Christian Schörgenhofer

VWF excess and ADAMTS13 deficiency: a unifying pathomechanism linking inflammation to thrombosis in DIC, malaria, and TTP

Absent or severely diminished activity of ADAMTS13 (A Disintegrin And Metalloprotease with a ThromboSpondin type 1 motif, member 13) resulting in the intravascular persistence and accumulation of highly thrombogenic ultra large von Willebrand factor (UL-VWF) multimers is the pathophysiological mechanism underlying thrombotic thrombocytopenic purpura. Reduced VWF-cleaving protease levels, however, are not uniquely restricted to primary thrombotic microangiopathy (TMA), e. g. thrombotic thrombocytopenic purpura, but also occur in other life-threatening thrombocytopenic conditions: severely decreased ADAMTS13 activity is seen in severe sepsis, disseminated intravascular coagulation (DIC) and complicated malarial infection. The clinical relevance of these secondary thrombotic microangiopathies is increasingly recognised, but its therapeutic implications have not yet been determined. The presence of a secondary TMA in certain diseases may define patient groups which possibly could benefit from ADAMTS13 replacement or a VWF-targeting therapy. This short-review focuses on the role of UL-VWF multimers in secondary TMA and discusses the potential of investigational therapies as candidates for the treatment of TTP. In conclusion, prospective clinical trials on the effectiveness of protease replacementin vivo seem reasonable. Carefully selected patients with secondary TMA may benefit from therapies primarily intended for the use in patients with TTP.

Asphyxia by Drowning Induces Massive Bleeding Due To Hyperfibrinolytic Disseminated Intravascular Coagulation

Objective: To date, no study has systematically investigated the impact of drowning-induced asphyxia on hemostasis. Our objective was to test the hypothesis that asphyxia induces bleeding by hyperfibrinolytic disseminated intravascular coagulation. Design: Observational study. Setting: A 2,100-bed tertiary care facility in Vienna, Austria, Europe. Patients: All cases of drowning-induced asphyxia (n = 49) were compared with other patients with cardiopulmonary resuscitation (n = 116) and to patients with acute promyelocytic leukemia (n = 83). Six drowning victims were investigated prospectively. To study the mechanism, a forearm-ischemia model was used in 20 volunteers to investigate whether hypoxia releases tissue plasminogen activator. Interventions: None. Measurements and Main Results: Eighty percent of patients with drowning-induced asphyxia developed overt disseminated intravascular coagulation within 24 hours. When compared with nondrowning cardiac arrest patients, drowning patients had a 13 times higher prevalence of overt disseminated intravascular coagulation at admission (55% vs 4%; p < 0.001). Despite comparable disseminated intravascular coagulation scores, acute promyelocytic leukemia patients had higher fibrinogen but lower d-dimer levels and platelet counts than drowning patients (p < 0.001). Drowning victims had a three-fold longer activated partial thromboplastin time (124 s; p < 0.001) than both nondrowning cardiac arrest and acute promyelocytic leukemia patients. Hyperfibrinolysis was reflected by up to 1,000-fold increased d-dimer levels, greater than 5-fold elevated plasmin antiplasmin levels, and a complete absence of thrombelastometric clotting patterns, which was reversed by antifibrinolytics and heparinase. Thirty minutes of forearm-ischemia increased tissue plasminogen activator 31-fold (p < 0.001). Conclusions: The vast majority of drowning patients develops overt hyperfibrinolytic disseminated intravascular coagulation, partly caused by hypoxia induced tissue plasminogen activator release. Antifibrinolytics and heparinase partially reverse the abnormal clotting patterns. Severe activated partial thromboplastin time prolongation may be a marker of combined hyperfibrinolytic afibrinogenemia and autoheparinization in drowning-related asphyxia.

Effect of preanalytical time-delay on platelet function as measured by multiplate, PFA-100 and VerifyNow.

Abstract Background and aims: Platelet function testing may help to identify poor responders to antiplatelet drugs. The aim of this study was to compare three commonly used platelet function tests with special focus on the pre-analytical influence of time-delay on the tested parameters. Methods: We assessed ADP-induced platelet function by the Multiplate, Platelet Function Analyzer-100 (PFA-100) and VerifyNow in nine healthy volunteers and 36 patients receiving clopidogrel or prasugrel 1 and 3 hours after sampling. Results: The PFA-100 demonstrated non-closure time in 23 patients. A more graded response could be detected with the two other devices. Aggregation in whole blood (Multiplate) decreased after 3 hours compared to 1 hour in all subjects (p < 0.05). Furthermore, aggregation levels obtained by the VerifyNow showed a decrease in patients taking P2Y12 inhibitors after 3 hours (p < 0.05), except in three patients, in whom an increase was observed. Conclusion: Responses to ADP are time-dependent after blood sampling for the Multiplate in all subjects and for the VerifyNow in patients on antiplatelet drugs. For both devices, platelet aggregation was reduced 3 hours after sampling which may affect data interpretation and clinical consequences.

Comparison between the impact of morning and evening doses of rivaroxaban on the circadian endogenous coagulation rhythm in healthy subjects.

Essentials It is unknown whether single rivaroxaban doses should best be administered in the morning or evening. Circadian rhythm of coagulation/fibrinolysis was measured after morning or evening intake of rivaroxaban. Evening intake of rivaroxaban leads to prolonged exposure to rivaroxaban concentrations. Evening intake of rivaroxaban better matches the morning hypofibrinolysis.

Tranexamic acid and fibrinogen restore clotting in vitro and in vivo in cardiac thrombus associated hyperfibrinolysis with overt bleedings

Tranexamic acid and fibrinogen restore clotting in vitro and in vivo in cardiac thrombus associated hyperfibrinolysis with overt bleedings -

Blockade of HLA Antibody-Triggered Classical Complement Activation in Sera From Subjects Dosed With the Anti-C1s Monoclonal Antibody TNT009—Results from a Randomized First-in-Human Phase 1 Trial

Background Complement may play a key role in antibody-mediated rejection. A promising therapeutic approach may be classical pathway (CP) inhibition at the level of early component C1. Methods In this first-in-human, double-blind, randomized placebo-controlled phase 1 trial, we evaluated the safety and complement inhibitory effect of TNT009, a humanized monoclonal anti-C1s antibody. Sixty-four adult healthy volunteers received either single (n = 48; 7 consecutive cohorts, 0.3-100 mg/kg) or 4 weekly infusions (n = 16; 2 consecutive cohorts, 30 and 60 mg/kg per infusion) of TNT009 or placebo. To assess the effect of treatment on complement activity, sera from dosed subjects were analyzed in a CP activation assay evaluating C3d deposition on HLA-coated microbeads spiked with alloantibodies. Results Single doses of TNT009 at 3 to 100 mg/kg uniformly and profoundly inhibited HLA antibody-mediated C3d deposition (≥86% after 60 minutes), whereby the duration of CP inhibition (2-14 days) was dose-dependent. Four weekly doses persistently blocked complement for 5 to 6 weeks. Ex vivo serum CP activity was profoundly inhibited when TNT009 concentrations exceeded 20 &mgr;g/mL. Infusions were well tolerated without serious or severe adverse events. Conclusions Treatment with TNT009 was safe and potently inhibited CP activity. Future studies in patients are required to assess the potential of TNT009 for preventing or treating antibody-mediated rejection.BACKGROUND Complement may play a key role in antibody-mediated rejection (ABMR). A promising therapeutic approach may be classical pathway (CP) inhibition at the level of early component C1. METHODS In this first-in-human, double-blind, randomized placebo-controlled phase 1 trial, we evaluated the safety and complement inhibitory effect of TNT009, a humanized monoclonal anti-C1s antibody. Sixty-four adult healthy volunteers received either single (n=48; 7 consecutive cohorts: 0.3-100 mg/kg) or 4 weekly infusions (n=16; 2 consecutive cohorts: 30 and 60 mg/kg per infusion) of TNT009 or placebo. To assess the effect of treatment on complement activity, sera from dosed subjects were analysed in a CP activation assay evaluating C3d deposition on HLA-coated microbeads spiked with alloantibodies. RESULTS Single doses of TNT009 at 3-100 mg/kg uniformly and profoundly inhibited HLA antibody-mediated C3d deposition (≥86% after 60 min), whereby the duration of CP inhibition (2-14 days) was dose-dependent. Four weekly doses persistently blocked complement for 5-6 weeks. Ex vivo serum CP activity was profoundly inhibited when TNT009 concentrations exceeded 20 μg/mL. Infusions were well tolerated without serious or severe adverse events. CONCLUSIONS Treatment with TNT009 was safe and potently inhibited CP activity. Future studies in patients are required to assess the potential of TNT009 for preventing or treating ABMR.This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives License 4.0 (CCBY-NC-ND), where it is permissible to download and share the work provided it is properly cited. The work cannot be changed in any way or used commercially without permission from the journal.

Evaluation of between-, within- and day-to-day variation of coagulation measured by rotational thrombelastometry (ROTEM)

Abstract Background and aims: The aim of this study was to assess the circadian variation and the between- and within-subject variation in 10 healthy subjects over a period of 8 weeks by ROTEM®. We further evaluated the influence of elevated body mass index and the effect of low molecular weight heparin and antithrombin on clot formation. Methods: Citrated blood samples were analysed in the NATEM® test system. The clotting time (CT), clot formation time (CFT), maximum clot firmness (MCF) and the maximum lysis (ML) were assessed. Results: Duplicate measurements showed that 23% of the CT and 31% of the CFT measurements had a coefficient of variation (CV) greater than 10%. The within-subject CV was 16% for the CT and 30% for the CFT. The MCF was fairly constant (6%), whereas ML showed more variation (18%). The between-subject CV was 6% for the CT and 20% for the CFT. Analytical variability was improved by summing up CT and CFT. Compared to morning values, CT, CFT and the sum of CT + CFT were shortened in the afternoon. High body mass index was associated with faster clotting. High concentrations of antithrombin had similar effects on clot formation as 0.2 IU/ml of enoxaparin. Conclusions: To overcome the influence of diurnal variation, we recommend obtaining blood samples at specified times in the morning. The within-subject variation should be taken into account, when serial measurements of drug effects are required.

Targeting von Willebrand Factor in Ischaemic Stroke: Focus on Clinical Evidence

Despite great efforts in stroke research, disability and recurrence rates in ischaemic stroke remain unacceptably high. To address this issue, one potential target for novel therapeutics is the glycoprotein von Willebrand factor (vWF), which increases in thrombogenicity especially under high shear rates as it bridges between vascular sub-endothelial collagen and platelets. The rationale for vWF as a potential target in stroke comes from four bodies of evidence. (1) Animal models which recapitulate the pathogenesis of stroke and validate the concept of targeting vWF for stroke prevention and the use of the vWF cleavage enzyme ADAMTS13 in acute stroke treatment. (2) Extensive epidemiologic data establishing the prognostic role of vWF in the clinical setting showing that high vWF levels are associated with an increased risk of first stroke, stroke recurrence or stroke-associated mortality. As such, vWF levels may be a suitable marker for further risk stratification to potentially fine-tune current risk prediction models which are mainly based on clinical and imaging data. (3) Genetic studies showing an association between vWF levels and stroke risk on genomic levels. Finally, (4) studies of patients with primary disorders of excess or deficiency of function in the vWF axis (e.g. thrombotic thrombocytopenic purpura and von Willebrand disease, respectively) which demonstrate the crucial role of vWF in atherothrombosis. Therapeutic inhibition of VWF by novel agents appears particularly promising for secondary prevention of stroke recurrence in specific sub-groups of patients such as those suffering from large artery atherosclerosis, as designated according to the TOAST classification.