Study on jararaca bites helps to elucidate the mechanisms of bleeding

Injury caused at the venom inoculation site can stimulate the release of a protein that plays an essential role in blood clotting.

By Fabio Reynol

Agência FAPESP – It has long been known that poison from snakes such as the jararaca (Bothrops jararaca) can cause damage to the tissue around the site of the bite and can stimulate bleeding. Understanding the causes of these effects and their etiology, however, is a complex challenge.

So says veterinarian Marcelo Larami Santoro, a researcher at the Butantan Institute in São Paulo. He led the project entitled “Importance of local damage induced by snake venom metalloproteinases in the induction of thrombocytopenia in envenomations” from 2011 to 2013 with funding from FAPESP through a regular research grant.

“In most cases, anti-ophidic serum is effective in treating jararaca bites; in more severe cases, however, the bleeding may be very heavy and may require special treatment,” the researcher said.

To understand how jararaca venom affects the clotting system and platelets (cells that help to control the loss of blood), experiments were conducted on rats using two inoculation channels: subcutaneous and intravenous. This study sought to confirm the importance of the local injury in inducing thrombocytopenia (a reduction in the blood platelet count) and of the alterations in the clotting system.

The study also tested the importance of the two main classes of toxins present in the venom: metalloproteinases and serine proteases. To do this, before being injected into the animals, the jararaca venom was incubated with the appropriate inhibitors. The purpose of incubating the venom was to promote the inhibition of certain enzymes. Both classes are known to present antihemostatic activity; in other words, they prevent the stoppage of blood loss, a reaction that occurs when the body tries to inhibit bleeding.

According to the findings, the two classes of toxins are not directly involved in the origin of the thrombocytopenia induced by jararaca venom, a fact that has led to the conclusion that other mechanisms or toxins from the venom must be responsible for reducing the number of platelets. However, the metalloproteinases in the venom have proven to be essential in the development of clotting disorders. This evidence challenges the widespread opinion held by physicians and scientists over the years: that serine proteases are the most important toxins for the consumption of fibrinogen, the protein involved in the process of blood clotting, and that this protein’s reduction promotes the hemorrhagic condition that arises from the bite of the jararaca.

Another important piece of information was that the injury caused at the site of the venom inoculation could stimulate the release of tissue factor into the bloodstream. Also known as thromboplastin, tissue factor is a substance found in tissues, monocytes and platelets that performs a basic role in blood clotting.

“The increase in circulating tissue factor makes the action of the venom stronger, increasing tissue damage by favoring coagulopathies, which are clotting disorders,” Santoro explained. He also emphasized that the study of the action of ophidic venoms throughout the 20th century has helped science to discover the mechanisms of blood clotting.

The article “Bothrops jararaca venom metalloproteinases are essential for coagulopathy and increased plasma tissue factor levels during envenomation”, describing all of these findings, is scheduled to be published in the journal PLOS Neglected Tropical Diseases.

Partnership with Argentina

The project involved the participation of researcher María Elisa Peichotto of Argentina’s National University of the Northeast (NDDE). The study was approved under the scientific cooperation agreement signed by FAPESP and the Argentine National Council for Scientific and Technical Research (CONICET) in 2010.

The Argentine author is the first author on a scientific article developed during the project “Inflammatory effects of patagonfibrase, a metalloproteinase from Philodryas patagoniensis (Patagonia Green Racer; Dipsadidae) venom”, published in the journal Experimental Biology and Medicine.

The partnership with Brazil’s neighbor also collaborated on the first “Biomedical investigation of poisonous animals in the Paraná jungle” workshop, held in the Argentine city of Puerto Iguaçu in May 2013.

Another important outcome of the project was the master’s research study “Pathogenesis of systemic hemostatic disturbances induced by Bothrops jararaca snake venom”, by master’s degree candidate Karine Miki Yamashita, funded by an FAPESP scholarship.

Santoro plans to continue research on tissue factor and the related mechanisms. “By understanding the venom better, we will be able to fight its actions in cases of poisoning,” he said.