Cell tagging with clinically approved iron oxides: feasibility and effect of lipofection, particle size, and surface coating on labeling efficiency.
OBJECTIVE
To evaluate the effect of lipofection, particle size, and surface coating on labeling efficiency of mammalian cells with superparamagnetic iron oxides (SPIOs).


METHODS
Institutional Review Board approval was not required. Different human cell lines (lung and breast cancer, fibrosarcoma, leukocytes) were tagged by using carboxydextran-coated SPIOs of various hydrodynamic diameters (17-65 nm) and a dextran-coated iron oxide (150 nm). Cells were incubated with increasing concentrations of iron (0.01-1.00 mg of iron [Fe] per milliliter), including or excluding a transfection medium (TM). Cellular iron uptake was analyzed qualitatively at light and electron microscopy and was quantified at atomic emission spectroscopy. Cell visibility was assessed with gradient- and spin-echo magnetic resonance (MR) imaging. Effects of iron concentration in the medium and of lipofection on cellular SPIO uptake were analyzed with analysis of variance and two-tailed Student t test, respectively.


RESULTS
Iron oxide uptake increased in a dose-dependent manner with higher iron concentrations in the medium. The TM significantly increased the iron load of cells (up to 2.6-fold, P < .05). For carboxydextran-coated SPIOs, larger particle size resulted in improved cellular uptake (65 nm, 4.37 microg +/- 0.08 Fe per 100 000 cells; 17 nm, 2.14 microg +/- 0.06 Fe per 100 000 cells; P < .05). Despite larger particle size, dextran-coated iron oxides did not differ from large carboxydextran-coated particles (150 nm, 3.81 microg +/- 0.46 Fe per 100 000 cells; 65 nm, 4.37 microg +/- 0.08 Fe per 100 000 cells; P > .05). As few as 10 000 cells could be detected with clinically available MR techniques by using this approach.


CONCLUSIONS
Lipofection-based cell tagging is a simple method for efficient cell labeling with clinically approved iron oxide-based contrast agents. Large particle size and carboxydextran coating are preferable for cell tagging with endocytosis- and lipofection-based methods.
Matuszewski
Lars
L
Department of Clinical Radiology, University Hospital Muenster, Albert-Schweitzer-Strasse 33, D-48129 Muenster, Germany.
Persigehl
Thorsten
T
Wall
Alexander
A
Schwindt
Wolfram
W
Tombach
Bernd
B
Fobker
Manfred
M
Poremba
Christopher
C
Ebert
Wolfgang
W
Heindel
Walter
W
Bremer
Christoph
C
D002478:Cells, Cultured; D003911:Dextrans; D005240:Feasibility Studies; D005290:Ferric Compounds; D052203:Ferrosoferric Oxide; D007501:Iron; D058185:Magnetite Nanoparticles; D010087:Oxides; D010316:Particle Size; D013194:Staining and Labeling / Q000379:methods*; D013499:Surface Properties
D003911:Dextrans; D005290:Ferric Compounds; D058185:Magnetite Nanoparticles; D010087:Oxides; C000499:ferric oxide; D007501:Iron; C065507:ferumoxides; D052203:Ferrosoferric Oxide