Quantitation of 20-hydroxy-5,8,11,14-eicosatetraenoic acid (20-HETE) produced by human polymorphonuclear leukocytes using electron capture ionization gas chromatography/mass spectrometry

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Abstract
Arachidonic acid can be enzymatically oxidized at the terminal methyl group by the cytochrome P450 system found in several tissues and cells, including the human polymorphonuclear leukocyte. The ω‐hydroxy metabolite, 20‐ hydroxy‐5,8,11,14‐eicosatetraenoic acid (20‐HETE) has recently been found to have interesting and diverse biological activities. Accurate measurement of quantities of this metabolite using physical chemical methods has not been previously described, but is necessary to assess biosynthesis of this eicosanoid from endogenous arachidonic acid. A procedure is described to quantitate 20‐HETE produced by the human polymorphonuclear leukocyte following physiological stimulation using (18O2)carboxy‐20‐HETE as internal standard. Since the human neutrophil produces relatively small amounts of this eicosanoid, such a study required substantial sensitivity in the quantitative assay. Following stimulation of the neutrophil, cell extracts and supernatants were purified by reverse‐phase high‐performance liquid chromatography, catalytically reduced then derivatized to the pentafluorobenzyl ester, trimethylsilyl ethers before electron capture ionization gas chromatography/mass spectrometry. Using selected ion monitoring, the amount of 20‐HETE present in a biological extract could be detected when as little as 60 pg per sample were available. Following stimulation of the human neutrophil with formyl‐methionyl‐leucyl‐phenylalanine (0.1 μM), platelet activating factor (0.1 μM) as well as with the calcium ionophore A23187 (2 μM), 20‐HETE was generated from endogenous arachidonate in concentrations of 1.2, 1.3 and 5.7 pg per 106 cells, respectively.