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Stability and modification of liposomal lipidic systems containing oxidized lipids upon binding and activity of the pore-forming protein sticholysin I

Grant number: 17/08460-1
Support type:Research Grants - Visiting Researcher Grant - International
Duration: October 16, 2017 - December 15, 2017
Field of knowledge:Biological Sciences - Biophysics
Principal Investigator:Rosangela Itri
Grantee:Rosangela Itri
Visiting researcher: Carlos Manuel Alvarez Valcarcel
Visiting researcher institution: Universidad de La Habana (UH), Cuba
Home Institution: Instituto de Física (IF). Universidade de São Paulo (USP). São Paulo , SP, Brazil

Abstract

Lipids of biological membranes contain high amounts of unsaturated fatty acids. These structures are prone to chemical and photoinduced oxidation leading to the formation of non-common oxidized lipid products (OxL). A determined amount of OxL is required for numerous cell functions; however, their uncontrolled production can have a deleterious effect on the functioning of cell and is involved in a variety of diseases. In fact, a correlation between lipid peroxidation and degenerative neurological disorders such as Parkinson´s and Alzheimer´s diseases has been documented. Both light and chemically induced oxidation usually starts with the formation of a lipid hydroperoxide, which can be further oxidized. Lipid hydroperoxides and derived OxL alter the properties of membranes by changing fluidity, lipid packing, lipidlipid interaction and lipid rafts structure and organization. Moreover, OxL can also lead to pore-formation and membrane disruption. Understanding and measuring how oxidation of the lipid bilayer affects permeability is key to recognize how oxidation alters the barrier properties of the membrane, potentially leading to cell damage. One experimental approach to assess the impact of OxL on membrane properties is to incorporate oxidized phospholipid species containing a hydroxyl, hydroperoxide, aldehyde or carboxylic groups in defined positions of one fatty acid chain. By these means, the oxidation process can be mimicked, yielding vesicles of controlled OxL composition and concentration. Model oxidized systems can be prepared either by the introduction of such OxL in their composition or promoting photo-oxidatively induced domains as has been largely explored by Prof. Itri´s laboratory at IF-USP. The characterization of the resulting structures can be crucial to understand damages derived from oxidation in cells and would contribute to develop potential treatments for diverse diseases. The proposed visit aims studying these changes by means of optical microscopy of giant unilamellar vesicles (GUV), permeabilization studies on GUV and large unilamellar vesicles (LUV) and binding assays in small unilamellar vesicles (SUV) with the proper lipid composition and subject to the action of a membranotropic agent such as the pore-forming protein sticholysin I (StI). St I is a pore-forming toxin largely characterized by the group of Prof. Alvarez at the Laboratory of Toxins and Liposomes (TLL), Center for Protein Studies (CEP) University of Havana (UH), Cuba, which is currently investigated for its potential biomedical applications. From previous projects between Profs. Itri´s and Alvarez´s laboratories, it has been possible to define the importance of lateral phase coexistence for StI activity and its remodeling action on membranes. Hence, it will also be of interest to explore the action of StI on photo-induced lipidic domain dynamics and stability as part of this proposed visit. The analysis of the fragility or changes in biophysical properties of model membranes containing oxidized lipids can be useful to understand and treat disorders where lipid oxidation is involved, ideally with the participation of StI. (AU)