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Lipid nanoparticle mediated small interfering RNA delivery as a potential therapy for Alzheimer's disease
Abstract
Alzheimer's disease (AD) is a neurodegenerative condition that exhibits a gradual decline in cognitive function and is prevalent among a significant number of individuals globally. The use of small interfering RNA (siRNA) molecules in RNA interference (RNAi) presents a promising therapeutic strategy for AD. Lipid nanoparticles (LNPs) have been developed as a delivery vehicle for siRNA, which can selectively suppress target genes, by enhancing cellular uptake and safeguarding siRNA from degradation. Numerous research studies have exhibited the effectiveness of LNP‐mediated siRNA delivery in reducing amyloid beta (Aβ) levels and enhancing cognitive function in animal models of AD. The feasibility of employing LNP‐mediated siRNA delivery as a therapeutic approach for AD is emphasized by the encouraging outcomes reported in clinical studies for other medical conditions. The use of LNP‐mediated siRNA delivery has emerged as a promising strategy to slow down or even reverse the progression of AD by targeting the synthesis of tau phosphorylation and other genes linked to the condition. Improvement of the delivery mechanism and determination of the most suitable siRNA targets are crucial for the efficacious management of AD. This review focuses on the delivery of siRNA through LNPs as a promising therapeutic strategy for AD, based on the available literature.
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In an ever-increasing aged world, Alzheimer’s disease (AD) represents the first cause of dementia and one of the first chronic diseases in elderly people. With 55 million people affected, the WHO considers AD to be a disease with public priority. Unfortunately, there are no final cures for this pathology. Treatment strategies are aimed to mitigate symptoms, i.e., acetylcholinesterase inhibitors (AChEI) and the N-Methyl-D-aspartate (NMDA) antagonist Memantine. At present, the best approaches for managing the disease seem to combine pharmacological and non-pharmacological therapies to stimulate cognitive reserve. Over the last twenty years, a number of drugs have been discovered acting on the well-established biological hallmarks of AD, deposition of β-amyloid aggregates and accumulation of hyperphosphorylated tau protein in cells. Although previous efforts disappointed expectations, a new era in treating AD has been working its way recently. The Food and Drug Administration (FDA) gave conditional approval of the first disease-modifying therapy (DMT) for the treatment of AD, aducanumab, a monoclonal antibody (mAb) designed against Aβ plaques and oligomers in 2021, and in January 2023, the FDA granted accelerated approval for a second monoclonal antibody, Lecanemab. This review describes ongoing clinical trials with DMTs and non-pharmacological therapies. We will also present a future scenario based on new biomarkers that can detect AD in preclinical or prodromal stages, identify people at risk of developing AD, and allow an early and curative treatment.
Alzheimer’s disease (AD) is a chronic neurodegenerative disorder that is accompanied by deficits in memory and cognitive functions. The disease is pathologically characterised by the accumulation and aggregation of an extracellular peptide referred to as amyloid-β (Aβ) in the form of amyloid plaques and the intracellular aggregation of a hyperphosphorelated protein tau in the form of neurofibrillary tangles (NFTs) that cause neuroinflammation, synaptic dysfunction, and oxidative stress. The search for pathomechanisms leading to disease onset and progression has identified many key players that include genetic, epigenetic, behavioural, and environmental factors, which lend support to the fact that this is a multi-faceted disease where failure in various systems contributes to disease onset and progression. Although the vast majority of individuals present with the sporadic (non-genetic) form of the disease, dysfunctions in numerous protein-coding and non-coding genes have been implicated in mechanisms contributing to the disease. Recent studies have provided strong evidence for the association of non-coding RNAs (ncRNAs) with AD. In this review, we highlight the current findings on changes observed in circular RNA (circRNA), microRNA (miRNA), short interfering RNA (siRNA), piwi-interacting RNA (piRNA), and long non-coding RNA (lncRNA) in AD. Variations in these ncRNAs could potentially serve as biomarkers or therapeutic targets for the diagnosis and treatment of Alzheimer’s disease. We also discuss the results of studies that have targeted these ncRNAs in cellular and animal models of AD with a view for translating these findings into therapies for Alzheimer’s disease.
Keywords: ncRNA; circRNA; miRNA; siRNA; piRNA; lncRNA; biomarkers; therapeutic targets
Alzheimer’s disease (AD) predominantly occurs as a late onset (LOAD) form involving neurodegeneration and cognitive decline with progressive memory loss. Risk factors that include aging promote accumulation of AD pathologies, such as amyloid-beta and tau aggregates, as well as inflammation and oxidative stress. Homeostatic glial states regulate and suppress pathology buildup; inflammatory states exacerbate pathology by releasing pro-inflammatory cytokines. Multiple stresses likely induce glial senescence, which could decrease supportive functions and reinforce inflammation. In this perspective, we hypothesize that aging first drives AD pathology burden, whereafter AD pathology putatively induces glial senescence in LOAD. We hypothesize that increasing glial senescence, particularly local senescent microglia accumulation, sustains and drives perpetuating buildup and spread of AD pathologies, glial aging, and further senescence. We predict that increasing glial senescence, particularly local senescent microglia accumulation, also transitions individuals from healthy cognition into mild cognitive impairment and LOAD diagnosis. These pathophysiological underpinnings may centrally contribute to LOAD onset, but require further mechanistic investigation.
In 2021, the US Food and Drug Administration (FDA) granted approval to aducanumab, an antiamyloid antibody for early-stage Alzheimer's disease, despite a lack of clear clinical evidence demonstrating the drug's cognitive benefits. The manufacturer initially priced the drug at a staggering $56,000 per year, a price that was later reduced to $28,200. Unfortunately, these costs do not include the additional expenses associated with monitoring the treatment. However, the Centers for Medicare and Medicaid Services (CMS) recently announced that they will only cover individuals enrolled in clinical trials and will limit coverage of future antiamyloid antibodies. This discrepancy between the FDA and CMS positions has caused confusion and concerns for patients who could potentially benefit from antiamyloid therapy. It is important to acknowledge the clinical and economic uncertainties surrounding aducanumab and its potential impacts on future antiamyloid drug development and approval processes. The FDA's approval, despite limited clinical evidence, raises questions about the integrity and rigor of the approval process. The drug's high cost also raises accessibility concerns, especially for those without insurance or sufficient financial resources. Given the CMS's limited coverage policy, it's critical to evaluate the long-term implications of this decision on future antiamyloid drug development. Without adequate support and coverage from insurance providers, the development and approval of future Alzheimer's treatments may be hindered. In summary, the approval and pricing of aducanumab, coupled with the CMS's limited coverage policy, has created a confusing and concerning landscape for Alzheimer's patients. It's important that stakeholders, including patients, clinicians, insurers, and regulatory bodies, work together to address these challenges and ensure that individuals with Alzheimer's have access to effective, affordable treatments.
RNA-delivery is a promising tool to develop therapies for difficult to treat diseases such as neurological disorders, by silencing pathological genes or expressing therapeutic proteins. However, in many cases RNA delivery requires a vesicle that could effectively protect the molecule from bio-degradation, bypass barriers i.e., the blood brain barrier, transfer it to a targeted tissue and efficiently release the RNA inside the cells. Many vesicles such as viral vectors, and polymeric nanoparticles have been mentioned in literature. In this review, we focus in the discussion of lipid-based advanced RNA-delivery platforms. Liposomes and lipoplexes, solid lipid nanoparticles and lipid nanoparticles are the main categories of lipidic platforms for RNA-delivery to the central nervous systems (CNS). A variety of surface particles’ modifications and routes of administration have been studied to target CNS providing encouraging results in vivo . It is concluded that lipid-based nanoplatforms will play a key role in the development of RNA neuro-therapies.
Alzheimer’s disease (AD), the most common form of dementia, is a progressive and multifactorial neurodegenerative disorder whose primary causes are mostly unknown. Due to the increase in life expectancy of world population, including developing countries, AD, whose incidence rises dramatically with age, is at the forefront among neurodegenerative diseases. Moreover, a definitive cure is not yet within reach, imposing substantial medical and public health burdens at every latitude. Therefore, the effort to devise novel and effective therapeutic strategies is still of paramount importance. Genetic, functional, structural and biochemical studies all indicate that new and efficacious drug delivery strategies interfere at different levels with various cellular and molecular targets. Over the last few decades, therapeutic development of nanomedicine at preclinical stage has shown to progress at a fast pace, thus paving the way for its potential impact on human health in improving prevention, diagnosis, and treatment of age-related neurodegenerative disorders, including AD. Clinical translation of nano-based therapeutics, despite current limitations, may present important advantages and innovation to be exploited in the neuroscience field as well. In this state-of-the-art review article, we present the most promising applications of polymeric nanoparticle-mediated drug delivery for bypassing the blood-brain barrier of AD preclinical models and boost pharmacological safety and efficacy. In particular, novel strategic chemical functionalization of polymeric nanocarriers that could be successfully employed for treating AD are thoroughly described. Emphasis is also placed on nanotheranostics as both potential therapeutic and diagnostic tool for targeted treatments. Our review highlights the emerging role of nanomedicine in the management of AD, providing the readers with an overview of the nanostrategies currently available to develop future therapeutic applications against this chronic neurodegenerative disease.
Alzheimer's disease (AD), as a progressive and irreversible brain disorder, remains the most universal neurodegenerative disease. No effective therapeutic methods are established yet due to the hindrance of the blood‐brain barrier (BBB) and the complex pathological condition of AD. Therefore, a multifunctional nanocarrier (Rapa@DAK/siRNA) for AD treatment is constructed to achieve small interfering RNA of β‐site precursor protein (APP) cleaving enzyme‐1 (BACE1 siRNA) and rapamycin co‐delivery into the brain, based on Aleuria aurantia lectin (AAL) and β‐amyploid (Aβ)‐binding peptides (KLVFF) modified PEGylated dendrigraft poly‐l‐lysines (DGLs) via intranasal administration. Nasal administration provides an effective way to deliver drugs directly into the brain through the nose‐to‐brain pathway. AAL, specifically binding to L‐fucose located in the olfactory epithelium, endows Rapa@DAK/siRNA with high brain entry efficiency through intranasal administration. KLVFF peptide as an Aβ targeting ligand and aggregation inhibitor enables nanoparticles to bind with Aβ, inhibit Aβ aggregation, and reduce toxicity. Meanwhile, the release of BACE1 siRNA and rapamycin is confirmed to reduce BACE1 expression, promote autophagy, and reduce Aβ deposition. Rapa@DAK/siRNA is verified to improve the cognition of transgenic AD mice after intranasal administration. Collectively, the multifunctional nanocarrier provides an effective and potential intranasal avenue for combination therapy of AD.
Lipid nanoparticle (LNP)-based drug delivery systems have become the most clinically advanced non-viral delivery technology. LNPs can encapsulate and deliver a wide variety of bioactive agents, including the small molecule drugs, proteins and peptides, and nucleic acids. However, as the physicochemical properties of small- and macromolecular cargos can vary drastically, every LNP carrier system needs to be carefully tailored in order to deliver the cargo molecules in a safe and efficient manner. Our group applied the combinatorial library synthesis approach and in vitro and in vivo screening strategy for the development of LNP delivery systems for drug delivery. In this Review, we highlight our recent progress in the design, synthesis, characterization, evaluation, and optimization of combinatorial LNPs with novel structures and properties for the delivery of small- and macromolecular therapeutics both in vitro and in vivo. These delivery systems have enormous potentials for cancer therapy, antimicrobial applications, gene silencing, genome editing, and more. We also discuss the key challenges to the mechanistic study and clinical translation of new LNP-enabled therapeutics.
Alzheimer’s disease (AD) is an irreversible and progressive neurodegenerative disorder. Most existing treatments only provide symptomatic solutions. Here, we introduce currently available commercial drugs and new therapeutics, including repositioned drugs, to treat AD. Despite tremendous efforts, treatments targeting the hallmarks of AD show limited efficacy. Challenges in treating AD are partly caused by difficulties in penetrating the blood–brain barrier (BBB). Recently, nanoparticle (NP)-based systems have shown promising potential as precision medicines that can effectively penetrate the BBB and enhance the targeting ability of numerous drugs. Here, we describe how NPs enter the brain by crossing, avoiding, or disrupting the BBB. In addition, we provide an overview of the action of NPs in the microenvironment of the brain for the treatment of AD. Diverse systems, including liposomes, micelles, polymeric NPs, solid-lipid NPs, and inorganic NPs, have been investigated for NP drug loading to relieve AD symptoms, target AD hallmarks, and target moieties to diagnose AD. We also highlight NP-based immunotherapy, which has recently gained special attention as a potential treatment option to disrupt AD progression. Overall, this review focuses on recently investigated NP systems that represent innovative strategies to understand AD pathogenesis and suggests treatment and diagnostic modalities to cure AD.
Alzheimer’s disease (AD) is the most common cause of dementia in the elderly, clinically defined by progressive cognitive decline and pathologically, by brain atrophy, neuroinflammation, and accumulation of extracellular amyloid plaques and intracellular neurofibrillary tangles. Neurotechnological approaches, including optogenetics and deep brain stimulation, have exploded as new tools for not only the study of the brain but also for application in the treatment of neurological diseases. Here, we review the current state of AD therapeutics and recent advancements in both invasive and non-invasive neurotechnologies that can be used to ameliorate AD pathology, including neurostimulation via optogenetics, photobiomodulation, electrical stimulation, ultrasound stimulation, and magnetic neurostimulation, as well as nanotechnologies employing nanovectors, magnetic nanoparticles, and quantum dots. We also discuss the current challenges in developing these neurotechnological tools and the prospects for implementing them in the treatment of AD and other neurodegenerative diseases.
Alzheimer's disease (AD) represents a particular therapeutic challenge because its aetiology is very complex, with dynamic progression from preclinical to clinical stages. Several potential therapeutic targets and strategies were tested for AD, in over 2000 clinical trials, but no disease-modifying therapy exists. This failure indicates that AD, as a multifactorial disease, may require multi-targeted approaches and the delivery of therapeutic molecules to the right place and at the right disease stage. Opportunities to meet the challenges of AD therapy appear to come from recent progress in knowledge and methodological advances in the design, synthesis, and targeting of brain mRNA and microRNA with synthetic antisense oligonucleotides (ASOs). Several types of ASOs allow the utilisation of different mechanisms of posttranscriptional regulation and offer enhanced effects over alternative therapeutics. This article reviews ASO-based approaches and targets in preclinical and clinical trials for AD, and presents the future perspective on ASO therapies for AD.
Drug delivery to central nervous system (CNS) diseases is very challenging since the presence of the innate blood–brain barrier (BBB) and the blood-cerebrospinal fluid barrier that impede drug delivery. Among new strategies to overcome these limitations and successfully deliver drugs to the CNS, nanotechnology-based drug delivery platform, offers potential therapeutic approach for the treatment of some common neurological disorders like Alzheimer’s disease, frontotemporal dementia, amyotrophic lateral sclerosis, Parkinson’s disease, Huntington’s disease. This review aimed to highlight advances in research on the development of nano-based therapeutics for their implications in therapy of CNS disorders. The challenges during clinical translation of nanomedicine from bench to bed side is also discussed.
Neurodegenerative disorders involve the slow and gradual degeneration of axons and neurons in the central nervous system (CNS), resulting in abnormalities in cellular function and eventual cellular demise. Patients with these disorders succumb to the high medical costs and the disruption of their normal lives. Current therapeutics employed for treating these diseases are deemed palliative. Hence, a treatment strategy that targets the disease’s cause, not just the symptoms exhibited, is desired. The synergistic use of nanomedicine and gene therapy to effectively target the causative mutated gene/s in the CNS disease progression could provide the much-needed impetus in this battle against these diseases. This review focuses on Parkinson’s and Alzheimer’s diseases, the gene/s and proteins responsible for the damage and death of neurons, and the importance of nanomedicine as a potential treatment strategy. Multiple genes were identified in this regard, each presenting with various mutations. Hence, genome-wide sequencing is essential for specific treatment in patients. While a cure is yet to be achieved, genomic studies form the basis for creating a highly efficacious nanotherapeutic that can eradicate these dreaded diseases. Thus, nanomedicine can lead the way in helping millions of people worldwide to eventually lead a better life.
The master regulator of the fibrosis cascade is the myocardin-related transcription factor/serum response factor (MRTF/SRF) pathway, making it a key target for anti-fibrotic therapeutics. In the past, inhibitors and small interfering RNAs (siRNAs) targeting the MRTF-B gene have been deployed to counter fibrosis in the eye, with the latter showing promising results. However, the biggest challenge in implementing siRNA therapeutics is the method of delivery. In this study, we utilised the novel, pH-sensitive, cationic lipid CL4H6, which has previously demonstrated potent targeting of hepatocytes and endosomal escape, to safely and efficiently deliver an MRTF-B siRNA into human conjunctival fibroblasts. We prepared two lipid nanoparticle (LNP) formulations, incorporating targeting cleavable peptide cY in one of them, and measured their physicochemical properties and silencing effect in human conjunctival fibroblasts. Both proved to be non-cytotoxic at a concentration of 50 nM and effectively silenced the MRTF-B gene in vitro, with the targeting cleavable peptide not affecting the silencing efficiency [LNP with cY: 62.1% and 81.5% versus LNP without cY: 77.7% and 80.2%, at siRNA concentrations of 50 nM (p = 0.06) and 100 nM (p = 0.09), respectively]. On the other hand, the addition of the targeting cleavable peptide significantly increased the encapsulation efficiency of the LNPs from 92.5% to 99.3% (p = 0.0005). In a 3D fibroblast-populated collagen matrix model, both LNP formulations significantly decreased fibroblast contraction after a single transfection. We conclude that the novel PEGylated CL4H6-MRTF-B siRNA-loaded LNPs represent a promising therapeutic approach to prevent conjunctival fibrosis after glaucoma filtration surgery.
Background
Successful development of agents that improve cognition and behavior in Alzheimer’s disease (AD) is critical to improving the lives of patients manifesting the symptoms of this progressive disorder.
Discussion
There have been no recent approvals of cognitive enhancing agents for AD. There are currently 6 cognitive enhancers in Phase 2 trials and 4 in phase 3. They represent a variety of novel mechanisms. There has been progress in developing new treatments for neuropsychiatric symptoms in AD with advances in treatment of insomnia, psychosis, apathy, and agitation in AD. There are currently 4 AD-related psychotropic agents in Phase 2 trials and 7 in Phase 3 trials. Many novel mechanisms are being explored for the treatment of cognitive and behavioral targets. Progress in trial designs, outcomes measures, and population definitions are improving trial conduct for symptomatic treatment of AD.
Conclusions
Advances in developing new agents for cognitive and behavioral symptoms of AD combined with enhanced trial methods promise to address the unmet needs of patients with AD for improved cognition and amelioration of neuropsychiatric symptoms.
Therapeutic small interfering RNAs (siRNAs) are double stranded RNAs capable of potent and specific gene silencing through activation of the RNA interference (RNAi) pathway. The potential of siRNA drugs has recently been highlighted by the approval of multiple siRNA therapeutics. These successes relied heavily on chemically modified nucleic acids and their impact on stability, delivery, potency, and off-target effects. Despite remarkable progress, clinical trials still face failure due to off-target effects such as off-target gene dysregulation. Each siRNA strand can downregulate numerous gene targets while also contributing towards saturation of the RNAi machinery, leading to the upregulation of miRNA-repressed genes. Eliminating sense strand uptake effectively reduces off-target gene silencing and helps limit the disruption to endogenous regulatory mechanisms. Therefore, our understanding of strand selection has a direct impact on the success of future siRNA therapeutics. In this review, the approaches used to improve strand uptake are discussed and effective methods are summarized.
Objective: This review summarizes recent findings on the epigenetics of Alzheimer's disease (AD) and provides therapeutic strategies for AD.
Methods: We searched the following keywords: “genetics,” “epigenetics,” “Alzheimer's disease,” “DNA methylation,” “DNA hydroxymethylation,” “histone modifications,” “non-coding RNAs,” and “therapeutic strategies” in PubMed.
Results: In this review, we summarizes recent studies of epigenetics in AD, including DNA methylation/hydroxymethylation, histone modifications, and non-coding RNAs. There are no consistent results of global DNA methylation/hydroxymethylation in AD. Epigenetic genome-wide association studies show that many differentially methylated sites exist in AD. Several studies investigate the role of histone modifications in AD; for example, histone acetylation decreases, whereas H3 phosphorylation increases significantly in AD. In addition, non-coding RNAs, such as microRNA-16 and BACE1-antisense transcript (BACE1-AS), are associated with the pathology of AD. These epigenetic changes provide us with novel insights into the pathogenesis of AD and may be potential therapeutic strategies for AD.
Conclusion: Epigenetics is associated with the pathogenesis of AD, including DNA methylation/hydroxymethylation, histone modifications, and non-coding RNAs, which provide potential therapeutic strategies for AD.
Toxic aggregated amyloid-β accumulation is a key pathogenic event in Alzheimer’s disease (AD), which derives from amyloid precursor protein (APP) through sequential cleavage by BACE1 (β-site APP cleavage enzyme 1) and γ-secretase. Small interfering RNAs (siRNAs) show great promise for AD therapy by specific silencing of BACE1. However, lack of effective siRNA brain delivery approaches limits this strategy. Here, we developed a glycosylated “triple-interaction” stabilized polymeric siRNA nanomedicine (Gal-NP@siRNA) to target BACE1 in APP/PS1 transgenic AD mouse model. Gal-NP@siRNA exhibits superior blood stability and can efficiently penetrate the blood-brain barrier (BBB) via glycemia-controlled glucose transporter-1 (Glut1)–mediated transport, thereby ensuring that siRNAs decrease BACE1 expression and modify relative pathways. Noticeably, Gal-NP@siBACE1 administration restored the deterioration of cognitive capacity in AD mice without notable side effects. This “Trojan horse” strategy supports the utility of RNA interference therapy in neurodegenerative diseases.
The field of nanomedicine is constantly expanding. Since the first work dated in 1999, almost 28 thousand articles have been published, and more and more are published every year: just think that only in the last five years 20,855 have come out (source PUBMED) including original research and reviews. The goal of this review is to present the current knowledge about nanomedicine in Alzheimer’s disease, a widespread neurodegenerative disorder in the over 60 population that deeply affects memory and cognition. Thus, after a brief introduction on the pathology and on the state-of-the-art research for NPs passing the BBB, special attention is placed to new targets that can enter the interest of nanoparticle designers and to new promising therapies. The authors performed a literature review limited to the last three years (2017–2020) of available studies with the intention to present only novel formulations or approaches where at least in vitro studies have been performed. This choice was made because, while limiting the sector to nanotechnology applied to Alzheimer, an organic census of all the relevant news is difficult to obtain.
The decrease and functional failure of the central cholinergic neurons caused by degeneration and necrosis, not only directly led to a series of clinical symptoms of Alzheimer's disease (AD), but also seriously affected the efficacy of cholinesterase inhibitors. At present, the clinical treatment of AD has extremely limited effect. In this work, a novel nanoparticle incorporating Nogo Receptor-siRNA (NgR-siRNA) and brain derived neurotrophic factor (BDNF) was designed and synthesized to realize the synergic treatment of AD with high efficiency. After brain-targeted modification, the nanoparticles overcome the blood-brain barrier were delivered into the basal forebrain and temporal hippocampus of the AD model by tail vein and brain-directed injection to achieve the effective promotion of the regeneration and repair of cholinergic neurons. The experimental results showed that the proposed nanoparticles could efficiently eliminate the limitations of currently AD treatment methods, enabling it a promising and reliable nanoplatform for AD treatment.
Treatment of brain diseases is always limited by the physiological nature of the highly selective blood-brain barrier (BBB) and the electrostatic charge of the nanoporous extracellular matrix. Nanomedical application provides a promising drug delivery revolution for the treatment of neurodegenerative diseases (NDDs). It depends on improving the pharmacokinetic distribution of drugs through the central nervous system. Nanotechnology offers various forms of nanoparticles, and these nanoparticles have brain-targeted and long-acting properties with minimal systemic adverse effects and motor complications. Gene delivery vehicles and nanocarriers including neurotrophic factors are promising therapeutics for many NDDs, and they can modulate neuronal survival and synaptic connectivity. Neurotrophic factors when integrated with the nanotechnological approaches can pass the BBB merely, representing a significant challenging track. Clinical trials proved that levodopa nanoparticles cause little motor complications which is a considerable drawback in treating Parkinson’s disease with levodopa. Recently, nanotechnology had patented new formulations and achieved various advanced procedures for management, and even prevention, of NDDs. Nanotechnology can be integrated into neuroscience to fight against neurodegenerative diseases. Primary research studies in using nanoparticles to cure Alzheimer disease (AD) are promising but are still in need for more investigations. The present paper aims to review, outline, and summarize various efforts done in the field of using nanoparticles in the management of Alzheimer.
Therapeutic drugs for Alzheimer’s disease have been extensively studied due to its recurrence and abundance among neurodegenerative diseases. It is thought that the accumulation of amyloid precursor protein (APP) products, a consequence of an up-regulation of the β-site APP-cleaving enzyme 1 (BACE1), is the main triggering mechanism during the early stages of the disease. This study aims to explore the ability of a multifunctional conjugate based on magnetite nanoparticles for the cellular delivery of siRNA against the expression of the BACE1 gene. We immobilized the siRNA strand on PEGylated magnetite nanoparticles and investigated the effects on biocompatibility and efficacy of the conjugation. Similarly, we co-immobilized the translocating protein OmpA on PEGylated nanoparticles to enhance cellular uptake and endosomal escape. BACE1 suppression was statistically significant in HFF-1 cells, without any presence of a cytotoxic effect. The delivery of the nanoconjugate was achieved through endocytosis pathways, where endosome formation was likely escaped due to the proton-sponge effect characteristic of PEGylated nanoparticles or mainly by direct translocation in the case of OmpA/PEGylated nanoparticles.
The effective treatment of Alzheimer's disease (AD) is hindered due to the hard blood–brain barrier (BBB) penetration and non‐selective distribution of drugs in the brain. Moreover, the complicated pathological mechanism of AD involves various pathway dysfunctions that limit the effectiveness of a single therapeutic drug. Herein, a dendrigraft poly‐l‐lysines (DGL)‐based siRNA and D peptide (Dp) loaded nanoparticle is designed that could target and penetrate through the BBB, enter the brain parenchyma, and further accumulate at the AD lesion. In this system, T7 peptide, which specifically targets transferrin receptors on the BBB, is linked to DGL via acid‐cleavable long polyethylene glycol (PEG) to achieve high internalization, quick escape from endo/lysosome, and effective transcytosis. Then, the Tet1, which specifically targets diseased neurons, is modified onto DGL by short PEG. After being exposed, Tet1 could drive the nanoparticles to the AD lesion and release the drugs. As a result, the production of β amyloid plaques (Aβ) is inhibited. Neurotoxicity induced by Aβ plaques and tau proten phosphorylation (p‐tau) tangle is also alleviated, and the cognition of AD mice is significantly improved. Overall, this system programmatically targets BBB and neurons, thus, significantly enhances the intracephalic drug accumulation and AD treatment efficacy.
Direct nose-to-brain (N-to-B) delivery enables the rapid transport of drugs to the brain, while minimizing systemic exposure. The objective of this work was to engineer a nanocarrier intended to enhance N-to-B delivery of RNA and to explore its potential utility for the treatment of neurological disorders. Our approach involved the formation of electrostatically driven nanocomplexes between a hydrophobic derivative of octaarginine (r8), chemically conjugated with lauric acid (C12), and the RNA of interest. Subsequently, these cationic nanocomplexes were enveloped (enveloped nanocomplexes, ENCPs) with different protective polymers, i.e. polyethyleneglycol - polyglutamic acid (PEG-PGA) or hyaluronic acid (HA), intended to enhance their stability and mucodiffusion across the olfactory nasal mucosa. These rationally designed ENCPs were produced in bulk format and also using a microfluidics-based technique. This technique enabled the production of a scalable nanoformulation, exhibiting; (i) a unimodal size distribution with a tunable mean size, (ii) the capacity to highly associate (100%) and protect RNA from degradation, (iii) the ability to preserve its physicochemical properties in biorelevant media and prevent the premature RNA release. Moreover, in vitro cell culture studies showed the capacity of ENCPs to interact and be efficiently taken-up by CHO cells. Finally, in vivo experiments in a mouse model of Alzheimer's disease provided evidence of a statistically significant increase of a potentially therapeutic miRNA mimic in the hippocampus area and its further effect on two mRNA targets, following its intranasal administration. Overall, these findings stress the value of the rational design of nanocarriers towards overcoming the biological barriers associated to N-to-B RNA delivery and reveal their potential value as therapeutic strategies in Alzheimer's disease.
The novel class of compounds represented by lipid nanoparticle (LNP)-encapsulated siRNA formulations has an enormous potential to target disease, notably of the liver. Endocytosis of LNPs is believed to be mediated by APOE, an important serum protein of lipoprotein homeostasis. APOE polymorphisms affect binding to hepatic receptors and have been associated with development of specific disease. Here, the role of APOE was investigated with regard to the efficacy of Patisiran, the first LNP-siRNA recently approved for clinical use in patients having transthyretin amyloidosis (ATTR amyloidosis). Patisiran was evaluated in the human hepatoma cell line HepG2 after knockdown of APOE. The APOE genotype was determined in ATTR amyloidosis patients treated with Patisiran. TTR knockdown was monitored in consecutive plasma up to week 12. Downregulation of APOE suppressed efficacy of Patisiran in HepG2 cells. TTR levels were found to be robustly reduced (84.7% ± 1%) following Patisiran treatment in patients plasma. Analysis of APOE polymorphisms in ATTR amyloidosis patients revealed three most frequent genotypes E3/3, E3/4 and E3/2. APOE stratification of patients did not show significant differences of TTR plasma concentrations following treatment. Our results suggest that APOE is an important mediator of TTR silencing by Patisiran, however efficacy is independent of the APOE genotype.
Background
Radiotherapy is commonly used for treating cancer. Novel sensitizers, such as gold nanoparticles (GNPs), are being used to enhance the local radiation dose. It is not known how the uptake and radiation dose enhancement of GNPs vary in synchronized vs unsynchronized (control) tumor cell populations. Successful application of GNPs in radiation therapy requires NPs to be accumulated within individual tumor cells at clinically feasible NP concentrations. Use of small GNPs as a radiation dose enhancer in the past required very high NP concentration, since the driving force for the uptake of smaller GNPs is low. We used a novel lipid-based NP of 50 nm diameter system as a Trojan horse to deliver smaller GNPs of size 5 nm (LNP–GNP) at 0.2 nM concentration. We investigated the changes in GNP uptake and survival fraction with the LNP delivery at different cell stages using human breast cancer as our tumor model and choosing the triple-negative MDA-MB-231 cell line.
Results
Using the LNP–GNP system resulted in a 39- and 73-fold enhancement in uptake of 5 nm GNPs in unsynchronized and synchronized tumor cell populations, respectively. The NP uptake per cell increased from 800 to 1200 and from 30,841 to 88,477 for individual 5 nm GNPs and 5 nm GNPs incorporated in LNPs, respectively. After a radiation dose of 2 Gy with 6 MeV photons, synchronized tumor cell populations incorporated with LNP–GNPs produced a 27% enhancement in tumor cell death compared to the control (unsynchronized; no GNPs; 2 Gy). The findings of our experimental results were supported by modeling predictions based on Monte Carlo calculations.
Conclusions
This study clearly shows that the cell cycle, GNPs, and radiation therapy can be combined to improve outcome of cancer therapy. Using the experimental data, we estimated the predicted improvement for a clinical treatment plan where 30 fractions of 2 Gy radiation dose were given over a period of time. Enhanced uptake and radiation sensitivity of a synchronous tumor cell population would produce a significant improvement in cell killing. For example, synchronizing cells and the addition of LNP–GNPs into tumor cells produced a 1000-fold enhancement in cell killing. Because the agents used for cell synchronization are in clinical practice, this approach may be a simple and cost-effective way to further enhance local radiation dose. Finally, this study provides a novel lipid-based NP platform to further improve GNP-mediated radiation therapy through synchronization of breast cancer cell population.
Drug combinations can improve the control of diseases involving redundant and highly regulated pathways. Validating a multi-target therapy early in drug development remains difficult. Small interfering RNAs (siRNAs) are routinely used to selectively silence a target of interest. Owing to the ease of design and synthesis, siRNAs hold promise for combination therapies. Combining siRNAs against multiple targets remains an attractive approach to interrogating highly regulated pathways. Currently, questions remain regarding how broadly such an approach can be applied, since siRNAs have been shown to compete with one another for binding to Argonaute2 (Ago2), the protein responsible for initiating siRNA-mediated mRNA degradation. Mathematical modeling, coupled with in vitro and in vivo experiments, led us to conclude that endosomal escape kinetics had the highest impact on Ago2 depletion by competing lipid-nanoparticle (LNP)-formulated siRNAs. This, in turn, affected the level of competition observed between them. A future application of this model would be to optimize delivery of desired siRNA combinations in vitro to attenuate competition and maximize the combined therapeutic effect.
An mRNA gene therapy represents a potentially promising therapeutic for curing inflammatory diseases. The transient nature of the gene expression of mRNA would be expected to be beneficial for avoiding undesired side effects. Since the mRNA is a vulnerable molecule, a development of a carrier that can deliver the mRNA to the cytoplasm has a high priority. We report herein on the development of a system for delivering mRNA to the inflammatory lesion in a dextran sulfate sodium (DSS)-induced colitis model. We modulated molecular structures of an ionizable lipid, an SS-cleavable and pH-activated lipid-like material (ssPalm). Among the fatty acids investigated, oleic acid scaffolds (ssPalmO) appeared to be more biocompatible than either myristic acid or linoleic acid scaffolds with the colitis model. The structural modification of the hydrophilic head groups from linear tertiary amines to piperazine rings (ssPalmO-Paz4-C2) resulted in a more than 10-fold higher increasing in the transgene activity in inflammatory colon. The most notable observation is that the transgene activity in the inflammatory colon is significantly higher than that in liver, the major clearance organ of lipid nanoparticles. Collectively, the ssPalmO-Paz4-C2 represents a promising material for the delivery of an mRNA to inflammatory lesions.
Alzheimer’s disease (AD) is a progressive neurodegenerative disease with a complex and heterogeneous pathophysiology. The number of people living with AD is predicted to increase; however, there are no disease-modifying therapies currently available and none have been successful in late-stage clinical trials. Fluid biomarkers measured in cerebrospinal fluid (CSF) or blood hold promise for enabling more effective drug development and establishing a more personalized medicine approach for AD diagnosis and treatment. Biomarkers used in drug development programmes should be qualified for a specific context of use (COU). These COUs include, but are not limited to, subject/patient selection, assessment of disease state and/or prognosis, assessment of mechanism of action, dose optimization, drug response monitoring, efficacy maximization, and toxicity/adverse reactions identification and minimization. The core AD CSF biomarkers Aβ42, t-tau, and p-tau are recognized by research guidelines for their diagnostic utility and are being considered for qualification for subject selection in clinical trials. However, there is a need to better understand their potential for other COUs, as well as identify additional fluid biomarkers reflecting other aspects of AD pathophysiology. Several novel fluid biomarkers have been proposed, but their role in AD pathology and their use as AD biomarkers have yet to be validated. In this review, we summarize some of the pathological mechanisms implicated in the sporadic AD and highlight the data for several established and novel fluid biomarkers (including BACE1, TREM2, YKL-40, IP-10, neurogranin, SNAP-25, synaptotagmin, α-synuclein, TDP-43, ferritin, VILIP-1, and NF-L) associated with each mechanism. We discuss the potential COUs for each biomarker.
Introduction:
A major challenge in treating central nervous system (CNS) disorders is to achieve adequate drug delivery across the blood-brain barrier (BBB). Receptor-mediated nanodrug delivery as a Trojan horse strategy has become an exciting approach. However, these nanodrugs do not accumulate significantly in the brain parenchyma, which greatly limits the therapeutic effect of drugs. Amplifying the efficiency of receptor-mediated nanodrug delivery across the BBB becomes the holy grail in the treatment of CNS disorders.
Areas covered:
In this review, we tend to establish links between dynamic BBB and receptor-mediated nanodrug delivery, starting with the delivery processes across the BBB, describing factors affecting nanodrug delivery efficiency, and summarizing potential strategies that may amplify delivery efficiency.
Expert opinion:
Receptor-mediated nanodrug delivery is a common approach to significantly enhance the efficiency of brain-targeting delivery. As BBB is constantly undergoing changes, it is essential to investigate the impact of diseases on the effectiveness of brain-targeting nanodrug delivery. More critically, there are several barriers to achieving brain-targeting nanodrug delivery in the five stages of receptor-mediated transcytosis (RMT), and the impacts can be conflicting, requiring intricate balance. Further studies are also needed to investigate the material toxicity of nanodrugs to address the issue of clinical translation.
This review provides an overview of recent advances in nanotechnology that are achieved to improve the therapeutic efficiency for treating Alzheimer's disease.
Last few decades unveiled the existence of diverse pool of non-coding RNAs, small RNAs, and repetitive elements which can play a pivotal role in maintaining the cellular homeostasis and dysfunction. Time- and tissue-dependent gene regulation by these small RNAs in-vivo made them a new class of pharmacological agents. The therapeutic effects of conventional treatment are fugitive as they are developed to target proteins rather than the actual underlying cause. On the other hand, nucleic acid-based therapeutics can procure long-term effect with much higher efficacy through gene silencing, editing. Thus, nucleic acid-based therapeutics are emerging as one of the most reliable on-target therapy for the treatment of genetically well-defined neurodegenerative diseases like Alzheimer’s disease, Huntington’s disease, Parkinson’s disease, amyotrophic lateral sclerosis, etc. Here, we will discuss the important nucleic acid-based therapies to treat neurodegenerative diseases along with the opportunities and challenges depending on the disease and the drug target. In addition, we will also accentuate the present-day application of these inhibitory small RNAs and antisense oligonucleotides in animal models and clinical trials.KeywordsAntisense oligonucleotidessiRNAAdeno-associated virus vectorsNeurodegenerative disease
Advances in genome sequencing have greatly facilitated the identification of genomic variants underlying rare neurodevelopmental and neurodegenerative disorders. Understanding the fundamental causes of rare monogenic disorders has made gene therapy a possible treatment approach for these conditions. RNA interference (RNAi) technologies such as small interfering RNA (siRNA), microRNA (miRNA), and short hairpin RNA (shRNA), and other oligonucleotide-based modalities such as antisense oligonucleotides (ASOs) are being developed as potential therapeutic approaches for manipulating expression of the genes that cause a variety of neurological diseases. Here, we offer a brief review of the mechanism of action of these RNAi approaches; provide deeper discussion of the advantages, challenges, and specific considerations related to the development of RNAi therapeutics for neurological disease; and highlight examples of rare neurological diseases for which RNAi therapeutics hold great promise.
Neurodegenerative disorders (NDs) lead to the progressive degeneration of the structural and physiological functions of the central and peripheral nervous systems, resulting in lifelong cognitive and motor dysfunction. Although comprehensive treatment of NDs is lacking, small interfering (si)RNA has shown therapeutic utility in the form of cellular nuclease-driven downregulation of mRNA levels. Various nanotechnologies have been used to modulate crucial physicochemical and biopharmaceutical properties of siRNA to provide protection and to enhance biomembrane interactions, residence times, tissue absorption, and cellular internalization for improved cytoplasm and/or nucleus interactions. In this review, we highlight advances in, and the role of, siRNA-based nanocarriers for the treatment of various NDs.
Alzheimer's disease (AD) is a neurodegenerative disorder that impairs mental ability development and interrupts neurocognitive function. This neuropathological condition is depicted by neurodegeneration, neural loss, and development of neurofibrillary tangles and Aβ plaques. There is also a greater risk of developing AD at a later age for people with cardiovascular diseases, hypertension and diabetes. In the biomedical sciences, effective treatment for Alzheimer's disease is a severe obstacle. There is no such treatment to cure Alzheimer's disease. The drug present in the market show only symptomatic relief. The cause of Alzheimer's disease is not fully understood and the blood-brain barrier restricts drug efficacy are two main factors that hamper research. Stem cell-based therapy has been seen as an effective, secure, and creative therapeutic solution to overcoming AD because of AD's multifactorial nature and inadequate care. Current developments in nanotechnology often offer possibilities for the delivery of active drug candidates to address certain limitations. The key nanoformulations being tested against AD include polymeric nanoparticles (NP), inorganic NPs and lipid-based NPs. Nano drug delivery systems are promising vehicles for targeting several therapeutic moieties by easing drug molecules' penetration across the CNS and improving their bioavailability. In this review, we focus on the causes of the AD and their treatment by different approaches.
Background:
Evidence from predominantly non-Hispanic White cohorts indicates healthcare utilization increases before Alzheimer's disease and related dementias (ADRD) is diagnosed. We investigated trends in healthcare utilization by Mexican-American Medicare beneficiaries before and after an incident diagnosis of ADRD.
Methods:
Data came from the Hispanic Established Populations for the Epidemiologic Study of the Elderly that has been linked with Medicare claims files from 1999-2016 (n=558 matched cases and controls). Piecewise regression and generalized linear mixed models were used to compare the quarterly trends in any (i.e., one or more) hospitalizations, emergency room (ER) admissions, and physician visits for one year before and one year after ADRD diagnosis.
Results:
The piecewise regression models showed that the per-quarter odds for any hospitalizations (OR=1.62, 95% CI=1.43-1.84) and any ER admissions (OR=1.40, 95% CI=1.27-1.54) increased before ADRD was diagnosed. Compared to participants without ADRD, the percentage of participants with ADRD who experienced any hospitalizations (27.2% vs 14.0%) and any ER admissions (19.0% vs 11.7%) was significantly higher at one-quarter and three-quarters before ADRD diagnosis, respectively. The per-quarter odds for any hospitalizations (OR=0.88, 95% CI=0.80-0.97) and any ER admissions (OR=0.89, 95% CI=0.82-0.97) decreased after ADRD was diagnosed. Trends for any physician visits before or after ADRD diagnosis were not statistically significant.
Conclusions:
Older Mexican-Americans show an increase in hospitalizations and ER admissions before ADRD is diagnosed, which is followed by a decrease after ADRD diagnosis. These findings support the importance of a timely diagnosis of ADRD for older Mexican-Americans.
Small interfering RNA (siRNA) has been expected to be a unique pharmaceutic for the treatment of broad-spectrum intractable diseases. However, its unfavorable properties such as easy degradation in the blood and negative-charge density are still a formidable barrier for clinical use. For disruption of this barrier, siRNA delivery technology has been significantly advanced in the past two decades. The approval of Patisiran (ONPATTRO™) for the treatment of transthyretin-mediated amyloidosis, the first approved siRNA drug, is a most important milestone. Since lipid-based nanoparticles (LNPs) are used in Patisiran, LNP-based siRNA delivery is now of significant interest for the development of the next siRNA formulation. In this review, we describe the design of LNPs for the improvement of siRNA properties, bioavailability, and pharmacokinetics. Recently, a number of siRNA-encapsulated LNPs were reported for the treatment of intractable diseases such as cancer, viral infection, inflammatory neurological disorder, and genetic diseases. We believe that these contributions address and will promote the development of an effective LNP-based siRNA delivery system and siRNA formulation.
Nucleic Acid (NA) based therapeutics are poised to disrupt modern medicine and augment traditional pharmaceutics in a meaningful way. However, a key challenge to advancing NA therapies into the clinical setting and on to the market is the safe and effective delivery to the target tissue and cell. Lipid Nanoparticles (LNP) have been extensively investigated and are currently the most advanced vector for the delivery of NA drugs, as evidenced by the approval of Onpattro for treatment of Amyloidosis in the US and EU in 2018. This article provides a comprehensive review of the state-of-the-art for LNP technology. We discuss key advances in the design and development of LNP, leading to a broad range of therapeutic applications. Finally, the current status of this technology in clinical trials and its future prospects are discussed.
IntroductionLipid based nanoparticles (LNPs) are clinically successful vectors for hepatic delivery of nucleic acids. These systems are being developed for non-hepatic delivery of mRNA for the treatment of diseases like cystic fibrosis or retinal degeneration as well as infectious diseases. Localized delivery to the lungs requires aerosolization. We hypothesized that structural lipids within LNPs would provide features of integrity which can be tuned for attributes required for efficient hepatic and non-hepatic gene delivery. Herein, we explored whether naturally occurring lipids that originate from the cell membrane of plants and microorganisms enhance mRNA-based gene transfection in vitro and in vivo and whether they assist in maintaining mRNA activity after nebulization.Methods
We substituted DSPC, a structural lipid used in a conventional LNP formulation, to a series of naturally occurring membrane lipids. We measured the effect of these membrane lipids on size, encapsulation efficiency and their impact on transfection efficiency. We further characterized LNPs after nebulization and measured whether they retained their transfection efficiency.ResultsOne plant-derived structural lipid, DGTS, led to a significant improvement in liver transfection of mRNA. DGTS LNPs had similar transfection ability when administered in the nasal cavity to conventional LNPs. In contrast, we found that DGTS LNPs had reduced transfection efficiency in cells pre-and post-nebulization while maintaining size and encapsulation similar to DSPC LNPs.Conclusions
We found that structural lipids provide differential mRNA-based activities in vitro and in vivo which also depend on the mode of administration. Understanding influence of structural lipids on nanoparticle morphology and structure can lead to engineering potent materials for mRNA-based gene therapy applications.
Aging is associated with a decrease in body and brain function and with a decline in insulin-like growth factor 1 levels. The observed associations between alterations in insulin-like growth factor 1 levels and cognitive functioning and Mild Cognitive Impairment suggest that altered insulin-like growth factor 1 signaling may accompany Alzheimer’s disease or is involved in the pathogenesis of the disease. Recent animal research has suggested a possible association between insulin-like growth factor 1 levels and the Apolipoprotein E ε4 allele, a genetic predisposition to Alzheimer’s disease. It is therefore hypothesized that a reduction in insulin-like growth factor 1 signaling may moderate the vulnerability to Alzheimer’s disease of human Apolipoprotein E ε4 carriers. We address the impact of age-related decline of insulin-like growth factor 1 levels on physical and brain function in healthy aging and Alzheimer’s disease and discuss the links between insulin-like growth factor 1 and the Apolipoprotein E ε4 polymorphism. Furthermore, we discuss lifestyle interventions that may increase insulin-like growth factor 1 serum levels, including physical activity and adherence to a protein rich diet and the possible benefits to the physical fitness and cognitive functioning of the aging population.
Introduction: Alzheimer’s Disease (AD) is a progressive neurodegenerative pathology characterised by the presence of neuritic plaques and neurofibrillary tangles. The most important markers in AD pathology include excessive accumulation of amyloid beta (Aβ42) and phosphorylated tau (P-tau) proteins. One of the possible therapeutic strategies entails the elimination of such deposits by inhibiting Aβ aggregation. For years, one of the major problems in the treatment of AD has been the limited ability to deliver drugs to the brain for reasons related to poor solubility, low bioavailability, and the impact of the blood-brain barrier (BBB).
Areas covered: In recent years, the authors have observed an increasing scientific interest in nanotechnological solutions as the factors potentially capable of facilitating the treatment of neurodegenerative diseases. The authors discuss recent reports regarding the use of nanotechnology in the therapy and treatment of AD.
Expert opinion: The current advances in nanotechnology promise a chance to overcome the obstacles posed by said limitations. The size and diversity of nanoparticles in terms of both composition and shape create new possibilities for a variety of therapeutic applications, also in the context of the treatment and diagnostics of neurodegenerative diseases, for instance in combination with magnetic resonance imaging.
Since health care systems dedicate substantial resources to Alzheimer's disease (AD), it poses an increasing challenge to scientists and health care providers worldwide, especially that many decades of research in the medical field revealed no optimal effective treatment for this disease. The intranasal administration route seems to be a preferable route of anti-AD drug delivery over the oral one as it demonstrates an ability to overcome the related obstacles reflected in low bioavailability, limited brain exposure and undesired pharmacokinetics or side effects. This delivery route can bypass the systemic circulation through the intraneuronal and extraneuronal pathways, providing truly needleless and direct brain drug delivery of the therapeutics due to its large surface area, porous endothelial membrane, the avoidance of the first-pass metabolism, and ready accessibility. Among the different nano-carrier systems developed, lipid-based nanosystems have become increasingly popular and have proven to be effective in managing the common symptoms of AD when administered via the nose-to-brain delivery route, which provides an answer to circumventing the BBB. The design of such lipid-based nanocarriers could be challenging since many factors can contribute to the quality of the final product. Hence, according to the authors, it is recommended to follow the quality by design methodology from the early stage of development to ensure high product quality while saving efforts and costs. This review article aims to draw attention to the up-to-date findings in the field of lipid-based nanosystems and the potential role of developing such forms in the management of AD by means of the nose-to-brain delivery route, in addition to highlighting the significant role of applying QbD methodology in this development.
Alzheimer's disease (AD) is an irreversible and progressive neurodegenerative disorder manifested by memory loss and cognitive impairment. Deposition of the amyloid β plaques has been identified as the most common AD pathology; however, the excessive accumulation of phosphorylated or total tau proteins, reactive oxygen species, and higher acetylcholinesterase activity are also strongly associated with Alzheimer's dementia. Several therapeutic approaches targeting these pathogenic mechanisms have failed in clinical or preclinical trials, partly due to the limited bioavailability, poor cell, and blood-brain barrier penetration, and low drug half-life of current regimens. The nanoparticles (NPs)-mediated drug delivery systems improve drug solubility and bioavailability, thus renders as superior alternatives. Moreover, NPs-mediated approaches facilitate multiple drug loading and targeted drug delivery, thereby increasing drug efficacy. However, certain NPs can cause acute toxicity damaging cellular and tissue architecture, therefore, NP material should be carefully selected. In this review, we summarize the recent NPs-mediated studies that exploit various pathologic mechanisms of AD by labeling, identifying, and treating the affected brain pathologies. The disadvantages of the select NP-based deliveries and the future aspects will also be discussed.
There is evidence that encapsulating glucocorticoids into nucleic acid-containing nanoparticles reduces the inflammatory toxicities of the nanoparticles. Herein, using betamethasone acetate (BA), a glucocorticoid, and a solid lipid nanoparticle formulation of siRNA, we confirmed that co-encapsulating BA into the siRNA solid lipid nanoparticles significantly reduced the proinflammatory activity of the siRNA nanoparticles in a mouse model. Using TNF-α siRNA, we then showed that the BA and TNF-α siRNA co-encapsulated into the solid lipid nanoparticles acted as a dual anti-inflammatory and synergistically reduced TNF-α release by mouse macrophages in culture following stimulation with lipopolysaccharide, as compared to solid lipid nanoparticles encapsulated with TNF-α siRNA or BA alone. Importantly, upon studying the effect of the ratio of BA and TNF-α siRNA on the proinflammatory activity of the resultant nanoparticles, we identified that BA and TNF-α siRNA co-encapsulated solid lipid nanoparticles prepared with a BA to TNF-α siRNA weight ratio of 2:1 induced the lowest proinflammatory cytokine production by macrophages in culture. This result was in comparison to nanoparticles prepared with BA to TNFα siRNA ratios both higher and lower than 2:1 (i.e. 4:1, 1:1, and 0.5:1), and is likely due to differences in molecular interactions among the various components in the BA and TNF-α-siRNA co-encapsulated solid lipid nanoparticles at these ratios. Encapsulating glucocorticoids into siRNA-nanoparticles represents a viable strategy to reduce the proinflammatory activity of the nanoparticles; however, the ratio of the glucocorticoid to siRNA in the nanoparticles requires optimization.
Delivering nucleic acid-based therapeutics to cells is an attractive approach to target the genetic cause of various diseases. In contrast to conventional small molecule drugs that target gene products (i.e., proteins), genetic drugs induce therapeutic effects by modulating gene expression. Gene silencing, the process whereby protein production is prevented by neutralizing its mRNA template, is a potent strategy to induce therapeutic effects in a highly precise manner. Importantly, gene silencing has broad potential as theoretically any disease-causing gene can be targeted. It was demonstrated two decades ago that introducing synthetic small interfering RNAs (siRNAs) into the cytoplasm results in specific degradation of complementary mRNA via a process called RNA interference (RNAi). Since then, significant efforts and investments have been made to exploit RNAi therapeutically and advance siRNA drugs to the clinic. Utilizing (unmodified) siRNA as a therapeutic, however, is challenging due to its limited bioavailability following systemic administration. Nuclease activity and renal filtration result in siRNA's rapid clearance from the circulation and its administration induces (innate) immune responses. Furthermore, siRNA's unfavorable physicochemical characteristics largely prevent its diffusion across cellular membranes, impeding its ability to reach the cytoplasm where it can engage the RNAi machinery. The clinical translation of siRNA therapeutics has therefore been dependent on chemical modifications and developing sophisticated delivery platforms to improve their stability, limit immune activation, facilitate internalization, and increase target affinity. These developments have resulted in last year's approval of the first siRNA therapeutic, called Onpattro (patisiran), for treatment of hereditary amyloidogenic transthyretin (TTR) amyloidosis. This disease is characterized by a mutation in the gene encoding TTR, a serum protein that transports retinol in circulation following secretion by the liver. The mutation leads to production of misfolded proteins that deposit as amyloid fibrils in multiple organs, resulting in progressive neurodegeneration. Patisiran's therapeutic effect relies on siRNA-mediated TTR gene silencing, preventing mutant protein production and halting or even reversing disease progression. For efficient therapeutic siRNA delivery to hepatocytes, patisiran is critically dependent on lipid nanoparticle (LNP) technology. In this Account, we provide an overview of key advances that have been crucial for developing LNP delivery technology, and we explain how these developments have contributed to the clinical translation of siRNA therapeutics for parenteral administration. We discuss optimization of the LNP formulation, particularly focusing on the rational design of ionizable cationic lipids and poly(ethylene glycol) lipids. These components have proven to be instrumental for highly efficient siRNA encapsulation, favorable LNP pharmacokinetic parameters, and hepatocyte internalization. Additionally, we pay attention to the development of rapid mixing-based methods that provide robust and scalable LNP production procedures. Finally, we highlight patisiran's clinical translation and LNP delivery technology's potential to enable the development of genetic drugs beyond the current state-of-the-art, such as mRNA and gene editing therapeutics.
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.
The success of Onpattro™ (patisiran) clearly demonstrates the utility of lipid nanoparticle (LNP) systems for enabling gene therapies. These systems are composed of ionizable cationic lipids, phospholipid, cholesterol, and polyethylene glycol (PEG)-lipids, and are produced through rapid-mixing of an ethanolic-lipid solution with an acidic aqueous solution followed by dialysis into neutralizing buffer. A detailed understanding of the mechanism of LNP formation is crucial to improving LNP design. Here we use cryogenic transmission electron microscopy and fluorescence techniques to further demonstrate that LNP are formed through the fusion of precursor, pH-sensitive liposomes into large electron-dense core structures as the pH is neutralized. Next, we show that the fusion process is limited by the accumulation of PEG-lipid on the emerging particle. Finally, we show that the fusion-dependent mechanism of formation also applies to LNP containing macromolecular payloads including mRNA, DNA vectors, and gold nanoparticles.
Lipid nanoparticles (LNPs) are one of the more promising technologies for efficiently delivering short interfering RNA (siRNA) in vivo. A pH-sensitive cationic lipid that facilitates the targeting of hepatocytes and endosomal escape, strongly influences the availability of siRNA, thus making it a key material for efficient siRNA delivery. A systematic knowledge regarding lipid structure-activity relationships would greatly facilitate the development of sophisticated pH-sensitive cationic lipids for use in siRNA-based therapeutics. The systemic derivatization of a hydrophilic head group and hydrophobic tails of YSK12-C4, a pH-sensitive cationic lipid that was developed in our laboratory, revealed that hydrophilic head significantly affected the apparent pKa of the final product, a key factor in both intrahepatic distribution and endosomal escape. The clogP value of a hydrophilic head group was found to be associated with the apparent pKa of the product. In contrast, the hydrophobic tail structure strongly affected intrahepatic distribution without depending on apparent pKa. A structure-activity relationship study enabled the selection of an adequate combination of a hydrophilic head group and hydrophobic tails and permitted a potent LNP composed of a pH-sensitive cationic lipid CL4H6 (CL4H6-LNPs) to be developed that showed efficient gene silencing activity (50% effective dose: 0.0025 mg/kg), biodegradability and was tolerated. In vivo experiments revealed that the CL4H6-LNPs showed a superior efficiency for endosomal escape, cytosolic release and the RNA-induced silencing for the complex-loading of siRNAs compared to the previously developed LNPs.