Plasminogen activation and plasmin activity are not necessary to prevent venous thrombosis/thromboembolism

Suppression of plasminogen activation and/or plasmin activity (PA) reduces blood loss and decreases hemorrhage-related death. However, whether the endogenous PA system is a biological mechanism to prevent intravascular thrombus formation is debated, and the potential that reduced PA may increase venous thrombosis/thromboembolism (VTE) risk cautions against the use of antifibrinolytic agents. We aimed to determine the contribution of PA to VTE. Type 1 plasminogen-deficient humans enrolled in the Hypoplasminogenemia International Retrospective and Prospective Cohort Study registry reported pathologic pseudomembrane formation, but not unprovoked VTE. When subjected to an experimental model of venous thrombosis, compared with Plg+/+ mice, neither partial (Plg+/-) nor complete (Plg-/-) deletion of plasminogen altered thrombus mass or thrombus nucleated cell, platelet, or fibrin(ogen) content at 24 or 6 hours after thrombus induction. Administration of tranexamic acid (TXA) to mouse plasma in vitro or healthy mice in vivo dose-dependently delayed and suppressed plasma plasmin generation for up to 3 hours. However, mice administered TXA did not have significantly altered thrombus mass or thrombus composition at 24 or 6 hours after thrombus induction, despite unexpectedly persistent TXA in plasma. In a genome-wide association study, variants in gene regions encoding PA pathway proteins were not significantly associated with VTE risk. In the UK Biobank repository, plasminogen protein levels were not significantly associated with VTE risk. These data from genetic, pharmacologic, and proteomic analyses of mice and humans indicate that perturbations in PA do not increase VTE risk. Collectively, these results suggest PA is not a molecular regulatory mechanism to protect against VTE. This trial was registered at www.clinicaltrials.gov as #NCT03797495).