Observation of granulocyte function during ex vivo thrombus formation for patients with ANKRD26-associated thrombocytopenia

ANKRD26-associated thrombocytopenia is a non-syndromic hereditary thrombocytopenia for which there are currently no formal diagnostic criteria. It is known that the probability of myeloid leukemia in patients with pathogenetic variants in the ANKRD26 gene significantly increases, however, studies of the functioning of granulocytes in this pathology have not been conducted. Aims: Analysis of the functioning of granulocytes and platelets during ex vivo thrombosis in patients with ANKRD26-associated thrombocytopenia. The study was approved by the Independent Ethics Committee of the Dmitry Rogachev National Medical Research Center of Pediatric Hematology, Oncology, and Immunology. Two patients and 10 healthy volunteers were included in the study. Intracellular signaling and platelet functional responses were observed by continuous flow cytometry. Ex vivo thrombus formation and granulocyte functioning were observed on a fluorescence microscope in parallel-plane flow chambers containing fibrillar collagen. Upon physiological activation (ADP, collagen) of patients’ platelets in vitro, there were no significant differences between the platelets of patients and healthy donors. However, the observed ex vivo size of platelet aggregates was significantly reduced in comparison with healthy donors and published data on patients with other thrombocytopenias. The observed number and activity (movement velocity) of granulocytes of patients was within normal values. However, significant morphological differences were observed for granulocytes of patients compared with granulocytes of healthy donors: there was an increased spreading of granulocytes, in particular, expressed in a large number of thin pseudopodia, as well as an increased curvature of the motion trajectories of granulocytes. Ex vivo observation of thrombus formation in patients with ANKRD26- associated thrombocytopenia, a significantly reduced thrombus size is observed with normal platelet activity and increased variability in the shape of granulocytes.

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Anticoagulant and antithrombotic properties of platelet protease nexin-1

Blood ◽

10.1182/blood-2009-04-217240 ◽

2010 ◽

Vol 115 (1) ◽

pp. 97-106 ◽

Cited By ~ 45

Author(s):

Yacine Boulaftali ◽

Frédéric Adam ◽

Laurence Venisse ◽

Véronique Ollivier ◽

Benjamin Richard ◽

...

Keyword(s):

Ex Vivo ◽

Thrombus Formation ◽

Human Platelets ◽

Platelet Surface ◽

Type Plasminogen Activator ◽

Healthy Donors ◽

Protease Nexin ◽

Deficient Mice

AbstractProtease nexin–1 (PN-1) is a serpin that inhibits plasminogen activators, plasmin, and thrombin. PN-1 is barely detectable in plasma but is expressed by platelets. Here, we studied platelet PN-1 in resting and activated conditions and its function in thrombosis. Studies on human platelets from healthy donors and from patients with a Gray platelet syndrome demonstrate that PN-1 is present both at the platelet surface and in α-granules. The role of PN-1 was investigated in vitro using human platelets incubated with a blocking antibody and using platelets from PN-1–deficient mice. Both approaches indicate that platelet PN-1 is active on thrombin and urokinase-type plasminogen activator. Blockade and deficiency of platelet PN-1 result in accelerated and increased tissue factor-induced thrombin generation as indicated by calibrated automated thrombography. Moreover, platelets from PN-1–deficient mice respond to subthreshold doses of thrombin, as assessed by P-selectin expression and platelet aggregation. Thrombus formation, induced ex vivo by collagen in blood flow conditions and in vivo by FeCl3-induced injury, is significantly increased in PN-1–deficient mice, demonstrating the antithrombotic properties of platelet PN-1. Platelet PN-1 is thus a key player in the thrombotic process, whose negative regulatory role has been, up to now, markedly underestimated.

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Biochemical and Pharmacological Properties of SANORG 34006, a Potent and Long-Acting Synthetic Pentasaccharide

Blood ◽

10.1182/blood.v91.11.4197 ◽

1998 ◽

Vol 91 (11) ◽

pp. 4197-4205 ◽

Cited By ~ 151

Author(s):

J.M. Herbert ◽

J.P. Hérault ◽

A. Bernat ◽

R.G.M. van Amsterdam ◽

J.C. Lormeau ◽

...

Keyword(s):

Thrombin Generation ◽

Ex Vivo ◽

Thrombus Formation ◽

Factor Xa ◽

Therapeutic Index ◽

Inhibitory Effect ◽

Experimental Models ◽

Treatment And Prevention ◽

Long Acting

Abstract SANORG 34006 is a new sulfated pentasaccharide obtained by chemical synthesis. It is an analog of the “synthetic pentasaccharide” (SR 90107/ ORG 31540) which represents the antithrombin (AT) binding site of heparin. SANORG 34006 showed a higher affinity to human AT than SR 90107/ORG 31540 (kd = 1.4 ± 0.3 v 48 ± 11 nmol/L), and it is a potent and selective catalyst of the inhibitory effect of AT on factor Xa (1,240 ± 15 anti–factor Xa U/mg v850 ± 27 anti-factor Xa U/mg for SR 90107/ORG 31540). In vitro, SANORG 34006 inhibited thrombin generation occurring via both the extrinsic and intrinsic pathway. After intravenous (IV) or subcutaneous (SC) administration to rabbits, SANORG 34006 displayed a long-lasting anti–factor Xa activity and inhibition of thrombin generation (TG) ex vivo. SANORG 34006 was slowly eliminated after IV or SC administration to rats, rabbits, and baboons, showed exceptionally long half-lives (between 9.2 hours in rats and 61.9 hours in baboons), and revealed an SC bioavailability near 100%. SANORG 34006 displayed antithrombotic activity by virtue of its potentiation of the anti–factor Xa activity of AT. It strongly inhibited thrombus formation in experimental models of thromboplastin/stasis-induced venous thrombosis in rats (IV) and rabbits (SC) (ED50values = 40.0 ± 3.4 and 105.0 ± 9.4 nmol/kg, respectively). The duration of its antithrombotic effects closely paralleled the ex vivo anti–factor Xa activity. SANORG 34006 enhanced rt-PA–induced thrombolysis and inhibited accretion of125I-fibrinogen onto a preformed thrombus in the rabbit jugular vein suggesting that concomitant use of SANORG 34006 during rt-PA therapy might be helpful in facilitating thrombolysis and preventing fibrin accretion onto the thrombus under lysis. Contrary to standard heparin, SANORG 34006 did not enhance bleeding in a rabbit ear incision model at a dose that equals 10 times the antithrombotic ED50 in this species and, therefore, exhibited a favorable therapeutic index. We suggest that SANORG 34006 is a promising compound in the treatment and prevention of various thrombotic diseases.

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ROLE OF NITRIC OXIDE (NO) IN CAPSAICIN MEDIATED ANTI-PLATELET ACTIVITY IN IN VITRO, IN VIVO, EX-VIVO MODEL OF PLATELET AGGREGATION ASSAY AND ARTERIAL THROMBOSIS IN RAT: POTENTIAL THERAPEUTIC TARGET?

International Journal of Pharmacy and Pharmaceutical Sciences ◽

10.22159/ijpps.2018v10i4.22474 ◽

2018 ◽

Vol 10 (4) ◽

pp. 44

Author(s):

Mihir K Patel ◽

Kiranj K. Chaudagar ◽

Anita A. Mehta

Keyword(s):

Platelet Aggregation ◽

Arterial Thrombosis ◽

Ex Vivo ◽

Platelet Activity ◽

Aggregation Assay ◽

Thrombosis Model ◽

Platelet Aggregation Assay

Objective: Although recent advances in the treatment of congestive heart disease, mortality among patients’ remains a questionable remark. Therefore, we evaluated the role of capsaicin on in vitro and ex vivo platelet aggregation induced by Adenosine Di-Phosphate (ADP) as well as in in vivo thrombosis models and role of NO, KATP was also identified in the capsaicin-induced anti-platelet animal model as well as in vivo model of arterial thrombosis.Methods: According to body weight wistar rats were divided into five groups. Group I and Group II was treated with saline and capsaicin (3 mg/kg, i. v), while animals from Group III were treated with N(ω)-nitro-L-arginine methyl ester (L-NAME) (30 mg/kg, i. v) 30 min before administration of capsaicin (3 mg/kg, i. v). Group IV animals were treated with glibenclamide (10 mg/kg,i. v) 30 min before administration of capsaicin (3 mg/kg, i. v). Group V was considered as a positive control and administered clopidogrel (30 mg/kg, p. o). Animals were subjected for in vitro, ex-vivo platelet aggregation assay. ADP (30µM) was utilized as an aggregating agent in these experiments. After these assays; animals of each group were subjected for subaqueous tail bleeding time in a rat model and FeCl3-induced arterial thrombosis model in rats.Results: In ADP-induced in vitro platelet aggregation, a significant reduction in % platelet aggregation was observed at 50µM (64.35±4.641) and 100µM (52.72±4.192) concentration of capsaicin as compared to vehicle control (85.82±3.716). Capsaicin (3 mg/kg, i. v) also showed a significant reduction (49.53±4.075) in ex-vivo ADP-induced platelet aggregation as compared to vehicle control (89.38±2.057). In FeCl3 induced arterial thrombosis model, Capsaicin (3 mg/kg, i. v) exhibited an increase in time to occlusion in this rodent model and presence of the L-NAME and glibenclamide had inhibited the activity of capsaicin.Conclusion: In our study, capsaicin (50 µM, 100µM) exhibited potent anti-platelet activity in ADP-induced platelet aggregation, similarly capsaicin exhibited significant anti-platelet action in the ex-vivo study. Moreover, the presence of L-NAME and glibenclamide inhibited the anti-thrombotic and anti-platelet action of capsaicin. Therefore, it was concluded that NO and KATP may be involved in the anti-thrombotic action of capsaicin.

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C5a and C5aR1 are key drivers of microvascular platelet aggregation in clinical entities spanning from aHUS to COVID-19

Blood Advances ◽

10.1182/bloodadvances.2021005246 ◽

2021 ◽

Author(s):

Sistiana Aiello ◽

Sara Gastoldi ◽

Miriam Galbusera ◽

Piero Luigi Ruggenenti ◽

Valentina Portalupi ◽

...

Keyword(s):

Endothelial Cells ◽

Bacterial Infections ◽

Viral Infections ◽

Ex Vivo ◽

Inflammatory Diseases ◽

Thrombus Formation ◽

Alternative Pathway ◽

Atypical Hemolytic Uremic Syndrome ◽

Uremic Syndrome

Unrestrained activation of the complement system till the terminal products, C5a and C5b-9, plays a pathogenetic role in acute and chronic inflammatory diseases. In endothelial cells, complement hyperactivation may translate into cell dysfunction, favoring thrombus formation. The aim of this study was to investigate the role of the C5a/C5aR1 axis as opposite to C5b-9 in inducing endothelial dysfunction and loss of anti-thrombogenic properties. In vitro and ex vivo assays with serum from patients with atypical hemolytic uremic syndrome (aHUS) -a prototype rare disease of complement-mediated microvascular thrombosis due to genetically determined alternative pathway dysregulation- and cultured microvascular endothelial cells, demonstrated that the C5a/C5aR1 axis is a key player of endothelial thromboresistance loss. C5a added to normal human serum, fully recapitulated the pro-thrombotic effects of aHUS serum. Mechanistic studies showed that C5a caused RalA-mediated exocytosis of vWF and P-selectin from Weibel-Palade bodies, which favored further vWF binding on the endothelium and platelet adhesion and aggregation. In patients with severe COVID-19 -who suffered from acute activation of complement triggered by SARS-CoV-2 infection- we found the same C5a-dependent pathogenic mechanisms. These results highlight C5a/C5aR1 as a common pro-thrombogenic effector spanning from genetic rare diseases to viral infections, and may have clinical implications. Selective C5a/C5aR1 blockade could have advantages over C5 inhibition, since the former preserves the formation of C5b-9 that is critical to control bacterial infections that often develop as comorbidities in severely ill patients. (Clinicaltrials.gov identifier NCT02464891)

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A Versatile Model of Microfluidic Perifusion System for the Evaluation of C-Peptide Secretion Profiles: Comparison Between Human Pancreatic Islets and HLSC-Derived Islet-Like Structures

Biomedicines ◽

10.3390/biomedicines8020026 ◽

2020 ◽

Vol 8 (2) ◽

pp. 26 ◽

Cited By ~ 2

Author(s):

Yonathan Gomez ◽

Victor Navarro-Tableros ◽

Ciro Tetta ◽

Giovanni Camussi ◽

Maria Felice Brizzi

Keyword(s):

High Glucose ◽

Ex Vivo ◽

C Peptide ◽

Healthy Donors ◽

Secretion Profile ◽

Lower Amplitude ◽

Peptide Secretion ◽

Perifusion System

A robust and easy-to-use tool for the ex vivo dynamic evaluation of pancreatic islet (PI) function is essential for further development of novel cell-based therapeutic approaches to treating diabetes. Here, we developed four different glucose perifusion protocols (GPPs) in a microfluidic perifusion system (MPS), based entirely on commercially available components. After validation, the GPPs were used to evaluate C-peptide secretion profiles of PIs derived from different donors (healthy, obese, and type 2 diabetic) and from human liver stem-cell-derived islet-like structures (HLSC-ILS). Using this device, we demonstrated that PIs derived from healthy donors displayed a physiological C-peptide secretion profile as characterized by the response to (a) different glucose concentrations, (b) consecutive pulses of high-glucose concentrations, (c) a glucose threshold ranging from 5–8 mM, and (d) a constant high-glucose perifusion in a biphasic manner. Moreover, we were able to detect a dysregulated secretion profile in PIs derived from both obese and type 2 diabetes mellitus (T2DM) donors. Finally, we also evaluated the kinetic secretion profiles of HLSC-ILS, demonstrating that, nonetheless, with a lower amplitude of secretion compared to PI derived from healthy donors, they were already glucose-responsive on day seven post-differentiation. In conclusion, we have provided evidence that our MPS is a versatile device and may represent a valuable tool to study insulin-producing cells in vitro.

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Severe platelet dysfunction in NHL patients receiving ibrutinib is absent in patients receiving acalabrutinib

Blood Advances ◽

10.1182/bloodadvances.2017011999 ◽

2017 ◽

Vol 1 (26) ◽

pp. 2610-2623 ◽

Cited By ~ 35

Author(s):

Alexander P. Bye ◽

Amanda J. Unsworth ◽

Michael J. Desborough ◽

Catherine A. T. Hildyard ◽

Niamh Appleby ◽

...

Keyword(s):

Platelet Function ◽

Ex Vivo ◽

Thrombus Formation ◽

Critical Role ◽

Platelet Dysfunction ◽

Non Hodgkin Lymphoma ◽

Healthy Donors ◽

Increased Risk ◽

Btk Inhibitor ◽

Size And Morphology

Abstract The Bruton tyrosine kinase (Btk) inhibitor ibrutinib induces platelet dysfunction and causes increased risk of bleeding. Off-target inhibition of Tec is believed to contribute to platelet dysfunction and other side effects of ibrutinib. The second-generation Btk inhibitor acalabrutinib was developed with improved specificity for Btk over Tec. We investigated platelet function in patients with non-Hodgkin lymphoma (NHL) receiving ibrutinib or acalabrutinib by aggregometry and by measuring thrombus formation on collagen under arterial shear. Both patient groups had similarly dysfunctional aggregation responses to collagen and collagen-related peptide, and comparison with mechanistic experiments in which platelets from healthy donors were treated with the Btk inhibitors suggested that both drugs inhibit platelet Btk and Tec at physiological concentrations. Only ibrutinib caused dysfunctional thrombus formation, whereas size and morphology of thrombi following acalabrutinib treatment were of normal size and morphology. We found that ibrutinib but not acalabrutinib inhibited Src family kinases, which have a critical role in platelet adhesion to collagen that is likely to underpin unstable thrombus formation observed in ibrutinib patients. We found that platelet function was enhanced by increasing levels of von Willebrand factor (VWF) and factor VIII (FVIII) ex vivo by addition of intermediate purity FVIII (Haemate P) to blood from patients, resulting in consistently larger thrombi. We conclude that acalabrutinib avoids major platelet dysfunction associated with ibrutinib therapy, and platelet function may be enhanced in patients with B-cell NHL by increasing plasma VWF and FVIII.

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Novel 12-LOX Inhibitor ML355 Attenuates Platelet Reactivity and Impairs Thrombus Growth, Stability and Vessel Occlusion In Vivo

Blood ◽

10.1182/blood.v126.23.3442.3442 ◽

2015 ◽

Vol 126 (23) ◽

pp. 3442-3442 ◽

Cited By ~ 1

Author(s):

Reheman Adili ◽

Theodore R Holman ◽

Michael Holinstat

Keyword(s):

Platelet Aggregation ◽

Platelet Function ◽

Platelet Adhesion ◽

Ex Vivo ◽

Platelet Reactivity ◽

Thrombus Formation ◽

Vessel Occlusion ◽

Growth Stability

Abstract Background: Adequate platelet reactivity is required for platelet adhesion and aggregation at the site of vascular injury to maintain hemostasis. However, excessive platelet reactivity can also lead to the formation of occlusive thrombi, the predominate underlying cause of myocardial infarction and stroke. While current anti-platelet treatments limit platelet function, they often result in an increased risk of bleeding. 12-lipoxygenase (12-LOX), an oxygenase highly expressed in the platelet, has been demonstrated by our lab and others to regulate PAR4 and GPVI-mediated platelet reactivity suggesting a role of 12-LOX in regulation of vivo thrombosis. However, the ability to pharmacologically target 12-LOX in vivo has not been established to date. Aims: To determine how 12-LOX regulates thrombus formation in vivo and whether platelet 12-LOX is an effective target for anti-platelet therapeutics, wild-type (WT) or 12-LOX deficient (12-LOX-/-) mice were treated with or without the 12-LOX inhibitor, ML355, and were assessed for inhibitory effects on platelet activation in vitro, ex-vivo and in vivo. Methods: The effect of the novel 12-LOX inhibitor ML355 on human platelet function was assessed in vitro by platelet aggregometry, ex vivo by perfusion chamber. In vivo thrombus formation and vessel occlusion in small and large vessels were studied in 12-LOX-/-, WT mice and mice treated with ML355 using intravital microscopy using the FeCl3 injury models. Results: Using in vitro platelet aggregation assays, ML355 dose dependently inhibited thrombin, PAR1-AP, and PAR4-AP-induced aggregation in washed human platelets. Interestingly, the negative regulatory effects of ML355 inhibition of 12-LOX can be overcome by high concentration of thrombin. Additionally, ML355 was able to attenuate ADP-induced platelet aggregation both in platelet-rich-plasma and whole blood. In ex vivo flow chamber assays, platelet adhesion and thrombus formation on collagen-coated surfaces at high shear was attenuated in both mouse and human whole blood after incubation with ML355. Further, platelet aggregation and thrombus growth in 12-LOX-/- mice was impaired in FeCl3-induced mesenteric or carotid artery thrombosis models. Thrombi in 12-LOX-/- mice were unstable and frequently form emboli, which resulted in impaired vessel occlusion or reopening. Additionally, thrombus formation and vessel occlusion was impaired in ML355 treated WT mice. Conclusions: The highly selective 12-LOX inhibitor ML355 inhibits platelets aggregation induced by various platelet agonists and ML355 inhibition of platelet function is not agonist specific. Platelet function at high shear in ex vivo conditions in both mice and human was attenuated in the presence of ML355. Thrombus growth, stability, and vessel occlusion was impaired in mice deficient for 12-LOX. Finally, the highly selective 12-LOX inhibitor ML355 attenuates thrombus formation and prevents vessel occlusion in vivo. Our data strongly indicates 12- LOX is an important determinant of platelet reactivity and inhibition of platelet 12-LOX may represent a new target for anti-platelet therapeutics. Disclosures No relevant conflicts of interest to declare.

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Platelet ADP receptors contribute to the initiation of intravascular coagulation

Blood ◽

10.1182/blood-2003-05-1385 ◽

2004 ◽

Vol 103 (2) ◽

pp. 594-600 ◽

Cited By ~ 80

Author(s):

Catherine Leon ◽

Meike Alex ◽

Antje Klocke ◽

Eberhard Morgenstern ◽

Christine Moosbauer ◽

...

Keyword(s):

Whole Blood ◽

Ex Vivo ◽

Thrombus Formation ◽

Intravascular Coagulation ◽

Adp Receptors ◽

Adp Receptor ◽

Deficient Mice ◽

Storage Pools

Abstract While the adenosine 5′-diphosphate (ADP) pathway is known to enhance thrombus formation by recruiting platelets and leukocytes to the primary layer of collagen-adhering platelets, its role for the initiation of coagulation has not been revealed. Ex vivo inhibition of the P2Y12 ADP receptor by clopidogrel administration diminished the rapid exposure of tissue factor (TF), the major initiator of coagulation, in conjugates of platelets with leukocytes established by the contact of whole blood with fibrillar collagen. Under in vitro conditions, the P2Y12 and P2Y1 ADP receptors were both found to be implicated in the exposure of TF in collagen-activated whole blood. Immunoelectron-microscopy revealed that collagen elicited the release of TF from its storage pools within the platelets. Functional activation of the intravascular TF was reduced by inhibition of the ADP receptors, partially due to the disruption of the platelet-neutrophil adhesions. Injection of collagen into the venous system of mice increased the number of thrombin-antithrombin complexes, indicative for the formation of thrombin in vivo. In P2Y1-deficient mice, the ability of collagen to enhance the generation of thrombin was impaired. In conclusion, the platelet ADP pathway supports the initiation of intravascular coagulation, which is likely to contribute to the concomitant formation of fibrin at the site of the growing thrombus.

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Increased Platelet S100A8/S100A9 Associated with Vasculitis in Granulomatosis with Polyangiitis (GPA)

Blood ◽

10.1182/blood-2021-152291 ◽

2021 ◽

Vol 138 (Supplement 1) ◽

pp. 3142-3142

Author(s):

Li Guo ◽

Ben Berger ◽

Jesse W Rowley ◽

Neal D Tolley ◽

Bhanu Kanth Manne ◽

...

Keyword(s):

Board Of Directors ◽

Granulomatosis With Polyangiitis ◽

Vascular Inflammation ◽

Differentially Expressed ◽

Functional Responses ◽

Advisory Committees ◽

Activated Platelets ◽

Healthy Donors ◽

Increased Risk

Abstract Granulomatosis with polyangiitis (GPA), formerly known as Wegener's Granulomatosis, is characterized by vasculitis that predominantly affects small- and medium-sized blood vessels in the sinuses, lungs, and kidneys. In addition to vascular inflammation, GPA is also characterized by an increased risk of thrombosis. The role of platelets in GPA pathogenesis remains incompletely understood. We aimed to better understand the changes in platelet gene expression and function in patients with GPA. Forty-two patients diagnosed with GPA (n=9 with active GPA and n=33 with GPA in remission) and 25 healthy, age-, gender-, and race-matched donors were enrolled. Patients with GPA showed typical disease manifestations, with an average Birmingham Vasculitis Activity Score of 1.6 (Mean±SD 1.6±3.5). One sixth of GPA patients (7/42) had a history of thrombosis. When stimulated with thrombin receptor activating peptide (TRAP, 50nM), platelets from patients with GPA showed significantly increased expression of P-selectin as compared to healthy controls (P-selectin+% Mean±SEM: Healthy 15.50±1.84 vs GPA 25.71±16.05, P<0.05). This suggests increased platelet activation in GPA, consistent with previous findings of increased platelet aggregation in vitro in GPA. In addition, released chemokines sCD40L and platelet-derived growth factor (PDGF) by activated platelets were increased in patients with GPA when we measured the cytokines in the platelet poor plasma using the Miliplex human cytokine Assay [sCD40L (ng/mL) Mean±SEM: Healthy 63.05±6.63 vs GPA 100.40±11.86, P<0.05, PDGF-AA (pg/mL) Mean±SEM: Healthy 137.50±46.52 vs GPA 357.30±79.65, P=0.052]. Next, we performed RNA-sequencing on platelets from GPA patients (n=8, 3 with active GPA disease and 5 in remission) and, for comparison, 4 healthy donors. We identified 75 genes that were significantly differentially expressed between GPA patients and healthy donors. The top 30 genes are listed in Figure 1A. S100A8 and S100A9 were the top two significantly differentially expressed transcripts in patients with GPA (Fig. 1B). These two genes encode proteins that form a heterodimer S100A8/S100A9 (commonly known as calprotectin) known to be increased in the plasma of GPA patients and associated with disease activity. Interestingly, platelets have not been identified as the cellular source of plasma calprotectin in GPA previously. Significantly increased RNA and protein expression of S100A8 and S100A9 in GPA patients was independently validated by qRT-PCR and immunoblot, respectively. The mRNA expression of S100A8 and S100A9 in platelets were significantly correlated with p-ANCA and anti-MPO antibodies, indicating platelet S100A8/S100A9 promotes neutrophil activation and inflammation (Mann-Whitney nonparametric test, P<0.05). As previously reported, plasma levels of calprotectin were also increased in GPA patients. To further evaluate if plateletS100A8/S100A9 mediates endothelial inflammation and vasculitis, we co-cultured platelets activated with thrombin (which increases S100A8/S100A9 secretion) with endothelial cells in the presence or absence of an anti-S100A8/S100A9 blocking antibody. Activated platelets triggered endothelial cell inflammation (e.g., increased expression of ICAM-1) that was significantly reduced when S100A8/S100A9 was blocked. In summary, the platelet transcriptome is altered in patients with GPA, with S100A8 and S100A9 being the top upregulated genes. Platelet functional responses are enhanced in patients with GPA, and our data suggests that increased plasma calprotectin levels in GPA patients may be platelet derived. Platelets and platelet S100A8/S100A9 appear to mediate vascular inflammation and thrombosis in GPA. Figure 1 Figure 1. Disclosures Rondina: Novartis: Research Funding; Platelet Biogenesis: Membership on an entity's Board of Directors or advisory committees; Acticor Biotech: Membership on an entity's Board of Directors or advisory committees; Platelet Transcriptomics: Patents & Royalties.

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A novel nucleotide-based thrombin inhibitor inhibits clot-bound thrombin and reduces arterial platelet thrombus formation

Blood ◽

10.1182/blood.v83.3.677.bloodjournal833677 ◽

1994 ◽

Vol 83 (3) ◽

pp. 677-682 ◽

Cited By ~ 1

Author(s):

WX Li ◽

AV Kaplan ◽

GW Grant ◽

JJ Toole ◽

LL Leung

Keyword(s):

Ex Vivo ◽

Platelet Rich Plasma ◽

Thrombus Formation ◽

Thrombin Inhibitors ◽

Thrombin Inhibitor ◽

Shear Rates ◽

High Shear Rates ◽

Dependent Inhibition ◽

Platelet Thrombus

A novel thrombin inhibitor based on single-stranded (ss) deoxynucleotides with the sequence GGTTGGTGTGGTTGG (thrombin aptamer) has been recently discovered. In this study, we tested its efficacy in inhibiting clot-bound thrombin activity and platelet thrombus formation in an ex vivo whole artery angioplasty model. The thrombin aptamer showed a specific dose-dependent inhibition of thrombin-induced platelet aggregation (0.5 U/mL) in human platelet-rich plasma, with an IC50 of approximately 70 to 80 nmol/L. In an in vitro clot-bound thrombin assay system, heparin, used at clinically relevant concentrations of 0.2 U/mL and 0.4 U/mL, was ineffective in inhibiting clot-bound thrombin (6.5% and 34.9% inhibition at 0.2 U/mL and 0.4 U/mL, respectively). In contrast, the thrombin aptamer at an equivalent anticoagulant concentration inhibited clot-bound thrombin (79.7% inhibition). In an ex vivo whole artery angioplasty model, the thrombin aptamer markedly suppressed the generation of fibrinopeptide A (FPA), whereas heparin at 2 U/mL was ineffective. Compared with a scrambled ssDNA control, the thrombin aptamer reduced platelet deposition by 34.5% +/- 5% (mean +/- SEM, n = 4, P = .09) at low shear rates (approximately 200 s-1) and 61.3% +/- 11% (mean +/- SEM, n = 4, P = .05) at high shear rates (approximately 850 s-1). Thrombin aptamers based on ssDNA molecules represent a new class of thrombin inhibitors with potent anticoagulant and antithrombotic properties.

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