| In mammalian cells, transmembrane flux of a variety of structurally diverse organic cations (e.g., metformin, tetraethylammonium, and 1-methy-4-phenylpyridinium) is mediated by organic cation transporters (OCTs). OCTs, including OCT1, OCT2 and OCT3, are thought to play a role in the absorption, distribution, elimination and tissue-specific targeting of organic cationic drugs. The goals of this dissertation were to characterize genetic variation in human OCT1 (SLC22A1) and to determine the pharmacological and physiological roles of the transporter. The findings contribute to the broader goal of understanding the pharmacogenetics of membrane transporters.; The first part of this dissertation described the identification and functional characterization of genetic variants of OCT1. OCT1 was found to be a highly polymorphic gene. Non-synonymous variants of OCT1 exhibited different rates of uptake of the model substrate MPP+ in Xenopus laevis oocytes. The non-synonymous variants were also evaluated with respect to chemical change, evolutionary conservation, and amino acid substitution scoring matrices. The data suggest that genetic variation in OCT1 may affect drug disposition.; The second part of this dissertation focused on determining the role of OCT1 in drug action. In particular, the role of OCT1 in the disposition and action of metformin, a drug used in the treatment of diabetes, was intensively investigated. Experiments in cell culture, Oct1 knockout mice, and human volunteers demonstrated that OCT1 was required for the therapeutic effects of metformin. OCT1 was a determinant of response to metformin in cell lines and in mouse primary hepatocytes. The glucose-lowering effect of metformin was abolished in Oct1-deficient mice. Importantly, OCT1 function or genotypes has a significant impact on the pharmacokinetics and pharmacodynamics of metformin in animals and in healthy volunteers.; In the final part of this dissertation, the role of OCT1 in hepatic triglyceride homeostasis was explored. A series of assays and measurements were performed in obese (ob/ob) and lean (OB/OB) mice in the presence or absence of the Oct1 allele. The data suggest that in addition to its function as a drug transporter, OCT1 is involved in nutrient, particularly triglyceride and glucose, homeostasis and may be important in the development of fatty liver. |
