Factor XII Activation Promotes Platelet Consumption in the Presence of Bacterial-Type Long-Chain Polyphosphate In Vitro and In Vivo

Abstract

Objective Terminal complications of bacterial sepsis include development of disseminated intravascular consumptive coagulopathy. Bacterial constituents, including long-chain polyphosphates (polyP), have been shown to activate the contact pathway of coagulation in plasma. Recent work shows that activation of the contact pathway in flowing whole blood promotes thrombin generation and platelet activation and consumption distal to thrombus formation ex vivo and in vivo. Here, we sought to determine whether presence of long-chain polyP or bacteria in the bloodstream promotes platelet activation and consumption in a coagulation factor (F)XII-dependent manner. Approach and Results Long-chain polyP promoted platelet P-selectin expression, microaggregate formation and platelet consumption in flowing whole blood in a contact activation pathway-dependent manner. Moreover, long-chain polyP promoted local fibrin formation on collagen under shear flow in a FXI-dependent manner. Distal to the site of thrombus formation, platelet consumption was dramatically enhanced in the presence of long-chain polyP in the blood flow in a FXI- and FXII-dependent manner. In a murine model, long-chain polyP promoted platelet deposition and fibrin generation in lungs in a FXII-dependent manner. Lastly, in a non-human primate model of bacterial sepsis, pretreatment of animals with an antibody blocking FXI activation by FXIIa reduced LD100 S. aureus-induced platelet and fibrinogen consumption. Conclusions This study demonstrates that bacterial-type long-chain polyP promotes platelet activation in a FXII-dependent manner in flowing blood, which may contribute to sepsis-associated thrombotic processes, consumptive coagulopathy and thrombocytopenia.

Antibody inhibition of contact factor XII reduces platelet deposition in a model of extracorporeal membrane oxygenator perfusion in nonhuman primates

“…Capillaries were washed with PBS and then blocked with 5 mg/mL denatured bovine serum albumin for 1 hour at RT before connecting them to a syringe pump and a blood reservoir. Human venous blood was drawn by venipuncture into syringes containing 3.8% (w/v) sodium citrate (one‐tenth of blood volume) in the absence or presence of 100 µg/mL 5C12; blood was recalcified prior to perfusion as previously described . After blood perfusion, capillaries were washed with PBS, fixed with 4% paraformaldehyde, and sealed with Fluoromount G. Platelet aggregates and fibrin formation in the capillaries were then imaged for analysis using a 63 × Zeiss Axio Imager M2 microscope as described …”

The contact pathway and sepsis

“…Certain bacterial cell components, including peptidoglycan and polyP, are also known to activate FXII and promote FXI activation . We have shown that bacterial‐type long‐chain polyP promotes platelet activation, microaggregate formation, and consumption in blood flow in a contact activation pathway–dependent manner in vitro . In a murine model, long‐chain polyP promoted platelet deposition and fibrin generation in the lungs in an FXII‐dependent manner.…”

“…In a murine model, long‐chain polyP promoted platelet deposition and fibrin generation in the lungs in an FXII‐dependent manner. In a nonhuman primate model of bacterial sepsis, pretreatment of animals with an antibody blocking FXI activation by FXIIa reduced Staphylococcus aureus –induced platelet and fibrinogen consumption . This work suggests that bacterial components, including long‐chain polyP, promote platelet activation in an FXII‐dependent manner in flowing blood, which may contribute to sepsis‐associated thrombotic processes, consumptive coagulopathy, and thrombocytopenia.…”

“…In human blood studies ex vivo and in primates in vivo, presence of microbial molecules (eg polyphosphates, potentiated thrombin generation and fibrin formation in FXII‐FXI axis–dependent manner …”

“…In human blood studies ex vivo and in primates in vivo, FXI potentiated thrombin generation at a local site of thrombus formation and led to platelet microaggregate formation and single platelet consumption in flowing blood distal to the local site of thrombus formation …”