Developing Laser Assisted - Rapid Evaporative Ionisation Mass Spectrometry (LA-REIMS) as a platform for the direct analysis of faecal metabolites in gastrointestinal health and disease

Abstract

Faecal metabolomics presents an avenue for the non-invasive study of the gastrointestinal (GI) tract, the gut microbiome, and their interactions with environmental factors (1).

This thesis serves as a first step towards developing Laser Assisted - Rapid Evaporative Ionisation Mass Spectrometry (LA-REIMS) as a platform for faecal metabolomics analysis in GI disease. Faecal LA-REIMS optimisation work was carried out and yielded improved signal-to-noise ratios and a decrease in % carry-over between samples. Further, pilot work on faecal water content in LA-REIMS analysis demonstrates the importance of correcting for variable water content. A novel application of LA-REIMS imaging for the real-time mapping of metabolites in whole fresh and frozen faecal samples was developed.

The results of the optimisation work were implemented in two large scale clinical datasets. In a cohort of 234 patients (control n=131, adenoma n=77, colorectal cancer n=26), LA-REIMS demonstrates the potential for accurate direct from faecal sample adenoma and colorectal cancer (CRC) detection; this could reduce the burden of unnecessary colonoscopy and optimise cancer referral pathways. In a cohort of 169 patients (Crohn’s disease n=60, Ulcerative Colitis n=60, and control n= 49), faecal LA-REIMS demonstrates moderate-to-high diagnostic accuracy for direct from sample inflammatory bowel disease (IBD) detection. Faecal LA-REIMS analysis has the potential to optimise IBD diagnostic pathways and could reduce the burden of unnecessary endoscopic, radiological, histological and laboratory investigations. This thesis presents the first study utilising optimised LA-REIMS faecal metabolomics analysis in CRC and IBD with several tentatively identified features significantly different between disease and control states. Patient-related modifiers of the faecal metabolome were investigated in both the CRC and IBD datasets.

Optimised faecal LA-REIMS analysis has potential as a rapid, preparation-free screening and diagnostic technique for CRC and IBD.