Maria E. Tsoumani

Pharmacodynamic properties of antiplatelet agents: current knowledge and future perspectives

Platelets play an important role in atherothrombotic disease. The currently available antiplatelet drugs target key steps of platelet activation including thromboxane A2 synthesis, ADP-mediated signaling, and glycoprotein IIb/IIIa-mediated platelet aggregation. The improvement of our understanding on the pharmacokinetic and pharmacodynamic characteristics of these drugs enables the tailoring of the most appropriate anti-thrombotic therapy to the individual patient and risk situation in the daily clinical practice. However, current antiplatelet therapies are associated with increased bleeding risk. Thus, further research on platelet functions may give rise to numerous new antiplatelet agents with high anti-thrombotic efficiency and low adverse hemorrhagic side effects.

Exploration of the antiplatelet activity profile of betulinic acid on human platelets

Betulinic acid, a natural pentacyclic triterpene acid, presents a diverse mode of biological actions including antiretroviral, antibacterial, antimalarial, and anti-inflammatory activities. The potency of betulinic acid as an inhibitor of human platelet activation was evaluated, and its antiplatelet profile against in vitro platelet aggregation, induced by several platelet agonists (adenosine diphosphate, thrombin receptor activator peptide-14, and arachidonic acid), was explored. Flow cytometric analysis was performed to examine the effect of betulinic acid on P-selectin membrane expression and PAC-1 binding to activated platelets. Betulinic acid potently inhibits platelet aggregation and also reduced PAC-1 binding and the membrane expression of P-selectin. Principal component analysis was used to screen, on the chemical property space, for potential common pharmacophores of betulinic acid with approved antithrombotic drugs. A common pharmacophore was defined between the NMR-derived structure of betulinic acid and prostacyclin agonists (PGI2), and the importance of its carboxylate group in its antiplatelet activity was determined. The present results indicate that betulinic acid has potential use as an antithrombotic compound and suggest that the mechanism underlying the antiplatelet effects of betulinic acid is similar to that of the PGI2 receptor agonists, a hypothesis that deserves further investigation.

Influence of high‐density lipoprotein and paraoxonase‐1 on platelet reactivity in patients with acute coronary syndromes receiving clopidogrel therapy

Summary.  Background: The paraoxonase activity of the enzyme paraoxonase‐1 (PON‐1) associated with high‐density lipoprotein (HDL) may significantly influence clopidogrel’s antiplatelet and clinical efficacy as a result of its involvement in the clopidogrel biotransformation to the pharmacologically active thiol metabolite. We evaluated the possible relationships of HDL levels as well as PON‐1 activities and the Q192R genotype with clopidogrel’s antiplatelet efficacy in acute coronary syndrome (ACS) patients. Methods and results: The platelet aggregation, P‐selectin expression and platelet/leukocyte conjugates as well as the clopidogrel response variability (evaluated by the VASP phosphorylation test and expressed as platelet reactivity index, PRI) were assessed in 74 ACS patients undergoing percutaneous coronary intervention (PCI) in relation to the PON‐1 Q192R genotype and to serum HDL‐cholesterol levels, and PON‐1 (paraoxonase and arylesterase) activities. Patients were loaded with 600 mg of clopidogrel followed by 75 mg per day. HDL‐cholesterol levels and PON‐1 activities at baseline (before clopidogrel loading) were not altered at 5‐ and 30‐day post‐clopidogrel loading, whereas baseline platelet activation parameters were significantly attenuated. At 5 days, 17 patients were clopidogrel non‐responders (PRI: 64.2 ± 11.1%). HDL‐cholesterol was inversely associated with platelet activation parameters independently on platelet response variability to clopidogrel whereas a negative association between platelet activation parameters and paraoxonase activity was observed in patients adequately responding to clopidogrel but not in clopidogrel non‐responders. Similarly, the platelet activation markers were significantly higher in PON‐1 Q192Q genotype carriers compared with those having one or two R alleles only in patients adequately responding to clopidogrel. Conclusions: PON‐1 is an important determinant of clopidogrel antiplatelet efficacy only in patients adequately responding to clopidogrel. These findings may be clinically important in ACS patients receiving clopidogrel therapy, especially the first days after the episode.

Platelet-Mediated Inflammation in Cardiovascular Disease. Potential Role of Platelet-Endothelium Interactions

Inflammation of the vascular wall is considered as the principal underlying mechanism in the development of atherosclerosis. Besides their specific functions in haemostasis via thrombus formation after an endothelial injury, a growing body of evidence indicates that platelets play an important role in the inflammatory reactions occurring in the vascular wall as well as in the subsequent tissue repair mechanisms. Platelets interact with activated endothelium as well as with circulating leukocytes and progenitor cells. These interactions, involve direct cell-to-cell interactions as well as autocrine and paracrine pathways, which lead to activation of platelets and their respective cellular counterpart. An increasing body of evidence suggests that antiplatelet therapy may reduce vascular inflammation primarily by inhibiting platelet activation. The aim of the present review is to highlight the molecular basis of platelet-mediated inflammatory response, focusing on the mechanisms underlying the platelet-endothelial cell interaction. The anti-inflammatory effects of current antiplatelet therapies will be also discussed.

Effect of clopidogrel besylate on platelet reactivity in patients with acute coronary syndromes. Comparison with clopidogrel hydrogen sulfate

Objective: The efficacy of clopidogrel therapy in patients with an acute coronary syndrome (ACS) has been established using the clopidogrel hydrogen sulfate (CHS) formulation. In this study we compared the antiplatelet effectiveness of a generic clopidogrel salt, clopidogrel besylate (CB), with the original CHS in patients with an ACS. Research design and methods: Ninety-six ACS patients were randomized to receive a 600-mg loading dose of either CHS (n = 45) or CB (n = 51), followed by 75 mg/day. Sixty-eight patients underwent a percutaneous coronary intervention (PCI), whereas 28 were treated conservatively. Platelet aggregatory response, vasodilator-stimulated phosphoprotein (VASP) phosphorylation, P-selectin expression and platelet–leucocyte conjugates were determined before clopidogrel loading (baseline), as well as at 5 days and at 1 month afterwards. Results: No difference in the clopidogrel response variability was observed between patients receiving CHS or CB either at 5 days or at 1 month of follow-up. Similarly, no difference in the inhibition of platelet aggregation, P-selectin expression or in the platelet–leucocyte conjugates was observed between CHS and CB group during the follow-up. Conclusions: There is no overall significant difference in the antiplatelet efficacy between CB and CHS during their administration in ACS patients for up to 1 month after the episode.

Antiplatelet Efficacy of Long-Term Treatment With Clopidogrel Besylate in Patients With a History of Acute Coronary Syndrome Comparison With Clopidogrel Hydrogen Sulfate

The efficacy of clopidogrel therapy in patients with an acute coronary syndrome (ACS) has been established using the clopidogrel hydrogen sulfate (CHS) formulation. We compared the antiplatelet effectiveness of long-term administration of the original CHS with a generic clopidogrel besylate (CB) salt formulation in 86 patients with a history of an ACS. At 1 month after the episode, patients receiving 75 mg/d CHS were randomized to continue with CHS (n = 41) or to switch to 75 mg/d CB (n = 45). Platelet aggregation, vasodilator-stimulated phosphoprotein (VASP) phosphorylation, P-selectin expression, and platelet–leucocyte conjugates were determined before randomization and at 6 months afterward. No difference in any platelet parameter studied was observed between the 2 groups either before randomization or after 6 months of treatment with CHS or CB. We conclude that there is no difference in the antiplatelet efficacy between CB and CHS during long-term administration in patients with a history of an ACS.

Clopidogrel Generic Formulations in the Era of New Antiplatelets: A Systematic Review

Clopidogrel is a thienopyridine that selectively and irreversibly inhibits the ADP purinergic receptor P2Y12 and the subsequent ADP-mediated platelet activation. Clopidogrel has been approved for clinical use as clopidogrel hydrogen sulfate (bisulfate) salt. The clinical usefulness of clopidogrel bisulfate salt has been proved in a wide variety of large scale clinical trials, thus clopidogrel bisulfate has been extensively used in a large spectrum of patients been under thrombotic risk. Recently, several generic clopidogrel formulations have been approved for clinical use. Consequently, clopidogrel is currently a cost-effective antiplatelet agent. Only small studies have compared the pharmacokinetic and pharmacodynamic properties of various clopidogrel generic salt formulations with the innovator bisulfate salt. In addition few data are available concerning the clinical efficacy and safety of these generic clopidogrel formulations in order to guide clinicians in deciding when generic substitution is appropriate. The aim of this review is to summarize the physicochemical properties as well as the pharmacokinetic and pharmacodynamic characteristics of the generic clopidogrel salts. We also critically present existing data on the clinical efficacy and safety of the generic clopidogrel formulations compared with the innovator clopidogrel bisulfate salt in patients with cardiovascular disease.

Generic Clopidogrel Besylate in the Secondary Prevention of Atherothrombotic Events: A 6-month Follow-up of a Randomised Clinical Trial.

BACKGROUND The aim of the present interim analysis was to compare the clinical efficacy and safety of the generic clopidogrel besylate (CB) with the innovator clopidogrel hydrogen sulphate (CHS) salt in patient groups eligible to receive clopidogrel. METHODS A 2-arm, multicenter, open-label, phase 4 clinical trial. Consecutive patients (n=1,864) were screened and 1,800 were enrolled in the trial and randomized to CHS (n=759) or CB (n=798). Primary efficacy end point was the composite of myocardial infarction, stroke or death from vascular causes, and primary safety end point was rate of bleeding events as defined by Bleeding Academic Research Consortium (BARC) criteria. RESULTS At 6-months follow-up no differences were observed between CB and CHS in primary efficacy end point (OR, 0.80; 95% CI, 0.37 to 1.71; p=0.57). Rates of BARC-1,-2,-3a and -5b bleeding were similar between the two study groups whereas no bleeding events according to BARC-3b, -3c, -4 and -5a were observed in either CHS or CB group. CONCLUSION The clinical efficacy and safety of the generic CB is similar to that of the innovator CHS salt, thus, it can be routinely used in the secondary prevention of atherothrombotic events for a period of at least 6 months. (Salts of Clopidogrel: Investigation to ENsure Clinical Equivalence, SCIENCE study Clinical Trials.gov Identifier: NCT02126982).

Antiplatelet agents and Anticoagulants: from pharmacology to clinical practice.

Thrombosis is the formation of potentially deadly blood clots in the artery (arterial thrombosis) or vein (venous thrombosis). Since thrombosis is one of the main causes of death worldwide, the development of antithrombotic agents is a global medical priority. They are subdivided into antiplatelet agents and anticoagulants. Antiplatelet agents inhibit clot formation by preventing platelet activation and aggregation, while anticoagulants primarily inhibit the coagulation cascade and fibrin formation. Therapeutics within each category differs with respect to the mechanism of action, time to onset, duration of effect and route of administration. In this review, we critically discuss their main pharmacodynamic and pharmacokinetic characteristics as well as recent advances in daily clinical practice.

Tailoring naringenin conjugates with amplified and triple antiplatelet activity profile: Rational design, synthesis, human plasma stability and in vitro evaluation

BACKGROUND The current standard-of-care antiplatelet therapy in cardiovascular disease patients is consisted of cyclooxygenase-1 (COX-1) inhibitor aspirin, along with a platelet receptor P2Y12 antagonist. Recently, the triple antiplatelet therapy with aspirin, a P2Y12 receptor antagonist and a protease activated receptor-1 (PAR-1) antagonist, has been suggested for the secondary prevention of atherothrombotic events, however presented an increased risk of bleeding. Therefore, the quest for novel antiplatelet agents simultaneously targeting the three pathways with improved efficacy/safety profile is of immense importance. Flavonoids as pre-validated ligands for numerous targets could serve as scaffolds targeting the three platelet activation pathways. METHODS Computational methods, Ultra High Performance Liquid Chromatography-Tandem Mass Spectrometry (UHPLC-MS/MS) plasma stability and in vitro platelet aggregation experiments were used to establish the antiplatelet activity of the flavonoid naringenin and its conjugates. RESULTS In silico studies indicated that naringenin could bear a potent triple antiplatelet activity by inhibiting different platelet aggregation mechanisms. However, we found that in human platelets naringenin has diminished activity. We rationally designed and synthesized different naringenin conjugates aiming to amplify the antiplatelet activity of the parent compound. UHPLC-MS/MS revealed a slow degradation rate for a docosahexaenoic acid (DHA) - naringenin conjugate in human plasma. The antiplatelet profile of the new analogues was evaluated against in vitro platelet aggregation induced by several platelet agonists. CONCLUSIONS The DHA - naringenin hybrid presented triple antiplatelet activity simultaneously targeting PAR-1, P2Y12 and COX-1 platelet activation pathways. GENERAL SIGNIFICANCE Natural products could offer a rich source for novel bioactives as a powerful alternative to the current combinatorial use of three different antiplatelet drugs.