15-hydroxy-11-alpha-9-alpha-(epoxymethano)prosta-5-13-dienoic-acid and Myeloproliferative-Disorders

Defects in glycoprotein (GP)IIb-IIIa or in its activation may cause abnormal platelet aggregation and a bleeding diathesis. We report studies in a 67-year-old man with a myeloproliferative disease and markedly abnormal platelet responses. By flow cytometry, platelet binding of two complex-specific anti-GPIIb-IIIa monoclonal antibodies (mAbs), A2A9 and 10E5, was approximately 50% of normal. An enzyme-linked immunosorbent assay (ELISA) using immobilized kistrin showed 18% of normal membrane GPIIb-IIIa complex. By immunoblot analysis, GPIIb and GPIIIa levels in platelet lysates and membranes were near normal. Activation of GPIIb-IIIa, monitored with mAb PAC-1, was markedly decreased (< 20% of normal) in response to ADP, thrombin and platelet-activating factor (PAF); expression of ligand-induced binding sites (LIBS) was < or = 30% of normal. Signal transduction-independent LIBS expression, induced by echistatin, was approximately 60% of normal, suggesting that the integrin present had intact ligand-binding capability. Sequence analysis of GPIIb and GPIIIa cDNA, and platelet mRNA levels for both subunits, were normal. These findings document an acquired combined defect in membrane expression (secondary to a defect in post-translational processing of the complex) and inside-out signalling-dependent activation of the GPIIb-IIIa complex.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Adenosine Diphosphate; Aged; Antibodies, Monoclonal; Binding Sites; Blood Platelets; Calcimycin; Diglycerides; DNA, Complementary; Enzyme Activators; Flow Cytometry; Humans; Immunoblotting; Intercellular Signaling Peptides and Proteins; Ionophores; Macrophage-1 Antigen; Male; Myeloproliferative Disorders; Neutrophils; Peptides; Platelet Activating Factor; Platelet Aggregation; Platelet Aggregation Inhibitors; Platelet Glycoprotein GPIIb-IIIa Complex; Polymerase Chain Reaction; Protein Binding; Protein Kinase C; Receptors, Thrombin; RNA, Messenger; Sequence Analysis, DNA; Serotonin; Signal Transduction

In patients with myeloproliferative disorders (MPD) an altered sensitivity of platelets to antiaggregatory prostaglandins and to the endoperoxide analogue U 46619 has been found. In this study we examined U 46619-induced platelet aggregation and binding of the endoperoxide/thromboxane A2 (TXA2) receptor antagonist SQ 29548 in 11 patients with MPD and 11 healthy controls. Although platelet responsiveness to U 46619 was significantly enhanced (p less than 0.05) in MPD, binding affinity and binding capacity of the corresponding endoperoxide/TXA2 receptor were not altered (Bmax 0.67 +/- 0.20 vs. 0.58 +/- 0.14 pmol/10(9) platelets, Kd 0.41 +/- 0.11 vs. 0.55 +/- 0.09 nM). These data exclude the possibility that changes in the presentation of endoperoxide/TXA2 receptors are responsible for the enhanced platelet sensitivity to endoperoxides found in MPD.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Adult; Aged; Blood Platelets; Bridged Bicyclo Compounds, Heterocyclic; Fatty Acids, Unsaturated; Female; Humans; Hydrazines; In Vitro Techniques; Kinetics; Male; Middle Aged; Myeloproliferative Disorders; Platelet Aggregation; Platelet Aggregation Inhibitors; Prostaglandin Endoperoxides, Synthetic; Receptors, Prostaglandin; Receptors, Thromboxane

In patients with myeloproliferative disorders (MPD) a group of related diseases of the bone marrow stem cell and recurrent haemorrhagic and/or thrombotic complications, the production of aggregating prostaglandins (PGs) may be normal or slightly reduced, while PGI2 production is normal. However, MPD platelet sensitivity to antiaggregatory PGs is still unknown. We studied the potency of PGD2, PGI2 and PGE1 as inhibitors of platelet aggregation induced by threshold aggregating concentrations of arachidonic acid and U-46619-analogue of the cyclic endoperoxide PGH2 in 20 patients with MPD in comparison with healthy controls, with the aim of evaluating the sensitivity of MPD platelets to antiaggregatory PGs. In these patients platelet prostanoid metabolism was normal. However, the functional response of platelets to aggregating and antiaggregating prostanoids was shifted towards potentially increased platelet aggregation response. These findings could have a clinical relevance in view of the haemostatic and thrombotic complications so frequent in MPD.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Adult; Aged; Arachidonic Acid; Arachidonic Acids; Chronic Disease; Female; Humans; Male; Middle Aged; Myeloproliferative Disorders; Platelet Aggregation; Prostaglandin Endoperoxides, Synthetic; Prostaglandins