Abstract
Cell tracking with magnetic resonance imaging (MRI) is important for evaluating the biodistribution of transplanted cells. Umbilical cord-derived mesenchymal stem cells (UC-MSCs) have emerged as a promising therapeutic tool in regenerative medicine. We examined the UC-MSCs labeled with superparamagnetic (SPIO) and ultrasmall superparamagnetic iron oxide (USPIO) in terms of cell functioning and imaging efficiency in vitro and in vivo. The UC-MSCs were co-incubated with SPIO or USPIO at a concentration of 50 or 100 µg/mL of label. Viability and proliferation were assessed by Trypan blue dye exclusion and MTT assay, respectively. Differentiation (chondrogenesis, osteogenesis, and adipogenesis) was induced to examine the impact of labelling on stemness. For in vitro experiments, we used 7-T MRI to assess the T2 values of phantoms containing various concentrations of cell suspensions. For in vivo experiments, nine neonatal rats were divided into the control, SPIO, and USPIO groups. The UC-MSCs were injected directly into the rat brains. MRI images were obtained immediately and at 7 and 14 days post injection. The UC-MSCs were successfully labeled with SPIO and USPIO after 24 h of incubation. Cell viability was not changed by labelling. Nevertheless, labelling with 100 µg/mL USPIO led to a significant decrease in proliferation. The capacity for differentiation into cartilage was influenced by 100 µg/mL of SPIO. MRI showed that labeled cells exhibited clear hypointense signals, unlike unlabeled control cells. In the USPIO-labeled cells, a significant (P < 0.05) decrease in T2 values (= improved contrast) was observed when compared with the controls and between phantoms containing the fewest and the most cells (0.5 × 106 versus 2.0 × 106 cells/mL). In vivo, the labeled cells were discernible on T2-weighted images at days 0, 7, and 14. The presence of SPIO and USPIO particles at day 14 was confirmed by Prussian blue staining. Microscopy also suggested that the regions occupied by the particles were not as large as the corresponding hypointense areas observed on MRI. Both labels were readily taken up by the UC-MSCs and identified well on MRI. While SPIO and USPIO provide improved results in MRI studies, care must be taken while labelling cells with high concentrations of these agents.
Highlights
Cell tracking with magnetic resonance imaging (MRI) is important for evaluating the biodistribution of transplanted cells
After 24 h, the Umbilical cord-derived mesenchymal stem cells (UC-Mesenchymal stem cells (MSCs)) were labeled with SPIO or ultrasmall superparamagnetic iron oxide (USPIO), as confirmed by microscopic examination (Fig. 1)
We evaluated the characteristics of UC-MSCs labeled with SPIO (Resovist) or USPIO (MIRB) by in vitro and in vivo experiments, to investigate the suitability of these agents for cell tracking
Summary
Cell tracking with magnetic resonance imaging (MRI) is important for evaluating the biodistribution of transplanted cells. While SPIO and USPIO provide improved results in MRI studies, care must be taken while labelling cells with high concentrations of these agents. MRI is widely used imaging modality for cell tracking, which can noninvasively observe the transplanted cells when they are labeled with contrast agents, such as superparamagnetic (SPIO) or ultrasmall superparamagnetic iron oxide (USPIO)[10].
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