A role for prostaglandins and thromboxanes in the exposure of platelet fibrinogen receptors.

769

274

A B S T R A C T To define better the role of the fibrinogen receptor in platelet physiology and to characterize it biochemically, a murine monoclonal antibody that completely blocks the binding of fibrinogen to the platelet surface was produced by the hybridoma technique with the aid of a functional screening assay. Purified F(ab')2 fragments and/or intact antibody completely blocked aggregation induced by ADP, thrombin, or epinephrine and the binding of radiolabeled fibrinogen to platelets induced by ADP. The antibody did not block agglutination of formaldehyde-fixed platelets by ristocetin or shape change induced by either ADP or thrombin. ADP-and epinephrine-induced release of ATP was completely inhibited by the antibody, but inhibition of release induced by collagen and thrombin was dose dependent and partial. The antibody also dramatically inhibited platelet retention in glass-bead columns, platelet adhesion to glass, and clot retraction. Thus, the antibody induced a thrombasthenic-like state. Immunofluorescent studies confirmed the specificity of the antibody for normal platelets and megakaryocytes and suggested that there is a marked decrease in detectable antigen in thrombasthenic platelets. Radiolabeled antibody bound to an average of -40,000 sites on normal platelets but it bound to <2,000 sites on the platelets of a patient with thrombasthenia. The antibody immunoprecipitated both glycoproteins IIb and IlIa, and both glycoproteins bound to an affinity column of the antibody. These Presented in part to the American Society of Hematology, San Antonio, TX, December 1981, and published in abstract form in Blood, 1981, 58:191a.

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A murine monoclonal antibody that completely blocks the binding of fibrinogen to platelets produces a thrombasthenic-like state in normal platelets and binds to glycoproteins IIb and/or IIIa.

Coller¹,

Peerschke²,

Scudder³

et al. 1983

769

274

“…6), and this drug impairs the binding of vWF only when platelets are exposed to some agents (Table II). Finally, the interaction of thromboxane or ADP with platelets is known to account only for 30-50% of the binding of fibrinogen or vWF observed in response to ADP or collagen (12)(13)(14)(15)44).…”

Section: Discussionmentioning

confidence: 99%

“…The interaction of fibrinogen with platelets plays a central role in platelet physiology (2)(3)(4)(5)(6)(7)(8)(9)(10)(11), and recent data (12)(13)(14)(15)(16) have emphasized the role of ADP, thromboxane (Tx),' and cAMP in the exposure of specific receptors for fibrinogen on the platelet surface. In this report we present evidence that ticlopidine almost suppresses the binding of fibrinogen to platelets without affecting the intraplatelet levels of cAMP, the formation of TxB2 and the secretion of nucleotides in response to high concentrations of collagen, arachidonic acid, ionophore A23187, or thrombin.…”

Section: Introductionmentioning

confidence: 99%

Functionally thrombasthenic state in normal platelets following the administration of ticlopidine.

Minno¹,

Cerbone²,

Mattioli³

et al. 1985

201

To elucidate the bleeding tendency that follows the administration of ticlopidine, we investigated the skin bleeding time and some ex vivo functions of platelets obtained from eight healthy volunteers before and 1 wk after daily administration of 500 mg of ticlopidine. We found the following: ticlopidine significantly (P < 0.001) prolonged the skin bleeding time and impaired the binding of radiolabeled fibrinogen and von Willebrand Factor, the clot retraction and the aggregation of platelets in response to ADP, epinephrine, thrombin, ionophore A23187, collagen, or arachidonic acid. In contrast, the administration of this drug did not affect intraplatelet levels of cAMP, agglutination and binding of von Willebrand Factor in response to ristocetin, shape change in response to ADP, collagen, thrombin, or arachidonic acid, or binding of prostaglandin El to resting platelets. Secretion of ATP in response to ADP or epinephrine was completely inhibited, whereas secretion as well as thromboxane synthesis in response to high concentrations of collagen, arachidonic acid, calcium ionophore A23187, or thrombin was unaffected. Studies with monoclonal antibodies showed that the glycoprotein IIb-IIIa complex (the putative receptor for fibrinogen and von Willebrand Factor on the surface of platelets exposed to naturally occurring aggregating agents) was quantitatively unaffected by ticlopidine. This observation was further confirmed by densitometric scannings of Periodic Acid-Schiff-stained gels of platelet suspensions. The onset, as well as the cessation of the inhibitory effect of ticlopidine on platelets was very slow, and reached a maximum after a 3-5-d administration. In addition, ticlopidine appeared to be a much more potent inhibitor when administered to subjects than when added in vitro to platelets. Finally, abnormalities comparable to those found in volunteers taking ticlopidine were observed when platelets from untreated subjects were incubated in the plasma of ticlopidine-treated subjects.We conclude that ticlopidine induces a thrombasthenic state in normal platelets without affecting the glycoprotein IlbIIIa complex quantitatively. Furthermore, our data suggest that one or more active metabolites rather than the native drug Portions of this work were presented at a symposium ("Ticlopidine: Quo vadis?") in Montpellier, France, 1983, and were published in abstract form in the proceedings of that symposium.Address reprint requests to Dr. Di Minno.

“…Platelets stimulated by ADP (1)(2)(3)(4), thrombin (5,6), epinephrine (2, 7), or prostaglandin endoperoxides (8,9) expose receptors specific for fibrinogen. These fibrinogen-binding sites were shown to be associated with glycoproteins (GP)' Ilb and IlIa of the platelet membrane (10)(11)(12)(13)(14).…”

Section: Introductionmentioning

confidence: 99%

Exposure of fibrinogen receptors in human platelets by surface proteolysis with elastase.

Kornecki¹,

Ehrlich²,

Mars³

et al. 1986

Human platelets that were preincubated with porcine elastase aggregated spontaneously upon the addition of fibrinogen. Maximal aggregation to fibrinogen was observed with platelets pretreated with an elastase concentration of 111 tg/ml, and halfmaximal aggregation occurred after treatment with 11 ,ug/ml elastase. Binding of radiolabeled fibrinogen to elastase-treated platelets was specific, saturable, and showed a single class of 48,400±9,697 fibrinogen-binding sites per platelet with a dissociation constant of 6.30±1.48 X i0-M. ATP, apyrase, and the stimulators of platelet adenylate cyclase forskolin, prostaglandin El, prostacyclin, and N6, 2'-O-dibutyryl cyclic AMP did not inhibit the fibrinogen-induced aggregation of elastase-treated platelets. EDTA completely blocked the initiation of aggregation and reversed the fibrinogen-induced aggregation of elastasetreated platelets. Monoclonal and polyclonal antibodies directed against glycoproteins (GP) Ilb and II1a completely blocked the fibrinogen-induced aggregation of elastase-treated platelets. Immunoprecipitates with these antibodies obtained from detergent extracts of surface-radiolabeled, intact, and elastase-treated platelets contained the glycoproteins IUb and IIIa. We conclude that surface proteolysis by low concentrations of elastase can expose fibrinogen-binding sites associated with GPIIb and GPIIIa on the platelet surface, resulting in spontaneous aggregation upon the addition of fibrinogen. These findings may be relevant to hemostatic changes observed in patients with increased levels of circulating elastase.