Factor XIIa Inhibitor Recombinant Human Albumin Infestin-4 Abolishes Occlusive Arterial Thrombus Formation Without Affecting Bleeding

Background-Blood coagulation is a tightly regulated process of sequentially activated serine proteases culminating in fibrin formation, which is critical for limiting posttraumatic blood loss but also may contribute to acute thrombotic diseases, most notably myocardial infarction and stroke. Recent studies with factor XII-deficient mice revealed that the factor XII-induced intrinsic coagulation pathway is essential for pathological thrombus formation but dispensable for hemostasis. Consequently, these findings led to the hypothesis that factor XII could be a promising pharmacological target for safe antithrombotic therapy. Methods and Results-The complementary DNA of the previously described factor XIIa inhibitor Infestin-4, cloned from the midgut of Triatoma infestans, was fused to recombinant human albumin (rHA) and analyzed in vitro. The resulting protein rHA-Infestin-4 specifically inhibits factor XIIa and causes prolonged activated partial thromboplastin time in human, mouse, and rat plasma. To assess its inhibitory potency in vivo, mice and rats were injected with rHA-Infestin-4 and challenged in pathological thrombus formation models. In addition, bleeding assays were performed. rHA-Infestin-4 completely abolished occlusive arterial thrombus formation in mice and rats while leaving hemostasis fully intact. Furthermore, rHA-Infestin-4 was highly protective in a murine model of ischemic stroke. Conclusion-These results identify rHA-Infestin-4 as a promising agent to achieve powerful protection from ischemic cardiovascular and cerebrovascular events without affecting hemostasis. (Circulation. 2010;121:1510-1517.)