Engineered aprotinin for improved stability of fibrin biomaterials

Fibrin has been long used clinically for hemostasis and sealing, yet extension of use in other applications has been limited due to its relatively rapid resorption in vivo, even with addition of aprotinin or other protease inhibitors. We report an engineered aprotinin variant that can be immobilized within fibrin and thus provide extended longevity. When recombinantly fused to a transglutaminase substrate domain from α2-plasmin inhibitor (α2PI1–8), the resulting variant, aprotinin-α2PI1–8, was covalently crosslinked into fibrin matrices during normal thrombin/factor XIIIa-mediated polymerization. Challenge with physiological plasmin concentrations revealed that aprotinin-α2PI1–8-containing matrices retained 78% of their mass after 3 wk, whereas matrices containing wild type (WT) aprotinin degraded completely within 1 wk. Plasmin challenge of commercial sealants Omrixil and Tisseel, supplemented with aprotinin-α2PI1–8 or WT aprotinin, showed extended longevity as well. When seeded with human dermal fibroblasts, aprotinin-α2PI1–8-supplemented matrices supported cell growth for at least 33% longer than those containing WT aprotinin. Subcutaneously implanted matrices containing aprotinin-α2PI1–8 were detectable in mice for more than twice as long as those containing WT aprotinin. We conclude that our engineered recombinant aprotinin variant can confer extended longevity to fibrin matrices more effectively than WT aprotinin in vitro and in vivo.