Protein C (PC) and protein S (PS) are vitamin K-dependent glycoproteins that play an important role in the regulation of blood coagulation as natural anticoagulants. PC is activated by thrombin and the resulting activated PC (APC) inactivates membrane-bound activated factor VIII and factor V. The free form of PS is an important cofactor of APC. Deficiencies in these proteins lead to an increased risk of venous thromboembolism; a few reports have also associated these deficiencies with arterial diseases. The degree of risk and the prevalence of PC and PS deficiency among patients with thrombosis and in those in the general population have been examined by several population studies with conflicting results, primarily due to methodological variability. The molecular genetic background of PC and PS deficiencies is heterogeneous. Most of the mutations cause type I deficiency (quantitative disorder). Type II deficiency (dysfunctional molecule) is diagnosed in approximately 5%-15% of cases. The diagnosis of PC and PS deficiencies is challenging; functional tests are influenced by several pre-analytical and analytical factors, and the diagnosis using molecular genetics also has special difficulties. Large gene segment deletions often remain undetected by DNA sequencing methods. The presence of the PS pseudogene makes genetic diagnosis even more complicated.

Two pentasaccharide sulfonic acids that were related to the antithrombin‐binding domain of heparin were prepared, in which two or three primary sulfate esters were replaced by sodium‐sulfonatomethyl moieties. The sulfonic‐acid groups were formed on a monosaccharide level and the obtained carbohydrate sulfonic‐acid esters were found to be excellent donors and acceptors in the glycosylation reactions. Throughout the synthesis, the hydroxy groups to be methylated were masked in the form of acetates and the hydroxy groups to be sulfated were masked with benzyl groups. The disulfonic‐acid analogue was prepared in a [2+3] block synthesis by using a trisaccharide disulfonic acid as an acceptor and a glucuronide disaccharide as a donor. For the synthesis of the pentasaccharide trisulfonic acid, a more‐efficient approach, which involved elongation of the trisaccharide acceptor with a non‐oxidized precursor of the glucuronic acid followed by post‐glycosidation oxidation at the tetrasaccharide level and a subsequent [1+4] coupling reaction, was elaborated. In vitro evaluation of the anticoagulant activity of these new sulfonic‐acid derivatives revealed that the disulfonate analogue inhibited the blood‐coagulation‐proteinase factor Xa with outstanding efficacy; however, the introduction of the third sulfonic‐acid moiety resulted in a notable decrease in the anti‐Xa activity. The difference in the biological activity of the disulfonic‐ and trisulfonic‐acid counterparts could be explained by the different conformation of their L‐iduronic‐acid residues.

Antithrombin (AT) is a serine protease inhibitor, its activity is highly accelerated by heparin. Mutations at the heparin-binding region lead to functional defect, type II heparin-binding site (IIHBS) AT deficiency. The aim of this study was to investigate and compare the molecular background of AT Budapest 3 (p.Leu131Phe, ATBp3), AT Basel (p.Pro73Leu), and AT Padua (p.Arg79His) mutations. Advanced in silico methods and heparin-binding studies of recombinant AT proteins using surface plasmon resonance method were used. Crossed immunoelectrophoresis and Differential Scanning Fluorimetry (NanoDSF) were performed in plasma samples. Heparin affinity of AT Padua was the lowest (KD = 1.08 × 10⁻⁶ M) and had the most severe consequences affecting the allosteric pathways of activation, moreover significant destabilizing effects on AT were also observed. KD values for AT Basel, ATBp3 and wild-type AT were 7.64 × 10⁻⁷ M, 2.15 × 10⁻⁸ M and 6.4 × 10⁻¹⁰ M, respectively. Heparin-binding of AT Basel was slower, however once the complex was formed the mutation had only minor effect on the secondary and tertiary structures. Allosteric activation of ATBp3 was altered, moreover decreased thermostability in ATBp3 homozygous plasma and increased fluctuations in multiple regions of ATBp3 were observed by in silico methods suggesting the presence of a quantitative component in the pathogenicity of this mutation due to molecular instability.

Background Deficiency of antithrombin increases risk of venous thromboembolism. We hypothesized that antithrombin deficiency affects fibrin clot structure and function. Methods We evaluated 148 patients (age: 38 [32–50] years; 70% women) with genetically confirmed antithrombin deficiency and 50 healthy controls. Fibrin clot permeability (K_s) and clot lysis time (CLT) along with thrombin generation capacity were assessed before and after antithrombin activity normalization in vitro. Results Antithrombin-deficient patients had lower antithrombin activity (−39%) and antigen levels (−23%) compared with controls (both p < 0.01). Prothrombin fragment 1 + 2 levels were 26.5% higher in patients with antithrombin deficiency than in controls along with 94% increased endogenous thrombin potential (ETP) and 108% higher peak thrombin (all p < 0.01). Antithrombin deficiency was associated with 18% reduced K_s and 35% prolonged CLT (both p < 0.001). Patients with type I (n = 65; 43.9%) compared with type II antithrombin deficiency (n = 83; 56.1%) had 22.5% lower antithrombin activity (p < 0.001) and despite similar fibrinogen levels, 8.4% reduced K_s, 18% prolonged CLT, and 30% higher ETP (all p < 0.01). Reduced K_s was associated with lower antithrombin antigen level (β = − 6.1, 95% confidence interval [CI]: −1.7 to −10.5), while prolonged CLT was associated with lower antithrombin antigen (β = − 69.6, 95% CI: −9.6 to −129.7), activity (β = − 2.4, 95% CI: −0.3 to −4.5), higher PAI-1 (β = 12.1, 95% CI: 7.7–16.5), and thrombin-activatable fibrinolysis inhibitor levels (β = 3.8, 95% CI: 1.9–5.7). Addition of exogenous antithrombin reduced ETP (−42%) and peak thrombin (−21%), and improved K_s (+8%) and CLT (−12%; all p < 0.01). Conclusion Our study suggests that enhanced thrombin generation and prothrombotic plasma fibrin clot phenotype can contribute to increased risk of thrombosis in patients with antithrombin deficiency. Conception and design of the study: M. Z.; data collection, analysis, and interpretation: J. N., J. C., M. E. M.-B., C. B.-P., Z. Ba., Z. Be., J. T., M. W., A. K., and A. U.; drafting the article: J. N. and M. Z.; revising the article: J. C., M. E. M.-B., C. B.-P., Z. Ba., Z. Be., J. T., M. W., A. K., and A. U. Received: 09 December 2022 Accepted: 26 March 2023 Article published online: 18 May 2023 © 2023. The Author(s). This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/) Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany