PRFF Peptide Mimic Interferes with Toxic Fibrin-Aβ42 Interaction by Emulating the Aβ Binding Interface on Fibrinogen

Delineating the tryptophan-galactosylamine conjugate mediated structural distortions in Aβ42 protofibrils

Amyloid-β (Aβ) fibrillation into neurotoxic soluble oligomers and mature fibrils is mainly responsible for the etiology of Alzheimer's disease (AD). A recent study revealed 61% disaggregation of the pre-formed Aβ42 fibrils upon incubating with a highly soluble tryptophan-galactosylamine conjugate, WGalNAc. WGalNAc displayed no toxicity and increased the viability of SH-SY5Y cells up to 62.9 ± 2% with an EC50 value of 2.3 μM against Aβ42 pre-formed fibrils. However, the key interactions and disruptive mechanism of WGalNAc against Aβ fibrils remain elusive. Thus, mechanistic insights into the disruptive potential of WGalNAc against Aβ42 protofibrils (PDB: 5OQV) were examined using molecular dynamics (MD) simulations. The molecular docking depicted a favourable binding energy (-6.60 kcal mol-1) and interaction of WGalNAc with the central hydrophobic core (CHC) region of chain A of the 5OQV protofibril. The MD simulations depicted that WGalNAc disrupted the contacts among Ala2, Phe4, Leu34, and Val36 in the hydrophobic core 1 of the 5OQV protofibril responsible for maintaining the stability of the LS-shaped 5OQV protofibril. WGalNAc binds favourably to the 5OQV protofibril (ΔGbinding = -21.76 ± 2.40 kcal mol-1) with a significant contribution from the van der Waals interaction term. Notably, the binding affinity between the neighbouring chains of the 5OQV protofibril was significantly reduced from -134.31 ± 11.12 to -121.88 ± 1.95 kcal mol-1 upon the incorporation of WGalNAc, which is consistent with the ThT kinetic results that revealed disaggregation of the pre-formed Aβ42 fibrils upon incubating with WGalNAc. The in silico ADMET properties of WGalNAc showed its ability as a promising therapeutic candidate due to its blood-brain barrier (BBB) permeability, extended half-life, and non-toxic profile. The MD simulations illuminated the binding interactions of WGalNAc with the 5OQV protofibril and provided mechanistic insights into the WGalNAc-mediated structural distortions in the 5OQV protofibril.

Modulating Amyloid-β Toxicity: In Vitro Analysis of Aβ42(G37V) Variant Impact on Aβ42 Aggregation and Cytotoxicity

Alzheimer's disease (AD) is primarily driven by the formation of toxic amyloid-β (Aβ) aggregates, with Aβ42 being a pivotal contributor to disease pathology. This study investigates a novel agent to mitigate Aβ42-induced toxicity by co-assembling Aβ42 with its G37V variant (Aβ42(G37V)), where Gly at position 37 is substituted with valine. Using a combination of Thioflavin-T (Th-T) fluorescence assays, Western blot analysis, atomic force microscopy (AFM)/transmission electron microscopy (TEM), and biochemical assays, we demonstrated that adding Aβ42(G37V) significantly accelerates Aβ42 aggregation rate and mass while altering the morphology of the resulting aggregates. Consequently, adding Aβ42(G37V) reduces the Aβ42 aggregates-induced cytotoxicity, as evidenced by improved cell viability assays. The possible mechanism for this effect is that adding Aβ42(G37V) reduces the production of reactive oxygen species (ROS) and lipid peroxidation, typically elevated in response to Aβ42, indicating its protective effects against oxidative stress. These findings suggest that Aβ42(G37V) could be a promising candidate for modulating Aβ42 aggregation dynamics and reducing its neurotoxic effects, providing a new avenue for potential therapeutic interventions in AD.

Molecular Integrative Study on Inhibitory Effects of Pentapeptides on Polymerization and Cell Toxicity of Amyloid-β Peptide (1-42)

Alzheimer's Disease (AD) is a multifaceted neurodegenerative disease predominantly defined by the extracellular accumulation of amyloid-β (Aβ) peptide. In light of this, in the past decade, several clinical approaches have been used aiming at developing peptides for therapeutic use in AD. The use of cationic arginine-rich peptides (CARPs) in targeting protein aggregations has been on the rise. Also, the process of peptide development employing computational approaches has attracted a lot of attention recently. Using a structure database containing pentapeptides made from 20 L-α amino acids, we employed molecular docking to sort pentapeptides that can bind to Aβ42, then performed molecular dynamics (MD) analyses, including analysis of the binding stability, interaction energy, and binding free energy to screen ligands. Transmission electron microscopy (TEM), circular dichroism (CD), thioflavin T (ThT) fluorescence detection of Aβ42 polymerization, MTT (3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) assay, and the flow cytometry of reactive oxygen species (ROS) were carried out to evaluate the influence of pentapeptides on the aggregation and cell toxicity of Aβ42. Two pentapeptides (TRRRR and ARRGR) were found to have strong effects on inhibiting the aggregation of Aβ42 and reducing the toxicity of Aβ42 secreted by SH-SY5Y cells, including cell death, reactive oxygen species (ROS) production, and apoptosis.

Structural Reorganization Mechanism of the Aβ42 Fibril Mediated by N-Substituted Oligopyrrolamide ADH-353

The inhibition of amyloid-β (Aβ) fibrillation and clearance of Aβ aggregates have emerged as a potential pharmacological strategy to alleviate Aβ aggregate-induced neurotoxicity in Alzheimer's disease (AD). Maity et al. shortlisted ADH-353 from a small library of positively charged N-substituted oligopyrrolamides for its notable ability to inhibit Aβ fibrillation, disintegrate intracellular cytotoxic Aβ oligomers, and alleviate Aβ-induced cytotoxicity in the SH-SY5Y and N2a cells. However, the molecular mechanism through which ADH-353 interacts with the Aβ42 fibrils, leading to their disruption and subsequent clearance, remains unclear. Thus, a detailed molecular mechanism underlying the disruption of neurotoxic Aβ42 fibrils (PDB ID 2NAO) by ADH-353 has been illuminated in this work using molecular dynamics simulations. Interestingly, conformational snapshots during simulation depicted the shortening and disappearance of β-strands and the emergence of a helix conformation, indicating a loss of the well-organized β-sheet-rich structure of the disease-relevant Aβ42 fibril on the incorporation of ADH-353. ADH-353 binds strongly to the Aβ42 fibril (ΔGbinding= -142.91 ± 1.61 kcal/mol) with a notable contribution from the electrostatic interactions between positively charged N-propylamine side chains of ADH-353 with the glutamic (Glu3, Glu11, and Glu22) and aspartic (Asp7 and Asp23) acid residues of the Aβ42 fibril. This aligns well with heteronuclear single quantum coherence NMR studies, which depict that the binding of ADH-353 with the Aβ peptide is driven by electrostatic and hydrophobic contacts. Furthermore, a noteworthy decrease in the binding affinity of Aβ42 fibril chains on the incorporation of ADH-353 indicates the weakening of interchain interactions leading to the disruption of the double-horseshoe conformation of the Aβ42 fibril. The illumination of key interactions responsible for the destabilization of the Aβ42 fibril by ADH-353 in this work will greatly aid in designing new chemical scaffolds with enhanced efficacy for the clearance of Aβ aggregates in AD.

Identification of new pentapeptides as potential inhibitors of amyloid-β42 aggregation using virtual screening and molecular dynamics simulations

Alzheimer's disease (AD) is a multifactorial neurodegenerative disease mainly characterized by extracellular accumulation of amyloid-β (Aβ) peptide. Previous studies reported pentapeptide RIIGL as an effective inhibitor of Aβ aggregation and neurotoxicity induced by Aβ aggregates. In this work, a library of 912 pentapeptides based on RIIGL has been designed and assessed for their efficacy to inhibit Aβ42 aggregation using computational techniques. The top hit pentapeptides revealed by molecular docking were further assessed for their binding affinity with Aβ42 monomer using MM-PBSA (molecular mechanics Poisson-Boltzmann surface area) method. The MM-PBSA analysis identified RLAPV, RVVPI, and RIAPA, which bind to Aβ42 monomer with a higher binding affinity -55.80, -46.32, and -44.26 kcal/mol, respectively, as compared to RIIGL (ΔGbinding = -41.29 kcal/mol). The residue-wise binding free energy predicted hydrophobic contacts between Aβ42 monomer and pentapeptides. The secondary structure analysis of the conformational ensembles generated by molecular dynamics (MD) depicted remarkably enhanced sampling of helical and no β-sheet conformations in Aβ42 monomer on the incorporation of RVVPI and RIAPA. Notably, RVVPI and RIAPA destabilized the D23-K28 salt bridge in Aβ42 monomer, which plays a crucial role in Aβ42 oligomer stability and fibril formation. The MD simulations highlighted that the incorporation of proline and arginine in pentapeptides contributed to their strong binding with Aβ42 monomer. Furthermore, RVVPI and RIAPA prevented conformational conversion of Aβ42 monomer to aggregation-prone structures, which, in turn, resulted in a lower aggregation tendency of Aβ42 monomer.

Mechanistic insights into the mitigation of Aβ aggregation and protofibril destabilization by a D–enantiomeric decapeptide rk10

According to clinical studies, the development of Alzheimer’s disease (AD) is linked to the abnormal aggregation of amyloid-β (Aβ) peptides into toxic soluble oligomers, protofibrils as well as mature fibrils....