Distinguishing levuglandins produced through the cyclooxygenase and isoprostane pathways

The cyclooxygenase (COX) pathway generates enantiomerically pure levuglandin (LG) E2 by a rearrangement of the prostaglandin (PG) endoperoxide PGH2. The isoprostane pathway generates racemic LGE2 together with stereoisomers, designated collectively as isoLGE2, through free radical-induced lipid oxidation. Within seconds, both LGs and isoLGs are rapidly sequestered by protein adduction. In theory, the diastereomeric purity of LGE2-protein adduct-derived lysyl lactams can reveal the relative contributions of the COX and isoprostane pathways to LGE2 stereoisomer production in vivo. Notably, however, the detection of LGE2-protein adducts does not provide a basis for inferring their formation through the isoprostane pathway in vivo unless the COX pathway can be rigorously excluded. In contrast, LGE2structural isomers, designated collectively as iso[n]LGE2s, are produced exclusively through the isoprostane pathway. Immunoassays that selectively recognize iso[n]LGE2-protein adducts are the only tools available to unambiguously detect and quantify the production of isolevuglandins in vivo through free radical-induced oxidation of arachidonates.