Distinction between enzymic and nonenzymic lipid peroxidation

Linoleic, linolenic and arachidonic acid were subjected to nonenzymic lipid peroxidation. After hydrogenation and derivatisation, the mixture of saturated monohydroxy acids was analyzed by gas chromatography-mass spectrometry. Typical alpha-cleavage fragments enabled quantification of single hydroxy compounds. This investigation revealed that not only oxidation products are found by removal of hydrogen from double allylically activated CH2 groups, but also that products are generated by removal of hydrogen from monoallylically activated CH2 groups. This reaction was previously unknown to occur with linolenic and arachidonic acid. The typical patterns of the monohydroxy acids derived after oxidation of polyunsaturated fatty acids allows distinction between an enzymic and a nonenzymic, induced lipid peroxidation process. In the first case usually only one hydroxy acid is produced preferentially while in nonenzymic processes two hydroperoxy acids (those with the hydroxy groups at ''outer position'') are generated in about equal yield.