Stem cell‐based cellular replacement strategies following traumatic brain injury (TBI)

Neurotrophins and neural stem cells in posttraumatic brain injury repair

Traumatic brain injury (TBI) is the main cause of disability, mental health disorder, and even death, with its incidence and social costs rising steadily. Although different treatment strategies have been developed and tested to mitigate neurological decline, a definitive cure for these conditions remains elusive. Studies have revealed that various neurotrophins represented by the brain-derived neurotrophic factor are the key regulators of neuroinflammation, apoptosis, blood-brain barrier permeability, neurite regeneration, and memory function. These factors are instrumental in alleviating neuroinflammation and promoting neuroregeneration. In addition, neural stem cells (NSC) contribute to nerve repair through inherent neuroprotective and immunomodulatory properties, the release of neurotrophins, the activation of endogenous NSCs, and intercellular signaling. Notably, innovative research proposals are emerging to combine BDNF and NSCs, enabling them to synergistically complement and promote each other in facilitating injury repair and improving neuron differentiation after TBI. In this review, we summarize the mechanism of neurotrophins in promoting neurogenesis and restoring neural function after TBI, comprehensively explore the potential therapeutic effects of various neurotrophins in basic research on TBI, and investigate their interaction with NSCs. This endeavor aims to provide a valuable insight into the clinical treatment and transformation of neurotrophins in TBI, thereby promoting the progress of TBI therapeutics.

Human umbilical cord blood cells rescued traumatic brain injury-induced cardiac and neurological deficits

Background

Traumatic brain injury (TBI) evokes neurological deficits and induces cardiac dysfunction. Treatment with human umbilical cord blood cells (HUCBCs) represents a potential therapeutic strategy for TBI-induced neurological deficits. The present study aimed to determine whether HUCBCs could ameliorate the cardiac dysfunction and neurological deficits induced by TBI.

Methods

Adult male C57BL/6J mice were subjected to controlled cortical impact (CCI)-induced TBI and were treated with either HUCBCs (1×10⁶) or phosphate-buffered saline (PBS), via tail vein injections, 3 days after TBI. Neurological and cognitive functions were subsequently evaluated at multiple time points after TBI and cardiac function was assessed by echocardiography 3 and 30 days after TBI. Brain and heart tissues were paraffin-embedded 30 days after TBI. Hematoxylin and eosin (H&E) staining was performed on brain tissue sections to calculate the brain damage volume, and Picro Sirius Red (PSR) staining was performed on heart tissue sections to evaluate myocardial fibrosis. Terminal deoxynucleotide transferase dUTP nick end labeling (TUNEL) staining was employed to assess cell apoptosis 30 days after TBI. Transforming growth factor-beta (TGF-β) and NADPH oxidase-2 (NOX2) levels were assessed to evaluate inflammation and oxidative stress levels 30 days after TBI.

Results

TBI elicited acute and chronic cardiac deficits, identified by decreased left ventricular ejection fraction (LVEF) and fractional shortening (LVFS) values 3 and 30 days after TBI, in addition to neurological and cognitive deficits. TBI mice treated with HUCBCs exhibited enhanced LVEF and FS values 30 days after TBI compared with untreated TBI controls. HUCBC treatment significantly improved neurological and cognitive functions and reduced cardiomyocyte apoptosis, inflammatory response, oxidative stress, and cardiac fibrosis in heart tissues 30 days after TBI.

Conclusions

TBI induced both neurological deficits and cardiac dysfunction in mice, which were ameliorated by HUCBC treatment. The anti-inflammatory activities of HUCBCs may contribute to these observed therapeutic effects.

Diffuse white matter response in trauma-injured brain to bone marrow stromal cell treatment detected by diffusional kurtosis imaging

Diffuse white matter (WM) response to traumatic brain injury (TBI) and transplantation of human bone marrow stromal cells (hMSCs) after the injury were non-invasively and dynamically investigated. Male Wistar rats (300-350 g) subjected to TBI were intravenously injected with 1 ml of saline (n = 10) or with hMSCs in suspension (∼3 × 106 hMSCs, n = 10) 1-week post-TBI. MRI measurements of T2-weighted imaging and diffusional kurtosis imaging (DKI) were acquired on all animals at multiple time points up to 3-months post-injury. Functional outcome was assessed using the Morris water maze test. DKI-derived metrics of fractional anisotropy (FA), axonal water fraction (AWF) and radial kurtosis (RK) longitudinally reveal an evolving pattern of structural alteration post-TBI occurring in the brain region remote from primary impact site. The progressive structural change is characterized by gradual disruption of WM integrity at an early stage (weeks post-TBI), followed by spontaneous recovery at a later stage (months post-TBI). Transplantation of hMSCs post-TBI promotes this structural plasticity as indicated by significantly increased FA and AWF in conjunction with substantially elevated RK at the later stage. Our long-term imaging data demonstrate that hMSC therapy leads to modified temporal profiles of these metrics, inducing an earlier presence of enhanced structural remodeling, which may contribute to improved functional recovery.

A dual-enzymatically cross-linked injectable gelatin hydrogel loaded with BMSC improves neurological function recovery of traumatic brain injury in rats

BMSC-laden gelatin hydrogels dual-enzymatically cross-linked by GOX and HRP could significantly promote the neurological function recovery of TBI in rats.

Human Neural Stem Cell Transplantation-Mediated Alteration of Microglial/Macrophage Phenotypes after Traumatic Brain Injury

Neural stem cells (NSCs) promote recovery from brain trauma, but neuronal replacement is unlikely the sole underlying mechanism. We hypothesize that grafted NSCs enhance neural repair at least partially through modulating the host immune response after traumatic brain injury (TBI). C57BL/6 mice were intracerebrally injected with primed human NSCs (hNSCs) or vehicle 24 h after a severe controlled cortical impact injury. Six days after transplantation, brain tissues were collected for Western blot and immunohistochemical analyses. Observations included indicators of microglia/macrophage activation, M1 and M2 phenotypes, axonal injury detected by amyloid precursor protein (APP), lesion size, and the fate of grafted hNSCs. Animals receiving hNSC transplantation did not show significant decreases of brain lesion volumes compared to transplantation procedures with vehicle alone, but did show significantly reduced injury-dependent accumulation of APP. Furthermore, intracerebral transplantation of hNSCs reduced microglial activation as shown by a diminished intensity of Iba1 immunostaining and a transition of microglia/macrophages toward the M2 anti-inflammatory phenotype. The latter was represented by an increase in the brain M2/M1 ratio and increases of M2 microglial proteins. These phenotypic switches were accompanied by the increased expression of anti-inflammatory interleukin-4 receptor α and decreased proinflammatory interferon-γ receptor β. Finally, grafted hNSCs mainly differentiated into neurons and were phagocytized by either M1 or M2 microglia/macrophages. Thus, intracerebral transplantation of primed hNSCs efficiently leads host microglia/macrophages toward an anti-inflammatory phenotype that presumably contributes to stem cell-mediated neuroprotective effects after severe TBI in mice.

Safety of neural stem cell transplantation in patients with severe traumatic brain injury

Neural stem cell (NSC) therapy is a promising treatment for traumatic brain injury (TBI). In addition, mesenchymal stem cells (MSCs) have been investigated for the treatment of TBI due to their functions in neural regeneration and their neurotrophic effect. In the present study, the safety, feasibility and biological effects of autologous MSC-derived NSC-like cell transplantation were investigated in 10 patients with severe TBI. All patients received intravenous or intrathecal injections of human NSC-like cells and were evaluated with physical and neurological examinations, routine laboratory tests and neuroradiological findings. The results indicated that the majority of patients experienced improved neurological function in different degrees during the follow-up period. No mortality or serious adverse events were observed in any patient subsequent to transplantation. Higher serum levels of nerve growth factor and brain-derived neurotrophic factor were detected following the transplantation, as compared with the levels prior to treatment. Overall, the present results suggest that transplantation of autologous NSC-like cells is feasible and appears to be safe for the treatment of non-acute severe TBI.

Transplantation of hUC-MSCs seeded collagen scaffolds reduces scar formation and promotes functional recovery in canines with chronic spinal cord injury

Spinal cord injury (SCI) can lead to locomotor deficits, and the repair of chronic SCI is considered one of the most challenging clinical problems. Although extensive studies have evaluated treatments for acute SCI in small animals, comparatively fewer studies have been conducted on large-animal SCI in the chronic phase, which is more clinically relevant. Here, we used a collagen-based biomaterial, named the NeuroRegen scaffold, loaded with human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) in a canine chronic SCI model. To generate chronic SCI, the T8 spinal cord segment was removed by complete transection of the spinal cord. Two months later, glial scar tissue was removed and a NeuroRegen scaffold was transplanted into the lesion area. Functionalized NeuroRegen scaffold implantation promoted both locomotor recovery and endogenous neurogenesis in the lesion area. Moreover, some newly generated neurons successfully matured into 5-HT-positive neurons at 1 year post-injury. In addition, many regenerated axon fibers in the lesion area exhibited remyelination and synapse formation at 1 year post-injury in the functionalized NeuroRegen scaffold group. In conclusion, the NeuroRegen scaffold functionalized with hUC-MSCs is a promising potential therapeutic approach to chronic SCI that promotes neuronal regeneration, reduces glial scar formation, and ultimately improves locomotor recovery.

Tracking and Quantification of Magnetically Labeled Stem Cells using Magnetic Resonance Imaging

Stem cell based therapies have critical impacts on treatments and cures of diseases such as neurodegenerative or cardiovascular disease. In vivo tracking of stem cells labeled with magnetic contrast agents is of particular interest and importance as it allows for monitoring of the cells' bio-distribution, viability, and physiological responses. Herein, recent advances are introduced in tracking and quantification of super-paramagnetic iron oxide (SPIO) nanoparticles-labeled cells with magnetic resonance imaging, a noninvasive approach that can longitudinally monitor transplanted cells. This is followed by recent translational research on human stem cells that are dual-labeled with green fluorescence protein (GFP) and SPIO nanoparticles, then transplanted and tracked in a chicken embryo model. Cell labeling efficiency, viability, and cell differentiation are also presented.

The migration and differentiation of hUC-MSCs(CXCR4/GFP) encapsulated in BDNF/chitosan scaffolds for brain tissue engineering

We previously developed a biomaterial scaffold that could effectively provide seed cells to a lesion cavity resulting from traumatic brain injury. However, we subsequently found that few transplanted human umbilical cord mesenchymal stem cells (hUC-MSCs) are able to migrate from the scaffold to the lesion boundary. Stromal derived-cell factor-1α and its receptor chemokine (C-X-C motif) receptor (CXCR)4 are chemotactic factors that control cell migration and stem cell recruitment to target areas. Given the low expression level of CXCR4 on the hUC-MSC membrane, lentiviral vectors were used to generate hUC-MSCs stably expressing CXCR4 fused to green fluorescent protein (GFP) (hUC-MSCs(CXCR4/GFP)). We constructed a scaffold in which recombinant human brain-derived neurotrophic factor (BDNF) was linked to chitosan scaffolds with the crosslinking agent genipin (CGB scaffold). The scaffold containing hUC-MSCs(CXCR4/GFP) was transplanted into the lesion cavity of a rat brain, providing exogenous hUC-MSCs to both lesion boundary and cavity. These results demonstrate a novel strategy for inducing tissue regeneration after traumatic brain injury.

Lipoic acid and bone marrow derived cells therapy induce angiogenesis and cell proliferation after focal brain injury

Abstract Introduction: Traumatic brain injury is a main cause of disability and death in developed countries, above all among children and adolescents. The intrinsic inability of the central nervous system to efficiently repair traumatic injuries renders transplantation of bone marrow-derived cells (BMDC) a promising approach towards repair of brain lesions. On the other hand, many studies have reported the beneficial effect of Lipoic acid (LA), a potent antioxidant promoting cell survival, angiogenesis and neuroregeneration.

METHODS

In this study, the cortex of adult mice was cryo-injured in order to mimic local traumatic brain injury. Vehicle or freshly prepared BMDC were grafted in the cerebral penumbra area 24 hours after unilateral local injury alone or combined with intra-peritoneal LA administration as a new regenerative strategy.

RESULTS

Differences were found in the process of cell proliferation, angiogenesis and glial scar formation after local injury depending of the applied treatment, either LA or BMDC alone or in combination.

CONCLUSION

The data presented here suggest that transplantation of BMDC is a good alternative and valid strategy to treat a focal brain injury when LA could not be prescribed due to its non-desired secondary effects.

Transient but not permanent benefit of neuronal progenitor cell therapy after traumatic brain injury: potential causes and translational consequences

Background: Numerous studies have reported a beneficial impact of neural progenitor cell transplantation on functional outcome after traumatic brain injury (TBI) during short and medium follow-up periods. However, our knowledge regarding long-term functional effects is fragmentary while a direct comparison between local and systemic transplantation is missing so far.

Objectives: This study investigated the long-term (12 week) impact of human fetal neuronal progenitor cell (hNPC) transplantation 24 h after severe TBI in rats.

Methods: Cells were either transplanted stereotactically (1 × 10⁵) into the putamen or systemically (5 × 10⁵) via the tail vein. Control animals received intravenous transplantation of vehicle solution.

Results: An overall functional benefit was observed after systemic, but not local hNPC transplantation by area under the curve analysis (p < 0.01). Surprisingly, this effect vanished during later stages after TBI with all groups exhibiting comparable functional outcomes 84 days after TBI. Investigation of cell-mediated inflammatory processes revealed increasing microglial activation and macrophage presence during these stages, which was statistically significant after systemic cell administration (p < 0.05). Intracerebral hNPC transplantation slightly diminished astrogliosis in perilesional areas (p < 0.01), but did not translate into a permanent functional benefit. No significant effects on angiogenesis were observed among the groups.

Conclusion: Our results suggest the careful long-term assessment of cell therapies for TBI, as well as to identify potential long-term detrimental effects of such therapies before moving on to clinical trials. Moreover, immunosuppressive protocols, though widely used, should be rigorously assessed for their applicability in the respective setup.

Repetitive long-term hyperbaric oxygen treatment (HBOT) administered after experimental traumatic brain injury in rats induces significant remyelination and a recovery of sensorimotor function

Cells in the central nervous system rely almost exclusively on aerobic metabolism. Oxygen deprivation, such as injury-associated ischemia, results in detrimental apoptotic and necrotic cell loss. There is evidence that repetitive hyperbaric oxygen therapy (HBOT) improves outcomes in traumatic brain-injured patients. However, there are no experimental studies investigating the mechanism of repetitive long-term HBOT treatment-associated protective effects. We have therefore analysed the effect of long-term repetitive HBOT treatment on brain trauma-associated cerebral modulations using the lateral fluid percussion model for rats. Trauma-associated neurological impairment regressed significantly in the group of HBO-treated animals within three weeks post trauma. Evaluation of somatosensory-evoked potentials indicated a possible remyelination of neurons in the injured hemisphere following HBOT. This presumption was confirmed by a pronounced increase in myelin basic protein isoforms, PLP expression as well as an increase in myelin following three weeks of repetitive HBO treatment. Our results indicate that protective long-term HBOT effects following brain injury is mediated by a pronounced remyelination in the ipsilateral injured cortex as substantiated by the associated recovery of sensorimotor function.

Combination therapy of human umbilical cord blood cells and granulocyte colony stimulating factor reduces histopathological and motor impairments in an experimental model of chronic traumatic brain injury

Traumatic brain injury (TBI) is associated with neuro-inflammation, debilitating sensory-motor deficits, and learning and memory impairments. Cell-based therapies are currently being investigated in treating neurotrauma due to their ability to secrete neurotrophic factors and anti-inflammatory cytokines that can regulate the hostile milieu associated with chronic neuroinflammation found in TBI. In tandem, the stimulation and mobilization of endogenous stem/progenitor cells from the bone marrow through granulocyte colony stimulating factor (G-CSF) poses as an attractive therapeutic intervention for chronic TBI. Here, we tested the potential of a combined therapy of human umbilical cord blood cells (hUCB) and G-CSF at the acute stage of TBI to counteract the progressive secondary effects of chronic TBI using the controlled cortical impact model. Four different groups of adult Sprague Dawley rats were treated with saline alone, G-CSF+saline, hUCB+saline or hUCB+G-CSF, 7-days post CCI moderate TBI. Eight weeks after TBI, brains were harvested to analyze hippocampal cell loss, neuroinflammatory response, and neurogenesis by using immunohistochemical techniques. Results revealed that the rats exposed to TBI treated with saline exhibited widespread neuroinflammation, impaired endogenous neurogenesis in DG and SVZ, and severe hippocampal cell loss. hUCB monotherapy suppressed neuroinflammation, nearly normalized the neurogenesis, and reduced hippocampal cell loss compared to saline alone. G-CSF monotherapy produced partial and short-lived benefits characterized by low levels of neuroinflammation in striatum, DG, SVZ, and corpus callosum and fornix, a modest neurogenesis, and a moderate reduction of hippocampal cells loss. On the other hand, combined therapy of hUCB+G-CSF displayed synergistic effects that robustly dampened neuroinflammation, while enhancing endogenous neurogenesis and reducing hippocampal cell loss. Vigorous and long-lasting recovery of motor function accompanied the combined therapy, which was either moderately or short-lived in the monotherapy conditions. These results suggest that combined treatment rather than monotherapy appears optimal for abrogating histophalogical and motor impairments in chronic TBI.

Transplantation of human mesenchymal stem cells loaded on collagen scaffolds for the treatment of traumatic brain injury in rats

Studies have suggested that mesenchymal stem cells (MSCs) have therapeutic effects following traumatic brain injury (TBI). However, cell distribution and survival rate are two major barriers to their success as therapeutic treatment. The improvement of cell therapy using collagen delivery matrices had been reported. However, we know very little about the mechanisms. We labeled human bone marrow-derived mesenchymal stem cells (hMSCs) with a positron emission tomography (PET) tracer, 18F-fluoro-2-deoxy-D-glucose (FDG). hMSCs were transplanted with or without collagen scaffolds into rats with experimental TBI and the whole-body nuclear images were compared. Collagen scaffolds increased the retention of hBMSC in the lesion site and limited its distribution at the transplanted region. Significantly more hMSCs were detected in the brain when transplanted with collagen scaffolds. The results showed collagen scaffolds also efficiently improved cell survival and neurite outgrowth in vivo, resulting in better neural functional recovery. In addition, brain metabolism also improved in the collagen scaffold implanted group, as evaluated by PET. We speculated that collagen scaffolds would improve early engraftment and support the survival of grafted cells post-transplantation.

Long-term benefit of human fetal neuronal progenitor cell transplantation in a clinically adapted model after traumatic brain injury

Experimental human fetal neural progenitor cell (hfNPC) transplantation has proven to be a promising therapeutic approach after traumatic brain injury (TBI). However, the long-term efficacy and safety, which are both highly important for clinical translation of this approach, have thus far not been investigated. This study investigated the effect of local (L, 1 × 10(5) cells) and systemic (S, 5 × 10(5) cells) administration of PKH-26-labeled pre-differentiated hfNPCs over a period of 12 weeks, beginning 24 h after severe controlled cortical impact TBI in Sprague-Dawley rats. Accelerating rotarod testing revealed a trend toward functional improvement beginning 1 week after transplantation, and persisting until the end of the experiment. The traumatic lesion volume as quantified by magnetic resonance imaging was smaller in both treatment groups compared to control (C) animals (C = 54.50 mm(3), L = 32 mm(3), S = 37.50 mm(3)). Correspondingly, neuronal (NeuN) staining showed increased neuronal survival at the border of the lesion in both transplanted groups (S = 92.4%; L = 87.2%; 72.5%). Histological analysis of the brain compartments revealed transiently increased angiogenesis and reduced astroglial reaction during the first 4 weeks post-transplantation. PKH-26-positive cells were detected exclusively after local transplantation without any evidence of tumor formation. However, graft differentiation was seen only in very rare cases. In conclusion, transplantation of hfNPCs improved the long-term functional outcome after TBI, diminished trauma lesion size, and increased neuronal survival in the border zone of the lesion. This therapeutic effect was not likely due to cell replacement, but was associated with transiently increased angiogenesis and reduced astrogliosis.

Transplantation of GABA-producing cells for seizure control in models of temporal lobe epilepsy

A high percentage of patients with temporal lobe epilepsy (TLE) are refractory to conventional pharmacotherapy. The progressive neurodegenerative processes associated with a lifetime of uncontrolled seizures mandate the development of alternative approaches to treat this disease. Transplantation of inhibitory cells has been suggested as a potential therapeutic strategy to achieve seizure suppression in humans with intractable TLE. Preclinical investigations over 20 years have demonstrated that multiple cell types from several sources can produce anticonvulsant, and antiepileptogenic, effects in animal models of TLE. Transplanting GABA-producing cells, in particular, has been shown to reduce seizures in several well-established models. This review addresses experimentation using different sources of transplantable GABAergic cells, highlighting progress with fetal tissue, neural cell lines, and stem cells. Regardless of the source of the GABAergic cells used in seizure studies, common challenges have emerged. Several variables influence the anticonvulsant potential of GABA-producing cells. For example, tissue availability, graft survival, immunogenicity, tumorigenicity, and varying levels of cell migration, differentiation, and integration into functional circuits and the microenvironment provided by sclerotic tissue all contribute to the efficacy of transplanted cells. The challenge of understanding how all of these variables work in concert, in a disease process that has no well-established etiology, suggests that there is still much basic research to be done before rational cell-based therapies can be developed for TLE.

Cell therapy for CNS trauma

Cell therapy plays an important role in multidisciplinary management of the two major forms of central nervous system (CNS) injury, traumatic brain injury and spinal cord injury, which are caused by external physical trauma. Cell therapy for CNS disorders involves the use of cells of neural or non-neural origin to replace, repair, or enhance the function of the damaged nervous system and is usually achieved by transplantation of the cells, which are isolated and may be modified, e.g., by genetic engineering, when it may be referred to as gene therapy. Because the adult brain cells have a limited capacity to migrate to and regenerate at sites of injury, the use of embryonic stem cells that can be differentiated into various cell types as well as the use of neural stem cells has been explored. Preclinical studies and clinical trials are reviewed. Advantages as well as limitations are discussed. Cell therapy is promising for the treatment of CNS injury because it targets multiple mechanisms in a sustained manner. It can provide repair and regeneration of damaged tissues as well as prolonged release of neuroprotective and other therapeutic substances.

Neuroprotection in traumatic brain injury

The management of traumatic brain injury (TBI) is challenging and there is a need for neuroprotective therapies. A better understanding of the pathomechanism of TBI, particularly of the evolution of secondary damage, is providing targets for new approaches and selected ones in clinical development are described. Clinical trials that have been discontinued in the past for lack of efficacy or other reasons are also listed. One of the problems has been the translation of promising animal experimental results into clinically successful therapies. The complexity of sequelae of TBI requires a multifaceted approach. In addition to the investigation of drugs for neuroprotective effect in TBI, new technologies based on cell/gene therapies, biomarkers and nanobiotechnology are being employed for the integration of neuroprotection with neuroregeneration and are promising.