Light Transmission Aggregometry Research Articles

Hemin promotes platelet activation and plasma membrane disintegration regulated by the subtilisin‐like proprotein convertase furin

AbstractPlatelet activation plays a critical role in thrombosis and hemostasis. Several pathophysiological situations lead to hemolysis, resulting in the liberation of free ferric iron‐containing hemin. Hemin has been shown to activate platelets and induce thrombo‐inflammation. Classical antiplatelet therapy failed to prevent hemin‐induced platelet activation. Thus, the aim of the present study was to characterize the mechanism of hemin‐induced platelet death (ferroptosis). We evaluated the in vitro effect of hemin on platelet activation, signaling, oxylipins, and plasma membrane destruction using light transmission aggregometry, ex vivo thrombus formation, multiparametric flow cytometry, micro‐UHPLC mass spectrometry for oxylipin profiling, and scanning ion conductance microscopy (SICM). We found that hemin induces platelet cell death indicated by increased ROS levels, phosphatidyl serine (PS) exposure, and loss of mitochondrial membrane potential (ΔΨm). Further, hemin causes lipid peroxidation and generation of distinct oxylipins, which strongly affects plasma membrane integrity leading to generation of platelet‐derived microvesicles. Interestingly, hemin‐dependent platelet death (ferroptosis) is specifically regulated by the subtilisin‐like proprotein convertase furin. In summary, platelet undergo a non‐apoptotic cell death mediated by furin. Inhibition of furin may offer a therapeutic strategy to control hemin‐induced thrombosis and thrombo‐inflammation at a site of hemolysis.

A study of platelet function in patients with chronic immune thrombocytopenia treated with thrombopoietin receptor agonists

BackgroundThrombopoietin 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. MethodsPlatelet 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. ResultsTPO-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 (rs = 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). ConclusionsThese 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.

Enhanced platelet sensitization is accompanied by increased expression of the transporter MRP4 and elevated plasma S1P levels in mild COVID-19 convalescents

Viral infections can lead to platelet activation and hemostatic complications. However, the extent to which platelet reactivity remains altered after convalescence, contributing to long-term health impairments as observed after COVID-19 is not yet fully understood. Therefore, we conducted a cohort study (DRKS00025217) to determine platelet function in individuals convalesced from mild COVID-19. Assays were performed ex vivo with blood from convalescents at 2–15 weeks and 6–10 months after convalescence, focusing on platelet aggregation, activation markers, and thrombin formation. In addition, two other potentially relevant factors for platelet function were examined: the immunomodulatory mediator sphingosine-1-phosphate (S1P) and the platelet expression of the transporter MRP4 (ABCC4). Our findings indicate that robust platelet functions, including platelet aggregation determined by light transmission aggregometry, and thrombin formation, were not altered in convalescents compared to matched control individuals. However, an elevation in subtle platelet activation markers, such as P-selectin surface expression and activation of glycoprotein IIb/IIIa, was observed 2–15 weeks after convalescence. This was accompanied by an increased expression of MRP4 in platelets and significantly elevated levels of S1P in platelet-poor plasma. Our findings suggest increased platelet sensitization and a pro-inflammatory state even after convalescence from mild COVID-19, pointing toward MRP4 and S1P as associated factors.

Hemin-induced platelet activation is regulated by the ACKR3 chemokine surface receptor and has implications for passivation of vulnerable atherosclerotic plaques.

In vulnerable atherosclerotic plaques, intraplaque hemorrhages (IPH) result in hemolysis of red blood cells and release of hemoglobin and free hemin. Hemin activates platelets and leads to thrombosis. Agonism of the inhibitory platelet receptor ACKR3 inhibits hemin-dependent platelet activation and thrombus formation. To characterize the effect of hemin and ACKR3 agonism on isolated human platelets, multi-color flow cytometry and classical experimental setup such as light transmission aggregometry and a flow chamber assay were used. Hemin induces platelet aggregation and ex vivo platelet-dependent thrombus formation on immobilized collagen under a low shear rate of 500 s-1, indicating that free hemin is a strong activator of platelet-dependent thrombosis. Recently, we described that ACKR3 is a prominent inhibitory receptor of platelet activation. Specific ACKR3 agonists but not conventional antiplatelet compounds such as COX-1 inhibitor (indometacin), ADP-receptor blocker (cangrelor), or PAR1 inhibitor (ML161) inhibit both hemin-dependent aggregation and thrombus formation. To further characterize the effect of hemin on platelet subpopulations, we established a multi-color flow cytometry assay. We found that hemin induces procoagulant (CD42bpos/PAC-1neg/AnnexinVpos), aggregatory (CD42bpos/PAC-1pos/AnnexinVneg), and inflammatory (CD42bpos/CXCR4pos/ACKR3pos/AnnexinVpos) platelet subpopulations. Treatment with ACKR3 agonists significantly decreased the formation of procoagulant and ACKR3pos platelets in response to hemin. We conclude that hemin is a strong activator for the formation of procoagulant platelets and thrombus formation which is dependent on the function of ACKR3. Activation of ACKR3 using specific agonists may offer a therapeutic strategy to regulate the vulnerability of atherosclerotic plaques in areas of IPH.

Functional characterization of a nanobody-based glycoprotein VI-specific platelet agonist

BackgroundGlycoprotein (GP)VI is a platelet-specific collagen receptor required for platelet activation during hemostasis. Platelet reactivity toward collagen is routinely assessed during diagnostic workup of platelet disorders. GPVI can be activated by inducing receptor clustering with suspensions of fibrillar collagen or synthetic cross-linked collagen-related peptide (CRP-XL). However, these suspensions are poorly standardized or difficult to produce. Nanobodies are small recombinant camelid-derived heavy-chain antibody variable regions. They are highly stable, specific, and ideal candidates for developing a stable GPVI agonist for diagnostic assays. ObjectivesDevelop a stable nanobody-based GPVI agonist. MethodsNanobody D2 (NbD2) was produced as dimers and purified. Tetramers were generated via C-terminal fusion of dimers with click chemistry. Nanobody constructs were functionally characterized with light transmission aggregometry (LTA) in platelet-rich plasma and whole blood flow cytometry. Diagnostic performance was assessed in patients with inherited platelet function disorders with LTA and flow cytometry. ResultsNbD2 was specific for human platelet GPVI. Dimers did not result in platelet activation in LTA or flow cytometry settings and fully inhibited CRP-XL-induced P-selectin expression and fibrinogen binding in whole blood and attenuated collagen-induced platelet aggregation in platelet-rich plasma. However, NbD2 tetramers caused full platelet aggregation, as well as P-selectin expression and fibrinogen binding. NbD2 tetramers were able to discriminate between inherited platelet function disorder patients and healthy controls based on fibrinogen binding, similar to CRP-XL. ConclusionNanobody tetramers to GPVI induce platelet activation and can be used to assess the GPVI pathway in diagnostic assays.

Dynamic Perioperative Platelet Activity and Cardiovascular Events in Peripheral Artery Disease

ObjectivePatients with peripheral artery disease (PAD) undergo lower extremity revascularization (LER) for symptomatic relief or limb salvage. Despite LER, patients remain at increased risk of platelet-mediated complications, such as major adverse cardiac and limb events (MACLE). Platelet activity is associated with cardiovascular events; yet little is known about the dynamic nature of platelet activity over time. We therefore investigated the change in platelet activity over time and its association with long-term cardiovascular risk. MethodsPatients with PAD undergoing LER were enrolled into the multicenter, prospective Platelet Activity and Cardiovascular Events (PACE) study. Platelet aggregation was assessed by light transmission aggregometry (LTA) to submaximal epinephrine (0.4μ M) immediately prior to LER, and on post-operative day 1 or 2 (POD1) and 30 (POD30). A hyperreactive platelet phenotype was defined as >60% aggregation. Patients were followed longitudinally for MACLE, defined as the composite of death, myocardial infarction, stroke, major lower extremity amputation, or acute limb ischemia leading to reintervention. ResultsAmong 287 patients undergoing LER, mean age was 70 ± 11 years, 33% were female, 61% were white, and 89% were on baseline antiplatelet therapy. Platelet aggregation to submaximal epinephrine induced a bimodal response; 15.5%, 16.8%, and 16.4% of patients demonstrated a hyperreactive platelet phenotype at baseline, POD1, and POD30, respectively. Platelet aggregation increased by 18.5% (P=0.001) from baseline to POD1, which subsequently returned to baseline at POD30. After a median follow-up of 19 months, MACLE occurred in 165 (57%) patients. After adjustment for demographics, clinical risk factors, procedure type, and antiplatelet therapy, platelet hyperreactivity at POD1 was associated with a significant hazard of long-term MACLE (aHR 4.61, 95% CI 2.08-10.20, P<0.001). ConclusionAmong patients with severe PAD, platelet activity increases following LER. Platelet hyperreactivity to submaximal epinephrine on POD1 is associated with long-term MACLE. Platelet activity following LER may represent a modifiable biomarker associated with excess cardiovascular risk.

Optimized Methodology to Produce Platelet-Rich Plasma and Perform Platelet Aggregation in Patients With Coronary Artery Disease.

Inter-individual differences in clopidogrel metabolism and platelet counts within platelet-rich plasma (PRP) intrigued us to optimize light transmittance aggregometry (LTA) assay in coronary artery disease (CAD) patients administered with clopidogrel and ticagrelor.The objective of the study was to optimize PRP preparation using separating gel PRP tubes to perform LTA among CAD patients on clopidogrel and ticagrelor. Initially, we optimized PRP preparation and platelet aggregation (PA) on healthy controls. To validate the protocol, we recruited 10 healthy controls and 28 CAD patients, comprising 16 on clopidogrel and 12 on ticagrelor regimen. Bio-X, India, supplied PRP tubes (9 mL) with 3.2% sodium citrate. PRP and autologous platelet-poor plasma (PPP) were prepared by centrifugation at 151 g for seven minutes and 3,780 g for 10 minutes, respectively. LTA was performed using platelet aggregometer TA-4V (Stago, Asnières-sur-Seine, France). Adenosine diphosphate (ADP) (10 µM) was used as an agonist. The mean maximum platelet aggregation (MPA) among controls, clopidogrel patients, and ticagrelor patients were 55.161±13.69%,53.17±22%, and 35.84±20.79% (p=0.042), respectively. The mean platelet volumes among groups were 9.34±2.51fL, 7.60±0.85fL, and 10.99±1.62fL (p≤0.01), respectively. We successfully optimized PRP preparation for the LTA assay using a PRP tube. Its application to measure PA routinely in a cardiology clinic seems propitious.

The effects of pathogen reduction technology on apheresis platelet concentrates stored in PAS.

The impact of pathogen reduction technology (PRT) such as Mirasol, and the effect of platelet additive solutions (PAS) on the activity and hemostatic profile of transfused apheresis platelets remain largely unknown. The aim of this study was to assess the in vitro hemostatic and metabolic profile of Mirasol treated platelets in PAS during a 7-day storage period. Ten split bags containing apheresis platelets stored in PAS were split into two groups; control platelets (No.=10 units) and PRT-treated platelets (No.=10 units). In vitro evaluation of the platelet components was performed on the 1st, 3rd, 5th, and 7th days of the storage period. Several metabolic parameters including pH, glucose, and lactate levels were evaluated, while assessment of their hemostatic capacity was performed using light transmission aggregometry (LTA) and viscoelastic studies such as rotational thromboelastometry (ROTEM) and thromboelastography (TEG). Last, Annexin V levels were measured though flow cytometry for evaluation of platelet activation. Clot strength, as reflected by the maximum clot firmness (MCF) and the maximum amplitude (MA) parameters of the viscoelastic studies was significantly decreased in the PRT-treated platelets compared to the control platelets (p<0.05). Clot strength based on MCF and MA values was also found to be decreasing over storage time in PRT-treated platelets (p<0.001), while this was not evident in control platelets. Moreover, the comparison between pH, glucose, and lactate levels were indicative of increased metabolic activity in PRT-treated platelets compared to control platelets (p<0.001). Last, Annexin-V was significantly higher in PRT-treated platelets compared to control platelets on the 7th day of the storage period (p<0.001). The results of this study indicate that increased PSL induced by PRT treatment leads to a decreased in vitro platelet hemostatic efficacy and increased metabolic activity. However, the clinical impact of these alterations needs further investigation.

Platelet aggregation response to cyclooxygenase inhibition and thromboxane receptor antagonism using impedance aggregometry: A pilot study.

Impedance aggregometry is an alternative to light transmission aggregometry that allows analysis of platelet function in whole blood samples. We hypothesized (1) impedance aggregometry would produce repeatable results, (2) inhibition of cyclooxygenase with aspirin would attenuate aggregation responses to collagen and abolish the aggregation response to arachidonic acid (AA), and (3) thromboxane receptor antagonism (terutroban) would attenuate the aggregation response to AA. Venous blood was obtained from 11 participants three times separated by at least 2 weeks. One sample followed 7-day-aspirin intervention (81 mg once daily; ASA), the others no intervention (control). Aggregation was induced using 1 μg/mL collagen ([col 1]), 5 μg/mL collagen ([col 5]), and 50 mM AA via impedance aggregometry to determine total aggregation (AUC) analyzed for intra-test repeatability, inter-test repeatability, intervention (ASA or control), and incubation (saline or terutroban). [col 1] showed high intra-test (p ≤ 0.03 visit 1 and 2) and inter-test repeatability (p < 0.01). [col 5] and AA showed intra- ([col 5] p < 0.01 visit 1 and 2; AA p < 0.001 visit 1 and 2) but not inter-test repeatability ([col 5] p = 0.48; AA p = 0.06). ASA attenuated AUC responses to [col 1] (p < 0.01), [col 5] (p = 0.03), and AA (p < 0.01). Terutroban attenuated AUC in response to AA (p < 0.01). [col 1] shows sufficient repeatability for longitudinal investigations of platelet function. [col 5] and AA may be used to investigate mechanisms of platelet function and metabolism at a single time point.

Fibrinolytic Platelet Decoys Reduce Cancer Metastasis by Dissociating Circulating Tumor Cell Clusters.

During metastasis, circulating tumor cells (CTCs) can travel in the bloodstream as individual cells or clusters, associated with fibrin and platelets. Clusters have a higher metastatic potential due to their increased ability to withstand shear stress and arrest in small vessels. Moreover, CTC-platelet interaction protects CTCs from shear stress and immune detection. The objective of this project is to develop a fibrinolytic platelet system to leverage platelet-CTC interactions and dissociate CTC clusters. For this approach, tissue plasminogen activator (tPA) is loaded onto two modified platelet systems: platelet Decoys and lyophilized platelets. The activities of the systems are characterized using a Förster Resonance Energy Transfer-based assay and an angiogenic assay. Furthermore, the ability of the system to dissociate cancer cell clusters in vitro is assessed using light transmission aggregometry. The data demonstrates that the fibrinolytic platelets can maintain tPA activity, interact with CTCs, and dissociate cancer cell clusters. Finally, fibrinolytic platelets are assessed in vivo, demonstrating a decreased tumor load and increased survival with tPA-Decoy treatment, which is selected as the optimal treatment based on favorable in vitro results and in vivo trials. Therefore, this fibrinolytic platelet approach is a promising method for leveraging platelet-CTC interactions to disperse CTC clusters and reduce metastasis.

Effect of toxins from different periodontitis-associated bacteria on human platelet function.

Periodontitis is caused by a dysbiosis of oral bacteria resulting in alveolar bone destruction and teeth loss. The role of platelets in pathogenesis of periodontitis is a subject of research. The release of toxins from periodontitis-associated bacteria may influence platelet function and contribute to the modulation of hemostatic or inflammatory responses. Therefore, we explored platelet function upon exposure to defined toxins: leukotoxin A from Aggregatibacter actinomycetemcomitans (LtxA), a synthetic version of the C14-Tri-LAN-Gly peptide from Fusobacterium nucleatum (C14), and lipopolysaccharides from Porphyromonas gingivalis (LPS). Light transmission aggregometry was performed after the addition of toxins to platelet-rich plasma in different doses. Flow cytometry was used to identify inhibitory effects of toxins by measuring phosphorylation of the vaso-dilator-stimulated phosphoprotein or to identify activating effects by the detection of CD62P expression. The release of chemokines derived from washed platelets was determined by immunoassays. Collagen-induced threshold aggregation values were diminished upon incubation with LtxA and C14, accompanied with an increase of vaso-dilator-stimulated phosphoprotein (VASP) phosphorylation, indicating platelet inhibition. In contrast, LPS did not affect aggregation but slightly enhanced CD62P expression under co-stimulation with low-dose thrombin pointing to slight platelet activation. The three toxins did not relevantly influence the secretion of chemokines. Although weak, the investigated toxins differently influenced human platelet function. LtxA and C14 mediated inhibitory effects, whereas LPS contributed to a slight activation of platelets. Further analysis of specific cellular responses mediated by bacterial toxins may render novel targets and suggestions for the treatment of periodontitis.

Evaluation of an automated platelet aggregation method for detection of congenital or acquired platelet function defects.

Light transmission aggregometry (LTA) is the most widely used laboratory method for an initial screening of patients with a suspected platelet function defect (PFD), and its use has also been proposed for assessing the efficacy of antiplatelet treatment (APT). An automated LTA method has been developed by Sysmex (Kobe, Japan) on a routine coagulation analyzer (CS-2400), together with a new research parameter called PAL (platelet aggregation level) to evaluate patients on APT. We evaluated the performance of CS-2400 compared to a stand-alone lumi-dual-aggregometer device in the diagnosis of PFD and in assessing the efficacy of APT. For these purposes, the study population was represented by a cohort of 23 patients with a previous diagnosis of PFD and a cohort of 28 patients on APT. Compared to healthy volunteers, patients with PFD showed a statistically significant reduction (p<0.05) in the maximal %light transmission, irrespective of the agonist used, both with the CS-2400 and the lumi-dual-aggregometer. As regards PFD patients, CS-2400 was effective in identifying the more severe defects, with a good sensibility and specificity, but less effective in identifying milder forms of PFD, such as platelet secretion defects. Patients on APT showed a statistically significant (p=0.001) reduced median %light transmission and PAL scores compared to healthy controls. Thanks to this LTA technology, CS-2400, a routine coagulation analyzer widely available in routine laboratories, could prove useful for initial assessment of patients with a suspected PFD. Moreover, the PAL scores were a fairly accurate reflection of the platelet response to APT.

Ticagrelor 60 vs. 90 mg in elderly ACS patients undergoing PCI: a randomized, crossover trial.

Although dual antiplatelet therapy with aspirin and a potent P2Y12 receptor inhibitor is currently recommended in patients with acute coronary syndrome (ACS), its use in elderly patients remains challenging. The aim of this trial is to evaluate the pharmacodynamic and pharmacokinetic profile of ticagrelor 60 vs. 90mg twice daily among elderly patients (≥75 years) with ACS undergoing percutaneous coronary intervention (PCI). PLINY The ELDER (NCT04739384) was a randomized, crossover trial testing the non-inferiority of a lower vs. standard dose of ticagrelor with respect to the primary endpoint of P2Y12 inhibition as determined by pre-dose P2Y12 reaction units (PRU) using the VerifyNow-P2Y12 (Accumetrics, San Diego, CA, USA). Other pharmacodynamic tests included light transmittance aggregometry, multiple electrode aggregometry, and response to aspirin. Plasma levels of ticagrelor and its active metabolite AR-C124910XX were also evaluated. A total of 50 patients (mean age 79.6±4.0 years, females 44%) were included in the trial. Ticagrelor 60mg was non-inferior to ticagrelor 90mg according to VerifyNow-P2Y12 results (PRU 26.4±32.1 vs. 30.4±39.0; least squares mean difference: -4; 95% confidence interval: -16.27 to 8.06; P for non-inferiority=0.002). Other pharmacodynamic parameters were similar between the two ticagrelor doses and there were no differences in response to aspirin. Plasma levels of ticagrelor (398.29±312.36ng/mL vs. 579.57±351.73ng/mL, P=0.006) and its active metabolite were significantly lower during treatment with ticagrelor 60mg. Although plasma concentrations were lower, ticagrelor 60mg twice daily provided a similar magnitude of platelet inhibition compared with ticagrelor 90mg twice daily among elderly patients undergoing PCI.

Whole Blood Aggregometry in Mice.

Aggregometry plays a crucial role in both clinical diagnostics and research within hematology, serving as a fundamental tool for understanding platelet function and its implications in physiological and pathological processes. In research, aggregometry provides insights into platelet aggregation dynamics and aids in understanding the underlying mechanisms of hemostasis, thrombosis, and related disorders. Light transmission aggregometry (LTA) and lumi-aggregometry, as well as whole blood aggregometry, are commonly employed methods. While LTA and lumi-aggregometry allow for specific platelet function assessment under controlled conditions, whole blood aggregometry provides a more physiologically relevant approach by evaluating platelet aggregation within the context of whole blood. Although both methodologies offer unique advantages, whole blood aggregometry allows for preservation of the native cellular environment, simplicity, and potential for better clinical correlation. In a clinical setting, with human blood samples, protocols are established for both LTA and whole blood aggregometry as they are frequently used diagnostic tools. A protocol for LTA and lumi-aggregometry in murine models has been described; however, to date, there is no standardized protocol for whole blood aggregometry in murine models accessible to hematology researchers. This article aims to outline a simple, basic protocol for murine whole blood aggregometry, offering an alternative method to the commonly used LTA aggregometry in research settings. Standardizing whole blood aggregometry protocols in murine models could enhance experimental reliability and facilitate translational research efforts in hematology. © 2024 Wiley Periodicals LLC. Basic Protocol 1: Whole blood aggregometry in mice Support Protocol: Phenylhydrazine-induced anemia in wild-type mice Basic Protocol 2: Hematocrit percentage in mice.

Point-of-Care Testing in Patients with Hereditary Disorders of Primary Hemostasis: A Narrative Review.

Inherited disorders of primary hemostasis, such as von Willebrand disease and congenital platelet disorders, can cause extensive, typically mucocutaneous bleeding. Assays to diagnose and monitor these disorders, such as von Willebrand factor activity assays and light transmission aggregometry, are performed in specialized hemostasis laboratories but are commonly not available in local hospitals. Due to the complexity and relative scarcity of these conventional assays, point-of-care tests (POCT) might be an attractive alternative in patients with hereditary bleeding disorders. POCTs, such as thromboelastography, are increasingly used to assess hemostasis in patients with acquired hemostatic defects, aiding clinical decision-making in critical situations, such as during surgery or childbirth. In comparison, the use of these assays in patients with hereditary hemostasis defects remains relatively unexplored. This review aims to give an overview of point-of-care hemostasis tests in patients with hereditary disorders of primary hemostasis. A summary of the literature reporting on the performance of currently available and experimental POCTs in these disorders is given, and the potential utility of the assays in various use scenarios is discussed. Altogether, the studies included in this review reveal that several POCTs are capable of identifying and monitoring severe defects in the primary hemostasis, while a POCT that can reliably detect milder defects of primary hemostasis is currently lacking. A better understanding of the strengths and limitations of POCTs in assessing hereditary defects of primary hemostasis is needed, after which these tests may become available for clinical practice, potentially targeting a large group of patients with milder defects of primary hemostasis.

The shear rate promotes pinocytosis of extracellular dextran in platelets.

Several conventional studies focused on platelet pinocytosis for possible utilization as drug delivery systems. Although platelet pinocytosis is important in such utilization, the impact of the shear rate on pinocytosis is unclear. Our objective was to investigate the relationship between shear rate and platelet pinocytosis in vitro. In addition, this study addressed the change in platelet aggregation reactivity with adenosine diphosphate (ADP) stimulation after pinocytosis. Porcine platelet-rich plasma was mixed with fluorescein isothiocyanate (FITC)-conjugated dextran and incubated for 15 min under shear conditions of 0, 500, and 1500 s-1. After incubation, confocal microscopic scanning and three-dimensional rendering were performed to confirm the internalization of FITC-dextran into platelets. The amount of FITC-dextran accumulated via platelet pinocytosis was compared using flow cytometry at each shear rate. In addition, light transmission aggregometry by ADP stimulation was applied to platelets after pinocytosis. The amount of intracellular FITC-dextran increased with higher shear rates. Platelets with increased amounts of intracellular FITC-dextran did not show changes in the aggregation reactivity to ADP. A higher shear rate promotes platelet pinocytosis, but enhanced pinocytosis does not affect aggregation sensitivity, which is stimulated by ADP.

Cardiorespiratory Fitness Is Associated with Decreased Platelet Reactivity.

Platelets are key mediators in cardiovascular disease (CVD). Low cardiorespiratory fitness (CRF) is a risk factor for CVD. The purpose of our study was to assess if CRF associates with platelet function. Platelet assays and cardiopulmonary exercise testing were conducted in the Framingham Heart Study (n = 3,014). Linear mixed effects models estimated associations between CRF (assessed by peak oxygen uptake [VO2]), and multiple platelet reactivity assays. Models were adjusted for multiple medications, risk factors, relatedness and prevalent CVD. Nineteen associations passed the significance threshold in the fully adjusted models, all indicating higher CRF associated with decreased platelet reactivity. Significant traits spanned multiple platelet agonists. Strongest associations were observed in Multiplate whole blood testing after TRAP-6 (e.g., velocity, beta = -0.563, 95% CI [-0.735,-0.391], p = 1.38E-10), ADP (e.g., velocity, beta = -0.514, 95% CI [-0.681,-0348], p = 1.41E-09), collagen (e.g., velocity, beta = -0.387, 95% CI [-0.549,-0.224], p = 3.01E-06), ristocetin (e.g., AUC, beta = -0.365, 95% CI [-0.522,-0.208], p = 5.17E-06) and arachidonic acid stimulation of platelets (e.g., velocity, beta = -0.298, 95% CI [-0.435,-0.162], p = 3.39E-04), and light transmission aggregometry (LTA) after ristocetin stimulation (e.g., max aggregation, beta = -0.362, 95% CI [-0.540,-0.184], p = 6.64E-05). One trait passed significance threshold in the aspirin sub-sample (LTA ristocetin primary slope, beta = -0.733, 95% CI [-1.134,-0.333], p = 3.30E-04), and another in a model including von Willebrand Factor levels as a covariate (U46619, a thromboxane receptor mimetic, AUC in the Optimul assay, beta = -0.36, 95%CI [-0.551,-0.168], p = 2.35E-04). No strong interactions were observed between the associations and sex, age or body mass index in formal interaction analyses. Our findings build on past work that shows CRF to be associated with reduced CVD by suggesting decreased platelet reactivity may play a mechanistic role. We found significant associations with multiple platelet agonists, indicating higher CRF may globally inhibit platelets; however, given multiple strong associations after TRAP-6 and ADP stimulation, PAR-1 and purinergic signaling may be most heavily involved. This is notable since each of these receptor pathways are tied to anti-coagulant (DOACs/thrombin inhibitors) and anti-platelet therapies (P2Y12/PAR1/PAR4 inhibitors) for CVD prevention.

Evaluation of clopidogrel response in healthy cats using a novel viscoelastic test and thromboelastography.

Cats with cardiomyopathy face an increased risk of arterial thromboembolism (ATE). Although clopidogrel is frequently utilized to mitigate this risk, feline responses to this therapy exhibit variability. This study evaluated 2 viscoelastic devices, thromboelastography (TEG) and Viscoelastic Coagulation Monitor (VCM), for monitoring clopidogrel in cats in comparison to light transmission aggregometry (LTA). Twenty-eight healthy cats received clopidogrel for 7 days. Blood was collected at baseline and after treatment for analysis by TEG, VCM, and LTA. On LTA, maximum amplitude, slope, and area under the curve (AUC) significantly decreased after treatment (p < 0.0001). On VCM, maximum clot firmness (MCF) significantly increased after treatment (p = 0.002). On TEG, R-time significantly prolonged (p = 0.024), while K and alpha angle significantly changed (p = 0.0002 and p = 0.0014, respectively). There was a moderate negative correlation between TEG R-time and LTA AUC (r = -0.39, p = 0.042). Eight cats were identified as non-responders to clopidogrel. Of the 8 non-responders, 6 (75%) had shortened R time after treatment. VCM appeared to be less discriminatory in identifying non-responders. LTA remained the gold standard of monitoring clopidogrel treatment in cats. Unexpected changes on VCM and TEG were likely related to high interindividual and assay variability and increased sensitivity of feline platelets. R-time on TEG may have potential utility for point-of-care monitoring of clopidogrel response in cats.

Lysophosphatidylcholine induces oxidative stress and calcium-mediated cell death in human blood platelets.

Platelets are essential component of circulation that plays a major role in hemostasis and thrombosis. During activation and its demise, platelets release platelet-derived microvesicles, with lysophosphatidylcholine (LPC) being a prominent component in their lipid composition. LPC, an oxidized low-density lipoprotein, is involved in cellular metabolism, but its higher level is implicated in pathologies like atherosclerosis, diabetes, and inflammatory disorders. Despite this, its impact on platelet function remains relatively unexplored. To address this, we studied LPC's effects on washed human platelets. A multimode plate reader was employed to measure reactive oxygen species and intracellular calcium using H2DCF-DA and Fluo-4-AM, respectively. Flow cytometry was utilized to measure phosphatidylserine expression, mitochondrial membrane potential (ΔΨm), and mitochondrial permeability transition pore (mPTP) formation using FITC-Annexin V, JC-1, and CoCl2/calcein-AM, respectively. Additionally, platelet morphology and its ultrastructure were observed via phase contrast and electron microscopy. Sonoclot and light transmission aggregometry were employed to examine fibrin formation and platelet aggregation, respectively. The findings demonstrate that LPC induced oxidative stress and increased intracellular calcium in platelets, resulting in increased phosphatidylserine expression and reduced ΔΨm. LPC triggered caspase-independent platelet death and mPTP opening via cytosolic and mitochondrial calcium, along with microvesiculation and reduced platelet counts. LPC increased the platelet's size, adopting a balloon-shaped morphology, causing membrane fragmentation and releasing its cellular contents, while inducing a pro-coagulant phenotype with increased fibrin formation and reduced integrin αIIbβ3 activation. Conclusively, this study reveals LPC-induced oxidative stress and calcium-mediated platelet death, necrotic in nature with pro-coagulant properties, potentially impacting inflammation and repair mechanisms during vascular injury.

The Effects of Aspirin dose in Children with Congenital and Acquired Heart Disease. Results from the Paediatric Study of Aspirin Efficacy using Diagnostic and Monitoring Tools (PAED-M).

The optimal dose of aspirin required in children with congenital and acquired heart disease is not known. The primary aim of this prospective observational study was to evaluate the effects of aspirin dose on platelet inhibition. The secondary aim was to determine the prevalence and clinical predictors of aspirin non-responsiveness. Measurements were by Thromboelastography with Platelet Mapping (TEGPM) only in children less than 2years (y) of age with particular emphasis on the parameter known as maximum amplitude with arachidonic acid (MAAA) and using both TEGPM, and light transmission aggregometry (LTA) in children greater than 2y. We prospectively studied 101 patients with congenital and acquired cardiac disease who were receiving empirical doses of aspirin for a minimum of 4weeks but no other antiplatelet agents. Patients were stratified according to dose concentration and age. There was a trend toward lower age in patients with no response or semi-response to aspirin. All patients were considered responsive to aspirin in the higher-dose quartile (Q4) with a median dose of 4.72 (4.18-6.05) mg/kg/day suggesting that patients in this age group may require 5mg/kg/day as an empirical dose. In children > 2y, there was no significant difference in inhibition found in patients dosed at higher doses in Q3 versus Q4 suggesting that patients in this cohort are responsive with 3mg/kg/day dose. The current practices may lead to reduced platelet inhibition in some children due to under-dosing or overdosing in others. In conclusion, younger children require higher doses of aspirin. Laboratory assessment is warranted in this population to mitigate against under and overdosing.