Snake venom, anticoagulants

Since predators of snakes (and humans) have to deal with snake venoms as defenses, they are included here, even though they serve in predation. Snake venoms are primarily enzymes (proteins), especially of the phospholipase A2 type, which breaks down cell membrane phospholipids hydrolytically. Other snake venoms such as cobrotoxin contain peptides with 60-70 amino acid residues. Pharmacologically, they have neurotoxic, cytotoxic, anticoagulant, and other effects. The neurotoxins, in turn, can have pre- or postsynaptic effects. Snake venoms with both neurotoxic and hemolytic effects on the heart are known as cardiotoxins. Cytotoxins attach to the cells of blood vessels and cause hemorrhage. Snake venom factors may stimulate or inhibit blood clotting. Finally, platelet-active factors can contribute to hemorrhage. 

Anticoagulant therapy in recent years has involved the use of either heparin or the oral anticoagulants, coumarln and indandione derivatives, on venous thrombosis. The only newer agents with clinical potential appear to be several snake venoms or venom fractions which act either through defibrlnogenatlon or inhibition of prothrombin activation. 

The anticoagulant properties of several snake venoms have previously been reported.4 The venom of Agkistrodon acutus contains a procoagulant principle as well as an anticoagulant fraction, both of which have been purified and studied. It has recently been found that the anticoagulant factor inhibits prothrombin activation by interfering with the interaction between prothrombin and its activation factors.49... 

D. Thrombin-Like Enzymes. Ancrod (arvin), a very specific snake venom component, has been investigated extensively for its anticoagulant action. Ancrod is a very specific protease whose action has some similarity to that of thrombin and occurs in the terminal sequence of a complex blood coagulation mechanism. Ancrod hydrolyzes only the Aa chain of fibrinogen and produces a polymer of the type (a Bp y)n rather than the (aPy)n type normal fibrin clot. The microclot produced by ancrod from fibrinogen is readily hydrolyzed by plasmin that was activated from tissue plasminogen. This results in a defibrination effect. This property is extensively used in the treatment of a patient who has suffered from myocardial infarction. 

Mizuno, H., Atoda, H., and Morita, T, 1991, Crystallization and preliminary X-ray study of blood coagulation factor IX/factor X-binding protein with anticoagulant activity from habu snake venom, J. Mol Biol 220 225-226. 

Denson, K.W.E., 1969, Coagulant and anticoagulant actions of snake venoms. Toxicon, 7 5. 

Marshall, L.R., Herrmann, R.P., 1983, Coagulant and anticoagulant actions of australian snake venoms. Thromb Haemostas, 50 707. 

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