Molecular dynamic simulations of oxidized skin lipid bilayer and permeability of reactive oxygen species.

Lipid peroxidation by reactive oxygen species (ROS) during oxidative stress is non-enzymatic damage that affects the integrity of biological membrane, and alters the fluidity and permeability. We conducted molecular dynamic simulation studies to evaluate the structural properties of the bilayer after lipid peroxidation and to measure the permeability of distinct ROS. The oxidized membrane contains free fatty acid, ceramide, cholesterol, and 5α-hydroperoxycholesterol (5α-CH). The result of unconstrained molecular dynamic simulations revealed that lipid peroxidation causes area-per-lipid of the bilayer to increase and bilayer thickness to decrease. The simulations also revealed that the oxidized group of 5α-CH (-OOH) moves towards the aqueous layer and its backbone tilts causing lateral expansion of the bilayer membrane. These changes are detrimental to structural and functional properties of the membrane. The measured free energy profile for different ROS (H2 O2 , HO2 , HO, and O2 ) across the peroxidized lipid bilayer showed that the increase in lipid peroxidation resulted in breaching barrier decrease for all species, allowing easy traversal of the membrane. Thus, lipid peroxidation perturbs the membrane barrier and imposes oxidative stress resulting into apoptosis. The collective insights increase the understanding of oxidation stress at the atomic level.