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Bleeding disorder of unknown cause (BDUC) is a diagnosis of exclusion after evaluation of plasma coagulation and platelet function. The underlying mechanisms are unclear, but increased fibrinolysis and abnormal clot formation may play a role. All BDUC patients (n=375) from the Vienna bleeding biobank were analyzed in comparison to healthy controls (HC, n=100) in this case-control study. Plasmin generation (PG) parameters were analyzed using calibrated fluorescence detection in citrated-plasma samples. Turbidimetric plasma clot formation/ lysis of 293 (78%) BDUC patients and confocal microscopy of clots from representative BDUC patients (n=6) and HC (n=9) were assessed. Fibrinolytic factors were measured using commercially available ELISAs. In PG analysis, BDUC patients exhibited lower velocity and peak plasmin, but a higher endogenous plasmin potential compared to HC. Peak plasmin correlated with maximum clot absorbance, but not with clot lysis time. Clot absorbance is an indicator of clot fiber density. Confocal microscopy analysis revealed that BDUC patients' clots had a tendency towards thicker fibers, which negatively correlated with peak plasmin (r=-0.561, p=0.030). Peak plasmin correlated weakly with FXIII, but not with the other fibrinolytic factors (alpha2-antiplasmin, thrombin activatable fibrinolysis inhibitor or plasminogen activator inhibitor 1) or bleeding severity. A model comprising fibrinogen and parameters of PG yielded high predictive power in discriminating BDUC patients from HC during 5-fold stratified cross validation (80% of data, mean AUC: 0.847). The same model generalized well to unseen data (20% of data, AUC: 0.856). Overall, BDUC patients exhibited counterintuitively reduced peak plasmin, potentially related to altered clot structure., (Copyright © 2024 American Society of Hematology.)

Background: Patients with primary immune thrombocytopenia (ITP) have an increased risk of thrombosis, which may be due to altered fibrinolysis., Objectives: To elucidate the clinical impact of delayed fibrinolysis in ITP patients., Methods: A turbidimetric clot formation and lysis assay and a fluorometric plasmin generation (PG) assay were performed, and levels of plasminogen activator inhibitor-1 (PAI-1), tissue plasminogen activator (tPA), tPA-PAI-1 complexes, α2-antiplasmin, thrombin activatable fibrinolysis inhibitor, and D-dimer were assessed in 86 adult primary ITP patients and 78 healthy controls (HCs)., Results: ITP patients showed significantly delayed clot formation, increased clot density, and prolonged clot lysis time (CLT) compared with HCs, with a median (IQR) CLT of 28.0 (13.7-34.7) minutes in patients and 17.3 (12.0-28.0) minutes in HCs, while in the PG assay, only the lag time was prolonged. In ITP patients compared with controls, PAI-1 was higher (1.2 [0.8-2.6] vs 1.1 [0.6-2.1] U/mL) and tPA antigen and activity were lower (tPA antigen: 2.6 [1.1-4.4] vs 3.7 [3.2-4.7] ng/mL; tPA activity ≤ 0 U/mL: 26% vs 7%). TPA-PAI-1 complex levels were positively associated with CLT in multiple linear regression analysis (β = 0.241; P = .019), whereas PG parameters were not associated with CLT. Six patients who developed thrombosis during follow-up had higher levels of tPA-PAI-1 complexes., Conclusion: Prolonged CLT and delayed onset of PG may indicate a hypofibrinolytic tendency in ITP patients, as also indicated by high PAI-1 and low tPA levels. No association was found between fibrinolytic potential and the bleeding phenotype, whereas higher tPA-PAI-1 complex levels were associated with prolonged CLT and increased in patients with future thrombosis., Competing Interests: Declaration of competing interests D.M. received honoraria for advisory board meetings and lectures from CSL Behring and travel support from Sobi, Novo Nordisk, Pfizer, and Roche. S.E.R. is supported by the American Heart Association postdoctoral award (23POST1019349). B.d.L. is an employee of Synapse Research Institute, which is a part of the Stago group that markets the Calibrated Automated Thrombography. A.S.W. is supported in part by a grant from the National Institutes of Health (R01HL126974). C.A. received personal fees for lectures and/or participation in advisory boards from Amgen, Novartis, and Sobi. I.P. has received honoraria from Bayer, CSL Behring, Novo Nordisk, Pfizer, Roche, Sobi, and Takeda for lectures and advisory board meetings. J.G. received honoraria for lectures and advisory board meetings, and research funding for the Medical University of Vienna from CSL Behring, Novartis, Amgen, and Sobi. T.S., J.R., C.d.M., M.F., and P.Q. have no conflicts of interest., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Background: Scott syndrome is a mild platelet-type bleeding disorder, first described in 1979, with only 3 unrelated families identified through defective phosphatidylserine (PS) exposure and confirmed by sequencing. The syndrome is distinguished by impaired surface exposure of procoagulant PS on platelets after stimulation. To date, platelet function and thrombin generation in this condition have not been extensively characterized., Objectives: Genetic and functional studies were undertaken in a consanguineous family with a history of excessive bleeding of unknown cause., Methods: A targeted gene panel of known bleeding and platelet genes was used to identify possible genetic variants. Platelet phenotyping, flow adhesion, flow cytometry, whole blood and platelet-rich plasma thrombin generation, and specialized extracellular vesicle measurements were performed., Results: We detected a novel homozygous frameshift variant, c.1943del (p.Arg648Hisfs∗23), in ANO6 encoding Anoctamin 6, in a patient with a bleeding history but interestingly with normal ANO6 expression. Phenotyping of the patient's platelets confirmed the absence of PS expression and procoagulant activity but also revealed other defects including reduced platelet δ granules, reduced ristocetin-mediated aggregation and secretion, and reduced P-selectin expression after stimulation. PS was absent on spread platelets, and thrombi formed over collagen at 1500/s. Reduced thrombin generation was observed in platelet-rich plasma and confirmed in whole blood using a new thrombin generation assay., Conclusion: We present a comprehensive report of a patient with Scott syndrome with a novel frameshift variant in AN06, which is associated with no platelet PS exposure and markedly reduced thrombin generation in whole blood, explaining the significant bleeding phenotype observed., Competing Interests: Declaration of competing interests A.G., D.H., and B.d.L. are employees of Synapse Research Institute, part of Diagnostica Stago S.A.S. All remaining authors declare no conflicts of interest., (Copyright © 2024 International Society on Thrombosis and Haemostasis. All rights reserved.)

Abstract: Plasma kallikrein (PKa) is an important activator of factor XII (FXII) of the contact pathway of coagulation. Several studies have shown that PKa also possesses procoagulant activity independent of FXII, likely through its ability to directly activate FIX. We evaluated the procoagulant activity of PKa using a mouse whole blood (WB) thrombin-generation (TG) assay. TG was measured in WB from PKa-deficient mice using contact pathway or extrinsic pathway triggers. PKa-deficient WB had significantly reduced contact pathway-initiated TG compared with that of wild-type controls and was comparable with that observed in FXII-deficient WB. PKa-deficient WB supported equivalent extrinsic pathway-initiated TG compared with wild-type controls. Consistent with the presence of FXII-independent functions of PKa, targeted blockade of PKa with either small molecule or antibody-based inhibitors significantly reduced contact pathway-initiated TG in FXII-deficient WB. Inhibition of activated FXII (FXIIa) using an antibody-based inhibitor significantly reduced TG in PKa-deficient WB, consistent with a PKa-independent function of FXIIa. Experiments using mice expressing low levels of tissue factor demonstrated that persistent TG present in PKa- and FXIIa-inhibited WB was driven primarily by endogenous tissue factor. Our work demonstrates that PKa contributes significantly to contact pathway-initiated TG in the complex milieu of mouse WB, and a component of this contribution occurs in an FXII-independent manner., (© 2024 by The American Society of Hematology. Licensed under Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0), permitting only noncommercial, nonderivative use with attribution. All other rights reserved.)

Background  Agonist-induced platelet activation, with the integrin αIIbβ3 conformational change, is required for fibrinogen binding. This is considered reversible under specific conditions, allowing a second phase of platelet aggregation. The signaling pathways that differentiate between a permanent or transient activation state of platelets are poorly elucidated. Objective  To explore platelet signaling mechanisms induced by the collagen receptor glycoprotein VI (GPVI) or by protease-activated receptors (PAR) for thrombin that regulate time-dependent αIIbβ3 activation. Methods  Platelets were activated with collagen-related peptide (CRP, stimulating GPVI), thrombin receptor-activating peptides, or thrombin (stimulating PAR1 and/or 4). Integrin αIIbβ3 activation and P-selectin expression was assessed by two-color flow cytometry. Signaling pathway inhibitors were applied before or after agonist addition. Reversibility of platelet spreading was studied by microscopy. Results  Platelet pretreatment with pharmacological inhibitors decreased GPVI- and PAR-induced integrin αIIbβ3 activation and P-selectin expression in the target order of protein kinase C (PKC) > glycogen synthase kinase 3 > β-arrestin > phosphatidylinositol-3-kinase. Posttreatment revealed secondary αIIbβ3 inactivation (not P-selectin expression), in the same order, but this reversibility was confined to CRP and PAR1 agonist. Combined inhibition of conventional and novel PKC isoforms was most effective for integrin closure. Pre- and posttreatment with ticagrelor, blocking the P2Y 12 adenosine diphosphate (ADP) receptor, enhanced αIIbβ3 inactivation. Spreading assays showed that PKC or P2Y 12 inhibition provoked a partial conversion from filopodia to a more discoid platelet shape. Conclusion  PKC and autocrine ADP signaling contribute to persistent integrin αIIbβ3 activation in the order of PAR1/GPVI > PAR4 stimulation and hence to stabilized platelet aggregation. These findings are relevant for optimization of effective antiplatelet treatment., Competing Interests: Conflict of Interest None declared., (The Author(s). This is an open access article published by Thieme under the terms of the Creative Commons Attribution License, permitting unrestricted use, distribution, and reproduction so long as the original work is properly cited. ( https://creativecommons.org/licenses/by/4.0/ ).)

Background: Life-long vitamin K antagonist (VKA) therapy is recommended as a standard of care in antiphospholipid syndrome (APS) patients with thrombosis. Concerns have been raised about the validity of international normalized ratio (INR) measurements in lupus anticoagulant (LA)-positive APS patients because LA may interfere with phospholipid-dependent coagulation tests and could elevate INR measurements., Objectives: Here, we aimed to determine the interference of antigen-specific monoclonal and isolated patient antibodies with LA activity on INR measurements., Methods: Pooled normal plasma and control plasma from patients on VKA (without LA) were incubated with monoclonal and isolated patient immunoglobulin G antiprothrombin and anti-beta-2-glycoprotein I antibodies that express LA activity. INR was determined before and after addition using 3 laboratory assays (Owren STA-Hepato Prest, Quick STA-NeoPTimal, and Quick STA-Neoplastine R) and 1 point-of-care test device (CoaguChek Pro II)., Results: Antiprothrombin and anti-beta-2-glycoprotein I antibodies with LA activity interfered with recombinant human thromboplastin reagents (Quick STA-Neoplastine R and CoaguChek Pro II), particularly when added to plasma of VKA-treated controls. This effect was most evident on point-of-care test INR measurements, while the recombinant Quick reagent exhibited a lesser degree of interference. In contrast, tissue-derived thromboplastin reagents (Owren STA-Hepato Prest and Quick STA-NeoPTimal) remained largely unaffected by these antibodies, both in pooled normal plasma and VKA anticoagulated control plasma. Among these reagents, the Owren INR reagent exhibited the lowest sensitivity to the influence of LA antibodies. This observed difference in sensitivity is independent of the plasma dilution factor or the presence of factor V or fibrinogen in Owren reagent., Conclusion: INR reagents that utilize recombinant human thromboplastin are more sensitive to the presence of monoclonal and patient-derived antibodies with LA activity. Consequently, APS patients positive for LA should be monitored using tissue-derived thromboplastin reagents, given its reduced susceptibility to interference by LA-causing antibodies., (© 2024 The Author(s).)

Background: Thrombin generation (TG) is used as a global test of coagulation and is an indicator of thrombosis and bleeding risk. Until now, data on the association of TG and mortality are inconclusive., Objectives: We investigated the association between TG and mortality in the prospective Moli-sani cohort (n = 21 920)., Methods: TG was measured using calibrated automated thrombinography using PPP-Reagent Low. Lag time (LT), endogenous thrombin potential (ETP), peak height, time-to-peak (TTP), and velocity index were quantified. The association of TG and mortality was studied by Cox regression and adjusted for sex, age, body mass index, smoking, contraceptives, and medical history (cardiovascular diseases, hypertension, hypercholesterolemia, diabetes, and cancer)., Results: LT and TTP were 4.1 ± 1.0 minutes and 6.6 ± 1.5 minutes, on average. The peak height was 364 ± 88 nM, velocity index was 163 ± 63 nM/min, and ETP was 1721 ± 411 nM·min. ETP was negatively associated with all-cause mortality (hazard ratio [HR], 0.86; 95% CI, 0.81-0.92; P < .001). Subjects in the lowest quintile of the ETP (ETP Q1 ) had a 1.3-fold higher mortality rate. Additionally, a high TTP/LT ratio was negatively associated with mortality (HR, 0.71; 95% CI, 0.57-0.89; P = .003). Individuals in quintile 1 of the TTP/LT ratio had a 1.4-fold higher mortality rate compared with the remainder of the cohort. Subjects that were both in ETP Q1 and TTP/LT Q1 had a 1.8-fold higher mortality rate, regardless of whether they reported history of cardiovascular disease at baseline (HR, 1.61 [CI: 1.07-2.42]) or not (HR, 1.89 [CI: 1.51-2.36])., Conclusion: Low ETP and TTP/LT ratios are independent risk factors for all-cause mortality in the general population., Competing Interests: Declaration of competing interests R.d.L.K., M.R., D.H., M.N., and B.d.L. are employees of Synapse Research Institute, part of Diagnostica Stago SAS. S.C., A. De Curtis, A. Di Castelnuovo, C.C., M.B.D., and L.I. have no conflict of interest to disclose., (Copyright © 2024 International Society on Thrombosis and Haemostasis. Published by Elsevier Inc. All rights reserved.)

Background:  Platelet glycoprotein VI (GPVI) stimulation activates the tyrosine kinases Syk and Btk, and the effector proteins phospholipase Cγ 2 (PLCγ2) and protein kinase C (PKC). Here, the activation sequence, crosstalk, and downstream effects of this Syk-Btk-PKC signalosome in human platelets were analyzed., Methods and Results:  Using immunoblotting, we quantified 14 regulated phospho-sites in platelets stimulated by convulxin with and without inhibition of Syk, Btk, or PKC. Convulxin induced fast, reversible tyrosine phosphorylation (pY) of Syk, Btk, LAT, and PLCγ2, followed by reversible serine/threonine phosphorylation (pS/T) of Syk, Btk, and downstream kinases MEK1/2, Erk1/2, p38, and Akt. Syk inhibition by PRT-060318 abolished all phosphorylations, except Syk pY352. Btk inhibition by acalabrutinib strongly decreased Btk pY223/pS180, Syk pS297, PLCγ2 pY759/Y1217, MEK1/2 pS217/221, Erk1/2 pT202/Y204, p38 pT180/Y182, and Akt pT308/S473. PKC inhibition by GF109203X abolished most pS/T phosphorylations except p38 pT180/Y182 and Akt pT308, but enhanced most Y-phosphorylations. Acalabrutinib, but not GF109203X, suppressed convulxin-induced intracellular Ca 2+ mobilization, whereas all three protein kinase inhibitors abolished degranulation and αIIbβ3 integrin activation assessed by flow cytometry. Inhibition of autocrine ADP effects by AR-C669931 partly diminished convulxin-triggered degranulation., Conclusion:  Kinetic analysis of GPVI-initiated multisite protein phosphorylation in human platelets demonstrates multiple phases and interactions of tyrosine and serine/threonine kinases with activation-altering feedforward and feedback loops partly involving PKC. The protein kinase inhibitor effects on multisite protein phosphorylation and functional readouts reveal that the signaling network of Syk, Btk, and PKC controls platelet granule exocytosis and αIIbβ3 integrin activation., Competing Interests: J.W.M.H. is a scientific advisor for Synapse Research Institute. P.Z. was supported by the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement TICARDIO no. 813409. P.Z. was enrolled in a joint PhD project of the Universities of Maastricht (NL) and Mainz (DE). The other authors declare no relevant conflicts of interest., (The Author(s). This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/).)

Background: Thromboembolic disease is a major complication in patients with pancreatic ductal adenocarcinoma (PDAC). Patients with PDAC often have altered blood cell counts, which are associated with venous thromboembolism (VTE) development. The high thrombotic risk in patients with PDAC may be partially caused by procoagulant blood cells., Objectives: The aim of this study was to compare blood cell-dependent coagulation between patients with PDAC (n = 18) and healthy controls matched for age and sex (n = 18)., Methods: Thrombin generation (TG) was measured in whole blood (WB) and plasma. The capacity of platelets to release granules (PGRCs) was measured in WB. We explored the occurrence of thromboembolic events in patients with PDAC during a 6-month follow-up., Results: Patients showed an increased endogenous thrombin potential in WB compared with controls. This difference was not observed in plasma, indicating a procoagulant effect of blood cells. Both in WB and plasma, the lag time was prolonged in patients compared with controls. Patients had hyperresponsive platelets, with a shorter time to peak granule release. Of the 18 patients with PDAC, 4 developed a venous thromboembolism (22%) and 1 developed an arterial thrombosis (6%). A shorter lag time in WB, but not in plasma, and an increased PGRC were associated with thromboembolic events., Conclusion: Patients with PDAC have an increased and delayed WB TG coagulation profile compared with controls. A shorter lag time in WB TG and increased PGRC are associated with the incidence of thromboembolic events. Platelets appear to be key players in thrombosis development. Measuring hemostasis in WB could improve thrombosis risk estimation in patients with PDAC., Competing Interests: Declaration of competing interests J.d.V.-G. has served as a consultant for Amgen, AstraZeneca, MSD, Pierre Fabre, and Servier and has received institutional research funding from Servier, all outside the submitted work. The other authors declare no conflicts of interest., (Copyright © 2024 International Society on Thrombosis and Haemostasis. Published by Elsevier Inc. All rights reserved.)

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive type of cancer and has a poor prognosis. Patients with PDAC are at high risk of developing thromboembolic events, which is a leading cause of morbidity and mortality following cancer progression. Plasma-derived coagulation is the most studied process in cancer-associated thrombosis. Other blood components, such as platelets, red blood cells, and white blood cells, have been gaining less attention. This narrative review addresses the literature on the role of cellular components in the development of venous thromboembolism (VTE) in patients with PDAC. Blood cells seem to play an important role in the development of VTE. Altered blood cell counts, i.e., leukocytosis, thrombocytosis, and anemia, have been found to associate with VTE risk. Tumor-related activation of leukocytes leads to the release of tissue factor-expressing microvesicles and the formation of neutrophil extracellular traps, initiating coagulation and forming a scaffold for thrombi. Tissue factor-expressing microvesicles are also thought to be released by PDAC cells. PDAC cells have been shown to stimulate platelet activation and aggregation, proposedly via the secretion of podoplanin and mucins. Hypofibrinolysis, partially explained by increased plasminogen activator inhibitor-1 activity, is observed in PDAC. In short, PDAC-associated hypercoagulability is a complex and multifactorial process. A better understanding of cellular contributions to hypercoagulability might lead to the improvement of diagnostic tests to identify PDAC patients at highest risk of VTE., Competing Interests: None declared., (Thieme. All rights reserved.)

Distinct platelet activation patterns are elicited by the tyrosine kinase-linked collagen receptor glycoprotein VI (GPVI) and the G-protein coupled protease-activated receptors (PAR1/4) for thrombin. This is reflected in the different platelet Ca 2+ responses induced by the GPVI agonist collagen-related peptide (CRP) and the PAR1/4 agonist thrombin. Using a 96 well-plate assay with human Calcium-6-loaded platelets and a panel of 22 pharmacological inhibitors, we assessed the cytosolic Ca 2+ signaling domains of these receptors and developed an automated Ca 2+ curve algorithm. The algorithm was used to evaluate an ultra-high throughput (UHT) based screening of 16,635 chemically diverse small molecules with orally active physicochemical properties for effects on platelets stimulated with CRP or thrombin. Stringent agonist-specific selection criteria resulted in the identification of 151 drug-like molecules, of which three hit compounds were further characterized. The dibenzyl formamide derivative ANO61 selectively modulated thrombin-induced Ca 2+ responses, whereas the aromatic sulfonyl imidazole AF299 and the phenothiazine ethopropazine affected CRP-induced responses. Platelet functional assays confirmed selectivity of these hits. Ethopropazine retained its inhibitory potential in the presence of plasma, and suppressed collagen-dependent thrombus buildup at arterial shear rate. In conclusion, targeting of platelet Ca 2+ signaling dynamics in a screening campaign has the potential of identifying novel platelet-inhibiting molecules., (© 2024. The Author(s).)

The endothelial regulation of platelet activity is incompletely understood. Here we describe novel approaches to find molecular pathways implicated on the platelet-endothelium interaction. Using high-shear whole-blood microfluidics, employing coagulant or non-coagulant conditions at physiological temperature, we observed that the presence of human umbilical vein endothelial cells (HUVEC) strongly suppressed platelet adhesion and activation, via the collagen receptor glycoprotein VI (GPVI) and the PAR receptors for thrombin. Real-time monitoring of the cytosolic Ca 2+ rises in the platelets indicated no major improvement of inhibition by prostacyclin or nitric oxide. Similarly under stasis, exposure of isolated platelets to HUVEC reduced the Ca 2+ responses by collagen-related peptide (CRP-XL, GPVI agonist) and thrombin (PAR agonist). We then analyzed the label-free phosphoproteome of platelets (three donors), exposed to HUVEC, CRP-XL, and/or thrombin. High-resolution mass spectrometry gave 5463 phosphopeptides, corresponding to 1472 proteins, with good correlation between biological and technical replicates (R > .86). Stringent filtering steps revealed 26 regulatory pathways (Reactome) and 143 regulated kinase substrates (PhosphoSitePlus), giving a set of protein phosphorylation sites that was differentially (44) or similarly (110) regulated by HUVEC or agonist exposure. The differential regulation was confirmed by stable-isotope analysis of platelets from two additional donors. Substrate analysis indicated major roles of poorly studied protein kinase classes (MAPK, CDK, DYRK, STK, PKC members). Collectively, these results reveal a resetting of the protein phosphorylation profile in platelets exposed to endothelium or to conventional agonists and to endothelium-promoted activity of a multi-kinase network, beyond classical prostacyclin and nitric oxide actors, that may contribute to platelet inhibition., (© 2024 The Authors. The FASEB Journal published by Wiley Periodicals LLC on behalf of Federation of American Societies for Experimental Biology.)

Abstract: Thrombosis is an important manifestation of the antiphospholipid syndrome (APS). The thrombin generation (TG) test is a global hemostasis assay, and increased TG is associated with thrombosis. APS is currently diagnosed based on clinical and laboratory criteria, the latter defined as anti-cardiolipin, anti-β2-glycoprotein I antibodies, or lupus anticoagulant (LA). APS testing is often performed after a thrombotic episode and subsequent administration of anticoagulation, which might hamper the interpretation of clotting assays used for LA testing. We set out to develop an artificial neural network (NN) that can diagnose APS in patients who underwent vitamin K antagonist (VKA) treatment, based on TG test results. Five NNs were trained to diagnose APS in 48 VKA-treated patients with APS and 64 VKA-treated controls, using TG and thrombin dynamics parameters as inputs. The 2 best-performing NNs were selected (accuracy, 96%; sensitivity, 96%-98%; and specificity, 95%-97%) and further validated in an independent cohort of VKA-anticoagulated patients with APS (n = 33) and controls (n = 62). Independent clinical validation favored 1 of the 2 selected NNs, with a sensitivity of 88% and a specificity of 94% for the diagnosis of APS. In conclusion, the combined use of TG and NN methodology allowed for us to develop an NN that diagnoses APS with an accuracy of 92% in individuals with VKA anticoagulation (n = 95). After further clinical validation, the NN could serve as a screening and diagnostic tool for patients with thrombosis, especially because there is no need to interrupt anticoagulant therapy., (© 2024 by The American Society of Hematology. Licensed under Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0), permitting only noncommercial, nonderivative use with attribution. All other rights reserved.)

Antifibrinolytic drugs are used extensively for on-demand treatment of severe acute bleeding. Controlling fibrinolysis may also be an effective strategy to prevent or lessen chronic recurring bleeding in bleeding disorders such as hemophilia A (HA), but current antifibrinolytics have unfavorable pharmacokinetic profiles. Here, we developed a long-lasting antifibrinolytic using small interfering RNA (siRNA) targeting plasminogen packaged in clinically used lipid nanoparticles (LNPs) and tested it to determine whether reducing plasmin activity in animal models of HA could decrease bleeding frequency and severity. Treatment with the siRNA-carrying LNPs reduced circulating plasminogen and suppressed fibrinolysis in wild-type and HA mice and dogs. In HA mice, hemostatic efficacy depended on the injury model; plasminogen knockdown improved hemostasis after a saphenous vein injury but not tail vein transection injury, suggesting that saphenous vein injury is a murine bleeding model sensitive to the contribution of fibrinolysis. In dogs with HA, LNPs carrying siRNA targeting plasminogen were as effective at stabilizing clots as tranexamic acid, a clinical antifibrinolytic, and in a pilot study of two dogs with HA, the incidence of spontaneous or excess bleeding was reduced during 4 months of prolonged knockdown. Collectively, these data demonstrate that long-acting antifibrinolytic therapy can be achieved and that it provides hemostatic benefit in animal models of HA.

In 2006, at a meeting in Sydney, Australia, consensus was reached by an international group of specialists to establish a number of serological criteria that identify patients with a history of thrombosis or pregnancy complications as having antiphospholipid syndrome (APS). These criteria were originally formulated for research purposes and to compare clinical trials in different centres. However, these same criteria are now generally used and accepted for the diagnosis and treatment of patients. The practice of using these criteria for direct patient care requires that these criteria are based on sound scientific evidence. Indeed, for all the autoantibodies that are officially included in the serological criteria, it has been shown that they induce thrombosis and fetal loss when infused into mice. There are also a number of additional autoantibodies that have been identified in these patients but for these antibodies there was not enough evidence to meet the official APS criteria in 2006. Seventeen years have now passed since the consensus meeting, therefore, this review examines whether additional studies performed with these 'non-criteria' autoantibodies have provided sufficient results to suggest the inclusion of these autoantibodies in the official serological criteria of APS., (© The Author(s) 2024. Published by Oxford University Press on behalf of the British Society for Rheumatology. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Background: α 2 -macroglobulin (α 2 M) is a versatile endopeptidase inhibitor that plays a role in cell growth, inflammation and coagulation. α 2 M is an inhibitor of key coagulation enzyme thrombin. Hypercoagulability due to an excess of thrombin production can cause thrombotic events. Therefore, we investigated the association of α 2 M levels and cardiovascular events in a subset of the general Italian population., Methods: We determined α 2 M levels in the baseline samples of a prospective cohort (n = 19,688; age: 55 ± 12 years; 47.8 % men) of the Moli-sani study and investigated the association with the cardiovascular events (n = 432, 2.2 %) in the median follow-up period of 4.3 years. Hazard ratios (HR) with 95 % confidence intervals (CI) were calculated by multivariable Cox regression and adjusted for a large panel of confounding factors., Results: α 2 M levels above the 90th percentile were significantly associated with cardiovascular disease (CVD) events after full adjustment for age, sex, current smoking, BMI, oral contraceptive use, cardiovascular diseases, hypertension, hypercholesterolemia, diabetes and history of cancer (HR: 1.36; CI: 1.06-1.74). Moreover, high α 2 M was associated with coronary heart disease (CHD; HR: 1.47; CI: 1.12-1.91), but not stroke. Stratification for CVD at baseline showed that high α 2 M levels are associated with CHD events in subjects without CVD at baseline (HR: 1.40; CI: 1.00-1.95) and subjects with CVD at baseline (HR: 1.58; CI: 1.02-2.44)., Conclusion: We show in a prospective cohort that high levels of α 2 M could be a risk factor for cardiovascular events, especially coronary heart disease events., Competing Interests: Declaration of competing interest RdLK, QY, and BdL are employees of Synapse Research Institute, part of Diagnostica Stago SAS. The other authors declare no competing interests., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Hypoxia plays an important role in several pathologies, e.g. chronic obstructive pulmonary disease and obstructive sleep apnea syndrome, and is linked to an increased thrombosis risk. Furthermore, oxygen deprivation is associated with hypercoagulability. In this study, we investigated the effect of gender and exercise on the coagulation potential under hypoxic conditions at high altitude by assessing thrombin generation (TG) and platelet activation. Hereto, ten healthy volunteers were included (50 % male, median age of 27.5 years). The measurements were conducted first at sea level and then twice at high altitude (3883 m), first after a passive ascent by cable car and second after an active ascent by a mountain hike. As expected, both the passive and active ascent resulted in a decreased oxygen saturation and an increased heart rate at high altitude. Acute mountain sickness symptoms were observed independently of the ascent method. After the active ascent, platelet, white blood cell and granulocyte count were increased, and lymphocytes were decreased, without a gender-related difference. FVIII and von Willebrand factor were significantly increased after the active ascent for both men and women. Platelet activation was reduced and delayed under hypobaric conditions, especially in women. TG analysis showed a prothrombotic trend at high altitude, especially after the active ascent. Women had a hypercoagulable phenotype, compared to men at all 3 timepoints, indicated by a higher peak height and endogenous thrombin potential (ETP), and shorter lag time and time-to-peak. In addition, ETP and peak inhibition by thrombomodulin was lower in women after the active ascent, compared to men. Interestingly, data normalisation for subject baseline values indicated an opposing effect of altitude-induced hypoxia on α2-macroglobulin levels and TG lag time between men and women, decreasing in men and increasing in women. We conclude that hypoxia increases TG, as well as FVIII and VWF levels in combination with exercise. In contrast, platelets lose their responsiveness at high altitude, which is most pronounced after heavy exercise. Women had a more pronounced prothrombotic phenotype compared to men, which we theorize is counterbalanced under hypobaric conditions by decreased platelet activation., Competing Interests: Declaration of competing interest All authors are employees of the Synapse Research Institute, Maastricht, The Netherlands; part of the Stago Diagnostica Group, Asnières-sur-Seine, France., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Background: Acquired factor FXIII (FXIII) deficiency can be immune- or non-immune mediated and may cause severe bleeding symptoms. The incidence of acquired FXIII deficiency and its etiology in patients with multiple myeloma (MM) are poorly understood., Objectives: To assess FXIII levels and the balance of fibrinolysis in newly diagnosed, untreated MM and monoclonal gammopathy of undetermined significance (MGUS) patients., Methods: FXIII activity, mixing studies, FXIII-A 2 B 2 antigen, total FXIII-B antigen were measured in platelet-poor plasma from 17 untreated MM patients, 33 untreated MGUS patients, and 30 age and sex-matched healthy controls. Besides routine laboratory measurements, the balance of coagulation and fibrinolysis was evaluated using quantitative fibrin monomer (FM) test, thrombin-antithrombin assay, α2-antiplasmin activity, plasmin-α2-antiplasmin (PAP) complex, D-dimer, plasmin generation assay, clot lysis assay, and ClotPro-TPA test., Results: FXIII-A 2 B 2 levels were significantly lower in MM patients compared to controls [median (IQR):14.6 (11.2-19.4) vs. 21.8 (17.1-26.4) mg/L, p = 0.0015], whereas total FXIII-B did not differ between groups. Decrease in FXIII activity was parallel to the decrease in FXIII-A 2 B 2 . An immune-mediated inhibitory mechanism was ruled out. Free/total FXIII-B was significantly higher in MM patients compared to MGUS and healthy controls, suggesting an etiology of FXIII-A consumption. In MM and MGUS patients, FM, D-dimer, and PAP complex were significantly elevated compared to controls, indicating hypercoagulability and ongoing fibrinolysis., Conclusions: Low FXIII levels due to consumption were observed in MM patients at diagnosis. Hypercoagulability and ongoing fibrinolysis were detected in MM and MGUS, indicating that a disturbed hemostasis balance is already present in the latter benign condition., Competing Interests: Declaration of competing interest The authors declare no competing interests., (Copyright © 2023 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Background: Patients with cirrhosis have a normal to increased thrombin generation (TG) capacity in platelet-poor plasma (PPP). By reflecting the contribution of all circulating blood cells, whole blood (WB) TG may allow a more physiological assessment of coagulation., Objectives: We compared WB-TG vs PPP-TG in patients with cirrhosis., Methods: Assessment of coagulation included routine tests, factor VIII, natural anticoagulants, PPP-TG, and WB-TG. TG assays were performed with and without thrombomodulin. Twenty-five healthy subjects were included as controls., Results: We included 108 patients (Child-Pugh A/B/C, 44/24/40). Compared with controls, patients had significantly lower platelet count, longer international normalized ratio, higher FVIII, and lower levels of protein C/S and antithrombin. Regarding thrombomodulin-modified TG assays, in compensated cirrhosis, both PPP-TG and WB-TG indicated an increased TG capacity, as reflected by an endogenous thrombin potential (ETP) significantly higher than controls. In contrast, in decompensated cirrhosis, PPP-TG indicated a hypercoagulable state with increased ETP, higher peak height, and shorter time-to-peak than controls, whereas WB-TG revealed a progressive impairment of TG kinetics and total capacity, ultimately resulting in a profound hypocoagulable state in patients with Child-Pugh C cirrhosis (ie, significant prolongation of lag time and time-to-peak with reduction of both ETP and peak height). In decompensated patients, bacterial infections and severity of anemia were associated with a further reduction of both ETP and peak height., Conclusion: Compensated cirrhosis is associated with an increased TG capacity. In decompensated cirrhosis, contrary to PPP-TG, which indicates hypercoagulability, WB-TG shows a significant hypocoagulable state. The clinical value of these findings deserves further investigation., Competing Interests: Declaration of competing interests There are no competing interests to disclose., (Copyright © 2023 International Society on Thrombosis and Haemostasis. Published by Elsevier Inc. All rights reserved.)

The platelet receptors, glycoprotein VI (GPVI) and integrin α2β1 jointly control collagen-dependent thrombus formation via protein tyrosine kinases. It is unresolved to which extent the ITIM (immunoreceptor tyrosine-based inhibitory motif) receptor PECAM1 and its downstream acting protein tyrosine phosphatase PTPN11 interfere in this process. Here, we hypothesized that integrin α2β1 has a co-regulatory role in the PECAM1- and PTPN11-dependent restraint of thrombus formation. We investigated platelet activation under flow on collagens with a different GPVI dependency and using integrin α2β1 blockage. Blood was obtained from healthy subjects and from patients with Noonan syndrome with a gain-of-function mutation of PTPN11 and variable bleeding phenotype. On collagens with decreasing GPVI activity (types I, III, IV), the surface-dependent inhibition of PECAM1 did not alter thrombus parameters using control blood. Blockage of α2β1 generally reduced thrombus parameters, most effectively on collagen IV. Strikingly, simultaneous inhibition of PECAM1 and α2β1 led to a restoration of thrombus formation, indicating that the suppressing signaling effect of PECAM1 is masked by the platelet-adhesive receptor α2β1. Blood from 4 out of 6 Noonan patients showed subnormal thrombus formation on collagen IV. In these patients, effects of α2β1 blockage were counterbalanced by PECAM1 inhibition to a normal phenotype. In summary, we conclude that the suppression of GPVI-dependent thrombus formation by either PECAM1 or a gain-of-function of PTPN11 can be overruled by α2β1 engagement., (© 2024. The Author(s).)

Pancreatic ductal adenocarcinoma (PDAC) is a highly fatal metastatic disease associated with robust activation of the coagulation and fibrinolytic systems. However, the potential contribution of the primary fibrinolytic protease plasminogen to PDAC disease progression has remained largely undefined. Mice bearing C57Bl/6-derived KPC (KRas G12D , TRP53 R172H ) tumors displayed evidence of plasmin activity in the form of high plasmin-antiplasmin complexes and high plasmin generation potential relative to mice without tumors. Notably, plasminogen-deficient mice (Plg - ) had significantly diminished KPC tumor growth in subcutaneous and orthotopic implantation models. Moreover, the metastatic potential of KPC cells was significantly diminished in Plg - mice, which was linked to reduced early adhesion and/or survival of KPC tumor cells. The reduction in primary orthotopic KPC tumor growth in Plg - mice was associated with increased apoptosis, reduced accumulation of pro-tumor immune cells, and increased local proinflammatory cytokine production. Elimination of fibrin(ogen), the primary proteolytic target of plasmin, did not alter KPC primary tumor growth and resulted in only a modest reduction in metastatic potential. In contrast, deficiencies in the plasminogen receptors Plg-RKT or S100A10 in tumor cells significantly reduced tumor growth. Plg-RKT reduction in tumor cells, but not reduced S100A10, suppressed metastatic potential in a manner that mimicked plasminogen deficiency. Finally, tumor growth was also reduced in NSG mice subcutaneously or orthotopically implanted with patient-derived PDAC tumor cells in which circulating plasminogen was pharmacologically reduced. Collectively, these studies suggest that plasminogen promotes PDAC tumor growth and metastatic potential, in part through engaging plasminogen receptors on tumor cells., (© 2023 The Authors. Molecular Oncology published by John Wiley & Sons Ltd on behalf of Federation of European Biochemical Societies.)

The anucleate human platelets contain a broad pattern of mRNAs and other RNA transcripts. The high quantitative similarity of mRNAs in megakaryocytes and platelets from different sources points to a common origin, and suggests a random redistribution of mRNA species upon proplatelet formation. A comparison of the classified platelet transcriptome (17.6k transcripts) with the identified platelet proteome (5.2k proteins) indicates an under-representation of: (i) nuclear but not of other organellar proteins; (ii) membrane receptors and channels with low transcript levels; (iii) transcription/translation proteins; and (iv) so far uncharacterized proteins. In this review, we discuss the technical, normalization and database-dependent possibilities and challenges to come to a complete, genome-wide platelet transcriptome and proteome. Such a reference transcriptome and proteome can serve to further elucidate intra-subject and inter-subject differences in platelets in health and disease. Applications may also lay in the aid of genetic diagnostics.

Genetic studies of platelet reactivity (PR) phenotypes may identify novel antiplatelet drug targets. However, such studies have been limited by small sample sizes (n < 5000) because of the complexity of measuring PR. We trained a model to predict PR from complete blood count (CBC) scattergrams. A genome-wide association study of this phenotype in 29 806 blood donors identified 21 distinct associations implicating 20 genes, of which 6 have been identified previously. The effect size estimates were significantly correlated with estimates from a study of flow cytometry-measured PR and a study of a phenotype of in vitro thrombus formation. A genetic score of PR built from the 21 variants was associated with the incidence rates of myocardial infarction and pulmonary embolism. Mendelian randomization analyses showed that PR was causally associated with the risks of coronary artery disease, stroke, and venous thromboembolism. Our approach provides a blueprint for using phenotype imputation to study the determinants of hard-to-measure but biologically important hematological traits., (© 2023 by The American Society of Hematology. Licensed under Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0), permitting only noncommercial, nonderivative use with attribution. All other rights reserved.)

About one-third of patients undergoing transcatheter aortic valve implantation (TAVI) use oral anticoagulants (OAC), mainly due to atrial fibrillation. General guidelines advise interrupting OAC in patients with a high risk of bleeding undergoing interventions. However, preliminary observational data suggest that the continuation of OAC during TAVI is safe and may reduce the risk of periprocedural thromboembolic events. The Periprocedural Continuation Versus Interruption of Oral Anticoagulant Drugs During Transcatheter Aortic Valve Implantation (POPular PAUSE TAVI) is a multicentre, randomised clinical trial with open-label treatment and blinded endpoint assessment. Patients are randomised 1:1 to periprocedural continuation versus interruption of OAC and are stratified for vitamin K antagonist or direct oral anticoagulant use. The primary endpoint is a composite of cardiovascular mortality, all stroke, myocardial infarction, major vascular complications and type 2-4 bleeding within 30 days after TAVI, according to the Valve Academic Research Consortium-3 criteria. Secondary endpoints include separate individual and composite outcomes, quality of life and cost-effectiveness. Since continuation of OAC is associated with the ancillary benefit that it simplifies periprocedural management, the primary outcome is first analysed for non-inferiority; if non-inferiority is proven, superiority will be tested. Recruitment started in November 2020, and the trial will continue until a total of 858 patients have been included and followed for 90 days. In summary, POPular PAUSE TAVI is the first randomised clinical trial to assess the safety and efficacy of periprocedural continuation versus interruption of OAC in patients undergoing TAVI.

Red blood cells (RBCs) and platelets contribute to the coagulation capacity in bleeding and thrombotic disorders. The thrombin generation (TG) process is considered to reflect the interactions between plasma coagulation and the various blood cells. Using a new high-throughput method capturing the complete TG curve, we were able to compare TG in whole blood and autologous platelet-rich and platelet-poor plasma to redefine the blood cell contributions to the clotting process. We report a faster and initially higher generation of thrombin and shorter coagulation time in whole blood than in platelet-rich plasma upon low concentrations of coagulant triggers, including tissue factor, Russell viper venom factor X, factor Xa, factor XIa, and thrombin. The TG was accelerated with increased hematocrit and delayed after prior treatment of RBC with phosphatidylserine-blocking annexin A5. RBC treatment with ionomycin increased phosphatidylserine exposure, confirmed by flow cytometry, and increased the TG process. In reconstituted blood samples, the prior selective blockage of phosphatidylserine on RBC with annexin A5 enhanced glycoprotein VI-induced platelet procoagulant activity. For patients with anemia or erythrocytosis, cluster analysis revealed high or low whole-blood TG profiles in specific cases of anemia. The TG profiles lowered upon annexin A5 addition in the presence of RBCs and thus were determined by the extent of phosphatidylserine exposure of blood cells. Profiles for patients with polycythemia vera undergoing treatment were similar to that of control subjects. We concluded that RBC and platelets, in a phosphatidylserine-dependent way, contribute to the TG process. Determination of the whole-blood hypo- or hyper-coagulant activity may help to characterize a bleeding or thrombosis risk., (© 2023 by The American Society of Hematology. Licensed under Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0), permitting only noncommercial, nonderivative use with attribution. All other rights reserved.)

Linking the genetic background of patients with bleeding diathesis and altered platelet function remains challenging. We aimed to assess how a multiparameter microspot-based measurement of thrombus formation under flow can help identify patients with a platelet bleeding disorder. For this purpose, we studied 16 patients presenting with bleeding and/or albinism and suspected platelet dysfunction and 15 relatives. Genotyping of patients revealed a novel biallelic pathogenic variant in RASGRP2 (splice site c.240-1G>A), abrogating CalDAG-GEFI expression, compound heterozygosity (c.537del, c.571A>T) in P2RY12, affecting P2Y12 signaling, and heterozygous variants of unknown significance in the P2RY12 and HPS3 genes. Other patients were confirmed to have Hermansky-Pudlak syndrome type 1 or 3. In 5 patients, no genetic variant was found. Platelet functions were assessed via routine laboratory measurements. Blood samples from all subjects and day controls were screened for blood cell counts and microfluidic outcomes on 6 surfaces (48 parameters) in comparison with those of a reference cohort of healthy subjects. Differential analysis of the microfluidic data showed that the key parameters of thrombus formation were compromised in the 16 index patients. Principal component analysis revealed separate clusters of patients vs heterozygous family members and control subjects. Clusters were further segregated based on inclusion of hematologic values and laboratory measurements. Subject ranking indicated an overall impairment in thrombus formation in patients carrying a (likely) pathogenic variant of the genes but not in asymptomatic relatives. Taken together, our results indicate the advantages of testing for multiparametric thrombus formation in this patient population., (© 2023 by The American Society of Hematology. Licensed under Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0), permitting only noncommercial, nonderivative use with attribution. All other rights reserved.)

Background: Platelets and neutrophils are the first blood cells accumulating at sites of arterial thrombus formation, and both cell types contribute to the pathology of thrombotic events. We aimed to identify key interaction mechanisms between these cells using microfluidic approaches., Methods: Whole-blood perfusion was performed over a collagen surface at arterial shear rate. Platelet and leukocyte (in majority neutrophil) activation were microscopically visualized using fluorescent markers. The contributions of platelet-adhesive receptors (integrin, P-selectin, CD40L) and chemokines were studied by using inhibitors or antibodies and using blood from patients with GT (Glanzmann thrombasthenia) lacking platelet-expressed αIIbβ3., Results: We observed (1) an unknown role of activated platelet integrin αIIbß3 preventing leukocyte adhesion, which was overcome by short-term flow disturbance provoking massive adhesion; (2) that platelet-expressed CD40L controls the crawling pattern and thrombus fidelity of the cells on a thrombus; (3) that continued secretion of platelet substances promotes activation of identified neutrophils, as assessed by (fMLP [ N -formylmethionyl-leucyl-phenylalanine, a potent chemotactic agent and leukocyte activator] induced) [Ca 2+ ] i rises and antigen expression; (4) and that platelet-released chemokines activate the adhered cells in the order of CXCL7>CCL5>CXCL4. Furthermore, postsilencing of the platelets in a thrombus suppressed the leukocyte activation. However, the leukocytes on thrombi did no more than limitedly form neutrophil extracellular traps, unless stimulated with phorbol ester or lipopolysaccharide., Conclusions: Together, these findings reveal a multifaceted regulation of adhesion and activation of neutrophils by platelets in a thrombus, with a balanced role of several platelet-adhesive receptors and a promoting role of platelet-released substances. This multivalent nature of neutrophil-thrombus interactions offers novel prospects for pharmacological intervention., Competing Interests: Disclosures J.W.M. Heemskerk is scientific advisor of the Synapse Research Institute Maastricht. The other authors report no conflicts.

Background: The acquired thrombotic risk factor known as lupus anticoagulant (LA) interferes with laboratory clotting assays and can be caused by autoantibodies against β2-glycoprotein I (β2GPI) and prothrombin. LA is associated with activated protein C (APC) resistance, which might contribute to thrombotic risk in patients with antiphospholipid syndrome. How antibodies against β2GPI and prothrombin cause APC resistance is currently unclear., Objectives: To investigate how anti-β2GPI and antiphosphatidylserine/prothrombin (PS/PT) antibodies induce APC resistance., Methods: The effects of anti-β2GPI and anti-PS/PT antibodies on APC resistance were studied in plasma (of patients with antiphospholipid syndrome) and with purified coagulation factors and antibodies., Results: APC resistance was observed in LA-positive patients with anti-β2GPI or anti-PS/PT antibodies and in normal plasma spiked with monoclonal anti-β2GPI or anti-PS/PT antibodies with LA activity. Analysis of factor (F)V cleavage patterns after APC incubation indicated that anti-β2GPI antibodies attenuated APC-mediated FV cleavage at R506 and R306. APC-mediated cleavage at R506 is required for FV cofactor activity during inactivation of FVIIIa. Assays with purified coagulation factors confirmed that anti-β2GPI antibodies interfered with the cofactor function of FV during FVIIIa inactivation but not with FVa inactivation. Anti-PS/PT antibodies attenuated APC-mediated FVa and FVIIIa inactivation. Analysis of FV(a) cleavage patterns after APC incubation indicated that anti-PS/PT antibodies interfere with APC-mediated cleavage of FV at positions R506 and R306., Conclusion: Anti-β2GPI antibodies with LA activity contribute to a procoagulant state by causing APC resistance via interference with the cofactor function of FV during FVIIIa inactivation. LA-causing anti-PS/PT antibodies interfere with the anticoagulant function of APC by preventing FV(a) cleavage., Competing Interests: Declaration of competing interests There are no competing interests to disclose., (Copyright © 2023 The Author(s). Published by Elsevier Inc. All rights reserved.)

Proteoglycans form a heterogeneous family of proteins with covalently bound sulfated glycosaminoglycans. The extracellular matrix proteoglycan perlecan has been proposed to bind to the platelet- and megakaryocyte-specific receptor G6bB, co-regulating platelet glycoprotein VI (GPVI) signaling. The derived non-sulfate proteoglycan endorepellin was previously shown to enhance platelet adhesion via the collagen receptor, integrin α2β1. Here, we compared the roles of perlecan and other matrix proteoglycans in platelet responses and thrombus formation. We used multi-color flow cytometry to measure the degranulation and integrin αIIbβ3 activation of washed platelets in response to various proteoglycans and collagen-related peptide (CRP), the GPVI agonist. Perlecan, but not endorepellin, enhanced the CRP-induced activation of platelets in a time- and concentration-dependent manner. Similar to collagen, immobilized perlecan, but not other proteoglycans, supported static platelet adhesion and spreading. In-flowed whole-blood perlecan diminished shear-dependent platelet adhesion, while it enforced GPVI-dependent thrombus formation-to a larger extent than endorepellin-to induce more contracted aggregates of activated platelets. We concluded that the sulfated proteoglycan perlecan enhances GPVI-dependent platelet responses extending to thrombus formation, but it does so at the expense of reduced adhesion of platelets under flow.

Introduction: The protein tyrosine phosphatase SHP2 (PTPN11) is a negative regulator of glycoprotein VI (GPVI)-induced platelet signal under certain conditions. Clinical trials with derivatives of the allosteric drug SHP099, inhibiting SHP2, are ongoing as potential therapy for solid cancers. Gain-of-function mutations of the PTPN11 gene are observed in part of the patients with the Noonan syndrome, associated with a mild bleeding disorder. Assessment of the effects of SHP2 inhibition in platelets from controls and Noonan syndrome patients., Materials and Methods: Washed human platelets were incubated with SHP099 and stimulated with collagen-related peptide (CRP) for stirred aggregation and flow cytometric measurements. Whole-blood microfluidics assays using a dosed collagen and tissue factor coating were performed to assess shear-dependent thrombus and fibrin formation. Effects on clot formation were evaluated by thromboelastometry., Results: Pharmacological inhibition of SHP2 did not alter GPVI-dependent platelet aggregation under stirring, but it enhanced integrin αIIbβ3 activation in response to CRP. Using whole-blood microfluidics, SHP099 increased the thrombus buildup on collagen surfaces. In the presence of tissue factor and coagulation, SHP099 increased thrombus size and reduced time to fibrin formation. Blood from PTPN11-mutated Noonan syndrome patients, with low platelet responsiveness, after ex vivo treatment with SHP099 showed a normalized platelet function. In thromboelastometry, SHP2 inhibition tended to increase tissue factor-induced blood clotting profiles with tranexamic acid, preventing fibrinolysis., Conclusion: Pharmacological inhibition of SHP2 by the allosteric drug SHP099 enhances GPVI-induced platelet activation under shear conditions with a potential to improve platelet functions of Noonan syndrome patients., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Background: Collagen-induced platelet activation is predominantly mediated by glycoprotein (GP) VI through formation of receptor clusters that coincide with the accumulation of signaling molecules and are hypothesized to drive strong and sustained platelet activation., Objectives: To determine the importance of GPVI clusters for thrombus formation in whole blood under shear., Methods: We utilized whole blood microfluidics and an anti-GPVI nanobody (Nb), Nb28, labeled with AlexaFluor 488, to assess the distribution of GPVI on the surface of platelets adhering to a range of collagen-like substrates with different platelet activation potentials., Results: Automated analysis of GPVI surface distribution on platelets supported the hypothesis that there is a relationship between GPVI cluster formation, thrombus size, and phosphatidylserine (PS) exposure. Substrates that supported the formation of macroclusters also induced significantly bigger aggregates, with increased amounts of PS-exposing platelets in comparison to substrates where no GPVI clusters were detected. Furthermore, we demonstrate that only direct inhibition of GPVI binding, but not of downstream signaling, is able to disrupt cluster formation., Conclusion: Labeled anti-GPVI Nb28 permits visualization of GPVI clustering under flow conditions. Furthermore, whilst inhibition of downstream signaling does not affect clustering, it does prevent thrombus formation. Therefore, GPVI macroclustering is a prerequisite for thrombus formation and platelet activation, namely, PS exposure, on highly GPVI-dependent collagen surfaces., Competing Interests: Declaration of competing interests S.P.W. and N.S.P. have a patent for the anti-GPVI nanobodies (WO2022/136457). R.W.F. is the Chief Scientific Officer of CambCol Laboratories Ltd. The other authors have no competing interests to disclose., (Copyright © 2023 The Author(s). Published by Elsevier Inc. All rights reserved.)

Background: Emerging data show an increased risk of ischemic stroke in patients with a new diagnosis of cancer. As the risk of stroke begins to increase 150 days before cancer is diagnosed, stroke may be the first clinical manifestation of undiagnosed cancer. About 6% of patients with cryptogenic ischemic stroke (unknown etiology after diagnostic evaluations) are diagnosed with cancer within one year. However, the optimal cancer screening strategy in this population is not known. We aim to conduct a scoping review of screening strategies for occult cancer in individuals with ischemic stroke., Methods: Electronic databases including MEDLINE (Ovid), EMBASE (Ovid), CINAHL (EBSCOhost) and Scopus will be systematically searched to identify articles that report on screening strategies for occult cancer in individuals with ischemic stroke. At least two investigators will independently perform two-stage study selection consisting of title/abstract screening and full-text review, followed by data extraction. Thereafter, a thematic analysis will be conducted to provide an overview of what diagnostic tests/strategies have been used, and their clinical utility in terms of positive and negative predictive value (when available)., Conclusion: We anticipate that the findings of this scoping review will identify strategies used to detect occult cancer in individuals with ischemic stroke and summarize their clinical utility (if reported). Addressing this knowledge gap will help guide the development of future clinical trials on occult cancer screening patients with ischemic stroke., Competing Interests: DMS received honoraria for educational presentations in the last 12 months (paid to institution) from BMS-Pfizer, Roche, and Servier. All other authors have declared that no competing interests exist,, (Copyright: © 2023 Leentjens et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Recent studies have shown that patients with pancreatic ductal adenocarcinoma (PDAC) treated with neoadjuvant chemo(radio)therapy followed by surgery have an improved outcome compared to patients treated with upfront surgery. Hence, patients with PDAC are more and more frequently treated with chemotherapy in the neoadjuvant setting. PDAC patients are at a high risk of developing venous thromboembolism (VTE), which is associated with decreased survival rates. As patients with PDAC were historically offered immediate surgical resection, data on VTE incidence and associated preoperative risk factors are scarce. Current guidelines recommend primary prophylactic anticoagulation in selected groups of patients with advanced PDAC. However, recommendations for patients with (borderline) resectable PDAC treated with chemotherapy in the neoadjuvant setting are lacking. Nevertheless, the prevention of complications is crucial to maintain the best possible condition for surgery. This narrative review summarizes current literature on VTE incidence, associated risk factors, risk assessment tools, and primary thromboprophylaxis in PDAC patients treated with neoadjuvant chemo(radio)therapy.

Background:  In secondary cardiovascular disease prevention, treatments blocking platelet-derived secondary mediators pose a risk of bleeding. Pharmacological interference of the interaction of platelets with exposed vascular collagens is an attractive alternative, with clinical trials ongoing. Antagonists of the collagen receptors, glycoprotein VI (GPVI), and integrin α2β1, include recombinant GPVI-Fc dimer construct Revacept, 9O12 mAb based on the GPVI-blocking reagent Glenzocimab, Syk tyrosine-kinase inhibitor PRT-060318, and anti-α2β1 mAb 6F1. No direct comparison has been made of the antithrombic potential of these drugs., Methods:  Using a multiparameter whole-blood microfluidic assay, we compared the effects of Revacept, 9O12-Fab, PRT-060318, or 6F1 mAb intervention with vascular collagens and collagen-related substrates with varying dependencies on GPVI and α2β1. To inform on Revacept binding to collagen, we used fluorescent-labelled anti-GPVI nanobody-28., Results and Conclusion:  In this first comparison of four inhibitors of platelet-collagen interactions with antithrombotic potential, we find that at arterial shear rate: (1) the thrombus-inhibiting effect of Revacept was restricted to highly GPVI-activating surfaces; (2) 9O12-Fab consistently but partly inhibited thrombus size on all surfaces; (3) effects of GPVI-directed interventions were surpassed by Syk inhibition; and (4) α2β1-directed intervention with 6F1 mAb was strongest for collagens where Revacept and 9O12-Fab were limitedly effective. Our data hence reveal a distinct pharmacological profile for GPVI-binding competition (Revacept), GPVI receptor blockage (9O12-Fab), GPVI signaling (PRT-060318), and α2β1 blockage (6F1 mAb) in flow-dependent thrombus formation, depending on the platelet-activating potential of the collagen substrate. This work thus points to additive antithrombotic action mechanisms of the investigated drugs., Competing Interests: M.P.G. is a co-inventor of Revacept and M.J.P. is a founder and scientific adviser for Acticor Biotech. S.P.W. and N.S.P. own a patent (WO2022/136457) for Nb28. R.W.F. is the Chief Scientific Officer of CambCol Laboratories Ltd., Ely, United Kingdom. J.W.M.H. is a consultant of Synapse B.V., (Thieme. All rights reserved.)

In platelets, elevated cytosolic Ca 2+ is a crucial second messenger, involved in most functional responses, including shape change, secretion, aggregation and procoagulant activity. The platelet Ca 2+ response consists of Ca 2+ mobilization from endoplasmic reticulum stores, complemented with store-operated or receptor-operated Ca 2+ entry pathways. Several channels can contribute to the Ca 2+ entry, but their relative contribution is unclear upon stimulation of ITAM-linked receptors such as glycoprotein VI (GPVI) and G-protein coupled receptors such as the protease-activated receptors (PAR) for thrombin. We employed a 96-well plate high-throughput assay with Fura-2-loaded human platelets to perform parallel [Ca 2+ ] i measurements in the presence of EGTA or CaCl 2 . Per agonist condition, this resulted in sets of EGTA, CaCl 2 and Ca 2+ entry ratio curves, defined by six parameters, reflecting different Ca 2+ ion fluxes. We report that threshold stimulation of GPVI or PAR, with a variable contribution of secondary mediators, induces a maximal Ca 2+ entry ratio of 3-7. Strikingly, in combination with Ca 2+ -ATPase inhibition by thapsigargin, the maximal Ca 2+ entry ratio increased to 400 (GPVI) or 40 (PAR), pointing to a strong receptor-dependent enhancement of store-operated Ca 2+ entry. By pharmacological blockage of specific Ca 2+ channels in platelets, we found that, regardless of GPVI or PAR stimulation, the Ca 2+ entry ratio was strongest affected by inhibition of ORAI1 (2-APB, Synta66) > Na + /Ca 2+ exchange (NCE) > P2× 1 (only initial). In contrast, inhibition of TRPC6, Piezo1/2 or STIM1 was without effect. Together, these data reveal ORAI1 and NCE as dominating Ca 2+ carriers regulating GPVI- and PAR-induced Ca 2+ entry in human platelets., Competing Interests: Declaration of Competing Interest MR is an employee of Synapse Research Institute. JWMH is a scientific advisor of Synapse Research Institute. The other authors report no relevant conflicts of interest., (Copyright © 2023. Published by Elsevier Ltd.)

Thrombin generation (TG) assays serve as a valuable tool to study the amplifying roles of intrinsic pathway factors in human coagulation and provide functional insights into the increased bleeding observed in individuals deficient in factors (F) XI, IX, or VIII. Mice are used extensively in hemostasis research owing to the availability of coagulation factor-deficient mice. However, phenotypic differences between mouse and human TG have become apparent. In this study, we describe a novel, calibrated mouse whole blood (WB) TG assay used to assess the amplifying roles of intrinsic pathway factors in mouse coagulation. WB- and plasma-TG was triggered with either silica or tissue factor (TF) in samples from wild-type mice and mice deficient for FXII, FXI, or FIX. Expectedly, silica-triggered WB-TG and platelet-poor plasma (PPP)-TG were significantly reduced by deficiencies for FXII, FXI, or FIX. FXII deficiency had no effect on WB-TG or PPP-TG when triggered with TF. However, FXI deficiency resulted in significantly reduced WB-TG triggered by low concentrations of TF but had no effect on TF-triggered PPP-TG. FIX deficiency profoundly reduced WB-TG when triggered by low or high concentrations of TF whereas TG in PPP or platelet-rich plasma was only moderately reduced under these conditions. In conclusion, we have developed a novel mouse WB-TG assay with enhanced sensitivity to FXI- and FIX-dependent amplification of coagulation compared with an established plasma-TG assay. The enhanced sensitivity of WB-TG to FXI and FIX-dependent amplification of coagulation suggests an important role of blood cells in this process., (© 2023 by The American Society of Hematology. Licensed under Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0), permitting only noncommercial, nonderivative use with attribution. All other rights reserved.)

Background: Especially in disease conditions, platelets can encounter activating agents in circulation., Objectives: To investigate the extent to which previously activated platelets can be reactivated and whether in-and reactivation applies to different aspects of platelet activation and thrombus formation., Methods: Short-and long-term effects of glycoprotein VI (GPVI) and G protein-coupled receptor (GPCR) stimulation on platelet activation and aggregation potential were compared via flow cytometry and plate-based aggregation. Using fluorescence and electron microscopy, we assessed platelet morphology and content, as well as thrombus formation., Results: After 30 minutes of stimulation with thrombin receptor activator peptide 6 (TRAP6) or adenosine diphosphate (ADP), platelets secondarily decreased in PAC-1 binding and were less able to aggregate. The reversibility of platelets after thrombin stimulation was concentration dependent. Reactivation was possible via another receptor. In contrast, cross-linked collagen-related peptide (CRP-XL) or high thrombin stimulation evoked persistent effects in α IIb β 3 activation and platelet aggregation. However, after 60 minutes of CRP-XL or high thrombin stimulation, when α IIb β 3 activation slightly decreased, restimulation with ADP or CRP-XL, respectively, increased integrin activation again. Compatible with decreased integrin activation, platelet morphology was reversed. Interestingly, reactivation of reversed platelets again resulted in shape change and if not fully degranulated, additional secretion. Moreover, platelets that were previously activated with TRAP6 or ADP regained their potential to contribute to thrombus formation under flow. On the contrary, prior platelet triggering with CRP-XL was accompanied by prolonged platelet activity, leading to a decreased secondary platelet adhesion under flow., Conclusion: This work emphasizes that prior platelet activation can be reversed, whereafter platelets can be reactivated through a different receptor. Reversed, previously activated platelets can contribute to thrombus formation., (Crown Copyright © 2023. Published by Elsevier Inc. All rights reserved.)

Bruton's tyrosine kinase (Btk) and spleen tyrosine kinase (Syk) are major signaling proteins in human platelets that are implicated in atherothrombosis and thrombo-inflammation, but the mechanisms controlling their activities are not well understood. Previously, we showed that Syk becomes phosphorylated at S297 in glycoprotein VI (GPVI)-stimulated human platelets, which limits Syk activation. Here, we tested the hypothesis that protein kinases C (PKC) and A (PKA) and protein phosphatase 2A (PP2A) jointly regulate GPVI-induced Btk activation in platelets. The GPVI agonist convulxin caused rapid, transient Btk phosphorylation at S180 (pS180↑), Y223 and Y551, while direct PKC activation strongly increased Btk pS180 and pY551. This increase in Btk pY551 was also Src family kinase (SFK)-dependent, but surprisingly Syk-independent, pointing to an alternative mechanism of Btk phosphorylation and activation. PKC inhibition abolished convulxin-stimulated Btk pS180 and Syk pS297, but markedly increased the tyrosine phosphorylation of Syk, Btk and effector phospholipase Cγ2 (PLCγ2). PKA activation increased convulxin-induced Btk activation at Y551 but strongly suppressed Btk pS180 and Syk pS297. PP2A inhibition by okadaic acid only increased Syk pS297. Both platelet aggregation and PLCγ2 phosphorylation with convulxin stimulation were Btk-dependent, as shown by the selective Btk inhibitor acalabrutinib. Together, these results revealed in GPVI-stimulated platelets a transient Syk, Btk and PLCγ2 phosphorylation at multiple sites, which are differentially regulated by PKC, PKA or PP2A. Our work thereby demonstrated the GPVI-Syk-Btk signalosome as a tightly controlled protein kinase network, in agreement with its role in atherothrombosis.

There is ongoing debate as to whether abacavir (ABC) increases the risk for cardiovascular disease(CVD) in people living with HIV (PLHIV) and the mechanisms underlying this possible association. We recently showed that the use of an ABC-containing regimen was independently associated with increased thrombin generation (TG). In the present study, we aim to explore these findings further, by studying the mechanistical processes that underly the global thrombin generation test via thrombin dynamics analysis. Thrombin dynamics analysis can pinpoint the cause of increased thrombin generation associated with ABC-use either to the procoagulant prothrombin conversion pathway or the anticoagulant thrombin inactivation pathway. In this cross-sectional study, 208 virally suppressed PLHIV were included, of whom 94 were on a ABC-containing regimen, 92 on a tenofovir disoproxil fumarate (TDF)-containing regimen, and the remainder on other regimens. We used Calibrated Automated Thrombinography to measure thrombin generation and perform thrombin dynamics analysis. The total amount of prothrombin conversion, as well as the maximum rate of prothrombin conversion were significantly increased in PLHIV on an ABC containing regimen compared to other treatment regimens. The levels of pro- and anticoagulant factors were comparable, indicating that the ABC-induced changes affect the kinetics of prothrombin conversion rather than procoagulant factor levels. Moreover, Von Willebrand Factor (VWF), active VWF and VWF pro-peptide levels were significantly higher in PLHIV than controls without HIV. However, they did not differ between ABC and non-ABC treated participants., Competing Interests: QY, SH, RL-K, MN, and BL are employees of Synapse Research Institute, part of Diagnostica Stago SAS. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Yan, Huang, van der Heijden, Ninivaggi, van de Wijer, de Laat-Kremers, Van der Ven, de Laat and de Mast.)

Platelets are small anucleate cell fragments (2-4 μm in diameter) in the blood, which play an essential role in thrombosis and hemostasis. Genetic or acquired platelet dysfunctions are linked to bleeding, increased risk of thromboembolic events and cardiovascular diseases. Advanced proteomic approaches may pave the way to a better understanding of the roles of platelets in hemostasis, and pathophysiological processes such as inflammation, metastatic spread and thrombosis. Further insights into the molecular biology of platelets are crucial to aid drug development and identify diagnostic markers of platelet activation. Platelet activation is known to be an extremely rapid process and involves multiple post-translational mechanisms at sub second time scale, including proteolysis and phosphorylation. Multi-omics technologies and biochemical approaches can be exploited to precisely probe and define these posttranslational pathways. Notably, the absence of a nucleus in platelets significantly reduces the number of present proteins, simplifying mass spectrometry-based proteomics and metabolomics approaches., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Background: The antiphospholipid syndrome (APS) is classified by the presence of antiphospholipid antibodies (aPL) and thrombotic and/or adverse obstetric outcomes. The diagnosis and risk assessment of APS is challenging. This systematic review investigated if the thrombin generation (TG) assay could be helpful for APS diagnosis and risk assessment., Methods: A systemic review was performed by searching two databases (MEDLINE and Embase) until March 31, 2022, using a search strategy with two concepts: APS and TG, and related keywords. Two reviewers independently screened the articles based on predefined inclusion and exclusion criteria. Data extraction and quality assessment with the Newcastle-Ottawa Scale (NOS) were performed independently. Synthesis Without Meta-analysis guidelines were followed for data synthesis reporting., Results: Fourteen studies with 677 APS and 1,349 control subjects were included with variable quality according to the NOS. Twelve studies measured TG via the calibrated automated thrombogram (CAT) method using a fluorogenic substrate, whereas two used a chromogenic substrate-based TG assay. One study compared the CAT assay to the fully-automated ST Genesia® (Stago, France). Two studies initiated TG using platelet-rich plasma, whereas the rest of the studies used platelet-poor plasma. Resistance to activated protein C (aPC) was examined in ten studies. They reported a significant increase in aPC-resistance in APS patients compared to healthy controls, aPL-carriers, and thrombotic controls. Based on two studies, the prevalence of aPC-resistance was higher in APS patients compared to healthy controls and thrombotic controls with odds ratios of 5.9 and 6.8-12.8, respectively ( p  < 0.05). In contrast, no significant difference in aPC-resistance was found between APS patients and autoimmune disease controls. Furthermore, 7/14 studies reported TG-parameters including peak height, endogenous thrombin potential, lag time, and time to peak, but these outcomes were highly variable between studies. Furthermore, TG methodology between studies differed greatly, impacting the comparability of the studies., Conclusion: aPC-resistance measured with TG was increased in APS patients compared to healthy and thrombotic controls, but the diagnostic and prognostic value is unclear compared to current diagnostic strategies. Studies of other TG-parameters were heterogeneous and more research is needed to identify their potential added value in APS diagnosis., Systematic Review Registration: https://www.PROSPERO/, identifier: CRD42022308363., Competing Interests: BDL and RG are employees of Synapse Research Institute, which is a part of the Stago group that markets the Calibrated Automated Thrombography and ST Genesia®. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (© 2023 Gehlen, Vandevelde, de Laat and Devreese.)

The American Trial Using Tranexamic Acid (TXA) in Thrombocytopenia (A-TREAT, NCT02578901) demonstrated no superiority of TXA over placebo in preventing World Health Organization (WHO) grade 2 or higher bleeding in patients with severe thrombocytopenia requiring supportive platelet transfusion following myeloablative therapy for hematologic disorders. In this ancillary study, we sought to determine whether this clinical outcome could be explained on the basis of correlative assays of fibrinolysis. Plasma was collected from A-TREAT participants (n = 115) before the initiation of study drug (baseline) and when TXA was at steady-state trough concentration (follow-up). Global fibrinolysis was measured by 3 assays: euglobulin clot lysis time (ECLT), plasmin generation (PG), and tissue-type plasminogen activator (tPA)-challenged clot lysis time (tPA-CLT). TXA was quantified in follow-up samples by tandem mass spectrometry. Baseline samples did not demonstrate fibrinolytic activation by ECLT or tPA-CLT. Furthermore, neither ECLT nor levels of plasminogen activator inhibitor-1, tPA, plasminogen, alpha2-antiplasmin, or plasmin-antiplasmin complexes were associated with a greater risk of WHO grade 2+ bleeding. TXA trough concentrations were highly variable (range, 0.7-10 μg/mL) and did not correlate with bleeding severity, despite the fact that plasma TXA levels correlated strongly with pharmacodynamic assessments by PG (Spearman r, -0.78) and tPA-CLT (r, 0.74). We conclude that (1) no evidence of fibrinolytic activation was observed in these patients with thrombocytopenia, (2) trough TXA concentrations varied significantly between patients receiving the same dosing schedule, and (3) tPA-CLT and PG correlated well with TXA drug levels., (© 2023 by The American Society of Hematology. Licensed under Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0), permitting only noncommercial, nonderivative use with attribution. All other rights reserved.)

Receptor diffusion plays an essential role in cellular signalling via the plasma membrane microenvironment and receptor interactions, but the regulation is not well understood. To aid in understanding of the key determinants of receptor diffusion and signalling, we developed agent-based models (ABMs) to explore the extent of dimerisation of the platelet- and megakaryocyte-specific receptor for collagen glycoprotein VI (GPVI). This approach assessed the importance of glycolipid enriched raft-like domains within the plasma membrane that lower receptor diffusivity. Our model simulations demonstrated that GPVI dimers preferentially concentrate in confined domains and, if diffusivity within domains is decreased relative to outside of domains, dimerisation rates are increased. While an increased amount of confined domains resulted in further dimerisation, merging of domains, which may occur upon membrane rearrangements, was without effect. Modelling of the proportion of the cell membrane which constitutes lipid rafts indicated that dimerisation levels could not be explained by these alone. Crowding of receptors by other membrane proteins was also an important determinant of GPVI dimerisation. Together, these results demonstrate the value of ABM approaches in exploring the interactions on a cell surface, guiding the experimentation for new therapeutic avenues., (© 2023. The Author(s).)

Background:  Coronavirus disease 2019 (COVID-19) is often associated with mild thrombocytopenia and increased platelet reactivity., Objective:  The aim of the current study was to investigate the adenosine triphosphate (ATP) release kinetics of platelets in hospitalized SARS-CoV-2-infected patients., Methods:  We studied time-dependent platelet activation in whole blood by monitoring the ATP release kinetics upon stimulation with a PAR1 receptor agonist in 41 hospitalized critically ill COVID-19 patients, 47 hospitalized noncritically ill COVID-19 patients, and 30 healthy controls., Results:  Our study demonstrated that platelets of critically ill COVID-19 patients were hyper-responsive with a shorter platelet response time (PRT) and a reduced platelet granule release capacity (GRC), probably due to chronic activation. The median PRT of COVID-19 patients admitted to the critical care unit was 10 and 7 seconds shorter than the median PRT in healthy controls and noncritical COVID-19 patients, respectively. Both PRT and GRC were also associated with D-dimer (Spearman r [ r s ] = -0.51, p  < 0.0001 and r s  = -0.23, p <  0.05), C-reactive protein (CRP) ( r s  = -0.59, p  < 0.0001 and r s  = -0.41, p  < 0.01), and neutrophil-to-lymphocyte ratio (NLR) ( r s  = -0.42, p  < 0.0001 and r s  = -0.26, p  < 0.05). Moreover, an increased PRT and a reduced GRC were associated with an increased mortality (odds ratio [OR]: 18.8, 95% confidence interval [CI]: 6.5-62.8, p <  0.0001 and OR: 4.0; 95% CI: 1.6-10.4, p <  0.01). These relationships remained significant after adjustment for age, sex, D-dimer, CRP, and NLR., Conclusion:  Using an accessible agonist-induced platelet granule ATP release assay, we show that platelet hyper-responsiveness and reduced platelet GRC in COVID-19 patients were associated with critical illness and mortality., Competing Interests: None declared., (Thieme. All rights reserved.)

Calibrated Automated Thrombography (CAT) is a versatile and sensitive method for analyzing coagulation reactions culminating in thrombin generation (TG). Here, we present a CAT method for analyzing TG in murine whole blood by adapting the CAT assay used for measuring TG in human plasma. The diagnostically used artificial and physiologic factor XII (FXII) contact activators kaolin, ellagic acid and polyphosphate (polyP) stimulated TG in murine blood in a dose-dependent manner resulting in a gradual increase in endogenous thrombin potential and peak thrombin, with shortened lag times and times to peak. The activated FXII inhibitor rHA-Infestin-4 and direct oral anticoagulants (DOACs) interfered with TG triggered by kaolin, ellagic acid and polyP and TG was completely attenuated in blood of FXII- ( F12 -/- ) and FXI-deficient ( F11 -/- ) mice. Moreover, reconstitution of blood from F12 -/- mice with human FXII restored impaired contact-stimulated TG. HEK293 cell-purified polyP also initiated FXII-driven TG in mouse whole blood and addition of the selective inhibitor PPX&#95;Δ12 ablated natural polyP-stimulated TG. In conclusion, the data provide a method for analysis of contact activation-mediated TG in murine whole blood. As the FXII-driven intrinsic pathway of coagulation has emerged as novel target for antithrombotic agents that are validated in mouse thrombosis and bleeding models, our novel assay could expedite therapeutic drug development., Competing Interests: Authors BL and MR are employees of Synapse Research Institute, part of Diagnostica Stago. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Konrath, Mailer, Beerens, Englert, Frye, Kuta, Preston, Maas, Butler, Roest, de Laat and Renné.)

Background: Trauma patients with abnormal fibrinolysis have increased morbidity and mortality. Knowledge of mechanisms differentiating fibrinolytic phenotypes is important to optimize treatment. We hypothesized that subjects with abnormal fibrinolysis identified by whole blood viscoelastometry can also be distinguished by plasma thrombin generation, clot structure, fibrin formation, and plasmin generation measurements., Methods: Platelet-poor plasma (PPP) from an observational cross-sectional trauma cohort with fibrinolysis shutdown (% lysis at 30 minutes [LY30] < 0.9, n = 11) or hyperfibrinolysis (LY30 > 3%, n = 9) defined by whole blood thromboelastography were studied. Noninjured control subjects provided comparative samples. Thrombin generation, fibrin structure and formation, and plasmin generation were measured by fluorescence, confocal microscopy, turbidity, and a fluorescence-calibrated plasmin assay, respectively, in the absence/presence of tissue factor or tissue plasminogen activator (tPA)., Results: Whereas spontaneous thrombin generation was not detected in PPP from control subjects, PPP from hyperfibrinolysis or shutdown patients demonstrated spontaneous thrombin generation, and the lag time was shorter in hyperfibrinolysis versus shutdown. Addition of tissue factor masked this difference but revealed increased thrombin generation in hyperfibrinolysis samples. Compared with shutdown, hyperfibrinolysis PPP formed denser fibrin networks. In the absence of tPA, the fibrin formation rate was faster in shutdown than hyperfibrinolysis, but hyperfibrinolysis clots lysed spontaneously; these differences were masked by addition of tPA. Tissue plasminogen activator-stimulated plasmin generation was similar in hyperfibrinolysis and shutdown samples. Differences in LY30, fibrin structure, and lysis correlated with pH., Conclusion: This exploratory study using PPP-based assays identified differences in thrombin generation, fibrin formation and structure, and lysis in hyperfibrinolysis and shutdown subgroups. These groups did not differ in their ability to promote tPA-triggered plasmin generation. The ability to characterize these activities in PPP facilitates studies to identify mechanisms that promote adverse outcomes in trauma., Level of Evidence: Prognostic/Epidemiological; Level III., (Copyright © 2022 Wolters Kluwer Health, Inc. All rights reserved.)