Electron microscopic analysis of nanoparticles delivering thioflavin-T after intrahippocampal injection in mouse: implications for targeting beta-amyloid in Alzheimer's disease

Nanotechnological approaches for targeting amyloid-β aggregation with potential for neurodegenerative disease therapy and diagnosis

Neurodegenerative disorders can arise as a result of amyloid-β production and misfolding of its protein. The complex anatomy of the brain and the unresolved mechanics of the central nervous system hinder drug delivery; the brain is sheathed in a highly protective blood-brain barrier, a tightly packed layer of endothelial cells that restrict the entry of certain substances into the brain. Nanotechnology has achieved success in delivery to the brain, with preclinical assessments showing an acceptable concentration of active drugs in the therapeutic range, and nanoparticles can be fabricated to inhibit amyloid and enhance the delivery of the therapeutic molecule. This review focuses on the interactions of nanoparticles with amyloid-β aggregates and provides an assessment of their theranostic potential.

In vitro and in vivo models for anti-amyloidosis nanomedicines

Amyloid diseases are global epidemics characterized by the accumulative deposits of cross-beta amyloid fibrils and plaques. Despite decades of intensive research, few solutions are available for the diagnosis, treatment, and prevention of these debilitating diseases. Since the early work on the interaction of human β₂-microglobulin and nanoparticles by Linse et al. in 2007, the field of amyloidosis inhibition has gradually evolved into a new frontier in nanomedicine offering numerous interdisciplinary research opportunities, especially for materials, chemistry and biophysics. In this review we summarise, for the first time, the in vitro and in vivo models employed thus far in the field of anti-amyloidosis nanomedicines. Based on this systematic summary, we bring forth the notion that, due to the complex and often overlapping physiopathologies of amyloid diseases, there is a crucial need for the appropriate use of in vitro and in vivo models for validating novel anti-amyloidosis nanomedicines, and there is a crucial need for the development of new animal models that reflect the behavioural, symptomatic and cross-talk hallmarks of amyloid diseases such as Alzheimer's (AD), Parkinson's (PD) diseases and type 2 diabetes (T2DM).

Nanoparticle-Based Technology Approaches to the Management of Neurological Disorders

Neurological disorders are the most devastating and challenging diseases associated with the central nervous system (CNS). The blood-brain barrier (BBB) maintains homeostasis of the brain and contributes towards the maintenance of a very delicate microenvironment, impairing the transport of many therapeutics into the CNS and making the management of common neurological disorders such as Alzheimer's disease (AD), Parkinson's disease (PD), cerebrovascular diseases (CVDs) and traumatic brain injury (TBI), exceptionally complicated. Nanoparticle (NP) technology offers a platform for the design of tissue-specific drug carrying systems owing to its versatile and modifiable nature. The prospect of being able to design NPs capable of successfully crossing the BBB, and maintaining a high drug bioavailability in neural parenchyma, has spurred much interest in the field of nanomedicine. NPs, which also come in an array of forms including polymeric NPs, solid lipid nanoparticles (SLNs), quantum dots and liposomes, have the flexibility of being conjugated with various macromolecules, such as surfactants to confer the physical or chemical property desired. These nanodelivery strategies represent potential novel and minimally invasive approaches to the treatment and diagnosis of these neurological disorders. Most of the strategies revolve around the ability of the NPs to cross the BBB via various influx mechanisms, such as adsorptive-mediated transcytosis (AMT) and receptor-mediated transcytosis (RMT), targeting specific biomarkers or lesions unique to that pathological condition, thereby ensuring high tissue-specific targeting and minimizing off-target side effects. In this article, insights into common neurological disorders and challenges of delivering CNS drugs due to the presence of BBB is provided, before an in-depth review of nanoparticle-based theranostic strategies.

Neurotherapeutic applications of nanomedicine for treating Alzheimer's disease

Alzheimer's disease (AD) is a progressive, irreversible, fatal brain disease which disturbs cognitive functions. It affects 35 million people worldwide and the number of people suffering may increase to 100 million by 2050 if no effective treatments are available. The present treatment improves cognitive functions and provide temporary symptomatic relief, but do not stop or delay the disease progression. Moreover, they are mainly available as conventional oral dosage forms and these conventional oral medications lack brain specificity and also produce side effects which leads to poor patient compliance. Brain drug targeting by nanomedicines is a promising approach to improve brain targeting specificity, brain bioavailability and patient compliance. The present review discuses about the currently available pharmacotherapy for AD and the neurotherapeutic applications as well as the advancements of nanomedicine for treating AD. It also highlights the recent advancements of various nanomedicines containing phytopharmaceuticals for treating AD. It is believed that nanomedicines containing approved drugs can be transformed into the clinics hence improve the life style of AD patients.

Nanogold Neuroprotection in Human Neural Stem Cells Against Amyloid-beta-induced Mitochondrial Dysfunction

Alzheimer's disease (AD) is a neuronal dementia with progressive memory loss. Amyloid-beta (Aβ) peptides has major effect in the neurodegenerative disorder, which are thought to promote mitochondrial dysfunction in AD brains. Anti-AD drugs acting upon the brain are generally difficult to develop, often cause serious side effects or lack therapeutic efficacy. Numerous studies have shown the beneficial therapeutic applications of gold nanoparticles (AuNPs), including for neuroprotective events and AD. The aim of this study is to understand how AuNPs could exert their neuroprotective role in AD, for which cell model have chosen human neural stem cells (hNSCs) as the experimental tool. We hypothesize AuNPs protect against Aβ-induced cellular impairment and mitochondrial dysfunction in hNSCs. Here, we show AuNPs increase the survival of hNSCs treated with Aβ via downregulation of caspase 3 and 9 activities. Moreover, AuNPs abrogated the Aβ-mediated decrease neuroprotective (CREB and Bcl-2) and mitochondrial (PGC1α, NRF-1 and Tfam) gene expressions in treated hNSCs. Importantly, co-treatment with AuNPs significantly rescued hNSCs from Aβ-mediated mitochondrial function and morphology. AuNPs also significantly normalizes the immunostaining of mitochondrial marker and mass in differentiated hNSCs with Aβ. The effects may be exerted by the AuNPs, as supported by its protective reversal of Aβ-induced cellular impairment and mitochondrial dysfunction in hNSCs. In fact, the results presented extend our understanding of the mechanisms through which AuNPs could exert their neuroprotective role in hNSCs treated with Aβ.

Nanotechnology-based Targeting of Neurodegenerative Disorders: A Promising Tool for Efficient Delivery of Neuromedicines

Traditional drug delivery approaches remained ineffective in offering better treatment to various neurodegenerative disorders (NDs). In this context, diverse types of nanocarriers have shown their great potential to cross the blood-brain barrier (BBB) and have emerged as a prominent carrier system in drug delivery. Moreover, nanotechnology-based methods usually involve numerous nanosized carrier platforms, which potentiate the effect of the therapeutic agents in the therapy of NDs especially in diagnosis and drug delivery with negligible side effects. In addition, nanotechnology-based techniques have offered several strategies to cross BBB to intensify the bioavailability of drug moieties in the brain. In the last few years, diverse kinds of nanoparticles (NPs) have been developed by incorporating various biocompatible components (e.g., polysaccharide-based NPs, polymeric NPs, selenium NPs, AuNPs, protein-based NPs, gadolinium NPs, etc.), that showed great therapeutic benefits against NDs. Eventually, this review provides deep insights to explore recent applications of some innovative nanocarriers enclosing active molecules for the efficient treatment of NDs.

Treatment of neurodegenerative disorders through the blood-brain barrier using nanocarriers

Neurodegenerative diseases refer to disorders of the central nervous system (CNS) that are caused by neuronal degradations, dysfunctions, or death. Alzheimer's disease, Parkinson's disease, and Huntington's disease (APHD) are regarded as the three major neurodegenerative diseases. There is a vast body of literature on the causes and treatments of these neurodegenerative diseases. However, the main obstacle in developing an effective treatment strategy is the permeability of the treatment components at the blood-brain barrier (BBB). Several strategies have been developed to improve this obstruction. For example, nanomaterials facilitate drug delivery to the BBB due to their size. They have been used widely in nanomedicine and as nanoprobes for diagnosis purposes among others in neuroscience. Nanomaterials in different forms, such as nanoparticles, nanoemulsions, solid lipid nanoparticles (SLN), and liposomes, have been used to treat neurodegenerative diseases. This review will cover the basic concepts and applications of nanomaterials in the therapy of APHD.

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.

Nanobiomaterials' applications in neurodegenerative diseases

The blood-brain barrier is the interface between the blood and brain, impeding the passage of most circulating cells and molecules, protecting the latter from foreign substances, and maintaining central nervous system homeostasis. However, its restrictive nature constitutes an obstacle, preventing therapeutic drugs from entering the brain. Usually, a large systemic dose is required to achieve pharmacological therapeutic levels in the brain, leading to adverse effects in the body. As a consequence, various strategies are being developed to enhance the amount and concentration of therapeutic compounds in the brain. One such tool is nanotechnology, in which nanostructures that are 1-100 nm are designed to deliver drugs to the brain. In this review, we examine many nanotechnology-based approaches to the treatment of neurodegenerative diseases. The review begins with a brief history of nanotechnology, followed by a discussion of its definition, the properties of most reported nanomaterials, their biocompatibility, the mechanisms of cell-material interactions, and the current status of nanotechnology in treating Alzheimer's, Parkinson's diseases, and amyotrophic lateral sclerosis. Of all strategies to deliver drug to the brain that are used in nanotechnology, drug release systems are the most frequently reported.

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.

Nanotechnology-based drug delivery systems for the treatment of Alzheimer's disease

Alzheimer's disease is a neurological disorder that results in cognitive and behavioral impairment. Conventional treatment strategies, such as acetylcholinesterase inhibitor drugs, often fail due to their poor solubility, lower bioavailability, and ineffective ability to cross the blood-brain barrier. Nanotechnological treatment methods, which involve the design, characterization, production, and application of nanoscale drug delivery systems, have been employed to optimize therapeutics. These nanotechnologies include polymeric nanoparticles, solid lipid nanoparticles, nanostructured lipid carriers, microemulsion, nanoemulsion, and liquid crystals. Each of these are promising tools for the delivery of therapeutic devices to the brain via various routes of administration, particularly the intranasal route. The objective of this study is to present a systematic review of nanotechnology-based drug delivery systems for the treatment of Alzheimer's disease.

Nanotechnological advances for the delivery of CNS therapeutics

Effective non-invasive treatment of neurological diseases is often limited by the poor access of therapeutic agents into the central nervous system (CNS). The majority of drugs and biotechnological agents do not readily permeate into brain parenchyma due to the presence of two anatomical and biochemical dynamic barriers: the blood-brain barrier (BBB) and blood-cerebrospinal fluid barrier (BCSFB). Therefore, one of the most significant challenges facing CNS drug development is the availability of effective brain targeting technology. Recent advances in nanotechnology have provided promising solutions to this challenge. Several nanocarriers ranging from the more established systems, e.g. polymeric nanoparticles, solid lipid nanoparticles, liposomes, micelles to the newer systems, e.g. dendrimers, nanogels, nanoemulsions and nanosuspensions have been studied for the delivery of CNS therapeutics. Many of these nanomedicines can be effectively transported across various in vitro and in vivo BBB models by endocytosis and/or transcytosis, and demonstrated early preclinical success for the management of CNS conditions such as brain tumors, HIV encephalopathy, Alzheimer's disease and acute ischemic stroke. Future development of CNS nanomedicines need to focus on increasing their drug-trafficking performance and specificity for brain tissue using novel targeting moieties, improving their BBB permeability and reducing their neurotoxicity.

Neurotherapeutic applications of nanoparticles in Alzheimer's disease

A rapid increase in incidence of neurodegenerative disorders has been observed with the aging of the population. Alzheimer's disease (AD) is the most common neurodegenerative disorder among the elderly. It is characterized by memory dysfunction, loss of lexical access, spatial and temporal disorientation and impairment of judgement clinically. Unfortunately, clinical development of drugs for the symptomatic and disease-modifying treatment of AD has resulted in both promise and disappointment. Indeed, a large number of drugs with differing targets and mechanisms of action were investigated with only a few of them being clinically available. The targeted drug delivery to the central nervous system (CNS), for the diagnosis and treatment of neurodegenerative disorders such as AD, is restricted due to the limitations posed by the blood-brain barrier (BBB) as well as due to opsonization by plasma proteins in the systemic circulation and peripheral side-effects. Over the last decade, nanoparticle-mediated drug delivery represents one promising strategy to successfully increase the CNS penetration of several therapeutic moieties. Different nanocarriers are being investigated to treat and diagnose AD by delivering at a constant rate a host of therapeutics over times extending up to days, weeks or even months. This review provides a concise incursion on the current pharmacotherapies for AD besides reviewing and discussing the literature on the different drug molecules that have been successfully encapsulated in nanoparticles (NPs). Some of them have been shown to cross the BBB and have been tested either for diagnosis or treatment of AD. Finally, the route of NPs administration and the future prospects will be discussed.

Nanotechnological applications for the treatment of neurodegenerative disorders

Nanotechnology employs engineered materials or devices that interact with biological systems at a molecular level and could revolutionize the treatment of neurodegenerative disorders (NDs) by stimulating, responding to and interacting with target sites to induce physiological responses while minimizing side-effects. Conventional drug delivery systems do not provide adequate cyto-architecture restoration and connection patterns that are essential for functional recovery in NDs, due to limitations posed by the restrictive blood-brain barrier. This review article provides a concise incursion into the current and future applications of nano-enabled drug delivery systems for the treatment of NDs, in particular Alzheimer's and Parkinson's diseases, and explores the application of nanotechnology in clinical neuroscience to develop innovative therapeutic modalities for the treatment of NDs.

Nanoparticle-chelator conjugates as inhibitors of amyloid-beta aggregation and neurotoxicity: a novel therapeutic approach for Alzheimer disease

Oxidative stress and amyloid-beta are considered major etiological and pathological factors in the initiation and promotion of neurodegeneration in Alzheimer disease (AD). Insomuch as causes of such oxidative stress, transition metals, such as iron and copper, which are found in high concentrations in the brains of AD patients and accumulate specifically in the pathological lesions, are viewed as key contributors to the altered redox state. Likewise, the aggregation and toxicity of amyloid-beta is dependent upon transition metals. As such, chelating agents that selectively bind to and remove and/or "redox silence" transition metals have long been considered as attractive therapies for AD. However, the blood-brain barrier and neurotoxicity of many traditional metal chelators has limited their utility in AD or other neurodegenerative disorders. To circumvent this, we previously suggested that nanoparticles conjugated to iron chelators may have the potential to deliver chelators into the brain and overcome such issues as chelator bioavailability and toxic side-effects. In this study, we synthesized a prototype nanoparticle-chelator conjugate (Nano-N2PY) and demonstrated its ability to protect human cortical neurons from amyloid-beta-associated oxidative toxicity. Furthermore, Nano-N2PY nanoparticle-chelator conjugates effectively inhibited amyloid-beta aggregate formation. Overall, this study indicates that Nano-N2PY, or other nanoparticles conjugated to metal chelators, may provide a novel therapeutic strategy for AD and other neurodegenerative diseases associated with excess transition metals.

Potential applications of nanotechnologies to Parkinson's disease therapy

Nanotechnology will play a key role in developing new diagnostic and therapeutic tools. Nanotechnologies use engineered materials with the smallest functional organization on the nanometre scale in at least one dimension. Some aspects of the material can be manipulated resulting in new functional properties. Nanotechnology could provide devices to limit and reverse neuropathological disease states, to support and promote functional regeneration of damaged neurons, to provide neuroprotection and to facilitate the delivery of drugs and small molecules across the blood-brain barrier. All of them are relevant to improve current therapy of Parkinson's disease (PD).

Nanoparticle iron chelators: a new therapeutic approach in Alzheimer disease and other neurologic disorders associated with trace metal imbalance

Accumulating evidence suggests that oxidative stress may be a major etiologic factor in initiating and promoting neurodegeneration in Alzheimer disease. Contributing to this, there is a dyshomeostasis of metal ions in Alzheimer disease with abnormally high levels of redox-active metals, particularly iron, in affected areas of the brain. Although it is unclear whether metal excesses are the sole cause of oxidative stress and neurodegeneration or a by-product of neuronal loss, the finding that metal chelators can partially solubilize amyloid-beta deposits in Alzheimer disease suggests a promising therapeutic role for chelating agents. However, the blood-brain barrier and toxicity of known chelators limit their utility. In this study, we suggest that covalent conjugation of iron chelators with nanoparticles may help overcome the limitations in blood-brain barrier permeability of existing chelation therapy. Using in vitro studies, we have shown that a chelator-nanoparticle system and the chelator-nanoparticle system complexed with iron, when incubated with human plasma, preferentially adsorb apolipoprotein E and apolipoprotein A-I, that would facilitate transport into and out of the brain via mechanisms used for transporting low-density lipoprotein. Our studies suggest a unique approach, utilizing nanoparticles, to transport chelators and chelator-metal complexes in both directions across the blood-brain barrier, thus providing safer and more effective chelation treatment in Alzheimer disease and other neurodegenerative diseases.

Thioflavins released from nanoparticles target fibrillar amyloid β in the hippocampus of APP/PS1 transgenic mice

For the delivery of drugs into the brain, the use of nanoparticles as carriers has been described as a promising approach. Here, we prepared nanoparticles as carriers for the model drugs thioflavin T and thioflavin S that bind fibrillar amyloid beta peptides (Abeta). These polymer colloids are composed of a polystyrene core and a degradable PBCA [poly(butyl-2-cyanoacrylate)] shell with a diameter of 90-100nm as shown by dynamic light scattering. Fluorescence spectrophotometric analysis revealed that encapsulated thioflavin T exhibited significantly stronger fluorescence than the free fluorophore. The enzymatic degradation of core-shell nanoparticles, as required in vivo, was shown after their treatment with porcine liver esterase, a non-specific esterase, in vitro. Shells of nanoparticles were dose-dependently degraded while their polystyrene cores remained intact. In the cortices of 7-14 months old APP/PS1 mice with age-dependent beta-amyloidosis, thioflavins selectively targeted fibrillar Abeta after biodegradation-induced release from their nanoparticulate carriers upon intracerebral injection. Collectively, our data suggest that core-shell nanoparticles with controlled degradation in vivo can become versatile tools to trace and clear Abeta in the brain.

Targeted nanoparticles for drug delivery through the blood–brain barrier for Alzheimer's disease

Alzheimer's disease (AD) is the most common cause of dementia among the elderly, affecting 5% of Americans over age 65, and 20% over age 80. An excess of senile plaques (beta-amyloid protein) and neurofibrillary tangles (tau protein), ventricular enlargement, and cortical atrophy characterizes it. Unfortunately, targeted drug delivery to the central nervous system (CNS), for the therapeutic advancement of neurodegenerative disorders such as Alzheimer's, is complicated by restrictive mechanisms imposed at the blood-brain barrier (BBB). Opsonization by plasma proteins in the systemic circulation is an additional impediment to cerebral drug delivery. This review gives an account of the BBB and discusses the literature on biodegradable polymeric nanoparticles (NPs) with appropriate surface modifications that can deliver drugs of interest beyond the BBB for diagnostic and therapeutic applications in neurological disorders, such as AD. The physicochemical properties of the NPs at different surfactant concentrations, stabilizers, and amyloid-affinity agents could influence the transport mechanism.

The contribution of microscopy to the study of Alzheimer's disease, amyloid plaques and Abeta fibrillogenesis

A broad survey is presented in this chapter, dealing with the impact that microscopy has made to the study of Alzheimer's disease, amyloid plaques and amyloid-beta fibrillogenesis. This includes classical light microscopy and the modem immunolabelling and confocal microscopies, together with the contribution of transmission electron microscopy and atomic force microscopy. Whilst usefully standing alone, the individual microscopies often contribute most effectively when they are integrated with cellular, biophysical and molecular approaches.