Superparamagnetic iron oxide labeling of neural stem cells and 4.7T MRI tracking in vivo and in vitro.

Neural stem cells were labeled with superparamagnetic iron oxide (SPIO) and tracked by MRI in vitro and in vivo after implantation. Rat neural stem cells were labeled with SPIO combined with PLL by the means of receptor-mediated endocytosis. Prussian blue staining and electron microscopy were conducted to identify the iron particles in these neural stem cells. SPIO-labeled cells were tracked by 4.7T MRI in vivo and in vitro after implantation. The subjects were divided into 5 groups, including 5 x 10(5) labeled cells cultured for one day after labeling, 5 x 10(5) same phase unlabeled cells, cell culture medium with 25 mug Fe/mL SPIO, cell culture medium without SPIO and distilled water. MRI scanning sequences included T(1)WI, T(2)WI and T(2)*WI. R(2) and R(2)* of labeled cells were calculated. The results showed: (1) Neural stem cells could be labeled with SPIO and labeling efficiency was 100%. Prussian blue staining showed numerous blue-stained iron particles in the cytoplasm; (2) The average percentage change of signal intensity of labeled cells on T(1)WI in 4.7T MRI was 24.06%, T2WI 50.66% and T(2)*WI 53.70% respectively; (3) T2 of labeled cells and unlabeled cells in 4.7T MRI was 516 ms and 77 ms respectively, R(2) was 1.94 s(-1) and 12.98 s(-1) respectively, and T(2)* was 109 ms and 22.9 ms, R(2)* was 9.17 s(-1) and 43.67 s(-1) respectively; (4) Remarkable low signal area on T(2)WI and T(2)*WI could exist for nearly 7 weeks and then disappeared gradually in the left brain transplanted with labeled cells, however no signal change in the right brain implanted with unlabeled cells. It was concluded that neural stem cells could be labeled effectively with SPIO. R2 and R(2)* of labeled cells were increased obviously. MRI can be used to track labeled cells in vitro and in vivo.