Impact of oxidized lipid in the structural parameters of biological model membranes as seen by Small Angle X-Ray Scattering (SAXS)

Full text: In this work, we investigated the alterations caused in membrane mimetic systems due to the presence of oxidized lipids in their composition. The study was performed using two different oxidized lipids: 1) hydroperoxide lipid of POPC (POPC-OOH) whose structure shows a hydroperoxide group in the 9-10 carbon region of one of the acyl chains, giving a more hydrophilic character in this region, 2) The lipid PAzPC (1-palmitoyl-2-azelaoylsn- glycero-3-phosphocholine) containing a carboxyl group at the end of one of the C9- truncated chains. Large unilamellar vesicles composed of POPC-OOH, POPC: PAzPC and POPC: POPC-OOH: PAzPC with different molar ratios were investigated by SAXS at the National Laboratory of Synchrotron Light (LNLS). The scattering curves for vesicles composed of oxidized lipids showed significant changes in the electron density profile. Vesicle analysis was performed via the 3-region model of different electron densities for the membrane (polar, CH2 and CH3 regions) relative to the density of the aqueous solvent using the GENFIT software. The results showed that there is a decrease in the thickness of the lipid bilayer as we increase the proportion of oxidized lipid in the membrane. For the POPC:POPC-OOH system, it was verified that the thickness of the lipid bilayer decreased from 46.8 Angs. For pure POPC membranes, to 42.4 Angs. When the membrane is composed of 33% POPC-OOH and 37.6 Angs. To 100% POPC-OOH. However, the systems composed of two oxidized lipids (POPC: POPC-OOH: PAzPC) showed a small displacement of the SAXS curve at higher scattering angles with the increase of the percentage of PAzPC in the membrane. The results indicate that the presence of POPC-OOH predominantly determines the observed changes. It is worth noting that the parameters obtained for the POPC / PAzPC membranes containing 25 mol% POPC-OOH are similar to those of POPC: POPC-OOH 67:33. Using a model considering the position of each chemical group in the membrane we could observe that both hydroperoxide and carboxyl groups are located at the interface hydrophob/hydrofilic region. (author)