The Significance of Preformed Aprotinin-Specific Antibodies in Cardiosurgical Patients

Human Kunitz-type protease inhibitor engineered for enhanced matrix retention extends longevity of fibrin biomaterials

Aprotinin is a broad-spectrum serine protease inhibitor used in the clinic as an anti-fibrinolytic agent in fibrin-based tissue sealants. However, upon re-exposure, some patients suffer from hypersensitivity immune reactions likely related to the bovine origin of aprotinin. Here, we aimed to develop a human-derived substitute to aprotinin. Based on sequence homology analyses, we identified the Kunitz-type protease inhibitor (KPI) domain of human amyloid-β A4 precursor protein as being a potential candidate. While KPI has a lower intrinsic anti-fibrinolytic activity than aprotinin, we reasoned that its efficacy is additionally limited by its fast release from fibrin material, just as aprotinin's is. Thus, we engineered KPI variants for controlled retention in fibrin biomaterials, using either covalent binding through incorporation of a substrate for the coagulation transglutaminase Factor XIIIa or through engineering of extracellular matrix protein super-affinity domains for sequestration into fibrin. We showed that both engineered KPI variants significantly slowed plasmin-mediated fibrinolysis in vitro, outperforming aprotinin. In vivo, our best engineered KPI variant (incorporating the transglutaminase substrate) extended fibrin matrix longevity by 50%, at a dose at which aprotinin did not show efficacy, thus qualifying it as a competitive substitute of aprotinin in fibrin sealants.

Efficacy and safety of aprotinin in cardiac surgery

Cardiac surgery and cardiopulmonary bypass produces bleeding and the need for allogenic blood product transfusions in many patients. Blood conservation is important in the perioperative management of patients. Aprotinin, a serine protease inhibitor isolated from bovine lung, is a complex protease inhibitor that is an antifibrinolytic, inhibits contact activation, and decreases the inflammatory response to cardiopulmonary bypass. Aprotinin reduces blood loss and transfusion requirements in adult and pediatric patients undergoing cardiac surgery with cardiopulmonary bypass. Full-dose aprotinin significantly reduces postoperative blood loss and has been demonstrated in multiple prospective blinded studies to be safe and effective. One of the major adverse effects is anaphylaxis that occurs on re-exposure to aprotinin.