Study of Pathway-Dependent Effects of Luminal Microbial Metabolites Including Short Chain Fatty Acids and Bile Acids in Irritable Bowel Syndrome Through Meta-omics Analysis of Fecal Specimens

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PROJECT SUMMARY The gut microbiome and its metabolites including short chain fatty acids (SCFA) and bile acids (BA) regulate gastrointestinal (GI) physiology and carry immense potential as diagnostic and therapeutic tools for irritable bowel syndrome (IBS), a common and chronic disorder of gut-brain interaction (or functional GI disorder). However, the precise mechanisms by which the gut microbiome and its intermediaries contribute to IBS symptoms are unclear. A mechanistically-informed understanding of microbiome-metabolome-host interactions will be essential to developing novel and targeted strategies to enhance the care of individuals with IBS. This R03 application is submitted in response to PAR-19-365. In this application, the PI proposes a hypothesis-driven research strategy to (1) identify functional pathways (genes) associated with fecal SCFA and BA levels/profiles and physiological traits in IBS and control volunteers and (2) confirm functional pathway analysis through untargeted fecal metabolite profiling. This study will complement the objectives of the PI's K23 research study which are to (1) identify changes in fecal microbiota composition that are associated with SCFA and BA profiles in IBS through 16S rRNA gene sequencing and targeted metabolite analysis, (2) establish SCFA as actionable IBS biomarkers, and (3) investigate interactions between SCFA and BA in IBS. The specific aims of this R03 proposal are to (1) identify differentially abundant metabolic pathways (genes) of SCFA production and BA biotransformation in IBS (IBS with diarrhea [IBS-D], IBS with constipation [IBS-C]) and control volunteers through functional profiling of metagenomic sequencing data and (2) compare if/how the end-products of the genomically- encoded functions of key microbial taxa differ in IBS-D, IBS-C, and controls through untargeted metabolomics. To achieve these aims, the PI will leverage her existing K23 cohort of prospectively-recruited and well- phenotyped IBS and matched-control volunteers. As part of the K23-funded study, all participants have submitted 2-day stool samples using standardized collection procedures for assessment of the fecal microbiota, fecal SCFA, and fecal BA. Residual specimens are archived and available for further analysis as described in this R03 proposal. The strategies proposed in this application will complement the PI's current career development activities and benefit from the continued mentorship from a multidisciplinary K23 mentorship panel. Findings will guide the approach for a subsequent R01 by identifying which features of the fecal microbiota could be refined into practical microbiota-based tools (e.g. third generation, long-read technology) that could be tested in a larger IBS and control volunteer cohort. Alternatively, if the genomically-encoded metabolic potential cannot be confirmed by metabolomics, findings will inform the need measure gene expression (i.e. metatranscriptomics) or quantitative microbial profiles to investigate microbial effects on IBS pathophysiology in a subsequent R01. At the conclusion of the project, the PI will be ideally positioned to become an independent physician investigator studying novel microbial and metabolomics biomarkers and targeted strategies to restore health in IBS.