Recombinant Destabilase from Hirudo medicinalis Is Able to Dissolve Human Blood Clots In Vitro

Leeches are amazing animals that can be classified as conditionally poisonous animals since the salivary cocktail they produce is injected directly into the victim, and its components have strictly defined biological purposes, such as preventing blood clot formation. Thrombolytic drugs are mainly aimed at treating newly formed blood clots. Aged clots are stabilized by a large number of isopeptide bonds that prevent the action of thrombolytics. These bonds are destroyed by destabilase, an enzyme of the leech’s salivary glands. Here, we conducted a pilot study to evaluate the feasibility and effectiveness of the use of destabilase in relation to blood clots formed during real pathological processes. We evaluated the isopeptidase activity of destabilase during the formation of a stabilized fibrin clot. We showed that destabilase does not affect the internal and external coagulation cascades. We calculated the dose–response curve and tested the ability of destabilase to destroy isopeptide bonds in natural blood clots. The effect of aged and fresh clots dissolving ability after treatment with destabilase coincided with the morphological characteristics of clots during surgery. Thus, recombinant destabilase can be considered as a potential drug for the treatment of aged clots, which are difficult to treat with known thrombolytics.

Postpartum Hemorrhage in Heterozygote Factor XIII Deficient Women Compared With Healthy Women. A Cross-Sectional Experience From Iran

Postpartum hemorrhage (PPH) is a major cause of maternal mortality, which is a common clinical manifestation in women with rare bleeding disorders. In this study, we compare PPH and its complications in heterozygote factor XIII (FXIII) deficient women with healthy women. In this cross sectional case study, 50 women with heterozygote FXIII deficiency and 50 healthy women are evaluated. Data were initially collected by interviewing the women who were receiving FXIII replacement therapy after their childbirths. Data were analysed using SPSS (Version 22) and a P-value of less than .05 was considered statistically significant. The mean age in the patient and control groups were 31.2 and 32.5 years respectively. The occurring rate of PPH in the patient group was significantly higher than the control group (34% vs 2%) (P-value <.0001). None of the confounding variables such as maternal age, gestational age, numbers, and types of delivery in women with PPH showed any significant differences between the control and patient groups. According to the results of this study, the risk of PPH (early and late), miscarriage, and menorrhagia in women who are heterozygous for FXIII deficiency is significantly higher than healthy women. However, the effect of other factors such as maternal age, gestational age, number, and type of delivery require further studies to delineate any confounding factors.

Acute spontaneous subdural hematoma as an inaugural presentation of systemic lupus erythematosus with acquired factor XIII deficiency: a case report

Acute spontaneous subdural hematoma is a rare clinical situation. Among its various etiologies, underlying coagulopathy is associated with a considerable risk of mortality. A 43-year-old female patient with no comorbidity and no personal or family history of bleeding disorders, consulted for acute and intense headache. The brain computed tomography (CT) scan showed a compressive left fronto-parietal acute subdural hematoma. The cerebral magnetic resonance angiography and routine hemostasis workup were normal. Factor XIII activity was low at 41% and the etiological investigation was consistent with the diagnosis of systemic lupus erythematosus. Surgical evacuation of the hematoma, factor XIII supplementation and systemic corticosteroid therapy with hydroxy chloroquine resulted in a favorable outcome. Acquired factor XIII deficiency should be systematically investigated for any acute spontaneous subdural hematoma with a normal hemostasis assessment in an adult with no personal or family history of hemorrhage.

Mild Acquired Factor XIII Deficiency and Clinical Relevance at the ICU-A Retrospective Analysis

Acquired FXIII deficiency is a relevant complication in the perioperative setting; however, we still have little evidence about the incidence and management of this rarely isolated coagulopathy. This study aims to help find the right value for the substitution of patients with an acquired mild FXIII deficiency. In this retrospective single-center cohort study, we enrolled critically ill patients with mild acquired FXIII deficiency (>5% and ≤70%) and compared clinical and laboratory parameters, as well as pro-coagulatory treatments. The results of the present analysis of 104 patients support the clinical relevance of FXIII activity out of the normal range. Patients with lower FXIII levels, beginning at <60%, had lower minimum and maximum hemoglobin values, corresponding to the finding that patients with a minimum FXIII activity of <50% needed significantly more packed red blood cells. FXIII activity correlated significantly with general coagulation markers such as prothrombin time, activated partial thromboplastin time, and fibrinogen. Nevertheless, comparing the groups with a cut-off of 50%, the amount of fresh frozen plasma, thrombocytes, PPSB, AT-III, and fibrinogen given did not differ. These results indicate that a mild FXIII deficiency occurring at any point of intensive care unit stay is also probably relevant for the total need of packed red blood cells, independent of pro-coagulatory management. In alignment with the ESAIC guidelines, the measurement of FXIII in critically ill patients with the risk of bleeding and early management, with the substitution of FXIII at levels <50%-60%, could be suggested.

Factor XIII Cross-Linked Adhesive Chitosan Hydrogels

Biomedical adhesives have been found to be an attractive alternative to suturing in several circumstances. However, to date most of the clinically approved formulations are based on synthetic and highly reactive toxic chemicals. In this work, we aimed to combine for the first time the bioactive properties of the cationic polysaccharide chitosan and its intrinsic electrostatic binding to negatively charged tissues with the biocompatible and clinically compliant enzymatic cross-linking scheme of fibrin glue. This synergistic activity led to the generation of a transglutaminase Factor XIII cross-linkable chitosan formulation with fast gelation kinetics, tunable mechanical properties, antibacterial activity, and strong adhesion to cartilage.

Pathological coagulation parameters in as many as 54 patients with autoimmune acquired factor XIII deficiency due to anti-factor XIII autoantibodies

INTRODUCTION

Autoimmune factor XIII (FXIII) deficiency (AiF13D) due to anti-FXIII autoantibodies is an extremely rare, life-threatening bleeding disorder that mostly occurs in the elderly. The number of patients diagnosed with AiF13D has been increasing in Japan, probably because of the nationwide survey on AiF13D supported by the Japanese Ministry of Health, Labour and Welfare.

AIM

To explore the pathologic characteristics of coagulation parameters in AiF13D.

METHODS

AiF13D-suspected cases were consulted, and underwent unified/integrated coagulation screening and were definitively diagnosed as AiF13D separately.

RESULTS

AiF13D patients had lower FXIII antigen levels than non-AiF13D patients, but their values overlapped. Among a series of 22-item screening tests and their resulting parameters, the 'FXIII inhibitory potential' yielded by a 1:1 mixing test of the patient's and healthy control's plasma and its 'residual FXIII activity' in 54 AiF13D cases were most distinguishable from 139 non-AiF13D cases, followed by FXIII activity per se and FXIII-specific activity. While the cross-linked α₂ -plasmin inhibitor level reduced, the levels of D-dimer, fibrin/fibrinogen degradation products and plasmin-plasmin inhibitor complex increased, probably because the patients' haematoma nonspecifically induced secondary fibrinolysis in both AiF13D and non-AiF13D patients.

CONCLUSION

AiF13D appears to induce a hypocoagulopathy combined with a hyper-fibrinolytic state secondary to severe FXIII deficiency caused by anti-FXIII autoantibodies, and the consequent bleeding further modifies its pathological conditions. In addition, the 1:1 mixing test of FXIII activity was confirmed to be a reliable screening method for AiF13D, especially when its derivative parameter, such as the 'FXIII inhibitory potential' or 'FXIII inhibitory potential ratio', is employed.

Factor XIII Activity Might Already Be Impaired before Veno-Venous ECMO in ARDS Patients: A Prospective, Observational Single-Center Cohort Study

Direct complications in patients receiving extracorporeal (veno-venous) membrane oxygenation (vvECMO) are mainly either due to bleeding or thromboembolism. We aimed to evaluate the course of routine coagulation parameters and the activity of different coagulation factors—with special focus on factor XIII (F XIII)—before, during and after vvECMO in acute respiratory distress syndrome (ARDS) patients. The activity of coagulation factors and rotational thrombelastometry were analyzed in 20 ECMO patients before (T-1) and 6 h (T0), one (T1), three (T3) and seven days (T7) after the implantation, as well as one and three days after the termination of ECMO. F XIII activity was already severely decreased to 37% (30/49) before ECMO. F XIII activity was the only coagulation factor continuously declining during vvECMO, being significantly decreased at T3 (31% (26/45) vs. 24% (18/42), p = 0.0079) and T7 (31% (26/45) vs. 23% (17/37), p = 0.0037) compared to T0. Three days after termination of vvECMO, platelet count and fibrinogen nearly doubled and factors II, V, XI and XIII showed spontaneous significant increases. Severe ARDS patients showed a considerably diminished factor XIII activity before vvECMO initiation and its activity continuously declined later on. Thus, incorporation of F XIII monitoring into the regular hemostaseologic routine during vvECMO therapy seems advisable. Due to the potential development of a hypercoagulatory state after the termination of vvECMO, tight hemostasiologic monitoring should persist in the initial phase after ECMO termination.

Incorporation of α2-Plasmin Inhibitor into Fibrin Clots and Its Association with the Clinical Outcome of Acute Ischemic Stroke Patients

Cross-linking of α2-plasmin inhibitor (α2-PI) to fibrin by activated factor XIII (FXIIIa) is essential for the inhibition of fibrinolysis. Little is known about the factors modifying α2-PI incorporation into the fibrin clot and whether the extent of incorporation has clinical consequences. Herein we calculated the extent of α2-PI incorporation by measuring α2-PI antigen levels from plasma and serum obtained after clotting the plasma by thrombin and Ca²⁺. The modifying effect of FXIII was studied by spiking of FXIII-A-deficient plasma with purified plasma FXIII. Fibrinogen, FXIII, α2-PI incorporation, in vitro clot-lysis, soluble fibroblast activation protein and α2-PI p.Arg6Trp polymorphism were measured from samples of 57 acute ischemic stroke patients obtained before thrombolysis and of 26 healthy controls. Increasing FXIII levels even at levels above the upper limit of normal increased α2-PI incorporation into the fibrin clot. α2-PI incorporation of controls and patients with good outcomes did not differ significantly (49.4 ± 4.6% vs. 47.4 ± 6.7%, p = 1.000), however it was significantly lower in patients suffering post-lysis intracranial hemorrhage (37.3 ± 14.0%, p = 0.004). In conclusion, increased FXIII levels resulted in elevated incorporation of α2-PI into fibrin clots. In stroke patients undergoing intravenous thrombolysis treatment, α2-PI incorporation shows an association with the outcome of therapy, particularly with thrombolysis-associated intracranial hemorrhage.

Fibrinogen Replacement Therapy for Traumatic Coagulopathy: Does the Fibrinogen Source Matter?

Fibrinogen is the first coagulation protein to reach critically low levels during traumatic haemorrhage. There have been no differential effects on clinical outcomes between the two main sources of fibrinogen replacement: cryoprecipitate and fibrinogen concentrate (Fg-C). However, the constituents of these sources are very different. The aim of this study was to determine whether these give rise to any differences in clot stability that may occur during trauma haemorrhage. Fibrinogen deficient plasma (FDP) was spiked with fibrinogen from cryoprecipitate or Fg-C. A panel of coagulation factors, rotational thromboelastography (ROTEM), thrombin generation (TG), clot lysis and confocal microscopy were performed to measure clot strength and stability. Increasing concentrations of fibrinogen from Fg-C or cryoprecipitate added to FDP strongly correlated with Clauss fibrinogen, demonstrating good recovery of fibrinogen (r² = 0.99). A marked increase in Factor VIII, XIII and α₂-antiplasmin was observed in cryoprecipitate (p < 0.05). Increasing concentrations of fibrinogen from both sources were strongly correlated with ROTEM parameters (r² = 0.78-0.98). Cryoprecipitate therapy improved TG potential, increased fibrinolytic resistance and formed more homogeneous fibrin clots, compared to Fg-C. In summary, our data indicate that cryoprecipitate may be a superior source of fibrinogen to successfully control bleeding in trauma coagulopathy. However, these different products require evaluation in a clinical setting.

Factor XIII and Fibrin Clot Properties in Acute Venous Thromboembolism

Coagulation factor XIII (FXIII) is converted by thrombin into its active form, FXIIIa, which crosslinks fibrin fibers, rendering clots more stable and resistant to degradation. FXIII affects fibrin clot structure and function leading to a more prothrombotic phenotype with denser networks, characterizing patients at risk of venous thromboembolism (VTE). Mechanisms regulating FXIII activation and its impact on fibrin structure in patients with acute VTE encompassing pulmonary embolism (PE) or deep vein thrombosis (DVT) are poorly elucidated. Reduced circulating FXIII levels in acute PE were reported over 20 years ago. Similar observations indicating decreased FXIII plasma activity and antigen levels have been made in acute PE and DVT with their subsequent increase after several weeks since the index event. Plasma fibrin clot proteome analysis confirms that clot-bound FXIII amounts associated with plasma FXIII activity are decreased in acute VTE. Reduced FXIII activity has been associated with impaired clot permeability and hypofibrinolysis in acute PE. The current review presents available studies on the role of FXIII in the modulation of fibrin clot properties during acute PE or DVT and following these events. Better understanding of FXIII’s involvement in the pathophysiology of acute VTE might help to improve current therapeutic strategies in patients with acute VTE.

Role, Laboratory Assessment and Clinical Relevance of Fibrin, Factor XIII and Endogenous Fibrinolysis in Arterial and Venous Thrombosis

Diseases such as myocardial infarction, ischaemic stroke, peripheral vascular disease and venous thromboembolism are major contributors to morbidity and mortality. Procoagulant, anticoagulant and fibrinolytic pathways are finely regulated in healthy individuals and dysregulated procoagulant, anticoagulant and fibrinolytic pathways lead to arterial and venous thrombosis. In this review article, we discuss the (patho)physiological role and laboratory assessment of fibrin, factor XIII and endogenous fibrinolysis, which are key players in the terminal phase of the coagulation cascade and fibrinolysis. Finally, we present the most up-to-date evidence for their involvement in various disease states and assessment of cardiovascular risk.

Trimester-specific thromboelastic values and coagulation activation markers in pregnancy compared across trimesters and compared to the nonpregnant state

INTRODUCTION

Rotational thromboelastometry (ROTEM) rapidly identifies deficits underlying coagulopathy during massive hemorrhage. Prompt coagulopathy correction is balanced with the risk of blood product overutilization, making the ability to quickly target therapy highly desirable. However, data about ROTEM reference ranges in pregnancy are limited. We hypothesized that ROTEM parameters change across trimesters of pregnancy and differ from the nonpregnant state. Also, we sought to identify which hemostatic test best predicts coagulation activation during pregnancy.

METHODS

A prospective cohort study in healthy pregnant patients in the first (n = 34), second (n = 34), and third trimesters (n = 41) against healthy, nonpregnant controls (n = 33) was performed. Citrated blood was collected, and ROTEM, complete blood count, and plasma-based assays of coagulation were performed. Mean ± SD or median [IQR] were compared across trimesters and between each trimester against the nonpregnant state. ROTEM parameters vs. plasma-based assays were also compared.

RESULTS

Maximum clot firmness and A10 in FIBTEM correlated strongly with fibrinogen level. INTEM and EXTEM values demonstrated only weak to modest correlation with corresponding tests using plasma assays. Thrombin antithrombin complex (TAT) increased from the first trimester onward, whereas other coagulation activation markers did not show difference compared with control group.

CONCLUSION

Rotational thromboelastometry parameters differ variably across trimesters of pregnancy and compared with the nonpregnant state. The development and use of pregnancy-specific values are critical to the proper clinical interpretation of ROTEM in women with serious hemorrhage during different stages in pregnancy. TAT was the earliest laboratory marker for coagulation activation among others.

Clinical Validation of an Automated Fluorogenic Factor XIII Activity Assay Based on Isopeptidase Activity

Hereditary factor XIII (FXIII) deficiency is a rare autosomal bleeding disorder which can cause life-threatening bleeding. Acquired deficiency can be immune-mediated or due to increased consumption or reduced synthesis. The most commonly used screening test is insensitive, and widely used quantitative assays have analytical limitations. The present study sought to validate Technofluor FXIII Activity, the first isopeptidase-based assay available on a routine coagulation analyser, the Ceveron s100. Linearity was evidenced throughout the measuring range, with correlation coefficients of >0.99, and coefficients of variation for repeatability and reproducibility were <5% and <10%, respectively. A normally distributed reference range of 47.0–135.5 IU/dL was derived from 154 normal donors. Clinical samples with Technofluor FXIII Activity results between 0 and 167.0 IU/dL were assayed with Berichrom^® FXIII Activity, a functional ammonia release assay, and the HemosIL^™ FXIII antigen assay, generating correlations of 0.950 and 0.980, respectively. Experiments with a transglutaminase inhibitor showed that Technofluor FXIII Activity can detect inhibition of enzymatic activity. No interference was exhibited by high levels of haemolysis and lipaemia, and interference by bilirubin was evident at 18 mg/dL, a level commensurate with severe liver disease. Technofluor FXIII Activity is a rapid, accurate and precise assay suitable for routine diagnostic use with fewer interferents than ammonia release FXIII activity assays.

Relation of α2-Antiplasmin Genotype and Genetic Determinants of Fibrinogen Synthesis and Fibrin Clot Formation with Vascular Endothelial Growth Factor Level in Axial Spondyloarthritis

Objective: Coagulation and fibrinolysis are interrelated with the expression of vascular endothelial growth factor (VEGF), which frequently is increased in axial spondyloarthritis (axSpA). We tested whether (i) α₂-antiplasmin (A2AP) Arg6Trp, (ii) fibrinogen, factor XIII A-subunit or B-subunit genotypes are associated with VEGF levels and assessed whether the known association between elevated VEGF and radiographic spinal progression in axSpA depends on genetic background. Methods: One hundred and eighty-six axSpA patients from the German Spondyloarthritis Inception Cohort were genotyped, characterized for VEGF levels, and statistically analyzed. The association between VEGF and radiographic spinal progression was assessed in dependence on genetic background in stratified analyses. Results: A2AP 6Trp carriage was associated with VEGF elevation (OR: 2.37, 95% CI: 1.06–5.29) and VEGF levels (6Trp, 455 ± 334 pg/mL; 6Arg/Arg, 373 ± 293 pg/mL; p < 0.008). Association between elevated VEGF and radiographic spinal progression in axSpA (OR: 3.11, 95% CI: 1.02–8.82) depended remarkably on the fibrinogen (FGA) genotype. When considering axSpA patients with elevated VEGF, in FGA rs6050A>G wild types, 42.1% of patients (8 of 19) progressed, while in G-allele carriers, no radiographic progression happened (0 of 13) (p < 0.04). Conclusions: The A2AP Arg6Trp genotype seems to influence VEGF levels in axSpA. The predictive value of VEGF elevations in respect of radiographic spinal progression in axSpA depends on FGA genotypes.

Terminal Phase Components of the Clotting Cascade in Patients with End-Stage Renal Disease Undergoing Hemodiafiltration or Hemodialysis Treatment

Hemostasis disorder in patients with end-stage renal disease (ESRD) is frequently associated with bleeding diathesis but it may also manifest in thrombotic complications. Analysis of individual coagulation and fibrinolytic factors may shed light on the background of this paradox situation. Here we explored components essential for fibrin formation/stabilization in ESRD patients being on maintenance hemodiafiltration (HDF) or hemodialysis (HD). Pre-dialysis fibrinogen, factor XIII (FXIII) antigen concentrations and FXIII activity were elevated, while α₂-plasmin inhibitor (α₂PI) activity decreased. The inflammatory status, as characterized by C-reactive protein (CRP) was a key determinant of fibrinogen concentration, but not of FXIII and α₂PI levels. During a 4-h course of HDF or HD, fibrinogen concentration and FXIII levels gradually elevated. When compensated for the change in plasma water, i.e., normalized for plasma albumin concentration, only FXIII elevation remained significant. There was no difference between HDF and HD treatments. Individual HDF treatment did not influence α₂PI activity, however after normalization it decreased significantly. HD treatment had a different effect, α₂PI activities became elevated but the elevation disappeared after normalization. Elevated fibrinogen and FXIII levels in ESRD patients might contribute to the increased thrombosis risk, while decreased α₂PI activity might be associated with elevated fibrinolytic potential.

Acquired factor XIII deficiency in patients under therapeutic plasma exchange: A poorly explored etiology

INTRODUCTION

Factor XIII (FXIII) deficiency may cause bleeding under certain clinical circumstances. Therapeutic plasma exchange (TPE) may lead to a transient deficiency.

OBJECTIVES

To describe the clinical evolution of patients with acquired FXIII deficiency secondary to TPE.

METHODS

We respectively studied a cohort of consecutive patients from 2014 to 2019 who were treated with TPE with FXIII levels <50%. The FXIII was measured after the start of the TPE course, on days between the TPE sessions, due to suspected acquired deficiency. All TPE were performed using continuous flow cell separator. In all cases, the initial replacement fluid applied was albumin. Apheresis procedures were held at 24to 48 hours intervals.

RESULTS

Eighteen patients were included, 13 of them were recipients of kidney transplants. The main TPE prescription was humoral rejection. Median FXIII at diagnosis (measured on days between sessions of the TPE course) was 19%(IQR17-25). The median of apheresis procedures before measurement of FXIII was 3(IQR2-4). Among the total cohort, 10 patients suffered hemorrhages. None of the patients without history of kidney transplants had bleeding (n = 5), however, 10/13 with kidney transplants did. Five kidney transplant patients received therapy with FXIII concentrate because of life-threatening bleeding. In all cases, the bleeding stopped within the first 24 hours. All patients had their FXIII levels measured again after finishing the TPE course, with normal results.

CONCLUSIONS

TPE is an under-diagnosed cause of acquired FXIII deficiency since routine coagulation tests remain unaltered. It might cause major bleeding, particularly in patients with a recent history of surgery like kidney transplants.

Autoimmune factor XIII deficiency with unusual laboratory and clinical phenotype

Hemorrhagic diathesis due to anti-factor XIII (FXIII) autoantibody is a rare but severe disorder. Challenges of the diagnosis and treatment is demonstrated by the case of a 67-year-old female without previous bleeding history, who suffered a huge muscular hematoma. Without blank subtraction 18% plasma FXIII activity was measured; however, after correction for blank the activity was below the limit of detection and the lack of fibrin cross-linking in the patient's plasma confirmed the latter result. FXIII-A2 antigen was not detectable by enzyme-linked immunosorbent assay (ELISA); however, it was well detected by western blotting. The autoantibody showed high affinity toward FXIII-A2 . Its considerable inhibitory activity was demonstrated by high titer in Bethesda units and the low immunoglobulin G concentration required for inhibition. The main biochemical effect was the inhibition of Ca2+ -induced activation. Eradication therapy was only partially successful. Four months after the last hemorrhagic event the patient suffered deep vein thrombosis complicated by pulmonary embolism.

The impact of prepartum factor XIII activity on postpartum blood loss

BACKGROUND

Postpartum hemorrhage (PPH), a major cause of maternal mortality, has several known risk factors but frequently occurs unexpectedly. PPH incidence and related maternal morbidity and mortality are rising worldwide.

OBJECTIVE

To evaluate the impact of defined prepartum blood coagulation parameters on postpartum blood loss.

METHODS

This single-center, prospective cohort study analyzed prepartum activities of coagulation factors II and XIII and fibrinogen levels in 1300 women. Blood samples were obtained at labor onset and analyzed only after the last patient had delivered, to prevent a potential treatment bias. Blood loss was quantified using a validated technique. The influence of coagulation factors on measured blood loss was assessed by continuous outcome logistic regression.

RESULTS

Prepartum factor XIII activity strongly influenced measured blood loss: every one unit (%) increase in prepartum factor XIII was associated with an odds ratio of 1.011 (95% confidence interval, 1.006-1.015; P < .001) to keep blood loss below any given cut-off level. For illustration, this suggests that a 30% increase in factor XIII activity increases the odds of not suffering PPH (defined as blood loss ≥500 mL) by 38.9%. This effect remained significant after stratification for the delivery mode, when correcting for other risk factors, and was independent of the statistical model used. Factor II but not fibrinogen had a partially comparable, but much less pronounced, effect.

CONCLUSION

In the largest population analyzed for the influence of prepartum coagulation factors on PPH to date, prepartum factor XIII activity had a strong impact on postpartum blood loss across every statistical model and clinical subgroup. Our hypothesis that early replenishment of factor XIII levels might constitute a new tool in the prevention and effective early treatment of PPH should be evaluated in future trials.

N-glycosylation of blood coagulation factor XIII subunit B and its functional consequence

BACKGROUND

The protective/inhibitory B subunits of coagulation factor XIII (FXIII-B) is a ~80 kDa glycoprotein containing two N-glycosylation sites. Neither the structure nor the functional role of the glycans on FXIII-B has been explored.

OBJECTIVE

To reveal the glycan structures linked to FXIII-B, to design a method for deglycosylating the native protein, to find out if deglycosylation influences the dimeric structure of FXIII-B and its clearance from the circulation.

METHODS

Asparagine-linked carbohydrates were released from human FXIIII-B by PNGase F digestion. The released N-linked oligosaccharides were fluorophore labeled and analyzed by capillary electrophoresis. Structural identification utilized glycan database search and exoglycosidase digestion based sequencing. The structure of deglycosylated FXIII-B was investigated by gel filtration. The clearance of deglycosylated and native FXIII-B from plasma was compared in FXIII-B knock out mice.

RESULTS

PNGase F completely removed N-glycans from the denatured protein. Deglycosylation of the native protein was achieved by repeated digestion at elevated PNGase F concentration. The total N-glycan profile of FXIII-B featured nine individual structures; three were fucosylated and each structure contained at least one sialic acid. Deglycosylation did not change the native dimeric structure of FXIII-B, but accelerated its clearance from the circulation of FXIII-B knock out mice.

CONCLUSION

Characterization of the glycan moieties attached to FXIII-B is reported for the first time. Complete deglycosylation of the native protein was achieved by a deglycosylation workflow. The associated glycan structure is not required for FXIII-B dimer formation, but it very likely prolongs the half-life of FXIII-B in the plasma.

Structure-Based Design of FXIIIa-Blockers: Addressing a Transient Hydrophobic Pocket in the Active Site of FXIIIa

Blood coagulation factor XIII (FXIII, F13) is considered to be a promising target for anticoagulants with reduced bleeding risk because of its unique position in the coagulation cascade downstream of thrombin. However, until now, no potent drug addressing FXIII has been available, indeed no compound has even entered clinical trials yet. In 2013, we published the co-crystal structure of FXIII in the active state (FXIIIa°), thereby providing a detailed map of the active site for the rational design of potent FXIIIa blockers. Here we report, for the first time, a structure-based approach to improving the affinity of FXIIIa inhibitors. FXIII was crystallized in complex with a methyl thiazole moiety to address a novel transient hydrophobic pocket close to the catalytic center. By subsequent structure-based design to rationalize the introduction of an ethyl ester, the potency of the inhibitor was improved significantly compared to that of the parent lead compound. The occupancy of the hydrophobic pocket described here might turn out to be a key step in the development of a potent reversible and orally available FXIIIa blocker.

The factor XIII-A Val34Leu polymorphism decreases whole blood clot mass at high fibrinogen concentrations

BACKGROUND

Factor XIII (FXIII) promotes fibrin crosslinking and red blood cell (RBC) retention in clots. The FXIII-A polymorphism, Val34Leu, is associated with protection against venous thrombosis. This effect is hypothesized to result from fibrinogen concentration-dependent changes in fibrin structure. Effects of the FXIII-A Val34Leu polymorphism in whole blood clots have not been investigated.

AIM

Characterize effects of FXIII-A Val34Leu polymorphism and fibrinogen on whole blood clots.

METHODS

We isolated platelet-poor plasmas from human donors (FXIIIVal/Val , FXIIIVal/Leu , FXIIILeu/Leu ), reconstituted plasmas with platelets and RBCs, and triggered clotting. We assessed contributions of gender, age, clotting times, thrombin generation, FXIII activity, FXIII-A Val34Leu polymorphism, and fibrinogen to clot mass. We also reconstituted FXIII-depleted plasma with platelets, RBCs, and purified FXIIIVal/Val or FXIIILeu/Leu , varied fibrinogen, and characterized effects on clot mass.

RESULTS

Clot mass was associated with age, fibrinogen, prothrombin time, and thrombin generation. Clots reconstituted with plasmas from individuals with FXIII-AVal/Val and FXIII-AVal/Leu did not differ in mass from clots with FXIII-ALeu/Leu . However, clots containing a 34Val allele demonstrated a fibrinogen concentration-dependent increase in mass, whereas clots with homozygous 34Leu did not. In plasmas with high fibrinogen, mass was higher for clots with 34Val alleles compared with clots with homozygous 34Leu. In clots reconstituted with purified FXIII, increasing fibrinogen enhanced clot mass in the presence of 34Val, but decreased mass in the presence of 34Leu.

CONCLUSIONS

FXIII 34Leu mitigates the effect of elevated fibrinogen on whole blood clot mass. The Val34Leu polymorphism may protect against venous thrombosis by reducing clot mass.

Combined presence of coagulation factor XIII V34L and plasminogen activator inhibitor 1 4G/5G gene polymorphisms significantly contribute to recurrent pregnancy loss in Serbian population

Background

Recurrent pregnancy loss (RPL) is a heterogeneous condition affecting up to 5% of women of reproductive age. Inherited thrombophilia have been postulated as one of the causes of RPL. Here we examined the prevalence of nine thrombophilic gene polymorphisms among women with history of recurrent miscarriages and fertile controls.

Methods

The study included 70 women with history of at least three early pregnancy losses and 31 fertile controls with no miscarriages. We investigated mutations in genes responsible for clotting and fibrinolysis, including factor V (FV) Leiden, FV H1299R, factor II (FII) G20210A, methylene tetrahydrofolate reductase (MTHFR) C677T and A1298C, factor XIII (FXIII) V34L, plasminogen activator inhibitor-1 (PAI-1) 4G/5G and endothelial protein C receptor (EPCR) H1 and H3 haplotypes using reverse polymerase chain reaction ViennaLab cardiovascular disease StrippAssays.

Results

Our results showed no significant increase in prevalence of tested polymorphisms in women with RPL. However, relative risk for PRL among women heterozygous for FXIII V34L was 2.81 times increased (OR 2.81, 95% CI 1.15-6.87, P=0.023). Haplotype analysis showed that combined presence of high-risk genotypes for FXIII and PAI-1 significantly increases risk for RPL (OR 13.98, CI 95% 1.11-17.46, P=0.044).

Conclusions

This is the first study in Serbian population that investigated prevalence of FVR2, A1298C, FXIII V34L and EPCR gene variants. Compound heterozygosity for FXIII V34L and PAI-1 4G is significant risk factor for recurrent miscarriage. Our results should be viewed in context of small case-control study, so further large prospective studies are need for confirmation of our findings.

Factor XIII deficiency does not prevent FeCl3-induced carotid artery thrombus formation in mice

BACKGROUND

The compositions of venous (red blood cell-rich) and arterial (platelet-rich) thrombi are mediated by distinct pathophysiologic processes; however, fibrin is a major structural component of both. The transglutaminase factor XIII (FXIII) stabilizes fibrin against mechanical and biochemical disruption and promotes red blood cell retention in contracted venous thrombi. Previous studies have shown factor XIII (FXIII) inhibition decreases whole blood clot mass and therefore, may be a therapeutic target for reducing venous thrombosis. The role of FXIII in arterial thrombogenesis is less studied, and the particular contribution of platelet FXIII remains unresolved.

OBJECTIVE

To determine whether FXIII reduction prevents experimental arterial thrombogenesis.

METHODS

Using wild-type mice and mice with genetically imposed deficiency in FXIII, we measured thrombus formation and stability following ferric chloride-induced arterial thrombosis. We also determined the impact of FXIII on the mass of contracted platelet-rich plasma clots.

RESULTS

Following vessel injury, F13a+/+ , F13a+/- , and F13a-/- mice developed occlusive arterial thrombi. FXIII deficiency did not significantly reduce the incidence or prolong the time to occlusion. FXIII deficiency also did not alter the timing of reflow events or decrease platelet-rich clot mass.

CONCLUSIONS

FXIII does not significantly alter the underlying pathophysiology of experimental arterial thrombus formation.

Novel inhibitor ZED3197 as potential drug candidate in anticoagulation targeting coagulation FXIIIa (F13a)

BACKGROUND

Factor XIII (FXIII) is the final enzyme of the coagulation cascade. While the other enzymatic coagulation factors are proteases, FXIII belongs to the transglutaminase family. FXIIIa covalently crosslinks the fibrin clot and represents a promising target for drug development to facilitate fibrinolysis. However, no FXIII-inhibiting compound has entered clinical trials. Here, we introduce the features of a peptidomimetic inhibitor of FXIIIa (ZED3197) as a potential drug candidate.

METHODS

The potency of ZED3197 against FXIIIa and the selectivity against other human transglutaminases were characterized using transamidation and isopeptidase assays. The inhibition of fibrin crosslinking was evaluated by biochemical methods and thromboelastometry. Further, the pharmacology of the compound was explored in a rabbit model of venous stasis and reperfusion.

RESULTS

ZED3197 proved to be a potent and selective inhibitor of human FXIIIa. Further, the compound showed broad inhibitory activity against cellular FXIIIA from various animal species. Rotational thromboelastometry in whole human blood indicated that the inhibitor, in a dose-dependent manner, prolonged clot formation, reduced clot firmness, and facilitated clot lysis without affecting the clotting time, indicating minimal impact on hemostasis. In vivo, the novel FXIIIa inhibitor effectively decreased the weight of clots and facilitated flow restoration without prolongation of the bleeding time.

CONCLUSIONS

ZED3197 is the first drug-like potent compound targeting FXIIIa, a yet untapped target in anticoagulation. Due to the function of FXIII downstream of thrombin the approach provides minimal impact on hemostasis. In vivo data imply that the inhibitor dissociates an antithrombotic effect from increased bleeding tendency.

Cellular Factor XIII, a Transglutaminase in Human Corneal Keratocytes

Cellular factor XIII (cFXIII, FXIII-A₂), a transglutaminase, has been demonstrated in a few cell types. Its main function is to cross-link proteins by isopeptide bonds. Here, we investigated the presence of cFXIII in cells of human cornea. Tissue sections of the cornea were immunostained for FXIII-A in combination with staining for CD34 antigen or isopeptide cross-links. Isolated corneal keratocytes were also evaluated by immunofluorescent microscopy and flow cytometry. FXIII-A in the corneal stroma was quantified by Western blotting. FXIII-A mRNA was detected by RT-qPCR. The cornea of FXIII-A-deficient patients was evaluated by cornea topography. FXIII-A was detected in 68 ± 13% of CD34+ keratocytes. Their distribution in the corneal stroma was unequal; they were most abundant in the subepithelial tertile. cFXIII was of cytoplasmic localization. In the stroma, 3.64 ng cFXIII/mg protein was measured. The synthesis of cFXIII by keratocytes was confirmed by RT-qPCR. Isopeptide cross-links were detected above, but not within the corneal stroma. Slight abnormality of the cornea was detected in six out of nine FXIII-A-deficient patients. The presence of cFXIII in human keratocytes was established for the first time. cFXIII might be involved in maintaining the stability of the cornea and in the corneal wound healing process.