Induced pluripotent stem cell-derived neural stem cells: new hope for stroke?

Emerging strategies for nerve repair and regeneration in ischemic stroke: neural stem cell therapy

Ischemic stroke is a major cause of mortality and disability worldwide, with limited treatment options available in clinical practice. The emergence of stem cell therapy has provided new hope to the field of stroke treatment via the restoration of brain neuron function. Exogenous neural stem cells are beneficial not only in cell replacement but also through the bystander effect. Neural stem cells regulate multiple physiological responses, including nerve repair, endogenous regeneration, immune function, and blood-brain barrier permeability, through the secretion of bioactive substances, including extracellular vesicles/exosomes. However, due to the complex microenvironment of ischemic cerebrovascular events and the low survival rate of neural stem cells following transplantation, limitations in the treatment effect remain unresolved. In this paper, we provide a detailed summary of the potential mechanisms of neural stem cell therapy for the treatment of ischemic stroke, review current neural stem cell therapeutic strategies and clinical trial results, and summarize the latest advancements in neural stem cell engineering to improve the survival rate of neural stem cells. We hope that this review could help provide insight into the therapeutic potential of neural stem cells and guide future scientific endeavors on neural stem cells.

Therapeutic role of neural stem cells in neurological diseases

The failure of endogenous repair is the main feature of neurological diseases that cannot recover the damaged tissue and the resulting dysfunction. Currently, the range of treatment options for neurological diseases is limited, and the approved drugs are used to treat neurological diseases, but the therapeutic effect is still not ideal. In recent years, different studies have revealed that neural stem cells (NSCs) have made exciting achievements in the treatment of neurological diseases. NSCs have the potential of self-renewal and differentiation, which shows great foreground as the replacement therapy of endogenous cells in neurological diseases, which broadens a new way of cell therapy. The biological functions of NSCs in the repair of nerve injury include neuroprotection, promoting axonal regeneration and remyelination, secretion of neurotrophic factors, immune regulation, and improve the inflammatory microenvironment of nerve injury. All these reveal that NSCs play an important role in improving the progression of neurological diseases. Therefore, it is of great significance to better understand the functional role of NSCs in the treatment of neurological diseases. In view of this, we comprehensively discussed the application and value of NSCs in neurological diseases as well as the existing problems and challenges.

Stem cell therapy for hepatocellular carcinoma and end-stage liver disease

Hepatocellular carcinoma (HCC) is a major health problem worldwide, especially for patients who are suffering from end-stage liver disease (ESLD). The ESLD is considered a great challenge for clinicians due to the limited chance for liver transplantation, which is the only curative treatment for those patients. Stem cell-based therapy as a part of regenerative medicine represents a promising application for ESLD patients. Many clinical trials were performed to assess the utility of bone marrow-derived stem cells as a potential therapy for patients with liver diseases. The aim of the present study is to present and review the various types of stem cell-based therapy, including the mesenchymal stem cells (MSCs), BM-derived mononuclear cells (BM-MNCs), CD34 + hematopoietic stem cells (HSCs), induced pluripotent stem cells (iPSCs), and cancer stem cells.Though this type of therapy achieved promising results for the treatment of ESLD, however still there is a confounding data regarding its clinical application. A large body of evidence is highly required to evaluate the stem cell-based therapy after long-term follow-up, with respect to the incidence of toxicity, immunogenicity, and tumorigenesis that developed in many patients.

Therapeutic Strategies in Huntington’s Disease: From Genetic Defect to Gene Therapy

Despite the identification of an expanded CAG repeat on exon 1 of the huntingtin gene located on chromosome 1 as the genetic defect causing Huntington’s disease almost 30 years ago, currently approved therapies provide only limited symptomatic relief and do not influence the age of onset or disease progression rate. Research has identified various intricate pathogenic cascades which lead to neuronal degeneration, but therapies interfering with these mechanisms have been marked by many failures and remain to be validated. Exciting new opportunities are opened by the emerging techniques which target the mutant protein DNA and RNA, allowing for “gene editing”. Although some issues relating to “off-target” effects or immune-mediated side effects need to be solved, these strategies, combined with stem cell therapies and more traditional approaches targeting specific pathogenic cascades, such as excitotoxicity and bioavailability of neurotrophic factors, could lead to significant improvement of the outcomes of treated Huntington’s disease patients.

Current and Possible Future Therapeutic Options for Huntington’s Disease

Huntington’s disease (HD) is an autosomal neurodegenerative disease that is characterized by an excessive number of CAG trinucleotide repeats within the huntingtin gene ( HTT). HD patients can present with a variety of symptoms including chorea, behavioural and psychiatric abnormalities and cognitive decline. Each patient has a unique combination of symptoms, and although these can be managed using a range of medications and non-drug treatments there is currently no cure for the disease. Current therapies prescribed for HD can be categorized by the symptom they treat. These categories include chorea medication, antipsychotic medication, antidepressants, mood stabilizing medication as well as non-drug therapies. Fortunately, there are also many new HD therapeutics currently undergoing clinical trials that target the disease at its origin; lowering the levels of mutant huntingtin protein (mHTT). Currently, much attention is being directed to antisense oligonucleotide (ASO) therapies, which bind to pre-RNA or mRNA and can alter protein expression via RNA degradation, blocking translation or splice modulation. Other potential therapies in clinical development include RNA interference (RNAi) therapies, RNA targeting small molecule therapies, stem cell therapies, antibody therapies, non-RNA targeting small molecule therapies and neuroinflammation targeted therapies. Potential therapies in pre-clinical development include Zinc-Finger Protein (ZFP) therapies, transcription activator-like effector nuclease (TALEN) therapies and clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated system (Cas) therapies. This comprehensive review aims to discuss the efficacy of current HD treatments and explore the clinical trial progress of emerging potential HD therapeutics.

Combination of stem cell therapy and acupuncture to treat ischemic stroke: a prospective review

Stroke is the second leading cause globally that leads to severe disability and death. Stem cell therapy has been developed over the recent years to treat stroke and diminish the mortality and disability rate of brain injuries. Acupuncture, which can activate endogenous recovery via physical stimuli, has been applied to enhance the recovery and rehabilitation of stroke patients. Attempts have been made to combine stem cell therapy and acupuncture to treat stroke patients and have shown the promising results. This prospective review will look into the possible mechanisms of stem cell therapy and acupuncture and intend to undercover the potential benefit of the combined therapy. It intends to bridge the modern emerging stem cell therapy and traditional acupuncture at cellular and molecular levels and to demonstrate the potential benefit to improve clinical outcomes.

Neural Stem Cells for Early Ischemic Stroke

Clinical treatments for ischemic stroke are limited. Neural stem cell (NSC) transplantation can be a promising therapy. Clinically, ischemia and subsequent reperfusion lead to extensive neurovascular injury that involves inflammation, disruption of the blood-brain barrier, and brain cell death. NSCs exhibit multiple potentially therapeutic actions against neurovascular injury. Currently, tissue plasminogen activator (tPA) is the only FDA-approved clot-dissolving agent. While tPA’s thrombolytic role within the vasculature is beneficial, tPA’s non-thrombolytic deleterious effects aggravates neurovascular injury, restricting the treatment time window (time-sensitive) and tPA eligibility. Thus, new strategies are needed to mitigate tPA’s detrimental effects and quickly mediate vascular repair after stroke. Up to date, clinical trials focus on the impact of stem cell therapy on neuro-restoration by delivering cells during the chronic stroke stage. Also, NSCs secrete factors that stimulate endogenous repair mechanisms for early-stage ischemic stroke. This review will present an integrated view of the preclinical perspectives of NSC transplantation as a promising treatment for neurovascular injury, with an emphasis on early-stage ischemic stroke. Further, this will highlight the impact of early sub-acute NSC delivery on improving short-term and long-term stroke outcomes.

How Knowledge about Stem Cells Influences Attitudes towards Breastfeeding: Case Study of Polish Women

Maternal breastfeeding is associated with multiple health benefits, both for the child and the mother. Since breastfeeding rates are declining, finding new, future-oriented strategies to strengthen and support mothers' positive attitudes towards breastfeeding need to be developed. In this paper, we describe how information about the presence of stem cells in breast milk can influence the willingness to breastfeed in the population of Polish pregnant women. A cross-sectional study involving a group of 150 pregnant women was conducted to assess the correlation between their knowledge about stem cells and their attitude towards breastfeeding. Among the respondents, only 6% claimed that they did not know anything about stem cells, but general knowledge about stem cells in the research group was poor. The survey results indicated that city residence, university degree, maternal experience and advanced pregnancy correlated with higher general knowledge regarding stem cells. Most respondents (77.3%) had no knowledge regarding the presence of stem cells in breast milk. Approximately two-thirds of mothers with earlier negative breastfeeding experience declared that information about the presence of stem cells in breast milk could have influenced the decision to continue and extend the time of breastfeeding. Hence highlighting the presence of stem cells in breast milk can be used to encourage breastfeeding as a unique activity.

Global trends in clinical trials involving pluripotent stem cells: a systematic multi-database analysis

Pluripotent stem cells (PSCs) hold great potential for novel therapeutic approaches to regenerate or replace functionally impaired tissues. Since the introduction of the induced pluripotent stem cell technology in 2006, the number of scientific publications on this topic has constantly been increasing. However, so far no therapy based on PSCs has found its way into routine clinical use. In this study, we examined research trends related to clinical trials involving PSCs based on data obtained from ClinicalTrials.gov, the ICTRP database from the World Health Organization, as well as from a search of all individual databases that are included in the ICTRP using a multistep search algorithm. Following a stringent inclusion/exclusion procedure 131 studies remained that could be classified as clinical trials involving PSCs. The magnitude of these studies (77.1%) was observational, which implies that no cells were transplanted into patients, and only a minority of studies (22.9%) were of an interventional study type. The number of clinical trials involving induced pluripotent stem cells (iPSCs, 74.8%) was substantially higher than the one involving embryonic stem cells (ESCs, 25.2%). However, the picture changes completely when focusing on interventional studies, where in the majority (73.3%) of cases ESCs were used. Interestingly, also the study duration was significantly shorter for interventional versus observational trials (p = 0.002). When focusing on the geographical study regions, it became obvious that the greatest part of all observational trials was performed in the USA (41.6%) and in France (16.8%), while the magnitude of interventional studies was performed in Asian countries (China 36.7%, Japan 13.3%, South Korea 10.0%) and in the field of ophthalmology. In summary, these results indicate that only a limited number of trials were focusing on the actual transplantation of PSCs into patients in a rather narrow field of diagnoses. The future will tell us, if the iPSC technology will ultimately overcome the current challenges and will finally make its way into routine clinical use.

Neural stem cell therapy for neurovascular injury in Alzheimer's disease

Alzheimer's disease (AD), the most common form of dementia, is characterized by progressive neurodegeneration leading to severe cognitive decline and eventual death. AD pathophysiology is complex, but neurotoxic accumulation of amyloid-β (Aβ) and hyperphosphorylation of Tau are believed to be main drivers of neurodegeneration in AD. The formation and deposition of Aβ plaques occurs in the brain parenchyma as well as in the cerebral vasculature. Thus, proper blood-brain barrier (BBB) and cerebrovascular functioning are crucial for clearance of Aβ from the brain, and neurovascular dysfunction may be a critical component of AD development. Further, neuroinflammation and dysfunction of angiogenesis, neurogenesis, and neurorestorative capabilities play a role in AD pathophysiology. Currently, there is no effective treatment to prevent or restore loss of brain tissue and cognitive decline in patients with AD. Based on multifactorial and complex pathophysiological cascades in multiple Alzheimer's disease stages, effective AD therapies need to focus on targeting early AD pathology and preserving cerebrovascular function. Neural stem cells (NSCs) participate extensively in mammalian brain homeostasis and repair and exhibit pleiotropic intrinsic properties that likely make them attractive candidates for the treatment of AD. In the review, we summarize the current advances in knowledge regarding neurovascular aspects of AD-related neurodegeneration and discuss multiple actions of NSCs from preclinical studies of AD to evaluate their potential for future clinical treatment of AD.

Therapeutic efficacy of intra-arterial administration of induced pluripotent stem cells-derived neural progenitor cells in acute experimental ischemic stroke in rats

Aim. Neural progenitor cells (NPC) are used for the development of cell therapies of neurological diseases. Their stereotaxic transplantation in the middle cerebral artery occlusion (MCAO) model imitating ischemic stroke results in symptom aleviation. However, exploration of less invasive transplantation options is essential, because stereotaxic transplantation is a complex procedure and can be applied to humans only by vital indications in a specialized neurological ward. The aim of the present study was to evaluate the efficacy of cell therapy of the experimental ischemic stroke by the intra-arterial transplantation of NPC.

Materials and methods. NPC for transplantation (IPSC-NPC) were derived by two-stage differentiation of cells of a stable line of human induced pluripotent stem cells. Stroke modeling in rats was carried out by transitory 90 min endovascular MCAO by a silicon-tipped filament. NPC were transplanted 24 hours after MCAO. Repetitive magnetic resonance tomography of experimental animals was made with the Bruker BioSpin ClinScan tomograph with 7 Tl magnetic field induction. Animal survival rate and neurological deficit (using mNSS standard stroke severity scale) were evaluated at the 1st (before IPSC-NPC transplantation), 7th and 14th day after transplantation. Histological studies were carried out following standard protocols.

Results. Intra-arterial transplantation of 7 × 105 IPSC-NPC in 1 ml at a constant 100 l/min rate in case of secured blood flow through the internal carotid artery did not cause brain capillary embolism, additional cytotoxic brain tissue edemas or other complications, while inducing increase of animal survival rate and enhanced revert of the neurological deficit. IPSC-NPC accumulation in brain after intra-arterial infusion was demonstrated. Some cells interacted with the capillary endothelium and probably penetrated through the blood-brain barrier.

Conclusion. Therapeutic efficacy of the systemic, intra-arterial administration of NPC in ischemic stroke has been experimentally proven. A method of secure intra-arterial infusion of cell material into the internal carotid artery middle in rats has been developed and tested.

Stem cells: past, present, and future

In recent years, stem cell therapy has become a very promising and advanced scientific research topic. The development of treatment methods has evoked great expectations. This paper is a review focused on the discovery of different stem cells and the potential therapies based on these cells. The genesis of stem cells is followed by laboratory steps of controlled stem cell culturing and derivation. Quality control and teratoma formation assays are important procedures in assessing the properties of the stem cells tested. Derivation methods and the utilization of culturing media are crucial to set proper environmental conditions for controlled differentiation. Among many types of stem tissue applications, the use of graphene scaffolds and the potential of extracellular vesicle-based therapies require attention due to their versatility. The review is summarized by challenges that stem cell therapy must overcome to be accepted worldwide. A wide variety of possibilities makes this cutting edge therapy a turning point in modern medicine, providing hope for untreatable diseases.

Comparative Analysis of the Effects of Intravenous Administration of Placental Mesenchymal Stromal Cells and Neural Progenitor Cells Derived from Induced Pluripotent Cells on the Course of Acute Ischemic Stroke in Rats

We compared the effects of placental mesenchymal stromal cells and neural progenitor cells derived from induced human pluripotent cells after their intravenous administration to rats in 24 h after transitory occlusion of the middle cerebral artery. The therapeutic effects were evaluated by the dynamics of animal survival, body weight, neurological deficit, and the volume of infarction focus in 7, 14, 30, and 60 days after surgery. Intravenous injection of neural progenitor cells produced a therapeutic effect on the course of experimental ischemic stroke by increasing animal survival in the most acute period and accelerating compensation of neurological deficit and body weight recovery. Neural progenitor cells were more effective than mesenchymal stromal cells from human placenta. The effectiveness of intravenous transplantation of neural progenitor cells in the model of occlusion of the middle cerebral artery is shown by us for the first time, although the therapeutic effect of their direct transplantation into the brain has already been described.

Neural stem cell therapy for subacute and chronic ischemic stroke

Neural stem cells (NSCs) play vital roles in brain homeostasis and exhibit a broad repertoire of potentially therapeutic actions following neurovascular injury. One such injury is stroke, a worldwide leading cause of death and disability. Clinically, extensive injury from ischemic stroke results from ischemia-reperfusion (IR), which is accompanied by inflammation, blood-brain barrier (BBB) damage, neural cell death, and extensive tissue loss. Tissue plasminogen activator (tPA) is still the only US Food and Drug Administration-approved clot-lysing agent. Whereas the thrombolytic role of tPA within the vasculature is beneficial, the effects of tPA (in a non-thrombolytic role) within the brain parenchyma have been reported as harmful. Thus, new therapies are needed to reduce the deleterious side effects of tPA and quickly facilitate vascular repair following stroke. The Stroke Treatment Academic Industry Roundtable (STAIR) recommends that stroke therapies "focus on drugs/devices/treatments with multiple mechanisms of action and that target multiple pathways". Thus, based on multifactorial ischemic cascades in various stroke stages, effective stroke therapies need to focus on targeting and ameliorating early IR injury as well as facilitating angiogenesis, neurogenesis, and neurorestorative mechanisms following stroke. This review will discuss the preclinical perspectives of NSC transplantation as a promising treatment for neurovascular injury and will emphasize both the subacute and chronic phase of ischemic stroke.

Application of Stem Cell Technology in Antiaging and Aging-Related Diseases

Stem cells are one kind of cells that have the potential of proliferation and differentiation. The human beings are originated from a totipotential stem cell-fertilized egg. After birth, the proliferation and differentiation of stem cells contribute to the development and maturation of individual tissues and organs. After maturation, aging is a phases of the life process, the stem cells within the individual's tissues ensure the metabolism of different cells and tissues, such as the hematopoietic stem cells in the bone marrow, which ensure there are still enough red blood cells (RBCs) being responsible for the mission of transporting oxygen after a single RBC has completed its 120-day physiological life cycle. After pathological damage and necrosis occurring on the intestinal epithelial cells or tubular epithelial cells, there will be regenerative epithelial cells continuing to maintain the integrity of the structure and function of the intestine and renal tubules. The role of stem cells in the regeneration and repair of tissues and organs is not only because of the ability of proliferation and differentiation of stem cells but also of the secretion function of stem cells, which secrete various growth factors and cytokines to regulate the tissue microenvironment. For example, mesenchymal stem cells derived from bone marrow are important regulators in bone marrow hematopoietic stem cell niche. Mesenchymal stem cells maintain the "stemness" of hematopoietic stem cells by secreting various cytokines.Aging is a phases of the life process, and all creatures obey this rule of nature. Different organs of the body have different time of entering into aging. Aging is reflected in structural changes and reduced function. Among them, the reduction of regeneration and repair capacity is the main feature of aging. As we age, the aging of stem cells in human tissues is a major cause of the decline in tissue regeneration capacity. Therefore, the elderly's ability of regenerate and repair can be improved by application of advance stem cell technology. It can delay the aging process and treat aged diseases (showed in Fig. 16.1).

Neural Stem Cell-Based Regenerative Approaches for the Treatment of Multiple Sclerosis

Multiple sclerosis (MS) is a chronic, autoimmune, inflammatory, and demyelinating disorder of the central nervous system (CNS), which ultimately leads to axonal loss and permanent neurological disability. Current treatments for MS are largely comprised of medications that are either immunomodulatory or immunosuppressive and are aimed at reducing the frequency and intensity of relapses. Neural stem cells (NSCs) in the adult brain can differentiate into oligodendrocytes in a context-specific manner and are shown to be involved in the remyelination in these patients. NSCs may exert their beneficial effects not only through oligodendrocyte replacement but also by providing trophic support and immunomodulation, a phenomenon now known as "therapeutic plasticity." In this review, we first provided an update on the current knowledge regarding MS pathogenesis and the role of immune cells, microglia, and oligodendrocytes in MS disease progression. Next, we reviewed the current progress on research aimed toward stimulating endogenous NSC proliferation and differentiation to oligodendrocytes in vivo and in animal models of demyelination. In addition, we explored the neuroprotective and immunomodulatory effects of transplanted exogenous NSCs on T cell activation, microglial activation, and endogenous remyelination and their effects on the pathological process and prognosis in animal models of MS. Finally, we examined various protocols to generate genetically engineered NSCs as a potential therapy for MS. Overall, this review highlights the studies involving the immunomodulatory, neurotrophic, and regenerative effects of NSCs and novel methods aiming at stimulating the potential of NSCs for the treatment of MS.

Delayed administration of neural stem cells after hypoxia-ischemia reduces sensorimotor deficits, cerebral lesion size, and neuroinflammation in neonatal mice

BACKGROUND

Hypoxic-ischemic (HI) encephalopathy causes mortality and severe morbidity in neonates. Treatments with a therapeutic window >6 h are currently not available. Here, we explored whether delayed transplantation of allogenic neural stem cells (NSCs) at 10 d after HI could be a tool to repair HI brain injury and improve behavioral impairments.

METHODS

HI was induced in 9-d-old mice. Animals received NSCs or vehicle intracranially in the hippocampus at 10 d post-HI. Sensorimotor performance was assessed by cylinder rearing test. Lesion size, synaptic integrity, and fate of injected NSCs were determined by immuno-stainings. Neuroinflammation was studied by immuno-stainings of brain sections, primary glial cultures, and TNFα ELISA.

RESULTS

NSC transplantation at 10 d post-insult induced long-term improvement of motor performance and synaptic integrity, and reduced lesion size compared to vehicle-treatment. HI-induced neuroinflammation was reduced after NSC treatment, at least partially by factors secreted by NSCs. Injected NSCs migrated toward and localized at the damaged hippocampus. Transplanted NSCs differentiated toward the neuronal lineage and formed a niche with endogenous precursors.

CONCLUSION

Our study provides evidence of the efficacy of NSC transplantation late after HI as a tool to reduce neonatal HI brain injury through regeneration of the lesion.

Transplantation of Induced Pluripotent Stem Cells Alleviates Cerebral Inflammation and Neural Damage in Hemorrhagic Stroke

BACKGROUND

Little is known about the effects of induced pluripotent stem cell (iPSC) treatment on acute cerebral inflammation and injuries after intracerebral hemorrhage (ICH), though they have shown promising therapeutic potentials in ischemic stoke.

METHODS

An ICH model was established by stereotactic injection of collagenase VII into the left striatum of male Sprague-Dawley (SD) rats. Six hours later, ICH rats were randomly divided into two groups and received intracerebrally 10 μl of PBS with or without 1 × 10(6) of iPSCs. Subsequently, neural function of all ICH rats was assessed at days 1, 3, 7, 14, 28 and 42 after ICH. Inflammatory cells, cytokines and neural apoptosis in the rats' perihematomal regions, and brain water content were determined on day 2 or 3 post ICH. iPSC differentiation was determined on day 28 post ICH. Nissl(+) cells and glial fibrillary acidic protein (GFAP)(+) cells in the perihematoma and the survival rates of rats in two groups were determined on post-ICH day 42.

RESULTS

Compared with control animals, iPSCs treatment not only improved neurological function and survival rate, but also resulted in fewer intracephalic infiltrations of neutrophils and microglia, along with decreased interleukin (IL)-1β, IL-6 and tumour necrosis factor-alpha (TNF-α), and increased IL-10 in the perihematomal tissues of ICH rats. Furthermore, brain oedema formation, apoptosis, injured neurons and glial scar formation were decreased in iPSCs-transplanted rats.

CONCLUSIONS

Our findings indicate that iPSCs transplantation attenuate cerebral inflammatory reactions and neural injuries after ICH, and suggests that multiple mechanisms including inflammation modulation, neuroprotection and functional recovery might be involved simultaneously in the therapeutic benefit of iPSC treatment against hemorrhagic stroke.

Stem cell transplantation for treating stroke: status, trends and development

The developing approaches of thrombolytic therapy, endovascular treatment, neuroprotective therapy, and stem cell therapy have enabled breakthroughs in stroke treatment. In this study, we summarize and analyze trends and progress in stem cell transplantation for stroke treatment by retrieval of literature from Thomson Reuters Web of Science database, the NIH Clinical Trial Planning Grant Program, and Clinical Trials Registration Center in North America. In the last 10 years, there has been an increasing number of published articles on stem cell transplantation for stroke treatment. In particular, research from the USA and China has focused on stem cell transplantation. A total of 2,167 articles addressing stem cell transplantation for stroke treatment from 2004 to 2013 were retrieved from the Thomson Reuters Web of Science database. The majority of these articles were from the USA (854, 39.4%), with the journal Stroke publishing the most articles (145, 6.7%). Of the published articles, 143 were funded by the National Institutes of Health (accounting for 6.6% of total publications), and 91 by the National Natural Science Foundation of China. Between 2013 and 2014, the National Institutes of Health provided financial support ($130 million subsidy) for 329 research projects on stroke therapy using stem cell transplantation. In 2014, 215 new projects were approved, receiving grants of up to $70,440,000. Ninety clinical trials focusing on stem cell transplantation for stroke were registered in the Clinical Trial Registration Center in North America, with 40 trials registered in the USA (ranked first place). China had the maximum number of registered research or clinical trials (10 projects).