Abstract 12649: Molecular Imaging Using Recombinant PSGL-1 as a Pan-selectin Targeting Moiety Provides Prolonged and Selective Tissue Enhancement for Detecting Recent Ischemia
Introduction: Molecular imaging of P-selectin with targeted microbubbles has been proposed for detecting ongoing or recent myocardial ischemia. We hypothesized that the time window for ischemic memory imaging could be extended by using a recombinant form of the PSGL-1 which targets selectins involved in the early (P-selectin) and late (E-selectin) post-ischemic response.
Methods: In vitro flow chamber studies (shear stress 0.5–8 dyne/cm2) were performed to assess the binding kinetics of targeted microbubbles bearing either P-selectin monoclonal antibody (MBAb) or recombinant dimeric selectin ligand PSGL-1 (MBP1). Similar in vivo studies were performed using intravital microscopy of cremasteric venules in wild-type mice. Contrast-enhanced ultrasound molecular imaging was performed in wild-type and P-selectin-deficient (P−/−) mice undergoing unilateral hindlimb ischemia (10 min) at 45, 90, 180 and 360 minutes after reperfusion. In select mice, a second ischemic insult was performed at 360 min with molecular imaging 45 min thereafter.
Results: Flow chamber attachment of MBAb and MBP1 to P-selectin IgG fusion protein was similar at all shear rates. On intravital microscopy, retention was similar for MBAb and MBP1 (13±2 vs 12±2 per 100 μm2, respectively) and differential fluorescent labeling illustrated regional colocalization of the site of attachment for the two agents. Molecular imaging signal early (45 min) after reperfusion in the ischemic leg was greater for MBAb than MBP1, although there was also more non-specific enhancement for MBAb in the contralateral non-ischemic leg. Signal for MBAb decreased progressively by >50% at 360 min, whereas signal from MBP1 remained unchanged. Signal for both agents increased again after ischemic re-challenge at 360 min. In P−/− mice, only MBP1 produced signal enhancement which occurred =180 min after reperfusion, indicating that E-selectin binding contributed to late signal enhancement for MBP1.
Conclusions: For molecular imaging of ischemic memory, the use of PSGL-1 as a targeting moiety allows binding to both early (P-selectin dominant) and late phase (E- and P-selectin) responses which provides a consistent signal over time. Recurrent ischemic injury can be detected by selectin-targeted imaging.
- © 2010 by American Heart Association, Inc.