Advances with RNA interference in Alzheimer's disease research

Self-Assembled Nanoscale Materials for Neuronal Regeneration: A Focus on BDNF Protein and Nucleic Acid Biotherapeutic Delivery

Enabling challenging applications of nanomedicine and precision medicine in the treatment of neurodegenerative disorders requires deeper investigations of nanocarrier-mediated biomolecular delivery for neuronal targeting and recovery. The successful use of macromolecular biotherapeutics (recombinant growth factors, antibodies, enzymes, synthetic peptides, cell-penetrating peptide–drug conjugates, and RNAi sequences) in clinical developments for neuronal regeneration should benefit from the recent strategies for enhancement of their bioavailability. We highlight the advances in the development of nanoscale materials for drug delivery in neurodegenerative disorders. The emphasis is placed on nanoformulations for the delivery of brain-derived neurotrophic factor (BDNF) using different types of lipidic nanocarriers (liposomes, liquid crystalline or solid lipid nanoparticles) and polymer-based scaffolds, nanofibers and hydrogels. Self-assembled soft-matter nanoscale materials show favorable neuroprotective characteristics, safety, and efficacy profiles in drug delivery to the central and peripheral nervous systems. The advances summarized here indicate that neuroprotective biomolecule-loaded nanoparticles and injectable hydrogels can improve neuronal survival and reduce tissue injury. Certain recently reported neuronal dysfunctions in long-COVID-19 survivors represent early manifestations of neurodegenerative pathologies. Therefore, BDNF delivery systems may also help in prospective studies on recovery from long-term COVID-19 neurological complications and be considered as promising systems for personalized treatment of neuronal dysfunctions and prevention or retarding of neurodegenerative disorders.

Inflammation and Alzheimer's Disease: Mechanisms and Therapeutic Implications by Natural Products

Alzheimer's disease (AD) is a neurodegenerative disorder with no clear causative event making the disease difficult to diagnose and treat. The pathological hallmarks of AD include amyloid plaques, neurofibrillary tangles, and widespread neuronal loss. Amyloid-beta has been extensively studied and targeted to develop an effective disease-modifying therapy, but the success rate in clinical practice is minimal. Recently, neuroinflammation has been focused on as the event in AD progression to be targeted for therapies. Various mechanistic pathways including cytokines and chemokines, complement system, oxidative stress, and cyclooxygenase pathways are linked to neuroinflammation in the AD brain. Many cells including microglia, astrocytes, and oligodendrocytes work together to protect the brain from injury. This review is focused to better understand the AD inflammatory and immunoregulatory processes to develop novel anti-inflammatory drugs to slow down the progression of AD.

siRNA Therapeutics: Future Promise for Neurodegenerative Diseases

Neurodegenerative diseases (ND), as a group of central nervous system (CNS) disorders, are among the most prominent medical problems of the 21st century. They are often associated with considerable disability, motor dysfunction and dementia and are more common in the aged population. ND imposes a psychologic, economic and social burden on the patients and their families. Currently, there is no effective treatment for ND. Since many ND result from the gain of function of a mutant allele, small interference RNA (siRNA) can be a potential therapeutic agent for ND management. Based on the RNA interference (RNAi) approach, siRNA is a powerful tool for modulating gene expression through gene silencing. However, there are some obstacles in the clinical application of siRNA, including unfavorable immune response, off-target effects, instability of naked siRNA, nuclease susceptibility and a need to develop a suitable delivery system. Since there are some issues related to siRNA delivery routes, in this review, we focus on the application of siRNA in the management of ND treatment from 2000 to 2020.

Trends in Therapeutic Conjugates: Bench to Clinic

In recent years, therapeutic conjugates have attracted considerable attention as a new class of drug due to their unique pharmacological properties, especially from the pharmaceutical community. Their molecular structure tunability, improved targeting specificity, and therapeutic efficacy have been demonstrated in a wide range of research and clinical applications. In this topical review, we summarize selected recent advances in bioconjugation strategies for the development of therapeutic conjugates, their emerging application in clinical settings, as well as perspectives on the direction of future research.

Glaucoma: Biological Trabecular and Neuroretinal Pathology with Perspectives of Therapy Innovation and Preventive Diagnosis

Glaucoma is a common degenerative disease affecting retinal ganglion cells (RGC) and optic nerve axons, with progressive and chronic course. It is one of the most important reasons of social blindness in industrialized countries. Glaucoma can lead to the development of irreversible visual field loss, if not treated. Diagnosis may be difficult due to lack of symptoms in early stages of disease. In many cases, when patients arrive at clinical evaluation, a severe neuronal damage may have already occurred. In recent years, newer perspective in glaucoma treatment have emerged. The current research is focusing on finding newer drugs and associations or better delivery systems in order to improve the pharmacological treatment and patient compliance. Moreover, the application of various stem cell types with restorative and neuroprotective intent may be found appealing (intravitreal autologous cellular therapy). Advances are made also in terms of parasurgical treatment, characterized by various laser types and techniques. Moreover, recent research has led to the development of central and peripheral retinal rehabilitation (featuring residing cells reactivation and replacement of defective elements), as well as innovations in diagnosis through more specific and refined methods and inexpensive tests.

Biodegradable Carriers for Delivery of VEGF Plasmid DNA for the Treatment of Critical Limb Ischemia

The safe and efficient delivery of therapeutic nucleic acid is a prerequisite for an effective DNA therapy. In this study, we condensed the low molecular weight polyethylenimine (PEI, 1.8k Da) with 2,6-pyridinedicarboxaldehyde (PDA), both of which are degradable in vivo, to synthesize a biodegradable polycationic material (PDAPEI) to deliver vascular endothelial growth factor (VEGF) plasmid DNA (pDNA). Particle size and zeta potential of this novel degradable PEI derivatives-pDNA nanoparticle were investigated and in vitro cytotoxicity was estimated on human umbilical vein endothelial cells (HUVECs). Using pDNA-encoding VEGF-A and green fluorescence protein (GFP), we also checked transfection efficiency of the vector (PDAPEI) and found its excellent performance at 40 w/w ratio. We successfully established peripheral ischemia animal model on C57/BL6J mice to evaluate the therapeutic effect of PDAPEI/pVEGF-A polyplex system on ischemic disease and a conclusion was made that PDAPEI is a promising gene vector in the treatment of peripheral ischemic artery disease (PAD).

Immune Activities of Polycationic Vectors for Gene Delivery

Polycationic vectors are used widely in the field of gene delivery, while currently their immune activities in vivo are poorly understood. In this comprehensive review, we aim to present an overview of existing mechanisms of adverse immune responses induced by the polycation/gene complexes, which includes the polycations themselves, the gene sequences and the ROS produced by them. These causes can induce pro-inflammatory cytokines, hypersensitivity as well as the activation of toll-like receptors, and finally the immunostimulation occur. In addition, we introduce some different opinions and research results on the immunogenicity of classical polycations such as polylysine (PLL), polyethyleneimine (PEI), polyamidoamine dendrimers (PAMAM), chitosan and gelatin, most of which have immunogenicity and can induce immunoreactions in vivo. The methods now used to adjust their immunogenicity are shown in the final part of this review. Nowadays, there is still no accurate conclusion on immunogenicity of polycations, which confuses researchers seriously in in vivo test. We conclude that further research is needed in order to skillfully utilize or inhibit the immunogenicity of these polycationic vectors.

Brain delivery of small interfering ribonucleic acid and drugs through intranasal administration with nano-sized polymer micelles

Recently, the development of effective strategies for enhancing drug delivery to the brain has been a topic of great interest in both clinical and pharmaceutical fields. In this review, we summarize our studies evaluating nose-to-brain delivery of drugs and small interfering ribonucleic acids in combination with cell-penetrating peptide-modified polymer micelles. Our findings show that the use of polymer micelles with surface modification with Tat peptide in the intranasal administration enables the non-invasive delivery of therapeutic agents to the brain by increasing the transfer of the administered drug or small interfering ribonucleic acid to the central nervous system from the nasal cavity.

New type of BACE1 siRNA delivery to cells

BACKGROUND

Small interfering RNA (siRNA) gene therapy is a new molecular approach in the search for an efficient therapy for Alzheimer disease (AD), based on the principle of RNA interference. Reducing BACE activity can have great therapeutic potential for the treatment of AD. In this study, receptor-mediated delivery was used to deliver opioid peptide-conjugated BACE 1 to INR-32 human neuroblastoma cells.

MATERIAL AND METHODS

An INR-32 human neuroblastoma cell line was stably transfected to express the APP cDNA coding fragment containing the predicted sites for cleavage by α, β, or γ-secretase. This was then treated with BACE 1 siRNA to silence BACE gene expression. BACE gene transcription and translation was determined using BACE-1 siRNA cross-linked with opioid peptide, together with RT-PCR, Western blot analysis, and ELISA.

RESULTS

Receptor-mediated delivery was used to introduce BACE1 siRNA to the APP - INR 32 human neuroblastoma cells. Decreased BACE mRNA and protein expression were observed after the cells were transfected with BACE1 siRNA.

CONCLUSIONS

Delivery of BACE1 siRNA appears to specifically reduce the cleavage of APP by inhibiting BACE1 activity.

Screening nylon-3 polymers, a new class of cationic amphiphiles, for siRNA delivery

Amphiphilic nucleic acid carriers have attracted strong interest. Three groups of nylon-3 copolymers (poly-β-peptides) possessing different cationic/hydrophobic content were evaluated as siRNA delivery agents in this study. Their ability to condense siRNA was determined in SYBR Gold assays. Their cytotoxicity was tested by MTT assays, their efficiency of delivering Alexa Fluor-488-labeled siRNA intracellularly in the presence and absence of uptake inhibitors was assessed by flow cytometry, and their transfection efficacies were studied by luciferase knockdown in a cell line stably expressing luciferase (H1299/Luc). Endosomal release was determined by confocal laser scanning microscopy and colocalization with lysotracker. All polymers efficiently condensed siRNA at nitrogen-to-phosphate (N/P) ratios of 5 or lower, as reflected in hydrodynamic diameters smaller than that at N/P 1. Although several formulations had negative zeta potentials at N/P 1, G2C and G2D polyplexes yielded >80% uptake in H1299/Luc cells, as determined by flow cytometry. Luciferase knockdown (20–65%) was observed after transfection with polyplexes made of the high molecular weight polymers that were the most hydrophobic. The ability of nylon-3 polymers to deliver siRNA intracellularly even at negative zeta potential implies that they mediate transport across cell membranes based on their amphiphilicity. The cellular uptake route was determined to strongly depend on the presence of cholesterol in the cell membrane. These polymers are, therefore, very promising for siRNA delivery at reduced surface charge and toxicity. Our study identified nylon-3 formulations at low N/P ratios for effective gene knockdown, indicating that nylon-3 polymers are a new, promising type of gene delivery agent.

Protein phosphorylation in neurodegeneration: friend or foe?

Protein misfolding and aggregation is a common hallmark in neurodegenerative disorders, including Alzheimer's disease (AD), Parkinson's disease (PD), and fronto-temporal dementia (FTD). In these disorders, the misfolding and aggregation of specific proteins occurs alongside neuronal degeneration in somewhat specific brain areas, depending on the disorder and the stage of the disease. However, we still do not fully understand the mechanisms governing protein aggregation, and whether this constitutes a protective or detrimental process. In PD, alpha-synuclein (aSyn) forms protein aggregates, known as Lewy bodies, and is phosphorylated at serine 129. Other residues have also been shown to be phosphorylated, but the significance of phosphorylation in the biology and pathophysiology of the protein is still controversial. In AD and in FTD, hyperphosphorylation of tau protein causes its misfolding and aggregation. Again, our understanding of the precise consequences of tau phosphorylation in the biology and pathophysiology of the protein is still limited. Through the use of a variety of model organisms and technical approaches, we are now gaining stronger insight into the effects of phosphorylation in the behavior of these proteins. In this review, we cover recent findings in the field and discuss how targeting phosphorylation events might be used for therapeutic intervention in these devastating diseases of the nervous system.

A synergic role of caspase-6 and caspase-3 in Tau truncation at D421 induced by H2O 2

Tau truncation is widely detected in Alzheimer's disease brain. Caspases activation is suggested to play a significant role in tau truncation at Aspartate 421 (D421) according to their ability to cleave recombinant tau in vitro. Ample evidence has shown that caspase-6 is involved in cognitive impairment and expressed in AD brain. Reactive oxygen species (ROS) can lead to caspase-6 activation and correlate with AD. Here, we transfected human embryonic kidney 293 (HEK 293) cells with Tau 441 plasmid and investigated the role of caspase-6 and caspase-3 in ROS-mediated tau truncation. Our data demonstrated that H2O2 induced oxidative stress and increased tau truncation. Caspase-6 and caspase-3 activity also increased in a dose-dependent manner in HEK 293/Tau cells during H2O2 insult. When cells were treated with an ROS inhibitor N-acetyl-L-cysteine, tau truncation was significantly suppressed. Compared with H2O2 (100 μM)/non-inhibitor group or single-inhibitor groups (z-VEID-fmk, caspase-6 inhibitor or z-DEVD-fmk, and caspase-3 inhibitor), tau truncation induced by H2O2 was effectively reduced in the combinative inhibitors group. Similar results were shown when cells were transfected with specific caspase-3 and caspase-6 siRNA. Inhibition of caspase-6 led to decline of caspase-3 activation. Taken together, our results suggest that the combination of caspase-6 and caspase-3 aggravates tau truncation at D421 induced by H2O2. Caspase-6 may play an important part in activating caspase-3. Further investigation of how the synergic role of caspase-6 and caspase-3 affects tau truncation may provide new visions for potential AD therapies.

RNA silencing of genes involved in Alzheimer's disease enhances mitochondrial function and synaptic activity

An age-dependent increase in mRNA levels of the amyloid precursor protein (APP), the microtubule-associated protein Tau, and voltage-dependent anion channel 1 (VDAC1) genes are reported to be toxic to neurons affected by Alzheimer's disease (AD). However, the underlying toxic nature of these genes is not completely understood. The purpose of our study was to determine the effects of RNA silencing of APP, Tau, and VDAC1 genes in AD pathogenesis. Using human neuroblastoma (SHSY5Y) cells, we first silenced RNA for APP, Tau, and VDAC1 genes, and then performed real-time RT-PCR analysis to measure mRNA levels of 34 genes that are involved in AD pathogenesis. Using biochemical assays, we also assessed mitochondrial function by measuring levels of H2O2 production, lipid peroxidation, cytochrome c oxidase activity, ATP production, and GTPase enzymatic activity. We found that increased mRNA expression of synaptic function and mitochondrial fission genes, and reduced levels of mitochondrial fusion genes in RNA silenced the SHSY5Y cells for APP, Tau and VDAC1 genes relative to the control SHSY5Y cells. In addition, RNA-silenced APP, Tau, and VDAC1 genes in SHSY5Y cells showed reduced levels of H2O2 production, lipid peroxidation, fission-linked GTPase activity, and increased cytochrome oxidase activity and ATP production. These findings suggest that a reduction of human APP, Tau, and VDAC1 may enhance synaptic activity, may improve mitochondrial maintenance and function, and may protect against toxicities of AD-related genes. Thus, these findings also suggest that the reduction of APP, Tau, and VDAC1 mRNA expressions may have therapeutic value for patients with AD.

Antisense gene silencing: therapy for neurodegenerative disorders?

Since the first reports that double-stranded RNAs can efficiently silence gene expression in C. elegans, the technology of RNA interference (RNAi) has been intensively exploited as an experimental tool to study gene function. With the subsequent discovery that RNAi could also be applied to mammalian cells, the technology of RNAi expanded from being a valuable experimental tool to being an applicable method for gene-specific therapeutic regulation, and much effort has been put into further refinement of the technique. This review will focus on how RNAi has developed over the years and how the technique is exploited in a pre-clinical and clinical perspective in relation to neurodegenerative disorders.