Synthetic Fibrin-Derived Bβ _15-42 Peptide Delays Thrombus Resolution in a Mouse Model

Abstract

Objective: Thrombus resolution is driven by leukocyte recruitment and thrombus angiogenesis. An effective inhibition of leukocyte transmigration in vitro is mediated by naturally occurring peptide Bβ 15-42 , which is a competitive inhibitor of the interaction between the N-terminus of the fibrin beta chain and vascular endothelial cadherin. We investigated the effect of Bβ 15-42 on thrombus resolution in a murine stagnant flow venous thrombosis model and studied Bβ 15-42 levels in venous thrombus of human patients. Approach and Results: We investigated 2 mouse models of subtotal inferior vena cava ligation. In the first model, we ligated the inferior vena cava. In the second model, we additionally ligated all visible inferior vena cava side and back branches. Study groups of 8 to 12 weeks old BALB/c mice were then injected intraperitoneal twice daily with 2.4 mg/kg of Bβ 15-42 , unrelated control peptide or saline. Bβ 15-42 attenuated thrombus resolution after inferior vena cava ligation. We observed decreased numbers of thrombus macrophages and microvessels and less urokinase-type plasminogen activator expression in mice that were injected with Bβ 15-42 . Mechanistic experiments demonstrated that Bβ 15-42 blocks monocyte transmigration through an endothelial cell monolayer. Measurements of Bβ 15-42 in red clot and plasma of chronic thromboembolic pulmonary hypertension cases indicated high concentrations compared with controls. Conclusions: Our data suggest that excess of the fibrin fragment Bβ 15-42 misguides thrombus resolution, presumably by inhibiting vascular endothelial cadherin-mediated leukocyte migration during early thrombus organization.

Monocyte/macrophage-mediated venous thrombus resolution

“…The peptide Bβ 15-42 was found to attenuate thrombus resolution probably through impeding monocyte endothelial transmigration, reducing macrophage numbers, microvessels, and uPA expression in the thrombus ( 111 ). Moreover, high levels of the fibrin fragment Bβ 15-42 were found in the red thrombus and plasma of patients with CTEPH ( 129 ). Therefore, fibrin fragments suppressing thrombolysis should be taken seriously in the treatment of CTEPH.…”