Usefulness of cell-penetrating peptides and penetration accelerating sequence for nose-to-brain delivery of glucagon-like peptide-2

Brain Delivery Strategies for Biomacromolecular Drugs: Intranasal Administration

Macromolecular Drugs (including monoclonal antibodies, recombinant proteins, and nucleic acid therapies) have become a cornerstone strategy for intervening in complex pathological mechanisms such as cancer, autoimmune diseases, and genetic disorders due to their high specificity for disease targets and low off-target toxicity. However, compared to traditional small-molecule drugs, the high molecular weight (>10 kDa) and structural complexity of macromolecular drugs result in extremely low transmembrane permeability. This is particularly challenging in the treatment of central nervous system (CNS) diseases, where the blood-brain barrier (BBB) imposes stringent selectivity, further limiting drug delivery efficiency. This review focuses on the breakthrough strategy of nose-to-brain (NtB) drug delivery. On one hand, the NtB pathway bypasses the BBB, enabling direct CNS drug delivery. On the other hand, nanocarrier technology can synergistically achieve systemic delivery and brain-targeted transport. Based on the latest research advances, this article systematically examines the feasibility of delivering macromolecular drugs via NtB administration. We comprehensively summarize relevant delivery carriers and discuss the potential advantages of intranasal-brain delivery for CNS disease treatment. Notably, while significant progress has been made in this field, further exploration is still needed regarding the mechanisms of NtB delivery and challenges in clinical translation.

Glucagon-like peptide-1 receptor agonists in neurodegenerative diseases: Promises and challenges

Glucagon-like peptide-1 (GLP-1) receptor agonists (GRA) belong to a class of compounds that reduce blood glucose and energy intake by simulating actions of endogenous incretin hormone GLP-1 after it is released by the gut following food consumption. They are used to treat type 2 diabetes mellitus (T2DM) and obesity and have systemic effects on various organs, including the brain, liver, pancreas, heart, and the gut. Patients with T2DM have a higher risk of developing neurodegenerative diseases (NDs), including Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS) and Huntington's disease (HD), accompanied by more severe motor deficits and faster disease progression, suggesting dysregulation of insulin signaling in these diseases. Experimental studies have shown that GRA have protective effects to modulate neuroinflammation, oxidative stress, mitochondrial and autophagic functions, and protein misfolding. Hence the compounds have generated enormous interest as novel therapeutic agents against NDs. To date, clinical trials have shown that three GRA, exenatide, liraglutide and lixisenatide can improve motor deficits as an add-on therapy in PD patients and liraglutide can improve cognitive function in AD patients. The neuroprotective effects of these and other GRA, such as PT320 (a sustained-released exenatide) and semaglutide, are still under investigation. The dual GLP-1/gastric inhibitory polypeptide (GIP) receptor agonists have been demonstrated to have beneficial effects in AD and PD mice models. Overall, GRA are highly promising novel drugs, but future clinical studies should identify which subsets of patients should be targeted as potential candidates for their symptomatic and/or neuroprotective benefits, investigate whether combinations with other classes of drugs can further augment their efficacy, and evaluate their long-term disease-modifying and adverse effects.

Advances in cell-penetrating peptide-based nose-to-brain drug delivery systems

The incidence of brain disorders has gained worldwide attention and the presence of the blood-brain barrier prevents numerous drugs from reaching the targeted brain. The specific physiology of the nasal cavity and the brain provides the feasibility of direct nose-brain delivery, a system that bypasses the blood-brain barrier in a non-invasive manner for brain-targeted drug delivery via intracellular and extracellular mechanisms. The use of CPPs provides further feasibility for naso-brain drug delivery studies, and liposomes, nanopolymer particles, and gels modified with CPPs have demonstrated significant brain-targeting capabilities after nasal delivery. In this paper, the physiology of the nasal cavity and brain, the pathways of naso-brain delivery and the influencing factors are discussed in detail. At the same time, the introduction, classification, mechanism of action and application of CPPs in the nasal-brain delivery system are discussed in detail to provide a theoretical basis for the in-depth study of the application of CPPs in the nasal-brain delivery system.

A Novel Method for Preparing Uniform Micro-Sized Dry Powder Formulations, Including Aggregation-Controlled VHH

BACKGROUND

The preparation of antibodies in powder form without changing their physicochemical properties may enable their use in new drug delivery system therapies or non-refrigerated storage. The variable domain of heavy-chain antibodies (VHHs) is more suited for this purpose than that of conventional antibodies because of VHHs' high thermal stability and ability to refold.

METHODS

In this report, the fine droplet drying (FDD) process was selected as the powderization technique because of its favorable features, such as mild drying conditions and the generation of uniform particle sizes. The aggregation, binding, particle, and in vitro inhalation properties of the prepared VHH powders (VHHps) were evaluated.

RESULTS

The amount of aggregated VHHs present in the VHHps depended on the flow temperature during the FDD process, with higher temperatures yielding a higher aggregation ratio. In contrast, no significant difference in binding activity was observed between each VHHp preparation and the native VHHs. However, this process degraded VHHs or inactivated their function, and ultimately, only about 30% of the original VHHs were functional, whereas the remaining VHHs that were not degraded showed little loss of functionality, even after storage at room temperature for more than two years. Analysis of the VHHp samples revealed that the particles were uniformly spherical with a single-micron size. The VHHps showed fine inhalation properties in the inhalation property test.

CONCLUSIONS

These findings suggest that the FDD process affords various VHH powder formulations, including pharmaceutical formulations.

Dodecyl creatine ester, a promising treatment to deliver creatine to neurons, achieves pharmacology efficacy in creatine transporter deficiency

Dodecyl creatine ester (DCE) is a creatine prodrug currently developed for brain diseases, including creatine transporter deficiency (CTD), an incurable rare genetic disease. A dual strategy combining a prodrug to bypass the non-functional creatine transporter and its delivery via the nose-to-brain pathway has been proposed to replenish creatine levels in cerebral cells, particularly in neurons of CTD patients. In vitro and in vivo studies in various animal models, including wild-type non-human primates and creatine transporter deficient mice, show that formulated DCE, when administered intranasally, achieves significant cerebral distribution up to the target cells, the neurons, and modulates the expression of neuronal markers related to cognitive function at doses intended for patients. These compelling results contribute to a better understanding of the pharmacokinetics and pharmacodynamics of DCE after nasal administration, with a particular focus on the crucial role of the nose-to-brain pathway in DCE distribution.

Tailored Borneol-Modified Lipid Nanoparticles Nasal Spray for Enhanced Nose-to-Brain Delivery to Central Nervous System Diseases

The nanodrug delivery system-based nasal spray (NDDS-NS) can bypass the blood-brain barrier and deliver drugs directly to the brain, offering unparalleled advantages in the treatment of central nervous system (CNS) diseases. However, the current design of NNDS-NS is excessively focused on mucosal absorption while neglecting the impact of nasal deposition on nose-to-brain drug delivery, resulting in an unsatisfactory nose-to-brain delivery efficiency. In this study, the effect of the dispersion medium viscosity on nasal drug deposition and nose-to-brain delivery in NDDS-NS was elucidated. The optimized formulation F5 (39.36 mPa·s) demonstrated significantly higher olfactory deposition fraction (ODF) of 23.58%, and a strong correlation between ODF and intracerebral drug delivery (R2 = 0.7755) was observed. Building upon this understanding, a borneol-modified lipid nanoparticle nasal spray (BLNP-NS) that combined both nasal deposition and mucosal absorption was designed for efficient nose-to-brain delivery. BLNP-NS exhibited an accelerated onset of action and enhanced brain targeting efficiency, which could be attributed to borneol modification facilitating the opening of tight junction channels. Furthermore, BLNP-NS showed superiority in a chronic migraine rat model. It not only provided rapid relief of migraine symptoms but also reversed neuroinflammation-induced hyperalgesia. The results revealed that borneol modification could induce the polarization of microglia, regulate the neuroinflammatory microenvironment, and repair the neuronal damage caused by neuroinflammation. This study highlights the impact of dispersion medium viscosity on the nose-to-brain delivery process of NDDS-NS and serves as a bridge between the formulation development and clinical transformation of NDDS-NS for the treatment of CNS diseases.

Cell-Penetrating Peptide-Mediated Biomolecule Transportation in Artificial Lipid Vesicles and Living Cells

Signal transduction and homeostasis are regulated by complex protein interactions in the intracellular environment. Therefore, the transportation of impermeable macromolecules (nucleic acids, proteins, and drugs) that control protein interactions is essential for modulating cell functions and therapeutic applications. However, macromolecule transportation across the cell membrane is not easy because the cell membrane separates the intra/extracellular environments, and the types of molecular transportation are regulated by membrane proteins. Cell-penetrating peptides (CPPs) are expected to be carriers for molecular transport. CPPs can transport macromolecules into cells through endocytosis and direct translocation. The transport mechanism remains largely unclear owing to several possibilities. In this review, we describe the methods for investigating CPP conformation, translocation, and cargo transportation using artificial membranes. We also investigated biomolecular transport across living cell membranes via CPPs. Subsequently, we show not only the biochemical applications but also the synthetic biological applications of CPPs. Finally, recent progress in biomolecule and nanoparticle transportation via CPPs into specific tissues is described from the viewpoint of drug delivery. This review provides the opportunity to discuss the mechanism of biomolecule transportation through these two platforms.

Intranasal delivery of glucagon-like peptide-1 to the brain for obesity treatment: opportunities and challenges

INTRODUCTION

Glucagon-like peptide-1 receptor agonists (GLP-1 RAs), approved by the US FDA for obesity treatment, are typically administered subcutaneously, an invasive method leading to suboptimal patient adherence and peripheral side effects. Additionally, this route requires the drug to cross the restrictive blood-brain barrier (BBB), limiting its safety and effectiveness in weight management and cognitive addiction disorders. Delivering the drug intranasally could overcome these drawbacks.

AREAS COVERED

This review summarizes GLP-1 RAs used as anti-obesity agents, focusing on the intranasal route as a potential pathway to deliver these biomolecules to the brain. It also discusses strategies to overcome challenges associated with nasal delivery.

EXPERT OPINION

Nose-to-brain (N2B) pathways can address limitations of the subcutaneous route for GLP-1 RAs. However, peptide delivery to the brain is challenging due to nasal physiological barriers and the drug's physicochemical properties. Innovative approaches, such as cell permeation enhancers, mucoadhesive systems, and nanocarriers in nasal formulations, along with efficient drug delivery devices, show promising preclinical results. Despite this, successful preclinical data does not guarantee clinical effectiveness, highlighting the need for comprehensive clinical investigations to optimize formulations and fully utilize the nose-to-brain interface for peptide delivery.

Covalent conjugation and non-covalent complexation strategies for intracellular delivery of proteins using cell-penetrating peptides

Therapeutic proteins provided new opportunities for patients and high sales volumes. However, they are formulated for extracellular targets. The lipophilic barrier of the plasma membrane renders the vast array of intracellular targets out of reach. Peptide-based delivery systems, namely cell-penetrating peptides (CPPs), have few safety concerns, and low immunogenicity, with control over administered doses. This study investigates CPP-based protein delivery systems by classifying them into CPP-protein "covalent conjugation" and CPP: protein "non-covalent complexation" categories. Covalent conjugates ensure the proximity of the CPP to the cargo, which can improve cellular uptake and endosomal escape. We will discuss various aspects of covalent conjugates through non-cleavable (stable) or cleavable bonds. Non-cleavable CPP-protein conjugates are produced by recombinant DNA technology to express the complete fusion protein in a host cell or by chemical ligation of CPP and protein, which ensures stability during the delivery process. CPP-protein cleavable bonds are classified into pH-sensitive and redox-sensitive bonds, enzyme-cleavable bonds, and physical stimuli cleavable linkers (light radiation, ultrasonic waves, and thermo-responsive). We have highlighted the key characteristics of non-covalent complexes through electrostatic and hydrophobic interactions to preserve the conformational integrity of the CPP and cargo. CPP-mediated protein delivery by non-covalent complexation, such as zippers, CPP adaptor methods, and avidin-biotin technology, are featured. Conclusively, non-covalent complexation methods are appropriate when a high number of CPP or protein samples are to be screened. In contrast, when the high biological activity of the protein is critical in the intracellular compartment, conjugation protocols are preferred.

Conditional Cell Penetration of Masked CPPs by an ADEPT-like Approach

The intracellular delivery of cargos via cell penetrating peptides (CPPs) holds significant promise as a drug delivery vehicle, but a major issue is their lack of cell type specificity, which can lead to detrimental off-target effects. We use an ADEPT-like concept to introduce conditional and selective activation of cellular uptake by using the lysine-rich, cationic, and amphiphilic L17E peptide as a model CPP. By masking the lysine residues of the L17E peptide with enzyme-cleavable acetyl protecting groups, the delivery of the covalently conjugated fluorophore TAMRA to HeLa cells was diminished. Recovery of cellular uptake could be achieved by deacetylation of the masked acetylated L17E peptide using the NAD-dependent sirtuin 2 (SirT2) deacetylase in vitro. Finally, trastuzumab-SirT2 and anti-B7H3-SirT2 antibody-enzyme conjugates were generated for the conditional and selective delivery of a cryptophycin cytotoxin by the L17E peptide. While the masked peptide still demonstrated some cytotoxicity, selective cell killing mediated by the antibody-enzyme conjugates was observed.

A new trivalent recombinant protein for type 2 diabetes mellitus with oral delivery potential: design, expression, and experimental validation

Glucagon-like peptide-1 (GLP-1) receptor agonists are increasingly used in clinical practice for the management of type 2 diabetes mellitus. However, the extremely short half-life of GLP-1 and the need for subcutaneous administration limit its clinical application. Thus, half-life extension and alternative delivery methods are highly desired. DARPin domains with high affinity for human serum albumin (HSA) have been selected for the half-life extension of therapeutic peptides and proteins. In the present study, novel trivalent fusion proteins as long-acting GLP-1 receptor agonists with potential for oral delivery were computationally engineered by incorporating a protease-resistant modified GLP-1, an anti-human serum albumin DARPin, and an approved cell-penetrating peptide (Penetratin, Tat, and Polyarginine) linked either by rigid or flexible linkers. Theoretical studies and molecular dynamics simulation results suggested that mGLP1-DARPin-Pen has acceptable quality and stability. Moreover, the potential affinity of the selected fusion proteins for GLP-1 receptor and human serum albumin was explored by molecular docking. The recombinant construct was cloned into the pET28a vector and expressed in Escherichia coli. SDS-PAGE analysis of the purified fusion protein matched its molecular size and was confirmed by western blot analysis. The results demonstrated that the engineered fusion protein could bind HSA with high affinity. Importantly, insulin secretion assays using a mouse pancreatic β-cell line (β-TC6) revealed that the engineered trivalent fusion protein retained the ability to stimulate cellular insulin secretion. Immunofluorescence microscopy analysis indicated the CPP-dependent cellular uptake of mGLP1-DARPin-Pen. These findings demonstrated that mGLP1-DARPin-Pen is a highly potent oral drug candidate that could be particularly useful in the treatment of type 2 diabetes mellitus.

GLP-1 derivatives with functional sequences transit and migrate through trigeminal neurons

Patients with dementia are increasing with the aging of the population, and dementia has become a disease with high unmet medical needs. Glucagon-like peptide-1 (GLP-1), a neuropeptide, has been reported to improve learning and memory following intracerebroventricular administration. We focused on intranasal administration, which can deliver drugs noninvasively and efficiently to the brain. Although much of the human nasal mucosa is occupied by respiratory epithelium, many capillaries are present in the paracellular route of respiratory epithelium. Therefore, to incorporate GLP-1 into cells, we created a GLP-1 derivative by adding cell-penetrating peptides (CPP) and penetration accelerating sequences (PAS) to GLP-1. We investigated in vitro and in vivo function of PAS-CPP-GLP-1 to enable the translocation of GLP-1 directly from nose to brain. PAS-CPP-GLP-1 enhanced cellular uptake by macropinocytosis with CPP, efficiently escaped from the endosomes due to PAS, and exited the cells. PAS-CPP-GLP-1 also transited trigeminal nerve cells through axon transport and migrated to the adjacent trigeminal nerve cell. Moreover, PAS-CPP-GLP-1 showed significant improvement in learning memory in mice within 20 min of intranasal administration. These results suggested CPP and PAS may be important for the efficient transfer of GLP-1 to the site of action in the brain following intranasal administration.

Cell-penetrating peptides for transmucosal delivery of proteins

Enabling non-invasive delivery of proteins across the mucosal barriers promises improved patient compliance and therapeutic efficacies. Cell-penetrating peptides (CPPs) are emerging as a promising and versatile tool to enhance protein and peptide permeation across various mucosal barriers. This review examines the structural and physicochemical attributes of the nasal, buccal, sublingual, and oral mucosa that hamper macromolecular delivery. Recent development of CPPs for overcoming those mucosal barriers for protein delivery is summarized and analyzed. Perspectives regarding current challenges and future research directions towards improving non-invasive transmucosal delivery of macromolecules for ultimate clinical translation are discussed.

Nanotechnology for enhanced nose-to-brain drug delivery in treating neurological diseases

Despite the increasing global incidence of brain disorders, achieving sufficient delivery towards the central nervous system (CNS) remains a formidable challenge in terms of translating into improved clinical outcomes. The brain is highly safeguarded by physiological barriers, primarily the blood-brain barrier (BBB), which routinely excludes most therapeutics from entering the brain following systemic administration. Among various strategies investigated to circumvent this challenge, intranasal administration, a noninvasive method that bypasses the BBB to allow direct access of drugs to the CNS, has been showing promising results. Nanotechnology-based drug delivery systems, in particular, have demonstrated remarkable capacities in overcoming the challenges posed by nose-to-brain drug delivery and facilitating targeted drug accumulation within the brain while minimizing side effects of systemic distribution. This review comprehensively summarizes the barriers of nose-to-brain drug delivery, aiming to enhance our understanding of potential physiological obstacles and improve the efficacy of nasal delivery in future trials. We then highlight cutting-edge nanotechnology-based studies that enhance nose-to-brain drug delivery in three key aspects, demonstrating substantial potential for improved treatment of brain diseases. Furthermore, the attention towards clinical studies will ease the regulatory approval process for nasal administration of nanomedicines targeting brain disease.

A comprehensive review of advanced nasal delivery: Specially insulin and calcitonin

Peptide drugs through nasal mucous membrane, such as insulin and calcitonin have been widely used in the medical field. There are always two sides to a coin. One side, intranasal drug delivery can imitate the secretion pattern in human body, having advantages of physiological structure and convenient use. Another side, the low permeability of nasal mucosa, protease environment and clearance effect of nasal cilia hinder the intranasal absorption of peptide drugs. Researchers have taken multiple means to achieve faster therapeutic concentration, lower management dose, and fewer side effects for better nasal preparations. To improve the peptide drugs absorption, various strategies had been explored via the nasal mucosa route. In this paper, we reviewed the achievements of 18 peptide drugs in the past decade about the perspectives of the efficacy, mechanism of enhancing intranasal absorption and safety. The most studies were insulin and calcitonin. As a result, absorption enhancers, nanoparticles (NPs) and bio-adhesive system are the most widely used. Among them, chitosan (CS), cell penetrating peptides (CPPs), tight junction modulators (TJMs), soft NPs and gel/hydrogel are the most promising strategies. Moreover, two or three strategies can be combined to prepare drug vectors. In addition, spray freeze dried (SFD), self-emulsifying nano-system (SEN), and intelligent glucose reaction drug delivery system are new research directions in the future.

The Role of Oxytocin in Alzheimer's Disease and Its Relationship with Social Interaction

Alzheimer's disease (AD)-the most common cause of dementia in the elderly-is characterized by progressive memory loss and β-amyloid protein (Aβ) accumulation in the brain. Recently, loneliness was found to be a high risk factor for AD, and social isolation has become a major cause of AD. AD. Oxytocin (OXT), the main hormone involved in social bonding, has been implicated in social interactions, notably in building trust and relationships. Moreover, social isolation or social enrichment modulates the activation of neurons related to OXT. Recently, we reported that OXT reverses learning and memory impairment in AD animal models. Based on the limited number of studies currently available, OXT might be a therapeutic target for AD. Further studies are necessary in order to better understand the role of oxytocin in AD. In this review, we described the relationships between OXT, AD, and social interaction.

Cell-Penetrating Peptides as Valuable Tools for Nose-to-Brain Delivery of Biological Drugs

Due to their high specificity toward the target and their low toxicity, biological drugs have been successfully employed in a wide range of therapeutic areas. It is yet to be mentioned that biologics exhibit unfavorable pharmacokinetic properties, are susceptible to degradation by endogenous enzymes, and cannot penetrate biological barriers such as the blood-brain barrier (i.e., the major impediment to reaching the central nervous system (CNS)). Attempts to overcome these issues have been made by exploiting the intracerebroventricular and intrathecal routes of administration. The invasiveness and impracticality of these procedures has, however, prompted the development of novel drug delivery strategies including the intranasal route of administration. This represents a non-invasive way to achieve the CNS, reducing systemic exposure. Nonetheless, biotherapeutics strive to penetrate the nasal epithelium, raising the possibility that direct delivery to the nervous system may not be straightforward. To maximize the advantages of the intranasal route, new approaches have been proposed including the use of cell-penetrating peptides (CPPs) and CPP-functionalized nanosystems. This review aims at describing the most impactful attempts in using CPPs as carriers for the nose-to-brain delivery of biologics by analyzing their positive and negative aspects.

Transferrin-modified chitosan nanoparticles for targeted nose-to-brain delivery of proteins

Nose-to-brain delivery presents a promising alternative route compared to classical blood-brain barrier passage, especially for the delivery of high molecular weight drugs. In general, macromolecules are rapidly degraded in physiological environment. Therefore, nanoparticulate systems can be used to protect biomolecules from premature degradation. Furthermore, targeting ligands on the surface of nanoparticles are able to improve bioavailability by enhancing cellular uptake due to specific binding and longer residence time. In this work, transferrin-decorated chitosan nanoparticles are used to evaluate the passage of a model protein through the nasal epithelial barrier in vitro. It was demonstrated that strain-promoted azide-alkyne cycloaddition reaction can be utilized to attach a functional group to both transferrin and chitosan enabling a rapid covalent surface-conjugation under mild reaction conditions after chitosan nanoparticle preparation. The intactness of transferrin and its binding efficiency were confirmed via SDS-PAGE and SPR measurements. Resulting transferrin-decorated nanoparticles exhibited a size of about 110-150 nm with a positive surface potential. Nanoparticles with the highest amount of surface bound targeting ligand also displayed the highest cellular uptake into a human nasal epithelial cell line (RPMI 2650). In an air-liquid interface co-culture model with glioblastoma cells (U87), transferrin-decorated nanoparticles showed a faster passage through the epithelial cell layer as well as increased cellular uptake into glioblastoma cells. These findings demonstrate the beneficial characteristics of a specific targeting ligand. With this chemical and technological formulation concept, a variety of targeting ligands can be attached to the surface after nanoparticle formation while maintaining cargo integrity.

Recent advances in selective and targeted drug/gene delivery systems using cell-penetrating peptides

Biological cell membranes are a natural barrier for living cells. In the last few decades, the cell membrane has been the main hurdle in the efficient delivery of bioactive and therapeutic agents. To increase the drug efficacy of these agents, additional mediators have been considered. Cell-penetrating peptides (CPPs), a series of oligopeptides composed of mostly hydrophobic and/or positively charged side chains, can increase the interaction with the cell membrane. CPP-based delivery platforms have shown great potential for the efficient and direct cytosol delivery of various cargos, including genes, proteins, and small molecule drugs. Bypassing endocytosis allows the CPP-based delivery systems greater defense against the degradation of protein-based drugs than other drug delivery systems. However, the delivery of CPPs exhibits intrinsically non-specific targeting, which limits their medical applications. To endow CPPs with specific targeting ability, the conjugation of pH-sensitive, enzyme-specific cleavable, and multiple targeting ligands has been reported. Optimization of the length and sequence of CPPs is still needed for various drugs of different sizes and surface charges. Toxicity issues in CPP-based delivery systems should be addressed carefully before clinical use.

Approaches for evaluation of novel CPP-based cargo delivery systems

Cell penetrating peptides (CPPs) can be broadly defined as relatively short synthetic, protein derived or chimeric peptides. Their most remarkable property is their ability to cross cell barriers and facilitate the translocation of cargo, such as drugs, nucleic acids, peptides, small molecules, dyes, and many others across the plasma membrane. Over the years there have been several approaches used, adapted, and developed for the evaluation of CPP efficacies as delivery systems, with the fluorophore attachment as the most widely used approach. It has become progressively evident, that the evaluation method, in order to lead to successful outcome, should concede with the specialties of the delivery. For characterization and assessment of CPP-cargo a combination of research tools of chemistry, physics, molecular biology, engineering, and other fields have been applied. In this review, we summarize the diverse, in silico, in vitro and in vivo approaches used for evaluation and characterization of CPP-based cargo delivery systems.

Application of Intranasal Administration in the Delivery of Antidepressant Active Ingredients

As a mental disease in modern society, depression shows an increasing occurrence, with low cure rate and high recurrence rate. It has become the most disabling disease in the world. At present, the treatment of depression is mainly based on drug therapy combined with psychological therapy, physical therapy, and other adjuvant therapy methods. Antidepressants are primarily administered peripherally (oral and intravenous) and have a slow onset of action. Antidepressant active ingredients, such as neuropeptides, natural active ingredients, and some chemical agents, are limited by factors such as the blood–brain barrier (BBB), first-pass metabolism, and extensive adverse effects caused by systemic administration. The potential anatomical link between the non-invasive nose–brain pathway and the lesion site of depression may provide a more attractive option for the delivery of antidepressant active ingredients. The purpose of this article is to describe the specific link between intranasal administration and depression, the challenges of intranasal administration, as well as studies of intranasal administration of antidepressant active ingredients.

Involvement of trigeminal axons in nose-to-brain delivery of glucagon-like peptide-2 derivative

In our previous study, we created a glucagon-like peptide-2 (GLP-2) derivative with the functional sequence PAS-CPP to achieve efficient uptake by the respiratory epithelium and trigeminal nerve. By using octaarginine for cell penetrating peptides (CPP) and FFLIPKG, a reverse sequence of a part of the cathepsin D sequence for the penetration accelerating sequence (PAS), we found that the derivative was taken up by the cells through macropinocytosis and efficiently escaped from the endosomes and exited the cells. Moreover, it showed drug effects by intranasal (in.) administration at the same dose as intracerebroventricular (icv.) administration, which is direct drug administration into the brain. The purpose of this study was to elucidate the cause of the drug effect of in. administered PAS-CPP-GLP-2 at the same dose as that by icv. Administration. The present results suggested that although icv. Administered PAS-CPP-GLP-2 entered the cerebrospinal fluid, it barely penetrated the perivascular space of the brain, and therefore, only a small amount of the administered dose may have reached the site of action in the brain. In contrast, it was qualitatively suggested that in. administered PAS-CPP-GLP-2 migrates from the trigeminal nerve to the central nervous system via the principal sensory trigeminal nucleus and then through the trigeminal lemniscus. The present results show that nose-to-brain delivery by trigeminal axons, which is assumed to be a transcellular pathway, may be possible. As the drug can be delivered into the nerve, it is expected to be applied not only as a central delivery route but also for the treatment of neurological diseases.

Intracerebroventricular administration of oxytocin and intranasal administration of the oxytocin derivative improve β-amyloid peptide (25-35)-induced memory impairment in mice

AIM

We previously reported that oxytocin, a peptide hormone, can reverse the β-amyloid peptide (25-35) (Aβ_25-35 )-induced impairments of the murine hippocampal synaptic plasticity. In this study, we examined the effects of oxytocin on the Aβ_25-35 -induced impairment of cognitive behavior in murine in order to investigate the potential of oxytocin as a clinical treatment tool for Alzheimer's disease (AD).

METHODS

The Y-maze and Morris water maze (MWM) tests were performed. Since the intracerebroventricular (ICV) administration is both invasive and impractical, we further utilized intranasal (IN) delivery to the brain. For this purpose, we prepared an oxytocin derivative containing cell-penetrating peptides and a penetration accelerating sequence, which was subsequently used in our IN administration experiments.

RESULTS

We herein showed that the ICV administration of oxytocin in mice exerted memory-improving effects on the Aβ_25-35 -induced amnesia in both the Y-maze and MWM tests. The IN administration of the oxytocin derivative exhibited memory-improving effects in the Y-maze test. Moreover, we acquired evidence that the fluorescein isothiocyanate-labeled oxytocin derivative was distributed throughout the mouse brain following its IN administration.

CONCLUSION

Our results suggest that the oxytocin derivative is effective for its IN delivery to the brain and may be particularly useful in the clinical treatment of cognitive impairment, such as that characterizing AD.

Mechanistic Insights into the Link between Gut Dysbiosis and Major Depression: An Extensive Review

Depression is a highly common mental disorder, which is often multifactorial with sex, genetic, environmental, and/or psychological causes. Recent advancements in biomedical research have demonstrated a clear correlation between gut dysbiosis (GD) or gut microbial dysbiosis and the development of anxiety or depressive behaviors. The gut microbiome communicates with the brain through the neural, immune, and metabolic pathways, either directly (via vagal nerves) or indirectly (via gut- and microbial-derived metabolites as well as gut hormones and endocrine peptides, including peptide YY, pancreatic polypeptide, neuropeptide Y, cholecystokinin, corticotropin-releasing factor, glucagon-like peptide, oxytocin, and ghrelin). Maintaining healthy gut microbiota (GM) is now being recognized as important for brain health through the use of probiotics, prebiotics, synbiotics, fecal microbial transplantation (FMT), etc. A few approaches exert antidepressant effects via restoring GM and hypothalamus–pituitary–adrenal (HPA) axis functions. In this review, we have summarized the etiopathogenic link between gut dysbiosis and depression with preclinical and clinical evidence. In addition, we have collated information on the recent therapies and supplements, such as probiotics, prebiotics, short-chain fatty acids, and vitamin B12, omega-3 fatty acids, etc., which target the gut–brain axis (GBA) for the effective management of depressive behavior and anxiety.

Bio-Membrane Internalization Mechanisms of Arginine-Rich Cell-Penetrating Peptides in Various Species

Recently, membrane-active peptides or proteins that include antimicrobial peptides (AMPs), cytolytic proteins, and cell-penetrating peptides (CPPs) have attracted attention due to their potential applications in the biomedical field. Among them, CPPs have been regarded as a potent drug/molecules delivery system. Various cargoes, such as DNAs, RNAs, bioactive proteins/peptides, nanoparticles and drugs, can be carried by CPPs and delivered into cells in either covalent or noncovalent manners. Here, we focused on four arginine-rich CPPs and reviewed the mechanisms that these CPPs used for intracellular uptake across cellular plasma membranes. The varying transduction efficiencies of them alone or with cargoes were discussed, and the membrane permeability was also expounded for CPP/cargoes delivery in various species. Direct membrane translocation (penetration) and endocytosis are two principal mechanisms for arginine-rich CPPs mediated cargo delivery. Furthermore, the amino acid sequence is the primary key factor that determines the cellular internalization mechanism. Importantly, the non-cytotoxic nature and the wide applicability make CPPs a trending tool for cellular delivery.

Brain Pathogenesis and Potential Therapeutic Strategies in Myotonic Dystrophy Type 1

Myotonic dystrophy type 1 (DM1) is the most common muscular dystrophy that affects multiple systems including the muscle and heart. The mutant CTG expansion at the 3'-UTR of the DMPK gene causes the expression of toxic RNA that aggregate as nuclear foci. The foci then interfere with RNA-binding proteins, affecting hundreds of mis-spliced effector genes, leading to aberrant alternative splicing and loss of effector gene product functions, ultimately resulting in systemic disorders. In recent years, increasing clinical, imaging, and pathological evidence have indicated that DM1, though to a lesser extent, could also be recognized as true brain diseases, with more and more researchers dedicating to develop novel therapeutic tools dealing with it. In this review, we summarize the current advances in the pathogenesis and pathology of central nervous system (CNS) deficits in DM1, intervention measures currently being investigated are also highlighted, aiming to promote novel and cutting-edge therapeutic investigations.