Brain targeting of nerve growth factor using poly(butyl cyanoacrylate) nanoparticles

Nanoparticles as carriers for drug delivery of macromolecules across the blood-brain barrier

Introduction: Current therapies of neurodegenerative or neurometabolic diseases are, to a large extent, hampered by the inability of drugs to cross the blood-brain barrier (BBB). This very tight barrier severely restricts the entrance of molecules from the blood into the brain, especially macromolecular substances (i.e. neurotrophic factors, enzymes, proteins, as well as genetic materials). Due to their size, physicochemical properties, and instability, the delivery of these materials is particularly difficult.Areas covered: Recent research showed that biocompatible and biodegradable nanoparticles possessing tailored surface properties can enable a delivery of drugs and specifically of macromolecules across the blood-brain barrier by using carrier systems of the brain capillary endothelium (Trojan Horse strategy). In the present review, the state-of-art of nanoparticle-mediated drug delivery of different macromolecular substances into the brain following intravenous injection is summarized, and different nanomedicines that are used to enable the transport of neurotrophic factors and enzymes across the blood-brain barrier into the CNS are critically analyzed.Expert opinion: Brain delivery of macromolecules by an intravenous application using nanomedicines is now a growing area of interest which could be really translated into clinical application if dedicated effort will be given to industrial scale-up production.

Targeted therapy in chronic diseases using nanomaterial-based drug delivery vehicles

The application of nanomedicines is increasing rapidly with the promise of targeted and efficient drug delivery. Nanomedicines address the shortcomings of conventional therapy, as evidenced by several preclinical and clinical investigations indicating site-specific drug delivery, reduced side effects, and better treatment outcome. The development of suitable and biocompatible drug delivery vehicles is a prerequisite that has been successfully achieved by using simple and functionalized liposomes, nanoparticles, hydrogels, micelles, dendrimers, and mesoporous particles. A variety of drug delivery vehicles have been established for the targeted and controlled delivery of therapeutic agents in a wide range of chronic diseases, such as diabetes, cancer, atherosclerosis, myocardial ischemia, asthma, pulmonary tuberculosis, Parkinson's disease, and Alzheimer's disease. After successful outcomes in preclinical and clinical trials, many of these drugs have been marketed for human use, such as Abraxane®, Caelyx®, Mepact®, Myocet®, Emend®, and Rapamune®. Apart from drugs/compounds, novel therapeutic agents, such as peptides, nucleic acids (DNA and RNA), and genes have also shown potential to be used as nanomedicines for the treatment of several chronic ailments. However, a large number of extensive clinical trials are still needed to ensure the short-term and long-term effects of nanomedicines in humans. This review discusses the advantages of various drug delivery vehicles for better understanding of their utility in terms of current medical needs. Furthermore, the application of a wide range of nanomedicines is also described in the context of major chronic diseases.

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.

110th Anniversary: Nanoparticle mediated drug delivery for the treatment of Alzheimer's disease: Crossing the blood-brain barrier

Alzheimer's disease is an irreversible neurodegenerative disorder affecting approximately 6 million Americans, 90% of which are over the age of 65. The hallmarks of the disease are represented by amyloid plaques and neurofibrillary tangles. While the neuronal characteristics of Alzheimer's disease are well known, current treatments only provide temporary relief of the disease symptoms. Many of the approved therapeutic agents for the management of cognitive impairments associated with the disease are based on neurotransmitter or enzyme modulation. However, development of new treatment strategies is limited due to failures associated with poor drug solubility, low bioavailability, and the inability to overcome obstacles present along the drug delivery route. In addition, treatment technologies must overcome the challenges presented by the blood-brain barrier. This complex and highly regulated barrier surveys the biochemical, physicochemical, and structural features of nearby molecules at the periphery, only permitting passage of select molecules into the brain. To increase drug efficacy to the brain, many nanotechnology-based platforms have been developed. These methods for assisted drug delivery employ sophisticated design strategies and offer serveral advantages over traditional methods. For example, nanoparticles are generally low-cost technologies, which can be used for non-invasive administrations, and formulations are highly tunable to increase drug loading, targeting, and release efficacy. These nanoscale systems can facilitate passage of drugs through the blood-brain barrier, thus improving the bioavailability, pharmacokinetics, and pharmacodynamics of therapeutic agents. Examples of such nanocarriers which are discussed herein include polymeric nanoparticles, dendrimers, and lipid-based nanoparticles.

Boosting Drug Discovery for Parkinson's: Enhancement of the Delivery of a Monoamine Oxidase-B Inhibitor by Brain-Targeted PEGylated Polycaprolactone-Based Nanoparticles

The current pharmacological treatments for Parkinson's disease only offer symptomatic relief to the patients and are based on the administration of levodopa and catechol-O-methyltransferase or monoamine oxidase-B inhibitors (IMAO-B). Since the majority of drug candidates fail in pre- and clinical trials, due largely to bioavailability pitfalls, the use of polymeric nanoparticles (NPs) as drug delivery systems has been reported as an interesting tool to increase the stealth capacity of drugs or help drug candidates to surpass biological barriers, among other benefits. Thus, a novel potent, selective, and reversible IMAO-B (chromone C27, IC50 = 670 ± 130 pM) was encapsulated in poly(caprolactone) (PCL) NPs by a nanoprecipitation process. The resulting C27-loaded PEGylated PCL NPs (~213 nm) showed high stability and no cytotoxic effects in neuronal (SH-SY5Y), epithelial (Caco-2), and endothelial (hCMEC/D3) cells. An accumulation of PEGylated PCL NPs in the cytoplasm of SH-SY5Y and hCMEC/D3 cells was also observed, and their permeation across Caco-2 and hCMEC/D3 cell monolayers, used as in vitro models of the human intestine and blood-brain barrier, respectively, was demonstrated. PEGylated PCL NPs delivered C27 at concentrations higher than the MAO-B IC50 value, which provides evidence of their relevance to solving the drug discovery pitfalls.

Nanodelivery of therapeutic agents in Parkinson's disease

Parkinson's disease (PD) as a motor disorder is pathologically featured by the loss of dopaminergic neurons of the substantia nigra compacta (SNc) and the consequent depletion of dopamine in the striatum. However, motor signs are detectable when the loss of dopaminergic striatal terminals exceeds to the dopaminergic neuronal degeneration in SN. Hence, recent evidences about the topological organization of the nigrostriatal system could provide novel insights about the progression of the neurodegenerative process as well as the correct application of the novel therapeutic strategies. Though dopaminergic drugs and different routes of administration have been proposed to treat PD, most of the effects are symptomatic with temporary effects resorting to invasive procedures to ameliorate the side effects. Since the blood-brain barrier (BBB) is the main obstacle for most of molecules to access to the brain, ongoing research is focused on halting the progression of PD through the use of those technologies that allow the effective delivery and diffusion of therapeutic molecules to the central nervous system for bypassing BBB and avoiding the side effects. In this context, nanotechnology is emerging as a promising tool for drug delivery. In fact, nanodelivery of restorative treatments in PD, such as gene therapy increased the effectiveness of neurotrophic factors for restoring the dopamine deficit and improving motor deficit in rodent models. Therefore, the present review is focused on the description and identification of the available nanotherapies developed in experimental models of PD which could suppose an important advance for controlled delivery of nanobioactive components into the brain and one more step for the clinical projection.

Overcoming the Blood–Brain Barrier. Challenges and Tricks for CNS Drug Delivery

Treatment of certain central nervous system disorders, including different types of cerebral malignancies, is limited by traditional oral or systemic administrations of therapeutic drugs due to possible serious side effects and/or lack of the brain penetration and, therefore, the efficacy of the drugs is diminished. During the last decade, several new technologies were developed to overcome barrier properties of cerebral capillaries. This review gives a short overview of the structural elements and anatomical features of the blood–brain barrier. The various in vitro (static and dynamic), in vivo (microdialysis), and in situ (brain perfusion) blood–brain barrier models are also presented. The drug formulations and administration options to deliver molecules effectively to the central nervous system (CNS) are presented. Nanocarriers, nanoparticles (lipid, polymeric, magnetic, gold, and carbon based nanoparticles, dendrimers, etc.), viral and peptid vectors and shuttles, sonoporation and microbubbles are briefly shown. The modulation of receptors and efflux transporters in the cell membrane can also be an effective approach to enhance brain exposure to therapeutic compounds. Intranasal administration is a noninvasive delivery route to bypass the blood–brain barrier, while direct brain administration is an invasive mode to target the brain region with therapeutic drug concentrations locally. Nowadays, both technological and mechanistic tools are available to assist in overcoming the blood–brain barrier. With these techniques more effective and even safer drugs can be developed for the treatment of devastating brain disorders.

Application of nanoscale polymer colloid carriers for targeted delivery of the brain-derived neurotrophic factor through the blood-brain barrier in experimental parkinsonism

Parkinson disease is one of the common age-related motor neurodegenerative diseases, in which dopamine neurons degeneration is considered to be pathognomic for the development of motor disfunction. Brain-derived neurotrophic factor (BDNF) is a member of the neurotrophin family, which is considered to be a key regulator of neuronal plasticity. BDNF, being a large molecule, does not pass through the blood-brain barrier (BBB). Synthetic polymer nanoparticles (NP), covered by surfactant, provide the phenomenon of “Trojan hoarse” and enable BDNF to penetrate into the brain tissue. For modelling of parkinsonism we used an intraperitoneal (i.p.) injection of neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) which was injected to the C57BL/6 mice with subsequest treatment with normal saline (group 1), BDNF (group 2), nanoparticulate BDNF (group 3) and surfactant-coated nanoparticulate BDNF (group 4). After 90 min, 24 hours, 72 hours and 7 days manifestations of parkinsonism were evaluated using behavioural tests of open field, rota-rod, assessment of the tremor, length of the body and pace. At the end of experiment the brain was sampled for histological evaluation of changes in the striatum and midbrain and concentration of BDNF in the brain tissues. The results of the experiments demonstrated that nanoparticulate BDNF covered with surfactant significanltly reduced rigidity of the skeletal muscles, oligokinesia and tremor, and also significantly increased BDNF concentration in the brain tissues.

Comparison between Polybutylcyanoacrylate Nanoparticles with Either Surface-Adsorbed or Encapsulated Brain-Derived Neurotrophic Factor on the Neural Differentiation of iPSCs

The brain-derived neurotrophic factor (BDNF) is vital in the neural differentiation of neural stem/progenitor cells, and together may have therapeutic potential for neural regeneration. In this study, a multiplexed polybutylcyanoacrylate nanoparticle (PBCA NP) delivery platform was constructed, incorporating either surface-adsorbed or encapsulated BDNF for the induction of neural differentiation in induced pleuripotent stem cells (iPSCs), where tween 80 (T80) and superparamagnetic iron oxide (SPIO) were added for central nervous system (CNS) targeting and magnetic resonance (MR) image tracking, respectively. Both methods by which the BDNF was carried resulted in loading efficiencies greater than 95%. The nanoparticle-mediated delivery of BDNF resulted in neural differentiation of iPSCs detected on immunofluorescence staining as early as 7 days, with enhanced differentiation efficiency by 1.3-fold compared to the control on flow cytometry; the delivery system of surface-adsorbed BDNF gave rise to cells that had the best neural development than the encapsulated formulation. T80-coating disrupted the in vitro blood–brain barrier model with a corresponding 1.5- to two-fold increase in permeability. SPIO-loaded PBCA NPs exhibited a concentration-dependent, rapid decay in signal intensity on the phantom MR experiment. This study demonstrates the versatility of the PBCA NP, and the surface-adsorption of BDNF is the preferred method of delivery for the differentiation of iPSCs.

Nanodelivery systems for overcoming limited transportation of therapeutic molecules through the blood-brain barrier

Due to the impermeable structure and barrier function of the blood-brain barrier (BBB), the delivery of therapeutic molecules into the CNS is extremely limited. Nanodelivery systems are regarded as the most effective and versatile carriers for the CNS, as they can transport cargo molecules across the BBB via various mechanisms. This review emphasizes the multi-functionalization strategies of nanodelivery systems and combinatorial approaches for the delivery of therapeutic drugs and genes into the CNS. The characteristics and functions of the BBB and underlying mechanisms of molecular translocation across the BBB are also described.

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.

Therapeutic strategies and nano-drug delivery applications in management of ageing Alzheimer's disease

In recent years, the incidental rate of neurodegenerative disorders has increased proportionately with the aging population. Alzheimer's disease (AD) is one of the most commonly reported neurodegenerative disorders, and it is estimated to increase by roughly 30% among the aged population. In spite of screening numerous drug candidates against various molecular targets of AD, only a few candidates - such as acetylcholinesterase inhibitors are currently utilized as an effective clinical therapy. However, targeted drug delivery of these drugs to the central nervous system (CNS) exhibits several limitations including meager solubility, low bioavailability, and reduced efficiency due to the impediments of the blood-brain barrier (BBB). Current advances in nanotechnology present opportunities to overcome such limitations in delivering active drug candidates. Nanodrug delivery systems are promising in targeting several therapeutic moieties by easing the penetration of drug molecules across the CNS and improving their bioavailability. Recently, a wide range of nano-carriers, such as polymers, emulsions, lipo-carriers, solid lipid carriers, carbon nanotubes, metal based carriers etc., have been adapted to develop successful therapeutics with sustained release and improved efficacy. Here, we discuss few recently updated nano-drug delivery applications that have been adapted in the field of AD therapeutics, and future prospects on potential molecular targets for nano-drug delivery systems.

Neuro-protective role of nanocapsulated curcumin against cerebral ischemia-reperfusion induced oxidative injury

Cerebral ischemia-reperfusion (CIR) accelerates the progression of neurodegeneration by causing mitochondrial dysfunction to overproduce reactive oxygen species (ROS). Curcumin shows protective effects against CIR-induced oxidative damage. Free curcumin (FC) is effective at high doses due to its poor bioavailability. Also the blood-brain barrier (BBB) limits the passage of substances from circulation into the cerebral region. Thus, formulation of curcumin within polyethylene glycol (PEG)-ylated polylactide-co-glycolide (PLGA) nanoparticles (NC) was applied orally to aged rats to explore its role against CIR injury. Mitochondrial damage was evaluated. The levels of pro-inflammatory cytokines and components of apoptotic pathway were studied. Unlike FC, NC pre-treatment exerted better neuro-protection by ameliorating ROS-mediated oxidative damage and prevented CIR-induced neuronal apoptosis. Therefore, curcumin incorporated PEGylated PLGA nanoparticles may be used as a suitable delivery vehicle to the brain as they can increase curcumin bioavalability and the released curcumin may confer protection to the neurons against CIR-induced oxidative damage.

Recent Status of Nanomaterial Fabrication and Their Potential Applications in Neurological Disease Management

Nanomaterials (NMs) are receiving remarkable attention due to their unique properties and structure. They vary from atoms and molecules along with those of bulk materials. They can be engineered to act as drug delivery vehicles to cross blood-brain barriers (BBBs) and utilized with better efficacy and safety to deliver specific molecules into targeted cells as compared to conventional system for neurological disorders. Depending on their properties, various metal chelators, gold nanoparticles (NPs), micelles, quantum dots, polymeric NPs, liposomes, solid lipid NPs, microparticles, carbon nanotubes, and fullerenes have been utilized for various purposes including the improvement of drug delivery system, treatment response assessment, diagnosis at early stage, and management of neurological disorder by using neuro-engineering. BBB regulates micro- and macromolecule penetration/movement, thus protecting it from many kinds of illness. This phenomenon also prevents drug delivery for the neurological disorders such as Alzheimer's disease (AD), Parkinson's disease (PD), multiple sclerosis, amyotrophic lateral sclerosis, and primary brain tumors. For some neurological disorders (AD and PD), the environmental pollution was considered as a major cause, as observed that metal and/or metal oxide from different sources are inhaled and get deposited in the lungs/brain. Old age, obesity, diabetes, and cardiovascular disease are other factors for rapid deterioration of human health and onset of AD. In addition, gene mutations have also been examined to cause the early onset familial forms of AD. AD leads to cognitive impairment and plaque deposits in the brain leading to neuronal cell death. Based on these facts and considerations, this review elucidates the importance of frequently used metal chelators, NMs and/or NPs. The present review also discusses the current status and future challenges in terms of their application in drug delivery for neurological disease management.

Application of nanodiagnostics and nanotherapy to CNS diseases

Alzheimer's disease, Parkinson's disease and stroke are the most common CNS diseases, all characterized by progressive cellular dysfunction and death in specific areas of the nervous system. Therapeutic development for these diseases has lagged behind other disease areas due to difficulties in early diagnosis, long disease courses and drug delivery challenges, not least due to the blood-brain barrier. Over recent decades, nanotechnology has been explored as a potential tool for the diagnosis, treatment and monitoring of CNS diseases. In this review, we describe the application of nanotechnology to common CNS diseases, highlighting disease pathogenesis and the underlying mechanisms and promising functional outcomes that make nanomaterials ideal candidates for early diagnosis and therapy. Moreover, we discuss the limitations of nanotechnology, and possible solutions.

Bioactivity-Guided Isolation of Neuritogenic Factor from the Seeds of the Gac Plant (Momordica cochinchinensis)

Nerve growth factor (NGF) is an endogenously produced protein with the capacity to induce central nervous system (CNS) neuronal differentiation and repair. NGF signaling involves its binding to tropomyosin-related kinase (Trk) receptors, internalization, and initiation of phosphorylation cascades which cause microtubule reorganization and neuronal outgrowth. Because NGF cannot cross the blood-brain barrier, its therapeutic use is limited. Synthetic peptides that can act as NGF receptor agonists (NGF mimetics) are known to attenuate neurodegenerative pathologies in experimental models of Alzheimer's disease and Parkinson's disease; however, the existence of plant-based NGF mimetics is uncertain. For this reason, we recently completed a high throughput screening of over 1100 nutraceuticals (vitamins, herbal plant parts, polyphenolics, teas, fruits, and vegetables) to identify neuritogenic factor using a PC-12 cell model. Remarkably we found only one, commonly known as the seed of Gac plant (Momordica cochinchinensis) (MCS). In the current study, we further investigated this seed for its neuritogenic effect using bioactivity-guided chemical separations. The data show no biological neuritogenic activity in any chemical solvent fraction, where activity was exclusive to the crude protein. MSC crude proteins were then separated by 1D electrophoresis, where the active neuritogenic activity was confirmed to have a molecular mass of approximately 17 kDa. Subsequently, the 17kDa band was excised, digested, and run on a UPLC-MS/MS with a Q Exactive Hybrid Quadrupole-Orbitrap Mass Spectrometer with data evaluated diverse tools such as X! Tandem, OMS, and K-score algorithms. Proteomic evaluation of the 17kDa band confirmed evidence for 11S globulin subunit beta, napin, oleosin, Momordica trypsin inhibitors (TI) MCoTI-I /II, and many isoforms of Two Inhibitor Peptide Topologies (TIPTOPs). While all peptides identified correspond to the genus/species, Momordica cochinchinensis and Cucumis Sativus, a significant limitation of the analysis is the nonexistence of full annotation for the Momordica cochinchinensis proteome. In conclusion, these findings demonstrate that there is a stable protein within MCS having a mass of 17kDa with the capacity to induce neurite outgrowth. Future work will be required to establish the therapeutic value of the MCS for the treatment of neurodegenerative diseases.

[Local injection of exogenous nerve growth factor improves early bone maturation of implants]

OBJECTIVE

To investigate the effects of nerve growth factor (NGF) in the osteogenic action of implants and the maturation and reconstruction changes in bone tissues in the early stage of osseointegration.

METHODS

The mouse implant model was established by placing titanium in the femoral head of the mouse and locally injecting NGF in the implant zone. On 1, 2 and 4 weeks after operation, stain samples were collected from animals using hematoxylin-eosin (HE) staining and Masson staining. The effect of NGF on the bone maturation was compared at different time points of early stage osseointegration.

RESULTS

The results of HE and Masson staining indicated that the local injection of external NGF can up-regulate bone mass, amount of bone trabecula, and bone maturity in the mouse model. The mature bone rate in treatment group of 1 week and 4 weeks after operation were significantly higher than those in the control group (P<0.05).

CONCLUSIONS

NGF can shorten the period of bone maturation.

Long-term delivery of brain-derived neurotrophic factor (BDNF) from nanoporous silica nanoparticles improves the survival of spiral ganglion neurons in vitro

Sensorineural hearing loss (SNHL) can be overcome by electrical stimulation of spiral ganglion neurons (SGNs) via a cochlear implant (CI). Restricted CI performance results from the spatial gap between the SGNs and the electrode, but the efficacy of CI is also limited by the degeneration of SGNs as one consequence of SHNL. In the healthy cochlea, the survival of SGNs is assured by endogenous neurotrophic support. Several applications of exogenous neurotrophic supply have been shown to reduce SGN degeneration in vitro and in vivo. In the present study, nanoporous silica nanoparticles (NPSNPs), with an approximate diameter of <100 nm, were loaded with the brain-derived neurotrophic factor (BDNF) to test their efficacy as long-term delivery system for neurotrophins. The neurotrophic factor was released constantly from the NPSNPs over a release period of 80 days when the surface of the nanoparticles had been modified with amino groups. Cell culture investigations with NIH3T3 fibroblasts attest a good general cytocompatibility of the NPSNPs. In vitro experiments with SGNs indicate a significantly higher survival rate of SGNs in cell cultures that contained BDNF-loaded nanoparticles compared to the control culture with unloaded NPSNPs (p<0.001). Importantly, also the amounts of BDNF released up to a time period of 39 days increased the survival rate of SGNs. Thus, NPSNPs carrying BDNF are suitable for the treatment of inner ear disease and for the protection and the support of SGNs. Their nanoscale nature and the fact that a direct contact of the nanoparticles and the SGNs is not necessary for neuroprotective effects, should allow for the facile preparation of nanocomposites, e.g., with biocompatible polymers, to install coatings on implants for the realization of implant-based growth factor delivery systems.

Collagen for brain repair: therapeutic perspectives

Biomaterials have increasingly become a focus of research on neuroprotection and neuroregeneration. Collagen, in terms of brain repair, presents many advantages such as being remarkably biocompatible, biodegradable, versatile and non-toxic. Collagen can be used to form injectable scaffolds and micro/nano spheres in order to: (i) locally release therapeutic factors with the aim of protecting degenerating neurons in neurodegenerative conditions such as Alzheimer's or Parkinson's diseases, (ii) encapsulate stem cells for safe delivery, (iii) encapsulate genetically modified cells to provide a long term source of trophic factors, (iv) fill in the voids from injury to serve as a structural support and provide a permissive microenvironment to promote axonal growth. This mini-review summarizes different applications of collagen biomaterial for central nervous system protection and repair, as well as the future perspectives. Overall, collagen is a promising natural biomaterial with various applications which has the potential to progress the development of therapeutic strategies in central nervous system injuries and degeneration.

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.

Emerging treatments for Alzheimer's disease for non-amyloid and non-tau targets

INTRODUCTION

The number of people with dementia, including Alzheimer's disease, is growing as a result of an ageing global population. Treatments available for AD only alleviate the symptoms of the disease, and are effective in some people with AD for a limited time. There is no disease-modifying treatment available, and despite research efforts, the underlying mechanisms of AD and optimal treatment targets have not been fully elucidated. Amyloid and tau are key pathological markers of AD with ongoing trials targeting both. However, there are also many trials at various stages of development that primarily target other markers and processes implicated in the disease, which are now being investigated. Areas covered: This review summarizes current treatment approaches for AD and explores both repositioned and novel therapies that target non amyloid and non tau mechanisms that are in the clinical trials pipeline. This includes treatments for cognitive and neuropsychiatric symptoms and potentially disease modifying therapies. The studies included in this review have been obtained from searches of PubMed and clinical trials databases. Expert commentary: There is a renewed energy in identifying better treatments for behavioural symptoms of AD using both novel drugs and repositioning existing drugs. Lack of success in clinical trials of drugs targeting amyloid and tau have led to a surge in targeting alternative mechanisms. Progress in the development of biomarkers will provide further tools for clinical trials of potential therapeutics for both symptomatic treatment and disease modification in AD.

The influence of surface charge on serum protein interaction and cellular uptake: studies with dendritic polyglycerols and dendritic polyglycerol-coated gold nanoparticles

Nanoparticles (NPs) have gained huge interest in the medical field, in particular for drug delivery purposes. However, binding of proteins often leads to fast NP uptake and rapid clearance, thereby hampering medical applications. Thus, it is essential to determine and control the bio-nano interface. This study investigated the serum protein interactions of dendritic polyglycerols (dPGs), which are promising drug delivery candidates by means of two dimensional gel electrophoresis (2DE) in combination with mass spectrometry. In order to investigate the influence of surface charge, sulfated (sulfated dendritic polyglycerol [dPGS]) and non-sulfated (dPGOH) surfaces were applied, which were synthesized on a gold core allowing for easier separation from unbound biomolecules through centrifugation. Furthermore, two different sizes for dPGS were included. Although size had only a minor influence, considerable differences were detected in protein affinity for dPGS versus dPGOH surfaces, with dPGOH binding much less proteins. Cellular uptake into human CD14+ monocytes was analyzed by flow cytometry, and dPGOH was taken up to a much lower extent compared to dPGS. By using a pull-down approach, possible cellular interaction partners of serum pre-incubated dPGS-Au20 NPs from the membrane fraction of THP-1 cells could be identified such as for instance the transferrin receptor or an integrin. Clathrin-mediated endocytosis was further investigated using chlorpromazine as an inhibitor, which resulted in a 50% decrease of the cellular uptake of dPGS. This study could confirm the influence of surface charge on protein interactions and cellular uptake of dPGS. Furthermore, the approach allowed for the identification of possible uptake receptors and insights into the uptake mechanism.

CNS Targeted Nanoparticle Drug Delivery

The idea of formulating brain permeable nanoparticles stems from the need to treat various neurological disorders like Parkinson's disease, Alzheimer's disease, schizophrenia, depression and brain tumors. Neuropeptides, antibiotics, anticancer drugs and many CNS active drugs cannot cross blood brain barrier (BBB). Studies have revealed that when these drugs are loaded on to nanoparticles they not only cross BBB, but also exhibit decreased side effects. The drug can be dissolved, dispersed, encapsulated inside the nanoparticle or attached on to surface of nanoparticles. In 1995, dalargin was the first drug to be delivered across blood brain barrier (BBB) using polysorbate 80 coated nanoparticles. The size of nanoparticles is usually between 10-1000nm. For crossing BBB it should be less than 300 nm.

Fluorescent polymeric nanovehicles for neural stem cell modulation

Nanomaterials are emerging as strong candidates for applications in drug delivery and offer an alternative platform to modulate the differentiation and activity of neural stem cells. Herein we report the synthesis and characterization of two different classes of polymeric nanoparticles: N-isopropylacrylamide-based thermoresponsive nanogels RM1 and P(TEGA)-b-P(_d,lLA)₂ nano-micelles RM2. We covalently linked the nanoparticles with fluorescent tags and demonstrate their ability to be internalized and tracked in neural stem cells from the postnatal subventricular zone, without affecting their proliferation, multipotency and differentiation characteristics up to 150 μg ml^-1. The difference in chemical structure of RM1 and RM2 does not appear to impact toxicity however it influences the loading capacity. Nanogels RM1 loaded with retinoic acid improve solubility of the drug which is released at 37 °C, resulting in an increase in the number of neurons, comparable to what can be obtained with a solution of the free drug solubilised with a small percentage of DMSO.

Prediction of new drug indications based on clinical data and network modularity

Drug repositioning is commonly done within the drug discovery process in order to adjust or expand the application line of an active molecule. Previous computational methods in this domain mainly focused on shared genes or correlations between genes to construct new drug-disease associations. We propose a method that can not only handle drugs or diseases with or without related genes but consider the network modularity. Our method firstly constructs a drug network and a disease network based on side effects and symptoms respectively. Because similar drugs imply similar diseases, we then cluster the two networks to identify drug and disease modules, and connect all possible drug-disease module pairs. Further, based on known drug-disease associations in CTD and using local connectivity of modules, we predict potential drug-disease associations. Our predictions are validated by testing their overlaps with drug indications reported in published literatures and CTD, and KEGG enrichment analysis are also made on their related genes. The experimental results demonstrate that our approach can complement the current computational approaches and its predictions can provide new clues for the candidate discovery of drug repositioning.

Nanomedicine in Central Nervous System (CNS) Disorders: A Present and Future Prospective

Purpose: For the past few decades central nervous system disorders were considered as a major strike on human health and social system of developing countries. The natural therapeutic methods for CNS disorders limited for many patients. Moreover, nanotechnology-based drug delivery to the brain may an exciting and promising platform to overcome the problem of BBB crossing. In this review, first we focused on the role of the blood-brain barrier in drug delivery; and second, we summarized synthesis methods of nanomedicine and their role in different CNS disorder. Method: We reviewed the PubMed databases and extracted several kinds of literature on neuro nanomedicines using keywords, CNS disorders, nanomedicine, and nanotechnology. The inclusion criteria included chemical and green synthesis methods for synthesis of nanoparticles encapsulated drugs and, their in-vivo and in-vitro studies. We excluded nanomedicine gene therapy and nanomaterial in brain imaging. Results: In this review, we tried to identify a highly efficient method for nanomedicine synthesis and their efficacy in neuronal disorders. SLN and PNP encapsulated drugs reported highly efficient by easily crossing BBB. Although, these neuro-nanomedicine play significant role in therapeutics but some metallic nanoparticles reported the adverse effect on developing the brain. Conclusion: Although impressive advancement has made via innovative potential drug development, but their efficacy is still moderate due to limited brain permeability. To overcome this constraint,powerful tool in CNS therapeutic intervention provided by nanotechnology-based drug delivery methods. Due to its small and biofunctionalization characteristics, nanomedicine can easily penetrate and facilitate the drug through the barrier. But still, understanding of their toxicity level, optimization and standardization are a long way to go.

Systems-level thinking for nanoparticle-mediated therapeutic delivery to neurological diseases

Neurological diseases account for 13% of the global burden of disease. As a result, treating these diseases costs $750 billion a year. Nanotechnology, which consists of small (~1-100 nm) but highly tailorable platforms, can provide significant opportunities for improving therapeutic delivery to the brain. Nanoparticles can increase drug solubility, overcome the blood-brain and brain penetration barriers, and provide timed release of a drug at a site of interest. Many researchers have successfully used nanotechnology to overcome individual barriers to therapeutic delivery to the brain, yet no platform has translated into a standard of care for any neurological disease. The challenge in translating nanotechnology platforms into clinical use for patients with neurological disease necessitates a new approach to: (1) collect information from the fields associated with understanding and treating brain diseases and (2) apply that information using scalable technologies in a clinically-relevant way. This approach requires systems-level thinking to integrate an understanding of biological barriers to therapeutic intervention in the brain with the engineering of nanoparticle material properties to overcome those barriers. To demonstrate how a systems perspective can tackle the challenge of treating neurological diseases using nanotechnology, this review will first present physiological barriers to drug delivery in the brain and common neurological disease hallmarks that influence these barriers. We will then analyze the design of nanotechnology platforms in preclinical in vivo efficacy studies for treatment of neurological disease, and map concepts for the interaction of nanoparticle physicochemical properties and pathophysiological hallmarks in the brain. WIREs Nanomed Nanobiotechnol 2017, 9:e1422. doi: 10.1002/wnan.1422 For further resources related to this article, please visit the WIREs website.

Development of novel HDL-mimicking α-tocopherol-coated nanoparticles to encapsulate nerve growth factor and evaluation of biodistribution

Nerve Growth Factor (NGF) is one of the members of the neurotrophin family with multifaceted functions. However, clinical application of NGF is hurdled by the challenge on formulation development. The objective of this study was to develop novel high-density lipoproteins (HDL)-mimicking nanoparticles (NPs) coated with α-tocopherol to incorporate NGF by a self-assembly approach. The NPs were prepared by an optimized self-assembly method that is simple and scalable. The composition of HDL-mimicking NPs was optimized. The prototype of the HDL-mimicking α-tocopherol-coated NPs contained phosphatidylserine (a negative charged phospholipid) and d-α-Tocopheryl polyethylene glycol succinate (a source of vitamin E) to enhance the entrapment efficiency of apolipoprotein A-I in the NPs. The entrapment efficiency of apolipoprotein A-I was about 30%. The NPs had particle size about 200nm with a relatively narrow size distribution. Finally, cationic ion-pair agents were optimized to form ion-pairs with NGF to facilitate the incorporation of NGF into the NPs. Protamine sodium salt USP formed an optimal ion-pair complex with NGF. The results showed that the novel HDL-mimicking α-tocopherol-coated NPs successfully encapsulated NGF with over 65% entrapment efficiency by using this ion-pair strategy. In vitro release studies demonstrated a slow release of NGF from NGF NPs in PBS containing 5% BSA at 37°C for 72 h. Further biodistribution studies showed that intravenously injected NGF NPs significantly increased NGF concentration in plasma and decreased the uptake in liver, spleen and kidney, compared to free NGF in mice.

Niosomal approach to brain delivery: Development, characterization and in vitro toxicological studies

The majority of active agents do not readily permeate into brain due to the presence of the blood-brain barrier and blood-cerebrospinal fluid barrier. Currently, the most innovative and promising non-invasive strategy in brain delivery is the design and preparation of nanocarriers, which can move through the brain endothelium. Niosomes can perform brain delivery, in fact polysorbates, can act as an anchor for apolipoprotein E from blood plasma. The particles mimic LDL and interact with the LDL receptor leading to the endothelial cells uptake. The efficacy of niosomes for anticancer therapeutic applications was correlated to their physicochemical and drug delivery properties. Dimensions and ζ-potential were characterized using dynamic light scattering and asymmetric flow-field fractionation system. Lipid bilayer was characterized measuring the fluidity, polarity and microviscosity by fluorescent probe spectra evaluation. Morphology and homogeneity were characterized using atomic force microscopy. Physicochemical stability and serum stability (45% v/v fetal bovine and human serum) were evaluated as a function of time using dynamic light scattering. U87-MG human glioblastoma cells were used to evaluate vesicle cytotoxicity and internalisation efficiency. From the obtained data, the systems appear useful to perform a prolonged (modified) release of biological active substances to the central nervous system.

Brain-derived neurotrophic factor delivered to the brain using poly (lactide-co-glycolide) nanoparticles improves neurological and cognitive outcome in mice with traumatic brain injury

Currently, traumatic brain injury (TBI) is the leading cause of death or disabilities in young individuals worldwide. The multi-complexity of its pathogenesis as well as impermeability of the blood-brain barrier (BBB) makes the drug choice and delivery very challenging. The brain-derived neurotrophic factor (BDNF) regulates neuronal plasticity, neuronal cell growth, proliferation, cell survival and long-term memory. However, its short half-life and low BBB permeability are the main hurdles to be an effective therapeutic for TBI. Poly (lactic-co-glycolic acid) (PLGA) nanoparticles coated by surfactant can enable the delivery of a variety of molecules across the BBB by receptor-mediated transcytosis. This study examines the ability of PLGA nanoparticles coated with poloxamer 188 (PX) to deliver BDNF into the brain and neuroprotective effects of BNDF in mice with TBI. C57bl/6 mice were subjected to weight-drop closed head injuries under anesthesia. Using enzyme-linked immunosorbent assay, we demonstrated that the intravenous (IV) injection of nanoparticle-bound BDNF coated by PX (NP-BDNF-PX) significantly increased BDNF levels in the brain of sham-operated mice (p < 0.001) and in both ipsi- (p < 0.001) and contralateral (p < 0.001) parts of brain in TBI mice compared to controls. This study also showed using the passive avoidance (PA) test, that IV injection of NP-BDNF-PX 3 h post-injury prolonged the latent time in mice with TBI thereby reversing cognitive deficits caused by brain trauma. Finally, neurological severity score test demonstrated that our compound efficiently reduced the scores at day 7 after the injury indicating the improvement of neurological deficit in animals with TBI. This study shows that PLGA nanoparticles coated with PX effectively delivered BDNF into the brain, and improved neurological and cognitive deficits in TBI mice, thereby providing a neuroprotective effect.

Biomaterials for the Treatment of Alzheimer's Disease

Alzheimer’s disease (AD) as a progressive and fatal neurodegenerative disease represents a huge unmet need for treatment. The low efficacy of current treatment methods is not only due to low drug potency but also due to the presence of various obstacles in the delivery routes. One of the main barriers is the blood–brain barrier. The increasing prevalence of AD and the low efficacy of current therapies have increased the amount of research on unraveling of disease pathways and development of treatment strategies. One of the interesting areas for the latter subject is biomaterials and their applications. This interest originates from the fact that biomaterials are very useful for the delivery of therapeutic agents, such as drugs, proteins, and/or cells, in order to treat diseases and regenerate tissues. Recently, manufacturing of nano-sized delivery systems has increased the efficacy and delivery potential of biomaterials. In this article, we review the latest developments with regard to the use of biomaterials for the treatment of AD, including nanoparticles and liposomes for delivery of therapeutic compounds and scaffolds for cell delivery strategies.

Advances in nanomedicine for the treatment of Alzheimer’s and Parkinson’s diseases

Alzheimer‘s disease and Parkinson’s disease are the most common neurodegenerative diseases worldwide. Despite all the efforts made by the scientific community, current available treatments have limited effectiveness, without halting the progression of the disease. That is why, new molecules such as growth factors, antioxidants and metal chelators have been raised as new therapeutical approaches. However, these molecules have difficulties to cross the blood–brain barrier limiting its therapeutic effect. The development of nanometric drug delivery systems may permit a targeted and sustained release of old and new treatments offering a novel strategy to treat these neurodegenerative disorders. This review summarized the main investigated drug delivery systems as promising approaches to treat Alzheimer‘s disease and Parkinson’s disease.

Improving drug delivery technology for treating neurodegenerative diseases

INTRODUCTION

Neurodegenerative diseases (NDs) represent intricate challenges for efficient uptake and transport of drugs to the brain mainly due to the restrictive blood-brain barrier (BBB). NDs are characterized by the loss of neuronal subtypes as sporadic and/or familial and several mechanisms of neurodegeneration have been identified.

AREAS COVERED

This review attempts to recap, organize and concisely evaluate the advanced drug delivery systems designed for treating common NDs. It highlights key research gaps and opinionates on new neurotherapies to overcome the BBB as an addition to the current treatments of countering oxidative stress, inflammation and apoptotic mechanisms.

EXPERT OPINION

Current treatments do not fully address the biological, drug and therapeutic factors faced. This has led to the development of vogue treatments such as nose-to-brain technologies, bio-engineered systems, fusion protein chaperones, stem cells, gene therapy, use of natural compounds, neuroprotectants and even vaccines. However, failure of these treatments is mainly due to the BBB and non-specific delivery in the brain. In order to increase neuroavailability various advanced drug delivery systems provide promising alternatives that are able to augment the treatment of Alzheimer's disease and Parkinson's disease. However, much work is still required in this field beyond the preclinical testing phase.

Nanoparticle transport across the blood brain barrier

While the role of the blood-brain barrier (BBB) is increasingly recognized in the (development of treatments targeting neurodegenerative disorders, to date, few strategies exist that enable drug delivery of non-BBB crossing molecules directly to their site of action, the brain. However, the recent advent of Nanomedicines may provide a potent tool to implement CNS targeted delivery of active compounds. Approaches for BBB crossing are deeply investigated in relation to the pathology: among the main important diseases of the CNS, this review focuses on the application of nanomedicines to neurodegenerative disorders (Alzheimer, Parkinson and Huntington's Disease) and to other brain pathologies as epilepsy, infectious diseases, multiple sclerosis, lysosomal storage disorders, strokes.

Nanoparticles combined with growth factors: recent progress and applications

Increasing attention has been focused on the applications of nanoparticles combined with growth factors (NPs/GFs) due to the substantial functions of GFs in regenerative medicine and disease treatments.

Cytotoxicity and apoptotic gene expression in an in vitro model of the blood-brain barrier following exposure to poly(butylcyanoacrylate) nanoparticles

Background Poly(butylcyanoacrylate) (PBCA) nanoparticles (NPs) loaded with doxorubicin (DOX) and coated with polysorbate 80 (PS80) have shown efficacy in the treatment of rat glioblastoma. However, cytotoxicity of this treatment remains unclear. Purpose The purpose of this study was to investigate cytotoxicity and apoptotic gene expression using a proven in vitro co-culture model of the blood-brain barrier. Methods The co-cultures were exposed to uncoated PBCA NPs, PBCA-PS80 NPs or PBCA-PS80-DOX NPs at varying concentrations and evaluated using a resazurin-based cytotoxicity assay and an 84-gene apoptosis RT-PCR array. Results The cytotoxicity assays showed PBCA-PS80-DOX NPs exhibited a decrease in metabolic function at lower concentrations than uncoated PBCA NPs and PBCA-PS80 NPs. The apoptosis arrays showed differential expression of 18 genes in PBCA-PS80-DOX treated cells compared to the untreated control. Discussion As expected, the cytotoxicity assays demonstrated enhanced dose-dependent toxicity in the DOX loaded NPs. The differentially expressed apoptotic genes participate in both the tumor necrosis factor receptor-1 and mitochondria-associated apoptotic pathways implicated in current DOX chemotherapeutic toxicity. Conclusion The following data suggest that the cytotoxic effect may be attributed to DOX and not the NPs themselves, further supporting the use of PBCA-PS80 NPs as an effective drug delivery vehicle for treating central nervous system conditions.

Current Neurogenic and Neuroprotective Strategies to Prevent and Treat Neurodegenerative and Neuropsychiatric Disorders

The adult central nervous system is commonly known to have a very limited regenerative capacity. The presence of functional stem cells in the brain can therefore be seen as a paradox, since in other organs these are known to counterbalance cell loss derived from pathological conditions. This fact has therefore raised the possibility to stimulate neural stem cell differentiation and proliferation or survival by either stem cell replacement therapy or direct administration of neurotrophic factors or other proneurogenic molecules, which in turn has also originated regenerative medicine for the treatment of otherwise incurable neurodegenerative and neuropsychiatric disorders that take a huge toll on society. This may be facilitated by the fact that many of these disorders converge on similar pathophysiological pathways: excitotoxicity, oxidative stress, neuroinflammation, mitochondrial failure, excessive intracellular calcium and apoptosis. This review will therefore focus on the most promising achievements in promoting neuroprotection and neuroregeneration reported to date.

Therapeutic targets and delivery challenges for Alzheimer’s disease

Dementia, including Alzheimer’s disease, the 21^st Century epidemic, is one of the most significant social and health crises which has currently afflicted nearly 44 million patients worldwide and about new 7.7 million cases are reported every year. This portrays the unmet need towards better understanding of Alzheimer’s disease pathomechanisms and related research towards more effective treatment strategies. The review thus comprehensively addresses Alzheimer’s disease pathophysiology with an insight of underlying multicascade pathway and elaborates possible therapeutic targets- particularly anti-amyloid approaches, anti-tau approaches, acetylcholinesterase inhibitors, glutamatergic system modifiers, immunotherapy, anti-inflammatory targets, antioxidants, 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase inhibitors and insulin. In spite of extensive research leading to identification of newer targets and potent drugs, complete cure of Alzheimer’s disease appears to be an unreached holy grail. This can be attributed to their ineffective delivery across blood brain barrier and ultimately to the brain. With this understanding, researchers are now focusing on development of drug delivery systems to be delivered via suitable route that can circumvent blood brain barrier effectively with enhanced patient compliance. In this context, we have summarized current drug delivery strategies by oral, transdermal, intravenous, intranasal and other miscellaneous routes and have accentuated the future standpoint towards promising therapy ultimately leading to Alzheimer’s disease cure.

Facilitation of Drug Transport across the Blood-Brain Barrier with Ultrasound and Microbubbles

Medical treatment options for central nervous system (CNS) diseases are limited due to the inability of most therapeutic agents to penetrate the blood–brain barrier (BBB). Although a variety of approaches have been investigated to open the BBB for facilitation of drug delivery, none has achieved clinical applicability. Mounting evidence suggests that ultrasound in combination with microbubbles might be useful for delivery of drugs to the brain through transient opening of the BBB. This technique offers a unique non-invasive avenue to deliver a wide range of drugs to the brain and promises to provide treatments for CNS disorders with the advantage of being able to target specific brain regions without unnecessary drug exposure. If this method could be applied for a range of different drugs, new CNS therapeutic strategies could emerge at an accelerated pace that is not currently possible in the field of drug discovery and development. This article reviews both the merits and potential risks of this new approach. It assesses methods used to verify disruption of the BBB with MRI and examines the results of studies aimed at elucidating the mechanisms of opening the BBB with ultrasound and microbubbles. Possible interactions of this novel delivery method with brain disease, as well as safety aspects of BBB disruption with ultrasound and microbubbles are addressed. Initial translational research for treatment of brain tumors and Alzheimer’s disease is presented.

Size, surface charge, and shape determine therapeutic effects of nanoparticles on brain and retinal diseases

Nanoparticles can be valuable therapeutic options to overcome physical barriers to reach central nervous system. Systemically administered nanoparticles can pass through blood-neural barriers; whereas, locally injected nanoparticles directly reach neuronal and perineuronal cells. In this review, we highlight the importance of size, surface charge, and shape of nanoparticles in determining therapeutic effects on brain and retinal diseases. These features affect overall processes of delivery of nanoparticles: in vivo stability in blood and other body fluids, clearance via mononuclear phagocyte system, attachment with target cells, and penetration into target cells. Furthermore, they are also determinants of nano-bio interfaces: they determine corona formation with proteins in body fluids. Taken together, we emphasize the importance of considerations on characteristics of nanoparticles more suitable for the treatment of brain and retinal diseases in the development of nanoparticle-based therapeutics.

FROM THE CLINICAL EDITOR

The central nervous system (CNS) remains an area where drug access and delivery are difficult clinically due to the blood brain barrier. With advances in nanotechnology, many researchers have designed and produced nanoparticle-based systems in an attempt to solve this problem. In this concise review, the authors described the current status of drug delivery to the CNS, based on particle size and shape. This article should stimulate more research to be done on future drug design.