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Ticagrelor has multiple indications, including for some patients with chronic coronary syndromes (CCS) at high risk of ischaemic events. Body mass can potentially affect pharmacodynamics (PD) and pharmacokinetics (PK). We investigated the influence of body mass (range 53-172 kg, 20.8-46.9 kg/m 2 ) on PD/PK in 221 CCS patients receiving ticagrelor 60 mg or 90 mg twice-daily (BD) during two randomised-controlled trials. Correlations between body weight (BW) or body mass index (BMI) and PD/PK measurements obtained during maintenance treatment at trough ('pre-dose') and peak effect ('post-dose') were assessed. BW and BMI correlated with P2Y 12 reactivity units at pre-dose (e.g. BW:R = 0.26, p = 0.008) but not post-dose timepoints. BW affected ticagrelor active metabolite (TAM) levels (e.g. 60 mg BD, post-dose:R = -0.39, p < 0.0001) and there was evidence of an inverse power law relationship between BW and TAM-to-ticagrelor ratio. PK with ticagrelor 60 mg correlated significantly with BMI. BW and BMI did not affect the chance of high platelet reactivity, which remained very low across the whole cohort. There was no difference in PRU between the two doses of ticagrelor within each weight or BMI group. Body mass has modest effects on the PK/PD response to ticagrelor in patients with CCS but currently-used regimens appear adequate across the range of BW/BMI studied., Competing Interests: Declaration of Competing Interest W.A.E. Parker reports institutional research grants and personal fees from AstraZeneca. D.J. Angiolillo has received consulting fees or honoraria from Abbott, Amgen, Aralez, AstraZeneca, Bayer, Biosensors, Boehringer Ingelheim, Bristol Myers Squibb, Chiesi, Daiichi-Sankyo, Eli Lilly, Haemonetics, Janssen, Merck, PhaseBio, PLx Pharma, Pfizer, Sanofi, and The Medicines Company; has received payments for participation in review activities from CeloNova and St Jude Medical; and his institution has received research grants from Amgen, AstraZeneca, Bayer, Biosensors, CeloNova, CSL Behring, Daiichi-Sankyo, Eisai, Eli Lilly, Gilead, Idorsia, Janssen, Matsutani Chemical Industry Co, Merck, Novartis, Osprey Medical, Renal Guard Solutions, and the Scott R. MacKenzie Foundation. F. Rollini declares that he has received honoraria from Chiesi. F. Franchi. declares that he has received consulting fees or honoraria from AstraZeneca, Bayer and Sanofi. He also declares that has received research grants from PLx Pharma and Scott R. MacKenzie Foundation. M.P. Bonaca is the Executive Director of CPC, a non-profit academic research organization affiliated with the University of Colorado, that receives research grant/consulting funding from: Abbott, Agios, Alexion Pharma, Alnylam, Amgen, Angionetics, ARCA Biopharma, Array, AstraZeneca, Atentiv, Audentes, Bayer, Better Therapeutics, Brigham and Women's Hospital, Bristol-Myers Squibb, Cardiol Therapeutics, CellResearch, Cook Medical, Cook, CSL Behring, Eidos Therapeutics, EP Trading Co, Esperion Therapeutics, EverlyWell, Faraday, Fortress Biotech, HDL Therapeutics, Heartflow, Hummingbird Bioscience, Insmed, Janssen, Kowa Research, Lexicon, Merck, Medtronic, Moderna, Novate Medical, NovoNordisk, Pfizer, PhaseBio, PPD Development, Prairie Education and Research, Prothena Ciosciences, Regeneron, Regio Biosciences, Sanifit Therapeutics, Sanofi, Smith and Nephew, Stealth BioTherapeutics, University of Colorado, Worldwide Clinical Trials, Wraser, Yale Cardiovascular Research Group. Dr. Bonaca also reports stock in Medtronic and Pfizer and consulting fees from Audentes. D.L. Bhatt discloses the following relationships - Advisory Board: AngioWave, Bayer, Boehringer Ingelheim, Cardax, CellProthera, Cereno Scientific, Elsevier Practice Update Cardiology, Janssen, Level Ex, Medscape Cardiology, Merck, MyoKardia, NirvaMed, Novo Nordisk, PhaseBio, PLx Pharma, Regado Biosciences, Stasys; Board of Directors: AngioWave (stock options), Boston VA Research Institute, DRS.LINQ (stock options), Society of Cardiovascular Patient Care, TobeSoft; Chair: Inaugural Chair, American Heart Association Quality Oversight Committee; Data Monitoring Committees: Acesion Pharma, Assistance Publique-Hôpitaux de Paris, Baim Institute for Clinical Research (formerly Harvard Clinical Research Institute, for the PORTICO trial, funded by St. Jude Medical, now Abbott), Boston Scientific (Chair, PEITHO trial), Cleveland Clinic (including for the ExCEED trial, funded by Edwards), Contego Medical (Chair, PERFORMANCE 2), Duke Clinical Research Institute, Mayo Clinic, Mount Sinai School of Medicine (for the ENVISAGE trial, funded by Daiichi Sankyo; for the ABILITY-DM trial, funded by Concept Medical), Novartis, Population Health Research Institute; Rutgers University (for the NIH-funded MINT Trial); Honoraria: American College of Cardiology (Senior Associate Editor, Clinical Trials and News, ACC.org; Chair, ACC Accreditation Oversight Committee), Arnold and Porter law firm (work related to Sanofi/Bristol-Myers Squibb clopidogrel litigation), Baim Institute for Clinical Research (formerly Harvard Clinical Research Institute; RE-DUAL PCI clinical trial steering committee funded by Boehringer Ingelheim; AEGIS-II executive committee funded by CSL Behring), Belvoir Publications (Editor in Chief, Harvard Heart Letter), Canadian Medical and Surgical Knowledge Translation Research Group (clinical trial steering committees), Cowen and Company, Duke Clinical Research Institute (clinical trial steering committees, including for the PRONOUNCE trial, funded by Ferring Pharmaceuticals), HMP Global (Editor in Chief, Journal of Invasive Cardiology), Journal of the American College of Cardiology (Guest Editor; Associate Editor), K2P (Co-Chair, interdisciplinary curriculum), Level Ex, Medtelligence/ReachMD (CME steering committees), MJH Life Sciences, Oakstone CME (Course Director, Comprehensive Review of Interventional Cardiology), Piper Sandler, Population Health Research Institute (for the COMPASS operations committee, publications committee, steering committee, and USA national co‑leader, funded by Bayer), Slack Publications (Chief Medical Editor, Cardiology Today's Intervention), Society of Cardiovascular Patient Care (Secretary/Treasurer), WebMD (CME steering committees), Wiley (steering committee); Other: Clinical Cardiology (Deputy Editor), NCDR-ACTION Registry Steering Committee (Chair), VA CART Research and Publications Committee (Chair); Research Funding: Abbott, Acesion Pharma, Afimmune, Aker Biomarine, Amarin, Amgen, AstraZeneca, Bayer, Beren, Boehringer Ingelheim, Boston Scientific, Bristol-Myers Squibb, Cardax, CellProthera, Cereno Scientific, Chiesi, CSL Behring, Eisai, Ethicon, Faraday Pharmaceuticals, Ferring Pharmaceuticals, Forest Laboratories, Fractyl, Garmin, HLS Therapeutics, Idorsia, Ironwood, Ischemix, Janssen, Javelin, Lexicon, Lilly, Medtronic, Merck, Moderna, MyoKardia, NirvaMed, Novartis, Novo Nordisk, Owkin, Pfizer, PhaseBio, PLx Pharma, Recardio, Regeneron, Reid Hoffman Foundation, Roche, Sanofi, Stasys, Synaptic, The Medicines Company, 89Bio; Royalties: Elsevier (Editor, Braunwald's Heart Disease); Site Co-Investigator: Abbott, Biotronik, Boston Scientific, CSI, Endotronix, St. Jude Medical (now Abbott), Philips, Svelte, Vascular Solutions; Trustee: American College of Cardiology; Unfunded Research: FlowCo, Takeda. P.G.Steg reports receiving research grants from Bayer, Merck, Sanofi, Servier and receiving consulting fees or honoraria from Amarin, Amgen, AstraZeneca, Bayer, Bristol-Myers-Squibb, Janssen, Kowa, Idorsia, Lexicon, Merck, Novartis, Novo-Nordisk, PhaseBio, Pfizer, Regeneron, Sanofi, Servier. M. R. Thomas reports institutional research grants from Novartis, Sanofi, Rigel and Acticor Pharmaceuticals and consultancy fees from Cytosorbents. M. S. Sabatine reports research grant support through Brigham and Women's Hospital from: Abbott; Amgen; Anthos Therapeutics; AstraZeneca; Bayer; Daiichi-Sankyo; Eisai; Intarcia; Ionis; Medicines Company; MedImmune; Merck; Novartis; Pfizer; Quark Pharmaceuticals. Consulting for: Althera; Amgen; Anthos Therapeutics; AstraZeneca; Beren Therapeutics; Bristol-Myers Squibb; DalCor; Dr. Reddy's Laboratories; Fibrogen; Intarcia; Merck; Moderna; Novo Nordisk; and Silence Therapeutics. R.F. Storey reports institutional research grants and personal fees from AstraZeneca, Cytosorbents, GlyCardial Diagnostics and Thromboserin; and personal fees from Alnylam, Bayer, Bristol Myers Squibb/Pfizer, Chiesi, CSL Behring, Hengrui, Idorsia, Novartis, PhaseBio, Portola, and Sanofi Aventis. The other authors have no relevant disclosures., (Copyright © 2023 Elsevier Inc. All rights reserved.)

A novel enoxaparin regimen consisting of intra-arterial bolus (0.75 mg/kg) followed by intravenous infusion (0.75 mg/kg/6 hours) has been developed as a possible solution to the delayed absorption of oral P2Y 12 inhibitors in opiate-treated ST-elevation myocardial infarction (STEMI) patients undergoing primary angioplasty. We aimed to study the feasibility of this regimen as an alternative to standard-of-care treatment (SOC) with unfractionated heparin ± glycoprotein IIb/IIIa antagonist (GPI). One hundred opiate-treated patients presenting with STEMI and accepted for primary angioplasty were randomized (1:1) to either enoxaparin or SOC. Fifty patients were allocated enoxaparin (median age 61, 40% females) and 49 allocated SOC (median age 62, 22% females). One developed stroke before angiography and was withdrawn. One SOC patient had a gastrointestinal bleed resulting in 1 g drop in hemoglobin and early cessation of GPI infusion. Two enoxaparin patients had transient minor bleeding: one transient gingival bleed and one episode of coffee ground vomit with no hemoglobin drop or hemodynamic instability. Two SOC and no enoxaparin group patients had acute stent thrombosis. These preliminary data support further study of this novel 6-hour enoxaparin regimen in opiate-treated PPCI patients.

Ticagrelor is an antagonist of both platelet adenosine diphosphate (ADP) receptor P2Y 12 and equilibrative nucleoside transporter-1. Optimal timing of ticagrelor cessation prior to coronary artery bypass grafting (CABG) remains unclear. We characterized the offset of ticagrelor's effects on platelets and cellular adenosine uptake in ticagrelor-treated patients (n = 13) awaiting CABG. Blood was drawn prior to CABG at multiple timepoints 2 to 120 (h) after the last dose of ticagrelor. Platelet function (n = 13) was assessed with multiple electrode aggregometry (MEA), expressed as arbitrary units (U) derived from area-under-the-curve (AUC) in response to ADP, and inhibition of adenosine uptake by high-performance liquid chromatography (n = 7). Mean±SD AUC was 20.3 ± 8.2 U (2 h post-ticagrelor), 33.0 ± 18.3U (24 h), 56.6 ± 30.6U (48 h), 61.4 ± 20.2U (72 h), 82.8 ± 24.2U (96 h) and 96.0 ± 15.3U (120 h). There was a significant difference between 72 h and 120 h ( p = .007), but not between 96 h and 120 h ( p > .99). By 96 h, all patients had AUC >31U, an accepted cutoff below which surgical bleeding risk is increased. Adenosine uptake showed no significant differences between the timepoints. These data suggest it takes 4 days for platelet reactivity to recover sufficiently after cessation of ticagrelor to avoid the excess risk of CABG-related bleeding. Discontinuing ticagrelor had no measurable effect on cellular adenosine uptake.

There is evidence for the effects of platelet inhibition on innate immune activation. Circulating microRNAs (miRNAs) have been implicated as markers of platelet and leukocyte activation. In the present study, we assessed the effects of P2Y 12 inhibitors on platelet and leukocyte miRNAs during endotoxemia. Healthy volunteers were randomly assigned to receive oral ticagrelor ( n = 10), clopidogrel ( n = 8) or no drug ( n = 8) for one week, followed by an intravenous bolus of 2 ng/kg endotoxin. Serum was collected at baseline, after one week of antiplatelet treatment and 6 and 24 h after endotoxin administration. MiRNAs were screened using LNA-based qPCR, followed by TaqMan-qPCR validation of candidates. Clinical validation was performed in 41 sepsis patients. Platelet-enriched miR-197, miR-223 and miR-223* were decreased in volunteers following antiplatelet therapy. Endotoxin increased platelet miRNAs, whilst the opposite effect was seen for leukocyte-enriched miR-150. Neither of these endotoxin-mediated effects were altered by P2Y 12 inhibitors. Sepsis patients with fatal outcomes ( n = 12) had reduced miR-150 levels compared with survivors ( n = 29). In conclusion, we show that miR-150 is downregulated in experimental endotoxemia and can predict survival in sepsis but is unaffected by P2Y 12 inhibition. While P2Y 12 inhibition reduces platelet-associated miRNAs in healthy volunteers, it fails to attenuate the response of platelet miRNAs to endotoxemia.

Higher aspirin doses may be inferior in ticagrelor-treated acute coronary syndrome (ACS) patients and reducing bleeding risk whilst maintaining antithrombotic benefits could improve outcomes. We characterized the pharmacodynamics of a novel dual-antiplatelet-therapy regimen consisting of very-low-dose twice-daily (BD) aspirin with standard-dose ticagrelor. A total of 20 ticagrelor-treated ACS patients entered a randomized crossover to take aspirin 20 mg BD (12-hourly) during one 14-day period and 75 mg once-daily (OD) in the other. After 14 days of treatment, serum thromboxane (TX)B 2 and light-transmittance aggregometry were assessed pre- and 2 h post-morning-dose, bleeding time was measured post-dose, and TXA 2 and prostacyclin stable metabolites were measured in urine collected 2 h post-morning-dose. Data are expressed as mean ± SD. After 14 days treatment, serum TXB 2 levels were significantly greater 2 h post-dosing with aspirin 20 mg BD vs. 75 mg OD (3.0 ± 3.6 ng/mL vs. 0.8 ± 1.9 ng/mL; p = 0.018) whereas pre-dosing levels were not significantly different (3.5 ± 4.1 ng/mL vs. 2.5 ± 3.1 ng/mL, p = 0.23). 1-mmol/L arachidonic acid-induced platelet aggregation was similarly inhibited by both regimens pre-dose (8.5 ± 14.3% vs. 5.1 ± 3.6%, p = 0.24) and post-dose (8.7 ± 14.2% vs. 6.6 ± 5.3%; p = 0.41). Post-dose bleeding time was shorter with 20 mg BD (680 ± 306 s vs. 834 ± 386 s, p = 0.02). Urinary prostacyclin and TX metabolite excretion were not significantly different. In conclusion, compared to aspirin 75 mg OD, aspirin 20 mg BD provided consistent inhibition of platelet TXA 2 release and aggregation, and improved post-dose hemostasis, in ticagrelor-treated ACS patients. Further studies are warranted to assess whether this regimen improves the balance of clinical efficacy and safety.

Background: Ticagrelor has superior efficacy to clopidogrel in the management of acute coronary syndromes but has not been assessed in patients undergoing percutaneous coronary intervention for stable coronary artery disease. We compared the pharmacodynamic effects of ticagrelor and clopidogrel in this stable population., Methods: One hundred eighty aspirin-treated stable coronary artery disease patients, who were planned to undergo elective percutaneous coronary intervention in a single center, were randomized 1:1:1 to either a standard clopidogrel regimen or 1 of 2 regimens of ticagrelor, either 90 mg (T90) or 60 mg twice daily (T60), both with a 180 mg loading dose. Cellular adenosine uptake was assessed, at the time of the procedure and pre- and postdose at 1 month, by adding adenosine 1 µmol/L to aliquots of anticoagulated whole blood and mixing with a stop solution at 0, 15, 30, and 60 seconds, then measuring residual plasma adenosine concentration by high-performance liquid chromatography. Systemic plasma adenosine concentration and platelet reactivity were assessed at the same timepoints. High-sensitivity troponin T was measured pre- and 18 to 24 hours postpercutaneous coronary intervention., Results: One hundred seventy-four patients underwent an invasive procedure, of whom 162 received percutaneous coronary intervention (mean age 65 years, 18% female, 21% with diabetes mellitus). No effect on in vitro adenosine uptake was seen postdose at 1 month for either ticagrelor dose compared with clopidogrel (residual adenosine at 15 seconds, mean±SD: clopidogrel 0.274±0.101 µmol/L; T90 0.278±0.134 µmol/L; T60 0.288±0.149 µmol/L; P =0.37). Similarly, no effect of ticagrelor on in vitro adenosine uptake was seen at other timepoints, nor was plasma adenosine concentration affected (all P >0.1). Both maintenance doses of ticagrelor achieved more potent and consistent platelet inhibition than clopidogrel (VerifyNow P2Y 12 reaction units, 1 month, mean±SD: predose, T60: 62±47, T90: 40±38, clopidogrel 181±44; postdose, T60: 34±30, T90: 24±21, clopidogrel 159±57; all P <0.0001 for ticagrelor versus clopidogrel). High platelet reactivity was markedly less with both T60 and T90 compared with clopidogrel (VerifyNow P2Y 12 reaction units>208, 1 month postdose: 0%, 0%, and 21%, respectively). Median (interquartile range) high-sensitivity troponin T increased 16.9 (6.5-46.9) ng/L for clopidogrel, 22.4 (5.5-53.8) ng/L for T60, and 17.7 (8.1-43.5) ng/L for T90 ( P =0.95). There was a trend toward less dyspnea with T60 versus T90 (7.1% versus 19.0%; P =0.09)., Conclusions: Maintenance therapy with T60 or T90 had no detectable effect on cellular adenosine uptake at 1 month, nor was there any effect on systemic plasma adenosine levels. Both regimens of ticagrelor achieved greater and more consistent platelet inhibition than clopidogrel but did not appear to affect troponin release after percutaneous coronary intervention., Clinical Trial Registration: URL: https://www., Clinicaltrials: gov. Unique identifier: NCT02327624.

Delayed onset of action of oral P2Y 12 inhibitors in ST-elevation myocardial infarction (STEMI) patients may increase the risk of acute stent thrombosis. Available parenteral anti-thrombotic strategies, to deal with this issue, are limited by added cost and increased risk of bleeding. We investigated the pharmacodynamic effects of a novel regimen of enoxaparin in STEMI patients undergoing primary percutaneous coronary intervention (PPCI). Twenty patients were recruited to receive 0.75 mg/kg bolus of enoxaparin (pre-PPCI) followed by infusion of enoxaparin 0.75 mg/kg/6 h. At four time points (pre-anti-coagulation, end of PPCI, 2-3 hours into infusion and at the end of infusion), anti-Xa levels were determined using chromogenic assays, fibrin clots were assessed by turbidimetric analysis and platelet P2Y 12 inhibition was determined by VerifyNow P2Y12 assay. Clinical outcomes were determined 14 hours after enoxaparin initiation. Nineteen of 20 patients completed the enoxaparin regimen; one patient, who developed no-reflow phenomenon, was switched to tirofiban after the enoxaparin bolus. All received ticagrelor 180 mg before angiography. Mean (± standard error of the mean) anti-Xa levels were sustained during enoxaparin infusion (1.17 ± 0.06 IU/mL at the end of PPCI and 1.003 ± 0.06 IU/mL at 6 hours), resulting in prolonged fibrin clot lag time and increased lysis potential. Onset of platelet P2Y 12 inhibition was delayed in opiate-treated patients. No patients had thrombotic or bleeding complications. In conclusion, enoxaparin 0.75 mg/kg bolus followed by 0.75 mg/kg/6 h provides sustained anti-Xa levels in PPCI patients. This may protect from acute stent thrombosis in opiate-treated PPCI patients who frequently have delayed onset of oral P2Y 12 inhibition., Competing Interests: R.F.S. reports research grants from AstraZeneca, PlaqueTec; Honoraria from AstraZeneca; Consultant/Advisory Board fees from AstraZeneca, Actelion, Avacta, Bayer, Bristol Myers Squibb/Pfizer, Idorsia, Novartis and The Medicines Company. Other authors have no disclosures., (Georg Thieme Verlag KG Stuttgart · New York.)

Diabetes increases cardiovascular risk and reduces pharmacodynamic response to some oral antiplatelet drugs. This study aimed to determine whether ticagrelor 60 mg twice daily (bid) provided potent and consistent platelet inhibition in patients with vs without diabetes in the PEGASUS-TIMI 54 platelet function substudy. Out of 180 patients studied, 58 patients were randomised to and had received at least four weeks of ticagrelor 60 mg bid, with 20 (34 %) having diabetes, 58 patients received ticagrelor 90 mg bid, with 12 (21 %) having diabetes, and 64 patients received placebo, with 18 (28 %) having diabetes. Blood was sampled pre- and 2 hours post-maintenance dose. In patients treated with ticagrelor 60 mg bid, on-treatment platelet reactivity to ADP, as determined by light transmission aggregometry (LTA), VerifyNow and VASP, was similar in patients with vs without diabetes (LTA post-dose, ADP 20 µM: 29 ± 14 vs 34 ± 10 %, respectively; p = 0.19). A consistent inhibitory effect of ticagrelor 60 mg bid was observed pre- and post-dose regardless of diabetes status, even in insulin-treated patients. Patients with diabetes did not have an increased incidence of high platelet reactivity in either ticagrelor group. Platelet reactivity was similar in patients with diabetes treated with ticagrelor 60 mg vs 90 mg bid. Pharmacokinetics of ticagrelor were not affected by diabetes status. In conclusion, ticagrelor 60 mg bid is equally effective at reducing platelet reactivity in patients with and without diabetes, yielding a consistently high level of platelet inhibition regardless of diabetes status.

The increasing use of antiplatelet therapy, particularly aspirin and oral P2Y 12 inhibitors, in the prevention and management of arterial thrombosis, has stimulated extensive pharmacodynamic studies and research into tailored antiplatelet regimens. Many different methodologies have been studied for monitoring antiplatelet drugs and some are now well validated and used in clinical practice. However, clinical studies of tailored antiplatelet therapy have not convincingly demonstrated a benefit of this approach in patients treated with aspirin and clopidogrel, coupled with the fact that more potent antiplatelet therapies have more consistent effects compared with clopidogrel and so may reduce the rationale for monitoring. On the other hand, the optimum timing of urgent surgery after cession of oral antiplatelet therapy may be informed by platelet function testing. This review discusses the different methodologies that have been used to monitor the effects of antiplatelet therapy and highlights the current position of platelet function testing in clinical practice., (Thieme Medical Publishers 333 Seventh Avenue, New York, NY 10001, USA.)

Delays in the onset of action of prasugrel during primary percutaneous coronary intervention (PPCI) have been reported and could be related to the effects of morphine on gastric emptying and subsequent intestinal absorption. The study objective was to determine whether morphine delays the onset of action of prasugrel in patients with a prior history of ST-elevation myocardial infarction (STEMI) treated with PPCI. This was a crossover study of 11 aspirin-treated patients with prior history of STEMI treated with PPCI, for which prasugrel and morphine had been previously administered. Patients were randomised to receive either morphine (5 mg) or saline intravenously followed by 60 mg prasugrel. Blood samples were collected before randomised treatment and over 24 hours after prasugrel administration. The inhibitory effects of prasugrel on platelets were determined using the VerifyNow P2Y12 assay and light transmission aggregometry. Plasma levels of prasugrel and prasugrel active metabolite were measured. Platelet reactivity determined by VerifyNow PRU, VerifyNow % Inhibition and LTA was significantly higher at 30-120 minutes (min) when morphine had been co-administered compared to when saline had been co-administered. Morphine, compared to saline, significantly delayed adequate platelet inhibition after prasugrel administration (158 vs 68 min; p = 0.006). Patients with delayed onset of platelet inhibition also had evidence of delayed absorption of prasugrel. In conclusion, prior administration of intravenous morphine significantly delays the onset of action of prasugrel. Intravenous drugs may be necessary to reduce the risk of acute stent thrombosis in morphine-treated STEMI patients undergoing PPCI.

Background: The PEGASUS-TIMI 54 (Prevention of Cardiovascular Events in Patients with Prior Heart Attack Using Ticagrelor Compared to Placebo on a Background of Aspirin-Thrombolysis In Myocardial Infarction 54) trial studied 2 doses of ticagrelor, 90 mg twice a day (bid) and 60 mg bid, for long-term prevention of ischemic events in patients with prior myocardial infarction. Both doses similarly reduced the rate of ischemic events versus placebo. The pharmacokinetics and pharmacodynamics of ticagrelor 60 mg bid have not been studied., Objectives: In this study, the authors sought to study the pharmacokinetics and pharmacodynamics for ticagrelor 60 mg compared with 90 mg bid., Methods: A total of 180 patients who received >4 weeks of study medication had blood sampling in the morning pre-maintenance dose and again 2 h post-dose. All patients received aspirin. Plasma levels of ticagrelor and its active metabolite AR-C124910XX were determined. P2Y12 inhibition was assessed by the VerifyNow P2Y12 assay (Accumetrics, Inc., San Diego, California) (P2Y12 reaction units [PRU]), light transmittance aggregometry (adenosine diphosphate 5 and 20 μmol/l and arachidonic acid), and vasodilator-stimulated phosphoprotein phosphorylation assays. VerifyNow Aspirin assays and serum thromboxane B2 measurements were performed., Results: Mean pre- and post-dose plasma levels of ticagrelor were 35% and 38% lower, respectively, with 60 mg versus 90 mg. Both doses achieved high levels of platelet inhibition pre- and post-dose, with numerically slightly more variability with 60 mg: mean (SD) pre-dose PRU values were 59 ± 63 and 47 ± 43 for ticagrelor 60 and 90 mg, respectively (p = 0.34). High platelet reactivity, determined as PRU >208, was rare with the 60-mg pre-dose and was absent post-dose. Platelet reactivity pre- and post-dose, as measured by light transmittance aggregometry or vasodilator-stimulated phosphoprotein assays, was numerically but not significantly lower with 90 mg than with 60 mg. Aspirin response was not affected by either dose., Conclusions: Ticagrelor 60 mg bid achieved high levels of peak and trough platelet inhibition in nearly all patients, similar to that with 90 mg bid, helping to explain the efficacy of the lower ticagrelor dose in PEGASUS-TIMI 54., (Copyright © 2016 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.)

Cangrelor is a rapid-acting, direct-binding, and reversible P2Y12 antagonist which has been studied for use during percutaneous coronary intervention (PCI) in patients with or without pretreatment with an oral P2Y12 antagonist. As cangrelor is administered intravenously, it is necessary to switch to an oral P2Y12 antagonist following PCI, such as the thienopyridines clopidogrel, and prasugrel or the non-pyridine ticagrelor. Previous studies have suggested a negative pharmacodynamic interaction between cangrelor and thienopyridines. This in vitro study evaluated the receptor-level interaction between cangrelor and the active metabolite (AM) of clopidogrel or prasugrel by assessing functional P2Y12 receptor number using a (33)P-2MeSADP binding assay. All P2Y12 antagonists studied resulted in strong P2Y12 receptor blockade (cangrelor: 93.6%; clopidogrel AM: 93.0%; prasugrel AM: 97.9%). Adding a thienopyridine AM in the presence of cangrelor strongly reduces P2Y12 receptor blockade by the AM (clopidogrel AM: 7%, prasugrel AM: 3.2%). The thienopyridine AMs had limited ability to compete with cangrelor for binding to P2Y12 (% P2Y12 receptor blockade after co-incubation with cangrelor 1000 nmol/L: 11.7% for clopidogrel AM 3 µmol/L; 34.1% for prasugrel AM 3 µmol/L). In conclusion, in vitro cangrelor strongly inhibits the binding of clopidogrel and prasugrel AMs to the P2Y12 receptor, consistent with the previous observation of a negative pharmacodynamic interaction. Care may need to be taken to not overlap exposure to thienopyridine AMs and cangrelor in order to reduce the risk of thrombotic complications following PCI.

Objective: Clinical studies suggest that platelet P2Y12 inhibitors reduce mortality from sepsis, although the underlying mechanisms have not been clearly defined in vivo. We hypothesized that P2Y12 inhibitors may improve survival from sepsis by suppressing systemic inflammation and its prothrombotic effects. We therefore determined whether clopidogrel and the novel, more potent P2Y12 inhibitor, ticagrelor, modify these responses in an experimental human model., Approach and Results: We randomized 30 healthy volunteers to ticagrelor (n=10), clopidogrel (n=10), or no antiplatelet medication (controls; n=10). We examined the effect of P2Y12 inhibition on systemic inflammation, which was induced by intravenous injection of Escherichia coli endotoxin. Both P2Y12 inhibitors significantly reduced platelet-monocyte aggregate formation and peak levels of major proinflammatory cytokines, including tumor necrosis factor α, interleukin-6, and chemokine (C-C motif) ligand 2. In contrast to clopidogrel, ticagrelor also significantly reduced peak levels of IL-8 and growth colony-stimulating factor and increased peak levels of the anti-inflammatory cytokine IL-10. In addition, ticagrelor altered leukocyte trafficking. Both P2Y12 inhibitors suppressed D-dimer generation and scanning electron microscopy revealed that ticagrelor also suppressed prothrombotic changes in fibrin clot ultrastructure., Conclusions: Potent inhibition of multiple inflammatory and prothrombotic mechanisms by P2Y12 inhibitors demonstrates critical importance of platelets as central orchestrators of systemic inflammation induced by bacterial endotoxin. This provides novel mechanistic insight into the lower mortality associated with P2Y12 inhibitors in patients with sepsis in clinical studies., (© 2015 American Heart Association, Inc.)

In the PLATO study, ticagrelor was associated with fewer pulmonary infections and subsequent deaths than clopidogrel. Neutrophils are a first-line defence against bacterial lung infection; ticagrelor inhibits cellular uptake of adenosine, a known regulator of neutrophil chemotaxis and phagocytosis. We assessed whether the inhibition of adenosine uptake by ticagrelor influences neutrophil chemotaxis and phagocytosis. Neutrophils and erythrocytes were isolated from healthy volunteers. Concentration-dependent effects of adenosine on IL-8-induced neutrophil chemotaxis were investigated and the involved receptors identified using adenosine receptor antagonists. The modulatory effects of ticagrelor on adenosine-mediated changes in neutrophil chemotaxis and phagocytosis of Streptococcus pneumoniae were determined in the presence of erythrocytes to replicate physiological conditions of cellular adenosine uptake. Low-concentration adenosine (10(-8)M) significantly increased IL-8-induced neutrophil chemotaxis (% neutrophil chemotaxis: adenosine 28.7%±4.4 vs. control 22.6%±2.4; p<0.01) by acting on the high-affinity A1 receptor. Erythrocytes attenuated the effect of adenosine, although this was preserved by ticagrelor and dipyridamole (another inhibitor of adenosine uptake) but not by control or by cangrelor. Similarly, in the presence of erythrocytes, a low concentration of adenosine (10(-8)M) significantly increased neutrophil phagocytic index compared to control when ticagrelor was present (37.6±6.6 vs. 28.0±6.6; p=0.028) but had no effect in the absence of ticagrelor. We therefore conclude that the inhibition of cellular adenosine reuptake by ticagrelor potentiates the effects of a nanomolar concentration of adenosine on neutrophil chemotaxis and phagocytosis. This represents a potential mechanism by which ticagrelor could influence host defence against bacterial lung infection., (Copyright © 2015. Published by Elsevier Inc.)

Thrombin-induced platelet activation is initiated by PAR1 and PAR4 receptors. Vorapaxar, a PAR1 antagonist, has been assessed in patients with acute coronary syndromes (ACS) and stable atherosclerotic disease in addition to standard-of-care treatment. In clinical trials, vorapaxar has been observed to reduce the frequency of ischaemic events in some subgroups though in others has increased the frequency of bleeding events. Among patients undergoing CABG surgery, which is associated with excess thrombin generation, bleeding was not increased. The aim of these studies was to investigate the effects of selective PAR1 antagonism on thrombin-induced platelet activation in patients receiving vorapaxar or placebo in the TRACER trial and to explore the roles of PAR1 and PAR4 in thrombin-induced platelet activation in healthy volunteers. ACS patients receiving vorapaxar or placebo in the TRACER trial were studied at baseline and 4 hours, 1 and 4 months during drug administration. Thrombin-induced calcium mobilisation in platelet-rich plasma was assessed by flow cytometry. In vitro studies were performed in healthy volunteers using the PAR1 antagonist SCH79797 or PAR4 receptor desensitisation. Vorapaxar treatment significantly inhibited thrombin-induced calcium mobilisation, leaving a residual, delayed response. These findings were consistent with calcium mobilisation mediated via the PAR4 receptor and were reproduced in vitro using SCH79797. PAR4 receptor desensitization, in combination with SCH79797, completely inhibited thrombin-induced calcium mobilisation confirming that the residual calcium mobilisation was mediated via PAR4. In conclusion vorapaxar selectively antagonises the PAR1-mediated component of thrombin-induced platelet activation, leaving the PAR4-mediated response intact, which may explain why vorapaxar is well tolerated in patients undergoing CABG surgery since higher thrombin levels in this setting may override the effects of PAR1 antagonism through PAR4 activation, thus preserving haemostasis. Further assessment may be warranted.

Aims: Platelets have a fundamental role in atherothrombosis, but their role in early atherogenesis is unclear. The P2Y12 receptor is responsible for amplifying and sustaining platelet activation and P2Y12 inhibition is crucial in modulating the vessel wall response to injury. We therefore examined the role of platelet vs. vessel wall P2Y12 in early atherogenesis and considered the use of P2Y12 antagonists ticagrelor and clopidogrel in modulating this process., Methods and Results: ApoE(-/-) and ApoE(-/-)P2Y12 (-/-) male mice underwent bone marrow transplantation and were fed a western diet for 4 weeks before assessing atherosclerotic burden. Compared with ApoE(-/-) controls, platelet P2Y12 deficiency profoundly reduced platelet reactivity but had no effect on atheroma formation, whereas vessel wall P2Y12 deficiency significantly attenuated atheroma in the aortic sinus and brachiocephalic artery (both P < 0.001). ApoE(-/-) and ApoE(-/-)P2Y12 (-/-) male mice fed western diet plus either twice-daily doses of ticagrelor (100 mg/kg) or daily clopidogrel (20 mg/kg) for 4 weeks exhibited no significant reduction in atheroma compared with control mice fed mannitol. Attenuated P-selectin expression confirmed platelet P2Y12 inhibition in drug-treated mice., Conclusions: Despite its major contribution to platelet reactivity, platelet P2Y12 has no effect on early atheroma formation, whereas vessel wall P2Y12 is important in this process. Ticagrelor and clopidogrel effectively reduced platelet reactivity but were unable to inhibit early atherogenesis, demonstrating that these P2Y12 inhibitors may not be effective in preventing early disease., (Published on behalf of the European Society of Cardiology. All rights reserved. © The Author 2014. For permissions please email: journals.permissions@oup.com.)

Vorapaxar is an antagonist of the protease activated receptor-1 (PAR-1), the principal platelet thrombin receptor. The Thrombin Receptor Antagonist for Clinical Event Reduction (TRACER) trial evaluated vorapaxar compared to placebo in non-ST-elevation (NSTE)-acute coronary syndrome (ACS) patients. It was the study's objective to assess the pharmacodynamic effects of vorapaxar versus placebo that included aspirin or a thienopyridine or, frequently, a combination of both agents in NSTE-ACS patients. In a substudy involving 249 patients, platelet aggregation was assessed by light transmittance aggregometry (LTA) in 85 subjects (41 placebo, 44 vorapaxar) using the agonists thrombin receptor activating peptide (TRAP, 15 μM), adenosine diphosphate (ADP, 20 μM), and the combination of collagen-related peptide (2.5 μg/ml) + ADP (5 μM) + TRAP (15 μM) (CAT). VerifyNow® IIb/IIIa and vasodilator-stimulated phosphoprotein (VASP) phosphorylation assays were performed, and platelet PAR-1 expression, plasma platelet/endothelial and inflammatory biomarkers were determined before and during treatment. LTA responses to TRAP and CAT and VerifyNow results were markedly inhibited by vorapaxar. Maximal LTA response to TRAP (median, interquartile range) 2 hours post loading dose: placebo 68% (53-75%) and vorapaxar 3% (2-6%), p<0.0001. ADP inhibition was greater in the vorapaxar group at 4 hours and one month (p<0.01). In contrast to the placebo group, PAR-1 receptor number in the vorapaxar group at one month was significantly lower than the baseline (179 vs 225; p=0.004). There were significant changes in selected biomarker levels between the two treatment groups. In conclusion, vorapaxar caused a potent inhibition of PAR-1-mediated platelet aggregation. Further studies are needed to explore vorapaxar effect on P2Y12 inhibition, PAR-1 expression and biomarkers and its contribution to clinical outcomes.

Dual antiplatelet therapy consisting of clopidogrel in addition to aspirin has previously been the standard of care for patients with acute coronary syndromes (ACS) but international guidelines have been evolving over the last 4 years with the introduction of prasugrel and ticagrelor. In October 2009, prasugrel was approved in the UK by the National Institute of Health and Clinical Excellence (NICE) for use in patients with ST-elevation myocardial infarction (STEMI) undergoing primary percutaneous coronary intervention (PCI), diabetic patients with non-ST-elevation (NSTE) ACS undergoing PCI and patients with stent thrombosis while other ACS patients were to continue receiving clopidogrel. Ticagrelor was approved in October 2011 by NICE for use in patients with moderate-to-high risk NSTE ACS and STEMI undergoing primary PCI and was recommended in preference to clopidogrel in European guidelines. These recommendations were adopted in our region, constituting a population of 1.8 million. We studied the effect of changing patterns of P2Y12 inhibitor usage on levels of platelet inhibition during maintenance therapy. Patients admitted to Northern General Hospital, Sheffield, with NSTE ACS or STEMI managed with primary PCI were enrolled over two periods of time: May 2010 to November 2011 (T1); and October 2012 to February 2013 (T2). Venous blood samples were obtained at 1 month after the onset of ACS. Light transmittance aggregometry (LTA) was performed and maximum aggregation response to ADP 20 μM was determined. A total of 116 patients were enrolled in T1 of whom 82 were receiving clopidogrel and 34 were receiving prasugrel. Twenty-nine patients were enrolled in T2, all of whom were receiving ticagrelor. Mean LTA results according to treatment with clopidogrel, prasugrel and ticagrelor were 57 ± 18%, 41 ± 20%, and 31 ± 12%, respectively. Prasugrel was associated with significantly lower platelet aggregation responses than clopidogrel (p < 0.001) and ticagrelor was associated with significantly lower platelet aggregation responses than both prasugrel (p = 0.015) and clopidogrel (p < 0.001). We conclude that international guidelines and NICE approval have led to increasing levels of P2Y12 inhibition in ACS patients in this UK centre between May 2010 and February 2013. Ticagrelor was associated with significantly greater P2Y12 inhibition than both clopidogrel and prasugrel during maintenance therapy.

VerifyNow (VN) P2Y12 is a point-of-care assay used to assess response to P2Y12 inhibitors. Sodium citrate (citrate) is the standard anticoagulant used for this assay but requires a pre-incubation period. Hirudin is an alternative anticoagulant for platelet function studies that maintains physiological divalent cation levels. We investigated whether hirudin anticoagulation might allow more rapid testing of P2Y₁₂ inhibition at the time of percutaneous coronary intervention (PCI). Blood was collected from the arterial sheath of aspirin-treated patients undergoing elective, urgent or emergency coronary angiography±PCI and aliquots were anticoagulated with either citrate or hirudin. For each anticoagulant, VN P2Y12 was performed both immediately and after 20 minutes. A total of 98 patients were included in this study following pre-treatment with clopidogrel (n=88), prasugrel (n=6) or no P2Y₁₂ inhibitor (n=4). PRU with hirudin immediately (PRU&#95;H&#95;Imm) and PRU with citrate 20 minutes post sampling (PRU&#95;C&#95;20) were very strongly correlated (R=0.95) though PRU&#95;H&#95;Imm tended to be lower than PRU&#95;C&#95;20 so that optimal correlation was estimated by the equation PRU&#95;H&#95;Imm=0.95xPRU&#95;C&#95;20 (p<0.001). Bland-Altman plots showed good agreement between PRU&#95;H&#95;Imm and (0.95xPRU&#95;C&#95;20). Platelet reactivity was more stable over the studied time course with hirudin as compared to citrate. We therefore conclude that VN P2Y12 with hirudin anticoagulation can be performed more rapidly and results are strongly correlated with delayed citrate measurements. Further studies are warranted to assess the utility of this method for improving clinical outcomes in patients undergoing PCI.

Objective: Our goal was to study the effects of ticagrelor on murine platelet function and thrombosis and characterize the time course of P2Y(12) inhibition required to inhibit neointima formation following vascular injury., Methods and Results: Mice were treated with ticagrelor or vehicle. Platelet aggregation and P-selectin expression were assessed over time, and thrombus formation was assessed in laser-injured cremasteric arterioles of P2Y(12)+/+ and P2Y(12)-/- mice. Neointima formation in FeCl(3)-injured carotid artery was assessed in C57BL/6 mice treated with different regimens of ticagrelor. Ticagrelor inhibited platelet aggregation and P-selectin expression in a dose-dependent, reversible manner. Ticagrelor inhibited thrombus formation to the same extent as seen in P2Y(12)-/- mice. Neointima formation was markedly reduced in mice treated with ticagrelor before and 4 hours after injury (neointima area: control, 39 921±22 749 μm(2), versus ticagrelor, 3705±2600 μm(2); P<0.01), whereas administration of ticagrelor either before injury only or from 4 hours postinjury was ineffective., Conclusions: Ticagrelor effectively and reversibly inhibits P2Y(12)-mediated platelet function and thrombosis in mice. P2Y(12) inhibition is required both at the time of and after injury to effectively inhibit neointima formation. Additional studies are warranted to evaluate the role of P2Y(12) inhibition in preventing restenosis.

The thienopyridine P2Y12 receptor antagonists clopidogrel and prasugrel prevent arterial thrombosis and are routinely used following percutaneous coronary intervention. However, the optimal level of P2Y12 blockade to effectively inhibit platelet function is unknown. These studies utilised the active metabolite of prasugrel (R-138727) to achieve a range of P2Y12 blockade in vitro and assessed several aspects of platelet function. Blood from healthy volunteers was incubated with R-138727 (0-10 microM). P2Y12 receptor number was assessed using a 33P-2MeSADP binding assay. Platelet aggregation (PA) was measured by optical aggregometry with ADP 2-20 microM. VASP phosphorylation, annexin V binding, microparticle formation and P-selectin expression were assessed by flow cytometry. Increasing numbers of unblocked receptors were required for a sustained aggregation response with decreasing concentrations of ADP. A P2Y12 receptor blockade of 60-80% resulted in strong inhibition of final PA response, P-selectin expression, microparticle formation and vasodilator-stimulated phosphoprotein (VASP). PA induced by ADP 2 microM and P-selectin expression were particularly sensitive to low levels of receptor blockade whereas the VASP phosphorylation assay was relatively insensitive, requiring 60% receptor blockade to achieve substantial inhibition. Different assays varied in their ability to discriminate particular ranges of P2Y12 blockade and 80% or greater P2Y12 receptor blockade is required for consistently strong inhibition of several aspects of platelet function. These data guide the interpretation of results from different assays used to monitor the effects of P2Y12 receptor antagonists.

The aim of these studies was to investigate the extent of platelet P2Y(12) receptor inhibition by the thienopyridine active metabolite of prasugrel, R-138727. Blood was taken from healthy volunteers and pre-incubated with R-138727 or cangrelor (AR-C66931MX). Platelet aggregation was assessed in platelet rich plasma (PRP) and whole blood (WB). Vasodilator stimulated phosphoprotein (VASP) phosphorylation, platelet procoagulant activity (annexin V binding and microparticle formation) and calcium mobilisation were measured by flow cytometry. Platelet-leukocyte co-aggregate formation and sCD40L release, both pro-inflammatory responses of platelets, were measured by flow cytometry and ELISA, respectively. P2Y(12) receptor antagonism was determined using a radioligand binding assay ((33)P 2-MeSADP) in resting and stimulated platelets and the effects of clopidogrel administration were also assessed. R-138727 yielded concentration-dependent inhibition of platelet aggregation, VASP phosphorylation inhibition, procoagulant activity and pro-inflammatory responses. In the presence of R-138727 or cangrelor there was increased calcium reuptake following agonist stimulation. R-138727 30 micromol/L and cangrelor 1 micromol/L completely inhibited (33)P 2-MeSADP binding, compared to partial inhibition following clopidogrel administration. Platelet activation and granule secretion did not expose an additional pool of P2Y(12) receptors. Prasugrel's active metabolite effectively blocks the P2Y(12) receptor with the highest concentrations tested yielding complete inhibition of P2Y(12)-mediated amplification of several important platelet responses.

The efficacy of the platelet P2Y12 receptor antagonist clopidogrel, which undergoes cytochrome-mediated metabolism to its active form, shows marked inter-individual variability. We investigated whether polymorphic variations in the P2Y12 gene, which have been linked to platelet aggregation phenotypes, or the cytochrome P450 3A5 gene 6986G > A polymorphism, which largely determines CYP3A5 expression, influence the response to clopidogrel therapy. Fifty-four patients listed for elective percutaneous coronary intervention were studied using ADP-induced optical aggregometry, whole-blood single platelet counting (WBSPC) aggregometry, and flow-cytometric analysis of platelet P-selectin expression and platelet-monocyte conjugate formation. Platelet reactivity was measured at baseline, 4 h post clopidogrel 300 mg, and 10 and 28 days following clopidogrel 75 mg daily. A further 55 patients were studied using ADP-induced WBSPC at baseline and 4 h post clopidogrel 600 mg. Patients were genotyped for P2Y12 haplotype and the CYP3A5 6986G > A single nucleotide polymorphism. Neither genotype was found to significantly influence the inhibition of platelet responses by either clopidogrel regimen. In conclusion, common sequence variations within the P2Y12 and CYP3A5 genes do not contribute any major effect to the inter-patient variability in clopidogrel efficacy.

This study aimed to establish the utility of a whole-blood single-platelet counting (WBSPC) assay, a measure of microaggregation, in monitoring the effects of tirofiban, comparing this with optical aggregometry (OA) and the Ultegra TRAP cartridge system (UTC), measures of macroaggregation. Fifty-nine patients with acute coronary syndrome scheduled for coronary angiography +/- angioplasty were studied. WBSPC assay (ADP 0.3-100 microM, Sysmex KX21 analyzer), OA (ADP 20 microM) and UTC were performed: before starting tirofiban; 30 min, 4 and 24 h after starting tirofiban; and 1 and 2 h after stopping tirofiban. Thirty minutes after starting tirofiban, there was substantial inhibition of platelet aggregation (40 +/- 30%; WBSPC, 2 minutes after addition of ADP 30 microM) and this remained stable at 4 and 24 h. OA (86 +/- 17%; inhibition of maximal aggregation, ADP 20 microM) and UTC (93 +/- 7%) showed marked inhibition with less inter-individual variation. There was no significant correlation between OA and UTC results (R(2) = 0.006), but fair correlation between OA and WBSPC results (R(2) = 0.37). Greater inhibition of macroaggregation (OA and UTC) was seen compared to microaggregation (WBSPC) such that WBSPC was more discriminating in the therapeutic range when macroaggregation was often completely inhibited. A WBSPC assay of platelet microaggregation shows promise for monitoring GPIIb/IIIa antagonists.

Glycoprotein IIb/IIIa (GPIIb/IIIa) antagonists, including abciximab and tirofiban, are administered concurrently with clopidogrel, a P2Y12 antagonist, and aspirin in some patients undergoing percutaneous coronary intervention. We studied the effects of, and interactions between, abciximab, tirofiban, aspirin and the P2Y12 antagonist cangrelor on platelet aggregation, alpha and dense granule secretion and procoagulant responses in vitro. Blood was obtained from healthy volunteers. Platelet aggregation, dense granule secretion, alpha granule secretion (PAI-1 and soluble CD40 ligand levels) and procoagulant responses (annexin-V and microparticle formation) were assessed using collagen and thrombin receptor activating peptide (TRAP) as agonists. All the antagonists used singularly inhibited collagen-induced responses. Combinations of abciximab or tirofiban with aspirin and/or cangrelor gave additive inhibition with the greatest effect seen when abciximab or tirofiban was combined with both aspirin and cangrelor. Cangrelor inhibited TRAP-induced responses and, again, there was additive inhibition of these parameters when abciximab or tirofiban were combined with cangrelor. The GPIIb/IIIa receptor plays an important role in amplification of platelet activation such that there are important interactions between GPIIb/IIIa antagonists and inhibitors of both P2Y12 receptor activation and, to a lesser extent, thromboxane A2 generation. These interactions are likely to have important influences on the safety and efficacy of combination anti-platelet therapies.

Inappropriate platelet activation is a feature of acute and chronic diseases such as disseminated intravascular coagulation (DIC) and atherosclerosis. Since proinflammatory microbial-derived agonists can be involved in the pathogenesis of these diseases, we examined the potential role of TLR4 (mediating responses to LPS) and TLR2 (which responds to bacterial lipopeptides) in platelet activation. Our data suggested low-level expression of TLR2 and TLR4 on platelets, determined by flow cytometry, and we also observed expression of TLR4 on a megakaryocytic cell line by both flow cytometry and immunohistochemistry. Stimulation of the platelets with the TLR4 agonist LPS, and the synthetic TLR2 agonist Pam3CSK4, resulted in no platelet aggregation, no increase in CD62P surface expression and no increase in the cytosolic concentration of Ca2+. The TLR agonists were also unable to directly activate platelets primed with epinephrine, or pretreated with a low concentration of ADP or PAF. Pretreatment of platelets with LPS or Pam3CSK4 also failed to modulate the platelet response to submaximal concentrations of the classical platelet agonists ADP and PAF. We conclude that the TLR agonists LPS and Pam3CSK4 have no direct effect on platelet activation and that platelet TLRs may be a remnant from megakaryocytes. TLR2 and TLR4 agonists are thought to have a significant role in diseases such as atherosclerosis and DIC, but our research suggests that this is through a mechanism other than direct platelet activation or by modification of platelet responses to other agonists.

We investigated whether statin type or dose influenced the inhibition of platelet function induced by clopidogrel in a prospective, open, parallel group study in patients undergoing elective percutaneous coronary intervention. Patients were taking CYP3A4 metabolised atorvastatin (n = 20) or simvastatin (n = 21), non-CYP3A4 metabolised pravastatin (n = 11) or fluvastatin (n = 2), or no statin therapy (n = 5). ADP and TRAP-induced platelet aggregation were measured using optical aggregometry, whole-blood single-platelet counting, and the Ultegra and Plateletworks point-of-care systems. Platelet pro-coagulant activity (annexin V binding and microparticle formation), P-selectin expression and platelet-leukocyte conjugate formation were assessed by flow cytometry. Platelet responses were measured at baseline, 4 h post clopidogrel 300 mg, and after 10 and 28 days with clopidogrel 75 mg daily. Clopidogrel significantly inhibited both ADP and TRAP-induced platelet responses over time, with steady state inhibition achieved by day 10. This was demonstrated by all techniques used. There was no significant effect of statin type or dose on platelet responses by any method at any time-point. In conclusion, statins do not influence the inhibitory effects of clopidogrel on multiple platelet responses, including aggregation, P-selectin expression, platelet-leucocyte conjugate formation and pro-coagulant responses, in patients undergoing elective PCI.

Platelet-leukocyte interactions are recognised to have pro-inflammatory effects, which may be important in the pathophysiology of ischaemic heart disease. Clopidogrel and the novel intravenous antithrombotic agent AR-C69931MX act at the level of the platelet P2Y12 receptor, which is known to amplify platelet activation, aggregation and other responses induced by numerous platelet agonists. We studied the effects of clopidogrel and aspirin on ADP-induced platelet-leukocyte conjugate formation and P-selectin expression in healthy volunteers. The effects of clopidogrel and AR-C69931MX administered to patients with ischaemic heart disease were also assessed. AR-C69931MX and aspirin were also studied in vitro. Clopidogrel and AR-C69931MX suppressed ADP-induced platelet aggregation, P-selectin expression and platelet-leukocyte conjugate formation whereas aspirin had no inhibitory effect. These effects of clopidogrel and AR-C69931MX may confer therapeutic benefits in the management of acute coronary syndromes.