Anti-Amyloidogenic and Fibril-Disaggregating Potency of the Levodopa-Functionalized Gold Nanoroses as Exemplified in a Diphenylalanine-Based Amyloid Model

Futuristic Alzheimer's therapy: acoustic-stimulated piezoelectric nanospheres for amyloid reduction

The degeneration of neurons due to the accumulation of misfolded amyloid aggregates in the central nervous system (CNS) is a fundamental neuropathology of Alzheimer's disease (AD). It is believed that dislodging/clearing these amyloid aggregates from the neuronal tissues could lead to a potential cure for AD. In the present work, we explored biocompatible polydopamine-coated piezoelectric polyvinylidene fluoride (DPVDF) nanospheres as acoustic stimulus-triggered anti-fibrillating and anti-amyloid agents. The nanospheres were tested against two model amyloidogenic peptides, including the reductionist model-based amyloidogenic dipeptide, diphenylalanine, and the amyloid polypeptide, amyloid beta (Aβ42). Our results revealed that DPVDF nanospheres could effectively disassemble the model peptide-derived amyloid fibrils under suitable acoustic stimulation. In vitro studies also showed that the stimulus activated DPVDF nanospheres could efficiently alleviate the neurotoxicity of FF fibrils as exemplified in neuroblastoma, SHSY5Y, cells. Studies carried out in animal models further validated that the nanospheres could dislodge amyloid aggregates in vivo and also help the animals regain their cognitive behavior. Thus, these acoustic stimuli-activated nanospheres could serve as a novel class of disease-modifying nanomaterials for non-invasive electro-chemotherapy of Alzheimer's disease.

Phenylalanine-based fibrillar systems

Phenylketonuria (PKU) is an inborn metabolic disorder characterized by excess accumulation of phenylalanine (Phe) and its fibril formation, resulting in progressive intellectual disability. Several research groups have approached from various directions to understand the formation of toxic amyloid fibrils from the essential amino acid Phe. Different parameters like the nature of the solvent, pH, Phe concentration, temperature, etc. influence the fibril formation kinetics. In this article, we have summarized all major findings regarding the formation of Phe-based fibrils in aqueous and organic media and discussed how non-covalent interactions are involved in the self-assembly process using spectroscopic and microscopic techniques. The toxicity of Phe-based fibrils is compared with other neurodegenerative peptides. It is noted that the Phe-based fibrils can also induce various globular proteins into toxic fibrils. Later, we discuss the different approaches to inhibit fibril formation and reduce its toxicity. The presence of polyphenolic compounds, drugs, amino acids, nanoparticles, metal ions, crown ethers, and others showed a remarkable inhibitory effect on fibril formation. To the best of our knowledge, this is the first-ever etymological analysis of the Phe-fibrillar system and its inhibition to create a strong database against PKU.

Design of Gallic Acid-Glutamine Conjugate and Chemical Implications for Its Potency Against Alzheimer's Amyloid-β Fibrillogenesis

Epigallocatechin-3-gallate (EGCG) has been widely recognized as a potent inhibitor of Alzheimer's amyloid-β (Aβ) fibrillogenesis. We found that gallic acid (GA) has superior inhibitory effects over EGCG at the same mass concentrations and assumed the pivotal role of the carboxyl group in GA. Therefore, we designed five GA-derivatives to investigate the significance of carboxyl groups in modulating Aβ fibrillogenesis, including carboxyl-amidated GA (GA-NH₂), GA-glutamic acid conjugate (GA-E), and GA-E derivatives with amidated either of the two carboxyl groups (GA-Q and GA-E-NH₂) or with two amidated-carboxyl groups (GA-Q-NH₂). Intriguingly, only GA-Q shows significantly stronger potency than GA and extends the life span of the AD transgenic nematode by over 30%. Thermodynamic studies reveal that GA-Q has a strong binding affinity for Aβ₄₂ with two binding sites, one stronger (site 1, K_a1 = 3.1 × 10⁶ M^-1) and the other weaker (site 2, K_a2 = 0.8 × 10⁶ M^-1). In site 1, hydrogen bonding, electrostatic interactions, and hydrophobic interactions all have contributions, while in site 2, only hydrogen bonding and electrostatic interactions work. The two sites are confirmed by molecular simulations, and the computations specified the key residues. GA-Q has strong binding to Asp23, Gly33, Gly38, Ala30, Ile31, and Leu34 via hydrogen bonding and electrostatic interactions, while it interacts with Phe19, Ala21 Gly25, and Asn27 via hydrophobic interactions. Consequently, GA-Q destroys Asp23-Lys28 salt bridges and restricts β-sheet/bridge structures. The thermodynamic and molecular insight into the GA-Q functions on inhibiting Aβ fibrillogenesis would pave a new way to the design of potent molecules against Alzheimer's amyloid.

Self-Fluorescent Lone Tryptophan Nanoparticles as Theranostic Agents Against Alzheimer's Disease

Aggregation of β-amyloid (Aβ42) peptide in the neural extracellular space leads to cellular dysfunction, resulting in Alzheimer's disease (AD). The hydrophobic core of the amyloidogenic Aβ42 peptide contains aromatic residues that play an important role in the self-assembly and subsequent aggregation of the peptide. Hence, targeting these hydrophobic core residues by potent low molecular agents can be a promising therapeutic approach toward AD. In the current work, we have developed self-fluorescent solo tryptophan nanoparticles (TNPs) as nanotheranostic systems against AD. We demonstrated that TNPs could significantly inhibit as well as disrupt the fibrils formed by both Aβ42 peptide and another reductionist approach-based amyloid model dipeptide, phenylalanine-phenylalanine (FF). More importantly, these nanostructures were nontoxic to neural cells and could protect the neurons from Aβ42 peptide and FF aggregate-induced cytotoxicity. In addition, efficacy studies performed in animal model further revealed that the TNPs could rescue spatial and learning memory in intracerebroventricular streptozotocin-administration-induced AD phenotype in rats. Moreover, our pharmacokinetics study further established the BBB permeability and brain delivery potency of TNPs. The inherent excellent fluorescent properties of these nanoparticles could be exploited further to use them as imaging modalities for tagging and detecting FF and Aβ42 peptide fibrils. Overall, our results clearly illustrated that the solo TNPs could serve as promising nanotheranostic agents for AD therapy.