Metabolomic profiling of biomarkers of liver X receptor-induced toxicity in mouse liver tissue

Methods based on matrix-assisted laser desorption/ionisation mass spectrometry (MALDI-MS), liquid chromatography coupled to an LTQ-Orbitrap mass spectrometer (LC-MS) and gas chromatography-mass spectrometry (GC-MS) were used to investigate changes in the small molecule profiles of mouse liver in response to administration of an LXR agonist. Mice were treated with either 0.3 mg/kg, 1 mg/kg, 10 mg/kg, 30 mg/kg or 60 mg/kg of an LXR test compound or saline (control) once daily, over a 5 day period, to investigate the effects of the drug on metabolism in the liver. It was possible to detect triacylglycerol accumulation in the livers of animals treated with the drug, even at the lowest concentrations using, in the first instance, MALDI MS. There was also an increase in the relative degree of triacylglycerol saturation in the drug-treated samples. Changes in the profiles of phosphatidylcholine lipids were also observed. The changes in lipid profiles were also confirmed by LC-MS and GC-MS, the latter revealing a large increase in the level of the free fatty acid oleic acid (C18:1) in the treated samples. All of the changes were dose-related. Polar metabolites in the samples were analysed by hydrophilic interaction (HILIC) chromatography in combination with an LTQ-Orbitrap mass spectrometer. There were many changes in the metabolite profiles, some of which might simply be related to generalised toxicity. The clearest marker compounds, which showed very marked changes with dose, were methylglutaryl carnitine (MGC) and hydroxymethylglutaryl carnitine (HMGC). Another marker of some interest was uridine diphosphate N-acetylglucosamine (UNGA).