Identification and profiling of targeted oxidized linoleic acid metabolites in rat plasma by quadrupole time-of-flight mass spectrometry (original) (raw)

2012, Biomedical Chromatography

Linoleic acid (LA) and LA-esters are the precursors of LA hydroperoxides, which are readily converted to 9-and 13-hydroxy-octadecadienoic acid (HODE) and 9-and 13-oxo-octadecadienoic acid (oxo ODE) metabolites in vivo. These four oxidized LA metabolites (OXLAMs) have been implicated in a variety of pathological conditions. Therefore, their accurate measurement may provide mechanistic insights into disease pathogenesis. Here we present a novel quadrupole timeof-flight mass spectrometry (Q-TOFMS) method for quantitation and identification of target OXLAMs in rat plasma. In this method, the esterified OXLAMs were base-hydrolyzed and followed by liquid-liquid extraction. Quantitative analyses were based on one-point standard addition with isotope dilution. The target metabolites were quantified by multiple reaction monitoring (MRM) extracted ion chromatograms generated post-acquisition with 10 ppm extraction window. The limit of quantitation was 9.7-35.9 nmol/L depending on the metabolite. The method was reproducible with coefficient of variation below 18.5%. Mean concentrations of target metabolites were 57.8, 123.2, 218.1, and 57.8 nmol/L for 9-HODE, 13-HODE, 9-oxoODE, and 13-oxoODE, respectively. Plasma levels of total OXLAMs were 456.9 nmol/L, which correlated well with published concentrations obtained by gas chromatography/mass spectrometry (GC/MS). The concentrations were also obtained utilizing a standard addition curve approach. The calibration curves were linear with correlation coefficients > 0.991. Concentrations of 9-HODE, 13-HODE, 9-oxoODE, and 13-oxoODE were 84.0, 138.6, 263.0, and 69.5 nmol/L, respectively, which were consistent with the results obtained from one-point standard addition. Target metabolites were simultaneously characterized based on accurate Q-TOFMS data. This is the first study of secondary LA metabolites using Q-TOFMS.