Platelet Aggregation In Healthy Volunteers Research Articles

The role of the hydrogen sulfide donor in adenosine diphosphate-induced platelet aggregation in patients with coronary heart disease

Introduction. Platelet activation is the initial stage of thrombotic complications in pathological conditions, primarily in atherosclerotic cardiovascular diseases. Endogenous hydrogen sulfide (H2S) is an antiplatelet agent, but the specific ways to realize its effects are not studied enoughAim: To study the effect of H2S on adenosine diphosphate (ADP)-induced platelet aggregation in patients with coronary heart disease (CHD) with blockers of Na+,K+,2Cl- cotransporter (NKCC), an anion exchanger, and a phosphodiesterase (PDE) inhibitor of cyclic nucleotides.Material and Methods. The study included 22 patients with CHD. The control group included 14 healthy volunteers. Platelet aggregation was determined by turbidimetric method. The degree of aggregation (%) and the size of aggregates (rel. units) were measured. ADP (2 μM) was an aggregation inductor. In some cases the incubation medium contained the hydrogen sulfide donor NaHS (1–100 μM) and aggregation modifierResults. The H2S donor at a concentration of 100 μM reduced the parameters of ADP-dependent platelet aggregation in healthy volunteers and increased it in patients with coronary artery disease. NKCC and anion exchanger blockers, as well as a PDE inhibitor, reduced ADP-dependent platelet aggregation in healthy volunteers. The combined action of these agents and NaHS enhanced the inhibitory effects of the applied modifiers. The results obtained for platelet aggregation in patients with coronary artery disease differed in different directionConclusion. The obtained data indicate that the antiaggregation effect of H2S is realized through the effect on the NKCC and anion exchanger, as well as due to the effect on the links of the signaling system mediated by cyclic nucleotides.

Rekombinant Granülosit Koloni-Stimüle Edici Faktör ve Granülosit-Makrofaj Koloni-Stimüle Edici Faktörün Sağlıklı Gönüllülerde Platelet Agregasyonu Üzerine Etkileri

Objective: Recombinant human granulocyte colony-stimulating factor (G-CSF) is increasingly used for stem cell mobilization in healthy donors for allogeneic stem cell transplantation. However, a possible association between thrombosis and G-CSF administration has been reported. This study was performed to investigate the in vitro effects of G-CSF and granulocyte-macrophagecolony-stimulating factor (GM-CSF) on platelet aggregation in healthy volunteers. Material and Methods: Platelet aggregation was induced by adenosinediphosphate (ADP) and collagen in platelet rich plasma (PRP) and whole blood (WB) samples from 26 healthy volunteers (20 volunteers for G-CSF, and 6 volunteers for GM-CSF study). Three concentrations of G-CSF solution (10, 50 and 100 ng/mL) and GM-CSF (5, 10 and 20 ng/mL) were prepared. Each concentration of G-CSF and GM-CSF solutions and the control diluent were incubated with PRP and WB samples. After incubation, aggregation responses were evaluated with ADP (1 µM and 5 µM) and collagen (1 µg/mL) in PRP and WB samples. Results: We found that G-CSF increased ADP and collagen induced platelet aggregation in PRP and ADP induced platelet aggregation rate in WB. GM-CSF didn't affect ADP and collagen induced platelet aggregation rate in whole blood and platelet-rich plasma in vitro. Conclusion: This study showed that G-CSF administration may lead to platelet hyperaggregability. The enhancing effect of G-CSF on platelet aggregation should be taken into consideration in clinical usage.

Precision and reliability of 5 platelet function tests in healthy volunteers and donors on daily antiplatelet agent therapy.

Anticoagulation protocols used during mechanical circulatory support call for titration of antiplatelet agents. We compared the precision and reliability of 5 platelet function tests in healthy volunteers and donors on daily antiplatelet therapy to distinguish their efficacy for titrating antiplatelet therapy. We assessed arachidonic acid-induced platelet function by light transmission aggregometry (LTA), Multiplate impedance aggregometry, VerifyNow, and platelet mapping by thromboelastography (TEG PM). We assessed ADP-induced platelet function by the same methods and flow cytometry. Forty healthy volunteers and 10-13 volunteers on daily aspirin and/or clopidogrel therapy were evaluated. We compared tests for intraassay precision, interassay precision (samples from 2 separate blood draws), and reliability coefficient. For arachidonic acid-induced platelet aggregation in healthy volunteers, intra- and interassay CVs were ≤ 10% for all methods. Intra- and interassay precision among donors on daily aspirin was ≤ 30% for all methods except LTA (38% interassay CV) and TEG PM (95% intraassay and 104% interassay CV). For ADP-induced platelet function, intra- and interassay precision was ≤ 10% and ≤ 30% for all methods. Only Multiplate demonstrated moderate or greater (R > 0.40) reliability coefficients for arachidonic acid-induced platelet function among all subjects. All methods of ADP-induced platelet function, except TEG PM, demonstrated substantial or greater (R > 0.60) reliability among all subjects. TEG PM is least suited to monitor effects of antiplatelet agents. Multiplate impedance aggregometry was the only method to demonstrate an acceptable reliability coefficient among healthy volunteers and donors on both aspirin and clopidogrel therapy.

α2A-Adrenergic receptor polymorphism potentiates platelet reactivity in patients with stable coronary artery disease carrying the cytochrome P450 2C19*2 genetic variant.

Platelet α2A-adrenergic receptors (ARs) mediate platelet aggregation in response to sympathetic stimulation. The 6.3-kb variant of α2A-AR gene is associated with increased epinephrine-induced platelet aggregation in healthy volunteers. The cytochrome P450 2C19*2 (CYP2C19*2) loss-of-function allele influences P2Y12-mediated platelet inhibition and hence the rate of major adverse cardiovascular events. We assessed the influence of 6.3-kb α2A-AR gene variant on platelet aggregation and its interaction with CYP2C19*2 loss-of-function allele in patients with stable angina on aspirin and clopidogrel (dual antiplatelet therapy). Aggregation to 5 increasing doses of epinephrine (from 0.156 to 10 μmol/L) was assessed in aggregation units by Multiplate Analyzer and platelet reactivity in P2Y12 reactivity units and % inhibition by VerifyNow P2Y12 assay before percutaneous revascularization. Gene polymorphisms were analyzed with TaqMan Drug Metabolism assay. Of 141 patients, aggregation was higher in 6.3-kb carriers (n=52) when compared with wild types (n=89) at all epinephrine doses (P<0.05) apart from 10 μmol/L (P=0.077). Percentage inhibition was lower (P=0.048) in 6.3-kb α2A-AR carriers. Percentage inhibition was lower (P=0.005) and P2Y12 reactivity units was higher (P=0.012) in CYP2C19*2 allele carriers. Higher P2Y12 reactivity units (P=0.037) and lower percentage inhibition (P=0.009) were observed in carriers of both 6.3-kb α2A-AR variant and CYP2C19*2 allele when compared with wild-type or with either mutation on its own. The 6.3-kb α2A-AR variant is associated with increased platelet reactivity to epinephrine and has an additive effect along with CYP2C19*2 loss-of-function allele on P2Y12-mediated platelet responses in patients with stable angina on dual antiplatelet therapy.

The effect of desmopressin on bleeding time and platelet aggregation in healthy volunteers administered ticagrelor

Ticagrelor is a reversibly binding and selective P2Y12 -receptor antagonist approved for the prevention of atherothrombotic events in patients with acute coronary syndromes. As bleeding events remain a hazard with antiplatelet therapy, this study investigated the effect of the vasopressin agonist, desmopressin, on ticagrelor-induced bleeding time prolongation. Desmopressin has previously been shown to improve primary haemostasis and is widely used as first-line therapy for individuals with bleeding disorders. In a randomized, double-blind, 2-period crossover study, healthy volunteers received ticagrelor (270mg loading dose; 180mgbid) for 5days. On Day 5, desmopressin (0·3μg/kg) or saline intravenous infusions were administered. The impact of desmopressin on bleeding time, inhibition of platelet aggregation (IPA), platelet function and ticagrelor pharmacokinetic parameters was investigated. Twenty-one volunteers (81% male) were enrolled. Median [range] bleeding times were slightly reduced with ticagrelor plus desmopressin compared with ticagrelor alone (7·50 [3-17] vs. 10·50 [3-25] min at 2·5h). Median reductions in bleeding time from baseline were generally similar between ticagrelor plus desmopressin compared with ticagrelor alone at all time points. Co-administration of desmopressin had no impact on IPA, although platelet reactivity was significantly increased (von Willebrand Factor antigen: GLS mean AUEC was 4667%.h for ticagrelor plus desmopressin compared with 2750%.h for ticagrelor alone). Desmopressin did not influence the pharmacokinetics of ticagrelor. Desmopressin had no significant effect on bleeding time or inhibition of platelet aggregation by ticagrelor, although primary haemostatic activity was significantly increased. Ticagrelor pharmacokinetic parameters were not affected by co-administration with desmopressin. Therefore, desmopressin is unlikely to be an effective therapeutic agent for control of the potential bleeding events associated with ticagrelor.

Etodolac, a well known cyclooxygenase inhibitor with preferential COX-2 inhibition, shows no influence on platelet aggregation in healthy volunteers

Etodolac, a well known cyclooxygenase inhibitor with preferential COX-2 inhibition, shows no influence on platelet aggregation in healthy volunteers

Role of the T744C polymorphism of the P2Y12 gene on platelet response to a 600-mg loading dose of clopidogrel in 597 patients with non-ST-segment elevation acute coronary syndrome

Background Variability in platelet response to clopidogrel and its clinical relevance have been well described. However, the underlying mechanisms remain unclear. Recently, the T744C polymorphism of the P2Y12 receptor gene has been associated with enhanced platelet aggregation in healthy volunteers, suggesting a possible mechanism for modulation of clopidogrel response. Aim of this study To assess whether the clopidogrel response may be influenced by the T744C P2Y12 gene polymorphism in patients with non ST elevation acute coronary syndrome (NSTE ACS). Methods 597 NSTE ACS patients were included in our study and were divided into 3 groups: CC homozygotes, CT heterozygotes ad TT homozygotes. All patients received loading doses of 600 mg clopidogrel and 250 mg aspirin at least 12 hours before blood samples. Clopidogrel response was assessed by post-treatment ADP 10 μmol/L-induced platelet aggregation (ADP-Ag), VASP phosphorylation (PRI VASP) and P-selectin expression (PS). Clopidogrel resistance was defined by persistence of High Post-treatment Platelet Reactivity (HPPR = ADP-Ag > 70%). Results Significant variability in the distribution of platelet parameters was observed in the overall study population. No significant difference in platelet parameter profiles was observed within patients having the same genotype, for ADP-Ag ( p = 0.39), PRI VASP ( p = 0.97) and PS ( p = 0.62). The genotype frequencies of the T744C polymorphism of the P2Y12 gene were similar in responders and non responders defining by HPPR ( p = 0.75). Conclusion Our study did not show any influence of the T744C polymorphism of the P2Y12 receptor gene on clopidogrel response assessed by ADP-Ag, PRI VASP or P-selectin expression in NSTE ACS patients.

Lack of effect of enteric coating on aspirin-induced inhibition of platelet aggregation in healthy volunteers

Aspirin inhibits platelet aggregation and is widely used in the treatment of cardiovascular disease. Some individuals are less responsive to aspirin's antiplatelet effect, a phenomenon termed aspirin resistance. It is not known whether the antiplatelet effect is fully preserved with the enteric-coated (EC) formulation. We performed a prospective randomized trial of 50 healthy volunteers using a crossover design to compare the EC with the standard aspirin formulations. The subjects received a 7-day course of each aspirin formulation (81-mg) (Bayer Corporation, Morristown, NJ) separated by a 3-week washout period. Platelet function was measured before and after each course using optical aggregometry (with arachidonic acid and adenosine diphosphate as agonists) and a point-of-care platelet assay. The assays were reproducible, and the variation in baseline platelet function was small to moderate between the subjects. There was no difference in the extent of platelet inhibition between the EC and standard formulations with any of the 3 assays. With the point-of-care platelet assay, the mean aspirin effect favoring the standard formulation (more aggregation inhibition) compared with the EC formulation was 1.6% +/- 15.8% (P = .60 for difference between the formulations). The corresponding optical aggregometry values were -3.4% +/- 39.5% (P = .97) and -1.4% +/- 16.6% (P = .75) for arachidonic acid and adenosine diphosphate, respectively. Compared with standard aspirin, EC aspirin appears to exhibit similar inhibition of platelet aggregation in healthy volunteers. Furthermore, point-of-care platelet assessment correlated well with the gold standard of laboratory-based optical platelet aggregometry.

The Genotypic Combination of Homozygous Carriers of Both H1 Haplotype and 34C Shows a Significantly Lower Responsiveness to ADP-Induced Platelet Aggregation Than Others in Healthy Volunteers.

BACKGROUND: The adenosine diphosphate (ADP) receptor, P2Y12, plays a central role in platelet activation and its blocker clopidogrel reduces the incidence of cardiovascular events. Recently, the polymorphisms of the P2Y12 gene (H1 and H2 haplotype) was shown to be associated with increased ADP-induced platelet aggregation in healthy volunteers. In addition, the polymorphism (C34T) of the P2Y12 gene was reportedly associated with higher numbers of cerebrovascular events in patients with PAD receiving clopidgrel therapy. However, it is totally unknown if there is any association between polymorphisms combination and platelet reactivity. In this study, we aimed to investigate in detail about the association between ADP-induced platelet aggregation and the polymorphisms of P2Y12 gene, haplotype and C34T, in healthy volunteers.METHODS AND RESULTS: We determined P2Y12 genotype and platelet reactivity in 267 healty volunteers. Genotyping was performed using direct sequencing or a single nucleotide primer extension (SNuPE). In previous study, H1 and H2 haplotype were defined by 4 polymorphisms, C139T, T744C and insertion801A in intron1 and G52T in exon2, and there were in complete linkage disequilibrium. Result of genotyping of haplotype, however, G52T was found not to be in complete linkage disequilibrium. Allele frequencies of H1 and H2 were 0.83 and 0.17, respectively. For C34T, allele frequencies of 34C and 34T were 0.75 and 0.25, respectively. Platelet reactivity was evaluated by optical aggregometry in platelet-rich plasma. Aggregation was induced by 2 or 5 μmol/L ADP to evaluate maximal aggregation (%) and the area under the aggregate curve (AUC) for 6 min. Maximal aggregation induced by 2 μmol/L ADP was similar in homozygous carriers of H1 haplotype and carriers of H2 haplotype (p=0.262). AUC induced by 2 μmol/L ADP was lower in homozygous carriers of H1 haplotype than carriers of H2 haplotype (p=0.074). However, haplotype was not associated with platelet reactivity induced by 5 μmol/L ADP. For C34T, whereas, maximal aggregation and AUC induced by 2 or 5 μmol/L ADP was lower in homozygous carriers of 34C than carriers of 34T (p=0.009 and p=0.006 or p=0.002 and p=0.003, respectively). Furthermore, for the genotypic combination of haplotype and genotype (C34T), maximal aggregation and AUC induced by 2 or 5 μmol/L ADP was significantly lower in homozygous carriers of both H1 haplotype and 34C than others (p=0.003 and p<0.001 or p=0.05 and p=0.007, respectively). When platelet aggregation was induced by 1 mg/mL Collagen, the same trends were observed.CONCLUSIONS: We demonstrated that polymorphisms of the P2Y12 gene are associated with increased ADP-induced platelet aggregation, moreover, that group with genotypic combination of homozygous carriers of both H1 haplotype and 34C shows a significantly lower responsiveness to ADP-induced platelet aggregation than others in healthy volunteers. This suggests the possibility that polymorphisms of the P2Y12 gene are related to the receptor expression of P2Y12.

P2Y12 gene H2 haplotype is not associated with increased adenosine diphosphate-induced platelet aggregation after initiation of clopidogrel therapy with a high loading dose

A large variability in the antiplatelet response to clopidogrel has been consistently reported. Recently, a P2Y12 haplotype was shown to be associated with enhanced adenosine diphosphate (ADP)-induced platelet aggregation in healthy volunteers. The aim of this study was to test in patients (n = 416) scheduled for coronary artery stenting whether P2Y12 haplotype H2 carriage is associated with increased ADP-induced platelet aggregation after administration of a 600 mg loading dose of clopidogrel. Blood was drawn from the arterial sheath at least 2 h after administration of 100 mg aspirin and 600 mg clopidogrel. ADP-induced platelet aggregation was assessed in platelet-rich plasma with light-transmission aggregometry. P2Y12 haplotypes (H1/H2) and P2Y12 C32T genotypes were determined with TaqMan assays. Haplotype combinations and genotypes were not associated with parameters of ADP-induced platelet aggregation after administration of a 600 mg loading dose of clopidogrel. Maximal ADP (5 mumol/l)-induced platelet aggregation was similar in patients carrying haplotype H2 and homozygous carriers of haplotype H1 (43.9 +/- 21.4 versus 43.2 +/- 21.1%, respectively; P = 0.77). Carriage of P2Y12 H2 haplotype does not seem to affect the platelet response to a 600 mg loading dose of clopidogrel in coronary artery disease patients prior to stenting.

Lack of association between the P2Y 12 receptor gene polymorphism and platelet response to clopidogrel in patients with coronary artery disease

Introduction Clopidogrel inhibits the ADP subtype P2Y 12 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 P2Y 12 receptor in patients treated with clopidogrel has not yet been assessed. Materials and methods The T744C polymorphism of the P2Y 12 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 P2Y 12 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.

Effects of armagnac or vodka on platelet aggregation in healthy volunteers: a randomized controlled clinical trial

Background Cardiovascular mortality is especially low in southwest France (the French Paradox). In previous experimental studies, we found that alcohol-free extracts of armagnac could inhibit human platelet function in vitro and experimental thrombosis in vivo. To test the possible relevance of these findings, we tested the effects of daily use of small quantities of armagnac against same alcohol strength, polyphenol-free vodka in healthy volunteers. MethodRandomized controlled trial comparing 5-year old armagnac (30 ml/day for 2 weeks) to same alcoholic strength vodka, in 20 healthy volunteers, on platelet aggregation induced by ADP, collagen, and thrombin, as well as bleeding time, partial thromboplastin time (pTT), and plasma lipids during and after consumption. Platelet testing was done blind. ResultsAfter 14 days, ADP-induced platelet aggregation was inhibited more in armagnac (−31±3.2% compared to pretreatment values, p<.01) than in vodka (−11.0±6.8%, NS) users ( p<.05, armagnac vs. vodka). A rebound increase of aggregation was found 2 weeks later in vodka but not in armagnac users. The same pattern was found for thrombin-induced aggregation, including post-treatment rebound. No effect was found on collagen-induced aggregation, bleeding time, pTT, or plasma lipids. Conclusion The chronic ingestion of moderate quantities of armagnac modified platelet aggregation to ADP in healthy volunteers. The difference with the effects of same alcohol degree vodka is in favour of an effect of the nonalcoholic fraction in the effects of armagnac, rather than just alcohol. All spirits may not be equal for cardioprotection.

Dark chocolate inhibits platelet aggregation in healthy volunteers

Cardiovascular disease is a leading cause of death in the UK. The flavonoids found in cocoa may produce a cardio-protective role for chocolate with a high cocoa content. Thirty healthy volunteers were randomised to receive 100 g of white, milk or dark chocolate, and assessments of platelet function were undertaken on venous blood samples before and after chocolate consumption. White and milk chocolate had no significant effect on platelets. However dark chocolate inhibited collagen-induced platelet aggregation in platelet rich plasma. In the future dark chocolate may have a role in prevention of cardiovascular and thromboembolic diseases.

Effects of D-003, a New Compound Purified from Sugarcane Wax, on Platelet Aggregation in Healthy Volunteers

Background D-003 is a mixture of long-chain aliphatic primary acids purified from sugarcane wax with experimentally demonstrated antiplatelet effects. D-003 shows hypocholesterolaemic effects in rabbits and healthy volunteers, lowering serum total cholesterol (TC) and low-density lipoprotein-cholesterol (LDL-C), but increasing high-density lipoprotein-cholesterol (HDL-C).

Effect of black tea on (iso-)prostaglandins and platelet aggregation in healthy volunteers

Flavonoids among others are found in tea. Many of them were shown to exhibit antioxidative action in vitro. We examined the effect of a 1-month consumption of 500 ml black tea containing 2.0 mg quercetin. While single tea consumption 2 h after finishing the intake did not affect any of the parameters (8-epi-PGF 2 α in plasma and serum, 11-DH-TXB 2 and ADP-induced platelet aggregation) examined at all, 1-week consumption and even more than 1 month regular tea intake significantly decreased most of the parameters. The effect was somewhat more pronounced for females as compared with males, the values for 11-dehydro-thromboxane B 2 (11-DH-TXB 2) and ADP-induced aggregation reached the level of significance in females only. These data show that regular daily black tea consumption for 1 month improves platelet function and decreases thromboxane and 8-epi-PGF 2 α to a varying extent indicating a reduced in vivo oxidation injury.

Meloxicam (Mobic): a review of its pharmacological and clinical profile

Meloxicam (Mobic) is a new nonsteroidal anti-inflammatory drug (NSAID) derived from enolic acid, exhibiting selectivity for cyclooxygenase (COX)-2 over COX-1. Meloxicam has shown potent anti-inflammatory and analgesic activity together with low gastrointestinal toxicity in animal models. It is a potent inhibitor not only of acute exudation in adjuvant arthritis in the rat, but also of bone and cartilage destruction. The therapeutic range of meloxicam in the rat, with regard to inhibition of adjuvant arthritis, was several times greater than that of other NSAIDs. Meloxicam in therapeutic doses was found to have no effect on bleeding time or platelet aggregation in healthy volunteers. In clinical studies, meloxicam has shown reliable efficacy against rheumatoid arthritis, osteoarthritis, lumbago (low back pain), scapulohumeral periarthritis, and neck-shoulder-arm syndrome with low gastrointestinal toxicity.

The Inhibitory Effect of Triflusal (Disgren)on the Platelet Aggregation in Healthy Volunteers: Impedance Method with the Whole Blood

The Inhibitory Effect of Triflusal (Disgren)on the Platelet Aggregation in Healthy Volunteers: Impedance Method with the Whole Blood

2.P.350 A therapeutic dosage (3 g/day) of borage oil supplementation has no effect on platelet aggregation in healthy volunteers

2.P.350 A therapeutic dosage (3 g/day) of borage oil supplementation has no effect on platelet aggregation in healthy volunteers