Electrochemical oxidation of phosphatidylethanolamines studied by mass spectrometry.

Phosphatidylethanolamines (PEs) are widely present in cellular membranes and lipoproteins. Oxidation of PE fatty acyl chains generates several oxidized products, exerting a vast number of biological functions, not totally unveiled yet. In vitro biomimetic models have been used to identify oxidized PEs and to develop analytical strategies for their targeted detection in vivo. Most of the models are based on oxidation by reactive oxygen species (ROS), but the oxidative metabolism of PE also relies on controlled reactions catalyzed by enzymes as lipoxygenase, which can be mimicked by electrochemical (EC) oxidation. In this study, 3 PE standards (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE), 1-palmitoyl-2-linoleoyl-sn-glycero-3-phosphoethanolamine (PLPE), and 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphoethanolamine (PAPE)) were oxidized by EC oxidation, using an EC flow-through cell system as a biomimetic model of oxidative injury. The new oxidation products were identified by online EC electrospray ionization mass spectrometry (EC-ESI-MS and MS/MS). Long-chain and short-chain oxidation products were identified, bearing modifications in the sn-2 acyl chains, whereas the oxidation pattern was dependent on the unsaturation level. Long-chain oxidation products of PEs (keto, hydroxy, hydroperoxy, poly-hydroperoxy derivatives) were identified, bearing up to 5, 7, and 10 oxygens for POPE, PLPE, and PAPE, respectively. Fourteen short-chain oxidation products, 7 from PLPE, and 7 from PAPE, including aldehydes, -hydroxy-,-aldehydes, and dicarboxylic acids were characterized. Some of these oxidized species were previously reported during the oxidative metabolism of PEs driven by ROS. The EC-ESI-MS platform was, therefore, able to mimic the oxidative metabolism of PEs mediated by ROS.