Metabolomics approach for gaining insights into pathological mechanisms of irritable bowel syndrome and inflammatory bowel disease

Abstract

Irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD) are two of the most commonly diagnosed chronic digestive disorders in Western countries with increasing prevalence among Canadians. However, the etiology of IBS and IBD remain poorly understood due to a complex interplay of genetic, psychosocial and environmental factors, which hampers efforts at early detection/screening, accurate diagnosis and effective treatments notably in children. This thesis aims to reveal new biochemical insights into the pathophysiology underlying IBS and IBD when using an untargeted metabolite profiling (i.e., metabolomics) approach on urine and stool specimens based on multisegment injection-capillary electrophoresis-mass spectrometry (MSI-CE-MS). Chapter I reviews brief history and current challenges in diagnosis and treatment, as well as current metabolomics literature of IBS and IBD. Chapter II first develops a robust method for high throughput profiling of anionic metabolites in human urine samples when using MSI-CE-MS. For the first time, we demonstrate that incidental capillary fractures are caused by irreversible aminolysis of the outer polyimide coating due to the frequent use of volatile ammonia based buffers under alkaline conditions (pH > 9) in electrospray ionization-MS. Chapter III subsequently applies this validated method to investigate differentially excreted urinary metabolites between adult IBS patients and healthy controls, which indicated significantly accelerated rates of collagen degradation and cell turn-over in IBS patients. Chapter IV later develops a novel stool extraction protocol for characterization of the fecal metabolome together with meta-genomic data for elucidating complex host-gut microflora interactions from a cohort of pediatric IBD patients, including Crohn’s disease and ulcerative colitis. In this pilot study, a panel of discriminating metabolites in urine is shown to allow for differential diagnosis of major pediatric IBD sub-types as an alternative to colonoscopy and histopathology that are invasive, expensive and prone to ambiguous test results. Finally, Chapter V involves a longitudinal metabolomics study that aims to identify metabolic trajectories that predict treatment responses of a cohort of pediatric Crohn’s disease patients following initiation of exclusive enteral nutrition (EEN) therapy. In the end, Chapter VI highlights major outcomes of thesis and future direction of metabolomics in IBS and IBD with a specific focus on improved stool specimen collection and validation of biomarker specificity relative to other related gastrointestinal disorders. In summary, this thesis has demonstrated metabolic processes that are associated with exacerbation of symptoms or remission in subset of IBS and pediatric IBD patients. With follow up studies with larger cohort of patients, potential biomarkers identified in this thesis will contribute the development of more accurate and non-invasive decision making process for diagnosis and treatment, resulting in long-lasting remission and improved quality of life of patients suffering from chronic digestive disorders.