125I-Fibrinogen Binding to Platelets in Myeloproliferative Disease

Abstract

SummaryRecent reports have suggested a variation in the density and affinity of fibrinogen binding sites in platelets from patients with myeloproliferative disorders (MPD) which may reflect platelet functional abnormalities in these subjects. We have investigated the binding of 125I-fibrinogen (125I-Fb) to gel-filtered platelets from a large relatively homogeneous group of patients with MPD compared to normal age matched controls. Twenty-two of the patients investigated had polycythaemia vera and four essential thrombocythaemia.The maximal density and affinity (Kd) of 125I-Fb binding was assessed by saturation analysis in gel-filtered platelets (GFP) stimulated with either 10 εM ADP or 150 mU thrombin. In addition the functional significance of the binding sites was studied by evaluating the response of GFP from the two experimental groups by assessing the effects of increasing concentrations of added fibrinogen on the response to 10 εM ADP using standard light transmission aggregometry.In both groups the density of fibrinogen binding sites expressed in response to thrombin stimulation was significantly higher (approximately 2-3 fold) than that found in response to ADP. However, fewer binding sites were detected in the MPD group as compared with the control group in response to both ADP and thrombin. The Kd for 125I-Fb was similar for both agonists in normal controls and was significantly lower than that found in the MPD subjects.Although the 125I-Fb binding study results indicate a significant reduction in both the number and affinity of fibrinogen binding sites in patients with myeloproliferative disorders, the clinical and functional significance of these findings remain uncertain.

The human platelet fibrinogen receptor: clinical and therapeutic significance.

“…We have shown that the EC50 for added fibrinogen supporting ADP induced aggregation in this way is approximately 60 mm which is very similar to the Kd for [1251]-fibrinogen binding in the presence of ADP to the high affinity binding site (70 nM) in the same platelets (Mistry et al, 1991). Several groups of workers have examined the density and affinity of fibrinogen binding sites on abnormal platelets from patients with myeloproliferative disorders (MPD) in an attempt to relate changes in this receptor to clinical abnormalities (Clezardin et al, 1985;Landolfi et al, 1988;Mazzucato et al, 1989;Mistry et al, 1991). These studies show conflicting results indicating a pathological correlation depending on whether high or low affinity binding is considered.…”

“…In situ on the platelet the complex exhibits the properties of a membrane binding site in that binding of fibrinogen is saturable, reversible and dependent on the presence of divalent cations in physiological concentrations (Marguerie et al, 1979;Peerschke et al, 1980). The characterisation of receptor density (Bma,) and affinity (Kd) on platelets has been undertaken in a number of laboratories using radioligand binding methods Marguerie et al, 1987;Mistry et al, 1991;Peerschke et al, 1980). Briefly the technique involves the preparation of gel-filtered platelets from citrated/aspirin treated blood followed by stimulation with agonists (usually ADP and thrombin) in the presence of millimolar concentrations of divalent ions and varying quantities of the radioligand.…”

“…In situ on the platelet the complex exhibits the properties of a membrane binding site in that binding of fibrinogen is saturable, reversible and dependent on the presence of divalent cations in physiological concentrations (Marguerie et al, 1979;Peerschke et al, 1980). The characterisation of receptor density (Bma,) and affinity (Kd) on platelets has been undertaken in a number of laboratories using radioligand binding methods Marguerie et al, 1987;Mistry et al, 1991;Peerschke et al, 1980 (Clezardin et al, 1985;Landolfi et al, 1988;Mazzucato et al, 1989;Mistry et al, 1991 (ii) Synthetic peptides comprising short amino acid sequences which compete with fibrinogen for the binding sites on the GPIIb/IIIa complexes are another class of compounds with potential antithrombotic clinical application . The peptide glycineproline-arginine-proline was the first short chain peptide shown to inhibit platelet fibrinogen binding (Ruggeri et al, 1986).…”

Relation of Platelet Abnormalities to Thrombosis and Hemorrhage in Chronic Myeloproliferative Disorders

“…96 Analysis of fibrinogen binding to platelets revealed a decreased number of binding sites in most stud ies. 94,97,98 Heterogeneous affinity of fibrinogen receptors was reported by Landolfi et al 97 in patients with PV and was attributed to platelet heterogeneity in this disease.…”

Recombinant activated factor VII for intractable bleeding post splenectomy in a patient with myeloproliferative disorder

“…Aggregation is mainly mediated through glycoprotein IIb/IIIa. Several authors have demonstrated that the glycoprotein IIb/IIIa complexes are decreased in patients with MPDs [9], in addition to a decrease in the binding of fibrinogen, which is the functional counterpart of decreased glycoprotein IIb/IIIa receptors on the platelet surface [9,10]. Some investigators demonstrated that MPD patients may not only have a quantitative decrease of glycoprotein IIb/IIIa receptors on the platelet surface, but also a qualitative defect [11].…”