Impedance Platelet Aggregation Research Articles

Increased Platelet Aggregation in Children and Adolescents with Sleep-disordered Breathing.

Rationale: Sleep-disordered breathing (SDB) is associated with increased vascular resistance in children and adults. Persistent increased vascular resistance damages vascular endothelial cells-a marker of which is increased platelet activation.Objectives: This study compared whole-blood impedance platelet aggregation in children with clinically diagnosed SDB warranting adenotonsillectomy and healthy control subjects.Methods: Thirty children who had SDB warranting intervention clinically diagnosed by experienced pediatric otolaryngologists were recruited from adenotonsillectomy waitlists, and 20 healthy children from the community underwent overnight polysomnography to determine SDB severity (obstructive apnea-hypopnea index). Snoring frequency was collected from parents. In the morning, a fasting blood sample was taken, and whole-blood platelet aggregation was measured.Measurements and Main Results: Children with SDB exhibited increased platelet aggregation to TRAP (thrombin receptor-activating peptide) (children with SDB = 114.8 aggregation units [AU] vs. control subjects = 98.0 AU; P < 0.05) and COL antibody (96.7 vs. 82.2 AU; P < 0.05) and an increased trend in ADP antibody (82.3 vs. 69.2 AU; P < 0.07) but not aspirin dialuminate (82.1 vs. 79.5 AU; P > 0.05). No significant association was observed between either the obstructive apnea-hypopnea index and any aggregation parameter, but parental report of snoring was positively associated with TRAP aggregation (Kendall's τ-c = 0.23; P < 0.05).Conclusions: The finding of increased platelet aggregation is consistent with endothelial damage. This suggests that the profile of cardiovascular changes noted in adults with SDB may also occur in children with SDB.

Effect of acetylsalicylic acid intake on platelet derived microvesicles in healthy subjects

Platelet-derived microvesicles (pMVs) are released from platelets in physiological and pathological conditions and exhibit a wide range of prothrombotic, antithrombotic, proatherogenic, and pro-inflammatory properties. Antiplatelet agents, such as acetylsalicylic acid (ASA), are widely used for the prevention and treatment of vascular diseases, but their impact on pMV release remains poorly understood and contradictory mainly because of discrepancies in the methodology and lack of well-standardized MV assessment protocols. The present study investigated the effects of ASA not only on total pMV release but also on their phenotypes defined using the surface expression of pro-inflammatory (CD40L, CD62P, CD31) and procoagulant (PS, PAC-1) markers in healthy subjects. Fifty healthy volunteers were enrolled in the study and received a daily dose of 150 mg ASA for 3 consecutive days. Circulating pMVs were characterized and quantified before and after the intervention period using flow cytometry. Serum levels of thromboxane B2 (TXB2) and whole blood impedance platelet aggregation under arachidonic acid (AA) stimulation were also investigated to assess ASA compliance. In general, ASA did not effect pMV numbers in healthy subjects despite its effective inhibition of platelet aggregation Moreover, in premenopausal women, we noticed an increase in the number of pMVs. Further studies are needed to assess whether dose modification of ASA or combinations or changes in antiplatelet therapy would reduce pMV formation, especially in patients with cardiovascular risk factors.

ASSOCIATION OF PLATELET-DERIVED MICROVESICLES WITH HIGH ON-TREATMENT PLATELET REACTIVITY IN CONVALESCENT ISCHEMIC STROKE PATIENTS TREATED WITH ACETYLSALICYLIC ACID

Elevated concentrations of platelet-derived microvesicles are found in cerebrovascular diseases. The impact of acetylsalicylic acid on these microvesicles remains inconsistent, despite its well-established effect on platelet aggregation. High residual platelet aggregation is defined as high on-treatment platelet reactivity, while “treatment failure” is the occurrence of vascular events despite antiplatelet treatment. The aim of this study was to determine whether the antiaggregatory effect of acetylsalicylic acid correlates with platelet-derived microvesicles in convalescent ischaemic stroke patients and cardiovascular risk factor controls as well as to evaluate the association between high on-treatment platelet reactivity and recurrent vascular events with the studied platelet-derived microvesicle parameters. The study groups consisted of 76 convalescent stroke patients and 74 controls. Total platelet-derived microvesicles, annexino-positive microvesicles number, and platelet-derived microvesicles with surface expression of proinflammatory (CD40L, CD62P, CD31) and procoagulant (PS, GPIIb/IIIa) markers were characterized and quantified using flow cytometry. Cyclooxygenase-1-specific platelet responsiveness, with whole blood impedance platelet aggregation under arachidonic acid stimulation and the serum concentration of thromboxane B2, were evaluated. Neither acetylsalicylic acid intake nor modification of its daily dose caused statistically significant differences in the studied microvesicle parameters. Additionally, no statistically significant differences in the studied microvesicle parameters were revealed between high on-treatment platelet reactivity and non-high on-treatment platelet reactivity subjects in either study subgroup. However, elevated concentrations of PAC-1+/CD61+, CD62P+/CD61+ and CD31+/CD61+ microvesicles were found in stroke patients with treatment failure, defined in this study as a recurrent vascular events in a one-year follow-up period. This study revealed no relationship between circulating microvesicle number and platelet aggregation. The procoagulant and proinflammatory phenotype of circulating platelet-derived microvesicles might contribute to acetylsalicylic acid treatment failure.

Platelet turnover and function in end-stage renal disease

Background/Aim. End-stage renal disease (ESRD) is characterized by significant impairment of platelet functions which may cause bleeding or thrombotic complications. The iam of this study was the aim of this study was the assessement of platelet turnover and function and their correlation with inflammatory and procoagulant markers in ESRD patients as well as platelet indicies comparison between ESRD diabetic and ESRD non-diabetic patients. Methods. The prospective, observational clinical study included 63 ESRD patients and 30 age and sex matched healthy volunteers. Following laboratory parameters of platelet turnover and function (platelet count, reticulated platelets, platelet indices, whole blood impedance platelet aggregation), inflammatory and procoagulant markers (number of neutrophils, neutrophil to lymphocyte ratio, C-reactive protein, plasma fibrinogen, D dimer, von Willebrand factor) were obtained. Results. Platelet turnover (% of reticulated platelets) was significantly higher (3.8 ? 2.3 vs. 2.3 ? 1.3; p &lt; 0.01) and platelet aggregation tests induced by thrombin receptor activiting peptide (TRAP) (p &lt; 0.01), adenosine diphospate (ADP) (p &lt; 0.05), arachidonic acid (ASPI) (p &lt; 0.05) and collagen (p &lt; 0.05) were markedly increased in the ESRD patients compared to the control group. The comparison of chronic inflammation and procoagulant markers revealed higher values in all patients comparing to the group of healthy subjects (p &lt; 0.01 regarding all parameters). There was no difference between the ESRD diabetic and ESRD non-diabetic patients. Conclusion. Results point out increased platelet turnover in ESRD as a consequence of platelet activation and consumption induced by clotting system hyperactivity and chronic inflammation. None of the examined parameters do not predict bleeding occurrence.

Changes in Cardiac Function After a Single Intravenous Administration of CKD-712 in Healthy Male Volunteers.

CKD-712, a candidate treatment for septic shock, acts by increasing cardiac output. This study investigated changes in the pharmacodynamics, pharmacokinetics, and tolerability of CKD-712 after a single intravenous administration. A dose-block-randomized, double-blind, placebo-controlled, single-dose escalation study was conducted in 44 healthy subjects receiving 20, 40, 80, 160, 240, or 320μg/kg CKD-712 or placebo. Pharmacodynamics were evaluated using computerized impedance cardiography, vital signs, platelet aggregation, and bleeding time. Serial blood and urine samples for pharmacokinetic analysis were collected up to 12 and 24h, respectively, after the initiation of intravenous drug infusion. Tolerability assessments were performed throughout the study. The area under the effect-time curve of the cardiac index (AUECCI) and systolic blood pressure (AUECSBP) changed significantly with the 160 and 320µg/kg doses of CKD-712 compared with placebo. Furthermore, the AUECCI and AUECSBP tended to increase as the systemic exposure of CKD-712 increased from 20 to 240µg/kg. The frequency of drug-related adverse events (AEs), including cardiovascular symptoms, was higher with the 320µg/kg dose. The pharmacological effects and on-target AEs of CKD-712 increased relative to the dose increments. The results of this study suggest that potentially therapeutic doses of CKD-712 could range from 160 to 240μg/kg.

Monitoring Residual Platelet Activity Among Patients With Acute Coronary Syndrome

Several medicines are currently used to inhibit the platelet activity. We aim to monitor the residual platelet activity (RPA) despite antiplatelet therapy and assess its relationship with major adverse events. The impedance platelet aggregation was employed to determine RPA. Totally, 202 patients with acute coronary syndrome (ACS) were followed up for 10 months for major clinical events of myocardial infarction, cerebrovascular accident (CVA), and all cause mortality, and RPA after clopidogrel loading was assessed in 30 patients. The RPA at 2 hours after 300 mg clopidogrel loading was 1 Ω (± 2.3 Ω) induced by adenosine diphosphate. Residual platelet activity of patients who experienced death, MI, or CVA was significantly higher than those who did not experience (P < .05). Cutoff values of RPA showed optimal negative predictive values (96%-97%) and poor positive predictive values (16%-29%). Therefore, RPA monitored by whole blood impedance platelet aggregation may have high exclusionary predictive value for the occurrence of major clinical events in patients with ACS.

Aspirin treatment influences platelet-related inflammatory biomarkers in healthy individuals but not in acute stroke patients

Objectives Platelet-leukocyte aggregation is believed to contribute to acute thrombotic events. While the effect of aspirin on platelet-to-platelet aggregation is well established, the impact of the drug on pro-inflammatory platelet function remains equivocal. Thus we investigated the effect of aspirin on selected platelet-related inflammatory biomarkers in both acute ischaemic stroke patients and healthy volunteers. Methods Using five-colour flow cytometry the platelet surface expression of CD62P and CD40L and subpopulations of leukocyte-platelet aggregates were assessed in 63 acute stroke patients and 40 healthy volunteers at baseline and after a 10-day period of aspirin intake at a daily dose of 150 mg. Simultaneously the plasma levels of soluble CD62P and CD40L, serum level of TxB 2, and whole blood impedance platelet aggregation under arachidonic acid (AA) stimulation were investigated. Results No differences in values of studied platelet-related inflammatory biomarkers in both resting platelets and those activated with TRAP after 10-day treatment with aspirin were confirmed in stroke subjects. In healthy individuals the resting platelet expression of CD62P, plasma level of soluble CD62P and percentage of circulating monocyte-platelet aggregates were lower after the aspirin intake period (P = 0.009; P = 0.04; P = 0.004, respectively). In both studied groups serum level of TxB 2 and platelet aggregation under AA stimulation were lower than before treatment (P < 0.001). Conclusion Despite effective inhibition of COX-1-dependent platelet aggregation, aspirin does not influence the platelet α-granule-derived inflammatory mediators and monocyte-platelet aggregation in acute stroke subjects, although it does in healthy individuals.

Functional Evaluation of Platelet Aspirin Resistance after On-Pump Coronary Bypass Grafting Using Multiple Aggregation Tests

The predominant mechanism of early graft failure after coronary artery bypass grafting (CABG) is associated with antiplatelet treatment using drugs such as acetylsalicylic acid (ASA). Impaired hemostasis of multiple etiologies is often present in patients undergoing on-pump cardiac surgery. We investigated the impact of intravenous ASA administration on platelet function in this setting. Forty-two patients were enrolled in the study. Patients received 100 mg oral ASA once daily, beginning in the early postoperative period. Noncompliance was eliminated by the administration of 300 mg ASA intravenously at 6-8 days post-operation. Blood was drawn immediately before, 1 h and 24 h after ASA administration. A platelet function analyzer (PFA-100™) was used to evaluate closure time (CT), turbidimetric platelet aggregation (TPA) and impedance platelet aggregation (IPA) induced by arachidonic acid (AA), collagen and ADP and results were compared with the respective values from 120 healthy individuals. At 1 h and 24 h after administration, we found that intravenous ASA caused CEPI-CT to be significantly prolonged with a reduction of AA and collagen-induced IPA. Despite postoperative oral ASA administration for 6-8 days, PFA-100™ CEPI and CADP-CT were significantly shorter and ADP-TPA and IPA values induced by any agonist were significantly greater in patients than in controls. Intravenous ASA had no significant influence on CADP-CT or ADP-induced IPA (ADP-IPA). Platelet tests for diagnosing patients as aspirin responders (ASA-R) or aspirin non-responders (ASA-NR) were found to be not comparable. Patients after CABG show augmented platelet dysfunction. Intravenous ASA administration may indicate a promising approach to reduce laboratory resistance after CABG procedure. The reason for this is not clear and requires additional clinical studies.

The impact of intravenous aspirin administration on platelet aspirin resistance after on-pump coronary artery bypass surgery

Aspirin resistance continues to be a major challenge in patients after coronary artery bypass grafting (CABG). We investigated the impact of intravenous aspirin on platelet function in this clinical setting. Forty-two patients received 100 mg of oral aspirin once daily, beginning on day 1 after the operation. Between day 6 and 8 post operation one oral dose was replaced by an intravenous dose of 300 mg. Platelet function analyzer (PFA-100™) closure times (CT), turbidimetric platelet aggregation (TPA) and impedance platelet aggregation (IPA) induced by arachidonic acid (AA), collagen and ADP were measured prior to and 1 h and 24 h after intravenous aspirin. Results obtained prior to the intravenous aspirin were compared with respective values from 120 healthy individuals. Despite the postoperative oral aspirin that was given once daily, ADP-induced TPA (ADPTPA) and IPA values induced by AA, ADP or collagen were significantly greater in patients than in controls, while PFA-100™ CT were significantly shorter. Intravenous aspirin induced a significant reduction of platelet aggregability as measured by collagen/epinephrine (CEPI) CT, TPA and IPA induced by AA and collagen 1 h and 24 h after administration. Intravenous aspirin was not found to influence collagen/ADP (CADP) CT and IPA induced by ADP. Concomitantly, the number of patients with laboratory aspirin resistance as measured by CEPI-CT and TPA but not by IPA induced by AA or collagen dropped significantly. Agreement in the detection of aspirin responders and non-responders among platelet function tests was poor. Our findings indicate that the intravenous aspirin appears to be a promising approach for reducing laboratory aspirin resistance during the postoperative phase of CABG.

Preservation of platelet aggregation and dense granule secretion during extended storage of blood samples in the presence of a synthetic dual inhibitor of factor Xa and thrombin

The clinical significance of platelet function tests may be limited by the use of citrate anticoagulant. We examined the influence of BAPA, a dual inhibitor of factor Xa and thrombin, on platelet responsiveness to agonists when measured between 2 and 48 h after venipuncture. Blood samples from 24 healthy individuals were anticoagulated with citrate or BAPA. Impedance platelet aggregation (IPA) and adenosine triphosphate (ATP) release induced by ADP, collagen and thrombin-receptor activating peptide (TRAP) were determined in whole blood after a storage period between 2 and 48 h after venipuncture. Citrate resulted in significantly reduced collagen or TRAP-induced IPA and ATP release when measured 32 h and 48 h after blood collection. ADP-induced IPA and ATP release in citrated blood dropped significantly between 8 and 24 h. The length of storage of BAPA-anticoagulated blood samples over 48 h had no significant influence on platelet response to collagen and TRAP. In BAPA-anticoagulated blood, ADP-induced IPA and ATP secretion in whole blood were maintained over a storage period of 32 h. No difference in ADP-induced ATP secretion in whole blood anticoagulated with citrate and BAPA was observed, but it was largely suppressed in BAPA-anticoagulated platelet rich plasma. IPA and ATP release remain stable for at least 32 h when whole blood is anticoagulated with a dual inhibitor of factor Xa and thrombin. This would allow shipment of samples for platelet function testing on the following day. Platelet secretion studies in whole blood may include platelet activation by ADP when BAPA is used as anticoagulant.

Assessing aspirin responsiveness using the Verify Now Aspirin assay

We read with great interest the study of Dyskiewicz-Korpanty et al. recently published in Thrombosis Research [1]. They evaluate aspirin responsiveness in 50 healthy subjects taking 325 mg/d during 3 days using whole blood impedance platelet aggregation and the rapid platelet function assay Verify Now™ Aspirin (RPFA, Accumetrics, San Diego, USA). Arachidonic acid-induced whole blood platelet aggregation (AA-aggregation) showed a 100% inhibition by aspirin in all subjects while there was a more limited effect when collagen was used as the agonist.

Impedance-Based Whole Blood and Optical-Based Platelet Rich Plasma Aggregation Methods for the Assessment of Celexocib Effects on Platelet Function: A Preliminary Report.

Cyclooxygenase-2 (COX-2) is the inducible cyclooxygenase isoform expressed by cells involved in inflammation. Platelets normally lack COX-2; however, the enzyme is expressed in megakaryocytes and newly formed platelets and may play a role in clinical syndromes associated with high platelet turnover (1, 2). Selective COX-2 inhibitors (coxibs), have become the mainstay for treatment of patients with arthritis and also have been widely used in cancer chemoprevention. Coxibs were found to have a safer GI toxicity profile when compared with classic NSAIDS; however, in some patients they may increase the risk of GI bleeding (3). The underlying mechanism has not yet been elucidated. Moreover, the role of coxibs in hemostatic alterations has been a subject of controversy. The aim of the study was to investigate the possible anti-platelet effects of celecoxib (200 mg/d for 7 days) in 7 healthy volunteers (2 females, 5 males; mean age = 35.7 ± 8; mean platelet count = 230 ± 23; mean Ht = 42.3 ± 6). A very sensitive whole blood impedance platelet aggregation assay, previously unused for this purpose, was employed for the assessment of celecoxib influence on platelet function. The test was performed along with a traditional, optical-based platelet rich plasma (PRP) aggregation method. Arachidonic acid (0.5; 0.25 mM), Collagen (2; 1mg/mL) and ADP (20, 10 mM) were used as platelet agonists in both tests.Celexocib did not affect platelet function in neither whole blood nor in PRP. The preliminary results of this study indicate that the increased bleeding tendency in patients treated with celecoxib is probably not related to platelet dysfunction.AssayArachidonic AcidCollagenADP0.5[mM]0.25[mM]2[μg/mL]1[μg/mL]20[μM]10[μ M]WB Impedance17.5±4.720.9±3.825.4±3.925.9±6.114.3±2.614.1±5Aggregation: Pre-drugPost-drug18±421±527.1±4.724±418.7±6.216.3±7PRP Optical118.1±10.3118.1±6.7101.4±13.7110±2.2104±15108±8.9Aggregation: Pre-drugPost-drug119.6±6.7112.9±10.2105.4±11.5110.4±7.5102.1±18.3107.7±9.6