Oxygen attachment dissociation (OAD) MS/MS in the identification of positional isomers of dysregulated lipids detected in an ethanol exposure metabolomics study in mice.

INTRODUCTION: In metabolic profiling studies the structural characterisation of lipids requires the identification of the head group, carbon number and the position(s) of carbon-carbon double bonds (C = C). Locating the position of double bonds is vital since minor structural differences between positional isomers can alter a lipid's biochemical function.

OBJECTIVES: Oxygen Attachment Dissociation (OAD) is a novel fragmentation technology that enables the localisation of C = C double bonds in lipids. To evaluate its use in the structural characterisation of lipids, OAD has been applied in a discovery-based untargeted analysis of the metabolic impact of acute ethanol exposure in a mouse model.

METHODS: UHPLC-OAD-MS/MS was used to enhance the identification of lipids found to be significantly altered by acute ethanol exposure in the gut, liver and pancreas tissues of male C57BL/6 mice receiving a Lieber-DeCarli liquid diet either containing 5% ethanol or an isocaloric control diet. Tissue extracts were analysed using untargeted UHPLC-DIA-MS/MS; UHPLC-OAD-MS/MS analysis was performed to further annotate lipids that were significantly increased or diminished in the animals exposed to ethanol.

RESULTS: UHPLC-DIA-MS/MS analysis of gut, liver and pancreas tissue revealed 101 lipids that were significantly increased or diminished in ethanol treated mice. Of the included 83 unsaturated lipids detected, UHPLC-OAD-MS/MS enabled the localisation of C = C double bonds in 61, including isomers indistinguishable by MS/MS with collision induced dissociation.

CONCLUSIONS: The results demonstrate the value of OAD-MS/MS in enhancing lipid identification. The resulting improvement may enable better understanding of the underlying biochemistry in the response of mice to exposure to ethanol.