High fibrinogen γ′ levels in patient plasma increase clot formation at arterial and venous shear

Fibrinogen γ' accounts for 3% to 40% of plasma fibrinogen. Earlier studies indicated that fibrinogen γ' forms altered fibrin clots under static conditions, whereas clinically, altered plasma γ' levels are associated with arterial and venous thrombosis. However, the effects of static vs flow conditions on the role of γ9 throughout the pathophysiological range is unknown. This study explores the effects of γ' levels on clot formation and structure in static and flow conditions. Coagulation of plasma samples with low (n 5 41; 3%), normal (n 5 45; 10%), or high (n 5 33; 30%) γ9 levels were compared with that of purified fibrinogen mixtures with increasing ratios of γ9 (3%, 10%, 30%). Clots were analyzed by confocal microscopy, permeation, turbidity, and lysis techniques. In a novel 2-step flow-perfusion model, fibrinogen-deficient plasma repleted with increasing ratios of g9 (3%, 10%, 30%) or plasmas with low (n 5 5, 3%) or high (n 5 5, 30%) γ9 were flowed over preformed platelet aggregates at arterial (500 s21) and venous (150 s21) shear rates. Increasing g9 percentages within the pathophysiological range (3%-30%) did not result in any change in clot-formation rates; however, it led to significantly higher clot density, thinner fibers, and slower lysis in static conditions. Under flow at arterial shear, high g9 (30%) led to faster (144.1%-75.3%) and increased (1104%-123%) fibrin deposition, with clots exhibiting a larger volume (1253%-655%) and height (1130%-146%). These trends were magnified at venous shear. Overall, our findings demonstrate the significant impact of pathophysiological fibrinogen γ9 levels on clot structure and provide new flow-dependent mechanisms to explain how γ9 increases thrombosis risk.