Joseph DiChiara

Evaluation of Dose-Related Effects of Aspirin on Platelet Function Results From the Aspirin-Induced Platelet Effect (ASPECT) Study

Background— The antiplatelet effect of aspirin is attributed to platelet cyclooxygenase-1 inhibition. Controversy exists on the prevalence of platelet resistance to aspirin in patients with coronary artery disease and effects of aspirin dose on inhibition. Our primary aim was to determine the degree of platelet aspirin responsiveness in patients, as measured by commonly used methods, and to study the relation of aspirin dose to platelet inhibition. Methods and Results— We prospectively studied the effect of aspirin dosing on platelet function in 125 stable outpatients with coronary artery disease randomized in a double-blind, double-crossover investigation (81, 162, and 325 mg/d for 4 weeks each over a 12-week period). At all doses of aspirin, platelet function was low as indicated by arachidonic acid (AA)-induced light transmittance aggregation, thrombelastography, and VerifyNow at any 1 dose. Resistance to aspirin was 0% to 6% in the overall group when AA was used as the agonist, whereas it was 1% to 27% by other methods [collagen and ADP-induced light transmittance aggregation, platelet function analyzer (PFA-100)]. Platelet response to aspirin as measured by collagen-induced light transmittance aggregation, ADP-induced light transmittance aggregation, PFA-100 (81 mg versus 162 mg, P≤0.05), and urinary 11-dehydrothromboxane B2 was dose-related (81 mg versus 325 mg, P=0.003). No carryover effects were observed. Conclusions— The assessment of aspirin resistance is highly assay-dependent; aspirin is an effective blocker of AA-induced platelet function at all doses, whereas higher estimates of resistance were observed with methods that do not use AA as the stimulus. The observation of dose-dependent effects despite nearly complete inhibition of AA-induced aggregation suggests that aspirin may exert antiplatelet properties through non–cyclooxygenase-1 pathways and deserves further investigation.

The Association of Cigarette Smoking With Enhanced Platelet Inhibition by Clopidogrel

OBJECTIVES The purpose of this study was to examine the effect of cigarette smoking on the platelet response to clopidogrel. BACKGROUND Response variability to clopidogrel therapy has been demonstrated. Clopidogrel is metabolically activated by several hepatic cytochrome P450 (CYP) isoenzymes, including CYP1A2. Cigarette smoking induces CYP1A2 and may, therefore, enhance the conversion of clopidogrel to its active metabolite. METHODS Among 259 consecutive patients undergoing elective coronary stenting; 120 were on chronic clopidogrel therapy and were not loaded; and 139 were clopidogrel naïve and were loaded with 600 mg. There were 104 current smokers (CS) and 155 nonsmokers (NS). The adenosine diphosphate (ADP)-stimulated platelet aggregation (PA) was assessed by conventional aggregometry. The ADP-stimulated total and active glycoprotein (GP) IIb/IIIa expression were assessed with flow cytometry. Low PA was defined as the lowest quartile of 5 micromol/l ADP-induced post-treatment PA. RESULTS Current smokers on chronic clopidogrel therapy displayed significantly lower PA and ADP-stimulated active GP IIb/IIIa expression compared with NS (p < or = 0.0008 for both). Similarly, CS treated with 600 mg of clopidogrel displayed greater platelet inhibition and lower active GP IIb/IIIa expression compared with NS (p < or = 0.05). In a multivariate Cox regression analysis, current smoking was an independent predictor of low PA (p = 0.0001). CONCLUSION Clopidogrel therapy in CS is associated with increased platelet inhibition and lower aggregation as compared with NS. The mechanism of the smoking effect deserves further study and may be an important cause of response variability to clopidogrel therapy.

The effect of aspirin dosing on platelet function in diabetic and nondiabetic patients: an analysis from the aspirin-induced platelet effect (ASPECT) study.

OBJECTIVE— Diabetic patients may have a higher prevalence of platelet aspirin resistance than nondiabetic patients. Our goal was to analyze platelet aspirin responsiveness to various aspirin doses in diabetic and nondiabetic patients. RESEARCH DESIGN AND METHODS— We examined the effect of aspirin (81, 162, and 325 mg/day for 4 weeks each) on platelet aspirin responsiveness in 120 stable outpatients (30 diabetic patients and 90 nondiabetic patients) with coronary artery disease (CAD) using light transmittance aggregometry (LTA), VerifyNow, platelet function analyzer (PFA)-100, and levels of urinary 11-dehydro-thromboxane B2 (11-dh-TxB2). RESULTS— In the total group, a low prevalence (0–2%) of aspirin resistance was observed with all aspirin doses as determined by arachidonic acid–induced LTA. Aspirin resistance was higher at the 81-mg dose in diabetic versus nondiabetic patients using collagen-induced LTA (27 vs. 4%, P = 0.001), VerifyNow (13 vs. 3%, P = 0.05), and urinary 11-dh-TxB2 (37 vs. 17%, P = 0.03). Diabetic patients treated with 81 mg exhibited higher platelet function measured by VerifyNow, collagen- and ADP-induced LTA, and 11-dh-TxB2 levels (P ≤ 0.02 for all comparisons). Higher aspirin doses significantly inhibited platelet function and decreased aspirin resistance in diabetic patients (P < 0.05). CONCLUSIONS— Diabetic patients with CAD treated with 81 mg aspirin exhibit a higher prevalence of aspirin resistance and have significantly higher ADP- and collagen-induced platelet aggregation, 11-dh-TxB2 levels, and aspirin reaction units measured by VerifyNow than nondiabetic patients. Increased aspirin dosing resulted in similar rates of resistance and platelet function levels between groups. These findings indicate that diabetic patients exhibit a global high platelet reactivity phenotype that may be partially overcome by higher aspirin doses.

Platelet reactivity to adenosine diphosphate and long-term ischemic event occurrence following percutaneous coronary intervention: A potential antiplatelet therapeutic target

Platelets play a central role in the genesis of post-percutaneous coronary intervention (PCI) ischemic events. High post-procedural platelet reactivity to adenosine diphosphate (HPRADP) may be a risk factor for ischemic events after PCI. The study was designed to evaluate a cutpoint of platelet reactivity that is associated with the occurrence of ischemic events after PCI. Post-procedural platelet reactivity to ADP was measured by conventional aggregometry in 297 consecutive patients undergoing non-emergent PCI. Patients were prospectively followed for up to 2 years for post-discharge ischemic events. All patients had received clopidogrel and aspirin therapy at the time of aggregation measurements. Eighty-one patients (27%) suffered ischemic events. Patients with ischemic events had higher 5 µM ADP-induced platelet aggregation (46 ± 14% vs. 30 ± 17%, p < 0.001) and 20 µM ADP-induced platelet aggregation (60 ± 13% vs. 43 ± 19%, p < 0.001) compared to patients without ischemic events. Using a combined receiver operator curve analysis, cutpoints of >46% aggregation following 5 µM ADP stimulation and >59% aggregation following 20 µM ADP stimulation (HPRADP) were associated with 58 and 54% of ischemic events, respectively. Multivariate Cox regression demonstrated a significant relation between event occurrence and post-procedural HPRADP cutpoints (5 µM ADP, OR=3.9, and 20 µM ADP, OR=3.8, p < 0.001 for both). High post-procedural platelet reactivity to ADP is an independent risk factor for ischemic events within 2 years of non-emergent PCI. These data support a potential therapeutic target for antiplatelet therapy based on the results of an ex vivo platelet function test. The study is a step towards a personalized medicine approach to guide the intensity of antiplatelet therapy.

Bivalirudin and Clopidogrel With and Without Eptifibatide for Elective Stenting: Effects on Platelet Function, Thrombelastographic Indexes, and Their Relation to Periprocedural Infarction: Results of the CLEAR PLATELETS-2 (Clopidogrel With Eptifibatide to Arrest the Reactivity of Platelets) Study

OBJECTIVES The primary objective of this study was to compare the effect of therapy with bivalirudin alone versus bivalirudin plus eptifibatide on platelet reactivity measured by turbidometric aggregometry and thrombin-induced platelet-fibrin clot strength (TIP-FCS) measured by thrombelastography in percutaneous coronary intervention (PCI) patients. The secondary aim was to study the relation of platelet aggregation and TIP-FCS to the occurrence of periprocedural infarction. BACKGROUND Bivalirudin is commonly administered alone to clopidogrel naïve (CN) patients and to patients on maintenance clopidogrel therapy (MT) undergoing elective stenting. The effect of adding eptifibatide to bivalirudin on platelet reactivity (PR) and TIP-FCS, and their relation to periprocedural infarction in these patients are unknown. METHODS Patients (n = 200) stratified to clopidogrel treatment status were randomly treated with bivalirudin (n = 102) or bivalirudin plus eptifibatide (n = 98). One hundred twenty-eight CN patients were loaded with 600 mg clopidogrel immediately after stenting, and 72 MT patients were not loaded. The PR, TIP-FCS, and myonecrosis markers were serially determined. RESULTS In CN and MT patients, bivalirudin plus eptifibatide was associated with markedly lower PR at all times (5- and 20-microM adenosine diphosphate-induced, and 15- and 25-microM thrombin receptor activator peptide-induced aggregation; p < 0.001 for all) and reduced mean TIP-FCS (p < 0.05). Patients who had a periprocedural infarction had higher mean 18-h PR (p < 0.0001) and TIP-FCS (p = 0.002). CONCLUSIONS For elective stenting, the addition of eptifibatide to bivalirudin lowered PR to multiple agonists and the tensile strength of the TIP-FCS, 2 measurements strongly associated with periprocedural myonecrosis. Future studies of PR and TIP-FCS for elective stenting may facilitate personalized antiplatelet therapy and enhance the selection of patients for glycoprotein IIb/IIIa blockade. (Peri-Procedural Myocardial Infarction, Platelet Reactivity, Thrombin Generation, and Clot Strength: Differential Effects of Eptifibatide + Bivalirudin Versus Bivalirudin [CLEAR PLATELETS-2]; NCT00370045.

Hypercoagulability, platelet function, inflammation and coronary artery disease acuity: results of the Thrombotic RIsk Progression (TRIP) study.

The objective of the study was to determine the relation of platelet reactivity, hypercoagulability and inflammation in various stages of coronary artery disease acuity (CAD). Thrombin-induced platelet-fibrin clot strength (MA), time to initial platelet-fibrin clot formation (R), C-reactive protein (CRP), prothrombotic factors, activated GPIIb/IIIa receptor expression and other biomarkers were studied in patients with asymptomatic stable CAD (AS), in patients undergoing PCI for stable (SA) and unstable angina (UA). MA and R were measured by thrombelastography, GPIIb/IIIa expression by flow cytometry and all other markers by fluorokine multianalyte profiling assays. An overall increase in all measurements from a clinically stable to an unstable disease state was observed. There was a distinct stepwise increment in MA [AS vs. SA (p = 0.02), SA vs. UA (p = 0.02) and AS vs. UA (p < 0.001)]. MA exhibited the strongest correlation with other prothrombotic markers (p ≤ 0.02), with CRP (p < 0.001) at all levels of CAD acuity. A distinct pathophysiological state of heightened platelet function, hypercoagulability and inflammation marks the presence of unstable cardiovascular disease requiring intervention. Further studies are required to investigate the primary mechanisms linking the above processes associated with a prothrombotic state resulting in clinical destabilization of the disease.

Platelet function measured by VerifyNow™ identifies generalized high platelet reactivity in aspirin treated patients

Selected aspirin treated patients may exhibit high platelet reactivity to agonists other than arachidonic acid. This study aimed to determine whether the VerifyNow™ identifies generalized high platelet reactivity supported by correlations with other established methods that stimulate platelets with various agonists. Stable outpatients with coronary artery disease (n = 110) were treated with aspirin in a two 3 × 3 Latin square design (81, 162 and 325 mg/day for 4 weeks each). VerifyNow™ (arachidonic acid (AA) cartridge); light transmittance aggregometry; thrombelastography; PFA-100®; flow cytometry; PlateletWorks®; and urinary 11- dehydro thromboxane levels were measured. Multianalyte profiling measured fibrinogen and von Willebrand factor (vWF). Patients with ≥550 ARU by VerifyNow™ had increased 5 mM AA-, 5 µM ADP-, and 2 µg/mL collagen-induced platelet aggregation compared to patients with <550 ARU (p ≤ 0.001). The highest ADP- and collagen-induced aggregation was present in the upper quartile by VerifyNow™ (p < 0.05). Fibrinogen or vWF levels did not differ between VerifyNow™ quartiles. Patients with high platelet reactivity to arachidonic acid identified by VerifyNow™ also exhibit increased reactivity to other important platelet agonists that is independent of fibrinogen and vWF levels. These data suggest that VerifyNow™ may identify a generalized high platelet reactivity phenotype.

The link between heightened thrombogenicity and inflammation: Pre-procedure characterization of the patient at high risk for recurrent events after stenting

Heightened thrombogenicity and biomarker evidence of inflammation have been independently associated with ischemic risk in patients with coronary artery disease. However, a study examining their relation has not been reported. We analysed the relation between measurements of thrombogenicity and biomarkers in patients undergoing stenting and followed for 24 months recurrent ischemic events. In 84 consecutive patients undergoing stenting, pre-procedure thrombogenicity was measured by thrombelastography (TEG) and conventional aggregometry whereas biomarkers were measured by fluorokine multi-analyte profiling. Patients were stratified into quartiles based on platelet-fibrin clot strength (MA) by TEG and correlated with ischemic event occurrence. Patients in the highest MA quartile (high MA) had greater ADP-induced platelet aggregation (57.5 ± 15.0% vs. 47.9 ± 17.6%, p = 0.05), C-reactive protein (25.0 ± 5.6 vs. 4.2 ± 1.0 μg/mL, p = 0.006) and interleukin-8 (23.8 ± 2.8 vs. 14.1 ± 1.6 pg/mL, p < 0.001) than patients within the lowest MA quartile (low MA). Epidermal growth factor (7.7 ± 2.2 vs. 1.2 ± 0.3 pg/mL, p = 0.006) and vascular endothelial growth factor (296 ± 35 vs. 190 ± 10 pg/mL, p = 0.05) were also higher. Patients with high-MA had an ischemic event more often than patients with low-MA (48% vs. 13%, p = 0.02). Our study suggests that a link is present between inflammation and heightened thrombogenicity measured pre-procedurally in the patient at high risk for recurrent ischemic events after stenting. Larger studies are required to solidify these observations and their clinical relevance.

Further Ex Vivo Evidence Supporting Higher Aspirin Dosing in Patients With Coronary Artery Disease and Diabetes

Aspirin remains the cornerstone antiplatelet agent for primary and secondary prevention in patients with diabetes mellitus (DM), a disease associated with heightened platelet reactivity, endothelial dysfunction, and inflammation.1,2 Patients with DM are at a greater risk of death, myocardial infarction, and stroke resulting from thrombotic event occurrence than are patients without diabetes. Because reactive platelets play a central role in the genesis of thrombotic events, the antiplatelet effects of various antiplatelet therapy regimens have been a focus of ex vivo investigations in this high-risk population. The current guidelines recommend aspirin (75 to 162 mg QD) for primary prevention in men aged >50 years and women aged >60 years with diabetes at increased cardiovascular risk (10-year risk >10%). Despite these recommendations, the clinical efficacy of the widely used low-dose aspirin regimen (75 to 81 mg QD) to treat the patient with diabetes remains a major source of controversy, and the optimal dose is unknown.3 Article see p 180 Previous investigations have examined the dose-related effects of aspirin on platelet reactivity. In stable patients with coronary artery disease (CAD), low-dose aspirin did not inhibit platelet function in a significant number, despite highly effective blockade of its primary platelet target cyclooxygenase-1 (COX-1).4,5 The ASPECT (Aspirin-Induced Platelet Effect) study, a double-blind, double-crossover, William design investigation of 81, 162, and 325 mg QD aspirin administered as single doses for 4 weeks, each over a 12-week period, was the largest serial pharmacodynamic investigation of the dose-related effects of aspirin on platelet function in patients with CAD.4 It was clearly demonstrated in the ASPECT study that aspirin inhibited platelet aggregation stimulated by agonists other than arachidonic acid in a dose-dependent manner; significant effects were observed for collagen- and shear-induced aggregation …

Response to the Letter Regarding Article, “Evaluation of Dose-Related Effects of Aspirin on Platelet Function: Results From the Aspirin-Induced Platelet Effect (ASPECT) Study”

BACKGROUND The antiplatelet effect of aspirin is attributed to platelet cyclooxygenase-1 inhibition. Controversy exists on the prevalence of platelet resistance to aspirin in patients with coronary artery disease and effects of aspirin dose on inhibition. Our primary aim was to determine the degree of platelet aspirin responsiveness in patients, as measured by commonly used methods, and to study the relation of aspirin dose to platelet inhibition. METHODS AND RESULTS We prospectively studied the effect of aspirin dosing on platelet function in 125 stable outpatients with coronary artery disease randomized in a double-blind, double-crossover investigation (81, 162, and 325 mg/d for 4 weeks each over a 12-week period). At all doses of aspirin, platelet function was low as indicated by arachidonic acid (AA)-induced light transmittance aggregation, thrombelastography, and VerifyNow. At any 1 dose, resistance to aspirin was 0% to 6% in the overall group when AA was used as the agonist, whereas it was 1% to 27% by other methods [collagen and ADP-induced light transmittance aggregation, platelet function analyzer (PFA-100)]. Platelet response to aspirin as measured by collagen-induced light transmittance aggregation, ADP-induced light transmittance aggregation, PFA-100 (81 mg versus 162 mg, P < or = 0.05), and urinary 11-dehydrothromboxane B2 was dose-related (81 mg versus 325 mg, P = 0.003). No carryover effects were observed. CONCLUSIONS The assessment of aspirin resistance is highly assay-dependent; aspirin is an effective blocker of AA-induced platelet function at all doses, whereas higher estimates of resistance were observed with methods that do not use AA as the stimulus. The observation of dose-dependent effects despite nearly complete inhibition of AA-induced aggregation suggests that aspirin may exert antiplatelet properties through non-cyclooxygenase-1 pathways and deserves further investigation.