Practical applications of snake venom toxins in haemostasis

Snake venom toxins affecting haemostasis have facilitated extensively the routine assays of haemostatic parameters in the coagulation laboratory. Snake venom thrombin-like enzymes (SVTLE) are used for fibrinogen/fibrinogen breakdown product assay and for the detection of fibrinogen dysfunction. SVTLE are not inhibited by heparin and can thus can be used for assaying antithrombin III and other haemostatic variables in heparin-containing samples. Snake venoms are a rich source of prothrombin activators and these are utilised in prothrombin assays, for studying dysprothrombinaemias and for preparing meizothrombin and non-enzymic forms of prothrombin. Russell's viper (Daboia russelli) venom (RVV) contains toxins which have been used to assay blood clotting factors V, VII, X, platelet factor 3 and, importantly, lupus anticoagulants (LA). Other prothrombin activators (from the taipan, Australian brown snake and saw-scaled viper) have now been used to assay LA. Protein C and activated protein C resistance can be measured by means of RVV and Protac^®, a fast acting inhibitor from Southern copperhead snake venom and von Willebrand factor can be studied with botrocetin^® from Bothrops jararaca venom. The disintegrins, a large family of Arg-Gly-Asp (RGD)-containing snake venom proteins, show potential for studying platelet glycoprotein receptors, notably, GPIIb/IIIa and Ib. Snake venom toxins affecting haemostasis are also used in the therapeutic setting: Ancrod (from the Malayan pit viper, Calloselasma rhodostoma), in particular, has been used as an anticoagulant to achieve ‘therapeutic defibrination’. Other snake venom proteins show promise in the treatment of a range of haemostatic disorders.