Phosphatidylethanolamine Modification by Oxidative Stress Product 4,5(E)-Epoxy-2(E)-heptenal

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Abstract
Phosphatidylethanolamine and ethanolamine were incubated with 4,5(E)-epoxy-2(E)-heptenal to analyze the changes produced in amino phospholipids as a consequence of their reaction with this lipid oxidation product. The reactions, which were followed by GC/MS or HPLC/MS, produced in a first step the corresponding imines, which later evolved into two main products. These products, which were isolated and characterized by 1H and 13C NMR and mass spectrometry, resulted in the corresponding phosphatidylethanolpyrroles (PEPs) and phosphatidylethanol-2-(1-hydroxypropyl)pyrroles (PEHPs). PEPs were relatively stable, but PEHPs polymerized spontaneously. This polymerization, which was followed in 4,5(E)-epoxy-2(E)-heptenal/ethanolamine incubations with the detection of the corresponding dimers and trimers, was related to the brown color and fluorescence development produced. In addition, when hydroxyalkylpyrroles were incubated in the presence of single pyrroles, mixed polymers of the two pyrroles were obtained, and these polymers were produced in a higher extent than those derived exclusively from PEHP. These results confirm that lipid oxidation products are able to react with amino phospholipids analogously to protein amino groups, and therefore, both amino phospholipids and proteins may compete for lipid oxidation products. Although these results do not demonstrate the formation of pyrrolyzed phospholipids in vivo, they suggest that analogously to pyrrolyzed proteins, these modified phospholipids are likely to be produced during the phospholipid peroxidation process. In addition, these results also provide new bases for assessing the role of phospholipid modification in certain diseases, pathophysiological conditions, and aging.