CHOLESTEROL PROTECTS THE PHOSPHOLIPID-BILAYER FROM OXIDATIVE DAMAGE

The measurement of fluorescence lifetime distribution of 1,6-diphenyl- 1,3,5-hexatriene is used for the detection of oxidative damage produce d in phospholipid membranes by ionizing radiation. The recently develo ped method is based on the linear relationship between the width of th e probe lifetime distribution and the logarithm of the dose. The molec ular origin of the damage resides in the production of hydroperoxide r esidues at the level of acyl chains double bonds. A chemiluminescence assay was used to quantitate the amount of produced hydroperoxides. Co nsequences of the produced damages include an increased disorder in th e upper portion of the bilayer, accompanied by the penetration of wate r molecules. In the presence of the physiological concentration of cho lesterol in phospholipid bilayers, the amount of hydroperoxides produc ed by ionizing radiation is dramatically reduced. The packing effect o f cholesterol in phospholipid bilayers is well recognized, as well as its influence on the reduction of water concentration in the bilayer. The dramatic reduction of hydroperoxides concentration observed when i rradiation is performed in the presence of cholesterol probably origin ates from a steric hindrance to the radical chain reaction through the unsaturated lipids due to the presence of cholesterol.