Echocardiographic Ischemic Memory Imaging Through Complement-Mediated Vascular Adhesion of Phosphatidylserine-Containing Microbubbles.

Abstract

OBJECTIVES: This study hypothesized that microvascular retention of phosphatidylserine-containing microbubbles (MB-PS) would allow detection of recent but resolved myocardial ischemia with myocardial contrast echocardiographic (MCE) molecular imaging. BACKGROUND: Techniques for ischemic memory imaging which can detect and spatially assess resolved myocardial ischemia are being developed for rapid evaluation of patients with chest pain. METHODS: MCE molecular imaging with MB-PS was performed 1.5 h, 3.0 h, and 6.0 h after brief (10 min) myocardial ischemia in mice; data were compared to selectin-targeted microbubbles. MCE molecular imaging with Sonazoid (GE Healthcare, Amersham, United Kingdom), a commercially produced phosphatidylserine (PS)&#xa0;- containing agent, was performed in separate mice at 1.5 h and 3.0 h after ischemia-reperfusion; and in dogs undergoing 135 min of ischemia and 60 min of reflow as well as in closed-chest nonischemic control dogs. The mechanism for MB-PS attachment was assessed by intravital microscopy of post-ischemic muscle and by flow cytometry analysis of cell-MB interactions. RESULTS: In mice undergoing ischemia-reperfusion without infarction, signal enhancement in the risk area for MB-PS and p-selectin glycoprotein ligand-1-targeted microbubbles was similar at reflow times of 1.5 h (23.3 &#xb1; 7.3 IU vs. 30.7&#xa0;&#xb1; 4.1 IU), 3.0 h (42.2 &#xb1; 6.2 IU vs. 33.9 &#xb1; 7.4 IU), and 6.0 h (24.1 &#xb1; 4.3 IU vs. 25.5 &#xb1; 4.7 IU). For both agents, signal in the&#xa0;risk area was significantly (p&#xa0;< 0.05) higher than remote region at all reflow times. Sonazoid also produced strong risk area enhancement at 1.5 h (34.7 &#xb1; 5.0 IU) and 3.0 h (52.5 &#xb1; 4.5 IU) which was approximately 3-fold greater than in the control region, and which correlated spatially with the microsphere-derived risk area. In dogs, Sonazoid signal in the risk area was >5-fold higher than in closed-chest control myocardium (42.2 &#xb1; 8.1 IU vs. 7.9 &#xb1; 3.3 IU; p&#xa0;< 0.001). Mechanistic studies indicated that MB-PS attached directly to venular endothelium and adherent leukocytes which was dependent on serum complement components C1q and C3. CONCLUSIONS: Ischemic memory imaging with MCE is possible using MB-PS which may obviate the need for ligand-directed targeting.