Paradox of omega-3 PUFA oxidation

The oxidative stability of polyunsaturated fatty acids (PUFAs) in micelles and in liposomes is dramatically different from that observed in the bulk phase and in organic solvents. In aqueous micelles, docosahexaenoic acid (DHA, 22:6n-3) is oxidatively most stable followed by EPA (20:5n-3), arachidonic acid (AA, 20:4n-6), alpha-linolenic acid (18:3n-3), gamma-linolenic acid (18:3n-6), and linoleic acid (LA, 18:2n-6), respectively. In phosphatidylcholine (PC) liposomes, DHA-PC showed the highest oxidative stability followed by AA-PC and LA-PC in that order. This order was completely opposite to that found in bulk and in organic solvent systems. NMR and GC-MS analysis and a computer modelling approach to hydroperoxide isomer composition suggest that the physical and stereochemical characteristics of DHA molecules in the aqueous phase are related to its unusually high oxidative stability. The possible mechanisms are a tight packing conformation ofDHAmolecules and the presence of water molecule near the double bonds of DHA, which may inhibit hydrogen abstraction from the bis-allylic positions of DHA.