Factor XIII Activity Research Articles

Prevalence of FXII-Deficiency and Its Relevance to Monitoring Anticoagulation in Adults Receiving Extracorporeal Membrane Oxygenation.

During extracorporeal membrane oxygenation (ECMO) blood is exposed to artificial surfaces, resulting in contact activation of the intrinsic coagulation pathway initiated by coagulation factor XII (FXII). Little is known about the prevalence of acquired FXII-deficiency, especially during ECMO. The primary outcome was the prevalence of acquired FXII-deficiency (FXII activity <60%) during ECMO. Secondary outcomes included differences in hemorrhagic/thromboembolic complications, doses of unfractionated heparin administered, and time points of anticoagulation within target ranges between patients with and without FXII-deficiency. Of 193 adults receiving ECMO therapy between 2013 and 2021, FXII testing was performed in 64 (33%) patients. Of these, 89% ( n = 57) had an acquired FXII-deficiency. Median complication-free intervals were not different between patients with and without acquired FXII-deficiency (bleeding: 28 days [6-145] vs. 12 days [11-not available], p = 0.85; thromboembolism: 16 days [8-54] vs. 13 days [3-15], p = 0.053). Patients with acquired FXII-deficiency received less heparin (16,554 IU/day vs. 25,839 IU/day; p = 0.009) and were less likely to be within aPTT-target ranges (23.1% [14.3%-36.4%] vs. 37.8% [33.7%-58.3%], p = 0.005). Acquired FXII-deficiency is common during ECMO and may affect monitoring of anticoagulation. The impact of FXII-activity on complications needs to be determined in future studies.

Heterozygosity in factor XIII genes and the manifestation of mild inherited factor XIII deficiency

BackgroundThe characterization of inherited mild factor XIII deficiency is more imprecise than its rare, inherited severe forms. It is known that heterozygosity at FXIII genetic loci results in mild FXIII deficiency, characterized by circulating FXIII activity levels ranging from 20% to 60%. There exists a gap in information on 1) how genetic heterozygosity renders clinical bleeding manifestations among these individuals and 2) the reversal of unexplained bleeding upon FXIII administration in mild FXIII-deficient individuals. ObjectivesTo assess the prevalence and burden of mild FXIII deficiency among the apparently healthy German-Caucasian population and correlate it with genetic heterozygosity at FXIII and fibrinogen gene loci. MethodsPeripheral blood was collected from 752 donors selected from the general population with essentially no bleeding complications to ensure asymptomatic predisposition. These were assessed for FXIII and fibrinogen activity, and FXIII and fibrinogen genes were resequenced using next-generation sequencing. For comparison, a retrospective analysis was performed on a cohort of mild inherited FXIII deficiency patients referred to us. ResultsThe prevalence of mild FXIII deficiency was high (∼0.8%) among the screened German-Caucasian population compared with its rare-severe forms. Although no new heterozygous missense variants were found, certain combinations were relatively dominant/prevalent among the mild FXIII-deficient individuals. ConclusionThis extensive, population-based quasi-experimental approach revealed that the burden of heterozygosity in FXIII and fibrinogen gene loci causes the clinical manifestation of inherited mild FXIII deficiency, resulting in ‘’unexplained bleeding’’ upon provocation.

Factors affecting progressive facial swelling immediately after orthognathic surgery: A retrospective cohort study

The aim of this study was to identify clinical factors associated with progressive facial swelling after orthognathic surgery. Patients diagnosed with jaw deformities and undergoing orthognathic surgery were retrospectively evaluated, and those with surgical site infection, Le Fort I osteotomy, or genioplasty only were excluded. Facial swelling volume was calculated by comparing facial volume preoperatively and three days postoperatively using 3D images and image analysis software (VECTRA H2). FXIII was measured within three days after surgery in only patients with unexplained postoperative bleeding or hematoma. The correlation between facial swelling volume and clinical factors was statistically analyzed. Facial swelling volume was examined in 78 patients. Univariate analysis showed a significant difference between facial swelling volume (mean = 41.6 cm3) and operation time (mean = 209.3 min, r = 0.283, p = 0.012), ΔHb level (mean = 1.18 g/dL, r = 0.235, p = 0.039), as well as decreased factor XIII activity (mean = 75.3%, p = 0.012). Multivariate analysis showed a significant difference between facial swelling volume and FXIII deficiency (standard error = 6.44, p = 0.031).Progressive facial swelling immediately after orthognathic surgery may be due to factor XIII deficiency.

OC 28.5 Exploring Interdomain Interactions Mediated by the Factor XIII Activation Peptide

OC 28.5 Exploring Interdomain Interactions Mediated by the Factor XIII Activation Peptide

Tackling the Root Cause of Surface-Induced Coagulation: Inhibition of FXII Activation to Mitigate Coagulation Propagation and Prevent Clotting.

Factor XII (FXII) is a zymogen present in blood that tends to adsorb onto the surfaces of blood-contacting medical devices. Once adsorbed, it becomes activated, initiating a cascade of enzymatic reactions that lead to surface-induced coagulation. This process is characterized by multiple redundancies, making it extremely challenging to prevent clot formation and preserve the properties of the surface. In this study, a novel modulatory coating system based on C1-esterase inhibitor (C1INH) functionalized polymer brushes, which effectively regulates the activation of FXII is proposed. Using surface plasmon resonance it is demonstrated that this coating system effectively repels blood plasma proteins, including FXII, while exhibiting high activity against activated FXII and plasma kallikrein under physiological conditions. This unique property enables the modulation of FXII activation without interfering with the overall hemostasis process. Furthermore, through dynamic Chandler loop studies, it is shown that this coating significantly improves the hemocompatibility of polymeric surfaces commonly used in medical devices. By addressing the root cause of contact activation, the synergistic interplay between the antifouling polymer brushes and the modulatory C1INH is expected to lay the foundation to enhance the hemocompatibility of medical device surfaces.

Increased Osteoclastogenesis in Absence of TG2 Is Reversed by Transglutaminase Inhibition-Evidence for the Role for TG1 in Osteoclast Formation.

Osteoclasts are multinucleated, bone-resorbing giant cells derived from monocyte-macrophage cell lines. Increased bone resorption results in loss of bone mass and osteoporosis. Osteoclast and bone marrow macrophages have been shown to express three TG enzymes (TG2, Factor XIII-A, and TG1) and TG activity to regulate osteoclast differentiation from bone marrow macrophages in vitro. In vivo and in vitro studies have demonstrated that the deletion of TG2 causes increased osteoclastogenesis and a significant loss of bone mass in mice (Tgm2-/- mice). Here, we confirm that TG2 deficiency results in increased osteoclastogenesis in vitro and show that this increase can be reversed by a TG inhibitor, NC9, suggesting that other TGs are responsible for driving osteoclastogenesis in the absence of TG2. An assessment of total TG activity with 5-(biotinamido)-pentylamine, as well as TG1 and FXIII-A activities using TG-specific Hitomi peptides (bK5 and bF11) in Tgm2-/- bone marrow flushes, bone marrow macrophages, and osteoclasts, showed a significant increase in total TG activity and TG1 activity. Factor XIII-A activity was unchanged. Aspartate proteases, such as cathepsins, are involved in the degradation of organic bone matrix and can be produced by osteoclasts. Moreover, Cathepsin D was shown in previous work to be increased in TG2-null cells and is known to activate TG1. We show that Pepstatin A, an aspartate protease inhibitor, blocks osteoclastogenesis in wild-type and Tgm2-/- cells and decreases TG1 activity in Tgm2-/- osteoclasts. Cathepsin D protein levels were unaltered in Tgm2-/-cells and its activity moderately but significantly increased. Tgm2-/- and Tgm2+/+ bone marrow macrophages and osteoclasts also expressed Cathepsin E, and Renin of the aspartate protease family, suggesting their potential involvement in this process. Our study brings further support to the observation that TGs are significant regulators of osteoclastogenesis and that the absence of TG2 can cause increased activity of other TGs, such as TG1.

Von Willebrand factor-binding protein (vWbp)-activated factor XIII and transglutaminase 2 (TG2) promote cross-linking between FnBPA from Staphylococcus aureus and fibrinogen

The secreted von Willebrand factor-binding protein (vWbp) from Staphylococcus aureus interacts with the coagulation factors prothrombin and fibrinogen (Fbg), leading to the non-proteolytic transglutaminase activation of Factor XIII (FXIII). In this study we found that vWbp-activated FXIII catalyses the incorporation of amino-donor dansylcadaverine into region A of fibronectin-binding protein A (FnBPA). Incubation of Fbg with recombinant region A of S. aureus Fbg-binding proteins FnBPA, FnBPB, ClfA or ClfB in presence of vWbp-activated FXIII resulted in the formation of high molecular heteropolymers with FnBPA only, suggesting a specificity of the cross-linking reaction between fibrin(ogen) and the staphylococcal surface. As previously observed, cross-linking sites were mapped to the α-chain and the N1 subdomain of fibrin(ogen) and region A of FnBPA, respectively. Comparable results were obtained when tissue tranglutaminase-2 (TG2) was tested for cross-linking of FnBPA and Fbg. Of note, FnBPA-mediated covalent cross-linking promoted by vWbp-activated FXIII was also observed when bacteria were allowed to attach to fibrin(ogen). Together these findings suggest a novel pathogenetic mechanism by which the transglutaminase action of FXIII and/or TG2 contributes to entrapment and persistence of S. aureus in blood and host tissues.

Fbg αC 389-402 Enhances Factor XIII Cross-Linking in the Fibrinogen αC Region Via Electrostatic and Hydrophobic Interactions.

Coagulation Factor XIII (FXIII) stabilizes blood clots by cross-linking glutamines and lysines in fibrin and other proteins. FXIII activity in the fibrinogen αC region (Fbg αC 221-610) is critical for clot stability and growth. Fbg αC 389-402 is a binding site for thrombin-activated FXIII, (FXIII-A*), with αC E396 promoting FXIII-A* binding and activity in αC. The current study aimed to discover additional residues within Fbg αC 389-402 that accelerate transglutaminase activity toward αC. Electrostatic αC residues (E395, E396, and D390), hydrophobic αC residues (W391 and F394), and residues αC 328-425 were studied by mutations to recombinant Fbg αC 233-425. FXIII activity was monitored through MS-based glycine ethyl ester (GEE) cross-linking and gel-based fluorescence monodansylcadaverine (MDC) cross-linking assays. Truncation mutations 403 Stop (Fbg αC 233-402), 389 Stop (Fbg αC 233-388), and 328 Stop (Fbg αC 233-327) reduced Q237-GEE and MDC cross-linking compared to wild-type (WT). Comparable cross-linking between 389 Stop and 328 Stop showed that FXIII is mainly affected by the loss of Fbg αC 389-402. Substitution mutations E396A, D390A, W391A, and F394A decreased cross-linking relative to WT, whereas E395A, E395S, E395K, and E396D had no effect. Similar FXIII-A* activities were observed for double mutants (D390A, E396A) and (W391A, E396A), relative to D390A and W391A, respectively. In contrast, cross-linking was reduced in (F394A, E396A), relative to F394A. In conclusion, Fbg αC 389-402 boosts FXIII activity in Fbg αC, with D390, W391, and F394 identified as key contributors in enhancing αC cross-linking.

Acquired Factor XIII Deficiency Is Common during ECMO Therapy and Associated with Major Bleeding Events and Transfusion Requirements.

Bleeding events are frequent complications during extracorporeal membrane oxygenation therapy (ECMO). To determine the rate of acquired factor XIII deficiency and its association with major bleeding events and transfusion requirements in adults undergoing ECMO therapy. A retrospective single centre cohort study. Adult patients receiving veno-venous or veno-arterial ECMO therapy during a 2-year period were analysed and screened for factor XIII activity measurements. Factor XIII deficiency was defined based on the lowest factor XIII activity measured during ECMO therapy. Among 84 subjects included into the analysis, factor XIII deficiency occurred in 69% during ECMO therapy. There were more major bleeding events (OR, 3.37; 95% CI, 1.16-10.56; p = 0.02) and higher transfusion requirements (red blood cells, 20 vs. 12, p < 0.001; platelets, 4 vs. 2, p = 0.006) in patients with factor XIII deficiency compared to patients with normal factor XIII activity. In a multivariate regression model, factor XIII deficiency was independently associated with bleeding severity (p = 0.03). In this retrospective single centre study, acquired factor XIII deficiency was observed in 69% of adult ECMO patients with a high bleeding risk. Factor XIII deficiency was associated with higher rates of major bleeding events and transfusion requirements.

Factor XIII and Endothelial Dysfunction in Patients with Systemic Sclerosis.

Systemic sclerosis (SSc, scleroderma) is a severe autoimmune connective tissue disease which affects the skin and internal organs. There has been evidence that coagulation factor XIII (FXIII) has a positive impact on clinical results in patients with SSc. In a single-center cohort study, we investigated the relationship between coagulation FXIII, endothelial dysfunction, and skin infection in SSc. Fifty-six patients could be included and were divided into two groups (with and without scleroderma). Markers of inflammation, coagulation, and endothelial dysfunction like C-reactive protein, leucocytes, fibrinogen, FVIII, VWF-Ag (von Willebrand factor antigen), D-dimers, and vascular endothelial growth factor were analyzed as well as MRSS (modified Rodnan skin scores) data were evaluated. Reduced daily activities were evaluated by the Scleroderma Health Assessment Questionnaire (SHAQ). There were no significant correlations between FXIII activity, MRSS, and SHAQ score. There were correlations between FXIII activity and Raynaud's phenomenon-related symptoms and a weak but not significant positive correlation with the level of pain. A significant correlation between VWF-Ag and lung-associated complaints (n = 56; p = 0.41, p < 0.0001) was found. Moreover, the study showed a correlation between VWF-Ag and MRSS (r [N = 48] = 0.4, p = 0.01), which means that higher VWF-Ag levels come along with more severe skin involvement. A trend toward a negative correlation between FXIII activity and VWF-Ag as marker of endothelial dysfunction was found (r [N = 56] = - 0.20, p = 0.15). In our cohort, there is no FXIII deficiency in patients with SSc. FXIII might have a role in improving cutaneous manifestations indirectly by means of a moderating influence on endothelial dysfunction. Further clinical evaluation is needed.

Antibodies against non-catalytic B subunit of factor XIII inhibit activation of factor XIII and fibrin crosslinking.

Coagulation factor XIII (FXIII) is a proenzyme of plasma transglutaminase. It comprises two catalytic A subunits (FXIII-A) and two carrier B subunits (FXIII-B). We previously reported that alloantibodies against FXIII-B could promote FXIII clearance in a patient with congenital FXIII-B deficiency who had received infusions of plasma-derived human FXIII (A2B2 heterotetramer). We aimed to investigate whether anti-FXIII-B antibodies affect the catalytic function of FXIII. FXIII activation and fibrin crosslinking were examined in the presence of patient plasma, isolated patient IgG, or rat anti-FXIII-B monoclonal antibodies. Alloantibody levels were increased by repeated infusions of plasma-derived A2B2 heterotetramer, which enhanced binding to the functionally important FXIII-B Sushi domains. The patient plasma strongly inhibited cleavage of the FXIII-A activation peptide, amine incorporation, and fibrin crosslinking in normal plasma. Further, anti-FXIII-B alloantibodies blocked the formation of the complex of FXIII-B with FXIII-A, and fibrinogen. Rat monoclonal antibodies against the 10th Sushi domain of FXIII-B inhibited the incorporation of FXIII-B to fibrin, FXIII activation (i.e., cleavage of FXIII-A activation peptide), and ultimately fibrin crosslinking in normal plasma, independent of their effect on heterotetramer assembly with FXIII-A. Alloantibody binding to the A2B2 heterotetramer blocked the access of thrombin to the FXIII-A cleavage site, as indicated by the reaction of the alloantibodies to the A2B2 heterotetramer and FXIII-B, but not to FXIII-A. Anti-FXIII-B antibodies binding to the A2B2 heterotetramer and FXIII-B inhibited FXIII activation and its crosslinking function despite being directed against its non-catalytic subunit (FXIII-B).

A site on factor XII required for productive interactions with polyphosphate

BackgroundDuring plasma contact activation, factor XII (FXII) binds to surfaces through its heavy chain and undergoes conversion to the protease FXIIa. FXIIa activates prekallikrein and factor XI (FXI). Recently, we showed that the FXII first epidermal growth factor-1 (EGF1) domain is required for normal activity when polyphosphate is used as a surface. ObjectivesThe aim of this study was to identify amino acids in the FXII EGF1 domain required for polyphosphate-dependent FXII functions. MethodsFXII with alanine substitutions for basic residues in the EGF1 domain were expressed in HEK293 fibroblasts. Wild-type FXII (FXII-WT) and FXII containing the EGF1 domain from the related protein Pro-HGFA (FXII-EGF1) were positive and negative controls. Proteins were tested for their capacity to be activated, and to activate prekallikrein and FXI, with or without polyphosphate, and to replace FXII-WT in plasma clotting assays and a mouse thrombosis model. ResultsFXII and all FXII variants were activated similarly by kallikrein in the absence of polyphosphate. However, FXII with alanine replacing Lys73, Lys74, and Lys76 (FXII-Ala73,74,76) or Lys76, His78, and Lys81 (FXII-Ala76,78,81) were activated poorly in the presence of polyphosphate. Both have <5% of normal FXII activity in silica-triggered plasma clotting assays and have reduced binding affinity for polyphosphate. Activated FXIIa-Ala73,74,76 displayed profound defects in surface-dependent FXI activation in purified and plasma systems. FXIIa-Ala73,74,76 reconstituted FXII-deficient mice poorly in an arterial thrombosis model. ConclusionFXII Lys73, Lys74, Lys76, and Lys81 form a binding site for polyanionic substances such as polyphosphate that is required for surface-dependent FXII function.

Perioperative therapeutic plasma exchange in a patient with rare Factor XIII inhibitor

IntroductionFactor XIII deficiency is a rare bleeding disorder which could be severe if inherited or less severe if acquired. We report a case of acquired Factor XIII inhibitor in a 75-year-old male with a suspicious left renal mass treated perioperatively with therapeutic plasma exchange (TPE). Patient and methodTo perform kidney biopsy and ablation of the renal mass, six daily TPE treatments were performed before and after biopsy to minimize bleeding risk because the patient did not respond to drug therapy. Both thromboelastography (TEG) and laboratory-based coagulation tests were performed to assess coagulation status prior to and after TPE. ResultsThe biopsy indicated oncocytoma which was removed by surgical procedure. Factor XIII activity remained below 15 % throughout TPE treatments, but Factor XIII inhibitor titer reduced from initial positive value of 1:40 to negative following the third TPE and remained negative through the sixth TPE. Unfortunately, the inhibitor titer was positive at 1:20 in the fifth month and 1:5 in the sixth month during follow-up. ConclusionsTPE is useful in removing XIII inhibitory factor, but the effects are only short term.

Peptidic Inhibitors and a Fluorescent Probe for the Selective Inhibition and Labelling of Factor XIIIa Transglutaminase.

Factor XIIIa (FXIIIa) is a transglutaminase of major therapeutic interest for the development of anticoagulants due to its essential role in the blood coagulation cascade. While numerous FXIIIa inhibitors have been reported, they failed to reach clinical evaluation due to their lack of metabolic stability and low selectivity over transglutaminase 2 (TG2). Furthermore, the chemical tools available for the study of FXIIIa activity and localization are extremely limited. To combat these shortcomings, we designed, synthesised, and evaluated a library of 21 novel FXIIIa inhibitors. Electrophilic warheads, linker lengths, and hydrophobic units were varied on small molecule and peptidic scaffolds to optimize isozyme selectivity and potency. A previously reported FXIIIa inhibitor was then adapted for the design of a probe bearing a rhodamine B moiety, producing the innovative KM93 as the first known fluorescent probe designed to selectively label active FXIIIa with high efficiency (kinact/KI = 127,300 M-1 min-1) and 6.5-fold selectivity over TG2. The probe KM93 facilitated fluorescent microscopy studies within bone marrow macrophages, labelling FXIIIa with high efficiency and selectivity in cell culture. The structure-activity trends with these novel inhibitors and probes will help in the future study of the activity, inhibition, and localization of FXIIIa.

Influence of the polymerization method on the properties of fibrin matrices

Highlights. We have proposed and patented a method for obtaining fully autologous fibrin without the use of exogenous thrombin, which can be implemented within the framework of a personalized approach in tissue engineering. Such fibrin, in addition to lower risk of infection and inflammation, possesses greater strength and resistance to degradation, as well as better hemocompatibility compared to fibrin polymerized with exogenous thrombin, which is an undoubted advantage when used as a coating for small-diameter vascular grafts.Background. Autologous fibrin can be used as a coating to impart biomimetic properties to various polymers used in vascular tissue engineering. Traditionally, fibrinogen polymerization is performed with the addition of exogenous thrombin and calcium chloride. Our patented method of obtaining fibrin without the use of exogenous thrombin allows us to obtain a completely autologous material that does not have the risk of infection. The differences in methods polymerization can change the fibrin properties.Aim. To compare the most important properties of vascular tissue engineering of fibrin obtained by various methods: using endogenous thrombin and exogenous thrombin in vitro.Methods. The fibrinogen precipitate was obtained with ethanol precipitation method using low concentration of ethanol. The content of fibrinogen in the precipitate was normalized to a final concentration in fibrin of 30 mg/mL. Polymerization of fibrin polymerized with exogenous thrombin was performed by adding 50 U/ mL and 0.2% calcium chloride to the thrombin precipitate, fibrin polymerized by activation of endogenous thrombin only by adding 0.2% calcium chloride. The strength properties of the samples were tested on a Z tensile tester (Zwick/ Roell). The structure of fibrin was studied using scanning electron microscopy, a quantitative analysis of the size of pores and fibers, the density of branching points was carried out. The quantitative content of FXIII in plasma and the resulting precipitate was determined by ELISA. FXIII activity was studied by the formation of γ-γ crosslinks by SDS-PAGE, the resistance of samples to proteolytic and fibrinolytic degradation. The ability of fibrin polymerized by activation of endogenous thrombin and fibrin polymerized with exogenous thrombin to activate contact coagulation and platelet aggregation was evaluated.Results. Thinner fibers predominated in the structure of the fibrin polymerized by activation of endogenous thrombin samples, while the samples were distinguished by greater strength and stiffness. The described features may be associated with a more efficient activation of FXIII, which is confirmed by the formation of a larger number of γ-γ dimers in fibrin polymerized by activation of endogenous thrombin samples, as well as resistance to proteolytic degradation compared to fibrin polymerized with exogenous thrombin. Moreover, fibrin polymerized by activation of endogenous thrombin samples in vitro activated platelets less than fibrin polymerized with exogenous thrombin.Conclusion. The method for obtaining and polymerizing fibrin using endogenous thrombin makes it possible to obtain a completely autologous material that has better physical and mechanical properties, resistance to proteolytic degradation and lower thrombogenicity compared to traditional fibrin polymerization.

Factor XII contributes to thrombotic complications and vaso-occlusion in sickle cell disease

AbstractA hypercoagulable state, chronic inflammation, and increased risk of venous thrombosis and stroke are prominent features in patients with sickle cell disease (SCD). Coagulation factor XII (FXII) triggers activation of the contact system that is known to be involved in both thrombosis and inflammation, but not in physiological hemostasis. Therefore, we investigated whether FXII contributes to the prothrombotic and inflammatory complications associated with SCD. We found that when compared with healthy controls, patients with SCD exhibit increased circulating biomarkers of FXII activation that are associated with increased activation of the contact pathway. We also found that FXII, but not tissue factor, contributes to enhanced thrombin generation and systemic inflammation observed in sickle cell mice challenged with tumor necrosis factor α. In addition, FXII inhibition significantly reduced experimental venous thrombosis, congestion, and microvascular stasis in a mouse model of SCD. Moreover, inhibition of FXII attenuated brain damage and reduced neutrophil adhesion to the brain vasculature of sickle cell mice after ischemia/reperfusion induced by transient middle cerebral artery occlusion. Finally, we found higher FXII, urokinase plasminogen activator receptor, and αMβ2 integrin expression in neutrophils of patients with SCD compared with healthy controls. Our data indicate that targeting FXII effectively reduces experimental thromboinflammation and vascular complications in a mouse model of SCD, suggesting that FXII inhibition may provide a safe approach for interference with inflammation, thrombotic complications, and vaso-occlusion in patients with SCD.

Distinguishing immune-mediated thrombotic thrombocytopenic purpura from septic disseminated intravascular coagulation using plasma levels of haptoglobin and factor XIII activity

BackgroundBoth immune-mediated thrombotic thrombocytopenic purpura (iTTP) and septic disseminated intravascular coagulation (DIC) are life-threatening disorders developed by platelet-consuming microvascular thrombi and necessitate immediate therapeutic interventions. Although severe deficiencies of plasma haptoglobin in iTTP and factor XIII (FXIII) activity in septic DIC have been reported, few studies have focused on the possibility of using these markers to distinguish between iTTP and septic DIC. ObjectivesWe investigated whether the plasma levels of haptoglobin and FXIII activity could be helpful for differential diagnosis. MethodsThirty-five patients with iTTP and 30 with septic DIC were enrolled in the study. Patient characteristics, coagulation, and fibrinolytic markers were collected from the clinical data. Plasma haptoglobin and FXIII activities were measured using chromogenic Enzyme-Linked Immuno Sorbent Assay and an automated instrument, respectively. ResultsThe median plasma haptoglobin level was 0.39 mg/dL and 54.20 mg/dL in the iTTP and septic DIC groups, respectively. The median plasma FXIII activities were 91.3% and 36.3% in the iTTP and septic DIC groups, respectively. In the receiver operating characteristic curve analysis, the cutoff level of plasma haptoglobin was 2.868 mg/dL and the area under the curve was 0.832. The cutoff level for plasma FXIII activity and the area under the curve were 76.0% and 0.931, respectively. The thrombotic thrombocytopenic purpura (TTP)/DIC index was defined by FXIII activity (percentage) and haptoglobin (milligrams per decilitre). Laboratory TTP was defined as an index ≥60 and laboratory DIC <60. The sensitivity and specificity of the TTP/DIC index were 94.3% and 86.7%, respectively. ConclusionThe TTP/DIC index, composed of plasma levels of haptoglobin and FXIII activity, is useful in differentiating iTTP from septic DIC.

Fbg αC 389-402 enhances factor XIII crosslinking in the fibrinogen αC region via electrostatic and hydrophobic interactions.

Coagulation Factor XIII (FXIII) hinders fibrinolysis via transglutaminase activity in fibrin and other proteins. FXIII activity in the fibrinogen αC region (Fbg αC 221-610) is critical for clot stability and growth. Fbg αC 389-402 acts as a binding site for thrombin-activated FXIII, (FXIII-A∗), with αC E396 promoting FXIII-A∗ binding and activity. The current study aimed to discover additional residues within Fbg αC 389-402 that accelerate transglutaminase activity toward αC (233-425). αC E395 and D390 were proposed to form ionic interactions with FXIII that improve binding. αC W391 and F394 were hypothesized to augment FXIII-fibrinogen αC binding through favorable hydrophobic contacts with FXIII residues. Truncated Fbg αC 328-425 was also examined for any potential impact on FXIII activity. Fbg αC D390, W391, F394, E395, E396, and residues 328-425 were studied by select mutations to recombinant Fbg αC 233-425. FXIII activity was quantified by monitoring glycine ethyl ester (GEE) crosslinking to αC Q237 over time by mass spectrometry. Truncation mutations “403 Stop” (Fbg αC 233-402), “389 Stop” (Fbg αC 233-388), and “328 Stop” (Fbg αC 233-327) experienced reduced Q237-GEE crosslinking compared to wild-type (WT). Comparable crosslinking between “389 Stop” and “328 Stop” shows that FXIII is mainly affected by the loss of Fbg αC 389-402. Substitution mutations E396A, D390A, W391A, and F394A decreased crosslinking relative to WT, whereas E395A, E395S, E395K, and E396D had no effect. Similar FXIII-A∗ activities were observed for double mutants (D390A,E396A) and (W391A,E396A), relative to D390A and W391A, respectively. In contrast, crosslinking was further reduced in (F394A,E396A), relative to F394A. In conclusion, Fbg αC 389-402 boosts FXIII activity in Fbg αC, with D390, W391, and F394 identified as additional residues that enhance αC crosslinking.

Factor XIII activation and substrate crosslinking can be influenced by amino acid substitutions from transglutaminase-2.

Factor XIII (FXIII) catalyzes formation of covalent crosslinks between reactive glutamines and lysines in plasma and cellular substrates. Related enzyme Transglutaminase 2 (TG2) also catalyzes crosslinking of cellular substrates, some common with FXIII. FXIII-A2 can be activated proteolytically to FXIII-A∗ by thrombin cleavage of the FXIII activation peptide (AP) and low mM CaCl2. FXIII-A2 can also be activated non-proteolytically by elevated Ca2+ levels (FXIII-A°) with up to three calcium binding sites Ca1, 2, and 3 filled. TG2 is allosterically regulated by Ca2+ and GTP. Kanchan et al (2013) reported that TG2 activity could be increased with a G224V substitution that improves Ca2+ binding. For the current project, two TG2 residues (V224 and N231) located near Ca3 were introduced into comparable positions of FXIII-A2. FXIII WT, G262V, K269N, and (G262V, K269N) were screened for their abilities to catalyze crosslinking of monodansylcadaverine (MDC, lysine mimic) into Fbg αC (233-425, glutamine substrate). For FXIII-A° generated with 100 mM CaCl2, MDC crosslinking ranked as FXIII G262V < FXIII WT ≪ FXIII K269N ≈ FXIII (G262V, K269N). FXIII V262 is proposed to impair a helical segment near Ca3 thus hindering the benefits of effective Ca2+ binding. FXIII K269N with its neutral N269 is hypothesized to enhance the lysine substrate binding surface near Ca3. Comparable crosslinkings occurred for FXIII-A∗ WT and FXIII-A∗ G262V likely due to presence of low mM Ca2+ that would primarily target Ca1 binding. The extent of MDC crosslinking ranked as FXIII-A∗ (WT ≈ G262V) ≪ (G262V, K269N) < K269N. For both FXIII-A∗ and A°, the K269N position in the vicinity of Ca3 and the lysine binding surface generated the greatest improvements in transglutaminase activity. Overall, TG2 substitutions were successfully used to tune properties of FXIII.

Transglutaminase Activities of Blood Coagulant Factor XIII Are Dependent on the Activation Pathways and on the Substrates.

Factor XIII (FXIII) catalyzes formation of γ-glutamyl-ε-lysyl crosslinks between reactive glutamines (Q) and lysines (K). In plasma, FXIII is activated proteolytically (FXIII-A*) by the concerted action of thrombin and Ca2+. Cellular FXIII is activated nonproteolytically (FXIII-A°) by elevation of physiological Ca2+ concentrations. FXIII-A targets plasmatic and cellular substrates, but questions remain on correlating FXIII activation, resultant conformational changes, and crosslinking function to different physiological substrates. To address these issues, the characteristics of FXIII-A* versus FXIII-A° that contribute to transglutaminase activity and substrate specificities were investigated. Crosslinking of lysine mimics into a series of Q-containing substrates were measured using in-gel fluorescence, mass spectrometry, and UV-Vis spectroscopy. Covalent incorporation of fluorescent monodansylcadaverine revealed that FXIII-A* exhibits greater activity than FXIII-A° toward Q residues within Fbg αC (233-425 WT, Q328P Seoul II, and Q328PQ366N) and actin. FXIII-A* and FXIII-A° displayed similar activities toward α2-antiplasmin (α2AP), fibronectin, and Fbg αC (233-388, missing FXIII-binding site αC 389-402). Furthermore, the N-terminal α2AP peptide (1-15) exhibited similar kinetic properties for FXIII-A* and FXIII-A°. MALDI-TOF mass spectrometry assays with glycine ethyl ester and Fbg αC (233-425 WT, αC E396A, and truncated αC (233-388) further documented that FXIII-A* exerts greater benefit from the αC 389-402 binding site than FXIII-A°. Conformational properties of FXIII-A* versus A° are proposed to help promote transglutaminase function toward different substrates. A combination of protein substrate disorder and secondary FXIII-binding site exposure are utilized to control activity and specificity. From these studies, greater understandings of how FXIII-A targets different substrates are achieved.