Fibrin, γ′-Fibrinogen, and Transclot Pressure Gradient Control Hemostatic Clot Growth during Human Blood Flow over a Collagen/Tissue Factor Wound

Abstract

Objective-Biological and physical factors interact to modulate blood response in a wounded vessel, resulting in a hemostatic clot or an occlusive thrombus. Flow and pressure differential (ΔP) across the wound from the lumen to the extravascular compartment may impact hemostasis and the observed core/shell architecture. We examined physical and biological factors responsible for regulating thrombin-mediated clot growth. Approach and Results-Using factor XIIa-inhibited human whole blood perfused in a microfluidic device over collagen/tissue factor at controlled wall shear rate and ΔP, we found thrombin to be highly localized in the P-selectin+ core of hemostatic clots. Increasing ΔP from 9 to 29 mm Hg (wall shear rate=400 s-1) reduced P-selectin+ core size and total clot size because of enhanced extravasation of thrombin. Blockade of fibrin polymerization with 5 mmol/L Gly-Pro-Arg-Pro dysregulated hemostasis by enhancing both P-selectin+ core size and clot size at 400 s-1 (20 mm Hg). For whole-blood flow (no Gly-Pro-Arg-Pro), the thickness of the P-selectin-negative shell was reduced under arterial conditions (2000 s-1, 20 mm Hg). Consistent with the antithrombin-1 activity of fibrin implicated with Gly-Pro-Arg-Pro, anti-γ′-fibrinogen antibody enhanced core-localized thrombin, core size, and overall clot size, especially at venous (100 s-1) but not arterial wall shear rates (2000 s-1). Pathological shear (15 000 s-1) and Gly-Pro-Arg-Pro synergized to exacerbate clot growth. Conclusions-Hemostatic clotting was dependent on core-localized thrombin that (1) triggered platelet P-selectin display and (2) was highly regulated by fibrin and the transclot ΔP. Also, γ′-fibrinogen had a role in venous but not arterial conditions.