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Adhesive interactions of platelets and their blockade
1Department of Microbiology and Immunology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-2363.
Insights
Platelet activation is key to cardiovascular diseases. New peptide analogs selectively block platelet receptors, preventing thrombus formation without harming endothelial cells, aiding vascular injury repair.
Area of Science:
- Cardiovascular Biology
- Hematology
- Pharmacology
Background:
- Thrombus formation, central to occlusive cardiovascular diseases, involves platelets and fibrinogen.
- Platelet activation occurs via multiple pathways, with only one sensitive to aspirin inhibition.
- Aspirin-insensitive pathways trigger platelet shape change and receptor exposure, crucial for thrombus development.
Purpose of the Study:
- To investigate selective blockade of platelet receptors for antithrombotic therapy.
- To develop agents that inhibit platelet aggregation without adverse effects on endothelial cells.
- To explore molecular modeling for improved antiplatelet drug design.
Main Methods:
- Utilized peptide analogs of human fibrinogen gamma chain (400-411) for selective platelet GPIIb-IIIa blockade.
- Assessed the impact of RGD-containing peptides and monoclonal antibodies on endothelial cell attachment and detachment.
- Focused on developing a molecular model of fibrinogen-GPIIb-IIIa interaction.
Main Results:
- Peptide analogs of fibrinogen gamma chain 400-411 selectively target platelet GPIIb-IIIa.
- These selective peptides do not cause endothelial cell detachment, unlike RGD peptides or antibodies.
- Selective blockade preserves endothelial regrowth in vascular injury zones post-thrombolysis/angioplasty.
Conclusions:
- Selective antiplatelet agents targeting GPIIb-IIIa are feasible and beneficial for vascular injury repair.
- Molecular modeling of fibrinogen-GPIIb-IIIa interactions can guide the development of potent and selective antithrombotic drugs.
- This approach offers a promising strategy to improve outcomes after procedures like angioplasty.
Abstract:
Formation of thrombi, which constitute the main mechanism of occlusive cardiovascular diseases, is mediated by blood platelets and fibrinogen. At least three stimulatory pathways can activate platelets, yet only one is sensitive to inhibition by aspirin (cyclooxygenase). Aspirin-insensitive pathways, mediated by protein kinase C and myosin light-chain kinase, lead to a change of platelet shape, with an attendant striking increase in their surface (pseudopods) followed by exposure of receptors for fibrinogen and vWf on GPIIb-IIIa. Another receptor for vWf (GPIb), independent of known pathways of platelet activation, seems to function primarily in vessels with a high shear rate. The multistep processes of platelet activation can be circumvented by the blockade of platelet receptors for adhesive molecules, present in subendothelium and in plasma. However, platelet receptors exposed on GPIIb-IIIa share common structural features with the endothelial receptor for vitronectin. Blockade of platelet GPIIb-IIIa with synthetic peptides containing the RGD sequence, or with certain monoclonal antibodies, may inadvertently cause detachment, or prevent attachment, of endothelial cells in a zone of vascular injury. The peptide analogs of human fibrinogen gamma chain sequence 400-411 possess high selectivity for platelet GPIIb-IIIa because they do not cause detachment of endothelial cells. Thus, endothelial regrowth in the zone of vascular injury following thrombolysis and/or angioplasty will go unperturbed. The significance of adhesive proteins interacting with their receptors transcends the issue of the fundamental mechanism of platelet aggregation of platelet thrombus formation. A molecular model of the adhesive interaction between fibrinogen domains and GPIIb-IIIa will probably be the most amenable to construction. Once such a model is established and its allosteric regulation is unraveled, its utility for further development of improved antiplatelet receptor blockers as antithrombotic drugs, that are both selective and potent will become a reality.