Ultrasound Detection of Myocardial Ischemic Memory Using an E-Selectin Targeting Peptide Amenable to Human...

Vascular endothelial leukocyte adhesion molecules, such as E-selectin, are acutely upregulated in myocardial ischemia/reperfusion and are thus "ischemic memory" biomarkers for recent cardiac ischemia. We sought to develop an ultrasound molecular imaging agent composed of microbubbles (MBs) targeted to E-selectin to enable the differential diagnosis of myocardial ischemia in patients presenting with chest pain of unclear etiology. Biodegradable polymer MBs were prepared bearing a peptide with specific human E-selectin affinity (MB_ESEL). Control MBs had scrambled peptide (MB_CTL) or nonspecific IgG (MB_IgG). MB_ESEL adhesion to activated rat endothelial cells (ECs) was confirmed in vitro in a flow system and in vivo with intravital microscopy of rat cremaster microcirculation. Ultrasound molecular imaging of recent myocardial ischemia was performed in rats 4 hours after transient (15 minutes) coronary occlusion. MB_ESEL adhesion was higher to inflamed versus normal ECs in vitro; there was no difference in MB_CTL or MB_IgG adhesion to inflamed versus normal ECs. There was greater adhesion of MB_ESEL to inflamed versus noninflamed microcirculation and minimal adhesion of MB_CTL or MB_IgG under any condition. Ultrasound imaging after injection of MB_SEL demonstrated persistent contrast enhancement of the previously ischemic region. Videointensity in postischemic myocardium after MB_ESEL was higher than that in the nonischemic bed (11.6 ± 2.7 dB vs 3.6 ± 0.8 dB, p < .02) and higher than that after MB_CTL (4.0 ± 1.0 dB, p < .03) or MB_IgG (1.7 ± 0.1 dB, p < .03). MBs targeted to E-selectin via a short synthetic peptide with human E-selectin binding affinity enables echocardiographic detection of recent ischemia, setting the stage for clinical myocardial ischemic memory imaging to identify acute coronary syndromes.