Abstract
F2-isoprostanes (F2-iPs) are prostaglandin (PG)-like products of non-enzymatic free radical-catalyzed peroxidation of arachidonic acid that are now widely used as indices of lipid peroxidation in vivo. Knowledge of the metabolic fate of F2-iPs in vivo is still scant, despite its importance for defining their overall formation and biological effects in vivo. Type III F2-iPs, which are diastereoisomers of cyclooxygenase-derived PGF2α, may be metabolized through the pathways of PG metabolism. We therefore studied the in vitro metabolism of eight synthetic Type III F2-iP diastereoisomers in comparison with PGF2α. We used gas chromatography-mass spectrometry and high performance liquid chromatography-electrospray-tandem mass spectrometry for structural identification of metabolites formed after incubation of the various compounds with isolated rat hepatocytes. PGF2α was metabolized to several known products, resulting from a combination of β-oxidation, reduction of Δ5 and/or Δ13 double bonds, and 15-OH oxidation, plus other novel products deriving from conjugation with taurine of PGF2α and its metabolites. Of the eight F2-iP diastereoisomers, some were processed similarly to PGF2α, whereas others showed peculiar metabolic profiles according to specific stereochemical configurations. These data represent the first evidence of biodegradation of selected Type III F2-iP isomers other than 8-epi-PGF2α, through known and novel pathways of PGF2α metabolism. The analytical characterization of these products may serve as a basis for identifying the most significant products formed in vivo. —Chiabrando, C., C. Rivalta, R. Bagnati, A. Valagussa, T. Durand, A. Guy, P. Villa, J-C. Rossi, and R. Fanelli. Identification of metabolites from Type III F2-isoprostane diastereoisomers by mass spectrometry.
Highlights
F2-isoprostanes (F2-iPs) are prostaglandin (PG)-like products of non-enzymatic free radical-catalyzed peroxidation of arachidonic acid that are widely used as indices of lipid peroxidation in vivo
The unconjugated products tentatively identified by this screening method were structurally identified after HPLC separation by examining the mass spectra of the product ions formed after collision-activated decomposition (CAD) of the carboxylate anions produced by electrospray ionization (HPLC-mass spectrometry (MS)/MS) (Table 1)
Chromatographic and mass spectral features of parent compounds, their metabolites, and authentic standards are summarized in Table 2 (GC-NICIMS) and Table 3 (HPLC-tandem mass spectrometry (MS/MS))
Summary
F2-isoprostanes (F2-iPs) are prostaglandin (PG)-like products of non-enzymatic free radical-catalyzed peroxidation of arachidonic acid that are widely used as indices of lipid peroxidation in vivo. Type III F2-iPs, which are diastereoisomers of cyclooxygenase-derived PGF2␣, may be metabolized through the pathways of PG metabolism. We studied the in vitro metabolism of eight synthetic Type III F2-iP diastereoisomers in comparison with PGF2␣. Of the eight F2-iP diastereoisomers, some were processed to PGF2␣, whereas others showed peculiar metabolic profiles according to specific stereochemical configurations. These data represent the first evidence of biodegradation of selected Type III F2-iP isomers other than 8-epi-PGF2␣, through known and novel pathways of PGF2␣ metabolism. Identification of metabolites from Type III F2-isoprostane diastereoisomers by mass spectrometry.
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