Abstract Number: PB0263
Meeting: ISTH 2020 Congress
Background: Binding to negatively charged surfaces activates contact coagulation factor (F)XII, which can trigger the inflammatory kallikrein-kinin system and intrinsic coagulation pathway via its substrates prekallikrein (PK) and factor (F)XI, respectively. Misfolded proteins have been recognized as contact system activators; however, the underlying mechanism remains to be established.
Aims: To assess effects and mechanisms of misfolded proteins on contact system activation.
Methods: Serum albumin was misfolded via glycation (SA-AGE). Conformational changes of denatured albumins were analysed by circular dichroism. Chromogenic assays in plasma and purified proteins examined activation of contact system components FXII(a), (pre)kallikrein, and FXI(a). Clotting assays in normal and contact system component deficient plasma samples were employed to determine the ability of SA-AGE to trigger coagulation via contact activation. SA-AGE effects on thrombus formation under flow was analysed in whole blood. Protamine sulfate was employed to neutralise the negative charge of SA-AGE to examine this effect on clot formation.
Results: SA-AGE induced autoactivation of FXII in a negative charge dependent manner and led to PK but not FXI activation. Addition of the positively charged protein protamine sulfate neutralised the negative charge of SA-AGE and interfered with FXII contact activation in plasma. SA-AGE inhibited FXIa, but not PKa or FXIIa, by a non-competitive inhibition mechanism. SA-AGE demonstrated an anticoagulant effect in plasma, and whole blood under flow conditions. SA-AGE dose dependently prolonged FXII contact activator silica-stimulated plasma clotting time indicating that SA-AGE inhibits downstream FXIIa mechanisms. Counterintuitively, we found that SA-AGE enhanced the extrinsic pathway, with a mechanism yet to be identified.
Conclusions: Albumin misfolding via glycation results in a clustering of negative charge, which can contact activate FXII leading to PK activation, and the subsequent cleavage of high-molecular-weight kininogen. SA-AGE inhibits FXIa, offering an explanation why some misfolded protein surfaces do activate the kallikrein-kinin system but not coagulation.
To cite this abstract in AMA style:Hardy L, Heal SL, Hethershaw E, Foster R, Longstaff C, Renne T, Philippou H. The Misfolded Protein Glycated Albumin Activates the Contact System Leading to Plasma Kallikrein Activity But Not Intrinsic Coagulation [abstract]. Res Pract Thromb Haemost. 2020; 4 (Suppl 1). https://abstracts.isth.org/abstract/the-misfolded-protein-glycated-albumin-activates-the-contact-system-leading-to-plasma-kallikrein-activity-but-not-intrinsic-coagulation/. Accessed February 21, 2024.
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