A novel chiral stationary phase HPLC-MS/MS method to discriminate between enzymatic oxidation and auto-oxidation of phosphatidylcholine.

To elucidate the role of enzymatic lipid peroxidation in disease pathogenesis and in food deterioration, we recently achieved stereoselective analysis of phosphatidylcholine hydroperoxide (PCOOH) possessing 13S-hydroperoxy-9Z,11E-octadecadienoic acid (13(S)-9Z,11E-HPODE) using HPLC-MS/MS with a CHIRALPAK OP (+) column. Because enzymatic oxidation progresses concurrently with auto-oxidation, we need to distinguish them further. Here, we attempted such an analysis. First, we used lipoxygenase, linoleic acid, and lysophosphatidylcholine (LPC) to synthesize the enzymatic oxidation product 13(S)-9Z,11E-HPODE PC, and the auto-oxidation products 13(RS)-9Z,11E-HPODE PC and 13(RS)-9E,11E-HPODE PC, which were used as standards to test the ability of various columns to separate the enzymatic oxidation product from auto-oxidation products. Separation was achieved by connecting in series two columns with different properties: CHIRALPAK OP (+) and CHIRALPAK IB-3. The CHIRALPAK OP (+) column separated 13(R)-9Z,11E-HPODE PC and 13(S)-9Z,11E-HPODE PC, whereas CHIRALPAK IB-3 enabled separation of 13(S)-9Z,11E-HPODE PC and 13(RS)-9E,11E-HPODE PC. The results for the analysis of both enzymatically oxidized and auto-oxidized lecithin (an important phospholipid mixture in vivo and in food) indicate that our method would be useful for distinguishing enzymatic oxidation and auto-oxidation reactions. Such information will be invaluable for elucidating the involvement of PCOOH in disease pathogenesis and in food deterioration.