Alteration of blood clotting and lung damage by protamine are avoided using the heparin and polyphosphate inhibitor UHRA

Manu Thomas Kalathottukaren, Libin Abraham, Piyushkumar R. Kapopara, Benjamin F.L. Lai, Rajesh A. Shenoi, Federico I. Rosell, Edward M. Conway, Edward L.G. Pryzdial, James H. Morrissey, Charles A. Haynes and Jayachandran N. Kizhakkedathu

Key points

  • Protamine, the clinically used heparin antidote, alters clot structure by direct incorporation, explaining its known adverse effects.

  • UHRA, a heparin antidote, neutralizes heparin anticoagulation without affecting clotting, clot structure and lung damage in mice.


Anticoagulant therapy associated bleeding and pathological thrombosis, pose serious risks to hospitalized patients. Both complications could be mitigated by developing new therapeutics that safely neutralize anticoagulant activity and inhibit activators of the intrinsic blood clotting pathway, such as polyphosphate (polyP) and extracellular nucleic acids. The latter strategy could reduce the use of anticoagulants, potentially decreasing bleeding events. However, previously described cationic inhibitors of polyP and extracellular nucleic acids, exhibit both non-specific binding and adverse effects on blood clotting that limit their use. Indeed, the polycation, protamine used to counteract heparin-associated bleeding in surgical settings, exhibit adverse side-effects. To address these clinical shortcomings, we developed a synthetic polycation, Universal Heparin Reversal Agent (UHRA), which is nontoxic and can neutralize the anticoagulant activity of heparins and the prothrombotic activity of polyP. Sharply contrasting protamine, we show that UHRA does not interact with fibrinogen, affect fibrin polymerization during clot formation or abrogate plasma clotting. Using scanning electron microscopy, confocal microscopy and clot lysis assays, we confirm that UHRA does not incorporate into clots, and clots are stable with normal fibrin morphology. Conversely, protamine binds to the fibrin clot, which could explain how protamine instigates clot lysis and increases bleeding after surgery. Finally, studies in mice reveal that UHRA reverses heparin anticoagulant activity without the lung injury seen with protamine. The data presented here illustrate that UHRA could be safely used as an antidote during adverse therapeutic modulation of hemostasis.

  • Submitted October 25, 2016.
  • Accepted December 19, 2016.