CHARACTERIZATION OF ORGANIC ANION TRANSPORTING POLYPEPTIDE 1A1 (OATP1A1) IN THE BILE ACID HOMEOSTASIS OF MICE

Organic anion transporting polypeptides (human: OATPs; all other species: Oatps; gene symbol: SLCO/Slco) are sodium-independent transport systems that mediate the transmembrane transport of a wide range of amphipathic endogenous and exogenous organic compounds. In mice, Oatp1a1, 1a4, and 1b2 are thought to account for the bulk of Na-independent bile acid (BA) uptake into liver during normal physiological conditions. The overall goal of this dissertation has focused on characterization of the in vivo role of mouse Oatp1a1 in BA homeostasis by using Oatp1a1-null mice. To achieve this overall goal, three specific aims were examined in the present dissertation. In the first specific aim, a simple and sensitive UPLC-MS/MS method was established and validated for the simultaneous analysis of various BAs, and applied to investigate liver BA content in C57BL/6 mice fed 1% cholic acid (CA), 0.3% deoxycholic acid (DCA), 0.3% chenodeoxycholic acid (CDCA), 0.3% lithocholic acid (LCA), 3% ursodeoxycholic acid (UDCA), or 2% cholestyramine (resin). The purpose of this study was to understand the BA metabolic pathways in mice by using this newly developed BA-quantification method, and thus to provide tools and knowledge for the future study in Oatp1a1-null mice. Gender differences in liver BA composition were observed after feeding CA, DCA, CDCA, and LCA, but were not prominent after feeding UDCA. Sulfation of CA and CDCA was found at the 7-OH position, and increased by feeding CA or CDCA more in male than female mice. In contrast, sulfation of LCA and taurolithocholic acid (TLCA) was female predominant, and increased by feeding UDCA and LCA. The metabolic pathways of each BA in vivo are proposed, and can be used to interpret BA-mediated gene regulation and hepatotoxicity. In the second specific aim, the hypothesis that Oatp1a1 is important in transporting unconjugated BAs was evaluated. The purpose of this study was to determine whether knockout of Oatp1a1 will alter BA metabolism in mice. To address this aim, the ...