The tissue factor pathway mediates both activation of coagulation and coagulopathy after injury.

BACKGROUND: The initiation of coagulation in trauma is thought to originate from exposed tissue factor (TF); recent data have led to the alternative hypothesis that damage-associated molecular patterns may contribute to postinjury coagulation. In acute traumatic coagulopathy, aberrant coagulation is mediated via the activated protein C (aPC) pathway; the upstream regulators of this process and its relation to TF remain uncharacterized. To examine the role of the TF pathway in mediating acute traumatic coagulopathy, we used specific antibody blockades in an established murine model of traumatic hemorrhagic shock, hypothesizing that both coagulation activation after injury and aPC-mediated coagulopathy are driven by TF via thrombin.

METHODS: Mice underwent an established model of trauma and hemorrhage and were subjected to either sham (vascular cannulation) or trauma-hemorrhage (cannulation, laparotomy, shock to mean arterial pressure of 35 mm Hg); they were monitored for 60 minutes before sacrifice. Mice in each group were pretreated with either targeted anti-TF antibody to block the TF pathway or hirudin for specific blockade of thrombin. Plasma was assayed for thrombin-antithrombin (TAT) and aPC by enzyme-linked immunosorbent assay.

RESULTS: Compared with controls, trauma-hemorrhage mice treated with anti-TF antibody had significantly reduced levels of TAT (2.3 ng/mL vs. 5.7 ng/mL, p = 0.016) and corresponding decreases in aPC (16.3 ng/mL vs. 31.6 ng/mL, p = 0.034), with reductions to levels seen in sham mice. Direct inhibition of thrombin yielded similar results, with reduction in aPC to levels below those seen in sham mice.

CONCLUSION: In this study, blockade of the TF pathway led to the attenuation of both thrombin production and aPC activation observed in traumatic shock. Specific thrombin inhibition achieved similar results, indicating that aPC-related coagulopathy is mediated via thrombin activated by the TF pathway. The near-complete blockade of TAT and aPC observed in this model argues for a dominant role of the TF-thrombin pathway in both coagulation activation after injury and traumatic coagulopathy.