Free radicals from 1-palmitoyl-2-arachidonoylphosphatidylcholine liposomes in Fe2+/ascorbic acid solution.

The generation of free radicals during the lipid peroxidation of liposomes composed of 1-palmitoyl-2-arachidonoylphosphatidylcholine (PAPC-liposome) in Fe2+/ascorbic acid (AsA) solution was studied by the ESR spin trapping technique. A carbon-centered radical adduct was observed using alpha-(4-pyridyl-1-oxide)-N-tert-butyl-nitorone (4-POBN) and 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), but no oxygen-centered radicals such as .OH, LO., and LOO. were observed. The lipid peroxidation evaluated as 2-thiobarbituric acid reactive substances was inhibited by the addition of 4-POBN. The intensity of this inhibitory effect was dependent on the time when 4-POBN was added to the mixture of PAPC-liposomes and Fe2+/AsA solution, and no inhibitory effect could be observed after 4 min. The signal intensity of the carbon-centered radical adduct was dependent on the lipid concentration of PAPC-liposomes. These results suggest that the alkyl radicals generated from PAPC-liposome peroxidation induced by Fe2+/AsA were trapped by DMPO or 4-POBN at an earlier stage of lipid peroxidation.