Homing of 111In-Labeled Bone Marrow Mesenchymal Stem Cells in Acute Brain Trauma Model

Abstract

This study was to evaluate the in vivo distribution of intravenously transplanted bone marrow-derived mesenchymal stem cells (BMSCs) in an acute brain trauma model by 111In-tropolone labeling and to perform the effect of 111In-labeling on the viability and functions of BMSCs. Rat BMSCs were labeled with 37 MBq 111In-tropolone. Their labeling efficiency and in vitro retention rate were measured. To evaluate dose-dependent effect of 111In-labeling, BMSCs were labeled with various doses (0.4-11.1 Bq/cell) of 111In-tropolone, and growth curve analysis, fluorescent activated cell sorter (FACS) analysis after staining with 5-bromo-2-deoxy-uridine (BrdU), and microscopic evaluation after 5-bromo-4-chloro-3-indolyl-D-galactopyranoside (X-gal) staining were performed until the 14th day. FACS analysis after staining with Annexin V- fluorescein isothiocyanate (FITC) and propidium iodide (PI) was performed at early (3 and 12 hr) and late (7 days) stages with higher doses of 111In (11.1 and 33.3 Bq/cell) to evaluate apoptotic or necrotic change of labeled BMSCs. The biodistribution of 111In-BMSCs in trauma models was compared with those in sham-operated rats and normal rats by gamma camera images. The migration of 111In-BMSCs to the traumatic brain was evaluated using confocal microscope. The labeling efficiency of 111In-BMSCs was 66 ± 5%, and their retention rate was 85.3% at 1 h after labeling. There was no difference in the number of viable cells between 111In-BMSCs and controls at 48 h after labeling. However, the proliferation of 111In-BMSCs was inhibited after the third day of labeling, and it did not reach confluency. For lower doses of 111In (0.4 and 1.1 Bq/cell), the growth of labeled stem cells was not significantly different from that of control, whereas, labeling with higher doses of 111In (4.4 and 11.1 Bq/cell) led to a significant proliferative inhibition from the 3rd day to the 14th day. FACS analysis also revealed less BrdU positive cells in BMSCs labeled with 1.1, 4.4 and 11.1 Bq/cell compared with controls on the 3rd day after labeling. Of these, the patterns of cell cycle in BMSCs labeled with 0.4 and 1.1 Bq/cell of 111In were restored similar to controls on the 14th day. On the contrary, BMSCs labeled with 4.4 and 11.1 Bq/cell of 111In could not recover from cell cycle arrest. Senescence-associated β-gal (SA- β-gal) staining was not prominent in all concentrations until the 14th day after labeling. FACS analysis with Annexin V-FITC and PI also revealed no significant apoptosis or necrosis in both early and late stages. On gamma camera images, most of the 111In-BMSCs uptake was observed in the liver and spleen at the second day of injection. The brain uptake of 111In-BMSCs was more prominent in trauma models (1.4%) than in sham-operated (0.5%) or normal rats (0.3%). Radiolabeled BMSCs were observed at the marginal region of traumatic brain on the confocal microscope. We observed the dose-dependent growth inhibition of BMSCs by 111In-labeling, which was developed by dose-dependent, transient cell cycle arrest, not by cellular senescence or apoptosis/necrosis. Although growth inhibition by 111In-labeling need to be evaluated further prior to use in humans, 111In-BMSCs are useful for the tracking of intravenously transplanted mesenchymal stem cells in brain disease models.