Tracking of Transplanted Mesenchymal Stem Cells Labeled with Fluorescent Magnetic Nanoparticle in Liver Cirrhosis Rat Model with 3T MRI

Abstract

"Purpose : Liver cirrhosis represents the end stage of chronic liver injury and the only therapeutic option for advanced liver cirrhosis is liver transplantation. As a new therapeutic approach, there have been many studies about the therapeutic effect of transplantation of bone marrow stem cells. In vivo visualization of transplanted stem cells with noninvasive technique is essential for the monitoring of cell implantation, homing and differentiation. This study was designed to track intrasplenically injected bone marrow mesenchymal stem cells labeled with fluorescent magnetic nanoparticle in liver cirrhosis rat model with 3 Tesla (3T) MR equipment.

Materials and Methods : For the evaluation of T2 and T2* relaxation time, 5 x 105 cells/ml mesenchymal stem cells (MSCs) were separately labeled for 12 hours using the ferumoxides and fluorescent magnetic nanoparticle containing rhodamine B isothiocyanate with 12.5, 25.0, 50.0 and 100 μg/ml concentrations. The T2 and T2* values were measured by using the conventional spin-echo (TR/TE = 2000 ms/10, 20, 30, 40, 50 and 60 ms) and gradient-echo sequences (TR/TE = 1000 ms/2, 5, 8, 11, 14 and 17 ms). Liver cirrhosis was induced in 10 male Sprague-Dawley rats with intraperitoneal injection of dimethylnitrosamine (DMN, 10 μg/g body weight) 3 times per week (3 consecutive daily injections and 4 days off) for 3 weeks. Approximately 3.0 x 106 BMSCs suspended in 0.5mL phosphate-buffered saline were slowly injected into the inferior tip of the spleen in group 1 (MNP-labeled BMSCs, n=6) and group 2 (unlabeled BMSCs, n=4). For stem cell tracking, transverse T2*-weighted gradient echo (26/9 ; section thickness, 2mm ; intersection gap, 2mm ; matrix, 256 x 256; field of view, 60 x 60 mm ; flip angle , 30°) sequences were performed before injection and at 3 hours, 5 hours, 1 day and 7 days after injection. A rat was sacrificed at 3 hours, 1 day and 7 days after stem cell injection for the evaluation of degree of liver fibrosis and detection of MNP-labeled MSCs within tissues.

Results : T2 and T2* relaxation times of MNP-labeled stem cells were 32 ± 20 and 16 ± 5 ms and shorter than those of ferumoxides, 36 ± 11 and 26 ± 6, respectively. Before injection, 3 and 5 hours and 1 and 7 days after injection, the respective liver-to-muscles CNRs were -6.95 ± 4.21, -28.74 ± 5.03, -20.7 ± 6.41, -7.89 ± 2.99 and -8.33 ± 1.59 for MNP-labeled group and -3.52 ± 1.29, -2.95 ± 1.65, -1.31 ± 2.42, -1.78 ± 3.04 and 2.58 ± 3.56 for non-labeled group. For the MNP-labeled group, CNR at 3 and 5 hours after injection was significantly lower than that of pre-injection and non-labeled group at 3 and 5 hours after injection (p<0.05). On confocal laser microscopic imaging of liver specimens obtained at 3 hours, 1 day and 7 days after MNP-labeled stem cell injection, stem cells arranged linearly forming multiple variable sized circles. We found that remained MNP-labeled stem cells were located in fibrous septa. Much more cells were observed in rat liver sacrificed at 3 hours after injection.

Conclusion : Intrasplenically injected MNP-labeled MSCs in an experimental rat model of liver cirrhosis can be effectively detected with 3T MRI.

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