Adenosine Diphosphate Stimuli Research Articles

Impact of diabetes mellitus on the pharmacodynamic effects of prasugrel and ticagrelor after switching from clopidogrel in patients with coronary artery disease

Switching P2Y12 inhibitors is common in clinical practice. However, data on the pharmacodynamic (PD) effects of switching in clinical settings characterized by high platelet reactivity, such as diabetes mellitus (DM), are limited. This is a post-hoc analysis from a prospective, randomized, open-label study conducted in coronary artery disease patients comparing the PD effects of loading dose (LD) and maintenance dose regimens of prasugrel vs ticagrelor according to DM status. A total of 110 patients were enrolled: 42 (38%) with DM and 68 (62%) without DM. All patients were on maintenance dual antiplatelet therapy with aspirin and clopidogrel. PD assessments were performed using whole blood vasodilator-stimulated phosphoprotein (VASP), with results quantified by the platelet reactivity index (PRI), VerifyNow P2Y12 (VN-P2Y12) with results reported as P2Y12 reaction units(PRU), and light transmittance aggregometry(LTA) following 20 and 5µM adenosine diphosphate stimuli with results reported as maximum platelet aggregation (MPA). PD assessments were performed at baseline (while on clopidogrel), 30min after LD, 2h after LD, and 1week after LD. Overall, platelet reactivity was higher in DM than in non-DM patients while on clopidogrel therapy. After switching to either prasugrel or ticagrelor, platelet reactivity dropped but remained significantly higher among patients with DM at 30min with all tests (VN-PRU p < 0.01, MPA 20µM p < 0.01, VASP-PRI p = 0.02) and at 2h with VN-PRU (p < 0.01) and LTA-MPA 20µM (p < 0.01) but not with VASP-PRI (p = 0.19). There were no significant differences between prasugrel and ticagrelor both among patients with or without DM, except for lower LTA-MPA 20 at 30min (p < 0.01) among non-DM patients treated with prasugrel. Patients with DM treated with clopidogrel have higher platelet reactivity compared to patients without DM. Although platelet reactivity markedly reduces to a similar extent after switching to prasugrel or ticagrelor, patients with DM persist with increased platelet reactivity compared to patients without DM.Study registration: ClinicalTrials.gov identifier: NCT01852175.

Pantoprazole Does Not Reduce the Antiplatelet Effect of Clopidogrel: A Randomized Controlled Trial in Korea.

Background/AimsConcerns that proton pump inhibitors (PPIs) diminish the efficacy of clopidogrel could hamper the appropriate prescription of PPIs. We evaluated the influence of pantoprazole on the antiplatelet effect of clopidogrel compared with ranitidine, which is regarded as safe, after stratification of the population according to the presence of a cytochrome (CYP) 2C19 polymorphism in Korea.MethodsForty patients who underwent dual antiplatelet therapy were randomized to receive pantoprazole (n=20) or ranitidine (n=20). Platelet aggregation was evaluated by impedance aggregometry at baseline (D0) and 8 days after acid-lowering treatments (D9). CYP2C19 was genotyped by polymerase chain reaction restriction fragment length polymorphism.ResultsAfter co-treatment, the percentage of clopidogrel low-response was 11.1% (2/18) in the pantoprazole group and 10.5% (2/19) in the ranitidine group (p=0.954). The impedance values with adenosine diphosphate stimulus after acid-lowering treatments did not significantly differ between the two groups. In a multiple regression analysis, only ST-elevation myocardial infarction was marginally associated with a reduced antiplatelet effect (odds ratio, 12.07; 95% confidence interval, 0.84 to 173.78). However, pantoprazole use did not affect the antiplatelet effect after correction for the CYP2C19 polymorphism.ConclusionsThis study showed that pantoprazole does not increase platelet aggregation in patients receiving dual antiplatelet therapy (ClinicalTrials.gov number: NCT02733640).

High residual platelet reactivity (HRPR) for adenosine diphosphate (ADP) stimuli is a determinant factor for long-term outcomes in acute ischemic stroke with anti-platelet agents: The meaning of HRPR after ADP might be more prominent in large atherosclerotic infarction than other subtypes of AIS.

High residual platelet activation (HRPA) after ADP stimuli has associated with recurrent vascular events in acute atherothrombosis with the use of antiplatelet agents (APAs). However, there has been little evidence supporting this association in acute ischemic stroke (AIS). In this study, we evaluated the influences of HRPR after ADP stimuli on the 1-year incidence of recurrent cardiovascular events and mortality in AIS with APAs. We conducted an observational, referral center cohort study on 968 AIS patients with APAs from January 2010 to December 2013 who were evaluated using optical platelet aggregometry (OPA). All patients received the dual APA combination of aspirin and clopidogrel or aspirin alone. We evaluated their platelet function 5days after hospital admission using OPA. HRPR after ADP stimuli was defined as platelet aggregation of 70% or greater according to OPA after 10µM ADP stimuli. The primary endpoint was a composite of all causes of death, myocardial infarction, and stroke at the 1-year follow-up. The secondary endpoints were each component of the primary endpoint. The event rate of primary endpoint was 11.3% (109/968). Its rate was significantly higher in the patients with HRPR (16.7%) than in those without (9.7%). HPRP was independently associated with the primary endpoint (OR=1.97, CI 1.22-3.18, p<0.01). According to the AIS subtype, the presence of HRPR was independently significant for the occurrence of the primary endpoint in the large artery atherosclerosis (LAA) subtype only (OR=2.26, CI 1.15-4.45, p=0.02). In this study, the presence of HRPR after ADP stimuli is associated with a poor long-term outcome after acute ischemic stroke. In particular, the influence of this factor might be more prominent in LAA compared with other types of AIS.

The in vitro effects of verbascoside on human platelet aggregation

Preliminary in vitro and animal studies have shown that verbascoside, a phenolic compound, may have several favourable biological activities, including an influence on endothelial function and on platelet aggregation. We sought to evaluate the effects of verbascoside, biotechnologically produced from plant cell cultures, on human platelet aggregation (PA). The blood from 40 aspirin-naïve volunteers with at least one cardiovascular risk factor was preincubated in vitro with verbascoside (1 and 2mg/dL) and aspirin (100μM). The blood from 20 patients with a prior diagnosis of coronary heart disease who were chronically assuming aspirin was preincubated in vitro with verbascoside (1 and 2mg/dL). PA is measured with a light transmission aggregometry and multiplate analyzer. As compared to reference, preincubation with verbascoside resulted in a significant inhibition of adenosine diphosphate (ADP) and arachidonic acid (AA)-induced PA (p<0.01 for both). Verbascoside 2mg/dL did not show a stronger effect as compared to verbascoside 1mg/dL (p=0.4). As expected, the in vitro addition of aspirin reduced AA induced PA (p<0.01), but not that induced by ADP (p=0.5). The addition of verbascoside to the blood of aspirin-treated patients did not improve the values of PA after AA stimulus (p=0.8), whereas it ensured a stronger inhibition after ADP stimulus (p<0.01). Verbascoside in vitro affects PA by mildly inhibiting aggregation, triggered both by ADP and AA. These preliminary data, while intriguing, require confirmation in subjects receiving verbascoside orally in order to determine whether these findings are clinically relevant.

Pharmacodynamic effects of cangrelor and clopidogrel: the platelet function substudy from the cangrelor versus standard therapy to achieve optimal management of platelet inhibition (CHAMPION) trials

Cangrelor is an intravenous antagonist of the P2Y(12) receptor characterized by rapid, potent, predictable, and reversible platelet inhibition. However, cangrelor was not superior to clopidogrel in reducing the incidence of ischemic events in the cangrelor versus standard therapy to achieve optimal management of platelet inhibition (CHAMPION) trials. A prospectively designed platelet function substudy was performed in a selected cohort of patients to provide insight into the pharmacodynamic effects of cangrelor, particularly in regard to whether cangrelor therapy may interfere with the inhibitory effects of clopidogrel. This pre-defined substudy was conducted in a subset of patients from the CHAMPION-PCI trial (n = 230) comparing cangrelor with 600 mg of clopidogrel administered before percutaneous coronary intervention (PCI) and from the CHAMPION-PLATFORM trial (n = 4) comparing cangrelor at the time of PCI and 600 mg clopidogrel given after the PCI. Pharmacodynamic measures included P2Y12 reaction units (PRU) assessed by VerifyNow P2Y12 testing (primary endpoint marker), platelet aggregation by light transmittance aggregometry following 5 and 20 μmol/L adenosine diphosphate stimuli, and markers of platelet activation determined by flow cytometry. The primary endpoint was the percentage of patients who achieved <20 % change in PRU between baseline and >10 h after PCI. The main trial was stopped early limiting enrollment in the platelet substudy. A total of 167 patients had valid pharmacodynamic assessments for the primary endpoint. The percent of individuals achieving <20 % change in PRU between baseline and >10 h after PCI was higher with cangrelor + clopidogrel (32/84, 38.1 %) compared with placebo + clopidogrel (21/83, 25.3 %), but this was not statistically significant (difference:12.79 %, 95 % CI: -1.18 %, 26.77 %;p = 0.076). All pharmacodynamic markers as well as the prevalence of patients with high on-treatment platelet reactivity were significantly lower in patients treated with cangrelor. A rapid platelet inhibitory effect was achieved during cangrelor infusion and a rapid offset of action after treatment discontinuation. This CHAMPION platelet function substudy represents the largest pharmacodynamic experience with cangrelor, demonstrating its potent P2Y(12) receptor inhibitory effects, and rapid onset/offset of action. Although there was no significant pharmacodynamic interaction when transitioning to clopidogrel therapy, further studies are warranted given that enrollment in this study was limited due to premature interruption of the main trial.

Pharmacodynamic Evaluation of Pantoprazole Therapy on Clopidogrel Effects

Background— Safety concerns have recently emerged based on a drug interaction between clopidogrel and proton pump inhibitors leading to reduced pharmacodynamic effects. However, whether such drug interaction is a class effect or a drug effect and if this can be modulated by timing of drug administration remains a matter of debate. The aim of this study was to assess the impact of high-dose pantoprazole therapy, a proton pump inhibitor with low potential to interfere with clopidogrel metabolism, administered concomitantly or staggered, on clopidogrel-mediated pharmacodynamic effects. Methods and Results— This was a prospective, randomized, crossover study conducted in 20 healthy volunteers. Subjects were randomly assigned to receive pantoprazole (80 mg daily) administered concomitantly (CONC) or staggered by 8 to 12 hours (STAG) for 1 week on a background of clopidogrel therapy (600-mg loading dose followed by a 75-mg maintenance dose during all phases) in a crossover fashion with a 2- to 4-week washout period between treatments. All subjects had a 1-week treatment phase with a clopidogrel-only regimen with a 2- to 4-week washout period from randomization sequence. Platelet function was assessed by flow cytometric analysis of the status of phosphorylation of the vasodilator-stimulated phosphoprotein, light transmittance aggregometry after adenosine diphosphate stimuli, and VerifyNow P2Y 12 system at 3 time points: baseline, 24 hours after loading dose, and 1 week after maintenance dose. The primary end point was the comparison of P2Y 12 reactivity index assessed by vasodilator-stimulated phosphoprotein at 1 week. After 1 week, there were no significant difference in P2Y 12 reactivity index between the CONC and STAG regimens (least-squares mean±SEM, 56.0±3.9% versus 56.1±3.9%; P =0.974), as well as when compared with the clopidogrel-only regimen (61.0±3.9%; P =0.100 versus CONC and P =0.107 versus STAG). Further, no differences were observed at baseline and 24 hours between regimens. Concordant results were obtained by light transmittance aggregometry and VerifyNow P2Y 12 assays. Conclusions— Pantoprazole therapy used at high doses is not associated with modulation of the pharmacodynamic effects of clopidogrel, irrespective of timing of drug administration. Clinical Trial Registration— URL: http://www.clinicaltrials.gov . Unique identifier: NCT01170533.

Platelet Inhibition by Adjunctive Cilostazol Versus High Maintenance-Dose Clopidogrel in Patients With Acute Myocardial Infarction According to Cytochrome P450 2C19 Genotype

The aim of this study was to assess the degree of platelet inhibition by adjunctive cilostazol in patients with acute myocardial infarction (AMI) according to hepatic cytochrome P450 2C19 (CYP2C19) genotype. Although adjunctive cilostazol intensifies platelet inhibition in AMI patients, it is not established whether this regimen can be free from the effect of CYP2C19 loss-of-function variants (*2/*3). We randomly assigned 126 AMI patients with available CYP2C19 genotyping to receive adjunctive cilostazol (triple group; n = 64) or high maintenance-dose (MD) clopidogrel of 150 mg/day (high-MD group; n = 62). Using conventional aggregometry and VerifyNow (Accumetrics Inc., San Diego, California), platelet reactivity was measured at pre-discharge and 30-day follow-up. Primary endpoint was change in maximal platelet aggregation (ΔAgg(max)) between pre-discharge and 30-day follow-up. High on-treatment platelet reactivity (HPR) was defined as 20 μmol/l adenosine diphosphate-induced maximal platelet aggregation (Agg(max)) >59%. In noncarriers, despite numerically greater inhibition by adjunctive cilostazol, changes in platelet measures and the rate of HPR did not significantly differ between the 2 groups. In carriers, ΔAgg(max) after 5 and 20 μmol/l adenosine diphosphate stimuli was significantly higher in the triple (n = 39) versus high-MD group (n = 38) (21.8 ± 13.9% vs. 9.0 ± 13.3%, p < 0.001, and 24.2 ± 17.2% vs. 7.7 ± 15.5%, p < 0.001, respectively). Likewise, changes in late platelet aggregation and P2Y12 reaction unit were consistently greater in the triple versus high-MD group. Fewer patients in the triple group met the criteria of HPR at 30-day follow-up than in the high-MD group (15.4% vs. 44.7%, p = 0.005). Compared with high-MD clopidogrel, adjunctive cilostazol significantly enhances platelet inhibition and reduces the rate of HPR, especially in AMI patients with CYP2C19 loss-of-function variants. (Adjunctive Cilostazol Versus High Maintenance-Dose Clopidogrel in Acute Myocardial Infarction (AMI) Patients According to CYP2C19 Polymorphism [ACCELAMI2C19]; NCT00915733).

Pharmacodynamic Effects of Different Aspirin Dosing Regimens in Type 2 Diabetes Mellitus Patients With Coronary Artery Disease

Patients with type 2 diabetes mellitus (T2DM) have reduced aspirin-induced pharmacodynamic effects. This may be attributed to increased platelet turnover rates resulting in an increased proportion of non-aspirin-inhibited platelets during the daily dosing interval. The hypothesis of this study was that an increase in the frequency of drug administration [twice daily (bid) versus once daily (od)] may provide more effective platelet inhibition in T2DM patients. T2DM patients with stable coronary artery disease were prospectively recruited. Patients modified their aspirin regimen on a weekly basis according to the following scheme: 81 mg/od, 81 mg/bid, 162 mg/od, 162 mg/bid, and 325 mg/od. Pharmacodynamic assessments included light-transmittance aggregometry after arachidonic acid, collagen and adenosine diphosphate stimuli; VerifyNow-Aspirin assay; and serum thromboxane B(2) (TXB(2)) levels. Twenty patients were analyzed. All patients were sensitive and compliant to aspirin irrespective of dose, as assessed by arachidonic acid-induced aggregation. When aspirin was administered once daily, there was no significant effect on platelet reactivity by increasing the once-daily dosing using aspirin-sensitive assays (collagen-induced aggregation and VerifyNow-Aspirin). An increase in aspirin dose by means of a second daily administration was associated with a significant reduction in platelet reactivity assessed by collagen-induced aggregation and VerifyNow-Aspirin between 81 mg/od and 81 mg/bid (P<0.05 for both assays) and between 81 mg/od and 162 mg/bid (P<0.05 for both assays). There was no impact of aspirin dosing regimens on adenosine diphosphate-induced aggregation. A dose-dependent effect of aspirin was observed on serum TXB(2) levels (P=0.003). Aspirin dosing regimens are associated with different pharmacodynamic effects in platelets from T2DM patients and stable coronary artery disease, with a twice-daily, low-dose aspirin administration resulting in greater platelet inhibition than once-daily administration as assessed by aspirin-sensitive assays and a dose-dependent effect on serum TXB(2) levels. The clinical implications of a modified aspirin regimen tailored to T2DM patients warrant further investigation. URL: http://www.clinicaltrials.gov. Unique identifier: NCT01201785.

The Impact of Smoking on Post-Clopidogrel Platelet Reactivity in Patients With Acute Myocardial Infarction

Background and ObjectivesSmoking increases inhibition of clopidogrel-induced platelet reactivity in patients undergoing elective coronary stenting. However, an association between pre-admission smoking (PS) and post-clopidogrel platelet reactivity in patients with acute myocardial infarction (AMI) has not been determined.Subjects and MethodsStudy cohorts were recruited from a pool of patients at our hospital who were undergoing coronary stenting for AMI (n=134). Immediately after arrival at the emergency room (ER), all patients received a 600 mg loading dose of clopidogrel followed by a maintenance dose of 75 mg/day. Platelet aggregation was measured with light transmittance aggregometry (LTA) after addition of 5 or 20 µmol/L adenosine diphosphate (ADP).ResultsMaximal platelet aggregation (Aggmax) was lower in PS patients after 5 µmol/L ADP (43.6±15.7% vs. 48.4±12.5%, p=0.096) and 20 µmol/L ADP stimuli (56.2±15.6% vs. 61.3±11.6%, p=0.073) compared with non-smoking (NS) patients. However, there were no differences in 5 µmol/L (42.6±16.3% vs. 43.8±15.6%, p=0.776) and 20 µmol/L ADP-induced Aggmax (54.8±14.3% vs. 56.5±15.9%, p=0.692) between PS patients <0.5 pack/day and ≥0.5 pack/day. Although more PS patients met the criteria for low post-clopidogrel platelet reactivity (LPPR) (≤37%; the lowest quartile of 5 µmol/L ADP-induced Aggmax) than NS patients (30.9% vs. 13.5%, p=0.048), advancing age was the only independent predictor of LPPR {odds ratio (OR) 0.960, 95% confidence interval (CI) 0.929 to 0.993, p=0.019}.ConclusionPS is significantly not associated with decreased residual platelet reactivity in AMI patients.

Functional impact of high clopidogrel maintenance dosing in patients undergoing elective percutaneous coronary interventions

The currently recommended maintenance dose of clopidogrel is often associated with inadequate platelet inhibition, suggesting the need for a higher dose. The aim of this pilot study was to assess the functional impact of a high (150 mg/day) maintenance dose of clopidogrel in patients undergoing elective percutaneous coronary intervention (PCI). This is a prospective, randomized, platelet function study which was performed in elective PCI patients assigned to treatment with either a 75 mg (n = 20) or 150 mg (n = 20) daily maintenance dose of clopidogrel for 30 days; afterwards, all patients resumed standard dosing. Platelet aggregation was performed using light transmittance aggregometry following 20 microM and 5 microM adenosine diphosphate (ADP) stimuli 30 days after randomization and 30 days after resuming standard dosing. Patients treated with 150 mg/day clopidogrel had lower 20 microM ADP-induced platelet aggregation compared to patients on 75 mg/day (52.1 +/- 9% vs. 64.0 +/- 8%; p < 0.001; primary endpoint). The dose-dependent effect was confirmed by the absolute and relative increase in platelet aggregation after resuming standard dosing (p < 0.001). No changes were observed in patients randomized to standard dosing. Parallel findings were observed following 5 microM ADP stimuli for all assessments. A broad variability in clopidogrel-induced antiplatelet effects was observed irrespective of dosing. In conclusion, a 150 mg/day maintenance dose regimen of clopidogrel is associated with reduced platelet reactivity and enhanced platelet inhibition compared to that achieved with the currently recommended 75 mg/day in patients undergoing elective PCI.

Impact of Platelet Reactivity on Cardiovascular Outcomes in Patients With Type 2 Diabetes Mellitus and Coronary Artery Disease

This study sought to determine the prognostic implications of high platelet reactivity (HPR) assessed in type 2 diabetes mellitus (T2DM) patients while in their steady-state phase of dual antiplatelet therapy. Type 2 diabetes mellitus patients have increased platelet reactivity compared with nondiabetic patients. Whether HPR assessed in T2DM while in their steady-state phase of dual antiplatelet therapy is associated with an increased risk of major adverse cardiovascular events (MACE) is unknown. Platelet function analyses, which included measures of platelet aggregation and activation, were performed in 173 T2DM patients with coronary artery disease on chronic treatment with aspirin and clopidogrel. The HPR was defined as the upper quartile of maximal platelet aggregation (Agg(max)) after 20 micromol/l adenosine diphosphate stimuli. Patients were followed up for 2 years and MACE were recorded. A total of 41 MACE occurred in 34 patients (19.7%) during the 2-year follow-up. The MACE occurred in 15.2%, 12.2%, 12.2%, and 37.7% of patients from the lowest to upper quartile, respectively (p = 0.005). The HPR was the strongest independent predictor of MACE (hazard ratio 3.35, 95% confidence interval [CI] 1.68 to 6.66, p = 0.001). Receiver-operating characteristic analysis indicated that a cutoff value of 62% Agg(max) best predicted MACE (37.8% vs. 13.2%, odds ratio 3.96, 95% CI 1.8 to 8.7, p < 0.001). Patients with HPR had up-regulation of multiple platelet signaling pathways (p < 0.0001 for all assays), indicative of a global hyperreactive platelet status. High platelet reactivity determined in T2DM patients with coronary artery disease while on chronic dual antiplatelet therapy is associated with a higher risk of long-term adverse cardiovascular events, suggesting the need for tailored antithrombotic drug regimens in these high-risk patients.

Reversibility of the Association of Fibrinogen With Rabbit Platelets Exposed to ADP

Fibrinogen enhances the adenosine diphosphate (ADP) induced aggregation of washed rabbit platelets and has previously been shown to associate with platelets upon the addition of ADP. This association has been investigated further by measuring the binding of 126I-flbnnogen to platelets exposed to ADP under physiologic conditions of aggregation and deaggregation. To determine the extent of 126I-fibrinogen binding, the platelets were removed by rapid centrifugation and the radioactivity in the platelet pellet was measured; trivalent chromium-51 was used as a space marker. If fibrinogen is present before ADP is added, the fibrinogen binds maximally to the platelets as they change shape in response to ADP. When ADP is not removed from the platelet suspension, deaggregation is slow, and fibrinogen also binds when added shortly after the ADP, but the amount that binds is less. The ability of the platelets to bind fibrinogen upon exposure to ADP is lost rapidly if an enzyme that removes the ADP is present in the suspension. A large portion of the 125I-fibrinogen bound to platelets during ADP stimulation, can be displaced by unlabeled fibrinogen added shortly after the ADP. Bound fibrinogen dissociates from platelets when they deaggregate upon removal of the ADP stimulus, and characterization of this fibrinogen by SDS-PAGE did not show any change resulting from its reactions with platelets. If the platelets are allowed to recover and then are stimulated a second time with ADP, they aggregate and bind fibrinogen to the same extent as platelets not previously aggregated with ADP. Thus, fibrinogen binding sites become available when platelets are exposed to ADP, become unavailable within a short time, and, if conditions are such that the platelets can recover, fibrinogen binding sites may become available again upon subsequent addition of ADP. It appears that neither the fibrinogen nor the fibrinogen binding site is permanently altered during the processes of aggregation and deaggregation.