In Vivo MR Imaging of Macrophages in Cardiac Ischemia/Reperfusion Injury with Paramagnetic Phosphatidylserine-Containing Liposomes

Tessa Geelen¹, Sin Yuin Yeo¹, Leonie E. Paulis¹, Bram F. Coolen¹, Klaas Nicolay¹, Gustav J. Strijkers¹

After a myocardial infarction, macrophages infiltrate the damaged tissue to remove dead cells and promote left ventricular remodeling. The aim of this study was to characterize the presence of these macrophages with MRI. Phosphatidylserine (PS) was incorporated in paramagnetic liposomes to promote uptake by macrophages. In vitro, liposomes containing 6 mol% PS showed the highest uptake by murine macrophages. These liposomes were applied after mouse cardiac ischemia/reperfusion injury and visualized with T₁-weighted MRI and confocal microscopy. PS-liposomes were specifically associated with macrophages in the infarcted myocardium 2.5 hours after injection. After 24 hours of circulation, passive accumulation was predominant.