Shiga toxin 2a binds antithrombin and heparin, but does not directly activate platelets

Area of Science:

• Microbiology
• Hematology
• Toxicology

Background:

• Escherichia coli-induced hemolytic uremic syndrome (eHUS) is a severe complication linked to Shiga toxin (Stx).
• Enhanced coagulation and platelet activation are suspected contributors to eHUS pathogenesis.
• The specific role of Stx2a in coagulation and platelet function remains debated.

Purpose of the Study:

• To investigate the effects of Stx2a on plasmatic coagulation and platelets.
• To elucidate the interaction between Stx2a, antithrombin (AT), and heparin.

Main Methods:

• Enzyme-linked immunosorbent assay (ELISA), co-immunoprecipitation, and quartz crystal microbalance with dissipation monitoring (QCM-D) for binding studies.
• Antithrombin activity assays and rotational thromboelastometry (ROTEM®) for coagulation assessment.
• Flow cytometry (FACS) and light-transmission aggregometry for platelet analysis.

Main Results:

• Stx2a directly binds to antithrombin (AT) and heparin.
• A mild reduction in AT activity against Factor Xa was observed in the presence of Stx2a.
• Stx2a binding to heparin impaired AT binding to heparin.
• ROTEM® analysis showed a moderate shortening of clotting time in Stx2a-treated plasma.
• No direct binding or activation of platelets by Stx2a was detected.

Conclusions:

• Stx2a interacts with AT and heparin, but does not cause major dysregulation of plasmatic coagulation.
• Stx2a does not directly interact with or activate platelets.
• The observed interaction of Stx2a with heparin may explain the limited efficacy of heparin therapy in eHUS patients.