Involvement of von Willebrand factor and botrocetin in the thrombocytopenia induced by Bothrops jararaca snake venom

Patients bitten by snakes consistently manifest a bleeding tendency, in which thrombocytopenia, consumption coagulopathy, mucous bleeding, and, more rarely, thrombotic microangiopathy, are observed. Von Willebrand factor (VWF) is required for primary hemostasis, and some venom proteins, such as botrocetin (a C-type lectin-like protein) and snake venom metalloproteinases (SVMP), disturb the normal interaction between platelets and VWF, possibly contributing to snakebite-induced bleedings. To understand the relationship among plasma VWF, platelets, botrocetin and SVMP from Bothrops jararaca snake venom (BjV) in the development of thrombocytopenia, we used (a) Wistar rats injected s.c. with BjV preincubated with anti-botrocetin antibodies (ABA) and/or Na2-EDTA (a SVMP inhibitor), and (b) VWF knockout mice (Vwf-/-) injected with BjV. Under all conditions, BjV induced a rapid and intense thrombocytopenia. In rats, BjV alone reduced the levels of VWF:Ag, VWF:CB, high molecular weight multimers of VWF, ADAMTS13 activity, and factor VIII. Moreover, VWF:Ag levels in rats that received BjV preincubated with Na2-EDTA and/or ABA tended to recover faster. In mice, BjV caused thrombocytopenia in both Vwf-/- and C57BL/6 (background control) strains, and VWF:Ag levels tended to decrease in C57BL/6, demonstrating that thrombocytopenia was independent of the presence of plasma VWF. These findings showed that botrocetin present in BjV failed to affect the extent or the time course of thrombocytopenia induced by envenomation, but it contributed to decrease the levels and function of plasma VWF. Thus, VWF alterations during B. jararaca envenomation are an ancillary event, and not the main mechanism leading to decreased platelet counts.
Author summary Envenomation by snakebites is a major burden to tropical and subtropical areas in the world. Many snake species produce venoms that, when injected into victims, cause bleedings and other associated symptoms and signs. This work aimed to understand the mechanisms that lead to a fall in blood platelet counts after bites by a snake that inhabits in southeastern Brazil, the lance-headed snake Bothrops jararaca (popularly known as jararaca). We used experimental approaches to understand the involvement of a protein from jararaca venom, called botrocetin, and a protein present in our blood (von Willebrand factor) in the fall of platelet counts. We observed that botrocetin alters von Willebrand factor, but this mechanism in not important for the decrease in platelet counts. We show that jararaca snake venom disturb blood platelets in a complex and intricate way, and that other venom compounds are involved in the decrease of platelet counts during snakebite envenomation.