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8th Seah Cheng Siang Memorial Lecture: new antithrombotic agents
1Center for Molecular and Vascular Biology, University of Leuven, Belgium. marc.verstraete@med.kuleuven.ac.be
Insights
Aspirin and clopidogrel are key antiplatelet drugs for preventing thromboembolic events. Glycoprotein (GPIIb/IIIa) receptor inhibitors offer advanced options, with varying efficacy and bleeding risks.
Area of Science:
- Cardiovascular Medicine
- Pharmacology
- Thrombosis Research
Background:
- Aspirin is the standard antiplatelet therapy for atherosclerotic vascular disease, inhibiting cyclooxygenase-dependent platelet aggregation.
- Clopidogrel demonstrates superior efficacy and comparable safety to aspirin in large-scale trials, acting via adenosine diphosphate (ADP) receptor blockade.
- Experimental anti-thrombotic agents targeting thromboxane pathways have shown limited predictive value for human outcomes.
Discussion:
- Platelet aggregation culminates in the activation of the glycoprotein (GPIIb/IIIa) receptor, a common final pathway for various stimuli.
- GPIIb/IIIa receptor inhibitors include monoclonal antibodies like abciximab and synthetic blockers (peptidic and non-peptidic).
- Abciximab provides prolonged platelet binding, while synthetic inhibitors offer oral activity but shorter ex vivo inhibition durations.
Key Insights:
- Large-scale trials confirm the efficacy of aspirin, dipyridamole, and clopidogrel in secondary atherothrombosis prevention.
- GPIIb/IIIa inhibitors, particularly abciximab combined with aspirin and heparin, significantly reduce ischemic events in high-risk cardiovascular interventions.
- Synthetic GPIIb/IIIa inhibitors have not demonstrated suppression of restenosis and are associated with higher bleeding rates compared to abciximab in current usage patterns.
Outlook:
- Further research is needed for direct comparative studies between synthetic GPIIb/IIIa inhibitors and abciximab.
- Optimizing the balance between antiplatelet efficacy and bleeding risk remains a critical challenge in managing atherothrombotic diseases.
- Development of novel antiplatelet strategies targeting specific pathways continues to be an active area of cardiovascular research.
Abstract:
For the long-term prevention of thromboembolic events in patients with atherosclerotic vascular disease, aspirin is the preferred antiplatelet drug. Only clopidogrel was shown to be more effective and at least as safe than medium-dose aspirin in direct comparative large-scale trials. Aspirin inhibits the cyclooxygenase dependent pathway of platelet aggregation while ticlopidine and clopidogrel selectively bind to adenosine diphosphate (ADP) receptors on the platelet surface. Compounds which inhibit the synthesis of thromboxane synthase, block the thromboxane receptor or have the dual activity were effective in experimental thrombosis models in animals but not predictive of results in humans. Activation of the platelet glycoprotein (GPIIb/IIIa) receptor on the platelet surface is the final pathway of platelet aggregation, regardless of the initiating stimulus. Inhibitors of GPIIb/IIIa receptors include monoclonal antibodies (abciximab) against this receptor and peptidic as well as non-peptidic synthetic specific receptor blockers. Abciximab exchanges between and binds to platelets for as long as two weeks whereas synthetic GPIIb/IIIa inhibitors inhibit ex vivo platelet aggregation for only a few hours after the end of infusion but have the advantage of being also orally active. In the secondary prevention of atherothrombosis, large scale trials were successfully conducted with aspirin, dipyridamole and clopidogrel. In the first large-scale trials with GPIIb/IIIa inhibitors with abciximab was investigated. In aggregate, this class of platelet inhibitors, combined with aspirin and heparin, was shown to reduce ischaemic events in patients with high- and low-risk coronary intervention, stents, unstable angina and non-Q-wave infarction with long-term preservation of the initial benefit. With synthetic GPIIb/IIIa inhibitors there is no suppression of clinical evident restenosis 6 months after the end of treatment. With the doses presently used, bleeding occurs more often with the synthetic GPIIb/IIIa inhibitors (used for 3 days) than with abciximab (used for 12 hours) but there are no direct comparisons between these drugs.