In vitro measurement of platelet glycoprotein IIb/IIIa receptor blockade by abciximab: interindividual variation and increased platelet secretion.

Background And Objectives: Inhibition of soluble fibrinogen binding to activated platelets represents the target of pharmacologic approach with antagonists of the glycoprotein IIb/IIIa (GPIIb/IIIa) complex. In this study we assessed the effects of abciximab, a recombinant chimeric Fab fraction of the antibody against GPIIb/IIIa, on several markers of platelet activation.

Design And Methods: The platelet surface expression of GPIIb/IIIa was measured by a flow cytometry technique using a two-color assay.

Proteolysis of von Willebrand factor and shear stress-induced platelet aggregation in patients with aortic valve stenosis.

Background: Excessive bleeding may complicate congenital cardiac defects. To explain the pathogenesis of this abnormality, we evaluated selected parameters of primary hemostasis in patients with aortic valve stenosis before and after corrective surgery.

Methods And Results: We examined shear-induced platelet aggregation with the filter aggregometer test and von Willebrand factor (vWF) structure by evaluating the multimeric distribution and extent of subunit proteolysis.

Effect of adenosine derivatives on in vitro thrombus formation induced by shear stress.

Background And Objective: Shear-stress is considered to be the first event of platelet aggregation in vivo and platelet adhesion may be enhanced under pathologic conditions (e.g. arterial occlusion).

Serum von Willebrand factor levels in patients with inflammatory bowel disease are related to systemic inflammation.

Background: Increased levels of circulating von Willebrand factor (vWF) have been found in patients with inflammatory bowel disease (IBD); this increase may reflect either endothelial damage or systemic inflammation. Our aim was to evaluate serum vWF levels in patients with IBD and their correlation with clinical and biochemical disease activity.

Methods: We evaluated serum vWF levels in 32 patients with ulcerative colitis (UC) (10 active with increased acute-phase reactants (APR), 6 active with normal APR, 16 in remission), 27 with Crohn disease (CD) (10 active, 12 quiescent, and 5 quiescent with increased APR), and 31 healthy controls.

Evaluation of the abnormal platelet function in von Willebrand disease by the blood filtration test.

We have evaluated platelet function in different subtypes of von Willebrand disease (vWD) by pushing blood through the capillary-sized channels of a glass filter. Patients, including those with type IIB vWD, showed lower than normal platelet retention and increased cumulative number of blood drops passing through the filter as a function of time. In contrast, shear-induced platelet aggregation, measured in the cone-and-plate viscometer, was paradoxically increased in type IIB patients.

Composition of platelet phospholipids after moderate consumption of red wine in healthy volunteers.

Objective: To evaluate the effect of moderate consumption of red wine on composition of platelet phospholipids, discriminating the effect of alcohol from that of non-alcoholic components.

Design: A randomised crossover study.

Setting: The Department of Food Science and Technology, University of Milan.

Porcine von Willebrand factor binding to human platelet GPIb induces transmembrane calcium influx.

Porcine von Willebrand factor (P-vWF) binds to human platelet glycoprotein (GP) Ib and, upon stirring (1500 rpm/min) at 37 degrees C, induces, in a dose-dependent manner, a transmembrane flux of Ca2+ ions and platelet aggregation with an increase in their intracellular concentration. The inhibition of P-vWF binding to GP Ib, obtained with anti GP Ib monoclonal antibody (LJ-Ib1), inhibits the increase of intracellular Ca2+ concentration ([Ca2+]i) and platelet aggregation. This effect is not observed with LJ-Ib10, an anti GP Ib monoclonal antibody which does not inhibit the vWF binding to GP Ib.

Effects of moderate consumption of red wine on platelet aggregation and haemostatic variables in healthy volunteers.

Objective: To evaluate the effect of moderate consumption of red wine on platelet aggregation and haemostatic variables, discriminating the effect of alcohol from that of non-alcoholic components.

Design: A randomised crossover study.

Setting: The Department of Food Science and Technology, University of Milan.

Platelet aggregation at high shear is impaired in patients with congenital defects of platelet secretion and is corrected by DDAVP: correlation with the bleeding time.

Techniques measuring platelet aggregation in vitro under the high shear rate conditions that can be found in the microcirculation could reflect the status of primary hemostasis better than the turbidimetric technique. We studied platelet aggregation at high shear in patients with prolonged bleeding time caused by congenital platelet secretion defects such as delta-storage pool deficiency and primary secretion defect. Two different techniques were used: shear-induced platelet aggregation in a cone-and-plate viscometer and the filter aggregation test.

Interaction of porcine von Willebrand factor with the platelet glycoproteins Ib and IIb/IIIa complex.

Porcine von Willebrand factor (PvWF) induces platelet aggregation which is thought to be responsible for the thrombocytopenia that occurs in haemophilic patients treated with commercial preparations of porcine factor VIII. This study demonstrates that such aggregation can be completely inhibited by a monoclonal antibody against human platelet glycoprotein GPIb and partially inhibited by an antibody directed against platelet GPIIb/IIIa. The interaction of PvWF with GPIb is also demonstrated by the inhibitory effect of purified glycocalycin on aggregation.

Prevention of hemoperitoneum during ovulation by oral contraceptives in women with type III von Willebrand disease and afibrinogenemia. Case reports.

The follicle ruptures at the time of ovulation and fills with blood, forming a corpus hemorrhagicum. Minor bleeding from the follicle into the abdominal cavity may cause peritoneal irritation and, when it occurs in a patient with a defect of primary hemostasis, hemoperitoneum can occur. Von Willebrand disease and afibrinogenemia are two important bleeding disorders in which both primary hemostasis and coagulation are involved.

Spontaneous platelet aggregation during pregnancy in a patient with von Willebrand disease type IIB can be blocked by monoclonal antibodies to both platelet glycoproteins Ib and IIb/IIIa.

Spontaneous platelet aggregation appeared in a patient with von Willebrand disease type IIB during the 37th week of pregnancy. This phenomenon was not associated with symptoms of thrombosis and the patient delivered by caesarean section with no complications. Her platelet-poor plasma (PPP) aggregated normal platelet-rich plasma (PRP) and washed platelets.

Effects of monoclonal antibodies against the platelet glycoprotein IIb/IIIa complex on thrombosis and hemostasis in the baboon.

To assess the hemostatic consequences and antithrombotic effectiveness of blocking the platelet glycoprotein (GP) IIb/IIIa receptor for fibrinogen and other adhesive glycoproteins in vivo, well characterized murine monoclonal antibodies against the platelet GP IIb/IIIa complex, AP-2 and LJ-CP8, were infused intravenously into baboons. Four animals each received doses of 0.2, 0.

Isolation and characterization of two domains of human von Willebrand factor that interact with fibrillar collagen types I and III.

We have identified four discrete proteolytic fragments of von Willebrand factor (vWF) that define two collagen-binding domains. Two of the fragments tested, T 96 kDa and T 55 kDa, were generated by digestion with trypsin, and two, Fragments I and III, with Staphylococcus aureus V8 protease. The larger Fragment III, a disulfide-linked homodimer, extends between residues 1 and 1365 of the 2050-residue vWF subunit and comprises the sequence of all the others.

Isolation and characterization of a collagen binding domain in human von Willebrand factor.

von Willebrand factor binds to fibrillar type I collagen in a rapid, temperature-independent, reversible, specific, and saturable manner. Evaluation of binding isotherms by Scatchard-type analysis demonstrated that 6-18 micrograms of von Willebrand factor bind per mg of collagen, with Ka between 2 and 8 X 10(8) M-1. Five distinct tryptic fragments, purified under denaturing and reducing conditions and representing over 75% of the molecular mass of the von Willebrand factor subunit, were tested for their capacity to inhibit the von Willebrand factor-collagen interaction.

A variant of von Willebrand's disease characterized by recessive inheritance and missing triplet structure of von Willebrand factor multimers.

A 10-yr-old girl had bleeding symptoms of moderate severity; her mother and maternal aunt had milder bleeding symptoms, and other members of the kindred were asymptomatic. In the child, factor VIII coagulant activity (VIII:C) and von Willebrand factor antigen (vWF:Ag) were normal, ristocetin cofactor very low, and the bleeding time (BT) markedly prolonged. These values were normal in the rest of the kindred, but the mother and maternal aunt had prolonged BT and a high VIII:C/vWF:Ag ratio.

Biochemical and metabolic aspects of platelet dysfunction in chronic myeloproliferative disorders.

Fifty-two patients with chronic myeloproliferative disorders (13 with polycythemia vera; 23 with primary thrombocythemia; 6 with myelofibrosis and 10 with chronic granulocytic leukemia) had low platelet levels of adenine nucleotides and serotonin and abnormal uptake and storage of the amine. The storage pool deficiency was confined to the substances contained in the platelet dense bodies, because alpha-granule and lysosome markers were present in normal amounts. In chronic granulocytic leukemia the storage defect was usually less marked but was accompanied by a decreased formation of thromboxane B2 and normal platelet aggregation in response to arachidonic acid.

Detection of circulating released platelets after renal transplantation.

In recipients of renal transplants, the biochemical defect(s) that underlies increased deposition of platelets in the graft and their shortened survival in the circulation are poorly understood. Forty-six recipients of kidney allografts, with and without rejection signs (13 acute rejections (ARs), 15 chronic rejections (CRs), and 18 functioning transplants (FTs), had lower platelet serotonin (5HT) and higher plasma beta-thromboglobulin than normal controls (NCs). These abnormalities were more pronounced in patients with ARs than with CRs but were also present in patients with FTs.

Acquired dysfunction due to the circulation of "exhausted" platelets.

An acquired platelet functional defect was found to be present in eight patients who presented with various clinical conditions--three with renal allograft rejection, three with the hemolytic uremic syndrome or thrombotic thrombocytopenic purpura, one with acute consumption coagulopathy due to an incompatible transfusion and one with systemic lupus erythematosus. They showed defective platelet aggregation and reduced levels of adenine nucleotides and serotonin with abnormal uptake and storage of the amine. The bleeding time was more prolonged than predicted from the platelet count.

Heightened interaction between platelets and factor VIII/von Willebrand factor in a new subtype of von Willebrand's disease.

The form of von Willebrand's disease characterized by a qualitative abnormality of Factor VIII/von Willebrand factor (FVIII/vWF) in plasma has been designated as Type II. We have now identified 20 persons from five families whose qualitatively abnormal FVIII/vWF shows heightened responsiveness to ristocetin. We have classified this form of the disease as Type IIB and reclassified as Type IIA the form previously described as Type II, in which the interaction of the abnormal FVIII/vWF with platelets is decreased or absent in the presence of ristocetin.

Congenital deficiency of thromboxane and prostacyclin.

Animal work suggests that with certain doses of aspirin the antithrombotic effect exerted via the inhibition of the proaggregatory platelet thromboxane A2 (TXA2) may be neutralised by the concomitant vascular reduction of the antiaggregatory prostacyclin (PGI2). Such a situation might result not only in therapeutic ineffectiveness but also in a thrombotic tendency. A patient with a bleeding disorder characterised by a mildly prolonged bleeding time and defective platelet-release reaction due to a congenital deficiency of cyclo-oxygenase provided an opportunity for studying this problem.