Membrane-Modulating Drugs can Affect the Size of Amyloid-β25–35 Aggregates in Anionic Membranes

Abstract

The formation of amyloid-β plaques is one of the hallmarks of Alzheimer’s disease. The presence of an amphiphatic cell membrane can accelerate the formation of amyloid-β aggregates, making it a potential druggable target to delay the progression of Alzheimer’s disease. We have prepared unsaturated anionic membranes made of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and 1,2-dimyristoyl-sn-glycero-3-phospho-L-serine (DMPS) and added the trans-membrane segment Aβ25–35. Peptide plaques spontaneously form in these membranes at high peptide concentrations of 20 mol%, which show the characteristic cross-β motif (concentrations are relative to the number of membrane lipids and indicate the peptide-to-lipid ratio). We used atomic force microscopy, fluorescence microscopy, x-ray microscopy, x-ray diffraction, UV-vis spectroscopy and Molecular Dynamics (MD) simulations to study three membrane-active molecules which have been speculated to have an effect in Alzheimer’s disease: melatonin, acetylsalicyclic acid (ASA) and curcumin at concentrations of 5 mol% (drug-to-peptide ratio). Melatonin did not change the structural parameters of the membranes and did not impact the size or extent of peptide clusters. While ASA led to a membrane thickening and stiffening, curcumin made membranes softer and thinner. As a result, ASA was found to lead to the formation of larger peptide aggregates, whereas curcumin reduced the volume fraction of cross-β sheets by ~70%. We speculate that the interface between membrane and peptide cluster becomes less favorable in thick and stiff membranes, which favors the formation of larger aggregates, while the corresponding energy mismatch is reduced in soft and thin membranes. Our results present evidence that cross-β sheets of Aβ25–35 in anionic unsaturated lipid membranes can be re-dissolved by changing membrane properties to reduce domain mismatch.

The Effects of Resveratrol, Caffeine, β‐Carotene, and Epigallocatechin Gallate (EGCG) on Amyloid‐β25--35 Aggregation in Synthetic Brain Membranes

“…The peptide segment A was added at a peptide concentration of 20 mol% (peptide‐to‐lipid ratio), which spontaneously lead to the formation of nano to micrometer‐sized cross‐β amyloid plaques. [ 53,54 ] Solid supported membranes were prepared for the microscopy and X‐ray experiments and liposomes were used in the UV–vis spectroscopy experiments.…”

“…The peptides were then re‐dissolved in ultrapure water at a concentration of 20 mg mL −1 . [ 53,54,56,57 ] Stock solutions of resveratrol, caffeine, β‐carotene, and EGCG were prepared at concentrations of 20 mg mL −1 and each solution was sonicated and vortexed until homogeneous. Liposomes of POPC and DMPS (97:3 mol per mol%) were prepared with 20 mol% of A and incubated for 2 h. After incubation, 5 mol% of resveratrol, caffeine, β‐carotene, or EGCG were added to each sample, vortexed until homogenous and incubated overnight.…”

“…BLADE used a 9 kW (45 kV, 200 mA) CuKα rotating anode at a wavelength of 1.5418 Å using a Rigaku HyPix‐3000 2D semiconductor detector with an area of 3000 mm 2 and 100 m pixel size. [ 54 ] Diffraction measurements were conducted under controlled temperature and humidity conditions (30 °C, 98% RH) in a custom‐built humidity chamber. The highly oriented membranes were aligned in the diffractometer such that the vertical axis () in the 2D scans was aligned perpendicular to the membranes and detected structure normal to the bilayers.…”

“…ThT was then added to the aliquot and a measurement was conducted. As ThT was found to induce aggregation, which plateaued out after 12 h, [ 54 ] all measurements were conducted 12 h after ThT deposition at 30 °C and all data were normalized to the ThT reference.…”

“…This procedure resulted in highly oriented membrane stacks that uniformly covered the silicon substrates. [53,54,56,57]…”