Breaking the fibrinolytic speed limit with microwheel co-delivery of tissue plasminogen activator and plasminogen

Abstract

Fibrinolysis is the enzymatic degradation of fibrin, the biopolymer that gives blood clots their mechanical integrity. To reestablish blood flow in vessels occluded by clots, tissue plasminogen activator (tPA) can be used; however, its efficacy is limited by transport to and into a clot and by the depletion of its substrate, plasminogen. To overcome these rate limitations, we design a platform to co-deliver tPA and plasminogen based on microwheels (μwheels), wheel-like assemblies of superparamagnetic colloidal beads that roll along surfaces at high speeds and carry therapeutic payloads in applied magnetic fields. By experimentally measuring fibrinolysis of plasma clots at varying concentrations of tPA and plasminogen, the biochemical speed limit was first determined. These data, in conjunction with measurements of μwheel translation, activity of immobilized tPA on beads, and plasminogen release kinetics from magnetic mesoporous silica nanoparticles (mMSN), were used in a mathematical model to identify the optimal tPA:plasminogen ratio and guide the coupling of plasminogen-loaded mMSN to tPA functionalized superparamagnetic beads. Once coupled, particle-bead assemblies form into a co-delivery vehicle that rolls to plasma clot interfaces and lyses them at rates comparable to the biochemical speed limit. With the addition of mechanical action provided by rotating μwheels to penetrate clots, this barrier was exceeded by rates 40-fold higher lysis by 50 nM tPA. This co-delivery of an immobilized enzyme and its substrate via a microbot capable of mechanical work has the potential to target and rapidly lyse clots that are inaccessible by mechanical thrombectomy devices or recalcitrant to systemic tPA delivery.

Fibrinolytic system and COVID-19: From an innovative view of epithelial ion transport

“…Administration of tPA, an available therapeutic schedule, improves fibrin dissolution and oxygenation, as well as accelerates rehabilitation in the early stage [66] , [67] . While at advanced stage, the administration of tPA can hardly ameliorate hemodynamics because the efficacy of tPA is limited by the depletion of plasminogen when blood flow is needed to reestablish in clot-occluded vessels [68] , [69] . Hence, except for giving tPA alone, systemic thrombolytic therapy is necessary for patients who have developed into severe progression.…”

Removing plasmin from the equation – Something to chew on…

“…These µwheels can be loaded with therapeutic agents that are delivered to the site of thrombosis 46 . The µwheels platform is being developed to co‐deliver tPA and plasminogen to overcome several limitations of current thrombolytic therapies, including plasminogen consumption 46,47 …”

“…46 The µwheels platform is being developed to co-deliver tPA and plasminogen to overcome several limitations of current thrombolytic therapies, including plasminogen consumption. 46,47 Targeting of inhibitors of fibrinolysis has been considered as an alternative to thrombolytics to promote fibrin degradation by enhancing endogenous plasmin generation or activity. Small molecules, peptides, monoclonal antibodies and antibody fragments have been used to modulate PAI-1 activity by interfering at different stages of the PAI-1/plasminogen activator interaction.…”

Magnetically powered chitosan milliwheels for rapid translation, barrier function rescue, and delivery of therapeutic proteins to the inflamed gut epithelium

“…In previous work, we have shown that magnetic microwheels (μ-wheels), disk-like assemblies of superparamagnetic polystyrene microparticles, can translate at speeds of 100’s μm/s along surfaces when driven by 1-10 mT rotating magnetic fields, 24–26 deliver therapeutic proteins, 27,28 and behave like swarms through complex vessels. 29 Here we build upon that work to create hydrogel-based milliwheels (m-wheels) designed for translation along mucosal tissues and controlled release of therapeutic proteins with swarm-like behavior.…”