Phosphorus and sulfur metabonomic profiling of tissue and plasma obtained from tumour-bearing mice using ultra-performance liquid chromatography/inductively coupled plasma mass spectrometry

RATIONALE: Metabonomic studies use complex biological samples (blood plasma/serum, tissues, etc.) that when analysed with high-performance liquid chromatography/mass spectrometry (HPLC/MS) or nuclear magnetic resonance (NMR) generate profiles that may contain many thousands of features. These profiles can be difficult to interpret with the majority of the features contributing little to the study. As such there is an argument for the development of techniques that can simplify the problem by targeting particular classes of compounds. METHODS: In this study ultra-performance liquid chromatography/inductively coupled plasma mass spectrometry (UPLC/ICP-MS) was used to profile tumour tissue and plasma samples for phosphorus- and sulfur-containing metabolites. These samples were xenograft tumours (derived from breast, lung and colon cell lines) and plasma obtained from nude mice. Plasma was also obtained from non-tumour-bearing mice as a control. Due to isobaric interferences this method took advantage of the dynamic reaction cell within the ICP-MS system to react the phosphorus and sulfur ions with oxygen. The PO+ and SO+ ions were then monitored free of interferences. The total phosphorus and sulfur within each sample was also recorded using flow injection ICP-MS. A robust quality control system based on pooled sample replicate analysis was used throughout the study. RESULTS: Determination of the total phosphorus and sulfur content of each sample was sufficient in itself for statistical differentiation between the majority of the cell lines analysed. Subsequent reversed-phase chromatographic profiling of the organic tumour and plasma extracts revealed the presence of a number of well-retained phosphorus-containing compounds that showed tumour-specific profiles. Reversed-phase profiling was not suitable for the sulfur-containing compounds which eluted with the solvent front. CONCLUSIONS: This study has shown the potential use of UPLC/ICP-MS to differentiate between tumour cell lines, using both plasma and tumour tissue samples, based solely on metabolites that contain phosphorus or sulfur. Whilst further work is required to identify these compounds this methodology shows the ability of the described methods to provide targets for future biomarker discovery studies.