hirudin and von-Willebrand-Diseases

The use of extracorporeal membrane oxygenation (ECMO) support for cardiac and respiratory failure has increased in recent years. Improvements in ECMO oxygenator and pump technologies have aided this increase in utilization. Additionally, reports of successful outcomes in supporting patients with respiratory failure during the 2009 H1N1 pandemic and reports of ECMO during cardiopulmonary resuscitation have led to increased uptake of ECMO. Patients requiring ECMO are a heterogenous group of critically ill patients with cardiac and respiratory failure. Bleeding and thrombotic complications remain a leading cause of morbidity and mortality in patients on ECMO. In this review, we describe the mechanisms and management of hemostatic, thrombotic and hemolytic complications during ECMO support.

Topics: Anticoagulants; Blood Coagulation; Blood Coagulation Tests; Cardiac Output, Low; Cardiac Tamponade; Extracorporeal Membrane Oxygenation; Hemolysis; Hemorheology; Hemorrhage; Heparin; Hirudins; Humans; Peptide Fragments; Purpura, Thrombocytopenic, Idiopathic; Recombinant Proteins; Respiratory Insufficiency; Thrombosis; von Willebrand Diseases

Von Willebrand factor (vWF) is synthesized in endothelial cells as pre-provWF and processed intracellularly to propeptide (vWFpp) and mature vWF. Building on previous studies indicating that recombinant provWF when infused into animals can also be processed extracellularly in vivo, we investigated the processing of provWF in vitro. Incubation of a recombinant provWF (rpvWF) preparation with canine and human vWF-deficient plasma induced a time-dependent decrease in provWF antigen and an increase in vWFpp antigen without changing total vWF antigen or collagen-binding activity. Multimer analysis showed the gradual transformation of the provWF multimers to mature vWF multimers and cleaved vWFpp was visualized on autoradiograms of SDS-polyacrylamide electrophoresis gels using 125-labeled provWF. Processing was facilitated by CaCl2 but prevented by a thrombin inhibitor and did not occur in prothrombin-depleted plasma. When recombinant provWF was incubated with increasing amounts of purified thrombin, the extent of provWF processing was dose-dependent. The specific cleavage of vWFpp was confirmed by immunoblots using an anti-vWFpp antibody and by amino terminal amino-acid analysis. Binding of provWF to collagen decreased the thrombin concentration necessary for propeptide removal to a concentration in the range of that found during blood clotting. Meizothrombin, an intermediate of prothrombin activation, was also able to induce dose-dependent removal of the propeptide from rpvWF. Hirudin preconditioning of vWF-deficient mice attenuated processing of infused rpvWF suggesting that thrombin plays a part in the processing events in vivo.

Topics: Animals; Biopolymers; Blood Protein Electrophoresis; Calcium Chloride; Collagen; Dog Diseases; Dogs; Enzyme Activation; Enzyme Inhibitors; Enzyme Precursors; Hirudins; Humans; Mice; Mice, Knockout; Protein Precursors; Recombinant Fusion Proteins; Species Specificity; Thrombin; von Willebrand Diseases; von Willebrand Factor

We have previously observed that von Willebrand factor (vWF) plays an important role in platelet deposition on subendothelium at low values of wall shear rate (200 to 400 seconds-1). In the present study, we have investigated the mechanism responsible for such a defect in platelet deposition at low shear rates in the absence of vWF. Blood from both normal and von Willebrand's disease (vWD) animals was exposed to de-endothelialized aorta from normal pigs for a range of shear rates (200 to 3,000 seconds-1) and exposure times (three to 30 minutes) in a tubular perfusion chamber. Variations in the method of inhibiting coagulation (none, heparin, citrate, hirudin, and EDTA) and of perfusing blood (in vitro v ex vivo) were compared by determining the influence of wall shear rate and vWF on the deposition of 111In-labeled platelets on subendothelium. Whereas platelet deposition was reduced in the absence of vWF for all experimental variations at high shear rates (greater than 850 seconds-1), a defect was observed at low shear rates only when heparinized blood was exposed by means of an ex vivo perfusion system. Maximum sensitivity of the measurement occurs under ex vivo perfusion conditions due to the reduced ability of platelets to deposit in normal blood when recirculated in vitro. Our results indicate that vWF mediates platelet-vessel wall interaction even at low shear rates and that such effect can only be observed in systems where platelet function is minimally affected by the experimental conditions.

Topics: Animals; Blood Coagulation; Blood Platelets; Blood Vessels; Heparin; Hirudins; Perfusion; Stress, Mechanical; Swine; von Willebrand Diseases; von Willebrand Factor