Effects of extended-release dipyridamole in vitro on thrombin indices measured by calibrated automated thrombography in poststroke survivors.

Randomized trials suggested superior stroke prevention with extended-release dipyridamole (ERD) in combination with low-dose aspirin than either with aspirin or dipyridamole alone. Thrombin generation (TG) is a critical step in clot formation and represents a cornerstone biomarker of atherothrombosis. We, therefore, sought to define the effect of ERD in escalating concentrations on the time course of TG using the Calibrated Automated Thrombogram (CAT) technology in patients after ischemic stroke. Serial plasma samples were obtained from 20 patients with ischemic stroke documented by neuroimaging and who were treated with aspirin for at least 30 days. The impact of 75-, 150-, 250-, and 300-nM ERD on TG was assessed using fluorogenic substrate CAT technology. The following integrated CAT indices were calculated for each ERD dose and compared with the vehicle: TGmax, start time (tstart) peak time (tpeak), and mean time (tmean). Preincubation of platelet-poor plasma with ERD resulted in a dose-dependent significant inhibition of TG. The TGmax was gradually reduced from 447 ± 21 nM at baseline to 354 ± 31 nM (P = 0.008) for 75-nM ERD, 298 ± 24 nM for 150-nM ERD, 248 ± 26 nM for 250-nM ERD, and finally to 240 ± 23 nM for 300-nM ERD (P < 0.0001 for all). The tmean was reduced only for the highest (250-300 nM) ERD concentrations. The tstart was only slightly delayed, but not different (1.5 vs. 1.8 vs.1.9 minutes; P = 0.09), for all ERD concentrations. The tpeak was not affected by ERD. ERD in vitro affects thrombin activity indices predominantly by a dose-dependent inhibition of endogenous thrombin potential and demonstrated a trend to delayed initiation of thrombin production. These preliminary data, while intriguing, require confirmation in poststroke patients receiving orally dosed ERD to determine whether these findings are clinically relevant.

Stability validation of paraformaldehyde-fixed samples for the assessment of the platelet PECAM-1, P-selectin, and PAR-1 thrombin receptor by flow cytometry.

Sample fixation for storage and/or transportation represents an unsolved challenge for multicenter clinical trials assessing serial changes in platelet activity, or monitoring various antiplatelet regimens. Whole blood flow cytometry represents a major advance in defining platelet function, although special training and expensive equipment is required. We sought to determine how fixation with 2% paraformaldehyde (PFA), and storage of blood samples over 1 week affects the flow cytometry readings for both intact and thrombin-activating four major surface platelet receptors. Whole blood platelet expression of PECAM-1, P-selectin, PAR-1 inactive receptor (SPAN-12), and cleaved (WEDE-15) epitope was assessed immediately after blood draw, after staining with 2% PFA, and at day 1, 3, 5, and 7. The study was performed in 6 volunteers with multiple risk factors for vascular disease, not receiving any antiplatelet agents. Staining with PFA resulted in a slight decrease of fluorescence intensity, especially for PECAM-1, while antigen expression at day 1, 3 and 5 remains consistent, and highly reproducible. At day 7 there was a small but inconsistent trend towards diminished fluorescence intensity. The platelet data were consistent while validated with the isotype-matched irrelevant antibody. These data suggest that there is a 5 day window to perform final flow cytometry readings of whole blood PFA-fixed inactivated platelet samples. In contrast, thrombin activation cause gradual loss of flow cytometry signal, and cannot be recommended for long-term storage. This is critical logistic information for conducting multicenter platelet substudies within the framework of major clinical trials.

Incidence and causes of new-onset dyspnea in 3,719 patients treated with clopidogrel and aspirin combination after coronary stenting.

The experimental oral antiplatelet agent AZD6140 causes dyspnea in randomized trials. Whether clopidogrel may also cause dyspnea remains controversial. We sought to define the incidence and causes of dyspnea in a large post-percutaneous coronary intervention (PCI) cohort based on open-labeled consecutive registry analysis of in-hospital charts and discharge diagnoses. Data were collected at six-month follow-up by means of telephone interviews or returned questionnaires during outpatient visits. Patients undergoing coronary stent implantation were loaded with 600 mg clopidogrel followed by 75 mg/daily in combination with 75-325 mg of aspirin daily for at least six months. Data from 3,719 patients were analyzed. Dyspnea was diagnosed in 157 (4.2%) patients caused by chronic obstructive pulmonary disease (n = 43 or 27% of the dyspnea group), heart failure (n = 30 or 19%), cancer (n = 22 or 14%), pneumonia (n = 17 or 11%); asthma (n = 8 or 5%), pulmonary hypertension (n = 8 or 5%); pericarditis (n = 5 or 3%); cardiac arrhythmias (n = 4 or 2.5%); pleural effusion (n = 1), pulmonary embolism (n = 1), anxiety (n = 1), or unknown (n = 17, or 11%). The incidence of dyspnea at six months in a post-stent cohort treated with aspirin and clopidogrel is low (4.2%). The majority of patients with dyspnea (140/157) exhibit a distinct underlying disease or condition, in contrast to only 17 patients (0.45% of total cohort) in whom the pathogenesis of dyspnea remained unidentified. These data closely match the frequency of dyspnea that was observed in the CAPRIE trial, suggesting that therapy with clopidogrel, and/or aspirin holds very small (if any) risk for dyspnea.

Baseline platelet activity and response after clopidogrel in 257 diabetics among 822 patients with coronary artery disease.

The objective was to describe the indices of platelet aggregation and activation in a large cohort of diabetic patients with coronary artery disease (CAD). Recently, a number of observations have indicated that patients with diabetes mellitus (DM) exhibit persistent platelet activation, and low response after antiplatelet therapy, although no randomized data exist. We sought to define the baseline platelet biomarkers, and the patterns of response to aspirin and clopidogrel therapy in DM versus non-diabetic patients. Secondary post-hoc analyses were made of platelet activity biomarkers in the dataset which consisted of patients with documented CAD (n = 822), including those with DM (n = 257). Patients with DM exhibited higher baseline platelet activity by adenosine diphosphate (ADP)- (p = 0.0002), and collagen-induced (p = 0.03) aggregometry; Ultegra- (p = 0.0001), and PFA-100 (p = 0.02) analyzers; and expression of platelet/endothelial cell adhesion molecule-1 (PECAM-1) (p = 0.01), glycoprotein (GP) IIb/IIIa antigen (p = 0.001), and activity (p = 0.02), vitronectin receptor (p = 0.03), P selectin (p = 0.02), and intact epitope of PAR-1 thrombin receptor (p = 0.02). Antiplatelet response after clopidogrel in diabetics was impaired when compared with non-diabetics. In conclusion, diabetic patients exhibit high pretreatment platelet activity, and do not respond well to the available antiplatelet regimens when compared with similar patients without DM. The clinical implications of these findings are unknown but are potentially important. Considering worsened outcomes in this high-risk population, clinical trials in DM are urgently needed in order to define the optimal degree of platelet inhibition and suitability for more aggressive antiplatelet regimens.