Development of Nonviral Vectors Targeting the Brain as a Therapeutic Approach For Parkinson's Disease and Other Brain Disorders

Topoisomeric Membrane-Active Peptides: A Review of the Last Two Decades

In recent decades, bioactive peptides have been gaining recognition in various biomedical areas, such as intracellular drug delivery (cell-penetrating peptides, CPPs) or anti-infective action (antimicrobial peptides, AMPs), closely associated to their distinct mode of interaction with biological membranes. Exploiting the interaction of membrane-active peptides with diverse targets (healthy, tumoral, bacterial or parasitic cell membranes) is opening encouraging prospects for peptides in therapeutics. However, ordinary peptides formed by L-amino acids are easily decomposed by proteases in biological fluids. One way to sidestep this limitation is to use topoisomers, namely versions of the peptide made up of D-amino acids in either canonic (enantio) or inverted (retroenantio) sequence. Rearranging peptide sequences in this fashion provides a certain degree of native structure mimicry that, in appropriate contexts, may deliver desirable biological activity while avoiding protease degradation. In this review, we will focus on recent accounts of membrane-active topoisomeric peptides with therapeutic applications as CPP drug delivery vectors, or as antimicrobial and anticancer candidates. We will also discuss the most common modes of interaction of these peptides with their membrane targets.

Novel systemic delivery of a peptide-conjugated antisense oligonucleotide to reduce α-synuclein in a mouse model of Alzheimer's disease

Neurodegenerative disorders of aging are characterized by the progressive accumulation of proteins such as α-synuclein (α-syn) and amyloid beta (Aβ). Misfolded and aggregated α-syn has been implicated in neurological disorders such as Parkinson's disease, and Dementia with Lewy Bodies, but less so in Alzheimer's Disease (AD), despite the fact that accumulation of α-syn has been confirmed in over 50% of postmortem brains neuropathologically diagnosed with AD. To date, no therapeutic strategy has effectively or consistently downregulated α-syn in AD. Here we tested the hypothesis that by using a systemically-delivered peptide (ApoB11) bound to a modified antisense oligonucleotide against α-syn (ASO-α-syn), we can downregulate α-syn expression in an AD mouse model and improve behavioral and neuropathologic phenotypes. Our results demonstrate that monthly systemic treatment with of ApoB11:ASO α-syn beginning at 6 months of age reduces expression of α-synuclein in the brains of 9-month-old AD mice. Downregulation of α-syn led to reduction in Aβ plaque burden, prevented neuronal loss and astrogliosis. Furthermore, we found that AD mice treated with ApoB11:ASO α-syn had greatly improved hippocampal and spatial memory function in comparison to their control counterparts. Collectively, our data supports the reduction of α-syn through use of systemically-delivered ApoB11:ASO α-syn as a promising future disease-modifying therapeutic for AD.

Cell-Penetrating and Targeted Peptides Delivery Systems as Potential Pharmaceutical Carriers for Enhanced Delivery across the Blood-Brain Barrier (BBB)

Among the challenges to the 21st-century health care industry, one that demands special mention is the transport of drugs/active pharmaceutical agents across the blood-brain barrier (BBB). The epithelial-like tight junctions within the brain capillary endothelium hinder the uptake of most pharmaceutical agents. With an aim to understand more deeply the intricacies of cell-penetrating and targeted peptides as a powerful tool for desirable biological activity, we provide a critical review of both CPP and homing/targeted peptides as intracellular drug delivery agents, especially across the blood-brain barrier (BBB). Two main peptides have been discussed to understand intracellular drug delivery; first is the cell-penetrating peptides (CPPs) for the targeted delivery of compounds of interest (primarily peptides and nucleic acids) and second is the family of homing peptides, which specifically targets cells/tissues based on their overexpression of tumour-specific markers and are thus at the heart of cancer research. These small, amphipathic molecules demonstrate specific physical and chemical modifications aimed at increased ease of cellular internalisation. Because only a limited number of drug molecules can bypass the blood-brain barrier by free diffusion, it is essential to explore all aspects of CPPs that can be exploited for crossing this barrier. Considering siRNAs that can be designed against any target RNA, marking such molecules with high therapeutic potential, we present a synopsis of the studies on synthetic siRNA-based therapeutics using CPPs and homing peptides drugs that can emerge as potential drug-delivery systems as an upcoming requirement in the world of pharma- and nutraceuticals.

Neuroinflammation, immune response and α-synuclein pathology: how animal models are helping us to connect dots

INTRODUCTION

A key pathological event occurring in Parkinson's disease (PD) is the transneuronal spreading of alpha-synuclein (α-syn). Other hallmarks of PD include neurodegeneration, glial activation, and immune cell infiltration in susceptible brain regions. Although preclinical models can mimic most of the key characteristics of PD, it is crucial to know the biological bases of individual differences between them when choosing one over another, to ensure proper interpretation of the results and to positively influence the outcome of the experiments.

AREAS COVERED

This review provides an overview of current preclinical models actively used to study the interplay between α-syn pathology, neuroinflammation and immune response in PD but also to explore new potential preclinical models or emerging therapeutic strategies intended to fulfill the unmet medical needs in this disease. Lastly, this review also considers the current state of the ongoing clinical trials of new drugs designed to target these processes and delay the initiation or progression of the disease.

EXPERT OPINION

Anti-inflammatory and immunomodulatory agents have been demonstrated to be very promising candidates for reducing disease progression; however, more efforts are needed to reduce the enormous gap between these and dopaminergic drugs, which have dominated the therapeutic market for the last sixty years.

Inhibition of α-Synuclein Seeding-Dependent Aggregation by ssDNA Aptamers Specific to C-Terminally Truncated α-Synuclein Fibrils

Neuropathologically, Parkinson's disease (PD) and dementia with Lewy bodies (DLB) are characterized by the accumulation of insoluble aggregates of α-synuclein (α-syn) in the Lewy bodies (LBs). In addition to full-length α-syn fibrils, C-terminally truncated α-syn is also abundant in the LBs that acts as seeds and facilitates the aggregation of the full-length α-syn in vitro and in vivo and induces toxicity. Hence, identifying molecules that can inhibit the seeding activity of these truncated forms is of great importance. Here, we report the first in vitro selection of aptamers targeting the fibrillar forms of different C-terminally truncated α-syn using systematic evolution by an exponential enrichment method followed by quantitative high-throughput DNA sequencing. We identify a panel of aptamers that bound with high specificity to different truncated forms of α-syn fibrils with no cross-reactivity toward other amyloid fibrils. Interestingly, two of the aptamers (named Apt11 and Apt15) show higher affinity to most C-terminally truncated forms of α-syn fibrils with an evident inhibition of α-syn-seeded aggregation in vitro by Apt11. This inhibition is further confirmed by circular dichroism, Congo red binding assay, and electronic microscopy. Moreover, Apt11 is also found to reduce the insoluble phosphorylated form of α-syn at Ser-129 (pS129-α-syn) in the cell model and also can inhibit α-syn aggregation using RT-QuIC reactions seeded with brain homogenates extracted from patients affected by PD. The aptamers discovered in this study represent potential useful tools for research and diagnostics or therapy toward PD and DLB.

Intronic enhancers of the human SNCA gene predominantly regulate its expression in brain in vivo

Evidence from patients with Parkinson's disease (PD) and our previously reported α-synuclein (SNCA) transgenic rat model support the idea that increased SNCA protein is a substantial risk factor of PD pathogenesis. However, little is known about the transcription control of the human SNCA gene in the brain in vivo. Here, we identified that the DYT6 gene product THAP1 (THAP domain-containing apoptosis-associated protein 1) and its interaction partner CTCF (CCCTC-binding factor) act as transcription regulators of SNCA. THAP1 controls SNCA intronic enhancers' activities, while CTCF regulates its enhancer-promoter loop formation. The SNCA intronic enhancers present neurodevelopment-dependent activities and form enhancer clusters similar to "super-enhancers" in the brain, in which the PD-associated single-nucleotide polymorphisms are enriched. Deletion of the SNCA intronic enhancer clusters prevents the release of paused RNA polymerase II from its promoter and subsequently reduces its expression drastically in the brain, which may provide new therapeutic approaches to prevent its accumulation and thus related neurodegenerative diseases defined as synucleinopathies.

Peptides as Pharmacological Carriers to the Brain: Promises, Shortcomings and Challenges

Central nervous system (CNS) diseases are among the most difficult to treat, mainly because the vast majority of the drugs fail to cross the blood-brain barrier (BBB) or to reach the brain at concentrations adequate to exert a pharmacological activity. The obstacle posed by the BBB has led to the in-depth study of strategies allowing the brain delivery of CNS-active drugs. Among the most promising strategies is the use of peptides addressed to the BBB. Peptides are versatile molecules that can be used to decorate nanoparticles or can be conjugated to drugs, with either a stable link or as pro-drugs. They have been used to deliver to the brain both small molecules and proteins, with applications in diverse therapeutic areas such as brain cancers, neurodegenerative diseases and imaging. Peptides can be generally classified as receptor-targeted, recognizing membrane proteins expressed by the BBB microvessels (e.g., Angiopep2, CDX, and iRGD), "cell-penetrating peptides" (CPPs; e.g. TAT_47-57, SynB1/3, and Penetratin), undergoing transcytosis through unspecific mechanisms, or those exploiting a mixed approach. The advantages of peptides have been extensively pointed out, but so far few studies have focused on the potential negative aspects. Indeed, despite having a generally good safety profile, some peptide conjugates may display toxicological characteristics distinct from those of the peptide itself, causing for instance antigenicity, cardiovascular alterations or hemolysis. Other shortcomings are the often brief lifetime in vivo, caused by the presence of peptidases, the vulnerability to endosomal/lysosomal degradation, and the frequently still insufficient attainable increase of brain drug levels, which remain below the therapeutically useful concentrations. The aim of this review is to analyze not only the successful and promising aspects of the use of peptides in brain targeting but also the problems posed by this strategy for drug delivery.

Peptide Shuttles for Blood–Brain Barrier Drug Delivery

The blood–brain barrier (BBB) limits the delivery of therapeutics to the brain but also represents the main gate for nutrient entrance. Targeting the natural transport mechanisms of the BBB offers an attractive route for brain drug delivery. Peptide shuttles are able to use these mechanisms to increase the transport of compounds that cannot cross the BBB unaided. As peptides are a group of biomolecules with unique physicochemical and structural properties, the field of peptide shuttles has substantially evolved in the last few years. In this review, we analyze the main classifications of BBB–peptide shuttles and the leading sources used to discover them.

Development of non-viral vectors for neuronal-targeted delivery of CRISPR-Cas9 RNA-proteins as a therapeutic strategy for neurological disorders

The aging population contributes to an increase in the prevalence of neurodegenerative diseases, such as Parkinson's disease (PD). Due to the progressive nature of these diseases and an incomplete understanding of their pathophysiology, current drugs are inefficient, with a limited efficacy and major side effects. In this study, CRISPR-Cas9 RNA-proteins (RNP) composed of a Cas9 nuclease and single-guide RNA were delivered with a non-viral targeted delivery system to rescue the PD-associated phenotype in neuronal cells. Here, we fused the cell-penetrating amphipathic peptide, PepFect14 (PF14), with a short fragment of the rabies virus glycoprotein (C2) previously shown to have an affinity towards nicotinic acetylcholine receptors expressed on neuronal cells and on the blood-brain barrier. The resultant peptide, C2-PF14, was used to complex with and deliver RNPs to neuronal cells. We observed that RNP/C2-PF14 complexes formed nanosized, monodispersed, and nontoxic nanoparticles that led to a specific delivery into neuronal cells. α-Synuclein (α-syn) plays a major role in the pathology of PD and is considered to be a target for therapy. We demonstrated that CRISPR/Cas9 RNP delivered by C2-PF14 achieved α-syn gene (SNCA) editing in neuronal cells as determined by T7EI assay and western blotting. Furthermore, RNP/C2-PF14 relieved PD-associated toxicity in neuronal cells in vitro. This is a proof-of-concept towards simple and safe targeted genome-editing for treating PD and other neurological disorders.

Gene-Based Therapeutics for Parkinson’s Disease

Parkinson’s disease (PD) is a complex multifactorial disorder that is not yet fully surmised, and it is only when such a disease is tackled on multiple levels simultaneously that we should expect to see fruitful results. Gene therapy is a modern medical practice that theoretically and, so far, practically, has demonstrated its capability in joining the battle against PD and other complex disorders on most if not all fronts. This review discusses how gene therapy can efficiently replace current forms of therapy such as drugs, personalized medicine or invasive surgery. Furthermore, we discuss the importance of enhancing delivery techniques to increase the level of transduction and control of gene expression or tissue specificity. Importantly, the results of current trials establish the safety, efficacy and applicability of gene therapy for PD. Gene therapy’s variety of potential in interfering with PD’s pathology by improving basal ganglial circuitry, enhancing dopamine synthesis, delivering neuroprotection or preventing neurodegeneration may one day achieve symptomatic benefit, disease modification and eradication.

The Role of Non-Coding RNAs in the Pathogenesis of Parkinson’s Disease: Recent Advancement

Parkinson’s disease (PD) is a prevalent neurodegenerative aging disorder that manifests as motor and non-motor symptoms, and its etiopathogenesis is influenced by non-coding RNAs (ncRNAs). Signal pathway and gene sequence studies have proposed that alteration of ncRNAs is relevant to the occurrence and development of PD. Furthermore, many studies on brain tissues and body fluids from patients with PD indicate that variations in ncRNAs and their target genes could trigger or exacerbate neurodegenerative pathogenesis and serve as potential non-invasive biomarkers of PD. Numerous ncRNAs have been considered regulators of apoptosis, α-syn misfolding and aggregation, mitochondrial dysfunction, autophagy, and neuroinflammation in PD etiology, and evidence is mounting for the determination of the role of competing endogenous RNA (ceRNA) mechanisms in disease development. In this review, we discuss the current knowledge regarding the regulation and function of ncRNAs as well as ceRNA networks in PD pathogenesis, focusing on microRNAs, long ncRNAs, and circular RNAs to increase the understanding of the disease and propose potential target identification and treatment in the early stages of PD.

Alpha-Synuclein Targeting Therapeutics for Parkinson's Disease and Related Synucleinopathies

α-Synuclein (asyn) is a key pathogenetic factor in a group of neurodegenerative diseases generically known as synucleinopathies, including Parkinson's disease (PD), dementia with Lewy bodies (DLB) and multiple system atrophy (MSA). Although the initial triggers of pathology and progression are unclear, multiple lines of evidence support therapeutic targeting of asyn in order to limit its prion-like misfolding. Here, we review recent pre-clinical and clinical work that offers promising treatment strategies to sequester, degrade, or silence asyn expression as a means to reduce the levels of seed or substrate. These diverse approaches include removal of aggregated asyn with passive or active immunization or by expression of vectorized antibodies, modulating kinetics of misfolding with small molecule anti-aggregants, lowering asyn gene expression by antisense oligonucleotides or inhibitory RNA, and pharmacological activation of asyn degradation pathways. We also discuss recent technological advances in combining low intensity focused ultrasound with intravenous microbubbles to transiently increase blood-brain barrier permeability for improved brain delivery and target engagement of these large molecule anti-asyn biologics.

Anti-Parkinsonian Therapy: Strategies for Crossing the Blood-Brain Barrier and Nano-Biological Effects of Nanomaterials

Parkinson's disease (PD), a neurodegenerative disease that shows a high incidence in older individuals, is becoming increasingly prevalent. Unfortunately, there is no clinical cure for PD, and novel anti-PD drugs are therefore urgently required. However, the selective permeability of the blood-brain barrier (BBB) poses a huge challenge in the development of such drugs. Fortunately, through strategies based on the physiological characteristics of the BBB and other modifications, including enhancement of BBB permeability, nanotechnology can offer a solution to this problem and facilitate drug delivery across the BBB. Although nanomaterials are often used as carriers for PD treatment, their biological activity is ignored. Several studies in recent years have shown that nanomaterials can improve PD symptoms via their own nano-bio effects. In this review, we first summarize the physiological features of the BBB and then discuss the design of appropriate brain-targeted delivery nanoplatforms for PD treatment. Subsequently, we highlight the emerging strategies for crossing the BBB and the development of novel nanomaterials with anti-PD nano-biological effects. Finally, we discuss the current challenges in nanomaterial-based PD treatment and the future trends in this field. Our review emphasizes the clinical value of nanotechnology in PD treatment based on recent patents and could guide researchers working in this area in the future.

Rapid Assessment of CRISPR Transfection Efficiency and Enrichment of CRISPR Induced Mutations Using a Dual-Fluorescent Stable Reporter System

The nuclease activity of the CRISPR-Cas9 system relies on the delivery of a CRISPR-associated protein 9 (Cas9) and a single guide RNA (sgRNA) against the target gene. CRISPR components are typically delivered to cells as either a Cas9/sgRNA ribonucleoprotein (RNP) complex or a plasmid encoding a Cas9 protein along with a sequence-specific sgRNA. Multiple transfection reagents are known to deliver CRISPR-Cas9 components, and delivery vectors are being developed for different purposes by several groups. Here, we repurposed a dual-fluorescence (RFP-GFP-GFP) reporter system to quantify the uptake level of the functional CRISPR-Cas9 components into cells and compare the efficiency of CRISPR delivery vectors. Using this system, we developed a novel and rapid cell-based microplate reader assay that makes possible real-time, rapid, and high throughput quantification of CRISPR nuclease activity. Cells stably expressing this dual-fluorescent reporter construct facilitated a direct quantification of the level of the internalized and functional CRISPR-Cas9 molecules into the cells without the need of co-transfecting fluorescently labeled reporter molecules. Additionally, targeting a reporter gene integrated into the genome recapitulates endogenous gene targeting. Thus, this reporter could be used to optimize various transfection conditions of CRISPR components, to evaluate and compare the efficiency of transfection agents, and to enrich cells containing desired CRISPR-induced mutations.

Development of an α-synuclein knockdown peptide and evaluation of its efficacy in Parkinson's disease models

Convincing evidence supports the premise that reducing α-synuclein levels may be an effective therapy for Parkinson's disease (PD); however, there has been lack of a clinically applicable α-synuclein reducing therapeutic strategy. This study was undertaken to develop a blood-brain barrier and plasma membrane-permeable α-synuclein knockdown peptide, Tat-βsyn-degron, that may have therapeutic potential. The peptide effectively reduced the level of α-synuclein via proteasomal degradation both in cell cultures and in animals. Tat-βsyn-degron decreased α-synuclein aggregates and microglial activation in an α-synuclein pre-formed fibril model of spreading synucleinopathy in transgenic mice overexpressing human A53T α-synuclein. Moreover, Tat-βsyn-degron reduced α-synuclein levels and significantly decreased the parkinsonian toxin-induced neuronal damage and motor impairment in a mouse toxicity model of PD. These results show the promising efficacy of Tat-βsyn-degron in two different animal models of PD and suggest its potential use as an effective PD therapeutic that directly targets the disease-causing process.

Dose-related biphasic effect of the Parkinson's disease neurotoxin MPTP, on the spread, accumulation, and toxicity of α-synuclein

BACKGROUND

Parkinson's disease (PD), the second most common progressive neurodegenerative disorder, is characterized by the abnormal accumulation of intraneuronal inclusions enriched in aggregated α-synuclein (α-syn), known as Lewy bodies (LBs) and Lewy neurites (LNs), and significant loss of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc) of the brain. Recent evidence suggests that the intrastriatal inoculation of α-syn preformed fibrils (PFF) in mice brain triggers endogenous α-syn in interconnected brain regions. 1-methyl, 4-phenyl, 1,2,3,6 tetrahydropyridine (MPTP), a mitochondrial neurotoxin, has been used previously to generate a PD mouse model. However, the common methods of MPTP exposure do not induce LB or α-syn aggregation in mice. In the present study, we evaluated the effect of different doses of MPTP (10 mg/kg.b.wt and/or 25 mg/kg.b.wt) on the spread, accumulation, and toxicity of endogenous α-syn in mice administered an intrastriatal injection of human α-syn PFF.

METHODS

We inoculated human WT α-syn PFF in mouse striatum. At 6 weeks post PFF injection, we challenged the animal with two different doses of MPTP (10 mg/kg.b.wt and 25 mg/kg.b.wt) once daily for five consecutive days. At 2 weeks from the start of the MPTP regimen, we collected the mice brain and performed immunohistochemical analysis, and Rotarod test to assess motor coordination and muscle strength before and after MPTP injection.

RESULTS

A single injection of human WT α-syn PFF in the mice striatum induced the propagation of α-syn, occurring as phosphorylated α-synuclein (pS129), towards the SNpc, within a very short time. Injection of a low dose of MPTP (10 mg/kg.b.wt) at 6 weeks post α-syn PFF inoculation further enhanced the spread, whereas a high dose of MPTP (25 mg/kg.b.wt.) reduced the spread. Majority of the accumulated α-syn were proteinase K resistant, as recognized using a conformation-specific α-syn antibody. Injection of α-syn PFF alone caused 12 % reduction in the number of tyrosine hydroxylase positive neurons while α-syn PFF + a low dose of MPTP caused 33 % reduction (loss), compared to the control mice injected with saline. This combination also reduced the motor coordination. Interestingly, a low dose of MPTP alone did not cause any significant reduction in the number of tyrosine hydroxylase positive neurons compared to saline treatment. Animals that received α-syn PFF and a high dose of MPTP showed massive activation of glial cells and decreased spread of α-syn, majority of which were detected in the nucleus.

CONCLUSION

Our results suggest that a combination of human WT α-syn PFF and a low dose of MPTP increases the pathological conversion and propagation of endogenous α-syn, and neurodegeneration, within a very short time. Our model can be used to study the mechanisms of α-syn propagation and screen for potential drugs against PD.

The Inclusion of a Matrix Metalloproteinase-9 Responsive Sequence in Self-assembled Peptide-based Brain-Targeting Nanoparticles Improves the Efficiency of Nanoparticles Crossing the Blood-Brain Barrier at Elevated MMP-9 Levels

This study investigated whether the inclusion of a matrix metalloproteinase-9 (MMP-9) responsive sequence in self-assembled peptide-based brain-targeting nanoparticles (NPs) would enhance the blood-brain barrier (BBB) penetration when MMP-9 levels are elevated both in the brain and blood circulation. Brain-targeting peptides were conjugated at the N-terminus to MMP-9-responsive peptides, and these were conjugated at the N-terminus to lipid moiety (cholesteryl chloroformate or palmitic acid). Two constructs did not have MMP-9-responsive peptides. NPs were characterised for size, charge, critical micelle concentration, toxicity, blood compatibility, neural cell uptake, release profiles, and in vitro BBB permeability simulating normal or elevated MMP-9 levels. The inclusion of MMP-9-sensitive sequences did not improve the release of a model drug in the presence of active MMP-9 from NPs compared to distilled water. ¹⁹F NMR studies suggested the burial of MMP-9-sensitive sequences inside the NPs making them inaccessible to MMP-9. Only cholesterol-GGGCKAPETALC (responsive to MMP-9) NPs showed <5% haemolysis, <1 pg/mL release of IL-1β at 500 μg/mL from THP1 cells, with 70.75 ± 5.78% of NPs crossing the BBB at 24 h in presence of active MMP-9. In conclusion, brain-targeting NPs showed higher transport across the BBB model when MMP-9 levels were elevated and the brain-targeting ligand was responsive to MMP-9.

Neuroprotective Effect of Curcumin on the Nigrostriatal Pathway in a 6-Hydroxydopmine-Induced Rat Model of Parkinson's Disease is Mediated by α7-Nicotinic Receptors

Parkinson’s disease (PD) is a common neurodegenerative disorder, characterized by selective degeneration of dopaminergic nigrostriatal neurons. Most of the existing pharmacological approaches in PD consider replenishing striatal dopamine. It has been reported that activation of the cholinergic system has neuroprotective effects on dopaminergic neurons, and human α7-nicotinic acetylcholine receptor (α7-nAChR) stimulation may offer a potential therapeutic approach in PD. Our recent in-vitro studies demonstrated that curcumin causes significant potentiation of the function of α7-nAChRs expressed in Xenopus oocytes. In this study, we conducted in vivo experiments to assess the role of the α7-nAChR on the protective effects of curcumin in an animal model of PD. Intra-striatal injection of 6-hydroxydopmine (6-OHDA) was used to induce Parkinsonism in rats. Our results demonstrated that intragastric curcumin treatment (200 mg/kg) significantly improved the abnormal motor behavior and offered neuroprotection against the reduction of dopaminergic neurons, as determined by tyrosine hydroxylase (TH) immunoreactivity in the substantia nigra and caudoputamen. The intraperitoneal administration of the α7-nAChR-selective antagonist methyllycaconitine (1 µg/kg) reversed the neuroprotective effects of curcumin in terms of both animal behavior and TH immunoreactivity. In conclusion, this study demonstrates that curcumin has a neuroprotective effect in a 6-hydroxydopmine (6-OHDA) rat model of PD via an α7-nAChR-mediated mechanism.

Alpha-Synuclein deficiency ameliorates chronic methamphetamine induced neurodegeneration in mice

The α-Synuclein (α-syn) and tau have synergistic effects on neurodegenerative diseases induced by environmental factors or genetic mutation. Thus, we investigated the role of α-syn and tau in neurodegeneration induced by chronic methamphetamine (METH) exposure (1.0∼20.0 mg/kg/d body weight, for 14 consecutive days). Here, we present a mice model with evidences of α-syn and tau participating in toxicology in chronic METH. METH increased α-syn level in the stratum oriens, pyramidal layer, stratum radiatum and stratum moleculare of hippocampal CA1, CA2 and CA3, polymorph layer of hippocampal dentate gyrus (DG), and substantia nigra (SN). The subcellular locations of the upregulated α-syn were mainly found in mitochondria and axons. The METH upregulated α-syn may directly induce mitochondrial damage, myelin sheath destruction, and synaptic failure. Also, the excess α-syn might indirectly promote tau phosphorylation through tau kinase GSK3β and CDK5, leading to microtubule depolymerization and eventually fusion deficit of autophagosome and lysosome. In the in vitro experiment, the autophagic vacuoles failed to fuse with the lysosome. The neuropathology induced by both the direct and indirect effects of α-syn could be alleviated by α-syn knockout. Taking together, these results indicate that the α-syn mediates the neurodegenerative process induced by chronic METH and that reducing α-syn might be a potential approach to protect the toxic effects of METH and also be, to a broader view, of therapeutic value in neurodegenerative diseases.

Targeting α-synuclein for PD Therapeutics: A Pursuit on All Fronts

Parkinson's Disease (PD) is characterized both by the loss of dopaminergic neurons in the substantia nigra and the presence of cytoplasmic inclusions called Lewy Bodies. These Lewy Bodies contain the aggregated α-synuclein (α-syn) protein, which has been shown to be able to propagate from cell to cell and throughout different regions in the brain. Due to its central role in the pathology and the lack of a curative treatment for PD, an increasing number of studies have aimed at targeting this protein for therapeutics. Here, we reviewed and discussed the many different approaches that have been studied to inhibit α-syn accumulation via direct and indirect targeting. These analyses have led to the generation of multiple clinical trials that are either completed or currently active. These clinical trials and the current preclinical studies must still face obstacles ahead, but give hope of finding a therapy for PD with time.

Systemic peptide mediated delivery of an siRNA targeting α-syn in the CNS ameliorates the neurodegenerative process in a transgenic model of Lewy body disease

Neurodegenerative disorders of the aging population are characterized by progressive accumulation of neuronal proteins such as α-synuclein (α-syn) in Parkinson's Disease (PD) and Amyloid ß (Aß) and Tau in Alzheimer's disease (AD) for which no treatments are currently available. The ability to regulate the expression at the gene transcription level would be beneficial for reducing the accumulation of these proteins or regulating expression levels of other genes in the CNS. Short interfering RNA molecules can bind specifically to target RNAs and deliver them for degradation. This approach has shown promise therapeutically in vitro and in vivo in mouse models of PD and AD and other neurological disorders; however, delivery of the siRNA to the CNS in vivo has been achieved primarily through intra-cerebral or intra-thecal injections that may be less amenable for clinical translation; therefore, alternative approaches for delivery of siRNAs to the brain is needed. Recently, we described a small peptide from the envelope protein of the rabies virus (C2-9r) that was utilized to deliver an siRNA targeting α-syn across the blood brain barrier (BBB) following intravenous injection. This approach showed reduced expression of α-syn and neuroprotection in a toxic mouse model of PD. However, since receptor-mediated delivery is potentially saturable, each allowing the delivery of a limited number of molecules, we identified an alternative peptide for the transport of nucleotides across the BBB based on the apolipoprotein B (apoB) protein targeted to the family of low-density lipoprotein receptors (LDL-R). We used an 11-amino acid sequence from the apoB protein (ApoB11) that, when coupled with a 9-amino acid arginine linker, can transport siRNAs across the BBB to neuronal and glial cells. To examine the value of this peptide mediated oligonucleotide delivery system for PD, we delivered an siRNA targeting the α-syn (siα-syn) in a transgenic mouse model of PD. We found that ApoB11 was effective (comparable to C2-9r) at mediating the delivery of siα-syn into the CNS, co-localized to neurons and glial cells and reduced levels of α-syn protein translation and accumulation. Delivery of ApoB11/siα-syn was accompanied by protection from degeneration of selected neuronal populations in the neocortex, limbic system and striato-nigral system and reduced neuro-inflammation. Taken together, these results suggest that systemic delivery of oligonucleotides targeting α-syn using ApoB11 might be an interesting alternative strategy worth considering for the experimental treatment of synucleinopathies.

Non-viral nucleic acid delivery to the central nervous system and brain tumors

Gene therapy is a rapidly emerging remedial route for many serious incurable diseases, such as central nervous system (CNS) diseases. Currently, nucleic acid medicines, including DNAs encoding therapeutic or destructive proteins, small interfering RNAs or microRNAs, have been successfully delivered to the CNS with gene delivery vectors using various routes of administration and have subsequently exhibited remarkable therapeutic efficiency. Among these vectors, non-viral vectors are favorable for delivering genes into the CNS as a result of their many special characteristics, such as low toxicity and pre-existing immunogenicity, high gene loading efficiency and easy surface modification. In this review, we highlight the main types of therapeutic genes that have been applied in the therapy of CNS diseases and then outline non-viral gene delivery vectors.

Micro- and nanotechnology approaches to improve Parkinson's disease therapy

Current therapies for Parkinson's disease are symptomatic and unable to regenerate the brain tissue. In recent years, the therapeutic potential of a wide variety of neuroprotective and neuroregenerative molecules such as neurotrophic factors, antioxidants and RNA-based therapeutics has been explored. However, drug delivery to the brain is still a challenge and the therapeutic efficacy of many drugs is limited. In the last decade, micro- and nanoparticles have proved to be powerful tools for the administration of these molecules to the brain, enabling the development of new strategies against Parkinson's disease. The list of encapsulated drugs and the nature of the particles used is long, and numerous studies have been carried out supporting their efficacy in treating this pathology. This review aims to give an overview of the latest advances and emerging frontiers in micro- and nanomedical approaches for repairing dopaminergic neurons. Special emphasis will be placed on offering a new perspective to link these advances with the most relevant clinical trials and with the real possibility of transferring micro- and nanoformulations to industrial scale-up processes. This review is intended as a contribution towards facing the challenges that still exist in the clinical translation of micro- and nanotechnologies to administer therapeutic agents in Parkinson's disease.

In vivo methods for acute modulation of gene expression in the central nervous system

Accurate and timely expression of specific genes guarantees the healthy development and function of the brain. Indeed, variations in the correct amount or timing of gene expression lead to improper development and/or pathological conditions. Almost forty years after the first successful gene transfection in in vitro cell cultures, it is currently possible to regulate gene expression in an area-specific manner at any step of central nervous system development and in adulthood in experimental animals in vivo, even overcoming the very poor accessibility of the brain. Here, we will review the diverse approaches for acute gene transfer in vivo, highlighting their advantages and disadvantages with respect to the efficiency and specificity of transfection as well as to brain accessibility. In particular, we will present well-established chemical, physical and virus-based approaches suitable for different animal models, pointing out their current and future possible applications in basic and translational research as well as in gene therapy.

SNCA, a novel biomarker for Group 4 medulloblastomas, can inhibit tumor invasion and induce apoptosis

Medulloblastoma (MB) is the most common malignant brain tumor in childhood. It contains at least four distinct molecular subgroups. The aim of this study is to explore novel diagnostic and potential therapeutic markers within each subgroup of MB, in particular within Group 4, the largest subgroup, to facilitate diagnosis together with gene therapy. One hundred and six MB samples were examined. Tumor subtype was evaluated with the NanoString assay. Several novel tumor related genes were shown to have high subgroup sensitivity and specificity, including PDGFRA,FGFR1, and ALK in the WNT group, CCND1 in the SHH group, and α‐synuclein (SNCA) in Group 4. Knockdown and overexpression assays of SNCA revealed the ability of this gene to inhibit tumor invasion and induce apoptosis. Methylation‐specific PCR and pyrosequencing analysis showed that epigenetic mechanisms, rather than DNA hypermethylation, might play the key role in the regulation of SNCA expression in MB tumors. In conclusion, we identify SNCA as a novel diagnostic biomarker for Group 4 MB. Some other subgroup signature genes have also been found as candidate therapeutic targets for this tumor.

Pressing diseases that represent promising targets for gene therapy

Over time, there has been a growing interest in the application of gene therapy within the healthcare industry as demonstrated by the nearly 3,000 clinical trials associated with gene therapy that are listed in clinicaltrials.gov. However, there are various difficulties associated with gene therapy that have limited the realization of licensed gene therapies to only a handful of treatments. Furthermore, efforts to develop gene therapeutics have been narrowly focused and most clinical trials have sought to develop treatments for cancer (64.6%), monogenic diseases (10.5%), infectious diseases (7.4%), and cardiovascular diseases (7.4%). In addition, nearly 70% of clinical trials have utilized viral-based delivery systems, despite various concerns associated with this strategy. Each of these factors highlights the lack of diversity in the development of gene therapeutics that should be addressed. In recent years, developments in gene manipulation and delivery such as CRISPR and non-viral vectors (e.g., liposomes) demonstrate promise for improving outcomes for gene therapy. The increased fidelity and capacity afforded by these technologies provide the potential to improve upon contemporary gene therapy approaches and enable the development of treatments for less-emphasized disorders. In this review, we provide a summary of gene delivery technology and discuss various developments in gene therapy technology. We conclude by proposing several genetic conditions that represent promising targets for gene therapy given recent developments in gene delivery and manipulation.

Polyethylenimine Nanoparticle-Mediated siRNA Delivery to Reduce α-Synuclein Expression in a Model of Parkinson's Disease

RNA interference (RNAi)-based strategies that mediate the specific knockdown of target genes by administration of small interfering RNAs (siRNAs) could be applied for treatment of presently incurable neurodegenerative diseases such as Parkinson’s disease. However, inefficient delivery of siRNA into neurons hampers in vivo application of RNAi. We have previously established the 4–12 kDa branched polyethylenimine (PEI) F25-LMW with superior transfection efficacy for delivery of siRNA in vivo. Here, we present that siRNA complexed with this PEI extensively distributes across the CNS down to the lumbar spinal cord after a single intracerebroventricular infusion. siRNA against α-synuclein (SNCA), a pre-synaptic protein that aggregates in Parkinson’s disease, was complexed with PEI F25-LMW and injected into the lateral ventricle of mice overexpressing human wild-type SNCA (Thy1-aSyn mice). Five days after the single injection of 0.75 μg PEI/siRNA, SNCA mRNA expression in the striatum was reduced by 65%, accompanied by reduction of SNCA protein by ∼50%. Mice did not show signs of toxicity or adverse effects. Moreover, ependymocytes and brain parenchyma were completely preserved and free of immune cell invasion, astrogliosis, or microglial activation. Our results support the efficacy and safety of PEI nanoparticle-mediated delivery of siRNA to the brain for therapeutic intervention.

Reducing Endogenous α-Synuclein Mitigates the Degeneration of Selective Neuronal Populations in an Alzheimer's Disease Transgenic Mouse Model

Alzheimer's disease (AD) is characterized by the progressive accumulation of amyloid β (Aβ) and microtubule associate protein tau, leading to the selective degeneration of neurons in the neocortex, limbic system, and nucleus basalis, among others. Recent studies have shown that α-synuclein (α-syn) also accumulates in the brains of patients with AD and interacts with Aβ and tau, forming toxic hetero-oligomers. Although the involvement of α-syn has been investigated extensively in Lewy body disease, less is known about the role of this synaptic protein in AD. Here, we found that reducing endogenous α-syn in an APP transgenic mouse model of AD prevented the degeneration of cholinergic neurons, ameliorated corresponding deficits, and recovered the levels of Rab3a and Rab5 proteins involved in intracellular transport and sorting of nerve growth factor and brain-derived neurotrophic factor. Together, these results suggest that α-syn might participate in mechanisms of vulnerability of selected neuronal populations in AD and that reducing α-syn might be a potential approach to protecting these populations from the toxic effects of Aβ.

SIGNIFICANCE STATEMENT

Reducing endogenous α-synuclein (α-syn) in an APP transgenic mouse model of Alzheimer's disease (AD) prevented the degeneration of cholinergic neurons, ameliorated corresponding deficits, and recovered the levels of Rab3a and Rab5 proteins involved in intracellular transport and sorting of nerve growth factor and brain-derived neurotrophic factor. These results suggest that α-syn might participate in mechanisms of vulnerability of selected neuronal populations in AD and that reducing α-syn might be a potential approach to protecting these populations from the toxic effects of amyloid β.

Blood-brain barrier peptide shuttles

Brain delivery is hampered by the presence of the blood-brain barrier (BBB), a natural defence of the brain that protects it and allows the entrance of nutrients by several mechanisms. Taking advantage of these mechanisms is an opportunity to treat brain related diseases. Among the different alternatives, BBB peptide shuttles are gaining attention to increase brain delivery of therapeutics. The most recent advances in the field are analysed here.

Andrographolide Activates Keap1/Nrf2/ARE/HO-1 Pathway in HT22 Cells and Suppresses Microglial Activation by Aβ42 through Nrf2-Related Inflammatory Response

Therapeutic approach of Alzheimer's disease (AD) has been gradually diversified. We examined the therapeutic and preventive potential of andrographolide, which is a lactone diterpenoid from Andrographis paniculata, and focused on the Kelch-like ECH-associated protein 1 (Keap1)/nuclear factor (erythroid-derived 2)-like 2 (Nrf2)-mediated heme oxygenase (HO)-1-inducing effects and the inhibitory activity of amyloid beta (Aβ)₄₂-induced microglial activation related to Nrf2 and nuclear factor κB (NF-κB)-mediated inflammatory responses. Andrographolide induced the expression and translocation of Nrf2 from the cytoplasm to the nucleus, thereby activating antioxidant response element (ARE) gene transcription and HO-1 expression in murine hippocampal HT22 cells. Andrographolide eliminated intracellular Aβ₄₂ in BV-2 cells and decreased the production of interleukin (IL)-6, IL-1β, prostaglandin (PG)E₂, and nitric oxide (NO) because of artificial phagocytic Aβ₄₂. It decreased pNF-κB accumulation in the nucleus and the expression of inducible nitric oxide synthase (i-NOS) and cyclooxygenase II (COX-II) in the microglial BV-2 cell line. In summary, andrographolide activates Nrf2-mediated HO-1 expression and inhibits Aβ₄₂-overexpressed microglial BV-2 cell activation. These results suggested that andrographolide might have the potential for further examination of the therapeutics of AD.

Epigenetic regulation in Parkinson's disease

Recent efforts have shed new light on the epigenetic mechanisms driving gene expression alterations associated with Parkinson's disease (PD) pathogenesis. Changes in gene expression are a well-established cause of PD, and epigenetic mechanisms likely play a pivotal role in regulation. Studies in families with PD harboring duplications and triplications of the SNCA gene have demonstrated that gene dosage is associated with increased expression of both SNCA mRNA and protein, and correlates with a fulminant disease course. Furthermore, it is postulated that even subtle changes in SNCA expression caused by common variation is associated with disease risk. Of note, genome-wide association studies have identified over 30 loci associated with PD with most signals located in non-coding regions of the genome, thus likely influencing transcript expression levels. In health, epigenetic mechanisms tightly regulate gene expression, turning genes on and off to balance homeostasis and this, in part, explains why two cells with the same DNA sequence will have different RNA expression profiles. Understanding this phenomenon will be crucial to our interpretation of the selective vulnerability observed in neurodegeneration and specifically dopaminergic neurons in the PD brain. In this review, we discuss epigenetic mechanisms, such as DNA methylation and histone modifications, involved in regulating the expression of genes relevant to PD, RNA-based mechanisms, as well as the effect of toxins and potential epigenetic-based treatments for PD.