Mass spectrometric quantitation and analysis of leukotrienes and other 5-lipoxygenase metabolites

Detailed studies fo the 5-lipoxygenase pathway of arachidonic acid metabolism is a difficult challenge, but nonetheless, an important pursuit. The leukotriense are perplexing compounds to quantitate due, in part, to their production in very small quantities by only certain cells, as well as to their chemical/biochemical instability. Several mass spectrometric techniques have been developed to quantitate 5-hydroxyeicosatetraenoic acid (5-HETE) and leukotriene b₄ (LTB₄). The mass spectral properties of terbutyldimethylsilyl derivatives of LTB₄ are reported here which are quite favorable for electron impact ionization. Catalytic reduction of LTB₄ prior to derivatization greatly improved capillary gas chromatographic behavior as well as electron impact mass spectral properties. Subpicomole quantities could be readily detected by selected ion recording of the M-57 ion, which is the most abundant ion in the mass spectrum. Lipoxygenase products labeled with oxygen-18 at the carboxyl moiety are uniquely stable to catalytic reduction and, thus, may serve as useful internal standards.