Cell-Penetrating Peptides: Promising Therapeutics and Drug-Delivery Systems for Neurodegenerative Diseases

Currently, one of the most significant and rapidly growing unmet medical challenges is the treatment of neurodegenerative diseases such as Alzheimer's disease (AD) and Parkinson's disease (PD). This challenge encompasses the imperative development of efficacious therapeutic agents and overcoming the intricacies of the blood-brain barrier for successful drug delivery. Here we focus on the delivery aspect with particular emphasis on cell-penetrating peptides (CPPs), widely used in basic and translational research as they enhance drug delivery to challenging targets such as tissue and cellular compartments and thus increase therapeutic efficacy. The combination of CPPs with nanomaterials such as nanoparticles (NPs) improves the performance, accuracy, and stability of drug delivery and enables higher drug loads. Our review presents and discusses research that utilizes CPPs, either alone or in conjugation with NPs, to mitigate the pathogenic effects of neurodegenerative diseases with particular reference to AD and PD.

Exploring the significance of potassium homeostasis in copper ion binding to human αB-Crystallin

αB-Crystallin (αB-Cry) is a small heat shock protein known for its protective role, with an adaptable structure that responds to environmental changes through oligomeric dynamics. Cu(II) ions are crucial for cellular processes but excessive amounts are linked to diseases like cataracts and neurodegeneration. This study investigated how optimal and detrimental Cu(II) concentrations affect αB-Cry oligomers and their chaperone activity, within the potassium-regulated ionic-strength environment. Techniques including isothermal titration calorimetry, differential scanning calorimetry, fluorescence spectroscopy, inductively coupled plasma atomic emission spectroscopy, cyclic voltammetry, dynamic light scattering, circular dichroism, and MTT assay were employed and complemented by computational methods. Results showed that potassium ions affected αB-Cry's structure, promoting Cu(II) binding at multiple sites and scavenging ability, and inhibiting ion redox reactions. Low concentrations of Cu(II), through modifications of oligomeric interfaces, induce regulation of surface charge and hydrophobicity, resulting in an increase in chaperone activity. Subunit dynamics were regulated, maintaining stable interfaces, thereby inhibiting further aggregation and allowing the functional reversion to oligomers after stress. High Cu(II) disrupted charge/hydrophobicity balance, sewing sizable oligomers together through subunit-subunit interactions, suppressing oligomer dissociation, and reducing chaperone efficiency. This study offers insights into how Cu(II) and potassium ions influence αB-Cry, advancing our understanding of Cu(II)-related diseases.

Design, optimization and characterization of a novel antibacterial chitosan-based hydrogel dressing for promoting blood coagulation and full-thickness wound healing: A biochemical and biophysical study

The use of hydrogel dressings has become increasingly popular as a scaffold for skin tissue engineering. Herein, we have developed an innovative wound dressing using chitosan, fibrinogen, nisin, and EDTA as an effective antibacterial scaffold for wound treatment. The structural and functional characteristics of the hydrogel, including morphology, mechanical strength, drug encapsulation and release, swelling behaviors, blood coagulation, cytotoxicity, and antibacterial activity, were studied. Spectroscopic studies indicated that the attachment of chitosan to fibrinogen is associated with minimal change in its secondary structure; subsequently, at higher temperatures, it is expected to preserve fibrinogen's conformational stability. Mechanical and blood coagulation analyses indicated that the incorporation of fibrinogen into the hydrogel resulted in accelerated clotting and enhanced mechanical properties. Our cell studies showed biocompatibility and non-toxicity of the hydrogel along with the promotion of cell migration. In addition, the prepared hydrogel indicated an antibacterial behavior against both Gram-positive and Gram-negative bacteria. Interestingly, the in vivo data revealed enhanced tissue regeneration and recovery within 17 days in the studied animals. Taken together, the results obtained from in vitro and histological assessments indicate that this innovatively designed hydrogel shows good potential as a candidate for wound healing.

Neuroprotective Effect of Propolis Polyphenol-Based Nanosheets in Cellular and Animal Models of Rotenone-Induced Parkinson's Disease

Considering the central role of oxidative stress in the onset and progress of Parkinson's diseases (PD), search for compounds with antioxidant properties has attracted a growing body of attention. Here, we compare the neuroprotective effect of bulk and nano forms of the polyphenolic fraction of propolis (PFP) against rotenone-induced cellular and animal models of PD. Mass spectrometric analysis of PFP confirmed the presence of multiple polyphenols including kaempferol, naringenin, coumaric acid, vanillic acid, and ferulic acid. In vitro cellular experiments indicate the improved efficiency of the nano form, compared to the bulk form, of PFP in attenuating rotenone-induced cytotoxicity characterized by a decrease in cell viability, release of lactate dehydrogenase, increased ROS generation, depolarization of the mitochondrial membrane, decreased antioxidant enzyme activity, and apoptosis induction. In vivo experiments revealed that while no significant neuroprotection was observed relating to the bulk form, PFP nanosheets were very effective in protecting animals, as evidenced by the improved behavioral and neurochemical parameters, including decreased lipid peroxidation, increased GSH content, and antioxidant enzyme activity enhancement. We suggest that improved neuroprotective effects of PFP nanosheets may be attributed to their increased water solubility and enrichment with oxygen-containing functional groups (such as OH and COOH), leading to increased antioxidant activity of these compounds.

Common Mechanisms Underlying α-Synuclein-Induced Mitochondrial Dysfunction in Parkinson's Disease

Parkinson's disease (PD) is the most common neurological movement disorder characterized by the selective and irreversible loss of dopaminergic neurons in substantia nigra pars compacta resulting in dopamine deficiency in the striatum. While most cases are sporadic or environmental, about 10% of patients have a positive family history with a genetic cause. The misfolding and aggregation of α-synuclein (α-syn) as a casual factor in the pathogenesis of PD has been supported by a great deal of literature. Extensive studies of mechanisms underpinning degeneration of the dopaminergic neurons induced by α-syn dysfunction suggest a complex process that involves multiple pathways, including mitochondrial dysfunction and increased oxidative stress, impaired calcium homeostasis through membrane permeabilization, synaptic dysfunction, impairment of quality control systems, disruption of microtubule dynamics and axonal transport, endoplasmic reticulum/Golgi dysfunction, nucleus malfunction, and microglia activation leading to neuroinflammation. Among them mitochondrial dysfunction has been considered as the most primary target of α-syn-induced toxicity, leading to neuronal cell death in both sporadic and familial forms of PD. Despite reviewing many aspects of PD pathogenesis related to mitochondrial dysfunction, a systemic study on how α-syn malfunction/aggregation damages mitochondrial functionality and leads to neurodegeneration is missing in the literature. In this review, we give a detailed molecular overview of the proposed mechanisms by which α-syn, directly or indirectly, contributes to mitochondrial dysfunction. This may provide valuable insights for development of new therapeutic approaches in relation to PD. Antioxidant-based therapy as a potential strategy to protect mitochondria against oxidative damage, its challenges, and recent developments in the field are discussed.

The anti-platelet drug ticlopidine inhibits FapC fibrillation and biofilm production: Highlighting its antibiotic activity

Multidrug resistance of bacteria and persistent infections related to biofilms, as well as the low availability of new antibacterial drugs, make it urgent to develop new antibiotics. Here, we evaluate the antibacterial and anti-biofilm properties of ticlopidine (TP), an anti-platelet aggregation drug, TP showed antibacterial activity against both gram-positive (MRSA) and gram-negative (E. coli, and P. aeruginosa) bacteria over a long treatment period. TP significantly reduced the survival of gram-negative bacteria in human blood though impact on gram-positives was more limited. TP may cause death in MRSA by inhibiting staphyloxanthin pigment synthesis, leading to oxidative stress, while scanning electron microscopy imaging indicate a loss of membrane integrity, damage, and consequent death due to lysis in gram-negative bacteria. TP showed good anti-biofilm activity against P. aeruginosa and MRSA, and a stronger biofilm degradation activity on P. aeruginosa compared to MRSA. Measuring fluorescence of the amyloid-reporter Thioflavin T (ThT) in biofilm implicated inhibition of amyloid formation as part of TP activity. This was confirmed by assays on the purified protein in P. aeruginosa, FapC, whose fibrillation kinetics was inhibited by TP. TP prolonged the lag phase of aggregation and reduced the subsequent growth rate and prolonging the lag phase to very long times provides ample opportunity to exert TP's antibacterial effect. We conclude that TP shows activity as an antibiotic against both gram-positive and gram-negative bacteria thanks to a broad range of activities, targeting bacterial metabolic processes, cellular structures and the biofilm matrix.

A dual responsive robust human serum albumin-based nanocarrier for doxorubicin

Targeted drug therapy against cancer has been introduced as a smart strategy to combat the unwanted side effects due to systemic administration of chemotherapeutics. A human serum albumin (HSA)-based nanocarrier was fabricated with the aim to target reductive media and acidic pH of the tumor tissues. α-Lipoic acid (LA) was applied to increase the number of disulfide bonds in the nanocarrier to target higher glutathione concentrations present in tumor tissues and polyethylene glycol was used to target the acidic pH of tumors. UV illumination, ethanol desolvation, oxygen bubbling, and a mixture of redox buffers were employed to prepare doxorubicin-loaded HSA-LA nanoparticles. The nanocarrier was supposed to release the loaded doxorubicin in reductive and acidic pH media. Fourier-transform infrared spectroscopy and energy dispersive X-ray analysis indicated successful attachment of LA to HSA. The prepared nanoplatform presented improved doxorubicin loading efficiency and content and successfully released the loaded doxorubicin in the expected conditions. Protein corona study indicated that positively charged plasma proteins with molecular weights of nearly 80 kDa are absorbed to the surface of the nanoparticles. Furthermore, it showed desirable UV and storage stability, which implied its robustness and improved shelf life if applied in nanomedicine.

A penetratin-derived peptide reduces the membrane permeabilization and cell toxicity of α-synuclein oligomers

Parkinson's disease is a neurodegenerative movement disorder associated with the intracellular aggregation of α-synuclein (α-syn). Cytotoxicity is mainly associated with the oligomeric species (αSOs) formed at early stages in α-syn aggregation. Consequently, there is an intense focus on the discovery of novel inhibitors such as peptides to inhibit oligomer formation and toxicity. Here, using peptide arrays, we identified nine peptides with high specificity and affinity for αSOs. Of these, peptides p194, p235, and p249 diverted α-syn aggregation from fibrils to amorphous aggregates with reduced β-structures and increased random coil content. However, they did not reduce αSO cytotoxicity and permeabilization of large anionic unilamellar vesicles. In parallel, we identified a non-self-aggregating peptide (p216), derived from the cell-penetrating peptide penetratin, which showed 12-fold higher binding affinity to αSOs than to α-syn monomers (K_d^app 2.7 and 31.2 μM, respectively). p216 reduced αSOs-induced large anionic unilamellar vesicle membrane permeability at 10^-1 to 10^-3 mg/ml by almost 100%, was not toxic to SH-SY5Y cells, and reduced αSOs cytotoxicity by about 20%. We conclude that p216 is a promising starting point from which to develop peptides targeting toxic αSOs in Parkinson's disease.

Bivalent metal ions induce formation of α-synuclein fibril polymorphs with different cytotoxicities

α-Synuclein (α-Syn) aggregates are key components of intracellular inclusion bodies characteristic of Parkinson’s disease (PD) and other synucleinopathies. Metal ions have been considered as the important etiological factors in PD since their interactions with α-Syn alter the kinetics of fibrillation. In the present study, we have systematically explored the effects of Zn²⁺, Cu²⁺, Ca²⁺, and Mg²⁺ cations on α-Syn fibril formation. Specifically, we determined fibrillation kinetics, size, morphology, and secondary structure of the fibrils and their cytotoxic activity. While all cations accelerate fibrillation, we observed distinct effects of the different ions. For example, Zn²⁺ induced fibrillation by lower t_lag and higher k_app and formation of shorter fibrils, while Ca²⁺ ions lead to formation of longer fibrils, as evidenced by dynamic light scattering and atomic force microscopy studies. Additionally, the morphology of formed fibrils was different. Circular dichroism and attenuated total reflection-Fourier transform infrared spectroscopies revealed higher contents of β-sheets in fibrils. Interestingly, cell viability studies indicated nontoxicity of α-Syn fibrils formed in the presence of Zn²⁺ ions, while the fibrils formed in the presence of Cu²⁺, Ca²⁺, and Mg²⁺ were cytotoxic. Our results revealed that α-Syn fibrils formed in the presence of different divalent cations have distinct structural and cytotoxic features.