Anticoagulant Activity of Endotoxin-Binding Synthetic Peptides

Abstract

We have purified 7kDa and 18kDa cationic antibacterial proteins (CAP-7 and CAP-18) with LPS-binding and LPS-neutralizing activities from rabbit granulocytes. CAP-7 was identified as the C-terminal 37 amino acid fragment of CAP-18. Synthetic peptide #197-1 (identical sequence to CAP-7, Gly1-Tyr37) and #36-1 (a truncation of CAP-7 consisting of 32 amino acid residues, Gly1-Ala32) showed LPS-binding activity. Both peptides inhibited tissue factor- and Xa-induced plasma clotting. Using synthetic chromogenic substrates, both CAP-7 peptides blocked the coagulation cascade at two sites, activation of factor X to Xa and conversion of Factor II (prothrombin) to factor IIa (thrombin). In vivo treatment of peptide #197-1 prevented acute lethality in mice injected with tissue factor. Two other peptides, #32-1 (Gly1-Phe9) and #50-2 (Ile13-Tyr37) failed to demonstrate LPS-binding and anticoagulant activities. The active peptides but not the inactive peptides maintain a putative heparin binding domain at their N-termini. This heparin binding domain is participated in the LPS-binding and anticoagulant activites of CAP-7. These active peptides may have therapeutic potential for treatment for DIC due to sepsis and endotoxin shock.