Stereochemistry and dose of bile acids (BA) influence probiotic growth and barrier function in human colon T84 cells
Authors: Farooq Zohaib , Moosani Ayesha , Leininger Alexander , Rehman Ebaad , Donner Faith , Rao Mrinalini , Narayanan Madhavan 
Published: May 2024

BA-associated diarrhea (BAD) occurs in ~1% of the population, where high [BA] alter the gut microbiota and epithelial barrier function. Probiotics are used to help restore the microbiome and alleviate diarrheal symptoms in these patients. Using T84 cells, we showed that the primary BA, chenodeoxycholic acid (CDCA; 500μM) increased apoptosis, oxidative stress (ROS) and proinflammatory cytokine IL-8 to disrupt tight junctions while its secondary BA, lithocholic acid (LCA), did not. We also showed that probiotics reversed the effects of CDCA in T84 cells (Physiol. 2023, 38, S1). In this study, we examined the dose-dependent effects of di-hydroxy (OH) BAs, CDCA, its 7-OH epimer ursodeoxycholic acid (UDCA) and its mono-OH BA, LCA, on microbial and epithelial cell function. We hypothesize that the differences in the -OH position (3, 7, or 12) and stereochemistry (α or β) will result in varied dose-dependent effects of these BAs. Probiotic strains in Up & Up supplement (30 billion CFUs of 10 strains) were grown in T84 cell culture media ± BA (50 - 500μM) in anaerobic conditions (37°C, 48h). The effect of BAs (50-500μM, 0–18h) on barrier function was studied in confluent T84 cells (TransEpithelial Resistance, TER >1000 Ω.cm2) as follows: i) apoptosis (Annexin-V, flow cytometry); ii. mitochondrial and nuclear ROS production (CellRox, flow cytometry) and iii) paracellular permeability (TER and FITC-10kD dextran fluxes (F10D)). The predominant bacterial species (Control media, CFU x 108: 7.5 ± 1) was Lactobacillus fermentum (L f) (16S rRNA sequencing). CDCA caused a dose-dependent (μM) reduction in growth rate (50: 0.6±0.2; 250: 0.06±0.04; 500: 0.05±0.01; p<0.01, n=3) and changed the predominant species to L. plantarum (L p). UDCA and LCA (50-500μM) alone had no effect but reversed the actions of CDCA on bacterial growth (only 50 LCA/UDCA ± 500 CDCA are shown; CFU x 108: LCA: 7±1; CDCA+LCA: 6.7±0.8; UDCA: 6.2±0.5; UDCA + CDCA: 6.5±1, n=3) and changed the predominant species to L f. In T84 cells, apical exposure of CDCA caused a dose-dependent increase in apoptosis while UDCA or LCA at any dose had no effect (% Annexin V+ cells, 18 H: DMSO: 10±1; CDCA 50: 14±2; CDCA 250: 20±2; CDCA 500: 25±2; UDCA 500: 13±4; LCA 500: 9±2; n=3). CDCA increased ROS starting at 50μM (% CellRox+ cells: DMSO: 12±0.5; CDCA 50: 25±0.1; CDCA 250: 30±0.1; CDCA 500: 36±2). UDCA and LCA (50-500μM) had no effect. Time- and dose-dependent studies show that CDCA decreased TER (% decrease: CDCA 50: 50±5, CDCA 250: 63±7; CDCA 500: 71±8) and increased F10D fluxes (apparent permeability (x 10−9) cm/sec: Control: 8±1; CDCA 50: 35±5; CDCA 250: 78±10; CDCA 500: 90±20). In contrast, UDCA and LCA alone (50-500μM) had no effect on paracellular permeability but restored CDCA-induced barrier dysfunction (apparent permeability (x 10−9) cm/sec: Control: 8±1; CDCA 50: 35±5; CDCA 250: 78±10; CDCA 500: 90±20; UDCA 500: 13±2; CDCA 500+UDCA: 41±12; LCA 500: 15±2; CDCA 500+LCA: 38±2, n>3). Comparing the effects of hydrophobic CDCA with that of its hydrophilic 7-b isomer, UDCA, highlighted the importance of stereochemistry of -OH groups in BA action. CDCA’s deleterious effects on microbiota and epithelia started as low as 50μM, while UDCA, like LCA, restores the microbiota and barrier function. Understanding and targeting the interplay of BA, microbiota and epithelia may open up new therapeutic avenues for the treatment of diarrheal diseases. Supported by Funds from UGSRF, APS to ZF, NSSRP Funds, BenU to ER, AL, MN, MP and JS, UIC Funds to MR. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.