  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.
