Influence of age on intestinal bile acid transport in C57BL/6 mice.

Intestinal and hepatic bile acid transporters are important for enterohepatic bile acid circulation and pharmacokinetics. Based on previous literature, we hypothesized that the expression of bile acid transporters and intestinal bile acid absorption are lower in older individuals. Here, we measured active taurocholate absorption across the ileum of male C57BL/6 mice in two different age cohorts - young (age range of 89-224 days) and old (age range of 613-953 days). Also examined in these mice were mRNA expression of the major bile acid transporters - Asbt and Ost/ in the ileum, and Ntcp, Oatp1b2 and Bsep in the liver. Mean intestinal taurocholate absorption was significantly lower (~50%) in mice in the older cohort compared to those in the younger cohort. In the ileum, the expression of Asbt was significantly lower in the older cohort, but expression of Ost/ was not affected by age. The lower capacity for intestinal bile acid absorption in the older animals is consistent with their lower expression level of Asbt. Of the hepatic bile acid transporters examined, expression of Ntcp and Oatp1b2 were significantly lower in the older mice. This is the first study to directly measure intestinal bile acid absorption as a function of age. The data suggest a lower capacity for intestinal bile acid absorption in older animals. Also, lower expression of Asbt, Ntcp, and Oatp1b2 in older individuals could influence pharmacokinetics of drug substrates.