Search

Peripheral arterial disease (PAD) affects approximately 236 million people worldwide. Therefore, this study aimed to investigate the relationship between CYP2C19 genotype polymorphisms and clopidogrel resistance (CR) following revascularization in patients with PAD. In total, 345 patients who underwent PAD revascularization were monitored for five years and risk factors for ischemic events were identified. Platelet reactivity and CYP2C19 genotypes were measured, and patients were classified as normal, intermediate, or poor metabolizers based on their genotypes. The study endpoint was defined as an ischemic event, that encompassed major adverse cardiovascular or limb events, or all-cause death. In this study, ischemic events following PAD revascularization were associated with patient age, prior minor amputation, the Rutherford category before revascularization, indications for revascularization, index ankle-branchial index before revascularization, CYP2C19 phenotypes, and CR. Intermediate and poor metabolism, the Rutherford category before revascularization, and CR were independent risk factors for ischemic events in patients after PAD revascularization. Similarly, intermediate and poor metabolism, the Rutherford category before revascularization, and CR were independent risk factors for ischemic events in patients with PAD after revascularization within five years. Intermediate and poor metabolizers had a higher platelet reactivity and risk of CR than normal metabolizers. However, poor metabolizers had a higher platelet reactivity and risk of CR than intermediate metabolizers. Furthermore, the hazard ratio for ischemic events increased with platelet reactivity. This effect was more prevalent in intermediate and poor metabolizers than in normal metabolizers. Ischemic events in patients after PAD revascularization were affected by independent risk factors. Decreased clopidogrel metabolism increased the platelet reactivity and CR in patients after PAD revascularization. Furthermore, high platelet reactivity was associated with an increased risk of ischemic events in patients with intermediate and poor metabolism. [Display omitted] • CYP2C19 phenotype and CR effects after revascularization for PAD remain unclear. • We evaluated these effects on ischemic events after revascularization over 5 years. • CYP2C19 phenotype and CR were independent risk factors for ischemic events. • Patients with impaired clopidogrel metabolism had a higher risk of CR. [ABSTRACT FROM AUTHOR]

The bleeding phenotype in immune thrombocytopenia (ITP) is heterogeneous, but usually mild and only partly dependent on the severity of thrombocytopenia. Platelet reactivity has previously been suggested to underly the mild phenotype. Platelet function was assessed as basal and agonist-induced surface expression of P-selectin and activation of GPIIb/IIIa via flow cytometry, and soluble (s)P-selectin levels were assessed in plasma of 77 patients with primary ITP, 19 hemato-oncologic thrombocytopenic controls (TC) and 20 healthy controls (HC). The association of platelet function with laboratory and clinical parameters such as bleeding manifestations at inclusion and previous thrombosis was analyzed. ITP patients showed tendency towards increased surface P-selectin and elevated levels of activated GPIIb/IIIa. Platelet activation after stimulation with all agonists including TRAP-6, ADP, arachidonic acid and CRP was decreased compared to HC. Compared to TC, only GPIIb/IIIa activation but not surface P-selectin was higher in ITP. Levels of soluble (s)P-selectin were significantly higher in ITP patients compared to TC, but similar to HC. Higher sP-selectin levels were associated with blood group O and current therapy, with highest levels in TPO-RA treated patients. Platelet reactivity was not associated with platelet count or size, platelet antibodies, treatment regime, or blood group. No correlation between platelet activation with the bleeding phenotype or previous thrombotic events could be observed. ITP patients did not have hyper-reactive platelets compared to HC, but partly higher reactivity compared to TC. Further studies are needed to understand the underlying mechanism behind the bleeding and pro-thrombotic phenotype in ITP. 250/250. [Display omitted] [ABSTRACT FROM AUTHOR]

Thrombopoietin receptor agonists (TPO-RAs) are widely used in immune thrombocytopenia (ITP) and are associated with increased thrombotic risk. However, data regarding their impact on platelet function is scarce. Platelet function was evaluated in chronic ITP patients enrolled over one year, using light transmission aggregometry and platelet-derived microparticle (PMP) levels measurement with flow cytometry. Aggregation responses to various concentrations of ADP, collagen, ristocetin, and PMP levels were compared between TPO-RA-treated patients, patients treated with other agents and healthy individuals. TPO-RA-treated patients (n = 24) displayed significantly reduced aggregation responses to 2.5 μM, 5 μM, and 10 μM of ADP and collagen compared to 15 healthy individuals (59.5 % vs. 87.6 %, p <.0001, 43.6 % vs. 79.9 %, p <.0001, 26.1 % vs. 75.2 %, p <.0001, 67.2 % vs. 86 %, p <.0001, respectively). Reduced responses to ADP and collagen were also recorded in patients treated with other agents (n = 16) compared to healthy controls but without difference between the two treatment groups. Aggregation response to ristocetin was normal in all three groups. None of the patients yielded enhanced platelet aggregation. In TPO-RA-treated patients, a strong positive correlation between platelet counts and aggregation response to ristocetin was observed (r s = 0.65, p =.0005). PMP levels were significantly elevated in TPO-RA-treated patients compared to patients treated with other agents (49.5 vs 4.5 events/uL, p <.0001) and healthy controls (5 events/uL, p <.0001). These results suggest that TPO-RAs may not enhance platelet aggregation responses, whereas impaired responses may be a disease feature. Furthermore, TPO-RAs may increase PMP levels and thus be implicated in the modulation of platelet function in ITP patients. • TPO-RAs lead to a significant increase in platelet microparticle levels. • TPO-RA treatment does not induce enhanced platelet aggregation responses. • TPO-RA-treated ITP patients yield impaired aggregation responses to ADP and collagen. • TPO-RAs may exert selective effects on ristocetin-induced aggregation. [ABSTRACT FROM AUTHOR]

Postoperative myocardial injury (PMI) after major vascular surgery, detected by elevated cardiac troponin (cTn), has been associated with morbidity and mortality. It is unclear whether the pathophysiology of PMI is determined by increased platelet activity. To examine the relationship between platelet activation (P-selectin expression) and PMI in patients undergoing elective open abdominal aortic surgery. This prospective, single-centre, observational, cohort study included 33 patients undergoing elective open abdominal aortic surgery between March 2018 and April 2021. Patients were routinely treated with aspirin. Unstimulated platelet activation was measured by platelet bound P-selectin expression (range 0–100 %). Explorative coagulation measurements were: stimulated platelet aggregation measured with the VerifyNow® assay (aspirin cartridge), with the Multiplate® analyzer (ASPI, ADP and TRAP) and stimulated coagulation status evaluated by the TEG® Hemostasis Analyzer System (global hemostasis cartridge). The primary outcome was cTn release assessed by the fifth generation high-sensitive cTn assay. Multivariable generalized linear mixed models were used to evaluate the association between platelet function and cTn concentrations over time. Ten patients (30.3 %) developed PMI. Increased P-selectin expression directly after surgery was associated with the cTn concentrations over 48 h (β = 1.39 (1.1–1.75), P = 0.0064). No association was found between P-selectin measured later after surgery (at 24 h or 48 h) and cTn concentrations. Furthermore, there was no association between the explorative coagulation parameters and cTn release. Platelet reactivity, assessed by P-selectin expression measured directly after surgery is associated with PMI, assessed by elevated cTn concentrations in the early postoperative period in patients undergoing elective open abdominal aortic surgery. [ABSTRACT FROM AUTHOR]

The coronavirus disease-2019 (COVID-19) is a systemic disease with severe implications on the vascular and coagulation system. A procoagulant platelet phenotype has been reported at least in the acute disease phase. Soluble P-selectin (sP-sel) in the plasma is a surrogate biomarker of platelet activation. Increased plasma levels of sP-sel have been reported in hospitalized COVID-19 patients associated with disease severity. Here, we evaluated in a longitudinal study the sP-sel plasma concentration in blood donors who previously suffered from moderate COVID-19. 154 COVID-19 convalescent and 111 non-infected control donors were recruited for plasma donation and for participation in the CORE research trial. First donation (T1) was performed 43–378 days after COVID-19 diagnosis. From most of the donors the second (T2) plasma donation including blood sampling was obtained after a time period of 21–74 days and the third (T3) donation after additional 22–78 days. Baseline characteristics including COVID-19 symptoms of the donors were recorded based on a questionnaire. Platelet function was measured at T1 by flow cytometry and light transmission aggregometry in a representative subgroup of 25 COVID-19 convalescent and 28 control donors. The sP-sel plasma concentration was determined in a total of 704 samples by using a commercial ELISA. In vitro platelet function was comparable in COVID-19 convalescent and control donors at T1. Plasma samples from COVID-19 convalescent donors revealed a significantly higher sP-sel level compared to controls at T1 (1.05 ± 0.42 ng/mL vs. 0.81 ± 0.30 ng/mL; p < 0.0001) and T2 (0.96 ± 0.39 ng/mL vs. 0.83 ± 0.38 ng/mL; p = 0.0098). At T3 the sP-sel plasma level was comparable in both study groups. Most of the COVID-19 convalescent donors showed a continuous decrease of sP-sel from T1 to T3. Increased sP-sel plasma concentration as a marker for platelet or endothelial activation could be demonstrated even weeks after moderate COVID-19, whereas, in vitro platelet function was comparable with non-infected controls. We conclude that COVID-19 and additional individual factors could lead to an increase of the sP-sel plasma level. [ABSTRACT FROM AUTHOR]

We sought to investigate the predictive value of platelet function assessment for bleeding in clopidogrel- or ticagrelor-treated patients undergoing off-pump coronary artery bypass grafting (OPCABG). This prospective study included patients treated with acetylsalicylic acid and clopidogrel or acetylsalicylic acid and ticagrelor and scheduled for OPCABG. The percentage of platelet aggregation was evaluated by thromboelastography. Postoperative blood loss was measured as the chest tube drainage (CTD) and excessive blood loss was settled as CTD with more than 600 mL at first postoperative 12 h. Major bleeding complications were defined by Bleeding Academic Research Consortium (BARC) type 4-CABG related bleeding or class 3 or class 4 bleeding in universal definition of perioperative bleeding (UDPB) in adult cardiac surgery. A total of 434 consecutive patients were included. There was a negative correlation (r = −0.133, P = 0.0056) between ADP-induced platelet aggregation and CTD at 12 h. The platelet aggregation exhibited a moderate performance (AUC = 0.616) for predicting excessive postoperative blood loss. Multivariable analysis showed that ADP-induced platelet aggregation <33.45% (OR = 2.976, 95% CI: 1.325–6.711, P = 0.008) was independently associated with excessive postoperative blood loss. However, the percentage of ADP-induced platelet aggregation predicted neither UDPB-defined nor BARC-defined major bleeding. Instead, P2Y 12 receptor antagonist discontinuation time was independently related to the risk of major bleeding complication. ADP-induced platelet aggregation detected by thromboelastography was negatively related to postoperative blood loss and platelet aggregation <33.45% was associated with excessive postoperative blood loss. However, platelet function assessment by thromboelastography failed to predict major bleeding complications. [ABSTRACT FROM AUTHOR]

The risk of recurrent cardiovascular events in patients with coronary artery disease (CAD) is determined by multiple factors including platelet function and turnover. MicroRNAs (miRs) may regulate both platelet function and turnover. We aimed to identify candidate miRs associating with platelet function and turnover in a cohort of stable CAD patients. Furthermore, we retrieved information on binding targets of the candidate miRs to obtain a more comprehensive biological insight into miR regulation of platelet function and turnover. Based on existing literature and a pilot study, we identified nine candidate miRs. Subsequently, we investigated the expression of the candidate miRs in whole blood and their relation to platelet function and turnover in 749 CAD patients. Platelet function was analysed using impedance aggregometry, optical aggregometry and serum thromboxane B 2 measurements. Platelet turnover markers (immature platelet count, immature platelet fraction and mean platelet volume) were measured using monochromatic automated flow cytometry. Expression of miR-93-5p, miR-126-3p, miR-150-5p, miR-423-3p and miR-1180-3p showed negative correlations with platelet function (p -values from <0.0001 to 0.0006, rho from −0.13 to −0.36). In addition, expression of miR-423-3p showed negative correlation with platelet turnover markers (p -values from 0.001 to 0.004, rho from −0.11 to −0.12). We identified several novel miRs that may regulate platelet function and turnover, thereby contributing to the increased risk of recurrent cardiovascular events in CAD patients. • Coronary artery disease patients are at risk of recurrent cardiovascular events. • The risk is determined by multiple factors including platelet function and turnover. • MicroRNAs (miRs) may influence the regulation of platelet function and turnover. • We identified several miRs that correlated with platelet function and turnover. • These miRs may regulate relevant genes important for platelet function and turnover. [ABSTRACT FROM AUTHOR]

Genetic differences between races have been hypothesized to contribute to differences in outcome from acute coronary syndromes (ACS). Our objective was to assess racial differences in genetic variations in the platelet serotonin transporter (5HTT) and receptor in patients with ACS. 127 consecutive patients, African Americans (AA) = 27; Caucasian (C) =100, admitted with ACS were evaluated for platelet function by serotonin (5HT) induced platelet activation. All patients were genotyped for two polymorphisms in the serotonin-transporter-linked polymorphic region (5-HTTLPR) S/L and L G /L A and one polymorphism of the serotonin 2A receptor (5-HT2A, T102C) gene. All patients were followed for major and minor adverse cardiac events at 12 months. AA when compared to C had a lower prevalence of the HTTLPR S allele (21% vs 45%, p = 0.0003) and a higher prevalence of the L G allele (24% vs 4.5%, p = 0.0001). Allelic frequency of the 5-HT2A T102C allele was not significantly different between the races. Platelet activation was lower in AA compared to C, median EC50 5HT was 12.08 μg vs 2.14 μg (p = 0.001). The 5-HTTLPR and the 5-HT2A polymorphisms were not associated with platelet functional responses to serotonin. There were no significant differences in major or minor adverse cardiac events in patients with serotonin transporter or receptor polymorphisms. We found a lower prevalence of the S allele and a higher prevalence of the G allele in AA with ACS. We also found decreased platelet activation in AA which did not correlate with serotonin-related platelet polymorphisms. It is unclear if other contributing factors may explain these platelet functional differences. • Genetic differences are hypothesized as factors contributing to ACS outcomes in African Americans • African Americans have significant differences in allele frequency of the platelet serotonin transporter • Decreased platelet activation in response to serotonin in African Americans is not related to serotonin polymorphisms • Alternative contributing factors may explain platelet serotonin response in African Americans [ABSTRACT FROM AUTHOR]

The contrast agents have different molarities and ionic structures. The high osmolar contrast agents could increase platelet aggregation but the ionic contrast agents decrease platelet aggregation. However there is insufficient data on whether the antiaggregan effect of P2Y12 inhibitors used during coronary interventions are affected by the contrast agents. This study aimed to evaluate the in vitro effects of different contrast agents on the antiaggregant activity of P2Y12 inhibitors (clopidogrel, ticagrelor and prasugrel). Thirty patients (who underwent percutaneous coronary interventions and were treated with a P2Y12 inhibitor for a minimum of 10 days) and five healthy volunteers were divided into four groups: the clopidogrel (10 patients), ticagrelor (10 patients), prasugrel (10 patients) and control (five volunteers) groups. Antiaggregant activity was measured by using the Verify-Now method and was represented as P2Y12 reaction unit (PRU) values. Three tubes of blood were collected from the participants in the three patient groups and in the control group; as the contrast material, 10% iohexol was added to a second tube, and 10% iodixanol was added to a third tube. PRU values of the control and the contrast tubes were measured at 5 min and at 30 min after the contrast material was added. Iohexol and iodixanol led to a significant decrease in the PRU values in the control group (iohexol: 188.4 ± 39.2 vs 142.4 ± 17.0, p =.04; iodixanol: 188.4 ± 39.2 vs 159.2 ± 33.7, p =.04) and in the clopidogrel group (iohexol: 140.8 ± 50.8 vs 106.3 ± 44.4, p =.04; iodixanol: 140.8 ± 50.8 vs 109.4 ± 47.6, p =.009) but not in the ticagrelor and prasugrel groups. The PRU values were significantly lower in the ticagrelor (23.1 ± 26.2) and prasugrel (23.4 ± 27.5) groups than in the clopidogrel (140.8 ± 50.8) and control (188.4 ± 39.2) groups (p <.01), and the PRU values for the ticagrelor and prasugrel groups were similar for both the 5-min and 30-min time periods (p >.05). The antiaggregant activities of iohexol and iodixanol were observed to be similar at the 5- and 30-minute time points for all of the groups (p >.05). Iohexol and iodixanol had in vitro antiaggregant effects, and their antiaggregant effects were similar. Iohexol and iodixanol increased the clopidogrel antiaggregant activity in vitro, but they did not significantly alter the antiaggregant activities of prasugrel and ticagrelor. • Iohexol and iodixanol have similar antiaggregant activity in in vitro setting. • Iohexol and iodixanol icrease the antiaggregant activity of clopidogrel in in vitro setting. • Iohexol and iodixanol did not change the antiaggregant activity of prasugrel and ticagrelor. • Iohexol antiaggregant activity occurs more rapidly than iodixanol. [ABSTRACT FROM AUTHOR]

• We established reference ranges of platelet function in healthy Japanese subjects. • The data of each sample were clearly shown by overlaying them on the reference ranges. • Visual and clear evaluation of platelet function will aid in clinical practices. [ABSTRACT FROM AUTHOR]

Abstract In randomised trials, bivalirudin has been associated with higher rates of acute stent thrombosis (AST) compared to unfractionated heparin (UFH), without mechanistic explanation. Furthermore, data are discrepant regards the antiplatelet effects of bivalirudin. This prespecified study, part of a larger HEAT-PPCI Platelet Substudy, aimed to compare the antiplatelet and antithrombotic effects of bivalirudin and UFH using short thrombelastography (s-TEG), an ex vivo whole blood platelet function assay. In HEAT-PPCI, patients were randomised to receive UFH or bivalirudin before angiography. Assay with s-TEG was performed in 184 patients (10.2%) at end of procedure (EOP) and repeated at 24 h. In addition to adenosine diphosphate- (ADP) and arachidonic acid- (AA) mediated platelet aggregation, thrombin-mediated clotting (TMC) was assessed using kaolin with and without heparinase. There were no significant differences between UFH and bivalirudin in ADP- and AA-mediated platelet aggregation at EOP or 24 h. Whilst UFH obliterated TMC at EOP, bivalirudin prolonged R time (19.7 min [15.9–25.4] vs. 8.4 min [7.5–10]; P < 0.0001), K time (2.4 min [1.9–3.4] vs. 2.2 min [1.8–2.7]; P = 0.007) and significantly increased maximum clot strength (MA 62.7 mm [58.7–67.4] vs. 58.6 [55–63]; P = 0.0005), compared to control. In conclusion, there were no significant differences in the antiplatelet effects of UFH and bivalirudin. However, whilst UFH obliterated TMC, bivalirudin prolonged clot initiation but potentiated maximum clot strength. As AST is likely multifactorial in aetiology, in patients treated with bivalirudin, increased clot strength may contribute to this hazard in some individuals and this observation warrants further investigation. Highlights • Comparing the antiplatelet and antithrombotic effects of bivalirudin and heparin • No significant differences in the antiplatelet effects of bivalirudin and heparin • Heparin totally obliterated thrombin-mediated clotting. • Bivalirudin prolonged clot initiation/propagation and increased clot strength. • Increased clot strength with bivalirudin may contribute to acute stent thrombosis. [ABSTRACT FROM AUTHOR]

Levosimendan has been developed for treatment of severe heart failure. The favorable hemodynamic effect of levosimendan is related to its unique dual mechanism of action – increase of the contractile force of the myocardium caused by enhanced sensitivity of myofilaments to calcium combined with vasodilatation caused by the opening of adenosine triphosphate - dependent potassium channels. Due to the structural similarities to phosphodiesterase inhibitors it may partly exert its action via inhibition of phosphodiesterase inhibitors III. Inhibition of the phosphodiesterase inhibitors III leads to an increase of intracellular concentration of cyclic adenosine monophosphate causing an anti-aggregatory effect. There are some contradictory or indirect and inconclusive reports related to the impact of levosimendan on platelet function. The aim of this systematic review was to critically discuss the impact of levosimendan on platelet function according to currently available knowledge based on the findings of experimental as well as observational and randomized clinical studies. [ABSTRACT FROM AUTHOR]

Introduction Remote ischaemic conditioning (RIC) protects against ischaemia-reperfusion injury through cellular protective pathways, but may also modulate haemostasis. We aimed to investigate the effect of long-term RIC on platelet function and fibrinolysis in patients with chronic ischaemic heart failure (CIHF). Material and methods In a prospective, outcome-assessor blinded, paired study, 16 patients with CIHF and 21 age- and gender-matched controls without ischaemic heart disease (IHD) were treated with RIC once daily for 28 ± 4 days. RIC was performed as four cycles of 5 min upper arm ischaemia and reperfusion. We evaluated collagen and arachidonic acid induced platelet aggregation (Multiplate® Analyzer), platelet turnover (Sysmex® XE-5000), platelet activation (plasma soluble-platelet-selectin) and fibrinolysis (clot lysis time, tissue plasminogen activator (t-PA) and plasminogen activator inhibitor-1 (PAI-1)). We compared blood samples assessed at baseline and following long-term RIC. Results Long-term RIC did not affect platelet aggregation, turnover or activation or PAI-1 in any study groups. Long-term RIC did not affect fibrin clot lysis time in patients with CIHF but reduced fibrin clot lysis time in matched controls without IHD (median: 773 s (interquartile range: 689–936) vs. 658 s (618–823), p = 0.03). t-PA was increased following long-term RIC in CIHF patients (2.5 (1.7–3.4) vs. 2.9 (1.8–4.0), p = 0.03) and in matched controls without IHD (1.5 (1.3–1.9) vs. 1.6 (1.4–2.3), p = 0.03). Conclusions While long-term RIC did not affect collagen or arachidonic acid induced platelet aggregation, platelet turnover or sP-selectin, fibrinolysis was increased although most consistently in matched controls without IHD. This finding suggests that RIC may stimulate fibrinolysis potentially reducing the risk of thrombosis. [ABSTRACT FROM AUTHOR]

Introduction Current guidelines recommend acetylsalicylic acid (ASA) treatment after coronary artery bypass grafting (CABG) to reduce thrombotic vein graft occlusion. The optimal dosage of ASA is not known. Materials and methods Forty-two patients undergoing elective CABG were randomized to receive either ASA 75 mg or 160 mg once daily (OD) or 75 mg twice daily (BID) after the operation. Platelet function testing was performed before, and one and three months after the operation. Results White blood cell counts increased during the initial postoperative days whereas platelet counts were initially slightly reduced after the operation but increased after one month without any major changes of mean platelet volumes. Serum thromboxane B 2 was more effectively suppressed at one and three months after the operation with ASA 75 mg BID or 160 mg OD than with 75 mg OD ( p < 0.001). ASA 75 mg BID and 160 mg OD were equally effective. Adenosine diphosphate stimulated platelet aggregation in whole blood (Multiplate®) was increased one and three months after the operation, and this was counteracted by ASA 75 mg BID but not by 75 or 160 mg OD. Arachidonic acid-induced aggregation was more effectively inhibited by 75 mg BID or 160 mg OD compared to 75 mg OD at three months. Conclusions Less effective inhibition of platelet activation was obtained with ASA 75 mg OD than with ASA 160 mg OD or 75 mg BID up to three months after CABG. Especially the latter dose is of interest f o r further studies of efficacy and clinical outcomes after CABG. [ABSTRACT FROM AUTHOR]

Introduction: In this prespecified BRAVE 4 substudy we examined the antiplatelet and anticoagulant efficacy of clopidogrel plus heparin vs. prasugrel plus bivalirudin in patients with ST-segment elevation myocardial infarction. Methods: 26 patients received clopidogrel/heparin, 25 patients received prasugrel/bivalirudin and 20 additional untreated patients served as controls. Platelet aggregation was tested using whole blood impedance aggregometry. Dynamic platelet adhesion and aggregate formation to collagen were quantified under flow conditions. Coagulation tests included activated partial thromboplastin time (aPTT), international normalized ratio (INR) as well as rotational thrombelastography (ROTEM®). Analyses were performed 3 and 72 h after drug administration. Results: At 3, but not at 72 h we observed a significant increase in the inhibition of platelet aggregation in response to adenosine diphosphate (P < 0.01), but not to arachidonic acid, collagen or thrombin receptor agonist in the prasugrel/bivalirudin group compared to the clopidogrel/heparin group. Inhibition of platelet adhesion to collagen under flow was significantly stronger in the prasugrel/bivalirudin group at 3 and 72 h after drug administration (P < 0.01). APTT was significantly higher in the clopidogrel/heparin group (P < 0.05) and INR was significantly higher in the prasugrel/bivalirudin group (P < 0.01) 3 h after drug administration. Concerning ROTEM® analysis the drug combinations did not differ in reducing clot formation time (CFT) and both combinations did not influence maximum clot firmness (MCF) compared to the controls. Conclusions: We could demonstrate a more pronounced inhibition of platelet aggregation as well as platelet adhesion and aggregate formation to collagen under flow in prasugrel plus bivalirudin treated patients. [ABSTRACT FROM AUTHOR]

Introduction Multiple electrode aggregometry (MEA) improves prediction of thrombosis and bleeding in cardiac patients. However, the causes of inter-individual variation in MEA results are incompletely understood. We explore whether low MEA results are associated with platelet G-protein coupled receptor (GPCR) gene variants. Methods The effects of P2Y 12 receptor (P2Y 12 ), thromboxane A 2 receptor (TPα) and protease-activated receptor 1 (PAR1) dysfunction on the MEA ADP-test, ASPI-test and TRAP-test were determined using receptor antagonists. Cardiac surgery patients with pre-operative MEA results suggesting GPCR dysfunction were selected for P2Y 12 ( P2RY12 ), TPα ( TBXA2R ) and PAR1 ( F2R ) sequencing. Results In control blood samples, P2Y 12 , TPα or PAR1 antagonists markedly reduced ADP-test, ASPI-test and TRAP-test results respectively. In the 636 patients from a cohort of 2388 cardiac surgery patients who were not receiving aspirin or a P2Y 12 blocker, the median ADP-test result was 75.1 U (range 4.8-153.2), ASPI-test 83.7 U (1.4-157.3) and TRAP-test 117.7 U (2.4-194.1), indicating a broad range of results unexplained by anti-platelet drugs. In 238 consenting patients with unexplained low MEA results, three P2RY12 variants occurred in 70/107 (65%) with suspected P2Y 12 dysfunction and four TBXA2R variants occurred in 19/22 (86%) with suspected TPα dysfunction although the later group was too small to draw meaningful conclusions about variant frequency. All the variants were synonymous and unlikely to cause GPCR dysfunction. There were no F2R variants in the 109 cases with suspected PAR1 dysfunction. Conclusion MEA results suggesting isolated platelet GPCR dysfunction were common in cardiac surgery patients, but were not associated with non-synonymous variants in P2RY12 or F2R . [ABSTRACT FROM AUTHOR]

Abstract: Background: Detection of both thrombosis and bleeding risk are essential in clinical cardiology. Thrombin generated by activated platelets and from the extrinsic coagulation pathway is the major determinant of thrombogenesis and hemostasis. Although novel oral anticoagulants further increase the bleeding risk of antiplatelet drugs, platelet function tests do not reliably predict hemorrhagic complications. It seems that in addition to platelet aggregation, true assessment of bleeding risks requires the measurement of both platelet and plasma derived thrombin activity. Objective: To adapt a novel, near-patient test for the assessment of both antithrombotic and anticoagulant effects of oral thrombin inhibitors. Methods: The point-of-care Global Thrombosis Test (GTT), which measures platelet reactivity to shear-activation in native blood, was used. Thrombin, generated from activated platelets (procoagulant activity) plays a pivotal role in GTT measurement. In order to assess endogenous thrombin potential, in a separate blood sample thrombin generation was induced by microparticles formed during hypotonic hemolysis. Thus two blood samples were tested to measure simultaneously platelet reactivity (occlusion time, OT) and hemolysis (microparticles)-induced endogenous thrombin potential (OT-H). Results: In healthy subjects (n=32), OT measured in native blood was reduced in hemolysed blood (100% vs. 43±4%; OT vs. OT-H respectively). Shortening of OT in hemolysed blood (OT-H) was dose-dependently inhibited by the in vitro added thrombin inhibitor argatroban. In patients receiving dabigatran (n=27), OT and, to a lesser extent, OT-H was prolonged, compared to healthy volunteers. Intra-assay variation of OT-H was low (4.5%), but interindividual variation was great, both in healthy subjects (61%) and in patients on dabigatran (65%). Thrombin inhibitors argatroban, heparin (in vitro) and dabigatran (in vivo) all prolonged both OT and OT-H. There was no correlation between the measured OT and OT-H data. Conclusions: Microparticles shed from erythrocytes during hypotonic lysis of native blood considerably shortened OT. In a direct proportion to the applied concentrations, various thrombin inhibitors prolonged both OT (antithrombotic effect) and to a lesser extent, OT-H (anticoagulant effect). Further large studies are required to evaluate the usefulness of this technique in a clinical setting, in assessing the anticoagulant and antithrombotic effects of medication and relating GTT results with observed thrombotic and bleeding events. [Copyright &y& Elsevier]

Background: Pulmonary hemorrhage (PHEM) complicates the hospital course of 3-5% of preterm infants with respiratory distress syndrome (RDS), and bears a high mortality rate. Impaired thrombin generation and poor clot formation in premature neonates affect PHEM severity. Objectives: We evaluated the impact of surfactant upon in-vitro clot formation in order to assess the role of surfactant in the pathogenesis of PHEM. Methods: Blood samples were obtained from healthy volunteers for measuring complete blood count, PT, PTT, and platelet function. Surfactant at increasing concentrations was added to blood samples, and whole blood clotting assays were performed using rotation thromboelastogram (ROTEM®, Pentapharm Munich, Germany) and whole blood platelet adhesion and aggregation (Impact-R®, Diamed, Switzerland). Results: The mean PT level increased from 10.05±033 to 11.64±0.85sec (p=0.06) in the presence of surfactant. Platelet aggregation with the agonists adenosine diphosphate and epinephrine significantly decreased with escalating surfactant concentration (p<0.001). Adhesion, manifested by surface coverage (SC), significantly decreased with increasing surfactant concentration: mean SC 9.25±2.96 compared to 6.1±0.96 and 0.05±0.058 with 0/0.1/5mg/ml surfactant, respectively, p<0.001 Whole blood ROTEM studies showed a trend towards lengthening of clotting time with increased surfactant concentration and lower clot strength. Conclusion: The presence of surfactant impairs coagulation in-vitro. The risk of PHEM may therefore be greater in extremely premature infants. Future studies are required to assess the clinical significance and relevance of our preliminary findings. [ABSTRACT FROM AUTHOR]

Multiple electrode aggregometry (MEA) is used to measure platelet function. Pneumatic tube transport systems (PTS) for delivery of patient samples to a central laboratory are often used to reduce turnaround time for vital analyses. We evaluated the effects of PTS transport on platelet function as measured by MEA. Duplicate samples were collected from 58 individuals. One sample was sent using PTS and the other was carried by personnel to the lab. Platelet function was measured by means of a Multiplate® analyzer using the ADP test, ASPI test, COL test, RISTO test and TRAP test. Samples transported using PTS showed a reduction of AUC-values of up to a 100% of the average as compared to samples carried by personnel and a majority showed reductions of AUC-values greater than 20% of the average. Bias±95% limits of agreement for the ADP test were 26±56% of the average. Bias±95% limits of agreement for the ASPI test were 16±58% of the average. Bias±95% limits of agreement for the COL test were 20±54% of the average. Bias±95% limits of agreement for the RISTO were 14±79% of the average. Bias±95% limits of agreement for the TRAP test were 19±45% of the average. We conclude that PTS transport affect platelet activity as measured by MEA. We advise against clinical decisions regarding platelet function on the basis of samples sent by PTS in our hospital settings. [ABSTRACT FROM AUTHOR]

Abstract: Introduction: Analyses of platelet aggregation in hirudin whole blood using Multiplate® was validated. Reference intervals for the most commonly used agonists were established, and the association between platelet aggregation, age, gender and haematological values was analysed. Material and methods: We included 121 healthy individuals to establish reference intervals and six healthy individuals for evaluation of the day-to-day variation. Platelet aggregation was evaluated on hirudin whole blood employing Multiplate® induced by arachidonic acid, ADP, collagen and ristocetin (RISTOlow and RISTOhigh). Measurements of haematological values were performed employing Sysmex K-4500. Results: We found no association between platelet aggregation and age (p>0.57 for all agonists, except RISTOlow: p=0.05). Platelet aggregation was significantly higher in women compared to men for all agonists (p<0.0003), except RISTOlow (p=0.05). A reference interval is presented as 95% confidence interval suitable for any age and both sex. Day-to-day variation was <11% for all agonists except for RISTOlow. No association was found between platelet aggregation and haematocrit or red blood cell count after adjusting for age and gender except for RISTOhigh. A positive significant association was found between platelet count and platelet aggregation (p<0.04). Finally, a significant positive association was found between platelet aggregation and white blood cell count for all agonists (p<0.05) except RISTOlow and RISTOhigh (p>0.05). Conclusion: Reference intervals for platelet aggregation in healthy individuals (age: 17 to 66years) were established in hirudin whole blood measured by Multiplate® employing the most commonly used agonists. [Copyright &y& Elsevier]

Abstract: Background: Thiazolidinediones (TZDs) are agonists of PPARγ and exert beneficial metabolic effects in patients with diabetes. They may also affect platelet function. Objectives: To characterize potential platelet inhibitory effect of pioglitazone alone and in the presence of aspirin. Methods: 20 normal and 20 diabetic subjects were enrolled in a prospective study. On day 1, a blood sample was obtained at baseline and a second one after ingestion of 30mg of pioglitazone. PRP was prepared and platelet aggregation and release were evaluated using ADP, collagen and arachidonic acid as agonists. Subjects returned at 6–9days later after ingesting a single 81mg dose of aspirin and a third blood sample was obtained. The subjects then again ingested 30mg of pioglitazone and a fourth and final blood sample was obtained. Platelet aggregation and release were measured. PRP was incubated with thrombin to activate platelets, and the serum was separated and assayed for thromboxane B2, TGFβ and CD40L Results: Pioglitazone alone did not affect aggregation with arachidonic acid. However, following ingestion of both aspirin and pioglitazone aggregation was significantly decreased compared to aspirin alone (P<0.0001). Pioglitazone also potentiated aspirin-induced inhibition of ATP release using either arachidonic acid or collagen. Following pioglitazone alone, TXB2 release was 32,719±3,585pg/ml which was significantly reduced compared to baseline (42,075±4,479, P=0.0004). Pioglitazone also potentiated the inhibition of TXB2 release by aspirin. Conclusion: Pioglitazone inhibits platelet function and potentiates the inhibitory effects of aspirin. [Copyright &y& Elsevier]

Abstract: Introduction: Apoptotic cell death is a highly regulated genetic program, which has been observed in mature megakaryocytes fragmenting into platelets. The clock gene Per2, a key component of core clock oscillator, was involved in affecting both cell cycle control and apoptosis. Thus, loss of Per2 function may be considered potential influence of platelet formation and function. Methods: Per2-null mice and C57BL/6 mice were used in the study. Bleeding time, platelet count, megakaryocyte count, megakaryocyte ploidy, megakaryocyte apoptosis, rate of proplatelet formation, clot retraction, platelet aggregation and secretion were performed to evaluate thrombopoiesis and hemostasis. Quantitative RT-PCR was employed to analyze genes expression in liver, bone marrow and enriched megakaryocytes. Results: The Per2-null mice had nearly 50% platelet counts in peripheral blood. Per2-null platelets were compromised in their ability to aggregate and secretion, consistent with a marked reduction in the number of dense and a-granules. Megakaryocytes from Per2-null mice showed no significant variation in number but increased in ploidy. Ultrastructural examination of Per2-null megakaryocytes revealed many vacuoles in demarcation membranes and reduction in platelet granules. Megakaryocytes from Per2-null bone marrow decreased the rate of proplatelet formation and impaired apoptosis. Per2-null mice showed increased both in Tpo in livers and its receptors C-mpl in bone marrow, and the megakaryocytes from these mice decreased P53 expression, consequently increased Bcl-xl and Bcl-2 level. Conclusions: The clock gene Per2 modulating the apoptosis of megakaryocytes was required for platelet formation and function. [ABSTRACT FROM AUTHOR]

Abstract: Cardiac surgery involving cardio pulmonary bypass (CPB) may be associated with development of a coagulopathy that increases risk of bleeding. In the present ex vivo study we investigated the influence of fibrinogen and rFVIIa, alone or in combination, on whole blood coagulation thromboelastometry using pre- and postoperative blood samples from 18 consecutive adult patients undergoing CPB surgery. Dynamic thromboelastometric clotting profiles were recorded using citrated whole blood activated with trace amounts of tissue factor (Innovin®, final dilution 1:17000). Blood samples were collected before surgery (control) and postoperative samples were obtained following in vivo neutralization of heparin with protamine sulphate. All blood samples were treated with heparinase to ensure neutralization of possible residual heparin effect. The post-operative blood samples were spiked with buffer, rFVIIa (2 µg/mL), fibrinogen (1 mg/mL), or the combination of rFVIIa and fibrinogen. Despite neutralization of heparin, CPB surgery left a measurable coagulopathy that was thromboelastometrically characterized by prolonged onset of clotting, reduced maximum velocity of clot formation (MaxVel), and decreased maximum clot firmness (MCF). Ex vivo spiking of the postoperative samples with rFVIIa shortened the clotting time. Fibrinogen also shortened the clotting time and, in addition, improved the MaxVel, and MCF. Finally, adding the combination of rFVIIa and fibrinogen to the postoperative samples corrected all thromboelastometric parameters to the preoperative range. In conclusion, the correction of whole blood clotting abnormalities that occurs with rFVIIa and/or fibrinogen suggests that future clinical trials on treatment of bleeding during CPB surgery should study the haemostatic effect of fibrinogen or possibly the combination of rFVIIa and fibrinogen. [Copyright &y& Elsevier]

Abstract: Objective: The purpose of the present study was to explore the platelet function during the perioperative period of orthotopic liver transplantation (OLT) due to the underlying liver disease. Methods: The blood coagulation parameters, platelet surface markers and the determination of platelet aggregation were analyzed in 34 patients who underwent OLT. Blood samples were drawn preoperatively, anhepatic, 10min and 1hour after reperfusion, 1day, 3 and 7days postoperatively. Conventional coagulation screens, thrombopoietin (TPO) serum levels, P-selectin, GPIIb/IIIa and GPIb binding sites on the surface of platelets as evaluated by flow cytometry and platelet aggregation response were measured. Results: Coagulation factors, maximum aggregation and rate of aggregation were significantly different before transplantation due to the underlying liver disease. Further we found a markedly depressed GPIIb/IIIa and P-selectin expression and a reduced rate of aggregation in all patients throughout the study. In contrast maximum aggregation of platelets was restored on the third day after reperfusion without intergroup differences and almost comparable to healthy controls. An inverse correlation was found between peripheral platelet count pre-transplantation and peak TPO concentrations one weak post-transplantation. Conclusions: In the entire process of OLT, coagulation factors, maximum aggregation and rate of platelet aggregation depend on the surgical phases during transplantation and on the underlying liver disease. The data obtained in this study might contribute to a better understanding of the pathophysiology and assessment of bleeding risk in OLT. [Copyright &y& Elsevier]

Abstract: Introduction: A simple, validated method to measure platelet function is unavailable for bedside use. Measurement of platelet retention rate using a column of collagen-coated beads and whole blood is a new, simple assay that reflects platelet aggregation. This study was aimed to examine the utility of this assay to assess efficacy of antiplatelet drug therapy. Methods: Citrated whole blood (1.5 ml) in a syringe was passed through a polyvinyl tube packed with collagen-coated beads for 40 seconds using a syringe pump. Platelet retention rate in the column was calculated from platelet counts in blood before and after passage. An increase in the retention rate reflects an increase in platelet activity. This new platelet retention assay and the traditional optical aggregometry assay were performed in 331 patients with stable coronary artery disease (CAD). Results: The retention rate was significantly reduced in patients taking dual antiplatelet therapy (aspirin plus clopidogrel or ticlopidine) compared with aspirin alone. There was a significant linear correlation between the platelet retention rate and platelet aggregability measured by the traditional method (r=0.44, p<0.001). In multivariate Cox proportional hazards analysis, higher platelet retention rate was an independent predictor of future cardiovascular events in patients on dual antiplatelet therapy (hazard ratio 3.9, 95% CI 1.6 to 9.5, p=0.003). Conclusions: Measurement of the platelet retention rate in a column of collagen-coated beads may be useful for monitoring the efficacy of antiplatelet drug therapy in patients with CAD. [Copyright &y& Elsevier]

Abstract: Introduction: There are some studies reporting that platelets might have a role in cases with recurrent fetal losses. The aim of this study is to evaluate the importance of platelet aggregation abnormalities in this patient group. Materials and methods: In this study, platelet aggregation abnormalities were compared in 56 cases with recurrent fetal losses (29 of these 56 patients have ≥3 losses) and in 33 healthy female controls with no previous history of fetal loss. Platelet aggregation studies were performed with optical turbidometric method by using ADP (5 μM), collagen (0.2 mg/ml) and epinephrine (10 μM). Results: We did not find any statistically significant difference between patient (56 cases with ≥2 fetal losses and 29 of them with ≥3 fetal losses) and control groups for platelet aggregation abnormalities. Conclusions: The data we have obtained suggest that severe platelet aggregation abnormalities are not the rule in patients with recurrent fetal losses. [Copyright &y& Elsevier]

Abstract: Introduction: We have previously demonstrated platelet hyperreactivity in cystic fibrosis (CF) patients. Carriers of one CF mutation (heterozygotes) have been shown to have abnormalities related to the presence of only one-half the normal amount of CF transmembrane conductance regulator protein. Platelet hyperreactivity in CF heterozygotes would be an important cardiovascular risk factor, since approximately 1 in 25 Caucasians is a CF carrier. Materials and methods: We used highly sensitive assays of platelet activation to assess the difference between 16 CF heterozygotes and 16 age- and sex-matched healthy controls without CF mutations. Results: We found no difference in platelet activation between CF heterozygotes and controls. Conclusions: The 50% reduction in the CF transmembrane conductance regulator protein in heterozygotes is insufficient to cause platelet activation. [Copyright &y& Elsevier]

Abstract: Aspirin resistance refers to less than expected suppression of thromboxane A2 production by aspirin and has been reported to be independently associated with an increased risk of adverse cardiovascular events. Possible causes of aspirin resistance include poor compliance, drug interaction, inadequate aspirin dose, increase turnover of platelets, genetic polymorphisms of cyclo-oxygenase-1, and upregulation of alternate (non-platelet) pathways of thromboxane production. Laboratory methods used to detect aspirin resistance include those that measure thromboxane A2 production and thromboxane A2-dependent platelet function. However, since there is currently no standardised approach to the diagnosis and there are no proven effective treatments for aspirin resistance that improve outcome, patients with cardiovascular disease receiving aspirin should not be routinely tested for aspirin resistance. Instead physicians should be aware of the factors that may impair aspirin function, ensure that they use an appropriate dose of aspirin and optimise compliance with aspirin therapy. Further research exploring the mechanisms of aspirin resistance is needed in order to better define and develop a standardised test for aspirin resistance that is specific, reliable, can be readily applied in routine laboratories and correlate with an increased risk of cardiovascular events. [Copyright &y& Elsevier]

Abstract: Introduction: The marked interindividual variability in platelet inhibition even after administration of high loading doses of clopidogrel raised the question whether monitoring of antiplatelet effects in patients undergoing percutaneous coronary intervention (PCI) can improve clinical outcome. Established methods for monitoring antiplatelet drug activity such as optical aggregometry and determination of surface protein expression are not suitable for routine bedside testing. Material and methods: We therefore compared the applicability of whole blood impedance aggregometry (20μmol/L ADP) and the whole blood bedside ULTEGRA assay with ADP-cartridges (20μmol/L) with optical aggregometry in platelet-rich plasma and determination of surface protein expression (P-Selectin and activated GPIIb/IIIa) by flow cytometry. We analyzed samples obtained from 27patients scheduled for elective PCI who received a loading dose of 600mg of clopidogrel. Blood samples were withdrawn before clopidogrel, before PCI and 24h thereafter. Results: Platelet aggregation assessed by optical aggregometry (20μmol/L ADP) declined from 65±9% (baseline) to 42±12% (PCI) and 45±13% (24h; p <0.01). Expression of surface proteins displayed a similar time course. Platelet aggregation determined by impedance aggregometry decreased from 4.6±4.0Ω (baseline) to 0.1±0.3Ω (PCI) and 0.5±1.1Ω (24h) with no detectable residual platelet aggregation during PCI in 88% of patients. The ULTEGRA assay showed only slight changes after administration of clopidogrel. Correlation analysis between the various assays revealed significant correlations only between optical aggregometry and flow cytometry. Conclusions: The results indicate that both of the whole blood assays cannot substitute for optical aggregometry or determination of surface proteins in the assessment of clopidogrel-induced platelet inhibition. [Copyright &y& Elsevier]

Abstract: Introduction: Platelet activation needs a high energy demand which is supplied by the degradation of glucose into lactate. Platelet response to agonists in patients with primary thrombocythemia is defective. We studied the production of lactate by the platelets of patients with this disease and defective platelet aggregation. Material and methods: Ten patients suffering from primary thrombocythemia and ten controls were included in this study. The lactate generation was measured in resting and thrombin activated platelets in absence or presence of glucose. Results: Resting platelets incubated for 30 min in phosphate-buffered saline (PBS) generated the same amount of lactate in patients (44.6±21.6 μmol/1011 cells) and controls (41.0±17.3 μmol/1011 cells). Addition of glucose led to similar increases in lactate formation by platelets in patients (82.2±26.4 μmol/1011 cells) and controls (88.1±34.5 μmol/1011 cells). The addition of thrombin in absence of glucose did not modify the lactate formation respective to PBS. Finally, the incubation of platelets with both glucose and thrombin caused further increases in the generation of lactate in both groups, patients (236.9±83.9 μmol/1011 cells) and controls (228.6±63.5 μmol/1011 cells) without differences between them. The production of lactate in both groups was also similar when platelets were incubated for 10 min or 20 min with both thrombin and glucose. However at 5 min, platelets of patients generated more lactate (97.8±23.7 μmol/1011 cells) than controls (66.5±38.7 μmol/1011 cells, p <0.05). Conclusions: These results suggest that thrombin is able to induce an initial hyperactivity of those pathways involved in the platelet energy production of patients with primary thrombocythemia. [Copyright &y& Elsevier]

Abstract: Background/Objectives: Bleeding problems during laparoscopic surgery are infrequent. We hypothesised that increased abdominal pressure during the application of the pneumoperitoneum would lead to an increased release of endogenous vasopressin which could then contribute to the hemostasis by increasing platelet reactivity, FVIII and von Willebrand-factor. Patients and methods: We compared the vasopressin levels, the platelet function as measured by the PFA-100-test, aPTT and FVIII in 39 consecutive patients who underwent elective hysterectomy (20 with the laparoscopic and 19 with the conventional, “open” method). Blood was sampled the day before surgery and 2, 4 and 72 h after the induction of anaesthesia. Results: After two hours, the PFA-100 closure times with collagen/ADP decreased to lower levels in the laparoscopic group (from 93±22 to 82±20, mean±SD) and even further down to 65±13 s (compared to 82±20 s) (p =0.024)) four hours after the beginning of surgery. Vasopressin levels and F VIII increased in both groups but there was no significant difference between the groups (21 vs. 17.8 pmol/l for vasopressin, differences of the mean). Bleeding was minimal, with a trend to lower Hb-levels in the laparotomy group. Conclusions: The procedural difference of laparoscopic vs. open hysterectomy appears to enhance platelet reactivity by other mechanisms than increased vasopressin levels and may contribute to an enhanced hemostatic competence in laparoscopic surgery. [Copyright &y& Elsevier]

Abstract: Introduction: Clopidogrel inhibits the ADP subtype P2Y12 receptor. Recently, polymorphisms of this receptor have been associated with different degrees of platelet aggregation in healthy volunteers and have been suggested to modulate clopidogrel response. However, the role of gene sequence variations of the P2Y12 receptor in patients treated with clopidogrel has not yet been assessed. Materials and methods: The T744C polymorphism of the P2Y12 receptor gene was assessed in 119 patients: 36 undergoing coronary stenting receiving a 300 mg loading dose (Group A) and 83 on long-term clopidogrel (75 mg/day) treatment (Group B). Patients were divided into 2 subgroups according to the presence or absence of the C allele: carriers (CT heterozygotes and CC homozygotes) and non-carriers (TT homozygotes). Platelet aggregation, assessed by light transmittance aggregometry following ADP, collagen, TRAP and epinephrine stimuli, and platelet activation (GP IIb/IIIa activation and P-selectin expression), assessed by whole blood flow cytometry in ADP and TRAP-stimulated platelets, were performed. Platelet function was assessed at baseline and 4 and 24 h following clopidogrel loading dose in Group A and when patients where on clopidogrel treatment for at least 1 month in Group B. Results: The genotype distribution of Group A was: 22/36 (61.1%) non-carriers and 14/36 (38.9%) carriers of the C allele; Group B: 57/83 (68.7%) non-carriers and 26/83 (31.3%) carriers of the C allele. There were no differences between groups for all the assessed platelet function assays. Conclusions: The T744C polymorphism of the P2Y12 receptor gene does not modulate platelet response to clopidogrel either in the early or long-term phases of treatment. This specific gene polymorphism alone is therefore unlikely to be the cause of variability in individual response to antiplatelet therapy. [Copyright &y& Elsevier]

Abstract: Introduction: Moderate and regular consumption of wine reduces the risk of acute coronary thrombotic events. The mechanism of the anti-thrombotic effect of wine is not clear. Extract or purified ingredients of grapes have not yet been studied for anti-thrombotic effect. Materials and methods: Anti-thrombotic effect of proanthocyanidin, a highly purified ingredient of grape seed, was assessed by a shear-induced thrombosis test in vitro and by a laser-induced thrombosis test in the mouse carotid artery, in vivo. Results and conclusions: Intravenously (20 mg/kg body weight, BW) or orally (2×200 mg/kg BW) administered proanthocyanidin significantly inhibited the laser-irradiation induced thrombus formation in the carotid artery (both P=0.01). Subsequent to oral administration of proanthocyanidin, in vitro platelet reactivity to shear stress has been inhibited. The latter suggests that the in vivo anti-thrombotic effect of proanthocyanidin may be due to a direct inhibitory effect on platelets. [Copyright &y& Elsevier]

Introduction: Platelets are involved in the pathogenesis of atherosclerosis. Although physical exercise is recommended to prevent atherosclerosis, the effect of exercise on platelet function and the underlying mechanisms of these effects are not completely understood. Accordingly, we aimed to examine the effect of different intensities acute arm exercises on platelet function. In addition, we evaluated the effect of lipid peroxidation and fluid shear rate on platelet response. Materials and methods: Twenty four healthy sedentary male volunteers aged 18–24 years performed submaximal and incremental exercises by upper extremity ergometer. The shear rate in the right artery was measured by Power Doppler Ultrasound (US) at rest and immediately after exercise. Pre and postexercise maximum intensities of ADP and collagen-induced platelet aggregation were measured using the impedance technique. Bioluminescent detection of thrombin-induced platelet ATP release and measurement of thromboxane B2 (TxB2) levels (as a marker of thromboxane A2 (TxA2) formation) by enzyme-linked immunoassay were performed before and after exercise. Results and conclusion: Shear rate increased after both submaximal and incremental exercise. Collagen-induced platelet aggregation increased after submaximal exercise, while ADP-induced aggregation and thromboxane B2 levels did not alter with this protocol. Incremental exercise caused increased collagen and ADP-induced platelet aggregation and thromboxane B2 levels. Neither of the protocols altered platelet ATP release. It was shown that acute upper extremity exercise increased platelet aggregation, without an increase in platelet release. Collagen-induced signalling pathways were more sensitive than those induced by ADP. The increase in thromboxane B2 after incremental exercise implied increase in thromboxane A2 formation and lipid peroxidation. Despite a significant correlation between platelet aggregation and thromboxane B2 levels at rest, we found no clear-cut relationship between thromboxane A2 formation, blood shear rate and platelet response to exercise. [Copyright &y& Elsevier]

Abstract: Introduction: Current guidelines still recommend the bolus and infusion administration of glycoprotein IIbIIIa inhibitors in patients with high-risk acute coronary syndrome undergoing percutaneous coronary intervention. We sought to evaluate the extent of platelet inhibition by a blocking and bridging strategy with intracoronary abciximab bolus-only administration and oral loading of adenosine diphosphate receptor antagonists. Patients and methods: Fifty-six consecutive high-risk acute coronary syndrome patients with bolus-only abciximab administration (0.25mg/kg i.c.) and loading with 600mg clopidogrel (55%) or 60mg prasugrel (45%) were included in this study. Platelet aggregation induced by thrombin receptor-activating peptide and adenosine diphosphate was measured by multiple electrode aggregometry up to 7days. Results: Thrombin receptor-activating peptide induced platelet aggregation was significantly suppressed for a minimum of 48h (45±17U) and returned to a normal range (>84U) after 6days (90±26U; p<0.001). Co-medication with prasugrel significantly reduced adenosine diphosphate-induced (p=0.002) and thrombin receptor-activating peptide-induced (p=0.02) platelet aggregation compared with clopidogrel throughout the observation period. No stent thrombosis or repeat myocardial infarction occurred at 30-day follow-up. Conclusions: Immediate blocking of platelet aggregation in high-risk acute coronary syndrome patients by intracoronary abciximab bolus-only administration and bridging to prolonged inhibition via oral blockade of ADP receptors effectively inhibited overall platelet reactivity for at least 48h, questioning the value of continuous abciximab infusion. Co-medication with prasugrel vs. clopidogrel synergistically augmented platelet inhibition. [Copyright &y& Elsevier]

Abstract: Interactions with exposed subendothelial extracellular proteins and cellular integrins (endothelial cells, platelets and lymphocytes) can cause alterations in the hemostatic system associated with atherothrombotic processes. Many molecules found in snake venoms induce pathophysiological changes in humans, cause edema, hemorrhage, and necrosis. Disintegrins are low molecular weight, non-enzymatic proteins found in snake venom that mediate changes by binding to integrins of platelets or other cells and prevent binding of the natural ligands such as fibrinogen, fibronectin or vitronectin. Disintegrins are of great biomedical importance due to their binding affinities resulting in the inhibition of platelet aggregation, adhesion of cancer cells, and induction of signal transduction pathways. RT-PCR was used to obtain a 216bp disintegrin cDNA from a C. s. scutulatus snake venom gland. The cloned recombinant disintegrin called r-mojastin 1 codes for 71 amino acids, including 12 cysteines, and an RGD binding motif. r-Mojastin 1 inhibited platelet adhesion to fibronectin with an IC50 of 58.3nM and ADP-induced platelet aggregation in whole blood with an IC50 of 46nM. r-Mojastin 1 was also tested for its ability to inhibit platelet ATP release using PRP resulting with an IC50 of 95.6nM. MALDI-TOF mass spectrum analysis showed that r-mojastin has a mass of 7.95676kDa. [ABSTRACT FROM AUTHOR]