Platelet P2Y12 receptor inhibition by thienopyridines: status and future

One immune cell to bind them all: platelet contribution to neurodegenerative disease

Alzheimer's disease (AD) and related dementias (ADRD) collectively affect a significant portion of the aging population worldwide. The pathological progression of AD involves not only the classical hallmarks of amyloid beta (Aβ) plaque buildup and neurofibrillary tangle development but also the effects of vasculature and chronic inflammatory processes. Recently, platelets have emerged as central players in systemic and neuroinflammation. Studies have shown that patients with altered platelet receptor expression exhibit accelerated cognitive decline independent of traditional risk factors. Additionally, platelets from AD patients exhibit heightened unstimulated activation compared to control groups. Platelet granules contain crucial AD-related proteins like tau and amyloid precursor protein (APP). Dysregulation of platelet exocytosis contributes to disease phenotypes characterized by increased bleeding, stroke, and cognitive decline risk. Recent studies have indicated that these effects are not associated with the quantity of platelets present in circulation. This underscores the hypothesis that disruptions in platelet-mediated inflammation and healing processes may play a crucial role in the development of ADRD. A thorough look at platelets, encompassing their receptors, secreted molecules, and diverse roles in inflammatory interactions with other cells in the circulatory system in AD and ADRD, holds promising prospects for disease management and intervention. This review discusses the pivotal roles of platelets in ADRD.

Platelet P2Y1 receptor exhibits constitutive G protein signaling and β-arrestin 2 recruitment

BACKGROUND

Purinergic P2Y₁ and P2Y₁₂ receptors (P2Y₁-R and P2Y₁₂-R) are G protein-coupled receptors (GPCR) activated by adenosine diphosphate (ADP) to mediate platelet activation, thereby playing a pivotal role in hemostasis and thrombosis. While P2Y₁₂-R is the major target of antiplatelet drugs, no P2Y₁-R antagonist has yet been developed for clinical use. However, accumulating data suggest that P2Y₁-R inhibition would ensure efficient platelet inhibition with minimal effects on bleeding. In this context, an accurate characterization of P2Y₁-R antagonists constitutes an important preliminary step.

RESULTS

Here, we investigated the pharmacology of P2Y₁-R signaling through Gq and β-arrestin pathways in HEK293T cells and in mouse and human platelets using highly sensitive resonance energy transfer-based technologies (BRET/HTRF). We demonstrated that at basal state, in the absence of agonist ligand, P2Y₁-R activates Gq protein signaling in HEK293T cells and in mouse and human platelets, indicating that P2Y₁-R is constitutively active in physiological conditions. We showed that P2Y₁-R also promotes constitutive recruitment of β-arrestin 2 in HEK293T cells. Moreover, the P2Y₁-R antagonists MRS2179, MRS2279 and MRS2500 abolished the receptor dependent-constitutive activation, thus behaving as inverse agonists.

CONCLUSIONS

This study sheds new light on P2Y₁-R pharmacology, highlighting for the first time the existence of a constitutively active P2Y₁-R population in human platelets. Given the recent interest of P2Y₁₂-R constitutive activity in patients with diabetes, this study suggests that modification of constitutive P2Y₁-R signaling might be involved in pathological conditions, including bleeding syndrome or high susceptibility to thrombotic risk. Thus, targeting platelet P2Y₁-R constitutive activation might be a promising and powerful strategy for future antiplatelet therapy.

Aminotransferase Level and the Effects of Dual Antiplatelet in Minor Stroke or Transient Ischemic Attack: A post hoc Analysis of a Randomized Control Trial

INTRODUCTION

This study was intended to evaluate whether the safety and efficacy of dual antiplatelet treatment in patients with minor ischemic stroke (MIS) or transient ischemic attack (TIA) could be modified by the aminotransferase level. Also, we sought to assess the interaction between aminotransferase level and CYP2C19 loss-of-function status on the efficacy of dual antiplatelet therapy.

METHODS

This study is a post hoc analysis of the Clopidogrel in High-Risk Patients With Acute Nondisabling Cerebrovascular Events (CHANCE) study, a double-blinded randomized control trial. We included 5,133 patients with a complete workup of baseline alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels. The primary outcome is stroke or TIA recurrence within 90 days. Cox proportional hazard models were used in the evaluation of the efficacy of antiplatelet treatment in patients with different aminotransferase levels and subgroups categorized by the aminotransferase level × CYP2C19 loss-of-function status.

RESULTS

The median age of all the included patients was 62 years; 66.3% of the patients were male. More recurrent stroke or TIA occurred in patients with elevated ALT and AST levels within 90 days compared to patients with normal ALT and AST levels (14.5 vs. 11.2%, p = 0.029). Dual antiplatelet treatment with aspirin and clopidogrel reduced recurrence compared with aspirin alone in patients with both normal (adjusted hazard ratio [HR], 95% confidence interval [CI]: 0.72 [0.60-0.86], p < 0.001) and elevated (adjusted HR [95% CI]: 0. 57 [0. 35-0. 92], p = 0. 020) ALT and AST levels (p = 0.64 for interaction). No significant difference in treatment efficacy on 90-day all-cause death or bleeding events was found.

CONCLUSIONS

Dual antiplatelet treatment was safe for minor stroke or high-risk TIA patients with mildly elevated aminotransferase. Mild elevation of ALT or AST did not undermine the protective efficacy of the dual antiplatelet regimen in reducing recurrent stroke or TIA within 90 days after MIS or TIA. The interaction between the CYP2C19 loss-of-function allele carrier status and aminotransferase level on the efficacy of dual antiplatelet treatment was not observed.

Ticagrelor induces paraoxonase-1 (PON1) and better protects hypercholesterolemic mice against atherosclerosis compared to clopidogrel

Ticagrelor (TIC), a P2Y purinoceptor 12 (P2Y₁₂)-receptor antagonist, has been widely used to treat patients with acute coronary syndrome. Although animal studies suggest that TIC protects against atherosclerosis, it remains unknown whether it does so through its potent platelet inhibition or through other pathways. Here, we placed hypercholesterolemic Ldlr^-/-Apobec1^-/- mice on a high-fat diet and treated them with either 25 mg/kg/day of clopidogrel (CLO) or 180 mg/kg/day of TIC for 16 weeks and evaluated the extent of atherosclerosis. Both treatments equally inhibited platelets as determined by ex vivo platelet aggregation assays. The extent of atherosclerosis, however, was significantly less in the TIC group than in the CLO group. Immunohistochemical staining and ELISA showed that TIC treatment was associated with less macrophage infiltration to the atherosclerotic intima and lower serum levels of CCL4, CXCL10, and TNFα, respectively, than CLO treatment. Treatment with TIC, but not CLO, was associated with higher serum activity and tissue level of paraoxonase-1 (PON1), an anti-atherosclerotic molecule, suggesting that TIC might exert greater anti-atherosclerotic activity, compared with CLO, through its unique ability to induce PON1. Although further studies are needed, TIC may prove to be a viable strategy in the prevention and treatment of chronic stable human atherosclerosis.

The mechanism and risk factors of clopidogrel-induced liver injury

CONTEXT AND OBJECTIVE

Clopidogrel (CLP) is a prodrug which is widely used as a platelet aggregation inhibitor. Hepatotoxicity is rare but a potentially serious adverse reaction that is associated with CLP. Thiophene in CLP (the thienopyridine derivative) is a group that is easily oxidated by cytochrome P450 enzymes (CYP450s) to generate reactive metabolites (RMs), it may be implicated in the mechanism of CLP-induced hepatotoxicity. CYP2C19 and CYP2B6 are important CYP450s involved in the metabolism and activation of CLP, and the aim of this study is to investigate whether the metabolites of CYP2C19 and CYP2B6 are associated with the CLP-induced liver injury.

METHOD

Primary rat hepatocytes are applied to evaluate the hepatotoxicity of CLP. Glutathione-depleted mouse model is used to evaluate whether this toxicity of CLP is metabolized by CYP450s. We also used HepG2 cells co-incubated with recombinant CYP2B6 and CYP2C19 enzymes to further assess whether the metabolites of CYP2C19 and CYP2B6 are associated with the CLP-induced hepatocellular toxicity.

RESULT

CLP in high dose (100 μM and 300 μM) showed cytotoxicity in primary rat hepatocytes assay. Administration of CLP with l-buthionine-S, R-sulfoxinine (BSO) for seven days enhanced the liver injury of CLP. The level of ALT, AST and TBIL in plasma increased significantly, and the histopathological results showed the obvious liver injury; Pretreatment of 1-aminobenzotriazole, a nonspecific inhibitor of CYP450s, suppressed CLP-induced hepatotoxicity; CLP showed a dose-dependent toxicity in HepG2/CYP2C19 enzyme and HepG2/CYP2B6 enzyme models.

CONCLUSION

High activities of CYP2C19 and CYP2B6 are the risk factors for hepatocellular toxicity of CLP.

Hepatocellular toxicity of clopidogrel: mechanisms and risk factors

Clopidogrel is a prodrug used widely as a platelet aggregation inhibitor. After intestinal absorption, approximately 90% is converted to inactive clopidogrel carboxylate and 10% via a two-step procedure to the active metabolite containing a mercapto group. Hepatotoxicity is a rare but potentially serious adverse reaction associated with clopidogrel. The aim of this study was to find out the mechanisms and susceptibility factors for clopidogrel-associated hepatotoxicity. In primary human hepatocytes, clopidogrel (10 and 100 μM) was cytotoxic only after cytochrome P450 (CYP) induction by rifampicin. Clopidogrel (10 and 100 μM) was also toxic for HepG2 cells expressing human CYP3A4 (HepG2/CYP3A4) and HepG2 cells co-incubated with CYP3A4 supersomes (HepG2/CYP3A4 supersome), but not for wild-type HepG2 cells (HepG2/wt). Clopidogrel (100 μM) decreased the cellular glutathione content in HepG2/CYP3A4 supersome and triggered an oxidative stress reaction (10 and 100 µM) in HepG2/CYP3A4, but not in HepG2/wt. Glutathione depletion significantly increased the cytotoxicity of clopidogrel (10 and 100 µM) in HepG2/CYP3A4 supersome. Co-incubation with 1 μM ketoconazole or 10mM glutathione almost completely prevented the cytotoxic effect of clopidogrel in HepG2/CYP3A4 and HepG2/CYP3A4 supersome. HepG2/CYP3A4 incubated with 100 μM clopidogrel showed mitochondrial damage and cytochrome c release, eventually promoting apoptosis and/or necrosis. In contrast to clopidogrel, clopidogrel carboxylate was not toxic for HepG2/wt or HepG2/CYP3A4 up to 100 µM. In conclusion, clopidogrel incubated with CYP3A4 is associated with the formation of metabolites that are toxic for hepatocytes and can be trapped by glutathione. High CYP3A4 activity and low cellular glutathione stores may be risk factors for clopidogrel-associated hepatocellular toxicity.

The discovery of a new class of synaptic transmitters in smooth muscle 50 years ago and amelioration of coronary artery thrombosis

Clopidogrel and ticagrelor, antagonists to P2Y(12) receptor molecules on platelet membranes, significantly ameliorate acute myocardial infarction due to coronary artery thrombosis, the most common cause of death in the developed world. A personal account is given here of the foundational research that lead to the identification of P2Y receptors, carried out 50 years ago in the Melbourne University Zoology Department headed by Geoffrey Burnstock. In Christmas 1962, I made the serendipitous observation of large hyperpolarizing changes across the membranes of smooth muscle cells in the taenia coli of the intestine on stimulating its nerve supply. I then showed that these potentials relaxed the muscle and were not due to noradrenaline or acetylcholine, which were then the only substances known to be released from nerves. I called these non-adrenergic, non-cholinergic (NANC) terminals in the laboratory and showed that this NANC transmitter acted at receptor molecules on the muscle cells, promoting efflux of potassium ions, and so the observed potential changes. In 1968, Graeme Campbell showed that ATP relaxed the taenia coli muscle, and in 1969, David Satchell, using purine chromatography, showed that ATP was likely to be released from NANC terminals. The receptor molecules involved were shown to be exceptionally sensitive to 2-methylthio-ATP (Satchell and Macguire, 1975, J Pharmacol Exp Ther, 195, 540), and so belonged to the class P2Y receptors as designated by Abbracchio and Burnstock, with subclasses P2Y(1)-P2Y(12). The discovery of the role of P2Y(12) receptors in increasing thrombosis lead to the focused research that resulted in clopidogrel and ticagrelor.

Clopidogrel and the risk of osteoporotic fractures: a nationwide cohort study

OBJECTIVES

The P2Y(12) inhibitor clopidogrel inhibits platelet aggregation and is used in the treatment and prevention of coronary artery disease. It is widely used and, in combination with acetylsalicylic acid, is the standard of care for acute coronary syndrome and percutaneous coronary intervention. The mode of action of clopidogrel involves pathways that are important to the metabolic activity in bone cells, although to our knowledge whether P2Y(12) receptors are involved in the regulation of bone metabolism has not yet been investigated. Therefore, the objective of the present study was to investigate the association between clopidogrel use and risk of fractures.

METHODS

We investigated the association between clopidogrel use and fracture incidence in a nationwide cohort study within the Danish population of approximately 5.3 million individuals. All patients who were prescribed clopidogrel during the years 1996-2008 were included in the study (n = 77 503), and three nonusers were randomly selected, matched for age and gender (n = 232 510), for each clopidogrel-treated subject.

RESULTS

Treatment with clopidogrel was associated with both increased overall fracture risk and increased risk of osteoporotic fractures, especially in subjects with a treatment duration of more than 1 year. However, individuals with low exposure to clopidogrel (<0.01 defined daily dose) had a lower risk of fracture than never users.

CONCLUSIONS

Use of the P2Y(12) inhibitor clopidogrel is associated with risk of fractures. There seems to be a biphasic relation so that lower doses are associated with decreased fracture risk, whereas higher doses (recommended dose range) are associated with increased risk. More studies are warranted to determine the potential in vivo effect of platelet aggregation inhibitors on bone metabolism.

Effects of prasugrel on platelet inhibition during systemic endotoxaemia: a randomized controlled trial

P2Y12 receptor antagonists have become a mainstay for the treatment of CVD (cardiovascular diseases). However, they have rarely been evaluated under pathophysiological conditions apart from arterial diseases. We hypothesized interactions between prasugrel and enhanced vWF (von Willebrand Factor) release in a model of systemic inflammation, and compared the pharmacodynamic effects of prasugrel against placebo on agonist-induced platelet aggregation and shear-induced platelet plug formation. A total of 20 healthy male volunteers were enrolled in a double-blind placebo-controlled two-way crossover trial. Each volunteer received either placebo or a 60 mg loading dose of prasugrel 2 h before endotoxin or placebo infusion. Platelet inhibition was measured with MEA (multiple electrode aggregometry), the PFA-100 system and the VASP (vasodilator-stimulated phosphoprotein) phosphorylation assay. Prasugrel blunted various platelet aggregation pathways, including those induced by ADP (−81%), AA (arachidonic acid) (−60%), ristocetin (−75%; P<0.001 for all) and, to a lesser degree, collagen or TRAP (thrombin-receptor-activating peptide). Prasugrel decreased shear-induced platelet plug formation, but vWF release during endotoxaemia partly antagonized the inhibitory effect of prasugrel as measured with the PFA-100 system. Endotoxaemia acutely decreased ristocetin and TRAP-induced platelet aggregation, and enhanced ristocetin-induced aggregation after 24 h. Strong in vivo blockade of P2Y12 inhibits a broad spectrum of platelet aggregation pathways. However, vWF release may reduce prasugrel's effects under high-shear conditions.

Clopidogrel-induced neutropenia after coronary stenting: is cilostazol a good alternative?

Dual antiplatelet therapy with aspirin plus thienopyridines has become the standard treatment of patients undergoing coronary stenting. Clopidogrel has mostly replaced the use of ticlopidine due to its more favourable adverse event profile. However, also the use of clopidogrel is not without side effects. Clopidogrel major adverse events are represented by marrow suppression, manifesting with aplastic anaemia, thrombocytopenia and neutropenia. When clopidogrel toxicity occurs, there are few and unsubstantiated alternative treatments and thus, in these cases, medical decisions may be very difficult. We report a case of clopidogrel-induced bone marrow toxicity manifesting with severe neutropenia in a patient treated with multiple coronary stents and provide suggestions for an alternative treatment.

Docking-based virtual screening of potential human P2Y12 receptor antagonists

Platelet plays essential roles in hemostasis and its dysregulation can lead to arterial thrombosis. P2Y12 is an important platelet membrane adenosine diphosphate receptor, and its antagonists have been widely developed as anti-coagulation agents. The current P2Y12 inhibitors available in clinical practice have not fully achieved satisfactory anti-thrombotic effects, leaving room for further improvement. To identify new chemical compounds as potential anti-coagulation inhibitors, we constructed a three-dimensional structure model of human P2Y12 by homology modeling based on the recently reported G-protein coupled receptor Meleagris gallopavo β1 adrenergic receptor. Virtual screening of the modeled P2Y12 against three subsets of small molecules from the ZINC database, namely lead-like, fragment-like, and drug-like, identified a number of compounds that might have high binding affinity to P2Y12. Detailed analyses of the top three compounds from each subset with the highest scores indicated that all of these compounds beard a hydrophobic bulk supplemented with a few polar atoms which bound at the ligand binding site via largely hydrophobic interactions with the receptor. This study not only provides a structure model of P2Y12 for rational design of anti-platelet inhibitors, but also identifies some potential chemicals for further development.

Use of the oral platelet inhibitors dipyridamole and acetylsalicylic acid is associated with increased risk of fracture

BACKGROUND

Platelet inhibitors are widely used in the treatment and prevention of coronary artery disease. In addition to acetylsalicylic acid, two major groups of platelet inhibitors are used; phosphodiesterase inhibitors including dipyridamole, and thienopyridines (ticlopidine and clopidogrel). Clopidogrel is the most widely used, and in combination with acetylsalicylic acid it is the standard of care for acute coronary syndromes and percutaneous coronary interventions. However, the modes of action involve pathways that are involved in the metabolic activity in bone cells and pharmacologic modulation of these pathways may therefore have effects on bone.

METHODS

In the current study, we assessed the association between platelet inhibitor use and fracture incidence in a population-based epidemiological study performed within the Danish population consisting of approximately 5.3 million individuals, where all patients sustaining a fracture during the year of 2000 were included (124,655 cases). The hypotheses were to investigate if use of thienopyridines or phosphodiesterase inhibitors were associated with increased risk of fractures after adjustment for potential confounders.

RESULTS

We found that treatment with dipyridamole is associated with increased overall fracture risk, but not to the risk of osteoporotic fractures. In contrast, low-dose acetylsalicylic acid is associated to increased risk of overall fractures and fractures of the hip. Finally, in the current study clopidogrel is not associated with increased fracture risk.

CONCLUSIONS

Use of some oral platelet inhibitors is associated with increased risk of fractures, and more studies are warranted to determine the potential effect of platelet inhibitors on bone metabolism in vivo.

Clopidogrel 150 vs. 75 mg day(-1) in patients undergoing percutaneous coronary intervention: a meta-analysis

BACKGROUND

Whether an increase in the daily oral maintenance dose of clopidogrel may improve clinical outcomes in patients undergoing percutaneous coronary intervention (PCI) is still debated.

OBJECTIVES

This meta-analysis aimed to estimate the relative effect of a 150- vs. 75-mg daily maintenance dosage of clopidogrel on clinical and laboratory end-points in patients undergoing PCI.

METHODS

We searched electronic and printed sources (up to 14 December 2010) for both randomized control trials and observational studies satisfying the predefined inclusion criteria.

RESULTS

We retrieved 12 reports of studies including a total of 23,814 patients. Clopidogrel, 150 mg day(-1), was associated with significant reductions in major adverse cardiac and/or cerebrovascular events (odds ratio [OR], 0.67; 95% confidence interval [CI], 0.48-0.94), myocardial infarction (OR, 0.72; 95% CI, 0.60-0.86), target vessel revascularization (OR, 0.27; 95% CI, 0.12-0.62) and stent thrombosis (OR, 0.64; 95% CI, 0.53-0.77) and decreased adenosine diphosphate-induced maximal platelet aggregation. However, as compared with 75 mg day(-1), the 150-mg daily maintenance dosage significantly increased the risk of minor bleeding (OR, 1.21; 95% CI, 1.08-1.36).

CONCLUSION

As compared with the currently recommended 75-mg day(-1) maintenance dosage of clopidogrel, the 150-mg day(-1) dosage can reduce major adverse cardiac and/or cerebrovascular events but may increase the risk of minor bleeding.

Review: Antiplatelet Drugs: What Comes Next?

Antiplatelet drugs are important components in the management of atherothrombotic vascular disease. However, several limitations restrict the safety and efficacy of current antiplatelet therapy in clinical practice. Interpatient variability and resistance to aspirin and/or clopidogrel has spurred efforts for the development of novel agents. Indeed, several antiplatelet drugs are at various stages of evaluation; those at advanced stage of development are the focus of this review.

Modern role for clopidogrel in management of atrial fibrillation and stroke reduction

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia. The prevalence of AF increases sharply in old age (prevalence approximately 10% among persons 80 years of age and older). The expected risk for ischemic stroke is increased five-fold by the presence of AF, primarily as a result of cardiogenic embolism. Multiple large-scale, randomized trials have been completed or are still underway to find optimal, efficacious, and relatively safe ways to reduce the risk of ischemic stroke and other systemic thromboembolic events related to AF. Antithrombotic strategies are accompanied by serious bleeding complications that threaten patients in need of medical stroke prevention. Treatment regimens for preventing thromboembolism in AF patients range from vitamin K antagonists such as warfarin or coumadins, antiplatelet drugs like aspirin or clopidogrel, to newly developed orally available antithrombotics like the direct thrombin inhibitor dabigatran, or the Factor Xa-inhibitor rivaroxaban. The available anticoagulant and antiplatelet drugs have different advantages and disadvantages. This review attempts to delineate the specific role of clopidogrel in patients with AF and at risk of stroke, taking into consideration new and ongoing trials in this important field of medical practice.