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Autoimmune factor XIII (FXIII) deficiency (AiF13D) is a rare hemorrhagic disease. The anti-FXIII autoantibodies that cause this disease are classified into three types: type Aa inhibits the heterotetramer assembly and activation of FXIII, type Ab inhibits the enzymatic activity of activated FXIII, and type B enhances the elimination of FXIII from the blood. The former two are FXIII inhibitors and may be lethal if overlooked by conventional functional assays. To reliably detect both types of FXIII inhibitors, a new assay was developed by incorporating 5-(biotinamido)pentylamine (BAPA) into α 2 -plasmin inhibitor (PI-BAPA assay). This assay was tested on plasma samples from 128 participants, including 60 healthy controls, 35 patients with non-immune acquired FXIII deficiency, and 33 patients with AiF13D (29 with type Aa inhibitors and 4 with type Ab inhibitors). The PI-BAPA assay successfully detected type Aa and Ab inhibitors in 5-step dilution cross-mixing tests between patient and normal plasma. This assay also showed comparable or superior inhibition rates in the 1:1 mixing test compared to conventional ammonia release and amine incorporation assays. Receiver operating characteristic curve analysis confirmed the excellent specificity and sensitivity of this assay for determining inhibition rates, and the assay has already been used for AiF13D diagnosis., (© 2024. Japanese Society of Hematology.)

Coagulation factor XIII (FXIII) is a fibrin-stabilizing factor with additional roles in wound healing and interactions between the decidua and fetus. Congenital FXIII deficiency is rare bleeding disorder. Inhibitor development against FXIII in inherited FXIII deficency is also uncommon, but may cause severe, life-threatening bleeding. FXIII is the last step in the coagulation cascade with normal coagulation paramaters (PT, aPTT), the detection of inhibitor to FXIII is quite difficult. The treatment of inhibitor-positive congenital FXIII deficiency is challenging due to the lack of a role of by-pass agents such as FVII. The best known ways of treatment in these cases are the use of high-dose FXIII concentrates and immunosuppression. Herein, we report the management of postoperative bleeding diathesis in a patient with FXIII deficiency who developed inhibitors, and to follow the clinical course of the disease with FXIII concentrate and immunosuppression.

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., (© 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

Essentials Corn Trypsin Inhibitor (CTI) is a selective inhibitor of coagulation Factor XII (FXII). Molecular modelling of the CTI-FXIIa complex suggested a canonical inhibitor binding mode. Mutagenesis revealed the CTI inhibitory loop and helices α1 and α2 mediate the interaction. This confirms that CTI inhibits FXII in canonical fashion and validates the molecular model., Summary: Background Corn trypsin inhibitor (CTI) has selectivity for the serine proteases coagulation factor XII and trypsin. CTI is in widespread use as a reagent that specifically inhibits the intrinsic pathway of blood coagulation but not the extrinsic pathway. Objectives To investigate the molecular basis of FXII inhibition by CTI. Methods We performed molecular docking of CTI, using its known crystal structure, with a model of the activated FXII (FXIIa) protease domain. The interaction model was verified by use of a panel of recombinant CTI variants tested for their ability to inhibit FXIIa enzymatic activity in a substrate cleavage assay. Results The docking predicted that: (i) the CTI central inhibitory loop P1 Arg34 side chain forms a salt bridge with the FXIIa S1 pocket Asp189 side chain; (ii) Trp22 from CTI helix α1 interacts with the FXIIa S3 pocket; and (iii) Arg43 from CTI helix α2 forms a salt bridge with FXIIa H1 pocket Asp60A. CTI amino acid substitution R34A negated all inhibitory activity, whereas the G32W, L35A, W22A and R42A/R43A substitutions reduced activity by large degrees of 108-fold, 41-fold, 158-fold, and 100-fold, respectively; the R27A, W37A, W39A and R42A substitutions had no effect. Synthetic peptides spanning CTI residues 20-44 had inhibitory activity that was three-fold to 4000-fold less than that of full-length CTI. Conclusions The data confirm the validity of a canonical model of the FXIIa-CTI interaction, with helix α1 (Trp22), central inhibitory loop (Arg34) and helix α2 (Arg43) of CTI being required for effective binding by contacting the S1, S3 and H1 pockets of FXIIa, respectively., (© 2017 The Authors. Journal of Thrombosis and Haemostasis published by Wiley Periodicals, Inc. on behalf of International Society on Thrombosis and Haemostasis.)

Autoimmune hemophilia-like disease (hemorrhaphilia) due to anti-factor XIII (FXIII) antibodies (AH13) is a very rare, life-threatening bleeding disorder. A 77-year-old woman developed macrohematuria and a right renal pelvic hematoma. The coagulation times were not prolonged, but FXIII activity and antigen levels were severely and moderately reduced to 9 and 29% of normal values, respectively. Accordingly, the FXIII-specific activity turned out to be low. FXIII inhibitor and anti-FXIII-A subunit autoantibodies were detected by a 1:1 crossmixing test and immunoblot and immunochromatographic assays. She was therefore diagnosed with "definite AH13" and treated with plasma-derived FXIII concentrates to arrest the hemorrhage. In addition to a highly compressed inferior vena cava by a huge renal pelvic hematoma, deep vein thrombosis (DVT) and pulmonary thromboembolism (PE) were identified by systemic computed tomography. The patient was immediately started on anticoagulation therapy with low-dose heparin. Emboli disappeared quickly, probably because under-crosslinked thrombi caused by severe FXIII deficiency are vulnerable to fibrinolysis. After about 1.5 years, anti-FXIII-A subunit autoantibodies still remained despite the use of rituximab, steroid pulse therapy, oral prednisolone, and oral cyclophosphamide treatments. In conclusion, an extremely rare AH13 case complicated by DVT and PE was successfully managed by balancing anticoagulation therapy with hemostatic therapy., (© 2017 S. Karger AG, Basel.)

Autoimmune acquired factor XIII (F13) deficiency or autoimmune hemophilia-like disease (hemorrhaphilia) resulted from the generation of anti-F13 antibodies (AH13) is a severe bleeding disorder that occurs mainly in the elderly. Although rare, the number of patients diagnosed with AH13 has recently increased. To improve understanding of this disease, the author summarized 93 ever reported/diagnosed AH13 cases. About 50% of cases were idiopathic. In the remaining half of the patients, autoimmune diseases and malignancies were the most common underlying diseases. Intramuscular and subcutaneous bleeding were the most frequently reported symptoms. Hemorrhage was the cause of death in 13 patients. In 4 patients, the diagnosis was established after hemorrhagic death. Therefore, physicians/hematologists must raise the awareness of AH13 as a life-threatening disease. Most patients were treated with F13 concentrates to arrest bleeding and with prednisolone and cyclophosphamide to eradicate anti-F13 autoantibodies. AH13 cases tend to become chronic and intractable and require close follow-up over an extended period., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

A novel class of potent FXIII-A inhibitors containing a (±) cis-bisamido epoxide pharmacophore is described. The compounds display highly potent inhibition of FXIII-A (IC50 = 5-500 nM) in an in vitro assay. In contrast to other types of previously described covalent transglutaminase inhibitors, the bis-amido epoxides exhibited no measurable reactivity with glutathione, therefore possibly rendering this class of compounds suitable for future in vivo investigations. Additionally, the compounds show selective inhibition for FXIII-A against the cysteine protease, cathepsin S although they proved to have similar potency with a closely related transglutaminase, TGII, to that observed for FXIII-A., (Copyright © 2015 Elsevier Masson SAS. All rights reserved.)

Perioral hematomas can lead to acute airway compromise and can present significant challenges in both direct and indirect approaches to airway instrumentation. In patients with normal cell counts and routine coagulation tests, spontaneous hematomas are rare, but when encountered, they elicit a limited differential diagnosis that includes von Willebrand factor deficiency, platelet dysfunction, and the acquired factor XIII (FXIII) deficiency. Although spontaneous hematoma formation resulting from FXIII inhibition has been reported, we describe what may be the first reported case of FXIII inhibitor-related hematoma leading to acute airway compromise. Successful management of this patient required multidisciplinary cooperation among anesthesiologists, intensivists, otolaryngologists, and hematologists.

Factor XIII/13 (FXIII or F13) is a plasma protransglutaminase, which stabilizes fibrin clots, and thus plays an important role in hemostasis. Autoimmune hemo(rrha)philia due to anti-F13 autoantibodies (AH13) has been on the rise in Japan, which has become the leading superaging society in the 21st century. The mean age of Japanese AH13 cases has risen to 70.4 years. A total of 83 AH13 cases have been diagnosed in the world as of July 2014. To raise the awareness of AH13, the author and members of the Japanese Collaborative Research Group first proposed "Criterion and Algorithm of Laboratory Tests for anti F13" in February 2012. AH13 is not just an acquired isolated defect of F13 molecule itself but a disturbance caused by autoantibodies. Accordingly, AH13 cases are diagnosed in patients with otherwise unexplained hemorrhages by a combination of a severe deficiency of F13 activity and the presence of anti-F13 autoantibodies. As patients with this disease manifest life-threatening bleeding symptoms, prompt diagnosis and proper treatment are essential. Because AH13 tends to become chronic and intractable, affected patients must be closely followed for a prolonged period., (Thieme Medical Publishers 333 Seventh Avenue, New York, NY 10001, USA.)

The in-vitro lysis of plasma clots in acetic acid generally indicates a Factor XIII deficiency that is confirmed by quantitative assay. However, there are two rare, poorly understood circumstances whereby clot lysis in acid occurs when factor XIII activity levels are normal: the presence of either an atypical antifactor XIII antibody, or an unknown acid-activated protease. Our centre has identified four patients with in-vitro clot lysis in acetic acid and normal FXIII levels by activity assay. Our aim was to determine whether the cause of this unusual result was an inhibitory antibody or an aspartic acid protease. In each case, we found an inhibitor that was not an IgG but showed characteristics of an acid protease, including that it was neutralized by pepstatin. The four patients had median pepsinogen I levels five-fold to 10-fold higher than the normal median of 89 μg/l. Pepsinogen II was increased by three-fold to six-fold, but from a lower baseline median of 6.5 μg/l. Cathepsin D levels were normal. Clot lysis in the acid test was observed when recombinant human pepsinogen I was added to normal plasma at similarly high concentrations as in patient samples, consistent with a role of an acid protease. Clot lysis also occurred with addition of pepsinogen II, but required four-fold to seven-fold more than in patient samples. Laboratories should be aware that a positive acid clot lysis test can be misleading if pepsinogen levels are raised and should not use this alone to diagnose FXIII deficiency.

Coagulation factor XIII (FXIII) is a protein that promotes fibrin stabilization by forming multiple covalent cross-links between fibrin monomers. Beside congenital FXIII deficiency, due to FXIII gene mutations, severe acquired FXIII deficiency has been described in association with autoantibodies against coagulation FXIII. These inhibitors, which occurs very rarely but may cause life-threatening bleeding complications, may arise spontaneously or in association with autoimmune and lymphoproliferative disorders or medications. The management of patients with acquired FXIII inhibitors is very demanding and treatment regimens must be focused on eradication of the inhibitor and to increase the plasma FXIII levels. In this systematic review, we analyse all the published case-reports on anti-FXIII autoantibodies focusing on the clinical features and treatment modalities of this acquired hemorrhagic condition.

Less than 60 cases of acquired factor (F)XIII deficiencies have been reported, most having distinct clinical features. To illustrate the therapeutic challenges of acquired FXIII inhibitors, we report a case of a 65-year-old patient with no previous bleeding history who suddenly developed massive haemorrhages associated to a strong and isolated FXIII inhibitor. No underlying disorder has been detected till now after three years of follow-up. Despite aggressive treatment with prednisone, rituximab, cyclophosphamide, immunoglobulin, immunoadsorption and immune tolerance his inhibitor is still present, although at low titre and with a clinical benefit since the patient has no more bleed since more than one year. Moreover the patient had a venous thromboembolic complication. After a review of the management of acquired FXIII deficiency patients and based on the management of acquired haemophilia we discuss a possible strategy for such difficult cases.

Factor XIII (FXIII) is a fibrin-stabilizing factor consisting of catalytic A subunits (FXIII-A) and carrier B subunits (FXIII-B). Congenital FXIII deficiency is a rare bleeding disorder. Acquired FXIII deficiency resulting from FXIII hypo-synthesis and/or hyperconsumption is a relatively common disorder in which patients seldom bleed. On the contrary, 'autoimmune/acquired hemorrhaphilia XIII/13 due to anti-FXIII antibodies (AH13)' is a rare but life-threatening bleeding disorder. Through a nationwide survey of AH13, we diagnosed aggressive AH13 in a 66-year-old woman. She consulted our department because of a spontaneous hematoma in her hand. After 1.5 months, she also developed an intramuscular hematoma but retained approximately half (52%) of the normal FXIII activities. The patient's bleeding symptoms were aggravated to catastrophic massive bleedings in the large abdominal muscles and intrapelvic and intraperitoneal spaces. Two months after the bleeding onset, she died despite undergoing plasma exchange, which was performed because we were deeply suspicious of the presence of an anti-FXIII inhibitor. Seven days after her death, extremely low FXIII activity (6%) and positive data on anti-FXIII inhibitor were reported by a commercial laboratory. Our dot blot assay detected anti-FXIII-A autoantibodies, afterwards. Thus, the diagnosis of aggressive AH13 as early as possible is necessary to save patients' lives.

Coagulation factor XIII/13 (FXIII/13) stabilizes fibrin molecules by creating crosslinks with other fibrin molecules as well as with α₂-plasmin inhibitor (α₂-PI). "Hemorrhagic acquired FXIII/13 deficiency" was formerly considered rare, but has been increasing recently in Japan. During the 10 months of our nationwide campaign, we diagnosed five new patients with "acquired hemorrhaphilia due to anti-FXIII/13 autoantibodies," after examining 20 newly suspected cases of "hemorrhagic acquired FXIII/13 deficiency." When FXIII/13 activity was reduced to less than 50% of normal, it was proportional to the difference in α₂-PI levels between plasma and serum (plasma-serum α₂-PI), likely due to its cross-linking to fibrin by activated FXIII/13. Accordingly, decreased amounts of the plasma-serum α₂-PI ex vivo may reflect reduced FXIII/13 activity in vivo. The plasma-serum α₂-PI may thus also be a useful diagnostic marker for severe FXIII/13 deficiency.

We developed a novel on-chip assay using protein arrays for quantitative and rapid analysis of blood coagulation factor XIII (FXIII) activity in human plasma. FXIII is activated by concerted action of thrombin and Ca(2+) and plays essential roles in hemostasis, angiogenesis, and wound healing. We fabricated protein arrays by immobilizing fibrinogen onto the 3-aminopropyltrimethoxysilane layer of well-type arrays and determined FXIII activity by analyzing biotinylated fibrinogen with Cy3-conjugated streptavidin. We determined optimal concentrations of Ca(2+), thrombin, and 5-(biotinamido)pentylamine (BAPA) for the on-chip activity assay, and the detection limit was 0.01 Lowey U/mL (9.9 pM). Using the on-chip activity assay, hepatocellular carcinoma patients (n = 24), but not hepatitis (n = 24) or liver cirrhosis patients (n = 41), had significantly lower FXIII activities (p < 0.001) than normal individuals (n = 41), indicating that FXIII activity is a possible diagnostic marker for hepatocellular carcinoma. In addition, we have successfully used this activity assay to reveal individual variations (37-57%, n = 65) in the inhibition rate of FXIII activity by isoniazid, the first-line antituberculosis agent. Thus, our optimized on-chip FXIII activity assay provides a quantitative and high-throughput approach to investigating the role(s) of FXIII in human diseases. Moreover, it has a strong potential to be applied toward FXIII-related personalized medicines.

Background: Thrombelastography has received renewed interest in the perioperative setting. The main determinants of thrombelastographic results are coagulation factor concentrations (various zymogens and fibrinogen) and platelet count; thus, platelet inhibition renders these assays mainly coagulation factor dependent. Assays with and without platelet inhibition are thus increasingly used to trigger and monitor replacement therapy with blood products. In this study, we evaluated the effect of factor XIII inhibition and additional glycoprotein (GP) IIb/IIIa blockade on (platelet-inhibited) whole blood thrombelastography and whether a modified routine assay (using factor XIII antibody) can be used to detect factor XIII deficiency., Methods: Normal whole blood was incubated with increasing amounts of a nonspecific antibody, an anti-GPIIb/IIIa antibody, or a neutralizing anti-factor XIII antibody; samples were analyzed with a tissue factor-activated and platelet-inhibited whole blood thrombelastographic assay. Clotting time, clot formation time, maximum clot firmness, and clot lysis at 60 min were evaluated in triplicate. Also, 25 whole blood routine samples were evaluated for factor XIII deficiency using a new thrombelastographic assay incorporating a factor XIII antibody and using a standard factor XIII assay for comparison., Results: Although GPIIb/IIIa inhibition did not alter the results of the platelet-inhibited whole blood thrombelastography, factor XIII inhibition significantly reduced maximum clot firmness (P = 0.020) and increased clot formation time (P = 0.025) and clot lysis (P = 0.007), leaving clotting time unchanged; a ceiling effect seemed to be present with increasing antibody concentrations in whole blood (but not plasma). The thrombelastographic assay for factor XIII deficiency (<70% activity) had a 90% sensitivity and negative predictive value (area under receiver operating characteristic curve 0.803, P = 0.0015); for a deficiency <60%, sensitivity and negative predictive value were 100% (area under receiver operating characteristic curve 0.84, P = 0.0037)., Conclusion: Factor XIII has significant impact on platelet-inhibited activated whole blood thrombelastography. This phenomenon should be considered when interpreting thrombelastographic results in the bleeding patient, especially when the results trigger procoagulant therapy. Antibody-mediated factor XIII inhibition can be used to establish thrombelastography-based assays to detect factor XIII deficiency.

The A subunit of plasma factor XIII (FXIII-A) is thought to function as an intracellular transglutaminase (TG) in the monocyte/macrophage lineage to regulate certain intracellular processes involving cytoskeleton remodeling, but its precise role and the functional consequences of its absence remain poorly understood. In the present study, we show that cellular FXIII (cFXIII) expression is largely upregulated during in vitro differentiation of monocytes into dendritic cells (DCs). Monodansyl-cadaverine, a competitive substrate of TG activity, inhibited basal and CCL19-stimulated migration of mature DCs. In agreement, FXIII-A-deficient DCs showed a reduced chemotactic response to CCL19. Consistent with these findings, CHO cells stably expressing human FXIII-A showed enhanced motility in transwell and scratch-wound assays. These cells displayed increased formation of membrane blebs, dynamic cell protrusions implicated in cell movement that were also observed in DCs. The results provide evidence suggesting that upregulation of cFXIII in DCs has a role in regulating cell motility.

Tissue transglutaminase was reported to act as protein disulfide isomerase (PDI). We studied whether plasma transglutaminase - coagulation factor XIII (FXIII) - has PDI activity as well. PDI activity was measured by determining the ability to renature reduced-denatured RNase (rdRNase). We found that FXIII can renature rdRNase, with efficiency comparable to commercial PDI. This PDI activity was inhibited by bacitracin. Like tissue transglutaminase, FXIII-mediated PDI activity is independent of its transglutaminase activity and is located on the A subunit. Surface-associated PDI has been previously shown to catalyse two distinct functions: transnitrosation with subsequent release of intracellular nitric oxide and disulfide bond rearrangement during platelet integrin ligation. Our results imply that FXIII-PDI activity may have a role in platelet function.

Direct thrombin inhibitors enhance fibrinolysis more efficiently than heparin. Direct thrombin inhibitors and heparin enhance fibrinolysis by inhibition of activation of thrombin activatable fibrinolysis inhibitor (TAFI); however, the role played by other thrombin-activated proteins [e.g., factor XIII (FXIII)] in fibrinolysis remained to be elucidated. Our goal was thus to define the roles of TAFI and FXIII in direct thrombin inhibitor-mediated fibrinolysis enhancement. Plasma was exposed to argatroban or heparin, with coagulation initiated with kaolin/tissue factor and fibrinolysis initiated with tissue plasminogen activator. Additional experiments utilized TAFI and FXIII-deficient plasmas. Coagulation/fibrinolysis kinetics were monitored with thrombelastography. Argatroban (1.25, 2.5 microg/ml) significantly decreased clot lysis time and increased the maximum rate of lysis compared with unexposed plasma, whereas heparin exposure only diminished clot lysis time. When changes in maximum rate of lysis were related to changes in the maximum rate of thrombus generation, argatroban was associated with a greater increase in maximum rate of lysis per decrease in maximum rate of thrombus generation compared with heparin. Experiments with TAFI-deficient and FXIII-deficient plasma demonstrated a sparing of thrombin-mediated FXIII activation with concurrent inhibition of TAFI activation. The mechanism by which argatroban more efficiently enhanced fibrinolysis was via a differential inhibition of thrombin-mediated activation of TAFI and FXIII.

A novel assay for factor XIII is described that utilizes exclusively small synthetic peptides as substrates for the cross-linking reaction catalyzed by activated factor XIII (FXIIIa). The acyl donor substrate (selection peptide) is immobilized on a microplate via biotin while the acyl acceptor substrate (detection peptide) is labeled with the fluorochrome Oregon green to allow sensitive detection without the need for secondary enzyme systems for signal amplification. Starting with an amino acid sequence from the fibrin gamma-chain (GQQHHLGGAKQAGDV) as a prototype peptide, the influence of amino acid exchanges were investigated with respect to their impact on the FXIIIa-catalyzed reaction. It was found that FXIIIa readily accepts a broad range of substrate peptides, with a proline neighboring the essential lysine having the most detrimental effect. The assay appears to be valuable for the molecular characterization of factor XIII and may be used for a deeper investigation into the substrate requirements of this final enzyme of wound repair, and eventually also for the characterization of other transglutaminases.

Chronic changes in blood flow induce an adaptation of vascular caliber. Thus, arteries show inward remodeling after a reduction in blood flow. We hypothesized that this remodeling depends on the crosslinking enzyme tissue-type transglutaminase (tTG). Flow-dependent remodeling was studied in wild-type (WT) and tTG-null mice using a surgically imposed change in blood flow in small mesenteric arteries. WT mice showed inward remodeling after 2 days of low blood flow, which was absent in arteries from tTG-null mice. Yet, after continued low blood flow for 7 days, inward remodeling was similar in arteries from WT and tTG-null mice. Studying the alternative pathways of remodeling, we identified a relatively high expression of the plasma transglutaminase factor XIII in arteries of WT and tTG-null mice. In addition, vessels from both WT and tTG-null mice showed the presence of transglutaminase-specific crosslinks. An accumulation of adventitial monocytes/macrophages was found in vessels exposed to low blood flow in tTG-null mice. Because monocytes/macrophages may represent a source of factor XIII, tTG-null mice were treated with liposome-encapsulated clodronate. Elimination of monocytes/macrophages with liposome-encapsulated clodronate reduced both the expression of factor XIII and inward remodeling in tTG-null mice. In conclusion, tTG plays an important role in the inward remodeling of small arteries associated with decreased blood flow. Adventitial monocytes/macrophages are a source of factor XIII in tTG-null mice and contribute to an alternative, delayed mechanism of inward remodeling when tTG is absent.

Objective: To review published literature evaluating the use of rituximab for treatment of acquired hemophilia., Data Sources: An English-language literature search was conducted using MEDLINE (1966-January 2006). References of identified articles were subsequently reviewed for additional data. Search terms included rituximab, acquired hemophilia, and inhibitors., Data Synthesis: Available data suggest that B-cell depletion by rituximab in patients with acquired hemophilia may contribute to the eradication of inhibitors to coagulation factors. B-cells have been shown to be essential in the development of autoimmunity or an acquired immune response. Beneficial effects of rituximab, after failure of established therapies, have been reported in case reports and one small, open-label trial., Conclusions: Although data are limited, administration of rituximab appears to be an effective option for treatment of patients with acquired hemophilia after established therapies have failed. Patients given rituximab experienced cessation of recurrent bleeding, normalization of factor VIII activity, and eradication of inhibitors. A complete response to rituximab (undetectable inhibitors, normalization of factor levels) generally occurred several weeks to months after initiation of therapy.

A new class of selective FXIIIa inhibitors with a bicyclic [1,2,4]-thiadiazole pharmacophore is described. At 160 muM, compound 8 caused 50% reduction in fibrin gamma-chain cross-linking and suppressed the polymerization of alpha chains in platelet-depleted human plasma clots. Fibrinolysis rates in response to tissue plasminogen activator were directly proportional to the concentration of 8 in plasma at the time of clotting.

Patients affected with the hemorrhagic syndrome caused by contact with caterpillars of the Lonomia genus show digestive, pulmonary and intraperitoneal bleeding in combination with hematomas and echymosis. Hematuria is also frequently seen. Blood coagulation tests show prolongation of PT, aPTT and ThT. There is a decrease of Fg, FV, FXIII, Pg and alpha 2AP. Factor VIII and FvW are increased while the platelet count is unaffected. FDP's are increased and D-dimers are present in most cases. Treatment with whole blood or fresh frozen plasma worsens the clinical picture causing a severe drop in the platelet count often leading to renal failure and death. However, if antifibrinolytics, either alone or in combination with cryoprecipitate or purified fibrinogen, are administered, no change in the platelet count can be detected and the patients recover rapidly. It is concluded that this syndrome is caused by a mild disseminated intravascular coagulation (DIC) in combination with a hyperfibrinolytic state; the former being partially obscured by the latter, that manifests on administration of whole blood or fresh frozen plasma. Activators of FII, FV and Pg, and compounds showing FXa, plasmin and kallikrein-like activities have been identified in the Lonomia achelous venom. Proteases capable of degrading FXIII and extracellular matrix protein and an inhibitor of FV have also been isolated from these species. In Lonomia oblique, activators of FII and FX and an enzyme with phospholipase-like activity have been identified. In rabbits, subcutaneous injection of crude extract and one of the chromatographically purified fractions of Lonomia achelous venom causes a decrease of Fg, Pg and FXIII. Intravenous administration of the same fraction causes lysis of preformed thrombus with decrease of Fg, Pg and FXIII in combination with inhibition of thrombus growth. It should be noted that, under the same conditions, injection of Lonomia obliqua prothrombin activator causes a DIC.

Background: The mechanism underlying decreased risk for myocardial infarction in carriers of the Leu34 polymorphism of the factor (F) XIII A-subunit is unclear. Given that acetylation of fibrinogen by aspirin can alter its clotting properties and the presence of fibrin stimulates thrombin-mediated activation of FXIII, we have tested the hypothesis that treatment with aspirin differentially modulates the influence of the FXIII Val34Leu polymorphism on its activation in vivo., Methods and Results: The rates of the disappearance of FXIIIA chain and the appearance of its activated form (FXIIIAa) in sequential 30-second blood samples collected at the site of microvascular injury were compared in 14 healthy carriers of the Leu34 allele and 23 Val34 homozygotes both before and after a 7-day aspirin ingestion (75 mg/d), with the use of quantitative Western blotting. The presence of the Leu34 allele was associated with a significant increase in the maximum rate of FXIII activation by thrombin. Although the Leu34-positive and -negative subjects were similar with respect to aspirin-related impairment of thrombin generation, aspirin led to a more pronounced inhibition of the activation of FXIII in the Leu34 carriers as compared with the Val34 homozygotes., Conclusions: Inhibition of FXIII activation by aspirin is enhanced in the Leu34 carriers in vivo, suggesting that these subjects might benefit more than the Leu34-negative subjects from the reduction in risk for myocardial infarction with low-dose aspirin.

Intracranial hemorrhage in a young woman with systemic lupus erythematosus necessitated two surgical evacuations. In the absence of a family history of bleeding, clot solubility in urea suggested a factor XIII (FXIII) inhibitor. The patient's IgG bound well to the virgin and the thrombin-modified zymogen ensemble (A(2)B(2) and A(2)'B(2)) and to the free rA(2) but reacted poorly with the thrombin-modified rA(2)'. Since the IgG did not block the thrombin-catalyzed proteolysis of A subunits nor the dissociation of the A(2)'B(2), its action might be to interfere with the release of activation peptides from the thrombin-cleaved zymogen, hindering the conformational change necessary for generating FXIIIa. Treatment with cryoprecipitate and cyclophosphamide arrested the hemorrhage and almost neutralized the antibody so that the patient's clot became insoluble in urea and showed a close to normally crosslinked gamma-gamma and alpha(n) fibrin chain profile. Nevertheless, she still has detectable anti-FXIII antibody and may be at risk for hemorrhage.

Contact with Lonomia achelous caterpillars venom induces a severe bleeding syndrome in humans. A constant finding in all reported cases is a marked decrease of blood coagulation factor XIII (FXIII), which has been attributed to the presence of a proteolytic enzyme, isolated and named Lonomin V, in the hemolymph and hair secretion. In this study, the effect of Lonomin V on transglutaminase activity from human plasma, rabbit plasma, and platelet FXIII was analyzed. The decrease of activity was more pronounced in platelet (A2) when compared with rabbit plasma (AB) and human plasma FXIII (A2B2). This finding might be explained by the differences in FXIII molecular structure. In addition, platelet FXIII molecule was degraded by Lonomin to several fragments of low molecular mass. Lonomin V was stable over a wide range of pH (6-8.5) and temperatures of -70 degrees C, -20 degrees C and between 4 to 24 degrees C, with a progressive decrease at 37 degrees C and total inactivation at 60 degrees C after 2 hours incubation. Diisopropyl fluoro-phosphate, phenylmethylsulfonyl fluoride, tosyl-l-lysine chloromethyl ketone, and iodoacetamide abolished the effect of Lonomin V on FXIII; in contrast dithiothreitol and EDTA-Na enhance the activity. We concluded that Lonomin V is a serine proteinase with a free Cys essential for the enzymatic activity. Due to its proteolytic activity on FXIII, with concomitant impairment of fibrin cross-linking, Lonomin V might be useful in association with thrombolytic drugs for preventing rethrombosis.

The plasma factor XIII (FXIII) is a transglutaminase which catalyzes the cross-linking of fibrin monomers during blood coagulation. S-nitrosylation of protein sulfhydryl groups has been shown to regulate protein function. Therefore, to establish whether nitric oxide (NO) affects the enzymatic activity of FXIII, we studied the effect of the NO-donor S-nitroso-N-acetylpenicillamine (SNAP) in a blood coagulation test in vitro. High concentrations of SNAP were found to have inhibitory effects on clot formation. Moreover, specific formation of gamma-dimers through the action of FXIII is selectively inhibited by high concentrations of SNAP, as revealed by Western blot. Purified activated FXIII and plasma preparations were then exposed to NO-donor compounds and the enzyme activity was assayed by measuring the incorporation of [3H] putrescine into dimethylcasein. The NO donors, SNAP, spermine-NO (SPER-NO) and 3-morpholinosydnonimine (SIN-1), and the NO-carrier, S-nitrosoglutathione (GSNO), inhibited FXIII activity in a dose-dependent manner, in both purified enzyme and plasma preparations. Titration of -SH groups of FXIII with [14C] iodoacetamide has shown that the number of titratable cysteines per monomer of FXIII decreased from 1 (in absence of NO donors) to 0 (in the presence of NO donors). These results demonstrate that blood coagulation FXIII is a target for NO both in vitro and in vivo, and that inhibition occurs by S-nitrosylation of a highly reactive cysteine residue. In conclusion, we show that inhibition of FXIII activity by NO may represent an additional regulatory mechanism for the formation of blood clot with physio-pathological implications.

Lonomia achelous caterpillar venom (LACV) causes a severe bleeding diathesis in humans. A constant finding in these cases is a profound depression of blood clotting Factor XIII (FXIII) activity. The molecular mechanisms by which LONOMIN V (a chromatographically purified fraction from LACV) alters the FXIII complex is the subject of the present study. Incubation of human purified FXIII with Lonomin V shows that both the zymogen and the activated forms of FXIII were proteolytically degraded, with the generation of peptidic fragments of low molecular weight. Both the A and B subunits of FXIII were degraded in a progressive, dose dependent manner. The B subunit was more resistant to the action of Lonomin V, requiring higher concentrations in order to achieve complete degradation. On the basis of these findings we postulate that the proteolysis of FXIII in vivo is one of the pathophysiological factors behind this bleeding syndrome.

Lonomia Achelous Caterpillar Venom (LACV) causes a severe acquired bleeding diathesis in exposed persons. The condition is characterized by prolonged bleeding from superficial wounds and mucous membranes. Intracranial or intra-abdominal hemorrhage is a common and often fatal complication. A constant finding in these cases is a profound decrease of clotting Factor XIII (FXIII) activity. In the present study, the effects of LACV on plasmatic and purified human FXIII has been evaluated. The results show that native LACV and one of its chromatographically purified fractions (termed FIID) produce a dose dependent decrease of FXIII activity accompanied with an impairment of fibrin(ogen) crosslinking. We conclude that the inactivation of FXIII by fraction FIID (which will be named Lonomin V), is one of the principal patho-physiological mechanisms behind the acquired bleeding diathesis seen in these cases.

An acquired IgG inhibitor to factor XIII was identified in a 30-year-old Vietnamese woman with systemic lupus erythematosus. The IgG fraction was isolated from plasma by chromatography on an agarose gel column and by protein G adsorption. The anti-factor XIII activity, identified within the IgG fraction, inhibited factor XIII from both normal plasma (a2b2) and platelets (a2). A normal level of the b subunit was measured by immunoelectrophoresis of the patient's plasma, but the a subunit was not detected. These results suggested the presence of an IgG immunoglobulin which recognized the a subunit and interfered with its activity.

Recurrent hemorrhage has been reported in humans as a result of acquired antibody inhibitors which interfere with the crosslinking of fibrin by factor XIII. One type of these inhibitors (Type III) prevents activated factor XIII from acting on fibrin. We have generated an antifibrin monoclonal antibody, called mAb 4A5, which binds to a peptide sequence at the carboxyl-terminus of human fibrinogen gamma-chains. MAb 4A5 acts like a Type III inhibitor and prevents proper factor XIII-mediated crosslinking. Pre-incubation of fibrinogen or pooled human plasma with mAb 4A5, but not mAb D2 (specific for the carboxyl terminus of fibrin alpha-chains), resulted in clots which are soluble in either 5 M urea or 1% monochloroacetic acid. SDS-PAGE and immunoblotting analysis of these clots confirmed that mAb 4A5 inhibited gamma-chain crosslinking in plasma clots and fibrin clots. Results from a factor XIII activity assay demonstrated that biotinylcadaverine crosslinking into fibrin by factor XIII could be inhibited by mAb 4A5 but not mAb D2, arguing that mAb 4A5 acted by binding the crosslinking site of factor XIII. Studies of the immunoreactivity of these mAbs with 12 different animal species showed that the gamma-chain epitope recognized by mAb 4A5 was more conserved than the alpha-chain epitope recognized by mAb D2. The species fibrinogens, recognized by mAb 4A5 in binding assays, also showed impaired crosslinking when mAb 4A5 was present during the clotting reaction

Although known to play a critical role in thrombosis, the precise role of factor XIII in other processes like wound healing and gestation remains to be elucidated. Because a specific, potent inhibitor could help define the function of factor XIII in these processes, or determine the potential benefits of factor XIII suppression in thrombotic disease, we have derived and characterized a monoclonal antibody inhibitor of factor XIII activation. This immunoinhibitor, 9C11, reacts specifically with both plasma and platelet forms of factor XIII. When added to human plasma, either as whole immunoglobulin or as Fab fragments, 9C11 completely prevented thrombin-activated factor XIII activity with small molecular weight substrates like 14C-putrescine. In addition, when clotted with plasma, 9C11 ablated the gamma chain crosslinking of fibrin catalyzed by factor XIII and markedly accelerated the fibrinolysis of plasma clots by urokinase. Studies of the mechanism of action showed that 9C11 inhibited the cleavage and activation of factor XIII by thrombin, but did not affect the catalytic function of previously activated factor XIII. Although it inhibited thrombin activation, experiments indicated that it bound comparably to both factor XIII zymogen and the thrombin-cleaved zymogen, and did not bind to the thrombin cleavage site of the molecule. Taken together these experiments indicated that 9C11 acted as an inhibitor of the thrombin cleavage and activation of the factor XIII A-subunit. Its potency and specificity make it a useful agent for studying thrombin-activatable factor XIII function in biological systems.

Efforts to develop an improved assay for plasma and tissue transglutaminase have led us to a convenient, sensitive microtiter plate assay for coagulation factor XIII using human fibrinogen as an immobilized substrate. Factor XIII was activated in the presence of calcium, thrombin, and immobilized fibrinogen and then assayed by adding biotinylcadaverine. The reaction was terminated by adding EDTA and the level of incorporated biotin was measured with streptavidin-beta-galactosidase. In this assay, the analytical range for human platelet factor XIII was 0.01-100 ng and 1-100 ng for guinea pig liver transglutaminase. Fibrinogen-coated plates gave more than 100-fold increase in sensitivity compared with N,N-dimethylcasein-coated microtiter plates. The intraassay coefficient of variation was less than 5% (n = 12) and interassay less than 6% (n = 4). The sensitivity of this assay reduced the volumes of plasma samples required and consequently eliminated the need to remove fibrinogen from such test samples. As expected, factor XIII activity could be inhibited by putrescine and antibodies against factor XIII as well as by a monoclonal antibody that bound to the carboxyl terminus of human fibrin gamma-chains. The assay provided a sensitive, simple, and rapid method for measuring factor XIII.

Coagulation factor XIII (FXIII) is of paramount importance in the process of fibrin stabilization, which is the final step of the coagulation cascade. The clinical significance of defective fibrin stabilization is highlighted by the severe hemorrhagic manifestations of congenital FXIII deficiency. In this paper we review the pathophysiology, clinical presentation and therapy of acquired plasma FXIII deficiencies, caused by specific inhibitors or associated with other clinical conditions. For acquired severe FXIII deficiency caused by factor-specific inhibitors, the need for prompt diagnosis and treatment is emphasized by the high hemorrhagic risk and mortality. For moderate reduction of FXIII secondary to other conditions, we discuss the relative importance of FXIII reduction in the development of clinical symptoms and the role of substitution treatment.

An 81-year-old woman, who presented with sudden episodes of spontaneous bleeding, was found to have a specific inhibitor of factor XIII. Her fibrin clots had approximately 70% gamma-gamma and no alpha polymer formation, under conditions where normal fibrin was fully cross-linked; the patient's clots were soluble in urea or monochloroacetic acid. Factor XIII activity in her plasma was 24%, measured by the dansylcadaverine incorporation assay. When mixed with normal plasma, the patient's plasma inhibited fibrin cross-linking; however, in mixtures of patient and normal plasma, there was no inhibition of factor XIII activity when assayed by the incorporation of dansylcadaverine into casein. Thus, this inhibitor was active against fibrin cross-linking but not against ligation of small molecules to casein. Consequently, gel electrophoresis of reduced, sodium dodecyl sulfate-solubilized fibrin clots was a simple, quantitative method that was used to measure inhibitor activity. This inhibitor is unique and has been designated inhibitor New Haven. It was neutralized by anti-IgG and anti-kappa. It did not inhibit the activation of factor XIII but did inhibit fibrin cross-linking. There was complex formation between the inhibitor and activated factor XIII (A', A*) but not between A2 or fibrinogen. Only A', A* and the 56-Kd fragment bound to affinity columns made with this IgG. The inhibitor significantly decreased the binding of A', A* to fibrin clots. These data indicate that the epitope for this inhibitor is in a fibrin binding site. It is hidden in the zymogen and expressed on A' and A*, indicating that the conformational change occurring with the cleavage of the activation peptide is sufficient to expose the fibrin binding site.

As the final enzyme in the coagulation cascade, activated fibrin stabilizing factor or factor XIII catalyzes the intermolecular cross-linking of fibrin chains. To study this enzyme in plasma, we derived a monoclonal antibody (MAb 309) against a peptide sequence (NH2-G-V-N-L-Q-E-F-C-COOH) in the thrombin activation site of factor XIII. Radioimmunoassays indicate that MAb 309 binds specifically to both platelet and plasma factor XIII. Peptide inhibition studies demonstrate that the MAb binds equally well to the factor XIII (FXIII) zymogen and the active form of FXIII (FXIIIa). In immunoblots of whole platelet lysates, MAb 309 binds only to FXIII and does not cross-react with other proteins. In saturation binding studies, the antibody shows a binding avidity of (1.75 +/- 0.35) x 10(9) M-1. MAb 309 also inhibited 99% of apparent FXIIIa activity in a standard transglutaminase assay. SDS-PAGE analysis of fibrin clots showed that MAb 309 inhibited fibrin gamma-gamma cross-linking. Moreover, MAb 309 accelerated the lysis of plasma clots, consistent with inhibition of fibrin-fibrin and fibrin-alpha 2-antiplasmin cross-linking. Immunoblotting experiments revealed that MAb 309 affected apparent FXIIIa activity by inhibiting the thrombin activation of the FXIII zymogen. In addition to its utility as a specific probe for the FXIII a-subunit, the strategy used to obtain MAb 309 may be used to generate MAbs that inhibit the activation of other coagulation factor zymogens.

A 63-year-old woman presented with extensive bruising. An inhibitor to factor XIII was detected. Subsequent subcutaneous bruising and soft tissue haemorrhage into the left foot were treated with infusions of pasteurized factor XIII concentrate with good effect. Immunosuppression with cyclophosphamide was attempted but in spite of this she suffered a right cerebral haemorrhage necessitating further intensive therapy with factor XIII concentrate. This overcame the inhibitor, adequate post-infusion factor XIII levels were achieved and she made an excellent recovery. Factor XIII concentrate was well tolerated with no evidence of transmission of hepatitis or HIV infection. The inhibitor appeared to interfere with haemostasis by hindering the fibrin binding site of factor XIII, resulting in interference in clot-solubility tests. Subsequently the inhibitor resolved.

Some physiological properties of a complex of factor XIII with heparin were studied in relatively pure system in vitro. The complex was shown to exhibite the fibrinolytic activity toward unstabilized fibrin in the presence or absence of xi-aminocapronic acid, optimal pH for the activity was at pH 6.5--7.5 The activity was still observed after heating at 60 degrees C for 30 min. An excess of heparin was found to block the specific hydrolytic activity of the complex studied. The possibility of transition of heparin from a complex adrenaline-heparin to factor XIII with formation of factor XIII--heparin complex was shown. As a result of interaction of heparin with factor XIII the latter lost the fibrin-stabilizing activity.

The variations of dilute blood clot lysis time (DBCLT) in 103 diabetic patients were investigated in terms of insulin dependency, body weight, serum lipids and presence of diabetic vascular diseases. The results showed that DBCLT was significantly longer in the 34 overweight diabetic patients (437 +/- 68 min) than in the 69 diabetics at or below the ideal body weight (240 +/- 28 min) or in the 76 normalipidemic normal weight control subjects (253 +/- 12 min). DBCLT was also longer in the hypertrigliceridemic diabetic patients than in the normolipidemic ones. The mean lysis time was similar in diabetic patients with and without retinopathy. However, a higher level of fibrinolytic inhibitors was found in patients with diabetic small vessel disease. In vitro inhibition of plasma factor XIII by p-chlormercuribenzoate (PCMB) caused an acceleration of DBCLT and the differences between lysis time in the overweight diabetics and in the controls were attenuated. These results suggested that deficient thrombolysis is rather due to overweight and to disturbances of lipid metabolism than to diabets and/or its vascular complications and that enhanced fibrin crosslinking is at least partially responsible for delayed clot lysis.