Blood-brain barrier penetration and in vivo activity of an NGF conjugate

Mechanistic insights into the potential role of dietary polyphenols and their nanoformulation in the management of Alzheimer's disease

Alzheimer's disease (AD) is a very common neurodegenerative disorder associated with memory loss and a progressive decline in cognitive activity. The two major pathophysiological factors responsible for AD are amyloid plaques (comprising amyloid-beta aggregates) and neurofibrillary tangles (consisting of hyperphosphorylated tau protein). Polyphenols, a class of naturally occurring compounds, are immensely beneficial for the treatment or management of various disorders and illnesses. Naturally occurring sources of polyphenols include plants and plant-based foods, such as fruits, herbs, tea, vegetables, coffee, red wine, and dark chocolate. Polyphenols have unique properties, such as being the major source of anti-oxidants and possessing anti-aging and anti-cancerous properties. Currently, dietary polyphenols have become a potential therapeutic approach for the management of AD, depending on various research findings. Dietary polyphenols can be an effective strategy to tackle multifactorial events that occur with AD. For instance, naturally occurring polyphenols have been reported to exhibit neuroprotection by modulating the Aβ biogenesis pathway in AD. Many nanoformulations have been established to enhance the bioavailability of polyphenols, with nanonization being the most promising. This review comprehensively provides mechanistic insights into the neuroprotective potential of dietary polyphenols in treating AD. It also reviews the usability of dietary polyphenol as nanoformulation for AD treatment.

Recent Advances in Delivery of Peptide and Protein Therapeutics to the Brain

The classes of neuropharmaceuticals known as proteins and peptides serve as diagnostic tools and are involved in specific communication in the peripheral and central nervous systems. However, due to tight junctions resembling epithelial cells found in the blood-brain barrier (BBB) in vivo, they are typically excluded from transport from the blood to the brain. The drugs having molecular weight of less than 400 Dalton are able to cross the BBB via lipid-mediated free diffusion. However, large molecule therapeutics are devoid of these characteristics. As an alternative, these substances may be carried via chimeric peptide drug delivery systems, and assist in transcytosis through BBB with the aid of linker strategies. With their recent developments, several forms of nanoparticles, including poly (ethylene glycol)-poly(ε-caprolactone) copolymers, nanogels, liposomes, nanostructured lipid carriers, poly (D, L-lactide-co-glycolide) nanoparticles, chitosan, and solid lipid nanoparticles, have also been considered for their therapeutic applications. Moreover, the necessity for physiologic optimization of current drug delivery methods and their carriers to deliver therapeutic doses of medication into the brain for the treatment of various neurologic illnesses has also been emphasized. Therapeutic use of proteins and peptides has no neuroprotective impact in the absence of all these methods. Each tactic, however, has unique drawbacks and considerations. In this review, we discuss different drug delivery methods for therapeutic distribution of pharmaceuticals, primarily neuroproteins and neuropeptides, through endothelial capillaries via blood-brain barrier. Finally, we have also discussed the challenges and future perspective of protein and peptide therapeutics delivery to the brain. SIGNIFICANCE STATEMENT: Very few reports on the delivery of therapeutic protein and peptide nanoformulations are available in the literature. Herein, we attempted to discuss these nanoformulations of protein and peptide therapeutics used to treat brain diseases.

BBB-PEP-prediction: improved computational model for identification of blood-brain barrier peptides using blending position relative composition specific features and ensemble modeling

BBPs have the potential to facilitate the delivery of drugs to the brain, opening up new avenues for the development of treatments targeting diseases of the central nervous system (CNS). The obstacle faced in central nervous system disorders stems from the formidable task of traversing the blood-brain barrier (BBB) for pharmaceutical agents. Nearly 98% of small molecule-based drugs and nearly 100% of large molecule-based drugs encounter difficulties in successfully penetrating the BBB. This importance leads to identification of these peptides, can help in healthcare systems. In this study, we proposed an improved intelligent computational model BBB-PEP-Prediction for identification of BBB peptides. Position and statistical moments based features have been computed for acquired benchmark dataset. Four types of ensembles such as bagging, boosting, stacking and blending have been utilized in the methodology section. Bagging employed Random Forest (RF) and Extra Trees (ET), Boosting utilizes XGBoost (XGB) and Light Gradient Boosting Machine (LGBM). Stacking uses ET and XGB as base learners, blending exploited LGBM and RF as base learners, while Logistic Regression (LR) has been applied as Meta learner for stacking and blending. Three classifiers such as LGBM, XGB and ET have been optimized by using Randomized search CV. Four types of testing such as self-consistency, independent set, cross-validation with 5 and 10 folds and jackknife test have been employed. Evaluation metrics such as Accuracy (ACC), Specificity (SPE), Sensitivity (SEN), Mathew's correlation coefficient (MCC) have been utilized. The stacking of classifiers has shown best results in almost each testing. The stacking results for independent set testing exhibits accuracy, specificity, sensitivity and MCC score of 0.824, 0.911, 0.831 and 0.663 respectively. The proposed model BBB-PEP-Prediction shown superlative performance as compared to previous benchmark studies. The proposed system helps in future research and research community for in-silico identification of BBB peptides.

Treatment of Parkinson's disease with biologics that penetrate the blood-brain barrier via receptor-mediated transport

Parkinson's disease (PD) is characterized by neurodegeneration of nigral-striatal neurons in parallel with the formation of intra-neuronal α-synuclein aggregates, and these processes are exacerbated by neuro-inflammation. All 3 components of PD pathology are potentially treatable with biologics. Neurotrophins, such as glial derived neurotrophic factor or erythropoietin, can promote neural repair. Therapeutic antibodies can lead to disaggregation of α-synuclein neuronal inclusions. Decoy receptors can block the activity of pro-inflammatory cytokines in brain. However, these biologic drugs do not cross the blood-brain barrier (BBB). Biologics can be made transportable through the BBB following the re-engineering of the biologic as an IgG fusion protein, where the IgG domain targets an endogenous receptor-mediated transcytosis (RMT) system within the BBB, such as the insulin receptor or transferrin receptor. The receptor-specific antibody domain of the fusion protein acts as a molecular Trojan horse to ferry the biologic into brain via the BBB RMT pathway. This review describes the re-engineering of all 3 classes of biologics (neurotrophins, decoy receptor, therapeutic antibodies) for BBB delivery and treatment of PD. Targeting the RMT pathway at the BBB also enables non-viral gene therapy of PD using lipid nanoparticles (LNP) encapsulated with plasmid DNA encoding therapeutic genes. The surface of the lipid nanoparticle is conjugated with a receptor-specific IgG that triggers RMT of the LNP across the BBB in vivo.

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

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

Receptor-mediated drug delivery of bispecific therapeutic antibodies through the blood-brain barrier

Therapeutic antibody drug development is a rapidly growing sector of the pharmaceutical industry. However, antibody drug development for the brain is a technical challenge, and therapeutic antibodies for the central nervous system account for ~3% of all such agents. The principal obstacle to antibody drug development for brain or spinal cord is the lack of transport of large molecule biologics across the blood-brain barrier (BBB). Therapeutic antibodies can be made transportable through the blood-brain barrier by the re-engineering of the therapeutic antibody as a BBB-penetrating bispecific antibody (BSA). One arm of the BSA is the therapeutic antibody and the other arm of the BSA is a transporting antibody. The transporting antibody targets an exofacial epitope on a BBB receptor, and this enables receptor-mediated transcytosis (RMT) of the BSA across the BBB. Following BBB transport, the therapeutic antibody then engages the target receptor in brain. RMT systems at the BBB that are potential conduits to the brain include the insulin receptor (IR), the transferrin receptor (TfR), the insulin-like growth factor receptor (IGFR) and the leptin receptor. Therapeutic antibodies have been re-engineered as BSAs that target the insulin receptor, TfR, or IGFR RMT systems at the BBB for the treatment of Alzheimer's disease and Parkinson's disease.

Transferrin receptor 1 targeted nanomedicine for brain tumor therapy

Achieving effective drug delivery to traverse the blood-brain barrier (BBB) and target tumor cells remains the greatest challenge for brain tumor therapy. Importantly, the overexpressed membrane receptors on the brain endothelial cells, especially transferrin receptor 1 (TfR1), which mediate their ligands/antibodies to overcome the BBB by transcytosis, have been emerging as promising targets for brain tumor therapy. By employing ligands (e.g., transferrin, H-ferritin), antibodies or targeting peptides of TfR1 or aptamers, various functional nano-formulations have been developed in the last decade. These agents showed great potential for the treatment of brain diseases due to their ideal size, high loading capacity, controlled drug release and suitable pharmacokinetics. Herein, we summarize the latest advances on TfR1-targeted nanomedicine for brain tumor therapy. Moreover, we also discuss the strategies of improving stability, targeting ability and accumulation of nano-formulations in brain tumors for better outcomes. In this review, we hope to provide inspiration for the rational design of TfR1-targeted nanomedicine against brain tumors.

Lessons from the Cerebrospinal Fluid Analysis of HTLV-1-Infected Individuals: Biomarkers of Inflammation for HAM/TSP Development

HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is a neurodegenerative disease that leads to motor impairment due to a chronic inflammatory process in the central nervous system (CNS). However, the HAM/TSP pathogenesis is not completely clear, and biomarkers to define the disease prognosis are still necessary. Thus, we aimed to identify biomarkers for HAM/TSP and potential mechanisms involved in disease development. To that end, the concentrations of VILIP-1, BDNF, VEGF, β-NGF, TGF-β1, fractalkine/CX3CL1, IL-6, IL-18, and TNF-α, and the soluble forms of TREM-1, TREM-2, and RAGE, were assessed using a multiplex bead-based immunoassay in paired cerebrospinal fluid (CSF) and serum samples from HAM/TSP patients (n = 20), asymptomatic HTLV-1 carriers (AC) (n = 13), and HTLV-1-seronegative individuals (n = 9), with the results analyzed according to the speed of HAM/TSP progression. HAM/TSP patients had elevated fractalkine in the serum but not in the CSF, particularly those with low neuroinflammatory activity (CSF/serum ratio of neopterin <1 and of CXCL10 < 2). HAM/TSP patients with normal CSF levels of neurofilament light chain (NfL) showed elevated β-NGF in serum, and serum BDNF levels were increased in HTLV-1-infected individuals, particularly in HTLV-1 AC. Both HTLV-1 AC and HAM/TSP patients had lower TGF-β1 levels in CSF compared to uninfected individuals, and HAM/TSP patients with active CNS inflammation showed higher CSF levels of IL-18, which correlated with markers of inflammation, neuronal death, and blood−brain-barrier permeability. Although none of the factors evaluated were associated with the speed of HAM/TSP progression, reduced TGF-β1 levels in CSF suggest that suppressive responses to control subclinical and/or active neurodegeneration are impaired, while increased CSF IL-18 indicates the involvement of inflammasome-mediated mechanisms in HAM/TSP development.

A Historical Review of Brain Drug Delivery

The history of brain drug delivery is reviewed beginning with the first demonstration, in 1914, that a drug for syphilis, salvarsan, did not enter the brain, due to the presence of a blood-brain barrier (BBB). Owing to restricted transport across the BBB, FDA-approved drugs for the CNS have been generally limited to lipid-soluble small molecules. Drugs that do not cross the BBB can be re-engineered for transport on endogenous BBB carrier-mediated transport and receptor-mediated transport systems, which were identified during the 1970s-1980s. By the 1990s, a multitude of brain drug delivery technologies emerged, including trans-cranial delivery, CSF delivery, BBB disruption, lipid carriers, prodrugs, stem cells, exosomes, nanoparticles, gene therapy, and biologics. The advantages and limitations of each of these brain drug delivery technologies are critically reviewed.

A Microglial Function for the Nerve Growth Factor: Predictions of the Unpredictable

Microglia are the only immune cell population present in the brain parenchyma. Their vantage position in the central nervous system (CNS) enables these myeloid cells to perform the most disparate of tasks: from the classical immune functions of fighting infections and surveilling the extracellular space for pathogens and damage, to sculpting the neuronal circuitry by pruning unnecessary synapses and assisting neurons in spine formation, aiding in the maintenance of brain homeostasis. The neurotrophin field has always been dominated by the neurocentric view that the primary target of these molecules must be neurons: this holds true even for the Nerve Growth Factor (NGF), which owes its popularity in the neuroscience community to its trophic and tropic activity towards sensory and sympathetic neurons in the peripheral nervous system, and cholinergic neurons in the CNS. The increasing evidence that microglia are an integral part of neuronal computation calls for a closer look as to whether these glial cells are capable of responding directly to NGF. In this review, we will first outline evidence in support of a role for NGF as a molecule mediating neuroimmune communication. Then, we will illustrate some of those non-immune features that have made microglial cells one of the hottest topics of this last decade. In conclusion, we will discuss evidence in support of a microglial function for NGF.

Current Chemical, Biological, and Physiological Views in the Development of Successful Brain-Targeted Pharmaceutics

One of the greatest challenges with successful pharmaceutical treatments of central nervous system (CNS) diseases is the delivery of drugs into their target sites with appropriate concentrations. For example, the physically tight blood-brain barrier (BBB) effectively blocks compounds from penetrating into the brain, also by the action of metabolizing enzymes and efflux transport mechanisms. However, many endogenous compounds, including both smaller compounds and macromolecules, like amino acids, sugars, vitamins, nucleosides, hormones, steroids, and electrolytes, have their peculiar internalization routes across the BBB. These delivery mechanisms, namely carrier-mediated transport and receptor-mediated transcytosis have been utilized to some extent in brain-targeted drug development. The incomplete knowledge of the BBB and the smaller than a desirable number of chemical tools have hindered the development of successful brain-targeted pharmaceutics. This review discusses the recent advancements achieved in the field from the point of medicinal chemistry view and discusses how brain drug delivery can be improved in the future.

A Review of Techniques for Biodelivery of Nerve Growth Factor (NGF) to the Brain in Relation to Alzheimer's Disease

Age-dependent progressive neurodegeneration and associated cognitive dysfunction represent a serious concern worldwide. Currently, dementia accounts for the fifth highest cause of death, among which Alzheimer's disease (AD) represents more than 60% of the cases. AD is associated with progressive cognitive dysfunction which affects daily life of the affected individual and associated family. The cognitive dysfunctions are at least partially due to the degeneration of a specific set of neurons (cholinergic neurons) whose cell bodies are situated in the basal forebrain region (basal forebrain cholinergic neurons, BFCNs) but innervate wide areas of the brain. It has been explicitly shown that the delivery of the neurotrophic protein nerve growth factor (NGF) can rescue BFCNs and restore cognitive dysfunction, making NGF interesting as a potential therapeutic substance for AD. Unfortunately, NGF cannot pass through the blood-brain barrier (BBB) and thus peripheral administration of NGF protein is not viable therapeutically. NGF must be delivered in a way which will allow its brain penetration and availability to the BFCNs to modulate BFCN activity and viability. Over the past few decades, various methodologies have been developed to deliver NGF to the brain tissue. In this chapter, NGF delivery methods are discussed in the context of AD.

Neuromodulation for Cognitive Disorders: In Search of Lazarus?

Alzheimer's disease (AD) and other forms of dementia can have a large impact on patients, their families, and for the society as a whole. Current medical treatments have not shown enough potential in treating or altering the course of the disease. Deep brain stimulation (DBS) has shown great neuromodulatory potential in Parkinson's disease, and there is a growing body of evidence for justifying its use in cognitive disorders. At the same time there is mounting interest at less invasive and alternative modes of neuromodulation for the treatment of AD. This manuscript is a brief review of the infrastructure of memory, the current understanding of the pathophysiology of AD, and the body of preclinical and clinical evidence for noninvasive and invasive neuromodulation modalities for the treatment of cognitive disorders and AD in particular.

A Neurotrophic Mechanism Directs Sensory Nerve Transit in Cranial Bone

The flat bones of the skull are densely innervated during development, but little is known regarding their role during repair. We describe a neurotrophic mechanism that directs sensory nerve transit in the mouse calvaria. Patent cranial suture mesenchyme represents an NGF (nerve growth factor)-rich domain, in which sensory nerves transit. Experimental calvarial injury upregulates Ngf in an IL-1β/TNF-α-rich defect niche, with consequent axonal ingrowth. In calvarial osteoblasts, IL-1β and TNF-α stimulate Ngf and downstream NF-κB signaling. Locoregional deletion of Ngf delays defect site re-innervation and blunted repair. Genetic disruption of Ngf among LysM-expressing macrophages phenocopies these observations, whereas conditional knockout of Ngf among Pdgfra-expressing cells does not. Finally, inhibition of TrkA catalytic activity similarly delays re-innervation and repair. These results demonstrate an essential role of NGF-TrkA signaling in bone healing and implicate macrophage-derived NGF-induced ingrowth of skeletal sensory nerves as an important mediator of this repair.

Treating brain diseases using systemic parenterally-administered protein therapeutics: Dysfunction of the brain barriers and potential strategies

The parenteral administration of protein therapeutics is increasingly gaining importance for the treatment of human diseases. However, the presence of practically impermeable blood-brain barriers greatly restricts access of such pharmaceutics to the brain. Treating brain disorders with proteins thus remains a great challenge, and the slow clinical translation of these therapeutics may be largely ascribed to the lack of appropriate brain delivery system. Exploring new approaches to deliver proteins to the brain by circumventing physiological barriers is thus of great interest. Moreover, parallel advances in the molecular neurosciences are important for better characterizing blood-brain interfaces, particularly under different pathological conditions (e.g., stroke, multiple sclerosis, Parkinson's disease, and Alzheimer's disease). This review presents the current state of knowledge of the structure and the function of the main physiological barriers of the brain, the mechanisms of transport across these interfaces, as well as alterations to these concomitant with brain disorders. Further, the different strategies to promote protein delivery into the brain are presented, including the use of molecular Trojan horses, the formulation of nanosystems conjugated/loaded with proteins, protein-engineering technologies, the conjugation of proteins to polymers, and the modulation of intercellular junctions. Additionally, therapeutic approaches for brain diseases that do not involve targeting to the brain are presented (i.e., sink and scavenging mechanisms).

Stimuli-Responsive Delivery of Growth Factors for Tissue Engineering

Growth factors (GFs) play a crucial role in directing stem cell behavior and transmitting information between different cell populations for tissue regeneration. However, their utility as therapeutics is limited by their short half-life within the physiological microenvironment and significant side effects caused by off-target effects or improper dosage. "Smart" materials that can not only sustain therapeutic delivery over a treatment period but also facilitate on-demand release upon activation are attracting significant interest in the field of GF delivery for tissue engineering. Three properties are essential in engineering these "smart" materials: 1) the cargo vehicle protects the encapsulated therapeutic; 2) release is targeted to the site of injury; 3) cargo release can be modulated by disease-specific stimuli. The aim of this review is to summarize the current research on stimuli-responsive materials as intelligent vehicles for controlled GF delivery; Five main subfields of tissue engineering are discussed: skin, bone and cartilage, muscle, blood vessel, and nerve. Challenges in achieving such "smart" materials and perspectives on future applications of stimuli-responsive GF delivery for tissue regeneration are also discussed.

Vascularized neural constructs for ex-vivo reconstitution of blood-brain barrier function

Ex-vivo blood-brain barrier (BBB) model is of great value for studying brain function and drug development, but it is still challenging to engineer macroscale three-dimensional (3D) tissue constructs to recapitulate physiological and functional aspects of BBB. Here, we describe a delicate 3D vascularized neural constructs for ex-vivo reconstitution of BBB function. The tissue-engineered tissue construct is based on a multicomponent 3D co-culture of four types of cells, which typically exist in the BBB and were spatially defined and organized to mimic the in vivo BBB structure and function. A porous polycaprolactone/poly (d,l-lactide-co-glycolide) (PCL/PLGA) microfluidic perfusion system works as the vasculature network, which was made by freeze-coating a 3D-printed sacrificial template. Endothelial cells were seeded inside the channels of the network to form 3D interconnected blood vessels; while other types of cells, including pericytes, astrocytes, and neurons, were co-cultured in a collagen matrix wrapping the vasculature network to derive a vascularized neural construct that recapitulates in vivo BBB function with great complexity and delicacy. Using this model, we successfully reconstituted BBB function with parameters that are similar to the in vivo condition, and demonstrated the identification of BBB-penetrating therapeutics by examining the molecular delivery to neuronal cells when relevant biologic molecules were applied to the vasculature circulation system of the neural construct.

Dietary Polyphenols: A Multifactorial Strategy to Target Alzheimer's Disease

Ageing is an inevitable fundamental process for people and is their greatest risk factor for neurodegenerative disease. The ageing processes bring changes in cells that can drive the organisms to experience loss of nutrient sensing, disrupted cellular functions, increased oxidative stress, loss of cellular homeostasis, genomic instability, accumulation of misfolded protein, impaired cellular defenses and telomere shortening. Perturbation of these vital cellular processes in neuronal cells can lead to life threatening neurological disorders like Alzheimer's Disease, Parkinson's Disease, Huntington's Disease, Lewy body dementia, etc. Alzheimer's Disease is the most frequent cause of deaths in the elderly population. Various therapeutic molecules have been designed to overcome the social, economic and health care burden caused by Alzheimer's Disease. Almost all the chemical compounds in clinical practice have been found to treat symptoms only limiting them to palliative care. The reason behind such imperfect drugs may result from the inefficiencies of the current drugs to target the cause of the disease. Here, we review the potential role of antioxidant polyphenolic compounds that could possibly be the most effective preventative strategy against Alzheimer's Disease.

A window into the brain: Tools to assess pre-clinical efficacy of biomaterials-based therapies on central nervous system disorders

Therapeutic conveyance into the brain is a cardinal requirement for treatment of diverse central nervous system (CNS) disorders and associated pathophysiology. Effectual shielding of the brain by the blood-brain barrier (BBB) sieves out major proportion of therapeutics with the exception of small lipophilic molecules. Various nano-delivery systems (NDS) provide an effective solution around this obstacle owing to their small size and targeting properties. To date, these systems have been used for several pre-clinical disease models including glioma, neurodegenerative diseases and psychotic disorders. An efficacy screen for these systems involves a test battery designed to probe into the multiple facets of therapeutic delivery. Despite their wide application in redressing various disease targets, the efficacy evaluation strategies for all can be broadly grouped into four modalities, namely: histological, bio-imaging, molecular and behavioural. This review presents a comprehensive insight into all of these modalities along with their strengths and weaknesses as well as perspectives on an ideal design for a panel of tests to screen brain nano-delivery systems.

Efficient Delivery of Nerve Growth Factors to the Central Nervous System for Neural Regeneration

The central nervous system (CNS) plays a central role in the control of sensory and motor functions, and the disruption of its barriers can result in severe and debilitating neurological disorders. Neurotrophins are promising therapeutic agents for neural regeneration in the damaged CNS. However, their penetration across the blood-brain barrier remains a formidable challenge, representing a bottleneck for brain and spinal cord therapy. Herein, a nanocapsule-based delivery system is reported that enables intravenously injected nerve growth factor (NGF) to enter the CNS in healthy mice and nonhuman primates. Under pathological conditions, the delivery of NGF enables neural regeneration, tissue remodeling, and functional recovery in mice with spinal cord injury. This technology can be utilized to deliver other neurotrophins and growth factors to the CNS, opening a new avenue for tissue engineering and the treatment of CNS disorders and neurodegenerative diseases.

Stimulating brain recovery after stroke using theranostic albumin nanocarriers loaded with nerve growth factor in combination therapy

For many years, delivering drug molecules across the blood brain barrier has been a major challenge. The neuropeptide nerve growth factor is involved in the regulation of growth and differentiation of cholinergic neurons and holds great potential in the treatment of stroke. However, as with many other compounds, the biomolecule is not able to enter the central nervous system. In the present study, nerve growth factor and ultra-small particles of iron oxide were co-encapsulated into a chemically crosslinked albumin nanocarrier matrix which was modified on the surface with apolipoprotein E. These biodegradable nanoparticles with a size of 212 ± 1 nm exhibited monodisperse size distribution and low toxicity. They delivered NGF through an artificial blood brain barrier and were able to induce neurite outgrowth in PC12 cells in vitro. In an animal model of stroke, the infarct size was significantly reduced compared to the vehicle control. The combination therapy of NGF and the small-molecular MEK inhibitor U0126 showed a slight but not significant difference compared to U0126 alone. However, further in vivo evidence suggests that successful delivery of the neuropeptide is possible as well as the synergism between those two treatments.

Induction of nerve growth factor by phorbol 12-myristate 13-acetate is dependent upon the mitogen activated protein kinase pathway

Several small molecules have been identified that induce glial cells to synthesize and secrete nerve growth factor (NGF), a critical neurotrophin that supports neuronal growth and survival, and as such show promise in the development of drugs for the chemoprevention of Alzheimer's disease. To map the signal transduction cascade leading to NGF synthesis and secretion, cultured human glial cells were stimulated by phorbol 12-myristate 13-acetate (PMA), an agonist of Protein Kinase C. Changes in intracellular protein phosphorylation states were evaluated by reverse phase protein microarrays (RPPA), selectively screening over 130 protein endpoints. Of these, 55 proteins showed statistically significant changes in phosphorylation state due to cellular exposure to PMA. A critical signal transduction pathway was identified, and subsequent validation by ELISA and qPCR revealed that the signaling proteins Raf, MEK, ERK, and the signal transduction factor CREB are all essential to the upregulation of NGF gene expression by PMA. Additionally, members of the RSK family of kinases appear to be involved in glial secretion (exocytosis) of the NGF protein. Furthermore, through RPPA, the effects of PMA on apoptosis signaling events and cell proliferation were differentiated from the pathway to NGF upregulation. Overall, this study reveals potential protein targets for the rational design of Alzheimer's therapeutics.

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.

Targeting the Cholinergic System to Develop a Novel Therapy for Huntington's Disease

In this review, we outline the role of the cholinergic system in Huntington’s disease, and briefly describe the dysfunction of cholinergic transmission, cholinergic neurons, cholinergic receptors and cholinergic survival factors observed in post-mortem human brains and animal models of Huntington’s disease. We postulate how the dysfunctional cholinergic system can be targeted to develop novel therapies for Huntington’s disease, and discuss the beneficial effects of cholinergic therapies in pre-clinical and clinical studies.

Regulatory role of NGFs in neurocognitive functions

Nerve growth factors (NGFs), especially the prototype NGF and brain-derived neurotrophic factor (BDNF), have a diverse array of functions in the central nervous system through their peculiar set of receptors and intricate signaling. They are implicated not only in the development of the nervous system but also in regulation of neurocognitive functions like learning, memory, synaptic transmission, and plasticity. Evidence even suggests their role in continued neurogenesis and experience-dependent neural network remodeling in adult brain. They have also been associated extensively with brain disorders characterized by neurocognitive dysfunction. In the present article, we aimed to make an exhaustive review of literature to get a comprehensive view on the role of NGFs in neurocognitive functions in health and disease. Starting with historical perspective, distribution in adult brain, implied molecular mechanisms, and developmental basis, this article further provides a detailed account of NGFs’ role in specified neurocognitive functions. Furthermore, it discusses plausible NGF-based homeostatic and adaptation mechanisms operating in the pathogenesis of neurocognitive disorders and has presents a survey of such disorders. Finally, it elaborates on current evidence and future possibilities in therapeutic applications of NGFs with an emphasis on recent research updates in drug delivery mechanisms. Conclusive remarks of the article make a strong case for plausible role of NGFs in comprehensive regulation of the neurocognitive functions and pathogenesis of related disorders and advocate that future research should be directed to explore use of NGF-based mechanisms in the prevention of implicated diseases as well as to target these molecules pharmacologically.

Neuroprotective Effects of Encapsulated CNTF-Producing Cells in a Rodent Model of Huntington's Disease are Dependent on the Proximity of the Implant to the Lesioned Striatum

Huntington's disease (HD) is a devastating genetic disorder with no effective treatments for preventing or lessening the underlying neuronal degeneration. Intracerebral delivery of CNTF in animal models of HD has shown considerable promise as a means of protecting striatal neurons that would otherwise be destined to die. The present study examines whether the neuroprotective effects of CNTF require that the delivery be immediately proximal to the lesion site or whether protective effects can be exerted when the delivery site is more distal to the site of injury. Encapsulated CNTF-producing cells were implanted into the lateral ventricle either ipsilateral or contralateral to an intrastriatal quinolinic acid (QA) injection. A robust neuroprotective effect was observed only in those animals receiving CNTF implants ipsilateral to the QA injection. In these animals, the loss of striatal ChAT and GAD activity as well as the behavioral impairments that resulted from QA were completely prevented. In contrast, no neurochemical or behavioral benefits were produced by implants of CNTF-producing cells in the contralateral ventricle. These data continue to support the use of cellular delivery of CNTF for HD but caution that delivery directly to the striatum may be needed if any clinical benefits are to be seen.

Rescuing cholinergic neurons from apoptotic degeneration by targeting of serotonin modulator-and apolipoprotein E-conjugated liposomes to the hippocampus

β-Amyloid (Aβ)-targeting liposomes (LIP) with surface serotonin modulator (SM) and apolipoprotein E (ApoE) were utilized to facilitate the delivery of nerve growth factor (NGF) across the blood-brain barrier (BBB) for neuroprotection in the hippocampus. The therapeutic efficacy of SM- and ApoE-grafted LIP carrying NGF (NGF-SM-ApoE-LIP) was assessed by an in vitro Alzheimer's disease (AD) model of degenerated SK-N-MC cells and an in vivo AD model of Aβ-insulted Wistar rats. The experimental evidences revealed that the modified SM and ApoE on the surface of LIP increased the permeation of NGF across the BBB without serious damage to structural integrity of tight junction. When compared with free NGF, NGF-SM-ApoE-LIP upregulated the expression of phosphorylated neurotrophic tyrosine kinase receptor type 1 on cholinergic neurons and significantly improved their survival. In addition, NGF-SM-ApoE-LIP could reduce the secretion of acetylcholinesterase and malondialdehyde and rescue hippocampal neurons from apoptosis in rat brains. The synergistic effect of SM and ApoE is promising in the induction of NGF to inhibit the neurotoxicity of Aβ and NGF-SM-ApoE-LIP can be a potent antiapoptotic pharmacotherapy for clinical care of patients with AD.

Comparison of Linear and Cyclic His-Ala-Val Peptides in Modulating the Blood-Brain Barrier Permeability: Impact on Delivery of Molecules to the Brain

The aim of this study is to evaluate the effect of peptide cyclization on the blood-brain barrier (BBB) modulatory activity and plasma stability of His-Ala-Val peptides, which are derived from the extracellular 1 domain of human E-cadherin. The activities to modulate the intercellular junctions by linear HAV4 (Ac-SHAVAS-NH2), cyclic cHAVc1 (Cyclo(1,8)Ac-CSHAVASC-NH2), and cyclic cHAVc3 (Cyclo(1,6)Ac-CSHAVC-NH2) were compared in in vitro and in vivo BBB models. Linear HAV4 and cyclic cHAVc1 have the same junction modulatory activities as assessed by in vitro MDCK monolayer model and in situ rat brain perfusion model. In contrast, cyclic cHAVc3 was more effective than linear HAV4 in modulating MDCK cell monolayers and in improving in vivo brain delivery of Gd-DTPA on i.v. administration in Balb/c mice. Cyclic cHAVc3 (t1/2 = 12.95 h) has better plasma stability compared with linear HAV4 (t1/2 = 2.4 h). The duration of the BBB modulation was longer using cHAVc3 (2-4 h) compared with HAV4 (<1 h). Both HAV4 and cHAVc3 peptides also enhanced the in vivo brain delivery of IRdye800cw-PEG (25 kDa) as detected by near IR imaging. The result showed that cyclic cHAVc3 peptide had better activity and plasma stability than linear HAV4 peptide.

Review : Gene Therapy: Applications to the Neurosciences and to Neurological Disease

Gene expression is involved in some way in every human disease. As our knowledge of gene structure and function has blossomed in the last 2 decades, so too has our potential genetically-based repertoire for combating disease. Gene therapy refers to the manipulation of gene expression, either by augmenting the expression of therapeutic genes or by diminishing the expression of deleterious genes. In some neurological diseases, such as trauma, ischemia, and neurodegenerative disorders, gene therapy might be used to express genes for such substances as growth factors or neurotransmitters to prevent neuronal degeneration or to compensate for lost function, respectively. In other cases, gene therapy could be used to block the expression of genes that cause disease such as β-amyloid precursor protein or the Huntingtin gene. In inherited diseases of the nervous system such as muscular dystrophy, normal gene copies could be placed into the nervous system to compensate for lost function resulting from abnormal gene expression. The tools for achieving well-targeted, sustained, and safe gene delivery in the nervous system are now becoming available, and this technology is likely to substantially alter the nature of neurological therapy in the future. NEUROSCIENTIST 4:398-407, 1998

The Evaluation of Nerve Growth Factor Over Expression on Neural Lineage Specific Genes in Human Mesenchymal Stem Cells

Objective

Treatment and repair of neurodegenerative diseases such as brain tumors, spinal cord injuries, and functional disorders, including Alzheimer’s disease, are challenging problems. A common treatment approach for such disorders involves the use of mesenchymal stem cells (MSCs) as an alternative cell source to replace injured cells. However, use of these cells in hosts may potentially cause adverse outcomes such as tumorigenesis and uncontrolled differentiation. In attempt to generate mesenchymal derived neural cells, we have infected MSCs with recombinant lentiviruses that expressed nerve growth factor (NGF) and assessed their neural lineage genes.

Materials and Methods

In this experimental study, we cloned the NGF gene sequence into a helper dependent lentiviral vector that contained the green fluorescent protein (GFP) gene. The recombinant vector was amplified in DH5 bacterial cells. Recombinant viruses were generated in the human embryonic kidney 293 (HEK-293) packaging cell line with the helper vectors and analyzed under fluorescent microscopy. Bone marrow mesenchymal cells were infected by recombinant viruses for three days followed by assessment of neural differentiation. We evaluated expression of NGF through measurement of the NGF protein in culture medium by ELISA; neural specific genes were quantified by real-time polymerase chain reaction (PCR).

Results

We observed neural morphological changes after three days. Quantitative PCR showed that expressions of NESTIN, glial derived neurotrophic factor (GDNF), glial fibrillary acidic protein (GFAP) and Microtubule-associated protein 2 (MAP2) genes increased following induction of NGF overexpression, whereas expressions of endogenous NGF and brain derived neural growth factor (BDNF) genes reduced.

Conclusion

Ectopic expression of NGF can induce neurogenesis in MSCs. Direct injection of MSCs may cause tumorigenesis and an undesirable outcome. Therefore an alternative choice to overcome this obstacle may be the utilization of differentiated neural stem cells.

Fcγ1 fragment of IgG1 as a powerful affinity tag in recombinant Fc-fusion proteins: immunological, biochemical and therapeutic properties

Affinity tags are vital tools for the production of high-throughput recombinant proteins. Several affinity tags, such as the hexahistidine tag, maltose-binding protein, streptavidin-binding peptide tag, calmodulin-binding peptide, c-Myc tag, glutathione S-transferase and FLAG tag, have been introduced for recombinant protein production. The fragment crystallizable (Fc) domain of the IgG1 antibody is one of the useful affinity tags that can facilitate detection, purification and localization of proteins and can improve the immunogenicity, modulatory effects, physicochemical and pharmaceutical properties of proteins. Fcγ recombinant forms a group of recombinant proteins called Fc-fusion proteins (FFPs). FFPs are widely used in drug discovery, drug delivery, vaccine design and experimental research on receptor-ligand interactions. These fusion proteins have become successful alternatives to monoclonal antibodies for drug developments. In this review, the physicochemical, biochemical, immunological, pharmaceutical and therapeutic properties of recombinant FFPs were discussed as a new generation of bioengineering strategies.

The neuritogenic and neuroprotective potential of senegenin against Aβ-induced neurotoxicity in PC 12 cells

BACKGROUND

Improved therapeutics aimed at ameliorating the devastating effects of neurodegenerative diseases, such as Alzheimer's disease (AD), are pertinent to help attenuate their growing prevalence worldwide. One promising avenue for such therapeutics lies in botanical medicines that have been efficaciously employed in the likes of traditional medicine doctrines for millennium. Integral to this approach is the necessity of neuritogenesis and/or neuroprotection to counterbalance the deleterious effects of amyloid-β (Aβ) proteins. Senegenin, a principle saponin of Polygala tenuifolia Willd., which has empirically shown to improve cognition and intelligence, was chosen to evaluate its cytoprotective potential and possible neuritogenic and neuroprotective effects.

METHODS

The purpose of the present study was then to analyze morphological changes in neurite development and altered protein expression of two proteins requisite to neuritogenesis, growth associated protein 43 (Gap-43) and microtubule-associated protein 2 (MAP2) in PC 12 cells. Neuritogenic analysis was conducted with immunofluorescence after incubation with Aβ (25-35) peptide, and to deduce information on cell viability and mitochondrial functionality MTT (3,(4,5-dimethylthiazol-2-yl)2,5-diphenyltetrazolium bromide) was employed.

RESULTS

This study found that cells pre-incubated with senegenin for 24 h (40 μg and 20 μg/ml) before introducing Aβ attenuated Aβ-cytotoxicity, and significantly increased cell viability by 23 % and 34 % (P < 0.001), respectively. In neurite outgrowth experiments, Aβ was compared to NGF positive control and senegenin treated groups which showed a drastic decrease in the quantity, average length and maximum length of neurites (P < 0.001). At concentrations of 1 μg/ml (P < 0.01) and 5 μg/ml (P < 0.05) senegenin triggered neuritogenesis with significant increases in total neurite number, average length and maximum length. This was additionally shown through the augmented expression of MAP2 and Gap-43.

CONCLUSIONS

These results suggest that senegenin possesses cytoprotective properties, can moderate neurite outgrowth and augment MAP2 and Gap-43, thus suggesting a potential therapeutic value for Polygala tenuifolia in neurodegenerative disorders.

Rescuing apoptotic neurons in Alzheimer's disease using wheat germ agglutinin-conjugated and cardiolipin-conjugated liposomes with encapsulated nerve growth factor and curcumin

Liposomes with cardiolipin (CL) and wheat germ agglutinin (WGA) were developed to permeate the blood–brain barrier and treat Alzheimer’s disease. WGA-conjugated and CL-incorporated liposomes (WGA-CL-liposomes) were used to transport nerve growth factor (NGF) and curcumin (CUR) across a monolayer of human brain-microvascular endothelial cells regulated by human astrocytes and to protect SK-N-MC cells against apoptosis induced by β-amyloid_1–42 (Aβ_1–42) fibrils. An increase in the CL mole percentage in lipids increased the liposomal diameter, absolute zeta potential value, entrapment efficiency of NGF and CUR, release of NGF, biocompatibility, and viability of SK-N-MC cells with Aβ_1–42, but decreased the atomic ratio of nitrogen to phosphorus and release of CUR. In addition, an increase in the WGA concentration for grafting enhanced the liposomal diameter, atomic ratio of nitrogen to phosphorus, and permeability of NGF and CUR across the blood–brain barrier, but reduced the absolute zeta potential value and biocompatibility. WGA-CL-liposomes carrying NGF and CUR could be promising colloidal delivery carriers for future clinical application in targeting the blood–brain barrier and inhibiting neurotoxicity.

Significantly lower nerve growth factor levels in patients with major depressive disorder than in healthy subjects: a meta-analysis and systematic review

INTRODUCTION

Since its discovery several decades ago, nerve growth factor (NGF) has been found to play roles in different areas, such as neurology, endocrinology, and immunology. There is some evidence linking NGF and psychiatry, including the role of NGF in subjects' response to stress, the alteration of NGF in different emotional states, and the penetration of NGF across the blood-brain barrier under specific conditions. There are many inconsistent findings regarding the differences in NGF in patients with major depressive disorder (MDD) at the present time. The aim of our study was to clarify whether NGF levels are different in MDD compared with healthy controls (HCs).

METHODS

We conducted a thorough literature search and compared peripheral NGF levels between MDD and HC through meta-analysis, and investigated possible confounding variables through meta-regression.

RESULTS

Seven studies were brought into the current meta-analysis comparing peripheral NGF in MDD and HCs. The main result was that the NGF levels were significantly lower in MDD than in HCs and that this had an inverse correlation with mean age and disease severity. In addition, meta-analysis of four articles found that the peripheral NGF levels did not change significantly before and after treatment.

CONCLUSION

Our study highlights the significant differences in peripheral NGF levels in patients with MDD. However, further exploration of the dynamic changes in peripheral NGF along with the disease course, and specific studies investigating the correlation of NGF in the peripheral and CNS environments are still needed.

Nerve growth factor and autophagy: effect of nasal anti-NGF-antibodies administration on Ambra1 and Beclin-1 expression in rat brain

Nerve growth factor (NGF) exerts protective actions in the healthy and diseased nervous system. Intranasal administration is a suitable and safe strategy to deliver NGF to CNS neurons. We investigated whether nasal anti-NGF-antibody (ANA) administration affects neuronal autophagy, in view of its putative regulatory role in this process. We focused on olfactory bulbs (OB), neocortex (Cx), hippocampus (HF) and septal complex (SC), known to be NGF-responsive and autophagically active. Our combined molecular/morphological results demonstrate that intranasally administered ANA reaches brain NGF-target neurons and lowers the levels of endogenous NGF and its receptors. Treatment also affects - in a brain region-dependent manner - the expression of the autophagic proteins Beclin-1 and Ambra1, as well as that of proteins belonging to the Bcl2 family, namely Bax and Bcl-2, reflecting apoptotic dysregulation. This study provides a nongenetically modified, NGF-defective animal model, representing a suitable tool to investigate novel properties of the neurotrophin, especially in relation to autophagy.

Potential therapeutic strategies for Alzheimer's disease targeting or beyond β-amyloid: insights from clinical trials

Alzheimer's disease (AD) is a progressive neurodegenerative disorder with two hallmarks: β-amyloid plagues and neurofibrillary tangles. It is one of the most alarming illnesses to elderly people. No effective drugs and therapies have been developed, while mechanism-based explorations of therapeutic approaches have been intensively investigated. Outcomes of clinical trials suggested several pitfalls in the choice of biomarkers, development of drug candidates, and interaction of drug-targeted molecules; however, they also aroused concerns on the potential deficiency in our understanding of pathogenesis of AD, and ultimately stimulated the advent of novel drug targets tests. The anticipated increase of AD patients in next few decades makes development of better therapy an urgent issue. Here we attempt to summarize and compare putative therapeutic strategies that have completed clinical trials or are currently being tested from various perspectives to provide insights for treatments of Alzheimer's disease.

A human blood-brain barrier transcytosis assay reveals antibody transcytosis influenced by pH-dependent receptor binding

We have adapted an in vitro model of the human blood-brain barrier, the immortalized human cerebral microvascular endothelial cells (hCMEC/D3), to quantitatively measure protein transcytosis. After validating the receptor-mediated transport using transferrin, the system was used to measure transcytosis rates of antibodies directed against potential brain shuttle receptors. While an antibody to the insulin-like growth factor 1 receptor (IGF1R) was exclusively recycled to the apical compartment, the fate of antibodies to the transferrin receptor (TfR) was determined by their relative affinities at extracellular and endosomal pH. An antibody with reduced affinity at pH5.5 showed significant transcytosis, while pH-independent antibodies of comparable affinities at pH 7.4 remained associated with intracellular vesicular compartments and were finally targeted for degradation.

Encapsulated cell therapy for neurodegenerative diseases: from promise to product

Delivering therapeutic molecules, including trophic factor proteins, across the blood brain barrier to the brain parenchyma to treat chronic neurodegenerative diseases remains one of the great challenges in biology. To be effective, delivery needs to occur in a long-term and stable manner at sufficient quantities directly to the target region in a manner that is selective but yet covers enough of the target site to be efficacious. One promising approach uses cellular implants that produce and deliver therapeutic molecules directly to the brain region of interest. Implanted cells can be precisely positioned into the desired region and can be protected from host immunological attack by encapsulating them and by surrounding them within an immunoisolatory, semipermeable capsule. In this approach, cells are enclosed within a semiporous capsule with a perm selective membrane barrier that admits oxygen and required nutrients and releases bioactive cell secretions while restricting passage of larger cytotoxic agents from the host immune defense system. Recent advances in human cell line development have increased the levels of secreted therapeutic molecules from encapsulated cells, and membrane extrusion techniques have led to the first ever clinical demonstrations of long-term survival and function of encapsulated cells in the brain parenchyma. As such, cell encapsulation is capable of providing a targeted, continuous, de novo synthesized source of very high levels of therapeutic molecules that can be distributed over significant portions of the brain.

Serum neurotrophic factors in adolescent depression: gender difference and correlation with clinical severity

BACKGROUND

Brain derived neurotrophic factor (BDNF), nerve growth factor (NGF), neurotrophin-3 (NT-3) and glial cell line derived neurotrophic factor (GDNF) play critical role in growth, differentiation, maintenance and synaptic plasticity in neuronal systems which is more relevant in adolescence. The present study was undertaken to verify the 'neurotrophin hypothesis' in adolescent depression by (i) comparing serum concentrations of neurotrophic factors in depression patients and healthy control, and (ii) analyzing correlations between clinical severity and serum neurotrophin levels.

METHODS

Eighty four adolescent (aged 13-18 years) depressed patients (56 males; 60 medication free/naive) and 64 healthy controls (39 males) were recruited. Severity of depression was measured by Beck's depression inventory, and anxiety by state-trait anxiety inventory. Measurement of serum neurotrophins was done by ELISA.

RESULTS

Adolescents with depression had significantly lower levels of BDNF: mean diff. (95% C.I.): 2093.9 (1074.0, 3113.9), NGF: 813.3 (343.1, 1283.6) and GDNF: 158.8 (77.2, 240.4) compared to controls. On gender based analysis female controls had significantly increased trait anxiety scores [-1.1 (-1.8, -0.1)], as compared to control males. In the patient group, female patients had far lower level of NGF: 919.6 (210.9, 1628.3) and NT-3: 1288.8 (145.4, 2432.3) compared to male. BDI-II score showed a statistically significant (p<0.01) negative correlation with all four neurotrophins in male patients while in female patients such negative correlation was observed only with NGF and GDNF (p<0.01).

LIMITATIONS

The study is cross-sectional from a tertiary care hospital.

CONCLUSION

The novelty of the study lies in its large number of exclusively adolescent depression patients showing significant reduction of BDNF, NGF and GDNF serum levels as compared to controls. A gender bias with much reduction in female has also been recorded.

Developing therapeutic antibodies for neurodegenerative disease

The central nervous system has been considered off-limits to antibody therapeutics. However, recent advances in preclinical and clinical drug development suggest that antibodies can cross the blood-brain barrier in limited quantities and act centrally to mediate their effects. In particular, immunotherapy for Alzheimer's disease has shown that targeting beta amyloid with antibodies can reduce pathology in both mouse models and the human brain, with strong evidence supporting a central mechanism of action. These findings have fueled substantial efforts to raise antibodies against other central nervous system targets, particularly neurodegenerative targets, such as tau, beta-secretase, and alpha-synuclein. Nevertheless, it is also apparent that antibody penetration across the blood-brain barrier is limited, with an estimated 0.1-0.2 % of circulating antibodies found in brain at steady-state concentrations. Thus, technologies designed to improve antibody uptake in brain are receiving increased attention and are likely going to represent the future of antibody therapy for neurologic diseases, if proven safe and effective. Herein we review briefly the progress and limitations of traditional antibody drug development for neurodegenerative diseases, with a focus on passive immunotherapy. We also take a more in-depth look at new technologies for improved delivery of antibodies to the brain.