Kinetic Analysis of Co-oxidation of Biomembrane Lipids Induced by Water-Soluble Radicals

Experiments on the oxidation of the biomembrane lipids, cholesterol (ChH) and phospholipids (LH), induced by water-soluble radicals were performed in three types of model liposome systems. To clarify mechanisms of sole LH and ChH oxidations and their co-oxidation, these systems were prepared using oxidizable LH and non-oxidizable ChH, non-oxidizable LH and oxidizable ChH, and oxidizable LH and ChH. Experimental results showed that sole oxidation of LH or ChH in the lipid phase was induced by water-soluble radicals and that ChH oxidation was strongly accelerated by LH oxidation. A kinetic model was constructed based on reaction mechanisms that considered mass transfer of water-soluble radicals from the water to lipid phases, a series of sole oxidations of LH and ChH initiated by transferred radicals in the lipid phase, and accelerated reactions between LH and ChH. The resulting model quantitatively described sole LH and ChH oxidations and their co-oxidation behaviors in liposome systems under various water-soluble radical concentrations.