Active transport of anionic and cationic drugs plays a critical role in their intestinal absorption, penetration across the blood-cerebrospinal fluid (CSF) and blood-brain barriers, and accumulation within excretory organs. In general, separate systems mediate the transport of charged organic solutes, the organic anion (OAT) and organic cation (OCT) transporter families. However, a number of drugs, e.g., the cation cimetidine, are transported by both systems. Using both Xenopus oocytes and cell lines expressing cloned drug transporters, we have examined their ability to handle several nucleoside phosphonate antiviral (NPA) drugs -- adefovir, cidofovir, and tenofovir. Of these drug transporters, only OAT1 and the ATP-driven drug pump, MRP2, transported the NPAs. None of the NPAs were transported by the OAT3 transporters from mouse, rat, or human. Thus, human nephrotoxicity of the NPAs reflects their avid (Km's ~5 uM) transport via OAT1. In the choroid plexus -- a component of the blood-CSF barrier, OAT3 is the predominant transporter expressed. Thus, choroid plexus shows limited accumulation of NPAs. This conclusion has now been confirmed in the OAT3 knockout mouse that shows no change in NPA transport despite nearly complete loss of the transport of mOAT3 substrates including taurocholate and estrone sulfate. This observation also indicates that other transporters, most likely the MRPs, are responsible for the limited penetration of the NPAs into the brain across the blood-brain and blood-CSF barriers. Our current focus is on the structural features of OAT1 and OAT3 that underlie their ability to descriminate between the NTAs and other OAT substrates shared by both isoforms. Molecular modeling based on the published crystal structures of related transport proteins have provided the basis for modeling of the binding pocket in OATs 1 and 3 and identification of amino acid residues putatively involved in substrate recognition and binding. These residues are currently being modified by site directed mutagenisis to assess their impact on transporter function.

Agency
National Institute of Health (NIH)
Institute
National Institute of Environmental Health Sciences (NIEHS)
Type
Intramural Research (Z01)
Project #
1Z01ES048014-05
Application #
7007953
Study Section
(LPC)
Project Start
Project End
Budget Start
Budget End
Support Year
5
Fiscal Year
2004
Total Cost
Indirect Cost
Name
U.S. National Inst of Environ Hlth Scis
Department
Type
DUNS #
City
State
Country
United States
Zip Code
Kimura, T; Perry, J; Anzai, N et al. (2007) Development and characterization of immobilized human organic anion transporter-based liquid chromatographic stationary phase: hOAT1 and hOAT2. J Chromatogr B Analyt Technol Biomed Life Sci 859:267-71
Aslamkhan, Amy G; Thompson, Deborah M; Perry, Jennifer L et al. (2006) The flounder organic anion transporter fOat has sequence, function, and substrate specificity similarity to both mammalian Oat1 and Oat3. Am J Physiol Regul Integr Comp Physiol 291:R1773-80
Perry, Jennifer L; Dembla-Rajpal, Neetu; Hall, Laura A et al. (2006) A three-dimensional model of human organic anion transporter 1: aromatic amino acids required for substrate transport. J Biol Chem 281:38071-9
Pritchard, John B; Miller, David S (2005) Expression systems for cloned xenobiotic transporters. Toxicol Appl Pharmacol 204:256-62
Bleasby, Kelly; Hall, Laura A; Perry, Jennifer L et al. (2005) Functional consequences of single nucleotide polymorphisms in the human organic anion transporter hOAT1 (SLC22A6). J Pharmacol Exp Ther 314:923-31
Dai, Jian; Park, Gyungse; Perry, Jennifer L et al. (2004) Molecular aspects of the transport and toxicity of ochratoxin a. Acc Chem Res 37:874-81
Sykes, Destiny; Sweet, Douglas H; Lowes, Simon et al. (2004) Organic anion transport in choroid plexus from wild-type and organic anion transporter 3 (Slc22a8)-null mice. Am J Physiol Renal Physiol 286:F972-8
Sweet, Douglas H; Chan, Lauretta M S; Walden, Ramsey et al. (2003) Organic anion transporter 3 (Slc22a8) is a dicarboxylate exchanger indirectly coupled to the Na+ gradient. Am J Physiol Renal Physiol 284:F763-9
Aslamkhan, Amy; Han, Yong-Hae; Walden, Ramsey et al. (2003) Stoichiometry of organic anion/dicarboxylate exchange in membrane vesicles from rat renal cortex and hOAT1-expressing cells. Am J Physiol Renal Physiol 285:F775-83
Sweet, Douglas H; Miller, David S; Pritchard, John B et al. (2002) Impaired organic anion transport in kidney and choroid plexus of organic anion transporter 3 (Oat3 (Slc22a8)) knockout mice. J Biol Chem 277:26934-43

Showing the most recent 10 out of 13 publications