Inhibition of Binding of ß2-Glycoprotein 1 to Phosphatidylserine by Polymyxin B, a Lupus-Like Anticoagulant.

Polymyxin B is a cationic peptide that inhibits phospholipid-dependent coagulation tests including activated partial thromboplastin time and to a lesser degree prothrombin time. Thrombin clotting time is insensitive to polymyxin B. ß2-glycoprotein 1 (ß2GP1) is a cofactor of antiphospholipid antibodies. Antiphospholipid autoantibodies also poses lupus anticoagulant activity through interactions with ß2GP1. Using affinity chromatography, polymyxin B can effectively decrease the binding of ß2GP1 to immobilize phosphatidylserine. Since then, anticoagulant effect of polymyxin B is most likely due to the binding to negatively charged phospholipids, preventing formation of coagulation complexes.