Effects of gender, and SLCO1B1 and CYP7A1 polymorphisms on plasma bile s in humans and the pharmacokinetics of therapeutic ursodeoxycholic

Bile s are important steroid-derived molecules essential for fat absorption in the small intestine. They are produced in the liver and secreted into the bile. Bile s are transported by bile flow to the small intestine, where they aid the digestion of lipids. Most bile s are reabsorbed in the small intestine and return to the liver through the portal vein. The whole recycling process is referred to as the enterohepatic circulation, during which only a small amount of bile s are removed from the body via faeces. The enterohepatic circulation of bile s involves the delicate coordination of a number of bile transporters expressed in the liver and the small intestine. Organic anion transporting polypeptide 1B1 (OATP1B1), encoded by the solute carrier organic anion transporter family, member 1B1 (SLCO1B1) gene, mediates the sodium independent hepatocellular uptake of bile s. Two common SNPs in the SLCO1B1 gene are well known to affect the transport activity of OATP1B1. Moreover, bile synthesis is an important elimination route for cholesterol. Cholesterol 7α-hydroxylase (CYP7A1) is the rate-limiting enzyme of bile production. The aim of this thesis was to investigate the effects of SLCO1B1 polymorphism on the fasting plasma levels of individual endogenous bile s and a bile synthesis marker, and the pharmacokinetics of exogenously administered ursodeoxycholic (UDCA). Furthermore, the effects of CYP7A1 genetic polymorphism and gender on the fasting plasma concentrations of individual endogenous bile s and the bile synthesis marker were evaluated. Firstly, a high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method for the determination of bile s was developed (Study I). A retrospective study examined the effects of SLCO1B1 genetic polymorphism on the fasting plasma concentrations of individual bile s and a bile synthesis marker in 65 healthy subjects (Study II). In another retrospective study with 143 healthy individuals, the effects of CYP7A1 genetic polymorphism and gender as well as SLCO1B1 polymorphism on the fasting plasma levels of individual bile s and the bile synthesis marker were investigated (Study III). The effects of SLCO1B1 polymorphism on the pharmacokinetics of exogenously administered UDCA were evaluated in a prospective genotype panel study including 27 healthy volunteers (Study IV). A robust, sensitive and simple HPLC-MS/MS method was developed for the simultaneous determination of 16 individual bile s in human plasma. The method validation parameters for all the analytes met the requirements of the FDA (Food and Drug Administration) bioanalytical guidelines. This HPLC-MS/MS method was applied in Studies II-IV. In Study II, the fasting plasma concentrations of several bile s and the bile synthesis marker seemed to be affected by SLCO1B1 genetic polymorphism, but these findings were not replicated in Study III with a larger sample size. Moreover, SLCO1B1 polymorphism had no effect on the pharmacokinetic parameters of exogenously administered UDCA. Furthermore, no consistent association was observed between CYP7A1 genetic polymorphism and the fasting plasma concentrations of individual bile s or the bile synthesis marker. In contrast, gender had a major effect on the fasting plasma concentrations of several bile s and also total bile s. In conclusion, gender, but not SLCO1B1 or CYP7A1 polymorphisms, has a major effect on the fasting plasma concentrations of individual bile s. Moreover, the common genetic polymorphism of CYP7A1 is unlikely to influence the activity of CYP7A1 under normal physiological conditions. OATP1B1 does not play an important role in the in vivo disposition of exogenously administered UDCA.