title: Vigabatrin transport across the human intestinal epithelial (Caco-2) brush-border membrane is via the H+ -coupled amino-acid transporter hPAT1.
abstract: The aim of this investigation was to determine if the human proton-coupled amino-acid transporter 1 (hPAT1 or SLC36A1) is responsible for the intestinal uptake of the orally-administered antiepileptic agent 4-amino-5-hexanoic acid (vigabatrin). The Caco-2 cell line was used as a model of the human small intestinal epithelium. Competition experiments demonstrate that [3H]GABA uptake across the apical membrane was inhibited by vigabatrin and the GABA analogues trans-4-aminocrotonic acid (TACA) and guvacine, whereas 1-(aminomethyl)cyclohexaneacetic acid (gabapentin) had no affect. Experiments with 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF)-loaded Caco-2 cells demonstrate that apical exposure to vigabatrin and TACA induce comparable levels of intracellular acidification (due to H+/amino-acid symport) to that generated by GABA, suggesting that they are substrates for a H+ -coupled absorptive transporter such as hPAT1. In hPAT1 and mPAT1-expressing Xenopus laevis oocytes [3H]GABA uptake was inhibited by vigabatrin, TACA and guvacine, whereas gabapentin failed to inhibit [3H]GABA uptake. In Na+ -free conditions, vigabatrin and TACA evoked similar current responses (due to H+/amino-acid symport) in hPAT1-expressing oocytes under voltage-clamp conditions to that induced by GABA (whereas no current was observed in water-injected oocytes) consistent with the ability of these GABA analogues to inhibit [3H]GABA uptake. This study demonstrates that hPAT1 is the carrier responsible for the uptake of vigabatrin across the brush-border membrane of the small intestine and emphasises the therapeutic potential of hPAT1 as a delivery route for orally administered, clinically significant GABA-related compounds.
authors.affiliation: Institute for Cell and Molecular Biosciences, Faculty of Medical Sciences, University of Newcastle upon Tyne, Newcastle upon Tyne NE2 4HH.
authors.forename: Emily L
authors.initials: EL
authors.lastname: Abbot
authors.forename: Danielle S
authors.initials: DS
authors.lastname: Grenade
authors.forename: David J
authors.initials: DJ
authors.lastname: Kennedy
authors.forename: Kelly M
authors.initials: KM
authors.lastname: Gatfield
authors.forename: David T
authors.initials: DT
authors.lastname: Thwaites
mesh_terms: D026905:Amino Acid Transport Systems / Q000037:antagonists & inhibitors / Q000502:physiology*; D001692:Biological Transport; D018938:Caco-2 Cells; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007408:Intestinal Absorption; D007413:Intestinal Mucosa / Q000378:metabolism / Q000648:ultrastructure; D008871:Microvilli / Q000378:metabolism; D011392:Proline / Q000378:metabolism; D027981:Symporters / Q000037:antagonists & inhibitors / Q000502:physiology*; D020888:Vigabatrin / Q000493:pharmacokinetics* / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
chemical_list: D026905:Amino Acid Transport Systems; C475905:SLC36A1 protein, human; D027981:Symporters; D005680:gamma-Aminobutyric Acid; D011392:Proline; D020888:Vigabatrin