Biotherapies in stroke

The antidepressant-like and glioprotective effects of the Y2 receptor antagonist SF-11 in the astroglial degeneration model of depression in rats: Involvement of glutamatergic inhibition

In this study, we explored the potential antidepressant-like properties of the brain-penetrant Y2 receptor (Y2R) antagonist SF-11 [N-(4-ethoxyphenyl)- 4-(hydroxydiphenylmethyl)- 1-piperidinecarbothioamide] in the astroglial degeneration model of depression with an emphasis on checking the possible mechanisms implicated in this antidepressant-like effect. The model of depression relies on the loss of astrocytes in the medial prefrontal cortex (mPFC) in Sprague-Dawley rats after administering the gliotoxin L-alpha-aminoadipic acid (L-AAA). SF-11 was administered intraperitoneally (i.p.) once (10 mg/kg) or for three consecutive days (10 mg/kg/day), and the effects of L-AAA and SF-11 injected alone or in combination were investigated using the forced swim test (FST), sucrose intake test (SIT), Western blotting, immunohistochemical staining, and microdialysis. SF-11 produced an antidepressant-like effect after single or three-day administration in rats subjected to astrocyte impairment, as demonstrated by the FST and SIT, respectively. Immunoblotting and immunohistochemical analyses showed that SF-11 reversed the L-AAA-induced astrocyte cell death in the mPFC, suggesting it is glioprotective. Microdialysis studies showed that SF-11 decreased extracellular glutamate (Glu) levels compared to basal value when administered alone and compared to the basal value and control group in LAAA-treated rats. The results from immunoblotting analysis indicated the involvement of Y2Rs in the astrocyte ablation model of depression and the antidepressant-like effect of SF-11. In addition, we observed the participation of the caspase-3 apoptotic pathway in the mechanism of gliotoxin action induced by L-AAA. These findings demonstrate that SF-11, a Y2R antagonist, elicited a rapid antidepressant-like response, possibly linked to its ability to inhibit glutamatergic neurotransmission.

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.

Modulation of neurotrophic factors in the treatment of dementia, stroke and TBI: Effects of Cerebrolysin

Neurotrophic factors (NTFs) are involved in the pathophysiology of neurological disorders such as dementia, stroke and traumatic brain injury (TBI), and constitute molecular targets of high interest for the therapy of these pathologies. In this review we provide an overview of current knowledge of the definition, discovery and mode of action of five NTFs, nerve growth factor, insulin-like growth factor 1, brain derived NTF, vascular endothelial growth factor and tumor necrosis factor alpha; as well as on their contribution to brain pathology and potential therapeutic use in dementia, stroke and TBI. Within the concept of NTFs in the treatment of these pathologies, we also review the neuropeptide preparation Cerebrolysin, which has been shown to resemble the activities of NTFs and to modulate the expression level of endogenous NTFs. Cerebrolysin has demonstrated beneficial treatment capabilities in vitro and in clinical studies, which are discussed within the context of the biochemistry of NTFs. The review focuses on the interactions of different NTFs, rather than addressing a single NTF, by outlining their signaling network and by reviewing their effect on clinical outcome in prevalent brain pathologies. The effects of the interactions of these NTFs and Cerebrolysin on neuroplasticity, neurogenesis, angiogenesis and inflammation, and their relevance for the treatment of dementia, stroke and TBI are summarized.

Intranasal erythropoietin protects granular cells and reduces astrogliosis in the dentate gyrus after ischemic damage, an effect associated with molecular changes in erythropoietin and its receptor

Within the hippocampus, the CA1 and dentate gyrus (DG) regions are considered the most and the least susceptible to damage by cerebral ischemia, respectively. In addition, it has been tested that rHuEPO exhibits neuroprotective properties. This work investigates the effect of different intranasal doses of rHuEPO, applied in different ischemic post-damage times in the DG, and the effect of the rHuEPO on astroglial reactivity after cerebral ischemia. Additionally, an effective dose for neuroprotection and an administration time was used to evaluate gene and protein expression changes of EPO and EPOR in the DG region. We observed a considerable loss of cells on the granular layer and an increased number of GFAP immunoreactive cells in this region only 72 h after the onset of ischemia/damage. When rHuEPO was administered, the number of morphologically abnormal cells and immunoreactivity decreased. In the analysis of protein and gene expression, there is no correlation between expression level of these molecules, although the rHuEPO amplifies the response to ischemia of EPO and EPOR gene for each evaluated time; in the case of the protein only at 2 h this effect was observed. We demonstrated the susceptibility of the DG to ischemia; so granular cells damage was observed, moreover of the astrocytic response, which is accompanied by molecular changes in signaling mediated by rHuEPO intranasal administration.

Functional hydrogels for the repair and regeneration of tissue defects

Tissue defects can be accompanied by functional impairments that affect the health and quality of life of patients. Hydrogels are three-dimensional (3D) hydrophilic polymer networks that can be used as bionic functional tissues to fill or repair damaged tissue as a promising therapeutic strategy in the field of tissue engineering and regenerative medicine. This paper summarises and discusses four outstanding advantages of hydrogels and their applications and advances in the repair and regeneration of tissue defects. First, hydrogels have physicochemical properties similar to the extracellular matrix of natural tissues, providing a good microenvironment for cell proliferation, migration and differentiation. Second, hydrogels have excellent shape adaptation and tissue adhesion properties, allowing them to be applied to a wide range of irregularly shaped tissue defects and to adhere well to the defect for sustained and efficient repair function. Third, the hydrogel is an intelligent delivery system capable of releasing therapeutic agents on demand. Hydrogels are capable of delivering therapeutic reagents and releasing therapeutic substances with temporal and spatial precision depending on the site and state of the defect. Fourth, hydrogels are self-healing and can maintain their integrity when damaged. We then describe the application and research progress of functional hydrogels in the repair and regeneration of defects in bone, cartilage, skin, muscle and nerve tissues. Finally, we discuss the challenges faced by hydrogels in the field of tissue regeneration and provide an outlook on their future trends.

Comparison of the Administration Route of Stem Cell Therapy for Ischemic Stroke: A Systematic Review and Meta-Analysis of the Clinical Outcomes and Safety

Stem cell treatment is emerging as an appealing alternative for stroke patients, but there still needs to be an agreement on the protocols in place, including the route of administration. This systematic review aimed to assess the efficacy and safety of the administration routes of stem cell treatment for ischemic stroke. A systematic review was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. A comprehensive literature search was undertaken using the PubMed, Scopus, and Cochrane databases. A total of 21 publications on stem cell therapy for ischemic stroke were included. Efficacy outcomes were measured using the National Institutes of Health Stroke Scale (NIHSS), the modified Rankin Scale (mRS), and the Barthel index (BI). Intracerebral administration showed a better outcome than other routes, but a greater number of adverse events followed due to its invasiveness. Adverse events were shown to be related to the natural history of stroke not to the treatment. However, further investigation is required, since studies have yet to compare the different administration methods directly.

Spatial Analysis of Neural Cell Proteomic Profiles Following Ischemic Stroke in Mice Using High-Plex Digital Spatial Profiling

Stroke is ranked as the fifth leading cause of death and the leading cause of adult disability in the USA. The progression of neuronal damage after stroke is recognized to be a complex integration of glia, neurons, and the surrounding extracellular matrix, therefore potential treatments must target the detrimental effects created by these interactions. In this study, we examined the spatial cellular and neuroinflammatory mechanisms occurring early after ischemic stroke utilizing Nanostring Digital Spatial Profiling (DSP) technology. Male C57bl/6 mice were subjected to photothrombotic middle cerebral artery occlusion (MCAO) and sacrificed at 3 days post-ischemia. Spatial distinction of the ipsilateral hemisphere was studied according to the regions of interest: the ischemic core, peri-infarct tissues, and peri-infarct normal tissue (PiNT) in comparison to the contralateral hemisphere. We demonstrated that the ipsilateral hemisphere initiates distinct spatial regulatory proteomic profiles with DSP technology that can be identified consistently with the immunohistochemical markers, FJB, GFAP, and Iba-1. The core border profile demonstrated an induction of neuronal death, apoptosis, autophagy, immunoreactivity, and early degenerative proteins. Most notably, the core border resulted in a decrease of the neuronal proteins Map2 and NeuN; an increase in the autophagy proteins BAG3 and CTSD; an increase in the microglial and peripheral immune invasion proteins Iba1, CD45, CD11b, and CD39; and an increase in the neurodegenerative proteins BACE1, APP, amyloid β 1-42, ApoE, and hyperphosphorylated tau protein S-199. The peri-infarct region demonstrated increased astrocytic, immunoreactivity, apoptotic, and neurodegenerative proteomic profiles, with an increase in BAG3, GFAP, and hyperphosphorylated tau protein S-199. The PiNT region displayed minimal changes compared to the contralateral cortex with only an increase in GFAP. In this study, we showed that mechanisms known to be associated with stroke, such as apoptosis and inflammation, occur in distinct spatial domains of the injured brain following ischemia. We also demonstrated the dysregulation of specific autophagic pathways that may lead to neurodegeneration in peri-infarct brain tissues. Taken together, these data suggest that identifying post-ischemic mechanisms occurring in a spatiotemporal manner may lead to more precise targets for successful therapeutic interventions to treat stroke.

Clinical outcome and safety of stem cell therapy for ischemic stroke: A systematic review and meta-analysis

Background:

Several reports on stem cell administration have emerged proving it to be an ideal therapeutic approach for improving neurological functions in ischemic stroke patients. However, some studies also show disappointing results, with some reporting no statistically significant improvements among several different parameters. Several challenges also arise relating to safety and nonscientific aspects, such as ethics.

Methods:

We performed a systematic review and meta-analysis to evaluate the effect of stem cell therapy on the clinical outcomes of ischemic stroke patients. A systematic review and meta-analysis were performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. A thorough literature search was conducted on PubMed, Scopus, and Cochrane databases. Articles were selected systematically based on the PRISMA protocol and reviewed completely. A total of 19 publications pertaining to stem cell therapy on the ischemic route were included and reviewed. Efficacy outcomes were measured with the National Institutes of Health Stroke Scale, modified Rankin Scale, or Barthel Index.

Results:

The results of the meta-analysis indicate that the efficacy outcomes suggest favorable results after stem cell therapy, although not all study results are statistically significant. Stem cell therapy in stroke cases showed a better outcome than standard conservative therapy alone, although our analysis shows that many factors can influence this outcome, and significant effects can only be seen after several months.

Conclusion:

The results of this study show promising and satisfying efficacy and a relatively low rate of serious adverse events.

Natural recovery and regeneration of the central nervous system

The diagnosis and management of CNS injuries comprises a large portion of psychiatric practice. Many clinical and preclinical studies have demonstrated the benefit of treating CNS injuries using various regenerative techniques and materials such as stem cells, biomaterials and genetic modification. Therefore it is the goal of this review article to briefly summarize the pathogenesis of CNS injuries, including traumatic brain injuries, spinal cord injuries and cerebrovascular accidents. Next, we discuss the role of natural recovery and regeneration of the CNS, explore the relevance in clinical practice and discuss emerging and cutting-edge treatments and current barriers in the field of regenerative medicine.

Neuroprotective and Neurorestorative Effects of Epo and VEGF: Perspectives for New Therapeutic Approaches to Neurological Diseases

BACKGROUND

Erythropoietin (Epo) and vascular endothelial growth factor (VEGF) are two vasoactive molecules with essential trophic effects for brain development. The expression and secretion of both molecules increase in response to neuronal damage and they exert protective and restorative effects, which may also be accompanied by adverse side effects.

OBJECTIVE

We review the most relevant evidence on the neuroprotective and neurorestorative effects of Epo and VEGF in three of the most frequent neurological disorders, namely, stroke, epilepsy and Alzheimer's disease, to develop new therapeutic approaches.

METHODS

Several original scientific manuscripts and reviews that have discussed the evidence in critical way, considering both the beneficial and adverse effects of Epo and VEGF in the selected neurological disorders, were analysed. In addition, throughout this review, we propose several considerations to take into account in the design of therapeutic approaches based on Epo and VEGF signalling.

RESULTS

Although the three selected disorders are triggered by different mechanisms, they evolve through similar processes: excitotoxicity, oxidative stress, neuroinflammation, neuronal death, glial reactivity and vascular remodelling. Epo and VEGF exert neuroprotective and neurorestorative effects by acting on these processes due to their pleiotropism. In general, the evidence shows that both Epo and VEGF reduce neuronal death but that at the vascular level, their effects are contradictory.

CONCLUSION

Because the Epo and VEGF signalling pathways are connected in several ways, we conclude that more experimental studies, primarily studies designed to thoroughly assess the functional interactions between Epo and VEGF in the brain under both physiological and pathophysiological conditions, are needed.

A Mechanistic Rationale for PDE-4 Inhibitors to Treat Residual Cognitive Deficits in Acquired Brain Injury

Patients with acquired brain injury (ABI) suffer from cognitive deficits that interfere significantly with their daily lives. These deficits are long-lasting and no treatment options are available. A better understanding of the mechanistic basis for these cognitive deficits is needed to develop novel treatments. Intracellular cyclic adenosine monophosphate (cAMP) levels are decreased in ABI. Herein, we focus on augmentation of cAMP by PDE4 inhibitors and the potentially synergistic mechanisms in traumatic brain injury. A major acute pathophysiological event in ABI is the breakdown of the blood-brain-barrier (BBB). Intracellular cAMP pathways are involved in the subsequent emergence of edema, inflammation and hyperexcitability. We propose that PDE4 inhibitors such as roflumilast can improve cognition by modulation of the activity in the cAMP-Phosphokinase A-Ras-related C3 botulinum toxin substrate (RAC1) inflammation pathway. In addition, PDE4 inhibitors can also directly enhance network plasticity and attenuate degenerative processes and cognitive dysfunction by increasing activity of the canonical cAMP/phosphokinase-A/cAMP Responsive Element Binding protein (cAMP/PKA/CREB) plasticity pathway. Doublecourtin and microtubule-associated protein 2 are generated following activation of the cAMP/PKA/CREB pathway and are decreased or even absent after injury. Both proteins are involved in neuronal plasticity and may consist of viable markers to track these processes. It is concluded that PDE4 inhibitors may consist of a novel class of drugs for the treatment of residual symptoms in ABI attenuating the pathophysiological consequences of a BBB breakdown by their anti-inflammatory actions via the cAMP/PKA/RAC1 pathway and by increasing synaptic plasticity via the cAMP/PKA/CREB pathway. Roflumilast improves cognition in young and elderly humans and would be an excellent candidate for a proof of concept study in ABI patients.

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.

Drug-like delivery methods of stem cells as biologics for stroke

Introduction: Stem cell therapy is an experimental treatment for brain disorders. Although a cellular product, stem cells can be classified as biologics based on the cells' secretion of therapeutic substances. Treatment with stem cell biologics may appeal to stroke because of the secondary cell death mechanisms, especially neuroinflammation, that are rampant from the onset and remain elevated during the progressive phase of the disease requiring multi-pronged biological targets to effectively abrogate the neurodegenerative pathology. However, the optimal delivery methods, among other logistical approaches (i.e. cell doses and timing of intervention), for stem cell therapy will need to be refined before stem cell biologics can be successfully utilized for stroke in large scale clinical trials. Areas covered: In this review, we discuss how the innate qualities of stem cells characterize them as biologics, how stem cell transplantation may be an ideal treatment for stroke, and the various routes of stem cell administration that have been employed in various preclinical and clinical investigations. Expert opinion: There is a need to optimize the delivery of stem cell biologics for stroke in order to guide the safe and effective translation of this therapy from the laboratory to the clinic.

Effects of GDNF-Transfected Marrow Stromal Cells on Rats with Intracerebral Hemorrhage

OBJECTIVE

The present study aimed to investigate the effects of Mesenchymal stem cells/glial cell line derived neurotrophic factor (MSCs/GDNF) transplantation on nerve reconstruction in rats with intracerebral hemorrhage.

METHODS

GDNF transduction to MSCs was using adenovirus vector pAdEasy-1-pAdTrack-CMV prepared. Intracerebral hemorrhage (ICH) was induced by injection of collagenase and heparin into the caudate putamen. At the third day after a collagenase-induced ICH, adult male SD rats were randomly divided into saline group, MSCs group and MSCs/GDNF group. Immunofluorescence and RT-PCR were performed to detect the differentiation of MSCs or MSCs with an adenovirus vector encoding GDNF gene in vivo and in vitro.

RESULT

After 6 hours of induction, both MSCs and MSCs/GDNF expressed neuro or glial specific markers and synaptic-associated proteins (SYN, GAP-43, PSD-95); additionally, they secreted bioactive compounds (BDNF, NGF-β). MSCs/GDNF transplantation, compared to MSCs and saline solution injection, significantly improved neurological functions after ICH. The grafted MSCs or MSCs/GDNF survived in the striatum after 2 weeks of transplantation and expressed the neural cell-specific biomarkers NSE, MAP2, and GFAP.

CONCLUSION

These findings demonstrate that MSCs/GDNF transplantation contributes to improved neurological function in experimental ICH rats. The mechanisms are possibly due to neuronal replacement and enhanced neurotrophic factor secretion.

Intranasal Erythropoietin Protects CA1 Hippocampal Cells, Modulated by Specific Time Pattern Molecular Changes After Ischemic Damage in Rats

Erythropoietin, a multitarget molecule exhibited neuroprotective properties, especially against cerebral ischemia. However, little effort has been made to determinate both the administration pathway and doses that diminishes neuronal damage. In this study, we investigate the effect on CA1 region of different intranasal doses of rHuEPO (500, 1000 and 2500 IU/kg) applied in distinct post-damage times (1, 6, and 24 h) against ischemic cellular damage. Furthermore, most effective dose and time were used to evaluate gen and protein expression changes in 3 key molecules (EPO, EPOR, and βcR). We established that CA1-region present histopathological damage in this ischemia model and that rHuEPO protects cells against damage, particularly at 1000 IU dose. Molecular data shows that EPO and EPOR gene expression are upregulated in a short term after damage treatment with rHuEPO (1 h); oppositely, BcR is upregulated in ischemic and Isc + EPO. Protein expression data displays no changes on EPO expression in evaluated times after treatment, but a tendency to increase 24 h after damage; in the opposite way, EPOR is upregulated significantly 6 h after treatment and this effect last until 24 h. So, our data suggest that a single intranasal dose of rHuEPO (1 h post-injury) provides histological neurorestoration in CA1 hippocampal region, even if we did not observe a dose-dependent dose effect, the medium dose evaluated (1000 UI/kg of b.w.) was more effective and sufficient for induces molecular changes that provides a platform for neuroprotection.

How to use stem cells for repair in stroke patients

Regenerative cell therapy is a promising therapeutic strategy in neurology, most notably to improve stroke recovery. Although tolerability and feasibility have apparently been validated, many questions remain as to what is the best type of cells to use, the best route and the post-stroke delay for administration. Two main strategies have currently emerged: intravenous injection of mesenchymal stem cells with systemic trophic support; and intracerebral grafting of neural stem cells with brain repair effects at the lesion site. Multicenter clinical trials have just begun and are starting to assess the efficacy of these treatments on functional recovery. However, experimental studies also need to be conducted in parallel to precisely identify the mechanisms of action regarding the pathophysiology of brain plasticity, notably when stroke occurs with comorbidities. Such studies should also evaluate the potential of cell grafting combined with injectable biomaterials.

Controlled clinical trials of cell therapy in stroke: Meta-analysis at six months after treatment

Background

Cell therapy is promising in experimental studies and has been assessed only in a few studies on humans.

Aims

To evaluate the effect of cell therapy in humans.

Methods

We included clinical trials with a control group that reported safety and efficacy six months following treatment. Quality was evaluated and clinical scales data were extracted. Quantitative analysis was based on the standardized means difference (SMD). Among 28 trials published from 1995 to 2016, nine studies (194 patients; 191 controls) were eligible. Publication biases were assessed with the funnel plot and pre-specified explanatory variables were tested with a group analysis and a meta-regression.

Results

The overall quality was moderate. Cell therapy had a positive effect on the outcome (SMD: 0.57, 95% CI: 0.22–0.92; p = 0.002). The sensitivity analysis showed an upper level of effect size of 0.81 (95% CI: 0.34–1.27; p = 0.001) and a lower level of 0.455 (95% CI: 0.04–0.87; p = 0.03). None of the pre-specified explanatory variable was significantly correlated to outcome: age, ratio infarction/hemorrhage, delay from stroke to treatment, route of administration, cell type, randomization, and blinded outcome assessment. The significant heterogeneity (p = 0.03) was not explained by publication biases (p = 0.09) and was more likely due to methodological and quality differences between the trials.

Conclusions

This result suggests that cell therapy is beneficial in stroke and is expected to help in the designing of stem cells controlled clinical trials (CCT) in large populations.

Cell therapies administered in the chronic phase after stroke: a meta-analysis examining safety and efficacy

Aim: To assess the safety and efficacy of cell therapies for chronic stroke. Methodology: Five databases were searched for treatments administered >90 days post-stroke. Reporting quality, adherence to research guidelines, treatment safety (risk ratios/pooled incidence rates) and neurological/functional efficacy (Hedge’s g) were all evaluated. Results: Twenty-three studies examined 17 treatments. Reporting quality scores were medium to high, but adherence to recommended guidelines was lower. Three treatments resulted in serious adverse events; four improved outcomes more than standard care. However, many studies were under-powered and individual patients varied in their response to some treatments. Conclusion: Preliminary findings suggest that some cell therapies may be relatively safe and effective, but larger double-blinded placebo-controlled studies are needed to establish the long-term risks and benefits.

Safety and efficacy of cell therapies administered in the acute and subacute stages after stroke: a meta-analysis

AIMS

To evaluate the safety and efficacy of cell therapies administered acutely/sub-acutely after stroke.

METHODS

Five databases were searched for studies examining the safety/efficacy of cell therapies administered ≤90 days post-stroke. Reporting quality and adherence to research guidelines were evaluated. Safety and efficacy were assessed using risk ratios/pooled incidence rates and Hedge's g, respectively.

RESULTS

11 therapies (Nstudies= 28) were trialed: reporting quality was high, but adherence to guidelines low. Serious adverse events were observed following five treatments; six improved outcomes. There was a trend toward larger treatment effects in non-blinded studies, younger participants, and higher dosages.

CONCLUSION

Although a number of therapies appear effective, many studies did not control for normal recovery (standard-care). Long-term safety also needs to be established.

Stem Cell Therapy and Administration Routes After Stroke

Cell-based therapy has demonstrated safety and efficacy in experimental animal models of stroke, as well as safety in stroke patients. However, various questions remain regarding the therapeutic window, dosage, route of administration, and the most appropriate cell type and source, as well as mechanisms of action and immune-modulation to optimize treatment based on stem cell therapy. Various delivery routes have been used in experimental stroke models, including intracerebral, intraventricular, subarachnoid, intra-arterial, intraperitoneal, intravenous, and intranasal routes. From a clinical point of view, it is necessary to demonstrate which is the most feasible, safest, and most effective for use with stroke patients. Therefore, further experimental studies concerning the safety, efficacy, and mechanisms of action involved in these therapeutic effects are required to determine their optimal clinical use.

Biomaterial Applications in Cell-Based Therapy in Experimental Stroke

Stroke is an important health issue corresponding to the second cause of mortality and first cause of severe disability with no effective treatments after the first hours of onset. Regenerative approaches such as cell therapy provide an increase in endogenous brain structural plasticity but they are not enough to promote a complete recovery. Tissue engineering has recently aroused a major interesting development of biomaterials for use into the central nervous system. Many biomaterials have been engineered based on natural compounds, synthetic compounds, or a mix of both with the aim of providing polymers with specific properties. The mechanical properties of biomaterials can be exquisitely regulated forming polymers with different stiffness, modifiable physical state that polymerizes in situ, or small particles encapsulating cells or growth factors. The choice of biomaterial compounds should be adapted for the different applications, structure target, and delay of administration. Biocompatibilities with embedded cells and with the host tissue and biodegradation rate must be considerate. In this paper, we review the different applications of biomaterials combined with cell therapy in ischemic stroke and we explore specific features such as choice of biomaterial compounds and physical and mechanical properties concerning the recent studies in experimental stroke.

Translational Hurdles in Stroke Recovery Studies

Emerging understanding of brain plasticity has opened new avenues for the treatment of stroke. The promising preclinical evidence with neuroprotective drugs has not been confirmed in clinical trials, thus nowadays, researchers, pharmaceutical companies, and funding bodies hesitate to initiate these expensive trials with restorative therapies. Since many of the previous failures can be traced to low study quality, a number of guidelines such as STAIR and STEPS were introduced to rectify these shortcomings. However, these guidelines stem from the study design for neuroprotective drugs and one may question whether they are appropriate for restorative approaches, which rely heavily on behavioral testing. Most of the recovery studies conducted in stroke patients have been small-scale, proof-of-concept trials. Consequently, the overall effect sizes of pooled phase II trials have proved unreliable and unstable in most meta-analyses. Although the methodological quality of trials in humans is improving, most studies still suffer from methodological flaws and do not meet even the minimum of evidence-based standards for reporting randomized controlled trials. The power problem of most phase II trials is mostly attributable to a lack of proper stratification with robust prognostic factors at baseline as well as the incorrect assumption that all patients will exhibit the same proportional amount of spontaneous neurological recovery poststroke. In addition, most trials suffer from insufficient treatment contrasts between the experimental and control arm and the outcomes have not been sufficiently responsive to detect small but clinically relevant changes in neurological impairments and activities. This narrative review describes the main factors that bias recovery studies, both in experimental animals and stroke patients.

Poststroke Cell Therapy of the Aged Brain

During aging, many neurodegenerative disorders are associated with reduced neurogenesis and a decline in the proliferation of stem/progenitor cells. The development of the stem cell (SC), the regenerative therapy field, gained tremendous expectations in the diseases that suffer from the lack of treatment options. Stem cell based therapy is a promising approach to promote neuroregeneration after brain injury and can be potentiated when combined with supportive pharmacological drug treatment, especially in the aged. However, the mechanism of action for a particular grafted cell type, the optimal delivery route, doses, or time window of administration after lesion is still under debate. Today, it is proved that these protections are most likely due to modulatory mechanisms rather than the expected cell replacement. Our group proved that important differences appear in the aged brain compared with young one, that is, the accelerated progression of ischemic area, or the delayed initiation of neurological recovery. In this light, these age-related aspects should be carefully evaluated in the clinical translation of neurorestorative therapies. This review is focused on the current perspectives and suitable sources of stem cells (SCs), mechanisms of action, and the most efficient delivery routes in neurorestoration therapies in the poststroke aged environment.