Detection of antecedent myocardial ischemia with multiselectin molecular imaging

Objectives: Our aim was to develop an echocardiographic molecular imaging approach for detecting recent myocardial ischemia by using recombinant P-selectin glycoprotein ligand (PSGL)-1 as a targeting ligand, which is a feasible approach for human use. Background: Ischemic memory imaging using human PSGL-1 as a targeting moiety may extend the time window for postischemic detection by targeting the early (P-selectin) and late (E-selectin) endothelial ischemic response. Methods: Lipid microbubbles bearing recombinant human PSGL-1 (MB_YSPSL) or P-selectin antibody (MB_Ab) were prepared. Targeted attachment was evaluated by using flow chamber and intravital microscopy. In vivo ultrasound molecular imaging was first performed in the hindlimb in wild-type and P-selectin-deficient (P^-/-) mice 45 to 360 min after brief ischemia-reperfusion injury. Myocardial contrast echocardiography molecular imaging was performed 1.5, 3, 6, and 18 h after brief left anterior descending coronary artery ischemia-reperfusion. Results: Microbubble attachment to P-selectin-immunoglobulin G fusion protein in flow chamber experiments (shear stress 0.5 to 8.0 dyne/cm²) and to activated venular endothelium on intravital microscopy were similar for MB _Ab and MB_YSPSL. Intense enhancement was seen for MB _Ab and MB_YSPSL in postischemic muscle and was more stable over time for MB_YSPSL. On myocardial contrast echocardiography, both MB_YSPSL and MB_Ab produced similar signal enhancement at 90 min and 3 h after ischemia, which spatially correlated with the postischemic risk area. Signal significantly decreased but was still present at 6 to 18 h. Conclusions: Echocardiographic molecular imaging with a human multi-selectin-targeted contrast agent bearing recombinant human PSGL-1 can detect myocardial ischemia hours after resolution. This approach may potentially be used for rapid bedside evaluation of patients with recent chest pain.