Investigation of the Differences in Antithrombin to Heparin Binding among Antithrombin Budapest 3, Basel, and Padua Mutations by Biochemical and In Silico Methods

Comparison of antithrombin activity assays in detection of patients with heparin binding site antithrombin deficiency: systematic review and meta-analysis

Antithrombin (AT) deficiency increases the risk for venous thromboembolism, therefore, a highly sensitive assay to identify this condition is crucial. The aim of this paper was to perform a meta-analysis comparing AT activities measured by different AT activity assays in patients with heparin binding site AT deficiency. In addition, the diagnostic sensitivity of selected assays was compared depending on the available data. An extensive literature search was performed considering results with publication date up to July 10, 2021. Seven relevant English-language observational studies, comparing AT activity measured by different AT activity assays in Caucasian Europeans with either the AT Budapest III or AT Padua I mutation were included in meta-analyses. There was no significant difference in AT activity between Labexpert and Innovance in patients with AT Budapest III (P = 0.567) and AT Padua I (P = 0.265), while AT activity determined by HemosIL was significantly higher compared to Innovance for both mutations (AT Budapest III: P < 0.001; AT Padua I: P < 0.001). These results are in line with the results of comparison of diagnostic sensitivity. In patients with AT Budapest III, the AT activity was also higher when measured with Berichrom compared to Innovance (P = 0.002), however, the results of comparison of diagnostic sensitivity across studies were variable. No significant difference (P = 0.117) in AT activity as well as diagnostic sensitivity was observed between Sta-Stachrom and Innovance. The results of our study suggest that Innovance, Labexpert and Sta-Stachrom are the most sensitive activity assays for detection of AT Budapest III and AT Padua I, whereas HemosIL showed considerably lower sensitivity for these two variants. As revealed in our study, the diagnostic sensitivity of AT activity assays to type II heparin binding site AT deficiency is different, and in some assays mutation dependent.

The Interaction of Factor Xa and IXa with Non-Activated Antithrombin in Michaelis Complex: Insights from Enhanced-Sampling Molecular Dynamics Simulations

The interaction between coagulation factors Xa and IXa and the activated state of their inhibitor, antithrombin (AT),have been investigated using X-ray diffraction studies. However, only mutagenesis data are available for non-activated AT. Our aim was to propose a model based on docking and advanced-sampling molecular dynamics simulations that can reveal the conformational behavior of the systems when AT is not binding a pentasaccharide. We built the initial structure for non-activated AT-FXa and AT-FIXa complexes using HADDOCK 2.4. The conformational behavior was studied using Gaussian accelerated molecular dynamics simulations. In addition to the docked complexes, two systems based on the X-ray structures were also simulated, with and without the ligand. The simulations revealed large variability in conformation for both factors. In the docking-based complex of AT-FIXa, conformations with stable Arg150-AT interactions can exist for longer time periods but the system also has a higher tendency for reaching states with very limited interaction with the "exosite" of AT. By comparing simulations with or without the pentasaccharide, we were able to gain insights into the effects of conformational activation on the Michaelis complexes. RMSF analysis and correlation calculations for the alpha-carbon atoms revealed important details of the allosteric mechanisms. Our simulations provide atomistic models for better understanding the conformational activation mechanism of AT against its target factors.

Antithrombin diagnostics by mass spectrometry: Development and analytical validation of a next-generation test

Background

Antithrombin deficiency is a rare but severe disorder leading to high risk of thrombosis. The current clinical care pathway relies on activity tests, which only provide overall functional information on the in vitro activity of antithrombin. However, antithrombin exists in many different forms, also known as proteoforms, with varying clinical phenotypes. Precision diagnostics, facilitated by mass spectrometry, provides a strategy to improve patient diagnostics by molecular characterization.

Objectives

To develop and analytically validate a mass spectrometry-based test for molecular characterization of antithrombin.

Methods

The test was analytically validated based on predefined analytical performance specifications. The validation covered imprecision, carryover, linearity, stability, analytical specificity, a provisional reference interval, and an explorative method comparison.

Results

The test passed the predefined analytical performance specifications with a mean within-laboratory imprecision of 5.9%, linearity between 0.08 and 2.58 μmol/L, and a provisional reference interval of 1.07 to 1.49 μmol/L. When measuring samples with a suspected quantitative deficiency, the test showed a good correlation with a commercial activity test (Pearson r = 0.88).

Conclusion

The test passed the validation, and we now envision the use of the test for exploration of the clinical relevance of specific antithrombin proteoforms. Puzzling cases of antithrombin deficiency, for instance, due to ambiguous activity results or an atypical clinical presentation, can be investigated by the LC-MRM mass spectrometry test serving as an add-on to the activity test and providing a molecular diagnosis. Clinical studies are planned to investigate the potential of the test to improve antithrombin diagnostics. Furthermore, the molecular information gained using the test may aid in establishing better risk stratification and a basis for personalized medicine.

Antithrombin Therapy: Current State and Future Outlook

Antithrombin (AT) is a natural anticoagulant pivotal in inactivating serine protease enzymes in the coagulation cascade, making it a potent inhibitor of blood clot formation. AT also possesses anti-inflammatory properties by influencing anticoagulation and directly interacting with endothelial cells. Hereditary AT deficiency is one of the most severe inherited thrombophilias, with up to 85% lifetime risk of venous thromboembolism. Acquired AT deficiency arises during heparin therapy or states of hypercoagulability like sepsis and premature infancy. Optimization of AT levels in individuals with AT deficiency is an important treatment consideration, particularly during high-risk situations such as surgery, trauma, pregnancy, and postpartum. Here, we integrate the existing evidence surrounding the approved uses of AT therapy, as well as potential additional patient populations where AT therapy has been considered by the medical community, including any available consensus statements and guidelines. We also describe current knowledge regarding cost-effectiveness of AT concentrate in different contexts. Future work should seek to identify specific patient populations for whom targeted AT therapy is likely to provide the strongest clinical benefit.

Computational analyses reveal fundamental properties of the AT structure related to thrombosis

Summary

Blood coagulation is a vital process for humans and other species. Following an injury to a blood vessel, a cascade of molecular signals is transmitted, inhibiting and activating more than a dozen coagulation factors and resulting in the formation of a fibrin clot that ceases the bleeding. In this process, antithrombin (AT), encoded by the SERPINC1 gene is a key player regulating the clotting activity and ensuring that it stops at the right time. In this sense, mutations to this factor often result in thrombosis-the excessive coagulation that leads to the potentially fatal formation of blood clots that obstruct veins. Although this process is well known, it is still unclear why even single residue substitutions to AT lead to drastically different phenotypes. In this study, to understand the effect of mutations throughout the AT structure, we created a detailed network map of this protein, where each node is an amino acid, and two amino acids are connected if they are in close proximity in the three-dimensional structure. With this simple and intuitive representation and a machine-learning framework trained using genetic information from more than 130 patients, we found that different types of thrombosis have emerging patterns that are readily identifiable. Together, these results demonstrate how clinical features, genetic data and in silico analysis are converging to enhance the diagnosis and treatment of coagulation disorders.

Supplementary information

Supplementary data are available at Bioinformatics Advances online.

Use of Real-World Data and Physiologically-Based Pharmacokinetic Modeling to Characterize Enoxaparin Disposition in Children With Obesity

Dosing guidance for children with obesity is often unknown despite the fact that nearly 20% of US children are classified as obese. Enoxaparin, a commonly prescribed low-molecular-weight heparin, is dosed based on body weight irrespective of obesity status to achieve maximum concentration within a narrow therapeutic or prophylactic target range. However, whether children with and without obesity experience equivalent enoxaparin exposure remains unclear. To address this clinical question, 2,825 anti-activated factor X (anti-Xa) surrogate concentrations were collected from the electronic health records of 596 children, including those with obesity. Using linear mixed-effects regression models, we observed that 4-hour anti-Xa concentrations were statistically significantly different in children with and without obesity, even for children with the same absolute dose (P = 0.004). To further mechanistically explore obesity-associated differences in anti-Xa concentration, a pediatric physiologically-based pharmacokinetic (PBPK) model was developed in adults, and then scaled to children with and without obesity. This PBPK model incorporated binding of enoxaparin to antithrombin to form anti-Xa and elimination via heparinase-mediated metabolism and glomerular filtration. Following scaling, the PBPK model predicted real-world pediatric concentrations well, with an average fold error (standard deviation of the fold error) of 0.82 (0.23) and 0.87 (0.26) in children with and without obesity, respectively. PBPK model simulations revealed that children with obesity have at most 20% higher 4-hour anti-Xa concentrations under recommended, total body weight-based dosing compared to children without obesity owing to reduced weight-normalized clearance. Enoxaparin exposure was better matched across age groups and obesity status using fat-free mass weight-based dosing.

Unraveling a borderline antithrombin deficiency case with quantitative mass spectrometry

Antithrombin deficiency diagnostics by first-line activity tests suffer from a lack of sensitivity sometimes resulting in diagnostic uncertainty. We here present a case of a woman with recurrent pregnancy loss who was screened for inherited thrombophilia. Antithrombin activity was borderline low, resulting in uncertainty about the correct diagnosis. Using a mass spectrometry-based test, the antithrombin protein of the patient was characterized at the molecular level and a heterozygous p.Pro73Leu mutation was identified. The mutation, also known as antithrombin "Basel," increases the risk of venous thromboembolism and obstetric complications. This case is illustrative of current antithrombin deficiency screening, in which diagnoses may be missed by traditional diagnostics. Next-generation protein diagnostics by mass spectrometry provides molecular insight into the proteoforms present in vivo. This information is essential for laboratory specialists and clinicians to unambiguously diagnose patients and will aid in evolving healthcare from traditional to precision diagnostics.

Ameliorative Effect of Flavonoid-rich Extracts from Gongronema latifolium Against Diabetic Cardiomyopathy via serpin A3 and socs3-a in Streptozocin Treated Rats

INTRODUCTION

The present study access the effect of the flavonoid-rich isolate from Gongronema latifolium against cardiomyopathy in a streptozotocin-rich extract.

MATERIAL AND METHODS

The flavonoid-rich isolate from G. latifolium leaf (FREGL) was prepared using a standard method. A single injection of streptozotocin was induced into the experimental rats. The experimental animals were divided into five groups as non-diabetic rats, diabetic control, diabetic rats administered low and high doses of FREGL (13 and 26 mg/kg), and metformin glibenclamide orally for 21 days. Hence, the experimental animals were sacrificed; blood and heart were harvested to determine diverse biochemical parameters, including the gene expressions of serpin A₃ and socs3-a as well as histological examination.

RESULTS

The results demonstrated that FREGL significantly (p < 0.05) reduced fasting blood glucose, total cholesterol, low density lipoprotein (LDL), triglyceride (TG), lipid peroxidation levels, as well as the activities of lactate dehydrogenase and creatine kinase-MB, including the relative gene expressions of serpin A₃ and Socs3-A in diabetic rats. Also, diabetic rats that received different doses of FREGL showed a substantial rise in insulin and high density lipoprotein (HDL) levels, and antioxidant enzyme activities, as well as, normal histoarchitecture of the heart tissues.

CONCLUSION

Therefore, FREGL may be beneficial in alleviating diabetic cardiomyopathy.