Decreased Platelet Reactivity Research Articles

Platelet Function in CKD: A Systematic Review and Meta-Analysis.

Patients with CKD are at high risk for thrombotic and hemorrhagic complications. Abnormalities in platelet function are central to these complications, but reports on platelet function in relation to CKD are conflicting, and vary from decreased platelet reactivity to normal or increased platelet responsiveness. The direct effects of uremic toxins on platelet function have been described, with variable findings. To help clarify how CKD affects platelet function, we conducted a systematic review and meta-analysis of platelet activity in CKD, with a focus on nondialysis-induced effects. We also performed an extensive literature search for the effects of individual uremic toxins on platelet function. We included 73 studies in the systematic review to assess CKD's overall effect on platelet function in patients; 11 of them described CKD's effect on ex vivo platelet aggregation and were included in the meta-analysis. Although findings on platelet abnormalities in CKD are inconsistent, bleeding time was mostly prolonged and platelet adhesion mainly reduced. Also, the meta-analysis revealed maximal platelet aggregation was significantly reduced in patients with CKD upon collagen stimulation. We also found that relatively few uremic toxins have been examined for direct effects on platelets ex vivo; ex vivo analyses had varying methods and results, revealing both platelet-stimulatory and inhibitory effects. However, eight of the 12 uremic toxins tested in animal models mostly induced prothrombotic effects. Overall, most studies report impaired function of platelets from patients with CKD. Still, a substantial number of studies find platelet function to be unchanged or even enhanced. Further investigation of platelet reactivity in CKD, especially during different CKD stages, is warranted.

Transferrin Saturation and Its Association with Platelet Reactivity

Introduction. While a plethora of risk factors have been well established as predictors for atherosclerosis and coronary heart disease, the possible association between body iron status and the risk of cardiovascular disease has yielded conflicting results. Epidemiological studies have found a significant negative association of transferrin saturation and coronary heart disease or myocardial infarction suggesting that higher body iron stores possibly confer a protective effect towards developing cardiovascular diseases. Despite the pivotal role of platelets on the pathogenesis of thrombotic complications, little information is available about the relationships between transferrin saturation and platelet reactivity. Aim of this study was to evaluate the influence of transferrin saturation on platelet function.Methods. The study included two groups: 32 healthy volunteers (17M/15F, age: 55±5 years) and 45 hereditary hemochromatosis (HH) patients (34M/11F, age: 62±2 years). HH patients were characterized by high prevalence of C282Y and/or H63D mutations of the hemochromatosis gene (HFE) and showed, just before the last therapeutic bloodletting, serum transferrin saturation and ferritin levels of 51±4% and 176±34 ng/ml, respectively.In platelet samples from healthy subjects and HH patients, we evaluated the effects of a 15-min preincubation with holotransferrin (holoTf) or apotransferrin (apoTf) (10-80 nmol/l) on: i) maximal aggregation to ADP (10 µmol/l), collagen (4 mg/l), epinephrine (5 µmol/l) and arachidonic acid (AA)(1 µmol/l) (Born's method); ii) expression of platelet activation marker CD62P in response to collagen (4mg/l) (flow-cytometry); iii) activation of signaling pathways PI-3K/Akt and MAPK/Erk-1/2 in response to collagen (4mg/l) and AA (100 µmol/l) (Western Blot); iv) reactive oxygen species (ROS) stimulated by AA (100 µmol/l) (DCF-DA fluorescence).Results. In healthy subjects we found that platelet exposure to holoTf, but not apoTf, significantly decreased platelet reactivity. In particular, 40 µmol/l HoloTf: i) reduced maximal aggregation by 39±1% to ADP, 40±4% to collagen, 49±3% to epinephrine, and 48±4% to AA (versus each agonist alone: p<0.05); ii) reduced platelet membrane expression of CD62P by 50±3% to collagen (p<0.0001); iii) reduced pAkt levels by 40±5% with collagen (p<0.001), and 38±2% with AA (p<0.0001); reduced pErk-2 levels by 66±5% with collagen (p<0.0001), and 38±4% with AA (p<0.005); iv) reduced the AA-induced ROS production by 35±3% (p<0.001). Also in platelets from HH patients holoTf significantly attenuated platelet reactivity. In fact, 40 µmol/l HoloTf: i) reduced platelet aggregation by 45±4% to ADP, 38±9% to collagen, 57±4% to epinephrine, and 49±5% to AA (versus each agonist alone: p<0.05); ii) reduced platelet membrane expression of CD62P by 54±6% to collagen (p<0.0001); iii) reduced pAkt levels by 37±6% with collagen (p<0.005), and 41±7% with AA (p<0.0001); reduced pErk-2 levels by 59±7% with collagen (p<0.0001), and 42±5% with AA (p<0.005); iv) reduced the AA-induced ROS production by 37±5% (p<0.001). The levels of transferrin saturation, but not of ferritin, were inversely correlated with the main platelet reactivity parameters; in particular, we found negative and significant correlations with the maximal aggregation to ADP (r:-0.332, p=0.05), collagen (r=-0.511, p=0.002), epinephrine (r=-0.404, p=0.02), AA (r=-0.460, p=0.009) and the CD62P expression at both basal conditions (r=-0.456, p=0.02) and after stimulation with collagen (r=-0.459, p=0.05) or AA (r=-0.629, p= 0.001).Conclusions. In healthy subjects, platelet exposure to holoTf, but not apoTf, reduced platelet reactivity as showed by a significant decrease of: i) aggregation, ii) membrane expression of CD62P, iii) activation of PI3K and MAPK pathways, and iv) oxidative stress. The effects of holoTf on platelet response were preserved in HH patients were transferrin saturation levels inversely correlated with platelet aggregation and activation. These results induce to hypothesize that in the association of high transferrin saturations and lower risk of cardiovascular diseases a role could be exerted by transferrin saturation effects on platelets. DisclosuresNo relevant conflicts of interest to declare.

A Combination of Aspirin and Clopidogrel Predict More Favorable Dynamics of Platelet Reactivity versus Clopidogrel Alone in the Acute Phase of Minor Stroke.

Background: The combined use of clopidogrel and aspirin is recommended for the short-term (21 days) therapy of minor stroke or transient ischemic attack. Previous studies have demonstrated its efficacy and superiority over treatment with a single antiplatelet agent. However, there is insufficient support for the advantages of such therapy based on platelet function testing. We aimed to compare the effect of the concomitant use of clopidogrel and aspirin versus clopidogrel alone on the dynamics of platelet reactivity over time to determine the appropriate antiplatelet treatment strategy for minor strokes. Methods: We enrolled 74 ischemic stroke subjects, including 38 minor strokes. Platelet reactivity was assessed by impedance aggregometry (Multiplate Analyzer) 48 and 96 h after a first 75 mg dose of clopidogrel, using the acetylsalicylic acid platelet inhibition (ASPI) test and the adenosine diphosphate (ADP) test. Dual antiplatelet therapy was strictly reserved only to minor strokes, as the other strokes received clopidogrel alone in the secondary prevention. The dynamics of platelet reactivity refer to the difference between two assessments, and a decrease in values over time was considered favorable. Results: The incidence of clopidogrel non-responsiveness was 64.8%, and this was similar in the group of minor strokes and the group of more disabling strokes. We indicated diabetes mellitus as an independent predictor of high on-clopidogrel platelet reactivity (Odds ratio OR 5.69 95% Confidence Interval CI 1.13–41.26, p = 0.0386). Among minor strokes treated with dual antiplatelet therapy, in relation to clopidogrel, we reported a trend toward more favorable dynamics of platelet reactivity over time compared to the group using clopidogrel alone (p = 0.0652 vs. p = 0.3384, respectively). We identified five predictors (sex, female; small-vessel disease; no diabetes; no hyperlipidemia; and no alcohol abuse) related to a significant decrease in platelet reactivity over time with respect to clopidogrel. No significant dynamics of platelet reactivity when using aspirin were found. Conclusions: Our findings, based on the favorable dynamics of platelet reactivity over time in relation to clopidogrel, confirm the usefulness of dual antiplatelet therapy in minor strokes and support the continuation of the secondary prevention with clopidogrel alone rather than aspirin, particularly among identified beneficiaries of such a strategy.

Thrombotic Events in COVID-19 Are Associated With a Lower Use of Prophylactic Anticoagulation Before Hospitalization and Followed by Decreases in Platelet Reactivity.

Background: Coronavirus disease of 2019 (COVID-19) is associated with a prothrombotic state and a high incidence of thrombotic event(s) (TE).Objectives: To study platelet reactivity in hospitalized COVID-19 patients and determine a possible association with the clinical outcomes thrombosis and all-cause mortality.Methods: Seventy nine hospitalized COVID-19 patients were enrolled in this retrospective cohort study and provided blood samples in which platelet reactivity in response to stimulation with ADP and TRAP-6 was determined using flow cytometry. Clinical outcomes included thrombotic events, and all-cause mortality.Results: The incidence of TE in this study was 28% and all-cause mortality 16%. Patients that developed a TE were younger than patients that did not develop a TE [median age of 55 vs. 70 years; adjusted odds ratio (AOR) = 0.96 per 1 year of age, 95% confidence interval (CI) 0.92–1.00; p = 0.041]. Furthermore, patients using preexisting thromboprophylaxis were less likely to develop a thrombotic complication than patients that were not (18 vs. 54%; AOR = 0.19, 95% CI 0.04–0.84; p = 0.029). Conversely, having asthma strongly increased the risk on TE development (AOR = 6.2, 95% CI 1.15–33.7; p = 0.034). No significant differences in baseline P-selectin expression or platelet reactivity were observed between the COVID-19 positive patients (n = 79) and COVID-19 negative hospitalized control patients (n = 21), nor between COVID-19 positive survivors or non-survivors. However, patients showed decreased platelet reactivity in response to TRAP-6 following TE development.Conclusion: We observed an association between the use of preexisting thromboprophylaxis and a decreased risk of TE during COVID-19. This suggests that these therapies are beneficial for coping with COVID-19 associated hypercoagulability. This highlights the importance of patient therapy adherence. We observed lowered platelet reactivity after the development of TE, which might be attributed to platelet desensitization during thromboinflammation.

Prostacyclin Analogues Inhibit Platelet Reactivity, Extracellular Vesicle Release and Thrombus Formation in Patients with Pulmonary Arterial Hypertension.

(1) Background: Prostacyclin analogues (epoprostenol, treprostinil, and iloprost) induce vasodilation in pulmonary arterial hypertension (PAH) but also inhibit platelet function. (2) Objectives: We assessed platelet function in PAH patients treated with prostacyclin analogues and not receiving prostacyclin analogues. (3) Methods: Venous blood was collected from 42 patients treated with prostacyclin analogues (49.5 ± 15.9 years, 81% female) and 38 patients not receiving prostacyclin analogues (55.5 ± 15.6 years, 74% female). Platelet reactivity was analyzed by impedance aggregometry using arachidonic acid (AA; 0.5 mM), adenosine diphosphate (ADP; 6.5 µM), and thrombin receptor-activating peptide (TRAP; 32 µM) as agonists. In a subset of patients, concentrations of extracellular vesicles (EVs) from all platelets (CD61+), activated platelets (CD61+/CD62P+), leukocytes (CD45+), and endothelial cells (CD146+) were analyzed by flow cytometry. Platelet-rich thrombus formation was measured using a whole blood perfusion system. (4) Results: Compared to controls, PAH patients treated with prostacyclin analogues had lower platelet reactivity in response to AA and ADP (p = 0.01 for both), lower concentrations of platelet and leukocyte EVs (p ≤ 0.04), delayed thrombus formation (p ≤ 0.003), and decreased thrombus size (p = 0.008). Epoprostenol did not affect platelet reactivity but decreased the concentrations of platelet and leukocyte EVs (p ≤ 0.04). Treprostinil decreased platelet reactivity in response to AA and ADP (p ≤ 0.02) but had no effect on the concentrations of EVs. All prostacyclin analogues delayed thrombus formation and decreased thrombus size (p ≤ 0.04). (5) Conclusions: PAH patients treated with prostacyclin analogues had impaired platelet reactivity, EV release, and thrombus formation, compared to patients not receiving prostacyclin analogues.

Impact of selected genetic factors on clopidogrel inactive metabolite level and antiplatelet response in patients after percutaneous coronary intervention

Background and objectiveClopidogrel is frequently used as part of optimal dual antiplatelet therapy in high-bleeding risk patients with the acute coronary syndrome. The concentration of the inactive carboxylic acid metabolite of clopidogrel might be useful to evaluate the response to clopidogrel therapy. Therefore, we sought to correlate the inhibition of platelet aggregation with the plasma level of the inactive metabolite of clopidogrel in patients after percutaneous coronary interventions (PCI) and their associations with the most frequently studied genetic polymorphisms. For this purpose, the fast and simple HPLC method for determining the concentration of the inactive metabolite was developed.MethodsThe effect of CYP2C19, CYP3A4/5, ABCB1 and PON1 genes on the plasma inactive metabolite concentration of clopidogrel and the platelet aggregation was investigated in 155 patients before and after PCI.ResultsThe concentration of the inactive metabolite of clopidogrel was not significantly different in the intermediate metabolizers (IM) of CYP2C19 compared with extensive metabolizers (EM) both before and after PCI, while inhibition of platelet aggregation was found to be significantly better in EM than in IM. The presence of the A allele at position 2677 in the ABCB1 gene was associated with a significantly lower concentration of inactive metabolite of clopidogrel before PCI.ConclusionThe CYP2C19*2 allele was associated with decreased platelet reactivity during clopidogrel therapy before and after PCI. Simultaneous determination of platelet aggregation and concentration of the inactive clopidogrel metabolite may be useful in clinical practice to find the cause of adverse effects or insufficient treatment effect in patients chronically treated with clopidogrel.

Adjunctive Cilostazol to Dual Antiplatelet Therapy to Enhance Mobilization of Endothelial Progenitor Cell in Patients with Acute Myocardial Infarction: A Randomized, Placebo-Controlled EPISODE Trial

Background: Endothelial progenitor cells (EPCs) have the potential to protect against atherothrombotic event occurrences. There are no data to evaluate the impact of cilostazol on EPC levels in high-risk patients. Methods: We conducted a randomized, double-blind, placebo-controlled trial to assess the effect of adjunctive cilostazol on EPC mobilization and platelet reactivity in patients with acute myocardial infarction (AMI). Before discharge, patients undergoing percutaneous coronary intervention (PCI) were randomly assigned to receive cilostazol SR capsule (200-mg) a day (n = 30) or placebo (n = 30) on top of dual antiplatelet therapy (DAPT) with clopidogrel and aspirin. Before randomization (baseline) and at 30-day follow-up, circulating EPC levels were analyzed using flow cytometry and hemostatic measurements were evaluated by VerifyNow and thromboelastography assays. The primary endpoint was the relative change in EPC levels between baseline and 30-day. Results: At baseline, there were similar levels of EPC counts between treatments, whereas patients with cilostazol showed higher levels of EPC counts compared with placebo after 30 days. Cilostazol versus placebo treatment displayed significantly higher changes in EPC levels between baseline and follow-up (ΔCD133+/KDR+: difference 216%, 95% confidence interval (CI) 44~388%, p = 0.015; ΔCD34+/KDR+: difference 183%, 95% CI 25~342%, p = 0.024). At 30-day follow-up, platelet reactivity was lower in the cilostazol group compared with the placebo group (130 ± 45 versus 169 ± 62 P2Y12 Reaction Unit, p = 0.009). However, there were no significant correlations between the changes of EPC levels and platelet reactivity. Conclusion: Adjunctive cilostazol on top of clopidogrel and aspirin versus DAPT alone is associated with increased EPC mobilization and decreased platelet reactivity in AMI patients, suggesting its pleiotropic effects against atherothrombotic events (NCT04407312).

P4556Thrombin generation and platelet function in patients on RAAS inhibitors

Abstract Background ACE inhibitors (ACEI) and angiotensin II receptor blockers (ARB) are beneficial for patients with cardiovascular disease. However, little is known about whether one of these drugs is superior. First analyses show that the inhibition of the renin-angiotensin-aldosterone system (RAAS) affects platelet reactivity. Therefore we evaluated the effects of ACEI and ARB on platelet reactivity and thrombin generation. Methods In a time series analysis, samples of 24 patients before, 4h and 24h after initial intake of ACEI were analysed. Also we included 10 patients with permanent ACEI treatment and 4h, 24h and 3 months after switching to ARB. Platelet reactivity was measured via light transmission aggregometry (LTA). Thrombin generation was measured as endogenous thrombin potential (ETP) by calibrated automated thrombogram. Protease-activated receptor (PAR) expression was analysed by flow cytometry. Thrombin-antithrombin (TAT) complexes were measured with an enzyme-linked immunosorbent assay. Results TRAP-6 induced platelet reactivity increased during ACEI treatment (prior vs. 4h post ACEI: 41.9±16.2% vs. 55.2±16.7%; p=0.003, prior vs. 24h post ACEI: 52.3±12.7%; p=0.003). Switching from chronic ACEI to ARB treatment decreased platelet reactivity (permanent ACEI vs. 3 months after switching: 50.3±20.9% vs. 34.7±20.9%; p=0.033). ACEI reduced ETP from prior to 3 months post ACEI (1527±437 nM*min vs. 1088±631 nM*min; p=0.025). ARB did not affect ETP (1526±587 nM*min vs. 1369±516 nM*min; p=0.3). PAR1 levels rose from 37.38±10.97% before to 49.53±6.04% after ACEI treatment (p=0.036). ARB did not have an effect on PAR1 (33.16±11.73 vs. 32.86±8.99; p=0.89). ACEI slightly decreased plasma thrombin concentration. ARB treatment showed a minor but again not significant decrease in TAT complexes as well. (TAT complexes prior vs. 3 months post ACEI: 8.4±11.9 μg/l vs. 6.3±6.8 μg/l; p=0.99, permanent ACEI vs. 3 months after switching to ARB: 4.3±1.9 μg/l vs. 3.0±1.0 μg/l; p=0.3). Conclusion ACEI increased platelet reactivity. This can be reversed by switching to ARB. The mechanism behind RAAS influencing platelet function needs to be further investigated in larger trials. Acknowledgement/Funding Medical Faculty of the Heinrich-Heine-University Düsseldorf

PS1582 DECREASED PLATELET REACTIVITY IS ASSOCIATED WITH AN INFLAMMATORY STATUS IN PATIENTS WITH CANCER

Background:Decreased platelet reactivity was observed in cancer patients at high risk of venous thromboembolism (VTE) and death. Prothrombotic and inflammatory mechanisms have been suggested to cooperate in the development of VTE, representing represent the hallmark of thromboinflammation.Aims:To assess whether platelet reactivity is associated with inflammatory parameters in cancer patients.Methods:Platelet reactivity was determined by whole blood flow cytometry in 62 newly diagnosed cancer patients (median age [interquartile range, IQR]: 63 [54–70] years, 48 % female) at several time points during the first 6 months of chemotherapy (total number of samples analyzed: 179). We measured platelet surface P‐selectin and activated glycoprotein (GP) IIb/IIIa expression in vivo and upon ex vivo stimulation with agonists of protease‐activated receptor (PAR) −1, −4, and GPVI. C‐reactive protein (CRP) and fibrinogen levels were analyzed in plasma samples from the corresponding blood draws.Results:Platelet reactivity, as determined by percentage of platelets expressing activated GPIIb/IIIa on the surface, upon stimulation with different agonists, correlated with significantly lower levels of CRP and fibrinogen (Table 1). Platelet surface P‐selectin expression upon stimulation of the GPVI receptor also showed a significant inverse correlation with CRP and fibrinogen (Table 1). Platelet activation in vivo (i.e. without ex vivo agonist activation) did not correlate with CRP and fibrinogen levels (Table 1).Summary/Conclusion:Our data indicate that there is an inverse relationship between platelet reactivity and inflammatory status in cancer patients, whereby platelets of patients with increased inflammatory parameters are less reactive to stimulation with platelet agonists. Further research is needed to better understand underlying pathophysiological mechanisms.image

Cigarette smoking reduces platelet reactivity independently of clopidogrel treatment in patients with non-ST elevation acute coronary syndromes

Smokers receiving clopidogrel show a lower residual platelet reactivity than non-smokers, a phenomenon generally ascribed to smoking-induced increased production of clopidogrel active metabolite, but also associated with the high hemoglobin levels of smokers, which decreases platelet reactivity in tests that measure platelet function in whole blood. We evaluated the impact of cigarette smoking and of hemoglobin levels on platelet reactivity index (PRI) measured by the vasodilator-stimulated phosphoprotein phosphorylation (VASP-P) assay in whole blood samples from patients with non-ST elevation acute coronary syndrome (NSTE-ACS) undergoing percutaneous coronary interventions, both before and after clopidogrel administration.PRI was measured in 718 clopidogrel-naïve NSTE-ACS patients, both before and 1 month after treatment with clopidogrel (75 mg daily). Smokers (n = 347, 48%) had significantly lower mean PRI levels at both baseline (57.7 ± 24.1 vs. 64.8 ± 19.8, p < 0.001) and 1 month (43.4 ± 20.3% vs. 46.8 ± 18.0%, p = 0.017) than non-smokers. After adjusting for potential confounders (age, sex, diabetes, chronic kidney disease, Syntax score>15), the β coefficient of smoke on PRI was −8.51 [−11.90 to −5.11, p < 0.001] at baseline and −3.41 [−6.30 to −0.51, p = 0.02] after 1 month. Hemoglobin was higher in smokers (13.8 ± 1.5 g/dL) than non-smokers (13.1 ± 1.7 g/dL, p < 0.001), but was not significantly correlated with PRI both at baseline (Rho = 0.02, p = 0.60) and at 1 month (Rho = 0.01, p = 0.80).Our analysis confirms that clopidogrel-treated smokers have lower platelet reactivity, measured by the VASP-P assay, compared to clopidogrel-treated non-smokers. However, smokers had lower platelet reactivity already before receiving clopidogrel treatment, suggesting that smoke affects platelet reactivity independently of its potential effect on the pharmacokinetics of clopidogrel. Our data also indicate that such an effect is not mediated by increased hemoglobin levels.

One-Year Outcome of Intensive Insulin Therapy Combined to Glucose-Insulin-Potassium in Acute Coronary Syndrome: A Randomized Controlled Study.

BackgroundA number of factors may offset the cardioprotective effects of glucose‐insulin‐potassium (GIK) on outcome of patients with acute coronary syndrome, such as hyperglycemia induced by this cocktail infusion. We performed a study to evaluate the effect of intensive insulin therapy in association with GIK on 1‐year outcome in patients hospitalized for acute coronary syndrome.Methods and ResultsIn a randomized prospective controlled trial we included 772 patients with non–ST‐segment elevation acute coronary syndrome. Patients were randomized into 3 groups: GIKI2 group, who received GIK with intensive insulin therapy for 24 hours; GIK group, who received GIK with nonintensive insulin therapy; and control group, who received usual care. The primary outcome criteria were the rates of major cardiovascular events combining death, reinfarction, and stroke rate at 1 year. In addition, we measured platelet function assay‐100 and plasminogen activator inhibitor‐1 at admission and 24 hours later. Based on an intention‐to‐treat analysis, major cardiovascular events at 1 year was 12.8% in the GIKI2 group, 15.5% in the GIK group, and 20.5% in the placebo group; the difference was significant between the GIK2 and control groups (P=0.01). Platelet function assay‐100 at 24 hours decreased significantly from baseline in the control group but not in the GIKI2 group. Plasminogen activator inhibitor‐1 decreased significantly in the GIKI2 group but significantly increased in the control group. Minor hypoglycemic events were more frequent in the GIKI2 group compared with other groups.ConclusionsGIKI2 led to improvement of 1‐year outcome rates in patients with non–ST‐segment elevation acute coronary syndrome. This beneficial effect was associated with a decrease in platelet reactivity and an increase on fibrinolysis tests.Clinical Trial RegistrationURL: https://www.clinicaltrials.gov. Unique identifier: NCT00965406.

Cryoablation decreases platelet reactivity in patients with atrial fibrillation compared with radiofrequency ablation: results from the Sparelife Project

Cryoablation decreases platelet reactivity in patients with atrial fibrillation compared with radiofrequency ablation: results from the Sparelife Project

LIPID LOWERING BY STATIN;

Objectives: To observe the effect of lipid lowering by atorvastatin administrationon platelet reactivity by measuring serum beta thromboglobulin concentration in male andfemale Sprague Dawley rats. Study Design: Randomized control trial (RCT). Place of study:The study was conducted at Physiology department, Army Medical College, Rawalpindi. Animalhandling, obesity induction, drug administration and sample collection were done at NationalInstitute of Health (NIH), Islamabad and biochemical assays were performed at Centre forResearch in Experimental and Applied Medicine (CREAM), Army Medical College, Rawalpindi.Period: 12 months. Material and Methods: Ninety healthy Sprague Dawley (male and female)rats were randomly selected and divided into three equal groups. Group I rats (normal control)were given normal chow diet for three weeks. Group II rats (obese control) were given high fatdiet for three weeks to induce obesity. Group III rats (obese treated) were given atorvastatinfor three weeks in a dose of 10 mg/kg/day orally by gavage method after obesity induction.Terminal blood sampling was done at the end of the study by intra-cardiac puncture. Bloodwas centrifuged to obtain serum and serum beta thromboglobulin was measured by usingEnzyme Linked Immunosorbant assay. Results: There was a significant (p &lt; 0.05) increasein serum B-TG concentration in obese rats as compared to normal control rats. Atorvastatinadministration to obese rats significantly (p &lt; 0.05) reduced serum B-TG concentration.Conclusions: Obesity increases and statin administration decreases platelet reactivity in highfat diet induced obese Sprague Dawley rats as reflected by serum B-TG concentration.

Decreased platelet reactivity in patients with cancer is associated with high risk of venous thromboembolism and poor prognosis.

Platelets are suggested to play a crucial role in cancer progression and the prothrombotic state of cancer patients. Here, we aimed to examine the activation status of platelets in cancer patients and investigate their association with risk of death and occurrence of venous thromboembolism (VTE) in a prospective observational cohort study. We measured platelet surface P-selectin, activated glycoprotein (GP) IIb/IIIa and monocyte-platelet aggregate (MPA) formation in vivo and platelet response to ex vivo stimulation with agonists of protease-activated receptor (PAR) -1, -4, and GPVI, by whole blood flow cytometry, before beginning of chemotherapy and repeatedly during the first six months thereafter (total number of samples analysed: 230). Endpoints of the study were occurrence of death or VTE during a two-year follow-up, respectively. Of 62 patients (median age [interquartile range, IQR]: 63 [54-70] years, 48 % female), 32 (51.6 %) died and nine (14.5 %) developed VTE. Association with a higher risk of death was found for lower platelet surface expression of P-selectin and activated GPIIb/IIIa in vivo and in response to PAR-1, -4 and GPVI activation, but not for MPA formation. Furthermore, reduced platelet responsiveness to PAR-1 and GPVI agonists was associated with higher risk of VTE (hazard ratio per decile increase of percentage P-selectin positive platelets: 0.73 [0.56-0.92, p=0.007] and 0.77 [0.59-0.98, p=0.034], respectively). In conclusion, cancer patients with a poor prognosis showed decreased platelet reactivity, presumably as a consequence of continuous activation. Our data suggest that decreased platelet reactivity is associated with increased mortality and VTE in cancer.

Inverse relationship between erythrocyte size and platelet reactivity in elderly

Previous work indicates that erythrocytes (RBCs) accumulate β-amyloid X-40 (Aβ40) in individuals with Alzheimer disease (AD) and to a lesser extent in healthy elderly. The toxin damages RBCs and increases their mean corpuscular volume (MCV). Furthermore, AD platelets demonstrate lower reactivity. This study investigated interactions between RBCs and platelets. Older individuals with moderate hypertension (n = 57) were classified into two groups, depending on MCV in whole blood: The MCVhigh group comprised individuals with higher MCV (n = 27; 97 ± 3(SD) fl) and MCVlow group had relatively lower MCV (n = 30; 90 ± 3(SD) fl). Flow cytometry was used to determine platelet reactivity, i.e., the surface binding of fibrinogen after provocation. Adenosine diphosphate (ADP) and a thrombin receptor-activating protein (TRAP-6) were used as agonists. Subsequently, blood cells were divided according to density into 17 subfractions. Intra-RBC Aβ40 content was analyzed and in all platelet populations surface-bound fibrinogen was determined to estimate platelet in vivo activity. We found Aβ40 inside RBCs of approximately 50% of participants, but the toxin did not affect MCV and platelet reactivity. In contrast, MCV associated inversely with platelet reactivity as judged from surface-attached fibrinogen after ADP (1.7 μmol/L) (p < 0.05) and TRAP-6 provocation (57 μmol/L (p = 0.01) and 74 μmol/L (p < 0.05)). In several density fractions (nos. 3, 4, 8, 11–13 (p < 0.05) and nos. 5–7 (p < 0.01)) MCV linked inversely with platelet-attached fibrinogen. In our community-dwelling sample, enhanced MCV associated with decreased platelet reactivity and lower in vivo platelet activity. It resembles RBCs and platelet behavior in AD-type dementia.

ATP‐binding cassette transporter 1 (ABCA1) deficiency decreases platelet reactivity and reduces thromboxane A2 production independently of hematopoietic ABCA1

ESSENTIALS: The role of ATP-binding cassette transporter 1 (ABCA1) in platelet functions is poorly characterized. We studied the impact of ABCA1 deficiency on platelet responses in a mouse model and two Tangier patients. ABCA1-deficient platelets exhibit reduced positive feedback loop mechanisms. This reduced reactivity is dependent on external environment and independent of hematopoietic ABCA1. The ATP-binding cassette transporter ABCA1 is required for the conversion of apolipoprotein A-1 to high-density lipoprotein (HDL), and its defect causes Tangier disease, a rare disorder characterized by an absence of HDL and accumulation of cholesterol in peripheral tissues. The role of ABCA1 in platelet functions remains poorly characterized. To determine the role of ABCA1 in platelet functions and to clarify controversies concerning its implication in processes as fundamental as platelet phosphatidylserine exposure and control of platelet membrane lipid composition. We studied the impact of ABCA1 deficiency on platelet responses in a mouse model and in two Tangier patients. We show that platelets in ABCA1-deficient mice are slightly larger in size and exhibit aggregation and secretion defects in response to low concentrations of thrombin and collagen. These platelets have normal cholesterol and major phospholipid composition, granule morphology, or calcium-induced phosphatidylserine exposure. Interestingly, ABCA1-deficient platelets display a reduction in positive feedback loop mechanisms, particularly in thromboxane A2 (TXA2) production. Hematopoietic chimera mice demonstrated that defective eicosanoids production, particularly TXA2, was primarily dependent on external environment and not on the hematopoietic ABCA1. Decreased aggregation and production of TXA2 and eicosanoids were also observed in platelets from Tangier patients. Absence of ABCA1 and low HDL level induce reduction of platelet reactivity by decreasing positive feedback loops, particularly TXA2 production through a hematopoietic ABCA1-independent mechanism.

CRT-200.33 Comparison of Platelet Reactivity on Ticagrelor in African-American Patients With Acute Coronary Syndromes Versus Stable Coronary Artery Disease

Ticagrelor significantly decreases platelet reactivity and improves clinical outcomes compared with clopidogrel, but little is known regarding the effects of ticagrelor upon platelet reactivity in African-Americans (AA) with an acute coronary syndrome (ACS). We therefore performed pharmacodynamic

Diabetes mellitus, CYP2C19 genotype, and response to escalating doses of clopidogrel. Insights from the ELEVATE-TIMI 56 Trial.

Both diabetes mellitus (DM) and carriage of the CYP2C19*2 allele are associated with a reduced response to clopidogrel. The relative contributions of these factors and whether higher clopidogrel doses can overcome both factors remain unknown. The objective of this study was to test the ability of clopidogrel doses up to 300 mg daily to decrease platelet reactivity in patients with DM and/or CYP2C19*2. ELEVATE-TIMI 56 randomised 333 patients with coronary artery disease to different maintenance doses of clopidogrel in four treatment periods, each lasting approximately 14 days. On-treatment platelet reactivity was compared between patients stratified by DM, CYP2C19*2 status and clopidogrel dose. Both DM and CYP2C19*2 were independently associated with elevated on-treatment platelet reactivity with clopidogrel 75 mg daily (p<0.0001 for each). With 75 mg, mean on-treatment PRU was progressively higher (p trend <0.001) when evaluating patients: with neither DM nor CYP2C19*2 (150.7; 95 % CI 140.5-162.6), with only DM (187.2; 95 % CI, 171.3-206.9), with only CYP2C19*2 (227.9; 95 % CI, 205.1-250.8), and with both DM and CYP2C19*2 (239.9; 95 % CI, 209.7-270.1). Notably, with 75 mg, patients with only CYP2C19*2 had higher on-treatment platelet reactivity than those with only DM (p=0.0068). To achieve on-treatment platelet reactivity similar to that seen with clopidogrel 75 mg in patients with neither DM nor CYP2C19*2, the following doses were required: 150 mg with only DM, 225 mg with only CYP2C19*2, and 300 mg with both DM and CYP2C19*2. Patients with both DM and CYP2C19*2 required a four-fold increase in clopidogrel maintenance dose as compared to patients without these factors to achieve a similar antiplatelet response.

The effects of angiotensin II signaling blockade on platelet activity in subjects with hypertension.

To investigate the effects of Angiotensin II receptor blockade (ARB) and angiotensin converting enzyme (ACE) inhibition on platelet reactivity in patients with mild to moderate hypertension. PFA-100 evaluates platelet function (expressed in seconds as closure time, CT) in anti-coagulated whole blood in vitro at high shear rates. The test cartridge is impregnated with either collagen and epinephrine (Col/Epi) or collagen and ADP (Col/ADP). 33 patients were randomized to perindopril 4mg (n = 9), valsartan 80mg/d (n = 9) and for lifestyle modification (n = 15) for 4 weeks. Platelet reactivity was measured at baseline and after 4 weeks by PFA-100. Normotensive controls (n = 11) were also tested at baseline to standardize PFA-100 CT. Haematocrit, platelet count and plasma vWF antigen levels were measured. There was no difference in baseline haematocrit, platelet count or vWF antigen level between the groups. The vWF antigen levels measured after 4 weeks showed no significant difference either. Significant blood pressure reduction was seen in the treated group (SBP P = 0.002 and DBP P = 0.005) when compared to the life style modification group (SBP P = 0.06 and DBP P = 0.04) after 4 weeks. There was no significant statistical difference in Col/ADP CT in treated and non-treated groups but increase in CT (P = 0.05) in treated group with Col/Epi seen after 4 weeks. In patients with mild to moderate hypertension, valsartan and perindopril compared to life style modification demonstrate a significant decrease in platelet reactivity.

Platelet reactivity in comatose survivors of cardiac arrest undergoing percutaneous coronary intervention and hypothermia.

To investigate the effects of clopidogrel and eptifibatide on platelet reactivity in patients resuscitated from cardiac arrest undergoing percutaneous coronary intervention (PCI) and hypothermia. VerifyNow® and Multiplate® aggregometry were used before, and 4, 12, 22 and 48 hours after 600 mg clopidogrel treatment in 28 post-cardiac arrest hypothermic patients and in 14 normothermic patients with acute coronary syndrome. Basal platelet reactivity after stimulation with iso-thrombin receptor-activating peptide (TRAP) and PAR4-activating peptide (BASE) was significantly lower in the post-cardiac arrest group and persisted up to 48 hours. The antiplatelet effect of clopidogrel measured by VerifyNow and expressed as % inhibition was significantly lower in the post-cardiac arrest group. It was close to zero with an increase to only around 10% after 48 hours. Post-cardiac arrest patients receiving eptifibatide showed profound platelet inhibition measured by both VerifyNow IIb/IIIa and Multiplate TRAP tests for at least 22 hours after administration. Post-resuscitation syndrome with ongoing hypothermia is associated with decreased platelet reactivity. Clopidogrel loading does not significantly affect platelet function during the first 48 hours. This is in contrast with eptifibatide which produces profound platelet inhibition, and may be used to bridge insufficient inhibition by clopidogrel.