All-trans Retinoic Acid Counteracts Diarrhea and Inhibition of Downregulated in Adenoma Expression in Gut Inflammation.

BACKGROUND: Intestinal epithelial apical membrane Cl-/HCO3- exchanger DRA (downregulated in adenoma, SLC26A3) has emerged as an important therapeutic target for diarrhea, emphasizing the potential therapeutic role of agents that upregulate DRA. All-trans retinoic acid (ATRA), a key vitamin A metabolite, was earlier shown by us to stimulate DRA expression in intestinal epithelial cells. However, its role in modulating DRA in gut inflammation has not been investigated. AIMS: Our aim was to analyze the efficacy of ATRA in counteracting inflammation-induced decrease in DRA in vitro and in vivo. METHODS: Interferon-γ (IFN-γ)-treated Caco-2 cells and dextran sulfate sodium (DSS)-treated C57BL/6J mice served as in vitro and in vivo models of gut inflammation, respectively. The effect of ATRA on IFN-γ-mediated inhibition of DRA function, expression, and promoter activity were elucidated. In the DSS colitis model, diarrheal phenotype, cytokine response, in vivo imaging, myeloperoxidase activity, and DRA expression were measured in the distal colon. RESULTS: All-trans retinoic acid (10 µM, 24 h) abrogated IFN-γ (30 ng/mL, 24 h)-induced decrease in DRA function, expression, and promoter activity in Caco-2 cells. All-trans retinoic acid altered IFN-γ signaling via blocking IFN-γ-induced tyrosine phosphorylation of STAT-1. All-trans retinoic acid cotreatment (1 mg/kg BW, i.p. daily) of DSS-treated mice (3% in drinking water for 7 days) alleviated colitis-associated weight loss, diarrheal phenotype, and induction of IL-1ß and CXCL1 and a decrease in DRA mRNA and protein levels in the colon. CONCLUSION: Our data showing upregulation of DRA under normal and inflammatory conditions by ATRA demonstrate a novel role of this micronutrient in alleviating IBD-associated diarrhea.