Novel Injury Site Targeted Fusion Protein Comprising Annexin V and Kunitz Inhibitor Domains Ameliorates Ischemia-Reperfusion Injury and Promotes Survival of Ischemic Rat Abdominal Skin Flaps

Appropriate antithrombotic therapy is critical for successful outcomes in reconstructive microsurgical procedures involving free tissue transfer. The annexin V-6L15 (ANV-6L15) fusion protein was developed as a targeted antithrombotic reagent. Annexin V specifically binds to exposed phosphatidylserine on apoptotic or injured cells, and prevents coagulation and cell adhesion, whereas 6L15 inhibits tissue factor-VIIa pathway within the coagulation cascade. The treatment efficacy of ANV-6L15 on rat island muscle and pedicled abdominal fasciocutaneous flaps following ischemic injury and ischemia-reperfusion injury (IRI) was evaluated. Materials and Methods: The effects of ANV-6L15 on survival of rat abdominal fasciocutaneous flaps subjected to 10 hours of critical ischemia were assessed on day 5. Near-IR imaging was applied to evaluate the distribution of ANV-6L15 and flap perfusion. The rat cremaster muscle island flap was used to evaluate the effect of ANV-6L15 on IRI-induced leukocyte-endothelial interactions via intravital microscopy. 2,3,5 triphenyl-tetrazolium chloride assay was used to determine the ratio between live-versus-dead tissue. Results: ANV-6L15 significantly increased the ratio of viable tissue (68.5 +/- 9.79% vs 84.8 +/- 5.14%, P < 0.05), and promoted survival of rat pedicled abdominal flaps (59.3 +/- 6.86 vs. 47.0 +/- 8.67, P < 0.05). Intravital microscopy demonstrated a significant decrease in the number of adhesive leukocytes (1.8 +/- 1.64 vs. 10.0 +/- 6.32, P < 0.05), and the percentage change of functional capillaries (16.4 +/- 15.1 vs. 47.3 +/- 18.3, P < 0.05) in ANV-6L15-treatment group. Conclusions: ANV-6L15 promoted survival of ischemic rat cremaster muscle and abdominal fasciocutaneous flaps and ameliorated leukocyte-related IRI. Future evaluation of potential clinical application of ANV-6L15 is warranted as a flap treatment adjunct.