Ursodiol is a commercially-available exogenous form of UDCA, the precursor of TUDCA. Although the compound has an established dosing, safety, tolerability and efficacy profile in patients with hepatobiliary disorders, gaps exist in the understanding of the pharmacokinetics / pharmacodynamics of the compound, particularly in patients with normal gastrointestinal function, and no human data exist for its therapeutic use in neurodegenerative disorders. The specific aims of this study are: