Selective thrombolysis through fibrin network destabilization: An unrecognized heparin analog mechanism.

Clinically approved thrombolytic agents carry significant bleeding risks due to systemic plasminogen activation. Heparin analogs prevent thrombus formation but lack direct thrombolytic activity. Here, we report a previously unrecognized thrombolytic mechanism of octaparin, a synthetic heparin analog. Studies demonstrated that octaparin exhibits potent anticoagulant and thrombolytic activity both in vitro and in vivo, with a lower bleeding risk compared to conventional heparin-based agents. Octaparin directly binds fibrin monomers, altering their secondary conformation to inhibit polymerization and destabilize preformed thrombi, while preserving tissue factor-driven coagulation. In murine models of pulmonary embolism and inferior vena cava thrombosis, octaparin both prevented and dose-dependently dissolved established clots without compromising hemostatic integrity, sharply contrasting with conventional thrombolytics that induce hemorrhage. Further analyses using molecular docking, microscale thermophoresis, and spectroscopy confirmed that octaparin induces changes in fibrin monomer folding that compromise fibrin network stability. In human systems, octaparin selectively prolonged intrinsic coagulation time, reduced clot retraction, did not induce platelet activation, and its effects were reversible with protamine sulfate. This study establishes targeted fibrin destabilization as a viable therapeutic strategy, revealing a previously unrecognized thrombolytic mechanism achievable through heparin-based molecular design.