Orélia carried out her research in the BIBAC and IDeAS teams at the Softmat laboratory.
On 16th of December, she defended her thesis entitled: “Oxidative interactions of peptides involved in Alzheimer’s disease with model membrane systems”
Alzheimer’s disease is a common neurodegenerative disorder in the elderly, characterised by senile plaques and neurofibrillary tangles. The plaques are composed of amyloid-β (Aβ) peptide interacting with metal ions, particularly copper. Its complexation with copper could play a central role in its toxicity by inducing the production of reactive oxygen species (ROS), such as the hydroxyl radical, which causes oxidative damage to both the peptide and plasma membranes.
This project aimed to study the interactions between Aβ peptide, Cu²⁺, and lipid vesicles (LUVs) — mimicking plasma membranes — under oxidative stress conditions, using ascorbate as a reducing agent. The study sought to determine the impact of these interactions on ROS production and the resulting oxidative damage.
In the first part, a model system was developed based on LUVs made of choline headgroup phospholipids (PLPC) or serine (PLPS), containing an unsaturated linoleic acid chain in an 80:20 molar ratio. In the presence of LUVs, the studied “Fenton-like” reaction involved ascorbate oxidation in the presence of Cu²⁺ ions and oxygen, which was monitored by UV-visible spectroscopy. A decrease in the initial rate of ascorbate consumption was observed when LUVs were present, and the kinetic system was modeled to extract the rate constants of each reaction. This study revealed potential interactions between PLPS and the metal ion.
In the second part, the model peptides Aβ1-28 or pre-oxidised Aβ1-28 were added to the reaction system. Two pathways of peptide addition were examined: pre-incubation of the peptide with LUVs or pre-incubation with copper. The results show that the complexation of copper with Aβ1-28 is a slow process, which is favored before ascorbate is introduced. Oxidative damage was examined at the molecular level using mass spectrometry. Oxidised forms of Aβ1-28 and PLPC were observed, suggesting potential competition between them for oxidation. Studies on pre-oxidised Aβ1-28 peptide are still under development.
In the final part, the toxicities of copper, Aβ1-28, and the complex were evaluated in SH-SY5Y cells. Cytotoxicity was observed for the peptide, Cu²⁺ ions, and the complex at concentrations above 60 µM for Aβ1-28 and 15 µM for Cu²⁺. Notably, the pre-oxidised form of the peptide proved to be toxic more quickly (from 1 µM).
Extruder for 100 nm diameter phospholipid vesicles
Finally, preliminary work was undertaken with the Aβ1-40 peptide, whose use is more complex due to its tendency to aggregate in solution. Two solubilisation methods were evaluated, and the peptide solutions were characterised by dynamic light scattering and field-flow fractionation.
In conclusion, this work highlights certain interactions between the Aβ peptide, copper, and LUVs, opening new perspectives for understanding the oxidative mechanisms related to Alzheimer’s disease.
Highlights of the thesis:
- Orélia presented her research work during the 33rd international symposium on Pharmaceutical and Biomedical Analysis, in Turkey in July 2023.
Congratulations to Orélia for the quality of her work!