Characterization of hydroxyeicosatetraenoic acids and hydroxyeicosatetraenoic acid phosphatidylcholines by liquid secondary ion tandem mass spectrometry

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Abstract
Arachidonic acid is oxidized to regioisomeric 5(S)-, 12(S)- and 15(S)-hydroxyeicosatetraenoic acids by the corresponding 5-, 12- and 15-lipoxygenases. These hydroxylated fatty acids can then be incorporated into cellular phos-pholipids. Negative liquid secondary ion tandem mass spectrometry using a high-energy collision regime in a tandem four-sector mass spectrometer was used to characterize regioisomeric hydroxyeicosatetraenoic acids and the corresponding hydroxyeicosatetraenoic phosphatidylcholine species. Collision-induced dissociation (CID) of the [M − H]− negative ion at m/z 319 from the hydroxyeicosatetraenoic acids regioisomers produced some similar product ions, such as m/z 301 [M − H − H2O]− and m/z 257 [M − H − (H2O + CO2)]-. In addition, product ions characteristic of the particular hydroxyeicosatetraenoic acid were formed from α cleavages adjacent to the hydroxyl moieties. Negative liquid secondary ion mass spectrometry of purified hydroxyeicosatetraenoate phosphatidylcholine species gave an ion at m/z 810 [M − CH3] -. CID of the m/z 810 ion gave product ions at m/z 283 and m/z 319, corresponding to stearate at the sn-1 position and hydroxyeicosatetraenoate at the sn-2 position, respectively. From CID of the negative ion at m/z 319 and examination of the product ion spectra, the hydroxyeicosatetraenoate regioisomer present in the phosphatidylcholine could be identified.

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