Sodium oleate, arachidonate, and linoleate enhance fibrinogenolysis by Russell's viper venom proteinases and inhibit FXIIIa; a role for phospholipase A 2 in venom induced consumption coagulopathy.

Life-threatening symptoms produced by Russell's viper (RV, Daboia russelii) envenomation result largely from venom induced consumption coagulopathy (VICC). VICC is thought to be mediated to a large degree by venom serine and metalloproteinases, as well as by snake venom phospholipase A(2) (svPLA(2)), the most abundant constituent of RV venom (RVV). The observation that the phenolic lipid anacardic acid markedly enhances proteolytic degradation of fibrinogen by RVV proteinases led us to characterize the chemical basis of this phenomenon with results indicating that svPLA(2) products may be major contributors to VICC. Results: Of the chemical analogs tested, the anionic detergents sodium dodecyl sulfate, sodium deoxycholate, N-lauryl sodium sarcosine, and the sodium salts of the fatty acids arachidonic, oleic and to a lesser extend linoleic acid were able to enhance fibrinogenolysis by RVV proteinases. Enhanced Fibrinogenolysis (EF) was observed with various venom size exclusion fractions containing different proteinases, and also with trypsin, indicating that conformational changes of the substrate and increased accessibility of otherwise cryptic cleavage sites are likely to be responsible for EF. In addition to enhancing fibrinogenolysis, sodium arachidonate and oleate were found to partially inhibit thrombin induced, factor XIIIa (FXIIIa) mediated ligation of fibrin chains. In clotting experiments with fresh blood RVV was found to disrupt normal coagulation, leading to small, partial clot formation, whereas RVV pretreated with the PLA(2) inhibitor Varespladib induced rapid and complete clot formation (after 5 min) compared to blood alone. Conclusion: The observations that fatty acid anions and anionic detergents induce conformational changes that render fibrin(ogen) more susceptible to proteolysis by RVV proteinases and that RVV-PLA(2) activity (which produces FFA) is required to render blood incoagulable in clotting experiments with RVV indicate a mechanism by which the activity of highly abundant RVV-PLA(2) promotes degradation and depletion of fibrin(ogen) resulting in incoagulable blood seen following RVV envenomation (VICC).