Characterization of lipoxins by combined gas chromatography and electron-capture negative ion chemical ionization mass spectrometry: formation of lipoxin A4 by stimulated human whole blood.

The lipoxins are a recent addition to the family of bioactive products derived from arachidonic acid. Here, we have prepared pentafluorobenzyl ester, trimethylsilyl ether derivatives of lipoxin A4, lipoxin B4 and pentadeuterolipoxin A4 and have characterized these products by electron-capture negative ion chemical ionization gas chromatography/mass spectrometry (NICI GC/MS). Lipoxin A4 (5S,6R,15S-trihydroxy-7,9,13-trans-11-cis-eicosa-tetraenoic acid; LXA4) was quantified following extraction from whole blood by stable isotopic dilution utilizing deuterium-labeled LXA4 as internal standard and selected ion monitoring of the [M--pentafluorobenzyl] anions. Studies with a second tritiated internal standard (e.g. [11,12-3H]LXA4) also showed that the recovery of LXA4 was greater than 80% following solid-phase extraction from whole blood, and greater than 90% from isolated cells. In addition, neither isolated neutrophils nor platelets oxidatively metabolized [11,12-3H]LXA4 when incubated in the presence or absence of stimuli. Whole blood incubated with either the ionophore of divalent cations (A23187), thrombin, or thrombin plus the chemotactic peptide formylmethionyl-leucine-phenylalanine generated both LXA4 and thromboxane, which were quantified by stable isotope dilution. The ratio of thromboxane to LXA4 formed by stimulated whole blood ranged from approximately 2:1 to 20:1. These results indicate that the lipoxins display suitable characteristics as their respective pentafluorobenzyl ester, trimethylsilyl ether derivatives for quantification by electron-capture NICI GC/MS. Moreover, they provide evidence that LXA4 can be generated from endogenous sources in whole blood following exposure to physiologically relevant stimuli.