Alpha-tocopherol inhibits pore formation in the oxidized bilayers

Abstract

In biological membranes, alpha-tocopherols ({\alpha}-toc; vitamin E) protect polyunsaturated lipids from free radicals. Although the interactions of {\alpha}-toc with non-oxidized lipid bilayers have been studied, their on oxidized bilayers remain unknown. In this study, atomistic molecular dynamics (MD) simulations of oxidized lipid bilayers were performed with varying concentrations of {\alpha}-toc. Bilayers with 1-palmitoyl-2-lauroyl-sn-glycero-3-phosphocholine (PLPC) lipids and its aldehyde derivatives at 1:1 ratio were studied. Our simulations show that oxidized lipids self-assemble into aggregates with a water pore rapidly developing across the lipid bilayer. The free energy of transporting an {\alpha}-toc molecule in a lipid bilayer suggests that {\alpha}-tocs can passively adsorb into the bilayer. When {\alpha}-toc molecules were present at low concentrations in bilayers containing oxidized lipids, the formation of water pores was slowed down. At high {\alpha}-toc concentra-tions, no pores were observed. Based on the simulations, we propose that the mechanism of how {\alpha}-toc inhibits pore formation in bilayers with oxidized lipids is the follow-ing: {\alpha}-tocs trap the polar groups of the oxidized lipids at the membrane-water interface resulting in a decreased probability for the oxidized lipids to reach contact with the two leaflets and initiate pore formation. This demon-strates that {\alpha}-toc molecules not only protect the bilayer from oxidation but also help to stabilize the bilayer after lipid peroxidation occurs. These results will help in de-signing more efficient molecules to protect membranes from oxidative stress.