Comparison of bile acids profiles in the enterohepatic circulation system of mice and rats

Bile acids (BAs) were selected as biomarkers for the diagnosis and prevention of multiple liver diseases, and they were also considered as an important signal transductor via "liver-gut" axis. As important factors for maintaining the normal function and tissue morphology, BA homeostasis throughout the enterohepatic circulation system was guaranteed by BA synthases and transporters, nuclear receptors (NRs) and gut microbiota, all of which presented significant species differences. Thus, we simultaneously quantify BA profiles in the enterohepatic circulation of SD rats and C57BL/6 mice to reveal the species differences of BA homeostasis between these two main rodents of preclinical studies. Our results showed that BA profiles of mice plasma, bile and liver were most dissimilar from these of rats. Meanwhile, BAs profiles also presented obvious species differences in the intestine of mice and rats, especially small intestine. Unlike rats, taurine-conjugated bile acids (T-BAs) were predominant in mice small intestine content and tissue, in which taurocholic acid (TCA) was the most prominent BAs. BAs dynamic analysis showed that compared with rats, mice showed stranger taurine and glycine de-conjugations in lager intestine. However, both the ratios of unconjugated bile acids (Un-BAs) to conjugated BAs, and secondary BAs to primary BAs in mice small content and tissue were all much lower than these in rats. Furthermore, ileum BAs profiles also showed significantly separation trend between rats and mice, whether content or tissue. Our data revealed that the patterns of BAs homeostasis in mice enterohepatic circulation system were significantly different from these in rats (especially in intestine), suggesting that more cautious should be paid to the selection of BAs as biomarkers for disease diagnosis or/and drug induced toxicity, and the certain role and mechanism of individual BA in the pathological process of BA-related diseases via "liver-gut" axis should be verified by using of multiple species.