Objective       To investigate the method of labeling endothelial progenitor cells (EPCs) with Gd-BOPTA and cytobiological characteristics of Gd-BOPTA-labeled EPCs

and to explore imaging characteristics of the labeled cells by magnetic resonance imaging (MRI) in vitro

fo

r providing experimental evidences for clinical application of EPCs transplantation.       Methods       EPCs were separated from human umbilical cord blood (HUCB) by density gradient centrifugation and adherence screening

and were cultured in vitro. EPCs were labeled with Gd-BOPTA via jetPEI

TM

-FluoF

and the effects of different concentration of Gd-BOPTA and different incubation time on cytobiological characteristics of Gd-BOPTA-labeled EPCs were examined. Unlabeled EPCs and EPCs labeled for 24 h were collected for MRI examination

and signal intensities of EPCs labeled with different concentration of Gd-BOPTA in different scanning sequence were compared.       Results       Green fluorescence particles were found in the cytoplasm of Gd-BOPTA-labeled EPCs under fluorescence microscope

and numerous Gd particles mainly scattered around Golgi apparatus and attached to internal surface of cell membrane by transmission electron microscopy. The labeling pattern of Gd-BOPTA was parabolic

indicating that before the labeling concentration reached 25 μg/ml and the labeling time reached 24 h [(88.2±1.6)%

the peak level

]

the labeling efficiency and Gd particles were increasing

but after that the labeling efficiency and Gd particles decreased. At concentrations of 12.5

25 and 37.5 μg/ml after labeling for 12 and 24 h

the labeling efficiency of Gd-BOPTA were (55.7±0.8)%

(80.8±0.5)%

(71.6±0.6)% and (67.4±1.7)%

(88.2±1.6)%

(73.2±2.2)%

respectively. The adhesion

migration and proliferation capacities of Gd-BOPTA-labeled EPCs showed no significant change when the labeling concentration was below 25 μg/ml (P0.05). The maximal signal intensity (SI) of Gd-BOPTA-labeled EPCs in T

1

WI sequence was obtained at the concentration of 25 μg/ml (161%)

and it was significantly different from that of unlabeled EPCs (P0.05). The △SI of Gd-BOPTA-labeled EPCs in T

2

WI and T

2

*WI was not significantly different from that in T

1

WI (P0.05).       Conclusion       EPCs can be efficien

tly labeled with Gd-BOPTA via jetPEI

TM

-FluoF. The major effect of Gd-BOPTA on MR imaging is in T

1

WI positive sequence

the optimal labeling concentration of Gd-BOPTA is 25 μg/ml and the best labeling time is 24 h.