A new measure for in vivo thrombin activity in comparison with in vitro thrombin generation potential in patients with hyper- and hypocoagulability

Characterization of a prothrombotic phenotype using thrombin generation and thrombin activity in cirrhosis and portal hypertension

BACKGROUND

Patients with advanced chronic liver disease (ACLD) may develop a prothrombotic phenotype that seems to be more pronounced with more severe liver dysfunction. An imbalance of endogenous pro- and anticoagulants is not fully captured by routine coagulation assays.

METHODS

In a cohort of ACLD patients undergoing hepatic venous pressure gradient (HVPG) measurement, we assessed thrombin generation (TGA) using two commercially available assays (Technothrombin and Thrombinoscope) with and without addition of soluble thrombomodulin (TM), as well as thrombin activity, alongside a panel of coagulation parameters.

RESULTS

The cohort encompassed 37 patients (median age 55.3 years, mean HVPG 16 ± 5 mm Hg). In the TM-modified Thrombinoscope TGA, the endogenous thrombin generation potential (ETP) was significantly increased in Child-Pugh-Score (CPS) B/C patients (N = 23, 62 %) compared to CPS A patients (N = 14, 38 %) (ETP: 546 nM∗min (443-696) vs. 404 nM∗min (289-573), p = 0.028). Using the Technothrombin TGA without TM, patients with CPS B/C had decreased ETP compared to CPS A patients (ETP: 2792 ± 1336 nM∗min vs. 5040 ± 816 nM∗min, p < 0.001) and with addition of TM (final concentration: 5 nM; ETP: 2545 ± 1327 nM∗min vs. 4824 ± 929 nM∗min, p < 0.001). Thrombin activity levels were 0.6pM in median (0.2-1.6pM) and above the level of detectability (0.10pM) in 94.6 % of patients but were not correlated to severity of cirrhosis (CPS A 0.7pM vs CPS B/C 0.4pM, p = 0.377) nor to parameters of TGA.

CONCLUSION

Thrombin plasma levels are elevated in liver disease patients without apparent correlation to TGA or severity of cirrhosis. TGAs can be modified with TM to enable protein C-dependent anticoagulation, but result in differences with regard to severity of liver disease.

Influence of direct oral anticoagulants on thrombin generation on Ceveron TGA

INTRODUCTION

Monitoring of direct oral anticoagulants (DOACs) with calibrated anti-Xa assay is limited by the high intra- and interindividual variations of the test results. Thrombin generation (TG) is a global hemostatic assay that reflects the patient´s individual coagulation status. The aim of this study was to investigate the influence of DOACs on TG measured with a fully automated assay system.

METHODS

All consecutive patients under apixaban and rivaroxaban coming to the outpatient coagulation center MVZ Limbach, Magdeburg, Germany between October 2017 and April 2020 were included. DOAC plasma levels were correlated with TG assessed using the fully automated Ceveron TG analyzer.

RESULTS

A total of 703 rivaroxaban and 252 apixaban containing plasma samples were included. There was a significant correlation between DOAC plasma levels and all TG parameters except for lag time regarding apixaban. Time to peak and peak thrombin followed an exponential regression curve, while this was linear for the endogenous thrombin potential (ETP). Apixaban showed a lower correlation coefficient for all TG parameters compared with rivaroxaban, and thrombin generation was less influenced by apixaban than rivaroxaban at plasma levels >100 ng/ml. The sensitivity and negative predictive value of normal TG parameters for the prediction of DOAC plasma levels <30 ng/ml was >85%.

CONCLUSION

The present data show a moderate predominantly nonlinear correlation between TG parameters and plasma levels of apixaban and rivaroxaban. Rivaroxaban has a stronger effect on TG than apixaban.

Femtomolar Detection of Thrombin in Serum and Cerebrospinal Fluid via Direct Electrocatalysis of Oxygen Reduction by the Covalent G4-Hemin-Aptamer Complex

Thrombin, a serine protease playing a central role in the coagulation cascade reactions and a potent neurotoxin produced by injured brain endothelial cells, is a recognized cardiac biomarker and a critical biomarker for Alzheimer's disease development. Both in vivo and in vitro, its low physiological concentrations and nonspecific binding of other components of physiological fluids complicate electroanalysis of thrombin. Here, femtomolar levels of thrombin in serum and an artificial cerebrospinal fluid (CSF) were detected by the indicator-free electrochemical methodology exploiting the O₂ reduction reaction directly, with no electron transfer mediators, electrocatalyzed by the covalent G4-hemin DNAzyme complex naturally self-assembling upon thrombin binding to the hemin-modified 29-mer DNA aptamer sequence tethered to gold via an alkanethiol linker. Coadsorbed PEG inhibited nonspecific protein binding and allowed the sought signal resolution. The proposed assay exploiting the "oxidase" activity of G4-hemin DNAzyme does not require any coreactants necessary for the traditional peroxidase activity-based assays with this DNAzyme, such as H₂O₂ and redox mediators, or solution deaeration and allows fast, overall 30 min analysis of thrombin in aerated buffer, CSF, and 1% human serum solutions. This pioneer approach exploiting the oxidase activity G4-hemin DNAzyme is simple, sensitive, and selective and represents a new tool for ultrasensitive electrocatalytic assays based on simple and efficient O₂-dependent DNAzyme labels.

Increased activity of procoagulant factors in patients with small cell lung cancer

Small cell lung cancer (SCLC) patients have augmented risk of developing venous thromboembolism, but the mechanisms triggering this burden on the coagulation system remain to be understood. Recently, cell-derived microparticles carrying procoagulant phospholipids (PPL) and tissue factor (TF) in their membrane have attracted attention as possible contributors to the thrombogenic processes in cancers. The aims of this study were to assess the coagulation activity of platelet-poor plasma from 38 SCLC patients and to provide a detailed procoagulant profiling of small and large extracellular vesicles (EVs) isolated from these patients at the time of diagnosis, during and after treatment compared to 20 healthy controls. Hypercoagulability testing was performed by thrombin generation (TG), procoagulant phospholipid (PPL), TF activity, Protein C, FVIII activity and cell-free deoxyribonucleic acid (cfDNA), a surrogate measure for neutrophil extracellular traps (NETs). Our results revealed a coagulation activity that is significantly increased in the plasma of SCLC patients when compared to age-related healthy controls, but no substantial changes in coagulation activity during treatment and at follow-up. Although EVs in the patients revealed an increased PPL and TF activity compared with the controls, the TG profiles of EVs added to a standard plasma were similar for patients and controls. Finally, we found no differences in the coagulation profile of patients who developed VTE to those who did not, i.e. the tests could not predict VTE. In conclusion, we found that SCLC patients display an overall increased coagulation activity at time of diagnosis and during the disease, which may contribute to their higher risk of VTE.

Peri-interventional Triple Therapy With Dabigatran Improves Vasomotion and Promotes Endothelialization in Porcine Coronary Stenting Model

Objective: We evaluated the short and long-term effect of peri-interventional dabigatran therapy on vasomotion, endothelialization, and neointimal formation in a porcine coronary artery stenting model. Background: Stenting of coronary arteries induces local inflammation, impairs vasomotion and delays endothelialization. Methods: Twenty-eight animals underwent percutaneous coronary intervention (PCI) with drug eluting stents. Sixteen pigs started dabigatran therapy 4 days prior to PCI and continued for 4 days post-stenting, while 12 animals served as controls. Post-stenting dual antiplatelet therapy (75 mg clopidogrel and 100 mg aspirin) was continued in both groups until termination. Immediately post-stenting and at day 3 optical coherence tomography (OCT) was performed in all animals, followed by euthanasia of 8 dabigatran and 4 control animals. The remaining pigs (8 of each group) were followed up for 1 month, with control angiography and OCT. Tissue burden (degree of peri-strut structure-thrombus and/or fibrin) was evaluated. After euthanasia coronary arteries were harvested for in-vitro myometry and histology. Results: Thrombin generation was lower (p < 0.001) and tissue burden (0.83 ± 0.98 vs. 3.0 ± 2.45; p = 0.031) was significantly decreased in dabigatran treated animals. After 3 days post-PCI endothelium-dependent vasodilation was significantly improved (77 ± 40% vs. 41 ± 31%, p = 0.02) in dabigatran animals. Neither quantitative angiography nor histomorphometry showed differences between the groups. Endothelialization was faster in the dabigatran group as compared with controls (p = 0.045). Conclusion: Short-term peri-interventional triple therapy with dabigatran, aspirin, and clopidogrel led to an enhanced endothelium dependent vasodilation and faster endothelialization. However, neointimal formation 1-month after stent implantation was comparable between groups.

Plasma levels do not predict thrombin generation in patients taking direct oral anticoagulants

BACKGROUND

The antithrombotic effect of direct oral anticoagulants (DOAC) in specific clinical scenarios is difficult to assess.

OBJECTIVE

This study aimed to evaluate the effect of DOAC on thrombin generation (TG) in relation to their plasma level.

METHODS

Eighty patients newly started on anticoagulation were included, 20 patients for each DOAC-apixaban, edoxaban, rivaroxaban, and dabigatran. Plasma was sampled before DOAC (baseline), at plasma peak time, 6 and 12 hours after starting DOAC for quantification of drug levels and TG.

RESULTS

The baseline TG before DOAC intake showed inter-individual variability. All DOACs significantly prolonged lag time (LT) and time to peak (TTP), but did not change endogenous thrombin potential (ETP). Anti-Xa inhibitors but not dabigatran reduced thrombin peak, but the effect of apixaban at plasma peak was less pronounced (factor 1.6). LT and TTP prolongation of dabigatran was lower compared to anti-Xa inhibitors. All DOACs showed a nonlinear dose-response relationship, with the greatest antithrombotic effect at lower DOAC plasma levels. The inhibition of TG parameters between baseline and peak was parallel between individual patients but the coefficient of variation of TG was lower compared to drug levels.

CONCLUSION

The antithrombotic effect at DOAC peak plasma level measured by TG depends on the patient-specific baseline TG level and the drug-specific inhibition by the particular DOAC. Although peak plasma levels have a high variability, the variation of TG is lower compared to drug levels. Therefore, TG assays may be superior to plasma levels in the assessment of the intensity of anticoagulation.

Characterization of circulating thrombin in patients with septic shock: a prospective observational study

Septic shock is characterized by a dysregulated response to infection, hypotension and activation of the coagulation system. Markers of coagulation activation are commonly used to diagnose and monitor ensuing coagulopathies. In this study, we sought to determine levels of circulating thrombin in patients with septic shock. To characterize levels of circulating, active thrombin in patients with septic shock. 48 patients with septic shock were included in this prospective, observational study. Blood samples were obtained on admission, day 1, day 3 and day 6. Levels of active thrombin were measured using a standardized, clinically applicable oligonucleotide (aptamer)-based enzyme-capture assay (OECA). Thrombin levels were correlated with established indirect thrombin parameters, conventional coagulation tests, laboratory parameters, patient characteristics and outcome. Elevated levels of thrombin were detected in 27 patients (56.3%) during the course of the study. Thrombin levels were positively correlated with thrombin-antithrombin complexes (r = 0.30, p < 0.05) and negatively associated with FVII levels (r = - 0.28, p < 0.05). Thrombin levels on admission did not predict 30-day mortality (OR 0.82, 95% CI 0.23-2.92, p = 0.77). Circulating levels of active thrombin can be measured in a subset of patients with septic shock. Although thrombin levels are correlated with established markers of coagulation, they do not provide additional prognostic information.

Nephrotic syndrome disease activity is proportional to its associated hypercoagulopathy

INTRODUCTION

Nephrotic syndrome (NS) is associated with an acquired hypercoagulopathy that drives its strong predilection for life-threatening thrombosis. We previously demonstrated that hypercoagulopathy is proportional to NS disease severity in animal models. Therefore, hypercoagulopathy and disease severity may inform thrombosis risk and better guide therapeutic decision making. The objective of this study was thus to establish the relationship between disease severity and hypercoagulopathy in human NS.

MATERIALS AND METHODS

Thrombin generation assays (TGA) were performed on biorepository plasma samples from a prospective longitudinal NS cohort study. TGA was also determined on a separate cohort of incident NS patients. Multivariable regression was used to build NS-hypercoagulopathy relationship models.

RESULTS

Endogenous thrombin potential (ETP) was the TGA parameter most strongly correlated with NS severity and was proportional to conventional measures of NS disease activity including proteinuria, hypercholesterolemia, and hypoalbuminemia. The overall disease activity model was well correlated with ETP (R² = 0.38). The relationship with disease activity was confirmed in the second cohort. These models further revealed that ETP is related to disease activity in a manner dependent on remission status.

CONCLUSION

Consistent with our previously reported animal model observations, we found that the combination of proteinuria, hypercholesterolemia, and hypoalbuminemia correlated with ETP-defined hypercoagulopathy. Hypercoagulopathy improved significantly with partial or complete NS remission. These data are expected to inform studies designed to stratify thrombotic risk for patients with NS.

Optical Fingerprints of Proteases and Their Inhibited Complexes Provided by Differential Cross-Reactivity of Fluorophore-Labeled Single-Stranded DNA

The detection of proteases and their complexes with inhibitor proteins is of great importance for diagnosis and medical-treatment applications. In this study, we report a fingerprint-based sensor using an array of single-stranded DNAs (ssDNAs) labeled with environment-responsive 3'-carboxytetramethylrhodamine (TAMRA) for the identification of proteases. Four TAMRA-modified ssDNAs with different sequences solubilized in two different buffer solutions were incorporated in an array that was capable of generating fluorescent fingerprints unique to the proteases through diverse cross-reactive interactions, allowing the discrimination of (i) 8 proteases and (ii) 12 different mixtures of trypsin and its inhibitor protein (α₁-antitrypsin) by multivariate analysis. Constructing an array with TAMRA-modified DNA aptamers that bind to different sites of human thrombin provides fluorescence fingerprints that reflect a reduction of the exposed surface area of thrombin upon complexation with antithrombin III, even in the presence of human serum. We finally demonstrate the potential of hybridization with complementary DNAs as an effective means to easily double the fingerprint information for proteases. Our approach based on the cross-reactive capability of ssDNAs enables high-throughput fingerprint-based sensing that can be flexibly designed and easily constructed, not only for the identification of a variety of proteins including proteases but also for the evaluation of their complexation ability.

Differential binding cell-SELEX method to identify cell-specific aptamers using high-throughput sequencing

Aptamers have in recent years emerged as a viable alternative to antibodies. High-throughput sequencing (HTS) has revolutionized aptamer research by increasing the number of reads from a few (using Sanger sequencing) to millions (using an HTS approach). Despite the availability and advantages of HTS compared to Sanger sequencing, there are only 50 aptamer HTS sequencing samples available on public databases. HTS data in aptamer research are primarily used to compare sequence enrichment between subsequent selection cycles. This approach does not take full advantage of HTS because the enrichment of sequences during selection can be due to inefficient negative selection when using live cells. Here, we present a differential binding cell-SELEX (systematic evolution of ligands by exponential enrichment) workflow that adapts the FASTAptamer toolbox and bioinformatics tool edgeR, which are primarily used for functional genomics, to achieve more informative metrics about the selection process. We propose a fast and practical high-throughput aptamer identification method to be used with the cell-SELEX technique to increase the aptamer selection rate against live cells. The feasibility of our approach is demonstrated by performing aptamer selection against a clear cell renal cell carcinoma (ccRCC) RCC-MF cell line using the RC-124 cell line from healthy kidney tissue for negative selection.

Aptamers in the Therapeutics and Diagnostics Pipelines

Aptamers are short single-stranded DNA or RNA oligonucleotides that can selectively bind to small molecular ligands or protein targets with high affinity and specificity, by acquiring unique three-dimensional structures. Aptamers have the advantage of being highly specific, relatively small in size, non-immunogenic and can be easily stabilized by chemical modifications, thus allowing expansion of their diagnostic and therapeutic potential. Since the invention of aptamers in the early 1990s, great efforts have been made to make them clinically relevant for diseases like macular degeneration, cancer, thrombosis and inflammatory diseases. Furthermore, owing to the aforementioned advantages and unique adaptability of aptamers to point-of-care platforms, aptamer technology has created a stable niche in the field of in vitro diagnostics by enhancing the speed and accuracy of diagnoses. The aim of this review is to give an overview on aptamers, highlight the inherent therapeutic and diagnostic opportunities and challenges associated with them and present various aptamers that have reached therapeutic clinical trials, diagnostic markets or that have immediate translational potential for therapeutics and diagnostics applications.

Simple Methods and Rational Design for Enhancing Aptamer Sensitivity and Specificity

Aptamers are structured nucleic acid molecules that can bind to their targets with high affinity and specificity. However, conventional SELEX (Systematic Evolution of Ligands by EXponential enrichment) methods may not necessarily produce aptamers of desired affinity and specificity. Thus, to address these questions, this perspective is intended to suggest some approaches and tips along with novel selection methods to enhance evolution of aptamers. This perspective covers latest novel innovations as well as a broad range of well-established approaches to improve the individual binding parameters (aptamer affinity, avidity, specificity and/or selectivity) of aptamers during and/or post-SELEX. The advantages and limitations of individual aptamer selection methods and post-SELEX optimizations, along with rational approaches to overcome these limitations are elucidated in each case. Further the impact of chosen selection milieus, linker-systems, aptamer cocktails and detection modules utilized in conjunction with target-specific aptamers, on the overall assay performance are discussed in detail, each with its own advantages and limitations. The simple variations suggested are easily available for facile implementation during and/or post-SELEX to develop ultrasensitive and specific assays. Finally, success studies of established aptamer-based assays are discussed, highlighting how they utilized some of the suggested methodologies to develop commercially successful point-of-care diagnostic assays.