Integrin αIIbβ3

Administration of a new nano delivery system coated with Tirofiban to prevent early thrombosis of vein graft

OBJECTIVE

To verify the administration of a new nano delivery system coated with Tirofiban on preventing early thrombosis in vein graft.

METHODS

Forty New Zealand white rabbits were randomly divided into five groups with eight rabbits in each group. The rabbits of all groups underwent jugular vein transplantation, except group I with only neck opening and closing operation. Vein grafts of group II were preprocessed by intravenous injection of normal saline; group III were preprocessed by tirofiban alone; group IV were preprocessed by unloaded nanoparticles of PLGA-PEG; group V were preprocessed by PLGA-PEG coated with tirofiban. Coagulation and platelet function of peripheral and vein graft blood were detected at 1, 2, 4, 12 h and 1, 3, 7, 10, 14 days after operation. Patency rate of vein graft and blood flow index were measured by vascular ultrasound at third, seventh, 10th, and 14th days after operation; two rabbits in each group were randomly sacrificed at the corresponding time of detection. Pathological differences of vein grafts were observed by HE stainin.

RESULTS

The patency rate of vein grafts in group V was significantly higher than that in group II to IV. The platelet and platelet aggregation rate in group V were inhibited in vein graft blood significantly. The post-operative PT and APTT in vein graft blood in group V were increased obviously while the FBG, D-dimer and FDP were significantly inhibited. Except group I, the lumen loss rate of vein grafts in group V was significantly lower than that in other groups, and vein graft blood in group V had a significant lower expression of platelet P-selectin and GP IIb/IIIa receptor than that in other groups.

CONCLUSION

This study proves that PEG-PLGA coated with tirofiban can effectively prevent early vein graft stenosis from thrombosis by inhibition of platelet function, coagulation function.

Biomechanical activation of blood platelets via adhesion to von Willebrand factor studied with mesoscopic simulations

Platelet adhesion and activation are essential initial processes of arterial and microvascular hemostasis, where high hydrodynamic forces from the bloodflow impede coagulation. The process relies on von Willebrand factor (VWF)-a linear multimeric protein of blood plasma plays a pivotal role in mechanochemical regulation of shear-induced platelet aggregation (SIPA). Adhesive interactions between VWF and glycoprotein receptors GPIb are crucial for platelet recruitment under high shear stress in fluid. Recent advances in experimental studies revealed that mechanical tension on the extracellular part of GPIb may trigger a cascade of biochemical reactions in platelets leading to activation of integrins [Formula: see text] (also known as GPIIb/IIIa) and strengthening of the adhesion. The present paper is aimed at investigation of this process by three-dimensional computer simulations of platelet adhesion to surface-grafted VWF multimers in pressure-driven flow of platelet-rich plasma. The simulations demonstrate that GPIb-mediated mechanotransduction is a feasible way of platelet activation and stabilization of platelet aggregates under high shear stress. Quantitative understanding of mechanochemical processes involved in SIPA would potentially promote the discovery of new anti-platelet medication and the development of multiscale numerical models of platelet thrombosis and hemostasis.

Platelet Apoptosis Can Be Triggered Bypassing the Death Receptors

In nucleated cells, the extrinsic pathway of the programmed cell death (apoptosis) is triggered by interaction of death ligands of the tumor necrosis factor superfamily with the death receptors on external cell surface membrane. In this review, we present evidence that, in contrast to nucleated cells, apoptosis in anucleate platelets can be induced through bypassing the death receptors, using instead specific receptors on the platelet surface mediating platelet activation, aggregation, and blood coagulation. These platelet surface receptors include the protease-activated receptor 1 of thrombin and glycoproteins IIbIIIa and Ibα, receptors of fibrinogen, and von Willebrand factor. The pro-apoptotic BH3 mimetic ABT-737 and calcium ionophore A23187 also trigger platelet apoptosis without using death receptors. These agents induce the intrinsic pathway of platelet apoptosis by direct targeting mitochondrial and extra-mitochondrial apoptotic responses.

Maximum likelihood approach suggests positive selection in platelet integrin αIIbβ3 in mammalian species

Platelet integrin αIIbβ3 is crucial for platelet aggregation. Although structural and functional characteristics of this protein have been extensively studied, the evolutionary pattern studies of this protein complex in mammals are scarce. Here, we addressed this question using maximum likelihood approaches to identify codons that are evolving under positive selection. Likelihood of positive selection was estimated using CODEML implemented in PAML software applied to integrin αIIbβ3 derived from nucleotide sequences of 10 different mammalian species. Four codons in mature αIIb-subunit (corresponding to residues 150, 184, 193, and 370) and three codons in mature β3-subunit (corresponding to residues 129, 440, and 444) showed signs of positive selection with posterior probabilities over 95%. The different amino acids observed for each of the positively selected residues detected showed different physicochemical properties. These results open new research avenues to understand the physiological importance of specific residues and should allow for a better understanding of the function and the different interactions of each residue within the mature protein.

New Fundamentals in Hemostasis

Hemostasis encompasses the tightly regulated processes of blood clotting, platelet activation, and vascular repair. After wounding, the hemostatic system engages a plethora of vascular and extravascular receptors that act in concert with blood components to seal off the damage inflicted to the vasculature and the surrounding tissue. The first important component that contributes to hemostasis is the coagulation system, while the second important component starts with platelet activation, which not only contributes to the hemostatic plug, but also accelerates the coagulation system. Eventually, coagulation and platelet activation are switched off by blood-borne inhibitors and proteolytic feedback loops. This review summarizes new concepts of activation of proteases that regulate coagulation and anticoagulation, to give rise to transient thrombin generation and fibrin clot formation. It further speculates on the (patho)physiological roles of intra- and extravascular receptors that operate in response to these proteases. Furthermore, this review provides a new framework for understanding how signaling and adhesive interactions between endothelial cells, leukocytes, and platelets can regulate thrombus formation and modulate the coagulation process. Now that the key molecular players of coagulation and platelet activation have become clear, and their complex interactions with the vessel wall have been mapped out, we can also better speculate on the causes of thrombosis-related angiopathies.

A systematic review of the management and outcomes of pregnancy in Glanzmann thrombasthenia

Glanzmann Thrombasthenia (GT) is a rare autosomal recessive disorder which usually manifests as severe mucocutaneous bleeding and is caused by deficiency of the platelet glycoprotein IIb-IIIa. Pregnancy in women with GT presents particular challenges as there is increased risk of both maternal and foetal bleeding. To improve understanding and clarify the optimum management of pregnancy in this disorder, we performed a systematic review of the world literature of pregnancy and GT. This identified three single-centre case series of patients with GT that included brief descriptions of women in pregnancy and 31 detailed case reports of 40 pregnancies in 35 women that resulted in 38 live births. Among the detailed case reports, ante-natal bleeding was described in 50% of pregnancies but was usually mild and occurred at mucocutaneous sites. Primary postpartum haemorrhage (PPH) was reported in 34% of pregnancies and secondary PPH in 24%. PPH was frequently severe and occurred up to 20 days after delivery. There was a wide variation in approach to prevention and treatment of PPH but most women received platelet transfusion, sometimes with additional recombinant FVIIa and anti-fibrinolytics. Maternal alloimmunization against platelet antigens was reported in 73% of pregnancies and was associated with four neonatal deaths. These data emphasize the need for multidisciplinary management of pregnancy in women with GT. Delivery plans should recognize the need for prevention and aggressive treatment of PPH and should minimize foetal bleeding risk in pregnancies complicated by alloimmunization.