A 13-Oxo-9,10-epoxytridecenoate Phospholipid Analogue of the Genotoxic 4,5-Epoxy-2E-decenal: Detection in Vivo, Chemical Synthesis, and Adduction with DNA

Often guided by analogy with non phospholipid products from oxidative cleavage of polyunsaturated fatty acids (PUFAs), we previously identified a variety of biologically active oxidatively truncated phospholipids. Previously, 4,5-epoxy-2(E)-decenal (4,5-EDE)1 was found to be produced by oxidative cleavage of 13-(S)-hydroperoxy-9,11-(Z,E)-octadeca-dienoic acid (13-HPODE). 4,5-EDE reacts with deoxy-adenosine (dAdo) and deoxy-guanosine (dGuo) to form mutagenic etheno derivatives. We hypothesized that a functionally similar and potentially mutagenic compound, i.e., 13-oxo-9,10-epoxytridecenoic acid (OETA) would be generated from 9-HPODE through an analogous fragmentation. We expected that an ester of 2-lysophosphatidylcoline (PC), OETA-PC, would be produced by oxidative cleavage of 9-HPODE-PC in biological membranes. An efficient, unambiguous total synthesis of trans-OETA-PC was first executed to provide a standard that could facilitate the identification of this phospholipid epoxyalkenal that was shown to be produced during oxidation of the linoleic acid ester of 2-lysoPC. Finally, trans-OETA-PC was detected in a lipid extract from rat retina. The identity of the naturally occurring oxidatively truncated phospholipid was further confirmed by derivatization with methoxylamine that produced characteristic mono and bis adducts. The average amount of trans-OETA-PC in rat retina, 0.33 pmol, is relatively low, compared to other oxidatively truncated PCs, e.g., the 4-hydroxy-7-oxohept-5-enoic acid PC ester (HOHA-PC, 2.5 pmol) or the 4-keto-7-oxohept-5-enoic acid PC ester (KOHA-PC, 1.7 pmol), derived from the docosahexaenoic acid ester of 2-lysoPC. This, most likely, is because docosahexaenoate PCs are particularly abundant in the retina compared to the linoleate PC ester precursor of OETA-PC. As predicted by analogy with 4,5-EDE, OETA-PC reacts with dAdo and dGuo, as well as with DNA, to form mutagenic etheno-adducts.