Porcine von Willebrand Factor Binding to Human Platelet GPIb Induces Transmembrane Calcium Influx

1996 ◽  
Vol 75 (04) ◽  
pp. 655-660 ◽  
Author(s):  
Mario Mazzucato ◽  
Luigi De Marco ◽  
Paola Pradella ◽  
Adriana Masotti ◽  
Francesco I Pareti
Keyword(s):  
Monoclonal Antibody ◽  
Shear Stress ◽  
Platelet Aggregation ◽  
Von Willebrand Factor ◽  
Human Platelet ◽  
Platelet Glycoprotein ◽  
Dependent Manner ◽  
Transmembrane Flux ◽  
Von Willebrand ◽  
Willebrand Factor

SummaryPorcine von Willebrand factor (P-vWF) binds to human platelet glycoprotein (GP) lb and, upon stirring (1500 rpm/min) at 37° 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 lb, obtained with anti GP lb 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 lb monoclonal antibody which does not inhibit the vWF binding to GP lb. An anti GP Ilb-IIIa monoclonal antibody (LJ-CP8) shown to inhibit the binding of both vWF and fibrinogen to the GP IIb-IIIa complex, had only a slight effect on the [Ca2+]i rise elicited by the addition of P-vWF. No inhibition was also observed with a different anti GP IIb-IIIa monoclonal antibody (LJ-P5), shown to block the binding of vWF and not that of fibrinogen to the GP IIb-IIIa complex. PGE1, apyrase and indomethacin show a minimal effect on [Ca2+]i rise, while EGTA completely blocks it. The GP lb occupancy by recombinant vWF fragment rvWF445-733 completely inhibits the increase of [Ca2+]i and large aggregates formation. Our results suggest that, in analogy to what is seen with human vWF under high shear stress, the binding of P-vWF to platelet GP lb, at low shear stress and through the formation of aggregates of an appropriate size, induces a transmembrane flux of Ca2+, independently from platelet cyclooxy-genase metabolism, perhaps through a receptor dependent calcium channel. The increase in [Ca2+]i may act as an intracellular message and cause the activation of the GP IIb-IIIa complex.

scholarly journals Shear stress-induced von Willebrand factor binding to platelet glycoprotein Ib initiates calcium influx associated with aggregation

Blood ◽  
1992 ◽  
Vol 80 (1) ◽  
pp. 113-120 ◽  
Author(s):  
TW Chow ◽  
JD Hellums ◽  
JL Moake ◽  
MH Kroll
Keyword(s):  
Monoclonal Antibody ◽  
Shear Stress ◽  
Platelet Aggregation ◽  
Von Willebrand Factor ◽  
Fluid Shear Stress ◽  
Platelet Glycoprotein ◽  
Platelet Surface ◽  
Von Willebrand ◽  
Induced Aggregation ◽  
Willebrand Factor

Platelets subjected to elevated levels of fluid shear stress in the absence of exogenous agonists will aggregate. Shear stress-induced aggregation requires von Willebrand factor (vWF) multimers, extracellular calcium (Ca2+), adenosine diphosphate (ADP), and platelet membrane glycoprotein (GP)Ib and GPIIb-IIIa. The sequence of interaction of vWF multimers with platelet surface receptors and the effect of these interactions on platelet activation have not been determined. To elucidate the mechanism of shear stress-induced platelet aggregation, suspensions of washed platelets were subjected to different levels of uniform shear stress (15 to 120 dyne/cm2) in an optically modified cone and plate viscometer. Cytoplasmic ionized calcium ([Ca2+]i) and aggregation of platelets were monitored simultaneously during the application of shear stress; [Ca2+]i was measured using indo-1 loaded platelets and aggregation was measured as changes in light transmission. Basal [Ca2+]i was approximately 60 to 100 nmol/L. An increase of [Ca2+]i (up to greater than 1,000 nmol/L) was accompanied by synchronous aggregation, and both responses were dependent on the shear force and the presence of vWF multimers. EGTA chelation of extracellular Ca2+ completely inhibited vWF-mediated [Ca2+]i and aggregation responses to shear stress. Aurin tricarboxylic acid, which blocks the GPIb recognition site on the vWF monomer, and 6D1, a monoclonal antibody to GPIb, also completely inhibited platelet responses to shear stress. The tetrapeptide RGDS and the monoclonal antibody 10E5, which inhibit vWF binding to GPIIb-IIIa, partially inhibited shear stress-induced [Ca2+]i and aggregation responses. The combination of creatine phosphate/creatine phosphokinase, which converts ADP to adenosine triphosphate and blocks the effect of ADP released from stimulated platelets, inhibited shear stress-induced platelet aggregation without affecting the increase of [Ca2+]i. Neither the [Ca2+]i nor aggregation response to shear stress was inhibited by blocking platelet cyclooxygenase metabolism with acetylsalicylic acid. These results indicate that GPIb and extracellular Ca2+ are absolutely required for vWF-mediated [Ca2+]i and aggregation responses to imposed shear stress, and that the interaction of vWF multimers with GPIIb-IIIa potentiates these responses. Shear stress-induced elevation of platelet [Ca2+]i, but not aggregation, is independent of the effects of release ADP, and both responses occur independently of platelet cyclooxygenase metabolism. These results suggest that shear stress induces the binding of vWF multimers to platelet GPIb and this vWF-GPIb interaction causes an increase of [Ca2+]i and platelet aggregation, both of which are potentiated by vWF binding to the platelet GPIIb-IIIa complex.

scholarly journals Shear stress-induced von Willebrand factor binding to platelet glycoprotein Ib initiates calcium influx associated with aggregation

Blood ◽  
1992 ◽  
Vol 80 (1) ◽  
pp. 113-120 ◽  
Author(s):  
TW Chow ◽  
JD Hellums ◽  
JL Moake ◽  
MH Kroll
Keyword(s):  
Monoclonal Antibody ◽  
Shear Stress ◽  
Platelet Aggregation ◽  
Von Willebrand Factor ◽  
Fluid Shear Stress ◽  
Platelet Glycoprotein ◽  
Platelet Surface ◽  
Von Willebrand ◽  
Induced Aggregation ◽  
Willebrand Factor

Abstract Platelets subjected to elevated levels of fluid shear stress in the absence of exogenous agonists will aggregate. Shear stress-induced aggregation requires von Willebrand factor (vWF) multimers, extracellular calcium (Ca2+), adenosine diphosphate (ADP), and platelet membrane glycoprotein (GP)Ib and GPIIb-IIIa. The sequence of interaction of vWF multimers with platelet surface receptors and the effect of these interactions on platelet activation have not been determined. To elucidate the mechanism of shear stress-induced platelet aggregation, suspensions of washed platelets were subjected to different levels of uniform shear stress (15 to 120 dyne/cm2) in an optically modified cone and plate viscometer. Cytoplasmic ionized calcium ([Ca2+]i) and aggregation of platelets were monitored simultaneously during the application of shear stress; [Ca2+]i was measured using indo-1 loaded platelets and aggregation was measured as changes in light transmission. Basal [Ca2+]i was approximately 60 to 100 nmol/L. An increase of [Ca2+]i (up to greater than 1,000 nmol/L) was accompanied by synchronous aggregation, and both responses were dependent on the shear force and the presence of vWF multimers. EGTA chelation of extracellular Ca2+ completely inhibited vWF-mediated [Ca2+]i and aggregation responses to shear stress. Aurin tricarboxylic acid, which blocks the GPIb recognition site on the vWF monomer, and 6D1, a monoclonal antibody to GPIb, also completely inhibited platelet responses to shear stress. The tetrapeptide RGDS and the monoclonal antibody 10E5, which inhibit vWF binding to GPIIb-IIIa, partially inhibited shear stress-induced [Ca2+]i and aggregation responses. The combination of creatine phosphate/creatine phosphokinase, which converts ADP to adenosine triphosphate and blocks the effect of ADP released from stimulated platelets, inhibited shear stress-induced platelet aggregation without affecting the increase of [Ca2+]i. Neither the [Ca2+]i nor aggregation response to shear stress was inhibited by blocking platelet cyclooxygenase metabolism with acetylsalicylic acid. These results indicate that GPIb and extracellular Ca2+ are absolutely required for vWF-mediated [Ca2+]i and aggregation responses to imposed shear stress, and that the interaction of vWF multimers with GPIIb-IIIa potentiates these responses. Shear stress-induced elevation of platelet [Ca2+]i, but not aggregation, is independent of the effects of release ADP, and both responses occur independently of platelet cyclooxygenase metabolism. These results suggest that shear stress induces the binding of vWF multimers to platelet GPIb and this vWF-GPIb interaction causes an increase of [Ca2+]i and platelet aggregation, both of which are potentiated by vWF binding to the platelet GPIIb-IIIa complex.

scholarly journals Platelet Aggregation Induced by a Monoclonal Antibody to the A1 Domain of von Willebrand Factor

Blood ◽  
1998 ◽  
Vol 91 (10) ◽  
pp. 3792-3799 ◽  
Author(s):  
Hilde Depraetere ◽  
Nadine Ajzenberg ◽  
Jean-Pierre Girma ◽  
Catherine Lacombe ◽  
Dominique Meyer ◽  
...  
Keyword(s):  
Shear Stress ◽  
Platelet Aggregation ◽  
Von Willebrand Factor ◽  
Inhibitory Effect ◽  
Platelet Glycoprotein ◽  
Rotational Viscometer ◽  
Induce Platelet Aggregation ◽  
Static Conditions ◽  
Von Willebrand ◽  
Willebrand Factor

Shear-induced platelet aggregation (SIPA) involves von Willebrand Factor (vWF) binding to platelet glycoprotein (GP)Ib at high shear stress, followed by the activation of αIIbβ3. The purpose of this study was to determine the vWF sequences involved in SIPA by using monoclonal antibodies (MoAbs) to vWF known to interfere with its binding to GPIb and to αIIbβ3. Washed platelets were exposed to shear rates between 100 and 4,000 seconds−1 in a rotational viscometer. SIPA was quantitated by flow cytometry as the disappearance of single platelets (DSP) in the sheared sample in the presence of vWF, relative to a control in the absence of shear and vWF. At a shear rate of 4,000 seconds−1, DSP was increased from 5.9% ± 3.5% in the absence of vWF to 32.7% ± 6.3% in the presence of vWF. This increase in SIPA was not associated with an elevation of P-selectin expression. vWF-dependent SIPA was completely abolished by MoAb 6D1 to GPIb and partially inhibited by MoAb 10E5 to αIIbβ3. Three MoAbs to vWF were compared for their effect on SIPA at 4,000 seconds−1 in the presence of vWF: MoAb 328, known to block vWF binding to GPIb in the presence of ristocetin, MoAb 724 blocking vWF binding to GPIb in the presence of botrocetin, and MoAb 9, an inhibitor of vWF binding to αIIbβ3. Similar to the effect of MoAb 6D1, MoAb 328 completely inhibited the effect of vWF, whereas MoAb 9 had a partial inhibitory effect, as MoAb 10E5 did. In contrast, MoAb 724, as well as its F(ab′)2 fragments, promoted shear-dependent platelet aggregation (165% of the DSP value obtained in the absence of MoAb 724), indicating that MoAb 724 was responsible for an enhanced aggregation, which was independent of binding to the platelet Fcγ receptor. In addition, the enhancement of aggregation induced by MoAb 724 was abrogated by MoAb 6D1 or 10E5 to the level of SIPA obtained in the presence of vWF incubated with a control MoAb to vWF. Finally, the activating effect of MoAb 724 was also found under static conditions at ristocetin concentrations too low to induce platelet aggregation. Our results suggested that on binding to a botrocetin-binding site on vWF, MoAb 724 mimics the effect of botrocetin by inducing an active conformation of vWF that is more sensitive to shear stress or to low ristocetin concentration.

scholarly journals Platelet Aggregation Induced by a Monoclonal Antibody to the A1 Domain of von Willebrand Factor

Blood ◽  
1998 ◽  
Vol 91 (10) ◽  
pp. 3792-3799 ◽  
Author(s):  
Hilde Depraetere ◽  
Nadine Ajzenberg ◽  
Jean-Pierre Girma ◽  
Catherine Lacombe ◽  
Dominique Meyer ◽  
...  
Keyword(s):  
Shear Stress ◽  
Platelet Aggregation ◽  
Von Willebrand Factor ◽  
Inhibitory Effect ◽  
Platelet Glycoprotein ◽  
Rotational Viscometer ◽  
Induce Platelet Aggregation ◽  
Static Conditions ◽  
Von Willebrand ◽  
Willebrand Factor

AbstractShear-induced platelet aggregation (SIPA) involves von Willebrand Factor (vWF) binding to platelet glycoprotein (GP)Ib at high shear stress, followed by the activation of αIIbβ3. The purpose of this study was to determine the vWF sequences involved in SIPA by using monoclonal antibodies (MoAbs) to vWF known to interfere with its binding to GPIb and to αIIbβ3. Washed platelets were exposed to shear rates between 100 and 4,000 seconds−1 in a rotational viscometer. SIPA was quantitated by flow cytometry as the disappearance of single platelets (DSP) in the sheared sample in the presence of vWF, relative to a control in the absence of shear and vWF. At a shear rate of 4,000 seconds−1, DSP was increased from 5.9% ± 3.5% in the absence of vWF to 32.7% ± 6.3% in the presence of vWF. This increase in SIPA was not associated with an elevation of P-selectin expression. vWF-dependent SIPA was completely abolished by MoAb 6D1 to GPIb and partially inhibited by MoAb 10E5 to αIIbβ3. Three MoAbs to vWF were compared for their effect on SIPA at 4,000 seconds−1 in the presence of vWF: MoAb 328, known to block vWF binding to GPIb in the presence of ristocetin, MoAb 724 blocking vWF binding to GPIb in the presence of botrocetin, and MoAb 9, an inhibitor of vWF binding to αIIbβ3. Similar to the effect of MoAb 6D1, MoAb 328 completely inhibited the effect of vWF, whereas MoAb 9 had a partial inhibitory effect, as MoAb 10E5 did. In contrast, MoAb 724, as well as its F(ab′)2 fragments, promoted shear-dependent platelet aggregation (165% of the DSP value obtained in the absence of MoAb 724), indicating that MoAb 724 was responsible for an enhanced aggregation, which was independent of binding to the platelet Fcγ receptor. In addition, the enhancement of aggregation induced by MoAb 724 was abrogated by MoAb 6D1 or 10E5 to the level of SIPA obtained in the presence of vWF incubated with a control MoAb to vWF. Finally, the activating effect of MoAb 724 was also found under static conditions at ristocetin concentrations too low to induce platelet aggregation. Our results suggested that on binding to a botrocetin-binding site on vWF, MoAb 724 mimics the effect of botrocetin by inducing an active conformation of vWF that is more sensitive to shear stress or to low ristocetin concentration.

THE PLATELET AGGREGATING PROPERTIES OF TYPE IIB VON WILLEBRAND FACTOR (vWF): THE ROLE OF PLATELET ACTIVATION, FIBRINOGEN AND TWO DISTINCT MEMBRANE RECEPTORS

1987 ◽  
Author(s):  
L De Marco ◽  
M Mazzucato ◽  
M G Del Ben ◽  
U Budde ◽  
A B Federici ◽  
...  
Keyword(s):  
Monoclonal Antibody ◽  
Platelet Aggregation ◽  
Von Willebrand Factor ◽  
Binding Domain ◽  
Platelet Glycoprotein ◽  
Induce Platelet Aggregation ◽  
Adhesive Proteins ◽  
Von Willebrand ◽  
Induced Aggregation ◽  
Willebrand Factor

Three preparations of purified von Willebrand factor (vWF), obtained from unrelated patients affected by type IIB von Willebrand disease, were found to have normal sialic acid content (between 129-190 nmoles/mg of vWF, as compared to 158 ± 17 nmoles/mg in four normal preparations) and to induce platelet aggregation in the presence of physiologic levels of divalent cations and without addition of ristocetin. A monoclonal antibody that blocks the vWF binding domain of the platelet glycoprotein (GP) Ib caused complete inhibition of IIB vWF-induced aggregation. On the contrary, a monoclonal antibody that blocks the receptor for adhesive proteins on the platelet GPIIb/IIIa complex failed to inhibit the initial response of platelets to high concentration of IIB vWF Moreover, IIB vWF caused agglutination of formalin-fixed platelets that was blocked only by the anti-GPIb antibody, suggesting that the binding of vWF to GPIb, even in the absence of ristocetin, results in platelet-platelet interaction that is followed by exposure of the GPIIb/IIIa receptors for adhesive proteins. Endogenous ADP, normally active platelet metabolism and fibrinogen binding to GPIIb/IIIa were necessary for maximal and irreversible platelet aggregation. In the absence of fibrinogen, however, aggregation was mediated by vWF binding to GPIIb/IIIa. A 52/48 kDa tryptic fragment containing the GPIb binding domain of normal vWF completely blocked the aggregation induced by all three IIB vWF preparations. The present study defines in detail the mechanisms involved in IIB vWF-induced platelet aggregation. Moreover, it establishes that the GPIb binding domain of normal and IIB vWF are closely related and that desialylation is not required for the direct interaction of IIB vWF with GPIb.

Fc-receptor Dependent Platelet Aggregation Induced by Monoclonal Antibodies against Platelet Glycoprotein Ib or von Willebrand Factor

2001 ◽  
Vol 85 (04) ◽  
pp. 679-685 ◽  
Author(s):  
Nancy Cauwenberghs ◽  
Agotha Schlammadinger ◽  
Stephan Vauterin ◽  
Susan Cooper ◽  
Gretel Descheemaeker ◽  
...  
Keyword(s):  
Platelet Aggregation ◽  
Platelet Activation ◽  
Von Willebrand Factor ◽  
Human Platelet ◽  
Platelet Rich Plasma ◽  
Fc Receptor ◽  
Platelet Glycoprotein ◽  
Protein Tyrosine Phosphorylation ◽  
Von Willebrand ◽  
Willebrand Factor

SummaryIn this paper we describe two pathways leading to platelet activation by crosslinking glycoprotein (GP) Ib to the platelet Fc-receptor (FcγRII). First the monoclonal antibody (MoAb) 9C8, raised against human platelet GPIbα, dose-dependently induced platelet aggregation of citrate-anticoagulated platelet-rich plasma, an effect that can be inhibited by several activation inhibitors. The FcγRII-inhibitory MoAb IV.3 was able to prevent the aggregatory effects of MoAb 9C8, indicating that crosslinking of the antigen GPIbαto the FcγII-receptor is necessary for the activating effect. Secondly we observed a synergistic activating effect of two anti-von Willebrand factor (vWF) MoAbs 1C1E7 and B724, both known to enhance vWF binding to GPIbαin the presence of shear or ristocetin. When these antibodies are added together to PRP, platelet aggregation is induced without further need for an additional modulator. This effect can be blocked by either MoAb IV.3 or an inhibitory anti-GPIbαMoAb, indicating that again the platelet activation results from signaling through FcγRII crosslinked to vWF bound to GPIbα. In addition, both the anti-GPIbαMoAb 9C8, or the two anti-vWF MoAbs 1C1E7 and B724 induce genuine platelet activation, as evidenced by the secretion of ATP and protein tyrosine phosphorylation. These findings with both anti-GPIbαand anti-vWF MoAbs add further proof to recent reports demonstrating an interaction between the platelet receptors GPIbαand FcγRII, suggesting a role for the FcγII-receptor in GPIb-related signaling.

Ristocetin-dependent, but not botrocetin-dependent, binding of von Willebrand factor to the platelet glycoprotein Ib-IX-V complex correlates with shear-dependent interactions

Blood ◽  
2001 ◽  
Vol 97 (1) ◽  
pp. 162-168 ◽  
Author(s):  
Jing-Fei Dong ◽  
Michael C. Berndt ◽  
Alicia Schade ◽  
Larry V. McIntire ◽  
Robert K. Andrews ◽  
...  
Keyword(s):  
Shear Stress ◽  
Platelet Aggregation ◽  
Von Willebrand Factor ◽  
Chinese Hamster Ovary Cells ◽  
Chinese Hamster ◽  
Platelet Glycoprotein ◽  
Extracellular Region ◽  
Static Conditions ◽  
Von Willebrand ◽  
Willebrand Factor

Abstract Under conditions of high shear stress, both hemostasis and thrombosis are initiated by the interaction of the platelet membrane glycoprotein (GP) Ib-IX-V complex with its adhesive ligand, von Willebrand factor (vWF), in the subendothelial matrix or plasma. This interaction involves the A1 domain of vWF and the N-terminal extracellular region of GP Ibα (His-1-Glu-282), and it can also be induced under static conditions by the modulators ristocetin and botrocetin. In this study, a panel of anti-vWF and anti-GP Ibα antibodies—previously characterized for their effects on ristocetin- and botrocetin-dependent vWF–GP Ib-IX-V interactions—was analyzed for their capacity to inhibit either the adhesion of Chinese hamster ovary cells expressing recombinant GP Ibα to surface-associated vWF under hydrodynamic flow or shear-stress–induced platelet aggregation. The combined results suggest that the shear-dependent interactions between vWF and GP Ibα closely correlate with ristocetin- rather than botrocetin-dependent binding under static conditions and that certain anti-vWF monoclonal antibodies are able to selectively inhibit shear-dependent platelet aggregation.

scholarly journals Aurin tricarboxylic acid: a novel inhibitor of the association of von Willebrand factor and platelets

Blood ◽  
1988 ◽  
Vol 72 (6) ◽  
pp. 1898-1903 ◽  
Author(s):  
MD Phillips ◽  
JL Moake ◽  
L Nolasco ◽  
N Turner
Keyword(s):  
Platelet Aggregation ◽  
Von Willebrand Factor ◽  
Competitive Inhibition ◽  
Platelet Rich Plasma ◽  
Tricarboxylic Acid ◽  
Platelet Glycoprotein ◽  
Dependent Manner ◽  
Von Willebrand ◽  
Induced Aggregation ◽  
Willebrand Factor

Abstract Shear stress activated platelets undergo aggregation in the presence of large or unusually large von Willebrand factor (vWF) multimers without the addition of ristocetin or any other exogenous chemical. This phenomenon may be analogous to the platelet aggregation that leads to thrombosis in the narrowed arteries and arterioles of patients with atherosclerosis or vasospasm. A triphenyl-methyl compound, aurin tricarboxylic acid (ATA), inhibits shear-induced, vWF-mediated platelet aggregation in platelet-rich plasma (PRP) in concentrations above 200 mumol/L and in buffer suspensions of washed platelets at a concentration of 0.1 mumol/L. In a concentration-dependent manner, ATA also inhibits ristocetin-induced, vWF-mediated platelet clumping in both fresh and formaldehyde-fixed platelet suspensions. This inhibition can be overcome by increasing the concentration of vWF, following the kinetics of first order competitive inhibition. ATA prevents the attachment to platelets of the largest vWF multimeric forms found in normal plasma and of the unusually large vWF multimers derived from endothelial cells. The rate of aggregation and degree of inhibition by ATA is not accounted for by the binding of ristocetin or calcium. Arachidonic acid- and adenosine diphosphate (ADP)-induced aggregation are not inhibited by ATA. Platelets incubated with ATA can be easily separated from the compound. However, ATA binds to large vWF multimeric forms and inhibits their ristocetin-induced interaction with platelet glycoprotein Ib. Because ATA also inhibits shear-induced, vWF-mediated platelet aggregation in vitro in the absence of ristocetin, it may be a useful prototype compound to impede the development of arterial thrombosis in vivo.

scholarly journals Aurin tricarboxylic acid: a novel inhibitor of the association of von Willebrand factor and platelets

Blood ◽  
1988 ◽  
Vol 72 (6) ◽  
pp. 1898-1903 ◽  
Author(s):  
MD Phillips ◽  
JL Moake ◽  
L Nolasco ◽  
N Turner
Keyword(s):  
Platelet Aggregation ◽  
Von Willebrand Factor ◽  
Competitive Inhibition ◽  
Platelet Rich Plasma ◽  
Tricarboxylic Acid ◽  
Platelet Glycoprotein ◽  
Dependent Manner ◽  
Von Willebrand ◽  
Induced Aggregation ◽  
Willebrand Factor

Shear stress activated platelets undergo aggregation in the presence of large or unusually large von Willebrand factor (vWF) multimers without the addition of ristocetin or any other exogenous chemical. This phenomenon may be analogous to the platelet aggregation that leads to thrombosis in the narrowed arteries and arterioles of patients with atherosclerosis or vasospasm. A triphenyl-methyl compound, aurin tricarboxylic acid (ATA), inhibits shear-induced, vWF-mediated platelet aggregation in platelet-rich plasma (PRP) in concentrations above 200 mumol/L and in buffer suspensions of washed platelets at a concentration of 0.1 mumol/L. In a concentration-dependent manner, ATA also inhibits ristocetin-induced, vWF-mediated platelet clumping in both fresh and formaldehyde-fixed platelet suspensions. This inhibition can be overcome by increasing the concentration of vWF, following the kinetics of first order competitive inhibition. ATA prevents the attachment to platelets of the largest vWF multimeric forms found in normal plasma and of the unusually large vWF multimers derived from endothelial cells. The rate of aggregation and degree of inhibition by ATA is not accounted for by the binding of ristocetin or calcium. Arachidonic acid- and adenosine diphosphate (ADP)-induced aggregation are not inhibited by ATA. Platelets incubated with ATA can be easily separated from the compound. However, ATA binds to large vWF multimeric forms and inhibits their ristocetin-induced interaction with platelet glycoprotein Ib. Because ATA also inhibits shear-induced, vWF-mediated platelet aggregation in vitro in the absence of ristocetin, it may be a useful prototype compound to impede the development of arterial thrombosis in vivo.

Shear Stress-Induced Binding of Large and Unusually Large von Willebrand Factor to Human Platelet Glycoprotein Ibα

2004 ◽  
Vol 32 (7) ◽  
pp. 961-969 ◽  
Author(s):  
Feng Li ◽  
Chester Q. Li ◽  
Joel L. Moake ◽  
José A. López ◽  
Larry V. McIntire
Keyword(s):  
Shear Stress ◽  
Von Willebrand Factor ◽  
Human Platelet ◽  
Platelet Glycoprotein ◽  
Von Willebrand ◽  
Willebrand Factor
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