Application of liquid chromatography-mass spectrometry-based metabolic profiling in inflammatory bowel disease

Abstract

The inflammatory bowel diseases (IBD), Crohn’s Disease (CD) and Ulcerative colitis (UC), are chronic inflammatory diseases of the gastrointestinal tract, whose aetiology has yet to be determined, but is widely thought to be the result of genetic, immune, microbial, metabolic and environmental influences. IBD has been the subject of microbial and metabolomic research for many years due to associations between UC, CD and alterations in the gut microbiome, as well as measurable changes in systemic metabolism. In this thesis, the breadth of metabolomic research in IBD across multiple human biosamples has been documented in a systematic review. The majority of studies have used untargeted ‘global profiling’ techniques and the review highlights potential advantages that a targeted metabolomic and lipidomic approach to IBD research may bring. The first IBD-specific and targeted liquid-chromatography mass-spectrometry method was developed and validated. The method also employed a novel application of a derivatizing agent to stool samples, as well as previously studied urine and blood components. The application of this method in multiple biosamples showed alterations in concentrations of key microbial and mammalian molecules, comparing IBD patients to healthy controls. The utility of this method when compared to untargeted approaches was also explored, demonstrating the potential advantages of targeted metabolomic methods in IBD research. Results from a lipidomic analysis of IBD stool samples showed significant differences in bioactive lipid species in the stool samples of both UC and CD patients compared to healthy controls. This analysis was integrated with 16S ribosomal RNA (16S rRNA) gene-based sequencing data, identifying correlations between IBD associated bacterial groups and significantly altered stool lipids. This study was also the first to attempt to measure oxylipins in human stool samples. The studies undertaken in this thesis demonstrate the potential of targeted metabolomic analyses in IBD, through novel mass spectrometry approaches.