Clot-Derived Contaminants in Transplanted Bone Marrow Mononuclear Cells Impair the Therapeutic Effect in Stroke

Cell Therapy and Functional Recovery of Stroke

Stroke is the most common cause of disability. Brain repair mechanisms are often insufficient to allow a full recovery. Stroke damage involve all brain cell type and extracellular matrix which represent the crucial "glio-neurovascular niche" useful for brain plasticity. Regenerative medicine including cell therapies hold great promise to decrease post-stroke disability of many patients, by promoting both neuroprotection and neural repair through direct effects on brain lesion and/or systemic effects such as immunomodulation. Mechanisms of action vary according to each grafted cell type: "peripheral" stem cells, such as mesenchymal stem cells (MSC), can provide paracrine trophic support, and neural stem/progenitor cells (NSC) or neurons can act as direct cells' replacements. Optimal time window, route, and doses are still debated, and may depend on the chosen medicinal product and its expected mechanism such as neuroprotection, delayed brain repair, systemic effects, or graft survival and integration in host network. MSC, mononuclear cells (MNC), umbilical cord stem cells and NSC are the most investigated. Innovative approaches are implemented concerning combinatorial approaches with growth factors and biomaterials such as injectable hydrogels which could protect a cell graft and/or deliver drugs into the post-stroke cavity at chronic stages. Through main publications of the last two decades, we provide in this review concepts and suggestions to improve future translational researches and larger clinical trials of cell therapy in stroke.

Gap Junction-Mediated Transport of Metabolites Between Stem Cells and Vascular Endothelial Cells

We have previously demonstrated that small molecular transfer, such as glucose, between hematopoietic stem cells (HSCs) or mesenchymal stem cells (MSCs) and vascular endothelial cells via gap junctions constitutes an important mechanism of stem cell therapy. Cell metabolites are high-potential small-molecule candidates that can be transferred to small molecules between stem cells and vascular endothelial cells. Here, we investigated the differences in metabolite levels between stem cells (HSCs and MSCs), vascular endothelial cells, and the levels of circulating non-hematopoietic white blood cells (WBCs). The results showed remarkable differences in metabolite concentrations between cells. Significantly higher concentrations of adenosine triphosphate (ATP), guanosine triphosphate (GTP), total adenylate or guanylate levels, glycolytic intermediates, and amino acids were found in HSCs compared with vascular endothelial cells. In contrast, there was no significant difference in the metabolism of MSCs and vascular endothelial cells. From the results of this study, it became clear that HSCs and MSCs differ in their metabolites. That is, metabolites that transfer between stem cells and vascular endothelial cells differ between HSCs and MSCs. HSCs may donate various metabolites, several glycolytic and tricarboxylic acid cycle metabolites, and amino acids to damaged vascular endothelial cells as energy sources and activate the energy metabolism of vascular endothelial cells. In contrast, MSCs and vascular endothelial cells regulate each other under normal conditions. As the existing MSCs cannot ameliorate the dysregulation during insult, exogenous MSCs administered by cell therapy may help restore normal metabolic function in the vascular endothelial cells by taking up excess energy sources from the lumens of blood vessels. Results of this study suggested that the appropriate timing of cell therapy is different between HSCs and MSCs.

Pre-Clinical Proof of Concept: Intra-Carotid Injection of Autologous CD34-Positive Cells for Chronic Ischemic Stroke

This study was conducted to evaluate the safety and efficacy of human peripheral blood CD34 positive (CD34⁺) cells transplanted into a murine chronic stroke model to obtain pre-clinical proof of concept, prior to clinical testing. Granulocyte colony stimulating factor (G-CSF) mobilized human CD34⁺ cells [1 × 10⁴ cells in 50 μl phosphate-buffered saline (PBS)] were intravenously (iv) or intra-carotid arterially (ia) transplanted 4 weeks after the induction of stroke (chronic stage), and neurological function was evaluated. In this study, severe combined immune deficiency (SCID) mice were used to prevent excessive immune response after cell therapy. Two weeks post cell therapy, the ia CD34⁺ cells group demonstrated a significant improvement in neurological functions compared to the PBS control. The therapeutic effect was maintained 8 weeks after the treatment. Even after a single administration, ia transplantation of CD34⁺ cells had a significant therapeutic effect on chronic stroke. Based on the result of this pre-clinical proof of concept study, a future clinical trial of autologous peripheral blood CD34⁺ cells administration in the intra-carotid artery for chronic stroke patients is planned.

Red blood cells and their releasates compromise bone marrow-derived human mesenchymal stem/stromal cell survival in vitro

PURPOSE

The use of bone marrow aspirate (BMA) and bone marrow aspirate concentrate (BMC) in the treatment of inflammatory orthopedic conditions has become a common practice. The therapeutic effect of BMA/BMC is thought to revolve primarily around the mesenchymal stem/stromal cell (MSC) population residing within the nucleated cell fraction. MSCs have the unique ability to respond to site of injury via the secretion of immunomodulating factors, resolving inflammation in diseased joints. Recently, the importance of hematocrit (HCT) in BMC has been debated, as the potential impact on MSC function is unknown. In the present study, we investigate MSC health over a short time-course following exposure to a range of HCT and red blood cell releasate (RBC_rel) conditions.

METHODS

Bone marrow-derived human MSCs in early passage were grown under conditions of 0%, 2.5%, 5%, 10%, 20% and 40% HCT and RBC_rel conditions for 3 days. At each day, the percentage of viable, apoptotic and necrotic MSCs was determined via flow cytometry. Relative viable MSC counts in each condition was determined to account for dynamic changes in overall MSC densities over the time-course. Statistical analysis was performed using a one-way ANOVA comparing test conditions to the control followed by a Dunnett's multiple comparison test.

RESULTS

Significant reductions in viable MSCs concurrent with an increase in necrotic MSCs in high HCT and RBC_rel conditions was observed within 24 h. At each successive timepoint, the percent and relative number of viable MSCs were reduced, becoming significant in multiple HCT and RBC_rel conditions by Day 3. Necrosis appears to be the initial mode of MSC death following exposure to HCT and RBC_rel, followed by apoptosis in surviving MSC fractions.

CONCLUSION

Various levels of HCT and RBC_rel severely compromise MSC health within 3 days and HCT should be controlled in the preparation of BMC products. Further, HCT of BMCs should be routinely recorded and tracked with patient outcomes along with routine metrics (e.g. nucleated cell counts, fibroblast-colony forming units). Differences in HCT may account for the inconsistencies in the efficacy of BMC reported when treating orthopedic conditions.

Bone Marrow Mononuclear Cells Transplantation and Training Increased Transplantation of Energy Source Transporters in Chronic Stroke

OBJECTIVES

Bone marrow mononuclear cells (BM-MNC) show a significant therapeutic effect in combination with training even in the chronic phase of stroke. However, the mechanism of this combination therapy has not been investigated. Here, we examined its effects on brain metabolism in chronic stroke mice.

MATERIALS AND METHODS

BM-MNC (1x105 cells in 100 µL of phosphate-buffered saline) were intravenously transplanted at 4 weeks (chronic stage) after the middle cerebral artery occlusion. At 3 h and 10 weeks after the administration of BM-MNC, we evaluated transcription changes of the metabolism-related genes, hypoxia inducible factor 1-α (Hif-1α), prolyl hydroxylase 3 (Phd3), pyruvate dehydrogenase kinase 1 (Pdk1), Na+/K+-ATPase (Atp1α1‒3), connexins, glucose transporters, and monocarboxylate transporters, in the brain during chronic phase of stroke using quantitative polymerase chain reaction.

RESULTS

The results showed transcriptional activation of the metabolism-related genes in the contralateral cortex at 3 h after BM-MNC transplantation. Behavioral tests were performed after cell therapy, and the brain metabolism of mice with improved motor function was examined at 10 weeks after cell therapy. The therapeutic efficacy of the combination therapy with BM-MNC transplantation and training was evident in the form of transcriptional activation of ipsilateral anterior cerebral artery (ACA) cortex.

CONCLUSIONS

BM-MNC transplantation combined with training for chronic stroke activated gene expression in both the ipsilateral and the contralateral side.

Intravenous Bone Marrow Mononuclear Cells Transplantation Improves the Effect of Training in Chronic Stroke Mice

There is no effective treatment for chronic stroke if the acute or subacute phase is missed. Rehabilitation alone cannot easily achieve a dramatic recovery in function. In contrast to significant therapeutic effects of bone marrow mononuclear cells (BM-MNC) transplantation for acute stroke, mild and non-significant effects have been shown for chronic stroke. In this study, we have evaluated the effect of a combination of BM-MNC transplantation and neurological function training in chronic stroke. The effect of BM-MNC on neurological functional was tested four weeks after permanent middle cerebral artery occlusion (MCAO) insult in mice. BM-MNC (1 × 10⁵cells in 100 μl PBS) were injected into the vein of MCAO model mice, followed by behavioral tests as functional evaluations. Interestingly, there was a significant therapeutic effect of BM-MNC only when repeated training was performed. This suggested that cell therapy alone was not sufficient for chronic stroke treatment; however, training with cell therapy was effective. The combination of these differently targeted therapies provided a significant benefit in the chronic stroke mouse model. Therefore, targeted cell therapy via BM-MNC transplantation with appropriate training presents a promising novel therapeutic option for patients in the chronic stroke period.

Recent Advances in Cell-Based Therapies for Ischemic Stroke

Stroke is the most prevalent cardiovascular disease worldwide, and is still one of the leading causes of death and disability. Stem cell-based therapy is actively being investigated as a new potential treatment for certain neurological disorders, including stroke. Various types of cells, including bone marrow mononuclear cells, bone marrow mesenchymal stem cells, dental pulp stem cells, neural stem cells, inducible pluripotent stem cells, and genetically modified stem cells have been found to improve neurological outcomes in animal models of stroke, and there are some ongoing clinical trials assessing their efficacy in humans. In this review, we aim to summarize the recent advances in cell-based therapies to treat stroke.

Intravenous Bone Marrow Mononuclear Cells Transplantation in Aged Mice Increases Transcription of Glucose Transporter 1 and Na+/K+-ATPase at Hippocampus Followed by Restored Neurological Functions

We recently reported that intravenous bone marrow mononuclear cell (BM-MNC) transplantation in stroke improves neurological function through improvement of cerebral metabolism. Cerebral metabolism is known to diminish with aging, and the reduction of metabolism is one of the presumed causes of neurological decline in the elderly. We report herein that transcription of glucose transporters, monocarboxylate transporters, and Na⁺/K⁺-ATPase is downregulated in the hippocampus of aged mice with impaired neurological functions. Intravenous BM-MNC transplantation in aged mice stimulated the transcription of glucose transporter 1 and Na⁺/K⁺-ATPase α1 followed by restoration of neurological function. As glucose transporters and Na⁺/K⁺-ATPases are closely related to cerebral metabolism and neurological function, our data indicate that BM-MNC transplantation in aged mice has the potential to restore neurological function by activating transcription of glucose transporter and Na⁺/K⁺-ATPase. Furthermore, our data indicate that changes in transcription of glucose transporter and Na⁺/K⁺-ATPase could be surrogate biomarkers for age-related neurological impairment as well as quantifying the efficacy of therapies.

Bone Marrow Mononuclear Cells Activate Angiogenesis via Gap Junction-Mediated Cell-Cell Interaction

Background and Purpose- Bone marrow mononuclear cells (BM-MNCs) are a rich source of hematopoietic stem cells and have been widely used in experimental therapies for patients with ischemic diseases. Activation of angiogenesis is believed to be one of major BM-MNC mode of actions, but the essential mechanism by which BM-MNCs activate angiogenesis have hitherto been elusive. The objective of this study is to reveal the mechanism how BM-MNCs activate angiogenesis. Methods- We have evaluated the effect of direct cell-cell interaction between BM-MNC and endothelial cell on uptake of VEGF (vascular endothelial growth factor) into endothelial cells in vitro. Cerebral ischemia model was used to evaluate the effects of direct cell-cell interaction with transplanted BM-MNC on endothelial cell at ischemic tissue. Results- The uptake of VEGF into endothelial cells was increased by BM-MNC, while being inhibited by blockading the gap junction. Low-molecular-weight substance was transferred from BM-MNC into endothelial cells via gap junctions in vivo, followed by increased expression of hypoxia-inducible factor-1α and suppression of autophagy in endothelial cells. The concentration of glucose in BM-MNC cytoplasm was significantly higher than in endothelial cells, and transfer of glucose homologue from BM-MNC to endothelial cells was observed. Conclusions- Our findings demonstrated cell-cell interaction via gap junction is the prominent pathway for activation of angiogenesis at endothelial cells after ischemia and provided novel paradigm that energy source supply by stem cell to injured cell is one of the therapeutic mechanisms of cell-based therapy. Visual Overview- An online visual overview is available for this article.