Binding of Platelet Agglutinating Protein p 37 from the Plasma of a Patient with Thrombotic Thrombocytopenic Purpura to Human Platelets

1991 ◽  
Vol 65 (01) ◽  
pp. 096-101 ◽  
Author(s):  
Eric C-Y Lian ◽  
Farooq A Siddiqui
Keyword(s):  
Thrombotic Thrombocytopenic Purpura ◽  
Helix Pomatia ◽  
Human Platelets ◽  
Scatchard Analysis ◽  
Thrombocytopenic Purpura ◽  
Specific Protease ◽  
Von Willebrand ◽  
Willebrand Factor ◽  
Helix Pomatia Lectin ◽  
Insight Into

SummaryWe have previously reported the purification of a 37 kDa platelet agglutinating protein (PAP p37) from the plasma of a patient with thrombotic thrombocytopenic purpura (TTP) that was shown to be present in a subset of TTP patients. To gain further insight into the interaction between PAP p37 and platelets, we have studied the properties of PAP p37 binding to platelets. Washed human platelets from two normal donors and two TTP patients after recovery were used for the experiments. The PAP p 37 binding to platelets was specific, concentration dependent and saturable. Scatchard analysis demonstrated about 20,564–27,090 PAP p37 binding sites per platelet. Stimulation of platelets with thrombin or ADP did not have any significant effect on its binding.Thiol- and serine-specific protease inhibitors did not inhibit PAP p37 binding to the platelets. Sugars such as glucose, fructose, mannose, and sialic acid, at 40 mM, inhibited its binding to platelets by 44%, 73%, 79%, and 91% respectively, but galactose and amino sugars did not have any significant effect. At 250 μg/ml, Concanavalin-A inhibited 42% of binding, but other lectins, such as phytohemagglutinin-P, potato lectin and helix pomatia lectin (snail), did not. Pre-incubation of 125I-PAP p37 with the adult human IgG, decreased its binding to the platelets. The monoclonal antibodies to GP Ib (6D1) and GP IIb-IIIa complex (10E5) did not inhibit the binding of 125I-PAP p37 to platelets. Fibrinogen and von Willebrand factor did not affect the binding either. These results suggest that PAP p37 binds to platelets on the sites other than GP lb or GP IIb-IIIa complex.

The Importance of the Carbohydrate Moiety of the Factor VIII/Von Willebrand Factor Protein in Binding to and Causing Agglutination of Human Platelets

1979 ◽  
Author(s):  
H.R. Gralnick ◽  
D.K. Morisato
Keyword(s):  
Factor Viii ◽  
Von Willebrand Factor ◽  
Binding Sites ◽  
Human Platelets ◽  
Galactose Oxidase ◽  
Scatchard Analysis ◽  
Human Fibrinogen ◽  
Number Of Binding Sites ◽  
Von Willebrand ◽  
Willebrand Factor

We have investigated the binding of radiolabelled factor VIII/von Willebrand factor (f. VIII/vWf) protein to human platelets (P) in the presence of ristocetin (R). In these atudies we have delineated the importance of the carbohydrate (CHO) moiety(s) in both the binding to the P and in cauaing agglutination of P. Binding of the f.VIII/vWf protein to human P was time and temperature dependent and dependent on the concentration of R. Binding was specific in that it could not be blocked by human fibrinogen but was inhibited by unlabelled f.VIII/vWf protein. In studies utilizing varying amounts of the f.VIII/vWf protein or by varying the number of P in the assay, the number of binding sites for the f. VIII/vWf protein were estimated at 9,500-9,800 per platelet. Scatchard analysis revealed 11,000 binding sites with 3,600 of high affinity and 7,400 of low affinity. Removal of the sialic acid of the f.VIII/vWf protein resulted in no significa nt change in its ability to bind to the P surface or cause agglutination in the presence, IR. Removal of the galactose by 6-galactosijase resulted in a 75% reduction of binding of the f.VIII/vWf protein and a 91% decrease in the agglutination of human P. Similar studies with galactose oxidase showed that oxidation of the penultimate galactose residue s results in a decrease in agglutination comparable to that seen with 6-galactosidase treatment. These studies indicate that the CHO moiety of the f.VIII/vWf protein is important in both binding to the P surface as well as causing agglutination of human P.

scholarly journals Cost effectiveness of caplacizumab in acquired thrombotic thrombocytopenic purpura

Blood ◽  
2020 ◽  
Author(s):  
George Goshua ◽  
Pranay Sinha ◽  
Jeanne Elise Hendrickson ◽  
Christopher A Tormey ◽  
Pavan Bendapudi ◽  
...  
Keyword(s):  
Cost Effectiveness ◽  
Thrombotic Thrombocytopenic Purpura ◽  
Von Willebrand Factor ◽  
Organ Damage ◽  
Hospital Length Of Stay ◽  
Sensitivity Analyses ◽  
Thrombocytopenic Purpura ◽  
Von Willebrand ◽  
Willebrand Factor ◽  
Relapse Rates

Acquired thrombotic thrombocytopenic purpura (TTP) is a life-threatening disease characterized by thrombotic microangiopathy leading to end-organ damage. The standard of care (SOC) treatment is therapeutic plasma exchange (TPE) alongside immunomodulation with steroids, with increasing use of rituximab +/- other immunomodulatory agents. The addition of caplacizumab, a nanobody targeting von Willebrand factor, was shown to accelerate platelet count recovery and reduce TPE treatments and hospital length of stay in TTP patients treated in the TITAN and HERCULES trials. The addition of caplacizumab to SOC also led to increased bleeding due to transient reductions in von Willebrand factor and increased relapse rates. Using data from TITAN and HERCULES on caplacizumab, we performed the first-ever cost effectiveness analysis in TTP. Over a 5-year period, the projected incremental cost effectiveness ratio (ICER) in our Markov model was $1,482,260, significantly above the accepted 2019 US willingness-to-pay of $195,300. One-way sensitivity analyses showed the utility of the well state and the cost of caplacizumab to have the largest effects on ICER, with a reduction in caplacizumab cost demonstrating the greatest impact on lowering the ICER. In a probabilistic sensitivity analysis, SOC was favored over caplacizumab in 100% of 10,000 iterations. Our data indicate that the addition of caplacizumab to SOC in treatment of acquired TTP is not cost effective due to the high cost of the medication and its failure to improve relapse rates. The potential impact of caplacizumab on health system cost using longer-term follow-up data merits further study.

The Binding Of 125I-Von Willebrand Factor To Human Platelets In The Presence Of Ristocetin

1981 ◽  
Author(s):  
P Silber ◽  
T H Finlay
Keyword(s):  
Von Willebrand Factor ◽  
Binding Sites ◽  
Binding Constant ◽  
Specific Binding ◽  
Human Platelets ◽  
Scatchard Analysis ◽  
Binding Data ◽  
Number Of Binding Sites ◽  
Von Willebrand ◽  
Willebrand Factor

The effect of ristocetin on the binding of 125I-porcine von Willebrand factor to human platelets was studied. Previously, we had shown that 125I-porcine von Willebrand factor binds to human platelets in the absence of ristocetin. The present work demonstrates that binding is stimulated by ristocetin and this stimulation is maximal at a ristocetin concentration of 2 mg/ml. At a ristocetin concentration of 0.5 mg/ml, Scatchard analysis indicates a binding constant of 5.18 × 10-9M and the presence of 105,000 binding sites. This compares with our previous finding, in the absence of ristocetin, of a binding constant of 2.92 × 10-7M and 4760 binding sites. These binding data assume the porcine von Willebrand factor to be a tetramer with a molecular weight of 9 × 105. This study indicates that ristocetin causes tighter binding and increases the number of binding sites on human platelets for porcine von Willebrand factor. Unlabelled porcine von Willebrand factor competitively inhibits the specific binding of the labelled protein and gives a binding constant of 0.17 × 10-9M. Similar results were obtained using human von Willebrand factor.

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