Lithocholic acid regulates colonic epithelial barrier function and apoptosis: Implications for inflammatory bowel disease
Authors: Ginley Natalia Lajczak‐Mc , Smyth Jessica , Fallon Ciara , Clerkin Caoimhe , Keely Stephen J 
Published: June 2021

BackgroundIncreased apoptosis and loss of epithelial barrier function are hallmark features in the pathogenesis of inflammatory bowel disease. While bile acids are classically known for their roles in facilitating digestion and absorption of fats, they have more recently become appreciated as a family of enterocrine hormones that regulate many aspects of intestinal function. However, even though changes in luminal bile acids are closely associated with IBD pathogenesis, their roles in regulating epithelial barrier function are still largely unknown. Lithocholic acid (LCA) is a secondary colonic bile acid whose luminal levels are decreased and which we have recently shown to be protective against the onset of intestinal inflammation. The aim of the current study was to investigate the effects of LCA on colonic epithelial barrier function and apoptosis.MethodsC57BL/6 mice were administered dextran sodium sulphate (DSS, 2.5%) in drinking water for 5 days to induce epithelial damage and intestinal inflammation and disease severity was measured as disease activity index (DAI). Mice received PBS or Na+‐lithocholate (LCA) via IP injection each day. Epithelial permeability was assessed by measuring the flux of orally‐gavaged FITC‐dextran from the lumen into the blood. Levels of cleaved PARP, measured by Western blotting, were used as a marker of apoptosis. To examine the effects of LCA on cytokine‐induced barrier dysfunction in vitro, monolayers of T84 colonic epithelial cells, treated INF‐ɣ and TNF‐α, were employed.ResultsAfter 5 days, animals treated with LCA had a significantly lower DAI score (5.12 ± 1.0) than those of mice treated with DSS alone (9.0 ± 0.5) (n = 12; p ≤ 0.001). DSS treatment increased the flux of FITC‐dextran from the lumen into the blood by 2.3 ± 0.7 fold and this was reduced to 1.3 ± 0.2 fold in LCA‐treated animals (n = 12). The apoptotic marker, cleaved‐PARP, was increased 19.9 ± 10.9 fold in mucosal tissues isolated from DSS treated mice and this was also reduced to 3.9 ± 1.1 fold by LCA treatment (n = 3 – 4; p ≤ 0.01). In monolayers of cultured T84 colonic epithelial cells, treatment with a combination of the proinflammatory cytokines, INF‐ɣ (40 ng/ml) and TNF‐α (20 ng/ml) increased FITC‐dextran flux from the apical to basolateral domain by 4.9 ± 0.7 fold of that in control cells, while treatment with LCA (10 μM) practically abolished this response to 1.3 ± 0.5 fold (n = 8; p ≤ 0.001). Levels of cleaved‐PARP were increased by 4.4 ± 1.8 fold in IFN/TNF treated cells but this was reduced to 1.9 ±0.1 fold in LCA treated cells (n = 4). Similarly, GW4064 (5 μM), an agonist of the nuclear bile acid receptor, FXR, also prevented IFN/TNF‐induced FITC‐dextran flux and PARP cleavage in cultured epithelial cells.ConclusionsBy virtue of its capacity to prevent cytokine‐induced epithelial apoptosis and disruption of barrier function, these data imply a protective role for LCA in conditions of colonic inflammation. Thus, LCA and its associated signalling pathways present promising targets for the development of new approaches to promote colonic barrier function in the treatment of IBD.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.