Covalent Binding of LTA4 to Nucleosides and Nucleotides

Leukotriene A4 (LTA4) is a chemically reactive conjugated triene epoxide that is formed by 5-lipoxygenase and is an intermediate in the formation of the biologically active eicosanoids leukotriene B4 and leukotriene C4. The present study was undertaken to determine whether or not LTA4 could serve as an electrophilic species that nucleosides and nucleotides could attack, ultimately resulting in a covalent adduct. Electrospray ionization mass spectrometry and tandem mass spectrometry were used to study the covalent binding of LTA4 with uridine, cytidine, adenosine, and guanosine. The reaction with guanosine was found to yield five major and at least six minor adduct species. Reversed phase HPLC and mass spectrometric data suggested that the guanosine attacked LTA4 either at carbon-12 or carbon-6 with opening the epoxide at carbon-5 to yield a series of adducts characterized by the molecular anion [M–H]− at m/z 600.3. Reactions of LTA4 with mixtures of nucleosides and nucleotides revealed that guanine-containing nucleosides were the most reactive toward LTA4. The facility of the reaction of guanine with LTA4 raises the possibility that this intermediate of leukotriene biosynthesis formed on or near the cellular nuclear envelope may react with nucleosides and nucleotides present in RNA or DNA.