Continuous thrombin infusion leads to a bleeding phenotype in sheep

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.

Dabigatran reduces endothelial permeability through inhibition of thrombin-induced cytoskeleton reorganization

Dabigatran etexilate (DE), a new oral anti-coagulant, is a direct thrombin inhibitor. Clinical trials showed the favorable benefit-to-risk profile of DE compared to warfarin for the prevention of ischemic stroke in patients with atrial fibrillation. Remarkably, patients treated with dabigatran showed reduced rates of intracerebral hemorrhage compared to warfarin. As the breakdown of endothelial barrier integrity is associated with hemorrhagic events and as thrombin increases endothelial permeability, we hypothesized that dabigatran preserves the endothelial barrier by inhibiting thrombin-induced permeability. We assessed leakage of fluorescein isothiocyanate (FITC)-dextran through the endothelial monolayer and measured trans-endothelial electrical resistance of the endothelial monolayer after treatment of thrombin or thrombin pre-incubated with dabigatran. Thrombin increased the permeability of endothelial cells. Dabigatran effectively blocked the ability of thrombin to increase permeability. Dabigatran inhibited the formation of actin stress fibers induced by thrombin and inhibited consequent destabilization of junctional protein complexes and intercellular gap formation. The interaction of thrombin with protease activated receptor-1 activates the Rho A guanosine triphosphate (GTP)ase-myosin light chain (MLC) phosphorylation signaling axis, leading to actin cytoskeleton changes. This signaling pathway was effectively inhibited by dabigatran in endothelial cells. Consistently, the number of phosphorylated MLC-positive cells was significantly decreased in ischemic tissue of rat brains. These results indicate dabigatran blocks the ability of thrombin to induce vascular permeability and the resulting underlying signaling cascade in endothelial cells. Our findings provide evidence that dabigatran may confer a lower risk of intracerebral hemorrhage by preserving endothelial barrier integrity.

Interplay between genetic and clinical variables affecting platelet reactivity and cardiac adverse events in patients undergoing percutaneous coronary intervention

Several clinical and genetic variables are associated with influencing high on treatment platelet reactivity (HTPR). The aim of the study was to propose a path model explaining a concurrent impact among variables influencing HTPR and ischemic events. In this prospective cohort study polymorphisms of CYP2C19*2, CYP2C19*17, ABCB1, PON1 alleles and platelet function assessed by Multiple Electrode Aggregometry were assessed in 416 patients undergoing percutaneous coronary intervention treated with clopidogrel and aspirin. The rates of major adverse cardiac events (MACE) were recorded during a 12-month follow up. The path model was calculated by a structural equation modelling. Paths from two clinical characteristics (diabetes mellitus and acute coronary syndrome (ACS)) and two genetic variants (CYP2C19*2 and CYP2C19*17) independently predicted HTPR (path coefficients: 0.11 0.10, 0.17, and -0.10, respectively; p<0.05 for all). By use of those four variables a novel score for prediction of HTPR was built: in a factor-weighted model the risk for HTPR was calculated with an OR of 3.8 (95%CI: 3.1–6.8, p<0.001) for a score level of ≥1 compared with a score of <1. While MACE was independently predicted by HTPR and age in the multivariate model (path coefficient: 0.14 and 0.13, respectively; p<0.05), the coexistence of HTPR and age ≥75 years emerged as the strongest predictor of MACE. Our study suggests a pathway, which might explain indirect and direct impact of variables on clinical outcome: ACS, diabetes mellitus, CYP2C19*2 and CYP2C19*17 genetic variants independently predicted HTPR. In turn, age ≥75 years and HTPR were the strongest predictors of MACE.

Recovery, safety, and tolerability of a solvent/detergent-treated and prion-safeguarded transfusion plasma in a randomized, crossover, clinical trial in healthy volunteers

BACKGROUND

Octaplas LG is a prion-depleted version of a previous generation product called Octaplas S/D. We compared the recovery, safety, and tolerability of these two pharmaceutical-grade plasmas.

STUDY DESIGN AND METHODS

In this comparative, block-randomized, open-label, active-controlled, crossover Phase I trial, 60 healthy adult volunteers received single transfusions of 1200 mL of parent product (in Period 1) and of the LG plasma product (in Period 2) or vice versa. In both periods, plasmapheresis (600 mL) preceded the transfusion. Blood samples were drawn before and after apheresis and 15 minutes, 2 hours, 24 hours, and 7 days after end of plasma transfusion, to assess recovery, safety, and tolerability. The primary efficacy endpoints were the changes in coagulation factors and hemostatic variables compared to baseline; their relative recovery was computed in the per-protocol analysis (n = 43). Safety and tolerability were assessed (n = 60).

RESULTS

Variations in coagulation factors and hemostatic variables over time were similar between the two treatments and within normal range; 90% confidence intervals for the derived recovery data were within predefined limits of equivalence. Both products were well tolerated. The advanced manufacturing process also significantly increased plasmin inhibitor concentrations after transfusion in vivo.

CONCLUSION

The LG plasma product was bioequivalent to its predecessor with respect to recovery of clotting factors and demonstrated comparable safety and tolerability in healthy volunteers. Both products compensated well for the loss of clotting factors after apheresis (NCT01063595).