Intranasal administration of nerve growth factor ameliorate β-amyloid deposition after traumatic brain injury in rats

The Neurovascular Unit as a Locus of Injury in Low-Level Blast-Induced Neurotrauma

Blast-induced neurotrauma has received much attention over the past decade. Vascular injury occurs early following blast exposure. Indeed, in animal models that approximate human mild traumatic brain injury or subclinical blast exposure, vascular pathology can occur in the presence of a normal neuropil, suggesting that the vasculature is particularly vulnerable. Brain endothelial cells and their supporting glial and neuronal elements constitute a neurovascular unit (NVU). Blast injury disrupts gliovascular and neurovascular connections in addition to damaging endothelial cells, basal laminae, smooth muscle cells, and pericytes as well as causing extracellular matrix reorganization. Perivascular pathology becomes associated with phospho-tau accumulation and chronic perivascular inflammation. Disruption of the NVU should impact activity-dependent regulation of cerebral blood flow, blood-brain barrier permeability, and glymphatic flow. Here, we review work in an animal model of low-level blast injury that we have been studying for over a decade. We review work supporting the NVU as a locus of low-level blast injury. We integrate our findings with those from other laboratories studying similar models that collectively suggest that damage to astrocytes and other perivascular cells as well as chronic immune activation play a role in the persistent neurobehavioral changes that follow blast injury.

Lost in Translation: Neurotrophins Biology and Function in the Neurovascular Unit

The neurovascular unit (NVU) refers to the functional building unit of the brain and the retina, where neurons, glia, and microvasculature orchestrate to meet the demand of the retina's and brain's function. Neurotrophins (NTs) are structural families of secreted proteins and are known for exerting neurotrophic effects on neuronal differentiation, survival, neurite outgrowth, synaptic formation, and plasticity. NTs include several molecules, such as nerve growth factor, brain-derived neurotrophic factor, NT-3, NT-4, and their precursors. Furthermore, NTs are involved in signaling pathways such as inflammation, apoptosis, and angiogenesis in a nonneuronal cell type. Interestingly, NTs and the precursors can bind and activate the p75 neurotrophin receptor (p75NTR) at low and high affinity. Mature NTs bind their cognate tropomyosin/tyrosine-regulated kinase receptors, crucial for maintenance and neuronal development in the brain and retina axis. Activation of p75NTR results in neuronal apoptosis and cell death, while tropomysin receptor kinase upregulation contributes to differentiation and cell growth. Recent findings indicate that modulation of NTs and their receptors contribute to neurovascular dysfunction in the NVU. Several chronic metabolic and acute ischemic diseases affect the NVU, including diabetic and ischemic retinopathy for the retina, as well as stroke, acute encephalitis, and traumatic brain injury for the brain. This work aims to review the current evidence through published literature studying the impact of NTs and their receptors, including the p75NTR receptor, on the injured and healthy brain-retina axis.

Intranasal human-recombinant NGF administration improves outcome in children with post-traumatic unresponsive wakefulness syndrome

BACKGROUND

Severe traumatic brain injury (TBI) is one of the most dramatic events in pediatric age and, despite advanced neuro-intensive care, the survival rate of these patients remains low. Children suffering from severe TBI show long-term sequelae, more pronounced in behavioral, neurological and neuropsychological functions leading to, in the most severe cases, an unresponsive wakefulness syndrome (UWS). Currently, no effective treatments can restore neuronal loss or produce significant improvement in these patients. In experimental animal models, human- recombinant Nerve Growth Factor (hr-NGF) promotes neural recovery supporting neuronal growth, differentiation and survival of brain cells and up-regulating the neurogenesis-associated processes. Only a few studies reported the efficacy of intranasal hr-NGF administration in children with post- traumatic UWS.

METHODS

Children with the diagnosis of post-traumatic UWS were enrolled. These patients underwent a treatment with intranasal hr-NGF administration, at a total dose of 50 gamma/kg, three times a day for 7 consecutive days. The treatment schedule was performed for 4 cycles, at one month distance each. Neuroradiogical evaluation by Positron Emission Tomography scan (PET), Single Photon Emission Computed Tomography (SPECT), Electroencephalography (EEG), and Power Spectral Density (PSD) was determined before the treatment and one month after the end. Neurological assessment was also deepened by using modified Ashworth Scale, Gross Motor Function Measure, and Disability Rating Scale.

RESULTS

Three children with post-traumatic UWS were treated. hr-NGF administration improved functional (PET and SPECT) and electrophysiological (EEG and PSD) assessment. Also clinical conditions improved, mainly for the reduction of spasticity and with the acquisition of voluntary movements, facial mimicry, attention and verbal comprehension, ability to cry, cough reflex, oral motility, and feeding capacity, with a significant improvement of their neurological scores. No side effects were reported.

CONCLUSION

These promising results and the ease of administration of this treatment make it worthwhile to be investigated further, mainly in the early stages from severe TBI and in patients with better baseline neurological conditions, to explore more thoroughly the benefits of this new approach on neuronal function recovery after traumatic brain damage.

Combined treatment of nerve growth factor and transcranical direct current stimulations to improve outcome in children with vegetative state after out-of-hospital cardiac arrest

BACKGROUND

Out-of-hospital cardiac arrest (OHCA) is one of the most dramatic events in pediatric age and, despite advanced neurointensive care, the survival rate remains low. Currently, no effective treatments can restore neuronal loss or produce significant improvement in these patients. Nerve Growth Factor (NGF) is a neurotrophin potentially able to counteract many of the deleterious effects triggered by OHCA. Transcranial Direct Current Stimulation (tDCS) has been reported to be neuroprotective in many neurological diseases, such as motor deficit and cognitive impairment. Children with the diagnosis of chronic vegetative state after OHCA were enrolled. These patients underwent a combined treatment of intranasal administration of human recombinant NGF (hr-NGF), at a total dose of 50 gamma/kg, and tDCS, in which current intensity was increased from zero to 2 mA from the first 5 s of stimulation and maintained constant for 20 min. The treatment schedule was performed twice, at one month distance each. Neuroradiogical evaluation with Positron Emission Tomography scan (PET), Single Photon Emission Computed Tomography (SPECT), Electroencephalography (EEG) and Power Spectral Density of the brain (PSD) was determined before the treatment and one month after the end. Neurological assessment was deepened by using modified Ashworth Scale, Gross Motor Function Measure, and Disability Rating Scale.

RESULTS

Three children with a chronic vegetative state secondary to OHCA were treated. The combined treatment with hr-NGF and tDCS improved functional (PET and SPECT) and electrophysiological (EEG and PSD) assessment. Also clinical conditions improved, mainly for the reduction of spasticity and with the acquisition of voluntary finger movements, improved facial mimicry and reaction to painful stimuli. No side effects were reported.

CONCLUSIONS

These promising preliminary results and the ease of administration of this treatment make it worthwhile to be investigated further, mainly in the early stages from OHCA and in patients with better baseline neurological conditions, in order to explore more thoroughly the benefits of this new approach on neuronal function recovery after OHCA.

Neurotrophic Factors as Regenerative Therapy for Neurodegenerative Diseases: Current Status, Challenges and Future Perspectives

Neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), multiple sclerosis (MS), spinal cord injury (SCI), and amyotrophic lateral sclerosis (ALS), are characterized by acute or chronic progressive loss of one or several neuronal subtypes. However, despite their increasing prevalence, little progress has been made in successfully treating these diseases. Research has recently focused on neurotrophic factors (NTFs) as potential regenerative therapy for neurodegenerative diseases. Here, we discuss the current state of knowledge, challenges, and future perspectives of NTFs with a direct regenerative effect in chronic inflammatory and degenerative disorders. Various systems for delivery of NTFs, such as stem and immune cells, viral vectors, and biomaterials, have been applied to deliver exogenous NTFs to the central nervous system, with promising results. The challenges that currently need to be overcome include the amount of NTFs delivered, the invasiveness of the delivery route, the blood-brain barrier permeability, and the occurrence of side effects. Nevertheless, it is important to continue research and develop standards for clinical applications. In addition to the use of single NTFs, the complexity of chronic inflammatory and degenerative diseases may require combination therapies targeting multiple pathways or other possibilities using smaller molecules, such as NTF mimetics, for effective treatment.

Acute intranasal treatment with nerve growth factor limits the onset of traumatic brain injury in young rats

BACKGROUND AND PURPOSE

Traumatic brain injury (TBI) comprises a primary injury directly induced by impact, which progresses into a secondary injury leading to neuroinflammation, reactive astrogliosis, and cognitive and motor damage. To date, treatment of TBI consists solely of palliative therapies that do not prevent and/or limit the outcomes of secondary damage and only stabilize the deficits. The neurotrophin, nerve growth factor (NGF), delivered to the brain parenchyma following intranasal application, could be a useful means of limiting or improving the outcomes of the secondary injury, as suggested by pre-clinical and clinical data.

EXPERIMENTAL APPROACH

We evaluated the effect of acute intranasal treatment of young (20-postnatal day) rats, with NGF in a TBI model (weight drop/close head), aggravated by hypoxic complications. Immediately after the trauma, rats were intranasally treated with human recombinant NGF (50 μg·kg^-1 ), and motor behavioural test, morphometric and biochemical assays were carried out 24 h later.

KEY RESULTS

Acute intranasal NGF prevented the onset of TBI-induced motor disabilities, and decreased reactive astrogliosis, microglial activation and IL-1β content, which after TBI develops to the same extent in the impact zone and the hypothalamus.

CONCLUSION AND IMPLICATIONS

Intranasal application of NGF was effective in decreasing the motor dysfunction and neuroinflammation in the brain of young rats in our model of TBI. This work forms an initial pre-clinical evaluation of the potential of early intranasal NGF treatment in preventing and limiting the disabling outcomes of TBI, a clinical condition that remains one of the unsolved problems of paediatric neurology.

Intranasal Leukemia Inhibitory Factor Attenuates Gliosis and Axonal Injury and Improves Sensorimotor Function After a Mild Pediatric Traumatic Brain Injury

Leukemia inhibitory factor (LIF) is a neuroprotective cytokine that is essential for appropriate glial responses, remyelination, and preservation of neuronal conductance after injury. The intranasal route for delivery of therapeutics to the central nervous system is of particular interest given that it bypasses the blood-brain barrier and peripheral clearance systems. We explored the possibility that LIF might improve neurological function when administered intranasally during the acute phase in a pediatric model of mild traumatic brain injury (mTBI). We tested two doses of LIF and evaluated behavioral outcomes. Here, we show that acute 40-ng intranasal LIF treatment twice a day for 3 days attenuates astrogliosis and microgliosis, protects against axonal damage, significantly improves sensorimotor function, and is well tolerated without detrimental effects on growth. Altogether, our studies provide pre-clinical evidence for the use of acute intranasal LIF treatment as a viable therapeutic for pediatric cases of mTBIs.

Amyloidogenesis and Neurotrophic Dysfunction in Alzheimer’s Disease: Do They have a Common Regulating Pathway?

The amyloid cascade hypothesis has predominately been used to describe the pathogenesis of Alzheimer’s disease (AD) for decades, as Aβ oligomers are thought to be the prime cause of AD. Meanwhile, the neurotrophic factor hypothesis has also been proposed for decades. Accumulating evidence states that the amyloidogenic process and neurotrophic dysfunction are mutually influenced and may coincidently cause the onset and progress of AD. Meanwhile, there are intracellular regulators participating both in the amyloidogenic process and neurotrophic pathways, which might be the common original causes of amyloidogenesis and neurotrophic dysfunction. In this review, the current understanding regarding the role of neurotrophic dysfunction and the amyloidogenic process in AD pathology is briefly summarized. The mutual influence of these two pathogenesis pathways and their potential common causal pathway are further discussed. Therapeutic strategies targeting the common pathways to simultaneously prevent amyloidogenesis and neurotrophic dysfunction might be anticipated for the disease-modifying treatment of AD.

A Narrative Review on Translational Research in Acute Brain Injury

There has been a constant endeavor to reduce the mortality and morbidity associated with acute brain injury. The associated complex mechanisms involving biomechanics, markers, and neuroprotective drugs/measures have been extensively studied in preclinical studies with an ultimate aim to improve the patients' outcomes. Despite such efforts, only few have been successfully translated into clinical practice. In this review, we shall be discussing the major hurdles in the translation of preclinical results into clinical practice. The need is to choose an appropriate animal model, keeping in mind the species, age, and gender of the animal, choosing suitable outcome measures, ensuring quality of animal trials, and carrying out systematic review and meta-analysis of experimental studies before proceeding to human trials. The interdisciplinary collaboration between the preclinical and clinical scientists will help to design better, meaningful trials which might help a long way in successful translation. Although challenging at this stage, the advent of translational precision medicine will help the integration of mechanism-centric translational medicine and patient-centric precision medicine.

Effects of the Notch Signaling Pathway on Secondary Brain Changes Caused by Spinal Cord Injury in Mice

Spinal cord injury (SCI) can cause secondary brain changes, leading to hypomyelination in the dorsolateral prefrontal cortex (dlPFC). Some studies have shown that notch signaling pathway activation can regulate oligodendrocyte maturation and myelination. The aim of this study was to investigate whether inhibition of the Notch signaling pathway can alleviate hypomyelination in the dlPFC caused by SCI. Moreover, we further investigated whether the changes in myelination in the dlPFC are associated with neuropathic pain following SCI. We established a mouse model of SCI and observed the changes in mechanical and thermal hyperalgesia. Western blotting and immunofluorescence were used to analyze the changes in myelination in the dlPFC. The results indicated the existence of a relationship between activation of the Notch signaling pathway and hypomyelination in the dlPFC and confirmed the existence of a relationship between hypomyelination in the dlPFC and decreases in mechanical and thermal hyperalgesia thresholds. In conclusion, these results suggested that the Notch signaling pathway is activated after SCI, leading to hypomyelination in the dlPFC, and that DAPT can inhibit the Notch signaling pathway and improve mechanical and thermal hyperalgesia thresholds. Our findings provide a new target for the treatment of neuropathic pain caused by SCI.

Intranasal neprilysin rapidly eliminates amyloid-beta plaques, but causes plaque compensations: the explanation why the amyloid-beta cascade may fail?

Neurodegenerative brain disorders are a major burden in our society, such as Alzheimer´s disease. In order to repair or prevent such diseases, drugs are designed which enter the brain, but the blood-brain barrier limits their entry and the search for alternative pathways is important. Recently, we reported that intranasal delivery of the amyloid-beta degrading enzyme neprilysin eliminated amyloid-beta plaques in transgenic Alzheimer´s disease mice. This review describes the anatomical structure of the intranasal pathway, explains the intranasal delivery of pure neprilysin, cell-loaded neprilysin (platelets) and collagen-embedded neprilysin to destruct amyloid-beta plaques in Alzheimer´s disease in transgenic APP_SweDI mice and hypothesizes why this may cause compensation and why the amyloid-beta cascade hypothesis may fail.

Intranasal Delivery of Nerve Growth Factor in Neurodegenerative Diseases and Neurotrauma

Since the 1980s, the development of a pharmacology based on nerve growth factor (NGF) has been postulated for the therapy of Alzheimer’s disease (AD). This hypothesis was based on the rescuing effect of the neurotrophin on the cholinergic phenotype of the basal forebrain neurons, primarily compromised during the development of AD. Subsequently, the use of NGF was put forward to treat a broader spectrum of neurological conditions affecting the central nervous system, such as Parkinson’s disease, degenerative retinopathies, severe brain traumas and neurodevelopmental dysfunctions. While supported by solid rational assumptions, the progress of a pharmacology founded on these hypotheses has been hampered by the difficulty of conveying NGF towards the brain parenchyma without resorting to invasive and risky delivery methods. At the end of the last century, it was shown that NGF administered intranasally to the olfactory epithelium was able to spread into the brain parenchyma. Notably, after such delivery, pharmacologically relevant concentration of exogenous NGF was found in brain areas located at considerable distances from the injection site along the rostral-caudal axis. These observations paved the way for preclinical characterization and clinical trials on the efficacy of intranasal NGF for the treatment of neurodegenerative diseases and of the consequences of brain trauma. In this review, a summary of the preclinical and clinical studies published to date will be attempted, as well as a discussion about the mechanisms underlying the efficacy and the possible development of the pharmacology based on intranasal conveyance of NGF to the brain.

Current knowledge and challenges associated with targeted delivery of neurotrophic factors into the central nervous system: focus on available approaches

During the last decades, numerous basic and clinical studies have been conducted to assess the delivery efficiency of therapeutic agents into the brain and spinal cord parenchyma using several administration routes. Among conventional and in-progress administrative routes, the eligibility of stem cells, viral vectors, and biomaterial systems have been shown in the delivery of NTFs. Despite these manifold advances, the close association between the delivery system and regeneration outcome remains unclear. Herein, we aimed to discuss recent progress in the delivery of these factors and the pros and cons related to each modality.

Repetitive low-level blast exposure improves behavioral deficits and chronically lowers Aβ42 in an Alzheimer's disease transgenic mouse model

Public awareness of traumatic brain injury (TBI) in the military increased recently because of the conflicts in Iraq and Afghanistan where blast injury was the most common mechanism of injury. Besides overt injuries, concerns also exist over the potential adverse consequences of subclinical blast exposures, which are common for many service members. TBI is a risk factor for the later development of neurodegenerative diseases, including Alzheimer's disease (AD)-like disorders. Studies of acute TBI in humans and animals have suggested that increased processing of the amyloid precursor protein (APP) towards the amyloid beta protein (Aβ) may explain the epidemiological associations with AD. However, in a prior study we found in both rat and mouse models of blast overpressure exposure (BOP), that rather than increasing, rodent brain Aβ42 levels were decreased following acute blast exposure. Here we subjected APP/presenilin 1 transgenic mice (APP/PS1 Tg) to an extended sequence of repetitive low-level blast exposures (34.5 kPa) administered three times per week over 8 weeks. If initiated at 20 weeks of age, these repetitive exposures, which were designed to mimic human subclinical blast exposures, reduced anxiety and improved cognition as well as social interactions in APP/PS1 Tg mice, returning many behavioral parameters in APP/PS1 Tg mice to levels of non-transgenic wild type mice. Repetitive low-level blast exposure was less effective at improving behavioral deficits in APP/PS1 Tg mice when begun at 36 weeks of age. While amyloid plaque loads were unchanged, Aβ42 levels and Aβ oligomers were reduced in brain of mice exposed to repetitive low-level blast exposures initiated at 20 weeks of age, although levels did not directly correlate with behavioral parameters in individual animals. These results have implications for understanding the nature of blast effects on the brain and their relationship to human neurodegenerative diseases.

Intranasal Delivery of Collagen-Loaded Neprilysin Clears Beta-Amyloid Plaques in a Transgenic Alzheimer Mouse Model

Alzheimer’s disease (AD) is pathologically characterized by extracellular beta-amyloid (Aβ) plaques and intraneuronal tau tangles in the brain. A therapeutic strategy aims to prevent or clear these Aβ plaques and the Aβ-degrading enzyme neprilysin is a potent drug to degrade plaques. The major challenge is to deliver bioactive neprilysin into the brain via the blood-brain barrier. The aim of the present study is to explore if intranasal delivery of neprilysin can eliminate plaques in a transgenic AD mouse model (APP_SweDI). We will test if collagen or platelets are useful vehicles to deliver neprilysin into the brain. Using organotypic brain slices from adult transgenic APP_SweDI mice, we show that neprilysin alone or loaded in collagen hydrogels or in platelets cleared cortical plaques. Intransasal delivery of neprilysin alone increased small Aβ depositions in the middle and caudal cortex in transgenic mice. Platelets loaded with neprilysin cleared plaques in the frontal cortex after intranasal application. Intranasal delivery of collagen-loaded neprilysin was very potent to clear plaques especially in the middle and caudal parts of the cortex. Our data support that the Aβ degrading enzyme neprilysin delivered to the mouse brain can clear Aβ plaques and intranasal delivery (especially with collagen as a vehicle) is a fast and easy application. However, it must be considered that intranasal neprilysin may also activate more plaque production in the transgenic mouse brain as a side effect.

Topical delivery of nerve growth factor for treatment of ocular and brain disorders

Neurotrophins are a family of proteins that support neuronal proliferation, survival, and differentiation in the central and peripheral nervous systems, and are regulators of neuronal plasticity. Nerve growth factor is one of the best-described neurotrophins and has advanced to clinical trials for treatment of ocular and brain diseases due to its trophic and regenerative properties. Prior trials over the past few decades have produced conflicting results, which have principally been ascribed to adverse effects of systemic nerve growth factor administration, together with poor penetrance of the blood-brain barrier that impairs drug delivery. Contrastingly, recent studies have revealed that topical ocular and intranasal nerve growth factor administration are safe and effective, suggesting that topical nerve growth factor delivery is a potential alternative to both systemic and invasive intracerebral delivery. The therapeutic effects of local nerve growth factor delivery have been extensively investigated for different ophthalmic diseases, including neurotrophic keratitis, glaucoma, retinitis pigmentosa, and dry eye disease. Further, promising pharmacologic effects were reported in an optic glioma model, which indicated that topically administered nerve growth factor diffused far beyond where it was topically applied. These findings support the therapeutic potential of delivering topical nerve growth factor preparations intranasally for acquired and degenerative brain disorders. Preliminary clinical findings in both traumatic and non-traumatic acquired brain injuries are encouraging, especially in pediatric patients, and clinical trials are ongoing. The present review will focus on the therapeutic effects of both ocular and intranasal nerve growth factor delivery for diseases of the brain and eye.

Management of Traumatic Brain Injury: From Present to Future

TBI (traumatic brain injury) is a major cause of death among youth in industrialized societies. Brain damage following traumatic injury is a result of direct and indirect mechanisms; indirect or secondary injury involves the initiation of an acute inflammatory response, including the breakdown of the blood–brain barrier (BBB), brain edema, infiltration of peripheral blood cells, and activation of resident immunocompetent cells, as well as the release of numerous immune mediators such as interleukins and chemotactic factors. TBI can cause changes in molecular signaling and cellular functions and structures, in addition to tissue damage, such as hemorrhage, diffuse axonal damages, and contusions. TBI typically disturbs brain functions such as executive actions, cognitive grade, attention, memory data processing, and language abilities. Animal models have been developed to reproduce the different features of human TBI, better understand its pathophysiology, and discover potential new treatments. For many years, the first approach to manage TBI has been treatment of the injured tissue with interventions designed to reduce the complex secondary-injury cascade. Several studies in the literature have stressed the importance of more closely examining injuries, including endothelial, microglia, astroglia, oligodendroglia, and precursor cells. Significant effort has been invested in developing neuroprotective agents. The aim of this work is to review TBI pathophysiology and existing and potential new therapeutic strategies in the management of inflammatory events and behavioral deficits associated with TBI.

Proneurotrophins Induce Apoptotic Neuronal Death After Controlled Cortical Impact Injury in Adult Mice

The p75 neurotrophin receptor (p75NTR) can regulate multiple cellular functions including proliferation, survival, and apoptotic cell death. The p75NTR is widely expressed in the developing brain and is downregulated as the nervous system matures, with only a few neuronal subpopulations retaining expression into adulthood. However, p75NTR expression is induced following damage to the adult brain, including after traumatic brain injury, which is a leading cause of mortality and disability worldwide. A major consequence of traumatic brain injury is the progressive neuronal loss that continues secondary to the initial trauma, which ultimately contributes to cognitive decline. Understanding mechanisms governing this progressive neuronal death is key to developing targeted therapeutic strategies to provide neuroprotection and salvage cognitive function. In this study, we demonstrate that a cortical impact injury to the sensorimotor cortex elicits p75NTR expression in apoptotic neurons in the injury penumbra, confirming previous studies. To establish whether preventing p75NTR induction or blocking the ligands would reduce the extent of secondary neuronal cell death, we used a noninvasive intranasal strategy to deliver either siRNA to block the induction of p75NTR, or function-blocking antibodies to the ligands pro-nerve growth factor and pro-brain-derived neurotrophic factor. We demonstrate that either preventing the induction of p75NTR or blocking the proneurotrophin ligands provides neuroprotection and preserves sensorimotor function.

Subchronic Pathobiological Response Following Chronic Repetitive Mild Traumatic Brain Injury in an Aged Preclinical Model of Amyloid Pathogenesis

Repetitive mild traumatic brain injury (r-mTBI) is a risk factor for Alzheimer disease (AD). The precise nature of how r-mTBI leads to, or precipitates, AD pathogenesis remains unclear. In this study, we explore subchronic effects of chronic r-mTBI (12-impacts) administered over 1-month in aged-PS1/APP mice and littermate controls. We investigate specific mechanisms that may elucidate the molecular link between AD and r-mTBI, focusing primarily on amyloid and tau pathology, amyloid processing, glial activation states, and associated clearance mechanisms. Herein, we demonstrate r-mTBI in aged PS1/APP mice does not augment, glial activation, amyloid burden, or tau pathology (with exception of pS202-positive Tau) 1 month after exposure to the last-injury. However, we observed a decrease in brain soluble Aβ42 levels without any appreciable change in peripheral soluble Aβ42 levels. This was accompanied by an increase in brain insoluble to soluble Aβ42 ratio in injured PS1/APP mice compared with sham injury. A parallel reduction in phagocytic receptor, triggering receptor expressed on myeloid cells 2, was also observed. This study demonstrates very subtle subchronic effects of r-mTBI on a preexisting amyloid pathology background, which may be on a continuum toward a slow and worsening neurodegenerative outcome compared with sham injury, and therefore, have many implications, especially in the elderly population exposed to TBI.

Traumatic Brain Injury by Weight-Drop Method Causes Transient Amyloid-β Deposition and Acute Cognitive Deficits in Mice

There has been growing awareness of the correlation between an episode of traumatic brain injury (TBI) and the development of Alzheimer's disease (AD) later in life. It has been reported that TBI accelerated amyloid-β (Aβ) pathology and cognitive decline in the several lines of AD model mice. However, the short-term and long-term effects of TBI by the weight-drop method on amyloid-β pathology and cognitive performance are unclear in wild-type (WT) mice. Hence, we examined AD-related histopathological changes and cognitive impairment after TBI in wild-type C57BL6J mice. Five- to seven-month-old WT mice were subjected to either TBI by the weight-drop method or a sham treatment. Seven days after TBI, the WT mice exhibited significantly lower spatial learning than the sham-treated WT mice. However, 28 days after TBI, the cognitive impairment in the TBI-treated WT mice recovered. Correspondingly, while significant amyloid-β (Aβ) plaques and amyloid precursor protein (APP) accumulation were observed in the TBI-treated mouse hippocampus 7 days after TBI, the Aβ deposition was no longer apparent 28 days after TBI. Thus, TBI induced transient amyloid-β deposition and acute cognitive impairments in the WT mice. The present study suggests that the TBI could be a risk factor for acute cognitive impairment even when genetic and hereditary predispositions are not involved. The system might be useful for evaluating and developing a pharmacological treatment for the acute cognitive deficits.

The delayed protective effect of GK-2, а dipeptide mimetic of Nerve Growth Factor, in a model of rat traumatic brain injury

The delayed protective effect of GK-2, a dipeptide mimetic of Nerve Growth Factor, was investigated on the model of focal one-sided traumatic brain injury (TBI) of the sensorimotor cortex region on the 180th day after the injury. TBI caused a reliably disruption of the functions of the limbs contralateral to injury focus. The intraperitoneal administration of GK-2 (1 mg/kg) from 1st to 4th and from 7th to 10th days after TBI reduced the impairment of the motor functions of the limbs. This therapeutic effect significant manifested itself from the 7th day and continued until the end of the experiment - on the 180th day after TBI. Morphological studies of the animal brains on the 180th day after TBI demonstrated a decrease in the number of neurons in the V layer of the cerebral cortex and a decrease in the thickness of the corpus callosum. The treatment of animals with GK-2 after TBI statistically significant prevented a decrease in the density of neurons in the ipsilateral hemisphere and a decrease in the thickness of the corpus callosum in the contralateral hemisphere in comparison with untreated animals. Additionally, we showed in vitro that GK-2 exhibits neuroprotective properties under oxidative stress in primary hippocampal cultures. Our results demonstrate that the use of GK-2 at the early stages of development of traumatic brain damage can prevent such delayed damage as neuronal and axonal degeneration as well as reduce TBI-related disruptions of brain functions.

Nerve Growth Factor: Early Studies and Recent Clinical Trials

Since its discovery, nerve growth factor (NGF) has long occupied a critical role in developmental and adult neurobiology for its many important regulatory functions on the survival, growth and differentiation of nerve cells in the peripheral and central nervous system. NGF is the first discovered member of a family of neurotrophic factors, collectively indicated as neurotrophins, (which include brain-derived neurotrophic factor, neurotrophin-3 and neurotrophin 4/5). NGF was discovered for its action on the survival and differentiation of selected populations of peripheral neurons. Since then, an enormous number of basic and human studies were undertaken to explore the role of purified NGF to prevent the death of NGF-receptive cells. These studies revealed that NGF possesses important therapeutic properties, after topical administration, on human cutaneous pressure ulcer, corneal ulcers, glaucoma, retinal maculopathy, Retinitis Pigmentosa and in pediatric optic gliomas and brain traumas. The aim of this review is to present our previous, recent and ongoing clinical studies on the therapeutic properties of NGF.

Gambogic amide, a selective TrkA agonist, does not improve outcomes from traumatic brain injury in mice

OBJECTIVES

There is evidence that treatment with nerve growth factor (NGF) may reduce neuroinflammation and apoptosis after a traumatic brain injury (TBI). NGF is thought to exert its effects via binding to either TrkA or p75 neurotrophin receptors. This study aimed to investigate the effects of a selective TrkA agonist, gambogic amide (GA), on TBI pathology and outcomes in mice following lateral fluid percussion injury.

METHODS

Male C57BL/6 mice were given either a TBI or sham injury, and then received subcutaneous injections of either 2 mg/kg of GA or vehicle at 1, 24, and 48 h post-injury. Following behavioural studies, mice were euthanized at 72 h post-injury for analysis of neuroinflammatory, apoptotic, and neurite outgrowth markers.

RESULTS

Behavioural testing revealed that GA did not mitigate motor deficits after TBI. TBI caused an increase in cortical and hippocampal expression of several markers of neuroinflammation and apoptosis compared to sham groups. GA treatment did not attenuate these increases in expression, possibly contributed to by our finding of TrkA receptor down-regulation post-TBI.

CONCLUSIONS

These findings suggest that GA treatment may not be suitable for attenuating TBI pathology and improving outcomes.

Nose-to-brain peptide delivery - The potential of nanotechnology

Nose-to-brain (N-to-B) delivery offers to protein and peptide drugs the possibility to reach the brain in a non-invasive way. This article is a comprehensive review of the state-of-the-art of this emerging peptide delivery route, as well as of the challenges associated to it. Emphasis is given on the potential of nanosized drug delivery carriers to enhance the direct N-to-B transport of protein or peptide drugs. In particular, polymer- and lipid- based nanocarriers are comparatively analyzed in terms of the influence of their physicochemical characteristics and composition on their in vivo fate and efficacy. The use of biorecognitive ligands and permeation enhancers in order to enhance their brain targeting efficiency is also discussed. The article concludes highlighting the early stage of this research field and its still unveiled potential. The final message is that more explicatory PK/PD studies are required in order to achieve the translation from preclinical to the clinical development phase.

Neurotrauma: The Crosstalk between Neurotrophins and Inflammation in the Acutely Injured Brain

Traumatic brain injury (TBI) is a major cause of morbidity and mortality among young individuals worldwide. Understanding the pathophysiology of neurotrauma is crucial for the development of more effective therapeutic strategies. After the trauma occurs, immediate neurologic damage is produced by the traumatic forces; this primary injury triggers a secondary wave of biochemical cascades together with metabolic and cellular changes, called secondary neural injury. In the scenario of the acutely injured brain, the ongoing secondary injury results in ischemia and edema culminating in an uncontrollable increase in intracranial pressure. These areas of secondary injury progression, or areas of “traumatic penumbra”, represent crucial targets for therapeutic interventions. Neurotrophins are a class of signaling molecules that promote survival and/or maintenance of neurons. They also stimulate axonal growth, synaptic plasticity, and neurotransmitter synthesis and release. Therefore, this review focuses on the role of neurotrophins in the acute post-injury response. Here, we discuss possible endogenous neuroprotective mechanisms of neurotrophins in the prevailing environment surrounding the injured areas, and highlight the crosstalk between neurotrophins and inflammation with focus on neurovascular unit cells, particularly pericytes. The perspective is that neurotrophins may represent promising targets for research on neuroprotective and neurorestorative processes in the short-term following TBI.

Pathophysiology Associated with Traumatic Brain Injury: Current Treatments and Potential Novel Therapeutics

Traumatic brain injury (TBI) is one of the leading causes of death of young people in the developed world. In the United States alone, 1.7 million traumatic events occur annually accounting for 50,000 deaths. The etiology of TBI includes traffic accidents, falls, gunshot wounds, sports, and combat-related events. TBI severity ranges from mild to severe. TBI can induce subtle changes in molecular signaling, alterations in cellular structure and function, and/or primary tissue injury, such as contusion, hemorrhage, and diffuse axonal injury. TBI results in blood-brain barrier (BBB) damage and leakage, which allows for increased extravasation of immune cells (i.e., increased neuroinflammation). BBB dysfunction and impaired homeostasis contribute to secondary injury that occurs from hours to days to months after the initial trauma. This delayed nature of the secondary injury suggests a potential therapeutic window. The focus of this article is on the (1) pathophysiology of TBI and (2) potential therapies that include biologics (stem cells, gene therapy, peptides), pharmacological (anti-inflammatory, antiepileptic, progrowth), and noninvasive (exercise, transcranial magnetic stimulation). In final, the review briefly discusses membrane/lipid rafts (MLR) and the MLR-associated protein caveolin (Cav). Interventions that increase Cav-1, MLR formation, and MLR recruitment of growth-promoting signaling components may augment the efficacy of pharmacologic agents or already existing endogenous neurotransmitters and neurotrophins that converge upon progrowth signaling cascades resulting in improved neuronal function after injury.

P2X1 Receptor-Mediated Ca2+ Influx Triggered by DA-9801 Potentiates Nerve Growth Factor-Induced Neurite Outgrowth

Nerve growth factor (NGF)-induced neuronal regeneration has emerged as a strategy to treat neuronal degeneration-associated disorders. However, direct NGF administration is limited by the occurrence of adverse effects at high doses of NGF. Therefore, development of a therapeutic strategy to promote the NGF trophic effect is required. In view of the lack of understanding of the mechanism for potentiating the NGF effect, this study investigated molecular targets of DA-9801, a well-standardized Dioscorea rhizome extract, which has a promoting effect on NGF. An increase in intracellular calcium ion level was induced by DA-9801, and chelation of extracellular calcium ions with ethylene-bis(oxyethylenenitrilo)tetraacetic acid (EGTA) suppressed the potentiating effect of DA-9801 on NGF-induced neurite outgrowth. In addition, EGTA treatment reduced the DA-9801-induced phosphorylation of extracellular signal-regulated kinase1/2 (ERK1/2), the major mediators of neurite outgrowth. To find which calcium ion-permeable channel contributes to the calcium ion influx induced by DA-9801, we treated PC12 cells with various inhibitors of calcium ion-permeable channels. NF449, a P2X1 receptor selective antagonist, significantly abolished the potentiating effect of DA-9801 on NGF-induced neurite outgrowth and abrogated the DA-9801-induced ERK1/2 phosphorylation. In addition, transfection with siRNA of P2X1 receptor significantly reduced the DA-9801-enhanced neurite outgrowth. In conclusion, calcium ion influx through P2X1 receptor mediated the promoting effect of DA-9801 on NGF-induced neurite outgrowth via ERK1/2 phosphorylation.

Permeability and distribution of nerve growth factor in the brain of neonatal rats by periphery venous injection in hypoxic-ischemic state

Objective

To investigate the permeability of β-NGF through blood–brain-barrier (BBB) in neonatal and adult rats, and the spatial distribution of β-NGF in different brain regions in hypoxic-ischemic (HI) and normal neonatal rats.

Methods

To investigate the overall permeability of β-NGF through BBB, β-NGF labeled with I¹²⁵ was injected into adult rats, neonatal rats and HI neonatal rats via tail vein. The radioactivity of brain tissue and blood was examined and analyzed 30 min after injection. Also, brain regions including the basal forebrain, frontal cortex, hippocampus, hypothalamus, cerebellum, bulbus olfactorius and hypophysis, of all the rats were dissected and radioactivity was examined to investigate the spatial specificity of NGF permeation through BBB.

Results

Statistically significant results were observed in I¹²⁵-β-NGF contents in brain tissues of adult rats group, neonatal rats group and HI neonatal rats group (P < 0.05). Compared to the HI neonatal rats’ brain with the highest I¹²⁵-β-NGF contents, normal neonatal rats ranks the second while the adult rats were the lowest. While for the spatial specificity examination part, I¹²⁵-β-NGF in both HI group and control group were widely distributed in basal forebrain, frontal cortex, hippocampus, cerebellum and bulbus olfactorius. But the radioactivity in frontal cortex, hippocampus and cerebellum of HI groups are statistically higher than control groups (P < 0.05).

Conclusion

β-NGF can more easily penetrate the BBB of newborn rats than adult rats via peripheral venous administration and this effect can be enhanced by HI insult. Also, this HI-induced permeation of β-NGF through BBB is more obvious in frontal cortex, hippocampus and cerebellum.

Pumping the Brakes: Neurotrophic Factors for the Prevention of Cognitive Impairment and Dementia after Traumatic Brain Injury

Traumatic brain injury (TBI) is the leading cause of disability and death worldwide, affecting as many as 54,000,000-60,000,000 people annually. TBI is associated with significant impairments in brain function, impacting cognitive, emotional, behavioral, and physical functioning. Although much previous research has focused on the impairment immediately following injury, TBI may have much longer-lasting consequences, including neuropsychiatric disorders and cognitive impairment. TBI, even mild brain injury, has also been recognized as a significant risk factor for the later development of dementia and Alzheimer's disease. Although the link between TBI and dementia is currently unknown, several proposed mechanisms have been put forward, including alterations in glucose metabolism, excitotoxicity, calcium influx, mitochondrial dysfunction, oxidative stress, and neuroinflammation. A treatment for the devastating long-term consequences of TBI is desperately needed. Unfortunately, however, no such treatment is currently available, making this a major area of unmet medical need. Increasing the level of neurotrophic factor expression in key brain areas may be one potential therapeutic strategy. Of the neurotrophic factors, granulocyte-colony stimulating factor (G-CSF) may be particularly effective for preventing the emergence of long-term complications of TBI, including dementia, because of its ability to reduce apoptosis, stimulate neurogenesis, and increase neuroplasticity.

Selective and differential interactions of BNN27, a novel C17-spiroepoxy steroid derivative, with TrkA receptors, regulating neuronal survival and differentiation

Nerve growth factor (NGF) holds a pivotal role in brain development and maintenance, been also involved in the pathophysiology of neurodegenerative diseases. Here, we provide evidence that a novel C17-spiroepoxy steroid derivative, BNN27, specifically interacts with and activates the TrkA receptor of NGF, inducing phosphorylation of TrkA tyrosine residues and down-stream neuronal survival-related kinase signaling. Additionally, BNN27 potentiates the efficacy of low levels of NGF, by facilitating its binding to the TrkA receptors and differentially inducing fast return of internalized TrkA receptors into neuronal cell membranes. Furthermore, BNN27 synergizes with NGF in promoting axonal outgrowth, effectively rescues from apoptosis NGF-dependent and TrkA positive sympathetic and sensory neurons, in vitro, ex vivo and in vivo in NGF null mice. Interestingly, BNN27 does not possess the hyperalgesic properties of NGF. BNN27 represents a lead molecule for the development of neuroprotective TrkA receptor agonists, with potential therapeutic applications in neurodegenerative diseases and in brain trauma.

Cerebral amyloid-β accumulation and deposition following traumatic brain injury--A narrative review and meta-analysis of animal studies

Traumatic brain injury (TBI) increases the risk of neurodegenerative disorders many years post-injury. However, molecular mechanisms underlying the relationship between TBI and neurodegenerative diseases, such as Alzheimer's disease (AD), remain to be elucidated. Nevertheless, previous studies have demonstrated a link between TBI and increased amyloid-β (Aβ), a protein involved in AD pathogenesis. Here, we review animal studies that measured Aβ levels following TBI. In addition, from a pool of initially identified 1209 published papers, we examined data from 19 eligible animal model studies using a meta-analytic approach. We found an acute increase in cerebral Aβ levels ranging from 24h to one month following TBI (overall log OR=2.97 ± 0.40, p<0.001). These findings may contribute to further understanding the relationship between TBI and future dementia risk. The methodological inconsistencies of the studies discussed in this review suggest the need for improved and more standardised data collection and study design, in order to properly elucidate the role of TBI in the expression and accumulation of Aβ.

C6 Glioma-Secreted NGF and FGF2 Regulate Neuronal APP Processing Through Up-Regulation of ADAM10 and Down-Regulation of BACE1, Respectively

Excessive accumulation of amyloid-β (Aβ) caused by cleavage of amyloid precursor protein (APP) is thought to be the primary cause of Alzheimer's disease (AD). Two key enzymes ADAM10 and BACE1 are involved in the initial cleavage of APP, resulting in the onset of two pathways, the amyloidogenic pathway and the non-amyloidogenic pathway, respectively. Altering APP metabolism towards the non-amyloidogenic pathway is thought to reduce Aβ production. It has been reported that, in vivo, exogenous neurotrophic factors make APP apt to entering the non-amyloidogenic pathway. Since astrocytes secrete a battery of neurotrophic factors, we investigated the role of astrocyte-derived factors in the dynamics of Aβ generation in neural cells. Results show that C6 glioma cell-conditioned medium (GCM), obtained from cultured astrocyte-derived C6 glioma cells, inhibit Aβ1-42 production and shift APP processing towards the non-amyloidogenic pathway in APPswe-HEK293 cells. Such effect is attributed to two key APP cleavage enzymes, ADAM10 and BACE1. Two neurotrophic factors in the GCM, nerve growth factor and fibroblast growth factor 2, are responsible for the up-regulation of ADAM10 and down-regulation of BACE1, respectively. Our findings enhance our understanding of the relationship between astrocytes and Aβ generation, indicating that stimulation of astrocytic neurotrophic factors could slow AD progression.

Correlation of mechanical impact responses and biomarker levels: A new model for biomarker evaluation in TBI

A modified Marmarou impact acceleration model was used to help screen biomarkers to assess brain injury severity. Anesthetized male Sprague-Dawley rats were subjected to a closed head injury from 1.25, 1.75 and 2.25 m drop heights. Linear and angular responses of the head were measured in vivo. 24h after impact, cerebrospinal fluid (CSF) and serum were collected. CSF and serum levels of phosphorylated neurofilament heavy (pNF-H), glial fibrillary acidic protein (GFAP), interleukin 6 (IL-6), and amyloid beta (Aβ) 1-42 were assessed by enzyme-linked immunosorbent assay (ELISA). Compared to controls, significantly higher CSF and serum pNF-H levels were observed in all impact groups, except between 1.25 m and control in serum. Furthermore, CSF and serum pNF-H levels were significantly different between the impact groups. For GFAP, both CSF and serum levels were significantly higher at 2.25 m compared to 1.75 m, 1.25 m and controls. There was no significant difference in CSF and serum GFAP levels between 1.75 m and 1.25 m, although both groups were significantly higher than control. TBI rats also showed significantly higher levels of IL-6 versus control in both CSF and serum, but no significant difference was observed between each impact group. Levels of Aβ were not significantly different between groups. Pearson's correlation analysis showed pNF-H and GFAP levels in CSF and serum had positive correlation with power (rate of impact energy), followed by average linear acceleration and surface righting (p<0.01), which were good predictors for traumatic axonal injury according to histologic assessment in our previous study, suggesting that they are directly related to the injury mechanism. The model used in this study showed a unique ability in elucidating the relationship between biomarker levels and severity of the mechanical trauma to the brain.

Intranasal administration of human umbilical cord mesenchymal stem cells-conditioned medium enhances vascular remodeling after stroke

Stem cell-based treatments have been reported to be a potential strategy for stroke. However, tumorigenic potential and low survival rates of transplanted cells could attenuate the efficacy of the stem cell-based treatments. The application of stem cell-condition medium (CM) may be a practicable approach to conquer these limitations. In this study, we investigated whether intranasal administration of human umbilical cord mesenchymal stem cells (hUCMSCs)-CM has the therapeutic effects in rats after stroke. Adult male rats were subjected to middle cerebral artery occlusion (MCAo) and were treated by intranasal routine with or without hUCMSCs-CM (1 ml/kg/d), starting 24h after MCAo and daily for 14 days. Neurological functional tests, blood brain barrier (BBB) leakage, were measured. Angiogenesis and angiogenic factor expression were measured by immunohistochemistry, and Western blot, respectively. hUCMSCs-CM treatment of stroke by intranasal routine starting 24h after MCAo in rats significantly enhances BBB functional integrity and promotes functional outcome but does not decrease lesion volume compared to rats in DMEM/F12 medium control group and saline control group. Treatment of ischemic rats with hUCMSCs-CM by intranasal routine also significantly decreases the levels of Ang2 and increases the levels of both Ang1 and Tie2 in the ischemic brain. To take together, increased expression of Ang1 and Tie2 and decreased expression of Ang2, induced by hUCMSCs-CM treatment, contribute to vascular remodeling in the ischemic brain which plays an important role in functional outcome after stroke.

Beneficial effects of hyperbaric oxygen on edema in rat hippocampus following traumatic brain injury

Hyperbaric oxygen (HBO) therapy helps alleviate secondary injury following brain trauma [traumatic brain injury (TBI)], although the mechanisms remain unclear. In this study, we assessed recovery of post-TBI spatial learning and memory in rats using the Morris water maze (MWM) and measured changes in apparent diffusion coefficient in the hippocampus by diffusion-weighted imaging (DWI) to evaluate possible therapeutic effects of HBO on TBI-associated brain edema. DWIs were obtained 8, 24, 48 h, 7 days, and 14 days post-TBI. Daily HBO therapy significantly improved post-TBI MWM performance and reduced edema in the ipsilateral hippocampus, suggesting that the therapeutic efficacy of HBO is mediated, at least in part, by a reduction in brain edema.

Intranasal gene delivery for treating Parkinson's disease: overcoming the blood-brain barrier

INTRODUCTION

Developing a disease-modifying gene therapy for Parkinson's disease (PD) has been a high priority for over a decade. However, due to the inability of large biomolecules to cross the blood-brain barrier (BBB), the only means of delivery to the brain has been intracerebral infusion. Intranasal administration offers a non-surgical means of bypassing the BBB to deliver neurotrophic factors, and the genes encoding them, directly to the brain.

AREAS COVERED

This review summarizes: i) evidence demonstrating intranasal delivery to the brain of a number of biomolecules having therapeutic potential for various CNS disorders; and ii) evidence demonstrating neuroprotective efficacy of a subset of biomolecules specifically for PD. The intersection of these two spheres represents the area of opportunity for development of new intranasal gene therapies for PD. To that end, our laboratory showed that intranasal administration of glial cell line-derived neurotrophic factor (GDNF), or plasmid DNA nanoparticles encoding GDNF, provides neuroprotection in a rat model of PD, and that the cells transfected by the nanoparticle vector are likely to be pericytes.

EXPERT OPINION

A number of genes encoding neurotrophic factors have therapeutic potential for PD, but few have been tested by the intranasal route and shown to be neuroprotective in a model of PD. Intranasal delivery provides a largely unexplored, promising approach for development of a non-invasive gene therapy for PD.

Low-frequency transcranial magnetic stimulation is beneficial for enhancing synaptic plasticity in the aging brain

In the aging brain, cognitive function gradually declines and causes a progressive reduction in the structural and functional plasticity of the hippocampus. Transcranial magnetic stimulation is an emerging and novel neurological and psychiatric tool used to investigate the neurobiology of cognitive function. Recent studies have demonstrated that low-frequency transcranial magnetic stimulation (≤1 Hz) ameliorates synaptic plasticity and spatial cognitive deficits in learning-impaired mice. However, the mechanisms by which this treatment improves these deficits during normal aging are still unknown. Therefore, the current study investigated the effects of transcranial magnetic stimulation on the brain-derived neurotrophic factor signal pathway, synaptic protein markers, and spatial memory behavior in the hippocampus of normal aged mice. The study also investigated the downstream regulator, Fyn kinase, and the downstream effectors, synaptophysin and growth-associated protein 43 (both synaptic markers), to determine the possible mechanisms by which transcranial magnetic stimulation regulates cognitive capacity. Transcranial magnetic stimulation with low intensity (110% average resting motor threshold intensity, 1 Hz) increased mRNA and protein levels of brain-derived neurotrophic factor, tropomyosin receptor kinase B, and Fyn in the hippocampus of aged mice. The treatment also upregulated the mRNA and protein expression of synaptophysin and growth-associated protein 43 in the hippocampus of these mice. In conclusion, brain-derived neurotrophic factor signaling may play an important role in sustaining and regulating structural synaptic plasticity induced by transcranial magnetic stimulation in the hippocampus of aging mice, and Fyn may be critical during this regulation. These responses may change the structural plasticity of the aging hippocampus, thereby improving cognitive function.

Investigational agents for treatment of traumatic brain injury

INTRODUCTION

Traumatic brain injury (TBI) is a major cause of death and disability worldwide. To date, there are no pharmacologic agents proven to improve outcomes from TBI because all the Phase III clinical trials in TBI have failed. Thus, there is a compelling need to develop treatments for TBI.

AREAS COVERED

The following article provides an overview of select cell-based and pharmacological therapies under early development for the treatment of TBI. These therapies seek to enhance cognitive and neurological functional recovery through neuroprotective and neurorestorative strategies.

EXPERT OPINION

TBI elicits both complex degenerative and regenerative tissue responses in the brain. TBI can lead to cognitive, behavioral, and motor deficits. Although numerous promising neuroprotective treatment options have emerged from preclinical studies that mainly target the lesion, translation of preclinical effective neuroprotective drugs to clinical trials has proven challenging. Accumulating evidence indicates that the mammalian brain has a significant, albeit limited, capacity for both structural and functional plasticity, as well as regeneration essential for spontaneous functional recovery after injury. A new therapeutic approach is to stimulate neurovascular remodeling by enhancing angiogenesis, neurogenesis, oligodendrogenesis, and axonal sprouting, which in concert, may improve neurological functional recovery after TBI.

Environmental enrichment aides in functional recovery following unilateral controlled cortical impact of the forelimb sensorimotor area however intranasal administration of nerve growth factor does not

PURPOSE

An injury to the forelimb sensorimotor cortex results in the impairment of motor function in animals. Recent research has suggested that intranasal administration of nerve growth factor (NGF), a protein naturally found in the brain, and placement into enriched environments (EE) improves motor and cognitive function after traumatic brain injury (TBI). The purpose of this study was to determine whether NGF, EE, or the combination of both was beneficial in the recovery of motor function following TBI.

RESULTS

Uninjured animals had fewer foot faults than injured animals, displaying a lesion effect. Injured animals housed in EE were shown to have fewer foot faults whether or not they received NGF. Injured animals also displayed an increased reliance on the non-impaired limb further validating a lesion effect.

CONCLUSION

EE is an effective treatment on the recovery of motor function after a TBI. Intranasal administration of NGF was found to not be an effective treatment for functional motor recovery after a TBI.

Anti-diabetes drug pioglitazone ameliorates synaptic defects in AD transgenic mice by inhibiting cyclin-dependent kinase5 activity

Cyclin-dependent kinase 5 (Cdk5) is a serine/threonine kinase that is activated by the neuron specific activators p35/p39 and plays many important roles in neuronal development. However, aberrant activation of Cdk5 is believed to be associated with the pathogenesis of several neurodegenerative diseases, including Alzheimer's disease (AD) and Parkinson's disease (PD). Here in the present study, enhanced Cdk5 activity was observed in mouse models of AD; whereas soluble amyloid-β oligomers (Aβ), which contribute to synaptic failures during AD pathogenesis, induced Cdk5 hyperactivation in cultured hippocampal neurons. Inhibition of Cdk5 activity by pharmacological or genetic approaches reversed dendritic spine loss caused by soluble amyloid-β oligomers (Aβ) treatment. Interestingly, we found that the anti-diabetes drug pioglitazone could inhibit Cdk5 activity by decreasing p35 protein level. More importantly, pioglitazone treatment corrected long-term potentiation (LTP) deficit caused by Aβ exposure in cultured slices and pioglitazone administration rescued impaired LTP and spatial memory in AD mouse models. Taken together, our study describes an unanticipated role of pioglitazone in alleviating AD and reveals a potential therapeutic drug for AD curing.

Brain Uptake of Neurotherapeutics after Intranasal versus Intraperitoneal Delivery in Mice

There is a growing global prevalence of neurodegenerative diseases such as Alzheimer's disease and dementia. Current treatment for neurodegenerative diseases is limited due to the blood brain barrier's ability to restrict the entry of therapeutics to the brain. In that context, direct delivery of drugs from nose to brain has gained emerging interest as an important alternative to oral and parenteral routes of administration. Although there are considerable reports showing promising results after intranasal drug delivery in various disease-models and investigatory human clinical trials, there are very few studies showing a detailed pharmacokinetics with regard to the uptake and retention of intranasally delivered material(s) within specific brain regions, which are critical determining factors for dosing conditions and optimal treatment regimen. This investigation compared a time-dependent brain uptake and resident time of various radiolabeled candidate neurotherapeutics after a single bolus intranasal or intraperitoneal administration in mice. Results indicate that the brain uptake of intranasally delivered therapeutic(s) is > 5 times greater than that after intraperitoneal delivery. The peak uptake and resident time of all intranasally delivered test therapeutics for all brain regions is observed to be between 30min-12h, depending upon the distance of brain region from the site of administration, followed by gradual fading of radioactive counts by 24h post intranasal administration. Current study confirms the usefulness of intranasal administration as a non- invasive and efficient means of delivering therapeutics to the brain to treat neurodegenerative diseases including Alzheimer's disease.

Effects of low-level blast exposure on the nervous system: is there really a controversy?

High-pressure blast waves can cause extensive CNS injury in human beings. However, in combat settings, such as Iraq and Afghanistan, lower level exposures associated with mild traumatic brain injury (mTBI) or subclinical exposure have been much more common. Yet controversy exists concerning what traits can be attributed to low-level blast, in large part due to the difficulty of distinguishing blast-related mTBI from post-traumatic stress disorder (PTSD). We describe how TBI is defined in human beings and the problems posed in using current definitions to recognize blast-related mTBI. We next consider the problem of applying definitions of human mTBI to animal models, in particular that TBI severity in human beings is defined in relation to alteration of consciousness at the time of injury, which typically cannot be assessed in animals. However, based on outcome assessments, a condition of "low-level" blast exposure can be defined in animals that likely approximates human mTBI or subclinical exposure. We review blast injury modeling in animals noting that inconsistencies in experimental approach have contributed to uncertainty over the effects of low-level blast. Yet, animal studies show that low-level blast pressure waves are transmitted to the brain. In brain, low-level blast exposures cause behavioral, biochemical, pathological, and physiological effects on the nervous system including the induction of PTSD-related behavioral traits in the absence of a psychological stressor. We review the relationship of blast exposure to chronic neurodegenerative diseases noting the paradoxical lowering of Abeta by blast, which along with other observations suggest that blast-related TBI is pathophysiologically distinct from non-blast TBI. Human neuroimaging studies show that blast-related mTBI is associated with a variety of chronic effects that are unlikely to be explained by co-morbid PTSD. We conclude that abundant evidence supports low-level blast as having long-term effects on the nervous system.

Adipokines: a link between obesity and dementia?

Being overweight or obese, as measured with body-mass index or central adiposity (waist circumference), and the trajectory of body-mass index over the life course have been associated with brain atrophy, white matter changes, disturbances of blood-brain barrier integrity, and risk of all-cause late-onset dementia and Alzheimer's disease. This observation leads us to question what it is about body-mass index that is associated with health of the brain and dementia risk. If high body-mass index and central adiposity represent an increase in adipose tissue, then the endocrine function of adipose tissue, mediated by adipose tissue hormones and adipokines, could be a clue to mechanisms that underlie the association with dementia and Alzheimer's disease. Hundreds of adipokines have been identified, creating a complexity that is a challenge to simplify. Nonetheless, adipokines are being investigated in association with clinical dementia outcomes, and with imaging-based measures of brain volume, structure, and function in human beings and in preclinical models of clinical dementia.