Abstract 3423: Monocyte Labeling and Tracking with Perfluorocarbon Nanobeacons for Therapeutic Angiogenesis in Mouse Hind Limb Ischemia
Bone marrow mononuclear cells (BM MNC), specifically monocytic cells, can augment new blood vessel formation in a hind limb ischemia model of angiogenesis. Approaches to track the activity of such cells in vivo with MRI have employed labeling with ferrous compounds to provide MR contrast effects. We propose a new labeling method utilizing perfluorocarbon nanoparticles (PFC NP) that avoids the ubiquitous background water signal and the susceptibility artifact that accompanies iron oxide particles, and also allows quantification of the signal to determine nanoparticle concentration,. The advantage of PFC NP is their inherent fluorine signal that can be analyzed using 19F MR imaging and spectroscopy. BM MNC’s isolated from the femur and tibia of donor mice were labeled in 6 hours without the use of transfection agents and without detriment to viability (>95% via dye exclusion). Analysis by flow cytometry showed that the PFC NP labeling efficiency for the Gr-1+ cells and CD11b+ cells (both monocytic markers in the bone marrow) was 44% and 37%, respectively. 19F MR spectroscopy identified the signal from as few as 15,000 cells in vitro (n=3 pellets), and 62,000 cells in vivo (n=2 mice) at 11.7 T. The therapeutic effect of these labeled cells on ischemic limb angiogenesis in 5 mice was comparable to that of unlabeled cells as analyzed with laser Doppler perfusion imaging, which confirmed a 100% augmentation of blood flow at day 7 following intravenous injection of 1 million cells over mice not receiving cells. We observed that 62,000 cells can be imaged 24 hours following intramuscular injection in vivo at 11.7 T. Accordingly, PFC NP show promise as an alternative to ferrous contrast agents for cell tracking in vivo as a nontoxic, unique, and quantifiable signal that can be imaged without obscuring background water signal.