Objective    To explore the optimal situation of labeling bone mesenchymal stem cells (BMSCs) with superparamagnetic iron oxides (SPIO) mediated by poly-L-lysine (PLL)

and determine the most optimal protocol of magnet

ic resonance imaging according to the patterns of MR in vitro.     Methods    BMSCs were isolated from white rat and purified

incubated with SPIO-PLL complexes at the range of concentrations (0

4.2

8.4

21

42

84 μg Fe per ml medium). The labeling ratio and distribution of SPIO particles in BMSCs

and the morphological evidence of abnormal visualization were evaluated by Prussian blue staining

fluorescent microscope and electron microscopy. MTT growth curves and magnetic resonance imagings were obtained at the range of concentrations. Trypan blue exclusion test was performed to elevate the viability of BMSCs labeled with PLL at the range of concentrations (0

0.05

0.25

0.5

1.0

5.0 μg PLL per ml medium).     Results    The cellular labeling ratio was strongly correlated to the concentrations of SPIO (P0.05). BMSCs labeled with SPIO had similar viability and proliferation profiles at the range of 0 to 42 μg Fe per ml medium

while the cellular viability was limited at the concentration of 84 μg/ml (P0.05). PLL could not affect the cellular viabilities when its concentration was in the range of 0 to 1.0 μg PLL per ml medium

but the viabilities of BMSCs were significantly limited at the concentration of 5.0 μg/ml of PLL. The signal intensities of cell suspension were strongly dependent on the concentrations of SPIO used for labeling in medium (P0.05). The signal intensity rates on T

2

WI and T

2

*WI were stronger than that on T

1

WI (P0.05)

especially on T

2

*WI.      Conclusion    SPIO can label BMSCs easily and efficiently mediated by PLL without interference on the cellular viability and proliferation. The optimal concentration of SPIO should range from 20 μg/ml to 40 μg/ml when incubation time was 24 h.