The function of factor XI in tissue factor-initiated thrombin generation

Area of Science:

• Biochemistry
• Hematology
• Thrombosis Research

Background:

• Thrombin generation is a critical process in hemostasis.
• Vitamin K-dependent proteins (VKDP) play a key role in coagulation.
• The role of factor XI (FXI) in thrombin generation under varying conditions is not fully elucidated.

Purpose of the Study:

• To investigate the influence of plasma and platelet factor XI (FXI) on thrombin generation.
• To evaluate the impact of elevated vitamin K-dependent proteins (VKDP) on thrombin generation.
• To assess the interplay between FXI, VKDP, and phospholipids/platelets in a synthetic coagulation model.

Main Methods:

• A synthetic coagulation model was used to initiate thrombin generation with 10 pM tissue factor (TF).
• Experiments involved either platelets or phospholipids at physiological concentrations.
• The effects of factor XI (FXI) and increased vitamin K-dependent proteins (VKDP) were assessed.

Main Results:

• At physiological VKDP concentrations, 30 nM FXI had no effect on thrombin generation.
• Elevated VKDP (up to 500%) prolonged thrombin generation initiation and decreased peak levels, primarily due to increased prothrombin and FIX.
• In the presence of phospholipids or platelets, FXI addition with elevated VKDP reversed the inhibitory effects, shortening initiation and increasing thrombin levels.

Conclusions:

• Factor XI (FXI) does not influence thrombin generation at low tissue factor (TF) concentrations with physiological vitamin K-dependent proteins (VKDP).
• Platelets and plasma FXI can effectively counteract the inhibitory impact of elevated VKDP on thrombin generation.
• These findings highlight a compensatory mechanism involving FXI in coagulation under specific conditions.