Detection of direct oral anticoagulants with the dilute Russels viper venom time – observations in a real life setting

Background

The detection of direct oral anticoagulants (DOACs) in emergency settings still remains challenging, especially when dedicated anti-Xa or anti-IIa tests are not readily available or the specific DOAC is unknown. The dilute Russel's viper venom time (dRVVT) is widely known in lupus anticoagulant (LA) testing and may also provide helpful information regarding the residual antithrombotic activity of DOACs. Yet real world data describing the effect of DOACs on the dRVVT is scarce.

Objective

The study aimed to evaluate the sensitivity and specificity of dRVVT for different DOAC plasma levels.

Methods

A total of 80 patients were recruited – 20 patients for each approved DOAC (apixaban, edoxaban, rivaroxaban and dabigatran). Blood plasma was sampled before (baseline), 6 and 12 hours after DOAC-intake and at plasma peak time. DRVVT was measured using the LA1 screening assay for lupus anticoagulant. Plasma levels were measured by calibrated anti-Xa or anti-IIa tests. Additionally, activated partial thromboplastin time (aPTT) and prothrombin time (PT) were measured.

Results

All DOACs significantly prolonged the dRVVT. The effects were more pronounced at higher DOAC plasma levels. The area under the receiver operating characteristic (ROC) curve regarding a plasma level cut-off of 30 ng/ml was 0.92 (95% confidence interval (CI) 0.823 to 1.00) for apixaban, 0.97 (95% CI 0.902 to 1.00) for edoxaban, 0.87 (95% CI 0.649 to 1.00) for rivaroxaban and 0.96 (95% CI 0.871 to 1.00) for dabigatran.

Conclusion

A dose dependent effect of all approved direct oral anticoagulants (DOACs) on the dilute Russel's viper venom time (dRVVT) was documented in our real world setting, while relevant DOAC plasma levels did not affect standard coagulation tests. The negative predictive value for the dRVVT was high even at low DOAC plasma levels. The dRVVT could therefore be helpful to rule out relevant antithrombotic plasma activity caused of DOACs in emergency situations.

Funding Acknowledgement

Type of funding sources: Public Institution(s). Main funding source(s): Universität Leipzig Figure 1. ROC curves

Thrombin generation and rotational thromboelastometry in the healthy adult population

Published data on thrombin generation variables and their correlation with thrombo - elastometry in the healthy population are scarce. This study aimed at assessing thrombin generation in adults and its correlation to classical rotational thromboelastometry (ROTEM).

Thrombin generation was measured in platelet-poor plasma from healthy volunteers using the calibrated automated thrombogram (CAT) with 1 and 5 pmol/l tissue factor final concentration. Lag time, thrombin peak, time to thrombin peak and endogenous thrombin potential (ETP) were analyzed. ROTEM was performed without activator (NATEM) and data for clotting time, alpha angle, clot formation time and maximum clot firmness were correlated with those of thrombin generation.

Altogether 132 persons (72 men, 60 women; median age: 48.0 years) were included. There was a positive non-linear correlation for age versus lag time (p < 0.001) and time to peak (p = 0.001), and almost linear correlation for age versus thrombin peak (p = 0.024) and ETP (p = 0.001), although with a moderate regression slope. Regarding ROTEM, there was a positive correlation between age and maximum clot firmness and alpha angle (p = 0.001), but a negative correlation between age and clotting time (p = 0.039). Comparing both assays, thrombin peak and ETP measured with a final tissue factor concentration of 5 pmol/l correlated significantly with alpha angle and maximum clot firmness.

The age-related changes in CAT and ROTEM variables among adults are not linear. There is a significant correlation, although with a moderate slope, between data from CAT measured with 5 pmol/l tissue factor and ROTEM.

Clot waveform analysis in patients with haemophilia A

Clot waveform analysis extends the interpretation of aPTT measurement curves. The curve is mathematically processed to obtain information about fibrin formation kinetics including semiquantitative determination of thrombin, prothrombinase and tenase activity.

PATIENTS, METHOD

In this study the feasibility of clot waveform analysis for monitoring of haemophilia A was investigated using blood samples from healthy controls as well as haemophilia A patients under various clinical conditions.

RESULTS

Thrombin, prothrombinase and tenase activity show a high correlation to factor VIII levels. Tenase activity was found to exhibit a linear relationship to factor VIII levels over a very large concentration range and was able to discriminate patients with severe, moderate and mild haemophilia.

CONCLUSION

Clot waveform analysis is an easy, fast and cheap method to access disturbances in clot formation and can be done without any additional measurements beside an aPTT.

Thrombin generation in severe sepsis

INTRODUCTION

Hemostasis and inflammation are two tightly interrelated systems in the host's response to infection. Thrombin generation in sepsis plays a crucial role in enhancing and modulation of inflammation. The present study aimed to investigate the course of thrombin generation in patients with severe sepsis, and its correlation with outcome.

MATERIALS AND METHODS

Thrombin generation was measured in platelet-poor plasma from 32 healthy controls and 75 patients with severe sepsis using the commercially available Calibrated Automated Thrombography. Samples were taken within 24 hours of the diagnosis of severe sepsis (t1) as well as on day 2 (t2), day 3 or 4 (t3) and between day 6 to 8 (t4), while this was done only once in healthy controls. The assay was run with and without the addition of thrombomodulin. Clinical data were also collected at the same time points.

RESULTS

Except for endogenous thrombin potential, there was significant difference between patients and controls regarding peak thrombin, lag time and time to thrombin peak. Twelve patients (16%) died in the ICU. There was no significant difference in endogenous thrombin potential between survivors and non-survivors of sepsis. Thrombin peak was higher in survivors than non-survivors at all time points, with a significant difference at t2 and t4. The lag time and time to thrombin peak were shorter in non-survivors than in survivors at t1 and t3.

CONCLUSIONS

While thrombin peak shows a positive correlation with survival, the lag phase and time to thrombin peak may be signs of impending DIC. The endogenous thrombin potential does not have any prognostic importance.

Aspirin resistance in secondary stroke prevention

BACKGROUND

We investigated the platelet function in stroke patients treated with aspirin [acetylsalicylic acid (ASA)] for secondary stroke prevention during a follow-up period of 1 year.

METHODS

In this prospective study 291 patients with first initiated aspirin therapy (300 mg/day) for secondary stroke prevention were included. Platelet aggregation measurements were performed 24 h, 3, 6, and 12 months after starting medication.

RESULTS

Twenty-one of 291 patients (7.2%) were identified as primary ASA-non-responders (initial insufficient platelet inhibition) and 4.1% as secondary ASA-non-responders (insufficient platelet inhibition during follow-up). There were no significant differences between ASA-responders and ASA-non-responders concerning age, gender, risk factors, and stroke characteristics.

CONCLUSION

Aspirin resistance in stroke patients is not uncommon. The clinical usefulness of routine platelet function tests needs to be proved by further trials.

Thioflavins released from nanoparticles target fibrillar amyloid β in the hippocampus of APP/PS1 transgenic mice

For the delivery of drugs into the brain, the use of nanoparticles as carriers has been described as a promising approach. Here, we prepared nanoparticles as carriers for the model drugs thioflavin T and thioflavin S that bind fibrillar amyloid beta peptides (Abeta). These polymer colloids are composed of a polystyrene core and a degradable PBCA [poly(butyl-2-cyanoacrylate)] shell with a diameter of 90-100nm as shown by dynamic light scattering. Fluorescence spectrophotometric analysis revealed that encapsulated thioflavin T exhibited significantly stronger fluorescence than the free fluorophore. The enzymatic degradation of core-shell nanoparticles, as required in vivo, was shown after their treatment with porcine liver esterase, a non-specific esterase, in vitro. Shells of nanoparticles were dose-dependently degraded while their polystyrene cores remained intact. In the cortices of 7-14 months old APP/PS1 mice with age-dependent beta-amyloidosis, thioflavins selectively targeted fibrillar Abeta after biodegradation-induced release from their nanoparticulate carriers upon intracerebral injection. Collectively, our data suggest that core-shell nanoparticles with controlled degradation in vivo can become versatile tools to trace and clear Abeta in the brain.

Redistribution of CB1 cannabinoid receptors during evolution of cholinergic basal forebrain territories and their cortical projection areas: A comparison between the gray mouse lemur (Microcebus murinus, primates) and rat

Endocannabinoid signaling, mediated by presynaptic CB1 cannabinoid receptors on neurons, is fundamental for the maintenance of synaptic plasticity by modulating neurotransmitter release from axon terminals. In the rodent basal forebrain, CB1 cannabinoid receptor-like immunoreactivity is only harbored by a subpopulation of cholinergic projection neurons. However, endocannabinoid control of cholinergic output from the substantia innominata, coincident target innervation of cholinergic and CB1 cannabinoid receptor-containing afferents, and cholinergic regulation of endocannabinoid synthesis in the hippocampus suggest a significant cholinergic-endocannabinergic interplay. Given the functional importance of the cholinergic modulation of endocannabinoid signaling, here we studied CB1 cannabinoid receptor distribution in cholinergic basal forebrain territories and their cortical projection areas in a prosimian primate, the gray mouse lemur. Perisomatic CB1 cannabinoid receptor immunoreactivity was unequivocally present in non-cholinergic neurons of the olfactory tubercule, and in cholecystokinin-containing interneurons in layers 2/3 of the neocortex. Significantly, CB1 cannabinoid receptor-like immunoreactivity was localized to cholinergic perikarya in the magnocellular basal nucleus. However, cortical cholinergic terminals lacked detectable CB1 cannabinoid receptor levels. A dichotomy of CB1 cannabinoid receptor distribution in frontal (suprasylvian) and parietotemporal (subsylvian) cortices was apparent. In the frontal cortex, CB1 cannabinoid receptor-containing axons concentrated in layers 2/3 and layer 6, while layer 4 and layer 5 were essentially devoid of CB1 cannabinoid receptor immunoreactivity. In contrast, CB1 cannabinoid receptors decorated axons in all layers of the parietotemporal cortex with peak densities in layer 2 and layer 4. In the hippocampus, CB1 cannabinoid receptor-containing terminals concentrated around pyramidal cell somata and proximal dendrites in the CA1-CA3 areas, and granule cell dendrites in the molecular layer of the dentate gyrus. CB1 cannabinoid receptors frequently localized to inhibitory GABAergic terminals while leaving glutamatergic boutons unlabeled. Aging did not affect either the density or layer-specific distribution of CB1 cannabinoid receptor-immunoreactive processes. We concluded that organizing principles of CB1 cannabinoid receptor-containing neurons and their terminal fields within the basal forebrain are evolutionarily conserved between rodents and prosimian primates. In contrast, the areal expansion and cytoarchitectonic differentiation of neocortical subfields in primates is associated with differential cortical patterning of CB1 cannabinoid receptor-containing subcortical and intracortical afferents.