Thrombin functions during tissue factor-induced blood coagulation

Quantification of the contribution of individual coagulation factors to haemostasis using a microchip flow chamber system and reconstituted blood from deficient plasma

BACKGROUND AND OBJECTIVES

Quantifying the contribution of individual coagulation factors to haemostasis may aid our understanding of the haemostatic function in patients with rare coagulation deficiencies (RCDs) and the exploration of suitable treatments.

MATERIALS AND METHODS

Reconstituted blood prepared from specific coagulation factor-deficient plasma (factor [F]II; prothrombin, FV, FVII, FVIII, FIX, FX, FXI or FXII) and red blood cell/platelet products were used to simulate the whole blood of patients with RCD. We prepared in vitro treatment models for patients with prothrombin deficiency using coagulation factor agents and fresh frozen plasma. Haemostatic function was measured using a microchip flow chamber system at 600 s-1.

RESULTS

The haemostatic function was low, especially in blood samples reconstituted with prothrombin- and FX-deficient plasma. In a plasma transfusion model of prothrombin deficiency, haemostatic function recovered after 10% replacement with normal plasma and reached a plateau at ≧60% replacement. A treatment model of prothrombin deficiency with prothrombin complex concentrates revealed dose-dependent therapeutic effects in the range of 0-50 IU/kg.

CONCLUSION

Microchip flow chamber system-based quantification of haemostatic function using reconstituted blood could predict haemostasis and therapeutic effects of treatments in patients with prothrombin deficiency.

Quantitative protein mass spectrometry for multiplex measurement of coagulation and fibrinolytic proteins towards clinical application: What, why and how?

Plasma proteins involved in coagulation and fibrinolysis are essential to hemostasis. Consequently, their circulating levels and functionality are critical in bleeding and thrombosis development. Well-established laboratory tests to assess these are available; however, said tests do not allow high multiplicity, require large volumes of plasma and are often costly. A novel technology to quantify plasma proteins is quantitative protein mass spectrometry (QPMS). Aided by stable isotope-labeled internal standards a large number of proteins can be quantified in one single analytical run requiring <30 μL of plasma. This provides an opportunity to improve insight in the etiology and prognosis of bleeding and thrombotic disorders, in which the balance between different proteins plays a crucial role. This manuscript aims to give an overview of the QPMS potential applications in thrombosis and hemostasis research (quantifying the 38 proteins assigned to coagulation and fibrinolysis by the KEGG database), but also to explore the potential and hurdles if designed for clinical practice. Advantages and limitations of QPMS are described and strategies for improved analysis are proposed, using as an example the test requirements for antithrombin. Application of this technology in the future could represent a step towards individualized patient care.

Protocol for a phase 3, randomised, active-control study of four-factor prothrombin complex concentrate versus frozen plasma in bleeding adult cardiac surgery patients requiring coagulation factor replacement: the LEX-211 (FARES-II) trial

INTRODUCTION

Reduced thrombin generation is an important component of post cardiopulmonary bypass (CPB) coagulopathy. To replenish coagulation factors and enhance thrombin generation in bleeding surgical patients, frozen plasma (FP) and four-factor prothrombin complex concentrate (4F-PCC) are used. However, the efficacy-safety balance of 4F-PCC relative to FP in cardiac surgery is unconfirmed.

METHODS AND ANALYSIS

LEX-211 (FARES-II) is an active-control, randomised, phase 3 study comparing two coagulation factor replacement therapies in bleeding adult cardiac surgical patients at 12 hospitals in Canada and the USA. The primary objective is to determine whether 4F-PCC (Octaplex/Balfaxar, Octapharma) is clinically non-inferior to FP for haemostatic effectiveness. Inclusion criteria are any index (elective or non-elective) cardiac surgery employing CPB and coagulation factor replacement with 4F-PCC or FP ordered in the operating room for bleeding management. Patients will be randomised to receive 1500 or 2000 international units of 4F-PCC or 3 or 4 units of FP, depending on body weight. The primary endpoint of haemostatic treatment response is 'effective' if no additional haemostatic intervention is required from 60 min to 24 hours after the first initiation of 4F-PCC or FP; or 'ineffective' if any other haemostatic intervention (including a second dose of study drug) is required. An estimated 410 evaluable patients will be required to demonstrate non-inferiority (one-sided α of 0.025, power ≥90%, non-inferiority margin 0.10). Secondary outcomes include transfusions, bleeding-related clinical endpoints, coagulation parameters and safety.

ETHICS AND DISSEMINATION

The trial has been approved by the institutional review boards of all participating centres. Trial completion is anticipated at the end of 2024, and results will be disseminated via publications in peer-reviewed journals and conference presentations in 2025. The results will advance our understanding of coagulation management in bleeding surgical patients, potentially reducing the need for allogeneic blood products and improving outcomes in surgical patients.

TRIAL REGISTRATION NUMBER

NCT05523297.

Fingerprint analysis of dang-gui-Si-Ni decoction and its anticoagulant activity in vivo-in vitro

ETHNOPHARMACOLOGICAL RELEVANCE

Dang-Gui-Si-Ni (DGSN) decoction is a classic prescription in the clinical practice of traditional Chinese Medicine (TCM). DGSN decoction is often used to relieve symptoms of cold coagulation and blood stasis recorded by Treatise on Febrile Diseases (Shang Han Lun) and treat Raynaud's disease, dysmenorrhea, arthritis, migraine in TCM clinic. Accumulated evidences have suggested that this diseases are related to microcirculation disturbance. However, the anticoagulant activity and underlying mechanisms of DGSN decoction responsible for the therapeutic not well understood.

AIM OF THE STUDY

The fingerprint and anticoagulant activity in vivo-in vitro of DGSN decoction were evaluated to strengthen the quality control and activity study of formulas.

MATERIALS AND METHODS

The chemical components of DGSN decoction were analyzed by HPLC and its fingerprint similarity were evaluated by "Chinese Medicine Chromatographic Fingerprint Similarity Evaluation Software (2012 Edition)". The anticoagulant activity of DGSN decoction was assessed by measuring four coagulation factors (PT, TT, APTT, FIB) in vitro. Zebrafish thrombosis model induced by punatinib was established to evaluate the activity of improving microvascular hemodynamics in vivo. Quantitative real-time polymerase chain reaction (q-PCR) were adopted to compare the changes in the RNA expression levels of coagulation factor II (FII), VII (FVII), IX (FIX) and X (FX) in zebrafish thrombosis model.

RESULTS

The fingerprint similarity evaluation method of DGSN decoction was established. The results showed that 18 samples had higher similarity (S1-S18 > 0.878). Pharmacodynamic results showed that DGSN decoction could extend PT, TT and APTT, and reduce FIB content in vitro. Meanwhile, it markedly enhanced the cardiac output and blood flow velocity at low dosage (500 μg mL-1) in vivo. q-PCR data demonstrated that DGSN decoction (500 μg mL-1) could downregulate the RNA expression of FII, FVII, FIX and FX. Interestingly, there were a bidirectional regulation of FII, FIX and FX in a certain concentration range. In general, DGSN decoction can significantly improve hemodynamics and downregulate coagulation factors, and the results were consistent both in vitro - in vivo.

CONCLUSION

The fingerprint study provide a new perspective for improving the quality control of DGSN decoction. DGSN decoction possess anticoagulant activity by regulating multiple coagulation factors simultaneously. Thus, it has the potential to develop into the novel raw material of anticoagulant drugs.

Semiphysical Design Concept for Developing Miniaturized Microrobots In Vivo

The miniaturization of biomedical microrobots is crucial for their in vivo applications. However, it is challenging to reduce their size while maintaining their biomedical functions. To resolve this contradiction, we propose a semiphysical design concept for developing miniaturized microrobots, in which invisible components such as light beams are utilized to replace most of the physical parts of a microrobot, thus minimizing its physical size without sacrificing its biomedical functions. According to this design, we have constructed a semiphysical microrobot (SPM) composed of main light beam, light-responsive microparticle, and auxiliary light beam, serving as the actuation system, recognition part, and surgical claws, respectively. Based on the functions of actuation, biosensing, and microsurgery, a SPM has been applied for a series of applications, including thrombus elimination at the branch vessel, stratified removal of multilayer thrombus, and biosensing-guided microsurgery. The proposed semiphysical design concept should bring new insight into the development of miniaturized biomedical microrobots.

Anti-thrombotic Effects Mediated by a Novel Dual-Target Peptide Inhibiting Both Platelet Aggregation and Thrombin Activity without Causing Bleeding

BACKGROUND

 Classical anticoagulants and antiplatelets are associated with high frequencies of bleeding complications or treatment failure when used as single agents. Thrombin plays an important role in the blood coagulation system. GP IIb/IIIa is the central receptor of platelets, which can recognize the Arg-Gly-Asp (RGD) sequence and activate platelets.

MATERIAL AND METHODS

 Molecular simulation and homology modeling were performed to design a novel dual-target anticoagulant short peptide (PTIP ). The activities of PTIP on coagulation and platelet in vitro were analyzed. The antithrombotic activity of PTIP was determined by pulmonary thromboembolism model, ferric chloride injury model and arteriovenous bypass thrombosis model. Bleeding effect and toxicity of PTIP were evaluated.

RESULTS

 We have constructed a novel dual-target peptide (PTIP) based on the direct thrombin inhibitor peptide (DTIP). PTIP was expressed at high levels in Pichia pastoris. PTIP interfered with thrombin-mediated coagulation and ADP-induced platelet aggregation in vitro. When injected intravenously or subcutaneously, PTIP showed potent and dose-dependent extension of aPTT and PT which were similar to DTIP; but only PTIP was capable of inhibiting platelet aggregation. PTIP (1.0 mg/kg) decelerated thrombosis formation in venous and arterial vessels induced by FeCl3 injury. PTIP (1.0 mg/kg) also prevented deep venous thrombosis and increased the survival rate associated with pulmonary thromboembolism. And PTIP effectively reduced thrombus length in arteriovenous bypass thrombosis model. Moreover, the antithrombotic dose of PTIP could not induce bleeding.

CONCLUSION

 These data establish that PTIP represents a novel antithrombotic agent whose effects involve both inhibition of platelet activation and reduction of fibrin generation. And PTIP not only can be used in venous thrombosis and arterial thrombosis, it can also replace the combined treatment of antiplatelet and anticoagulant drugs in thrombotic diseases.

Comparative analysis of andexanet alfa and prothrombin complex concentrate in reversing anticoagulation by rivaroxaban ex vivo

BACKGROUND

The comparative effectiveness of the specific antidote andexanet alfa vs the nonspecific therapy four-factor prothrombin complex concentrates (4F-PCCs) as reversal agents for direct factor Xa (FXa) inhibitors in severely bleeding patients is unclear. We hypothesised that specific reversal using andexanet alfa would be more effective than a high dose of PCC (50 IU kg-1) for reversing the FXa inhibitor rivaroxaban.

METHODS

The reversal potential of andexanet alfa, various 4F-PCCs, and activated PCC was investigated ex vivo in human blood anticoagulated with rivaroxaban (37.5, 75, 150, and 300 ng ml-1) using a panel of coagulation parameters, including conventional coagulation assays, thrombin generation, and a newly developed viscoelastometric device. We simulated in vivo conditions of coagulation activation and fibrin formation using flow chamber experiments of thrombogenicity potential under arterial flow conditions.

RESULTS

The 4F-PCCs normalised clotting profiles only at low rivaroxaban concentrations, whereas andexanet alfa and activated PCC significantly shortened clotting time at all rivaroxaban concentrations. Only andexanet alfa restored thrombin generation to baseline. Flow chamber results showed that various 4F-PCCs concentration-dependently restored clot formation.

CONCLUSIONS

In contrast to thrombin generation measurements, haemostatic reversal of rivaroxaban using high-dose 4F-PCCs exhibited similar efficacy as andexanet alfa in flow chamber experiments. The haemostatic effects of 4F-PCCs and andexanet alfa in the context of bleeding patients taking FXa inhibitors requires further study.

Coagulation management during liver transplantation: monitoring and decision making for hemostatic interventions

PURPOSE OF REVIEW

Rebalanced hemostasis describes the precarious balance of procoagulant and antithrombotic proteins in patients with severe liver failure. This review is aimed to discuss currently available coagulation monitoring tests and pertinent decision-making process for plasma coagulation factor replacements during liver transplantation (LT).

RECENT FINDINGS

Contemporary viscoelastic coagulation monitoring systems have demonstrated advantages over conventional coagulation tests in assessing the patient's coagulation status and tailoring hemostatic interventions. There is increasing interest in the use of prothrombin complex and fibrinogen concentrates, but it remains to be proven if purified factor concentrates are more efficacious and safer than allogeneic hemostatic components. Furthermore, the decision to use antifibrinolytic therapy necessitates careful considerations given the risks of venous thromboembolism in severe liver failure.

SUMMARY

Perioperative hemostatic management and thromboprophylaxis for LT patients is likely to be more precise and patient-specific through a better understanding and monitoring of rebalanced coagulation. Further research is needed to refine the application of these tools and develop more standardized protocols for coagulation management in LT.

Integration of fluorescence and MALDI imaging for microfluidic chip-based screening of potential thrombin inhibitors from natural products

The microfluidic technology provides an ideal platform for in situ screening of enzyme inhibitors and activators from natural products. This work described a surface-modified ITO glass-PDMS hybrid microfluidic chip for evaluating thrombin interaction with its potential inhibitors by fluorescence imaging and matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI MSI). The fluorescence-labeled substrate was immobilized on a conductive ITO glass slide coated with gold nanoparticles/thiol-β-cyclodextrin modified TiO2 nanowires (Au-β-CD@TiO2 NWs) via Au-S bonds. A PDMS microchannel plate was placed on top of the modified ITO slide. The premixed solutions of thrombin and candidate thrombin inhibitors were infused into the microchannels to form a microreactor environment. The enzymatic reaction was rapidly monitored by fluorescence microscopy, and MALDI MS was used to validate and quantify the enzymatic hydrolysate of thrombin to determine the enzyme kinetic process and inhibitory activities of selected flavonoids. The fluorescence and MALDI MS results showed that luteolin, cynaroside, and baicalin have good thrombin inhibitory activity and their half-maximal inhibitory concentrations (IC50) were below 30 μM. The integration of fluorescence imaging and MALDI MSI for in situ monitoring and quantifying the enzymatic reaction in a microfluidic chip is capable of rapid and accurate screening of thrombin inhibitors from natural products.

Cell Surface Platelet Tissue Factor Expression: Regulation by P2Y12 and Link to Residual Platelet Reactivity

BACKGROUND

ADP-induced platelet activation leads to cell surface expression of several proteins, including TF (tissue factor). The role of ADP receptors in platelet TF modulation is still unknown. We aimed to assess the (1) involvement of P2Y1 and P2Y12 receptors in ADP-induced TF exposure; (2) modulation of TFpos-platelets in anti-P2Y12-treated patients with coronary artery disease. Based on the obtained results, we revisited the intracellular localization of TF in platelets.

METHODS

The effects of P2Y1 or P2Y12 antagonists on ADP-induced TF expression and activity were analyzed in vitro by flow cytometry and thrombin generation assay in blood from healthy subjects, P2Y12-/-, and patients with gray platelet syndrome. Ex vivo, P2Y12 inhibition of TF expression by clopidogrel/prasugrel/ticagrelor, assessed by VASP (vasodilator-stimulated phosphoprotein) platelet reactivity index, was investigated in coronary artery disease (n=238). Inhibition of open canalicular system externalization and electron microscopy (TEM) were used for TF localization.

RESULTS

In blood from healthy subjects, stimulated in vitro by ADP, the percentage of TFpos-platelets (17.3±5.5%) was significantly reduced in a concentration-dependent manner by P2Y12 inhibition only (-81.7±9.5% with 100 nM AR-C69931MX). In coronary artery disease, inhibition of P2Y12 is paralleled by reduction of ADP-induced platelet TF expression (VASP platelet reactivity index: 17.9±11%, 20.9±11.3%, 40.3±13%; TFpos-platelets: 10.5±4.8%, 9.8±5.9%, 13.6±6.3%, in prasugrel/ticagrelor/clopidogrel-treated patients, respectively). Despite this, 15% of clopidogrel good responders had a level of TFpos-platelets similar to the poor-responder group. Indeed, a stronger P2Y12 inhibition (130-fold) is required to inhibit TF than VASP. Thus, a VASP platelet reactivity index <20% (as in prasugrel/ticagrelor-treated patients) identifies patients with TFpos-platelets <20% (92% sensitivity). Finally, colchicine impaired in vitro ADP-induced TF expression but not α-granule release, suggesting that TF is open canalicular system stored as confirmed by TEM and platelet analysis of patients with gray platelet syndrome.

CONCLUSIONS

Data show that TF expression is regulated by P2Y12 and not P2Y1; P2Y12 antagonists downregulate the percentage of TFpos-platelets. In clopidogrel good-responder patients, assessment of TFpos-platelets highlights those with residual platelet reactivity. TF is stored in open canalicular system, and its membrane exposure upon activation is prevented by colchicine.

Monitoring prothrombin activation in plasma through loss of Förster resonance energy transfer

BACKGROUND

Current assays that monitor thrombin generation in plasma rely on fluorogenic substrates to follow the kinetics of zymogen activation, which may be complicated by substrate cleavage from other proteases. In addition, these assays depend on activation following cleavage at the prothrombin R320 site and fail to report the cleavage at the alternative R271 site, leading to the shedding of the auxiliary Gla and kringle domains of prothrombin.

OBJECTIVES

To develop a plasma assay that directly monitors prothrombin activation independent of fluorogenic substrate hydrolysis.

METHODS

Cleavage at the R271 site of prothrombin is monitored through loss of Förster resonance energy transfer in plasma coagulated along the extrinsic or intrinsic pathway.

RESULTS

The availability of factor (F)V in plasma strongly influences the rate of prothrombin activation. The rate of thrombin formation is equally perturbed in FV or prothrombin-depleted plasma, implicating that the thrombin-catalyzed feedback reactions that amplify the coagulation response play an important role in generating sufficient amounts of FVa required for the assembly of prothrombinase. Congenital deficiencies in FVIII and FIX significantly slow down cleavage at R271 in plasma coagulated along the extrinsic and intrinsic pathways. Prothrombin activation in FXI-deficient plasma is only perturbed when coagulation is triggered along the intrinsic pathway.

CONCLUSION

The Förster resonance energy transfer assay enables direct monitoring of prothrombin activation through cleavage at R271 without the need for fluorogenic substrates. The assay is sensitive enough to assess how deficiencies in coagulation factors affect thrombin formation.

Augmented Degradation of Factors VIII and IX in the Intermittent Movement State

The most common clinical presentation of hemophilia A and hemophilia B is bleeding in large joints and striated muscles. It is unclear why bleeding has a predilection to affect joints and muscles. As muscles and joints are involved in intermittent movement, we explored whether this phenomenon could be associated with an impact on factor VIII and IX levels. Purified proteins and a mouse model were assessed using coagulation assays, Western blot analysis and immuno-staining. Movement caused an increase in thrombin activity and a decrease in factor VIII and factor IX activity. The decrease in factor VIII activity was more significant in the presence of thrombin and during movement. Under movement condition, sodium ions appeared to enhance the activity of thrombin that resulted in decreased factor VIII activity. Unlike factor VIII, the reduction in factor IX levels in the movement condition was thrombin-independent. High factor VIII levels were found to protect factor IX from degradation and vice versa. In mice that were in movement, factor VIII and IX levels decreased in the microcirculation of the muscle tissue compared with other tissues and to the muscle tissue at rest. Movement had no effect on von Willebrand factor levels. Movement induces reduction in factor VIII and IX levels. It enables an increase in the binding of sodium ions to thrombin leading to enhanced thrombin activity and augmented degradation of factor VIII. These data suggest a potential mechanism underlying the tendency of hemophilia patients to bleed in muscles and joints.

Low dose rivaroxaban for the management of atherosclerotic cardiovascular disease

Atherosclerotic cardiovascular disease is characterized by some risk of major adverse events despite the availability of effective medical therapies for secondary prevention. There is emerging evidence suggesting that thrombin partly contributes to this residual risk. In fact, thrombin (i.e., activated coagulation factor II) triggers not only the conversion of fibrinogen to fibrin but also platelet activation and various pathways responsible for pro-atherogenic and/or pro-inflammatory effects through interaction with protease activated receptors. To reduce the risk associated with thrombin activation, oral anticoagulants antagonists of vitamin K showed promise, but were associated with unacceptable bleeding rates. Direct oral anticoagulants targeting the activated factors X and II carry a lower risk of bleeding than vitamin K antagonists. Rivaroxaban, a direct inhibitor of activated factor X approved at the dose of 20 mg once daily for the prevention of thromboembolic events, has been also investigated at a reduced dose of 2.5 mg twice daily in several alternative scenarios of atherosclerotic cardiovascular disease, in combination with standard of care. Current guidelines recommend that low-dose rivaroxaban is given in an adjunct to standard therapy to patients with stable atherosclerosis and acute coronary syndromes at low bleeding risk. Several studies are underway to evaluate its putative benefits in other clinical settings.

Monitoring the Formation of Fibrin Clots as Part of the Coagulation Cascade Using Fluorescent Single-Walled Carbon Nanotubes

Blood coagulation is a critical defense mechanism against bleeding that results in the conversion of liquid blood into a solid clot through a complicated cascade, which involves multiple clotting factors. One of the final steps in the coagulation pathway is the conversion of fibrinogen to insoluble fibrin mediated by thrombin. Because coagulation disorders can be life-threatening, the development of novel methods for monitoring the coagulation cascade dynamics is of high importance. Here, we use near-infrared (NIR)-fluorescent single-walled carbon nanotubes (SWCNTs) to image and monitor fibrin clotting in real time. Following the binding of fibrinogen to a tailored SWCNT platform, thrombin transforms the fibrinogen into fibrin monomers, which start to polymerize. The SWCNTs are incorporated within the clot and can be clearly visualized in the NIR-fluorescent channel, where the signal-to-noise ratio is improved compared to bright-field imaging in the visible range. Moreover, the diffusion of individual SWCNTs within the fibrin clot gradually slows down after the addition of thrombin, manifesting a coagulation rate that depends on both fibrinogen and thrombin concentrations. Our platform can open new opportunities for coagulation disorder diagnostics and allow for real-time monitoring of the coagulation cascade with a NIR optical signal output in the biological transparency window.

Development of Host-Cleavable Antibody-Bactericide Conjugates against Extracellular Pathogens

Novel antimicrobial agents with potent bactericidal activity are needed to treat infections caused by multidrug-resistant (MDR) extracellular pathogens, such as Pseudomonas aeruginosa. Antimicrobial peptides (AMPs) and peptidomimetics are promising alternatives to traditional antibiotics, but their therapeutic use is limited due to the lack of specificity and resulting off-target effects. The incorporation of an antibody into the drug design would alleviate these challenges by localizing the AMP to the target bacterial cells. Antibody-drug conjugates (ADCs) have already achieved clinical success as anticancer therapeutics, due to the ability of the antibody to deliver the payload directly to the cancer cells. This strategy involves the selective delivery of highly cytotoxic drugs to the target cells, which enables a broad therapeutic window. This platform can be translated to the treatment of infections, whereby an antibody is used to deliver an antimicrobial agent to the bacterial antigen. Herein, we propose the development of an antibody-bactericide conjugate (ABC) in which the antibacterial oligothioetheramide (oligoTEA), BDT-4G, is coupled to an anti-P. aeruginosa antibody via a cleavable linker. The drug BDT-4G was chosen based on its efficacy against a range of P. aeruginosa isolates and its ability to evade mechanisms conferring resistance to the last-resort agent polymyxin B. We demonstrate that the ABC binds to the bacterial cell surface, and following cleavage of the peptide linker, the oligoTEA payload is released and exhibits antipseudomonal activity.

Plasma Angiotensin Converting Enzyme 2 (ACE2) Activity in Healthy Controls and Patients with Cardiovascular Risk Factors and/or Disease

Angiotensin converting enzyme 2 (ACE2) is an endogenous negative regulator of the renin-angiotensin system, a key factor in the development of cardiovascular disease (CVD). ACE2 is also used by SARS-CoV-2 for host cell entry. Given that COVID-19 is associated with hypercoagulability, it is timely to explore the potential relationship between plasma ACE2 activity and the coagulation profile. In this cross-sectional study, ACE2 activity and global coagulation assays (GCA) including thromboelastography, thrombin, and fibrin generation were measured in adult healthy controls (n = 123; mean age 41 ± 17 years; 35% male) and in patients with cardiovascular risk factors and/or disease (n = 258; mean age 65 ± 14 years; 55% male). ACE2 activity was significantly lower in controls compared to patients with cardiovascular risk factors and/or disease (median 0.10 (0.02, 3.33) vs. 5.99 (1.95, 10.37) pmol/mL/min, p < 0.001). Of the healthy controls, 48% had undetectable ACE2 activity. Controls with detectable ACE2 had lower maximum amplitude (p < 0.001). In patients with cardiovascular risk factors and/or disease, those in the 3rd tertile were older and male (p = 0.002), with a higher Framingham grade and increased number of cardiovascular risk factors (p < 0.001). In conclusion, plasma ACE2 activity is undetectable to very low in young healthy controls with minimal clinically relevant associations to GCA. Patients with cardiovascular risk factors and/or disease have increased plasma ACE2 activity, suggesting that it may be an important biomarker of endothelial dysfunction and atherosclerosis.

The Role of Antiplatelet Therapy in Patients With MINOCA

Myocardial infarction with non-obstructive coronary arteries (MINOCA) is a heterogeneous group of clinical entities characterized by the common clinical evidence of myocardial infarction (MI) with non-obstructive coronary arteries on coronary angiography and without an overt cause for the MI. Platelets play a cornerstone role in the pathophysiology of MI with obstructive coronary arteries. Accordingly, antiplatelet therapy is recommended for treating patients with MI and obstructive coronary disease. However, the role of platelets in the pathophysiology of MINOCA patients is not fully defined, questioning the role of antiplatelet therapy in this setting. In this review, we will assess the role of antiplatelet therapy in MINOCA with a focus on the pathophysiology, therapeutic targets, current evidence, and future directions according to its different etiologies.

Development of an Innovative Quantification Assay Based on Aptamer Sandwich and Isothermal Dumbbell Exponential Amplification

Detecting blood biomarkers such as proteins with high sensitivity and specificity is of the utmost importance for early and reliable disease diagnosis. As molecular probes, aptamers are raising increasing interest for biosensor applications as an alternative to antibodies, which are used in classical enzyme-linked immuno-sorbent assays (ELISA). We have developed a sensitive and antibody-free molecular quantification assay that combines the specificity of aptamers and the sensitivity of the loop-mediated isothermal amplification (LAMP). For the proof-of-concept, we consider two types of biomarkers: (i) a model of oligonucleotide mimicking nucleic acid targets and (ii) the thrombin involved in the complex coagulation cascade as a model protein for which two relevant aptamers form a stable sandwich. The assay protocol is based on a few successive steps, similar to sandwich ELISA. First, aptamer-coated magnetic beads are added to the sample to specifically capture the targets. Then, the sandwich complex is formed by adding the second aptamer. This secondary aptamer is integrated in a larger oligonucleotide dumbbell sequence designed for LAMP detection using only two primers. After a proper rinsing step, the isothermal dumbbell exponential amplification is performed to detect and quantify a low amount of targets (limit of detection ∼ 1 pM for the oligonucleotide and ∼100 pM for thrombin). This study demonstrates that our innovative aptamero-LAMP assay could be relevant for the detection of different types of biomarkers and their quantification at physiological levels. This may also pave the way for antibody-free molecular assays.

Vascular Endothelial Cells Produce Coagulation Factors That Control Their Growth via Joint Protease-Activated Receptor and C5a Receptor 1 (CD88) Signaling

As per the classical view of the coagulation system, it functions solely in plasma to maintain hemostasis. An experimental approach modeling vascular reconstitution was used to show that vascular endothelial cells (ECs) endogenously synthesize coagulation factors during angiogenesis. Intracellular thrombin generated from this synthesis promotes the mitotic function of vascular endothelial cell growth factor A (VEGF-A). The thrombin concurrently cleaves C5a from EC-synthesized complement component C5 and unmasks the tethered ligand for EC-expressed protease-activated receptor 4 (PAR4). The two ligands jointly trigger EC C5a receptor-1 (C5ar1) and PAR4 signaling, which together promote VEGF receptor 2 growth signaling. C5ar1 is functionally associated with PAR4, enabling C5a or thrombin to elicit Gαi and/or Gαq signaling. EC coagulation factor and EC complement component synthesis concurrently down-regulate with contact inhibition. The connection of these processes with VEGF receptor 2 signaling provides new insights into mechanisms underlying angiogenesis. Knowledge of endogenous coagulation factor/complement component synthesis and joint PAR4/C5ar1 signaling could be applied to other cell types.

Reduced thrombogenicity of surface-treated Nitinol implants steered by altered protein adsorption

Blood-contacting medical implants made of Nitinol and other titanium alloys, such as neurovascular flow diverters and peripheral stents, have the disadvantage of being highly thrombogenic. This makes the use of systemic (dual) anti-platelet/anticoagulant therapies inevitable with related risks of device thrombosis, bleeding and other complications. Meeting the urgent clinical demand for a less thrombogenic Nitinol surface, we describe here a simple treatment of standard, commercially available Nitinol that renders its surface ultra-hydrophilic and functionalized with phosphate ions. The efficacy of this treatment was assessed by comparing standard and surface-treated Nitinol disks and braids, equivalent to flow diverters. Static and dynamic (Chandler loop) blood incubation tests showed a drastic reduction of thrombus formation on treated devices. Surface chemistry and proteomic analysis indicated a key role of phosphate and calcium ions in steering blood protein adsorption and avoiding coagulation cascade activation and platelet adhesion. A good endothelialization of the surface confirmed the biocompatibility of the treated surface. STATEMENT OF SIGNIFICANCE: Titanium alloys such as Nitinol are biocompatible and show favorable mechanical properties, which led to their widespread use in medical implants. However, in contact with blood their surface triggers the activation of the intrinsic coagulation cascade, which may result in catastrophic thrombotic events. The presented results showed that a phosphate functionalization of the titanium oxide surface suppresses the activation of both coagulation cascade and platelets, avoiding the subsequent formation of a blood clot. This novel approach has therefore a great potential for mitigating the risks associated to either thrombosis or bleeding complications (due to systemic anticoagulation) in patients with cardiovascular implants.

Control of Blood Coagulation by Hemocompatible Material Surfaces-A Review

Hemocompatibility of biomaterials in contact with the blood of patients is a prerequisite for the short- and long-term applications of medical devices such as cardiovascular stents, artificial heart valves, ventricular assist devices, catheters, blood linings and extracorporeal devices such as artificial kidneys (hemodialysis), extracorporeal membrane oxygenation (ECMO) and cardiopulmonary bypass. Although lower blood compatibility of materials and devices can be handled with systemic anticoagulation, its side effects, such as an increased bleeding risk, make materials that have a better hemocompatibility highly desirable, particularly in long-term applications. This review provides a short overview on the basic mechanisms of blood coagulation including plasmatic coagulation and blood platelets, as well as the activation of the complement system. Furthermore, a survey on concepts for tailoring the blood response of biomaterials to improve the hemocompatibility of medical devices is given which covers different approaches that either inhibit interaction of material surfaces with blood components completely or control the response of the coagulation system, blood platelets and leukocytes.

Coagulation in Lymphatic System

The lymphatic system maintains homeostasis of the internal environment between the cells in tissues and the blood circulation. The coagulation state of lymph is determined by conditions of coagulation factors and lymphatic vessels. Internal obliteration, external compression or abnormally increased lymphatic pressure may predispose to localized lymphatic coagulation. In physiological conditions, an imbalance of antithrombin and thrombokinase reduces lymphatic thrombosis. However, the release of factor X by lymphatic endothelium injury may trigger coagulation casacade, causing blockage of lymphatic vessels and lymphedema. Heterogeneity of lymphatic vessels in various tissues may lead to distinct levels and patterns of coagulation in specific lymphatic vessels. The quantitative and qualitative measurement of clotting characteristic reveals longer time for clotting to occur in the lymph than in the blood. Cancer, infections, amyloidosis and lymph node dissection may trigger thrombosis in the lymphatic vessels. In contrast to venous or arterial thrombosis, lymphatic thrombosis has rarely been reported, and its actual prevalence is likely underestimated. In this review, we summarize the mechanisms of coagulation in lymphatic system, and discuss the lymphatic thrombosis-related diseases.

Thrombin Generation Following Severe Trauma: Mechanisms, Modulators, and Implications for Hemostasis and Thrombosis

ABSTRACT

Thrombin is the central coagulation enzyme that catalyzes the conversion of fibrinogen to form insoluble fibrin blood clots. In vivo, thrombin production results from the concerted effort of plasma enzymatic reactions with essential contributions from circulating and vessel wall cells. The relative amount of thrombin produced directly dictates the structure and stability of fibrin clots; therefore, sufficient thrombin generation is essential for normal hemostasis to occur. Examination of thrombin generation phenotypes among severely injury trauma patients reveals important relationships between the potential for generating thrombin and risks of bleeding and thrombotic complications. Thus, understanding determinants of thrombin generation following traumatic injury is of high clinical importance. This review will focus on patterns and mechanisms of thrombin generation in severely injured patients, the role of fluid resuscitation in modulating thrombin generation and implications for outcomes.

Bioactive Natural Compounds with Antiplatelet and Anticoagulant Activity and Their Potential Role in the Treatment of Thrombotic Disorders

Natural anticoagulant drugs can be obtained from plants, rich in secondary bioactive metabolites which, in addition to being effective antioxidants, also possess anticoagulant and antiplatelet properties and, for this reason, can be excellent candidates for the treatment of thrombotic diseases. This review reports an overview of the hemostatic process and thrombotic disorders together with data on plants, more and less common from around the world, containing bioactive compounds characterized by antiplatelet and anticoagulant activity. The reported literature was obtained from Medline, PubMed, Elsevier, Web of Science, Google Scholar considering only articles in the English language, published in peer-reviewed journals. The number of citations of the articles and the impact factor of the journals were other parameters used to select the scientific papers to be included in the review. The analysis of the literature data selected demonstrates that many plants' bioactive compounds show antiplatelet and anticoagulant activity that make them potential candidates to be used as new natural compounds able to interfere with both primary and secondary hemostasis. Moreover, they could be used together with anticoagulants currently administered in clinical practice to increase their efficacy and to reduce complications in the treatment of thrombotic disorders.

Ratiometric Bioluminescent Indicator for a Simple and Rapid Measurement of Thrombin Activity Using a Smartphone

Hemostasis is an essential function that repairs tissues and maintains the survival of living organisms. To prevent diseases caused by the abnormality of the blood coagulation mechanism, it is important to carry out a blood test periodically by a method that is convenient and less burdensome for examiners. Thrombin is a protease that catalyzes the conversion of fibrinogen, and its cleavage activity can be an index of coagulation activity. Here, we developed a ratiometric bioluminescent indicator, Thrombastor (thrombin activity sensing indicator), which reflects the thrombin cleavage activity in blood by changing the emission color from green to blue. Compared to the current thrombin activity indicator, the rapid color change of the emission indicated a 2.5-fold decrease in the K_m for thrombin, and the cleavage rate was more than two times faster. By improving the absolute bioluminescence intensity, detection from a small amount of plasma could be achieved with a smartphone camera. Using Thrombastor and a versatile device, an effective diagnosis for preventing coagulation disorders can be provided.

Changes in Maternal Platelet Physiology during Gestation and Their Interaction with Trophoblasts

Upon activation, maternal platelets provide a source of proinflammatory mediators in the intervillous space of the placenta. Therefore, platelet-derived factors may interfere with different trophoblast subtypes of the developing human placenta and might cause altered hormone secretion and placental dysfunction later on in pregnancy. Increased platelet activation, and the subsequent occurrence of placental fibrinoid deposition, are linked to placenta pathologies such as preeclampsia. The composition and release of platelet-derived factors change over gestation and provide a potential source of predicting biomarkers for the developing fetus and the mother. This review indicates possible mechanisms of platelet-trophoblast interactions and discusses the effect of increased platelet activation on placenta development.

Rheological and clot microstructure evaluation of heparin neutralization by UHRA and protamine

The current study reports the use of small amplitude oscillatory rheometry to investigate the dynamics of blood clot formation upon heparin neutralization under three different oscillatory frequencies, two of which were mimicking physiological heart rates. We utilized two different heparin antidotes, namely protamine and newly developed universal heparin reversal agent (UHRA-7), at different concentrations to determine the quality of blood clot formed upon heparin neutralization by analyzing several key rheological parameters. Scanning electron microscopy (SEM) was used to determine the morphology and microstructure of the blood clot after heparin neutralization to support the rheological observations. The current study revealed that the structure of blood clots formed had significant differences when an oscillatory frequency that mimicked the physiological heart rate was used in comparison to a lower frequency commonly used in current clinical measurements. The limited working dose range for protamine and its intrinsic anticoagulation behaviour was observed. The neutralization profile of UHRA-7 showed a large window of activity. The global assessment of rheological parameters and microstructure of the clot together revealed additional details describing anticoagulant reversal and blood coagulation dynamics by relating the blood clot's fiber thickness and the oscillatory measurements, including storage modulus and blood clot's contractile force. Additionally, a mechanical characterization was conducted to provide a further assessment of blood coagulation using the rheological data.

Using Rotational Thromboelastometry to Identify Early Allograft Dysfunction after Living Donor Liver Transplantation

Background: Diagnostic tests for early allograft dysfunction (EAD) after living donor liver transplantation (LDLT) vary widely. We aimed to evaluate the predictive value of rotational thromboelastometry (ROTEM)-derived parameters in EAD. Materials and Methods: A total of 121 patients were reviewed. The definition of EAD proposed by Olthoff et al. included the presence of any of the following at postoperative day 7: bilirubin level ≥ 10 mg/dL, INR ≥ 1.6, or serum AST or ALT levels > 2000 IU/L. All patients underwent ROTEM assay, which consisted of an extrinsically activated thromboelastometric test (EXTEM) before and 24 h after LDLT. Results: The 1-year/2-year OS were 68.%8/64.5% and 94.4%/90.8% for the EAD and non-EAD groups, respectively (p = 0.001). Two independent risks were identified for EAD, the postoperative clotting time (CT, p = 0.026) and time to maximum clot firmness (maximum clot firmness (MCF)-t, p = 0.009) on the EXTEM. CT yielded a specificity of 82.0% and negative predictive value of 83.0%, and MCF-t displayed a specificity of 76.4% and negative predictive value of 81.9% in diagnosing EAD. The use of the 24 h post-LDLT ROTEM increased the effectiveness of predicting overall survival (OS) compared to using the Olthoff’s EAD criteria alone (p < 0.001). Conclusion: We conclude that CT and MCF on EXTEM were independent predictors of EAD. The 24 h post-LDLT ROTEM can be used with conventional laboratory tests to diagnose EAD. It increases the effectiveness of predicting OS.

Bleeding phenotype of patients with moderate haemophilia A and B assessed by thromboelastometry and thrombin generation

INTRODUCTION

Predicting the bleeding phenotype is crucial for the management of patients with moderate haemophilia. Global coagulation assays evaluate haemostasis more comprehensively than conventional methods.

AIM

To explore global coagulation assays and the bleeding phenotype of patients with moderate haemophilia A (MHA) and B (MHB).

METHODS

The MoHem study is a cross-sectional, multicentre study covering Nordic patients with MHA and MHB. Thromboelastometry in whole blood and thrombin generation (TG) in platelet-poor plasma (1, 2.5 and 5 pM tissue factor (TF)) were compared with joint health (Haemophilia Joint Health Score (HJHS)) and treatment modality.

RESULTS

We report on 61 patients from Oslo and Helsinki: 24 MHA and 37 MHB. By TG (2.5 pM TF), patients who had been without replacement therapy during the previous 12 months depicted higher endogenous thrombin potential (P = .03). In contrast, those who had low ETP (< median) captured higher HJHS (P = .02). Patients who had undergone orthopaedic surgery generated least thrombin (P = .02). By thromboelastometry, those without the need of factor consumption had short clotting times, and quick times to maximum velocity (< median values) (P = .03). Factor VIII/factor IX activity (FVIII/FIX:C) did not align with the bleeding phenotype, but FIX:C ≤ 3 IU/dL was associated with lower peak thrombin (P = .03).

CONCLUSION

TG differentiated patients with moderate haemophilia according to HJHS, annual factor consumption, and whether orthopaedic surgery had been performed. Thromboelastometry differentiated according to factor consumption only. Global coagulation assays may assist predicting the bleeding phenotype in moderate haemophilia.

Systematic Approach to DNA Aptamer Design Using Amino Acid-Nucleic Acid Hybrids (ANHs) Targeting Thrombin

Chemical modifications of innate DNA/RNA aptamers facilitate the improvement of their function. Herein, we report our modular strategy to manipulate a thrombin-binding DNA aptamer (TBA) to improve its anticoagulation activity and binding affinity. A set of amino acid conjugates, termed amino acid-nucleic acid hybrids or ANHs, was synthesized and incorporated into a TBA loop sequences. We found that substitutions with hydrophobic amino acids in the loop region possessed significantly enhanced antithrombin activity, up to 3-fold higher than the native TBA. We investigated the correlations between thrombin-binding affinity and the features of our amino-acid conjugates using experimental techniques including circular dichroism spectroscopy, surface plasmon resonance assay, and molecular modeling. The present study demonstrates a systematic approach to aptamer design based on amino-acid characteristics, allowing the development of advanced aptamers.

Thrombin Generation Kinetics are Predictive of Rapid Transfusion in Trauma Patients Meeting Critical Administration Threshold

INTRODUCTION

We hypothesize that a patient (pt) with accelerated thrombin generation, time to peak height (ttPeak), will have a greater odds of meeting critical administration threshold (CAT) criteria (> 3 packed red blood cell [pRBC] transfusions [Tx] per 60 min interval), within the first 24 h after injury, independent of international normalized ratio (INR).

METHODS

In a prospective cohort study, trauma patients were enrolled over a 4.5-year period and serial blood samples collected at various time points. We retrospectively stratified pts into three categories: CAT+, CAT- but receiving some pRBC Tx, receiving no Tx within the first 24 h. Blood collected prior to Tx was analyzed for thrombin generation parameters and prothrombin time (PT)/INR.

RESULTS

A total of 484 trauma pts were analyzed: injury severity score = 13 [7,22], age = 48 [28, 64] years, and 73% male. Fifty pts met criteria for CAT+, 64 pts CAT-, and 370 received no Tx. Risk factors for meeting CAT+: decreased arrival systolic blood pressure (OR 2.82 [2.17, 3.67]), increased INR (OR 2.09, [1.66, 2.62]) and decreased time to peak OR 2.27 [1.74, 2.95]). These variables remained independently associated with increased risk of requiring Tx in a multivariable logistic model, after adjusting for sex and trauma type.

CONCLUSIONS

Pts in hemorrhagic shock, who meet CAT+ criteria, are characterized by accelerated thrombin generation. In our multivariable analysis, both ttPeak and PT/INR have a complementary role in predicting those injured patients who will require a high rate of Tx.

Complex and prolonged hypercoagulability in coronavirus disease 2019 intensive care unit patients: A thromboelastographic study

BACKGROUND

A high number of thrombotic complications have been reported in critically ill patients with coronavirus disease 2019 (COVID-19) and appear to be related to a hypercoagulable state. Evidence regarding detection, management, and monitoring of COVID-19-associated coagulopathy is still missing. We propose to describe the thrombus viscoelastic properties to investigate the mechanisms of hypercoagulability in patients with COVID-19.

METHODS

Thromboelastography (TEG) was performed in 24 consecutive patients admitted to a single intensive care unit for COVID-19 pneumonia, and 10 had a second TEG before being discharged alive from the intensive care unit.

RESULTS

Compared with a group of 20 healthy participants, patients with COVID-19 had significantly decreased values of reaction time, coagulation time, and lysis index and increased values of α angle, maximum amplitude, clot strength, and coagulation index. Velocity curves were consistent with increased generation of thrombin. These values persisted in surviving patients despite their good clinical course.

DISCUSSION

In patients with COVID-19, TEG demonstrates a complex and prolonged hypercoagulable state including fast initiation of coagulation and clot reinforcement, low fibrinolysis, high potential of thrombin generation, and high fibrinogen and platelet contribution. The antithrombotic strategy in patients with COVID-19 during intensive care hospitalisation and after discharge should be investigated in further studies.

Global coagulation assays in healthy controls: are there compensatory mechanisms within the coagulation system?

Global coagulation assays (GCAs) may provide a more comprehensive individual hemostatic profiling. We aim to evaluate GCAs (thromboelastography, thrombin generation) in healthy controls, and correlate results with age, gender, lipid status, tissue factor pathway inhibitor (TFPI) and P-selectin. Blood samples were collected from healthy controls (> 18 years of age) not taking anticoagulation or antiplatelet agents and without known cardiovascular disease. Thromboelastography (TEG) was performed on citrated whole blood while calibrated automated thrombogram (CAT), P-selectin (endothelial marker) and TFPI (principle inhibitor of tissue factor-initiated coagulation) were performed on platelet-poor plasma. 153 healthy controls (mean age 42 years, 98 females (64%)) were recruited. Female controls demonstrated more hypercoagulable TEG and CAT parameters while those over 50 years of age demonstrated more hypercoagulable TEG parameters despite comparable thrombin generation. Paradoxically, individuals with "flattened" thrombin curves (lower velocity index (rate of thrombin generation) despite preserved endogenous thrombin potential (amount of thrombin)) were more likely to be male (49% vs 20%, p = 0.003) with increased low-density lipoprotein cholesterol (3.3 vs 2.6 mmol/L, p = 0.003), P-selectin (54.2 vs 47.3 ng/mL, p = 0.038) and TFPI (18.7 vs 8.6 ng/ml, p = 0.001). In addition to reduced velocity index and thrombin peak, controls in the highest TFPI tertile also demonstrated a poorer lipid profile. GCAs can detect subtle changes of the hemostatic profile. Interestingly, reduced thrombin generation was paradoxically associated with increased cardiovascular risk factors, possibly attributable to increased TFPI. This finding may suggest compensation by the coagulation system in response to endothelial activation and represent a biomarker for early cardiovascular disease. A larger prospective study evaluating these assays in the cardiovascular disease population is ongoing.

Inhibitory Effects of P2Y12 Receptor Antagonist on PAR1- and PAR4-AP-Induced Platelet Aggregation in Patients with Stroke or TIA

OBJECTIVES

The inhibitory effects of P2Y12 receptor antagonist on PAR1- and PAR4-activating peptide (AP)-induced platelet aggregation have not been fully elucidated. The present study aimed to investigate the inhibitory effects of P2Y12 receptor antagonist on PAR1- and PAR4-AP-induced platelet aggregation using platelet-rich plasma (PRP) from individuals including patients with stroke or transient ischemic attack (TIA).

MATERIALS AND METHODS

PRP was given to 10 healthy individuals pretreated in vitro with cangrelor, then stimulated with adenosine diphosphate (ADP), PAR4-AP, or PAR1-AP. Moreover, 20 patients were enrolled from 148 consecutive patients with acute ischemic stroke or TIA admitted to our institute between December 2017 and April 2019. PRP obtained from each patient before and >7 days after initiation of clopidogrel was similarly stimulated with these agonists. Platelet aggregation was measured using an automatic coagulation analyzer in all participants.

RESULTS

In healthy individuals, ADP- and PAR4-AP-induced platelet aggregations were significantly inhibited depending on the cangrelor concentration in vitro, while PAR1-AP-induced platelet aggregation was slightly inhibited. In patients with stroke or TIA, clopidogrel inhibited ADP-induced platelet aggregation at all concentrations, and significantly inhibited PAR4-AP-induced platelet aggregation at 50 µmol/L of PAR4-AP (p<0.05), especially in 5 patients who showed high reactivity to PAR4-AP. PAR1-AP-induced platelet aggregation was also slightly inhibited.

CONCLUSIONS

We showed significant inhibitory effects on PAR4-AP-induced platelet aggregation by clopidogrel in patients with stroke or TIA who had high reactivity to PAR4-AP.

Evaluation of coagulation function by rotation thromboelastometry in critically ill patients with severe COVID-19 pneumonia

Critically ill patients with COVID-19 pneumonia suffered both high thrombotic and bleeding risk. The effect of SARS-CoV-2 on coagulation and fibrinolysis is not well known. We conducted a retrospective study of critically ill patients admitted to an intensive care unit (ICU) a cause of severe COVID-19 pneumonia and we evaluated coagulation function using rotational thromboelastometry (ROTEM) on day of admission (T0) and 5 (T5) and 10 (T10) days after admission to ICU. Coagulation standard parameters were also evaluated. Forty patients were enrolled into the study. The ICU and the hospital mortality were 10% and 12.5%, respectively. On ICU admission, prothrombin time was slightly reduced and it increased significantly at T10 (T0 = 65.1 ± 9.8 vs T10 = 85.7 ± 1.5, p = 0.002), while activated partial thromboplastin time and fibrinogen values were higher at T0 than T10 (32.2 ± 2.9 vs 27.2 ± 2.1, p = 0.017 and 895.1 ± 110 vs 332.5 ± 50, p = 0.002, respectively); moreover, whole blood thromboelastometry profiles were consistent with hypercoagulability characterized by an acceleration of the propagation phase of blood clot formation [i.e., CFT below the lower limit in INTEM 16/40 patients (40%) and EXTEM 20/40 patients (50%)] and significant higher clot strength [MCF above the upper limit in INTEM 20/40 patients (50%), in EXTEM 28/40 patients (70%) and in FIBTEM 29/40 patients (72.5%)]; however, this hypercoagulable state persists in the first five days, but it decreases ten day after, without returning to normal values. No sign of secondary hyperfibrinolysis or sepsis induced coagulopathy (SIC) were found during the study period. In six patients (15%) a deep vein thrombosis and in 2 patients (5%) a thromboembolic event, were found; 12 patients (30%) had a catheter-related thrombosis. ROTEM analysis confirms that patients with severe COVID-19 pneumonia had a hypercoagulation state that persisted over time.

Modeling Thrombin Generation in Plasma under Diffusion and Flow

We investigate the capacity of published numerical models of thrombin generation to reproduce experimentally observed threshold behavior under conditions in which diffusion and/or flow are important. Computational fluid dynamics simulations incorporating species diffusion, fluid flow, and biochemical reactions are compared with published data for thrombin generation in vitro in 1) quiescent plasma exposed to patches of tissue factor and 2) plasma perfused through a capillary coated with tissue factor. Clot time is correctly predicted in individual cases, and some models qualitatively replicate thrombin generation thresholds across a series of tissue factor patch sizes or wall shear rates. Numerical results suggest that there is not a genuine patch size threshold in quiescent plasma-clotting always occurs given enough time-whereas the shear rate threshold observed under flow is a genuine physical limit imposed by flow-mediated washout of active coagulation factors. Despite the encouraging qualitative results obtained with some models, no single model robustly reproduces all experiments, demonstrating that greater understanding of the underlying reaction network, and particularly of surface reactions, is required. In this direction, additional simulations provide evidence that 1) a surface-localized enzyme, speculatively identified as meizothrombin, is significantly active toward the fluorescent thrombin substrate used in the experiments or, less likely, 2) thrombin is irreversibly inhibited at a faster-than-expected rate, possibly explained by a stimulatory effect of plasma heparin on antithrombin. These results highlight the power of simulation to provide novel mechanistic insights that augment experimental studies and build our understanding of complex biophysicochemical processes. Further validation work is critical to unleashing the full potential of coagulation models as tools for drug development and personalized medicine.

Targeted inhibition of thrombin attenuates murine neonatal necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is an inflammatory bowel necrosis of premature infants and an orphan disease with no specific treatment. Most patients with confirmed NEC develop moderate-severe thrombocytopenia requiring one or more platelet transfusions. Here we used our neonatal murine model of NEC-related thrombocytopenia to investigate mechanisms of platelet depletion associated with this disease [K. Namachivayam, K. MohanKumar, L. Garg, B. A. Torres, A. Maheshwari, Pediatr. Res. 81, 817-824 (2017)]. In this model, enteral administration of immunogen trinitrobenzene sulfonate (TNBS) in 10-d-old mouse pups produces an acute necrotizing ileocolitis resembling human NEC within 24 h, and these mice developed thrombocytopenia at 12 to 15 h. We hypothesized that platelet activation and depletion occur during intestinal injury following exposure to bacterial products translocated across the damaged mucosa. Surprisingly, platelet activation began in our model 3 h after TNBS administration, antedating mucosal injury or endotoxinemia. Platelet activation was triggered by thrombin, which, in turn, was activated by tissue factor released from intestinal macrophages. Compared to adults, neonatal platelets showed enhanced sensitivity to thrombin due to higher expression of several downstream signaling mediators and the deficiency of endogenous thrombin antagonists. The expression of tissue factor in intestinal macrophages was also unique to the neonate. Targeted inhibition of thrombin by a nanomedicine-based approach was protective without increasing interstitial hemorrhages in the inflamed bowel or other organs. In support of these data, we detected increased circulating tissue factor and thrombin-antithrombin complexes in patients with NEC. Our findings show that platelet activation is an important pathophysiological event and a potential therapeutic target in NEC.

Protease-activated prodrugs: strategies, challenges, and future directions

Proteases play critical roles in virtually all biological processes, including proliferation, cell death and survival, protein turnover, and migration. However, when dysregulated, these enzymes contribute to the progression of multiple diseases, with cancer, neurodegenerative disorders, inflammation, and blood disorders being the most prominent examples. For a long time, disease-associated proteases have been used for the activation of various prodrugs due to their well-characterized catalytic activity and ability to selectively cleave only those substrates that strictly correspond with their active site architecture. To date, versatile peptide sequences that are cleaved by proteases in a site-specific manner have been utilized as bioactive linkers for the targeted delivery of multiple types of cargo, including fluorescent dyes, photosensitizers, cytotoxic drugs, antibiotics, and pro-antibodies. This platform is highly adaptive, as multiple protease-labile conjugates have already been developed, some of which are currently in clinical use for cancer treatment. In this review, recent advancements in the development of novel protease-cleavable linkers for selective drug delivery are described. Moreover, the current limitations regarding the selectivity of linkers are discussed, and the future perspectives that rely on the application of unnatural amino acids for the development of highly selective peptide linkers are also presented.

Continuous Detection of Increasing Concentrations of Thrombin Employing a Label-Free Photonic Crystal Aptasensor

Thrombin generation is a complex and finely regulated pathway that provokes dynamical changes of thrombin concentration in blood when a vascular injury occurs. In order to characterize the initiation phase of such process, when thrombin concentration is in the nM range, a label-free optical aptasensor is proposed here. This aptasensor combines a 1D photonic crystal structure consisting of a silicon corrugated waveguide with thrombin binding aptamers on its surface as bioreceptors. As a result, this aptasensor has been demonstrated to specifically detect thrombin concentrations ranging from 270 pM to 27 nM with an estimated detection limit of 33.5 pM and a response time of ~2 min. Furthermore, it has also been demonstrated that this aptasensor is able to continuously respond to consecutive increasing concentrations of thrombin and to detect binding events as they occur. All these features make this aptasensor a good candidate to continuously study how thrombin concentration progressively increases during the initiation phase of the coagulation cascade.

VE-1902-A direct thrombin inhibitor with reversible covalent mechanism of action shows efficacy with reduced bleeding in rodent models of thrombosis

INTRODUCTION

High incidence of bleeding events remains a key risk for patients taking anticoagulants, especially those in need of long-term combination therapy with antiplatelet agents. As a consequence, patients may not receive clinically indicated combination antithrombotic therapy. Here, we report on VE-1902, a member of a novel class of precision oral anticoagulants (PROACs) that combines effective anticoagulation with reduced bleeding in preclinical testing.

METHODS AND RESULTS

Acting through covalent, reversible active-site modification of thrombin similar to a previously described molecule [1], VE-1902 shows potency and selectivity for thrombin inhibition in human plasma comparable to clinically relevant direct thrombin inhibitors (DTI) such as argatroban and dabigatran (thrombin generation assay ETP EC₅₀ = 1.3 μM compared to 0.36 μM and 0.31 μM for argatroban and dabigatran; >100-fold selectivity against related serine proteases). Unlike the current anticoagulants, VE-1902 does not significantly inhibit thrombin-mediated platelet activation in in vivo models of thrombosis. In the thrombin generation assay, the compound inhibits thrombin formation without significantly delaying the initiation phase of the clotting cascade. These features are possibly responsible for the observed reduced bleeding in tail bleeding and saphenous vein bleeding models. Consistent with this novel pharmacological profile, VE-1902 shows efficacious anticoagulation in several fibrin-driven animal models of thrombosis (arteriovenous shunt, venous stasis thrombosis, and thrombin-induced thromboembolism models), whereas it does not significantly prevent arterial occlusion in the platelet dependent FeCl₃ model.

CONCLUSIONS

By leaving platelet activation following vascular injury mostly unaffected, VE-1902, and the PROACs more generally, represent a new generation of precision anticoagulants with reduced bleeding risk.

Limited factor VIIa surface localization requirement of the factor VIIa-induced overall thrombin generation in platelet-rich hemophilia A plasma

BACKGROUND

Thrombin generation assay (TGA) and thrombelastography (TEG) are increasingly employed, global, in vitro methods for assessment of the procoagulant potential of plasma/blood and possibly ideally suited tools to monitor, for example, therapy with recombinant factor VIIa (FVIIa). It remains controversial to what extent results obtained with spiked and postinfusion samples reflect the outcome in patients.

OBJECTIVE

To characterize the TGA response to FVIIa in hemophilic plasma and compare with TEG data.

METHODS

Hemophilia A (HA) was induced in platelet-rich plasma (PRP) from healthy volunteers, followed by spiking with FVIIa, γ-carboxyglutamic acid (Gla)-domainless FVIIa or V158D/E296V/M298Q-FVIIa (FVIIaDVQ). Samples were triggered with tissue factor and analyzed by TGA and TEG in parallel.

RESULTS

Addition of 25 nmol L-1 FVIIa to HA PRP normalized TEG parameters angle and R time, as well as TGA lag time, but had poor effects on the thrombin peak height and velocity index. All parameters (at least) returned to normal levels either upon adding a much higher concentration of FVIIa (~1500 nmol L-1) or by using the superactive variant FVIIaDVQ. Surprisingly, Gla-domainless derivatives of FVIIa and FVIIaDVQ also yielded considerable effects in HA PRP.

CONCLUSIONS

The good general responses to clinically effective concentrations of FVIIa (25 and 75 nmol L-1) seen in TEG analyses, as well as for TGA lag time, were accompanied by far-from-normal thrombin peaks. A near-normal thrombin peak response required the presence of considerably higher FVIIa activity but, intriguingly, relied only marginally on a functional Gla domain (ie, on platelet surface localization).

Reactive microglia and astrocytes in neonatal intraventricular hemorrhage model are blocked by mesenchymal stem cells

Severe intraventricular hemorrhage (IVH) in premature infants triggers reactive gliosis, causing acute neuronal death and glial scar formation. Transplantation of mesenchymal stem cells (MSCs) has often showed improved CNS recovery in an IVH model, but whether this response is related to reactive glial cells is still unclear. Herein, we suggest that MSCs impede the response of reactive microglia rather than astrocytes, thereby blocking neuronal damage. Astrocytes alone showed mild reactiveness under hemorrhagic conditions mimicked by thrombin treatment, and this was not blocked by MSC-conditioned medium (MSC-CM) in vitro. In contrast, thrombin-induced microglial activation and release of proinflammatory cytokines were inhibited by MSC-CM. Interestingly, astrocytes showed greater reactive response when co-cultured with microglia, and this was abolished in the presence of MSC-CM. Gene expression profiles in microglia revealed that transcript levels of genes for immune response and proinflammatory cytokines were altered by thrombin treatment. This result coincided with the robust phosphorylation of STAT1 and p38 MAPK, which might be responsible for the production and release of proinflammatory cytokines. Furthermore, application of MSC-CM diminished thrombin-mediated phosphorylation of STAT1 and p38 MAPK, supporting the acute anti-inflammatory role of MSCs under hemorrhagic conditions. In line with this, activation of microglia and consequent cytokine release were impaired in Stat1-null mice. However, reactive response in Stat1-deficient astrocytes was maintained. Taken together, our results demonstrate that MSCs mainly block the activation of microglia involving STAT1-mediated cytokine release and subsequent reduction of reactive astrocytes.

Compact Grating-Coupled Biosensor for the Analysis of Thrombin

A compact optical biosensor for direct detection of thrombin in human blood plasma (HBP) is reported. This biosensor platform is based on wavelength spectroscopy of diffraction-coupled surface plasmons on a chip with a periodically corrugated gold film that carries an antifouling thin polymer layer consisting of poly[(N-(2-hydroxypropyl)methacrylamide)-co-(carboxybetaine methacrylamide)] (poly(HPMA-co-CBMAA)) brushes. This surface architecture provides superior resistance to nonspecific and irreversible adsorption of abundant compounds in the analyzed HBP samples in comparison to standard surface modifications. The carboxylate groups along the polymer brushes were exploited for the covalent immobilization of aptamer ligands. These ligands were selected to specifically capture the target thrombin analyte from the analyzed HBP sample in a way that does not activate the coagulatory process at the biosensor surface with poly(HPMA-co-CBMAA) brushes. Direct label-free analysis of thrombin in the medically relevant concentration range (1-20 nM) is demonstrated without the need for diluting the HBP samples or using additional steps for signal enhancement. The reported platform constitutes the first step toward a portable and sensitive point-of-care device for direct detection of thrombin in human blood.

p38/TF/HIF-α Signaling Pathway Participates in the Progression of CIPN in Mice

Chemotherapy induced peripheral neuropathy (CIPN) is a serious adverse effect of chemotherapeutics with limited pathogenetic mechanism been known. Whether microcirculatory disturbance is involved in CIPN has not been reported. Considering that tissue factor (TF) is an endogenous coagulation factor, we hypothesize CIPN may be induced by the high expression of TF in macrophages and sciatic nerve, which induces the molecular signal related to ischemia and hypoxia. Oxaliplatin (L-OHP) was used to establish CIPN model. Von Frey Hairs was used to measure nociception. The murine macrophage cell line Raw 264.7 was used for cell experiments. Gelatin zymography and western blotting were used to measure the activity or expression of protein. TF expression and MMP-9/2 activity in sciatic nerve and blood are significantly increased by L-OHP. L-OHP increased the release of HSP70 from macrophage and enhanced the expression of p-p38 and HIF-1α in vivo and in vitro. Hirudin significantly suppressed the overexpression of p38, HIF-1α and activation of MMP-9/2 induced by L-OHP and attenuated CIPN in mice. This study suggests that a novel HSP70-TLR-4-p38-TF-HIF-1a axis may play a pivotal role in the pathological process of CIPN. It is also shown that the use of anticoagulant Hirudin can inhibit the above mechanisms and improve CIPN.

Idarucizumab, but not procoagulant concentrates, fully restores dabigatran-altered platelet and fibrin components of hemostasis

BACKGROUND

Comparative studies on the restoration of hemostasis with different reversal agents after dabigatran therapy have not been performed. We compared the efficacy and prothrombotic potential of the specific antidote idarucizumab with that of previously recommended non-specific procoagulant concentrates.

STUDY DESIGN AND METHODS

We explored the in vitro effects of dabigatran (184 ng/mL) on fibrin and platelet-aggregate formation onto a damaged vessel under flow conditions (600 s^-1 ). The reversal mechanisms and efficacy of idarucizumab (0.3-3 mg/mL) were compared with that of the non-specific procoagulant concentrates aPCC (25-75 U/Kg), PCC (70 U/Kg), or rFVIIa (120 μg/Kg). Generation of thrombin and prothrombin fragment (F1 + 2), and thromboelastometry parameters of clot formation were measured.

RESULTS

Dabigatran caused pronounced reductions in fibrin (87%) and platelet interactions (36%) with damaged vessels (p < 0.01) and significantly impaired thrombin generation and thromboelastometric parameters (delayed dynamics and reduced firmness). Idarucizumab completely normalized rates of fibrin and platelet coverage to baseline values in flow studies; and reversed the alterations in thrombin generation, F1 + 2 and thromboelastometry parameters produced by dabigatran. In comparison, aPCC and PCC only partially compensated for the dabigatran-induced alterations in fibrin deposition, but were unable to fully restore them to baseline values. Reversal with aPCC or PCC improved the majority of alterations in coagulation-related tests, but tended to overcompensate thrombin generation kinetics and significantly increased F1 + 2 levels.

CONCLUSION

Idarucizumab antagonizes alterations of direct and indirect biomarkers of hemostasis caused by dabigatran. In our studies, idarucizumab was clearly more efficacious than strategies with non-specific procoagulant concentrates and devoid of the excessive procoagulant tendency observed with the latter.

Hemodilution and Endothelial Cell Regulation of Whole Blood Coagulation

Background

Beyond localized damage to the circulatory system and surrounding tissue, trauma stresses endothelial cells throughout the vasculature, potentially leading to hemorrhagic or thrombotic complications away from the injury site.

Objective

Use a whole blood endothelial cell model to define the effects of crystalloid fluid therapy on protein C pathway regulation of tissue factor-initiated coagulation.

Methods

Tissue factor-initiated coagulation was studied in the presence of EA.hy926 cells. Blood was diluted to 70% or 40% using normal saline or lactated ringers. Analyses of coagulation dynamics included clot times, thrombin formation (thrombin-antithrombin complex), FV activation/inactivation, fibrinogen consumption, FXIII activation, and platelet activation.

Results

In all donors, the onset of thrombin generation was not altered in 70% blood using either diluent; with the blood component reduced to 40%, clot time was prolonged two-fold when normal saline was utilized but was unchanged with lactated ringers. The timing of the activations of FV, fibrinogen, and platelets paralleled the effects of dilution on clot times. Extensive inactivation of FVa was observed in undiluted blood and where lactated ringers was the diluent but not in trials with 40% blood/60% normal saline.

Conclusion

Feedback inhibition of tissue factor-initiated coagulation by the protein C pathway is not compromised by hemodilution with crystalloids.