Therapeutic Potential of Human Stem Cell Implantation in Alzheimer's Disease

Mesenchymal Stem Cell-Derived Exosomes as a Neuroregeneration Treatment for Alzheimer's Disease

BACKGROUND

Alzheimer's disease (AD) is the most prevalent kind of dementia and is a long-term degenerative disease. Pathologically, it is defined by the development of extracellular amyloid-β plaques and intracellular neurofibrillary tangles made up of hyperphosphorylated tau protein. This causes neuronal death, particularly in the hippocampus and cortex. Mesenchymal stem cell (MSC)-derived exosomes have been identified as possibly therapeutic and have promise for Alzheimer's disease due to their regenerative characteristics.

METHODS

A systematic retrieval of information was performed on PubMed. A total of 60 articles were found in a search on mesenchymal stem cells, exosomes, and Alzheimer's disease. A total of 16 ongoing clinical trials were searched and added from clinicaltrials.gov. We added 23 supporting articles to help provide information for certain sections. In total, we included 99 articles in this manuscript: 50 are review articles, 13 are preclinical studies, 16 are clinical studies, 16 are ongoing clinical trials, and 4 are observational studies. Appropriate studies were isolated, and important information from each of them was understood and entered into a database from which the information was used in this article. The clinical trials on mesenchymal stem cell exosomes for Alzheimer's disease were searched on clinicaltrials.gov.

RESULTS

Several experimental investigations have shown that MSC-Exo improves cognitive impairment in rats. In this review paper, we summarized existing understanding regarding the molecular and cellular pathways behind MSC-Exo-based cognitive function restoration, with a focus on MSC-Exo's therapeutic potential in the treatment of Alzheimer's disease.

CONCLUSION

AD is a significant health issue in our culture and is linked to several important neuropathological characteristics. Exosomes generated from stem cells, such as mesenchymal stem cells (MSCs) or neural stem cells (NSCs), have been examined more and more in a variety of AD models, indicating that they may be viable therapeutic agents for the treatment of diverse disorders. Exosome yields may be increased, and their therapeutic efficacy can be improved using a range of tailored techniques and culture conditions. It is necessary to provide standardized guidelines for exosome manufacture to carry out excellent preclinical and clinical research.

Emerging Pro-neurogenic Therapeutic Strategies for Neurodegenerative Diseases: A Review of Pre-clinical and Clinical Research

The neuroscience community has largely accepted the notion that functional neurons can be generated from neural stem cells in the adult brain, especially in two brain regions: the subventricular zone of the lateral ventricles and the subgranular zone in the dentate gyrus of the hippocampus. However, impaired neurogenesis has been observed in some neurodegenerative diseases, particularly in Alzheimer's, Parkinson's, and Huntington's diseases, and also in Lewy Body dementia. Therefore, restoration of neurogenic function in neurodegenerative diseases emerges as a potential therapeutic strategy to counteract, or at least delay, disease progression. Considering this, the present study summarizes the different neuronal niches, provides a collection of the therapeutic potential of different pro-neurogenic strategies in pre-clinical and clinical research, providing details about their possible modes of action, to guide future research and clinical practice.

Evolving therapeutic interventions for the management and treatment of Alzheimer's disease

Alzheimer's Disease (AD) patients experience diverse symptoms, including memory loss, cognitive impairment, behavioral abnormalities, mood changes, and mental issues. The fundamental objective of this review is to discuss novel therapeutic approaches, with special emphasis on recently approved marketed formulations for the treatment of AD, especially Aducanumab, the first FDA approved moiety that surpasses the blood-brain barrier (BBB) and reduces amyloid plaques in the brain, thereby reducing associated cognitive decline. However, it is still in the phase IV trial and is to be completed by 2030. Other drugs such as lecanemab are also under clinical trial and has recently been approved by the FDA and is also discussed here. In this review, we also focus on active and passive immunotherapy for AD as well as several vaccines, such as amyloid-beta epitope-based vaccines, amyloid-beta DNA vaccines, and stem cell therapy for AD, which are in clinical trials. Furthermore, ongoing pre-clinical trials associated with AD and other novel strategies such as curcumin-loaded nanoparticles, Crispr/ cas9, precision medicine, as well as some emerging therapies like anti-sense therapy are also highlighted. Additionally, we discuss some off-labeled drugs like non-steroidal anti-inflammatory drugs (NSAID), anti-diabetic drugs, and lithium, which can manage symptoms of AD and different non-pharmacological approaches are also covered which can help to manage AD. In summary, we have tried to cover all the therapeutic interventions which are available for the treatment and management of AD under sections approved, clinical phase, pre-clinical phase or futuristic interventions, off-labelled drugs, and non-pharmacological interventions for AD, offering positive findings and well as challenges that remain.

Adipose tissue-derived mesenchymal stem cells ameliorate cognitive impairment in Alzheimer's disease rat model: Emerging role of SIRT1

Alzheimer's disease (AD) is a complex form of neurodegenerative dementia. Growing body of evidence supports the cardinal role of sirtuin1 (SIRT1) in neurodegeneration and AD development. Recently, adipose tissue-derived mesenchymal stem cells (Ad-MSCs) have made their mark for a wide array of regenerative medicine applications, including neurodegenerative disorders. Therefore, the present study aimed to investigate the therapeutic potential of Ad-MSCs in AD rat model, and to explore the possible implication of SIRT1. Ad-MSCs were isolated from rat epididymal fat pads and properly characterized. Aluminum chloride was used to induce AD in rats, and afterward, a group of AD-induced rats received a single dose of Ad-MSCs (2 × 106 cell, I.V per rat). One month after Ad-MSCs transplantation, behavioral tests were done, brain tissues were collected, then histopathological and biochemical assessments were performed. Amyloid beta and SIRT1 levels were determined by enzyme-linked immunosorbent assay. Whereas expression levels of neprilysin, BCL2 associated X protein, B-cell lymphoma-2, interleukin-1β, interleukin-6, and nerve growth factor in hippocampus and frontal cortex brain tissues were assessed using reverse transcriptase quantitative polymerase chain reaction. Our data demonstrated that transplantation of Ad-MSCs alleviated cognitive impairment in AD rats. Additionally, they exhibited anti-amyloidogenic, antiapoptotic, anti-inflammatory, as well as neurogenic effects. Furthermore, Ad-MSCs were found to possibly mediate their therapeutic effects, at least partially, via modulating both central and systemic SIRT1 levels. Hence, the current study portrays Ad-MSCs as an effective therapeutic approach for AD management and opens the door for future investigations to further elucidate the role of SIRT1 and its interrelated molecular mediators in AD.

An update on stem cell and stem cell-derived extracellular vesicle-based therapy in the management of Alzheimer's disease

Globally, neurological diseases pose a major burden to healthcare professionals in terms of the management and prevention of the disorder. Among neurological diseases, Alzheimer's disease (AD) accounts for 50%-70% of dementia and is the fifth leading cause of mortality worldwide. AD is a progressive, degenerative neurological disease, with the loss of neurons and synapses in the cerebral cortex and subcortical regions. The management of AD remains a debate among physicians as no standard and specific "disease-modifying" modality is available. The concept of 'Regenerative Medicine' is aimed at regenerating the degenerated neural tissues to reverse the pathology in AD. Genetically modified engineered stem cells modify the course of AD after transplantation into the brain. Extracellular vesicles (EVs) are an emerging new approach in cell communication that involves the transfer of cellular materials from parental cells to recipient cells, resulting in changes at the molecular and signaling levels in the recipient cells. EVs are a type of vesicle that can be transported between cells. Many have proposed that EVs produced from mesenchymal stem cells (MSCs) may have therapeutic promise in the treatment of AD. The biology of AD, as well as the potential applications of stem cells and their derived EVs-based therapy, were explored in this paper.

Molecular, Translational and Clinical Research on the Two Most Common Forms of Neurodegenerative Dementia: Alzheimer's Disease and Dementia with Lewy Bodies

While not a specific disease, dementia is a term used to describe the deterioration of cognitive function beyond what would be expected because of natural biological aging [...].

Depletion of gut microbiota resistance in 5×FAD mice enhances the therapeutic effect of mesenchymal stem cell-derived exosomes

Mesenchymal stem cell-derived exosomes (MSCs-exo) can be used for treating Alzheimer's disease (AD) by promoting amyloid-β (Aβ) degradation, modulating immune responses, protecting neurology, promoting axonal growth, and improving cognitive impairment. Increasing evidence suggests that the alteration of gut microbiota is closely related to the occurrence and development of Alzheimer's disease. In this study, we hypothesized that dysbiosis of gut microbiota might limit the therapy of MSCs-exo, and the application of antibiotics would improve the therapy.

METHODS

In this original research study, we used MSCs-exo to treat 5 ×FAD mice and fed them antibiotic cocktails for 1 week to detect cognitive ability and neuropathy. The mice's feces were collected to investigate alterations in the microbiota and metabolites.

RESULTS

The results revealed that the AD gut microbiota eliminated the therapeutic effect of MSCs-exo, whereas antibiotic modulation of disordered gut microbiota and associated metabolites enhanced the therapeutic effect of MSCs-exo.

CONCLUSIONS

These results encourage the research of novel therapeutics to enhance MSCs-exo treatment for AD, which could benefit a broader range of patients with AD.

Nanotherapeutic and Stem Cell Therapeutic Strategies in Neurodegenerative Diseases: A Promising Therapeutic Approach

Neurodegeneration is characterized by progressive, disabling, and incurable neurological disorders with the massive loss of specific neurons. As one of the most promising potential therapeutic strategies for neurodegenerative diseases, stem cell therapy exerts beneficial effects through different mechanisms, such as direct replacement of damaged or lost cells, secretion of neurotrophic and growth factors, decreased neuroinflammation, and activation of endogenous stem cells. However, poor survival and differentiation rates of transplanted stem cells, insufficient homing ability, and difficulty tracking after transplantation limit their further clinical use. The rapid development of nanotechnology provides many promising nanomaterials for biomedical applications, which already have many applications in neurodegenerative disease treatment and seem to be able to compensate for some of the deficiencies in stem cell therapy, such as transport of stem cells/genes/drugs, regulating stem cell differentiation, and real-time tracking in stem cell therapy. Therefore, nanotherapeutic strategies combined with stem cell therapy is a promising therapeutic approach to treating neurodegenerative diseases. The present review systematically summarizes recent advances in stem cell therapeutics and nanotherapeutic strategies and highlights how they can be combined to improve therapeutic efficacy for the treatment of neurodegenerative diseases.

A consolidated review on stem cell therapy for treatment and management of Alzheimer's disease

Alzheimer's disease (AD) is one of the most common forms of dementia and affects around 50 million people around the globe. AD is diagnosed mainly through imaging techniques and to date only five drugs are approved for management of AD but no promising treatment is available for AD. So in this review, we are focusing on stem cell therapy for AD. This review will cover all stem cells like mesenchymal stem cells, embryonic stem cells, induced pluripotent stem cells, and neural stem cells. Clinical trials of AD have also been discussed. Finally, limitations of stem cells are discussed with ongoing clinical trials, and in the future stem cell therapy can be used for treatment of AD.

Adipose tissue-derived stem cells as a potential candidate in treatment of Alzheimer's disease: A systematic review on preclinical studies

In recent years, numerous investigations have evaluated the efficacy of adipose tissue-derived stem cells (ADSCs) and their exosome transplantation in managing Alzheimer's disease (AD) in different animal models. However, there are still many contradictions among the studies that hinder reaching a reliable conclusion. Therefore, we aimed to systematically review the existing evidence regarding the efficacy of ADSCs administration in treatment of AD. The systematic search was conducted in the databases of Medline (via PubMed), Embase, Scopus, and Web of Science, in addition to the manual search in Google and Google scholar, to find articles published until March 13, 2021. Preclinical studies were included and two independent reviewers summarized the eligible papers. Ten articles were included in our review. The treatment strategies varied between isolated ADSC, ADSCs exosomes, ADSCs conditioned medium, and combination therapy (ADSCs plus conditioned medium in one study, and ADSCs plus melatonin in another study). Overview of the included articles showed promising results of ADSCs and its conditioned medium/exosome administration in animal models of AD. These studies showed significant learning and memory improvements through ADSCs and their conditioned medium/exosome administration in animal models of AD. In addition, the application of ADSCs reduced the amyloid-beta plaque deposits in the hippocampus and neocortex of these animals. Based on the aforementioned evidence, studies have suggested potential beneficial effects of ADSCs in the treatment of AD, particularly through decreasing the size of Aβ plaques and improvement of cognitive deficits. Further investigations regarding the subject are encouraged to achieve more accurate conclusions.

The Monkey Head Mushroom and Memory Enhancement in Alzheimer’s Disease

Alzheimer’s disease (AD) is a neurodegenerative disorder, and no effective treatments are available to treat this disorder. Therefore, researchers have been investigating Hericium erinaceus, or the monkey head mushroom, an edible medicinal mushroom, as a possible treatment for AD. In this narrative review, we evaluated six preclinical and three clinical studies of the therapeutic effects of Hericium erinaceus on AD. Preclinical trials have successfully demonstrated that extracts and bioactive compounds of Hericium erinaceus have potential beneficial effects in ameliorating cognitive functioning and behavioral deficits in animal models of AD. A limited number of clinical studies have been conducted and several clinical trials are ongoing, which have thus far shown analogous outcomes to the preclinical studies. Nonetheless, future research on Hericium erinaceus needs to focus on elucidating the specific neuroprotective mechanisms and the target sites in AD. Additionally, standardized treatment parameters and universal regulatory systems need to be established to further ensure treatment safety and efficacy. In conclusion, Hericium erinaceus has therapeutic potential and may facilitate memory enhancement in patients with AD.

Placenta-Derived Mesenchymal-like Adherent Stromal Cells as an Effective Cell Therapy for Cocaine Addiction in a Rat Model

Recent research points to mesenchymal stem cells’ potential for treating neurological disorders, especially drug addiction. We examined the longitudinal effect of placenta-derived mesenchymal stromal-like cells (PLX-PAD) in a rat model for cocaine addiction. Sprague–Dawley male rats were trained to self-administer cocaine or saline daily until stable maintenance. Before the extinction phase, PLX-PAD cells were administered by intracerebroventricular or intranasal routes. Neurogenesis was evaluated, as was behavioral monitoring for craving. We labeled the PLX-PAD cells with gold nanoparticles and followed their longitudinal migration in the brain parallel to their infiltration of essential peripheral organs both by micro-CT and by inductively coupled plasma-optical emission spectrometry. Cell locations in the brain were confirmed by immunohistochemistry. We found that PLX-PAD cells attenuated cocaine-seeking behavior through their capacity to migrate to specific mesolimbic regions, homed on the parenchyma in the dentate gyrus of the hippocampus, and restored neurogenesis. We believe that intranasal cell therapy is a safe and effective approach to treating addiction and may offer a novel and efficient approach to rehabilitation.

Stem Cell Homing in Intrathecal Applications and Inspirations for Improvement Paths

A transplanted stem cell homing is a directed migration from the application site to the targeted tissue. Intrathecal application of stem cells is their direct delivery to cerebrospinal fluid, which defines the homing path from the point of injection to the brain. In the case of neurodegenerative diseases, this application method has the advantage of no blood–brain barrier restriction. However, the homing efficiency still needs improvement and homing mechanisms elucidation. Analysis of current research results on homing mechanisms in the light of intrathecal administration revealed a discrepancy between in vivo and in vitro results and a gap between preclinical and clinical research. Combining the existing research with novel insights from cutting-edge biochips, nano, and other technologies and computational models may bridge this gap faster.

Role of melatonin in Alzheimer's disease: From preclinical studies to novel melatonin-based therapies

Melatonin and novel melatonin-based therapies such as melatonin-containing hybrid molecules, melatonin analogues, and melatonin derivatives have been investigated as potential therapeutics against Alzheimer's disease (AD) pathogenesis. In this review, we examine the developmental trends of melatonin therapies for AD from 1997 to 2021. We then highlight the neuroprotective mechanisms of melatonin therapy derived from preclinical studies. These mechanisms include the alleviation of amyloid-related burden, neurofibrillary tangle accumulation, oxidative stress, neuroinflammation, apoptosis, mitochondrial dysfunction, and impaired neuroplasticity and neurotransmission. We further illustrate the beneficial effects of melatonin on behavior in animal models of AD. Next, we discuss the clinical effects of melatonin on sleep, cognition, behavior, psychiatric symptoms, electroencephalography findings, and molecular biomarkers in patients with mild cognitive impairment and AD. We then explore the effectiveness of novel melatonin-based therapies. Lastly, we discuss the limitations of current melatonin therapies for AD and suggest two emerging research themes for future study.

Hippocampal neurogenesis and pro-neurogenic therapies for Alzheimer's disease

Adult hippocampal neurogenesis (AHN) facilitates hippocampal circuits plasticity and regulates hippocampus-dependent cognition and emotion. However, AHN malfunction has been widely reported in both human and animal models of Alzheimer's disease (AD), the most common form of dementia in the elderly. Pro-neurogenic therapies including rescuing innate AHN, cell engraftment and glia-neuron reprogramming hold great potential for compensating the neuronal loss and rewiring the degenerated neuronal network in AD, but there are still great challenges to be overcome. This review covers recent advances in unraveling the involvement of AHN in AD and highlights the prospect of emerging pro-neurogenic remedies.

Regenerative Neurology and Regenerative Cardiology: Shared Hurdles and Achievements

From the first success in cultivation of cells in vitro, it became clear that developing cell and/or tissue specific cultures would open a myriad of new opportunities for medical research. Expertise in various in vitro models has been developing over decades, so nowadays we benefit from highly specific in vitro systems imitating every organ of the human body. Moreover, obtaining sufficient number of standardized cells allows for cell transplantation approach with the goal of improving the regeneration of injured/disease affected tissue. However, different cell types bring different needs and place various types of hurdles on the path of regenerative neurology and regenerative cardiology. In this review, written by European experts gathered in Cost European action dedicated to neurology and cardiology-Bioneca, we present the experience acquired by working on two rather different organs: the brain and the heart. When taken into account that diseases of these two organs, mostly ischemic in their nature (stroke and heart infarction), bring by far the largest burden of the medical systems around Europe, it is not surprising that in vitro models of nervous and heart muscle tissue were in the focus of biomedical research in the last decades. In this review we describe and discuss hurdles which still impair further progress of regenerative neurology and cardiology and we detect those ones which are common to both fields and some, which are field-specific. With the goal to elucidate strategies which might be shared between regenerative neurology and cardiology we discuss methodological solutions which can help each of the fields to accelerate their development.

Extracellular Vesicles Released from Neprilysin Gene-Modified Human Umbilical Cord-Derived Mesenchymal Stem Cell Enhance Therapeutic Effects in an Alzheimer's Disease Animal Model

Alzheimer's disease (AD) animal studies have reported that mesenchymal stem cells (MSCs) have therapeutic effects; however, clinical trial results are controversial. Neprilysin (NEP) is the main cleavage enzyme of β-amyloid (Aβ), which plays a major role in the pathology and etiology of AD. We evaluated whether transplantation of MSCs with NEP gene modification enhances the therapeutic effects in an AD animal model and then investigated these pathomechanisms. We manufactured NEP gene-enhanced human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) and intravenously transplanted them in Aβ_1-42-injected AD animal models. We compared the differences in behavioral tests and immunohistochemical assays between four groups: normal, Aβ_1-42 injection, naïve hUC-MSCs, and NEP-enhanced hUC-MSCs. Both naïve and NEP-enhanced hUC-MSC groups showed significant improvements in memory compared to the Aβ_1-42 injection group. There was no significant difference between naïve and NEP-enhanced hUC-MSC groups. There was a significant decrease in Congo red, BACE-1, GFAP, and Iba-1 and a significant increase in BDNF, NeuN, and NEP in both hUC-MSC groups compared to the Aβ_1-42 injection group. Among them, BDNF, NeuN, GFAP, Iba-1, and NEP showed more significant changes in the NEP-enhanced hUC-MSC group than in the naïve group. After stem cell injection, stem cells were not found. Extracellular vesicles (EVs) were equally observed in the hippocampus in the naïve and NEP-enhanced hUC-MSC groups. However, the EVs of NEP-enhanced hUC-MSCs contained higher amounts of NEP as compared to the EVs of naïve hUC-MSCs. Thus, hUC-MSCs affect AD animal models through stem cell-released EVs. Although there was no significant difference in cognitive function between the hUC-MSC groups, NEP-enhanced hUC-MSCs had superior neurogenesis and anti-inflammation properties compared to naïve hUC-MSCs due to increased NEP in the hippocampus by enriched NEP-possessing EVs. NEP gene-modified MSCs that release an increased amount of NEP within EVs may be a promising therapeutic option in AD treatment.