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In a factor XIIIa (FXIIIa) generation assay with recombinant FXIII-A2 (rFXIII-A2 ) free FXIII activation peptide (fAP-FXII) prolonged the time to peak (TTP) but did not affect the area under the curve (AUC) or concentration at peak (CP). Addition of recombinant factorXIII-B2 (rFXIII-B2 ) restored the characteristics of the FXIIIa generation parameters (AUC, TTP and CP) to those observed for plasma FXIII (FXIII-A2 B2 ). FXIII-A2 B2 reconstituted from rFXIII-A2 and rFXIII-B2 showed a similar effect on AUC, TTP and CP in the presence of fAP-FXII as observed for plasma FXIII-A2 B2 , indicating a role for FXIII-B in this observation. An effect of fAP-FXIII on thrombin, the proteolytic activator of FXIII, was excluded by thrombin generation assays and clotting experiments. In a purified system, fAP-FXIII did not interfere with the FXIIIa activity development of thrombin-cleaved rFXIII-A2 (rFXIII-A2 ') also excluding direct inhibition of FXIIIa. However, FXIIIa activity development of FXIII-A2 'B2 was inhibited in a concentration-dependent manner by fAP-FXIII, indicating that an interaction between AP-FXIII and FXIII-B2 contributes to the overall stability of FXIII-A2 'B2 . In addition to its well-known role, FXIII-B also contributes to FXIII-A2 B2 stability or dissociation depending on fAP-FXIII and calcium concentrations., (© 2015 John Wiley & Sons Ltd.)

Background: Gelatin solution impairs coagulation. The mechanism of coagulopathy is incompletely defined. The purpose of this study was to evaluate the capacity of single coagulation factors to reverse gelatin-promoted whole-blood coagulation disorders in vitro., Methods: Venous blood was withdrawn from 12 volunteers in a crossover study. Four percent succinylated gelatin was added to citrated whole-blood samples to make a 40 vol% end-concentration of gelatin. The baseline and 40 vol% samples, and samples with addition of fresh-frozen plasma (FFP), fibrinogen, coagulation factors XIII (FXIII) or VIII, together with the von Willebrand factor (FVIII+vWF), were analysed by thromboelastometry (ROTEM. Coagulation was initiated by tissue thromboplastin (ExTEM with and without cytochalasin to determine the functional component of fibrinogen (FibTEM., Results: Initiation of coagulation and fibrin formation were delayed at 40 vol% gelatin dilution. At this stage, the median (25th-75th percentiles) maximum clot firmness (MCF) was 76.3 (65.9-80.0) and 32.5 (27.4-45.0)% of the pre-dilution value in ExTEM and FibTEM thromboelastometry, respectively. Coagulation time was corrected by addition of fibrinogen and FFP in ExTEM and FibTEM analysis, whereas FVIII or FXIII had minimal effects. MCF was partly restored only by FFP in ExTEM. In FibTEM analysis, MCF improved more by fibrinogen than by FVIII+VWF, FXIII or FFP., Conclusions: Gelatin-induced whole-blood coagulation disorder in vitro is mainly dependent on the initial fibrinogen-fibrin interaction. The proposed mechanism might suggest not to reverse gelatin coagulopathy solely by fibrinogen administration. The administration of FFP, a mixture of different coagulation factors, reversed the gelatin-induced in vitro coagulopathy the best.

Background: Hydroxyethyl starch (HES) administration has resulted in decreased hemostasis and fibrinogen (FI)-thrombin-(FIIa)-Factor XIII (FXIII) interactions. I proposed to determine the hemostatic effect of hemodilution with PentaLyte (6% HES, mean molecular weight 220 kDa) and Voluven (6% HES, 130 kDa)., Methods: Rabbits were intravenously administered 20 ml/kg PentaLyte or Voluven (n = 8 per fluid) over 10 min. Plasma was obtained prior to, 1 min and 1 h after hemodilution. Thrombelastography was performed, with clot initiation (R, sec), clot propagation (alpha, degrees), and clot strength (shear elastic modulus, G, dynes/cm2) determined over 20 min. Celite-activated samples had either no additions or addition of FI, FIIa or activated FXIII (FXIIIa) to restore protein content to pre-diluted values., Results and Conclusions: While there were no significant differences between the groups, R significantly decreased 1 h after hemodilution compared with values observed before and 1 min after hemodilution, whereas alpha and G significantly decreased 1 min after hemodilution and then significantly, but only partially, increased 1 h after hemodilution compared with pre-dilution values. Addition of FI, FIIa and FXIIIa significantly decreased R in both groups. alpha and G 1 min after hemodilution were significantly enhanced by FI, FIIa, FXIIIa in both groups; however, 1 h after hemodilution, rabbits administered PentaLyte had alpha and G enhanced only by FI and FXIIIa addition, whereas animals administered Voluven had alpha and G significantly enhanced by FI addition. PentaLyte and Voluven hemodilution initially diminishes FIIa-FI and FXIIIa-fibrin, but within an hour primarily inhibit FXIIIa-fibrin interactions in the rabbit.

We report a new case of severe bleeding diathesis due to an acquired inhibitor of fibrin crosslinking. The patient, an 80-year-old woman, was admitted to the hospital for a massive subcutaneous hematoma, with severe anemia requiring red cell transfusion; a subsequent retroperitoneal hematoma developed 2 weeks later. Coagulation studies were normal except for a thromboelastographic pattern suggestive of FXIII deficiency. Clot solubility test was abnormal even after 1:1 mix with normal plasma. Immunochemical studies confirmed the presence of a monoclonal IgG lambda inhibitor directed against FXIII activity (type II FXIII inhibitor). The patient IgG fraction selectively inhibited FXIII transamidating activity but did not inhibit the thrombin-mediated activation of FXIII. The patient was treated with high doses of FXIII concentrate to overcome the inhibitor and immunosuppressive therapy with cyclophosphamide and discharged in good conditions. High doses of commercially available FXIII appear to be a safe and effective method of controlling acute episodes of bleeding in patients with acquired FXIII deficiency.

Factor XIII is present in plasma as a proenzyme, which when activated catalyses the formation of epsilon(gamma-glutamyl)lysyl bonds in fibrin. In this study the activation of purified plasma factor XIII was examined quantitatively with the fluorescent amine incorporation assay. Activation products were examined by polyacrylamide gel electrophoresis. The serin proteases, thrombin, trypsin, chymotrypsin, and factor Xa, and also Reptilase were tested for their ability to activate factor XIII. Highly purified thrombins activated purified factor XIII; this reaction was not calcium dependent. Trypsin was also a potent activator, but no transglutaminase activity was found with chymotrypsin. The most highly purified preparations of Reptilase had no effect on factor XIII activity. Less purified Reptilase preparations activated factor XIII, which suggests the presence of another enzyme in these Reptilase preparations. Highly purified factor Xa was found to be an effective activator of purified factor XIII. In contrast to thrombin activation, this reaction required calcium. It may be that under certain circumstances factor XIIIa could be formed in vivo directly by the alternative pathway of factor Xa. Factor XIIIa could then crosslink fibrinogen, which would also provide an alternative pathway for thrombus formation. Also, the activation of factor XIII by both factor Xa and thrombin provides a further point of control in the blood coagulation process.