Published online Feb 26, 2019. doi: 10.4252/wjsc.v11.i2.100
Peer-review started: October 23, 2018
First decision: November 14, 2018
Revised: December 5, 2018
Accepted: December 17, 2018
Article in press: December 17, 2018
Published online: February 26, 2019
Mesenchymal stem cells (MSCs) have been widely tested for therapeutic efficacy in the ischemic brain, providing several benefits. A major obstacle for the clinical translation of these therapies has been the inability to noninvasively monitor the best route, cell doses, and collateral effects, while ensuring survival and effective biological functioning of the transplanted stem cells. Combined image modalities have improved the accuracy of cellular therapy, allowed the in vivo monitoring of the biodistribution and viability of transplanted stem cells due to associated new tracers such as multimodal nanoparticles with new labels and covers, resulting in low toxicity and longtime residence in cells.
Although meta-analyses have examined the benefits of cell transplantation in experimental stroke, low viable cell retention after transplantation in ischemic brain areas still represents the major obstacle to the successful clinical translation of cell-based stroke repair approaches. The multimodal imaging techniques provide morpho-functional information for studying pathological events following ischemia, associated with new tracers. These innovations will contribute to further our comprehension of stem cell transplantation, allowing the assessment of therapeutic effects on a molecular scale.
In this study, we aim to evaluate the sensitivity of triple-modal imaging of stem cells labeled with multimodal nanoparticles with different iron concentrations and their cellular viability in vitro as well as the correlation of the quantification of the iron load between different techniques (ICP-MS, MRI and NIRF. In addition, we seek to verify whether these images of stem cells labeled with multimodal nanoparticles maintain the same properties after application in a stroke model. The results will help us to better understand the biodistribution, sensitivity and viability of stem cells labeled with nanoparticles in sham and stroke models.
Isolated and immunophenotypically characterized hBM-MSCs were transduced with a lentivirus for BLI evaluation in vitro and in vivo. In addition, MNP-IR750 that had previously been characterized (hydrodynamic size, zeta potential, and optical properties) were used for labeling these cells and analyzing cell viability via MTT and BLI assays. The internalization process and quantification of the iron load in different concentrations of MNP-IR750 were analyzed via MRI, NIRF, and ICP-MS. In the in vivo study, the same labeled cells were implanted in the sham group and stroke group at different times and MNP-IR750 concentrations (after 4 h and after 6 d of cell implantation) to evaluate the sensitivity of triple-modal images.
The collection and isolation of hBM-MSCs after immunophenotypic characterization was demonstrated to be adequate for human bone marrow samples. After the transduction of these cells with luciferase, we detected a maximum BLI intensity of 2.0 × 108 photons/s in 106 hBM-MSC samples. Evaluation of the physicochemical characteristics of MNP-IR750 showed an average hydrodynamic diameter of 38.2 ± 0.5 nm, a zeta potential of +29.2 ± 1.9 mV and adequate colloidal stability, without agglomeration over 18 h. The iron load internalization process in hBM-MSCs showed a strong relationship of the signal with the corresponding MNP labeling concentration based on MRI, ICP-MS and NIRF. Cellular viability in the highest MNP-IR750 concentration showed a reduction of less than 10% compared to the control. The correlation analysis of the MNP-IR750 load internalized by hBM-MSCs between the MRI, ICP-MS and NIRF techniques showed the same correlation coefficient of 0.99. The evaluation of BLI, NIRF, and MRI signals in vivo and ex vivo after labeled hBM-MSCs were implanted in the animals showed sensitivity in the detection of MNP-IR750 concentrations of 5, 20 and 50 µg Fe/mL at 4 h and 6 d in the sham groups, with significant results regarding the time and image effect as well as the group effect when the sham and stroke groups were compared at 6 d.
Our study demonstrates that MNP-IR750 can be used to monitor cell grafts noninvasively, longitudinally, and repetitively, enabling the assessment of cell graft conditions in vivo after stroke for multimodal imaging assessment. The BLI signal of hBM-MSCLuc showed the best imaging technique for functional and longitudinal assessment.
In summary, we highlight the importance of quantification of multimodal nanoparticles internalized by cells and the efficacy of signal detection under the triple-image modality in a stroke model. However, the applicability of multimodal imaging should always be analyzed in accordance with the limitations and advantages of each technique involved.