Evaluation of Direct from Sample Metabolomics of Human Faeces using Rapid Evaporative Ionisation Mass Spectrometry (REIMS)

Simon J S Cameron, James L. Alexanders, Frances Bolt, Adam Burke, Hutan Ashrafian, Julian P Teare, Julian R Marchesi, James M Kinross, Jia V Li, Zoltan Takats

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Abstract

Mass spectrometry is a powerful tool in the investigation of the human faecal metabolome. However, current approaches require time-consuming sample preparation, chromatographic separations, and consequently long analytical run times. Rapid evaporative ionisation mass spectrometry (REIMS) is a method of ambient ionisation mass spectrometry and has been utilised in the metabolic profiling of a diverse range of biological materials, including human tissue, cell culture lines, and microorganisms. Here, we describe the use of an automated, high-throughput REIMS robotic platform for direct analysis of human faeces. Through the analysis of faecal samples from five healthy male participants, REIMS analytical parameters were optimised and used to assess the chemical information obtainable using REIMS. Within the faecal samples analysed, bile acids, including primary, secondary, and conjugate species were identified, and phospholipids of possible bacterial origin were detected. In addition, the effect of storage conditions and consecutive freeze/thaw cycles was determined. Within the REIMS mass spectra, the lower molecular weight metabolites, such as fatty acids, were shown to be significantly affected by storage conditions for prolonged periods at temperatures above -80°C, and consecutive freeze/thaw cycles. However, the complex lipid region was shown to be unaffected by these conditions. A further cohort of 50 faecal samples, collected from patients undergoing bariatric surgery, were analysed using the optimised REIMS parameters, and the complex lipid region mass spectra used for multivariate modelling. This analysis showed a predicted separation between pre- and post-surgery specimens, suggesting that REIMS analysis can detect biological differences, such as microbiome-level differences, which have traditionally been reliant upon methods utilising extensive sample preparations and chromatographic separations and/or DNA sequencing.

Original languageEnglish
JournalAnalytical Chemistry
Early online date04 Oct 2019
DOIs
Publication statusEarly online date - 04 Oct 2019

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