Decreased antithrombin activity and inflammation in cats

OBJECTIVES

The objective of this study was to determine if inflammatory markers are associated with antithrombin activity in cats.

METHODS

For a retrospective population of 231 cats admitted to a referral hospital, antithrombin activity was classified as decreased (n = 77), intermediate (n = 97) or in the upper quartile (n = 57). Odds ratios (ORs) were calculated for an association between decreased or upper quartile activity and hypoalbuminemia, hyperfibrinogenemia, band neutrophilia and toxic change. Multiple logistic regression was performed to determine if an association between band neutrophilia and decreased antithrombin activity was independent of decreased hepatic synthesis, consumptive coagulopathy or protein loss.

RESULTS

Cats with decreased antithrombin activity were more likely than cats with intermediate-to-upper quartile activity to have band neutrophilia (OR 2.85, P = 0.0050), hypoalbuminemia (OR 12.1, P <0.0001) or toxic neutrophils (OR 4.47, P <0.0001). Cats with antithrombin activity in the upper quartile were less likely than those with intermediate-to-low activity to have hypoalbuminemia (OR 0.31, P = 0.0023) or toxic neutrophils (OR 0.44, P = 0.033). In a regression model that included other mechanisms for decreased antithrombin, band neutrophilia remained associated with decreased antithrombin activity (adjusted OR 2.62, P = 0.013).

CONCLUSIONS AND RELEVANCE

Contrary to previous studies suggesting antithrombin is a feline positive acute phase protein, this study demonstrates an association between decreased antithrombin activity and inflammation. Further studies are needed to determine the mechanistic basis of this association.

Pharmacokinetic modeling and simulation support for age- and weight-adjusted dosing of dabigatran etexilate in children with venous thromboembolism

BACKGROUND

Dabigatran etexilate (DE), a direct oral thrombin inhibitor, has been evaluated in children with venous thromboembolism (VTE) using oral solution, pellets, or capsules.

OBJECTIVES

This study evaluated DE pharmacokinetics (PK) in children with VTE and the appropriateness of a DE pediatric age- and weight-based dosing algorithm.

PATIENTS/METHODS

A population PK model was fitted to data from four single-arm and one randomized, comparative pediatric VTE studies (358 children aged birth to <18 years; 2748 PK observations) and one healthy-adult study (32 males aged <40 years; 1523 PK observations) using nonlinear mixed-effects modeling. A stepwise, covariate, model-building procedure evaluated the influence of covariates (e.g., age, body weight, body surface area [BSA]-normalized renal function, and sex). The final model was used to evaluate the pediatric dosing algorithm, with simulations comparing pediatric trough exposure with reference exposure defined for the pediatric studies.

RESULTS

The population PK of dabigatran was adequately described by a two-compartment model with first-order elimination and absorption. Age, weight, BSA-normalized renal function, and sex were statistically significant covariates (all P < .05). Apparent clearance increased with age (independently of body weight), diminished with decreasing BSA-normalized renal function, and was lower in females than males. All disposition parameters increased with body weight escalation (allometric scaling). Simulations confirmed that for all DE formulations, the final pediatric dosing algorithms achieved reference exposure without dose adjustment.

CONCLUSIONS

Using a population PK model of DE for children with VTE, simulations showed that the final dosing algorithms were appropriate for all DE formulations; no dose titration was needed.

Skeletal muscle myosin and cardiac myosin attenuate heparin's antithrombin-dependent anticoagulant activity

BACKGROUND

Heparin enhances the ability of the plasma protease inhibitor, antithrombin, to neutralize coagulation factor Xa and thrombin. Skeletal muscle myosin binds unfractionated heparin.

OBJECTIVES

The aim of this study was to investigate the influence of myosin binding to heparin on antithrombin's anticoagulant activity.

METHODS

Inhibition of factor Xa and thrombin by antithrombin in the presence of different heparins and skeletal muscle myosin or cardiac myosin was studied by measuring inhibition of each enzyme's chromogenic substrate hydrolysis.

RESULTS AND CONCLUSIONS

Skeletal muscle myosin and cardiac myosin neutralized unfractionated heparin's enhancement of antithrombin's inhibition of purified factor Xa and thrombin. Skeletal muscle myosin also reduced the inhibition of factor Xa and thrombin by antithrombin in the presence of heparan sulfate. These two myosins did not protect factor Xa from antithrombin inhibition when tested in the presence of smaller heparins (eg, low molecular weight heparin, heparin pentasaccharide). This chain length dependence for skeletal muscle myosin's ability to reduce heparin's anticoagulant activity might have potential implications for therapy for patients who experience increases in plasma myosin levels (eg, acute trauma patients). In addition to the chain length, the type and extent of sulfation of glycosaminoglycans influenced the ability of skeletal muscle myosin to neutralize the polysaccharide's ability to enhance antithrombin's activity. In summary, these studies show that skeletal muscle myosin and cardiac myosin can influence antithrombin's anticoagulant activity against factor Xa and thrombin, implying that they may significantly influence the hemostatic balance involving bleeding vs clotting.

Anticoagulant and signaling functions of antithrombin

Antithrombin (AT) is a major plasma glycoprotein of the serpin superfamily that regulates the proteolytic activity of the procoagulant proteases of both intrinsic and extrinsic pathways. Two important structural features that participate in the regulatory function of AT include a mobile reactive center loop that binds to active site of coagulation proteases, trapping them in the form of inactive covalent complexes, and a basic D-helix that binds to therapeutic heparins and heparan sulfate proteoglycans (HSPGs) on vascular endothelial cells. The binding of D-helix of AT by therapeutic heparins promotes the reactivity of the serpin with coagulation proteases by several orders of magnitude by both a conformational activation of the serpin and a template (bridging) mechanism. In addition to its essential anticoagulant function, AT elicits a potent anti-inflammatory signaling response when it binds to distinct vascular endothelial cell HSPGs, thereby inducing prostacyclin synthesis. Syndecans-4 has been found as a specific membrane-bound HSPG receptor on endothelial cells that relays the signaling effect of AT to the relevant second messenger molecules in the signal transduction pathways inside the cell. However, following cleavage by coagulation proteases and/or by spontaneous conversion to a latent form, AT loses both its anti-inflammatory activity and high-affinity interaction with heparin and HSPGs. Interestingly, these low-affinity heparin conformers of AT elicit potent proapoptotic and antiangiogenic activities by also binding to specific HSPGs by unknown mechanisms. This review article will summarize current knowledge about mechanisms through which different conformers of AT exert their serine protease inhibitory and intracellular signaling functions in these biological pathways.

Management and outcomes of newborns at risk for inherited antithrombin deficiency

BACKGROUND

As levels of antithrombin (AT) are low at birth, diagnosing inherited AT deficiency in newborns is challenging. In Stockholm, Sweden, pregnant women with known AT deficiency are referred to the Karolinska University Hospital, where local guidelines for management of newborns at risk of inherited AT deficiency have been established. Data on pregnancy, obstetric, and neonatal outcomes are recorded in a registry.

OBJECTIVES

We aimed to evaluate the current practice at the Karolinska University Hospital for managing delivery of newborns at risk for AT deficiency, the predictive value of AT levels at birth, and the neonatal outcomes of newborns with AT deficiency.

PATIENTS/METHODS

This was an observational, retrospective study. All children born to mothers with AT deficiency at the Karolinska University Hospital 2003-2018 were identified from the registry and included in the study. Data were collected from the medical records and the registry. AT activity was measured postnatally and after 6 months of age.

RESULTS

The total study cohort included 41 newborns. There was a significant association between low AT values postnatally and after 6 months of age (P = .001). Half (21/41) of the children were diagnosed with AT deficiency; two suffered from sinus thrombosis, which presented at 10 days of age. Both children with sinus thrombosis were delivered using vacuum extraction.

CONCLUSIONS

The current practice of testing newborns can in most cases predict inherited AT deficiency. The risk for thrombosis during the neonatal period is enhanced by the use of instrumental delivery.

Plasmodium falciparum histidine rich protein HRPII inhibits the anti-inflammatory function of antithrombin

BACKGROUND

It has been reported that histidine-rich protein II (HRPII), secreted by the malaria parasite, Plasmodium falciparum (Pf), inhibits the heparin-dependent anticoagulant activity of antithrombin (AT) in vitro and in plasma-based assay systems.

OBJECTIVE

The objective of this study was to test the hypothesis that HRPII may also interact with the AT-binding vascular glycosaminoglycans (GAGs), thereby inhibiting the anti-inflammatory signaling function of the serpin.

METHODS

We expressed HRPII in bacteria, purified it to homogeneity and studied its effect on endothelial cell signaling in the absence and presence of AT employing established signaling assays.

RESULTS

We demonstrate that a low concentration of HRPII potently disrupts the barrier permeability function of endothelial cells. Moreover, HRPII competitively inhibits the protective effect of AT by a concentration-dependent manner. Similarly, AT inhibits the pro-inflammatory activity of HRPII by a concentration-dependent manner. The siRNA knockdown of 3-O-sulfotransferase 1 (3-OST-1), the enzyme responsible for the essential 3-O-sulfation of the AT-binding GAGs, downregulates the pro-inflammatory function of HRPII in endothelial cells, supporting the hypothesis that HRPII competitively inhibits the interaction of AT with 3-OS containing vascular GAGs. Histidine-rich protein II elicits its barrier-disruptive effect by the Src-dependent phosphorylation of vascular endothelial (VE)-cadherin and AT counteracts this effect. We further demonstrate that inorganic polyphosphates bind HRPII with a high affinity to amplify the pro-inflammatory signaling function of HRPII in both cellular and in vivo permeability models.

CONCLUSION

We postulate that Pf-derived HRPII and polyphosphate can contribute to the pathogenesis of malaria infection by downregulating the AT-dependent anti-inflammatory and anticoagulant pathways.

Choice of access site and type of anticoagulant in acute coronary syndromes with advanced Killip class or out-of-hospital cardiac arrest

INTRODUCTION AND OBJECTIVES

Patients who are vulnerable to hemodynamic or electrical disorders (VP) are often excluded from clinical trials and data on the optimal access-site or antithrombotic treatment are limited. We assessed outcomes of transradial vs transfemoral access and bivalirudin vs unfractionated heparin (UFH) in VP with acute coronary syndrome undergoing invasive management.

METHODS

The MATRIX trial randomized 8404 patients to radial or femoral access and 7213 patients to bivalirudin or UFH. Among them, 934 (11.1%) were deemed VP due to advanced Killip class (n = 808), cardiac arrest (n = 168), or both (n = 42). The 30-day coprimary outcomes were major adverse cardiovascular and cerebrovascular events (MACE: death, myocardial infarction, or stroke) and net adverse clinical events (NACE: MACE or major bleeding).

RESULTS

MACE and NACE were similarly reduced with radial vs femoral access in VP and non-VP. Transradial access was also associated with consistent relative benefits in all-cause and cardiovascular mortality or Bleeding Academic Research Consortium (BARC) 3 or 5 bleeding with greater absolute benefits in VP. The effects of bivalirudin vs UFH on MACE and NACE were consistent in VP and non-VP. Bivalirudin was associated with lower all-cause and cardiovascular mortality in VP but not in non-VP, with borderline interaction testing. Bivalirudin reduced bleeding in both VP and non-VP with a larger absolute benefit in VP.

CONCLUSIONS

In acute coronary syndrome patients undergoing invasive management, the effects of randomized treatments were consistent in VP and non-VP, but absolute risk reduction with radial access and bivalirudin were greater in VP, with a 5- to 10-fold lower number needed to treat for benefits. Trial registry number: NCT01433627.

Wavy small-diameter vascular graft made of eggshell membrane and thermoplastic polyurethane

In this study, a small-diameter, double-layered eggshell membrane/thermoplastic polyurethane (ESM/TPU) vascular graft with a wavy structure was developed. The avian eggshell membrane, a fibrous structure similar to the extracellular matrix (ECM), has the potential to yield rapid endothelialization in vitro. The dopamine and heparin modification of the ESM surface not only promoted human umbilical vein endothelial cell (HUVEC) proliferation via cytocompatibility assessment, but also improved its anticoagulation properties as verified in platelet adhesion tests. The biomimetic mechanical properties of the vascular graft were provided by the elastic TPU fibers via electrospinning using a wavy cross-section rotating collector. The advantage of combining these two materials is to make use of the bioactivity of ESM as the internal membrane and the tunable mechanical properties of TPU as the external layer. The circumferentially wavy structure of the vascular graft produced a toe region in the non-linear section of the stress-strain curve similar to that of natural blood vessels. The ESM/TPU graft's circumferential ultimate strength was 2.57 MPa, its strain was 339% mm/mm, and its toe region was found to be around 20% mm/mm. Cyclical tension tests showed that the vascular graft could maintain good mechanical properties and showed no structural damage under repeated extension tests.

The prevention and management of asparaginase-related venous thromboembolism in adults: Guidance from the SSC on Hemostasis and Malignancy of the ISTH

Venous thromboembolism is a common complication of asparaginase-based chemotherapy regimens for the treatment of acute lymphoblastic leukemia. Thrombosis associated with asparaginase administration poses a number of specific and often clinically challenging management decisions. This review provides guidance on the prevention and treatment of thrombosis associated with asparaginase in adults including discussions on antithrombin repletion, pharmacologic thromboprophylaxis, cerebral venous thrombosis, and therapeutic anticoagulation.

[Peculiarities of the treatment of venous thromboembolism with direct oral anticoagulants in challenging patients: senile age, renal failure, fragility]

The paper is a narrative review of the literature on the use of direct oral anticoagulants (DOACs) for the VTE treatment in challenging patients: senile age (≥75 years), impaired renal function (estimated glomerular filtration rate ≤50 ml/min), fragility (one of the previous characteristics and/or bodyweight ≤50 kg). The paper discusses the studies of EINSTEIN DVT and PE (rivaroxaban), AMPLIFY (apixaban), HOKUSAI-VTE (edoxaban), RE-COVER I and II (dabigatran) in the focus of the secondary analysis in the pre-specified patient's subgroups, as well as their pooled analyzes and meta-analyzes. Based on the results of this review, it was concluded that in a subgroup of senile age patients, dabigatran increases the risk of major bleeding by 4.8 times and has no advantages over vitamin K antagonists (VKA); rivaroxaban and apixaban retain superiority over VKA on the safety outcomes and reduce the risk of major bleeding by 73% and 77%. In the subgroup of patients with impaired renal function, the use of apixaban and dabigatran is associated with an increase in the risk of major bleeding by 6.5 and 7.3 times, and these DOACs do not have advantages over VKA; rivaroxaban retains its superiority over VKA and reduces the risk of major bleeding by 78%. For fragile patients, a secondary analysis is available only for rivaroxaban, which remains superior to VKA on safety endpoints and reduces the risk of major bleeding by 73%. In the absence of direct comparisons between the available DOACs, the presented data can be used as a rational approach for the choice of appropriate treatment for VTE in challenging patients.

Partial rescue of naturally occurring active site factor X variants through decreased inhibition by tissue factor pathway inhibitor and antithrombin

BACKGROUND

Activated coagulation factor X (FXa) is the serine protease component of prothrombinase, the physiological activator of prothrombin. Factor X Nottingham (A404T) and Taunton (R405G) are two naturally occurring mutations, identified in families with a bleeding phenotype.

OBJECTIVE

To characterize these FX variants functionally.

METHODS

The activity and inhibition of recombinant FX variants were quantified in plasma-based and pure component assays.

RESULTS

The prothrombin times in FX-depleted plasma supplemented with FX Nottingham and Taunton were greatly increased compared to that of wild-type (WT) FX. Kinetic investigations of activated variants in the prothrombinase complex showed kcat /Km reduced ~50-fold and ~5-fold, respectively, explaining the prolonged prothrombin time (PT). The substituted residues are located in the protease domain Na+ -binding loop, important for the activity of FXa, as well as its inhibition. Both FXa Nottingham and Taunton showed reduced affinity for Na+ . Plasma-based thrombin generation assays triggered with 1 pmol/L tissue factor (TF) demonstrated only small differences in activities compared to WT FX, but large reductions at 10 pmol/L TF. Severely reduced inhibition of both FXa Nottingham and Taunton by tissue factor pathway inhibitor (TFPI) and antithrombin (AT), was shown in pure-component FXa inhibition assays. Factor Xa Nottingham and Taunton produced higher amounts of thrombin than WT FXa in pure-component prothrombinase assays in the presence of TFPI and AT, explaining the results from the plasma-based assay.

CONCLUSIONS

Factor X Nottingham and Taunton both display decreased proteolytic activity. However, their reduced activity in plasma triggered by low TF can be rescued by decreased inhibition by the natural FXa inhibitors, TFPI and AT.

Recommendations for clinical laboratory testing for antithrombin deficiency; Communication from the SSC of the ISTH

Hereditary deficiency of antithrombin, a natural anticoagulant, causes a thrombophilia with a high risk for venous thromboembolism. Guidance for laboratory testing to diagnose antithrombin deficiency include the use of an activity assay for initial testing, performing an antigen test and activity-to-antigen ratio when the activity level is low, using pediatric reference ranges until the age of 6 months, excluding acquired causes of low antithrombin (e.g. liver dysfunction, proteinuria, heparin, disseminated intravascular coagulation, thrombosis, surgery) or falsely normal/elevated results (e.g. argatroban, bivalirudin, dabigatran in factor IIa-based assays; rivaroxaban, apixaban, edoxaban, but not betrixaban in Xa-based assays). Molecular testing, if available, may help determine the risk for thrombosis as this might vary among the different mutations. Moreover, it will identify mutations that can be missed by traditional activity assays. Strategies for interpreting laboratory test results are provided.

Microfluidic Point-of-Care Ecarin-Based Clotting and Chromogenic Assays for Monitoring Direct Thrombin Inhibitors

Direct thrombin inhibitors (DTIs), such as bivalirudin and dabigatran, have maintained steady inpatient and outpatient use as substitutes for heparin and warfarin, respectively, because of their high bioavailability and relatively safe "on-therapy" range. Current clinical methods lack the capacity to directly quantify plasma DTI concentrations across wide ranges. At present, the gold standard is the ecarin clotting time (ECT), where ecarin maximizes thrombin activity and clotting time is evaluated to assess DTIs' anticoagulation capability. This work focused on the development of a microfluidic paper analytic device (µPAD) that can quantify the extent of anticoagulation as well as DTI concentration within a patient's whole blood sample. Capillary action propels a small blood sample to flow through the nitrocellulose paper channels. Digital images of whole blood migration are then captured by our self-coded Raspberry Pi and/or the Samsung Galaxy S8 smartphone camera. Both the flow length and the blue absorbance from the plasma front on the μPAD were measured, allowing simultaneous, dual assays: ecarin clotting test (ECT) and ecarin chromogenic assay (ECA). Statistically significant (p < .05) changes in flow and absorbance were observed within our translational research study. Currently, there are no quantitative, commercially available point-of-care tests for the ECT and ECA within the United States. Both the ECT and ECA assays could be instrumental to differentiate between supratherapeutic and subtherapeutic incidents during bridging anticoagulant therapy and limit the unwarranted use of reversal agents.

Use of idarucizumab in clinical practice: a case report

Budd-Chiari syndrome is a serious condition which in chronic course leads to the development of liver cirrhosis. Anti-coagulant treatment of this syndrome is fully indicated and in the treatment can be used dabigatran. Advanced cirrhosis of the liver due to this disease can be an indication for a liver transplant. In this case, it is a great advantage the existence of an antidote to dabigatran (idarucizumab) in order to adjust the coagulation ratios and prevent bleeding disorders. Referred to a case report describes the first experience with idarucizumab in context with liver transplant in a patient with Budd-Chiari syndrome.

Drug therapy in anticoagulation: which drug for which patient?

Four non-vitamin K oral anticoagulants (NOACs) are now licensed and available in the UK, offering unprecedented choices in anticoagulant therapy for clinicians and patients. NOACs have many clear benefits over warfarin, the most striking being the reduction in intracranial haemorrhage. However, a number of uncertainties remain: their efficacy in certain situations, utility of drug assays, significance of drug interactions and management of bleeding. In the absence of any direct comparative trials, it is not clear that any of the NOACs is significantly better than the others in any of the licensed indications. The differential activities, pharmacokinetics, metabolism, excretion and side effects of the agents should be considered when selecting the most appropriate anticoagulant. In this article, we discuss how, with careful selection for the relevant indication, NOACs can simplify therapy while improving outcomes. We aim to provide clinicians with the information needed to select the most suitable anticoagulant drug for an individual patient in a given situation.