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.