In vivo labelling of resting monocytes in the reticuloendothelial system with fluorescent iron oxide nanoparticles prior to injury reveals that they are mobilized to infarcted myocardium.
OBJECTIVE
To evaluate the feasibility of loading resting monocytes/macrophages by intravenous (i.v.) injection of fluorescent iron oxide nanoparticles prior to injury and tracking of these cells in the very same animal to myocardial infarction (MI) by magnetic resonance imaging (MRI) and optical imaging.


RESULTS
Rats were injected with fluorescent iron oxide nanoparticles (10 mg/kg) (n = 15) prior to injury. After disappearance of the nanoparticles from the blood, MI was induced. Monocytes/macrophages were then tracked in the very same animal by MRI and optical imaging. Control groups were (i) non-injected animals (n = 15), (ii) injected animals associated with a sham operation (n = 8), and (iii) animals treated with an anti-inflammatory agent (n = 6). The presence of iron-loaded cells can be detected by MRI in vivo in the infarcted myocardium. Here, we showed that the detection of inflammatory cells in vivo correlated well with ex vivo imaging (MRI and reflectance fluorescence) and histology. We also showed that the method is robust enough to depict changes in the inflammatory response.


CONCLUSIONS
This study demonstrates that resting monocytes/macrophages can be loaded in vivo by a simple i.v. injection of fluorescent superparamagnetic iron oxide nanoparticles prior to injury and then tracked, in the same animal, in a model of ischaemia-reperfusion leading to myocardial infarct. Although previous studies of macrophages infiltration following MI have labelled the macrophages after injury, this study, for the first time, has pre-load the resting monocytes with fluorescent iron oxide nanoparticles.
Montet-Abou
Karin
K
Radiology Department, Geneva University Hospital, Geneva, Switzerland.
Daire
Jean-Luc
JL
Hyacinthe
Jean-Noël
JN
Jorge-Costa
Manuel
M
Grosdemange
Kerstin
K
Mach
François
F
Petri-Fink
Alke
A
Hofmann
Heinrich
H
Morel
Denis R
DR
Vallée
Jean-Paul
JP
Montet
Xavier
X
D000818:Animals; D015703:Antigens, CD; D015214:Antigens, Differentiation, Myelomonocytic; D002465:Cell Movement / Q000502:physiology*; D005290:Ferric Compounds; D005453:Fluorescence; D008264:Macrophages / Q000378:metabolism* / Q000502:physiology; D008279:Magnetic Resonance Imaging; D053768:Metal Nanoparticles; D009000:Monocytes / Q000378:metabolism* / Q000502:physiology; D012157:Mononuclear Phagocyte System; D009203:Myocardial Infarction / Q000175:diagnosis*; D015428:Myocardial Reperfusion Injury / Q000175:diagnosis; D051381:Rats; D017208:Rats, Wistar; D000097382:CD68 Molecule
D015703:Antigens, CD; D015214:Antigens, Differentiation, Myelomonocytic; D005290:Ferric Compounds; C067980:CD68 antigen, human; D000097382:CD68 Molecule; C000499:ferric oxide