P2Y12 inhibitors: differences in properties and mechanisms of action and potential consequences for clinical use

Coronary artery bypass grafting in acute coronary syndromes: modern indications and approaches

PURPOSE OF REVIEW

Acute coronary syndromes (ACS) are a leading cause of morbidity and mortality worldwide, with approximately 1.2 million hospitalizations annually in the U.S. This review aims to explore the contemporary evidence regarding revascularization strategies, including percutaneous coronary intervention (PCI) and coronary artery bypass grafting (CABG), in ACS patients. It also addresses the unresolved questions concerning the optimal procedural aspects of surgery and antithrombotic therapy for secondary prevention postsurgery.

RECENT FINDINGS

Recent studies highlight that while PCI is generally preferred for its timeliness in high-risk non-ST-elevation ACS (NSTE-ACS) patients, CABG offers a benefit in terms of cardiovascular events in those with multivessel disease, particularly in the presence of diabetes and higher coronary disease complexity. For ST-elevation myocardial infarction (STEMI), CABG is less frequently utilized due to the preference for primary PCI, but it remains crucial for patients with complex anatomy or failed PCI. Furthermore, the optimal timing and type of antiplatelet therapy post-CABG remain controversial, with current evidence supporting the use of dual antiplatelet therapy (DAPT) to reduce ischemic events but necessitating careful management to balance bleeding risks.

SUMMARY

In patients with ACS, the choice between PCI and CABG depends on the complexity of coronary disease and patient comorbidities. CABG is particularly beneficial for multivessel disease in NSTE-ACS and specific STEMI cases where PCI is not feasible. The management of antiplatelet therapy postsurgery requires a nuanced approach to minimize bleeding risks while preventing thrombotic complications. Further randomized clinical trials are needed to solidify these findings and guide clinical practice.

Platelets isolation and ectonucleotidase assay: Revealing functional aspects of the communication between the vasculature and the immune system

Platelets are enucleated fragments of cells with a diversity of internal granules. They are responsible for functions related to hemostasis, coagulation, and inflammation. The activation of these processes depends on a cascade coordinated by cytokines, chemokines, and components of purinergic signaling, such as ATP, ADP, and adenosine. Platelets express distinct components of the purinergic system: P2X1, P2Y1, PY12, and P2Y14 receptors; and the ectonucleotidases NTPDase, NPP, and 5NTE (ecto-5'-nucleotidase). Except for P2Y14, which has not yet exhibited a known function, all other components relate to the biological processes mentioned before. Platelets are known to display specific responses to microorganisms, being capable of recognizing pathogen-associated molecular patterns (PAMPs), engulfing certain classes of viruses, and participating in NETosis. Platelet function dysregulation implicates various pathophysiological processes, including cardiovascular diseases (CVDs) and infections. In COVID-19 patients, platelets exhibit altered purinergic signaling and increased activation, contributing to inflammation. Excessive platelet activation can lead to complications from thrombosis, which can affect the circulation of vital organs. Therefore, controlling the activation is necessary to end the inflammatory process and restore homeostasis. Ectonucleotidases, capable of hydrolyzing ATP, ADP, and AMP, are of fundamental importance in activating platelets, promising pharmacological targets for clinical use as cardiovascular protective drugs. In this review, we revisit platelet biology, the purinergic receptors and ectonucleotidases on their surface, and their importance in platelet activity. Additionally, we describe methods for isolating platelets in humans and murine, as well as the main techniques for detecting the activity of ectonucleotidases in platelets. Considering the multitude of functions revealed by platelets and their potential use as potent bioreactors able to secrete and present molecules involved in the communication of the vasculature with the immune system, it is crucial to deeply understand platelet biology and purinergic signaling participation to contribute to the developing of therapeutic strategies in diseases of the cardiovascular, inflammatory, and immune systems.

Clinical implications of combination proton pump inhibitor and triple therapies in patients with atrial fibrillation following percutaneous intervention: a guide for clinicians

INTRODUCTION

Patients on systemic oral anticoagulation with vitamin K antagonists (VKA) or non-vitamin K oral anticoagulants (NOAC) often require triple therapy following percutaneous coronary intervention, substantially increasing the risk of bleeding. Gastroprotective agents like proton pump inhibitors (PPI) are often employed to mitigate this risk, despite potential competitive inhibition between P2Y12-receptor inhibitors, NOACs, and VKAs. While the interactions and clinical outcomes of PPIs and DAPT have been frequently explored in literature, not many studies have evaluated the same outcomes for triple therapy.

AREAS COVERED

This comprehensive narrative review of three studies on PPIs and triple from the PubMed/MEDLINE database supplemented by 23 other relevant studies aims to use the available literature to analyze the potential interactions between PPIs and triple therapy while shedding light on their mechanisms, clinical implications, and areas for optimization.

EXPERT OPINION

If triple therapy is indicated following PCI, then patients at high-risk for bleeding may benefit from transition to apixaban and a PPI to lower the risk of gastrointestinal bleeding. More research is needed to determine the role of PPIs in triple therapies in prevention of gastrointestinal bleeding or potentiation of other adverse outcomes.

Should We Use Aspirin or P2Y12 Inhibitor Monotherapy in Stable Ischemic Heart Disease?

PURPOSE OF REVIEW

To summarize the recent evidence and guideline recommendations on aspirin or P2Y12 inhibitor monotherapy in patients with stable ischemic heart disease and provide insights into future directions on this topic, which involves transition to a personalized assessment of bleeding and thrombotic risks.

RECENT FINDINGS

It has been questioned whether the evidence for aspirin as the foundational component of secondary prevention in patients with coronary artery disease aligns with contemporary pharmaco-invasive strategies. The recent HOST-EXAM study randomized patients who had received dual antiplatelet therapy for 6 to 18 months without ischemic or major bleeding events to either clopidogrel or aspirin for a further 24 months, and demonstrated that the patients in the clopidogrel arm had significantly lower rates of both thrombotic and bleeding complications compared to those in the aspirin arm. The patient-level PANTHER meta-analysis showed that in patients with established coronary artery disease, P2Y12 inhibitor monotherapy was associated with lower rates of myocardial infarction, stent thrombosis as well as gastrointestinal bleeding and hemorrhagic stroke compared to aspirin monotherapy, albeit with similar rates of all-cause mortality, cardiovascular mortality and major bleeding. Long-term low-dose aspirin is recommended for secondary prevention in patients with stable ischemic heart disease, with clopidogrel monotherapy being acknowledged as a feasible alternative. Dual antiplatelet therapy for six months after percutaneous coronary intervention remains the standard recommendation for patients with stable ischemic heart disease. However, the duration of dual antiplatelet therapy may be shortened and followed by P2Y12 inhibitor monotherapy or prolonged based on individualized evaluation of the patient's risk profile.

How to undertake procedures while on antiplatelet agents: a hematologist's view

Cardiovascular diseases (CVDs) are the leading cause of mortality globally while also contributing to excess health system costs. Significant advancements have been made in the understanding and prevention of deaths from CVD. In addition to risk factor modifications, one of the key developments in this area is the appropriate prescribing of antiplatelet medications for secondary prevention of CVD. With the advent of vascular devices, there has been an increased use of potent antiplatelet agents to mitigate thrombosis risk. A well-recognized, albeit rare complication of antiplatelet drugs is the heightened risk of bleeding. This adverse effect is particularly relevant when a patient receiving these medications may require an urgent surgery. In addition, for elective surgeries, although these drugs can be withheld, there may be some situations when interruption of antiplatelet agents, even for short duration, may lead to thrombotic events. There are no robust guidelines on how to manage these clinical scenarios, although there have been some important studies published recently in this area. In this review, we provide our approach to patients on antiplatelet drugs who may require urgent surgeries or surgical interventions.

An update on oral antiplatelet drug interactions with proton pump inhibitors: what are the risks?

INTRODUCTION

Aspirin and anti-P2Y12 are widely prescribed in cardiovascular patients, often in combination with proton pump inhibitors (PPIs) to limit the risk of upper gastrointestinal bleedings. The potential interaction between PPIs and antiplatelet agents has been widely discussed, but doubts remain as to whether PPIs may reduce the cardiovascular protection provided by aspirin, prasugrel, ticagrelor, and clopidogrel.

AREAS COVERED

Many pharmacokinetic (PK) and pharmacodynamic (PD) studies have confirmed the interaction, especially between PPIs and clopidogrel, but with uncertain consequences on clinical outcomes. Therefore, we aimed to summarize the evidence for the widespread combined use of oral antiplatelet drugs and PPIs, to outline the current evidence supporting or opposing drug-drug interaction, and to discuss the clinical implications of such interactions.

EXPERT OPINION

A large body of evidence describes the PK/PD interaction of antiplatelet drugs with PPIs and its potential role in increasing clinical cardiovascular adverse events, but no solid clinical data have confirmed these effects. In the light of the published studies, there seems to be no restriction on the choice of PPI with aspirin, prasugrel, and/or ticagrelor. The choice of a PPI with no (or minimal) interference with the hepatic cytochrome P450 2C19 is preferred in patients receiving clopidogrel.

Clinical Outcomes of Aspirin and Clopidogrel among Patients with Chronic Obstructive Lung Disease: Insights from a Meta-Analysis

(1) Background: Aspirin and clopidogrel have been found helpful in improving clinical outcomes among patients with chronic obstructive lung disease (COPD). However, the evidence on the efficacy of aspirin and/or clopidogrel on clinical outcomes has not been synthesized and summarized in the prior reviews. Hence, we undertook a meta-analysis of the research studies examining the effect of aspirin and/or clopidogrel on varying clinical outcomes among COPD patients; (2) Methods: Using key search terms, we searched databases, including MEDLINE, CINAHL, Google Scholar, and EMBASE to find observational studies and RCTs. Our search was limited to research written in English. We used a random effect model to calculate the 95% confidence intervals and pooled hazard ratio; (3) Results: We included 12 eligible research studies (33,8008 patients) in the current meta-analysis. Among COPD patients, the hazard of all-cause mortality among users of aspirin or clopidogrel was 17% lower (HR: 0.83; 95% CIs (0.70, 0.97; I2 = 73%, X2: 33.34) compared to non-users of anticoagulants (aspirin or clopidogrel). The hazard of dyspnea among users of aspirin or clopidogrel was 3% lower (HR: 0.97; 95% CIs (0.27, 3.49; I2 = 93%, X2: 42.15) compared to non-users of anticoagulants (aspirin or clopidogrel). There was no statistically significant effect of aspirin on other clinical outcomes such as myocardial infarction (HR: 2.04; 95% CIs (0.02, 257.33) and major bleeding (HR: 1.93; 95% CIs (0.07, 1002.33). The funnel plot and Egger's regression test did not show any evidence of publication bias; (4) Conclusions: Overall, we found a positive and beneficial effect of aspirin and/or clopidogrel in reducing all-cause mortality among COPD patients. However, there is uncertainty of evidence for other clinical outcomes such as exacerbation of dyspnea, myocardial infarction, and major bleeding. A limited number of studies examining other clinical outcomes warrant conducting more robust epidemiological studies to assess the efficacy and safety of aspirin and clopidogrel on other clinical outcomes among COPD patients.

Safety, Tolerability, and Pharmacodynamics of AZD3366 (Optimized Human CD39L3 Apyrase) Alone and in Combination With Ticagrelor and Acetylsalicylic Acid: A Phase 1, Randomized, Placebo-Controlled Study

BACKGROUND

ADP and ATP are importantly involved in vascular and thrombotic homeostasis, via multiple receptor pathways. Blockade of ADP P2Y12 receptors inhibits platelet aggregation and represents an effective cardiovascular disease prevention strategy. AZD3366 (APT102), a long-acting recombinant form of an optimized CD39L3 human apyrase, has effectively reduced ATP, ADP, and platelet aggregation and provided tissue protection in preclinical models, features that could be very beneficial in treating patients with cardiovascular disease.

METHODS AND RESULTS

We conducted this phase 1, first-in-human study of single ascending doses of intravenous AZD3366 or placebo, including doses added to dual antiplatelet therapy with ticagrelor and acetylsalicylic acid. The primary objective was safety and tolerability; secondary and exploratory objectives included pharmacokinetics, pharmacodynamics (measured as inhibition of platelet aggregation), adenosine diphosphatase (ADPase) activity, and ATP/ADP metabolism. In total, 104 participants were randomized. AZD3366 was generally well tolerated, with no major safety concerns observed. ADPase activity increased in a dose-dependent manner with a strong correlation to AZD3366 exposure. Inhibition of ADP-stimulated platelet aggregation was immediate, substantial, and durable. In addition, there was a prompt decrease in systemic ATP concentration and an increase in adenosine monophosphate concentrations, whereas ADP concentration appeared generally unaltered. At higher doses, there was a prolongation of capillary bleeding time without detectable changes in the ex vivo thromboelastometric parameters.

CONCLUSIONS

AZD3366 was well tolerated in healthy participants and demonstrated substantial and durable inhibition of platelet aggregation after single dosing. Higher doses prolonged capillary bleeding time without detectable changes in ex vivo thromboelastometric parameters.

REGISTRATION

URL: https://www.clinicaltrials.gov; Unique Identifier: NCT04588727.

Optimizing Dual Antiplatelet Therapy in the Perioperative Period for Spine Surgery After Recent Percutaneous Coronary Intervention: A Comprehensive Review, Synthesis, and Catalyst for Protocol Formulation

The increased incidence of spine surgery within the past decade has highlighted the importance of robust perioperative management to improve patient outcomes overall. Coronary artery disease is a common medical comorbidity present in the population of individuals who receive surgery for spinal pathology that is often treated with dual antiplatelet therapy (DAPT) after percutaneous coronary intervention. Discontinuation of DAPT before surgical intervention is typically indicated; however, contradictory evidence exists in the literature regarding the timing of DAPT use and discontinuation in the perioperative period. We review the most recent cardiac and spine literature on the intricacies of percutaneous coronary intervention and its associated risks in the postoperative period. We further propose protocols for DAPT use after both elective and urgent spine surgery to optimize perioperative care.

Blood oxygen regulation via P2Y12R expressed in the carotid body

BACKGROUND

Peripheral blood oxygen monitoring via chemoreceptors in the carotid body (CB) is an integral function of the autonomic cardiorespiratory regulation. The presence of the purinergic P2Y12 receptor (P2Y12R) has been implicated in CB; however, the exact role of the receptor in O2 sensing and signal transduction is unknown.

METHODS

The presence of P2Y12R was established by immunoblotting, RT qPCR and immunohistochemistry. Primary glomus cells were used to assess P2Y12R function during hypoxia and hypercapnia, where monoamines were measured by HPLC; calcium signal was recorded utilizing OGB-1 and N-STORM Super-Resolution System. Ingravescent hypoxia model was tested in anaesthetized mice of mixed gender and cardiorespiratory parameters were recorded in control and receptor-deficient or drug-treated experimental animals.

RESULTS

Initially, the expression of P2Y12R in adult murine CB was confirmed. Hypoxia induced a P2Y12R-dependent release of monoamine transmitters from isolated CB cells. Receptor activation with the endogenous ligand ADP promoted release of neurotransmitters under normoxic conditions, while blockade disrupted the amplitude and duration of the intracellular calcium concentration. In anaesthetised mice, blockade of P2Y12R expressed in the CB abrogated the initiation of compensatory cardiorespiratory changes in hypoxic environment, while centrally inhibited receptors (i.e. microglial receptors) or receptor-deficiency induced by platelet depletion had limited influence on the physiological adjustment to hypoxia.

CONCLUSIONS

Peripheral P2Y12R inhibition interfere with the complex mechanisms of acute oxygen sensing by influencing the calcium signalling and the release of neurotransmitter molecules to evoke compensatory response to hypoxia. Prospectively, the irreversible blockade of glomic receptors by anti-platelet drugs targeting P2Y12Rs, propose a potential, formerly unrecognized side-effect to anti-platelet medications in patients with pulmonary morbidities.

Off-Target Effects of P2Y12 Receptor Inhibitors: Focus on Early Myocardial Fibrosis Modulation

Several studies have demonstrated that, beyond their antithrombotic effects, P2Y12 receptor inhibitors may provide additional off-target effects through different mechanisms. These effects range from the preservation of endothelial barrier function to the modulation of inflammation or stabilization of atherosclerotic plaques, with an impact on different cell types, including endothelial and immune cells. Many P2Y12 inhibitors have been developed, from ticlopidine, the first thienopyridine, to the more potent non-thienopyridine derivatives such as ticagrelor which may promote cardioprotective effects following myocardial infarction (MI) by inhibiting adenosine reuptake through sodium-independent equilibrative nucleoside transporter 1 (ENT1). Adenosine may affect different molecular pathways involved in cardiac fibrosis, such as the Wnt (wingless-type)/beta (β)-catenin signaling. An early pro-fibrotic response of the epicardium and activation of cardiac fibroblasts with the involvement of Wnt1 (wingless-type family member 1)/β-catenin, are critically required for preserving cardiac function after acute ischemic cardiac injury. This review discusses molecular signaling pathways involved in cardiac fibrosis post MI, focusing on the Wnt/β-catenin pathway, and the off-target effect of P2Y12 receptor inhibition. A potential role of ticagrelor was speculated in the early modulation of cardiac fibrosis, thanks to its off-target effect.

Intravenous cangrelor use for neuroendovascular procedures: a two-center experience and updated systematic review

Background

The optimal antiplatelet therapy regimen for certain neuroendovascular procedures remains unclear. This study investigates the safety and feasibility of intravenous dose-adjusted cangrelor in patients undergoing acute neuroendovascular interventions.

Methods

We conducted a retrospective chart review of all consecutive patients on intravenous cangrelor for neuroendovascular procedures between September 1, 2020, and March 13, 2022. We also conducted an updated systematic review and meta-analysis using PubMed, Scopus, Web of Science, Embase and the Cochrane Library up to February 22, 2023.

Results

In our cohort, a total of 76 patients were included [mean age (years): 57.2 ± 18.2, males: 39 (51.3), Black: 49 (64.5)]. Cangrelor was most used for embolization and intracranial stent placement (n = 24, 32%). Approximately 44% of our patients had a favorable outcome with a modified Rankin Scale (mRS) score of 0 to 2 at 90 days (n = 25/57); within 1 year, 8% of patients had recurrent or new strokes (n = 5/59), 6% had symptomatic intracranial hemorrhage [sICH] (4/64), 3% had major extracranial bleeding events (2/64), and 3% had a gastrointestinal bleed (2/64). In our meta-analysis, 11 studies with 298 patients were included. The pooled proportion of sICH and intraprocedural thromboembolic complication events were 0.07 [95% CI 0.04 to 1.13] and 0.08 [95% CI 0.05 to 0.15], respectively.

Conclusion

Our study found that intravenous cangrelor appears to be safe and effective in neuroendovascular procedures, with low rates of bleeding and ischemic events. However, further research is needed to compare different dosing and titration protocols of cangrelor and other intravenous agents.

Novel strategies in antithrombotic therapy: targeting thrombosis while preserving hemostasis

Antithrombotic therapy is a delicate balance between the benefits of preventing a thrombotic event and the risks of inducing a major bleed. Traditional approaches have included antiplatelet and anticoagulant medications, require careful dosing and monitoring, and all carry some risk of bleeding. In recent years, several new targets have been identified, both in the platelet and coagulation systems, which may mitigate this bleeding risk. In this review, we briefly describe the current state of antithrombotic therapy, and then present a detailed discussion of the new generation of drugs that are being developed to target more safely existing or newly identified pathways, alongside the strategies to reverse direct oral anticoagulants, showcasing the breadth of approaches. Combined, these exciting advances in antithrombotic therapy bring us closer than we have ever been to the "holy grail" of the field, a treatment that separates the hemostatic and thrombotic systems, preventing clots without any concurrent bleeding risk.

Evaluating the pharmacokinetic and pharmacodynamic impact of different modes of ticagrelor administration

INTRODUCTION

Alternative administration modes for oral P2Y12 inhibitors, particularly ticagrelor, have emerged as a potential alternative to overcome the limitations associated with the delayed onset of action of these drugs in patients who are unable to swallow or with impaired absorption.

AREAS COVERED

This comprehensive literature review aims to provide an overview of the current state of knowledge on the pharmacokinetics and administration modes of ticagrelor, including factors that may affect its action. It also compares the pharmacokinetics of ticagrelor with that of other drugs with similar uses to provide a comprehensive understanding of the potential advantages and limitations of different modalities of P2Y12 administration. For this purpose, Embase, Medline, Web of Science Core Collection, Cochrane Central Register of Controlled Trials, Google Scholar, and ClinicalTrials.gov were searched from database inception to July 2023.

EXPERT OPINION

Among the different alternatives, crushed formulations, especially for ticagrelor, have emerged as the most promising option, showing early and robust platelet inhibition. However, important questions remain unanswered, such as the comparative clinical benefits of crushed ticagrelor versus standard administration, the cost-effectiveness of alternative modes compared to intravenous P2Y12 inhibitors such as cangrelor, and the important limitations associated with the concomitant use of opioids, who have been proven to impair even the action of crushed ticagrelor.

Is It Really Safe to Discontinue Antiplatelet Therapy 12 Months After Percutaneous Coronary Intervention in Patients with Atrial Fibrillation?

The prevalence of AF in patients with coronary artery disease is high. The guidelines from many professional groups, including the European Society of Cardiology, American College of Cardiology/American Heart Association and Heart Rhythm Society, recommend a maximum duration of 12 months of combination single antiplatelet and anticoagulation therapy in patients who undergo percutaneous coronary intervention and who have concurrent AF, followed by anticoagulation alone beyond 1 year. However, the evidence that anticoagulation alone without antiplatelet therapy adequately reduces the well-documented attritional risk of stent thrombosis after coronary stent implantation is relatively sparse, particularly given that very late stent thrombosis (>1 year from stent implantation) is the commonest type. By contrast, the elevated risk of bleeding from combined anticoagulation and antiplatelet therapy is clinically important. The aim of this review is to assess the evidence for long-term anticoagulation alone without antiplatelet therapy 1 year post-percutaneous coronary intervention in patients with AF.

Antiplatelet Therapy in Coronary Artery Disease: Now and Then

Cardiovascular disease, particularly coronary artery disease (CAD), remains the leading cause of mortality and morbidity in industrialized countries. Platelet activation and aggregation at the site of endothelial injury play a key role in the processes ultimately resulting in thrombus formation with vessel occlusion and subsequent end-organ damage. Consequently, antiplatelet therapy has become a mainstay in the pharmacological treatment of CAD. Several drug classes have been developed over the last decades and a broad armamentarium of antiplatelet agents is currently available. This review portrays the evolution of antiplatelet therapy, and provides an overview on previous and current antiplatelet drugs and strategies.

Comparative Risk of Hospitalized Bleeding of P2Y12 Inhibitors for Secondary Prophylaxis in Acute Coronary Syndrome After Percutaneous Coronary Intervention

In closely monitored randomized controlled trials (RCTs), newer P2Y12 agents (ticagrelor and prasugrel) reduced cardiovascular outcomes compared with clopidogrel following percutaneous coronary intervention (PCI) in acute coronary syndrome. However, these RCTs indicated a higher bleeding risk with these newer agents. This study evaluated the comparative safety of each P2Y12 inhibitor on hospitalizations due to major bleeding in a real-world population. This retrospective, propensity score-matched (PSM) cohort study utilized the IBM MarketScan database over 6 years (2013-2018) to identify incident users of P2Y12 inhibitors with age ≥18 years. The primary safety outcome was hospitalization due to any major bleeding event including gastrointestinal, intracranial, and other serious forms of bleeding. In pairwise comparisons using Cox-proportional hazards models, ticagrelor, prasugrel, and clopidogrel users were compared for the primary safety outcome at 30, 90, and 180 days following the first prescription of P2Y12 inhibitor after PCI. There were 21,719 (ticagrelor vs. clopidogrel), 11,513 (prasugrel vs. clopidogrel), and 11,065 (prasugrel vs. ticagrelor) PSM pairs. Overall, the risk of major bleeding was similar for all P2Y12 inhibitors. Hospitalization for major bleeding was generally lower among ticagrelor users vs. clopidogrel and higher among prasugrel users compared with clopidogrel. Importantly, a 66% higher risk of major bleeding at 90 days is suggested with prasugrel compared with clopidogrel (hazard ratio 1.66; 95% confidence interval, 1.11-2.48). This study indicated a higher short-term bleeding risk with prasugrel compared with clopidogrel, which concurs with the results of RCTs.

Pharmacogenetics of P2Y12 receptor inhibitors

Oral P2Y12 inhibitors are commonly prescribed for cardiovascular disease and include clopidogrel, prasugrel, and ticagrelor. Each of these drugs has its strengths and weaknesses. Prasugrel and ticagrelor are more potent inhibitors of platelet aggregation and were shown to be superior to clopidogrel in preventing major adverse cardiovascular events after an acute coronary syndrome and percutaneous coronary intervention (PCI) in the absence of genotyping. However, both are associated with an increased risk for non-coronary artery bypass-related bleeding. Clopidogrel is a prodrug requiring bioactivation, primarily via the CYP2C19 enzyme. Approximately 30% of individuals have a CYP2C19 no function allele and decreased or no CYP2C19 enzyme activity. Clopidogrel-treated carriers of a CYP2C19 no function allele have decreased exposure to the clopidogrel active metabolite and lesser inhibition of platelet aggregation, which likely contributed to reduced clopidogrel efficacy in clinical trials. The pharmacogenetic data for clopidogrel are most robust in the setting of PCI, but evidence is accumulating for other indications. Guidance is available from expert consensus groups and regulatory agencies to assist with integrating genetic information into P2Y12 inhibitor prescribing decisions, and CYP2C19 genotype-guided antiplatelet therapy after PCI is one of the most common examples of clinical pharmacogenetic implementation. Herein, we review the evidence for pharmacogenetic associations with clopidogrel response and outcomes with genotype-guided P2Y12 inhibitor selection and describe guidance to assist with pharmacogenetic implementation. We also describe processes for applying genotype data for P2Y12 inhibitor therapy selection and remaining gaps in the field. Ultimately, consideration of both clinical and genetic factors may guide selection of P2Y12 inhibitor therapy that optimally balances the atherothrombotic and bleeding risks.

Monitoring antiplatelet therapy: where are we now?

Single antiplatelet therapy represents the cornerstone of thrombosis prevention in atherosclerotic cardiovascular disease. Dual antiplatelet therapy (DAPT), consisting of aspirin plus a P2Y12 inhibitor, is the standard of care for patients with acute coronary syndrome or undergoing both coronary and peripheral percutaneous interventions. Recent data suggest the efficacy of DAPT also after minor stroke. In this setting, a large body of evidence has documented that genetic and acquired patients' characteristics may affect the magnitude of platelet inhibition induced by antiplatelet agents. The implementation of tools allowing the identification and prediction of platelet inhibition has recently been shown to improve outcomes, leading to an optimal balance between antithrombotic efficacy and bleeding risk. We are therefore clearly moving towards tailored antiplatelet therapy. The aim of this paper is to summarize the available evidence on the evaluation of platelet inhibition in patients with coronary, peripheral, or cerebrovascular atherosclerosis. We will here focus on antiplatelet therapy based on both aspirin and P2Y12 inhibitors. In addition, we provide practical insights into the clinical settings in which it appears reasonable to implement antiplatelet therapy monitoring.

The Role of the Coagulation System in Peripheral Arterial Disease: Interactions with the Arterial Wall and Its Vascular Microenvironment and Implications for Rational Therapies

Peripheral artery disease (PAD) is a clinical manifestation of atherosclerotic disease with a large-scale impact on the economy and global health. Despite the role played by platelets in the process of atherogenesis being well recognized, evidence has been increasing on the contribution of the coagulation system to the atherosclerosis formation and PAD development, with important repercussions for the therapeutic approach. Histopathological analysis and some clinical studies conducted on atherosclerotic plaques testify to the existence of different types of plaques. Likely, the role of coagulation in each specific type of plaque can be an important determinant in the histopathological composition of atherosclerosis and in its future stability. In this review, we analyze the molecular contribution of inflammation and the coagulation system on PAD pathogenesis, focusing on molecular similarities and differences between atherogenesis in PAD and coronary artery disease (CAD) and discussing the possible implications for current therapeutic strategies and future perspectives accounting for molecular inflammatory and coagulation targets. Understanding the role of cross-talking between coagulation and inflammation in atherosclerosis genesis and progression could help in choosing the right patients for future dual pathway inhibition strategies, where an antiplatelet agent is combined with an anticoagulant, whose role, despite pathophysiological premises and trials' results, is still under debate.

The NO/cGMP/PKG pathway in platelets: The therapeutic potential of PDE5 inhibitors in platelet disorders

Platelets are the "guardians" of the blood circulatory system. At sites of vessel injury, they ensure hemostasis and promote immunity and vessel repair. However, their uncontrolled activation is one of the main drivers of thrombosis. To keep circulating platelets in a quiescent state, the endothelium releases platelet antagonists including nitric oxide (NO) that acts by stimulating the intracellular receptor guanylyl cyclase (GC). The latter produces the second messenger cyclic guanosine-3',5'-monophosphate (cGMP) that inhibits platelet activation by stimulating protein kinase G, which phosphorylates hundreds of intracellular targets. Intracellular cGMP pools are tightly regulated by a fine balance between GC and phosphodiesterases (PDEs) that are responsible for the hydrolysis of cyclic nucleotides. Phosphodiesterase type 5 (PDE5) is a cGMP-specific PDE, broadly expressed in most tissues in humans and rodents. In clinical practice, PDE5 inhibitors (PDE5i) are used as first-line therapy for erectile dysfunction, pulmonary artery hypertension, and lower urinary tract symptoms. However, several studies have shown that PDE5i may ameliorate the outcome of various other conditions, like heart failure and stroke. Interestingly, NO donors and cGMP analogs increase the capacity of anti-platelet drugs targeting the purinergic receptor type Y, subtype 12 (P2Y12) receptor to block platelet aggregation, and preclinical studies have shown that PDE5i inhibits platelet functions. This review summarizes the molecular mechanisms underlying the effect of PDE5i on platelet activation and aggregation focusing on the therapeutic potential of PDE5i in platelet disorders, and the outcomes of a combined therapy with PDE5i and NO donors to inhibit platelet activation.

Assessment of immediate clotting after flapless extraction using piezosurgery or turbine handpiece in patients receiving dual antiplatelet therapy

PURPOSE

This study aimed to investigate the efficacy of piezosurgery (PI) in promoting immediate clotting after flapless extraction in patients undergoing dual antiplatelet therapy (DAPT).

METHODS

In this randomized controlled trial, 80 DAPT patients were equally divided into the PI and turbine handpiece (TH) groups. Accordingly, flapless extraction of a single tooth using PI or TH was performed on each patient, and the immediate clotting status was evaluated. The results of the preoperative hematological examinations, surgery-related variables and postoperative complications were recorded for analysis.

RESULTS

Both groups presented with low platelet aggregation and similar coagulation functions. The PI group exhibited a higher proportion of patients with normal intra-alveolar clotting (≤30 min) (70% vs. 40%, P = 0.007) and fewer intraoperative complications (25% vs. 47.5%, P = 0.036) than that in the TH group. Logistic regression analysis indicated that the applied instrument was an independent risk factor for prolonged immediate bleeding (odds ratio = 3.10, 95% confidence interval: 1.20-8.00, P = 0.019). Intergroup differences were insignificant in terms of the other surgery-related variables and postoperative complications, except for the longer surgical duration in the PI group.

CONCLUSION

The application of PI may contribute to better immediate clotting in DAPT patients after flapless extraction compared with the use of TH.

Clinical pharmacology of antiplatelet drugs

INTRODUCTION

Platelets play a key role in arterial thrombosis and antiplatelet therapy is pivotal in the treatment of cardiovascular disease. Current antiplatelet drugs target different pathways of platelet activation and show specific pharmacodynamic and pharmacokinetic characteristics, implicating clinically relevant drug-drug interactions.

AREAS COVERED

This article reviews the role of platelets in hemostasis and cardiovascular thrombosis, and discusses the key pharmacodynamics, drug-drug interactions and reversal strategies of clinically used antiplatelet drugs.

EXPERT OPINION

Antiplatelet therapies target distinct pathways of platelet activation: thromboxane A₂ synthesis, adenosine diphosphate-mediated signaling, integrin α_IIbβ₃ (GPIIb/IIIa), thrombin-mediated platelet activation via the PAR1 receptor and phosphodiesterases. Key clinical drug-drug interactions of antiplatelet agents involve acetylsalicylic acid - ibuprofen, clopidogrel - omeprazole, and morphine - oral P2Y₁₂ inhibitors, all of which lead to an attenuated antiplatelet effect. Platelet function and genetic testing and the use of scores (ARC-HBR, PRECISE-DAPT, ESC ischemic risk definition) may contribute to a more tailored antiplatelet therapy. High on-treatment platelet reactivity presents a key problem in the acute management of ST-elevation myocardial infarction (STEMI). A treatment strategy involving early initiation of an intravenous antiplatelet agent may be able to bridge the gap of insufficient platelet inhibition in high ischemic risk patients with STEMI.

Efficacy of ticagrelor compared to clopidogrel in improving endothelial function in patients with coronary artery disease: a systematic review

BACKGROUND

Ticagrelor and clopidogrel are antiplatelet drugs that act by binding to the adenosine diphosphate P2Y12 receptor. Previous studies have compared between them regarding the endothelial function effect.

OBJECTIVES

This systematic review aims to summarize the evidence comparing the efficacy of ticagrelor vs. clopidogrel in improving endothelial function in patients with coronary artery disease (CAD).

METHODS

In August 2021, the Scopus, PubMed, Web of Science, and Cochrane library were searched systematically for eligible trials. We included randomized controlled trials that compared the efficacy of ticagrelor vs. clopidogrel in improving endothelial function in patients with CAD.

RESULTS

Seven trials (n = 511) were included in our systematic review. Ticagrelor resulted in a greater elevation of the level of progenitor cells CD34+ KDR+ and CD34+ 133+ (P = 0.036 and P = 0.019, respectively), with a lower rate of endothelial cell apoptosis rate (P < 0.001). Moreover, ticagrelor showed superiority regarding nitric oxide, radical oxygen species, and soluble P-selectin levels (P = 0.03, P = 0.02, and P = 0.019, respectively). Flow-mediated dilation findings differed between the studies (P = 0.004 vs. P = 0.39).

CONCLUSION

Ticagrelor appears to exert an additional improvement in endothelial function compared with clopidogrel in patients with coronary heart disease.

Antiplatelet Agents in Acute ST Elevation Myocardial Infarction

Platelet aggregation and thrombus formation represent the basic mechanism for clinical, electrocardiographic, and biomarker changes consistent with acute coronary syndrome. Various oral and intravenous formulations of platelet function inhibitors have been developed to help decrease platelet aggregation due to acute atherosclerotic plaque rupture. In this article, we review the various mechanisms, pharmacokinetics/pharmacodynamics, and the key clinical trials related to the platelet inhibitors that form the basis for current recommendations of their use in the ST elevation myocardial infarction guidelines by the American College of Cardiology/American Heart Association.

P2Y12 Antagonists in Cardiovascular Disease—Finding the Best Balance Between Preventing Ischemic Events and Causing Bleeding

Dual antiplatelet therapy comprising of aspirin and oral P2Y₁₂ receptor antagonists are an established cornerstone of therapy in acute coronary syndromes and percutaneous coronary intervention. As a result, the platelet P2Y₁₂ receptor remains a key therapeutic target in cardiovascular medicine since pharmacological antagonists were first developed in the 1990’s. With a greater understanding of platelet biology and the role played by the P2Y₁₂ receptor in the amplification of platelet activation and thrombus formation, there has been progressive refinement in the development of P2Y₁₂ receptor antagonists with greater potency and consistency of antiplatelet effect. However, challenges remain in the utilization of these agents particularly in balancing the need for greater protection from ischemic events whilst minimizing the bleeding risk and present a real opportunity for the institution of individualized medicine. Future drug developments will provide clinicians with greater avenues to achieve this.

Platelet reactivity testing in peripheral artery disease

DISCLAIMER

In an effort to expedite the publication of articles related to the COVID-19 pandemic, AJHP is posting these manuscripts online as soon as possible after acceptance. Accepted manuscripts have been peer-reviewed and copyedited, but are posted online before technical formatting and author proofing. These manuscripts are not the final version of record and will be replaced with the final article (formatted per AJHP style and proofed by the authors) at a later time.

PURPOSE

Oral antiplatelet therapy is routinely used to prevent adverse cardiovascular events in patients with peripheral artery disease (PAD). Several laboratory tests are available to quantify the degree of platelet inhibition following antiplatelet therapy. This article aims to provide a review of the literature surrounding platelet functional testing in patients with PAD receiving oral P2Y12 inhibitors and to offer guidance to clinicians for the use and interpretation of these tests.

SUMMARY

A literature search of PubMed and the Web of Science Core Collection database was conducted. All studies that performed platelet function testing and reported clinical outcomes in patients with PAD were included. Evaluation of the data suggests that, among the available testing strategies, the VerifyNow platelet reactivity unit (PRU) test is the most widely used. Despite numerous investigations attempting to define a laboratory threshold indicating suboptimal response to antiplatelet therapy, controversy exists about which PRU value best correlates with cardiovascular outcomes (ie, mortality, stent thrombosis, etc). In the PAD literature, the most commonly used PRU thresholds are 208 or higher and 235 or higher. Nonetheless, adjusting antiplatelet regimens based on suboptimal P2Y12 reactivity values has yet to be proven useful in reducing the incidence of adverse cardiovascular outcomes. This review examines platelet function testing in patients with PAD and discusses the interpretation and application of these tests when monitoring the safety and efficacy of P2Y12 inhibitors.

CONCLUSION

Although platelet functional tests may be simple to use, clinical trials thus far have failed to show benefit from therapy adjustments based on test results. Clinicians should be cautioned against relying on this test result alone and should instead consider a combination of laboratory, clinical, and patient-specific factors when adjusting P2Y12 inhibitor therapy in clinical practice.

Antiplatelet Therapy for Atherothrombotic Disease in 2022—From Population to Patient-Centered Approaches

Antiplatelet agents, with aspirin and P2Y₁₂ receptor antagonists as major key molecules, are currently the cornerstone of pharmacological treatment of atherothrombotic events including a variety of cardio- and cerebro-vascular as well as peripheral artery diseases. Over the last decades, significant changes have been made to antiplatelet therapeutic and prophylactic strategies. The shift from a population-based approach to patient-centered precision medicine requires greater awareness of individual risks and benefits associated with the different antiplatelet strategies, so that the right patient gets the right therapy at the right time. In this review, we present the currently available antiplatelet agents, outline different management strategies, particularly in case of bleeding or in perioperative setting, and develop the concept of high on-treatment platelet reactivity and the steps toward person-centered precision medicine aiming to optimize patient care.

Current and Novel Antiplatelet Therapies for the Treatment of Cardiovascular Diseases

Over the last decades, antiplatelet agents, mainly aspirin and P2Y₁₂ receptor antagonists, have significantly reduced morbidity and mortality associated with arterial thrombosis. Their pharmacological characteristics, including pharmacokinetic/pharmacodynamics profiles, have been extensively studied, and a significant number of clinical trials assessing their efficacy and safety in various clinical settings have established antithrombotic efficacy. Notwithstanding, antiplatelet agents carry an inherent risk of bleeding. Given that bleeding is associated with adverse cardiovascular outcomes and mortality, there is an unmet clinical need to develop novel antiplatelet therapies that inhibit thrombosis while maintaining hemostasis. In this review, we present the currently available antiplatelet agents, with a particular focus on their targets, pharmacological characteristics, and patterns of use. We will further discuss the novel antiplatelet therapies in the pipeline, with the goal of improved clinical outcomes among patients with atherothrombotic diseases.

Safety of Oral P2Y12 Inhibitors in Interventional Neuroradiology: Current Status and Perspectives

In the field of interventional neuroradiology, antiplatelet agents are commonly used to prepare patients before the implantation of permanent endovascular materials. Among the available drugs, clopidogrel is the most frequently used one, but resistance phenomena are considered to be relatively common. Prasugrel and ticagrelor were recently added to the pharmacologic arsenal, but the safety of these agents in patients undergoing neurointerventional procedures is still a subject of discussion. The cumulative experience with both drugs is less extensive than that with clopidogrel, and the experience with patients in the neurology field is less extensive than in the cardiology domain. In the present article, we provide a narrative review of studies that investigated safety issues of oral P2Y12 inhibitors in interventional neuroradiology and discuss potential routes for future research.

Coronary Heart Disease (CHD) in Elderly Patients: Which Drug to Choose, Ticagrelor and Clopidogrel? A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Background: A new generation P2Y12 receptor inhibitor (ticagrelor) is recommended in current therapeutic guidelines to treat patients with coronary heart disease (CHD). However, it is unknown if ticagrelor is more effective than clopidogrel in elderly patients. Therefore, a systematic review was done to assess the effectiveness and safety of ticagrelor and clopidogrel in older patients with CHD to determine the appropriate antiplatelet treatment plan. Methodology: We performed a systematic review of randomized controlled trials (RCTs) to compare the effectiveness and safety of ticagrelor vs. clopidogrel in elderly patients with CHD. We selected eligible RCTs based on specified study criteria following a systematic search of PubMed and Scopus databases from January 2007 to May 2021. Primary efficacy outcomes assessed were major adverse cardiovascular events (MACEs), myocardial infarction (MI), stent thrombosis (ST), and all-cause death. The secondary outcome assessed was major bleeding events. We used RevMan 5.3 software to conduct a random-effects meta-analysis and estimated the pooled incidence and risk ratios (RRs) with 95% confidence intervals (CIs) for ticagrelor and clopidogrel. Results: Data from 6 RCTs comprising 21,827 elderly patients were extracted according to the eligibility criteria. There was no significant difference in the MACE outcome (incidence: 9.23% vs. 10.57%; RR = 0.95, 95% CI = 0.70–1.28, p = 0.72), MI (incidence: 5.40% vs. 6.23%; RR = 0.94, 95% CI= 0.69–1.27, p = 0.67), ST (incidence: 2.33% vs. 3.17%; RR = 0.61, 95% CI= 0.32–1.17, p = 0.13), and all-cause death (4.29% vs. 5.33%; RR = 0.86, 95% CI = 0.65–1.12, p = 0.25) for ticagrelor vs. clopidogrel, respectively. In addition, ticagrelor was not associated with a significant increase in the rate of major bleeding (incidence: 9.98% vs. 9.33%: RR = 1.37, 95% CI = 0.97–1.94, p = 0.07) vs. clopidogrel. Conclusions: This study did not find evidence that ticagrelor is significantly more effective or safer than clopidogrel in elderly patients with CHD.

Treatment of In-Stent Stenosis Following Flow Diversion of Intracranial Aneurysms with Cilostazol and Clopidogrel

In-stent stenosis is a feared complication of flow diversion treatment for cerebral aneurysms. We present 2 cases of patients treated with pipeline flow diversion for unruptured cerebral aneurysms. Initial perioperative dual antiplatelet therapy (DAPT) consisted of standard aspirin plus clopidogrel. At 6-month follow-up cerebral angiography, the patients were noted to have developed significant in-stent stenosis (63% and 53%). The patients were treated with cilostazol and clopidogrel for at least 6 months. Subsequent angiography at 1-year post-treatment showed significant improvement of the in-stent stenosis from 63% to 34% and 53% to 21%. The role of cilostazol as treatment of intracranial in-stent stenosis has not been previously described. Cilostazol’s vasodilatory effect and suppression of vascular smooth muscle proliferation provides ideal benefits in this setting. Cilostazol plus clopidogrel may be a safe and effective alternative to standard DAPT for treatment of in-stent stenosis following flow diversion and warrants further consideration and investigation.

Guided and unguided de-escalation from potent P2Y12 inhibitors among patients with ACS: a meta-analysis

AIM

Optimal dual antiplatelet therapy (DAPT) in patients undergoing percutaneous coronary intervention (PCI) for acute coronary syndrome (ACS) intends to balance ischemic and bleeding risks. Various DAPT de-escalation strategies, defined as switching from a full-dose potent to a reduced dose or less potent P2Y12 inhibitor, have been evaluated in several ACS-PCI trials. We aimed to compare DAPT de-escalation to standard DAPT with full dose potent P2Y12 inhibitors in ACS patients who underwent PCI.

METHODS & RESULTS

PubMed, Google Scholar and Cochrane Central Register of Controlled Trials were searched for eligible randomised controlled trials. Aspirin monotherapy trials were excluded. Five randomised trials (n = 10,779 patients) that assigned DAPT de-escalation (genetically guided to clopidogrel n = 1,242; platelet function guided to clopidogrel n = 1,304; unguided to clopidogrel n = 1,672; unguided to lower dose n = 1,170) versus standard DAPT (control group n = 5,391) were included in this analysis. DAPT de-escalation was associated with a significant reduction in Bleeding Academic Research Consortium ≥ 2 bleeding (HR 0.57, 95% CI 0.42-0.78; I2 = 77%) as well as major adverse cardiac events, represented in most trials by the composite of cardiovascular mortality, myocardial infarction, stent thrombosis and stroke (HR 0.77, 95% CI 0.62-0.96; I2 = 0%). Notwithstanding the limited power, consistency was noted across various de-escalation strategies.

CONCLUSION

De-escalation of DAPT after PCI for ACS, both unguided and guided by genetic or platelet function testing, was associated with lower rates of clinically relevant bleeding and ischemic events as compared to standard DAPT with potent P2Y12 inhibitors based on five open-label RCTs reviewed.

A Clinical Update on Antiplatelet Therapy in Secondary Prevention of Ischemic Stroke

PURPOSE OF REVIEW

Antiplatelet therapy remains the standard of care in secondary stroke prevention for non-cardioembolic ischemic stroke and transient ischemic attack. We aim to examine the use of antiplatelet agents in secondary prevention through highlighting relevant clinical trials and meta-analyses as well as providing commentary regarding our practice.

RECENT FINDINGS

In the POINT and CHANCE trials, dual antiplatelet therapy reduced recurrent stroke compared to aspirin monotherapy. Sub-analyses of these trials suggest that genetic polymorphisms could play a role in diminishing the effectiveness of clopidogrel. Similarly, THALES demonstrated better outcomes with ticagrelor-aspirin combination therapy over aspirin monotherapy. Combination antiplatelet therapy with aspirin and the P2Y12 inhibitors, clopidogrel and ticagrelor, reduced stroke recurrence in those presenting with mild ischemic stroke or high risk TIA. Genetic polymorphisms may play a role in determining the appropriate regimen. Questions remain regarding the optimal duration of combination antiplatelet therapy for various stroke etiologies.

Ischemic and bleeding outcomes of potent P2Y12 inhibitor antiplatelet agents versus clopidogrel in elderly patients with acute coronary syndrome: A meta-analysis of randomized trials

BACKGROUND

The role of P2Y12 inhibition in acute coronary syndrome (ACS) has been well described in literature. However, the agent of choice is less clear among elderly patients (>65 years) who are at increased risk of bleeding. This meta-analysis was designed to investigate the efficacy and safety of potent P2Y12 inhibitors vs. clopidogrel in this population.

METHODS AND RESULTS

PubMed, Cochrane Central Register of Clinical Trials, EMBASE, and ClinicalTrial.gov (inception through February 25, 2021) were searched for randomized studies comparing potent oral P2Y12 inhibitors to clopidogrel in elderly population presenting with ACS. Study endpoints included major adverse cardiac events (MACE), major bleeding, all-cause mortality, cardiovascular mortality, myocardial infarction, and stroke. Hazard ratios (HRs) with 95% confidence intervals (CIs) were computed and p<0.05 was considered significant. Eight randomized studies with a total 10,081 patients were included in the final analysis. At mean follow up of 26 months, there were no significant differences between potent oral P2Y12 inhibitors and clopidogrel in MACE (HR 0.97, 95% CI [0.82-1.15]; p=0.73), all-cause mortality (HR 0.91, 95% CI [0.75-1.10]; p=1.00), MI (HR 0.95, 95% CI [0.78-1.17]; p=0.64), and stroke (HR 1.24, 95% CI [0.82-1.86]; p=0.31). However, potent oral P2Y₁₂ inhibitors were associated with a reduction in cardiovascular mortality (HR 0.82, 95% CI [0.68-0.98]; p=0.03), and an increase in major bleeding events (HR 1.32, 95% CI [1.09-1.59]; p<0.01).

CONCLUSION

In comparison with clopidogrel, the use of potent oral P2Y12 inhibitors in elderly patients with ACS, is associated with a reduction in the risk of cardiovascular mortality with increased risk of bleeding events and no significant change in MACE outcomes.

Purinergic Receptors of the Central Nervous System: Biology, PET Ligands, and Their Applications

Purinergic receptors play important roles in central nervous system (CNS). These receptors are involved in cellular neuroinflammatory responses that regulate functions of neurons, microglial and astrocytes. Based on their endogenous ligands, purinergic receptors are classified into P1 or adenosine, P2X and P2Y receptors. During brain injury or under pathological conditions, rapid diffusion of extracellular adenosine triphosphate (ATP) or uridine triphosphate (UTP) from the damaged cells, promote microglial activation that result in the changes in expression of several of these receptors in the brain. Imaging of the purinergic receptors with selective Positron Emission Tomography (PET) radioligands has advanced our understanding of the functional roles of some of these receptors in healthy and diseased brains. In this review, we have accumulated a list of currently available PET radioligands of the purinergic receptors that are used to elucidate the receptor functions and participations in CNS disorders. We have also reviewed receptors lacking radiotracer, laying the foundation for future discoveries of novel PET radioligands to reveal these receptors roles in CNS disorders.

The Molecular Aspects of Disturbed Platelet Activation through ADP/P2Y12 Pathway in Multiple Sclerosis

Epidemiological studies confirm a high risk of ischemic events in secondary-progressive multiple sclerosis (SP MS) patients, directly associated with an increased level of pro-thrombotic activity of platelets. Our work aimed to verify potential molecular abnormalities of the platelet P2Y₁₂ receptor expression and functionality as a cause of an increased risk of thromboembolism observed in the course of MS. We have demonstrated an enhanced platelet reactivity in response to adenosine diphosphate (ADP) in SP MS relative to controls. We have also shown an increased mRNA expression for the P2RY12 gene in both platelets and megakaryocytes, as well as enhanced density of these receptors on the platelet surface. We postulate that one of the reasons for the elevated risk of ischemic events observed in MS may be a genetically or phenotypically reinforced expression of the platelet P2Y₁₂ receptor. In order to analyze the effect of the PAR1 (protease activated receptor type 1) signaling pathway on the expression level of P2Y₁₂, we also analyzed the correlation parameters between P2Y₁₂ expression and the markers of platelet activation in MS induced by selective PAR1 agonist (thrombin receptor activating peptide-6, TRAP-6). Identifying the molecular base responsible for the enlarged pro-thrombotic activity of platelets in SP MS could contribute to the implementation of prevention and targeted treatment, reducing the development of cardiovascular disorders in the course of the disease.

Analysis of the clinical characteristics of acute arthritis induced by clopidogrel

WHAT IS KNOWN AND OBJECTIVE

Knowledge regarding the association between clopidogrel exposure and acute arthritis is based mainly on case reports. The purpose of this article was to assess the clinical characteristics of clopidogrel-induced acute arthritis.

METHODS

We collected literature from 1998 to 2020 in Chinese and English on acute arthritis induced by clopidogrel for retrospective analysis.

RESULTS AND DISCUSSION

The median age of 21 patients (6 females and 15 males) was 63 years (range 34-77). The median time of symptom onset was 10 days (range 0.21-21) overall. The median onset time of symptoms of clopidogrel-induced arthritis was 14 days (range 3-21) and 3 days (range 0.21-7) in patients with and without a loading dose of clopidogrel, respectively. Arthralgias (100%), joint swelling (61.9%), fever (57.1%), rash (33.3%) and pruritus (28.6%) were the most common accompanying symptoms. Most cases were accompanied by different degrees of acute inflammation markers: the median ESR was 68 mm/h (range 10-120), and the median CRP was 142.4 mg/L (range 2.3-408). X-ray films were unremarkable. Symptoms disappeared completely in all patients at a median time of 4 days (range 0.17-30) after the discontinuation of clopidogrel. Prasugrel, ticagrelor and ticlopidine can be used as safe alternatives to clopidogrel in patients with clopidogrel-induced acute arthritis with no recurrence of arthritis.

WHAT IS NEW AND CONCLUSION

Clopidogrel-induced arthritis is a rare adverse reaction and should be suspected in patients with arthralgia and fever during clopidogrel use.

Management of patients receiving novel antithrombotic treatment in endodontic practice: Review and clinical recommendations

Cardiovascular diseases are a major component of non-communicable diseases and death, with thrombosis constituting the most common underlying pathosis of the three major cardiovascular disorders: ischaemic heart disease (acute coronary syndrome), stroke and venous thromboembolism (VTE). The introduction of direct oral anticoagulants (DOACs) in recent years has necessitated a more complex approach to periprocedural and perioperative anticoagulation management and the need for revised management strategies and protocols. Currently, patients taking classic oral anticoagulants are advised to stop taking the drugs and have their INR values checked 72 h prior to dental surgery (e.g., apical surgery, tooth extraction, and periodontal surgery) and checked again 24 h prior to the procedure to ensure it is within the therapeutic range. However, the current incorporation of these novel DOACs in routine medical practice requires changes in the way patients are managed preoperatively in dentistry, and specifically in endodontic surgery. The methodology applied in this review included searching for relevant articles in the PubMed database using keywords listed in the Entree Terms databases. Articles published on human blood clotting mechanism, antithrombotic drugs, as well as treatment guidelines and recommendations for dentistry were retrieved. In addition, textbooks and guidelines that may not have surfaced in the online search were searched manually. The aim of this paper was to review the mechanisms of action of classic and novel antithrombotic medications and their impact on endodontic treatment and the management of local haemostasis in endodontics.

Oral Antiplatelet Therapy After Acute Coronary Syndrome: A Review

IMPORTANCE

Acute coronary syndrome (ACS) is a major cause of morbidity and mortality in the United States with an annual incidence of approximately 1 million. Dual antiplatelet therapy (DAPT), consisting of aspirin and a P2Y12 inhibitor (clopidogrel, ticagrelor, or prasugrel) reduces cardiovascular event rates after ACS.

OBSERVATIONS

In 2016, the updated guidelines from the American College of Cardiology/American Heart Association (ACC/AHA) recommended aspirin plus a P2Y12 inhibitor for at least 12 months for patients with ACS. Since these recommendations were published, new randomized clinical trials have studied different regimens and durations of antiplatelet therapy. Recommendations vary according to the risk of bleeding. If bleeding risk is low, prolonged DAPT may be considered, although the optimal duration of prolonged DAPT beyond 1 year is not well established. If bleeding risk is high, shorter duration (ie, 3-6 months) of DAPT may be reasonable. A high risk of bleeding traditionally is defined as a 1-year risk of serious bleeding (either fatal or associated with a ≥3-g/dL drop in hemoglobin) of at least 4% or a risk of an intracranial hemorrhage of at least 1%. Patients at higher risk are 65 years old or older; have low body weight (BMI <18.5), diabetes, or prior bleeding; or take oral anticoagulants. The newest P2Y12 inhibitors, prasugrel and ticagrelor, are more potent, with high on-treatment residual platelet reactivity of about 3% vs 30% to 40% with clopidogrel and act within 30 minutes compared with 2 hours for clopidogrel. Clinicians should avoid prescribing prasugrel to patients with a history of stroke or transient ischemic attack because of an increased risk of cerebrovascular events (6.5% vs 1.2% with clopidogrel, P = .002) and should avoid prescribing it to patients older than 75 years or who weigh less than 60 kg. The ISAR-REACT-5 trial found that prasugrel reduced rates of death, myocardial infarction, or stroke at 1 year compared with ticagrelor among patients with ACS undergoing percutaneous coronary intervention (9.3% vs 6.9%, P = .006) with no significant difference in bleeding. Recent trials suggested that discontinuing aspirin rather than the P2Y12 inhibitor may be associated with better outcomes.

CONCLUSIONS AND RELEVANCE

Dual antiplatelet therapy reduces rates of cardiovascular events in patients with acute coronary syndrome. Specific combinations and duration of dual antiplatelet therapy should be based on patient characteristics-risk of bleeding myocardial ischemia.

Comparison of Light Transmission Aggregometry With Impedance Aggregometry in Patients on Potent P2Y12 Inhibitors

Since data on the agreement between light transmission aggregometry (LTA) and multiple electrode aggregometry (MEA) in patients on the more potent P2Y₁₂ inhibitors are missing so far, we investigated if the evaluation of the responsiveness to therapy by LTA can be replaced by MEA in 160 acute coronary syndrome (ACS) patients on dual antiplatelet therapy with aspirin and prasugrel or ticagrelor (n = 80 each). Cut-off values for high on-treatment residual platelet reactivity (HRPR) in response to adenosine diphosphate (ADP) or arachidonic acid (AA) were defined according to previous studies showing an association of HRPR with the occurrence of adverse ischemic outcomes. ADP- inducible platelet aggregation was 33% and 37% (P = 0.07) by LTA and 19 AU and 20 AU (P = 0.38) by MEA in prasugrel- and ticagrelor-treated patients, respectively. AA- inducible platelet aggregation was 2% and 3% by LTA and 15 AU and 16 AU by MEA, (all P ≥ 0.3) in patients on prasugrel and ticagrelor, respectively. By LTA, HRPR ADP and HRPR AA were seen in 5%/5% and in 4%/ 13% of patients receiving prasugrel- and ticagrelor, respectively. By MEA, HRPR ADP and HRPR AA were seen in 3%/ 25% and 0%/24% of prasugrel- and ticagrelor-treated patients, respectively. ADP-inducible platelet reactivity by MEA correlated significantly with LTA ADP in prasugrel-treated patients (r = 0.4, P < 0.001), but not in those receiving ticagrelor (r = 0.09, P = 0.45). AA-inducible platelet aggregation by LTA and MEA did not correlate in prasugrel- and ticagrelor-treated patients. Sensitivity/specificity of HRPR by MEA to detect HRPR by LTA were 25%/99% for MEA ADP and 100%/79% for MEA AA in prasugrel-treated patients, and 0%/100% for MEA ADP and 70%/83% for MEA AA in ticagrelor-treated patients. In conclusion, on-treatment residual ADP-inducible platelet reactivity by LTA and MEA shows a significant correlation in prasugrel- but not ticagrelor-treated patients. However, in both groups LTA and MEA revealed heterogeneous results regarding the classification of patients as responders or non-responders to P2Y₁₂ inhibition.

Purinergic signaling orchestrating neuron-glia communication

This review discusses the evidence supporting a role for ATP signaling (operated by P₂X and P₂Y receptors) and adenosine signaling (mainly operated by A₁ and A_2A receptors) in the crosstalk between neurons, astrocytes, microglia and oligodendrocytes. An initial emphasis will be given to the cooperation between adenosine receptors to sharpen information salience encoding across synapses. The interplay between ATP and adenosine signaling in the communication between astrocytes and neurons will then be presented in context of the integrative properties of the astrocytic syncytium, allowing to implement heterosynaptic depression processes in neuronal networks. The process of microglia 'activation' and its control by astrocytes and neurons will then be analyzed under the perspective of an interplay between different P₂ receptors and adenosine A_2A receptors. In spite of these indications of a prominent role of purinergic signaling in the bidirectional communication between neurons and glia, its therapeutical exploitation still awaits obtaining an integrated view of the spatio-temporal action of ATP signaling and adenosine signaling, clearly distinguishing the involvement of both purinergic signaling systems in the regulation of physiological processes and in the control of pathogenic-like responses upon brain dysfunction or damage.

Efficacy and safety of newer P2Y12 inhibitors for acute coronary syndrome: a network meta-analysis

Whether newer P2Y₁₂ inhibitors are more efficacious and safer than clopidogrel and whether there is a superior one remain uncertain. We compared the effect of P2Y₁₂ inhibitors on clinical outcomes in patients with acute coronary syndrome (ACS). Randomized controlled trials comparing clopidogrel, prasugrel, ticagrelor, or cangrelor, in combination with aspirin were searched. Sixteen trials with altogether 77,896 patients were included. Compared to clopidogrel, cardiovascular mortality was reduced with prasugrel (OR 0.85, 95% CI 0.75–0.97) and ticagrelor (0.82, 0.73–0.93). Myocardial infarction (0.75, 0.63–0.89) and major adverse cardiovascular events (0.80, 0.69–0.94) were reduced by prasugrel. Stent thrombosis was reduced by prasugrel (0.49, 0.38–0.63), ticagrelor (0.72, 0.57–0.90), and cangrelor (0.59, 0.43–0.81). It was reduced more by prasugrel than ticagrelor (0.69, 0.51–0.93). There were more major bleeds with prasugrel (1.24, 1.05–1.48). Thrombolysis in Myocardial Infarction (TIMI) major bleeding was increased with prasugrel compared to clopidogrel (1.36, 1.11–1.66) and ticagrelor (1.33, 1.06–1.67). TIMI minor bleeding was increased with prasugrel (1.44, 1.16–1.77) and cangrelor (1.47, 1.01–2.16) compared to clopidogrel while it was increased with prasugrel compared to ticagrelor (1.32, 1.01–1.72). Prasugrel is preferable to those ACS patients at low bleeding risk to reduce cardiovascular events whereas ticagrelor is a relatively safe antiplatelet drug of choice for most patients.