The action of Echis carinatus venom on the blood coagulation system. Demonstration of an activator of factor X

Comparative study of anticoagulant and procoagulant properties of 28 snake venoms from families Elapidae, Viperidae, and purified Russell's viper venom-factor X activator (RVV-X)

Snake venoms consist of numerous molecules with diverse biological functions used for capturing prey. Each component of venom has a specific target, and alters the biological function of its target. Once these molecules are identified, characterized, and cloned; they could have medical applications. The activated clotting time (ACT) and clot rate were used for screening procoagulant and anticoagulant properties of 28 snake venoms. Crude venoms from Daboia russellii siamensis, Bothrops asper, Bothrops moojeni, and one Crotalus oreganus helleri from Wrightwood, CA, had procoagulant activity. These venoms induced a significant shortening of the ACT and showed a significant increase in the clot rate when compared to the negative control. Factor X activator activity was also measured in 28 venoms, and D. r. siamensis venom was 5-6 times higher than those of B. asper, B. moojeni, and C. o. helleri from Wrightwood County. Russell's viper venom-factor X activator (RVV-X) was purified from D. r. siamensis venom, and then procoagulant activity was evaluated by the ACT and clot rate. Other venoms, Crotalus atrox and two Naja pallida, had anticoagulant activity. A significant increase in the ACT and a significant decrease in the clot rate were observed after the addition of these venoms; therefore, the venoms were considered to have anticoagulant activity. Venoms from the same species did not always have the same ACT and clot rate profiles, but the profiles were an excellent way to identify procoagulant and anticoagulant activities in snake venoms.

The action of Lonomia achelous caterpillars venom on human factor V

The bleeding syndrome produced by contact with the Lonomia achelous caterpillars is characterized by a decrease of fibrinogen, factor XIII, plasminogen, and factor V with normal platelets. In this study, we report the effect of crude hemolymph and some semipurified chromatographic fractions on human factor V. Incubation of factor V with crude hemolymph resulted in an increase in procoagulant activity, followed by a subsequent decline in factor V activity. Identical results were obtained with fraction I, whereas with fraction II there was only a decrease in activity reaching its minimum at 30 minutes. fraction III did not modify the activity of factor V. All concentrations of fraction I tested produced an initial rise and subsequent fall in activity. However, at lower relative concentrations of fraction I, more sustained increases in activity were observed. The activator and inactivator activities present in fraction I show differences in temperature and pH stability, susceptibility to different inhibitors, and in SDS/PAGE pattern. The factor V activator is a thermostable protein, with maximum activity at acid pH and is inhibited by o-phenantroline, EDTA, and EGTA, while the factor V inactivator is thermolabile, presents maximum activity at basic pH, precipitates at pH 5.0, and is completely inhibited by iodoacetic acid and TLCK. It is partially blocked by diisopropyl fluorophosphate, phenylmethylsulfonyl fluoride, and p-chloromercuribenzoic acid. These results suggest that the activator should be a metallo-proteinase, while the inactivator is a serine or cysteine proteinase with a serine, histidine, or cysteine residue in the active site.

Prothrombin and factor X activator activities in the venoms of Viperidae snakes

A Ca(2+)-dependent prothrombin activator, carinactivase-1 (CA-1), was previously found in the venom of Echis carinatus leucogaster. In the present study, the activities of CA-1-like enzymes were screened in the venoms of various Viperidae snakes. The addition of 1 mM Ca2+ ions to the venoms of only Echis snakes in Viperidae produced considerably high prothrombin activator activity, indicating that only the Echis snake venoms contain not only the Ca(2+)-independent prothrombin activator, ecarin, but also Ca(2+)-dependent activator(s). CA-1-like activators and ecarin in the venom of each Echis snake were efficiently separated by Blue Sepharose column chromatography. The venoms of the various Viperidae snakes were also examined for factor X activator activity. The venoms of genera Daboia, Vipera, Cerastes, Echis, Calloselasma and Bothrops contained factor X activator activity in the presence of Ca2+ ions. Cerastes cerastes and Calloselasma rhodostoma venoms also had Ca(2+)-independent factor X activator activity.

The effect on blood clotting of some west African plants used against snakebite

Aqueous extracts of the bark of Schumanniophyton magnificum and the leaves of Mucuna pruriens var. utilis, Strophanthus gratus and Strophanthus hispidus show a dose related ability to prolong the time taken to clot for blood treated with a standardised dose of the venom of Echis carinatus. Strophanthus hispidus was shown to be the most potent of the plants tested. The dose-response profiles obtained showed that the increased clotting time was due to different processes for the different plant extracts.

Structural and functional properties of snake venom prothrombin activators

In this review we have summarized the current knowledge about the prothrombin activating principles present in the venom of a large number of different snake species. It appears that snake venom prothrombin activators can be classified into four different groups based on their structural properties and on their functional properties in prothrombin activation. Group I activators efficiently convert prothrombin into meizothrombin and their activity is not influenced by the non-enzymatic cofactors of the prothrombinase complex (CaCl2, factor Va and phospholipid). Group II and III activators can cleave both peptide bonds in prothrombin necessary to convert prothrombin into thrombin. The prothrombin-converting activity of Group II activators is strongly stimulated by phospholipids and factor Va in the presence of CaCl2, whereas the activity of group III activators is only stimulated by CaCl2 and phospholipid. Group IV consists of snake venom proteases which do not convert prothrombin into enzymatically active products but cleave peptide bonds in prothrombin, resulting in the formation of inactive precursor forms of thrombin.

Procoagulant activities in venoms from central Asian snakes

The venoms from central Asian snakes (Echis carinatus, Echis multisquamatus, Vipera ursini, Vipera lebetina, Agkistrodon halys halys and Naja naja oxiana) contain several enzymes with amidolytic- and procoagulant activity. We have characterized the activities and the mol. wts of the venom enzymes that are able to convert a number of commercially available chromogenic substrates for activated coagulation factors. The chromogenic substrate cleavage patterns obtained for the crude venoms may be helpful tools in the further identification of venom fractions and venom enzymes with procoagulant activity. The crude venoms were also tested for their ability to clot fibrinogen, to lyse fibrin polymers and to activate the coagulation factors prothrombin, factor X and factor V. The products of venom-catalyzed coagulation factor activation were structurally characterized by SDS gel electrophoresis and were compared with activated coagulation factors that are generated under physiological conditions.

Hemostatic changes due to the venom gland extract of the red-necked keelback snake (Rhabdophis subminiatus)

After a bite by the aglyphous red-necked keelback snake Rhabdophis subminiatus a complete defibrinogenation syndrome with severe hemorrhagic diathesis developed in a 25-year-old man. In vitro studies showed that the venom gland extract of the snake contains a very active prothrombin (Factor II) activator. The thrombin generated is inhibited neither by antithrombin III nor the antithrombin-III-heparin complex. The venom gland extract stimulated also the tissue plasminogen activator; however, it did not cause direct activation of plasminogen, protein C, Factor X or direct degradation of fibrinogen.

An investigation of the coagulant activity of the venom of the saw-scaled viper (Echis carinatus) from Saudi Arabia

Unlike the venom of Echis carinatus from India, Pakistan, Nigeria, Kenya, Iran and Oman, Saudi Arabian E. carinatus venom is a poor activator of prothrombin. However, it possesses similar defibrinogenating activity to the other venoms. This is because the venom from Saudi Arabian snakes contains a calcium-dependent factor X activator. It is suggested that in future studies of the coagulant activity of venoms, the determination of plasma coagulant activity should be carried out in the presence of added calcium ions. This applies particularly to those venoms which do not act on plasma or fibrinogen, but which do cause in vivo defibrinogenation.

Determination of factor X activator in the venom of the saw-scaled viper (Echis carinatus)

Factor X activator in Echis carinatus venom was determined by incubating the zymogen 'factor X' with venom, interrupting the activation process by ethylenediaminetetraacetic acid and measuring the generated proteinase 'factor Xa' by means of a synthetic chromogenic substrate. A comparison of factor X- and prothrombin-activating potencies in E. carinatus venoms of five different geographic origins revealed no correlation between these two procoagulant activities.

Chromogenic assay for the prothrombin activator ecarin from the venom of the saw-scaled viper (Echis carinatus)

Ecarin, by limited proteolysis and subsequent autocatalytic reactions, causes the conversion of prothrombin into three products with amidolytic activity: meizothrombin, meizothrombin 1 and lpha-thrombin. Ecarin action may be abolished by ethylenediaminetetraacetic acid and the activity of alpha-thrombin can, with a high degree of selectivity, be inhibited by heparin. Thus, ecarin potency may be assayed by measuring the meizothrombin activity generated by ecarin action on human plasma in the presence of heparin. The chromogenic substrate Tosyl-glycyl-L-prolyl-L-arginine-p-nitroanilide (Chromozym TH) is used in this assay.