Distinct features of bivalent direct thrombin inhibitors, hirudin and bivalirudin, revealed by clot waveform analysis and enzyme kinetics in coagulation assays

Comparison of clot waveform analysis with or without adjustment between prothrombin time and activated partial thromboplastin time assays to assess in vitro effects of direct oral anticoagulants

BACKGROUND

Clot waveform analysis (CWA) reportedly enhances the interpretation of clotting time measurement. This study aimed to compare CWA between prothrombin time (PT) and activated partial thromboplastin time (APTT) assays for better understanding how to apply CWA for assessing effects of direct oral anticoagulants (DOACs).

METHODS

Samples were prepared by spiking plasma with rivaroxaban, apixaban, edoxaban, or dabigatran. To compensate the influence of fibrinogen, CWA parameters were adjusted by unifying maximum changes in transmittance in clotting reaction curves detected by the optical system.

RESULTS

Non-adjusted PT-CWA parameters unexpectedly rose at low drug concentrations but declined at high drug concentrations while adjusted PT-CWA parameters exhibited dose-dependent decrease. Both non-adjusted and adjusted APTT-CWA parameters showed dose-dependent decrease. Adjusted CWA parameters were applicable to Hill plot analysis. All DOACs exhibited Hill coefficients indicating positively cooperative effects regarding most adjusted PT-CWA parameters. Regarding adjusted APTT-CWA parameters, rivaroxaban, apixaban, and edoxaban exhibited Hill coefficients indicating no or negatively cooperative effects. The observed differences between PT-CWA and APTT-CWA suggested the implication of thrombin positive feedback in DOAC effects.

CONCLUSION

The results revealed distinct features of DOAC effects in extrinsic and intrinsic pathways. To ascertain the clinical implication, further studies using clinical samples are needed.

Cellular mechanisms of fibrin (ogen): insight from neurodegenerative diseases

Neurodegenerative diseases are prevalent and currently incurable conditions that progressively impair cognitive, behavioral, and psychiatric functions of the central or peripheral nervous system. Fibrinogen, a macromolecular glycoprotein, plays a crucial role in the inflammatory response and tissue repair in the human body and interacts with various nervous system cells due to its unique molecular structure. Accumulating evidence suggests that fibrinogen deposits in the brains of patients with neurodegenerative diseases. By regulating pathophysiological mechanisms and signaling pathways, fibrinogen can exacerbate the neuro-pathological features of neurodegenerative diseases, while depletion of fibrinogen contributes to the amelioration of cognitive function impairment in patients. This review comprehensively summarizes the molecular mechanisms and biological functions of fibrinogen in central nervous system cells and neurodegenerative diseases, including Alzheimer's disease, Multiple Sclerosis, Parkinson's disease, Vascular dementia, Huntington's disease, and Amyotrophic Lateral Sclerosis. Additionally, we discuss the potential of fibrinogen-related treatments in the management of neurodegenerative disorders.

Early growth response factor 1 upregulates pro-fibrotic genes through activation of TGF-β1/Smad pathway via transcriptional regulation of PAR1 in high-glucose treated HK-2 cells

Tubulointerstitial fibrosis (TIF) makes a key role in diabetic kidney disease (DKD). In this study, we revealed that the expressions of Egr1 and protease-activated receptor 1 (PAR1) were increased in renal tissues of DKD rats. In vitro experiments demonstrated that both Egr1 overexpression and high glucose (HG) condition could promote the expressions of PAR1, fibronectin (FN) and collagen I (COL I). Furthermore, HG stimulation enhanced the binding capacity of Egr1 to PAR1 promoter. Both HG condition and Egr1 upregulation could increase, and thrombin inhibitor did not affect activity of TGF-β1/Smad pathway via PAR1. Collectively, Egr1 is involved in TIF of DKD partly through activating TGF-β1/Smad pathway via transcriptional regulation of PAR1 in HG treated HK-2 cells.

Clot waveform analysis for perioperative hemostatic monitoring in a hemophilia A patient on emicizumab undergoing liver transplantation

How to optimize perioperative factor VIII (FVIII) replacement through hemostatic monitoring is critically important to manage hemophilia A patients. The bispecific antibody emicizumab binds activated FIX (FIXa) and FX to functionally mimic FVIIIa. While being used for hemostatic control in hemophilia A, this therapeutic antibody inconveniently interferes with coagulation tests using human FIXa and FX, such as activated partial thromboplastin time (APTT) and FVIII activity measurement based on one-stage clotting assays. Clot waveform analysis (CWA) extends the interpretation of measurement curves for coagulation time to provide global information. We performed APTT-CWA to monitor perioperative hemostasis in a hemophilia A patient on emicizumab undergoing liver transplantation. Plasma samples were treated with anti-idiotype monoclonal antibodies against emicizumab to enable accurate coagulation assays. Kinetics of maximum coagulation velocity and acceleration mimicked that of FVIII activity. These CWA parameters better correlated with FVIII activity than APTT. The plateaus of them were observed at FVIII activity of 100% or more, supporting the protocol for perioperative FVIII replacement. Thus, CWA may measure coagulation potential in hemophilia A patients undergoing liver transplantation, aiding in optimizing perioperative hemostasis.

Hirudin, a thrombin inhibitor, attenuates TGF-β-induced fibrosis in renal proximal tubular epithelial cells by inhibition of protease-activated receptor 1 expression via S1P/S1PR2/S1PR3 signaling

Renal interstitial fibrosis (RIF) is the final common outcome of numerous chronic kidney diseases, contributing to end-stage renal disease. Hirudin, a thrombin inhibitor, has attracted increased attention as a potential treatment approach for renal fibrosis. The present study aimed to investigate the molecular mechanism underlying the effect of hirudin on fibrosis in renal proximal tubular epithelial cells. An in vivo mouse RIF model established using unilateral ureteral obstruction (UUO) and an in vitro of RIF using the renal tubular epithelial cell line HK-2 treated with TGF-β were used. Expressions of sphingosine-1-phosphate (S1P) receptors (S1PR)1-4 and protease-activated receptor 1 (PAR1) were measured by reverse transcription-quantitative PCR and western blotting in mice with UUO and TGF-β induced HK-2 cells. Western blotting was used to detect the expression of N-cadherin, Slug, E-cadherin, Collagen IV, fibronectin, MMP9 and monocyte chemoattractant protein-1. Immunofluorescence staining was conducted to measure α-SMA level expression. The results demonstrated that the expression levels of S1PR1, S1PR2, S1PR3, S1PR4 and PAR1 were upregulated in both TGF-β-induced HK-2 cells and renal tissues from mice with unilateral ureteral ligation. Notably, hirudin inhibited TGF-β-induced PAR1, S1PR2 and S1PR3 upregulation in both HK-2 cells and renal tissues. Additionally, the inhibition of S1PR2 and S1PR3 resulted in PAR1 downregulation. Furthermore, treatment with S1P and PAR1 agonists abolished the effect of hirudin on the expression of EMT, fibrosis-related proteins and monocyte chemoattractant protein 1. In conclusion, hirudin attenuated TGF-β-induced fibrosis in proximal renal tubular epithelial HK-2 cells by inhibiting PAR1 expression via the S1P/S1PR2/S1PR3 signaling pathway. Therefore, hirudin may be considered as a promising therapeutic agent for RIF.

Update on the Clot Waveform Analysis

The activated partial thromboplastin time (APTT)–clot waveform analysis (CWA) was previously reported to be associated with the early detection of disseminated intravascular coagulation and was also reported to be able to measure very low levels of coagulation factor VIII activity. The software program for the analysis for the APTT-CWA allows the associated first and second derivative curves (first and second DCs) to be displayed. The first and second DC reflect the velocity and acceleration, respectively. The height of the first DC reflects the “thrombin burst” and bleeding risk, while that of the second DC is useful for detecting any coagulation factor deficiency and abnormal enhancement of coagulation by phospholipids. Activated partial thromboplastin time-CWA aids in making a differential diagnosis which is difficult to do using only the routine APTT. The CWA is currently used for many applications in the clinical setting, including the monitoring of hemophilia patients and patients receiving anticoagulant therapy and the differential diagnosis of diseases.

A phase I, single and continuous dose administration study on the safety, tolerability, and pharmacokinetics of neorudin, a novel recombinant anticoagulant protein, in healthy subjects

The aim of this study was to evaluate the tolerability, safety, and pharmacokinetics of single and continuous dose administration of recombinant neorudin (EPR-hirudin, EH) by intravenous administration in healthy subjects, and to provide a safe dosage range for phase II clinical research. Forty-four subjects received EH as a single dose of between 0.2 and 2.0 mg/kg by intravenous bolus and drip infusion. In addition, 18 healthy subjects were randomly divided into three dose groups (0.15, 0.30, and 0.45 mg/kg/h) with 6 subjects in each group for the continuous administration trial. Single or continuous doses of neorudin were generally well tolerated by healthy adult subjects. There were no serious adverse events (SAEs), and all adverse events (AEs) were mild to moderate. Moreover, no subjects withdrew from the trial because of AEs. There were no clinically relevant changes in physical examination results, clinical chemistry, urinalysis, or vital signs. The incidence of adverse events was not significantly related to drug dose or systemic exposure. After single-dose and continuous administration, the serum EH concentration reached its peak at 5 min, and the exposure increased with the increase in the administered dose. The mean half-life (T_1/2 ), clearance (Cl), and apparent volume of distribution (Vd) of EH ranged from 1.7 to 2.5 h, 123.9 to 179.7 ml/h/kg, and 402.7 to 615.2 ml/kg, respectively. The demonstrated safety, tolerability, and pharmacokinetic characteristics of EH can be used to guide rational drug dosing and choose therapeutic regimens in subsequent clinical studies. Clinical trial registration: Chinadrugtrials.org identifier: CTR20160444.

Characterisation of antithrombin-dependent anticoagulants through clot waveform analysis to potentially distinguish them from antithrombin-independent inhibitors targeting activated coagulation factors

AIMS

While antithrombin (AT)-independent inhibitors targeting thrombin or activated factor X have been assessed through clot waveform (CWA), there are no reports on assessment with respect to AT-dependent anticoagulants. The present study aims to characterise AT-dependent anticoagulants through CWA to distinguish them from AT-independent inhibitors.

METHODS

CWA was applied to the activated partial thromboplastin time (APTT) assay of plasma samples spiked with each of AT-dependent drugs (unfractionated heparin, enoxaparin and fondaparinux) and AT-independent drugs (rivaroxaban, apixaban, edoxaban, dabigatran, argatroban, hirudin and bivalirudin), which was performed using the CS-5100 or CN-6000 (Sysmex). The APTT-CWA data were automatically gained by the analyser program. The positive mode of clotting reaction curves was defined as the direction towards fibrin generation.

RESULTS

Regarding dose-response curves in AT-dependent anticoagulants, the maximum positive values of the first and secondary derivatives (Max1 and Max_p2, respectively) and the maximum negative values of the secondary derivative (Max_n2) seemed to drop to zero without making an asymptotic line, consistent with the irreversibility. Such a feature was observed also in hirudin, as reported previously. Notably, the symmetric property of Max1 peaks in the waveforms was distorted dose dependently in AT independent but not AT-dependent drugs. A plot of Max_p2 logarithm versus Max_n2 logarithm was linear. The slope was about 1 in AT-dependent drugs while that was more than 1 in AT-independent drugs. These features made it possible to distinguish AT-dependent and AT-independent drugs.

CONCLUSIONS

The results aid in further understanding of the pharmacological aspects of anticoagulation and in screening of candidates for novel anticoagulants.

Enhanced anticoagulant activity of hirudin-i analogue co-expressed with arylsulfotransferase in periplasm of E. coli BL21(DE3)

Hirudin, a blood anticoagulant, is the most potent natural thrombin inhibitor of leech origin. Its application is limited because it is difficult to obtain abundant natural hirudin directly from the leech. Although some bioengineering methods can significantly increase the production of hirudin, the reduced efficacy of recombinant hirudin (rH) remains a critical shortcoming. The lack of sulfation of tyrosine 63 in rH is an important cause of its inadequate performance. This article is the first report of periplasmic co-expression of an rH-I analogue with arylsulfotransferase (ASST) in E. coli BL21(DE3). Co-expressed rH-I analogue with sulfate donor substrate (p-nitrophenyl sulfate potassium) showed anticoagulant (rabbit and goat serum) activity twice more than rH-I analogue expressed without ASST, indicating its potential periplasmic sulfation. Moreover, purified rH-I analogue showed above 4.5 times higher anticoagulant activity compared to therapeutic anti-thrombotic heparin (HE). At the same time, pH-dependent differential solubility was employed to purify rH analogues from fermentation broth, which is a simple, fast and inexpensive purification technology, and can potentially be used for larger scale purification. This will also greatly improve the application of rH in clinical treatment.

A novel thrombin inhibitory peptide discovered from leech using affinity chromatography combined with ultra-high performance liquid chromatography-high resolution mass spectroscopy

Thrombin (THR) inhibitors play an important role in the treatment of thrombotic diseases. This study established a THR-based bio-specific extraction coupled with affinity chromatography and ultra-high performance liquid chromatography-high resolution mass spectroscopy (UPLC-HR-MS) analysis method to screen and identify THR ligands in Leech. After evaluating the reliability of the screening method using positive control drug (hirudin), it was successfully used to screen the potential active constituents in leech. And a comprehensive analysis of the peptides in leech elution was performed by UPLC-HR-MS, a total of 34 peptides were identified. At the same time, anti-THR activity was explored and inferred by searching databases and published literature. As a result, six peptides were discovered to be potential active compounds in leech. Further, the six peptides were synthesized and in vitro enzymatic activity assay was performed. Finally, SYELPDGQVITIGNER was screened as an anti-THR peptide with an IC50 value of 255.75 µM and it was discovered for the first time from Whitmania pigra Whitman and Hirudo nipponica Whitman. The molecular docking study showed that THR inhibitory activity of the polypeptide was mainly attributed to the hydrogen bond interactions, van der Waals forces and electrostatic interactions interaction between polypeptide and THR. These results suggest that the polypeptide is a potential natural THR inhibitor that can be used as anticoagulant.

Application of clot-fibrinolysis waveform analysis to assessment of in vitro effects of direct oral anticoagulants on fibrinolysis

INTRODUCTION

Acceleration of fibrinolysis by direct oral anticoagulants (DOACs) has been reported by several groups, suggesting contribution of not only anticoagulant but also fibrinolytic effects to the therapeutic efficacy. The present study aims to evaluate the usability of clot-fibrinolysis waveform analysis (CFWA) for assessment of in vitro effects of DOACs on fibrinolysis.

METHODS

The experimental conditions were optimized according to how t-PA concentrations and a time length after t-PA adjustment affect parameters of CFWA. Addition of the activated partial thromboplastin time (APTT) reagent followed by that of calcium and t-PA was done to obtain clotting and fibrinolytic reaction curves which were mathematically differentiated for CFWA (APTT-CFWA). The positive and negative modes of waveforms were defined as the direction toward fibrin generation and that toward fibrin degradation, respectively. The maximum positive and negative values (Max_p 1 and Max_n 1) correspond to the maximum coagulation velocity and the maximum fibrinolysis velocity, respectively. Plasma spiked with each of DOACs (rivaroxaban, apixaban, edoxaban, and dabigatran) was subjected to APTT-CFWA.

RESULTS

Optimization of t-PA use was based on Max_n 1. Roughly biphasic effects of rivaroxaban and dabigatran but not apixaban or edoxaban on fibrinolysis were observed through Max_n 1 and the fibrinolysis peak time, which was defined as a time length from the time when Max_p 1 (Max_p 1 time) to the time when Max_n 1 appears (Max_n 1 time).

CONCLUSION

The results suggest the usability of CFWA for assessment of DOAC effects and provide insights into relevance of anticoagulation to therapeutic efficacy and bleeding risk from the perspective of fibrinolysis.