In vivo imaging with cellular resolution of bone marrow cells transplanted into the ischemic brain of a mouse

Evaluation of Alginate Hydrogel Microstrands for Stromal Cell Encapsulation and Maintenance

Mesenchymal stromal cells (MSCs) have displayed potential in regenerating organ function due to their anti-fibrotic, anti-inflammatory, and regenerative properties. However, there is a need for delivery systems to enhance MSC retention while maintaining their anti-fibrotic characteristics. This study investigates the feasibility of using alginate hydrogel microstrands as a cell delivery vehicle to maintain MSC viability and phenotype. To accommodate cell implantation needs, we invented a Syringe-in-Syringe approach to reproducibly fabricate microstrands in small numbers with a diameter of around 200 µm and a porous structure, which would allow for transporting nutrients to cells by diffusion. Using murine NIH 3T3 fibroblasts and primary embryonic 16 (E16) salivary mesenchyme cells as primary stromal cell models, we assessed cell viability, growth, and expression of mesenchymal and fibrotic markers in microstrands. Cell viability remained higher than 90% for both cell types. To determine cell number within the microstrands prior to in vivo implantation, we have further optimized the alamarBlue assay to measure viable cell growth in microstrands. We have shown the effect of initial cell seeding density and culture period on cell viability and growth to accommodate future stromal cell delivery and implantation. Additionally, we confirmed homeostatic phenotype maintenance for E16 mesenchyme cells in microstrands.

Cell Therapy for Ischemic Stroke: How to Turn a Promising Preclinical Research into a Successful Clinical Story

Stroke is a major public health issue with limited treatment. The pharmacologically or mechanically removing of the clot is accessible to less than 10% of the patients. Stem cell therapy is a promising alternative strategy since it increases the therapeutic time window but many issues remain unsolved. To avoid a new dramatic failure when translating experimental data on the bedside, this review aims to highlight the indispensable checkpoints to make a successful clinical trial based on the current preclinical literature. The large panel of progenitors/ stem cells at the researcher's disposal is to be used wisely, regarding the type of cells, the source of cells, the route of delivery, the time window, since it will directly affect the outcome. Mechanisms are still incompletely understood, although recent studies have focused on the inflammation modulation of most cells types.

MSCs: Delivery Routes and Engraftment, Cell-Targeting Strategies, and Immune Modulation

Mesenchymal stem cells (MSCs) are currently being widely investigated both in the lab and in clinical trials for multiple disease states. The differentiation, trophic, and immunomodulatory characteristics of MSCs contribute to their therapeutic effects. Another often overlooked factor related to efficacy is the degree of engraftment. When reported, engraftment is generally low and transient in nature. MSC delivery methods should be tailored to the lesion being treated, which may be local or systemic, and customized to the mechanism of action of the MSCs, which can also be local or systemic. Engraftment efficiency is enhanced by using intra-arterial delivery instead of intravenous delivery, thus avoiding the "first-pass" accumulation of MSCs in the lung. Several methodologies to target MSCs to specific organs are being developed. These cell targeting methodologies focus on the modification of cell surface molecules through chemical, genetic, and coating techniques to promote selective adherence to particular organs or tissues. Future improvements in targeting and delivery methodologies to improve engraftment are expected to improve therapeutic results, extend the duration of efficacy, and reduce the effective (MSC) therapeutic dose.

Delayed Intranasal Delivery of Hypoxic-Preconditioned Bone Marrow Mesenchymal Stem Cells Enhanced Cell Homing and Therapeutic Benefits after Ischemic Stroke in Mice

Stem cell transplantation therapy has emerged as a potential treatment for ischemic stroke and other neurodegenerative diseases. Effective delivery of exogenous cells and homing of these cells to the lesion region, however, have been challenging issues that hinder the efficacy and efficiency of cell-based therapy. In the present investigation, we tested a delayed treatment of noninvasive and brain-targeted intranasal delivery of bone marrow mesenchymal stem cells (BMSCs) in a mouse focal cerebral ischemia model. The investigation tested the feasibility and effectiveness of intranasal delivery of BMSCs to the ischemic cortex. Hypoxia preconditioning (HP) of BMSCs was performed before transplantation in order to promote their survival, migration, and homing to the ischemic brain region after intranasal transplantation. Hoechst dye-labeled normoxic- or hypoxic-pretreated BMSCs (1 × 106 cells/animal) were delivered intranasally 24 h after stroke. Cells reached the ischemic cortex and deposited outside of vasculatures as early as 1.5 h after administration. HP-treated BMSCs (HP-BMSCs) showed a higher level of expression of proteins associated with migration, including CXC chemokine receptor type 4 (CXCR4), matrix metalloproteinase 2 (MMP-2), and MMP-9. HP-BMSCs exhibited enhanced migratory capacities in vitro and dramatically enhanced homing efficiency to the infarct cortex when compared with normoxic cultured BMSCs (N-BMSCs). Three days after transplantation and 4 days after stroke, both N-BMSCs and HP-BMSCs decreased cell death in the peri-infarct region; significant neuroprotection of reduced infarct volume was seen in mice that received HP-BMSCs. In adhesive removal test of sensorimotor functional assay performed 3 days after transplantation, HP-BMSC-treated mice performed significantly better than N-BMSC- and vehicle-treated animals. These data suggest that delayed intranasal administration of stem cells is feasible in the treatment of stroke and hypoxic preconditioning of transplanted cells, significantly enhances cell's homing to the ischemic region, and optimizes the therapeutic efficacy.

Interleukin-1beta and tumor necrosis factor-alpha are expressed by different subsets of microglia and macrophages after ischemic stroke in mice

BACKGROUND

Interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) are expressed by microglia and infiltrating macrophages following ischemic stroke. Whereas IL-1beta is primarily neurotoxic in ischemic stroke, TNF-alpha may have neurotoxic and/or neuroprotective effects. We investigated whether IL-1beta and TNF-alpha are synthesized by overlapping or segregated populations of cells after ischemic stroke in mice.

METHODS

We used flow cytometry and immunohistochemistry to examine cellular co-expression of IL-1beta and TNF-alpha at 6, 12 and 24 hours after permanent middle cerebral artery occlusion in mice, validating the results by the use of bone marrow chimeric mice.

RESULTS

We found that IL-1beta and TNF-alpha were expressed in largely segregated populations of CD11b+CD45dim microglia and CD11b+CD45high macrophages, with cells expressing both cytokines only rarely. The number of Gr1+ granulocytes producing IL-1beta or TNF-alpha was very low, and we observed no IL-1beta- or TNF-alpha-expressing T cells or astrocytes.

CONCLUSION

Taken together, the results show that IL-1beta and TNF-alpha are produced by largely segregated populations of microglia and macrophages after ischemic stroke in mice. Our findings provide evidence of a functional diversity among different subsets of microglia and macrophages that is potentially relevant to future design of anti-inflammatory therapies in stroke.

Dual-modality monitoring of targeted intraarterial delivery of mesenchymal stem cells after transient ischemia

BACKGROUND AND PURPOSE

In animal models of stroke, functional improvement has been obtained after stem cell transplantation. Successful therapy depends largely on achieving a robust and targeted cell engraftment, with intraarterial (IA) injection being a potentially attractive route of administration. We assessed the suitability of laser Doppler flow (LDF) signal measurements and magnetic resonance (MR) imaging for noninvasive dual monitoring of targeted IA cell delivery.

METHODS

Transient cerebral ischemia was induced in adult Wistar rats (n=25) followed by IA or intravenous (IV) injection of mesenchymal stem cells (MSCs) labeled with superparamagnetic iron oxide. Cell infusion was monitored in real time with transcranial laser Doppler flowmetry while cellular delivery was assessed with MRI in vivo (4.7 T) and ex vivo (9.4 T).

RESULTS

Successful delivery of magnetically labeled MSCs could be readily visualized with MRI after IA but not IV injection. IA stem cell injection during acute stroke resulted in a high variability of cerebral engraftment. The amount of LDF reduction during cell infusion (up to 80%) was found to correlate well with the degree of intracerebral engraftment, with low LDF values being associated with significant morbidity.

CONCLUSIONS

High cerebral engraftment rates are associated with impeded cerebral blood flow. Noninvasive dual-modality imaging enables monitoring of targeted cell delivery, and through interactive adjustment may improve the safety and efficacy of stem cell therapy.

Vascular fate of adipose tissue-derived adult stromal cells in the ischemic murine brain: A combined imaging-histological study

Increasing evidence indicates that fat tissue can provide a novel source of progenitor cells with therapeutic potential. Here, the fate of adipose tissue-derived stromal cells (ADSCs) transplanted into the mouse ischemic cortex was monitored in the long term using in vivo imaging, and subsequently characterized. The left middle cerebral artery (MCA) was occluded in C57BL/6J mice equipped with a closed cranial window chronically implanted over the left parietal cortex (n = 20). ADSCs expressing the green fluorescent protein (GFP) (approximately 18 x 10(3) cells in 0.5 microl) were transplanted into the ipsilateral cortex, 24 h after MCA occlusion. GFP+-ADSCs were monitored through the window using confocal fluorescence microscopy to assess their single fate in vivo. Co-localization of GFP with vascular, neuronal, glial or proliferation markers was investigated immunohistochemically. Repeated in vivo imaging revealed that GFP+-ADSCs migrated over 1 week toward the lesion, survived for at least 4 weeks, and exhibited a particular tropism for vessels. About 5% of the transplanted GFP+-ADSCs were scattered in the peri-ischemic area on histological sections. Immunohistochemistry evidenced that perivascular GFP+-ADSCs enfolded CD31-labeled endothelial cells, always outside their basal lamina, and occasionally expressed smooth muscle alpha-actin. Less than 1% GFP and BrdU co-labeling indicated a low proliferation rate of ADSCs. These results demonstrate that cerebral ischemia induces ADSCs survival, migration toward the lesion, especially toward microvessels, and occasional differentiation into smooth muscle cells.