Stem cell-based therapies for ischemic stroke: a systematic review and meta-analysis of clinical trials

Neural Stem Cell-Derived Small Extracellular Vesicles: key Players in Ischemic Stroke Therapy - A Comprehensive Literature Review

Ischemic stroke, being a prominent contributor to global disability and mortality, lacks an efficacious therapeutic approach in current clinical settings. Neural stem cells (NSCs) are a type of stem cell that are only found inside the nervous system. These cells can differentiate into various kinds of cells, potentially regenerating or restoring neural networks within areas of the brain that have been destroyed. This review begins by providing an introduction to the existing therapeutic approaches for ischemic stroke, followed by an examination of the promise and limits associated with the utilization of NSCs for the treatment of ischemic stroke. Subsequently, a comprehensive overview was conducted to synthesize the existing literature on the underlying processes of neural stem cell-derived small extracellular vesicles (NSC-sEVs) transplantation therapy in the context of ischemic stroke. These mechanisms encompass neuroprotection, inflammatory response suppression, and endogenous nerve and vascular regeneration facilitation. Nevertheless, the clinical translation of NSC-sEVs is hindered by challenges such as inadequate targeting efficacy and insufficient content loading. In light of these limitations, we have compiled an overview of the advancements in utilizing modified NSC-sEVs for treating ischemic stroke based on current methods of extracellular vesicle modification. In conclusion, examining NSC-sEVs-based therapeutic approaches is anticipated to be prominent in both fundamental and applied investigations about ischemic stroke.

Efficacy and safety of stem cells in the treatment of ischemic stroke: A meta-analysis

BACKGROUND

Stem cell therapy on ischemic stroke has long been studied using animal experiments. The efficacy and safety of this treatment in ischemic stroke patients remain uncertain.

METHODS

We searched for all clinical randomized controlled trials published before October 2023, on PubMed, EMBASE, and the Cochrane Library using predetermined search terms, and performed a meta-analysis of the efficacy of stem cell therapy in ischemic stroke patients.

RESULTS

13 studies that included 592 ischemic stroke patients were reviewed. The mRS (MD -0.32, 95% CI -0.64 to 0.00, I2 = 63%, P = .05), NIHSS (MD -1.63, 95% CI -2.69 to -0.57, I2 = 58%, P = .003), and BI (MD 14.22, 95% CI 3.95-24.48, I2 = 43%, P = .007) showed effective stem cell therapy. The mortality (OR 0.42, 95% CI 0.23-0.79, I2 = 0%, P = .007) showed improved prognosis and reduce mortality with stem cell therapy.

CONCLUSION

Stem cell therapy reduces mortality and improves the neurological prognosis of ischemic stroke patients. However, due to the different types of stem cells used and the limited data in the reported studies, the safety of clinical applications of stem cells in patients with ischemic stroke must be carefully evaluated. Future randomized controlled trials with large sample sizes from controlled cell sources are warranted to validate this finding.

Stem cell-based ischemic stroke therapy: Novel modifications and clinical challenges

Ischemic stroke (IS) causes severe disability and high mortality worldwide. Stem cell (SC) therapy exhibits unique therapeutic potential for IS that differs from current treatments. SC's cell homing, differentiation and paracrine abilities give hope for neuroprotection. Recent studies on SC modification have enhanced therapeutic effects for IS, including gene transfection, nanoparticle modification, biomaterial modification and pretreatment. These methods improve survival rate, homing, neural differentiation, and paracrine abilities in ischemic areas. However, many problems must be resolved before SC therapy can be clinically applied. These issues include production quality and quantity, stability during transportation and storage, as well as usage regulations. Herein, we reviewed the brief pathogenesis of IS, the "multi-mechanism" advantages of SCs for treating IS, various SC modification methods, and SC therapy challenges. We aim to uncover the potential and overcome the challenges of using SCs for treating IS and convey innovative ideas for modifying SCs.

Efficacy and safety of mesenchymal stem cells in patients with acute ischemic stroke: a meta-analysis

OBJECTIVE

This meta-analysis and systematic review were conducted to comprehensively evaluate the efficacy and safety of mesenchymal stem cells in patients with acute ischemic stroke.

METHOD

We conducted a manual search of electronic databases, including PubMed, Embase, the Cochrane Library, and Web of Science, with a search deadline set for February 1, 2023. Data analysis was performed using Stata version 15.0.

RESULT

A total of 9 randomized controlled studies were included, involving a total of 316 people, including 159 mesenchymal stem cells and 147 control groups. Results of meta-analysis: Compared to a placebo group, the administration of mesenchymal stem cells resulted in a significant reduction in the National Institutes of Health Stroke Scale (NIHSS) scores among patients diagnosed with acute ischemic stroke [SMD=-0.99,95% CI (-1.93, -0.05)]. Compared to placebo, barthel index [SMD = 0.48,95% CI (-0.55,1.51)], modified rankin score [SMD = 0.45, 95% CI (1.11, 0.21)], adverse events (RR = 0.68, 95% CI (0.40, 1.17)] the difference was not statistically significant.

CONCLUSION

Based on current studies, mesenchymal stem cell transplantation can ameliorate neurological deficits in patients with ischemic stroke to a certain extent without increasing adverse reactions. However, there was no significant effect on Barthel index and Modified Rankin score.

Extracellular vesicles and their microRNA cargo in ischaemic stroke

Acute ischaemic stroke (AIS) is a leading cause of death and disability. MicroRNAs (miRNAs) are short non-coding RNAs which hold the potential to act as a novel biomarker in AIS. The majority of circulating miRNAs are actively encapsulated by extracellular vesicles (EVs) produced by many cells and organs endogenously. EVs released by mesenchymal stem cells (MSCs) have been extensively studied for their therapeutic potential. In health and disease, EVs are vital for intercellular communication, as the cargo within EVs can be exchanged between neighbouring cells or transported to distant sites. It is clear here from both current preclinical and clinical studies that AIS is associated with specific EV-derived miRNAs, including those transported via MSC-derived EVs. In addition, current studies provide evidence to show that modulating levels of specific EV-derived miRNAs in AIS provides a novel therapeutic potential of miRNAs in the treatment of stroke. Commonalities exist in altered miRNAs across preclinical and clinical studies. Of those EV-packaged miRNAs, miRNA-124 was described both as an EV-packaged biomarker and as a potential EV-loaded therapeutic in experimental models. Alterations of miRNA-17 family and miRNA-17-92 cluster were identified in preclinical, clinical and MSC-EV-mediated neuroprotection in experimental stroke. Finally, miRNA-30d and -30a were found to mediate therapeutic effect when overexpressed from MSC and implicated as a biomarker clinically. Combined, EV-derived miRNAs will further our understanding of the neuropathological processes triggered by AIS. In addition, this work will help determine the true clinical value of circulating EV-packaged miRNAs as biomarkers of AIS or as novel therapeutics in this setting.

Potential Therapeutic Use of Stem Cells for Prion Diseases

Prion diseases are neurodegenerative disorders that are progressive, incurable, and deadly. The prion consists of PrPSc, the misfolded pathogenic isoform of the cellular prion protein (PrPC). PrPC is involved in a variety of physiological functions, including cellular proliferation, adhesion, differentiation, and neural development. Prion protein is expressed on the membrane surface of a variety of stem cells (SCs), where it plays an important role in the pluripotency and self-renewal matrix, as well as in SC differentiation. SCs have been found to multiply the pathogenic form of the prion protein, implying their potential as an in vitro model for prion diseases. Furthermore, due to their capability to self-renew, differentiate, immunomodulate, and regenerate tissue, SCs are prospective cell treatments in many neurodegenerative conditions, including prion diseases. Regenerative medicine has become a new revolution in disease treatment in recent years, particularly with the introduction of SC therapy. Here, we review the data demonstrating prion diseases' biology and molecular mechanism. SC biology, therapeutic potential, and its role in understanding prion disease mechanisms are highlighted. Moreover, we summarize preclinical studies that use SCs in prion diseases.

Mesenchymal Stem Cells Overexpressing FGF21 Preserve Blood-Brain Barrier Integrity in Experimental Ischemic Stroke

Blood-brain barrier (BBB) disruption is a prominent pathophysiological mechanism in stroke. Transplantation of mesenchymal stem cells (MSCs) preserves BBB integrity following ischemic stroke. Fibroblast growth factor 21 (FGF21) has been shown to be a potent neuroprotective agent that reduces neuroinflammation and protects against BBB leakage. In this study, we assessed the effects of transplantation of MSCs overexpressing FGF21 (MSCs-FGF21) on ischemia-induced neurological deficits and BBB breakdown. MSCs-FGF21 was injected into the rat brain via the intracerebroventricular route 24 h after middle cerebral artery occlusion (MCAO) surgery. The behavioral performance was assessed using modified neurological severity scores and Y-maze tests. BBB disruption was measured using Evans blue staining, IgG extravasation, and brain water content. The levels of tight junction proteins, aquaporin 4, and neuroinflammatory markers were analyzed by western blotting and immunohistochemistry. The activity of matrix metalloproteinase-9 (MMP-9) was determined using gelatin zymography. At day-5 after MCAO surgery, intraventricular injection of MSCs-FGF21 was found to significantly mitigate the neurological deficits and BBB disruption. The MCAO-induced loss of tight junction proteins, including ZO-1, occludin, and claudin-5, and upregulation of the edema inducer, aquaporin 4, were also remarkably inhibited. In addition, brain infarct volume, pro-inflammatory protein expression, and MMP-9 activation were effectively suppressed. These MCAO-induced changes were only marginally improved by treatment with MSCs-mCherry, which did not overexpress FGF21. Overexpression of FGF21 dramatically improved the therapeutic efficacy of MSCs in treating ischemic stroke. Given its multiple benefits and long therapeutic window, MSC-FGF21 therapy may be a promising treatment strategy for ischemic stroke.

Functional reconstruction of the impaired cortex and motor function by hMGEOs transplantation in stroke

Stroke is the leading cause of death and long-term disability worldwide. But treatments are not available to promote functional recovery, and efficient therapies need to be investigated. Stem cell-based therapies hold great promise as potential technologies to restore function in brain disorders. Loss of GABAergic interneurons after stroke may result in sensorimotor defects. Here, by transplanting human brain organoids resembling the MGE domain (human MGE organoids, hMGEOs) derived from human induced pluripotent stem cells (hiPSCs) into the infarcted cortex of stroke mice, we found that grafted hMGEOs survived well and primarily differentiated into GABAergic interneurons and significantly restored the sensorimotor deficits of stroke mice for a long time. Our study offers the feasibility of stem cell replacement therapeutics strategy for stroke.

From Hair to the Brain: The Short-Term Therapeutic Potential of Human Hair Follicle-Derived Stem Cells and Their Conditioned Medium in a Rat Model of Stroke

The short-term therapeutic impacts of stem cells and their derivatives were frequently reported in preclinical investigations of ischemic stroke (IS); however, several drawbacks including accessibility, abundancy, and ethical concerns limited their clinical application. We describe here for the first time the therapeutic potential of human hair follicle-derived stem cells (hHFSCs) and their conditioned medium (CM) in a rat model of IS. Furthermore, we hypothesized that a combination of cell therapy with repeated CM administration might enhance the restorative efficiency of this approach compared to each treatment alone. Middle cerebral artery occlusion was performed for 30 min to induce IS. Immediately after reperfusion, hHFSCs were transplanted through the intra-arterial route and/or hHFSC-CM administered intranasally. The neurological outcomes, short-term spatial working memory, and infarct size were evaluated. Furthermore, relative expression of seven target genes in three categories of neuronal markers, synaptic markers, and angiogenic markers was assessed. The hHFSCs and hHFSC-CM treatments improved neurological impairments and reduced infarct size in the IS rats. Moreover, molecular data elucidated that IS was accompanied by attenuation in the expression of neuronal and synaptic markers in the evaluated brain regions and the interventions rescued these expression changes. Although there was no considerable difference between hHFSCs and hHFSC-CM treatments in the improvement of neurological function and decrement of infarct size, combination therapy was more effective to reduce infarction and elevation of target gene expression especially in the hippocampus. These findings highlight the curative potential of hHFSCs and their CM in a rat model of IS.

Inflammation and immunomodulation in central nervous system injury - B cells as a novel therapeutic opportunity

Acute injury to the central nervous system (CNS) remains a complex and challenging clinical need. CNS injury initiates a dynamic neuroinflammatory response, mediated by both resident and infiltrating immune cells. Following the primary injury, dysregulated inflammatory cascades have been implicated in sustaining a pro-inflammatory microenvironment, driving secondary neurodegeneration and the development of lasting neurological dysfunction. Due to the multifaceted nature of CNS injury, clinically effective therapies for conditions such as traumatic brain injury (TBI), spinal cord injury (SCI), and stroke have proven challenging to develop. No therapeutics that adequately address the chronic inflammatory component of secondary CNS injury are currently available. Recently, B lymphocytes have gained increasing appreciation for their role in maintaining immune homeostasis and regulating inflammatory responses in the context of tissue injury. Here we review the neuroinflammatory response to CNS injury with particular focus on the underexplored role of B cells and summarize recent results on the use of purified B lymphocytes as a novel immunomodulatory therapeutic for tissue injury, particularly in the CNS.

Outcomes of autologous bone marrow mononuclear cell administration in the treatment of neurologic sequelae in children with spina bifida

BACKGROUND

To evaluate the safety and efficacy of autologous bone marrow mononuclear cell (BMMNC) infusion in the management of neurological sequelae in children with spina bifida (SB).

METHODS

BMMNCs were harvested from bilateral anterior iliac crests. Two intrathecal BMMNC administrations were performed with an interval of 6 months. The measurements of outcomes included clinical assessments, cystomanometry and rectomanometry.

RESULTS

Eleven children with SB underwent autologous BMMNC infusions from 2016 to 2020. There were no severe adverse events during the study period. The number of patients requiring assistance to expel stools decreased from 11 before cell infusion to 3 after the second cell infusion. The number of patients who had urine leakage decreased from 9 patients at baseline to 3 patients after the second BMMNC infusion. The mean bladder capacity increased from 127.7 ± 59.2 ml at baseline to 136.3 ± 54.8 ml at six months and to 158.3 ± 56.2 ml at 12 months after BMMNC infusions. Detrusor pressure (pdet) decreased from 32.4 ± 22.0 cm H₂O at baseline to 21.9 ± 11.8 cm H₂O after 12 months of follow-up. At baseline, six patients could walk independently. After the 2nd infusion, eight patients could walk independently.

CONCLUSION

Intrathecal infusions of autologous bone marrow mononuclear cells are safe and may improve bowel, bladder, and motor function in children with SB.

TRIAL REGISTRATION

NCT, NCT05472428. Registered July 25, 2022- Retrospectively registered, https://www.

CLINICALTRIALS

gov/ct2/show/NCT05472428 .

Perspective insights into hydrogels and nanomaterials for ischemic stroke

Ischemic stroke (IS) is a neurological disorder prevalent worldwide with a high disability and mortality rate. In the clinic setting, tissue plasminogen activator (tPA) and thrombectomy could restore blood flow of the occlusion region and improve the outcomes of IS patients; however, these therapies are restricted by a narrow time window. Although several preclinical trials have revealed the molecular and cellular mechanisms underlying infarct lesions, the translatability of most findings is unsatisfactory, which contributes to the emergence of new biomaterials, such as hydrogels and nanomaterials, for the treatment of IS. Biomaterials function as structural scaffolds or are combined with other compounds to release therapeutic drugs. Biomaterial-mediated drug delivery approaches could optimize the therapeutic effects based on their brain-targeting property, biocompatibility, and functionality. This review summarizes the advances in biomaterials in the last several years, aiming to discuss the therapeutic potential of new biomaterials from the bench to bedside. The promising prospects of new biomaterials indicate the possibility of an organic combination between materialogy and medicine, which is a novel field under exploration.

Advanced molecular therapies for neurological diseases: focus on stroke, alzheimer's disease, and parkinson's disease

Neurological diseases (NDs) are one of the leading causes of disability and the second leading cause of death globally. Among these stroke, Alzheimer's disease (AD), and Parkinson's disease (PD) are the most common NDs. A rise in the absolute number of individuals affected with these diseases indicates that the current treatment strategies in management and prevention of these debilitating diseases are not effective sufficiently. Therefore, novel treatment strategies are being explored to cure these diseases by addressing the causative mechanisms at the molecular level. Advanced therapies like gene therapy (gene editing and gene silencing) and stem cell therapies aim to cure diseases by gene editing, gene silencing and tissue regeneration, respectively. Gene editing results in the deletion of the aberrant gene or insertion of the corrected gene which can be executed using the CRISPR/Cas gene editing tool a promising treatment strategy being explored for many other prevalent diseases. Gene silencing using siRNA silences the gene by inhibiting protein translation, thereby silencing its expression. Stem cell therapy aims to regenerate damaged cells or tissues because of their ability to divide into any type of cell in the human body. Among these approaches, gene editing and gene silencing have currently been applied in vitro and to animal models, while stem cell therapy has reached the clinical trial stage for the treatment of NDs. The current status of these strategies suggests a promising outcome in their clinical translation.

Biomaterial application strategies to enhance stem cell-based therapy for ischemic stroke

BACKGROUND

Ischemic stroke is a condition in which an occluded blood vessel interrupts blood flow to the brain and causes irreversible neuronal cell death. Transplantation of regenerative stem cells has been proposed as a novel therapy to restore damaged neural circuitry after ischemic stroke attack. However, limitations such as low cell survival rates after transplantation remain significant challenges to stem cell-based therapy for ischemic stroke in the clinical setting. In order to enhance the therapeutic efficacy of transplanted stem cells, several biomaterials have been developed to provide a supportable cellular microenvironment or functional modification on the stem cells to optimize their reparative roles in injured tissues or organs.

AIM

To discuss state-of-the-art functional biomaterials that could enhance the therapeutic potential of stem cell-based treatment for ischemic stroke and provide detailed insights into the mechanisms underlying these biomaterial approaches.

METHODS

The PubMed, Science Direct and Scopus literature databases were searched using the keywords of “biomaterial” and “ischemic stroke”. All topically-relevant articles were then screened to identify those with focused relevance to in vivo, in vitro and clinical studies related to “stem cells” OR “progenitor cells” OR “undifferentiated cells” published in English during the years of 2011 to 2022. The systematic search was conducted up to September 30, 2022.

RESULTS

A total of 19 articles matched all the inclusion criteria. The data contained within this collection of papers comprehensively represented 19 types of biomaterials applied on seven different types of stem/progenitor cells, namely mesenchymal stem cells, neural stem cells, induced pluripotent stem cells, neural progenitor cells, endothelial progenitor cells, neuroepithelial progenitor cells, and neuroblasts. The potential major benefits gained from the application of biomaterials in stem cell-based therapy were noted as induction of structural and functional modifications, increased stem cell retention rate in the hostile ischemic microenvironment, and promoting the secretion of important cytokines for reparative mechanisms.

CONCLUSION

Biomaterials have a relatively high potential for enhancing stem cell therapy. Nonetheless, there is a scarcity of evidence from human clinical studies for the efficacy of this bioengineered cell therapy, highlighting that it is still too early to draw a definitive conclusion on efficacy and safety for patient usage. Future in-depth clinical investigations are necessary to realize translation of this therapy into a more conscientious and judicious evidence-based therapy for clinical application.

A Study on the Protective Effect of sRAGE-MSCs in a Rodent Reperfusion Model of Myocardial Infarction

Acute myocardial infarction (AMI) is one of the major leading causes of death in humans globally. Recently, increased levels of recruited macrophages and AGE-albumin were observed in the hearts of humans and animals with acute myocardial infarction. Thus, the purposes of this study were to investigate whether the elevated levels of AGE-albumin from activated macrophage cells are implicated in ischemia-induced cardiomyocyte death and to develop therapeutic strategies for AMI based on its underlying molecular mechanisms with respect to AGEs. The present study demonstrated that activated macrophages and AGE-albumin were observed in heart tissues obtained from humans and rats with AMI incidences. In the cellular model of AMI, it was found that increased expression of AGE-albumin was shown to be co-localized with macrophages, and the presence of AGE-albumin led to increased expression of RAGE through the mitogen-activated protein kinase pathway. After revealing cardiomyocyte apoptosis induced by toxicity of the AGE-RAGE system, sRAGE-secreting MSCs were generated using the CRISPR/Cas9 platform to investigate the therapeutic effects of sRAGE-MSCs in an AMI rat model. Gene-edited sRAGE-MSCs showed greater therapeutic effects against AMI pathogenesis in rat models compared to mock MSCs, and promising results of the functional improvement of stem cells could result in significant improvements in the clinical management of cardiovascular diseases.

Dental pulp stem cell transplantation facilitates neuronal neuroprotection following cerebral ischemic stroke

OBJECTIVES

This study aimed to identify and evaluate the intracranial transplantation of dental pulp stem cells (DPSCs) as a possible ischemic stroke therapy that mitigates neuronal death/apoptosis.

MATERIALS AND METHODS

DPSCs were isolated from the impacted third molars of healthy volunteers and then intracranially injected at 24 h post-ischemic stroke to Sprague Dawley rats that had been subjected to 2 h of middle cerebral artery occlusion. Neurological functional deficits were assessed using the modified neurological severity score (mNSS), and cerebral edema was quantified using brain water content. Neuronal death/apoptosis was indicated by TdT-mediated dUTP Nick-End Labeling (TUNEL) staining, NeuN immunofluorescence and immunohistochemistry, and Western blot analysis of the protein expression of anti-apoptotic indicator of Bcl-2 and apoptotic indicators of Bax and caspase 3.

RESULTS

DPSC transplantation could ameliorate neurological dysfunction and brain edema, reduce infarct volume, decrease the percentage of TUNEL-positive nuclei, increase the number and percentage of NeuN-positive cells in ischemic penumbra, increase the ratio of Bcl-2 and Bax and down-regulate the production of caspase 3 in the cortical infarct zone.

CONCLUSIONS

DPSC therapy via intracranial injection exerted remarkably neuroprotection mainly by inhibiting neuronal death/apoptosis.

The Efficacy and Safety of Ischemic Stroke Therapies: An Umbrella Review

Background: Ischemic stroke is a leading cause of morbidity and mortality in neurological diseases. Numerous studies have evaluated the efficacy and safety of ischemic stroke therapies, but clinical data were largely inconsistent. Therefore, it is necessary to summarize and analyze the published clinical research data in the field.

Objective: We aimed to perform an umbrella review to evaluate the efficacy and safety of ischemic stroke therapies.

Methods: We conducted a search for meta-analyses and systematic reviews on PubMed, the Cochrane Library, and the Web of Science to address this issue. We examined neurological function deficit and cognitive function scores, quality of life, and activities of daily living as efficacy endpoints and the incidence of adverse events as safety profiles.

Results: Forty-three eligible studies including 377 studies were included in the umbrella review. The results showed that thrombolytic therapy (tPA; alteplase, tenecteplase, and desmoteplase), mechanical thrombectomy (MTE), edaravone with tPA, stem cell-based therapies, stent retrievers, acupuncture with Western medicines, autologous bone marrow stromal cells, antiplatelet agents (aspirin, clopidogrel, and tirofiban), statins, and Western medicines with blood-activating and stasis-dispelling herbs (NaoShuanTong capsule, Ginkgo biloba, Tongqiao Huoxue Decoction, Xuesaitong injection) can improve the neurological deficits and activities of daily living, and the adverse effects were mild for the treatment of ischemic stroke. Moreover, ligustrazine, safflower yellow, statins, albumin, colchicine, MLC601, salvianolic acids, and DL-3-n-butylphthalide showed serious adverse events, intracranial hemorrhage, or mortality in ischemic stroke patients.

Conclusion: Our study demonstrated that tPA, edaravone and tPA, tPA and MTE, acupuncture and Western medicines, and blood-activating and stasis-dispelling herbs with Western medicines are the optimum neurological function and activities of daily living medication for patients with ischemic stroke.

Systematic Review Registration: https://inplasy.com/, identifier [INPLASY202250145].

Conditioned Medium of Human Pluripotent Stem Cell-Derived Neural Precursor Cells Exerts Neurorestorative Effects against Ischemic Stroke Model

Previous studies have shown that early therapeutic events of neural precursor cells (NPCs) transplantation to animals with acute ischemic stroke readily protected neuronal cell damage and improved behavioral recovery through paracrine mechanisms. In this study, we tested the hypothesis that administration of conditioned medium from NPCs (NPC-CMs) could recapitulate the beneficial effects of cell transplantation. Rats with permanent middle cerebral artery occlusion (pMCAO) were randomly assigned to one of the following groups: PBS control, Vehicle (medium) controls, single (NPC-CM(S)) or multiple injections of NPC-CM(NPC-CM(M)) groups. A single intravenous injection of NPC-CM exhibited strong neuroregenerative potential to induce behavioral recovery, and multiple injections enhanced this activity further by suppressing inflammatory damage and inducing endogenous neurogenesis leading to histopathological and functional recovery. Proteome analysis of NPC-CM identified a number of proteins that are known to be associated with nervous system development, neurogenesis, and angiogenesis. In addition, transcriptome analysis revealed the importance of the inflammatory response during stroke recovery and some of the key hub genes in the interaction network were validated. Thus, our findings demonstrated that NPC-CM promoted functional recovery and reduced cerebral infarct and inflammation with enhanced endogenous neurogenesis, and the results highlighted the potency of NPC-CM in stroke therapy.

Exosomes Derived From Mesenchymal Stem Cells: Novel Effects in the Treatment of Ischemic Stroke

Ischemic stroke is defined as an infarction in the brain, caused by impaired cerebral blood supply, leading to local brain tissue ischemia, hypoxic necrosis, and corresponding neurological deficits. At present, revascularization strategies in patients with acute ischemic stroke include intravenous thrombolysis and mechanical endovascular treatment. However, due to the short treatment time window (<4.5 h) and method restrictions, clinical research is focused on new methods to treat ischemic stroke. Exosomes are nano-sized biovesicles produced in the endosomal compartment of most eukaryotic cells, containing DNA, complex RNA, and protein (30-150 nm). They are released into surrounding extracellular fluid upon fusion between multivesicular bodies and the plasma membrane. Exosomes have the characteristics of low immunogenicity, good innate stability, high transmission efficiency, and the ability to cross the blood-brain barrier, making them potential therapeutic modalities for the treatment of ischemic stroke. The seed sequence of miRNA secreted by exosomes is base-paired with complementary mRNA to improve the microenvironment of ischemic tissue, thereby regulating downstream signal transduction activities. With exosome research still in the theoretical and experimental stages, this review aims to shed light on the potential of exosomes derived from mesenchymal stem cells in the treatment of ischemic stroke.

Treatment with outgrowth endothelial cells protects cerebral barrier against ischemic injury

BACKGROUND AND AIMS

We have previously reported that outgrowth endothelial cells (OECs) restore cerebral endothelial cell integrity through effective homing to the injury site. This study further investigates whether treatment with OECs can restore blood-brain barrier (BBB) function in settings of ischemia-reperfusion injury both in vitro and in vivo.

METHODS

An in vitro model of human BBB was established by co-culture of astrocytes, pericytes, and human brain microvascular endothelial cells (HBMECs) before exposure to oxygen-glucose deprivation alone or followed by reperfusion (OGD±R) in the absence or presence of exogenous OECs. Using a rodent model of middle cerebral artery occlusion (MCAO), we further assessed the therapeutic potential of OECs in vivo.

RESULTS

Owing to their prominent antioxidant, proliferative, and migratory properties, alongside their inherent capacity to incorporate into brain vasculature, treatments with OECs attenuated the extent of OGD±R injury on BBB integrity and function, as ascertained by increases in transendothelial electrical resistance and decreases in paracellular flux across the barrier. Similarly, intravenous delivery of OECs also led to better barrier protection in MCAO rats as evidenced by significant decreases in ipsilateral brain edema volumes on day 3 after treatment. Mechanistic studies subsequently showed that treatment with OECs substantially reduced oxidative stress and apoptosis in HBMECs subjected to ischemic damages.

CONCLUSION

This experimental study shows that OEC-based cell therapy restores BBB integrity in an effective manner by integrating into resident cerebral microvascular network, suppressing oxidative stress and cellular apoptosis.

Mesenchymal Stromal Cells in Ischemic Brain Injury

Ischemic brain injury represents a major cause of death worldwide with limited treatment options with a narrow therapeutic window. Accordingly, novel treatments that extend the treatment from the early neuroprotective stage to the late regenerative phase may accommodate a much larger number of stroke patients. To this end, stem cell-based regenerative therapies may address this unmet clinical need. Several stem cell therapies have been tested as potentially exhibiting the capacity to regenerate the stroke brain. Based on the long track record and safety profile of transplantable stem cells for hematologic diseases, bone marrow-derived mesenchymal stromal cells or mesenchymal stromal cells have been widely tested in stroke animal models and have reached clinical trials. However, despite the translational promise of MSCs, probing cell function remains to be fully elucidated. Recognizing the multi-pronged cell death and survival processes that accompany stroke, here we review the literature on MSC definition, characterization, and mechanism of action in an effort to gain a better understanding towards optimizing its applications and functional outcomes in stroke.

Mesenchymal Stem Cells: Therapeutic Mechanisms for Stroke

Due to aging of the world’s population, stroke has become increasingly prevalent, leading to a rise in socioeconomic burden. In the recent past, stroke research and treatment have become key scientific issues that need urgent solutions, with a sharp focus on stem cell transplantation, which is known to treat neurodegenerative diseases related to traumatic brain injuries, such as stroke. Indeed, stem cell therapy has brought hope to many stroke patients, both in animal and clinical trials. Mesenchymal stem cells (MSCs) are most commonly utilized in biological medical research, due to their pluripotency and universality. MSCs are often obtained from adipose tissue and bone marrow, and transplanted via intravenous injection. Therefore, this review will discuss the therapeutic mechanisms of MSCs and extracellular vehicles (EVs) secreted by MSCs for stroke, such as in attenuating inflammation through immunomodulation, releasing trophic factors to promote therapeutic effects, inducing angiogenesis, promoting neurogenesis, reducing the infarct volume, and replacing damaged cells.

Exploring the Role of Stem Cell Therapy in Treating Neurodegenerative Diseases: Challenges and Current Perspectives

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Several human neurological disorders, such as Parkinson’s disease, Alzheimer’s disease, amyotrophic lateral sclerosis, Huntington’s disease, spinal cord injury, multiple sclerosis, and brain stroke, are caused by the injury to neurons or glial cells. The recent years have witnessed the successful generation of neurons and glia cells driving efforts to develop stem-cell-based therapies for patients to combat a broad spectrum of human neurological diseases. The inadequacy of suitable cell types for cell replacement therapy in patients suffering from neurological disorders has hampered the development of this promising therapeutic approach. Attempts are thus being made to reconstruct viable neurons and glial cells from different stem cells, such as embryonic stem cells, mesenchymal stem cells, and neural stem cells. Dedicated research to cultivate stem cell-based brain transplantation therapies has been carried out. We aim at compiling the breakthroughs in the field of stem cell-based therapy for the treatment of neurodegenerative maladies, emphasizing the shortcomings faced, victories achieved, and the future prospects of the therapy in clinical settings.

Current status of ischemic stroke treatment: From thrombolysis to potential regenerative medicine

Ischemic stroke is a major cause of death and disability worldwide and is expected to increase in the future with the aging population. Currently, there are no clinically available treatments for damage sustained during an ischemic stroke, but much research is being conducted in this area. In this review, we will introduce current ischemic stroke treatments along with their limitations, as well as research on potential short and long-term future treatments. There are advantages and disadvantages in these potential treatments, but our understanding of these methods and their effectiveness in clinical trials are improving. We are confident that some future treatments introduced in this review will become commonly used in clinical settings in the future.

Endovascular Stem Cell Therapy Post Stroke Rescues Neurons from Endoplasmic Reticulum Stress-Induced Apoptosis by Modulating Brain-Derived Neurotrophic Factor/Tropomyosin Receptor Kinase B Signaling

Ischemic stroke is devastating, with serious long-term disabilities affecting millions of people worldwide. Growing evidence has shown that mesenchymal stem cells (MSCs) administration after stroke provides neuroprotection and enhances the quality of life in stroke patients. Previous studies from our lab have shown that 1 × 10⁵ MSCs administered intra-arterially (IA) at 6 h post stroke provide neuroprotection through the modulation of inflammasome and calcineurin signaling. Ischemic stroke induces endoplasmic reticulum (ER) stress, which exacerbates the pathology. The current study intends to understand the involvement of brain-derived neurotrophic factor/tropomyosin receptor kinase B (BDNF/TrkB) signaling in preventing apoptosis induced by ER stress post stroke following IA MSCs administration. Ischemic stroke was induced in ovariectomized female Sprague Dawley rats. The MSCs were administered IA, and animals were sacrificed at 24 h post stroke. Infarct area, neurological deficit score, motor coordination, and biochemical parameters were evaluated. The expression of various genes and proteins was assessed. An inhibition study was also carried out to confirm the involvement of BDNF/TrkB signaling in ER stress-induced apoptosis. IA-administered MSCs improved functional outcomes, reduced infarct area, increased neuronal survival, and normalized biochemical parameters. mRNA and protein expression of ER stress markers were reduced, while those of BDNF and TrkB were increased. Reduction in ER stress-mediated apoptosis was also observed. The present study shows that IA MSCs administration post stroke provides neuroprotection and can modulate ER stress-mediated apoptosis via the BDNF/TrkB signaling pathway.

Mesenchymal Stem/Stromal Cell Therapy in Blood-Brain Barrier Preservation Following Ischemia: Molecular Mechanisms and Prospects

Ischemic stroke is the leading cause of mortality and long-term disability worldwide. Disruption of the blood-brain barrier (BBB) is a prominent pathophysiological mechanism, responsible for a series of subsequent inflammatory cascades that exacerbate the damage to brain tissue. However, the benefit of recanalization is limited in most patients because of the narrow therapeutic time window. Recently, mesenchymal stem cells (MSCs) have been assessed as excellent candidates for cell-based therapy in cerebral ischemia, including neuroinflammatory alleviation, angiogenesis and neurogenesis promotion through their paracrine actions. In addition, accumulating evidence on how MSC therapy preserves BBB integrity after stroke may open up novel therapeutic targets for treating cerebrovascular diseases. In this review, we focus on the molecular mechanisms of MSC-based therapy in the ischemia-induced prevention of BBB compromise. Currently, therapeutic effects of MSCs for stroke are primarily based on the fundamental pathogenesis of BBB breakdown, such as attenuating leukocyte infiltration, matrix metalloproteinase (MMP) regulation, antioxidant, anti-inflammation, stabilizing morphology and crosstalk between cellular components of the BBB. We also discuss prospective studies to improve the effectiveness of MSC therapy through enhanced migration into defined brain regions of stem cells. Targeted therapy is a promising new direction and is being prioritized for extensive research.

[18F]FDG-labelled stem cell PET imaging in different route of administrations and multiple animal species

Stem cell therapy holds great promise for tissue regeneration and cancer treatment, although its efficacy is still inconclusive and requires further understanding and optimization of the procedures. Non-invasive cell tracking can provide an important opportunity to monitor in vivo cell distribution in living subjects. Here, using a combination of positron emission tomography (PET) and in vitro 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) direct cell labelling, the feasibility of engrafted stem cell monitoring was tested in multiple animal species. Human mesenchymal stem cells (MSCs) were incubated with phosphate-buffered saline containing [18F]FDG for in vitro cell radiolabelling. The pre-labelled MSCs were administrated via peripheral vein in a mouse (n = 1), rats (n = 4), rabbits (n = 4) and non-human primates (n = 3), via carotid artery in rats (n = 4) and non-human primates (n = 3), and via intra-myocardial injection in rats (n = 5). PET imaging was started 10 min after cell administration using a dedicated small animal PET system for a mouse and rats. A clinical PET system was used for the imaging of rabbits and non-human primates. After MSC administration via peripheral vein, PET imaging revealed intense radiotracer signal from the lung in all tested animal species including mouse, rat, rabbit, and non-human primate, suggesting administrated MSCs were trapped in the lung tissue. Furthermore, the distribution of the PET signal significantly differed based on the route of cell administration. Administration via carotid artery showed the highest activity in the head, and intra-myocardial injection increased signal from the heart. In vitro [18F]FDG MSC pre-labelling for PET imaging is feasible and allows non-invasive visualization of initial cell distribution after different routes of cell administration in multiple animal models. Those results highlight the potential use of that imaging approach for the understanding and optimization of stem cell therapy in translational research.

Bone Marrow-Derived IL-1Ra Increases TNF Levels Poststroke

Tumor necrosis factor (TNF) and interleukin-1 receptor antagonist (IL-1Ra) are key players in stroke, a disease in which cell-based therapies have shown great potential. Having shown an infarct-reducing effect of bone marrow (BM) cells, especially cells with high IL-1Ra expression, we here investigated the effect of BM cells on TNF and other stroke-related mediators in mice after transient middle cerebral artery occlusion (tMCAo) and in vitro using adult microglial cultures. We analyzed stroke-related genes and inflammatory mediators using qPCR stroke Tier panels, electrochemiluminescence, or enzyme-linked immunosorbent assays. We found a significant correlation and cellular colocalization between microglial-derived TNF and IL-1Ra, though IL-1Ra production was TNF independent. BM treatment significantly increased TNF, interleukin (IL)-10, and IL-4 levels, while C-X-C motif ligand 1 (CXCL1), IL-12p70, and Toll-like receptor 2 (TLR2) decreased, suggesting that BM treatment favors an anti-inflammatory environment. Hierarchical clustering identified Tnf and IL-1rn within the same gene cluster, and subsequent STRING analysis identified TLR2 as a shared receptor. Although IL-1Ra producing BM cells specifically modulated TNF levels, this was TLR2 independent. These results demonstrate BM cells as modulators of poststroke inflammation with beneficial effects on poststroke outcomes and place TNF and IL-1Ra as key players of the defense response after tMCAo.

Insight Into the Mechanisms and the Challenges on Stem Cell-Based Therapies for Cerebral Ischemic Stroke

Strokes are the most common types of cerebrovascular disease and remain a major cause of death and disability worldwide. Cerebral ischemic stroke is caused by a reduction in blood flow to the brain. In this disease, two major zones of injury are identified: the lesion core, in which cells rapidly progress toward death, and the ischemic penumbra (surrounding the lesion core), which is defined as hypoperfusion tissue where cells may remain viable and can be repaired. Two methods that are approved by the Food and Drug Administration (FDA) include intravenous thrombolytic therapy and endovascular thrombectomy, however, the narrow therapeutic window poses a limitation, and therefore a low percentage of stroke patients actually receive these treatments. Developments in stem cell therapy have introduced renewed hope to patients with ischemic stroke due to its potential effect for reversing the neurological sequelae. Over the last few decades, animal tests and clinical trials have been used to treat ischemic stroke experimentally with various types of stem cells. However, several technical and ethical challenges must be overcome before stem cells can become a choice for the treatment of stroke. In this review, we summarize the mechanisms, processes, and challenges of using stem cells in stroke treatment. We also discuss new developing trends in this field.