Uncommon defibrinogenation and coagulopathy caused by Trimeresurus stejnegeri stejnegeri envenomation in a patient with swelling above the ankle.

In Taiwan, Trimeresurus stejnegeri stejnegeri (Stejneger's Bamboo pitviper) is responsible for more than half of all venomous snakebites annually. This species often causes local envenoming characterized by tissue swelling and pain, occasional local ecchymosis, bullae and blister formation, and lymphangitis and lymphadenitis. The pathophysiology and treatment of potentially life-threatening coagulopathy and defibrinogenation induced by T. s. stejnegeri systemic envenoming have not been specifically addressed. Here, we describe the case of a man who was bitten by T. s. stejnegeri on his right first toe, which later developed into swelling above the ankle. It was found that there was severe hypofibrinogenemia, prolonged prothrombin time, and reduced activities of factors V and XI, plasminogen, and α2-antiplasmin. Even though a favorable outcome was achieved after repeatedly administering specific antivenom, fresh frozen plasma, and cryoprecipitate, probably low effectiveness of antivenom against the coagulopathy and prodigious amounts of replacement products were observed. To control coagulopathy early and avoid the needless replacement of coagulation factor, which are associated with inherent adverse reactions, more frequent serial blood assessment (e.g., every 6 h) and higher initial antivenom doses may be helpful. Knowledge of the specific coagulation factor deficiencies may improve our understanding of the relationship between hemotoxins and the resulting envenoming syndromes in this snakebite.

Population divergence in venom bioactivities of elapid snake Pseudonaja textilis: role of procoagulant proteins in rapid rodent prey incapacitation.

This study looked at how toxic proteins in venoms of adult Australian eastern Brown snakes Pseudonaja textilis from South Australian and Queensland populations interact with physiological functions of the lab SD rat Rattus norvegicus. Circulatory collapse and incoagulable blood occurred instantly after injection of venom under the dorsal skin of anaesthetised and mechanically ventilated rats in an imitation of a P. textilis bite. Intravenous injection of purified P. textilis (Mackay, QLD) venom prothrombin activator proteins caused instant failure of circulation, testifying of high toxicity of these proteins and suggesting their role in rapid incapacitation of rodent prey. The hypothesis is further supported by circulatory collapse occurring instantly despite artificial respiration in envenomed rats and the finding of extremely high venom procoagulant potency in rat plasma. LC-MS and physiology assays revealed divergent venom composition and biological activity of South Australian (Barossa locality) and Queensland (Mackay locality) populations, which may be driven by selection for different prey. The Queensland venom of P. textilis was found to be more procoagulant and to exhibit predominately presynaptic neurotoxicity, while the South Australian venom contained diverse postsynaptic type II and III α-neurotoxins in addition to the presynaptic neurotoxins and caused significantly faster onset of neuromuscular blockade in the rat phrenic nerve-diaphragm preparation. LC-MS analysis found evidence of multiple coagulation factor X-like proteins in P. textilis venoms, including a match to P. textilis coagulation factor X isoform 2, previously known to be expressed only in the liver.

A novel therapeutic approach combining human plasma-derived Factors VIIa and X for haemophiliacs with inhibitors: evidence of a higher thrombin generation rate in vitro and more sustained haemostatic activity in vivo than obtained with Factor VIIa alone.

BACKGROUND AND OBJECTIVES: Therapy with recombinant Factor VIIa (rFVIIa) for haemophiliacs with inhibitors still has some unresolved problems, such as the requirement for frequent infusions of rFVIIa every 2-3 h to sustain haemostatic activity for an extended time-period and that the therapeutic dose of rFVIIa is not always predictable. In the present study, we searched for an effective combination of plasma-derived FVIIa with other blood coagulation factors, and demonstrated that a therapeutic approach combining plasma-derived FVIIa and Factor X (FX) was more useful for treating haemophiliacs with inhibitors than FVIIa alone. MATERIALS AND METHODS: The haemostatic effects of FVIIa and FX were evaluated in vitro and in vivo. In in vitro experiments we assessed the following: the ability to enhance the thrombin generation rate in a reconstituted blood coagulation model without Factor VIII (FVIII) or Factor IX (FIX); the ability to correct the activated partial prothrombin time (APTT) of FVIII-depleted plasma or FIX-depleted plasma; and the ability to correct the clotting time of haemophilia-like whole blood using thromboelastography (TEG). In in vivo experiments, the haemostatic activity of the combination treatment of FVIIa and FX was determined by measuring the bleeding time and TEG using a monkey haemophilia B model produced by the injection of anti-human FIX polyclonal antibodies. The degree of thrombogenicity of the combination was evaluated using the rabbit stasis model. RESULTS: The addition of FX to FVIIa dramatically enhanced the thrombin generation rate in the reconstituted blood coagulation model and corrected the prolonged APTTs of FVIII- and FIX-depleted plasmas to levels achieved by the replacement therapies. In contrast, the addition of prothrombin to FVIIa did not show such enhancing activity. Furthermore, FVIIa-induced whole blood clotting times in the FVIII- and FIX-inhibited states were also shortened by the addition of FX in a concentration-dependent manner. Finally, the co-administration of FVIIa (80 microg/kg) and FX (800 microg/kg) in a monkey haemophilia B model resulted in a more robust and persistent haemostatic effect on the secondary bleeding time and whole-blood clotting time of TEG than that of FVIIa alone. The results of rabbit stasis tests for evaluating the risk of thrombogenicity showed that the combination of FVIIa and FX was less thrombogenic than FEIBA. CONCLUSIONS: The present study demonstrated that the combination of FVIIa and FX appeared to have a higher and more sustainable haemostatic potential than FVIIa alone, and less thrombogenicity than FEIBA. A therapeutic approach combining FVIIa and FX could be a promising and novel approach to compensate for the disadvantages of rFVIIa and FEIBA for haemophiliacs with inhibitors.

Thrombogenicity of a factor IX concentrate quantitated in a canine model.

Dose-ranging studies with a batch of factor IX concentrate have been performed in a canine non-stasis model of thrombogenicity. Doses between 50 and 200 IU/kg were infused over a 30 min period, and beagles were found to be more sensitive than greyhounds with regard to subsequent alterations in haemostatic parameters over a 150 min period. In beagles we detected significant increases in plasma fibrin(ogen) degradation products and reduction in fibrinogen concentrations in a dose-related manner after infusion of factor IX concentrate over the range 50-150 IU/kg. Plasma fibrinopeptide A was the most sensitive marker of activation of coagulation with significantly increased levels after factor IX at 50 IU/kg compared with control infusions of albumin. Recovery of infused factor IX was similar to values reported in man. In these experiments, measurement of urinary fibrinopeptide A did not prove to be a useful indicator of thrombogenicity. In conclusion, the beagle non-stasis model will provide a sensitive method to quantify the unwanted thrombogenic activities associated with the use of high doses of certain factor IX concentrates.

Thrombogenicity of factor IX complex: in vivo investigation.

Factor IX Complex therapy has been associated with thrombosis when used in patients with liver disease, hemophilia B and hemophilia A with inhibitors to Factor VIII when administered repetitively and in high doses. Three mechanisms for inducing thrombogenicity have been proposed: activated coagulants, coagulant-active phospholipid content and/or the high zymogen level attained in recipients. A new animal model using Russel Viper Venom (RVV) as an in vivo stimulus of coagulation has been used to investigate the role of high levels of zymogens in the induction of thrombosis. The quantity of RVV tolerated by rabbits infused with Factor IX Complex is reduced 100-fold. Infusion of Factor X or prothrombin also reduces the lethal dose of RVV. In contrast, Coagulation Factor IX devoid of other coagulants has little effect. However other animal data indicate that the amount of activated coagulants can play a role in the in vivo thrombogenicity of Factor IX Complex.