Contribution à l'e′tude des proprie′te′s antioxydantes ou pro-oxydantes des phospholipides

Abstract

Oxidation properties of phospholipids: mechanistic studies. The antioxidant effects of phospholipids in the dark have been investigated by kinetic studies in a model system. The oxidation of methyl linoleate, thermally induced at 60°C by azobisisobutyronitrile (AIBN), was performed in heptanol or in ethyl heptanoate in the presence of phosphorylated diacylglycerols. The diphenyl ester of dipalmitoyl phosphatidic acid (DPPAPh₂) showed no significant activity, under all experimental conditions used. In heptanol, the dibutyryl phosphatidylcholine (DBPC) was slightly antioxidant , but all dipalmitoyl phospholipids (except DPPAPh₂) exhibited a pro-oxidant activity. However, such a negative effect did not occur in ethyl heptanoate.

The effects of phospholipids (5×10^-4 M) on the radical scavenging activity of vitamin E (4×10^-4 M) were investigated at 60°C by the same kinetic studies. In heptanol, the results were closely related to the chemical class of phospholipids: compounds that contained an amino group synergistically extended the induction period arising from vitamin E, whereas other compounds were pro-oxidant or ineffective. In ethyl heptanoate, all phospholipids, except DPPAPh₂ and DBPC, showed negative synergism when methyl linoleate and vitamin E were used simultaneously. Hence, the results were hardly affected by the fatty acid chain length within the phospholipids.

The effect of the addition of dipalmitoyl phosphatidylethanolamine (DPPE, 5×10^-4 M) together with vitamin E (4×10^-4 M) on the non-induced oxidation of methyl linoleate was investigated at 60°C in heptanol or in ethyl heptanoate. DPPE acted synergistically with vitamin E in both solvents.

It is suggested that the enhanced effect of aminophospholipids R′R″R‴N for vitamin E in heptanol results from the complexation of peroxyl free radicals ROO by the amino group: ROO+R′R″R‴NC yielding complexed radicals C, which are less reactive toward vitamin E than the uncomplexed ones. In ethyl heptanoate, it is suggested that the amphiphilic phospholipid molecules aggregate to form reverse micelles, thereby enhancing the accessibility of vitamin E to linoleylperoxyl radicals.