In vivo MR tracking of mesenchymal stem cells in rat liver after intrasplenic transplantation

Purpose: To prospectively track in vivo in rats intrasplenically transplanted stem cells labeled with superparamagnetic particles by using magnetic resonance (MR) imaging.

Materials and methods: The study was approved by the institutional Committee on Animal Research. Liver damage in 12 rats was induced with subcutaneous injection of carbon tetrachloride (CCl4). Intrasplenic transplantation of 6x10(6) rodent bone mesenchymal stem cells (BMSCs) with (n=6) and without (n=6) superparamagnetic particle Fe2O3-poly-L-lysine (PLL) labeling was performed via direct puncture. Cell labeling efficiency was assessed in vitro by using Prussian blue stain and an atomic absorption spectrometer. MR examinations were performed immediately before and 3 hours and 3, 7, and 14 days after transplantation. Liver-to-muscle contrast-to-noise ratios (CNRs) on T2*-weighted MR images obtained before and after injection were measured and correlated with histomorphologic studies. Statistical analyses were performed by using repeated-measures analysis of variance.

Results: Rat BMSCs could be effectively labeled with approximately 100% efficiency. Migration of transplanted labeled cells to the liver was successfully documented with in vivo MR imaging. CNRs on T2*-weighted images decreased significantly in the liver 3 hours after injection of BMSCs (P<.05) and returned gradually to the level achieved without labeled cell injection in 14 days. Histologic analyses confirmed the presence of BMSCs in the liver. The labeled cells primarily localized in the sinusoids of periportal areas and the foci of CCl4-induced liver damage. Quantitative analysis of Prussian blue-stained cells indicated gradual decrease of dye pigments from 3 hours to 3, 7, and 14 days after injection. No free iron particles were found in the interstitium or within hepatic microvessels.

Conclusion: The rat BMSCs could be efficiently labeled with Fe2O3-PLL and the relocation of the labeled cells to rat livers after intrasplenic transplantation could be depicted at in vivo MR imaging.