Cholesterol Inhibits Peroxidation of Egg Phosphatidylcholine in MultilamellarLiposomes

Overview

The effect of cholesterol (CHOL) on the rate of autoperoxidation of chromatographically purephosphatidylcholine from hen egg yolks (EYPC) in aerated multilamellar liposomes was examinedat eight CHOL:EYPC molar ratios from 0.1 up to 1.0 at 45 °C. Autoperoxidation was measured asconjugated diene (CD) formation by UV-VIS spectrophotometry. In the presence of cholesterol, theinitiation and propagation phases of autoperoxidation were prolonged, the autoperoxidation rate inthe propagation phase was decreased, and the CD concentration in the termination phase waslowered. The inhibition of EYPC autoperoxidation by cholesterol can originate a) from the increasedlateral separation of polyunsaturated EYPC acyl chains caused by intercalation of cholesterolbetween EYPC molecules, b) from the increased molecular packing of both the bilayer polar andhydrophobic regions due to the reduced bilayer hydration, c) from the decreased concentration ofthe molecular oxygen in the bilayer interior, and d) from the cholesterol epoxidation and hydroperoxidationinduced by the oxidation products of EYPC polyunsaturated acyl chains.

Key words:
peroxidation – liposome – phosphatidylcholine – cholesterol – conjugated dienes