{
  "abstract": "Introduction Bile acid diarrhoea (BAD) is a common, debilitating condition caused by excess bile acids entering the colon, leading to urgency, diarrhoea, and poor quality of life. The mechanisms by which excess colonic bile acids drive symptoms in humans are poorly understood. This study investigates how dysregulated bile acid environments impact colonic epithelial barrier function using human colonic organoids.Methods Physiologically relevant bile acid cocktails were formulated to model normal (BA-N; ~10 μM) and high (BA-H; ~150 μM) bile acid environments representative of healthy and BAD mucosal tissues. Human tissue–derived colonic organoids were established and cultured in stem or differentiated states before exposure to BA-N or BA-H for 1–5 days.The effect of BA-N and BA-H on organoid viability (CellTiter-Glo 3D), growth dynamics (Incucyte live cell imaging), extracellular vesicle (EV) release (nanoparticle tracking analysis) and cellular senescence (Ki67/GLF16 immunohistochemistry) were assessed (organoids derived from n=3-5 donors). Transcriptional responses in stem-state organoids cultured in BA-N and BA-H for 24 hours (n=5) were assessed using qPCR for stem cell markers. Transcriptomic responses in differentiated organoids were analysed by qPCR and RNA-sequencing, focusing on BA receptor, barrier integrity, secretory and inflammatory pathway expression (n=5). Barrier function was assessed through transepithelial electrical resistance (TEER) measurements of colonic organoid-derived Transwell monolayers (n=2).Results Colonic organoids expressed bile acid receptors ( TGR5, FXR, PXR, VDR) with no change in expression following exposure to BA-H. Organoid viability was also unchanged following BA-H exposure. However, altered growth dynamics, including increased darkness and reduced eccentricity were observed. Targeted qPCR analysis revealed no changes in epithelial differentiation markers (CDH1, MUC2, LYZ, CHGA) or permeability markers (CLDN2, CLDN4, OCLN, TJP1) induced by BA-H, nor changes in functional permeability (TEER). Inflammatory markers (IL33, IL1B, IL18) and secreted EV size and quantity were unaltered following BA-H exposure.Differentiated organoids exposed to BA-H showed a significant increase in FGF19 mRNA (p=0.01), a key negative regulator of bile acid synthesis, suggesting a compensatory response to excess BAs may exist in the colon. In line with this, RNA sequencing identified increased FABP6 (p=0.04) in BA-H organoids, further supporting altered bile acid handling in response to excess bile acids.Stem-state organoids exhibited reduced LGR5 (p=0.02) and ASCL2 (p=0.04) following BA-H exposure, suggesting excess BAs also reduce colonic stemness.Conclusions Excess bile acids induce adaptive bile-acid handling responses and reduced stemness in the colon that warrant further investigation of potential druggable mechanisms contributing to BAD.",
  "authors": [
    {
      "affiliations": [
        "University of Dundee, Dundee, United Kingdom"
      ],
      "name": "Claire Mobbs"
    },
    {
      "affiliations": [
        "University of Dundee, Dundee, United Kingdom"
      ],
      "name": "Simon Powis"
    },
    {
      "affiliations": [
        "University of Dundee, Dundee, United Kingdom"
      ],
      "name": "Stephen Keely"
    },
    {
      "affiliations": [
        "University of Dundee, Dundee, United Kingdom"
      ],
      "name": "Julian Walters"
    },
    {
      "affiliations": [
        "University of Dundee, Dundee, United Kingdom"
      ],
      "name": "Mairi McLean"
    }
  ],
  "title": "P414 Excess bile acids alter epithelial function in human colonic organoids",
  "uid": "9c211088-0cc7-547d-b2ad-50b6ed55a7c8"
}