Activated Protein C Inhibits Local Coagulation after Intrapulmonary Delivery of Endotoxin in Humans

Abstract

Rationale: Acute lung injury and pneumonia are associated with pulmonary activation of coagulation and suppression of fibrinolysis, resulting in fibrin deposition in the lung. Activated protein C (APC) has systemic anticoagulant effects in patients with sepsis. Objective: To determine the effect of systemic administration of recombinant human APC on endotoxin-induced hemostatic alterations in the bronchoalveolar space in humans. Methods: Healthy humans received intravenous APC (24 μg/kg/hour; n = 8) or vehicle (n = 7); all subjects were administered saline in one lung subsegment and endotoxin (4 ng/kg) into the contralateral lung. Bronchoalveolar lavage was performed 16 hours after saline and endotoxin administration. Measurements and Main Results: Endotoxin induced local activation of coagulation, as reflected by elevated levels of thrombin–antithrombin complexes (1.9 ± 0.1 ng/ml) and soluble tissue factor (15.0 ± 0.6 pg/ml) in bronchoalveolar lavage fluid, which was inhibited by APC (1.4 ± 0.1 ng/ml and 12.3 ± 0.4 pg/ml, respectively; both p < 0.01). Concurrently, endotoxin suppressed fibrinolysis, as indicated by reduced bronchoalveolar levels of plasminogen activator activity accompanied by elevated levels of plasminogen activator inhibitor type I activity. APC diminished the rise in plasminogen activator inhibitor type I activity (from 3.9 ± 0.1 to 3.0 ± 0.2 ng/ml, p = 0.002), while not significantly influencing plasminogen activator activity levels. Endotoxin reduced bronchoalveolar protein C concentrations, which was prevented by APC. Protein C did not influence the endotoxin-induced rise in local soluble thrombomodulin levels. Conclusion: APC exerts an anticoagulant effect in the human lung challenged with endotoxin.