Jararaca GPIb-binding protein causes thrombocytopenia during Bothrops jararaca envenomation

Area of Science:

• Toxicology
• Hematology
• Biochemistry

Background:

• Bothrops jararaca snake venom (BjV) is known to cause thrombocytopenia.
• The specific BjV toxins responsible for in vivo thrombocytopenia remain unidentified.
• Previous studies indicated that common inhibitors and antibodies did not prevent BjV-induced thrombocytopenia.

Purpose of the Study:

• To identify and characterize the specific toxins in BjV that induce thrombocytopenia in vivo.
• To investigate the mechanism of action of these toxins on platelets.

Main Methods:

• Ultrafiltration of BjV to isolate proteins by molecular mass.
• Chromatography of the 50 kDa fraction to isolate active proteins.
• Mass spectrometry to identify the isolated proteins.
• Thrombocytopenia induction assays in mice (including Vwf-/- mice).
• Platelet aggregation studies in human and mouse blood.

Main Results:

• Proteins between 30-50 kDa from BjV induced thrombocytopenia in mice without hemorrhagic or coagulating activity.
• Two fractions, D and E, isolated from the 50 kDa ultrafiltrate, induced thrombocytopenia in mice.
• Neither fraction D nor E caused platelet aggregation in vitro.
• Fraction E was identified as a jararaca glycoprotein Ib (GPIb)-binding protein.
• Thrombocytopenia was induced in both control and Vwf-/- mice, indicating the GPIb-von Willebrand factor axis is not involved.

Conclusions:

• Specific BjV toxins, particularly fraction E (a GPIb-binding protein), are responsible for inducing thrombocytopenia in vivo.
• The mechanism of thrombocytopenia induction by these toxins does not involve direct platelet aggregation or the GPIb-von Willebrand factor pathway.
• Further research is required to elucidate the precise in vivo mechanism of action for these identified toxins.