Inhibition of Amyloid β-Induced Lipid Membrane Permeation and Amyloid β Aggregation by K162

Design of an electrochemical aptasensor in the presence of an array of gold nanostructure and a GO-MWCNTs nanocomposite: application in diagnosis of Alzheimer's disease

Alzheimer's disease (AD) is considered one of the main progressive chronic diseases in elderly individuals. Early diagnosis using related biomarkers, specifically beta-amyloid peptide (Aβ), allows finding expected treatment routes. Here, we developed an electrochemical aptasensing platform for AD by employing a glassy carbon electrode (GCE) modified with a layer of jagged gold (JG) nanostructure (diameter: 60-185 nm) and graphene oxide-carboxylic acid functionalized multiwalled carbon nanotubes (GO-c-MWCNTs) nanocomposite. These surface modifications acted as the signal amplifier and provided an optimum nano-interface substrate for immobilizing aptamer strands. The measurements of Aβ were performed via differential pulse voltammetry (DPV), and the aptasensor detected the analyte in a linear range from 0.1 pg mL-1 to 1 ng mL-1, with an estimated limit of detection (LOD) of about 0.088 pg mL-1 (S/N = 3). The aptasensor showed sufficient stability (11 days), reversibility (three times), and reproducibility (five times re-fabrication with relative standard deviation (RSD): 1.27). The potential interfering agents showed negligible impact on the sensing performance. Finally, the application of the aptasensor was evaluated in the presence of 10 serum samples, and the recovery values were from 93 to 110.1%.

Regioselective Tip-Enhanced Raman Spectroscopy of Lipid Membranes with Sub-Nanometer Axial Resolution

Noninvasive and label-free analysis of cell membranes at the nanoscale is essential to comprehend vital cellular processes. However, conventional analytical tools generally fail to meet this challenge due to the lack of required sensitivity and/or spatial resolution. Herein, we demonstrate that tip-enhanced Raman spectroscopy (TERS) is a powerful nanoanalytical tool to analyze dipalmitoylphosphatidylcholine (DPPC) bilayers and human cell membranes with submolecular resolution in the vertical direction. Unlike the far-field Raman measurements, TERS spectra of the DPPC bilayers reproducibly exhibited a uniquely shaped C-H band. These unique spectral features were also reproducibly observed in the TERS spectrum of human pancreatic cancer cells. Spectral deconvolution and DFT simulations confirmed that the TERS signal primarily originated from vibrations of the CH₃ groups in the choline headgroup of the lipids. The reproducible TERS results obtained in this study unequivocally demonstrate the ultrahigh sensitivity of TERS for nanoanalysis of lipid membranes under ambient conditions.

Role of phosphatidylserine in amyloid-beta oligomerization at asymmetric phospholipid bilayers

Amyloid-beta (Aβ_1-42) aggregation triggers neurotoxicity and is linked to Alzheimer's disease. Aβ_1-42 oligomers, rather than extended fibrils, adhere to the cell membrane, causing cell death. Phosphatidylserine (PS), an anionic phospholipid, is prevalent in neuronal membranes (< 20 molar percentage) and, while isolated to the cytoplasmic leaflet of the membrane in healthy cells, its exposure in apoptotic cells and migration to exoplasmic leaflet is triggered by oxidative damage to the membrane. It is widely believed that PS plays a crucial role in the Aβ peptide interaction in the membranes of neuronal cells. However, due to the complexity of the cell membrane, it can be challenging to address molecular level understanding of the PS-Aβ binding and oligomerization processes. Herein, we use microcavity supported lipid bilayers (MSLBs) to analyse PS and Aβ_1-42 binding, oligomer formation, and membrane damage. MSLBs are a useful model to evaluate protein-membrane interactions because of their cell-like dual aspect fluidity, their addressability and compositional versatility. We used electrochemical impedance spectroscopy (EIS) and confocal fluorescence microscopy to compare the impact of Aβ_1-42 on simple zwitterioinic membrane, dioleoylphosphatidylcholine (DOPC), with MSLBs comprised of transversally asymmetric binary DOPC and dioleoylphosphatidylserine (DOPS). Monomeric Aβ_1-42 adsorbs weakly to the pristine zwitterionic DOPC membrane without aggregation. Using a membrane integrity test, with pyranine trapped within the cavities beneath the membrane, Aβ_1-42 exposure did not result in pyranine leakage, indicating that DOPC membranes were intact. When 10 mol% DOPS was doped asymmetrically into the membrane's outer leaflet, oligomerization of Aβ_1-42 monomer was evident in EIS and atomic force microscopy (AFM), and confocal imaging revealed that membrane damage, resulted in extensive pyranine leakage from the pores. The effects were time, and DOPS and Aβ_1-42 concentration-dependent. Membrane pore formation was visible within 30 minutes, and oligomerization, membrane-oligomer multilayer, and Aβ_1-42 fibril formation evident over 3 to 18 hours. In asymmetric membranes with DOPS localized to the lower leaflet, optothermally (laser induced) damage increased local DOPS concentrations at the distal leaflet, promoting Aβ_1-42 aggregation.

Synthesis of Fluorenes and Dibenzo[g,p]chrysenes through an Oxidative Cascade

We have developed robust, operationally simple syntheses of fluorenes and of dibenzo[g,p]chrysenes through oxidative cascade processes. These structures that are commonly encountered in optoelectronic materials, dyes, and pharmaceutical products are accessible from 1,4-dioxaspiro[4.5]decan-8-one. The reactions are conducted open to air with inexpensive, safe CuBr₂ or CuCl₂.

A Ratiometric Fluorescent Conjugated Oligomer for Amyloid β Recognition, Aggregation Inhibition, and Detoxification

The sensitive recognition and effective inhibition of toxic amyloid β protein (Aβ) aggregates play a critical role in early diagnosis and treatment of neurodegenerative diseases. In this work, a new conjugated oligo(fluorene-co-phenylene) (OFP) modified with 1,8-naphthalimide (NA) derivative OFP-NA-NO₂ is designed and synthesized as a ratiometric fluorescence probe for sensing Aβ, inhibiting the assembly of Aβ, and detoxicating the cytotoxicity of Aβ aggregates. In the presence of Aβ, the active ester group on the side chain of OFP-NA-NO₂ can covalently react with the amino group on Aβ, effectively inhibiting the formation of Aβ aggregates and degrading the preformed fibrils. In this case, the fluorescence intensity ratio of NA to OFP (I_NA /I_OFP ) increases greatly. The detection limit is calculated to be 89.9 nM, presenting the most sensitive ratiometric recognition of Aβ. Interestingly, OFP-NA-NO₂ can dramatically recover the cell viability of PC-12 and restore the Aβ-clearing ability of microglia. Therefore, this ratiometric probe exhibits the targeted recognition of Aβ, effective inhibition of Aβ aggregates, and detox effect, which is potential for early diagnosis and treatment of neurodegenerative diseases.

Mechanistic Understanding from Molecular Dynamics in Pharmaceutical Research 2: Lipid Membrane in Drug Design

We review the use of molecular dynamics (MD) simulation as a drug design tool in the context of the role that the lipid membrane can play in drug action, i.e., the interaction between candidate drug molecules and lipid membranes. In the standard "lock and key" paradigm, only the interaction between the drug and a specific active site of a specific protein is considered; the environment in which the drug acts is, from a biophysical perspective, far more complex than this. The possible mechanisms though which a drug can be designed to tinker with physiological processes are significantly broader than merely fitting to a single active site of a single protein. In this paper, we focus on the role of the lipid membrane, arguably the most important element outside the proteins themselves, as a case study. We discuss work that has been carried out, using MD simulation, concerning the transfection of drugs through membranes that act as biological barriers in the path of the drugs, the behavior of drug molecules within membranes, how their collective behavior can affect the structure and properties of the membrane and, finally, the role lipid membranes, to which the vast majority of drug target proteins are associated, can play in mediating the interaction between drug and target protein. This review paper is the second in a two-part series covering MD simulation as a tool in pharmaceutical research; both are designed as pedagogical review papers aimed at both pharmaceutical scientists interested in exploring how the tool of MD simulation can be applied to their research and computational scientists interested in exploring the possibility of a pharmaceutical context for their research.

Potential Anti-Alzheimer Agents from Guanidinyl Tryptophan Derivatives with Activities of Membrane Adhesion and Conformational Transition Inhibitions

Guanidinyl tryptophan derivatives TGN1, TGN2, TGN3, and TGN4 were synthesized, and these compounds were shown to possess in vitro inhibitory activity for amyloid aggregation in a previous study. Nevertheless, the influence of the TGN series of compounds on the binding and permeation behaviors of an Aβ monomer to the cell membranes was not elucidated. In this study, we investigated the effect of compounds in the TGN series on the behavior of an Aβ monomer regarding its toxicity toward the bilayer lipid membrane using molecular dynamics (MD) simulation. MD simulations suggest that TGN4 is a potential agent that can interfere with the movement of the Aβ monomer into the membrane. The MM-GBSA result demonstrated that TGN4 exhibits the highest affinity to the Aβ_1–42 monomer but has the lowest affinity to the bilayer. Moreover, TGN4 also contributes to a decrease in the binding affinity between the Aβ_1–42 monomer and the POPC membrane. Regarding the results of the binding mode and conformational analyses, a high number of amino-acid residues were shown to provide the binding interactions between TGN4 and the Aβ_1–42 monomer. TGN4 also reduces the conformational transition of the Aβ_1–42 monomer by means of interacting with the monomer. The present study presents molecular-level insights into how the TGN series of compounds affect the membrane adsorption and the conformational transition of the Aβ_1–42 monomer, which could be valuable for the further development of new anti-Alzheimer agents.