.

Background: Immune thrombotic thrombocytopenic purpura (iTTP) in children is a rare, severe thrombotic microangiopathy. This condition is characterized by microangiopathic hemolytic anemia, severe thrombocytopenia, and organ ischemia due to reduced activity of the von Willebrand factor-cleaving protease ADAMTS13., Methods: A retrospective case series evaluating data collected from the medical files of 4 children diagnosed with iTTP., Results: The presented case series depicts a variety of iTTP presentations: 1 case of primary iTTP, 1 case induced by Shiga toxin, 1 associated with RAS-associated autoimmune leukoproliferative disease (RALD), and 1 initial manifestation of systemic lupus erythematosus (SLE). Notably, 2 patients recovered without undergoing plasma exchange., Conclusion: Early ADAMTS13 testing in children with unexplained hemolysis or thrombocytopenia is crucial. The diverse underlying causes, including infections and autoimmune disorders, underscore the complexity of iTTP in the pediatric population. These cases highlight the necessity for personalized treatment approaches that consider each patient's unique clinical situation and potential alternatives or modifications to conventional therapeutic regimens., (Copyright © 2024 Wolters Kluwer Health, Inc. All rights reserved.)

Pro- and anticoagulant factors are core components of hemostasis [...].