Secondary bile acids (SBAs) with high hydrophobicity are abundant in the colonic lumen. However, both aggravating and protective roles of SBAs have been proposed in the pathogenesis of inflammatory bowel diseases (IBDs). We observed that oral administration of hyodeoxycholic acid (HDCA), a hydrophilic bile acid, prevented the development of dextran sulfate sodium (DSS)-induced colitis in mice. We then examined the individual effects of DSS and HDCA as well as their combined effects on fecal bile acid profile in mice. HDCA treatment increased the levels of most of fecal bile acids, whereas DSS treatment had limited effects on the levels of fecal bile acids. The combined treatment with DSS and HDCA synergistically increased the levels of fecal chenodeoxycholic acid (CDCA) and deoxycholic acid (DCA) in feces, which are potent activators of the farnesoid X receptor (FXR) and Takeda G-protein-coupled receptor 5 (TGR5). The overall hydrophobicity of fecal bile acids was not modified by any treatments. Our data suggest that the preventive effect of HDCA on DSS-induced colitis in mice is due to the synergism between DSS and HDCA in increasing the levels of the fecal bile acids with potencies to activate FXR and TGR5.
Keywords: Takeda G-protein-coupled receptor 5; chenodeoxycholic acid; deoxycholic acid; farnesoid X receptor; hydrophobicity.