Coagulation factor activity patterns of venom-induced consumption coagulopathy in naturally occurring tiger snake (Notechis scutatus) envenomed dogs treated with antivenom

BACKGROUND

Venom-induced consumption coagulopathy (VICC) from tiger snake (Notechis scutatus) envenomation results in a dose-dependent coagulopathy that is detectable on coagulometry. However, individual coagulation factor activities in dogs with tiger snake envenomation have not been determined. This study aimed to characterise VICC and the time course of recovery in tiger snake envenomed dogs and to investigate an association between tiger snake venom (TSV) concentrations and factor activity.

METHODS

This was a prospective, observational, cohort study. The study cohort was 11 dogs of any age, breed, sex, body weight >10 kg, confirmed serum TSV on ELISA and treated with antivenom. Blood was collected at enrolment before antivenom administration, then at 3, 12 and 24 h after antivenom administration. Tiger snake venom concentrations were detected with a sandwich ELISA. Fibrinogen was measured using a modified Clauss method, and coagulation factors (F) II, V, VII, VIII and X were measured with factor-deficient human plasma using a modified prothrombin (PT) and activated partial thromboplastin (aPTT) method. Linear mixed models, with multiple imputations of censored observations, were used to determine the effect of time and TSV concentration on the coagulation times and factor activity. This cohort was compared to 20 healthy controls.

RESULTS

At enrolment, there were severe deficiencies in fibrinogen, FV and FVIII, with predicted recovery by 10.86, 11.75 and 13.14 h after antivenom, respectively. There were modest deficiencies in FX and FII, with predicted recovery by 20.57 and 32.49 h after antivenom, respectively. No changes were detected in FVII. Prothrombin time and aPTT were markedly prolonged with predicted recovery of aPTT by 12.58 h. Higher serum TSV concentrations were associated with greater deficiencies in FII, FV and FVIII, and greater prolongations in coagulation times. The median (range) serum TSV concentration was 57 (6-2295) ng/mL.

CONCLUSIONS

In tiger snake envenomed dogs, we detected a profound, TSV-concentration-related consumption of select coagulation factors, that rapidly recovered toward normal. These findings allowed further insight into tiger snake VICC in dogs.

Differential heme-mediated modulation of Deinagkistrodon, Dispholidus, Protobothrops and Pseudonaja hemotoxic venom activity in human plasma

Envenomation by vipers with hemotoxic enzymes continues to be a worldwide source of morbidity and mortality. The present work examined the effects of exposure of venom enzymes to carbon monoxide and O-phenylhydroxylamine, agents that modulate the biometal heme, by forming carboxyheme and metheme, respectively. Four venoms obtained from medically important, diverse snake venom found in Africa, Asia and Australia were analyzed. The species that had venom tested in human plasma with thrombelastography and heme modulating agents were Deinagkistrodon acutus, Protobothrops mucrosquamatus, Dispholidus typus and Pseudonaja textilis. These venoms varied four hundred-fold in potency (ng-µg/ml) to exert procoagulant effects on human plasma; further, there was species specific variability in venom inhibition after exposure to carboxyheme or metheme agents. Lastly, using a wide range of carbon monoxide concentrations, it was determined that the factor V component of P. textilis venom was likely inhibited before the factor X component. Further investigation using this thrombelastograph-based, venom "kinetomic" methodology involving heme modulation will demonstrate in time its laboratory and clinical utility.

Carbon monoxide inhibits hemotoxic activity of Elapidae venoms: potential role of heme

Envenomation by hemotoxic enzymes continues to be a major cause of morbidity and mortality throughout the world. With regard to treatment, the gold standard to abrogate coagulopathy caused by these venoms is still the administration of antivenom; however, despite antivenom therapy, coagulopathy still occurs and recurs. Of interest, this laboratory has demonstrated in vitro and in vivo that coagulopathy inducing venom derived from snakes of the family Viperidae exposed to carbon monoxide (CO) is inhibited, potentially by an attached heme. The present investigation sought to determine if venoms derived from snakes of the Elapidae family (taipans and cobras) could also be inhibited with CO or with the metheme inducing agent, O-phenylhydroxylamine (PHA). Assessing changes in coagulation kinetics of human plasma with thrombelastography, venoms from Elapidae snakes were exposed in isolation to CO (five species) or PHA (one specie) and placed in human plasma to assess changes in procoagulant or anticoagulant activity. The procoagulant activity of two taipan venoms and anticoagulant activity of three cobra venoms were significantly inhibited by CO. The venom of the inland taipan was also inhibited by PHA. In sum, these data demonstrate indirectly that the biometal heme is likely bound to these disparate venoms as an intermediary modulatory molecule. In conclusion, CO may not just be a potential therapeutic agent to treat envenomation but also may be a potential modulator of heme as a protective mechanism for venomous snakes against injury from their own proteolytic venoms.

Elucidation of procoagulant mechanism and pathophysiological significance of a new prothrombin activating metalloprotease purified from Daboia russelii russelii venom

The procoagulant proteases present in Russell's Viper venom (RVV) are responsible for promoting consumption coagulopathy in victims. In this study, a procoagulant metalloprotease (Rusviprotease) possessing prothrombin activating and α-fibrinogenase properties has been purified and characterized from RVV. Rusviprotease is a 26.8 kDa glycoprotein which also exists in other multimeric forms. The peptide mass fingerprinting and secondary structure analyses of Rusviprotease revealed its similarity with snake venom prothrombin activators and metalloproteases. Similar to group A prothrombin activators, Rusviprotease cleaved prothrombin independent of any co-factor requirement generating meizothrombin which is further cleaved to form thrombin. The Km and Vmax values of Rusviprotease towards prothrombin were determined to be 1.73 μM, and 153.5 nM thrombin generated/min/μmoles of Rusviprotease, respectively. The Km and Vmax values of Rusviprotease towards fibrinogen were calculated to be 3.14 μM and 78.7 nmol/min, respectively. Spectrofluorometric study provided the evidence of interaction between Rusviprotease and factor Xa with a Kd value of 6.64 nM. This interaction augmented the prothrombin activating property of the factor Xa-prothrombinase-Rusviprotease complex by 2.5 fold. Intravenous injection of Rusviprotease to BALB/c mice (0.1 mg/kg) resulted in in vivo defibrinogenation rendering the blood incoagulable. In conclusion, Rusviprotease is the first example of a prothrombin activator with fibrinogenolytic property purified from Daboia russelii russelii venom.

Prothrombin activator-like toxin appears to mediate cardiovascular collapse following envenoming by Pseudonaja textilis

Brown snake (Pseudonaja spp.)-induced early cardiovascular collapse is a life-threatening medical emergency in Australia. We have previously shown that this effect can be mimicked in animals and is mediated via the release of endogenous mediators. In the present study, we aimed to purify and characterize the component in Pseudonaja textilis venom which induces cardiovascular collapse following envenoming. The component (fraction 3) was isolated using a combination of techniques including hydroxyapatite and reverse phase chromatography. Fraction 3 (10 or 20 μg/kg, i.v.) produced a rapid decrease in mean arterial pressure (MAP) followed by cardiovascular collapse. Fraction 3-induced early collapse was abolished by prior administration of smaller priming doses of fraction 3 (i.e. 2 and 5 μg/kg, i.v.) or heparin (300 units/kg, i.v.). P. textilis whole venom (1 and 3 μg/ml), but not fraction 3 (1 or 3 μg/ml), induced endothelium-dependent relaxation in isolated rat mesenteric arteries. SDS-PAGE gel indicated the presence of 9-10 protein bands of fraction 3. Using proteomic based analysis some protein bands of fraction 3 were identified as subunits of venom prothrombin activator, pseutarin C of P. textilis venom. Our results conclude that prothrombin activator-like toxin is likely to be a contributor to the rapid collapse induced by P. textilis venom.