Abstract 18539: Molecular Imaging of Factor XIII for Early Diagnosis of Coronary Microvascular Disease in Mice

Abstract

Background: Coronary microvascular disease (MVD) remains a major clinical challenge, involving endothelial cell (ECs) dysfunction and microthrombosis. We hypothesize that active FXIII can be a specific biomarker for MVD and its activity can be evaluated by a FXIII targeted radiolabeled probe ( 99m Tc-NC100668). We also hypothesize that a murine MVD model can be established through photodynamic therapy (PDT). Methods: To optimize the PDT parameters, primary ECs from the heart were isolated and treated with various concentrations of rose bengal, different illumination times, multiple combinations of rose bengal and illumination times (PDT), or nothing to evaluate cell viability and production of reactive oxygen species (ROS). The optimal parameters were translated for in vivo MVD model establishment. 52 female mice were assigned to one of four groups: 1) rose bengal, 2) green light, 3) combination, or 4) nothing. Microvascular injury was evaluated by fluorescent myocardial perfusion, coronary microCT angiography, and electron microscopy. To validate the efficacy of this tracer for the diagnosis of coronary MVD, an additional 124 female mice with MVD were injected either 0.1mCi 99m Tc-NC100668 or 99m Tc-AH110563 (an inactive analog), at 3 hrs, 24 hrs, 3, 7, or 14 days, for ex vivo gamma well counting (GWC, n=100) to assess regional myocardial activity as %injection dose/mg (id/mg), or in vivo microSPECT/CT (n=24) to visualize active FXIII. Results: PDT were capable of injuring primary ECs by over-producting ROS in vitro . Coronary MVD developed only in PDT mice with focal “no flow phenomena”. microCT demonstrated arteriole rarefaction and Electron Microscopy showed luminal microthrombi and loss of endothelial integrity in PDT-treated myocardium. GWC demonstrated 99m Tc-NC100668 activity within endothelial-damaged myocardium, compared to an inactive tracer at early time points (3 hours: 9.33±1.98 vs. 2.84±1.97% id/mg, p<0.01; 3 days: 3.3±2.23 vs. 0.275±0.072% id/mg, p<0.05). In vivo microSPECT/CT images confirmed focal myocardial uptake up to day 3. Conclusions: We successfully established a murine model of coronary MVD. Molecular imaging of the activated FXIII allowed visualization of acute and sub-acute coronary micro-thrombi, a hallmark of MVD.